Fuel cell system with circulation means

Abstract

This fuel cell system (2) comprises: - a fuel cell stack (6) comprising an anode and a cathode, - a housing (8), in which the stack is arranged, having a ventilation inlet (10) and a ventilation outlet (12), - a water separator (24) connected to an outlet pipe (7b) of the cathode and configured to separate an incoming cathode gas flow (26) into a first outgoing flow comprising water-rich air, exiting through a first outlet (28a) of the water separator (24), and a second outgoing flow comprising water-poor air, exiting through a second outlet (28b) of the water separator (24), and - an ejector (30) comprising a primary inlet (32a) connected to the first outlet (28a) of the water separator (24) and a secondary inlet (32b) connected to the ventilation outlet (12) of the housing (8). Figure for abstract: Figure 1

Description

Title of the invention: Fuel cell system with circulation means

[0001] The invention relates to the field of fuel cells such as proton exchange membrane fuel cells. More specifically, the invention relates to a fuel cell system intended to equip a mobile element such as a vehicle, as well as to a vehicle comprising such a fuel cell system.

[0002] A proton exchange membrane fuel cell, generally abbreviated as "PEMFC" from the English term "polymer electrolyte membrane fuel cell", typically comprises an electrode membrane arranged between two unipolar half-plates. An electrode membrane comprises an electrolytic solution contained in a proton-conducting membrane arranged between an anode and a cathode. A set of fuel cells forms what is commonly called a fuel cell stack, also called a "fuel cell stack" in English. In a fuel cell stack, several fuel cells are mounted in parallel in the stack and are electrically connected in series so that the fuel cell stack produces sufficient electrical energy.In a known manner, the anode is supplied with a hydrogen-rich gas (H2) and the cathode is supplied with a gas containing oxygen (O2), atmospheric air for example, in order to produce electricity and, in particular, water at a cathode outlet, water being a reaction product of each fuel cell. In the case where atmospheric air is used as the oxygen-containing gas, nitrogen is another product present at an anode outlet. Indeed, in this case, the nitrogen present in the air migrates from the cathode to the anode through the electrode membrane.

[0003] Since hydrogen is particularly volatile, it may happen that a quantity of hydrogen circulating in the fuel cell stack escapes from it. It then spreads into a housing in which the fuel cell stack is arranged and remains confined inside this housing. Although the risk of such a leak occurring is generally low, an accumulation of hydrogen inside the housing constitutes a considerable danger which must be avoided because it could cause an explosion in the event of combustion.

[0004] To this end, it is known from the prior art to constantly ventilate the housing of the fuel cell stack, for example using a fan arranged to generate an air flow passing through the housing to evacuate the hydrogen therefrom. This thus makes it possible to prevent the hydrogen concentration inside the housing from reaching dangerous values.

[0005] The fan of the prior art thus makes it possible to remedy the danger caused by potential hydrogen leaks in the housing of the fuel cell stack, but this comes with new problems. Indeed, the fan needs to be supplied with electrical energy to operate, so that its presence has the indirect effect of reducing the overall energy efficiency of the fuel cell system. In addition, the fan forms a relatively bulky component which can be complex to arrange in the fuel cell system, especially if the system is fitted to a vehicle, itself comprising drastic space constraints. Furthermore, the presence of the fan and its electrical connections significantly increases the manufacturing cost of the fuel cell system, which is generally preferable to avoid.

[0006] The invention aims in particular to remedy these drawbacks by providing a fuel cell system preventing the accumulation of hydrogen in the housing of the fuel cell stack using means which are less energy-intensive, more compact and less expensive than those of the prior art.

[0007] To this end, the invention relates in particular to a fuel cell system comprising:

[0008] - a fuel cell stack comprising an anode and a cathode,

[0009] - a housing, in which the stack of fuel cells is arranged, having a ventilation inlet and a ventilation outlet,

[0010] - a water separator connected to a cathode outlet pipe and configured to separate an incoming cathode gas stream into a first outgoing stream comprising air rich in liquid water, exiting through a first outlet of the water separator, and a second outgoing stream comprising air lean in liquid water, exiting through a second outlet of the water separator, and

[0011] - an ejector comprising a primary inlet connected to the first outlet of the se water separator and a secondary inlet connected to the ventilation outlet of the housing.

