EP4193405A1 - Method for operating a fuel cell system, and fuel cell system - Google Patents

Method for operating a fuel cell system, and fuel cell system

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Publication number
EP4193405A1
EP4193405A1 EP21754701.7A EP21754701A EP4193405A1 EP 4193405 A1 EP4193405 A1 EP 4193405A1 EP 21754701 A EP21754701 A EP 21754701A EP 4193405 A1 EP4193405 A1 EP 4193405A1
Authority
EP
European Patent Office
Prior art keywords
zeolite
valve
fuel cell
path
reservoir
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP21754701.7A
Other languages
German (de)
French (fr)
Inventor
Mark Hellmann
Matthias Rink
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Bosch GmbH filed Critical Robert Bosch GmbH
Publication of EP4193405A1 publication Critical patent/EP4193405A1/en
Pending legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
    • H01M8/04156—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying with product water removal
    • H01M8/04171—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying with product water removal using adsorbents, wicks or hydrophilic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04253—Means for solving freezing problems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H01M8/04402—Pressure; Ambient pressure; Flow of anode exhausts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0444—Concentration; Density
    • H01M8/04462—Concentration; Density of anode exhausts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04037—Electrical heating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H01M8/04373—Temperature; Ambient temperature of auxiliary devices, e.g. reformers, compressors, burners
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H01M8/04425—Pressure; Ambient pressure; Flow at auxiliary devices, e.g. reformers, compressors, burners
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the invention relates to a method for operating a fuel cell system having the features of the preamble of claim 1.
  • the invention also relates to a fuel cell system which is suitable for carrying out the method according to the invention or can be operated using the method according to the invention.
  • a fuel cell converts hydrogen into electrical energy with the help of oxygen.
  • the fuel cell has a membrane-electrode assembly with an anode and a cathode.
  • Hydrogen which is stored in a suitable tank, is fed to the anode via an anode path.
  • a large number of fuel cells for example 200 to 400 fuel cells, are installed in a stacked arrangement to form a fuel cell stack. This is traversed by several channels that serve to supply the fuel cells with the required gases and to discharge the exhaust gases exiting the fuel cells. Since the exhaust gas exiting the anode side contains unused hydrogen, the anode exhaust gas is generally recirculated. The pressure loss in the anode path is overcome actively by means of a blower and/or passively by means of a jet pump. Fresh hydrogen from the tank is added to the recirculated material before it enters the anode.
  • Fuel cell systems with hydrogen-based fuel cells are considered to be the mobility concept of the future, since they essentially only emit water as exhaust gas and also enable fast refueling times.
  • Condensate separators are usually used to discharge the water that occurs during operation, with the help of which liquid water is collected at defined points in the system and released into the environment at defined times via so-called drain valves. After a vehicle is parked, additional water accumulates due to cooling of the system and condensation of vaporous water in a gas phase. This water or condensate must also be removed to avoid blockages caused by accumulations of liquid water when the vehicle is restarted. At low outside temperatures there is also a risk that the condensate will freeze.
  • the adsorption of water using a zeolite storage tank is exothermic, which means that the storage tank is heated to around 160°C.
  • the storage tank then has to be regenerated with the addition of heat (endothermic reaction), with the water previously absorbed by means of adsorption being desorbed.
  • a temperature level of 200°C to 250°C is typically required for this.
  • the object of the present invention is to optimize the regeneration of a zeolite-based water reservoir in a fuel cell system.
  • energy-optimized regeneration should take place.
  • condensation of desorbed water should be avoided and—as far as possible—the operation of the fuel cell system should not be impaired thereby.
  • At least one fuel cell is supplied with hydrogen via an anode path and oxygen via a cathode path.
  • Anode waste gas exiting the fuel cell is recirculated via a recirculation path, water vapor contained in the anode waste gas being adsorbed by means of a zeolite storage device.
  • the following steps are carried out to regenerate the zeolite reservoir: a) separating the zeolite reservoir from the recirculation path by closing at least one shut-off valve and/or switching a directional control valve, b) heating the zeolite reservoir by means of an electrical heating device so that previously adsorbed water is desorbed, and c) Removal of desorbed water from the system by switching the directional control valve again and/or by opening at least one flushing valve.
  • this process can be carried out largely independently of the operation of the fuel cell system. This means that the operation of the fuel cell system is not limited or only limited to a small extent by the regeneration process. Furthermore, desorbed water can be safely discharged without the risk of the anode being flooded or liquid water being released at the anode inlet. In addition, less hydrogen is trapped in the zeolite reservoir and discharged when the zeolite reservoir is regenerated, so that less hydrogen is lost.
  • a zeolite reservoir can be used, for example, which has a bed of zeolite material.
  • the zeolite reservoir can also include a ceramic or metal support structure that is coated with a zeolite material.
  • the zeolite storage device can be used in a fuel cell system with active and/or passive recirculation.
  • At least one shut-off valve is provided upstream of the zeolite reservoir to separate the zeolite reservoir from the recirculation path of the fuel cell system. Closing the shut-off valve prevents recirculated material from flowing through the zeolite reservoir and the additional volume created by the zeolite reservoir is separated, so that the system behaves less sluggishly. In this way, the behavior of the system can be positively influenced at the same time.
  • a further shut-off valve or a directional valve, in particular a 3/2-way valve, is preferably arranged downstream of the zeolite reservoir.
  • a connection of the zeolite reservoir to the at least one flushing valve can be interrupted during desorption.
  • the shut-off valve and the at least one flushing valve can be opened, so that desorbed water is discharged via it.
  • a directional valve is provided instead of a second shut-off valve, this can be switched in such a way that a flushing path for discharging the desorbed water is released.
  • step a) is only initiated when the hydrogen concentration falls below a maximum and/or a maximum hydrogen partial pressure in the recirculation path. This is the case, for example, in the lower load range of the fuel cell system or shortly before the system is flushed. In this way, the hydrogen consumption can be further reduced or minimized. It is also ensured that the amount of hydrogen trapped in the zeolite storage tank is sufficiently diluted before it is discharged.
  • step b) the zeolite reservoir is heated to a temperature of approximately 250° C. in order to promote the desorption of the previously adsorbed water or water vapor.
  • at least one heating cartridge integrated into the zeolite reservoir be used as an electrical heating device to heat the zeolite reservoir is used. With the help of at least one integrated heating cartridge, the heating of the zeolite storage can be accelerated.
  • the at least one heating cartridge can be arranged, for example, in a zeolite bed of the zeolite store.
  • the zeolite reservoir was separated from the system before initiating step b), heat losses caused by convection and/or interaction with the remaining volume are avoided or kept low.
  • the heating of the zeolite reservoir is possible independently of the system operation, in particular independently of the pressure, the temperature and/or the volume flow in the system.
  • the zeolite reservoir releases the previously adsorbed water as water vapor to the volume of the zeolite reservoir.
  • the pressure in the zeolite storage increases.
  • the pressure in the zeolite reservoir can thus be used as a measured variable for the amount of water desorbed.
  • the pressure and/or the temperature in the zeolite reservoir are therefore preferably measured and the amount of water desorbed in the zeolite reservoir is deduced from the measured values.
  • the heating of the zeolite reservoir can then be terminated.
  • step c Before initiating step c), it is preferably first checked whether specific conditions, in particular dilution conditions, exist for opening a flushing valve. This is because the discharge of water or water vapor from the system is usually subject to the condition that the hydrogen contained therein is sufficiently diluted (“dilution constraint”). Only when this condition is met can the at least one flushing valve be opened.
  • specific conditions in particular dilution conditions
  • step c) desorbed water is introduced via the directional control valve and/or the at least one flushing valve into a cathode exhaust gas path or discharged to the environment.
  • the introduction into the cathode exhaust gas path can, for example, via the scavenging valve usually provided for scavenging the recirculation path be effected. If this is opened for flushing, no or only limited operation of the fuel cell system is possible.
  • a further flushing valve is provided for opening an additional flushing path.
  • Desorbed water can then also be introduced into the cathode exhaust gas path or discharged to the environment via the additional rinsing path. Opening the additional purge path does not affect system operation. This means that the regeneration of the zeolite reservoir and the operation of the fuel cell system can take place separately from one another. This enables more degrees of freedom in the operation of the fuel cell system.
  • the functions of the second shut-off valve and the further flushing valve can be combined in the previously proposed directional valve arranged downstream of the zeolite reservoir.
  • the additional flushing path can be released by switching the directional valve accordingly.
  • the directional valve is preferably designed as a 3/2-way valve. Depending on the switching position of the directional control valve, desorbed water is then introduced from the zeolite reservoir into the additional flushing path or fed to one flushing valve.
  • shut-off valve is opened in step c) so that desorbed water from the zeolite reservoir is fed to the at least one flushing valve.
  • step c the shut-off valve arranged downstream of the zeolite reservoir and a flushing valve are opened.
  • both shut-off valves and one rinsing valve can also be opened.
  • this increases the risk of liquid water condensation at the anode inlet.
  • Steps a) to c) are preferably repeated at least once, preferably several times, until the desired amount of water has been expelled from the zeolite reservoir and/or the regeneration of the zeolite reservoir is complete. Because with increasing regeneration of the zeolite reservoir, the pressure when heating the zeolite reservoir is less strong increases as the temperature, the characteristic behavior of pressure and temperature increase can be used to monitor the regeneration process.
  • the following criteria can be used, which indicate that the regeneration of the zeolite reservoir has been completed: at constant temperature, the pressure does not rise or hardly increases, which means that no more water passes into the gas phase in the volume of the zeolite reservoir; the temperature increases significantly or quickly above the desorption temperature, which means that the rate of change of the temperature increase dT/dt of the zeolite storage device exceeds a specific threshold value and less water is desorbed.
  • the method according to the invention can also be carried out without a pressure sensor for measuring the pressure in the volume of the zeolite reservoir. If the heat output and the thermal behavior of the zeolite storage are known, the temperature gradient or course alone can be used to estimate how much water vapor is present in the zeolite storage at any given time and what its state of regeneration is.
  • the zeolite reservoir is preferably repeatedly heated and desorbed water is removed from the zeolite reservoir by flushing. Residual hydrogen is also flushed out with the flushing volume, with the residual hydrogen content being the highest when flushing for the first time. In the subsequent rinsing processes, the residual hydrogen content continues to decrease, since preferably no hydrogen-containing recirculate flows into the zeolite reservoir upstream of the zeolite reservoir due to the closed shut-off valve.
  • a combined scavenging strategy can therefore also be used, particularly when scavenging for the first time, when the residual hydrogen content is particularly high.
  • a first scavenging valve opening into the cathode exhaust gas path and—if provided—a second scavenging valve opening into an additional scavenging path can be opened at the same time.
  • Flushing valve and a second flushing valve are opened during repeated flushing.
  • the first scavenging valve can in particular be a scavenging valve that opens into the cathode exhaust gas path, since the residual hydrogen content is still very high when scavenging for the first time.
  • the amount of scavenging mixes with the air present there, so that the residual hydrogen is sufficiently diluted.
  • the scavenging volume can then be introduced into an additional scavenging path via the second scavenging valve.
  • the introduction into an additional scavenging path has the advantage that the subsequent scavenging process--unlike the first scavenging process--can be carried out independently of the operation of the fuel cell system. Accordingly, the operation of the fuel cell system is not restricted.
