Water electrolysis system

Abstract

This water electrolysis system comprises: a water electrolysis cell stack; a water separator that is connected to the water electrolysis cell stack and separates water discharged from the water electrolysis cell stack from gas; a water circulation path that is provided with a water circulation pump and circulates the water separated by the water separator; a water supply path that is separate from the water circulation path, is provided with a water supply pump, and supplies the water to the water electrolysis cell stack; an ion exchange resin provided in the water circulation path; a first heat exchanger that is provided on the upstream side of the ion exchange resin in the water circulation path and cools the water in the water circulation path; and a second heat exchanger that is provided in the water circulation path and that performs heat exchange between the water delivered from the ion exchange resin and the water before being cooled by the first heat exchanger.

Description

Water electrolysis system

[0001] The present disclosure relates to a water electrolysis system that electrolyzes water to generate hydrogen and oxygen.

[0002] Conventionally, water splitting systems have been proposed that electrolyze water into hydrogen and oxygen using a water electrolysis cell stack that uses a solid polymer electrolyte membrane. In these water splitting systems, when water discharged from the water electrolysis cell stack is circulated for use, ions in the circulating water are removed using an ion exchange resin to maintain high-purity water.

[0003] Generally, the temperature at which ion exchange resins function efficiently is lower than the temperature at which a water electrolysis cell stack operates efficiently, and therefore, some ingenuity is required regarding the water temperature.

[0004] For example, in Japanese Patent No. 4347972, the purity of the circulating water is maintained without using ion exchange resin by supplying pure water at room temperature and discharging a portion of the circulating water.

[0005] However, since a part of the circulating water is discharged, waste occurs.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a water electrolysis system that is capable of efficiently operating a water electrolysis cell stack without wasting circulating water.

[0007] A water electrolysis system according to a first aspect includes a water electrolysis cell stack; a water separator connected to the water electrolysis cell stack and configured to separate water discharged from the water electrolysis cell stack from gas; a water circulation channel provided with a water circulation pump and configured to circulate the water separated by the water separator; a water supply channel separate from the water circulation channel and provided with a water supply pump, configured to supply water to the water electrolysis cell stack; an ion exchange resin provided in the water circulation channel; a first heat exchanger provided in the water circulation channel upstream of the ion exchange resin and configured to cool the water in the water circulation channel; and a second heat exchanger provided in the water circulation channel and configured to exchange heat between the water discharged from the ion exchange resin and the water before being cooled by the first heat exchanger.

[0008] In a water electrolysis system according to a first aspect, a water separator separates water discharged from the water electrolysis cell stack from gas. A water circulation channel for circulating the water separated by the water separator and a water supply channel for supplying water to the water electrolysis cell stack are separate paths, and an ion exchange resin is provided in the water circulation channel. A first heat exchanger is provided in the water circulation channel upstream of the ion exchange resin, and the water in the water circulation channel is cooled in the first heat exchanger. The water circulation channel also includes a second heat exchanger for heat exchange between the water discharged from the ion exchange resin and the water before being cooled by the first heat exchanger. In this way, by providing a water supply channel for supplying water to the water electrolysis cell stack and a water circulation channel provided with an ion exchange resin as separate paths and cooling the water in the water circulation channel by the first heat exchanger, the water temperatures in the water supply channel and the water circulation channel can be made different. This enables efficient operation of the water electrolysis cell stack while performing ion exchange without discharging circulating water. In addition, heat exchange is carried out in the second heat exchanger between the water sent out from the ion exchange resin and the water before being cooled in the first heat exchanger, so that the water sent out to the first heat exchanger can be cooled and the water returned to the water separator can be heated, thereby reducing heat loss.

[0009] In the water electrolysis system of a second aspect, the first heat exchanger cools the water in the water circulation channel based on the temperature of the water supplied from the water supply channel to the water electrolysis cell stack.

[0010] According to the water electrolysis system of the second aspect, by cooling the water in the water circulation channel based on the temperature of the water supplied from the water supply channel to the water electrolysis cell stack, it is possible to adjust the water temperature to a level that allows the water electrolysis cell stack to operate efficiently, and also to cool the water supplied to the ion exchange resins.

