Water electrolysis system and method for controlling the water electrolysis system

Abstract

To provide a technique by which a change of state of an electrolyte membrane can be detected in an early stage.SOLUTION: A water electrolysis system comprises: a water electrolysis unit for generating oxygen and hydrogen by electrolyzing water using an electrolyte membrane; a hydrogen gas-liquid separation unit for separating a mixture of hydrogen and water generated in the water electrolysis unit into hydrogen and water; a measurement unit for measuring the quality of the water separated from hydrogen by the hydrogen gas-liquid separation unit; and a control unit for controlling the water electrolysis system. The control unit includes: estimating a state of the electrolyte membrane based on the measurement result by the measurement unit; and controlling the generation of the oxygen and hydrogen by the water electrolysis unit according to the state of the polymer electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water electrolysis system and a method for controlling a water electrolysis system. [Background technology]

[0002] Conventionally, water electrolysis systems that generate hydrogen by electrolysis of water using an electrolyte membrane have been known. For example, Patent Documents 1 and 2 disclose water electrolysis systems in which water that has not reacted in the electrolyte membrane is circulated within the water electrolysis system and resupplied to the electrolyte membrane. In these water electrolysis systems, the impurity concentration in the circulating water is determined from the measurement results of the conductivity of the circulating water circulating between the oxygen gas-liquid separator and the water electrolysis cell, and if the impurity concentration is high, control is performed to remove the impurities using a filter, ion exchange resin, or the like.

[0003] Furthermore, technologies for preventing damage and deterioration of water electrolysis systems have also been proposed. For example, Patent Document 3 discloses a water electrolysis system that prevents negative pressure within the water electrolysis device when water electrolysis operation is stopped by providing a pressure adjustment channel connecting a hydrogen-side gas-liquid separation tank and an oxygen-side gas-liquid separation tank. Patent Document 4 discloses a water electrolysis device that applies a shutdown voltage to prevent deterioration of the electrolyte membrane while the water electrolysis reaction is stopped. Patent Document 5 discloses a power supplier that is used in a water electrolysis device, and that disperses current to prevent damage to the electrolyte membrane due to high temperatures. Patent Document 6 discloses a water electrolysis device in which the catalyst layer is covered with a porous material to absorb the load applied to the electrolyte membrane when the pressure difference between the cathode electrode catalyst layer side and the anode electrode catalyst layer side increases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-48506 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-105578 [Patent Document 3] Patent Publication No. 2021-46602 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-199697 [Patent Document 5] Japanese Patent Application Laid-Open No. 2011-127215 [Patent Document 6] Japanese Patent Application Publication No. 2019-157213 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Documents 3 to 6 only disclose methods for preventing damage and deterioration of water electrolysis systems, and do not consider detecting the state of the electrolyte membrane. Furthermore, Patent Documents 1 and 2 measure the conductivity of circulating water, but this circulating water is used in the electrolysis reaction in the water electrolysis cell and is appropriately diluted with fresh pure water to maintain its purity. Therefore, even if the water quality of the circulating water, such as the conductivity, is measured, it is difficult to detect indicators of the state of the electrolyte membrane, and there is a risk that changes in the state of the electrolyte membrane cannot be detected early. Therefore, there is a need for a water electrolysis system that can detect changes in the state of the electrolyte membrane early. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) One aspect of the present invention provides a water electrolysis system including a water electrolysis unit that produces oxygen and hydrogen by electrolyzing water using an electrolyte membrane, a hydrogen-gas-liquid separation unit that separates a mixture of hydrogen and water produced in the water electrolysis unit into hydrogen and water, a measurement unit that measures the quality of hydrogen-separated water that is water separated in the hydrogen-gas-liquid separation unit, and a controller that controls the water electrolysis system, wherein the controller estimates a state of the electrolyte membrane based on the measurement results by the measurement unit and controls the production of oxygen and hydrogen by the water electrolysis unit based on the state of the electrolyte membrane.

[0008] According to this configuration, the quality of the hydrogen-separated water, which is water separated in the hydrogen-gas-liquid separation unit, is measured, and the production of oxygen and hydrogen by the water electrolysis unit is controlled according to the state of the electrolyte membrane estimated from the measurement results. Because the quality of the hydrogen-separated water changes in accordance with changes in the state of the electrolyte membrane, this configuration makes it possible to accurately determine the state of the electrolyte membrane. Furthermore, because the water in the hydrogen-gas-liquid separation unit is not diluted and information indicating the state of the electrolyte (e.g., elution) is directly reflected in the hydrogen-separated water, changes in the state of the electrolyte membrane can be determined with high sensitivity. In other words, because changes in the state of the electrolyte can be detected as soon as they begin to occur, changes in the state of the electrolyte membrane can be detected early.

[0009] (2) In the water electrolysis system of the above aspect, the state of the electrolyte membrane may include whether or not the electrolyte is damaged, and if the electrolyte membrane is damaged, the control unit may stop the production of oxygen and hydrogen by the water electrolysis unit or slow down the rate at which oxygen and hydrogen are produced by the water electrolysis unit. With this configuration, the state of the electrolyte membrane can be estimated as the presence or absence of damage to the electrolyte membrane. If the electrolyte membrane is damaged, the production of oxygen and hydrogen by the water electrolysis unit is stopped or the production rate is reduced, thereby preventing the damage to the electrolyte membrane from spreading.

