WO2010108605A2

WO2010108605A2 - Fuel cell system having at least one fuel cell

Info

Publication number: WO2010108605A2
Application number: PCT/EP2010/001551
Authority: WO
Inventors: Thorsten Tüxen; Cosimo Mazzotta; Thomas Baur; Klaus Scherrbacher; Matthias Jesse
Original assignee: Daimler Ag; Ford Global Technologies, Llc
Priority date: 2009-03-24
Filing date: 2010-03-11
Publication date: 2010-09-30
Also published as: DE102009014590A1; WO2010108605A3

Abstract

The invention relates to a fuel cell system (1) comprising at least one fuel cell (2) having an anode chamber (3) and a cathode chamber (4). A recirculation line (7) is provided, through which exhaust gas from the anode chamber (3) can be returned to an area ahead of the anode chamber (3). At least one means for discharging media is provided in the area of the recirculation line (7) and/or the anode chamber (3). According to the invention, the at least one means is designed as a valve device (13) comprising a switchable flow path (19) and an overflow path (21).

Description

Fuel cell system with at least one fuel cell

The invention relates to a fuel cell system having at least one fuel cell according to the type defined in more detail in the preamble of claim 1. Furthermore, the invention relates to a method for operating such a fuel cell system, as well as a use thereof.

Such a construction of a fuel cell system with a recirculation line for returning the anode exhaust gas into the anode inlet is known, for example, from DE 101 15 336 A1. In such systems with a so-called anode loop, nitrogen and water accumulate in the recirculated anode exhaust gas over time. Therefore, it is known from the general state of the art and described in the above-mentioned document that in the region of the recirculation line valve devices are arranged, which are opened from time to time to the nitrogen from the area of the recirculation line and the area of the anode space to blow off accordingly. According to DE 101 15 336 A1, the "disposal" of this waste gas from the region of the anode loop can take place in different regions which typically each have a catalytic surface or are in connection with another component which has such a catalytic surface is therefore common because together with the nitrogen there will always also be a small amount of hydrogen in the vented gas, which can be rendered harmless in this way .. In order to be able to remove the product water of the fuel cell arising in the region of the anode exhaust gas, DE Furthermore, a water separator in the region of the recirculation line is described.

The above construction requires at least one valve device for blowing off the nitrogen (purge) and at least one further valve device for the purge Draining the accumulated in the water separator (drain). In addition to the cost of providing these components in the system, the components cause additional effort in terms of their control and any necessary sensor technology. In addition, corresponding line elements must be present from the valve devices into the respective areas into which the media are discharged. This requires corresponding components and corresponding installation space. To be able to ensure a safe start and secure functionality of the system even at temperatures below freezing, these line elements must also be made correspondingly insulated and / or heated. This also causes great expense in terms of cost, complexity and weight in the fuel cell system shown above.

International Application WO 2008/052578 A1 likewise discloses a fuel cell system with an anode loop, which is referred to herein as a fuel circuit. The special feature of this design is that the functionality of the water separator with a drain valve for discharging the water and the functionality of the blow-off valve for blowing off the nitrogen-containing gas are combined. The structure provides that a water separator is provided with a corresponding valve device. Whenever a correspondingly large amount of water has accumulated, it is drained from the water separator via the valve device. In addition, after the water is drained, gas exits the anode loop via the valve means of the water separator before it is closed again. The functionality, which was distributed in the above-mentioned writing on two separate components, is thereby integrated into a single component.

This structure already represents a significant improvement over the above-mentioned construction. However, a corresponding sensor for detecting the water level in the separator is also necessary here. Experience in practice has shown that this sensor is extremely easily contaminated with deposits from the fuel cell system, and that very often leads to a malfunction of the sensor and thus too frequent or too rare discharge of the accumulated water. Again, this is correspondingly problematic in terms of reliability of such a system. In addition, the use of such a sensor always represents a certain amount of effort, especially since a level sensor in Water separator typically has to be designed in the form of two individual sensors, which in turn is associated with the corresponding costs.

