Method for operating an anode subsystem, control device

Abstract

The invention relates to a method for operating an anode subsystem (1), in which an anode gas is recirculated via an anode circuit (2) and water contained in the anode gas is separated from the anode gas by means of a water separator (3) integrated into the anode circuit (2) and is collected in a container (4) of the water separator (3), wherein, depending on the fill level in the container (4), which is detected by means of a fill level sensor (5), the container (4) is emptied by virtue of a valve (6) being opened, and wherein dirt particles entrained by the water are removed by means of a filter (7) positioned upstream of the valve (6). According to the invention, in order to diagnose the loading state of the filter (7), the emptying rate during the emptying of the container (4) is detected and compared with a reference value. The invention also relates to a control device for a fuel cell system (10).

Description

[0001] Description

[0002] title

[0003] Method for operating an anode subsystem, control unit

[0004] The invention relates to a method for operating an anode subsystem with the features of the preamble of claim 1. Furthermore, the invention relates to a control unit for executing steps of the method.

[0005] The preferred application area of ​​the invention is fuel cell systems, in particular mobile fuel cell systems or fuel cell vehicles.

[0006] State of the art

[0007] Hydrogen-based fuel cells convert hydrogen and oxygen into electrical energy, heat, and water. To increase electrical output, multiple fuel cells are stacked together to form a fuel cell stack. The hydrogen is supplied to an anode section of the stack, and the oxygen—in the form of ambient air—is supplied to a cathode section.

[0008] The anode area of ​​a fuel cell stack is supplied with hydrogen via an anode subsystem. This subsystem comprises an anode circuit through which fresh hydrogen is supplied from a tank and anode gas, still containing hydrogen, exiting the stack is recirculated. Over time, the recirculated anode gas becomes enriched with nitrogen, which diffuses from the cathode side to the anode side, and with water. This water is product water, a byproduct of the electrochemical reaction in the fuel cells. A water separator is integrated into the anode circuit to remove the water from the anode gas and the anode subsystem. The separated water is collected in a container within the water separator. A valve, which may be a drain valve, is provided for emptying the container.

[0009] Since the anode gas recirculated via the anode circuit can also contain solid components or dirt particles (initial dirt from production and assembly and / or operational dirt due to wear and aging), a filter can be installed between the water separator and the drain valve to protect it. The filter is intended to prevent the solid components from entering the valve and impairing its function. The problem that arises when using such a filter is that its loading level cannot be determined without disassembling the system.

[0010] The present invention therefore addresses the problem of providing an alternative method for detecting the filter's loading state. To solve this problem, the method with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. Furthermore, a control unit for executing steps of the method is specified.

[0011] Disclosure of the invention

[0012] In the proposed method for operating an anode subsystem, an anode gas is recirculated via an anode circuit, and water contained in the anode gas is separated from the anode gas by means of a water separator integrated into the anode circuit and collected in a container of the water separator. Depending on the fill level in the container, which is detected by a level sensor, the container is emptied by opening a valve. A filter upstream of the valve removes dirt particles carried by the water. According to the invention, the emptying rate during the emptying of the container is recorded and compared with a reference value to diagnose the filter's loading status.

[0013] Dirt particles carried along by the water when the container is emptied are trapped by the filter, preventing them from entering the valve. Over time, more and more dirt particles accumulate on the filter surface, increasing the filter's loading level. This impairs the water flow through the filter. To maintain the flow, the differential pressure would have to increase continuously. If the differential pressure across the filter is kept constant, the flow rate, or water volume flow through the filter, decreases. This, in turn, reduces the emptying rate of the water separator container. The emptying rate, i.e., the change in the fill level in the water separator container over time, thus provides information about the filter's loading level. For evaluation purposes, the measured emptying rate is compared to a reference value.

[0014] According to a preferred embodiment of the invention, the signal from the level sensor is evaluated to determine the emptying rate. The level sensor detects when a maximum fill level is reached and the container needs to be emptied. This means that the emptying process is initiated via the level sensor. Simultaneously, the level sensor detects when a minimum fill level is reached, so that the duration of the emptying process can be determined from the level sensor signals. The volume to be emptied is assumed to be known, so that the emptying rate can be determined from this information.

[0015] When carrying out the proposed procedure, a measurement previously taken with an unloaded filter can be used as a reference value for the emptying rate. The reference value thus corresponds to the emptying rate with an unloaded filter. If the measured emptying rate deviates from the reference value, this indicates a loaded filter.

[0016] Alternatively or additionally, it is proposed that a previously recorded emptying rate be used as a reference value for the current emptying rate. In this case, the currently recorded emptying rate can be compared to the previously recorded emptying rate, thus revealing whether the load level has increased further.

[0017] Advantageously, the discharge rate is only recorded in a defined operating state of the system, thus ensuring comparability between the recorded discharge rates. If the reference value was previously measured with the filter still empty, the measurement is preferably carried out under identical operating conditions to guarantee comparability. This results in increased diagnostic accuracy. A defined operating state exists, in particular, during system startup, for example, during the initial flow through the anode, or during system shutdown, for example, during a drying process. Preferably, the discharge rate is recorded in an operating state in which no further product water is generated and introduced into the anode circuit, so that a constant differential pressure prevails across the filter.

