Method for operating a fuel cell system, fuel cell system

Abstract

The present invention relates to a method for operating a fuel cell system, in which at least one fuel cell (1) receives a supply of hydrogen via an anode path (2) and a supply of oxygen via a cathode path, anode exhaust gas from the fuel cell (1) is recirculated via a recirculation path (3), and water vapor contained in the anode exhaust gas is adsorbed by a zeolite container (4). According to the present invention, the following steps are performed to regenerate the zeolite container (4): a) isolating the zeolite container (4) from the recirculation path (3) by closing at least one isolation valve (5, 6) and / or switching a directional control valve (7), b) heating the zeolite container (4) with an electric heating device (8), thereby desorbing previously adsorbed water, and c) removing the desorbed water from the system by again switching the directional control valve (7) and / or opening at least one flush valve (9, 10). The present invention also relates to a fuel cell system suitable for carrying out this method.

Description

[Technical field]

[0001] The present invention relates to a method for operating a fuel cell system having the features of the preamble of claim 1. Furthermore, the present invention relates to a fuel cell system which is suitable for carrying out the method according to the invention or which can be operated according to the method according to the invention. [Background technology]

[0002] Fuel cells convert hydrogen into electrical energy with the aid of oxygen. To this end, they have a membrane-electrode structure that includes an anode and a cathode. The anode is supplied with hydrogen, stored in a suitable tank, via the anode passage. The cathode is supplied with ambient air, which acts as the oxygen source, via the cathode passage.

[0003] To improve performance, a large number of fuel cells, for example 200 to 400 fuel cells, are usually built in a stacked configuration to form a fuel cell stack. It is penetrated by passages that serve to supply the fuel cells with the necessary gases and to carry away the exhaust gases leaving the fuel cells. Since the exhaust gases leaving the anode side contain unconsumed hydrogen, the anode exhaust gases are usually recirculated. The pressure loss in the anode path is then overcome actively by means of a fan and / or passively by means of a jet pump. Fresh hydrogen is added to the recirculation from a tank before the anode inlet.

[0004] Fuel cell systems with hydrogen-based fuel cells are considered the mobility concept of the future, as they essentially only emit hydrogen as exhaust gas and allow fast tank filling times. To convey away the water generated during operation, condensate separators are usually used, with which the water is collected at a defined point in the system and discharged to the environment at a defined time via a so-called drain valve. Additional water is generated after the vehicle has been stopped by cooling the system and by condensation of evaporated water from the gas phase. This water, or condensate, must also be removed to avoid blockages caused by the accumulation of liquid water when the vehicle is restarted. Furthermore, there is a risk of the condensate freezing at low outside temperatures.

[0005] It has therefore already been proposed in the prior art to adsorb the residual moisture present after the fuel cell has been switched off by means of a zeolite-based adsorption unit and to utilize the heat released during adsorption for heating the fuel cell during the subsequent start-up phase.

[0006] The adsorption of water by the zeolite container is carried out in an exothermic reaction, which heats up the container to approximately 160° C. The container must then be regenerated under a heat supply (endothermic reaction), during which the water previously absorbed by adsorption is desorbed, typically at temperature levels of 200° C. to 250° C. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Patent Application Publication No. 102008007024A1 Summary of the Invention [Problem to be solved by the invention]

[0008] Given the above-mentioned state of the art, the object of the present invention is to optimize the regeneration of zeolite-based water reservoirs in fuel cell systems. In particular, it is intended to achieve an energy-optimized regeneration. Furthermore, condensation of the desorbed water should be avoided so that - as far as possible - the operation of the fuel cell system is not adversely affected thereby. [Means for solving the problem]

[0009] To achieve this object, a method is proposed having the features of claim 1 as well as a fuel cell system having the features of claim 10. Preferred developments of the invention emerge from the respective dependent claims.

