Mechanical load take-up system integrated into a plurality of sub-stacks of high-temperature SOEC / SOFC solid oxide cells placed one on top of the other

Abstract

The invention relates to a mechanical load take-up system (100) integrated into a plurality of sub-stacks (20a) of high-temperature SOEC / SOFC solid oxide cells forming a modular stack (20), which system comprises: - a thermal enclosure (102); - a plurality of sub-stacks (20a); - a plurality of end plates (40), each having an upper face (40s) and a lower face (40i), the surface area of an upper face (40s) being larger in size than the surface area of a lower face (20ai) of a sub-stack (20a) and the surface area of a lower face (40i) being larger in size than the surface area of an upper face (20as) of a sub-stack (20a) so as to obtain one or more free surfaces (40l) that are not positioned on top of a sub-stack (20a); - a plurality of supporting members (103); and - a plurality of resilient return members (104) arranged between one or more supporting members (103) and one or more free surfaces (40l).

Description

[0001] DESCRIPTION

[0002] TITLE: Integrated mechanical load transfer system within a plurality of superimposed high-temperature SOEC / SOFC type solid oxide cell substacks

[0003] TECHNICAL FIELD OF THE INVENTION

[0004]

[0001] The present invention relates to the general field of high temperature electrolysis (HTE), in particular high temperature steam electrolysis (HTE), designated by the English terms "High Temperature Electrolysis" (HTE) and "High Temperature Steam Electrolysis" (HTSE), of carbon dioxide (CO₂) electrolysis, or even of high temperature co-electrolysis of water vapor and carbon dioxide (CO₂).

[0005]

[0002] More specifically, the invention relates to the field of high-temperature solid oxide electrolyzers, usually designated by the acronym SOEC (for "Solid Oxide Electrolysis Cell" in English).

[0006]

[0003] It also relates to the field of high-temperature solid oxide fuel cells, usually referred to by the acronym SOFC (for "Solid Oxide Fuel Cells" in English).

[0007]

[0004] Thus, more generally, the invention relates to the field of SOEC / SOFC type solid oxide cell stacks operating at high temperature.

[0008]

[0005] More specifically, the invention relates to a mechanical load recovery system for a plurality of superimposed SOEC / SOFC type solid oxide cell sub-stacks operating at high temperature, allowing the simultaneous operation of the sub-stacks with mechanical load recovery.

[0009] STATE OF THE ART

[0010]

[0006] In a high-temperature solid oxide electrolyzer (SOEC), the process involves converting water vapor (H2O) into dihydrogen (H2) and dioxygen (O2) by means of an electric current within the same electrochemical device, and / or converting carbon dioxide (CO2) into carbon monoxide (CO) and dioxygen (O2). In a high-temperature solid oxide fuel cell (SOFC), the operation is reversed, producing an electric current and heat when supplied with dihydrogen (H2) or other fuels such as methane (CH4), natural gas, biogas, and dioxygen (O2), typically air. For the sake of simplicity, the following description focuses on the operation of a high-temperature solid oxide electrolyzer (SOEC) performing the electrolysis of water vapor.However, this principle is applicable to the electrolysis of carbon dioxide (CO2), and even to the co-electrolysis of high-temperature steam (HTS) with carbon dioxide (CO2). Furthermore, this principle can be applied to the case of a high-temperature solid oxide fuel cell (SOFC).

[0011]

[0007] To perform water electrolysis, it is advantageous to carry it out at high temperature, typically between 600 and 1000°C, because it is more economical to electrolyze steam than liquid water and because some of the energy required for the reaction can be supplied by heat, which is cheaper than electricity.

[0008] To implement high-temperature steam electrolysis (HTSE), a high-temperature solid oxide electrolyzer (SOEC) of the SOEC type consists of a stack of elementary units, each comprising a solid oxide electrolysis cell, or electrochemical cell, made up of three anode / electrolyte / cathode layers stacked one on top of the other, and interconnecting plates made of metallic alloys, also called bipolar plates or interconnectors. Each electrochemical cell is sandwiched between two interconnecting plates.A high-temperature solid oxide electrolyzer (SOEC) is an alternating stack of electrochemical cells and interconnectors. A high-temperature solid oxide fuel cell (SOFC) consists of the same type of stacking of elementary units. Because this high-temperature technology is reversible, the same stack can operate in electrolysis mode, producing hydrogen and oxygen from water and electricity, or in fuel cell mode, producing electricity from hydrogen and oxygen.

