JP7552079B2 - Water Electrolysis System - Google Patents

Description

The present invention relates to a water electrolysis system.

Conventionally, water electrolysis systems that generate hydrogen and oxygen by electrolysis of water are known (see, for example, Patent Documents 1 and 2). Patent Document 1 discloses a technology in which, when the water electrolysis system is shut down, air introduced from an air blower is used to discharge water present in the water circulation path and the water electrolysis stack, thereby preventing damage to the water electrolysis stack due to freezing of water in the water electrolysis stack. Patent Document 2 discloses a technology in which a gas-driven water supply device driven by generated gas transports water electrolyzed in the water electrolysis device.

JP 2019-123899 A JP 2018-178231 A

In the water electrolysis system described in Patent Document 2, when water electrolysis is stopped, water is present in the water supply flow path and the water electrolysis cell. For example, metal piping such as stainless steel is often used for the water supply flow path, and a power supply such as a metal mesh is often provided in the water electrolysis cell. Therefore, if water electrolysis is stopped for a long time, metal ions may be eluted from the metal piping as the water supply flow path and the metal mesh in the water electrolysis cell into the water supply flow path and the accumulated water in the water electrolysis cell, and the conductivity of the accumulated water may increase. When water electrolysis is started in the water electrolysis system, when water is supplied to the water electrolysis cell, the accumulated water is also supplied to the water electrolysis cell. Therefore, if the conductivity of the accumulated water increases, the conductivity of the water supplied to the water electrolysis cell increases, and there is a risk of the electrodes of the water electrolysis cell deteriorating.

The present invention has been made to solve the above-mentioned problems, and aims to provide a technology that suppresses an increase in the conductivity of water supplied to an electrolysis cell in a water electrolysis system.

The present invention has been made to solve at least some of the above problems, and can be realized in the following form.

(1) According to one aspect of the present invention, a water electrolysis system is provided. The water electrolysis system includes an electrolysis cell that includes an oxygen electrode, an oxygen electrode side flow path, a hydrogen electrode, and a hydrogen electrode side flow path, and that generates oxygen and hydrogen by electrolyzing water; a water storage unit that is connected to the oxygen electrode side flow path of the electrolysis cell via a water supply flow path and that stores water to be supplied to the electrolysis cell, and a water supply unit that supplies the water in the water storage unit to the electrolysis cell via the water supply flow path; an oxygen side processing unit that is connected to the oxygen electrode side flow path of the electrolysis cell via an oxygen side flow path and that is connected to the water supply flow path and the oxygen supply flow path, stores oxygen generated by the electrolysis cell in the first oxygen storage unit via the oxygen side flow path, and supplies oxygen in the first oxygen storage unit to the water supply flow path via the oxygen supply flow path; and a control unit that controls the oxygen side processing unit to supply oxygen in the oxygen storage unit to the water supply flow path when electrolysis of water by the electrolysis cell is stopped.

According to this configuration, when the electrolysis of water by the electrolysis cell is stopped, oxygen in the oxygen storage unit of the first oxygen side processing unit is supplied to the water supply flow path. The water supply flow path is connected to the oxygen electrode side flow path of the electrolysis cell, and the oxygen side flow path is connected to the oxygen electrode side flow path, so that the supplied oxygen flows through the water supply flow path, the oxygen electrode side flow path of the electrolysis cell, and the oxygen side flow path. Therefore, when the electrolysis of water by the electrolysis cell is stopped, at least a portion of the water present in the water supply flow path, the oxygen electrode side flow path of the electrolysis cell, and the oxygen side flow path can be discharged from those flow paths by the oxygen generated by water electrolysis. Therefore, while the electrolysis of water by the electrolysis cell is stopped, the amount of water remaining in the water supply flow path, the oxygen electrode side flow path of the electrolysis cell, and the oxygen side flow path can be reduced, and an increase in the conductivity of the water supplied to the electrolysis cell at the start of water electrolysis can be suppressed.

(2) In the water electrolysis system of the above embodiment, the oxygen-side processing unit further includes an oxygen-side exhaust flow path connected to the oxygen-side flow path, and when the control unit stops the electrolysis of water by the electrolysis cell and then starts the electrolysis of water by the electrolysis cell, the control unit controls the water supply unit to supply water in the water storage unit to the oxygen electrode-side flow path of the electrolysis cell via the water supply flow path, and controls the oxygen-side processing unit to discharge water that has flowed from the oxygen electrode-side flow path of the electrolysis cell into the oxygen-side flow path to the outside of the water electrolysis system via the oxygen-side exhaust flow path.

In this way, when the electrolysis of water by the electrolytic cell is started, the water in the water storage unit flows through the water supply flow path, the oxygen electrode side flow path of the electrolytic cell, and the oxygen side flow path, and is discharged outside the water electrolysis system via the oxygen side discharge flow path. Therefore, even if the water supply flow path, the oxygen electrode side flow path of the electrolytic cell, and the oxygen side flow path are purged using oxygen in the first oxygen storage unit when the electrolysis of water by the electrolytic cell is stopped, the water remains in those flow paths, and while the electrolysis of water by the electrolytic cell is stopped, the water that has accumulated in those flow paths and has an increased conductivity can be discharged outside the water electrolysis system by the water. Therefore, the increase in the conductivity of the water supplied to the electrolytic cell when the electrolysis of water starts can be further suppressed.

(3) In the water electrolysis system of the above embodiment, the oxygen-side processing unit further includes a second oxygen storage unit connected to the oxygen electrode-side flow path of the electrolysis cell via the oxygen-side flow path, and stores oxygen generated in the electrolysis cell in the second oxygen storage unit at a pressure lower than the pressure of the first oxygen storage unit. When electrolysis of water by the electrolysis cell is stopped, the control unit may control the oxygen-side processing unit to supply oxygen in the first oxygen storage unit to the water supply flow path due to the pressure difference between the first oxygen storage unit and the second oxygen storage unit.

In this way, oxygen in the first oxygen storage unit can be supplied to the water supply flow path without using a pump to supply oxygen in the first oxygen storage unit to the water supply flow path. This contributes to the miniaturization and cost reduction of the water electrolysis system. In addition, the energy required to drain water from the flow path can be reduced compared to when an electric pump is used.

(4) The water electrolysis system of the above embodiment includes a first hydrogen storage unit connected to the hydrogen electrode side flow path of the electrolysis cell via a hydrogen side flow path and connected to the hydrogen electrode side flow path of the electrolysis cell via a hydrogen supply flow path, and further includes a hydrogen side processing unit that stores hydrogen generated in the electrolysis cell in the first hydrogen storage unit via the hydrogen side flow path and supplies hydrogen in the first hydrogen storage unit to the hydrogen electrode side flow path of the electrolysis cell via the hydrogen supply flow path, and the control unit may control the hydrogen side processing unit to supply hydrogen in the first hydrogen storage unit to the hydrogen electrode side flow path of the water electrolysis cell when electrolysis of water by the electrolysis cell is stopped.

In this way, when the electrolysis of water by the electrolysis cell is stopped, hydrogen in the hydrogen storage unit of the first hydrogen side processing unit is supplied to the hydrogen electrode side flow path of the electrolysis cell. Since the hydrogen side flow path is connected to the hydrogen electrode side flow path, the supplied hydrogen flows through the hydrogen electrode side flow path and the hydrogen side flow path of the electrolysis cell. Therefore, when the electrolysis of water by the electrolysis cell is stopped, at least a part of the water in the hydrogen electrode side flow path and the hydrogen side flow path of the electrolysis cell can be discharged from those flow paths by the hydrogen generated by the water electrolysis. Therefore, while the electrolysis of water by the electrolysis cell is stopped, the amount of water retained in the hydrogen electrode side flow path of the electrolysis cell can be reduced, and deterioration of the hydrogen electrode due to an increase in the conductivity of the retained water can be suppressed. In addition, while the electrolysis of water by the electrolysis cell is stopped, the amount of water retained in the hydrogen side flow path can be reduced, and for example, when the water flowing into the hydrogen side processing unit from the water electrolysis cell is reused as water to be supplied to the water electrolysis cell, the increase in the conductivity of the water supplied to the electrolysis cell can be suppressed.

(5) In the water electrolysis system of the above embodiment, the hydrogen-side processing unit further includes a hydrogen-side discharge flow path connected to the hydrogen-side flow path, and when electrolysis of water by the electrolysis cell is started after the control unit has stopped electrolysis of water by the electrolysis cell, the control unit controls the hydrogen-side processing unit to supply hydrogen in the first hydrogen storage unit to the hydrogen electrode-side flow path of the electrolysis cell via the hydrogen supply flow path, and to discharge hydrogen that has flowed from the hydrogen electrode-side flow path of the electrolysis cell to the hydrogen-side flow path to the outside of the water electrolysis system via the hydrogen-side discharge flow path.

In this way, when the electrolysis of water by the electrolysis cell is started, the hydrogen in the hydrogen storage unit flows through the hydrogen electrode side flow path and the hydrogen side flow path of the electrolysis cell and is discharged to the outside of the water electrolysis system via the hydrogen side discharge flow path. Therefore, even if the hydrogen in the first hydrogen storage unit is used to purge the hydrogen electrode side flow path and the hydrogen side flow path of the electrolysis cell when the electrolysis of water by the electrolysis cell is stopped, the hydrogen still remains in those flow paths, and the water that remains in those flow paths while the electrolysis of water by the electrolysis cell is stopped and has an increased conductivity can be discharged to the outside of the water electrolysis system by the hydrogen generated by the water electrolysis. Therefore, for example, when the water flowing into the hydrogen side treatment unit from the water electrolysis cell is reused as water to be supplied to the water electrolysis cell, the increase in the conductivity of the water to be supplied to the electrolysis cell can be further suppressed.

(6) In the water electrolysis system of the above embodiment, the hydrogen-side processing unit further includes a second hydrogen storage unit connected to the hydrogen electrode-side flow path of the electrolysis cell via the hydrogen-side flow path, and stores hydrogen generated in the electrolysis cell at a pressure lower than the pressure of the first hydrogen storage unit. When the electrolysis of water by the electrolysis cell is stopped, the control unit may control the hydrogen-side processing unit to supply hydrogen in the first hydrogen storage unit to the hydrogen electrode-side flow path of the electrolysis cell due to the pressure difference between the first hydrogen storage unit and the second hydrogen storage unit.

In this way, hydrogen in the first hydrogen storage unit can be supplied to the electrolysis cell without using a pump for supplying hydrogen in the first hydrogen storage unit to the electrolysis cell . This contributes to downsizing and cost reduction of the water electrolysis system. Furthermore, the energy required for draining water from the flow path can be reduced compared to when an electric pump is used.

(7) According to another aspect of the present invention, a water electrolysis system is provided. The water electrolysis system includes an electrolysis cell that includes an oxygen electrode, an oxygen electrode side flow path, a hydrogen electrode, and a hydrogen electrode side flow path, and that generates oxygen and hydrogen by electrolyzing water; a water storage unit that is connected to the oxygen electrode side flow path of the electrolysis cell via a water supply flow path and that stores water to be supplied to the electrolysis cell; a water supply unit that supplies water in the water storage unit to the electrolysis cell via the water supply flow path; an oxygen storage unit that is connected to the oxygen electrode side flow path of the electrolysis cell via an oxygen side flow path; and an oxygen side exhaust flow path that is connected to the oxygen side flow path. The system includes an oxygen-side processing unit that stores the oxygen generated in the electrolysis cell in the oxygen storage unit via the oxygen-side flow path, and a control unit that controls the water supply unit to supply the water in the water storage unit to the oxygen electrode-side flow path of the electrolysis cell via the water supply flow path when electrolysis of water by the electrolysis cell is started after the electrolysis of water by the electrolysis cell is stopped, and controls the oxygen-side processing unit to discharge the water that has flowed from the oxygen electrode-side flow path of the electrolysis cell to the oxygen-side flow path outside the water electrolysis system via the oxygen-side discharge flow path.

