Fuel cell system with improved humidification

Abstract

A fuel cell system is proposed, comprising at least one fuel cell with an anode, a cathode, a membrane arranged between the anode and the cathode, a cathode inlet, a cathode outlet, an anode inlet and an anode outlet, which is characterized according to the invention in that the water occurring at the anode outlet is at least partially directed to at least one humidification connection in an oxidant tube connected to the cathode inlet, so as to humidify the oxidant stream flowing to the cathode inlet.

Description

Technical Field

[0001] The present invention relates to a fuel cell system including at least one fuel cell.

Background Art

[0002] Vehicles are known in which power is provided by a fuel cell system and driven by a drive motor. At that time, hydrogen catalytically combines with an oxidant, usually oxygen in ambient air, to form water, and in this case, power is provided. The ambient air is supplied to the fuel cell system using an air conveyance system or an air compression system. Hydrogen is usually stored in a high-pressure tank and supplied to the fuel cell system via pipes and valves. Further, hydrogen can be recirculated in the anode circuit or in the anode passage.

[0003] A fuel cell system based on a PEM fuel cell requires a sufficiently wet membrane in order to be able to conduct protons. For this reason, sufficient water management in the fuel cell system, particularly in the cathode passage and in the membrane, is essential for the operation of the fuel cell system. The risk of drying is particularly high in the cathode inlet region. It is known to operate the fuel cell system using a membrane humidifier and / or to set the system pressure higher in order to reduce the water absorption capacity from the air. Further, internal humidification by flow passages in individual fuel cells requires a fairly high system pressure and a relatively thin membrane. For this reason, for example, when the ambient temperature is high, when driving on a mountain road, when the fuel cell is deteriorated, etc., the fuel cell system may become inoperable in some operating regions, or may become inoperable unless the output is reduced.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Accordingly, an object of the present invention is to propose a fuel cell or a fuel cell system in which improvement of humidification is achieved in order to expand the achievable operating limit, and in this case, not to increase or significantly increase the complexity and cost of the fuel cell system as much as possible.

Means for Solving the Problem

[0005] This problem is solved by a fuel cell system having the configuration of independent claim 1. Advantageous embodiments and further configurations can be read from the dependent claims and the following description.

[0006] A fuel cell system having at least one fuel cell including an anode, a cathode, a membrane disposed between the anode and the cathode, a cathode inlet, a cathode outlet, an anode inlet, and an anode outlet is proposed. According to the present invention, this fuel cell system is characterized in that water generated at the anode outlet is at least partially guided to at least one humidification connection portion in an oxidant pipe connected to the cathode inlet, and as a result, is formed to humidify an oxidant flow flowing to the cathode inlet.

[0007] Accordingly, the at least one fuel cell is a polymer electrolyte membrane (PEM) type fuel cell. In this case, a gas having hydrogen or hydrogen is supplied to the anode side, and a gas having oxygen or oxygen is supplied to the cathode side. During operation, water is also generated at the anode, and this water is used to humidify the oxidant flow according to the present invention.

[0008] The oxidant flow may be realized in the form of air or oxygen. In the case of a vehicle operating on the ground or outdoors, air is particularly considered as an oxidant. This is because air is provided in a sufficient amount and can be pressurized through a compressor in some cases.

[0009] At least one humidification connection part may have only one humidification connection part, but may also have a plurality of humidification connection parts. These may be provided at different locations of the oxidant pipe. It is conceivable that the first humidification connection part is arranged immediately upstream of the cathode inlet. This may also be immediately upstream of a first metering valve that is coupled to the cathode inlet and selectively discharges water from the anode outlet. The second humidification connection part may be connected after the intercooler, and the third humidification connection part may be connected before the intercooler. The fourth humidification connection part may be connected before a compressor that pressurizes the oxidant flow and conveys it into the oxidant pipe. Further, a fifth humidification connection part may also be arranged before the air filter. Of course, further humidification connection parts are conceivable, and it is also conceivable to use a plurality of humidification connection parts simultaneously.

[0010] The classification numbers "first", "second", "third", "fourth", "fifth" used in this disclosure should not be understood as an order, but are only for identifying components of the same type that may be provided at different positions, for different purposes, or in different embodiments.

