Water electrolysis system

Abstract

To provide a water electrolysis system capable of rapidly detecting anomalies indicating potential damage to an electrolyte membrane.SOLUTION: A water electrolysis system comprises a water electrolyzer for electrolyzing water to generate oxygen and hydrogen, a water-pressure changer capable of changing the pressure of water to be supplied to the water electrolyzer, a pressure monitor for monitoring the pressure of the supply water, a voltage monitor for monitoring the voltage of the water electrolyzer, and a determination unit for determining the presence or absence of an anomaly in the water electrolysis system using the voltage of the water electrolyzer varying according to the varying water pressure in the supply water.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Conventionally, a water electrolysis system that generates oxygen and hydrogen by electrolyzing water has been known. In Patent Document 1, when it is considered that an accident such as damage may have occurred in the electrolyte membrane, the safety is improved by closing the regulating valves provided in the hydrogen extraction line and the oxygen extraction line. A solid polymer type water electrolysis device is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The deterioration of the electrolyte membrane progresses gradually over a relatively long period of time, but the breakage of the electrolyte membrane progresses rapidly within a relatively short period of time. Therefore, it is highly likely that the breakage will be recognized after it has occurred without recognizing the abnormality that is a precursor to the breakage. For this reason, in order to prevent the electrolyte membrane from being damaged, a technique capable of early detecting an abnormality that is a precursor to the breakage has been demanded. In the solid polymer type water electrolysis device of Patent Document 1, no consideration is given to early detection of an abnormality that is a precursor to breakage of the electrolyte membrane.

[0005] The present invention has been made to solve at least a part of the above-described problems, and an object thereof is to provide a water electrolysis system capable of early detecting an abnormality that is a precursor to breakage when the abnormality occurs in the electrolyte membrane.

Means for Solving the Problems

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

[0007] (1) According to one embodiment of the present invention, a water electrolysis system is provided. This water electrolysis system comprises a water electrolysis unit that generates oxygen and hydrogen by electrolysis of water, a water pressure fluctuation unit that can fluctuate the water pressure of the supply water supplied to the water electrolysis unit, a pressure measuring unit that measures the water pressure of the supply water, a voltage measuring unit that measures the voltage of the water electrolysis unit, and a determination unit that determines whether or not there is an abnormality in the water electrolysis system using the voltage of the water electrolysis unit which fluctuates in accordance with the fluctuation of the water pressure of the supply water.

[0008] The voltage fluctuations of the water electrolysis unit, which respond to fluctuations in the water supply pressure, exhibit unusual behavior if there is an abnormality in the electrolyte membrane that could indicate impending damage. These fluctuations in water supply pressure, which cause the voltage fluctuations in the water electrolysis unit, can be triggered at any time and for a short duration, as long as water is being supplied to the unit. Therefore, with this configuration, the fluctuating voltage of the water electrolysis unit is used as an indicator to determine whether or not there is an abnormality in the water electrolysis system, allowing for high-frequency determination. Consequently, abnormalities that could indicate impending damage to the electrolyte membrane can be detected early, thus preventing damage to the electrolyte membrane.

[0009] (2) In the water electrolysis system of the above form, the determination unit may output a statement indicating that there is an abnormality in the water electrolysis system if the difference between the maximum voltage and the minimum voltage included in the voltage of the water electrolysis unit in each period, which fluctuates in accordance with the periodic fluctuation of the water pressure of the supplied water, is greater than a preset upper limit. In this configuration, the presence or absence of an abnormality in the water electrolysis system is determined by comparing the difference in voltage fluctuations in the water electrolysis section with a preset upper limit. If a difference larger than the upper limit exists, the abnormality that caused it is highly likely to be a precursor to electrolyte membrane damage. Therefore, this configuration allows for early detection of such abnormalities, thereby preventing electrolyte membrane damage.

[0010] (3) In the water electrolysis system of the above configuration, the determination unit may output a statement indicating that there is an abnormality in the water electrolysis system if the difference value is smaller than a preset lower limit value. With this configuration, the presence or absence of an abnormality in the water electrolysis system is determined by comparing the difference in voltage fluctuations in the water electrolysis section with a preset lower limit. If a difference smaller than the lower limit exists, it is highly likely that the abnormality that caused it is in the water pressure fluctuation section. Therefore, with this configuration, in addition to detecting abnormalities that are precursors to electrolyte membrane damage, abnormalities in the water pressure fluctuation section can also be detected.

[0011] (4) In the water electrolysis system of the above configuration, the determination unit may output a statement indicating that there is an abnormality in the water electrolysis system if the absolute value of the difference between the period voltage, which is the voltage for one period of each period of the water electrolysis unit that fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, and a reference period voltage that is set in advance as a reference for the voltage of the water electrolysis unit that fluctuates during one period, is greater than a set threshold. In this configuration, the presence or absence of an abnormality in the water electrolysis system is determined by comparing the absolute value of the difference between the periodic voltage of the water electrolysis unit and the reference periodic voltage with a preset threshold. If an absolute value greater than the threshold exists, the abnormality that caused it is highly likely to be a precursor to electrolyte membrane damage. Therefore, this configuration allows for the early detection of such abnormalities, thereby preventing electrolyte membrane damage.

