Hydrogen production system and hydrogen production method

Abstract

The purpose of the present invention is to improve the energy efficiency of a hydrogen production system as a whole. A hydrogen production system (1) produces hydrogen. The hydrogen production system (1) is provided with: an SOEC (10) that is supplied with an oxidizing gas and steam and generates hydrogen by electrolyzing the supplied steam; a steam generation unit (20) that generates the steam supplied to the SOEC (10) by heating feed water; and a power supply device (40) that supplies power to the SOEC (10) so that the SOEC (10) operates at an operation point exceeding a thermal neutral point. The steam generation unit (20) uses heat generated in the SOEC (10) to heat the feed water, and generates the steam without using heat supplied from outside of the hydrogen production system (1).

Description

DescriptionTitle of Invention: HYDROGEN PRODUCTION SYSTEM AND HYDROGEN PRODUCTION METHOD Technical Field

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

[0002] Electrolysis cells for producing hydrogen and oxygen by electrochemically decomposing water are hydrogen production methods not accompanied by discharge of carbon dioxide and have excellent environmental characteristics. Among these, in a solid oxide electrolysis cell (SOEC), ceramics such as yttria-stabilized zirconia is used as an electrolyte and high-temperature steam is used as a feedstock, and thus the SOEC can produce hydrogen with higher efficiency than the other electrolysis cells. Further, co-electrolysis is also possible in which carbon dioxide (CO2) is used as a feedstock for the purpose of decarbonization and electrolytic hydrogen is used as a reducing agent to directly produce carbon monoxide (CO).

[0003] As an electrolytic system including the SOEC, for example, an electrolytic system described in Patent Document 1 is known. Patent Document 1 describes a system including 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 resistive heating element, or an inductive heating element.Citation ListPatent Literature

[0004] Patent Document 1: JP 2022-180316 A Summary of InventionTechnical Problem

[0005] In order to produce hydrogen in an SOEC, steam is required. Therefore, it is necessary to generate steam from feed water and supply the steam to the SOEC, except for a case where steam from an outside of a system (for example, a steam feed line of a factory) is supplied to the SOEC.As a method for generating steam, for example, as in Patent Document 1, a method is also conceivable in which a device in which power such as an AC or DC resistive heating element is used is used. However, in such a method, there is a possibility that power consumption of the entire system increases due to the use of power, and energy efficiency of the entire system decreases.

[0006] The present disclosure has been made in view of such circumstances, and an object thereof is to provide a hydrogen production system and a hydrogen production method that can improve energy efficiency of the entire hydrogen production system. Solution to Problem

[0007] In order to solve the above-described problems, the hydrogen production system and the hydrogen production method of the present disclosure employ the following means.A hydrogen production system according to an aspect of the present disclosure is a hydrogen production system for producing hydrogen that includes a solid oxide electrolysis cell supplied with an oxidizing gas and steam and configured to electrolyze the supplied steam to generate hydrogen, a steam generation unit configured to generate steam to be supplied to the solid oxide electrolysis cell by heating feed water, and a power supply unit configured to supply power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell is operated at an operating point exceeding a thermal neutral point in which the steam generation unit heats the feed water by using heat generated in the solid oxide electrolysis cell, and generates steam without using heat to be supplied from an outside of the hydrogen production system.

[0008] A hydrogen production method according to an aspect of the present disclosure is a method for producing hydrogen in a hydrogen production system, the hydrogen production system including a solid oxide electrolysis cell to which an oxidizing gas and steam are supplied and that electrolyzes the supplied steam to generate hydrogen, a steam generation unit that generates steam to be supplied to the solid oxide electrolysis cell by heating feed water, and a power supply unit that supplies power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell is operated at an operating point exceeding a thermal neutral point, the hydrogen production method including a hydrogen generation step of generating hydrogen by electrolyzing the supplied steam in the solid oxide electrolysis cell, a steam generation step of generating steam to be supplied to the solid oxide electrolysis cell by heating the feed water, and a power supply step of supplying power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point in which the steam generation step heats the feed water by using heat generated in the solid oxide electrolysis cell, and generates steam without using heat to be supplied from an outside of the hydrogen production system. Advantageous Effects of Invention

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

[0010] FIG. 1 is a schematic configuration diagram illustrating a hydrogen production system according to an embodiment of the present disclosure.FIG. 2 is a diagram illustrating an aspect of a cell stack according to the embodiment of the present disclosure. Description of Embodiments

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

[0012] As illustrated in FIG. 1, a hydrogen production system 1 according to the present 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 feed water to the steam generation unit 20, a power supply unit 40 that supplies power to the SOEC 10, and a compression device 50 that compresses air to be supplied to the SOEC 10.

