Method for standby of an electrolysis system, control device and electrolysis system

Abstract

A method is disclosed for a standby of an electrolysis plant (400, 600), wherein the electrolysis plant comprises an electrolysis unit (1) and an oxygen gas separator (2) for separating oxygen gas and electrolyte, and the electrolysis unit (1) is connected to a power connection (4) for an energy supply (E) for electrolysis in the electrolysis unit (1). The procedure comprises: - Determining a hydrogen gas content (c(H2)) in the oxygen gas separator and / or an oxygen gas content (c(O2)) in the oxygen gas separator (2), - Receiving a signal to interrupt the electrolysis of the electrolysis unit (1) for standby, - Lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) in response to the signal to interrupt depending on the hydrogen gas content (c(H2)) in the oxygen gas separator (2) and / or depending on the oxygen gas content (c(O2)) in the oxygen gas separator (2).Furthermore, a control device and an electrolysis plant are disclosed.

Description

[0001] The present disclosure relates to a method for the standby operation of an electrolysis plant, a control device, and an electrolysis plant with which the standby method can be carried out. The electrolysis plant is designed for water electrolysis, in particular alkaline pressure electrolysis (pressure alkaline electrolysis).

[0002] In water electrolysis, the electrolysis gases hydrogen and oxygen are obtained from an aqueous electrolyte through the electrochemical splitting of water in a cell stack of the electrolysis plant. The separation of the two electrolysis gases takes place within the cell stack using a membrane. Subsequently, the electrolyte (liquid phase) is separated from the respective electrolysis gas (gaseous phase) in gas separators. At least one oxygen and one hydrogen gas separator, connected to the cell stack, are provided for this purpose.

[0003] Electrolysis plants are typically designed for continuous operation, where electrolysis is not interrupted and fresh electrolysis gas flows continuously into the respective gas separator, thus minimizing the risk of a hydrogen-oxygen reaction. With the increase in renewable energy sources and growing demands on the stability of energy grids, more flexible operating modes for electrolysis plants are required, enabling rapid interruption and restart of the electrolysis process. However, in such standby mode, there is an increased risk that hydrogen and oxygen gas will mix to form an explosive mixture in the gas separator if less or no fresh electrolysis gas flows into the separator.

[0004] It is desirable to specify an electrolysis plant and a method for improving the gas quality in the oxygen gas separator, which in particular enables an efficient and safe standby of the electrolysis operation.

[0005] Embodiments of the disclosure relate to methods for an electrolysis plant comprising at least one electrolysis unit and at least one oxygen gas separator for separating oxygen gas and electrolyte. Furthermore, an energy source for supplying energy to the electrolysis in the electrolysis unit is connected to the at least one electrolysis unit via an energy supply device. The energy is generally provided as electrical energy in the form of direct current. The energy source can, for example, be a power supply network or one or more power generators.

[0006] The electrolysis unit can be an electrolysis cell stack, also referred to simply as a cell stack. If the cell stack is divided into cell sub-stacks in which the electrolysis or energy supply can be controlled independently, in particular interrupted and continued, then an electrolysis unit can also be a cell sub-stack.

[0007] The standby procedure for the oxygen gas separator involves determining the hydrogen gas content c(H₂) of the gas phase within the oxygen gas separator. Additionally or alternatively, the oxygen gas content c(O₂) of the gas phase within the oxygen gas separator is determined. Additionally or alternatively, the ratio of these gas contents, e.g., c(H₂) / c(O₂) or c(O₂) / c(H₂), is determined. For improved process control, the measurement of the hydrogen gas content c(H₂), the oxygen gas content c(O₂), and / or their ratio can be performed, for example, at defined intervals, particularly periodic ones, or essentially continuously.

[0008] The determination of the hydrogen gas content c(H₂), the oxygen gas content c(O₂), and / or their ratio can be initiated in response to a signal to interrupt the electrolysis of the electrolysis unit for standby mode. That is, the acquisition of the value(s) starts as soon as the interruption signal is received. If the value(s) are already being determined before the signal is received, the acquisition continues after the interruption signal is received.

[0009] The interruption signal can be triggered, for example, by user input from an operator or user of the electrolysis plant via a user interface. Alternatively or additionally, the interruption signal can be generated and / or triggered by a control device based on state and / or time parameters of the electrolysis plant and / or the electrical power supplied to the electrolysis system. The interruption signal can be triggered, for example, when no more electrical power is available for electrolysis and / or no more electrolysis gas is being requested and the production rate is to be reduced to zero. For example, the interruption signal is sent and / or received by the control device disclosed herein. For example, the control device may have several control sections.One of the control sections is configured to send the interrupt signal when a predefined condition is met, or when several predefined conditions are met. Another control section is configured to receive the interrupt signal and to perform or initiate further steps, in particular to reduce the hydrogen content in the oxygen gas separator. Once the electrolysis plant is ready for standby, the electrolysis is actually interrupted in response to the received interrupt signal. Thus, it is possible that a period of, for example, a few seconds or more may elapse between receiving the interrupt signal and the actual interruption. It is also possible that no interruption of the electrolysis is actually implemented in response to the received interrupt signal, for example, if the electrolysis plant does not reach a standby-ready state.

[0010] The hydrogen gas content c(H₂) denotes the proportion of hydrogen gas in the gas phase separated in the oxygen gas separator; the same applies to the oxygen gas content c(O₂). The hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) can be determined directly or indirectly in the separated gas phase in the oxygen gas separator, e.g., by in-line measurement. Alternatively or additionally, it is possible to extract a portion of the gas phase from the oxygen gas separator and determine the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) within it, e.g., by online measurement.

[0011] The gas contents c(H₂) and / or c(O₂) can be determined as volume concentrations, mass or molar concentrations, or partial pressures and, if necessary, converted to another reference quantity, and the disclosed method can be carried out depending on these quantities. In multi-stage gas separators, the gas contents of the gas volumes of the respective separator stages of the gas separator can be determined, and the disclosed method can be carried out depending on the highest hydrogen gas contents c(H₂) and / or the lowest oxygen gas contents c(O₂) of the separator stages.

[0012] For standby mode, electrolysis in at least one electrolysis unit is interrupted depending on the measured hydrogen gas content c(H₂) and / or oxygen gas content c(O₂), if the hydrogen gas content c(H₂), the oxygen gas content c(O₂), and / or their ratio in the oxygen gas separator are outside the range for a hydrogen / oxygen oxyhydrogen reaction. Electrolysis is interrupted by disconnecting or switching off the power supply to at least one electrolysis unit. With the interruption of electrolysis, no more oxygen gas is produced in the electrolysis unit and introduced into the oxygen gas separator.

[0013] The interruption / shutdown of the power supply can occur abruptly or through a gradual or continuous reduction of the electrolysis current and / or voltage for the electrolysis unit. Accordingly, a state before the interruption of the electrolysis or power supply refers, for example, to a state in which the electrolysis or power supply of the electrolysis unit is not yet completely interrupted or switched off. This can also include the process of interrupting the electrolysis or power supply, for example, if this occurs through a gradual or continuous reduction. A state after the interruption of the electrolysis or power supply refers, for example, to a state after the electrolysis or power supply has ceased.The power supply has been interrupted and is still interrupted, and no more oxygen is being produced in the electrolysis unit and fed into the oxygen gas separator. For example, the electrolysis current value is zero during the interruption / shutdown of the power supply. Alternatively, the electrolysis current value during the interruption / shutdown may be greater than zero and less than the minimum current required to start or begin electrolysis.

[0014] If the electrolysis process or the power supply is interrupted, at least one electrolysis unit can also be shut off from the oxygen gas separator. An oxygen supply line is provided between the electrolysis unit and the oxygen gas separator to transfer oxygen from the electrolysis unit to the oxygen gas separator. This line connects the electrolysis unit to the oxygen gas separator, so that oxygen gas produced during electrolysis is transferred from the electrolysis unit to the oxygen gas separator. Electrolyte that was not consumed during electrolysis is also introduced into the oxygen gas separator via this supply line.

[0015] An oxygen inlet valve can be arranged on the oxygen supply line. This valve is designed to control, and in particular interrupt, the flow of oxygen and electrolyte from the electrolysis unit into the oxygen gas separator. Control can be achieved via the control device. The oxygen inlet valve can be controlled depending on the electrolysis current I. It can be closed when the electrolysis or the power supply to the electrolysis unit is interrupted, in order to isolate the electrolysis unit from the oxygen gas separator. For example, the oxygen inlet valve remains closed as long as the electrolysis or the power supply is interrupted and only reopens when the electrolysis unit restarts and the interruption of the electrolysis or the power supply ends.

[0016] In addition to the oxygen supply line, the oxygen gas separator has an electrolyte drain line through which the electrolyte can be transferred from the oxygen gas separator to the electrolysis unit or recirculated. An electrolyte treatment device can also be provided between the oxygen gas separator and the electrolysis unit. In one embodiment, the oxygen supply line and the electrolyte drain line can be connected via a bypass line with a bypass valve. The oxygen inlet valve is then located between the bypass line and the oxygen gas separator. An electrolyte drain valve can be located on the electrolyte drain line between the bypass line and the oxygen gas separator. The electrolyte drain valve and the bypass valve can also be controlled by the control device.To isolate the electrolysis unit from the oxygen gas separator, the bypass valve can be closed when the electrolysis or power supply to the electrolysis unit is interrupted.

[0017] Shutting off the oxygen supply lines prevents oxygen and electrolyte from entering the oxygen gas separator from the electrolysis unit during standby mode. This would prevent uncontrolled changes to the hydrogen content (g(H₂)) and hinder the measurement of the hydrogen gas content (c(H₂)) and / or the oxygen gas content (c(O₂)) for the standby process. Closing the bypass valve prevents gas from entering the oxygen gas separator via the bypass line and the electrolyte drain line. If no bypass valve is present, or for added safety, the electrolyte drain valve can also be closed in addition to the oxygen inlet valve when electrolysis or the power supply to the electrolysis unit is interrupted.

[0018] The electrolysis system can also include a hydrogen gas separator, which, analogous to the oxygen gas separator, has a hydrogen supply line and an electrolyte drain line. A hydrogen inlet valve can be arranged on the hydrogen supply line, designed to control, and in particular interrupt, the flow of hydrogen and electrolyte from the electrolysis unit. The hydrogen inlet valve can be controlled depending on the electrolysis current I. It can be closed when the electrolysis or the power supply to the electrolysis unit is interrupted, in order to isolate the electrolysis unit from the hydrogen gas separator and to prevent excessively high differential pressures between the anode and cathode compartments in the cells. The hydrogen inlet valve can remain closed as long as the electrolysis or the power supply to the electrolysis unit is interrupted and only be opened again when the electrolysis unit is restarted.If the hydrogen supply line and the electrolyte drain line of the hydrogen gas separator are also connected to each other via a bypass line and a bypass valve, and an electrolyte drain valve is provided on the electrolyte drain line, then this bypass valve and / or the electrolyte drain valve can also be closed when the electrolysis or power supply is interrupted.

[0019] For safe standby operation, the hydrogen content g(H₂) in the oxygen gas separator can be reduced before and / or after the interruption of electrolysis or the standby power supply, depending on the respective determined hydrogen gas content c(H₂), the respective determined oxygen gas content c(O₂), and / or their ratio, in the disclosed process. This reduces the risk of a hydrogen-oxygen oxyhydrogen reaction, and the interruption of electrolysis, as well as the restart after the interruption of electrolysis, can be carried out more quickly and safely.

[0020] The total hydrogen content g(H₂) in the oxygen gas separator also includes the hydrogen dissolved in the electrolyte within the separator. Depending on the method used to reduce the hydrogen content, the hydrogen content g(H₂) is lowered in the gas phase, in the electrolyte, or in both, thereby also reducing the hydrogen gas content c(H₂). Under normal operating conditions, the gas phase of the oxygen gas separator contains only oxygen and hydrogen. Impurities from other gases are negligible, so the gas contents c(H₂) and c(O₂) can be converted into each other, e.g., c(H₂) = 100 vol% - c(O₂). Therefore, it is sufficient to determine either the hydrogen gas content c(H₂) or the oxygen gas content c(O₂). However, for increased security, both values ​​can be measured or determined, thus enabling redundant work.

[0021] For example, the hydrogen content g(H₂) in the oxygen gas separator is reduced such that the hydrogen gas content c(H₂) in the oxygen gas separator and / or the oxygen gas content c(O₂) in the oxygen gas separator are outside the range for a hydrogen / oxygen oxyhydrogen reaction. The respective hydrogen or oxygen gas content is specifically set below a lower explosive limit (LEL). If the ratios of the gas contents are adjusted, e.g., B. c(H 2 ) / c(O 2 ) or c(O 2 ) / c(H 2 ), if the hydrogen content g(H 2 ) can be reduced and / or the oxygen content g(O 2 ) increased in such a way that the gas contents c(H 2 ), c(O 2 ) are outside a range for a hydrogen / oxygen oxyhydrogen reaction, in particular below a lower explosive limit (LEL).

[0022] For example, before interrupting electrolysis or the standby power supply, the hydrogen content g(H₂) in the oxygen gas separator is reduced if a first threshold c₁(H₂) of the hydrogen gas content in the oxygen gas separator is exceeded, and / or a first threshold of the oxygen gas content c₁(O₂) in the oxygen gas separator is undershot, and / or a predetermined first time duration t₁ is reached. If the gas content ratios are determined, the hydrogen content g(H₂) is reduced before interrupting electrolysis or the power supply if a first threshold for the ratio is reached, e.g., a first threshold r₁ for the ratio c(H₂) / c(O₂) is exceeded, and / or a first threshold 1 / r₁ for the ratio c(O₂) / c(H₂) is undershot.

[0023] The exceeding or falling below the threshold values ​​does not usually have to occur as a sharp threshold, but can also be a smooth, continuous transition, which can even be controlled or regulated, for example with a PID control method (PID: proportional, integrating, and differentiating). For the predetermined time period t1 or the predetermined time interval until a first time t1, a time period is generally used starting from a reference time tV0 = 0, which is typically the reception of the signal to interrupt the process. The first time period or the first time t1 can be chosen such that the reduction of the hydrogen content g(H2) occurs immediately after the reception of the signal to interrupt the process.However, it may also be possible to initiate the reduction of the hydrogen content g(H₂) with a time delay in order to first query and check current state parameters of the electrolysis plant, in particular state parameters of at least one electrolysis unit, on which the implementation of the hydrogen content reduction g(H₂) may depend. Time-based control can also be used, for example, as a backup control in case the determination of the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) should fail.

[0024] Furthermore, it is planned that before the electrolysis or energy supply is interrupted, the hydrogen content g(H₂) in the oxygen gas separator is reduced until a second threshold c₂(H₂) of the hydrogen content in the oxygen gas separator is undershot, and / or a second threshold c₂(O₂) of the oxygen gas content in the oxygen gas separator is exceeded, and / or a second time period has elapsed or a second time point t₂ is reached. If a ratio of the gas contents is determined, the hydrogen content g(H₂) is reduced before the electrolysis or energy supply is interrupted until a second threshold for the ratio is reached, e.g. B. until a second threshold r 2 for the ratio c(H 2 ) / c(O 2 ) is undershot and / or a second threshold 1 / r 2 for the ratio c(O 2 ) / c(H 2 ) is exceeded.The first and second thresholds behave such that, for example, the first threshold for hydrogen gas content c₁(H₂) is typically greater than the second threshold c₂(H₂) for hydrogen gas content, and / or the first threshold c₁(O₂) for oxygen gas content is less than the second threshold c₂(O₂) for oxygen gas content. Similarly, the first threshold r₁ for the ratio c(H₂) / c(O₂) can be greater than the second threshold r₂ for the ratio c(H₂) / c(O₂), and vice versa for the reciprocal ratio c(O₂) / c(H₂).

[0025] The predetermined second time period between the first time t 1 and the second time t 2 can, for example, be empirically determined for the respective electrolysis plant, such that for the respective plant after the second time period the second limit c 2 (H 2 ) for which the hydrogen gas content in the oxygen gas separator is undershot, the second threshold c 2 (O 2 ) for the oxygen gas content in the oxygen gas separator is exceeded and / or the second threshold for the ratio of the gas contents is reached, e.g. the second threshold r 1 for the ratio c(H 2 ) / c(O 2 ) is undershot and / or the second threshold 1 / r 1 for the ratio c(O 2 ) / c(H 2 ) is exceeded.The time duration can be predetermined for the respective electrolysis plant or determined depending on the measured hydrogen gas content c(H₂) and / or the measured oxygen gas content c(O₂) in the oxygen gas separator, for example at time tV₀ and / or t1. If the gas content(s) are measured at different times, e.g., tV₀ and t1, the second time duration can be determined, in particular, depending on a gradient of the gas content c(H₂) and / or c(O₂) over a period between tV₀ and t1. The determination of the second time duration can be carried out by the control device in which the measured gas contents are also stored.

[0026] The electrolysis or energy supply is only interrupted for standby mode, for example, when the second threshold c₂(H₂) of the hydrogen gas content in the oxygen gas separator falls below a certain level, the second threshold c₂(O₂) of the oxygen gas content in the oxygen gas separator is exceeded, the second threshold for the ratio of the gas contents is reached (e.g., the second threshold for the ratio c(H₂) / c(O₂) falls below a certain level), and / or the second threshold for the ratio c(O₂) / c(H₂) is exceeded, and / or the predetermined second time period has expired. The electrolysis, and thus gas production, is therefore only stopped, for example, when a specific gas quality or gas composition is reached in the oxygen gas separator. The second thresholds for the hydrogen gas content and / or...or the oxygen gas content is below a lower explosive limit for a hydrogen / oxygen reaction. The same applies to the ratios of the gas contents.

[0027] The standby process can be carried out with electrolysis systems in which exactly one electrolysis unit is assigned to each oxygen gas separator, meaning that oxygen from the electrolysis in a single electrolysis unit is introduced into the oxygen gas separator. However, in some embodiments, the process can also be carried out with electrolysis systems in which several electrolysis units, e.g., cell stacks and / or cell substacks, are connected to one oxygen gas separator.

[0028] For example, two or more cell stacks of a module can be connected to an oxygen gas separator. In some configurations, at least one cell stack can also contain cell sub-stacks, each connected to the oxygen gas separator. The electrolysis or energy supply in each cell sub-stack can be controlled independently, in particular, interrupted and resumed. The cell sub-stacks can be thermally, hydraulically, and electrically isolated from each other and, for example, connected electrically in parallel.

[0029] In such an electrolysis system, the electrolysis process or the standby power supply is interrupted in all electrolysis units connected to the oxygen gas separator, preventing oxygen from entering the separator. This interruption occurs when the second threshold c₂(H₂) of the hydrogen gas content in the oxygen gas separator falls below a certain level, when the second threshold c₂(O₂) of the oxygen gas content in the oxygen gas separator is exceeded, when the second threshold for the gas content ratio is reached (e.g., when the second threshold for the ratio c(H₂) / c(O₂) falls below a certain level), and / or when the second threshold for the ratio c(O₂) / c(H₂) is exceeded, and / or when the predetermined second time period has expired.

[0030] The standby procedure is performed, for example, from a normal operating state of the electrolysis plant, i.e., immediately following normal operation. The standby procedure is therefore not performed, for example, during the initial commissioning of the electrolysis plant or electrolysis unit, nor is it performed following an emergency shutdown of the electrolysis plant or electrolysis unit.

[0031] In normal operation, the electrolysis gases hydrogen and oxygen are produced in at least one electrolysis unit. The electrolysis unit is connected to the power supply device, which is configured to provide energy from a power source for the electrolysis process within the electrolysis unit. The electrolysis unit is also connected to the oxygen gas separator, so that during electrolysis, oxygen from the at least one electrolysis unit is introduced into the oxygen gas separator, usually continuously. The oxygen inlet valve to the oxygen gas separator is open.

[0032] Electrolysis in the electrolysis unit is carried out at an operating temperature Tunit and an operating pressure punit. The pressure in the oxygen gas separator typically corresponds to the operating pressure punit during normal operation. In electrolysis units consisting of cell stacks with cell sub-stacks, state parameters such as the operating temperature, operating pressure, and electrolysis current refer to the respective cell sub-stack. For alkaline electrolysis, the operating temperature of the electrolysis unit is typically between 40 °C and 90 °C during normal operation. The operating temperature Tunit usually refers to an average value of the temperatures in the cells of the electrolysis unit. However, in some embodiments, the maximum temperature in the electrolysis unit can also be used as the operating temperature Tunit.The electrolysis unit also has an operating temperature Tunit and an operating pressure punit while electrolysis is interrupted. The respective values ​​of the operating temperature Tunit during electrolysis and during the interruption of electrolysis, and the operating pressure punit during electrolysis and during the interruption of electrolysis, can differ from each other.

[0033] The operating pressure in atmospheric alkaline electrolysis can range from 0.02 bar to 0.1 bar gauge during normal operation, while in alkaline pressure electrolysis it typically ranges from 20 bar to 35 bar gauge. The operating pressure punit usually refers to the average pressure in the cells of the electrolysis unit. However, in some configurations, the maximum pressure of the electrolysis unit can also be used as the operating pressure pstack.

[0034] According to embodiments of the method, normal operation with multiple electrolysis units is carried out such that the electrolysis units are operated alternately when the electrolysis plant is operating at partial load. Partial load operation means that in at least one electrolysis unit connected to the oxygen gas separator, the electrolysis or power supply is interrupted, while at least a second electrolysis unit is in operation, i.e., the electrolysis or power supply of this second electrolysis unit is not interrupted. Reasons for such partial load operation can be, for example, low demand for hydrogen and / or oxygen from the user or low availability of electrical power for the electrolysis power supply, which does not necessitate or allow full load operation.Alternating operation ensures that the electrolysis units are in a state that allows for safe standby.

[0035] In alternating operation, electrolysis units take turns operating. This can occur, firstly, when an electrolysis unit or group of electrolysis units, whose electrolysis or energy supply is interrupted, reaches a certain state (alternating operation 1), and / or secondly, when the number of electrolysis units whose electrolysis or energy supply is interrupted or which are in operation changes (alternating operation 2).

[0036] The switching process can depend on a state of the electrolysis units, such as the operating pressure punit, the operating temperature Tunit, the hydrogen and / or oxygen gas contents cano (H2), cano (O2), ckato (H2), ckato (O2) on the anode and / or cathode side, a mechanical stress ounit, the electrolysis current I, and / or the electrolysis gas flow rate of the electrolysis units. At least one of these state parameters can be recorded and compared with a threshold value for the switching process. Alternatively or additionally, it is possible to perform the switching process depending on several of the state parameters, in particular depending on the operating pressure punit and the operating temperature Tunit of the electrolysis units. Which state parameter is considered for the switching process can be defined system-specifically and / or user-specifically and depend on the equipment of the electrolysis plant.For example, in systems with gas analysis for the electrolysis units, in addition to the operating pressure p unit and the operating temperature T unit, a gas content in the electrolysis units can also be taken into account for a change.

[0037] The following describes first the alternating operation 1, which can be carried out when a first electrolysis unit, whose electrolysis or energy supply is interrupted, reaches a certain state.

[0038] If at least one electrolysis unit, whose electrolysis or energy supply is interrupted, reaches a certain state, this first electrolysis unit is restarted. "Starting up" means that the interruption of the electrolysis or energy supply is ended and the first electrolysis unit is supplied with energy for electrolysis, so that electrolysis continues, oxygen is produced in the electrolysis unit, and fed into the oxygen gas separator. Instead of interrupting the electrolysis or energy supply of at least one first electrolysis unit, the electrolysis or energy supply of at least one second electrolysis unit is then interrupted. The first and second electrolysis units thus alternate in electrolysis operation. However, the oxygen gas separator does not go into standby mode because oxygen continues to be fed into the oxygen gas separator from the first electrolysis unit.

[0039] The start-up of the first electrolysis unit can be triggered, for example, by the control device, which contains the current recorded state parameters of the electrolysis units connected to the oxygen gas separator, such as operating pressure p unit, operating temperature T unit, anode and / or cathode-side gas contents, mechanical stress o, electrolysis current I and / or the electrolysis gas throughput produced by the electrolysis units.

[0040] A state at which the first electrolysis unit is started can be reached, for example, when the operating pressure punit in the first electrolysis unit reaches or falls below a specific pressure value pW1_on for the changeover and / or decreases at a specific rate, when the operating temperature Tunit of the first electrolysis unit reaches or falls below a specific temperature value TW1_on for the changeover and / or decreases at a specific rate, and / or when a mechanical stress of the electrolysis unit reaches or falls below a specific voltage oW1_on for the changeover. Furthermore, starting the first electrolysis unit can be triggered when the first electrolysis unit reaches a specific state with respect to the gas composition within the electrolysis unit. Since the gas in the electrolysis unit essentially consists only of the electrolysis gases hydrogen and oxygen, the gas concentrations can be converted into one another, e.g.,...B. cano(H2) = 100 vol% - cano(O2). For the gas composition, it is sufficient to determine one of the gas contents, the hydrogen gas content or the oxygen gas content, e.g., cano(H2) / cano(O2) = cano(H2) / [100 vol% - cano(H2)].

[0041] A first electrolysis unit can be started, for example, when the hydrogen gas content cano(H2) on the anode side reaches or exceeds a certain hydrogen gas content cW1anoon(H2) for the changeover, and / or when the oxygen gas content cano(O2) on the anode side reaches or falls below a certain oxygen gas content cW1anoon(O2) for the changeover. "Anode side" means in an anode compartment of an electrolysis cell of the electrolysis unit, between an anode compartment and an oxygen supply line, and / or in the oxygen supply line between the electrolysis unit and the oxygen gas separator, in particular between the electrolysis unit and an oxygen inlet valve in the oxygen gas separator.Furthermore, a first electrolysis unit can be started up in which, on the cathode side, the hydrogen gas content ckato(H2) has reached or fallen below a specific hydrogen gas content cW1kato_on(H2) for the changeover, and / or, on the cathode side, the oxygen gas content ckato(O2) has reached or exceeded a specific oxygen gas content cW1kato_on(O2). "Cathode side" means in a cathode compartment of an electrolysis cell of the electrolysis unit, between a cathode compartment and a hydrogen supply line, and / or in the hydrogen supply line between the electrolysis unit and the hydrogen gas separator, in particular between the electrolysis unit and a hydrogen inlet valve in the hydrogen gas separator. Alternatively or additionally, the electrolysis or energy supply of a first electrolysis unit can be started up when a time period tW1 has elapsed since the interruption of the electrolysis or...The energy supply to the electrolysis unit has expired. The duration t W1_on can, for example, be empirically determined such that the pressure p W1_on , the temperature T W1_on , the voltage o W1_on and / or at least one of the gas contents c W1ano_on (H 2 ), c ​​W1ano_on (O 2 ), c ​​W1kato_on (H 2 ), c ​​W1kato_on (O 2 ) in the first electrolysis unit is reached.

[0042] The first electrolysis unit is then started up, for example, in such a way that it produces at least the same throughput of oxygen gas and / or hydrogen gas as the second electrolysis unit produced before the electrolysis or energy supply of the latter is interrupted. Instead of the throughput of electrolysis gas, which can also be referred to as the production rate, the electrolysis current of the first electrolysis unit can also be increased to an electrolysis current IW1_on that, for example, corresponds at least to the electrolysis current IW1_on with which the second electrolysis unit was operated before its electrolysis or energy supply was interrupted.

