Alkaline water electrolysis system and method for operating an alkaline water electrolysis system

Abstract

An alkaline water electrolysis system (70) is provided with: a rectifier (74) connected to a variable power source to convert alternating current into direct current; two or more bipolar electrolytic cells (50_1) to (50_N) that generate hydrogen and oxygen by electrolysis of water using an electrolyte based on a prescribed direct current voltage supplied by the rectifier (74); a gas-liquid separation tank (72) connected to the two or more bipolar electrolytic cells (50_1) to (50_N) to separate hydrogen and oxygen from the electrolyte and store the electrolyte; and an on-off valve (62) provided between the gas-liquid separation tank (72) and the bipolar electrolytic cells (50).

Description

Technical Field

[0001] This invention relates to an alkaline water electrolysis system and a method for operating the alkaline water electrolysis system. Background Technology

[0002] In recent years, in order to address issues such as global warming caused by greenhouse gases such as carbon dioxide and the depletion of fossil fuel reserves, technologies that utilize renewable energy, such as wind power and solar power, have received attention.

[0003] Renewable energy sources are highly dependent on climate conditions and fluctuate significantly. Therefore, it is difficult to transmit electricity generated from renewable energy sources to the general power system, potentially leading to social impacts such as imbalances in electricity supply and demand and instability in the power system. Consequently, research has been conducted on storing electricity and converting it into a transmittable form for use; for example, studies have explored the production of hydrogen through the electrolysis of water and its utilization as an energy source or feedstock.

[0004] Hydrogen has been widely used industrially in petroleum refining, chemical synthesis, and metal refining. In recent years, its potential applications in hydrogen refueling stations for fuel cell vehicles, smart communities, and hydrogen power plants have also been expanding. Therefore, there is high hope for developing technologies that obtain hydrogen, especially from renewable energy sources.

[0005] As a method of water electrolysis, known methods include solid polymer membrane water electrolysis, high-temperature steam electrolysis, and alkaline water electrolysis. Alkaline water electrolysis is considered particularly advantageous due to its industrialization over several decades ago, its ability to be implemented on a large scale, and its lower cost compared to other electrolysis methods. Alkaline water electrolysis refers to the following electrolysis method: using an alkaline aqueous solution containing dissolved alkaline salts (alkaline water) as the electrolyte, water is electrolyzed, thereby producing hydrogen gas from the cathode and oxygen gas from the anode.

[0006] For example, Patent Document 1 discloses a hydrogen production device comprising: a water electrolysis unit having two or more battery stacks connected in series or parallel; a power supply unit supplying power to the water electrolysis unit; a voltage control unit that variably controls the voltage supplied to the water electrolysis unit; and a stack number control unit that selects the number of battery stacks used to ensure that the voltage and current acting on the battery stacks meet specified ranges. This improves energy efficiency.

[0007] For example, Patent Document 2 discloses a hydrogen production system comprising: a power generation device that converts renewable energy into electrical energy; two or more hydrogen production devices connected in series or parallel to produce hydrogen using the electrical energy; a switching element that switches the connection of the two or more hydrogen production devices; a voltage application unit that applies voltage to the hydrogen production devices; and a control device that controls the switching element and the voltage application unit. This suppresses the occurrence of reverse reactions in the hydrogen production devices.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2005-126792

[0011] Patent Document 2: International Publication No. 2013 / 046958 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, existing systems with more than two electrolyzers have the following problems: with the overall shutdown of the system, the frequency of purging of inactive gases is high, making it difficult to maintain the supply of high-purity hydrogen.

[0014] In view of the above, the object of the present invention is to provide an alkaline water electrolysis system capable of continuously producing high-purity hydrogen and a method for operating the alkaline water electrolysis system.

[0015] Methods for solving problems

[0016] That is, the present invention is as follows.

[0017] One embodiment of the alkaline water electrolysis system is characterized by comprising:

[0018] A rectifier, connected to a variable power source, converts alternating current (AC) into direct current (DC).

[0019] Two or more bipolar electrolyzers, which use an electrolyte to produce hydrogen and oxygen by electrolyzing water based on a specified DC voltage supplied by the aforementioned rectifier;

[0020] A gas-liquid separator, connected to two or more of the aforementioned bipolar electrolyzers, separates the hydrogen and oxygen from the electrolyte and stores the electrolyte; and

[0021] An on / off valve is installed between the gas-liquid separator and the bipolar electrolytic cell.

[0022] Furthermore, in one embodiment of the alkaline water electrolysis system, it is characterized by further comprising a pressure regulating valve that regulates the internal pressure of the aforementioned gas-liquid separator.

[0023] Furthermore, in one embodiment of the alkaline water electrolysis system, it is characterized by further comprising a control device that determines the DC voltage and controls the operation or shutdown of the bipolar electrolyzer.

[0024] Furthermore, in one embodiment of the alkaline water electrolysis system, the control device controls the operation or shutdown of the bipolar electrolyzer so that the current used to operate the alkaline water electrolysis system is consistent with the target current.

[0025] Furthermore, in one embodiment of the alkaline water electrolysis system, the control device controls the operation or shutdown of the bipolar electrolyzer based on the ratio of the current density of the bipolar electrolyzer during operation to the maximum current density.

[0026] Furthermore, in one embodiment of the alkaline water electrolysis system, the control device operates all of the bipolar electrolyzers when the power supplied to the alkaline water electrolysis system is at or above a first threshold.

[0027] When the power supplied to the alkaline water electrolysis system is less than the first threshold, a portion of the bipolar electrolyzers are operated.

[0028] Furthermore, in one embodiment of the alkaline water electrolysis system, the control device is characterized in that, when power is supplied to the alkaline water electrolysis system,

[0029] If the current density of the aforementioned bipolar electrolytic cell that has started operation is above the second threshold, then the number of the aforementioned bipolar electrolytic cells in operation is increased.

[0030] The number of bipolar electrolytic cells that continue to operate when the current density of the bipolar electrolytic cell that has started operating is less than the second threshold.

[0031] Furthermore, in one embodiment of the alkaline water electrolysis system, it is characterized by further comprising a heating device that heats the electrolyte stored inside the gas-liquid separator.

[0032] Furthermore, in one embodiment of the alkaline water electrolysis system, the renewable energy supplied to the alkaline water electrolysis system is energy obtained from at least one of wind power, solar energy, hydropower, tidal power, wave power, ocean currents, and geothermal energy.

[0033] Furthermore, in one embodiment of the alkaline water electrolysis system, the characteristic is that each of the two or more of the above-mentioned bipolar electrolyzers has an individual rectifier.

[0034] One embodiment of the operation method of an alkaline water electrolysis system is characterized by comprising:

[0035] The steps of a rectifier connected to a variable power source to convert alternating current (AC) into direct current (DC);

[0036] Two or more bipolar electrolyzers, based on a specified DC voltage supplied by the aforementioned rectifier, use an electrolyte to generate hydrogen and oxygen through the electrolysis of water.

[0037] The steps of separating hydrogen and oxygen from the electrolyte and storing the electrolyte in a gas-liquid separator connected to two or more of the above-mentioned bipolar electrolyzers; and

[0038] The step of the on / off valve installed between the gas-liquid separator and the bipolar electrolyzer to suppress the conduction of the electrolyte, hydrogen and oxygen between the gas-liquid separator and the bipolar electrolyzer.

[0039] Furthermore, in one embodiment of the alkaline water electrolysis system operation method, the method is characterized by further comprising: controlling the operation or shutdown of two or more of the above-mentioned bipolar electrolytic cells by a control device, closing the inlet opening / closing valve and the outlet opening / closing valve among the above-mentioned opening / closing valves, or closing either the inlet opening / closing valve or the outlet opening / closing valve.

[0040] Furthermore, in one embodiment of the operation method of the alkaline water electrolysis system, the method is characterized by further comprising: when the control device is filled with the electrolyte in the bipolar electrolyzer, closing the inlet valve and the outlet valve, or closing either the inlet valve or the outlet valve.

[0041] Furthermore, in one embodiment of the operation method of the alkaline water electrolysis system, the method is characterized by further comprising the step of adjusting the temperature of the electrolyte using a heat exchanger disposed inside the gas-liquid separator.

[0042] Furthermore, in one embodiment of the alkaline water electrolysis system operation method, the gas-liquid separator is located above two or more of the above-mentioned bipolar electrolytic cells.

[0043] The effects of the invention

[0044] According to the present invention, an alkaline water electrolysis system capable of continuously producing high-purity hydrogen and a method for operating the alkaline water electrolysis system can be provided. Attached Figure Description

[0045] Figure 1A This is a diagram illustrating an example of the configuration of the alkaline water electrolysis system of this embodiment.

[0046] Figure 1B This is a diagram illustrating an example of the configuration of the alkaline water electrolysis system of this embodiment.

[0047] Figure 2 This is a diagram illustrating an example of the mechanism used to maintain the high purity of the gas in this embodiment.

[0048] Figure 3A This is a graph illustrating an example of the relationship between current load and impurity concentration when all bipolar electrolyzers are in operation in the alkaline water electrolysis system of this embodiment.

[0049] Figure 3B This is a diagram illustrating an example of the relationship between current load and impurity concentration in the alkaline water electrolysis system of this embodiment, where some bipolar electrolyzers are in operation and some bipolar electrolyzers are stopped.

[0050] Figure 4 This is a diagram showing an example of the configuration of the bipolar electrolytic cell of this embodiment.

[0051] Figure 5A This is a diagram showing an example of the configuration of the electrolysis unit in this embodiment.

[0052] Figure 5B This is a diagram showing an example of the configuration of the electrolysis unit in this embodiment.