[0013] The SOEC 10 is supplied with a high-temperature and high-pressure oxidizing gas (in the present embodiment, air as an example) and high-temperature and high-pressure steam. The SOEC 10 electrolyzes the steam using high-temperature solid electrolyte to generate hydrogen.

[0014] The SOEC 10 includes a plurality of cell stacks 101, a steam supply header 12, a hydrogen exhaust header 13, an oxidizing gas supply header 14, an oxidizing gas exhaust header 15, and a housing 16 provided with the plurality of cell stacks 101 inside thereof.

[0015] Upstream ends of the plurality of cell stacks 101 are connected to the steam supply header 12. Further, downstream ends of the plurality of cell stacks 101 are connected to the hydrogen exhaust header 13. Further, the oxidizing gas supply header 14 and the oxidizing gas exhaust header 15 communicate with a space (reaction chamber) formed inside the housing 16.

[0016] Next, the cell stack 101 will be described with reference to FIG. 2.Hereinafter, as an example according to the present embodiment, a tubular cell stack in which a substrate tube is used will be described. When the substrate tube is not used, for example, a fuel electrode may be formed thick to serve also as the substrate tube, and the present embodiment is not limited to the use of the substrate tube. In addition, although the substrate tube in the present embodiment is described as having a tubular shape, the substrate tube only needs to have a cylindrical shape, and a cross section is not necessarily limited to a circular shape, and may have, for example, an elliptical shape. A cell stack such as a flat tubular cell stack in which a circumferential side surface of a tube is vertically crushed may also be used. Here, FIG. 2 illustrates an aspect of the cell stack according to the embodiment. The cell stack 101 includes, as an example, a substrate tube 103 having a tubular shape, a plurality of electrolysis cells 105 formed at an outside surface of the substrate tube 103, and an interconnector 107 formed between the electrolysis cells 105 adjacent to each other. The electrolysis cell 105 is formed by stacking a cathode 109, an electrolyte 111, and an anode 113. Additionally, the cell stack 101 includes a lead film 115 electrically connected via the interconnector 107 to the anode 113 of the electrolysis cell 105 formed at one outermost end in an axial direction of the substrate tube 103 among the plurality of electrolysis cells 105 formed at the outside surface of the substrate tube 103, and includes the lead film 115 electrically connected to the cathode 109 of the electrolysis cell 105 formed at another outermost end.Although a gas supplied to and discharged from the cathode 109 often contains hydrogen in addition to steam used for electrolysis, in the following description, a feed gas containing hydrogen is referred to as "supply steam" and a hydrogen gas containing the steam discharged from the cathode 109 is referred to as "generated hydrogen" for the sake of avoiding confusion.

[0017] The substrate tube 103 is made of a porous material and includes, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ + NiO), Y2O3-stabilized ZrO2 (YSZ), MgAl2O4, or the like as a main component. The substrate tube 103 supports the electrolysis cell 105, the interconnector 107, and the lead film 115, and diffuses supply steam supplied to an inside surface of the substrate tube 103 to the cathode 109 formed at the outside surface of the substrate tube 103 through pores of the substrate tube 103.

[0018] The cathode 109 is made of an oxide of a composite material of Ni and a zirconia-based electrolyte material, and for example, Ni / YSZ is used. A thickness of the cathode 109 is 50 μm to 250 μm, and the cathode 109 may be formed by screen printing a slurry.As the electrolyte 111, YSZ is mainly used which has gas tightness, and high oxygen ion conductivity at high temperatures. The electrolyte 111 moves oxygen ions (O2-) generated at the cathode 109 to the anode 113. A thickness of the electrolyte 111 located on a surface of the cathode 109 is 5 μm to 100 μm, and the electrolyte 111 may be formed by screen printing a slurry.The anode 113 is made of, for example, LaSrMnO3-based oxides or LaCoO3-based oxides, and the anode 113 is formed into a slurry and applied by screen-printing or using a disperser. The anode 113 may have a two-layer structure. In this case, an anode layer (anode intermediate layer) on the electrolyte 111 side is made of a material that exhibits high ion conductivity and is excellent in catalytic activity. The anode intermediate layer may be made of ceria doped with Sm exhibiting high ion conductivity, and an anode layer (anode conductive layer) on the anode intermediate layer may be made of perovskite oxides such as Sr and Ca doped LaMnO3.

