Hydrogen production system and hydrogen production method

Abstract

To improve the energy efficiency of the entire hydrogen production system.SOLUTION: A hydrogen production system 1 produces hydrogen. The hydrogen production system 1 comprises: a solid oxide electrolysis cell (SOEC) 10 which is supplied with an oxidizing gas and steam and generates hydrogen by electrolyzing the supplied steam; a steam generation unit 20 which generates steam supplied to the SOEC 10 by heating feed water; and a power supply device 40 which supplies electric power to the SOEC 10 so that the SOEC 10 operates at an operating point exceeding a thermoneutral point. The steam generation unit 20 heats the feed water using heat generated in the SOEC 10 and generates steam without using heat supplied from the outside of the hydrogen production system 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a hydrogen production system and a hydrogen production method. [Background technology]

[0002] Electrolysis cells, which produce hydrogen and oxygen by electrochemically decomposing water, are a hydrogen production method that does not involve carbon dioxide emissions and has excellent environmental properties. Among these, solid oxide electrolysis cells (SOECs) use ceramics such as yttria-stabilized zirconia as the electrolyte and can produce hydrogen more efficiently than other electrolysis cells because they use high-temperature steam as the feedstock. Furthermore, for the purpose of decarbonization, co-electrolysis is also possible, using carbon dioxide (CO2) as the feedstock and electrolytic hydrogen as the reducing agent to directly produce carbon monoxide (CO).

[0003] As an electrolysis system equipped with an SOEC, for example, the electrolysis system described in Patent Document 1 is known. Patent Document 1 describes a system equipped with an electrolysis cell (SOEC) stack and a steam generator that generates steam to be supplied to the stack. The steam generator includes an AC or DC resistance heating element or an induction heating element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-180316 Summary of the Invention [Problem to be solved by the invention]

[0005] To produce hydrogen in an SOEC, water vapor is required. Therefore, unless water vapor is supplied to the SOEC from outside the system (e.g., from a factory steam supply line), water vapor must be generated from feedwater and supplied to the SOEC. One possible method for generating water vapor is to use an electric power device such as an AC or DC resistance heating element, as described in Patent Document 1. However, in such a method, the use of electric power increases the power consumption of the entire system, potentially reducing the energy efficiency of the entire system.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a hydrogen production system and a hydrogen production method that can improve the energy efficiency of the entire hydrogen production system. [Means for solving the problem]

[0007] In order to solve the above problems, the hydrogen production system and hydrogen production method of the present disclosure employ the following measures. A hydrogen production system according to one aspect of the present disclosure is a hydrogen production system that produces hydrogen and includes: a solid oxide electrolysis cell that receives an oxidizing gas and water vapor and generates hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit that heats feedwater to generate water vapor to be supplied to the solid oxide electrolysis cell; and a power supply device that supplies power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell operates at an operating point above a thermal neutral point, wherein the water vapor generation unit heats the feedwater using heat generated by the solid oxide electrolysis cell and generates water vapor without using heat supplied from outside the hydrogen production system.

[0008] A hydrogen production method according to one aspect of the present disclosure is a method of producing hydrogen using a hydrogen production system, the hydrogen production system comprising: a solid oxide electrolysis cell that receives an oxidizing gas and water vapor and generates hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit that heats feedwater to generate water vapor to be supplied to the solid oxide electrolysis cell; and a power supply device that supplies power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell operates at an operating point above a thermal neutral point. The method comprises: a hydrogen generation step of producing hydrogen in the solid oxide electrolysis cell by electrolyzing supplied water vapor; a steam generation step of heating feedwater to generate water vapor to be supplied to the solid oxide electrolysis cell; and a power supply step of supplying power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell operates at an operating point above a thermal neutral point. The steam generation step uses heat generated in the solid oxide electrolysis cell to heat the feedwater and generates water vapor without using heat supplied from outside the hydrogen production system. [Effects of the Invention]

[0009] According to the present disclosure, the energy efficiency of the entire hydrogen production system can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram illustrating a hydrogen production system according to an embodiment of the present disclosure. [Figure 2] FIG. 1 illustrates an aspect of a cell stack according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a hydrogen production system and a hydrogen production method according to the present disclosure will be described with reference to the drawings.

[0012] As shown in FIG. 1, the hydrogen production system 1 according to this embodiment includes a solid oxide electrolysis cell (SOEC) 10, a steam generation unit 20 that generates steam to be supplied to the SOEC 10, a water supply device 30 that supplies water to the steam generation unit 20, a power supply device 40 that supplies power to the SOEC 10, and a compressor 50 that compresses air to be supplied to the SOEC 10.