According to this configuration, when the electrolysis of water by the electrolysis cell starts, the water in the water storage section flows through the water supply flow path, the oxygen electrode side flow path of the electrolysis cell, and the oxygen side flow path, and is discharged outside the water electrolysis system via the oxygen side discharge flow path. Therefore, while the electrolysis of water by the electrolysis cell is stopped, the water that has accumulated in the water supply flow path, the oxygen electrode side flow path of the electrolysis cell, and the oxygen side flow path and has increased conductivity can be discharged outside the water electrolysis system by the water. Therefore, the increase in the conductivity of the water supplied to the electrolysis cell when the electrolysis of water starts can be further suppressed.

(8) The water electrolysis system of the above embodiment includes a first hydrogen storage unit connected to the hydrogen electrode side flow path of the electrolysis cell via a hydrogen side flow path and connected to the hydrogen electrode side flow path of the electrolysis cell via a hydrogen supply flow path, and further includes a hydrogen side processing unit that stores hydrogen generated in the electrolysis cell in the first hydrogen storage unit via the hydrogen side flow path and supplies hydrogen in the first hydrogen storage unit to the hydrogen electrode side flow path of the electrolysis cell via the hydrogen supply flow path, and when electrolysis of water by the electrolysis cell is started after the control unit stops electrolysis of water by the electrolysis cell, the control unit may control the hydrogen side processing unit to supply hydrogen in the hydrogen storage unit to the hydrogen electrode side flow path of the electrolysis cell via the hydrogen supply flow path and discharge hydrogen that has flowed from the hydrogen electrode side flow path of the electrolysis cell to the hydrogen side flow path outside the water electrolysis system via the hydrogen side discharge flow path.

In this way, when the electrolysis of water by the electrolysis cell is started, the hydrogen in the hydrogen storage unit flows through the hydrogen electrode side flow path and the hydrogen side flow path of the electrolysis cell and is discharged to the outside of the water electrolysis system via the hydrogen side discharge flow path. Therefore, even if the hydrogen in the first hydrogen storage unit is used to purge the hydrogen electrode side flow path and the hydrogen side flow path of the electrolysis cell when the electrolysis of water by the electrolysis cell is stopped, the hydrogen still remains in those flow paths, and the water that remains in those flow paths while the electrolysis of water by the electrolysis cell is stopped and has an increased conductivity can be discharged to the outside of the water electrolysis system by the hydrogen generated by the water electrolysis. Therefore, for example, when the water flowing into the hydrogen side treatment unit from the water electrolysis cell is reused as water to be supplied to the water electrolysis cell, the increase in the conductivity of the water to be supplied to the electrolysis cell can be further suppressed.

The present invention can be realized in various forms, such as a method for controlling a water electrolysis system, a water electrolysis method, a computer program for causing a computer to perform water electrolysis, a server device for distributing the computer program, a non-transitory storage medium on which the computer program is stored, etc.

1 is an explanatory diagram illustrating a schematic configuration of a water electrolysis system according to a first embodiment; FIG. 2 is an explanatory diagram of a water electrolysis process in the water electrolysis system. FIG. 2 is an explanatory diagram of a water electrolysis stopping process in the water electrolysis system. FIG. 2 is an explanatory diagram of a water electrolysis starting process in the water electrolysis system. FIG. 11 is an explanatory diagram showing a schematic configuration of a water electrolysis system according to a second embodiment. FIG. 2 is an explanatory diagram of a water electrolysis stopping process in the water electrolysis system. FIG. 13 is an explanatory diagram showing a schematic configuration of a water electrolysis system according to a third embodiment. FIG. 2 is an explanatory diagram of a water electrolysis stopping process in the water electrolysis system. FIG. 13 is an explanatory diagram showing a schematic configuration of a water electrolysis system according to a fourth embodiment. FIG. 2 is an explanatory diagram of a water electrolysis starting process in the water electrolysis system.

First Embodiment
FIG. 1 is an explanatory diagram showing a schematic configuration of a water electrolysis system 1 of the first embodiment. The water electrolysis system 1 includes an electrolysis cell 10, an oxygen-side treatment section 20, a hydrogen-side treatment section 30, a water supply section 40, and a control section 50. In the water electrolysis system 1 of the present embodiment, oxygen and hydrogen are generated by electrolyzing water in the electrolysis cell 10. The oxygen discharged from the electrolysis cell 10 together with the water that was not electrolyzed is separated into water in the oxygen-side treatment section 20 and stored in the oxygen-side treatment section 20. On the other hand, the hydrogen discharged from the electrolysis cell 10 together with the water that was not electrolyzed is separated into water in the hydrogen-side treatment section 30 and stored in the hydrogen-side treatment section 30. In addition, the water separated in the oxygen-side treatment section 20 and the hydrogen-side treatment section 30 is sent to the water supply section 40 and is supplied again to the electrolysis cell 10 for electrolysis in the electrolysis cell 10. In the water electrolysis system 1 of the present embodiment, in order to efficiently generate hydrogen and oxygen with high purity, electrolysis is performed on pure water with a low impurity content and high purity, but the purity of the water to be electrolyzed is not limited thereto. In this specification, the electrolysis of water is also referred to as "water electrolysis."

The electrolysis cell 10 is a PEM (Polymer Electrolyte Membrane) type water electrolysis cell, and has a membrane electrode assembly (hereinafter referred to as "MEA") 11. The MEA 11 is formed by bonding an oxygen electrode 11b, which generates oxygen from oxygen ions generated by electrolysis of water, and a hydrogen electrode 11c, which generates hydrogen from hydrogen ions, to both sides of an electrolyte membrane 11a that allows hydrogen ions and water to pass through. The oxygen electrode 11b has an oxygen electrode side flow path 12, such as a groove or a pore of a porous material. The hydrogen electrode 11c has a hydrogen electrode side flow path 13, such as a groove or a pore of a porous material, similar to the oxygen electrode side flow path 12. The electrolysis cell 10 is provided with a power source 14 that supplies power to the oxygen electrode 11b and hydrogen electrode 11c of the MEA 11.

In the electrolysis cell 10, when the water supplied by the water supply unit 40 flows through the oxygen electrode side flow path 12, power is supplied to the oxygen electrode 11b and the hydrogen electrode 11c of the MEA 11, and water is electrolyzed at the oxygen electrode 11b to generate oxygen and hydrogen ions. The generated oxygen is discharged to the outside of the electrolysis cell 10 through the oxygen electrode side flow path 12 together with a portion of the water that was not electrolyzed. The hydrogen ions generated at the oxygen electrode 11b move from the oxygen electrode 11b to the hydrogen electrode 11c together with the water that was not electrolyzed and was not discharged to the outside of the electrolysis cell 10 (produced water), and are combined with electrons at the hydrogen electrode 11c to become hydrogen. The hydrogen generated at the hydrogen electrode 11c is discharged to the outside of the electrolysis cell 10 together with the produced water through the hydrogen electrode side flow path 13. In this embodiment, the flow direction of oxygen and water in the oxygen electrode side flow path 12 is the direction indicated by the dotted arrow A12 in FIG. 1, and the flow direction of hydrogen and associated water in the hydrogen electrode side flow path 13 is the direction indicated by the dotted arrow A13 in FIG. 1.

When electrolysis of water is performed in the electrolysis cell 10, a portion of the water supplied to the oxygen electrode side flow path 12 becomes a refrigerant that cools the electrolysis cell 10, which is heated to a high temperature due to overvoltage. That is, the water supply unit 40 of this embodiment supplies the electrolysis cell 10 with water to be electrolyzed and water for cooling the electrolysis cell 10. The water that has cooled the electrolysis cell 10 is discharged to the outside of the electrolysis cell 10 together with oxygen or hydrogen as the water that was not electrolyzed as described above. The mixture of oxygen and water discharged from the oxygen electrode side flow path 12 is sent to the oxygen side treatment unit 20. The mixture of hydrogen and water discharged from the hydrogen electrode side flow path 13 is sent to the hydrogen side treatment unit 30.

The water supply unit 40 includes a water tank 41, a supply pump 43, an ion exchanger 45, a liquid delivery pump 77, and an ion exchanger 79. The water supply unit 40 temporarily stores the water to be supplied to the electrolysis cell 10 and supplies water W70 to the electrolysis cell 10. The water tank 41 in this embodiment is also referred to as the "water storage unit."

The water tank 41 temporarily stores water (dotted arrow F40 in FIG. 1) supplied from an external water supply device (not shown). Water separated from the gas and liquid in the oxygen side treatment unit 20 and water separated from the gas and liquid in the hydrogen side treatment unit 30 are also sent to the water tank 41. The water tank 41 is connected to the electrolysis cell 10 via the water supply flow path 40a, the water supply flow path 40d, the supply pump 43, and the water supply flow path 40b. The water W70 in the water tank 41 is pressurized by the supply pump 43 and supplied to the oxygen electrode side flow path 12 of the electrolysis cell 10. The water tank 41 is connected to the supply pump 43 via the water supply flow path 40a and the water supply flow path 40b.

The supply pump 43 is a diaphragm-type pump that is driven by the pressure of hydrogen supplied from the hydrogen-side processing unit 30. Note that the driving method of the supply pump 43 is not limited to this. The water W70 stored in the water tank 41 may be pressurized by rotating gears or a turbine using the flow of hydrogen, and the pressurized water may be supplied to the electrolysis cell 10.

A three-way valve 44 is disposed in the water supply flow passage 40b that connects the supply pump 43 and the electrolysis cell 10. The three-way valve 44 directs a portion of the water flowing through the water supply flow passage 40b to the bypass flow passage 40c. The ion exchanger 45 disposed in the bypass flow passage 40c reduces the conductivity of the water flowing through the bypass flow passage 40c by ion exchange. This makes it possible to suppress deterioration of the electrodes of the electrolysis cell 10.

The liquid delivery pump 77 and the ion exchanger 79 are provided in the oxygen side flow path 20c that connects the oxygen side processing unit 20 and the water tank 41. The liquid delivery pump 77 is a diaphragm type pump that is driven by the pressure of oxygen supplied from the oxygen side processing unit 20. The liquid delivery pump 77 pressurizes the water supplied from the oxygen side processing unit 20 and sends the pressurized water to the water tank 41. The ion exchanger 79 reduces the conductivity of the water that the liquid delivery pump 77 sends to the water tank 41 by ion exchange. Note that the driving method of the liquid delivery pump 77 is not limited to this. Water may be pressurized and sent to the water tank 41 by rotating a gear or a turbine with oxygen.

The control unit 50 is a computer including a ROM, a RAM, and a CPU. The control unit 50 controls the entire water electrolysis system 1, including the water electrolysis process, the water electrolysis stop process, and the water electrolysis start process (described later).

The oxygen-side processing unit 20 includes a heat exchanger 21, an oxygen-side gas-liquid separator 23, a first oxygen tank 63, and a second oxygen tank 65. The oxygen-side processing unit 20 separates oxygen from a mixture of oxygen and water discharged from the oxygen electrode-side flow path 12 of the electrolysis cell 10, stores the separated oxygen, and sends the water W20 obtained by gas-liquid separation to the water tank 41 of the water supply unit 40. The oxygen-side processing unit 20 also supplies a portion of the stored oxygen to the liquid feed pump 77 of the water supply unit 70. The oxygen-side processing unit 20 also supplies oxygen in the first oxygen tank 63 to the water supply flow path 40d of the water supply unit 40. The oxygen-side processing unit 20 can also discharge the water discharged from the electrolysis cell 10 to the outside of the water electrolysis system 1. In this embodiment, the first oxygen tank 63 is also called the "first oxygen storage unit" or "oxygen storage unit", and the second oxygen tank 65 is also called the "second oxygen storage unit".