[0010] (3) The water electrolysis system of the above aspect may further include an oxygen-gas-liquid separation unit that separates a mixture of oxygen and water produced in the water electrolysis unit into oxygen and water; a reflux path that supplies the hydrogen-separated water from the hydrogen-gas-liquid separation unit to the oxygen-gas-liquid separation unit; and a supply path that supplies water containing the hydrogen-separated water from the oxygen-gas-liquid separation unit to the water electrolysis unit. With this configuration, hydrogen-separated water is supplied from the hydrogen-gas-liquid separation unit to the oxygen-gas-liquid separation unit, and water containing hydrogen-separated water is supplied from the oxygen-gas-liquid separation unit to the water electrolysis unit. Therefore, water that was sent to the hydrogen-gas-liquid separation unit because it did not react in the electrolyte membrane can be supplied to the water electrolysis unit and reused for the water electrolysis reaction. This reduces the cost of producing oxygen and hydrogen through the water electrolysis reaction.

[0011] (4) In the water electrolysis system of the above aspect, a shut-off valve may be provided in the return path and capable of shutting off the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit, the state of the electrolyte membrane may include whether or not the electrolyte is damaged, and if the electrolyte membrane is damaged, the control unit may close the shut-off valve to stop the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit. According to this configuration, if the electrolyte membrane is damaged, the hydrogen-separated water contains eluted materials and the like resulting from the damage to the electrolyte membrane, and therefore, such hydrogen-separated water can be prevented from circulating within the water electrolysis system via the oxygen-gas-liquid separation section.

[0012] (5) The water electrolysis system of the above aspect may include a plurality of the water electrolysis units; a plurality of hydrogen-gas-liquid separation units provided corresponding to the water electrolysis units, each separating a mixture of hydrogen and water produced in the water electrolysis units into hydrogen and water; a plurality of measuring units provided corresponding to the hydrogen-gas-liquid separation units, each measuring a water quality of the hydrogen-separated water separated in the hydrogen-gas-liquid separation unit; the control unit estimating a state of the electrolyte membrane in each of the water electrolysis units based on measurement results by each of the measuring units and controlling production of oxygen and hydrogen by each of the water electrolysis units based on the state of the electrolyte membrane; the oxygen-gas-liquid separation unit; a plurality of return paths for supplying the hydrogen-separated water from each of the hydrogen-gas-liquid separation units to the oxygen-gas-liquid separation unit; and the supply path for supplying water containing the hydrogen-separated water from the oxygen-gas-liquid separation unit to each of the water electrolysis units. With this configuration, hydrogen-separated water is supplied from each hydrogen-gas-liquid separation unit to the oxygen-gas-liquid separation unit, and water containing hydrogen-separated water is supplied from the oxygen-gas-liquid separation unit to the water electrolysis unit. Therefore, water that was sent to each hydrogen-gas-liquid separation unit because it was unreacted in the electrolyte membrane can be supplied to the electrolyte membrane and reused for the water electrolysis reaction. This reduces the cost of producing oxygen and hydrogen through the water electrolysis reaction.

[0013] (6) In the water electrolysis system of the above aspect, the state of the electrolyte membrane may include whether or not the electrolyte is damaged. If any of the water electrolysis units has damaged electrolyte membranes, the control unit may stop the water electrolysis unit from producing oxygen and hydrogen or reduce the rate at which the water electrolysis unit produces oxygen and hydrogen. According to this configuration, if there is a water electrolysis unit with damaged electrolyte membrane, the production of oxygen and hydrogen by that water electrolysis unit is stopped or the production rate is reduced, thereby preventing the damage to the electrolyte membrane from spreading.

[0014] (7) The water electrolysis system of the above aspect may further include a plurality of shut-off valves provided in the return paths, each capable of shutting off the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit, and when a water electrolysis unit with damaged electrolyte membrane is present, the control unit may close the shut-off valve in the return path through which the hydrogen-separated water originating from the water electrolysis unit flows, thereby stopping the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit. According to this configuration, if a water electrolysis unit with damaged electrolyte membrane is present, the hydrogen-separated water derived from that water electrolysis unit will contain leachables, etc., which are information indicating damage to the electrolyte membrane. Therefore, such hydrogen-separated water can be prevented from circulating within the water electrolysis system via the oxygen-gas-liquid separation unit.

[0015] The present invention can be realized in various forms, such as a method for controlling a water electrolysis system, a computer program for controlling water electrolysis in a water electrolysis system, a server device for distributing the computer program, and a non-transitory storage medium on which the computer program is stored. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a first embodiment. [Figure 2] FIG. 4 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a second embodiment. [Figure 3] FIG. 10 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a third embodiment. [Figure 4] FIG. 10 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment 1 is an explanatory diagram illustrating the configuration of a water electrolysis system 1 according to one embodiment of the present invention. The water electrolysis system 1 is a system that produces oxygen and hydrogen by electrolysis of water. The water electrolysis system 1 includes a storage tank 5, an oxygen-gas-liquid separation unit 10, a water electrolysis unit 11, a DC power supply 13, heat exchangers 15o, 15h, and 17, an ion exchange unit 19, a hydrogen-gas-liquid separation unit 20, and a control unit 40.

