Method and device for operating an electrolysis system

Abstract

The invention relates to a method (1000) for operating an electrolysis system (10) which has at least one electrolyzer stack (100), with an air side (120) and a reactant side (130), and different operating situations. The method (1000) has the steps of detecting the operating situation of the electrolysis system (10) and controlling the electrolysis system (10) on the basis of the detected operating situation. In the method (1000), the operating situation of the electrolysis system (10) is determined to be a special operating situation if the detected operating situation deviates from a normal operation of the electrolysis system (10) for generating a synthesis gas from a reactant as intended. For the detected special operating situation, at least one electric heater (221, 222) is controlled so as to control the temperature of air which can be supplied to the air side (120) in order to control the temperature of the electrolyzer stack (100). Furthermore, for the special operating situation, a heating gas is guided to the reactant side (130), said heating gas having at least one protective gas. The invention also relates to a computer program product, to a control device (20) for carrying out the method (1000), and to an electrolysis system (10) comprising the control device (20).

Description

[0001] Method and device for operating an electrolysis system

[0002] The present invention relates to a method for operating an electrolysis system, as well as a computer program product and a control device for carrying out such a method. The invention further relates to an electrolysis system with the control device according to the invention.

[0003] Replacing crude oil with synthetically produced hydrocarbons represents a way to reduce dependence on fossil fuels and emissions in energy production. Synthetic hydrocarbons can be produced from synthesis gas, which is generated in a fuel cell through the electrolysis of carbon dioxide and water with the addition of electricity. The synthesis gas produced in this way is often referred to as "syngas" and contains, in particular, hydrogen and carbon monoxide. The synthetic hydrocarbons are obtained from the synthesis gas in a synthesis process following electrolysis, such as the Fischer-Tropsch process. High-temperature electrolysis is the preferred method for electrolysis, for which solid oxide electrolyzer cells (SOECs) are preferably used.These are solid oxide fuel cells (SOFCs) that operate in reverse mode to electrolyze water and carbon dioxide. Like solid oxide fuel cells, solid oxide electrolyzer cells operate particularly efficiently at temperatures between 500°C and 900°C.

[0004] It is known from the state of the art to operate electrolysis systems in different operating states, such as a resting state or an active operating state. Due to the high temperatures required for high-temperature electrolysis, the intermediate states that occur between such a resting state and an active operating state pose technical challenges for an operating strategy for controlling the electrolysis system. Startup and shutdown processes, in particular, must be designed with consideration for temperature-sensitive components and system safety. Disadvantages of existing operating strategies are that the startup and shutdown processes implemented in them take a relatively long time and consequently require high energy. Furthermore, startup and shutdown processes of the fuel cell system can often only be controlled imprecisely.This makes it particularly difficult to reliably maintain temperature gradients within permissible ranges during heating or cooling of system components. This can subject the electrolysis system's components to relatively high thermal and mechanical stress.

[0005] The object of the present invention is to at least partially remedy the disadvantages described above. In particular, the object of the present invention is to improve the efficiency and safety of high-temperature electrolysis systems as well as the control of start-up and run-back processes, particularly with regard to permissible temperature gradients.

[0006] The above object is achieved by a method having the features of claim 1, a computer program product having the features of claim 13, a control device having the features of claim 14 and by an electrolysis system having the features of claim 15.

[0007] Further advantages and features of the invention emerge from the dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the computer program product according to the invention, with the control device according to the invention, and with the electrolysis system according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other and can be made to each other.

[0008] A first aspect of the present invention relates to a method for operating an electrolysis system. The electrolysis system has at least one electrolyzer stack with an air side and a reactant side. The electrolysis system further has various operating situations. The method comprises a step of detecting an operating situation of the electrolysis system. Furthermore, the method comprises controlling the electrolysis system depending on the detected operating situation. An operating situation of the electrolysis system is detected as a special operating situation if the detected operating situation deviates from normal operation of the electrolysis system for generating a specified synthesis gas from a reactant that can be supplied to the reactant side via a reactant supply path of the electrolysis system.For the detected special operating situation, the electrolysis system is controlled, with at least one electric heater controlling the air temperature of air that can be supplied to the air side via an air supply path of the electrolysis system being controlled in order to control a temperature of the electrolyzer stack. Furthermore, a heating gas comprising at least one protective gas is supplied to the reactant side via the reactant supply path.

[0009] In other words, the invention provides a method for operating an electrolysis system with which, for example, an operating strategy for the electrolysis system can be implemented.

[0010] In this context, "operating a system" can preferably be understood as instructing the system to operate. The electrolysis system can be, for example, a fuel cell electrolyzer system, a high-temperature fuel cell electrolyzer system, an SOEC, or a CO-SOEC system. Furthermore, the electrolysis system can preferably be a reversible fuel cell system, such as an rSOC system.

[0011] The electrolysis system comprises at least one electrolyzer stack with an air side and a reactant side. The electrolysis system has various operating situations.

[0012] Within the scope of the invention, an “operating situation” can be understood in particular as a situation or circumstances that occur during operation of the electrolysis system. An operating situation can be defined by the current condition and / or a control state of the electrolysis system. An operating situation can also be defined, for example, by physical variables such as actual pressures or actual temperatures that occur in the electrolysis system and / or by a control command. The electrolysis system has a plurality of different operating situations. Preferably, the electrolysis system can only ever have one operating situation at a time. An operating situation can be defined such that circumstances that occur in the electrolysis system can only be assigned to one operating situation. Within the scope of the invention, an operating situation can also be predetermined, for example, from outside.Thus, within the scope of the invention, detecting is preferably also understood to mean specifying.

[0013] According to the invention, an operating situation of the electrolysis system is detected as a special operating situation if the detected operating situation deviates from normal operation of the electrolysis system. Normal operation is intended to generate a suitable synthesis gas from reactant, which can be supplied to the reactant side via a reactant supply path of the electrolysis system.

[0014] Within the scope of the invention, "detecting an operating situation" can be understood in particular as registering an operating situation. For example, in addition to recording and / or measuring information pertaining to operating situations, detecting can preferably also comprise evaluating or classifying this information. For example, an operating situation can be determined from the current and / or historical information recorded for an operating situation. Within the scope of the invention, a "path" can be understood in particular as a flow path between a starting point and at least one or more end points.

[0015] Within the scope of the invention, a "special operating situation" can be understood in particular as an operating situation that deviates from normal operation of the electrolysis system. A special operating situation can thus particularly involve rest and / or transitional states of the electrolysis system, for example, which occur before and / or after normal operation.

[0016] In the context of the invention, "normal operation" can be understood to mean, in particular, stationary or at least semi-stationary operation of the electrolysis system. During normal operation, the electrolysis system generates a synthesis gas as intended from reactant. Normal operation can preferably comprise operation of the electrolysis system at partial load (preferably at least 5%, 10%, 20%, 30%, 40%, or 50% of production capacity) and / or full load.

[0017] Within the scope of the invention, a "designated synthesis gas" can preferably be understood as a gas or gas mixture generated from the supplied reactant for further processing. Normal operation for generating a synthesis gas can preferably be provided as the designated synthesis gas. Furthermore, the electrolysis system is preferably designed and / or intended for generating this synthesis gas. The reactant can be supplied via a reactant supply path, such as a reactant supply line. The "reactant" can preferably be understood as a gaseous mixture which comprises, in particular, water and carbon dioxide. This is preferably also referred to as a reactant-gas-carbon dioxide mixture or reactant-gas mixture.

[0018] Within the scope of the invention, fuel can also advantageously be understood as a reactant.

[0019] The composition of the reactant may depend on the desired composition of the synthesis gas.

[0020] According to the invention, the electrolysis system is controlled depending on the detected operating situation.

[0021] In the context of the invention, “controlling” can be understood in particular as controlling and / or regulating input variables, parameters and / or components of the electrolysis system.

[0022] For the detected special operating situation, at least one electric heater is controlled to control the air temperature of air that can be supplied to the air side via an air supply path of the electrolysis system, in order to control a temperature of the electrolyzer stack. Preferably, for the detected special operating situation, a temperature of the electrolyzer stack can be controlled using at least the electric heater.

[0023] The temperature of the electrolyzer stack can, in particular, be a temperature measurable locally on the electrolyzer stack or an average temperature calculated from locally different measured temperatures. The air supply path can, for example, be provided as an air supply line.

