Water electrolysis system

Abstract

SOLUTION: A water electrolysis system (10) comprises a flow rate control valve (47) that relatively changes a first flow rate, which is the flow rate of water flowing through a first flow path portion (52a) extending from a first water outlet portion (26), and a second flow rate, which is the flow rate of water flowing through a second flow path portion (52b) extending from a second water outlet portion (28).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 below discloses a water electrolysis system including a water electrolysis stack. This water electrolysis stack includes a plurality of stacked water electrolysis cells. The water electrolysis stack is installed so that the stacking direction of the water electrolysis cells is along the vertical direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2019-123899 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, there has been a demand for efficient water electrolysis.

[0005] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0006] An aspect of the present disclosure is a water electrolysis system comprising a water electrolysis stack having a plurality of water electrolysis cells stacked in a vertical direction, a water inlet portion, a first water outlet portion, and a second water outlet portion, wherein the first water outlet portion is provided on an upper side of the water electrolysis stack and the second water outlet portion is provided on a lower side of the water electrolysis stack, and the water inlet portion is provided between the first water outlet portion and the second water outlet portion in the stacking direction of the water electrolysis cells, and the water electrolysis system further comprises a flow rate control valve that relatively changes a first flow rate, which is the flow rate of water flowing through a first flow path portion extending from the first water outlet portion, and a second flow rate, which is the flow rate of water flowing through a second flow path portion extending from the second water outlet portion. [Effects of the Invention]

[0007] According to the aspects of the present disclosure, electrolysis can be performed efficiently. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a water electrolysis system according to one embodiment. [Figure 2] FIG. 2 is a flowchart showing the procedure for changing the opening degree of the flow rate adjusting valve. [Figure 3] FIG. 3A is a graph showing the behavior of the voltage or resistance of the water electrolysis cell, and FIG. 3B is a graph showing the behavior of the flow rate of water discharged from the water electrolysis stack. DETAILED DESCRIPTION OF THE INVENTION

[0009] Fig. 1 is a diagram showing a water electrolysis system 10 according to one embodiment. In Fig. 1, the direction of arrow A1 indicates the direction of gravity, and the direction of arrow A2 indicates the direction opposite to the direction of gravity. The water electrolysis system 10 includes a water electrolysis stack 12 that produces oxygen (atmospheric pressure) and hydrogen (at a higher pressure than oxygen) by electrolyzing water.

[0010] The water electrolysis stack 12 has a plurality of stacked water electrolysis cells 14. Each water electrolysis cell 14 is formed, for example, in a disk shape. Although detailed illustration is omitted, each water electrolysis cell 14 includes a membrane electrode assembly, and an anode separator and a cathode separator disposed on either side of the membrane electrode assembly. The membrane electrode assembly includes an electrolyte membrane, and an anode power supply (anode electrode) and a cathode power supply (cathode electrode) disposed on either side of the electrolyte membrane in the thickness direction. In this embodiment, the water electrolysis cell 14 is a PEM cell using a proton exchange membrane as the electrolyte membrane.

[0011] The water electrolysis stack 12 is installed so that the stacking direction of the water electrolysis cells 14 is along the vertical direction (the direction of arrow A). An electrolysis power supply 16, which is a DC power supply, is connected to the water electrolysis stack 12. The electrolysis power supply 16 is connected, for example, to both ends of the water electrolysis cells 14 that are connected in series. End plates 18a, 18b are disposed at both ends of the stacking direction of the multiple water electrolysis cells 14. A hydrogen outlet channel 20 that communicates with the cathode side (high-pressure hydrogen generation side) of each water electrolysis cell 14 is connected to the upper end plate 18a.

[0012] The water electrolysis stack 12 is provided with a water introduction section 22 and a water discharge section 24. The water introduction section 22 is provided with a water inlet 22a for introducing water into the water electrolysis stack 12. The water inlet 22a is connected to a water introduction communication hole 25 provided to penetrate the water electrolysis cells 14 in the stacking direction. The water introduction communication hole 25 allows water introduced from the water inlet 22a of the water introduction section 22 to flow in the stacking direction. The water introduction communication hole 25 is connected to the anode inlet side (water supply inlet side) of each water electrolysis cell 14.

