Hydrogen production system and hydrogen production method

Abstract

This technology maintains the heat exchange rate between the primary helium gas and the second heat transfer medium while suppressing creep failure of the heat exchanger tubes that exchange heat between the steam supplied to the high-temperature steam electrolysis device and the second heat transfer medium. [Solution] According to this embodiment, the hydrogen production system comprises a first circulation system, a second circulation system, an intermediate heat exchanger, a depressurization section, a high-temperature steam electrolysis device, and a first heat exchanger. The first circulation system has a first circulation path through which primary helium gas at 700°C or higher circulates. The second circulation system has a second circulation path through which a second heat transfer medium circulates. The intermediate heat exchanger exchanges heat between the primary helium gas of the first circulation system and the second heat transfer medium of the second circulation system. The depressurization section reduces the pressure of the second heat transfer medium in the second circulation system. The high-temperature steam electrolysis device produces hydrogen and oxygen. The first heat exchanger exchanges heat between the second heat transfer medium, which has been depressurized in the depressurization section, and at least steam supplied to the stack of the high-temperature steam electrolysis device via heat exchanger heat transfer tubes.

Description

Technical Field

[0001] Embodiments of the present invention relate to a hydrogen production system and a hydrogen production method.

Background Art

[0002] As a nuclear reactor that plays a role in the green energy transformation, a high-temperature gas reactor with high safety has attracted attention. The high-temperature gas reactor uses helium as a coolant and has a higher operating temperature than a light water reactor, so heat utilization for various industrial applications is considered. One of them is the application to a hydrogen production device, which is being promoted.

[0003] As hydrogen production methods, the reforming method, the IS method, etc. have been put into practical use (see Patent Document 1), and a methane reforming method using high-temperature steam has been invented. However, since the reforming method uses natural gas or the like as a raw material, it cannot be said to be carbon-free, and the combination with a high-temperature gas reactor does not result in green energy transformation. On the other hand, the IS method can be combined with a high-temperature gas reactor due to the high required temperature, but corrosion of pipes due to substances after the chemical reaction occurs.

[0004] As one of the hydrogen production technologies, there is the high-temperature steam electrolysis method. This high-temperature steam electrolysis method has the advantage that the raw material is water and carbon dioxide (CO2) is not generated in the hydrogen production process. However, since the high-temperature steam electrolysis method generates hydrogen by electrolysis, the cost of electric energy becomes high.

[0005] Therefore, it is conceivable to reduce the electric energy required for electrolysis by electrolyzing high-temperature steam of 700 °C or higher. A hydrogen production system using a high-temperature gas reactor that electrolyzes high-temperature steam is generally known (see Patent Document 2), and high-efficiency hydrogen production can be achieved by efficiently recovering heat from the high-temperature gas reactor.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Patent No. 3964657 [Patent Document 2] Patent No. 7374150 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in order to recover the large amount of thermal energy generated in the reactor, the first heat transfer medium needs to be compressed, and the second heat transfer medium also needs to be under high pressure to maintain the heat exchange efficiency of the heat exchanger. In contrast, the steam supplied to the high-temperature steam electrolysis unit is at near atmospheric pressure, so when the thermal energy of the second heat transfer medium is used to heat the steam, the pressure difference between the second heat transfer medium and the steam being heated becomes large. As a result, the stress on the heat exchanger heat transfer tubes is large, and because they are exposed to high temperatures, there is a risk of creep failure.