The heat exchanger 21 is connected to the oxygen electrode side flow path 12 of the electrolysis cell 10 via the oxygen side flow path 20a and the oxygen side flow path 20d. The heat exchanger 21 has a heat exchange pipe 21a through which a heat exchange fluid flows. In the heat exchanger 21, heat is recovered from a mixture of oxygen and water that is relatively hot due to cooling the electrolysis cell 10 whose temperature has risen, by using the heat exchange fluid flowing through the heat exchange pipe 21a. The heat recovered by the heat exchange fluid is used, for example, to store heat in an external heat storage body (not shown) or to directly heat an external object (not shown). Since the electrolysis cell 10 is at a high temperature due to overvoltage, part of the water discharged from the oxygen electrode side flow path 12 of the electrolysis cell 10 is water vapor. The heat exchanger 21 converts at least a part of the water vapor discharged from the electrolysis cell 10 into liquid water. The heat exchanger 21 is connected to the oxygen side gas-liquid separator 23 via the oxygen side flow path 20b.

The oxygen-side gas-liquid separator 23 is, for example, a cyclone-type gas-liquid separator, which separates the mixture of oxygen and water after passing through the heat exchanger 21 into oxygen and water. As described above, the water vapor is converted into liquid water by the heat exchanger 21, so the humidity (water vapor content) of the oxygen flowing into the oxygen-side gas-liquid separator 23 is lower than the oxygen discharged from the electrolysis cell 10. In other words, the oxygen separated into gas and liquid by the oxygen-side gas-liquid separator 23 can be called dry oxygen. In the oxygen-side gas-liquid separator 23 of this embodiment, oxygen accumulates on the upper side of the oxygen-side gas-liquid separator 23, and water W20 accumulates on the lower side. Note that the method of gas-liquid separation by the oxygen-side gas-liquid separator 23 is not limited to the cyclone type, and may be a method using a filter, a method using centrifugal force, or a cooling type.

The oxygen-side gas-liquid separator 23 is connected to the water supply unit 40 via the oxygen-side flow path 20c. The oxygen-side gas-liquid separator 23 is provided with a water level gauge 22a that detects the water level of the water W20 in the oxygen-side gas-liquid separator 23. In addition, the oxygen-side flow path 20c is provided with an on-off valve 22 that is controlled to open and close by the control unit 50. When the water level of the water W20 detected by the water level gauge 22a is equal to or lower than a predetermined water level, the control unit 50 closes the on-off valve 22 to cut off the oxygen-side gas-liquid separator 23 and the water supply unit 40. On the other hand, when the water level of the water W20 detected by the water level gauge 22a exceeds the predetermined water level, the control unit 50 opens the on-off valve 22, and the water W20 in the oxygen-side gas-liquid separator 23 is sent to the water supply unit 40 via the oxygen-side flow path 20c.

The oxygen-side gas-liquid separator 23 is connected to the first oxygen tank 63 via the oxygen-side flow path 60a and the oxygen-side flow path 60b, and is connected to the second oxygen tank 65 via the oxygen-side flow path 60a, the oxygen-side flow path 60d, and the oxygen-side flow path 60e. The oxygen separated into gas and liquid by the oxygen-side gas-liquid separator 23 flows into the first oxygen tank 63 via the oxygen-side flow path 60a and the oxygen-side flow path 60b while the water electrolysis process is being performed, and flows into the second oxygen tank 65 via the oxygen-side flow path 60a, the oxygen-side flow path 60d, and the oxygen-side flow path 60e while the water electrolysis process is stopped (described in detail later). A check valve 24 is disposed in the oxygen-side flow path 60a. The check valve 24 allows the flow of fluid from the oxygen-side gas-liquid separator 23 to the first oxygen tank 63 and the second oxygen tank 65, while blocking the flow of fluid from the first oxygen tank 63 and the second oxygen tank 65 to the oxygen-side gas-liquid separator 23.

The oxygen-side gas-liquid separator 23 is also provided with a pressure gauge 68 that detects the oxygen pressure in the oxygen-side gas-liquid separator 23. The pressure gauge 68 outputs the detected oxygen pressure to the control unit 50.

The first oxygen tank 63 stores the oxygen obtained by gas-liquid separation in the oxygen-side gas-liquid separator 23 at a relatively high pressure. The first oxygen tank 63 is connected to the second oxygen tank 65 via the oxygen-side flow path 60c. The oxygen-side flow path 60c is provided with a back pressure valve 67 that maintains the pressure of the first oxygen tank 63 at or below a predetermined pressure. When the pressure of the oxygen stored in the first oxygen tank 63 exceeds a predetermined value, the back pressure valve 67 opens and oxygen flows from the first oxygen tank 63 to the second oxygen tank 65. In other words, the second oxygen tank 65 stores oxygen at a lower pressure than the pressure of the oxygen stored in the first oxygen tank 63. Here, the predetermined pressure is a pressure at which water can be sent to the water tank 41 using the liquid delivery pump 77.

The first oxygen tank 63 is connected to the liquid supply pump 77 of the water supply unit 70 via the oxygen supply flow path 60f and the oxygen side flow path 60g, and is connected to the water supply flow path 40d of the water supply unit 40 via the oxygen supply flow path 60f and the oxygen supply flow path 60i. A portion of the oxygen in the first oxygen tank 63 is supplied to the liquid supply pump 77 and used to drive the liquid supply pump 77. A portion of the oxygen in the first oxygen tank 63 is supplied to the water supply flow path 40a and used to purge the water supply flow path, the oxygen electrode side flow path 12 of the electrolysis cell 10, and the oxygen side flow path (described in detail later).

The second oxygen tank 65 is also connected to the oxygen side gas-liquid separator 23 via the oxygen side flow path 60a, the oxygen side flow path 60d, and the oxygen side flow path 60e, and the oxygen (oxygen supplied from the first oxygen tank 63) used to purge the water supply flow path, the oxygen electrode side flow path 12 of the electrolysis cell 10, and the oxygen side flow path, from which the liquid water has been separated by the oxygen side gas-liquid separator 23, is also stored in the second oxygen tank 65.

The second oxygen tank 65 is also connected to the liquid pump 77 of the water supply unit 70 via the oxygen side flow path 60e and the oxygen side flow path 60h, and stores the low-pressure oxygen used to drive the liquid pump 77. The oxygen stored in the second oxygen tank 65 is discharged to the outside of the water electrolysis system 1 as needed (dotted arrow F20 in FIG. 1) and is used, for example, for the oxidation of chemicals or for adjusting the composition in a converter during steelmaking.

A check valve 68 is disposed in the oxygen side flow path 60h that connects the second oxygen tank 65 and the liquid delivery pump 77. The check valve 68 allows fluid to flow from the liquid delivery pump 77 to the second oxygen tank 65, while blocking the flow of fluid from the second oxygen tank 65 to the liquid delivery pump 77.

The hydrogen-side processing unit 30 includes a hydrogen-side gas-liquid separator 31, a first hydrogen tank 33, and a second hydrogen tank 35. The hydrogen-side processing unit 30 separates hydrogen from a mixture of hydrogen and water discharged from the hydrogen electrode-side flow path 13 of the electrolysis cell 10, stores the separated hydrogen, and sends the water obtained by gas-liquid separation to a water tank 41 of the water supply unit 40. The hydrogen-side processing unit 30 also supplies a portion of the stored hydrogen to a supply pump 43 of the water supply unit 40. The hydrogen-side processing unit 30 also supplies hydrogen in the first hydrogen tank 33 to the hydrogen electrode-side flow path 13 of the electrolysis cell 10. The hydrogen-side processing unit 30 can also discharge water discharged from the electrolysis cell 10 to the outside of the water electrolysis system 1. In this embodiment, the first hydrogen tank 33 is also called the "first hydrogen storage unit" or "hydrogen storage unit," and the second hydrogen tank 35 is also called the "second hydrogen storage unit."

The hydrogen-side gas-liquid separator 31 is connected to the hydrogen electrode-side flow path 13 of the electrolysis cell 10 via the hydrogen-side flow path 30a and the hydrogen-side flow path 30n. The hydrogen-side gas-liquid separator 31 is, for example, a cyclone-type gas-liquid separator, which separates the mixture of hydrogen and water discharged from the hydrogen electrode-side flow path 13 into hydrogen and water. In the hydrogen-side gas-liquid separator 31 of this embodiment, hydrogen accumulates on the upper side of the hydrogen-side gas-liquid separator 31, and water W30 accumulates on the lower side. Note that the method of gas-liquid separation of the hydrogen-side gas-liquid separator 31 is not limited to the cyclone type, as with the oxygen-side gas-liquid separator 23, and may be a method using a filter, a method using centrifugal force, or a cooling type.

The hydrogen-side gas-liquid separator 31 is connected to the water tank 41 of the water supply unit 40 via the hydrogen-side flow path 30b. The hydrogen-side gas-liquid separator 31 is provided with a water level gauge 32a that detects the water level of the water W30 in the hydrogen-side gas-liquid separator 31. The hydrogen-side flow path 30b is also provided with an on-off valve 32 that is controlled to open and close by the control unit 50. When the water level of the water W30 detected by the water level gauge 32a is equal to or lower than a predetermined water level, the control unit 50 closes the on-off valve 32 to shut off the hydrogen-side gas-liquid separator 31 and the water supply unit 40. On the other hand, when the water level of the water W30 detected by the water level gauge 32a exceeds the predetermined water level, the control unit 50 opens the on-off valve 32 to send the water W30 in the hydrogen-side gas-liquid separator 31 to the water tank 41 via the hydrogen-side flow path 30b.

The hydrogen-side gas-liquid separator 31 is connected to the first hydrogen tank 33 via the hydrogen-side flow path 30c and the hydrogen-side flow path 30g, and is connected to the second hydrogen tank 35 via the hydrogen-side flow path 30c, the hydrogen-side flow path 30h, and the hydrogen-side flow path 30i. The hydrogen separated into gas and liquid by the hydrogen-side gas-liquid separator 31 flows into the first hydrogen tank 33 via the hydrogen-side flow path 30c and the hydrogen-side flow path 30g while the water electrolysis process is being performed, and flows into the second hydrogen tank 35 via the hydrogen-side flow path 30c, the hydrogen-side flow path 30h, and the hydrogen-side flow path 30i while the water electrolysis process is stopped (described in detail later). A check valve 34 is disposed in the hydrogen-side flow path 30c. The check valve 34 allows the flow of fluid from the hydrogen-side gas-liquid separator 31 to the first hydrogen tank 33 and the second hydrogen tank 35, while blocking the flow of fluid from the first hydrogen tank 33 and the second hydrogen tank 35 to the hydrogen-side gas-liquid separator 31.

The first hydrogen tank 33 stores hydrogen obtained by gas-liquid separation in the hydrogen-side gas-liquid separator 31 at a relatively high pressure. The first hydrogen tank 33 is connected to the second hydrogen tank 35 via the hydrogen-side flow path 30e. The hydrogen-side flow path 30e is provided with a back pressure valve 37 that maintains the pressure of the first hydrogen tank 33 at or below a predetermined pressure. When the pressure of the hydrogen stored in the first hydrogen tank 33 exceeds a predetermined value, the back pressure valve 37 opens and hydrogen flows from the first hydrogen tank 33 to the second hydrogen tank 35. That is, the second hydrogen tank 35 stores hydrogen at a lower pressure than the pressure of the hydrogen stored in the first hydrogen tank 33. Here, the predetermined pressure is a pressure at which water can be supplied to the electrolysis cell 10 using the supply pump 43.

