FUEL CELL SYSTEM HAVING ACTIVE HOUSING PURGING

Abstract

A fuel cell system including a fuel cell stack having cathode and anode sides, a housing surrounding the fuel cell stack, a housing purging air inlet, an air-conveying installation disposed on the housing purging air inlet, a housing purging air outlet, an oxidation catalyst, a temperature sensor, and a control unit. The air-conveying installation continuously directs an airflow into the housing purging air inlet. The oxidation catalyst is disposed downstream of the housing purging air outlet and catalytically combusts hydrogen and oxygen. The temperature sensor is disposed on the oxidation catalyst and detects the oxidation catalyst temperature as an information item pertaining to a volumetric hydrogen flow occurring outside a fuel cell process and to be discharged. The control unit couples to the temperature sensor and to the air-conveying installation and receives the temperature detected by the temperature sensor and to therefrom determine variations of a hydrogen concentration.

Claims

1. A fuel cell system, comprising at least one fuel cell stack having a cathode side and an anode side, a housing which surrounds the at least one fuel cell stack, a housing purging air inlet, an air-conveying installation which is disposed on the housing purging air inlet, a housing purging air outlet, an oxidation catalyst, at least one temperature sensor, and a control unit, wherein the air-conveying installation is configured to continuously direct an airflow into the housing purging air inlet, wherein the oxidation catalyst is disposed downstream of the housing purging air outlet and is configured to catalytically combust hydrogen and oxygen, wherein the at least one temperature sensor is disposed on the oxidation catalyst and is configured to detect a temperature of the oxidation catalyst as an item of information pertaining to a volumetric flow of hydrogen that occurs outside a fuel cell process and is to be discharged, and wherein the control unit is coupled to the at least one temperature sensor and to the air-conveying installation and is configured to receive a temperature detected by the at least one temperature sensor and to therefrom determine variations of a concentration of hydrogen.

2. The fuel cell system as claimed in claim 1, wherein the at least one temperature sensor is disposed in an outlet pipe which directly succeeds the oxidation catalyst.

3. The fuel cell system as claimed in claim 1, further comprising a flashback arrester which is disposed upstream of the oxidation catalyst and is configured to prevent any ignition of hydrogen upstream of the flashback arrester.

4. The fuel cell system as claimed in claim 1, further comprising an anode purging device, coupled to the control unit, for purging the anode side of the at least one fuel cell stack, wherein the anode purging device has at least one purging valve which is disposed between an anode outlet and the oxidation catalyst, and wherein the control unit, by selectively opening the at least one purging valve, is configured to direct a flow of hydrogen through the anode side to the oxidation catalyst, to purge the anode side.

5. The fuel cell system as claimed in claim 4, wherein the at least one fuel cell stack comprises a plurality of fuel cell stacks, wherein the at least one purging valve comprises a plurality of purging valves which are coupled to different fuel cell stacks, and wherein the control unit is configured to open the plurality of purging valves at least one of successively or not simultaneously.

6. The fuel cell system as claimed in claim 1, wherein the control unit is configured to determine from a measured temperature of the at least one temperature sensor a momentary concentration of hydrogen of a gas mixture flowing into the oxidation catalyst.

7. The fuel cell system as claimed in claim 1, wherein the control unit is configured to influence an operation of the air-conveying installation as a function of the determined concentration of hydrogen.

8. The fuel cell system as claimed in claim 4, wherein the control unit is configured to influence the operation of the air-conveying installation as a function of a determined concentration of hydrogen, and wherein the control unit is configured to at least temporarily close the at least one purging valve, and, with the at least one purging valve closed, to determine a momentary concentration of hydrogen in the interior of the housing.

9. The fuel cell system as claimed in claim 8, wherein the control unit is configured to compare the momentary concentration of hydrogen in the interior of the housing with a tolerable value, and, if the tolerable value is exceeded, to increase a volumetric flow of air provided by the air-conveying installation.

10. The fuel cell system as claimed in claim 8, wherein the control unit is configured to operate the fuel cell system with a reduced output if the momentary concentration of hydrogen in the interior of the housing exceeds a pre-definable threshold value.