[0008] Therefore, the problem that this embodiment aims to solve is to provide a hydrogen production system and a hydrogen production method that can suppress creep failure of heat exchanger heat transfer tubes that exchange heat between steam supplied to a high-temperature steam electrolysis apparatus and the second heat transfer medium, while maintaining the heat exchange rate between the first heat transfer medium and the second heat transfer medium. [Means for solving the problem]

[0009] The hydrogen production system according to this embodiment comprises a first circulation system, a second circulation system, an intermediate heat exchanger, a depressurization section, a high-temperature steam electrolyzer, and a first heat exchanger. The first circulation system has a first circulation path through which a first heat transfer medium at 700°C or higher circulates. The second circulation system has a second circulation path through which a second heat transfer medium circulates. The intermediate heat exchanger exchanges heat between the first heat transfer medium of the first circulation system and the second heat transfer medium of the second circulation system. The depressurization section reduces the pressure of the second heat transfer medium in the second circulation system. The high-temperature steam electrolyzer produces hydrogen and oxygen. The first heat exchanger exchanges heat between the second heat transfer medium, which has been depressurized in the depressurization section, and at least steam supplied to the stack of the high-temperature steam electrolyzer, using heat exchanger heat transfer tubes. [Effects of the Invention]

[0010] This method maintains the heat exchange rate between the first and second heat transfer fluids while suppressing creep failure of the heat exchanger tubes that exchange heat between the steam supplied to the high-temperature steam electrolysis apparatus and the second heat transfer fluid. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram showing an example configuration of a hydrogen production system according to the first embodiment. [Figure 2] A flowchart illustrating an example of a hydrogen production system. [Figure 3] A diagram showing an example configuration of a hydrogen production system according to the second embodiment. [Figure 4] A diagram showing an example configuration of a hydrogen production system according to the third embodiment. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same and similar components will be denoted by the same reference numerals, and components that have already been described will be omitted from the description as appropriate.

[0013] (First Embodiment) <Hydrogen Production System> Figure 1 shows an example of the configuration of a hydrogen production system according to the first embodiment. As shown in Figure 1, the hydrogen production system 1 has a first circulation system 2, a second circulation system 3, and a hydrogen production system 4. In this embodiment, the circulation region of the second heat transfer medium (secondary helium gas) in the second circulation system 3 is indicated by the dashed line L10.

[0014] The first circulation system 2 has a first circulation path through which a first heat medium (primary helium gas) at about 700°C to 900°C circulates. That is, this first circulation system 2 is a system that supplies heat to the second circulation system 3 using the primary helium gas heated to 700°C or higher. The second circulation system 3 has a second circulation path through which secondary helium gas circulates. That is, this second circulation system 3 is a system that减压 the secondary helium gas supplied from the first circulation system 2 and supplies heat to the hydrogen production system 4. The hydrogen production system 4 is a system that generates hydrogen and oxygen by a high-temperature steam electrolyzer 100 using the heat supplied from the secondary helium gas.

[0015] Thus, the hydrogen production system 1 includes a high-temperature gas furnace 5, an intermediate heat exchanger 10, a generator 11, a prime mover 20, a compressor 21, a pressure reduction unit 22, a plurality of heat exchangers 30 to 34, a high-temperature steam electrolyzer 100, and a hydrogen separation device 200.

[0016] The first circulation system 2 and the second circulation system 3 are separated by the intermediate heat exchanger 10, and the second circulation system 3 and the hydrogen production system 4 are separated by a plurality of heat exchangers 30 to 32. Thereby, the hydrogen production system 1 according to the present embodiment form can减压 the secondary helium gas and exchange heat with the heat exchange tubes of the heat exchanger of the hydrogen production system 4 while maintaining the heat exchange rate between the primary helium gas and the secondary helium gas.

[0017] In the following description, for convenience of explanation, the heat exchanger will be described as a configuration on the upstream side of heat. For example, the intermediate heat exchanger 10 has a circulation path for the primary helium gas and the secondary helium gas, but will be described as a configuration of the first circulation system 2 on the upstream side of heat. Similarly, the plurality of heat exchangers 30 to 32 will be described as a configuration of the second circulation system 3.

[0018] <First Circulation System> More specifically, the first circulation system 2 according to the present embodiment includes a high-temperature gas reactor 5, an intermediate heat exchanger 10, and a generator 11. The high-temperature gas reactor 5 is, for example, a nuclear reactor that uses helium as a coolant and graphite as a moderator. The high-temperature gas reactor 5 can generate primary helium gas at 900°C or higher. In the present embodiment, the heat medium of the first circulation system 2 and the second circulation system 3 is helium gas, but it is not limited thereto.

