Hydrogen generation system and control method thereof

Abstract

Provided is a hydrogen generation system that can be shut down without gas replacement using air, nitrogen, or the like to remove water vapor. [Solution] The hydrogen generation system 100 comprises an electrolysis cell having a hydrogen electrode 11, an oxygen electrode 12, and an electrolyte layer 13 arranged between the hydrogen electrode 11 and the oxygen electrode 12, and is equipped with an electrolysis module 19 that supplies water vapor to the hydrogen electrode 11 to generate hydrogen by water vapor electrolysis, a hydrogen electrode side vacuum pump 62 that reduces the pressure in the hydrogen electrode space 11a to which the hydrogen electrode 11 contacts, and a control device 80 that operates the hydrogen electrode side vacuum pump 62 to control the pressure in the hydrogen electrode space 11a to a pressure lower than the saturated vapor pressure of water when performing shutdown control to stop the generation of hydrogen by the electrolysis module 19.

Description

[Technical field]

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

[0002] Solid oxide electrolysis cells (SOECs) are known as hydrogen generation systems that generate hydrogen through steam electrolysis. With the recent progress toward a decarbonized society, it is expected that the demand for SOECs will increase, and with the increase in renewable energy electricity, it is expected that SOECs will be required to be operated with start-stop operations.

[0003] In an SOEC, in order to protect the cell stack of the cells during start-up or shutdown, when the temperature drops, it is necessary to remove steam to prevent the steam from becoming drained (see, for example, Patent Document 1).

[0004] In Patent Document 1, in order to remove steam from the cell stack of the SOEC, an operation is performed in which the internal fluid on the fuel electrode side is replaced with air. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7282968 Summary of the Invention [Problem to be solved by the invention]

[0006] In operations that require replacing the fuel electrode with air during shutdown, the introduction of air cools the fuel electrode, which means that it must be heated again the next time it is started, making a rapid restart difficult.

[0007] If air is replaced with nitrogen, nitrogen is consumed every time the system is shut down, resulting in a huge amount of nitrogen consumption. Also, when the system is started up, the nitrogen must be discharged and replaced with water vapor, which is inefficient.

[0008] If large-capacity hydrogen production becomes necessary in the future, there will be a problem that as SOECs become larger, the amount of nitrogen required as a utility will also become even larger.

[0009] The present disclosure has been made in consideration of the above circumstances, and aims to provide a hydrogen generation system and a control method thereof that can be shut down without performing gas replacement using air, nitrogen, etc. to remove water vapor. [Means for solving the problem]

[0010] A hydrogen generation system according to one aspect of the present disclosure includes an electrolysis module that includes an electrolysis cell having a hydrogen electrode, an oxygen electrode, and an electrolyte layer disposed between the hydrogen electrode and the oxygen electrode, and that generates hydrogen by water vapor electrolysis by supplying water vapor to the hydrogen electrode, a hydrogen electrode-side pressure reduction device that reduces the pressure in the hydrogen electrode space in contact with the hydrogen electrode, and a control unit that operates the hydrogen electrode-side pressure reduction device to control the pressure in the hydrogen electrode space to a pressure lower than the saturated vapor pressure of water when performing stop control to stop hydrogen generation by the electrolysis module.

[0011] A control method for a hydrogen generation system according to one aspect of the present disclosure is a control method for a hydrogen generation system including an electrolysis module that includes an electrolysis cell having a hydrogen electrode, an oxygen electrode, and an electrolyte layer disposed between the hydrogen electrode and the oxygen electrode, and that supplies water vapor to the hydrogen electrode to generate hydrogen by water vapor electrolysis, and a hydrogen electrode-side pressure reduction device that reduces the pressure in the hydrogen electrode space in contact with the hydrogen electrode, and when performing stop control to stop hydrogen generation by the electrolysis module, the hydrogen electrode-side pressure reduction device is operated to control the pressure in the hydrogen electrode space to a pressure lower than the saturated vapor pressure of water. Effect of the Invention

[0012] The operation can be stopped without gas replacement with air, nitrogen, etc. to remove water vapor. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram showing a hydrogen generation system according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a partially enlarged vertical cross-sectional view showing an example of the cylindrical electrolysis module shown in FIG. [Diagram 3] 4 is a flowchart showing the stop control of the hydrogen generation system. [Figure 4] 4 is a flowchart showing the startup control of the hydrogen generation system. [Diagram 5] 4 is a flowchart showing the startup control of the hydrogen generation system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. 1 shows a schematic configuration of a hydrogen generation system 100 according to this embodiment. The hydrogen generation system 100 includes an electrolysis module 19, a power supply unit 18, a water vapor supply unit 20, a hydrogen separation facility 30, a hydrogen storage facility (hydrogen supply unit) 40, an adjustment unit 50, an air supply unit (heating medium supply unit) 70, and a control device (control unit) 80. Note that, although a system including a hydrogen storage facility (hydrogen supply unit) is shown in this embodiment, the hydrogen storage facility (hydrogen supply unit) 40 may be a hydrogen pipeline, and hydrogen may be extracted from the pipeline and supplied to this system, or the generated hydrogen may be directly supplied to the hydrogen pipeline.

[0015] A solid oxide electrolysis cell (hereinafter simply referred to as "electrolysis cell") 10 is an element constituting a solid oxide electrolysis module 19 (hereinafter simply referred to as "electrolysis module 19") that supplies water vapor from a water vapor supply unit 20 to a hydrogen electrode 11 to generate hydrogen and oxygen by water vapor electrolysis, and has a hydrogen electrode 11, an oxygen electrode 12, and an electrolyte layer 13 disposed between the hydrogen electrode 11 and the oxygen electrode 12. The electrolysis module 19 is an assembly of electrolysis cells 10. Water vapor electrolysis is the reverse reaction of a fuel cell that generates electricity, and the electrolysis cell 10 can use substantially the same configuration and materials as a solid oxide fuel cell (SOFC).

