Method for suppressing methane formation in electrolytic cell stacks, electrolytic cell cartridges, electrolytic cell modules, and electrolytic cell stacks.

Abstract

The present invention provides an electrolytic cell stack, an electrolytic cell cartridge, an electrolytic cell module, and a method for suppressing methanation in an electrolytic cell stack, which can suppress the methanation reaction of the generated gas even when a methanation catalyst is present in the flow path through which the generated gas produced at the hydrogen electrode by co-electrolysis flows. [Solution] The electrolytic cell stack 101 according to the present disclosure comprises an electrolytic cell 105 in which a hydrogen electrode, a solid electrolyte, and an oxygen electrode are stacked in order; a flow passage 117 through which the gas generated at the hydrogen electrode flows; and a hollow tube 140 arranged within the flow passage 117 so that the gas generated at the hydrogen electrode can flow. The member 103 defining the outer casing of the flow passage 117 contains a methanation catalyst, while the hollow tube 140 does not contain a methanation catalyst.

Description

[Technical Field]

[0001] This disclosure relates to an electrolytic cell stack, an electrolytic cell cartridge, an electrolytic cell module, and a method for suppressing methanation in an electrolytic cell stack. [Background technology]

[0002] This disclosure relates to an electrolytic cell stack, an electrolytic cell cartridge, an electrolytic cell module, and a method for manufacturing an electrolytic cell stack.

[0003] Water electrolysis, which electrochemically decomposes water to produce hydrogen and oxygen, is a hydrogen production method that does not emit carbon dioxide and has excellent environmental characteristics. There are various types, including alkaline electrolysis and solid polymer electrolysis, which electrolyze liquid water, and steam electrolysis, which electrolyzes water vapor.

[0004] In particular, solid oxide electrolysis cells (SOECs), which electrolyze high-temperature steam, use oxygen ion conductive ceramics such as yttria-stabilized zirconia as a solid electrolyte. Because they can utilize the thermal energy of high-temperature steam as part of the energy required for the electrolytic reaction, they can produce hydrogen with higher efficiency compared to other electrolysis methods. Electrolysis cells using solid electrolytes can also be used for ammonia electrolysis.

[0005] Furthermore, the electrolytic cell can also be supplied with a mixed gas of high-temperature steam and carbon dioxide (CO2) (raw material gas), and the hydrogen produced by electrolysis reacts with carbon dioxide on the electrolytic cell to directly produce carbon monoxide (CO) or hydrocarbon compounds in a co-electrolytic manner (see Patent Document 1).

[0006] Electrolytic cells using solid electrolytes can simultaneously electrolyze CO2 / H2O as a co-electrolysis to produce H2 / CO synthesis gas necessary for Fischer-Tropsch (FT) synthesis, which is used in the production of synthetic fuels (e-fuels) such as sustainable aviation fuel (SAF). This may simplify the system compared to production processes using reverse shift reactions from water electrolysis. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-50701 [Overview of the project] [Problems that the invention aims to solve]

[0008] In Patent Document 1, the electrode layer (hydrogen electrode) material contains Ni, and the metal support supporting the hydrogen electrode contains Fe. Ni and Fe act as catalysts (methanization catalysts) in the reaction in which methane is synthesized from hydrogen and carbon monoxide.

[0009] The product gas generated in the CO2 / H2O co-electrolysis contains hydrogen and carbon monoxide. Therefore, when the product gas comes into contact with a structure containing a methanation catalyst, the methanation reaction proceeds.

[0010] In pressurized operation, which facilitates integration with FT synthesis, a problem arises because the methanation reaction occurs due to the action of the methanation catalyst, producing methane and reducing the H2 / CO yield.

[0011] To prevent the methanation reaction, the methanation catalyst can be removed from the hydrogen electrode and metal support. However, Ni and Fe may serve purposes other than catalysis, such as controlling the coefficient of thermal expansion or adjusting porosity, so they cannot be easily removed.

[0012] This disclosure has been made in view of these circumstances and aims to provide an electrolytic cell stack, an electrolytic cell cartridge, an electrolytic cell module, and a method for suppressing methanation in an electrolytic cell stack, which can suppress the methanation reaction of the generated gas even when a methanation catalyst is included in the flow path through which the generated gas produced at the hydrogen electrode by co-electrolysis flows. [Means for solving the problem]

[0013] To solve the above problems, the following means are employed for the methane suppression method in the electrolytic cell stack, electrolytic cell cartridge, electrolytic cell module, and electrolytic cell stack of this disclosure.

[0014] This disclosure provides an electrolytic cell stack comprising: an electrolytic cell in which a hydrogen electrode, a solid electrolyte, and an oxygen electrode are stacked in order; a flow passage through which a gas generated by the hydrogen electrode flows; and a hollow tube disposed within the flow passage so that the gas generated by the hydrogen electrode can flow, wherein the member defining the outer casing of the flow passage includes a methanation catalyst, and the hollow tube does not include a methanation catalyst.

[0015] This disclosure provides an electrolytic cell cartridge comprising the above-described electrolytic cell stack.

[0016] This disclosure provides an electrolytic cell module equipped with the above-mentioned electrolytic cell cartridge.

[0017] This disclosure provides a method for suppressing methanation in an electrolytic cell stack, wherein the methane concentration and / or hydrogen concentration and carbon monoxide concentration in the gas discharged from the electrolytic cell stack are measured, and the length of the hollow tube is set based on the measured values. [Effects of the Invention]

[0018] Even if a methane catalyst is present in the flow path through which the product gas generated at the hydrogen electrode by co-electrolysis flows, the methane reaction of the product gas can be suppressed by placing a hollow tube within the flow path.

