Method for operating water electrolysis apparatus, control device for water electrolysis apparatus, and hydrogen production facility

Abstract

A method for operating a water electrolysis apparatus that comprises an electrolytic bath for electrolyzing water, a hydrogen separator to which hydrogen generated in the electrolytic bath is guided, an oxygen separator to which oxygen generated in the electrolytic bath is guided, and a vent line for discharging gas from the hydrogen separator or the oxygen separator and a vent valve provided to the vent line, the method comprising: a step for halting electrolysis of water in the electrolytic bath; and a step for determining whether or not a first index indicating the amount of increase in the concentration of oxygen in gas in the hydrogen separator or the concentration of hydrogen in gas in the oxygen separator has exceeded a first threshold after the electrolysis has been halted. When the first index exceeds the first threshold, the pressure in the hydrogen separator or the oxygen separator is lowered to a first prescribed value by opening the vent valve.

Description

Method for operating a water electrolysis device, control device for a water electrolysis device, and hydrogen production facility

[0001] This disclosure relates to a method for operating a water electrolysis device, a control device for a water electrolysis device, and hydrogen production equipment. This application claims priority based on Japanese Patent Application No. 2024-029700, filed with the Japan Patent Office on February 29, 2024, the contents of which are incorporated herein by reference.

[0002] In a water electrolysis apparatus used to produce hydrogen, there is a risk of explosion if the concentration ratio of hydrogen gas to oxygen gas falls within a predetermined range in the anode chamber, the cathode chamber, etc. To avoid such a problem, for example, an operating method has been proposed to suppress the mixing of hydrogen gas into the gas on the anode side where oxygen gas is produced, or the mixing of oxygen gas into the gas on the cathode side where hydrogen gas is produced.

[0003] Patent Literature 1 describes that after stopping the electrolysis of water in a water electrolysis module (water electrolysis device), hydrogen gas in the cathode chamber and the cathode-side gas-liquid separator is released to the atmosphere and water is supplied to the cathode chamber. In this way, the amount of hydrogen gas in the cathode chamber is reduced and the water supplied to the cathode chamber prevents the hydrogen gas from moving from the cathode chamber to the anode chamber, thereby suppressing the hydrogen gas on the cathode side from mixing with the oxygen gas on the anode side while electrolysis is stopped.

[0004] Japanese Patent Application Laid-Open No. 2020-186418

[0005] If the oxygen gas concentration in the gas on the cathode side or the hydrogen gas concentration in the gas on the anode side increases during shutdown of the water electrolysis device, increasing the risk of explosion, an interlock set in accordance with the oxygen / hydrogen concentrations in the gas may be activated, resulting in an emergency shutdown (trip), even if an attempt is made to restart the operation of the water electrolysis device, and it may take some time before the operation of the water electrolysis device can be restarted and product hydrogen gas can be supplied. In this regard, the method described in Patent Document 1 is designed to suppress mixing of hydrogen gas with oxygen gas on the anode side during shutdown of the water electrolysis device, thereby suppressing an increase in the hydrogen concentration in the gas on the anode side and potentially avoiding the above-mentioned trip.

[0006] On the other hand, in the method described in Patent Document 1, when water electrolysis in the water electrolysis device is stopped, hydrogen gas in the cathode chamber is released to the atmosphere and water is supplied to the cathode chamber. Therefore, when the operation of the water electrolysis device is subsequently restarted, it is necessary to discharge water from the cathode chamber and increase the pressure in the gas-liquid separator on the cathode side, and therefore it takes a long time before product hydrogen gas can be supplied.

[0007] In view of the above circumstances, at least one embodiment of the present invention aims to provide an operation method for a water electrolysis device, a control device for the water electrolysis device, and hydrogen production equipment that enable the supply of product hydrogen gas to be resumed promptly when the operation of the water electrolysis device is restarted after being stopped.

[0008] At least one embodiment of the present invention relates to a method for operating a water electrolysis apparatus including: an electrolytic cell for electrolyzing water; a hydrogen separator to which hydrogen produced in the electrolytic cell is introduced; an oxygen separator to which oxygen produced in the electrolytic cell is introduced; a vent line for discharging gas from the hydrogen separator or the oxygen separator; and a vent valve provided in the vent line, the method comprising the steps of: stopping the electrolysis of water in the electrolytic cell; and determining whether a first index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator since the electrolysis was stopped has exceeded a first threshold value; and if the first index exceeds the first threshold value, opening the vent valve to reduce the pressure in the hydrogen separator or the oxygen separator to a first specified value.

[0009] Furthermore, at least one embodiment of the present invention provides a control device for a water electrolysis apparatus including: an electrolytic cell for electrolyzing water; a hydrogen separator to which hydrogen produced in the electrolytic cell is introduced; an oxygen separator to which oxygen produced in the electrolytic cell is introduced; a vent line for discharging gas from the hydrogen separator or the oxygen separator; and a vent valve provided in the vent line, the control device comprising: an index acquisition unit configured to acquire a first index that indicates an amount of increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after electrolysis of water in the electrolytic cell is stopped; and a determination unit configured to determine whether the first index has exceeded a first threshold value; and when the determination unit determines that the first index has exceeded the first threshold value, the control device is configured to open the vent valve to reduce the pressure in the hydrogen separator or the oxygen separator to a first specified value.

[0010] Furthermore, at least one embodiment of the present invention provides a hydrogen production facility comprising: a water electrolysis device including: an electrolytic cell for electrolyzing water; a hydrogen separator to which hydrogen produced in the electrolytic cell is introduced; an oxygen separator to which oxygen produced in the electrolytic cell is introduced; a vent line for discharging gas from the hydrogen separator or the oxygen separator, and a vent valve provided in the vent line; and the above-described control device for controlling the water electrolysis device.

[0011] At least one embodiment of the present invention provides a method for operating a water electrolysis apparatus, a control device for a water electrolysis apparatus, and hydrogen production equipment that enable early resumption of supply of product hydrogen gas when restarting operation of the water electrolysis apparatus after shutdown.

[0012] FIG. 1 is a schematic configuration diagram of a hydrogen production facility according to an embodiment; FIG. 2 is a schematic configuration diagram of a control device according to an embodiment; FIG. 3 is a flowchart showing a method for operating a water electrolysis device according to an embodiment; FIG. 4 is a graph showing an example of a change in separator pressure over time in the operating method according to an embodiment; FIG. 5 is a graph showing an example of a change in separator pressure over time in the operating method according to an embodiment; FIG. 6 is a flowchart showing a method for operating a water electrolysis device according to an embodiment; FIG. 7 is a graph showing an example of a change in separator pressure over time in the operating method according to an embodiment;

[0013] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0014] (Configuration of Hydrogen Production Facility) Fig. 1 is a schematic configuration diagram of a hydrogen production facility according to one embodiment. As shown in Fig. 1, the hydrogen production facility 1 according to one embodiment includes a water electrolysis device 10 for electrolyzing water and a control device 50 for controlling the water electrolysis device 10.

[0015] 1 includes an electrolytic cell 12 for electrolyzing water, a hydrogen separator 14 (gas-liquid separator) to which hydrogen (gas) produced in the electrolytic cell 12 is introduced, and an oxygen separator 26 (gas-liquid separator) to which oxygen (gas) produced in the electrolytic cell 12 is introduced. The water electrolysis device 10 also includes a vent line 22 for discharging gas from the hydrogen separator 14 and a vent valve 24 provided in the vent line 22, and a vent line 36 for discharging gas from the oxygen separator 26 and a vent valve 38 provided in the vent line 36. The vent line 22 may be provided so as to branch off from a hydrogen gas line 20 described below. The vent line 36 may be provided so as to branch off from an oxygen gas line 32 described below.

[0016] Water to be electrolyzed (make-up water) is supplied to the water electrolysis apparatus 10 including the electrolytic cell 12 via a make-up water line (not shown). The make-up water line may be connected to the hydrogen separator 14 or the oxygen separator 26.

