Water electrolysis system and method of operating water electrolysis system

Abstract

To secure the insulation property of an electrical insulation mechanism in a water electrolysis system over a long period of time.SOLUTION: The water electrolysis system 1 includes one or more water electrolysis stacks 10, a water line 13 for supplying water to each water electrolysis stack 10, an oxygen line 14 for discharging oxygen gas and excess water generated in each water electrolysis stack 10, a hydrogen line 15 for discharging hydrogen gas and excess water generated in each water electrolysis stack 10, an insulating pipe 16 for electrically insulating the water electrolysis stack 10 from pipes of the water line 13, the oxygen line 14, and the hydrogen line 15, and a DC power supply 11 for supplying DC power to the water electrolysis stack 10 to drive the water electrolysis stack 10. During operation of the water electrolysis system 1, water is supplied to a portion of the hydrogen line 15 upstream of the insulating pipe 16, where hydrogen gas and excess water are mixed in the water electrolysis stack 10 or the hydrogen line 15.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water electrolysis system and a method for operating the water electrolysis system. [Background technology]

[0002] Unlike fossil fuels, hydrogen is a clean energy source that does not emit carbon dioxide when burned. For this reason, hydrogen has attracted attention as a clean energy source to combat global warming, and technological development is underway regarding the production, transportation, and use of hydrogen.

[0003] Hydrogen that minimizes carbon dioxide emissions during the production process is also called CO2-free hydrogen. To produce CO2-free hydrogen, it is necessary to produce it using energy sources such as renewable energy or nuclear power. One method of producing hydrogen is a water electrolysis system. In recent years, water electrolysis systems have become larger, and construction projects for water electrolysis systems of several hundred megawatts or larger are being planned. It is expected that water electrolysis systems will continue to grow in size in the future. Furthermore, conventional water electrolysis stacks (water electrolyzers) used in large-scale water electrolysis systems require a low-voltage, high-current DC power supply of several hundred volts and several thousand amperes.

[0004] Water electrolysis systems are becoming larger in order to reduce hydrogen production costs, which requires larger water electrolysis stacks and reduced equipment costs. As mentioned above, water electrolysis stacks require a low-voltage, high-current DC power supply, but such DC power supplies are for special applications and cost reductions are not progressing. For this reason, large-scale water electrolysis systems need to be connected to a power grid of several tens of kV to ensure power. However, connecting to a power grid of several tens of kV requires multi-stage transformers to reduce the voltage, which increases the equipment costs as the water electrolysis system becomes larger. For this reason, there is a demand for lowering the cost of power supply equipment.

[0005] In large-scale water electrolysis systems, the need to operate multiple water electrolysis stacks with a single power supply has been advocated for high-efficiency operation of power sources. One method for operating multiple water electrolysis stacks simultaneously is to electrically connect them in series (hereinafter referred to as "multiple series connection"). By connecting multiple water electrolysis stacks in series to increase voltage, it may be possible to reduce the number of step-down transformers and rectifiers when drawing power from the power grid. This could potentially enable large-scale hydrogen production at low cost. However, when connecting multiple water electrolysis stacks in series to increase voltage, electrical insulation between the high-voltage water electrolysis stacks and the ground or piping at earth potential becomes an issue.

[0006] Patent Document 1 describes an insulation configuration for obtaining high-voltage output in a fuel cell stack. In the fuel cell stack described in Patent Document 1, an insulating plate is provided between the lower end plate (housing) of the fuel cell stack and the installation base (ground) to ensure electrical insulation of the fuel cell stack, and an insulating mechanism is provided in part of the metal piping for supplying fuel gas and air to the fuel cell stack. This insulating plate ensures electrical insulation between the lower end plate and the support frame. Furthermore, this insulating mechanism makes it possible to avoid electrical connection between the upper and lower end plates of each fuel cell stack via the metal piping in a fuel cell in which multiple fuel cell stacks are connected in series. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-87863 Summary of the Invention [Problem to be solved by the invention]

[0008] The fuel cell stack described in Patent Document 1 is a fuel cell that operates in a high-temperature atmosphere of 600°C or higher, like a solid oxide fuel cell, and is a system that does not contain water. On the other hand, a water electrolysis stack that operates at low temperatures electrolyzes water to produce hydrogen, so water must be supplied to the oxygen gas system. In addition, a small amount of water is discharged into the system for hydrogen gas produced by water electrolysis as produced water accompanying the movement of protons (hydrogen ions). The resistivity of pure water is lower than that of gas, and is 17.5 to 18.2 MΩ·cm for ultrapure water.

[0009] Therefore, when a water electrolysis stack is operated at a high voltage using a configuration similar to that described in Patent Document 1, a current determined by the applied voltage and the volume resistivity of pure water flows through the water. This current causes electrolytic corrosion in the metal piping. Metal ions eluted by electrolytic corrosion not only deteriorate the water electrolysis stack, but may also deposit on the insulating mechanism installed in the piping, reducing the insulating properties of the insulating mechanism. Furthermore, cations such as metal ions eluted in the water of the oxygen gas system may pass through the diaphragm and electrolyte and migrate to the hydrogen gas system, where they may be concentrated in the water of the hydrogen gas system.

[0010] In particular, if the insulation of the insulation mechanism installed in the piping deteriorates and breakdowns, the entire water electrolysis system must be shut down. However, if a large-scale water electrolysis system is suddenly disconnected from the power grid, it may cause a disturbance to the power grid. Therefore, a system is needed to prevent the entire water electrolysis system from shutting down due to insulation breakdown.

[0011] The present invention has been made in view of the above background, and an object of the present invention is to ensure the insulation properties of an electrical insulation mechanism in a water electrolysis system for a long period of time. [Means for solving the problem]

[0012] In order to solve the above problems, one aspect of the present invention provides a water electrolysis system comprising: one or more water electrolysis stacks that produce hydrogen gas and oxygen gas from water; water lines that supply water to each water electrolysis stack; oxygen lines that discharge the oxygen gas produced in each water electrolysis stack and excess water; hydrogen lines that discharge the hydrogen gas produced in each water electrolysis stack and excess water; insulating piping that electrically insulates the water electrolysis stack from the piping of the water line, the oxygen line, and the hydrogen line; and a DC power supply that supplies DC power to the water electrolysis stack to drive it. During operation of the water electrolysis system, water is supplied to a portion of the water electrolysis stack or the hydrogen line, upstream of the insulating piping of the hydrogen line, where hydrogen gas and excess water are mixed. [Effects of the Invention]