[0012]

[0009] Each electrochemical cell corresponds to an electrolyte / electrode assembly, which is typically a multilayer ceramic assembly in which the electrolyte is formed by a central ion-conducting layer. This layer is solid, dense, and impermeable, and is sandwiched between the two porous layers forming the electrodes. It should be noted that additional layers may exist, but these serve only to improve one or more of the layers already described.

[0013]

[0010] The electrical and fluidic interconnecting devices are electronic conductors that ensure, from an electrical point of view, the connection of each electrochemical cell of elementary motif in the stack of elementary motifs, guaranteeing electrical contact between one face and the cathode of one cell and between the other face and the anode of the next cell, and from a fluidic point of view, the supply of reactants and the removal of products for each of the cells. The interconnectors thus perform the functions of supplying and collecting electrical current and delimit gas circulation compartments for distribution and / or collection.

[0014]

[0011] More specifically, the interconnectors have the main function of ensuring the passage of electric current but also the circulation of gases in the vicinity of each cell (namely: injected water vapor, extracted hydrogen and oxygen for EHT electrolysis; air and fuel including injected hydrogen and extracted water vapor for a SOFC cell), and of separating the anodic and cathodic compartments of two adjacent cells, which are the gas circulation compartments on the anode and cathode sides of the cells respectively.

[0015]

[0012] In particular, for a high-temperature solid oxide electrolyzer (SOEC), the cathode compartment contains water vapor and hydrogen, products of the electrochemical reaction, while the anode compartment contains a draining gas, if present, and oxygen, another product of the electrochemical reaction. For a high-temperature solid oxide fuel cell (SOFC), the anode compartment contains the fuel, while the cathode compartment contains the oxidizer.

[0016]

[0013] To perform high-temperature steam electrolysis (HTE), steam (H2O) is injected into the cathode compartment. Under the effect of the electric current applied to the cell, the dissociation of water molecules into steam occurs at the interface between the hydrogen electrode (cathode) and the electrolyte: this dissociation produces dihydrogen gas (H₂) and oxygen ions (O₂). 2The dihydrogen (H₂) is collected and discharged from the hydrogen compartment outlet. The oxygen ions (O₂) 2 ) migrate through the electrolyte and recombine into dioxygen (O2) at the interface between the electrolyte and the oxygen electrode (anode). A draining gas, such as air, can circulate at the anode and thus collect the oxygen generated in gaseous form at the anode.

[0017]

[0014] To ensure the operation of a solid oxide fuel cell (SOFC), air (oxygen) is injected into the cathode compartment of the cell and hydrogen into the anodic compartment. The oxygen from the air will dissociate into O₂ ions 2 These ions migrate in the electrolyte from the cathode to the anode to oxidize hydrogen and form water, simultaneously producing electricity. In a SOFC fuel cell, as in SOEC electrolysis, water vapor is found in the hydrogen (H2) compartment. Only the polarity is reversed.

[0018]

[0015] By way of illustration, Figure 1 represents a schematic view showing the operating principle of a high-temperature solid oxide electrolyzer of the SOEC type. The function of such an electrolyzer is to transform water vapor into hydrogen and oxygen according to the following electrochemical reaction: 2 H2O 2 H2+ O2.

[0019]

[0016] This reaction is carried out electrochemically in the cells of the electrolyzer. As shown schematically in Figure 1, each elementary electrolysis cell 1 consists of a cathode 2 and an anode 4, placed on either side of a solid electrolyte 3. The two electrodes (cathode and anode) 2 and 4 are electronic and / or ionic conductors made of a porous material, and the electrolyte 3 is gas-tight, an electronic insulator, and an ionic conductor. The electrolyte 3 can, in particular, be an anionic conductor, more precisely an anionic conductor of O₂ ions 2' and the electrolyzer is then called an anionic electrolyzer, as opposed to proton electrolytes (H + ).

[0020]

[0017] The electrochemical reactions take place at the interface between each of the electronic conductors and the ionic conductor.

[0021]

[0018] At cathode 2, the half-reaction is as follows:

[0022] 2 H2O + 4 e → 2 H2 + 2 O 2 '.

[0023]

[0019] At anode 4, the half-reaction is as follows:

[0024] 2 O 2 ^ O2+ 4 e\

[0025]

[0020] Electrolyte 3, intercalated between the two electrodes 2 and 4, is the site of migration of the O ions 2 ' under the effect of the electric field created by the potential difference imposed between the anode 4 and the cathode 2.

[0026]

[0021] As illustrated in parentheses in Figure 1, the water vapor at the cathode inlet may be accompanied by hydrogen (H2), and the hydrogen produced and recovered at the outlet may be accompanied by water vapor. Similarly, as illustrated by the dashed line, a draining gas, such as air, may also be injected at the anode inlet to remove the oxygen produced. The injection of a draining gas has the additional function of acting as a thermal regulator.

