Water electrolysis system

Abstract

To provide a water electrolysis system capable of suppressing the deterioration of a cell while suppressing the cost increase when reusing water from which hydrogen is separated, for electrolysis in a water electrolysis tank.SOLUTION: The water electrolysis system comprises a water electrolysis stack, an oxygen gas / liquid separator for separating a mixture of oxygen generated in the water electrolysis stack and water into oxygen and water, a hydrogen gas / liquid separator for separating a mixture of hydrogen generated in the water electrolysis stack and water into hydrogen and water, a circulation flow path for circulating water between the oxygen gas / liquid separator and the water electrolysis stack, an ion exchanger disposed outside the circulation flow path to reduce the conductivity of supply water supplied from outside to the circulation flow path, by exchanging ions, and a return flow path for sending hydrogen separated water, i.e., water separated from hydrogen in the hydrogen gas / liquid separator, to the upstream side of the ion exchanger. The circulation flow path is supplied with clean water of reduced conductivity reduced by the ion exchanger and hydrogen separated water as feed water.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, water electrolysis systems that generate oxygen and hydrogen by electrolysis of water have been known. Patent Document 1 discloses a solid polymer water electrolysis device in which an ion exchanger is installed between a circulation pump and a water electrolysis cell as a water electrolysis system. Patent Document 2 discloses a solid polymer water electrolysis device in which a branch line is provided for extracting a portion of water supplied to a water electrolysis cell that performs water electrolysis, passing the portion through an ion exchanger, and then supplying the portion to an oxygen gas-liquid separator as a water electrolysis system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-143852 A [Patent Document 2] JP 2002-173788 A Summary of the Invention [Problem to be solved by the invention]

[0004] Hydrogen-separated water, which is water separated by the hydrogen gas-liquid separator, may have a higher electrical conductivity than water flowing through a circulation flow path that circulates water between the oxygen gas-liquid separator and the water electrolytic cell. In Patent Documents 1 and 2, the hydrogen-separated water is mixed with water flowing through the circulation flow path and is used again for electrolysis in the water electrolytic cell, which may accelerate the deterioration of the cells that constitute the water electrolytic layer. As a countermeasure, it is possible to provide a separate ion exchanger for lowering the electrical conductivity of the hydrogen-separated water in addition to the ion exchanger for lowering the electrical conductivity of the clean water used for water electrolysis, but this leads to an increase in costs due to expansion and maintenance. For this reason, there has been a demand for a technology that can suppress the deterioration of the cells while suppressing an increase in costs when the hydrogen-separated water is used again for electrolysis in the water electrolytic cell.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to provide a water electrolysis system that can suppress deterioration of a cell while suppressing an increase in costs when hydrogen-separated water is reused for electrolysis in a water electrolytic cell. [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 forms.

[0007] (1) According to one aspect of the present invention, there is provided a water electrolysis system comprising: a water electrolysis stack that generates oxygen and hydrogen by electrolysis of water; an oxygen gas-liquid separator that separates a mixture of oxygen and water generated by the water electrolysis stack into oxygen and water; a hydrogen gas-liquid separator that separates a mixture of hydrogen and water generated by the water electrolysis stack into hydrogen and water; a circulation flow path that circulates water between the oxygen gas-liquid separation unit and the water electrolysis stack; an ion exchanger that is disposed outside the circulation flow path and that reduces the electrical conductivity of supply water supplied from the outside to the circulation flow path by ion exchange; and a reflux flow path that sends hydrogen-separated water, which is water separated from hydrogen by the hydrogen gas-liquid separation unit, to a side upstream of the ion exchange unit, and the circulation flow path is supplied with clean water whose electrical conductivity has been reduced by the ion exchanger and the hydrogen-separated water as the supply water.

[0008] In general, a water electrolysis system includes an ion exchanger for reducing the conductivity of clean water used for water electrolysis. According to this configuration, the hydrogen-separated water is supplied upstream of the ion exchanger via the reflux flow path, so that the ion exchanger can reduce the conductivity of the hydrogen-separated water as well as the clean water. That is, the ion exchanger used for ion exchange of the clean water can also be used for ion exchange of the hydrogen-separated water. Therefore, when the hydrogen-separated water is used again for electrolysis in the water electrolysis stack, deterioration of each cell constituting the water electrolysis stack can be suppressed while suppressing an increase in costs due to the installation and maintenance of an additional ion exchanger in addition to the ion exchanger for reducing the conductivity of the clean water used for water electrolysis.

