CLOSURE DEVICE DESIGNED FOR MOUNTING IN A FLUID CIRCULATION CHANNEL OF A FUEL CELL STACK, AND METHOD FOR CLOSING

Description

Technical field

[0001] The present invention relates to the field of repairing fuel cells, in particular, on board an aircraft in order to provide propulsive and non-propulsive energy.

[0002] A fuel cell produces electrical energy from an electrochemical reaction between different fluids. Typically, a fuel cell is supplied with hydrogen and oxygen, which react in the fuel cell to generate electrical energy. A fuel cell comprises a stack comprising a plurality of cells aligned along a stacking axis. The stack of cells, referred to as a "Stack", enables the electrochemical reaction from the fluids.

[0003] Each cell comprises an ion-conducting electrolyte surrounded by two electrodes which are themselves surrounded by interconnection plates. For example, in the case of a proton exchange membrane fuel cell (PEMFC), the electrolyte is in the form of a proton-conducting polymer membrane and the electrodes are in the form of a porous medium carrying a catalyst such as platinum. The electrolyte and electrode assembly is called a Membrane Electrode Assembly (MEA). Each MEA is brought into contact with reactive gases on its two opposite faces (for example, hydrogen and oxygen possibly contained in the air) thanks to the interconnection plates to form a cell.

[0004] As is known, the assembly of two interconnecting plates, belonging to two adjacent cells, is called a bipolar plate. Thus, a bipolar plate is interposed between the cathode of one MEA and the anode of the adjacent MEA. A bipolar plate supplies, on the one hand, a first MEA on the anode side with fuel (hydrogen) and, on the other hand, a second MEA on the cathode side with oxidant (oxygen). Generally, each bipolar plate has an internal cooling circuit in which a heat transfer fluid circulates, used to supply heat or extract the heat produced by the exothermic reaction.

[0005] The current generated by the cells is collected at both ends of the stack by conductive plates called collectors. The electrical power delivered by the fuel cell depends on the number of cells (delivered voltage capacity), the active surface area of the cells (delivered current capacity) and the flow rates of the reactive fluids (importance of the electrochemical reaction that produces the current).

[0006] The entire cell stack is held compressed between two plates called end plates connected by tie rods that hold the assembly together and ensure the stack is watertight. This watertightness is ensured by gaskets inserted between the bipolar plates and the cell MEAs. The end plates are typically massive because they must apply uniform pressure to the cell surface and be dimensionally stable under the effect of the internal pressure of the cell and temperature variations.

[0007] The reactant and heat transfer fluids are introduced and evacuated at the end plates, which distribute them into circulation chimneys passing through the stack. These circulation chimneys result from the stacking of openings formed in the cells. For example, three chimneys introduce the fluids on one side of the stack (two reactant fluids and one heat transfer fluid if necessary) to pass into the cells, while three other chimneys evacuate the fluids on the other side of the stack.

[0008] In a known manner, a fuel cell comprises a stack comprising a plurality of cells aligned along a stack axis. Tie rods connect an outer portion of the end plates peripherally in order to apply a constant compressive force to the stack. The end plates comprise circulation pipes which open into the circulation chimneys of the stack.

[0009] During the electrochemical reaction in the fuel cell, the reactive fluids are charged with traces of acid that are part of the composition of the MEAs. These traces of phosphoric acid are present in the circulation chimneys corresponding to the outlets of the two fuel fluid circuits, in particular, in the form of water vapor in the case of a high-temperature fuel cell. This acid can crystallize, in particular during a fuel cell start-up / stop step during which the temperature is lower than the normal operating temperature, which can block the circulation chimneys. Such blockage is likely to cause damage that can lead to the creation of hot spots with a risk of perforation of the MEA. In addition to a loss of fuel cell efficiency, the probability of fire and leak risks is increased.

[0010] In the event of damage to one or more cells, it is necessary to isolate these cells from the circulation of reactive fluids so that they no longer produce electricity or allow fluid communication between the reactants. From an electrical point of view, these cells must be shunted so as not to interrupt the electrical generation in the Stack.