[0027]

[0022] An elementary electrolyzer, or electrolysis reactor, consists of an elementary cell as described above, with a cathode 2, an electrolyte 3, and an anode 4, and two interconnectors which provide the electrical and fluidic distribution functions.

[0028]

[0023] To increase the flow rates of hydrogen and oxygen produced, it is known to stack several elementary electrolysis cells one on top of the other, separating them with interconnectors. The assembly is positioned between two end interconnection plates that support the electrical and gas supplies of the electrolyzer (electrolysis reactor).

[0029]

[0024] A high-temperature solid oxide electrolyzer of the SOEC type thus comprises at least one, generally a plurality of electrolysis cells stacked one on top of the other, each elementary cell being formed of an electrolyte, a cathode and an anode, the electrolyte being intercalated between the anode and the cathode.

[0030]

[0025] As previously stated, the fluid and electrical interconnection devices which are in electrical contact with one or more electrodes generally provide the functions of supplying and collecting electrical current and delimit one or more gas circulation compartments.

[0031]

[0026] Thus, the so-called cathodic compartment has the function of distributing the electric current and water vapor as well as recovering hydrogen at the cathode in contact.

[0032]

[0027] The so-called anodic compartment has the function of distributing the electric current as well as recovering the oxygen produced at the anode in contact, possibly with the help of a draining gas.

[0033]

[0028] Figure 2 shows an exploded view of elementary motifs of a high-temperature solid oxide electrolyzer of the SOEC type according to the prior art. This electrolyzer comprises a plurality of elementary electrolysis cells C1, C2, of the solid oxide cell (SOEC) type, stacked alternately with interconnectors 5. Each cell C1, C2 consists of a cathode 2.1, 2.2 and an anode (only the anode 4.2 of cell C2 is shown), between which is disposed an electrolyte (only the electrolyte 3.2 of cell C2 is shown).

[0034]

[0029] The interconnector 5 is a metal alloy component that provides the separation between the cathode compartment 50 and the anode compartment 51, defined by the volumes between the interconnector 5 and the adjacent cathode 2.1 and between the interconnector 5 and the adjacent anode 4.2, respectively. It also ensures the distribution of gases to the cells. The injection of water vapor into each elementary motif takes place in the cathode compartment 50. The collection of the hydrogen produced and the residual water vapor at the cathode 2.1, 2.2 is carried out in the cathode compartment 50 downstream of the cell C1, C2 after the water vapor has been dissociated by the latter. The collection of the oxygen produced at the anode 4.2 is carried out in the anode compartment 51 downstream of the cell C1, C2 after the water vapor has been dissociated by the latter.The interconnector 5 ensures the passage of current between cells C1 and C2 by direct contact with the adjacent electrodes, i.e. between the anode 4.2 and the cathode 2.1.

[0035]

[0030] Since the operating conditions of a high-temperature solid oxide electrolyzer (SOEC) are very similar to those of a solid oxide fuel cell (SOFC), the same technological constraints apply.

[0031] Thus, the proper functioning of such stacks of SOEC / SOFC-type solid oxide cells operating at high temperatures primarily requires meeting the points stated below.

[0036]

[0032] First, electrical insulation is necessary between two successive interconnectors to avoid short-circuiting the electrochemical cell. Good electrical contact and a sufficient contact surface between a cell and an interconnector are also required. The lowest possible ohmic resistance is sought between cells and interconnectors.

[0037]

[0033] Furthermore, a seal must be provided between the anodic and cathodic compartments, otherwise there will be a recombination of the gases produced, leading to a decrease in efficiency and, above all, the appearance of hot spots damaging the stack.

[0038]

[0034] Finally, it is essential to have a good distribution of gases both in the input and in the recovery of the products under penalty of loss of yield, inhomogeneity of pressure and temperature within the different elementary motifs, or even of prohibitive degradation of the electrochemical cells.

[0039]

[0035] The gases entering and exiting a high-temperature electrolysis (SOEC) or fuel cell (SOFC) stack operating at high temperature can be managed by means of devices such as the one illustrated with reference to Figure 3. The device 13 thus comprises cold parts PF and hot parts PC, the latter including the furnace floor 11, the furnace bell 10, a loop tube 12 to manage the gas inlets and outlets and the stack 20, also called “stack”, of high-temperature electrolysis (SOEC) or fuel cell (SOFC).

[0040]

[0036] Furthermore, Figure 4 illustrates an example of an assembly 80 comprising such a stack 20 and a clamping system 60 for it. Such an assembly 80 may be as described in French patent application FR 3 045 215 A1.