[0024] For the detected special operating situation, a heating gas is supplied to the reactant side via the reactant supply path, which comprises at least one protective gas.

[0025] In the context of the invention, a "heating gas" can be understood in particular as a gas or gas mixture capable of transporting heat. A "protective gas" in the context of the invention can be understood in particular as a gas or gas mixture that does not react with the surfaces over which the fluid flows and with substances present in the system under normal operating conditions and is preferably also suitable for displacing reactive substances, in particular gases such as air or oxygen. The protective gas can be, for example, an inert gas such as argon or nitrogen.

[0026] The method according to the invention makes it possible to identify operating situations that deviate from normal operation and to control them in a situation-specific manner. A particular advantage is that the temperature of the electrolyzer stack can be controlled precisely, quickly, and efficiently, especially in operating situations that occur during transitions to and from normal operation, since the air temperature can be regulated relatively precisely and quickly using electric heaters. This also makes it possible to maintain temperature gradients, so that the thermal load on components of the electrolysis system during heating and cooling processes can be reduced. Furthermore, the time at which chemical reactions in the electrolyzer stack begin can be controlled via the air temperature.Supplying the reactant side with heating gas in special operating situations allows heat to be transported into and out of the electrolyzer stack, allowing the electrolysis system to be indirectly heated or cooled with the heating gas. Since the heating gas is mixed with a protective gas for special operating situations, it can be ensured that only the intended substances enter the reactant lines and are converted in the electrolyzer stack. Contamination of the reactant by any residual gas in the reactant supply and reactant conversion can thus be prevented. Accordingly, the method according to the invention can be used to optimize the energy consumption and safety during operation of the electrolysis system.

[0027] Preferably, the at least one electric heater can be controlled according to a temperature profile for the heated air. For this purpose, a temperature profile can be specified, for example. Furthermore, a maximum permissible temperature gradient of the temperature profile can preferably be the minimum of component-dependent maximum heating and / or cooling rates. Within the scope of the invention, the heater can also be designed, for example, as a torch with a heat exchanger. Therefore, it does not necessarily have to be an electric heater.

[0028] It can thus be achieved that temperature changes of components run through as quickly as permissible in order to reduce their thermal stress and avoid damage to or malfunctions of the components. According to a preferred embodiment, a first warm-up operating situation preceding normal operation can be detected in the method when a process request to heat the electrolyzer stack to a warm-up temperature is issued. The special operating situation can comprise the first warm-up operating situation. For the detected first warm-up operating situation, monitoring the electrolysis system can preferably comprise monitoring a composition of the heating gas, in which the heating gas comprises only the protective gas, preferably nitrogen, in a first time period, and in a second time period the heating gas comprises a gas mixture of hydrogen and the protective gas.The gas mixture can preferably have a composition of up to 95% nitrogen as the protective gas and up to 5% hydrogen in order to at least partially reduce a surface of the electrode on the reactant side, preferably within the second time period. The gas mixture can preferably be provided in a composition of up to 95% nitrogen as the protective gas and up to 5% hydrogen as a gas mixture, which is also sold, for example, under the name "Areal F5." The second time period can preferably begin when the electrolyzer stack has reached a reduction temperature. The second time period can preferably last at least 10 minutes.

[0029] Advantageously, the electrolysis system can also be heated from the start with a gas mixture containing up to 95% nitrogen as the protective gas and up to 5% hydrogen as the gas mixture, i.e., with Area F5. Alternatively, it is also conceivable for the electrolysis system to be heated only with nitrogen as the gas, which is then reduced with hydrogen shortly before operation begins.

[0030] Within the scope of the invention, a "process request" can preferably be understood as a control command, in particular a control command issued, for example, by a user of the electrolysis system. Furthermore, "controlling a composition" can be understood as providing and combining gas components to form a gas mixture with defined volume fractions of the gas components.

[0031] This makes it possible to initially purge the electrolyzer stack on the reactant side with a protective gas for a defined period of time at the start of a heating process, for example to remove any residual oxygen from the reactant side. In a subsequent reduction process, the electrode on the reactant side can be reduced using hydrogen mixed with the heating gas, with oxidized electrode surface sections reacting with the hydrogen. For example, the electrode surface on the reactant side can contain nickel oxide before being subjected to the heating gas flow and contain only nickel after reduction. In this way, the internal resistance of the electrode can be reduced and the efficiency of the electrolysis increased. At the same time, the air side can be purged with air, and the electrolyzer stack can be heated using the electrically heated air.This allows the electrolysis system to be brought into a defined state on the material side and slowly heated up. At the same time, a pressure difference can be adjusted within the electrolyzer stack. These steps can increase the safety and efficiency of the electrolysis system's operation.

[0032] Alternatively or additionally, the heating gas can be recirculated in a recirculation path of the electrolysis system. The recirculation path can extend between a synthesis gas section on the reactant side for discharging the synthesis gas and a reactant feed section on the reactant side for feeding the reactant. Preferably, heating gas or synthesis gas can be recirculated for a special operating situation, such as the initial warm-up operating situation, and / or for normal operation.

[0033] This enables efficient and effective heating of the reactant side. In particular, the heating gas in the electrolyzer stack can absorb heat from the electrically heated air. The thus heated heating gas can then be passed through the synthesis gas path and, via recirculation, also into at least part of the reactant feed path. Furthermore, the already heated heating gas is mixed with the newly supplied heating gas from the reactant feed path, so that the previously supplied heat energy is retained in the electrolysis system. This can increase the efficiency of the electrolysis system's operation.

[0034] According to a further preferred embodiment, a second warm-up operating situation preceding normal operation for warming up the electrolysis system can be detected in the method if the heating gas discharged from the reactant side has at least a warm-up temperature and / or if a surface of the electrode on the reactant side has a minimum electrical conductivity. For this purpose, the electrical resistance of the electrolyzer stack can preferably be measured. Further preferably, a second warm-up operating situation can follow a first warm-up operating situation. The special operating situation can comprise the second warm-up operating situation. For the second warm-up operating situation, monitoring the electrolysis system can comprise supplying water vapor to the reactant side. Furthermore, monitoring a composition of the heating gas as a gas mixture can take place.The gas mixture can, for example, comprise steam, protective gas, and hydrogen. The gas mixture can preferably have a composition containing at least 3% hydrogen. The heating temperature can preferably be at least 110°C.

[0035] This makes it possible to purge the fuel side with steam and adjust it to a desired temperature. At the same time, pressure equalization can be achieved between the reactant side and the air side. Furthermore, a stable steam supply can be established. This allows the electrolyzer stack to be efficiently prepared for active operation during the second warm-up operating situation.

[0036] According to a preferred embodiment, a standby operating situation preceding normal operation can be detected in the method if the temperature of the electrolyzer stack has at least one minimum stack temperature and preferably at least one stack operating temperature. The special operating situation can preferably comprise the standby operating situation. Furthermore, a standby operating situation can preferably follow a second warm-up operating situation. For the standby operating situation, monitoring the electrolysis system can comprise monitoring a composition of the heating gas as a gas mixture. The gas mixture can comprise water vapor, protective gas, and hydrogen. Preferably, the gas mixture can have a composition with at least 3% hydrogen. Furthermore, a flow rate of the heated air and / or the heating gas can be controlled to a minimum.The minimum flow rate can correspond to a flow rate at which the temperature of the electrolyzer stack is maintained between the minimum stack temperature and the stack operating temperature. The minimum stack temperature can preferably be at least 770°C. The stack operating temperature can preferably be at least 830°C. This makes it possible to maintain the electrolysis system in a standby state, from which it can, for example, be switched to active operation. The resources required to maintain this state can be reduced to the minimum necessary for this purpose.

[0037] According to a further preferred embodiment, a start-up operating situation preceding normal operation for commissioning the electrolysis system can be detected in the method when a process request to generate the intended synthesis gas is issued. Preferably, the special operating situation can comprise a start-up operating situation. Furthermore, a start-up operating situation can preferably follow a standby operating situation. For the start-up operating situation, monitoring the electrolysis system can comprise monitoring a composition of the heating gas as a gas mixture. Preferably, the gas mixture can comprise water vapor, hydrogen, and protective gas. A flow rate of the heating gas through the reactant supply path can be monitored. Preferably, the flow rate can be monitored as a function of a target flow rate.The target flow rate can be specified according to a preset function or as a minimum flow rate. The preset function can, for example, have a ramp that increases over time.