[0016] 1 diagrammatically illustrates the relationship between an electrolysis module 19, an electrolysis cell 10, a hydrogen electrode 11, an oxygen electrode 12, and an electrolyte layer 13. The electrolysis module 19 can be, for example, a cylindrical cell stack in which the hydrogen electrode 11 is arranged in a cylindrical tube made of a porous material, the electrolyte layer 13 is arranged on the hydrogen electrode 11, and the oxygen electrode 12 is arranged on the electrolyte layer 13. The electrolysis module 19 also has a temperature sensor 17 that measures the operating temperature.

[0017] 2 is a partially enlarged vertical cross-sectional view showing an example of a cylindrical electrolysis module 19 according to this embodiment. The electrolysis module 19 includes, as an example, a cylindrical base tube 14, electrolysis cells 10 formed at multiple locations on the outer peripheral surface of the base tube 14, and interconnectors 15 formed between adjacent electrolysis cells 10. The electrolysis cells 10 are formed by stacking a hydrogen electrode 11, an electrolyte layer 13, and an oxygen electrode 12 on the surface of the base tube 14.

[0018] Of the multiple electrolytic cells 10 formed on the outer peripheral surface of the base tube 14, a lead film 16 is electrically connected via an interconnector 15 to the oxygen electrode 12 of the electrolytic cell 10 formed at the end closest to the axial direction of the base tube 14, and a lead film 16 is electrically connected to the hydrogen electrode 11 of the electrolytic cell 10 formed at the other end closest to the axial direction of the base tube 14. In the following description, "supplying a medium (air, water vapor, hydrogen, etc.) to the hydrogen electrode 11" means supplying the medium to the hydrogen electrode 11 formed on the outer peripheral surface of the base tube 14 by circulating the medium in the space inside the base tube 14 and diffusing the medium in the pores of the base tube 14.

[0019] The base tube 14 is made of a porous material and is mainly composed of, for example, CaO-stabilized ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), Y2O3-stabilized ZrO2 (YSZ), MgAl2O4, etc. This base tube 14 supports the electrolytic cell 10, the interconnector 15, and the lead film 16, and diffuses water vapor supplied to the inner peripheral surface of the base tube 14 through the pores of the base tube 14 to the hydrogen electrode 11 formed on the outer peripheral surface of the base tube 14.

[0020] The hydrogen electrode 11 is made of a composite oxide of a metal material (such as Ni) and a zirconia-based electrolyte material, for example, Ni / YSZ. The oxygen electrode 12 is made of, for example, a LaSrMnO3-based oxide or a LaCoO3-based oxide. The electrolyte layer 13 is mainly made of YSZ, which has gas-tightness that makes it difficult for gas to pass through and high oxygen ion conductivity at high temperatures.

[0021] The interconnector 15 is, for example, a M such as SrTiO3. 1-x L x It is made of a conductive perovskite oxide represented by TiO3 (M is an alkaline earth metal element, and L is a lanthanoid element). The interconnector 15 is a dense film that prevents water vapor and air (oxidizing gas) from mixing.

[0022] Furthermore, the interconnector 15 has stable durability and electrical conductivity in both an oxidizing atmosphere and a reducing atmosphere. The interconnector 15 electrically connects the oxygen electrode 12 of one electrolytic cell 10 to the hydrogen electrode 11 of the other electrolytic cell 10, thereby connecting the adjacent electrolytic cells 10 in series.

[0023] The lead film 16 has electronic conductivity and is made of a composite material of Ni and zirconia-based electrolyte material such as Ni / YSZ, or M1-xLxTiO3 (M is an alkaline earth metal element, L is a lanthanoid element) such as SrTiO3. The lead film 16 supplies DC power to the multiple electrolysis cells 10 connected in series by the interconnectors 15.

[0024] When power is supplied from the outside between the hydrogen electrode 11 and the oxygen electrode 12 via the lead film 16, part of the high-temperature water vapor supplied to the hydrogen electrode 11 receives electrons and is separated into hydrogen and oxygen ions, generating hydrogen. The separated oxygen ions move inside the electrolyte layer 13 to the oxygen electrode 12 and release electrons to generate oxygen.

[0025] 1 is a sensor that detects the temperature of the electrolysis module 19 (the temperature of the electrolysis cell 10 itself, or the ambient temperature of the space in which the electrolysis cell 10 is placed). The temperature of the electrolysis module 19 detected by the temperature sensor 17 is transmitted to the control device 80.

[0026] The power supply unit 18 is a device that supplies power for performing steam electrolysis to the electrolysis module 19. The state of power supply from the power supply unit 18 to the electrolysis module 19 is controlled by a control device 80.

[0027] The water vapor supply unit 20 is a device that generates water vapor and supplies the water vapor to the electrolysis module 19. The water vapor is supplied to the hydrogen electrode space 11a in contact with the hydrogen electrode 11 of the electrolysis module 19 via a water vapor supply pipe 21. The temperature of the hydrogen electrode inlet gas supplied to the hydrogen electrode space 11a is, for example, 400° C. or higher.

[0028] The electrolysis module 19 is provided with a hydrogen electrode side pressure sensor 23 that measures the pressure in the hydrogen electrode space 11a. The output of the hydrogen electrode side pressure sensor 23 is transmitted to the control device 80. The electrolysis module 19 is provided with an oxygen electrode side pressure sensor 24 that measures the pressure in the oxygen electrode space 12a that is in contact with the oxygen electrode 12. The output of the oxygen electrode side pressure sensor 24 is transmitted to the control device 80. The hydrogen electrode side pressure sensor 23 does not need to be provided in the hydrogen electrode space 11a, and may be located at a position where the pressure in the hydrogen electrode space 11a can be obtained by calculation or the like. Similarly, the oxygen electrode side pressure sensor 24 does not need to be provided in the oxygen electrode space 12a, and may be located at a position where the pressure in the oxygen electrode space 12a can be obtained by calculation or the like.

