Assembly comprising a plurality of high-temperature SOEC / SOFC solid oxide stacks and a bypass

Abstract

The invention relates to an assembly (100) comprising: a module (80) comprising a plurality of SOEC / SOFC solid oxide stacks (20a, 20b, 20c, 20d) electrically connected in series, each stack (20a, 20b, 20c, 20d) comprising a gas inlet (EG) and a gas outlet (SG); a heat exchanger (10); a heating device (30) for heating the gases (G), and a bypass duct (40) configured to supply gas (G) in a controlled manner to only a portion of the gas inlets (EG) of the stacks (20a, 20b, 20c, 20d), wherein the bypass duct (40) comprises control means (45) intended to control the supply of gas (G) from the bypass duct (40) to the portion of the gas inlets (EG).

Description

[0001] DESCRIPTION

[0002] TITLE: Assembly comprising a plurality of high-temperature SOEC / SOFC type solid oxide stacks and a bypass

[0003] TECHNICAL FIELD OF THE INVENTION

[0004]

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

[0008]

[0005] More specifically, the invention relates to an assembly comprising a plurality of high-temperature SOEC / SOFC type solid oxide stacks and a bypass duct, as well as a method for controlling the inlet temperature of the gases of the SOEC / SOFC type solid oxide stacks of such an assembly.

[0009] STATE OF THE ART

[0010]

[0006] In a high-temperature solid oxide electrolyzer (SOEC), the process involves transforming water vapor (H₂O) into dihydrogen (H₂) and dioxygen (O₂) by means of an electric current within the same electrochemical device, and / or transforming 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) and dioxygen (O₂), typically air and natural gas, namely methane (CH₄). For the sake of simplicity, the following description focuses on the operation of a high-temperature solid oxide electrolyzer (SOEC) performing water electrolysis.However, this principle is applicable to the electrolysis of carbon dioxide (CO₂), and even to the co-electrolysis of high-temperature water (HTW) with carbon dioxide (CO₂). Furthermore, this principle can be transposed to the case of a high-temperature solid oxide fuel cell (SOFC).

[0011]

[0007] To carry out the electrolysis of water, it is advantageous to carry it out at high temperature, typically between 600°C and 1000°C, and preferably between 650°C and 850°C, because it is more advantageous to electrolyze water vapor than liquid water and because part of the energy required for the reaction can be supplied by heat, which is cheaper than electricity.

[0012]

[0008] To implement high-temperature water electrolysis (HTW), a high-temperature solid oxide electrolyzer (SOEC) 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 of the SOEC type is thus an alternating stack of electrochemical cells and interconnectors. A high-temperature solid oxide fuel cell (SOFC) of the SOEC type consists of the same type of stack of elementary units.Because this high-temperature technology is reversible, the same stack can operate in electrolysis mode and produce hydrogen and oxygen from water and electricity, or in fuel cell mode and produce electricity from hydrogen and oxygen.

[0013]

[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.

[0014]

[0010] The electrical and fluidic interconnection devices are electronic conductors that ensure, from an electrical point of view, the connection of each electrochemical cell of elementary pattern in the stack of elementary patterns, 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, thus combining the output of each of the cells. The interconnectors thus ensure the functions of supplying and collecting electrical current and delimit gas circulation compartments for distribution and / or collection.

[0015]

[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.

[0016]

[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.

[0017]

[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). 2'). Dihydrogen (H₂) is collected and discharged from the hydrogen compartment outlet. 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.

[0018]

[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.

[0019]

[0015] By way of illustration, Figure 1 shows a schematic view illustrating 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:

[0020] 2 H2O 2 H2+ O2.

[0021]

[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 ions2 ' and the electrolyzer is then called an anionic electrolyzer, as opposed to proton electrolytes (H + ).

[0022]

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

[0023]

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

[0024] 2 H2O + 4 e → 2 H2 + 2 O 2 '.

[0025]

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

[0026] 2 O 2 ^ O2+ 4 e .

[0027]

[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.

[0028]

[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 inlet to remove the oxygen produced. The injection of a draining gas has the additional function of acting as a thermal regulator.

[0029]

[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, hydraulic and thermal distribution functions.

[0030]

[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).

