Method of operating a fuel cell device and fuel cell device

Abstract

The present invention provides a method of operating a fuel cell apparatus (10), comprising ensuring (S1) a predetermined hydrogen concentration in the anode circuit of a fuel cell stack (BS), switching off (S4) hydrogen recirculation in the anode circuit or reducing the hydrogen recirculation in the anode circuit to a predetermined recirculation volumetric flow rate or below a predetermined recirculation volumetric flow rate (S4a), and drying (S5) the cathode of the fuel cell stack (BS).

Description

[Technical Field]

[0001] The present invention relates to a method of operating a fuel cell device and to a fuel cell device. [Background technology]

[0002] Known fuel cells can operate on a hydrogen basis, emitting only water as an exhaust gas, allowing for fast refueling times and are therefore considered a mobility concept for the future.

[0003] Known fuel cell systems require air and hydrogen for the chemical reaction, and the waste heat of the fuel cell stack can typically be removed using a cooling circuit and vented to the ambient environment by a main vehicle cooler. It can be advantageous to heat the stack as quickly as possible, particularly during startup of the fuel cell system below 0°C. In this regard, rapid heating can eliminate or substantially eliminate the accumulation of water or ice that would otherwise make startup difficult or impossible. However, the risk of icing can only be reduced or avoided if the coolant is heated above 0°C and pumped into the stack, thereby reducing or avoiding freezing conditions.

[0004] In such a conventional cold start below 0°C (Gefrierstart), the coolant can be heated either externally to the stack or by an electrochemical reaction in the stack. This can prolong the start-up process in both cases (e.g., at -30°C, reaching 50% load after 30 seconds). Furthermore, in this case, the cells (and the system) may need to have a higher ice tolerance in order to continue cooling below 0°C. This can be achieved, for example, by incorporating an ice buffer in the cell and a heater in the system.

[0005] Patent Document 1 describes a tank having a joint and a valve, the valve being attached to the joint. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent No. 112006003013 Summary of the Invention

[0007] The present invention provides a method for operating a fuel cell device as claimed in claim 1 and a fuel cell device as claimed in claim 10 .

[0008] Preferred developments are the subject of the dependent claims.

[0009] The idea underlying the present invention is to provide a method for operating a fuel cell device and a fuel cell device, which can achieve an operating strategy for shutting down a vehicle and, in the process, reduce the humidity inside the fuel cell stack during the drying process of the fuel cell stack.

[0010] The method according to the invention and the fuel cell device designed therefor can achieve a faster drying process of the fuel cell stack, which can lead to an increase in the energy efficiency of the fuel cell. In this case, a comfortable after-run behavior of the control device can also be achieved by reducing the duration of unattended operation of components with associated noise levels after the vehicle is shut down (the fuel cell control unit (FCCU) can perform after-run operations to dry the fuel cell operation after the vehicle is shut down).

[0011] Furthermore, the cell drying can be made more reliable, which can lead to more reliable and robust cold starts, especially in extreme external conditions (low temperatures).

[0012] Furthermore, for example, ice buffer measures in the stack and system can be omitted or the effort required for such measures can be significantly reduced, thereby achieving a reduction in the cost of the fuel cell device.

[0013] Additionally, during cold start-up, the useful life of the stack can be extended by shortening the duration of the drying process with reduced localized drying of the membrane and preventing or reducing cell icing that can lead to irreversible failure.

[0014] According to the invention, a method includes ensuring a predetermined hydrogen concentration in the anode circuit of a fuel cell stack, switching off hydrogen recirculation in the anode circuit or reducing the hydrogen recirculation in the anode circuit to a predetermined recirculation volumetric flow rate or below a predetermined recirculation volumetric flow rate, and drying the cathode of the fuel cell stack.

[0015] According to this method, the hydrogen concentration can be increased, for example, by a relatively long purge process, to operate the fuel cell device. In this case, the purge process can be used to ensure and to exchange hydrogen in the anode circuit, whereby the amount of hydrogen extracted or introduced can be taken into account, thereby inferring the pressure situation and / or hydrogen concentration in the anode circuit after the purge process. If the hydrogen concentration can be measured, during this increase / guarantee, the detected hydrogen concentration is compared with a specified hydrogen concentration value or a specified interval and the hydrogen concentration in the anode circuit is assimilated to at least the specified value or the specified interval, and the hydrogen recirculation in the anode circuit is switched off or reduced to a specified recirculation volumetric flow rate or below the recirculation volumetric flow rate, and the cathodes of the fuel cell stack are dried.