The first hydrogen tank 33 is connected to the supply pump 43 of the water supply unit 40 via the hydrogen supply flow path 30d and the hydrogen side flow path 30k, and is connected to the electrolysis cell 10 via the hydrogen supply flow path 30d and the hydrogen supply flow path 30j. A flow rate adjustment valve 36 is disposed in the hydrogen supply flow path 30d to adjust the flow rate of hydrogen flowing through the hydrogen supply flow path 30d in response to a command from the control unit 50. In response to a command from the control unit 50, the three-way valve 39a connects the hydrogen supply flow path 30d and the hydrogen side flow path 30k, and the flow rate adjustment valve 36 opens to a predetermined flow rate, thereby supplying a portion of the hydrogen in the first hydrogen tank 33 to the supply pump 43. The hydrogen in the first hydrogen tank 33 supplied to the supply pump 43 is used to drive the supply pump 43.

In addition, an on-off valve 39b that opens and closes in response to a command from the control unit 50 is disposed in the hydrogen supply flow path 30j. In response to a command from the control unit 50, the three-way valve 39a connects the hydrogen supply flow path 30d to the hydrogen supply flow path 30j, the flow rate control valve 36 opens to a predetermined flow rate, and the on-off valve 39b opens, so that a portion of the hydrogen in the first hydrogen tank 33 is supplied to the electrolysis cell 10 and used to purge the hydrogen electrode side flow path 13 and the hydrogen side flow path (described in detail later).

The second hydrogen tank 35 is connected to the hydrogen side gas-liquid separator 31 via the hydrogen side flow path 30c, the hydrogen side flow path 30h, and the hydrogen side flow path 30i. The hydrogen used to purge the hydrogen electrode side flow path 13 and the hydrogen side flow path (hydrogen supplied from the first hydrogen tank 33) from which the liquid water has been separated by the hydrogen side gas-liquid separator 31 is also stored in the second hydrogen tank 35.

The second hydrogen tank 35 is also connected to the supply pump 43 of the water supply unit 40 via the hydrogen side flow path 30i and the hydrogen side flow path 30f, and also stores low-pressure hydrogen used to drive the supply pump 43. The hydrogen stored in the second hydrogen tank 35 is discharged to the outside of the water electrolysis system 1 as needed (dotted arrow F30 in FIG. 1) and is used, for example, for the production of hydrocarbon compounds or the reduction of chemicals.

A check valve 38 is disposed in the hydrogen side flow path 30f that connects the second hydrogen tank 35 and the supply pump 43. The check valve 38 allows fluid to flow from the supply pump 43 to the second hydrogen tank 35, while blocking fluid flow from the second hydrogen tank 35 to the supply pump 43.

Figure 2 is an explanatory diagram of the water electrolysis process in the water electrolysis system 1. In Figure 2, the flow of fluid during the water electrolysis process is illustrated by thick arrows. In the water electrolysis system 1, the water supply unit 40 electrolyzes water supplied to the oxygen electrode side flow path 12 of the electrolysis cell 10 via the water supply flow paths 40a, 40d, and 40b, generating oxygen at the oxygen electrode 11b and hydrogen at the hydrogen electrode 11c. At this time, water that was not electrolyzed in the electrolysis cell 10 is discharged to the oxygen side flow path 20a together with the generated oxygen in the oxygen electrode side flow path 12, and is discharged to the hydrogen side flow path 30a together with the generated hydrogen in the hydrogen electrode side flow path 13.

When the control unit 50 receives an instruction to start water electrolysis, it starts water electrolysis. When water electrolysis starts, the control unit 50 controls the three-way valve 61 provided in the oxygen-side processing unit 20 to connect the oxygen-side flow path 20a and the oxygen-side flow path 20d, controls the three-way valve 62 to connect the oxygen-side flow path 60a and the oxygen-side flow path 60b, and controls the three-way valve 69 to connect the oxygen supply flow path 60f and the oxygen-side flow path 60g. The control unit 50 also controls the three-way valve 47 provided in the water supply unit 40 to connect the water supply flow path 40a and the water supply flow path 40d.

The control unit 50 also controls the three-way valve 39e provided in the hydrogen side processing unit 30 to connect the hydrogen side flow path 30a and the hydrogen side flow path 30n, controls the three-way valve 39c to connect the hydrogen side flow path 30c and the hydrogen side flow path 30g, controls the three-way valve 39a to connect the hydrogen supply flow path 30d and the hydrogen side flow path 30k, and closes the on/off valve 39b.

Next, the control unit 50 controls the power source 14 to supply power to the electrolysis cell 10. Then, when the control unit 50 opens the on/off valve 46 of the water supply unit 40 and the flow rate control valve 36 of the hydrogen side treatment unit 30, the supply pump 43 is driven, and the water W70 in the water tank 41 is supplied to the oxygen electrode side flow path 12 of the electrolysis cell 10 via the water supply flow path 40a, the water supply flow path 40d, and the water supply flow path 40b, and water electrolysis in the electrolysis cell 10 is started. Here, the control unit 50 adjusts the flow rate of the flow rate control valve 36 according to the state of electrolysis of water in the electrolysis cell 10 and opens it. For example, when the power source 14 is a power source derived from renewable energy such as solar, hydroelectric, wind, wave, biomass, or geothermal, the amount of power supplied from the power source derived from renewable energy is likely to fluctuate greatly. Therefore, the control unit 50 adjusts the opening of the flow rate control valve 36 according to the amount of power supplied from the power source 14, thereby adjusting the amount of hydrogen supplied to the supply pump 43 and controlling the amount of water supplied from the water tank 41 to the electrolysis cell 10. The type of power source 14 is not particularly limited, and may be a commercial power source.

The oxygen generated in the electrolysis cell 10 flows through the oxygen electrode side flow path 12 together with water that was not electrolyzed in the electrolysis cell 10, and is discharged to the oxygen side flow path 20a. The mixture of oxygen and water flowing through the oxygen side flow path 20a is cooled in the heat exchanger 21 and then sent to the oxygen side gas-liquid separator 23. In the oxygen side gas-liquid separator 23, gas and liquid are separated from the mixture of oxygen and water. The oxygen obtained by gas-liquid separation passes through the oxygen side flow path 60a and the oxygen side flow path 60b and is stored in the first oxygen tank 63. When the pressure of the oxygen stored in the first oxygen tank 63 reaches or exceeds a predetermined value, the back pressure valve 67 opens, and oxygen flows from the first oxygen tank 63 to the second oxygen tank 65.

Meanwhile, the water W20 obtained by gas-liquid separation is sent to the water tank 41 through the oxygen side flow path 20c. More specifically, the water W20 from the oxygen side gas-liquid separator 23 is sent to the water tank 41 according to the water level of the water W20 in the oxygen side gas-liquid separator 23. Specifically, when the water level of the water W20 detected by the water level gauge 22a exceeds a predetermined water level, the control unit 50 opens the on-off valve 22. At this time, the water W20 from the oxygen side gas-liquid separator 23 flows through the oxygen side flow path 20c, pushed out by the internal oxygen pressure in the oxygen side gas-liquid separator 23, and is sent to the water tank 41 via the ion exchanger 79.

When the water W20 in the oxygen-side gas-liquid separator 23 is sent to the water tank 41, if the amount of water sent from the oxygen-side gas-liquid separator 23 to the water tank 41, i.e., the amount of water flowing through the oxygen-side flow path 20c, is less than a predetermined value, the control unit 50 drives the liquid supply pump 77 to increase the amount of water flowing through the oxygen-side flow path 20c. Specifically, the control unit 50 determines whether the amount of water flowing through the oxygen-side flow path 20c is less than a predetermined value from the oxygen pressure of the oxygen-side gas-liquid separator 23 detected by the pressure gauge 68 when the water W20 is sent to the water tank 41. When the control unit 50 determines that the amount of water flowing through the oxygen-side flow path 20c is less than a predetermined value, it opens the flow rate adjustment valve 66 so that the oxygen stored in the first oxygen tank 63 is supplied to the liquid supply pump 77. When the oxygen in the first oxygen tank 63 is sent to the liquid supply pump 77, the liquid supply pump 77 is driven and the water flowing through the oxygen-side flow path 20c is pressurized. This increases the amount of water flowing through the oxygen side flow path 20c. The water that flows from the oxygen side gas-liquid separator 23 into the oxygen side flow path 20c has its conductivity reduced by the ion exchanger 79 and is sent to the water tank 41. The oxygen used to drive the liquid delivery pump 77 flows into the second oxygen tank 65 via the oxygen side flow path 60h and the oxygen side flow path 60e.

The hydrogen generated in the electrolysis cell 10 flows through the hydrogen electrode side flow path 13 together with water that was not electrolyzed in the electrolysis cell 10, and is discharged to the hydrogen side flow path 30a. The mixture of hydrogen and water flowing through the hydrogen side flow path 30a is separated into gas and liquid from the hydrogen and water mixture in the hydrogen side gas-liquid separator 31. The hydrogen obtained by gas-liquid separation passes through the hydrogen side flow path 30c and is stored in the first hydrogen tank 33. When the pressure of the hydrogen stored in the first hydrogen tank 33 reaches or exceeds a predetermined value, the back pressure valve 37 opens, and oxygen flows from the first hydrogen tank 33 to the second hydrogen tank 35.

Here, the pressure of hydrogen stored in the first hydrogen tank 33 will be described. Hydrogen obtained by gas-liquid separation flows into the first hydrogen tank 33 through the hydrogen side flow path 30c in which the check valve 34 is arranged. This gas-liquid separated hydrogen is continuously generated by electrolysis of water in the electrolysis cell 10, so hydrogen is also continuously supplied to the first hydrogen tank 33. On the other hand, a back pressure valve 37 is arranged in the hydrogen side flow path 30e through which hydrogen flows from the first hydrogen tank 33, and hydrogen does not flow in the hydrogen side flow path 30e unless the pressure of hydrogen from the first hydrogen tank 33 becomes greater than the pressure value preset in the back pressure valve 37. In addition, a flow rate adjustment valve 36 that adjusts the flow rate of hydrogen flowing through the hydrogen supply flow path 30d is arranged in the hydrogen supply flow path 30d through which hydrogen flows from the first hydrogen tank 33, and hydrogen does not flow in the hydrogen supply flow path 30d unless there is a command from the control unit 50. Thus, in the water electrolysis system 1 of this embodiment, hydrogen is continuously supplied to the first hydrogen tank 33, while only a limited amount of hydrogen is discharged from the first hydrogen tank 33, so the hydrogen pressure in the first hydrogen tank 33 becomes relatively high.

The hydrogen stored in the first hydrogen tank 33 is supplied to the supply pump 43 via the hydrogen supply flow path 30d and the hydrogen side flow path 30k. The supply pump 43 pressurizes the water stored in the water tank 41 using hydrogen supplied from the first hydrogen tank 33. In this embodiment, the supply pump 43 is driven by the high-pressure hydrogen described above, and therefore can supply a sufficient amount of water to the electrolysis cell 10 to achieve both the electrolysis of water and the cooling of the electrolysis cell 10.

The hydrogen used to drive the supply pump 43 is at a relatively low pressure and is sent to the second hydrogen tank 35 via the hydrogen side flow path 30f and the hydrogen side flow path 30i. That is, in the second hydrogen tank 35, the back pressure valve 37 is opened to store hydrogen sent from the first hydrogen tank 33 and hydrogen sent from the supply pump 43.

Meanwhile, the water W30 obtained by gas-liquid separation is sent to the water tank 41 through the hydrogen side flow path 30b. More specifically, the water W30 from the hydrogen side gas-liquid separator 31 is sent to the water tank 41 according to the water level of the water W30 in the hydrogen side gas-liquid separator 31. Specifically, when the water level of the water W30 detected by the water level gauge 32a exceeds a predetermined water level, the control unit 50 opens the on-off valve 32. At this time, the water W30 from the hydrogen side gas-liquid separator 31 is pushed out by the internal hydrogen pressure in the hydrogen side gas-liquid separator 31 and sent to the water tank 41 through the hydrogen side flow path 30b.

