Hydrogen production system and hydrogen production method

Abstract

To reduce cost.SOLUTION: The hydrogen production system includes a SOEC10 that generates ammonia and generates hydrogen by electrolyzing supplied water vapor, a water vapor supplying system 90 that guides supplied water to the SOEC10, a condenser 60 to which hydrogen containing ammonia discharged from the SOEC10 is guided and which condenses ammonia by cooling the hydrogen containing ammonia, and a condensed water line L32 that guides the ammonia condensed by the condenser 60 to the water vapor supplying system 90.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] Known examples of electrolysis systems equipped with an SOEC include the electrolysis system described in Patent Document 1. Patent Document 1 discloses a system equipped with an SOEC that produces hydrogen from a gas containing water vapor, and a condenser that condenses the water vapor contained in the gas produced by the SOEC. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-98433 Summary of the Invention [Problem to be solved by the invention]

[0005] A hydrogen generation system equipped with an SOEC that generates hydrogen from such steam requires a steam generator that generates the steam to be supplied to the SOEC. The steam generator, the feedwater supplied to the steam generator, and the facilities through which the steam generated by the steam generator circulate may experience corrosion due to the feedwater. Therefore, one approach to suppress corrosion in the steam generator is to inject a corrosion-suppressing chemical into the feedwater supplied to the steam generator. However, injecting a corrosion-suppressing chemical into the feedwater supplied to the steam generator may increase costs.

[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 reduce costs. [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 includes a solid oxide electrolysis cell that generates ammonia and produces hydrogen by electrolyzing supplied water vapor; a water vapor supply system that introduces water vapor to the solid oxide electrolysis cell; a condenser that receives ammonia-containing hydrogen discharged from the solid oxide electrolysis cell and cools the ammonia-containing hydrogen to condense the ammonia; and a condensed water line that introduces the ammonia condensed in the condenser to the water vapor supply system.

[0008] A hydrogen production method according to one aspect of the present disclosure includes a generation step of generating ammonia in a solid oxide electrolysis cell and producing hydrogen by electrolyzing supplied water vapor; a water vapor introduction step of introducing water vapor to the solid oxide electrolysis cell through a water vapor supply system; a condensation step of condensing ammonia by cooling ammonia-containing hydrogen discharged from the solid oxide electrolysis cell; and an ammonia introduction step of introducing the ammonia condensed in the condensation step to the water vapor supply system. [Effects of the Invention]

[0009] According to the present disclosure, costs can be reduced. [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] 1, a hydrogen production system 1 according to this embodiment includes a solid oxide electrolysis cell (SOEC) 10, a steam generator 20 that generates steam to be supplied to the SOEC 10, a water supply device 30 that supplies water to the steam generator 20, a power supply device 40 that supplies power to the SOEC 10, a compressor 50 that compresses air to be supplied to the SOEC 10, a condenser 60 that separates steam from steam-containing hydrogen generated in the SOEC 10, a nitrogen supplier 70 that supplies nitrogen to the steam to be supplied to the SOEC 10, and a controller 80. The steam generator 20, together with a first steam supply line L10 and a second steam supply line L11 (described later), are included in a steam supply system 90 that supplies steam 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. Below, a cylindrical cell stack using a substrate tube will be described as an example according to this embodiment. When a substrate tube is not used, for example, the fuel electrode may be formed thick and used as the substrate tube, and the use of a substrate tube is not limited. Furthermore, although the substrate tube in this embodiment is described as having a cylindrical shape, the substrate tube may be tubular 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 shape, in which the peripheral side surface of a cylinder is crushed vertically, may also be used.

[0017] 1 shows one embodiment of a cell stack according to the present invention. The cell stack 101 includes, for example, a cylindrical substrate tube 103, a plurality of electrolysis cells 105 formed on the outer peripheral surface of the substrate tube 103, and an interconnector 107 formed between adjacent electrolysis cells 105. Each 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 the interconnector 107 to the oxygen electrode 113 of the electrolysis cell 105 formed at the outer peripheral surface of the substrate tube 103, which is located at the end of the electrolysis cell 105 in the axial direction of the substrate tube 103, and a lead film 115 electrically connected to the hydrogen electrode 109 of the electrolysis cell 105 located at the other end of the electrolysis cell 105.

