FR3116388A1 - SPRING ELEMENT, CLAMPING DEVICE FOR AN ELECTROCHEMICAL STACK, AND ASSEMBLY FORMED BY THE CLAMPING DEVICE AND THE ELECTROCHEMICAL STACK - Google Patents

Abstract

The invention relates to a spring element (500) provided with two bellows called, respectively, internal bellows (501) and external bellows (502), mounted coaxially around an axis of revolution XX', and between which is arranged a annular space forming a fluidic circuit (510). Figure for abstract: Figure 6 .

Description

SPRING ELEMENT, CLAMPING DEVICE FOR AN ELECTROCHEMICAL STACK, AND ASSEMBLY FORMED BY THE CLAMPING DEVICE AND THE ELECTROCHEMICAL STACK

The present invention relates to the field of clamping devices and in particular to clamping devices for electrochemical stacks. Said electrochemical stacks considered are in particular stacks of the SOEC or SOFC type capable of operating at temperatures above 700° C.

The invention relates in particular to a clamping device provided with a spring element intended to exert a force leading to the clamping, or even to the crushing of the electrochemical stack. The spring element, according to the terms of the present invention, is in particular an assembly of two spring washers of generally frustoconical shape and whose taper is oriented in two opposite directions. This spring element is also provided with thermalization means, and more particularly with a fluid conduit in which a cooling fluid is capable of flowing in order to maintain said spring element in a range of temperatures for which the force exerted by said element varies little.

PRIOR ART

There represents an electrochemical device 100 known from the state of the art and described in document [1] cited at the end of the description.

The electrochemical device comprises a stack 200 of solid oxides operating at high temperature clamped between two clamping plates 300 and 310 able to operate either in electrolyser mode or in fuel cell mode. Clamping rods, extending between the two clamping plates, are also implemented in order to maintain the clamping of the stack by the clamping plates.

The electrochemical device 100 is generally referred to by one or other of the acronyms "SOEC" ("Solid Oxide Electrolyser Cell") or "SOFC" ("Solid Oxide Full Cell") when it operates, respectively, in electrolyser mode or in fuel cell mode.

Stack 200, as shown in , comprises a stack 200 of elementary electrochemical cells 210 between which are interposed interconnectors 230 intended to ensure electrical contact between the elementary electrochemical cells. These interconnectors also comprise channels allowing the evacuation and/or the distribution of gas at the level of the elementary cells.

Each elementary electrochemical cell comprises an electrolyte 210e interposed between an anode 210a and a cathode 210c.

Throughout the description of the present application, by "anode", "cathode" and "electrolyte" is meant elements of generally flat shape, for example in the form of a layer, which comprise two essentially parallel main faces and connected by an outline.

The anode and the cathode of each elementary electrochemical cell generally comprise a porous layer, while the electrolyte forms a dense and tight layer.

Each interconnector arranged on either side of an electrochemical cell forms, respectively, with the anode an anode compartment 230a for gas distribution and collection, and with the cathode a cathode compartment 230c for gas distribution and collection.

In operation, the anode and the cathode are the site of electrochemical reactions, while the electrolyte allows the transport of ions from the cathode to the anode, or vice versa depending on whether the electrochemical device operates in electrolyser mode or in battery mode. fuel.

Thus in electrolyser mode, the cathode compartment allows a supply of water vapor and an evacuation of the water reduction products, in particular hydrogen, while the anode compartment ensures, via a draining gas, the evacuation of the dioxygen produced from the oxidation of O ^2- ions migrating from the cathode to the anode.

The electrolysis mechanism (“SOEC” mode) of water vapor by an elementary electrochemical cell is illustrated in . During this electrolysis, the elementary electrochemical cell is powered by a current flowing from the cathode to the anode. The water vapor distributed by the cathode compartment is then reduced under the effect of the current according to the following half-reaction:
[Chem 1]
2 H ₂ O + 4 e ^- → 2 H ₂ + 2 O ^2- .
The dihydrogen produced during this reaction is then evacuated, while the O ^2- ions produced during this reduction migrate from the cathode to the anode, via the electrolyte, where they are oxidized to dioxygen according to the half-reaction:
[Chem 2]
2 O ^2- → O ₂ + 4 e ^- .
The oxygen thus formed is evacuated by the draining gas circulating in the anode compartment.