[0018] The storage tank 5 is a tank for storing pure water. The flow path F1 connects the storage tank 5 and the oxygen-gas-liquid separation unit 10. A shutoff valve S1 and a water supply pump R1 are provided in the piping forming the flow path F1. The shutoff valve S1 can adjust the flow rate in the piping forming the flow path F1 and can also shut off the flow in the piping depending on the degree of opening or closing. Hereinafter, shutoff valves with different reference numerals from the shutoff valve S1 will be assumed to have the same function. The water supply pump R1 supplies water to the oxygen-gas-liquid separation unit 10. Pure water is supplied to the oxygen-gas-liquid separation unit 10 from the storage tank 5 via the flow path F1. The oxygen-gas-liquid separation unit 10 separates the mixture of oxygen and water generated in the water electrolysis unit 11, which will be described later, into oxygen and water. The separated oxygen is sent to the outside of the water electrolysis system 1 via the flow path F2. When the separated water is sent to the outside of the water electrolysis system 1, a shutoff valve S2 provided in the piping forming the flow path F3 is opened. The water level sensor L1 detects the water level in the oxygen gas-liquid separator .

[0019] Flow path F4 is a flow path for supplying water separated in the oxygen-gas-liquid separation unit 10 to the water electrolysis unit 11. The piping forming flow path F4 is provided with a shutoff valve S3, a circulation pump R2, a pressure sensor P1, a temperature sensor T1, and a shutoff valve S4. The circulation pump R2 sends water from the oxygen-gas-liquid separation unit 10 to the water electrolysis unit 11. The pressure sensor P1 and the temperature sensor T1 detect the pressure and temperature in the piping forming flow path F4. Hereinafter, pressure sensors and temperature sensors with different reference numerals from the pressure sensor P1 and the temperature sensor T1 will be assumed to have the same functions. Flow path F5 is a flow path branched off from flow path F4 and connected to a heat exchanger 17 that reduces the temperature of water passing therethrough. The piping forming flow path F5 is provided with a shutoff valve S5. The ion exchange unit 19 is connected to the heat exchanger 17 via flow path F6 and reduces the conductivity of water passing therethrough by ion exchange. The water that has passed through the ion exchange unit 19 is sent to the oxygen-gas-liquid separation section 10 via flow path F7. When the shut-off valve S5 is open, at least a portion of the water sent from the oxygen-gas-liquid separation section 10 to flow path F4 passes through the heat exchanger 17 and the ion exchange unit 19 and is circulated to the oxygen-gas-liquid separation section 10. The bypass flow path B1 is a flow path branched off from flow path F4, and is connected to flow path F8 that connects the water electrolysis section 11 and the heat exchanger 15o. The piping that forms the bypass flow path B1 is provided with a shut-off valve S6. The piping that forms flow path F8 is provided with a pressure sensor P2 and a temperature sensor T2.

[0020] The water electrolysis unit 11 generates oxygen and hydrogen by electrolysis (electrolysis) of pure water using an electrolyte membrane. As described above, water used in the electrolysis reaction is supplied from the oxygen-gas-liquid separation unit 10 via flow path F4. The mixture of oxygen and water generated in the water electrolysis unit 11 is sent to the heat exchanger 15o via flow path F8 and cooled, and then sent to the oxygen-gas-liquid separation unit 10 via flow path F9. On the other hand, the mixture of hydrogen and water generated in the water electrolysis unit 11 is sent to the heat exchanger 15h via flow path F10 and cooled, and then sent to the hydrogen-gas-liquid separation unit 20 via flow path F11.

[0021] The hydrogen-gas-liquid separation unit 20 separates the mixture of hydrogen and water produced in the water electrolysis unit 11 into hydrogen and water. The separated hydrogen is sent to the outside of the water electrolysis system 1 via a flow path F12. A water level sensor L2 detects the water level in the hydrogen-gas-liquid separation unit 20. A flow path F13 is a flow path connected to the hydrogen-gas-liquid separation unit 20. When the water separated in the hydrogen-gas-liquid separation unit 20 is sent to the outside of the water electrolysis system 1, a shutoff valve S7 provided in a pipe forming the flow path F13 is opened.

[0022] Flow path F14 is a flow path branched from flow path F13 and connected to the oxygen-gas-liquid separation unit 10. Flow path F14 is a return flow path that supplies hydrogen-separated water, which is water separated in the hydrogen-gas-liquid separation unit 20, from the hydrogen-gas-liquid separation unit 20 to the oxygen-gas-liquid separation unit 10. The piping that forms flow path F14 is provided with a water pump R3, a shutoff valve S8, and a measurement unit M1. The water pump R3 sends water from the hydrogen-gas-liquid separation unit 20 to the oxygen-gas-liquid separation unit 10. The shutoff valve S8 is a shutoff valve that can shut off the supply of hydrogen-separated water to the oxygen-gas-liquid separation unit 10. The measurement unit M1 measures the water quality of the hydrogen-separated water. In this embodiment, the measurement unit M1 is a conductivity meter that measures the conductivity of water.

[0023] The hydrogen-separated water supplied to the oxygen-gas-liquid separation unit 10 via flow path F14 is mixed in the oxygen-gas-liquid separation unit 10 with water separated from the oxygen-water mixture and pure water supplied from the storage tank 5, and then supplied to the water electrolysis unit 11 via flow path F4. In other words, flow path F4 is a supply channel for supplying water containing hydrogen-separated water from the oxygen-gas-liquid separation unit 10 to the water electrolysis unit 11.

