Steam electrolysis system

Abstract

To provide a steam electrolysis system that can effectively collect the exhaust heat of a steam electrolytic cell.SOLUTION: A steam electrolysis system 1 comprises a steam electrolytic cell 2 and a heat exchanger 3. The steam electrolytic cell 2 includes a hydrogen electrode chamber 22 for generating hydrogen from steam W1 and an oxygen electrode chamber 23 for generating oxygen from air A1, with a solid electrolyte 21 having ion conductivity therebetween. The heat exchanger 3 includes: a steam supply channel 31 for supplying the steam W1 to the hydrogen electrode chamber 22; a hydrogen discharge channel 32 for discharging hydrogen mixed steam W2 from the hydrogen electrode chamber 22; an air supply channel 33 for supplying the air A1 to the oxygen electrode chamber 23; and an oxygen discharge channel 34 for discharging an oxygen mixed air A2 from the oxygen electrode chamber 23. At least three of the steam supply channel 31, the air supply channel 33, the hydrogen discharge channel 32, and the oxygen discharge channel 34 are stacked next to each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a steam electrolysis system. [Background technology]

[0002] Fuel cell systems include SOFCs (Solid Oxide Fuel Cells), which generate electricity using an electrochemical reaction between hydrogen and oxygen, and SOECs (Solid Oxide Electrolysis Cells), which electrolyze high-temperature steam to produce hydrogen and generate electricity. A steam electrolysis system is composed of a steam electrolysis cell (SOEC) made of a solid electrolyte with a hydrogen electrode and an oxygen electrode, and a heat exchanger for recovering the exhaust heat from the steam electrolysis cell. In the steam electrolysis cell, high-temperature steam that comes into contact with the hydrogen electrode is decomposed into hydrogen and oxide ions, and electrons are released when the oxide ions pass through the solid electrolyte toward the oxygen electrode, generating electricity.

[0003] In order to increase the thermal efficiency of the steam electrolysis system, the exhaust heat from the steam electrolysis cell is recovered by a heat exchanger. For example, in the high-temperature steam electrolysis system described in Patent Document 1, the hydrogen regeneration heat exchanger heats water for generating steam to be supplied to the hydrogen electrode chamber of the high-temperature steam electrolysis cell with hydrogen-enriched steam discharged from the high-temperature steam electrolysis cell. In addition, the oxygen regeneration heat exchanger heats air to be supplied to the oxygen electrode chamber of the high-temperature steam electrolysis cell with oxygen-enriched air discharged from the high-temperature steam electrolysis cell. This configuration makes it possible to eliminate the need for a heat exchanger for heating air and to supply air and steam to the high-temperature steam electrolysis cell at approximately the same temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-120900 A Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors' research has revealed that there is room for improvement in the efficiency of recovering exhaust heat from a steam electrolysis cell depending on the configuration of the heat exchanger of the steam electrolysis system described in Patent Document 1 and the like. In Patent Document 1, heat exchange is performed only in the path leading to the hydrogen electrode chamber, and only in the path leading to the oxygen electrode chamber. However, it has been found that in order to more effectively recover exhaust heat from a steam electrolysis cell, it is effective to also take into account the difference in heat capacity between the fluids, namely, steam, hydrogen-enriched steam, air, and oxygen-enriched air. Therefore, further ingenuity is required to effectively recover exhaust heat from a steam electrolysis cell.

[0006] The present invention has been made in view of the above problems, and aims to provide a steam electrolysis system capable of effectively recovering exhaust heat from a steam electrolysis cell. [Means for solving the problem]

[0007] One aspect of the present invention is a water vapor electrolysis cell (2) including a hydrogen electrode chamber (22) in which hydrogen is produced from water vapor (W1) and an oxygen electrode chamber (23) in which oxygen is produced from air (A1), with an ion-conductive solid electrolyte body (21) interposed therebetween; a heat exchanger (3) formed with a water vapor supply passage (31) for supplying the water vapor to the hydrogen electrode chamber, a hydrogen discharge passage (32) through which hydrogen-mixed water vapor (W2) is discharged from the hydrogen electrode chamber, an air supply passage (33) for supplying the air to the oxygen electrode chamber, and an oxygen discharge passage (34) through which oxygen-mixed air (A2) is discharged from the oxygen electrode chamber, At least three of the steam supply flow path, the air supply flow path, the hydrogen discharge flow path and the oxygen discharge flow path are stacked adjacent to one another in the steam electrolysis system (1). Effect of the Invention

[0008] In the steam electrolysis system of the above aspect, at least three of the water vapor supply channel, the air supply channel, the hydrogen exhaust channel, and the oxygen exhaust channel are stacked adjacent to one another. With this configuration, the heat exchanger can perform heat exchange between at least three of water vapor, hydrogen-mixed water vapor, air, and oxygen-mixed air, each of which has a different heat capacity. In other words, heat exchange can also be performed between water vapor or hydrogen-mixed water vapor connected to the hydrogen electrode chamber and air or oxygen-mixed air connected to the oxygen electrode chamber.