The electrolysis of water vapor responds to the following reaction:
[Chem 3]
_2H2O → _2H2 + _O2 .
In fuel cell (“SOFC”) mode, air is injected into the cathode compartment where the oxygen is then reduced to O ^2- ions. These O ^2- ions then migrate towards the anode and react with dihydrogen circulating in the anode compartment to form water.

Operation in fuel cell mode allows the production of an electric current.

The optimization of the operation of such an electrochemical device known from the state of the art must however meet certain constraints.

In particular, it is necessary to have an electrical insulation between two successive interconnectors under penalty of short-circuiting the elementary electrochemical cell. Good electrical contact and a sufficient contact surface between an elementary electrochemical cell and an interconnector may also be necessary. The lowest possible ohmic resistance is then sought between cells and interconnectors. This depends on the facing materials but also on the level of tightness of the stack.

In addition, it is necessary to have a seal between the anode and cathode compartments under penalty of having a recombination of the gases produced leading to a drop in efficiency and especially the appearance of hot spots damaging the stack. Again, this tightness depends on the design of the joints and the materials used, but also on the level of tightness of the stack.

Finally, it is preferable to have a good distribution of the gases both at the inlet and at the recovery of the products, under penalty of loss of yield, of inhomogeneity of pressure and temperature within the various elementary electrochemical cells, even of prohibitive degradations. of said cells.

The electrochemical device 100 as shown in , by a choice of materials forming the rods and the clamping plates, makes it possible to respond favorably to the aforementioned requirements as long as the stack 200 contains less than 25 elementary electrochemical cells. However, when the stack comprises a number of elementary electrochemical cells exceeding 25, the latter is liable to exhibit an expansion at high temperature which is difficult to predict, and consequently makes the dimensioning of the rods and clamping plates complicated.

The object of the invention is therefore to propose a clamping device for clamping an electrochemical stack making it possible to accommodate a large number, for example greater than 25, of elementary electrochemical cells.

The invention also aims to provide a clamping device whose expansion remains limited when it is subjected to high temperatures and in particular temperatures above 700°C.

The invention also aims to propose an assembly which comprises the clamping device and an electrochemical stack.

The aims are, at least in part, achieved by a spring element provided with two bellows called, respectively, internal bellows and external bellows, mounted coaxially around an axis of revolution XX′, and between which an annular space is provided. forming a fluid circuit.

According to one embodiment, the annular space is also delimited at a first end and a second end by, respectively, a first base and a second base, the first base and the second base each having a symmetry of revolution around the axis of revolution XX'.

According to one embodiment, said spring element comprises a fluid supply orifice and a discharge orifice of said fluid cooperating with the fluidic circuit.

According to one embodiment, the supply orifice is formed in the first base while the discharge orifice is formed in the second base.

According to one embodiment, the spring element comprises a supply channel connected to the supply orifice and an evacuation channel connected to the evacuation orifice, said supply channel and evacuation channel being intended to be connected to a heat transfer fluid circulation system, advantageously, the supply channel and the evacuation channel are made in one piece with the internal bellows, the external bellows, the first base and the second base.

According to one embodiment, the spring element comprises at least one of the materials chosen from: a nickel-based superalloy, for example Inconel®718.

The invention also relates to a clamping device for an electrochemical stack, said device comprises:
- two clamping plates called, respectively, upper clamping plate and lower clamping plate, facing each other by one of their faces, called, respectively, upper internal face and lower internal face, and between which is intended to be enclosed in an electrochemical stack;
- the spring element according to the present invention, said spring element being arranged to clamp the two clamping plates against the electrochemical stack capable of being clamped between said clamping plates;
- A holding means intended to maintain the clamping, imposed by the spring element on the clamping plates.

