Water electrolysis system and control method for the water electrolysis system

Abstract

This invention provides a more suitable configuration and control method for a water electrolysis system capable of high-voltage drive. [Solution] The water electrolysis system of the present invention comprises a hydrogen production apparatus having a water electrolysis stack section containing one or more water electrolysis stacks that generate oxygen and hydrogen by an electrolysis reaction; a power supply that supplies DC power to one or more water electrolysis stacks; a pure water supply piping system that supplies pure water; an oxygen outlet piping system that discharges oxygen generated in the water electrolysis stack section to the outside; a hydrogen outlet piping system that discharges hydrogen generated in the water electrolysis stack section to the outside; an insulating section that electrically insulates the hydrogen production apparatus from the ground; a first insulating pipe having electrical insulation properties provided in a part of the pure water supply piping system; a second insulating pipe having electrical insulation properties provided in a part of the oxygen outlet piping system; and a third insulating pipe having electrical insulation properties provided in a part of the hydrogen outlet piping system.

Description

Technical Field

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

Background Art

[0002] In recent years, with the increase in the emission of greenhouse gases such as carbon dioxide, environmental problems such as global warming and energy problems such as the depletion of oil resources have attracted attention. From these problems, hydrogen energy has attracted attention as a clean alternative energy. However, since a large amount of hydrogen is required to replace existing fossil fuels with hydrogen energy, the large-scale expansion of water electrolysis systems has been promoted for the purpose of reducing the cost of hydrogen production.

[0003] By the way, conventionally, as water electrolysis methods, various methods such as solid polymer type water electrolysis method, high-temperature steam electrolysis method, and alkaline type water electrolysis method have been proposed. Among these, the alkaline type water electrolysis method has attracted attention as one of the particularly promising methods because, for example, it has been industrialized for decades or more, the scale of the device can be increased, and it is less expensive than other water electrolysis systems. However, in this method, it is necessary to drive the water electrolysis stack at a large current and low voltage, and the DC power supply for realizing this is for special use, so it is expected that cost reduction will not progress.

[0004] As a method for solving the above cost reduction problem, there is a method of electrically connecting a large number of water electrolysis stacks in series and driving the water electrolysis system at a high voltage. In this method, the number of step-down transformers, rectifiers, etc. required when inputting power from the power grid to a large number of water electrolysis stacks connected in series can be reduced, and large-scale hydrogen production at low cost can be realized. Therefore, conventionally, various technologies have been proposed for a water electrolysis system in which a plurality of water electrolysis stacks are connected in series (see, for example, Patent Document 1). Patent Document 1 discloses an insulating pipe that connects a water electrolysis stack and auxiliary equipment to improve the robustness of the water electrolysis system.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-51868 [Overview of the project] [Problems that the invention aims to solve]

[0006] As mentioned above, various technologies have been proposed for high-voltage-driven water electrolysis systems. Furthermore, in this field, there is a need for further optimization of the configuration and control methods of high-voltage-driven water electrolysis systems.

[0007] This invention has been made in view of the above circumstances, and the object of this invention is to provide a more suitable configuration and control method for a water electrolysis system that can be driven by a high voltage. [Means for solving the problem]

[0008] To solve the above problems, the water electrolysis system of the present invention comprises a hydrogen production apparatus section having a water electrolysis stack section containing one or more water electrolysis stacks that generate oxygen and hydrogen by an electrolysis reaction, and a power supply that supplies DC power to one or more water electrolysis stacks. Furthermore, the water electrolysis system of the present invention comprises a pure water supply piping system that supplies pure water to the hydrogen production apparatus section, an oxygen outlet piping system that discharges oxygen generated in the water electrolysis stack section to the outside, and a hydrogen outlet piping system that discharges hydrogen generated in the water electrolysis stack section to the outside. Furthermore, the water electrolysis system of the present invention comprises an insulating section that electrically insulates the hydrogen production apparatus section from the ground, and a first insulating pipe having electrical insulation properties provided in a part of the pure water supply piping system. In addition, the water electrolysis system of the present invention comprises a second insulating pipe having electrical insulation properties provided in a part of the oxygen outlet piping system, and a third insulating pipe having electrical insulation properties provided in a part of the hydrogen outlet piping system.

[0009] Furthermore, in order to solve the above problems, the control method for the water electrolysis system of the present invention is a control method executed by a control unit of the water electrolysis system of the present invention, which further comprises a control unit that performs operation control and stop control of the hydrogen production apparatus. The control method for the water electrolysis system of the present invention includes the control unit disconnecting the hydrogen production apparatus from the power supply when stopping the hydrogen production apparatus. The control method for the water electrolysis system of the present invention also includes the control unit performing discharge control of the charge accumulated in one or more water electrolysis stacks after disconnecting the hydrogen production apparatus from the power supply. Furthermore, the control method for the water electrolysis system of the present invention includes the control unit setting the hydrogen production apparatus to ground potential after performing the discharge control. [Effects of the Invention]

[0010] According to the present invention with the above configuration, a more suitable configuration and control method can be provided for a water electrolysis system that can be driven by a high voltage. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a water electrolysis system according to the first embodiment of the present invention. [Figure 2] This figure shows the configuration of the insulating frame for a water electrolysis system according to the first embodiment of the present invention. [Figure 3] This is a schematic diagram of a water electrolysis system according to a second embodiment of the present invention. [Figure 4] This is a schematic diagram of a water electrolysis system according to a third embodiment of the present invention. [Figure 5] This is a schematic diagram of a water electrolysis system according to a fourth embodiment of the present invention. [Figure 6] This is a functional block diagram of the system control device for a water electrolysis system according to a fourth embodiment of the present invention. [Figure 7] This is a hardware configuration diagram of a computer device applicable as a system control device for a water electrolysis system according to a fourth embodiment of the present invention. [Figure 8]This flowchart shows the procedure for control processing when a water electrolysis system is shut down according to the fourth embodiment of the present invention. [Modes for carrying out the invention]

[0012] Below, water electrolysis systems and their control methods according to various embodiments of the present invention will be described in detail with reference to the drawings. The water electrolysis systems described in the following embodiments are water electrolysis systems that produce hydrogen by alkaline water electrolysis.

[0013] 1. First Embodiment [Configuration of a water electrolysis system] Figure 1 is a schematic diagram of a water electrolysis system 101 according to a first embodiment of the present invention. For the sake of simplicity, only the components related to the water electrolysis operation and the insulating function of the water electrolysis system 101 are shown here. In Figure 1, electrical wiring connecting the components is shown with solid lines, and piping is shown with dashed and dotted lines. In the schematic diagrams of the water electrolysis system shown in Figures 3 to 5 described later, the meaning of the solid, dashed, and dotted lines connecting the components is the same as in Figure 1.

[0014] As shown in Figure 1, the water electrolysis system 101 comprises a DC power supply 1, a pure water pump 2, multiple hydrogen production units 3, pure water supply piping 4, oxygen outlet piping 5, and hydrogen outlet piping 6.

[0015] In the water electrolysis system 101, each of the multiple hydrogen production units 3 has one water electrolysis stack 10 (water electrolysis stack unit), and as shown in Figure 1, the water electrolysis stacks 10 provided in each hydrogen production unit 3 are electrically connected in series with each other. A DC power supply 1 is electrically connected between the anode (not shown) of the water electrolysis stack 10 provided at one end of the multiple water electrolysis stacks 10 provided in series and the cathode (not shown) of the water electrolysis stack 10 provided at the other end. In addition, each hydrogen production unit 3 is connected to a pure water pump 2 via a pure water supply pipe 4. Furthermore, each hydrogen production unit 3 is connected to an oxygen outlet pipe 5 and a hydrogen outlet pipe 6.

[0016] The DC power supply 1 is a power supply for driving a plurality of water electrolysis stacks 10 connected in series. The DC power supply 1 applies a DC voltage to the plurality of water electrolysis stacks 10 connected in series. At this time, the DC power supply 1 can apply a voltage corresponding to the value obtained by integrating the DC voltage (cell voltage) applied to each water electrolysis stack 10 and the number of water electrolysis stacks 10 connected in series as the maximum voltage to the plurality of water electrolysis stacks 10. Therefore, although the entire water electrolysis system 101 is driven at a high voltage, the voltage applied from the DC power supply 1 is divided for each water electrolysis stack 10, so that each water electrolysis stack 10 can be driven at a low voltage. Note that the DC power supply 1 may be a power supply with a constant output voltage, but since the operating voltage of the water electrolysis system 101 (each water electrolysis stack 10) changes depending on the energization current, operating temperature, etc., it may be composed of a variable voltage power supply.

[0017] The pure water pump 2 supplies the pure water produced by a pure water production device (not shown) to each hydrogen production unit 3 through a pure water supply pipe 4 in order to replenish the water consumed by water electrolysis in each hydrogen production unit 3. The pure water supplied to the water electrolysis system 101 may be, for example, ion-exchanged water or RO (Reverse Osmosis) water.

