Fuel cell system; method for operating a fuel cell system

Abstract

Fuel cell system (100) with at least one fuel cell stack (11) and an anode system (200) in which a purge line (23) is arranged, and a cathode system (300) in which a cathode recirculation line (34) and a cathode recirculation valve (35) are arranged, wherein the purge line (23) is connected to the cathode recirculation line (34).

Description

[0001] The invention relates to a fuel cell system having the features of the preamble of independent claim 1. Furthermore, the invention relates to a method for operating a fuel cell system having the features of the preamble of independent claim 5. State of the art

[0002] It is known from the prior art that fuel cell systems exist that have an anode system and a cathode system. The anode system consists of an anode feed line that supplies fuel to a fuel cell stack, and an anode recirculation line that recirculates anode exhaust gas to the anode feed line via a feed unit.

[0003] The cathode system consists of a cathode supply line, which can house a compressor and supply air to the fuel cell stack. Furthermore, the cathode system consists of a cathode outlet line through which cathode exhaust gas is transported from the cathode system into the exhaust system. Disclosure of the invention

[0004] The fuel cell system according to the invention according to independent claim 1 and the method according to the invention for operating a fuel cell system with the features according to independent claim 5 have the advantage that anode exhaust gas, which contains a proportion of hydrogen, is at least partially fed into the cathode system and can react on a catalyst layer to form water (H2O). The catalyst layer is arranged in the fuel cell stack.

[0005] In the fuel cell system according to the invention, a purge line is connected to a cathode recirculation line, so that anode exhaust gas is introduced into the cathode recirculation line by setting a purge valve arranged in the purge line to an open switching position.

[0006] It is advantageous if the purge line is connected to the cathode recirculation line upstream of a cathode recirculation valve. This ensures a fluidically efficient connection between the purge line and the cathode recirculation line.

[0007] A cathode outlet line advantageously branches off from the cathode recirculation line, and the purge line is advantageously connected to the cathode recirculation line upstream of the cathode outlet line, which branches off from the cathode recirculation line. This makes it possible to efficiently direct a proportion of the anode exhaust gas into the cathode recirculation line and to discharge a proportion of the anode exhaust gas into the cathode outlet line.

[0008] It is advantageous to introduce anode exhaust gas from the purge line into the cathode recirculation line by setting the cathode recirculation valve to at least a partially open position. This allows the amount of anode exhaust gas to be precisely controlled or regulated.

[0009] A hydrogen concentration is measured in the cathode outlet line, and the cathode recirculation valve is advantageously set to an at least partially open switching position when the hydrogen concentration exceeds a limit value. This allows the method according to the invention to be carried out more efficiently, since anode exhaust gas is only fed into the cathode recirculation line when the limit value, which represents a maximum permissible hydrogen concentration, is exceeded.

[0010] It is advantageous if a hydrogen sensor is arranged in the cathode outlet line and the hydrogen concentration is determined using a hydrogen concentration sensor. A hydrogen sensor is an established component that enables efficient and accurate determination of the hydrogen concentration and can be made available to the method according to the invention.

[0011] Advantageously, the limit value is stored in a cloud-based table. This allows the limit value to be easily retrieved and adjusted as conditions change.

[0012] It is advantageous to set the cathode recirculation valve to at least a partially open position if a purge process is expected within a defined period of time. This can specifically ensure that at least a portion of the anode exhaust gas flows into the cathode recirculation line. Description of the drawings

[0013] The fuel cell system and the method according to the invention are explained in more detail below with reference to drawings with preferred embodiments.

[0014] They show: Fig. 1 a first schematic topology of the fuel cell system and Fig. 2 a flowchart of the method according to the invention.

[0015] In Fig. 1 shows a schematic topology of a fuel cell system 100 with at least one fuel cell stack 11, an anode system 200, a cathode system 300 and a cooling circuit, not shown.

[0016] The cathode system 300 supplies a cathode chamber K with oxygen (O2) as a reactant. Oxygen is a component of air. By supplying air to the fuel cell system 100, the oxygen is made available to the system as a reactant.

[0017] In the cathode system 300, a cathode supply line 31, a cathode outlet line 32 and a cathode recirculation line 34 are arranged.

[0018] 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 cathode compressor 33 is located within the cathode supply line 31. The cathode compressor 33 pumps air into the fuel cell stack 11.

[0019] 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.

