Method and device for operating a fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (10) that comprises at least one fuel cell stack (100) having an air side (120) and having a fuel side (130). The fuel cell system (10) is operated in various operating situations which include a normal operating situation (BS350) for outputting electrical power and numerous special operating situations during transitions from or to the normal operating situation (BS350). The method comprises detecting a present operating situation of the fuel cell system (10) and controlling the fuel cell system (10) in accordance with the detected present operating situation. For a detected special operating situation, an air temperature of air that can be fed to the fuel cell system (10) via an air inlet portion (112) is controlled by means of at least one electric heater (223, 243). Furthermore, a course of at least one flow path of the thus-heated air in the fuel cell system (10) is selected from at least two possible flow path courses in the fuel cell system (10) in accordance with the special operating situation. The invention also relates to a computer program product and to a control device (20) for carrying out the method. The invention also relates to a fuel cell system (10).

Description

[0001] Method and device for operating a fuel cell system

[0002] The present invention relates to a method for operating a fuel cell system, and to a computer program product and a control device for implementing this method. The invention further relates to a fuel cell system.

[0003] Fuel cells represent a suitable solution for generating electrical energy from energy sources such as natural gas or biomethane while avoiding emissions. Natural gas or biomethane can be converted into hydrogen in a reformer to supply the fuel cell. In the fuel cell, the electrochemical reaction of hydrogen and oxygen produces electricity, water, and heat, as well as no environmentally harmful emissions such as carbon dioxide.

[0004] Solid oxide fuel cells (SOFCs for short) have proven to be particularly advantageous, as they operate particularly efficiently at temperatures between 500°C and 900°C.

[0005] It is known from the prior art to operate such fuel cell 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, intermediate states that occur between a resting state and an active operating state pose particular technical challenges for the operating strategy for controlling the fuel cell system. For example, start-up and shutdown processes must be designed specifically for temperature-sensitive components, and system safety must be ensured.

[0006] Disadvantages of existing operating strategies are that the start-up and shut-down processes implemented in them take a relatively long time and require a high level of energy. This places relatively high thermal and mechanical stress on the components of the fuel cell system. Furthermore, a protective gas or inert gas is often required during the start-up and shut-down processes in order to operate the fuel cell system safely in such transient states. This has the disadvantage that the fuel cell system must be designed and controlled accordingly in order to use the protective gas. This leads to a high level of complexity in the control software and the fuel cell system. This correspondingly increases the costs for designing, manufacturing, and operating the fuel cell system. Furthermore, the use of protective gases can also be associated with additional energy consumption, which can lead to a reduction in the efficiency of the fuel cell system.

[0007] It is therefore an object of the present invention to at least partially remedy the disadvantages described above. In particular, the present invention aims to increase the efficiency of high-temperature fuel cell systems in a cost-effective and simple manner. Furthermore, the invention preferably provides a solution that makes it possible to dispense with the use of protective or inert gases during transient states during operation of the fuel cell system.

[0008] 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 a fuel cell system having the features of claim 15.

[0009] 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 fuel cell system according to the invention, and vice versa, so that with regard to the disclosure of individual aspects of the invention, reference is always made or can be made to each other.

[0010] One aspect of the invention relates to a method for operating a fuel cell system. The fuel cell system has at least one fuel cell stack with an air side and a fuel side. The fuel cell system is operated in various operating situations, which include a normal operating situation for electrical power output and a plurality of special operating situations during transitions from or to the normal operating situation. In the method, a current operating situation of the fuel cell system is detected. The fuel cell system is controlled depending on the detected current operating situation. For a detected special operating situation, an air temperature of air that can be supplied to the fuel cell system via an air inlet section is controlled at least by means of an electric heater.For the detected special operating situation, at least one course of a flow path of the heated air in the fuel cell system is selected from at least two possible flow path courses of the fuel cell system as a function of the detected special operating situation.

[0011] In other words, a method for operating a fuel cell system is provided. The method can, for example, implement an operating strategy.

[0012] In this context, "operating a system" can preferably be understood as instructing the system to operate. The fuel cell system can, for example, be a high-temperature fuel cell system or an SOFC fuel cell system.

[0013] The fuel cell system comprises at least one fuel cell stack with an air side and a fuel side, as well as various operating situations.

[0014] Within the scope of the invention, an "operating situation" can be understood in particular as an operating method or operating mode. An operating situation can be defined by a current control sequence of the fuel cell system. An operating situation can also be defined, for example, by physical variables, such as actual pressures or actual temperatures, which occur in the fuel cell system, and / or by a control command. The fuel cell system has a multitude of different operating situations. Preferably, the fuel cell system can only have one operating situation at a time.

[0015] According to the invention, an operating situation is detected as a special operating situation if the detected operating situation deviates from normal operation of the fuel cell system for electrical power output.

[0016] Within the scope of the invention, “detecting a current operating situation” can be understood in particular as registering an actual operating situation. For example, in addition to recording and / or measuring information relating to operating situations, detecting can preferably also comprise evaluating or classifying this information. For example, an operating situation can be determined from the information recorded relating to an operating situation. 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 fuel cell system. A special operating situation can therefore particularly be idle and / or transitional states of the fuel cell system that occur, for example, before and / or after normal operation.In particular, the special operating situations can be operating situations during a heating process or a cooling process. Within the scope of the invention, "normal operation" can be understood in particular as stationary or at least semi-stationary operation of the fuel cell system. During normal operation, the fuel cell system converts chemical energy into electrical energy as intended and outputs it as electrical current. Normal operation can preferably comprise operation of the fuel cell system under full load and / or partial load (preferably at least 50% production capacity).

[0017] According to the invention, the fuel cell system is controlled depending on the detected operating situation.

[0018] In the context of the invention, “regulation” can be understood in particular as controlling and / or monitoring input variables, parameters, manipulated variables and / or components of the fuel cell system.

[0019] For the detected special operating situation, the temperature of air that can be supplied to the fuel cell system via an air inlet section is regulated by means of at least one electric heater. Furthermore, for the detected special operating situation, at least one flow path of the electrically heated air in the fuel cell system is selected from at least two possible flow path profiles of the fuel cell system, depending on the detected special operating situation with regard to its course in the fuel cell system.

[0020] Within the scope of the invention, a "flow path" can be understood in particular to mean a flow and / or flow path of a fluid, such as air or another cathode gas here. The flow path can preferably extend between two points, which are preferably part of the route between the source and sink of the flow. Within the scope of the invention, a "course" can be understood in particular to mean an extension or a connection between two points. Within the scope of the invention, "selecting a course" can be understood in particular to mean a targeted specification and / or setting of one of several possible flow paths in the fuel cell system. By specifically selecting the course, the electrically heated air can be given a flow path from the number of flow paths possible in the fuel cell system. For this purpose, the electric heater can be connected to at least two separate lines.

[0021] With the method according to the invention, operating situations that do not correspond to normal operation can be identified and regulated in a situation-specific manner. In operating situations that occur during transitions to and from normal operation, electric heaters are used for heating, which can quickly and precisely provide a defined amount of heat. Furthermore, by selecting the flow path, the heat can be distributed locally and specifically within the fuel cell system. The combination of the aforementioned design features makes it possible to dispense with protective gas or inert gas, since sections and / or components of the fuel cell system can be heated and cooled specifically and in a predeterminable sequence. Accordingly, the method allows heating and cooling processes to be implemented solely using operating resources from normal operation.As a result, energy consumption and operating costs can be reduced without having to compromise on system safety.

