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 to separate water discharged from the water electrolysis cell stack from gas; a water circulation path that is provided with a water circulation pump, circulates the water separated by the water separator, and supplies water to the water electrolysis cell stack; an ion exchange resin that is provided upstream of the water electrolysis cell stack in the water circulation path; a first heat exchanger that is provided upstream 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 to perform heat exchange between the water delivered from the ion exchange resin and the water prior to cooling 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 a gas; a water circulation channel provided with a water circulation pump and configured to supply the water separated by the water separator to the water electrolysis cell stack; an ion exchange resin provided in the water circulation channel upstream of the water electrolysis cell stack; 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 the water electrolysis system of the first aspect, the water separator separates water discharged from the water electrolysis cell stack from gas. The water separated by the water separator is supplied to the water electrolysis cell stack through a water circulation path. An ion exchange resin is provided in the water circulation path upstream of the water electrolysis cell stack, thereby removing impurities from the water supplied to the water electrolysis cell stack and maintaining the purity of the water without discharging the circulating water.

[0009] In addition, since the first heat exchanger for cooling the water in the water circulation path is provided upstream of the ion exchange resin in the water circulation path, the temperature of the water supplied to the ion exchange resin can be made lower than the temperature of the water in the water separator. Furthermore, the water circulation path is provided with a second heat exchanger for exchanging heat between the water sent from the ion exchange resin and the water before being cooled by the first heat exchanger, so that the water sent to the first heat exchanger can be cooled and the water returned to the water separator can be heated, thereby reducing heat loss.

[0010] In the water electrolysis system of a second aspect, the first heat exchanger cools the water in the water circulation path based on the temperature of the water supplied from the water circulation path to the water electrolysis cell stack.

[0011] 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 circulation 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.

[0012] In the water electrolysis system of the third aspect, 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 becomes an optimum temperature for the ion exchange resin.

[0013] In the water electrolysis system of the third aspect, the flow rate of 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, thereby allowing the ion exchange resin to function efficiently with simple control.

[0014] The water electrolysis system of a fourth aspect includes a bypass passage through which water delivered from the water separator is delivered to the first heat exchanger without passing through the second heat exchanger.

[0015] According to the water electrolysis system of the fourth aspect, the amount of heat exchanged in the second heat exchanger can be adjusted by diverting the water from the water separator to the bypass passage.

[0016] In a fifth aspect of the water electrolysis system, the water circulation pump controls the flow rate of water circulated through the water circulation channel in accordance with the flow rate of hydrogen produced in the water electrolysis cell stack, and controls the flow rate of water flowing through the bypass channel so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

[0017] In the water electrolysis system of the fifth aspect, the flow rate of the water circulation pump is controlled in accordance with the flow rate of hydrogen produced in the water electrolysis cell stack, and the flow rate of water flowing through the bypass passage is controlled so that the temperature of the water supplied to the ion exchange resins is an optimum temperature for the ion exchange resins. This enables a stable supply of water to the stack and allows the ion exchange resins to function efficiently.

[0018] In a sixth aspect of the water electrolysis system, the water circulation pump controls the flow rate of water circulated through the water circulation channel 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 controls the flow rate of water flowing through the bypass channel so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin.

[0019] According to the water electrolysis system of the sixth aspect, the flow rate of the water circulation pump is controlled 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 flow rate of the water flowing through the bypass passage is controlled so that the temperature of the water supplied to the ion exchange resin is an optimum temperature for the ion exchange resin. This enables a stable supply of water to the stack and allows the ion exchange resin to function efficiently.

[0020] According to the water electrolysis system of the present invention, the water electrolysis cell stack can be operated efficiently without wasting circulating water.

[0021] 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 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; FIG. 5 is a block diagram showing the configuration of a water electrolysis system according to a third embodiment; FIG. 6 is a block diagram showing the connection with a controller of the water electrolysis system according to the third embodiment;

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] [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 resin 16, a first heat exchanger 24, and a second heat exchanger 44. Note that the dotted lines in Figs. 1, 3, and 5 may indicate functional relationships that differ from the actual connection relationships.

