Method for 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 exhaust gas and allowing for fast refuelling 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 usually be extracted using a cooling circuit and can be radiated to the surrounding environment with a main vehicle cooler. In that case, it can be advantageous to be able to heat up the stack as quickly as possible, especially during start-up of the fuel cell system below 0° C. In this regard, rapid heating can result in no or almost no accumulation of water or ice that would make it difficult or prevent continued start-up. However, the risk of icing can only be reduced or avoided if a coolant is heated above 0° C. and pumped into the stack, thereby reducing or avoiding freezing conditions.

[0004] In such a conventional sub-0°C cold start (Gefrierstart), the coolant can be heated either externally in the stack or by electrochemical reactions in the stack. This can prolong the start-up process in both cases (e.g. at -30°C, reaching 50% load after 30s). Furthermore, in that case it may be necessary to increase the ice tolerance of the cells (and the system) in order to continue to cool below 0°C. This can be achieved, for example, by incorporating ice buffers (Eispuffers) in the cells and heaters 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, a reduction in humidity inside the fuel cell stack during the drying process of the fuel cell stack.

[0010] By the method according to the invention and the fuel cell device designed therefor, a faster drying process of the fuel cell stack can be achieved, which can lead to an increase in the energy efficiency of the fuel cell, and in that case, a comfortable after-run behavior of the control device can also be achieved by reducing the duration of unattended operation of the 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 drying of the cells can be made more reliable, which can lead to more reliable and robust cold starts, especially in extreme external conditions (low temperatures).

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

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

[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 the method, in order to operate the fuel cell device, an increase in the hydrogen concentration can be performed, for example by a relatively long purge process. In that case, the purge process can be used to ensure and an exchange of hydrogen in the anode circuit can be performed, in which case the amount of hydrogen drawn off or introduced can be taken into account, so that the pressure situation and / or the hydrogen concentration in the anode circuit after the purge process can be inferred. If the hydrogen concentration is measurable, during this increase / guarantee, a comparison of the detected hydrogen concentration with a defined value or a defined interval of the hydrogen concentration and an assimilation of the hydrogen concentration in the anode circuit at least to the defined value or defined interval are performed, the hydrogen recirculation in the anode circuit is switched off or reduced to a predetermined recirculation volume flow rate or below the recirculation volume flow rate, and the cathode of the fuel cell stack is dried.

[0016] The specified values ​​or specified intervals can be preset by the manufacturer or user of the fuel cell stack, can be stored in the control device or can be receivable by the control device and can be set in such a way that the expected functional form and the desired functional range of the operation of the fuel cell stack can be achieved while respecting the specified values ​​or specified intervals. The assimilation of the hydrogen concentration can be achieved by a valve, for example by a valve releasing or injecting hydrogen into the anode circuit from a hydrogen supply or into 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, or average, or desired operating mode / performance of the fuel cell stack and that is selected by the manufacturer or user and that as such can be stored in or received by 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 periods as well as to the start-up phase which follows a relatively long period, for example in the case of low external temperatures.

[0020] According to a preferred embodiment of the method, the assurance involves a comparison of the hydrogen concentration with a defined value or a 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, a recognition of the need for drying a cathode of a fuel cell stack of a fuel cell device and a subsequent initiation of an operating mode of the fuel cell stack to dry are provided, 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 a cathode of the fuel cell stack should be dried and / or whether a command to dry the cathode of the fuel cell stack is 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 that 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 supply volumetric flow rate or below a predetermined supply volumetric flow rate.

[0027] According to a preferred embodiment of the method, after switching off or reducing the hydrogen supply, the anode pressure of the hydrogen in the anode circuit at the anode is monitored until it reaches or falls below a lower defined value of the anode pressure, then it is detected whether the drying is complete, and if so, the 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, then the anode pressure is monitored until it exceeds or reaches an upper defined 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 defined 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 discontinued, 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 defined values ​​is repeated until the drying is complete.

[0029] The method can be in a loop process as long as the drying is not yet complete, in other words as long as the corresponding parameter of the drying has not yet reached its target value or is above / below the target value. The adjustment of the anode pressure between the upper and lower specified values ​​can be performed according to the invention during the control of the hydrogen recirculation and / or supply. To recognize 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, measurements of the cathode or anode outlet humidity, water in the exhaust system, visual observation of the membrane impedance, etc. can be performed, and the degree of dryness can be inferred.

[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 especially meaningful 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 the hydrogen circulation is performed in a sawtooth pattern, whereby the advantages of the method, for example in the case of low hydrogen circulation, can be combined with the possibility of transporting water out of the anode circuit in phases of high hydrogen circulation.

[0033] According to the 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 invention.

[0034] According to a preferred embodiment of the fuel cell device, it is equipped with a pressure sensor at the anode, and the control device can sense the anode pressure by means of the pressure sensor and compare the anode pressure with an upper and / or lower defined value for the anode pressure.

