DEVICE FOR AIR SUPPLY OF A FUEL CELL

Description

[0001] The invention relates to a device for supplying air to a fuel cell according to the type defined in the preamble of claim 1. It also relates to a fuel cell system comprising such a device.

[0002] Fuel cells are typically supplied with air via an air conveying device, such as a turbomachine, which is driven by an electric motor and can optionally also be supported by an exhaust air turbine. This design is generally known as an electric turbocharger, or ETC, or motor-assisted turbocharger. After compression, the supply air to the fuel cell is heated accordingly. In a low-temperature fuel cell, particularly a PEM fuel cell, this is a serious disadvantage, and many conventional designs incorporate an intercooler. This cools the air before it flows through a humidifier and is humidified for use in the fuel cell. This design is large, complex, and causes pressure losses in the supply air stream.A charge air cooler, in particular, has the disadvantage of placing additional strain on the fuel cell system's cooling circuit. Since dissipating the fuel cell system's waste heat is already difficult at the relatively low temperature level of this waste heat, usually below 100 to 120°C, the additional heat input from the charge air cooler represents a significant disadvantage.

[0003] DE 10 2004 038 633 B4 now proposes humidifying the air by injecting the condensate from the fuel cell system into the heat exchanger used as a charge air cooler. This not only consumes the fuel cell's product water, but also eliminates the need for a humidifier, such as a membrane humidifier designed as a gas / gas humidifier. However, the load on the cooling circuit remains.

[0004] DE 10 2017 214 312 A1 humidifies the supply air flow to a fuel cell using water that condenses from the fuel cell system and is injected into the volume flow downstream of the compressor via an injection valve. This achieves the humidification, eliminating the need for a conventional humidifier. The topic of charge air cooling plays no role here and is not mentioned.

[0005] From DE 10 2012 011 863 A1, a fuel cell system with at least one fuel cell is known, which comprises a membrane electrode assembly arranged between a first separator plate with distribution channels for distributing a fuel and a second separator plate with distribution channels for distributing an oxidizing agent, wherein a humidification device for humidifying a membrane of the membrane electrode assembly with a humidification medium comprises at least two further channels for the humidification medium, which are formed in at least one of the two separator plates, and the channels open into the distribution channels assigned to this separator plate at different locations from one another.

[0006] Further prior art is disclosed in the documents DE 102 23 353 A1 and JP 2001 283887 A.

[0007] The object of the present invention is to provide an improved device for supplying air to a fuel cell according to the type defined in more detail in the preamble of claim 1.

[0008] According to the invention, this object is achieved by a device having the features of claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments of the device are set forth in the dependent claims. Claim 10 further specifies a fuel cell system with such a device.

[0009] The device according to the invention uses a nozzle to humidify the supply air flow, similar to the prior art. According to the invention, an array of dual-fluid nozzles for supplying the condensed water is formed in the cross-section of the supply air flow. A separate cross-section is available for each dual-fluid nozzle, so that each nozzle is specifically targeted by its own air flow. This makes it simple and highly efficient to design the dual-fluid nozzle to suit the volume flow of air it is intended to humidify. Each of the separate cross-sections comprises a valve seat and a valve body, which experiences a restoring force in the direction of the valve seat, counter to the flow, for example, through a spring or other restoring element.

[0010] According to an exceptionally advantageous development of the device according to the invention, the individual restoring forces can be individually specified during design for each of the separated flow-through cross-sections, so that, depending on the pressure and volume flow generated by the air conveying device, only one or the other, or a specific number of valve bodies, are lifted from the valve seats in order to flow through the respective two-fluid nozzle and atomize the water supplied to it. Once all valve bodies in all separated flow-through cross-sections have been lifted from their valve seats, a corresponding cross-section must be available that is designed for the maximum air volume flow and at which all two-fluid nozzles in the field of two-fluid nozzles are supplied with water and humidify the volume flow.

[0011] It has been shown that humidification of the hot volume flow downstream of the flow compressor, which can, for example, have temperatures in the range of 150 to 250°C, is ideal. The supplied water, which according to an advantageous development of the concept can be preheated via a heat exchanger, in particular using waste heat from the fuel cell system, can then be ideally evaporated in the volume flow. This ensures, on the one hand, humidification of the supply air flow and, on the other hand, cools it downstream of the air conveying device. Depending on the required supply air flow, suitable humidification can be ensured due to the number of separate flow-through cross-sections through which the air flows, matching this volume flow. This allows for ideal adaptation.In particular, an air supply system designed in this way can dispense with both the charge air cooler and the humidifier, thus efficiently reducing the pressure losses in the supply air flow. Furthermore, the components and the space required for them can be saved, thus providing further advantages.