  • a fuel cell system with at least one fuel cell to which hydrogen can be supplied via an anode path and oxygen can be supplied via a cathode path.
  • the fuel cell system also includes a recirculation path, via which anode exhaust gas exiting the fuel cell can be recirculated, and a zeolite storage device, by means of which water vapor contained in the anode exhaust gas can be adsorbed.
  • the zeolite reservoir can be switched on and off via at least one shut-off valve and/or a directional control valve. By switching on the zeolite storage, the water vapor contained in the recirculated material can be adsorbed.
  • the zeolite storage can be regenerated by means of desorption, independently of the operation of the fuel cell system. This means that the regeneration of the zeolite storage does not lead to a restriction of the system operation.
  • the zeolite storage is not connected in series, but in parallel.
  • the parallel connection has the advantage, among other things, that the pressure loss in the anode path is kept low.
  • the zeolite storage is connected in parallel by means of the valves mentioned, which enable the zeolite storage to be completely separated from the recirculation path.
  • the valves include at least one shut-off valve, which is arranged upstream of the zeolite reservoir and in the closed position Flow through the zeolite storage with recirculation prevented.
  • a further shut-off valve or a directional valve, preferably a 3/2-way valve, can be arranged downstream of the zeolite reservoir. If a further shut-off valve is provided, the water desorbed during the regeneration of the zeolite reservoir can be discharged via the flushing valve, which is usually provided and opens into the cathode exhaust gas path.
  • the desorbed water can also be introduced into an additional flushing path via a further flushing valve.
  • a further flushing valve If an additional scavenging path is provided, the functions of the shut-off valve arranged downstream of the zeolite reservoir and of the further scavenging valve can also be implemented by means of the directional control valve.
  • the proposed fuel cell system is particularly suitable for carrying out the method according to the invention described above. Accordingly, the same advantages can be achieved with the aid of the fuel cell system. Furthermore, the zeolite reservoir can be designed analogously to the zeolite reservoir described above and/or connected to the system.
  • an electrical heating device be integrated into the zeolite storage unit, so that the zeolite storage unit can be heated for desorption of water.
  • the zeolite storage device can be quickly brought to the temperature of about 250° C. required for desorption by means of the electrical heating device.
  • the zeolite storage device can also be preheated with the aid of the electrical heating device.
  • the electrical heating device comprises at least one heating cartridge. This can easily be integrated into a bed of zeolite material in the zeolite store.
  • the zeolite reservoir is connected to a cathode exhaust gas path and/or to the environment via the directional control valve and/or at least one purge valve, so that desorbed water from the zeolite reservoir can be introduced into the cathode exhaust gas path or discharged to the environment.
  • the flushing volume is preferably in the Initiated cathode exhaust path to dilute the residual hydrogen contained with the air present there.
  • FIG. 1 shows a schematic representation of a first fuel cell system according to the invention for carrying out the method according to the invention
  • FIG. 2 the implementation of the method according to the invention with the aid of the fuel cell system of FIG. 1,
  • FIG. 3 shows a schematic representation of a second fuel cell system according to the invention for carrying out the method according to the invention
  • FIG. 4 shows the implementation of the method according to the invention with the aid of the fuel cell system of FIG. 3,
  • FIGS. 5 shows an alternative implementation of the method according to the invention using the fuel cell system of FIGS.
  • FIG. 6 shows a schematic representation of a third fuel cell system according to the invention for carrying out the method according to the invention.
  • the fuel cell system shown in FIG. 1 comprises at least one fuel cell 1 which can be supplied on the anode side via an anode path 2 with an anode gas, namely with hydrogen from a tank 11 .
  • the supply of fresh hydrogen can be controlled via a valve 12. Since the anode waste gas emerging from the fuel cell 1 still contains a residue of hydrogen, this is recirculated via a recirculation path 3 or reintroduced into the anode path 2 . In the present case, the recirculation is actively supported by means of a recirculation fan 13 . In the anode path 2, fresh hydrogen from the tank 11 is added to the recirculated material.
  • the fuel cell system shown in FIG. 1 also has a zeolite storage device 4 for dehumidifying the recirculated material.
  • the zeolite reservoir 4 is connected to the recirculation path 3 or connected in parallel via a first shut-off valve 5 and a second shut-off valve 6 .
  • the shut-off valves 5, 6 are in the open position, the recirculated material flows through the zeolite reservoir 4, with the water contained therein being withdrawn by means of adsorption. This generates heat that can be used, for example, when the system is cold started, to bring the system up to operating temperature more quickly.
  • the zeolite storage device 4 can be heated by means of an integrated electrical heating device 8 . This is particularly advantageous in the case of a freezing start.
  • the anode gas can also be enriched with nitrogen during operation of the fuel cell system, which diffuses, for example, from the cathode side (not shown) to the anode side, the anode path 2 and the recirculation path 3 must be purged from time to time.
  • a purge valve 9 is provided on the outlet side, which preferably opens into a cathode exhaust gas path (not shown). The amount of scavenging discharged via the scavenging valve 9 is then replaced by fresh hydrogen from the tank 11 .
  • the scavenging valve 9 shown in FIG. 1 is also used to regenerate the zeolite reservoir 4 in the present case.
  • the zeolite reservoir 4 is separated from the recirculation path 3 and then brought to a temperature of approximately 250° C. by means of the electrical heating device 8, so that previously adsorbed water is desorbed.
  • the amount of water desorbed 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 rinsing of the zeolite store 4 is repeated several times until the desorbed quantity has been completely removed from the zeolite store 4 .
  • the temperature and/or the pressure in the zeolite reservoir 4 can be monitored.
  • a temperature sensor 14 and a pressure sensor 15 are provided on the zeolite storage device 4 .
  • the precise sequence of the adsorption and desorption phases of the zeolite storage device 4 shown is explained below with reference to the diagram in FIG.
  • the times t0 to t9 are plotted on the timeline.
  • the system is required to extract water or water vapor from the recirculated anode waste gas and, if necessary, to introduce heat, for example when starting to freeze.
  • the two shut-off valves 5, 6 are opened so that the zeolite reservoir 4 is flowed through by recirculated anode waste gas.
  • the exothermic adsorption begins, with the zeolite reservoir 4 heating up to approximately 160° C. by time t2.
  • two operating modes can be distinguished:
  • variant 1 the kinetics of the adsorption process for heating the zeolite storage 4 are sufficient, so that variant 1 can be followed.
  • variant 2 proves to be advantageous.
  • the system-side request to store water in the zeolite reservoir 4 is withdrawn because, for example, no more water can be stored or there is no longer any need for it. Since the check valves 5, 6 are still open, the flow through the zeolite storage tank 4 continues. Because to close the check valves 5, 6, a suitable time is awaited. This is reached, for example, when a maximum hydrogen concentration Xns.max in the zeolite reservoir 4 is undershot. In this way, the hydrogen losses during the subsequent regeneration of the zeolite store 4 can be kept low. After the two shut-off valves 5, 6 have been closed at the point in time tshut-off, the gas composition in the zeolite reservoir 4 initially no longer changes.
  • the zeolite storage device 4 is to be regenerated at time t3.
  • the zeolite material is heated to approximately 250° C. by means of the electrical heating device 8 in order to desorb water from the zeolite storage unit 4 . Because both check valves 5, 6 are closed, heat losses are kept to a minimum. The heating of the zeolite storage 4 is also possible independently of the system.
  • the desorption temperature of 250° C. is reached and the zeolite reservoir 4 releases the previously adsorbed water back into the volume of the zeolite reservoir 4 as water vapor.
  • the pressure in the zeolite reservoir 4 increases, which can be used as a measured variable for the amount of water desorbed.
  • a maximum pressure and/or a maximum temperature in the zeolite reservoir 4 is or are exceeded, so that the electrical heating device 8 is switched off.
  • a query is sent to the system as to whether the required dilution conditions (“dilution constraint”) for flushing the system are present. If there is positive feedback, 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 reservoir 4 . In this phase, no or only limited operation of the fuel cell system is possible.
  • the check valve 6 is closed again at time t6 and the processes of heating the zeolite reservoir 4 and rinsing are repeated until the desired amount of water is expelled from the zeolite reservoir 4 and the regeneration of the zeolite reservoir 4 is complete.
  • the characteristic behavior of the temperature and pressure increase in the zeolite storage device 4 during the heating-up phase from t3 to t4 or from t6 to t7 etc. can be used as a debit criterion. Because with increasing regeneration of the zeolite storage 4, the pressure rises less than the temperature.
  • FIG. 3 shows a modification of the system of FIG.
  • the modification consists in 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 store 4 .
  • the further scavenging valve 10 thus enables more degrees of freedom in the operation of the fuel cell system.
  • the processes during operation of the fuel cell system of FIG. 3 are shown in FIG.
  • the adsorption phase A, the valve closing phase B and the heating phase C proceed analogously to the corresponding phases in FIG. 2, so that reference is made to the description of FIG.
  • the only differences are with regard to the desorption phase D.
  • the hydrogen-water vapor gas mixture is discharged here via the further flushing valve 10 into the additional flushing path 16. Certain dilution conditions must also be observed here, but these can differ from those mentioned above. Depending on the design of the zeolite storage 4 and the choice of Xns.max, it is even possible to release the gas mixture directly into the environment.
  • a combined scavenging strategy can also be used with the aid of the system in FIG. 3 .
  • both flushing valves 9, 10 are opened, with a time delay.
  • scavenging is carried out via the first scavenging valve 9.
  • flushing takes place via the further flushing valve 10 .
  • This strategy is optimal to ensure the necessary dilution of the residual hydrogen.
  • the scavenging quantity mixes with the air present there.
  • the normal operation of the fuel cell system is thereby interrupted or disturbed. It therefore proves to be advantageous if the scavenging quantity is discharged via the further scavenging valve 10 and the scavenging path 16 in the further course of the regeneration of the zeolite reservoir 4 . Because this process does not affect the operation of the fuel cell system.
  • FIG. A further modification of the fuel cell system according to the invention is shown in FIG. Here the functions of the shut-off valve 6 and the additional flushing valve 10 are implemented by a 3/2-way valve 7 .
  • the structure of the fuel cell system can be simplified as a valve is saved.

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  • Fuel Cell (AREA)

Abstract

The invention relates to a method for operating a fuel cell system in which at least one fuel cell (1) is supplied with hydrogen via an anode path (2) and with oxygen via a cathode path, and in which anode exhaust gas exiting the fuel cell (1) is recirculated via a recirculation path (3), wherein steam contained in the anode exhaust gas is adsorbed by means of a zeolite container (4). According to the invention, the following steps are carried out in order to regenerate the zeolite container (4): a) separating the zeolite container (4) from the recirculation path (3) by closing at least one shut-off valve (5, 6) and/or switching a directional control valve (7), b) heating the zeolite container (4) by means of an electric heating device (8) such that previously adsorbed water is desorbed, and c) removing the desorbed water from the system by switching the directional control valve (7) again and/or by opening at least one flushing valve (9, 10). The invention additionally relates to a fuel cell system which is suitable for carrying out the method.