[0041]

[0037] Thus, the stack 20 comprises a plurality of electrochemical cells 41, each formed of a cathode, an anode, and an electrolyte interposed between the cathode and the anode, and a plurality of intermediate interconnectors 42, each arranged between two adjacent electrochemical cells 41. Furthermore, it comprises an upper terminal plate 43 and a lower terminal plate 44, also referred to respectively as the upper stack terminal plate 43 and the lower stack terminal plate 44, between which the plurality of electrochemical cells 41 and the plurality of intermediate interconnectors 42 are sandwiched, i.e., between which the stack is located.

[0042]

[0038] The clamping system 60 comprises an upper clamping plate 45 and a lower clamping plate 46, between which the stack 20 is clamped. Each clamping plate 45, 46 has four clamping holes 54 through which clamping rods 55, or tie rods, extend. Clamping means 56, 57, 58 are provided at the ends of these rods.

[0043]

[0039] In general, to date, stacks 20 have a limited number of electrochemical cells 41. Typically, the Applicant implements stacks 20 with 25 electrochemical cells 41 of 100 cm³ 2active surface area. The conditioning step is carried out individually, with each stack placed alone in a conditioning bench. The applied cycle performs both the sealing step and the reduction step of the electrochemical cells 41. The cycle concludes with various electrochemical measurements to characterize the stack's performance before it is delivered for use.

[0044]

[0040] Before it can operate, the stack 20 must undergo at least one heat treatment step, known as a reduction step, in order to bring the electrochemical cells 41 to their reduced form, and not to their initially oxidized state. This reduction step can be a thermomechanical cycle under a reducing gas for the hydrogen electrode and air or a neutral gas for the oxygen electrode. Such a heat treatment step has, for example, been described in European patent application EP 2 870 650 A1.

[0045]

[0041] Furthermore, the 20 stacks implemented to date generally use, at each of their levels, seals that must guarantee the seal between two adjacent and distinct gas circulation compartments, i.e., an anodic compartment and a cathodic compartment. Such seals were described in European patent application EP 3 078 071 A1. These seals have the particularity of requiring thermal conditioning during which they are compressed.

[0046]

[0042] Furthermore, the contact elements, such as the layers described in patent application EP 2 900 846 A1 or the nickel grids, are also compressed during thermal conditioning and during operation of the stack 20, which ensures their proper positioning. The elements that serve as contact elements in the hydrogen chamber are also compressed.

[0047]

[0043] In other words, during the heat conditioning step, a stack of 20 is compressed by several centimeters. To date, given the relatively small number of stacked cells, the compression is proceeding correctly.

[0048]

[0044] However, the Applicant has considered implementing stacks with a larger number of electrochemical cells, typically beyond 25 cells. In this case, the expected displacement during stack tightening can lead to mechanical jamming problems of the buttressing type on the guide rods. These jams then prevent proper thermal conditioning and, consequently, normal operation of the stack.

[0049]

[0045] One solution to these drawbacks is to use a stacking concept in which several sub-stacks are assembled, by means of stiffening plates, so as to manage large crushing forces. However, it is then necessary to condition each sub-stack separately, and thus a significant number of stacks and sub-stacks must be produced.

[0050]

[0046] However, conditioning such a stack is a lengthy and costly process because heating requires energy. Furthermore, current devices only allow for the conditioning of one stack or sub-stack at a time.

[0051]

[0047] Consequently, there is still a need to improve the conditioning and operating principle of high-temperature electrolysis stacks (SOEC) or fuel cell stacks (SOFC), in particular to condition and operate several sub-stacks at the same time.

[0052] DESCRIPTION OF THE INVENTION

[0053]

[0048] The invention aims to remedy, at least partially, the aforementioned needs and the drawbacks of prior art implementations.

[0049] The invention thus relates, according to one of its aspects, to a mechanical load-bearing system for a plurality of sub-stacks of SOEC / SOFC type solid oxide cells operating at high temperature, together forming a modular stack of high-temperature SOEC / SOFC type solid oxide cells, in particular a mechanical load-bearing system integrated into such a plurality of SOEC / SOFC type solid oxide cell sub-stacks, each sub-stack comprising a plurality of electrochemical cells, each formed of a cathode, an anode, and an electrolyte interposed between the cathode and the anode, and a plurality of intermediate interconnectors arranged between two adjacent electrochemical cells, characterized in that the system comprises:

[0054] - a thermal enclosure delimiting an internal volume,

[0055] - a plurality of substacks placed in the internal volume, at least two substacks being at least partially superimposed on each other, each substack having a top face and a bottom face,