[0038] This allows the electrolysis system to be controlled in an operating situation from which it is to be ramped up to active operation. Flow rate control allows the system to pass through endothermic operating ranges as quickly as possible, thus reducing the energy required for operation.

[0039] According to a preferred embodiment, a low-power operating situation preceding normal operation for commissioning the electrolysis system can be detected in the method if the heating gas has a flow rate through the reactant supply path that is at least necessary for charge exchange between the electrodes of the reactant side and the air side connected by a closed electrical connection. Preferably, the special operating situation can comprise the low-power operating situation. Furthermore, the low-power operating situation can follow the start-up operating situation. For the low-power operating situation, controlling the electrolysis system can comprise supplying carbon dioxide to the reactant side. Furthermore, a composition of the heating gas can be controlled as a gas mixture. Preferably, the gas mixture can comprise the protective gas, water vapor, hydrogen, and carbon dioxide.The amount of carbon dioxide added can preferably follow a feed curve. The gas mixture can further preferably comprise a heating gas exhaust that has been recirculated via the recirculation path. Furthermore, electrical current can be supplied to the electrolyzer stack. The electrical current can preferably be added according to a power curve. The feed curve for the amount of carbon dioxide added can, for example, be linearly correlated with the consumption of the reactant and / or the supplied electrical current.

[0040] In the context of the invention, an "addition curve" can be understood, for example, as a predetermined concentration curve. This curve can depend, for example, on another variable, such as time, temperature, or concentrations of other substances.

[0041] The inventive control of the electrolysis system makes it possible to protect the electrolyzer stack and avoid endothermic operating regimes. Furthermore, a current ramp with a relatively steep rise can be implemented, allowing reactant utilization to be increased quickly.

[0042] According to a further preferred embodiment, a normal operation operating situation corresponding to normal operation can be detected in the method if the electrolyzer stack has at least a minimum electrical stack current and preferably the synthesis gas has a minimum operating temperature. Preferably, a normal operation operating situation can follow a low-power operating situation. The minimum electrical stack current can, for example, be at least 63.5 A. Further preferably, a normal operation operating situation can be detected if, alternatively or additionally, a process request with a process quantity specification is issued. Preferably, the process request can comprise a request to operate the electrolysis system at full load or partial load (preferably at least 5%, 10%, 20%, 30%, 40%, or 50% of full load operation).

[0043] For a normal operation situation corresponding to normal operation, controlling the electrolysis system may include supplying carbon dioxide and water vapor to the reactant side as the reactants. Furthermore, the composition of the reactant may be controlled as a gas mixture. Preferably, the gas mixture may include carbon dioxide, water vapor, and preferably synthesis gas recirculated via the recirculation path.

[0044] Controlling in a normal operating situation may further comprise controlling the temperature of the electrolyzer stack by means of catalytic heating. Controlling the temperature may comprise supplying residual gas from a synthesis process, in which synthesis gas is converted into hydrocarbons, to a catalyst of the electrolysis system and catalytically combusting the residual gas by means of the catalyst. Heat from a catalyst exhaust stream from the catalytic combustion can then be transferred to the air to be supplied and / or the reactant to be supplied by means of at least one heat exchanger.

[0045] For a normal operation operating situation corresponding to normal operation, controlling the electrolysis system may further comprise supplying air, reactant, and electric current to the electrolyzer stack. A synthesis gas, preferably a synthesis gas, can be generated from the supplied air, reactant, and electric current by means of the electrolyzer stack. The at least one electric heater may be deactivated in a normal operation operating situation.

[0046] In the context of the invention, "catalytic heating" can be understood in particular as the introduction of heat into the electrolysis system by means of heat generation in a catalyst. A "synthesis process" can be understood in particular as a process for producing synthetic hydrocarbons from a synthesis gas. In this synthesis process, typically not all of the synthesis gas can be converted and / or short-chain hydrocarbons are formed, which are separated. This separated gas portion can be referred to, for example, as "residual gas" (also known in English as "tail gas") in the context of the invention. Of course, the invention is not limited to such a gas.

[0047] Thus, in the context of the invention, "residual gas" can be understood in particular as a gas mixture containing carbon dioxide and / or short-chain hydrocarbons. The residual gas can also comprise, for example, methane or natural gas. The residual gas can, for example, be a functionally equivalent gas or gas mixture to a residual gas, originating, for example, from a synthesis process in which synthesis gas is converted into hydrocarbons. Furthermore, "deactivating the electric heater" can be understood in particular as interrupting the power supply to the electric heater.

[0048] This process design makes it possible to generate the intended synthesis gas in the electrolyzer stack to a significant extent during active operation of the electrolysis system, while utilizing the relatively high calorific value of the residual gas to provide heat in the high-temperature electrolysis. This can increase the efficiency of the electrolysis system.

[0049] According to a preferred embodiment, a reversing operating situation following normal operation can be detected in the method if the electrolyzer stack has an electrical stack current less than a minimum stack current or a process request to terminate the operation of the electrolyzer stack is issued. The electrical minimum stack current can, for example, be at least 63.5 A. Preferably, the special operating situation can comprise a reversing operating situation. The electrical stack current less than a minimum stack current is generally an operator input value.

[0050] Controlling the electrolysis system for a reverse operating situation can comprise, as a step, controlling the composition of the heating gas as a gas mixture. The gas mixture can preferably comprise protective gas, carbon dioxide, and water vapor. Furthermore, the gas mixture can preferably also comprise heating gas exhaust gas recirculated via the recirculation path. Preferably, the proportions of carbon dioxide and water vapor in the heating gas can be reduced; in particular, the proportions of carbon dioxide are quickly set to at least approximately zero and the proportions of water vapor are set to a minimum value (similar to that of hot standby). Preferably, the reduction of the respective component can be carried out according to a respective associated decrease curve. Flow rates of the air and heating gas, as well as the electrical current supplied to the electrolyzer stack, can also be reduced.The electric current can preferably be reduced according to a power reduction curve until no more current is supplied. Furthermore, in the reverse operating situation, the air temperature can preferably be additionally controlled by means of a further electric heater arranged in the air supply path to heat the air. Thus, the method can provide an operating situation in which the electrolyzer stack and other temperature-sensitive components are cooled sufficiently slowly. Furthermore, a balance can be struck between the thermal inertia of the electrolysis system and the adjustment of the mass flows in the electrolysis system.

[0051] According to a further preferred embodiment, the method can detect a first cooling operating situation following normal operation for cooling the electrolysis system when the electrical connection for charge exchange between the electrodes on the reactant side and the air side is open. Preferably, the special operating situation can comprise a first cooling operating situation. Furthermore, a first cooling operating situation can preferably follow a reversing operating situation.

[0052] Controlling the electrolysis system for a first cooling operating situation can comprise, as a step, controlling the composition of the heating gas as a gas mixture. The gas mixture can comprise a protective gas and hydrogen. Furthermore, the air temperature can preferably be additionally controlled by means of a further electric heater arranged in the air supply path.

[0053] Thus, in particular, the electrolyzer stack can be cooled safely and with low risk of oxidation of the electrode surface by using a heating gas with a composition of protective gas and hydrogen.

[0054] According to a preferred embodiment, the method can detect a second cooling operating situation following normal operation for cooling the electrolysis system when the temperature of the electrolyzer stack is between a first stack temperature and a second stack temperature. Preferably, the special operating situation can comprise a second cooling operating situation. Furthermore, a second cooling operating situation can preferably follow a first cooling operating situation. The first stack temperature can, for example, comprise a temperature of 650°C and the second stack temperature a temperature of 50°C.

[0055] Checking the electrolysis system for a second cooling operating situation can include checking the composition of the heating gas so that the heating gas only contains protective gas. This is carried out, in particular, until a target temperature is reached, so that the system can be safely switched to cold standby or shut down.

[0056] Thus, the electrolyzer stack can be safely cooled further and at the same time the course of chemical reactions in the reactant path can be stopped by the heating gas only containing protective gas to displace other gaseous substances.

[0057] According to a further preferred embodiment, a safety shutdown operating situation can be detected in the method when the electrolysis system enters a critical state.