From the further general state of the art DE 103 11 785 A1 is also known. Therein a connection of the cathode region to the anode region of a fuel cell is described, in particular a fuel cell, which is operated with a hydrogen-containing gas from a gas generating device. Such hydrogen usually has some contamination with carbon monoxide, which damages the catalyst in the region of the anode space. Therefore, if necessary, air is introduced into the hydrogen via the compound, which oxidizes this carbon monoxide to carbon dioxide and thus minimizes the amount of carbon monoxide harmful to the catalyst. The control takes place via a corresponding pressure difference between the region of the anode and the region of the cathode, so that at lower pressure in the region of the anode air flows through the opening in the region of the anode (Airbleed). On the other hand, this structure can also be used to allow gas to flow from the region of the anode into the region of the cathode, namely whenever the pressure conditions are reversed (purge). This is also used in the structure according to DE 103 11 785 A1, for example, to blow off the resulting carbon dioxide, or in the case of an anode loop, the nitrogen which accumulates, together with the carbon dioxide, into the region of the cathode.

It is now the object of the present invention to provide a fuel cell system with an anode loop, in which with minimal expenditure on components and low costs media from the area of the recirculation line and / or the anode compartment can be safely and reliably discharged.

According to the invention this object is achieved by the features mentioned in the characterizing part of claim 1. A method of operating such a fuel cell system according to the invention is indicated by the features in the characterizing part of claim 13. A preferred use for the fuel cell system according to the invention and / or the method according to the invention is mentioned in claim 18. The respective dependent claims describe advantageous embodiments and further developments of the invention. Characterized in that the at least one means according to the invention is designed as a valve device which also has an overflow in addition to their usually existing switchable flow path, a valve device is formed with a bypass. This valve device with bypass is now used according to the invention to integrate both the purge and the drain in a single valve device according to the invention. This creates a very simple and compact design. In usually present operation, the discharge of the media will generally take place via the overflow path, which is provided with a correspondingly narrow cross section. In addition, for example, a shutter or the like may be integrated into the overflow path to firmly set a corresponding cross section which matches the volumetric flows in the present fuel cell system. Thus, one and the same valve device for different sized fuel cell systems can be used by simply replacing the panel. It is important to ensure that the flow factor (kv value) for the overflow or bypass suitable for the respective fuel cell system is designed so that no too high hydrogen concentrations occur in the gas discharged.

The opening of the switchable flow path of the valve is typically always carried out only when necessary, that is, for example, if there is too low a hydrogen concentration in the region of the recirculation line and / or the anode compartment in order to realize the required power generation in the fuel cell of the fuel cell system. By opening the switchable flow path, drain water is then expelled very quickly and the purge function is started very quickly.

In principle, a plurality of such valve devices may be provided in the region of the recirculation line and / or the anode compartment. However, the construction can be realized in a particularly efficient, simple and cost-effective manner if exactly one valve device is provided in the region of the recirculation line and / or the anode chamber according to a particularly favorable embodiment of the invention. About this one valve device as a combined drain / purge valve can then be realized with minimal effort in terms of space, the sensor and the control a very simple, compact and efficient design. Due to the Überströmwegs in the valve device, it comes to a continuous outflow, first of the water and then a corresponding amount of gas. This can be dispensed with elaborate sensors, such as level sensors, for the water level. On the one hand, this saves costs and, on the other hand, makes it possible to free oneself of possible malfunctions of the very slightly polluting level sensors.

In the simplest embodiment of the invention, the overflow path can have a solid cross-section which is predetermined by the fuel cell system and can be flowed through. In a particularly advantageous embodiment of the invention, it is further provided that this durchströmbare cross section is designed as a diaphragm, wherein the diaphragm is realized as a flexible diaphragm whose opening cross-section changes automatically depending on the pressure difference on the two sides of the diaphragm. Such a flexible diaphragm is still a passive device which does not require active driving or the like. It is therefore still very easy to implement cost-effectively and without the problem of malfunction.

The structure may for example be constructed in the form of a membrane, which deflects depending on the pressure difference between the one side and the other side accordingly. If one or more openings are now provided in the region of the membrane, its cross-section will be correspondingly larger in the case of a deflected membrane than in the case of a membrane that is not deflected. In extreme cases, it is thus possible to close the overflow path when the system is turned off so that, for example, no gases are exchanged between the areas connected via the valve device via the overflow path. Only when the system is put into operation and a corresponding pressure difference between the one side and the other side occurs, the membrane will deform accordingly in the direction of lower pressure and the flexible diaphragm creates the flow-through opening cross-section, which flows through the overflow, for example allowed by drain water and purge gas.