[0056] - a plurality of end plates, each substack being arranged between an upper end plate and a lower end plate, each end plate having an upper face and a lower face, at least one of which is in contact with at least one substack, the surface area of ​​an upper face of an end plate being larger than the surface area of ​​a lower face of a substack and the surface area of ​​a lower face of an end plate being larger than the surface area of ​​an upper face of a substack, such that each upper face and each lower face of an end plate in contact with at least one substack has one or more free surfaces not superimposed on a substack and not in contact with a substack,

[0057] - a plurality of supports, also called matrix-forming supports or matrices, arranged on one or more free surfaces of the upper faces of the terminal plates in contact with at least one substack,

[0058] - a plurality of elastic return elements arranged between one or more supports and one or more free surfaces of the lower faces of the terminal plates.

[0059]

[0050] The mechanical load recovery system according to the invention may further comprise one or more of the following characteristics taken individually or in any possible technical combinations.

[0060]

[0051] The elastic return elements may have identical shapes.

[0061]

[0052] The first stage of the modular stack, associated with the first sub-stack, starting from the top of the modular stack, may be without support and elastic return element.

[0062]

[0053] Furthermore, the elastic restoring members associated with a third sub-stack, located below a second sub-stack, may have a number and / or stiffness of elastic restoring members greater than the number and / or stiffness of the elastic restoring members associated with the second sub-stack superimposed above the third sub-stack.

[0063]

[0054] The number of elastic return elements and / or the stiffness of the elastic return elements can be increasing from the top of the modular stack to the bottom of the modular stack.

[0064]

[0055] Furthermore, the elastic return elements associated with the same sub-stack can be arranged symmetrically with respect to the two vertical planes meeting on the central axis of the modular stack, in particular formed by the extension of a force rod applying a compressive force on the modular stack, and which pass through the midpoints of the four sides of the sub-stack.

[0065]

[0056] Furthermore, the elastic return elements can be made of metal, in particular Inconel®, or preferably of ceramic.

[0066]

[0057] Furthermore, the number of sub-stacks to be stacked is not limited by design. However, in order to take into account the acceptable height of the conditioning bench, the number of sub-stacks may preferably be between 2 and 20.

[0067]

[0058] The modular stack can be arranged between a main load distribution top plate and a base plate.

[0068]

[0059] In addition, the thermal enclosure can consist of a furnace floor, forming the lower horizontal wall of the thermal enclosure, an upper horizontal wall and side walls, together defining the internal volume.

[0069]

[0060] The system may also include a force rod to apply a compressive force on the modular stack, in particular on a main load distribution top plate.

[0070]

[0061] The stiffness of each elastic return element can be between 0.1 N / mm and 1000 N / mm, in particular between 1 N / mm and 40 N / mm. Furthermore, the length of each elastic return element can be between 10 mm and 80 mm, in particular between 20 mm and 40 mm.

[0071]

[0062] Advantageously, the modular stack of high-temperature SOEC / SOFC type solid oxide cells is pre-conditioned during the integration of the mechanical load-bearing system. In other words, the stack conditioning, in particular the sealing and electrochemical activation, is advantageously already carried out so that the stack does not undergo a significant change in height, for example, on the order of a few millimeters compared to several centimeters in the case of a stack that has not been pre-conditioned. The mechanical load-bearing system can thus advantageously be applied to a stack that has already been conditioned throughout its entire production lifespan.

[0072]

[0063] Furthermore, the load recovery system according to the invention can limit the mechanical stresses on the sub-stacks during the operation of the stack, and thus extend its service life by limiting the sagging and degradation of the sealing joints present between the electrochemical cells.

[0073]

[0064] Furthermore, according to another aspect of the invention, a method for clamping a plurality of sub-stacks of SOEC / SOFC type solid oxide cells operating at high temperature, forming a modular stack, by means of a mechanical load-bearing system as defined above, characterized in that it comprises the step of applying a vertical compressive force to the sub-stacks with load transfer by means of elastic return elements bearing on supports.

[0065] The method can advantageously be implemented under a neutral gas, directly inside the sub-stacks or via the thermal chamber rendered completely inert.

[0074] BRIEF DESCRIPTION OF THE FIGURES

[0075]

[0066] Other advantages, objects and particular features of the invention will become apparent from the following non-limiting description of at least one embodiment of the present invention, with reference to the accompanying figures, in which: Figure 1 is a schematic view showing the operating principle of a high-temperature solid oxide electrolyzer (SOEC), Figure 2 is an exploded schematic view of a part of a high-temperature solid oxide electrolyzer (SOEC) comprising interconnectors according to the prior art, Figure 3 illustrates the principle of the architecture of a device on which a stack of high-temperature electrolysis cells (SOEC) or high-temperature fuel cells (SOFC) is placed, Figure 4 represents, in perspective and by observation from above, an example of a stack of SOEC / SOFC type solid oxide cells according to the prior art with a stack clamping system,Figure 5 schematically represents, in partial cross-section, an example of a mechanical load-bearing system according to the invention, consisting of a plurality of sub-stacks of SOEC / SOFC type solid oxide cells operating at high temperature.