[0022] According to a preferred embodiment, a first warm-up operating situation for warming up the fuel cell system can be detected as one of the special operating situations for the transition to the normal operation operating situation. The special operating situation can thus have a first warm-up operating situation. The first warm-up operating situation can precede the normal operation operating situation. The fuel cell system can preferably be operated in the first warm-up operating situation after a process request to warm up the fuel cell system is issued. In the first warm-up operating situation, the fuel cell system can preferably heat a primary electric heater to a heater temperature. Furthermore, in a first warm-up operating situation, the air temperature can preferably be controlled by means of a secondary electric heater. A catalyst warm-up curve can preferably be used to control the air temperature.A flow path of the air heated by the secondary heater can be selected to flow to a catalyst of the fuel cell system, which is provided for the catalytic combustion of fuel exhaust gas, in order to heat the catalyst to its catalyst activation temperature. Operation in the first warm-up operating situation can preferably continue at least until the catalyst reaches a catalyst start temperature.

[0023] Thus, in the first warm-up operating situation, a catalyst in the fuel exhaust path can be heated to its catalyst activation temperature by the at least one electric heater by passing the heated air from the at least one electric heater to the catalyst.

[0024] In the context of the invention, a “process request” can be understood in particular as a programming command or control command by the user, which can be transmitted, for example, to a control device.

[0025] This makes it possible to heat the catalyst to the activation temperature at the beginning of a heating process. Reaching the activation temperature makes it possible to supply the fuel cell system with additional operating materials without fear of releasing harmful substances from the fuel cell system, as the catalyst can be operated in a chemically active manner. At the same time, heat can be generated in the fuel cell system through catalytic combustion and distributed from the catalyst. This allows the heating process to be accelerated and carried out safely.

[0026] According to a further preferred embodiment, a second warm-up operating situation for warming up the fuel cell system can be detected as one of the special operating situations for the transition to the normal operation operating situation. This can precede the normal operation operating situation and preferably follow the first warm-up operating situation. The special operating situation can be a second warm-up operating situation. The fuel cell system can be operated in the second warm-up operating situation as soon as the catalyst has at least one catalyst start temperature of a catalyst of the fuel cell system for the catalytic combustion of fuel exhaust gas.

[0027] For the second warm-up operating situation, a heating gas, such as methane, can be supplied via a fuel line to a fuel supply section on the fuel side for supplying the fuel to absorb heat from the heated air in the fuel cell stack. The heating gas supplied in this way can further be recirculated in a recirculation line of the fuel cell system to heat fuel-carrying lines of the fuel cell system. The recirculation line can extend between a fuel exhaust section on the fuel side for discharging the fuel exhaust gas and a section of the fuel line upstream of the fuel supply section. Furthermore, the air temperature can be regulated at least by means of a primary electric heater. Preferably, a fuel line warm-up curve can be used for temperature control.In addition, a flow path for the heated air can be selected, which runs from the preferably primary heater to an air supply section on the air side. Preferably, the fuel cell system can be operated in the second warm-up operating situation at least until the recirculation line and the fuel line have a minimum line temperature. Preferably, the minimum line temperature can be at least a water vapor condensation temperature. Preferably, the water vapor condensation temperature can be defined by the operating pressure in the fuel line.

[0028] Thus, in the second warm-up operating situation, fuel-carrying lines of the fuel cell system can be heated by directing the heated air from the at least one electric heater to the air side of the fuel cell stack and, furthermore, supplying a heating gas from the fuel side to the fuel cell stack to absorb heat from the heated air there, wherein the heating gas thus heated is recirculated via a recirculation line between the fuel exhaust gas section and a section of the fuel line. This makes it possible to heat the fuel line to a specific temperature. In particular, it can be prevented that water vapor, which is to be supplied to a reformer for reforming, condenses in the fuel line. It is advantageous here that the heating gas in the fuel cell stack can absorb heat and can be repeatedly used for warming up via the recirculation.This allows the heating process to be accelerated and carried out safely. The heating gas can be an anode gas, which is also preferably used during normal operation.

[0029] According to a preferred embodiment, the fuel cell system can further be operated in a third warm-up operating situation for warming up the fuel cell system. The third warm-up operating situation can precede the normal operation operating situation and preferably follow the second warm-up operating situation. The special operating situation can be a third warm-up operating situation. The third warm-up operating situation can be detected as one of the special operating situations for the transition to the normal operation operating situation. Operation in the third warm-up operating situation can preferably take place when a fuel line and a recirculation line of the fuel cell system have at least one minimum line temperature. The minimum line temperature can preferably be the water vapor condensation temperature.

[0030] For the third warm-up operating situation, the air temperature can preferably be regulated by means of at least one secondary electric heater. A flow path for the air, which is preferably heated by the secondary heater, can be selected such that it runs from the heater to an inlet of a reformer heat exchanger of a reformer in order to heat the reformer to its reformer activation temperature. The reformer can be provided in the fuel cell system for generating fuel to be supplied to the fuel side. Alternatively or additionally, the flow path can be selected such that it runs from the heater to a catalyst of the fuel cell system for the catalytic combustion of fuel exhaust gas.Furthermore, the temperature of the reformer can be regulated to a reformer start temperature, such as its reformer activation temperature, by controlling the flow rate of the heated air through the reformer heat exchanger, preferably by means of a control valve. The control valve can be provided along the flow path upstream of the inlet of the reformer heat exchanger. The reformer temperature can thus be regulated preferably according to a reformer warm-up curve. Steam can be supplied to the reformer as soon as the reformer reaches the reformer start temperature.

[0031] Thus, in the third warm-up operating situation, a reformer for producing fuel can be heated to its activation temperature by passing the heated air from the at least one electric heater to a reformer heat exchanger of the reformer in order to heat the reformer to its activation temperature.

[0032] This allows the reformer to heat up to its activation temperature. Fast heat-up times can be achieved because heat from both the (secondary) heater and the fuel cell stack can be utilized. Regulating the reformer temperature using a control valve enables simple and precise temperature control. Since steam is added when the reformer's activation temperature is reached, carbonization of the reformer's catalyst surface can be prevented. This allows the heat-up process to be achieved quickly and safely.

[0033] According to a preferred embodiment, the fuel cell system can further be operated in a fourth warm-up operating situation for warming up the fuel cell system. The fourth warm-up operating situation can precede the normal operation operating situation and preferably follow the third warm-up operating situation. The special operating situation can thus be a fourth warm-up operating situation. The fourth warm-up operating situation can be detected as one of the special operating situations for the transition to the normal operation operating situation. Operation in the fourth warm-up operating situation can preferably take place when a reformer of the fuel cell system has at least one reformer start temperature, such as the reformer activation temperature, for generating fuel to be supplied to the fuel side.

[0034] For the fourth warm-up operating situation, the air temperature can preferably be regulated by means of a primary electric heater and / or a secondary electric heater until a minimum stack temperature of the fuel cell stack is reached. A flow path for the air heated by the heater(s) can be selected to run to a conduit section that is heat-transferringly or fluidly coupled to a section of an air supply path leading to the air side. Furthermore, steam and fuel gas can be supplied to the reformer to generate the fuel. Furthermore, the fuel and heated air thus generated can be supplied to the fuel cell stack.

[0035] Thus, in the fourth warm-up operating situation, the fuel cell stack can be heated to a minimum stack temperature by supplying the heated air from the electric heater to the air side, and further supplying water vapor and a heating gas to the reformer to generate a fuel, wherein the generated fuel is supplied to the fuel side to release heat while generating electrical power in the fuel cell stack.

[0036] In this way, a synthesis gas can be generated as a reformate in the reformer. This synthesis gas and heated air can be used to further heat the fuel cell stack. The air can be heated both electrically and indirectly through catalytic combustion of the synthesis gas in the catalyst.

