Fuel cell system comprising an oxygen supply device in the anode system; method for operating such a fuel cell system

Abstract

The invention relates to a fuel cell system (100) comprising at least one fuel cell stack (11), each of which comprises a cathode system (300) and an anode system (200) with an anode supply line (24), an anode discharge line (22) and a recirculation line (21), wherein an oxygen supply device (28) and an oxygen supply line (26) are disposed in the anode system. The fuel cell system further relates to a method for operating a fuel cell system (100).

Description

[0001] Description

[0002] title

[0003] Fuel cell system with an oxygen supply device in the anode system; method for operating such a fuel cell system

[0004] 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 7.

[0005] State of the art

[0006] It is known from the prior art that fuel cell systems exist that have an anode system and a cathode system. The anode system typically consists of an anode supply line that supplies fuel gas to a fuel cell stack, and an anode outlet line that recirculates anode exhaust gas to the anode supply line via a conveying unit. Furthermore, the cathode system typically consists of a cathode supply line, in which a compressor may be located, and a cathode outlet line through which cathode exhaust gas is conveyed from the cathode system into the exhaust system.

[0007] It is known that contaminants present in the ambient air and fuel can lead to degradation in the fuel cell system, reducing its performance. Disclosure of the Invention

[0008] It is advantageous if a fuel cell system includes an oxygen supply device. The oxygen supply device can reverse the aging of the fuel cell system caused by contaminants such as hydrocarbons or compounds such as CO, HCl, H2S, NOx, SOx, and NH3, thus restoring the efficiency of the fuel cell system. The oxygen supply device can also extend the service life of the fuel cell system. The oxygen supply device eliminates the need for costly and large filters in the fuel cell system's cathode system, as these are no longer required to reduce and separate contaminants.

[0009] Advantageously, the oxygen supply device can achieve greater robustness against contamination of the fuel with contaminants, since the aging of the fuel cell system caused by contaminants is reversible by the oxygen supply device and the associated process.

[0010] Advantageously, the oxygen supply device is a pump, in particular a rotary pump or a wheel pump, since this is an established and cost-effective technology that is regularly a component of a fuel cell system.

[0011] It is advantageous if the oxygen supply device is designed as a jet pump or a combined valve jet pump arrangement, since jet pumps and combined valve jet pump arrangements enable an efficient supply of oxygen to the anode system. Jet pumps require a driving medium that adjusts the volume flow of a suction medium through momentum exchange. Fuel or anode exhaust gas can be used as the driving medium for the jet pump in the anode system. The combined valve jet pump arrangement typically includes a metering valve and a jet pump.

[0012] Advantageously, an additional valve is arranged upstream of the oxygen supply device in the direction of flow. This additional valve ensures that oxygen is supplied to the fuel cell system in a targeted manner. The additional valve can be used to further regulate the amount of oxygen or oxygen-containing gas mixture. When there is no oxygen demand, the additional valve can assume a closed switching position, thus further increasing the reliability against unwanted oxygen ingress into the fuel cell system, especially the anode system.

[0013] It is advantageous if the oxygen supply device is located in the recirculation line of the anode system upstream of the second feed unit. In the recirculation line, the pressure within the anode system upstream of the second feed unit is lowest, thus facilitating oxygen supply.

[0014] It is advantageous if the oxygen supply device is located in the anode inlet line within the anode system. If the anode system's structural configuration does not allow for the oxygen supply device to be located in the recirculation line, this provides an alternative arrangement.

[0015] It is advantageous to activate an oxygen supply device in the anode system to regenerate the fuel cell stack, especially the catalyst. This restores the efficiency of the fuel cell system and extends its service life.

[0016] Advantageously, the oxygen supply device can be operated in a continuous and / or discontinuous mode. This allows a suitable operating mode to be selected depending on the ambient conditions, in particular the composition of the ambient air supplied to the fuel cell system and the composition of the fuel, which has a beneficial effect on the operation of the fuel cell system.

[0017] It is advantageous if parameters are used to activate and / or decide on the operating variant. This can be a GPS signal, since information about the ambient air can be obtained indirectly using the GPS signal. It can be assumed that higher levels of ambient air pollution can be expected in urban operation of the fuel cell system than in rural areas. Country-specific differences may also be possible, or local peculiarities may be taken into account when selecting the operating variant. It is advantageous if cell voltage values ​​of the fuel cell stack are used to determine the operating variant.If the measurement of cell voltages is part of the fuel cell system, the efficiency of the fuel cell system can be measured efficiently without additional structural measures and the oxygen supply device can be specifically activated if the efficiency of the fuel cell system drops.