[0012] Furthermore, the present invention can be realized in various forms, for example, as a control method for a water electrolysis system, a computer program for controlling the electrolysis of water in a water electrolysis system, a server device for distributing the computer program, a non-temporary storage medium storing the computer program, and so on. [Brief explanation of the drawing]

[0013] [Figure 1] This is an explanatory diagram showing the configuration of the water electrolysis system according to the first embodiment. [Figure 2] This is an explanatory diagram showing the detailed configuration of the water electrolysis cell that makes up the water electrolysis unit. [Figure 3] This is an explanatory diagram showing the voltage of a water electrolysis cell that fluctuates in response to changes in the water pressure of the supply water. [Figure 4] This is an explanatory diagram showing the voltage of a water electrolysis cell that fluctuates in response to changes in the water pressure of the supply water. [Figure 5] This is an explanatory diagram showing the voltage of a water electrolysis cell that fluctuates in response to changes in the water pressure of the supply water. [Figure 6] This is an explanatory diagram showing the voltage of a water electrolysis cell that fluctuates in response to changes in the water pressure of the supply water. [Figure 7] This is an explanatory diagram illustrating the calculation of the absolute value of the difference. [Figure 8] This is a flowchart showing the procedure for the first decision-making process. [Figure 9] This flowchart shows the procedure for the second decision-making process. [Figure 10] This is an explanatory diagram showing the voltages of multiple water electrolysis cells that fluctuate in response to changes in the water pressure of the supply water. [Modes for carrying out the invention]

[0014] <First Embodiment> FIG. 1 is an explanatory diagram showing the configuration of a water electrolysis system 1 according to a first embodiment of the present invention. The water electrolysis system 1 is a system that generates oxygen and hydrogen by electrolyzing water. The water electrolysis system 1 includes a storage tank 5, an oxygen gas-liquid separation unit 10, a water electrolysis unit 20, a hydrogen gas-liquid separation unit 30, a control unit 40, and a DC power source 50.

[0015] The storage tank 5 is a tank that stores water. The flow path F1 is a flow path that connects the storage tank 5 and the oxygen gas-liquid separation unit 10. A regulating valve S1 and a supply pump R1 are provided in a pipe (not shown) forming the flow path F1. The regulating valve S1 can adjust the flow rate in the pipe forming the flow path F1 according to the degree of opening and closing, and can also block the flow in the pipe. The supply pump R1 sends water to the oxygen gas-liquid separation unit 10.

[0016] Water is supplied from the storage tank 5 to the oxygen gas-liquid separation unit 10. The oxygen gas-liquid separation unit 10 separates a mixture of oxygen and water generated in the water electrolysis unit 20 described later into oxygen and water. The separated oxygen is sent outside the water electrolysis system 1 through a flow path F2 connected to the upper part in the gravitational direction of the oxygen gas-liquid separation unit 10. The separated water and the water supplied from the storage tank 5 are supplied to the water electrolysis unit 20 described later through a flow path F3. The flow path F3 is a flow path through which the water supplied from the oxygen gas-liquid separation unit 10 to the water electrolysis unit 20 flows. Hereinafter, the water supplied from the oxygen gas-liquid separation unit 10 to the water electrolysis unit 20 is referred to as supply water.

[0017] A regulating valve S2, a supply pump R2, and a pressure sensor P are provided in a pipe (not shown) forming the flow path F3. Similar to the regulating valve S1, the regulating valve S2 can adjust the flow rate in the pipe forming the flow path F3 according to the degree of opening and closing, and can also block the flow in the pipe. The supply pump R2 sends the supply water to the water electrolysis unit 20. In the present embodiment, the supply pump R2 corresponds to a water pressure fluctuation unit that can vary the water pressure of the supply water flowing in the flow path F3. The pressure sensor P measures the water pressure of the supply water flowing in the pipe forming the flow path F3. In the present embodiment, the pressure sensor P corresponds to a pressure measurement unit.

[0018] The water electrolysis unit 20 generates oxygen and hydrogen by electrolyzing water (electrolysis). The mixture of oxygen and water generated in the water electrolysis unit 20 is sent to the oxygen gas-liquid separation unit 10 via a flow path F4 described later. The mixture of hydrogen and water generated in the water electrolysis unit 20 is sent to the hydrogen gas-liquid separation unit 30 via a flow path F5 described later. The flow path F4 is a flow path for supplying the mixture of oxygen and water generated in the water electrolysis unit 20 to the oxygen gas-liquid separation unit 10. A regulating valve S3 is provided in a pipe (not shown) forming the flow path F4. The flow path F5 is a flow path for supplying the mixture of hydrogen and water generated in the water electrolysis unit 20 to the hydrogen gas-liquid separation unit 30. A regulating valve may also be provided in the pipe (not shown) forming the flow path F4. The plurality of cell voltage sensors 21V measure the voltage of each of the water electrolysis cells 21 (described in FIG. 2) constituting the water electrolysis unit 20 as a voltage measurement unit. In the present embodiment, a cell voltage sensor 21V is provided corresponding to each of the water electrolysis cells 21. That is, the voltage of each of the water electrolysis cells 21 can be measured individually.