[0019] By applying a negative voltage to the cathode 109 and a positive voltage to the anode 113, the steam contained in the supply steam receives electrons and is electrolyzed at the cathode 109, thereby generating hydrogen molecules and oxygen ions (O2-) (see the following reaction formula (1)). The generated hydrogen is taken out to an outside together with the supply steam.On the other hand, the oxygen ions pass through the electrolyte 111 due to a potential difference, move to the anode 113, and release the electrons to become oxygen molecules (see the following reaction formula (2)). The generated oxygen is discharged to the outside together with an oxidizing gas supplied to the anode 113.H2O + 2e- → H2 + O2- (1)2O2- → O2 + 4e- (2)

[0020] The oxidizing gas does not directly participate in an electrolytic reaction, but supplies heat necessary for the electrolytic reaction (endothermic reaction) and discharges excess heat generated by the electrolytic reaction. The gas usually contains about 15% to 30% of oxygen, and typically, air is suitable, but a mixed gas of combustion exhaust gas and air, a mixed gas of oxygen and air, an inert gas such as nitrogen, or the like can be used in addition to air.

[0021] The interconnector 107 is made of, for example, a conductive perovskite-type oxide represented by M1-xLxTiO3 (M is an alkaline earth metal element, and L is a lanthanoid element) such as SrTiO3-based oxide, or lanthanum chromite (LaCrO3), and is formed into a slurry and is screen printed. The interconnector 107 is in the form of a dense film so that the supply steam and the oxidizing gas do not mix. In addition, the interconnector 107 has stable durability and electronic conductivity in both an oxidizing atmosphere and a reducing atmosphere. The interconnector 107 electrically connects the anode 113 of one electrolysis cell 105 and the cathode 109 of another electrolysis cell 105 in the adjacent electrolysis cells 105, and connects the adjacent electrolysis 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 thus is made of a composite material of Ni and a zirconia-based electrolyte material, such as Ni / YSZ, or M1-xLxTiO3 such as SrTiO3-based material (M is an alkaline earth metal element and L is a lanthanoid element). The lead film 115 applies DC power necessary for the electrolytic reaction to the plurality of electrolysis cells 105 connected in series through the interconnectors 107 from an end portion of the cell stack 101. Further, a surface on the oxidizing gas side may be protected with an airtight oxidation-resistant material so that a metal material such as Ni is not oxidized.

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

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

[0025] The first heat exchanging unit 21, the second heat exchanging unit 22, and the third heat exchanging unit 23 are provided at an intermediate position of a first steam supply line L10. The first heat exchanging unit 21, the second heat exchanging unit 22, and the third heat exchanging unit 23 are provided in parallel. Specifically, the first steam supply line L10 branches into three diverging lines L10a at the intermediate position, and the diverging lines L10a are provided with one first heat exchanging unit 21, one second heat exchanging unit 22, and one third heat exchanging unit 23, respectively. The diverging lines L10a are merged on a downstream side of the respective heat exchanging units.

[0026] The first heat exchanging unit 21 heats the feed water to generate steam by performing heat exchange between the feed water flowing through the first steam supply line L10 (specifically, the diverging line L10a) and the oxidizing gas flowing through an oxidizing gas exhaust line L21.The second heat exchanging unit 22 heats the feed water to generate steam by performing heat exchange between the feed water flowing through the first steam supply line L10 (specifically, the diverging line L10a) and hydrogen flowing through a hydrogen discharge line L30.The third heat exchanging unit 23 heats the feed water to generate steam by performing heat exchange between the feed water flowing through the first steam supply line L10 (specifically, the diverging line L10a) and the oxidizing gas flowing through an oxidizing gas supply line L20.

[0027] The water supply device 30 is a device that stores and supplies water (the feed water). The feed water is heated by the steam generation unit 20 to become steam. An upstream end of the first steam supply line L10 is connected to the water supply device 30.

[0028] The power supply unit 40 is a device that supplies power to be used for steam electrolysis to the SOEC 10. The power supply unit 40 supplies power to the SOEC 10 so that the SOEC 10 is operated at an operating point exceeding a thermal neutral point. The thermal neutral point means an operating point of the SOEC 10 at which Joule heat generated in the SOEC 10 and an amount of heat absorbed by an endothermic reaction accompanying the electrolysis of the SOEC 10 become equal. The power supply unit 40 of the present embodiment supplies more power than the power supplied when the SOEC 10 is operated at the thermal neutral point in order for the SOEC 10 to be operated at an operating point exceeding the thermal neutral point. A method of increasing the power is not particularly limited. For example, a current flowing to the SOEC 10 may be increased, or a 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. Examples of the oxidizing gas include 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 coupled to each other by the same rotor shaft, and the compressor 51 is configured to be driven by rotation of the turbine 52. The electric motor 53 is configured to drive the compressor 51 or assist the driving of the compressor 51 when output of the turbine 52 is low (for example, when the hydrogen production system 1 is started).