[0010] In the proposed method of operating a fuel cell system, at least one fuel cell receives a supply of hydrogen via an anode path and a supply of oxygen via a cathode path. The anode exhaust gas leaving the fuel cell is recirculated via a recirculation path, and the water vapor contained in the anode exhaust gas is adsorbed by the zeolite container. To regenerate the zeolite container, according to the invention the following steps are carried out: a) isolating the zeolite container from the recirculation path by closing at least one shutoff valve and / or by switching a directional control valve; b) heating the zeolite container with an electric heating device, thereby desorbing the previously adsorbed water; c) The desorbed water is removed from the system by a fresh switching of the directional control valve and / or by opening of at least one flush valve.

[0011] The proposed separation of the zeolite container from the recirculation path during the regeneration process allows this process to be carried out almost independently of the operation of the fuel cell system, i.e. the operation of the fuel cell system is not or only to a small extent restricted by the regeneration process. Furthermore, the desorbed water can be reliably transported away without any risk of flooding the anode or of liquid water at the anode inlet. Furthermore, less hydrogen is trapped in the zeolite container and transported away during the regeneration of the zeolite container, so that less hydrogen is lost.

[0012] To carry out the proposed method, a zeolite container can be utilized, which has a bulk material made of, for example, zeolite material, or alternatively, the zeolite container can include a ceramic or metal support structure coated with a zeolite material.

[0013] The zeolite container can be integrated into fuel cell systems with active and / or passive recirculation based on the prior art described at the beginning.

[0014] At least one shut-off valve is preferably provided upstream of the zeolite container to separate the zeolite container from the recycle path of the fuel cell system. Closing the shut-off valve prevents the recycle from passing through the zeolite container and cuts off the additional volume provided by the zeolite container, thereby reducing the sluggishness of the system, which can thus also have a positive effect on the system's behavior.

[0015] A further shut-off valve or directional control valve, in particular a 3 / 2 directional control valve, is preferably arranged downstream of the zeolite container. By means of a further shut-off valve or also by means of a directional control valve, the connection between the at least one flushing valve and the zeolite container during desorption can be interrupted. To remove the desorbed water from the zeolite container, the shut-off valve and the at least one flushing valve can be opened, through which the desorbed water is conveyed away. If a directional control valve is provided instead of the second shut-off valve, it can be switched so that the flushing path for conveying away the desorbed water is open.

[0016] In a preferred embodiment of the invention, step a) is only started when the maximum hydrogen concentration and / or maximum hydrogen partial pressure in the recirculation path is below the maximum hydrogen concentration and / or maximum hydrogen partial pressure. This is the case, for example, in the lower load region of the fuel cell system or immediately before a cleaning process of the system. In this way, the hydrogen consumption can be further reduced or minimized. Furthermore, it is ensured that the amount of hydrogen contained in the zeolite container is sufficiently diluted before being discharged.

[0017] It is further proposed that in step b) the zeolite container is heated to a temperature of about 250° C. in order to facilitate desorption of the previously adsorbed water / water vapor. Alternatively or additionally, it is proposed that at least one heating cartridge integrated in the zeolite container is used as an electric heating device in order to heat the zeolite container. The at least one integrated heating cartridge can be used to facilitate heating of the zeolite container. The at least one heating cartridge can for example be arranged in the zeolite bulk material of the zeolite container.

[0018] By separating the zeolite container from the system before the start of step b), heat losses caused by convection and / or interaction with the remaining volume are avoided or minimized, and furthermore heating of the zeolite container is possible regardless of the system operation, in particular regardless of the system pressure, temperature and / or volumetric flow rate.

[0019] Upon reaching a temperature of approximately 250° C., the zeolite container releases the previously adsorbed water again as water vapor into the volume of the zeolite container. This results in an increase in the pressure in the zeolite container. The pressure in the zeolite container can thus be used as a measuring quantity representative of the amount of desorbed water. The same applies correspondingly to the temperature of the zeolite container. Therefore, the pressure and / or temperature of the zeolite container are preferably measured and the amount of water desorbed in the zeolite container is deduced from the measured values. The heating of the zeolite container can then be terminated upon reaching a predefined maximum pressure and / or temperature limit value in the zeolite container.

[0020] Before the start of step c), it is preferably first checked whether certain conditions for opening the flushing valves exist, in particular dilution conditions. The withdrawal of water or water vapor from the system is then usually linked to the condition that the hydrogen contained therein is sufficiently diluted (English: "dilution constraint"). Only when this condition is fulfilled can the at least one flushing valve be opened.

