Hydrogen production system and hydrogen production method

Abstract

The purpose of this disclosure is to improve the overall energy efficiency of a hydrogen production system. The hydrogen production system (1) produces hydrogen. The hydrogen production system (1) includes: an SOEC (10) supplied with an oxidizing gas and water vapor, which generates hydrogen by electrolyzing the supplied water vapor; a water vapor generating unit (20) that heats the supplied water, thereby generating water vapor supplied to the SOEC (10); and a power supply unit (40) that supplies electricity to the SOEC (10) in a manner that enables the SOEC (10) to operate at an operating point above thermal neutrality. The water vapor generating unit (20) generates water vapor by utilizing the heat generated in the SOEC (10) to heat the supplied water without using heat supplied from outside the hydrogen production system (1).

Description

Technical Field

[0001] This disclosure relates to hydrogen production systems and methods. Background Technology

[0002] Electrolytic cells that produce hydrogen and oxygen through the electrochemical decomposition of water are hydrogen production methods that do not involve the emission of carbon dioxide, offering excellent environmental characteristics. Among these, solid oxide electrolytic cells (SOECs) use yttrium oxide-stabilized zirconia and other ceramics as the electrolyte and high-temperature steam as the feedstock, thus producing hydrogen with higher efficiency compared to other electrolytic cells. Alternatively, co-electrolysis can be used for decarbonization, employing carbon dioxide (CO2) as a feedstock and electrolyzed hydrogen as a reducing agent to directly produce carbon monoxide (CO).

[0003] As an electrolysis system equipped with SOEC, the electrolysis system described in Patent Document 1 is known, for example. Patent Document 1 describes a system that includes an SOEC stack and a steam generator for generating steam to be supplied to the stack. The steam generator includes AC (Alternating Current) or DC (Direct Current) resistance heating elements or induction heating elements.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-180316 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] To produce hydrogen in a SOEC, steam is required. Therefore, except in cases where steam from outside the system (e.g., steam transmission lines from the plant) is supplied to the SOEC, steam needs to be generated from the water supply and supplied to the SOEC.

[0009] As a method for generating water vapor, methods using electric devices such as AC or DC resistance heating elements, as in Patent Document 1, are also considered. However, in such methods, the overall power consumption of the system increases due to the use of electricity, and the overall energy efficiency of the system may decrease.

[0010] This disclosure was made in view of the following circumstances, and its purpose is to provide a hydrogen production system and a hydrogen production method that can improve the overall energy efficiency of a hydrogen production system.

[0011] Solution for solving the problem

[0012] To address the aforementioned issues, the hydrogen production system and method disclosed herein employ the following approach.

[0013] One aspect of this disclosure is a hydrogen production system for producing hydrogen, comprising: a solid oxide electrolyzer supplied with an oxidizing gas and water vapor, which generates hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit that heats the supplied water, thereby generating water vapor to be supplied to the solid oxide electrolyzer; and a power supply device that supplies electricity to the solid oxide electrolyzer in a manner that enables it to operate at an operating point above thermal neutrality, wherein the water vapor generation unit generates water vapor by using the heat generated in the solid oxide electrolyzer to heat the supplied water without using heat supplied from outside the hydrogen production system.

[0014] One method of hydrogen production disclosed herein is a method of producing hydrogen using a hydrogen production system, wherein the hydrogen production system comprises: a solid oxide electrolyzer, supplied with an oxidizing gas and water vapor, and generating hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit, which heats the supplied water to generate water vapor supplied to the solid oxide electrolyzer; and a power supply unit, which supplies electricity to the solid oxide electrolyzer in a manner that operates the solid oxide electrolyzer at an operating point above thermal neutrality. The hydrogen production method comprises: a hydrogen generation step, in which the supplied water vapor is electrolyzed in the solid oxide electrolyzer to generate hydrogen; a steam generation step, in which the supplied water is heated to generate water vapor supplied to the solid oxide electrolyzer; and an electricity supply step, in which electricity is supplied to the solid oxide electrolyzer in a manner that operates the solid oxide electrolyzer at an operating point above thermal neutrality. The steam generation step generates water vapor by using the heat generated in the solid oxide electrolyzer to heat the supplied water without using heat supplied from outside the hydrogen production system.

[0015] Invention Effects

[0016] According to this disclosure, the overall energy efficiency of hydrogen production systems can be improved. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the configuration of a hydrogen production system according to an embodiment of the present disclosure.

[0018] Figure 2 This is a diagram illustrating one embodiment of the battery stack according to the present disclosure. Detailed Implementation

[0019] Hereinafter, with reference to the accompanying drawings, one embodiment of the hydrogen production system and hydrogen production method of this disclosure will be described.

[0020] like Figure 1 As shown, the hydrogen production system 1 of this embodiment includes: a solid oxide electrolysis cell (SOEC) 10; a steam generation unit 20 for generating steam to be supplied to the SOEC 10; a water supply unit 30 for supplying water to the steam generation unit 20; a power supply unit 40 for supplying electricity to the SOEC 10; and a compression unit 50 for compressing the air supplied to the SOEC 10.