[0018] Each of the plurality of hydrogen production units 3 produces hydrogen by the alkaline water electrolysis method using the electric power (DC power) supplied from the DC power supply 1. And each hydrogen production unit 3 causes the produced hydrogen to flow out into a hydrogen outflow pipe 6. Also, at this time, each hydrogen production unit 3 causes the oxygen generated by water electrolysis to flow out into an oxygen outflow pipe 5. In the present embodiment, it is assumed that each of the plurality of hydrogen production units 3 has the same configuration, but the present invention is not limited to this, and some or all of the plurality of hydrogen production units 3 may have different configurations. The internal configuration of each hydrogen production unit 3 will be described in detail later.

[0019] The pure water supply pipe 4 discharges the pure water flowing in from the pure water pump 2 to each hydrogen production unit 3, specifically, to the cleaning tower 16 described later. The oxygen outflow pipe 5 discharges the oxygen flowing in from each hydrogen production unit 3 to the outside. Further, although not shown in the figure, the hydrogen outflow pipe 6 is connected to, for example, a hydrogen compressor, a hydrogen storage tank, a hydrogen supply point, etc., and discharges the hydrogen flowing in from each hydrogen production unit 3 to the hydrogen compressor, the hydrogen storage tank, the hydrogen supply point, etc.

[0020] [Configuration of Hydrogen Production Unit] The hydrogen production unit 3 is composed of a hydrogen production device unit including various main devices related to the production of oxygen and hydrogen, a piping unit connected to each main device, and an insulating unit for ensuring electrical insulation of the hydrogen production device unit with respect to the ground. Further, the piping unit of the hydrogen production unit 3 includes a pure water supply piping system for supplying pure water to the hydrogen production device unit and an electrolytic solution supply piping system for supplying an electrolytic solution to the water electrolysis stack 10. Furthermore, the piping unit includes an oxygen outflow piping system for discharging the oxygen generated in the water electrolysis stack 10 to the oxygen outflow pipe 5 and a hydrogen outflow piping system for discharging the hydrogen generated in the water electrolysis stack 10 to the hydrogen outflow pipe 6.

[0021] As shown in FIG. 1, the hydrogen production device unit of the hydrogen production unit 3 includes, as main devices related to the production of oxygen and hydrogen, a water electrolysis stack 10, a liquid feed pump 11, an oxygen gas-liquid separator 12, an oxygen demister 13, a hydrogen gas-liquid separator 14, a hydrogen demister 15, and a cleaning tower 16. The configuration and operation of these main devices will be described in detail later. In the hydrogen production unit 3, a potassium hydroxide aqueous solution (electrolytic solution) with a concentration of 20 to 50% is circulated from the liquid feed pump 11 to the water electrolysis stack 10, and oxygen and hydrogen are generated by an electrolysis reaction in the water electrolysis stack 10. In this embodiment, an example of using a potassium hydroxide aqueous solution as the electrolytic solution is described, but the present invention is not limited thereto, and for example, other alkaline aqueous solutions such as a sodium hydroxide aqueous solution may be used as the electrolytic solution.

[0022] The electrolyte supply piping system of the hydrogen production unit 3 includes, as shown by the dashed line in Figure 1, a pipe 30 connecting the oxygen gas-liquid separator 12 and the hydrogen gas-liquid separator 14 to the liquid transfer pump 11, and a pipe 31 connecting the liquid transfer pump 11 to the water electrolysis stack 10. The pure water supply piping system of the hydrogen production unit 3 includes a pipe 32 connecting the scrubbing tower 16 to the pure water supply pipe 4, and a pipe 33 connecting the scrubbing tower 16 to the pipe 31.

[0023] The oxygen outlet piping system of the hydrogen production unit 3 includes, as shown by the dashed line in Figure 1, a pipe 41 connecting the water electrolysis stack 10 and the oxygen gas-liquid separator 12, a pipe 42 connecting the oxygen gas-liquid separator 12 and the oxygen demister 13, and a pipe 43 connecting the oxygen demister 13 and the oxygen outlet piping 5. The hydrogen outlet piping system of the hydrogen production unit 3 also includes a pipe 51 connecting the water electrolysis stack 10 and the hydrogen gas-liquid separator 14, a pipe 52 connecting the hydrogen gas-liquid separator 14 and the hydrogen demister 15, a pipe 53 connecting the hydrogen demister 15 and the scrubbing tower 16, and a pipe 54 connecting the scrubbing tower 16 and the hydrogen outlet piping 6.

[0024] Furthermore, the various pipes (excluding the insulated pipes described later) and the gas-liquid separators within the hydrogen production apparatus that constitute the water electrolysis system 101 are generally made of SUS (Steel Use Stainless) for reasons such as preventing leakage of hydrogen and electrolyte and ensuring robustness. In addition, a resin lining layer is provided on the various pipes and gas-liquid separators to provide corrosion resistance to the electrolyte. Fluorine-based resin is preferred as the material for forming the resin lining layer.

[0025] Furthermore, in the pure water supply piping system of the hydrogen production unit 3, as shown in Figure 1, a first insulating pipe 61 is provided in a portion of the pipe 32 connecting the scrubbing tower 16 and the pure water supply pipe 4. In the oxygen outlet piping system of the hydrogen production unit 3, a second insulating pipe 62 is provided in a portion of the pipe 43 connecting the oxygen demister 13 and the oxygen outlet pipe 5. Also, in the hydrogen outlet piping system of the hydrogen production unit 3, a third insulating pipe 63 is provided in a portion of the pipe 54 connecting the scrubbing tower 16 and the hydrogen outlet pipe 6. Each insulating pipe is made of an electrically insulating material such as ceramics, fluororesin, polyethylene, or polyvinyl chloride. The length of each insulating pipe can be set arbitrarily.

[0026] Furthermore, the insulating section of the hydrogen production unit 3 is composed of an insulating frame 20 for mounting various main devices (hydrogen production equipment section) involved in the production of oxygen and hydrogen, as shown in Figure 1. The configuration of the insulating frame 20 will be described in detail later.

[0027] [Configuration and operation of each part of the hydrogen production equipment] The water electrolysis stack 10 generates oxygen and hydrogen by electrolyzing an electrolyte (a 20-50% potassium hydroxide aqueous solution) using a cell voltage applied from a DC power supply 1. The water electrolysis stack 10 then discharges the generated oxygen to the oxygen gas-liquid separator 12 via piping 41. At this time, the oxygen discharges from the water electrolysis stack 10 to the oxygen gas-liquid separator 12 in a state mixed with the electrolyte. The water electrolysis stack 10 also discharges the generated hydrogen to the hydrogen gas-liquid separator 14 via piping 51. At this time, the hydrogen discharges from the water electrolysis stack 10 to the hydrogen gas-liquid separator 14 in a state mixed with the electrolyte.

[0028] The liquid transfer pump 11 supplies (discharges) the electrolyte (20-50% concentration potassium hydroxide aqueous solution) that flows in through the piping 30 to the water electrolysis stack 10 through the piping 31.

[0029] The oxygen gas-liquid separator 12 separates the mixture of oxygen and electrolyte flowing in from the water electrolysis stack 10 into oxygen and electrolyte. The oxygen gas-liquid separator 12 discharges the separated oxygen to the oxygen demister 13 via piping 42. At this time, the oxygen after gas-liquid separation contains mist derived from the electrolyte. The oxygen gas-liquid separator 12 also discharges the separated electrolyte to the liquid transfer pump 11 via piping 30.

[0030] The oxygen demister 13 removes mist from the mixture of oxygen flowing in from the oxygen gas-liquid separator 12 and mist derived from the electrolyte. Besides using a demister, other methods for removing mist may be employed, such as condensing the mist using a heat exchanger. The oxygen demister 13 then discharges the mist-free oxygen into the oxygen outlet pipe 5 via the piping 43 and a second insulated piping 62 provided in part of it.

[0031] The hydrogen gas-liquid separator 14 separates the mixture of hydrogen and electrolyte flowing in from the water electrolysis stack 10 into hydrogen and electrolyte. The hydrogen gas-liquid separator 14 discharges the separated hydrogen to the hydrogen demister 15 via piping 52. At this time, the hydrogen after gas-liquid separation contains mist derived from the electrolyte. The hydrogen gas-liquid separator 14 also discharges the separated electrolyte to the liquid transfer pump 11 via piping 30.

[0032] The hydrogen demister 15 removes mist from the mixture of hydrogen flowing in from the hydrogen gas-liquid separator 14 and mist derived from the electrolyte. The hydrogen demister 15 then discharges the hydrogen, from which the mist has been removed, to the scrubbing tower 16 via the piping 53.