[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, with the electrolyte being intercalated between the anode and the cathode.

[0031]

[0025] As previously stated, the fluidic 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.

[0032]

[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.

[0033]

[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.

[0034]

[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 type (SOEC), 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).

[0035]

[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.

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

[0036]

[0031] Thus, the proper functioning of such SOEC / SOFC type solid oxide stacks operating at high temperature mainly requires compliance with the points stated below.

[0037]

[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.

[0038]

[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.

[0039]

[0034] Furthermore, it is essential to have a good distribution of gases both in the inlet 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.

[0040]

[0035] Finally, it is necessary to carefully control the gas inlet temperature to limit thermomechanical stresses in the electrochemical cell. In particular, it is desirable that the gas inlet temperature be very close to the cell's operating temperature. This is especially important since the electrochemical cell is composed of ceramic elements that are sensitive to temperature gradients.

[0041]

[0036] The gases entering and exiting a high-temperature SOEC or SOFC stack operating at high temperature can be managed by means of appropriate devices of a furnace such as that illustrated with reference to Figure 3.

[0042]

[0037] The furnace 15 thus comprises cold sections PF and hot sections PC, the latter including in particular the furnace floor 11, a loop tube 12 for managing gas inlets and outlets, and the high-temperature electrolysis (SOEC) or fuel cell (SOFC) stack 20. It should be noted that, in this Figure 3, the upper part located above the furnace floor 11 has only been partially shown in order to visualize the stack 20 and the loop tube 12. Also, although not visible here, the hot sections PC also include insulation and heating means.

[0043]

[0038] A stack formed from a set of electrochemical cells and interconnectors can also be referred to by the English term "stack". There are usually between 25 and 1000, and typically about 75, electrochemical cells in a stack.

[0044]

[0039] In order, for example, to enable large-scale hydrogen production, it is necessary to increase the number of electrochemical cells, and therefore stacks, within the same production unit. The stacks are then assembled into modules, each module being able to contain several dozen stacks.

[0045]

[0040] From an electrical point of view, all these stacks are generally connected in series. Since the voltage across an electrochemical cell is on the order of 1.3 V, approximately 800 to 1000 cells are needed to obtain operating voltages of around 1000 V for the electrolyzer, which corresponds to approximately 10 to 12 stacks connected electrically in series, with approximately 75 cells per stack. This results in modules of 10 to 12 stacks connected electrically in series, these modules being powered in parallel.

[0046]

[0041] From a fluidics perspective, the objective is to limit pressure-related stresses, as these induce mechanical stresses and leaks in the stacks. To achieve this, it is necessary to limit pressure losses within the stack. Besides the stack's design, one solution is to fluidize all the electrochemical cells in a single stack in parallel, and also to fluidize all the stacks in a single module in parallel. Ultimately, the pressure stresses encountered are limited solely to those related to the pressure losses of a single cell; therefore, there is no cumulative effect.

[0047]

[0042] Furthermore, the operating temperature of the stacks is of major importance. As mentioned previously, a module can contain several dozen stacks, and all these stacks can exhibit different performance levels. Initially, there may be variations in the manufacturing process or in the batches of electrochemical cells or materials used. Over time, the stacks may exhibit different aging curves. Moreover, it may be necessary to replace some of the stacks, for example, following a major defect in one of them, thus requiring the coexistence of stacks with different degrees of aging, and therefore different performance levels.

[0043] However, it should be noted that for a stack operating in SOEC mode, if the electric current, gas composition, and gas flow rates are fixed, then the operating temperature is determined by the performance level, and the voltage across the stack will approach a reference voltage called the "thermo-neutral voltage." The term "thermo-neutral voltage" refers to the electrical voltage that must be applied across the stack for the electrolysis reaction to occur at a constant temperature: at this voltage, all the energy required for the electrolysis reaction is supplied electrically. In a stack operating in SOFC mode, these three parameters are fixed: the composition of the inlet gases, the electric current (because it determines the production of dihydrogen (H₂)), and the gas flow rates (because all the electrochemical cells are in parallel).Therefore, having stacks with different performance levels leads to stacks with different operating temperatures. However, the gas inlet temperature is the same for all stacks, resulting in thermal gradients within them, which is detrimental to their lifespan, as explained previously.