Brief Description of the Drawings

[0019] [Figure 1] It is a partial schematic cross-sectional view showing an example of an electrolytic cell stack according to the first embodiment. [Figure 2] It is an overall schematic cross-sectional view of the cell stack of FIG. 1. [Figure 3] It is a schematic diagram of a hollow tube. [Figure 4] It is an overall schematic cross-sectional view of an electrolytic cell stack according to the second embodiment. [Figure 5] It is a diagram for explaining a method for suppressing methanation according to the third embodiment. [Figure 6] It is a diagram showing one aspect of an electrolytic cell cartridge provided with an electrolytic cell stack. [Figure 7] It is a diagram showing one aspect of an electrolytic cell module provided with the electrolytic cell cartridge of FIG. 6.

Modes for Carrying Out the Invention

[0020] An embodiment of an electrolytic cell stack, an electrolytic cell cartridge, an electrolytic cell module, and a method for suppressing methanation in an electrolytic cell stack will be described with reference to the drawings.

[0021] For the sake of convenience of explanation, the positional relationship of each component described using the expressions "upper" and "lower" based on the paper surface indicates the vertically upper side and the vertically lower side, respectively. Also, in this embodiment, for those that can obtain the same effect in the vertical and horizontal directions, the vertical direction on the paper surface is not necessarily limited to the vertically up-and-down direction, and may correspond to, for example, a horizontal direction orthogonal to the vertical direction.

[0022] 〔First Embodiment〕 FIG. 1 is a partial schematic cross-sectional view showing an example of an electrolytic cell stack (hereinafter referred to as a cell stack). The cell stack 101 includes, for example, a cylindrical base tube 103, multiple electrolytic cells 105 formed on the outer surface of the base tube 103, and an interconnector 107 formed between adjacent electrolytic cells 105. The electrolytic cell 105 is formed by stacking a hydrogen electrode 109, a solid electrolyte membrane 111, and an oxygen electrode 113.

[0023] The cell stack 101 comprises a plurality of electrolytic cells 105 formed on the outer circumferential surface of the base tube 103. The lead film 115 is electrically connected via an interconnector 107 to the oxygen electrode 113 of the electrolytic cell 105 formed at one end of the base tube 103 in the axial direction, and the lead film 115 is electrically connected to the hydrogen electrode 109 of the electrolytic cell 105 formed at the other end.

[0024] The base tube 103 is made of a porous material, and its main components are, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), Y2O3-stabilized ZrO2 (YSZ), or MgAl2O4. This base tube 103 supports the electrolytic cell 105, the interconnector 107, and the lead film 115, and also diffuses the raw material gas supplied to the inner circumferential surface 104 of the base tube 103 through the pores of the base tube 103 to the hydrogen electrode 109 formed on the outer circumferential surface of the base tube 103.

[0025] In the cell stack 101 shown in Figure 1, the electrolytic cell 105 is supported by a base tube 103. However, for example, the hydrogen electrode may be made thicker and serve as the base tube, and the use of a base tube is not limited to this configuration. Furthermore, although the base tube in this embodiment is described as being cylindrical, the base tube can be cylindrical, and its cross-section is not necessarily limited to a circle; for example, it may be elliptical. A cell stack of a flat tubular, for example, with the circumferential surface of a cylinder flattened vertically, may also be used.

[0026] The hydrogen electrode 109 is composed of an oxide of a composite material of Ni and a zirconia-based electrolyte material, for example, Ni / YSZ is used. The thickness of the hydrogen electrode 109 is 50 μm to 250 μm, and the hydrogen electrode 109 may be formed by screen printing of a slurry.

[0027] The solid electrolyte membrane 111 is mainly made of YSZ, which has airtightness that prevents gas from passing through and high oxygen ion conductivity at high temperatures. This solid electrolyte membrane 111 is made of oxygen ions (O) generated at the hydrogen electrode 109. 2- This transfers the ) to the oxygen electrode 113. The thickness of the solid electrolyte membrane 111 located on the surface of the hydrogen electrode 109 is 5 μm to 100 μm, and the solid electrolyte membrane 111 may be formed by screen printing of a slurry.

[0028] The oxygen electrode 113 is composed of, for example, a LaSrMnO3-based oxide or a LaCoO3-based oxide, and the oxygen electrode 113 is applied as a slurry using screen printing or a dispenser. The oxygen electrode 113 can also have a two-layer structure. In this case, the oxygen electrode layer (oxygen electrode intermediate layer) on the solid electrolyte membrane 111 side is composed of a material that exhibits high ionic conductivity and excellent catalytic activity. The oxygen electrode intermediate layer may be composed of Sm-doped ceria that exhibits high ionic conductivity, and the oxygen electrode layer (oxygen electrode conductive layer) on the oxygen electrode intermediate layer may be composed of a perovskite-type oxide such as Sr and Ca-doped LaMnO3.

[0029] Oxidizing gases do not directly participate in the electrolytic reaction, but they supply the heat necessary for the electrolytic reaction (endothermic reaction) and dissipate excess heat generated during the electrolytic reaction. Typically, these gases contain approximately 15% to 30% oxygen, and air is the most suitable choice. However, other gases such as mixtures of combustion exhaust gas and air, mixtures of oxygen and air, and inert gases such as nitrogen can also be used.