[0018] The gas supplied to and discharged from the hydrogen electrode 109 often contains hydrogen in addition to the water vapor used in 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."

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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)

[0025] 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.

[0026] 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.

[0027] 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.

[0028] As shown in FIG. 1 , the steam generation unit 20 generates steam to be supplied to the SOEC 10 by heating the feedwater supplied from the water supply device 30. The steam generation unit 20 generates steam by heating the feedwater using heat generated in the SOEC 10. The steam generation unit 20 is provided at a midpoint of the first steam supply line L10. The first steam supply line L10 guides the feedwater stored in the water supply device 30 to the second steam supply line L11. The first steam supply line L10 has a water supply line L10a that is upstream of the steam generation unit 20 and through which the feedwater W flows, and a steam line L10b that is downstream of the steam generation unit 20 and through which the water vapor S1 flows.

[0029] The steam generating 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, and a second heat exchange section 22 that exchanges heat between the hydrogen generated in the SOEC 10 and the feed water.

[0030] The first heat exchange section 21 and the second heat exchange section 22 are provided at a midpoint of the first steam supply line L10. The first heat exchange section 21 and the second heat exchange section 22 are provided in parallel. In detail, the first steam supply line L10 branches into two branch lines at a midpoint, and each branch line is provided with one first heat exchange section 21 and one second heat exchange section 22. The branch lines merge downstream of each heat exchange section.

[0031] The first heat exchanger 21 heats the feedwater flowing through the first steam supply line L10 (more specifically, one of the branch lines) and the oxidizing gas flowing through the oxidizing gas discharge line L21, thereby heating the feedwater and generating steam. The second heat exchanger 22 heats the feedwater flowing through the first steam supply line L10 (more specifically, the other branch line where the first heat exchanger 21 is located) and the hydrogen flowing through the hydrogen discharge line L30, thereby generating steam. The first heat exchanger 21 and the second heat exchanger 22 may be arranged in series or may be configured integrally.

[0032] 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.

[0033] The first steam supply line L10 is provided with, in order from the upstream side, a feedwater flow meter 33, an electrical conductivity meter (electrical conductivity measuring unit) 34, a pH meter (pH measuring unit) 35, and a steam generating unit 20. A chemical liquid injector 36 may be provided between the feedwater flow meter 33 and the electrical conductivity meter 34.

[0034] The feedwater flow meter 33 measures the flow rate of the feedwater W flowing through the first steam supply line L10. The electrical conductivity meter 34 measures the electrical conductivity of the feedwater W flowing through the first steam supply line L10. The pH meter 35 measures the pH of the feedwater W flowing through the first steam supply line L10. The chemical liquid injector 36 injects a chemical liquid (e.g., ammonia) into the feedwater W flowing through the first steam supply line L10 to adjust the pH of the feedwater W.

[0035] The compression device 50 is a device that compresses the oxidizing gas supplied to the SOEC 10. An example of the oxidizing gas is air. In the following description, the oxidizing gas is air. The compression device 50 has a compressor 51, a turbine 52, and an electric motor 53. The compressor 51 and the turbine 52 are connected 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).

[0036] The condenser 60 is provided at a midpoint on the hydrogen discharge line L30. Specifically, the condenser 60 is provided downstream of the point on the hydrogen discharge line L30 where heat exchange takes place in the second heat exchange section 22.

[0037] The condenser 60 cools the hydrogen (specifically, a mixed gas of hydrogen and water vapor) by exchanging heat with a cooling medium (for example, water), thereby condensing the water vapor contained in the hydrogen. The condensed water vapor (hereinafter referred to as "condensed water") accumulates in the lower part of the condenser 60. On the other hand, the hydrogen accumulates in the upper part of the condenser 60. In this way, the condenser 60 separates the hydrogen from the water vapor.

[0038] There are no particular limitations on the manner of heat exchange in the condenser 60. For example, the condenser 60 may exchange heat between the hydrogen containing water vapor and the cooling medium via a heat transfer tube, or may exchange heat by directly contacting the hydrogen containing water vapor with the cooling medium.