[0024] The control unit 40 controls the operation of the entire water electrolysis system 1 based on information obtained from various sensors included in the water electrolysis system 1. Examples of control by the control unit 40 include controlling the opening and closing of each shut-off valve and controlling the power supply from the DC power supply 13 to the water electrolysis unit 11. The control unit 40 estimates the state of the electrolyte membrane in the water electrolysis unit 11 based on the measurement results from the measurement unit M1, and controls the production of oxygen and hydrogen by the water electrolysis unit 11 based on the state of the electrolyte membrane. In this embodiment, the state of the electrolyte membrane includes whether or not the electrolyte membrane is damaged. When the electrolyte membrane begins to be damaged, materials constituting the electrolyte membrane leach into the water flowing through the water electrolysis unit 11. Examples of leachates from the electrolyte membrane include fluoride ions, sulfate ions, and nitrate ions. The conductivity of water sent from the water electrolysis unit 11 to the oxygen gas-liquid separation unit 10 or the hydrogen gas-liquid separation unit 20 changes depending on the amount of leachates contained in the water. The control unit 40 acquires information indicating the conductivity of the hydrogen-separated water, which is the measurement result by the measurement unit M1, and estimates whether the electrolyte membrane is damaged based on whether the conductivity is greater than a reference value (a preset value for conductivity). If the electrolyte membrane is damaged, the control unit 40 stops the production of oxygen and hydrogen by the water electrolysis unit 11. The control unit 40 stops the production of oxygen and hydrogen by the water electrolysis unit 11 by closing the shut-off valves S3 and S4 and stopping the supply of power from the DC power supply 13 to the water electrolysis unit 11. Note that the production may be stopped by either closing one of the shut-off valves S3 and S4 or by stopping the supply of power from the DC power supply 13. Furthermore, if the electrolyte membrane is damaged, the control unit 40 stops the production of oxygen and hydrogen by the water electrolysis unit 11 and also closes the shut-off valve S8 to stop the supply of hydrogen-separated water to the oxygen-gas-liquid separation unit 10.

[0025] As described above, the water electrolysis system 1 of the first embodiment measures the quality of the hydrogen-separated water, which is water separated in the hydrogen-gas-liquid separation unit 20, and controls the production of oxygen and hydrogen by the water electrolysis unit 11 based on the state of the electrolyte membrane estimated from the measurement results. Because the quality of the hydrogen-separated water changes with changes in the state of the electrolyte membrane, the water electrolysis system 1 of the first embodiment can accurately determine the state of the electrolyte membrane. Furthermore, because the water in the hydrogen-gas-liquid separation unit 20 is not diluted and information indicating the state of the electrolyte (e.g., elution) is directly reflected in the hydrogen-separated water, changes in the state of the electrolyte membrane can be determined with high sensitivity. In other words, changes in the state of the electrolyte membrane can be detected as soon as they begin to occur, allowing early detection of changes in the state of the electrolyte membrane. Note that, if the open time of at least one of the shutoff valves S7 and S8 is controlled to be longer during measurement by the measurement unit M1 to constantly reduce the amount of water in the hydrogen-gas-liquid separation unit 20, information indicating the state of the electrolyte membrane can be reflected in the hydrogen-separated water with even greater immediacy.

[0026] When measuring the water quality (e.g., conductivity) of the circulating water circulating between the oxygen gas-liquid separation unit 10 and the water electrolysis unit 11, this circulating water is used in the electrolysis reaction in the water electrolysis unit 11 and is appropriately diluted with fresh pure water sent from the storage tank 5 to maintain its purity. Therefore, even if the water quality of this circulating water is measured, it is likely that information indicating the state of the electrolyte membrane is also diluted, making it difficult to estimate the state of the electrolyte membrane from the measurement results of the circulating water. In other words, it is difficult to detect changes in the state of the electrolyte membrane early using the measurement results of the circulating water. If damage to the electrolyte membrane cannot be detected early as a change in the state of the electrolyte membrane, the damage may progress and a large amount of leachate may be generated from the ruptured electrolyte membrane. This large amount of leachate may spread throughout the water electrolysis system via water circulating within the water electrolysis system, causing contamination due to deposition or adhesion of the leachate at various locations. On the other hand, the water electrolysis system 1 of the first embodiment detects damage to the electrolyte membrane early as a change in the state of the electrolyte membrane, thereby preventing the electrolyte membrane from rupturing. This prevents a large amount of elution from the electrolyte membrane into water. Even if damage occurs, if the amount of elution is small, the water electrolysis system 1 can likely be reused by simply cleaning the entire system.

[0027] Furthermore, in the water electrolysis system 1 of the first embodiment, the presence or absence of damage to the electrolyte membrane can be estimated as the state of the electrolyte membrane. If the electrolyte membrane is damaged, the production of oxygen and hydrogen by the water electrolysis unit 11 is stopped or the production rate is reduced, thereby preventing the damage to the electrolyte membrane from spreading.

[0028] Furthermore, in the water electrolysis system 1 of the first embodiment, hydrogen-separated water is supplied from the hydrogen-gas-liquid separation unit 20 to the oxygen-gas-liquid separation unit 10, and water containing hydrogen-separated water is supplied from the oxygen-gas-liquid separation unit 10 to the water electrolysis unit 11. Therefore, water that was sent to the hydrogen-gas-liquid separation unit 20 because it did not react in the electrolyte membrane can be supplied to the water electrolysis unit 11 and reused for the water electrolysis reaction. When protons migrate to the hydrogen electrode through the electrolyte membrane during the water electrolysis reaction, four to five water molecules migrate with each proton, and therefore a relatively large amount of water is sent to the hydrogen-gas-liquid separation unit 20. In the water electrolysis system 1 of the first embodiment, such water is reused, thereby reducing the cost of producing oxygen and hydrogen through the water electrolysis reaction.