[0009] Therefore, according to the steam electrolysis system of the above aspect, the exhaust heat of the steam electrolysis cell can be effectively recovered.

[0010] In addition, the symbols in parentheses for each component shown in one aspect of the present invention indicate a correspondence with the symbols in the figures in the embodiment, but do not limit each component to only the contents of the embodiment. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of a steam electrolysis system according to a first embodiment. [Diagram 2] FIG. 2 is a perspective view illustrating a schematic diagram of a steam electrolysis system according to the first embodiment. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a steam electrolysis system according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A preferred embodiment of the above-mentioned steam electrolysis system will be described with reference to the drawings. <Embodiment 1> As shown in Fig. 1 and Fig. 2, the water vapor electrolysis system 1 of this embodiment includes a water vapor electrolysis cell 2 and a heat exchanger 3. The water vapor electrolysis cell 2 includes a hydrogen electrode chamber 22 in which hydrogen is produced from water vapor W1 and an oxygen electrode chamber 23 in which oxygen is produced from air A1, with a solid electrolyte body 21 having ion conductivity therebetween. The heat exchanger 3 includes a water vapor supply flow path 31 for supplying water vapor W1 to the hydrogen electrode chamber 22, a hydrogen discharge flow path 32 for discharging hydrogen-mixed water vapor W2 from the hydrogen electrode chamber 22, an air supply flow path 33 for supplying air A1 to the oxygen electrode chamber 23, and an oxygen discharge flow path 34 for discharging oxygen-mixed air A2 from the oxygen electrode chamber 23. At least three of the water vapor supply flow path 31, the air supply flow path 33, the hydrogen discharge flow path 32, and the oxygen discharge flow path 34 are stacked adjacent to one another.

[0013] The steam electrolysis system 1 of this embodiment will be described in detail below. (Steam electrolysis system 1) 1 and 2, a steam electrolysis system 1 is configured to generate power using a steam electrolysis cell 2 serving as a solid oxide electrolysis cell (SOEC), and to recover exhaust heat from the steam electrolysis cell 2 using a heat exchanger 3. The steam electrolysis system 1 may operate as a hydrogen production system, since hydrogen is produced in a hydrogen electrode chamber 22. The hydrogen produced in the hydrogen electrode chamber 22 may be extracted through a hydrogen discharge passage 32 and used for various purposes. In addition, oxygen produced in the oxygen electrode chamber 23 may be extracted through an oxygen discharge passage 34 and used for various purposes.

[0014] (Steam electrolysis cell 2) As shown in Fig. 1, the water vapor electrolysis cell 2 has a solid electrolyte body 21 provided with a hydrogen electrode 221 and an oxygen electrode 231, a hydrogen electrode chamber 22 formed adjacent to one side of the solid electrolyte body 21 in a state in which the hydrogen electrode 221 is housed, and an oxygen electrode chamber 23 formed adjacent to the other side of the solid electrolyte body 21 in a state in which the oxygen electrode 231 is housed. The solid electrolyte body 21 contains oxide ions (O 2-) and is formed in a plate shape. The hydrogen electrode 221 is provided on one surface of the solid electrolyte body 21 and serves to generate hydrogen and oxide ions from water vapor W1. The oxygen electrode 231 is provided on the other surface of the solid electrolyte body 21 and serves to generate oxygen from oxide ions that permeate the solid electrolyte body 21.

[0015] The solid electrolyte body 21 is made of a perovskite-type oxide, yttria-stabilized zirconia, yttria-partially-stabilized zirconia, etc. The hydrogen electrode 221 is made of a material such as a metal or a metal compound having catalytic activity against water vapor W1, and the oxygen electrode 231 is made of a material such as a metal or a metal compound having catalytic activity against oxygen.