[0021] SOEC10 is supplied with a high-temperature, high-pressure oxidizing gas (air, as an example in this embodiment) and high-temperature, high-pressure water vapor. SOEC10 uses a high-temperature solid electrolyte to electrolyze the water vapor, thereby generating hydrogen.

[0022] SOEC10 includes multiple battery stacks 101, a water vapor supply manifold 12, a hydrogen generation discharge manifold 13, an oxidizing gas supply manifold 14, an oxidizing gas discharge manifold 15, and a housing 16 for housing the multiple battery stacks 101.

[0023] The upstream ends of the multiple battery stacks 101 are connected to the steam supply manifold 12. Furthermore, the downstream ends of the multiple battery stacks 101 are connected to the hydrogen generation exhaust manifold 13. Additionally, the oxidizing gas supply manifold 14 and the oxidizing gas exhaust manifold 15 communicate with a space (reaction chamber) formed inside the housing 16.

[0024] Next, refer to Figure 2 The battery stack 101 will be described.

[0025] The following description, as an example of this embodiment, illustrates a cylindrical battery stack using a substrate tube. In the absence of a substrate tube, the fuel electrode can be formed to a greater thickness to also function as a substrate tube, and the method is not limited to using a substrate tube. Furthermore, regarding the substrate tube in this embodiment, a cylindrical substrate tube is used for explanation; however, any cylindrical substrate tube is acceptable, and its cross-section is not necessarily limited to a circle; for example, it can be elliptical. A flat tubular battery stack, or similar structure, can also be used, formed by vertically flattening the circumferential side of a cylinder. Figure 2This is a diagram illustrating one embodiment of a battery stack. As an example, the battery stack 101 includes: a cylindrical substrate tube 103; multiple electrolytic cells 105 formed on the outer peripheral surface of the substrate tube 103; and interconnects 107 formed between adjacent electrolytic cells 105. Each electrolytic cell 105 is formed by stacking a hydrogen electrode 109, a solid electrolyte membrane 111, and an oxygen electrode 113. Furthermore, the battery stack 101 includes a lead film 115 electrically connected via the interconnects 107 to the oxygen electrode 113 of the electrolytic cell 105 formed axially at the outer peripheral surface of the substrate tube 103, and also includes a lead film 115 electrically connected to the hydrogen electrode 109 formed at the other end of the electrolytic cell 105.

[0026] In addition to water vapor used for electrolysis, the gas supplied / discharged relative to the hydrogen electrode 109 mostly contains hydrogen. However, in the following description, to avoid confusion, the supply gas containing hydrogen will be referred to as "supply water vapor", and the hydrogen gas containing water vapor discharged from the hydrogen electrode 109 will be referred to as "generated hydrogen".

[0027] The substrate tube 103 is made of a porous material, such as CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), Y2O3-stabilized ZrO2 (YSZ), or MgAl2O4 as the main components. The substrate tube 103 supports the electrolytic cell 105, the interconnect 107, and the lead film 115, and allows the water vapor supplied to the inner peripheral surface of the substrate tube 103 to diffuse through the fine pores of the substrate tube 103 to the hydrogen electrode 109 formed on the outer peripheral surface of the substrate tube 103.

[0028] The hydrogen electrode 109 is composed of an oxide of a composite material of Ni and a zirconium oxide electrolyte material, such as Ni / YSZ. Alternatively, the thickness of the hydrogen electrode 109 can be 50 μm to 250 μm, and the hydrogen electrode 109 can be formed by screen printing a paste.

[0029] The solid electrolyte membrane 111 primarily uses YSZ, which possesses excellent airtightness, preventing gas from passing through, and high oxygen ion conductivity at high temperatures. This solid electrolyte membrane 111 allows oxygen ions (O2) generated at the hydrogen electrode 109 to pass through... 2- It moves to the oxygen electrode 113. Alternatively, the solid electrolyte membrane 111 on the surface of the hydrogen electrode 109 has a thickness of 5 μm to 100 μm and is formed by screen printing the paste.

[0030] The oxygen electrode 113 is composed, for example, of LaSrMnO3-based oxides or LaCoO3-based oxides. For the oxygen electrode 113, the slurry-formed material is applied using screen printing or a distributor. The oxygen electrode 113 can also be composed of two layers. In this case, the oxygen electrode layer (oxygen electrode intermediate layer) on the solid electrolyte membrane 111 side is composed of a material exhibiting high ionic conductivity and excellent catalytic activity. The oxygen electrode intermediate layer can also be composed of Sm-doped cerium dioxide exhibiting high ionic conductivity, and the oxygen electrode layer (oxygen electrode conductive layer) on the oxygen electrode intermediate layer can also be composed of perovskite-type oxides such as Sr and Ca-doped LaMnO3.