As described above, in the water electrolysis system 1, among the water that is not electrolyzed in the electrolysis cell 10 during the water electrolysis process, the water that is sent from the oxygen side treatment unit 20 to the water tank 41 and reused has its conductivity reduced by the ion exchanger 79. In addition, a portion of the water supplied from the water tank 41 to the electrolysis cell 10 is ion exchanged in the ion exchanger 45 to reduce its conductivity. Therefore, when the water electrolysis process is performed in the water electrolysis system 1, water with low conductivity is supplied to the electrolysis cell 10.

When the control unit 50 receives an instruction to end the water electrolysis process, it closes the on/off valve 46 of the water supply unit 40, closes the flow rate adjustment valve 36 and on/off valve 39b of the hydrogen side treatment unit 30, and stops the power supply from the power source 14. This stops water electrolysis by the electrolysis cell 10. The control unit 50 also closes the flow rate adjustment valve 66 and on/off valve 22 of the oxygen side treatment unit 20, and the on/off valve 32 of the hydrogen side treatment unit 30 to end the water electrolysis process and transitions to the water electrolysis stop process described below.

For example, when the power source 14 is a power source derived from renewable energy, the amount of power varies greatly, so that when the output power of the power source 14 exceeds a predetermined threshold, the water electrolysis process may be started, and when the output power of the power source 14 falls below the predetermined threshold, the water electrolysis process may be ended. That is, the control unit 50 may receive an instruction to start and an instruction to end the water electrolysis process according to the output power of the power source 14. Also, the water electrolysis system 1 may be started, and the water electrolysis process may be started after a predetermined time has elapsed, and the water electrolysis process may be ended when an instruction to stop the operation of the water electrolysis system 1 is input (for example, the start switch of the water electrolysis system 1 is turned off).

Figure 3 is an explanatory diagram of the water electrolysis stop process in the water electrolysis system 1. In Figure 3, the thick arrows indicate the flow of fluids during the water electrolysis stop process. In the water electrolysis system 1, in the water electrolysis stop process, the control unit 50 stops the power supply from the power source 14 to the electrolysis cell 10 and stops the water supply from the water supply unit 40 to the electrolysis cell 10. This stops the electrolysis of water by the electrolysis cell 10. Then, the control unit 50 uses the oxygen stored in the first oxygen tank 63 to purge the water supply flow path, the oxygen electrode side flow path 12, and the oxygen side flow path, and uses the hydrogen stored in the first hydrogen tank 33 to purge the hydrogen electrode side flow path 13 and the hydrogen side flow path.

When the water electrolysis stop process starts, the control unit 50 controls the three-way valve 61 provided in the oxygen-side processing unit 20 to connect the oxygen-side flow path 20a and the oxygen-side flow path 20d, controls the three-way valve 62 to connect the oxygen-side flow path 60a and the oxygen-side flow path 60d, and controls the three-way valve 69 to connect the oxygen supply flow path 60f and the oxygen supply flow path 60i. The control unit 50 also controls the three-way valve 47 provided in the water supply unit 40 to connect the oxygen supply flow path 60i and the water supply flow path 40d, and closes the on-off valve 46.

When the control unit 50 opens the flow rate control valve 66, the high-pressure oxygen in the first oxygen tank 63 flows through the oxygen supply flow path 60f, the oxygen supply flow path 60i, the water supply flow path 40d, the supply pump 43, and the water supply flow path 40b and enters the electrolysis cell 10. The oxygen then flows through the oxygen electrode side flow path 12 and enters the oxygen side flow path 20a, and then flows through the oxygen side flow path 20d, the heat exchanger 21, and the oxygen side flow path 20b into the oxygen side gas-liquid separator 23. When the oxygen flows through the above-mentioned flow paths, the water in the flow paths is discharged by the oxygen into the oxygen side gas-liquid separator 23. That is, the above-mentioned flow paths are purged by the oxygen in the first oxygen tank 63. The oxygen from which the water has been separated in the oxygen side gas-liquid separator 23 flows into the second oxygen tank 65 through the oxygen side flow path 60a, the oxygen side flow path 60d, and the oxygen side flow path 60e.

As described above, when the electrolysis of water is stopped, the oxygen side flow path 60a is connected to the second oxygen tank 65 via the oxygen side flow path 60d and the oxygen side flow path 60e. That is, the first oxygen tank 63 and the second oxygen tank 65 are connected via the oxygen supply flow path 60f, the oxygen supply flow path 60i, the water supply flow path 40d, the supply pump 43, the water supply flow path 40b, the oxygen electrode side flow path 12, the oxygen side flow path 20a, the oxygen side flow path 20d, the heat exchanger 21, the oxygen side flow path 20b, the oxygen side gas-liquid separator 23, the oxygen side flow path 60a, the oxygen side flow path 60d, and the oxygen side flow path 60e. Therefore, by utilizing the pressure difference between the first oxygen tank 63 and the second oxygen tank 65, the oxygen in the first oxygen tank 63 can flow from the first oxygen tank 63 to the second oxygen tank 65 via the above-mentioned path. As a result, the water in the water supply flow path, the supply pump 43, the oxygen electrode side flow path 12, the oxygen side flow path, and the heat exchanger 21 can be discharged.

When the water electrolysis stop process starts, the control unit 50 controls the three-way valve 39e provided in the hydrogen-side processing unit 30 to connect the hydrogen-side flow path 30a and the hydrogen-side flow path 30n, controls the three-way valve 39c to connect the hydrogen-side flow path 30c and the hydrogen-side flow path 30h, and controls the three-way valve 39a to connect the hydrogen supply flow path 30d and the hydrogen supply flow path 30j.

When the control unit 50 opens the flow control valve 36 and the on-off valve 39b, the high-pressure hydrogen in the first hydrogen tank 33 flows through the hydrogen supply flow path 30d and the hydrogen supply flow path 30j and into the electrolysis cell 10. The hydrogen then flows through the hydrogen electrode side flow path 13 into the hydrogen side flow path 30a, and flows through the hydrogen side flow path 30n into the hydrogen side gas-liquid separator 31. When hydrogen flows through the hydrogen side flow path, the water in the flow path is discharged by the hydrogen into the hydrogen side gas-liquid separator 31. That is, the flow path is purged by the hydrogen in the first hydrogen tank 33. The hydrogen from which the water has been separated in the hydrogen side gas-liquid separator 31 flows into the second hydrogen tank 35 through the hydrogen side flow path 30c, the hydrogen side flow path 30h, and the hydrogen side flow path 30i.

As described above, when the electrolysis of water is stopped, the hydrogen side flow path 30c is connected to the second hydrogen tank 35 via the hydrogen side flow path 30h and the hydrogen side flow path 30i. That is, the first hydrogen tank 33 and the second hydrogen tank 35 are connected via the hydrogen supply flow path 30d, the hydrogen supply flow path 30j, the hydrogen electrode side flow path 13, the hydrogen side flow path 30a, the hydrogen side flow path 30n, the hydrogen side gas-liquid separator 31, the hydrogen side flow path 30c, the hydrogen side flow path 30h, and the hydrogen side flow path 30i. Therefore, by utilizing the pressure difference between the first hydrogen tank 33 and the second hydrogen tank 35, the hydrogen in the first hydrogen tank 33 can be flowed from the first hydrogen tank 33 to the second hydrogen tank 35 via the above-mentioned route. As a result, the water in the hydrogen electrode side flow path 13 and the hydrogen side flow path can be discharged.

After a predetermined time has elapsed, the control unit 50 closes the flow control valve 66 of the oxygen side processing unit 20, the flow control valve 36 of the hydrogen side processing unit 30, and the on/off valve 39b to terminate the water electrolysis stop process.

Figure 4 is an explanatory diagram of the water electrolysis start process in the water electrolysis system 1. In Figure 4, the thick arrows indicate the flow of fluids during the water electrolysis start process. In the water electrolysis system 1, the water electrolysis start process is performed immediately before restarting the water electrolysis process, in other words, when the electrolysis of water by the electrolysis cell 10 is started after the electrolysis of water by the electrolysis cell 10 is stopped. In the water electrolysis start process, the control unit 50 uses the water W70 stored in the water tank 41 to drain the water remaining in the water supply flow path, the oxygen electrode side flow path 12, and the oxygen side flow path, and uses the hydrogen stored in the first hydrogen tank 33 to drain the water remaining in the hydrogen electrode side flow path 13 and the hydrogen side flow path.

When the water electrolysis start process is started, the control unit 50 controls the three-way valve 61 provided in the oxygen-side processing unit 20 to connect the oxygen-side flow path 20a and the oxygen-side exhaust flow path 20e. The control unit 50 also controls the three-way valve 47 provided in the water supply unit 40 to connect the water supply flow path 40a and the water supply flow path 40d. The control unit 50 also controls the three-way valve 39e provided in the hydrogen-side processing unit 30 to connect the hydrogen-side flow path 30a and the hydrogen-side exhaust flow path 30m, and controls the three-way valve 39a to connect the hydrogen supply flow path 30d and the hydrogen supply flow path 30j.

When the control unit 50 opens the flow rate adjustment valve 36 of the hydrogen-side processing unit 30 and also opens the on-off valve 39b, the high-pressure hydrogen in the first hydrogen tank 33 flows into the electrolysis cell 10 via the hydrogen supply flow path 30d and the hydrogen supply flow path 30j. The hydrogen then flows through the hydrogen electrode-side flow path 13 into the hydrogen-side flow path 30a, and is discharged outside the water electrolysis system 1 through the hydrogen-side discharge flow path 30m. When the hydrogen in the first hydrogen tank 33 flows through the above-mentioned flow paths, the water in the flow paths is swept away by the hydrogen, and is discharged outside the water electrolysis system 1 together with the hydrogen.

After a predetermined time has elapsed, the control unit 50 closes the flow rate control valve 36 and the on-off valve 39b, and controls the three-way valve 39a to connect the hydrogen supply flow path 30d and the hydrogen side flow path 30k. When the control unit 50 then opens the flow rate control valve 36, the hydrogen in the first hydrogen tank 33 flows into the supply pump 43 via the hydrogen supply flow path 30d and the hydrogen side flow path 30k. The supply pump 43 pressurizes the water stored in the water tank 41 using the hydrogen supplied from the first hydrogen tank 33. When the control unit 50 opens the on-off valve 46 and hydrogen is supplied from the first hydrogen tank 33 to the supply pump 43, the water W70 in the water tank 41 flows through the water supply flow path 40a, the water supply flow path 40d, the supply pump 43, and the water supply flow path 40b and into the electrolysis cell 10. The water supplied from the water tank 41 flows through the oxygen electrode side flow path 12 into the oxygen side flow path 20a, and is discharged outside the water electrolysis system 1 through the oxygen side exhaust flow path 20e. When the water supplied from the water tank 41 flows through the above flow paths, the water remaining in the flow paths is swept away by the water supplied from the water tank 41, and is discharged outside the water electrolysis system 1. The hydrogen supplied to the supply pump 43 flows into the second hydrogen tank 35 via the hydrogen side flow path 30f and the hydrogen side flow path 30i.

In this way, in the water electrolysis start process, the hydrogen in the first hydrogen tank 33 can be used to drain the stagnant water in the hydrogen electrode side flow path 13 and the hydrogen side flow path, and the water in the water tank 41 can be used to drain the stagnant water in the water supply flow path, the oxygen electrode side flow path 12, and the oxygen side flow path.

After a predetermined time has elapsed, the control unit 50 closes the on/off valve 46 of the water supply unit 40 and closes the flow rate control valve 36 and on/off valve 39b of the hydrogen side processing unit 30, terminating the water electrolysis start process and transitioning to the water electrolysis process described above.

The program for implementing the above-mentioned water electrolysis process, water electrolysis stop process, and water electrolysis start process may be pre-stored in the control unit 50. The program may also be provided by a program provider via a communication network. The program may also be stored in a commercially available portable storage medium. In this case, the portable storage medium may be set in an external or built-in reading device, and the program may be read and executed by the control unit 50. Various types of storage media can be used as the portable storage medium, such as CD-ROM, DVD-ROM, flexible disk, optical disk, magneto-optical disk, IC card, and USB memory device. The program stored in such a storage medium is read by the reading device.

