Method for operating a fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (100) comprising: at least one fuel cell stack (11); an anode system (200) in which an anode feed line (22) through which anode gas flows into an anode chamber (A), and a recirculation line (21) through which anode exhaust gas can flow out of the anode chamber (A) and into the anode feed line (22) are arranged; and a cathode system (300), in which method the following steps are carried out at least once: a. determining a pressure difference in the fuel cell system (100), b. comparing the pressure difference with a first limit value which describes the maximum permissible pressure difference, and c. reducing the mass flow of the anode gas in the anode feed line (22) if the pressure difference exceeds the first limit value.

Description

[0001]

[0002] title

[0003] Procedures for operating a

[0004] The invention relates to a method for operating a fuel cell system with the features of the preamble of independent claim 1.

[0005] State of the art

[0006] It is known from the prior art that fuel cell systems exist which have an anode system and a cathode system. The anode system consists of an anode supply line, which supplies fuel, in particular hydrogen, to a fuel cell stack, and a recirculation line, which returns anode exhaust gas to the anode supply line via a pumping unit. Furthermore, the cathode system consists of a cathode supply line, through which ambient air is introduced into the fuel cell stack, and a cathode outlet line, through which cathode exhaust gas is conveyed from the cathode system into the exhaust stream.

[0007] During operation of the fuel cell system, the reactants fuel and air flow into the fuel cell stack to obtain electrical energy in a cold combustion reaction.

[0008]

[0009] The inventive method for operating a fuel cell system according to independent claim 1 has the advantage that an excessively high pressure difference across a membrane arranged in a fuel cell stack between an anode compartment A and a cathode compartment K can be avoided, thus increasing the service life of the membrane.

[0010] The inventive method supplies the fuel cell stack with sufficient reactants, in particular fuel and air, and at the same time ensures that the supplied flow rates do not have a damaging effect on the membrane.

[0011] Particularly in counterflow operation of the fuel cell stack, where the reactants fuel and air flow in opposite directions within the stack, a local pressure gradient can build up, which can damage the membrane. For example, mechanical aging due to fluctuating pressure acting on the membrane can promote the formation of cracks and holes.

[0012] In the context of the invention, anode exhaust gas is understood to be the gas exiting from the anode chamber A into a recirculation line.

[0013] In the context of the invention, an anode gas is understood to be a gas mixture of fuel and anode exhaust gas in variable mixing ratios.

[0014] An excessive pressure differential across the membrane between the anode and cathode compartments can be avoided by performing the following steps at least once: a. Determine the pressure differential in the fuel cell system. b. Compare the pressure differential with a first limit value that defines a maximum permissible pressure differential. c. Reduce the anode gas flow rate in an anode supply line if the pressure differential exceeds the first limit value. Advantageously, the following steps are also performed: d. Determine the anode gas flow rate in the anode supply line. e. Compare the anode gas flow rate in the anode supply line with a second limit value that defines a minimum flow rate in the anode supply line. f. Reduce the anode gas flow rate in the anode supply line to a value that does not fall below the second limit value.

[0015] By carrying out the additional steps d., e. and f., it can be ensured that the flow rate of the anode gas in the anode supply line is sufficient to discharge water that has formed in the anode chamber A during the operation of the fuel cell system.

[0016] It is advantageous to reduce the flow rate of anode gas in the anode supply line by reducing the flow rate of anode exhaust gas flowing into the anode supply line via the recirculation line. This allows for an efficient reduction of the flow rate without additional components.

[0017] Advantageously, the flow rate of fuel, particularly hydrogen, being fed from a tank into the anode supply line will be kept constant if the flow rate of anode gas in the anode supply line is reduced. This ensures that sufficient fuel is available to the fuel cell stack.

[0018] It is advantageous to reduce the flow rate of the anode gas in the anode supply line by at least partially closing a first metering valve, which is arranged upstream of a jet pump in a first section of the anode supply line. This allows the method according to the invention to be carried out using existing components and ensures a cost-effective design of the fuel cell system.

[0019] Advantageously, the anode gas flow rate in the anode supply line is reduced by reducing the power output of a pump located in the recirculation line. Reducing the pump output allows for this reduction in anode gas flow rate to be achieved using existing components within the fuel cell system, ensuring a more cost-effective and compact design. Furthermore, reducing the pump output increases the efficiency of the fuel cell system, as the pump consumes less power.

[0020] It is advantageous to maintain a constant fuel flow rate by at least partially opening a second metering valve located in a second section of the anode supply line. This partial opening of the second metering valve allows the amount of fuel supplied to the fuel cell stack to be kept constant without enriching the anode gas with anode exhaust gas and thereby increasing the flow rate in the anode supply line.