[0021] It is further proposed that in step c) the desorbed water is introduced into the cathode exhaust gas path via a directional control valve and / or at least one flushing valve or discharged to the environment. The introduction into the cathode exhaust gas path can be effected, for example, via a flushing valve which is usually provided for flushing the recirculation path. When this is open for flushing, no operation of the fuel cell system is possible or only a restricted operation is possible.

[0022] In order not to restrict the system operation while the desorbed water is being conveyed out of the zeolite container, a further development of the invention proposes that a further flushing valve is provided for opening an additional flushing path, via which the desorbed water can then also be introduced into the cathode exhaust gas path or discharged to the environment. The opening of the additional flushing path does not adversely affect the system operation, i.e. the regeneration of the zeolite container and the operation of the fuel cell system can proceed separately from each other, which allows for even greater flexibility in the operation of the fuel cell system.

[0023] Alternatively, the functions of the second shutoff valve and the further flushing valve can be combined in the already proposed directional control valve, which is arranged downstream of the zeolite container. The further flushing path can then be opened by a corresponding switch of the directional control valve. For this purpose, the directional control valve is preferably made as a 3 / 2 directional control valve. Depending on the switch position of the directional control valve, the desorbed water is then led from the zeolite container into the further flushing path or fed to one of the flushing valves.

[0024] If a second shut-off valve is arranged downstream of the zeolite container instead of a directional control valve, it is proposed that in step c) at least one shut-off valve is opened, so that the desorbed water is fed from the zeolite container to at least one flushing valve, i.e. for flushing at least one shut-off valve arranged downstream of the zeolite container as well as one flushing valve are opened. During flushing, both shut-off valves as well as one flushing valve can be opened, although this increases the risk of liquid water condensation at the anode inlet.

[0025] Steps a) to c) are preferably repeated at least once, preferably multiple times, until the desired amount of water is expelled from the zeolite container and / or until the regeneration of the zeolite container is complete. As the regeneration of the zeolite container proceeds, the pressure does not increase as much as the temperature under heating of the zeolite container, so that the characteristic behavior of the pressure increase and the temperature increase can be utilized to monitor the regeneration process. Furthermore, the following criteria can be utilized to estimate the completion of the regeneration of the zeolite container:

[0026] - At a constant temperature there is no or very little increase in pressure, i.e. water does not pass into the gas phase within the volume of the zeolite container. - The temperature is increasing significantly or rapidly above the desorption temperature, i.e. the rate of change of temperature increase of the zeolite container dT / dt is above a certain threshold and less water is being desorbed.

[0027] Alternatively, the method according to the invention can be carried out without a pressure sensor for measuring the pressure in the volume of the zeolite container, since if the heating power and the thermal behavior of the zeolite container are known, it is possible to estimate, via the temperature gradient or temperature progression alone, how much water vapor is present in the zeolite container at any given time and what regeneration state it has.

[0028] For complete regeneration, the zeolite container is preferably repeatedly heated and the desorbed water is removed from the zeolite container by washing. With each wash, the residual hydrogen is also washed out, with the first wash having the highest residual hydrogen content. With subsequent wash processes, the residual hydrogen content gradually decreases, in particular because no additional hydrogen-containing recycle flows into the zeolite container due to the closed shutoff valve upstream of the zeolite container.

[0029] Thus, especially during the first flushing when the residual hydrogen content is particularly high, a hybrid flushing strategy can be implemented, for example by simultaneously opening a first flushing valve opening into the cathode exhaust gas path and - if provided - a second flushing valve opening into the additional flushing path.