[0013] A high-temperature, high-pressure oxidizing gas (in this embodiment, air is used as an example) and high-temperature, high-pressure water vapor are supplied to the SOEC 10. The SOEC 10 generates hydrogen by electrolyzing the water vapor using a high-temperature solid electrolyte.

[0014] The SOEC 10 includes a plurality of cell stacks 101, a steam supply header 12, a produced hydrogen discharge header 13, an oxidizing gas supply header 14, an oxidizing gas discharge header 15, and a housing 16 in which the plurality of cell stacks 101 are arranged.

[0015] The upstream ends of the multiple cell stacks 101 are connected to the water vapor supply header 12. The downstream ends of the multiple cell stacks 101 are connected to the produced hydrogen discharge header 13. The oxidizing gas supply header 14 and the oxidizing gas discharge header 15 are connected to a space (reaction chamber) formed inside the housing 16.

[0016] Next, the cell stack 101 will be described with reference to FIG. The following describes a cylindrical cell stack using a substrate tube as an example according to this embodiment. When a substrate tube is not used, for example, the fuel electrode may be formed thick and serve as the substrate tube, and the use of a substrate tube is not limited. Furthermore, while the substrate tube in this embodiment is described as being cylindrical, the substrate tube may have any shape as long as it is cylindrical, and the cross section is not necessarily limited to a circular shape, and may be, for example, an elliptical shape. A cell stack such as a flat tubular cell formed by vertically crushing the circumferential surface of a cylinder is also possible. Here, FIG. 1 shows one aspect of a cell stack according to this embodiment. The cell stack 101 includes, for example, a cylindrical substrate tube 103, multiple electrolysis cells 105 formed on the outer circumferential surface of the substrate tube 103, and interconnectors 107 formed between adjacent electrolysis cells 105. The electrolysis cell 105 is formed by stacking a hydrogen electrode 109, a solid electrolyte membrane 111, and an oxygen electrode 113. The cell stack 101 also includes a lead film 115 electrically connected via an interconnector 107 to the oxygen electrode 113 of the electrolytic cell 105 formed at one end of the electrolytic cell 105 at the extreme end in the axial direction of the substrate tube 103 among the multiple electrolytic cells 105 formed on the outer peripheral surface of the substrate tube 103, and a lead film 115 electrically connected to the hydrogen electrode 109 of the electrolytic cell 105 formed at the other extreme end. The gas supplied to and discharged from the hydrogen electrode 109 often contains hydrogen in addition to the water vapor used for electrolysis, but in the following explanation, to avoid confusion, the supply gas containing hydrogen will be called "supplied water vapor" and the hydrogen gas containing water vapor discharged from the hydrogen electrode 109 will be called "produced hydrogen."

[0017] The base tube 103 is made of a porous material, and its main component is, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), Y2O3-stabilized ZrO2 (YSZ), or MgAl2O4. The base tube 103 supports the electrolytic cell 105, the interconnector 107, and the lead film 115, and also diffuses the supply steam supplied to the inner circumferential surface 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.

[0018] The hydrogen electrode 109 is made of a composite oxide of Ni and a zirconia-based electrolyte material, for example, Ni / YSZ. The thickness of the hydrogen electrode 109 is 50 μm to 250 μm, and the hydrogen electrode 109 may be formed by screen printing a slurry. YSZ, which has gas-tightness that makes it difficult for gas to pass through and high oxygen ion conductivity at high temperatures, is mainly used for the solid electrolyte membrane 111. This solid electrolyte membrane 111 transfers oxygen ions (O2-) generated at the hydrogen electrode 109 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 a slurry. The oxygen electrode 113 is made of, for example, a LaSrMnO3-based oxide or a LaCoO3-based oxide, and the oxygen electrode 113 is formed by screen printing or by applying a slurry using a dispenser. The oxygen electrode 113 may 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 made of a material that exhibits high ionic conductivity and excellent catalytic activity. The oxygen electrode intermediate layer may be made of Sm-doped ceria, which exhibits high ionic conductivity, and the oxygen electrode layer (oxygen electrode conductive layer) on the oxygen electrode intermediate layer may be made of a perovskite-type oxide such as Sr- and Ca-doped LaMnO3.

[0019] By applying a negative voltage to the hydrogen electrode 109 and a positive voltage to the oxygen electrode 113, the water vapor contained in the supplied water vapor receives electrons at the hydrogen electrode 109 and is electrolyzed to generate hydrogen molecules and oxygen ions (O2-) (see reaction formula (1) below). The generated hydrogen is extracted to the outside together with the supplied water vapor. 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 (see reaction formula (2) below). The generated oxygen is discharged to the outside together with the oxidizing gas supplied to the oxygen electrode 113. H2O+2e- → H2+O2- (1) 2O2- → O2 + 4e- (2)

[0020] The oxidizing gas is not directly involved in the electrolysis reaction, but supplies the heat necessary for the electrolysis reaction (endothermic) and discharges excess heat generated by the electrolysis reaction. It is usually a gas containing approximately 15% to 30% oxygen, and air is a typical example, but other gases that can be used include a mixture of combustion exhaust gas and air, a mixture of oxygen and air, and inert gases such as nitrogen.