[0011] To reach a defective cell, it is necessary to descend along each of the chimneys to intervene individually on each of the circulation openings of the defective cell. This intervention is complex given the height of the chimneys (up to 300 mm) and their section (from 300 to 1000 mm 2< ).

[0012] A method for repairing a defective cell is known in the prior art in which an electric shock is applied to the defective cell so as to pierce the membrane. The circulation openings are individually sealed by depositing resin. US 4761350A describes such a sealing method.

[0013] Although attractive in theory, this solution is complex to implement. One objective of the present invention is to enable a defective cell to be isolated from a stack in a practical and rapid manner. PRESENTATION OF THE INVENTION

[0014] An isolation device configured to be mounted in a fluid circulation chimney of a fuel cell comprising a stack comprising a plurality of cells aligned along a stack axis and a plurality of fluid circulation chimneys in the stack.

[0015] The isolation device is remarkable in that it comprises a peripherally shaped belt configured to close the fluid communication between the circulation chimney and at least one circulation opening of a cell to be isolated from the stack, the belt being deformable between a first configuration, called rest configuration, and a second configuration, called tightened configuration, the section of which is smaller than in the first configuration.

[0016] Preferably, such an isolation device can be conveniently positioned at the desired position in a circulation stack to isolate a cell from the stack. A peripheral belt allows localized sealing while allowing fluid to circulate through the belt to supply the other cells. Its deformable nature allows convenient and rapid positioning without risk of damage to the inner surface of the circulation stack. The belt allows a plurality of circulation openings of a cell to be conveniently and simultaneously sealed.

[0017] Preferably, in the first configuration, the section of the belt is substantially similar to the section of the circulation chimney in which the isolation device is configured to be mounted. Thus, the belt naturally fits, without excessive stress or deformation, the interior surface of the circulation chimney, which makes it possible to seal the cell in a practical manner and without risk of damage to the surrounding area.

[0018] In one aspect, the isolation device includes a spring member configured to constrain the belt in the first configuration. Thus, the belt deploys automatically when the operator does not constrain the belt. This is particularly advantageous when the cell to be isolated is far from the access opening of the circulation stack and it is desired to manipulate the isolation device easily.

[0019] Preferably, the spring member is in the form of a leaf spring of simple design. A leaf spring may be positioned on the inner surface of the belt to avoid contact with the inner surface of the chimney.

[0020] Preferably, the isolation device comprises an indexing member configured to ensure precise positioning of the isolation device in the circulation chimney, in particular, opposite an opening of one or more circulation openings of the cell to be isolated. Preferably, a cell comprises two seals on either side of the circulation openings, the indexing member is configured to cooperate with the seals.

[0021] This is particularly advantageous for ensuring precise positioning when the cell to be insulated is far from the access opening of the circulation chimney. Preferably, the indexing member is in the form of a peripheral tongue extending projecting from the outer surface of the belt. Thus, the indexing member allows cooperation by complementary shapes with the sealing joints.

[0022] Preferably, the isolation device comprises a plurality of guide members configured to cooperate with an interior surface of the circulation chimney. Preferably, the circulation chimney having a section defining a plurality of corners, the guide members are configured to cooperate with the corners of the circulation chimney. Thus, the belt is precisely angularly positioned in the chimney, which ensures optimal sealing.

[0023] The invention also relates to a fuel cell assembly comprising a stack comprising a plurality of cells aligned along a stack axis and a plurality of fluid circulation chimneys in the stack and an isolation device, as presented previously, positioned in the circulation chimney to close the fluid communication between the circulation chimney and at least one cell to be isolated from the stack.

[0024] Preferably, the stack comprises an alternation of bipolar plates and membrane electrode assemblies defining the cells of the stack. The isolation device is positioned in the circulation chimney so as to close the fluid communication between the circulation chimney and a bipolar plate to be isolated. Thus, the fluid supply to the bipolar plate is stopped.

[0025] Preferably, the isolation device has a thickness, defined along the stacking axis in the mounted position, which is greater than the thickness of a bipolar plate so as to prevent any circulation of fluid in the latter.

[0026] According to a preferred aspect, sealing gaskets being interposed between the bipolar plates, the sealing gaskets extend projecting into the circulation chimney so as to participate in the watertight sealing of the bipolar plate.