According to a particularly favorable and advantageous embodiment and development of the invention, the region of the recirculation line in this case has a water separator, wherein the valve device is arranged in the outlet region of the water separator. With this structure, the merging of drain and purge can be realized particularly efficiently in a single component. Separated water collects in the water separator, so that it can be assumed that the largest Amount of present in the region of the recirculation line and / or the anode chamber water collects in the region of this separator. In the outflow region of the separator, typically in the direction of gravity below, the valve device is then arranged, which allows by its Überströmweg a continuous outflow of water. If there is no more water in the separator, it also comes to a blow-off of the enriched in the recirculation line gases, in particular nitrogen and optionally a certain residual amount of hydrogen come. From the described functionality, the construction with the water separator can do without the pollution-critical and cost-intensive level sensors, as a continuous flow of the accumulating water is ensured via the overflow. With appropriate selection of the diameter of the overflow so a very simple and efficient structure can be achieved, in which only minimal amounts of hydrogen flow from the recirculation line.

In the method according to the invention, it is provided to use the structure according to the invention in such a way that media in two different states of aggregation are discharged via the valve device. Due to the nature of the liquids and the gases, with a suitable arrangement of the valve device, preferably in a water separator, the drainage function will always be carried out first until no more water is present in the corresponding lines to the valve device. Only after the water has flowed out via the valve device will there be a blow off of gases from the region of the recirculation line and / or the anode chamber. By means of a corresponding design of the overflow path and here in particular of the flow-through cross section, it can be achieved that no large amounts of hydrogen leave the region of the recirculation line and / or the anode compartment. This will result in a continuous outflow of the accumulating water, while only comparatively small amounts of enriched nitrogen are blown off via the overflow. Since a certain amount of hydrogen is always lost together with the blowing off of the inert gases, this is particularly favorable since the loss of hydrogen should, of course, be kept as low as possible.

Typically, therefore, the switchable flow path of the valve device in normal operation is not or only in exceptional circumstances, such as the operation of the Fuel cell system with high electrical power, opened accordingly. Therefore, it is provided according to a particularly favorable and advantageous development of the method that the switchable flow path of the valve device is always opened only when the hydrogen concentration in the recirculation line and / or the anode compartment falls below a predetermined value. The drop in hydrogen concentration indicates the presence of a large volume of inert gas, especially nitrogen. If this is the case, then a very fast blowing off of this gas can be achieved by opening the switchable flow path. Only in such cases, therefore, the opening of the switchable flow path, so that losses of hydrogen from the region of the recirculation line and / or the anode compartment can be largely minimized.

As stated above, the structure of the fuel cell system according to the invention and the operation of the method according to the invention are characterized in particular by simplicity, reliability and compactness. Therefore, both the fuel cell system and the method of operating such a system are particularly suitable for use in land, water and air transport. Since such means of transport, in particular passenger cars, are always realized under high cost pressure and rather small available installation space, these advantages play a particularly important role here. The fuel cell system can typically provide the drive energy for such a means of transport, but it is also conceivable to generate only electrical energy for auxiliary drives via the fuel cell system, while the propulsion energy is otherwise obtained, for example, by internal combustion engines, turbomachines or the like.

Further advantageous embodiments of the invention will become apparent from the remaining dependent claims and will be apparent from the embodiment, which will be explained in more detail below with reference to FIGS.

Showing:

Fig. 1 is a schematic representation of a fuel cell system in a possible

Embodiment according to the invention; Fig. 2 shows a structure of a valve device in a first embodiment according to the

Invention; Fig. 3 shows a structure of a valve device in a second embodiment according to the

Invention; Fig. 4 shows a structure of a valve device in a third embodiment according to the

Invention; and FIG. 5 shows a construction of a flow path with a flexible diaphragm.