[0030] Alternatively, it is proposed that a first flushing valve is opened during the first flushing and a second flushing valve is opened during the repeated flushing, i.e. the first and second flushing valves are opened one after the other in successive flushing processes. The first flushing valve is in particular a flushing valve that opens into the cathode exhaust gas path, since during the first flushing the residual hydrogen content is still very high. In the cathode exhaust gas path, the flushing volume is mixed with the air present there, so that the residual hydrogen is sufficiently diluted. Then, in at least one subsequent flushing process, when the residual hydrogen content has already decreased, the flushing volume can be introduced into the additional flushing path via the second flushing valve. The introduction into the additional flushing path has the advantage that the subsequent flushing processes - unlike the first flushing process - can be carried out independently of the operation of the fuel cell system. The operation of the fuel cell system is accordingly not restricted.

[0031] In addition to the above, in order to solve the problem mentioned at the beginning, a fuel cell system is proposed having at least one fuel cell to which hydrogen can be supplied via the anode path and oxygen can be supplied via the cathode path. The fuel cell system further comprises a recirculation path in which the anode exhaust gas from the fuel cell can be recirculated, as well as a zeolite container in which water vapor contained in the anode exhaust gas can be adsorbed. According to the invention, the zeolite container can be connected and disconnected via at least one shutoff valve and / or directional control valve. The connection of the zeolite container makes it possible to adsorb water vapor contained in the recirculation. The disconnection or separation of the zeolite container from the recirculation path makes it possible to regenerate the zeolite container by desorption, which is independent of the operation of the fuel cell system. That is to say, the regeneration of the zeolite container does not lead to any constraints on the operation of the system.

[0032] In the proposed fuel cell system, the zeolite containers are connected in parallel rather than in series, which has the advantage that the pressure loss is reduced, especially in the anode path.

[0033] The parallel piping of the zeolite containers is carried out by the above-mentioned valves, which allow a complete separation of the zeolite containers from the recirculation path. These valves include at least one shutoff valve, which is arranged upstream of the zeolite container and prevents the recirculation from passing through the zeolite container when in the closed position. A further shutoff valve or a directional control valve, preferably a 3 / 2 directional control valve, may be arranged downstream of the zeolite container. If a further shutoff valve is provided, the water desorbed during the regeneration of the zeolite containers can be conveyed off via the normally provided wash valve, which opens into the cathode exhaust gas path. Alternatively or additionally, the desorbed water can also be introduced into the additional wash path via a further wash valve. If an additional wash path is provided, the functions of the shutoff valve and the further wash valve arranged downstream of the zeolite container can be embodied by a directional control valve.

[0034] The proposed fuel cell system is particularly suitable for carrying out the method according to the invention as described above. The same advantages can be realized by the fuel cell system accordingly. Furthermore, the zeolite container can be manufactured according to the zeolite container described above and / or can be connected to the system.

[0035] In a development of the fuel cell system according to the invention, it is proposed that an electric heating device is integrated into the zeolite container, which can be heated for the desorption of water. The electric heating device allows the zeolite container to be quickly brought to the temperature of about 250° C. required for desorption. Furthermore, in the case of adsorption, the zeolite container can be preheated by the electric heating device, especially when performing a cold start.

[0036] In a particularly preferred embodiment, the electric heating device comprises at least one heating cartridge, which can be easily integrated into the bulk material of the zeolite container made of zeolite material.

[0037] It is further proposed that the zeolite container is connected to the cathode exhaust gas path and / or the surroundings via a directional control valve and / or at least one flushing valve, so that the desorbed water can be introduced from the zeolite container into the cathode exhaust gas path or discharged into the surroundings. The latter is possible because the content of residual hydrogen is usually very low, especially after the first flushing process. During the first flushing, the flushing volume is preferably introduced into the cathode exhaust gas path to dilute the residual hydrogen contained therein with the air present therein.

[0038] The invention and its advantages will now be described in more detail with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 is a schematic diagram showing a first fuel cell system according to the invention for carrying out a method according to the invention. [Diagram 2] 2 is an embodiment of the method according to the invention using the fuel cell system of FIG. 1. [Diagram 3] FIG. 2 is a schematic diagram showing a second fuel cell system according to the invention for carrying out the method according to the invention. [Figure 4] 4 is an embodiment of the method according to the invention using the fuel cell system of FIG. [Diagram 5] 4 is an alternative implementation of the method according to the invention using the fuel cell system of FIG. 3. [Figure 6] FIG. 4 is a schematic diagram showing a third fuel cell system according to the invention for carrying out the method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The fuel cell system shown in Fig. 1 comprises at least one fuel cell 1, to which on the anode side anode gas, i.e. hydrogen, can be supplied from a tank 11 via an anode path 2. The supply of fresh hydrogen can be controlled via a valve 12. The anode exhaust gas leaving the fuel cell 1 still contains residual hydrogen and is therefore recirculated via a recirculation path 3 or introduced again into the anode path 2. The recirculation is actively supported in this example by a recirculation fan 13. In the anode path 2, fresh hydrogen from the tank 11 is added to the recirculation.