[0011] In the water electrolysis system of a third aspect, the water supply pump keeps the flow rate of water supplied to the water electrolysis cell stack constant, and the water circulation pump controls the flow rate of water circulating through the water circulation path so that the temperature of the water supplied to the ion exchange resin becomes an optimum temperature for the ion exchange resin.

[0012] According to the water electrolysis system of the third aspect, the water supply pump is operated to maintain a constant flow rate, and the water circulation pump is controlled to control the flow rate of water supplied to the ion exchange resins so that the temperature of the water is optimum for the ion exchange resins. This enables stable supply of water to the water electrolysis cell stack with simple control.

[0013] In a fourth aspect of the water electrolysis system, the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack in accordance with the flow rate of hydrogen produced in the water electrolysis cell stack, and the water circulation pump controls the flow rate of water circulating through the water circulation path so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

[0014] According to the water electrolysis system of the fourth aspect, the water supply pump controls the flow rate in accordance with the flow rate of hydrogen produced in the water electrolysis cell stack, and the water circulation pump controls the flow rate so that the temperature of water supplied to the ion exchange resins is an optimum temperature for the ion exchange resins. This enables the ion exchange resins to function efficiently with simple control.

[0015] In a fifth aspect of the water electrolysis system, the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack in accordance with the temperature difference between the water supplied to the water electrolysis cell stack and the water discharged from the water electrolysis cell stack, and the water circulation pump controls the flow rate of water circulating through the water circulation path so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

[0016] In the water electrolysis system of the fifth aspect, the water supply pump controls the flow rate in accordance with the temperature difference between the water supplied to the water electrolysis cell stack and the water discharged from the water electrolysis cell stack, and the water circulation pump controls the flow rate so that the temperature of the water supplied to the ion exchange resins is an optimum temperature for the ion exchange resins. This enables the ion exchange resins to function efficiently with simple control.

[0017] In a sixth aspect of the water electrolysis system, the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack in accordance with a temperature difference between the water supplied to the water electrolysis cell stack and the water discharged from the water electrolysis cell stack, and the water circulation pump controls the flow rate of water circulating through the water circulation conduit so that the ratio of the flow rate of water circulating through the water circulation conduit to the flow rate in the water supply conduit is constant.

[0018] In the water electrolysis system of the sixth aspect, the water supply pump controls the flow rate in accordance with the temperature difference between the water supplied to the water electrolysis cell stack and the water discharged from the water electrolysis cell stack, and the water circulation pump controls the flow rate so that the ratio of the flow rate of water circulating through the water circulation channel to the flow rate in the water supply channel is constant, thereby enabling a stable supply of water to the water electrolysis cell stack.

[0019] In a seventh aspect of the water electrolysis system, the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack so that the ratio of the flow rate of water circulating through the water circulation conduit to the flow rate of water in the water supply conduit is constant, and the flow rate of water circulating through the water circulation conduit is controlled so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

[0020] In the water electrolysis system of the seventh aspect, the water supply pump is flow-controlled so that the ratio of the flow rate of water circulating through the water circulation channel to the flow rate in the water supply channel is constant, and the water circulation pump is flow-controlled so that the temperature of water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin, thereby enabling a stable supply of water to the water electrolysis cell stack.

[0021] According to the water electrolysis system of the present invention, the water electrolysis cell stack can be operated efficiently without wasting circulating water.

[0022] Fig. 1 is a block diagram schematically showing the configuration of a water electrolysis system according to a first embodiment; Fig. 2 is a block diagram showing the connection with a controller of the water electrolysis system according to the first embodiment; Fig. 3 is a block diagram schematically showing the configuration of a water electrolysis system according to a second embodiment; Fig. 4 is a block diagram showing the connection with a controller of the water electrolysis system according to the second embodiment;

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] First Embodiment Fig. 1 shows a water electrolysis system 10A according to a first embodiment of the present invention. The water electrolysis system 10A includes a water electrolysis cell stack 12, a water separator 14, ion exchange resins 16, a first heat exchanger 24, and a second heat exchanger 44. Note that the dotted lines in Figs. 1 and 3 may indicate functional relationships that differ from the actual connection relationships.