[0039] A second hydrogen compressor 61 is provided on the hydrogen discharge line L30 downstream of the condenser 60. The downstream end of the hydrogen discharge line L30 is connected to a hydrogen storage unit 62. The hydrogen storage unit 62 stores the hydrogen (product hydrogen) produced in the hydrogen production system 1.

[0040] The upstream end of a condensed water line L32 is connected to the lower part of the condenser 60. The downstream end of the condensed water line L32 is connected to the first steam supply line L10. Specifically, the downstream end of the condensed water line L32 is connected to the first steam supply line L10 between the feedwater pump 31 and the feedwater flow meter 33. The condensed water line L32 connects the condenser 60 and the first steam supply line L10. The condensed water line L32 guides the condensed water containing ammonia that is condensed in the condenser 60 and stored in the lower part of the condenser 60 to the first steam supply line L10.

[0041] The condensed water line L32 is provided with a condensed water pump 63 that is driven by a driving force from a motor 64. The condensed water introduced into the condensed water line L32 is supplied to the first steam supply line L10 by the driving force of the condensed water pump 63.

[0042] The nitrogen supply device (nitrogen-containing gas supply unit) 70 supplies nitrogen gas to the mixed gas S2 flowing through the second steam supply line L11. That is, the nitrogen gas is supplied to the steam supplied to the SOEC 10. The amount of nitrogen gas supplied by the nitrogen supply device 70 is controlled by the control device 80. The gas supplied from the nitrogen supply device 70 may be any gas containing nitrogen (for example, air).

[0043] The hydrogen production system may also be provided with a nitrogen facility for purging the SOEC 10 with nitrogen, which is an inert gas, when the system is started or stopped. Nitrogen gas may be supplied to the nitrogen supply device 70 from the nitrogen facility.

[0044] The control device 80 receives information acquired by the electrical conductivity meter 34, the pH meter 35, and the feedwater flow meter 33. The control device 80 controls the amount of chemical liquid supplied from the chemical liquid injector 36 to the feedwater W flowing through the first water vapor supply line L10 by controlling the chemical liquid injector 36. The control device 80 also controls the nitrogen supply device 70 to control the amount of nitrogen supplied from the nitrogen supply device 70 to the mixed gas S2 flowing through the second water vapor supply line L11.

[0045] The control device 80 may adjust the amount of nitrogen supplied from the nitrogen supply device 70 to the mixed gas S2 flowing through the second water vapor supply line L11 based on information acquired by the electrical conductivity meter 34, the pH meter 35, or the feedwater flow meter 33. Specifically, the control device 80 may control the nitrogen supply device 70 based on information acquired by the electrical conductivity meter 34 and / or the pH meter 35 and / or the feedwater flow meter 33 so that the pH of the feedwater supplied to the water vapor generation unit 20 approaches a predetermined value, and adjust the amount of nitrogen supplied to the mixed gas S2 flowing through the second water vapor supply line L11. The predetermined value may be a value that can suppress the occurrence of corrosion in the water vapor generating unit 20.

[0046] The control device 80 (Controller) includes, for example, a CPU (Central Processing Unit: Processor), a main memory, a secondary storage, etc. Furthermore, the control device 80 may include a communication unit for transmitting and receiving information to and from other devices.

[0047] The primary storage device is composed of writable memory such as cache memory and RAM (Random Access Memory), and is used as a working area for reading the CPU's execution program and writing data processed by the execution program. The secondary storage device is a non-transitory computer-readable storage medium, such as a magnetic disk, magneto-optical disk, CD-ROM, DVD-ROM, or semiconductor memory.

[0048] For example, a series of processes for realizing various functions is stored in a secondary storage device in the form of a program, and the CPU reads this program into the main storage device and executes information processing and arithmetic operations to realize various functions. Note that the program may be pre-installed in the secondary storage device, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0049] 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 feed water and steam supplied to the SOEC 10. In the following, the fluid flowing through the first steam supply line L10 is liquid water (feed water) in the feed water line L10a, which is upstream of the steam generation unit 20, and gaseous steam in the steam line L10b, which is downstream of the steam generation unit 20. Therefore, in the following, the feed water will be denoted by the symbol "W" and the steam will be denoted by the symbol "S1."