[0030] Next, a fluid flow in the hydrogen production system 1 according to the present embodiment will be described.First, a flow of the feed water and the steam supplied to the SOEC 10 will be described. Note that in the following description, a fluid flowing through an inside of the first steam supply line L10 is the feed water on an upstream side of the steam generation unit 20, and is the steam on a downstream side of the steam generation unit 20, and thus, a reference sign "W" is given to the feed water and the same reference sign "S1" is given to the steam.

[0031] Feed water 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 feed water W introduced into the first steam supply line L10 is supplied to the steam generation unit 20 by a driving force of the feedwater pump 60.

[0032] The feed water W supplied to the steam generation unit 20 is heat exchanged with a mixed gas A2 flowing through the oxidizing gas exhaust line L21 in the first heat exchanging unit 21, and is evaporated to become steam S1 (a steam generation step). In addition, the feed water W is heat exchanged with hydrogen H flowing through the hydrogen discharge line L30 in the second heat exchanging unit 22, and thus is evaporated to become the steam S1. In addition, the feed water W is heat exchanged with an oxidizing gas A1 flowing through the oxidizing gas supply line L20 in the third heat exchanging unit 23, and is evaporated to become the steam S1. Note that in consideration of heat loss in the first steam supply line L10 and a second steam supply line L11, the steam S1 at an outlet of each heat exchanging unit may be brought into a superheated state.

[0033] The steam S1 generated in each heat exchanging unit is merged on a downstream side of the steam generation unit 20. The merged steam S1 is introduced into the second steam supply line L11 via the first steam supply line L10. At this time, the hydrogen H supplied via a hydrogen supply line L31 is added. A mixed gas S2 of the steam S1 and the hydrogen H is supplied to the SOEC 10 (specifically, the steam supply header 12) via the second steam supply line L11.The SOEC 10 is supplied with power from the power supply unit 40 (a power supply step). The SOEC 10 is operated at an operating point exceeding the thermal neutral point.

[0034] The high-temperature and 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 exchanging unit 23 of the steam generation unit 20. The oxidizing gas A1 supplied to the third heat exchanging unit 23 is cooled by being heat exchanged with the feed water W flowing through the first steam supply line L10. The oxidizing gas A1 cooled in the third heat exchanging unit 23 is supplied to the SOEC 10 (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 in an internal space of the housing 16 and is introduced into the oxidizing gas exhaust header 15. When the oxidizing gas flows through the internal space of the housing 16, oxygen is added to the oxidizing gas. The mixed gas A2 of the oxidizing gas A1 and oxygen introduced into the oxidizing gas exhaust header 15 is discharged to the oxidizing gas exhaust line L21. The mixed gas A2 introduced into the oxidizing gas exhaust line L21 is supplied to the first heat exchanging unit 21 of the steam generation unit 20. The mixed gas A2 supplied to the first heat exchanging unit 21 is cooled by being heat exchanged with the feed water W flowing through the first steam supply line L10. The mixed gas A2 cooled in the first heat exchanging unit 21 is supplied to the turbine 52 of the compression device 50 via the oxidizing gas exhaust line L21. The mixed gas A2 supplied to the turbine 52 rotationally drives the turbine 52.

[0036] On the other hand, the mixed gas S2 of the steam S1 and the hydrogen H supplied to the steam supply header 12 flows through an inside of each cell stack 101. At this time, the steam S1 contained in the mixed gas S2 is electrolyzed to generate hydrogen (a hydrogen generation step). The generated high-temperature hydrogen H (including steam) is introduced into the hydrogen exhaust header 13. The hydrogen H introduced into the hydrogen exhaust header 13 is discharged to the hydrogen discharge line L30. The hydrogen H introduced into the hydrogen discharge line L30 is supplied to the second heat exchanging unit 22 of the steam generation unit 20. The hydrogen H supplied to the second heat exchanging unit 22 is cooled by being heat exchanged with the feed water W flowing through the first steam supply line L10. The steam contained in the cooled hydrogen H is condensed, and thus the steam is separated. The hydrogen with the steam separated (strictly speaking, containing steam corresponding to a saturated steam pressure) is supplied to a hydrogen storage facility (not illustrated) via the hydrogen discharge line L30.

[0037] Moreover, the hydrogen supply line L31 is connected to the second heat exchanging unit 22. The hydrogen supply line L31 guides a part (containing steam) of the hydrogen H flowing through the hydrogen discharge line L30 to the second steam supply line L11. Therefore, a part of the hydrogen H introduced into the second heat exchanging unit 22 is introduced into the second steam 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 a driving force of the booster 62.