[0025] The water electrolysis cell stack 12 is formed by stacking water electrolysis cells, each forming an anode and a cathode with an electrolyte membrane sandwiched therebetween. In the water electrolysis cell stack 12, water supplied to the anode is electrolyzed by applying current, generating oxygen at the anode and hydrogen at the cathode. The water electrolysis cell stack 12 is connected to a control unit 40 via a DC power supply DC, and the control unit 40 controls the amount of current and therefore the amount of water electrolysis. One end of a water supply channel 32 is connected to the anode side inlet of the water electrolysis cell stack 12, and water is supplied from the water supply channel 32. A hydrogen delivery channel 12A is connected to the cathode side outlet of the water electrolysis cell stack 12, and hydrogen is delivered from the hydrogen delivery channel 12A. One end of a water / oxygen delivery channel 12B is connected to the anode side outlet of the water electrolysis cell stack 12, and oxygen and water are delivered from the water / oxygen delivery channel 12B. The other end of the water / oxygen delivery channel 12B is connected to a water separator 14.

[0026] The water separator 14 separates the oxygen and water from the water / oxygen delivery channel 12B and stores the separated water. The oxygen delivery channel 14A is connected to the water separator 14, and oxygen is delivered from the oxygen delivery channel 14A. The other end of the water supply channel 32 is connected to the water separator 14, and a water supply pump 38 is provided in the water supply channel 32. The water supply pump 38 supplies water from the water separator 14 to the water electrolysis cell stack 12. The water supply pump 38 is connected to a control unit 40, and its output is controlled by the control unit 40. In this embodiment, the water supply pump 38 is set to provide a constant flow rate. Hereinafter, the flow rate of water delivered by the water supply pump 38 will be referred to as the "water supply flow rate F2."

[0027] A pure water supply device 20 is connected to the water separator 14 via a pure water supply line 22. An adjustment valve 21 is provided on the pure water supply line 22. A water level gauge 23 is provided on the water separator 14, and when the water level detected by the water level gauge 23 falls below a predetermined level, the adjustment valve 21 is opened and pure water is supplied from the pure water supply device 20 to the water separator 14.

[0028] One end and the other end of a water circulation line 30 are connected to the water separator 14, and a water circulation pump 36 is provided in the water circulation line 30. The water circulation pump 36 sends water out of the water separator 14, passes through a heat exchanger 24 (described below) and an ion exchange resin 16, and returns the water to the water separator 14. Hereinafter, the flow rate of water circulated by the water circulation pump 36 is referred to as the "water circulation flow rate F1." The water circulation pump 36 is connected to a control unit 40, and its output is controlled by the control unit 40.

[0029] The other end (downstream end) of the water circulation path 30 may be connected to the water supply path 32 upstream of a water supply pump 38, which will be described later.

[0030] An ion exchange resin 16 is provided downstream of the water circulation pump 36 in the water circulation path 30. The ion exchange resin 16 performs ion exchange treatment on the water to remove impurities from the circulating water and maintain the electrical resistivity at a value close to that of theoretically pure water.

[0031] A first heat exchanger 24 is provided in the water circulation path 30 upstream of the ion exchange resin 16 and downstream of the water circulation pump 36. The first heat exchanger 24 cools the water flowing through the water circulation path 30 using a heat medium supplied therein. The flow rate of the heat medium supplied into the first heat exchanger 24 is adjusted by a flow control valve 26.

[0032] The first heat exchanger 24 may use air as cooling, like a radiator, instead of cooling water. In this case, the degree of cooling can be adjusted by changing the rotation speed of the fan.

[0033] A second heat exchanger 44 is provided on the water circulation path 30 upstream of the first heat exchanger 24 and downstream of the water circulation pump 36. The second heat exchanger 44 exchanges heat between the water before being supplied to the first heat exchanger 24 and the water delivered from the ion exchange resin 16. Specifically, the water delivered from the water separator 14 is cooled by the water delivered from the ion exchange resin 16 before being supplied to the first heat exchanger 24, and the water delivered from the ion exchange resin 16 is heated by the water delivered from the water separator 14 before being returned to the water separator 14.