[0031] A negative voltage is applied to the hydrogen electrode 109 and a positive voltage is applied to the oxygen electrode 113. Thus, in the hydrogen electrode 109, the water vapor contained in the supplied water vapor accepts electrons and is electrolyzed to generate hydrogen molecules and oxygen ions (O2). 2- (Refer to the following reaction formula (1)). The generated hydrogen is extracted to the outside along with the supplied water vapor.

[0032] On the other hand, due to the potential difference, oxygen ions pass through the solid electrolyte membrane 111 and move toward the oxygen electrode 113, releasing electrons to become oxygen molecules (refer to the reaction formula (2) below). The generated oxygen is discharged to the outside along with the oxidizing gas supplied to the oxygen electrode 113.

[0033] H2O + 2e - →H2+O 2- ...(1)

[0034] 2O 2- →O2+4e - ...(2)

[0035] Oxidizing gases do not directly participate in the electrolysis reaction, but they supply the heat required for the electrolysis reaction (endothermic) and remove the excess heat generated during the electrolysis reaction. They are typically gases containing approximately 15% to 30% oxygen, with air being the most preferred. However, in addition to air, mixtures of combustion exhaust gas and air, mixtures of oxygen and air, inert gases such as nitrogen, etc., can also be used.

[0036] Interconnector 107 is made of SrTiO3 or similar M 1-x L xThe conductive perovskite-type oxide, represented by TiO3 (M being an alkaline earth metal element and L being a lanthanide element) and lanthanum chromate (LaCrO3), is used to screen print the slurry-like material. The interconnect 107 is a dense film to prevent the supply of water vapor from mixing with oxidizing gases. Furthermore, the interconnect 107 exhibits stable durability and electronic conductivity under both oxidizing and reducing atmospheres. This interconnect 107 electrically connects the oxygen electrode 113 of one adjacent electrolytic cell 105 to the hydrogen electrode 109 of another, thus connecting the adjacent electrolytic cells 105 in series.

[0037] The lead film 115 needs to have electronic conductivity and its coefficient of thermal expansion needs to be close to that of the other materials constituting the battery stack 101. Therefore, it is made of composite materials of Ni and zirconium oxide electrolytes such as Ni / YSZ, or SrTiO3-based electrolytes. 1-x L x It is composed of TiO3 (M is an alkaline earth metal element, L is a lanthanide element). The lead film 115 connects multiple electrolytic cells 105 in series via interconnect 107, applying the DC power required for the electrolysis reaction to the end of the battery stack 101. In addition, the surface on the oxidizing gas side can be protected by an airtight, oxidation-resistant material to prevent the oxidation of metal materials such as Ni.

[0038] like Figure 1 As shown, the steam generating unit 20 heats the water supplied from the water supply device 30, thereby generating steam that is supplied to the SOEC 10. The steam generating unit 20 uses the heat generated in the SOEC 10 to heat the water supply, thereby generating steam.

[0039] The steam generation unit 20 includes: a first heat exchange unit 21 for exchanging heat between the oxidizing gas discharged from SOEC 10 and the water supply; a second heat exchange unit 22 for exchanging heat between the hydrogen generated by SOEC 10 and the water supply; and a third heat exchange unit 23 for exchanging heat between the oxidizing gas compressed by the compression device 50 and the water supply.

[0040] The first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 are located midway along the first steam supply pipeline L10. These three sections are connected in parallel. Specifically, the first steam supply pipeline L10 branches into three branch pipelines L10a midway along its length, with each of the three heat exchange sections located on its respective branch pipeline L10a. The branch pipelines L10a merge downstream of each heat exchange section.

[0041] The first heat exchange unit 21 performs heat exchange between the water supply flowing in the first steam supply line L10 (more specifically, the branch line L10a) and the oxidizing gas flowing in the oxidizing gas discharge line L21, thereby heating the water supply to generate steam.

[0042] The second heat exchange section 22 performs heat exchange between the water supply flowing in the first steam supply line L10 (more specifically, branch line L10a) and the hydrogen flowing in the hydrogen discharge line L30, thereby heating the water supply to generate steam.

[0043] The third heat exchange section 23 performs heat exchange between the water supply flowing in the first steam supply line L10 (more specifically, branch line L10a) and the oxidizing gas flowing in the oxidizing gas supply line L20, thereby heating the water supply to generate steam.

[0044] The water supply device 30 is a device for storing and transporting water (water supply). The water is heated into steam by the steam generating unit 20. The upstream end of the first steam supply line L10 is connected to the water supply device 30.

[0045] The power supply unit 40 is a device that supplies electricity for steam electrolysis to the SOEC 10. The power supply unit 40 supplies electricity to the SOEC 10 in a manner that allows it to operate at an operating point above the thermal neutral point. The thermal neutral point is the operating point of the SOEC 10 where the Joule heat generated in the SOEC 10 is equal to the heat absorbed in the endothermic reaction accompanying the electrolysis of the SOEC 10. In this embodiment, the power supply unit 40 supplies more electricity than would be supplied when operating at the thermal neutral point, thereby allowing the SOEC 10 to operate at an operating point above the thermal neutral point. The method of increasing the electricity is not particularly limited. For example, the current flowing to the SOEC 10 can be increased, or the voltage applied to the SOEC 10 can be increased. Furthermore, both the current and voltage can be increased.