[0053] Figure 6 This is a flowchart illustrating an example of the operation method of the alkaline water electrolysis system of this embodiment. Detailed Implementation

[0054] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that, in principle, the same reference numerals are used to label the same constituent elements, and repeated descriptions are omitted. In the figures, for ease of explanation, the aspect ratios of each component are exaggerated relative to the actual proportions.

[0055] In addition, in the following description, "vertical" refers to the direction parallel to the Z-axis shown in the coordinate axes depicted in the attached figures, "up" refers to the positive direction of the Z-axis, and "down" refers to the negative direction of the Z-axis. "Horizontal" refers to the direction parallel to the XY plane shown in the coordinate axes depicted in the attached figures. "Inclined" refers to the direction forming a specified angle (other than 0°, 90°, 180°, and 270°) relative to the XY plane shown in the coordinate axes depicted in the attached figures. "Left" refers to the negative direction of the X-axis shown in the coordinate axes depicted in the attached figures, and "right" refers to the positive direction of the X-axis shown in the coordinate axes depicted in the attached figures. However, "vertical," "horizontal," "inclined," "up," "down," "right," and "left" are used for convenience only and should not be interpreted restrictively.

[0056] Composition of an alkaline water electrolysis system

[0057] Reference Figures 1A to 5B An example of the configuration of the alkaline water electrolysis system 70 of this embodiment will be described.

[0058] The alkaline water electrolysis system 70 includes two or more rectifiers 74_1 to 74_N, two or more bipolar electrolytic cells 50_1 to 50_N, an on / off valve 62, a gas-liquid separator 72, a heat exchanger 79, a control device 30, a temperature regulating valve 61, a pressure gauge 78, a pressure regulating valve 80, and a circulating pump 90. It should be noted that... Figure 1A and Figure 1B In this example, a configuration in which two or more bipolar electrolytic cells are connected to different rectifiers is described, but a configuration in which two or more bipolar electrolytic cells are connected to the same rectifier is also possible. Furthermore, there is no particular limitation on the number of bipolar electrolytic cells.

[0059] [Rectifier]

[0060] Two or more rectifiers 74_1 to 74_N are electrically connected to two or more bipolar electrolytic cells 50_1 to 50_N. Additionally, two or more rectifiers 74_1 to 74_N are electrically connected to a control device 30.

[0061] The rectifier 74 is connected to a variable power source and converts alternating current (AC) to direct current (DC) when variable power (e.g., renewable energy) is supplied from outside the alkaline water electrolysis system 70. Renewable energy sources include, for example, at least one of wind, solar, hydro, tidal, wave, ocean current, and geothermal energy. Renewable energy sources are prone to power fluctuations, thus allowing for the random supply of a wide range of power densities, from low to high, to the alkaline water electrolysis system 70.

[0062] The rectifier 74 applies a specified DC current between the anode and cathode terminals in the bipolar electrolytic cell 50. The specified DC voltage is determined by the control device 30.

[0063] For example, the rectifier 74 has a distance of 10 kA / m between the anode and cathode terminals in the bipolar electrolytic cell 50, determined by the control device 30. 2 A current density of ] is applied. As a result, the bipolar electrolytic cell 50 operates at 100% capacity.

[0064] For example, the rectifier 74 has a distance of 5 kA / m between the anode and cathode terminals in the bipolar electrolytic cell 50, determined by the control device 30. 2 A current density of ] is applied. As a result, the bipolar electrolytic cell 50 operates at a 50% operating rate.

[0065] For example, the rectifier 74 has a distance of 3 [kA / m] between the anode and cathode terminals in the bipolar electrolytic cell 50, determined by the control device 30. 2 A current density of ] is applied. As a result, the bipolar electrolytic cell 50 operates at a working rate of 30%.

[0066] For example, the rectifier 74 does not apply voltage between the anode and cathode terminals in the bipolar electrolytic cell 50, thereby stopping the bipolar electrolytic cell 50.

[0067] As described above, a predetermined DC voltage, determined by the control device 30, is applied between the anode and cathode terminals in the bipolar electrolytic cell 50 via the rectifier 74, thereby controlling the operation or shutdown of the bipolar electrolytic cell 50. It should be noted that, in this specification, controlling the operation or shutdown of the bipolar electrolytic cell 50 not only means simple on / off control of the bipolar electrolytic cell 50, but also includes controlling the operating rate of the bipolar electrolytic cell 50 during operation.

[0068] [Bipolar Electrolyzer]

[0069] Two or more bipolar electrolyzers 50_1 to 50_N are installed at the lower part of the gas-liquid separator 72 and are electrically connected to two or more rectifiers 74_1 to 74_N respectively. In addition, the two or more bipolar electrolyzers 50_1 to 50_N are connected to the oxygen separator 72o via on / off valves 62o (inlet on / off valve 62oi, outlet on / off valve 62oo) and to the hydrogen separator 72h via on / off valves 62h (inlet on / off valve 62hi, outlet on / off valve 62ho).

[0070] The bipolar electrolyzer 50, based on a predetermined DC voltage supplied by the rectifier 74, uses an electrolyte to produce oxygen from the anode side and hydrogen from the cathode side through the electrolysis of water. The bipolar electrolyzer 50 has two or more electrolysis units 65 (see reference). Figure 4 It should be noted that the details of the composition of the bipolar electrolytic cell 50 and the electrolysis unit 65 are described later.

[0071] The electrolyte is an alkaline aqueous solution containing a dissolved alkali salt, such as an aqueous solution of NaOH or KOH. The concentration of the alkali salt is preferably 20% to 50% by mass, more preferably 25% to 40% by mass. Considering ionic conductivity, kinematic viscosity, and freezing at low temperatures, the electrolyte is particularly preferably an aqueous solution of KOH with a concentration of 25% to 40% by mass, or an aqueous solution of NaOH with a concentration of 10% to 40% by mass.

[0072] Two or more bipolar electrolyzers 50_1 to 50_N are controlled to operate or stop via a control device 30. For example, the operation or stop of each of the two or more bipolar electrolyzers 50_1 to 50_N is controlled by the control device 30 to ensure that the current used to operate the alkaline water electrolysis system 70 matches a target current. For example, the operation or stop of each of the two or more bipolar electrolyzers 50_1 to 50_N is controlled by the control device 30 based on the ratio of the current density of the operating bipolar electrolyzer to the maximum current density. For example, the operation or stop of each of the two or more bipolar electrolyzers 50_1 to 50_N is controlled by the control device 30 based on the power supplied to the alkaline water electrolysis system 70.

[0073] In this way, by appropriately controlling the operation or shutdown of each of the two or more bipolar electrolyzers 50_1 to 50_N through the control device 30, the alkaline water electrolysis system 70 can continuously produce high-purity hydrogen.

[0074] [On / Off Valve]

[0075] An on / off valve 62 is disposed between the bipolar electrolyzer 50 and the gas-liquid separator 72. For example, an on / off valve 62o is disposed between the bipolar electrolyzer 50 and the oxygen separator 72o. For example, an on / off valve 62h is disposed between the bipolar electrolyzer 50 and the hydrogen separator 72h. For example, an inlet on / off valve 62oi is disposed between the bipolar electrolyzer 50 and the gas-liquid separator 72o via a circulation pump 90. For example, an inlet on / off valve 62hi is disposed between the bipolar electrolyzer 50 and the gas-liquid separator 72h via a circulation pump 90.

[0076] The on / off valve 62 is controlled by the control device 30. When the on / off valve 62 is open, the electrolyte flows between the bipolar electrolyzer 50 and the gas-liquid separator 72. When the on / off valve 62 is closed, the flow of electrolyte between the bipolar electrolyzer 50 and the gas-liquid separator 72 is stopped. With the on / off valve 62 closed, not only is the flow of electrolyte between the bipolar electrolyzer 50 and the gas-liquid separator 72 stopped, but gas diffusion between the bipolar electrolyzer 50 and the gas-liquid separator 72 is also suppressed, preventing gas from entering the interior of the bipolar electrolyzer. As a result, gas contamination is also reduced.

[0077] The on / off valve 62 is closed when the bipolar electrolyzer 50 is filled with electrolyte. Therefore, the diaphragm inside the bipolar electrolyzer 50 is always immersed in the electrolyte, which inhibits the diffusion of oxygen and hydrogen into the bipolar electrolyzer 50 through the diaphragm. As a result, gas contamination can be further reduced.

[0078] The inlet valves 62hi and 62oi have the following effects: preventing electrolyte from shifting into the gas-liquid separator 72 due to its own weight, ensuring that the bipolar electrolyzer 50 is always full, and keeping the diaphragm constantly immersed in the electrolyte. The outlet valves 62ho and 62oo have the effect of preventing the diffusion of hydrogen and oxygen in the piping. The effect is maximized by completely closing the inlet valves 62hi and 62oi and the outlet valves 62ho and 62oo, but the effect is also achieved even when only the inlet valves 62hi and 62oi and only the outlet valves 62ho and 62oo are closed.

[0079] The circulating pump 90 delivers electrolyte to the bipolar electrolytic cell 50. By driving the circulating pump, the following effects are achieved: in addition to filling the bipolar electrolytic cell 50 with water using electrolyte, it also replenishes the water consumed by electrolysis, making the electrolyte concentration uniform, and cooling the bipolar electrolytic cell 50 through electrolyte circulation.

[0080] [Gas-Liquid Separator]

[0081] The gas-liquid separator 72 is preferably located above two or more bipolar electrolyzers 50_1 to 50_N and connected to them. The gas-liquid separator 72 separates the generated gases (hydrogen and oxygen) from the electrolyte and stores the electrolyte flowing into the two or more bipolar electrolyzers 50_1 to 50_N. The gas-liquid separator 72 includes an oxygen separator 72o and a hydrogen separator 72h. One oxygen separator 72o is connected to two or more bipolar electrolyzers 50_1 to 50_N, and one hydrogen separator 72h is connected to two or more bipolar electrolyzers 50_1 to 50_N. It should be noted that the position of the gas-liquid separator 72 relative to the two or more bipolar electrolyzers 50_1 to 50_N is not particularly limited. For example, as... Figure 1B Similar to the alkaline water electrolysis system 70B shown, the gas-liquid separator 72 can also be installed at the lower part of two or more bipolar electrolyzers 50_1 to 50_N and connected to the two or more bipolar electrolyzers 50_1 to 50_N.