[0058] Controlling the electrolysis system for a safety shutdown operating situation can comprise the step of supplying protective gas, preferably nitrogen, through the reactant supply path. This serves to equalize the pressure in the reactant path when everything is sealed and the system is cooling. For this purpose, the reactant supply path can preferably be connected to a pressurized protective gas reservoir. Furthermore, the supply of air to the air side can be prevented, and the at least one electric heater can be deactivated. In this case, an inlet and an outlet on the reactant side are preferably also closed. In addition, the supply of electrical current to the electrolyzer stack can be interrupted. Preferably, passive pressure control of the pressure occurring in the electrolyzer stack can be carried out in order to compensate for a negative pressure in the electrolyzer stack caused by cooling.

[0059] In the context of the invention, a “critical condition” can be understood as meaning, in particular, the occurrence of component failure, leaks or temperatures, pressures or reaction products outside the operating limits of the electrolysis system.

[0060] This makes it possible to place the electrolysis system into a safe operating range if conditions arise within the electrolysis system that could have potentially dangerous consequences for the system and / or people. A particular advantage here is that the protective gas can both displace reaction gases and cool the electrolysis system. This further increases the safety of the electrolysis system's operation.

[0061] According to a further preferred embodiment, a check operating situation can be detected in the method when a process request to check the functionality of the electrolyzer stack is issued. A check operating situation can preferably precede a special operating situation and a normal operating situation.

[0062] Checking the electrolysis system for a verification operating situation can comprise, as a step, at least one of checking the actual operating parameters of the electrolyzer stack with regard to their operating limits. Preferably, the actual operating parameters can include at least an actual temperature of the electrolyzer stack and / or an actual pressure occurring in the electrolyzer stack.

[0063] It is also advisable to check and / or verify whether all actuators are controllable, whether all sensors are providing (correct) values, and whether the lockout has been released. It may also be beneficial to activate heating strips around the actuators if they are frozen and immobile.

[0064] This makes it possible to check the electrolysis system at regular intervals, especially before commissioning, for its functionality and proper condition. This can further increase the safety of the electrolysis system's operation.

[0065] A further aspect of the invention relates to a use of the aforementioned method to produce electricity-based synthetic fuels.

[0066] A further aspect of the invention relates to a computer program product which has instructions which, when the program is executed by a computer, cause the computer to carry out the method described above.

[0067] A further aspect of the invention relates to a control device for operating an electrolysis system. The electrolysis system operable by the control device comprises at least one electrolyzer stack with an air side and a reactant side. Furthermore, the electrolysis system comprises an air supply path for supplying air to the air side. At least one electric heater for controlling the air temperature is arranged in the air supply path. The electrolysis system also comprises a reactant supply path for supplying reactants to the reactant side. The electrolysis system also comprises various operating situations. The control device for operating an electrolysis system comprises a detection module for detecting an operating situation of the electrolysis system.The detection module is configured to detect an operating situation as a special operating situation if the detected operating situation deviates from normal operation of the electrolysis system for generating a specified synthesis gas from the reactant. Furthermore, the control device comprises a situation control module for controlling the electrolysis system depending on the detected operating situation. For the detected special operating situation, the situation control module is configured to at least control the electric heater to control a temperature of the electrolyzer stack and to supply a heating gas comprising at least one protective gas to the reactant side via the reactant supply path.

[0068] A further aspect of the invention relates to an electrolysis system. The electrolysis system has at least one electrolyzer stack with an air side and a reactant side. Furthermore, the electrolysis system has an air supply path for supplying air to the air side. At least one electric heater for controlling the air temperature is arranged in the air supply path. The electrolysis system also has a reactant supply path for supplying reactants to the reactant side. The electrolysis system has various operating situations, which include at least one normal operation situation, which corresponds to normal operation, and at least one special operating situation, which deviates from normal operation of the electrolysis system for generating a specified synthesis gas from the reactant. The electrolysis system further has the control device according to the invention described above.

[0069] With the use, the computer program product and the device and the system described above, all of the advantages already explained for the method according to the invention can be achieved.

[0070] The electrolysis system can preferably be a fuel cell electrolyzer system. It can be a high-temperature fuel cell electrolyzer system, such as an SOEC or CO-SOEC system. Preferably, the electrolysis of water can take place at temperatures around 900 degrees Celsius. By providing the high thermal energy, the power required to carry out the electrolysis can be reduced and the efficiency increased.

[0071] The electrolysis system may comprise at least two electrolysis cell packs, each with two electrolyzer stacks. The electrolysis system may be configured to produce electricity-based synthetic fuels.

[0072] According to a preferred embodiment, the air supply path can have a primary air supply path with one or more air heat exchangers for heating the air to be supplied. Furthermore, the air supply path can have a secondary air supply path, and the at least one electric heater can be provided in the secondary air supply path. The primary air supply path and the secondary air supply path can be fluidly connected to one another via a mixing section. The air temperature can be controlled by mixing cold air from the primary air supply path and heated air from the secondary air supply path at a mixing section of the air supply path.

[0073] This allows the temperature of the electrolyzer stack to be controlled quickly, efficiently and safely.

[0074] In order to distinguish components or elements of the same kind or type from one another, such as heat exchangers, shut-off devices, partial paths or bypass paths, components or elements of the same kind or type are numbered consecutively below and are referred to as first component, second component, third component, etc., for example first heat exchanger, second heat exchanger, etc. This designation based on the numbering serves solely to distinguish components or elements of the same kind or type, but in no way represents a restriction with regard to their nature.

[0075] The connections mentioned herein are fluid-conducting, particularly gas-conducting, connections. The connections can be established via various paths or lines, such as pipes or hoses, which are each coupled to one another. Various flow-influencing devices, such as those mentioned herein, such as shut-off devices, can be arranged in the connections.

[0076] To the extent that reference is made herein to the arrangement of a heat exchanger in one connection and the thermal coupling of the heat exchanger to another connection, these features are to be understood as synonymous due to the function of the heat exchanger. This is because the heat exchanger exchanges the heat of two flows in the respective connections, for example, in countercurrent. In this respect, the heat exchanger is actually arranged in each of the two connections, and the heat exchanger also thermally couples both connections.

[0077] The aforementioned shut-off devices serve at least to stop or allow the flow of the respective fluid, especially gas, flowing through the connections. Depending on the design of the shut-off device used, the flow rate can also be controlled. For this purpose, the shut-off devices can be equipped with appropriate control electronics and sensors. The shut-off device can be designed in a variety of ways, for example, as a valve, gate valve, shut-off cock, or butterfly valve.

[0078] Further advantages, features, and details of the invention will become apparent from the following description. The description describes exemplary embodiments of the invention in detail with reference to the figures. They show schematically:

[0079] Fig. 1 shows an embodiment of a method according to the invention,

[0080] Fig. 2 shows an embodiment of the electrolysis system according to the invention and its operation in a test operating situation according to the invention,

[0081] Fig. 3 shows the electrolysis system of Figure 2 during operation in a first warm-up operating situation according to the invention,

[0082] Fig. 4 shows the electrolysis system of Figure 2 during operation in a second warm-up operating situation, in a standby operating situation and in a start-up operating situation, each according to the invention,

[0083] Fig. 5 the electrolysis system from Figure 2 during operation in a

[0084] Low power operating situation according to the invention,

[0085] Fig. 6 the electrolysis system from Figure 2 during operation in a

[0086] Normal operation operating situation according to the invention, Fig. 7 the electrolysis system from Figure 2 during operation in a reverse operating situation according to the invention,

[0087] Fig. 8 shows the electrolysis system of Figure 2 during operation in a first cooling operating situation according to the invention,

[0088] Fig. 9 shows the electrolysis system of Figure 2 during operation in a second cooling operating situation according to the invention,

[0089] Fig. 10 shows the electrolysis system of Figure 2 during operation in a safety shutdown operating situation according to the invention.

[0090] A first aspect of the present invention relates to a method 1000 for operating an electrolysis system. The method 1000 may, for example, be an implementation of an operating strategy.

[0091] Figures 2 to 10 show, by way of example, an electrolysis system 10 that can be operated using the method 1000. An electrolysis system operable using the method 1000 and shown by way of example in Figures 2 to 10 can be a CO-SOEC system, although the invention is not limited thereto.