[0048]

[0044] Prior art solutions for controlling the inlet temperature of gases in stacks are known. US patent application 2018 / 0287179 A1 discloses a heat management method for a SOEC and / or SOFC stack in which the required steam is supplied by an external source and an exhaust gas stream is cooled after the stack. This application describes a heat management solution for operation in SOFC mode, without the presence of a gas heater. Furthermore, European patent application EP 3 956 497 A1 discloses a method for operating an SOEC stack with operation controlled by modulating electrical power. This application does not address operation with multiple stacks, does not perform gas temperature control and adjustment for these stacks, and does not allow for regulation.

[0049]

[0045] Thus, there is still a need to enable control and control of the inlet temperature of the gases at the inlet of each stack of a multi-stack module, or stacks, of high-temperature electrolysis (SOEC) or fuel cell (SOFC).

[0050] DESCRIPTION OF THE INVENTION

[0051]

[0046] The invention aims to remedy at least partially the needs mentioned above and the disadvantages relating to the achievements of the prior art.

[0052]

[0047] The invention aims in particular to control and regulate the gas temperature at the inlet of each stack in a multi-stack module arranged with a parallel fluidic supply and a gas heater for the stacks. Specifically, it aims to achieve a gas inlet temperature very close to the operating temperature of each stack.

[0053]

[0048] The invention thus relates, according to one of its aspects, to an assembly, characterized in that it comprises:

[0054] - a module comprising a plurality of high-temperature SOEC / SOFC type solid oxide stacks, electrically connected in series, each stack comprising a plurality of electrochemical cells, each consisting 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, each stack comprising a gas inlet and a gas outlet, the gas supply to the stacks being carried out in parallel through each gas inlet, and the gas evacuation from the stacks being carried out in parallel through each gas outlet,

[0055] - a heat exchanger, comprising a first gas inlet to receive the gases from the gas outlets of the stacks, a first gas outlet, downstream of the first gas inlet and fluidically connected, in particular by a direct fluidic communication, that is to say by an uninterrupted or continuous fluidic path, that is to say still without element interrupting the fluidic continuity, to the first gas inlet, a second gas inlet and a second gas outlet, downstream of the second gas inlet and fluidly connected, in particular by a direct fluidic communication, that is to say by an uninterrupted or continuous fluidic path, that is to say still without element interrupting the fluidic continuity, to the second gas inlet, to supply gas to the gas inlets of the stacks,

[0056] - a gas heating device, in particular a gas heater, comprising a gas inlet to be heated, downstream of the heat exchanger and fluidically connected, in particular by direct fluid communication, i.e. by an uninterrupted or continuous fluid path, i.e. still without any element interrupting the fluid continuity, to the second gas outlet of the heat exchanger, and a heated gas outlet, upstream of the gas inlets of the stacks and fluidly connected, in particular by direct fluid communication, i.e. by an uninterrupted or continuous fluid path, i.e. still without any element interrupting the fluid continuity, to the gas inlets of the stacks,

[0057] - a bypass conduit configured to supply gas in a regulated manner to only a portion of the gas inlets of the stacks, the bypass conduit comprising regulating means for controlling the gas supply from the bypass conduit to said portion of the gas inlets.

[0049] The assembly according to the invention may further comprise one or more of the following features taken individually or in any possible technical combinations.

[0058]

[0050] Advantageously, the bypass duct can fluidly connect the second gas inlet of the heat exchanger and said portion of the gas inlets of the stacks.

[0051] Furthermore, the stack(s) having a gas inlet belonging to said portion of the gas inlets may exhibit different operating performance from the operating performance of the stack(s) having a gas inlet not belonging to said portion of the gas inlets.

[0059]

[0052] The stack or stacks comprising a gas inlet not belonging to said part of the gas inlets may exhibit substantially identical operating performance.

[0060]

[0053] Furthermore, said part of the gas inlets may include a single gas inlet from a stack.

[0061]

[0054] Alternatively, said portion of the gas inlets may include at least two gas inlets. The assembly may include at least two bypass conduits. Each bypass conduit may fluidly connect the second gas inlet of the heat exchanger and a gas inlet of said portion of the gas inlets. Each bypass conduit may include control means for regulating the gas supply from the bypass conduit to the associated gas inlet.