[0012] In the design variant described above, in which the condensed water is preheated accordingly using waste heat from the fuel cell system itself, the design also allows for a reduction in the load on the fuel cell's cooling circuit. This is not only relieved by the option of omitting the charge air cooler, but also by using heat from the fuel cell's cooling circuit to preheat the condensed water before atomization. This greatly helps to further optimize the cooling circuit configuration in low-temperature fuel cells, which is already critical with regard to waste heat dissipation.

[0013] Another crucial advantage of the design is the use of valve bodies and valve seats, which are opened as needed by the volume flow delivered by the air delivery system. If this volume flow drops below a certain limit or is completely absent, the valve bodies are pushed or pulled onto the valve seats, sealing the design. Thus, as an additional benefit of the device according to the invention, a passive cathode shutoff valve is created, which efficiently prevents air flow through the fuel cell whenever the air delivery system is not in operation and, accordingly, no air flow is desired.

[0014] Conventional valves of this type that open automatically when pressure is applied can, for example, operate via a spring. This has the disadvantage that with increasing volume flow and increasing opening cross-section between the valve seat and the valve body, the spring's restoring force also increases. This can cause the valve body to oscillate and thus result in uneven flow, which can be detrimental to downstream components and / or dosing accuracy due to the resulting pressure fluctuations. According to an exceptionally advantageous development of the device according to the invention, a magnetic force is therefore used as the restoring force.This then acts between a switchable and / or permanent magnet, for example in the area of ​​the valve body but preferably in the area of ​​the valve seat, and a magnetizable material such as a steel or iron alloy in the area of ​​the valve seat or preferably in the area of ​​the valve body. The valve body is therefore designed, for example, in the form of a hollow iron or steel sphere, preferably with a chemically resistant coating, for example made of plastic. It is then held on the valve seat by permanent magnets and / or electromagnetic means. As the volume flow increases, the valve body, which has a low mass due to its design as a hollow sphere and therefore reacts dynamically, lifts off from the valve seat and opens up a cross-section through which flow occurs. As the volume flow increases, this cross-section through which flow occurs becomes larger.Unlike a spring-loaded ball, with a magnetic restoring force the restoring force also decreases with the distance of the valve body from the valve seat, so that a degressive force-displacement characteristic curve of the respective valve is created, which is ideal for the applications mentioned, on the one hand for controlling the supply air flow to the respective two-fluid nozzle and on the other hand as a cathode shut-off valve.

[0015] Another very advantageous embodiment of the device according to the invention can further provide that the water can be conveyed to the dual-fluid nozzles via a conveying device directly or via a collecting line. The amount of water for humidification can thus be adjusted depending on the conveying pressure and the conveyed volume flow. In particular, the use of a collecting line also enables the use of the water in other areas of a system surrounding the device, in particular a fuel cell system surrounding the device. Such a use of water with a water collecting line is fundamentally described, for example, in DE 10 2020 206 156 A1 by the applicant.

[0016] The collected water can and should pass through appropriate purification devices and filters, for example, to mechanically retain impurities and to remove ions that have accumulated in the water. For example, a combination of a water filter with an ion exchange cartridge can be provided and can be arranged, for example, in the area of ​​the collecting line or between the individual water separators of such a system and a preferably heated collecting tank, in particular one comprising the aforementioned heat exchanger.

[0017] According to a very advantageous development of the concept, the individual, separated flow-through cross-sections, with their respective dual-fluid nozzles and valves, can be arranged directly at the outlet of a flow compressor as an air conveying device. "Direct" in this context means that no additional components are interposed. In particular, the device according to the invention can be designed such that the separated cross-sections, with their valves and dual-fluid nozzles, are flange-mounted directly at the outlet of the flow compressor, in order to then feed the cooled and humidified supply air directly or via a short line into the cathode chamber of the fuel cell.In this area immediately after the outlet of the flow compressor, the highest temperature of the supply air is present, so that the evaporation of the preheated water can take place ideally in order to humidify this supply air on the one hand and to cool it to a temperature level suitable for the fuel cell on the other.

[0018] According to an exceptionally advantageous development of the device, at least two air conveying devices and / or humidifying devices can be arranged as a sequential cascade. Two such consecutive humidifying nozzles and / or charging stages can then be used for a conventional register charging system. This allows for greater variability of the design and allows for efficient humidification of different material flows.

[0019] The respective air delivery device can be part of an electrically assisted turbocharger with the air delivery device, an exhaust air turbine and an electric machine. Such a setup, which is also commonly known under the term ETC (Electric Turbo Charger) or motor-assisted turbocharger, is ideal for efficiently supplying air to the fuel cell. In addition to the drive power typically required from the electric machine, energy recovered from the exhaust air can be used via the turbine for compression. If there is more energy in the turbine area than is needed to drive the air delivery device, the electric machine can also be operated as a generator in order to recover this energy in the form of electrical energy and store it temporarily. This applies whether two or one air delivery device is used.