[0076]

[0067] Throughout these figures, identical references may designate identical or analogous elements.

[0077]

[0068] Furthermore, the different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.

[0078] DETAILED DESCRIPTION OF THE INVENTION

[0079]

[0069] Figures 1 to 4 have already been described previously in the section relating to the prior art and the technical context of the invention. It is specified that, for Figures 1 and 2, the symbols and arrows for supplying water vapor H2O, distributing and recovering dihydrogen H2, oxygen O2, air, and electric current are shown for the sake of clarity and precision, to illustrate the operation of the devices shown.

[0080]

[0070] Furthermore, it should be noted that all the constituents (anode / electrolyte / cathode) of a given electrochemical cell are preferably ceramics. The operating temperature of a high-temperature SOEC / SOFC stack is also typically between 600 and 1000°C.

[0071] Moreover, the terms "upper" and "lower" should be understood here in terms of the normal orientation of a substack or SOEC / SOFC stack when in its operating configuration.

[0081]

[0072] We will now describe an example of a mechanical load recovery system 100 according to the invention of several sub-stacks 20a of type SOEC / SOFC to form a modular stack 20 with reference to figure 5.

[0082]

[0073] We generally consider here the conditioning of three substacks 20a. However, the number of substacks 20a is not limited by design but rather by the need to take into account the acceptable height of the conditioning bench. Therefore, the number of substacks 20a is preferably between 2 and 20.

[0083]

[0074] As described previously in the part relating to the prior art and the technical context of the invention, each substack 20a comprises a plurality of electrochemical cells 41 each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of intermediate interconnectors 42 arranged each between two adjacent electrochemical cells 41.

[0084]

[0075] The three substacks 20a are placed in the internal volume Vi of a thermal enclosure 102 of the mechanical load recovery system 100. This thermal enclosure 102 is here made up of a furnace floor 11, as described previously, which forms the lower horizontal wall of the thermal enclosure 102, and an upper horizontal wall 102s and side walls 1021, together defining the internal volume Vi, as seen in Figure 5.

[0085]

[0076] Thus, the three sub-stacks 20a are placed in the internal volume Vi of the thermal enclosure 102 by being totally superimposed on each other.

[0086]

[0077] Each of the substacks 20a has a top face 20as and a bottom face 20ai, here with identical surfaces.

[0087]

[0078] Furthermore, the system 100 comprises four terminal plates 40, interleaved with the sub-stacks 20a. More precisely, each sub-stack 20a is arranged between an upper terminal plate 40 and a lower terminal plate 40, the same terminal plate 40 therefore being able to act as both the upper terminal plate for one sub-stack 20a and the lower terminal plate for another sub-stack 20a.

[0088]

[0079] Each terminal plate 40 has an upper face 40s and a lower face 40i, here of identical surfaces, and of which at least one is in contact with a sub-stack 20a.

[0089]

[0080] Furthermore, the modular stack 20 thus obtained is arranged between a main load distribution top plate 110 and a stack base bottom plate 120. The stack base bottom plate 120 is arranged on the furnace floor 11.

[0090]

[0081] In addition, the system 100 includes a force rod 130, of rounded shape, for applying a compressive force on the modular stack 20, in particular on the upper main load distribution plate 110. The force rod 130 allows in particular a ball-and-socket support on the main load distribution plate 110.

[0091]

[0082] In normal operation, SOFC or SOEC mode, the pre-conditioned modular stack 20, composed of numerous sub-stacks 20a, will subject the lower sub-stacks 20a to significant mechanical pressure caused by the cumulative weight of the upper sub-stacks 20a. To distribute this mechanical load evenly among the sub-stacks 20a, the invention seeks to utilize the laterally protruding portions of the end plates 40 on two opposite sides of the sub-stacks 20a to insert springs mounted on long supports. In this way, the mechanical load experienced by each sub-stack 20a is almost entirely offset by the compressive force required to compress the springs.The number of springs per substack 20a can then be a function of the maximum load they can support individually, their stiffness constant, their maximum deformation and their height, these characteristics being able to be individually tested beforehand.