[0092] The electrolysis system 10 shown as an example in the figures has at least one electrolyzer stack 100. The electrolyzer stack 100 has an air side 120, at which an electrode can be supplied with air via an air supply section 122. Such an air electrode is not shown in the figures for the sake of clarity. The electrolyzer stack 100 further has a reactant side 130, at which another electrode can be supplied with reactants via a reactant supply section 131. Such a reactant electrode is not shown in the figures for the sake of clarity. Depending on the operating mode as an electrolyzer cell or fuel cell, the electrodes can function as an anode in one case and as a cathode in the other case. In the case of operation as an electrolyzer cell, for example, the air side 120 can have the air electrode as the anode and the reactant side 130 can have the reactant electrode as the cathode.

[0093] Preferably, the electrolysis system 10 can also have more than one electrolyzer stack 100, preferably two electrolysis modules with two electrolyzer stacks each.

[0094] The electrolyzer stack 100 can be connected to a power source 510 by an electrical connection 511 via an electrode terminal 512. The electrical connection 511 can include a relay 514. To simplify the illustration, the negative and positive potential connections to the electrical connection 511 are shown in the figures as a common connection.

[0095] The air can be introduced into the electrolysis system 10 from an air inlet section 2201, for example, from the environment. The air is guided to the air side 120 via an air supply path 2200. The air supply path 2200 can have various sections. For example, a first supply air heater 201 and a second supply air heater 202, as well as an air filter 203, can be provided in an air supply line section 2202. The filtered and preheated air can be conveyed along the air supply path 2200 by an air blower 204. The air can be directed optionally into a primary air supply path 2210 and / or a secondary air supply path 2220 at a branching point 207. In the primary air supply path 2210, two air heat exchangers 421, 422 can be arranged, which can be coupled to this line section in a heat-transfer manner.Upstream of the air heat exchangers 421, 422, a shut-off device 215 can be provided, for example, to regulate the amount of air to be discharged from the branching point 207. At least one electric heater is provided in the air supply path 2200. In Figures 2 to 10, two electric heaters 221, 222 for heating the air are provided in parallel in the secondary air supply path 2220. The electric heaters 221, 222 can have identical or different heating capacities. A shut-off device 224, 225 can be connected upstream of each of the heaters 221, 222 after a branching point 223 downstream of the branching point 207, for example, to regulate the amount of air to be supplied to the respective heater 221, 222. The volume flows can be reunited at a connection point 226.Air from the primary air supply path 2210 and the secondary air supply path 2220 can be combined at a mixing section 213. For example, air with a first temperature from the primary air supply path 2210 and air with a second temperature from the secondary air supply path 2220 can be mixed together so that the air can achieve a mixed temperature. The thus tempered air can be supplied to the air supply section 122 via an air supply line section 2212. The air consumed in the electrolyzer stack 100 can be removed as air exhaust gas via an air exhaust section 125 from the air side 120 along an air exhaust discharge path 2500. For this purpose, the air exhaust discharge path 2500 can have an air exhaust discharge line section 2510. The air exhaust gas can be guided through a further air exhaust gas discharge line section 2520 in which a catalyst 412 is arranged for the catalytic combustion of the air exhaust gas.

[0096] The air exhaust gas can be mixed with various gas components along the air exhaust gas discharge path 2500 in order to further utilize the air exhaust gas, for example, in the electrolysis system 10. For example, a residual gas can be supplied to the air exhaust gas, which enables catalytic combustion in one or more catalysts 411, 412 described in more detail below. Preheated or unheated air from the air supply path 2200 can also be supplied to the air exhaust gas, for example, for the precise adjustment of stoichiometric ratios and / or temperatures.

[0097] Thus, the air exhaust gas can preferably be enriched with warm air from the air supply path 2200. For this purpose, the air supply path 2200 can have a branching point 206 upstream of the branching point 207, from which air is guided along an additional air heater heat path 2530 to a branching point 233 arranged in the air exhaust gas discharge path 2500. A further electric heater 231 can be provided in the additional air heater heat path 2530. The further electric heater 231 can thus be fluidly coupled to the air supply path 2200 and a section of the air exhaust gas discharge path 2500. A controllable shut-off device 235 can also be arranged between the further electric heater 231 and the branching point 206. The air exhaust gas can further be enriched with a residual gas.For this purpose, the air exhaust gas discharge path 2500 can have a connection point 251, to which the residual gas can be guided from a residual gas connection section 401 along a residual gas supply line 4110 and preferably a residual gas line branching section 4112. The connection point 251 can preferably be arranged between the air exhaust section 125 and the catalyst 412. Furthermore, the connection point 251 can preferably be arranged downstream of the connection point 233.

[0098] The air exhaust section 125 may further include a reactant heat exchanger 420 downstream of the catalyst 412 to heat the reactant to be supplied with the exhaust gas from the catalyst 412. The air exhaust may be guided to another catalyst 411 via air exhaust discharge line sections 2540 and 2560.

[0099] Downstream of the further catalyst 411, the two air heat exchangers 421, 422 can be provided. The exhaust gas from the catalyst 411 can thus be used to heat the air in the primary air supply path 2210. Preferably, the air exhaust gas upstream of the further catalyst 411 can be mixed with air from the air supply path 2200. For this purpose, the electrolysis system 10 can have an additional air heater heat path 2550 in which a further electric heater 241 is provided. For this purpose, a branching point 205 can be provided upstream of the branching points 206, 207. A shut-off device 245 can be provided between the branching point 206 and the further heater 241.

[0100] In an adjoining air exhaust line section 2570, two further heat exchangers 423, 424, namely a steam heat exchanger 423 and a carbon dioxide heat exchanger 424, can be provided. The exhaust gas from the catalyst 411 can thus be used again for heat transfer. The heat exchanger 424 can also be used, for example, during commissioning of the electrolysis system 10 to preheat an inert gas instead of carbon dioxide. Downstream of the heat exchangers 423, 424, the air exhaust gas can be guided into the air exhaust line section 2580 and finally released to the environment via an air exhaust outlet section 2501.

[0101] The figures also show that natural gas can optionally be added to the air exhaust gas upstream of the catalysts 411, 412. For this purpose, natural gas can be introduced via a natural gas section 402 and guided in an associated natural gas supply line 4210. The natural gas can be added, for example, as a replacement gas or bridging gas for the residual gas. The natural gas can also be added, in particular, during partial load operation. Residual gas can also be added to the air exhaust gas via residual gas branching sections 4111, 4112 upstream of the catalysts 411, 412.

[0102] The composition of the reactant for the electrolyzer stack 100 can be provided differently depending on the operating situation.

[0103] To generate synthesis gas, carbon dioxide (hereinafter referred to as CO2) and water vapor are used as reactants in the figures. For this purpose, CO2 can be introduced into the electrolysis system 10 via a CO2 feed section 3101. The CO2 can then be supplied to the

[0104] Reactant supply section 131 of the electrolyzer stack 100. The electrolysis system 10 has a reactant supply path 3100 for this purpose.

[0105] Steam can be introduced into the electrolysis system 10 via a steam inlet section 3105. The steam can be guided via steam supply lines 3151, 3152 via a connection point 307 into the reactant supply path 3100. For this purpose, the steam can be guided through the previously described steam heat exchanger 423 and further heated. The steam supply line 3151 can have a shut-off device 355. Furthermore, protective gas can be supplied to the reactant supply path 3100 from a first, second, and third protective gas supply section 3102, 3103, 3104. For this purpose, corresponding supply lines, such as a first protective gas supply line 3112, a second protective gas supply line 3113, and a third protective gas supply line 3114, can be provided, which open into the reactant supply path 3100 at connection points 305, 306. A heat exchanger 320 and an ejector 372 may further be provided in the reactant supply path 3100.

[0106] In the electrolyzer stack 100, a synthesis gas can be generated from the reactant in the reactant side 130. The synthesis gas can preferably be a synthesis gas. The synthesis gas can be conducted from a synthesis gas section 132 of the reactant side 130 via a synthesis gas discharge path 3200 to a synthesis gas outlet section 3201, which can preferably be fluidly connected to a synthesis system. Before leaving the electrolysis system 10, the synthesis gas can be passed through a synthesis gas cooler 321. A coolant can flow through the synthesis gas cooler 321, which can be introduced via a coolant supply section 801 and discharged again downstream of the synthesis gas cooler 321 via a coolant discharge section 801. The synthesis gas discharge path 3200 can further comprise the heat exchanger 320 to transfer heat from the synthesis gas to the reactant.The electrolysis system 10 may further include a recirculation path 3700 for conducting synthesis gas from the synthesis gas section 132 back to the reactant feed section 131 via the ejector 372. Instead of the ejector 372 shown as an example, other suitable components may of course also be provided. For example, a gas blower device could be provided. A shut-off device 371 may also be provided in the recirculation path 3700.