[0013] According to at least one aspect of the present invention, it is possible to ensure the insulation properties of the electrical insulation mechanism in the water electrolysis system for a long period of time. Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiments of the invention. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing a schematic configuration example of a water electrolysis system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating an example of the hardware configuration of a computer included in the water electrolysis system according to the first embodiment of the present invention. [Figure 3] FIG. 1 is a diagram showing an example of the configuration of ceramic insulating piping used in a water electrolysis system according to a first embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing an example of the configuration of an insulating resin pipe used in a water electrolysis system according to a first embodiment of the present invention. [Figure 5] 4 is a graph showing an example of changes over time in leakage current flowing through insulating pipes in the water electrolysis system according to the first embodiment of the present invention. [Figure 6] FIG. 4 is a diagram showing an example of the schematic configuration of a water electrolysis system according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a block diagram showing an example of the internal configuration of a system control unit of a water electrolysis system according to a third embodiment of the present invention. [Figure 8] 10 is a flowchart showing an example of the control process performed by a system controller of a water electrolysis system according to a third embodiment of the present invention. [Figure 9] 10 is a flowchart showing an example of the control process performed by a system controller of a water electrolysis system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, examples of modes for carrying out the present invention (hereinafter referred to as "embodiments") will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, common or similar components are given the same reference numerals, and redundant explanations may be omitted or only explanations focusing on the differences may be given. Furthermore, when there are multiple identical or similar components, they may be described using the same reference numerals with different subscripts. Note that when it is not necessary to distinguish between these multiple components, the subscripts may be omitted in the description. The number of each component may be singular or plural unless otherwise specified.

[0016] First Embodiment First, a water electrolysis system according to a first embodiment of the present invention will be described with reference to FIGS. The water electrolysis system according to this embodiment is a multi-connection water electrolysis system configured by connecting multiple water electrolysis stacks (water electrolysis cells). Water electrolysis stacks used in water electrolysis systems include alkaline, solid polymer, and anion exchange membrane types. While the present invention is applicable to any type of water electrolysis stack, a solid polymer type, which has excellent output responsiveness, is shown here as an example.

[0017] [Outline of water electrolysis system] FIG. 1 is a diagram showing a schematic configuration example of a water electrolysis system according to a first embodiment of the present invention. The water electrolysis system 1 is mainly composed of a water electrolysis stack 10, a DC power supply 11, and auxiliary equipment such as an ultrapure water supply system (not shown), a gas-liquid separator (not shown), a gas tank (not shown), a dehumidifier (not shown), and a water supply pump (not shown).

[0018] The water electrolysis system 1 includes a water electrolysis stack 10 that electrolyzes water. The water electrolysis stack 10 is connected to a DC power supply 11 by a power cable 12. The DC power supply 11 is configured to draw power (e.g., 66 kV) from a power grid 27 via a transformer 26 and a rectifier 25. A self-commutated converter may be used instead of the rectifier 25. The DC power supply 11 uses power from the power grid 27 to supply DC power to the water electrolysis stack 10.

[0019] Although Fig. 1 shows a configuration in which a plurality of water electrolysis stacks 10 are connected in series to a DC power source 11, the water electrolysis stacks 10 may be connected singly, in parallel, or in a series-parallel configuration. In the figure, water electrolysis stacks 10-1, 10-2, ..., 10-n are arranged as the water electrolysis stack 10. When there is no need to distinguish between the water electrolysis stacks 10-1, 10-2, ..., 10-n, they will simply be referred to as "water electrolysis stack 10."

[0020] The water electrolysis stack 10 has a structure in which, for example, multiple thin components (water electrolysis cells) that electrolyze water to produce hydrogen and oxygen are stacked. The water electrolysis stack 10 is made by stacking water electrolysis cells (not shown) each including a proton-permeable membrane, and is a device that produces hydrogen and oxygen using water as a raw material. An example of a water electrolysis stack is a polymer electrolyte membrane (PEM)-type water electrolysis stack.

[0021] Ultrapure water is supplied to the water electrolysis stack 10 from an ultrapure water supply facility (not shown) through a pure water line 13. Oxygen gas and hydrogen gas generated by electrolysis in the water electrolysis stack 10 flow through an oxygen line 14 and a hydrogen line 15, respectively, and are supplied to a gas tank (not shown) or a supply destination (not shown) via a gas-liquid separator (not shown) and a dehumidifier (not shown) provided in each line. In this specification, the pure water line 13, oxygen line 14, and hydrogen line 15 will be simply referred to as "lines" unless they are to be particularly distinguished from one another.

[0022] When the number of water electrolysis cells (not shown) in the water electrolysis stack 10 is increased or when the water electrolysis stacks 10 are connected in series as shown in FIG. 1 , the voltage applied by the DC power supply 11 increases, and the water electrolysis stack 10 is at a high potential. In this case, the maximum voltage applied to the water electrolysis stack 10 is calculated as (number of cells in the water electrolysis stack) x (cell voltage). The voltage of a water electrolysis cell is dependent on the current, temperature, etc., and therefore varies depending on the current flowing through it and the operating temperature. The voltages applied to the water electrolysis stacks 10-1, 10-2, ..., 10-n are measured by voltmeters 18-1, 18-2, ..., 18-n connected to each of the water electrolysis stacks. When the voltmeters 18-1, 18-2, ..., 18-n are not to be distinguished from one another, they will simply be referred to as "voltmeter 18."

[0023] Generally, SUS (Steel Use Stainless Steel) is used for the piping of the pure water line 13, oxygen line 14, and hydrogen line 15 from the viewpoints of preventing leakage of ultrapure water and robustness. However, if the water electrolysis stack 10 is at a high potential, and metal piping is directly connected to the water electrolysis stack 10, there is a risk of electrical conduction between the piping and excessive leakage current. In addition, there is a risk of electric shock when workers touch auxiliary equipment such as an ultrapure water supply system (not shown) or a gas-liquid separator (not shown).

[0024] Therefore, it is necessary to ensure electrical insulation between the water electrolysis stack 10 and the pure water line 13, oxygen line 14, and hydrogen line 15, and therefore insulated piping 16 is required. In FIG. 1 , the insulated piping 16 includes an insulated piping 16-kw for the pure water line 13, an insulated piping 16-ko for the oxygen line 14, and an insulated piping 16-kh for the hydrogen line 15. "k" corresponds to "k" (k = 1 to n) in the water electrolysis stack 10-k. Furthermore, since insulation between the water electrolysis stack 10 and the ground is also required, insulators In1 and In2 (examples of insulators) are provided between the water electrolysis stack 10 and the ground to ensure electrical insulation. The pure water line 13 and the oxygen line 14 may be made of resin as long as they satisfy physical specifications. In this case, the present invention applies only to the piping of the hydrogen line 15.

[0025] To describe the water electrolysis system 1 more specifically, an insulating pipe 16-1w is arranged on the pure water supply side of the pure water line 13 connected to the water electrolysis stack 10-1, an insulating pipe 16-1o is arranged on the oxygen output side of the oxygen line 14, and an insulating pipe 16-1h is arranged on the hydrogen output side of the hydrogen line 15. An insulating pipe 16-2w is arranged on the pure water supply side of the pure water line 13 connected to the water electrolysis stack 10-2, an insulating pipe 16-2o is arranged on the oxygen output side of the oxygen line 14, and an insulating pipe 16-2h is arranged on the hydrogen output side of the hydrogen line 15. In addition, an insulating pipe 16-nw is arranged on the pure water supply side of the pure water line 13 connected to the water electrolysis stack 10-n, an insulating pipe 16-no is arranged on the oxygen output side of the oxygen line 14, and an insulating pipe 16-nh is arranged on the hydrogen output side of the hydrogen line 15. When there is no need to distinguish between the insulating pipe 16-kw of the pure water line 13, the insulating pipe 16-ko of the oxygen line 14, and the insulating pipe 16-kh of the hydrogen line 15, they will simply be referred to as "insulating pipes 16."