[0046] The compression device 50 is a device for compressing the oxidizing gas supplied to the SOEC 10. Examples of oxidizing gases include, for instance, air. Hereinafter, air will be used as the oxidizing gas in the description.

[0047] The compression unit 50 includes a compressor 51, a turbine 52, and an electric motor 53.

[0048] The compressor 51 and the turbine 52 are connected by the same rotating shaft, and are configured to drive the compressor 51 by the rotation of the turbine 52. The electric motor 53 is configured to drive the compressor 51 when the output of the turbine 52 is low (e.g., when the hydrogen production system 1 is started) or to assist in driving the compressor 51.

[0049] Next, the flow of fluid in the hydrogen production system 1 of this embodiment will be described.

[0050] First, the flow of water and steam supplied to SOEC10 will be described. It should be noted that, in the following description, the fluid flowing in the first steam supply line L10 is water upstream of the steam generation section 20 and steam downstream of the steam generation section 20. Therefore, water will be labeled with the reference numeral "W" and steam with the same reference numeral "S1".

[0051] Water W stored in water supply device 30 is introduced into first steam supply line L10. A water supply pump 60, driven by a driving force from motor 61, is provided in first steam supply line L10. Water W introduced into first steam supply line L10 is supplied to steam generation unit 20 by the driving force of water supply pump 60.

[0052] The water W supplied to the steam generation unit 20 undergoes heat exchange with the mixed gas A2 flowing in the oxidizing gas discharge line L21 in the first heat exchange unit 21, thereby evaporating into water vapor S1 (steam generation process). Furthermore, in the second heat exchange unit 22, it undergoes heat exchange with hydrogen H flowing in the hydrogen discharge line L30, thereby evaporating into water vapor S1. Additionally, in the third heat exchange unit 23, it undergoes heat exchange with the oxidizing gas A1 flowing in the oxidizing gas supply line L20, thereby evaporating into water vapor S1. It should be noted that, considering heat losses in the first steam supply line L10 and the second steam supply line L11, the water vapor S1 at the outlet of each heat exchange unit can also be set to a superheated state.

[0053] The water vapor S1 generated by each heat exchanger merges downstream of the water vapor generation unit 20. The merged water vapor S1 is introduced into the second water vapor supply line L11 via the first water vapor supply line L10. At this time, hydrogen H is supplied via the hydrogen supply line L31. The mixture S2 of water vapor S1 and hydrogen H is supplied to SOEC 10 (specifically, water vapor supply manifold 12) via the second water vapor supply line L11.

[0054] Power is supplied from power supply unit 40 to SOEC10 (power supply process). SOEC10 operates at an operating point above thermal neutrality.

[0055] The high-temperature, high-pressure oxidizing gas A1, compressed by compressor 51, is introduced into oxidizing gas supply line L20. The oxidizing gas A1 introduced into oxidizing gas supply line L20 is supplied to the third heat exchange section 23 of the steam generation section 20. The oxidizing gas A1 supplied to the third heat exchange section 23 exchanges heat with the water supply W flowing in the first steam supply line L10, thereby being cooled. The oxidizing gas A1 cooled in the third heat exchange section 23 is supplied to SOEC 10 (specifically, oxidizing gas supply manifold 14) via oxidizing gas supply line L20.

[0056] Oxidizing gas A1 supplied to oxidizing gas supply manifold 14 flows upward within the internal space of housing 16 and is introduced into oxidizing gas discharge manifold 15. Oxygen is added to the oxidizing gas as it flows within the internal space of housing 16. The mixture A2 of oxidizing gas A1 and oxygen introduced into oxidizing gas discharge manifold 15 is discharged into oxidizing gas discharge line L21. The mixture A2 introduced into oxidizing gas discharge line L21 is supplied to the first heat exchange section 21 of steam generation section 20. The mixture A2 supplied to the first heat exchange section 21 exchanges heat with the water supply W flowing in the first steam supply line L10, thereby being cooled. The cooled mixture A2 in the first heat exchange section 21 is supplied to the turbine 52 of compression device 50 via oxidizing gas discharge line L21. The mixture A2 supplied to turbine 52 drives turbine 52 to rotate.

[0057] On the other hand, a mixture of water vapor S1 and hydrogen H, supplied to the water vapor supply manifold 12, flows inside each battery stack 101. At this time, the water vapor S1 contained in the mixture S2 is electrolyzed to generate hydrogen (hydrogen generation process). The generated high-temperature hydrogen H (containing water vapor) is introduced into the hydrogen generation discharge manifold 13. The hydrogen H introduced into the hydrogen generation discharge manifold 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 exchanges heat with the water supply W flowing in the first water vapor supply line L10, thereby being cooled. The cooled hydrogen H is separated from water vapor by condensation of the water vapor it contains. The hydrogen after the water vapor is separated (strictly speaking, water vapor containing a portion of the saturated vapor pressure) is supplied to the hydrogen storage device (not shown) via the hydrogen discharge line L30.