[0029] The hydrogen separation equipment 30 is equipment that separates hydrogen from a mixed gas of hydrogen and water vapor generated at the hydrogen electrode 11 of the electrolysis module 19. When the hydrogen discharge valve 31 is opened, hydrogen generated at the hydrogen electrode 11 is supplied to the hydrogen separation equipment 30 via a hydrogen discharge pipe 33. The hydrogen separated in the hydrogen separation equipment 30 is supplied to the hydrogen storage equipment 40 by a hydrogen booster 32. The hydrogen separation equipment 30 cools the mixed gas of hydrogen and water vapor supplied from the hydrogen discharge pipe 33, for example, and condenses the water vapor contained in the mixed gas to recover it as recovered water.

[0030] The hydrogen storage equipment 40 is equipment that stores hydrogen generated by the electrolysis module 19 and supplies hydrogen to a hydrogen supply destination via a hydrogen supply pipe 41. The hydrogen storage equipment 40 can also supply hydrogen to the hydrogen electrode 11 via a hydrogen supply pipe 42 and a water vapor supply pipe 21. The hydrogen storage equipment 40 can also supply hydrogen to the oxygen electrode 12 of the electrolysis module 19 via a hydrogen supply pipe (hydrogen system) 43. The hydrogen supplied from the hydrogen storage equipment 40 to the hydrogen electrode 11 is preferably heated in the process of flowing through the hydrogen supply pipe 42 and then supplied to the water vapor supply pipe 21 in order to maintain the hydrogen electrode 11 at a desired temperature.

[0031] The adjustment unit 50 is a device that adjusts the amount of water vapor supplied from the water vapor supply unit 20, the amount of hydrogen supplied from the hydrogen storage equipment 40 to the hydrogen electrode 11, the amount of hydrogen supplied from the hydrogen storage equipment 40 to the oxygen electrode 12, the amount of air (oxidizing gas) supplied from the air supply unit 70 to the oxygen electrode 12, and the amount of air supplied from the air supply unit 70 to the hydrogen electrode 11.

[0032] The adjustment section 50 includes a water vapor adjustment valve 51 arranged in the water vapor supply pipe 21, a hydrogen adjustment valve 52 arranged in the hydrogen supply pipe 42, a hydrogen adjustment valve (or gate valve) 53 arranged in a position close to the water vapor supply pipe 21 downstream of the hydrogen supply pipe 42, an air adjustment valve 54 arranged in the air supply pipe 72 for the hydrogen electrode, an air side discharge adjustment valve 55 for the hydrogen electrode vent gas arranged in the air discharge pipe 73, a hydrogen supply valve 56, and an air adjustment valve 57.

[0033] The hydrogen regulating valve 53 is a valve that is closed when water vapor is supplied to the hydrogen electrode but hydrogen is not supplied. By closing the hydrogen regulating valve 53, it is possible to prevent water vapor from entering the hydrogen supply pipe 42 when water vapor is supplied to the hydrogen electrode but hydrogen is not supplied.

[0034] The hydrogen supply valve 56 is a valve that adjusts the amount of hydrogen supplied from the hydrogen storage equipment 40 to the oxygen electrode 12 via the hydrogen supply pipe 43 and the air supply pipe 74. The hydrogen supplied to the air supply pipe 74 is supplied to the oxygen electrode 12 side of the electrolysis module 19. The hydrogen supplied to the oxygen electrode 12 of the electrolysis module 19 and the oxygen electrode 12 side of the base tube 14 is combusted by catalytic action, increasing the temperature of the electrolysis module 19.

[0035] 1 supplies hydrogen stored in the hydrogen storage facility 40 to the oxygen electrode 12 and the oxygen electrode 12 side of the substrate tube 14 by opening the hydrogen supply valve 56, but other configurations are also possible. For example, a fuel supply unit (not shown) that supplies hydrogen or other fuel gas (methane gas, etc.) may be provided, and the fuel gas may be supplied from the fuel supply unit to the oxygen electrode 12 side of the electrolysis module 19 and combusted by catalytic action.

[0036] The air supply unit 70 supplies air heated to a high temperature (for example, less than 400° C.) to the oxygen electrode 12. That is, the air supplied from the air supply unit 70 is supplied to the oxygen electrode space 12a of the electrolysis module 19 via an air supply pipe 74. The air supplied from the air supply unit 70 can also be supplied to the hydrogen electrode space 11a via a hydrogen electrode air supply pipe 72. The amount of air supplied from the air supply unit 70 to the oxygen electrode space 12a and the hydrogen electrode space 11a is adjusted by the air regulating valve 57. The amount of air supplied from the air supply unit 70 to the hydrogen electrode space 11a is adjusted by the air regulating valve 54.

[0037] A vacuum piping 60 is connected to the hydrogen discharge pipe 33. Specifically, the upstream end of the vacuum piping 60 is connected to the upstream side of the hydrogen discharge valve 31. A hydrogen electrode side vacuum pump (hydrogen electrode side pressure reduction device) 62 is connected to the vacuum piping 60.

[0038] The hydrogen electrode side vacuum pump 62 is used when the hydrogen generation system 100 is stopped or started, and is controlled by commands from the control device 80. The hydrogen electrode side vacuum pump 62 sucks gas from the hydrogen electrode space 11a via the hydrogen exhaust pipe 33, creating a vacuum in the hydrogen electrode space 11a. The exhaust from the hydrogen electrode side vacuum pump 62 is led to the hydrogen recovery section 64 via an exhaust pipe 63. The hydrogen recovery section 64 recovers hydrogen remaining in the hydrogen electrode space 11a. The hydrogen recovered in the hydrogen recovery section 64 is stored and used when the hydrogen generation system 100 is started up, as described below.