[0011] In the realized fuel cell system, it is possible to select an appropriate humidification connection part suitable for the pressure expected at the anode outlet. If the expected pressure is relatively low, for example, it may be worth considering providing the humidification connection part upstream of the compressor rather than downstream of the compressor.

[0012] The anode may be supplied with a pressure that is at least slightly higher than that of the cathode. Thus, there is a positive pressure difference, i.e., an overpressure, between the anode outlet and the oxidant pipe immediately upstream of the cathode inlet. According to the present invention, this overpressure can be utilized to mix the water generated at the anode into the oxidant stream without any special treatment. Thereby, the configuration space and the additionally required peripheral equipment can be significantly reduced. This can clearly simplify the fuel cell system according to the present invention compared to known fuel cell systems and enable cost - favorable manufacturing. Further, due to the humidification of the oxidant stream, no significant pressure loss occurs in the air supply path. Also, a membrane humidifier is not required, and as a result, the configuration space can be saved. The operating range of the fuel cell system can be extended to the operating limit, or the expected output reduction for the operating range can be considerably delayed. The output required for the compressor inside the fuel cell system can be reduced, and / or the design of at least one fuel cell at the full - load point can be improved. Because by sufficiently eliminating the required pressure drop and the parasitic output of the air compression system, the overall required output is reduced. Therefore, the fuel cell system according to the present invention is optimized with respect to the operating range and the operating limit, and thus with respect to hydrogen consumption, without significantly increasing the system cost.

[0013] It is advantageous if a mixing unit for homogenizing the oxidant - water mixture is arranged after at least one humidification connection. The mixing unit enables homogenizing the oxidant - water mixture in order to avoid the intrusion of water droplets into at least one fuel cell. Further, the mixing unit can promote evaporation / vaporization. The mounting position of the mixing unit may be different from each other in a plurality of embodiments. For example, it is possible to arrange the mixing unit immediately upstream of the cathode inlet or immediately upstream of the shut - off valve. By using the cathode bypass described below, the mixing unit may be arranged upstream of the draw - in location of the cathode bypass.

[0014] Furthermore, it is advantageous if, behind at least one humidification connection part, a porous humidification body through which an oxidant flow passes is arranged in order to promote the evaporation or vaporization of water. The pressure difference between the anode outlet and the humidification connection part may be too small in order to prevent the injection or spraying of water into the oxidant pipe. For example, by using a porous humidification body implemented in a sponge-like form, the water wets a very large surface area, which facilitates vaporization or evaporation by the oxidant flow. In an advantageous embodiment, the humidification body locally completely fills the cross-section of the oxidant pipe, so that the oxidant flow has to pass through the humidification body.

[0015] In a further advantageous embodiment, a metering unit is arranged in front of at least one humidification connection part and is formed to meter and pressurize water and discharge it into at least one humidification connection part. The metering unit can enable a fine spray of water by increasing the pressure. The pressure increase can be achieved in various ways. For example, the metering unit may have a pump nozzle unit or something similar. For example, a pressure increase injector having a piezo actuator is conceivable. Similarly, a small pump or a volumetric transport diaphragm pump is conceivable. The latter embodiment has a special advantage, namely that the pump stroke is precisely defined and the amount of metered water can be accurately quantified. In the market, diaphragm pumps with a predetermined transport volume or metering volume, which are cost-effective and particularly resistant to ice pressure, are already available for use in vehicles. The metering unit can be used in combination with a metering valve or instead of a metering valve. Especially when using the above-mentioned diaphragm pump, its cost is reasonable. The advantage of the embodiment with the possibility of spraying, which increases this pressure, is that - compared to the above-mentioned mixer - no pressure loss occurs.

[0016] Furthermore, the metering unit and / or at least one humidification connection part may have an injection device or a spraying device for injecting or spraying water. This assists in the homogenization of the oxidant-water mixture. The injection device or the spraying device may be implemented in the form of an injector.

[0017] In a further advantageous embodiment, the metering unit may be coupled to a buffer storage system that at least temporarily collects water. This may be a separate container that is constantly filled with water from the anode outlet. However, the discharge pipe coupled to the anode outlet may be implemented such that it has sufficient buffering capacity for water there. In this case, the metering unit can operate continuously advantageously because water collected therein is continuously supplied from the buffer storage system.