[0030] Interconnector 107 is M for SrTiO3 series, etc. 1-x L xThe interconnector 107 is composed of conductive perovskite-type oxides represented by TiO3 (where M is an alkaline earth metal element and L is a lanthanide element) or lanthanum chromite (LaCrO3), and the slurry is screen printed. The interconnector 107 has a dense film to prevent mixing of the source gas and the oxidizing gas. Furthermore, the interconnector 107 has stable durability and electronic conductivity under both oxidizing and reducing atmospheres. In adjacent electrolytic cells 105, the interconnector 107 electrically connects the oxygen electrode 113 of one electrolytic cell 105 to the hydrogen electrode 109 of the other electrolytic cell 105, thereby connecting adjacent electrolytic cells 105 in series.

[0031] The lead film 115 needs to possess electronic conductivity and have a coefficient of thermal expansion similar to that of the other materials constituting the cell stack 101. Therefore, composite materials of Ni and zirconia-based electrolyte materials such as Ni / YSZ or M such as SrTiO3 are used. 1-x L x It is composed of TiO3 (where M is an alkaline earth metal element and L is a lanthanide element). This lead film 115 applies the DC power necessary for the electrolytic reaction to the ends of the cell stack 101 to multiple electrolytic cells 105 connected in series by an interconnector 107. In addition, the surface on the oxidizing gas side may be protected with an airtight, oxidation-resistant material to prevent oxidation of metal materials such as Ni.

[0032] Figure 2 shows a schematic cross-sectional view of the cell stack 101. In Figure 2, the base pipe 103 is connected via connection points (120, 121) to a supply pipe 122 that supplies gas into the base pipe 103 and a discharge pipe 123 that discharges gas from inside the base pipe 103.

[0033] The inner surface 104 of the base tube 103 defines the outer edge of the gas flow passage 117. In a cell stack where the hydrogen electrode 109 is formed thickly and also serves as the base tube, the inner surface of the hydrogen electrode 109 defines the outer edge of the flow passage.

[0034] The gas (raw material gas) supplied into the base tube 103 flows from right to left on the page and is electrolyzed in the electrolytic cell 105. The gas (product gas) generated at the hydrogen electrode by electrolysis, along with the unelectrolyzed raw material gas that did not contribute to the electrolytic reaction, is discharged to the outside through the discharge pipe 123. Hereafter, the gas discharged to the outside from the base tube 103 will be referred to as "product gas" even if it contains unelectrolyzed raw material gas.

[0035] In this embodiment, the base tube 103 is divided into three areas along its axial direction. The area where the electrolytic cell 105 is formed is called the electrolytic section 130, the area upstream of the electrolytic section 130 is called the upper lead section 131, and the area downstream of the electrolytic section 130 is called the lower lead section 132. The generated gas flows through the base tube 103 located in the lower lead section 132.

[0036] A hollow tube 140 is positioned inside the base tube 103 located at the lower lead portion 132, allowing gas flowing through the base tube 103 to pass through. In Figure 2, the hollow tube 140 is coaxially positioned with the base tube 103. One end of the hollow tube 140 is fixed to the connection portion 121 with ceramic adhesive. The hollow tube 140 may also be fixed to the inner circumferential surface 104 of the base tube 103 with ceramic adhesive.

[0037] In Figure 2, the hollow tube 140 is arranged over almost the entire area of ​​the lower lead portion 132, but this is not limited to this arrangement, and the hollow tube 140 may be partially arranged in a portion of the lower lead portion 132. Also, the end of the hollow tube 140 may extend into the area of ​​the electrolytic section 130.

[0038] Figure 3 shows a schematic diagram of the hollow tube 140. Figure 3(a) is a front view, and Figure 3(b) is a side view. The outer diameter R of the hollow tube 140 is smaller than the inner diameter of the base tube 103. A clearance may exist between the hollow tube 140 and the base tube 103. This clearance is smaller than the inner diameter of the hollow tube 140. That is, the flow area of ​​the clearance between the inner circumferential surface 104 (flow passage 117) of the base tube 103 and the hollow tube 140 is smaller than the flow area inside the hollow tube 140. The clearance is within a range that does not impose a physical load on the base tube 103 due to the thermal expansion of the hollow tube 140 at the operating temperature of the cell stack 101. Within this range, a smaller clearance is better.

[0039] The hollow tube 140 does not contain a methanation catalyst. A methanation catalyst is a catalyst for the reaction that produces methane from hydrogen (H2) and carbon monoxide (CO). Examples of methanation catalysts include Ni, Fe, Co, Ru, etc.

[0040] The coefficient of linear expansion of the hollow tube 140 is less than or equal to that of the base tube 103. During operation of the cell stack 101, the hollow tube 140 will not expand more than the base tube 103. Preferably, the hollow tube 140 is made of a material whose coefficient of linear expansion is approximately the same as that of the base tube 103 (the member defining the outer casing of the flow passage 117). "Approximately the same" means 2 × 10⁻⁶ -6 This means it is within / ℃.

[0041] The material of the hollow tube 140 may be a ceramic such as zirconia (ZrO2).

[0042] The hollow tube 140 may be made of a material that has thermal conductivity and corrosion resistance.

[0043] The material of the hollow tube 140 may be metal such as SUS.

[0044] The electrolytic reaction in the cell stack 101 described above and the effects of having a hollow tube will be explained.

[0045] The gas (raw material gas) supplied into the base tube 103 (hydrogen electrode 109) contains water vapor and carbon dioxide. The raw material gas may contain hydrogen.