[0062]

[0055] The assembly may advantageously include a single heating device, in particular in the form of a gas heater.

[0063]

[0056] Furthermore, the control means may include a control valve. Alternatively, the control means may include any type of control mechanism.

[0064]

[0057] Regulation may, for example, consist of updating the opening of a control valve, for example manually, at a frequency of a few weeks or a few months.

[0065]

[0058] Furthermore, the assembly may include at least one furnace to which one or more stacks are coupled for the inlet and outlet of the gases. The control means may advantageously be located outside the furnace. Advantageously, the control means may thus be in the form of a control valve located on the external part of the furnace, for example at a temperature of approximately 150°C, and may thus be a conventionally designed, simple, robust, and low-cost control valve.

[0059] Alternatively, the control means may be located inside the furnace, either entirely or partially, in particular in the form of a control valve adapted to high temperatures, for example in the range of 700°C to 800°C.

[0066]

[0060] The assembly may in particular be a high-temperature SOEC / SOFC type solid oxide production unit comprising a plurality of modules electrically powered in parallel. Each module may comprise a plurality of stacks electrically connected in series.

[0067]

[0061] Each module can, for example, comprise between 4 and 20 stacks.

[0068]

[0062] The electrochemical cells of the same stack can advantageously be supplied fluidically with gas in parallel.

[0069]

[0063] Furthermore, the invention also relates, according to another aspect, to a method for controlling the inlet temperature of the gases of a plurality of SOEC / SOFC type solid oxide stacks operating at high temperature of an assembly as defined above, characterized in that it comprises the following steps:

[0070] - regulation of the heating device's power output so that the gas inlet temperature is substantially equal to the operating temperature of the stack(s) having a gas inlet not belonging to said part of the gas inlets, and / or,

[0071] - injection of gas through the control means of the bypass duct to said part of the gas inlets fluidly connected to the bypass duct to modify the inlet temperature of the gases of said part of the gas inlets so that the modified inlet temperature of the gases is substantially equal to the operating temperature of the stack(s) comprising a gas inlet belonging to said part of the gas inlets.

[0072]

[0064] The stack(s) having a gas inlet belonging to said portion of the gas inlets may have a lower operating temperature than the operating temperature of the stack(s) having a gas inlet not belonging to said portion of the gas inlets. Furthermore, the process may include the step of injecting gas through the bypass duct at a temperature lower than the outlet temperature of the heating device.

[0073]

[0065] Furthermore, the stack(s) having a gas inlet belonging to said part of the gas inlets may exhibit superior operating performance compared to the stack(s) having a gas inlet not belonging to said part of the gas inlets.

[0066] Moreover, the gas injection stage can be controlled by means of regulation means driven by the measurement of the gas inlet temperature of the stacks.

[0074] BRIEF DESCRIPTION OF THE FIGURES

[0075]

[0067] Other advantages, purposes 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 furnace on which a high-temperature electrolysis stack (SOEC) or high-temperature fuel cell (SOFC) is placed, and Figure 4 schematically illustrates an example of an embodiment of an assembly according to the invention comprising high-temperature SOEC / SOFC type solid oxide stacks.

[0076]

[0068] Throughout these figures, identical references may designate identical or analogous elements.

[0077]

[0069] 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]

[0070] Figures 1 to 3 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]

[0071] 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°C and 1000°C, and preferably between 650°C and 850°C.

[0081]

[0072] Furthermore, the terms "upper" and "lower" are to be understood here in terms of the normal orientation of a SOEC / SOFC-type stack when in its operating configuration.

[0073] With reference to Figure 4, we will now describe an example of an embodiment of an assembly 100 according to the invention and explain a principle of the method for controlling the inlet temperature TE, TE' of the gases G of a plurality of SOEC / SOFC-type solid oxide stacks 20a, 20b, 20c, 20d operating at high temperature in this assembly 100.