[0017] In the water electrolysis device 10, water in the electrolytic cell 12 is electrolyzed by applying a voltage between electrodes provided in the electrolytic cell 12, generating hydrogen on the cathode side and oxygen on the anode side. The water in the electrolytic cell 12 may be water in which an electrolyte is dissolved (electrolyte solution). The electrolyte may be an alkaline substance such as potassium hydroxide (KOH).

[0018] The hydrogen gas generated on the cathode side, containing water (electrolyte solution, etc.), is introduced to the hydrogen separator 14 via the cathode side line 16. In the hydrogen separator 14, the water-containing hydrogen gas is separated into hydrogen gas and water. The hydrogen gas (product hydrogen gas) separated by the hydrogen separator 14 is discharged from the hydrogen separator 14 via the hydrogen gas line 20. The water (electrolyte solution) separated by the hydrogen separator 14 is returned to the electrolytic cell 12 via the return line 18. The hydrogen gas discharged from the hydrogen separator 14 may be supplied via the hydrogen gas line 20 to a hydrogen storage unit (not shown) for storing hydrogen gas, or to a hydrogen consumption facility (not shown) configured to consume hydrogen as fuel, etc.

[0019] The oxygen gas generated on the anode side, containing water (electrolyte solution, etc.), is introduced to the oxygen separator 26 via the anode side line 28. In the oxygen separator 26, the water-containing oxygen gas is separated into oxygen gas and water. The oxygen gas separated by the oxygen separator 26 is discharged from the oxygen separator 26 via an oxygen gas line 32. The water (electrolyte solution) separated by the oxygen separator 26 is returned to the electrolytic cell 12 via a return line 30. The oxygen gas discharged from the oxygen separator 26 may be supplied to an oxygen reservoir (not shown) or an oxygen consumption facility (not shown) via the oxygen gas line 32.

[0020] As shown in the figure, the hydrogen gas line 20 may be provided with a hydrogen supply valve 21, or the oxygen gas line 32 may be provided with an oxygen supply valve 33. In addition, the return line 18 may be provided with a pump 19 for pumping water, and the return line 30 may be provided with a pump 31 for pumping water.

[0021] There are no limitations on the type of the water electrolysis device 10 constituting the hydrogen production facility 1. The water electrolysis device 10 may be, for example, an alkaline water electrolysis device, a polymer electrolyte membrane (PEM) water electrolysis device, or an anion exchange membrane (AEM) water electrolysis device.

[0022] The above-described vent valve 24 or vent valve 38 may be electrically connected to a control device 50 so that the opening / closing or opening degree of the vent valve 24 or vent valve 38 is controlled by the control device 50 .

[0023] The hydrogen production facility 1 may include a temperature sensor for measuring the temperature of the water (electrolyte solution, etc.) in the water electrolysis device 10. For example, as shown in FIG. 1 , the hydrogen production facility 1 may include, as the above-mentioned temperature sensor, a temperature sensor 62 configured to measure the temperature of the water (electrolyte solution, etc.) in the cathode side line 16 and / or a temperature sensor 64 configured to measure the temperature of the water (electrolyte solution, etc.) in the anode side line 28. Alternatively, in some embodiments, the above-mentioned temperature sensor may be configured to measure the temperature of the water (electrolyte solution, etc.) in the return line 18, the return line 30, the electrolytic cell 12, the hydrogen separator 14, or the oxygen separator 26.

[0024] The hydrogen production facility 1 may include a pressure sensor configured to measure the pressure of the hydrogen separator 14 or the oxygen separator 26. For example, as shown in FIG. 1 , the hydrogen production facility 1 may include a pressure sensor 66 configured to measure the pressure of the hydrogen separator 14 and / or a pressure sensor 68 configured to measure the pressure of the oxygen separator 26.

[0025] The temperature sensors 62, 64 and / or the pressure sensors 66, 68 may be electrically connected to the controller 50 so that signals indicative of measurements made by the temperature sensors 62, 64 and / or the pressure sensors 66, 68 are sent to the controller 50.

[0026] In some embodiments, the water electrolysis apparatus 10 may include an inert gas supply unit 40 for supplying an inert gas to the hydrogen separator 14 or the oxygen separator 26. The inert gas may include, for example, nitrogen or argon. As shown in FIG. 1 , the inert gas supply unit 40 may include, for example, an inert gas reservoir 42 in which the inert gas is stored, a supply line 44 provided between the inert gas reservoir 42 and the hydrogen separator 14 or the oxygen separator 26, and a supply valve 46 provided on the supply line 44.

[0027] 1 , the supply line 44 includes a first branch 48a connected to the hydrogen separator 14 and a second branch 48b connected to the oxygen separator 26, and the first branch 48a and the second branch 48b are provided with a first valve 49a and a second valve 49b, respectively. Thus, the inert gas supply unit 40 may be capable of supplying the inert gas from the inert gas storage unit 42 to the hydrogen separator 14 and the oxygen separator 26, and may be capable of individually adjusting the amount of inert gas supplied to the hydrogen separator 14 and the amount of inert gas supplied to the oxygen separator 26. For example, the amount of inert gas supplied to the hydrogen separator 14 can be adjusted by adjusting the aperture of the supply valve 46 and / or the first valve 49a. Alternatively, the amount of inert gas supplied to the oxygen separator 26 can be adjusted by adjusting the aperture of the supply valve 46 and / or the second valve 49b.

[0028] The supply valve 46, the first valve 49a and / or the second valve 49b may be electrically connected to the control device 50, and the opening / closing or opening degree of the supply valve 46, the first valve 49a and / or the second valve 49b may be controlled by the control device 50.

[0029] 2 is a schematic diagram of a control device 50 according to an embodiment. As shown in FIG. 2, the control device 50 includes an index acquisition unit 52 and a determination unit 54.

[0030] The control device 50 includes a computer equipped with a processor (such as a CPU), a main memory device (such as a memory device; such as a RAM), an auxiliary memory device, an interface, and the like. The control device 50 receives signals indicating measurement results from the temperature sensors 62, 64 and / or the pressure sensors 66, 68 via the interface. The processor is configured to process the signals received in this manner. The processor is also configured to process a program loaded in the main memory device. This realizes the functions of the control device 50, including the index acquisition unit 52 and / or the determination unit 54 described above.

[0031] The processing contents of the control device 50 are implemented as programs executed by the processor. The programs may be stored in, for example, an auxiliary storage device. When the programs are executed, they are loaded into the main storage device. The processor reads the programs from the main storage device and executes the instructions contained in the programs.

[0032] The control device 50 may be configured to control the stopping and restarting of water electrolysis by the water electrolysis device 10 (i.e., the stopping and restarting of application of voltage between the electrodes provided in the electrolytic cell 12). The control device 50 may be configured to receive a stop command to stop or a restart command to restart water electrolysis in the water electrolysis device 10 from, for example, a higher-level control device (not shown), and to control the water electrolysis device 10 based on the stop command or the restart command.

[0033] Furthermore, the control device 50 may be configured to operate the vent valve 24, the vent valve 38, the supply valve 46, the first valve 49a and / or the second valve 49b based on the determination result by the determination unit 54 described below.

[0034] The index acquisition unit 52 is configured to acquire a first index indicating the amount of increase in the oxygen concentration in the gas in the hydrogen separator 14 or the hydrogen concentration in the gas in the oxygen separator 26 after the electrolysis of water in the electrolytic cell 12 is stopped when the electrolysis is stopped.

[0035] The first index may include the time elapsed since electrolysis in the electrolytic bath 12 was stopped, or the temperature of the water in the water electrolysis apparatus 10. The index acquiring unit 52 may acquire the time elapsed since electrolysis in the electrolytic bath 12 was stopped, using a timer built into the control device 50. The index acquiring unit 52 may acquire the measurement result by the temperature sensor 62 or the temperature sensor 64 as the temperature of the water in the water electrolysis apparatus 10.

[0036] The determination unit 54 is configured to determine whether the first index acquired by the index acquisition unit 52 exceeds a first threshold value T1. The first threshold value T1 may be a value determined based on past operating records so as to prevent the water electrolysis apparatus 10 from tripping due to high oxygen / hydrogen concentrations in the gas.