[0024] 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 between them. 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 circulation channel 30 is connected to the anode side inlet of the water electrolysis cell stack 12, and water is supplied from the water circulation channel 30. 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 as part of the water circulation channel 30, 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.

[0025] The water separator 14 separates the oxygen and water from the water / oxygen delivery line 12B and stores the separated water. The oxygen delivery line 14A is connected to the water separator 14, and oxygen is delivered from the oxygen delivery line 14A. The other end of the water circulation line 30 is connected to the water separator 14, and the stored water is supplied to the water electrolysis cell stack 12.

[0026] 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.

[0027] The water separator 14 is provided with a water circulation pump 36. The water circulation pump 36 sends water out of the water separator 14, passes through a second heat exchanger 44 (cooling), the first heat exchanger 24, the ion exchange resin 16, and the second heat exchanger 44 (heating), which will be described later, and is then supplied to the water electrolysis cell stack 12. 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 the control unit 40, and its output is controlled by the control unit 40.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] A second heat exchanger 44 is provided in 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 resins 16. Specifically, the water delivered from the water separator 14 is cooled by the water delivered from the ion exchange resins 16 before being supplied to the first heat exchanger 24, and the water delivered from the ion exchange resins 16 is heated by the water delivered from the water separator 14 before being supplied to the water electrolysis cell stack 12.

[0032] A stack temperature sensor 32T is provided on the water circulation path 30 upstream of the water electrolysis cell stack 12 and downstream of the heated water outlet of the second heat exchanger 44. The stack temperature sensor 32T detects the temperature of the water flowing through the water circulation path 30 immediately before being 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.

[0033] 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 .

[0034] 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.

[0035] 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).

[0036] 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 .

[0037] 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.

[0038] The optimum temperature T1 for the ion exchange resin is set to be lower than the optimum temperature T2 for water electrolysis. For example, the optimum temperature T2 for water electrolysis can be set to 70°C to 80°C, and the optimum temperature T1 for the ion exchange resin can be set to about 50°C to 60°C.

[0039] 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, and the water circulation pump 36. 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.

[0040] 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.

[0041] 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 temperature T1 for ion exchange resin, the optimum temperature T2 for water electrolysis, and the water circulation flow rate F1). The control programs and various data may also be stored in the ROM 42.

[0042] In the water electrolysis system 10A of this embodiment, the first heat exchanger 24 is provided upstream of the ion exchange resins 16 to cool the water supplied to the ion exchange resins 16. This allows the ion exchange resins 16 to function efficiently.

[0043] 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.

[0044] Furthermore, in this embodiment, the water supplied to the water electrolysis cell stack 12 is heated by the second heat exchanger 44, so that the water electrolysis cell stack 12 can be operated efficiently.

[0045] Furthermore, in this embodiment, heat exchange is performed in the second heat exchanger between the water delivered from the ion exchange resin 16 and the water before being cooled in the first heat exchanger 24. This allows the water delivered to the first heat exchanger 24 to be cooled and the water supplied to the water electrolysis cell stack 12 to be heated, thereby reducing heat loss.

[0046] Furthermore, in the present embodiment, the output of the water circulation pump 36 is controlled based on the temperature detected by the ion exchange temperature sensor 30T. This enables the water electrolysis system 10A to be operated with simple control.

[0047] 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.

[0048] In the water electrolysis system 10B of this embodiment, the water circulation pump 36 varies the water circulation flow rate F1 in accordance with the load on the water electrolysis cell stack 12. In this case, the water circulation flow rate F1 delivered by the water circulation pump 36 is varied in accordance with the amount of hydrogen generated input to the control unit 40.

[0049] 3 , the water electrolysis system 10B of this embodiment is provided with a bypass path 46 in the water circulation path 30 that bypasses the second heat exchanger 44. The bypass path 46 is provided upstream of the ion exchange resin 16, from downstream of the water circulation pump 36 and upstream of the second heat exchanger 44 to upstream of the first heat exchanger 24 and downstream of the second heat exchanger 44, such that part of the water circulation path 30 bypasses the second heat exchanger 44. The bypass path 46 is provided with a bypass flow rate valve 48. The bypass flow rate valve 48 is connected to the ion exchange temperature sensor 30T and adjusts the flow rate of water diverted to the bypass path 46 (bypass flow rate F3) based on the temperature measured by the ion exchange temperature sensor 30T.