[0041] Since the recycled anode exhaust gas contains water, i.e. liquid and gaseous water or water vapor, in addition to hydrogen, the fuel cell system shown in FIG. 1 additionally has a zeolite container 4 for removing water from the recycle. The zeolite container 4 is connected to the recycle path 3 via a first shut-off valve 5 and a second shut-off valve 6 or is connected in parallel. When the shut-off valves 5, 6 are in the open position, the zeolite container 4 is passed through by the recycle and the water contained therein is removed by adsorption. The heat generated in this process can be used, for example, during a cold start of the system, to bring the system up to operating temperature more quickly. Additionally, the zeolite container 4 can be heated by an integrated electric heating device 8. This is particularly advantageous during a freeze start.

[0042] Furthermore, during operation of the fuel cell system, the anode channel 2 and the recirculation channel 3 must be flushed from time to time, since the anode gas can become enriched with nitrogen, which diffuses from the cathode side (not shown) to the anode side, for example. For this purpose, a flushing valve 9 is provided on the outlet side, which preferably opens into the cathode exhaust gas channel (not shown). The flushing volume carried off via the flushing valve 9 is then replaced by fresh hydrogen from a tank 11.

[0043] The flushing valve 9 shown in FIG. 1 is further used in this example to regenerate the zeolite container 4. The zeolite container 4 is first isolated from the recirculation path 3 and then brought to a temperature of about 250° C. by means of an electric heating device 8, whereby the previously adsorbed water is desorbed. The desorbed amount of water can then be introduced into the cathode exhaust gas path by opening the shut-off valve 6 and the flushing valve 9. The heating and flushing of the zeolite container 4 is usually repeated several times until the adsorbed amount is completely removed from the zeolite container 4. When this is the case can be monitored by means of the temperature and / or pressure of the zeolite container 4. For this purpose, the zeolite container 4 is provided with a temperature sensor 14 and a pressure sensor 15, respectively.

[0044] Next, the detailed progression of the adsorption and desorption stages of the illustrated zeolite container 4 will be explained with reference to the graph of FIG.

[0045] The time series is plotted from time t0 to t9. At time t0, a requirement arises on the system side to remove water or water vapor from the recycled anode exhaust gas and possibly to inject heat, for example in the case of a freeze start. Both shut-off valves 5, 6 are opened, so that the recycled anode exhaust gas flows through the zeolite container 4. At time t1, exothermic adsorption begins, with the zeolite container 4 being heated to approximately 160° C. by time t2. Depending on the requirements with regard to the dynamics and / or the initial temperature, two operating modes can then be distinguished:

[0046] 1. Electrical Energy P elektr. No supply (solid line T Z ), whereby the zeolite container 4 is heated only through exothermic adsorption. 2. Electrical Energy P elektr. There is an initial supply of (dashed line T Z ), whereby the zeolite container 4 absorbs heat and absorbs the electrical energy P elektr. and is heated by.

[0047] In principle, option 1 can be followed, since the kinetics of the adsorption process are sufficient to heat the zeolite container 4. At particularly low ambient temperatures, e.g. -40°C, option 2 has proven to be preferable, when the kinetics are very slow and the system requirements regarding the dynamic behavior of the zeolite container 4 cannot be met otherwise.