[0009] (2) In the water electrolysis system of the above aspect, a heat exchanger may be provided in the pipe forming the reflux flow path. According to this configuration, the heat exchanger can lower the temperature of the hydrogen-separated water before it is introduced into the ion exchanger, thereby improving the ion exchange efficiency of the hydrogen-separated water in the ion exchanger, thereby further suppressing deterioration of each cell that constitutes the water electrolysis stack.

[0010] 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 description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is an explanatory diagram showing the configuration of a water electrolysis system according to a second embodiment of the present invention. [Diagram 3] FIG. 11 is an explanatory diagram showing the configuration of a water electrolysis system according to a third embodiment of the present invention. [Figure 4] FIG. 11 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a fourth embodiment of the present invention. [Diagram 5] FIG. 11 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a fifth embodiment of the present invention. [Figure 6] FIG. 13 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a sixth embodiment of the present invention. [Figure 7] FIG. 2 is an explanatory diagram showing the configuration of a water electrolysis system of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment Fig. 1 is an explanatory diagram showing the configuration of a water electrolysis system 1 according to a first embodiment of the present invention. The water electrolysis system 1 is a system for producing oxygen and hydrogen by electrolysis of water. The water electrolysis system 1 includes an RO unit 11, a pure water tank 12, an ion exchanger 13, a pump 15, an ion exchanger 16, a water electrolysis stack 17, an oxygen gas-liquid separator 18, and a hydrogen gas-liquid separator 19.

[0013] The RO unit 11 includes a reverse osmosis membrane such as an RO (Reverse Osmosis Membrane). The RO unit 11 removes ion components from clean water sent from outside the water electrolysis system 1. Clean water refers to water obtained by purifying groundwater, river water, lake water, seawater, etc., and is, for example, tap water purified at a water purification plant.

[0014] The pure water tank 12 is connected to the RO unit 11 via a flow path F1. The pure water tank 12 stores water from which ionic components have been removed by the RO unit 11 (RO water).

[0015] The ion exchanger 13 is connected to the pure water tank 12 via a flow path F2. The ion exchanger 13 reduces the conductivity of the water sent from the pure water tank 12 by ion exchange. An on-off valve (not shown) is provided in the pure water tank 12 itself or in the piping forming the flow path F2, and the flow rate in the piping can be adjusted and the flow in the piping can be blocked depending on the opening and closing degree of the on-off valve. The on-off valve (not shown) may be provided in the piping forming the flow path F3 instead of or in addition to the piping forming the flow path F2.

[0016] The oxygen-gas-liquid separator 18 is connected to the ion exchanger 13 via a flow path F3. The oxygen-gas-liquid separator 18 separates a mixture of oxygen and water generated in the water electrolysis stack 17 (described below) into oxygen and water. The separated oxygen is sent to the outside of the water electrolysis system 1 via a flow path F8o connected to an upper part of the oxygen-gas-liquid separator 18 in the direction of gravity. The separated water is sent to the pump 15 via a flow path F4.

[0017] The pump 15 is connected to the oxygen-gas-liquid separator 18 via flow path F4. The pump 15 sends the water sent from the oxygen-gas-liquid separator 18 via flow path F4 toward the ion exchanger 16. The water sent to the pump 15 via flow path F4 contains water from which oxygen has been separated in the oxygen-gas-liquid separator 18 and water supplied to the oxygen-gas-liquid separator 18 via flow path F3.

[0018] The ion exchanger 16 is connected to the pump 15 via flow path F5. The ion exchanger 16 reduces the conductivity of the water sent from the pump 15 via flow path F5 by ion exchange. The water that has passed through the ion exchanger 16 is sent to the water electrolysis stack 17 via flow path F6.