In the illustration according to FIG. 1, a fuel cell system 1 is indicated in highly schematic form in a section relevant to the present invention. The most important component of the fuel cell system 1 is a fuel cell 2, which is typically designed as a stack of individual fuel cells, as a so-called fuel cell stack. The fuel cell 2 has an anode space 3 and a cathode space 4, which in the exemplary embodiments illustrated here should each be separated from one another by a proton-conducting membrane. The fuel cell 2 is therefore a so-called PEM fuel cell stack.

The anode compartment 3 of the fuel cell 2 is supplied with hydrogen from the hydrogen storage device 5 from a hydrogen storage device 5 via a metering valve 6 and a line element. In the region of the anode chamber 3, unreacted hydrogen passes via a recirculation line 7 back into the region in which the fresh hydrogen flows via the metering valve 6 to the anode chamber 3. The recirculation line 7 thus leads in a manner known per se unused gas from the region of the anode chamber 3 back into the anode space, wherein the gas mixed with fresh hydrogen from the hydrogen storage device 5. To compensate for the pressure loss in the anode chamber 3, a recirculation conveyor 8 is arranged in the region of the recirculation line 7, which ensures the return of the unused gas from the anode chamber 3. The recirculation conveyor 8 can be designed as a hydrogen recirculation fan, as indicated in FIG. Additionally or alternatively, a gas jet pump would be conceivable, which is driven by the hydrogen from the hydrogen storage device 5, and sucks the gas from the region of the recirculation line 7, mixed with the fresh hydrogen and the anode chamber 3 feeds.

The cathode compartment 4 of the fuel cell 2 is supplied with air in the exemplary embodiment shown here. The oxygen contained in the air serves as an oxidizing agent for the chemical reaction in the interior of the fuel cell 2 and forms together with the Hydrogen in a conventional manner, water, wherein electric power is released, which can be tapped at the fuel cell 2 accordingly. The air for the cathode compartment 4 is compressed accordingly via an air conveyor 9 and fed to the cathode compartment 4. For the preparation of the air while other components such as air filters or the like may be present, their representation has been omitted here for simplicity. The air conveyor 9 can be designed as a compressor, for example as a screw compressor. In the embodiment shown here, however, the air conveying device 9 should be designed as a flow compressor, which is combined via a shaft with an electric machine 10 and a turbine 11. This construction, which is also known from the prior art, is also referred to as an electric turbocharger (ETC = Electric Turbo Charger). Via the turbine 11, existing energy in the form of pressure and heat can be correspondingly recovered in the exhaust gas from the cathode compartment 4. The air conveyor 9 can then be operated via the turbine 11 or the operation can be supported at least via the turbine 11. The remaining energy remaining, or if the turbine 11 does not provide energy all the energy for driving the air conveyor 9, can also be provided via the electric machine 10. If the turbine 11 provides an excess of energy, so that more energy is generated at the turbine 11 than is needed to operate the air compressor 9, then the electric machine 10 can be operated as well as a generator to convert this resulting mechanical energy into electrical energy, which then in example, a battery of the fuel cell system 1 is stored accordingly or other electrically operated ancillaries can be provided.

In the region of the recirculation line 7, a water separator 12 is also provided, which during operation liquid water, which accumulates in the region of the anode chamber 3 and is discharged via the recirculation line 7, collects. This liquid water can thus not clog gas ducts and the like in the region of the anode compartment 3, so that its safe and reliable operation can be guaranteed. In the region of the water separator 12, a valve device 13 is provided in the outlet region of the water separator 12, typically in the direction of gravity below, for discharging this water. This valve device 13, which is the core of the one described here Represents system structure, it has a special design, which will be discussed later on comprehensive.

In the region of the supply of air from the air conveyor 9 in the cathode compartment 4, a further component 14 is also arranged, which is flowed through by both the supply air flow to the cathode compartment 4 and the exhaust air flow from the cathode compartment 4. This component 14 is intended to be a combined intercooler and humidifier. In principle, it would also be conceivable to design the two components individually one after the other. The task of the component 14 is to cool and humidify the air which is comparatively hot and dry after the air conveying device 9 with the rather cold and moist exhaust air from the cathode chamber 4. For this purpose, the two gas streams flow through the component 14 in separate regions, which are separated from one another by means of partitions which are at least partially permeable to heat and water vapor. Thus, the heat of the compressed supply air can be transferred to the exhaust air. At the same time, moisture present in the exhaust air, which is there due to the product water produced primarily in the region of the cathode compartment 4, is transferred to the dry supply air, so that it flows into the cathode compartment 4 in a correspondingly humidified manner and thus does not damage the sensitive membranes. The advantage of the structure with the turbine 11 is that used in the component 14 from the supply air flow to the exhaust air flow energy used in the area of the turbine 11 and at least partially made available again for the air conveyor 9 available.

