Fuel cell system and method for operating a fuel cell system

Abstract

Fuel cell system (100) comprising at least one fuel cell stack (11) and a cathode system (300) having a cathode supply line (31) in which a first delivery unit (35) and a second delivery unit (36) and a cooler (39) are arranged, wherein the first delivery unit (35) and the second delivery unit (36) are arranged in parallel and in series via a line system (31, 33, 34).

Description

[0001] R. 417018

[0002] - 1 -

[0003] Description

[0004] title

[0005] Fuel cell system and method for operating a fuel cell system

[0006] The invention relates to a fuel cell system having the features of the preamble of independent claim 1 and a method for operating a fuel cell system having the features of the preamble of independent claim 9.

[0007] State of the art

[0008] It is known from the prior art that fuel cell systems include a fuel cell stack, an anode system, a cathode system and a cooling circuit.

[0009] 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.

[0010] From the patent application DE10 2021 201 306 A1, a fuel cell system is known in which two compressors are arranged in the cathode supply line, which can be driven by an electric motor or by a turbine.

[0011] Disclosure of the invention

[0012] The fuel cell system according to the invention and the method according to the invention for operating a fuel cell system have the advantage that a series arrangement of a first conveying unit and a second conveying unit via a piping system in a cathode system of the fuel cell system as well as a parallel arrangement of the first conveying unit and R. 417018

[0013] - 2 - of the second conveying unit via the piping system in the cathode system of the fuel cell system.

[0014] By using a serial arrangement of the first pumping unit and the second pumping unit in the cathode supply line, a high pressure of the cathode gas in the cathode system of, for example, up to 5 bar can be achieved.

[0015] By using a parallel arrangement of the first and second pumping units, the fuel cell system can be operated without reducing the power output ("derating") at a reduced air density of the supplied ambient air.

[0016] Advantageously, the piping system has one line configured to deliver cathode gas to the first pumping unit and a second line configured to deliver cathode gas to the second pumping unit. This allows for maximum flexibility in the distribution of the cathode gas mass flow within the piping system.

[0017] It is advantageous if, in the piping system, the first line is arranged parallel to the first pumping unit and the second line is arranged parallel to the second pumping unit. This allows cathode gas to be supplied to the cathode system via the piping system and the cathode gas to be diverted around the first compressor and the second compressor as needed.

[0018] Advantageously, the first line connects to the cathode supply line upstream of the second pumping unit, and the second line connects to the cathode supply line downstream of the first pumping unit. This allows both the first and second pumping units to deliver an increased mass flow of cathode gas through the piping system.

[0019] Advantageously, the system is switched from series to parallel operation by having the flow pass through a first line and a second line simultaneously. This allows for flexible use of the first and second pumping units and enables optimized distribution of the cathode gas mass flow within the piping system. R. 417018

[0020] - 3 -

[0021] It is advantageous to have a first means of regulating the mass flow rates in the piping system, in particular a first valve in the first line. It is also advantageous to have a second means of regulating the mass flow rates in the piping system. This allows the mass flow rate of the cathode gas to be precisely controlled.

[0022] It is advantageous if the first mass flow control device, in particular a first valve located in the first line, is set to at least a partially open switching position, and the second mass flow control device is set to a switching position such that cathode gas flows at least partially from the cathode supply line into the second line. This allows for a cost-effective design of the fuel cell system using established components and enables efficient regulation and control of the cathode gas mass flow.

[0023] It is advantageous if the second means for regulating the mass flows is designed as a 3-way valve, with the 3-way valve connecting the second line to the cathode supply line. Advantageously, switching from series operation to parallel operation is achieved by setting the 3-way valve to a switching position, allowing at least a portion of the cathode gas to flow from the cathode supply line into the second line. This enables a cost-effective design of the fuel cell system through the use of established components and allows for efficient regulation and control of the cathode gas mass flows.