[0019] The water electrolysis stack 17 is connected to the ion exchanger 16 via a flow path F6. The water electrolysis stack 17 produces oxygen and hydrogen by electrolysis (electrolysis) of water. The water electrolysis stack 17 is connected to the oxygen gas-liquid separator 18 via a flow path F7L. A mixture of oxygen and water produced in the water electrolysis stack 17 is sent to the oxygen gas-liquid separator 18 via the flow path F7L. In addition, the water electrolysis stack 17 is connected to the hydrogen gas-liquid separator 19 via a flow path F7R. A mixture of hydrogen and water produced in the water electrolysis stack 17 is sent to the hydrogen gas-liquid separator 19 via the flow path F7R.

[0020] The hydrogen-gas-liquid separator 19 separates the mixture of hydrogen and water generated in the water electrolysis stack 17 into hydrogen and water. The separated hydrogen is sent to the outside of the water electrolysis system 1 via a flow path F9o connected to an upper part of the hydrogen-gas-liquid separator 19 in the direction of gravity. The hydrogen-gas-liquid separator 19 is also connected to the pure water tank 12 via a flow path F9. The water separated from hydrogen in the hydrogen-gas-liquid separator 19 is sent to the pure water tank 12 via the flow path F9. In the following description, the water separated from hydrogen in the hydrogen-gas-liquid separator 19 is referred to as hydrogen-separated water. The flow path F9 is a reflux flow path that sends the hydrogen-separated water upstream of the ion exchanger 13. Here, the upstream side refers to the upstream side in the direction in which water flows from the RO unit 11 toward the ion exchanger 13.

[0021] As described above, the mixture of oxygen and water generated in the water electrolysis stack 17 is sent to the oxygen-liquid separator 18 via F7L and then separated into oxygen and water. The separated water is sent back to the water electrolysis stack 17 via flow paths F4, F5, and F6. In this embodiment, the flow paths F4, F5, F6, and F7L correspond to a circulation flow path that circulates water between the oxygen-liquid separator 18 and the water electrolysis stack 17. In addition, water whose conductivity has been reduced through the RO unit 11 and the ion exchanger 13 arranged outside the circulation flow path is supplied to this circulation flow path. In the following description, water supplied from outside the circulation flow path to the circulation flow path is referred to as supply water. In addition, supplying the supply water to the circulation flow path from outside the circulation flow path includes not only directly supplying the supply water from outside the circulation flow path to the circulation flow paths (flow paths F4, flow paths F5, flow paths F6 and flow paths F7L) but also supplying the supply water to each component (oxygen gas-liquid separator 18, etc.) connected by the circulation flow paths (flow paths F4, flow paths F5, flow paths F6 and flow paths F7L).

[0022] As described above, the hydrogen separated water is supplied to the upstream side of the ion exchanger 13 through the flow path F9. In particular, in this embodiment, the hydrogen separated water is supplied to the pure water tank 12 arranged upstream of the ion exchanger 13 through the flow path F9. The hydrogen separated water is then supplied to the pure water tank 12 and then sent to the ion exchanger 13. That is, the clean water whose conductivity has been reduced by the RO unit 11 and the ion exchanger 13 and the hydrogen separated water whose conductivity has been reduced by the ion exchanger 13 are supplied to the circulation flow path as the supply water. In other words, the supply water includes the clean water and the hydrogen separated water. Of the supply water, the hydrogen separated water may have a higher conductivity than the water flowing through the circulation flow path, but by passing through the ion exchanger 13, it becomes water with the same conductivity as the water flowing through the circulation flow path before being supplied to the circulation flow path.

[0023] In general, a water electrolysis system includes an ion exchanger for reducing the conductivity of clean water used for water electrolysis. According to the water electrolysis system 1 of the first embodiment described above, the hydrogen-separated water is supplied upstream of the ion exchanger 13 for reducing the conductivity of the clean water via a reflux flow path (flow path F9 in this embodiment), so that the ion exchanger 13 can reduce the conductivity of the hydrogen-separated water in addition to the clean water. That is, the ion exchanger 13 used for ion exchange of the clean water can also be used for ion exchange of the hydrogen-separated water. Therefore, when the hydrogen-separated water is used again for electrolysis in the water electrolysis stack 17, deterioration of each cell constituting the water electrolysis stack 17 can be suppressed while suppressing an increase in costs due to the installation and maintenance of an additional ion exchanger in addition to the ion exchanger 13 for reducing the conductivity of the clean water used for water electrolysis.