[0027] Preferably, the indexing member cooperates with the sealing gaskets to ensure tight isolation. Thus, the positioning of the isolation device is precise to tightly isolate a bipolar plate.

[0028] The invention also relates to a method of isolating a cell of a fuel cell comprising a stack comprising a plurality of cells aligned along a stack axis and a plurality of fluid circulation chimneys in the stack, the method comprising the steps of: Deforming the isolation device, as previously presented, from the first configuration to the second configuration, so as to reduce its section so that it is less than the section of the circulation chimney, Moving said isolation device according to the second configuration in the circulation chimney so as to align it with at least one circulation opening of the cell to be isolated and Releasing the constraint to deform the isolation device from the second configuration to the first configuration so as to press the belt against an interior surface of the circulation chimney in order to close the fluid communication between the circulation chimney and the circulation opening of the defective cell.

[0029] Preferably, the isolation method comprises a step of electrically connecting the cell to be isolated to another cell in the stack, preferably an adjacent cell. Thus, the defective cell is electrically isolated to enable the stack to provide an electrical voltage. PRESENTATION OF FIGURES

[0030] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects. There [ Fig. 1 ] is a schematic representation of a fuel cell according to the invention. The [ Fig.2 ] is a first schematic cross-sectional representation of a fluid circulation chimney with an insulation device. The [ Fig.3] is a second schematic cross-sectional representation of a fluid circulation chimney with an insulation device. The [ Fig.4 ] is a third schematic cross-sectional representation of a fluid circulation chimney with an insulation device. The [ Fig.5 ] is a first schematic representation of an isolation device. The [ Fig.6 ] is a second schematic representation of an isolation device.

[0031] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0032] The invention relates to the field of fuel cells of the proton exchange membrane type known by its English abbreviation PEMFC for "Proton Exchange Membrane Fuel Cell". Preferably, the fuel cell is installed in an aircraft in order to provide energy to propulsion equipment.

[0033] With reference to the [ Fig. 1 ], a fuel cell 1 is shown comprising a stack 2 comprising a plurality of cells aligned along a stack axis X. Each cell comprises a plurality of fluid circulation openings, said fluid circulation openings being aligned parallel to the stack axis X in order to form a plurality of fluid circulation chimneys 20 in the stack 2.

[0034] The stack 2 of cells, called "Stack" in English, allows the electrochemical reaction from fluids, in particular, hydrogen and oxygen. In this example, each cell comprises a Membrane Electrode Assembly, known by its abbreviation AME. Each AME is brought into contact with reactive gases on its two opposite faces (for example hydrogen and oxygen possibly contained in the air) thanks to the interconnection plates to form a cell. In a known manner, the assembly of two interconnection plates, belonging to two adjacent cells, is called a bipolar plate. Thus, a bipolar plate is interposed between the cathode of an AME and the anode of the adjacent AME. Thus, a bipolar plate supplies, on the one hand, a first AME on the anode side with fuel (hydrogen) and, on the other hand, a second AME on the cathode side with oxidant (oxygen).Generally, each bipolar plate comprises an internal cooling circuit in which a heat transfer fluid circulates, used to supply heat or extract the heat produced by the exothermic reaction. Such a stack 2, formed by alternating AMEs and bipolar plates, is known from the prior art and will not be presented in more detail.

[0035] In this example, with reference to the [ Fig. 1 ], the fuel cell 1 further comprises collector plates 4, positioned at the ends of the stack 2, so as to collect the current generated by the cells. In a known manner, the electrical power delivered by the fuel cell 1 is a function of the number of cells (delivered voltage capacity) and the flow rates of the reactive fluids (importance of the electrochemical reaction which produces the current).

[0036] With reference to the [ Fig. 1], the fuel cell 1 further comprises two end plates 3 placed at the ends of the stack 2 along the stack axis X and a plurality of traction members connecting the end plates 3 together in order to compress the stack 2.

[0037] In reference to the figures 2 to 6 , an isolation device 9 according to the invention will be presented for isolating a defective cell from a stack 2.

[0038] As a reminder, as previously stated, a cell comprises a membrane electrode assembly (MEA) and two interconnection plates. Two adjacent interconnection plates form a bipolar plate.