[0037] The longer the time that has elapsed since electrolysis in the electrolytic bath 12 was stopped, the greater the amount of oxygen molecules that migrate to the cathode chamber or the amount of hydrogen molecules that migrate to the anode chamber through the diaphragm in the electrolytic bath 12, and therefore the higher the oxygen / hydrogen concentration in the gas tends to be. Therefore, when the first indicator is the time that has elapsed since electrolysis in the electrolytic bath 12 was stopped, the determination unit 54 may determine that the first indicator has exceeded the first threshold value T1 when the first indicator becomes greater than the first threshold value T1. The same applies to the second indicator and second threshold value T2, and the third indicator and third threshold value T3, which will be described later.

[0038] Furthermore, the lower the temperature of the water in the water electrolysis apparatus 10, the higher the dissolved oxygen concentration and dissolved hydrogen concentration in the liquid phase, and the greater the amount of oxygen molecules moving to the cathode chamber or the amount of hydrogen molecules moving to the anode chamber through the diaphragm in the electrolytic cell 12, which tends to increase the oxygen / hydrogen concentration in the gas. Therefore, when the first indicator is the temperature of the water in the water electrolysis apparatus 10, the determination unit 54 may determine that the first indicator has exceeded the first threshold value T1 when the first indicator is smaller than the first threshold value T1. The same applies to the second indicator and second threshold value T2, and the third indicator and third threshold value T3, which will be described later.

[0039] The control device 50 may be configured to open the vent valve 24 or 38 to reduce the pressure of the hydrogen separator 14 or the oxygen separator 26 to a first specified value P1 when the judgment unit 54 determines that the first indicator has exceeded the first threshold value T1.

[0040] The control device 50 may be configured to operate the pump 19 or the pump 31 so that water circulates between the electrolytic cell 12 and the hydrogen separator 14 or the oxygen separator 26 when the pressure of the hydrogen separator 14 or the oxygen separator 26 is reduced to the first specified value P1 as described above.

[0041] The above-mentioned index acquisition unit 52 may be configured to acquire a second index indicating the amount of increase in the oxygen concentration in the gas in the hydrogen separator 14 or the hydrogen concentration in the gas in the oxygen separator 26 after the pressure in the hydrogen separator 14 or the oxygen separator 26 reaches the first specified value P1.

[0042] The second index may include the time elapsed since the pressure in the hydrogen separator 14 or the oxygen separator 26 reached the first specified value P1, or the temperature of the water in the water electrolysis apparatus 10. The index acquisition unit 52 may acquire the time elapsed since the pressure in the hydrogen separator 14 or the oxygen separator 26 reached the first specified value P1, using the measurement results from the pressure sensor 66 or 68 and a timer built into the control device 50. The index acquisition unit 52 may acquire the measurement results from the temperature sensor 62 or the temperature sensor 64 as the temperature of the water in the water electrolysis apparatus 10.

[0043] The determination unit 54 may be configured to determine whether the second index acquired by the index acquisition unit 52 exceeds a second threshold value T2. The second threshold value T2 may be a value determined based on past operating records so as to prevent the water electrolysis apparatus 10 from tripping due to high oxygen / hydrogen concentrations in the gas.

[0044] The control device 50 may be configured to, when the judgment unit 54 determines that the second indicator has exceeded the second threshold value T2, appropriately operate the vent valve 24 or 38 and the supply valve 46, etc., to replace at least a portion of the gas in the hydrogen separator 14 or the oxygen separator 26 with an inert gas.

[0045] The control device 50 may be configured to determine whether or not the replacement of the gas in the hydrogen separator 14 or the oxygen separator 26 with an inert gas is completed when the replacement is performed.

[0046] The above-mentioned index acquisition unit 52 may be configured to acquire a third index that indicates the amount of increase in the oxygen concentration in the gas in the hydrogen separator 14 or the hydrogen concentration in the gas in the oxygen separator 26 after the replacement of the gas in the hydrogen separator 14 or the oxygen separator 26 with an inert gas is completed.

[0047] The third index may include the time elapsed since the completion of the substitution, or the temperature of the water in the water electrolysis apparatus 10. The index acquiring unit 52 may acquire the time elapsed since the completion of the substitution using a timer built into the control device 50. The index acquiring unit 52 may acquire the measurement result by the temperature sensor 62 or the temperature sensor 64 as the temperature of the water in the water electrolysis apparatus 10.

[0048] The determination unit 54 may be configured to determine whether the third index acquired by the index acquisition unit 52 exceeds a third threshold value T3. The third threshold value T3 may be a value determined based on past operating records so as to prevent the water electrolysis apparatus 10 from tripping due to high oxygen / hydrogen concentrations in the gas.

[0049] The control device 50 may be configured to, when the judgment unit 54 determines that the third indicator has exceeded the third threshold value T3, appropriately operate the vent valve 24 or 38 and the supply valve 46, etc., to again replace at least a portion of the gas in the hydrogen separator 14 or the oxygen separator 26 with an inert gas.

[0050] (Operation Method of Water Electrolysis Apparatus) Next, an operation method of a water electrolysis apparatus according to some embodiments will be described with reference to Figures 3 to 8. Note that, although the following describes a case in which the operation of the water electrolysis apparatus 10 is controlled using the control device 50, in some embodiments, some or all of the procedures described below may be performed manually.

[0051] In the following, the operation of the hydrogen system including the hydrogen separator 14 will be described, but the same explanation can be applied to the oxygen system including the oxygen separator 26.

[0052] Fig. 3 is a flowchart showing an operation method of the water electrolysis system 10 according to one embodiment. Figs. 4 and 5 are graphs each showing an example of the change in separator pressure over time when an operation method according to one embodiment is performed (solid line 101 in Fig. 4 , solid line 102 in Fig. 5 , dashed lines 201 and 202 in Figs. 4 and 5 ).

[0053] 3 , in one embodiment, first, the control device 50 stops the electrolysis of water by the water electrolysis device 10 (i.e., stops the operation of the water electrolysis device 10; S2; time t10 in FIG. 4 and time t20 in FIG. 5 ). The control device 50 may stop the electrolysis of water by the water electrolysis device 10 based on a stop command from, for example, a higher-level control device.

[0054] During normal operation of the water electrolysis system 10, i.e., when voltage is applied to the electrodes of the electrolytic cell 12 to electrolyze water and supply product hydrogen gas to the destination (the period up to times t10 and t20 in FIGS. 4 and 5 ), the vent valve 24 is closed and the hydrogen supply valve 21 is open, and the pressure in the hydrogen separator 14 is substantially constant at the operating pressure P0. When electrolysis by the water electrolysis system 10 is stopped in step S2, the application of voltage to the electrodes of the electrolytic cell 12 is stopped and the hydrogen supply valve 21 is closed to stop the supply of product hydrogen gas. The vent valve 24 is maintained in a closed state.

[0055] Next, the determination unit 54 determines whether a first index indicating the increase in oxygen concentration in the gas in the hydrogen separator 14 since electrolysis was stopped has exceeded a first threshold value T1 (S4). In this embodiment, the first index is the elapsed time since electrolysis in the electrolytic cell 12 was stopped. Furthermore, a value that is preset based on the operating history of the water electrolysis system 10 is used as the first threshold value T1.

[0056] If water electrolysis in the water electrolysis device 10 is restarted in response to a restart command from a higher-level control device or the like before the first index exceeds the first threshold T1 (Yes in step S4), water electrolysis is restarted while the vent valve 24 remains closed since electrolysis was stopped in step S2 (i.e., voltage application to the electrodes of the electrolytic cell 12 is restarted; S22). The change in pressure in the hydrogen separator 14 in this case is represented by the dashed line 201 in Figures 4 and 5.

[0057] In this case, the vent valve 24 is kept closed to prevent gas from being released from within the hydrogen separator 14, and electrolysis of water in the water electrolysis apparatus 10 is resumed without reducing the separator pressure. This shortens the time required for the separator internal pressure to be increased to the operating pressure P0 after electrolysis is resumed.