According to one embodiment, the holding means comprises a base plate, the spring element bearing on the one hand against an internal face of the base plate and, on the other hand, against an upper external face of the base plate. upper clamping, and opposite to the upper inner face.

According to one embodiment, the at least one holding means further comprises at least two tie rods arranged to adjust the distance between the base plate and the lower clamping plate in order to impose compression on the spring element.

According to one embodiment, the at least two tie rods are pivotally mounted, by a first end, on a peripheral contour of the lower clamping plate, while the base plate comprises notches intended to be traversed by the tie rods, each tie rod comprises a thread which extends from a second end, opposite the first end and cooperating with a nut.

The invention also relates to an electrochemical assembly which comprises:
- a clamping device according to the present invention,
- an electrochemical stack with solid oxides of the SOEC/SOFC type operating at high temperature and comprising at least one elementary electrochemical cell, said stack being clamped between the upper clamping plate and the lower clamping plate, and so as to exert a force of predetermined crushing on said stack.

According to one embodiment, an upper end plate and a lower end plate are inserted between the electrochemical stack and, respectively, the upper clamping plate and the lower clamping plate.

Other characteristics and advantages will appear in the following description of a spring element, given by way of non-limiting examples, with reference to the appended drawings in which:

shows, in a perspective view, an electrochemical device known from the state of the art (document [1]), and on which the present invention is likely to be implemented;

is an exploded schematic view of a stack of two basic electrochemical cells known from the state of the art and capable of being implemented within the scope of the present invention;

is a schematic view showing the principle of operation of an elementary electrochemical cell in high temperature solid oxide electrolyser (SOEC) mode, the arrows represent the circulation of gases at the level of the electrodes, in particular the arrows in solid lines represent the circulation of reactive gases or reaction products, while the arrow in broken lines represents the circulation of draining gas;

is a schematic representation according to a sectional plane of a clamping device clamping an electrochemical stack according to the present invention;

is a schematic representation in perspective of a spring element capable of being implemented within the scope of the present invention;

is a schematic representation according to a sectional plane passing through an axis of revolution XX′ of a spring element capable of being implemented within the scope of the present invention;

is a schematic representation, according to a perspective view, of a clamping device implementing the spring element of the ;

is a graphic representation of the force (E in N on the vertical axis) exerted by the spring element as a function of crushing (D in mm, on the horizontal axis) of an electrochemical stack of 25 elementary cells ;

are schematic representations of two compression phases of an electrochemical stack with the clamping device according to the present invention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The present invention relates to a spring element formed by two bellows, respectively called internal bellows and external bellows, mounted coaxially, and between which is formed an annular space forming a fluidic circuit.

The fluidic circulation circuit allows in particular the circulation of a heat transfer fluid between an inlet orifice and an outlet orifice for the purpose of thermalizing said spring element.

The present invention also relates to a clamping device provided with two clamping plates between which a stack, for example an electrochemical stack, is intended to be clamped. In particular, the device according to the present invention comprises the spring element. The spring element is in particular arranged to transmit a force to the clamping plates, in order to impose a crushing on said electrochemical stack.

The fluidic circuit of the spring element thus allows the circulation of a fluid in the volume of the spring element so as to limit, or even prevent, the expansion of said spring element when it is subjected to high temperatures, and in particular to temperatures above 700°C.

Thus, the clamping device is advantageously implemented in an assembly which comprises an electrochemical stack sandwiched between the two clamping plates.

The rest of the statement describes, in relation to Figures 4 to 8, 9a and 9b, a clamping device 400.

Said clamping device 400 is represented with a stack, and in particular an electrochemical stack 200, clamped between two clamping plates called, respectively, upper clamping plate 410 and lower clamping plate 420.

By "clamping plate" is meant a plate of generally flat shape, which comprises two main faces connected by an outline, and which when they are assembled in pairs are intended to maintain the cohesion of a stack, for example of an electrochemical stack.

“Electrochemical stack” means a stack of elementary electrochemical cells.

The upper clamping plate 410 comprises two main faces called, respectively, upper internal face 410a and an upper external face 410b essentially parallel and connected by an upper outline 410c.