[0016] In the steam electrolysis cell 2 of this embodiment, the solid electrolyte body 21, the hydrogen electrode chamber 22, and the oxygen electrode chamber 23 are formed in a shape that is elongated in the axial direction L. The axial direction L refers to the longitudinal direction of the steam electrolysis cell 2. The steam electrolysis cell 2 is formed as a cell stack in which a plurality of cells are stacked. The plurality of cells that constitute the steam electrolysis cell 2 of this embodiment are stacked in a direction perpendicular to the axial direction L.

[0017] The hydrogen electrode chamber 22 is formed with a water vapor inlet 222 through which water vapor W1 is introduced, and a hydrogen outlet 223 through which water vapor W1 mixed with hydrogen is discharged. The oxygen electrode chamber 23 is formed with an air inlet 232 through which air A1 is introduced, and an oxygen outlet 233 through which air A1 mixed with oxygen is discharged. The water vapor inlet 222, hydrogen outlet 223, air inlet 232, and oxygen outlet 233 of this embodiment are disposed distributed on both sides of the axial direction L of the water vapor electrolysis cell 2.

[0018] At the hydrogen electrode 221 of the water vapor electrolysis cell 2, H2O+2e - →H2+O 2- At the oxygen electrode 231 of the water vapor electrolysis cell 2, 2- →1 / 2O2+2e -The electrolytic reaction of the water vapor W1 is an endothermic reaction, while the water vapor electrolysis cell 2 generates heat due to Joule heat caused by the electrical resistance generated in the solid electrolyte body 21 and the overvoltage generated in the hydrogen electrode 221 and the oxygen electrode 231 during power generation. By balancing the heat absorption due to the electrolytic reaction and the heat generated by Joule heat, it is possible to maintain a predetermined operating temperature and a predetermined operating voltage without heating the water vapor electrolysis cell 2 with a heat source.

[0019] Heat may be provided from an external source during start-up of the water vapor electrolysis cell 2. The water vapor W1 sent to the heat exchanger 3 may be generated by heating water using a heating device or the like connected to the heat exchanger 3.

[0020] (heat exchanger 3) 1, the heat exchanger 3 performs heat exchange of at least three of the water vapor W1, hydrogen-mixed water vapor W2, air A1, and oxygen-mixed air A2. The heat exchanger 3 of this embodiment is configured to perform heat exchange of four of the water vapor W1, hydrogen-mixed water vapor W2, air A1, and oxygen-mixed air A2. Specifically, the water vapor supply passage 31, the air supply passage 33, the hydrogen discharge passage 32, and the oxygen discharge passage 34 are stacked adjacent to each other in the order of a first supply side passage S1 which is one of the water vapor supply passage 31 or the air supply passage 33, a first discharge side passage E1 which is one of the hydrogen discharge passage 32 or the oxygen discharge passage 34, a second supply side passage S2 which is the other of the water vapor supply passage 31 or the air supply passage 33, and a second discharge side passage E2 which is the other of the hydrogen discharge passage 32 or the oxygen discharge passage 34.

[0021] This configuration allows heat exchange to occur between the four fluids, namely, water vapor W1, hydrogen-mixed water vapor W2, air A1, and oxygen-mixed air A2, which flow in and out of the water vapor electrolysis cell 2. This makes it easier for the temperatures of the four fluids flowing in and out of the water vapor electrolysis cell 2 to reach equilibrium, making it easier to recover waste heat from the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2 into the water vapor W1 and air A1.

[0022] The heat capacity of a fluid is expressed by the product of density, flow rate, and specific heat, and the heat quantity of a fluid is expressed by the product of heat capacity and temperature difference. The density of each fluid is highest in the order of oxygen-mixed air A2, air A1, water vapor W1, and hydrogen-mixed water vapor W2. The specific heat of each fluid is highest in the order of hydrogen-mixed water vapor W2, water vapor W1, air A1, and oxygen-mixed air A2. The temperature of each fluid is highest in the order of hydrogen-mixed water vapor W2 and oxygen-mixed air A2, water vapor W1, and air A1.

[0023] The oxygen-mixed air A2 has the highest heat capacity among the four fluids flowing in and out of the steam electrolysis cell 2. Therefore, in order to effectively recover the exhaust heat from the steam electrolysis cell 2, it is preferable to perform heat exchange between the oxygen exhaust flow path 34 and the steam supply flow path 31 and the air supply flow path 33.