[0021] The interconnector 107 is made of a conductive perovskite oxide represented by M1-xLxTiO3 (M is an alkaline earth metal element, L is a lanthanoid element) such as SrTiO3 or lanthanum chromite (LaCrO3), and is screen-printed as a slurry. The interconnector 107 is a dense film that prevents the supplied water vapor and oxidizing gas from mixing. The interconnector 107 also has stable durability and electronic conductivity in both oxidizing and reducing atmospheres. This interconnector 107 electrically connects the oxygen electrode 113 of one electrolytic cell 105 to the hydrogen electrode 109 of the other electrolytic cell 105, connecting the adjacent electrolytic cells 105 in series.

[0022] The lead film 115 is required to have electronic conductivity and a thermal expansion coefficient close to that of the other materials constituting the cell stack 101, and is therefore made of a composite material of Ni and a zirconia-based electrolyte material, such as Ni / YSZ, or an M1-xLxTiO3 (M is an alkaline earth metal element, L is a lanthanoid element) such as an SrTiO3-based material. This lead film 115 applies DC power required for the electrolysis reaction to the multiple electrolysis cells 105 connected in series by the interconnectors 107 to the end of the cell stack 101. Furthermore, 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.

[0023] 1, the steam generating unit 20 generates steam to be supplied to the SOEC 10 by heating the feedwater supplied from the water supply device 30. The steam generating unit 20 generates steam by heating the feedwater using heat generated in the SOEC 10.

[0024] The steam generation section 20 has a first heat exchange section 21 that exchanges heat between the oxidizing gas discharged from the SOEC 10 and the feed water, a second heat exchange section 22 that exchanges heat between the hydrogen generated in the SOEC 10 and the feed water, and a third heat exchange section 23 that exchanges heat between the oxidizing gas compressed in the compression device 50 and the feed water.

[0025] The first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 are provided at a midpoint of the first steam supply line L10. The first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 are provided in parallel. In detail, the first steam supply line L10 branches into three branch lines L10a at a midpoint, and each branch line L10a is provided with one first heat exchange section 21, one second heat exchange section 22, and one third heat exchange section 23. The branch lines L10a join downstream of each heat exchange section.

[0026] The first heat exchange section 21 heats the feedwater flowing through the first steam supply line L10 (more specifically, the branch line L10a) and generates steam by exchanging heat between the feedwater flowing through the oxidizing gas discharge line L21 and the oxidizing gas. The second heat exchange section 22 heats the feedwater and generates steam by exchanging heat between the feedwater flowing through the first steam supply line L10 (more specifically, the branch line L10a) and hydrogen flowing through the hydrogen discharge line L30. The third heat exchange section 23 heats the feedwater and generates steam by exchanging heat between the feedwater flowing through the first steam supply line L10 (more specifically, the branch line L10a) and the oxidizing gas flowing through the oxidizing gas supply line L20.

[0027] The water supply device 30 is a device that stores and delivers water (supply water). This supply water is heated to become steam in the steam generating section 20. The water supply device 30 is connected to the upstream end of a first steam supply line L10.

[0028] The power supply 40 supplies the SOEC 10 with power used for steam electrolysis. The power supply 40 supplies power to the SOEC 10 so that the SOEC 10 operates at an operating point above the thermal neutral point. The thermal neutral point refers to the operating point of the SOEC 10 at which the Joule heat generated in the SOEC 10 is equal to the amount of heat absorbed by the endothermic reaction accompanying electrolysis in the SOEC 10. The power supply 40 of this embodiment supplies more power than that supplied when operating at the thermal neutral point so that the SOEC 10 operates at an operating point above the thermal neutral point. The method for increasing the power is not particularly limited. For example, the current flowing through the SOEC 10 may be increased, or the voltage applied to the SOEC 10 may be increased. Alternatively, both the current and the voltage may be increased.

[0029] The compression device 50 is a device that compresses the oxidizing gas supplied to the SOEC 10. The oxidizing gas may be, for example, air. In the following description, the oxidizing gas is air. The compression device 50 includes a compressor 51 , a turbine 52 and an electric motor 53 . The compressor 51 and the turbine 52 are connected to one another by the same rotating shaft, and the compressor 51 is driven by the rotation of the turbine 52. The electric motor 53 is configured to drive the compressor 51 or to assist in driving the compressor 51 when the output of the turbine 52 is low (for example, when the hydrogen production system 1 is started up).