[0024] FIG. 7 is an explanatory diagram showing a configuration of a water electrolysis system 1p of a comparative example. The water electrolysis system 1p of the comparative example is the same as the water electrolysis system 1 of the first embodiment, except that, compared to the water electrolysis system 1 of the first embodiment, the water electrolysis system 1p of the comparative example includes a flow path F9p for sending hydrogen separated water from the hydrogen gas-liquid separator 19 to the oxygen gas-liquid separator 18 instead of the flow path F9. In such a water electrolysis system 1p, if an ion exchanger is provided in the piping forming the flow path F9p in order to reduce the conductivity of the hydrogen separated water before it is introduced into the oxygen gas-liquid separator 18, there is a concern that the cost will increase. In addition, if the ion exchanger 16 is used to reduce the conductivity of the water increased by adding the hydrogen separated water to the oxygen gas-liquid separator 18, the size of the ion exchanger 16 needs to be increased. This is because the ion exchange efficiency of the ion exchanger 16 disposed in the circulation flow path, which is generally assumed to be at a high temperature, is considered to be relatively poor, and unless the size of the ion exchanger 16 is increased by the amount of the hydrogen separated water added to the oxygen gas-liquid separator 18 as the target of ion exchange by the ion exchanger 16, there is a risk that the conductivity increased by the addition of the hydrogen separated water cannot be sufficiently reduced. Of course, increasing the size of the ion exchanger 16 also raises concerns about an increase in costs. On the other hand, according to the water electrolysis system 1 of the first embodiment, the ion exchanger 13 used for ion exchange of clean water is also used for ion exchange of hydrogen-separated water, which makes it possible to suppress deterioration of each cell constituting the water electrolysis stack 17 while suppressing an increase in costs.

[0025] <Second embodiment> 2 is an explanatory diagram showing the configuration of a water electrolysis system 1a according to a second embodiment of the present invention. The water electrolysis system 1a according to the second embodiment differs from the water electrolysis system 1 according to the first embodiment mainly in that the water electrolysis system 1a according to the second embodiment includes a pure water tank 14.

[0026] The pure water tank 14 is connected to the ion exchanger 13 via a flow path F3a. The pure water tank 14 stores the water sent from the ion exchanger 13. In the second embodiment, the pump 15 is connected to the pure water tank 14 via a flow path F4a. An on-off valve (not shown) is provided in the pure water tank 14 itself or in the piping forming the flow path F4a, and depending on the opening and closing degree of the on-off valve, the flow rate in the piping can be adjusted and the flow in the piping can be blocked.

[0027] In the second embodiment, the oxygen gas-liquid separator 18 is connected to the pure water tank 14 via a flow path F8. The water separated in the oxygen gas-liquid separator 18 is sent to the pure water tank 14 via the flow path F8. In the second embodiment, the flow paths F4a, F5, F6, F7L, and F8 correspond to circulation flow paths.

[0028] In the water electrolysis system 1a according to the second embodiment described above, when the hydrogen-separated water is reused for electrolysis in the water electrolysis stack 17, deterioration of each cell constituting the water electrolysis stack 17 can be suppressed while suppressing an increase in costs.

[0029] <Third embodiment> 3 is an explanatory diagram showing the configuration of a water electrolysis system 1b according to a third embodiment of the present invention. The water electrolysis system 1b according to the third embodiment differs from the water electrolysis system 1a according to the second embodiment mainly in that the water electrolysis system 1b according to the third embodiment does not include an ion exchanger 16, as compared with the water electrolysis system 1 according to the first embodiment.

[0030] In the third embodiment, the pump 15 is connected to the water electrolysis stack 17 via flow path F5b. In the third embodiment, the flow paths F4a, F5b, F7L, and F8 correspond to the circulation flow paths. In the water electrolysis system 1b of the third embodiment, when the hydrogen-separated water is reused for electrolysis in the water electrolysis stack 17, deterioration of each cell constituting the water electrolysis stack 17 can be suppressed while suppressing an increase in costs.