[0048] At time t2, the request of the system to fill the zeolite container 4 with water is cancelled, for example because it is no longer possible or necessary to fill it further. The shut-off valves 5, 6 are still open, so that the flow through the zeolite container 4 continues, since a suitable time is awaited for closing the shut-off valves 5, 6. This time is reached, for example, when the maximum hydrogen concentration X H2,max In this way, hydrogen loss during the subsequent regeneration of the zeolite container 4 can be kept small. shut-off After both shut-off valves 5, 6 are closed, the gas composition in the zeolite container 4 remains unchanged for the time being.

[0049] At time t3, it is intended that the zeolite container 4 is regenerated. For that purpose, the zeolite material is heated by the electric heating device 8 to about 250° C. in order to desorb water from the zeolite container 4. Both shut-off valves 5, 6 are closed, thereby minimizing heat losses. Furthermore, heating of the zeolite container 4 is possible independently of the system.

[0050] At time t4, the desorption temperature of 250° C. is reached and the zeolite container 4 releases the previously adsorbed water again as water vapor into the volume of the zeolite container 4. This results in an increase in pressure within the zeolite container 4, which can be used as a measure of the amount of water desorbed.

[0051] At time t5 or when the maximum pressure and / or maximum temperature is exceeded in the zeolite container 4, the electric heating device 8 is switched off. Furthermore, a query is sent to the system as to whether the required dilution constraint for rinsing the system exists. If an affirmative response message arrives, the shut-off valve 6 and the flushing valve 9 are opened and the hydrogen-water vapor-gas mixture is flushed out of the zeolite container 4. At this stage, no operation of the fuel cell system is possible or only a restricted operation is possible.

[0052] After the first cleaning process, at time t6, the shutoff valve 6 is closed again and the process of heating and cleaning the zeolite container 4 is repeated until the desired amount of water has been expelled from the zeolite container 4 and the regeneration of the zeolite container 4 is completed, with the stopping criterion being the characteristic behavior of the temperature and pressure increase in the zeolite container 4 during the heating stages from t3 to t4 or t6 to t7 etc., since the increase in pressure compared to the temperature becomes slower as the regeneration of the zeolite container 4 progresses.

[0053] The successive stages are designated in Figure 2 as A for the adsorption stage, B for the valve closure stage, C for the heating stage, and D for the desorption stage, which can be followed by stage E either by shutting down the system or by continued operation.

[0054] In figure 3 one can see a modification of the system of figure 1. The essence of this modification is that a further flushing valve 10 is provided which opens into an additional flushing path 16. The further flushing valve 10 can be opened independently of the first flushing valve 9, and thus independently of the operation of the fuel cell system, in order to regenerate the zeolite container 4. The further flushing valve 10 thus allows for an even greater degree of freedom in the operation of the fuel cell system.

[0055] The progression in the operation of the fuel cell system of FIG. 3 is shown in FIG. 4. The adsorption stage A, the valve closing stage B and the heating stage C proceed in accordance with the corresponding stages of FIG. 2, so reference is made to the description of FIG. 2. Differences exist only with respect to the desorption stage D. The discharge of the hydrogen-water vapor-gas mixture now takes place via a further flushing valve 10 into an additional flushing channel 16. Certain dilution conditions must also be observed in this case, which can differ from those listed above. Depending on the design of the zeolite container 4 and the X-ray suction, the dilution conditions can be varied. H2,max Depending on the choice of the gas mixture, it is even possible to release the gas mixture directly into the environment.

[0056] Alternatively, a hybrid flushing strategy can be used with the system of FIG. 3, as shown by way of example in FIG. 5. Here, both flushing valves 9, 10 are opened during the desorption phase D, i.e. offset in time. When the hydrogen concentration in the zeolite container 4 is high, flushing is first carried out via the first flushing valve 9 at least in the first flushing process. In the second and each subsequent flushing process (when the hydrogen concentration is low or negligible) flushing is carried out via the other flushing valve 10. Such a strategy is best for ensuring the necessary dilution of the residual hydrogen, since when the first flushing valve 9 is opened and the flushing volume is introduced into the cathode exhaust gas path (not shown), it mixes with the air present there. However, this interrupts or interferes with the normal operation of the fuel cell system. It has therefore proven to be preferable if in the further course of regeneration of the zeolite container 4 the flushing volume is discharged via the other flushing valve 10 and flushing path 16, since this process does not affect the operation of the fuel cell system.