[0019] The hydrogen gas-liquid separation unit 30 separates the mixture of hydrogen and water generated in the water electrolysis unit 20 into hydrogen and water. The separated hydrogen is sent to the outside of the water electrolysis system 1 via a flow path F6 connected to the upper portion in the gravitational direction of the hydrogen gas-liquid separation unit 30. The separated water is supplied to the water electrolysis unit 20 via the flow path F7. The separated water may be supplied to the oxygen gas-liquid separation unit 10 via the flow path F7.

[0020] The control unit 40 controls the operation of the entire water electrolysis system 1 based on information obtained from various sensors provided in the water electrolysis system 1. Examples of the control by the control unit 40 include opening / closing control of the regulating valves S1 to S3, delivery control of the supply pumps R1 and R2, and control of power supply from the DC power supply 50 to the water electrolysis unit 20.

[0021] Figure 2 is an explanatory diagram showing the detailed configuration of the water electrolysis cell 21 that constitutes the water electrolysis unit 20. The water electrolysis unit 20 is composed of multiple water electrolysis cells 21 stacked on top of each other. The water electrolysis cell 21 is a PEM (Polymer Electrolyte Membrane: solid polymer electrolyte membrane) type water electrolysis cell. The water electrolysis cell 21 has a membrane electrode assembly (hereinafter referred to as "MEA") 22. The MEA 22 is a proton (H + An electrolyte membrane 24 that can pass water is joined to both sides of an oxygen electrode 26 that decomposes water to generate oxygen, hydrogen ions, and electrons, and a hydrogen electrode 28 that generates hydrogen from hydrogen ions and electrons. On the surface of the oxygen electrode 26 opposite to the electrolyte membrane 24, a power supply body 26f made of a metal mesh or the like is provided. A gasket 26g is provided around the oxygen electrode 26 and the power supply body 26f. On the other hand, on the surface of the hydrogen electrode 28 opposite to the electrolyte membrane 24, a power supply body 28f is similarly provided, and a gasket 28g is provided around the hydrogen electrode 28 and the power supply body 28f.

[0022] The assembled structure of gasket 26g, power supply unit 26f, MEA 22, gasket 28g, and power supply unit 28f is sandwiched between separator 26s provided on the oxygen electrode 26 side and separator 28s provided on the hydrogen electrode 28 side. In this sandwiched state, separator 26s forms a channel Fc through which the supply water supplied to the water electrolysis unit 20 and the mixture of oxygen and water generated in the water electrolysis unit 20 flow. Separator 28s forms a channel Fa through which the mixture of hydrogen and water generated in the water electrolysis unit 20 flows. Separators 26s and 28s are so-called bielectrode plates. The contact portion Ct shown in Figure 2 will be described later.

[0023] Figure 3 is an explanatory diagram illustrating an example of the voltage of a water electrolysis cell 21 fluctuating in response to fluctuations in the water pressure of the supply water. In Figure 3, the horizontal axis of each graph represents time. In the upper graph of Figure 3, the vertical axis represents the water pressure of the supply water measured by the pressure sensor P, and the dashed line L1 shows the water pressure of the supply water periodically fluctuated by the supply pump R2. In the lower graph of Figure 3, the vertical axis represents the voltage of a single water electrolysis cell 21 measured by the cell voltage sensor 21V, and the dashed line L2 shows the voltage of the water electrolysis cell 21 fluctuating in response to periodic fluctuations in the water pressure of the supply water.

[0024] In the upper graph of Figure 3, the water pressure of the supply water fluctuates periodically, as shown by the portions of the dashed line L1 that fall within each of the periods P1 to P3. The length of periods P1 to P3 can be adjusted by the supply pump R2, which is the water pressure fluctuation section. Also, in the lower graph of Figure 3, the voltage of the water electrolysis cell 21 fluctuates periodically in accordance with the fluctuations in the water pressure of the supply water, as shown by the portions of the dashed line L2 that fall within each of the periods P4 to P6 (periods corresponding to periods P1 to P3). The voltage of the water electrolysis cell 21 fluctuates from a maximum voltage M2 to a minimum voltage m2 in each of the periods P4 to P6.

[0025] The voltage fluctuations of the water electrolysis unit 20 (water electrolysis cell 21) in response to fluctuations in the water supply pressure exhibit unusual behavior if there is an abnormality in the electrolyte membrane 24 that is a precursor to damage. One such abnormality is poor contact between the separator 26s and the power supply unit 26f. Figure 2 shows the contact portion Ct between the separator 26s, which is a bipolar plate, and the power supply unit 26f. Current flows from the separator 26s to the oxygen electrode 26 through this contact portion Ct. However, if there is poor contact between the separator 26s and the power supply unit 26f, the contact portion Ct may decrease in response to an increase in the water supply pressure. In such cases, the current density flowing through the reduced contact portion Ct increases, causing a voltage increase in the water electrolysis unit 20 (water electrolysis cell 21). Normally, the voltage of the water electrolysis unit 20 (water electrolysis cell 21) increases in accordance with the increase in the water pressure of the supply water. However, when a contact failure occurs, the voltage of the water electrolysis unit 20 (water electrolysis cell 21) increases even more significantly than the increase in accordance with the increase in the water pressure of the supply water. The dashed line L3 shown in Figure 3 represents the voltage of the water electrolysis cell 21 that fluctuates in accordance with the periodic fluctuations in the water pressure of the supply water when such a contact failure occurs. In this state, the voltage of the water electrolysis cell 21 fluctuates from the maximum voltage M3 (> maximum voltage M2) to the minimum voltage m2 in each of the periods P4 to P6. In contrast, the dashed line L2 represents the voltage of the water electrolysis cell 21 that fluctuates in accordance with the periodic fluctuations in the water pressure of the supply water when there is no abnormality in the electrolyte membrane 24 that would indicate impending damage.