[0037] For example, the fuel cell system can also be operated in a standby operating situation. The standby operating situation can precede the normal operation operating situation and preferably follow the fourth warm-up operating situation. The standby operating situation can preferably be recorded as a special operating situation or a further normal operation operating situation. The standby operating situation can preferably be applied for operation when the temperature of the fuel cell stack has at least a minimum stack temperature. For a standby operating situation, steam and fuel gas can be supplied to the reformer to generate the fuel. Furthermore, the fuel thus generated and electrically or catalytically heated air can be supplied to the fuel cell stack.In addition, the flow rate of heated air and fuel to the fuel cell stack can be regulated to minimum flow rates at which the fuel cell stack maintains at least the minimum stack temperature. Thus, the fuel cell system can be maintained in a standby state, from which it can, for example, be switched to normal operation as active operation. The resources required to maintain this state can be reduced to the minimum necessary.

[0038] According to a preferred embodiment, the fuel cell system can be operated in the normal operation operating situation corresponding to normal operation, preferably when the fuel cell stack has at least a minimum stack temperature. A normal operation operating situation can preferably follow a low-power operating situation. The normal operation operating situation can be detected.

[0039] In a normal operating situation, air and fuel can be supplied to the fuel cell stack. Electric current can be generated in the fuel cell stack from the supplied air and fuel. The temperature of the fuel cell stack can be regulated by means of catalytic heating. Accordingly, the at least one electric heater can preferably be deactivated. Catalytic heating can be achieved, for example, by conducting air exhaust gas from an air outlet section on the air side and fuel exhaust gas from a fuel exhaust section on the fuel side to a catalyst of the fuel cell system. Heat from the fuel exhaust gas can be transferred to the fuel to be supplied by means of at least one fuel heat exchanger. The fuel heat exchanger can preferably be arranged in a section of a fuel line upstream of the fuel cell stack.The fuel exhaust gas can be catalytically combusted by the catalyst. Heat from the resulting catalyst exhaust gas stream can be transferred to the supply air by means of at least one air heat exchanger. The air heat exchanger can preferably be arranged in a section of an air supply line upstream of the fuel cell stack.

[0040] Thus, for normal operation, the at least one electric heater can be deactivated and the temperature of the fuel cell stack can be regulated by transferring at least heat from the exhaust stream of a catalyst arranged in the fuel exhaust path to the air to be supplied and to the fuel to be supplied by means of heat exchangers. Within the scope of the invention, "catalytic heating" can be understood in particular as the introduction of heat into the fuel cell system by means of heat generation in a catalyst. "Deactivating the electric heater" can be understood in particular as interrupting the power supply to the electric heater.

[0041] Thus, by actively operating the fuel cell system, chemical energy can be converted into electrical energy in the fuel cell stack as intended and released to the outside.

[0042] The fuel cell system may further comprise a low-power operating situation. A low-power operating situation may preferably immediately precede or follow the normal operation operating situation. Alternatively or additionally, a low-power operating situation may follow the standby operating situation or the normal operation operating situation. The low-power operating situation may, for example, be used for operation when a process request is made to generate and deliver electrical power. For the low-power operating situation, the generated fuel and heated air may be supplied to the fuel cell stack. Electrical power may be generated in the fuel cell stack from the supplied air and fuel. The flow rate of the heated air and fuel to the fuel cell stack may preferably be regulated according to a stack power delivery curve.

[0043] Thus, the fuel cell system can be guided towards or away from active operation while taking endothermic regions into account.

[0044] According to a preferred embodiment, the fuel cell system can further be operated in a first cooling operating situation for cooling the fuel cell system. The first cooling operating situation can preferably follow the normal operation operating situation and further preferably follow the low-power operating situation. The first cooling operating situation can preferably be detected as one of the special operating situations for the transition from the normal operation operating situation. The fuel cell system can be operated in the first cooling operating situation when a process request to cool down the fuel cell system is issued. In the first cooling operating situation, the air temperature can preferably be regulated according to a cooling curve by means of at least one electric heater. The electric heater can preferably be a secondary heater of two electric heaters.Furthermore, a flow path for the heated air can be selected that leads to an inlet of a reformer heat exchanger. The reformer heat exchanger is preferably provided by a reformer of the fuel cell system, which is provided for generating fuel to be supplied to the fuel side. Furthermore, air exhaust from the air side can be supplied to the inlet of the reformer heat exchanger. The temperature of the reformer can be regulated by controlling a flow rate of the gas mixture consisting of the heated air and the air exhaust through the reformer heat exchanger using a control valve. The control valve can be provided along the flow path upstream of the inlet of the reformer heat exchanger. Preferably, the temperature of the reformer can be regulated according to a reformer cooling curve. The temperature of the fuel cell stack can also be regulated to a first stack cooling temperature.This can preferably be carried out according to a stack cooling curve. Furthermore, the first stack cooling temperature can preferably be lower than the minimum stack temperature for normal operation. To regulate the temperature of the fuel cell stack, a flow rate of fuel to be supplied to the fuel side can be regulated. The first cooling operating situation can preferably continue until the first stack cooling temperature is reached. The fuel can preferably be fuel produced in the reformer. The first stack cooling temperature can preferably be 377°C.

[0045] Thus, in the first cooling operating situation, a temperature of a reformer for generating fuel can be controlled by the at least one electric heater by supplying the heated air to an inlet of a reformer heat exchanger of the reformer and further supplying air exhaust gas from the air side to the inlet of the reformer heat exchanger.

[0046] In this way, the fuel cell stack can be cooled by the reformate from the reformer. Excessive or rapid cooling of the reformer's temperature can be prevented by heat transfer from the exhaust air and electrically heated air to the reformer. The control valve enables quick and efficient control.

[0047] According to a further preferred embodiment, the fuel cell system can further be operated in a second cooling operating situation for cooling the fuel cell system. The second cooling operating situation can follow normal operation and preferably the first cooling operating situation. Preferably, the second cooling operating situation can be a special operating situation. The second cooling operating situation can be detected as one of the special operating situations for the transition from normal operation. Preferably, the fuel cell stack can be operated in the second cooling operating situation when the fuel cell stack has a first stack cooling temperature.

[0048] In the second cooling operating situation, the air temperature can preferably be controlled by means of a secondary electric heater. The air temperature can preferably be controlled according to a cooling curve. Furthermore, a flow path for the heated air can be selected that runs from the electric heater to a catalyst of the fuel cell system for the catalytic combustion of fuel exhaust gas in order to enable its operation above its catalyst activation temperature. Furthermore, a temperature of a reformer of the fuel cell system for generating fuel to be supplied to the fuel side can be controlled to a reformer start temperature, such as a reformer activation temperature, by supplying fuel gas and water vapor to the reformer for heat removal. This can preferably be continued until the reformer has a temperature of at most the reformer start temperature.As soon as the reformer has a temperature lower than the reformer start temperature, the supply of steam to the reformer can be stopped.

[0049] In the second cooling operating situation, a catalyst can thus be heated by the electric heater to continue catalyst operation above the catalyst activation temperature. Heating occurs by directing heated air from the at least one electric heater to the catalyst. Furthermore, the temperature of the reformer can be lowered by supplying it with heating gas and steam. In this way, the reformer can be cooled below its activation temperature. Carbonization of the reformer's catalyst surface can be prevented by shutting off the steam supply early on.

[0050] According to a preferred embodiment, the fuel cell system can further be operated in a third cooling operating situation for cooling the fuel cell system, preferably when a temperature of a reformer of the fuel cell system for generating fuel to be supplied to the fuel side is lower than a reformer activation temperature. The third cooling operating situation can preferably follow the normal operation operating situation and preferably the second cooling operating situation. The third cooling operating situation can preferably be a special operating situation. A third cooling operating situation can be detected as one of the special operating situations for the transition from the normal operation operating situation.