[0082] The oxygen separator 72o separates oxygen into the upper gas phase and electrolyte into the lower liquid phase from the mixture of oxygen and electrolyte flowing in from the bipolar electrolyzer 50. The separated oxygen is discharged from the outlet located at the top of the oxygen separator 72o. The separated electrolyte accumulates inside the oxygen separator 72o and flows out from the outlet located at the bottom of the oxygen separator 72o, flowing back into the bipolar electrolyzer 50.

[0083] The hydrogen separator 72h separates hydrogen into the upper gas phase and electrolyte into the lower liquid phase from the mixture of hydrogen and electrolyte flowing in from the bipolar electrolyzer 50. The separated hydrogen is discharged from the outlet located at the top of the hydrogen separator 72h. The separated electrolyte accumulates inside the hydrogen separator 72h and flows out from the outlet located at the bottom of the hydrogen separator 72h, flowing back into the bipolar electrolyzer 50.

[0084] It should be noted that the oxygen or hydrogen discharged from the outlet of the gas-liquid separator 72 is in a state containing alkaline mist. Therefore, the gas-liquid separator 72 is preferably equipped with a device such as a mist separator or a cooler on the downstream side of the outlet, which can liquefy the remaining mist and return it to the gas-liquid separator 72.

[0085] The degree of gas-liquid separation in the gas-liquid separator 72 is determined by factors such as the amount of electrolyte stored inside, the floating velocity of gas bubbles, and the residence time of the gas. If the degree of gas-liquid separation is properly determined, adverse situations such as a decrease in gas purity due to the mixing of oxygen and hydrogen can be avoided when the electrolyte flows from the bipolar electrolyzer 50 into the gas-liquid separator 72.

[0086] If volume is taken into consideration, the gas-liquid separator 72 is preferably small in capacity. However, if the volume is too small, the fluctuation of the electrolyte level inside the gas-liquid separator 72 will increase due to changes in pressure or current. Therefore, the capacity of the gas-liquid separator 72 is preferably designed to account for the fluctuation of the electrolyte level. It should be noted that the gas-liquid separator 72 may also be further equipped with a level gauge for measuring the height of the electrolyte level inside.

[0087] The gas-liquid separator 72 can be any shape that can at least store electrolyte inside, such as a cylindrical shape. The gas-liquid separator 72 is preferably made of an alkali-resistant metal material, such as nickel or SUS.

[0088] The gas-liquid separator 72 preferably has a resin lining on its inner surface. If the gas-liquid separator 72 has a resin lining on its inner surface, its outer surface is preferably covered with an insulating material.

[0089] The thickness of the resin liner is preferably 0.5 mm to 4.0 mm, more preferably 1.0 mm to 2.0 mm. When the thickness is less than 0.5 mm, the inner surface of the gas-liquid separator 72 is prone to deterioration due to gas and electrolyte. When the thickness is greater than 4.0 mm, residual stress is released through high temperature and alkali, thereby increasing the possibility of deformation or peeling. By ensuring the resin liner thickness falls within this range, the durability of the gas-liquid separator 72 can be improved.

[0090] The standard deviation of the resin liner thickness is preferably 1.0 mm or less, more preferably 0.5 mm or less. By suppressing the deviation in the resin liner thickness, the durability of the gas-liquid separator 72 can be improved. It should be noted that the deviation in the resin liner thickness can be suppressed by appropriately adjusting the conditions of the sandblasting treatment performed on the surface of the gas-liquid separator 72 before the resin liner is formed.

[0091] The resin liner is preferably formed in two or more layers. The resin liner can be formed using known methods. Examples of such methods include, for instance, rotary sintering, powder coating, liquid coating, and spray coating. It should be noted that before forming the resin liner, the inner surface of the gas-liquid separator 72 may undergo one or more of the following treatments: degreasing, sandblasting, or primer coating.

[0092] The resin liner is preferably formed of a fluorinated resin material. Examples of fluorinated resin materials include at least one selected from the group consisting of polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). By forming the resin liner from a fluorinated resin material, the durability of the gas-liquid separator 72 to the electrode liquid can be improved.

[0093] The insulation material can be any known thermal insulation material, such as glass wool or foam. The inner surface of the gas-liquid separator 72, especially under high-temperature conditions, becomes significantly degraded due to gas and electrolyte. By covering the outer surface of the gas-liquid separator 72 with insulation material, this deterioration can be suppressed.

[0094] As described above, the gas-liquid separator 72 is preferably located above two or more bipolar electrolyzers 50_1 to 50_N. This guides the denser liquid to the lower side and the less dense gas to the upper side, ensuring stable electrolyte circulation even when variable power is supplied to the alkaline water electrolysis system 70, thus promoting self-circulation. Furthermore, when the bipolar electrolyzer 50 is stopped, the density difference between the gas-liquid separator 72 and the bipolar electrolyzer 50 allows the electrolyte held in the gas-liquid separator 72 to keep the bipolar electrolyzer 50 fully saturated, thereby suppressing gas diffusion through the diaphragm. Additionally, it prevents undesirable mixing of impurity gases between the oxygen separator 72o and the hydrogen separator 72h via the bipolar electrolyzer 50. Furthermore, when the bipolar electrolyzer 50 is located above the gas-liquid separator 72, maintenance of the bipolar electrolyzer 50 requires lifting it to the top of the gas-liquid separator 72 using a crane, making maintenance complicated. However, when the bipolar electrolyzer 50 is located below the gas-liquid separator 72, maintenance can be carried out smoothly because it is not necessary to lift the bipolar electrolyzer 50 using a crane.

[0095] Furthermore, as described above, the gas-liquid separator 72 is connected to two or more bipolar electrolytic cells 50_1 to 50_N, and a large amount of high-purity gas generated in the two or more bipolar electrolytic cells 50_1 to 50_N flows into the gas-liquid separator 72. Therefore, assuming that even if the impurity concentration increases in any of the bipolar electrolytic cells 50, a large amount of high-purity gas can be used inside the gas-liquid separator 72 to dilute the low-purity gas in one go, and the gas discharged from the gas-liquid separator 72 can be made into a high-purity gas (see reference). Figure 2 This reduces the frequency of purging inactive gases that accompany system shutdowns, improving the sustainability of high-purity hydrogen supply. Therefore, an alkaline water electrolysis system 70 capable of continuously producing high-purity hydrogen can be realized.

[0096] [Heat Exchanger]

[0097] The heat exchanger 79 is preferably located inside the gas-liquid separator 72. The heat exchanger 79 controls the heat exchange via the control device 30 to regulate the temperature of the electrolyte stored inside the gas-liquid separator 72. In this case, the heat exchanger 79 can be controlled by the control device 30 based on the flow rate of the electrolyte measured by a flow meter (not shown).

[0098] With the heat exchanger 79o installed inside the oxygen separator 72o, the heat exchanger 79o regulates the temperature of the electrolyte stored inside the oxygen separator 72o. By connecting the oxygen separator 72o to two or more bipolar electrolyzers 50_1 to 50_N, the heat exchanger 79o can effectively regulate the electrolyte temperature. Furthermore, by installing the heat exchanger 79o inside the oxygen separator 72o, the overall system footprint can be reduced.

[0099] With the heat exchanger 79h installed inside the hydrogen separator 72h, the heat exchanger 79h regulates the temperature of the electrolyte stored inside the hydrogen separator 72h. By connecting the hydrogen separator 72h to two or more bipolar electrolyzers 50_1 to 50_N, the heat exchanger 79h can effectively regulate the electrolyte temperature. Furthermore, by installing the heat exchanger 79h inside the hydrogen separator 72h, the overall system footprint can be reduced.

[0100] For example, if all the bipolar electrolyzers 50 are operated at 100% capacity, the temperature of the electrolyte in all the operating bipolar electrolyzers 50 will rise. Therefore, in this case, the heat exchanger 79 cools the electrolyte stored inside the gas-liquid separator 72. For example, if some of the bipolar electrolyzers 50 are operated at 100% capacity and some are stopped, the temperature of the electrolyte in the stopped bipolar electrolyzers 50 will drop. Therefore, in this case, the heat exchanger 79 heats the electrolyte stored inside the gas-liquid separator 72. In this way, by appropriately adjusting the temperature of the electrolyte according to the operation or stoppage of two or more bipolar electrolyzers 50_1 to 50_N, the temperature of the electrolyte throughout the system can be maintained at an appropriate level. Thus, an alkaline water electrolysis system 70 capable of high-efficiency operation can be achieved.

[0101] As described above, by installing the heat exchanger 79 inside the gas-liquid separator 72, which is connected to two or more bipolar electrolyzers 50_1 to 50_N, the temperature of the electrolyte stored inside the gas-liquid separator 72 can be easily maintained at an appropriate temperature. For example, even if the alkaline water electrolysis system 70 stops and restarts, no unnecessary electricity is consumed, thus enabling the alkaline water electrolysis system 70 to operate efficiently and continuously.

[0102] [Control Device]

[0103] The control device 30 can be any computer capable of performing prescribed processes through a program, such as a laptop computer (personal computer), smartphone, tablet, or other mobile phone used by the operator. The control device 30 controls all components of the alkaline water electrolysis system 70.