[0026] Figure 4 is an explanatory diagram showing the voltage of the water electrolysis cell 21, which fluctuates with a delay in response to fluctuations in the water pressure of the supply water. In Figure 3, for the sake of explanation, the dashed lines L1 and L2 were shown as being in phase (the start and end timings of periods P1-P3 and P4-P6 were the same), but the dashed lines L1 and L2 shown in Figure 4 are not in phase. In the water electrolysis system 1, the pressure sensor P and the cell voltage sensor 21V are far apart. Therefore, the further the cell voltage sensor 21V is from the pressure sensor P, the greater the delay in time between the start of fluctuations in the water pressure of the supply water and the start of fluctuations in the voltage of the water electrolysis cell 21. In other words, in the water electrolysis system 1, as shown in Figure 4, the phase shown by dashed line L2 lags behind the phase shown by dashed line L1. Figure 4 shows that when the water pressure of the supply water increases at timing ta and then repeatedly increases and decreases at intervals of periods P1 to P3, the voltage of the water electrolysis cell 21 increases at timing tb after a delay time De has elapsed from timing ta, and then repeatedly increases and decreases at intervals of the same length as periods P1 to P3. The intervals of the same length as periods P1 to P3 in this case correspond to periods P4 to P6. Furthermore, the length of this delay time De increases as the cell voltage sensor 21V is farther from the pressure sensor P. Here, we have explained the phase lag of the dashed line L2 relative to the phase of the dashed line L1, but of course the same applies to the case of the dashed line L3.

[0027] The control unit 40, acting as a determination unit, uses the voltage of the water electrolysis unit 20 (water electrolysis cell 21), which fluctuates in accordance with fluctuations in the water pressure of the supply water, to determine whether or not there is an abnormality in the water electrolysis system 1. Specifically, the control unit 40 outputs a message indicating that there is an abnormality in the water electrolysis system 1 if the difference value Df between the maximum voltage and the minimum voltage included in the voltage of the water electrolysis unit 20 (water electrolysis cell 21), which fluctuates in accordance with the periodic fluctuations in the water pressure of the supply water, is greater than a preset upper limit value U. In the dashed line L2, the difference value Df for each period is the difference between the maximum voltage M2 and the minimum voltage m2. In the dashed line L3, the difference value Df for each period is the difference between the maximum voltage M3 and the minimum voltage m2. The upper limit value U, which is compared with the difference value Df, is set to a value smaller than the difference value Df expected when the voltage of the water electrolysis cell 21 is fluctuated in a state where there is poor contact between the separator 26s and the power supply 26f. This assumed difference value Df can also be obtained by preparing and measuring a water electrolysis cell 21 that actually has a contact failure. Figure 4 illustrates an example of the upper limit value U. Note that in Figures 3 and 4, the dashed lines L2 and L3 are shown where the difference value Df for each period is the same, but in reality, the difference value Df for each period is more often different. Also, in Figures 3 and 4, the minimum voltage of dashed line L3 is the same minimum voltage m2 as that of dashed line L2, but the minimum voltage of dashed line L3 may be a minimum voltage m3 that is different from the minimum voltage m2. The minimum voltage m3 can be either greater than the minimum voltage m2 or less than the minimum voltage m2. Of course, in either case, the difference value Df is the difference between the maximum voltage M3 and the minimum voltage m3.

[0028] When a difference value Df greater than the upper limit value U exists, the output indicating an abnormality in the water electrolysis system 1 may be a notification to the administrator of the water electrolysis system 1. Preferably, this notification includes information indicating that an abnormality that is a precursor to damage has occurred in the electrolyte membrane 24, and information identifying the water electrolysis cell 21 that is experiencing the abnormality among the water electrolysis cells 21 constituting the water electrolysis unit 20. The water electrolysis cell 21 experiencing the abnormality is identified based on the cell voltage sensor 21V which measures a voltage fluctuation in which the difference value Df is greater than the upper limit value U. In addition, the output indicating an abnormality in the water electrolysis system 1 may also be a control to stop the power supply from the DC power supply 50 to the water electrolysis unit 20 or a control to stop the water supply in order to stop electrolysis by the water electrolysis unit 20. The control to stop the water supply includes the control of closing the regulating valves S1 to S3 and the control to stop the discharge from the supply pumps R1 and R2.