[0051] In the third cooling operating situation, the air temperature can be regulated to a catalyst activation temperature, preferably by means of a secondary electric heater. In this case, a cooling curve can preferably be followed. Furthermore, a flow path for the heated air can be selected, which runs from the (secondary) heater to a catalyst of the fuel cell system for the catalytic combustion of fuel exhaust gas. Furthermore, the temperature of the fuel cell stack can be regulated to a second stack cooling temperature by regulating the flow rates of a heating gas, which can be supplied to a fuel supply section on the fuel side, and of the air. Preferably, the fuel cell system can be operated in the third cooling operating situation until the second stack cooling temperature is reached. In this case, a stack cooling curve can preferably be followed.

[0052] Thus, in the third cooling operating situation, the fuel cell stack can preferably be cooled to room temperature, with the electric heater continuing to supply the catalyst with electrically heated air in order to operate the catalyst above the catalyst activation temperature and thus maintain the catalytic conversion in the catalyst. The temperature of the fuel cell stack can be controlled simultaneously by regulating the flow rates of the heating gas and the air until a second stack cooling temperature, preferably room temperature, is reached. This allows the fuel cell stack to be cooled with air and heating gas (e.g., natural gas). At the same time, it can be ensured that the temperature of the catalyst does not fall below its activation temperature, so that only non-combustible substances leave the fuel cell system. This can increase the safety and efficiency of the fuel cell system.

[0053] According to a further preferred embodiment, the fuel cell system can further be operated in a fourth cooling operating situation for cooling the fuel cell system, preferably when the fuel cell stack has a temperature of at most a second stack cooling temperature. Preferably, the second stack cooling temperature can be at most room temperature (i.e., for example, 19°C to 22°C). The fourth cooling operating situation can follow the normal operation operating situation and / or preferably follow the third cooling operating situation. Preferably, the fourth cooling operating situation can be a special operating situation. A fourth cooling operating situation can be detected as one of the special operating situations for the transition from the normal operation operating situation.

[0054] For the fourth cooling operating situation, the air temperature can be regulated to a catalyst rest temperature by means of the at least one electric heater, which can preferably be a secondary heater. A cooling curve can preferably be followed. A flow path for the heated air can be selected, which runs from the heater to a catalyst of the fuel cell system for the catalytic combustion of fuel exhaust gas in order to cool the catalyst below its catalyst activation temperature. Furthermore, the temperature of the catalyst can be regulated to the catalyst rest temperature, preferably according to a catalyst cooling curve, by regulating flow rates of a heating gas, which can be supplied to a fuel supply section on the fuel side, and of the air.Preferably, the fuel cell system can be operated in the fourth cooling operating situation until the second stack cooling temperature is reached in the catalyst.

[0055] This allows the catalyst to be further cooled and the fuel cell system to be brought into a safe state.

[0056] According to a preferred embodiment, the fuel cell system can additionally be operated in a safety shutdown operating situation. A safety shutdown operating situation can be configured to be detected when the fuel cell system enters a critical state. For the safety shutdown operating situation, the supply of air to the air side and the supply of fuel to the fuel side can be prevented.

[0057] In the context of the invention, a “critical condition” can be understood as meaning, in particular, the occurrence of component failure, leaks, temperatures, pressures or reaction products outside the operating limits of the fuel cell system.

[0058] This makes it possible to place the fuel cell system into a safe operating range if conditions arise within the fuel cell system that could have potentially dangerous consequences for the system and / or people. This further increases the safety of the fuel cell system's operation.

[0059] According to a further preferred embodiment, the fuel cell system can also be operated in a check operating situation. A check operating situation can precede a special operating situation and / or a normal operating situation. A check operating situation can be adapted to be detected when a process request to check the functionality of the fuel cell stack is issued. In a check operating situation, actual operating parameters of the fuel cell stack, preferably at least its actual temperature and / or the actual pressure occurring therein, can be compared with respect to operating limits.

[0060] This makes it possible to check the fuel cell system for functionality and condition at regular intervals, especially before commissioning. This can further increase the safety of the fuel cell system's operation.

[0061] According to a further preferred embodiment, the fuel cell system can have two electric heaters, each arranged in one of two parallel line sections of the air supply path. For the particular operating situation detected, a primary electric heater and / or a secondary electric heater can be selected as the electric heater(s) for regulating the air temperature, depending on the particular operating situation.

[0062] This allows the heat generation capacity of two electric heaters to be utilized during operation. Depending on the heat demand, operation can be carried out using either one or both heaters. Furthermore, individual heaters can be connected to different components, allowing specific components to be supplied with heat from specific heaters.

[0063] According to a preferred embodiment, in special operating situations for warming up the fuel cell system, heat can be provided by the at least one electric heater in a heating sequence. Using this heating sequence, a catalyst for catalytic combustion of fuel exhaust gas, fuel-carrying lines, a reformer for fuel generation, and the fuel cell stack can each be heated to their operating temperature for normal operation.

[0064] Accordingly, for these special operating situations, the flow paths for the heated air can be selected depending on the heating sequence.

[0065] This eliminates the need for protective or inert gases during the heating process. A heating sequence can be understood, in particular, as a sequence or predefined order for components of the fuel cell system. A schedule for the heating process can preferably be created based on this sequence or prioritization.

[0066] A further aspect of the invention relates to a computer program product with 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 a fuel cell system. The fuel cell system has at least one fuel cell stack with an air side and a fuel side, and at least one electric heater for regulating the air temperature of air that can be supplied to the fuel cell system via an air inlet section. The fuel cell system is further operated in various operating situations. The operating situations include a normal operating situation for electrical power output and a plurality of special operating situations during transitions from or to the normal operating situation. The control device has a detection module for detecting a current operating situation of the fuel cell system. Furthermore, the control device has a situation control module for regulating the fuel cell system depending on the detected current operating situation.The situation control module is configured to regulate the air temperature for a detected special operating situation using the at least one electric heater. Furthermore, the situation control module is configured to select a course of at least one flow path of the electrically heated air in the fuel cell system from at least two possible flow path courses of the fuel cell system depending on the detected special operating situation.

[0068] A further aspect of the invention relates to a fuel cell system. The fuel cell system comprises at least one fuel cell stack having an air side and a fuel side. Furthermore, the fuel cell system comprises at least one electric heater for regulating the air temperature of air that can be supplied to the fuel cell system via an air inlet section. The fuel cell system also comprises the previously described control device for operating the fuel cell system in the aforementioned various operating situations. The fuel cell system can, for example, be an SOFC or SOEC fuel cell system.

[0069] With the aforementioned computer program product, fuel cell system and control device, all of the advantages already explained for the method according to the invention can be achieved.

[0070] 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 and are referred to as first component, second 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 and therefore does not limit their nature.

[0071] The connections mentioned herein are fluid-carrying, such as gas-carrying, connections. The connections can be established via various paths or lines, such as pipes or hoses, which are each coupled to one another. Flow-influencing devices, such as shut-off devices, can be arranged in the connections.

[0072] 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.

[0073] Shut-off devices serve, at a minimum, 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, flow rate control is also possible. For this purpose, the shut-off devices can be equipped with appropriate control electronics and sensors. The shut-off device can take various forms, for example, as a valve, gate valve, shut-off cock, or butterfly valve.