As described above, according to the water electrolysis system 1 of this embodiment, when the water electrolysis process is performed in the electrolysis cell 10, the product gas (oxygen, hydrogen) generated in the electrolysis cell 10 is stored, and when the water electrolysis process in the electrolysis cell 10 is stopped, the stored product gas can be used to purge the oxygen side flow path, the water supply flow path, the hydrogen side flow path, the electrolysis cell 10, and the like. Specifically, the water supply flow path 40d, the supply pump 43, the water supply flow path 40b, the oxygen electrode side flow path 12, the oxygen side flow path 20a, the oxygen side flow path 20d, the heat exchanger 21, and the oxygen side flow path 20b can be purged using the oxygen stored in the first oxygen tank 63. On the other hand, the hydrogen electrode side flow path 13, the hydrogen side flow path 30a, and the hydrogen side flow path 30n can be purged using the hydrogen stored in the first hydrogen tank 33.

In the water electrolysis system 1 of this embodiment, further, at the start of the water electrolysis process by the electrolysis cell 10 (immediately before the start), a water electrolysis start process is performed, and the water remaining in the water supply flow path, the oxygen electrode side flow path, the oxygen side flow path, etc. is drained using the water in the water tank 41, and the water remaining in the hydrogen electrode side flow path and the hydrogen side flow path is drained using the hydrogen in the first hydrogen tank 33. Specifically, in the water electrolysis system 1, the water remaining in the water supply flow path 40a, the water supply flow path 40d, the supply pump 43, the water supply flow path 40b, the oxygen electrode side flow path 12, and the oxygen side flow path 20a can be discharged using the water in the water tank 41. On the other hand, on the hydrogen side of the water electrolysis system 1, the water remaining in the hydrogen electrode side flow path 13 and the hydrogen side flow path 30a can be discharged using the hydrogen stored in the first hydrogen tank 33.

In the water electrolysis system 1, water is present in the water supply flow path 40a, the water supply flow path 40d, the supply pump 43, the water supply flow path 40b, and the oxygen electrode side flow path 12, through which water flows, when electrolysis of the electrolysis cell 10 is stopped, in order to supply water to the electrolysis cell 10. In addition, oxygen generated on the oxygen electrode 11b side of the electrolysis cell 10 flows into the oxygen side flow path 20a together with water, and flows through the oxygen side flow path 20d, the heat exchanger 21, and the oxygen side flow path 20b into the oxygen side gas-liquid separator 23. Therefore, when electrolysis of the electrolysis cell 10 is stopped, water is also present in the oxygen side flow path 20a, the oxygen side flow path 20d, the heat exchanger 21, and the oxygen side flow path 20b. In addition, water supplied to the oxygen electrode 11b side of the electrolysis cell 10 permeates the electrolyte membrane 11a and moves to the hydrogen electrode 11c side, so the hydrogen generated on the hydrogen electrode 11c side flows into the hydrogen side flow passage 30a together with the water, flows through the hydrogen side flow passage 30n, and flows into the hydrogen side gas-liquid separator 31. Therefore, when electrolysis of the electrolysis cell 10 is stopped, water is also present in the hydrogen electrode side flow passage 13, the hydrogen side flow passage 30a, and the hydrogen side flow passage 30n.

Metal pipes such as stainless steel are often used for the water supply flow path, oxygen side flow path, and hydrogen side flow path, and a power supply such as a metal mesh is often provided inside the electrolysis cell 10. Therefore, if electrolysis is stopped for a long time, metal ions may be eluted from the metal pipes as the water supply flow path, oxygen side flow path, and hydrogen side flow path, and the metal mesh in the water electrolysis cell into the water that is retained in the water supply flow path and the water electrolysis cell (oxygen electrode side flow path 12, hydrogen electrode side flow path 13), and the conductivity of the retained water may increase. When water electrolysis is started in the water electrolysis system 1, when water is supplied to the electrolysis cell 10, the retained water is also supplied to the electrolysis cell 10. Therefore, when the conductivity of the retained water increases, the conductivity of the water supplied to the electrolysis cell 10 increases. When water with high conductivity is supplied to the electrolysis cell 10 when the water electrolysis process is resumed, there is a risk that the efficiency of water electrolysis will decrease due to the adsorption of impurity ions to the electrodes and the deterioration of the electrodes due to oxidation. There is also a risk that impurity gas components will be mixed into the gas generated by water electrolysis.

In contrast, according to the water electrolysis system 1 of this embodiment, when the water electrolysis process in the electrolysis cell 10 is stopped, the water supply path, the oxygen side path, the hydrogen side path, and the path in the electrolysis cell 10 are purged by the water electrolysis stop process, so that the amount of water in these paths can be reduced when the water electrolysis process is stopped. Therefore, the amount of retained water in these paths can be reduced during the stop of the water electrolysis process. By reducing the amount of retained water in the electrolysis cell 10, deterioration of the electrolysis cell 10 due to the elution of metal ions caused by contact between the electrodes or the power supply and the retained water can be suppressed. Furthermore, in the water electrolysis system 1, the water electrolysis start process is performed at the start of the water electrolysis process by the electrolysis cell 10 (immediately before the start), and the retained water that remains in the path and retains even after the water electrolysis stop process is performed can be discharged immediately before the start of the water electrolysis process. In other words, the retained water with high conductivity can be discharged before the start of the water electrolysis process. As a result, it is possible to suppress an increase in the conductivity of the water supplied to the electrolysis cell 10 when the water electrolysis process is restarted, suppress deterioration of the electrodes of the electrolysis cell 10, and improve the durability of the electrolysis cell 10. In the water electrolysis system 1, it is preferable to always maintain the conductivity of the water supplied to the electrolysis cell 10 at less than 1 μS/cm (pure water state).

In the water electrolysis system 1, the supply pump 43 can also be purged in order to allow the oxygen in the first oxygen tank 63 to flow into the water supply line connecting the water tank 41 and the supply pump 43. If the supply pump 43 is made of metal, purging can be performed to suppress an increase in the conductivity of the water supplied to the electrolysis cell 10.

When a power source derived from renewable energy such as solar power is used as the power source 14 that supplies power to the electrolysis cell 10, power is not supplied at night, and the water electrolysis process is stopped for a relatively long time until power supply from the power source 14 is started again. If water is present in the water electrolysis system 1 when the water electrolysis process is stopped and remains in the water electrolysis system 1 for a long time, there is a high possibility that the conductivity of the retained water will increase. Therefore, when a power source derived from renewable energy is used as the power source 14, it is preferable to adopt the water electrolysis system 1, since this can suppress the increase in the conductivity of the retained water. Note that even when the power source 14 is a commercial power source, the increase in the conductivity of the retained water due to the stop of the water electrolysis process can be appropriately suppressed.

In addition, in the water electrolysis system 1, oxygen is used to purge the oxygen side flow path, the water supply flow path, and the oxygen electrode side flow path 12 during the water electrolysis stop process, and hydrogen is used to purge the hydrogen side flow path and the hydrogen electrode side flow path 13. That is, the flow path connected to the oxygen electrode side flow path 12 on the oxygen electrode 11b side where oxygen is generated by water electrolysis is purged with oxygen, and the flow path connected to the hydrogen electrode side flow path 13 on the hydrogen electrode 11c side where hydrogen is generated by water electrolysis is purged with hydrogen. Therefore, when the water electrolysis process is started, the gas discharged from the electrolysis cell 10 is oxygen on the oxygen side and hydrogen on the hydrogen side. Therefore, for example, the purity of the oxygen and hydrogen discharged from the electrolysis cell 10 by the water electrolysis process can be improved compared to when air is used to purge each flow path in the water electrolysis system 1.

In addition, the water electrolysis system 1 uses oxygen and hydrogen, which are generated by water electrolysis in the electrolysis cell 10 and stored, to purge the flow paths within the water electrolysis system 1. Therefore, compared to purging using an inert gas such as nitrogen, helium, or argon, no storage tank or the like is required to store the purge gas, which contributes to miniaturization and cost reduction of the water electrolysis system 1.

In addition, oxygen generated by water electrolysis that is used to purge the flow paths of the water electrolysis system 1 during the water electrolysis stopping process is stored in the second oxygen tank 65. In addition, hydrogen generated by water electrolysis that is used to purge the flow paths of the water electrolysis system 1 during the water electrolysis stopping process is stored in the second hydrogen tank 35. In other words, the oxygen and hydrogen used for purging are not discarded. Therefore, it is possible to suppress a decrease in the amount of oxygen and hydrogen that can be supplied outside the water electrolysis system 1 and used among the oxygen and hydrogen generated by water electrolysis.

In addition, the water remaining in the flow paths and the like of the water electrolysis system 1 is discharged outside the water electrolysis system 1 and is not reused. This makes it possible to suppress an increase in the electrical conductivity of the water in the water tank 41.

Furthermore, in the water electrolysis system 1, during the water electrolysis start process, water in the water tank 41 is used to drain the water remaining in the water supply flow path, the oxygen electrode side flow path 12, and the oxygen side flow path. That is, at the start of water electrolysis (immediately before the start of water electrolysis), pure water with low conductivity is supplied to the oxygen electrode side flow path 12. Therefore, compared to the case where gas is used to drain the water remaining in the water supply flow path, the oxygen electrode side flow path 12, and the oxygen side flow path, the electrolyte membrane 11a can be kept in a good wet state, and a decrease in water electrolysis efficiency can be suppressed.

The water electrolysis system 1 of this embodiment also includes an ion exchanger 45 and an ion exchanger 79, and reduces the conductivity of the water supplied to the electrolysis cell 10 by ion exchange. As described above, in the water electrolysis system 1, the water electrolysis stop process and the water electrolysis start process can suppress an increase in the conductivity of the water supplied to the electrolysis cell 10, so that the frequency of replacement of the ion exchanger 45 and the ion exchanger 79 can be suppressed, and the cost of producing pure water can be reduced.

The oxygen-side processing unit 20 of the water electrolysis system 1 includes a first oxygen tank 63 that stores oxygen at high pressure and a second oxygen tank 65 that stores oxygen at a lower pressure than the first oxygen tank 63, and supplies oxygen in the first oxygen tank 63 to the water supply flow path by utilizing the pressure difference between the first oxygen tank 63 and the second oxygen tank 65. Similarly, the hydrogen-side processing unit 30 of the water electrolysis system 1 includes a first hydrogen tank 33 that stores hydrogen at high pressure and a second hydrogen tank 35 that stores hydrogen at a lower pressure than the first hydrogen tank 33, and supplies hydrogen in the first hydrogen tank 33 to the electrolysis cell 10 by utilizing the pressure difference between the first hydrogen tank 33 and the second hydrogen tank 35. Therefore, compared to a case where a pump or the like is separately provided to discharge water from the flow path, etc., this can contribute to miniaturization, cost reduction, and energy reduction of the water electrolysis system 1.

In addition, according to the water electrolysis system 1 of this embodiment, water discharged from the oxygen electrode side flow path 12 of the electrolysis cell 10 without being electrolyzed is separated from oxygen by the oxygen side gas-liquid separator 23 and sent to the water tank 41. In addition, water discharged from the hydrogen electrode side flow path 13 of the electrolysis cell 10 is separated from hydrogen by the hydrogen side gas-liquid separator 31 and sent to the water tank 41. The water sent from the oxygen side gas-liquid separator 23 and the hydrogen side gas-liquid separator 31 to the water tank 41 is supplied again to the electrolysis cell 10 and electrolyzed. The water used in the water electrolysis system 1 is highly pure water, and therefore requires a lot of cost for production. Therefore, by reusing the water discharged from the electrolysis cell 10 without being electrolyzed for electrolysis, the production costs of oxygen and hydrogen can be reduced.