[0012] Thus, the fuel cell system according to the invention uses one of the flows leaving the water separator to generate, using the ejector, a venturi effect continuously sucking the gas contained in the housing of the fuel cell stack through the secondary inlet of the ejector. The water separator being a component already present in a conventional system, only the ejector constitutes an additional component compared to such a system. The ejector being a passive component, that is to say not requiring an energy supply to operate, it has no negative impact on the energy efficiency of the system unlike the fan of the prior art. In addition, the ejector is much more compact than the fan and does not require electrical connections, so it is simpler to arrange it in the fuel cell system. Finally, the ejector constitutes a less expensive component than the vent prior art activator, and thus contributes to reducing the manufacturing cost of the fuel cell system.

[0013] Advantageously, the fuel cell system further comprises a compression device arranged upstream of a cathode inlet pipe and a heat exchanger arranged between the compression device and the cathode inlet pipe.

[0014] It is thus possible to control the pressure and temperature parameters of the cathode gas flow supplying the cathode inlet pipe, which helps to optimize the performance of the fuel cell system.

[0015] Advantageously, the ventilation inlet of the housing is connected to a first supply point located upstream of the compression device.

[0016] If the first flow leaving the water separator has a sufficiently high flow rate, the venturi effect generated by its passage through the ejector is sufficiently powerful to draw air through the housing, via the secondary inlet of the ejector, before it is compressed by the compression device. This avoids unnecessary compression of this volume of air and therefore a reduction in the energy efficiency of the fuel cell system.

[0017] Advantageously, the fuel cell system further comprises a non-return valve arranged between the ventilation inlet of the housing and the first supply point.

[0018] This prevents any untimely leakage of hydrogen contained in the housing into the rest of the fuel cell system, using simple and passive means.

[0019] Advantageously, the ventilation inlet of the housing is connected to a second supply point located downstream of the heat exchanger.

[0020] It may happen that the first flow leaving the water separator has a flow rate that is not sufficiently large to generate a venturi effect by its passage through the ejector powerful enough to draw air through the housing, via the secondary inlet of the ejector, before it is compressed by the compression device. This is the case when the fuel cell system operates at low speed. In this case, the ejector is allowed to draw compressed air through the compression device, which is possible even with a relatively weak venturi effect.

[0021] Preferably, the fuel cell system further comprises a valve arranged between the ventilation inlet of the housing and the second supply point.

[0022] It is thus possible to simply control the opening and closing of access to the second supply point. For example, the opening and closing of the valve can be controlled dynamically as a function of a measurement of the flow rate of the first stream leaving the water separator and a comparison of this measured value with a predetermined threshold value.

[0023] Preferably, the valve is a proportional valve configured to control the flow rate at the ventilation inlet of the housing based on a target flow rate value.

[0024] This allows for finer management of the ventilation of the housing.

[0025] Advantageously, the fuel cell system further comprises a humidifier arranged between the heat exchanger and the cathode inlet pipe.

[0026] This allows for management of the humidification of the cathode gas flow supplying the cathode inlet pipe, which contributes to improving the operation, efficiency and lifetime of the fuel cell system.

[0027] Advantageously, the ejector is a venturi pump or suction jet pump.

[0028] The ejector is thus produced with simple means.

[0029] Advantageously, the fuel cell system further comprises a turbine arranged downstream of the second outlet of the water separator.

[0030] It is thus possible to recover part of the kinetic energy of the second flow leaving the water separator, which contributes to increasing the energy efficiency of the fuel cell system.

[0031] The invention also provides a vehicle comprising an electric powertrain and an electrical energy storage element, comprising a fuel cell system as defined above.

[0032] The invention also provides a method for managing a fuel cell system, the fuel cell system comprising:

[0033] - a fuel cell stack comprising an anode and a cathode,

[0034] - a housing, in which the stack of fuel cells is arranged, having a ventilation inlet and a ventilation outlet,

[0035] - a water separator connected to a cathode outlet pipe, configured to separating an incoming cathode gas stream into a first outgoing stream comprising air rich in liquid water, exiting through a first outlet of the water separator, and a second outgoing stream comprising air lean in liquid water, exiting through a second outlet of the water separator, and

[0036] - an ejector comprising a primary inlet connected to the first outlet of the se water separator and a secondary inlet connected to the ventilation outlet of the housing,

[0037] the method implementing the step according to which the ejector sucks the gas contained in the housing by venturi effect caused by the circulation of the flow entering through the primary inlet through the ejector.

[0038] Advantageously, the fuel cell system further comprises:

[0039] - a compression device arranged upstream of an inlet pipe of the cathode, and

[0040] - a heat exchanger arranged between the compression device and the pipe cathode input, the ventilation inlet of the housing being connected to a first supply point located upstream of the compression device via a non-return valve and to a second supply point located downstream of the heat exchanger via a valve.