[0024] It is advantageous if the second means for regulating the mass flows is designed as a second valve and a third valve, with the second valve being arranged in the second line and the third valve being arranged in the cathode supply line upstream of the first line's entry into the cathode supply line. Advantageously, switching from series operation to parallel operation is achieved by at least partially opening the second valve and placing the third valve in a closed switching position. In an alternative embodiment, this allows for a cost-effective design of the fuel cell system using established components and enables efficient regulation and control of the cathode gas mass flows.

[0025] It is advantageous if the first and second conveyor units are switched from series operation to parallel operation when a required R. 417018

[0026] - 4 -

[0027] Mass flow of the cathode gas m stack exceeds a limit value. The limit value corresponds to a mass flow rate of cathode gas. Specifically, the limit value corresponds to the maximum pumpable mass flow rate of cathode gas for the first and second pumping units in series operation. By operating the first and second pumping units in parallel, the mass flow rate of cathode gas can be increased above the limit value, so that the mass flow rate of cathode gas delivered to the fuel cell stack is greater than the limit value.

[0028] Description of the drawings

[0029] The fuel cell system and the method according to the invention are explained in more detail below with reference to drawings with preferred embodiments.

[0030] They show:

[0031] Fig. 1 shows a first embodiment of the fuel cell system according to the invention and

[0032] Fig. 2 shows a second embodiment of the fuel cell system according to the invention and

[0033] Fig. 3 shows a third embodiment of the fuel cell system according to the invention and

[0034] Fig. 4 shows an embodiment of the method according to the invention.

[0035] Figure 1 shows a schematic topology of a first embodiment of a fuel cell system 100 according to the invention, comprising at least one fuel cell stack 11, a cathode system 300, a cooling circuit (not shown) and an anode system (not shown).

[0036] The cathode system 300 supplies a cathode compartment in at least one fuel cell stack 11 with oxygen (O2) as a reactant. Oxygen is a component of air. R. 417018

[0037] - 5 -

[0038] In the cathode system 300 a cathode outlet 32 ​​and a conduction system 31 , 33, 34 is arranged, wherein in the conduction system 31 , 33, 34 a cathode inlet 31 , a first conductor 33 and a second conductor 34 are arranged.

[0039] The cathode lead 31 terminates in at least one fuel cell stack.

[0040] 11. Oxygen is supplied to the at least one fuel cell stack 11 via the cathode supply line 31. A first conveying unit 35, in particular a first compressor 35, and a second conveying unit 36, in particular a second compressor 36, are arranged in the cathode supply line 31.

[0041] In the illustrated first embodiment of the first exemplary embodiment, the first conveying unit 35 is electrically driven. The second conveying unit 36 ​​is connected to a turbine 40 via a shaft and can be driven by the turbine 40.

[0042] In a second embodiment, an electric shaft is arranged on the first conveying unit 35 and on the second conveying unit 36.

[0043] In a third embodiment, the first conveying unit 35 and the second conveying unit 36 ​​are connected to each other via a common electrical shaft and can be driven.

[0044] In a fourth embodiment, the second conveying unit 36 ​​can be driven by an electric motor. The first conveying unit 35 is connected to a turbine 40 via a shaft and can be driven by the turbine 40.

[0045] The first line 33 is configured to direct cathode gas past the first pumping unit 35 and the second line 34 is configured to direct cathode gas past the second pumping unit 36.

[0046] The first line 33 is arranged parallel to the first conveying unit 35 and the second line 34 is arranged parallel to the second conveying unit 36.

[0047] The first line 33 opens into the cathode supply line 31 upstream of the second pumping unit 36, and the second line 34 opens into the cathode supply line 31 downstream of the first pumping unit 35. R. 417018

[0048] - 6 -

[0049] In the piping system 31, 33, 34, a first means for regulating the mass flows 37 is arranged. In the first embodiment, the first means for regulating the mass flows 37 is designed as a first valve 37, wherein the first valve 37 is arranged in the first piping 33.