[0104] The control device 30 includes a control unit and a storage unit. The control unit can be constructed using dedicated hardware, or it can be constructed using a general-purpose processor or a processor dedicated to specific processing. The storage unit includes one or more memories, such as semiconductor memories, magnetic memories, optical memories, etc. Each memory included in the storage unit can function as a main memory device, an auxiliary memory device, or a cache memory, for example. Each memory does not necessarily need to be located inside the control device 30; it can also be configured to be located outside the control device 30.

[0105] The control device 30 generates control signals for controlling the operation or shutdown of the bipolar electrolytic cell 50 and outputs them to the rectifier 74. For example, the control device 30 outputs a control signal to the rectifier 74 to operate the bipolar electrolytic cell 50 at 100% operating rate. For example, the control device 30 outputs a control signal to the rectifier 74 to operate the bipolar electrolytic cell 50 at 50% operating rate. For example, the control device 30 outputs a control signal to the rectifier 74 to operate the bipolar electrolytic cell 50 at 30% operating rate. For example, the control device 30 outputs a control signal to the rectifier 74 to shut down the bipolar electrolytic cell 50. Thus, the control device 30 controls the operation (or operating rate) or shutdown of each of the two or more bipolar electrolytic cells 50_1 to 50_N by appropriately determining the prescribed DC voltage supplied to each.

[0106] For example, such as Figure 3A As shown, when the alkaline water electrolysis system 70 has six bipolar electrolyzers, the control device 30 controls bipolar electrolyzers 50_1, 50_2, 50_3, 50_4, 50_5, and 50_6 to operate at 100% capacity. In this case, the current load in the alkaline water electrolysis system 70 is (600% / 600%) × 100 = 100%.

[0107] For example, such as Figure 3B As shown, in the case where the alkaline water electrolysis system 70 has six bipolar electrolyzers, the control device 30 controls bipolar electrolyzer 50_1 to operate at a 30% operating rate, and controls bipolar electrolyzers 50_2, 50_3, 50_4, 50_5, and 50_6 to stop. In this case, the current load in the alkaline water electrolysis system 70 is (30% / 600%) × 100 = 5%.

[0108] Here, a typical solid line graph representing the relationship between current load and impurity concentration is used. The horizontal axis represents current load [%], and the vertical axis represents impurity concentration [H2 / O2]. Low impurity concentration is preferred, but the impurity concentration tends to be higher as the current load decreases.

[0109] Depend on Figure 3A It can be seen that in bipolar electrolytic cells 50_1 to 50_6, when the current load is 100%, the black circle representing the impurity concentration is at a very low position compared to the dashed line representing the allowable range of impurity concentration.

[0110] Depend on Figure 3B It can be seen that in the bipolar electrolytic cell 50_1, when the current load is 30%, the black circle representing the impurity concentration is at a lower position compared to the dashed line representing the allowable range of impurity concentration. Furthermore, in the bipolar electrolytic cells 50_2 to 50_6, when the current load is 0%, it can be seen that the black circle representing the impurity concentration is at an extremely low position compared to the dashed line representing the allowable range of impurity concentration.

[0111] Depend on Figure 3A and Figure 3B It can be seen that in the alkaline water electrolysis system 70, by appropriately controlling the operation or shutdown of two or more bipolar electrolyzers 50_1 to 50_N by the control device 30, for example, even if the current load in the overall system is reduced from 100% to 5%, the impurity concentration inside all bipolar electrolyzers 50 can be maintained at an extremely low level. Therefore, it can be seen that an alkaline water electrolysis system 70 capable of operating over a wide range can be realized.

[0112] That is, it is shown that an alkaline water electrolysis system 70 capable of continuously producing high-purity hydrogen can be realized by having two or more bipolar electrolyzers 50_1 to 50_N that produce high-purity gas during operation and become full of liquid when stopped, and a gas-liquid separator 72 connected to the two or more bipolar electrolyzers 50_1 to 50_N and capable of diluting low-purity gas with a large amount of high-purity gas at one time.

[0113] The control device 30 controls the operation or shutdown of the bipolar electrolyzer 50, using a current that matches the target current (e.g., 10 kA) to operate the alkaline water electrolysis system 70. For example, the control device 30 outputs control signals to the rectifier 74 to operate or shut down two or more bipolar electrolyzers 50_1 to 50_N individually, so that the target current is evenly distributed to the operating bipolar electrolyzers 50. Alternatively, the control device 30 outputs control signals to the rectifier 74 to operate or shut down two or more bipolar electrolyzers 50_1 to 50_N individually, so that the target current is unevenly distributed to the operating bipolar electrolyzers 50.

[0114] The control device 30 is based on the current density of the bipolar electrolyzer 50 during operation relative to the maximum current density (e.g., 10 kA / m³). 2 The control device 30 controls the operation or shutdown of the bipolar electrolytic cell 50 by adjusting the ratio of the current density of the bipolar electrolytic cell 50 to the maximum current density. For example, when the current density of the bipolar electrolytic cell 50 in operation is less than 40% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to stop the bipolar electrolytic cell 50 in operation; when the current density of the bipolar electrolytic cell 50 in operation is greater than 40% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to stop the bipolar electrolytic cell 50 in operation. For example, when the current density of the bipolar electrolytic cell 50 in operation is less than 20% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to stop the bipolar electrolytic cell 50 in operation; when the current density of the bipolar electrolytic cell 50 in operation is greater than 20% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to stop the bipolar electrolytic cell 50 in operation. For example, when the current density of the operating bipolar electrolytic cell 50 is less than 10% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to stop the operating bipolar electrolytic cell 50; when the current density of the operating bipolar electrolytic cell 50 is greater than 10% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to allow the operating bipolar electrolytic cell 50 to continue operating as before. For example, when the current density of the operating bipolar electrolytic cell 50 is less than 5% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to stop the operating bipolar electrolytic cell 50; when the current density of the operating bipolar electrolytic cell 50 is greater than 5% of the maximum current density, the control device 30 outputs a control signal to the rectifier 74 to allow the operating bipolar electrolytic cell 50 to continue operating as before. It should be noted that the ratio is not limited to 40%, 20%, 10%, or 5%, and can be arbitrarily set by the control device 30.

[0115] The control device 30 controls the operation or shutdown of the bipolar electrolyzers 50 based on the power supplied to the alkaline water electrolysis system 70. For example, when the power supplied to the alkaline water electrolysis system 70 is above a first threshold, the control device 30 outputs a control signal to the rectifier 74 to operate all the bipolar electrolyzers 50. In this case, the control device 30 can control each bipolar electrolyzer 50 to make the current flow uniformly to all the bipolar electrolyzers 50, or it can control each bipolar electrolyzer 50 to make the current flow unevenly to all the bipolar electrolyzers 50. For example, when the power supplied to the alkaline water electrolysis system 70 is less than the first threshold, the control device 30 outputs a control signal to the rectifier 74 to operate a portion of the bipolar electrolyzers 50 and to stop the remaining bipolar electrolyzers 50. In this configuration, the control device 30 can arbitrarily control the number of bipolar electrolytic cells 50 in operation and the number of bipolar electrolytic cells 50 that are stopped. It should be noted that the first threshold can be arbitrarily set by the control device 30, and its value is not particularly limited.

[0116] When supplying power to the alkaline water electrolysis system 70, the control device 30 controls the number of operating bipolar electrolyzers 50 based on the current density of the bipolar electrolyzers 50 that have started operation. For example, if the current density of an operating bipolar electrolyzer 50 (e.g., the third bipolar electrolyzer) is above a second threshold, the control device 30 decides to increase the number of operating bipolar electrolyzers 50. Furthermore, the control device 30 outputs control signals to the rectifier 74 for starting a new bipolar electrolyzer 50 (e.g., the fourth bipolar electrolyzer) and for maintaining the operation of existing bipolar electrolyzers 50 (e.g., the first to third bipolar electrolyzers). For example, if the current density of an operating bipolar electrolyzer 50 (e.g., the third bipolar electrolyzer) is below the second threshold, the control device 30 decides to maintain the number of operating bipolar electrolyzers 50. Furthermore, the control device 30 outputs a control signal to the rectifier 74 to ensure that the bipolar electrolytic cells 50 (e.g., the first to the third bipolar electrolytic cells) that have already started operating continue to operate as before. It should be noted that the second threshold can be arbitrarily set by the control device 30, and its value is not particularly limited.

[0117] The control device 30 generates a control signal for controlling the on / off valve 62 and outputs it to the on / off valve 62. For example, if the control device 30 outputs a control signal to the on / off valve 62 to open the valve, then the on / off valve 62 becomes open. This allows the electrolyte to flow between the bipolar electrolyzer 50 and the gas-liquid separator 72. Conversely, if the control device 30 outputs a control signal to the on / off valve 62 to close the valve, then the on / off valve 62 becomes closed. This prevents the flow of electrolyte between the bipolar electrolyzer 50 and the gas-liquid separator 72.

[0118] Control device 30 generates a control signal for controlling pressure regulating valve 80 and outputs it to pressure regulating valve 80. For example, control device 30 controls pressure regulating valve 800 connected to oxygen separator 720 based on the measurement result of pressure gauge 780 measuring the internal pressure of oxygen separator 720. Thus, the internal pressure of oxygen separator 720 is regulated to an appropriate pressure (e.g., 100 kPa). Similarly, control device 30 controls pressure regulating valve 80h connected to hydrogen separator 72h based on the measurement result of pressure gauge 78h measuring the internal pressure of hydrogen separator 72h. Thus, the internal pressure of hydrogen separator 72h is regulated to an appropriate pressure (e.g., 100 kPa).