The fuel cell system 1 according to FIG. 1 also shows an electronic control system

15, which is indicated here by way of example and is in communication with corresponding components of the fuel cell system 1. In addition, three sensors are exemplary

16, 17, 18, which provide corresponding values to the control electronics 15, which can then be used to control, for example, the air conveyor 9, the recirculation conveyor 8, the metering valve 6, the turbine 11 or the like. The sensors 16 and 17 should represent corresponding pressure sensors, while the sensor 18 a

Hydrogen concentration sensor symbolizes. The control electronics 15 is connected in a conventional manner with the fuel cell 2 itself and can monitor the functionality of the entire fuel cell system 1 and control or regulate. When used in a vehicle, the control electronics 15 is also with a vehicle control unit are in communication in order to implement the corresponding requirements of the vehicle to the fuel cell system 1, for example, by the fuel cell system 1, the power demand imposed by the vehicle accordingly. Thus, the desired propulsion energy can be generated by the Brenπstoffzellensystem 1, if this provides at least a portion of the drive power for the motor vehicle. In equally conceivable use of the fuel cell system 1 as auxiliary power system, a corresponding request could be made by the electrical auxiliary unit of the vehicle, for example an air conditioning system or a corresponding electronic component.

This structure described so far corresponds to the corresponding part of a fuel cell system 1, as it is also known from the prior art. Due to the fact that the cathode chamber 4 air is supplied, and that the hydrogen is passed through the recirculation line 7, in a so-called anode loop to the anode chamber 3, it comes with time to an accumulation of nitrogen in the recirculation line 7 and the Anode space 3, since nitrogen diffuses through the membrane from the air in the cathode space 4 in the region of the anode space 3. In addition, a portion of the resulting product water will arise in the region of the anode compartment 3, although most of the product water in the cathode compartment 4 is obtained. Due to the circulation of the gas around the anode compartment 3, there is now an accumulation of nitrogen and water in the region of the anode loop. In order nevertheless to ensure a sufficient amount of hydrogen or a sufficiently high hydrogen concentration in the anode compartment 3 of the fuel cell 2, this nitrogen must be blown off in conventional systems from time to time (purge). Also, the accumulating water must be drained from time to time (drain). The drain and the purge take place in the structure according to FIG. 1 by means of the valve device 13, which is attached to the water separator 12 in the exemplary embodiment shown here.

In the illustration of Figure 2, the detailed structure of the valve device 13 can be seen in a schematically illustrated embodiment. In this case, the valve device 13 has two flow paths, namely a switchable flow path 19 with a valve element 20 and an overflow path 21, which in the exemplary embodiment shown here is intended to have a fixed predetermined flow-through cross-section via an orifice 22. The switchable flow path 19 and the overflow 21 are guided in parallel in the valve device 13, so that even when the valve 20 is closed, a flow through the overflow 21, which could also be referred to as a bypass, may occur. Via the valve device 13, the water separator 12 is now connected to the region of the supply air to the cathode chamber 4. In regular operation, with closed switchable flow path 19, accumulating water accumulating in the water separator 12 will flow out of the water separator via the overflow path 21 and reach the cathode chamber 4 in the region of the supply air. In particular, in the area of the merge after the air conveyor 9, the supply air will be hot and dry accordingly, so that the moisture introduced or the water introduced from the area of the water separator 12 is cooling and humidifying the supply air, which is for the conditioning of the supply air, which then typically flows through a charge air cooler and / or a humidifier, is quite beneficial. After the water separator is correspondingly empty through the Überströmweg 21, so that the water in it was largely drained, also a part of the gas from the region of the recirculation line 7 is blown over the Überströmweg 21 of the valve means 13, which also in the supply air reaches the cathode compartment 4. This gas will primarily consist of inert gases, especially nitrogen. In general, however, a small amount of hydrogen will be included. This is mixed in the supply air to the cathode compartment 4 according to the supply air. At the present in the cathode compartment 4 catalysts, the mixture of oxygen and residual hydrogen in the purge gas can then react to water without the exhaust duct from the cathode compartment 4 emissions of hydrogen to the environment would be feared.