[0020] The entire structure of the device can be integrated into a fuel cell system with a fuel cell, in particular a stack of individual cells, a so-called fuel cell stack. The fuel cell system itself can be used for various stationary or mobile applications. In particular, it can be used to provide electrical drive energy for a vehicle. Particularly in such vehicle applications, it is advantageous, on the one hand, to reuse the collected product water so that it does not have to be discharged onto the road. On the other hand, the decisive advantages with regard to construction volume, weight, energy efficiency, and the savings in components provided by the device according to the invention are a particularly significant advantage here.

[0021] Further advantageous embodiments of the device according to the invention also emerge from the exemplary embodiment which is described in more detail below with reference to the figures.

[0022] Showing: Fig. 1 shows a schematically indicated fuel cell system in a vehicle with a device according to the invention; Fig. 2 shows a sectional view through a part of the device according to the line II-II in Fig. 1 ; and Fig. 3 a schematic sectional view along the line III-III in Fig. 2 .

[0023] In the presentation of the Figure 1a very schematically indicated vehicle 1, for example a commercial vehicle or a passenger car, can be seen. At least part of its electrical drive power is supplied to this vehicle 1 by a fuel cell system 2, which is only partially indicated here and is highly simplified. This comprises a fuel cell 3 as its core, which is constructed, for example, as a stack of individual cells using PEM technology, as a so-called fuel cell stack. Purely by way of example, a common cathode chamber 4 and a common anode chamber 5 are indicated here. Hydrogen from a hydrogen storage system 6 is supplied to the anode chamber 5, and residual hydrogen leaves the system via an exhaust line 7 with a water separator 8. Other variants of the anode side are of course possible. Since these are of minor importance for the invention, they will not be discussed further here.However, it is clear to the person skilled in the art that various storage systems for the hydrogen, various dosing devices as well as an anode circuit with one or more recirculation conveyor devices and the like are conceivable and possible here.

[0024] Air is supplied to the cathode chamber 4 as an oxygen supplier via an air supply device 10. Part of this device 10 is an air conveying device 11, which can be designed, for example, as part of a so-called electric turbocharger 12. This known electric turbocharger 12 comprises, in addition to the air conveying device 11, which is preferably designed as a flow compressor, an exhaust air turbine 13 and an electric machine 14. Its principle of operation is known, so it need not be discussed further here.

[0025] After the air conveying device 11, a hot and dry compressed supply air stream is provided to the cathode chamber 4 of the fuel cell 3. This air then passes, preferably directly after the air conveying device 11, into an array of individual flow-through cross-sections, each with a two-fluid nozzle. In the schematic cross-section of the Figure 2 is this in Figure 1The field labeled 15 is indicated again. The individual flow-through cross sections are designated here with the reference numerals 161 - 168. They can, for example, be round and arranged within the flow cross section of the supply air. In the center of each individual separated flow-through cross section 161 - 168 there is a two-component nozzle 171 - 178, which is on the one hand flowed through by the volume flow of the hot and dry air flowing through the flow-through cross section 161 - 168 after the air conveying device 11 and on the other hand via a conveying device 18, as shown in the illustration of the Figure 1 This water is deionized water, which is condensed and collected in the fuel cell system 2. Purely as an example, the illustration of the Figure 1Two water separators are indicated. On the one hand, this is the already mentioned water separator 8 on the anode side, and on the other hand, this is a cathode-side water separator, designated here by 9, in an exhaust air line 19 connecting the cathode chamber 4 to the exhaust air turbine 13. The product water collected in this way reaches, for example, a tank, indicated here as an example and designated 20, and is preheated in this tank or downstream of it in the flow direction via a heat exchanger 21. It then reaches the area of ​​the feed pump 18 in order to be fed to the respective dual-fluid nozzles 171-178 depending on the generated feed pressure and the generated volume flow. This can be done, for example, for each of the dual-fluid nozzles 171-178 directly and, if necessary, switchably via a valve, or via a collecting line from which the corresponding dual-fluid nozzles are supplied.

[0026] This design of device 10 could also be varied in that two or possibly more of the air conveying devices are connected in series as a sequential cascade. These would then each be followed by a corresponding dual-fluid nozzle 171-178 to humidify the corresponding air flow and provide the other functionalities described here.