[0046] By applying a negative voltage to the hydrogen electrode 109 and a positive voltage to the oxygen electrode 113, at the hydrogen electrode 109, the water vapor contained in the raw material gas receives electrons and is electrolyzed to generate hydrogen molecules and oxygen ions (O 2- ). (Refer to the following reaction formula (1)). Also, the carbon dioxide contained in the raw material gas receives electrons and is electrolyzed to generate carbon monoxide molecules and oxygen ions (O 2- ). (Refer to the following reaction formula (2)). H2O + 2e - →H2 + O 2- ···(1) CO2 + 2e - →CO + O 2- ···(2)

[0047] On the other hand, the oxygen ions pass through the solid electrolyte membrane 111 due to the potential difference, move to the oxygen electrode 113, release electrons, and become oxygen molecules. (Refer to the following reaction formula (3)). The generated oxygen is discharged to the outside together with the oxidizing gas supplied to the oxygen electrode 113. 2O 2- →O2 + 4e - ···(3)

[0048] Although electrolysis is an endothermic reaction, if an electric current continues to flow through the electrolytic cell 105 for the electrolysis reaction, heat is generated due to the electrical resistance. Therefore, the temperature of the electrolysis part 130, particularly the central part in the axial direction of the base tube 103, becomes higher than that of the upper lead part 131. For example, when the upper lead part 131 is 550 °C, at the central part in the axial direction of the electrolysis part 130, it is 900 °C to 950 °C, and on the lower lead part 132 side of the electrolysis part 130, it is 850 °C. On the other hand, the temperature gradually decreases at the lower lead part 132. For example, the temperature near the opening on the lower lead part 132 side is about 550 °C.

[0049] The product gas generated at the hydrogen electrode 109 by electrolysis can become a raw material for the methanation reaction as it flows through the substrate tube 103 containing the methanation catalyst (Ni). According to the inventors' simulation results, the methanation reaction proceeds most readily in the lower lead section 132, during the process of the temperature decreasing from high temperature (850°C) to low temperature (550°C).

[0050] In the cell stack 101 according to this embodiment, a hollow tube 140 is placed inside the base tube 103 located at the lower lead portion 132. Since the pressure drop inside the hollow tube 140 is smaller than outside the hollow tube, the generated gas is preferentially introduced into the hollow tube 140. This reduces the amount of generated gas that comes into contact with the low-temperature base tube 103, thereby suppressing the methane reaction.

[0051] By making the linear expansion coefficient of the hollow tube 140 approximately the same as that of the base tube 103 (the member that defines the outer perimeter of the flow passage), the outer diameter of the hollow tube 140 can be brought closer to the inner diameter of the base tube 103. If the outer diameter of the hollow tube 140 is larger, the clearance between the hollow tube 140 and the base tube 103 decreases, making it easier for the generated gas to be introduced into the hollow tube 140. This reduces the opportunities for the generated gas to come into contact with the methane catalyst.

[0052] If the hollow tube 140 is made of a metal such as SUS, its high thermal conductivity can promote the cooling (defrosting) of the generated gas passing through the base tube 103 located in the lower lead section 132. Lowering the temperature of the generated gas at the outlet of the base tube 103 can reduce thermal damage to metal components that fix the base tube 103.

[0053] [Second Embodiment] The electrolytic cell stack according to this embodiment differs from the first embodiment in that a core is arranged inside the hollow tube. In the following description, the components common to both the first embodiment and this embodiment will not be explained.

[0054] Figure 4 shows a schematic cross-sectional view of the cell stack. In the cell stack 150, as in Figure 2, a supply pipe 122 that supplies gas into the base pipe 103 and a discharge pipe 123 that discharges gas from inside the base pipe 103 are connected to the base pipe 103 via connection parts (120, 121), as in Figure 2.

[0055] A hollow tube 140 is positioned inside the base tube 103 at the location of the lower lead portion 132, as in Figure 2. A core 151 is positioned inside the hollow tube 140 so that the generated gas can flow through it.

[0056] The core 151 may be made of metal or a non-metal. The material of the core 151 may be, for example, a metal that has thermal conductivity and high corrosion resistance. For example, the core 151 may be a rod made of SUS (stainless steel).

[0057] By placing a core, the heat transfer coefficient on the inner surface of the hollow tube 140 can be increased (by reducing the clearance between the hollow tube and the core, thereby increasing the convective heat transfer coefficient), thus promoting heat exchange of the supplied gas. If the core 151 is made of metal, the thermal conductivity of the core 151 itself increases, further promoting the cooling of the generated gas.

[0058] [Third Embodiment] Figure 5 illustrates the methane suppression method according to this embodiment. The cell stack 101 in Figure 5 has the same configuration as in Figure 2 of the first embodiment. A methane concentration measuring means 160 is provided in the discharge pipe 123 of the cell stack 101.

[0059] In this embodiment, the methane concentration contained in the gas (generated gas) discharged from the base tube 103 during the operation of the cell stack 101 is measured, and the (axial) length of the hollow tube 140 is set according to the measured value.

[0060] The methane concentration measuring device is an apparatus for measuring the methane concentration in the gas (product gas) discharged from the base tube 103. Methane concentration can be measured by gas chromatography, semiconductor laser absorption spectroscopy, Raman scattering, etc. In particular, Raman scattering is suitable for the direct measurement of gas under high temperature and high pressure conditions.

[0061] The methane concentration may be obtained by directly measuring methane (CH4), or it may be obtained indirectly by measuring the carbon monoxide (CO) concentration and hydrogen (H2) concentration.

[0062] In the methane suppression method according to this embodiment, if the methane concentration in the gas discharged from the base tube 103 is high, a long hollow tube 140 is placed inside the base tube 103. If the methane concentration is low, a short hollow tube 140 is placed inside. The length of the hollow tube 140 should be adjusted so that the methane concentration in the gas discharged from the base tube 103 is lower than a desired value.