[0016] The specified value or specified interval can be preset by the manufacturer or user of the fuel cell stack, stored in the control device, or receivable by the control device, and can be set so that the expected functional form and desired functional range of the fuel cell stack operation can be achieved while respecting this specified value or specified interval. The assimilation of the hydrogen concentration can be achieved by a valve, for example, by a valve that releases or injects hydrogen into the anode circuit from a hydrogen supply or to a hydrogen release.

[0017] Cathode drying is accomplished by passing a stream of air through the stack in significant excess of stoichiometry.

[0018] The predetermined recirculation volumetric flow rate may correspond to such a recirculation volumetric flow rate in the anode circuit that is required for the normal, average, or desired operating mode / performance of the fuel cell stack and that is selected by the manufacturer or user and can be stored or received as such in the controller.

[0019] A suitably effective drying process during the vehicle shutdown phase can be decisive, which corresponds to the cessation of vehicle operation and the subsequent vehicle and drive shutdown period, as well as the start-up phase that follows after a relatively long time, for example when the external temperature is low.

[0020] According to a preferred embodiment of the method, the assurance involves a comparison of the hydrogen concentration with a defined value or defined interval of the hydrogen concentration and an assimilation of the hydrogen concentration in the anode circuit to at least the defined value or defined interval.

[0021] According to a preferred embodiment of the method, the fuel cell device includes a fuel cell stack cathode drying requirement, followed by initiation of a fuel cell stack drying operation mode, which can be triggered, for example, by an ambient temperature being below 0° C. or expected to be below 0° C.

[0022] The operating mode of the fuel cell stack for drying can correspond to the drying of the cathode according to the invention with monitoring methods (loop methods) for the recirculation and / or supply of hydrogen in the anode circuit.

[0023] According to a preferred embodiment of the method, before switching off the fuel cell process, it is detected via an ambient environment check device whether drying of the cathodes of the fuel cell stack should be carried out and / or whether a command to dry the cathodes of the fuel cell stack has been received from a user.

[0024] According to a preferred embodiment of the method, a cold start of the fuel cell stack is performed after shutting down the operation of the fuel cell stack to dry out.

[0025] In this case, cold start corresponds to the initiation of operation of the fuel cell stack (the necessary supply of reactant gases and operation of the components / parts required therefor) when the vehicle's ambient environment is below 0°C.

[0026] According to a preferred embodiment of the method, after switching off or reducing the hydrogen recirculation, or in order to reduce the hydrogen recirculation, the hydrogen supply to the anode circuit is switched off or reduced to a predetermined feed volumetric flow rate or below a predetermined feed volumetric flow rate.

[0027] According to a preferred embodiment of the method, after switching off or reducing the hydrogen supply, the anode pressure of hydrogen in the anode circuit at the anode is monitored until it reaches or falls below a lower specified value of the anode pressure, and then it is detected whether drying is complete, and if so, drying is subsequently terminated.

[0028] According to a preferred embodiment of the method, if it is detected that the drying is not yet complete, the hydrogen supply is switched on or increased again, after which the anode pressure is monitored until it exceeds or reaches an upper specified value for the anode pressure, then the hydrogen circulation is reduced or switched off again, the hydrogen supply is reduced or switched off, the anode pressure is monitored until it falls below or reaches a lower specified value for the anode pressure, then it is detected again whether the drying is complete, if it is detected that the drying is complete, then the drying is stopped, and if it is detected that the drying is not yet complete, the hydrogen supply is increased or switched on again, and the control of the anode pressure between the upper and lower specified values ​​is repeated until the drying is complete.

[0029] The method can remain in a loop as long as the drying is not yet complete, i.e., as long as the corresponding drying parameter has not yet reached or is above / below its target value. According to the present invention, the anode pressure can be adjusted between an upper and lower setpoint during the control of the hydrogen recirculation and / or supply. To determine whether the drying is not yet complete, for example, the operation can be time-controlled, interrupted after a certain drying time, and the success of the next cold start can be checked. Meanwhile, the degree of dryness can be estimated by measuring the cathode or anode outlet humidity, visually observing the water in the exhaust system, or visually observing the membrane impedance.