[0029] Furthermore, the control unit 40, acting as a determination unit, outputs a message indicating that there is an abnormality in the water electrolysis system 1 if a difference value Df smaller than a preset lower limit value (not shown) exists. One example of a case where a difference value Df smaller than the lower limit value exists is when an abnormality occurs in the supply pump R2, which is the water pressure fluctuation unit, causing the range of water pressure fluctuations (the range between the maximum and minimum water pressure) of the supplied water by the supply pump R2 to become smaller than the normal range, and consequently, the difference value Df also becomes smaller. For this reason, the lower limit value compared with the difference value Df is set to a value larger than the difference value Df expected when the voltage of the water electrolysis cell 21 is fluctuated while the supply pump R2 is malfunctioning. This expected difference value Df may be obtained by preparing a water electrolysis cell 21 in which the supply pump R2 is actually malfunctioning and measuring it. When a difference value Df smaller than the lower limit exists, the output indicating an abnormality in the water electrolysis system 1 may include notification to the administrator of the water electrolysis system 1 or control of the water electrolysis unit 20 to stop electrolysis, similar to the case when a difference value Df larger than the upper limit U exists. Preferably, this notification includes notification that an abnormality has occurred in the supply pump R2, which is the water pressure fluctuation unit.

[0030] Figure 5 is an explanatory diagram showing another example of the voltage of the water electrolysis cell 21 fluctuating in response to fluctuations in the water pressure of the supply water. Figure 5 is the same as Figure 3, except that the dashed line L4 is shown instead of the dashed lines L2 and L3. Abnormalities that may indicate impending damage to the electrolyte membrane 24 include poor contact between the separator 26s and the power supply 26f, as well as a reduction in the flow path Fc (see Figure 2) due to deformation of the electrolyte membrane 24. If the MEA 22 is not held in place by the separator 26s or the power supply 26f, the power supply 26f may be pushed into the flow path Fc due to swelling of the electrolyte membrane 24 or deformation of the electrolyte membrane 24 due to differential pressure (the pressure on the hydrogen electrode 28 side is higher than the pressure on the oxygen electrode 26 side), thereby reducing the flow path Fc. In such a case, the voltage change of the water electrolysis unit 20 (water electrolysis cell 21) in response to increases and decreases in the water pressure of the supply water is hindered. In other words, the voltage of the water electrolysis cell 21 does not fluctuate smoothly as shown by the dashed line L2 (Figures 3 and 4), but rather fluctuates more erratically than the dashed line L2. The dashed line L4 shown in Figure 5 shows the voltage of the water electrolysis cell 21 fluctuating in response to fluctuations in the water pressure of the supply water when the flow path Fc is reduced. The reason why the dashed line L4 has a more erratic waveform than the dashed line L2 is that the flow path Fc is reduced by the power supply 26f, and the power supply 26f is irregularly pushed back towards the electrolyte membrane 24 by the water pressure of the supply water, causing the flow path Fc to temporarily expand.

[0031] Figure 6 is an explanatory diagram showing the voltage of the water electrolysis cell 21, which fluctuates with a delay in response to fluctuations in the water pressure of the supply water. In Figure 5, the dashed lines L1 and L4 were in phase, but in Figure 6, the dashed lines L1 and L4 are not in phase. In Figure 5, for the sake of explanation, the dashed lines L1 and L4 were shown as being in phase, but of course, in the case of dashed line L4, as with dashed lines L2 (L3) explained in Figure 4, its phase lags behind the phase of dashed line L1. In Figure 6, when the increase in the water pressure of the supply water starts at timing ta and the increase and decrease in the water pressure of the supply water are repeated at intervals of period P1 to P3, the increase in the voltage of the water electrolysis cell 21 starts at timing tb after a delay time De has elapsed from timing ta, and the increase and decrease in the voltage of the water electrolysis cell 21 are repeated at intervals of the same length as period P1 to P3. The intervals of the same length as period P1 to P3 in this case correspond to period P7 to P9 in dashed line L4.

[0032] Figure 7 is an explanatory diagram illustrating the calculation of the absolute value Ab of the difference between the voltage of each period of the water electrolysis unit 20 (water electrolysis cell 21) and the reference period voltage ST. The control unit 40, as a determination unit, outputs a message indicating that there is an abnormality in the water electrolysis system 1 if the absolute value Ab of the difference between the period voltage PV, which is the voltage for one period of each period of the water electrolysis unit 20 (water electrolysis cell 21) that fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, and the reference period voltage ST, which is set in advance as a reference for the voltage of the water electrolysis unit 20 (water electrolysis cell 21) that fluctuates during one period, is greater than a preset threshold Th. Here, the period voltage PV is the voltage for one period of each period of the water electrolysis unit 20 (water electrolysis cell 21) that fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water (periods P4~P6 in the dashed lines L2 and L3, and period P7~P9 in the dashed line L4). The periodic voltage PV is extracted from a series of fluctuating voltages of the water electrolysis unit 20, indicated by the dashed lines L2 to L4. Specifically, each voltage that fluctuates during intervals of the same length as periods P1 to P3 (corresponding to periods P4 to P6 in Figure 4 and periods P7 to P9 in Figure 6), from the timing after the delay time set for each cell voltage sensor 21V (corresponding to delay time De in Figure 4 and 6) has elapsed (corresponding to timing tb in Figure 4 and 6) starting from the timing when the water pressure of the supply water starts to increase (corresponding to timing ta in Figures 4 and 6) to the timing after the delay time set for each cell voltage sensor 21V (corresponding to delay time De in Figures 4 and 6) has elapsed (corresponding to timing tb in Figures 4 and 6), is extracted as the periodic voltage PV.