[0013] The water inlet section 22 is provided in one of the water electrolysis cells 14 located between both ends (middle) in the stacking direction. Specifically, the water inlet section 22 is provided in one of the water electrolysis cells 14 located in a central region in the stacking direction. The central region refers to, for example, the middle region obtained by dividing the water electrolysis cells 14 into thirds in the stacking direction. However, the central region may also be, for example, the middle region obtained by dividing the water electrolysis cells 14 into thirds in a 1:2:1 ratio in the stacking direction.

[0014] The water outlet 24 has a first water outlet 26 and a second water outlet 28. The first water outlet 26 is provided in the water electrolysis cell 14 (the upper end side of the water electrolysis stack 12) that is located at the upper end (one end) of the multiple water electrolysis cells 14 in the stacking direction. That is, the first water outlet 26 is located above the water inlet 22 (in the direction of arrow A2). The first water outlet 26 is formed with a first water outlet 26a for discharging unreacted water (excess water) that has not been electrolyzed from the water electrolysis stack 12.

[0015] The second water outlet 28 is provided in the water electrolysis cell 14 (the lower end of the water electrolysis stack 12) that is located at the lower end (the other end) of the multiple water electrolysis cells 14 in the stacking direction. That is, the second water outlet 28 is located lower (in the direction of arrow A1) than the water inlet 22 and the first water outlet 26. The second water outlet 28 is formed with a second water outlet 28a for discharging unreacted water (excess water) that has not been electrolyzed from within the water electrolysis stack 12.

[0016] The first water outlet 26 and the second water outlet 28 are each provided at a position that is 180° out of phase with the water inlet 22 in the circumferential direction of the water electrolysis stack 12. The first water outlet 26a and the second water outlet 28a each communicate with a water outlet communication hole 30 that is provided to penetrate the water electrolysis cells 14 in the stacking direction. The water outlet communication hole 30 communicates with the anode outlet side (water and oxygen discharge side) of each water electrolysis cell 14, and circulates unreacted water that has not been electrolyzed in the stacking direction to guide it to the first water outlet 26 and the second water outlet 28.

[0017] The water electrolysis system 10 includes a water supply device 32, a water supply channel 34, a water circulation circuit 36, an air blower 38, an air supply channel 40, an air discharge channel 42, a drain channel 44, an on-off valve 46, and a flow rate adjustment valve 47.

[0018] The water supply device 32 introduces water to the water circulation circuit 36. The water may be pure water. The water circulation circuit 36 ​​includes a gas-liquid separator 48, a water supply channel 50, a water discharge channel 52, and a circulation pump 54. The water supply channel 34 is connected to the upper part of the gas-liquid separator 48. The gas-liquid separator 48 functions as a tank for storing water. In the case of an AEM cell that uses an anion exchange membrane as the electrolyte membrane, alkaline water may be supplied to the water electrolysis cell 14.

[0019] The water supply channel 50 connects the bottom of the gas-liquid separator 48 to the water inlet 22. The water supply channel 50 guides water stored in the gas-liquid separator 48 to the water inlet 22. The water discharge channel 52 connects the first water outlet 26 and the second water outlet 28 to the upper part of the gas-liquid separator 48. The water discharge channel 52 guides the mixed fluid into the gas-liquid separator 48. The mixed fluid contains unreacted water that was not electrolyzed, oxygen generated by the reaction, and hydrogen that has permeated from the cathode side to the anode side.

[0020] The water discharge channel 52 includes a first flow path portion 52a extending from the first water discharge portion 26, a second flow path portion 52b extending from the second water discharge portion 28, and a third flow path portion 52c connecting the first flow path portion 52a and the second flow path portion 52b. The second flow path portion 52b is located lower than the first flow path portion 52a and the third flow path portion 52c. In other words, the second flow path portion 52b is located at the lowermost position of the water discharge channel 52.