[0018] Particularly advantageously, a control unit may be formed and coupled to at least one metering valve or the aforementioned metering unit to control the amount of water flowing into the oxidant pipe depending on the operating state of at least one fuel cell. The control unit can achieve adaptation of the humidification. The metering may be performed depending on the operating state or operating point of the fuel cell system or at least one fuel cell. If at least one fuel cell is configured to self-humidify in most of the operating range, the metering of water may advantageously be performed at the limits of the operating range to avoid output reduction or drying in this limit range. However, if at least one fuel cell is conveniently configured such that it can always utilize somewhat humidified oxidant, humidification may be applied over the entire operating range starting from the water at the anode outlet. Further, over the entire life of the fuel cell system, it is necessary to adapt the operating strategy based on the degradation of at least one fuel cell. The metering may be performed adaptively and sequentially as appropriate over the life. For example, in the new state of at least one fuel cell, metering may be performed only at some operating points and at more parts of the operating range as the life progresses. The control unit may be formed to perform one or more of these processes.

[0019] In an advantageous embodiment, a water supply detection unit is provided which is formed to detect or sense the amount of water flowing into the oxidant tube. Knowledge about the amount of water flowing into the oxidant tube is useful for adaptively controlling the humidification by the humidifying device. Alternatively to direct detection, the amount of water may be calculated based on existing data / sensor data and the activation control of the metering unit via model-based evaluation. For example, an actuator whose flow is monitored within the metering unit or within the metering valve may be evaluated as to whether water or gas is being metered based on the flow characteristics during metering or during the conveying process. Due to the significantly different densities of the fluids, different flow characteristics are obtained each time that allow for the estimation of the medium state (liquid or gaseous). For example, if there is no water for metering and dispensing, this information feedback may be considered to adapt the operating strategy. Of course, it is also possible to monitor the metering of water using a suitable sensor.

[0020] Furthermore, it may be advantageous if the fuel cell system is formed to increase the pressure difference between the anode and the cathode during a predetermined time interval and to induce water into at least one humidification connection during said time interval. This is particularly effective when implementing a fuel cell system without a metering unit in particular. Thereby, the driving force acting on the water can be increased in a short time.

[0021] Furthermore, a cathode bypass may be provided which is formed to selectively couple the cathode outlet to the oxidant tube in order to carry excess water out into the exhaust gas passage or directly to the surroundings. For this purpose, the cathode bypass may extend directly, i.e., past the stack, to the surroundings or to the exhaust gas passage. Any corresponding metering valve or metering unit or any other mechanism for introducing water may melt frozen water by drawing hot air into the cathode bypass if it is necessary to have a temperature below the freezing point or if it is necessary to contain frozen water.

[0022] Further measures for improving the present invention will be shown in more detail below together with the description of the advantageous embodiments of the present invention with reference to the drawings.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0024] FIG. 1 schematically shows a fuel cell system 2. The fuel cell system 2 has a fuel cell 4, and the fuel cell has an anode 6, a cathode 8, and a cooling unit 10. A membrane 12 is disposed between the anode 6 and the cathode 8. Hydrogen is supplied to the anode 6 through an anode inlet 14, and the hydrogen is at least partially discharged again from an anode outlet 16. A recirculation pipe 18 performs recirculation of hydrogen from the anode outlet 16 to the anode inlet 14 using a compressor 20 and a jet pump 22. Hydrogen from a hydrogen tank (not shown here) is mixed through the jet pump 22.

[0025] Ambient air 24 is supplied to a compressor 28 through an air filter 26. The compressor is driven here, for example, by an electric motor 30 that receives a voltage supply from an inverter 32. Thereby, the pressurized air is supplied to an oxidant pipe 34 formed as an air pipe.