[0033] The reference periodic voltage ST is a periodic voltage PV extracted from a series of voltages measured in advance by periodically fluctuating the water pressure of the supply water under normal conditions, when there is no abnormality in the supply pump R2, which is the water pressure fluctuation unit, and no abnormality that would indicate impending damage to the electrolyte membrane 24. The absolute value Ab of the difference between the periodic voltage PV and the reference periodic voltage ST is calculated for each phase, as shown by the arrows in Figure 6. The periodic voltage PV shown in Figure 7 is one of the periodic voltages PV for each period (periods P7 to P9) indicated by the dashed line L4 (see Figure 6). Note that if the periodic voltage PV is a periodic voltage PV measured under normal conditions, the absolute value Ab of the difference between that periodic voltage PV and the reference periodic voltage ST will be close to 0 for all phases. The threshold Th, which is compared with the absolute value Ab, is set to a value that is smaller than some of the absolute values ​​Ab for each phase when the absolute values ​​Ab for each phase are calculated using the periodic voltage PV (one of the periodic voltages PV from periods P7 to P9) and the reference periodic voltage ST that are assumed to occur when the flow path Fc is reduced. Figure 7 illustrates an example of the threshold Th.

[0034] In Figures 5 and 6, the dashed line L4 is shown to represent the periodic fluctuation of the voltage at the water electrolysis unit 20 when the water pressure of the supply water is varied while the flow path Fc is narrowed. However, in such a state, the voltage at the water electrolysis unit 20 may not fluctuate periodically. Even in such cases, the dashed lines representing the voltage measured over time by the cell voltage sensor 21V will be used as the periodic voltage PV, representing the voltages that fluctuate within the same length as periods P1 to P3 from the timing after the delay time set for each cell voltage sensor 21V (corresponding to delay time De in Figure 6) has elapsed (corresponding to timing tb in Figure 6) from the timing when the water pressure of the supply water starts to increase (corresponding to timing ta in Figure 6), and will be used for comparison with the reference periodic voltage ST.

[0035] Figure 8 is a flowchart showing the procedure for the first determination process. The first determination process is a process to determine whether or not an abnormality that indicates impending damage has occurred in the electrolyte membrane 24. The first determination process is performed periodically while electrolysis is being carried out by the water electrolysis unit 20.

[0036] When the first determination process is initiated, the control unit 40 first controls the supply pump R2 to impart periodic fluctuations to the water pressure of the supply water flowing through the flow path F3 (step S11). Next, the control unit 40 divides the voltages of a series of water electrolysis cells 21 measured while the water pressure of the supply water is being periodically fluctuated into periods (periods P4 to P6 and periods P7 to P9 as described above) based on the period of fluctuation of the water pressure of the supply water (periods P1 to P3 as described above), and then calculates the difference value Df between the maximum voltage and the minimum voltage of the voltage in each period (step S12). In other words, this division is a division that occurs after the delay time set for each cell voltage sensor 21V has elapsed since the start of the periodic water pressure fluctuation, and after the length of one period of the periodic water pressure fluctuation has elapsed, and is a division that is generated by the same process as the extraction of the periodic voltage PV as described above.

[0037] After calculating the difference value Df, the control unit 40 determines whether or not there is a difference value Df greater than the upper limit value U (step S13). If there is no difference value Df greater than the upper limit value U (step S13: NO), the control unit 40 determines whether or not there is a difference value Df smaller than the lower limit value (step S14). If there is a difference value Df greater than the upper limit value U (step S13: YES), or if there is a difference value Df smaller than the lower limit value (step S14: YES), the control unit 40 outputs a message indicating that there is an abnormality in the water electrolysis system 1 (step S15). After that, the control unit 40 terminates the first determination process. On the other hand, if there is no difference value Df smaller than the lower limit value (step S15: NO), the control unit 40 terminates the first determination process.

[0038] Figure 9 is a flowchart showing the procedure for the second determination process. The second determination process, like the first determination process, is a process to determine whether or not an abnormality that indicates impending damage has occurred in the electrolyte membrane 24. The second determination process is performed simultaneously with the first determination process while electrolysis is being performed by the water electrolysis unit 20.

[0039] When the second determination process is started, the control unit 40 first extracts periodic voltages PV from a series of voltages of the water electrolysis cells 21 measured while periodic fluctuations are applied to the water pressure of the supply water by step S11 of the first determination process (step S21). Next, as shown in Figure 7, the control unit 40 calculates the absolute value Ab of the difference between each extracted periodic voltage PV and the reference periodic voltage ST (step S22).

[0040] Next, the control unit 40 determines whether or not there is an absolute value Ab greater than the threshold Th (step S23). If there is an absolute value Ab greater than the threshold Th (step S23: YES), the control unit 40 outputs a message indicating that there is an abnormality in the water electrolysis system 1 (step S24), and then terminates the second determination process. On the other hand, if there is no absolute value Ab greater than the threshold Th (step S23: NO), the control unit 40 terminates the second determination process.