[0018] It is advantageous to use values ​​from mapped voltages to determine the operating variant. The cell voltage curve can be compared with the mapped voltage, allowing the oxygen supply system to be activated in a targeted and optimized manner only when needed.

[0019] It is advantageous if the values ​​from at least one contamination sensor are used to determine the operating mode. The contamination sensor can reliably detect whether the ambient air contains a high proportion of contaminants, so that, for example, a continuous operating mode can be specifically activated if the contaminant content is high.

[0020] Advantageously, the oxygen supply device is activated when the fuel cell system is started up, so that continuous regeneration of the fuel cell system takes place without additional measures.

[0021] Advantageously, the oxygen supply device is activated when a first specified time period is exceeded, thus ensuring in an optimized and reliable manner that regular contamination cleaning takes place in the fuel cell system.

[0022] Advantageously, the oxygen supply device is activated when a specified voltage drop of the fuel cell stack is exceeded over a specified time interval, so that any loss of efficiency of the fuel cell system that has occurred is specifically regenerated.

[0023] Description of the drawings

[0024] The fuel cell system and method according to the invention are explained in more detail below with reference to drawings with preferred embodiments. They show:

[0025] Fig. 1 shows a first schematic topology of a fuel cell system according to a first embodiment;

[0026] Fig. 2 shows a second schematic topology of a fuel cell system according to a second embodiment;

[0027] Fig. 3 shows a third schematic topology of a fuel cell system according to a third embodiment;

[0028] Fig. 4 is a flow chart of the method according to the invention;

[0029] Figure 1 shows a schematic topology of a fuel cell system 100 with at least one fuel cell stack 11. The at least one fuel cell stack 11 has a cathode system 300 and an anode system 200.

[0030] The cathode system 300 requires oxygen (O2) as a reactant. Oxygen is a component of ambient air. By supplying ambient air to the fuel cell system 100, oxygen is made available to it as a reactant.

[0031] A cathode supply line 32 is arranged in the cathode system 300 and leads into the fuel cell stack 11. Oxygen is supplied to the fuel cell stack 11 via the cathode supply line 32.

[0032] A cathode compressor 31 is located within the cathode supply line. The cathode compressor 31 transports air into the fuel cell stack 11. The cathode compressor 31 can be used to vary the air flow rate. Increasing the power of the cathode compressor 31 results in an increased air flow rate being supplied to the fuel cell stack 11 via the cathode supply line 32. Reducing the power of the cathode compressor 31 results in a reduced air flow rate being supplied to the fuel cell stack 11. A cathode outlet line 33 is arranged in the cathode system 300. 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 33.

[0033] The anode system 200 requires fuel or anode fluid, in particular hydrogen (H2), as a reactant. By supplying fuel to the fuel cell system 100, the fuel is made available to the system as a reactant.

[0034] An anode supply line 24 is arranged in the anode system 200 and leads into the fuel cell stack 11. Fuel is supplied to the fuel cell stack 11 via the anode supply line 24.

[0035] A recirculation line 21 is arranged in the anode system 200. The recirculation line 21 is connected to the anode inlet line 24 via a first conveying unit 25. The first conveying unit 25 is arranged in the anode supply line 24 and connects it to the recirculation line 21.

[0036] The first delivery unit 25 is preferably designed as a jet pump or a combined valve jet pump arrangement. A combined valve jet pump arrangement typically includes a metering valve and a jet pump. The metering valve is firmly connected to the jet pump, for example, by means of a screw connection.

[0037] With the aid of the first feed unit 25, the ratio of fuel and anode exhaust gas in the anode feed line 24 downstream of the first feed unit 25 is varied.

[0038] If the first feed unit 25 is designed as a jet pump or combined valve jet pump arrangement, an increase in the volume flow of the supplied fuel into the first feed unit 25 also results in an increase in the volume flow of the anode exhaust gas into the anode feed line 24.

[0039] A second conveying unit 23 is optionally arranged within the recirculation line 21. The second conveying unit 23 can be a compressor configured as a blower, pump, and / or compressor. The second conveying unit 23 supports the recirculation of the anode exhaust gas from the recirculation line 21 into the anode supply line 24.