[0019] <Circulation of primary helium gas> The first circulation system 2 according to the present embodiment has a primary helium gas circulation path through which primary helium gas circulates along circulation paths L40 to L42. The primary helium gas circulation path according to the present embodiment corresponds to the first circulation path. The circulation paths L40 and L42 of the primary helium gas are connected to the high-temperature gas reactor 5. The primary helium gas is transported from the high-temperature gas reactor 5 to the intermediate heat exchanger 10 via the primary helium gas circulation path L40.

[0020] The intermediate heat exchanger 10 extracts heat from the primary helium gas heated to about 700°C to 900°C in the high-temperature gas reactor 5 and supplies the heat to the secondary helium gas. The intermediate heat exchanger 10, for example, supplies heat from the primary helium gas at 900°C and raises the temperature of the secondary helium gas to 800°C. Thus, the intermediate heat exchanger 10 exchanges heat between the primary helium gas of the first circulation system 2 and the secondary helium gas of the second circulation system 3.

[0021] The primary helium gas heat-exchanged in the intermediate heat exchanger 10 is transported to the generator 11 via the primary helium gas circulation path L41. The generator 11 is integrated with a turbine and generates electricity using the primary helium gas. The primary helium gas passing through the generator 11 returns to the high-temperature gas reactor 5 via the primary helium gas circulation path L42.

[0022] <Second circulation system> The second circulation system 3 according to the present embodiment includes a prime mover 20, a compressor 21, a decompression unit 22, and a plurality of heat exchangers 30 to 32.

[0023] <Circulation of secondary helium gas> The second circulation system 3 according to this embodiment has a secondary helium gas circulation path through circulation paths L60 to L69. The secondary helium gas circulation path according to this embodiment corresponds to the second circulation path.

[0024] In the second circulation system 3, the circulation path for secondary helium gas connects the intermediate heat exchanger 10, the prime mover 20, the compressor 21, the pressure reducing unit 22, and the exchanger 30 via series piping L60, 61, 62, 68, and 69. Meanwhile, heat exchangers 31 and 32 are connected to parallel piping L64, 65 and L66, 67 between the supply header 23 and the return header 24, respectively.

[0025] More specifically, L60 and L69, which are one end of the secondary helium gas circulation path, are connected to the intermediate heat exchanger 10. The secondary helium gas generated in the intermediate heat exchanger 10 is transported to the prime mover 20 via the secondary helium gas circulation path L60.

[0026] The prime mover 20 consumes the thermal energy of the secondary helium gas and converts it into kinetic energy, which is then consumed by the connected compressor 21. The secondary helium gas that has done work in the prime mover 20 is transported to the depressurization section 22 via the secondary helium gas circulation path L61.

[0027] <Decompression of secondary helium gas> The pressure reducing unit 22 is, for example, a pressure reducing valve, which reduces the pressure of the secondary helium gas to a predetermined pressure, for example, 0.3 MPa. The secondary helium gas reduced in pressure by the pressure reducing unit 22 is transported to the first heat exchanger (steam heater) 30 via the secondary helium gas circulation path L62.

[0028] <Generation of superheated steam at atmospheric pressure> The steam heater 30 is a heat exchanger using heat exchanger tubes, and it transfers heat from the secondary helium gas to the steam. Since the secondary helium gas has already been depressurized in the depressurization section 22, there is no need to pressurize the steam, which is the recipient of the heat exchange. In this embodiment, the steam heater 30 corresponds to the first heat exchanger.

[0029] <Suppression of creep failure in heat exchangers> In this way, the pressure reduction section 22 reduces the pressure of the secondary helium gas. Therefore, the steam pressure can be adjusted to the pressure required for the purpose. This eliminates the need to reinforce the heat exchanger tubes of the steam heater 30 to withstand pressure. In addition, since the pressure reduction section 22 reduces the pressure of the secondary helium gas, the risk of creep failure in the heat exchanger tubes can be reduced.