Furthermore, according to the water electrolysis system 1 of this embodiment, the hydrogen-side gas-liquid separator 31 is used to remove water from the hydrogen before it is stored in the first hydrogen tank 33. Similarly, the oxygen-side gas-liquid separator 23 is used to remove water from the oxygen before it is stored in the first oxygen tank 63. This allows the flow paths in the water electrolysis system 1 to be purged using hydrogen and oxygen with low humidity.

Furthermore, according to the water electrolysis system 1 of this embodiment, hydrogen from the first hydrogen tank 33 is supplied to the supply pump 43, which pressurizes the water W70 in the water tank 41 to send it to the electrolysis cell 10. This is because the amount of hydrogen generated is greater than the amount of oxygen generated during the electrolysis of water, such that 0.5 mol of oxygen and 1 mol of hydrogen are produced by the electrolysis of 1 mol of water. As a result, when the internal volume of the first hydrogen tank 33 and the internal volume of the first oxygen tank 63 are the same, the pressure of the hydrogen in the first hydrogen tank 33 is likely to be higher than the pressure of the oxygen in the first oxygen tank 63, making it easier to drive the supply pump 43.

Second Embodiment
5 is an explanatory diagram showing a schematic configuration of a water electrolysis system 1A of the second embodiment. The water electrolysis system 1A includes an electrolysis cell 10, an oxygen-side treatment unit 20A, a hydrogen-side treatment unit 30, a water supply unit 40A, and a control unit 50. The water electrolysis system 1A of the second embodiment differs from the water electrolysis system 1 of the first embodiment in that the oxygen-side treatment unit 20A does not include the second oxygen tank 65 but includes an oxygen supply pump 80, and that the water supply unit 40A does not include the liquid feed pump 77 and the ion exchanger 79. The same components as those of the first embodiment are denoted by the same reference numerals, and the preceding description is to be referred to.

The oxygen supply pump 80 provided in the oxygen side processing unit 20A is an electric pump. The oxygen supply pump 80 is provided in the oxygen supply flow path 60f and is controlled by the control unit 50 to cause the oxygen in the first oxygen tank 63 to flow into the water supply flow path 40d via the oxygen supply flow path 60f.

The water supply unit 40A does not include the liquid delivery pump 77 and ion exchanger 79 in the first embodiment, so the water W20 obtained by gas-liquid separation passes through the oxygen side flow path 20c and is sent directly to the water tank 41.

Figure 6 is an explanatory diagram of the water electrolysis stopping process in the water electrolysis system 1A. In Figure 6, thick arrows indicate the flow of fluids during the water electrolysis stopping process. When the water electrolysis stopping process starts, the control unit 50 controls the three-way valve 61 provided in the oxygen-side processing unit 20A to connect the oxygen-side flow path 20a and the oxygen-side flow path 20d, controls the three-way valve 47 provided in the water supply unit 40A to connect the oxygen supply flow path 60f and the water supply flow path 40d, and closes the on-off valve 46.

When the control unit 50 opens the flow rate control valve 66 and drives the oxygen supply pump 80, the oxygen in the first oxygen tank 63 flows through the oxygen supply flow path 60f, the water supply flow path 40d, the supply pump 43, and the water supply flow path 40b and into the electrolysis cell 10. The oxygen then flows through the oxygen electrode side flow path 12 and into the oxygen side flow path 20a, and flows into the oxygen side gas-liquid separator 23 through the oxygen side flow path 20d, the heat exchanger 21, and the oxygen side flow path 20b. When the oxygen flows through the above-mentioned flow paths, the water in the flow paths is discharged by the oxygen into the oxygen side gas-liquid separator 23. That is, the above-mentioned flow paths are purged by the oxygen in the first oxygen tank 63. The oxygen from which the water has been separated in the oxygen side gas-liquid separator 23 flows into the first oxygen tank 63 through the oxygen side flow path 60a.

The control of the hydrogen side treatment section 30 and the fluid flow are the same as in the first embodiment, so please refer to the preceding description.

As described above, the water electrolysis system 1A of this embodiment can also discharge at least a portion of the water in the electrolysis cell 10, flow paths, etc., by the water electrolysis stop process, thereby reducing the amount of water in these flow paths, etc., when the water electrolysis process is stopped. Therefore, the amount of water retained in these flow paths, etc., can be reduced while the water electrolysis process is stopped. By reducing the amount of retained water in the electrolysis cell 10, deterioration of the electrolysis cell 10 due to the elution of metal ions caused by contact between the electrodes or power supply and the retained water can be suppressed. In addition, by reducing the amount of retained water in the water electrolysis system 1A, an increase in the conductivity of the water supplied to the electrolysis cell 10 when the water electrolysis process is resumed can be suppressed.

Third Embodiment
7 is an explanatory diagram showing a schematic configuration of a water electrolysis system 1B of the third embodiment. The water electrolysis system 1B includes an electrolysis cell 10, an oxygen-side treatment unit 20B, a hydrogen-side treatment unit 30, a water supply unit 40A, and a control unit 50. The water electrolysis system 1B of the third embodiment differs from the water electrolysis system 1A of the second embodiment in that the oxygen-side treatment unit 20B does not include the first oxygen tank 63. The same components as those of the first and second embodiments are denoted by the same reference numerals, and the preceding descriptions are to be referred to.

The oxygen-side gas-liquid separator 23 provided in the oxygen-side processing unit 20B is connected to the water supply flow path 40d via the oxygen supply flow path 60f. In detail, the oxygen supply flow path 60f is relatively higher than the oxygen-side gas-liquid separator 23 and is connected to a portion where the oxygen resulting from gas-liquid separation is stored. The oxygen-side gas-liquid separator 23 in this embodiment is also referred to as the "first oxygen storage section" or the "oxygen storage section."

Figure 8 is an explanatory diagram of the water electrolysis stopping process in the water electrolysis system 1B. In Figure 8, thick arrows indicate the flow of fluids during the water electrolysis stopping process. When the water electrolysis stopping process starts, the control unit 50 controls the three-way valve 61 provided in the oxygen-side processing unit 20B to connect the oxygen-side flow path 20a and the oxygen-side flow path 20d, controls the three-way valve 47 provided in the water supply unit 40A to connect the oxygen supply flow path 60f and the water supply flow path 40d, and closes the on-off valve 46.

When the control unit 50 opens the flow control valve 66 and drives the oxygen supply pump 80, the oxygen in the oxygen-side gas-liquid separator 23 flows through the oxygen supply flow path 60f, the water supply flow path 40d, the supply pump 43, and the water supply flow path 40b and enters the electrolysis cell 10. The oxygen then flows through the oxygen electrode side flow path 12 and enters the oxygen side flow path 20a, and then flows through the oxygen side flow path 20d, the heat exchanger 21, and the oxygen side flow path 20b and into the oxygen-side gas-liquid separator 23. When oxygen flows through the above-mentioned flow paths, the water in the flow paths is discharged by the oxygen into the oxygen-side gas-liquid separator 23. That is, the above-mentioned flow paths are purged by the oxygen in the oxygen-side gas-liquid separator 23. The mixture of oxygen and water that flows into the oxygen-side gas-liquid separator 23 is separated into gas and liquid by the oxygen-side gas-liquid separator 23.

The control of the hydrogen side treatment section 30 and the fluid flow are the same as in the first embodiment, so please refer to the preceding description.

As described above, the water electrolysis system 1B of this embodiment can also discharge at least a portion of the water in the electrolysis cell 10, flow paths, etc., by the water electrolysis stop process, thereby reducing the amount of water in these flow paths, etc., when the water electrolysis process is stopped. Therefore, the amount of water retained in these flow paths, etc., can be reduced while the water electrolysis process is stopped. By reducing the amount of retained water in the electrolysis cell 10, deterioration of the electrolysis cell 10 due to the elution of metal ions caused by contact between the electrodes or power supply and the retained water can be suppressed. In addition, by reducing the amount of retained water in the water electrolysis system 1A, an increase in the conductivity of the water supplied to the electrolysis cell 10 when the water electrolysis process is resumed can be suppressed.

In addition, in the water electrolysis system 1B of this embodiment, the oxygen-side gas-liquid separator 23 functions as a first oxygen storage section and an oxygen storage section, which contributes to miniaturization and cost reduction of the water electrolysis system 1B.

Fourth Embodiment
9 is an explanatory diagram showing a schematic configuration of a water electrolysis system 1C of the fourth embodiment. The water electrolysis system 1C includes an electrolysis cell 10, an oxygen-side treatment section 20C, a hydrogen-side treatment section 30, a water supply section 40C, and a control section 50. The water electrolysis system 1C of the fourth embodiment differs from the water electrolysis system 1 of the first embodiment in that the oxygen-side treatment section 20C does not include the oxygen supply flow path 60i. The same components as those of the first embodiment are denoted by the same reference numerals, and the preceding description is to be referred to.

Because the oxygen-side treatment unit 20C does not have an oxygen supply flow path 60i, the oxygen in the first oxygen tank 63 does not flow into the water supply flow path 40d. That is, in the water electrolysis system 1C of the fourth embodiment, the water electrolysis stop process performed in the water electrolysis system 1 of the first embodiment is not performed. In the water electrolysis system 1C of this embodiment, when the water electrolysis process is terminated, the water present in the water electrolysis system 1C remains there while the water electrolysis process is stopped. Then, when the water electrolysis process is resumed, the water electrolysis start process is performed and the retained water is discharged.

Figure 10 is an explanatory diagram of the water electrolysis start process in the water electrolysis system 1C. In Figure 10, the thick arrows indicate the flow of fluids during the water electrolysis start process. At the start of the water electrolysis process, in the water electrolysis system 1C, as in the water electrolysis system 1 of the first embodiment, the control unit 50 uses the water W70 stored in the water tank 41 to drain the water remaining in the water supply flow path, the oxygen electrode side flow path 12, and the oxygen side flow path, and uses the hydrogen stored in the first hydrogen tank 33 to drain the water remaining in the hydrogen electrode side flow path 13 and the hydrogen side flow path.

As described above, the water electrolysis system 1C of this embodiment can also discharge at least a portion of the water remaining in the electrolysis cell 10, flow path, etc., to the outside of the water electrolysis system 1C by the water electrolysis start process. Therefore, it is possible to suppress an increase in the conductivity of the water supplied to the electrolysis cell 10 when the water electrolysis process is restarted.

<Modifications of this embodiment>
The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

- In the above embodiment, an example was shown in which both the water electrolysis stop process and the water electrolysis start process are performed in the water electrolysis system 1, but only one of the water electrolysis stop process and the water electrolysis start process may be performed. Even in this way, an increase in the conductivity of the water supplied to the electrolysis cell 10 can be suppressed.

- In the above embodiment, an example was shown in which water was discharged from the oxygen side flow path and the water supply flow path, and water was discharged from the hydrogen side flow path, but water does not have to be discharged from the hydrogen side flow path. This is because in water electrolysis, water is supplied to the oxygen electrode side of the electrolysis cell, and the amount of water present in the hydrogen side flow path is smaller than the amount of water present in the oxygen side flow path and the water supply flow path.

- In the above second embodiment, an example was shown in which the oxygen side treatment section 20A does not have a second oxygen tank 65 and the oxygen supply pump 80 is used to pump out the oxygen in the first oxygen tank 63. However, in other forms, the hydrogen side treatment section 30 may similarly not have a second hydrogen tank 35 and may use a hydrogen supply pump to pump out the hydrogen in the first hydrogen tank 63. Also, in both the oxygen treatment section and the hydrogen treatment section, a pump may be used to pump out the gas (oxygen or hydrogen) in the tank.