[0033] The scrubbing tower 16 washes the hydrogen flowing in from the hydrogen demister 15 with pure water supplied from the pure water pump 2 through the pure water supply pipe 4, and through the pipe 32 and a first insulating pipe 61 provided in part thereof, thereby increasing the concentration of hydrogen. The scrubbing tower 16 then discharges the washed hydrogen into the hydrogen outlet pipe 6 through the pipe 54 and a third insulating pipe 63 provided in part thereof.

[0034] Furthermore, the scrubbing tower 16 allows pure water supplied from the pure water pump 2 through the pure water supply piping 4, and through piping 32 and a first insulating piping 61 provided in part of it, to flow out into piping 30 via piping 33. As a result, pure water is mixed with the electrolyte circulating in piping 30 connecting the oxygen gas-liquid separator 12 and the hydrogen gas-liquid separator 14 to the liquid transfer pump 11, allowing for efficient adjustment of the electrolyte concentration. If the hydrogen production unit 3 does not have a scrubbing tower 16, the system may be configured to supply pure water to the oxygen gas-liquid separator 12 and the hydrogen gas-liquid separator 14.

[0035] [Configuration of the insulating frame] The insulating frame 20 is a device for electrically insulating the various main devices (hydrogen production equipment section) involved in the production of oxygen and hydrogen within the hydrogen production section 3 from the ground. Figure 2 is a side view showing the schematic configuration of the insulating frame 20.

[0036] As shown in Figure 2, the insulating frame 20 has a plate-shaped insulating frame body 21 (frame) and a plurality of insulating members 22. In this embodiment, the insulating frame body 21 may be made of, for example, a metal plate-shaped member, or a resin plate-shaped member as long as strength is maintained. The insulating members 22 can be made of insulating insulators such as ceramic insulators or epoxy resin insulators.

[0037] On one side of the insulating frame body 21, the hydrogen production equipment section 3a of the hydrogen production section 3, specifically the main equipment such as the water electrolysis stack 10, liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister 15, and scrubbing tower 16, is mounted. In Figure 2, for the sake of simplicity, only the water electrolysis stack 10, oxygen gas-liquid separator 12, and hydrogen gas-liquid separator 14 are shown as the main equipment mounted on the insulating frame body 21, and the other main equipment is omitted from the illustration.

[0038] Multiple insulating members 22 are placed between the other side of the insulating frame body 21 and the ground 200. In this case, the insulating frame body 21 is placed on the multiple insulating members 22 so that the insulating frame body 21 does not come into contact with the ground 200. This ensures electrical insulation (hereinafter simply referred to as "insulation") between the hydrogen production equipment 3a (various main devices involved in the production of hydrogen and oxygen) of the hydrogen production unit 3, which is placed on the insulating frame body 21, and the ground 200.

[0039] Furthermore, in this embodiment, as shown in Figure 2, a side wall portion 21a is provided at the side end of the insulating frame body portion 21, projecting toward the ground 200 side perpendicular to the surface of the insulating frame body portion 21. By providing the side wall portion 21a, it is possible to prevent the electrolyte, which has high conductivity, from adhering to the side wall of the insulating member 22, etc., in the event of leakage of the electrolyte, thereby reducing the insulating properties of the insulating frame 20 and preventing dielectric breakdown.

[0040] [Insulation function of water electrolysis system] Next, a method (insulation function) for ensuring insulation between each hydrogen production unit 3 and the ground 200 in the water electrolysis system 101 of this embodiment will be described.

[0041] Typically, in water electrolysis systems using alkaline water electrolysis stacks, potassium hydroxide solution is present in both the hydrogen and oxygen effluent systems produced by electrolysis of a highly conductive potassium hydroxide solution (electrolyte). Therefore, when such a water electrolysis stack is driven at a high voltage, leakage current may occur depending on the applied voltage and the volume resistance of the potassium hydroxide solution.

[0042] When leakage current occurs, it causes electrolytic corrosion in the metal piping that makes up the water electrolysis system. When electrolytic corrosion occurs, the ions dissolved by the corrosion not only degrade the water electrolysis stack, but can also deposit on the insulating mechanism in the piping (metal piping section), potentially reducing the insulation performance of the piping. Furthermore, if dielectric breakdown occurs, the entire water electrolysis system must be shut down. In this case, instantaneously disconnecting a large-scale water electrolysis system from the power grid could cause significant disruption to the power grid. For these reasons, ensuring the insulation performance of the water electrolysis system is a challenge when driving alkaline water electrolysis systems with high voltage.

[0043] It should be noted that, not limited to the water electrolysis stack 10 of this embodiment, general water electrolysis stacks are provided with an insulating section (not shown) inside the water electrolysis stack, and have insulating performance that can withstand normal self-generated voltages. However, if a voltage that cannot be handled by the insulating performance of the water electrolysis stack is applied, leakage current will occur. Furthermore, in a configuration in which a large number of water electrolysis stacks 10 are connected in series, as in this embodiment, if leakage current occurs due to insufficient insulating performance of the insulating section of each water electrolysis stack 10, the leakage current will increase, which may lead to a decrease in the durability and reliability of the entire water electrolysis system 101. In particular, in alkaline water electrolysis systems 101, the 20-50% potassium hydroxide aqueous solution used as the electrolyte has high conductivity, so when the water electrolysis system 101 is driven at high voltage, a very large leakage current may occur. As a solution to this problem, a method of reinforcing the insulating section of each water electrolysis stack 10 to increase resistance to high voltage can be considered, but considering, for example, material processing and manufacturing costs, this method is not practical.

[0044] To suppress the generation of leakage current in the water electrolysis stack 10 during high-voltage operation as described above, the water electrolysis system 101 of this embodiment is provided with an insulating frame 20, a first insulating pipe 61, a second insulating pipe 62, and a third insulating pipe 63.

[0045] When the water electrolysis stack 10 reaches a high potential, the electrolyte also reaches a high potential in the liquid transfer pump 11, the oxygen gas-liquid separator 12, and the hydrogen gas-liquid separator 14, which flow directly with the water electrolysis stack 10. Furthermore, since the electrolyte flows in the form of mist to the oxygen demister 13 and the hydrogen demister 15, if the mist condenses and adheres to the inner wall surface of the piping through which the mist flows, these demisters also become nearly conductive through the piping and reach a high potential. In addition, the piping from the water electrolysis stack 10 to the oxygen demister 13, and the piping from the water electrolysis stack 10 to the hydrogen demister 15, may also reach a high potential because condensed electrolyte adheres to their inner wall surfaces. Therefore, if the piping is grounded in this state, a large leakage current will flow through the piping to the earth 200.

[0046] Therefore, in order to suppress the leakage currents mentioned above, it is necessary to ensure insulation between the main equipment involved in the generation of hydrogen and oxygen (hydrogen production equipment section 3a), such as the water electrolysis stack 10, liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister 15, and scrubbing tower 16 of each hydrogen production section 3, and the ground 200. Furthermore, in order to suppress the leakage currents mentioned above, it is also necessary to ensure insulation between the piping connected to these main equipment, i.e., piping that may become high potential, and the ground 200. Specifically, it is necessary to ensure insulation between the piping for pure water supplied to the system including the water electrolysis stack 10 (hydrogen production equipment section 3a), and the piping provided in the respective distribution systems for oxygen and hydrogen flowing out from the water electrolysis stack 10.

[0047] Therefore, in the water electrolysis system 101 of this embodiment, first, as shown in Figures 1 and 2, the hydrogen production equipment section 3a of each hydrogen production unit 3 (water electrolysis stack 10, liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister, and scrubbing tower 16) is placed on an insulating frame 20 provided for each hydrogen production unit 3. At this time, the hydrogen production equipment section 3a is placed on an insulating frame main body 21 that ensures insulation from the ground 200, so that the hydrogen production equipment section 3a is insulated from the ground 200.

[0048] Furthermore, in the water electrolysis system 101 of this embodiment, as shown in Figure 1, a first insulating pipe 61 is provided in a part of the piping 32 for supplying pure water to the hydrogen production apparatus 3a. In addition, a second insulating pipe 62 is provided in a part of the piping 43 connected to the oxygen outlet end of the oxygen demister 13, and a third insulating pipe 63 is provided in a part of the piping 54 connected to the hydrogen outlet end of the scrubbing tower 16. Therefore, in this embodiment, the first insulating pipe 61, the second insulating pipe 62, and the third insulating pipe 63 ensure insulation of the piping provided in each hydrogen production unit 3 from the ground 200.