About the aperture 22 in Überströmweg 21 of the valve device 13 is typically always first that accumulating water flow. Only then is a blowing off of gas from the area of the recirculation line 7. This is so intentional in the general operating conditions, in particular in the partial load range of the fuel cell system 1 and typically also both in terms of the drain and with respect to the Purgs sufficient. In special situations, when a corresponding amount of inert gas has accumulated in the recirculation line 7, the valve 20 of the switchable flow path can be opened correspondingly via the control device 15. Then, in addition to a blow off a larger volume, also here first of the water and then the gas. Because of the control device 15 corresponding values the system such as pressures, temperatures and the like are known, an opening of the valve 20 in the switchable flow path 19 can be controlled so that it takes place at a time in which the appropriate conditions in the cathode compartment 4, so on the one hand the introduced moisture and on the other hand can be reacted accordingly with introduced residual hydrogen in the purge gas in the cathode chamber 4, without affecting the operation of the fuel cell 2 massively. As a trigger for such purge through the valve 20 in the switchable flow path 9, for example, the hydrogen concentration in the region of the recirculation line 7 can be used. Such can, as exemplified here, be measured in accordance with a hydrogen concentration sensor 18 and processed in the control electronics 15. If the hydrogen concentration decreases due to a large amount of enriched nitrogen in the recirculation line 7, opening of the valve 20 in the switchable flow path 19 of the valve device 13, a blowing off of this nitrogen can be realized parallel to the otherwise always open flow path through the overflow 21 with its aperture 22 ,

As an alternative or in addition to the measurement of the hydrogen concentration, opening of the valve 20 can also take place if a corresponding amount of water is present in the region of the water separator 12 and the recirculation line 7. Since it is intended to dispense with the typically very sensitive level sensors in the region of the water separator 12, a corresponding deterioration of the fuel cell performance or simply a time-controlled opening of the valve 20 for the drain can then be provided.

The orifice 22 is selected with regard to its permeable diameter in accordance with the respective system conditions of the present fuel cell system 1. In particular, the flow factor must be chosen so that always the best possible drainage of the water is guaranteed and that in coordination with the volume flow in the recirculation line 7 is also ensured that only a small amount of hydrogen via the overflow 21 from the area of the anode space. 3 and the recirculation line 7 is discharged. In a small fuel cell system 1, therefore, a smaller aperture will be used than in a large fuel cell system 1 with larger volume flows through the fuel cell 2. Overall, this results in a very simple and efficient structure of a fuel cell system 1, which allows a correspondingly secure functionality and in particular is not controlled in response to very sensitive to contamination level sensors. The construction of the valve device 13 can be realized as shown in FIG. In this case, both a construction with a valve 20 and a bypass line placed around it as Überströmweg 21 is conceivable. In parallel, the overflow 21 may also be integrated into the valve 20, for example as a bypass channel in the valve housing. In addition, it would be conceivable to integrate the overflow path 21 directly into the valve 20, so that an integrated and extremely compact valve device 13 is created. Figures 3 and 4 show possible embodiments of such a valve device 13. The illustration of Figure 3 and Figure 4 shows a valve housing 23, in which by way of example a valve seat 24 and a valve seat 24 corresponding with this valve stem 25 are shown. As indicated by the double arrow in a shaft 26 of the valve stem 25, the valve stem 25 can be moved accordingly, so that between the valve stem 25 and the valve seat 24, a flow-through cross section is released. The valve stem 25 can be moved according to magnetic forces, for example, so that a solenoid valve is present. In the illustration of Figure 3 it can be seen that in the valve stem 25, a groove 27 is provided. Through this groove 27 as a recess of the overflow 21 is formed even when the valve 20 is closed, that is, whenever the valve stem 25 - as shown in Figures 3 and 4 - abuts the valve seat 24. The groove 27 can be provided in each case once or several times in the valve lifter 25. Their cross-section defines the flow factor and replaces the aperture 22 shown in FIG. 2. The representation in FIG. 4 is essentially analogous to the representation in FIG. 3. Instead of the groove 27 here a bore 28 is mounted in the valve stem 25. The bore 28 allows a small amount of medium to flow continuously through the valve means 13, even when the valve 20 is closed and the valve stem 25 sealingly abuts the valve seat 24. In this case, a plurality of holes 28 can be provided analogously to the example shown above.