[0043] The first electrolysis unit can, for example, be started up with an initial electrolysis current I0 > 0 A, which is increased by an electrolysis current ramp until it is at least equal to the electrolysis current of the second electrolysis unit before its electrolysis or power supply is interrupted. The current ramp, i.e., the increase in current over time, can, for example, be greater than a current ramp during the initial start-up of the electrolysis unit or when starting up the electrolysis unit from a pressureless state (punit ≈ 1 atm). For alkaline pressure electrolysis, a ramp can, for example, be greater than 0.6% Imax / s (percent per second) relative to the maximum electrolysis current Imax. Preferably, the ramp slope can also be greater than 2% or greater than 10% of the maximum electrolysis current Imax per second; more preferably, it can even be 15% of the maximum electrolysis current per second or more.For alkaline pressure electrolysis with a maximum electrolysis current I max of 10 kA, this could be, for example, an electrolysis current ramp in a range from 60 A / s to 1500 A / s or more, such as a ramp of ≥200 A / s, ≥500 A / s, ≥1000 A / s or ≥1500 A / s.

[0044] If a group of first electrolysis units is started up simultaneously, it can be started up in such a way that it produces at least the same total throughput of oxygen gas and / or hydrogen gas as a group of second electrolysis units before their electrolysis or energy supply is interrupted. The total throughput can be determined, for example, from the sum of the respective throughputs of the individual electrolysis units in the respective group.

[0045] Instead of starting up the first electrolysis unit, the electrolysis or power supply is interrupted in a second electrolysis unit for the switchover. The selection of which electrolysis unit's electrolysis or power supply is interrupted can be predetermined by the control device. This selection can depend, for example, on the current state of the electrolysis units connected to the oxygen gas separator and / or on a time parameter. Regarding the state parameters, the interruption of the electrolysis or power supply can depend, in particular, on the hydrogen and / or oxygen gas content on the anode and / or cathode side, the operating temperature Tunit, the operating pressure punit, a mechanical stress ounit, the electrical power for the electrolysis, especially the electrolysis current I, and / or the electrolysis gas flow rate of the electrolysis units.

[0046] For example, the electrolysis or energy supply of an electrolysis unit can be interrupted if its condition is particularly favorable because, on the anode side, there is a low hydrogen gas concentration with a certain threshold value cW1ano_off(H2) or below, and / or a high oxygen gas concentration with a threshold value cW1ano_off(O2) or above, and / or on the cathode side, there is a low oxygen gas concentration with a threshold value cW1kato_off(O2) or below, and / or a high hydrogen gas concentration with a threshold value cW1kato_off(H2) or above, where the gas concentrations are in each case outside the explosive range of a hydrogen / oxygen reaction. The threshold values ​​of the gas concentrations are typically chosen such that cW1ano_off(H2)<c W1ano_on (H 2 ), c W1ano_off (O 2 )> c W1ano_on (O 2 ) or c W1kato_off (O2)<c W1kato_on (O 2 ), c W1kato_off (H 2 )> c W1kato_on ( H 2 ).

[0047] For example, the electrolysis or energy supply of an electrolysis unit can be interrupted if it exhibits a maximum or minimum state parameter relative to all electrolysis units connected to the oxygen gas separator. This could be an electrolysis unit with the highest oxygen gas content |cano(O2)|max on the anode side and / or the lowest hydrogen gas content |cano(H2)|min on the anode side and / or the lowest oxygen gas content |ckato(O2)|min or the highest hydrogen gas content |ckato(H2)|max on the cathode side.

[0048] Alternatively or additionally to the hydrogen gas content and / or oxygen gas content, the operating temperature Tunit, the operating pressure punit, the mechanical stress ounit, the electrical power for electrolysis, and / or the electrolysis gas throughput of the electrolysis unit can also be taken into account for interrupting the electrolysis or energy supply. It can be provided that the electrolysis or energy supply for an electrolysis unit is interrupted if it has at least a predetermined operating pressure pw1_off, a predetermined operating temperature TW1_off, and / or a specific mechanical stress oW1_off, and / or if it is operated with at least a specific electrolysis current IW1_off, and / or if it has at least a specific electrolysis gas throughput. The electrolysis current can, for example, be the maximum electrolysis current Imax for the electrolysis, i.e.,An electrolysis current for full-load operation of the electrolysis unit. This typically corresponds to a maximum electrolysis gas flow rate, in particular a maximum hydrogen gas flow rate, so that instead of the maximum electrolysis current, a maximum electrolysis gas flow rate can also be used. The threshold values ​​for pressure, temperature, and / or mechanical stress can be chosen such that: PW1_off > pW1_on, TW1_off > TW1_on, oW1_off > oW1_on.

[0049] The operating pressure pW1_off for alkaline electrolysis can be, for example, at least 80%, at least 90%, or at least 95% of the maximum operating pressure pmax of the electrolysis unit. The operating temperature TW1_off can be, for example, at least 66% or at least 80% of the maximum operating temperature Tmax of the electrolysis unit. The mechanical stress can be defined, for example, as the stress in the longitudinal direction of the electrolysis unit, i.e., in the longitudinal direction of a cell stack and / or cell sub-stack, which is proportional to the operating temperature Tunit and / or the operating pressure punit.

[0050] In one example configuration, the electrolysis or energy supply is interrupted for each electrolysis unit whose operating pressure (p unit), operating temperature (T unit), mechanical stress (o unit), hydrogen gas flow rate, oxygen gas flow rate, and / or electrolysis current (I) are at their maximum relative to all electrolysis units of the oxygen gas separator or electrolysis plant. In any case, however, the electrolysis or energy supply is only interrupted if the gas concentrations on the anode and cathode sides are within a safe range, in particular outside the explosive limit for a hydrogen / oxygen reaction.

[0051] In one exemplary embodiment of the process, the electrolysis or the energy supply of an electrolysis unit is only interrupted if the respective state parameter is reached for at least a certain period of time. The electrolysis or energy supply is therefore only interrupted if a predetermined hydrogen gas content CW1ano_off (H2) and / or cW1kato_off (H2), oxygen gas content cW1ano_off (O2) and / or cW1kato_off (O2), operating pressure pW1_off, operating temperature TW1_off, mechanical stress OW1_off, electrical power for the electrolysis or electrolysis current IW1_off, and / or electrolysis gas throughput, in particular a maximum oxygen and / or hydrogen throughput and / or a maximum electrolysis current Imax, has already been reached for a predetermined period of time in the electrolysis unit.This ensures that each electrolysis unit is in a stable state before being switched off for the changeover. Due to its condition, such an electrolysis unit can remain in an interrupted electrolysis state for a particularly long time. Therefore, if standby mode follows the alternating operation, the standby can be carried out safely for at least a certain period before one of the electrolysis units reaches a critical state and the standby mode is terminated. The described alternating operation thus enables a safe standby mode.

[0052] If none of the operating electrolysis units is in a favorable state, the state of one electrolysis unit can be improved to interrupt the electrolysis or energy supply in that unit. For this purpose, the electrolysis current I of an electrolysis unit can, for example, be increased to an electrolysis current IW1ini > I, in particular to the maximum electrolysis current IW1ini = Imax.The electrolysis unit can then be operated with the increased electrolysis current I W1ini until the operating pressure p unit of the electrolysis unit has increased to a pressure of at least p W1_off, the operating temperature T unit of the electrolysis unit has increased to a temperature of at least T W1_off, the mechanical stress o unit has increased to a stress of at least o W1_off, the anode-side oxygen gas content c ano (O 2 ) has increased to at least c W1ano_off (O 2 ), the anode-side hydrogen gas content c ano (H 2 ) has decreased to c W1ano_off (H 2 ) or below, the cathode-side hydrogen gas content c kato (H 2 ) has increased to at least c W1ano_off (H 2 ) and / or the cathode-side oxygen gas content c kato (O 2 ) has decreased to c W1ano_off (O 2 ) or below. Then the electrolysis or energy supply to the electrolysis unit can be interrupted.

[0053] Alternatively, it may also be possible to operate the electrolysis unit with the increased electrolysis current I W1ini for a certain period of time t W1ini.The time period t W1ini can be determined depending on the electrolysis current I W1ini and at least one measured state parameter, p unit , T unit , o unit , c ano (O 2 ), c ​​ano (H 2 ), c ​​kato (O 2 ), c ​​kato (H 2 ), such that during the time period t W1ini the operating pressure p unit of the electrolysis unit increases to a pressure of at least p W1_off , the operating temperature T unit of the electrolysis unit increases to a temperature of at least T W1_off , the mechanical stress o unit increases to a stress of at least o W1_off , the anode-side oxygen gas content c ano (O 2 ) increases to at least c W1ano_off (O 2 ), the anode-side hydrogen gas content c ano (H 2 ) decreases to c W1ano_off (H 2 ) or below , and the cathode-side hydrogen gas content c kato (H₂) rises to at least cW1kato_off(H₂) and / or the cathode-side oxygen gas content ckato(O₂) falls to cW1kato_off(O₂) or below. Then electrolysis or...The power supply to the electrolysis unit will be interrupted.

[0054] For a particularly reliable standby mode, the electrolysis current I of an electrolysis unit can be increased each time before electrolysis or the power supply to the electrolysis unit is interrupted, regardless of the unit's state. The electrolysis unit's state can also be improved to a state where the operating pressure punit, the operating temperature Tunit, the voltage ounit, and / or the gas contents are significantly improved beyond the threshold values ​​for switching, in particular to a maximum or minimum value, e.g.The maximum operating pressure pmax, the maximum operating temperature Tmax, a maximum stress omax, a maximum anode-side oxygen gas content cano_max (O2) and / or maximum cathode-side hydrogen gas content ckato_max (H2) and / or minimum anode-side hydrogen gas content cano_min (H2) and / or minimum cathode-side oxygen gas content ckato_min (O2) can be improved. However, this takes time, so for a faster changeover, the changeover thresholds can be set less strictly, e.g., pW1_off. <p max ; T W1_off <T max . o W1_off <o max , c W1ano_off (O2)<c ano _ max (O 2 ), c W1kato_off (H2)<c kato_max (H 2 ), c W1ano_off (H 2 > c ano_min (H 2 ) and / or c W1kato_off (O 2 ) <c kato_min (O 2 ).

[0055] To improve or increase the operating temperature T unit, the operating pressure p unit and the tension o unit, cooling of the electrolysis unit can be reduced or switched off in addition to or as an alternative to increasing the electrolysis current I.

[0056] In another embodiment, a change in the electrolysis units can occur when the number of electrolysis units whose electrolysis or energy supply is interrupted, or which are in electrolysis operation, changes. Such a switching operation is described below. A change in the number of electrolysis units whose electrolysis or energy supply is interrupted, or which are in electrolysis operation, can be triggered, for example, if the amount of electrolysis gas to be produced changes and / or the electrical power available for electrolysis changes.

[0057] In a first step, it is checked whether a setpoint for a number x of electrolysis units to be operated—i.e., whose electrolysis or energy supply should not be interrupted—is zero. The setpoint can be determined in the control device, for example, depending on the electrical power available for electrolysis and / or a required production rate for the electrolysis gases hydrogen and / or oxygen. The electrical power and / or production rate can be stored in the control device or specified by a user via user input. Instead of a setpoint x for the number of electrolysis units to be operated, a setpoint y can also be defined for the number of electrolysis units whose electrolysis or energy supply should be interrupted.From the difference between a total number S of electrolysis units connected to the oxygen gas separator and the setpoint y, the setpoint x can be determined, x=Sn.

[0058] If the setpoint x is zero (x=0), no electrolysis units are required in electrolysis mode. The standby procedure is then started, for example, by means of the interrupt signal.

[0059] If the setpoint x is not zero, the next step involves comparing the setpoint x with an actual value n of the number of electrolysis units connected to the oxygen gas separator and currently operating in electrolysis mode, meaning their electrolysis or energy supply is not currently interrupted. If the difference between the setpoint and actual value (xn) > 0, or x > n, electrolysis units whose electrolysis or energy supply is currently interrupted must be activated to reach the setpoint x. If the difference between the setpoint and actual value (xn) < 0, or x <n, so muss die Elektrolyse bzw. Energieversorgung von Elektrolyseeinheiten unterbrochen werden, die aktuell in Betrieb sind, um den Sollwert x zu erreichen.

[0060] In the first case, when x > n, a number (xn) of electrolysis units connected to the oxygen gas separator, whose electrolysis or power supply is interrupted, are activated. The selection of which electrolysis units are activated can depend on a current state parameter of the electrolysis units connected to the oxygen gas separator and / or on a time parameter. It can be determined, for example, in the control device where the state parameters are available.

[0061] For example, electrolysis units can be started up whose operating pressure p unit, operating temperature T unit and / or voltage o unit is below a pressure p W2_on, a temperature T W2_on or a voltage o W2_on for a changeover, whose anode-side hydrogen gas content c ano (H 2 ) and / or cathode-side oxygen gas content c kato (O 2 ) is above a hydrogen gas content c W2kato_on (H 2 ) or oxygen gas content c W2ano_on (O 2 ) for a changeover, and / or whose anode-side oxygen gas content c ano (O 2 ), and / or cathode-side hydrogen gas content c kato (H 2 ) is below an oxygen gas content c W2ano_on (O 2 ) or hydrogen gas content c W2kato_on (H 2 ) for a changeover. If fewer than (xn) electrolysis units meet at least one of these criteria, electrolysis units whose state parameters do not meet the aforementioned criteria can also be used.These are electrolysis units that are in a more favorable state. They are started up secondarily. Priority is given to electrolysis units that are in a less favorable state, so that the continuation of electrolysis brings them back to a favorable state, which then allows for safe standby operation.

[0062] Alternatively, those (xn) electrolysis units can be selected whose operating pressure p unit, operating temperature T unit, and / or voltage o unit is particularly low, especially the lowest of the n electrolysis units, and / or whose anode-side hydrogen gas content c ano (H₂) and / or cathode-side oxygen gas content c kato (O₂) is particularly high, especially the highest of the n electrolysis units, and / or whose anode-side oxygen gas content c ano (O₂) and / or cathode-side hydrogen gas content c kato (H₂) is particularly low, especially the lowest of the n electrolysis units. These are electrolysis units that are in an unfavorable condition.

[0063] Alternatively or additionally to at least one of the state parameters, the time elapsed since the interruption of electrolysis or the interruption of the energy supply to the electrolysis units can also be used when selecting which electrolysis units to start up. For example, electrolysis units can be started up whose operating time has exceeded a certain time tW2_on, meaning their electrolysis or energy supply has already been interrupted for at least a time tW2_on. tW2_on can be chosen such that a specific state of the electrolysis unit has been reached since the interruption of electrolysis or the energy supply, e.g., pW2_on, TW2_on, oW2_on, cW2ano_on (O2) and / or cW2kato_on (H2) has been reached or fallen below, and / or cW2ano_on (H2) and / or cW2kato_on (O2) has been reached or exceeded.

[0064] In one configuration of the alternating operation, for example (xn) electrolysis units can be started up whose duration since the interruption of electrolysis or energy supply is the maximum in relation to the durations of all n electrolysis units, whose electrolysis or energy supply has therefore already been interrupted for the longest time.

[0065] By performing the changeover solely based on the difference (nx) or (xn) between the n requested electrolysis units and the x electrolysis units currently operating, the changeover can be carried out very quickly. Alternatively, the changeover can also be performed by identifying, from the total number S of electrolysis units connected to the oxygen gas separator, n electrolysis units that are in an unfavorable state, and then selecting those electrolysis units whose electrolysis is interrupted.

[0066] The electrolysis current I, to which the electrolysis units are started, can be determined or specified by the control device. If several electrolysis units are started, they can each be started at the same or different electrolysis currents I. The electrolysis units can, for example, be started with an initial electrolysis current I0 > 0 A, which is increased by an electrolysis current ramp until the electrolysis current Imax required for electrolysis is reached. The current ramp can, for example, be a steep electrolysis current ramp. For alkaline pressure electrolysis, this can be, for example, a ramp with a gradient > 0.6% Imax / s (percent per second) relative to the maximum electrolysis current Imax. Preferably, the ramp gradient can also be ≥2% Imax / s or ≥10% Imax / s of the maximum electrolysis current Imax per second, and preferably even ≥15% of the maximum electrolysis current per second.For alkaline pressure electrolysis with a maximum electrolysis current I max of 10 kA, this could be, for example, an electrolysis current ramp in a range from 60 A / s to 1500 A / s or more, such as a ramp of ≥200 A / s, ≥500 A / s, ≥1000 A / s or ≥1500 A / s.

[0067] In the second case, when n > x, the electrolysis or energy supply is interrupted for a number (nx) of electrolysis units connected to the oxygen gas separator. The selection of which electrolysis unit is activated can also depend on a current state parameter of the electrolysis units connected to the oxygen gas separator and / or on a time parameter. It can be determined, for example, in the control device where the state parameters are available.

[0068] For example, the electrolysis or energy supply of at least one electrolysis unit can be interrupted if its operating pressure punit, operating temperature Tunit, and mechanical stress ounit are at least at a pressure pW2_off, a temperature TW2_off, and / or a mechanical stress oW2_off for a changeover, and if its anode-side hydrogen gas content cano (H2) and / or cathode-side oxygen gas content ckato (O2) is at or below a hydrogen gas content cW2kato_on (H2) or an oxygen gas content cW2ano_off (O2), and / or if its anode-side oxygen gas content cano (O2) and / or cathode-side hydrogen gas content ckato (H2) is at or below an oxygen gas content cW2ano_off (O2). W2kato_off (H 2 ) or above.Alternatively or additionally, the electrolysis current I or an electrolysis gas flow rate (hydrogen and / or oxygen flow rate) can also be considered when selecting electrolysis units, and, for example, the electrolysis or energy supply of electrolysis units operating with at least one electrolysis current IW2_off, in particular with the maximum electrolysis current Imax, or producing a specific electrolysis gas flow rate, in particular a maximum flow rate, can be interrupted. These are electrolysis units that are in a favorable state for interrupting the electrolysis or energy supply. For example, the electrolysis or energy supply is interrupted in electrolysis units that meet at least two, for example at least three, of these criteria, in particular an operating pressure punit ≥ pW2_off and an operating temperature Tunit ≥ TW2_off, as well as the maximum electrolysis current Imax.

[0069] In one example configuration, the electrolysis or energy supply for at least one electrolysis unit is interrupted when its operating pressure punit, operating temperature Tunit, mechanical stress ounit, hydrogen gas flow rate, oxygen gas flow rate, electrolysis current I, anode-side oxygen gas content cano(H2) and / or cathode-side hydrogen gas content ckato(H2) is at its maximum relative to all electrolysis units of the oxygen gas separator, and / or its anode-side hydrogen gas content cano(H2) and / or cathode-side oxygen gas content ckato(O2) is at its minimum relative to all electrolysis units connected to the oxygen gas separator. In any case, however, the electrolysis or energy supply is only interrupted when the anode-side and cathode-side gas contents are within a safe range, in particular outside the explosive limit for a hydrogen / oxygen reaction.

[0070] In one exemplary embodiment of the process, the electrolysis or the energy supply of an electrolysis unit is only interrupted if the respective state parameter is reached for at least a certain period of time. The electrolysis or energy supply is therefore only interrupted if at least a predetermined hydrogen gas content cW2ano_off (H2) and / or cW2kato_off (H2), oxygen gas content c1ano_on (O2) and / or cW2kato_off (O2), operating pressure pW2_off, operating temperature TW2_off, mechanical stress oW2_off, electrolysis current IW2_off, and / or electrolysis gas throughput, in particular a maximum oxygen and / or hydrogen throughput and / or a maximum electrolysis current Imax, has already been reached for a predetermined period of time in the electrolysis unit.This ensures that the respective electrolysis unit is in a stable state, and that a subsequent standby can be carried out safely for at least a certain period of time.

[0071] If fewer than (nx) electrolysis units meet at least one or all of these criteria for a favorable state, the state of an electrolysis unit can be improved before the electrolysis or energy supply for that electrolysis unit is interrupted. For this purpose, the electrolysis unit, as previously described for change 1, can be operated for a certain period with the increased electrolysis current IW2ini, in particular with the maximum electrolysis current Imax, until the state has improved and / or a time period tW2ini is reached that is necessary to improve the state, in particular such that punit ≥ pW2_off, Tunit ≥ TW2_off, ounit ≥ oW2_off, cano(O2) ≥ cW2ano_off(O2), cano(H2) ≤ cW2ano_off(H2), ckato(H2) ≥ cW2kato_off(H2) and / or ckato(O2) ≤ cW2kato_off(O2).

[0072] Similar to switching 1, in a version of switching 2, an increase in the electrolysis current I of an electrolysis unit can be carried out each time before the electrolysis or energy supply of the electrolysis unit is interrupted, regardless of the state of the electrolysis unit.

[0073] The state of the electrolysis unit can also be improved to a state where it is significantly improved beyond the threshold values ​​for the changeover, in particular to a maximum or minimum value, e.g., p unit = p max, T unit = T max, a maximum voltage o unit = o max, c ano (O 2 ) = c ano_max (O 2 ), c ​​kato (H 2 ) = c kato_max (H 2 ), c ​​ano (H 2) = c ano_min (H 2 ) and / or c kato (O 2 ) = c kato_min (O 2 ). The maximum and minimum gas contents are the gas contents that can be achieved with the electrolysis unit at the respective electrolysis current I W2ini. However, such a procedure takes time, so for a faster changeover, the threshold values ​​for the changeover can be set less strictly, e.g.p W2_off <p max , T W2_off <T max , o W2_off <o max , c W2ano_off (O 2 )<c ano_max (O 2 ), c W2kato_off (H 2 )<c kato_max (H 2 ), c W2ano_off (H 2 )> c ano_min (H 2 ) and / or c W2kato_off (O 2 ) <c kato_min (O 2 ).

[0074] In addition or alternatively to increasing the electrolysis current I, cooling of the electrolysis unit can also be reduced or switched off to increase the operating temperature T unit, the operating pressure p unit and the voltage o unit.

[0075] Alternating operation 1 and / or alternating operation 2 can be performed simultaneously. If both alternating operation 1 and 2 are configured, the threshold values ​​for alternating operation 1 are disregarded during alternating operation 2. For example, the threshold values ​​for starting up in alternating operation 1 can be set more stringent than the threshold values ​​for starting up in alternating operation 2. This generally allows alternating operation 2 to be performed more quickly. Furthermore, the threshold values ​​for starting up can be set more stringent than the critical threshold values ​​for starting up from standby.

[0076] Alternating operation ensures that the electrolysis units are kept in good condition during normal operation before standby mode is triggered, allowing for safe subsequent standby operation for a specific period. Alternatively or additionally to the described alternating operation, the risk of an oxyhydrogen reaction during standby can also be reduced by lowering the hydrogen content g(H₂) in the oxygen gas separator when standby mode is triggered. The hydrogen content g(H₂) can be reduced by one or more of the measures described below. These measures allow them to be implemented even with electrolysis systems that only have a single electrolysis unit, where alternating operation of multiple electrolysis units is not possible: According to embodiments, before the electrolysis is interrupted, or...For standby power supply, a degassed electrolyte is used for electrolysis. This can be supplied to the at least one electrolysis unit whose electrolysis or power supply is interrupted for standby, as well as to other electrolysis units that may be connected to the oxygen gas separator. For example, a degassed electrolyte is used for electrolysis in all electrolysis units connected to the oxygen gas separator. Thus, less hydrogen gas escapes from the electrolyte during standby, i.e., after interruption of electrolysis or power supply, and also when starting up from standby, and the hydrogen gas content c(H₂) in the oxygen gas separator is reduced. The degassed electrolyte can, for example, have a dissolved hydrogen H₂ content of at most 5 × 10⁻⁷ wt.%, or at most 1 × 10⁻⁷ wt.%.-%, for example of at most 1 x 10 -8< wt.%.

[0077] The degassed electrolyte can be supplied to the respective electrolysis unit in addition to, or instead of, the electrolyte recirculated from the oxygen gas separator, for example, from a separate storage tank. Alternatively, it is also possible to use the electrolyte recirculated during electrolysis and reduce the concentration of dissolved gases in this electrolyte in a separate degassing unit. "Separate" in this context means that the degassing takes place outside the electrolysis unit and the oxygen gas separator, thus ensuring that the operating pressure in the electrolysis unit and the oxygen gas separator is not affected, allowing the production of electrolysis gas to continue. In some configurations, the electrolyte preparation device can be designed as a degassing unit or can include one.

[0078] After the electrolysis or power supply is interrupted, i.e., when the electrolysis or power supply is interrupted for standby, the electrolysis unit can also be heated with degassed electrolyte.

[0079] According to embodiments, the hydrogen content g(H₂) in the oxygen gas separator is reduced by lowering the operating temperature Tunit and / or the operating pressure punit of at least one electrolysis unit before the electrolysis or standby power supply is interrupted. If several electrolysis units are connected to the oxygen gas separator, the operating temperatures Tunit and / or the operating pressure punit of all electrolysis units in electrolysis operation are lowered. This allows hydrogen gas dissolved in the electrolyte to degas in a controlled manner before the electrolysis or power supply is interrupted and to be removed from the oxygen gas separator along with the oxygen gas, thus reducing the hydrogen content g(H₂) in the oxygen gas separator.

[0080] In contrast to the previously described method, the electrolyte is degassed only in the electrolysis unit and the gas separator, and is not supplied to the electrolysis unit as a degassed electrolyte. The operating temperature Tunit is typically reduced to a temperature of at least 70% of the maximum operating temperature Tmax, and / or the operating pressure punit is reduced to a pressure of at least 73% of the maximum operating pressure pmax.

[0081] The maximum operating temperature Tmax can be understood as the maximum temperature of the electrolysis cells in the cell stack at which electrolysis in the electrolysis unit can be operated continuously, or at least for 1 to 10 years, without damage or failure of the electrolysis cells. For alkaline pressure electrolysis with aqueous alkaline solutions, such as potassium hydroxide (KOH), as the electrolyte, this temperature is typically in the range of 60 °C to 90 °C.

[0082] The operating pressure pstack is the pressure in the anode and cathode compartments of the electrolysis cells. The maximum operating pressure pmax is the maximum pressure in the electrolysis cells of the electrolysis unit at which electrolysis can be operated continuously, or at least for 1 to 10 years, without damage or failure of the electrolysis cells. It is usually dependent on the design of the electrolysis unit and can be between 85% and 95% of the design pressure. For atmospheric alkaline electrolysis, the maximum operating pressure pmax can, for example, be in the range of 0.05 bar to 0.1 bar gauge pressure, while for alkaline pressure electrolysis it can be in the range of 25 bar to 35 bar gauge pressure.

[0083] Alternatively or additionally to reducing the operating pressure p unit and / or the operating temperature T unit, an electrolyte with an increased concentration c L of dissolved alkali salt, e.g., potassium hydroxide (KOH), can be used for electrolysis before the electrolysis or power supply is interrupted for standby, and / or the concentration of the dissolved alkali salt in the electrolyte can be increased to the concentration c L before the electrolysis or power supply is interrupted. For alkaline electrolysis, an increased concentration c L could, for example, be a KOH concentration in the range of 25 wt% to 30 wt%, or in the range of 27 wt% to 30 wt%, or even 30 wt%.

[0084] The electrolyte concentration can be increased by replacing the electrolyte recirculated from the oxygen gas separator with an electrolyte of higher concentration cL, which may also be degassed. Alternatively, the electrolyte concentration can be increased by adding a more concentrated electrolyte with a concentration greater than cL to the electrolyte recirculated from the gas separator, by adding less or no distilled / deionized water, and / or by adding alkali salts.