[0074] Further advantages, features, and details of the invention will become apparent from the following description. The description describes exemplary embodiments of the invention with reference to the figures. They show schematically:

[0075] Fig. 1 shows an embodiment of the method according to the invention,

[0076] Fig. 2 shows an embodiment of the fuel cell system according to

[0077] Invention and an embodiment of the control device according to the invention, Fig. 3 shows a further embodiment of the fuel cell system according to the invention and its operation according to the invention in a check operating situation,

[0078] Fig. 4 shows the fuel cell system of Figure 3 during operation according to the invention in a first warm-up and a fourth cool-down operating situation,

[0079] Fig. 5 shows the fuel cell system of Figure 3 during operation in a second warm-up operating situation according to the invention,

[0080] Fig. 6 shows the fuel cell system of Figure 3 during operation in a third warm-up operating situation according to the invention,

[0081] Fig. 7 shows the fuel cell system of Figure 3 during operation in a fourth warm-up operating situation according to the invention,

[0082] Fig. 8 shows the fuel cell system from Figure 3 during operation in a normal operation situation,

[0083] Fig. 9 shows the fuel cell system of Figure 3 during operation in a first cooling operating situation according to the invention,

[0084] Fig. 10 shows the fuel cell system of Figure 3 during operation in a second cooling operating situation according to the invention, and

[0085] Fig. 11 shows the fuel cell system from Figure 3 during operation in a third cooling operating situation according to the invention.

[0086] The figures show different aspects and embodiments of the invention.

[0087] The invention relates to a method 1000 for operating a fuel cell system in various operating situations. The fuel cell system 10 shown in Figures 2 to 11 can, for example, be operated using the method 1000. Operating situations can be illustrated in a first approximation step as situations that may occur during normal operation, idle operation, or during operating transitions. In the method 1000, an operating situation of the fuel cell system 10 is first detected, and the fuel cell system 10 is controlled based on this. Figure 1 shows exemplary operating situations that are detected and controlled in the method 1000.

[0088] In method 1000, a current operating situation of the fuel cell system 10 is detected. The current operating situation can be a normal operating situation for electrical power output or one of a plurality of special operating situations during transitions from or to the normal operating situation. The fuel cell system 10 has at least one fuel cell stack 100 with an air side 110 and a fuel side 130. Depending on the detected special operating situation, the temperature and the course of a flow path of air, which can be supplied to the fuel cell system 10 via an air inlet section 2101, are then regulated by means of at least one electric heater 223, 243. This embodiment of method 1000 can be seen in particular in Figures 4 to 7 and 9 to 11, which show the control of the fuel cell system 10 for special operating situations.Figure 8, on the other hand, shows a control for a normal operation situation.

[0089] The method 1000 is described below using the exemplary operating cycle from Figure 1 for the fuel cell system 10 from Figures 2 and 3. The exemplary operating cycle comprises a start from a cold standby mode (BS80), from which the fuel cell system 10 is first heated (BS201 to BS204; Figures 4 to 7), an active operation (BS350; Figure 8), and the return to the cold standby mode, for which the fuel cell system 10 must be cooled down again (Figures 9 to 11).

[0090] Figure 4 shows exemplary steps of the method 1000 when a special operating situation in the form of a first warm-up operating situation BS201 is detected. This can be executed when, for example, a process request for heating is received in cold standby mode. In the first warm-up operating situation BS201, a catalyst 511 provided in the fuel cell system 10 is preferably to be heated. For this purpose, air from the air inlet section 2101 is heated with a secondary electric heater 243. For this purpose, the air can preferably first be passed through an air filter 210 and transported by an air blower 211. In order to heat the catalyst 511 with the heated air, a flow path of the heated air is directed from the secondary heater 243 to the catalyst 511. For this purpose, for example, connection points 241, 246, 512 and shut-off devices along the flow path can be controlled accordingly.The catalyst 511 is heated in this way to a catalyst start temperature. Reaching the catalyst start temperature enables catalytic combustion of fuel exhaust gas. Figure 4 shows, with thick lines, the air flow path from the air inlet section 2101, through which the air enters the fuel cell system 10, via the catalyst 511 along an exhaust gas discharge path 3500 to an exhaust gas discharge section 3502, via which the exhaust gas leaves the fuel cell system 10. Furthermore, in the first warm-up operating situation BS201, a further primary electric heater 223 can preferably be heated to a heater temperature.

[0091] Figure 5 shows exemplary steps of method 1000 when a special operating situation in the form of a second warm-up operating situation BS202 is detected. The second warm-up operating situation BS202 is carried out, for example, when at least the catalyst start temperature is detected at the catalyst 511. In the second warm-up operating situation BS202, fuel-carrying lines should preferably be heated. To produce a hydrogen-rich fuel, a mixture of steam and natural gas is often used. The fuel-carrying lines must therefore be preheated before the steam is supplied to avoid any possibility of condensation. Part of the heat required for this can be provided by the primary electric heater 223. A flow path of the air heated in this way is directed from the primary electric heater 223 to an air supply section 112 of the air side 110.Figure 5 shows the corresponding flow path with thick lines. Since the catalyst 511 is ready for catalytic conversion into non-combustible gases, the heating gas can be introduced into the fuel cell system 10 via a heating gas supply section 3101. The heating gas can be conducted through a fuel line 3100 to a fuel supply section 131 of the fuel side 130. Here, the heating gas can absorb heat from the heated air. The thus heated heating gas can leave the fuel cell stack 100 again via a fuel exhaust section 132 and be recirculated by a recirculation fan 311 through a recirculation line 3700. Accordingly, the fuel line 3100 and the recirculation line 3700 can be heated to a minimum line temperature. The minimum line temperature can be a temperature above which condensation of water vapor is prevented.Preferably, the recirculation line 3700 can extend from a branching point 371 of the fuel exhaust gas discharge path 3200 and open into a connection point 317 of the fuel line 3100.

[0092] Figure 6 shows exemplary steps of the method 1000 when a special operating situation in the form of a third warm-up operating situation BS203 is detected. The third warm-up operating situation BS203 is carried out, for example, when the fuel line 3100 and the recirculation line 3700 have at least a minimum line temperature. In the third warm-up operating situation BS203, in particular a reformer 314, which is provided for generating fuel for the fuel cell stack 100, is to be heated to its activation temperature. The heat required for this is provided at least partially by the secondary electric heater 243. Figure 6 shows the corresponding flow path by thick lines. Furthermore, heated air leaving the air side 110 can also provide heat. For example, fuel entering the fuel side 130 can be preheated by an air heat exchanger 214.The heated air from the fuel cell stack 100 can also be, for example, air that is guided through the second air line section 230, in which the air heat exchanger 235 is provided. The air heat exchanger 235 can transfer heat from the exhaust gas of the catalyst 511, which is hot due to catalytic combustion. The air thus heated is guided to an inlet of a reformer heat exchanger 248 of the reformer 314. Preferably, the air is also further supplied to the catalyst 511. It is advantageous here that the secondary electric heater 243 is connected in series with both the catalyst 511 and the reformer heat exchanger 248. Branching point 246 can divide the air flow into two streams. The actual control of the heating process of the reformer 314 can be achieved by controlling the opening of a control valve 247. The opening of the control valve 247 can thus regulate the heating ramp of the reformer 314.The control valve 247 can be arranged between the branching point 246 and the reformer heat exchanger 248. As soon as the reformer 314 reaches the activation temperature (also referred to as the reformer start temperature), steam can be supplied to prevent carbon formation (carbonization) on the catalytic surface of the reformer 314. This is indicated in Figure 6 by open arrowheads. The steam can be generated in a steam generator 330. The steam thus generated can be introduced into the fuel line 3100 via a connection point 331.