11. A vehicle comprising at least one fuel cell system as claimed in claim 1.

12. The vehicle as claimed in claim 11, wherein the vehicle is an aircraft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Exemplary embodiments will be discussed in more detail hereunder by means of the appended drawings. The illustrations are schematic and not to scale. Identical reference signs relate to identical or equivalent elements. In the drawings:

[0027] FIGS. 1-5 show schematic illustrations of a fuel cell system in a plurality of variants, and

[0028] FIG. 6 shows an aircraft having a fuel cell system disposed therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] FIG. 1 shows a fuel cell system 2 having a fuel cell stack 4 which comprises an anode side 6, a cathode side 8, a heat transfer element 10, and an electric terminal 12. It is noted here that the fuel cell stack 4 presently is only schematically illustrated and is, in fact, composed of a series of fuel cells which by means of bipolar plates are electrically connected to one another and supplied with reactants.

[0030] The anode side 6 at an anode inlet 14 is supplied with hydrogen which emanates from a hydrogen source 16 which, by way of a hydrogen connector 18, is connected to the fuel cell system 2. One or a plurality of hydrogen valves 20, which, by actuation, is/are configured to deliver in a metered manner fresh hydrogen to the anode inlet 14, adjoins/adjoin the hydrogen connector 18. This assembly, optionally having further components, is referred to as a “balance of plant”.

[0031] Air from an air source 22, which is humidified by a humidifier 24 in order to guarantee the integrity of a membrane situated in the fuel cell stack 4, is fed to the cathode side 8. The pre-humidified air makes its way into a cathode inlet 26. After a proportion of oxygen has been consumed, exhaust air from a cathode outlet 28 makes its way into the humidifier 24 and in the latter dispenses water vapor to the fresh intake air.

[0032] For example, the heat transfer element 10 may be integrated in the previously mentioned bipolar plates, and by means of a pump 30 is passed through by a flow of coolant. To this end, the coolant flows into a coolant inlet 32, is heated in the fuel cell stack 4, and flows out again from a coolant outlet 34. The heat absorbed by the coolant can be discharged to the environment again by way of a heat exchanger 36.

[0033] The fuel cell system 2 furthermore has a housing 38 which here, in an exemplary manner, encloses the fuel cell stack 4 and the hydrogen valves 20. The housing 38 may preferably be designed as compact as possible and provide an available interior space which is not unnecessarily large. The housing 38 on the lower side thereof has a housing purging air inlet 40 on which is provided an air-conveying installation 42 which actively directs ambient air into the housing 38. The ambient air leads to the gas situated in the housing 38 being purged out of a housing purging air outlet 44, the latter in an exemplary manner being disposed on the upper side thereof This housing purging air outlet 44 may open into a corresponding outlet pipe 46.

[0034] A flashback arrester 48, which is adjoined by an oxidation catalyst 50, is disposed in the outlet pipe 46. A temperature sensor 52 is disposed directly downstream. Hydrogen which flows through the housing purging air outlet 44 is converted to water with oxygen by the oxidation catalyst 50, while generating heat. The temperature sensor 52 here detects the temperature of the exhaust gas downstream of the oxidation catalyst 50, such that a control unit 54, which is coupled to the temperature sensor 52, by means of the detected temperature can determine a variation of a concentration of hydrogen or a level of the concentration of hydrogen. A hydrogen sensor 56, which is likewise coupled to the control unit 54, can additionally also be disposed within the housing 38.

[0035] FIG. 2 shows a somewhat modified view in a schematic block diagram, in which even more details are apparent. A purging valve 58, which is coupled to an anode outlet 60, can be utilized for purging the anode side 6 if required, in particular for removing nitrogen and water from the fuel cells. To this end, the purging valve 58, which can be connected to the control unit 54, is connected to an outlet 62 which supplies the purging gas to the environment.