[0092]

[0083] According to the invention, the conditioning of the modular stack 20 by assembling several sub-stacks 20a one on top of the other is therefore carried out in such a way as to minimize the footprint of the conditioning bench, while allowing to be carried out independently for each sub-stack 20a a controlled mechanical tightening.

[0093]

[0084] Also, a distribution of the main mechanical load is provided between the different sub-stacks 20a during the crushing during the conditioning of the stack 20 so as to allow a resumption of the forces.

[0094]

[0085] Specifically, the main mechanical compression provided by the force rod 130 is distributed between the sub-stacks 20a by dedicated elastic return elements 104, which can have different stiffnesses. It is then possible to compensate for the gravitational load experienced at each sub-stack 20a by the force required for the elastic deformation of a device resistant to temperatures close to 900°C.

[0095]

[0086] Thus, advantageously, the surface area of ​​an upper face 40s of an end plate 40 is larger than the surface area of ​​a lower face 20ai of a substack 20a. Similarly, the surface area of ​​a lower face 40i of an end plate 40 is larger than the surface area of ​​an upper face 20as of a substack 20a.

[0087] In this way, each upper face 40s and each lower face 40i of an end plate 40 in contact with at least one substack 20a has one or more free surfaces 401 that are not superimposed on a substack 20a and are not in contact with a substack 20a. These free surfaces 401 are shown in Figure 5. They correspond to the parts extending laterally from a substack 20a on its four sides formed on the terminal plates 40.

[0096]

[0088] Thus, supports 103 are arranged on these free surfaces 401. In the example of Figure 5, two long supports 103 are provided per substack 20a level, namely one in front of and one behind the substack 20a. However, in this example of Figure 5, the first substack 20a level, namely the one in the immediate vicinity of the main load distribution plate 110, i.e. the first substack 20a from the top of the stack, is without a support 103.

[0097]

[0089] The supports 103 may have a height substantially equal to that of the stack after packaging. The supports 103 are advantageously metallic, for example made of Inconel®.

[0098]

[0090] Advantageously still, a plurality of elastic return elements 104, here in the form of springs 104, is arranged between the supports 103 and the free areas 401 of the lower faces 40i of the terminal plates 40 in contact with the substacks 20a.

[0099]

[0091] These springs 104 interposed between the sub-stacks 20a have adequate stiffness to compensate for the mechanical force generated by the weight of the sub-stacks positioned on them.

[0100]

[0092] In the example in Figure 5, the springs 104 can all be identical. Here, they can be made of ceramic, which is desirable in normal operation of the stack 20 in SOEC or SOFC mode.

[0101]

[0093] However, it should be noted that the distribution of the main mechanical compression force supplied by the force rod 130 between the sub-stacks 20a is done by springs 104 with a number differentiated per sub-stack 20a, this number being therefore proportional to the mechanical load suffered.

[0102]

[0094] Specifically, for the second substack 20a, starting from the top of the stack, the force to be compensated can be a maximum of 200 N. This compensation is achieved by one or more pairs of springs 104 arranged symmetrically with respect to the two vertical planes meeting on the axis formed by the extension of the force rod 130 and passing through the midpoints of the four sides of the substack 20a. Here, for this second stage of substack 20a, four springs 104 are used, two on each side, but this number can be higher.

[0095] Thus, for this second substack 20a, one can, for example, consider a maximum vertical stack deformation of 1 mm between ambient temperature and standard operating conditions at 700°C and under gas. For 104 springs with a stiffness constant of around 24.5 N / mm, a total of 8 104 springs will be needed to approach, without exceeding, the gravitational force to be compensated of 200 N.

[0103]

[0096] Furthermore, the spring(s) 104 chosen will advantageously have characteristics designed to withstand one or more of the following stresses:

[0104] - a minimum height, in mm, namely the minimum height that the spring 104 can have under stress, which is strictly less than the sum of the height of the support 103 and the distance between the end plates 40 at room temperature,

[0105] - the maximum possible deformation of the spring(s) 104, in mm, which is strictly greater than the maximum deformation of the sub-stack 20a, with, in particular for safety, an additional 1 mm, i.e. at least 2 mm,

[0106] - the maximum load that can be borne, in N, which multiplied by the number of springs 104 is greater than 200 N.

[0107]

[0097] For the third sub-stack 20a, starting from the top of the stack, it may have a force to compensate of 400 N added to the mass of all the springs 104 and their supports 103 implemented at the level of the second sub-stack 20a. Then, the same constraints for the choice of the type and number of springs 104 as for the second sub-stack 20a must be respected.

[0108]

[0098] For any subsequent sub-stacks 20a, the same logic is used, given that each level of sub-stack 20a adds a force to be compensated of at least 200 N. As one moves down the stack, the stiffness and / or the number of springs 104 will then increase.