[0093] Figure 7 shows exemplary steps of the method 1000 when a special operating situation in the form of a fourth warm-up operating situation BS204 is detected. The fourth warm-up operating situation BS204 can be carried out, for example, when the reformer 314 has at least the reformer start temperature. In the fourth warm-up operating situation BS204, the fuel cell stack 100 is to be heated up to a minimum stack temperature. The heat required for this can be provided at least partially by the primary electric heater 223. Alternatively or additionally, it is also conceivable to provide the heat with the secondary electric heater 243 (not shown in Figure 7). The heated air from the primary heater 223 can be provided directly to the fuel cell stack 100 via air supply path 2100. Figure 7 shows the corresponding flow path by thick lines.Furthermore, thermal energy can be released by generating fuel from water vapor and fuel gas in the reformer 314 and supplying the fuel thus generated as well as the heated air to the fuel cell stack 100.

[0094] Figure 8 shows exemplary steps of the method 1000 when a normal operation operating situation BS350, which corresponds to normal operation, is detected. The normal operation operating situation BS350 can be carried out, for example, when the fuel cell stack 100 has at least a minimum stack temperature. During normal operation, air and fuel are supplied to the fuel cell stack 100 in order to generate electrical current therefrom. Preferably, no electrical heaters 223, 243 are required to maintain normal operation. The necessary thermal energy can, for example, be provided solely by catalytic heating by the catalyst 511. Catalytic heating can be achieved, for example, by conducting air exhaust gas from the air outlet section 115 of the air side 110 and fuel exhaust gas from a fuel exhaust gas section 132 of the fuel side 130 to the catalyst 511.Thus, the heat from the catalyst exhaust stream of the catalytic combustion in the catalyst 511 can be transferred to the air being supplied by means of the air heat exchanger 235. Heat from the fuel exhaust gas can be transferred to the fuel being supplied by means of two fuel heat exchangers 315, 316. The fuel heat exchanger 315 can be arranged in a section of the fuel exhaust gas discharge path 3200. The fuel heat exchanger 316 can preferably be arranged in a section of the recirculation line 3700. The generated electrical current can be conducted to a current output 610 via an electrical connection 611 with a relay 614. Figure 8 shows active components and flow paths using bold lines.

[0095] Figure 9 shows exemplary steps of the method 1000 when a special operating situation in the form of a first cooling operating situation BS471 is detected, in which the fuel cell system 10 is to be cooled. The first cooling operating situation BS471 can be executed, for example, when a process request to cool down the fuel cell system 10 is issued. In the first cooling operating situation BS471, the fuel cell stack 100 is primarily to be cooled to a first stack cooling temperature (e.g., 377°C) while maintaining temperature gradients. The air and fuel supplied to the fuel cell stack 100 can be used for this purpose. For example, the flow rate of fuel can be regulated until the first stack cooling temperature is reached. The temperature of the fuel and the reformer 314 can be regulated primarily by means of the secondary electric heater 243.For this purpose, a flow path of the air heated by the secondary heater 243 can be guided to the reformer heat exchanger 248. Figure 9 shows the corresponding flow path by thick lines. Furthermore, the increasingly cooled air exhaust gas from the air outlet section 115 can be guided from the air side 110 to the inlet of the reformer heat exchanger 248. The temperature of the reformer 314 can be adjusted by controlling the control valve 247. Figure 10 shows exemplary steps of the method 1000 when a special operating situation in the form of a second cooling operating situation BS472 is detected. The second cooling operating situation BS472 can be executed, for example, when the fuel cell stack 100 has cooled down to the first stack cooling temperature. In the second cooling operating situation BS472, the reformer 314 is to be cooled below its activation temperature.For this purpose, the air temperature is adjusted using the secondary electric heater 243 and directed to the catalyst 511 to enable it to continue operating above its activation temperature. Figure 10 shows the corresponding flow path with thick lines. At the same time, the control valve 247, which is preferably open in the first cooling operating situation BS471, is closed so that the reformer 314 can be cooled to a reformer start temperature by the heating gas and steam. The steam supply is preferably interrupted as soon as the reformer 314 has dropped to the reformer start temperature, so that no carbon formation can occur.

[0096] Figure 11 shows exemplary steps of method 1000 when a special operating situation in the form of a third cooling operating situation BS473 is detected. The third cooling operating situation BS473 can be carried out, for example, when a temperature of the reformer 314 is lower than the reformer start temperature. In the third cooling operating situation BS473, the fuel cell stack 100 should more preferably be cooled to room temperature. For this purpose, the air temperature is set to at least the activation temperature of the catalyst 511 by means of the secondary electric heater 243, and a corresponding flow path of the thus heated air is guided to the catalyst 511 in order to maintain the catalytic conversion in the catalyst 511. Figure 11 shows the corresponding flow path by thick lines.The temperature of the fuel cell stack 100 is controlled by regulating the flow rates of the heating gas and the air until a second stack cooling temperature (preferably room temperature) is reached by the fuel cell stack 100. Thus, the fuel cell stack 100 can be cooled by the supplied air and the heating gas.

[0097] Figure 4, already discussed, also shows, by way of example, steps of method 1000 when a special operating situation in the form of a fourth cooling operating situation BS474 is detected. The fourth cooling operating situation BS474 can be carried out, for example, when the fuel cell stack 100 has a temperature of at most the second stack cooling temperature. In the fourth cooling operating situation BS474, the catalyst 511 should now also be brought to a temperature below its activation temperature and in particular to room temperature. For this purpose, heat can be provided by the secondary electric heater 243. A flow path for the air heated in this way is directed to the catalyst 511. Figure 4 shows the corresponding flow path with thick lines. At the same time, further heating gas is supplied to the catalyst 511 and the flow rate is regulated in order to further cool the catalyst 511.

[0098] Figure 1 shows further operating situations, which are briefly described below:

[0099] For example, at the beginning of method 1000, a check operating situation BS10 can be recorded if a process request to check the functionality of the fuel cell system 10 has been issued. Components can then be checked. Figure 3 can be used as an example to illustrate this operating situation.

[0100] Furthermore, the fuel cell system 10 can also exhibit a cold standby operating state BS80 outside of diagnostic cycles. This operating state is detected, for example, when there is no process request for heating or operation and the fuel cell system 10 is at room temperature.

[0101] A standby operating situation BS330 can be implemented when the fuel cell system 10 has a sufficiently high temperature and is waiting for a request to enter normal operation. In this operating situation, the primary goal is to maintain the temperature, pressure, and media distribution.

[0102] A low-power operating situation (BS340, BS360) can be executed immediately before or after normal operation. The electrical output can be slowly ramped up or down.

[0103] In order to be able to react to errors during operation, a safety shutdown operating situation BS500 can also be detected in the method 1000. Depending on the error, a first critical operating situation BS501, a second critical operating situation BS502 and a third critical operating situation BS503 can be detected. In the first critical operating situation BS501, for example, operation can be abruptly interrupted and the fuel cell system 10 can be transferred to a safe state. With the second critical operating situation BS502, in particular critical events such as a power failure can be handled during full-load or partial-load operation. In the third critical operating situation BS503, in particular critical events such as a power failure can be handled during heating or cooling processes.

[0104] A control device 20 according to the invention with a detection module 21 and a situation control module 22 is shown by way of example in Figure 2. The control device 20 can be connected to the fuel cell system 10 via a control connection 23. The control device 20 is preferably configured to carry out the method 1000 according to the invention.