[0085] In a further embodiment of the process, the recirculated electrolyte already has an increased concentration cL. Thus, the electrolysis process is carried out with an electrolyte of concentration cL even before or at the beginning of the standby process, particularly during normal operation. For example, the electrolysis system can already be started up with the increased electrolyte concentration cL. A complex control system for increasing the concentration can therefore be omitted, and the standby process can be carried out more simply and quickly.

[0086] Alternatively or additionally, the hydrogen content g(H₂) in the oxygen gas separator is reduced before the electrolysis or power supply is interrupted for standby mode by lowering the electrolyte volume in the oxygen gas separator before the electrolysis or power supply is interrupted. Such a reduction in the electrolyte level in the oxygen gas separator is carried out, for example, when no inert gas is introduced into the oxygen gas separator. The electrolyte volume can be reduced, in particular, to a level lower than the electrolyte volume at the time the interruption signal is received. For example, it is reduced to a level lower than during normal operation. With the reduced electrolyte volume, the amount of dissolved hydrogen that can escape from the electrolyte is reduced, thereby lowering the hydrogen gas content c(H₂) in the oxygen gas separator.

[0087] Under normal operating conditions, the electrolyte volume or level in the gas separators (oxygen and / or hydrogen gas separator) is typically set to ensure reliable transfer such that the liquid volume of electrolyte in the gas separators or their separation chambers is larger than the gas volume of the gas phase. The liquid levels in the gas separators can be equal. In the disclosed process, the electrolyte volume is reduced such that the liquid volume of electrolyte is smaller than the gas volume of oxygen in the oxygen gas separator. In particular, the electrolyte volume in the oxygen gas separator can also be smaller than the electrolyte volume in a hydrogen gas separator to which the electrolysis unit is connected.

[0088] In hydraulically coupled oxygen and hydrogen gas separators, at least one electrolyte-filled shuttle line should be provided between the gas separators to lower the fill level in the oxygen gas separator. This shuttle line connects the gas separators via the electrolyte in the shuttle line, based on the principle of communicating vessels. The shuttle line can be connected as low as possible on the separation chamber of each gas separator, for example, at the lowest point. This allows for very large fill level differences between the oxygen and hydrogen gas separators. This makes it possible to generate a large gas volume in the oxygen gas separator without unnecessarily increasing the size of the separation chamber, and also prevents the two electrolysis gases from mixing due to insufficient fill levels.

[0089] The fill levels can be adjusted by controlling the flow rates of the electrolysis gases supplied to and extracted from the gas separators. For example, to lower the fill level in the oxygen gas separator, the outflow rate q out of the oxygen gas separator can be reduced. This outflow rate can be controlled via the gas outlet valve on the oxygen gas separator. Alternatively or additionally, more hydrogen gas can be extracted from the hydrogen gas separator. This outflow rate can also be controlled via a gas outlet valve on the hydrogen gas separator.

[0090] In electrolysis plants where the oxygen gas separator and the hydrogen gas separator are not hydraulically coupled, the fill levels can be adjusted by controlling the amount of electrolyte withdrawn from or supplied to a separate container. For example, to lower the fill level in the oxygen gas separator, electrolyte can be withdrawn and transferred to the separate electrolyte storage tank, resulting in a larger gas volume than electrolyte volume in the oxygen gas separator.

[0091] Alternatively or additionally, before interrupting electrolysis or the standby power supply, the hydrogen content g(H₂) in the oxygen gas separator is reduced by operating the electrolysis unit with an increased electrolysis current I, specifically with a maximum electrolysis current Imax, i.e., at full load. This means that the electrolysis current I, insofar as it does not yet correspond to the maximum electrolysis current Imax, is increased to a value higher than the electrolysis current at the time the interruption signal is received, specifically to the maximum electrolysis current Imax. By operating with an increased electrolysis current, more oxygen gas is produced in the electrolysis unit and introduced into the oxygen gas separator, thereby reducing the hydrogen content g(H₂), specifically the hydrogen gas content c(H₂).If several electrolysis units are connected to the oxygen gas separator, in particular all of the electrolysis units whose electrolysis or energy supply is not interrupted can be operated with maximum electrolysis current I max.

[0092] The maximum electrolysis current Imax is the maximum current at which electrolysis in the electrolysis unit can be operated continuously, or at least for one to ten years, without damage to or failure of the electrolysis cells. It depends on the electrode surface area and is limited by the maximum heat that the electrolysis system can dissipate; typical current densities for alkaline pressure electrolysis are in the range of 0.2 to 1.2 A / cm².

[0093] In a further embodiment, the hydrogen content g(H₂) in the oxygen gas separator is reduced before the electrolysis or standby power supply is interrupted by introducing inert gas into the oxygen gas separator before the electrolysis or power supply is interrupted. The gas separator can be purged with the inert gas, i.e., the inert gas can be introduced into the gas separator and a gas mixture of inert gas, hydrogen, and oxygen can be extracted from the gas separator, thus reducing the hydrogen content g(H₂) in the oxygen gas separator.

[0094] An inert gas is, for example, a gas that does not form an explosive mixture with oxygen gas, such as nitrogen and / or compressed air. Introducing inert gas into the oxygen gas separator, just like the measures described previously, can reduce the hydrogen content g(H₂), and in particular the hydrogen gas content c(H₂), in the oxygen gas separator before interrupting electrolysis or the standby power supply. Introducing inert gas can be carried out as a standalone measure or in conjunction with one or more of the previously described measures for reducing the hydrogen content. In some configurations, inert gas can also be introduced during an interruption of electrolysis or the power supply, especially if this is achieved by gradually or continuously reducing the electrolysis current and / or voltage in the electrolysis unit.

[0095] For example, the inert gas is introduced into the oxygen gas separator at a pressure pfill of at least 80%, at least 90%, or at least 95% of the maximum operating pressure pmax. The inert gas can be supplied as a pressurized gas for this purpose. It can be introduced into the oxygen gas separator, for example, using a stepwise or a continuous flow process.

[0096] In the stepwise process, the inert gas content in the oxygen gas separator is increased stepwise. Preferably, in a first step, with the gas outlet valve on the oxygen gas separator closed and the oxygen inlet valve between the oxygen gas separator and the electrolysis unit closed, the inert gas is introduced into the oxygen gas separator via an open inert gas inlet valve. In a second step, with the gas outlet valve open, a gas mixture is discharged from the oxygen gas separator. The inert gas is typically introduced into the oxygen gas separator in such a way that it mixes with the gas volume within the oxygen gas separator to form a gas mixture. In the second step, this gas mixture is discharged from the oxygen gas separator through the gas outlet valve. For example, the first and second steps are repeated.An electrolyte drain valve for returning the electrolyte from the oxygen gas separator to an electrolyte preparation device or to the electrolysis unit is usually closed in both steps.

[0097] In an oxygen gas separator that is hydraulically coupled, for example via a shuttle line, to a second gas separator, such as a hydrogen gas separator, the first step can be carried out, for instance, until the liquid level of the electrolyte in the oxygen gas separator has dropped to a specific level. The gas pressure in the oxygen gas separator can, for example, be kept constant during this process. In self-contained oxygen gas separators, i.e., oxygen gas separators that are not hydraulically coupled to hydrogen gas separators, the first step can be carried out, for example, until a specific gas pressure is reached in the oxygen gas separator.

[0098] In the second step, the gas pressure in the oxygen gas separator is not reduced below, for example, 80%, 90%, or 95% of the maximum operating pressure pmax. This keeps the oxygen gas separator at a high pressure level close to the operating pressure, allowing the electrolysis unit to quickly restart from standby to normal operation and oxygen to be introduced into the gas separator. In the case of an oxygen gas separator that is hydraulically coupled to a second gas separator, the gas pressure in the oxygen gas separator is kept constant in the second step.

[0099] In the stepwise process, the introduction of the inert gas between the first and second steps can be stopped or at least reduced, so that in the second step no inert gas or less inert gas than in the first step is introduced into the oxygen gas separator. In the first and / or second step, the inert gas can be introduced into the oxygen gas separator at a continuous flow rate or, for better mixing, at a variable flow rate, e.g., pulsed. The flow rate q fill can be varied periodically or aperiodically in such a way as to force changing turbulences, e.g., in a turbulent flow, and thus achieve improved mixing of the gases in the oxygen gas separator.

[0100] Instead of gradually increasing the inert gas concentration by alternately opening and closing the gas outlet valve, it is also possible to increase the inert gas concentration c(inert) continuously. For example, the oxygen gas separator can be continuously permeated with inert gas.

[0101] In the flow-through process, the inert gas is continuously introduced into the oxygen gas separator, while a gas outlet valve continuously discharges the gas mixture of oxygen and nitrogen, and possibly hydrogen, from the oxygen gas separator into a discharge line. The gas pressure in the oxygen gas separator remains constant or close to the operating pressure. For example, it is not reduced below 80% of the maximum operating pressure pmax. It is maintained at ≥90% or ≥95% of the maximum operating pressure pmax. In alkaline electrolysis with KOH solution as the electrolyte, the maximum operating pressure pmax is typically in the range of 25 bar to 35 bar gauge pressure, for example, in the range of 29 bar to 33 bar gauge pressure, or in the range of 30 bar to 32.5 bar gauge pressure. Due to the high pressure level in the oxygen gas separator during the inert gas introduction and / or discharge,-Rinsing allows for a rapid start-up from standby and the electrolyte levels in the gas separators (hydrogen and oxygen) remain balanced, provided the gas separators are hydraulically coupled.

[0102] In the flow-through method, the continuous introduction of inert gas into the oxygen gas separator can, for example, be achieved with a constant inflow rate q fill > 0. However, it is also possible to vary the inflow rate q fill over time, particularly to pulse it for better mixing, e.g., to vary it periodically or aperiodically between upper and lower threshold values, so that, for example, alternating turbulence occurs in the gas volume or the gas phase of the oxygen gas separator.

[0103] For both step and flow processes, it may be necessary to raise the electrolyte level in the oxygen gas separator to reduce the gas volume and thus limit the purging time and the inert gas usage, i.e., the inert gas inflow rate q fill and / or the duration of the inert gas injection. Any outgassing of dissolved hydrogen from the electrolyte is not critical because it is diluted with the inert gas and discharged from the gas separator. The electrolyte level can, for example, be raised so that there is a larger electrolyte volume than gas volume in the oxygen gas separator.

[0104] Raising the fill level can be performed before introducing the inert gas. In hydraulically coupled gas separators, this can be achieved, for example, by increasing the gas outflow rate qout from the oxygen gas separator or by decreasing the gas outflow rate from the hydrogen gas separator. In flow-through systems, raising the fill level can also be performed during the introduction of the inert gas, for example, by increasing the gas outflow rate qout from the oxygen gas separator relative to the inert gas inflow rate qfill. In self-contained gas separators, the fill level in the oxygen gas separator can be raised by adding electrolyte or water from an external source.

[0105] Once the inert gas injection process is complete, the electrolyte level in the oxygen gas separator can be lowered again. This can be achieved, in particular, by increasing the amount of inert gas injected into the oxygen gas separator, for example, by increasing the inflow rate q fill and / or decreasing the gas outflow rate q out. Alternatively or additionally, in hydraulically coupled gas separators, the electrolyte level in the hydrogen gas separator can also be raised, for example, by injecting the inert gas into the oxygen gas separator at a pressure higher than the gas pressure in the hydrogen gas separator. In the stepwise process, this can be done particularly in the final step, when inert gas is injected into the oxygen gas separator.

[0106] For standby operation, one or more of the previously described measures to reduce the hydrogen content g(H 2 ) in the oxygen gas separator can be carried out before the electrolysis or power supply is interrupted.

[0107] If several measures are implemented to reduce the hydrogen content, at least two measures can be carried out partially or completely simultaneously, or sequentially. For this purpose, each of the measures to be implemented, M i (i=1,2,3...), is assigned its own first and second threshold values.

[0108] Each measure M i (i=1,2,3,...) can be assigned first threshold values ​​c Mi_1 (H 2 ) for the hydrogen gas content in the oxygen gas separator, c Mi_1 (O 2 ) for the oxygen gas content in the oxygen gas separator, or r Mi_1 for the ratio of hydrogen gas content and oxygen gas content in the oxygen gas separator and / or 1 / r Mi_1 for the reciprocal ratio of the gas contents, as well as second threshold values ​​c Mi_2 (H 2 ) for the hydrogen gas content in the oxygen gas separator, c Mi_2 (O 2 ) for the oxygen gas content in the oxygen gas separator, or r Mi_2 for the ratio of hydrogen gas content and oxygen gas content in the oxygen gas separator and / or 1 / r Mi_2 for the reciprocal ratio of these gas contents. The respective measure M i is carried out as long as the hydrogen gas content c(H 2 ) and / oror the oxygen gas content c(O 2 ) in the oxygen gas separator is a value between the respective first and second threshold values, that is, if the detected hydrogen gas content c(H 2 ) is between c Mi_1 (H 2 ) and c Mi_2 (H 2 ), the detected oxygen gas content c(O 2 ) is between c Mi_1 (O 2 ) and c Mi_2 (O 2 ), and / or a ratio of these gas contents is between the first and second threshold values ​​for the respective ratio, e.g. c(H 2 ) / c(O 2 ) between r Mi_1 and r Mi_2 and / or c(O 2 ) / c(H 2 ) between 1 / r Mi_1 and 1 / r Mi_2 . In addition or instead of these threshold values, for a measure M i (i=1,2,3,...) a first time point t Mi_1 and / or a second time point t Mi_2 can also be used, between which the respective measure M i is carried out.

[0109] The time duration or interval between the first and second time parameters is determined such that the second threshold values ​​cMi_2 (H2) and cMi_2 (O2) are reached with the respective action Mi. The determination of the time duration between tMi_1 and tMi_2 can depend on the further actions Mj (ji) that are carried out simultaneously with the respective action Mi. The reference time tV0 = 0 for the times tMi_1 and tMi_2 before the interruption of the power supply is typically the reception or generation of the signal to interrupt. The first times tMi_1 can be determined such that a defined sequence of actions Mi is specified.

[0110] In the case of a measure M i, which is carried out at least temporarily simultaneously with one or more other measures M j (j=1,2,3..., j≠i), the measure M i has first or second threshold values ​​for the hydrogen gas content c Mi_1 (H 2 ), c ​​Mi_2 (H 2 ) and / or the oxygen gas content c Mi_1 (O 2 ), c ​​Mi_2 (O 2 ) which correspond to or lie between the first or second threshold values ​​of the further measure or measures M j: c Mj_2 (H 2 ) ≤ c Mi_1 (H 2 ) ≤ c Mj_1 (H 2 ) and / or c Mj_2 (H 2 ) ≤ c Mi_2 (H 2 ) ≤ c Mj_1 (H 2 ) or c Mj_1 (O 2 ) ≤ c Mi_1 (O 2 ) ≤ c Mj_2 (O 2 ) and / or c Mj_1 (O 2 )≤ c Mi_2 (O 2 )≤ c Mj_2 (O 2 ) and, if time parameters are given, the measure M i has a first or second time point t Mi_1 , t Mi_2 or a time interval between the first and second time point t Mi_1 , t Mi_2, which is related to a first or second time point t Mj_1 , t Mj_2 or the The time interval between these points in time t Mj_1 , t Mj_2 of the further measure or measures M j coincides: t Mj _ 1 ≤ t Mi _ 1 ≤ t Mj _ 2 oder t Mj _ 1 ≤ t Mi _ 2 ≤ t Mj _ 2 or t Mi _ 1 ≤ t Mj _ 1 und t Mi _ 2 ≤ t Mj _ 2 .

[0111] For measures that are carried out sequentially, the first and second thresholds c Mi_1 (H 2 ), c ​​Mi_2 (H 2 ) and c Mi_1 (O 2 ), c ​​Mi_2 (O 2 ) of a measure M i each lie outside the first and second thresholds c Mj_1 (H 2 ), c ​​Mj_2 (H 2 ) and c Mj_1 (O 2 ), c ​​Mj_2 (O 2 ) of the subsequent measure or measures M j (j=1,2,3..., j≠i), and, if time parameters are given, the times t Mi_1 , t Mi_2 or the time interval between the times do not overlap with the times t Mj_1 , t Mj_2 or the time interval between these times of the subsequent measure or measures M j : c Mi_2 (H 2 ) > c Mj_1 (H 2 ) or c Mi_1 (H 2 ) < c Mj_2 (H 2 ) or c Mi_1 (O 2 ) > c Mj_2 (O 2 ) or c Mj_2 (O 2 ) < c Mj_1 (O 2 ) and / or t Mi_1 > t Mj_2 or t Mi_2 < t Mj_1.

[0112] In one embodiment of the process, at least two measures M i for reducing the hydrogen content in the oxygen gas separator can be carried out simultaneously. They therefore have the same first threshold values ​​c Mi_1 (H 2 ) and second threshold values ​​c Mi_2 (H 2 ) for the hydrogen gas content c(H 2 ) in the oxygen gas separator. If the process is carried out depending on the oxygen gas content c(O 2 ) and / or a time parameter, the measures M i also have the same first threshold values ​​c Mi_1 (O 2 ) and second threshold values ​​c Mi_2 (O 2 ) for the oxygen gas content c(O 2 ) in the oxygen gas separator, or the same first and second time parameters t Mi_1 , t Mi_2. By simultaneously implementing measures, the hydrogen content g(H 2 ) and in particular the hydrogen gas content c(H 2 ) in the oxygen gas separator can be reduced very quickly, and the standby procedure can be carried out in a time-efficient manner.Furthermore, the redundancy of the measures improves the security of the standby procedure.

[0113] Measures that can be implemented simultaneously include, in particular, those that do not reduce the hydrogen production rate and / or do not involve the introduction of inert gas into the oxygen gas separator. For example, at least two of the following measures, which do not reduce the hydrogen production rate, can be implemented simultaneously, for instance, as the only measures: Use of degassed electrolyte; increase of the electrolysis current I, in particular to the maximum electrolysis current I max; use of an electrolyte with increased concentration c L and / or increase of the electrolyte concentration to c L; reduction of the fill level in the oxygen gas separator.

[0114] In one exemplary embodiment, the measures to be implemented, Mi, are carried out simultaneously. They therefore have the same threshold values ​​cMi_1(H2) = c1(H2), cMi_2(O2) = c2(O2), ratios for the threshold values ​​rMi_1 = r1, rMi_2 = r2, and time parameters tMi_1 = t1, tMi_2 = t2. Due to the simultaneity of the measures and the limited set of threshold values ​​and time parameters, the standby procedure can be carried out particularly quickly and with minimal effort for control and monitoring. The time interval between t1 and t2 can, for example, be chosen such that the first and / or second threshold values ​​c2(H2), c2(O2), r2, 1 / r2 are exceeded or fallen below within this time interval. t 1 can, for example, be chosen such that the measures to reduce the hydrogen content are started immediately after receiving the signal to interrupt (t 1 =t V0 ).However, it is also possible to start the measures with a time delay (t 1 >t V0 ) in order to first record, for example, current state parameters of the electrolysis plant, in particular state parameters of the at least one electrolysis unit, on which the implementation of the measures may depend.

[0115] In a further embodiment of the standby procedure, at least two measures can be carried out sequentially. For this purpose, the measure Mm that can be carried out first has a second threshold value cMm_2(H2) (m=1,2,3...) for the hydrogen gas content c(H2) in the oxygen gas separator, which is smaller than the first threshold value cMn_1(H2) for the hydrogen gas content c(H2) in the oxygen gas separator of measure Mn (n=1,2,3... , n≠m), which can be carried out or is carried out after this measure Mm. If the standby procedure is carried out depending on the oxygen gas content c(O 2 ) and / or a time parameter, the measure M m has a second threshold c Mm_2 (O 2 ) for the oxygen gas content c(O 2 ) in the oxygen gas separator which is smaller than the first threshold c Mn_1 (O 2 ) for the oxygen gas content c(O 2 ) of the measure M n ora second time parameter t Mm_1 which is smaller than the first time parameter t Mn_1 of the measure M n. This allows, for example, a sequence of measures M m and M n to be specified.

[0116] As soon as inert gas is introduced into the oxygen gas separator as measure M i to reduce the hydrogen content, the further measures M j (j≠i) to reduce the hydrogen content before and / or after the interruption of electrolysis or energy supply are carried out, for example, only depending on the measured hydrogen gas content c(H 2 ) or depending on the respective threshold values ​​for the hydrogen gas content c Mj_1 (H 2 ), c ​​Mj_2 (H 2 ). If the measures M j are based on the time parameter t Mj_2, they are determined such that the respective second threshold value of the hydrogen gas content c Mj_2 (H 2 ) of measure M j is undercut.

[0117] By introducing inert gas into the oxygen gas separator, a gas mixture of oxygen, nitrogen, and hydrogen is present in the separator in both stepwise and continuous flow processes. This reduces not only the hydrogen gas content but also the oxygen gas content in the separator. Therefore, the oxygen gas content c(O₂) can no longer be determined solely from the hydrogen gas content c(H₂). It can be determined or measured, for example, as a function of the inert gas inflow rate qfill and the gas outflow rate qout from the oxygen gas separator, as well as the gas volume in the separator or the electrolyte level and total volume of the oxygen gas separator.

[0118] If the inert gas injection process continues until a second time parameter tMi_2 for the inert gas injection is reached, the second time parameter tMi_2 can be determined, for example, depending on the total volume, gas volume and / or electrolyte volume or electrolyte level in the oxygen gas separator, the inflow rate qfill of inert gas into the oxygen gas separator and the outflow rate qout of gas mixture from the oxygen gas separator, such that the second threshold cMi_2 (H2) for the hydrogen gas content and / or the second threshold cMi_2 (O2) of the oxygen gas content is undershot within the second time period and / or a defined gas content of inert gas c2 (Inert) is reached or exceeded.c 2 (Inert) is chosen such that when c 2 (Inert) is reached, the gas mixture in the oxygen gas separator is outside a range for a hydrogen / oxygen oxyhydrogen reaction, in particular below a lower explosive limit (LEL).

[0119] The standby procedure can be carried out depending on the gas concentration(s) c(H₂) and c(O₂) and / or their ratio, as well as depending on the first and second time parameters. In some embodiments, the standby procedure can also be carried out either solely depending on the gas concentration(s) c(H₂) and c(O₂) and / or their ratio, regardless of the time parameters, or solely depending on the time parameters, regardless of the gas concentration(s) c(H₂) and c(O₂) and / or their ratio.

[0120] If the procedure is carried out independently of the time parameters, depending on the gas content(s) c(H 2 ), c(O 2 ) and / or their ratio, then at least one measure M i (i=1,2,3...) to reduce the hydrogen content in the oxygen gas separator is carried out when the respective gas content(s) c(H 2 ), c(O 2 ) and / or their ratio lie between the first threshold c Mi_1 (H 2 ), c ​​Mi_1 (O 2 ) and / or r Mi_1 or 1 / r Mi_1 , and the second threshold c Mi_2 (H 2 ), c ​​Mi_2 (O 2 ) and / or r Mi_2 or 1 / r Mi_2 of measure M i . The electrolysis or energy supply is interrupted when the hydrogen gas content c(H₂) in the oxygen gas separator reaches the minimum of the second threshold values ​​|c Mi₂(H₂)| min (i=1,2,3...The electrolysis process is interrupted if the minimum threshold value of all measures to be implemented, Mi, is not exceeded, and / or if – provided no inert gas has been or is being introduced into the oxygen gas separator – the oxygen gas content c(O2) in the oxygen gas separator exceeds the maximum of the second threshold values ​​|cMi_2(O2)|max (i=1,2,3...) of all measures to be implemented, Mi. The same applies to the gas ratios, provided no inert gas is introduced into the oxygen gas separator. For example, if the ratio c(H2) / c(O2) is considered, the electrolysis or energy supply is interrupted if the minimum threshold value |rMi_2|min (i=1,2,3...) of all measures to be implemented, Mi, is not exceeded. For the reciprocal ratio, the electrolysis or energy supply is interrupted if the maximum threshold value for the reciprocal ratio is exceeded.

[0121] As an alternative to a minimum or maximum threshold, a threshold for interrupting the electrolysis or energy supply can be defined. If this threshold is reached, fallen below, or exceeded, the electrolysis or energy supply is interrupted. For example, a threshold for the hydrogen gas content coff (H2) and / or 1 / roff for the ratio of hydrogen gas to oxygen gas in the oxygen gas separator, if this threshold is not reached, interrupts the electrolysis or energy supply. Alternatively, a threshold for the oxygen gas content coff (O2) and / or 1 / roff for the ratio of oxygen gas to hydrogen gas in the oxygen gas separator, if this threshold is exceeded, interrupts the electrolysis or energy supply. If inert gas is introduced into the oxygen gas separator, the electrolysis or energy supply can be interrupted when a threshold for the inert gas content coff (Inert) is reached or exceeded.In embodiments, this can, for example, correspond to the second threshold c 2 (Inert) for introducing inert gas to reduce the hydrogen content.

[0122] Such a standby procedure, dependent on the gas concentration(s) c(H₂), c(O₂) and / or their ratio, allows the standby procedure to be carried out particularly efficiently, because no time parameters need to be determined and achieved. Furthermore, real-time determination or monitoring of the gas concentrations enables reliable process control.

[0123] If, in the standby procedure, the first and second time parameters tMi_1 and tMi_2 are used instead of the threshold values ​​for the gas content(s) or their ratio, the respective action Mi is carried out within the time interval between and including tMi_1 and tMi_2. Electrolysis or the energy supply is interrupted when the maximum of the second time parameter |tMi_2|max (i=1,2,3...) of all actions Mi to be carried out is reached, i.e., at the latest time for carrying out all actions Mi. This may be necessary, for example, if determining or recording the gas content is not possible or is faulty. The first time parameter tMi_1 can define the sequence of the actions, while the duration of the actions is determined by the second time parameter tMi_2.

[0124] In an exemplary embodiment, the at least one measure M i for reducing the hydrogen content g(H 2 ) in the oxygen gas separator and the interruption of the electrolysis or energy supply is only carried out depending on the first and second time parameters t Mi_1 , t Mi_2 if the determination of the gas content(s) c(H 2 ), c(O 2 ) is disturbed, e.g. if no current recorded values ​​for the gas content(s) or their ratios are available in the control device, and is otherwise carried out depending on the gas content(s) c(H 2 ), c(O 2 ) and / or their ratio, i.e. independently of the first and second time parameters t Mi_1 , t Mi_2 .

[0125] In a further embodiment of the procedure, the standby process can be implemented depending on the gas concentrations and / or one of their ratios, and depending on time parameters. The respective measure Mi is then carried out in the time interval between and including tMi_1 and tMi_2, as soon as the hydrogen gas concentration c(H₂) in the oxygen gas separator exceeds the first threshold cMi_1 (H₂) and / or, if no inert gas is introduced into the oxygen gas separator, the oxygen gas concentration c(O₂) in the oxygen gas separator falls below the first threshold cMi_1 (O₂). The measure is terminated when the second time parameter or point tMi_2 is reached and the hydrogen gas concentration c(H₂) falls below the second threshold cMi_2 (H₂) and / or the oxygen gas concentration c(O₂) exceeds the first threshold cMi_2 (O₂).Alternatively or additionally to the gas concentrations, the ratio of the gas concentrations or the first and second threshold values ​​of the ratio can also be used. The time parameters and threshold values ​​of the gas concentrations and / or their ratio can thus be used not only to define a sequence of measures, but also to prioritize them.