[0021] The circulation pump 54 is provided, for example, in the water supply channel 50. The circulation pump 54 circulates water such that the water stored in the gas-liquid separator 48 is supplied from the water inlet 22 through the water supply channel 50 into the water electrolysis stack 12, and unreacted water that has not been electrolyzed in the water electrolysis stack 12 is discharged from the water outlet 24 through the water discharge channel 52 to the gas-liquid separator 48.

[0022] In such a water circulation circuit 36, the second water outlet section 28 is located below the gas-liquid separator 48, the water supply channel 50, and the circulation pump 54, and is connected to the lowest part of the water discharge channel 52 (second flow path section 52b).

[0023] The air blower 38 is an air supply device that introduces air for dilution into the gas-liquid separator 48 via the air supply path 40. The air supply path 40 and the air discharge path 42 are connected to the top of the gas-liquid separator 48. The oxygen and hydrogen in the gas-liquid separator 48 are discharged into the air discharge path 42 together with the air introduced from the air blower 38.

[0024] The drain flow path 44 is a flow path for discharging water from the water circulation circuit 36 ​​and the water electrolysis stack 12 to the outside. The drain flow path 44 is connected to the lowermost part (second flow path portion 52b) of the water discharge path 52. The on-off valve 46 is provided in the drain flow path 44. The on-off valve 46 is configured as a solenoid valve that opens and closes the drain flow path 44.

[0025] The flow rate adjustment valve 47 is provided in the second flow path section 52b. The flow rate adjustment valve 47 adjusts the flow rate of water flowing through the second flow path section 52b by changing the opening degree of the second flow path section 52b. When the flow rate of water flowing through the second flow path section 52b decreases, the flow rate of water flowing through the first flow path section 52a inevitably increases. Conversely, when the flow rate of water flowing through the second flow path section 52b increases, the flow rate of water flowing through the first flow path section 52a inevitably decreases. In other words, the flow rate adjustment valve 47 relatively changes the first flow rate, which is the flow rate of water flowing through the first flow path section 52a, and the second flow rate, which is the flow rate of water flowing through the second flow path section 52b.

[0026] The water electrolysis system 10 includes a controller 55 that controls the overall operation of the water electrolysis system 10. The controller 55 is a calculator including a microcomputer. The controller 55 has a CPU (Central Processing Unit) and memories such as ROM and RAM. A detector 56 is connected to the controller 55. The detector 56 detects information indicating the resistance (or voltage) of each of the multiple water electrolysis cells 14. The detector 56 includes a voltage sensor that detects the voltage of the water electrolysis cell 14. The detector 56 may also include a resistance sensor that detects the resistance of the water electrolysis cell 14. The detector 56 may also include a current sensor that detects the current flowing through the electrolysis power supply 16.

[0027] When the CPU reads and executes the program stored in the ROM, the controller 55 operates as a first acquisition unit 58, a second acquisition unit 60, a calculation unit 62, and a control unit 64. Note that at least one of the first acquisition unit 58, the second acquisition unit 60, the calculation unit 62, and the control unit 64 can also be configured as a function realization unit in the form of hardware.

[0028] The first acquisition unit 58 acquires information indicating the resistance of the upper cell 14U using the detection unit 56. When gas in the mixed fluid accumulates on the upper cell 14U side, the cross-sectional area of ​​the current flowing through the anode power supply (anode electrode) and the cathode power supply (cathode electrode) decreases, resulting in an increase in resistance. The upper cell 14U is one of the multiple water electrolysis cells 14 that is located at the top in the stacking direction. The upper cell 14U may be the uppermost water electrolysis cell 14 in the stacking direction. The second acquisition unit 60 acquires information indicating the resistance of the lower cell 14D using the detection unit 56. The lower cell 14D is one of the multiple water electrolysis cells 14 that is located at the bottom in the stacking direction. The lower cell 14D may be the lowermost water electrolysis cell 14 in the stacking direction.

[0029] The calculation unit 62 performs calculations based on information indicating the resistance acquired by the first acquisition unit 58 and information indicating the resistance acquired by the second acquisition unit 60. The control unit 64 controls the driving and stopping of the circulation pump 54, controls the driving and stopping of the air blower 38, and controls the opening and closing operation of the on-off valve 46. The control unit 64 also controls the opening degree changing operation of the flow rate adjustment valve 47. The opening degree changing operation of the flow rate adjustment valve 47 is an operation to change the opening degree of the flow rate adjustment valve 47 with respect to the second flow path portion 52b.