[0105] Figure 2 further shows connections and coupling points of the fuel cell system 10 with external supply units. For example, a heating gas supply 9310 can supply the heating gas supply section 3101 with an anode gas or heating gas, such as natural gas or methane. A water supply 9330 can supply a water supply section 3301 of the fuel cell system 10 with water for steam generation. The fuel cell system 10 can be supplied with air from the environment 9500 via the air inlet section 2101. The exhaust gas from the fuel cell system 10 can be discharged into the environment 9500 via the exhaust gas discharge section 3502. A coolant supply 9800 can conduct coolant for cooling the exhaust gas to the fuel cell system 10 via a coolant supply section 801 and out of the fuel cell system 10 again via a coolant discharge section 802. As shown by way of example in Figure 3, an exhaust gas cooler 350 is fed by the coolant.

[0106] Figure 3 shows further details of an exemplary fuel cell system 10 according to the invention, which has the control device 10. It can be particularly emphasized that the secondary electric heater 243 can supply both components with heat simultaneously due to the parallel routing of the catalyst 511 and the reformer heat exchanger 248. The air supply path 2100 can in particular have four air line sections 220, 230, 240, 250, each having a shut-off device 222, 232, 242, 252. The fourth air line section 250 can preferably have a heat exchanger 253 to transfer heat from the heating gas to the air upstream of the air side 110. The air thus heated can be introduced into the second air line section 230 via a connection point 236 upstream of the air heat exchanger 235. The second air line section 230 can feed the air side 110 directly.Static mixers 213, 312, 510 may also be provided in the fuel cell system 10.

[0107] The above explanation of the embodiments describes the present invention exclusively by way of examples.

[0108] List of reference symbols

[0109] 1000 procedures

[0110] BS10 Review-Operating Situation

[0111] BS80 cold standby operating situation

[0112] BS201 first warm-up operating situation

[0113] BS202 second warm-up operating situation

[0114] BS203 third warm-up operating situation

[0115] BS204 fourth warm-up operating situation

[0116] BS330 Standby operating situation

[0117] BS340 Low Power Operating Situation

[0118] BS350 Normal Operation Operating Situation

[0119] BS360 low power operating situation

[0120] BS471 first cooling operating situation

[0121] BS472 second cooling operating situation

[0122] BS473 third cooling operating situation

[0123] BS474 fourth cooling operating situation

[0124] BS500 safety shutdown operating situation

[0125] BS501 first critical operating situation

[0126] BS502 second critical operating situation

[0127] BS503 third critical operating situation

[0128] 10 Fuel cell system

[0129] 100 fuel cell stacks

[0130] 110 Airside

[0131] 112 Air intake section

[0132] 115 Air outlet section

[0133] 130 Fuel side

[0134] 131 Fuel supply section

[0135] 132 Fuel exhaust section

[0136] 210 air filter

[0137] 211 air blowers

[0138] 213 static air mixer

[0139] 214 additional air heat exchangers

[0140] 220 first air line section shut-off device primary electric heater second air line section shut-off device

[0141] Air heat exchanger

[0142] Connection point Connection point third air line section Connection point shut-off device secondary electric heater Branching point control valve

[0143] Reformer heat exchanger connection point fourth air line section shut-off device further air heat exchanger recirculation fan static fuel mixer reformer, 316 fuel heat exchanger connection point steam generator connection point exhaust gas cooler

[0144] Branching point static exhaust gas mixer catalyst

[0145] Connection point power output electrical connection relay coolant supply section 802 coolant discharge section

[0146] 2100 Air supply path

[0147] 2101 Air intake section

[0148] 3101 Heating gas supply section

[0149] 3200 Fuel exhaust gas discharge path

[0150] 3301 Water supply section

[0151] 3500 exhaust gas discharge path

[0152] 3502 Exhaust gas discharge section

[0153] 3700 recirculation line

[0154] 9310 Heating gas supply

[0155] 9330 Water supply

[0156] 9500 surroundings

[0157] 9800 coolant supply

[0158] 20 Control device

[0159] 21 Recording module

[0160] 22 Situation Control Module

[0161] 23 Control connection

Claims

Patent claims 1. A method (1000) for operating a fuel cell system (10) which has at least one fuel cell stack (100) with an air side (110) and a fuel side (130), and which is operated in various operating situations, which have a normal operation operating situation (BS350) for electrical power output and a plurality of special operating situations during transitions from or to the normal operation operating situation (BS350), the method (1000) comprising the steps: - Recording a current operating situation of the fuel cell system (10); - Controlling the fuel cell system (10) as a function of the detected current operating situation, wherein for a detected special operating situation o the air temperature of air which can be supplied to the fuel cell system (10) via an air inlet section (2101) is controlled by means of at least one electrical heater (223, 243), and o a course of at least one flow path of the electrically heated air in the fuel cell system (10) is selected from at least two possible flow path courses of the fuel cell system (10) as a function of the detected special operating situation.

2. Method (1000) according to claim 1, characterized in that - a first warm-up operating situation (BS201) for warming up the fuel cell system (10) is recorded as one of the special operating situations for the transition to normal operation; and - for the first warm-up operating situation (BS201), a flow path for the heated air is selected as the detected special operating situation, which flow path leads from the at least one heater (243) to a catalyst (511) of the Fuel cell system (10) for the catalytic combustion of fuel exhaust gas in order to heat the catalyst (511) to its catalyst activation temperature, o the first warm-up operating situation (BS201) preferably continues at least until the catalyst (511) has the catalyst activation temperature, and o the air temperature is preferably regulated by means of the electric heater (223) according to a catalyst warm-up curve.

3. Method (1000) according to one of the preceding claims, characterized in that - a second warm-up operating situation (BS202) for warming up the fuel cell system (10) is detected as one of the special operating situations for the transition to normal operation, wherein the second warm-up operating situation (BS202) preferably follows immediately after the first warm-up operating situation (BS201); and - for the second warm-up operating situation (BS202) as the detected special operating situation o a heating gas, preferably methane, is supplied via a fuel line (3100) to a fuel supply section (131) of the fuel side (130) in order to absorb heat from the heated air in the fuel cell stack (100); o the supplied heating gas is recirculated in a recirculation line (3700) of the fuel cell system (10), which extends between a fuel exhaust gas section (132) of the fuel side (130) for discharging the fuel exhaust gas and a section of the fuel line (3100) upstream of the fuel supply section (131), in order to heat fuel-carrying lines (3100, 3700) of the fuel cell system (10); o preferably, the air temperature is regulated according to a fuel line warm-up curve by means of the at least one electric heater (243); and o a flow path for the heated air is selected which runs from the at least one heater (243) to an air supply section (112) of the air side (110), o preferably, the second warm-up operating situation (BS202) continues until at least the recirculation line (3700) and the fuel line (3100) have a minimum line temperature, which is further preferably at least a water vapor condensation temperature.

4. Method (1000) according to one of the preceding claims, characterized in that - a third warm-up operating situation (BS203) for warming up the fuel cell system (10) is detected as one of the special operating situations for the transition to normal operation, wherein the third warm-up operating situation (BS203) preferably follows immediately after the second warm-up operating situation (BS202); and - for the third warm-up operating situation (BS203), a flow path for the heated air is selected as the detected special operating situation o, which flow path runs from the at least one heater (243) to an inlet of a reformer heat exchanger (248) of a reformer (314) of the fuel cell system (10) for generating fuel to be supplied to the fuel side (130) in order to heat the reformer (314) to its reformer activation temperature, and preferably further an additional flow path is selected for the heated air, which flow path runs from the at least one heater (243) to a catalyst (511) of the fuel cell system (10) for the catalytic combustion of fuel exhaust gas; o a temperature of the reformer (314) is controlled to a reformer activation temperature, preferably according to a reformer warm-up curve, by controlling a flow rate of the heated air through the reformer heat exchanger (248); and o water vapor is supplied to the reformer (314) as soon as the reformer (314) has the reformer activation temperature.