[0082]

[0074] This assembly 100 can particularly be a high-temperature SOEC / SOFC type solid oxide production unit, comprising a plurality of modules 80, only one module 80 being shown in Figure 4, electrically powered in parallel, and each module 80 comprising a plurality of stacks 20a, 20b, 20c, 20d, here only four stacks (also called towers) are shown, which are electrically connected to each other in series. These stacks 20a, 20b, 20c, 20d are also fluidically powered in parallel.

[0083]

[0075] Each module 80 can, for example, comprise between 4 and 20 stacks 20a, 20b, 20c, 20d. Each stack 20a, 20b, 20c, 20d comprises a plurality of electrochemical cells 1, for example, between approximately 25 and 1000 cells, typically about 75 cells, each consisting of a cathode, an anode, and an electrolyte intercalated between the cathode and the anode, and a plurality of intermediate interconnectors 5 arranged between two adjacent electrochemical cells 1, as described previously. Advantageously, the electrochemical cells 1 of the same stack 20a, 20b, 20c, 20d are fluidically supplied with gas G in parallel.

[0084]

[0076] As can be seen in Figure 4, each stack 20a, 20b, 20c, 20d has a gas inlet EG and a gas outlet SG. The gas supply G to the four stacks 20a, 20b, 20c, 20d is carried out in parallel through each gas inlet EG, and the gas G is evacuated from the four stacks 20a, 20b, 20c, 20d is carried out in parallel through each gas outlet SG.

[0085]

[0077] At least one heat exchanger 10 is also provided which includes a first gas inlet 10a to receive the gases G from the gas outlets G of the stacks 20a, 20b, 20c, 20d. The heat exchanger 10 further includes a first gas outlet 10b, downstream of the first gas inlet 10a and fluidically connected to the first gas inlet 10a, by a direct fluidic communication, i.e. by a continuous fluidic path, without any element interrupting the fluidic continuity.

[0086]

[0078] Furthermore, the heat exchanger 10 includes a second gas inlet 10c and a second gas outlet 10d, downstream of the second gas inlet 10c and fluidically connected to the second gas inlet 10c, by a direct fluidic communication, that is to say by a continuous fluidic path, without element interrupting the fluidic continuity, to supply gas G to the gas inlets EG of the stacks 20a, 20b, 20c, 20d.

[0087]

[0079] The assembly 100 also includes a gas heating device 30 for the gases G, here a single gas heater 30. This includes a gas inlet to be heated 30a, downstream of the heat exchanger 10 and fluidically connected to the second gas outlet 10d of the heat exchanger 10, by a direct fluidic communication, i.e. by a continuous fluidic path, without any element interrupting the fluidic continuity, and a heated gas outlet 30b, upstream of the gas inlets EG of the stacks 20a, 20b, 20c, 20d and fluidly connected to the gas inlets EG of the stacks 20a, 20b, 20c, 20d, by a direct fluidic communication, i.e. by a continuous fluidic path, without any element interrupting the fluidic continuity.

[0088]

[0080] Finally, the assembly 100 comprises one or more bypass conduits 40; here, only one bypass conduit 40 is shown, which is, for example, fluidically supplied by the second gas inlet 10c of the heat exchanger 10, configured to supply gas G in a regulated manner to only a portion of the gas inlets EG of the stacks 20a, 20b, 20c, 20d. Thus, each bypass conduit 40 can supply, in a regulated manner, a single gas inlet EG of a given stack 20b.

[0089]

[0081] The bypass duct(s) 40 may have a small diameter, in particular smaller than the diameter of the other main gas supply lines G, and may be thermally insulated or of short length. Advantageously, the bypass duct(s) 40 allow the circulation of gas G at a temperature TC lower than the temperature TE of the gas G at the outlet of the gas heater 30.

[0090]

[0082] The bypass duct(s) 40 may advantageously include control means 45 provided to control the supply of gas G from the bypass duct(s) 40 to only a part of the gas inlets EG.

[0091]

[0083] The control means 45 may include, in particular, a control valve or any type of control mechanism. This control may, for example, consist of updating the opening of the control valve, for example manually, at a frequency of a few weeks or a few months.

[0092]

[0084] Such a control valve 45 can advantageously be located outside a furnace 15 as described above, in the cold part, for example at a temperature TC of approximately 150°C, thus allowing for a conventionally designed, simple, and robust valve. Alternatively, it can also be located inside such a furnace 15, in the hot part.