[0020] The cathode recirculation line 34 is connected to the cathode chamber K and the cathode supply line 31. In the first embodiment, the cathode recirculation line 34 opens according to the Fig. 1 in the flow direction upstream of the cathode compressor 33 into the anode feed line 31.

[0021] In an alternative embodiment, the cathode recirculation line 34 can open into the cathode supply line 31 downstream of the cathode compressor 33.

[0022] In an alternative embodiment, a recirculation conveying unit may additionally be arranged in the recirculation line 34. The recirculation conveying unit may assist the flow of cathode exhaust gas from the cathode recirculation line 34 into the cathode supply line 31.

[0023] The cathode outlet line 32 is connected to and branches off from the cathode recirculation line 34. Gases such as cathode exhaust gas and / or product water are discharged from the cathode system via the cathode outlet line 32.

[0024] A cathode recirculation valve 35 is arranged within the cathode recirculation line 34.

[0025] The cathode recirculation valve 35 can be used to adjust the flow of the cathode exhaust gas from the cathode recirculation line 34 into the cathode supply line 31. When the cathode recirculation valve 35 is in a closed position, no cathode exhaust gas can flow into the cathode supply line 31. When the cathode recirculation valve 35 is in an at least partially open position, the cathode exhaust gas flows at least partially into the cathode supply line 31.

[0026] The anode system 200 supplies an anode compartment A of the fuel cell stack 11 with a fuel or anode fluid, 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.

[0027] An anode supply line 22, an anode recirculation line 21 and a purge line 23 are arranged in the anode system.

[0028] The anode supply line 22 leads into the fuel cell stack 11. Fuel is supplied to the fuel cell stack 11 via the anode supply line 22.

[0029] The anode recirculation line 21 is connected to the anode chamber A and the anode supply line 22.

[0030] The fuel supply to the fuel cell stack 11 can be superstoichiometric, so that the anode exhaust gas still contains fuel. To make the fuel contained in the anode exhaust gas available to the anode system 200, the anode exhaust gas is recirculated from the anode recirculation line 21 into the anode supply line 22.

[0031] A recirculation conveying unit 25 is optionally arranged within the anode recirculation line 21. The recirculation conveying unit 25 supports the recirculation of the anode exhaust gas from the anode recirculation line 21 into the anode supply line 22.

[0032] A jet pump with a metering valve 26 is arranged in the anode supply line 22. The jet pump with a metering valve 26 is arranged between the anode supply line 22 and the anode recirculation line 21 and connects them to each other.

[0033] The purge line 23 is connected to the anode recirculation line 21 and to the cathode recirculation line 34. In the first exemplary embodiment, the purge line 23 opens into the cathode recirculation line 34 upstream of the cathode outlet line 32, which branches off from the cathode recirculation line 34. Anode exhaust gas is discharged from the anode system 200 via the purge line 23.

[0034] A purge valve 24 is arranged in the purge line 23. When the purge valve 24 is opened, anode exhaust gas is discharged from the anode system 200 and can flow into the cathode recirculation line 34. The jet pump with metering valve 26 doses fuel into the anode system 200 accordingly to maintain a continuous flow rate.

[0035] In an alternative embodiment, the purge line 23 opens into the cathode recirculation line 34 in the flow direction between the cathode recirculation valve 35 and the cathode outlet line 32.

[0036] A control unit 500 is provided to regulate and control all control-related processes in the fuel cell system 100. This also includes the processing of information for executing the method according to the invention.

[0037] The control unit 500 can communicate with the sensors in the fuel cell system 100 to monitor sensor values. The control unit 500 can control the actuators in the fuel cell system 100 to carry out the method according to the invention accordingly.

[0038] In addition, the control unit 500 can be in a communication connection with an external computing unit in order to outsource process steps and / or calculations in whole or in part to the external computing unit.

[0039] In Fig. 2 shows an embodiment of the method according to the invention.

[0040] The method according to the invention enables anode exhaust gas, which contains a proportion of hydrogen, to be conducted at least partially from the anode system 200 into the cathode system 300 and to react with a catalyst layer arranged in the fuel cell stack 11, forming water (H2O). This allows the proportion of hydrogen discharged from the fuel cell system 100 into the environment to be reduced.

[0041] The method is initiated in step S100. The method according to the invention is initiated or executed during operation of the fuel cell system 100.