[0024] Furthermore, the hydrogen-mixed air A1 has the lowest heat capacity among the four fluids that flow in and out of the steam electrolysis cell 2. Therefore, in order to minimize heat radiation from the steam electrolysis cell 2 to the outside, it is preferable to place the hydrogen discharge flow path 32 at the outermost position farthest from the steam electrolysis cell 2 among the steam supply flow path 31, the air supply flow path 33, the hydrogen discharge flow path 32, and the oxygen discharge flow path 34 that constitute the heat exchanger 3.

[0025] In order to effectively recover the exhaust heat of the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2 to the water vapor W1 and the air A1, it is effective to perform heat exchange between the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2 and the water vapor W1 and the air A1 in an integrated manner. To achieve this, four flow paths, a first supply side flow path S1, a first discharge side flow path E1, a second supply side flow path S2, and a second discharge side flow path E2, are formed adjacent to each other in sequence.

[0026] As shown in Figs. 1 and 2, the heat exchanger 3 of this embodiment is formed in a ring shape surrounding the steam electrolysis cell 2. More specifically, the heat exchanger 3 of this embodiment is formed in a cylindrical shape surrounding the central axis of the steam electrolysis cell 2. The central axis of the steam electrolysis cell 2 refers to an imaginary line passing through the center position of the steam electrolysis cell in the axial direction L. The first supply side flow passage S1, the first discharge side flow passage E1, the second supply side flow passage S2, and the second discharge side flow passage E2 are stacked adjacent to each other in the radial direction R centered on the steam electrolysis cell 2. The first supply side flow passage S1, the first discharge side flow passage E1, the second supply side flow passage S2, and the second discharge side flow passage E2 are each formed in a cylindrical shape overlapping each other in the radial direction R. The first supply side flow passage S1, the first discharge side flow passage E1, the second supply side flow passage S2, and the second discharge side flow passage E2 are each formed by being partitioned by a partition wall 35.

[0027] In this embodiment, the water vapor supply passage 31 is the first supply side passage S1, the oxygen discharge passage 34 is the first discharge side passage E1, the air supply passage 33 is the second supply side passage S2, and the hydrogen discharge passage 32 is the second discharge side passage E2. In the cylindrical heat exchanger 3, the water vapor supply passage 31, the oxygen discharge passage 34, the air supply passage 33, and the hydrogen discharge passage 32 are sequentially stacked from the inner periphery side in the radial direction R centered on the central axis of the water vapor electrolysis cell 2. With this configuration, in the heat exchanger 3, the water vapor supply passage 31 and the air supply passage 33 are stacked adjacent to each other on both sides of the oxygen discharge passage 34. With this configuration, the exhaust heat of the oxygen-mixed air A2 flowing through the oxygen discharge passage 34 can be effectively recovered. In addition, since the hydrogen discharge passage 32 is disposed on the outermost side of the heat exchanger 3 in the radial direction R, heat radiation from the heat exchanger 3 to the outside can be suppressed.

[0028] 1, the first supply flow path S1, the first discharge flow path E1, the second supply flow path S2, and the second discharge flow path E2 are configured so that adjacent flow paths form countercurrents in which the fluids, namely, water vapor W1, hydrogen-mixed water vapor W2, air A1, or oxygen-mixed air A2, flow in opposite directions. This configuration makes it possible to more effectively exchange heat between the fluids on the supply side of the water vapor W1 and air A1 and the fluids on the discharge side of the hydrogen-mixed water vapor W2 and oxygen-mixed air A2.

[0029] The flow inlets 311, 331 in the first supply side flow passage S1 and the second supply side flow passage S2 are formed on one side of the axial direction L of the heat exchanger 3, and the flow inlets 321, 341 in the first discharge side flow passage E1 and the second discharge side flow passage E2 are formed on the other side of the axial direction L of the heat exchanger 3. The flow outlets 312, 332 in the first supply side flow passage S1 and the second supply side flow passage S2 are formed on the other side of the axial direction L of the heat exchanger 3, and the flow outlets 322, 342 in the first discharge side flow passage E1 and the second discharge side flow passage E2 are formed on one side of the axial direction L of the heat exchanger 3. The fluids in the first supply side flow passage S1 and the second supply side flow passage S2 flow from one side to the other side of the axial direction L of the heat exchanger 3, and the fluids in the first discharge side flow passage E1 and the second discharge side flow passage E2 flow from the other side to one side of the axial direction L of the heat exchanger 3.