[0050] A second means for regulating the mass flows 21, 22, 23 is arranged in the piping system 31, 33, 34. In the first embodiment, the second means for regulating the mass flows 21, 22, 23 is designed as a 3-way valve 21, wherein the 3-way valve 21 connects the second line 34 to the cathode supply line 31. The 3-way valve 21 is arranged downstream of the first conveying unit 35 in the direction of flow.

[0051] A cooler 39 is arranged in the cathode supply line 31 upstream of the at least one fuel cell stack 11. The cooler 39 allows the cathode gas to be tempered before entering the at least one fuel cell stack 11. The cooler 39 can be designed as a heat exchanger 39, in particular a gas-water heat exchanger 39, wherein the heat exchanger 39 is connected to the cooling circuit of the fuel cell stack 11 (not shown) or to a separate cooling circuit (not shown).

[0052] The cathode outlet 32 ​​is connected to at least one 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 32.

[0053] In the first embodiment, the first conveying unit 35 and the second conveying unit 36 ​​are arranged in series via the piping system 31, 33, 34. When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in series, essentially only cathode gas flows through the cathode supply line 31 in the piping system 31, 33, 34. When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in series, the first mass flow control device 37 is in a closed switching position, so that essentially no cathode gas can flow through the first line 33. When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in series, the second mass flow control device 21 assumes a switching position in which no cathode gas can flow from the cathode supply line 31 into the second line 34. R. 417018

[0054] - 7 -

[0055] The cooling circuit (not shown) contains a first cooling circuit line, which forms a closed fluid circuit. A coolant is circulated in this cooling circuit line by means of a pump. A bypass line allows the coolant to be routed at least partially or completely away from the vehicle radiator.

[0056] The anode system (not shown) supplies an anode compartment of the at least one fuel cell stack 11 with a fuel, in particular hydrogen (H2), as a reactant. By supplying fuel to the anode compartment, the fuel is made available to the fuel cell system 10 as a reactant.

[0057] 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.

[0058] 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.

[0059] Figure 2 shows a schematic topology of a second embodiment of the fuel cell system 100 according to the invention. The second embodiment corresponds to the first embodiment except for the differences mentioned below.

[0060] In the second embodiment, the first conveying unit 35 and the second conveying unit 36 ​​are arranged in parallel via the piping system 31 , 33, 34.

[0061] When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in parallel, the mass flow of cathode gas in the cathode supply line is interrupted in the piping system 31, 33, 34. The mass flow of cathode gas is interrupted in the cathode supply line 31 between the second mass flow control device 21 and the connection point of the first line 33 with the cathode supply line 31. R. 417018

[0062] - 8 -

[0063] When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in parallel, cathode gas flows through the first line 33 and the second line 34.

[0064] When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in parallel, the first mass flow control device 37 has a switching position that is at least partially open, allowing cathode gas to flow through the first line 33. When the first conveying unit 35 and the second conveying unit 36 ​​are arranged in parallel, the second mass flow control device 21 assumes a switching position in which cathode gas can flow from the cathode supply line 31 into the second line 32.

[0065] Figure 3 shows a schematic topology of a third embodiment of the fuel cell system 100 according to the invention. The third embodiment corresponds to the second embodiment except for the differences mentioned below.

[0066] In the third embodiment, the second means for regulating the mass flows 21, 22, 23 is designed as a second valve 22 and a third valve 23, wherein the second valve 22 is arranged in the second line 34 and the third valve 23 is arranged in the cathode supply line 31 in the flow direction before the entry of the first line 33 into the cathode supply line 31.

[0067] In the third embodiment, the first conveying unit 35 and the second conveying unit 36 ​​are arranged in parallel via the line system 31 , 33, 34, in that the second valve 22 in the second line 34 assumes a switching position that is at least partially open and the third valve 23 in the cathode supply line 31 assumes a switching position that is closed.