[0041] The voltage fluctuations of the water electrolysis unit 20 (water electrolysis cell 21) in response to fluctuations in the water supply pressure exhibit unusual behavior, as shown by the dashed lines L3 and L4, when an abnormality that indicates impending damage to the electrolyte membrane 24 occurs. These fluctuations in the water supply pressure that cause the voltage fluctuations of the water electrolysis unit 20 (water electrolysis cell 21) can be made to occur at any time and for a short period of time, as long as water is being supplied to the water electrolysis unit 20. Therefore, according to the water electrolysis system 1 of the first embodiment described above, the presence or absence of abnormalities in the water electrolysis system 1 is determined using the fluctuating voltage of the water electrolysis unit 20 (water electrolysis cell 21) as an indicator, and this determination can be performed at a high frequency. Consequently, when an abnormality that indicates impending damage to the electrolyte membrane 24 occurs, it can be detected early, thereby preventing damage to the electrolyte membrane 24.

[0042] If abnormalities that indicate the impending failure of the electrolyte membrane cannot be detected early, the likelihood of the electrolyte membrane failing increases. When the electrolyte membrane fails, oxygen and hydrogen may mix and combust. Such combustion can generate a large amount of leached material from various components of the electrolysis unit, and this large amount of leached material can spread throughout the water electrolysis system via the water circulating within the system, potentially causing large-scale contamination. On the other hand, according to the water electrolysis system 1 of the first embodiment, abnormalities that indicate the impending failure of the electrolyte membrane 24 can be detected early. Therefore, by preventing the failure of the electrolyte membrane 24, contamination of the entire water electrolysis system 1 can be prevented.

[0043] Furthermore, according to the water electrolysis system 1 of the first embodiment described above, the presence or absence of an abnormality in the water electrolysis system 1 is determined by comparing the difference value Df in the voltage fluctuation of the water electrolysis unit 20 (water electrolysis cell 21) with a preset upper limit value U. If a difference value Df greater than the upper limit value U exists, the abnormality that caused it is highly likely to be an abnormality that foreshadows the damage of the electrolyte membrane 24. Therefore, according to the water electrolysis system 1 of the above embodiment, by detecting such an abnormality early, it is possible to prevent the damage of the electrolyte membrane 24.

[0044] Furthermore, according to the water electrolysis system 1 of the first embodiment described above, the presence or absence of an abnormality in the water electrolysis system 1 is determined by comparing the difference value Df in the voltage fluctuation of the water electrolysis unit 20 (water electrolysis cell 21) with a preset lower limit value. If a difference value Df smaller than the lower limit value exists, it is highly likely that the abnormality that caused it is an abnormality in the supply pump R2, which is the water pressure fluctuation unit. Therefore, according to the water electrolysis system 1 of the first embodiment described above, in addition to detecting abnormalities that are precursors to damage to the electrolyte membrane 24, it is also possible to detect abnormalities in the supply pump R2.

[0045] Furthermore, according to the water electrolysis system 1 of the first embodiment described above, the presence or absence of an abnormality in the water electrolysis system 1 is determined by comparing the absolute value Ab of the difference between the periodic voltage PV of the water electrolysis unit 20 (water electrolysis cell 21) and the reference periodic voltage ST with a preset threshold Th. If an absolute value Ab greater than the threshold Th exists, the abnormality that caused it is highly likely to be an abnormality that foreshadows the damage of the electrolyte membrane 24. Therefore, according to the water electrolysis system 1 of the first embodiment described above, by detecting such an abnormality early, it is possible to prevent the damage of the electrolyte membrane 24.

[0046] <Second Embodiment> Figure 10 is an explanatory diagram showing the voltages of multiple water electrolysis cells 21 that fluctuate in response to fluctuations in the water pressure of the supply water. The water electrolysis system of the second embodiment is the same as the water electrolysis system 1 of the first embodiment, except that the target used for the reference periodic voltage ST is different.

[0047] The dashed lines L5 to L9 shown in Figure 10 indicate the voltages that fluctuate in each of the water electrolysis cells 21 constituting the water electrolysis unit 20 in accordance with fluctuations in the water pressure of the supply water. In the first embodiment, the reference periodic voltage ST was a periodic voltage PV extracted from a series of voltages measured in advance by periodically fluctuating the water pressure of the supply water under normal conditions. On the other hand, in the second embodiment, the reference periodic voltage ST is a periodic voltage PV extracted from a series of voltages measured in other water electrolysis cells 21 included in the same water electrolysis unit 20 as the water electrolysis cell 21 that is the target of the second judgment process. Furthermore, it is assumed that the periodic voltage PV of the other water electrolysis cell 21 used as the reference periodic voltage ST and the periodic voltage PV of the water electrolysis cell 21 that is the target of the second judgment process are generated by water pressure fluctuations at the same timing. In this water electrolysis system of the second embodiment, as in the first embodiment, if an abnormality that is a precursor to damage occurs in the electrolyte membrane 24, the abnormality can be detected early, thereby preventing damage to the electrolyte membrane 24.

[0048] <Modified form of this embodiment> The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit, for example, the following modifications are also possible.

[0049] In the embodiment described above, the water pressure fluctuation unit was the supply pump R2, but it is not limited to this. For example, the water pressure fluctuation unit may be replaced by, or in addition to, the supply pump R2, the supply pump R1 or the control valves S1 to S3.