[0030] In Fig. 1, the flow path inlet of the water vapor supply flow path 31 (first supply side flow path S1) is indicated by reference numeral 311, and the flow path outlet of the water vapor supply flow path 31 (first supply side flow path S1) is indicated by reference numeral 312. The flow path inlet of the oxygen exhaust flow path 34 (first exhaust side flow path E1) is indicated by reference numeral 341, and the flow path outlet of the oxygen exhaust flow path 34 (first exhaust side flow path E1) is indicated by reference numeral 342. The flow path inlet of the air supply flow path 33 (second supply side flow path S2) is indicated by reference numeral 331, and the flow path outlet of the air supply flow path 33 (second supply side flow path S2) is indicated by reference numeral 332. The flow path inlet of the hydrogen exhaust flow path 32 (second exhaust side flow path E2) is indicated by reference numeral 321, and the flow path outlet of the hydrogen exhaust flow path 32 (second exhaust side flow path E2) is indicated by reference numeral 322.

[0031] Here, in Fig. 1, the positions of the flow passage inlets 311, 321, 331, and 341 and the flow passage outlets 312, 322, 332, and 342 are shown diagrammatically for the sake of simplicity. Also, in Fig. 2, a radiation heat recovery device 4, a heat transfer suppressing layer 5, and a heat dissipation suppressing layer 6, which will be described later, are omitted.

[0032] The water vapor supply flow path 31, the oxygen exhaust flow path 34, the air supply flow path 33, and the hydrogen exhaust flow path 32 are each connected to the steam electrolysis cell 2 via a pipe 7. For each of the water vapor supply flow path 31, the oxygen exhaust flow path 34, the air supply flow path 33, and the hydrogen exhaust flow path 32, the flow path inlets 311, 321, 331, and 341 and the flow path outlets 312, 322, 332, and 342 are formed at positions that are 180° apart in the circumferential direction C of the heat exchanger 3. This configuration makes it possible to appropriately ensure the flow paths of each fluid in each of the flow paths 31, 32, 33, and 34. The circumferential direction C refers to the direction around the central axis of the steam electrolysis cell 2.

[0033] (Radiative heat recovery device 4) During operation, the steam electrolysis cell 2 reaches a high temperature of about 700°C, and the heat is released to the outside as radiant heat. The heat exchanger 3 in this embodiment is formed in a cylindrical shape surrounding the steam electrolysis cell 2 for the purposes of reducing heat release from the steam electrolysis cell 2 to the outside and for the purposes of reducing the size of the steam electrolysis system 1.

[0034] As shown in Fig. 1, a radiant heat recovery device 4 is stacked on the inner periphery of the cylindrical heat exchanger 3 in order to minimize heat radiation from the steam electrolysis cell 2 to the outside. In other words, the radiant heat recovery device 4 is disposed in the cylindrical heat exchanger 3 at a position closest to the steam electrolysis cell 2, for recovering radiant heat emitted from the steam electrolysis cell 2. By using the radiant heat recovery device 4, it is possible to effectively recover radiant heat from the steam electrolysis cell 2. The air A1 from which radiant heat is recovered may be the air A1 flowing through the air supply flow path 33. The air A1 flowing through the air supply flow path 33 has the lowest temperature of the four fluids flowing in and out of the steam electrolysis cell 2, and is therefore easy to recover heat from.

[0035] The radiant heat recovery device 4 is formed in a cylindrical shape along the inner circumferential surface of the cylindrical heat exchanger 3. The radiant heat recovery device 4 has a plurality of recovery flow paths 41 formed to overlap in the radial direction R of the heat exchanger 3. The recovery flow paths 41 are formed to be folded back in the axial direction L. The recovery flow paths 41 may be formed to be serpentine in the axial direction L. The formation of a plurality of recovery flow paths 41 to be overlapped in the radial direction R lengthens the path through which the air A1 flows in the radiant heat recovery device 4. This allows the radiant heat from the water vapor electrolysis cell 2 to be effectively recovered into the air A1 flowing through the recovery flow paths 41.

[0036] The air supply passage 33 of the heat exchanger 3 is connected to a recovery passage 41 of the radiant heat recovery device 4 via a pipe 7, and the recovery passage 41 is connected to the oxygen electrode chamber 23 of the steam electrolysis cell 2 via a pipe 7. In other words, the radiant heat recovery device 4 is disposed at a position that relays between the air supply passage 33 and the oxygen electrode chamber 23.

[0037] The radiant heat recovery device 4 in this embodiment serves as a preheater for heating the air A1 after it has flowed through the air supply flow path 33, using radiant heat from the steam electrolysis cell 2. With this configuration, the radiant heat from the steam electrolysis cell 2 can be recovered more effectively.