[0030] Next, the flow of fluid in the hydrogen production system 1 according to this embodiment will be described. First, we will explain the flow of feedwater and steam supplied to the SOEC 10. In the following, the fluid flowing through the first steam supply line L10 is feedwater upstream of the steam generating unit 20 and steam downstream of the steam generating unit 20, so the feedwater will be denoted by the symbol "W" and the steam will be denoted by the same symbol "S1".

[0031] The feedwater W stored in the water supply device 30 is introduced into the first steam supply line L10. The first steam supply line L10 is provided with a feedwater pump 60 driven by a driving force from a motor 61. The feedwater W introduced into the first steam supply line L10 is supplied to the steam generation unit 20 by the driving force of the feedwater pump 60.

[0032] The feedwater W supplied to the steam generation unit 20 evaporates into steam S1 in the first heat exchange unit 21 by heat exchange with the mixed gas A2 flowing through the oxidizing gas discharge line L21 (steam generation process). Furthermore, in the second heat exchange unit 22, the feedwater W evaporates into steam S1 by heat exchange with hydrogen H flowing through the hydrogen discharge line L30. Furthermore, in the third heat exchange unit 23, the feedwater W evaporates into steam S1 by heat exchange with the oxidizing gas A1 flowing through the oxidizing gas supply line L20. Taking into account heat loss in the first steam supply line L10 and the second steam supply line L11, the steam S1 at the outlet of each heat exchange unit may be superheated.

[0033] The steam S1 generated in each heat exchange section joins together downstream of the steam generation section 20. The joined steam S1 is introduced into the second steam supply line L11 via the first steam supply line L10. At this time, hydrogen H supplied via the hydrogen supply line L31 is added. A mixed gas S2 of the steam S1 and hydrogen H is supplied to the SOEC 10 (more specifically, the steam supply header 12) via the second steam supply line L11. Power is supplied to the SOEC 10 from the power supply device 40 (power supply step). The SOEC 10 is operated at an operating point above the thermal neutral point.

[0034] The high-temperature, high-pressure oxidizing gas A1 compressed by the compressor 51 is introduced into the oxidizing gas supply line L20. The oxidizing gas A1 introduced into the oxidizing gas supply line L20 is supplied to the third heat exchange section 23 of the steam generation section 20. The oxidizing gas A1 supplied to the third heat exchange section 23 is cooled by heat exchange with the feedwater W circulating through the first steam supply line L10. The oxidizing gas A1 cooled in the third heat exchange section 23 is supplied to the SOEC 10 (more specifically, the oxidizing gas supply header 14) via the oxidizing gas supply line L20.

[0035] The oxidizing gas A1 supplied to the oxidizing gas supply header 14 flows upward through the internal space of the casing 16 and is introduced into the oxidizing gas discharge header 15. As the oxidizing gas flows through the internal space of the casing 16, oxygen is added to the oxidizing gas. The mixed gas A2 of the oxidizing gas A1 and oxygen introduced into the oxidizing gas discharge header 15 is discharged into the oxidizing gas discharge line L21. The mixed gas A2 introduced into the oxidizing gas discharge line L21 is supplied to the first heat exchange section 21 of the steam generation section 20. The mixed gas A2 supplied to the first heat exchange section 21 is cooled by heat exchange with the feedwater W flowing through the first steam supply line L10. The mixed gas A2 cooled in the first heat exchange section 21 is supplied to the turbine 52 of the compression device 50 via the oxidizing gas discharge line L21. The mixed gas A2 supplied to the turbine 52 drives the turbine 52 to rotate.

[0036] Meanwhile, the mixed gas S2 of water vapor S1 and hydrogen H supplied to the water vapor supply header 12 flows inside each cell stack 101. At this time, the water vapor S1 contained in the mixed gas S2 is electrolyzed to generate hydrogen (hydrogen generation process). The generated high-temperature hydrogen H (containing water vapor) is introduced into the generated hydrogen discharge header 13. The hydrogen H introduced into the generated hydrogen discharge header 13 is discharged into the hydrogen discharge line L30. The hydrogen H introduced into the hydrogen discharge line L30 is supplied to the second heat exchange section 22 of the water vapor generation section 20. The hydrogen H supplied to the second heat exchange section 22 is cooled by heat exchange with the feed water W flowing through the first water vapor supply line L10. The water vapor contained in the cooled hydrogen H condenses, separating the water vapor. The hydrogen from which the water vapor has been separated (strictly speaking, containing water vapor at the saturated vapor pressure) is supplied to a hydrogen storage facility (not shown) via the hydrogen discharge line L30.