[0068] In the third embodiment, the first conveying unit 35 and the second conveying unit 36 ​​can be arranged in series via the piping system 31, 33, 34 by placing the second valve 22 in the second line 34 in a closed switching position and the third valve 23 in the cathode supply line 31 in an open switching position. The first conveying unit 35 and the second conveying unit 36 ​​are arranged in series via the piping system 31, 33, 34 by placing the first valve 37 in a closed switching position. R. 417018

[0069] - 9 -

[0070] Figure 4 shows an embodiment of the method according to the invention.

[0071] By means of a serial arrangement of the first pumping unit 35 and the second pumping unit 36, a high pressure of, for example, up to 5 bar can be achieved in the cathode system 300. The exponential increase in the saturation vapor pressure of water with increasing temperature necessitates an increase in the operating pressure of the fuel cell system 100, from, for example, 1.5 bar at 60°C to 4 bar at an operating temperature of 90°C, in order to maintain a sufficiently high relative humidity in the cathode system 300, particularly in the cathode compartment of the at least one fuel cell stack 11, and to protect the at least one fuel cell stack 11 from drying out.

[0072] By means of a parallel arrangement of the first conveying unit 35 and the second conveying unit 36, operation of the fuel cell system 100 can be maintained without reduction of the power supply (“derating”) at a reduced air density of the ambient air supplied to the cathode system 300 as cathode gas.

[0073] For example, a substantially reduced air density of the ambient air supplied as cathode gas occurs during the operation of the fuel cell system 100 at altitudes above 2000m above sea level.

[0074] The oxygen requirement for operating the fuel cell system 100 depends on the power output of the fuel cell system 100. Even with a significantly reduced air density, it is necessary to continue supplying the fuel cell system 100 with a high mass flow of ambient air supplied as cathode gas via the cathode system 300, as otherwise the power output of the fuel cell system 100 will be reduced. However, due to the lower air density of the supplied ambient air, the maximum mass flow that can be conveyed by the first conveying unit 35 and the second conveying unit 36 ​​in series arrangement decreases.

[0075] Using the method according to the invention, the required mass flow rate of the cathode gas m can be determined. stackThe material can be conveyed via the parallel operation of the first conveying unit 35 and the second conveying unit 36 ​​even at lower air density of the supplied ambient air compared to sea level. R. 417018

[0076] - 10 -

[0077] The first conveying unit 35 and the second conveying unit 36 ​​can convey a lower mass flow rate in the series arrangement than in the parallel arrangement before a blocking limit and / or a speed limit of the first conveying unit 35 and the second conveying unit 36 ​​is reached.

[0078] In step S100, the process is initiated. The process according to the invention takes place during the operation of the fuel cell system 100. The process according to the invention can be carried out specifically when the fuel cell system 100 is located at an altitude of, for example, 2000 m or more.

[0079] In step S200, a required mass flow rate of the cathode gas m is determined.stack determined so that it is available for the further course of the process. The required mass flow rate of the cathode gas m stack is the mass flow of ambient air that must be supplied to the fuel cell system 100 in order to provide power.

[0080] The electrical stack power P stack is calculated as follows:

[0081] The voltage U stack The voltage depends on the current I via the current-voltage characteristic. A current I requires a certain mass flow rate of the cathode gas m. stack The required mass flow rate of the cathode gas m stack This corresponds to the air mass flow of ambient air required by the fuel cell stack 11 to provide the corresponding power.

[0082] To ensure an adequate supply of ambient air to the fuel cell stack 11, a stoichiometry A greater than 1 is chosen. Furthermore, M denotes air the molar mass of the ambient air, x 02 the mole fraction of oxygen in the ambient air, n ce u s The number of cells in the fuel cell stack 11 and F the Faraday constant. R. 417018

[0083] - 11 -

[0084] When the air density of the ambient air supplied as cathode gas is reduced compared to sea level, an adjustment of the ambient air supplied as cathode gas is necessary to determine the required corrected mass flow rate of the cathode gas m. corr take place.