Description

Beschreibung description
Verfahren zum Betreiben eines Brennstoffzellensystems, Brennstoffzellensystem Method for operating a fuel cell system, fuel cell system
Die Erfindung betrifft ein Verfahren zum Betreiben eines Brennstoffzellensystems mit den Merkmalen des Oberbegriffs des Anspruchs 1. Darüber hinaus betrifft die Erfindung ein Brennstoffzellensystem, das zur Durchführung des erfindungsgemäßen Verfahrens geeignet ist bzw. nach dem erfindungsgemäßen Verfahren betreibbar ist. The invention relates to a method for operating a fuel cell system having the features of the preamble of claim 1. The invention also relates to a fuel cell system which is suitable for carrying out the method according to the invention or can be operated using the method according to the invention.
Stand der Technik State of the art
Eine Brennstoffzelle wandelt Wasserstoff mit Hilfe von Sauerstoff zu elektrischer Energie. Die Brennstoffzelle weist hierzu eine Membran-Elektroden-Anordnung mit einer Anode und einer Kathode auf. Der Anode wird über einen Anodenpfad Wasserstoff zugeführt, der einem geeigneten Tank bevorratet wird. Der Kathode wird über einen Kathodenpfad Umgebungsluft zugeführt, die als Sauerstofflieferant dient. A fuel cell converts hydrogen into electrical energy with the help of oxygen. For this purpose, the fuel cell has a membrane-electrode assembly with an anode and a cathode. Hydrogen, which is stored in a suitable tank, is fed to the anode via an anode path. Ambient air, which serves as an oxygen supplier, is supplied to the cathode via a cathode path.
Zur Leistungssteigerung werden in der Regel eine Vielzahl von Brennstoffzellen, beispielsweise 200 bis 400 Brennstoffzellen, in gestapelter Anordnung zu einem Brennstoffzellenstapel verbaut. Dieser ist von mehreren Kanälen durchzogen, die der Versorgung der Brennstoffzellen mit den benötigten Gasen sowie dem Abführen der aus den Brennstoffzellen austretenden Abgase dienen. Da das anodenseitig austretende Abgas unverbrauchten Wasserstoff enthält, wird das Anodenabgas in der Regel rezirkuliert. Der Druckverlust im Anodenpfad wird dabei aktiv mittels Gebläse und/oder passiv mittels einer Strahlpumpe überwunden. Vor dem Anodeneintritt wird dem Rezirkulat frischer Wasserstoff aus dem Tank beigemischt. To increase performance, a large number of fuel cells, for example 200 to 400 fuel cells, are installed in a stacked arrangement to form a fuel cell stack. This is traversed by several channels that serve to supply the fuel cells with the required gases and to discharge the exhaust gases exiting the fuel cells. Since the exhaust gas exiting the anode side contains unused hydrogen, the anode exhaust gas is generally recirculated. The pressure loss in the anode path is overcome actively by means of a blower and/or passively by means of a jet pump. Fresh hydrogen from the tank is added to the recirculated material before it enters the anode.
Brennstoffzellensysteme mit wasserstoffbasierten Brennstoffzellen gelten als Mobilitätskonzept der Zukunft, da sie im Wesentlichen nur Wasser als Abgas emittieren und zudem schnelle Betankungszeiten ermöglichen. Um das im Betrieb anfallende Wasser auszutragen, werden in der Regel Kondensatabscheider eingesetzt, mit deren Hilfe flüssiges Wasser an definierten Stellen des Systems gesammelt und zu definierten Zeitpunkten über sogenannte Drain-Ventile an die Umgebung abgegeben wird. Nach dem Abstellen eines Fahrzeugs fällt zusätzlich Wasser durch Auskühlen des Systems und durch Kondensation von dampfförmigem Wasser einer Gasphase an. Dieses Wasser bzw. Kondensat muss ebenfalls entfernt werden, um bei einem erneuten Starten des Fahrzeugs Blockaden zu vermeiden, die durch Ansammlungen von flüssigem Wasser hervorgerufen werden. Bei tiefen Außentemperaturen besteht zudem die Gefahr, dass das Kondensat gefriert. Fuel cell systems with hydrogen-based fuel cells are considered to be the mobility concept of the future, since they essentially only emit water as exhaust gas and also enable fast refueling times. To the im Condensate separators are usually used to discharge the water that occurs during operation, with the help of which liquid water is collected at defined points in the system and released into the environment at defined times via so-called drain valves. After a vehicle is parked, additional water accumulates due to cooling of the system and condensation of vaporous water in a gas phase. This water or condensate must also be removed to avoid blockages caused by accumulations of liquid water when the vehicle is restarted. At low outside temperatures there is also a risk that the condensate will freeze.
Im Stand der Technik wurde daher bereits vorgeschlagen, nach Abschalten einer Brennstoffzelle vorhandene Restfeuchte mittels einer zeolithbasierten Adsorptionseinheit zu adsorbieren und die bei der Adsorption freiwerdende Wärme in der nachfolgenden Startphase zur Erwärmung der Brennstoffzelle zu nutzen. Beispielhaft wird hier auf die Offenlegungsschrift DE 10 2008 007 024 Al verwiesen. It has therefore already been proposed in the prior art to adsorb residual moisture present after a fuel cell has been switched off by means of a zeolite-based adsorption unit and to use the heat released during adsorption to heat the fuel cell in the subsequent start-up phase. By way of example, reference is made here to the published application DE 10 2008 007 024 A1.
Die Adsorption von Wasser mittels eines Zeolithspeichers erfolgt exotherm, wodurch sich der Speicher auf etwa 160°C erwärmt. Danach muss der Speicher unter Wärmezufuhr (endotherme Reaktion) regeneriert werden, wobei das zuvor mittels Adsorption aufgenommene Wasser desorbiert wird. Hierzu ist typischerweise ein Temperaturniveau von 200°C bis 250°C erforderlich. The adsorption of water using a zeolite storage tank is exothermic, which means that the storage tank is heated to around 160°C. The storage tank then has to be regenerated with the addition of heat (endothermic reaction), with the water previously absorbed by means of adsorption being desorbed. A temperature level of 200°C to 250°C is typically required for this.
Ausgehend von dem vorstehend genannten Stand der Technik liegt der vorliegenden Erfindung die Aufgabe zugrunde, die Regeneration eines zeolithbasierten Wasserspeichers in einem Brennstoffzellensystem zu optimieren. Insbesondere soll energieoptimiert regeneriert werden. Ferner soll die Kondensation von desorbiertem Wasser vermieden werden und - soweit möglich - soll dadurch der Betrieb des Brennstoffzellensystems nicht beeinträchtigt werden. Proceeding from the prior art mentioned above, the object of the present invention is to optimize the regeneration of a zeolite-based water reservoir in a fuel cell system. In particular, energy-optimized regeneration should take place. Furthermore, the condensation of desorbed water should be avoided and—as far as possible—the operation of the fuel cell system should not be impaired thereby.
Zur Lösung der Aufgabe werden das Verfahren mit den Merkmalen des Anspruchs 1 sowie das Brennstoffzellensystem mit den Merkmalen des Anspruchs 10 vorgeschlagen. Vorteilhafte Weiterbildungen der Erfindung sind den jeweiligen Unteransprüchen zu entnehmen. Offenbarung der Erfindung To solve the problem, the method with the features of claim 1 and the fuel cell system with the features of claim 10 are proposed. Advantageous developments of the invention can be found in the respective dependent claims. Disclosure of Invention
Bei dem vorgeschlagenen Verfahren zum Betreiben eines Brennstoffzellensystems wird mindestens einer Brennstoffzelle über einen Anodenpfad Wasserstoff und über einen Kathodenpfad Sauerstoff zugeführt. Aus der Brennstoffzelle austretendes Anodenabgas wird über einen Rezirkulationspfad rezirkuliert, wobei im Anodenabgas enthaltener Wasserdampf mittels eines Zeolithspeichers adsorbiert wird. Zur Regeneration des Zeolithspeichers werden erfindungsgemäß folgende Schritte ausgeführt: a) Trennen des Zeolithspeichers vom Rezirkulationspfad durch Schließen mindestens eines Absperrventils und/oder Schalten eines Wegeventils, b) Erwärmen des Zeolithspeichers mittels einer elektrischen Heizeinrichtung, so dass zuvor adsorbiertes Wasser desorbiert wird, und c) Entfernen von desorbiertem Wasser aus dem System durch erneutes Schalten des Wegeventils und/oder durch Öffnen mindestens eines Spülventils. In the proposed method for operating a fuel cell system, at least one fuel cell is supplied with hydrogen via an anode path and oxygen via a cathode path. Anode waste gas exiting the fuel cell is recirculated via a recirculation path, water vapor contained in the anode waste gas being adsorbed by means of a zeolite storage device. According to the invention, the following steps are carried out to regenerate the zeolite reservoir: a) separating the zeolite reservoir from the recirculation path by closing at least one shut-off valve and/or switching a directional control valve, b) heating the zeolite reservoir by means of an electrical heating device so that previously adsorbed water is desorbed, and c) Removal of desorbed water from the system by switching the directional control valve again and/or by opening at least one flushing valve.
Durch die vorgeschlagene Trennung des Zeolithspeichers vom Rezirkulationspfad während des Regenerationsvorgangs kann dieser Vorgang weitgehend unabhängig vom Betrieb des Brennstoffzellensystems durchgeführt werden. Das heißt, dass der Betrieb des Brennstoffzellensystems durch den Regenerationsvorgang nicht oder in nur geringem Maße eingeschränkt wird. Ferner kann desorbiertes Wasser sicher abgeführt werden, ohne, dass die Gefahr besteht, dass die Anode geflutet wird bzw. flüssiges Wasser am Anodeneintritt freigesetzt wird. Zudem wird weniger Wasserstoff im Zeolithspeicher eingeschlossen und bei der Regeneration des Zeolithspeichers ausgetragen, so dass weniger Wasserstoff verloren geht. Due to the proposed separation of the zeolite storage from the recirculation path during the regeneration process, this process can be carried out largely independently of the operation of the fuel cell system. This means that the operation of the fuel cell system is not limited or only limited to a small extent by the regeneration process. Furthermore, desorbed water can be safely discharged without the risk of the anode being flooded or liquid water being released at the anode inlet. In addition, less hydrogen is trapped in the zeolite reservoir and discharged when the zeolite reservoir is regenerated, so that less hydrogen is lost.
Zur Durchführung des vorgeschlagenen Verfahrens kann beispielsweise ein Zeolithspeicher eingesetzt werden, der eine Schüttung aus Zeolithmaterial aufweist. Alternativ kann der Zeolithspeicher auch eine keramische oder metallische Trägerstruktur umfassen, die mit einem Zeolithmaterial beschichtet ist. Der Zeolithspeicher kann gemäß dem eingangs beschriebenen Stand der Technik in ein Brennstoffzellensystem mit aktiver und/oder passiver Rezirkulation eingesetzt werden. To carry out the proposed method, a zeolite reservoir can be used, for example, which has a bed of zeolite material. Alternatively, the zeolite reservoir can also include a ceramic or metal support structure that is coated with a zeolite material. According to the prior art described above, the zeolite storage device can be used in a fuel cell system with active and/or passive recirculation.