[0039] A hydrogen reuse pipe 66 is connected to the hydrogen recovery unit 64. The downstream end of the hydrogen reuse pipe 66 is connected to the water vapor supply pipe 21. A hydrogen reuse valve 67 is provided on the hydrogen reuse pipe 66. The hydrogen reuse valve 67 is opened and closed by a control device 80. The hydrogen reuse valve 67 is normally closed, and is opened within a predetermined period of time, for example, at start-up. This allows the hydrogen stored in the hydrogen recovery unit 64 to be guided to the hydrogen electrode space 11a.

[0040] The upstream end of the evacuation pipe 65 is connected to an oxygen exhaust pipe 68 that exhausts oxygen-enriched air from the oxygen electrode space 12a. An oxygen electrode side vacuum pump (oxygen electrode side pressure reduction device) 69 is connected to the evacuation pipe 65. A gate valve 68a is provided on the oxygen exhaust pipe 68 downstream of the connection position of the evacuation pipe 65. The gate valve 68a is controlled to change from fully open to fully closed by a command from the control device 80 when the oxygen electrode side vacuum pump 69 is operated.

[0041] The oxygen electrode side vacuum pump 69 is used when the oxygen electrode is stopped or started, and is controlled by commands from the control device 80. The oxygen electrode side vacuum pump 69 sucks gas from the oxygen electrode space 12a through the oxygen exhaust pipe 68, creating a vacuum in the oxygen electrode space 12a. The exhaust gas from the oxygen electrode side vacuum pump 69 is discharged to the outside.

[0042] The control device 80 is a device that controls the hydrogen generation system 100. The control device 80 is composed of, for example, a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, for example, and the CPU reads the program into the RAM or the like and executes information processing and arithmetic processing to realize various functions. The program may be installed in a ROM or other storage medium in advance, may be provided in a state stored in a computer-readable storage medium, or may be distributed via a wired or wireless communication means. The computer-readable storage medium may be a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

[0043] <Stop control> The stop control of the hydrogen generation system 100 having the above configuration will be described with reference to FIG.

[0044] When the stop control is started, first, in step S101, the control device 80 controls the power supply unit 18 to reduce the current in order to stop the power supply from the power supply unit 18 to the electrolysis module 19.

[0045] In step S102, the control device 80 determines whether the current from the power supply unit 18 has stopped, and proceeds to step S103 after the current has become zero.

[0046] In step S103, the control device 80 starts adjusting the amount of hydrogen supplied from the hydrogen storage equipment 40 to the hydrogen electrode space 11a (inside the substrate tube 14) and starts operating the hydrogen adjustment valve 52 to bring the hydrogen concentration to a predetermined value so that the hydrogen electrode space 11a becomes a reducing atmosphere. Next, in step S104, the control device 80 reduces the supply of water vapor from the water vapor supply unit 20 to the hydrogen electrode space 11a, and closes the water vapor regulating valve 51 so that the water vapor concentration in the hydrogen electrode space 11a becomes a predetermined value.

[0047] In step S105, the control device 80 determines whether the temperature Ta of the electrolysis module 19 detected by the temperature sensor 17 is lower than Temp10, and if the temperature Ta is lower than Temp10, the process proceeds to step S106. Temp10 is, for example, a temperature not lower than 350° C. and not higher than 400° C. Temp10 is set lower than the temperature at which the metal components contained in the hydrogen electrode 11 react with water vapor and oxidize.

[0048] When it is determined in step S105 that the temperature Ta has fallen below Temp10, the supply of hydrogen and water vapor to the hydrogen electrode space 11a is stopped. At this time, the hydrogen regulating valves 52, 53 and the water vapor regulating valve 51 are fully closed. Then, in step S106, all valves connected to the hydrogen electrode space 11a are fully closed so that the space including the hydrogen electrode space 11a becomes a closed space. Specifically, in addition to the hydrogen regulating valves 52, 53 and the water vapor regulating valve 51, the hydrogen discharge valve 31 is also fully closed. The air regulating valve 54, the air-side discharge regulating valve 55, and the hydrogen reuse valve 67 are maintained fully closed.

[0049] In step S116, all valves connected to the oxygen electrode space 12a are fully closed so that the space including the oxygen electrode space 12a is closed. Specifically, the air adjustment valve 57 and the gate valve 68a are fully closed. The air discharge adjustment valve 55 and the hydrogen supply valve 56 are kept fully closed.

[0050] Then, in step S107, the hydrogen electrode side vacuum pump 62 is started to reduce the pressure in the hydrogen electrode space 11a to create a vacuum. The degree of vacuum is measured by the hydrogen electrode side pressure sensor 23, and is set so that the pressure in the hydrogen electrode space 11a is lower than the saturated vapor pressure of water at the temperature Ta in the hydrogen electrode space 11a. The operation of the hydrogen electrode side vacuum pump 62 is controlled to maintain the set degree of vacuum, and the hydrogen electrode space 11a is stored at a predetermined temperature (step S108). The temperature during this storage does not need to be replaced with nitrogen or air, and can be maintained at a relatively high temperature due to the insulating effect of the vacuum.

[0051] The hydrogen exhausted from the hydrogen electrode side vacuum pump 62 is guided to and stored in the hydrogen recovery section 64. At this time, water vapor is removed from the exhaust. For example, if the hydrogen electrode side vacuum pump 62 is a water-sealed type, the water vapor guided together with the hydrogen can be separated as drain water.