[0031] <Fourth embodiment> 4 is an explanatory diagram showing the configuration of a water electrolysis system 1c according to a fourth embodiment of the present invention. The water electrolysis system 1c according to the fourth embodiment differs from the water electrolysis system 1b according to the third embodiment mainly in that the water electrolysis system 1c according to the fourth embodiment includes a heat exchanger H1.

[0032] In the fourth embodiment, a heat exchanger H1 is provided in the piping forming the flow path F9. A piping (not shown) to which cooling water is supplied as a refrigerant and a piping (not shown) to which the cooling water is discharged are connected to the heat exchanger H1. That is, the heat exchanger H1 cools the hydrogen-separated water flowing through the flow path F9. Note that in the fourth embodiment, as in the third embodiment, the flow paths F4a, F5b, F7L, and F8 correspond to circulation flow paths.

[0033] In the water electrolysis system 1c of the fourth embodiment described above, when the hydrogen-separated water is reused for electrolysis in the water electrolysis stack 17, deterioration of each cell constituting the water electrolysis stack 17 can be suppressed while suppressing an increase in costs.

[0034] Furthermore, in the water electrolysis system 1c of the fourth embodiment, the heat exchanger H1 can reduce the temperature of the hydrogen-separated water before it is introduced into the ion exchanger 13, thereby improving the ion exchange efficiency of the hydrogen-separated water in the ion exchanger 13. As a result, deterioration of each cell in the water electrolysis stack 17 can be further suppressed.

[0035] <Fifth embodiment> 5 is an explanatory diagram showing the configuration of a water electrolysis system 1d according to a fifth embodiment of the present invention. The water electrolysis system 1d according to the fifth embodiment differs from the water electrolysis system 1a according to the second embodiment mainly in that the water electrolysis system 1d according to the fifth embodiment includes a heat exchanger H2.

[0036] In the fifth embodiment, a heat exchanger H2 is provided in a pipe (not shown) forming a flow path F5 (a flow path connecting the pump 15 and the ion exchanger 16). Unlike the heat exchanger H1 described in the fourth embodiment, the heat exchanger H2 is connected to a pipe (not shown) to which a heat medium is supplied and a pipe (not shown) to which the heat medium is discharged. That is, the heat exchanger H2 heats the water flowing through the flow path F5. Note that in the fifth embodiment, like the second embodiment, the flow paths F4a, F5, F6, F7L, and F8 correspond to circulation flow paths.

[0037] In the water electrolysis system 1d of the fifth embodiment described above, when the hydrogen-separated water is reused for electrolysis in the water electrolysis stack 17, deterioration of each cell constituting the water electrolysis stack 17 can be suppressed while suppressing an increase in costs.

[0038] Furthermore, in the water electrolysis system 1d of the fifth embodiment, the heat exchanger H2 can increase the temperature of the water before it is introduced into the water electrolysis stack 17. As a result, the efficiency of producing oxygen and hydrogen through electrolysis (endothermic reaction) in the water electrolysis stack 17 can be improved.

[0039] Sixth Embodiment 6 is an explanatory diagram showing the configuration of a water electrolysis system 1e according to a sixth embodiment of the present invention. The water electrolysis system 1e according to the sixth embodiment differs from the water electrolysis system 1a according to the second embodiment mainly in that the water electrolysis system 1e according to the sixth embodiment includes a flow path F9e that is different from the flow path F9.

[0040] Like flow path F9, flow path F9e is a reflux flow path that sends the hydrogen separated water upstream of the ion exchanger 13, but differs from flow path F9 in that it connects the hydrogen gas-liquid separator 19 to flow path F2. In the sixth embodiment, like the second embodiment, flow paths F4a, F5, F6, F7L, and F8 correspond to circulation flow paths. In the water electrolysis system 1e of the sixth embodiment, when the hydrogen separated water is reused for electrolysis in the water electrolysis stack 17, deterioration of each cell constituting the water electrolysis stack 17 can be suppressed while suppressing an increase in costs.