[0109]

[0099] Thus, without modification of the conditioning bench, the system 100 allows the mechanical load to be distributed uniformly between the sub-stacks 20a composing the overall modular stack 20 during its compression and operation. The system 100 can operate without damage to the lower sub-stacks 20a and the sealing joints that compose it, caused by the weight of the upper sub-stacks 20a.

[0110]

[0100] Of course, the invention is not limited to the embodiment just described. Various modifications can be made to it by a person skilled in the art.

Claims

DEMANDS 1. A mechanical load-bearing system (100) integrated into a plurality of sub-stacks (20a) of high-temperature SOEC / SOFC type solid oxide cells forming together a modular stack (20) of high-temperature SOEC / SOFC type solid oxide cells, each sub-stack (20a) comprising a plurality of electrochemical cells (41) each formed of a cathode, an anode and an electrolyte intercalated between the cathode and the anode, and a plurality of intermediate interconnectors (42) each arranged between two adjacent electrochemical cells (41), characterized in that the system (100) comprises: - a thermal enclosure (102) delimiting an internal volume (Vi), - a plurality of substacks (20a) placed in the internal volume (Vi), at least two substacks (20a) being at least partially superimposed on each other, each substack (20a) having a top face (20as) and a bottom face (20ai), - a plurality of end plates (40), each substack (20a) being arranged between an upper end plate (40) and a lower end plate (40), each end plate (40) having an upper face (40s) and a lower face (40i), at least one of which is in contact with at least one substack (20a), the surface area of ​​an upper face (40s) of an end plate (40) being larger than the surface area of ​​a lower face (20ai) of a substack (20a), and the surface area of ​​a lower face (40i) of an end plate (40) being larger than the surface area of ​​an upper face (20as) of a substack (20a), such that each upper face (40s) and each lower face (40i) of an end plate (40) in contact with at least one substack (20a) has one or more surfaces free (401) not superimposed on a substack (20a) and without contact with a substack (20a), - a plurality of supports (103) arranged on one or more free surfaces (401) of the upper faces (40s) of the terminal plates (40) in contact with at least one sub-stack (20a), - a plurality of elastic return elements (104) arranged between one or more supports (103) and one or more free surfaces (401) of the lower faces (40i) of the terminal plates (40).

2. System according to claim 1, characterized in that the elastic return members (104) have identical shapes.

3. System according to claim 1 or 2, characterized in that the first stage of the modular stack (20), associated with the first sub-stack (20a), starting from the top of the modular stack (20), is devoid of support (103) and elastic return member (104).

4. System according to any one of the preceding claims, characterized in that the elastic return members (104) associated with a third sub-stack (20a), located below a second sub-stack (20a), have a number and / or stiffness of elastic return members (104) greater than the number and / or stiffness of elastic return members (104) associated with the second sub-stack (20a) superimposed above the third sub-stack (20a).

5. System according to any one of the preceding claims, characterized in that the number of elastic return members (104) and / or the stiffness of the elastic return members (104) are increasing from the top of the modular stack (20) to the bottom of the modular stack (20).

6. System according to any one of the preceding claims, characterized in that the elastic return members (104) associated with the same sub-stack (20a) are arranged symmetrically with respect to the two vertical planes meeting on the central axis of the modular stack (20), in particular formed by the extension of a force rod (130) applying a compressive force on the modular stack (20), and which pass through the midpoints of the four sides of the sub-stack (20a).

7. System according to any one of the preceding claims, characterized in that the elastic return elements (104) are made of ceramic or metal, in particular Inconel®.

8. System according to any one of the preceding claims, characterized in that the number of substacks (20a) is between 2 and 20.

9. System according to any one of the preceding claims, characterized in that the modular stack (20) is arranged between a main load distribution top plate (110) and a base bottom plate (120).

10. System according to any one of the preceding claims, characterized in that the thermal enclosure (102) consists of a furnace floor (11), forming the lower horizontal wall of the thermal enclosure (102), an upper horizontal wall (102s) and side walls (1021), together defining the internal volume (Vi).

11. System according to any one of the preceding claims, characterized in that it comprises a force rod (130) for applying a compressive force on the modular stack (20), in particular on a main load distribution top plate (110).

12. Method of clamping a plurality of sub-stacks (20a) of SOEC / SOFC type solid oxide cells operating at high temperature forming a modular stack (20) by means of a mechanical load recovery system (100) according to any one of the preceding claims, characterized in that it comprises the step of exerting a vertical compressive force on the sub-stacks (20a) with a recovery of forces by means of the elastic return members (104) bearing on the supports (103).

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