[0038] According to the present embodiment, the following operational effects are obtained.In the present embodiment, the steam generation unit 20 heats feed water by using heat that is generated in the hydrogen production system 1 (heat that is generated in the SOEC 10 and the compression device 50), thereby generating steam that is to be supplied to the SOEC 10. Accordingly, steam can be generated by using waste heat of the SOEC 10. Therefore, energy efficiency of the entire hydrogen production system 1 can be improved as compared with a case where the waste heat of the SOEC 10 is not used, or a case where heat supplied from a separately provided device (for example, an electric boiler or the like) that supplies heat for generating steam to the steam generation unit 20 is used. Further, in the present embodiment, the SOEC 10 is operated at an operating point exceeding the thermal neutral point, so an amount of hydrogen generated can be increased. In this way, in the present embodiment, it is possible to improve the energy efficiency of the entire system while increasing hydrogen generation volume.

[0039] Further, since the cell stack 101 of the present embodiment has a tubular shape, the cell stack 101 can be used at a higher temperature as compared with a cell stack having another shape (for example, a flat plate shape) in terms of structure. Therefore, the SOEC 10 can be operated at an operating point exceeding the thermal neutral point in a suitable manner.

[0040] In addition, Joule heat is generated in the SOEC 10 as current flows. On the other hand, electrolysis of steam in the SOEC 10 is an endothermic reaction. Therefore, in the SOEC 10, the generated Joule heat is absorbed by the endothermic reaction. Therefore, in the SOEC 10, the Joule heat is effectively used in the electrolysis until the Joule heat generated exceeds an amount of heat absorbed in the endothermic reaction. Note that an operating point at which the amount of heat absorbed by the endothermic reaction is equal to the Joule heat generated is referred to as the "thermal neutral point". When the SOEC 10 is operated at an operating point exceeding the thermal neutral point, the generated Joule heat cannot be fully absorbed by the endothermic reaction, and thus, an excess amount of Joule heat (hereinafter referred to as "excess heat generation") is generated. Therefore, in the related art, in order to suppress energy loss due to the excess heat generation, it was common to operate the SOEC 10 to achieve the thermal neutral point.On the other hand, in the present embodiment, the power supply unit 40 that supplies power to the SOEC 10 is provided so that the SOEC 10 is operated at an operating point exceeding the thermal neutral point. That is, the SOEC 10 is operated at an operating point exceeding the thermal neutral point. Therefore, the excess heat generation occurs in the SOEC 10. In the present embodiment, the steam generation unit 20 heats the feed water by using the heat generated in the SOEC 10, and therefore, the feed water can be heated by effectively using this excess heat generation. Therefore, a part or all of an amount of heat required for generating the steam can be covered by the excess heat generation of the SOEC 10. Therefore, an amount of heat to be supplied to the steam generation unit 20 from a device (for example, an electric boiler or the like) that is separately provided outside the hydrogen production system 1 and supplies heat for steam generation can be decreased or made unnecessary. Therefore, the device can be downsized or made unnecessary, and thus equipment costs and operating costs of the hydrogen production system 1 can be decreased.

[0041] As described above, in the present embodiment, the SOEC 10 is operated at an operating point exceeding the thermal neutral point, and thus the excess amount of Joule heat is generated in the SOEC 10. The excess amount of Joule heat is consumed in the form of heating of the fluid (for example, the oxidizing gas, the steam, the hydrogen, or the like) flowing through the SOEC 10.In the present embodiment, the steam generation unit 20 includes the first heat exchanging unit 21 that performs heat exchange between the oxidizing gas discharged from the SOEC 10 and the feed water, and the second heat exchanging unit 22 that performs heat exchange between the hydrogen generated in the SOEC 10 and the feed water. Thus, in the first heat exchanging unit 21, the excess amount of Joule heat consumed for heating the oxidizing gas can be recovered, to be used for generating steam. Further, similarly, in the second heat exchanging unit 22, the excess amount of Joule heat consumed for heating hydrogen can be recovered, to be used for generating steam. Therefore, a part or all of the amount of heat required for generating the steam can be covered by the excess heat generation of the SOEC 10. Therefore, the amount of heat to be supplied from the separately provided device (for example, an electric boiler or the like) that supplies an amount of heat for generating steam can be reduced or made unnecessary. Therefore, the device can be downsized or made unnecessary, and thus the equipment costs and the operating costs of the hydrogen production system 1 can be decreased.

[0042] In the present embodiment, the steam generation unit 20 includes the third heat exchanging unit 23 that performs heat exchange between the oxidizing gas compressed by the compression device 50 and the feed water. Accordingly, steam can be generated by using heat generated by the compression in the compression device 50. Therefore, the energy efficiency of the entire hydrogen production system 1 can be further improved. In addition, the hydrogen generation volume can be further increased.