Vorteilhafterweise ist zum Trennen des Zeolithspeichers vom Rezirkulationspfad des Brennstoffzellensystems mindestens ein Absperrventil stromaufwärts des Zeolithspeichers vorgesehen. Durch Schließen des Absperrventils wird ein Durchströmen des Zeolithspeichers mit Rezirkulat verhindert und das durch den Zeolithspeicher geschaffene zusätzliche Volumen wird abgetrennt, so dass sich das System weniger träge verhält. Auf diese Weise lässt sich zugleich das Verhalten des Systems positiv beeinflussen. Advantageously, at least one shut-off valve is provided upstream of the zeolite reservoir to separate the zeolite reservoir from the recirculation path of the fuel cell system. Closing the shut-off valve prevents recirculated material from flowing through the zeolite reservoir and the additional volume created by the zeolite reservoir is separated, so that the system behaves less sluggishly. In this way, the behavior of the system can be positively influenced at the same time.
Stromabwärts des Zeolithspeichers ist vorzugsweise ein weiteres Absperrventil oder ein Wegeventil, insbesondere ein 3/2-Wegeventil, angeordnet. Mit Hilfe des weiteren Absperrventils, aber auch mit Hilfe des Wegeventils, kann während der Desorption eine Verbindung des Zeolithspeichers mit dem mindestens einen Spülventil unterbrochen werden. Zum Entfernen von desorbiertem Wasser aus dem Zeolithspeicher können das Absperrventil und das mindestens eine Spülventil geöffnet werden, so dass desorbiertes Wasser hierüber abgeführt wird. Ist anstelle eines zweiten Absperrventils ein Wegeventil vorgesehen, kann dieses derart geschaltet werden, dass ein Spülpfad zum Abführen des desorbierten Wassers freigegeben wird. A further shut-off valve or a directional valve, in particular a 3/2-way valve, is preferably arranged downstream of the zeolite reservoir. With the help of the further shut-off valve, but also with the help of the directional control valve, a connection of the zeolite reservoir to the at least one flushing valve can be interrupted during desorption. In order to remove desorbed water from the zeolite reservoir, the shut-off valve and the at least one flushing valve can be opened, so that desorbed water is discharged via it. If a directional valve is provided instead of a second shut-off valve, this can be switched in such a way that a flushing path for discharging the desorbed water is released.
Gemäß einer bevorzugten Ausführungsform der Erfindung wird Schritt a) erst mit Unterschreiten einer maximalen Wasserstoffkonzentration und/oder eines maximalen Wasserstoffpartialdrucks im Rezirkulationspfad eingeleitet. Dies ist beispielsweise im unteren Lastbereich des Brennstoffzellensystems der Fall oder kurz vor einem Spülvorgang des Systems. Auf diese Weise kann der Wasserstoffverbrauch weiter gesenkt bzw. minimiert werden. Ferner ist sichergestellt, dass die im Zeolithspeicher eingeschlossene Wasserstoffmenge vor dem Abführen ausreichend verdünnt wird. According to a preferred embodiment of the invention, step a) is only initiated when the hydrogen concentration falls below a maximum and/or a maximum hydrogen partial pressure in the recirculation path. This is the case, for example, in the lower load range of the fuel cell system or shortly before the system is flushed. In this way, the hydrogen consumption can be further reduced or minimized. It is also ensured that the amount of hydrogen trapped in the zeolite storage tank is sufficiently diluted before it is discharged.
Des Weiteren wird vorgeschlagen, dass in Schritt b) der Zeolithspeicher auf eine Temperatur von etwa 250°C erwärmt wird, um die Desorption des zuvor adsorbierten Wassers bzw. Wasserdampfs zu fördern. Alternativ oder ergänzend wird vorgeschlagen, dass zum Erwärmen des Zeolithspeichers mindestens eine in den Zeolithspeicher integrierte Heizpatrone als elektrische Heizeinrichtung verwendet wird. Mit Hilfe der mindestens einen integrierten Heizpatrone kann die Erwärmung des Zeolithspeichers beschleunigt werden. Die mindestens eine Heizpatrone kann beispielsweise in einer Zeolithschüttung des Zeolithspeichers angeordnet werden. Furthermore, it is proposed that in step b) the zeolite reservoir is heated to a temperature of approximately 250° C. in order to promote the desorption of the previously adsorbed water or water vapor. As an alternative or in addition, it is proposed that at least one heating cartridge integrated into the zeolite reservoir be used as an electrical heating device to heat the zeolite reservoir is used. With the help of at least one integrated heating cartridge, the heating of the zeolite storage can be accelerated. The at least one heating cartridge can be arranged, for example, in a zeolite bed of the zeolite store.
Dadurch, dass der Zeolithspeicher vor Einleiten des Schritts b) vom System getrennt wurde, werden durch Konvektion und/oder Interaktion mit dem restlichen Volumen bedingte Wärmeverluste vermieden bzw. geringgehalten. Das Erwärmen des Zeolithspeichers ist zudem unabhängig vom Systembetrieb, insbesondere unabhängig von dem Druck, der Temperatur und/oder dem Volumenstrom im System möglich. Because the zeolite reservoir was separated from the system before initiating step b), heat losses caused by convection and/or interaction with the remaining volume are avoided or kept low. In addition, the heating of the zeolite reservoir is possible independently of the system operation, in particular independently of the pressure, the temperature and/or the volume flow in the system.
Mit Erreichen der Temperatur von etwa 250°C gibt der Zeolithspeicher das zuvor adsorbierte Wasser wieder als Wasserdampf an das Volumen des Zeolithspeichers ab. Dies hat zur Folge, dass der Druck im Zeolithspeicher ansteigt. Der Druck im Zeolithspeicher kann somit als Messgröße für die desorbierte Wassermenge verwendet werden. Gleiches gilt analog für die Temperatur im Zeolithspeicher. Bevorzugt werden daher der Druck und/oder die Temperatur im Zeolithspeicher gemessen und von den Messwerten wird auf die desorbierte Wassermenge im Zeolithspeicher geschlossen. Mit Erreichen eines vorgegebenen maximalen Druck- und/oder Temperaturgrenzwerts im Zeolithspeicher kann dann die Erwärmung des Zeolithspeichers beendet werden. When the temperature of about 250°C is reached, the zeolite reservoir releases the previously adsorbed water as water vapor to the volume of the zeolite reservoir. As a result, the pressure in the zeolite storage increases. The pressure in the zeolite reservoir can thus be used as a measured variable for the amount of water desorbed. The same applies analogously to the temperature in the zeolite storage tank. The pressure and/or the temperature in the zeolite reservoir are therefore preferably measured and the amount of water desorbed in the zeolite reservoir is deduced from the measured values. When a predetermined maximum pressure and/or temperature limit value is reached in the zeolite reservoir, the heating of the zeolite reservoir can then be terminated.
Vor Einleiten von Schritt c) wird vorzugsweise erst geprüft wird, ob bestimmte Bedingungen, insbesondere Verdünnungsbedingungen, zum Öffnen eines Spülventils vorliegen. Denn das Ausleiten von Wasser bzw. Wasserdampf aus dem System ist in der Regel an die Bedingungen geknüpft, dass hierin enthaltener Wasserstoff ausreichend verdünnt ist (engl.: „dilution constraint“). Erst wenn diese Bedingung erfüllt ist, kann das mindestens eine Spülventil geöffnet werden. Before initiating step c), it is preferably first checked whether specific conditions, in particular dilution conditions, exist for opening a flushing valve. This is because the discharge of water or water vapor from the system is usually subject to the condition that the hydrogen contained therein is sufficiently diluted (“dilution constraint”). Only when this condition is met can the at least one flushing valve be opened.
Des Weiteren wird vorgeschlagen, dass in Schritt c) desorbiertes Wasser über das Wegeventil und/oder das mindestens eine Spülventil in einen Kathodenabgaspfad eingeleitet oder an die Umgebung abgegeben wird. Die Einleitung in den Kathodenabgaspfad kann beispielsweise über das üblicherweise zum Spülen des Rezirkulationspfads vorgesehene Spülventil bewirkt werden. Wird dieses zum Spülen geöffnet, ist kein oder nur ein eingeschränkter Betrieb des Brennstoffzellensystems möglich. Furthermore, it is proposed that in step c) desorbed water is introduced via the directional control valve and/or the at least one flushing valve into a cathode exhaust gas path or discharged to the environment. The introduction into the cathode exhaust gas path can, for example, via the scavenging valve usually provided for scavenging the recirculation path be effected. If this is opened for flushing, no or only limited operation of the fuel cell system is possible.
Um während des Abführens von desorbiertem Wasser aus dem Zeolithspeicher den Systembetrieb nicht einzuschränken, wird in Weiterbildung der Erfindung vorgeschlagen, dass ein weiteres Spülventil zum Öffnen eines zusätzlichen Spülpfads vorgesehen ist. Über den zusätzlichen Spülpfad kann dann desorbiertes Wasser ebenfalls in den Kathodenabgaspfad eingeleitet oder an die Umgebung abgegeben werden. Das Öffnen des zusätzlichen Spülpfads beeinträchtigt den Systembetrieb nicht. Das heißt, dass die Regeneration des Zeolithspeichers und der Betrieb des Brennstoffzellensystems getrennt voneinander ablaufen können Dies ermöglicht mehr Freiheitsgrade im Betrieb des Brennstoffzellensystems. In order not to restrict the system operation during the removal of desorbed water from the zeolite reservoir, it is proposed in a development of the invention that a further flushing valve is provided for opening an additional flushing path. Desorbed water can then also be introduced into the cathode exhaust gas path or discharged to the environment via the additional rinsing path. Opening the additional purge path does not affect system operation. This means that the regeneration of the zeolite reservoir and the operation of the fuel cell system can take place separately from one another. This enables more degrees of freedom in the operation of the fuel cell system.
Alternativ können die Funktionen des zweiten Absperrventils und des weiteren Spülventils in dem bereits vorgeschlagenen, stromabwärts des Zeolithspeichers angeordneten Wegeventil zusammengefasst werden. Der zusätzliche Spülpfad kann in diesem Fall durch entsprechendes Schalten des Wegeventils freigegeben werden. Das Wegeventil ist hierzu bevorzugt als 3/2-Wegeventil ausgeführt. In Abhängigkeit von der Schaltstellung des Wegeventils wird dann desorbiertes Wasser aus dem Zeolithspeicher in den zusätzlichen Spülpfad eingeleitet oder dem einen Spülventil zugeführt. Alternatively, the functions of the second shut-off valve and the further flushing valve can be combined in the previously proposed directional valve arranged downstream of the zeolite reservoir. In this case, the additional flushing path can be released by switching the directional valve accordingly. For this purpose, the directional valve is preferably designed as a 3/2-way valve. Depending on the switching position of the directional control valve, desorbed water is then introduced from the zeolite reservoir into the additional flushing path or fed to one flushing valve.
Sofern stromabwärts des Zeolithspeichers kein Wegeventil, sondern ein zweites Absperrventil angeordnet ist, wird vorgeschlagen, dass in Schritt c) mindestens ein Absperrventil geöffnet wird, so dass desorbiertes Wasser aus dem Zeolithspeicher dem mindestens einen Spülventil zugeführt wird. Das heißt, dass zum Spülen zumindest das stromabwärts des Zeolithspeichers angeordnete Absperrventil sowie ein Spülventil geöffnet wird. Beim Spülen können auch beide Absperrventile sowie ein Spülventil geöffnet werden. Allerdings erhöht sich dadurch die Gefahr einer Flüssigwasserkondensation am Anodeneintritt. If no directional control valve but a second shut-off valve is arranged downstream of the zeolite reservoir, it is proposed that at least one shut-off valve is opened in step c) so that desorbed water from the zeolite reservoir is fed to the at least one flushing valve. This means that for flushing at least the shut-off valve arranged downstream of the zeolite reservoir and a flushing valve are opened. When rinsing, both shut-off valves and one rinsing valve can also be opened. However, this increases the risk of liquid water condensation at the anode inlet.