[0029] Furthermore, in the water electrolysis system 1 of the first embodiment, if the electrolyte membrane is damaged, the shut-off valve S8 is closed to stop the supply of hydrogen-separated water to the oxygen-gas-liquid separation unit 10. If the electrolyte membrane is damaged, the hydrogen-separated water contains eluted substances and the like resulting from the damage to the electrolyte membrane. Therefore, it is possible to prevent such hydrogen-separated water from circulating within the water electrolysis system 1 via the oxygen-gas-liquid separation unit 10.

[0030] Another advantage of measuring the water quality of the hydrogen-separated water is described below. As described above, a relatively large amount of water is sent from the water electrolysis unit 11 to the hydrogen-gas-liquid separation unit 20. Therefore, if the electrolyte membrane is damaged, a large amount of eluate will be sent to the hydrogen-gas-liquid separation unit 20. Therefore, measuring the water quality of the hydrogen-separated water allows for early detection of changes in the state of the electrolyte membrane. Furthermore, measuring the hydrogen-separated water also makes it possible to accurately determine changes in the state of the electrolyte membrane without including errors or omissions caused by oxygen bubbles.

[0031] Second Embodiment 2 is an explanatory diagram illustrating the configuration of a water electrolysis system 1a according to a second embodiment. The configuration of the water electrolysis system 1a according to the second embodiment is the same as that of the water electrolysis system 1 according to the first embodiment ( FIG. 1 ), except that the water electrolysis system 1a according to the second embodiment does not include a flow path F14 and includes a measurement unit M2.

[0032] The water electrolysis system 1a does not include a flow path F14, and therefore does not include a measurement unit M1 that is provided in the piping that forms the flow path F14. Instead of the measurement unit M1, the water electrolysis system 1a includes a measurement unit M2. The measurement unit M2 is provided in the flow path F13 and measures the water quality of the hydrogen-separated water. Like the measurement unit M1 in the first embodiment, the measurement unit M2 is a conductivity meter that measures the conductivity of water. The control unit 40 controls the production of oxygen and hydrogen by the water electrolysis unit 11 based on the measurement results from the measurement unit M2.

[0033] The water electrolysis system 1a of the second embodiment as described above can also determine changes in the state of the electrolyte membrane with high sensitivity, allowing for early detection of changes in the state of the electrolyte membrane. Furthermore, since the water electrolysis system 1a of the second embodiment does not include the flow path F14, even if eluates are generated due to damage to the electrolyte membrane, the hydrogen-separated water containing the eluates is not supplied to the oxygen-gas-liquid separation unit 10. Therefore, the amount of eluates flowing into the oxygen-gas-liquid separation unit 10 when the electrolyte membrane is damaged can be reduced.

[0034] Third Embodiment 3 is an explanatory diagram illustrating the configuration of a water electrolysis system 1b according to a third embodiment. The configuration of the water electrolysis system 1b according to the third embodiment is the same as that of the water electrolysis system 1 according to the first embodiment (FIG. 1), except that the water electrolysis system 1b according to the third embodiment mainly includes a water electrolysis unit 21, a DC power supply 23, heat exchangers 25o and 25h, and a hydrogen gas-liquid separation unit 30.

[0035] Similar to the water electrolysis unit 11, the water electrolysis unit 21 produces oxygen and hydrogen by electrolysis (electrolysis) of pure water. Water used in the electrolysis reaction is supplied from the oxygen-gas-liquid separation unit 10 via a flow path F15 branching off from the flow path F4. The flow path F15 is a flow path for supplying the water separated in the oxygen-gas-liquid separation unit 10 to the water electrolysis unit 21. A pressure sensor P3, a temperature sensor T3, and a shutoff valve S9 are provided in the piping forming the flow path F15. A bypass flow path B2 is a flow path branching off from the flow path F15 and is connected to a flow path F16 that connects the water electrolysis unit 21 and the heat exchanger 25o. A shutoff valve S10 is provided in the piping forming the bypass flow path B2. A pressure sensor P4 and a temperature sensor T4 are provided in the piping forming the flow path F16.

[0036] The mixture of oxygen and water produced in the water electrolysis unit 21 is sent via flow path F16 to the heat exchanger 25o where it is cooled, and then sent via flow path F17 to the oxygen gas-liquid separation unit 10. On the other hand, the mixture of hydrogen and water produced in the water electrolysis unit 21 is sent via flow path F18 to the heat exchanger 25h where it is cooled, and then sent via flow path F19 to the hydrogen gas-liquid separation unit 30.

[0037] Similar to the hydrogen-gas-liquid separation unit 20, the hydrogen-gas-liquid separation unit 30 separates the mixture of hydrogen and water produced in the water electrolysis unit 21 into hydrogen and water. The separated hydrogen is sent to the outside of the water electrolysis system 1b via a flow path F20. Similar to the water level sensor L2, the water level sensor L3 detects the water level in the hydrogen-gas-liquid separation unit 30. A flow path F21 is connected to the hydrogen-gas-liquid separation unit 30. When the water separated in the hydrogen-gas-liquid separation unit 30 is sent to the outside of the water electrolysis system 1b, a shutoff valve S11 provided in a pipe forming the flow path F21 is opened.