[0107] The electrolysis system 10 has various operating situations. Figure 1 shows some examples of such operating situations and their relationships to one another.

[0108] In the method 1000, an operating situation is detected and the electrolysis system 10 is controlled depending on the detected operating situation.

[0109] An operating situation is detected as a special operating situation if the detected operating situation deviates from the normal operation of the electrolysis system 10. If such a special operating situation is detected, at least one of the electric heaters 221, 222 is controlled for controlling the air temperature of the air in the air supply path 2200 in order to control a temperature of the electrolyzer stack 100. Furthermore, a heating gas comprising at least one protective gas is supplied to the reactant side 130 via the reactant supply path 3100.

[0110] Figures 2 to 10 show examples of how the electrolysis system 10 can be controlled for various operating situations. Inactive components of the electrolysis system 10 are shown grayed out in such situations.

[0111] Figure 3 shows an embodiment according to the invention for special operating situations, using a first warm-up operating situation BS222 as an example, which is detected in the method 1000 as soon as, for example, the operator of the electrolysis system 10 issues a process request to warm the electrolyzer stack 100 to a warm-up temperature. The electric heater 221 is switched on, and air from the air supply path 2200 is heated in the secondary air supply path 2220. A predeterminable heating curve can be followed in order not to exceed maximum permissible temperature gradients. The heated air can also be mixed with air from the primary air supply path 2210 in the mixing section 213 in order to adjust the air temperature even more precisely. The electrolyzer stack 100 is thus heated by the air.At the same time, a heating gas is supplied to the reactant side 130 for purging the reactant side 130, which is recirculated via the recirculation path 3700 to accelerate the warming up of the reactant side 130. During a first time period, the heating gas consists solely of protective gas (e.g., nitrogen). In Figure 3, the protective gas is supplied from the second protective gas supply section 3103. Subsequently, in a second time period, the composition of the heating gas can be changed so that it comprises a mixture of protective gas and hydrogen in order to reduce the electrode surface on the reactant side 130. For example, "Areal F5" can be introduced into the reactant supply path 3100 from the third protective gas supply section 3104 via connection point 333.The heating gas can thus, on the one hand, clean the reactant side 130 and reactant lines of foreign substances, and, on the other hand, absorb heat from the electrolyzer stack 100 and the heat exchangers 420 to 424 arranged along the air exhaust gas discharge path 2500. In this way, the reactant-related part of the electrolysis system 10 can also be heated. Branch line 3115, which has a connection point 353 to the steam introduction section 3105, can enable heating of the steam-related part of the electrolysis system 10.

[0112] Figure 4 shows an embodiment according to the invention for special operating situations, using a second warm-up operating situation BS223 as an example, which is detected in the method 1000 as soon as, for example, the heating gas discharged from the reactant side 130 has at least the warm-up temperature and the surface of the electrode of the reactant side 130 has a minimum electrical conductivity. Air is also supplied to the electrolyzer stack 100 by means of at least the electric heater 221. A supply of steam is initiated, so that in addition to the previously described area F5, steam is also supplied to the reactant side 130.

[0113] Figure 4 also shows an embodiment according to the invention for a standby operating situation BS330, which occurs when the temperature of the electrolyzer stack 100 reaches at least a minimum stack temperature and stack operating temperature. In this operating situation, the system typically waits for a request from the operator to produce the synthesis gas, i.e., the request to transition to normal operation. In addition to the electric heater 221, just enough heating gas in the aforementioned composition is supplied to the reactant side to maintain the temperature of the electrolyzer stack 100.

[0114] Figure 4 also shows an embodiment according to the invention for a start-up operating situation BS341 for commissioning the electrolysis system 10. This operating situation occurs when the aforementioned process request to generate the intended synthesis gas in a specific quantity is issued. The flow rate of the heating gas is progressively increased, so that electrical operation with the electrolyzer stack 100 becomes possible. For this purpose, a default function for the flow rates can be specified. The air side 120 continues to be supplied with air heated by the electric heater 221.

[0115] Figure 5 shows an inventive embodiment of the method 1000 for a low-power operating situation BS342. This operating situation occurs, for example, when the heating gas has a minimum flow rate through the reactant supply path 3100, which is required for a charge exchange between the electrodes of the reactant side 130 and the air side 120, which are connected by a closed electrical connection. When the aforementioned condition occurs, CO2 is also added to the reactant side 130 in addition to protective gas and water vapor. For this purpose, a feed curve can preferably be used to adjust the amount of CO2 to be added. At the same time, the amount of protective gas in the heating gas can be reduced. If the heating gas is recirculated, the heating gas results as a gas mixture with a composition including protective gas, CO2, water vapor, hydrogen, and recirculated heating gas exhaust gas. Furthermore, electrical current can be supplied to the electrolyzer stack 100.For this purpose, a power curve can be used to regulate the power flow. The synthesis gas generated in the electrolyzer stack 100 during this operation can be delivered to a synthesis plant for further processing. Since no or only insufficient amounts of residual gas may be present at this time, catalytic heating with the catalysts 411, 412 does not yet take place in the low-power operating situation BS342. The air side 120 is therefore still supplied with electrically heated air.

[0116] Figure 6 shows an inventive embodiment of the method 1000 for a normal operation operating situation BS350. This is not a special operating situation, since the normal operation operating situation BS350 corresponds to normal operation. The normal operation operating situation BS350 is detected as soon as the electrolyzer stack 100 has a minimum electrical stack current and the synthesis gas has a minimum operating temperature. In the normal operation operating situation BS350, no more protective gas is supplied to the reactant side 130, and no electrically heated air is supplied to the air side 120. Instead, residual gas from the synthesis process is supplied to the catalysts 411, 412 to enable catalytic heating. For this purpose, the air exhaust gas can be mixed with the residual gas. Accordingly, the secondary air supply path 2200 can be used to convey cold air to the mixing section 213.The heat of a catalyst exhaust stream from the catalysts 411, 412 can be transferred to the air and / or reactant to be supplied by means of the heat exchangers 420, 421, 422. Air, reactant, and electrical current are fed to the electrolyzer stack 100, thereby generating the intended synthesis gas. The reactant comprises carbon dioxide and water vapor, as well as recirculated synthesis gas. Operation can take place at full or partial load.

[0117] Figure 7 shows an inventive embodiment of the method 1000 for a reversing operating situation BS360. The reversing operating situation BS360 is a special operating situation and is detected when, for example, a process request to terminate the operation of the electrolyzer stack 100 is issued. Area F5 is now increasingly supplied to the reactant as a protective gas in order to use it as heating gas in the electrolysis system 10, also for cooling the electrolyzer stack 100. At the same time, the proportions of carbon dioxide and water vapor in the heating gas are reduced to "zero" according to corresponding decrease curves. Furthermore, the flow rates of the air and heating gas as well as the supplied amount of electrical current are reduced. The current reduction continues until no more current is supplied, i.e., the current intensity is "zero."In addition to the electric heater 221, the additional electric heater 241 shown in Figure 7 is used to control the temperature of the electrolyzer stack 100. Component-dependent maximum temperature gradients are preferably not exceeded. The third electric heater 241 can be used, for example, in a warm-up or cool-down process of the electrolysis system 10 to heat the catalyst 411.

[0118] Figure 8 shows an inventive embodiment of the method 1000 for a first cooling operating situation BS471 for cooling the electrolysis system 10. This special operating situation is detected if, for example, the electrical connection 511 has been interrupted after the process request to terminate. The heating gas composition is adjusted for this operating situation such that it only comprises area F5. The temperature of the electrolyzer stack 100 is controlled by means of the electric heater 221 and the further electric heater 241.

[0119] Figure 9 shows an inventive embodiment of the method 1000 for a second cooling operating situation BS472. This special operating situation is detected when, for example, the temperature of the electrolyzer stack 100 is between a first and a second stack temperature. In this operating situation, only a protective gas, such as nitrogen, is supplied to the reactant side 130. At the same time, the heating of air with the electric heaters 221 and 241 is increasingly reduced. When the permissible temperatures of the electrolyzer stack 100 are reached, the heating gas supply and air supply can be interrupted.