[0063] Furthermore, in the methane suppression method according to this embodiment, for example, the CH4 concentration (and / or H2 concentration and CO concentration) in the generated gas can be monitored during the operation of the cell stack 101, and if the methane concentration increases, the length of the hollow tube 140 located in the base tube 103 can be changed.

[0064] If an increase in CH4 concentration relative to CO and H2 concentrations is observed due to deterioration of the cell stack 101, the suppression of the methane reaction can be maintained by changing the length of the hollow tube 140.

[0065] Furthermore, the methanation suppression method according to this embodiment may also be applied to the cell stack 150 of the second embodiment.

[0066] [Fourth Embodiment] In this embodiment, an electrolytic cell cartridge and an electrolytic cell module equipped with an electrolytic cell stack will be described. Figure 6 shows one embodiment of the electrolytic cell cartridge. Figure 7 shows one embodiment of the electrolytic cell module.

[0067] The electrolytic cell stack has the same configuration as in the first to third embodiments. In Figure 6, the hollow tube is omitted for simplification of the figure. The hollow tube 140 is positioned between the lower end of the electrolytic section 130 and the lower end of the cell stack 101 within the base tube 103. The connection parts (120, 121) shown in Figures 2, 4, and 5 correspond to the lower end of the base tube 103 in Figure 6. The outer circumferential surface of the lower end of the hollow tube 140 is fixed to the inner circumferential surface of the base tube 103 by ceramic adhesive.

[0068] (Electrolytic cell cartridge) As shown in Figure 6, the cartridge 203 comprises a plurality of cell stacks 101, an electrolysis chamber 215, a raw material gas supply header 217, a generated gas discharge header 219, an oxidizing gas (air) supply header 221, and an oxidizing gas discharge header 223. The cartridge 203 also comprises an upper tube sheet 225a, a lower tube sheet 225b, an upper insulator 227a, and a lower insulator 227b. In this embodiment, the cartridge 203 is structured so that the raw material gas and oxidizing gas flow in opposition to each other on the inside and outside of the cell stack 101, as shown in Figure 6, by arranging the raw material gas supply header 217, the generated gas discharge header 219, the oxidizing gas supply header 221, and the oxidizing gas discharge header 223. However, this is not necessarily required, and for example, the gases may flow parallel to each other on the inside and outside of the cell stack 101, or the oxidizing gas may flow in a direction perpendicular to the longitudinal direction of the cell stack 101.

[0069] The electrolytic chamber 215 is a region formed between the upper insulator 227a and the lower insulator 227b. This electrolytic chamber 215 is the region where the electrolytic cells 105 of the cell stack 101 are located, and it is the region where the raw material gas is electrolyzed to produce product gases (hydrogen and carbon monoxide). The temperature near the center of the cell stack 101 in the longitudinal direction of this electrolytic chamber 215 may also be monitored by the temperature measurement unit 620 (temperature sensor, thermocouple, etc.), and during steady-state operation of module 201, the atmosphere becomes high-temperature, approximately 700°C to 1000°C.

[0070] The raw material gas supply header 217 is the region enclosed by the upper casing 229a and upper tube sheet 225a of the cartridge 203, and is connected to the raw material gas supply branch pipe 207a by the raw material gas supply pipe 231a provided on the upper part of the upper casing 229a. In addition, the multiple cell stacks 101 are joined together by the upper tube sheet 225a and the upper sealing member 237a, and the raw material gas supply header 217 guides the raw material gas supplied from the raw material gas supply branch pipe 207a via the raw material gas supply pipe 231a into the base pipe 103 of the multiple cell stacks 101 at a substantially uniform flow rate, thereby substantially equalizing the generated gas performance of the multiple cell stacks 101.

[0071] The generated gas discharge header 219 is the region enclosed by the lower casing 229b and lower tube sheet 225b of the cartridge 203, and is connected to the generated gas discharge branch pipe 209a by the generated gas discharge pipe 231b provided in the lower casing 229b. In addition, the multiple cell stacks 101 are joined together by the lower tube sheet 225b and the lower sealing member 237b, and the generated gas discharge header 219 collects the generated gas that passes through the inside of the base tube 103 of the multiple cell stacks 101 and is supplied to the generated gas discharge header 219, and guides it to the generated gas discharge branch pipe 209a via the generated gas discharge pipe 231b.

[0072] The oxidizing gas supply main pipe (not shown) branches off a predetermined flow rate of oxidizing gas corresponding to the operating temperature of module 201 to oxidizing gas supply branch pipes (not shown) and supplies it to multiple cartridges 203. The oxidizing gas supply header 221 is the region surrounded by the lower casing 229b, lower tube sheet 225b, and lower insulator 227b of the SOEC cartridge 203, and is connected to an oxidizing gas supply branch pipe (not shown) by an oxidizing gas supply pipe 233a provided on the side of the lower casing 229b. This oxidizing gas supply header 221 guides the oxidizing gas supplied from the oxidizing gas supply branch pipe (not shown) via the oxidizing gas supply pipe 233a to the electrolysis chamber 215 via an oxidizing gas lower penetration section 235a, which will be described later.

[0073] The oxidizing gas discharge header 223 is the region enclosed by the upper casing 229a, upper tube sheet 225a, and upper insulator 227a of the cartridge 203, and is connected to an oxidizing gas discharge branch pipe (not shown) by an oxidizing gas discharge pipe 233b provided on the side of the upper casing 229a. This oxidizing gas discharge header 223 guides the exhaust oxidizing gas supplied from the electrolysis chamber 215 to the oxidizing gas discharge header 223 via the oxidizing gas upper penetration section 235b (described later) to an oxidizing gas discharge branch pipe (not shown) via the oxidizing gas discharge pipe 233b.