[0050] The feedwater W stored in the water supply device 30 is introduced into a first steam supply line L10 (more specifically, a feedwater line L10a). The first steam supply line L10 is provided with a feedwater pump 31 driven by a driving force from a motor 32. 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 31.

[0051] At this time, condensed water containing ammonia water is supplied to the feed water flowing through the first steam supply line L10 (specifically, the feed water line L10a) via the condensed water line L32. That is, the feed water supplied to the steam generation unit 20 is mixed with ammonia water. Furthermore, a chemical liquid (ammonia water or the like) may be injected from a chemical liquid injector 36 into the feed water flowing through the first steam supply line L10 (specifically, the feed water line L10a).

[0052] The feedwater W supplied to the steam generating section 20 evaporates into steam S1 in the first heat exchange section 21 by heat exchange with the mixed gas A2 flowing through the oxidizing gas discharge line L21 (steam generating step). In addition, in the second heat exchange section 22, the feedwater W evaporates into steam S1 by heat exchange with hydrogen H flowing through the hydrogen discharge line L30.

[0053] 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 (more specifically, the steam line L10b). At this time, hydrogen H supplied via the hydrogen supply line L31 is added. The hydrogen supply line L31 is provided with a first hydrogen compressor 25 driven by a driving force from a motor 26.

[0054] The hydrogen introduced into the hydrogen supply line L31 is supplied to the second steam supply line L11 by the driving force of the first hydrogen compressor 25. The 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. At this time, nitrogen is supplied from the nitrogen supplier 70 to the mixed gas S2 flowing through the second steam supply line L11.

[0055] Power is supplied to the SOEC 10 from the power supply device 40 (power supply step).

[0056] 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 SOEC 10 (more specifically, the oxidizing gas supply header 14) via the oxidizing gas supply line L20.

[0057] 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.

[0058] On the other hand, a mixed gas S2 of water vapor S1 and hydrogen H (more precisely, a gas in which nitrogen is further mixed with the mixed gas S2 (hereinafter referred to as "nitrogen mixed gas")) supplied to the water vapor supply header 12 flows inside each cell stack 101. At this time, the water vapor S1 contained in the nitrogen mixed gas is electrolyzed to generate hydrogen (hydrogen generation process). In addition, the nitrogen and hydrogen contained in the nitrogen mixed gas react to generate ammonia.

[0059] Due to thermal equilibrium, in the region of the solid oxide electrolysis cell (SOEC) 10 where the electrolysis cell 105 (see FIG. 2) is provided, the nitrogen mixed gas has a high temperature, so a chemical reaction in which ammonia is decomposed into hydrogen and nitrogen is likely to occur. On the other hand, in the region of the solid oxide electrolysis cell (SOEC) 10 downstream of the region where the electrolysis cell 105 (see FIG. 2) is provided (the lead portion on the discharge side), the nitrogen mixed gas has a relatively low temperature, so a chemical reaction in which hydrogen and nitrogen combine to produce ammonia is likely to occur.

[0060] The generated high-temperature hydrogen H (including water vapor and ammonia gas) 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 circulating through the first water vapor supply line L10. The cooled hydrogen H is introduced into the condenser 60.

[0061] 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.

[0062] In the condenser 60, the contained water vapor and ammonia are condensed, and the water vapor and ammonia are separated from the hydrogen. The hydrogen from which the water vapor and ammonia have been separated is supplied to the hydrogen storage unit 62 via the hydrogen discharge line L30.

[0063] On the other hand, the water vapor and ammonia condensed in the condenser 60 (hereinafter referred to as "condensed water") are supplied to the first water vapor supply line L10 via a condensed water line L32.

[0064] According to this embodiment, the following advantageous effects are achieved. In this embodiment, a condensed water line L32 is provided that guides the ammonia condensed in the condenser 60 to the steam supply system 90 (specifically, the feed water line L10a). This allows the ammonia to be guided to the steam supply system 90 (specifically, the feed water line L10a, the steam generating unit 20, the steam line L10b, and the second steam supply line L11) via the feed water line L10a. Therefore, the pH of the feed water and / or steam supplied to the steam supply system 90 can be maintained within a predetermined range, and corrosion in the steam supply system 90 can be suppressed.