[0085] The required corrected mass flow rate of the cathode gas m corr can be determined using the following formula:

[0086] The required corrected mass flow rate of the cathode gas m corrtakes into account the environmental conditions of the fuel cell system 100 under which the first conveying unit 35 and the second conveying unit 36 ​​supply ambient air to the fuel cell system 100.

[0087] A current print p in This corresponds to the pressure currently present in the vicinity of the fuel cell system 100.

[0088] A reference pressure p inire f corresponds to the pressure at sea level. For a pressure at sea level, 1.013 mbar is used as the standard reference.

[0089] A current temperature T in corresponds to the temperature currently present in the vicinity of the fuel cell system 100.

[0090] A reference temperature T in re f corresponds, for example, to the standard reference of the I SA standard atmosphere of 15°C.

[0091] The mass flow that can be conveyed by the first conveying unit 35 and the second conveying unit 36 ​​depends on the respective inlet conditions p. in and T in off. For example, if the ambient pressure p decreases in As the temperature drops below normal levels, the required corrected mass flow rate of the cathode gas increases. corr an. R. 417018

[0092] - 12 -

[0093] The speed limit of the first conveying unit 35 and the second conveying unit 36 ​​depends on the required corrected mass flow rate of the cathode gas m corr off, thereby, for example, the required mass flow rate of the cathode gas m stack from the first conveying unit 35 and the second conveying unit 36 ​​in serial arrangement at decreasing ambient pressure p in They will no longer be hired.

[0094] In step S300, the required corrected mass flow rate of the cathode gas m is determined. corr m't compared to a limit value. The limit value corresponds to a mass flow rate of the cathode gas. In particular, the limit value corresponds to a maximum deliverable corrected mass flow rate of cathode gas m corr max of the first conveying unit 35 and the second conveying unit 36 ​​in serial operation. When the required corrected mass flow of the cathode gas m corr If the limit is exceeded, a step S400 is then performed.

[0095] In step S400, the operation of the first conveying unit 35 and the second conveying unit 36 ​​is switched from series operation to parallel operation, as the required corrected mass flow of the cathode gas m corr exceeds the limit.

[0096] The operation is switched from the serial operation of the first conveying unit 35 and the second conveying unit 36 ​​to the parallel operation of the first conveying unit 35 and the second conveying unit 36 ​​by flowing through a first line 33 and a second line 34 in the line system 31 , 33 , 34.

[0097] A first means for regulating the mass flows 37, in particular a first valve 37, which is arranged in the first line 33, is placed at least partially in an open switching position and a second means for regulating the mass flows 22, 23, 24 is placed in a switching position so that cathode gas flows at least partially from the cathode supply line 31 into the second line 34.

[0098] In a first embodiment, the second means for regulating the mass flows 21, 22, 23 is designed as a 3-way valve 21 and is set to a switching position such that cathode gas flows at least partially from the cathode supply line 31 into the second line 34. R. 417018

[0099] - 13 -

[0100] In a second embodiment, the second means for controlling the mass flows 21, 22, 23 is designed as a second valve 22 and a third valve 23, and the second valve 22 is opened at least partially and the third valve 23 is placed in a closed switching position.

[0101] If, in step S300, it is determined that the required corrected mass flow rate of the cathode gas m corr If the limit value is not exceeded or step S400 has been executed, step S500 is then executed.

[0102] In step S500, the process according to the invention is terminated. The process according to the invention can be terminated when the fuel cell system 100 is shut down or is in an operational standstill. The process according to the invention can be terminated when the fuel cell system 100 is at sea level or the required corrected mass flow m corr falls below the limit value. If the inventive method is terminated while the fuel cell system 100 is in operation, the first conveying unit 35 and the second conveying unit 36 ​​can be connected in series in step S500.

[0103] 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.

[0104] 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.