[0085] In the example shown in Figure 4, it is assumed that the stack 20b has a gas inlet EG belonging to the aforementioned portion of the gas inlets EG defined above. It is assumed that this stack 20b exhibits different operating performance from the operating performance of the three other stacks 20a, 20c, and 20d, which have a gas inlet EG not belonging to the aforementioned portion of the gas inlets EG, in particular superior operating performance, for example, due to a better gas supply or a lower number of operating hours, among other things.

[0093]

[0086] So, if all the stacks 20a, 20b, 20c, 20d operate at a point close to their thermoneutral temperature then the stack 20b will have the lowest operating temperature.

[0094]

[0087] However, the gases G from the heater 30 have the same temperature TE at the inlet EG of each stack 20a, 20b, 20c, 20d, here approximately 800°C. This is therefore detrimental to the service life of the stack 20b, which has a lower operating temperature and therefore requires an inlet temperature TE' lower than the inlet temperature TE in order to correspond substantially to its operating temperature.

[0095]

[0088] The method of controlling the inlet temperature TE, TE' then consists of regulating the power of the heater 30, supplied with gas G at a temperature TD of about 800°C, so that the outlet temperature TE can correspond to the operating temperature of the hottest stacks 20a, 20c, 20d, and of injecting a certain quantity of cold gas G at the inlet EG of the stack 20b, via the regulating valve 45 and the bypass conduit containing gas G at a lower temperature TC, for example about 150°C, in order to lower the temperature TE' of the gases entering the stack 20b, this temperature TE' being for example of the order of 750°C and corresponding to the operating temperature of the stack 20b.

[0096]

[0089] After passing through the stacks 20a, 20b, 20c, 20d, the gases G are at an outlet temperature TS, for example of the order of 800°C, then reach a lower temperature TB, for example of about 200°C, after passing through the heat exchanger 10.

[0090] The stacks 20a, 20c and 20d have substantially identical operating performance, and therefore a substantially similar operating temperature.

[0097]

[0091] Advantageously, it is therefore possible to control and manage the temperature TE, TE' at the inlet of each stack 20a, 20b, 20c, 20d by regulating the operation of the gas heater 30 and by injecting cold gases upstream of each predetermined stack 20b through one or more bypass conduits 40. The flow rate of the cold gases G circulating in the bypass conduit 40 is controlled by means of the regulating valve 45, itself controlled by the measurement of the temperature TE, TE' at the inlet of the stacks 20a, 20b, 20c, 20d.

[0098]

[0092] It is thus possible to adjust the temperature TE, TE' of the inlet gases G to the operating temperature of each stack 20a, 20b, 20c, 20d. This adjustment of the temperature TE, TE' can limit mechanical stresses and extend the service life of the stacks 20a, 20b, 20c, 20d.

[0099]

[0093] It is also possible to use stacks 20a, 20b, 20c, 20d with different operating performance without affecting the overall lifespan of the module 80 or the assembly 100. If the difference in operating temperature between two stacks is too great, it is also possible to provide thermal insulation between them in order to limit energy exchanges which would be detrimental to their thermal homogeneity and therefore to their lifespan.

[0100]

[0094] It is possible to calculate an example of the injection flow rate at the bypass conduit 40. If we assume that the stacks 20a, 20c and 20d operate at an operating temperature of 800°C, the regulation temperature of the gases TE at the outlet of the heater 30 will be 800°C. The temperature of the gases TC upstream of the heat exchanger 10 is usually 150°C, as it is typically superheated steam.

[0101]

[0095] Furthermore, it is assumed that the operating temperature of the stack 20b is 750°C. Therefore, to lower the temperature of the inlet gases by injecting a low flow rate into the bypass duct 40, the calculation of the injected flow rate will be as follows, with an energy balance on the flow rates: % flow rate = 800 750 ~ 8%.

[0102] ' 5 800-150

[0103]

[0096] Consequently, approximately 8% of the main mass flow rate is required to lower the temperature by approximately 50°C and to go from the temperature TE equal to 800°C to the temperature TE' equal to 750°C at the gas inlet EG of the stack 20b.