[0034] A stack temperature sensor 32T is provided downstream of the water supply pump 38 on the water supply path 32. The stack temperature sensor 32T detects the temperature of water flowing through the water supply path 32 immediately before it is supplied to the water electrolysis cell stack 12. The stack temperature sensor 32T is connected to the flow rate control valve 26. The flow rate control valve 26 controls the flow rate of the heat medium supplied to the first heat exchanger 24 based on the temperature detected by the stack temperature sensor 32T.

[0035] The temperature of the water supplied to the water electrolysis cell stack 12 can also be estimated from the temperature of the water discharged from the water electrolysis cell stack 12 .

[0036] Specifically, the flow rate of the heat medium supplied into the first heat exchanger 24 is set by constantly feeding back the temperature detected by the stack temperature sensor 32T so that the temperature of the water supplied to the water electrolysis cell stack 12 is the optimum water electrolysis temperature T2. The optimum water electrolysis temperature T2 is set as an efficient operating temperature of the water electrolysis cell stack 12 (a temperature that increases energy efficiency during water electrolysis) and is set in the range of 70°C to 100°C. If the temperature detected by the stack temperature sensor 32T is higher than the optimum water electrolysis temperature T2, the aperture of the flow control valve 26 is increased to increase the amount of heat exchange in the first heat exchanger 24, thereby further cooling the circulating water. If the temperature detected by the stack temperature sensor 32T is lower than the optimum water electrolysis temperature T2, the aperture of the flow control valve 26 is decreased to reduce the amount of heat exchange in the first heat exchanger 24, thereby limiting the degree of cooling of the circulating water.

[0037] An ion exchange temperature sensor 30T is provided in the water circulation path 30 upstream of the ion exchange resin 16 and downstream of the first heat exchanger 24. The ion exchange temperature sensor 30T detects the temperature of the water flowing through the water circulation path 30 immediately before it is supplied to the ion exchange resin 16. The ion exchange temperature sensor 30T is connected to a water circulation pump 36. The output of the water circulation pump 36 is controlled based on instructions from the control unit 40 and the temperature detected by the ion exchange temperature sensor 30T, thereby controlling the flow rate of water circulating through the water circulation path 30 (water circulation flow rate F1).

[0038] The temperature of the water supplied to the ion exchange resin 16 can also be estimated from the temperature of the water downstream of the ion exchange resin 16 .

[0039] Specifically, the water circulation flow rate F1 is adjusted so that the temperature of the water supplied to the ion exchange resin 16 is equal to the optimum ion exchange resin temperature T1, which is the optimum temperature for the ion exchange resin 16. The optimum ion exchange resin temperature T1 is set as a temperature at which the ion exchange resin 16 functions efficiently (a temperature at which ion exchange can be promoted), and is set in the range of 40°C to 70°C. If the temperature detected by the ion exchange temperature sensor 30T is higher than the optimum ion exchange resin temperature T1, the output of the water circulation pump 36 is reduced to lengthen the time the circulating water passes through the first heat exchanger 24, thereby causing the circulating water to be cooled more by the first heat exchanger 24 before being discharged. If the temperature detected by the ion exchange temperature sensor 30T is lower than the optimum ion exchange resin temperature T1, the output of the water circulation pump 36 is increased to shorten the time the circulating water passes through the first heat exchanger 24, thereby limiting the degree of cooling of the circulating water in the first heat exchanger 24 before being discharged.

[0040] The optimum ion exchange resin temperature T1 is set lower than the optimum water electrolysis temperature T2, and the flow rate of water circulated through the water circulation channel 30 by the water circulation pump 36 (circulated water flow rate F1) is set lower than the flow rate of water supplied to the water electrolysis cell stack 12 by the water supply pump 38 (supply water flow rate F2). As an example, if the electrical resistivity of the water supplied to the water electrolysis cell stack 12 is to be equal to or higher than 10 MΩ cm, which is within the allowable range, the optimum water electrolysis temperature T2 can be set to 70°C to 80°C, and the optimum ion exchange resin temperature T1 can be set to approximately 50°C to 60°C, and the circulation water flow rate F1 can be set to 20% to 100% of the supply water flow rate F2.