[0040] The second feed unit 23 can be used to vary the volume flow of the anode exhaust gas flowing from the recirculation line 21 into the anode inlet line 24. Increasing the power of the second feed unit 23 results in an increased volume flow of anode exhaust gas being supplied to the fuel cell stack 11 via the recirculation line 21. Reducing the power of the second feed unit 23 results in a reduced volume flow of anode exhaust gas being supplied to the fuel cell stack 11.

[0041] The fuel supply to the fuel cell stack 11 occurs at a superstoichiometric rate, so that the anode exhaust gas still contains fuel. To make this fuel available to the anode system 200, the anode exhaust gas is recirculated from the recirculation line 21 into the anode inlet line 24.

[0042] In an alternative embodiment, it is also possible to vary the arrangement of the conveyor units by adding or omitting conveyor units.

[0043] The fuel cell system 100 includes an oxygen supply line 26. In the first exemplary embodiment, the oxygen supply line 26 opens into the anode supply line 24 in the flow direction and is connected thereto. The oxygen supply line 26 is arranged upstream of the first delivery unit 25 in the flow direction.

[0044] An oxygen supply device 28 is arranged in the oxygen supply line 26.

[0045] Pure oxygen (O2) or an oxygen-containing gas mixture can be supplied via the oxygen supply device, without this variation limiting the method according to the invention. Oxygen is a component of ambient air, so ambient air is preferably supplied via the oxygen supply device 28. By using ambient air, additional tank devices can be dispensed with. In the following, the term "oxygen-containing gas mixture" refers to both pure oxygen and gas mixtures containing oxygen, such as ambient air.

[0046] In the first exemplary embodiment, the oxygen supply device 28 is designed as a pump, in particular as a rotary pump and / or wheel pump. With the aid of the oxygen supply device 28, the volume flow of the oxygen-containing gas mixture flowing from the oxygen supply line 26 into the anode inlet line 24 can be varied. Increasing the power of the oxygen supply device 28 results in an increased volume flow of the oxygen-containing gas mixture being supplied to the fuel cell stack 11 via the anode inlet line 24. Reducing the power of the oxygen supply device 28 results in a reduced volume flow of the oxygen-containing gas mixture being supplied to the fuel cell stack 11.

[0047] An additional valve 27 is optionally arranged downstream of the oxygen supply device 28 in the flow direction. Using the additional valve 27, the volume flow of the oxygen-containing gas mixture flowing from the oxygen supply line 26 into the anode inlet line 24 can be varied. When the additional valve 27 is closed, no volume flow of the oxygen-containing gas mixture can flow via the oxygen supply line 26 into the anode inlet line 24. Depending on the design of the additional valve 27, for example, as a throttle valve, the volume flow can also be varied.

[0048] An anode outlet line 22 is arranged in the anode system 200. The anode outlet line 22 is connected to the recirculation line 21. Gases, such as anode exhaust gas and / or fluids, such as product water, are discharged from the anode system 200 via the anode outlet line 22.

[0049] A control unit 400 is provided to regulate and control all control and regulation processes in the fuel cell system 100.

[0050] This also includes the processing of at least one measurement signal for implementing the method according to the invention. Figure 2 shows a second schematic topology of the fuel cell system 100 according to a second exemplary embodiment. The fuel cell system 100 shown in Figure 2 corresponds to the fuel cell system 100 shown in Figure 1, except for the differences mentioned below.

[0051] The fuel cell system 100 includes an oxygen supply line 26. In the second embodiment, the oxygen supply line 26 opens into the oxygen supply device 28 in the flow direction and is connected thereto.

[0052] An additional valve 27 is optionally arranged in the oxygen supply line 26. Using the additional valve 27, the volume flow of the oxygen-containing gas mixture flowing from the oxygen supply line 26 via the oxygen supply device 28 into the recirculation line 21 can be varied. When the additional valve 27 is closed, no volume flow of the oxygen-containing gas mixture can flow via the oxygen supply line 26 into the recirculation line 21. Depending on the design of the additional valve 27, for example, as a throttle valve, the volume flow of the oxygen-containing gas mixture flowing into the oxygen supply device 28 can also be varied.

[0053] The oxygen supply device 28 is arranged in the recirculation line 21 and is located in the flow direction upstream of the second conveying unit 23.

[0054] In the second embodiment, the oxygen supply device 28 is designed as a jet pump or combined valve jet pump arrangement.