[0104]

[0097] The composition of the gases G at the outlet of the heater 30 and that at the outlet of the bypass duct(s) 40 are advantageously identical: they come from the same original gas line at the heat exchanger 10. Thus, there is no change in the composition of the gases G at the inlet of the stacks 20a, 20b, 20c, 20d.

[0105]

[0098] The control means 45, here the control valve 45, can be placed in parallel with the heat exchanger 10 and the heating device 30, here the gas heater 30. Advantageously, the pressure drop across the control means 45, here the control valve 45, is less than the pressure drop across the heating device 30, here the gas heater 30, so that gas can bypass the heating device 30, thus allowing a reduction in temperature at the inlet of the stacks 20a, 20b, 20c, 20d. Therefore, there is no compressor or other similar equipment that could allow the gas to be bypassed. A suitable choice is made between the characteristics of the control means 45 and those of the heating device 30.The available pressure difference at the control means 45, here the control valve 45, corresponds to the sum of the pressure losses of the heat exchanger 10 and the heating device 30, here the gas heater 30. Therefore, the flow coefficient of the control means 45, here the control valve 45, often called the Kv or Cv coefficient, must be chosen in order to allow the gas flow in the bypass line 40, typically 8% of the main flow in this example, under a pressure difference corresponding to the sum of the pressure losses of the heat exchanger 10 and the heating device 30, here the gas heater 30, typically between 40 and 80 mbar on this type of installation.

[0106]

[0099] Of course, the invention is not limited to the embodiments just described. Various modifications can be made to them by a person skilled in the art.

[0107]

[0100] In particular, the bypass conduit 40 can supply only part of the gas inlets EG of the stacks 20a, 20b, 20c, 20d, in particular the gas inlet EG of the stack 20b, with a gas mixture of a different composition than that of the gases G supplying the other gas inlets EG, for example a mixture containing 100% dihydrogen H? or 100% water H2O, thus making it possible to act on the composition of the fluid in addition to acting on the temperature.

Claims

DEMANDS 1. Set (100), characterized in that it comprises: - a module (80) comprising a plurality of high-temperature SOEC / SOFC-type solid oxide stacks (20a, 20b, 20c, 20d) electrically connected in series, each stack (20a, 20b, 20c, 20d) comprising a plurality of electrochemical cells (1) each formed of a cathode, an anode, and an electrolyte interposed between the cathode and the anode, and a plurality of intermediate interconnectors (5) each arranged between two adjacent electrochemical cells (1), each stack (20a, 20b, 20c, 20d) comprising a gas inlet (EG) and a gas outlet (SG), the gas supply (G) to the stacks (20a, 20b, 20c, 20d) being provided in parallel through each gas inlet (EG), and gas evacuation (G) from the stacks (20a, 20b, 20c, 20d) being carried out in parallel via each gas outlet (SG), - a heat exchanger (10), comprising a first gas inlet (10a) to receive the gases (G) from the gas outlets (G) of the stacks (20a, 20b, 20c, 20d), a first gas outlet (10b), downstream of the first gas inlet (10a) and fluidically connected to the first gas inlet (10a), a second gas inlet (10c) and a second gas outlet (1 Od), downstream of the second gas inlet (10c) and fluidly connected to the second gas inlet (10c), to supply gas (G) to the gas inlets (EG) of the stacks (20a, 20b, 20c, 20d), - a gas heating device (30) (G), comprising a gas inlet to be heated (30a), downstream of the heat exchanger (10) and fluidly connected to the second gas outlet (1 Od) of the heat exchanger (10), and a heated gas outlet (30b), upstream of the gas inlets (EG) of the stacks (20a, 20b, 20c, 20d) and fluidly connected to the gas inlets (EG) of the stacks (20a, 20b, 20c, 20d), - a bypass conduit (40) configured to supply gas (G) in a regulated manner to only a portion of the gas inlets (EG) of the stacks (20a, 20b, 20c, 20d), the bypass conduit (40) having control means (45) provided to control the supply of gas (G) from the bypass conduit (40) to said portion of the gas inlets (EG), in which the stack(s) (20b) having a gas inlet (EG) belonging to said portion of the gas inlets (EG) have different operating temperatures from the operating temperatures of the stack(s) (20a, 20c, 20d) having a gas inlet (EG) not belonging to said portion of the gas inlets (EG).