[0052] In step S117, the oxygen electrode side vacuum pump 69 is started to reduce the pressure in the oxygen electrode space 12a to create a vacuum. The degree of vacuum is measured by the oxygen electrode side pressure sensor 24 and set so that the pressure difference between the oxygen electrode space 12a and the hydrogen electrode space 11a measured by the hydrogen electrode side pressure sensor 23 is equal to or less than a predetermined value, i.e., is equal to the degree of vacuum in the hydrogen electrode space 11a. The operation of the oxygen electrode side vacuum pump 69 is controlled to maintain the set degree of vacuum, and the oxygen electrode space 12a is stored at a predetermined temperature (step S118). The temperature during this storage does not need to be replaced with nitrogen or air, and can be maintained at a relatively high temperature due to the insulating effect of the vacuum.

[0053] With the above, the shutdown control of the hydrogen generation system 100 is completed.

[0054] <Launch Control> Next, the startup control executed by the control device 80 of this embodiment at the time of startup of the hydrogen generation system 100 will be described with reference to FIGS.

[0055] At start-up, first in step S201, the control device 80 determines whether the temperature Ta of the electrolysis module 19 detected by the temperature sensor 17 exceeds Temp1. Temp1 is set to a temperature higher than the dew point of water vapor in the hydrogen electrode space 11a and the oxygen electrode space 12a so that water vapor does not become drained inside. Temp1 is, for example, a temperature not lower than 150°C and not higher than 200°C. Temp2, which will be described later, is set to a temperature higher than Temp1.

[0056] As described above, since the hydrogen electrode space 11a and the oxygen electrode space 12a are kept in a vacuum during the shutdown control, the temperature Ta of the electrolysis module 19 becomes higher than Temp1 in the normal state (YES in step S201). In this case, the process proceeds to step S202, where the supply of water vapor to the hydrogen electrode space 11a and the supply of air to the oxygen electrode space 12a are started. The control device 80 opens the water vapor regulating valve 51 so as to start the supply of water vapor from the water vapor supply unit 20 to the hydrogen electrode 11. The control device 80 controls the regulating unit 50 to open the air regulating valve 54 and the air-side discharge regulating valve 55, and to close the hydrogen regulating valve 52 and the hydrogen regulating valve (or gate valve) 53. The control device 80 also controls the air regulating valve 57 to be open, and the hydrogen discharge valve 31 and the hydrogen supply valve 56 to be closed.

[0057] The air supplied from the air supply unit 70 to the oxygen electrode 12 heats the oxygen electrode 12, and thus the entire electrolysis module 19 and the base tube 14, and is then discharged to the outside. The hydrogen electrode air supply pipe 72 is a system that supplies air from the air supply unit 70 to the hydrogen electrode 11. The air supplied from the air supply unit 70 through the hydrogen electrode air supply pipe 72 into the base tube 14 heats the base tube 14, thereby heating the entire electrolysis module 19 including the hydrogen electrode 11, and is then discharged to the outside through the air discharge pipe 73.

[0058] On the other hand, for example, if the stop time is long, heat dissipation progresses despite storage in a vacuum, and in step S201, if the temperature Ta of the electrolysis module 19 becomes lower than Temp1 (NO), the process proceeds to step S203, and air supply to the hydrogen electrode space 11a and the oxygen electrode space 12a is started. The control device 80 controls the adjustment unit 50 to open the air adjustment valve 54 and the air-side discharge adjustment valve 55, and to close the water vapor adjustment valve 51, the hydrogen adjustment valve 52, and the hydrogen adjustment valve (or gate valve) 53. The control device 80 also controls the air adjustment valve 57 to be open, and the hydrogen discharge valve 31 and the hydrogen supply valve 56 to be closed.

[0059] Then, when the temperature Ta on the hydrogen electrode 11 side becomes greater than Temp1 (YES in step S204), in step S205, the control device 80 begins to close the air regulating valve 54 from the open state so as to stop the supply of air from the air supply unit 70 to the hydrogen electrode space 11a (inside the substrate tube 14).

[0060] Subsequently, in step S206, the controller 80 starts the operation of opening the water vapor regulating valve 51 from the closed state so as to start the supply of water vapor from the water vapor supply unit 20 to the hydrogen electrode 11.

[0061] In step S207, the control device 80 determines whether the temperature Ta of the electrolysis module 19 detected by the temperature sensor 17 exceeds Temp2, and if the temperature Ta exceeds Temp2, the process proceeds to step S208. Temp2 is a temperature lower than the temperature at which the metal components contained in the hydrogen electrode 11 oxidize. Temp2 is, for example, a temperature not lower than 350°C and not higher than 400°C. Temp2 is set lower than the temperature at which the rate at which the metal components contained in the hydrogen electrode 11 react with water vapor and oxidize increases significantly.

[0062] If the temperature Ta of the electrolysis module 19 is greater than Temp1 in step S201 (YES), the process proceeds to step S207 via step S202. That is, in this case, the process proceeds to step S207 without passing through steps S204 to S206. This allows for faster startup.

[0063] In step S208, the control device 80 starts the supply of hydrogen from the hydrogen storage equipment 40 to the hydrogen electrode space 11a, and starts opening the hydrogen regulating valve 52 and the hydrogen regulating valve (or gate valve) 53 from the closed state so that the hydrogen concentration in the hydrogen electrode space 11a reaches a predetermined value. At this time, the hydrogen reuse valve 67 is opened by command of the control device 80, and hydrogen stored in the hydrogen recovery unit 64 at the time of shutdown control is supplied to the hydrogen electrode space 11a.

[0064] Next, as shown in FIG. 5, in step S209, the control device 80 reduces the supply of water vapor from the water vapor supply unit 20 to the hydrogen electrode space 11a, and closes the water vapor regulating valve 51 from an open state so that the water vapor concentration in the hydrogen electrode space 11a becomes a predetermined value.