[0043] In this way, in the present embodiment, all of latent heat and sensible heat required when steam to be supplied to the SOEC 10 from the feed water is generated is covered by the heat generated in the hydrogen production system 1 (the heat generated in the SOEC 10 and the compression device 50). Specifically, the feed water is heated only by the steam generation unit 20 (including heat by the heat exchange in the first heat exchanging unit 21 and the second heat exchanging unit 22, and heat by the heat exchange in the third heat exchanging unit 23 as necessary) without using heat from the outside of the hydrogen production system 1, thereby generating steam. Therefore, heat to be supplied from the separately provided device (for example, an electric boiler or the like) that supplies heat for generating steam can be made unnecessary. Therefore, the device can be made unnecessary, and thus the equipment costs and the operating costs of the hydrogen production system 1 can be further decreased.

[0044] Note that the present disclosure is not limited to the above-described embodiments and can be modified as required without departing from the gist of the disclosure.For example, in the above-described embodiment, the example in which the first heat exchanging unit 21, the second heat exchanging unit 22, and the third heat exchanging unit 23 are provided in parallel has been described, but the present disclosure is not limited thereto. For example, the first heat exchanging unit 21, the second heat exchanging unit 22, and the third heat exchanging unit 23 may be provided in series. That is, the steam and / or the feed water that has been subjected to heat exchange in the first heat exchanging unit 21 may be introduced into the second heat exchanging unit 22, and the steam and / or the feed water that has been subjected to the heat exchange in the second heat exchanging unit 22 may be introduced into the third heat exchanging unit 23. Note that when the respective heat exchanging units are provided in series, the order of providing the respective heat exchanging units is not limited to the above-described order.Further, some of the first heat exchanging unit 21, the second heat exchanging unit 22, and the third heat exchanging unit 23 may be provided in parallel. That is, two of the three heat exchanging units may be provided in parallel, and the remaining one may be provided on an upstream side or a downstream side of the heat exchanging units provided in parallel.

[0045] Further, as for each of the first heat exchanging unit 21, the second heat exchanging unit 22, and the third heat exchanging unit 23, a structure divided into a preheating unit, a steam generation unit, and a superheating unit may be adopted.

[0046] Furthermore, in the above-described embodiment, the example in which the steam generation unit 20 includes the third heat exchanging unit 23 has been described, but the present disclosure is not limited thereto. For example, the third heat exchanging unit 23 may be omitted. That is, in the present modification example, the steam generation unit 20 does not use the heat generated by the compression device 50. Therefore, the steam generation unit 20 generates steam by heating the feed water only by the heat generated in the SOEC 10. That is, all of the latent heat and sensible heat required when steam to be supplied from the feed water to the SOEC 10 is generated can be covered by the excess heat generation of the SOEC 10. Therefore, heat to be supplied from the separately provided device (for example, an electric boiler or the like) that supplies heat for generating steam can be made unnecessary. Therefore, the device can be made unnecessary, and thus the equipment costs and the operating costs of the hydrogen production system 1 can be further decreased.

[0047] The hydrogen production system and the hydrogen production method, which have been described in the embodiment described above, are understood as follows, for example.A hydrogen production system according a first aspect of the present disclosure is a hydrogen production system (1) for producing hydrogen that includes a solid oxide electrolysis cell (10) supplied with an oxidizing gas and steam and configured to electrolyze the supplied steam to generate hydrogen, a steam generation unit (20) configured to generate steam to be supplied to the solid oxide electrolysis cell (10) by heating feed water, and a power supply unit (40) configured to supply power to the solid oxide electrolysis cell (10) so that the solid oxide electrolysis cell (10) is operated at an operating point exceeding a thermal neutral point in which the steam generation unit (20) heats the feed water by using heat generated in the solid oxide electrolysis cell (10), and generates steam without using heat to be supplied from an outside of the hydrogen production system (1).

[0048] In the above-described configuration, a steam generation unit heats the feed water by using the heat generated in the solid oxide electrolysis cell, and generates the steam to be supplied to the solid oxide electrolysis cell without using heat to be supplied from the outside of the hydrogen production system. Accordingly, steam can be generated by using waste heat of the solid oxide electrolysis cell. Therefore, energy efficiency of the entire hydrogen production system can be improved as compared with a case where the waste heat of the solid oxide electrolysis cell is not used. In addition, in the above-described configuration, the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point, and thus an amount of hydrogen generated can be increased. In this way, in the above-described configuration, it is possible to improve the energy efficiency of the entire system while increasing hydrogen generation volume.