The lower clamping plate 420 comprises two main faces called, respectively, lower internal face 420a and a lower external face 420b essentially parallel and connected by a lower contour 420c.

The upper clamping plate 410 and the lower clamping plate 420 are in particular arranged so that the upper internal face 410a and the lower internal face 420a face each other.

The space delimited by the upper internal face 410a and the lower internal face 420a is intended to accommodate the stack, and more particularly the electrochemical stack 200.

The clamping device 400 also comprises a spring element 500. The spring element 500 is in particular arranged to exert a force which leads to the clamping of the electrochemical stack 200 by the upper clamping plate 410 and the lower clamping plate 420 ( ).

The spring element 500 is provided with two bellows called, respectively, internal bellows 501 and external bellows 502, mounted coaxially around an axis of revolution XX', and between which an annular space is provided forming a fluidic circuit 510 ( figures 5 and 6). The annular space is also delimited at a first end 521 and a second end 522 by, respectively, a first base 521a and a second base 522a.

The first base 521a and the second base 522a each comprise two main faces connected by an outline. More particularly, each of these bases 521a and 522a has a symmetry of revolution around the axis of revolution XX', said axis of revolution XX' being perpendicular to the main faces of each of the bases 521a and 522a. Each base can also comprise a through opening giving access to an internal volume of the internal bellows.

The spring element 500 also comprises a fluid supply orifice 541 and a discharge orifice 542 of said fluid cooperating with the fluidic circuit.

Advantageously, the supply orifice 541 is formed in the first base 521a while the discharge orifice 542 is formed in the second base 522a.

More particularly, the supply orifice 541 emerges from the contour of the first base 521a, while the evacuation orifice 542 emerges from the contour of the second base 522a.

Spring member 500 may also include a supply channel 551 connected to supply port 541 and an exhaust channel 552 connected to exhaust port 542 ( ). The supply channel 551 and evacuation channel 552 are in particular intended to be connected to a circulation system for a heat transfer fluid. Advantageously, the supply channel 551 and the evacuation channel 552 are made in one piece with the internal bellows, the external bellows, the first base and the second base.

The implementation of the fluidic circuit 510 thus makes it possible to impose the circulation of a fluid, in the fluidic circuit 510 for the purpose of thermalizing the spring element 500 ( ).

In a particularly advantageous manner, it is possible to impose the circulation of a cooling fluid in the fluidic circuit 510. The circulation of the cooling fluid can in particular be adapted to maintain the spring element 500 in a range of temperatures for which the mechanical properties undergo little or no variation. In other words, the circulation of a cooling fluid in the fluidic circuit 510 makes it possible to limit the variation of the force exerted by the spring element 500 when the latter is close to a heat source. In this regard, an electrochemical stack 200 with solid oxides of the SOEC/SOFC type is known to operate at high temperature, and in particular at temperatures above 700° C., and can, consequently, generate heating, by radiation or by conduction, of the spring element 500. This heating, a source of expansion of the spring element 500, results, without other precautions, generally in a variation in the force exerted by the latter which ultimately risks causing a rupture of sealing within the electrochemical stack. The implementation of a thermalization of the spring element 500 by the circulation of a cooling fluid thus makes it possible to limit the risk of rupture of the seal.

The spring element 500 can advantageously comprise at least one of the alloys chosen from: 310s, Inconel 718, Inconel 625.

In this regard, Inconel 718 exhibits corrosion resistance and mechanical properties over a wide temperature range that make it the alloy of choice when the applications under consideration involve temperatures up to 700°C.

The spring element 500 can be formed by an additive manufacturing technique, and in particular by 3D manufacturing. The dimensioning of the spring element 500 can be carried out so that the latter has a given stiffness. For example, the spring element can be dimensioned so as to be able to apply a sufficient force to seal the electrochemical stack clamped between the two clamping plates 410 and 420. In this respect, the is a graphic representation of a crushing D of an electrochemical stack formed of 25 elementary electrochemical cells as a function of the force exerted by the spring element 500.