[0026] Even if insulating piping 16 is inserted between the water electrolysis stack 10, which is at a high potential, and the piping at ground potential, a leakage current will flow that corresponds to the volume resistivity of the fluid flowing inside the insulating piping 16 and the potential difference between the water electrolysis stack 10 and the piping at ground potential. That is, if the volume resistivity of the fluid is ρ, the potential difference between the water electrolysis stack 10 and the piping at ground potential is V, the length of the insulating piping 16 is L, and the radius of the piping is r, when the insulating piping 16 is filled with a specific fluid, a leakage current I expressed by equation (1) will flow.

[0027]

number

[0028] In the case of the insulating pipe 16 provided on the oxygen line 14 or the hydrogen line 15, pure water and oxygen, or pure water and hydrogen, are mixed in the insulating pipe 16. Generally, pure water has a lower volume resistivity than gas. Therefore, in this case, a leakage current roughly proportional to the volume resistivity of the pure water in the insulating pipe 16 flows.

[0029] In the case of the insulating pipes 16 installed in the pure water line 13, oxygen line 14, and hydrogen line 15, ultrapure water, ultrapure water and oxygen, and ultrapure water and hydrogen are mixed in each insulating pipe 16. Generally, water has a lower volume resistivity than gas. Therefore, in this case, a leakage current roughly proportional to the volume resistivity of the ultrapure water in the insulating pipes 16 flows.

[0030] The leakage current flowing through the insulating pipe 16 causes electrolytic corrosion in the metal housing of the water electrolysis stack 10 and the metal pipe 30, resulting in the elution of metal ions. When the eluted metal ions flow into the water electrolysis stack 10, they not only cause deterioration of the water electrolysis stack 10 but also increase the conductivity of the ultrapure water due to the metal ions. Furthermore, when metal ions are precipitated in the insulating pipe 16, this leads to a deterioration in the insulation characteristics.

[0031] Typically, a large amount of ultrapure water circulates through the pure water line 13 and the oxygen line 14, so even if metal ions leach out, they are diluted to a very low concentration. Therefore, an increase in the conductivity of the ultrapure water and metal ion precipitation are unlikely to occur. On the other hand, ultrapure water is generally not supplied to the hydrogen line 15. In the water electrolysis stack 10, a small amount of water seeps from the oxygen gas system side through a diaphragm or the like into the hydrogen gas system side, gradually accumulating in the hydrogen line 15 and then being discharged outside the water electrolysis stack 10. Therefore, the concentration of metal ions eluted by electrolytic corrosion in the water electrolysis stack 10 is higher in the hydrogen line 15 than in the pure water line 13 and the oxygen line 14. Therefore, the increase in the conductivity of the ultrapure water and the precipitation of metal ions are accelerated in the hydrogen line 15. Furthermore, even small amounts of cations contained in the ultrapure water are concentrated in the hydrogen line 15 by ionic conduction during water electrolysis, resulting in a high cation concentration in the hydrogen line 15.

[0032] These effects may cause a deterioration in the insulating properties of the insulating pipe 16 of the hydrogen line 15, and if a breakdown occurs, the high-potential water electrolysis stack 10 may be grounded, making it difficult to continue operating the water electrolysis system 1.

[0033] Therefore, the present invention employs a configuration in which, during operation of the water electrolysis system, water is supplied to a portion of the hydrogen line upstream of the insulating piping, where hydrogen gas and excess water are mixed in the water electrolysis stack or the hydrogen line.

[0034] As a specific configuration, in this embodiment, a portion of the ultrapure water in the pure water line 13 is supplied to a portion of the hydrogen line 15 between the water electrolysis stack 10 and the insulating pipe 16 in the metal pipe 30, thereby diluting the water stagnating in the hydrogen line 15 with the ultrapure water in the pure water line 13. In other words, the ultrapure water is supplied to the hydrogen line 15 upstream of the insulating pipe 16. The amount (flow rate) of ultrapure water to be supplied to the hydrogen line 15 is calculated and set in advance. Basically, ultrapure water is supplied to each hydrogen line 15 while the water electrolysis system 1 is in operation. Although the amount of ultrapure water supplied has been described as being set in advance, the amount of ultrapure water supplied may be increased as the leakage current increases.

[0035] 1, ultrapure water is supplied from the pure water line 13 to between the water electrolysis stack 10-1 on the metal pipe 30 of the hydrogen line 15 and the insulating pipe 16-1h via a valve 40-1 such as a check valve and an insulating pipe 41-1. Similarly, ultrapure water is supplied from the pure water line 13 to between the water electrolysis stack 10-2 on the metal pipe 30 of the hydrogen line 15 and the insulating pipe 16-2h via a valve 40-2 and an insulating pipe 41-2. Furthermore, ultrapure water is supplied from the pure water line 13 to between the water electrolysis stack 10-n on the metal pipe 30 of the hydrogen line 15 and the insulating pipe 16-nh via a valve 40-n and an insulating pipe 41-n.

[0036] When there is no need to distinguish between valves 40-1, 40-2, and 40-n, they will simply be referred to as "valves 40." The opening and closing operations of each valve 40 are controlled by a system control unit 80, and the amount of ultrapure water supplied to each hydrogen line 15 is adjusted. When there is no need to distinguish between insulating pipes 41-1, 41-2, and 41-n, they will simply be referred to as "insulating pipes 41." The insulating pipes 41 can have the same structure as the insulating pipes 16.

[0037] Supplying ultrapure water to the hydrogen line 15 in this manner reduces the concentrations of metal ions and cations in the water accumulating in the hydrogen line 15, thereby suppressing an increase in the conductivity of the ultrapure water in the piping and metal ion deposition. Therefore, even when the operating voltage of the water electrolysis stack 10 increases, it is possible to prevent a decrease in the electrical insulation of the insulating piping 16 that electrically insulates the water electrolysis stack 10 from the piping. As a result, it is possible to ensure the insulation of the electrical insulation mechanism in the water electrolysis system for a long period of time and prevent the entire system from shutting down due to insulation breakdown.

[0038] A valve (not shown) may be provided on each of the insulating pipes 16-1w to 16-nw on the opposite side from the water electrolysis stacks 10-1 to 10-n. The valves (not shown) can adjust the amount of ultrapure water supplied to the water electrolysis stacks 10-1 to 10-n through the insulating pipes 16-1w to 16-nw. Alternatively, the pure water line 13 may have only one valve for adjusting the amount of ultrapure water supplied.