[0055] With the aid of the oxygen supply device 28, the ratio of anode exhaust gas and oxygen-containing gas mixture in the recirculation line 21 downstream of the oxygen supply device 28 is varied.

[0056] If the volume flow of the supplied anode exhaust gas into the oxygen supply device 28 increases, the volume flow of the oxygen-containing gas mixture in the recirculation line 21 also increases.

[0057] In an alternative embodiment, the oxygen supply device 28 can also be arranged in the anode inlet line 24. Figure 3 shows a third schematic topology of the fuel cell system 100 according to a third exemplary embodiment. The fuel cell system 100 shown in Figure 3 corresponds to the fuel cell system 100 shown in Figure 1, except for the differences mentioned below.

[0058] The fuel cell system 100 includes an oxygen supply line 26. In the third embodiment, the oxygen supply line 26 opens into the recirculation line 21 in the flow direction and is connected thereto.

[0059] An additional valve 27 is optionally arranged in the oxygen supply line 26. Using the additional valve 27, the volume flow of the oxygen-containing gas mixture flowing from the oxygen supply line 26 into the recirculation line 21 can be varied. When the additional valve 27 is closed, no volume flow of the oxygen-containing gas mixture can flow via the oxygen supply line 26 into the recirculation line 21. Depending on the design of the additional valve 27, for example, as a throttle valve, the volume flow of the oxygen-containing gas mixture flowing into the recirculation line 21 can also be varied.

[0060] The oxygen supply device 28 is arranged in the recirculation line 21 and is located in the flow direction upstream of the first conveying unit 25.

[0061] In the third embodiment, the oxygen supply device 28 is designed as a pump, in particular as a rotary pump and / or wheel pump, and replaces the second delivery unit 23.

[0062] With the aid of the oxygen supply device 28, the volume flow of the oxygen-containing gas mixture flowing from the oxygen supply line 26 into the recirculation line 21 can be varied. Increasing the power of the oxygen supply device 28, when configured as a pump, results in an increased volume flow of oxygen-containing gas mixture being supplied to the fuel cell stack 11 via the oxygen supply line 26, the recirculation line 21, and the anode inlet line 24. Reducing the power of the oxygen supply device 28, when configured as a pump, results in a reduced volume flow of oxygen-containing gas mixture being supplied to the fuel cell stack 11. Figure 4 shows a flow diagram of the method according to the invention.

[0063] The method is started in a step S100, so that step S100 represents the start.

[0064] In step S200, a check is made to determine whether regeneration is required. A distinction can be made between a continuous operating mode and a discontinuous operating mode.

[0065] In the continuous operating mode, a permanent contamination cleaning takes place, preferably from the start of operation of the fuel cell system 100 until the stop of operation of the fuel cell system 100, i.e. a standstill of the fuel cell system 100.

[0066] In the discontinuous operating mode, contamination removal takes place intermittently during fuel cell operation. In the discontinuous operating mode, regeneration may be required for contamination removal after a specified period of time has elapsed. It is also possible for the oxygen supply device 28 to be activated when a specified voltage drop of the fuel cell stack 11 has occurred over a specified period of time.

[0067] It is also possible to switch between continuous and discontinuous operating modes during fuel cell operation in order to respond to changing environmental conditions. Changing environmental conditions can arise, for example, because the oxygen-containing gas mixture is supplied to the fuel cell system 100 in the form of ambient air, and this ambient air varies in its composition.

[0068] At least one GPS signal can be used to decide on the operating variant, since it can be assumed that the contamination of ambient air varies locally. For example, higher levels of ambient air contamination with contaminants can be expected in urban areas and country-specific deviations in the composition of the ambient air are possible. To decide on the operating variant, a comparison can be made with a voltage stored in the characteristic map. The voltage curve of the cell voltages is compared with a voltage stored in the characteristic map. The characteristic map can be a stored voltage value table. If the voltage of the fuel cell stack 11 has exceeded a specified deviation from the characteristic map, the discontinuous operating mode is activated until the cell voltages have returned to the initial level.

[0069] The cell voltage values ​​of the fuel cell stack 11 can be used to determine the operating variant, so that the cell voltages are observed at a constant load point. The previous cell voltages reached under the same load point are compared with the current cell voltages. If a voltage drop, e.g., of >0.5 mV, has occurred, the discontinuous operating mode is activated until the cell voltages have returned to the initial level.