Bevorzugt werden die Schritte a) bis c) mindestens einmal, vorzugsweise mehrmals, wiederholt, und zwar so lange, bis die gewünschte Wassermenge aus dem Zeolithspeicher ausgetrieben und/oder die Regeneration des Zeolithspeichers abgeschlossen ist. Da mit zunehmender Regeneration des Zeolithspeichers der Druck beim Erwärmen des Zeolithspeichers weniger stark ansteigt als die Temperatur, kann das charakteristische Verhalten von Druck- und Temperaturanstieg zur Überwachung des Regenerationsvorgangs genutzt werden. Ferner können folgende Kriterien herangezogen werden, die auf einen Abschluss der Regeneration des Zeolithspeichers schließen lassen: bei konstanter Temperatur steigt der Druck nicht oder kaum noch an, das heißt, dass im Volumen des Zeolithspeichers kein Wasser mehr in die Gasphase übergeht; die Temperatur steigt deutlich bzw. schnell über die Desorptionstemperatur an, das heißt, dass die Änderungsrate der Temperaturerhöhung dT/dt des Zeolithspeichers einen bestimmten Schwellwert übersteigt und weniger Wasser desorbiert wird. Steps a) to c) are preferably repeated at least once, preferably several times, until the desired amount of water has been expelled from the zeolite reservoir and/or the regeneration of the zeolite reservoir is complete. Because with increasing regeneration of the zeolite reservoir, the pressure when heating the zeolite reservoir is less strong increases as the temperature, the characteristic behavior of pressure and temperature increase can be used to monitor the regeneration process. Furthermore, the following criteria can be used, which indicate that the regeneration of the zeolite reservoir has been completed: at constant temperature, the pressure does not rise or hardly increases, which means that no more water passes into the gas phase in the volume of the zeolite reservoir; the temperature increases significantly or quickly above the desorption temperature, which means that the rate of change of the temperature increase dT/dt of the zeolite storage device exceeds a specific threshold value and less water is desorbed.
Die Durchführung des erfindungsgemäßen Verfahrens ist aber auch ohne Drucksensor zur Messung des Drucks im Volumen des Zeolithspeichers möglich. Denn bei bekannter Heizleistung und bei bekanntem thermischen Verhalten des Zeolithspeichers kann allein über den Temperaturgardienten bzw. -verlauf abgeschätzt werden, wie viel Wasserdampf zum jeweiligen Zeitpunkt im Zeolithspeicher vorliegt und welchen Regenerationszustand dieser hat. However, the method according to the invention can also be carried out without a pressure sensor for measuring the pressure in the volume of the zeolite reservoir. If the heat output and the thermal behavior of the zeolite storage are known, the temperature gradient or course alone can be used to estimate how much water vapor is present in the zeolite storage at any given time and what its state of regeneration is.
Zur vollständigen Regeneration wird vorzugsweise der Zeolithspeicher wiederholt erwärmt und desorbiertes Wasser aus dem Zeolithspeicher durch Spülen entfernt. Mit der Spülmenge wird auch Restwasserstoff ausgespült, wobei beim erstmaligen Spülen der Restwasserstoffgehalt am höchsten ist. In den nachfolgenden Spülvorgängen nimmt der Restwasserstoffgehalt immer weiter ab, da vorzugsweise aufgrund des geschlossenen Absperrventils stromaufwärts des Zeolithspeichers kein wasserstoffhaltiges Rezirkulat in den Zeolithspeicher nachströmt. For complete regeneration, the zeolite reservoir is preferably repeatedly heated and desorbed water is removed from the zeolite reservoir by flushing. Residual hydrogen is also flushed out with the flushing volume, with the residual hydrogen content being the highest when flushing for the first time. In the subsequent rinsing processes, the residual hydrogen content continues to decrease, since preferably no hydrogen-containing recirculate flows into the zeolite reservoir upstream of the zeolite reservoir due to the closed shut-off valve.
Insbesondere beim erstmaligen Spülen, wenn der Restwasserstoffgehalt besonders hoch ist, kann daher auch eine kombinierte Spülstrategie gefahren werden. Beispielsweise können gleichzeitig ein in den Kathodenabgaspfad öffnendes erstes Spülventil und - sofern vorgesehen - ein in einen zusätzlichen Spülpfad öffnendes zweites Spülventil geöffnet werden. A combined scavenging strategy can therefore also be used, particularly when scavenging for the first time, when the residual hydrogen content is particularly high. For example, a first scavenging valve opening into the cathode exhaust gas path and—if provided—a second scavenging valve opening into an additional scavenging path can be opened at the same time.
Alternativ wird vorgeschlagen, dass beim erstmaligen Spülen ein erstesAlternatively, it is proposed that the first flush a first
Spülventil und beim wiederholten Spülen ein zweites Spülventil geöffnet werden. Das heißt, dass erstes und zweites Spülventil nacheinander in aufeinanderfolgenden Spülvorgängen geöffnet werden. Bei dem ersten Spülventil kann es sich insbesondere um ein in den Kathodenabgaspfad öffnendes Spülventil handeln, da beim erstmaligen Spülen der Restwasserstoffgehalt noch sehr hoch ist. Im Kathodenabgaspfad vermischt sich die Spülmenge mit der dort vorhandenen Luft, so dass der Restwasserstoff ausreichend verdünnt wird. In dem mindestens einen nachfolgenden Spülvorgang, wenn der Restwasserstoffgehalt bereits gesunken ist, kann dann über das zweite Spülventil die Spülmenge in einen zusätzlichen Spülpfad eingeleitet werden. Das Einleiten in einen zusätzlichen Spülpfad besitzt den Vorteil, dass der nachfolgende Spülvorgang - anders als der erste Spülvorgang - unabhängig vom Betrieb des Brennstoffzellensystems vorgenommen werden kann. Der Betrieb des Brennstoffzellensystems wird demnach nicht eingeschränkt. Flushing valve and a second flushing valve are opened during repeated flushing. This means that the first and second scavenging valves are opened one after the other in successive scavenging processes. The first scavenging valve can in particular be a scavenging valve that opens into the cathode exhaust gas path, since the residual hydrogen content is still very high when scavenging for the first time. In the cathode exhaust gas path, the amount of scavenging mixes with the air present there, so that the residual hydrogen is sufficiently diluted. In the at least one subsequent scavenging process, when the residual hydrogen content has already fallen, the scavenging volume can then be introduced into an additional scavenging path via the second scavenging valve. The introduction into an additional scavenging path has the advantage that the subsequent scavenging process--unlike the first scavenging process--can be carried out independently of the operation of the fuel cell system. Accordingly, the operation of the fuel cell system is not restricted.
Zur Lösung der eingangs genannten Aufgabe wird darüber hinaus ein Brennstoffzellensystem mit mindestens einer Brennstoffzelle vorgeschlagen, der über einen Anodenpfad Wasserstoff und über einen Kathodenpfad Sauerstoff zuführbar ist. Das Brennstoffzellensystem umfasst zudem einen Rezirkulationspfad, über den aus der Brennstoffzelle austretendes Anodenabgas rezirkulierbar ist, sowie einen Zeolithspeicher, mittels dessen im Anodenabgas enthaltener Wasserdampf adsorbierbar ist. Erfindungsgemäß ist der Zeolithspeicher über mindestens ein Absperrventil und/oder ein Wegeventil zu- und abschaltbar. Durch Zuschalten des Zeolithspeichers kann im Rezirkulat enthaltener Wasserdampf adsorbiert werden. Durch Abschalten bzw. Trennen des Zeolithspeichers vom Rezirkulationspfad kann mittels Desorption der Zeolithspeicher regeneriert werden, und zwar unabhängig vom Betrieb des Brennstoffzellensystems. Das heißt, dass die Regeneration des Zeolithspeichers nicht zu einer Einschränkung des Systembetriebs führt. In order to achieve the object mentioned at the outset, a fuel cell system with at least one fuel cell is also proposed, to which hydrogen can be supplied via an anode path and oxygen can be supplied via a cathode path. The fuel cell system also includes a recirculation path, via which anode exhaust gas exiting the fuel cell can be recirculated, and a zeolite storage device, by means of which water vapor contained in the anode exhaust gas can be adsorbed. According to the invention, the zeolite reservoir can be switched on and off via at least one shut-off valve and/or a directional control valve. By switching on the zeolite storage, the water vapor contained in the recirculated material can be adsorbed. By switching off or separating the zeolite storage from the recirculation path, the zeolite storage can be regenerated by means of desorption, independently of the operation of the fuel cell system. This means that the regeneration of the zeolite storage does not lead to a restriction of the system operation.
Bei dem vorgeschlagenen Brennstoffzellensystem ist der Zeolithspeicher nicht in Reihe, sondern parallel geschaltet. Die Parallelschaltung besitzt unter anderem den Vorteil, dass der Druckverlust im Anodenpfad gering gehalten wird. In the proposed fuel cell system, the zeolite storage is not connected in series, but in parallel. The parallel connection has the advantage, among other things, that the pressure loss in the anode path is kept low.
Die Parallelschaltung des Zeolithspeichers erfolgt mittels der genannten Ventile, die eine vollständige Trennung des Zeolithspeichers vom Rezirkulationspfad ermöglichen. Die Ventile umfassen mindestens ein Absperrventil, das stromaufwärts des Zeolithspeichers angeordnet ist und in Schließstellung ein Durchströmen des Zeolithspeichers mit Rezirkulat verhindert. Stromabwärts des Zeolithspeichers kann ein weiteres Absperrventil oder ein Wegeventil, vorzugsweise ein 3/2-Wegeventil, angeordnet sein. Sofern ein weiteres Absperrventil vorgesehen ist, kann das während der Regeneration des Zeolithspeichers desorbierte Wasser über das üblicherweise vorgesehene, in den Kathodenabgaspfad öffnende Spülventil abgeführt werden. Alternativ oder ergänzend kann das desorbierte Wasser auch über ein weiteres Spülventil in einen zusätzlichen Spülpfad eingeleitet werden. Sofern ein zusätzlicher Spülpfad vorgesehen ist, können die Funktionen des stromabwärts des Zeolithspeichers angeordneten Absperrventils und des weiteren Spülventils auch mittels des Wegeventils realisiert werden. The zeolite storage is connected in parallel by means of the valves mentioned, which enable the zeolite storage to be completely separated from the recirculation path. The valves include at least one shut-off valve, which is arranged upstream of the zeolite reservoir and in the closed position Flow through the zeolite storage with recirculation prevented. A further shut-off valve or a directional valve, preferably a 3/2-way valve, can be arranged downstream of the zeolite reservoir. If a further shut-off valve is provided, the water desorbed during the regeneration of the zeolite reservoir can be discharged via the flushing valve, which is usually provided and opens into the cathode exhaust gas path. Alternatively or additionally, the desorbed water can also be introduced into an additional flushing path via a further flushing valve. If an additional scavenging path is provided, the functions of the shut-off valve arranged downstream of the zeolite reservoir and of the further scavenging valve can also be implemented by means of the directional control valve.