[0036] With the purging valve 58 closed, residual hydrogen gas from the anode outlet 60 makes its way into a mixing point 64 where fresh hydrogen is added to the residual hydrogen gas, the mixture flowing to the anode inlet 14. The mixing point 64 may also be embodied as a jet pump. In order for the residual hydrogen gas to be conveyed, a recirculation fan 66 is coupled to the anode outlet 60 such that a recirculating circuit is formed. Additionally provided here is a water separator 68 which is disposed upstream of the mixing point 64 and at least partially dehumidifies the anode exhaust gas, or separates condensate from a supply line, respectively.

[0037] In the oxidation catalyst 50, leaked hydrogen 70, which accumulates in the interior of the housing 38, is combined with fresh intake air 72, the latter making its way into the housing 38 by way of the air-conveying installation 42, so as to form water. Consequently, air with water vapor contained therein is directed to the outside by way of the outlet pipe 46.

[0038] Furthermore, by way of example, a first switch-off valve 74 is disposed downstream of the humidifier 24. A second switch-off valve 76 is disposed downstream of the cathode output 28. In order for the fuel cell system 2 to be switched off, the two switch-off valves 74 and 76 can be closed in addition to the hydrogen valves 20. A water separator 78, which separates water from the cathode exhaust air and, in an exemplary manner, supplies the water to the humidifier 24, is disposed downstream of the second switch-off valve 76.

[0039] An electric load 80 is connected to the electrical terminal 12 and is supplied with electric power from the latter.

[0040] A somewhat modified fuel cell system 82 is shown in FIGS. 3 and 4. The purging valve 58 here is fluidically connected to the oxidation catalyst 50. This means that purging gases from the fuel cell stack 4 are guided directly into the outlet pipe 46 and rendered harmless by the oxidation catalyst 50. The temperature of the gas flowing out into the environment may increase somewhat further as a result. By way of example, the hydrogen sensor 56 is disposed downstream of the oxidation catalyst 50.

[0041] FIG. 5 shows a combination, illustrated only in a schematic manner, of a plurality of fuel cell stacks 4 in the fuel cell system 82, wherein each fuel cell stack 4, by way of example, is equipped with a purging valve 58. The individual purging valves 58 are fluidically connected to the oxidation catalyst 50 such that hydrogen contained in the purging gases is converted directly into water by air. The control unit 54 can sequentially actuate the purging valves such that the purging valves 58 open and close in a specific order, in particular opening successively and particularly preferably not simultaneously. In this way, an approximately consistent, additional input of hydrogen into the oxidation catalyst can take place, this leading to approximately consistent additional heating.

[0042] Finally, FIG. 6 shows an aircraft 84 in which a fuel cell system 2 or 82 is installed.

[0043] It should additionally be pointed out that “comprising” or “including” do not rule out other elements or steps, and “a” or “one” does not rule out a multitude. It should also be pointed out that features or steps that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other above-described exemplary embodiments.

[0044] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

[0045] List of reference signs [0046] 2 Fuel cell system [0047] 4 Fuel cell stack [0048] 6 Anode side [0049] 8 Cathode side [0050] 10 Heat transfer element [0051] 12 Terminal [0052] 14 Anode inlet [0053] 16 Hydrogen source [0054] 18 Hydrogen connector [0055] 20 Hydrogen valve [0056] 22 Air source [0057] 24 Humidifier [0058] 26 Cathode inlet [0059] 28 Cathode outlet [0060] 30 Pump [0061] 32 Coolant inlet [0062] 34 Coolant outlet [0063] 36 Heat exchanger [0064] 38 Housing [0065] 40 Housing purging air inlet [0066] 42 Air-conveying installation [0067] 44 Housing purging air outlet [0068] 46 Outlet pipe [0069] 48 Flashback arrester [0070] 50 Oxidation catalyst [0071] 52 Temperature sensor [0072] 54 Control unit [0073] 56 Hydrogen sensor [0074] 58 Purging valve [0075] 60 Anode outlet [0076] 62 Outlet [0077] 64 Mixing point [0078] 66 Recirculation fan [0079] 68 Water separator [0080] 70 Leaked hydrogen [0081] 72 Intake air [0082] 74 First switch-off valve [0083] 76 Second switch-off valve [0084] 78 Water separator [0085] 80 Electric load [0086] 82 Fuel cell system [0087] 84 Aircraft