[0026] The cooled and pressurized air enters a mixing unit 38 that homogenizes the air-water mixture via an intercooler 36. Hereinafter, the types of water conduction will be described in detail. For example, within the mixing unit 38, the water contained in the air swirls, and as a result, extremely small droplets or mist are formed, promoting the vaporization or evaporation of the water. A first shut-off valve 40 coupled to a cathode inlet 42 is connected downstream of the mixing unit 38. The exhaust air exiting from the cathode 8 enters into an air discharge pipe 48 via a cathode outlet 44 and via a second shut-off valve 46. This air discharge pipe may have a regulating valve 50 for supplying the air back to the ambient air 24 again.

[0027] The air pipe 34 here has a plurality of humidification connection parts, and water from the anode outlet 16 can be supplied to the air flow via these humidification connection parts. The water is supplied here to a discharge pipe 52, and the discharge pipe is coupled, for example, to a metering unit 56 via a first metering valve 54. The metering unit 56 may be configured to pressurize the amount of water discharged from the discharge pipe 52 at a first humidification connection part 58 located immediately upstream of the first shut-off valve 40 or immediately upstream of the mixing unit 38 and guide it into a second humidification connection part 60. Similarly, a third humidification connection part 62 may be arranged immediately upstream of the intercooler 36. A fourth humidification connection part 64 may be positioned immediately upstream of the compressor 28. Further, a fifth humidification connection part 66 may be provided immediately upstream of the air filter 26. Depending on the pressure difference between the anode outlet 16 and the cathode inlet 42, one of the humidification connection parts 58, 60, 62, 64, or 66 to be used may be selected. A plurality may be used simultaneously or depending on the operating state.

[0028] Humidification can be controlled by the first metering valve 54 and / or the metering unit 56. Excess water may be taken out from the discharge pipe 52 via the second metering valve 68 for supply to the ambient air 24 through the air discharge pipe 48. Moreover, the discharge pipe 52 may be completely emptied through it if there is a risk of freezing. A purge gas / washing gas valve 70 may be provided to wash the purge gas / washing gas for reducing the nitrogen content in the anode circulation system coming from the anode 6 and similarly supply it to the ambient air 24. The discharge pipe 52 may be sized such that it has a certain storage capacity for water and is thus sized to be usable as a buffer storage system. Accordingly, the reference sign 52 also applies to the buffer storage system.

[0029] A cathode bypass 72 with a bypass valve 74 may be provided to heat the air pipe 34 and the components arranged therein, such as the first shut-off valve 40 or the mixing unit 38, if necessary.

[0030] Furthermore, a control unit 76 may be provided to control the fuel cell system 2, and the control unit is coupled to the valves 40, 46, 50, 54, 68, 74 shown here, the metering unit 56, the inverter 32 and optionally sensors (not shown here).

[0031] The metering unit 56 may be omitted. In this case, the introduction of water may be carried out only by the pressure difference between the anode outlet 16 and the cathode inlet 42. For this purpose, the details shown in FIG. 3 are useful.

[0032] The introduction of water into the air stream can be controlled by the control unit 32. For this purpose, in particular, parameters of the air mass flow in the air pipe 34, parameters of the pressure in the cathode 8, parameters of the pressure in the wet state of the membrane 12, and parameters of stoichiometry may be considered. The metering can be carried out in a clockwise operation via the valve 54, and in this case, the injection time or the number of strokes and frequency of the metering pump can be changed.

[0033] Figure 2 shows one possible detail of the fuel cell system 2 according to the present invention. Here, an exhaust pipe 52 connected to a buffer storage system 78 is shown. The buffer storage system guides water to a metering unit 56, and the metering unit has an injector 80 that meters water into the air pipe 34. Thereby, water can be injected, and as a result, the injector 80 can be used as an injection device or a spraying device. As a location suitable for metering and dispensing, a second humidification connection 60 arranged upstream of the mixing unit 38 is selected. Water is introduced upstream of the cathode bypass 72. This has the advantage that by opening the bypass valve 74 to open the cathode bypass 72 for a short time, water that does not require humidification can be introduced into the air exhaust pipe 48, and in this case, the metering valve 68 can be omitted. Alternatively, the mixing unit 38 may be located downstream of the second humidification connection 60 and upstream of the cathode bypass 72. Also, it is conceivable to divert the second metering valve 68 into the air exhaust pipe 48. In this case, the versatility of the system 2 is higher, but however, it is necessary to use two active components, for example, two metering valves 54 and 68, or the second metering valve 68 and the metering unit 56.