[0030] According to a preferred embodiment of the method, immediately after increasing or switching on the hydrogen supply, the hydrogen recirculation is also increased or switched on.

[0031] In a loop process, after each increase or switch-on of the hydrogen supply, the hydrogen recirculation can also be increased or switched on. This can be particularly useful for systems where the hydrogen recirculation is passive or partially passive, since the recirculation can be maintained as long as the hydrogen supply can remain switched on.

[0032] According to a preferred embodiment of the method, the reduction and / or increase of the hydrogen supply and / or hydrogen circulation is performed in a sawtooth pattern, which allows the advantages of the method, for example, in the case of low hydrogen circulation, to be combined with the possibility of transporting water out of the anode circuit in phases of high hydrogen circulation.

[0033] According to the present invention, a fuel cell device comprises a fuel cell stack having an anode and a cathode, a hydrogen recirculation circuit at the anode, a hydrogen supply connected to the anode and / or the hydrogen recirculation circuit, a water outlet at the cathode, and a control device connected to the hydrogen supply and / or the hydrogen recirculation circuit and / or the water outlet and configured to carry out the method according to the present invention.

[0034] According to a preferred embodiment of the fuel cell device, it is provided with a pressure sensor at the anode, and the control device can detect the anode pressure using the pressure sensor and compare the anode pressure with an upper and / or lower specified anode pressure value.

[0035] The fuel cell device may also feature the features and advantages described above relating to the method, and vice versa.

[0036] Other features and advantages of embodiments of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0037] [Figure 1] 1 is a schematic diagram of a fuel cell device according to an exemplary embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a method procedure according to an exemplary embodiment of the present invention; [Figure 3] 3 is a block diagram of method steps of a method of operating a fuel cell device according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The invention will now be explained in more detail on the basis of exemplary embodiments shown in the diagrammatic drawings.

[0039] In the figures, identical or functionally identical elements are provided with the same reference numerals.

[0040] FIG. 1 shows a schematic diagram of a fuel cell device according to an exemplary embodiment of the present invention.

[0041] The fuel cell device 10 comprises a fuel cell stack BS having an anode A and a cathode K, a hydrogen recirculation circuit WZK at the anode A, a hydrogen supply WZ connected to the anode and / or the hydrogen recirculation circuit WZK, a water outlet WA at the cathode K, and a control device SE, the control device being connected to the hydrogen supply WZ (e.g., a valve for hydrogen supply) and / or the hydrogen recirculation circuit WZK and / or the water outlet WA for discharging water and thereby drying the cathode, and configured to perform the method according to the present invention and to control the components. The fuel cell device 10 may comprise a pressure sensor DS at the anode A, which the control device can use to detect the anode pressure, and the anode pressure can be detected at an upper and / or lower predetermined anode pressure value. The control device SE may also be connected to further valves, sensors, and pumps in the fuel cell device.

[0042] The water outlet WA component can also be located in the anode-side hydrogen recirculation circuit WZK, for which the anode-side water separator can include a first valve V1 for hydrogen and a second valve V2 for water (respectively for discharge) or multiple valves. The hydrogen supply can be connected to a circulation pump ZP.

[0043] Figure 2 shows a schematic diagram of the steps of a method according to an exemplary embodiment of the present invention. In Figure 2, a loop method is shown, and the method according to the present invention can be carried out in such or similar loop fashion.

[0044] According to the method of Fig. 2, the drying process of the fuel cell, generally before the vehicle is shut down and before the operation of the fuel cell is stopped, can be divided into several operating and method steps between the switch-on (start) of drying ST and the end of drying EN, which can then be reached when a predetermined humidity has been released from the cell and / or from the exhaust gas on the cathode side or when a predetermined permissible residual moisture value or residual water content has fallen below the cathode side.

[0045] Before switching off or on the fuel cell process, it can be detected via an ambient environment checking device (sensor, user interface, or optical or electronic monitoring device) whether a drying of the cathodes of the fuel cell stack should be performed and / or whether a command to dry the cathodes of the fuel cell stack is received from the user. This can be advantageously done in conjunction with the recognition of an impending relatively long vehicle shutdown with the fuel cell device switched off. After the operation of the fuel cell stack has stopped, a cold start of the fuel cell stack can be performed after such a drying process.