[0119] Control device 30 generates a control signal for controlling temperature regulating valve 61 and outputs it to temperature regulating valve 61. For example, control device 30 controls temperature regulating valve 61, which is connected to heat exchanger 79, based on the flow rate of the electrolyte measured by a flow meter. As a result, the temperature of the electrolyte stored inside oxygen separator 72 is adjusted to an appropriate temperature (e.g., 80 degrees Celsius). Similarly, control device 30 controls temperature regulating valve 61h, which is connected to heat exchanger 79h, based on the flow rate of the electrolyte measured by a flow meter. As a result, the temperature of the electrolyte stored inside hydrogen separator 72h is adjusted to an appropriate temperature (e.g., 80 degrees Celsius).

[0120] The control device 30 generates a control signal for controlling the heat exchange of the heat exchanger 79 and outputs it to the heat exchanger 79. For example, the control device 30 controls the heat exchange of the heat exchanger 79o installed inside the oxygen separator 72o based on the flow rate of the electrolyte measured by a flow meter. As a result, the electrolyte stored inside the oxygen separator 72o is cooled, heated, or kept warm. For example, the control device 30 controls the heat exchange of the heat exchanger 79h installed inside the hydrogen separator 72h based on the flow rate of the electrolyte measured by a flow meter. As a result, the electrolyte stored inside the hydrogen separator 72h is cooled, heated, or kept warm.

[0121] In addition to the aforementioned bipolar electrolyzer 50, rectifier 74, on / off valve 62, pressure regulating valve 80, temperature regulating valve 61, and heat exchanger 79, the control device 30 also controls all components of the alkaline water electrolysis system 70.

[0122] [Temperature regulating valve]

[0123] Temperature regulating valve 61 is controlled by control device 30. Connected to heat exchanger 79, temperature regulating valve 61 regulates the temperature of the electrolyte to maintain the temperature of the electrolyte stored inside gas-liquid separator 72 within a specified range (e.g., 50°C to 90°C, preferably 60°C to 80°C, more preferably 75°C to 85°C). For example, temperature regulating valve 61o is connected to heat exchanger 79o and controlled by control device 30 based on the electrolyte flow rate measured by a flow meter, thereby regulating the temperature of the electrolyte stored inside oxygen separator 72o. Similarly, temperature regulating valve 61h is connected to heat exchanger 79h and controlled by control device 30 based on the electrolyte flow rate measured by a flow meter, thereby regulating the temperature of the electrolyte stored inside hydrogen separator 72h. By appropriately controlling temperature regulating valve 61 by control device 30, excessive rise or fall of electrolyte temperature can be prevented, ensuring the electrolyte temperature is at an appropriate level.

[0124] [pressure gauge]

[0125] A pressure gauge 78 is disposed on the upper part of the gas-liquid separator 72 and connected to the gas-liquid separator 72. For example, pressure gauge 78 measures the internal pressure of oxygen separator 72 and outputs the measurement result to control device 30. Based on the measurement result, control device 30 controls pressure regulating valve 80, thereby maintaining the internal pressure of oxygen separator 72 at an appropriate pressure. For example, pressure gauge 78h measures the internal pressure of hydrogen separator 72h and outputs the measurement result to control device 30. Based on the measurement result, control device 30 controls hydrogen separator 72h, thereby maintaining the internal pressure of hydrogen separator 72h at an appropriate pressure.

[0126] [Pressure regulating valve]

[0127] Pressure regulating valve 80 is controlled by control device 30. Pressure regulating valve 80 is located at the top of gas-liquid separator 72 and connected to it. For example, pressure regulating valve 80o is connected to oxygen separator 72o, and is controlled by control device 30 based on the internal pressure of oxygen separator 72o measured by pressure gauge 78o, thereby regulating the internal pressure of oxygen separator 72o. Similarly, pressure regulating valve 80h is connected to hydrogen separator 72h, and is controlled by control device 30 based on the internal pressure of hydrogen separator 72h measured by pressure gauge 78h, thereby regulating the internal pressure of hydrogen separator 72h.

[0128] By appropriately adjusting the pressure regulating valve 80 using the control device 30, excessive pressure rises or drops inside the gas-liquid separator 72 can be prevented, ensuring that the pressure inside the gas-liquid separator 72 is at an appropriate level. Furthermore, even if the pressure inside the gas-liquid separator 72 exceeds the design pressure due to gas generated from water electrolysis, the pressure can be safely reduced.

[0129] [Flow meter]

[0130] A flow meter is installed at the lower part of the bipolar electrolyzer 50 and connected to it. The flow meter measures the flow rate of the electrolyte circulating in the bipolar electrolyzer 50 and outputs the measurement result to the control device 30. Based on the measurement result, the control device 30 controls the heat exchanger 79h and the temperature regulating valve 61h, thereby maintaining the electrolyte stored inside the oxygen separator 72h at an appropriate temperature. Additionally, based on the measurement result, the control device 30 controls the heat exchanger 79h and the temperature regulating valve 61h, thereby maintaining the electrolyte stored inside the hydrogen separator 72h at an appropriate temperature.

[0131] The flow meter appropriately outputs measurement results to the control device 30, which then appropriately controls the temperature of the electrolyte based on these results. This ensures stable electrolyte circulation and promotes self-circulation even when variable power is supplied to the alkaline water electrolysis system 70. Consequently, an alkaline water electrolysis system 70 capable of high-efficiency operation and the production of high-purity hydrogen can be achieved.

[0132] [Heating device]

[0133] A heating device is installed at the bottom of the gas-liquid separator 72 to heat the electrolyte stored inside the separator 72. The heating device is, for example, a heater. By utilizing not only the heat exchanger 79 and the temperature regulating valve 61, but also the heating device to heat the electrolyte stored inside the gas-liquid separator 72, the temperature of the cooled electrolyte can be instantly restored to a certain temperature, for example. Thus, an alkaline water electrolysis system 70 capable of high-efficiency operation can be achieved. Furthermore, for example, even if the alkaline water electrolysis system 70 stops and restarts, no unnecessary electricity is consumed, thus enabling a highly efficient and continuously operating alkaline water electrolysis system 70.

[0134] [Other components]

[0135] In addition to the components mentioned above, the alkaline water electrolysis system 70 may also include a water supply device, an oxygen concentration meter, a hydrogen concentration meter, and a detector. These components can be well-known, therefore detailed descriptions are omitted.

[0136] The alkaline water electrolysis system 70 of this embodiment, by having the above-described configuration, can reduce the frequency of purging inactive gases that occur when the entire system stops, and can improve the sustainability of the high-purity hydrogen supply. Thus, an alkaline water electrolysis system 70 capable of continuously producing high-purity hydrogen can be realized.

[0137] <Composition of a bipolar electrolytic cell>

[0138] Next, refer to Figure 4 , Figure 5A and Figure 5B Here is a detailed description of an example of the configuration of the bipolar electrolytic cell 50 in this embodiment.

[0139] In the bipolar electrolytic cell 50, two or more bipolar elements 60 are arranged between an anode terminal element (anode terminal) 51a and a cathode terminal element (cathode terminal) 51c. The anode terminal element 51a and the cathode terminal element 51c are electrically connected to a rectifier 74. Furthermore, the anode terminal element 51a is electrically connected to the leftmost anode 2a, and the cathode terminal element 51c is electrically connected to the rightmost cathode 2c. Current flows from the anode terminal element 51a through the cathode 2c and anode 2a included in the two or more bipolar elements 60 to the cathode terminal element 51c.

[0140] The bipolar electrolytic cell 50 is arranged from left to right as follows: a fixed head 51g1, an insulating plate 51i1, an anode terminal element 51a, an anode-side gasket 7a, a diaphragm 4, a cathode-side gasket 7c, two or more bipolar elements 60, an anode-side gasket 7a, a diaphragm 4, a cathode-side gasket 7c, a cathode terminal element 51c, an insulating plate 51i2, and a movable head 51g2. The two or more bipolar elements 60 are arranged such that the cathode 2c faces the anode terminal element 51a and the anode 2a faces the cathode terminal element 51c. The bipolar electrolytic cell 50 is integrally fastened by a pull rod 51r. It should be noted that a hydraulic cylinder or the like can also be used as the fastening mechanism. In addition, the bipolar electrolytic cell 50 can be arbitrarily changed from either the anode side or the cathode side, and is not limited to the above order.

[0141] Compared to unipolar electrolyzers, bipolar electrolyzers 50 can reduce the power supply current and can produce compounds and specified substances in large quantities in a short time. Therefore, in industry, using bipolar electrolyzers can achieve cost reduction compared to unipolar electrolyzers.

[0142] [Bipolar Device]

[0143] The bipolar element 60 includes an anode 2a, a cathode 2c, a partition 1 separating the anode 2a and the cathode 2c, and an outer frame 3 edging the partition 1. One side of the bipolar element 60 is the anode 2a, and the other side is the cathode 2c.

[0144] The number of pairs of bipolar elements 60 is not particularly limited, as long as the number of pairs required for the design production quantity is repeated. Preferably, it is 50 to 500, more preferably 70 to 300, and particularly preferably 100 to 200.

[0145] When the number of pairs of bipolar elements 60 is small, the adverse effects of leakage current on gas purity can be mitigated. However, when the number of pairs of bipolar elements 60 is large, it becomes difficult to evenly distribute the electrolyte into each electrolysis unit 65. Furthermore, an excessive number of pairs of bipolar elements 60 makes the manufacture of the bipolar electrolytic cell 50 difficult. If a large number of poorly manufactured bipolar elements 60 are piled up, the sealing surface pressure in the bipolar electrolytic cell 50 becomes uneven, easily leading to electrolyte and gas leakage. Therefore, by ensuring the number of pairs of bipolar elements 60 meets the aforementioned range, self-discharge generated when power supply is stopped can be reduced, and the electrical control system can be stabilized. Additionally, pump power and leakage current can be reduced, enabling efficient power storage.