[0038] Flow path F22 is a flow path branching off from flow path F21 and connected to the oxygen-gas-liquid separation unit 10. Like flow path F14, flow path F22 is a return flow path that supplies hydrogen-separated water from the hydrogen-gas-liquid separation unit 30 to the oxygen-gas-liquid separation unit 10. The piping that forms flow path F22 is provided with a water pump R4, a shutoff valve S12, and a measurement unit M3. The water pump R4 sends water from the hydrogen-gas-liquid separation unit 30 to the oxygen-gas-liquid separation unit 10. Like the shutoff valve S8, the shutoff valve S12 is a shutoff valve that can shut off the supply of hydrogen-separated water to the oxygen-gas-liquid separation unit 10. Like the measurement unit M1, the measurement unit M3 is a conductivity meter that measures the conductivity of the hydrogen-separated water.

[0039] The hydrogen-separated water supplied to the oxygen-gas-liquid separation unit 10 via flow paths F14 and F22 is mixed in the oxygen-gas-liquid separation unit 10 with water separated from the oxygen-water mixture and pure water supplied from the storage tank 5, and then supplied to the water electrolysis units 11 and 21 via flow paths F4 and F15.

[0040] As described above, the water electrolysis system 1b is provided with two water electrolysis units 11, 21, and two hydrogen-gas-liquid separation units 20, 30 corresponding to the water electrolysis units 11, 21, which separate hydrogen and water from a mixture of hydrogen and water produced in the water electrolysis units 11, 21. The water electrolysis system 1b also is provided with two measurement units M1, M3 corresponding to the two hydrogen-gas-liquid separation units 20, 30, which measure the quality of the hydrogen-separated water from each of the hydrogen-gas-liquid separation units 20, 30. The water electrolysis system 1b is also provided with flow paths F14, 22 for supplying hydrogen-separated water from each of the two hydrogen-gas-liquid separation units 20, 30 to the oxygen-gas-liquid separation unit 10, shut-off valves S8, 12 capable of shutting off each of the flow paths F14, 22, and flow paths F4, 15 for supplying water containing hydrogen-separated water from the oxygen-gas-liquid separation unit 10 to each of the water electrolysis units 11, 21.

[0041] The control unit 40 estimates the state of the electrolyte membrane in each of the water electrolysis units 11 and 21 based on the measurement results from each of the measurement units M1 and M3, and controls the production of oxygen and hydrogen by the water electrolysis units 11 and 21 based on the state of each electrolyte membrane. In the second embodiment, as in the first embodiment, the state of the electrolyte membrane also includes whether or not the electrolyte membrane is damaged. If a water electrolysis unit with a damaged electrolyte membrane is present, the control unit 40 stops the production of oxygen and hydrogen by that water electrolysis unit.

[0042] If the electrolyte membrane of the water electrolysis unit 11 is damaged, the control unit 40 closes the shutoff valve S4 and opens the shutoff valve S6, and stops the supply of power from the DC power supply 13 to the water electrolysis unit 11, thereby stopping the production of oxygen and hydrogen by the water electrolysis unit 11. At this time, the control unit 40 also closes the shutoff valve S8 of the flow path F14, through which the hydrogen-separated water derived from the water electrolysis unit 11 flows, thereby stopping the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit 10.

[0043] On the other hand, if the electrolyte membrane of the water electrolysis unit 21 is damaged, the control unit 40 closes the shutoff valve S9 and opens the shutoff valve S10, and stops the supply of power from the DC power supply 23 to the water electrolysis unit 21, thereby stopping the production of oxygen and hydrogen by the water electrolysis unit 21. At this time, the control unit 40 also closes the shutoff valve S12 of the flow path F22, through which the hydrogen-separated water originating from the water electrolysis unit 21 flows, thereby stopping the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit 10. Furthermore, if the electrolyte membrane of at least one of the water electrolysis units 11, 21 is damaged, the control unit 40 may adjust the output of the various pumps R1 to R4.

[0044] The water electrolysis system 1b of the third embodiment as described above can also determine changes in the state of the electrolyte membrane with high sensitivity, thereby enabling early detection of changes in the state of the electrolyte membrane. Furthermore, in the water electrolysis system 1b of the third embodiment, hydrogen-separated water is supplied from each of the hydrogen-gas-liquid separation units 20 and 30 to the oxygen-gas-liquid separation unit 10, and water containing hydrogen-separated water is supplied from the oxygen-gas-liquid separation unit 10 to the water electrolysis units 11 and 21. Therefore, similar to the first embodiment, the cost of producing oxygen and hydrogen through the electrolysis reaction of water can be reduced.

[0045] Furthermore, in the water electrolysis system 1b of the third embodiment, a mixture of hydrogen and water produced in each of the water electrolysis units 11, 21 is sent to each of the hydrogen gas-liquid separation units 20, 30, while a mixture of oxygen and water produced in each of the water electrolysis units 11, 21 is sent to a single oxygen gas-liquid separation unit 10. That is, the hydrogen gas-liquid separation units 20, 30 are provided corresponding to each of the water electrolysis units 11, 21, but only one oxygen gas-liquid separation unit 10 is provided for each of the water electrolysis units 11, 21. Therefore, compared to a water electrolysis system including multiple water electrolysis units and a pair of a hydrogen gas-liquid separation unit and an oxygen gas-liquid separation unit corresponding to each of the water electrolysis units, the water electrolysis system 1b of the third embodiment can reduce the number of oxygen gas-liquid separation units, thereby enabling reduction in manufacturing costs of the water electrolysis system 1b.