[0126] For example, several measures can have the same or at least overlapping time intervals between, including, the first and second time parameters tMi_1 and tMi_2, and the same or at least overlapping ranges between the first and second threshold values ​​of the gas concentrations c(H2) and c(O2) and / or a ratio of the gas concentrations, so that these measures can be carried out simultaneously, at least temporarily. This allows for redundancy of the measures, which improves the reliability, functionality, and operational safety of the electrolysis plant in standby mode and also when starting up from standby. Furthermore, by carrying out several measures simultaneously, at least temporarily, the hydrogen concentration in the oxygen gas holder is reduced more quickly.

[0127] Alternatively or additionally, it can be stipulated that several measures for reducing the hydrogen content have the same or at least overlapping time intervals between their respective first and second time parameters, and that the ranges of the first to second threshold values ​​of the gas contents c(H₂), c(O₂), and / or a ratio of the gas contents do not overlap for these measures. If the gas quality deteriorates, i.e., if the hydrogen gas content c(H₂) in the oxygen gas separator increases, the measure with the lowest first threshold value cMi_1(H₂) of the hydrogen gas content is then implemented first. Further measures with higher first threshold values ​​are only implemented if the hydrogen content c(H₂) continues to rise and reaches the higher threshold values. If the hydrogen gas content does not increase further, the subsequent measures are not implemented.Measures with lower initial threshold values ​​c Mi_1 (H 2 ) are thus implemented, while measures with higher initial threshold values ​​serve as backup measures. Such prioritization of measures allows the process to be adapted particularly efficiently to the respective electrolysis plant.

[0128] Regarding the oxygen gas content, provided no inert gas is introduced into the oxygen gas separator, measures with the highest first threshold values ​​c Mi_1 (O 2 ) of the oxygen gas content are implemented first. Further measures with lower threshold values ​​are only implemented once the oxygen gas content continues to decrease and the respective first threshold value of the oxygen gas content for the next measure in the oxygen gas separator is reached. The same applies to the ratios of the gas contents. If the ratio c(H 2 ) / c(O 2 ) is considered, measures with the lowest first threshold values ​​for this ratio are implemented first when the hydrogen gas content in the oxygen gas separator decreases. Conversely, for the ratio c(O 2 ) / c(H 2 ), measures with the highest first threshold values ​​for this ratio are implemented first.Monitoring the ratios of the gas contents allows changes in the gas composition to be detected more quickly if the oxygen gas content c(O 2 ) and the hydrogen gas content c(H 2 ) are determined or recorded separately and the ratio is calculated.

[0129] The electrolysis or energy supply can be interrupted when the maximum of the second time parameter |t Mi_2 | max (i=1,2,3...) is reached and the minimum of the second threshold values ​​|c Mi_2 (H 2 )| min (i=1,2,3...) for the hydrogen gas content is undershot and / or the maximum of the second threshold values ​​|c Mi_2 (O 2 )| max (i=1,2,3...) for the oxygen gas content is exceeded. The respective action M i is then carried out despite falling below the second threshold value c Mi_2 (H 2 ) and / or exceeding the second threshold value c M1_2 (O 2 ) until the respective second time parameter t Mi_2 is reached. This ensures a high level of process reliability. Alternatively, the electrolysis or energy supply can also be interrupted to accelerate the process even before reaching the maximum time parameter |t Mi_2 | max (i=1, 2,3...).The interruption occurs when the hydrogen gas content c(H₂) in the oxygen gas separator falls below the minimum of the second threshold values ​​|cMi₂(H₂)|min (i=1,2,3...) or the defined threshold coff(H₂) for interruption, and / or, provided no inert gas is introduced into the oxygen gas separator, when the oxygen gas content c(O₂) in the oxygen gas separator exceeds the maximum of the second threshold values ​​|cMi₂(O₂)|max (i=1,2,3...) or the defined threshold coff(O₂) for interruption. Alternatively or additionally, as described above, a ratio of the gas contents can also be used.

[0130] In an exemplary further development of the procedure, the measure(s) for reducing the hydrogen content in the oxygen gas separator are carried out depending on the gas contents and / or one of their ratios and depending on time parameters. The respective measure M i is carried out in the time interval between t Mi_1 and t Mj_2 if the respective determined or measured gas contents c(H 2 ), c(O 2 ) and / or their ratio between the first threshold value c Mi_1 (H 2 ), c ​​Mi_1 (O 2 ) and / or r Mi_1 or 1 / r Mi_1 , and the second threshold value c Mi_2 (H 2 ), c ​​Mi_2 (O 2 ) and / or r Mi_2 or 1 / r Mi_2 of the respective measure M i is / are If the second threshold value c Mi_2 (H 2 ) or r Mi_2 is not exceeded and / or if the second threshold value of c Mi_2 (O 2 ) is exceeded, respectively,At 1 / r Mi_2, the respective measure M i is terminated, and the time parameters whose time has not yet been reached at time t=t Vnew of the termination of measure M i are recalculated. The procedure is then continued with the newly calculated time parameters t Mi_1 (t Vnew ), t Mi_2 (t Vnew ). The new time parameters correspond to the difference between the respective previous time parameter and t Vnew : t Mi_1 (t Vnew ) = t Mi_1 - t Vnew and t Mi_2 (t Vnew ) = t Mi_2 - t Vnew for all t Mi_1 , t Mj_2 . >= t Vnew , i=1,2,3,... .

[0131] Time points that have already been reached, or whose duration has already elapsed since the reference time t V0 = 0, remain the same: t Mi_1 ( Vnew ) = t Mi_1 and t Mi_2 (t Vnew ) = t Mi_2 for all t Mi_1 , t Mi_2 < t Vnew , i=1,2,3,...

[0132] As an alternative to recalculating the first and second time parameters, the reference time t V0 can also be adjusted: t V0new =t V0 -t Vnew for all t Mi_1 , t Mj_2 >= t Vnew , i=1,2,3,...

[0133] By adjusting the time parameters, the process, similar to control based solely on gas content thresholds or their ratios, can be executed particularly quickly because the second time parameter is no longer waited for once the respective second threshold or ratio is exceeded or fallen below. Unlike control based exclusively on gas content or its ratios, the first time parameters allow for a predefined sequence of actions, and the control can be implemented using the first and second time parameters if necessary, for example, if gas content measurement is disrupted and no current values ​​are available. Furthermore, the second time parameters can be used to detect malfunctions in the measures for reducing the hydrogen content.Thus, if the respective second threshold value c Mi_2 for the gas content(s) and / or a ratio of the gas contents is not exceeded or fallen below by the second time t Mi_2, an error message and / or error routine can be triggered.

[0134] For example, the fault routine may include carrying out another of the measures M i to reduce the hydrogen content in the oxygen gas separator, e.g. by introducing inert gas into the oxygen gas separator, or aborting the standby and venting the gas from the gas separator.

[0135] The previously described measures M i for reducing the hydrogen content in the oxygen gas separator can be carried out before the electrolysis or power supply is interrupted. In embodiments of the process, they can also be carried out during the interruption of the power supply, with the exception of the measure of increasing the electrolysis current I, particularly if the interruption of the electrolysis or power supply of the respective electrolysis unit is effected by a gradual or continuous reduction of the electrolysis current I and / or the electrolysis voltage. Furthermore, in embodiments of the process, it is possible for one or more of the measures to be carried out multiple times, e.g., repeated or at a later time with different first and / or second threshold values ​​for the gas content(s) and / or their ratio.

[0136] For this purpose, at least one measure M i can have several sets (k=1,2,3,...) of first and second threshold values ​​c Mik_1 (H 2 ), c ​​Mik_2 (H 2 ), c ​​Mik_1 (O 2 ), c ​​Mik_2 (O 2 ), r Mik_1 , r Mik_2 , 1 / r Mik_1 , 1 / r Mik_2 and / or time parameters t Mik_1 and t Mik_2. The sequence and duration of the implementation of the measures M i can be determined via these threshold values ​​and / or time parameters.

[0137] If the measure M i is carried out depending on time parameters and depending on threshold values ​​for the gas content(s) and / or for a ratio of the gas contents, then the parameters of a set, i.e., the parameters with the same index k, are assigned to each other. The measure M i is then carried out, for example, in the time interval from t Mik_1 to t Mik_2 if the respective first threshold value c Mik_1 (H 2 ), c ​​Mik_1 (O 2 ), r Mik_1 , 1 / r Mik_2 is below or exceeded.

[0138] The selection, sequence, and prioritization of the measures M i to be carried out in the process can be plant-specific and / or user-specific. The measures M i to be carried out are, in principle, chosen so that they can be performed with the electrolysis plant. This means that the process only includes those measures M i for which the electrolysis plant is designed. In one embodiment of the process, for example, the process may only include those measures M i for which no separate electrolyte degassing devices and / or no inert gas supply device are provided.

[0139] Regarding the sequence of measures to be implemented, M i, it may be planned, for example, to first implement those measures that are suitable for reducing the hydrogen content g(H₂) in the oxygen gas separator particularly quickly, i.e., faster than other measures to be implemented, and / or in a particularly energy- and / or cost-efficient manner. Further measures can then be implemented. These may have larger initial time parameters and / or smaller initial thresholds for the hydrogen gas content c(H₂) and / or the ratio of hydrogen content to oxygen content and / or larger initial thresholds for the oxygen gas content c(O₂) and / or the ratio of oxygen gas content to hydrogen gas content.

[0140] Measures that can reduce the hydrogen content particularly quickly include increasing the electrolysis current I, lowering the fill level in the oxygen gas separator, or reducing the operating pressure p unit, as well as introducing inert gas into the oxygen gas separator. The continuous use of an electrolyte with an increased concentration c L can be implemented as soon as the electrolysis plant is commissioned, thus also saving time. If one or more of these measures are carried out first, the transition to standby mode can be significantly faster. The process can also consist solely of one or more of these measures.

[0141] Alternatively or additionally, the selection and / or prioritization of measures can also be based on the availability of energy, auxiliary materials, and / or raw materials for carrying out the respective measure, such as depending on the availability of degassed electrolyte or cooling or cooling water for lowering the temperature Tunit of the electrolysis unit. In one embodiment of the process, for example, measures can be carried out first or exclusively in which no degassed electrolyte is used, no inert gas is introduced into the oxygen gas separator, no temperature reduction of the operating temperature Tunit occurs, and / or no increase in the electrolysis current Ic occurs. Measures that do not require auxiliary materials include, for example, lowering the fill level, lowering the operating pressure punit, or increasing the electrolysis current Ic.One measure that can be carried out with low energy expenditure is lowering the fill level in the oxygen gas separator.

[0142] In one exemplary embodiment of the process, the first threshold value c Mi_1 (H 2 ) of the hydrogen gas content for the inert gas injection before the interruption of electrolysis or energy supply can be greater than the first threshold value c Mj_1 (H 2 ) of the hydrogen gas content in the oxygen gas separator of at least one measure, for example, of all measures, M j (j≠i), that are to be carried out before the interruption of electrolysis or energy supply to reduce the hydrogen content g(H 2 ). Alternatively or additionally, the injection of the inert gas can also be started depending on a first threshold value c Mi_1 (O 2 ) of the oxygen gas content in the oxygen gas separator that is lower than a first threshold value c Mj_1 (O 2 ) of the oxygen gas content of at least one, for example, of all measures, M j (j≠i), that are to be carried out before the interruption of electrolysis or energy supply.Energy supply measures are implemented to reduce the hydrogen gas content. This ensures that, prioritizing measures Mj(j#i) for reducing the hydrogen content, which do not require inert gas, are carried out before the energy supply is interrupted. Inert gas injection serves only as an emergency measure if the hydrogen gas content c(H2) cannot be reduced below the second threshold value(s) cMj_2(H2) and / or can be increased above the second threshold value(s) cMj_2(O2), particularly within a specific time period, for example, until the second time parameter tMj_2 is reached. This allows for a reduction in inert gas consumption or even the complete elimination of its use.

[0143] Alternatively or additionally, the selection and / or prioritization of measures can be carried out in such a way that the production rate of electrolysis gases, i.e., the hydrogen gas throughput, does not decrease due to the measures taken to reduce the hydrogen content before the interruption of the energy supply. For example, the hydrogen content in the oxygen gas separator can be reduced before the interruption of electrolysis or the energy supply by increasing the electrolyte concentration, by reducing the electrolyte volume or level in the oxygen gas separator, and / or by increasing the electrolysis current I before the interruption of electrolysis or the energy supply, in particular to a maximum electrolysis current Imax, before the electrolysis or the energy supply is then interrupted for standby.

[0144] Alternatively or additionally, the selection and / or prioritization of measures can depend on at least one state parameter of the electrolysis plant. The selection and / or prioritization of measures can be made by the control device in which the state parameters are available. State parameters can include, for example, the concentration of dissolved hydrogen in the electrolyte, the electrolysis current, the operating pressure and / or the operating temperature of the at least one electrolysis unit, the concentration of the electrolyte, or the electrolyte level in the oxygen gas separator and / or hydrogen gas separator.

[0145] For example, it may be stipulated that the reduction of the hydrogen content in the oxygen gas separator by means of a degassed electrolyte only occurs if the electrolyte in the electrolysis plant, particularly in the oxygen gas separator and / or in the cell stack, is not already degassed. Furthermore, the reduction of the hydrogen content by means of a degassed electrolyte may be carried out depending on whether degassed electrolyte and / or electrolyte degassing are available and / or operational. The increase of the electrolysis current I, particularly to the maximum electrolysis current Imax, only occurs if the electrolysis unit whose electrolysis or energy supply is to be interrupted is not already operating at the maximum electrolysis current Imax.To reduce the operating pressure punit and / or the operating temperature Tunit of the electrolysis unit and / or the electrolyte level in the oxygen gas separator, it may be stipulated that these adjustments only occur if the respective state parameter is not already below a certain threshold value. For example, in pressure alkaline electrolysis, the operating pressure punit may not already be below 73% (e.g., not below 80%) of the maximum operating pressure pmax, or the temperature Tunit may not be below 70% (e.g., not below 75%) of the maximum operating temperature Tmax. Similarly, an increase in the electrolyte concentration is only carried out if the concentration is not yet above a certain threshold value cL, e.g., above 30% in alkaline pressure electrolysis.

[0146] In some implementations of the procedure, the selection and / or prioritization of measures can be carried out by an operator or user of the electrolysis plant. For this purpose, user input can be made via a user interface of the electrolysis plant, where the user selects one or more measures M i to be implemented from at least one list. The list can, for example, only contain those measures M i that are feasible with the currently recorded state parameters of the electrolysis plant or the at least one electrolysis unit. Whether a measure is feasible can be determined, for example, by the control device based on state parameters as described above.

[0147] Alternatively or additionally, at least one list can be compiled according to further criteria. For example, it can only include measures M i that can be implemented particularly quickly and / or that do not reduce the production rate of electrolysis gases and / or that do not introduce inert gas into the oxygen gas separator. In one embodiment, the measures on the list can also be arranged in a specific sequence so that the process can be carried out as quickly as possible and / or, for example, through redundancy of measures, be carried out particularly safely.

[0148] The previously described measures M i concern the reduction of the hydrogen content before the interruption of electrolysis or the power supply. In an exemplary further development of the process, the hydrogen content g(H₂), in particular the hydrogen gas content c(H₂), in the oxygen gas separator is also reduced after the interruption of electrolysis or the power supply, when the electrolysis or power supply is interrupted for standby. For this purpose, for example, inert gas can be introduced into the oxygen gas separator.

[0149] The introduction of the inert gas into the oxygen gas separator can be continuous or stepwise. In particular, it can be carried out in the same manner as the previously described introduction of the inert gas before the interruption of the electrolysis or power supply, for example, using the described stepwise or flow-through method. In the case of pressurized alkaline electrolysis, the gas pressure in the oxygen gas separator is, for example, at least 80%, at least 90%, or at least 95% of the maximum operating pressure pmax of the electrolysis unit.

[0150] The reduction of the hydrogen content by introducing inert gas after interrupting electrolysis or the power supply is initiated when a third threshold c3(H2) of the hydrogen gas content c(H2) in the oxygen gas separator is exceeded, and / or a third threshold c3(O2) of the oxygen gas content c(O2) in the oxygen gas separator is undershot. Alternatively or additionally, a third time period t3 can be used. This third time period t3 is generally defined as the time elapsed since the interruption of electrolysis or the power supply at time tN0 = 0. A purely time-based control can be implemented as a precaution in case the measurement or determination of the gas contents c(H2) and c(O2) malfunctions.

[0151] In one exemplary embodiment of the process, the third threshold c3(H2) is greater than or equal to a second threshold cMi_2(H2), (i=1,2,3...) of at least one measure Mi for reducing the hydrogen gas content before the interruption of electrolysis or energy supply, in particular greater than or equal to the maximum of the thresholds |cMi_2(H2)|max. Additionally or alternatively, the first threshold of the oxygen gas content c(O2) is less than or equal to a second threshold cMi_2(O2), (i=1,2,3...) for the oxygen gas content c(O2) in the oxygen gas separator of at least one measure Mi before the interruption of electrolysis or energy supply, in particular less than or equal to the minimum of the thresholds |cMi_2(O2)|min. This means that at least one threshold value c Mi_2 (O 2 ), c ​​Mi_2 (H 2 ) before the interruption of electrolysis or energy supply is chosen more strictly than the threshold values ​​c 3 (H 2 ) or c 3 (H 2 ).c3(O2) after the interruption of electrolysis or energy supply, such that the hydrogen gas content c(H2) after the interruption of electrolysis or energy supply is below the third threshold c3(H2) for the start of inert gas injection and / or, if no inert gas was injected before the interruption of electrolysis or energy supply, the oxygen gas content c(O2) is above the third threshold c3(O2) for the start of inert gas injection after the interruption of electrolysis or energy supply: c(H2, tN0=0) < c3(H2) and / or c(O2, tN0=0) > c3(O2).

[0152] The gas quality in the oxygen gas separator is thus improved before the interruption of electrolysis or energy supply by one or more measures M i to reduce the hydrogen content to such an extent that in standby, after the interruption of electrolysis or energy supply, inert gas is only introduced if the gas quality deteriorates so much after the interruption of electrolysis or energy supply that the values ​​of the gas contents c(H 2 ) are again above c 3 (H 2 ) or c(O 2 ) are again below c 3 (O 2 ).

[0153] It is therefore possible for standby mode to occur after an interruption of electrolysis or power supply even without the introduction of inert gas, for example, at values ​​of cMi_2(H2) ≤ 1 vol.% and cMi_2(H2) < c3(H2) ≤ 2 vol.%. Here, cMi_2(H2) and c3(H2) denote process-dependent constants, of which cMi_2(H2) has a value less than or equal to 1 vol.% and c3(H2) has a value less than or equal to 2 vol.%, where c3(H2) is greater than cMi_2(H2). If the hydrogen gas content c(H 2 ) remains below c 3 (H 2 ), for example because the interruption of the electrolysis or energy supply and thus the standby only lasts a short time or hardly any hydrogen escapes from the electrolyte in the oxygen gas separator, then no inert gas needs to be used with this procedure.This means that when starting up from standby, inert gas does not first have to be blown out of the oxygen gas separator, but rather a high oxygen content is still present, allowing oxygen gas of high quality to be quickly drawn from the gas separator again.

[0154] The same applies to the oxygen gas content c(O2). Before the power supply is interrupted, the oxygen gas content c(O2) can be increased, for example, to cMi_2 (O2) = 99 vol.% or above by lowering the hydrogen content using one of the measures described above. After the power supply is interrupted, the introduction or purging with inert gas should only begin when the oxygen gas content falls below a third threshold c3 (O2), which is smaller than cMi_2 (O2), for example, c3 (O2) ≤ 98 vol.%. If the oxygen gas content c(O₂) remains above c₃(O₂), for example because the interruption of electrolysis or power supply and thus the standby phase is only brief, or because hardly any hydrogen is released from the electrolyte in the oxygen gas separator, then no inert gas is introduced into the oxygen gas separator using this procedure. This approach can therefore reduce inert gas consumption.

[0155] According to embodiments, the reduction of the hydrogen content g(H₂) by introducing inert gas into the oxygen gas separator is started after the interruption of electrolysis or power supply when the third threshold value of the hydrogen gas content for inert gas introduction or purging c₃(H₂) is exceeded and / or the third threshold value of the oxygen gas content for inert gas introduction or purging c₃(O₂) is undershot, wherein the third threshold value c₃(H₂) is smaller than the second threshold values ​​cₐMi₂(H₂) for the hydrogen gas content, i.e., in particular, smaller than the minimum of the second threshold values ​​|cₐMi₂(H₂)| min , and / or the third threshold of the oxygen content c 3 (O 2 ) is greater than the second thresholds c Mi_2 (O 2 ) for the oxygen gas content, in particular greater than the maximum of the second thresholds |c Mi_2 (O 2 )| max .This means that the threshold values ​​for inert gas introduction c3(H2) and c3(O2) are chosen to be stricter than or equal to the second threshold values ​​cMi_2(H2) and cMi_2(O2), so that after the interruption of electrolysis or the power supply, inert gas is introduced into the oxygen gas separator in any case to further reduce the hydrogen gas content, for example to a fourth threshold value for inert gas purging c4(H2). The introduction of the inert gas can be carried out stepwise, for example in the stepwise method, or continuously, for example in the flow-through method.

[0156] According to embodiments, after the interruption of electrolysis or energy supply, the hydrogen content g(H₂) in the oxygen gas separator is reduced by introducing inert gas into the oxygen gas separator until a fourth threshold value of the hydrogen gas content for inert gas introduction c₄(H₂) in the oxygen gas separator and / or a fourth threshold value of the oxygen gas content c₄(O₂) in the oxygen gas separator is undershot, and / or a fourth time period t₄ has elapsed. The threshold values ​​c₄(H₂) and / or c₄(O₂) are selected such that the gas contents c(H₂) and c(O₂) in the oxygen gas separator are outside the range for a hydrogen / oxygen oxyhydrogen reaction when one or both threshold values ​​are reached, in particular below a lower explosive limit (LEL).

[0157] The fourth time parameter, t4, is determined empirically for the process, whereby the time duration from t3 to t4 is chosen to be long enough so that at least one of the fourth threshold values, c4(H2) or c4(O2), is reached for the respective electrolysis plant. This time duration can depend, in particular, on the hydrogen gas content c(H2) and / or oxygen gas content c(O2) in the oxygen gas separator at the beginning of the inert gas introduction, on the total volume, the gas volume, and / or the electrolyte volume or level in the oxygen gas separator, the inflow rate qfill of the inert gas into the oxygen gas separator, and the outflow rate qout of the gas mixture from the oxygen gas separator. Furthermore, the time duration can also be determined based on the measures Mi for reducing the hydrogen content that were carried out before the interruption of the power supply.

[0158] If the inert gas is introduced into the oxygen gas separator using either a stepwise or continuous flow process, the respective process can be carried out until the fourth threshold value for the hydrogen gas content in the oxygen gas separator, c4(H2), and / or the fourth threshold value for the oxygen gas content, c4(O2), is undershot, and / or the fourth time parameter, t4, is reached. Instead of the fourth threshold values ​​for the hydrogen gas and / or oxygen gas content or the fourth time parameter, the introduction of inert gas can also be stopped when a defined inert gas content, c4(Inert), is reached or exceeded. c4(Inert) is selected such that, upon reaching c4(Inert), the gas mixture in the oxygen gas separator is outside the range for a hydrogen / oxygen oxyhydrogen reaction, in particular below a lower explosive limit (LEL).

[0159] In one iteration of the process, the inert gas injection can be carried out multiple times after the interruption of electrolysis or the power supply, i.e., repeated at a later time interval. For each iteration, a set of third and fourth threshold values ​​cI3(H2), cI3(O2), cI4(H2), cI4(O2) for the gas concentration(s) and / or third and fourth time parameters tI3, tI4 can be defined. The parameters of a set are each designated with the same index I = 1, 2, 3...

[0160] In another embodiment, the introduction of inert gas after an interruption of electrolysis or the power supply only occurs if inert gas is available for introduction into the oxygen gas separator and / or an inert gas supply device is available and functional. These parameters can be stored and verified, particularly in the control device.

[0161] In a further exemplary embodiment of the process, the introduction of inert gas into the oxygen gas separator to reduce the hydrogen content in the oxygen gas separator before, during, and after the interruption of electrolysis or the power supply is not required. Instead, one or more of the previously described measures M i for reducing the hydrogen content in the oxygen gas separator, which do not require the introduction of inert gas, are implemented. Thus, no inert gas needs to be stored. An inert gas supply device for introducing and removing the inert gas, as well as for providing the inert gas, can be omitted.

[0162] If the hydrogen gas content c(H₂) cannot be reduced below the lowest of the second threshold values ​​|cMi_2(H₂)|min by the measure(s) Mi, and / or the oxygen gas content c(O₂) cannot be increased above the highest of the threshold values ​​|cMi_2(O₂)|max, then the standby procedure cannot be continued as before. Depending on the measured hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) in the oxygen gas separator and / or their ratio, the at least one electrolysis unit can then remain in normal operation – the electrolysis or energy supply of the at least one electrolysis unit is therefore not interrupted. Alternatively, the at least one electrolysis unit or the entire electrolysis plant can be shut down. Shutdown can be initiated, in particular, by a shutdown command. This command can, for example, be generated or received in the control device.

[0163] In the previously described embodiments of the process, it is possible to select the first and / or second threshold values ​​for the gas concentration(s) c(H₂), c(O₂) and / or their ratio in such a way that a measure to reduce the hydrogen concentration in the oxygen gas separator before interrupting the electrolysis or the energy supply does not only begin when the respective first threshold value is exceeded or fallen below, but begins as soon as a first threshold value is reached; and / or a measure to reduce the hydrogen concentration does not only end when the respective second threshold value is exceeded or fallen below, but ends as soon as a second threshold value is reached. The respective time parameters can be selected such that, instead of the reaching of the time parameter or duration, the trigger is the exceeding of a duration or time parameter.The interruption of electrolysis or energy supply can therefore also depend on reaching the second threshold and / or exceeding the second time parameter.

[0164] Similarly, for the inert gas injection after the interruption of electrolysis or the power supply, the third and / or fourth threshold values ​​for the gas concentration(s) c(H₂), c(O₂) and / or their ratio can be selected such that the inert gas injection does not begin only when the third threshold is exceeded or fallen below, but rather as soon as a third threshold is reached, and / or does not end only when the respective fourth threshold is exceeded or fallen below, but rather as soon as a fourth threshold is reached. The third and / or fourth time period can be selected such that the inert gas injection depends on exceeding the specified time period or point in time.

[0165] According to embodiments, temperature monitoring and / or voltage monitoring is performed during or after an interruption of the electrolysis or the power supply. The temperature monitoring detects the operating temperature Tunit of the at least one electrolysis unit. If this temperature reaches or falls below a critical temperature Tcrit, the electrolysis unit is heated to an operating temperature Tunit that is higher than the critical temperature Tcrit.

[0166] In stress monitoring, a mechanical stress of the electrolysis unit o unit is detected and the electrolysis unit is heated when a critical threshold o krit of the stress is reached or fallen below, until the detected stress o unit is greater than the critical stress o krit.

[0167] For example, stress monitoring can be provided on a tensioning device of the electrolysis unit. The mechanical stress of the unit can be measured, for example, on tension rods or anchors of the tensioning device using stress sensors. A mechanical stress, or its component in the longitudinal direction of the tension rods, can be measured. The tension rods or anchors are typically guided through openings in end plates at opposite ends of a cell stack, so that they tension the end plates and the electrolysis cells of the cell stack against each other.