[0039] In reference to the figures 2 to 4, the stack 2 comprises an alternation of bipolar plates 21 and membrane electrode assemblies AME 22 to generate electrical energy. The stack 2 comprises several circulation chimneys 20 extending along the stacking axis X and putting each of the bipolar plates 21 into fluid communication which then feed the AME 22. Seals 23 are provided between the bipolar plates 21 so as to ensure a seal between them. The seals 23 are elastic and participate in the indexing of the isolation device 9 as will be presented later. Preferably, the seals 23 extend projecting into the circulation chimney 20, which facilitates the formation of a seal with the isolation device 9.Each bipolar plate 21 has circulation openings 210 opening into the circulation chimneys 20 in order to allow the bipolar plates 21 to be supplied with the fluids circulating in the circulation chimneys 20.

[0040] In practice, a circulation chimney 20 supplies reactive fluid to a single face of a bipolar plate 21 and the AME 22 in contact with it, the other face being supplied with another reactive fluid via another circulation chimney 20.

[0041] In this example, with reference to the figures 2 to 4 , a bipolar plate 21 is configured to supply the AME 22 located above it for this circulation chimney 20. It goes without saying that this could be different for another circulation chimney 20.

[0042] When an AME 22d is defective, it is likely to create a hot spot and present risks for the fuel cell 1. It is therefore necessary to isolate the cell to which the defective AME 22d belongs, in particular, the bipolar plate 21a which supplies it. In this example, the bipolar plate 21a which supplies the defective AME 22d is located under the defective AME 22d.

[0043] In this example, stopping the supply of a single reactive fluid to a defective MEA 22d is sufficient to isolate it. It goes without saying, however, that the supply of all the reactive fluids to the defective MEA 22d could also be stopped by using an isolation device 9 in another circulation chimney 20. Preferably, the isolation is carried out in the circulation chimney 20 carrying the hydrogen.

[0044] According to the invention, with reference to the figures 2 to 4, an isolation device 9 is used according to one embodiment of the invention in order to close all of the fluid circulation openings 210 of at least one bipolar plate 21 adjacent to the defective AME 22d. In this example, the bipolar plate 21 located below the defective AME 22d will be isolated since it is the latter which supplies the defective AME 22d. Subsequently, the bipolar plate to be isolated is referenced 21a.

[0045] In reference to the Figures 5 and 6 , the isolation device 9 comprises a belt 90 of peripheral shape. The belt 90 has a thickness, defined along the stacking axis X in the mounted position, which is greater than the thickness of a bipolar plate 21 so as to prevent any circulation of fluid in the latter. In particular, the belt 90 makes it possible to cooperate with the sealing joints 23 which are adjacent to the bipolar plate to be isolated 21a as illustrated in [ Fig.4]. Thus, the circulation chimney 20 is no longer in fluid communication with the circulation openings 210 of the bipolar plate to be isolated 21a. The bipolar plate 21 is no longer supplied with fluid and can no longer supply the defective AME 22d. Due to its peripheral shape, the belt 90 still allows the supply of fluid to the bipolar plates 21 located above and below the isolation device 9, the fluid being able to circulate in the center of the belt 90.

[0046] Preferably, the belt 90 is configured to be deformable between a first configuration, called rest configuration, and a second configuration, called tightened, the cross-section of which is smaller than in the first configuration. Preferably, the cross-section of the first configuration is substantially similar to the cross-section of the circulation chimney 20 in which the isolation device 9 is configured to be mounted so as to closely match its contour. Preferably, the belt 90 is formed from a deformable elastic material, for example, elastomer or rubber which also has good sealing performance.

[0047] Preferably, the isolation device 9 comprises a spring member 91 configured to constrain the belt 90 in the first configuration. In this example, as illustrated in Figures 5 and 6, the spring member 91 is in the form of a spring blade. Preferably, the spring member 91 is mounted in a groove 94 formed in the belt 90, in particular, in an inner face so as not to come into contact with the inner surface of a circulation chimney 20. The spring member 91 preferably comprises projecting ends 91a allowing the operator to constrain the spring member 91 in a practical manner in order to deform the belt 90 in the second configuration.