[0070] It is also possible to use the signal from at least one sensor, particularly a gas sensor, to decide on the operating variant. The gas sensor determines the composition of the ambient air. If the ambient air contains elevated levels of contaminants, the operating mode can be switched from discontinuous to continuous, or, in discontinuous operation, an initial specified time period can be reduced. The initial specified time period is the time that elapses until the contamination removal process is activated.

[0071] In step S300, the oxygen supply device 28 is activated. The oxygen supply device 28 conveys the oxygen-containing gas mixture, such as ambient air, into the anode system 200. The oxygen-containing gas mixture flows into the fuel cell stack via the anode supply line 24 and ensures regeneration of the fuel cell stack 11, in particular the catalyst.

[0072] The fuel cell stack 11 is aged by contaminants introduced from the ambient air or from the fuel. These contaminants are hydrocarbons or compounds such as CO, HCl, H2S, NOx, SOx, and NH3. Aging of the fuel cell system occurs when the efficiency of the fuel cell system 100 decreases. During aging, contaminants accumulate on the surface of the catalyst and block the reaction of hydrogen and / or fuel there.

[0073] By supplying oxygen (O2) contained in ambient air, regeneration of the fuel cell stack 11, in particular of the catalyst, takes place. By supplying ambient air, the contaminants on the surface of the catalyst react, and the performance and efficiency of the fuel cell stack are restored. For the method according to the invention, it is sufficient to supply a small amount of ambient air into the anode system 200, such as supplying 0.5 vol.% of ambient air relative to the total volume flow in the anode system.

[0074] In step S400, a check is made to determine whether an event triggering the end of the method has occurred. An event triggering the end of the method can be the stoppage of operation of the fuel cell system 100, so that when the fuel cell system 100 stops operating, the oxygen supply device 28 is deactivated.

[0075] In discontinuous operating mode, an event triggering the end of the procedure can be the exceeding of a second specified time period. The second specified time period specifies how long the oxygen supply device 28 should remain activated. If the second specified time period is exceeded, the oxygen supply device 28 is deactivated.

[0076] In the discontinuous operating mode, an event triggering the end of the process can also be the reaching of a specified voltage of the fuel cell stack 11, so that when a specified voltage is reached, the performance of the fuel cell stack has been sufficiently restored.

[0077] In step S500, the method according to the invention is terminated, so that step S500 represents the end. In step S500, the oxygen supply device is deactivated. In step S500, the additional valve 27 can optionally assume a closed switching position.

Claims

Claims Fuel cell system (100) with at least one fuel cell stack (11), each having a cathode system (300) and an anode system (200) with an anode supply line (24), an anode outlet line (22) and a recirculation line (21), characterized in that an oxygen supply device (28) and an oxygen supply line (26) are arranged in the anode system (200). Fuel cell system (100) according to claim 1, characterized in that the oxygen supply device (28) is designed as a pump, in particular as a rotary pump or as a wheel pump. Fuel cell system (100) according to claim 1, characterized in that the oxygen supply device (28) is designed as a jet pump or combined valve jet pump arrangement. Fuel cell system (100) according to claim 1, characterized in that an additional valve (27) is arranged upstream of the oxygen supply device (28) in the flow direction.Fuel cell system (100) according to claim 1, characterized in that the oxygen supply device (28) is arranged in the recirculation line (21). Fuel cell system (100) according to claim 1, characterized in that the oxygen supply device (28) is arranged in the anode inlet line (24). Method for operating a fuel cell system (100) according to claim 1, characterized in that an oxygen supply device (28) is arranged in the. Anode system (200) is activated to carry out a regeneration of the fuel cell stack (11), in particular of the catalyst. Method according to claim 7, characterized in that the oxygen supply device (28) is operated in a continuous and / or discontinuous operating variant. Method according to claim 8, characterized in that the following parameters are used for activating and / or deciding on the operating variant: a GPS signal and / or Values ​​of cell voltages of the fuel cell stack (11) and / or values ​​of characteristic field voltages and / or Values ​​from at least one contamination sensor. Method according to claim 7, characterized in that the oxygen supply device (28) is activated when the fuel cell system (100) starts operating. Method according to claim 7, characterized in that the oxygen supply device (28) is activated when a first predetermined time period is exceeded. Method according to claim 7, characterized in that the oxygen supply device (28) is activated when a predetermined voltage drop of the fuel cell stack (11) is exceeded over a predetermined time interval.

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