[0035] The fuel cell device may also feature the features and advantages described above in relation 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 description 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. [Diagram 2] FIG. 2 is a schematic diagram of a method procedure according to an exemplary embodiment of the present invention. [Diagram 3] 2 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 PREFERRED EMBODIMENTS

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

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

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

[0041] The fuel cell arrangement 10 comprises a fuel cell stack BS with 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, which is 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 is configured to perform the method according to the invention and to control said components accordingly. The fuel cell arrangement 10 may comprise a pressure sensor DS at the anode A, by means of which the anode pressure can be sensed by the control device, which can be sensed at an upper and / or lower defined value of the anode pressure. The control device SE may also be connected to further valves and sensors and pumps in the fuel cell arrangement.

[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 outlet) 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 invention. In Figure 2, a loop method is shown, and the method according to the invention can be carried out in such or a similar loop fashion.

[0044] According to the method of Fig. 2, the drying process of the fuel cell, generally before shutting down the vehicle and before ceasing operation of the fuel cell, can be divided into several operating and method steps between switching on (starting) drying ST and end of drying EN, whereby the end of drying EN can be reached when a predefined humidity has been released from the cell and / or from the exhaust gas on the cathode side or when it has fallen below a predefined permissible residual moisture value or residual water content on 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 cathode of the fuel cell stack should be performed and / or whether a command is received from the user that a drying of the cathode of the fuel cell stack should be performed. This can advantageously be done in conjunction with the recognition of an impending relatively long stop time of the vehicle with the fuel cell device switched off. After stopping the operation of the fuel cell stack, 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 a comparison (S2) of the detected hydrogen concentration with a specified value or interval of hydrogen concentration and an assimilation (S3) of the hydrogen concentration in the anode circuit to at least the specified value or interval, at which the hydrogen concentration can be increased, decreased or maintained. This step can advantageously provide SL1 the required hydrogen concentration in the anode circuit, which may be necessary for the drying process and / or for 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 next step SL2a, it is now possible to switch off the hydrogen supply to the anode circuit or to reduce the hydrogen supply to the anode circuit to a predefined supply volumetric flow rate or below a predefined supply volumetric flow rate.

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

[0050] Also after the increase or switching on of the hydrogen supply or the optional switching on or increasing of the recirculation in step SL5a, in the next step SL6 the anode pressure is monitored until it exceeds or reaches an upper defined value of the anode pressure, then step SL2 is carried out again, the hydrogen circulation is again reduced or switched off 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, or else the loop is carried out again with steps SL5 to SL6, again going to step SL2 and the next loop for switching off or reducing the recirculation and being carried out.

[0051] Thus, after the drying process has been started, 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. The recirculation can then be switched off or significantly reduced, for example by switching off the recirculation fan. This can thereby be switched off or significantly reduced in the interior of the cell, and the water can be efficiently removed from the cell by drying the cathode. An additional optional measure can be the switching off or reduction of the hydrogen supply. This is particularly meaningful for systems in which the hydrogen recirculation is passive or partially passive, since the 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, for example, 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 thus cell degradation does not occur or that the risk of this is at least reduced. If the anode pressure exceeds or reaches a threshold, i.e. an upper specified value of, for example, 1.4 bar, 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 of this is at least reduced.

[0053] Alternatively to the mentioned operating strategy, the hydrogen recycle or hydrogen supply can be switched off and on in the loop or on a time basis independently of the loop. Moreover, 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 recycle or hydrogen supply can be performed in a sawtooth manner.

[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 invention.

[0055] The method for operating a fuel cell device includes ensuring S1 a predetermined hydrogen concentration in the anode circuit of the fuel cell stack, 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, and drying S5 the cathode of the fuel cell stack. The ensuring S1 can include comparing S2 the hydrogen concentration with a predetermined value or a predetermined interval of hydrogen concentration and assimilating S3 the hydrogen concentration in the anode circuit to at least the predetermined value or a predetermined interval.

[0056] Although the present invention has been completely described above based on the 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, V2 valves WA water discharge section 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 given 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); The method includes:

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

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

4. 2. The method of claim 1, wherein the shutdown of the drying fuel cell stack (BS) is followed by a cold start of the fuel cell stack.

5. 2. The method according to claim 1, wherein after the switching off or reduction of the hydrogen recirculation or for reducing 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.

6. 6. The method according to claim 5, wherein after the switching off or reduction of 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 defined value of the anode pressure, and then it is detected whether the drying is complete, and if it is detected that the drying is complete, then the drying is terminated.

7. 7. The method according to claim 5 or 6, wherein 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 an upper defined value of 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 defined value of the anode pressure, then it is detected again 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 the control of the anode pressure between the upper and lower defined values ​​is repeated until the drying is complete.

8. 8. The method of claim 7, wherein immediately after increasing or switching on the hydrogen supply, hydrogen recirculation is also increased or switched on.

9. 9. The method according to any one of claims 5 to 8, wherein the reduction and / or increase of the hydrogen supply and / or the hydrogen circulation is performed in a sawtooth pattern.

10. 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 a method according to any one of claims 1 to 9.

11. 11. The fuel cell device (10) of claim 10, further comprising a pressure sensor at the anode (A), the pressure sensor being capable of being used by a control device to detect the anode pressure and to compare the anode pressure with an upper specified value and / or a lower specified value for the anode pressure.

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