[0105] According to another aspect, the invention provides a computer program product comprising instructions which, when the computer program product is executed by a computer, such as the arithmetic unit of the control unit 500, cause the computer to carry out the method which proceeds as described above R. 417018

[0106] - 14 - can. The same advantages described above in connection with the inventive method and / or the inventive control unit 500 can be achieved with the aid of the computer program product. These advantages are referred to in full hereto.

Claims

R. 417018 - 15 - Claims 1. Fuel cell system (100) with at least one fuel cell stack (11) and a cathode system (300) with a cathode supply line (31) in which a first pumping unit (35) and a second pumping unit (36) and a cooler (39) are arranged, characterized in that the first pumping unit (35) and the second pumping unit (36) are arranged in parallel and in series via a line system (31, 33, 34).

2. Fuel cell system (100) according to claim 1 , characterized in that in the piping system (31 , 33, 34) a first piping (33) is configured to direct cathode gas past the first conveying unit (35) and a second piping (34) is configured to direct cathode gas past the second conveying unit (36).

3. Fuel cell system (100) according to claim 1 , characterized in that in the piping system (31 , 33, 34) the first piping (33) is arranged parallel to the first conveying unit (35) and the second piping (34) is arranged parallel to the second conveying unit (36).

4. Fuel cell system (100) according to claim 2, characterized in that the first line (33) opens into the cathode supply line (31) upstream of the second pumping unit (36) in the direction of flow and the second line (34) opens into the cathode supply line (31) downstream of the first pumping unit (35) in the direction of flow.

5. Fuel cell system (100) according to claim 1 , characterized in that a first means for controlling the mass flows (37), in particular a first valve (37) in the first line (33), is arranged in the piping system (31 , 33, 34).

6. Fuel cell system (100) according to claim 1 , characterized in that a second means for controlling the mass flows (21 , 22, 23) is arranged in the piping system (31 , 33, 34). R. 417018 - 16 - 7. Fuel cell system (100) according to claim 6, characterized in that the second means for controlling the mass flows (21 , 22, 23) is designed as a 3-way valve (21), wherein the 3-way valve (21) connects the second line (34) to the cathode supply line (31).

8. Fuel cell system according to claim 6, characterized in that the second means for controlling the mass flows (21 , 22, 23) is designed as a second valve (22) and a third valve (23), wherein the second valve (22) is arranged in the second line (34) and the third valve (23) is arranged in the cathode supply line (31) in the flow direction upstream of the entry of the first line (33) into the cathode supply line (31).

9. Method for operating a fuel cell system (100) with at least one fuel cell stack (11) with a cathode supply line (31) in which a first pumping unit (35) and a second pumping unit (36) and a cooler (39) are arranged, characterized in that the first pumping unit (35) and the second pumping unit (36) can be connected and operated in series and in parallel via a line system (31 , 33, 34).

10. Method according to claim 9, characterized in that the operation is switched from serial to parallel operation when a required corrected mass flow rate of the cathode gas m corr exceeds a limit value.

11. Method according to claim 9, characterized in that switching from serial operation to parallel operation is carried out by passing current through a first line (33) and a second line (34) in the line system (31, 33, 34).

12. Method according to claim 11, characterized in that a first means for controlling the mass flows (37), in particular a first valve (37) arranged in the first line (33), is placed in an at least partially open switching position and a second means for controlling the mass flows (22, 23, 24) is placed in a switching position such that cathode gas flows at least partially from the cathode supply line (31) into the second line (34). R. 417018 - 17 - 13. Method according to claim 12, characterized in that the second means for controlling the mass flows (21 , 22, 23) is designed as a 3-way valve (21) and is placed in a switching position so that cathode gas flows at least partially from the cathode supply line (31) into the second line (34).

14. Method according to claim 12, characterized in that the second means for controlling the mass flows (21 , 22, 23) is designed as a second valve (22) and a third valve (23) and the second valve (22) is opened at least partially and the third valve (23) is placed in a closed switching position.

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