[0058] After electrolysis is stopped, during the period until the first index exceeds the first threshold T1 (from t10 to t11 in FIG. 4 and from t20 to t21 in FIG. 5 ), the separator pressure gradually decreases despite the vent valve 24 being closed. This is because the application of voltage to the electrodes is stopped, preventing current from flowing through the electrodes and the water in the electrolytic cell 12, and the temperatures of the water in the water electrolysis device 10 and the water electrolysis device 10 gradually decrease.

[0059] On the other hand, if water electrolysis in the water electrolysis device 10 is not resumed before the first index exceeds the first threshold T1 and the first index exceeds the first threshold T1 (No in step S4; t11 in FIG. 4 and t21 in FIG. 5 ), the vent valve 24 is opened to reduce the pressure in the hydrogen separator 14 to a first specified value P1 (S8). At this time, the aperture of the vent valve 24 may be adjusted based on the measurement results of the pressure sensor 66. Once the pressure in the hydrogen separator 14 has reduced to the first specified value P1, the vent valve 24 is closed (t12 in FIG. 4 and t22 in FIG. 5 ), and the vent valve 24 is maintained closed (S10).

[0060] In this way, when the first index exceeds the first threshold T1 and the oxygen concentration in the gas increases to a certain extent, the vent valve 24 is opened to reduce the separator pressure to the first specified value P1, and then electrolysis of water in the water electrolysis device 10 is resumed in step S22. This makes it possible to resume operation of the water electrolysis device 10 in a state where an increase in the oxygen concentration in the gas in the hydrogen separator 14 is suppressed. This makes it easier to avoid tripping due to a high oxygen concentration in the gas when the water electrolysis device 10 resumes operation.

[0061] If the first index exceeds the first threshold value T1 (No in step S4), water may be circulated between the electrolytic cell 12 and the hydrogen separator 14 (S6). Then, in step S8, the pressure in the hydrogen separator 14 may be reduced to a first specified value P1 while water is circulating between the electrolytic cell 12 and the hydrogen separator 14.

[0062] In step S6, the pump 19 may be operated to circulate water between the electrolytic cell 12 and the hydrogen separator 14 via the cathode side line 16 and the return line 18.

[0063] Next, the determination unit 54 determines whether a second index, which indicates the amount of increase in the oxygen concentration in the gas inside the hydrogen separator 14 since the separator pressure reached the first specified value P1, has exceeded a second threshold value T2 (S12). In this embodiment, the second index is the elapsed time since the pressure in the hydrogen separator 14 reached the first specified value P1 (i.e., from t12 in FIG. 4 or t22 in FIG. 5). Furthermore, the second threshold value T2 is a value that is preset based on the operating history of the water electrolysis system 10.

[0064] If water electrolysis in the water electrolysis device 10 is restarted in response to a restart command from a higher-level control device or the like before the second index exceeds the second threshold T2 (Yes in step S12), water electrolysis is restarted (S22) without replacing the gas in the hydrogen separator 14 with an inert gas (i.e., without replacing the gas in the separator with an inert gas, as described in step S14 below). The change in pressure in the hydrogen separator 14 in this case is represented by the dashed line 202 in Figures 4 and 5.

[0065] In this case, water electrolysis in the water electrolysis device 10 is resumed without replacing the gas in the hydrogen separator 14 with an inert gas. Therefore, compared to when the gas in the hydrogen separator 14 is replaced with an inert gas, the procedure of increasing the purity of the hydrogen gas by reducing the inert gas concentration in the hydrogen separator 14 after electrolysis is resumed can be omitted, and the amount of inert gas consumed can be reduced.

[0066] On the other hand, if water electrolysis in the water electrolysis device 10 is not resumed before the second index exceeds the second threshold value T2 and the second index exceeds the second threshold value T2 (No in step S12; t13 in FIG. 4 and t23 in FIG. 5), at least a portion of the gas in the hydrogen separator 14 is replaced with an inert gas (S14).

[0067] In this way, when the second index exceeds the second threshold T2 and the oxygen concentration in the gas increases to a certain extent, the increase in the oxygen concentration in the gas in the hydrogen separator 14 can be suppressed by replacing at least a portion of the gas in the hydrogen separator 14 with an inert gas. This makes it easier to avoid tripping due to a high oxygen concentration in the gas when the water electrolysis apparatus 10 restarts operation.

[0068] In step S14, as shown in FIG. 4 , the vent valve 24 may be opened to reduce the pressure inside the hydrogen separator 14 (the period after t13 in FIG. 4 ), and then, with the vent valve 24 closed, an inert gas may be supplied from the inert gas supply unit 40 to the hydrogen separator 14 to increase the pressure inside the hydrogen separator 14 to a second specified value P2. In this case, when the pressure inside the hydrogen separator 14 reaches the second specified value P2 (time t14 in FIG. 4 ), it may be determined that the replacement of the gas inside the hydrogen separator 14 has been completed, and the supply of inert gas to the hydrogen separator 14 may be stopped. In the example shown in FIG. 4 , the second specified value P2 is the same value as the first specified value P1, but the second specified value P2 may be a value different from the first specified value P1.

[0069] Alternatively, in step S14, as shown in FIG. 5 , the vent valve 24 may be opened (time t23 in FIG. 5 ), and the inert gas may be supplied from the inert gas supply unit 40 to the hydrogen separator 14 while the vent valve 24 is left open. At this time, the inert gas may be supplied to the hydrogen separator 14 so that the pressure in the hydrogen separator 14 is maintained at the second specified value P2. In this case, if the elapsed time since the supply of the inert gas to the hydrogen separator 14 started (t23 in FIG. 5 ) exceeds the threshold value Tp (time t24 in FIG. 5 ), it may be determined that the replacement of the gas in the hydrogen separator 14 is complete, and the vent valve 24 may be closed and the supply of the inert gas to the hydrogen separator 14 may be stopped. In the example shown in FIG. 5 , the second specified value P2 is the same as the first specified value P1, but the second specified value P2 may be a value different from the first specified value P1.

[0070] After the replacement of gas in the hydrogen separator 14 is started in step S14, the water electrolysis in the water electrolysis device 10 may be restarted (S22) upon receiving a restart command or the like from the upper control device (Yes in step S16). Note that when restarting water electrolysis in the water electrolysis device 10 while an inert gas is being supplied to the hydrogen separator 14, the supply valve 46 or the like may be closed to stop the supply of the inert gas, and, if the vent valve 24 is open, the vent valve 24 may be closed before restarting water electrolysis.

[0071] If water has been circulating between the electrolytic cell 12 and the hydrogen separator 14 after step S6, the electrolysis of water in the water electrolysis device 10 may be resumed in step S22 without stopping the pump 19. Alternatively, the pump 19 may be stopped to stop the circulation of water between the electrolytic cell 12 and the hydrogen separator 14, and the electrolysis of water in the water electrolysis device 10 may be resumed in step S22.

[0072] According to the above-described method, after the electrolysis of water in the water electrolysis apparatus 10 is stopped, it is determined whether the first index, which indicates the increase in the oxygen concentration in the gas in the hydrogen separator 14, has exceeded the first threshold value T1, and if so, the vent valve 24 is opened to reduce the pressure in the hydrogen separator 14 to the first specified value P1. Therefore, before the first index exceeds the first threshold value T1, the gas in the hydrogen separator 14 is maintained without being released, and electrolysis of water in the water electrolysis apparatus 10 can be resumed without reducing the separator pressure, and therefore the time required for increasing the separator internal pressure to the operating pressure P0 after electrolysis is resumed is short. Furthermore, when the first indicator exceeds the first threshold T1 and the oxygen content in the gas increases to a certain extent, the vent valve 24 is opened to reduce the separator pressure to the first specified value P1, thereby reducing the amount of oxygen gas present in the hydrogen separator 14 and the cathode chamber or the anode chamber of the electrolytic cell 12, thereby reducing the amount of oxygen gas moving through the diaphragm separating the cathode chamber and the anode chamber of the electrolytic cell 12. This suppresses an increase in the oxygen concentration in the gas in the hydrogen separator 14, making it easier to avoid tripping due to high oxygen content in the gas when the water electrolysis device 10 is restarted. This allows the supply of product hydrogen gas to be resumed quickly when the water electrolysis device 10 is restarted after being shut down.