[0168] For both temperature and voltage monitoring, the electrolysis unit can be heated by passing electrolyte at a temperature TL through it. The temperature TL of the introduced electrolyte is higher than the critical temperature Tcrit. The electrolyte can be heated directly to temperature TL, for example, by means of pipe tracing or a flow heater, or indirectly via hot water or another hot medium that is in thermal exchange with the electrolyte via a heat exchanger.

[0169] If the electrolysis unit is a cell part stack of a cell stack, then, for example, all cell part stacks of the cell stack will be heated.

[0170] A drop in temperature within the electrolysis unit would lead to a decrease in pressure and the release of hydrogen from the electrolyte. After the electrolysis process or power supply is interrupted, the released hydrogen gas would no longer be carried out of the electrolysis unit along with oxygen, thus increasing the risk of an oxyhydrogen reaction both within the electrolysis unit and during start-up in the oxygen gas separator.

[0171] This outgassing due to a temperature drop is prevented or reduced by temperature and / or voltage monitoring and heating. Temperature and / or voltage monitoring thus enables safe standby mode and also safe start-up from standby. Furthermore, the electrolysis unit remains at a high temperature level close to its operating temperature, allowing for a quick restart.

[0172] To determine the critical temperature Tcrit, at which point heating begins, it is recommended to set it at least 65%, for example at least 70%, for example at least 75% of the maximum operating temperature Tmax of the electrolysis unit. For alkaline electrolysis, especially alkaline pressure electrolysis, the critical temperature Tcrit can be, for example, above 60 °C, for example above 78 °C, for example above 80 °C. The temperature to which the electrolysis unit is heated can be, for example, 85% to 98% of the maximum operating temperature Tmax.

[0173] The mechanical stress of the electrolysis unit depends on the temperature Tunit within the electrolysis unit. The critical mechanical stress ocrit can be selected such that it corresponds to a mechanical stress at the critical temperature Tcrit, ocrit (Tcrit). For heating purposes, the electrolyte can be introduced, for example, until the mechanical stress ounit of the electrolysis unit corresponds to a stress of the electrolysis unit at an operating temperature Tunit above 60 °C, for example above 78 °C, for example above 80 °C, and in particular at an operating temperature Tunit between 85% and 98% of the maximum operating temperature Tmax.

[0174] According to embodiments, the pressure punit in the at least one electrolysis unit after interruption of the electrolysis or the power supply, while the electrolysis or power supply is interrupted, is at least 73%, for example at least 80%, for example at least 90% of a maximum operating pressure pmax. These pressure ranges are maintained by heating the electrolysis unit, i.e., increasing Tunit, or by restarting the electrolysis unit, i.e., resuming electrolysis as soon as the pressure in the electrolysis unit drops faster than a critical rate and / or reaches or falls below a critical value pcrit.

[0175] Heating can be achieved in the same way as temperature monitoring. The electrolysis unit can therefore be heated not only when a critical temperature Tcrit is reached or fallen below, but also when a critical pressure punit is reached or fallen below. For example, an electrolyte with a temperature TL higher than the critical temperature Tcrit can be passed through the electrolysis unit. Heating then increases not only the temperature Tunit in the electrolysis unit, but also the pressure punit within the electrolysis unit.

[0176] If a temperature increase is not possible, the electrolysis unit can be started by ending the interruption of the electrolysis or the power supply to the electrolysis unit and resuming the electrolysis. In particular, the electrolysis unit can be started using the disclosed method after receiving a start-up command. The start-up command can, for example, be received or generated in the control device as soon as the pressure punit in the electrolysis unit decreases faster than a critical rate and / or falls below a critical value pcrit.

[0177] This design ensures that the pressure in the electrolysis unit does not drop too drastically after an interruption of electrolysis or the power supply, thus preventing hydrogen gas from escaping the electrolyte. Furthermore, the electrolysis unit can return from standby to normal operation as quickly as possible.

[0178] The critical pressure drop rate is generally determined using the average pressure in the electrolysis unit. In one embodiment, for electrolysis systems with separate electrolyte circuits, in addition to the pressure in the electrolysis unit, the differential pressure between the anode and cathode compartments in the electrolysis cells of the electrolysis unit can also be determined. If a critical pressure difference is exceeded, the standby mode is terminated and electrolysis is resumed.

[0179] According to embodiments, for the detection or determination of the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) of the gas phase in the oxygen gas separator, a gas volume Vmess (sample volume) is extracted from the oxygen gas separator at a sampling frequency fmess, and the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) of the gas phase of the oxygen gas separator is determined in this extracted gas volume Vmess, wherein the sampling frequency fmess and / or the gas volume Vmess is lower after the interruption of the electrolysis or power supply than before the interruption of the electrolysis or power supply, particularly if no inert gas is introduced into the oxygen gas separator to reduce the hydrogen content after the interruption of the electrolysis or power supply. A reduction in the gas volume Vmess and / or the sampling frequency fmess also reduces the pressure drop in the oxygen gas separator.This reduces the risk of hydrogen outgassing and therefore also the risk of an oxyhydrogen reaction in the oxygen gas separator.

[0180] The gas volume Vmess and / or the sampling frequency fmess can be reduced, for example, so that a maximum of 0.7 vol% of the gas phase is extracted from the oxygen gas separator per hour, for example, only a maximum of 0.5 vol% of the gas phase, or for example, a maximum of 0.2 vol% of the gas phase. By reducing the gas volume, it is possible to determine both the hydrogen gas content c(H2) and the oxygen gas content c(O2) in the extracted gas volume Vmess. If no inert gas is introduced into the oxygen gas separator, the procedure can be carried out depending on a ratio of these gas contents, e.g., c(H2) / c(O2) or c(O2) / c(H2), since larger changes occur at these ratios, which are easier to identify.

[0181] The measures and procedures described above are carried out, for example, before or during an interruption of the electrolysis or power supply, when the oxygen gas separator is in standby mode. However, the standby procedure can also be designed to ensure a safe restart from standby, i.e., when the interruption of the electrolysis or power supply is ended, one or more electrolysis units are started up, and oxygen is once again fed into the oxygen gas separator.

[0182] When the electrolysis unit is started up, the interruption of the electrolysis or energy supply for at least one electrolysis unit is ended, and this electrolysis unit is supplied with energy for electrolysis. The start-up occurs, for example, in response to a received control signal to end the interruption. The control signal to end the interruption of the electrolysis unit is received, in particular, while the electrolysis is interrupted for standby.

[0183] The control signal, hereinafter also referred to as a command, can be generated and / or received, for example, in the control device. The control signal can be generated within the electrolysis unit and sent and received internally, for example, when predefined thresholds are exceeded or fallen below. The control signal can also be received from outside the electrolysis unit, for example, from the control device or an external controller. Starting up one or more electrolysis units can occur for various reasons: Firstly, at least one electrolysis unit may need to be started up if it reaches a critical state. Secondly, starting up at least one electrolysis unit may be necessary if the oxygen gas separator reaches a critical state. A start-up can also be triggered if the operation of a larger number of electrolysis units is requested.This can occur, for example, if the available electrical power for electrolysis increases or a higher hydrogen gas throughput is required, thus necessitating an increase in the production rate of electrolysis gas.

[0184] As previously described, restarting an electrolysis unit due to a critical condition can occur, for example, if the pressure punit in the electrolysis unit decreases faster than a critical rate and / or reaches or falls below a critical value pcrit. In alkaline pressure electrolysis, this critical pressure pcrit can be 73%, 80%, or 90% of the maximum operating pressure pmax.

[0185] Critical conditions of an electrolysis unit can also include a gas composition with an increased risk of oxyhydrogen gas in the electrolysis unit, cooling of the temperature T unit to or below the critical temperature T crit, if, for example, no temperature monitoring with heating is provided, or if this is faulty and no heating takes place, and / or falling below a critical voltage o crit.A critical gas composition may exist, for example, if the anode-side hydrogen gas content cano(H2) in an electrolysis unit reaches or exceeds a certain value ccrit_ano(H2), if the anode-side oxygen gas content cano(O2) in an electrolysis unit reaches or falls below a certain value ccrit_ano(O2), if the cathode-side hydrogen gas content ckato(H2) in an electrolysis unit reaches or falls below a certain value ccrit_kato(H2), and / or if the cathode-side oxygen gas content ckato(O2) in an electrolysis unit reaches or exceeds a certain value ccrit_kato(O2).

[0186] For the standby procedure, at least one of the following state parameters—punit, Tunit, ocrit, cano(H2), cano(O2), ckato(H2), and / or ckato(O2)—is detected and compared with the critical threshold of the state parameter to determine whether a critical state exists. This comparison can be performed by the control device, which, if a critical state is detected, then generates a command to start the respective electrolysis unit that is in a critical state. If several of the state parameters of the electrolysis units, e.g., the pressure punit and the temperature Tunit, are monitored for a critical state, then a critical state exists as soon as one of these state parameters reaches, exceeds, or falls below its critical threshold, e.g., punit ≤ pcrit or Tunit ≤ Tcrit.

[0187] The critical thresholds of the state parameters can, for example, be chosen to maximize the duration of the electrolysis or standby power supply interruption. In one example implementation of the method, the critical state parameters can be determined depending on the design and / or other state parameters of the respective electrolysis unit, such as the maintenance status, age, number of operating hours, and / or the number of electrolysis or power supply interruptions of the respective electrolysis unit.

[0188] If several electrolysis units are operated alternately before the electrolysis or standby power supply is interrupted, then in one embodiment of the method at least one threshold value for starting the electrolysis units in alternating operation can be chosen more strictly than a critical threshold value for starting the electrolysis units from standby: p W 1 _ on > p krit , T W 1 _ on > T krit , c W 1 ano _ on H 2 < c krit _ ano H 2 , c W 1 ano _ on O 2 > c krit _ ano O 2 , c W 1 kato _ on H 2 > c krit _ kato H 2 und / oder c W 1 kato _ on O 2 < c krit _ kato O 2 bzw . p W 2 _ on > p krit , T W 2 _ on > T krit , c W 2 ano _ on H 2 < c krit _ ano H 2 , c W 2 ano _ on O 2 > c krit _ ano O 2 , c W 2 kato _ on H 2 > c krit _ kato H 2 und / oder c W 2 kato _ on O 2 < c krit _ kato O 2 .

[0189] This ensures that the electrolysis units are maintained in a favorable state during alternating operation, preventing the standby mode from being immediately terminated due to a critical condition. Instead, it can be safely maintained for a certain period. For example, during alternating operation, an electrolysis unit can be started up as soon as it reaches a pressure pW1_on of 80% of the maximum operating pressure pmax, whereas in standby mode, a critical pressure pcrit of 73% of the maximum operating pressure is still permissible. Therefore, the electrolysis unit's power supply can remain safely interrupted during standby until its pressure punit drops from 80% to 73% of the maximum operating pressure pmax, before the standby mode is terminated due to the critical pressure condition and the electrolysis unit is started up.

[0190] In an alternative implementation of the procedure, the threshold values ​​for alternating operation are as strict or less strict than the critical state parameters for starting an electrolysis unit from standby: p W 1 _ on ≤ p krit , T W 1 _ on ≤ T krit , c W 1 ano _ on H 2 ≥ c krit _ ano H 2 , c W 1 ano _ on O 2 ≤ c krit _ ano O 2 , c W 1 kato _ on H 2 ≤ c krit _ kato H 2 und / oder c W 1 kato _ on O 2 ≥ c krit _ kato O 2 bzw . p W 2 _ on ≤ p krit , T W 2 _ on ≤ T krit , c W 2 ano _ on H 2 ≥ c krit _ ano H 2 , c W 2 ano _ on O 2 ≤ c krit _ ano O 2 , c W 2 kato _ on H 2 ≤ c krit _ kato H 2 und / oder c W 2 kato _ on O 2 ≥ c krit _ kato O 2 .

[0191] This can be particularly useful if measures are taken before and / or after interrupting the electrolysis or power supply for standby mode to improve the condition of the electrolysis units. One such measure could be heating the electrolysis unit if the critical pressure pcrit, critical temperature Tcrit, and / or critical stress ocrit are reached or fall below. Standby mode then continues as long as heating raises the pressure, temperature, and / or stress above the critical values ​​pcrit, Tcrit, and / or ocrit. Standby mode is only terminated when heating can no longer resolve the critical condition. For example, the electrolysis unit is only started up when the critical pressure pcrit, critical temperature Tcrit, and / or critical stress ocrit are reached or fall below for a specific duration tcrit.The time period t krit can be determined such that within the time period t krit, after falling below the respective critical value p krit, T krit and / or o krit, a pressure, temperature and / or stress above the respective critical threshold p krit, T krit, o krit is reached by heating the electrolysis unit.

[0192] Standby mode can be terminated when an electrolysis unit reaches a critical state and is started up. Starting up an electrolysis unit may also be necessary if the oxygen gas separator reaches a critical state. This start-up can be triggered by a start-up command. Such a command can be generated, for example, when a critical threshold ccrit(H2) of the hydrogen gas content in the oxygen gas separator is exceeded, or when the ratio of hydrogen gas content to oxygen gas content c(H2) / c(O2) in the oxygen gas separator exceeds a critical ratio rcrit. If inert gas is introduced into the oxygen gas separator after an interruption of the electrolysis or power supply, the start-up command can also be generated and / or received if the fourth threshold c4(H2) is not undercut by the fourth time interval t4.Alternatively, if no inert gas has been or is being introduced into the oxygen gas separator, i.e., only oxygen and hydrogen gas are present in the gas phase of the oxygen gas separator, a critical threshold ccrit(O2) of the oxygen gas content in the oxygen gas separator may fall below a critical threshold ccrit(O2) or the ratio of oxygen gas content to hydrogen gas content c(O2) / c(H2) in the oxygen gas separator may fall below a critical ratio 1 / rcrit.

[0193] Alternatively or additionally, it can be stipulated that a threshold value for another state parameter of the oxygen gas separator and / or a time parameter is reached, exceeded, or fallen below. For example, a lower limit of the temperature and / or pressure in the oxygen gas separator and / or in the hydrogen gas separator can be reached, thereby triggering a start-up.

[0194] A restart from standby mode can also be triggered if a larger number of electrolysis units are required for electrolysis operation. This might occur, for example, if the available electrical power for electrolysis increases or a higher throughput of electrolysis gas (hydrogen and / or oxygen) is required, thus necessitating an increased production rate. The hydrogen and / or oxygen throughput can be requested via user input on a user interface or determined by the control unit, with the gas quantity being determined, for example, based on the consumption of the respective electrolysis gas.

[0195] If several electrolysis units are connected to the oxygen gas separator, only the number of electrolysis units necessary to provide a specific amount of hydrogen and / or oxygen, e.g., as requested by the user, and / or to utilize a specific available electrical power for electrolysis, will be activated.

[0196] The start-up process can also be initiated by a start-up command. This command can be generated and / or received, for example, by the control device. The selection of which electrolysis units are started can depend on a time parameter, gas content, and / or state parameter of the electrolysis units. This selection can be made by the control device or be predefined.

[0197] For example, at least one electrolysis unit can be started up in which a certain hydrogen gas concentration has been reached or exceeded and / or a certain oxygen gas concentration has been reached or fallen below. Similar to alternating operation, electrolysis units with unfavorable conditions can be started first, for example, because there is a high hydrogen gas concentration cano (H2) and / or a low oxygen gas concentration cano (O2) on the anode side and / or a high oxygen gas concentration ckato (O2) and / or a low hydrogen gas concentration ckato (H2) on the cathode side.

[0198] For example, electrolysis units of an oxygen gas separator can be activated that exhibit a maximum or minimum state parameter relative to all electrolysis units of the oxygen gas separator and / or the electrolysis plant. These can be, in particular, electrolysis units that have the lowest oxygen gas content |cano(O2)|min on the anode side or the highest hydrogen gas content |cano(H2)|max, and / or, on the cathode side, the highest oxygen gas content |ckato(O2)|max or the lowest, especially minimum, hydrogen gas content |ckato(H2)|min. However, only electrolysis units whose gas composition is within a safe range on both the anode and cathode sides may be activated, especially below the lower explosive limit (LEL) for a hydrogen-oxygen reaction.

[0199] The same applies to the hydrogen and oxygen gas content of an electrolysis unit if the electrolysis unit is connected to only a single oxygen gas separator. An electrolysis unit is only started up if the gas composition on both the anode and cathode sides is outside the explosive range for a hydrogen / oxygen mixture.

[0200] If the electrolysis unit cannot be started, for example due to a defect, the oxygen gas separator can be shut down. In electrolysis systems where several electrolysis units are connected to a single oxygen gas separator for introducing oxygen from the electrolysis process, it should first be checked whether another electrolysis unit can be started as a replacement. The oxygen gas separator should only be shut down if no other electrolysis unit can be started as a replacement.

[0201] The restart, i.e., the end of the interruption of the electrolysis or energy supply, only occurs in all cases if the hydrogen gas content c(H₂) in the oxygen gas separator is below a value c STOP (H₂) for an emergency shutdown. The value c STOP (H₂) for the emergency shutdown is greater than the critical threshold value c krit (H₂) of the hydrogen gas content for the restart. Provided that no inert gas has been or will be introduced into the oxygen gas separator, start-up can also take place if the oxygen gas content c(O 2 ) is above a value c STOP (O 2 ) for an emergency shutdown, the ratio of hydrogen gas content to oxygen gas content c(H 2 ) / c(O 2 ) in the oxygen gas separator is below a ratio r STOP for an emergency shutdown, and / or the ratio of oxygen gas content to hydrogen gas content c(O 2 ) / c(H 2 ) in the oxygen gas separator is above a ratio 1 / r STOP for an emergency shutdown.The value c STOP (O 2 ) for emergency shutdown is less than the critical threshold c krit (O 2 ) for start-up. The value r STOP for emergency shutdown is greater than the critical value r krit for start-up. The gas concentrations or ratios of gas concentrations for emergency shutdown are each outside the range for a hydrogen / oxygen oxyhydrogen reaction in the oxygen gas separator, in particular below the lower explosive limit (LEL).

[0202] For example, a further development of the standby procedure may include the following: to ensure safe restart after the interruption of electrolysis or the power supply, i.e., when the electrolysis unit is again supplied with energy for electrolysis, the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) in the oxygen gas separator are monitored, and an emergency shutdown command is triggered or generated if the hydrogen gas content c(H₂) exceeds a threshold value c STOP (H₂) for the emergency shutdown, for example, c STOP (H₂) = 4 vol.%. Alternatively or additionally, if no inert gas has been or is being introduced into the oxygen gas separator, the emergency shutdown command can be triggered if the oxygen gas content c(O₂) reaches a critical value c STOP (O₂), e.g., c STOP (O₂) = 96 vol.%.%, falls below, the ratio of hydrogen gas content to oxygen gas content c(H 2 ) / c(O 2 ) in the oxygen gas separator exceeds a ratio r STOP , e.g. 0.041, or the ratio of oxygen gas content to hydrogen gas content c(O 2 ) / c(H 2 ) in the oxygen gas separator falls below a critical ratio 1 / r STOP.

[0203] According to embodiments, after the power supply is interrupted, at least one electrolysis unit is started up with an increased or steep electrolysis current ramp. An increased electrolysis current ramp is a ramp that is greater than the ramp during pressureless start-up or initial commissioning of the system or electrolysis unit. For alkaline electrolysis, this ramp is typically < 0.5 Imax % / s based on the maximum electrolysis current Imax. A steep or increased electrolysis current ramp can therefore, for example, be a ramp with a gradient > 0.6% Imax / s (percent per second) based on the maximum electrolysis current Imax. Preferably, the ramp gradient can also be ≥2% or ≥10% of the maximum electrolysis current, and preferably even ≥15% of the maximum electrolysis current per second.For alkaline pressure electrolysis with a maximum electrolysis current I max of 10 kA, this could be, for example, an electrolysis current ramp in a range of 60 A / s to 1500 A / s or more, e.g., a ramp of ≥200 A / s, ≥500 A / s, ≥1000 A / s or ≥1500 A / s.

[0204] For example, the electrolysis current ramp starts at an initial electrolysis current I 0 > 0 A, for example at an electrolysis current of ≥10 % of the maximum electrolysis current I max or for example at ≥20% or ≥30 % of the maximum electrolysis current I max .

[0205] In another exemplary embodiment, the at least one electrolysis unit being started up is operated for a specific period at the maximum electrolysis current Imax, i.e., the electrolysis current is increased up to the maximum electrolysis current Imax. This allows the electrolysis unit and the oxygen gas separator to be supplied with oxygen gas very quickly, so that the pressure punit in the electrolysis unit and in the gas separator is rapidly increased, thereby preventing further outgassing of hydrogen gas. Due to the increased oxygen production rate at full load operation at Imax, the oxygen produced in the at least one electrolysis unit also has a lower hydrogen content than in partial load operation, which also rapidly improves the gas quality in the oxygen gas separator.

[0206] In one exemplary further development of the process, the oxygen gas separator and the associated electrolysis unit(s) are shut down in response to a shutdown command. This shutdown command can be triggered by user input, a time parameter, and / or at least one state parameter of the electrolysis system, in particular a state parameter of the at least one electrolysis unit and / or the oxygen gas separator. The shutdown command can be generated internally, for example by the control device, or received externally. For instance, a user request to shut down might trigger a shutdown. Exceeding a threshold value for the hydrogen gas content and / or a time period after the interruption of electrolysis or the power supply, such as...The fourth threshold c 4 (H 2 ) of the hydrogen gas content, the fourth time period t 4 for the introduction of the intergas and / or the time t crit when heating an electrolysis unit, can trigger the shutdown command.

[0207] For example, the shutdown, in particular the cessation of the inert gas injection, is only triggered if the hydrogen gas content c(H 2 ) in the oxygen gas separator is less than a threshold value for an emergency shutdown c STOP (H 2 ) or if the ratio of hydrogen gas content to oxygen gas content c(H 2 ) / c(O 2 ) in the oxygen gas separator is below a ratio r STOP for an emergency shutdown, i.e., if the gas quality in the oxygen gas separator is sufficiently high and the shutdown can therefore be carried out safely without an oxyhydrogen reaction. If no inert gas is introduced into the oxygen gas separator, shutdown can also occur if the oxygen gas content c(O₂) exceeds a value c STOP (O₂) for an emergency shutdown, or if the ratio of oxygen gas content to hydrogen gas content c(O₂) / c(H₂) in the oxygen gas separator exceeds a ratio of 1 / r STOP for an emergency shutdown. The gas contents or...The gas concentration ratios for the emergency shutdown are in each case outside the range for a hydrogen / oxygen oxyhydrogen reaction, in particular below the lower explosive limit (LEL).

[0208] To shut down the system, any oxygen supply from all electrolysis units connected to the oxygen gas separator is stopped. This can be achieved by stopping the electrolysis process or the power supply to the respective electrolysis unit, so that no more oxygen is produced in the electrolysis unit, and / or by diverting the oxygen from the electrolysis unit so that no more oxygen enters the oxygen gas separator. Additionally, the operating pressure in the oxygen gas separator is reduced to ambient pressure, and the introduction of inert gas, if present, is stopped.

[0209] In alkaline pressure electrolysis, the pressure reduction to ambient pressure is achieved, for example, with a low pressure reduction ramp, such as a pressure reduction ramp of less than 0.4 bar per second, or even less than 0.1 bar per second. The pressure reduction ramp can be adjusted via a defined flow rate at the gas outlet valve of the oxygen gas separator.

[0210] If electrolysis or the power supply to the electrolysis unit is stopped, the electrolysis unit can also be brought to ambient pressure, for example, by keeping it connected to the oxygen gas separator while the pressure in the separator is reduced. When electrolysis or the power supply to the electrolysis unit is stopped, other functions or devices of the electrolysis unit or the electrolysis system can also be terminated or switched off. For example, temperature monitoring or voltage monitoring can also be stopped, and the electrolysis unit can be brought to ambient temperature.

[0211] Embodiments of the disclosure relate to an electrolysis plant. The electrolysis plant is suitable for carrying out the process described above. It has at least one oxygen gas separator to which at least one electrolysis unit is connected, such that during electrolysis, oxygen gas is introduced from the electrolysis unit into the oxygen gas separator. The electrolysis unit can be a cell stack or a cell sub-stack in which several electrolysis cells are electrically and hydraulically connected to one another for electrolysis. For electrolysis, the electrolysis unit is connected to a power supply device that provides energy for the electrolysis.

[0212] The electrolysis system is also designed to detect the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) in the oxygen gas separator. Furthermore, it is designed to trigger an interruption of the power supply to at least one electrolysis unit, thereby also interrupting the electrolysis process within that unit. For example, it can also be designed to reduce the hydrogen content g(H₂) in the oxygen gas separator before and / or after the interruption of the electrolysis or power supply. The reduction of the hydrogen content can depend on the detected hydrogen gas content c(H₂) in the oxygen gas separator, the detected oxygen gas content c(O₂) in the oxygen gas separator, and / or on a ratio of these gas contents to each other, e.g., c(H₂) / c(O₂) or c(O₂) / c(H₂).

[0213] For example, the electrolysis plant is equipped with a control device configured to trigger the interruption and / or termination of the electrolysis or energy supply to the at least one electrolysis unit, depending on the hydrogen gas content c(H₂) in the oxygen gas separator, the oxygen gas content c(O₂) in the oxygen gas separator, and / or a ratio of these gas contents to each other. Furthermore, the electrolysis plant, and in particular the control device, can include a timer device configured to monitor the time parameters tV₀, tN₀, t1, tMi₁ or tMik₁ (i=1,2,3; k=1,2,3...), t2, tMi₂ or tMik₂, t3, t4, tW₁_on, tW₂_on, and / or tcrit. The control device can be configured to trigger and / or terminate the reduction of the hydrogen content in the oxygen gas separator depending on at least one of these time parameters.Additionally or alternatively, it can be designed to trigger the interruption and termination of the energy supply depending on at least one of the time parameters.

[0214] The oxygen gas separator is designed to separate a stream of oxygen gas produced by electrolysis, along with electrolyte introduced into the oxygen gas separator from the electrolysis unit, into a liquid phase and a gas phase within a separation chamber of the oxygen gas separator. The hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) in the oxygen gas separator are determined for this gas phase. For this purpose, the electrolysis system, and in particular the oxygen gas separator, can include a gas measurement system designed to detect the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) of the gas phase of the oxygen gas separator. The gas content(s) can be measured either within the oxygen gas separator itself or in a gas volume Vm of the gas phase taken from the oxygen gas separator.

[0215] Alternatively or additionally, the electrolysis plant can be configured to indirectly determine the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂). For example, if no inert gas is present in the oxygen gas separator, the oxygen gas content c(O₂) can be calculated from the hydrogen gas content c(H₂). Furthermore, the gas measurement system can be configured to detect the inert gas content c(Inert) of the gas phase in the oxygen gas separator.

[0216] In addition to the gas measuring system, the electrolysis plant, in particular the oxygen gas separator, may also have a device for level determination, which is designed to determine, in particular to measure, the level of the liquid phase, i.e. the level of separated electrolyte, in the oxygen gas separator.