[0041] According to a first embodiment of the invention, the valve is closed so that the secondary inlet of the ejector is supplied with gas coming from the first supply point.

[0042] According to a second embodiment of the invention, the valve is opened so that the secondary inlet of the ejector is supplied with gas coming from the second supply point.

[0043] As indicated in the above, the first and second supply points make it possible to take into account the flow rate of the first flow leaving the separator and the power of the venturi effect generated in the ejector, which makes possible more precise management of the ventilation of the housing.

[0044] Also provided according to the invention is a computer program comprising instructions which, when the program is executed by a computer, cause the latter to implement the steps of the method as defined above, as well as a computer-readable recording medium comprising instructions which, when executed by a computer, cause the latter to implement the steps of the method as defined above. Brief description of the figures

[0045] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0046] [Fig-1] is a schematic view of a fuel cell system according to the invention in which a method for managing the latter is implemented according to a first embodiment, and

[0047] [Fig.2] is a schematic view of a fuel cell system according to the invention in which a method for managing the latter is implemented according to a second embodiment. Detailed description

[0048] In the following description, the expressions "downstream" and "upstream" refer to the direction of circulation of the different fluids in the fuel cell system, these circulation directions being represented by simple arrows in the figures.

[0049] [Fig. 1] shows a fuel cell system 2 according to the invention which equips, in the present case, a vehicle 4 of the type comprising an electric powertrain and an electrical energy storage element. The fuel cell system 2 comprises a stack of fuel cells 6 comprising an anode and a cathode, the latter being in particular provided with a conduit inlet 7a of the cathode and an outlet duct 7b of the cathode. What enters and leaves the cathode through the ducts 7a and 7b is a cathode gas. The cathode gas is a mixture of air and water. As indicated above, the operating principle of the fuel cell stack for the production of electrical energy is known per se, it will therefore not be described in more detail in the following. The fuel cell stack 6 is housed in a housing 8 having a ventilation inlet 10 and a ventilation outlet 12. Disregarding the ventilation inlet 10 and the ventilation outlet 12, the housing 8 defines a sealed volume encompassing the entire fuel cell stack 6.

[0050] The fuel cell system 2 comprises means 14 for supplying a gas containing oxygen, for example atmospheric air, to the inlet pipe 7a of the cathode. Downstream of the air supply means 14, the fuel cell system 2 comprises a filter 16 for filtering residues possibly contained in the air coming from the air supply means 14 in order to prevent their intrusion into the system.

[0051] Downstream of the filter 16, the fuel cell system 2 comprises a compression device 18, for example an electric turbocharger, configured to compress the air coming from the air supply means 14 before it is supplied to the inlet pipe 7a of the cathode. Downstream of the compression device 18, the fuel cell system 2 comprises a heat exchanger 20, for example a charge air cooler, also called a "charge air cooler" in English, configured to heat the air before it is supplied to the inlet pipe 7a of the cathode. The fuel cell system 2 comprises a humidifier 22, arranged between the heat exchanger 20 and the inlet pipe 7a of the cathode, configured to humidify the air before it is supplied to the inlet pipe 7a of the cathode.Compressing, heating and humidifying the air before supplying it to the cathode inlet line 7a allows the operation of the fuel cell stack 6 to be optimized.

[0052] At the cathode, water is produced by the reaction between oxygen in the air and hydrogen ions from the anode, such that the cathode gas exiting through the cathode outlet line 7b comprises water-enriched, oxygen-depleted air. Downstream of the cathode outlet line 7b, the fuel cell system 2 comprises a water separator 24 configured to separate the incoming cathode gas stream 26 into a first outgoing stream comprising liquid water-rich air, exiting through a first outlet 28a of the water separator 24, and a second outgoing stream comprising liquid water-lean air, exiting through a second outlet 28b of the water separator 24.

[0053] Downstream of the first outlet 28a of the water separator 24, the fuel cell system fuel cell system 2 comprises an ejector 30 comprising a primary inlet 32a connected to the first outlet 28a of the water separator 24 and a secondary inlet 32b connected to the ventilation outlet 12 of the housing 8. The ejector 30 further comprises an ejection outlet 34 opening onto an exhaust pipe 36 of the fuel cell system 2 exiting therefrom. The ejector 30 is here a venturi pump or a suction jet pump.

[0054] Downstream of the second outlet 28b of the water separator 24, the fuel cell system 2 comprises a turbine 38 configured to recover a portion of the kinetic energy of the second flow exiting through the second outlet 28b of the water separator 24 comprising air low in liquid water before the latter is discharged towards the exhaust pipe 36.