[0046] First, the hydrogen concentration in the anode circuit of the fuel cell stack (e.g., the inlet flow to the anode and the recirculation flow) can be ensured (S1), followed by or during the comparison (S2) of the detected hydrogen concentration with a predetermined value or predetermined interval of hydrogen concentration and the assimilation (S3) of the hydrogen concentration in the anode circuit to at least the predetermined value or predetermined interval, and the hydrogen concentration can be increased, decreased, or maintained at this predetermined value or predetermined interval. This step can advantageously provide the anode circuit with the hydrogen concentration SL1 required, which may be necessary for the drying process and / or the operation of the fuel cell.

[0047] In a next step SL2, the hydrogen recirculation in the anode circuit can be switched off or reduced to a predetermined recirculation volumetric flow rate or below a predetermined recirculation volumetric flow rate (S4, S4a).

[0048] In a further optional subsequent step SL2a, the hydrogen supply to the anode circuit can now be switched off or reduced to a predetermined supply volume flow rate or below a predetermined supply volume flow rate.

[0049] Furthermore, in the next step SL3, after the hydrogen supply has been switched off or reduced, or if step SL2a of switching off the hydrogen supply has not been performed and only the recirculation has been reduced or switched off, the anode pressure of hydrogen in the anode circuit at the anode is monitored until it reaches or falls below a specified anode pressure value, and if the anode pressure is within this value range, then in the next step SL4 it is detected whether drying is complete, and if it is detected that drying is complete (condition j), then in step EN drying is terminated and if it is detected that drying is not yet complete (condition n), then in the next step SL5 the hydrogen supply is switched on again or increased, and then, optionally, in the next step SL5a hydrogen recirculation can be switched on or increased.

[0050] Also after increasing or switching on the hydrogen supply or optionally switching on or increasing the recirculation in step SL5a, in the next step SL6 the anode pressure is monitored until the anode pressure exceeds or reaches the upper specified value of the anode pressure, then step SL2 is performed again, the hydrogen circulation is reduced or switched off again and the already mentioned steps SL2 to SL4 can be repeated, and if the drying process is completed, the drying is ended after step SL4 in EN, otherwise the loop is performed again with steps SL5 to SL6, and again step SL2 and the next loop are executed to switch off or reduce the recirculation.

[0051] Thus, after the drying process has begun, it can first be ensured that the hydrogen concentration in the anode circuit is sufficiently high, which can be achieved by sufficient introduction of hydrogen and / or by so-called sufficient "purging" and corresponding measurement of the hydrogen concentration. Subsequently, the recirculation can be switched off or significantly reduced, for example, by switching off the recirculation fan. This can switch off or significantly reduce the humidity inside the cell, and the drying of the cathode can efficiently remove water from the cell. An additional optional measure can be to switch off or reduce the hydrogen supply. This is particularly useful for systems in which hydrogen recirculation is passive or partially passive, since recirculation can be maintained as long as the hydrogen supply remains switched on.

[0052] If the hydrogen supply is completely switched off and the anode pressure falls below a certain threshold or reaches a certain threshold, for example, a lower specified value of 1.1 bar, and the drying process is not yet complete, the hydrogen supply is switched on again or increased, or optionally the hydrogen recirculation is increased again. These measures may be necessary to ensure that hydrogen starvation and therefore cell degradation does not occur or that the risk is at least reduced. If the anode pressure exceeds or reaches a threshold, i.e., an upper specified value of 1.4 bar, for example, the hydrogen recirculation or hydrogen supply can be switched off again. This control can also ensure that the pressure difference with the cathode is not too high (for example, above 0.5 bar) or that the risk is at least reduced.

[0053] Alternatively to the mentioned operating strategy, the hydrogen recirculation or hydrogen supply can be switched off and on on a time basis during the loop or independently of the loop. Furthermore, this can be controlled using indirect or direct detection of the hydrogen concentration in the anode circuit. Furthermore, the reduction or increase of the hydrogen recirculation or hydrogen supply can be performed in a sawtooth pattern.

[0054] FIG. 3 shows a block diagram of method steps of a method of operating a fuel cell device according to an exemplary embodiment of the present invention.