[0073] Furthermore, according to the above-described method, after the first index exceeds the first threshold value T1, the separator pressure is reduced to the first specified value P1 and then the vent valve 24 is maintained in a closed state. This prevents the separator pressure from being significantly reduced from the first specified value P1, thereby preventing a long time from being required to increase the separator pressure to the operating pressure P0 when the water electrolysis apparatus 10 is restarted.

[0074] In addition, in the above-described method, it is determined whether a second index indicating the amount of increase in oxygen concentration in the gas after the separator pressure reaches a first specified value P1 exceeds a second threshold value T2, and if it does, at least a portion of the gas in the hydrogen separator 14 is replaced with an inert gas.

[0075] Therefore, before the second index exceeds the second threshold T2, water electrolysis in the water electrolysis device 10 can be resumed without replacing the gas in the hydrogen separator 14 with an inert gas. This eliminates the need to reduce the inert gas concentration in the hydrogen separator 14 to increase the purity of the hydrogen gas after electrolysis is resumed, as compared to replacing the gas in the hydrogen separator 14 with an inert gas, and reduces the amount of inert gas consumed. Furthermore, when the second index exceeds the second threshold T2 and the oxygen concentration in the gas increases to a certain extent, at least a portion of the gas in the hydrogen separator 14 is replaced with an inert gas, which prevents an increase in the oxygen concentration in the gas in the hydrogen separator 14. This makes it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device 10 is restarted. This allows the supply of product hydrogen gas to be resumed quickly when the water electrolysis device 10 is restarted after being shut down.

[0076] Fig. 6 is a flowchart showing an operation method of the water electrolysis system 10 according to one embodiment. Figs. 7 and 8 are graphs showing the change in separator pressure over time when an operation method according to one embodiment is performed (solid line 103 in Fig. 7 , solid line 104 in Fig. 8 , and dashed lines 201 to 206 in Figs. 7 and 8 ).

[0077] In the embodiment shown in Fig. 6, steps S2 to S12 and step S22 are similar to those in the embodiment shown in Fig. 3, and therefore their explanations will be omitted. Also, the range of times t30 to t34 in the graph of Fig. 7 and the range of times t50 to t54 in the graph of Fig. 8 are similar to the range of times t10 to t14 in the graph of Fig. 4 and the range of times t20 to t24 in the graph of Fig. 5, and therefore their explanations will be omitted.

[0078] 6 , if, in step S12, water electrolysis in the water electrolysis device 10 is not resumed before the second index exceeds the second threshold value T2 and the second index exceeds the second threshold value T2 (No in step S12; t33 in FIG. 7 and t53 in FIG. 8 ), at least a portion of the gas in the hydrogen separator 14 is replaced with an inert gas ((i=1)th replacement) (S14′). Note that, as described below, step S14′ may be repeated multiple times depending on the situation.

[0079] 3, in step S14', the vent valve 24 may be opened to reduce the pressure inside the hydrogen separator 14 (the period after t33 in FIG. 7), and then, with the vent valve 24 closed, inert gas may be supplied from the inert gas supply unit 40 to the hydrogen separator 14 to increase the pressure inside the hydrogen separator 14 to the second specified value P2. In this case, when the pressure inside the hydrogen separator 14 reaches the second specified value P2 (time t34 in FIG. 7), it may be determined that the replacement of the gas inside the hydrogen separator 14 has been completed, and the supply of inert gas to the hydrogen separator 14 may be stopped.

[0080] Alternatively, in step S14', similar to step S14 in Fig. 3 , the vent valve 24 may be opened (time t53 in Fig. 8 ), and inert gas may be supplied from the inert gas supply unit 40 to the hydrogen separator 14 while the vent valve 24 is left open. At this time, inert gas may be supplied to the hydrogen separator 14 so that the pressure in the hydrogen separator 14 is maintained at the second specified value P2. In this case, when the elapsed time since the supply of inert gas to the hydrogen separator 14 started (t53 in Fig. 8 ) exceeds the threshold value Tp (time t54 in Fig. 8 ), it may be determined that the replacement of the gas in the hydrogen separator 14 has been completed, and the vent valve 24 may be closed and the supply of inert gas to the hydrogen separator 14 may be stopped.

[0081] Next, the determination unit 54 determines whether the third index, which indicates the increase in the oxygen concentration in the gas in the hydrogen separator 14 after the completion of the i-th gas replacement in the hydrogen separator 14 (t34 in FIG. 7 , t54 in FIG. 8 ), has exceeded a third threshold value T3(i) (S12). That is, the third threshold value when i=1 (first replacement) is T3(1). In this embodiment, the elapsed time since the completion of the i-th gas replacement in the hydrogen separator 14 (i.e., from t34 in FIG. 7 , t54 in FIG. 8 ) is used as the third index. Furthermore, a value that is preset based on the operating history of the water electrolysis system 10 is used as the third threshold value T3(i).

[0082] After the i-th replacement of the gas in the hydrogen separator 14 is completed, if water electrolysis in the water electrolysis device 10 is restarted in response to a restart command from a higher-level control device or the like before the third index exceeds the third threshold value T3(i) (Yes in step S18), water electrolysis is restarted (S22). In this case, the changes in pressure in the hydrogen separator 14 are represented by dashed lines 203 (i=1), 204 (i=2), 205 (i=3), and 206 (i=4) in Figures 7 and 8.

[0083] On the other hand, if water electrolysis in the water electrolysis device 10 is not resumed before the third index exceeds the third threshold T3(i) and the third index exceeds the third threshold T3(i) (No in step S18; t35 in FIG. 10, t55 in FIG. 8, etc.), at least a portion of the gas in the hydrogen separator 14 is again replaced with an inert gas (S14'). That is, the (i+1)th replacement is performed.

[0084] Then, until water electrolysis in the water electrolysis device 10 is resumed in response to a restart command or the like from the upper control device, step S18 of determining whether the third index has exceeded the third threshold value T3(i) and step S14′ of performing the (i+1)th replacement of the gas in the hydrogen separator 14 (step S14′) if the third index has exceeded the third threshold value T3(i) are repeatedly performed (see t33 to t41 in FIG. 7 and t53 to t62 in FIG. 8 ).

[0085] When step S18 is repeatedly performed as described above, each third threshold value T3(i) (T3(1), T3(2), T3(3), ..., etc.) may be a common value or may be a different value.

[0086] According to the above-described method, when it is determined that the replacement of the gas in the hydrogen separator 14 with the inert gas is complete, it is determined whether the third indicator, which indicates the increase in oxygen concentration in the gas since the replacement was completed, exceeds the third threshold T3(i). If the third indicator exceeds the third threshold T3(i), at least a portion of the gas in the hydrogen separator is replaced with the inert gas again. In other words, even if time has passed since the completion of the first replacement, the gas in the hydrogen separator is replaced with the inert gas again, thereby maintaining a state in which the increase in the oxygen concentration in the gas in the hydrogen separator is suppressed. This makes it easier to avoid tripping due to a high oxygen concentration in the gas when the water electrolysis system 10 is restarted. Therefore, the supply of product hydrogen gas can be resumed early when the water electrolysis system 10 is restarted after being shut down.

[0087] The contents described in each of the above embodiments can be understood, for example, as follows.