5. Method (1000) according to one of the preceding claims, characterized in that - a fourth warm-up operating situation (BS204) for warming up the fuel cell system (10) is detected as one of the special operating situations for the transition to normal operation, wherein the fourth warm-up operating situation (BS204) preferably follows immediately after the third warm-up operating situation (BS203); and - for the fourth warm-up operating situation (BS204) as the detected special operating situation o a flow path for the heated air is selected which runs from the at least one electric heater (223) to the air side (110) in order to heat the fuel cell stack (100) to a minimum stack temperature; o water vapor and heating gas are supplied to the reformer (314) in order to generate fuel for supply to the fuel side (130); o the generated fuel and the heated air are each supplied to the fuel cell stack (100), and o preferably the fourth warm-up operating situation (BS204) continues until the fuel cell stack (100) has the minimum stack temperature.

6. Method (1000) according to one of the preceding claims, characterized in that - the normal operation operating situation (BS350) corresponding to normal operation is recorded; and - for the detected normal operation situation (BS350) o air and fuel are supplied to the fuel cell stack (100); o electrical current is generated in the fuel cell stack (100) from the supplied air and fuel; o preferably the at least one electrical heater (223, 243) is deactivated; and o the temperature of the fuel cell stack (100) is regulated by means of catalytic heating.

7. Method (1000) according to one of the preceding claims, characterized in that - a first cooling operating situation (BS471) for cooling the fuel cell system (10) is recorded as one of the special operating situations for the transition from normal operation; and - for the first cooling operating situation (BS471) as the detected special operating situation o preferably the air temperature is regulated according to a cooling curve by means of the at least one electric heater (243); o a flow path for the heated air is selected which runs from the at least one heater (243) to an inlet of a reformer heat exchanger (248) of a reformer (314) of the fuel cell system (10) for generating fuel to be supplied from the fuel side (130), o air exhaust gas from the air side (110) is also supplied to the inlet of the reformer heat exchanger (248); o a temperature of the reformer (314) is regulated, preferably according to a reformer cooling curve, by regulating a flow rate of a gas mixture of the supplied heated air and the air exhaust gas through the reformer heat exchanger (248); o the temperature of the fuel cell stack (100) is regulated to a first stack cooling temperature, preferably according to a stack cooling curve, by regulating a flow rate of fuel, which is to be supplied to the fuel side (130), preferably from the reformer (314), wherein the first stack cooling temperature is lower than a minimum stack temperature for normal operation; and o preferably the first cooling operating situation (BS471) continues until the first stack cooling temperature is reached.

8. Method (1000) according to one of the preceding claims, characterized in that - a second cooling operating situation (BS472) for cooling the fuel cell system (10) is recorded as one of the special operating situations for the transition from normal operation; and - for the second cooling operating situation (BS472) as the detected special operating situation o preferably the air temperature is regulated according to a cooling curve by means of the at least one electric heater (243); o a flow path for the heated air is selected which runs from the at least one heater (243) to a catalyst (511) of the fuel cell system (10) for the catalytic combustion of fuel exhaust gas in order to operate the catalyst (511) above its catalyst activation temperature; o a temperature of a reformer (314) of the fuel cell system (10) for generating fuel for the fuel side (130) to a reformer activation temperature is controlled by supplying a heating gas and water vapor to the reformer (314) for heat dissipation until the reformer (314) has a temperature of at most the reformer activation temperature; and o no further water vapor is supplied to the reformer (314) as soon as the reformer (314) has a temperature lower than the reformer activation temperature.

9. Method (1000) according to one of the preceding claims, characterized in that - a third cooling operating situation (BS473) for cooling the fuel cell system (10) is recorded as one of the special operating situations for the transition from normal operation; and - for the third cooling operating situation (BS473) as the detected special operating situation o the air temperature is regulated to a catalyst activation temperature, preferably according to a cooling curve, by means of the at least one electric heater (243); o a flow path for the heated air is selected which runs from the at least one heater (243) to a catalyst (511) of the fuel cell system (10) for the catalytic combustion of fuel exhaust gas in order to maintain active operation of the catalyst (511); and o the temperature of the fuel cell stack (100) is regulated to a second stack cooling temperature, preferably according to a stack cooling curve, by regulating flow rates of a heating gas, which can be supplied to a fuel supply section (131) of the fuel side (130), and of the air.

10. Method (1000) according to one of the preceding claims, characterized by - a fourth cooling operating situation (BS474) for cooling the fuel cell system (10) is recorded as one of the special operating situations for the transition from normal operation; and - for the fourth cooling operating situation (BS474) as the detected special operating situation o a flow path for the heated air is selected which runs from the at least one heater (243) to a catalyst (511) of the fuel cell system (10) for the catalytic combustion of fuel exhaust gas in order to cool the catalyst (511) below its catalyst activation temperature; and o the air temperature is preferably regulated according to a cooling curve by means of the at least one electric heater (243) to a temperature below the catalyst activation temperature; o a temperature of the catalyst (511) is regulated to the catalyst rest temperature, preferably according to a catalyst cooling curve, by regulating flow rates of a heating gas which can be supplied to a fuel supply section (131) of the fuel side (130), and of the air through the catalyst (511).

11. Method (1000) according to one of the preceding claims, characterized in that the fuel cell system (10) has two electric heaters (223, 243), which are each arranged in one of two parallel line sections (220, 240) in an air supply path (2100) of the fuel cell system (10), and for the respectively detected special operating situation, a primary electric heater (223) and / or a secondary electric heater (243) is / are used as the or the electric heaters (223, 243) are selected depending on the respective special operating situation for regulating the air temperature.

12. The method (1000) according to any one of the preceding claims, characterized in that in special operating situations during warm-up of the fuel cell system (10), heat is provided for heating by the at least one electric heater (223, 243) in a heating sequence, wherein, with the heating sequence, a catalyst (511) for catalytic combustion of fuel exhaust gas, fuel-carrying lines (3100, 3700), a reformer (314) for generating fuel and the fuel cell stack (100) are heated one after the other to their operating temperature for normal operation, and for these special operating situations, the flow paths for the heated air are selected in each case as a function of the heating sequence.

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 a fuel cell system (10) with at least one fuel cell stack (100), which has an air side (110) and a fuel side (130), and with at least one electric heater (223, 243) for regulating the air temperature of air which can be supplied to the fuel cell system (10) via an air inlet section (112), wherein the fuel cell system (10) is operated in various operating situations which have a normal operating situation (BS350) for electrical power output and a plurality of special operating situations during transitions from or to the normal operating situation (BS350), characterized by - a detection module (21) for detecting a current operating situation of the fuel cell system (10), and - a situation control module (22) for regulating the fuel cell system (10) depending on the detected current operating situation, wherein the situation control module (22) is configured to regulate the air temperature by means of the at least one electric heater (223, 243) for a detected special operating situation, and to select a course of at least one flow path of the electrically heated air in the fuel cell system (10) from at least two possible flow path courses of the fuel cell system (10) depending on the detected special operating situation.

15. Fuel cell system (10), preferably a SOFC fuel cell system, comprising: - at least one fuel cell stack (100) having an air side (110) and a fuel side (130), and - at least one electric heater (223, 243) for regulating the air temperature of air which can be supplied to the fuel cell system (10) via an air inlet section (112), characterized by - a control device (20) according to claim 14, for operating the fuel cell system (10) in different operating situations, which have a normal operating situation (BS350) for electrical power output and a plurality of special operating situations during transitions from or to the normal operating situation (BS350).

Images