[0046] Furthermore, in the water electrolysis system 1b of the third embodiment, if a water electrolysis unit with a damaged electrolyte membrane is present, the production of oxygen and hydrogen by the water electrolysis unit is stopped or the production rate is reduced, thereby preventing the damage to the electrolyte membrane from spreading.

[0047] Furthermore, in the water electrolysis system 1b of the third embodiment, if a water electrolysis unit with a damaged electrolyte membrane is present, the hydrogen-separated water derived from the water electrolysis unit will contain leachables, which are information indicating the damage to the electrolyte membrane. Therefore, such hydrogen-separated water can be prevented from circulating within the water electrolysis system 1b via the oxygen gas-liquid separation unit 10.

[0048] <Fourth embodiment> 4 is an explanatory diagram illustrating the configuration of a water electrolysis system 1c according to a fourth embodiment. The configuration of the water electrolysis system 1c according to the fourth embodiment is the same as that of the water electrolysis system 1b according to the third embodiment (FIG. 3), except that the water electrolysis system 1c does not include flow paths F14 and F22 and includes measuring units M4 and M5.

[0049] The water electrolysis system 1c does not include flow paths F14 and F22, and therefore does not include measuring units M1 and M3 that are provided in the flow paths F14 and F22. Instead of the measuring units M1 and M3, the water electrolysis system 1c includes measuring units M4 and M5. The measuring units M4 and M5 are provided in the flow paths F13 and F21, respectively, and measure the water quality of the hydrogen-separated water. The measuring units M4 and M5 are conductivity meters that measure the conductivity of water, similar to the measuring units M1 to M3 in the first to third embodiments. The control unit 40 controls the production of oxygen and hydrogen by the water electrolysis units 11 and 21 based on the measurement results of the measuring units M4 and M5.

[0050] The water electrolysis system 1c of the fourth embodiment as described above can also determine changes in the state of the electrolyte membrane with high sensitivity, allowing for early detection of changes in the state of the electrolyte membrane. Furthermore, since the water electrolysis system 1c of the fourth embodiment does not include flow paths F14 and F22, even if eluates are generated due to damage to the electrolyte membrane, the hydrogen-separated water containing the eluates is not supplied to the oxygen-gas-liquid separation unit 10. Therefore, the amount of eluates flowing into the oxygen-gas-liquid separation unit 10 when the electrolyte membrane is damaged can be reduced.

[0051] <Modification 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 of the invention. For example, the following modifications are also possible.

[0052] [Variation 1] In the above embodiment, the water quality of the hydrogen-separated water measured by the measuring unit M1 and the like is conductivity, but this is not limited to this. For example, the water quality of the hydrogen-separated water to be measured may be resistivity, pH, or impurity concentration. The impurity concentration is the concentration of fluoride ions, sulfate ions, nitrate ions, and the like, which are eluted from the electrolyte membrane.

[0053] [Variation 2] In the above embodiment, the measuring unit M1 and the like are provided in the pipe forming the flow path, but this is not limiting. For example, in addition to or instead of being provided in the pipe forming the flow path, the measuring unit may be provided at a position where it can measure the water in the hydrogen gas-liquid separator.

[0054] [Variation 3] In the above embodiment, the control unit 40 stops the production of oxygen and hydrogen by the water electrolysis unit 11 when the electrolyte membrane is damaged, but this is not limited to this. For example, when the electrolyte membrane is damaged, the control unit 40 may slow down the rate at which oxygen and hydrogen are produced by the water electrolysis unit 11. In this case, the load caused by the operation of the water electrolysis unit 11 is reduced, thereby slowing down the progression of damage to the electrolyte membrane.

[0055] [Variation 4] In the above embodiment, the state of the electrolyte membrane includes whether or not the electrolyte membrane is damaged. However, this is not limiting. For example, the state of the electrolyte membrane may include whether or not the electrolyte membrane is degraded and the degree of degradation of the electrolyte membrane. The production of oxygen and hydrogen by the water electrolysis unit may be controlled based on the state of the electrolyte membrane. Degradation of the electrolyte membrane refers to degradation of the electrolyte membrane due to the influence of impurities or reaction heat. The degree of degradation of the electrolyte membrane refers to the current production efficiency compared to the production efficiency at the beginning of operation. When degradation of the electrolyte membrane occurs or depending on the degree of degradation of the electrolyte membrane, information indicating the state of the electrolyte (e.g., elution) reflected in the hydrogen-separated water may be measured in advance, and the degradation and degree of degradation of the electrolyte membrane may be estimated using this information as an index. When degradation of the electrolyte membrane occurs, the production of oxygen and hydrogen by the water electrolysis unit may be stopped or the production rate may be slowed. Furthermore, the higher the degree of degradation, the more the amount of power supplied from the DC power source to the water electrolysis unit or the amount of water supplied to the water electrolysis unit may be reduced, thereby achieving a supply of power and water that is just enough for the electrolysis reaction in the degraded electrolyte membrane.

[0056] [Variation 5] In the water electrolysis systems 1b and 1c (FIGS. 3 and 4) of the third and fourth embodiments, two water electrolysis units 11 and 21 and hydrogen gas-liquid separation units 20 and 30 corresponding to the water electrolysis units 11 and 21 are provided for one oxygen gas-liquid separation unit 10, but this is not limiting. For example, the water electrolysis system may be provided with three or more water electrolysis units and hydrogen gas-liquid separation units corresponding to the water electrolysis units for one oxygen gas-liquid separation unit.