2. Assembly (100) according to claim 1, wherein the bypass conduit (40) fluidly connects the second gas inlet (10c) of the heat exchanger (10) and said part of the gas inlets (EG) of the stacks (20a, 20b, 20c, 20d).

3. Assembly (100) according to claim 1 or 2, in which the stack(s) (20a, 20c, 20d) comprising a gas inlet (EG) not belonging to said part of the gas inlets (EG) have substantially identical operating temperatures.

4. Assembly (100) according to any one of the preceding claims, wherein said portion of the gas inlets (EG) comprises a single gas inlet (EG) of a stack (20b).

5. Assembly (100) according to any one of claims 1 to 3, wherein said gas inlet portion (EG) comprises at least two gas inlets (EG), the assembly (80) comprising at least two bypass conduits (40), each bypass conduit (40) fluidly connecting the second gas inlet (10c) of the heat exchanger (10) and a gas inlet (EG) of said gas inlet portion (EG), each bypass conduit (40) comprising control means (45) provided for controlling the gas supply (G) from the bypass conduit (40) to the associated gas inlet (EG).

6. Assembly (100) according to any one of the preceding claims, wherein the assembly (80) comprises a single heating device (30), in particular in the form of a gas heater.

7. Assembly (100) according to any one of the preceding claims, wherein the control means (45) comprise a control valve.

8. Assembly according to any one of the preceding claims, wherein the available pressure difference at the level of the control means (45) corresponds to the sum of the pressure losses of the heat exchanger (10) and the heating device (30).

9. Assembly (100) according to any one of the preceding claims, wherein the assembly (100) comprises at least one oven (15) on which one or more stacks (20a, 20b, 20c, 20d) are coupled for the supply and outlet of gases (G), the regulating means (45) being located outside the furnace (15).

10. Assembly (100) according to any one of the preceding claims, wherein the assembly (100) is a high-temperature SOEC / SOFC type solid oxide production unit comprising a plurality of modules (80) electrically powered in parallel, each module (80) comprising a plurality of stacks (20a, 20b, 20c, 20d) electrically connected in series.

11. Method for controlling the inlet temperature (TE, TE') of the gases (G) of a plurality of SOEC / SOFC type solid oxide stacks (20a, 20b, 20c, 20d) operating at high temperature of an assembly (100) according to any one of the preceding claims, characterized in that it comprises the following steps: - regulation of the heating device's power (30) so that the inlet temperature (TE) of the gases (G) is substantially equal to the operating temperature of the stack(s) (20a, 20c, 20d) comprising a gas inlet (EG) not belonging to said part of the gas inlets (EG), and / or, - injection of gas (G) through the control means (45) of the bypass conduit (40) to said part of the gas inlets (EG) fluidly connected to the bypass conduit (40) to modify the inlet temperature (TE') of the gases (G) of said part of the gas inlets (EG) so that the modified inlet temperature (TE') of the gases (G) is substantially equal to the operating temperature of the stack(s) (20b) comprising a gas inlet (EG) belonging to said part of the gas inlets (EG).

12. Method according to claim 11, wherein the stack(s) (20b) comprising a gas inlet (EG) belonging to said part of the gas inlets (EG) have a lower operating temperature than the operating temperature of the stack(s) (20a, 20c, 20d) comprising a gas inlet (EG) not belonging to said part of the gas inlets (EG), and wherein the method comprises the step of injecting gas (G) through the bypass conduit (40) at a temperature (TC) lower than the outlet temperature (TE) of the heating device (30).

13. A method according to claim 12, wherein the stack(s) (20b) comprising a gas inlet (EG) belonging to said part of the gas inlets (EG) exhibit superior operating performance compared to the stack(s) (20a, 20c, 20d) comprising a gas inlet (EG) not belonging to said part of the gas inlets (EG).

14. A method according to any one of claims 11 to 13, wherein the gas injection step (G) is controlled by means of the control means (45) driven by the measurement of the inlet temperature (TE, TE') of the gases (G) of the stacks (20a, 20b, 20c, 20d).

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