[0030] The secondary helium gas that passes through the steam heater 30 is transported via the secondary helium gas circulation path L63 and then splits into two branches at the supply header 23. One branch is transported to the steam generator 31 via the secondary helium gas circulation path L64. The other branch is transported to the second air heater 32 via the secondary helium gas circulation path L66.

[0031] <Steam Generation> The second heat exchanger (steam generator) 31 is a heat exchanger using heat exchanger tubes, which transfers heat from secondary helium gas to water to generate steam. In the steam generator 31, heat exchange is performed with the already depressurized secondary helium gas, so pressurization of the steam, which is the recipient of the heat exchange, is not necessary. This eliminates the need to make the heat exchanger tubes of the steam generator 31 pressure-resistant. In addition, since the pressure of the secondary helium gas is reduced by the depressurization section 22, the risk of creep failure in the heat exchanger tubes of the steam generator 31 can be reduced.

[0032] <Generation of heated air> The third heat exchanger (second air heater) 32 is a heat exchanger using heat exchanger tubes, which transfers heat from secondary helium gas to air. In the second air heater 32, heat is exchanged with already depressurized secondary helium gas, so pressurization of the air, which is the recipient of the heat exchange, is not necessary. This eliminates the need to make the heat exchanger tubes of the second air heater 32 pressure-resistant. In addition, since the pressure of the secondary helium gas is reduced by the depressurization section 22, the risk of creep failure in the heat exchanger tubes of the second air heater 32 can be reduced.

[0033] The secondary helium gas that has passed through the steam generator 31 returns to the return header 24 via the secondary helium gas circulation path L65. Similarly, the secondary helium gas that has passed through the second air heater 32 also returns to the return header 24 via the secondary helium gas circulation path L67. The secondary helium gas that has merged in the return header 24 is transported to the compressor 21 via the secondary helium gas circulation path L68.

[0034] <Pressurization with secondary helium gas using a compressor> As mentioned above, the kinetic energy obtained by the prime mover 20 upstream is transmitted to the compressor 21, thereby compressing the secondary helium gas. For example, the secondary helium gas can be pressurized to 7 MPa. The secondary helium gas pressurized by the compressor 21 returns to the intermediate heat exchanger 10 via the secondary helium gas circulation path L69.

[0035] Furthermore, since the intermediate heat exchanger 10, the prime mover 20, the compressor 21, and the pressure reducing unit 22 are connected in series via circulation paths L60-63 and L68-69, it is possible to more efficiently reduce and increase the pressure of the secondary helium gas passing through the intermediate heat exchanger 10. In addition, the kinetic energy obtained by the prime mover 20 upstream is transmitted to the compressor 21, enabling energy generation. Thus, since the intermediate heat exchanger 10, the prime mover 20, the compressor 21, and the pressure reducing unit 22 are connected in series via circulation paths, the energy of the secondary helium gas from the prime mover 20 can drive the compressor 21 to increase the pressure of the secondary helium gas, and furthermore, the pressure reducing unit 22 can reduce the pressure of the secondary helium gas to the desired pressure.

[0036] In this way, because the secondary helium gas is depressurized, the connection relationship between the heat exchangers 30-32 between the second circulation system 3 and the hydrogen production system 4 can be freely configured. This makes it possible to suppress the generation of creek in the heat exchanger tubes of the heat exchangers 30-32 while improving the efficiency of hydrogen production in the high-temperature steam electrolysis device 100.

[0037] <Hydrogen production system> The hydrogen production system 4 according to this embodiment includes a high-temperature steam electrolysis device 100, a hydrogen separation device 200, and a plurality of heat exchangers 33 to 34.