[0021] Advantageously, the pressure difference corresponds to the pressure difference between a cathode compartment K, which is arranged in the fuel cell stack, and the anode compartment A. This allows for a very precise determination of the pressure difference across the membrane via the cathode compartment K and the anode compartment A.

[0022] It is advantageous if the pressure difference corresponds to the pressure difference between the anode supply line and the recirculation line. This allows for a reliable determination of the pressure difference across the membrane's surface.

[0023] Advantageously, the pressure difference is calculated from two pressure values, which are measured using sensors and / or determined using a model. Measuring pressure values ​​with sensors allows for a precise determination of pressure values. Model-based determination of pressure values, with optimized use of sensors, also makes it possible to calculate the pressure difference.

[0024] The method according to the invention is explained in more detail below with reference to drawings with preferred embodiments.

[0025] They show:

[0026] Fig. 1 shows a schematic topology of a fuel cell system and

[0027] Fig. 2 shows a first embodiment of a method according to the invention.

[0028] Figure 1 shows a schematic topology of the fuel cell system 100 with at least one fuel cell stack 11 and an anode system 200. Furthermore, the fuel cell system 100 includes a highly schematic cathode system 300 and a cooling circuit (not shown).

[0029] The cathode system 300 supplies a cathode chamber K with oxygen (O2) as a reactant. Oxygen is a component of air.

[0030] In the cathode system 300, a cathode supply line 31 and a cathode outlet line 32 are arranged. The cathode supply line 31 leads into the fuel cell stack 11. Oxygen is supplied to the fuel cell stack 11 via the cathode supply line 31. A first sensor 33 can be arranged in the cathode supply line 31.

[0031] The cathode outlet line 32 is connected to the fuel cell stack 11. Gases, such as cathode exhaust gas and / or fluids, such as product water, are discharged from the cathode system 300 via the cathode outlet line 32. A second sensor 34 can be arranged in the cathode outlet line 32.

[0032] The anode system 200 supplies an anode compartment A of the fuel cell stack 11 with a fuel, in particular hydrogen (H2), as a reactant. By supplying fuel to the anode compartment A, the fuel is made available to the fuel cell system 100 as a reactant.

[0033] The anode system 200 comprises a fuel line 17, an anode supply line 22, a recirculation line 21, and an anode outlet line 23. The anode supply line 22 leads into the fuel cell stack 11. Anode gas is supplied to the fuel cell stack 11 via the anode supply line 22.

[0034] The recirculation line 21 is connected to the anode compartment A. The anode exhaust gas flowing from the anode compartment A is transported via the recirculation line 21 into the anode outlet line 23.

[0035] Fuel can be supplied to the fuel cell stack 11 superstoichiometrically, so that fuel is still contained in the anode exhaust gas. In order to make the fuel contained in the anode exhaust gas available to the anode system 200, an anode exhaust gas is recirculated from the recirculation line 21 into the anode supply line 22.

[0036] In the recirculation line 21, a third sensor 28 can be arranged behind the anode chamber A in the direction of flow.

[0037] A recirculation pumping unit 25 is optionally arranged within the recirculation line 21. The recirculation pumping unit 25 supports the recirculation of the anode exhaust gas from the recirculation line 21 into the anode supply line 22.

[0038] Fuel line 17 feeds fuel from tank 16 into the anode system 200. Upstream of the anode supply line 22, fuel line 17 splits into a first line section 20 and a second line section 29. A jet pump 26 and a first metering valve 19 are located in the first line section 20. A second metering valve 18 is located in the second line section 29.

[0039] A fourth sensor 27 can be arranged in the anode supply line 22 upstream of the anode chamber A in the direction of flow. The first line section 20 and the second line section 29 connect upstream of the fourth sensor 27 to form the anode supply line 22 in the direction of flow.

[0040] The anode outlet line 23 is connected to the recirculation line 21. Gases, such as anode exhaust gas, and / or fluids, such as water, are discharged from the anode system 200 via the anode outlet line 23. A drain valve 24 is arranged in the anode outlet line 23. When the drain valve 24 opens, water is discharged from the anode system 200.

[0041] In an alternative embodiment, the drain valve 24 can be designed as a combined purge-drain valve 24, so that anode exhaust gas and / or water can be discharged from the anode system 200 via the combined purge-drain valve 24.

[0042] In fuel cell stack 11, a membrane is arranged between anode compartment A and cathode compartment K, connecting them. The membrane is proton-conducting.