[0065] As described above, when the temperature Ta of the electrolysis module 19 exceeds Temp2, the supply state is controlled to switch from a water vapor supply state to a state in which hydrogen, which is a reducing gas, is mixed in. By switching from a water vapor supply state to a state in which hydrogen, which is a reducing gas, is mixed in, the hydrogen electrode 11 is maintained in a reduced state, and water vapor oxidation of the hydrogen electrode by oxygen contained in the water vapor is prevented.

[0066] On the other hand, on the oxygen electrode 12 side, as shown in Fig. 4, after step S202 or step S203, in step S210, the control device 80 determines whether the temperature Ta of the electrolysis module 19 detected by the temperature sensor 17 exceeds Temp3, and if the temperature Ta exceeds Temp3, the process proceeds to step S211. Temp3 is, for example, a temperature not less than 400°C and not more than 500°C.

[0067] In step S211, the control device 80 switches the hydrogen supply valve 56 from the closed state to the open state so as to start the supply of hydrogen from the hydrogen storage facility 40 to the oxygen electrode 12. The hydrogen supplied to the oxygen electrode 12 of the electrolysis module 19 is combusted due to the catalytic action of the oxygen electrode 12, and the temperature of the electrolysis module 19 on the oxygen electrode 12 side is increased.

[0068] 5, in step S212, on the hydrogen electrode 11 side, the control device 80 determines whether the temperature Ta of the electrolysis module 19 detected by the temperature sensor 17 exceeds Temp4, and if the temperature Ta exceeds Temp4, the process proceeds to step S213. Temp4 is a temperature higher than the temperature at which the electrolysis module 19 can produce hydrogen by steam electrolysis, and is, for example, a temperature equal to or higher than 600°C and equal to or lower than 700°C.

[0069] In step S213, the control device 80 increases the amount of water vapor supplied from the water vapor supply unit 20 to the hydrogen electrode 11 so as to match the electrolysis start condition. The control device 80 adjusts the valve aperture of the water vapor regulating valve 51, and also adjusts the aperture of the hydrogen regulating valve 52, which controls the amount of hydrogen supplied from the hydrogen storage facility 40 to the hydrogen electrode 11, so as to match the hydrogen concentration in the hydrogen electrode space 11a to the electrolysis start condition.

[0070] In step S214, the control device 80 determines whether the temperature Ta of the electrolysis module 19 exceeds Temp5, whether the hydrogen concentration in the hydrogen electrode space 11a and the amount of supplied water vapor meet the electrolysis start conditions, and whether preparations are complete to start power supply. If all of these conditions are met, the control device 80 proceeds to step S215.

[0071] In step S215, the control device 80 starts power supply from the power supply unit 18 to the electrolysis module 19, and controls the power supply unit 18 to gradually increase the amount of current. The electrolysis module 19, to which power is supplied from the power supply unit 18, starts generating hydrogen and oxygen by steam electrolysis. In step S215, the valve aperture of the water vapor regulating valve 51 is adjusted to control the amount of water vapor supplied to the hydrogen electrode 11, and the aperture of the hydrogen regulating valve 52 is adjusted to control the hydrogen concentration in the hydrogen electrode space 11a.

[0072] In step S216, the control device 80 determines whether the temperature Ta of the electrolysis module 19 detected by the temperature sensor 17 exceeds Temp6 or whether the amount of current supplied to the electrolysis module 19 exceeds a predetermined value, and if either condition is met, proceeds to step S217. Temp6 is, for example, a temperature not less than 650° C. and not more than 750° C. In step S217, the supply of hydrogen to the oxygen electrode space 12a is stopped.

[0073] Thereafter, in step S218, when the amount of current supplied to the electrolysis module 19 reaches a target value, start-up is completed and the electrolysis module 19 enters a rated operation state. Note that before the amount of current reaches the rated value, the controller 80 controls the water vapor regulating valve 51 and the hydrogen regulating valve 52 so that the amount of water vapor supplied to the hydrogen electrode 11 and the hydrogen concentration in the hydrogen electrode space 11a are at rated conditions. Here, the apertures of the water vapor regulating valve 51 and the hydrogen regulating valve 52 may be controlled as a function of the amount of current.

[0074] The effects of the present embodiment described above are as follows. When hydrogen generation by the electrolysis module 19 performing steam electrolysis is stopped, the hydrogen electrode space 11a in contact with the hydrogen electrode 11 is depressurized and cooled. Since water vapor remains in the hydrogen electrode space 11a, when the temperature of the hydrogen electrode space 11a falls below the dew point due to the depressurization and cooling, the water vapor condenses and becomes drain water. Therefore, during the stop control, the vacuum pump 62 communicating with the hydrogen electrode space 11a is operated to make the hydrogen electrode space 11a at a pressure lower than the saturated vapor pressure of water, thereby lowering the partial pressure of the water vapor and lowering the dew point. This makes it possible to suppress the generation of drain water in the hydrogen electrode space 11a and prevent damage to the electrolysis cell 10 including the hydrogen electrode 11. In addition, since it is not necessary to introduce other fluids such as air or nitrogen into the hydrogen electrode space 11a during the stop control, the power and equipment costs can be reduced. Furthermore, the temperature drop in the hydrogen electrode space 11a due to the introduction of other fluids can be suppressed as much as possible, and it is possible to prepare for restart.

[0075] The pressure in the hydrogen electrode space 11a is reduced so that the temperature in the hydrogen electrode space 11a becomes higher than the saturation temperature of water vapor, thereby making it possible to suppress the generation of drain water in the hydrogen electrode space 11a.

[0076] Since the pressure in the hydrogen electrode space 11a is maintained at a pressure lower than the saturated vapor pressure of water until the next startup control, water vapor can be prevented from becoming a drain.

[0077] Since the hydrogen recovery section 64 is provided for recovering hydrogen discharged from the hydrogen electrode space 11a during shutdown control, hydrogen generated in the electrolysis module 19 is not wasted.