[0217] The flow of oxygen gas and electrolyte is typically supplied to the oxygen gas separator from the electrolysis unit via an oxygen inlet valve located on an oxygen supply line between the electrolysis unit and the oxygen gas separator. In addition to this inlet valve, the oxygen gas separator also has an electrolyte drain valve through which the separated electrolyte can be recirculated from the oxygen gas separator into the electrolysis unit. Before the electrolyte is returned to the electrolysis unit, it can be processed in an electrolyte preparation device. The electrolyte preparation device can, for example, be configured to collect the electrolyte from the oxygen gas separator, temper it, degas it, and / or adjust it to a specific electrolyte concentration, particularly an increased concentration cL, e.g.,by adding alkali salt and / or a more concentrated electrolyte. In the electrolyte preparation device, the electrolyte from the oxygen gas separator can also be mixed with electrolyte from a hydrogen gas separator of the electrolysis plant. The mixed electrolyte can then be divided into two fractions (divided circles process), one fraction of which is supplied to the anode compartments and the other fraction to the cathode compartments of the electrolysis cells in the electrolysis unit.

[0218] However, systems are also possible in which the electrolyte streams from the gas separators are not mixed. The electrolyte from the oxygen gas separator is fed exclusively to the anode compartments of the electrolysis cells, and the electrolyte from the hydrogen gas separator is fed exclusively to the cathode compartments of the electrolysis cells. The electrolyte streams thus circulate in separate circuits ("separate circuits" process) within the electrolysis system, without mixing. Before being introduced into the electrolysis cells of the electrolysis unit, the electrolyte streams can be treated separately. For this purpose, for example, two separate electrolyte treatment devices can be provided: one for the electrolyte from the oxygen gas separator and a second for the electrolyte from the hydrogen gas separator.

[0219] Alternatively, cross-flow electrolysis plants are also possible, as known, for example, from EP 4 004 259 A1. In this system, the electrolyte streams are circulated in separate circuits without mixing within the electrolysis plant, similar to the separated-circuit process. However, the electrolyte from the oxygen gas separator is fed to the cathode compartments of the electrolysis cells, and the electrolyte from the hydrogen gas separator is fed to the anode compartments of the electrolysis cells. The electrolyte streams can be treated in electrolyte conditioning devices before being introduced into the electrolysis unit.

[0220] Alternatively or additionally to degassing and / or temperature control in an electrolyte preparation device, the electrolysis plant may also include a separate degassing unit for degassing the electrolyte and / or a separate temperature control unit for maintaining the electrolyte temperature, particularly for heating during temperature and / or stress monitoring. Furthermore, the oxygen gas separator and / or the hydrogen gas separator may also be configured to maintain a specific electrolyte concentration, particularly an increased concentration cL, in the separated electrolyte.

[0221] In some configurations, the oxygen gas separator can be designed as a gravity separator, for example, as a gas bubble separator, in which oxygen gas bubbles rise due to the density difference between the electrolyte and the oxygen gas and are thus separated from the electrolyte. The hydrogen gas separator of the electrolysis plant can also be designed as a gravity separator, in particular as a gas bubble separator. The hydrogen gas separator can be connected to the electrolysis unit via a hydrogen supply line. A hydrogen inlet valve can be arranged on the hydrogen supply line, which can be used to control, in particular to interrupt, the introduction of hydrogen from the electrolysis unit into the hydrogen gas separator.In some configurations, the oxygen gas separator and the hydrogen gas separator can be hydraulically coupled to each other, for example via at least one pendulum line at the bottom of their separation chambers, where the separated electrolyte collects.

[0222] In one example, the electrolysis plant is equipped with an inert gas supply device designed to introduce inert gas into the oxygen gas separator. The inert gas supply device can have an inert gas inlet line connected to an inert gas source, such as an inert gas tank. It can also have an inert gas inlet valve designed to supply the inert gas from the inert gas inlet line to the oxygen gas separator. The inert gas can be introduced directly into the separation chamber of the gas separator. Alternatively, the inert gas can be supplied to the oxygen gas separator via the oxygen inlet line, which carries the oxygen from the electrolysis unit to the oxygen gas separator. In this case, the inert gas inlet valve is located on an inert gas inlet line leading to the oxygen inlet line.In both cases, the inert gas can be introduced by introducing it into the gas volume of the gas phase in the oxygen gas separator. Alternatively or additionally, it is also possible to introduce the inert gas into the liquid phase in the oxygen gas separator, so that the liquid phase is permeated and degassed by the inert gas.

[0223] In addition to the inert gas inlet valve, the inert gas supply device also features a gas outlet valve designed to discharge the gas mixture from the oxygen gas separator. The gas outlet valve can be positioned, for example, on a discharge line at the oxygen gas separator. Both the inert gas inlet valve and the gas outlet valve can be controlled by the control device. The control device can be configured, in particular, to control the opening and closing of the inert gas inlet valve and the gas outlet valve for the stepwise or continuous flow process depending on the hydrogen gas content c(H₂), oxygen gas content c(O₂), a ratio of these gas contents, at least a time duration tMi_1, tMi_2 and / or t3, t4, a flow rate qfill through the inert gas inlet valve and / or a flow rate qout through the gas outlet valve, an electrolyte level or volume in the oxygen gas separator, and / or...or to control a pressure in the gas phase in the oxygen gas separator.

[0224] In addition to sensors for measuring these state parameters, the electrolysis plant may also include further measuring systems or control devices, in particular a measuring system for determining the operating pressure p unit and the operating temperature T unit of the at least one electrolysis unit, a measuring system for determining the electrolyte concentration, a measuring and control system for determining and controlling the electrolysis current I, and / or a measuring system for determining the tension o unit of the electrolysis unit, in particular a tensile stress on at least one tie rod and / or a tie rod of a tensioning device of the electrolysis unit. The state parameters measured by the respective system may be stored in the control device, i.e., transmitted to it from the systems, for example, continuously.

[0225] In some embodiments, the control device may have several control units, e.g.: a gas control device for regulating the electrolysis gas flows (H₂, O₂), the pressure and temperature of the electrolysis gases, and the distribution of inert gas (e.g., N₂) into the oxygen gas separator and / or hydrogen gas separator, in particular the flow rate and pressure of inert gas into the oxygen gas separator and / or hydrogen gas separator and the gas mixture from the oxygen gas separator and / or hydrogen gas separator; a liquid control device for regulating the flow rate and distribution of cooling water and deionized water for electrolyte preparation at the at least one cell stack and, if applicable,other units of the electrolysis plant, an electrolyte control device for regulating the temperature, concentration, flow rate and distribution as well as monitoring the pressure of the electrolyte to the at least one electrolysis unit, an operating control device for regulating the operating temperature and operating pressure in the electrolysis unit and / or a control device for controlling the energy supply of the at least one electrolysis unit, in particular the electrolysis current and / or the electrolysis voltage, and, if applicable, the distribution of the energy to several electrolysis units.

[0226] In one embodiment, the electrolysis plant is equipped with a user interface through which a user can trigger a signal to interrupt standby, start from standby, or shut down from standby, and / or request a specific quantity of hydrogen gas and / or oxygen gas. The command can be received by the control device. The user interface can also be configured to allow a user to select the procedure for reducing the hydrogen content in the oxygen gas separator from at least one list displayed on the interface and send it to the control device. The list can include at least one measure M i for reducing the hydrogen content in the oxygen gas separator.

[0227] Further advantages, features, and developments will emerge from the following examples, which are explained in conjunction with the figures. Identical, similar, and similarly effective elements can be marked with the same reference symbols across different figures. Fig. 1 An electrolysis plant with a schematically represented electrolysis unit and its clamping device, Fig. 2 An electrolysis plant with several schematically represented electrolysis units, Fig. 3 The values ​​for a lower explosion limit depending on a hydrogen gas content in mol% in a hydrogen / oxygen gas mixture, Fig. 4 Explosion ranges and limits for hydrogen / oxygen / nitrogen gas mixtures, Fig. 5 In a flowchart, an example of a sequence for a standby procedure before the interruption of the electrolysis or the standby power supply, Fig. 6 In a flowchart, another example of a sequence for a standby procedure before the interruption of the electrolysis or the standby power supply, Fig. 7 In a flowchart, another example of a sequence for a standby procedure before the interruption of the electrolysis or the standby power supply, Fig.8 in a flowchart an example of a process for temperature monitoring and / or stress monitoring, Fig. 8 the continuation of the standby procedure from . Figure 5 , 6 or 7 after the interruption of electrolysis or the power supply, Fig. 10 the continuation of the standby process from Figure 9 after the interruption of the electrolysis or the power supply, and Fig. 11 shows an overview of the control of several electrolysis units for a standby.

[0228] Figure 1 Figure 400 shows a schematic view of an electrolysis plant 400. The electrolysis plant 400 comprises at least one electrolysis unit 1 with a [missing information - likely a specific component or element] in the Figure 1The diagram shows a schematically represented clamping device. The electrolysis unit 1 is connected to an oxygen gas separator 2, which is equipped with a gas measuring system. The gas measuring system detects the hydrogen gas content c(H₂) and / or oxygen gas content c(O₂) of the gas phase of the oxygen gas separator. It can also measure an inert gas content c(Inert) of the gas phase.

[0229] The connection between electrolysis unit 1 and oxygen gas separator 2 is made via an oxygen supply line with an oxygen inlet valve 9A, through which the flow of oxygen and electrolyte from electrolysis unit 1 to oxygen gas separator 2 can be adjusted, in particular interrupted. The oxygen is typically taken from the anode side of the electrolysis cells of electrolysis unit 1 and contains both oxygen and electrolyte.

[0230] The electrolysis unit 1 can consist of a single unit comprising all the cells of a cell stack 1, or it can consist of cell sub-stacks, each of which can carry out electrolysis independently. The cell sub-stacks of a cell stack can, for example, be electrically isolated from one another and connected in parallel. Furthermore, the electrolysis system can have multiple electrolysis units 1, as exemplified in Figure 2 shown. These can be connected individually or as a group to the oxygen gas separator 2.

[0231] The oxygen gas separator 2 is designed to separate the oxygen gas and the electrolyte and has a gas outlet valve 11A through which the separated oxygen can be withdrawn from the oxygen gas separator 2. The oxygen gas separator 2 is further connected to an electrolyte preparation arrangement 200 via an electrolyte drain line and an electrolyte drain valve 12A. This arrangement includes an electrolyte preparation device 7 to which the separated liquid electrolyte can be discharged. From the electrolyte preparation device 7, electrolyte is fed back to the electrolysis unit 1 together with water from a water supply 8, i.e., recirculated. The water supply 8 can provide distilled / deionized water for the electrolyte preparation. By reducing the amount of water supplied, an increased concentration c L of the electrolyte can be set in the electrolyte preparation device 7.The electrolyte concentration can also be adjusted by adding electrolyte with a higher concentration. If an electrolysis plant does not have an electrolyte treatment device 7, it may also be possible to prepare the electrolyte in a gas separator, the oxygen and / or hydrogen gas separator, as in the example of . Figure 2 , to prepare it, i.e. to add water and, if necessary, lye or its salt.

[0232] In the electrolyte preparation device 7 of the Figure 1 The electrolyte is also heated to provide it for heating the electrolysis unit 1 to a specific temperature TL. If the electrolysis system does not have an electrolyte preparation device 7, a separate temperature control unit may be provided in which the electrolyte is heated, as for example in the Figure 2The temperature control unit can be, for example, a plate heat exchanger or a pipe heater.

[0233] In the electrolyte preparation device 7, the Figure 1The electrolyte can also be degassed and pressurized to a specific pressure in a pressure-controlled container of the electrolyte preparation device 7, in particular to an operating pressure p unit of the electrolysis unit 1. An inert gas supply line 22 can be provided for this purpose. Excess gas can be discharged from a pressure-controlled container of the electrolyte preparation device 7 via a vent valve 20C. Alternatively, the electrolyte can be degassed via vent valves 20A, 20B in the bypass lines, which are located at the highest point of the respective bypass line. As an alternative to degassing, a degassed electrolyte can be supplied to the recirculating electrolyte, or the recirculated electrolyte can be replaced by a degassed electrolyte, which is then supplied to the electrolysis unit 1.

[0234] During electrolysis, the electrolyte is circulated in a closed loop. It is drawn from electrolysis unit 1 along with the produced oxygen gas, fed into the oxygen gas separator, separated from the oxygen gas there, processed, and returned to electrolysis unit 1. However, if no oxygen is produced, it is also possible to circulate the electrolyte without passing it through oxygen gas separator 2. For this purpose, the electrolyte drain line and oxygen supply line are connected via a bypass line and a bypass valve 19A. The electrolyte drain valve 12A and the oxygen inlet valve 9A are then located between the bypass valve 19A and oxygen gas separator 2. Electrolysis unit 1 can be isolated from oxygen gas separator 2 by closing the oxygen inlet valve 9A and the bypass valve 19A.If the bypass valve 19A is opened and the electrolyte drain valve 12A is closed, the electrolyte can be circulated through the bypass line without passing through the oxygen gas separator 2.

[0235] The electrolyte supply to the electrolysis unit 1 can be controlled via an electrolyte inlet valve 18, which is arranged between the electrolyte preparation device 7 and the electrolysis unit 1. By closing the electrolyte inlet valve 18, the electrolysis unit 1 can be isolated from the electrolyte preparation device 7. If no electrolyte preparation device 7 with an electrolyte inlet valve 18 is provided, the electrolyte supply from the oxygen gas separator 2 to the electrolysis unit 1 can also be controlled via the electrolyte outlet valve 12A and the bypass valve 19A.

[0236] The electrolysis unit 1 is also connected to a hydrogen gas separator 3 via a hydrogen supply line. A hydrogen inlet valve 9B is arranged on the hydrogen supply line, allowing the flow rate of hydrogen and electrolyte into the hydrogen gas separator 3 to be adjusted. The hydrogen is typically drawn from the cathode side of the electrolysis cells of the electrolysis unit 1 and contains both hydrogen and electrolyte. In the hydrogen gas separator 3, the hydrogen is separated from the electrolyte and withdrawn from the system via a gas outlet valve 11B. Electrolyte is withdrawn from the hydrogen gas separator 3 via an electrolyte drain valve 12B and fed back to the electrolyte preparation device 7 and then to the electrolysis unit 1. Similar to the oxygen gas separator, a bypass valve 19B can also be provided on a bypass line between the hydrogen inlet valve 9B and the electrolyte drain valve 12B.The bypass line connects the hydrogen supply line and the electrolyte drain line of the hydrogen gas separator. Closing the hydrogen inlet valve 9B and electrolyte drain valve 12B isolates the electrolysis unit 1 from the hydrogen gas separator 3. If no electrolyte conditioning device 7 and electrolyte inlet valve 18 are provided, the electrolyte supply from the hydrogen gas separator 3 to the electrolysis unit 1 can also be controlled via the electrolyte drain valve 12B on the hydrogen gas separator 3.

[0237] In the exemplary embodiment of the Figure 1The electrolyte is supplied to and removed from the cathode and anode compartments of the electrolysis cells in separate electrolyte fractions. The removed electrolyte fractions are separated from the electrolysis gases in the gas separators 2, 3 and then mixed together, e.g., in a common tank of the electrolyte preparation device 7, before two fractions are again formed from the mixed electrolyte, one of which is supplied back to the anode compartments and the other to the cathode compartments (also known as the "divided circles" process).

[0238] Alternatively, arrangements are also possible in which the electrolyte preparation takes place without mixing, and the electrolyte streams from the oxygen gas separator 2 and the hydrogen gas separator 3 are circulated in separate circuits within the electrolysis system (also known as "separate circuits" processes). In this case, the electrolyte from the oxygen gas separator 2 is fed unmixed to the anode compartments of the electrolysis cells, and the electrolyte from the hydrogen gas separator 3 is fed unmixed to the cathode compartments of the electrolysis cells. The electrolysis system can also be designed for a cross-flow of the electrolyte streams. In this case, the electrolyte from the oxygen gas separator 2 is fed unmixed to the cathode compartments of the electrolysis cells, and the electrolyte from the hydrogen gas separator 3 is fed unmixed to the anode compartments of the electrolysis cells.

[0239] The gas separators 2, 3 can be single- or multi-stage gravity separators, in particular gas bubble separators. They can be hydraulically coupled to each other, for example via at least one shuttle line. The gas separators 2, 3 are connected to each other via a liquid column according to the principle of communicating vessels or tubes, allowing an exchange of the separated electrolyte between the gas separators 2, 3. However, it is also possible for the gas separators 2, 3 to be independent, i.e., not hydraulically connected to each other.

[0240] A power connection 4 for an energy supply E is in the Figure 1schematically represented. Here, it can be provided that the electrical power input to the electrolysis plant is monitored. The entire electrolysis plant is controlled by a control unit 5, which is shown schematically. The control unit 5 is specifically designed to control the electrical supply to the electrolysis unit 1, such as the start and end of the electrolysis interruption or power supply interruption, as well as all inlet and outlet valves. The measurement data from the gas measurement system, the fill level measurement, and other state parameters are also available to the control unit 5 for processing. Other state parameters can include the concentration of dissolved hydrogen gas in the circulating electrolyte, the temperature of the electrolyte, the electrolysis current, the operating pressure p unit, and / or...or the operating temperature T unit of the at least one electrolysis unit 1, the concentration of the electrolyte for electrolysis, the mechanical stress o unit of the at least one electrolysis unit 1, the flow rate q fill through the inert gas inlet valve (10A to oxygen gas separator 2 and 10B to hydrogen gas separator 3), the flow rate q out through the gas outlet valve (11A from oxygen gas separator 2 and 11B from hydrogen gas separator 3), the pressure in the oxygen gas separator 2 and / or in the hydrogen gas separator 3, and / or the gas composition in the electrolysis unit 1, in particular the anode-side and / or cathode-side content of hydrogen gas and / or oxygen gas.

[0241] The temperature T unit of electrolysis unit 1 can be measured using a surface thermometer on a pipe of the electrolysis unit or with a weld-in thermometer in the pipe close to the electrolysis unit. For direct measurement of the electrolysis unit's temperature, the temperature of the individual cells can be measured using infrared sensors, or a thermometer can be inserted in the cell frame or directly inside the cell. Temperature monitoring and other parameters can be controlled, for example, using a PID controller.

[0242] The gas contents in electrolysis unit 1 can be determined by simulations based on the operating conditions and the geometry of the respective cell stack or cell substack that forms the electrolysis unit. Measurement is also possible by connecting a gas analysis system, similar to the gas measurement system for the hydrogen and / or oxygen gas content of the oxygen gas separator. The tension of electrolysis unit 1 can be measured, for example, with a measuring system 15 on the tensioning device, such as on at least one tie rod or tie rod 14 of the tensioning device. The tie rods or tie rods 14 are typically guided through end plates 13 at the ends of a cell stack, so that the stack is compressed between the end plates 13 and the cells in the cell stack are sealed against each other.

[0243] The control device 5 of the electrolysis plant can have or be connected to at least one user interface 16. This user interface 16 can be configured, in particular, to receive user input for standby, starting from standby, or shutting down and forward it as a command to the control device 5. The user interface can also be configured to allow a user to request a specific quantity of hydrogen gas and / or oxygen gas via the user interface 16 and / or to select the procedure for reducing the hydrogen content in the oxygen gas separator 2 from at least one list displayed via the user interface 16 and send it to the control device 5. The control device 5 can be subdivided into several control units in various embodiments.

[0244] In Figure 2A further embodiment of an electrolysis plant 600 is shown schematically. The electrolysis plant 600 is like the plant 400 from the example of the Figure 1The system is constructed in a single unit but comprises several electrolysis units 1. The electrolysis units 1 can be connected to each other by a common clamping device. However, it is also possible for each electrolysis unit 1 to be equipped with its own clamping device. The electrolysis units 1 are supplied with energy for electrolysis via a power supply. Electrolysis can be carried out independently in each electrolysis unit 1, in particular, it can be interrupted and resumed. For electrolysis, the electrolysis units 1 can also be supplied independently with electrolyte, which can be fed to the respective electrolysis unit 1 via an electrolyte inlet valve 18. The electrolyte can be pumped around in an electrolyte preparation arrangement 200 by a pump 21 and heated to a specific temperature TL by a temperature control unit 17.The electrolyte preparation arrangement 200 can also optionally include a pressure-controlled container 25 with an inert gas supply line 22.

[0245] The electrolysis units 1 are connected to the oxygen gas separator 2 via oxygen supply lines, so that oxygen produced in the anode compartments of the electrolysis units 1 during electrolysis is introduced into the oxygen gas separator. The oxygen supply lines are equipped with oxygen inlet valves 9A1 and 9A2, which can be controlled independently of each other by the control device 5. The electrolysis units 1 are also connected to the hydrogen gas separator 3 via hydrogen supply lines, so that hydrogen produced in the cathode compartments of the electrolysis units 1 during electrolysis is introduced into the hydrogen gas separator 3 along with electrolyte. The hydrogen inlet valves 9B1 and 9B2 are located on the hydrogen supply lines and can be controlled independently of each other by the control device 5.

[0246] The oxygen supply lines and electrolyte drain lines are each connected to each other via bypass lines. Bypass valves 19A1 and 19A2 are attached to the bypass lines. The electrolyte from the electrolyte drain line of the oxygen gas separator and the hydrogen gas separator is combined and then recirculated to the electrolysis units 1. Valves 24A and 24B control which of the electrolysis units 1 receives the electrolyte. Before the electrolyte is introduced into the electrolysis units 1, it can be degassed via vent valves 20A and 20B and / or heated in the electrolyte conditioning units 200 using heaters 17.

[0247] In the electrolysis plant 600 of the Figure 2For electrolysis, a potassium hydroxide solution with an increased concentration cL in the range of 25 wt% to 30 wt%, for example, in the range of 27 wt% to 30 wt%, or 30 wt%, is used. The water for electrolysis is supplied to the electrolyte in the oxygen gas separator 2. The concentration is adjusted so that the electrolyte introduced into the electrolysis unit 1 has a concentration cL.

[0248] Figure 3 The diagram shows the explosion limits of hydrogen / oxygen gas mixtures. It is taken from the publication by Volkmar Schröder, "Explosion Limits of Hydrogen and Hydrogen / Methane Mixtures," Research Report 253, published by the Federal Institute for Materials Research and Testing (BAM 2002). The diagram illustrates the pressure dependence of the explosion limits at 20°C and 80°C in the range of 1 bar to 200 bar.

[0249] The lower explosive limit (LEL) allows the determination of the respective gas concentrations for hydrogen and oxygen gas, which must be below (in the case of hydrogen gas) or above (in the case of oxygen gas) to prevent a hydrogen / oxygen reaction. For electrolysis with an operating temperature above 80°C, the values ​​can be extrapolated, or, for safety, the values ​​for 80°C can be used. Schröder's publication also describes the measurement method for determining the explosive limits at specific pressures and temperatures.

[0250] Fig. 4This shows the explosion range and explosion limits for a hydrogen / oxygen / nitrogen gas mixture according to Schröder, "Explosion Limits of Hydrogen and Hydrogen / Methane Mixtures", Research Report 253, published by the Federal Institute for Materials Research and Testing (BAM 2002). The lower explosion limit (LEL) is the limit with a lower hydrogen gas content than oxygen gas content.

[0251] Figure 5Figure 1 shows a flowchart for the standby procedure. The oxygen gas separator is referred to as the "O₂ gas separator" in this and subsequent figures. The procedure begins with the reception of a signal to interrupt the electrolysis of electrolysis unit 1, e.g., a standby command, in procedure step 100 at time tV0 = 0. In the subsequent step 102, the hydrogen gas content c(H₂) and / or the oxygen gas content c(O₂) in the oxygen gas separator is measured, which is then carried out essentially continuously or at discrete time intervals. In step 104, the measured values ​​for the hydrogen gas content c(H₂) and / or oxygen gas content c(O₂) are compared with initial threshold values ​​c1(H₂) and / or c1(O₂).In particular, it is determined whether the current hydrogen gas content c(H₂) exceeds the first threshold c₁(H₂) and / or the current oxygen gas content c(O₂) exceeds the first threshold c₁(O₂). Instead of the gas contents c(H₂) and c(O₂), a ratio of the gas contents, e.g., c(H₂) / c(O₂) or c(O₂) / c(H₂), can also be compared with a first threshold r₁ or 1 / r₁ for the ratio, in particular whether c(H₂) / c(O₂) exceeds the first threshold r₁ and / or c(O₂) / c(H₂) falls below the first threshold 1 / r₁. Alternatively or additionally, the time started in step 100 with t V0 = 0 is also compared with a first time threshold t 1, in particular whether it has reached or exceeded the first time threshold or the first time duration t 1 since t V0 = 0.

[0252] If one or more of these queries are fulfilled, i.e., answered in the affirmative, the process continues to step 106. In step 106, the hydrogen content g(H₂), in particular the hydrogen gas content c(H₂), in the oxygen gas separator is reduced. Measures to reduce the hydrogen content may include using a degassed electrolyte for electrolysis, increasing the electrolysis current I, in particular to the maximum electrolysis current Imax, reducing the operating pressure of the electrolysis unit punit and / or the operating temperature of the electrolysis unit Tunit, using an electrolyte with an increased electrolyte concentration cL, and / or lowering the electrolyte level in the oxygen gas separator.Alternatively or in addition to these measures, step 106 may also involve introducing inert gas, in particular nitrogen and / or air, into the oxygen gas separator to reduce the hydrogen content in the oxygen gas separator.

[0253] The reduction of the hydrogen content in step 106 continues until, in process step 108, the value determined for the hydrogen gas content c(H₂) is less than a second threshold c₂(H₂) and / or the value determined for the oxygen gas content c(O₂) is greater than a second threshold c₂(O₂). Alternatively or additionally, the reduction of the hydrogen content can also be carried out until a ratio of the gas contents falls below or is below a second threshold, e.g., c(H₂) / c(O₂) is less than a second threshold r₂ and / or c(O₂) / c(H₂) is greater than 1 / r₂.

[0254] In the process of Figure 5It can also be queried whether the time t started at the beginning of standby is now equal to or greater than a second time limit t₂ (step 108) and / or whether a command to terminate standby has been issued (step 110). If neither of these conditions is met, the process continues with the reduction of the hydrogen content in process step 106. If the optional query 110 indicates that standby should be terminated, the end of the standby process is initiated in process step 112. If it turns out that standby should not be terminated, an interruption of the electrolysis is initiated in step 114. The electric current I for electrolysis in electrolysis unit 1 is reduced to such an extent that no more electrolysis gas is produced in electrolysis unit 1, or the energy supply for electrolysis in electrolysis unit 1 is completely interrupted (I = 0 A).

[0255] If several electrolysis units 1 are connected to the oxygen gas separator 2, the electrolysis of all these electrolysis units is interrupted. Optionally, a temperature and / or voltage monitoring can also be initiated in step 114. An example of the procedure for such monitoring is shown in Figure 7 schematically represented. Furthermore, the gas volume Vmess and / or the sampling frequency fmess of a sample taken from the oxygen gas separator for determining the gas content can be reduced in order to maintain the pressure in the gas separator for as long as possible. This is particularly useful when no inert gas is introduced into the oxygen gas separator.

[0256] The measures for reducing the hydrogen content, in particular the hydrogen gas content c(H₂), in the oxygen gas separator in process step 106 are explained in more detail below: 1. Degassed electrolyte: The use of a degassed electrolyte can be achieved, for example, via fresh electrolyte, i.e., an electrolyte that is supplied to the electrolysis unit in addition to or instead of the electrolyte recirculated from the gas separator for electrolysis, for example, from a separate storage tank. Alternatively, it is also possible to use the electrolyte recirculated during operation and to reduce the concentration of dissolved gases in this electrolyte in a degassing unit, which can, for example, be part of the electrolyte preparation arrangement 200, without affecting the operating pressure in the electrolysis unit.The electrolysis unit 1 is isolated from the gas separators 2 and 3, valves 11A, 12A, 9A, 11B, 9B, and 12B are closed, and valves 19A and 19B are open. The electrolyte pressure is reduced via valves 19A and 19B. Degassing takes place either via a pressureless, pressure-controlled container 7 or 25 of the electrolyte preparation arrangement 200, or via the degassing valves 20A and 20B (which are connected, for example, at the highest point of a siphon). Subsequently, the electrolyte is pumped out via a dedicated pump in the pressure-controlled container or via an external pump 17. Figure 2 ) is brought back to the operating pressure of electrolysis unit 1 and flows back into it.