[0039] In this embodiment, the leakage current flowing through the insulating pipes 16 of each line is measured to monitor the deterioration state of the insulation structure, including the insulating pipes 16. To measure the leakage current, an ammeter 20 for measuring the leakage current is provided on the opposite side of the insulating pipes 16 provided near the water electrolysis stack 10 from the water electrolysis stack 10. In FIG. 1 , the ammeters 20 include an ammeter 20w provided on the pure water line 13, an ammeter 20o provided on the oxygen line 14, and an ammeter 20h provided on the hydrogen line 15. The ammeter 20w measures the leakage current flowing through the insulating pipe 16 of the pure water line 13 connected to the water electrolysis stack 10. The ammeter 20o measures the leakage current flowing through the insulating pipe 16 of the oxygen line 14 connected to the water electrolysis stack 10. The ammeter 20h measures the leakage current flowing through the insulating pipe 16 of the hydrogen line 15 connected to the water electrolysis stack 10. For example, these ammeters may be configured to measure the current value based on the result of measuring the potential difference across a shunt resistor.

[0040] To accurately measure the leakage current flowing through the insulating pipes 16, insulating pipes 17aw, 17ao, and 17ah are provided on the opposite side of the insulating pipes 16 from the water electrolysis stack 10 in each line. Preferably, the leakage current is measured between each insulating pipe 16 and the insulating pipes 17aw, 17ao, and 17ah using ammeters 20 connected to leakage current measurement sections 24w, 24o, and 24h. The leakage current measurement sections 24w, 24o, and 24h are parts of the metal pipes 30 constituting each line, and are the sections where the leakage current of each line is to be measured (for example, the current collector 100, which will be described later). When the insulating pipes 17aw, 17ao, and 17ah are not to be distinguished from one another, they are simply referred to as "insulating pipes 17a."

[0041] 1, an insulating pipe 17aw is provided at leakage current measurement location 24w of the pure water line 13. Furthermore, an insulating pipe 17ao is provided at leakage current measurement location 24o of the oxygen line 14, and an insulating pipe 17ah is provided at leakage current measurement location 24h of the hydrogen line 15. By providing the insulating pipes 17aw, 17ao, and 17ah, safety during maintenance can be ensured, and the location of leakage current flow in each line can be determined from the positional relationship with the insulating pipe 16.

[0042] Here, the length of the insulating pipe 17a is selected so that the internal resistance of the ammeter 20 for measuring the leakage current is sufficiently smaller than the volume resistance of the fluid flowing through the insulating pipe 17a.

[0043] The leakage current value measured by the leakage current measuring ammeter 20 is then transmitted to the system control unit 80 via the signal line 21 shown by the dashed line, and is compared with a preset leakage current threshold value in the system control unit 80. In this embodiment, if a leakage current exceeding the threshold value is detected, the output of the DC power supply 11 is reduced or stopped via the system control unit 80, and the insulating pipe 16 is maintained before insulation breakdown occurs. Note that the signal line 21 may be wired or wireless.

[0044] The system control unit 80 transmits information such as the leakage current value and the comparison result between the leakage current value and a threshold value via the data communication unit 90 to an external device (not shown) such as a monitoring center.

[0045] [Hardware configuration of the water electrolysis system control system] Next, the hardware configuration of the control system of the water electrolysis system 1 will be described with reference to Fig. 2. Here, the hardware configuration of the computer that functions as the system control unit 80 (see Fig. 1) will be described.

[0046] FIG. 2 is a diagram illustrating an example of a hardware configuration of a computer. In the illustrated computer 50, each block may be selected according to the function and purpose of each device. The computer 50 may be, for example, a personal computer or a microcontroller.

[0047] The computer 50 includes a CPU (Central Processing Unit) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a non-volatile storage 56, and a communication interface 57. The components within the computer 50 are connected via a system bus so that they can send and receive data to and from each other.

[0048] The CPU 51, ROM 52, RAM 53, and non-volatile storage 56 constitute a system control unit 80. The system control unit 80 is used as an example of a computer that controls the operation of each unit of the water electrolysis system 1. The CPU 51 reads out a software program that realizes the functions of the system control unit 80 from the ROM 52, and loads the program into the RAM 53 for execution.

[0049] The ROM 52 is used as an example of a non-volatile memory (recording medium). The ROM 52 stores an OS (Operating System), various parameters, programs for operating each device, and the like. The RAM 53 is used as an example of a volatile memory. Variables, parameters, and the like generated during the arithmetic processing of the CPU 51 are temporarily written into the RAM 53. Instead of the CPU 51, another processor such as an MPU (Micro Processing Unit) may be used as the arithmetic processing device.

[0050] The nonvolatile storage 56 is an example of a recording medium, and is capable of storing data used by a program, data obtained by executing a program, and the like. For example, the nonvolatile storage 56 stores information related to the operation and measurements of the water electrolysis system 1. The nonvolatile storage 56 may also store an OS or a program executed by the CPU 51. Examples of the nonvolatile storage 56 include a hard disk drive (HDD), a solid state drive (SSD), an optical (and magnetic) disk, and a semiconductor memory card. The program may be provided via a wired or wireless transmission medium, such as a local area network (LAN), the Internet, or digital satellite broadcasting.

[0051] The communication interface 57 may be, for example, a network interface card (NIC). The communication interface 57 is configured to be able to transmit and receive various data to and from an external device via a communication network such as a LAN or the Internet to which a terminal is connected, or via a dedicated line. The communication means may be either wireless communication such as Wi-Fi (registered trademark) or LTE (Long Term Evolution) (registered trademark), or wired communication. The data communication unit 90 is realized using the communication interface 57.

[0052] A display device 54 and an input device 55, shown by dashed lines, may be connected to the computer 50. The display device 54 is a monitor such as a liquid crystal display, and displays a GUI screen, the results of processing performed by the CPU 51, etc. The input device 55 generates an input signal in response to an operation by an operator or the like, and outputs the signal to the CPU 51. The input device 55 may be, for example, a mouse or a keyboard, and the operator or the like can operate the input device 55 to input information and instructions. The display device 54 and the input device 55 may be integrated into a touch panel.

[0053] [Configuration of insulated piping] The configuration of the insulating pipe 16 used in the water electrolysis system 1 according to this embodiment will now be described with reference to FIGS. As the insulating pipe 16, in addition to ceramic pipe, resin pipe using polyethylene, vinyl chloride, fluorine-based, ethylene vinyl alcohol copolymer, glass fiber reinforced plastic, etc. may be considered.