[0038] <Water supply to the steam generator and steam generation> The water supplied to the steam generator 31 is transported from the feedwater valve 25 to the fourth heat exchanger (feedwater heater) 33 via the feedwater path L70. The feedwater heater 33 is a heat exchanger using heat exchanger tubes, and it heats the water by extracting the heat from the generated and separated hydrogen. The water heated in the feedwater heater 33 is transported to the steam generator 31 via the feedwater path L71. In the steam generator 31, as described above, the heat from the secondary helium gas is transferred to the water to generate steam.

[0039] <Steam supply to high-temperature steam electrolysis equipment> The steam generated in the steam generator 31 merges with the steam supply path L74 via the steam supply path L72. The steam that merges with the steam supply path L74 is transported to the connected steam heater 30. In the steam heater 30, as described above, superheated steam is generated by transferring heat from secondary helium gas to the steam via a heat exchanger. The superheated steam generated in the steam heater 30 is transported to the hydrogen electrode side cavity of the high-temperature steam electrolysis device 100 via the steam supply path L73.

[0040] <Preheating of air> The fifth heat exchanger (first air heater) 34 is a heat exchanger using heat exchanger tubes, and the high-temperature air supplied to the high-temperature steam electrolysis device 100 is preheated by the first air heater 34 in order to minimize heat loss as much as possible. The intake air is transported to the second air heater 32 via the air supply path L80.

[0041] In this way, the first air heater 34 extracts the heat from the oxygen gas electrolyzed and produced in the high-temperature steam electrolysis device 100 through heat exchange and preheats the intake air. The air preheated in the first air heater 34 is transported to the second air heater 32 via the air supply path L81.

[0042] <Supply of High-Temperature Air to High-Temperature Steam Electrolysis Device> As described above, in the second air heater 32, the air preliminarily heated by the heat of the secondary helium gas is further heated by heat exchange. In the second air heater 32, the heated high-temperature air is transported to the oxygen electrode side cavity of the high-temperature steam electrolysis device 100 via the air supply path L82.

[0043] <Steam Electrolysis in SOEC Stack> In the high-temperature steam electrolysis device 100, a solid oxide type electrochemical cell (SOEC: Solid Oxide Electrolysis Cell) is used to produce hydrogen by electrolysis from the supplied superheated steam and high-temperature air at a high temperature of about 700°C to 800°C. Note that the high-temperature steam electrolysis device 100 may be referred to as a high-temperature steam electrolysis device SOEC cell.

[0044] The supply electricity for electrolysis is generated by the generator 11 from the primary helium gas generated in the high-temperature gas furnace 5 and supplied to the high-temperature steam electrolysis device 100 via the electricity supply path L50. In the solid oxide type electrochemical cell, the steam supplied to the hydrogen electrode side cavity is electrolyzed, and the reaction of chemical formula (1) occurs.

[0045] Hydrogen electrode side: 2H2O + 4e - → 2H2 + 2O2 - (1) The electrolyzed oxygen ions O2- are conducted through the electrolyte membrane made of ceramic, and the reaction of chemical formula (2) occurs on the oxygen electrode side.

[0046] Oxygen electrode side: 2O2 - → O2 + 4e - (2) From the above, hydrogen is generated on the hydrogen electrode side and oxygen is generated on the oxygen electrode side. <(

[0047] <Exhaust of Oxygen from Oxygen Electrode Side of High-Temperature Steam Electrolysis Device> The oxygen gas generated in the solid oxide electrochemical cell is transported to the oxygen circulation path L93 by high-temperature air supplied to the oxygen electrode side cavity of the high-temperature steam electrolysis device 100. At the same time, the high-temperature air maintains the electrode temperature of the oxygen electrode at a high temperature, compensating for the heat absorbed during electrolysis. By discharging oxygen from the oxygen electrode side cavity and diluting the oxygen concentration in the oxygen electrode atmosphere, it is possible to prevent the open-circuit voltage from rising and the operating voltage range from narrowing.