[0058] Furthermore, a hydrogen supply line L31 is connected to the second heat exchange section 22. The hydrogen supply line L31 guides a portion of the hydrogen H (containing water vapor) flowing in 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.

[0059] A booster 62, driven by a motor 63, is provided in the hydrogen supply line L31. Hydrogen H introduced into the hydrogen supply line L31 is supplied to the second steam supply line L11 by the driving force of the booster 62.

[0060] According to this implementation method, the following effects will be achieved.

[0061] In this embodiment, the steam generation unit 20 uses the heat generated in the hydrogen production system 1 (the heat generated in the SOEC 10 and the compression unit 50) to heat the supply water, thereby generating steam to be supplied to the SOEC 10. Thus, steam can be generated using the exhaust heat of the SOEC 10. Therefore, compared to cases where the exhaust heat of the SOEC 10 is not utilized, or where heat is supplied to the steam generation unit 20 from a separately provided device for generating steam (e.g., an electric boiler), the overall energy efficiency of the hydrogen production system 1 can be improved. Furthermore, in this embodiment, the SOEC 10 is operated at an operating point above the thermal neutral point, thus increasing the hydrogen production rate. In this way, in this embodiment, the hydrogen production rate can be increased, and the overall energy efficiency of the system can be improved.

[0062] Furthermore, the battery stack 101 in this embodiment is cylindrical, thus structurally allowing it to be used at higher temperatures compared to battery stacks of other shapes (e.g., flat plates). Therefore, the SOEC10 can be appropriately operated above the thermal neutral point.

[0063] Furthermore, in SOEC10, Joule heat is generated along with the flow of electric current. On the other hand, the electrolysis of water vapor in SOEC10 is an endothermic reaction. Therefore, the Joule heat generated by SOEC10 is absorbed through the endothermic reaction. Thus, in SOEC10, Joule heat is effectively utilized in electrolysis until the generated Joule heat exceeds the heat absorbed through the endothermic reaction. It should be noted that the operating point where the generated Joule heat equals the heat absorbed through the endothermic reaction is called the "thermal neutral point". When SOEC10 is operated above the thermal neutral point, the generated Joule heat cannot be completely absorbed through the endothermic reaction, thus generating residual Joule heat (hereinafter referred to as "residual heat"). Therefore, conventionally, in order to suppress energy loss caused by residual heat, SOEC10 is usually operated in a manner that reaches the thermal neutral point.

[0064] On the other hand, in this embodiment, a power supply device 40 is provided, which supplies electricity to the SOEC10 in a manner that causes it to operate at an operating point above the thermal neutral point. That is, the SOEC10 is operated at an operating point above the thermal neutral point. Therefore, residual heat is generated in the SOEC10. In this embodiment, the steam generation unit 20 uses the heat generated in the SOEC10 to heat the water supply, thus effectively utilizing this residual heat to heat the water supply. Therefore, some or all of the heat required for steam generation can be provided using the residual heat of the SOEC10. Therefore, the heat supplied to the steam generation unit 20 from a device (e.g., an electric boiler) located outside the hydrogen production system 1 for supplying heat for steam generation can be reduced or eliminated. Therefore, the device can be miniaturized or eliminated altogether, thereby reducing the equipment cost and operating cost of the hydrogen production system 1.

[0065] As described above, in this embodiment, the SOEC10 is operated at an operating point above the thermal neutral point, thus generating residual Joule heat within the SOEC10. This residual Joule heat is consumed in the form of heating the fluid flowing within the SOEC10 (e.g., oxidizing gas, water vapor, hydrogen, etc.).

[0066] In this embodiment, the steam generation unit 20 includes: a first heat exchange unit 21 for exchanging heat between the oxidizing gas discharged from the SOEC 10 and the supplied water; and a second heat exchange unit 22 for exchanging heat between the hydrogen generated by the SOEC 10 and the supplied water. Thus, in the first heat exchange unit 21, the remaining Joule heat consumed in heating the oxidizing gas can be recovered, and the recovered heat can be used for steam generation. Similarly, in the second heat exchange unit 22, the remaining Joule heat consumed in heating the hydrogen can be recovered, and the recovered heat can be used for steam generation. Therefore, some or all of the heat required for steam generation can be provided using the residual heat from the SOEC 10. Therefore, the heat supplied from a separately provided device for generating steam (e.g., an electric boiler) can be reduced or eliminated. Therefore, the device can be miniaturized or eliminated altogether, thereby reducing the equipment cost and operating cost of the hydrogen production system 1.

[0067] In this embodiment, the steam generation unit 20 includes a third heat exchange unit 23, which exchanges heat between the oxidizing gas compressed by the compression device 50 and the supplied water. This allows steam to be generated using the heat produced by compression by the compression device 50. Therefore, the overall energy efficiency of the hydrogen production system 1 can be further improved. Furthermore, the hydrogen production capacity can be further increased.