[0146] [Electrolysis Unit]

[0147] The electrolysis unit 65 includes: a partition wall 1, an anode chamber 5a, and an anode 2a included in an adjacent bipolar element 60; a cathode 2c, a cathode chamber 5c, and a partition wall 1 included in another adjacent bipolar element 60; an outer frame 3; a diaphragm 4; and a gasket 7. The cathode chamber 5c includes a current collector 2r, a conductive elastomer 2e, and a rectifier plate 6. The electrolysis unit 65 may include a baffle 8.

[0148] The temperature of the electrolyte inside the electrolysis unit 65 is preferably 40°C or higher, more preferably 80°C or higher. Furthermore, the temperature of the electrolyte inside the electrolysis unit 65 is preferably 110°C or lower, more preferably 95°C or lower. By ensuring that the temperature of the electrolyte inside the electrolysis unit 65 meets this range, high electrolysis efficiency can be maintained while effectively suppressing the deterioration of various components in the alkaline water electrolysis system 70 due to heat.

[0149] The lower limit of the current density provided by the electrolysis unit 65 is preferably 1 kA / m 2 ]Above, more preferably 8 [kA / m 2 The above. Furthermore, the upper limit of the current density provided by the electrolysis unit 65 is preferably 15 kA / m³. 2 Below, and more preferably 10 kA / m 2The following applies. In particular, as with the alkaline water electrolysis system 70, when using a variable power source, it is preferable to set the upper limit of the current density to the range described above.

[0150] The internal pressure of the electrolysis unit 65 is preferably 3 kPa to 1000 kPa, more preferably 3 kPa to 300 kPa.

[0151] -next door-

[0152] The partition 1 separates the anode 2a and the cathode 2c. The partition 1 is electrically connected to the current collector 2r via the rectifier plate 6.

[0153] The partition 1 is preferably made of a conductive material. Examples of conductive materials include nickel, nickel alloys, mild steel, and nickel alloys plated with nickel. By making the partition 1 a conductive material, a uniform power supply can be achieved. The material of the part of the partition 1 that comes into contact with the electrolyte is particularly preferably made of nickel. This improves alkali resistance, heat resistance, and other properties.

[0154] The shape of the partition 1 is not particularly limited, but it is preferably a plate with a specified thickness. In addition, the top view shape of the partition 1 can be, for example, rectangular, circular, or elliptical. In the case of a rectangle, the corners can also be rounded.

[0155] -electrode-

[0156] An anode 2a is disposed in an anode chamber 5a, and a cathode 2c is disposed in a cathode chamber 5c. The anode 2a and cathode 2c belonging to one electrolysis unit 65 are electrically connected to each other. In addition, the cathode 2c is electrically connected to the current collector 2r via a conductive elastomer 2e.

[0157] To increase the surface area for water electrolysis, and to effectively remove the gas generated by water electrolysis from the surface of electrode 2, electrode 2 is preferably a porous body. Examples of porous bodies include plain woven mesh, perforated metal, metal mesh, and metal foam.

[0158] Electrode 2 can be the substrate itself, preferably having a highly reactive catalyst layer on the surface of the substrate.

[0159] From the perspective of resistance to the operating environment, the substrate is preferably formed of materials such as mild steel, stainless steel, nickel, or nickel-based alloys.

[0160] The catalyst layer of the anode 2a is preferably formed of a material with high oxygen production capacity and good durability. Examples of such materials include nickel or cobalt, iron or platinum group elements. Furthermore, as materials for achieving the desired catalytic activity and durability, examples include elemental metals such as palladium, iridium, platinum, gold, ruthenium, rhodium, cerium, nickel, cobalt, tungsten, iron, molybdenum, silver, copper, zirconium, titanium, hafnium, and lanthanides, compounds such as oxides, composite oxides or alloys composed of two or more metal elements, or mixtures thereof, and carbon materials such as graphene.

[0161] The catalyst layer of cathode 2c is preferably formed of a material with high hydrogen production capacity. Examples of such materials include nickel or cobalt, iron or platinum group elements. Furthermore, materials used to achieve the desired catalytic activity, durability, etc., include, for example, elemental metals, compounds such as oxides, composite oxides or alloys composed of two or more metal elements, or mixtures thereof. Specifically, examples include: porous coatings made by plasma spraying using Raney nickel, Raney alloys composed of two or more materials such as nickel and aluminum or nickel and tin, nickel compounds or cobalt compounds as raw materials; alloys or composite compounds of nickel with elements selected from cobalt, iron, molybdenum, silver, copper, etc.; metals or oxides of platinum group elements such as platinum or ruthenium with high hydrogen production capacity; and mixtures of these platinum group element metals or oxides with compounds of other platinum group elements such as iridium and palladium, compounds of rare earth metals such as lanthanum or cerium; carbon materials such as graphene, etc. To achieve high catalytic activity and durability, two or more catalyst layers formed from the above materials can be laminated, or two or more materials can be mixed within the catalyst layers. Furthermore, to improve durability and adhesion to the substrate, the material may also contain organic materials such as polymers.

[0162] The electrolysis voltage largely depends on the performance of electrode 2. By reducing the electrolysis voltage, energy consumption can be reduced in the alkaline water electrolysis system 70. Besides the theoretically required voltage for water electrolysis, the electrolysis voltage also includes overvoltages for the anodic reaction (oxygen production), overvoltages for the cathodic reaction (hydrogen production), and the voltage based on the distance between the electrodes of anode 2a and cathode 2c. Here, overvoltage refers to the voltage that needs to be applied in excess, exceeding the theoretical decomposition potential, when a certain current is flowing. By reducing the overvoltage, the electrolysis voltage can be reduced.

[0163] Electrode 2 preferably possesses properties such as high conductivity, high oxygen or hydrogen generation capacity, and high wettability of the electrolyte on its surface. By giving electrode 2 these properties, the aforementioned overvoltage can be reduced. Furthermore, electrode 2 preferably possesses properties such as resistance to corrosion of the substrate and catalyst layer, catalyst layer detachment, dissolution in the electrolyte, and adhesion of inclusions to the membrane 4, even when supplied with unstable power such as renewable energy sources.

[0164] -Current collector-

[0165] The current collector 2r has the following functions: while conducting electricity to the conductive elastomer 2e and the electrode 2, it supports the load borne by the conductive elastomer 2e and the electrode 2, allowing the gas generated by the electrode 2 to pass unimpeded to the partition wall 1 side.

[0166] The current collector 2r preferably has the shape of a metal mesh or a stamped perforated plate. The aperture ratio of the current collector 2r is preferably within a range that allows the hydrogen gas generated by the electrode 2 to be extracted unimpeded to the partition wall 1 side. If the aperture ratio is too large, problems such as reduced strength of the current collector 2r or reduced conductivity to the conductive elastomer 2e may occur; if the aperture ratio is too small, gas discharge will be poor. Therefore, the aperture ratio of the current collector 2r is preferably set appropriately with these problems in mind.

[0167] From the perspective of conductivity and alkali resistance, the current collector 2r is preferably made of materials such as nickel, nickel alloy, stainless steel, or mild steel. From the perspective of corrosion resistance, the current collector 2r is preferably nickel-plated on nickel, mild steel, or stainless steel / nickel alloy.

[0168] -Conductive elastomer-

[0169] The conductive elastomer 2e is in contact with the current collector 2r and the electrode 2, and is disposed between the current collector 2r and the cathode 2c. The conductive elastomer 2e has the following function: by applying appropriate pressure to the electrode 2 evenly without damaging the diaphragm 4, the diaphragm 4 is sealed tightly to the electrode 2.

[0170] The conductive elastomer 2e preferably has conductivity with respect to the electrode 2 and does not impede the diffusion of gas generated by the electrode 2. If the diffusion of gas is impeded by the conductive elastomer 2e, the resistance increases, the area of ​​the electrode 2 used for water electrolysis decreases, and thus the electrolysis efficiency decreases.

[0171] The composition of the conductive elastomer 2e is not particularly limited and can be any known composition. For example, the conductive elastomer 2e can be a cushioning pad made of an article woven from nickel wire with a diameter of about 0.05 mm to 0.5 mm and then corrugated.

[0172] -Outer frame-

[0173] The outer frame 3 is configured to surround the partition 1 along its outer edge. The outer frame 3 can be any shape that can surround the partition 1, and its shape is not particularly limited, but it is preferably shaped to have an inner surface that spans the outer edge of the partition 1 in a direction perpendicular to the plane of the partition 1. The outer frame 3 is preferably appropriately set according to the top view shape of the partition 1.

[0174] The outer frame 3 is preferably made of a conductive material, such as nickel, nickel alloy, mild steel, or nickel alloy. From the perspective of alkali resistance and heat resistance, the outer frame 3 is further preferably plated with nickel, such as nickel, nickel alloy, mild steel, or nickel alloy.

[0175] -Septum-

[0176] The diaphragm 4 divides the anode chamber 5a, which has an anode 2a, into a cathode chamber 5c, which has a cathode 2c. The diaphragm 4 is disposed between the anode terminal element 51a and the repolarizing element 60, between adjacent repolarizing elements 60, and between the repolarizing element 60 and the cathode terminal element 51c. The diaphragm 4 is ion-permeable, allowing ions to pass through while isolating hydrogen and oxygen. The diaphragm 4 is composed of an ion-exchange membrane with ion exchange capacity, a porous membrane capable of permeating electrolyte, etc. Preferably, the diaphragm 4 has low gas permeability, high ion conductivity, low electronic conductivity, and high strength.

[0177] --porous membrane--

[0178] Porous membranes have the following structure: they possess two or more microscopic through-pores that allow electrolyte to permeate. Examples of porous membranes with this structure include polymer porous membranes, inorganic porous membranes, woven fabrics, and nonwoven fabrics. These membranes are formed using known techniques.