[0048] <Hydrogen emissions from the hydrogen electrode side of a high-temperature steam electrolysis device> The steam-hydrogen mixed gas generated by electrolysis in the solid oxide electrochemical cell is transported to the steam-hydrogen mixed gas circulation path L90 by steam supplied to the hydrogen electrode side cavity of the high-temperature steam electrolysis device 100.

[0049] <Separation of steam and hydrogen> The vapor-hydrogen mixed gas produced by electrolysis in a solid oxide electrochemical cell is transported to a hydrogen separator 200 via a vapor-hydrogen mixed gas circulation path L90. The hydrogen separator 200 separates the vapor from the hydrogen. The hydrogen separator 200 is composed of, for example, a separation membrane, or a hydrogen storage alloy.

[0050] <Reflux of high-temperature steam> The high-temperature steam from which hydrogen has been separated in the hydrogen separator 200 is returned to the steam heater 30 via the steam supply path L74. This allows for the effective utilization of waste heat.

[0051] <Hydrogen waste heat recovery> The hydrogen separated in the hydrogen separator 200 is transported to the feedwater heater 33 via the hydrogen circulation path L91. In the feedwater heater 33, as described above, the water supplied to the steam generator 31 is heated using the heat from the hydrogen through a heat exchanger. This allows for the effective utilization of the waste heat from the hydrogen. In the steam generator 31, the hydrogen recovered from the waste heat is recovered from the hydrogen circulation path L92.

[0052] <Oxygen waste heat recovery> The oxygen electrolyzed and produced in the solid oxide electrochemical cell is transported to the first air heater 34 via the oxygen circulation path L93. In the first air heater 34, as described above, the supply air is preheated using the heat from the oxygen through heat exchange. This allows for the effective utilization of the waste heat from the oxygen. The oxygen recovered from the waste heat in the first air heater 34 is recovered from the oxygen circulation path L94.

[0053] Figure 2 is a flowchart showing an example of the hydrogen production system 1. As shown in Figure 2, primary helium gas heated to over 700°C circulating in the primary helium gas circulation path and secondary helium gas circulating in the secondary helium gas circulation path exchange heat in the intermediate heat exchanger 10 (step S100).

[0054] Next, the depressurization unit 22 depressurizes the secondary helium gas in the secondary helium gas circulation path (step S102) and supplies it to the multiple heat exchangers 30-32, where it exchanges heat with water vapor and air (step S104).

[0055] The high-temperature steam electrolysis apparatus 100 generates hydrogen and oxygen using steam and air heated in multiple heat exchangers 30 to 32 (step S106).

[0056] As described above, according to this embodiment, the first circulation system 2 in which primary helium gas circulates and the second circulation system 3 in which secondary helium gas circulates are separated by an intermediate heat exchanger 10, and the second circulation system 3 and the hydrogen production system 4 are separated by a plurality of heat exchangers 30 to 32. In addition, the pressure of the second heat transfer medium suitable for heat exchange in the intermediate heat exchanger 10 is reduced in the pressure reduction section 22 to a pressure suitable for the plurality of heat exchangers 30 to 32 used for heat exchange with the hydrogen production system 4. This makes it possible to suppress creep failure of the heat exchanger tubes in the heat exchangers 30 to 32 that exchange heat between steam, air supplied to the high-temperature steam electrolysis apparatus 100 and secondary helium gas, while maintaining the heat exchange rate between primary helium gas and secondary helium gas.

[0057] (Second Embodiment) The hydrogen production system according to the second embodiment is different from the hydrogen production system according to the first embodiment in that the SOEC stack heater 35 is further configured in the high-temperature steam electrolyzer 100. Hereinafter, the differences from the hydrogen production system according to the first embodiment will be described.

[0058] FIG. 2 is a diagram showing a configuration example of the hydrogen production system according to the second embodiment. As shown in FIG. 2, the SOEC stack heater 35 is further configured. In the present embodiment, the circulation region of the secondary helium gas in the second circulation system 3 is indicated by a one-dot chain line L20.