[0050] In the embodiment described above, multiple cell voltage sensors 21V corresponding to each of the water electrolysis cells 21 were provided, but the embodiment is not limited to this. Instead of multiple cell voltage sensors 21V, a single voltage sensor may be provided for the entire water electrolysis unit 20. That is, when the water pressure of the supply water fluctuates periodically, the voltage may be measured for the entire water electrolysis unit 20 as a single unit, rather than measuring the voltage of each of the water electrolysis cells 21. In this case, the first and second determination processes are performed based on a series of voltages of the water electrolysis unit 20 measured while the water pressure of the supply water is periodically fluctuating.

[0051] In the embodiment described above, the pressure sensor P and the cell voltage sensor 21V were far apart, but this is not limited to this. The pressure sensor P and the cell voltage sensor 21V may be placed in the same position. Of course, even in such a case, if there is a delay time between the start of fluctuations in the water pressure of the supply water and the output of the voltage fluctuation of the water electrolysis cell 21 as a measured value by the sensor, such a delay time should be taken into consideration when extracting the periodic voltage PV, etc.

[0052] In the embodiment described above, the first and second determination processes were executed simultaneously, but this is not limited to this. For example, the first and second determination processes may be executed separately. In this case, when executing the second determination process, the process from step S22 onward is executed by extracting the periodic voltage PV from the voltages of a series of water electrolysis cells 21 measured during the last executed first determination process (step S21), or by adding a periodic fluctuation to the water pressure of the supply water before the process in step S21 (corresponding to step S11 of the first determination process) and extracting the periodic voltage PV from the voltages of a series of water electrolysis cells 21 measured (step S21).

[0053] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0054] The present invention can also be realized in the following forms. [Application Example 1] A water electrolysis system, A water electrolysis unit that generates oxygen and hydrogen by the electrolysis of water, A water pressure fluctuation unit capable of fluctuating the water pressure of the supply water supplied to the water electrolysis unit, A pressure measuring unit for measuring the water pressure of the supply water, A voltage measuring unit for measuring the voltage of the water electrolysis unit, A water electrolysis system comprising: a determination unit that determines whether or not there is an abnormality in the water electrolysis system using the voltage of the water electrolysis unit which fluctuates in accordance with fluctuations in the water pressure of the supplied water. [Application Example 2] The water electrolysis system described in Application Example 1, The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the difference between the maximum voltage and the minimum voltage included in the voltage of the water electrolysis unit in each cycle, which fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, is greater than a preset upper limit. [Application Example 3] A water electrolysis system as described in Application Example 1 or Application Example 2, The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the difference value is smaller than a preset lower limit. [Application Example 4] A water electrolysis system as described in any of Application Examples 1 to 3, The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the absolute value of the difference between the period voltage, which is the voltage for one period of each period of the water electrolysis unit that fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, and a reference period voltage that is set in advance as a reference for the voltage of the water electrolysis unit that fluctuates during one period, is greater than a set threshold. [Explanation of Symbols]

[0055] 1…Water electrolysis system 5…Storage tanks 10…Oxygen-liquid separation unit 20...Water electrolysis section 21...Water electrolysis cell 21V...Cell voltage sensor 24...Electrolyte membrane 26…Oxygen electrode 26f,28f…Power supply 26g, 28g... gasket 26s, 28s... Separator 28…Hydrogen electrode 30…Hydrogen gas-liquid separation section 40... Control Unit 50…DC power supply F1~F7...flow channels P... Pressure sensor R1, R2… Supply pumps S1~S3... Adjustment valve

Claims

1. A water electrolysis system, A water electrolysis unit that generates oxygen and hydrogen by the electrolysis of water, A water pressure fluctuation unit capable of fluctuating the water pressure of the supply water supplied to the water electrolysis unit, A pressure measuring unit for measuring the water pressure of the supply water, A voltage measuring unit for measuring the voltage of the water electrolysis unit, The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system using the voltage of the water electrolysis unit, which fluctuates in accordance with fluctuations in the water pressure of the supplied water. The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the difference between the maximum voltage and the minimum voltage included in the voltage of the water electrolysis unit in each cycle, which fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, is greater than a preset upper limit.

2. A water electrolysis system, A water electrolysis unit that generates oxygen and hydrogen by the electrolysis of water, A water pressure fluctuation unit capable of fluctuating the water pressure of the supply water supplied to the water electrolysis unit, A pressure measuring unit for measuring the water pressure of the supply water, A voltage measuring unit for measuring the voltage of the water electrolysis unit, The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system using the voltage of the water electrolysis unit, which fluctuates in accordance with fluctuations in the water pressure of the supplied water. The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the difference between the maximum voltage and the minimum voltage included in the voltage of the water electrolysis unit in each cycle, which fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, is smaller than a preset lower limit.

3. A water electrolysis system, A water electrolysis unit that generates oxygen and hydrogen by the electrolysis of water, A water pressure fluctuation unit capable of fluctuating the water pressure of the supply water supplied to the water electrolysis unit, A pressure measuring unit for measuring the water pressure of the supply water, A voltage measuring unit for measuring the voltage of the water electrolysis unit, The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system using the voltage of the water electrolysis unit, which fluctuates in accordance with fluctuations in the water pressure of the supplied water. The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the absolute value of the difference between the period voltage, which is the voltage for one period of each period of the water electrolysis unit that fluctuates in accordance with the periodic fluctuations of the water pressure of the supply water, and a reference period voltage, which is set in advance as a reference for the voltage of the water electrolysis unit that fluctuates during one period, is greater than a set threshold.

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