[0068] In this embodiment, the heat generated in the hydrogen production system 1 (the heat generated in the SOEC 10 and the compression unit 50) is used to provide all the latent and sensible heat required to generate steam supplied to the SOEC 10 from the water supply. Specifically, heat from outside the hydrogen production system 1 is not used; steam is generated solely by heating the water supply through the steam generation unit 20 (including heat generated through heat exchange in the first heat exchange unit 21 and the second heat exchange unit 22, and, if necessary, heat generated through heat exchange in the third heat exchange unit 23). Therefore, heat supplied from a separately provided device for generating steam (e.g., an electric boiler) is not required. This eliminates the need for such a device, further reducing the equipment cost and operating cost of the hydrogen production system 1.

[0069] It should be noted that this disclosure is not limited to the above-described embodiments, and appropriate modifications can be made without departing from its spirit.

[0070] For example, in the above embodiment, an example of the first heat exchange unit 21, the second heat exchange unit 22, and the third heat exchange unit 23 being arranged in parallel was described, but this disclosure is not limited to this. For example, the first heat exchange unit 21, the second heat exchange unit 22, and the third heat exchange unit 23 may also be arranged in series. That is, steam and / or water supply that has completed heat exchange in the first heat exchange unit 21 may be introduced into the second heat exchange unit 22, and steam and / or water supply that has completed heat exchange in the second heat exchange unit 22 may be introduced into the third heat exchange unit 23. It should be noted that when the heat exchange units are arranged in series, the order in which the heat exchange units are arranged is not limited to the order described above.

[0071] Alternatively, a portion of the first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 may be connected in parallel. That is, two of the three heat exchange sections may be connected in parallel, with the remaining one located upstream or downstream of the parallel heat exchange sections.

[0072] In addition, the first heat exchange section 21, the second heat exchange section 22, and the third heat exchange section 23 may also be constructed as preheating section, evaporation section, and superheating section, respectively.

[0073] Furthermore, in the above embodiment, an example of the steam generation unit 20 having a third heat exchange unit 23 has been described, but this disclosure is not limited to this. For example, the third heat exchange unit 23 may be omitted. That is, in this modified example, the steam generation unit 20 does not utilize the heat generated by the compression device 50. Therefore, the steam generation unit 20 heats the supply water solely through the heat generated in the SOEC 10, thereby generating steam. That is, all the latent heat and sensible heat required to generate steam supplied to the SOEC 10 from the supply water can be provided by the residual heat of the SOEC 10. Therefore, it is not necessary to supply heat from a separately provided device for supplying heat for generating steam (e.g., an electric boiler). Therefore, this device is not required, thus further reducing the equipment cost and operating cost of the hydrogen production system 1.

[0074] The hydrogen production system and hydrogen production method described in the above embodiments are understood for example as follows.

[0075] The hydrogen production system of the first aspect of this disclosure is a hydrogen production system (1) for producing hydrogen, wherein the hydrogen production system (1) comprises: a solid oxide electrolyzer (10) supplied with an oxidizing gas and water vapor, and generating hydrogen by electrolyzing the supplied water vapor; a water vapor generating unit (20) for heating the supplied water, thereby generating water vapor supplied to the solid oxide electrolyzer (10); and a power supply device (40) for supplying electricity to the solid oxide electrolyzer (10) in a manner that causes the solid oxide electrolyzer (10) to operate at an operating point above the thermal neutral point, wherein the water vapor generating unit (20) generates water vapor by heating the supplied water using the heat generated in the solid oxide electrolyzer (10) without using heat supplied from outside the hydrogen production system (1).

[0076] In the above configuration, the steam generation unit generates steam supplied to the solid oxide electrolyzer by heating the water supply using heat generated in the solid oxide electrolyzer, without using heat supplied from outside the hydrogen production system. This allows steam to be generated using the heat dissipation from the solid oxide electrolyzer. Therefore, compared to cases where the heat dissipation from the solid oxide electrolyzer is not utilized, the overall energy efficiency of the hydrogen production system can be improved. Furthermore, in the above configuration, the solid oxide electrolyzer is operated at an operating point above the thermal neutrality point, thus increasing the hydrogen production rate. In this way, the above configuration increases the hydrogen production rate and improves the overall energy efficiency of the system.

[0077] Furthermore, in a solid oxide electrolytic cell, Joule heat is generated along with the flow of current. On the other hand, the electrolysis of water vapor in the solid oxide electrolytic cell is an endothermic reaction. Therefore, the Joule heat generated in the solid oxide electrolytic cell is absorbed through the endothermic reaction. Thus, in a solid oxide electrolytic cell, Joule heat is effectively utilized in electrolysis until the generated Joule heat exceeds the heat absorbed through the endothermic reaction. It should be noted that the operating point where the generated Joule heat equals the heat absorbed through the endothermic reaction is called the "thermal neutral point." When the solid oxide electrolytic cell is operated above the thermal neutral point, the generated Joule heat cannot be completely absorbed through the endothermic reaction, thus generating residual Joule heat (hereinafter referred to as "residual heating"). Therefore, conventionally, in order to suppress energy loss caused by residual heating, the solid oxide electrolytic cell is usually operated in a manner that achieves thermal neutrality.