[0179] The porous membrane preferably comprises at least one polymeric resin selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone. This allows for the maintenance of excellent ion permeability.

[0180] Porous membranes exhibit ionic conductivity through electrolyte permeation; therefore, it is preferable to appropriately control the porous structure, including pore size, porosity, and hydrophilicity. By appropriately controlling the porous structure, not only can electrolyte permeation be facilitated in porous membranes, but the barrier properties for generated gases can also be improved.

[0181] The thickness of the porous membrane is not particularly limited, but is preferably 200 μm or more and 700 μm or less. If the thickness of the porous membrane is 250 μm or more, superior barrier properties can be obtained, and the membrane's impact resistance can be further improved. From this perspective, the lower limit of the porous membrane thickness is more preferably 300 μm or more, more preferably 350 μm or more, and even more preferably 400 μm or more. On the other hand, if the thickness of the porous membrane is 700 μm or less, during the operation of the alkaline water electrolysis system 70, the permeability of ions is not easily hindered due to the resistance of the electrolyte contained within the pores, thus maintaining superior ion permeability. From this perspective, the upper limit of the porous membrane thickness is more preferably 600 μm or less, more preferably 550 μm or less, and even more preferably 500 μm or less.

[0182] --Ion exchange membrane--

[0183] Ion exchange membranes can be either cation exchange membranes that selectively allow cations to pass through or anion exchange membranes that selectively allow anions to pass through.

[0184] The material of the ion exchange membrane is not particularly limited, and known materials can be used. For example, ion exchange membranes are preferably formed from fluorinated resins or modified resins of polystyrene-divinylbenzene copolymer. From the perspective of superior heat resistance and chemical resistance, ion exchange membranes formed from fluorinated resins are particularly preferred.

[0185] -Electrode Chamber-

[0186] Electrode chamber 5 allows electrolyte to pass through and is defined by partition wall 1, outer frame 3, diaphragm 4, etc. The defined area of ​​electrode chamber 5 varies depending on the structure of outer frame 3 located at the outer end of partition wall 1. Electrode chamber 5 has an electrolyte inlet for introducing electrolyte into electrode chamber 5 and an electrolyte outlet for discharging electrolyte from electrode chamber 5 at its boundary with outer frame 3. For example, anode chamber 5a has an anolyte inlet for introducing electrolyte into anode chamber 5a and an anolyte outlet for discharging electrolyte from anode chamber 5a. For example, cathode chamber 5c has a cathode electrolyte inlet for introducing electrolyte into cathode chamber 5c and a cathode electrolyte outlet for discharging electrolyte from cathode chamber 5c.

[0187] The electrode chamber 5 may also be equipped with a baffle 8 for adjusting the gas-liquid ratio inside the bipolar electrolyzer 50. Additionally, the electrode chamber 5 may also be equipped with an internal distributor inside the bipolar electrolyzer 50 for uniformly distributing the electrolyte onto the surface of the electrode 2. Furthermore, to homogenize the electrolyte concentration and temperature, or to promote degassing of the gas adhering to the electrode 2 and the diaphragm 4, the electrode chamber 5 may also be equipped with protrusions for creating Karman vortices inside the bipolar electrolyzer 50.

[0188] It should be noted that the current collector 2r can be provided not only inside the cathode chamber 5c, but also inside the anode chamber 5a. The current collector 2r can be made of the same material and have the same structure as the current collector provided inside the cathode chamber 5c. Alternatively, the anode 2a itself can function as a current collector.

[0189] -Rectifier-

[0190] The rectifier plate 6 supports the anode 2a and is disposed between the anode 2a and the partition wall 1. In addition, the rectifier plate 6 supports the cathode 2c and the current collector 2r and is disposed between the current collector 2r and the partition wall 1.

[0191] The rectifier plate 6 is installed in a partition wall 1 of an adjacent electrolysis unit 65. For example, in the anode chamber 5a, a structure in which the partition wall 1, the rectifier plate 6, and the anode 2a overlap sequentially from left to right can be adopted. The partition wall 1, the rectifier plate 6, and the anode 2a can be electrically connected and physically directly connected. As a method for directly installing these components together, welding is an example. It should be noted that in the anode chamber 5a, a structure in which the partition wall 1, the rectifier plate 6, the current collector 2r, the conductive elastomer 2e, and the anode 2a overlap sequentially from left to right can also be adopted.

[0192] The rectifier plate 6 is mounted on another partition wall 1 of the adjacent electrolysis unit 65. For example, in the cathode chamber 5c, a structure can be adopted in which the cathode 2c, conductive elastomer 2e, current collector 2r, rectifier plate 6, and partition wall 1 overlap sequentially from left to right. The cathode 2c, conductive elastomer 2e, current collector 2r, rectifier plate 6, and partition wall 1 can be electrically connected and physically directly connected. As a method for directly mounting these components to each other, welding or the like can be cited.

[0193] By installing a rectifier plate 6 in the electrolysis chamber 5, current can easily flow from the partition wall 1 to the anode 2a or from the cathode 2c to the partition wall 1. In addition, by installing a rectifier plate 6 in the electrolysis chamber 5, convection generated inside the electrolysis chamber 5 due to turbulence of gas-liquid flow can be reduced, thus suppressing the rise in local electrolyte temperature.

[0194] The rectifier plate 6 is preferably formed of a conductive metallic material. Examples of such materials include, for instance, nickel-plated mild steel, stainless steel, and nickel.

[0195] The rectifier plate 6 preferably has at least a portion that is conductive, and more preferably all of it is conductive. By making the rectifier plate 6 conductive, the voltage rise in the electrolysis unit 65 caused by electrode deflection can be suppressed.

[0196] -Gasket-

[0197] The gasket 7 is disposed on the outer frame 3 that edges the partition 1. The gasket 7 has the functions of preventing electrolyte and generated gas from leaking to the outside of the bipolar electrolytic cell 50 and preventing gas mixing between the anode chamber 5a and the cathode chamber 5c.

[0198] The gasket 7 corresponds to the surface that contacts the outer frame 3 and has a quadrilateral shape or ring shape that extends through the electrode 2. The diaphragm 4 can be sandwiched between two gaskets, thereby stacking the diaphragm 4 between adjacent bipolar elements 60.

[0199] The gasket 7 preferably has a slit portion capable of accommodating the diaphragm 4 to hold the diaphragm 4 in place. Furthermore, the gasket 7 preferably has openings that allow the diaphragm 4 to protrude from both surfaces of the gasket 7. By providing openings in the gasket 7, the edge of the diaphragm 4 can be accommodated within the slit portion, and the end face of the edge of the diaphragm 4 can be covered. This reliably prevents electrolyte and gas from leaking from the end face of the edge of the diaphragm 4.

[0200] There are no particular restrictions on the material of gasket 7; any known insulating rubber or resin material can be selected. Specifically, rubber or resin materials such as natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), nitrile rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene propylene diene monomer (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), polyurethane rubber (UR), and chlorosulfonated polyethylene rubber (CSM) can be used; fluoropolymers such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and trifluorochloroethylene-ethylene copolymer (ECTFE); and resins such as polyphenylene sulfide (PPS), polyethylene, polyimide, and polyacetal are preferred. Among these, ethylene propylene diene monomer (EPDM) and fluororubber (FR) are particularly preferred in terms of elastic modulus and alkali resistance.

[0201] -Baffle-

[0202] Baffle 8 is a partition that restricts the flow of electrolyte inside electrode chamber 5. Baffle 8 adjusts the ratio of electrolyte to gas inside electrode chamber 5, for example, separating the electrolyte and gas in a manner where only electrolyte flows to the back side and both electrolyte and gas flow to the front side. That is, by using baffle 8 to retain gas at a predetermined location, the electrolyte can circulate internally within electrode chamber 5, resulting in a more uniform electrolyte concentration.

[0203] Baffle 8 is disposed, for example, inside the cathode chamber 5c. Preferably, baffle 8 is disposed obliquely or parallel to the partition wall 1 relative to the transverse direction of the cathode chamber 5c between the cathode 2c and the partition wall 1. In the space near the cathode 2c separated by baffle 8, if water electrolysis occurs, the concentration of the electrolyte decreases, producing hydrogen. This can sometimes result in a difference in specific gravity between the gas and liquid, but by arranging baffle 8 inside the cathode chamber 5c, internal circulation of the electrolyte can be promoted within the cathode chamber 5c, resulting in a more uniform concentration distribution of the electrolyte within the cathode chamber 5c.

[0204] The above provides a detailed description of one example of the configuration of the bipolar electrolyzer 50, but the bipolar electrolyzer 50 is not limited to the above configuration. In addition to the above-described components, the bipolar electrolyzer 50 may also include, for example, a header for dispensing or collecting the electrolyte.

[0205] Operation Methods of Alkaline Water Electrolysis Systems

[0206] Reference Figure 6 An example of the operation method of the alkaline water electrolysis system 70 of this embodiment will be described.

[0207] In step S101, if variable power is supplied from outside the alkaline water electrolysis system 70, two or more rectifiers 74_1 to 74_N convert the alternating current into direct current. Furthermore, the two or more rectifiers 74_1 to 74_N apply a predetermined direct current voltage between the anode and cathode terminals in two or more bipolar electrolytic cells 50_1 to 50_N.

[0208] In step S102, two or more bipolar electrolyzers 50_1 to 50_N generate oxygen from the anode side and hydrogen from the cathode side using an electrolyte through the electrolysis of water, based on a predetermined DC voltage applied by two or more rectifiers 74_1 to 74_N. The operation or shutdown of each bipolar electrolyzer 50 is controlled by the control device 30.