[0074] The upper tube sheet 225a is fixed to the side plate of the upper casing 229a between the top plate of the upper casing 229a and the upper insulator 227a, such that the upper tube sheet 225a, the top plate of the upper casing 229a, and the upper insulator 227a are substantially parallel to each other. The upper tube sheet 225a also has multiple holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and each cell stack 101 is inserted into one of these holes. This upper tube sheet 225a airtightly supports one end of each of the cell stacks 101 via either the upper sealing member 237a or an adhesive member, or both, and also isolates the raw material gas supply header 217 from the oxidizing gas discharge header 223.

[0075] The upper insulator 227a is positioned at the lower end of the upper casing 229a such that the upper insulator 227a, the top plate of the upper casing 229a, and the upper tube sheet 225a are substantially parallel, and is fixed to the side plate of the upper casing 229a. The upper insulator 227a is also provided with multiple holes corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameter of these holes is set to be larger than the outer diameter of the cell stacks 101. The upper insulator 227a includes an oxidizing gas upper penetration portion 235b formed between the inner surface of these holes and the outer surface of the cell stacks 101 inserted into the upper insulator 227a.

[0076] The upper insulator 227a separates the electrolytic chamber 215 from the oxidizing gas exhaust header 223, preventing the atmosphere around the upper tube sheet 225a from becoming too hot, which would reduce its strength and increase corrosion due to oxidizing agents in the oxidizing gas. In addition, to prevent thermal deformation of the upper tube sheet 225a and other components due to temperature differences when exposed to the high temperatures inside the electrolytic chamber 215, a metal material with high temperature resistance, such as a Ni-based alloy, may be used. The upper insulator 227a guides the exhaust oxidizing gas, which has passed through the electrolytic chamber 215 and been exposed to high temperatures, through the upper oxidizing gas penetration section 235b to the oxidizing gas exhaust header 223.

[0077] According to this embodiment, the structure of the cartridge 203 described above allows the raw material gas and the oxidizing gas to flow in opposition to each other on the inside and outside of the cell stack 101. As a result, the exhaust oxidizing gas exchanges heat with the raw material gas supplied to the electrolytic chamber 215 through the inside of the base tube 103, and is cooled to a temperature at which damage to the upper tube sheet 225a, etc., made of metal material, due to stress is prevented before being supplied to the oxidizing gas discharge header 223. In addition, the raw material gas is heated by heat exchange with the exhaust oxidizing gas discharged from the electrolytic chamber 215 and supplied to the electrolytic chamber 215. As a result, the raw material gas, which has been preheated to the temperature necessary for the electrolytic reaction, can be supplied to the electrolytic chamber 215 without the use of heaters or the like.

[0078] The lower tube sheet 225b is fixed to the side plate of the lower casing 229b between the bottom plate of the lower casing 229b and the lower insulator 227b, such that the lower tube sheet 225b, the bottom plate of the lower casing 229b, and the lower insulator 227b are substantially parallel to each other. The lower tube sheet 225b also has a number of holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and each cell stack 101 is inserted into a respective hole. This lower tube sheet 225b airtightly supports the other end of each of the cell stacks 101 via either the lower sealing member 237b or the adhesive member, or both, and also isolates the generated gas discharge header 219 from the oxidizing gas supply header 221.

[0079] The lower insulator 227b is positioned at the upper end of the lower casing 229b such that the lower insulator 227b, the bottom plate of the lower casing 229b, and the lower tube sheet 225b are substantially parallel, and is fixed to the side plate of the lower casing 229b. The lower insulator 227b is also provided with multiple holes corresponding to the number of cell stacks 101 provided in the SOEC cartridge 203. The diameter of these holes is set to be larger than the outer diameter of the cell stacks 101. The lower insulator 227b includes an oxidizing gas lower penetration portion 235a formed between the inner surface of these holes and the outer surface of the cell stacks 101 inserted through the lower insulator 227b.

[0080] The lower insulator 227b separates the electrolytic chamber 215 from the oxidizing gas supply header 221, preventing the atmosphere around the lower tube sheet 225b from becoming too hot, which would reduce its strength and increase corrosion due to the oxidizing agent contained in the oxidizing gas. In addition, to prevent thermal deformation of the lower tube sheet 225b due to temperature differences when it is exposed to the high temperature inside the electrolytic chamber 215, a metal material with high temperature durability, such as a Ni-based alloy, may be used. The lower insulator 227b guides the oxidizing gas supplied to the oxidizing gas supply header 221 through the lower oxidizing gas penetration section 235a to the electrolytic chamber 215.

[0081] According to this embodiment, the structure of the SOEC cartridge 203 described above causes the generated gas and the oxidizing gas to flow in opposition to each other on the inside and outside of the cell stack 101. As a result, the generated gas that has passed through the inside of the base tube 103 and through the electrolytic chamber 215 undergoes heat exchange with the oxidizing gas supplied to the electrolytic chamber 215, and is cooled to a temperature at which damage to the lower tube sheet 225b, etc., made of metal material, due to stress is prevented, and then supplied to the generated gas discharge header 219. In addition, the oxidizing gas is heated by heat exchange with the generated gas and supplied to the electrolytic chamber 215. As a result, the oxidizing gas heated to the temperature necessary for the electrolytic reaction can be supplied to the electrolytic chamber 215 without using a heater or the like.