[0041] 2 , the control unit 40 is connected to the DC power supply DC, the adjustment valve 21, the water level gauge 23, the flow rate adjustment valve 26, the ion exchange temperature sensor 30T, the stack temperature sensor 32T, the water circulation pump 36, and the water supply pump 38. The control unit 40 is also connected to the water electrolysis cell stack 12 via the DC power supply DC. The control unit 40 includes a central processing unit (CPU) 41, a read-only memory (ROM) 42, a random access memory (RAM) 43, an input / output interface (I / O) 44, and a storage unit 45.

[0042] The CPU 41, ROM 42, RAM 43, and I / O 44 are connected to each other via a bus 46. The I / O 44 is connected to various functional units including a storage unit 45. These functional units can communicate with the CPU 41 via the I / O 44.

[0043] The storage unit 45 may, for example, be a hard disk drive (HDD), a solid state drive (SSD), or a flash memory. The storage unit 45 stores control programs for controlling the various components of the water electrolysis system 10A and various data (e.g., the optimum ion exchange resin temperature T1, the optimum water electrolysis temperature T2, the water circulation flow rate F1, and the water supply flow rate F2). The control programs and various data may also be stored in the ROM 42.

[0044] In the water electrolysis system 10A of this embodiment, the water supply channel 32 that supplies water to the water electrolysis cell stack 12 and the water circulation channel 30 provided with the ion exchange resin 16 are separate channels, and the water in the water circulation channel 30 is cooled by the first heat exchanger 24. Therefore, the water temperatures in the water supply channel 32 and the water circulation channel 30 can be made different, and the optimum ion exchange resin temperature T1 can be made lower than the optimum water electrolysis temperature T2, allowing the ion exchange resin 16 to function efficiently and the water electrolysis cell stack 12 to operate efficiently.

[0045] Furthermore, in this embodiment, the water discharged from the water electrolysis cell stack 12 is circulated and used while removing impurities with the ion exchange resin 16, so there is no need to discard the water, and the circulated water can be used without waste.

[0046] In addition, in this embodiment, heat exchange is performed in the second heat exchanger between the water sent out from the ion exchange resin 16 and the water before being cooled in the first heat exchanger 24, so that the water sent out to the first heat exchanger 24 can be cooled and the water returned to the water separator 14 can be heated, thereby reducing heat loss.

[0047] Furthermore, in this embodiment, the water supply flow rate F2 delivered by the water supply pump 38 is set to a constant flow rate, so that water can be easily and stably supplied to the water electrolysis cell stack 12.

[0048] In this embodiment, the water supply flow rate F2 delivered by the water supply pump 38 is set to a constant flow rate, but the water supply flow rate F2 may be varied depending on the load on the water electrolysis cell stack 12. In this case, the water supply flow rate F2 delivered by the water supply pump 38 is varied depending on the amount of hydrogen generated input to the control unit 40.

[0049] Second Embodiment Next, a second embodiment will be described. In this embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0050] As shown in Fig. 3 , the water electrolysis system 10B of this embodiment is provided with a stack discharge temperature sensor 33T in the water / oxygen delivery path 12B. The stack discharge temperature sensor 33T detects the temperature of the water / oxygen mixed fluid delivered from the water electrolysis cell stack 12 to the water / oxygen delivery path 12B. The stack discharge temperature sensor 33T is connected to the stack temperature sensor 32T and the water supply pump 38. The output of the water supply pump 38 is controlled based on a difference between the temperature detected by the stack discharge temperature sensor 33T and the temperature detected by the stack temperature sensor 32T, in accordance with an instruction from the control unit 40. Specifically, the water supply flow rate F2 is varied so that the difference between the temperature detected by the stack discharge temperature sensor 33T and the temperature detected by the stack temperature sensor 32T is maintained within a predetermined temperature rise range.