[0037] A hydrogen supply line L31 is also connected to the second heat exchange section 22. The hydrogen supply line L31 guides a portion of the hydrogen H (including water vapor) flowing through the hydrogen discharge line L30 to the second water vapor supply line L11. Therefore, a portion of the hydrogen H introduced into the second heat exchange section 22 is introduced into the second water vapor supply line L11 via the hydrogen supply line L31. The hydrogen supply line L31 is provided with a booster 62 driven by a driving force from a motor 63. The hydrogen H introduced into the hydrogen supply line L31 is supplied to the second steam supply line L11 by the driving force of the booster 62.

[0038] According to this embodiment, the following advantageous effects are achieved. In this embodiment, the steam generator 20 generates steam to be supplied to the SOEC 10 by using heat generated in the hydrogen production system 1 (heat generated in the SOEC 10 and the compressor 50) to heat the feedwater. This allows steam to be generated using the exhaust heat of the SOEC 10. Therefore, the energy efficiency of the entire hydrogen production system 1 can be improved compared to when the exhaust heat of the SOEC 10 is not used or when heat supplied to the steam generator 20 from a separately provided device that supplies heat for steam generation (e.g., an electric boiler) is used. Furthermore, in this embodiment, the SOEC 10 is operated at an operating point above the thermal neutral point, which allows the amount of hydrogen generated to be increased. In this way, this embodiment allows the energy efficiency of the entire system to be improved while increasing the amount of hydrogen generated.

[0039] Furthermore, the cell stack 101 of this embodiment is cylindrical, and therefore structurally can be used at higher temperatures than cell stacks of other shapes (e.g., flat plate shapes). This allows the SOEC 10 to be operated at an operating point above the thermal neutral point.

[0040] Furthermore, in the SOEC 10, Joule heat is generated as current flows. Meanwhile, the electrolysis of water vapor in the SOEC 10 is an endothermic reaction. Therefore, in the SOEC 10, the generated Joule heat is absorbed by an endothermic reaction. Therefore, in the SOEC 10, Joule heat is effectively utilized by electrolysis until the amount of generated Joule heat exceeds the amount of heat absorbed by the endothermic reaction. The operating point at which the amount of generated Joule heat is equal to the amount of heat absorbed by the endothermic reaction is called the "thermal neutral point." When the SOEC 10 is operated at an operating point beyond the thermal neutral point, the generated Joule heat cannot be absorbed by the endothermic reaction, resulting in the generation of excess Joule heat (hereinafter referred to as "excess heat"). For this reason, in the past, it was common to operate the SOEC 10 so as to reach the thermal neutral point in order to suppress energy loss due to excess heat generation. On the other hand, in this embodiment, a power supply device 40 is provided that supplies power to the SOEC 10 so that the SOEC 10 operates at an operating point above the thermal neutral point. That is, the SOEC 10 is operated at an operating point above the thermal neutral point. Therefore, excess heat is generated in the SOEC 10. In this embodiment, the steam generation unit 20 heats the feedwater using the heat generated in the SOEC 10, and this excess heat can be effectively used to heat the feedwater. Therefore, part or all of the heat required for steam generation can be supplied by the excess heat generated by the SOEC 10. Therefore, the amount of heat supplied to the steam generation unit 20 from a separate device (e.g., an electric boiler) for generating steam, which is provided outside the hydrogen production system 1, can be reduced or eliminated. Therefore, the device can be made smaller or eliminated, thereby reducing the equipment costs and operating costs of the hydrogen production system 1.

[0041] As described above, in this embodiment, the SOEC 10 is operated at an operating point above the thermal neutral point, which generates excess Joule heat in the SOEC 10. The excess Joule heat is consumed by heating the fluid (e.g., oxidizing gas, steam, hydrogen, etc.) flowing through the SOEC. In this embodiment, the steam generation unit 20 includes a first heat exchange unit 21 that exchanges heat between the oxidizing gas discharged from the SOEC 10 and the feedwater, and a second heat exchange unit 22 that exchanges heat between the hydrogen generated in the SOEC 10 and the feedwater. This allows the first heat exchange unit 21 to recover excess Joule heat consumed for heating the oxidizing gas and use the recovered heat for steam generation. Similarly, the second heat exchange unit 22 recovers excess Joule heat consumed for heating the hydrogen and use the recovered heat for steam generation. Therefore, part or all of the heat required for steam generation can be met by the excess heat generated by the SOEC 10. This reduces or eliminates the need for a separate device (e.g., an electric boiler) that supplies heat for steam generation. This allows the device to be downsized or eliminated, thereby reducing the equipment and operating costs of the hydrogen production system 1.

[0042] In this embodiment, the steam generating unit 20 has a third heat exchange unit 23 that exchanges heat between the oxidizing gas compressed by the compressor 50 and the feed water. This makes it possible to generate steam by utilizing the heat generated by compression by the compressor 50. This can further improve the energy efficiency of the entire hydrogen production system 1. It can also further increase the amount of hydrogen produced.