The structure of the fuel cell system 1 in the embodiment shown here is now comparatively critical with regard to the design of the overflow path 21, since, as already mentioned several times, this must be designed such that no more hydrogen is emitted the area of the recirculation line 7 is lost as absolutely necessary. However, it is the case that different amounts of water and nitrogen in the region of the recirculation line 7 will occur over different operating conditions of the fuel cell system 1. It would therefore be desirable to provide different diameters of the overflow path for different operating conditions. In principle, this would be possible by providing a plurality of overflow paths in parallel, with individual overflow paths being switched on or off correspondingly via corresponding valve devices. However, this would largely consume the advantage of the small number of components and the simple system. Therefore, it may be provided according to a particularly advantageous embodiment of the system that the aperture 22 is designed as a flexible aperture. In the illustration of Figure 5, the aperture 22 is exemplified as such a flexible diaphragm. The flexible diaphragm may be formed as an opening 29 in a membrane 30. The membrane 30 itself is neither permeable to water nor to gas, so that the cross section of the overflow 21 is determined by the size of the opening 29. If a corresponding pressure, which is higher than the pressure in the region downstream of the valve device 13, in particular the pressure in the region of the cathode feed, now occurs in the region of the water separator 12, the membrane 30 will correspondingly deform and, for example, the dashed line in FIG Assume position 30 '. As can be seen, the opening then designated 29 'becomes larger, so that the diaphragm 22 in accordance with the pressure difference between the two sides of the diaphragm 22 its corresponding opening cross-section 29, 29' changed accordingly. This is done passively and without a control of the aperture 22 would be necessary for example by means of magnets or the like. However, the process can be specifically influenced by the pressures in the region of the cathode 4 and the anode 3 are influenced accordingly via the control electronics 15, so that there is a deflection of the membrane 30, 30 'in the region of the flexible diaphragm 22. Thus, the flow through the overflow 21 can be adjusted accordingly fine. Since the pressures between cathode 4 and anode 3 are constantly monitored anyway and can be adjusted via the air conveyor 9, the turbine 11, which usually has a variable turbine geometry, and thus the back pressure in Katzhodenraum, and the supply of hydrogen via the metering device 6 are adjusted accordingly can, this scheme for fine adjustment of the discharged amount of water and gas through the valve device 13 only a minimal additional effort with which, however, the functionality of the system over the simple variant with fixed aperture 22 can be increased again.

In particular, when the pressure in the region of the recirculation line 7 and thus also in the region of the anode chamber 3 is increased accordingly, a larger opening of the flexible diaphragm 22 is desirable. In the opposite case, but rather not. In order to achieve with the structure shown in Figure 5, that the aperture 22 only opens further, if in the region of the recirculation line 7, a correspondingly higher pressure is present, in the region of the diaphragm 22, a stabilizing means 31 introduced, for example in the form of a grid or perforated plate become. This stabilizing means 31 can be designed so that the membrane 30 rests with a balanced pressure difference in the region of the stabilizing means 31. If there is now an overpressure on the side of the cathode feed air or of the cathode space 4, the membrane is held in its position by the stabilizing means 31 and can not bulge in the direction of the recirculation line 7 and the water separator 12. Thus, the opening 29 remains in its defined opening cross section, although there is a pressure difference between the two sides. In the case of a pressure difference with a different sign, the stabilizing means 31 in its arrangement according to FIG. 5 does not disturb the function described above.