[0018] Furthermore, the emptying rate is preferably monitored over several driving cycles and / or over the filter's lifetime. This allows for the detection of a critical loading level or filter clogging, enabling corrective action to be taken. For example, a workshop can be visited to replace the filter.

[0019] Preferably, if the emptying rate of the container falls below a predefined lower limit, a service alert is displayed. This means the driver is informed that service is due or that a workshop visit is required. This prevents the water separator container from overflowing due to insufficient emptying.

[0020] Furthermore, a control unit for a fuel cell system is provided, wherein the control unit is configured to execute steps of a method according to the invention. In particular, the signals from the fill level sensor can be evaluated with the aid of the control unit in order to determine the emptying rate. A reference value can also be stored in the control unit to compare the determined emptying rate with the reference value. The emptying rates recorded over several driving cycles and / or over the lifetime of the system can also be stored in the control unit so that they are available as reference values ​​for comparison.

[0021] The invention and its advantages are described in more detail below with reference to the accompanying drawing. This shows a schematic representation of a fuel cell system with an anode subsystem that can be operated according to a method according to the invention.

[0022] Detailed description of the drawing

[0023] The figure shows an example of a fuel cell system 10 with a fuel cell stack 11 and several subsystems for supplying the fuel cell stack 11 with media. A first subsystem forms an air system 20 that supplies the fuel cell stack 11 with air. The air is supplied via a supply air path 12, into which an air compressor 13 for compressing the air and a humidifier 14 for humidifying the air supplied to the fuel cell stack 11 are integrated. The moist air exiting the fuel cell stack 11, or exhaust air, is discharged via an exhaust air path 15, whereby the moist exhaust air is passed through the humidifier 14 and used to humidify the air in the supply air path 12. A pressure regulator 16 integrated into the exhaust air path 15 regulates the pressure in the exhaust air path 15.

[0024] A cooling system 21 for dissipating the waste heat from the fuel cell stack 11 forms a further subsystem. It comprises a cooling circuit 17, into which a coolant pump 18 and a radiator 19 are integrated. The heat absorbed by the coolant of the cooling circuit 17 in the fuel cell stack 11 is transferred to the environment via the radiator 19.

[0025] As a further subsystem through which the fuel cell stack 11 is supplied with hydrogen, the fuel cell system 10 shown in the figure has an anode subsystem 1. The hydrogen is stored in a tank 9, and via an anode circuit 2 of the anode subsystem 1, not only is fresh hydrogen taken from the tank 9 supplied to the fuel cell stack 11 as anode gas, but also anode gas escaping from the fuel cell stack 11, which is recirculated for this purpose by means of a recirculation blower 8 integrated into the anode circuit 2. Over time, the recirculated gas becomes enriched with, among other things, water, which is product water. To remove the water from the anode gas, a water separator 3 with a container 4 in which the separated water is collected is integrated into the anode circuit 2.The fill level in container 4 is monitored by means of a level sensor 5, so that when a maximum fill level is reached, container 4 can be emptied. For this purpose, a valve 6 is opened, which is preceded by a filter 7 to protect the valve 6 from dirt particles.

[0026] The level sensor 5 protects the water separator 3 from overflowing by opening the valve 6 in a timely manner. Furthermore, timely

[0027] At the end of the emptying process, the valve 6 is kept open for too long, thus preventing unnecessary outflow of hydrogen-containing anode gas. After all the water has been removed from the container 4, anode gas escapes through the open valve 6. Closing the valve 6 in a timely manner minimizes hydrogen loss, thereby increasing system efficiency.

[0028] In the method according to the invention, the level sensor 5 fulfills a further purpose. The emptying rate during the emptying of the container 4 is detected using the signals from the level sensor 5. The emptying rate allows conclusions to be drawn about the loading state of the filter 7, so that the loading state of the filter 7 can be monitored using the level sensor signals.

Claims

Claims 1. A method for operating an anode subsystem (1) in which an anode gas is recirculated via an anode circuit (2) and water contained in the anode gas is separated from the anode gas by means of a water separator (3) integrated into the anode circuit (2) and collected in a container (4) of the water separator (3), wherein, depending on the fill level in the container (4), which is detected by means of a fill level sensor (5), the container (4) is emptied by opening a valve (6), and wherein dirt particles carried by the water are removed by means of a filter (7) upstream of the valve (6), characterized in that, for the purpose of diagnosing the loading state of the filter (7), the emptying rate during the emptying of the container (4) is detected and compared with a reference value.

2. Method according to claim 1, characterized in that the signal from the level sensor (5) is evaluated to determine the emptying rate.

3. Method according to claim 1 or 2, characterized in that a measured value is used as a reference value for the emptying rate which was previously measured with an unloaded filter.

4. Method according to one of the preceding claims, characterized in that a previously recorded emptying rate is used as a reference value for the emptying rate.

5. Method according to one of the preceding claims, characterized in that the emptying rate is only recorded in a defined operating state of the system, for example during the starting or stopping of the system.

6. A method according to any one of the preceding claims, characterized in that the emptying rate is monitored over several driving cycles and / or over the lifetime of the container.

7. A method according to any one of the preceding claims, characterized in that a service call is displayed if a predefined lower limit for the emptying rate of the container is undershot.

8. A control unit for a fuel cell system (10), wherein the control unit is configured to execute steps of a method according to any one of the preceding claims.

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