- In the above third embodiment, an example was shown in which the oxygen side treatment section 20B does not include the first oxygen tank 63, and oxygen stored in the oxygen side gas-liquid separator 23 is supplied to the water supply flow path 40d. However, in other embodiments, the hydrogen side treatment section 30 may similarly not include the first hydrogen tank 33, and hydrogen stored in the hydrogen side gas-liquid separator 31 may be supplied to the electrolysis cell 10. In addition, in both the oxygen treatment section and the hydrogen treatment section, the gas (oxygen or hydrogen) in the gas-liquid separator may be sent out.

- In the above embodiment, an example is shown in which the water separated in the gas-liquid separator is sent to the water tank 41 and then supplied again to the electrolysis cell 10, but the water separated in the gas-liquid separator does not have to be sent to the water tank 41. Also, the water separated in the gas-liquid separator does not have to be supplied to the electrolysis cell 10.

- In the above embodiment, an example was shown in which the oxygen in the first oxygen tank 63 was made to flow into the water supply passage connecting the water tank 41 and the supply pump 43, but it may also be made to flow into the water supply passage 40b connecting the supply pump 43 and the electrolysis cell 10.

- In the above embodiment, an example is shown in which the oxygen-side exhaust flow path 20e is connected to the oxygen-side flow path connecting the electrolysis cell 10 and the heat exchanger 21, but the oxygen-side exhaust flow path 20e may also be connected to the oxygen-side flow path 20b connecting the heat exchanger 21 and the oxygen-side gas-liquid separator 23. In this way, the water remaining in the oxygen-side flow path 20d, the heat exchanger 21, and the oxygen-side flow path 20b can also be discharged outside the water electrolysis system 1.

The present invention has been described above based on the embodiments and modifications, but the embodiments of the above-mentioned aspects are intended to facilitate understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the claims, and the present invention includes equivalents. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

1, 1A, 1B, 1C... Water electrolysis system 10... Electrolytic cell 11a... Electrolyte membrane 11b... Oxygen electrode 11c... Hydrogen electrode 12... Oxygen electrode side flow path 13... Hydrogen electrode side flow path 14... Power source 20, 20A, 20B, 20C... Oxygen side treatment unit 20a, 20b, 20c, 20d... Oxygen side flow path 20e... Oxygen side exhaust flow path 21... Heat exchanger 21a... Heat exchange pipe 22, 32, 39b, 46... On/off valve 22a, 32a... Water level gauge 23... Oxygen side gas-liquid separator 24, 34, 38, 68... Check valve 30... Hydrogen side treatment unit 30a, 30b, 30c, 30e, 30f, 30g, 30h, 30i, 30k, 30n... Hydrogen side flow path 30d, 30j... Hydrogen supply flow path 30m... Hydrogen side discharge flow path 31... Hydrogen side gas-liquid separator 33... First hydrogen tank 35... Second hydrogen tank 36, 66... Flow rate control valve 37, 67... Back pressure valve 39a, 39c, 39e, 44, 47, 61, 62, 69... Three-way valve 40, 40A, 40C... Water supply unit 40a, 40b, 40d... Water supply flow path 40c... Bypass flow path 41... Water tank 43... Supply pump 45, 79... Ion exchanger 50... Control unit 60a, 60b, 60c, 60d, 60e, 60g, 60h... Oxygen side flow path 60f, 60i... Oxygen supply flow path 63... First oxygen tank 65... Second oxygen tank 68... Pressure gauge 70... Water supply unit 77... Liquid supply pump 80... Oxygen supply pump

Claims (8)

A water electrolysis system comprising:
an electrolysis cell including an oxygen electrode, an oxygen electrode-side flow path, a hydrogen electrode, and a hydrogen electrode-side flow path, and configured to generate oxygen and hydrogen by electrolyzing water;
a water supply unit that is connected to the oxygen electrode side flow path of the electrolysis cell via a water supply flow path, the water supply unit including a water storage unit that stores water to be supplied to the electrolysis cell, and that supplies the water in the water storage unit to the electrolysis cell via the water supply flow path;
an oxygen-side treatment unit comprising a first oxygen storage unit connected to the oxygen electrode-side flow path of the electrolysis cell via an oxygen-side flow path and connected to the water supply flow path via an oxygen supply flow path, the first oxygen storage unit storing oxygen generated in the electrolysis cell via the oxygen-side flow path and supplying oxygen in the first oxygen storage unit to the water supply flow path via the oxygen supply flow path;
a control unit that controls the oxygen-side processing unit to supply oxygen in the first oxygen storage unit to the water supply flow path when electrolysis of water by the electrolysis cell is stopped;
Equipped with
The oxygen side treatment section includes:
Further comprising an oxygen-side exhaust flow path connected to the oxygen-side flow path,
The control unit is
when electrolysis of water by the electrolytic cell is started after electrolysis of water by the electrolytic cell is stopped, the water supply unit is controlled to supply water in the water storage unit to the oxygen electrode side flow path of the electrolytic cell via the water supply flow path, and to discharge water that has flowed from the oxygen electrode side flow path of the electrolytic cell into the oxygen side flow path to the outside of the water electrolysis system via the oxygen side discharge flow path .
Water electrolysis system. A water electrolysis system comprising:
an electrolysis cell including an oxygen electrode, an oxygen electrode-side flow path, a hydrogen electrode, and a hydrogen electrode-side flow path, and configured to generate oxygen and hydrogen by electrolyzing water;
a water supply unit that is connected to the oxygen electrode side flow path of the electrolysis cell via a water supply flow path, the water supply unit including a water storage unit that stores water to be supplied to the electrolysis cell, and that supplies the water in the water storage unit to the electrolysis cell via the water supply flow path;
an oxygen-side treatment unit comprising a first oxygen storage unit connected to the oxygen electrode-side flow path of the electrolysis cell via an oxygen-side flow path and connected to the water supply flow path via an oxygen supply flow path, the first oxygen storage unit storing oxygen generated in the electrolysis cell via the oxygen-side flow path and supplying oxygen in the first oxygen storage unit to the water supply flow path via the oxygen supply flow path;
a control unit that controls the oxygen-side processing unit to supply oxygen in the first oxygen storage unit to the water supply flow path when electrolysis of water by the electrolysis cell is stopped;
Equipped with
The oxygen side treatment section includes:
A second oxygen storage section that stores the oxygen generated in the electrolysis cell at a pressure lower than the pressure of the first oxygen storage section ,
The control unit is
when electrolysis of water by the electrolysis cell is stopped, the oxygen-side treatment unit is controlled to connect the first oxygen storage unit and the second oxygen storage unit via the oxygen supply flow path, the water supply flow path, and the oxygen electrode-side flow path, thereby circulating oxygen in the first oxygen storage unit through the oxygen supply flow path, the water supply flow path, and the oxygen electrode-side flow path due to a pressure difference between the first oxygen storage unit and the second oxygen storage unit .
Water electrolysis system. The water electrolysis system according to claim 1 ,
The oxygen side treatment section includes:
A second oxygen storage section that stores the oxygen generated in the electrolysis cell at a pressure lower than the pressure of the first oxygen storage section,
The control unit is
when electrolysis of water by the electrolysis cell is stopped, the oxygen-side treatment unit is controlled to connect the first oxygen storage unit and the second oxygen storage unit via the oxygen supply flow path, the water supply flow path, and the oxygen electrode-side flow path, so that oxygen in the first oxygen storage unit is circulated through the oxygen supply flow path, the water supply flow path, and the oxygen electrode-side flow path by a pressure difference between the first oxygen storage unit and the second oxygen storage unit .
Water electrolysis system. The water electrolysis system according to any one of claims 1 to 3,
a hydrogen-side treatment unit that comprises a first hydrogen storage unit connected to the hydrogen electrode-side flow path of the electrolytic cell via a hydrogen-side flow path and connected to the hydrogen electrode-side flow path of the electrolytic cell via a hydrogen supply flow path, and that stores hydrogen produced in the electrolytic cell in the first hydrogen storage unit via the hydrogen-side flow path and supplies hydrogen in the first hydrogen storage unit to the hydrogen electrode-side flow path of the electrolytic cell via the hydrogen supply flow path,
The control unit is
when electrolysis of water by the electrolysis cell is stopped, the hydrogen-side treatment unit is controlled to supply hydrogen in the first hydrogen storage unit to the hydrogen electrode-side flow path of the electrolysis cell.
Water electrolysis system. The water electrolysis system according to claim 4,
The hydrogen side treatment section includes:
A hydrogen-side exhaust flow path connected to the hydrogen-side flow path,
The control unit is
when electrolysis of water by the electrolytic cell is started after electrolysis of water by the electrolytic cell is stopped, the hydrogen-side processing unit is controlled to supply hydrogen in the first hydrogen storage unit to the hydrogen electrode-side flow path of the electrolytic cell via the hydrogen supply flow path, and to discharge hydrogen that has flowed from the hydrogen electrode-side flow path of the electrolytic cell to the hydrogen-side flow path to outside the water electrolysis system via the hydrogen-side discharge flow path.
Water electrolysis system. The water electrolysis system according to claim 4 or 5,
The hydrogen side treatment section includes:
a second hydrogen storage section that stores hydrogen generated in the electrolysis cell at a pressure lower than the pressure of the first hydrogen storage section;
The control unit is
when electrolysis of water by the electrolysis cell is stopped, the hydrogen-side treatment unit is controlled to connect the first hydrogen storage unit and the second hydrogen storage unit via the hydrogen supply flow path and the hydrogen electrode-side flow path, so that hydrogen in the first hydrogen storage unit is circulated through the hydrogen supply flow path and the hydrogen electrode-side flow path by a pressure difference between the first hydrogen storage unit and the second hydrogen storage unit.
Water electrolysis system. A water electrolysis system comprising:
an electrolysis cell including an oxygen electrode, an oxygen electrode-side flow path, a hydrogen electrode, and a hydrogen electrode-side flow path, and configured to generate oxygen and hydrogen by electrolyzing water;
a water supply unit that is connected to the oxygen electrode side flow path of the electrolysis cell via a water supply flow path, the water supply unit including a water storage unit that stores water to be supplied to the electrolysis cell, and that supplies the water in the water storage unit to the electrolysis cell via the water supply flow path;
an oxygen-side treatment section including an oxygen storage section connected to the oxygen electrode-side flow path of the electrolysis cell via an oxygen-side flow path, and an oxygen-side discharge flow path connected to the oxygen-side flow path, and configured to store oxygen generated in the electrolysis cell in the oxygen storage section via the oxygen-side flow path;
a control unit that controls the water supply unit to supply water in the water storage unit to the oxygen electrode-side flow path of the electrolytic cell via the water supply flow path and to discharge water that has flowed from the oxygen electrode-side flow path of the electrolytic cell into the oxygen-side flow path to the outside of the water electrolysis system via the oxygen-side discharge flow path when electrolysis of water by the electrolytic cell is started after electrolysis of water by the electrolytic cell is stopped;
Equipped with
Water electrolysis system. The water electrolysis system according to claim 7 ,
a first hydrogen storage unit connected to the hydrogen electrode side flow path of the electrolytic cell via a hydrogen side flow path and connected to the hydrogen electrode side flow path of the electrolytic cell via a hydrogen supply flow path, and a hydrogen side discharge flow path connected to the hydrogen side flow path, the hydrogen side processing unit storing hydrogen generated in the electrolytic cell in the first hydrogen storage unit via the hydrogen side flow path and supplying hydrogen in the first hydrogen storage unit to the hydrogen electrode side flow path of the electrolytic cell via the hydrogen supply flow path,
The control unit is
when electrolysis of water by the electrolytic cell is started after electrolysis of water by the electrolytic cell is stopped, the hydrogen-side processing unit is controlled to supply hydrogen in the hydrogen storage unit to the hydrogen electrode-side flow path of the electrolytic cell via the hydrogen supply flow path, and to discharge hydrogen that has flowed from the hydrogen electrode-side flow path of the electrolytic cell into the hydrogen-side flow path to the outside of the water electrolysis system via the hydrogen-side discharge flow path.
Water electrolysis system.

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