[0054] (ceramic insulated piping) FIG. 3 is a diagram showing an example of the configuration of the ceramic insulating pipe 16. As shown in FIG. In this example, ceramic tubes 60 are arranged as insulating pipes 16 to ensure electrical insulation between the metal pipes 30. To simplify the leakage current measurement location 24 shown in FIG. 1, a current collecting unit 100 made of a conductor such as metal may be provided between the ceramic tubes 60. Connecting the current collecting unit 100 to a ground wire enables the leakage current flowing through the insulating pipes 16 to be measured with a simple structure. This allows the length of the metal pipes 30 of each line connected to the water electrolysis stack 10 to be shortened. For example, by using the current collecting unit 100 as the leakage current measurement location 24 of the metal pipe 30 (see FIG. 1), the voltage between the current collecting unit 100 and ground can be measured, and the value of the current (leakage current) flowing through the current collecting unit 100 can be calculated from the measured voltage and the resistance of the current collecting unit 100.

[0055] (Resin insulating piping) FIG. 4 is a diagram showing an example of the configuration of the insulating pipe 16 made of resin. When resin is selected as the insulating material, a typical structure is one in which a packing (a sealing member such as an O-ring) is sandwiched between a flange formed at the end of the metal pipe 30 and a flange provided at the end of the resin pipe, and the two are tightened with fastening bolts to form a seal. As with the ceramic insulating pipe, a metal current collecting part 100 may be provided in the middle of the resin pipe.

[0056] 4, a configuration is adopted in which resin pipes 61 and 62 are arranged between metal pipes 30 as insulating pipes 16. A current collecting unit 100 is arranged between resin pipes 61 and 62. More specifically, a packing 32 (sealing member) is sandwiched between a flange 31R of metal pipe 30 and a flange 61L provided on resin pipe 61, and fastened with fastening bolts 33. Further, a packing 32 is sandwiched between flange 31L of metal pipe 30 and flange 62R provided on resin pipe 62, and fastened with fastening bolts 33. Furthermore, a packing 32 is sandwiched between flange 61R of resin pipe 61 and current collecting unit 100, and between flange 62L of resin pipe 62 and current collecting unit 100, and fastened with fastening bolts 33.

[0057] The joints connecting the metal pipe 30 and the resin pipes 61, 62 are not limited to flange structures and may be mechanical joints or other joints that prevent leakage of the flowing fluid. An example of a mechanical joint is a means that uses a sealing member (packing) and a nut. Mechanical joints are preferably used for pipes with a diameter of 1 inch or less.

[0058] The configuration of the insulating pipe 16 has been described, but the insulating pipe 17a can also have the same configuration as the insulating pipe 16 except for the current collecting part 100. However, the current collecting part 100 may be disposed in the insulating pipe 17a and the insulating pipe 43 shown in Fig. 6, which will be described later.

[0059] [Changes in leakage current over time] 5 is a graph showing an example of changes over time in the leakage current flowing through the insulating pipes 16 of the water electrolysis system 1. In the graph, the horizontal axis represents the operating time of the water electrolysis stack 10, and the vertical axis represents the leakage current flowing through the insulating pipes 16.

[0060] As described above, when the water electrolysis stack 10 is operated, leakage current flows through the insulating piping 16, causing electrolytic corrosion of the metal piping. Metal ions eluted by electrolytic corrosion increase the conductivity of the ultrapure water, resulting in a larger leakage current. In particular, the flow rate of ultrapure water in the hydrogen line 15 is lower than that in the oxygen line 14. Therefore, in a structure in which ultrapure water accumulates in the insulating piping 16 of the hydrogen line 15, the metal ion concentration in the ultrapure water does not decrease, and the leakage current gradually increases. As the operation time increases, the leakage current increases as shown in Figure 5, and eventually the leakage current value exceeds the output suppression threshold preset in the system control unit 80.

[0061] When the leakage current value exceeds the output suppression threshold in this manner, the system control unit 80 suppresses the output of the DC power supply 11. This reduces the voltage applied to the water electrolysis stack 10, thereby reducing the amount of leakage current. As a result, it is possible to prevent dielectric breakdown in the insulating pipes 16 or lengthen the time until dielectric breakdown occurs. In addition, during this time, it is possible to consider and perform appropriate maintenance methods. In this way, in this embodiment, the soundness (insulating properties) of the insulation mechanism of the water electrolysis system can be evaluated, and operation of the water electrolysis system can be controlled according to the degree of deterioration of the insulating properties.

[0062] This output suppression threshold may be the same as a threshold (for example, a threshold at the time of initial determination) that is compared with the measured value of the leakage current in step S2 shown in Fig. 8 (to be described later). Furthermore, the output control of the DC power supply 11 according to the leakage current value by the system control unit 80 in this embodiment may be applied to other embodiments.

[0063] At this time, the system control unit 80 displays the measurement value of the leakage current flowing through the insulating pipe 16, measured by the ammeter 20 or the like, on the display device 54. Then, the system control unit 80 controls the amount of DC power supplied from the DC power supply 11 to the water electrolysis stack 10 based on the measurement value of the leakage current.

[0064] <Second embodiment> Next, a second embodiment of a water electrolysis system according to the present invention will be described with reference to Fig. 6. The water electrolysis system according to the second embodiment is a modified example of the first embodiment (see Fig. 1). In the water electrolysis system according to the second embodiment, parts that are the same as or similar to those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0065] [Outline of water electrolysis system] FIG. 6 is a diagram showing a schematic configuration example of a water electrolysis system according to a second embodiment of the present invention. In the first embodiment, a portion of the ultrapure water in the pure water line 13 is supplied to the hydrogen line 15 between the water electrolysis stack 10 and the insulating piping 16, and the water accumulated in the hydrogen line 15 is diluted with the ultrapure water in the pure water line 13. This reduces the concentrations of metal ions and cations in the water accumulated in the hydrogen line 15, thereby suppressing an increase in the conductivity of the ultrapure water and metal ion precipitation. In this case, the water accumulated on the hydrogen gas system side of the water electrolysis stack 10 is not diluted, so the concentrations of metal ions and cations in the accumulated water cannot be reduced. Typically, the ultrapure water in the pure water line 13 is configured to be supplied to the oxygen electrode sides of the water electrolysis stacks 10-1 to 10-n through piping.

[0066] Therefore, in this embodiment, a portion of the ultrapure water in the pure water line 13 is directly supplied to the hydrogen gas system side of the water electrolysis stack 10, thereby diluting the water accumulating on the hydrogen gas system side of the water electrolysis stack 10 with the ultrapure water in the pure water line 13. This reduces the concentrations of metal ions and cations in the water accumulating on the hydrogen gas system side of the water electrolysis stack 10. This makes it possible to suppress an increase in the conductivity and metal ion deposition in the water accumulating on the hydrogen gas system side and in the hydrogen line 15 of the water electrolysis stack 10.

[0067] Specifically, a metal pipe 30 is provided in parallel with the insulating pipe 16-1w on the pure water line 13, and an insulating pipe 43-1 and a valve 42-1 are arranged on the metal pipe 30. The valve 42-1 is arranged on the opposite side of the insulating pipe 43-1 from the water electrolysis stack 10-1. Furthermore, a metal pipe 30 is provided in parallel with the insulating pipe 16-2w on the pure water line 13, and an insulating pipe 43-2 and a valve 42-2 are arranged on the metal pipe 30. The valve 42-2 is arranged on the opposite side of the insulating pipe 43-2 from the water electrolysis stack 10-2. Similarly, a metal pipe 30 is provided in parallel with the insulating pipe 16-nw on the pure water line 13, and an insulating pipe 43-n and a valve 42-n are arranged on the metal pipe 30.