[0049] In addition, in the solid oxide electrolysis cell, Joule heat is generated as current flows. On the other hand, the electrolysis of steam in the solid oxide electrolysis cell is an endothermic reaction. Therefore, in the solid oxide electrolysis cell, the generated Joule heat is absorbed by the endothermic reaction. Therefore, in the solid oxide electrolysis cell, the Joule heat is effectively used in the electrolysis until the Joule heat generated exceeds an amount of heat absorbed in the endothermic reaction. Note that an operating point at which the amount of heat absorbed by the endothermic reaction is equal to the Joule heat generated is referred to as a "thermal neutral point". When the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point, the generated Joule heat cannot be fully absorbed by the endothermic reaction, and thus, an excess amount of Joule heat (hereinafter referred to as "excess heat generation") is generated. Therefore, in the related art, in order to suppress energy loss due to the excess heat generation, it was common to operate the solid oxide electrolysis cell to achieve the thermal neutral point.On the other hand, in the above-described configuration, the power supply unit that supplies power to the solid oxide electrolysis cell is provided so that the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point. That is, the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point. Therefore, the excess heat generation occurs in the solid oxide electrolysis cell. In the above-described configuration, the steam generator heats the feed water by using the heat generated in the solid oxide electrolysis cell, and therefore the feed water can be heated by using this excess heat generation. Therefore, a part or all of an amount of heat required for generating steam can be covered by the excess heat generation of the solid oxide electrolysis cell. Therefore, an amount of heat to be supplied from a separately provided device (for example, an electric boiler or the like) that supplies an amount of heat for generating steam to the steam generation unit can be decreased or made unnecessary. Therefore, the device can be downsized or made unnecessary, and thus equipment costs and operating costs of the hydrogen production system can be reduced.In particular, in the above-described configuration, since steam is generated without using heat to be supplied from the outside of the hydrogen production system, the entire amount of heat required for generating steam can be covered by the excess heat generation of the solid oxide electrolysis cell. Therefore, the amount of heat to be supplied from the separately provided device (for example, an electric boiler or the like) that supplies the amount of heat for generating steam to the steam generation unit can be made unnecessary. Therefore, the device can be made unnecessary, and thus the equipment costs and the operating costs of the hydrogen production system can be significantly reduced.

[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 exchanging unit (21) configured to perform heat exchange between the oxidizing gas discharged from the solid oxide electrolysis cell (10) and the feed water, and a second heat exchanging unit (22) configured to perform heat exchange between the hydrogen generated in the solid oxide electrolysis cell (10) and the feed water.

[0051] As described above, in the above-described configuration, the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point, and thus, the excess amount of Joule heat is generated in the solid oxide electrolysis cell. The excess amount of Joule heat is consumed in the form of heating of the fluid (for example, the oxidizing gas, the steam, the hydrogen, or the like) flowing through the SOEC.In the above-described configuration, the steam generation unit includes the first heat exchanging unit that performs heat exchange between the oxidizing gas discharged from the solid oxide electrolysis cell and the feed water, and the second heat exchanging unit that performs heat exchange between the hydrogen generated in the solid oxide electrolysis cell and the feed water. Thus, in the first heat exchanging unit, the excess amount of Joule heat consumed for heating the oxidizing gas can be recovered, to be used for generating steam. Further, similarly, in the second heat exchanging unit, the excess amount of Joule heat consumed for heating the hydrogen can be recovered, to be used for generating steam. Therefore, a part or all of the amount of heat required for generating the steam can be covered by the excess heat generation of the solid oxide electrolysis cell. Therefore, the amount of heat to be supplied from the separately provided device (for example, an electric boiler or the like) that supplies the amount of heat for generating steam can be reduced or made unnecessary. Therefore, the device can be downsized or made unnecessary, and thus the equipment costs and the operating costs of the hydrogen production system can be reduced.

[0052] Further, since the generated hydrogen is cooled in the second heat exchanging unit, the steam contained in the hydrogen can be condensed. This makes it possible to separate the hydrogen and the steam from each other, and thus to improve quality of the produced hydrogen.

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

[0054] In the above-described configuration, the steam generation unit generates steam by heating the feed water only by the heat generated in the solid oxide electrolysis cell. That is, all of latent heat and sensible heat required when steam to be supplied to the solid oxide electrolysis cell from the feed water is generated can be covered by excess heat generation of the solid oxide electrolysis cell. Therefore, the amount of heat to be supplied from the separately provided device (for example, an electric boiler or the like) that supplies the amount of heat for generating steam can be made unnecessary. Therefore, the device can be made unnecessary, and thus the equipment costs and the operating costs of the hydrogen production system can be further reduced.

[0055] A hydrogen production system according to a fourth aspect of the present disclosure, in the first or second aspect, includes a compression device (50) configured to compress the oxidizing gas to be supplied to the solid oxide electrolysis cell (10), in which the steam generation unit (20) includes a third heat exchanging unit (23) that performs heat exchange between the oxidizing gas compressed by the compression device and the feed water.