[0038] (Heat transfer suppression layer 5, heat dissipation suppression layer 6) As shown in FIG. 1, a heat transfer suppression layer 5 for suppressing heat transfer between the heat exchanger 3 and the radiation heat recovery device 4 is disposed between the heat exchanger 3 and the radiation heat recovery device 4. The formation of the heat transfer suppression layer 5 allows the recovery of exhaust heat of the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2 in the heat exchanger 3 to be appropriately separated from the recovery of radiant heat by the radiation heat recovery device 4. This allows the exhaust heat of the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2 to be appropriately recovered. The heat transfer suppression layer 5 of this embodiment is formed as a heat insulating layer filled with a gas such as air A1. The heat transfer suppression layer 5 has a cylindrical shape and is formed by being sandwiched between the heat exchanger 3 and the radiation heat recovery device 4 in the radial direction R.

[0039] A heat-dissipation suppression layer 6 for suppressing heat dissipation from the heat exchanger 3 to the outside is disposed at the outermost position of the heat exchanger 3 farthest from the steam electrolysis cell 2. The formation of the heat-dissipation suppression layer 6 can suppress heat dissipation from the heat exchanger 3 to the outside as much as possible. The hydrogen discharge flow passage 32 is disposed at the outermost side in the radial direction R of the heat exchanger 3. The heat-dissipation suppression layer 6 suppresses the exhaust heat of the hydrogen-mixed steam W2 flowing through the hydrogen discharge flow passage 32 from being discharged to the outside. The heat-dissipation suppression layer 6 of this embodiment is formed as a heat insulating layer filled with a gas such as air A1. The heat-dissipation suppression layer 6 has a cylindrical shape and is laminated on the outer peripheral side in the radial direction R of the hydrogen discharge flow passage 32 of the heat exchanger 3.

[0040] The heat transfer suppressing layer 5 and the heat radiation suppressing layer 6 may be made of various heat insulating materials other than the heat insulating layer.

[0041] (Operation of steam electrolysis system 1) When power is generated and hydrogen is produced by the water vapor electrolysis system 1, water vapor W1 is sent from the water vapor supply passage 31 of the heat exchanger 3 to the hydrogen electrode chamber 22 of the water vapor electrolysis cell 2. In addition, air A1 is sent from the air supply passage 33 of the heat exchanger 3 to the oxygen electrode chamber 23 of the water vapor electrolysis cell 2 via the recovery passage 41 of the radiant heat recovery device 4. In the water vapor electrolysis cell 2, hydrogen is produced from the water vapor W1 in contact with the hydrogen electrode 221, and oxide ions permeate the solid electrolyte body 21 and move to the oxygen electrode 231, generating power.

[0042] The exhaust heat of the hydrogen-mixed water vapor W2 discharged from the hydrogen electrode chamber 22 is transferred to the air A1 flowing in the air supply passage 33 via the partition wall 35 when the hydrogen-mixed water vapor W2 flows through the hydrogen discharge passage 32 of the heat exchanger 3. In addition, the exhaust heat of the oxygen-mixed air A2 discharged from the oxygen electrode chamber 23 is transferred to the air A1 flowing in the air supply passage 33 and the water vapor W1 flowing in the water vapor supply passage 31 via the partition wall 35 when the oxygen-mixed air A2 flows through the oxygen discharge passage 34 of the heat exchanger 3.

[0043] (Action and effect) In the water vapor electrolysis system 1 of this embodiment, four flow paths, namely, a water vapor supply flow path 31, an air supply flow path 33, a hydrogen discharge flow path 32, and an oxygen discharge flow path 34, are stacked adjacent to one another. Furthermore, a supply side flow path which is the first supply side flow path S1 or the second supply side flow path S2 and a discharge side flow path which is the first discharge side flow path E1 or the second discharge side flow path E2 are stacked adjacent to one another alternately. With this configuration, in the heat exchanger 3, heat exchange can be effectively performed between the water vapor W1, the hydrogen-mixed water vapor W2, the air A1, and the oxygen-mixed air A2, which have different heat capacities.

[0044] In particular, by integrally stacking the four flow paths, the heat of the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2 can be effectively transferred to the water vapor W1 and the air A1 in the heat exchanger 3. In addition, in the heat exchanger 3, it becomes possible to recover almost all of the exhaust heat of the hydrogen-mixed water vapor W2 and the oxygen-mixed air A2.