[0068] When there is no need to distinguish between the insulating pipes 43-1, 43-2, and 43-n, they will simply be referred to as "insulating pipes 43." The insulating pipes 43 can have the same structure as the insulating pipes 16. When there is no need to distinguish between the valves 42-1, 42-2, and 42-n, they will simply be referred to as "valves 42."

[0069] The metal pipe 30 of the pure water line 13, which is provided with the insulating pipe 43 and the valve 42, is connected to the vicinity of the connection portion of the water electrolysis stack 10 with the hydrogen line 15, which is provided with the insulating pipe 16. This allows ultrapure water to be supplied to the connection portion of each water electrolysis stack 10 with the hydrogen line 15 (the portion where water seeping from the oxygen gas system side accumulates). This makes it possible to dilute the water remaining on the hydrogen gas supply side of each water electrolysis stack 10. The opening and closing operations of each valve 42 are controlled by the system control unit 80, and the amount of ultrapure water supplied is adjusted.

[0070] By adopting the above-described configuration, the present embodiment, like the first embodiment, can make it difficult for the electrical insulation of the insulating piping 16 that electrically insulates the water electrolysis stack 10 from the piping of the hydrogen line 15 to deteriorate, even when the operating voltage of the water electrolysis stack 10 is increased. As a result, it is possible to prevent the entire system from shutting down due to insulation breakdown. In this way, the present embodiment can evaluate the soundness (insulation) of the insulation mechanism of the water electrolysis system and control the operation of the water electrolysis system in accordance with the degree of deterioration of the insulation.

[0071] As in the first embodiment, a valve (not shown) may be provided on each of the insulating pipes 16-1w to 16-nw on the side opposite to the water electrolysis stacks 10-1 to 10-n. Alternatively, the pure water line 13 may have only one valve for adjusting the supply amount of ultrapure water.

[0072] <Third embodiment> Next, a third embodiment of the water electrolysis system according to the present invention will be described with reference to FIGS. 1, 7 and 8. FIG.

[0073] The configuration of the water electrolysis system according to the third embodiment is basically the same as that of the water electrolysis system 1 according to the first embodiment (see FIG. 1). In the water electrolysis system according to the third embodiment, parts that are the same as or similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. However, the configuration of this embodiment is not limited to the first embodiment, and can also be applied to the second embodiment (see FIG. 6).

[0074] [Internal structure of the system control unit] FIG. 7 is a block diagram showing an example of the internal configuration of the system control unit 80 of the water electrolysis system according to this embodiment. The system control unit 80 (an example of a control unit) includes a calculation unit 81 and a storage unit . The calculation unit 81 includes an operation control unit 81a, a threshold setting unit 81b, and an operation continuation determination unit 81c. A control program 82p and a control data table 82d are stored in the storage unit 82. The storage unit 82 is configured using the ROM 52 or the non-volatile storage 56 (see FIG. 2). For example, the control program 82p and the control data table 82d of the storage unit 82 are provided from a recording medium 85 that is detachable from the system control unit 80 (computer 50 in FIG. 2). The recording medium 85 may be a USB (Universal Serial Bus) memory, a disk medium, or the like.

[0075] The control program 82p is a program for controlling the operation of the water electrolysis system. The control data table 82d is a lookup table that associates leakage current thresholds with control details of the water electrolysis system for each threshold. The control details include, for example, the amount of ultrapure water to be supplied, resetting of the threshold, and shutdown of operation. The control data table 82d may also include control data such as the correspondence between the required amount of hydrogen generation and the output of the DC power supply 11.

[0076] The functions of each block of the calculation unit 81 are realized by the CPU 51 (see FIG. 2) executing a control program 82p stored in the storage unit 82. In the process of executing the control program 82p, necessary control data is read out as appropriate from the control data table 82d.

[0077] Based on instructions from an operator or a control program, the operation control unit 81a sets the amount of ultrapure water to be supplied to the hydrogen line 15, etc., and controls the output of the DC power supply 11. Furthermore, the operation control unit 81a controls the operation or stop of the water electrolysis system based on the determination result of the operation continuation determination unit 81c.

[0078] The threshold setting unit 81b resets the threshold for the amount of leakage current based on the determination result of the operation continuation determination unit 81c. Note that the threshold setting unit 81b may set the threshold for the amount of leakage current based on input from an operator, engineer, or the like, or based on a control program, or may set the relationship between the threshold and the amount of ultrapure water supplied to the hydrogen line 15, etc.

[0079] The operation continuation determination unit 81c determines whether to continue operation of the water electrolysis system under the current operating conditions and notifies the operation control unit 81a of the determination result. Then, based on the determination result of the operation continuation determination unit 81c, the operation control unit 81a adjusts the amount of ultrapure water supplied to the hydrogen line 15 or stops the operation of the water electrolysis system.

[0080] [Control processing of water electrolysis system] Next, the control process of the water electrolysis system 1 according to this embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing an example of the control process procedure performed by the system controller 80 of the water electrolysis system 1 according to this embodiment.

[0081] The system control unit 80 measures and monitors the value of the leakage current flowing through the insulating pipe 16 shown in FIG. 1 and adjusts the amount of ultrapure water supplied from the pure water line 13 to the hydrogen line 15 between the water electrolysis stack 10 and the insulating pipe 16 according to the amount of leakage current. With this configuration, the water retained in the hydrogen line 15 can be diluted with ultrapure water at a flow rate corresponding to the concentrations of metal ions and cations in the retained water. This makes it possible to suppress an increase in the conductivity of the ultrapure water and the deposition of metal ions while controlling the concentrations of metal ions and cations in the retained water.

[0082] 8, after the operation of the water electrolysis system 1 is started, the operation control unit 81a obtains the amount of leakage current in the insulating pipe 16 using the leakage current measurement ammeter 20 (step S1). The amount of leakage current measured by the leakage current measurement ammeter 20 is transmitted to the system control unit 80 via the signal line 21. Here, it is assumed that after the operation of the water electrolysis system 1 is started, ultrapure water is supplied to the hydrogen line 15 via the valve 40 and the insulating pipe 41 (see FIG. 1).

[0083] Next, after acquiring the leakage current of the insulating pipe 16, the operation control unit 81a compares the measurement data of the leakage current amount with a threshold value (corresponding to the first threshold value in the first measurement) preset in the storage unit 82 (step S2). If the leakage current amount is equal to or less than the threshold value (NO in step S2), the operation control unit 81a continues measuring the leakage current amount in step S1. Because the leakage current of the insulating pipe 16 is expected to increase due to a decrease in insulation caused by electrolytic corrosion, as described above, measurement may be performed at intervals of several tens of minutes or several hours.