[0257] Alternatively, degassing can be performed only on the anolyte side. For this, valves 11A, 9A, 12A, 9B, 12B, 11B, and 19B are closed, while valve 19A is open. The electrolyte pressure is reduced via valve 19A. Degassing occurs either through the unpressurized pressure-controlled vessel or the degassing valve 20A (which, for example, is connected to a siphon). Subsequently, the electrolyte is pressurized back to the pressure of the respective electrolysis unit 1 via a dedicated pump in the pressure-controlled vessel or via pump 17 and flows back into it.

[0258] In systems with separate electrolyte circuits for the anode and cathode sides, there is inherently less electrolyte contamination by unwanted gases. In these systems, the pressure in the oxygen gas separator can be reduced independently of the operating pressure (p unit) of the electrolysis unit and the pressure in the hydrogen gas separator to degas the anode-side electrolyte (anolyte). For example, the membranes of the electrolysis cells in the electrolysis unit can be separated from the electrolyte circuit to protect them from damage caused by increased pressure differentials between the anode and cathode sides. While the use of additional separate components, such as a storage tank, separate degassing device, or separate electrolyte circuits, is more complex in design, it ensures that the operating parameters in the electrolysis unit are not affected and thus hydrogen production remains constant.

[0259] Degassed means, in particular for the dissolved hydrogen content, for alkaline electrolysis with potassium hydroxide (KOH) as the electrolyte: ≤ 6.579 × 10⁻⁶ < kg H₂ / per kilogram at 85°C, 25 wt% KOH, 35 bar (absolute), for example ≤ 6.579 × 10⁻⁶ < kg(H₂) / kg at 85°C, 25 wt% KOH, 35 bar (absolute), further for example ≤ 4.745 × 10⁻⁶ < kg(H₂) / kg at 85°C, 30 wt% KOH, 35 bar (a), for example ≤ 3.707 × 10⁻⁶ < kg(H₂) / kg at 60°C, 25 wt% KOH, 26 bar (absolute), for example ≤ 2.532 × 10⁻⁶ < kg(H₂) / kg at 60°C, 30 wt% KOH, 26 bar (absolute).

[0260] 2. Increasing the electric current for electrolysis: Another way to reduce the hydrogen content is to apply an increased electrolysis current I or even the maximum electrolysis current Imax, i.e., operating the respective electrolysis unit at full load. This increased gas production results in improved gas quality with a higher oxygen content before standby, which also reduces the hydrogen content in the oxygen gas separator. The electrolysis current Imax is typically increased relative to the electrolysis current I(tV0) at time tV0 = 0, when the signal to interrupt is received or generated, or at the start of gas content measurement. If the electrolysis plant includes several electrolysis units connected to the oxygen gas separator, the current can be increased before the electrolysis is interrupted.For standby power supply, for example, all of these electrolysis units can be operated with an increased electrolysis current I, in particular with Imax. In alkaline pressure electrolysis, the maximum electrolysis current Imax can, for example, be in the range of 5 kA to 15 kA.

[0261] 3. Reduction of operating pressure and / or operating temperature: In process step 106, the operating pressure p unit of the electrolysis unit and / or the operating temperature T unit of the electrolysis unit can also be reduced to lower the hydrogen content. These are operating parameters that lead to outgassing of the electrolyte. Reducing the operating temperature (typically to a temperature ≥70% of the maximum operating temperature for alkaline electrolysis) can generally be achieved by increased cooling, for example, by increasing the cooling water flow through heat exchangers, which lowers the process temperature of the electrolysis process.

[0262] A reduction in operating pressure can be achieved by changing a threshold value of the pressure control. For alkaline pressure electrolysis, the pressure can be reduced, for example, within a range of 25 to 34 bar gauge, e.g., to 32.5 bar gauge, 28 bar gauge, or 25 bar gauge. The oxygen can be vented from the oxygen gas separator via a blow-off valve while gas is still being produced in the electrolysis process. This is necessary because otherwise, the pressure reduction would contaminate the oxygen gas separator with outgassing hydrogen.

[0263] In electrolysis plants where multiple electrolysis units are connected to the oxygen gas separator, the operating pressure p unit is reduced to the same pressure in all electrolysis units that are in electrolysis operation and whose power supply is therefore not interrupted. Electrolysis units that are not in electrolysis operation and whose power supply or electrolysis is therefore interrupted are shut off from the oxygen gas separator, and in the case of hydraulically coupled gas separators, also from the hydrogen gas separator. For this purpose, the oxygen inlet valve 9A and, for example, the hydrogen inlet valve 9B are closed.

[0264] 4. Increasing the electrolyte concentration cL: An increased electrolyte concentration cL can be set before the electrolysis unit is put into operation. For example, in alkaline electrolysis with KOH as the electrolyte, a concentration range of 25 to 30 wt%, e.g., 27 wt%, e.g., 30 wt%, can be set so that the electrolyte concentration is already increased when the power supply is switched off, regardless of any standby demand. This can be achieved by filling the electrolysis unit and the associated system with an electrolyte at the selected concentration cL before commissioning.

[0265] Alternatively or additionally, the electrolyte concentration can be increased during standby operation before the electrolysis process is shut down or interrupted. This can be achieved by adding less or no distilled / deionized water to the recirculated electrolyte during electrolyte preparation. This water would normally replace the water consumed during electrolysis. Furthermore, an alkali salt or an electrolyte with a higher concentration can be added, thus increasing the concentration to c L. When using degassed electrolyte, for example, the degassed electrolyte from the storage tank can have a higher concentration, or the electrolyte concentration can be increased during degassing in a degassing unit.

[0266] 5. Level Reduction in the Oxygen Gas Separator: As a measure in process step 106, the electrolyte level in the oxygen gas separator can also be reduced. This reduction is relative to the level of the oxygen gas separator during normal operation, particularly at time tV0 = 0. For hydraulically coupled gas separators, the shuttle lines should be connected as low as possible to the respective separator vessel, for example, at the lowest point of the separation chamber between the oxygen and hydrogen gas separators. This allows for very large level differences between the oxygen and hydrogen gas separators by controlling the withdrawal rates from the gas separators, thus generating the largest possible gas volumes in the oxygen gas separator and preventing the electrolysis gases from mixing due to insufficient levels.

[0267] If the oxygen gas separator 2 is hydraulically connected to the hydrogen gas separator 3, the fill level can be lowered, for example, by reducing the flow rate of oxygen gas from the oxygen gas separator 2. The flow rate can be controlled via the gas outlet valve 11A on the oxygen gas separator. Alternatively or additionally, more hydrogen gas can be drawn from the hydrogen gas separator 3. The flow rate can be controlled via a gas outlet valve 11B on the hydrogen gas separator. If the oxygen gas separator 2 and the hydrogen gas separator 3 are not hydraulically coupled, the fill levels can be adjusted by controlling the flow rate of electrolyte from the gas separators 2 and 3.To lower the fill level in the oxygen gas separator 2, for example, more electrolyte can be removed from the oxygen gas separator 2 than in normal operation, so that there is a larger gas volume than electrolyte volume in the oxygen gas separator 2.

[0268] 6. Introducing inert gas: As an alternative or in addition to one or more of the described measures M i (i=1,2,3...), inert gas can also be introduced into the oxygen gas separator in step 106 to reduce the hydrogen content, for example, using a stepwise or continuous flow process. Once inert gas is introduced into the oxygen gas separator to reduce the hydrogen content, the previously described measures are only carried out depending on the threshold values ​​for the hydrogen gas content c(H 2 ), since the oxygen gas content in the gas separator decreases instead of increasing. A hydrogen-free gas, such as nitrogen or air, can be used as the inert gas.

[0269] In the stepwise process, inert gas is first introduced into the oxygen gas separator 2 via the inert gas inlet valve 10A. The gas outlet valve 11A and the oxygen inlet valve 9A are closed during this step. With hydraulically coupled gas separators, e.g., via a shuttle line, the liquid level in the oxygen gas separator decreases and the liquid level in the hydrogen gas separator increases. With a hydraulically decoupled (self-contained) oxygen gas separator, the electrolyte level remains constant, and the pressure in the oxygen gas separator increases, but not beyond the pressure limit of the separator vessel.In the second step, the gas outlet valve 11A of the oxygen gas separator is opened, allowing the inert gas / oxygen mixture to flow towards the discharge line until the fill level in the oxygen gas separator has risen to a defined limit or a defined pressure in the oxygen gas separator has been reached, in particular a pressure not less than 70% of the operating pressure, for example, not less than 85% or not less than 90% of the operating pressure. The process is then repeated until, depending on the pressure and volume in the gas separator, a certain threshold c₂(H₂) for the hydrogen gas content, for example, 2 vol%, is reached. For the second step, the inert gas inflow rate can be reduced or, for example, the inert gas inflow can be interrupted. In contrast to the stepwise method, the gas outlet valve 11A remains continuously open in the flow-through method.

[0270] For both processes, the fill level in the oxygen gas separator 2 can be raised before the inert gas is introduced to reduce inert gas consumption. In hydraulically coupled gas separators 2, 3, this can be achieved, for example, by increasing the oxygen gas outflow rate qout from the oxygen gas separator 2 and / or by decreasing the hydrogen gas outflow rate from the hydrogen gas separator 3. In the flow-through process, the fill level can also be raised during introduction by reducing the gas outflow rate qout from the oxygen gas separator 2 relative to the inert gas inflow rate qfil. In self-contained gas separators, the fill level in the oxygen gas separator 2 can be raised by adding electrolyte or water from an external source into the oxygen gas separator.

[0271] In the example of the Figure 5In process step 106, one or more of the described measures are carried out simultaneously to reduce the hydrogen content. This means that the threshold values ​​c1 (H2), c2 (H2), c1 (O2), c2 (O2), r1, r2, and / or the time parameters t1, t2 are the threshold values ​​or time parameters for all measures to be carried out. For example, only those measures are carried out in which no inert gas is introduced into the oxygen gas separator. For instance, the only measures that can be carried out simultaneously are electrolysis with an increased electrolysis current I and an increased electrolyte concentration cL, as well as an increase in the fill level.

[0272] Which measure is implemented and whether an inert gas injection takes place is already determined in step 100, for example, due to user or system requirements, or is determined in step 105 after a threshold value has been exceeded or fallen below, depending on at least one currently determined state parameter of the electrolysis plant, in particular a state parameter of electrolysis unit 1. Due to the limited parameter set of threshold values ​​c1 (H2), c2 (H2), c1 (O2), c2 (O2), r1, r2 and / or time parameters t1, t2, the standby process can react quickly to changes in the hydrogen content in the oxygen gas separator.

[0273] In the Figure 6An embodiment is shown in which, in process step 106, one or more measures M i for reducing the hydrogen content can be carried out sequentially and / or at least partially simultaneously. For this purpose, each measure M i (i=1, 2, 3...) is assigned sets (k=1, 2, 3...) of its own first and second threshold values ​​and / or first and second time parameters. The index i denotes the same measure, and the index k denotes the k-th execution of measure M i.

[0274] In step 104, the currently recorded values ​​of the gas contents c(H₂) and c(O₂) are compared with first threshold values ​​cMik_1(H₂) and / or cMik_1(O₂) of a set k for the respective measure Mi. In step 108, the currently determined values ​​of the gas contents are compared with second threshold values ​​cMik_2(H₂) and / or cMik_2(O₂) of the set k for the respective measure Mi. Alternatively, in steps 104 and / or 108, ratios of the gas contents, e.g., c(H₂) / c(O₂) or c(O₂) / c(H₂), can also be compared with first or second threshold values ​​for the ratios rMik_1, rMik_2, or 1 / rMik_1, 1 / rMik_2, respectively. In steps 106 and / or 108, alternatively or additionally to the threshold values ​​for the gas contents or their ratios, first time parameters t Mik_1 for a measure M i and second time parameters t Mik_2 for a measure M i may be provided for the measures M i.

[0275] The respective measures Mi can be implemented depending on the threshold values ​​of the gas concentrations, their ratio, and / or the time parameters. For example, they can be implemented when values ​​for the gas concentrations c(H2) and / or c(O2) are recorded that lie within the interval [cMik_1(H2), cMik_2(H2)] or [cMik_1(O2), cMik_2(O2)]. Alternatively, the measures Mi can be implemented within the time interval [tMik_1(H2), tMik_2(H2)]. The duration of this time interval is chosen such that the respective threshold value cMik_2(H2) and / or cMik_2(O2) is reached when time tMik_2(H2) is reached.In another alternative, the measures M i are initiated when the first threshold c Mik_1 (H 2 ) for the hydrogen gas content c(H 2 ) is exceeded in the time interval [t Mik_1 (H 2 ), t Mik_2 (H 2 )] and / or the first threshold c Mik_1 (O 2 ) for the oxygen gas content c(O 2 ) is undershot. The measures are carried out until their second time parameter or point t Mik_2 is reached and the hydrogen gas content c(H 2 ) has undershot the second threshold c Mik_2 (H 2 ) and / or the oxygen gas content c(O 2 ) has exceeded the first threshold c Mik_2 (O 2 ).

[0276] The threshold values ​​for gas concentrations and / or time parameters define a sequence and thus a prioritization of the measures M i. This sequence, along with the selection of measures to be implemented, allows for the optimized operation of the electrolysis plant for specific operating modes. The selection and sequence of measures M i can be determined by the control device and / or user input. For example, one or more measures can be implemented exclusively or with priority, ensuring that the hydrogen production rate does not decrease and / or that no inert gas injection is necessary. E.g.: Use of degassed electrolyte; increase of the electrolysis current I, in particular to the maximum electrolysis current I max; use of an electrolyte with increased concentration c L and / or increase of the electrolyte concentration to c L; reduction of the fill level in the oxygen gas separator.

[0277] In Figure 7Figure 1 illustrates an embodiment of the standby procedure, in which the procedure is carried out with particular time efficiency. A measure Mi is initiated whenever the first threshold cMik_1(H2) is exceeded within the time interval [tMik_1(H2), tMik_2(H2)] and / or the first threshold cMik_1(O2) is undershot. The measure is carried out until the hydrogen gas content c(H2) falls below the second threshold cMik_2(H2) and / or the oxygen gas content c(O2) exceeds the first threshold cMik_2(O2). If this occurs before the second time parameter or point tMik_2 is reached, the procedure continues with newly calculated time parameters (step 116) without waiting for the time to elapse until the second time parameter tMik_2 is reached.If the second threshold values ​​for gas content are not reached by the second time point, an error message can be issued and / or another / further measure can be initiated as a support measure.

[0278] Figure 8 shows a procedural excerpt of the procedure of Figures 5 to 7, in which temperature and / or stress monitoring is performed. During or after an interruption, the operating temperature Tunit and / or the mechanical stress ounit of at least one electrolysis unit is detected. Upon reaching or falling below a critical temperature Tcrit and / or stress ocrit, the electrolysis unit is heated until the detected temperature Tunit is greater than the critical temperature Tcrit and / or the detected mechanical stress ounit is greater than the critical stress ocrit. The critical stress ocrit can, in particular, correspond to the stress at the critical temperature Tcrit. The stress can be detected at the tensioning device of the electrolysis unit. It can be measured, for example, with stress sensors on tension rods or anchors of the tensioning device, for instance, in the longitudinal direction of a cell stack or cell sub-stack of the electrolysis unit.

[0279] When the critical temperature Tcrit and / or stress ocrit of the electrolysis unit is reached or falls below the critical temperature Tcrit, heating of the electrolysis unit is initiated. For this heating, electrolyte with a temperature TL > Tcrit is circulated through the electrolysis unit. The electrolyte is circulated through the bypass line of the respective electrolysis unit with the bypass valve 19A open. The oxygen supply valve 12A and the electrolyte drain valves 9A are closed. The temperature TL of the circulated electrolyte can be set in an electrolyte conditioning device 7 or a temperature control unit 17.

[0280] In Figure 9 This shows the continuation of the standby process after the interruption of electrolysis or the power supply.

[0281] By choosing the threshold values ​​c 3 (H 2 ) and c 3 (O 2 ) in comparison to the critical threshold values ​​c Mik_2 (H 2 ) and c Mik_2 (O 2 ), two different scenarios can be created for gas exchange with inert gas after the interruption of electrolysis or energy supply: Scenario 1:The third threshold values ​​c3(H2) and c3(O2) are chosen to be equal to or less stringent than the second threshold values ​​cMik_2(H2) and cMik_2(O2), in particular c3(H2) ≥ |cMik_2(H2)|max and / or c3(O2) ≤ |cMik_2(O2)|min. In this scenario, the gas quality is improved before the interruption of electrolysis or the power supply to such an extent that, during standby, inert gas is only introduced into the oxygen gas separator if the gas quality deteriorates during standby, after the interruption of electrolysis or the power supply, to such an extent that the gas concentrations c(H2) > c3(H2) or c(O2) < c3(O2). It is therefore possible for standby mode to occur even without the introduction of inert gas. Example values ​​are |c Mik_2 (H 2 )| max ≤ 1 vol.-% and |c Mik_2 (H 2 )| max ≤ c 3 (H 2 ) ≤ 2 vol.-%.

[0282] Scenario 2In the second scenario, the third threshold values ​​c3(H2), c3(O2) are chosen more strictly than the second threshold values ​​cMik_2(H2), cMik_2(O2), i.e., c3(H2) < |cMik_2(H2)|min and / or c3(O2) > |cMik_2(O2)|max. The gas quality is improved by the measures already explained above, but gas exchange with inert gas still occurs after the electrolysis or energy supply is shut down. However, the measures can improve the gas quality to such an extent that less inert gas is consumed.

[0283] The two procedures described above also result from the flowchart according to Figure 9In step 120, the interruption of the electrolysis or energy supply is triggered at time t = t N0 = 0. Simultaneously, temperature and / or voltage monitoring is started. In query 122, the measured hydrogen gas content c(H₂) and / or oxygen gas content c(O₂) are compared with the third threshold values ​​c₃(H₂) and c₃(O₂), and / or the elapsed time is compared with a specific time duration t₃. If the hydrogen gas content exceeds the third threshold c 3 (H 2 ) and / or the oxygen gas content falls below the corresponding third threshold c 3 (O 2 ), then a continuous or stepwise introduction of inert gas into the oxygen gas separator takes place until the detected hydrogen gas content c(H 2 ) is less than a fourth threshold c 4 (H 2 ), the detected oxygen gas content c(O 2 ) is less than a fourth threshold c 4 (O 2 ) and / or a fourth time period t 4 is reached.As an alternative to the threshold values ​​c 4 (H 2 ), c ​​4 (O 2 ) and / or the time parameter t 4 , the content of inert gas can also be measured and the introduction of inert gas can be carried out until a threshold value for the inert gas content c 4 (Inert) in the oxygen gas separator is reached or exceeded.

[0284] Depending on the choice of the second threshold values ​​c Mik_2 (H 2 ) and c Mik_2 (O 2 ) of the measures M i before the interruption of electrolysis or energy supply, the following sequence of steps can occur in Figure 5 result: Scenario 1: 122, 128 Scenario 2: 122, 124, 126, 128.

[0285] Whether or not an inert gas purge takes place in step 124 also depends on the absolute values ​​of the threshold values ​​c Mik_2 (H 2 ) and c Mik_2 (O 2 ).

[0286] Step 128 checks whether a request to end standby mode exists. If so, a procedure to end standby mode is initiated in step 130.

[0287] The end of standby operation in process step 130 is initiated by receiving a command to terminate standby operation. This command can be, for example, a command to start up at least one electrolysis unit, a command to shut down the electrolysis plant, or a command for an emergency shutdown. The commands can be triggered by the operator or user of the electrolysis plant and / or dependent on an external power supply (wind turbine, solar park, electricity provider, etc.) and / or generated by the control device 5 based on measured and / or calculated state parameters of the electrolysis plant or by time parameters.

[0288] In a system where multiple electrolysis units are connected to the oxygen gas separator, restarting from standby mode can be performed for individual electrolysis units or for groups of electrolysis units. A restart can be initiated for various reasons. At least one electrolysis unit can be restarted when a critical state is reached within that electrolysis unit, when a critical state of the oxygen gas separator is reached, and / or when a specific time period has elapsed. This time period can be, in particular, the shortest time within which an electrolysis unit reaches a critical state. In normal operation, it can be determined from the interruption of electrolysis or the interruption of the power supply to the electrolysis unit; in standby mode, from the beginning of standby, e.g., from the receipt of the signal to interrupt operation or from the start of gas content measurement in the oxygen gas separator for standby.

[0289] A critical state in an electrolysis unit can occur, for example, if the pressure punit, temperature Tunit, and / or voltage ounit of the electrolysis unit decreases faster than a critical rate and / or reaches or falls below a critical value pcrit, Tcrit, or ocrit, respectively. A critical state can also be caused by a gas composition in the electrolysis unit that poses an increased risk of hydrogen explosion.A critical gas composition may exist, for example, if the anode-side hydrogen gas content cano(H2) in an electrolysis unit reaches or exceeds a certain value ccrit_ano(H2), if the anode-side oxygen gas content cano(O2) in an electrolysis unit reaches or falls below a certain value ccrit_ano(O2), if the cathode-side hydrogen gas content ckato(H2) in an electrolysis unit reaches or falls below a certain value ccrit_kato(H2), and / or if the cathode-side oxygen gas content ckato(O2) in an electrolysis unit reaches or exceeds a certain value ccrit_kato(O2).

[0290] A critical state of the oxygen gas separator can occur, for example, when a critical hydrogen gas concentration ccrit (H2) in the oxygen gas separator is exceeded, or when a critical temperature TGScrit and / or the critical pressure pcrit in the oxygen gas separator is reached or falls below a critical level. If no inert gas is or has been introduced into the oxygen gas separator, a critical state can also occur when the oxygen gas concentration ccrit (O2) in the oxygen gas separator falls below a critical level. In electrolysis plants with multiple electrolysis units, it may be sufficient to start up one of the electrolysis units to resolve the critical state. The selection of which electrolysis unit should be started up can be determined, for example, as in alternating operation of the Figure 11This can occur (setpoint x=1 at n=0). However, several electrolysis units can also be started up (setpoint x>1 at n=0), for example, if an overproduction of electrolysis gases is acceptable or to end the critical state of the oxygen gas separator as quickly and safely as possible.

[0291] Another reason for starting up a system can be an increase in the number of electrolysis units required. Such a change can occur, for example, when hydrogen production is needed again and / or when electrical power is available for electrolysis. The target value for the number of electrolysis units to be started up can be determined by or stored in the control device. The selection of which electrolysis unit(s) should be started up can be configured, for example, as in alternating operation. Figure 11 This occurs (target value x>0 at n=0).

[0292] In any case, it is important that the respective electrolysis unit is started up quickly and safely.

[0293] In Figure 10 The diagram schematically illustrates the start-up process. For safe start-up, at least one electrolysis unit is started with an increased electrolysis current ramp. The increased electrolysis current ramp means that the electrolysis current is higher compared to a pressureless start-up, which typically has a ramp gradient of <0.5 Imax % / s. A rapid start-up with a steeper ramp, e.g., ≥0.6% Imax / s, ≥2% Imax / s, ≥10% Imax / s, or ≥15% Imax / s, enables a rapid improvement in gas quality in the oxygen gas separator.

[0294] The steep electrolysis current ramp can be maintained until a specific electrolysis current is reached. This electrolysis current can be a current suitable for operating the electrolysis unit at partial load, particularly when insufficient power is available for full-load operation, or a maximum electrolysis current (Imax) suitable for full-load operation. Preferably, after start-up, the at least one electrolysis unit is operated at maximum electrolysis current (Imax) for at least a certain period of time in order to produce as much oxygen as possible and introduce it into the oxygen gas separator, thereby improving the gas quality in the electrolysis unit and the oxygen gas separator as quickly as possible.Alternatively or additionally, a faster improvement in gas quality can also be achieved by starting the electrolysis current not with an initial current of 0 A, but with an initial electrolysis current of I0 > 0 A, for example, I0 ≥ 10%, I0 ≥ 20%, or I0 ≥ 30% of the maximum electrolysis current Imax. The initial electrolysis current I0 can, for example, be an electrolysis current at which electrolysis takes place, i.e., electrolysis gas is formed.

[0295] Furthermore, the safety of the start-up process can be improved by lowering the electrolyte level in the oxygen gas separator. This reduces the risk of an oxyhydrogen reaction because, firstly, there is a smaller volume of liquid from which hydrogen can escape, and secondly, there is a larger volume of gas in which the escaping hydrogen is diluted. The electrolyte level can be lowered to such an extent that, during start-up, there is a smaller volume of liquid than gas in the oxygen gas separator. This is particularly useful when starting up a large number of electrolysis units or all of the electrolysis units connected to the oxygen gas separator.

[0296] As a further measure for rapid start-up, the thresholds for emergency shutdown can be adjusted so that they are less stringent than during normal operation and / or during an interruption of electrolysis or the power supply. This means that the threshold for the hydrogen gas content c STOP (H₂) during start-up is higher than during normal operation and / or during an interruption of electrolysis or the power supply, and the threshold c STOP (O₂) for the oxygen gas content is correspondingly lower, provided no inert gas has been introduced into the gas separator. For example, in pressure alkaline electrolysis at 30 bar, a value ≥4 vol.% for c STOP (H₂) and / or a value ≤ 96 vol.% for c STOP (O₂) can be chosen. However, the thresholds are set below the lower explosive limit (see [reference]). Figure 2 The adjusted threshold values ​​help avoid unnecessary emergency shutdowns.

[0297] If the gas volume V and / or the sampling frequency f for taking samples from the oxygen gas separator to determine the gas contents c(H 2 ), c(O 2 ) and / or c(Inert) were reduced for standby, these can now be increased again when starting up.

[0298] In Figure 11 The diagram schematically illustrates how, when the number of electrolysis units required for operation changes, it can be selected for which electrolysis unit the electrolysis or power supply is interrupted, and for which electrolysis unit this interruption is ended, i.e., a restart occurs. This alternating operation (alternating operation 2) can be carried out before standby in normal operation to keep the electrolysis units in sufficiently good condition to ensure a safe standby mode for a certain period.

[0299] The first step is to determine whether standby mode should be initiated. This involves checking whether any electrolysis units are still operating (actual value n>0) and whether the number of electrolysis units to be operated is zero (target value x=0). If these conditions are met, standby mode is initiated, for example, in response to receiving the interrupt signal, and the standby procedure is executed.

[0300] Otherwise, in a second step, it is determined whether the requested number x of electrolysis units is less than the number n of electrolysis units currently operating. This can be done, for example, in the control device. If more electrolysis units n are operating than the requested x, the electrolysis or energy supply is interrupted for the difference (nx) of electrolysis units; otherwise, a command to start is issued for the difference of (xn) electrolysis units. The electrolysis or energy supply is then interrupted in each case.The power supply is interrupted in those electrolysis units that operate with a high or the highest electrolysis current I, a high or the highest temperature T unit, a high or the highest pressure p unit, a high or the highest voltage o unit, a high or the highest anode-side oxygen gas content c ano (O 2 ), a high or the highest cathode-side hydrogen gas content c kato (H 2 ), a low or the lowest anode-side hydrogen gas content c ano (H 2 ), and / or a low or the lowest cathode-side oxygen gas content c kato (O 2 ). High or low values ​​can be values ​​that meet at least a threshold value, which e.g. B. p W2_off , T W2_off , o W2_off , c W2ano_off (O 2 ), c ​​W2kato_off (H 2 ) reach or exceed and / or c W2ano_off (H 2 ) c W2kato_off (O 2 ) reach or fall below.