[0082] (Electrolytic cell module) As shown in Figure 7, the electrolytic cell module (module) 201 includes, for example, a plurality of cartridges (electrolytic cell cartridges) 203, a module container 205 that houses these plurality of cartridges 203, and an insulating material (not shown) provided inside the module container 205 to insulate the plurality of cartridges 203. The module 201 also includes a raw material gas supply main pipe 207 and a plurality of raw material gas supply branch pipes 207a, and a generated gas discharge main pipe 209 and a plurality of generated gas discharge branch pipes 209a. Furthermore, the SOEC module 201 includes an oxidizing gas supply main pipe (not shown) and a plurality of oxidizing gas supply branch pipes (not shown).

[0083] The raw material gas supply main pipe 207 is located inside the module container 205 and is connected to a raw material gas supply unit that supplies raw material gas of a predetermined gas composition and flow rate corresponding to the amount of raw material gas generated by the SOEC module 201. It is also connected to a plurality of raw material gas supply branch pipes 207a. This raw material gas supply main pipe 207 branches and guides the raw material gas supplied from the aforementioned raw material gas supply unit at a predetermined flow rate to a plurality of raw material gas supply branch pipes 207a. The raw material gas supply branch pipes 207a are connected to the raw material gas supply main pipe 207 and are also connected to the raw material gas supply pipes 231a of a plurality of cartridges 203. These raw material gas supply branch pipes 207a guide the raw material gas supplied from the raw material gas supply main pipe 207 to the plurality of cartridges 203 at a substantially equal flow rate, thereby substantially equalizing the electrolysis voltage of the plurality of cartridges 203.

[0084] The generated gas discharge branch pipe 209a is connected to the generated gas discharge pipes 231b of multiple cartridges 203 and is also connected to the generated gas discharge main pipe 209. This generated gas discharge branch pipe 209a guides the generated gas discharged from the cartridges 203 to the generated gas discharge main pipe 209. The generated gas discharge main pipe 209 is connected to the multiple generated gas discharge branch pipes 209a and a portion of it is located outside the module container 205. This generated gas discharge main pipe 209 guides the generated gas discharged from the generated gas discharge branch pipes 209a at a substantially uniform flow rate to the outside of the module container 205.

[0085] The module container 205 is operated at an internal pressure of atmospheric pressure to several MPa and a surface temperature of ambient temperature to approximately 300°C, and is preferably made of materials such as carbon steel from the viewpoint of cost reduction.

[0086] In this embodiment, a configuration in which multiple cartridges 203 are assembled and stored in a module container 205 has been described, but the embodiment is not limited to this, and for example, the cartridges 203 can be stored in the module container 205 without being assembled.

[0087] The DC power required for the electrolytic reaction is supplied to the module after the supplied power is converted to a predetermined voltage by a power conversion device such as a power conditioner. The power supplied to the module is distributed according to the number of series and parallel connections of each cartridge. In each cartridge 203, power is supplied to a power supply member (not shown) via a power supply plate (not shown), and after current is passed through lead films 115 made of Ni / YSZ or the like provided on multiple electrolytic cells 105 to near the ends of the cell stack 101, it is supplied to the electrolytic cells 105.

[0088] In the first to fourth embodiments, a cylindrical transverse-striped electrolytic cell stack was described, but the shape of the electrolytic cell stack is not necessarily limited to this, as long as it has a configuration corresponding to a flow passage containing a methanation catalyst through which the generated gas passes, such as the lower lead portion. For example, a hollow tube may be placed at the position corresponding to the lower lead portion of a flat plate, cylindrical flat plate, or cylindrical vertical-striped electrolytic cell stack so as to avoid contact between the generated gas and the methanation catalyst. In particular, it is preferable that the hollow tube be placed in a region of the electrolytic cell stack that does not contribute to the electrolysis.

[0089] <Note> The method for suppressing methane formation in the electrolytic cell stack, electrolytic cell cartridge, electrolytic cell module, and electrolytic cell stack described in the embodiments above can be understood, for example, as follows.

[0090] An electrolytic cell stack (101) according to a first aspect of the present disclosure comprises an electrolytic cell (105) in which a hydrogen electrode (109), a solid electrolyte (111), and an oxygen electrode (113) are stacked in order; a flow passage (117) through which the gas produced by the hydrogen electrode flows; and a hollow tube (140) arranged within the flow passage so as to allow the gas produced by the hydrogen electrode to flow, wherein the member (103) defining the outer casing of the flow passage includes a methanation catalyst, and the hollow tube does not include a methanation catalyst.

[0091] The raw material gas supplied to the electrolytic cell stack is electrolyzed in the electrolytic cell. The gas produced at the hydrogen electrode (product gas containing hydrogen and carbon monoxide) is discharged to the outside through the flow passage. By placing the hollow tubes within the flow passage, the product gas preferentially flows into the hollow tubes, which have low pressure drop. This reduces the opportunities for the product gas to come into contact with the methane catalyst contained in the flow passage. As a result, the methane reaction of the product gas is suppressed, and the amount of methane produced can be reduced. In such an electrolytic cell stack, the decrease in H2 / CO yield is suppressed.

[0092] Hollow pipes may be installed throughout or in part within the flow path. Hollow pipes may extend outside the flow path.

[0093] The placement of hollow tubes within the flow path is straightforward. According to the above disclosure, the methanation reaction caused by the methanation catalyst downstream of the electrolytic cell can be suppressed by the simple operation of placing hollow tubes. Since there is no need to apply additional films to the electrolytic cell stack, defects such as film peeling do not occur.

[0094] In the first embodiment, the electrolytic cell stack according to a second aspect of the present disclosure has a flow path area of ​​clearance between the flow passage and the hollow tube that is smaller than the flow path area inside the hollow tube.