[0027] In the presentation of the Figure 3One of the separated flow-through cross-sections is now shown again in a sectional view, here, for example, cross-section 164. It comprises the two-substance nozzle 174 and a valve 22 consisting of a valve body 23 and a valve seat 24. The valve body 23 can preferably be designed as a hollow steel sphere with a plastic casing. In the area of ​​the valve seat 24 there is a permanent magnet 25, which is designed, for example, as a circumferential ring. This exerts an attractive force on the valve body 23, so that when there is little or no volume flow via the valve 22, the respective flow-through cross-section 161 - 168 is closed. This is particularly the case when the air conveying device 11 is not in operation.This prevents air from flowing through the cathode chamber 4, for example, due to airflow during purely electric operation of the vehicle 1 or due to external wind effects when the vehicle is parked. This is crucial for preventing fresh oxygen from entering the fuel cell 3, which would lead to a so-called air-to-air start during a later restart and damage the fuel cell 3.

[0028] Now, with increasing volume flow from the air conveying device 11, first one and then several of the valves 22 in the respective flow-through cross-sections 161 - 168 open accordingly. In particular, the restoring forces can be adjusted such that, depending on the respective volume flow from the air conveying device 11, a suitable number of the flow-through cross-sections 161 - 168 are opened by their valves 22, for example, first the central flow-through cross-section 161 and then increasingly the flow-through cross-sections 161 - 168 arranged centrally around it until, at the maximum volume flow from the air conveying device 11, all flow-through cross-sections 161 - 168 are opened by their respective valves 22. As soon as the respective flow-through cross-section 161 - 168 is opened via the valve 22, air flows through it.If water is supplied at the same time, it is atomized accordingly via the dual-fluid nozzle 171 - 178 in the hot and dry air stream downstream of the air conveying device 11, so that the water particles atomized into fine droplets can evaporate in the volume flow. This results in very efficient cooling of the supply air stream on the one hand and very good humidification of the supply air stream on the other. The dual-fluid nozzles 171 - 178 can be designed such that they are adapted to the respective volume flow, so that ideal atomization of the water and thus ideal humidification and cooling always occurs. This applies to every volume flow of the supplied air, since only the number of flow-through cross-sections matching the respective volume flow is passively released by the valves 22. At the same time, when the air conveying device is switched off, all valves 22 together seal off the cathode chamber 4 from the environment.

[0029] This results in a finely stepped characteristic curve, which allows for appropriate control via the delivery pressure and volume flow of the air delivery device 11 as well as via the delivery pressure and volume flow of the delivery pump 18, in order to use preheated water from the fuel cell system 1 in the warm, compressed air to humidify the supply air flow. Preheating can take place, in particular, in the heat exchanger 21 using waste heat from the fuel cell 3 itself, so that this additional use of waste heat relieves the load on the cooling system of the fuel cell system 2 and thus of the vehicle 1.

Claims

1. A device (10) for supplying air to a fuel cell (3), having at least one air conveying device (11) and at least one humidifying device, which is configured to supply condensed product water from the fuel cell (3) to the compressed supply air flow by means of at least one nozzle (171-178), characterized in that a field (15) of two-substance nozzles (171-178) for the supply of water is formed in the flow cross section of the supply air flow, wherein a separated cross section (161-168) through which flow can take place is formed for each of the two-substance nozzles (171-178) and wherein each of the separated cross sections (161-168) through which flow can take place comprises a valve (22) having a valve seat (24) and a valve body (23), which is pressed counter to the flow by a restoring force in the direction of the valve seat (24).

2. The device (10) according to claim 1, characterized in that the restoring force is formed as a magnetic force between a switchable and / or permanent magnet in the area of the valve body (23) or preferably in the area of the valve seat (24) and a magnetizable material of the valve seat (24) or preferably the valve body (23).

3. The device (10) according to claim 2, characterized in that the valve body (24) is designed as a hollow ball made of a magnetizable material.

4. The device (10) according to claim 1, 2, or 3, characterized in that the restoring force for each of the separated cross sections (161-168) through which flow can take place is predetermined, wherein at least two of the separated cross sections (161-168) through which flow can take place have different specifications and / or cross sectional areas.

5. The device (10) according to any one of claims 1 to 4, characterized in that the water can be conveyed via a conveying pump (18) directly or via a collecting line to the two-substance nozzles (171-178).

6. The device (10) according to any one of claims 1 to 5, characterized in that the water flows upstream of the two-component nozzles (171-178) through a heat exchanger (21), which is preferably operable by means of waste heat from a fuel cell system (2) comprising the fuel cell (3).

7. The device (10) according to any one of claims 1 to 6, characterized in that the separated cross sections (161-168) through which flow can take place are arranged directly in the outlet of a flow compressor used as an air conveying device (11).

8. The device (10) according to any one of claims 1 to 7, characterized in that at least two air conveying devices (11) and / or humidifying devices are provided as a sequential cascade.

9. The device (10) according to any one of claims 1 to 8, characterized in that the supply air flow is free of an intercooler and a membrane humidifier.

10. A fuel cell system (2) having a fuel cell (3) and a device (10) as claimed in any one of claims 1 to 9, in particular for supplying a vehicle (1) with at least part of its electrical driv