[0043] A control unit 500 is provided to regulate and control all control processes in the fuel cell system 100. This also includes the processing of a measured value for the execution of the method according to the invention.

[0044] In an alternative embodiment, more than one fuel cell stack 11 can also be arranged in the fuel cell system 100 without restricting the implementation of the method according to the invention.

[0045] In an alternative embodiment, the sensors (27, 28, 33, 34) can be partially or completely omitted. This can be the case, in particular, if the pressure values ​​are determined using a model.

[0046] Figure 2 shows an embodiment of the method according to the invention.

[0047] The method according to the invention enables the pressure difference across the membrane to be limited during operation of the fuel cell system 100, thereby extending the membrane's service life. For example, limiting the pressure difference can reduce mechanical stress peaks during operation of the fuel cell stack 11, which has a positive effect on its service life. The membrane is arranged in the fuel cell stack 11 between anode compartment A and cathode compartment K. This makes it possible to determine the pressure difference across the membrane indirectly, either by measuring the pressure difference between anode compartment A and cathode compartment K or via anode compartment A.This is particularly the case with an arrangement of anode system 200 and cathode system 300 in countercurrent operation, where the reactants fuel and air flow in opposite directions to each other in the fuel cell stack 11. In such a scenario, a local pressure gradient can build up that has a damaging effect on the membrane. For example, mechanical aging due to fluctuating pressure acting on the membrane can promote the formation of cracks and holes in the membrane.

[0048] The process begins in step S100.

[0049] In step S200, a first pressure value and a second pressure value are determined. Using the first and second pressure values, a pressure difference in the fuel cell system 100 is calculated. The first and second pressure values ​​are preferably measured at the following locations: in the anode inlet 22 upstream of the anode compartment A and / or in the anode outlet 21 downstream of the anode compartment A and / or in the cathode inlet 31 upstream of the cathode compartment K and / or in the cathode outlet 32 ​​downstream of the cathode compartment K

[0050] The first pressure value and the second pressure value are measured using sensors (27, 28, 33, 34) and / or are determined using a model.

[0051] In step S300, the pressure difference is determined using the first pressure value and the second pressure value in the fuel cell system 100.

[0052] In a first and a second embodiment, the pressure difference between a cathode chamber K, arranged in the fuel cell stack 11, and the anode chamber A is determined. In the first embodiment, the first pressure value in the anode supply line 22 upstream of the anode chamber A is measured using the fourth sensor, and the second pressure value in the cathode supply line 31 upstream of the cathode chamber K is measured using the first sensor 33.

[0053] In the second embodiment, the first pressure value is in the anode outlet line.

[0054] 21 in the direction of flow behind the anode chamber A using the third sensor 28 and the second pressure value in the cathode outlet line 32 in the direction of flow behind the cathode chamber K using the second sensor 34.

[0055] In a third embodiment, the pressure difference between the anode supply line is

[0056] The pressure difference across the anode chamber A is determined between the anode supply line 22 and the recirculation line 21 and corresponds approximately to the pressure difference across the diaphragm. The first pressure value is measured in the anode supply line 22 using the fourth sensor 27, and the second pressure value is measured in the recirculation line 21 using the third sensor 28.

[0057] In step S400, the pressure difference is compared with a first limit value that describes a maximum permissible pressure difference.

[0058] If the pressure difference exceeds a first limit value, step S500 is then carried out.

[0059] If the pressure difference in step S400 is less than or equal to the first limit value, there is no reduction in the flow rate of the anode gas in the anode supply line 22 and the process is terminated in step S800.

[0060] In step S500, the flow rate in the anode supply line 22 is determined. The flow rate in the anode supply line 22 can be measured using a sensor and / or determined using a model.

[0061] Subsequently, in step S600, the flow rate is compared with a second limit value. The second limit value describes a minimum flow rate in the anode supply line 22. The minimum flow rate is the flow rate that must pass through the anode chamber A so that sufficient water can be discharged from the anode chamber A.

[0062] If the flow rate is greater than or equal to the second limit, step S700 is then performed. If the flow rate is less than the second limit, step S601 is performed and the flow rate is increased so that it is at least equal to the second limit. The process then terminates in step S800.

[0063] In step S700, the flow rate of the anode gas in the anode supply line 22 is reduced because the pressure difference exceeds the first limit value. The flow rate of the anode gas in the anode supply line 22 is reduced to a value that lies between the first and second limit values.

[0064] The flow rate of the anode gas in the anode supply line 22 is reduced in step S700 by reducing the flow rate of anode exhaust gas flowing into the anode supply line 22 via the recirculation line 21.