[0055] The method for operating a fuel cell device includes ensuring a predetermined hydrogen concentration in the anode circuit of the fuel cell stack (S1), switching off the hydrogen recirculation in the anode circuit (S4) or reducing the hydrogen recirculation in the anode circuit to a predetermined recirculation volumetric flow rate or below a predetermined recirculation volumetric flow rate (S4a), and drying the cathodes of the fuel cell stack (S5). The ensuring (S1) can include comparing the hydrogen concentration with a predetermined value or a predetermined interval of hydrogen concentration (S2), and assimilating the hydrogen concentration in the anode circuit to at least the predetermined value or a predetermined interval (S3).

[0056] Although the present invention has been fully described above based on preferred exemplary embodiments, the present invention is not limited thereto and can be modified in various ways. [Explanation of symbols]

[0057] 10 Fuel cell device A Anode K cathode DS Pressure Sensor BS fuel cell stack SE control device ST Drying switch on EN End of drying V1 and V2 valves WA water discharge part WZ Hydrogen Supply Department WZK Hydrogen Recirculation Circuit ZP Circulation Pump

Claims

1. A method of operating a fuel cell device (10) comprising the steps of: - ensuring (S1) a predetermined hydrogen concentration in the anode circuit of the fuel cell stack (BS); - switching off (S4) the hydrogen recirculation in the anode circuit or reducing (S4a) the hydrogen recirculation in the anode circuit to a predetermined recirculation volumetric flow rate or below a predetermined recirculation volumetric flow rate, - drying (S5) the cathode of said fuel cell stack (BS); It encompasses after said switching off or reduction of the hydrogen recirculation, or in order to reduce the hydrogen recirculation, the hydrogen supply to the anode circuit is switched off or reduced to a predetermined supply volumetric flow rate or below a predetermined supply volumetric flow rate, After the switching off or reduction of the hydrogen supply, the anode pressure of hydrogen in the anode circuit is monitored until it reaches or falls below a lower predetermined value of the anode pressure, and then, when the anode pressure reaches or falls below the lower predetermined value, it is detected whether the drying is complete, and if it is detected that the drying is complete, then the drying is terminated, If it is detected that the drying is not yet complete, the hydrogen supply is switched on or increased again, then the anode pressure is monitored until it exceeds or reaches the upper predetermined value of the anode pressure, then the hydrogen recirculation is reduced or switched off again, the hydrogen supply is reduced or switched off, and the anode pressure is monitored until it falls below or reaches the lower predetermined value of the anode pressure, then when the anode pressure reaches or is below the lower predetermined value, it is again detected whether the drying is complete, if it is detected that the drying is complete, then drying is stopped, if it is detected that the drying is not yet complete, the hydrogen supply is increased or switched on again, and control of the anode pressure between the upper and lower predetermined values ​​is repeated until the drying is complete. method.

2. 2. The method according to claim 1, wherein the ensuring (S1) comprises comparing (S2) the hydrogen concentration with a specified value (VW) or specified interval of the hydrogen concentration (WK), and / or assimilating (S3) the hydrogen concentration in the anode circuit to at least the specified value (VW) or the specified interval.

3. 3. The method according to claim 1 or 2, wherein before switching off or on a fuel cell process, it is detected via an ambient environment check device whether drying of the cathodes of the fuel cell stack should be performed and / or whether a command to dry the cathodes of the fuel cell stack is received from a user.

4. 3. The method according to claim 1 or 2, wherein the stopping of the operation of the fuel cell stack (BS) to be dried is followed by a cold start of the fuel cell stack.

5. 3. The method according to claim 1 or 2, wherein immediately after increasing or switching on the hydrogen supply, hydrogen recirculation is also increased or switched on.

6. 3. The method of claim 1, wherein the reduction and / or increase of the hydrogen supply and / or the hydrogen recirculation is performed in a sawtooth pattern.

7. A fuel cell device (10), comprising: a fuel cell stack (BS) having an anode (A) and a cathode (K), a hydrogen recirculation circuit (WZK) at said anode (A), a hydrogen supply (WZ) connected to said anode and / or to said hydrogen recirculation circuit (WZK); a water outlet (WA) at said cathode (K), - a control device (SE) connected to the hydrogen supply (WZ) and / or the hydrogen recirculation circuit (WZK) and / or the water discharge (WA) and configured to carry out the method according to claim 1 or 2.

8. 8. The fuel cell device (10) of claim 7, wherein the anode (A) is provided with a pressure sensor, and the control device is capable of detecting the anode pressure using the pressure sensor and comparing the anode pressure with an upper specified value and / or a lower specified value for the anode pressure.

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