[0048] Such a spring member 91 is not mandatory and the belt 90 could deform the sealing joints 23, elastically, when the isolation device 9 is put in place.

[0049] Preferably, the isolation device 9 comprises an indexing member 92 configured to be housed between two seals 23 so as to ensure precise positioning of the isolation device 9 in the circulation chimney 20, that is to say, aligned with the circulation openings 210 of the bipolar plate to be isolated 21a. In this example, the indexing member 92 is in the form of a peripheral tongue extending in projection from the outer surface of the belt 90. Preferably, the indexing member 92 is made from the material of the belt 90, which makes it possible to reduce its manufacturing cost and to retain its sealing properties. Such an indexing member 92 advantageously makes it possible to index itself relative to the seals 23 and to deform them. A tab shape optimizes contact with the seals 23 to improve sealing.

[0050] In reference to the Figures 5 and 6, the isolation device 9 comprises a plurality of guide members 93 configured to cooperate with the inner surface of the circulation chimney 20 without completely closing the circulation openings 210 of the bipolar plates adjacent to the bipolar plate to be isolated 21a. In this example, the guide members 93 are elementary and not continuous so as to allow circulation of fluid between them. The guide members 93 are preferably positioned at each corner of the shape defined by the section of the circulation chimney 20. In this example, the circulation chimney 20 has a parallelogram section defining four corners. Also, as illustrated in Figures 5 and 6, the isolation device 9 comprises four guide members 93 in order to provide rigidity and improve the cooperation of the isolation device 9 with the concave zones (the corners) of the circulation chimney 20. Precise guidance and positioning make it possible to significantly improve the sealing. As illustrated in Figures 5 and 6 , the guide members 93 are in the form of portions extending vertically from an upper wall of the belt 90 so that they can be conveniently handled by an operator. Preferably, the guide members 93 are made from the material of the belt 90, which makes it possible to reduce its manufacturing cost.

[0051] An example of implementing a method for isolating a cell from a stack 2 will now be presented. In this example, with reference to the [ Fig.4], a circulation chimney 20 has a defective membrane electrode assembly (MEA) 22d which must be insulated. The circulation chimney 20 extends vertically and is accessible from its upper opening. Preferably, the insulation is carried out in the circulation chimney 20 conducting the hydrogen.

[0052] The method comprises a step of deforming the insulation device 9, from a first configuration to a second configuration, so as to reduce its section so that it is less than the section of the circulation chimney 20. The deformation is carried out simply by the operator by acting on the spring member 91, in particular on the ends 91a of the spring member 91.

[0053] The method comprises a step of moving the isolation device 9 according to the second configuration in the circulation chimney 20 so that the indexing member 92 is aligned with the bipolar plate to be isolated 21a located under the defective AME 22d.

[0054] The method comprises a step of releasing the stress applied to the isolation device 9 which, in the rest position, returns to the first configuration with a rest section which is substantially equal to that of the circulation chimney 20. When the stress is released, the belt 90 presses against the seals 23 so as to prevent any circulation of fluid between the circulation chimney 20 and the bipolar plate to be isolated 21a located under the defective AME 22d. The presence of the indexing member 92 allows precise positioning between the seals 23 and optimal sealed cooperation. The guide members 93 make it possible to guide the expansion of the belt 90 in the first configuration by positioning themselves in the concave zones of the circulation chimney 20, in particular, in its 4 corners.This limits the risk of a positioning fault of the isolation device 9 in particular when the circulation chimney 20 has a great height and the defective AME 22d is far from access to the circulation chimney 20.

[0055] Once the isolation device 9 is in position, all fluid circulation between the circulation chimney 20 and the bipolar plate 21a located under the defective AME 22d is stopped, which makes it possible to avoid supplying the AMEs 22 positioned adjacent to the bipolar plate 21a. Thus, the defective AME 22d is no longer supplied, which avoids forming a hot spot.

[0056] Preferably, the method comprises a step of electrically connecting the adjacent bipolar plates 21 to the defective MEA 22d so as to ensure electrical continuity in the fuel cell 1. Preferably, an electrical cable 10 is used to electrically connect the bipolar plates 21 as illustrated in [ Fig.4 ]. In other words, the bipolar plate 21a is no longer supplied with fluid and is electrically shunted, which ensures isolation of the defective cell allowing the fuel cell 1 to operate with one less cell.