In a further development of this idea, it may also be provided that in this rest state, the opening 29 of the flexible diaphragm 22 is selected so that it opens only when a certain deflection of the diaphragm 30 is realized. This could then be achieved that the valve device 13 in the parked state of the fuel cell system 1, when both sides are depressurized, is closed accordingly, so it does not cause a mixture of gases in the recirculation line 7 and thus in the region of the anode chamber 3 and the gases comes in the region of the cathode compartment 4.

The specific embodiments of FIGS. 3, 4 and 5 are merely examples of possible embodiments for implementation. It is obvious that the person skilled in alternative embodiments are familiar, or can be easily derived by this, which meet the same purpose with a different structural design. It goes without saying that these alternative embodiments are also covered by the invention.

Claims

claims

A fuel cell system having at least one fuel cell, which has an anode space and a cathode space, wherein a recirculation line is provided, through which exhaust gas from the anode space in an area in front of the anode space is traceable, and wherein at least one in the region of the recirculation line and / or the anode space Means is provided for discharging media, characterized in that the at least one means as a valve means (13) is formed, which has a switchable flow path (19) and an overflow path (21).

2. Fuel cell system according to claim 1, characterized in that the region of the recirculation line (7) and / or the anode chamber (3) has exactly one valve device (13).

3. Fuel cell system according to claim 1 or 2, characterized in that the overflow (21) is formed as an independent line element to the switchable flow path (19) of the valve device (13).

4. Fuel cell system according to claim 1, 2 or 3, characterized in that the overflow (21) as a channel element in the valve device (13) integrated around the switchable flow path (19) of the valve device (13) is formed.

5. Fuel cell system according to claim 4, characterized in that the overflow path (21) is designed as a specific opening (27, 28) in the switchable flow path (19) of the valve device (13).

6. Fuel cell system according to claim 5, characterized in that the targeted opening as a recess (27) or bore (28) in the region of a valve tappet (25) and / or a valve seat (24) is formed.

7. Fuel cell system according to one of claims 1 to 6, characterized in that the overflow (21) has a diaphragm (22) through which its flow-through cross section is fixed.

8. Fuel cell system according to claim 6, characterized in that the diaphragm (22) is designed as a fixed diaphragm.

9. Fuel cell system according to one of claims 1 to 7, characterized in that the diaphragm (22) is designed as a flexible diaphragm whose opening cross-section (29) automatically changes depending on the pressure difference on the two sides of the diaphragm (22).

10. Fuel cell system according to claim 9, characterized in that the aperture (22) increases its flow-through cross-section (29) with increasing pressure in the region of the recirculation line (7) and / or the anode space (3).

11. Fuel cell system according to one of claims 1 to 10, characterized in that the region of the recirculation line (7) has a water separator (12), wherein the valve device (13) in the outlet region of the water separator (12) is arranged.

12. Fuel cell system according to one of claims 1 to 11, characterized in that by the valve means (13) of the region of the recirculation line (7) and / or the anode chamber (3) with the region of the cathode (4), in particular the region of the supply air to the cathode (4) is connected.

13. A method for operating a fuel cell system according to one of claims 1 to 12, characterized in that, are discharged via the valve means (13) media in two different states of aggregation.

14. The method according to claim 13, characterized in that the discharge of the media from the region of the region of the recirculation line (7) and / or the anode chamber (3) in the region of the cathode (4), in particular in the region of the supply air to the cathode (4).

15. The method according to claim 13 or 14, characterized in that the switchable flow path (19) of the valve device (13) is always opened only when the hydrogen concentration in the recirculation line (7) and / or the anode compartment (3) under a predetermined value falls.

16. The method according to claim 13, 14 or 15, characterized in that the switchable flow path (19) of the valve device (13) is always opened only when the amount of water in the recirculation line (7) and / or the anode compartment (3) rises above a predetermined value.

17. The method according to claim 14, 15 or 16, characterized in that the through the overflow (21) flowing volume flow by an active change in the pressures in the region of the recirculation line (7) and / or the anode chamber (3) and in the region of the cathode (4), in particular the region of the supply air to the cathode (4), is influenced.

18. Use of a fuel cell system according to any one of claims 1 to 12 or a method according to any one of claims 13 to 17, in a means of transport on land, in the water or in the air.

19. Use according to claim 18, characterized in that via the fuel cell system (1) electrical energy is generated for the drive.