[0030] The water electrolysis system 10 configured as above operates as follows.

[0031] When the circulation pump 54 is driven, water in the gas-liquid separator 48 is supplied to the water inlet 22 (inside the water electrolysis cell 14 located approximately in the center in the stacking direction) via the water supply channel 50. The water supplied to the water inlet 22 flows into the water inlet passage 25, flows upward and downward (in the stacking direction), and is distributed to the anode inlet side of each water electrolysis cell 14.

[0032] When a voltage is applied to the water electrolysis stack 12 by the electrolysis power supply 16, water is electrolyzed on the anode side of each water electrolysis cell 14. When water is electrolyzed, hydrogen ions, electrons, and oxygen are produced on the anode side of each water electrolysis cell 14. Meanwhile, on the cathode side of each water electrolysis cell 14, the hydrogen ions combine with electrons to produce hydrogen. This hydrogen is extracted to the hydrogen output path 20 and becomes dry hydrogen (product hydrogen), which is supplied to a fuel cell electric vehicle (not shown) or the like.

[0033] Meanwhile, oxygen produced by the reaction, unreacted water that was not electrolyzed, and permeated hydrogen flow at the anode outlet. This mixed fluid containing oxygen, water, and hydrogen is discharged into the water discharge communication hole 30 and flows upward and downward (in the stacking direction). The mixed fluid that flows upward through the water discharge communication hole 30 is guided to the first flow path section 52a via the first water discharge section 26. The mixed fluid that flows downward through the water discharge communication hole 30 is guided to the second flow path section 52b via the second water discharge section 28.

[0034] The mixed fluid in the first flow path portion 52a and the mixed fluid in the second flow path portion 52b join together in the third flow path portion 52c and are guided to the upper portion of the gas-liquid separator 48, where they are separated into liquid (water) and gas (oxygen and hydrogen). In this case, the on-off valve 46 closes the drain flow path 44.

[0035] The water separated from the mixed fluid is stored in the gas-liquid separator 48. The water stored in the gas-liquid separator 48 is discharged into the water supply channel 50 by the circulation pump 54. The oxygen and hydrogen separated from the mixed fluid are discharged to the outside from the air discharge channel 42 by the air blower 38.

[0036] Next, a description will be given of the operation of changing the opening degree of the flow rate adjustment valve 47. The operation of changing the opening degree of the flow rate adjustment valve 47 is performed during operation of the water electrolysis system 10. Figure 2 is a flowchart showing the procedure for the operation of changing the opening degree of the flow rate adjustment valve 47.

[0037] In step S1, the first acquisition unit 58 starts acquiring the first information. The second acquisition unit 60 starts acquiring the second information. The first information is information indicating the resistance of the upper cell 14U detected by the detection unit 56 when a predetermined current is flowing through the upper cell 14U. The second information is information indicating the resistance of the lower cell 14D detected by the detection unit 56 when a predetermined current is flowing through the lower cell 14D. The first information and the second information are stored in memory together with the time of acquisition. A current sensor (not shown) that detects the current flowing through the electrolytic power supply 16 may be used to acquire the first information and the second information. Once acquisition of the first information and the second information has started, the process proceeds to step S2, a voltage value comparison process.

[0038] In step S2, the calculation unit 62 calculates the difference (degree of deviation) in voltage values ​​between the upper cell 14U and the lower cell 14D based on the first information and second information most recently stored in memory. The difference in voltage values ​​may be the absolute value of the difference in voltage values. The calculation unit 62 may also calculate the difference in resistance values ​​between the upper cell 14U and the lower cell 14D. The difference in resistance values ​​may be the absolute value of the difference in resistance values.