[0088] [1] According to at least one embodiment of the present invention, there is provided a method for operating a water electrolysis apparatus (10) including an electrolytic cell (12) for electrolyzing water, a hydrogen separator (14) to which hydrogen produced in the electrolytic cell is introduced, an oxygen separator (26) to which oxygen produced in the electrolytic cell is introduced, and a vent line (22, 36) for discharging gas from the hydrogen separator or the oxygen separator, and a vent valve (24, 38) provided in the vent line, the method comprising: a step (S2) of stopping the electrolysis of water in the electrolytic cell; and a step (S4) of determining whether a first index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator since the electrolysis was stopped has exceeded a first threshold value; and when the first index exceeds the first threshold value (T1), the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator to a first specified value (P1).

[0089] According to the method [1] above, after stopping the electrolysis of water in the water electrolysis apparatus, it is determined whether a first index indicating the amount of increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator (hereinafter also referred to as the oxygen / hydrogen concentration in the gas) has exceeded a first threshold, and if so, the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator (hereinafter also referred to as the separator pressure) to a first specified value. Therefore, before the first index exceeds the first threshold, the gas in the separator is maintained without being released, and water electrolysis in the water electrolysis apparatus can be resumed without reducing the separator pressure, thereby shortening the time required to increase the separator pressure to the operating pressure after resumption of electrolysis. Furthermore, when the first indicator exceeds the first threshold and the oxygen / hydrogen concentrations in the gas increase to a certain level, the vent valve is opened to reduce the separator pressure to the first specified value, thereby reducing the amount of oxygen gas or hydrogen gas present in the hydrogen separator or oxygen separator and the cathode chamber or anode chamber of the electrolytic cell, thereby reducing the amount of oxygen gas or hydrogen gas moving through the diaphragm separating the cathode chamber and the anode chamber of the electrolytic cell. This suppresses an increase in the oxygen / hydrogen concentrations in the gas in the separator, making it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device is restarted. This allows the supply of product hydrogen gas to be resumed early when the water electrolysis device is restarted after being shut down.

[0090] [2] In some embodiments, in the method of [1] above, the method of operating the water electrolysis apparatus further comprises a step (S22) of restarting the electrolysis of water in the electrolytic cell, wherein if the electrolysis of water is restarted before the first indicator exceeds the first threshold, the electrolysis of water is restarted while the vent valve is kept closed since the electrolysis was stopped, and if the electrolysis of water is restarted after the first indicator exceeds the first threshold, the vent valve is opened after the first indicator exceeds the first threshold, and the pressure in the hydrogen separator or the oxygen separator is reduced to the first specified value before the electrolysis of water is restarted.

[0091] According to the method [2] above, before the first indicator exceeds the first threshold, the vent valve is closed to maintain the gas in the separator without releasing it, and electrolysis of water in the water electrolysis apparatus is resumed without reducing the separator pressure. This shortens the time it takes for the pressure in the separator to be increased to the operating pressure after electrolysis is resumed. Furthermore, when the first indicator exceeds the first threshold and the oxygen / hydrogen concentrations in the gas increase to a certain extent, the vent valve is opened to reduce the separator pressure to a first specified value before restarting water electrolysis in the water electrolysis apparatus. This suppresses the increase in the oxygen / hydrogen concentrations in the gas in the separator when the water electrolysis apparatus is resumed, making it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis apparatus is resumed. This allows the supply of product hydrogen gas to be resumed quickly when the water electrolysis apparatus is restarted after being shut down.

[0092] [3] In some embodiments, in the method of [1] or [2] above, the first indicator includes the elapsed time since the electrolysis was stopped or the temperature of the water in the water electrolysis device.

[0093] Dissolved hydrogen gas in the water (solution) in the cathode chamber of the electrolytic cell, or dissolved oxygen gas in the water in the anode chamber of the electrolytic cell, can gradually migrate to the anode chamber or cathode chamber, respectively, through the diaphragm separating the cathode chamber and the anode chamber. While the water electrolysis device is stopped (i.e., while water electrolysis is stopped), if the separator pressure and the pressures in the anode chamber and cathode chamber do not decrease significantly, the oxygen / hydrogen concentrations in the gas in the anode chamber or cathode chamber and in the separator are thought to gradually increase due to the migration of hydrogen gas or oxygen gas through the diaphragm. Therefore, the time elapsed since electrolysis in the water electrolysis device was stopped can be appropriately used as a first indicator of the increase in the oxygen / hydrogen concentrations in the gas in the separator since electrolysis was stopped. Furthermore, after the operation of the water electrolysis device is stopped, the temperature of the water in the water electrolysis device gradually decreases, but the dissolved hydrogen gas concentration or dissolved oxygen gas concentration increases as the water temperature decreases. Therefore, it is believed that the migration of dissolved hydrogen gas or dissolved oxygen gas in the water through the diaphragm becomes more likely, and the oxygen / hydrogen concentrations in the gas in the anode chamber or cathode chamber and the separator gradually increase. Therefore, the water temperature in the water electrolysis device can be appropriately used as a first indicator that indicates the increase in the oxygen / hydrogen concentrations in the gas in the separator since electrolysis in the water electrolysis device was stopped. Therefore, according to the method [3] above, a first indicator including the time elapsed since electrolysis was stopped or the water temperature in the water electrolysis device is used. Therefore, by comparing the first indicator with a first threshold, it is possible to appropriately determine whether the oxygen / hydrogen concentrations in the gas in the separator have increased by a predetermined amount.

[0094] [4] In some embodiments, in any of the methods [1] to [3] above, the method of operating the water electrolysis apparatus comprises: a step (S10) of reducing the pressure in the hydrogen separator or the oxygen separator to the first specified value after the first indicator has exceeded the first threshold, and then maintaining the vent valve in a closed state; and a step (S12) of determining whether a second indicator, which indicates an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after the pressure has reached the first specified value, has exceeded a second threshold (T2), and if the second indicator has exceeded the second threshold, a substitution step (S14, S14') is carried out of substituting at least a portion of the gas in the hydrogen separator or the oxygen separator with an inert gas.

[0095] In the method [4] described above, after the first indicator exceeds the first threshold, the separator pressure is reduced to a first specified value and then the vent valve is kept closed, thereby preventing the separator pressure from decreasing significantly from the first specified value. This prevents a long time required to increase the separator pressure to the operating pressure when restarting the water electrolysis apparatus. Furthermore, a determination is made as to whether a second indicator, which indicates an increase in the oxygen / hydrogen concentration in the gas after the separator pressure reaches the first specified value, has exceeded a second threshold. If the second indicator has exceeded the second threshold, at least a portion of the gas in the separator is replaced with an inert gas. Therefore, before the second indicator exceeds the second threshold, water electrolysis in the water electrolysis apparatus can be resumed without replacing the gas in the separator with an inert gas. This eliminates the need to reduce the inert gas concentration in the separator to increase the purity of hydrogen gas or oxygen gas after electrolysis is resumed, and reduces the amount of inert gas consumed, compared to replacing the gas in the separator with an inert gas. Furthermore, when the second index exceeds the second threshold and the oxygen / hydrogen concentrations in the gas increase to a certain extent, at least a portion of the gas in the separator is replaced with an inert gas, thereby suppressing an increase in the oxygen / hydrogen concentrations in the gas in the separator. This makes it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis apparatus is restarted. This allows the supply of product hydrogen gas to be resumed quickly when the water electrolysis apparatus is restarted after being shut down.

[0096] [5] In some embodiments, in the method of [4] above, when the electrolysis of water is resumed before the second indicator exceeds the second threshold, the electrolysis of water is resumed without replacing the gas in the hydrogen separator or the oxygen separator with an inert gas; and when the electrolysis of water is resumed after the second indicator exceeds the second threshold, the replacement step is carried out after the second indicator exceeds the second threshold, and then the electrolysis of water is resumed.

[0097] According to the method [5], before the second index exceeds the second threshold, water electrolysis in the water electrolysis device is resumed without replacing the gas in the separator with an inert gas. This eliminates the need to reduce the inert gas concentration in the separator to increase the purity of hydrogen gas or oxygen gas after electrolysis is resumed, as compared to replacing the gas in the separator with an inert gas, and reduces the amount of inert gas consumed. Furthermore, when the second index exceeds the second threshold and the oxygen / hydrogen concentrations in the gas increase to a certain extent, at least a portion of the gas in the separator is replaced with an inert gas before water electrolysis is resumed. This allows the water electrolysis device to resume operation in a state where the increase in the oxygen / hydrogen concentrations in the gas in the separator is suppressed, making it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device is resumed. This allows the supply of product hydrogen gas to be resumed early when the water electrolysis device is restarted after being shut down.