[0057] When using the fuel cell 1, fluid circulates in the circulation chimney 20 to supply the cells that are not insulated in order to produce electrical energy. The fluid pressure makes it possible to force the belt 90 radially outwards in order to press it against the circulation openings 210, which ensures optimal sealing.

[0058] An isolation of a cell whose AME 22d is defective has been presented, but it goes without saying that the invention also applies to a cell or several cells whose bipolar plate 21 is defective. The isolation device 9 advantageously makes it possible to stop the supply of fluid to said bipolar plate 21 and to the associated cell.

[0059] When several adjacent AME 22 are defective, the isolation device 9 has a greater height and an indexing member 92 for each bipolar plate to be isolated.

Claims

1. Isolation device (9) configured to be mounted in a fluid flow channel (20) of a fuel cell (1) comprising a stack (2) comprising a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow channels (20) in the stack (2), the isolation device (9) comprising a belt (90) which is peripheral and configured to block the fluid communication between the flow channel (20) and at least one flow opening of a cell to be isolated from the stack (2), the belt (90) having a cross-section defined as the surface delimited by the periphery of the belt (90), the belt (90) being deformable between: • a first configuration, referred to as an idle configuration, wherein the cross-section of the belt (90) is substantially analogous to the cross-section of the flow channel (20) wherein the isolation device (9) is configured to be mounted, and • a second configuration, referred to as a constricted configuration, wherein the cross-section of the belt (90) is smaller than in the first configuration.

2. Isolation device (9) according to claim 1, wherein the isolation device (9) comprises a spring member (91) configured to constrain the belt (90) in the first configuration.

3. Isolation device (9) according to one of claims 1 to 2, wherein the isolation device (9) comprises an indexing member (92) configured to provide precise positioning of the isolation device (9) in the flow channel (20).

4. Isolation device (9) according to one of claims 1 to 3, wherein the isolation device (9) comprises a plurality of guiding members (93) configured to cooperate with an inner surface of the flow channel (20).

5. Isolation device (9) according to claim 4, wherein the flow channel (20) having a section defining a plurality of corners, the guiding members (93) are configured to cooperate with the corners of the flow channel (20).

6. Fuel cell assembly (1) comprising a stack (2) comprising a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow channels (20) in the stack (2) and an isolation device (9), according to one of claims 1 to 5, positioned in the flow channel (20) to seal the fluid communication between the flow channel (20) and at least one cell to be isolated from the stack (2)7. Assembly according to claim 6, wherein the stack (2) comprising an alternation of bipolar plates (21) and membrane electrode assemblies (22) defining the cells of the stack (2), the isolation device (9) is positioned in the flow channel (20) so as to block the fluid communication between the flow channel (20) and a bipolar plate to be isolated (21a).

8. Assembly according to claim 7, wherein, seals (23) being inserted between the bipolar plates (21), the seals (23) extend protruding into the flow channel (20).

9. Assembly according to claim 8, wherein, the isolation device (9) comprising an indexing member (92) configured to ensure a precise positioning of the isolation device (9) in the flow channel (20), the indexing member (92) cooperates with the seals (23) to provide a tight isolation.

10. Method of isolating a cell from a fuel cell (1) comprising a stack (2) comprising a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow channels (20) in the stack (2), the method comprising the steps consisting of: • Deforming the isolation device (9) according to one of claims 1 to 5, from the first configuration to the second configuration, so as to reduce its cross-section so that it is smaller than the cross-section of the flow channel (20), • Moving said isolation device (9) according to the second configuration in the flow channel (20) so as to align it with at least one flow opening of the cell to be isolated and • Releasing the constraint to deform the isolation device (9) from the second configuration to the first configuration so as to press the belt (90) against an inner surface of the flow channel (20) in order to block the fluid communication between the flow channel (20) and the flow opening of the defective cell.

11. Method of isolating according to claim 10 comprising a step of electrically connecting the cell to be isolated to another cell of the stack (2), preferably, an adjacent cell.