[0051] As in the first embodiment, the flow rate of water circulated through the water circulation path 30 by the water circulation pump 36 (water circulation flow rate F1) is controlled based on the temperature detected by the ion exchange temperature sensor 30T so that the temperature of the water supplied to the ion exchange resins 16 becomes the optimum ion exchange resin temperature T1. Also, as in the first embodiment, the flow rate of the heat medium supplied into the first heat exchanger 24 is controlled based on the temperature detected by the stack temperature sensor 32T so that the temperature of the water supplied to the water electrolysis cell stack 12 becomes the optimum water electrolysis temperature T2.

[0052] As shown in FIG. 4 , the control unit 40 is connected to the DC power supply DC, the adjustment valve 21, the water level gauge 23, the flow rate adjustment valve 26, the ion exchange temperature sensor 30T, the stack temperature sensor 32T, the stack discharge temperature sensor 33T, the water circulation pump 36, and the water supply pump 38.

[0053] According to the water electrolysis system 10B of this embodiment, the output of the water supply pump 38 is controlled to vary the water supply flow rate F2 based on the difference between the temperature detected by the stack discharge temperature sensor 33T and the temperature detected by the stack temperature sensor 32T. This allows the water electrolysis cell stack 12 to be stably cooled and operated with the supply water.

[0054] In this embodiment, as in the first embodiment, the output of the water circulation pump 36 is controlled based on the temperature detected by the ion exchange temperature sensor 30T, but the output of the water circulation pump 36 may also be controlled so that the ratio between the water circulation flow rate F1 and the water supply flow rate F2 is constant.

[0055] Furthermore, as in the first embodiment, the output of the water circulation pump 36 may be controlled based on the temperature detected by the ion exchange temperature sensor 30T so that the temperature of the water supplied to the ion exchange resin 16 becomes the optimum temperature T1 for the ion exchange resin, while the output of the water supply pump 38 may be controlled so that the ratio between the water circulation flow rate F1 and the water supply flow rate F2 is constant.

[0056] The disclosure of Japanese Patent Application No. 2024-015573 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A water electrolysis system comprising: a water electrolysis cell stack; a water separator connected to the water electrolysis cell stack and configured to separate water discharged from the water electrolysis cell stack from gas; a water circulation path provided with a water circulation pump and configured to circulate the water separated by the water separator; a water supply path separate from the water circulation path and provided with a water supply pump and configured to supply water to the water electrolysis cell stack; an ion exchange resin provided in the water circulation path; a first heat exchanger provided in the water circulation path upstream of the ion exchange resin and configured to cool the water in the water circulation path; and a second heat exchanger provided in the water circulation path and configured to exchange heat between the water discharged from the ion exchange resin and the water before being cooled by the first heat exchanger.

2. The water electrolysis system according to claim 1, wherein the first heat exchanger cools the water in the water circulation path based on the temperature of the water supplied from the water supply path to the water electrolysis cell stack.

3. The water electrolysis system according to claim 2, wherein the flow rate of water supplied to the water electrolysis cell stack by the water supply pump is kept constant, and the flow rate of water circulated through the water circulation path by the water circulation pump is controlled so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

4. The water electrolysis system according to claim 2, wherein the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack in accordance with the flow rate of hydrogen produced in the water electrolysis cell stack, and the water circulation pump controls the flow rate of water circulating through the water circulation path so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

5. The water electrolysis system according to claim 2, wherein the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack in accordance with the temperature difference between the water supplied to the water electrolysis cell stack and the water discharged from the water electrolysis cell stack, and the water circulation pump controls the flow rate of water circulating through the water circulation path so that the temperature of the water supplied to the ion exchange resin becomes an optimum temperature for the ion exchange resin.

6. The water electrolysis system according to claim 2, wherein the water supply pump controls the flow rate of water supplied to the water electrolysis cell stack in accordance with the temperature difference between the water supplied to the water electrolysis cell stack and the water discharged from the water electrolysis cell stack, and the water circulation pump controls the flow rate of water circulating through the water circulation path so that the ratio of the flow rate of water circulating through the water circulation path to the flow rate in the water supply path is constant.

7. The water electrolysis system according to claim 2, wherein the flow rate of water supplied to the water electrolysis cell stack by the water supply pump is controlled so that the ratio of the flow rate of water circulating through the water circulation path to the flow rate in the water supply path is constant, and the flow rate of water circulating through the water circulation path is controlled so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

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