[0078] The hydrogen recovered by the hydrogen recovery unit 64 during the shutdown control is led to the hydrogen electrode space 11a during the next startup control. This allows the hydrogen recovered during the shutdown control to be used effectively. Also, the consumption of the reducing agent (hydrogen) during the startup control can be reduced.

[0079] The pressure in the hydrogen electrode space 11a and the pressure in the oxygen electrode space 12a are controlled to be equal, thereby making it possible to prevent the electrolysis cell 10 from being damaged by a pressure difference.

[0080] In the above-described embodiment, the configuration includes the hydrogen recovery unit 64, the hydrogen reuse piping 66, and the hydrogen reuse valve 67 as shown in FIG. 1. However, if hydrogen is not recovered and reused from the gas exhausted by the vacuum pump 62, the hydrogen recovery unit 64, the hydrogen reuse piping 66, and the hydrogen reuse valve 67 can be omitted. Further, the vacuum pumps 62, 69 have been used as an example of devices for reducing the pressure in the hydrogen electrode space 11a and the oxygen electrode space 12a, but other pressure reducing devices such as an ejector may also be used. In addition, although the vacuum pump 62 is provided on the exhaust side of the hydrogen electrode space 11a, it may be provided on the inlet side (hydrogen supply side) of the hydrogen electrode space 11a. Similarly, for the oxygen electrode space 12a, the vacuum pump 69 may be provided on the inlet side (oxygen supply side) of the oxygen electrode space 12a.

[0081] The hydrogen generation system and the control method thereof described in each of the above-described embodiments can be understood, for example, as follows.

[0082] A hydrogen generation system (100) according to a first aspect of the present disclosure includes an electrolysis cell (10) having a hydrogen electrode (11), an oxygen electrode (12), and an electrolyte layer (13) disposed between the hydrogen electrode and the oxygen electrode, an electrolysis module (19) that supplies water vapor to the hydrogen electrode to generate hydrogen by water vapor electrolysis, a hydrogen electrode-side pressure reduction device (62) that reduces the pressure in a hydrogen electrode space (11a) in contact with the hydrogen electrode, and a control unit (80) that operates the hydrogen electrode-side pressure reduction device (62) to control the pressure in the hydrogen electrode space (11a) to a pressure lower than the saturated vapor pressure of water when performing stop control to stop the generation of hydrogen by the electrolysis module.

[0083] When hydrogen generation by the electrolysis module performing steam electrolysis is stopped, the hydrogen electrode space in contact with the hydrogen electrode is depressurized and cooled. Since water vapor remains in the hydrogen electrode space, when the temperature of the hydrogen electrode space falls below the dew point due to the depressurization and cooling, the water vapor condenses and becomes drain water. Therefore, during the stop control, the hydrogen electrode side pressure reducing device is operated to make the hydrogen electrode space at a pressure lower than the saturated vapor pressure of water, thereby lowering the partial pressure of the water vapor and lowering the dew point. This makes it possible to suppress the generation of drain water in the hydrogen electrode space and prevent damage to the electrolysis cell including the hydrogen electrode. In addition, since it is not necessary to introduce other fluids such as air or nitrogen into the hydrogen electrode space during the stop control, the power and equipment costs can be reduced. Furthermore, the temperature drop in the hydrogen electrode space due to the introduction of other fluids can be suppressed as much as possible, and it is possible to prepare for restart. The hydrogen electrode side pressure reducing device may be, for example, a vacuum device such as a vacuum pump or an ejector. When the pressure in the hydrogen electrode space is maintained at atmospheric pressure, the pressure in the hydrogen electrode space is preferably negative.

[0084] The hydrogen generation system (100) according to the second aspect of the present disclosure, in the first aspect, includes a temperature sensor (17) that measures the temperature of the hydrogen electrode space (11a) and a pressure sensor (23) that measures the pressure of the hydrogen electrode space (11a), and the control unit (80) reduces the pressure of the hydrogen electrode space (11a) so that the temperature of the hydrogen electrode space (11a) obtained from the temperature sensor (23) becomes higher than the saturation temperature of water vapor in the hydrogen electrode space (11a) obtained from the pressure sensor (23).

[0085] The pressure in the hydrogen electrode space is reduced so that the temperature in the hydrogen electrode space becomes higher than the saturation temperature of water vapor, thereby making it possible to suppress the generation of drain water in the hydrogen electrode space.

[0086] In the hydrogen generation system (100) according to a third aspect of the present disclosure, in the first or second aspect, the control unit (80) maintains the pressure in the hydrogen electrode space (11a) at a pressure lower than the saturated vapor pressure of water during the period from the shutdown control to the next startup control.

[0087] Since the pressure in the hydrogen electrode space is maintained at a pressure lower than the saturated vapor pressure of water until the next startup control, water vapor can be prevented from becoming a drain.

[0088] A hydrogen generation system (100) according to a fourth aspect of the present disclosure is any one of the first to third aspects, and is provided with a hydrogen recovery section (64) that recovers hydrogen discharged from the hydrogen electrode space (11a) during the stop control.

[0089] Since a hydrogen recovery section is provided for recovering hydrogen discharged from the hydrogen electrode space during shutdown control, hydrogen generated in the electrolysis module is not wasted.

[0090] In the hydrogen generation system (100) according to a fifth aspect of the present disclosure, in the fourth aspect, the control unit (80) guides the hydrogen recovered in the hydrogen recovery unit (64) to the hydrogen electrode space (11a) during the next startup control.

[0091] The hydrogen recovered in the hydrogen recovery section during shutdown control is led to the hydrogen electrode space during the next startup control. This allows the hydrogen recovered during shutdown to be used effectively. It also reduces the consumption of reducing agent (hydrogen) during startup.