On this graph, it appears that a crushing D of 50 mm of the electrochemical stack 200 is associated with a force exerted by the spring element of 2000 N. This stack, when it is subjected to a heating, in particular a heating at a temperature equal to 900° C., is liable to undergo an expansion of approximately 2 mm which results in a negligible variation in the force actually exerted by the spring element 500.

The clamping device 400 also comprises a holding means 600 intended to maintain the clamping imposed by the spring element 500 on the clamping plates ( ).

In particular, the holding means 600 comprises at least two tie rods 610a and 610b, as well as a base plate 620. The base plate 620 is provided with two main faces called, respectively, internal face 620a and external face 620b and connected by a outline 620c. More particularly, the base plate 620 is facing the upper outer face 410b by its inner face 620a, and the spring element 500 is located between the base plate 620 and the upper clamping plate 410, resting, respectively, against the internal face 620a and the upper external face 410b.

Furthermore, the at least two tie rods 610a and 610b extend between the lower clamping plate and the base plate to allow assembly of said plates and to adjust the distance which separates them. More particularly, this adjustment of the distance between the lower clamping plate and the base plate is intended to put the spring element 500 under compression so that the latter exerts a force which results in the clamping of the electrochemical stack between the clamping plates 410 and 420.

The at least two tie rods 610a and 610b can, according to a first aspect, pass through through openings made in the base plate 620 and the upper clamping plate 410, and cooperate with clamping means, for example nuts, at the level of the openings through.

According to a second aspect, the at least two tie rods 610a and 610b can advantageously be pivotally mounted, via a first end, on the contour 420c of the lower clamping plate 420 (FIG. 4). According to this second aspect, the base plate 620 comprises notches 612a and 612b intended to be crossed by the tie rods 610a and 610b ( ). Like the first aspect, clamping means, for example nuts, cooperate with the at least two tie rods at the notches 612a and 612b.

Advantageously, the base plate 620, the upper clamping plate 410 and the spring element 500 can form a single piece. This one-piece part can be obtained by an additive manufacturing process, and in particular by 3D manufacturing. According to this arrangement, a fluid, and in particular a cooling fluid, can circulate in the fluidic channel 510 of the spring element 500. During this circulation, the cooling fluid, for example water, undergoes a heating likely to transform it into steam into water vapour. This water vapor can advantageously be injected into the electrochemical stack 200.

In a particularly advantageous manner, the base plate comprises an orifice, called mounting orifice 630 ( ), in alignment with the axis of revolution XX' of the spring element 500. This mounting orifice is implemented in particular for crushing the electrochemical stack 200.

In this regard, Figures 9a and 9b are illustrations of the assembly of an electrochemical stack 200 and the clamping device.

This assembly comprises, initially, a phase of compression of the electrochemical stack 200 placed between the two clamping plates 410 and 420. apply a force, for example 2000 N, against the upper outer face 410b so as to crush the electrochemical stack 200 ( ). This compression phase may involve thermal cycles. For example, the compression may initially take place at room temperature or at a temperature below 200°C. The assembly thus compressed can be heated, for example to a temperature above 700° C., then cooled to its initial temperature while maintaining the force exerted by the jack.

The assembly also includes a second phase during which the tie rods 610a and 610b are positioned in the notches 612a and 612b so as to assemble the lower clamping plate 420 with the base plate 620. This second phase also includes the positioning of nuts 611a and 611b cooperating with the tie rods 610a and 610b at the level of the upper external face 610b so that the spring element 500 applies the force initially exerted by the jack.

The clamping device 400 according to the present invention thus makes it possible to exert a constant force on the electrochemical stack independently of the temperature of said stack. This device also makes it possible to envisage the stacking of a relatively large number, in particular greater than 25 or even greater than 50, of elementary electrochemical cells.

Furthermore, the cooling liquid circulating in the fluid circulation channel may comprise water. The latter, released in the form of water vapor at the level of the second end of the spring, can not advantageously be recovered, and in particular be injected into the electrochemical stack as a reagent. This aspect contributes to improving the energy efficiency of the electrochemical stack.