Das vorgeschlagene Brennstoffzellensystem ist insbesondere zur Durchführung des zuvor beschriebenen erfindungsgemäßen Verfahrens geeignet. Mit Hilfe des Brennstoffzellensystems sind demnach die gleichen Vorteile erzielbar. Ferner kann der Zeolithspeicher analog dem zuvor beschriebenen Zeolithspeicher ausgeführt und/oder an das System angebunden sein. The proposed fuel cell system is particularly suitable for carrying out the method according to the invention described above. Accordingly, the same advantages can be achieved with the aid of the fuel cell system. Furthermore, the zeolite reservoir can be designed analogously to the zeolite reservoir described above and/or connected to the system.
In Weiterbildung des erfindungsgemäßen Brennstoffzellensystems wird vorgeschlagen, dass in den Zeolithspeicher eine elektrische Heizeinrichtung integriert ist, so dass der Zeolithspeicher zur Desorption von Wasser erwärmbar ist. Mittels der elektrischen Heizeinrichtung kann der Zeolithspeicher schnell auf die zur Desorption erforderliche Temperatur von etwa 250°C gebracht werden. Im Adsorptionsfall, insbesondere bei einem Kaltstart, kann zudem der Zeolithspeicher mit Hilfe der elektrischen Heizeinrichtung vorgeheizt werden. In a further development of the fuel cell system according to the invention, it is proposed that an electrical heating device be integrated into the zeolite storage unit, so that the zeolite storage unit can be heated for desorption of water. The zeolite storage device can be quickly brought to the temperature of about 250° C. required for desorption by means of the electrical heating device. In the case of adsorption, in particular in the case of a cold start, the zeolite storage device can also be preheated with the aid of the electrical heating device.
In einer besonders bevorzugten Ausgestaltung umfasst die elektrische Heizeinrichtung mindestens eine Heizpatrone. Diese kann einfach in eine Schüttung des Zeolithspeichers aus Zeolithmaterial integriert werden. In a particularly preferred embodiment, the electrical heating device comprises at least one heating cartridge. This can easily be integrated into a bed of zeolite material in the zeolite store.
Des Weiteren wird vorgeschlagen, dass der Zeolithspeicher über das Wegeventil und/oder mindestens ein Spülventil an einen Kathodenabgaspfad und/oder an die Umgebung angebunden ist, so dass desorbiertes Wasser aus dem Zeolithspeicher in den Kathodenabgaspfad einleitbar oder an die Umgebung abgebbar ist. Letzteres ist möglich, da der Gehalt an Restwasserstoff, insbesondere nach einem ersten Spülvorgang, in der Regel sehr gering ist. Beim erstmaligen Spülen wird vorzugsweise die Spülmenge in den Kathodenabgaspfad eingeleitet, um den enthaltenen Restwasserstoff mit der dort vorhandenen Luft zu verdünnen. It is also proposed that the zeolite reservoir is connected to a cathode exhaust gas path and/or to the environment via the directional control valve and/or at least one purge valve, so that desorbed water from the zeolite reservoir can be introduced into the cathode exhaust gas path or discharged to the environment. The latter is possible because the residual hydrogen content is usually very low, in particular after a first rinsing process. When rinsing for the first time, the flushing volume is preferably in the Initiated cathode exhaust path to dilute the residual hydrogen contained with the air present there.
Die Erfindung und ihre Vorteile werden nachfolgend anhand der beigefügten Zeichnungen näher erläutert. Diese zeigen: The invention and its advantages are explained in more detail below with reference to the accompanying drawings. These show:
Fig. 1 eine schematische Darstellung eines ersten erfindungsgemäßen Brennstoffzellensystems zur Durchführung des erfindungsgemäßen Verfahrens, 1 shows a schematic representation of a first fuel cell system according to the invention for carrying out the method according to the invention,
Fig. 2 die Umsetzung des erfindungsgemäßen Verfahrens mit Hilfe des Brennstoffzellensystems der Fig. 1, FIG. 2 the implementation of the method according to the invention with the aid of the fuel cell system of FIG. 1,
Fig. 3 eine schematische Darstellung eines zweiten erfindungsgemäßen Brennstoffzellensystems zur Durchführung des erfindungsgemäßen Verfahrens, 3 shows a schematic representation of a second fuel cell system according to the invention for carrying out the method according to the invention,
Fig. 4 die Umsetzung des erfindungsgemäßen Verfahrens mit Hilfe des Brennstoffzellensystems der Fig. 3, 4 shows the implementation of the method according to the invention with the aid of the fuel cell system of FIG. 3,
Fig. 5 eine alternative Umsetzung des erfindungsgemäßen Verfahrens mit Hilfe des Brennstoffzellensystems der Fig. 3 und 5 shows an alternative implementation of the method according to the invention using the fuel cell system of FIGS
Fig. 6 eine schematische Darstellung eines dritten erfindungsgemäßen Brennstoffzellensystems zur Durchführung des erfindungsgemäßen Verfahrens. 6 shows a schematic representation of a third fuel cell system according to the invention for carrying out the method according to the invention.
Ausführliche Beschreibung der Zeichnungen Detailed description of the drawings
Das in der Fig. 1 dargestellte Brennstoffzellensystem umfasst mindestens eine Brennstoffzelle 1, die anodenseitig über einen Anodenpfad 2 mit einem Anodengas, und zwar mit Wasserstoff aus einem Tank 11 versorgbar ist. Die Versorgung mit frischen Wasserstoff ist über ein Ventil 12 steuerbar. Da das aus der Brennstoffzelle 1 austretende Anodenabgas noch einen Rest an Wasserstoff enthält, wird dieses über einen Rezirkulationspfad 3 rezirkuliert bzw. wieder in den Anodenpfad 2 eingeleitet. Die Rezirkulation wird vorliegend aktiv mittels eines Rezirkulationsgebläses 13 unterstützt. Im Anodenpfad 2 wird dem Rezirkulat frischer Wasserstoff aus dem Tank 11 beigemischt. Da das rezirkulierte Anodenabgas neben Wasserstoff auch Wasser, und zwar flüssiges sowie gasförmiges Wasser bzw. Wasserdampf, enthält, weist das in der Fig. 1 dargestellte Brennstoffzellensystem darüber hinaus einen Zeolithspeicher 4 zum Entfeuchten des Rezirkulats auf. Der Zeolithspeicher 4 ist über ein erstes Absperrventil 5 und ein zweites Absperrventil 6 an den Rezirkulationspfad 3 angebunden bzw. parallel geschaltet. In Offenstellung der Absperrventile 5, 6 wird der Zeolithspeicher 4 von dem Rezirkulat durchströmt, wobei diesem das enthaltene Wasser mittels Adsorption entzogen wird. Hierbei entsteht Wärme, die beispielsweise beim Kaltstart des Systems dazu genutzt werden kann, das System schneller auf Betriebstemperatur zu bringen. Ergänzend kann der Zeolithspeicher 4 mittels einer integrierten elektrischen Heizeinrichtung 8 erwärmt werden. Dies ist insbesondere bei einem Gefrierstart von Vorteil. The fuel cell system shown in FIG. 1 comprises at least one fuel cell 1 which can be supplied on the anode side via an anode path 2 with an anode gas, namely with hydrogen from a tank 11 . The supply of fresh hydrogen can be controlled via a valve 12. Since the anode waste gas emerging from the fuel cell 1 still contains a residue of hydrogen, this is recirculated via a recirculation path 3 or reintroduced into the anode path 2 . In the present case, the recirculation is actively supported by means of a recirculation fan 13 . In the anode path 2, fresh hydrogen from the tank 11 is added to the recirculated material. Since the recirculated anode waste gas also contains water in addition to hydrogen, namely liquid and gaseous water or water vapor, the fuel cell system shown in FIG. 1 also has a zeolite storage device 4 for dehumidifying the recirculated material. The zeolite reservoir 4 is connected to the recirculation path 3 or connected in parallel via a first shut-off valve 5 and a second shut-off valve 6 . When the shut-off valves 5, 6 are in the open position, the recirculated material flows through the zeolite reservoir 4, with the water contained therein being withdrawn by means of adsorption. This generates heat that can be used, for example, when the system is cold started, to bring the system up to operating temperature more quickly. In addition, the zeolite storage device 4 can be heated by means of an integrated electrical heating device 8 . This is particularly advantageous in the case of a freezing start.
Da sich das Anodengas im Betrieb des Brennstoffzellensystems ferner mit Stickstoff anreichern kann, der beispielsweise von der (nicht dargestellten) Kathodenseite auf die Anodenseite diffundiert, müssen der Anodenpfad 2 und der Rezirkulationspfad 3 von Zeit zu Zeit gespült werden. Hierzu ist austrittsseitig ein Spülventil 9 vorgesehen, das vorzugsweise in einen (nicht dargestellten) Kathodenabgaspfad öffnet. Die über das Spülventil 9 abgeführte Spülmenge wird dann durch frischen Wasserstoff aus dem Tank 11 ersetzt. Since the anode gas can also be enriched with nitrogen during operation of the fuel cell system, which diffuses, for example, from the cathode side (not shown) to the anode side, the anode path 2 and the recirculation path 3 must be purged from time to time. For this purpose, a purge valve 9 is provided on the outlet side, which preferably opens into a cathode exhaust gas path (not shown). The amount of scavenging discharged via the scavenging valve 9 is then replaced by fresh hydrogen from the tank 11 .
Das in der Fig. 1 dargestellte Spülventil 9 wird vorliegend ferner zur Regeneration des Zeolithspeichers 4 genutzt. Zunächst wird der Zeolithspeicher 4 vom Rezirkulationspfad 3 getrennt und dann mittels der elektrischen Heizeinrichtung 8 auf eine Temperatur von etwa 250°C gebracht, so dass zuvor adsorbiertes Wasser desorbiert wird. Die desorbierte Wassermenge kann anschließend durch Öffnen des Absperrventils 6 und des Spülventils 9 in den Kathodenabgaspfad eingeleitet werden. In der Regel wird das Aufheizen und Spülen des Zeolithspeichers 4 mehrfach wiederholt, bis die desorbierte Menge vollständig aus dem Zeolithspeicher 4 entfernt ist. Wann dies der Fall ist, kann mit Hilfe der Temperatur und/oder des Drucks im Zeolithspeicher 4 überwacht werden. Hierzu sind am Zeolithspeicher 4 jeweils ein Temperatursensor 14 und ein Drucksensor 15 vorgesehen. The scavenging valve 9 shown in FIG. 1 is also used to regenerate the zeolite reservoir 4 in the present case. First, the zeolite reservoir 4 is separated from the recirculation path 3 and then brought to a temperature of approximately 250° C. by means of the electrical heating device 8, so that previously adsorbed water is desorbed. The amount of water desorbed can then be introduced into the cathode exhaust gas path by opening the shut-off valve 6 and the flushing valve 9 . As a rule, the heating and rinsing of the zeolite store 4 is repeated several times until the desorbed quantity has been completely removed from the zeolite store 4 . When this is the case, the temperature and/or the pressure in the zeolite reservoir 4 can be monitored. For this purpose, a temperature sensor 14 and a pressure sensor 15 are provided on the zeolite storage device 4 .