[0050] Specifically, the bypass flow rate F3 is adjusted so that the temperature of the water supplied to the ion exchange resin 16 becomes the optimum ion exchange resin temperature T1, which is the optimum temperature for the ion exchange resin 16. If the temperature detected by the ion exchange temperature sensor 30T is higher than the optimum ion exchange resin temperature T1, the bypass flow rate F3 is reduced and the flow rate of water passing through the second heat exchanger 44 is increased to cool the water. If the temperature detected by the ion exchange temperature sensor 30T is lower than the optimum ion exchange resin temperature T1, the bypass flow rate F3 is increased and the flow rate of water passing through the second heat exchanger 44 is reduced to limit the degree of cooling.

[0051] 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 water circulation pump 36, and the bypass flow rate valve 48.

[0052] In the water electrolysis system 10B of this embodiment, the bypass 46 is provided, and the amount of heat exchanged in the second heat exchanger 44 can be adjusted so that the temperature of the water supplied to the ion exchange resin 16 becomes the optimum temperature T1 for the ion exchange resin.

[0053] Furthermore, the water electrolysis system 10B of this embodiment can stably supply water to the water electrolysis cell stack 12 in accordance with the load on the water electrolysis cell stack 12 .

[0054] Third Embodiment Next, a third embodiment will be described. In this embodiment, the same parts as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0055] As shown in Fig. 5 , the water electrolysis system 10C 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 circulation pump 36. The output of the water circulation pump 36 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 circulation flow rate F1 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.

[0056] The flow rate of the water diverted to the bypass passage 46 (bypass flow rate) is adjusted so that the temperature of the water supplied to the ion exchange resin 16 becomes the optimum temperature T1 for the ion exchange resin.

[0057] As shown in FIG. 6 , 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 bypass flow rate valve 48.

[0058] According to the water electrolysis system 10C of this embodiment, the output of the water circulation pump 36 is controlled to vary the water circulation flow rate F1 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 enables the water electrolysis cell stack 12 to be stably cooled and operated with circulating water.

[0059] The disclosure of Japanese Patent Application No. 2024-015574 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 channel provided with a water circulation pump and configured to supply the water separated by the water separator to the water electrolysis cell stack; an ion exchange resin provided in the water circulation channel upstream of the water electrolysis cell stack; 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, wherein the first heat exchanger cools the water in the water circulation channel based on the temperature of the water supplied from the water circulation channel to the water electrolysis cell stack after heat exchange in the second heat exchanger.

2. 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 channel provided with a water circulation pump and configured to supply the water separated by the water separator to the water electrolysis cell stack; an ion exchange resin provided in the water circulation channel upstream of the water electrolysis cell stack; 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; wherein the flow rate of water circulating through the water circulation channel is controlled by the water circulation pump so that the temperature of the water supplied to the ion exchange resin is optimum for the ion exchange resin.

3. 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 channel provided with a water circulation pump and configured to supply water separated by the water separator to the water electrolysis cell stack; an ion exchange resin provided in the water circulation channel upstream of the water electrolysis cell stack; 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 delivered from the ion exchange resin and water before being cooled by the first heat exchanger, and further comprising a bypass channel for delivering the water delivered from the water separator to the first heat exchanger without passing through the second heat exchanger.

4. The water electrolysis system according to claim 3, wherein the flow rate of water circulated through the water circulation path by the water circulation pump is controlled in accordance with the flow rate of hydrogen produced in the water electrolysis cell stack, and the flow rate of water flowing through the bypass 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.

5. The water electrolysis system according to claim 3, wherein the flow rate of water circulated through the water circulation path by the water circulation pump is controlled 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 flow rate of water flowing through the bypass 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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