[0045] Therefore, according to the steam electrolysis system 1 of this embodiment, the exhaust heat of the steam electrolysis cell 2 can be effectively recovered.

[0046] <Embodiment 2> This embodiment describes a steam electrolysis system 1 in which the position of the heat exchanger 3 arranged opposite the steam electrolysis cell 2 is different from that of the first embodiment. As shown in FIG. 3, the heat exchanger 3 in this embodiment is arranged opposite the steam electrolysis cell 2 in the axial direction L. The steam electrolysis cell 2 is arranged at the center of a ring-shaped radiation heat recovery device 4. More specifically, the radiation heat recovery device 4 is formed in a cylindrical shape surrounding the central axis of the steam electrolysis cell 2. A heat dissipation suppression layer 6A for suppressing heat dissipation from the radiation heat recovery device 4 to the outside is formed on the outer periphery of the radiation heat recovery device 4 in the radial direction R. The heat dissipation suppression layer 6A is composed of a thermal insulation layer.

[0047] In the heat exchanger 3 of this embodiment, the first supply side flow passage S1, which is one of the water vapor supply flow passage 31 or the air supply flow passage 33, the first discharge side flow passage E1, which is one of the hydrogen discharge flow passage 32 or the oxygen discharge flow passage 34, the second supply side flow passage S2, which is the other of the water vapor supply flow passage 31 or the air supply flow passage 33, and the second discharge side flow passage E2, which is the other of the hydrogen discharge flow passage 32 or the oxygen discharge flow passage 34, are stacked adjacent to each other in sequence. In other words, the supply side flow passage, which is the first supply side flow passage S1 or the second supply side flow passage S2, and the discharge side flow passage, which is the first discharge side flow passage E1 or the second discharge side flow passage E2, are stacked adjacent to each other alternately. With this configuration, in the heat exchanger 3, heat exchange between the water vapor W1, the hydrogen-mixed water vapor W2, the air A1, and the oxygen-mixed air A2, which have different heat capacities, can be effectively performed.

[0048] A heat-dissipation suppressing layer 6B is formed on the inner side of the heat exchanger 3 facing the steam electrolysis cell 2 and on the outer side opposite the inner side. The heat-dissipation suppressing layer 6B is formed of a thermal insulating layer.

[0049] In this embodiment, the heat exchanger 3 is disposed opposite the steam electrolysis cell 2 in the axial direction L, thereby reducing heat radiation from the steam electrolysis cell 2 to the outside and achieving a reduction in the size of the steam electrolysis system 1. The heat exchangers 3 may be disposed opposite both sides of the steam electrolysis cell 2 in the axial direction L.

[0050] Other configurations, functions, effects, etc. of the steam electrolysis system 1 of this embodiment are similar to those of embodiment 1. In this embodiment, too, components denoted by the same reference numerals as those in embodiment 1 are similar to those in embodiment 1.

[0051] <Other embodiments> In the heat exchanger 3, as long as three of the water vapor supply flow path 31, the air supply flow path 33, the hydrogen discharge flow path 32, and the oxygen discharge flow path 34 are formed by stacking them on one another, the remaining one does not need to be stacked. Adjacent flow paths in the first supply side flow path S1, the first discharge side flow path E1, the second supply side flow path S2, and the second discharge side flow path E2 may form parallel flows rather than counter flows. The heat exchanger 3 may be formed in a rectangular tube shape such as a square, other than a cylindrical shape.

[0052] The order in which the water vapor supply passage 31, the air supply passage 33, the hydrogen discharge passage 32, and the oxygen discharge passage 34 are stacked may be various orders in which the supply side passages S1, S2 and the discharge side passages E1, E2 are alternately arranged. At least three of the water vapor supply passage 31, the air supply passage 33, the hydrogen discharge passage 32, and the oxygen discharge passage 34 in the heat exchanger 3 may be stacked in the circumferential direction C at multiple locations in the circumferential direction C of the heat exchanger 3. In the heat exchanger 3, instead of the water vapor supply passage 31 and the air supply passage 33 being stacked adjacent to each other on both sides of the radial direction R of the oxygen discharge passage 34, the water vapor supply passage 31 and the air supply passage 33 may be stacked adjacent to each other on both sides of the radial direction R of the hydrogen discharge passage 32.