Der genaue Ablauf der Adsorbtions- und Desorptionsphasen des dargestellten Zeolithspeichers 4 wird nachfolgend anhand des Diagramms der Fig. 2 erklärt. Auf dem Zeitstrahl sind die Zeitpunkte tO bis t9 aufgetragen. Zum Zeitpunkt tO tritt systemseitig die Anforderung auf, dem rezirkulierten Anodenabgas Wasser bzw. Wasserdampf zu entziehen und ggf. Wärme einzubringen, beispielsweise bei einem Gefrierstart. Die beiden Absperrventile 5, 6 werden geöffnet, so dass der Zeolithspeicher 4 von rezirkuliertem Anodenabgas durchströmt wird. Zum Zeitpunkt tl setzt die exotherme Adsorption ein, wobei sich der Zeolithspeicher 4 bis zum Zeitpunkt t2 auf etwa 160°C erwärmt. Je nach Anforderung an die Dynamik und/oder Initialtemperatur können dabei zwei Betriebsarten unterschieden werden: The precise sequence of the adsorption and desorption phases of the zeolite storage device 4 shown is explained below with reference to the diagram in FIG. The times t0 to t9 are plotted on the timeline. At time tO, the system is required to extract water or water vapor from the recirculated anode waste gas and, if necessary, to introduce heat, for example when starting to freeze. The two shut-off valves 5, 6 are opened so that the zeolite reservoir 4 is flowed through by recirculated anode waste gas. At time t1, the exothermic adsorption begins, with the zeolite reservoir 4 heating up to approximately 160° C. by time t2. Depending on the requirements for dynamics and/or initial temperature, two operating modes can be distinguished:
1. ohne Zuführung von elektrischer Energie Peiektr. (durchgezogene Linie Tz), so dass sich der Zeolithspeicher 4 allein über die exotherme Adsorption erwärmt; und 1. without the supply of electrical energy Peiektr. (solid line Tz), so that the zeolite storage device 4 heats up solely via the exothermic adsorption; and
2. mit initialer Zuführung elektrischer Energie Peiektr. (gestrichelte Linie Tz), so dass sich der Zeolithspeicher 4 durch die exotherme Adsorption und der von außen hinzugeführten elektrischen Energie Peiektr. erwärmt. 2. with initial supply of electrical energy Peiektr. (Dashed line Tz), so that the zeolite storage 4 Peiektr by the exothermic adsorption and the electrical energy supplied from the outside. heated.
Grundsätzlich reicht die Kinetik des Adsorptionsprozesses zur Erwärmung des Zeolithspeichers 4 aus, so dass der Variante 1 gefolgt werden kann. Bei besonders tiefen Außentemperaturen, beispielsweise bei -40°C, wenn die Kinetik sehr langsam ist und die Anforderungen des Systems an das dynamische Verhalten des Zeolithspeichers 4 sonst nicht erfüllt werden, erweist sich Variante 2 als vorteilhaft. Basically, the kinetics of the adsorption process for heating the zeolite storage 4 are sufficient, so that variant 1 can be followed. At particularly low outside temperatures, for example at -40° C., when the kinetics are very slow and the system requirements for the dynamic behavior of the zeolite storage device 4 are otherwise not met, variant 2 proves to be advantageous.
Zum Zeitpunkt t2 wird die systemseitige Anforderung, Wasser in den Zeolithspeicher 4 einzulagern zurückgenommen, da beispielsweise kein Wasser mehr eingelagert werden kann oder kein solcher Bedarf mehr besteht. Da die Absperrventile 5, 6 weiterhin geöffnet sind, wird der Zeolithspeicher 4 weiterhin durchströmt. Denn zum Schließen der Absperrventile 5, 6 wird ein geeigneter Zeitpunkt abgewartet. Dieser ist beispielsweise dann erreicht, wenn eine maximale Wasserstoffkonzentration Xns.max im Zeolithspeicher 4 unterschritten wird. Auf diese Weise können die Wasserstoffverluste bei der nachfolgenden Regeneration des Zeolithspeichers 4 gering gehalten werden. Nach dem Schließen der beiden Absperrventile 5, 6 zum Zeitpunkt tshut-off ändert sich die Gaszusammensetzung im Zeolithspeicher 4 zunächst nicht mehr. Zum Zeitpunkt t3 soll der Zeolithspeicher 4 regeneriert werden. Dazu wird das Zeolithmaterial mittels der elektrischen Heizeinrichtung 8 auf etwa 250°C erwärmt, um Wasser aus dem Zeolithspeicher 4 zu desorbieren. Dadurch, dass beide Absperrventile 5, 6 geschlossen sind, werden Wärmeverluste minimal gehalten. Das Erhitzen des Zeolithspeichers 4 ist zudem unabhängig vom System möglich. At time t2, the system-side request to store water in the zeolite reservoir 4 is withdrawn because, for example, no more water can be stored or there is no longer any need for it. Since the check valves 5, 6 are still open, the flow through the zeolite storage tank 4 continues. Because to close the check valves 5, 6, a suitable time is awaited. This is reached, for example, when a maximum hydrogen concentration Xns.max in the zeolite reservoir 4 is undershot. In this way, the hydrogen losses during the subsequent regeneration of the zeolite store 4 can be kept low. After the two shut-off valves 5, 6 have been closed at the point in time tshut-off, the gas composition in the zeolite reservoir 4 initially no longer changes. The zeolite storage device 4 is to be regenerated at time t3. For this purpose, the zeolite material is heated to approximately 250° C. by means of the electrical heating device 8 in order to desorb water from the zeolite storage unit 4 . Because both check valves 5, 6 are closed, heat losses are kept to a minimum. The heating of the zeolite storage 4 is also possible independently of the system.
Zum Zeitpunkt t4 wird die Desorptionstemperatur von 250°C erreicht und der Zeolithspeicher 4 gibt das zuvor adsorbierte Wasser wieder als Wasserdampf an das Volumen des Zeolithspeichers 4 ab. Dies hat zur Folge, dass der Druck im Zeolithspeicher 4 ansteigt, was als Messgröße für die desorbierte Wassermenge verwendet werden kann. At time t4, the desorption temperature of 250° C. is reached and the zeolite reservoir 4 releases the previously adsorbed water back into the volume of the zeolite reservoir 4 as water vapor. The consequence of this is that the pressure in the zeolite reservoir 4 increases, which can be used as a measured variable for the amount of water desorbed.
Zum Zeitpunkt t5 wird bzw. werden ein maximaler Druck und/oder eine maximale Temperatur im Zeolithspeicher 4 überschritten, so dass die elektrische Heizeinrichtung 8 abgestellt wird. Ferner wird eine Anfrage an das System gestellt, ob die geforderten Verdünnungsbedingungen („dilution constraint“) zum Spülen des Systems vorliegen. Ergeht eine positive Rückmeldung, werden das Absperrventil 6 und das Spülventil 9 geöffnet und das Wasserstoff- Wasserdampf-Gasgemisch wird aus dem Zeolithspeicher 4 herausgespült. In dieser Phase ist kein oder nur ein eingeschränkter Betrieb des Brennstoffzellensystems möglich. At time t5, a maximum pressure and/or a maximum temperature in the zeolite reservoir 4 is or are exceeded, so that the electrical heating device 8 is switched off. In addition, a query is sent to the system as to whether the required dilution conditions (“dilution constraint”) for flushing the system are present. If there is positive feedback, 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 reservoir 4 . In this phase, no or only limited operation of the fuel cell system is possible.
Nach einem ersten Spülvorgang wird zum Zeitpunkt t6 das Absperrventil 6 wieder geschlossen und die Vorgänge Aufheizen des Zeolithspeichers 4 und Spülen solange wiederholt, bis die gewünschte Wassermenge aus dem Zeolithspeicher 4 ausgetrieben und die Regeneration des Zeolithspeichers 4 abgeschlossen ist. Als Abbuchkriterium kann dabei das charakteristische Verhalten von Temperatur- und Druckanstieg im Zeolithspeicher 4 während der Aufheizphase von t3 bis t4 bzw. von t6 bis t7 usw. herangezogen werden. Denn mit zunehmender Regeneration des Zeolithspeichers 4 steigt der Druck im Vergleich zur Temperatur weniger stark an. After a first rinsing process, the check valve 6 is closed again at time t6 and the processes of heating the zeolite reservoir 4 and rinsing are repeated until the desired amount of water is expelled from the zeolite reservoir 4 and the regeneration of the zeolite reservoir 4 is complete. The characteristic behavior of the temperature and pressure increase in the zeolite storage device 4 during the heating-up phase from t3 to t4 or from t6 to t7 etc. can be used as a debit criterion. Because with increasing regeneration of the zeolite storage 4, the pressure rises less than the temperature.
Die aufeinanderfolgenden Phasen sind in der Fig. 2 mit A für Adsorptionsphase, B für Ventilschließphase, C für Aufheizphase und D für Desorptionsphase bezeichnet. Hieran kann sich als Phase E der Shutdown oder Weiterbetrieb des Systems anschließen. Der Fig. 3 ist eine Abwandlung des Systems der Fig. 1 zu entnehmen. Die Abwandlung besteht darin, dass ein weiteres Spülventil 10 vorgesehen ist, das in einen zusätzlichen Spülpfad 16 öffnet. Das weitere Spülventil 10 kann zur Regeneration des Zeolithspeichers 4 unabhängig vom ersten Spülventil 9 und damit unabhängig vom Betrieb des Brennstoffzellensystems geöffnet werden. Das weitere Spülventil 10 ermöglicht somit mehr Freiheitsgrade im Betrieb des Brennstoffzellensystems. The successive phases are denoted in FIG. 2 by A for the adsorption phase, B for the valve closing phase, C for the heating-up phase and D for the desorption phase. This can be followed as phase E by the shutdown or continued operation of the system. FIG. 3 shows a modification of the system of FIG. The modification consists in 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 store 4 . The further scavenging valve 10 thus enables more degrees of freedom in the operation of the fuel cell system.
Die Abläufe im Betrieb des Brennstoffzellensystems der Fig. 3 sind in der Fig. 4 dargestellt. Die Adsorptionsphase A, die Ventilschließphase B und die Aufheizphase C laufen analog den entsprechenden Phasen in der Fig. 2 ab, so dass auf die Beschreibung der Fig. 2 verwiesen wird. Unterschiede bestehen lediglich hinsichtlich der Desorptionsphase D. Die Austragung des Wasserstoff- Wasserdampf-Gasgemischs erfolgt hier über das weitere Spülventil 10 in den zusätzlichen Spülpfad 16. Auch dabei müssen bestimmte Verdünnungsbedingungen eingehalten werden, diese können sich jedoch von den zuvor genannten unterscheiden. Je nach Auslegung des Zeolithspeichers 4 und nach Wahl von Xns.max ist es sogar möglich, das Gasgemisch direkt an die Umgebung abzugeben. The processes during operation of the fuel cell system of FIG. 3 are shown in FIG. The adsorption phase A, the valve closing phase B and the heating phase C proceed analogously to the corresponding phases in FIG. 2, so that reference is made to the description of FIG. The only differences are with regard to the desorption phase D. The hydrogen-water vapor gas mixture is discharged here via the further flushing valve 10 into the additional flushing path 16. Certain dilution conditions must also be observed here, but these can differ from those mentioned above. Depending on the design of the zeolite storage 4 and the choice of Xns.max, it is even possible to release the gas mixture directly into the environment.