[0043] As described above, in this embodiment, all of the latent heat and sensible heat required to generate steam from feedwater to be supplied to the SOEC 10 is provided by the heat generated in the hydrogen production system 1 (heat generated in the SOEC 10 and the compression device 50). Specifically, the feedwater is heated to generate steam only in the steam generation unit 20 (including heat from heat exchange in the first heat exchange unit 21 and the second heat exchange unit 22, and, if necessary, heat from heat exchange in the third heat exchange unit 23), without using heat from outside the hydrogen production system 1. Therefore, it is possible to eliminate the need for heat supplied from a separate device (such as an electric boiler) that supplies heat for steam generation. Therefore, since this device can be eliminated, the equipment costs and operating costs of the hydrogen production system 1 can be further reduced.

[0044] The present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure. For example, in the above embodiment, an example has been described in which the first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 are provided in parallel, but the present disclosure is not limited to this. For example, the first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 may be provided in series. That is, the steam and / or feedwater that has completed heat exchange in the first heat exchange section 21 may be introduced into the second heat exchange section 22, and the steam and / or feedwater that has completed heat exchange in the second heat exchange section 22 may be introduced into the third heat exchange section 23. Note that when the heat exchangers are provided in series, the order in which the heat exchangers are provided is not limited to the order described above. Furthermore, the first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 may be partially arranged in parallel. That is, two of the three heat exchangers may be arranged in parallel, and the remaining one may be arranged upstream or downstream of the heat exchange sections arranged in parallel.

[0045] Furthermore, the first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 may each have a structure divided into a preheating section, an evaporating section, and a superheating section.

[0046] Furthermore, in the above embodiment, an example has been described in which the steam generation unit 20 includes the third heat exchange unit 23, but the present disclosure is not limited thereto. For example, the third heat exchange unit 23 may be omitted. That is, in this modification, the steam generation unit 20 does not utilize the heat generated by the compression device 50. Therefore, the steam generation unit 20 generates steam by heating the feedwater only using the heat generated in the SOEC 10. That is, all of the latent heat and sensible heat required to generate steam from the feedwater to be supplied to the SOEC 10 can be covered by the surplus heat generated by the SOEC 10. Therefore, heat supplied from a separately provided device (e.g., an electric boiler) that supplies heat for steam generation can be eliminated. Therefore, since this device can be eliminated, the equipment costs and operating costs of the hydrogen production system 1 can be further reduced.

[0047] The hydrogen production system and the hydrogen production method described in the above-described embodiment can be understood, for example, as follows. A hydrogen production system according to a first aspect of the present disclosure is a hydrogen production system (1) that produces hydrogen, and includes: a solid oxide electrolysis cell (10) that receives an oxidizing gas and water vapor and generates hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit (20) that heats feedwater to generate water vapor to be supplied to the solid oxide electrolysis cell (10); and a power supply device (40) that supplies power to the solid oxide electrolysis cell (10) so that the solid oxide electrolysis cell (10) operates at an operating point above a thermal neutral point. The water vapor generation unit (20) heats the feedwater by utilizing heat generated in the solid oxide electrolysis cell (10) and generates water vapor without using heat supplied from outside the hydrogen production system (1).

[0048] In the above configuration, the steam generator heats the feedwater using heat generated in the solid oxide electrolysis cell, and generates steam to be supplied to the solid oxide electrolysis cell without using heat supplied from outside the hydrogen production system. This allows steam to be generated using the waste heat from the solid oxide electrolysis cell. Therefore, the energy efficiency of the entire hydrogen production system can be improved compared to a system that does not use the waste heat from the solid oxide electrolysis cell. Furthermore, in the above configuration, the solid oxide electrolysis cell is operated at an operating point above the thermal neutral point, which increases the amount of hydrogen generated. Thus, the above configuration allows the energy efficiency of the entire system to be improved while increasing the amount of hydrogen produced.