[0049] Furthermore, the placement of the first insulating pipe 61 is not limited to the example shown in Figure 1, and can be set to any position as long as it is part of the piping included in the pure water supply system (pure water supply piping system) that supplies pure water to the hydrogen production equipment section 3a. The placement of the second insulating pipe 62 is not limited to the example shown in Figure 1, and can be set to any position as long as it is part of the piping included in the oxygen supply system (oxygen outflow piping system) that flows out of the water electrolysis stack 10. Similarly, the placement of the third insulating pipe 63 is not limited to the example shown in Figure 1, and can be set to any position as long as it is part of the piping included in the hydrogen supply system (hydrogen outflow piping system) that flows out of the water electrolysis stack 10.

[0050] However, as shown in the example in Figure 1, if the second insulating pipe 62 is installed downstream of the oxygen demister 13 in the oxygen flow path, and the third insulating pipe 63 is installed downstream of the hydrogen demister 15 in the hydrogen flow path, then gas with the highly conductive electrolyte largely removed flows out downstream of the demister. This offers advantages such as making it easier to ensure the insulation of the pipes and reducing the possibility of electrolyte-derived contaminants adhering to the inner wall surface of the insulating pipes, thereby degrading their insulation performance.

[0051] Furthermore, in this embodiment, for example, if the insulating frame body portion 21 of the insulating frame 20 is formed of a metal material, it is necessary to keep the insulating frame body portion 21 in non-contact with the ground 200. However, if the insulating frame body portion 21 is formed of an electrically insulating resin material, the insulating frame body portion 21 may be in contact with the ground 200. However, from the viewpoint of ensuring insulation in the event of electrolyte leakage in the hydrogen production apparatus placed on the insulating frame body portion 21, a configuration in which the insulating frame body portion 21 is in non-contact with the ground 200, as in this embodiment, is superior regardless of the material used to form the insulating frame body portion 21.

[0052] [effect] As described above, in the water electrolysis system 101 of this embodiment, an insulating frame 20 is provided for each hydrogen production unit 3, ensuring insulation from the ground 200, and various main devices (hydrogen production equipment unit 3a) involved in the generation of hydrogen and oxygen within the hydrogen production unit 3 are placed on the insulating frame 20. Furthermore, in this embodiment, in each hydrogen production unit 3, insulating piping is provided for a portion of the piping in the flow system that supplies pure water to the hydrogen production unit 3, a portion of the piping in the flow system for oxygen generated in the water electrolysis stack 10, and a portion of the piping in the flow system for hydrogen generated in the water electrolysis stack 10.

[0053] Therefore, in this embodiment, insulation can be ensured between the various main devices involved in the generation of hydrogen and oxygen within each hydrogen production unit 3 and the ground 200, and insulation can also be ensured between the piping connected to each main device and the ground 200. As a result, even when the water electrolysis system 101, which consists of multiple water electrolysis stacks 10 connected in series, is driven at a high voltage, leakage current can be suppressed, and deterioration of the water electrolysis stacks 10 due to electrolytic corrosion and shutdown of the water electrolysis system 101 due to dielectric breakdown can be prevented. In other words, the configuration of the water electrolysis system 101 in this embodiment described above is a more suitable configuration as a water electrolysis system that can be driven at a high voltage.

[0054] 2. Second Embodiment In the first embodiment described above, an example configuration was described in which a liquid transfer pump 11, an oxygen gas-liquid separator 12, an oxygen demister 13, a hydrogen gas-liquid separator 14, a hydrogen demister 15, a washing tower 16, and an insulating frame 20 are provided for one water electrolysis stack 10 in each hydrogen production unit 3, but the present invention is not limited thereto. For example, each hydrogen production unit 3 may be provided with multiple water electrolysis stacks, and the liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister 15, washing tower 16, and insulating frame 20 may be provided in common for these multiple water electrolysis stacks. In the second embodiment, one example configuration will be described.

[0055] Figure 3 is a schematic diagram of a water electrolysis system 102 according to a second embodiment of the present invention. For the sake of simplicity, only the components related to the water electrolysis operation and the insulating function of the water electrolysis system 102 are shown here. In addition, in the water electrolysis system 102 of this embodiment shown in Figure 3, the same reference numerals are used for components that are the same as those for the water electrolysis system 101 of the first embodiment shown in Figure 1, and their descriptions are omitted.

[0056] As is clear from comparing Figure 3 with Figure 1, the water electrolysis system 102 of this embodiment has a configuration in which two water electrolysis stacks are provided in each hydrogen production unit 3 of the water electrolysis system 101 of the first embodiment. Here, an example in which two water electrolysis stacks are provided in each hydrogen production unit is described, but the present invention is not limited to this. The number of water electrolysis stacks provided in each hydrogen production unit can be appropriately set, for example, according to the DC voltage applied to each hydrogen production unit and the insulation performance of the water electrolysis stacks, so that the voltage applied to each water electrolysis stack does not exceed the insulation performance of the insulator inside the water electrolysis stack. Furthermore, here, an example in which multiple water electrolysis stacks are connected in series in each hydrogen production unit is described, but the present invention is not limited to this, and at least some of the multiple water electrolysis stacks may be connected in parallel.

[0057] In the water electrolysis system 102 of this embodiment, two water electrolysis stacks 71 and 72 within each hydrogen production unit 7 are electrically connected in series. Between adjacent hydrogen production units 7, the cathode (not shown) of the water electrolysis stack 72 located in one hydrogen production unit 7 is electrically connected to the anode (not shown) of the water electrolysis stack 71 located in the other hydrogen production unit 7. In other words, between multiple hydrogen production units 7 provided in the water electrolysis system 102, groups of water electrolysis stacks (water electrolysis stack sections) consisting of two series-connected water electrolysis stacks 71 and 72 located in each hydrogen production unit 7 are electrically connected in series. A DC power supply 1 is electrically connected between the anode (not shown) of the water electrolysis stack 71 located at one end of the water electrolysis stack group and the cathode (not shown) of the water electrolysis stack 72 located at the other end of the water electrolysis stack group.

[0058] Furthermore, in this embodiment, as shown in Figure 3, the liquid transfer pump 11 is connected to two water electrolysis stacks 71 and 72 via piping 34, and supplies electrolyte to each of the two water electrolysis stacks 71 and 72.

[0059] The oxygen outlet end of the water electrolysis stack 71 is connected to the oxygen gas-liquid separator 12 via piping 45a, and the oxygen produced in the water electrolysis stack 71 flows out to the oxygen gas-liquid separator 12 via piping 45a. Similarly, the hydrogen outlet end of the water electrolysis stack 71 is connected to the hydrogen gas-liquid separator 14 via piping 55a, and the hydrogen produced in the water electrolysis stack 71 flows out to the hydrogen gas-liquid separator 14 via piping 55a. On the other hand, the oxygen outlet end of the water electrolysis stack 72 is connected to the oxygen gas-liquid separator 12 via piping 45b, and the oxygen produced in the water electrolysis stack 72 flows out to the oxygen gas-liquid separator 12 via piping 45b. Similarly, the hydrogen outlet end of the water electrolysis stack 72 is connected to the hydrogen gas-liquid separator 14 via piping 55b, and the hydrogen produced in the water electrolysis stack 72 flows out to the hydrogen gas-liquid separator 14 via piping 55b.

[0060] In this embodiment, as shown in Figure 3, an insulating frame 20 is provided for each hydrogen production unit 7, similar to the first embodiment, and various main devices involved in the generation of hydrogen and oxygen within the hydrogen production unit 7 (two water electrolysis stacks 71 and 72, a liquid transfer pump 11, an oxygen gas-liquid separator 12, an oxygen demister 13, a hydrogen gas-liquid separator 14, a hydrogen demister, and a scrubbing tower 16) are placed on the insulating frame 20 (insulating frame main body 21). In this embodiment as well, a first insulating pipe 61 is provided in a portion of the piping 32 that supplies pure water to each hydrogen production unit 7. Furthermore, in each hydrogen production unit 7, insulating pipes (the second insulating pipe 62 and the third insulating pipe 63 in Figure 3) are provided in a portion of the piping (piping 43 and piping 54 in Figure 3) that are provided in the respective distribution systems for oxygen and hydrogen generated by the two water electrolysis stacks 71 and 72. Therefore, the same effects as in the first embodiment can be obtained in this embodiment as well.

[0061] 3. Third Embodiment The liquid transfer pumps used in water electrolysis systems are generally driven by commercial power supplies of 200V or 100V AC. However, as mentioned above, in alkaline water electrolysis systems, the liquid transfer pump comes into contact with an electrolyte (potassium hydroxide aqueous solution) that has high conductivity, and is therefore approximately equipotential with the water electrolysis stack. Therefore, when operating a water electrolysis system at high voltage, if the water electrolysis stack and the liquid transfer pump are not driven under conditions where they are approximately equipotential, an excessive potential difference may occur in the liquid transfer pump, potentially leading to failure of the liquid transfer pump and other equipment. For example, if the liquid transfer pump is driven by commercial power connected to a ground terminal, the water electrolysis stack and the liquid transfer pump will not be approximately equipotential, and current may flow from the water electrolysis stack to the ground via the commercial power supply's ground terminal, potentially leading to failure of the liquid transfer pump and other equipment. In the third embodiment, an example configuration of a water electrolysis system that can solve this problem will be described.