Alternativ kann mit Hilfe des Systems der Fig. 3 auch eine kombinierte Spülstrategie gefahren werden. Diese ist beispielhaft in der Fig. 5 dargestellt. Hier werden in der Desorptionsphase D beide Spülventile 9, 10 geöffnet, und zwar zeitversetzt. Bei hohen Wasserstoffkonzentrationen im Zeolithspeicher 4 wird zunächst, zumindest beim ersten Spülvorgang, über das erste Spülventil 9 gespült. Beim zweiten und jedem weiteren Spülvorgang (mit geringer bis vernachlässigbarer Wasserstoffkonzentration) wird über das weitere Spülventil 10 gespült. Diese Strategie ist optimal, um die erforderliche Verdünnung des Restwasserstoffs sicherzustellen. Denn mit Öffnen des ersten Spülventils 9 und Einleiten der Spülmenge in den (nicht dargestellten) Kathodenabgaspfad vermischt sich die Spülmenge mit der dort vorhandenen Luft. Der Normalbetrieb des Brennstoffzellensystems wird dadurch allerdings unterbrochen bzw. gestört. Daher erweist es sich als vorteilhaft, wenn im weiteren Verlauf der Regeneration des Zeolithspeichers 4 die Spülmenge über das weitere Spülventil 10 und den Spülpfad 16 abgeführt wird. Denn dieser Vorgang beeinflusst den Betrieb des Brennstoffzellensystems nicht. Eine weitere Abwandlung des erfindungsgemäßen Brennstoffzellensystems ist in der Fig. 6 dargestellt. Hier werden die Funktionen des Absperrventils 6 und des weiteren Spülventils 10 durch ein 3/2-Wegeventil 7 realisiert. Der Aufbau des Brennstoffzellensystems kann dadurch vereinfacht werden, da ein Ventil eingespart wird. Alternatively, a combined scavenging strategy can also be used with the aid of the system in FIG. 3 . This is shown as an example in FIG. Here, in the desorption phase D, both flushing valves 9, 10 are opened, with a time delay. In the case of high hydrogen concentrations in the zeolite reservoir 4, at least during the first scavenging process, scavenging is carried out via the first scavenging valve 9. During the second and every further flushing process (with a low to negligible hydrogen concentration), flushing takes place via the further flushing valve 10 . This strategy is optimal to ensure the necessary dilution of the residual hydrogen. Because when the first scavenging valve 9 is opened and the scavenging quantity is introduced into the cathode exhaust gas path (not shown), the scavenging quantity mixes with the air present there. However, the normal operation of the fuel cell system is thereby interrupted or disturbed. It therefore proves to be advantageous if the scavenging quantity is discharged via the further scavenging valve 10 and the scavenging path 16 in the further course of the regeneration of the zeolite reservoir 4 . Because this process does not affect the operation of the fuel cell system. A further modification of the fuel cell system according to the invention is shown in FIG. Here the functions of the shut-off valve 6 and the additional flushing valve 10 are implemented by a 3/2-way valve 7 . The structure of the fuel cell system can be simplified as a valve is saved.

Claims

Ansprüche Expectations
1. Verfahren zum Betreiben eines Brennstoffzellensystems, bei dem mindestens einer Brennstoffzelle (1) über einen Anodenpfad (2) Wasserstoff und über einen Kathodenpfad Sauerstoff zugeführt wird und bei dem aus der Brennstoffzelle (1) austretendes Anodenabgas über einen Rezirkulationspfad (3) rezirkuliert wird, wobei im Anodenabgas enthaltener Wasserdampf mittels eines Zeolithspeichers (4) adsorbiert wird, dadurch gekennzeichnet, dass zur Regeneration des Zeolithspeichers (4) folgende Schritte ausgeführt werden: a) Trennen des Zeolithspeichers (4) vom Rezirkulationspfad (3) durch Schließen mindestens eines Absperrventils (5, 6) und/oder Schalten eines Wegeventils (7), b) Erwärmen des Zeolithspeichers (4) mittels einer elektrischen Heizeinrichtung (8), so dass zuvor adsorbiertes Wasser desorbiert wird, und c) Entfernen von desorbiertem Wasser aus dem System durch erneutes Schalten des Wegeventils (7) und/oder durch Öffnen mindestens eines Spülventils (9, 10). 1. A method for operating a fuel cell system, in which at least one fuel cell (1) is supplied with hydrogen via an anode path (2) and oxygen via a cathode path, and in which anode exhaust gas exiting the fuel cell (1) is recirculated via a recirculation path (3), wherein the water vapor contained in the anode exhaust gas is adsorbed by means of a zeolite store (4), characterized in that the following steps are carried out to regenerate the zeolite store (4): a) separating the zeolite store (4) from the recirculation path (3) by closing at least one shut-off valve (5 , 6) and/or switching a directional control valve (7), b) heating the zeolite storage device (4) by means of an electric heating device (8) so that previously adsorbed water is desorbed, and c) removing desorbed water from the system by switching again of the directional control valve (7) and/or by opening at least one flushing valve (9, 10).
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass Schritt a) mit Unterschreiten einer maximalen Wasserstoffkonzentration (Xns.max) und/oder eines maximalen Wasserstoffpartialdrucks (pns) im Rezirkulationspfad (3) eingeleitet wird. 2. The method as claimed in claim 1, characterized in that step a) is initiated when the concentration falls below a maximum hydrogen concentration (Xns.max) and/or a maximum hydrogen partial pressure (pns) in the recirculation path (3).
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass in Schritt b) der Zeolithspeicher (4) auf eine Temperatur von etwa 250°C erwärmt wird und/oder zum Erwärmen des Zeolithspeichers (4) mindestens eine in den Zeolithspeicher (4) integrierte Heizpatrone als elektrische Heizeinrichtung (8) verwendet wird. 3. The method according to claim 1 or 2, characterized in that in step b) the zeolite storage (4) is heated to a temperature of about 250 ° C and / or for heating the zeolite storage (4) at least one in the zeolite storage (4) integrated heating cartridge is used as an electrical heating device (8).
4. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der Druck und/oder die Temperatur im Zeolithspeicher (4) gemessen werden und von den Messwerten auf die desorbierte Wassermenge im Zeolithspeicher (4) geschlossen wird. 4. The method as claimed in one of the preceding claims, characterized in that the pressure and/or the temperature in the zeolite reservoir (4) are measured and the amount of water desorbed in the zeolite reservoir (4) is inferred from the measured values.
5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass mit Erreichen eines vorgegebenen maximalen Druck- und/oder Temperaturgrenzwerts im Zeolithspeicher (4) die Erwärmung des Zeolithspeichers (4) beendet wird. 5. The method according to any one of the preceding claims, characterized in that when a predetermined maximum pressure and / or temperature limit in the zeolite storage (4) heating of the zeolite storage (4) is terminated.
6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass vor Einleiten von Schritt c) geprüft wird, ob bestimmte Bedingungen, insbesondere Verdünnungsbedingungen, zum Öffnen eines Spülventils (9, 10) vorliegen. 6. The method according to any one of the preceding claims, characterized in that before initiating step c) it is checked whether certain conditions, in particular dilution conditions, for opening a flushing valve (9, 10) are present.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass in Schritt c) desorbiertes Wasser über das Wegeventil (7) und/oder das mindestens eine Spülventil (9, 10) in einen Kathodenabgaspfad eingeleitet oder an die Umgebung abgegeben wird. 7. The method according to any one of the preceding claims, characterized in that in step c) desorbed water via the directional valve (7) and / or the at least one purge valve (9, 10) is introduced into a cathode exhaust gas path or discharged to the environment.
8. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass in Schritt c) mindestens ein Absperrventil (5, 6) geöffnet wird, so dass desorbiertes Wasser aus dem Zeolithspeicher (4) dem mindestens einen Spülventil (9, 10) zugeführt wird. 8. The method according to any one of the preceding claims, characterized in that in step c) at least one shut-off valve (5, 6) is opened so that desorbed water from the zeolite reservoir (4) is fed to the at least one flushing valve (9, 10).
9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Schritte a) bis c) mindestens einmal, vorzugsweise mehrmals, wiederholt wird, wobei vorzugsweise beim erstmaligen Spülen ein erstes Spülventil (9) und beim wiederholten Spülen ein zweites Spülventil (10) geöffnet werden. - 18 - 9. The method according to any one of the preceding claims, characterized in that steps a) to c) are repeated at least once, preferably several times, with a first flushing valve (9) preferably being used for the first flushing and a second flushing valve (10) for repeated flushing. be opened. - 18 -
10. Brennstoffzellensystem mit mindestens einer Brennstoffzelle (1), der über einen Anodenpfad (2) Wasserstoff und über einen Kathodenpfad Sauerstoff zuführbar ist, umfassend einen Rezirkulationspfad (3), über den aus der Brennstoffzelle (1) austretendes Anodenabgas rezirkulierbar ist, sowie einen Zeolithspeicher (4), mittels dessen im Anodenabgas enthaltener Wasserdampf adsorbierbar ist, dadurch gekennzeichnet, dass der Zeolithspeicher (4) über mindestens ein Absperrventil (5, 6) und/oder ein Wegeventil (7) zu- und abschaltbar ist. 10. Fuel cell system with at least one fuel cell (1), to which hydrogen can be supplied via an anode path (2) and oxygen via a cathode path, comprising a recirculation path (3) via which anode exhaust gas exiting the fuel cell (1) can be recirculated, and a zeolite storage device (4) by means of which the water vapor contained in the anode waste gas can be adsorbed, characterized in that the zeolite reservoir (4) can be switched on and off via at least one shut-off valve (5, 6) and/or a directional control valve (7).
11. Brennstoffzellensystem nach Anspruch 10, dadurch gekennzeichnet, dass in den Zeolithspeicher (4) eine elektrische Heizeinrichtung (8), vorzugsweise mindestens eine Heizpatrone, integriert ist, so dass der Zeolithspeicher (4) zur Desorption von Wasser erwärmbar ist. 11. The fuel cell system as claimed in claim 10, characterized in that an electrical heating device (8), preferably at least one heating cartridge, is integrated into the zeolite storage unit (4), so that the zeolite storage unit (4) can be heated for the desorption of water.
12. Brennstoffzellensystem nach Anspruch 10 oder 1, dadurch gekennzeichnet, dass der Zeolithspeicher (4) über das Wegeventil (7) und/oder mindestens ein Spülventil (9, 10) an einen Kathodenabgaspfad und/oder an die Umgebung angebunden ist, so dass desorbiertes Wasser aus dem Zeolithspeicher (4) in den Kathodenabgaspfad einleitbar oder an die Umgebung abgebbar ist. 12. Fuel cell system according to claim 10 or 1, characterized in that the zeolite storage (4) via the directional valve (7) and / or at least one purge valve (9, 10) is connected to a cathode exhaust gas path and / or to the environment, so that desorbed Water from the zeolite reservoir (4) can be introduced into the cathode exhaust gas path or released into the environment.
EP21754701.7A 2020-08-06 2021-07-19 Method for operating a fuel cell system, and fuel cell system Pending EP4193405A1 (en)

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