[0057] A further modification of the fuel cell system according to the invention is shown in Fig. 6. Here, the functions of the shut-off valve 6 and of the separate flushing valve 10 are embodied by a 3 / 2 directional control valve 7. This allows the construction of the fuel cell system to be simplified, since one valve is eliminated. [Explanation of symbols]

[0058] 1 fuel cell 2 Anode Path 3 Recirculation Path 4 Zeolite Container 5,6 Shut-off valve 7. Directional Control Valve 8 Electric heating device 9,10 Cleaning valve

Claims

1. A method for operating a fuel cell system, comprising: at least one fuel cell (1) receiving a supply of hydrogen via an anode passage (2) and a supply of oxygen via a cathode passage; an anode exhaust gas from said fuel cell (1) being recirculated via a recirculation passage (3); and water vapor contained in the anode exhaust gas being adsorbed by a zeolite container (4), To regenerate the zeolite container (4), the following steps are carried out: a) the zeolite container (4) is isolated from the recirculation path (3) by closing at least one shutoff valve (5, 6) and / or by switching a directional control valve (7), b) heating the zeolite container (4) by means of an electric heating device (8), thereby desorbing the previously adsorbed water; c) the desorbed water is removed from the system by a further switching of the directional control valve (7) and / or by opening at least one flush valve (9, 10); 4. A method according to claim 3, characterized in that step a) is initiated upon falling below a maximum hydrogen concentration (X H2,max ) in the recirculation line (3) and / or upon falling below a maximum hydrogen partial pressure (pH2).

2. 2. The method according to claim 1, characterized in that in step b) the zeolite container (4) is heated to a temperature of about 250° C. and / or at least one heating cartridge integrated in the zeolite container (4) is utilized as an electric heating device (8) for heating the zeolite container (4).

3. 3. A method according to claim 1 or 2, characterized in that the pressure and / or temperature of the zeolite container (4) is measured and the amount of water desorbed in the zeolite container (4) is deduced from the measurements.

4. A method for operating a fuel cell system, comprising: at least one fuel cell (1) receiving a supply of hydrogen via an anode pathway (2) and a supply of oxygen via a cathode pathway; anode exhaust gas from said fuel cell (1) being recirculated via a recirculation pathway (3); and water vapor contained in the anode exhaust gas being adsorbed by a zeolite container (4), To regenerate the zeolite container (4), the following steps are carried out: a) the zeolite container (4) is isolated from the recirculation path (3) by closing at least one shutoff valve (5, 6) and / or by switching a directional control valve (7), b) heating the zeolite container (4) by means of an electric heating device (8), thereby desorbing the previously adsorbed water; c) the desorbed water is removed from the system by a further switching of the directional control valve (7) and / or by opening at least one flush valve (9, 10); 4. A method according to claim 3, characterized in that the pressure and / or temperature of said zeolite container (4) is measured and the amount of water desorbed in said zeolite container (4) is deduced from the measurements.

5. 5. The method according to claim 1, wherein the heating of the zeolite container (4) is terminated upon reaching a predetermined maximum pressure and / or temperature limit in the zeolite container (4).

6. A method for operating a fuel cell system, comprising: at least one fuel cell (1) receiving a supply of hydrogen via an anode pathway (2) and a supply of oxygen via a cathode pathway; anode exhaust gas from said fuel cell (1) being recirculated via a recirculation pathway (3); and water vapor contained in the anode exhaust gas being adsorbed by a zeolite container (4), To regenerate the zeolite container (4), the following steps are carried out: a) the zeolite container (4) is isolated from the recirculation path (3) by closing at least one shutoff valve (5, 6) and / or by switching a directional control valve (7), b) heating the zeolite container (4) by means of an electric heating device (8), thereby desorbing the previously adsorbed water; c) the desorbed water is removed from the system by a further switching of the directional control valve (7) and / or by opening at least one flush valve (9, 10); 13. A method according to claim 12, characterized in that the heating of the zeolite container (4) is terminated upon reaching a predetermined maximum pressure and / or temperature limit in the zeolite container (4).