[0065] Furthermore, in this embodiment, the ammonia produced in the SOEC 10 is introduced to the steam generation unit 20 via the condenser 60 or the like. This reduces the amount of ammonia supplied to the steam generation unit 20 from a separately provided ammonia supply device or eliminates the need for such a device. This allows the device to be made smaller or eliminated, thereby reducing the equipment cost of the hydrogen production system 1. Furthermore, the amount of ammonia supplied from a separately provided ammonia supply device to the steam generating unit 20 can be reduced or eliminated, thereby reducing the operating cost.

[0066] In this embodiment, a nitrogen supply device 70 is provided to supply nitrogen gas to the SOEC 10. This causes nitrogen and hydrogen to combine to produce ammonia in the SOEC 10. Therefore, ammonia can be suitably produced in the SOEC 10.

[0067] In this embodiment, a control device 80 is provided that controls the nitrogen supply device 70 so that an amount of nitrogen gas based on the pH measured by the pH meter 35 is supplied to the SOEC 10. This allows the amount of nitrogen gas supplied from the nitrogen supply device 70 to be an amount based on the pH of the feedwater introduced to the steam generation unit 20. Therefore, the pH of the feedwater introduced to the steam generation unit 20 can be easily adjusted to a desired value, making it easier to suppress the occurrence of corrosion in the steam generation unit 20. The control device 80 may determine the amount of nitrogen gas based on the pH measured by the pH meter 35 so that the pH of the feedwater introduced to the steam generating unit 20 approaches a predetermined value. The predetermined value may be a value that can suppress corrosion in the water vapor generating unit 20.

[0068] In this embodiment, a control device 80 is provided that controls the nitrogen supply device 70 so that an amount of nitrogen gas based on the pH measured by the electrical conductivity meter 34 is supplied to the SOEC 10. This allows the amount of nitrogen gas supplied from the nitrogen supply device 70 to be the amount based on the electrical conductivity meter 34 of the feedwater introduced to the steam generation unit 20. Electrical conductivity and pH are correlated. Therefore, it is easy to adjust the pH of the feedwater introduced to the steam generation unit 20 to a desired value, making it easier to suppress the occurrence of corrosion in the steam generation unit 20. The control device 80 may determine the amount of nitrogen gas based on the electrical conductivity measured by the electrical conductivity meter 34 so that the pH of the feedwater introduced to the steam generating unit 20 approaches a predetermined value. The predetermined value may be a value that can suppress corrosion in the water vapor generating unit 20.

[0069] The present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present disclosure. For example, in the above-described embodiment, an example in which the chemical liquid injector 36 is provided between the feedwater flow meter 33 and the electrical conductivity meter 34 in the first steam supply line L10 has been described, but the present disclosure is not limited thereto. If a sufficient corrosion suppression effect in the steam generation unit 20 can be obtained by supplying the ammonia-containing condensed water condensed in the condenser 60 to the first steam supply line L10, the chemical liquid injector 36 may be omitted.

[0070] Furthermore, in the above embodiment, an example has been described in which the condensed water line L32 is connected to the water supply line L10a, but the present disclosure is not limited thereto. The condensed water line L32 may be connected to any one of the steam supply systems 90. For example, the condensed water line L32 may be connected to the steam line L10b or the second steam supply line L11. The condensed water line L32 may also be connected to the steam generator 20. With this configuration, ammonia can be supplied to a portion of the steam supply system 90 downstream of the connection portion of the condensed water line L32, thereby suppressing corrosion of that portion.

[0071] 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 includes a solid oxide electrolysis cell (10) that produces ammonia and generates hydrogen by electrolyzing supplied water vapor, a water vapor supply system (20, L10, L11) that introduces water vapor to the solid oxide electrolysis cell (10), a condenser (60) that introduces ammonia-containing hydrogen discharged from the solid oxide electrolysis cell (10) and cools the ammonia-containing hydrogen to condense the ammonia, and a condensed water line (L32) that introduces the ammonia condensed in the condenser (60) to the water vapor supply system (20, L10, L11).

[0072] In the above configuration, a condensed water line is provided to guide the ammonia condensed in the condenser to the steam supply system, thereby enabling the ammonia to be guided to the steam supply system, thereby suppressing corrosion in the steam supply system.