[0041] <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.

[0042] In the description of the first embodiment, the clean water from which the RO unit 11 removes ionic components is sent from outside the water electrolysis system 1, but this is not limited to the above. For example, the water electrolysis system 1 may include a tank for storing clean water upstream of the RO unit 11, and the RO unit 11 may remove ionic components from the clean water sent from the tank.

[0043] In the above embodiment, clean water and hydrogen-separated water, the conductivity of which has been reduced by the ion exchanger 13, are supplied as feed water to the oxygen gas-liquid separator 18 or the pure water tank 14, thereby supplying the feed water to the circulation flow path from outside the circulation flow path, but this is not limited to this. The feed water may be supplied to the circulation flow path from outside the circulation flow path by directly supplying the feed water to the circulation flow path (for example, flow path F4 or flow path F4a).

[0044] Although the water electrolysis systems 1b to 1e according to the third to sixth embodiments include the pure water tank 14, the present invention is not limited to this. The water electrolysis systems 1b to 1e according to the third to sixth embodiments do not necessarily need to include the pure water tank 14.

[0045] Although the water electrolysis system 1 of the first embodiment includes the ion exchanger 16, the present invention is not limited to this. The water electrolysis system 1 of the first embodiment does not necessarily need to include the ion exchanger 16.

[0046] Although the water electrolysis systems 1, 1a, 1d, and 1e of the first, second, fifth, and sixth embodiments do not include the heat exchanger H1, this is not limited thereto. The water electrolysis systems 1, 1a, 1d, and 1e of the first, second, fifth, and sixth embodiments may include the heat exchanger H1.

[0047] Although the water electrolysis systems 1, 1b, 1c, and 1e of the first, third, fourth, and sixth embodiments do not include the heat exchanger H2, this is not limited thereto. The water electrolysis systems 1, 1b, 1c, and 1e of the first, third, fourth, and sixth embodiments may include the heat exchanger H2.

[0048] In the water electrolysis systems 1, 1a to 1d of the first to fifth embodiments, the reflux flow path for sending the hydrogen-separated water upstream of the ion exchanger 13 is the flow path F9, but is not limited to this. In the water electrolysis systems 1, 1a to 1d of the first to fifth embodiments, the reflux flow path may be the flow path F9e. Furthermore, the reflux flow path may be connected to any position as long as it is connected upstream of the ion exchanger 13.

[0049] Although the present aspect has been described above based on the embodiment and modified examples, the above-mentioned embodiment of the aspect is intended to facilitate understanding of the present aspect and does not limit the present aspect. The present aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents are included in the present aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0050] 1, 1a to 1e...Water electrolysis system 11…RO unit 12…Pure water tank 13…Ion exchanger 14…Pure water tank 15…Pump 16…Ion exchanger 17…Water electrolysis stack 18...Oxygen gas-liquid separator 19...Hydrogen gas-liquid separator F1~F6, F7L, F7R, F8, F9...flow path F3a, F4a, F5b, F8o, F9e, F9o...flow path H1,H2…Heat exchanger

Claims

1. A water electrolysis system, a water electrolysis stack that generates oxygen and hydrogen by electrolyzing water, an oxygen gas-liquid separator that separates a mixture of oxygen and water generated in the water electrolysis stack into oxygen and water, a hydrogen gas-liquid separator that separates a mixture of hydrogen and water generated in the water electrolysis stack into hydrogen and water, a circulation flow path that circulates water between the oxygen gas-liquid separation section and the water electrolysis stack, an ion exchanger that is disposed outside the circulation flow path and reduces the conductivity of supply water supplied from the outside to the circulation flow path by ion exchange, a reflux flow path that sends hydrogen separation water, which is water separated from hydrogen in the hydrogen gas-liquid separation section, to an upstream side of the ion exchange section, and a water electrolysis system in which the circulation flow path is supplied with service water whose conductivity has been reduced by the ion exchanger and the hydrogen separation water as the supply water.

2. The water electrolysis system according to claim 1, wherein a heat exchanger is provided in a pipe forming the reflux flow path.

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