[0120] Figure 1, Figure 2 and Figure 10 show further special operating situations which should preferably not be regarded as special operating situations.

[0121] For example, Figure 1 shows a cold standby operating situation BS80, in which the electrolysis system 10 is in a sleep state. In the sleep state, the electrolysis system 10 may, for example, be in sleep mode or switched off, so that, for example, no operating fluids are pumped through the electrolysis system 10.

[0122] Figure 2 shows a check operating situation BS10, which occurs, for example, when a process request is made to check the functionality of the electrolyzer stack 100 and the components of the electrolysis system 10 (such as valves, sensors, etc.). In this operating situation, actual operating parameters of the electrolyzer stack 100, such as actual temperatures or actual pressures, are recorded, compared with stored operating limits, and evaluated accordingly. This check can preferably be performed at regular intervals.

[0123] Figure 10 shows a safety shutdown operating situation BS500, which occurs when the electrolysis system 10 enters a critical state. In this operating situation, pressurized protective gas, preferably nitrogen, is passed through the reactant supply path 3100 from the first protective gas supply section 3102. Furthermore, the air supply and power supply are prevented, and the electric heaters 221, 222, 241 are deactivated. Active pressure control can be implemented to prevent undue pressure differences from occurring in the electrolyzer stack 100 due to the sudden cooling and interruption of operation.

[0124] A further aspect of the invention relates to a control device 20 for operating an electrolysis system. This is illustrated by way of example in Figures 2 to 10. The control device 20 is designed in particular to carry out the previously described method 1000. The control device 20 can be connected to the components of the electrolysis system 10 via signaling.

[0125] Also shown in Figures 2 to 10 is an embodiment of the electrolysis system 10 according to the invention.

[0126] The above explanation of the embodiments describes the present invention exclusively by way of examples. Of course, individual features of the embodiments can be freely combined with one another, provided they are technically feasible, without departing from the scope of the present invention.

[0127] List of reference symbols

[0128] 10 Electrolysis system

[0129] 20 Control device

[0130] 100 electrolyzer stacks

[0131] 120 airside

[0132] 122 Air supply section

[0133] 125 Air exhaust section

[0134] 130 Reactant side

[0135] 131 Reactant feed section

[0136] 132 Synthesis gas section

[0137] 201 first flow air heater

[0138] 202 second flow air heater

[0139] 203 Air filter

[0140] 204 air blowers

[0141] 205 branching point

[0142] 206 branching point

[0143] 207 branch point

[0144] 213 mixing section

[0145] 215 shut-off device

[0146] 221 first electric heater

[0147] 222 second electric heater

[0148] 223 branching point

[0149] 224 shut-off device

[0150] 225 shut-off device

[0151] 226 junction

[0152] 231 additional electric heaters

[0153] 233 liaison office

[0154] 235 Shut-off device

[0155] 241 additional electric heaters

[0156] 245 Shut-off device

[0157] 251 liaison office

[0158] 305 junction

[0159] 306 junction

[0160] 307 Connection point 320 Heat exchanger

[0161] 321 Synthesis gas cooler

[0162] 333 liaison office

[0163] 353 liaison office

[0164] 355 shut-off device

[0165] 371 shut-off device

[0166] 372 Ejector

[0167] 401 residual gas connection section

[0168] 402 Natural Gas Section

[0169] 411 Catalyst

[0170] 412 Catalyst

[0171] 420 reactant heat exchanger

[0172] 421 Air heat exchanger

[0173] 422 air heat exchanger

[0174] 423 Steam heat exchanger

[0175] 424 CO2 heat exchangers

[0176] 510 power source

[0177] 511 electrical connection

[0178] 512 Electrode connection

[0179] 514 Relay

[0180] 801 Coolant supply section

[0181] 802 Coolant discharge section

[0182] 1000 procedures

[0183] 2200 air supply path

[0184] 2201 Air intake section

[0185] 2202 Air supply line section

[0186] 2210 primary air supply path

[0187] 2212 Air supply section

[0188] 2220 secondary air supply path

[0189] 2500 air exhaust gas discharge path

[0190] 2501 Air exhaust outlet section

[0191] 2510 Air exhaust pipe section

[0192] 2520 Air exhaust gas discharge line section

[0193] 2530 Additional air heater heat path 2540 Air exhaust gas discharge line section

[0194] 2550 Additional air heater heat path

[0195] 2560 Air exhaust gas discharge line section

[0196] 2570 Air exhaust gas discharge line section

[0197] 2580 Air exhaust gas discharge line section

[0198] 3100 Reactant feed path

[0199] 3101 CO2 supply section

[0200] 3102 first shielding gas supply section

[0201] 3103 second shielding gas supply section

[0202] 3104 third shielding gas supply section

[0203] 3105 Steam introduction section

[0204] 3110 CO2 supply line

[0205] 3112 first shielding gas supply line

[0206] 3113 second shielding gas supply line

[0207] 3114 third shielding gas supply line

[0208] 3115 branch line

[0209] 3151 steam supply line

[0210] 3152 steam supply line

[0211] 3200 Synthesis gas discharge path

[0212] 3201 Synthesis gas outlet section

[0213] 3700 Recirculation path

[0214] 4110 residual gas supply line

[0215] 4111 Residual gas pipeline branching section

[0216] 4112 residual gas pipeline branching section

[0217] 4210 Natural gas supply line

[0218] BS10 Review-Operating Situation

[0219] BS80 cold standby operating situation

[0220] BS222 first warm-up operating situation

[0221] BS223 second warm-up operating situation

[0222] BS330 Standby operating situation

[0223] BS341 Start-up operating situation

[0224] BS342 Low power operating situation

[0225] BS350 Normal Operation Operating Situation

[0226] BS360 reversing operating situation BS471 first cooling operating situation

[0227] BS472 second cooling operating situation

[0228] BS500 safety shutdown operating situation

Claims

Patent claims 1. A method (1000) for operating an electrolysis system (10) having at least one electrolyzer stack (100) with an air side (120) and a reactant side (130) and various operating situations, comprising the steps: - Recording an operating situation of the electrolysis system (10), - Control of the electrolysis system (10) depending on the detected operating situation, characterized by the steps: - detecting an operating situation of the electrolysis system (10) as a special operating situation if the detected operating situation deviates from a normal operation of the electrolysis system (10) for generating a designated synthesis gas from a reactant which can be supplied to the reactant side (130) via a reactant supply path (3100) of the electrolysis system (10), and - Controlling the electrolysis system (10) for the detected special operating situation, comprising the steps of: o Controlling at least one electric heater (221, 222) for controlling the air temperature of air which can be supplied to the air side (120) via an air supply path (2200) of the electrolysis system (10) in order to control a temperature of the electrolyzer stack (100); and o Supplying a heating gas to the reactant side (130) via the reactant supply path (3100), which heating gas comprises at least one protective gas.

2. Method (1000) according to claim 1, characterized by - detecting a special operating situation in the form of a first warm-up operating situation (BS222) preceding normal operation when a process request to warm up the electrolyzer stack (100) to a warm-up temperature is made; - Controlling the electrolysis system (10) for the first warm-up operating situation (BS222), comprising the steps: o Controlling a composition of the heating gas such that the heating gas comprises only the protective gas, preferably nitrogen, in a first time period and comprises a gas mixture of hydrogen and the protective gas in a second time period, wherein the gas mixture preferably has a composition of up to 95% nitrogen as the protective gas and up to 5% hydrogen, in order to at least partially reduce a surface of the electrode of the reactant side (130), preferably within the second time period; and / or - Recirculating the heating gas in a recirculation path (3700) of the electrolysis system (10), which extends between a synthesis gas section (132) of the reactant side (130) for discharging the synthesis gas and a reactant feed section (131) of the reactant side (130) for feeding the reactant.

3. Method (1000) according to claim 1 or claim 2, characterized by - detecting a special operating situation in the form of a second warm-up operating situation (BS223) preceding normal operation for warming up the electrolysis system (10), which preferably follows the first warm-up operating situation (BS222) when the heating gas discharged from the reactant side (130) has at least one warm-up temperature and / or a surface of the electrode of the reactant side (130) has a minimum electrical conductivity; - Controlling the electrolysis system (10) for the second warm-up operating situation (BS223), comprising the steps of: o supplying water vapor to the reactant side (130); and o controlling a composition of the heating gas as a gas mixture comprising water vapor, protective gas and hydrogen preferably a gas mixture having a composition of at least 3% hydrogen.