[0073] Furthermore, in the above configuration, ammonia produced in the solid oxide electrolysis cell is introduced into the steam supply system via a condenser or the like. This reduces or eliminates the amount of ammonia supplied from a separately provided ammonia supply device to the steam supply system. This allows the device to be made smaller or eliminated, thereby reducing the equipment costs of the hydrogen production system. Furthermore, this reduces or eliminates the amount of ammonia supplied from a separately provided ammonia supply device to the steam supply system, thereby reducing the operating costs.

[0074] In addition, in the hydrogen production system according to a second aspect of the present disclosure, in the above-described first aspect, the steam supply system (20, L10, L11) includes a steam generation unit (20) that heats feedwater to generate steam to be supplied to the solid oxide electrolysis cell (10), and a water supply line (L10a) that supplies feedwater to the steam generation unit (20), and the condensed water line (L32) is connected to the water supply line (L10a).

[0075] In the above configuration, the condensation line is connected to the water supply line, which allows ammonia to be guided to the steam generator via the water supply line, thereby suppressing corrosion in the water supply line and the steam generator.

[0076] Furthermore, the hydrogen production system according to a third aspect of the present disclosure is the first or second aspect, further comprising a nitrogen-containing gas supply unit (70) that supplies a nitrogen-containing gas to the solid oxide electrolysis cell (10), and the solid oxide electrolysis cell (10) produces ammonia using the nitrogen-containing gas supplied from the nitrogen-containing gas supply unit (70).

[0077] The above configuration includes a nitrogen-containing gas supply unit that supplies a nitrogen-containing gas to the solid oxide electrolysis cell. This allows nitrogen and hydrogen to combine in the solid oxide electrolysis cell to produce ammonia. Therefore, ammonia can be suitably produced in the solid oxide electrolysis cell.

[0078] Furthermore, a hydrogen production system according to a fourth aspect of the present disclosure is the same as that of the third aspect, and further includes: a pH measurement unit (35) that measures a pH of feedwater or steam circulating through the steam supply system (20, L10, L11); and a control device (80) that controls the nitrogen-containing gas supply unit (70) so that an amount of nitrogen-containing gas based on the pH measured by the pH measurement unit (35) is supplied to the solid oxide electrolysis cell (10).

[0079] The above configuration includes a control device that controls the nitrogen gas supply unit so that an amount of nitrogen-containing gas based on the pH measured by the pH measurement unit is supplied to the solid oxide electrolysis cell. This allows the amount of nitrogen gas supplied from the nitrogen gas supply unit to be based on the pH of the feedwater or steam circulating through the steam supply system. This makes it easier to adjust the pH of the feedwater or steam introduced into the steam supply system to a desired value, making it easier to suppress corrosion in the steam supply system. The control device may also determine the amount of nitrogen-containing gas based on the pH measured by the pH measurement unit so that the pH of the feedwater or steam circulating through the steam supply system approaches a predetermined value. The predetermined value may be a value that suppresses corrosion in the steam supply system.

[0080] Furthermore, a hydrogen production system according to a fifth aspect of the present disclosure is the hydrogen production system of the third or fourth aspect, further comprising: an electrical conductivity measurement unit (34) that measures electrical conductivity of feedwater or steam circulating through the steam supply system (20, L10, L11); and a control device (80) that controls the nitrogen-containing gas supply unit (70) so that an amount of nitrogen-containing gas based on the electrical conductivity measured by the electrical conductivity measurement unit (34) is supplied to the solid oxide electrolysis cell (10).

[0081] The above configuration includes a control device that controls the nitrogen gas supply unit so that an amount of nitrogen-containing gas based on the pH measured by the electrical conductivity measurement unit is supplied to the solid oxide electrolysis cell. This allows the amount of nitrogen gas supplied from the nitrogen gas supply unit to be an amount based on the electrical conductivity measurement unit of the feedwater or steam circulating through the water vapor supply system. Electrical conductivity and pH are correlated. Therefore, the pH of the feedwater or steam circulating through the water vapor supply system can be easily adjusted to a desired value, making it easier to suppress corrosion in the water vapor supply system. The control device may determine the amount of nitrogen-containing gas based on the electrical conductivity measured by the electrical conductivity measuring unit so that the pH of the feedwater or steam flowing through the steam supply system approaches a predetermined value. The predetermined value may be a value that can suppress corrosion in the steam supply system.