[0098] [6] In some embodiments, in the method of [4] or [5] above, the second indicator includes the elapsed time since the pressure of the hydrogen separator or the oxygen separator reached the first specified value, or the temperature of the water in the water electrolysis device.

[0099] During shutdown of the water electrolysis device, if the separator pressure and the pressures in the anode chamber and cathode chamber do not decrease significantly, it is believed that the oxygen / hydrogen concentrations in the gas in the anode chamber or cathode chamber and in the separator will gradually increase due to the movement of hydrogen gas or oxygen gas through the diaphragm. Therefore, the time elapsed since the separator pressure reached the first specified value can be appropriately used as a second indicator of the increase in the oxygen / hydrogen concentrations in the gas in the separator after the separator pressure reached the first specified value. Furthermore, as the temperature of the water in the water electrolysis device decreases, the dissolved hydrogen gas concentration or the dissolved oxygen gas concentration increases with the water temperature, making it easier for the dissolved hydrogen gas or dissolved oxygen gas in the water to move through the diaphragm. Therefore, the temperature of the water in the water electrolysis device can be appropriately used as a second indicator of the increase in the oxygen / hydrogen concentrations in the gas in the separator after the separator pressure reached the first specified value. Therefore, according to the method [6] above, the second index including the time elapsed since the separator pressure reached the first specified value or the temperature of the water in the water electrolysis apparatus is used, and by comparing the second index with the second threshold value, it is possible to appropriately determine whether the oxygen / hydrogen in the gas in the separator has increased to a predetermined level.

[0100] [7] In some embodiments, in any of the methods [4] to [6] above, in the replacement step, the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator, and then, with the vent valve closed, an inert gas is supplied to the hydrogen separator or the oxygen separator to increase the pressure in the hydrogen separator or the oxygen separator to a second specified value (P2).

[0101] According to the method [7] above, the vent valve is opened to release the gas in the hydrogen separator or oxygen separator to reduce the pressure, and then the vent valve is closed and an inert gas is supplied to the hydrogen separator or oxygen separator to increase the separator pressure to the second specified value, thereby appropriately replacing at least a portion of the gas in the separator with the inert gas.

[0102] [8] In some embodiments, in any of the methods [4] to [6] above, in the replacing step, the vent valve is opened, and an inert gas is supplied to the hydrogen separator or the oxygen separator while the vent valve is kept open.

[0103] According to the method [8] above, by opening the vent valve and supplying an inert gas to the hydrogen separator or the oxygen separator while keeping the vent valve open, at least a portion of the gas in the separator can be appropriately replaced with the inert gas.

[0104] [9] In some embodiments, in any of the methods [4] to [7] above, the method of operating the water electrolysis apparatus comprises the steps of: determining whether replacement of at least a portion of the gas in the hydrogen separator or the oxygen separator with an inert gas in the replacement step has been completed; and determining (S18) whether a third index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after completion of the replacement has exceeded a third threshold value (T3), and if the third index has exceeded the third threshold value, the replacement step (S14') is performed again.

[0105] According to the method [9] above, when it is determined that the replacement of the gas in the hydrogen separator or oxygen separator with an inert gas is complete, it is determined whether a third indicator, which indicates the increase in the oxygen / hydrogen concentration in the gas since the replacement is complete, exceeds a third threshold. If the third indicator exceeds the third threshold, at least a portion of the gas in the separator is replaced with an inert gas again. That is, even if time has passed since the completion of the first replacement, the gas in the separator is replaced with an inert gas again, thereby maintaining a state in which the increase in the oxygen / hydrogen concentration in the gas in the separator is suppressed. This makes it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis system is restarted. This allows the supply of product hydrogen gas to be resumed quickly when the water electrolysis system is restarted after being shut down.

[0106]

[10] In some embodiments, in the method of [9] above, when the electrolysis of water is resumed after the third indicator exceeds the third threshold, the replacement step is carried out again after the third indicator exceeds the third threshold, and then the electrolysis of water is resumed.

[0107] According to the method

[10] above, after it is determined that replacement of the gas in the hydrogen separator or the oxygen separator with the inert gas is completed, if a third index indicating the increase in the oxygen / hydrogen concentration in the gas since the replacement is completed exceeds a third threshold, at least a portion of the gas in the separator is replaced with the inert gas again and water electrolysis is resumed. This allows the water electrolysis device to resume operation in a state in which the increase in the oxygen / hydrogen concentration in the gas in the separator is suppressed, making it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device is restarted. This allows the supply of product hydrogen gas to be resumed promptly when the water electrolysis device is restarted after being shut down.

[0108]

[11] In some embodiments, in the method of any one of [1] to

[10] above, when the vent valve is opened to reduce the pressure of the hydrogen separator or the oxygen separator to the first specified value after the first indicator exceeds the first threshold, the water is circulated between the electrolytic cell and the hydrogen separator or the oxygen separator.

[0109] According to the method

[11] , after the electrolysis of water in the water electrolysis device is stopped and the first indicator exceeds the first threshold, when the vent valve is opened to reduce the separator pressure to the first specified value, water is circulated between the electrolytic cell and the separator. This allows dissolved oxygen gas and dissolved hydrogen gas in the liquid phase to be easily released into the gas phase. This reduces the concentrations of dissolved oxygen gas and dissolved hydrogen gas in the water, making it difficult for the dissolved hydrogen gas or dissolved oxygen gas in the water to migrate through the diaphragm. This makes it difficult for the oxygen / hydrogen concentrations in the gas in the anode chamber or cathode chamber and the separator to increase. Therefore, the method

[11] makes it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device is restarted. This makes it easier to quickly resume the supply of product hydrogen gas when the water electrolysis device is restarted after being stopped.

[0110]

[12] A control device (50) for a water electrolysis apparatus according to at least one embodiment of the present invention is a control device for a water electrolysis apparatus including: an electrolytic cell (12) for electrolyzing water; a hydrogen separator (14) to which hydrogen produced in the electrolytic cell is introduced; an oxygen separator (26) to which oxygen produced in the electrolytic cell is introduced; a vent line (22, 36) for discharging gas from the hydrogen separator or the oxygen separator, and a vent valve (24, 38) provided in the vent line; and the control device comprises: an index acquisition unit (52) configured to acquire a first index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after electrolysis of water in the electrolytic cell is stopped; and a determination unit (54) configured to determine whether the first index has exceeded a first threshold value. When the judgment unit determines that the first indicator has exceeded the first threshold, the vent valve is opened to reduce the pressure of the hydrogen separator or the oxygen separator to a first specified value (P1).

[0111] According to the configuration

[12] above, after electrolysis of water in the water electrolysis apparatus is stopped, it is determined whether a first index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator (hereinafter also referred to as the oxygen / hydrogen concentration in the gas) exceeds a first threshold, and if so, the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator (hereinafter also referred to as the separator pressure) to a first specified value. Therefore, before the first index exceeds the first threshold, gas in the separator is maintained without being released, and electrolysis of water in the water electrolysis apparatus can be resumed without reducing the separator pressure, thereby shortening the time required to increase the separator pressure to the operating pressure after electrolysis is resumed. Furthermore, when the first indicator exceeds the first threshold and the oxygen / hydrogen concentrations in the gas increase to a certain level, the vent valve is opened to reduce the separator pressure to the first specified value, thereby reducing the amount of oxygen gas or hydrogen gas present in the hydrogen separator or oxygen separator and the cathode chamber or anode chamber of the electrolytic cell, thereby reducing the amount of oxygen gas or hydrogen gas moving through the diaphragm separating the cathode chamber and the anode chamber of the electrolytic cell. This suppresses an increase in the oxygen / hydrogen concentrations in the gas in the separator, making it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device is restarted. This allows the supply of product hydrogen gas to be resumed early when the water electrolysis device is restarted after being shut down.