[0084] On the other hand, if the amount of leakage current is greater than the threshold (YES in step S2), the operation control unit 81a sets the supply amount of ultrapure water corresponding to the amount of leakage current from the control data table 82d (step S3). Then, based on the set supply amount of ultrapure water, the operation control unit 81a adjusts the amount of ultrapure water supplied from the pure water line 13 to between the water electrolysis stack 10 and the insulating piping 16 on the hydrogen line 15. The operation control unit 81a adjusts the aperture of each valve 40 based on the changed supply amount. As described above, in this embodiment, the operation control unit 81a adjusts the amount of ultrapure water to be supplied based on the value of the leakage current flowing through the insulating piping 16 of the hydrogen line 15 measured by the current measurement unit (ammeter 20).

[0085] In step S3, the operation control unit 81a may set the changed supply rate (second supply rate) by adding a preset supply rate (step width) to the current supply rate (first supply rate).

[0086] Next, the operation continuation determination unit 81c determines whether to stop the operation of the water electrolysis system (step S4). In step S4, the operation continuation determination unit 81c determines whether to stop the operation based on whether the amount of leakage current has reached a threshold for maintaining the insulating pipes 16. If the amount of leakage current is greater than the threshold, it can be said that the electrical insulation of any of the insulating pipes 16 has deteriorated to a certain degree.

[0087] If the operation continuation determination unit 81c determines to continue operation of the water electrolysis system (NO determination in step S4), the operator operates the input device 55 (see FIG. 2) to reset the threshold value (second threshold value) and stores it in the memory unit 82 (step S5). In step S5, the threshold setting unit 81b (see FIG. 7) may automatically reset the threshold (second threshold) by adding a preset current amount (step width) to the current threshold (first threshold). After the threshold is reset, the system control unit 80 returns to step S1 of measuring the leakage current. Then, in step S2, the reset threshold (second threshold) and the leakage current amount are compared.

[0088] The first threshold value is a leakage current value that takes into consideration a predetermined tolerance for dielectric breakdown of the insulating pipe 16. For example, if the leakage current value that is expected to cause dielectric breakdown is 100% and the tolerance is 30%, the first threshold value is set to 70% of that leakage current value.

[0089] The second threshold is a leakage current value based on a smaller margin (e.g., 25%) than the first threshold. For example, if the leakage current value at which dielectric breakdown is expected to occur is 100% and the margin is 25%, the second threshold is set to 75% of that leakage current value.

[0090] The second threshold may be set to a current value that requires the water electrolysis system (or a specific water electrolysis stack) to be immediately stopped. In this case, if the leakage current amount is determined to be greater than the threshold in the next determination process of step S2, an alert is output to the display device 54, and the operator (or the operation control unit 81a) issues a command to immediately stop operation. At least the first threshold is determined in advance by experiment or simulation and stored in the storage unit 82 or the like. The step size of the threshold may also be set in advance and stored in the storage unit 82 or the like.

[0091] As described above, in this embodiment, a first threshold value is set as the threshold value used for comparison, taking into consideration the tolerance for the value of leakage current that is expected to cause insulation breakdown of the insulating pipe 16, and when the measured value of the leakage current exceeds the first threshold value, a second threshold value is set based on a tolerance smaller than the tolerance of the first value.

[0092] On the other hand, if the operation continuation determination unit 81c determines that the operation of the water electrolysis system should be stopped (YES determination in step S4), the operation continuation determination unit 81c outputs an operation stop command to the operation control unit 81a. As described in the first embodiment, the operation control unit 81a stops the power supply from the DC power supply 11 in accordance with the operation stop command (step S6). If the water electrolysis system is configured so that the operation / stop of each water electrolysis stack can be controlled individually, an operation is performed to disconnect only the water electrolysis stack with a large leakage current from the system. After step S6 is performed, the process ends.

[0093] After shutting down the operation of the water electrolysis system, workers perform maintenance on the system. Since the water electrolysis stack still retains a potential even after shutting down, the potential is monitored using a voltmeter 18 installed in the water electrolysis stack 10 until the potential drops to prevent electric shock. After confirming that the potential of the water electrolysis stack 10 has dropped, maintenance such as replacing or cleaning the insulating piping with reduced insulation is performed.

[0094] <Fourth embodiment> Next, a fourth embodiment of a water electrolysis system according to the present invention will be described with reference to Fig. 1 and Fig. 9. The fourth embodiment is an example in which a maintenance schedule is created by calculating a maintenance timing that reflects a supply amount of ultrapure water that is set corresponding to the amount of leakage current.

[0095] The configuration of the water electrolysis system according to the fourth embodiment is basically the same as that of the first embodiment (see FIG. 1). In the water electrolysis system according to the fourth embodiment, parts that are the same as or similar to those of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. However, the configuration of this embodiment is not limited to the first embodiment, and can also be applied to the second embodiment (see FIG. 6).

[0096] [Control processing of water electrolysis system] Next, the control process of the water electrolysis system 1 according to this embodiment will be described with reference to FIG. 9 is a flowchart showing an example of the control process procedure by the system controller 80 of the water electrolysis system 1 according to this embodiment. This flowchart includes a flow up to determining when to perform maintenance on the insulating pipes 16.

[0097] In FIG. 9, after the operation of the water electrolysis system 1 is started, the operation control unit 81a executes the processes of steps S1 to S3 in the same manner as in the flow of FIG.

[0098] Next, the operation control unit 81a displays the maintenance timing for the insulating pipe 16 on the display device 54 (step S11). In step S11, the operation control unit 81a determines that the amount of leakage current is greater than the threshold (i.e., the electrical insulation of the insulating pipe 16 has deteriorated), and therefore calculates the maintenance timing before the insulation breakdown of the insulating pipe 16 occurs based on the amount of leakage current, and displays (presents) the maintenance timing on the display device 54. For example, from the relationship between the rising curve of leakage current shown in FIG. 5 and the threshold, it is possible to predict the time until the leakage current value reaches a value (not shown) that is expected to cause insulation breakdown in the insulating pipe 16. The maintenance timing needs to be set based on this predicted time (time) so that it occurs before the insulation breakdown of the insulating pipe 16 occurs.

[0099] Furthermore, by increasing the amount of ultrapure water supplied to the hydrogen line 15 etc. in accordance with the amount of leakage current, the concentration of metal ions and cations in the water accumulating in the hydrogen line 15 can be reduced, and the maintenance interval for the insulating pipe 16 can be expected to be extended. In this embodiment, the operation control unit 81a diagnoses the maintenance timing taking into account the impact of changes in the amount of ultrapure water supplied to the hydrogen line 15 etc., and this can lead to subsequent maintenance planning. In particular, it becomes possible to diagnose the maintenance timing for the insulating pipe 16 provided in the hydrogen line 15, taking into account the amount of ultrapure water supplied to the hydrogen line 15 etc.