[0095] By reducing the flow area of ​​the clearance between the hollow tube and the flow passage, it is possible to suppress the flow of generated gas between the hollow tube and the flow passage.

[0096] In the third aspect of the present disclosure, the electrolytic cell stack, in the first aspect, has a coefficient of thermal expansion of the hollow tube that is approximately equal to the coefficient of thermal expansion of the member defining the outer casing of the flow passage.

[0097] The smaller the clearance between the hollow tube and the flow passage, the more effectively the generated gas can be prevented from flowing between the hollow tube and the flow passage, allowing more of the generated gas to be introduced into the hollow tube. On the other hand, if two components with a large difference in linear expansion are placed in close proximity, there is a risk of damage due to temperature changes during the use of the electrolytic cell stack.

[0098] The above disclosure states that by reducing the difference in linear expansion between the hollow tube and the flow passage, the possibility of damage due to temperature changes during use can be reduced, thus allowing for a smaller clearance between the hollow tube and the flow passage.

[0099] In the fourth aspect of the present disclosure, the electrolytic cell stack, in the first aspect, is made of a metal material for the hollow tube.

[0100] Hollow metal tubes have high thermal conductivity. By placing such hollow tubes in the flow path of the generated gas, the cooling of the generated gas can be promoted. This reduces the thermal impact on the components that fix and support the electrolytic cell stack.

[0101] An electrolytic cell stack (150) according to a fifth aspect of this disclosure, in any of the first to fourth aspects, has a metal core 151 arranged inside the hollow tube so that the gas generated at the hydrogen electrode can flow through the hollow tube.

[0102] By incorporating a metal core, the thermal conductivity can be further increased. This, in turn, further accelerates the cooling of the generated gas.

[0103] An electrolytic cell cartridge (203) according to the sixth aspect of this disclosure comprises an electrolytic cell stack according to any of the first to fifth aspects.

[0104] An electrolytic cell module (201) according to the seventh aspect of this disclosure comprises an electrolytic cell cartridge as described in the sixth aspect.

[0105] A method for suppressing methanation in an electrolytic cell stack according to the eighth aspect of this disclosure is a method for suppressing methanation in an electrolytic cell stack according to any one of the first to fifth aspects, wherein the methane concentration and / or hydrogen concentration and carbon monoxide concentration in the gas discharged from the electrolytic cell stack are measured, and the length of the hollow tube is set based on the measured values.

[0106] By measuring the methane concentration and / or hydrogen and carbon monoxide concentrations, the amount of methane produced by the catalytic reaction of the generated gases can be determined directly or indirectly. If an increase in methane concentration is confirmed by this measurement, the length of the hollow tube can be increased to enhance the suppression effect of the methanation reaction. This can suppress the decrease in the H2 / CO yield. [Explanation of symbols]

[0107] 101,150 cell stack 103 Base tube (member that defines the outer casing) 104 Inner surface of the base tube 105 Electrolytic Cells 107 Interconnector (Separator) 109 Hydrogen electrode 111 Solid electrolyte membrane 113 Oxygen electrode 115 Lead film 117 Distribution path 120,121 Connection part 122 Supply pipe 123 Discharge pipe 130 Electrolytic section 131 Upper lead section 132 Lower lead section 140 Hollow tube 151 Core 160 Methane concentration measuring means 201 Modules 203 Cartridge 205 Module Container 207 Raw material gas supply main pipe 207a Raw material gas supply branch pipe 209 Generative gas discharge main pipe 209a Gas discharge branch pipe 215 Electrolysis chamber 217 Raw material gas supply header 219. Generated gas emission header 221 Oxidizing gas supply header 223 Oxidizing gas emission header 225a Upper tube plate 225b Lower tube sheet 227a Upper insulation 227b Lower insulation 229a Upper casing 229b Lower casing 231a Raw material gas supply pipe 231b Gas discharge pipe 233a Oxidizing gas supply pipe 233b Oxidizing gas exhaust pipe 235a Lower penetration for oxidizing gas 235b Upper penetration for oxidizing gas 237a Upper sealing member 237b Lower sealing member

Claims

1. An electrolytic cell in which a hydrogen electrode, a solid electrolyte, and an oxygen electrode are stacked in that order, A flow passage through which the gas generated at the hydrogen electrode flows, A hollow tube is provided within the flow passage through which the gas generated at the hydrogen electrode can flow, Equipped with, The member defining the outer perimeter of the flow passage includes a methane catalyst. The hollow tube is an electrolytic cell stack that does not contain a methane catalyst.

2. The electrolytic cell stack according to claim 1, wherein the flow path area of ​​the clearance between the flow passage and the hollow tube is smaller than the flow path area inside the hollow tube.

3. The electrolytic cell stack according to claim 1, wherein the coefficient of linear expansion of the hollow tube is substantially equal to the coefficient of linear expansion of the member defining the outer casing of the flow passage.

4. The electrolytic cell stack according to claim 1, wherein the material of the hollow tube is metal.

5. The electrolytic cell stack according to claim 1, wherein a metal core is arranged inside the hollow tube so that the gas generated at the hydrogen electrode can flow through the hollow tube.

6. An electrolytic cell cartridge comprising an electrolytic cell stack according to any one of claims 1 to 5.

7. An electrolytic cell module comprising the electrolytic cell cartridge described in claim 6.

8. A method for suppressing methane formation in an electrolytic cell stack according to any one of claims 1 to 5, A method for suppressing methane formation in an electrolytic cell stack, comprising measuring the methane concentration and / or hydrogen concentration and carbon monoxide concentration in the gas discharged from the electrolytic cell stack, and setting the length of the hollow tube based on the measured values.

Images