[0039] The control unit 64 compares the difference in voltage value between the upper cell 14U and the lower cell 14D calculated by the calculation unit 62 with a threshold value. If the difference in voltage value between the upper cell 14U and the lower cell 14D is less than the threshold value (step S2: NO), the opening degree changing operation does not proceed to step S3. In this case, the calculation by the calculation unit 62 and the comparison by the control unit 64 are repeated. On the other hand, if the difference in voltage value between the upper cell 14U and the lower cell 14D is equal to or greater than the threshold value (step S2: YES), it is determined that gas in the mixed fluid is accumulating on the upper cell 14U side, and the operation proceeds to the opening degree changing operation of step S3.

[0040] In step S3, the control unit 64 sets the aperture of the flow rate adjustment valve 47 so that the first flow rate (the flow rate of water flowing through the first flow path portion 52a) is greater than the second flow rate (the flow rate of water flowing through the second flow path portion 52b). Specifically, the control unit 64 sets the aperture of the flow rate adjustment valve 47 to be smaller than a predetermined aperture. Once the aperture of the flow rate adjustment valve 47 has been set, the process proceeds to a voltage value comparison step in step S4.

[0041] In step S4, the calculation unit 62 calculates the difference (degree of deviation) in the voltage values ​​between the upper cell 14U and the lower cell 14D based on the first information and second information most recently stored in memory. The control unit 64 compares the difference in the voltage values ​​between the upper cell 14U and the lower cell 14D calculated by the calculation unit 62 with a threshold value. If the difference in the voltage values ​​between the upper cell 14U and the lower cell 14D remains equal to or greater than the threshold value (step S4: NO), the opening degree change operation does not proceed to step S5. In this case, the calculation by the calculation unit 62 and the comparison by the control unit 64 are repeated. On the other hand, if the difference in the voltage values ​​between the upper cell 14U and the lower cell 14D becomes less than the threshold value (step S4: YES), it is determined that the gas remaining on the upper cell 14U side has been discharged, and the opening degree change operation proceeds to step S5.

[0042] In step S5, the control unit 64 sets the opening degree of the flow rate adjustment valve 47 so that the first flow rate (the flow rate of water flowing through the first flow path portion 52a) approaches the second flow rate (the flow rate of water flowing through the second flow path portion 52b). Specifically, the control unit 64 sets the opening degree of the flow rate adjustment valve 47 to a predetermined opening degree. Once the opening degree of the flow rate adjustment valve 47 is set, the opening degree changing operation proceeds to step S2.

[0043] FIG. 3A is a graph showing the behavior of the voltage or resistance of the water electrolysis cell 14, and FIG. 3B is a graph showing the behavior of the flow rate of water discharged from the water electrolysis stack 12.

[0044] Oxygen generated on the anode side of the water electrolysis cell 14 by water electrolysis exists as bubbles in the water supplied to the anode side. Bubbles rise due to buoyancy. Therefore, the higher the water electrolysis cell 14 is positioned in the stacking direction, the more likely it is that bubbles that have risen through the water outlet communication holes 30 will accumulate near the anode power supply. As shown in FIG. 3A , bubbles accumulate on the anode power supply over time, increasing the resistance or voltage of the water electrolysis cell 14. This is because the accumulation of bubbles on the anode power supply reduces the contact area between the anode power supply and the water. In other words, bubbles can act as a resistor. Therefore, the more bubbles accumulate on the anode power supply, the lower the electrolysis efficiency of the water electrolysis cell 14.

[0045] In this embodiment, the calculation unit 62 calculates the difference between the voltage value of the upper cell 14U when a predetermined current is flowing and the voltage value of the lower cell 14D when a predetermined current is flowing, thereby making it possible to accurately estimate the degree to which bubbles have accumulated on the anode power supply.

[0046] Furthermore, in this embodiment, when the difference is equal to or greater than the threshold value, the control unit 64 sets the aperture of the flow rate adjustment valve 47 to be smaller than the predetermined aperture. Therefore, as shown in FIG. 3B, the first flow rate (the flow rate of water flowing through the first flow path section 52a) increases over time. Meanwhile, the second flow rate (the flow rate of water flowing through the second flow path section 52b) decreases over time. In other words, the first flow rate is changed to be larger than the second flow rate. This allows bubbles that accumulate on the anode power supply to be efficiently discharged from the water electrolysis stack 12. As a result, water can be electrolyzed efficiently.