[0059] Hereinafter, the circulation path of the secondary helium gas will be described.

[0060] <Circulation of secondary helium gas> The secondary helium gas generated in the intermediate heat exchanger 10 is transported to the prime mover 20 via the secondary helium gas circulation path L60. The secondary helium gas that has worked in the prime mover 20 is transported to the decompression unit 22 via the secondary helium gas circulation path L61. In the decompression unit 22, the secondary helium gas is decompressed to a predetermined pressure, for example, 0.3 MPa.

[0061] <Heating of SOEC> The secondary helium gas decompressed in the decompression unit 22 is transported to the SOEC stack heater 35 via the secondary helium gas circulation path L62a. In the SOEC stack heater 35, the SOEC itself is heated using the heat of the secondary helium gas. During electrolysis in the SOEC stack 102, the temperature decreases due to an endothermic reaction, so the SOEC stack heater 35 can suppress unnecessary heat loss.

[0062] The secondary helium gas that has passed through the SOEC stack heater 35 is transported to the steam heater 30 via the secondary helium gas circulation path L62b. Downstream of this in the circulation path of the secondary helium gas is the same as in the first embodiment.

[0063] As described above, according to this embodiment, the SOEC stack 102 is heated by the SOEC stack heater 35, making it possible to suppress heat loss and further improve hydrogen production efficiency.

[0064] (Third embodiment) The hydrogen production system according to the third embodiment differs from the hydrogen production system according to the first embodiment in that the prime mover 20 generates prime mover power using superheated steam generated in the steam heater 30. The differences from the hydrogen production system according to the first embodiment will be explained below.

[0065] Figure 3 shows an example configuration of a hydrogen production system according to the fourth embodiment. As shown in Figure 2, the prime mover 20 recovers its power from the thermal energy of the superheated steam generated in the steam heater 30. In this embodiment, the circulation region of the secondary helium gas in the second circulation system 3 is indicated by the dashed line L30.

[0066] The circulation and vapor supply pathways for secondary helium gas will be described in more detail. <Secondary helium gas circulation> The secondary helium gas generated in the intermediate heat exchanger 10 is transported to the depressurization section 22 via the secondary helium gas circulation path L60. Downstream from this point, the configuration is the same as in the first embodiment.

[0067] <Steam supply path> In the steam heater 30, superheated steam is generated by transferring heat from secondary helium gas to the steam through heat exchange. The superheated steam generated in the steam heater 30 is transported to the steam supply header 26 via the steam supply path L73. The superheated steam, which is split into two at the steam supply header 26, is transported to the SOEC stack 102 via the steam supply path L75, and the other is transported to the prime mover 20 via the steam supply path L76.

[0068] <Steam recovery> The prime mover 20 recovers the thermal energy of the superheated steam supplied from the steam supply path L76 and converts it into kinetic energy. The superheated steam from which the thermal energy has been recovered becomes saturated steam and partially condensed water droplets, which then pass through the steam supply path L77 and merge with the steam supply path L70, where it is heated again in the feedwater heater 33.

[0069] As described above, according to this embodiment, a portion of the heated steam generated by the steam heater 30 is converted into kinetic energy for the prime mover 20, and this kinetic energy is consumed by the connected compressor 21. This makes it possible to drive the prime mover 20 with steam at a pressure equivalent to that of the steam supplied to the SOEC stack 102.

[0070] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0071] 1: Hydrogen production system, 2: First circulation system, 3: Second circulation system, 4: Hydrogen production system, 5: High-temperature gas reactor, 10: Intermediate heat exchanger, 11: Generator, 20: Prime mover, 21: Compressor, 22: Pressure reducing section, 23: Supply header, 24: Return header, 25: Feedwater valve, 26: Steam supply header, 30: First heat exchanger (steam heater), 31: Second heat exchanger (steam generator), 32: Third heat exchanger (second air heater), 33: Fourth heat exchanger (feedwater heater), 34: Fifth heat exchanger (first air heater), 35: SOEC stack heater, 100: High Hot water steam electrolysis unit, 200: Hydrogen separator, L40, L41, L42: Primary helium gas circulation path, L50: Electricity supply path, L60, L61, L62, L62a, L62b, L63, L64, L65, L66, L67, L68, L69: Secondary helium gas circulation path, L70, L71: Water path, L72, L73, L74, L75, L76, L77: Steam supply path, L80, L81, L82: Air supply path, L90: Hydrogen / steam mixed gas circulation path, L91, L92: Hydrogen circulation path, L93, L94: Oxygen circulation path