[0082] Furthermore, the hydrogen production method according to the first aspect of the present disclosure includes a generation step of generating ammonia in a solid oxide electrolysis cell (10) and producing hydrogen by electrolyzing supplied water vapor; a steam introduction step of introducing water vapor to the solid oxide electrolysis cell (10) through a steam supply system (20, L10, L11); a condensation step of condensing ammonia by cooling the ammonia-containing hydrogen discharged from the solid oxide electrolysis cell (10); and an ammonia introduction step of introducing the ammonia condensed in the condensation step to the steam supply system (20, L10, L11). [Explanation of symbols]

[0083] 1. Hydrogen production system 10 Solid Oxide Electrolysis Cell (SOEC) 12 Steam supply header 13 Produced hydrogen discharge header 14 Oxidizing gas supply header 15 Oxidizing gas discharge header 16 Case 20 Steam generation unit 21 1st heat exchange section 22 Second heat exchange section 25 No. 1 hydrogen compressor 26 Motor 30 Water supply equipment 31 Water supply pump 32 motor 33 Water supply flow meter 34 Electrical conductivity measuring instrument (electrical conductivity measuring part) 35 pH meter (pH measurement unit) 36 Chemical injection device 40 Power supply 50 Compression Device 51 Compressor 52 Turbine 53 Electric motor 60 Condenser 61 Second hydrogen compressor 62 Hydrogen storage unit 63 Condensate Pump 64 motor 70 Nitrogen supply device (nitrogen-containing gas supply unit) 80 Control device 90 Steam supply system 101 Cell Stack 103 Base tube 105 Electrolysis Cell 107 Interconnector 109 Hydrogen electrode 111 Solid electrolyte membrane 113 Oxygen electrode 115 Lead Film L10 First steam supply line L10a: Water supply line L10b: Water vapor line L11 Second steam supply line L20 Oxidizing gas supply line L21 Oxidizing gas exhaust line L30 Hydrogen discharge line L31 Hydrogen supply line L32 Condensate line

Claims

1. a solid oxide electrolysis cell that generates ammonia and electrolyzes supplied water vapor to generate hydrogen; a steam supply system for introducing steam into the solid oxide electrolysis cell; a condenser to which the ammonia-containing hydrogen discharged from the solid oxide electrolysis cell is introduced and which cools the ammonia-containing hydrogen to condense the ammonia; a condensed water line that guides the ammonia condensed in the condenser to the steam supply system.

2. the water vapor supply system includes a water vapor generating unit that generates water vapor to be supplied to the solid oxide electrolysis cell by heating feed water, and a water supply line that supplies feed water to the water vapor generating unit; The hydrogen production system according to claim 1 , wherein the condensed water line is connected to the water supply line.

3. a nitrogen-containing gas supply unit that supplies a nitrogen-containing gas to the solid oxide electrolysis cell, 2. The hydrogen production system according to claim 1, wherein the solid oxide electrolysis cell produces ammonia using the nitrogen-containing gas supplied from the nitrogen-containing gas supply unit.

4. a pH measuring unit that measures the pH of the feed water or steam flowing through the steam supply system; a control device that controls the nitrogen-containing gas supply unit so that an amount of nitrogen-containing gas based on the pH measured by the pH measurement unit is supplied to the solid oxide electrolysis cell.

5. an electrical conductivity measuring unit that measures the electrical conductivity of the feedwater or steam flowing through the steam supply system; a control device that controls the nitrogen-containing gas supply unit so that an amount of nitrogen-containing gas based on the electrical conductivity measured by the electrical conductivity measurement unit is supplied to the solid oxide electrolysis cell.

6. a generation step of generating ammonia in a solid oxide electrolysis cell and generating hydrogen by electrolyzing the supplied water vapor; a steam introducing step of introducing steam into the solid oxide electrolysis cell by a steam supply system; a condensation step of condensing ammonia by cooling the ammonia-containing hydrogen discharged from the solid oxide electrolysis cell; an ammonia introducing step of introducing the ammonia condensed in the condensing step into the steam supply system.

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