[0034] The injector 80 is electrically start-controlled and is connected to a control unit 76. Through the flow characteristics that directly change with the water volume flow, the control unit 76 can detect or detect the magnitude of the current water volume flow. At that time, the pressure of the released water becomes extremely high.

[0035] Alternatively, instead of this, as schematically illustrated in FIG. 3, a porous humidifying body 82 may be incorporated into the air pipe 34. Water is supplied to the humidifying body by the metering unit 56, for example, via a valve. There, a very large surface containing water is reticulated and evaporated or vaporized by the air flow. At that time, the discharge of water is solely propelled by the pressure difference between the anode outlet 16 and the cathode inlet 42.

Explanation of reference numerals

[0036] 2 Fuel cell system 4 Fuel cell 6 Anode 8 Cathode 12 Membrane 14 Anode inlet 16 Anode outlet 24 Surroundings 34 Oxidant pipe 38 Mixing unit 42 Cathode inlet 44 Cathode outlet 48 Air discharge pipe (exhaust gas passage) 52 Discharge pipe 54 First metering valve 56 Metering unit 58 First humidification connection 60 Second humidification connection 62 Third humidification connection 64 Fourth humidification connection 66 Fifth humidification connection 68 Second metering valve 72 Cathode bypass 76 Control unit 78 Buffer storage system 80 Injector (spray device or atomizer) 82 Humidifying body

Claims

1. A fuel cell system (2) having at least one fuel cell (4) comprising an anode (6), a cathode (8), a membrane (12) disposed between the anode (6) and the cathode (8), a cathode inlet (42), a cathode outlet (44), an anode inlet (14), and an anode outlet (16), wherein the fuel cell system (2) guides at least partially the water generated at the anode outlet (16) to at least one humidification connection (58, 60, 62, 64, 66) within an oxidant pipe (34) coupled to the cathode inlet (42), thereby forming to humidify the oxidant flow flowing into the cathode inlet (42), a cathode bypass (72) is provided which is formed to selectively couple the cathode outlet (44) to the oxidant pipe (34) for discharging excess water into the exhaust gas passage (48) or directly to the surroundings (24), The fuel cell system (2) is characterized in that the cathode bypass (72) is disposed downstream of the at least one humidification connection (58, 60, 62, 64, 66).

2. The fuel cell system (2) according to claim 1, characterized in that a mixing unit (38) for homogenizing the oxidant-water mixture is disposed after the at least one humidification connection (58, 60, 62, 64, 66).

3. The fuel cell system (2) according to claim 1 or 2, characterized in that a porous humidification body (82) through which the oxidant flow passes is disposed after the at least one humidification connection (58, 60, 62, 64, 66) to promote evaporation or vaporization of water.

4. The fuel cell system (2) according to any one of claims 1 to 3, characterized in that a metering unit (56) is disposed before the at least one humidification connection (58, 60, 62, 64, 66) and is formed to meter and pressurize water and discharge it into the at least one humidification connection (58, 60, 62, 64, 66).

5. The fuel cell system (2) according to claim 4, characterized in that the metering unit (56) and / or the at least one humidification connection (58, 60, 62, 64, 66) has an injection device or a spraying device (80) for injecting or spraying water.

6. The fuel cell system (2) according to claim 4 or 5, characterized in that the metering unit (56) is coupled to a buffer storage system (52, 78) that at least temporarily collects water.

7. The fuel cell system (2) according to any one of claims 4 to 6, characterized in that at least one metering valve (54, 68) or a control unit (76) operatively coupled to the metering unit (56) is provided, and the control unit is configured to control the amount of water flowing into the oxidant pipe (34) depending on the operating state of the at least one fuel cell (4).

8. The fuel cell system (2) according to claim 7, characterized in that the control unit (76) is configured to detect or sense the amount of water flowing into the oxidant pipe (34).

9. The fuel cell system (2) according to any one of claims 1 to 8, characterized in that it is configured to increase the pressure difference between the anode (6) and the cathode (8) during a predetermined time interval and to induce water into the at least one humidification connection (58, 60, 62, 64, 66) during the time interval.

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