[0062] [Configuration of a water electrolysis system] Figure 4 is a schematic diagram of a water electrolysis system 103 according to a third embodiment of the present invention. For the sake of simplicity, only the components related to the water electrolysis operation and the insulating function of the water electrolysis system 103 are shown here. In addition, in the water electrolysis system 103 of this embodiment shown in Figure 4, the same reference numerals are used for components that are the same as those for the water electrolysis system 101 of the first embodiment shown in Figure 1, and their descriptions are omitted.

[0063] As is clear from comparing Figure 4 with Figure 1, the water electrolysis system 103 of this embodiment has a configuration in which the liquid transfer pump 11 in each hydrogen production unit 3 of the water electrolysis system 101 of the first embodiment is connected to the AC power supply 81 (driving power supply) via the transformer 80.

[0064] In each hydrogen production unit 8 of the water electrolysis system 103 of this embodiment, as shown in Figure 4, the secondary winding of the transformer 80 is electrically connected to the liquid transfer pump 11. In this embodiment, the primary windings of the transformer 80 are connected in series between multiple hydrogen production units 8. An AC power supply 81 is electrically connected between the primary winding at one end of the series-connected primary windings and the primary winding at the other end. In this configuration, the liquid transfer pump 11 is electrically isolated from the AC power supply 81 by the transformer 80.

[0065] [effect] In the water electrolysis system 103 of this embodiment, as shown in Figure 4, similar to the first embodiment, an insulating frame 20 is provided for each hydrogen production unit 8, and various main devices involved in the generation of hydrogen and oxygen within the hydrogen production unit 8 (water electrolysis stack 10, liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister, and scrubbing tower 16) are placed on the insulating frame 20 (insulating frame main body 21). In addition, in this embodiment, a first insulating pipe 61 is provided in part of the piping 32 that supplies pure water to each hydrogen production unit 8. Furthermore, in this embodiment, in each hydrogen production unit 8, insulating pipes (the second insulating pipe 62 and the third insulating pipe 63 in Figure 4) are provided in part of the piping (piping 43 and piping 54 in Figure 4) that are provided in the respective flow systems of oxygen and hydrogen generated in the water electrolysis stack 10. Therefore, the same effects as in the first embodiment can be obtained in this embodiment as well.

[0066] Furthermore, in the above configuration of the water electrolysis system 103 of this embodiment, the liquid transfer pump 11 in each hydrogen production unit 8 is electrically isolated from the AC power supply 81. Therefore, in this embodiment, the liquid transfer pump 11 can be operated at approximately the same potential as the water electrolysis stack 10, thereby preventing equipment failure.

[0067] 4. Fourth Embodiment When a water electrolysis system (water electrolysis stack) is shut down, the charge accumulated between the anode (not shown) and cathode (not shown) of the water electrolysis stack during operation causes a current (reverse current) to flow in the opposite direction to the current flowing, and consequently, the potential of the water electrolysis stack converges to a predetermined potential. At this time, the potential passes through a potential range that causes corrosion of the electrodes (not shown) in the water electrolysis stack over a certain period of time. Therefore, the reverse current generated in the water electrolysis stack when the water electrolysis system (water electrolysis stack) is shut down becomes a factor in the deterioration of the water electrolysis stack.

[0068] Furthermore, in the various embodiments of the water electrolysis system described above, each hydrogen production unit is insulated from the ground 200 by providing an insulating frame 20 and a first insulating pipe 61 to a third insulating pipe 63 for each hydrogen production unit. However, when performing maintenance on the water electrolysis system, it is preferable to set the potential of each hydrogen production unit to the ground potential in order to ensure the safety of the workers.

[0069] In the fourth embodiment, an example configuration of a water electrolysis system that can resolve the various problems described above will be described.

[0070] [Configuration of a water electrolysis system] Figure 5 is a schematic diagram of a water electrolysis system 104 according to the fourth embodiment of the present invention. For the sake of simplicity, only the components related to the water electrolysis operation and the insulating function of the water electrolysis system 104 are shown here. In addition, in the water electrolysis system 104 of this embodiment shown in Figure 5, the same reference numerals are used for components that are the same as those for the water electrolysis system 101 of the first embodiment shown in Figure 1, and their descriptions are omitted.

[0071] As shown in Figure 5, the water electrolysis system 104 comprises a hydrogen production device 105 and a system control device 110. The system control device 110 is electrically connected to the hydrogen production device 105 and controls the operation and shutdown of the hydrogen production device 105, as well as monitoring the operating status of the hydrogen production device 105.

[0072] In this embodiment, an example of a configuration in which the hydrogen production apparatus 105 and the system control device 110 are directly electrically connected is described. However, the hydrogen production apparatus 105 and the system control device 110 may also be connected via communication, for example. In this case, the operation and shutdown control of the hydrogen production apparatus 105 is performed based on control signals transmitted from the system control device 110 to the hydrogen production apparatus 105. In this case, the hydrogen production apparatus 105 is monitored based on various information indicating the operating status of the water electrolysis system 104 transmitted from the hydrogen production apparatus 105 to the system control device 110.

[0073] [Configuration of a hydrogen production system] The hydrogen production apparatus 105 of this embodiment is driven by applying a DC voltage from a DC power supply 1 to a plurality of water electrolysis stacks 10 connected in series, similar to the water electrolysis system 101 of the first embodiment shown in Figure 1. Furthermore, as is clear from comparing Figure 5 with Figure 1, the hydrogen production apparatus 105 of this embodiment is configured in the same way as the water electrolysis system 101 of the first embodiment, with each hydrogen production unit further provided with a circuit switch 90, a discharge circuit 91, a grounding circuit 92, a stack voltage measurement unit 93, a ground voltage measurement unit 94, and a current measurement unit 95. The other configurations are the same as those of the water electrolysis system 101 of the first embodiment.

[0074] Therefore, the various main devices involved in the generation of hydrogen and oxygen within each hydrogen production unit 9 of this embodiment (water electrolysis stack 10, liquid transfer pump 11, gas-liquid separator for oxygen 12, oxygen demister 13, gas-liquid separator for hydrogen 14, hydrogen demister and scrubbing tower 16: hydrogen production equipment unit) have the same configuration as those in each hydrogen production unit 3 of the first embodiment shown in Figure 1. In the hydrogen production apparatus 105 of this embodiment as well, an insulating frame 20 is provided for each hydrogen production unit 9, and the various main devices (hydrogen production equipment unit) are placed on the insulating frame 20 (insulating frame main body 21).

[0075] Furthermore, in the hydrogen production apparatus 105 of this embodiment, the configuration of the piping in the distribution system that supplies pure water to the hydrogen production unit 9, and the configuration of the piping provided in the respective oxygen and hydrogen distribution systems, are the same as those of the water electrolysis system 101 of the first embodiment shown in Figure 1. That is, in each hydrogen production unit 9, a first insulating pipe 61 is provided in part of the piping 32 that supplies pure water to the hydrogen production unit 9, a second insulating pipe 62 is provided in part of the piping 43 that discharges the oxygen produced in the water electrolysis stack 10, and a third insulating pipe 63 is provided in part of the piping 54 that discharges the hydrogen produced in the water electrolysis stack 10.

[0076] Furthermore, the electrical connection configuration between the DC power supply 1 and the multiple hydrogen production units 9 (water electrolysis stacks 10) in the hydrogen production apparatus 105 of this embodiment is basically the same as that of the first embodiment, as shown in Figure 5.

[0077] However, in this embodiment, as shown in Figure 5, a circuit changer 90 is provided on the electrical wiring connected to the anode (not shown) side of the water electrolysis stack 10 in each hydrogen production unit 9. A discharge circuit 91 and a stack voltage measurement unit 93 are electrically connected in parallel between the electrical wiring connected to the anode (not shown) side and the electrical wiring connected to the cathode (not shown) side of the water electrolysis stack 10. In addition, a grounding circuit 92 and a ground voltage measurement unit 94 are electrically connected in parallel between the insulating frame 20 (insulating frame main body 21) and the ground 200. Furthermore, in this embodiment, a current measurement unit 95 is provided on the electrical wiring connected to the anode of the DC power supply 1.

[0078] The circuit changer 90 consists of a changeover switch and the like, and turns the application of DC voltage to the water electrolysis stack 10 on and off. Specifically, when the hydrogen production apparatus 105 is in operation (when the water electrolysis stack 10 is driven), the circuit changer 90 is in the ON state, and the DC power supply 1 is connected to the multiple hydrogen production units 9. On the other hand, when the hydrogen production apparatus 105 is stopped (when the water electrolysis stack 10 is stopped), the circuit changer 90 is in the OFF state, and the DC power supply 1 is disconnected from the multiple hydrogen production units 9.