[0042] In step S200, anode exhaust gas from the purge line 23 is introduced into the cathode recirculation line 34 by setting the purge valve 24 to an open switching position.

[0043] In a first embodiment, anode exhaust gas from the purge line 23 is introduced into the cathode recirculation line 34 by additionally setting the cathode recirculation valve 35 to an at least partially open switching position.

[0044] Optionally, it can be checked whether the cathode recirculation valve 35 was already set to an open switching position before the execution of step S200, so that the cathode recirculation valve 35 remains open in step S200 instead of being set to an open switching position.

[0045] In a second embodiment, a hydrogen concentration in a cathode outlet line 32 is measured, and the cathode recirculation valve 35 is set to an at least partially open switching position when the hydrogen concentration exceeds a threshold value. The hydrogen concentration can be determined using a hydrogen concentration sensor 36. The threshold value can be stored in a cloud-based table.

[0046] In a third embodiment, the cathode recirculation valve 35 is set to an at least partially open switching position when a purge process, in which the purge valve 24 is set to at least a partially open switching position, is to be expected within a defined period of time.

[0047] Subsequently, a step S300 is executed. In step S300, the method according to the invention is terminated.

[0048] If it has been determined in the second embodiment of the method according to the invention that the hydrogen concentration does not exceed the limit value, step S300 is carried out without the purge valve 24 being set to an open switching position.

[0049] The described embodiments can be combined with each other.

[0050] The method according to the invention can be carried out in a fuel cell system 100 in several fuel cell stacks 11 in parallel or sequentially.

[0051] The method may further 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 a code can be stored in a memory unit of the control unit 500, which, when the code is executed by a computing unit of the Control unit 500 performs a method which can proceed as described above The control unit 500 can achieve the same advantages as described above in connection with the method according to the invention. These advantages are incorporated herein by reference in their entirety.

[0052] The control unit 500 may be in communication with the sensors of the fuel cell system 100 to monitor the sensor values.

[0053] The control unit 500 can control the actuators in the fuel cell system 100 in order to carry out the method accordingly.

[0054] In addition, the control unit 500 can be in communication with an external computing unit in order to outsource some process steps and / or calculations in whole or in part to the external computing unit.

[0055] According to a further aspect, the invention provides a computer program product comprising instructions that, when the computer program product is executed by a computer, such as the processing unit of the control unit 500, cause the computer to perform the method, which can proceed as described above. The computer program product can achieve the same advantages as described above in connection with the method according to the invention and / or the control unit 500 according to the invention. These advantages are incorporated herein by reference.

Claims

[1] Fuel cell system (100) with at least one fuel cell stack (11) and an anode system (200) in which a purge line (23) is arranged, and a cathode system (300) in which a cathode recirculation line (34) and a cathode recirculation valve (35) are arranged, characterized by that the purge line (23) is connected to the cathode recirculation line (34). [2] Fuel cell system (100) according to claim 1, characterized by that the purge line (23) is connected to the cathode recirculation line (34) upstream of the cathode recirculation valve (35) in the flow direction. [3] Fuel cell system (100) according to claim 1, characterized by that a cathode outlet line (32) branches off from the cathode recirculation line (34) and the purge line (23) is connected to the cathode recirculation line (34) upstream of the cathode outlet line (32) which branches off from the cathode recirculation line (34). [4] Fuel cell system (100) according to claim 3, characterized by that a hydrogen sensor (36) is arranged in the cathode outlet line (32). [5] Method according to one of the above claims, characterized by that anode exhaust gas from the purge line (23) is introduced into the cathode recirculation line (34) by setting the purge valve (24) to an open switching position. [6] Method claim 5, characterized by that anode exhaust gas from the purge line (23) is introduced into the cathode recirculation line (34) by setting the cathode recirculation valve (35) to an at least partially open switching position. [7] Method according to claim 6, characterized bythat a hydrogen concentration in a cathode outlet line (32) is measured, and the cathode recirculation valve (35) is set to an at least partially open switching position when the hydrogen concentration exceeds a limit value. [8] Method according to claim 7, characterized by that the hydrogen concentration is determined by means of a hydrogen concentration sensor (36). [9] Method according to claim 7, characterized by that the limit is stored in a cloud-based table. [10] Method according to claim 6, characterized by that the cathode recirculation valve (35) is set to an at least partially open switching position when a purging process is to be expected within a defined period of time.

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