7. 7. The method according to claim 1, further comprising checking, before the start of step c), whether certain conditions for opening the flushing valve (9, 10) exist.

8. A method for operating a fuel cell system, comprising: at least one fuel cell (1) receiving a supply of hydrogen via an anode pathway (2) and a supply of oxygen via a cathode pathway; anode exhaust gas from said fuel cell (1) being recirculated via a recirculation pathway (3); and water vapor contained in the anode exhaust gas being adsorbed by a zeolite container (4), To regenerate the zeolite container (4), the following steps are carried out: a) the zeolite container (4) is isolated from the recirculation path (3) by closing at least one shutoff valve (5, 6) and / or by switching a directional control valve (7), b) heating the zeolite container (4) by means of an electric heating device (8), thereby desorbing the previously adsorbed water; c) the desorbed water is removed from the system by a further switching of the directional control valve (7) and / or by opening at least one flush valve (9, 10); 4. A method according to claim 3, characterized in that before the start of step c), it is checked whether certain conditions for opening the flushing valve (9, 10) exist.

9. 7. The method according to claim 1, further comprising checking, before the start of step c), whether the dilution conditions for opening the flushing valve (9, 10) are met.

10. A method for operating a fuel cell system, comprising: at least one fuel cell (1) receiving a supply of hydrogen via an anode path (2) and a supply of oxygen via a cathode path; anode exhaust gas from said fuel cell (1) being recirculated via a recirculation path (3); and water vapor contained in the anode exhaust gas being adsorbed by a zeolite container (4), To regenerate the zeolite container (4), the following steps are carried out: a) the zeolite container (4) is isolated from the recirculation path (3) by closing at least one shutoff valve (5, 6) and / or by switching a directional control valve (7), b) heating the zeolite container (4) by means of an electric heating device (8), thereby desorbing the previously adsorbed water; c) the desorbed water is removed from the system by a further switching of the directional control valve (7) and / or by opening at least one flush valve (9, 10); 2. A method according to claim 1, characterized in that before the start of step c), it is checked whether the dilution conditions for opening the flushing valves (9, 10) are met.

11. 11. The method according to claim 1, characterized in that in step c) the desorbed water is introduced into the cathode exhaust gas path via the directional control valve (7) and / or at least one of the flushing valves (9, 10) or discharged to the environment.

12. 12. The method according to claim 1, characterized in that in step c) at least one shut-off valve (5, 6) is opened, whereby desorbed water is supplied from the zeolite container (4) to at least one of the wash valves (9, 10).

13. 13. The method according to any one of claims 1 to 12, characterized in that steps a) to c) are repeated at least one time.

14. A method according to any one of claims 1 to 12, characterized in that steps a) to c) are repeated multiple times, the first flushing valve (9) being opened during the first flushing and the second flushing valve (10) being opened during the repeated flushing.

15. A fuel cell system having at least one fuel cell (1) to which hydrogen can be supplied via an anode path (2) and oxygen can be supplied via a cathode path, the fuel cell system including a recirculation path (3) capable of recirculating an anode exhaust gas from the fuel cell (1), and a zeolite container (4) capable of adsorbing water vapor contained in the anode exhaust gas, The zeolite container (4) is connectable and disconnectable via at least one shutoff valve (5, 6) and / or directional control valve (7), A fuel cell system, characterized in that it is operated by a method according to any one of claims 1 to 14.

16. 16. The fuel cell system according to claim 15, characterized in that the zeolite container (4) is equipped with an electric heating device (8) by means of which the zeolite container (4) can be heated for the desorption of water.

17. 16. The fuel cell system according to claim 15, characterized in that the zeolite container (4) is equipped with at least one heating cartridge, by means of which the zeolite container (4) can be heated for the desorption of water.

18. 18. The fuel cell system according to claim 15, characterized in that the zeolite container (4) is connected to the cathode exhaust gas path and / or to the surroundings via the directional control valve (7) and / or at least one flushing valve (9, 10), whereby desorbed water can be introduced from the zeolite container (4) into the cathode exhaust gas path or discharged to the surroundings.

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