[0079] The discharge circuit 91 (discharge circuit section) consists of a discharge resistor 91a and a discharge switch 91b, and the two discharge resistors 91a are electrically connected in series. The end of the discharge resistor 91a opposite to the discharge switch 91b is electrically connected to the anode (not shown) side of the water electrolysis stack 10, and the end of the discharge switch 91b opposite to the discharge resistor 91a side is electrically connected to the cathode (not shown) side of the water electrolysis stack 10.

[0080] The discharge resistor 91a is a resistive element that consumes the charge accumulated when the water electrolysis stack 10 is energized when the system is stopped. The discharge changeover 91b consists of a changeover switch or the like and switches the on / off operation of the discharge circuit 91. Specifically, the discharge changeover 91b is in the off state when the hydrogen production device 105 is in operation (when the water electrolysis stack 10 is driven) and is in the on state when the hydrogen production device 105 is stopped.

[0081] In other words, when the hydrogen production apparatus 105 is shut down, the circuit changer 90 is turned off and the discharge changer 91b is turned on. As a result, after the hydrogen production apparatus 105 is shut down, current flows from the anode (not shown) side of the water electrolysis stack 10 to the cathode (not shown) side via the discharge circuit 91, and the charge accumulated in the water electrolysis stack 10 when it was energized is consumed by the discharge resistor 91a. In this case, the generation of the aforementioned reverse current in the water electrolysis stack 10 can be suppressed after the hydrogen production apparatus 105 is shut down.

[0082] In this embodiment, an example of a configuration in which the connection destination of the water electrolysis stack 10 is switched to either the power supply circuit (DC power supply circuit section) or the discharge circuit 91 by controlling both the circuit changer 90 and the discharge changer 91b on / off, that is, an example in which the circuit switching function unit is configured with both the circuit changer 90 and the discharge changer 91b, has been described, but the present invention is not limited thereto. For example, a circuit changer capable of switching between the power supply circuit and the discharge circuit 91 may be provided at the connection point between the electrical wiring connected to the anode side of the water electrolysis stack 10 and the discharge circuit 91. In this case, the circuit switching function unit can be configured with a single circuit changer instead of the circuit changer 90 and the discharge changer 91b.

[0083] The stack voltage measurement unit 93 consists of a voltage measuring instrument and measures (monitors) the DC voltage value applied to the water electrolysis stack 10.

[0084] The grounding circuit 92 (grounding circuit section) consists of a grounding resistor 92a and a grounding switch 92b, and the grounding resistor 92a and the grounding switch 92b are electrically connected in series. The end of the grounding resistor 92a opposite to the grounding switch 92b is electrically connected to the insulating frame body 21 of the insulating frame 20 (see Figure 2), and the end of the grounding switch 92b opposite to the grounding resistor 92a is electrically connected to the earth 200 (grounded).

[0085] The grounding resistor 92a is a resistive element used to dissipate the charge accumulated in the insulating frame body 21 and the various main devices involved in hydrogen and oxygen production (water electrolysis stack 10, liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister, and scrubbing tower 16: hydrogen production equipment section) when the system is shut down. It is preferable that the grounding resistor 92a be made of a high-resistance element in order to reduce the ground fault current flowing from the water electrolysis stack 10 to the ground 200 when the grounding circuit 92 is accidentally switched on while charge remains in the main devices such as the water electrolysis stack 10.

[0086] The grounding switch 92b is composed of a changeover switch or the like and switches the on / off operation of the grounding circuit 92. Specifically, the grounding switch 92b is in the off state when the hydrogen production device 105 is in operation (when the water electrolysis stack 10 is driven) and is in the on state when the hydrogen production device 105 is stopped. In this embodiment, after the hydrogen production device 105 is stopped, when the potential of the water electrolysis stack 10, i.e., the value measured by the stack voltage measurement unit 93, falls below a predetermined threshold voltage, the grounding switch 92b switches from the off state to the on state. In this case, when the grounding switch 92b is on, the ground fault current flowing from the insulating frame body 21 (water electrolysis stack 10) to the earth 200 can be reduced.

[0087] As described above, in this embodiment, when the hydrogen production apparatus 105 is shut down, the grounding switch 92b is turned ON, and the potential of the insulating frame body 21 and the various main devices involved in the generation of hydrogen and oxygen in each hydrogen production unit 9 placed thereon becomes the ground potential. This ensures the safety of workers during maintenance of the water electrolysis system 104 performed after shutdown. In this embodiment, an example of a configuration in which the grounding circuit 92 is electrically connected to the insulating frame body 21 (see Figure 2) of the insulating frame 20 is described, but the present invention is not limited to this. For example, the grounding circuit 92 may also be connected to each of the main devices such as the water electrolysis stack 10, the liquid transfer pump 11, the oxygen gas-liquid separator 12, the oxygen demister 13, the hydrogen gas-liquid separator 14, the hydrogen demister 15, and the scrubbing tower 16.

[0088] The ground voltage measurement unit 94 measures the potential (voltage) of the insulating frame body 21 (see Figure 2) of the insulating frame 20. In this embodiment, the grounding state after the water electrolysis system 104 is stopped is determined based on the measurement value of the ground voltage measurement unit 94. In addition, the current measurement unit 95 monitors (measures) the current (current flowing through) the water electrolysis stack 10 when the water electrolysis system 104 is in operation.

[0089] [Functional Configuration of System Control Unit] Figure 6 is a functional block diagram of the system control device 110. For the sake of simplicity, only the components related to the operation control and shutdown control of the hydrogen production apparatus 105 performed by the system control device 110 are shown here.

[0090] As shown in Figure 6, the system control device 110 includes a control unit 111 and a display and operation unit 112 that is electrically connected to the control unit 111.

[0091] The control unit 111 performs various control processes related to the operation and stopping of the water electrolysis system 104. Therefore, the switching operations of the circuit switch 90, discharge switch 91b, and ground switch 92b described above during the operation and stopping of the water electrolysis system 104 are also controlled by the control unit 111. In addition, the display and operation unit 112 performs operations such as displaying various information indicating the operating status of the water electrolysis system 104 and outputting control command information for the water electrolysis system 104 to the control unit 111.

[0092] The control unit 111 includes a calculation unit 121 and a storage unit 122. Functionally, the calculation unit 121 includes an operation control unit 131, a value setting unit 132, and a determination unit 133, while the storage unit 122 functionally includes a control program unit 141 and a reference information unit 142.

[0093] The operation control unit 131 performs various processes related to the operation and stopping of the water electrolysis system 104. The value setting unit 132 sets various parameters used in the control processing of the water electrolysis system 104 performed by the operation control unit 131. The determination unit 133 determines, based on various measurement data, whether or not it is necessary to perform operations such as raising or lowering the output voltage of the DC power supply 1 or switching the circuit changer 90.

[0094] The control program unit 141 stores programs and the like for realizing the functions of the operation control unit 131, value setting unit 132, and determination unit 133 as described above, using the calculation unit 121. The reference information unit 142 stores various information that is referenced when the operation control unit 131 controls the water electrolysis system 104 and when the value setting unit 132 sets various parameters.

[0095] Furthermore, the display and operation unit 112 includes a display unit 151 and an operation unit 152. The display unit 151 displays information indicating the operating status of the water electrolysis system 104, such as measured data of each part of the water electrolysis system 104, including temperature, pressure, flow rate, current, and voltage, as well as control command values. The operation unit 152 outputs information such as operation command values ​​for the water electrolysis system 104 to the control unit 111.

[0096] [System control unit hardware configuration] The system control device 110 of this embodiment described above can be configured as an information processing device such as a computer device equipped with calculation and communication functions. Figure 7 is a block diagram showing an example of the hardware configuration of a computer device 160 that can be used as the system control device 110.

[0097] As shown in Figure 7, the computer device 160 includes a CPU (Central Processing Unit) 161, ROM (Read Only Memory) 162, and RAM (Random Access Memory) 163 connected to the bus line 168. The computer device 160 also includes a network interface 164, an operating device 165, a display device 166, and non-volatile storage 167, all connected to the bus line 168. Although not shown in Figure 7, the computer device 160 also includes various interfaces used for inputting and outputting various types of data (various types of information) with external devices.

[0098] The CPU 161 reads program code for the software that implements the various processing functions of the system control unit 110 from the ROM 162 into the RAM 163 and executes it. At this time, various data such as variables and parameters that occur during the calculation process are temporarily written to the RAM 163. In other words, the calculation unit 121 of the system control unit 110 is included in the CPU 161, and the storage unit 122 is included in the ROM 162 and RAM 163.

[0099] Network I / F164 is composed of, for example, a NIC (Network Interface Card) and transmits and receives various types of data between connected devices via wireless communication.