[0209] In step S103, oxygen separator 72o separates oxygen from the mixture of oxygen and electrolyte flowing into the bipolar electrolyzer 50. The separated oxygen is discharged from the outlet located above oxygen separator 72o. The separated electrolyte accumulates inside oxygen separator 72o. Meanwhile, hydrogen separator 72h separates hydrogen from the mixture of hydrogen and electrolyte flowing into the bipolar electrolyzer 50. The separated hydrogen is discharged from the outlet located above hydrogen separator 72h. The separated electrolyte accumulates inside hydrogen separator 72h.

[0210] In step S104, heat exchanger 79o adjusts the electrolyte stored inside oxygen separator 72o to an appropriate temperature. Additionally, heat exchanger 79h adjusts the electrolyte stored inside hydrogen separator 72h to an appropriate temperature.

[0211] According to the operation method of the alkaline water electrolysis system 70 of this embodiment, even when the overall current load of the system 70 is reduced, the impurity concentration can be maintained at an extremely low level inside all the bipolar electrolyzers 50. This reduces the frequency of purging inactive gases that occur when the entire system stops, and improves the sustainability of the high-purity hydrogen supply. Therefore, by applying the operation method of the alkaline water electrolysis system 70 of this embodiment, high-purity hydrogen can be continuously produced.

[0212] The above embodiments have been described as representative examples, but those skilled in the art will obviously be able to make many changes and substitutions within the spirit and scope of this disclosure. Therefore, the present invention should not be construed as being limited to the above embodiments, and various modifications or alterations can be made without departing from the claims. For example, two or more constituent blocks shown in the structural diagrams of the embodiments can be combined into one, or a constituent block can be divided. In addition, two or more steps shown in the flowcharts of the embodiments can be combined into one, or a step can be divided.

[0213] Industrial applicability

[0214] According to the present invention, an alkaline water electrolysis system capable of continuously producing high-purity hydrogen can be realized. Therefore, in addition to fields such as petroleum refining, chemical synthesis, and metal refining, it is also particularly useful for applications such as hydrogen refueling stations for fuel cell vehicles, smart communities, and hydrogen power plants.

[0215] Symbol Explanation

[0216] 1. Next door

[0217] 2 electrodes

[0218] 2a anode

[0219] 2C cathode

[0220] 2e conductive elastomer

[0221] 2r current collector

[0222] 3 outer frame

[0223] 4 diaphragms

[0224] 5 electrode chambers

[0225] 5a Anode Chamber

[0226] 5c cathode chamber

[0227] 6 rectifier boards

[0228] 6a anode rectifier plate

[0229] 6C cathode rectifier plate

[0230] 7 gaskets

[0231] 8 baffles

[0232] 30 control devices

[0233] 50 bipolar electrolytic cell

[0234] 51g1 fixing head

[0235] 51g2 loose head

[0236] 51i1 Insulation Board

[0237] 51i2 Insulation Board

[0238] 51a anode terminal element

[0239] 51c cathode terminal element

[0240] 51r pull rod

[0241] 60 bipolar components

[0242] 61 Temperature regulating valve

[0243] 61o temperature regulating valve

[0244] 61h temperature regulating valve

[0245] 62 On / Off Valve

[0246] 62o on / off valve

[0247] 62h on / off valve

[0248] 62oi inlet on / off valve

[0249] 62hi inlet on / off valve

[0250] 62oo outlet on / off valve

[0251] 62ho outlet on / off valve

[0252] 65 electrolysis units

[0253] 70 Alkaline Water Electrolysis System

[0254] 70B Alkaline Water Electrolysis System

[0255] 72 gas-liquid separator

[0256] 72° Oxygen Separator

[0257] 72h hydrogen separator

[0258] 74 rectifier

[0259] 78 pressure gauge

[0260] 78o pressure gauge

[0261] 78h pressure gauge

[0262] 79 heat exchanger

[0263] 79o heat exchanger

[0264] 79h heat exchanger

[0265] 80 pressure regulating valve

[0266] 80° pressure regulating valve

[0267] 80h pressure regulating valve

[0268] 90 circulating pump

Claims

1. An alkaline water electrolysis system, comprising: A rectifier, connected to a variable power source, converts alternating current (AC) into direct current (DC). Two or more bipolar electrolyzers, which use an electrolyte to produce hydrogen and oxygen by electrolyzing water based on a specified DC voltage supplied by the rectifier; A gas-liquid separator, which is connected to two or more of the aforementioned bipolar electrolyzers, separates the hydrogen and oxygen from the electrolyte and stores the electrolyte; and An on / off valve, which is located between the gas-liquid separator and the bipolar electrolytic cell, has an inlet on / off valve and an outlet on / off valve. A control device that determines the DC voltage and controls the operation or shutdown of the bipolar electrolytic cell.

2. The alkaline water electrolysis system as described in claim 1 further comprises a pressure regulating valve for regulating the internal pressure of the gas-liquid separator.

3. The alkaline water electrolysis system as described in claim 1 or 2, wherein, The control device controls the operation or shutdown of the bipolar electrolyzer to ensure that the current used to operate the alkaline water electrolysis system is consistent with the target current.

4. The alkaline water electrolysis system as described in claim 1 or 2, wherein, The control device controls the operation or shutdown of the bipolar electrolytic cell based on the ratio of the current density of the bipolar electrolytic cell during operation to the maximum current density.

5. The alkaline water electrolysis system as described in claim 1 or 2, wherein, When the power supplied to the alkaline water electrolysis system is above a first threshold, the control device activates all the bipolar electrolyzers. When the power supplied to the alkaline water electrolysis system is less than the first threshold, a portion of the bipolar electrolyzers are operated.

6. The alkaline water electrolysis system as described in claim 1 or 2, wherein, When power is supplied to the alkaline water electrolysis system, the control device If the current density of the bipolar electrolytic cell that has started operation is above the second threshold, the number of operating bipolar electrolytic cells shall be increased. The number of bipolar electrolyzers that continue to operate when the current density of the bipolar electrolyzer that has started operating is less than the second threshold.

7. The alkaline water electrolysis system as claimed in claim 1, further comprising a heating device for heating the electrolyte stored inside the gas-liquid separator.

8. The alkaline water electrolysis system as described in claim 1, wherein, The renewable energy supplied to the alkaline water electrolysis system is energy obtained from at least one of wind power, solar power, hydropower, tidal power, wave power, ocean currents, and geothermal energy.

9. The alkaline water electrolysis system as described in claim 1, wherein, Each of the two or more bipolar electrolytic cells has its own rectifier.

10. The alkaline water electrolysis system as described in claim 1, wherein, A heat exchanger is installed inside the gas-liquid separator.

11. The alkaline water electrolysis system as described in claim 10, wherein, It also includes a temperature regulating valve, which is connected to the heat exchanger to regulate the temperature of the electrolyte so that the temperature of the electrolyte stored inside the gas-liquid separator is within a specified range.

12. The alkaline water electrolysis system as described in claim 1, wherein, The gas-liquid separator is located above two or more of the bipolar electrolytic cells.

13. The alkaline water electrolysis system as described in claim 1, wherein, A flow meter is installed at the bottom of the bipolar electrolytic cell.

14. The alkaline water electrolysis system as described in claim 1, wherein, The on / off valve closes when the bipolar electrolyzer is filled with electrolyte.

15. The alkaline water electrolysis system as described in claim 1 or 2, wherein, The opening and closing of the valve is controlled by a control device.

16. A method for operating an alkaline water electrolysis system, comprising: The steps of a rectifier connected to a variable power source to convert alternating current (AC) into direct current (DC); Two or more bipolar electrolyzers, based on a specified DC voltage supplied by the rectifier, use an electrolyte to produce hydrogen and oxygen through the electrolysis of water; The steps of separating hydrogen and oxygen from the electrolyte and storing the electrolyte in a gas-liquid separator connected to two or more of the aforementioned bipolar electrolyzers; and The step of the on / off valve located between the gas-liquid separator and the bipolar electrolyzer inhibits the conduction of the electrolyte, hydrogen, and oxygen between the gas-liquid separator and the bipolar electrolyzer; It also includes the steps of: controlling the operation or shutdown of two or more of the bipolar electrolytic cells by the control device, closing the inlet and outlet valves of the on / off valves, or closing either the inlet or outlet valves.

17. The method of operating the alkaline water electrolysis system as described in claim 16, further comprising: The control device, when the interior of the bipolar electrolyzer is filled with the electrolyte, performs the steps of closing the inlet valve and the outlet valve, or closing either the inlet valve or the outlet valve.

18. The method of operating the alkaline water electrolysis system as described in claim 16 or 17, further comprising: The step of adjusting the temperature of the electrolyte using a heat exchanger installed inside the gas-liquid separator.

19. The method of operating the alkaline water electrolysis system as described in claim 16 or 17, wherein, The gas-liquid separator is located above two or more of the bipolar electrolytic cells.

20. The method of operating the alkaline water electrolysis system as described in claim 16, wherein, The degree of gas-liquid separation in a gas-liquid separator is determined by the internal electrolyte bundle, the floating velocity of gas bubbles, and the residence time of the gas.

21. The method of operating the alkaline water electrolysis system as described in claim 16, wherein, When the power supplied to the alkaline water electrolysis system is above a first threshold, the control device activates all the bipolar electrolyzers. When the power supplied to the alkaline water electrolysis system is less than the first threshold, a portion of the bipolar electrolyzers are operated.

22. The method of operating the alkaline water electrolysis system as described in claim 16, wherein, When power is supplied to the alkaline water electrolysis system, the control device If the current density of the bipolar electrolytic cell that has started operation is above the second threshold, the number of operating bipolar electrolytic cells shall be increased. The number of bipolar electrolyzers that continue to operate when the current density of the bipolar electrolyzer that has started operating is less than the second threshold.

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