[0049] Furthermore, in a solid oxide electrolysis cell, Joule heat is generated as a result of the flow of current. On the other hand, the electrolysis of water vapor in a solid oxide electrolysis cell is an endothermic reaction. Therefore, in a solid oxide electrolysis cell, the generated Joule heat is absorbed by an endothermic reaction. Therefore, in a solid oxide electrolysis cell, Joule heat is effectively utilized in electrolysis until the amount of generated Joule heat exceeds the amount of heat absorbed by the endothermic reaction. The operating point at which the amount of generated Joule heat is equal to the amount of heat absorbed by the endothermic reaction is called the "thermal neutral point." When a solid oxide electrolysis cell is operated at an operating point beyond the thermal neutral point, the generated Joule heat cannot be absorbed by the endothermic reaction, resulting in the generation of excess Joule heat (hereinafter referred to as "excess heat"). For this reason, in the past, it was common to operate a solid oxide electrolysis cell so that the cell was at the thermal neutral point in order to suppress energy loss due to excess heat generation. On the other hand, the above configuration includes a power supply device that supplies power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell operates at an operating point above the thermal neutral point. That is, the solid oxide electrolysis cell is operated at an operating point above the thermal neutral point. Therefore, excess heat is generated in the solid oxide electrolysis cell. In the above configuration, the steam generating unit heats the feedwater using the heat generated in the solid oxide electrolysis cell, and this excess heat can be used to heat the feedwater. Therefore, part or all of the heat required for steam generation can be supplied by the excess heat generated by the solid oxide electrolysis cell. This makes it possible to reduce or eliminate the amount of heat supplied to the steam generating unit from a separately provided device that supplies heat for steam generation (e.g., an electric boiler). This allows the device to be downsized or eliminated, thereby reducing the equipment and operating costs of the hydrogen production system. In particular, in the above configuration, steam is generated without using heat supplied from outside the hydrogen production system, so the heat required for steam generation can be entirely met by the surplus heat generated by the solid oxide electrolysis cell. This eliminates the need for heat to be supplied to the steam generation unit from a separate device (e.g., an electric boiler) that supplies heat for steam generation. This elimination of the device allows for significant reductions in the equipment and operating costs of the hydrogen production system.

[0050] In a hydrogen production system according to a second aspect of the present disclosure, in the above-described first aspect, the steam generation unit (20) includes a first heat exchange unit (21) that exchanges heat between the oxidizing gas discharged from the solid oxide electrolysis cell (10) and the feed water, and a second heat exchange unit (22) that exchanges heat between the hydrogen generated in the solid oxide electrolysis cell (10) and the feed water.

[0051] As described above, in the above configuration, the solid oxide electrolysis cell is operated at an operating point above the thermal neutral point, which generates excess Joule heat in the solid oxide electrolysis cell, which is consumed by heating the fluid (e.g., oxidizing gas, water vapor, hydrogen, etc.) circulating in the SOEC. In the above configuration, the steam generation unit includes a first heat exchange unit that exchanges heat between the oxidizing gas discharged from the solid oxide electrolysis cell and the feedwater, and a second heat exchange unit that exchanges heat between the hydrogen generated in the solid oxide electrolysis cell and the feedwater. This allows the first heat exchange unit to recover excess Joule heat consumed for heating the oxidizing gas and use the recovered heat for steam generation. Similarly, the second heat exchange unit can recover excess Joule heat consumed for heating the hydrogen and use the recovered heat for steam generation. Therefore, part or all of the heat required for steam generation can be met by the excess heat generated by the solid oxide electrolysis cell. This reduces or eliminates the need for a separate device (e.g., an electric boiler) that supplies heat for steam generation. This allows the device to be downsized or eliminated, thereby reducing the equipment and operating costs of the hydrogen production system.

[0052] Furthermore, since the generated hydrogen is cooled in the second heat exchange section, the water vapor contained in the hydrogen can be condensed, which allows the hydrogen and water vapor to be separated, improving the quality of the generated hydrogen.

[0053] A hydrogen production system according to a third aspect of the present disclosure is the hydrogen production system according to the first or second aspect, wherein the water vapor generation unit (20) generates water vapor by heating feedwater using only heat generated in the solid oxide electrolysis cell (10).

[0054] In the above configuration, the steam generator generates steam by heating the feedwater using only the heat generated in the solid oxide electrolysis cell. That is, all of the latent heat and sensible heat required to generate steam from the feedwater to be supplied to the solid oxide electrolysis cell can be provided by the surplus heat generated by the solid oxide electrolysis cell. This eliminates the need for heat supplied from a separate device (e.g., an electric boiler) that supplies heat for steam generation. This elimination of the device further reduces the equipment costs and operating costs of the hydrogen production system.

[0055] A hydrogen production system according to a fourth aspect of the present disclosure is the hydrogen production system of the first or second aspect, further comprising a compression device (50) that compresses an oxidizing gas to be supplied to the solid oxide electrolysis cell (10), and the steam generation unit (20) has a third heat exchange unit (23) that exchanges heat between the oxidizing gas compressed by the compression device and feedwater.

[0056] In the above configuration, the steam generating unit has a third heat exchange unit that exchanges heat between the oxidizing gas compressed by the compressor and the feedwater. This allows steam to be generated using the heat generated by compression in the compressor. This further improves the energy efficiency of the entire hydrogen production system. In addition, the amount of hydrogen produced can be further increased.