[0100] The operating device 165 is composed of, for example, keys and buttons, and generates an operation signal corresponding to the operation content input by the operator and supplies the operation signal to the CPU 161. The display device 166 is composed of, for example, a liquid crystal panel, and displays characters, images, etc. on the screen. Alternatively, the display device 166 may be configured as a touch panel, in which case the display device 166 and the operating device 165 are configured as an integrated unit. That is, the display unit 151 of the system control device 110 is included in the display device 166, and the operation unit 152 is included in the operating device 165.

[0101] The non-volatile storage 167 can consist of, for example, an HDD (Hard disk drive), an SSD (Solid State Drive), a flexible disk, an optical disk, a magneto-optical disk, a CD (Compact Disc)-ROM, a CD-R, magnetic tape, or non-volatile memory. The non-volatile storage 167 stores the OS (Operating System), various parameters, and various programs for making the computer device 160 function as a system control unit 110. In addition to the ROM 162 and the non-volatile storage 167, information (data) such as programs, tables, and files for realizing each function of the system control unit 110 may be stored on recording media such as an IC (Integrated Circuit) card, an SD card, or a DVD (Digital Versatile Disc).

[0102] [Control flow when shutting down a water electrolysis system] Next, the specific details of the control processing performed when the water electrolysis system 104 of this embodiment is shut down will be explained with reference to the drawings. Figure 8 is a flowchart showing the procedure of the control processing performed when the water electrolysis system 104 is shut down. The control processing performed when the water electrolysis system 104 is shut down, as described below, is executed by the calculation unit 121 (CPU 161) of the system control device 110 in software.

[0103] First, the calculation unit 121 (operation control unit 131) stops the operation of the water electrolysis system 104 (S1). Specifically, the calculation unit 121 stops the power supply from the DC power supply 1 to each hydrogen production unit 9.

[0104] Next, the calculation unit 121 (operation control unit 131) turns off the power supply connection (S2). Specifically, the calculation unit 121 turns off the circuit switch 90 provided for each hydrogen production unit 9. As a result, the DC power supply 1 is disconnected from the multiple hydrogen production units 9.

[0105] Next, the calculation unit 121 (operation control unit 131) turns on the discharge circuit 91 of each hydrogen production unit 9 (S3). Specifically, the calculation unit 121 turns on the discharge switch 91b in the discharge circuit 91 provided for each hydrogen production unit 9. As a result, the charge accumulated in the water electrolysis stack 10 when the operation is stopped is consumed by the discharge resistor 91a.

[0106] Next, the calculation unit 121 (determination unit 133) determines whether the voltage Vs (hereinafter referred to as "stack voltage Vs") between the anode (not shown) and cathode (not shown) of the water electrolysis stack 10 of each hydrogen production unit 9 is below a predetermined threshold voltage (S4). This determination process is performed based on the measured value of the stack voltage measurement unit 93. The predetermined threshold voltage can be set to a value of, for example, 0.1V or less. However, the present invention is not limited thereto, and the predetermined threshold voltage can be set to any voltage value that can prevent a situation in which a reverse current is generated in the water electrolysis stack 10 after the operation of the water electrolysis system 104 is stopped, causing corrosion of the electrodes (not shown).

[0107] In the S4 determination process, it is determined whether the stack voltage Vs in all hydrogen production units 9 (water electrolysis stacks 10) included in the water electrolysis system 104 is below a predetermined threshold voltage. If the stack voltage Vs in all hydrogen production units 9 included in the water electrolysis system 104 is below the predetermined threshold voltage, the determination result in S4 is Yes. On the other hand, if there is even one hydrogen production unit 9 whose stack voltage Vs is not below the predetermined threshold voltage, the determination result in S4 is No.

[0108] In the process of S4, if the calculation unit 121 determines that the stack voltage Vs of each hydrogen production unit 9 is not below a predetermined threshold voltage (i.e., if S4 is determined to be No), the calculation unit 121 (determination unit 133) repeats the process of S4.

[0109] On the other hand, if the calculation unit 121 determines that the stack voltage Vs of each hydrogen production unit 9 is below a predetermined threshold voltage (if S4 is determined to be Yes), the calculation unit 121 (operation control unit 131) turns on the grounding circuit 92 (S5). Specifically, the calculation unit 121 turns on the grounding switch 92b of the grounding circuit 92 provided for each hydrogen production unit 9. As a result of this process, in each hydrogen production unit 9, the potential of the insulating frame body 21 of the insulating frame 20 and the various main devices (hydrogen production equipment) placed on it that are involved in the generation of hydrogen and oxygen become the ground potential.

[0110] Next, the calculation unit 121 (determination unit 133) determines whether the voltage Vf (hereinafter referred to as "frame voltage Vf") of the insulating frame body 21 (see Figure 2) of the insulating frame 20 of each hydrogen production unit 9 is 0 (ground potential) (S6). This determination process is performed based on the measured value of the ground voltage measurement unit 94.

[0111] In the S6 determination process, it is determined whether the stand voltage Vf is 0 in all hydrogen production units 9 included in the water electrolysis system 104. If the stand voltage Vf is 0 in all hydrogen production units 9 included in the water electrolysis system 104, the determination result in S6 is Yes. On the other hand, if there is even one hydrogen production unit 9 whose stand voltage Vf is not 0, the determination result in S6 is No.

[0112] In the process of S6, if the calculation unit 121 determines that the frame voltage Vf of each hydrogen production unit 9 is not 0 (i.e., if S6 is determined to be No), the calculation unit 121 (determination unit 133) repeats the process of S6.

[0113] On the other hand, in the process of S6, if the calculation unit 121 determines that the frame voltage Vf of each hydrogen production unit 9 is 0 (i.e., if S6 is determined to be Yes), the calculation unit 121 (operation control unit 131) controls the display unit 151 to display information indicating that grounding is complete (S7). After the process of S7, the calculation unit 121 (operation control unit 131) terminates the control process after the operation of the water electrolysis system 104 has been stopped.

[0114] In this embodiment, the determination process in S4 describes an example of determining whether the stack voltage Vs of all hydrogen production units 9 included in the water electrolysis system 104 is below a predetermined threshold voltage, but the present invention is not limited thereto. For example, the determination process in S4 is repeated for each hydrogen production unit 9, and if the determination result of S4 is No for the hydrogen production unit 9 to be determined, the hydrogen production unit 9 to be determined is changed and the determination process in S4 is repeated. On the other hand, if the determination result of S4 is Yes for the hydrogen production unit 9 to be determined, the process in S5 (turning on the grounding circuit 92) may be performed on the grounding circuit 92 in the hydrogen production unit 9 to be determined. That is, the process of turning on the grounding circuit 92 (the process of setting the frame voltage Vf to 0) may be performed sequentially for the hydrogen production units 9 whose stack voltage Vs is below a predetermined threshold voltage.

[0115] Furthermore, although this embodiment describes an example in which the control processing for when the water electrolysis system 104 is shut down by the system control device 110 described above is performed in software, the present invention is not limited thereto. For example, some or all of the control processing may be configured in hardware.

[0116] [effect] In the water electrolysis system 104 of this embodiment, as shown in Figure 5, similar to the first embodiment, an insulating frame 20 is provided for each hydrogen production unit 9, and various main devices involved in the generation of hydrogen and oxygen within the hydrogen production unit 9 (water electrolysis stack 10, liquid transfer pump 11, oxygen gas-liquid separator 12, oxygen demister 13, hydrogen gas-liquid separator 14, hydrogen demister, and scrubbing tower 16) are placed on the insulating frame 20 (insulating frame main body 21). In addition, in this embodiment, a first insulating pipe 61 is provided in part of the piping 32 that supplies pure water to each hydrogen production unit 9. Furthermore, in this embodiment, in each hydrogen production unit 9, insulating pipes (the second insulating pipe 62 and the third insulating pipe 63 in Figure 5) are provided in part of the piping (piping 43 and piping 54 in Figure 5) that are provided in the respective flow systems of oxygen and hydrogen generated in the water electrolysis stack 10. Therefore, the same effects as in the first embodiment can be obtained in this embodiment as well.

[0117] Furthermore, in this embodiment, when the water electrolysis system 104 is shut down, the circuit changer 90 is turned off to disconnect the multiple hydrogen production units 9 (water electrolysis stacks 10) from the DC power supply 1, and then the discharge circuit 91 is turned on to dissipate the charge accumulated when the water electrolysis stacks 10 were energized using the discharge resistor 91a. This suppresses the generation of reverse current in the water electrolysis stacks 10 after the hydrogen production apparatus 105 is shut down, preventing corrosion of the electrodes (not shown) of the water electrolysis stacks 10 and suppressing deterioration of the water electrolysis stacks 10.