Claims

1. A first circulation system having a first circulation path through which a first heat transfer medium heated to over 700°C circulates, A second circulation system having a second circulation path through which a second heat transfer medium circulates, An intermediate heat exchanger that exchanges heat between the first heat transfer medium of the first circulation system and the second heat transfer medium of the second circulation system, A pressure reduction section that reduces the pressure of the second heat transfer medium in the second circulation system, A high-temperature steam electrolysis apparatus for producing hydrogen and oxygen, A first heat exchanger exchanges heat between the second heat transfer medium, which has been depressurized in the depressurization section, and at least steam supplied to the high-temperature steam electrolysis apparatus, using heat exchanger heat transfer tubes. A hydrogen production system equipped with the following features.

2. The system further includes a compressor that increases the pressure of the second heat transfer medium, The hydrogen production system according to claim 1, wherein the second heat transfer medium, after its pressure has been increased by the compressor, is supplied to the intermediate heat exchanger.

3. The system further comprises a prime mover that uses the second heat transfer medium in the second circulation path between the intermediate heat exchanger and the pressure reduction section, The hydrogen production system according to claim 2, wherein the compressor is driven by the prime mover.

4. A second heat exchanger exchanges heat between the second heat transfer medium that has passed through the first heat exchanger and the steam supplied to the first heat exchanger via heat exchanger heat transfer tubes, The hydrogen production system according to claim 2, further comprising the above.

5. A third heat exchanger exchanges heat between the second heat transfer medium, which has been depressurized in the aforementioned depressurization section, and the air supplied to the high-temperature steam electrolysis apparatus, using heat exchanger heat transfer tubes. The hydrogen production system according to claim 4, further comprising the above.

6. The second circulation path is branched by a heat transfer medium supply header, the second heat exchanger exchanges heat between the second heat transfer medium in one branch path and the steam, and the third heat exchanger exchanges heat between the second heat transfer medium in the other branch path and the air. The hydrogen production system according to claim 5, wherein the one branch path and the other branch path merge at a heat transfer medium return header, and the compressor increases the pressure of the second heat transfer medium after the merger.

7. The apparatus further includes a hydrogen separator for separating the hydrogen from a mixed gas of hydrogen electrolyzed in the high-temperature steam electrolysis apparatus and unreacted steam, The hydrogen production system according to claim 1, wherein the steam gas after the hydrogen has been separated by the hydrogen separator is supplied to the first heat exchanger via a steam supply path.

8. The hydrogen production system according to claim 1, further comprising a stack heating device for heating the high-temperature steam electrolysis device using the second heat transfer medium that has been depressurized in the depressurization section.

9. The system further comprises a prime mover that uses at least a portion of the steam supplied from the first heat exchanger, The hydrogen production system according to claim 2, wherein the compressor is driven by the prime mover.

10. The hydrogen production system according to any one of claims 1 to 9, wherein the first heat transfer medium and the second heat transfer medium are helium gas.

11. A first heat transfer medium heated to over 700°C circulates in the first circulation path, and a second heat transfer medium circulating in the second circulation path undergoes primary heat exchange. The pressure of the second heat transfer medium in the second circulation path is reduced, A method for producing hydrogen, wherein at least steam supplied to a high-temperature steam electrolysis apparatus for producing hydrogen and oxygen undergoes secondary heat exchange with the second heat transfer medium whose pressure has been reduced.

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