[0092] A hydrogen generation system (100) according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, includes an oxygen electrode side pressure reduction device (69) that reduces the pressure in an oxygen electrode space (12a) in contact with the oxygen electrode (12), and the control unit (80) controls the pressure in the oxygen electrode space (12a) using the oxygen electrode side pressure reduction device (69) so that the pressure is equivalent to the pressure in the hydrogen electrode space (11a).

[0093] The pressure in the hydrogen electrode space and the oxygen electrode space are controlled to be equal, which makes it possible to prevent the electrolysis cell from being damaged by a pressure difference.

[0094] A control method for a hydrogen generation system (100) according to a first aspect of the present disclosure is a control method for a hydrogen generation system (100) including an electrolysis cell (10) having a hydrogen electrode (11), an oxygen electrode (12), and an electrolyte layer (13) disposed between the hydrogen electrode and the oxygen electrode, an electrolysis module (19) that supplies water vapor to the hydrogen electrode to generate hydrogen by water vapor electrolysis, and a hydrogen electrode-side pressure reduction device (62) that reduces the pressure in a hydrogen electrode space (11a) in contact with the hydrogen electrode, wherein, when performing stop control to stop hydrogen generation by the electrolysis module (19), the hydrogen electrode-side pressure reduction device (62) is operated to control the pressure in the hydrogen electrode space (11a) to a pressure lower than the saturated vapor pressure of water. [Explanation of symbols]

[0095] 10 Electrolysis Cell 11 Hydrogen electrode 11a Hydrogen polar space 12 Oxygen electrode 12a Oxygen polar space 13 Electrolyte layer 14 Base tube 15 Interconnector 16 Lead Film 17 Temperature Sensor 18 Power supply section 19 Electrolysis Module 20 Steam supply section 21 Steam supply pipe 23 Hydrogen electrode pressure sensor 24 Oxygen electrode pressure sensor 30 Hydrogen separation equipment 31 Hydrogen exhaust valve 32 Hydrogen booster 33 Hydrogen exhaust pipe 40 Hydrogen storage equipment (hydrogen supply section) 41 Hydrogen supply pipe 42 Hydrogen supply pipe 43 Hydrogen supply pipe (hydrogen system) 50 Adjustment section 51 Steam Regulating Valve 52 Hydrogen Regulating Valve 53 Hydrogen Regulating Valve (or Gate Valve) 54 Air Regulating Valve 55 Air side discharge control valve for hydrogen electrode vent gas 56 Hydrogen supply valve 57 Air Regulating Valve 60 Vacuum piping 62 Hydrogen electrode side vacuum pump (hydrogen electrode side pressure reducing device) 63 Exhaust pipe 64 Hydrogen Recovery Section 65 Vacuum piping 66 Hydrogen Reuse Piping 67 Hydrogen Recycle Valve 68 Oxygen exhaust pipe 68a Gate valve 69 Oxygen electrode side vacuum pump (Oxygen electrode side pressure reducing device) 70 Air supply section 72 Air supply pipe for hydrogen electrode 73 Air exhaust pipe 74 Air supply pipe 80 Control device (control unit) 100 Hydrogen Generation System Ta Temperature of electrolysis module

Claims

1. an electrolysis module including an electrolysis cell having a hydrogen electrode, an oxygen electrode, and an electrolyte layer disposed between the hydrogen electrode and the oxygen electrode, the electrolysis module supplying water vapor to the hydrogen electrode to generate hydrogen by water vapor electrolysis; a hydrogen electrode side pressure reducing device for reducing the pressure of a hydrogen electrode space in contact with the hydrogen electrode; a control unit that operates the hydrogen electrode side pressure reduction device to control the pressure in the hydrogen electrode space to a pressure lower than the saturated vapor pressure of water when performing stop control to stop hydrogen production by the electrolysis module; A hydrogen generation system comprising:

2. A temperature sensor for measuring the temperature of the hydrogen electrode space; a pressure sensor for measuring the pressure in the hydrogen electrode space; Equipped with 2. The hydrogen generation system according to claim 1, wherein the control unit reduces the pressure in the hydrogen electrode space so that the temperature of the hydrogen electrode space obtained from the temperature sensor becomes higher than the saturation temperature of water vapor in the hydrogen electrode space obtained from the pressure sensor.

3. The hydrogen generation system according to claim 1 , wherein the control unit maintains the pressure in the hydrogen electrode space at a pressure lower than the saturated vapor pressure of water during the period from the shutdown control to the next startup control.

4. 2. The hydrogen generation system according to claim 1, further comprising a hydrogen recovery section that recovers hydrogen discharged from the hydrogen electrode space during the stop control.

5. The hydrogen generation system according to claim 4 , wherein the control unit guides the hydrogen recovered in the hydrogen recovery unit to the hydrogen electrode space at the time of the next startup control.

6. an oxygen electrode side pressure reducing device for reducing the pressure of an oxygen electrode space in contact with the oxygen electrode, The hydrogen generation system according to claim 1 , wherein the control unit controls the pressure in the oxygen electrode space by using the oxygen electrode side pressure reducing device so that the pressure in the oxygen electrode space is equal to the pressure in the hydrogen electrode space.

7. an electrolysis module including an electrolysis cell having a hydrogen electrode, an oxygen electrode, and an electrolyte layer disposed between the hydrogen electrode and the oxygen electrode, the electrolysis module supplying water vapor to the hydrogen electrode to generate hydrogen by water vapor electrolysis; a hydrogen electrode side pressure reducing device for reducing the pressure of a hydrogen electrode space in contact with the hydrogen electrode; A method for controlling a hydrogen generation system comprising: A control method for a hydrogen generation system, comprising: operating the hydrogen electrode side pressure reducing device to control the pressure in the hydrogen electrode space to a pressure lower than the saturated vapor pressure of water when performing stop control to stop hydrogen generation by the electrolysis module.

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