[0078] On the other hand, in the above configuration, a power supply device is included that supplies electricity to the solid oxide electrolyzer in a manner that operates it above the thermal neutral point. That is, the solid oxide electrolyzer is operated above the thermal neutral point. Therefore, residual heat is generated in the solid oxide electrolyzer. In this configuration, the steam generation unit utilizes the heat generated in the solid oxide electrolyzer to heat the supply water, thus the residual heat can be used to heat the supply water. Therefore, some or all of the heat required for steam generation can be provided using the residual heat from the solid oxide electrolyzer. Therefore, the heat supplied to the steam generation unit from a separately provided device for supplying heat for steam generation (e.g., an electric boiler) can be reduced or eliminated. Therefore, the device can be miniaturized or eliminated altogether, thereby reducing equipment costs and operating costs of the hydrogen production system.

[0079] In particular, in the above configuration, steam is generated without using heat supplied from outside the hydrogen production system, thus utilizing the residual heat from the solid oxide electrolyzer to provide all the heat required for steam generation. Therefore, it is not necessary to supply heat to the steam generation unit from a separately installed device for supplying heat for steam generation (e.g., an electric boiler). This eliminates the need for such a device, thereby significantly reducing equipment costs and operating costs of the hydrogen production system.

[0080] In the second embodiment of the hydrogen production system disclosed herein, in the first embodiment described above, the steam generation unit (20) includes: a first heat exchange unit (21) for exchanging heat between the oxidizing gas discharged from the solid oxide electrolytic cell (10) and the water supply; and a second heat exchange unit (22) for exchanging heat between the hydrogen generated by the solid oxide electrolytic cell (10) and the water supply.

[0081] As described above, in the above configuration, the solid oxide electrolytic cell is operated at an operating point above the thermal neutral point, thus generating residual Joule heat in the solid oxide electrolytic cell. The residual Joule heat is consumed in the form of heating the fluid flowing within the SOEC (e.g., oxidizing gas, water vapor, hydrogen, etc.).

[0082] In the above configuration, the steam generation unit includes: a first heat exchange unit for exchanging heat between the oxidizing gas discharged from the solid oxide electrolyzer and the supplied water; and a second heat exchange unit for exchanging heat between the hydrogen generated by the solid oxide electrolyzer and the supplied water. Thus, in the first heat exchange unit, the remaining Joule heat consumed in heating the oxidizing gas can be recovered and used for steam generation. Similarly, in the second heat exchange unit, the remaining Joule heat consumed in heating the hydrogen can be recovered and used for steam generation. Therefore, some or all of the heat required for steam generation can be provided using the residual heat from the solid oxide electrolyzer. Therefore, the heat supplied from a separately installed device for generating steam (e.g., an electric boiler) can be reduced or eliminated. Therefore, the device can be miniaturized or eliminated altogether, thereby reducing equipment costs and operating costs of the hydrogen production system.

[0083] Furthermore, in the second heat exchange section, the generated hydrogen is cooled, thus condensing the water vapor contained in the hydrogen. This allows for the separation of hydrogen and water vapor, thereby improving the quality of the generated hydrogen.

[0084] For the hydrogen production system of the third aspect of this disclosure, in the first or second aspect described above, the water vapor generation unit (20) uses only the heat generated in the solid oxide electrolysis cell (10) to heat the water supply, thereby generating water vapor.

[0085] In the above configuration, the steam generation unit uses only the heat generated in the solid oxide electrolyzer to heat the supply water, thereby generating steam. That is, the residual heat from the solid oxide electrolyzer can be used to provide all the latent and sensible heat required to generate steam from the supply water and supply it to the solid oxide electrolyzer. Therefore, it is not necessary to supply heat from a separately installed device (e.g., an electric boiler) for generating steam. Thus, this device is unnecessary, further reducing equipment costs and operating costs of the hydrogen production system.

[0086] In the hydrogen production system of the fourth embodiment of this disclosure, in the first or second embodiment described above, the hydrogen production system includes a compression device (50) that compresses the oxidizing gas supplied to the solid oxide electrolytic cell (10), and the water vapor generation unit (20) has a third heat exchange unit (23) that allows the oxidizing gas compressed by the compression device to exchange heat with the supplied water.

[0087] In the above configuration, the steam generation unit includes a third heat exchange unit that allows the oxidizing gas compressed by the compressor to exchange heat with the supplied water. This allows steam to be generated using the heat produced by compression. Therefore, the overall energy efficiency of the hydrogen production system can be further improved. Furthermore, the hydrogen production capacity can be further increased.