[0112]

[13] A hydrogen production facility (1) according to at least one embodiment of the present invention comprises: a water electrolysis device (10) including: an electrolytic cell (12) for electrolyzing water; a hydrogen separator (14) to which hydrogen produced in the electrolytic cell is introduced; an oxygen separator (26) to which oxygen produced in the electrolytic cell is introduced; a vent line (22, 36) for discharging gas from the hydrogen separator or the oxygen separator, and a vent valve (24, 38) provided in the vent line; and a control device (50) according to the above

[12] for controlling the water electrolysis device.

[0113] According to the configuration

[13] above, after electrolysis of water in the water electrolysis apparatus is stopped, it is determined whether a first index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator (hereinafter also referred to as the oxygen / hydrogen concentration in the gas) exceeds a first threshold, and if so, the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator (hereinafter also referred to as the separator pressure) to a first specified value. Therefore, before the first index exceeds the first threshold, gas in the separator is maintained without being released, and electrolysis of water in the water electrolysis apparatus can be resumed without reducing the separator pressure, thereby shortening the time required to increase the separator pressure to the operating pressure after electrolysis is resumed. Furthermore, when the first indicator exceeds the first threshold and the oxygen / hydrogen concentrations in the gas increase to a certain level, the vent valve is opened to reduce the separator pressure to the first specified value, thereby reducing the amount of oxygen gas or hydrogen gas present in the hydrogen separator or oxygen separator and the cathode chamber or anode chamber of the electrolytic cell, thereby reducing the amount of oxygen gas or hydrogen gas moving through the diaphragm separating the cathode chamber and the anode chamber of the electrolytic cell. This suppresses an increase in the oxygen / hydrogen concentrations in the gas in the separator, making it easier to avoid tripping due to high oxygen / hydrogen concentrations in the gas when the water electrolysis device is restarted. This allows the supply of product hydrogen gas to be resumed early when the water electrolysis device is restarted after being shut down.

[0114] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0115] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0116] REFERENCE SIGNS LIST 1 Hydrogen production equipment 10 Water electrolysis device 12 Electrolyzer 14 Hydrogen separator 16 Cathode side line 18 Return line 19 Pump 20 Hydrogen gas line 21 Hydrogen supply valve 22 Vent line 24 Vent valve 26 Oxygen separator 28 Anode side line 30 Return line 31 Pump 32 Oxygen gas line 33 Oxygen supply valve 36 Vent line 38 Vent valve 40 Inert gas supply section 42 Inert gas storage section 44 Supply line 46 Supply valve 48a First branch section 48b Second branch section 49a First valve 49b Second valve 50 Control device 52 Index acquisition section 54 Determination section 62 Temperature sensor 64 Temperature sensor 66 Pressure sensor 68 Pressure sensor

Claims

1. A method for operating a water electrolysis apparatus including an electrolytic cell for electrolyzing water, a hydrogen separator to which hydrogen produced in the electrolytic cell is introduced, an oxygen separator to which oxygen produced in the electrolytic cell is introduced, a vent line for discharging gas from the hydrogen separator or the oxygen separator, and a vent valve provided in the vent line, comprising the steps of: stopping the electrolysis of water in the electrolytic cell; and determining whether a first index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator since the electrolysis was stopped has exceeded a first threshold value; and if the first index exceeds the first threshold value, opening the vent valve to reduce the pressure in the hydrogen separator or the oxygen separator to a first specified value.

2. The method of operating a water electrolysis apparatus according to claim 1, further comprising the step of restarting the electrolysis of water in the electrolytic cell, wherein if the electrolysis of water is restarted before the first index exceeds the first threshold, the electrolysis of water is restarted while the vent valve is kept closed after the electrolysis has been stopped, and if the electrolysis of water is restarted after the first index exceeds the first threshold, the vent valve is opened after the first index exceeds the first threshold, and the pressure in the hydrogen separator or the oxygen separator is reduced to the first specified value before the electrolysis of water is restarted.

3. The method for operating a water electrolysis device according to claim 1 or 2, wherein the first indicator includes the time elapsed since the electrolysis was stopped or the temperature of the water in the water electrolysis device.

4. A method for operating a water electrolysis system according to claim 1 or 2, comprising the steps of: after the first indicator exceeds the first threshold, reducing the pressure in the hydrogen separator or the oxygen separator to the first specified value and then maintaining the vent valve closed; and determining whether a second indicator, which indicates the amount of increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after the pressure reaches the first specified value, has exceeded a second threshold, wherein if the second indicator exceeds the second threshold, a substitution step is carried out in which at least a portion of the gas in the hydrogen separator or the oxygen separator is replaced with an inert gas.

5. The method for operating a water electrolysis system according to claim 4, wherein, when water electrolysis is resumed before the second index exceeds the second threshold, water electrolysis is resumed without replacing the gas in the hydrogen separator or the oxygen separator with an inert gas, and when water electrolysis is resumed after the second index exceeds the second threshold, the replacement step is carried out after the second index exceeds the second threshold, and then water electrolysis is resumed.

6. The method for operating a water electrolysis system according to claim 4, wherein the second indicator includes the time elapsed since the pressure in the hydrogen separator or the oxygen separator reached the first specified value, or the temperature of the water in the water electrolysis system.

7. The method of operating a water electrolysis system according to claim 4, wherein in the substitution step, the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator, and then, with the vent valve closed, an inert gas is supplied to the hydrogen separator or the oxygen separator to increase the pressure in the hydrogen separator or the oxygen separator to a second specified value.

8. The method for operating a water electrolysis system according to claim 4, wherein in the replacing step, the vent valve is opened, and an inert gas is supplied to the hydrogen separator or the oxygen separator while the vent valve is kept open.

9. A method for operating a water electrolysis apparatus according to claim 4, comprising the steps of: determining whether replacement of at least a portion of the gas in the hydrogen separator or the oxygen separator with an inert gas in the replacement step has been completed; and determining whether a third index indicating an increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after completion of the replacement has exceeded a third threshold; and if the third index exceeds the third threshold, performing the replacement step again.

10. The method for operating a water electrolysis apparatus according to claim 9, wherein, when water electrolysis is resumed after the third index exceeds the third threshold, the replacement step is carried out again after the third index exceeds the third threshold, and then water electrolysis is resumed.

11. A method for operating a water electrolysis apparatus according to claim 1 or 2, wherein after the first indicator exceeds the first threshold, the water is circulated between the electrolytic cell and the hydrogen separator or the oxygen separator when the vent valve is opened to reduce the pressure in the hydrogen separator or the oxygen separator to the first specified value.

12. A control device for a water electrolysis apparatus including an electrolytic cell for electrolyzing water, a hydrogen separator to which hydrogen produced in the electrolytic cell is introduced, an oxygen separator to which oxygen produced in the electrolytic cell is introduced, a vent line for discharging gas from the hydrogen separator or the oxygen separator, and a vent valve provided in the vent line, the control device comprising: an index acquisition unit configured to acquire a first index that indicates an amount of increase in the oxygen concentration in the gas in the hydrogen separator or the hydrogen concentration in the gas in the oxygen separator after electrolysis of water in the electrolytic cell is stopped; and a determination unit configured to determine whether the first index has exceeded a first threshold value; and when it is determined by the determination unit that the first index has exceeded the first threshold value, the control device for a water electrolysis apparatus is configured to open the vent valve to reduce the pressure in the hydrogen separator or the oxygen separator to a first specified value.

13. A hydrogen production facility comprising: a water electrolysis device including an electrolytic cell for electrolyzing water; a hydrogen separator to which hydrogen produced in the electrolytic cell is introduced; an oxygen separator to which oxygen produced in the electrolytic cell is introduced; a vent line for discharging gas from the hydrogen separator or the oxygen separator and a vent valve provided in the vent line; and a control device according to claim 12 for controlling the water electrolysis device.

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