[0065] In a first embodiment, the flow rate of the anode gas in the anode supply line 22 is reduced by at least partially closing a first metering valve 19, which is arranged upstream of a jet pump 26 in a first line section 20. When the first metering valve 19 is at least partially closed, less anode exhaust gas flows into the anode supply line 22 via the recirculation line 21 and the first line section 20.

[0066] In a second embodiment, the flow rate of the anode gas in the anode supply line 22 is reduced by reducing the power of a pumping unit 25 located in the recirculation line 21. The pumping unit 25 assists the flow of the anode exhaust gas; when the power of the pumping unit 25 is reduced, the flow rate is reduced.

[0067] During the execution of step S700, the fuel flow rate, in particular hydrogen, which is fed from a tank 16 into the fuel line 17, can be kept constant. The fuel flow rate can be kept constant by at least partially opening a second metering valve 18, which is arranged in a second line section 29, so that at least a portion of the fuel flow passes through the second line section 29.

[0068] The inventive method is then terminated in step S800.

[0069] The method according to the invention can be terminated when a predefined number of iterations have been completed. The method according to the invention can also be terminated when the fuel cell system 100 is shut down or enters an operational standstill.

[0070] The method according to the invention can also be carried out, at least in part, by the control unit 500 of the fuel cell system 100. A computer program in the form of code can be stored in a memory unit of the control unit 500. When executed by a processing unit of the control unit 500, this code performs a process that can proceed as described above. The same advantages described above in connection with the method according to the invention can be achieved using the control unit 500. These advantages are fully referenced herein.

[0071] The control unit 500 can be in communication link with the sensors 27, 28, 33, 34 of the fuel cell system 100 in order to monitor the sensor values.

[0072] The control unit 500 can control the actuators in the fuel cell system 100 in order to carry out the procedure accordingly.

[0073] Furthermore, the control unit 500 can be in a communication link with an external computing unit in order to outsource some process steps and / or calculations completely or partially to the external computing unit.

[0074] According to another aspect, the invention provides a computer program product comprising instructions which, when executed by a computer, such as the processing unit of the control unit 500, cause the computer to carry out the method, which can proceed as described above. The computer program product offers the same advantages described above in connection with the method and / or the control unit 500 according to the invention. These advantages are fully referenced herein.

Claims

Claims 1.) Method for operating a fuel cell system (100) with at least one a fuel cell stack (11) and an anode system (200) in which an anode supply line (22), through which an anode gas flows into an anode chamber A, and a recirculation line (21), through which anode exhaust gas from the anode chamber A can flow into the anode supply line (22), and a cathode system 300 are arranged, characterized in that the following steps are carried out at least once: a. Determining a pressure difference in the fuel cell system (100) b. Comparing the pressure difference with a first limit value that describes a maximum permissible pressure difference c. Reducing the flow rate of the anode gas in the anode supply line (22) if the pressure difference exceeds the first limit value 2.) Method according to claim 1, characterized in that the following are additionally The following steps are performed: d. Determining the flow rate in the anode supply line (22) e. Comparing the flow rate in the anode supply line (22) with a second limit value that describes a minimum flow rate in the anode supply line (22) f. Reducing the flow rate of the anode gas in the anode supply line (22) to a value that does not fall below the second limit 3.) Method according to claim 1, characterized in that the quantity flow of the The anode gas in the anode supply line (22) is reduced by reducing the quantity flow of anode exhaust gas that flows into the anode supply line (22) via the recirculation line (21). The method of claim 3, characterized in that the flow rate of fuel, in particular hydrogen, which is fed from a tank (16) into the fuel line (17) remains constant. The method of claim 3, characterized in that the flow rate of the The anode gas in the anode supply line (22) is reduced by at least partially closing a first metering valve (19) which is arranged upstream of a jet pump (26) in a first line section (20). Method according to claim 3, characterized in that the flow rate of the The anode gas flow in the anode supply line (22) is reduced by reducing the power of a pumping unit (25) arranged in the recirculation line (21). Method according to claim 4, characterized in that the flow rate at Fuel remains constant by at least partially opening a second metering valve (18) arranged in a second line section (29). Method according to claim 1, characterized in that the pressure difference corresponds to a pressure difference between a cathode chamber K arranged in the fuel cell stack (11) and the anode chamber A. Method according to claim 1, characterized in that the pressure difference corresponds to a pressure difference between the anode supply line (22) and the recirculation line (21). Method according to claim 2 or 3, characterized in that the pressure difference is calculated from two pressure values ​​measured by sensors and / or determined using a model.

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