[0055] The ventilation inlet 10 of the housing 8 is connected in parallel to two air supply points of the fuel cell system 2. A first supply point 40 is located upstream of the compression device 18 and downstream of the filter 16. A non-return valve 42 is arranged between the ventilation inlet 10 of the housing 8 and the first supply point 40 and is configured to prevent any circulation of fluid from the ventilation inlet 10 of the housing 8 to the first supply point 40. A second supply point 44 is located downstream of the heat exchanger 20 and upstream of the humidifier 22. A valve 46 is arranged between the ventilation inlet 10 of the housing 8 and the second supply point 44. The valve 46 here comprises a proportional valve configured to control the flow rate at the ventilation inlet 10 of the housing 8 as a function of a target flow rate value.The valve 46 is for example a valve actuated by a hydraulic, pneumatic or, preferably, electric actuator.

[0056] We will now describe a method for managing the fuel cell system 2 allowing the ventilation of the housing 8.

[0057] The passage of the first flow leaving the water separator 24 into the ejector 30 through its primary inlet 32a generates, by venturi effect, a depression inside the latter which is all the greater the greater the flow rate of the first flow leaving the water separator 24. This depression makes it possible to suck in the gas contained in the housing 8, provided that this depression is sufficiently great to allow the displacement of the gas contained in the housing, through the secondary inlet 32b of the ejector 30.

[0058] According to a first embodiment of this method illustrated in [Fig.l], the flow rate of the first flow leaving the water separator 24 is greater than a predetermined value such that the depression generated by the venturi effect in the ejector 30 is sufficiently large to allow the gas contained in the housing 8 to be sucked in through the secondary inlet 32b of the ejector 30, without it being necessary to increase its pressure. This first embodiment corresponds for example to the situation in which the fuel cell system 2 operates at high speed.

[0059] Under these conditions, the valve 46 is closed or kept closed so that the gas sucked from the housing 8 is renewed by air coming from the first supply point 40 free of hydrogen, or at least having a negligible concentration of hydrogen, as indicated by the double arrow shown in [Fig.l]. The gas sucked from the housing 8 enters the ejector 30 through the secondary inlet 32b, is mixed with the first flow leaving the water separator 24, and leaves the ejector 30 through the ejection outlet 34 to be discharged into the exhaust pipe 36.

[0060] [Fig. 2] shows a second embodiment of the method for managing the fuel cell system 2 allowing the ventilation of the housing 8. The system itself is the same as that illustrated in [Fig. 1]. According to the second embodiment of the method, the flow rate of the first flow leaving the water separator 24 is lower than the predetermined value, such that the depression generated by the venturi effect in the ejector 30 is not sufficiently large to allow the gas contained in the housing 8 to be sucked in through the secondary inlet 32b of the ejector 30 without it being necessary to increase its pressure. This second embodiment corresponds, for example, to the situation in which the fuel cell system 2 operates at low speed.

[0061] Under these conditions, the valve 46 is opened or kept open so that the housing 8 is in communication with the outlet of the heat exchanger 20 and, above all, the outlet of the compression device 18. This has the effect of increasing the gas pressure inside the housing 8 sufficiently so that the depression generated by the venturi effect in the ejector 30 allows it to suck, through the secondary inlet 32b, the gas from the housing 8, which is then renewed by air coming from the second supply point 44 which is also free of hydrogen, as indicated by the double arrow shown in [Fig. 2]. The opening of the proportional valve 46 is controlled to control the flow rate at the ventilation inlet 10 of the housing 8 as a function of a target flow rate value.The target flow rate value is determined based on operating parameters of the fuel cell system 2 such as, for example, the pressure at the system inlet or the temperature at the system inlet. In the same manner as in the first embodiment, the gas drawn from the housing 8 enters the ejector 30 through the secondary inlet 32b, is mixed with the first flow exiting the water separator 24, and exits the ejector 30 through the ejection outlet 34 to be discharged into the exhaust pipe 36.

[0062] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art.