[0047] The above embodiment may be modified as follows.

[0048] For example, the control unit 64 may set the opening of the flow rate adjustment valve 47 so that the first flow rate becomes larger than the second flow rate as the difference increases, thereby reducing the accumulation of bubbles in the anode power supply.

[0049] Alternatively, the calculation unit 62 may calculate the difference between a first flow rate detected by a first flow rate sensor provided in the first flow path section 52a and a second flow rate detected by a second flow rate sensor provided in the second flow path section 52b.

[0050] Alternatively, the flow rate adjustment valve 47 may be provided in the first flow path section 52a instead of the second flow path section 52b. In this case, for example, the flow rate adjustment valve 47 is provided in the first flow path section 52a, which has a larger cross-sectional area than the cross-sectional area of ​​the second flow path section 52b. Furthermore, the predetermined opening degree of the flow rate adjustment valve 47 is set so that the cross-sectional area of ​​the first flow path section 52a is equal to the cross-sectional area of ​​the second flow path section 52b. Furthermore, in step S3, the control unit 64 sets the opening degree of the flow rate adjustment valve 47 to be larger than the predetermined opening degree. In this way, the same effects as those of the above embodiment can be obtained.

[0051] Alternatively, the water electrolysis cell 14 may be an AEM type cell. In this case, the water supply device 32 introduces alkaline water into the water circulation circuit 36.

[0052] Alternatively, the anode power supply (anode electrode) and the cathode power supply (cathode electrode) in the water electrolysis stack 12 may be reversed. In this case, the water inlet passage 25 is connected to the cathode inlet side of each water electrolysis cell 14. Water is electrolyzed on the cathode side of each water electrolysis cell 14. When water is electrolyzed, hydrogen is produced on the cathode side of each water electrolysis cell 14. Meanwhile, oxygen is obtained on the anode side of each water electrolysis cell 14. This oxygen is extracted to the hydrogen outlet path 20.

[0053] As described above, the present embodiment is provided with the flow rate adjustment valve 47 that changes the relative flow rate of water flowing through the first flow path portion 52a in the upper part of the water electrolysis stack 12 and the second flow path portion 52b in the lower part of the water electrolysis stack 12. This makes it possible to make the flow rate of water in the upper part of the water electrolysis stack 12 greater than the flow rate of water in the lower part of the water electrolysis stack 12. Therefore, even if gas present as bubbles in the water due to electrolysis of water rises due to buoyancy, the gas can be discharged to the first flow path portion 52a without accumulating in the water electrolysis cell 14 located above. This reduces interference with water electrolysis caused by bubbles, resulting in efficient water electrolysis.

[0054] The following additional notes are further disclosed regarding the above embodiment.

[0055] (Appendix 1) The water electrolysis system (10) of the present disclosure comprises a water electrolysis stack (12) having a plurality of water electrolysis cells (14) stacked in a vertical direction, a water inlet (22), a first water outlet (26), and a second water outlet (28), wherein the first water outlet is provided on an upper side of the water electrolysis stack, the second water outlet is provided on a lower side of the water electrolysis stack, and the water inlet is provided between the first water outlet and the second water outlet in the stacking direction of the water electrolysis cells, and the water electrolysis system comprises a flow rate control valve (47) that relatively changes a first flow rate, which is the flow rate of the water flowing through a first flow path portion (52a) extending from the first water outlet, and a second flow rate, which is the flow rate of the water flowing through a second flow path portion (52b) extending from the second water outlet.

[0056] (Appendix 2) The water electrolysis system according to Supplementary Note 1 may include a detection unit (56) that detects information indicating the resistance of each of the water electrolysis cells; a first acquisition unit (58) that acquires the information about an upper cell (14U) that is the water electrolysis cell located above in the stacking direction, the information being detected by the detection unit when a predetermined current flows through the upper cell; a second acquisition unit (60) that acquires the information about a lower cell (14D) that is the water electrolysis cell located below in the stacking direction, the information being detected by the detection unit when a predetermined current flows through the lower cell (14D) that is the water electrolysis cell located below in the stacking direction; a calculation unit (62) that calculates a difference in voltage or resistance between the upper cell and the lower cell, based on the information acquired by the first acquisition unit and the information acquired by the second acquisition unit; and a control unit (64) that sets an aperture of the flow rate control valve based on the difference.