[0057] A hydrogen production method according to a first aspect of the present disclosure is a method for producing hydrogen in a hydrogen production system (1), the hydrogen production system (1) including: a solid oxide electrolysis cell (10) that receives an oxidizing gas and water vapor and generates hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit (20) that heats feedwater to generate water vapor to be supplied to the solid oxide electrolysis cell (10); and a power supply device (40) that supplies power to the solid oxide electrolysis cell (10) so that the solid oxide electrolysis cell (10) operates at an operating point above a thermal neutral point. The hydrogen production system (1) includes a hydrogen production step of electrolyzing supplied steam in a solid oxide electrolysis cell (10) to produce hydrogen; a steam production step of heating feedwater to produce steam to be supplied to the solid oxide electrolysis cell (10); and a power supply step of supplying power to the solid oxide electrolysis cell (10) so that the solid oxide electrolysis cell (10) operates at an operating point above a thermal neutral point, wherein the steam production step heats the feedwater using heat generated in the solid oxide electrolysis cell (10) to produce steam without using heat supplied from outside the hydrogen production system (1). [Explanation of symbols]

[0058] 1: Hydrogen production system 10: SOEC (Solid Oxide Electrolysis Cell) 12: Steam supply header 13: Produced hydrogen discharge header 14: Oxidizing gas supply header 15: Oxidizing gas discharge header 16: Housing 20: Steam generation unit 21: 1st heat exchange section 22:Second heat exchange section 23:Third heat exchange section 30: Water supply device 40: Power supply 50: Compression device 51: Compressor 52: Turbine 53: Electric motor 60: Water supply pump 61: Motor 101: Cell stack 103:Base tube 105: Electrolytic cell 107: Interconnector 109: Hydrogen electrode 111: Solid electrolyte membrane 113: Oxygen electrode 115: Lead film L10: First steam supply line L10a: Branch line L11: Second steam supply line L20: Oxidizing gas supply line L21: Oxidizing gas exhaust line L30: Hydrogen discharge line L31: Hydrogen supply line A1: Oxidizing gas A2: Mixed gas H: Hydrogen S1: Water vapor S2: Mixed gas W: Water supply

Claims

1. A hydrogen production system for producing hydrogen, A solid oxide electrolytic cell is supplied with an oxidizing gas and water vapor, and hydrogen is produced by electrolyzing the supplied water vapor. A steam generation unit that generates steam to be supplied to the solid oxide type electrolytic cell by heating the water supply, The system includes a power supply device that supplies power to the solid oxide electrolytic cell so that the solid oxide electrolytic cell operates at an operating point above its thermal neutral point, The steam generation unit includes a first heat exchange unit that exchanges heat between the oxidizing gas discharged from the solid oxide electrolytic cell and feedwater, and a second heat exchange unit that exchanges heat between the hydrogen produced in the solid oxide electrolytic cell and feedwater. The steam generation unit is a hydrogen production system that heats feedwater using the heat generated in the solid oxide electrolytic cell and generates steam without using heat supplied from outside the hydrogen production system.

2. The hydrogen production system according to claim 1, wherein the steam generation unit generates steam by heating the feedwater solely by the heat generated in the solid oxide electrolytic cell.

3. The system includes a compressor for compressing the oxidizing gas supplied to the solid oxide electrolytic cell, The hydrogen production system according to claim 1, wherein the steam generation unit has a third heat exchange unit that exchanges heat between the oxidizing gas compressed by the compressor and feedwater.

4. A method for producing hydrogen in a hydrogen production system, The aforementioned hydrogen production system A solid oxide electrolytic cell is supplied with an oxidizing gas and water vapor, and hydrogen is produced by electrolyzing the supplied water vapor. A steam generation unit that generates steam to be supplied to the solid oxide type electrolytic cell by heating the water supply, The system includes a power supply device that supplies power to the solid oxide electrolytic cell so that the solid oxide electrolytic cell operates at an operating point above its thermal neutral point, The steam generation unit includes a first heat exchange unit that exchanges heat between the oxidizing gas discharged from the solid oxide electrolytic cell and feedwater, and a second heat exchange unit that exchanges heat between the hydrogen produced in the solid oxide electrolytic cell and feedwater. In the aforementioned solid oxide type electrolytic cell, a hydrogen generation step is performed to generate hydrogen by electrolyzing supplied water vapor, A steam generation step that generates steam to be supplied to the solid oxide type electrolytic cell by heating the water supply, The system includes a power supply step of supplying power to the solid oxide electrolytic cell so that the solid oxide electrolytic cell operates at an operating point above its thermal neutral point, The steam generation step is a hydrogen production method that uses the heat generated in the solid oxide electrolytic cell to heat feedwater and generates steam without using heat supplied from outside the hydrogen production system.

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