[0053] The present invention is not limited to the respective embodiments, and further different embodiments can be configured without departing from the scope of the present invention. The present invention also includes various modified examples, modifications within the scope of equivalents, etc. Furthermore, the combinations and forms of various components envisioned from the present invention are also included in the technical spirit of the present invention. [Explanation of symbols]

[0054] 1. Steam electrolysis system 2. Steam electrolysis cell 21 Solid electrolyte body 22 Hydrogen electrode chamber 23 Oxygen Chamber 3 Heat exchanger 31 Water vapor supply passage 32 Hydrogen exhaust flow path 33 Air supply passage 34 Oxygen exhaust flow path

Claims

1. a water vapor electrolysis cell (2) including a hydrogen electrode chamber (22) in which hydrogen is produced from water vapor (W1) and an oxygen electrode chamber (23) in which oxygen is produced from air (A1) with an ion-conductive solid electrolyte body (21) interposed therebetween; a heat exchanger (3) in which a water vapor supply flow path (31) for supplying the water vapor to the hydrogen electrode chamber, a hydrogen discharge flow path (32) through which hydrogen-mixed water vapor (W2) is discharged from the hydrogen electrode chamber, an air supply flow path (33) for supplying the air to the oxygen electrode chamber, and an oxygen discharge flow path (34) through which oxygen-mixed air (A2) is discharged from the oxygen electrode chamber are formed, At least three of the steam supply flow path, the air supply flow path, the hydrogen discharge flow path, and the oxygen discharge flow path are stacked adjacent to one another.

2. The water vapor electrolysis system according to claim 1 , wherein the water vapor supply flow path and the air supply flow path are stacked adjacent to each other on both sides of the oxygen discharge flow path.

3. 3. The water vapor electrolysis system according to claim 1 or 2, wherein the water vapor supply flow path, the air supply flow path, the hydrogen discharge flow path, and the oxygen discharge flow path are stacked adjacent to each other in the following order: a first supply side flow path (S1) which is one of the water vapor supply flow path or the air supply flow path, a first discharge side flow path (E1) which is one of the hydrogen discharge flow path or the oxygen discharge flow path, a second supply side flow path (S2) which is the other of the water vapor supply flow path or the air supply flow path, and a second discharge side flow path (E2) which is the other of the hydrogen discharge flow path or the oxygen discharge flow path.

4. the heat exchanger is formed in an annular shape surrounding the steam electrolysis cell; 4. The steam electrolysis system according to claim 3, wherein the first supply side flow path, the first discharge side flow path, the second supply side flow path, and the second discharge side flow path are stacked adjacent to each other in a radial direction (R) around the steam electrolysis cell.

5. the heat exchangers are disposed at positions opposing each other in an axial direction (L) of the steam electrolysis cell or in a radial direction (R) perpendicular to the axial direction, The steam electrolysis system according to claim 3 , wherein the first supply side flow path, the first discharge side flow path, the second supply side flow path, and the second discharge side flow path are stacked adjacent to each other in this order.

6. 6. The steam electrolysis system according to claim 3, wherein adjacent flow paths among the first supply side flow path, the first discharge side flow path, the second supply side flow path, and the second discharge side flow path are configured to form counter flows in which flows of a fluid, which is the water vapor, the hydrogen-mixed water vapor, the air, or the oxygen-mixed air, flow in opposite directions to each other.

7. 7. The steam electrolysis system according to claim 1, wherein the hydrogen discharge flow path is disposed at an outermost position farthest from the steam electrolysis cell among the steam supply flow path, the air supply flow path, the hydrogen discharge flow path and the oxygen discharge flow path which constitute the heat exchanger.

8. The steam electrolysis system according to any one of claims 1 to 7, wherein a radiant heat recovery device (4) for recovering radiant heat emitted from the steam electrolysis cell is disposed in the heat exchanger at a position closest to the steam electrolysis cell.

9. 9. The steam electrolysis system according to claim 8, wherein the radiant heat recovery device constitutes a preheater for heating the air after it has flowed through the air supply passage with radiant heat from the steam electrolysis cell.

10. 10. The steam electrolysis system according to claim 8 or 9, further comprising a heat transfer suppression layer (5) disposed between the heat exchanger and the radiation heat recovery device for suppressing heat transfer between the heat exchanger and the radiation heat recovery device.

11. The steam electrolysis system according to any one of claims 1 to 10, wherein a heat dissipation suppression layer (6) for suppressing heat dissipation from the heat exchanger to the outside is disposed in an outer position of the heat exchanger that is farthest from the steam electrolysis cell.

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