[0088] The first embodiment of this disclosure discloses a hydrogen production method that produces hydrogen using a hydrogen production system (1), wherein the hydrogen production system (1) comprises: a solid oxide electrolyzer (10) supplied with an oxidizing gas and water vapor, and generating hydrogen by electrolyzing the supplied water vapor; a water vapor generation unit (20) that heats the supplied water to generate water vapor supplied to the solid oxide electrolyzer (10); and a power supply device (40) that supplies electricity to the solid oxide electrolyzer (10) in a manner that causes the solid oxide electrolyzer (10) to operate at an operating point above the thermal neutral point. The hydrogen production method comprises: The hydrogen generation process involves electrolyzing supplied water vapor in the solid oxide electrolyzer (10) to generate hydrogen; the steam generation process involves heating the supplied water to generate water vapor supplied to the solid oxide electrolyzer (10); and the power supply process involves supplying electricity to the solid oxide electrolyzer (10) in a manner that causes it to operate at an operating point above the thermal neutral point. In the steam generation process, water vapor is generated by heating the supplied water using the heat generated in the solid oxide electrolyzer (10) without using heat supplied from outside the hydrogen production system (1).

[0089] Explanation of reference numerals in the attached figures

[0090] 1: Hydrogen production system;

[0091] 10: SOEC (Solid Oxide Electrolyte Cell);

[0092] 12: Steam supply manifold;

[0093] 13: Hydrogen is generated and discharged from the manifold;

[0094] 14: Oxidizing gas supply manifold;

[0095] 15: Oxidizing gas exhaust manifold;

[0096] 16: Shell;

[0097] 20: Water vapor generation section;

[0098] 21: First heat exchange section;

[0099] 22: Second heat exchange section;

[0100] 23: Third heat exchange section;

[0101] 30: Water supply device;

[0102] 40: Power supply device;

[0103] 50: Compression device;

[0104] 51: Compressor;

[0105] 52: Turbine;

[0106] 53: Electric motor;

[0107] 60: Water supply pump;

[0108] 61: Motor;

[0109] 101: Battery stack;

[0110] 103: Matrix tube;

[0111] 105: Electrolytic cell;

[0112] 107: Interconnector;

[0113] 109: Hydrogen electrode;

[0114] 111: Solid electrolyte membrane;

[0115] 113: Oxygen pole;

[0116] 115: Lead film;

[0117] L10: First steam supply pipeline;

[0118] L10a: Branch pipeline;

[0119] L11: Second steam supply pipeline;

[0120] L20: Oxidizing gas supply line;

[0121] L21: Oxidizing gas exhaust pipeline;

[0122] L30: Hydrogen discharge pipeline;

[0123] L31: Hydrogen supply pipeline;

[0124] A1: Oxidizing gas;

[0125] A2: Mixed gas;

[0126] H: Hydrogen;

[0127] S1: Water vapor;

[0128] S2: Mixed gas;

[0129] W: Water supply.

Claims

1. A hydrogen production system for producing hydrogen, said hydrogen production system comprising: A solid oxide electrolytic cell is supplied with oxidizing gas and water vapor, and hydrogen is generated by electrolyzing the supplied water vapor; A steam generation unit heats the supplied water, thereby generating steam to be supplied to the solid oxide electrolytic cell; and A power supply device that supplies electricity to the solid oxide electrolyzer in a manner that enables it to operate above its thermal neutrality point. The steam generation unit generates steam by using the heat generated in the solid oxide electrolysis cell to heat the water supply instead of using heat supplied from outside the hydrogen production system.

2. The hydrogen production system according to claim 1, wherein, The steam generation unit includes: a first heat exchange unit, which allows the oxidizing gas discharged from the solid oxide electrolytic cell to exchange heat with the supplied water; The second heat exchange section allows the hydrogen generated by the solid oxide electrolysis cell to exchange heat with the supplied water.

3. The hydrogen production system according to claim 1 or claim 2, wherein, The steam generation unit uses only the heat generated in the solid oxide electrolytic cell to heat the water supply, thereby generating steam.

4. The hydrogen production system according to claim 1 or claim 2, wherein, The hydrogen production system includes a compression device that compresses the oxidizing gas supplied to the solid oxide electrolyzer. The steam generation unit has a third heat exchange unit, which allows the oxidizing gas compressed by the compression device to exchange heat with the water supply.

5. A method for producing hydrogen, wherein the method is a method of producing hydrogen using a hydrogen production system, wherein, The hydrogen production system includes: A solid oxide electrolytic cell is supplied with oxidizing gas and water vapor, and hydrogen is generated by electrolyzing the supplied water vapor; A steam generation unit heats the supplied water, thereby generating steam that is supplied to the solid oxide electrolytic cell; and A power supply device that supplies electricity to the solid oxide electrolyzer in a manner that enables it to operate above its thermal neutrality point. The hydrogen production method comprises: In the hydrogen generation process, water vapor supplied is electrolyzed in the solid oxide electrolytic cell, thereby generating hydrogen. In the steam generation process, the water supply is heated to generate steam that is supplied to the solid oxide electrolytic cell. and The power supply process supplies power to the solid oxide electrolyzer in a manner that allows it to operate at an operating point above thermal neutrality. In the steam generation process, water vapor is generated by heating the water supply using the heat generated in the solid oxide electrolysis cell, without using heat supplied from outside the hydrogen production system.

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