4. Method (1000) according to one of the preceding claims, characterized by - detecting a special operating situation in the form of a standby operating situation (BS330) preceding normal operation, which preferably follows the second warm-up operating situation (BS223) when the temperature of the electrolyzer stack (100) has at least one minimum stack temperature and preferably at least one stack operating temperature; - Controlling the electrolysis system (10) for the standby operating situation (BS330), comprising the steps of: o Controlling a composition of the heating gas as a gas mixture comprising water vapor, protective gas, and hydrogen, preferably in a composition with at least 3% hydrogen; and o Controlling a flow rate of the heated air and / or the heating gas to a minimum at which the temperature of the electrolyzer stack (100) is maintained between the minimum stack temperature and the stack operating temperature.

5. Method (1000) according to one of the preceding claims, characterized by - detecting a special operating situation in the form of a start-up operating situation (BS341) preceding normal operation for commissioning the electrolysis system (10), which preferably follows the standby operating situation (BS330) when a process request to generate the intended synthesis gas is made; - Controlling the electrolysis system (10) for the start-up operating situation (BS341), comprising the steps of: o Controlling a composition of the heating gas as a gas mixture comprising water vapor, hydrogen and protective gas; and o Controlling a flow rate of the heating gas through the reactant feed path (3100), wherein preferably the flow rate is controlled as a function of a target flow rate which is specified according to a preset function or as a minimum flow rate.

6. Method (1000) according to one of the preceding claims, characterized by - detecting a special operating situation in the form of a low-power operating situation (BS342) preceding normal operation for commissioning the electrolysis system (10), which preferably follows the start-up operating situation (BS341) when the heating gas has a flow rate through the reactant feed path (3100) which is at least necessary for a charge exchange between the electrodes of the reactant side (130) and the air side (120) connected by means of a closed electrical connection; - Controlling the electrolysis system (10) for the low-power operating situation (BS341), comprising the steps of: o supplying carbon dioxide to the reactant side (130); o controlling a composition of the heating gas as a gas mixture comprising protective gas, carbon dioxide, preferably in an amount following a supply curve, water vapor, hydrogen, and heating gas exhaust gas recirculated preferably via a recirculation path (3700); and o supplying electrical current to the electrolyzer stack (100), preferably according to a power curve.

7. Method (1000) according to one of the preceding claims, characterized by - detecting a normal operation operating situation (BS350) corresponding to a normal operation, which preferably follows the low-power operating situation (BS341) when the electrolyzer stack (100) has at least one electrical minimum stack current and preferably the synthesis gas has a minimum operating temperature; and / or - Controlling the electrolysis system (10) for the normal operation operating situation (BS350) corresponding to normal operation, comprising the steps: o Supplying carbon dioxide and water vapor as the reactant to the reactant side (130); o Controlling a composition of the reactant as a gas mixture comprising carbon dioxide, water vapor, and synthesis gas preferably recirculated via a recirculation path (3700); o Controlling the temperature of the electrolyzer stack (100) during normal operation by means of catalytic heating, comprising: ■ Feeding residual gas from a synthesis process in which synthesis gas is converted into hydrocarbons to a catalyst (411, 412) of the electrolysis system (10); ■ catalytic combustion of the residual gas by means of the catalyst (411, 412); ■ Transferring heat of a catalyst exhaust gas stream of the catalytic combustion by means of at least one heat exchanger (420, 421, 422) to the air to be supplied and / or the reactant to be supplied; o Supplying the air, the reactant and electrical current to the electrolyzer stack (100); o Generating the synthesis gas, preferably synthesis gas, by means of the electrolyzer stack (100) from the supplied air, the reactant and the electrical current, and o preferably deactivating the electrical heater (221, 222).

8. Method (1000) according to one of the preceding claims, characterized by - detecting a special operating situation in the form of a reversing operating situation (BS360) following normal operation if the electrolyzer stack (100) has an electrical stack current less than a minimum stack current or a process request to terminate the operation of the electrolyzer stack (100) is issued; - Controlling the electrolysis system (10) for the reverse operating situation (BS360), comprising the steps of: o controlling a composition of the heating gas as a gas mixture comprising protective gas, carbon dioxide, water vapor and heating gas exhaust gas preferably recirculated via a recirculation path (3700); o preferably reducing the proportions of carbon dioxide and water vapor in the heating gas, preferably according to reduction curves; o reducing flow rates of the air and the heating gas; o reducing the electrical current supplied to the electrolyzer stack (100), preferably according to a power reduction curve until no more current is supplied; o preferably additionally controlling the air temperature by means of a further electrical heater (231) arranged in the air supply path (2200) for heating the air.

9. Method (1000) according to one of the preceding claims, characterized by - detecting a special operating situation in the form of a first cooling operating situation (BS471) following normal operation for cooling the electrolysis system (10), which preferably follows the reversing operating situation (BS360) when an electrical connection (511) for a charge exchange between the electrodes of the reactant side (130) and the air side (120) is open; and Check the electrolysis system (10) for the first cooling Operating situation (BS471), comprising the steps: o Controlling a composition of the heating gas as a gas mixture comprising protective gas and hydrogen; o Preferably, additionally controlling the air temperature by means of a further electric heater (231) arranged in the air supply path (2200).

10. Method (1000) according to one of the preceding claims, characterized by - detecting a special operating situation in the form of a second cooling operating situation (BS472) following normal operation for cooling the electrolysis system (10), which preferably follows the first cooling operating situation (BS471) when the temperature of the electrolyzer stack (100) is between a first stack temperature and a second stack temperature; and - Controlling the electrolysis system (10) for the second cooling operating situation (BS472), comprising: o Controlling a composition of the heating gas such that it only comprises protective gas.

11. Method (1000) according to one of the preceding claims, characterized by - detecting a safety shutdown operating situation (BS500) when the electrolysis system (10) enters a critical state; - Controlling the electrolysis system (10) for the safety shutdown operating situation, comprising: o supplying protective gas, preferably nitrogen, through the reactant supply path (3100); o preventing the supply of air to the air side (120); o deactivating the electric heater (221, 222, 231); and o preventing the supply of electrical current to the electrolyzer stack (100).

12. Method (1000) according to one of the preceding claims, characterized by - detecting a check operating situation (BS10), which preferably precedes a special operating situation and a normal operation operating situation (BS350), when a process request to check the functionality of the electrolyzer stack (100) is made; - Checking the electrolysis system (10) for checking the operating situation, comprising: o Checking actual operating parameters of the electrolyzer stack (100), at least its actual temperature and / or the actual pressure occurring, with regard to operating limits.

13. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method (1000) according to any one of the preceding claims 1 to 12.

14. Control device (20) for operating an electrolysis system (10) with at least one electrolyzer stack (100) having an air side (120) and a reactant side (130), with an air supply path (2200) for supplying air to the air side (120), wherein at least one electric heater (221, 222) for controlling the air temperature is arranged in the air supply path (2200), and with a reactant supply path (3100) for supplying reactant to the reactant side (130), wherein the electrolysis system (10) has various operating situations, characterized by - a detection module (21) for detecting an operating situation of the electrolysis system (10), wherein the detection module (21) is configured to detect an operating situation as a special operating situation if the detected operating situation deviates from a normal operation of the electrolysis system (10) for generating a specified synthesis gas from the reactant; and - a situation control module (22) for controlling the electrolysis system (10) depending on the detected operating situation, wherein the situation control module (22) for the detected special operating situation is configured to control at least the electric heater (221, 222) for controlling a temperature of the electrolyzer stack (100), and further to supply a heating gas comprising at least one protective gas to the reactant side (130) via the reactant supply path (3100).

15. Electrolysis system (10), preferably a SOEC or CO-SOEC system, comprising: - at least one electrolyzer stack (100) having an air side (120) and a reactant side (130), - an air supply path (2200) for supplying air to the air side (120), wherein at least one electric heater (221, 222, 241) for controlling the air temperature is arranged in the air supply path (2200), - a reactant supply path (3100) for supplying reactant to the reactant side (130), and - different operating situations, comprising at least one normal operation operating situation (BS350) corresponding to a normal operation, and at least one special operating situation which deviates from a normal operation of the electrolysis system (10) for generating a specified synthesis gas from the reactant, characterized by a control device (20) according to claim 14.

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