[0100] Next, the operator checks the maintenance schedule displayed on the display device 54, formulates a maintenance plan (step S12), and determines whether to stop operation of the water electrolysis system (step S4). For example, if the displayed maintenance schedule is still far in the future and the measured leakage current value does not indicate that insulation breakdown of the insulated piping 16 will occur in the near future, the operator determines to continue operation; otherwise, the operator determines to stop operation. Note that if the determination in step S2 is NO, the maintenance schedule for the insulated piping 16 is the standard maintenance schedule initially set.

[0101] In this embodiment, in steps S12 and S4, an operator formulates a maintenance plan and determines whether to shut down the plant, but these processes may be executed by the system control unit 80. For example, step S12 is executed by the operation control unit 81a, and step S4 is executed by the operation continuation determination unit 81c.

[0102] If it is determined that the operation of the water electrolysis system should be continued (NO determination in step S4), the operator operates the input device 55 (see FIG. 2) to reset the threshold value (second threshold value) and store it in the storage unit 82 (step S5). After the processing in step S5, the process returns to step S1.

[0103] On the other hand, if it is determined that the operation of the water electrolysis system should be stopped (YES in step S4), the operation continuation determination unit 81c outputs an operation stop command to the operation control unit 81a. The operation control unit 81a stops the power supply from the DC power supply 11 in accordance with the operation stop command (step S6). Then, after the operation of the water electrolysis system is stopped, an operator performs maintenance on the water electrolysis system.

[0104] With the above configuration, a deterioration in the electrical insulation of the insulating piping, which electrically insulates the water electrolysis stack from the piping of each line, can be detected from the measured leakage current value of the insulating piping, and the deterioration can be displayed to the operator for maintenance. That is, the operator can obtain information related to a maintenance plan for the insulating piping. Then, the operator can formulate a maintenance plan based on the displayed content (maintenance timing) and take the necessary measures (step S5 or S6), thereby preventing the entire water electrolysis system from being shut down due to insulation breakdown.

[0105] As described above, the present invention is not limited to the above-described embodiments, and various other modifications and applications are possible without departing from the spirit of the invention as defined in the claims. For example, the above-described embodiments have been described in detail and specifically to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the components described. Furthermore, it is possible to replace part of the configuration of one embodiment with a component of another embodiment. It is also possible to add a component of another embodiment to the configuration of one embodiment. It is also possible to add, replace, or delete other components from part of the configuration of each embodiment.

[0106] Furthermore, the above-described configurations, functions, processing units, etc. may be partially or entirely realized in hardware, for example, by designing them as integrated circuits, etc. As the hardware, a broad processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used. [Explanation of symbols]

[0107] 1,1A...Water electrolysis system, 10,10-1 to 10-n...Water electrolysis stack, 11...DC power supply, 13...Pure water line, 14...Oxygen line, 15...Hydrogen line, 16,16-1w,16-1o,16-1h,16-2w,16-2o,16-2h,16-nw,16-no,16-nh...Insulated piping, 17aw,17ao,17ah...Insulated piping, 18-1,18-2,18-n...Voltmeter, 19...Ammeter, 20,20w,20o,20h...Ammeter (for measuring leakage current), 24...Leakage current measurement location, 25...Rectifier, 26...Transformer, 27...Power system, 30...Metal piping, 40-1 to 40-n...Valve, 41-1 to 41-n...insulating pipes, 42-1 to 42-n...valves, 43-1 to 43-n...insulating pipes, 50...computer, 51...CPU, 54...display device, 55...input device, 80...system control unit, 81...calculation unit, 81a...operation control unit, 81b...threshold value setting unit, 81c...operation continuation determination unit, 82...storage unit, 82p...control program, 82d...control data table, 90...data communication unit, 100...current collection unit, In1, In2...insulator

Claims

1. one or more water electrolysis stacks that produce hydrogen gas and oxygen gas from water; a water line for supplying water to each water electrolysis stack; an oxygen line for discharging oxygen gas and excess water generated in each water electrolysis stack; A hydrogen line for discharging the hydrogen gas and excess water generated in each water electrolysis stack; insulating piping that electrically insulates the water electrolysis stack from piping for the water line, the oxygen line, and the hydrogen line; a DC power supply that supplies DC power to the water electrolysis stack to drive the water electrolysis stack; A water electrolysis system comprising: During operation of the water electrolysis system, water is supplied to a portion of the hydrogen line upstream of the insulating pipe, where the hydrogen gas and the excess water are mixed in the water electrolysis stack or the hydrogen line. Water electrolysis system.

2. During operation of the water electrolysis system, water is supplied to the hydrogen line piping between the water electrolysis stack and the insulating piping. The water electrolysis system according to claim 1 .

3. During operation of the water electrolysis system, water is supplied to a connection portion of the water electrolysis stack with the hydrogen line. The water electrolysis system according to claim 1 .

4. a current measuring unit that measures a leakage current flowing through the insulating pipe; a control unit, The control unit adjusts the amount of water to be supplied based on the value of the leakage current flowing through the insulating pipe of the hydrogen line measured by the current measurement unit. The water electrolysis system according to any one of claims 1 to 3.

5. The control unit compares the value of the leakage current flowing through the insulating pipe of the hydrogen line measured by the current measurement unit with a leakage current threshold, and sets the amount of water to be supplied based on the comparison result. The water electrolysis system according to claim 4.

6. The control unit increases the amount of water supplied between the water electrolysis stack and the insulating pipe of the hydrogen line as the value of the leakage current increases. The water electrolysis system according to claim 4.

7. The control unit compares the value of the leakage current flowing through the insulating pipe of the hydrogen line measured by the current measurement unit with a leakage current threshold, and diagnoses the maintenance timing of the insulating pipe based on the comparison result. The water electrolysis system according to claim 4.

8. The control unit diagnoses the maintenance timing of the insulating pipe by reflecting a set value of the amount of water to be supplied. The water electrolysis system according to claim 4.

9. a current collecting section made of a conductor for measuring leakage current flowing through the insulating pipe, at least in a part of the insulating pipe of the hydrogen line; The water electrolysis system according to claim 4.

10. one or more water electrolysis stacks that produce hydrogen gas and oxygen gas from water; a water line for supplying water to each water electrolysis stack; an oxygen line for discharging oxygen gas and excess water generated in each water electrolysis stack; A hydrogen line for discharging the hydrogen gas and excess water generated in each water electrolysis stack; insulating piping that electrically insulates the water electrolysis stack from piping for the water line, the oxygen line, and the hydrogen line; a DC power supply that supplies DC power to the water electrolysis stack to drive the water electrolysis stack; a current measuring unit that measures a leakage current flowing through the insulating pipe; A control unit; A method for operating a water electrolysis system comprising: supplying water to a portion of the hydrogen line upstream of the insulating pipe, where the hydrogen gas and the excess water are mixed, in the water electrolysis stack or the hydrogen line, during operation of the water electrolysis system; The control unit adjusts the amount of water to be supplied based on the value of the leakage current flowing through the insulating pipe of the hydrogen line measured by the current measurement unit. How to operate a water electrolysis system.

Images