[0063] The invention is particularly applicable to mobile equipment, such as road vehicles including cars and trucks, rail vehicles, vehicles marine, aircraft and spacecraft, as well as stationary, such as power plants or generators. List of references

[0064] 2: fuel cell system 4: vehicle 6: Fuel cell stack 7a: cathode inlet pipe 7b: cathode outlet pipe 8: case 10: ventilation inlet 12: ventilation outlet 14: means of air supply 16: filter 18: compression device 20: heat exchanger 22: humidifier 24: water separator 26: incoming cathode gas flow 28a: first outlet of the water separator 28b: second outlet of the water separator 30: ejector 32a: primary ejector inlet 32b: secondary ejector inlet 34: ejection outlet 36: exhaust pipe 38: turbine 40: first power point 42: non-return valve 44: second power point 46: valve

Claims

Claims

1. Fuel cell system (2), characterized in that it comprises: - a fuel cell stack (6) comprising an anode and a cathode, - a housing (8), in which the fuel cell stack is arranged, having a ventilation inlet (10) and a ventilation outlet (12), - a water separator (24) connected to an outlet pipe (7b) of the cathode and configured to separate an incoming cathode gas flow (26) into a first outgoing flow comprising air rich in liquid water, exiting through a first outlet (28a) of the water separator (24), and a second outgoing flow comprising air poor in liquid water, exiting through a second outlet (28b) of the water separator (24), and - an ejector (30) comprising a primary inlet (32a) connected to the first outlet (28a) of the water separator (24) and a secondary inlet (32b) connected to the ventilation outlet (12) of the housing (8).

2. The fuel cell system (2) of claim 1, further comprising a compression device (18) arranged upstream of an inlet pipe (7a) of the cathode and a heat exchanger (20) arranged between the compression device (18) and the inlet pipe (7a) of the cathode.

3. Fuel cell system (2) according to claim 2, wherein the ventilation inlet (10) of the housing (8) is connected to a first supply point (40) located upstream of the compression device (18).

4. Fuel cell system (2) according to claim 3, further comprising a non-return valve (42) arranged between the ventilation inlet (10) of the housing (8) and the first supply point (40).

5. Fuel cell system (2) according to any one of claims 2 to 4, wherein the ventilation inlet (10) of the housing (8) is connected to a second supply point (44) located downstream of the heat exchanger (20).

6. A fuel cell system (2) according to claim 5, further comprising a valve (46) arranged between the ventilation inlet (10) of the housing (8) and the second supply point (44).

7. The fuel cell system (2) of claim 6, wherein the valve (46) is a proportional valve configured to control the flow rate at the ventilation inlet (10) of the housing (8) as a function of a target flow rate value.

8. A fuel cell system (2) according to any one of claims 2 to 7, further comprising a humidifier (22) arranged between the heat exchanger (20) and the cathode inlet pipe (7a).

9. A fuel cell system (2) according to any preceding claim, wherein the ejector (30) is a venturi pump or suction jet pump.

10. A fuel cell system (2) according to any preceding claim, further comprising a turbine (38) arranged downstream of the second outlet (28b) of the water separator (24).

11. Vehicle (4) comprising an electric powertrain and an electrical energy storage element, characterized in that the vehicle comprises a fuel cell system (2) according to any one of the preceding claims.

12. A method for managing a fuel cell system (2), characterized in that the fuel cell system comprises: - a fuel cell stack (6) comprising an anode and a cathode, - a housing (8), in which the fuel cell stack (6) is arranged, having a ventilation inlet (10) and a ventilation outlet (12), - a water separator (24) connected to an outlet pipe (7b) of the cathode, configured to separate an incoming cathode gas flow (26) into a first outgoing flow comprising air rich in liquid water, exiting through a first outlet (28a) of the water separator (24), and a second outgoing flow comprising air poor in liquid water, exiting through a second outlet (28b) of the water separator (24), and - an ejector (30) comprising a primary inlet (32a) connected to the first outlet (28a) of the water separator (24) and a secondary inlet (32b) connected to the ventilation outlet (12) of the housing (8),the method implementing the step according to which the ejector (30) sucks the gas contained in the housing (8) by venturi effect caused by the circulation of the flow entering through the primary inlet (32a) through the ejector (30).,

13. A method of managing a fuel cell system (2) according to the preceding claim, wherein the fuel cell system (2) further comprises: - a compression device (18) arranged upstream of an inlet pipe (7a) of the cathode, and - a heat exchanger (20) arranged between the compression device (18) and the inlet pipe (7a) of the cathode, the ventilation inlet (10) of the housing (8) being connected to a first supply point (40) located upstream of the compression device (18) via a non-return valve (42) and to a second supply point (44) located downstream of the heat exchanger (20) via a valve (46).

14. A method of managing a fuel cell system according to claim 13, wherein the valve (46) is closed so that the secondary inlet (32b) of the ejector (30) is supplied with gas from the first supply point (40).

15. A method of managing a fuel cell system according to claim 13, wherein the valve (46) is opened so that the secondary inlet (32b) of the ejector (30) is supplied with gas from the second supply point (44).

16. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement the steps of the method according to any one of claims 12 to 15.

17. A computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of claims 12 to 15.

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