[0301] During start-up, the electrolysis units in an unfavorable condition can be started first. These can be electrolysis units exhibiting, for example, a low or the lowest temperature (T unit), a low or the lowest pressure (p unit), a low or the lowest voltage (o unit), a low or the lowest anode-side oxygen gas content (cano(O2), a low or the lowest cathode-side hydrogen gas content (ckato(H2), a high or the highest anode-side hydrogen gas content (cano(H2), and / or a high or the highest cathode-side oxygen gas content (ckato(O2). High or low values ​​can be those that meet at least one threshold value, e.g.,... B. p W2_on , T W2_on , o W2_on , c W2ano_on (O 2 ), c ​​W2kato_on (H 2 ) reach or fall below and / or c W2ano_on (H 2 ) reach or exceed c W2kato_on (O 2 ).Instead of threshold values ​​for interrupting the electrolysis or energy supply, a time period can also be reached which is determined in such a way that the respective threshold value in the electrolysis unit is reached, exceeded, or fallen below.

[0302] By performing the changeover with only a number of electrolysis units corresponding to the difference (nx) or (xn) between the n requested electrolysis units and the x electrolysis units currently operating, the changeover can be carried out very quickly. Alternatively, the changeover can be performed by identifying, from the total number of electrolysis units connected to the oxygen gas separator, n electrolysis units that are in an unfavorable state and then switching to those electrolysis units whose electrolysis is still interrupted.

[0303] The in Figure 11The described selection procedure for starting up can also be applied when an electrolysis unit reaches a critical state and needs to be started up. This can be a start-up from standby (n=0) or a start-up in normal operation (n>0), in which, instead of the electrolysis unit switching to electrolysis operation, the electrolysis or energy supply of another electrolysis unit is interrupted. In this alternating operation, in which one electrolysis unit is started up and the electrolysis or energy supply of another electrolysis unit is interrupted (alternating operation 1), the number of electrolysis units in electrolysis operation remains constant. Furthermore, the electrolysis gas production can also remain constant, as the electrolysis unit being started up produces electrolysis gas with the same electrolysis gas flow rate as the electrolysis unit whose electrolysis or energy supply is interrupted.The power supply is interrupted.

[0304] For alternating operation 1, the same threshold values ​​of the state parameters can be chosen as for alternating operation 2, or separate threshold values ​​can be set, in particular stricter threshold values: p W 1 _on > p W 2 _on , T W 1 _on > T W 2 _on , c W 1 ano_on O 2 > c W 2 ano_on O 2 , c W 1 kato_on H 2 > c W 2 kato_on H 2 , c W 1 ano_on H 2 < c W 2 ano_on H 2 und / oder c W 2 kato_on O 2 < c W 2 kato_on O 2 .

[0305] The threshold values ​​can also be chosen to be stricter than a critical threshold for starting up the electrolysis unit during standby. p W 1 _on > p krit , T W 1 _on > T krit , c W 1 ano_on H 2 < c krit_ano H 2 , c W 1 ano_on O 2 > c krit_ano O 2 , c W 1 kato_on H 2 > c krit_kato H 2 und / oder c W 1 kato_on O 2 < c krit_kato O 2 bzw . p W 2 _on > p krit , T W 2 _on > T krit , c W 2 ano_on H 2 < c krit_ano H 2 , c W 2 ano_on O 2 > c krit_ano O 2 , c W 2 kato_on H 2 > c krit_kato H 2 und / oder c W 2 kato_on O 2 < c krit_kato O 2 .

[0306] This ensures that the electrolysis units are kept in such good condition during normal operation that they do not need to be started up immediately when in standby mode, but can instead be safely maintained for a certain period. This is particularly beneficial for electrolysis plants with multiple electrolysis units, where the electrolysis or power supply to individual units may be interrupted during normal operation (partial load operation). For electrolysis plants with only a single electrolysis unit connected to the oxygen gas separator, alternating operation is not possible. In these cases, standby mode can be safely maintained primarily due to measures taken to reduce the hydrogen content (g(H₂)).

[0307] For example, the electrolysis system includes electrolysis unit 1 and oxygen gas separator 2 for separating oxygen gas and electrolyte. For example, electrolysis unit 1 is connected to power supply terminal 4 for the energy supply E for electrolysis in electrolysis unit 1.

[0308] The procedure for a standby mode of an electrolysis system 400, 600 includes, for example: Determining a hydrogen gas content c(H₂) in the oxygen gas separator and / or an oxygen gas content c(O₂) in the oxygen gas separator 2, receiving a signal to interrupt the electrolysis of electrolysis unit 1 for standby, lowering the hydrogen content g(H₂) in the oxygen gas separator 2 in response to the signal to interrupt depending on the hydrogen gas content c(H₂) in the oxygen gas separator 2 and / or depending on the oxygen gas content c(O₂) in the oxygen gas separator 2.

[0309] For example, the process includes lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2, such that the hydrogen gas content c(H 2 ) in the oxygen gas separator 2 and / or the oxygen gas content c(O 2 ) in the oxygen gas separator 2 are outside a range for an oxyhydrogen reaction.

[0310] For example, the procedure includes interrupting the electrolysis in electrolysis unit 1 in response to the signal to interrupt the electrolysis.

[0311] For example, the procedure includes blocking a fluid connection between the electrolysis unit 1 and the oxygen gas separator 2 in response to the signal to interrupt electrolysis.

[0312] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 involves introducing a degassed electrolyte into the electrolysis unit 1.

[0313] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 before interrupting electrolysis in the electrolysis unit 1 involves reducing an operating temperature T unit in the electrolysis unit 1.

[0314] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 before interrupting electrolysis in the electrolysis unit 1 involves reducing an operating pressure p unit in the electrolysis unit 1.

[0315] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 before interrupting electrolysis in the electrolysis unit 1 includes operating the electrolysis in the electrolysis unit 1 with an electrolyte having a concentration c L of dissolved alkali salt of at least 25 wt.%.

[0316] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 before interrupting electrolysis in the electrolysis unit 1 involves reducing a volume of the electrolyte in the oxygen gas separator 2.

[0317] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 before interrupting electrolysis in the electrolysis unit 1 includes increasing an electric electrolysis current I for the electrolysis in the electrolysis unit 1 and / or operating the electrolysis in the electrolysis unit 1 with a maximum electrolysis current I max .

[0318] For example, lowering the hydrogen content g(H 2 ) in the oxygen gas separator 2 involves introducing an inert gas into the oxygen gas separator 2.

[0319] For example, the introduction of the inert gas is carried out in a step-by-step process.

[0320] For example, the introduction of the inert gas is carried out using a flow-through process.

[0321] For example, the procedure includes increasing the electrolyte level in the oxygen gas separator 2.

[0322] For example, the procedure includes: Providing a temperature threshold Tcrit for electrolysis unit 1, after interrupting electrolysis in electrolysis unit 1, determining an operating temperature Tunit of electrolysis unit 1, comparing the determined operating temperature Tunit with the temperature threshold Tcrit, and if the determined operating temperature Tunit is equal to or less than the temperature threshold Tcrit: increasing the operating temperature of the electrolysis unit Tunit.

[0323] For example, the procedure includes: Providing a stress threshold ocrit for electrolysis unit 1, after interrupting electrolysis in electrolysis unit 1, determining a mechanical stress ounit of electrolysis unit 1, comparing the determined stress ounit with the stress threshold ocrit, and if the determined stress ounit is equal to or less than the stress threshold ocrit: increasing the operating temperature Tunit of electrolysis unit 1.

[0324] For example, the procedure includes: Providing a pressure threshold for electrolysis unit 1, after interrupting electrolysis in electrolysis unit 1, determining a pressure p unit in electrolysis unit 1, comparing the determined pressure p unit with the pressure threshold, and if the determined pressure p unit is less than or equal to the stress threshold o crit: increasing the pressure p unit in electrolysis unit 1.

[0325] For example, the method for operating the electrolysis plant 400, 600 includes receiving a control signal to terminate an interruption of the electrolysis of electrolysis unit 1 while the electrolysis in electrolysis unit 1 is interrupted.

[0326] For example, the procedure includes: Providing a pressure threshold pcrit for electrolysis unit 1, determining a pressure punit in electrolysis unit 1, comparing the determined pressure punit with the pressure threshold pcrit, and if the determined pressure punit is less than or equal to the pressure threshold pcrit: sending the control signal.

[0327] For example, the procedure includes: Providing a temperature threshold Tcrit for electrolysis unit 1, determining an operating temperature Tunit of electrolysis unit 1, comparing the determined operating temperature Tunit with the temperature threshold Tcrit, and if the determined operating temperature Tunit is equal to or less than the temperature threshold Tcrit: sending the control signal.

[0328] For example, the procedure includes: Providing a stress threshold o crit for electrolysis unit 1, determining a mechanical stress o unit of electrolysis unit 1, comparing the determined stress o unit with the stress threshold o crit, and if the determined stress o unit is equal to or less than the stress threshold o crit: sending the control signal.

[0329] For example, the procedure includes: Providing one or more threshold values ​​from: an anode hydrogen threshold ccrit_ano(H2), an anode oxygen threshold ccrit_ano(O2), a cathode hydrogen threshold ccrit_kato(H2), and a cathode oxygen threshold ccrit_kato(O2); sending the control signal when an anode-side hydrogen gas content cano(H2) in electrolysis unit 1 is equal to or greater than the anode hydrogen threshold ccrit_ano(H2); when an anode-side oxygen gas content cano(O2) in electrolysis unit 1 is equal to or less than the anode oxygen threshold ccrit_ano(O2); when a cathode-side hydrogen gas content ckato(H2) in electrolysis unit 1 is equal to or less than the anode oxygen threshold ccrit_ano(O2). (1) equal to or less than the cathode hydrogen threshold ccrit_cato(H2),and / or if the cathode-side oxygen gas content c kato (O 2 ) in electrolysis unit 1 is equal to or greater than the cathode oxygen threshold c krit_kato (O 2 ).

[0330] For example, the procedure includes: Sending the control signal after a time period predefined such that an anode-side hydrogen gas content cano(H2) in electrolysis unit 1 is equal to or greater than an anode hydrogen threshold ccrit_ano(H2), if an anode-side oxygen gas content cano(O2) in electrolysis unit 1 is equal to or less than an anode oxygen threshold ccrit_ano(O2), if a cathode-side hydrogen gas content ckato(H2) in electrolysis unit 1 is equal to or less than a cathode hydrogen threshold ccrit_kato(H2), if a cathode-side oxygen gas content ckato(O2) in electrolysis unit 1 is equal to or greater than a cathode oxygen threshold ccrit_kato(O2). and / or a critical temperature Tcrit and / or a critical pressure pcrit in the electrolysis unit 1 is reached or falls below a certain level.

[0331] For example, the procedure includes: Providing one or more threshold values ​​from: a hydrogen threshold ccrit(H2), a ratio threshold rcrit, and an oxygen threshold ccrit(O2) for the gas content in the oxygen gas separator 2; sending the control signal when a hydrogen gas content c(H2) in the oxygen gas separator 2 is greater than the hydrogen threshold ccrit(H2), a ratio of hydrogen gas content c(H2) to oxygen gas content c(O2) in the oxygen gas separator 2 is greater than the ratio threshold rcrit, an oxygen gas content c(O2) in the oxygen gas separator 2 is less than the oxygen threshold ccrit(O2), and / or a ratio of oxygen gas content c(O2) to hydrogen gas content c(H2) in the oxygen gas separator 2. 2 is smaller than the reciprocal of the ratio threshold r crit .

[0332] For example, the method includes providing the threshold or several thresholds for the gas content such that the gas content is outside a range for an oxyhydrogen reaction.

[0333] For example, the procedure includes: Sending the control signal after a predetermined time period, which is set such that a hydrogen gas content c(H 2 ) in the oxygen gas separator 2 is not greater than the hydrogen threshold c krit (H 2 ), a ratio of hydrogen gas content c(H 2 ) to oxygen gas content c(O 2 ) in the oxygen gas separator 2 is not greater than the ratio threshold r krit , an oxygen gas content c(O 2 ) in the oxygen gas separator 2 is not less than the oxygen threshold c krit (O 2 ), and / or a ratio of an oxygen gas content c(O 2 ) to a hydrogen gas content c(H 2 ) in the oxygen gas separator 2 is not less than the reciprocal of the ratio threshold r krit .

[0334] For example, the method includes operating the electrolysis unit 1 with an electric current I in response to receiving the control signal, wherein the electric current I has a greater increase per unit of time than during the initial start-up of the electrolysis unit 1.

[0335] For example, the method includes operating the electrolysis unit 1 with an electric current I in response to receiving the control signal, wherein the electric current I corresponds to a maximum electrolysis current I max.

[0336] For example, the method includes operating the electrolysis unit 1 with an electric current I in response to receiving the control signal, wherein the electric current I is increased from a starting value I 0, where the starting value I 0 is greater than zero amperes.

[0337] For example, a procedure for a standby of the electrolysis system includes 400, 600: Receiving a signal to interrupt the electrolysis of electrolysis unit 1 for standby, lowering the hydrogen content g(H₂) in the oxygen gas separator 2 in response to the interruption signal when a first threshold c₁(H₂), cₐMi₁(H₂) for a hydrogen gas content in the oxygen gas separator 2 is exceeded, when a first threshold for an oxygen gas content c₁(O₂), cₐMi₁(O₂) in the oxygen gas separator 2 is undershot, when a predetermined first time (t₁) is reached, when a first threshold r₁, rₐMi₁ for a ratio c(H₂) / c(O₂) of hydrogen gas content to oxygen gas content in the oxygen gas separator 2 is exceeded, and / or when a first threshold 1 / r₁, 1 / rₐMi₁ for a ratio c(O 2 ) / c(H 2 ) of oxygen gas content to hydrogen gas content in oxygen gas separator 2 is undershot, and then the electrolysis of electrolysis unit 1 is interrupted.

[0338] For example, the procedure includes: Lowering the hydrogen content g(H₂) in the oxygen gas separator 2 in response to the signal to interrupt until a second threshold c₂(H₂), cₐMi₂(H₂) for the hydrogen content in the oxygen gas separator 2 is undershot, until a second threshold c₂(O₂), cₐMi₂(O₂) for the oxygen gas content in the oxygen gas separator 2 is exceeded, until a predetermined second time t₂ is reached, until a second threshold r₂, rₐMi₂ for the ratio c(H₂) / c(O₂) of hydrogen gas content to oxygen gas content in the oxygen gas separator 2 is undershot, and / or until a second threshold 1 / r₂, 1 / rₐMi₂ for the ratio c(O₂) / c(H₂) of oxygen gas content to The hydrogen gas content in oxygen gas separator 2 has been exceeded.

[0339] For example, the second threshold c 2 (H 2 ), c ​​Mi_2 (H 2 ) for the hydrogen gas content is set such that the second threshold c 2 (H 2 ), c ​​Mi_2 (H 2 ) for the hydrogen gas content is outside a range for a hydrogen / oxygen oxyhydrogen reaction, and / or the second threshold c 2 (O 2 ), c ​​Mi_2 (O 2 ) for the oxygen gas content is set such that the second threshold c 2 (O 2 ), c ​​Mi_2 (O 2 ) for the oxygen gas content is outside a range for a hydrogen / oxygen oxyhydrogen reaction, and / or the second time t 2 is chosen such that in the time interval between the first time t 1 and the second time t 2, a hydrogen gas content c(H 2 ) and / or an oxygen gas content c(O 2 ) is present in the oxygen gas separator 2. 2) is reached, which is outside a range for a hydrogen / oxygen oxyhydrogen reaction.

[0340] For example, the procedure includes blocking the interruption of the electrolysis if the second threshold c 2 (H 2 ), c ​​Mi_2 (H 2 ) for the hydrogen content in the oxygen gas separator is exceeded, if the second threshold c 2 (O 2 ), c ​​Mi_2 (O 2 ) for the oxygen gas content in the oxygen gas separator is not reached, if the time interval between the first time t 1 and the second time t 2 has not yet elapsed, if the second threshold r 2 , r Mi_2 for the ratio c(H 2 ) / c(O 2 ) is exceeded, and / or if the second threshold 1 / r 2 , 1 / r Mi_2 for the ratio c(O 2 ) / c(H 2 ) is not reached.

[0341] For example, the procedure includes: Selecting two or more measures M i to reduce the hydrogen content g(H 2 ) in the oxygen gas separator 2, specifying for each measure M i a second threshold c Mi_2 (H 2 ) for the hydrogen gas content, a second threshold c Mi_2 (O 2 ) for the oxygen gas content, a second threshold r Mi_2 for the ratio of hydrogen gas content to oxygen gas content and / or a second threshold 1 / r Mi_2 for the ratio of oxygen gas content to hydrogen gas content in the oxygen gas separator 2.

[0342] For example, the procedure includes Selecting two or more measures M i , M j to reduce the hydrogen content g(H 2 ) in the oxygen gas separator 2, specifying for each measure M i of the measures M i , M j a first time t Mi_1 and a second time t Mi_2 , between which the measure M i , M j is carried out.

[0343] For example, the procedure includes specifying the respective first time point t Mi_1 and the respective second time point t Mi_2 depending on one or more further measures M i , M j which are carried out simultaneously with the respective measure M i , M j.

[0344] For example, the procedure includes specifying the respective first time point t Mi_1 depending on a given sequence of measures M i , M j .

[0345] For example, the procedure includes specifying the same first threshold values ​​c Mi_1 (H 2 ) and second threshold values ​​c Mi_2 (H 2 ) for the hydrogen gas content c(H 2 ) in the oxygen gas separator 2, the same first threshold values ​​c Mi_1 (O 2 ) and second threshold values ​​c Mi_2 (O 2 ) for the oxygen gas content c(O 2 ) in the oxygen gas separator 2, and / or the same first and second time points t Mi_1 , t Mi_2 for the two or more measures M i , M j .

[0346] For example, the procedure includes interrupting the electrolysis if the hydrogen gas content c(H 2 ) in the oxygen gas separator 2 falls below the minimum of the second threshold values ​​|c Mi_2 (H 2 )| min of the two or more measures M i, the oxygen gas content c(O 2 ) in the oxygen gas separator exceeds the maximum of the second threshold values ​​|c Mi_2 (O 2 )| max of two or more measures M i, and / or the minimum of the threshold values ​​|r Mi_2 | min of the two or more measures M i for the ratio is not reached.

[0347] For example, the procedure includes interrupting the electrolysis when the maximum of the second time points |t Mi_2 | max of the two or more measures M i is reached.

[0348] For example, the procedure includes determining a new first time point t Mi_1 (t Vnew ) and / or a new second time point t Mi_2 (t Vnew ) if the second threshold c Mi_2 (H 2 ) for the hydrogen gas content is undershot, the second threshold r Mi_2 for the ratio of hydrogen gas content to oxygen gas content is undershot, the second threshold c Mi_2 (O 2 ) for the oxygen gas content is exceeded, and / or the second threshold 1 / r Mi_2 for the ratio of oxygen gas content to hydrogen gas content is exceeded before the second time point t Mi_2 is reached.

[0349] For example, the procedure includes: Specifying two or more sets of first and second thresholds c Mik_1 (H 2 ), c ​​Mik_2 (H 2 ), c ​​Mik_1 (O 2 ), c ​​Mik_2 (O 2 ), r Mik_1 , r Mik_2 , 1 / r Mik_1 , 1 / r Mik_2 and / or time points t Mik_1 , t Mik_2 , Repeating the execution of one measure M i of the two or more measures M i , M j , applying the thresholds of a common set for each execution.

[0350] For example, the procedure includes specifying a sequence for carrying out the two or more measures M i , M j .

[0351] For example, the procedure after interrupting electrolysis includes: Introducing inert gas into the oxygen gas separator 2 when at least one of the following conditions is met: the hydrogen gas content c(H 2 ) in the oxygen gas separator 2 is greater than a third threshold c 3 (H 2 ) for the hydrogen gas content c(H 2 ), an oxygen gas content c(O 2 ) in the oxygen gas separator 2 is less than a third threshold c 3 (O 2 ) for the oxygen gas content c(O 2 ), and a predetermined third time period t 3 has elapsed.

[0352] For example, the procedure includes: Specifying the third threshold c 3 (H 2 ) for the hydrogen gas content c(H 2 ) equal to or greater than the second threshold c 2 (H 2 ), c ​​Mi_2 (H 2 ) of the hydrogen content, and / or specifying the third threshold c 3 (O 2 ) for the oxygen gas content c(O 2 ) equal to or less than the second threshold c 2 (O 2 ), c ​​Mi_2 (O 2 ) of the oxygen gas content.

[0353] For example, the procedure includes: Specifying the third threshold c 3 (H 2 ) for the hydrogen gas content c(H 2 ) less than the second threshold c 2 (H 2 ), c ​​Mi_2 (H 2 ) of the hydrogen content, and / or specifying the third threshold c 3 (O 2 ) for the oxygen gas content c(O 2 ) greater than the second threshold c 2 (O 2 ), c ​​Mi_2 (O 2 ) of the oxygen gas content.

[0354] For example, the procedure includes: Selecting two or more measures M i , M j to reduce the hydrogen content g(H 2 ) in the oxygen gas separator 2, specifying for each measure M i , M j a first threshold c Mi_1 (H 2 ) for the hydrogen gas content, a first threshold c Mi_1 (O 2 ) for the oxygen gas content, a first threshold r Mi_1 for the ratio of hydrogen gas content to oxygen gas content, and / or a first threshold 1 / r Mi_1 for the ratio of oxygen gas content to hydrogen gas content.

[0355] For example, a control device is adapted to carry out a procedure according to one or more of the preceding examples.

[0356] The electrolysis system 400, 600, for example, includes the control device and the electrolysis unit 1, which is coupled to the control device 5 via signal technology, as well as the oxygen gas separator 2 for separating oxygen gas and electrolyte, which is fluidly coupled to the electrolysis unit 1 and is coupled to the control device 5 via signal technology.

[0357] The electrolysis plant 400, 600, for example, has the electrolyte preparation arrangement 200, wherein the electrolyte preparation arrangement 200 comprises at least one of: an electrolyte preparation device 7, a heater 17, a pump 21 and a pressure-controlled container.

Claims

1. Method for standby operation of an electrolysis plant (400, 600), wherein the electrolysis plant comprises an electrolysis unit (1) and an oxygen gas separator (2) for separating oxygen gas and electrolyte, and the electrolysis unit (1) is connected to a power supply (4) for energy supply (E) for electrolysis in the electrolysis unit (1), the method comprising: - determining a hydrogen gas content (c(H2)) in the oxygen gas separator and / or an oxygen gas content (c(O2)) in the oxygen gas separator (2), - receiving a signal to interrupt the electrolysis of the electrolysis unit (1) for standby operation, - lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) in response to the interruption signal depending on the hydrogen gas content (c(H2)) in the oxygen gas separator (2) and / or depending on the oxygen gas content (c(O2)) in the oxygen gas separator (2).

2. The method of claim 1, comprising: - lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) such that the hydrogen gas content (c(H2)) in the oxygen gas separator (2) and / or the oxygen gas content (c(O2)) in the oxygen gas separator (2) are outside a range for an oxyhydrogen reaction.

3. Method according to any of the preceding claims, comprising: - interrupting the electrolysis in the electrolysis unit (1) in response to the signal to interrupt the electrolysis.

4. Method according to any of the preceding claims, comprising: - blocking a fluid connection between the electrolysis unit (1) and the oxygen gas separator (2) in response to the signal to interrupt the electrolysis.

5. Method according to any of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: - introducing a degassed electrolyte into the electrolysis unit (1).

6. A method according to any of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: reducing an operating temperature (T) before interrupting electrolysis in the electrolysis unit (1). unit ) in the electrolysis unit (1).

7. A method according to one of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: - reducing an operating pressure (p) before interrupting electrolysis in the electrolysis unit (1). unit ) in the electrolysis unit (1).

8. A method according to any of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: - prior to interrupting electrolysis in the electrolysis unit (1) operation of the electrolysis in the electrolysis unit (1) with an electrolyte having a concentration (c L ) contains at least 25% by weight of dissolved alkali salt.

9. Method according to any of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: - reducing a volume of the electrolyte in the oxygen gas separator (2) before interrupting electrolysis in the electrolysis unit (1).

10. A method according to any of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: - before interrupting electrolysis in the electrolysis unit (1), increasing an electric electrolysis current (I) for the electrolysis in the electrolysis unit (1) and / or operating the electrolysis in the electrolysis unit (1) with a maximum electrolysis current (I max ).

11. Method according to any of the preceding claims, wherein lowering the hydrogen content (g(H2)) in the oxygen gas separator (2) comprises: - introducing an inert gas into the oxygen gas separator (2).

12. The method of claim 11, wherein the introduction of the inert gas is carried out in a step-by-step process.

13. The method of claim 11, wherein the introduction of the inert gas is carried out in a flow-through process.

14. Method according to any one of claims 11 to 13, comprising: - increasing the electrolyte level in the oxygen gas separator (2).

15. Method according to any one of the preceding claims, comprising: - providing a temperature threshold (T krit ) for the electrolysis unit (1), after interrupting electrolysis in the electrolysis unit (1) determining an operating temperature (T unit ) of the electrolysis unit (1), - comparing the determined operating temperature (T unit ) with the temperature threshold (T krit ), and - if the determined operating temperature (T unit ) equal to or less than the temperature threshold (T krit ) is: Increasing the operating temperature of the electrolysis unit (T unit ).

16. Method according to any one of the preceding claims, comprising: - providing a stress threshold (o krit) for the electrolysis unit (1), after interrupting electrolysis in the electrolysis unit (1) Determining a mechanical stress (o unit ) of the electrolysis unit (1), - comparing the determined voltage (o unit ) with the stress threshold (o krit ), and - if the determined tension (o unit ) equal to or less than the stress threshold (o krit ) is: Increasing the operating temperature (T unit ) of the electrolysis unit (1).

17. Method according to any one of the preceding claims, comprising: - providing a pressure threshold for the electrolysis unit (1), - after interrupting electrolysis in the electrolysis unit (1) determining a pressure (p unit ) in the electrolysis unit (1), - comparing the determined pressure (p unit ) with the pressure threshold value, and - if the determined pressure (p unit ) less than or equal to the stress threshold (okrit ) is: Increasing the pressure (p unit ) in the electrolysis unit (1).

18. Control device (5) for an electrolysis plant (1), wherein the control device (5) is adapted to carry out a method according to one of the preceding claims.

19. Electrolysis system (400, 600), comprising: - a control device (5) according to claim 18, - an electrolysis unit (1) which is coupled to the control device (5) via a signal connection, - an oxygen gas separator (2) for separating oxygen gas and electrolyte, which is fluidly coupled to the electrolysis unit (1) and which is coupled to the control device (5) via a signal connection.

20. Electrolysis system (400, 600) according to claim 19, comprising an electrolyte preparation arrangement (200), wherein the electrolyte preparation arrangement (200) comprises at least one of: an electrolyte preparation device (7), a heater (17), a pump (21) and a pressure-controlled container.

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