Finally, this clamping device remains relatively compact.

The invention also relates to an electrochemical assembly which comprises:
- a clamping device 400 according to the present invention,
- an electrochemical stack 200 with solid oxides of the SOEC/SOFC type operating at high temperature and comprising at least one elementary electrochemical cell, said stack being clamped between the upper clamping plate and the lower clamping plate, and so as to exert a force predetermined crush on said stack.

The assembly can also comprise an upper end plate and a lower end plate which are inserted between the electrochemical stack 200 and, respectively, the upper clamping plate 410 and the lower clamping plate 420.

REFERENCES

[1] FR 3 045 215

Claims (12)

Spring element (500) provided with two bellows called, respectively, internal bellows (501) and external bellows (502), mounted coaxially around an axis of revolution XX', and between which is provided an annular space forming a circuit fluidics (510). Spring element according to Claim 1, in which the annular space is also delimited at the level of a first end (521) and a second end (522) by, respectively, a first base (521a) and a second base ( 522a), the first base and the second base each having a symmetry of revolution around the axis of revolution XX'. Spring element according to Claim 2, in which the said spring element (500) comprises a fluid supply orifice (541) and a discharge orifice (542) of said fluid cooperating with the fluidic circuit (510). A spring element according to claim 3, wherein the supply port (541) is formed in the first base (521a) while the discharge port (542) is formed in the second base (522a). Spring element according to claim 3 or 4, wherein the spring element (500) comprises a supply channel (551) connected to the supply port (541) and an exhaust channel (552) connected to the evacuation orifice (542), said supply channel (551) and evacuation channel (552) being intended to be connected to a circulation system for a heat transfer fluid, advantageously, the supply channel and the evacuation channel are made in one piece with the inner bellows, the outer bellows, the first base and the second base. Spring element according to one of Claims 1 to 5, in which the spring element (500) comprises at least one of the materials chosen from: a nickel-based superalloy, for example Inconel®718. Clamping device (400) for an electrochemical stack (200), said device comprises:
- two clamping plates (410, 420) called, respectively, upper clamping plate (410) and lower clamping plate (420), facing each other by one of their faces, called, respectively, face upper internal face (420a) and lower internal face (420b), and between which an electrochemical stack (200) is intended to be clamped;
- the spring element (500) according to one of claims 1 to 6, said spring element (500) being arranged to clamp the two clamping plates (410, 420) against the electrochemical stack (200) capable of being clamped between said clamping plates (410, 420);
- a holding means (600) intended to maintain the clamping imposed by the spring element (500) on the clamping plates (410, 420). Device according to Claim 7, in which the holding means comprises a base plate (620), the spring element (500) bearing on the one hand against an internal face of the base plate and, on the other hand, against an upper outer face (410b) of the upper clamping plate (410), and opposite to the upper inner face (420a). Device according to Claim 8, in which the at least one holding means further comprises at least two tie rods (610a, 610b) arranged to adjust the distance between the base plate (620) and the lower clamping plate (420) in order to to impose a compression on the spring element (500). Device according to Claim 9, in which the at least two tie rods (610a, 610b) are pivotally mounted, by a first end, on a peripheral contour (420c) of the lower clamping plate (420), while the base plate ( 620) comprises notches (612a, 612b) intended to be traversed by the tie rods (610a, 610b), each tie rod (610a, 610b) comprises a thread which extends from a second end, opposite the first end and cooperating with a nut. Electrochemical assembly which includes:
- a clamping device according to one of claims 7 to 10,
- an electrochemical stack (200) with solid oxides of the SOEC/SOFC type operating at high temperature and comprising at least one elementary electrochemical cell, said stack being clamped between the upper clamping plate (410) and the lower clamping plate (420) , and so as to exert a predetermined crushing force on said stack. Assembly according to claim 11, in which an upper terminal plate and a lower terminal plate are inserted between the electrochemical stack and, respectively, the upper clamping plate (410) and the lower clamping plate (420).