[0056] In the above-described configuration, the steam generation unit includes the third heat exchanging unit that performs the heat exchange between the oxidizing gas compressed by the compression device and the feed water. Accordingly, steam can be generated by using heat generated by the compression in the compression device. Therefore, the energy efficiency of the entire hydrogen production system can be further improved. In addition, the hydrogen generation volume 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) to which an oxidizing gas and steam are supplied and that electrolyzes the supplied steam to generate hydrogen, a steam generation unit(20) that generates steam to be supplied to the solid oxide electrolysis cell (10) by heating feed water, a power supply unit (40) that supplies power to the solid oxide electrolysis cell (10) so that the solid oxide electrolysis cell (10) is operated at an operating point exceeding a thermal neutral point, the hydrogen production method including a hydrogen generation step of generating hydrogen by electrolyzing the supplied steam in the solid oxide electrolysis cell (10), a steam generation step of generating steam to be supplied to the solid oxide electrolysis cell (10) by heating the feed water, and a power supply step of supplying power to the solid oxide electrolysis cell (10) so that the solid oxide electrolysis cell (10) is operated at an operating point exceeding the thermal neutral point in which the steam generation step heats the feed water by using heat generated in the solid oxide electrolysis cell (10), and generates steam without using heat to be supplied from an outside of the hydrogen production system (1). Reference Signs List

[0058] 1 Hydrogen production system10 Solid oxide electrolysis cell (SOEC)12 Steam supply header13 Hydrogen exhaust header14 Oxidizing gas supply header15 Oxidizing gas exhaust header16 Housing20 Steam generation unit21 First heat exchanging unit22 Second heat exchanging unit23 Third heat exchanging unit30 Water supply device40 Power supply unit50 Compression device51 Compressor52 Turbine53 Electric motor60 Feedwater pump61 Motor101 Cell stack103 Substrate tube105 Electrolysis cell107 Interconnector109 Cathode111 Electrolyte113 Anode115 Lead filmL10 First steam supply lineL10a Diverging lineL11 Second steam supply lineL20 Oxidizing gas supply lineL21 Oxidizing gas exhaust lineL30 Hydrogen discharge lineL31 Hydrogen supply lineA1 Oxidizing gasA2 Mixed gasH HydrogenS1 SteamS2 Mixed gasW Feed water  

Claims

 

1. A hydrogen production system for producing hydrogen, comprising:a solid oxide electrolysis cell supplied with an oxidizing gas and steam and configured to electrolyze the supplied steam to generate hydrogen;a steam generation unit configured to generate steam to be supplied to the solid oxide electrolysis cell by heating feed water; anda power supply unit configured to supply power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell is operated at an operating point exceeding a thermal neutral point, whereinthe steam generation unit heats the feed water by using heat generated in the solid oxide electrolysis cell, and generates steam without using heat to be supplied from an outside of the hydrogen production system. 

2. The hydrogen production system according to claim 1, whereinthe steam generation unit includes a first heat exchanging unit that performs heat exchange between the oxidizing gas discharged from the solid oxide electrolysis cell and the feed water, and a second heat exchanging unit that performs heat exchange between the hydrogen generated in the solid oxide electrolysis cell and the feed water. 

3. The hydrogen production system according to claim 1 or 2, whereinthe steam generation unit generates steam by heating the feed water only by heat generated in the solid oxide electrolysis cell. 

4. The hydrogen production system according to claim 1 or 2 comprising a compression device configured to compress the oxidizing gas to be supplied to the solid oxide electrolysis cell, whereinthe steam generation unit includes a third heat exchanging unit that performs heat exchange between the oxidizing gas compressed by the compression device and the feed water. 

5. A hydrogen production method that is a method for producing hydrogen in a hydrogen production system,the hydrogen production system includinga solid oxide electrolysis cell to which an oxidizing gas and steam are supplied and that electrolyzes the supplied steam to generate hydrogen,a steam generation unit that generates steam to be supplied to the solid oxide electrolysis cell by heating feed water, anda power supply unit that supplies power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell is operated at an operating point exceeding a thermal neutral point, the hydrogen production method comprising:a hydrogen generation step of generating hydrogen by electrolyzing the supplied steam in the solid oxide electrolysis cell;a steam generation step of generating steam to be supplied to the solid oxide electrolysis cell by heating the feed water; anda power supply step of supplying power to the solid oxide electrolysis cell so that the solid oxide electrolysis cell is operated at an operating point exceeding the thermal neutral point, whereinthe steam generation step heats the feed water by using heat generated in the solid oxide electrolysis cell, and generates steam without using heat to be supplied from an outside of the hydrogen production system. 

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