[0057] (Appendix 3) In the water electrolysis system according to Supplementary note 2, when the difference is equal to or greater than a threshold, the controller may set an aperture of the flow rate adjustment valve so that the first flow rate is greater than the second flow rate.

[0058] (Appendix 4) In the water electrolysis system according to Supplementary Note 3, when the difference, which has become equal to or greater than the threshold value, becomes less than the threshold value, the controller may set the aperture of the flow rate adjustment valve so that the first flow rate approaches the second flow rate.

[0059] (Appendix 5) In the water electrolysis system according to Supplementary Note 2, the controller may set an aperture of the flow rate adjustment valve such that the first flow rate becomes larger than the second flow rate as the difference increases.

[0060] (Appendix 6) In the water electrolysis system according to Supplementary Note 2, the upper cell may be the water electrolysis cell located at the top in the stacking direction, and the lower cell may be the water electrolysis cell located at the bottom in the stacking direction.

[0061] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments. [Explanation of symbols]

[0062] 10...Water electrolysis system 12...Water electrolysis stack 14...Water electrolysis cell 14U...Upper cell 14D...lower cell 22...water inlet 24...Water outlet part 26...First water outlet part 28...Second water outlet section 36...Water circulation circuit 38...Air blower 44...Drain passage 46...Shut-off valve 47...Flow control valve 48... Gas-liquid separator 50... Water supply line 52...Water discharge channel 52a...First flow path section 52b... second flow path portion 54... circulation pump 56...detection unit 58...first acquisition unit 60...Second acquisition section 62...Calculation section 64...Control unit

Claims

1. a water electrolysis stack including a plurality of water electrolysis cells stacked in a vertical direction, a water inlet portion, a first water outlet portion, and a second water outlet portion; a water electrolysis system, wherein the first water outlet is provided above the water electrolysis stack, the second water outlet is provided below the water electrolysis stack, and the water introduction part is provided between the first water outlet and the second water outlet in a stacking direction of the water electrolysis cells, a flow rate adjusting valve that relatively changes a first flow rate, which is the flow rate of water flowing through a first flow path portion extended from the first water outlet portion, and a second flow rate, which is the flow rate of the water flowing through a second flow path portion extended from the second water outlet portion; A water electrolysis system comprising:

2. The water electrolysis system according to claim 1, a detection unit that detects information indicating the resistance of each of the plurality of water electrolysis cells; a first acquisition unit that acquires the information about the upper cell detected by the detection unit in a state where a predetermined current flows through the upper cell, which is the water electrolysis cell located above in the stacking direction; a second acquisition unit that acquires the information about the lower cell detected by the detection unit in a state where a predetermined current flows through the lower cell, which is the water electrolysis cell located lower in the stacking direction; a calculation unit that calculates a difference in voltage value or resistance value between the upper cell and the lower cell based on the information acquired by the first acquisition unit and the information acquired by the second acquisition unit; a control unit that sets an opening degree of the flow rate adjustment valve based on the difference; A water electrolysis system comprising:

3. The water electrolysis system according to claim 2, When the difference is equal to or greater than a threshold, the controller sets the aperture of the flow rate adjustment valve so that the first flow rate is greater than the second flow rate.

4. The water electrolysis system according to claim 3, When the difference, which has become equal to or greater than the threshold, becomes less than the threshold, the controller sets the aperture of the flow rate adjustment valve so that the first flow rate approaches the second flow rate.

5. The water electrolysis system according to claim 2, the control unit sets the aperture of the flow rate adjustment valve so that the first flow rate becomes greater than the second flow rate as the difference increases.

6. The water electrolysis system according to claim 2, the upper cell is the water electrolysis cell located at the top in the stacking direction, the lower cell is the water electrolysis cell located at the bottom in the stacking direction.

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