[0118] Furthermore, in this embodiment, when the water electrolysis system 104 is shut down, the grounding circuit 92 (grounding switch 92b) can be turned on, and the potential of the insulating frame main body 21 of each hydrogen production unit 9 and the various main devices (hydrogen production equipment unit) placed thereon that are involved in the generation of hydrogen and oxygen can be set to the ground potential. Therefore, in this embodiment, the safety of workers can be ensured during maintenance and repair of the water electrolysis system 104 performed after shutdown.

[0119] In other words, in the water electrolysis system 104 of this embodiment, by providing the circuit changer 90, discharge circuit 91, and grounding circuit 92 with the above-described configuration, and using the above-described control method for when the system is stopped, various problems that may arise due to the charge accumulated in the insulating frame main body 21 and the various main devices placed thereon when the system is stopped can be resolved. Therefore, the configuration of the water electrolysis system 104 of this embodiment and its operation control method are even more suitable as a water electrolysis system capable of high-voltage driving.

[0120] 5. Various variations Although various embodiments of the water electrolysis system and its control method during shutdown have been described above, the present invention is not limited thereto, and various other modifications can be made as long as they do not depart from the gist of the present invention as described in the claims. For example, the following various modifications can be adopted, and the same effects as the above embodiments can be obtained in the following various modifications.

[0121] In the water electrolysis systems of the various embodiments described above, an example configuration was described in which a water electrolysis stack section, consisting of one or more water electrolysis stacks provided in each water electrolysis production section, is electrically connected in series between multiple water electrolysis production sections. However, the present invention is not limited thereto. For example, a configuration in which at least a portion of multiple water electrolysis stack sections is electrically connected in parallel between multiple water electrolysis production sections may be used. Alternatively, for example, a water electrolysis stack section may be constructed by electrically connecting multiple water electrolysis stacks in parallel in each water electrolysis production section, and the water electrolysis stack sections of each water electrolysis production section may be electrically connected in series between multiple water electrolysis production sections.

[0122] In the water electrolysis systems of the various embodiments described above, an example configuration in which one insulating stand 20 is installed for each hydrogen production unit has been explained, but the present invention is not limited thereto. For example, one insulating stand may be installed for each main device (equipment) involved in the generation of hydrogen and oxygen within each hydrogen production unit. Alternatively, depending on the size of each hydrogen production unit, one insulating stand may be provided for each of several hydrogen production units that are arranged adjacent to each other.

[0123] In the above embodiments, examples have been described in which the above-mentioned configurations, such as insulation function, discharge circuit, and grounding circuit, and control methods during shutdown are applied to a water electrolysis system that produces hydrogen by alkaline water electrolysis. However, the present invention is not limited thereto. The above-described configurations, such as insulation function, discharge circuit, and grounding circuit, and control methods during shutdown are also applicable to water electrolysis systems that produce hydrogen by other methods, such as solid polymer water electrolysis and high-temperature steam electrolysis.

[0124] Furthermore, the various embodiments described above are detailed and specific explanations of the device's configuration in order to clearly illustrate the present invention, and are not necessarily limited to devices having all the configurations described. The positions, sizes, shapes, and ranges of the components shown in the drawings may not represent the actual positions, sizes, shapes, and ranges, in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, and ranges disclosed in the drawings. [Explanation of Symbols]

[0125] 1...DC power supply, 2...pure water pump, 3,7~9...hydrogen production section, 3a...hydrogen production equipment section, 4...pure water supply piping, 5...oxygen outlet piping, 6...hydrogen outlet piping, 10,71,72...water electrolysis stack, 11...liquid transfer pump, 12...gas-liquid separator for oxygen, 13...demister for oxygen, 14...gas-liquid separator for hydrogen, 15...demister for hydrogen, 16...washing tower, 20...insulating frame, 21...insulating frame main body, 22...insulating material, 30~34,41~43,45a,45b,51~54, 55a, 55b... Piping, 61... First insulated piping, 62... Second insulated piping, 63... Third insulated piping, 80... Transformer, 81... AC power supply, 90... Circuit changer, 91... Discharge circuit, 92... Grounding circuit, 93... Stack voltage measurement unit, 94... Voltage to ground measurement unit, 95... Current measurement unit, 101~104... Water electrolysis system, 105... Hydrogen production equipment, 110... System control device, 111... Control unit, 112... Display / operation unit, 131... Operation control unit, 133... Judgment unit, 200... Ground

Claims

1. A hydrogen production apparatus having a water electrolysis stack section containing one or more water electrolysis stacks that generate oxygen and hydrogen by an electrolysis reaction, A power supply that supplies DC power to the one or more water electrolysis stacks, A pure water supply piping system that supplies pure water to the hydrogen production apparatus, An oxygen outlet piping system for releasing oxygen generated in the water electrolysis stack to the outside, A hydrogen outlet piping system for releasing hydrogen generated in the aforementioned water electrolysis stack to the outside, An insulating section that electrically insulates the hydrogen production apparatus from the ground, A first electrically insulating pipe provided in a part of the aforementioned pure water supply piping system, A second electrically insulating pipe provided in a part of the oxygen outflow piping system, The system comprises a third electrically insulating pipe provided in a part of the hydrogen discharge piping system. Water electrolysis system.

2. The insulating portion comprises a frame on which the hydrogen production apparatus is mounted and which is not in contact with the ground, and an insulating insulator provided between the frame and the ground to ensure electrical insulation between the frame and the ground. The water electrolysis system according to claim 1.

3. The sides of the frame are provided with side walls that protrude toward the ground and do not come into contact with the ground. The water electrolysis system according to claim 2.

4. The hydrogen production apparatus includes a liquid supply pump for supplying electrolyte to the water electrolysis stack, an oxygen gas-liquid separator for separating the oxygen generated in the water electrolysis stack from the electrolyte, an oxygen demister for removing mist from the mixture of oxygen and mist separated by the oxygen gas-liquid separator, a hydrogen gas-liquid separator for separating the hydrogen generated in the water electrolysis stack from the electrolyte, and a hydrogen demister for removing mist from the mixture of hydrogen and mist separated by the hydrogen gas-liquid separator. The second insulating pipe is provided on the oxygen outlet side of the oxygen demister, The third insulating pipe is provided on the hydrogen outlet side of the hydrogen demister. The water electrolysis system according to claim 2.

5. The hydrogen production apparatus further includes a washing tower for washing the hydrogen that has leaked out of the hydrogen demister. The third insulating pipe is provided on the hydrogen outlet side of the scrubbing tower. The water electrolysis system according to claim 4.

6. The system comprises multiple hydrogen production apparatus units, Multiple hydrogen production apparatus units are electrically connected in series with multiple water electrolysis stack units. The water electrolysis system according to claim 5.

7. The water electrolysis stack section includes a plurality of water electrolysis stacks electrically connected in series. The water electrolysis system according to claim 5.

8. The aforementioned liquid transfer pump is connected to the power supply for the liquid transfer pump via a transformer. The water electrolysis system according to claim 5.

9. Furthermore, a discharge circuit section is electrically connected in parallel to the water electrolysis stack section, A circuit switching function unit that switches the electrical connection destination of the water electrolysis stack unit to either the DC power supply side circuit unit or the discharge circuit unit, The system includes a grounding circuit that electrically connects the hydrogen production equipment to the ground when the hydrogen production equipment is being stopped, During operation control of the hydrogen production apparatus, the circuit switching function unit connects the water electrolysis stack to the DC power supply circuit unit. When the hydrogen production apparatus is being shut down, the circuit switching function unit connects the water electrolysis stack to the discharge circuit unit. The water electrolysis system according to claim 5.

10. A water electrolysis system comprising: a hydrogen production apparatus having a water electrolysis stack section containing one or more water electrolysis stacks that generate oxygen and hydrogen by electrolysis reaction; a power supply that supplies DC power to the one or more water electrolysis stacks; a pure water supply piping system that supplies pure water to the hydrogen production apparatus section; an oxygen outlet piping system that discharges oxygen generated in the water electrolysis stack section to the outside; a hydrogen outlet piping system that discharges hydrogen generated in the water electrolysis stack section to the outside; an insulating section that electrically insulates the hydrogen production apparatus section from the ground; a first insulating pipe having electrical insulation properties provided in a part of the pure water supply piping system; a second insulating pipe having electrical insulation properties provided in a part of the oxygen outlet piping system; a third insulating pipe having electrical insulation properties provided in a part of the hydrogen outlet piping system; and a control unit that performs operation control and stop control of the hydrogen production apparatus section, wherein the control unit disconnects the hydrogen production apparatus section from the power supply when stopping the hydrogen production apparatus section. The control unit, after disconnecting the hydrogen production apparatus from the power supply, performs discharge control of the charge accumulated in the one or more water electrolysis stacks. The control unit includes setting the hydrogen production apparatus to ground potential after the discharge control has been executed. A method for controlling a water electrolysis system.

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