[0057] [Variation 6] In the water electrolysis systems 1 and 1a (FIGS. 1 and 2) of the first and second embodiments, a flow path F5 is provided branching from flow path F4, and water sent to flow path F5 passes through a heat exchanger 17, flow path F6, an ion exchange unit 19, and flow path F7, before circulating to the oxygen-gas-liquid separation unit 10. On the other hand, in the water electrolysis systems 1b and 1c of the third and fourth embodiments, a flow path corresponding to flow path F5 is not branched from flow path F15, but this is not limited thereto. A branch flow path corresponding to flow path F5 in flow path F4 may be provided in flow path F15. The water sent to this branch flow path passes through a heat exchanger and an ion exchange unit, before circulating to the oxygen-gas-liquid separation unit 10.

[0058] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0059] 1, 1a to 1c...Water electrolysis system 5...Storage tank 10...Oxygen gas-liquid separation section 11...Water electrolysis section 13…DC power supply 15o,15h…Heat exchanger 17...Heat exchanger 19...Ion exchange unit 20...Hydrogen gas-liquid separation section 21...Water electrolysis section 23…DC power supply 25o,25h…Heat exchanger 30...Hydrogen gas-liquid separation section 40...Control unit B1, B2...Bypass flow path F1~F22...flow path L1~L3...Water level sensors M1~M5...Measuring section P1 to P4: Pressure sensors R1...Water supply pump R2...Circulation pump R3, R4...Water pump S1 to S12: Shut-off valves T1 to T4: Temperature sensors

Claims

1. A water electrolysis system, a water electrolysis unit that generates oxygen and hydrogen by electrolysis of water using an electrolyte membrane; a hydrogen gas-liquid separation unit that separates the mixture of hydrogen and water produced in the water electrolysis unit into hydrogen and water; a measuring unit that measures the water quality of hydrogen-separated water, which is water separated in the hydrogen-gas-liquid separation unit; a control unit that controls the water electrolysis system; an oxygen gas-liquid separation unit that separates the mixture of oxygen and water produced in the water electrolysis unit into oxygen and water; a return path for supplying the hydrogen-separated water from the hydrogen-gas-liquid separation section to the oxygen-gas-liquid separation section, The measuring unit is provided in a pipe forming the return path, The control unit estimates a state of the electrolyte membrane based on a measurement result by the measurement unit, and controls production of oxygen and hydrogen by the water electrolysis unit based on the state of the electrolyte membrane.

2. The water electrolysis system according to claim 1, The state of the electrolyte membrane includes whether or not the electrolyte is damaged; When the electrolyte membrane is damaged, the control unit stops the production of oxygen and hydrogen by the water electrolysis unit or reduces the rate at which oxygen and hydrogen are produced by the water electrolysis unit.

3. The water electrolysis system according to claim 1 or 2, further comprising: a supply path for supplying water containing the hydrogen-separated water from the oxygen gas-liquid separation unit to the water electrolysis unit.

4. The water electrolysis system according to claim 3, further comprising: a shutoff valve provided in the return path and capable of shutting off the supply of the hydrogen-separated water to the oxygen-gas-liquid separation section; The state of the electrolyte membrane includes whether or not the electrolyte is damaged; When the electrolyte membrane is damaged, the control unit closes the shutoff valve to stop the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit.

5. The water electrolysis system according to claim 3, A plurality of the water electrolysis units; a plurality of hydrogen gas-liquid separation units provided corresponding to each of the water electrolysis units, the hydrogen gas-liquid separation units separating a mixture of hydrogen and water produced in each of the water electrolysis units into hydrogen and water; a plurality of measuring units provided corresponding to the hydrogen-gas-liquid separation units, each measuring the quality of the hydrogen-separated water separated by the hydrogen-gas-liquid separation units; the control unit estimates a state of the electrolyte membrane in each of the water electrolysis units in accordance with a measurement result by each of the measurement units, and controls production of oxygen and hydrogen by each of the water electrolysis units in accordance with the state of the electrolyte membrane; The oxygen gas-liquid separation unit; a plurality of return paths for supplying the hydrogen-separated water from each of the hydrogen-gas-liquid separation sections to the oxygen-gas-liquid separation section; the supply path for supplying water containing the hydrogen-separated water from the oxygen gas-liquid separation unit to each of the water electrolysis units, a water electrolysis system, wherein each of the pipes forming the return path is provided with a corresponding one of the measuring units.

6. The water electrolysis system according to claim 5, The state of the electrolyte membrane includes whether or not the electrolyte is damaged; When any of the water electrolysis units has damaged electrolyte membranes, the control unit stops the production of oxygen and hydrogen by the water electrolysis unit or reduces the rate at which oxygen and hydrogen are produced by the water electrolysis unit.

7. The water electrolysis system according to claim 6, further comprising: a plurality of shutoff valves provided in each of the return paths and capable of shutting off the supply of the hydrogen-separated water to the oxygen-gas-liquid separation section; and when the electrolyte membrane of one of the water electrolysis units is damaged, the control unit closes the shut-off valve in the return path through which the hydrogen-separated water originating from the water electrolysis unit flows, thereby stopping the supply of the hydrogen-separated water to the oxygen-gas-liquid separation unit.

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