JP7470818B2 - Alkaline water electrolysis system and method for operating the alkaline water electrolysis system - Google Patents

Description

The present invention relates to an alkaline water electrolysis system and a method for operating an alkaline water electrolysis system.

In recent years, technologies that utilize renewable energy sources, such as wind power generation and solar power generation, have been attracting attention in order to solve problems such as global warming caused by greenhouse gases such as carbon dioxide and dwindling reserves of fossil fuels.

Renewable energy fluctuates greatly depending on weather conditions. For this reason, it is difficult to transport electricity generated using renewable energy to the general power grid, and there are concerns about social impacts such as an imbalance in electricity supply and demand and instability in the power grid. As a result, research is being conducted into storing electricity and using it in a transportable form. For example, hydrogen is being generated by electrolysis of water and used as an energy source or raw material.

Hydrogen is widely used industrially in fields such as petroleum refining, chemical synthesis, and metal refining, and in recent years, the possibility of its use in hydrogen stations for fuel cell vehicles, smart communities, hydrogen power plants, etc. is expanding. For this reason, there are high expectations for the development of technology to obtain hydrogen, in particular, from renewable energy sources.

Well-known methods of water electrolysis include solid polymer membrane water electrolysis, high-temperature steam electrolysis, and alkaline water electrolysis, but alkaline water electrolysis is considered to be one of the most promising methods because it has been industrialized for over several decades, can be carried out on a large scale, and is inexpensive compared to other electrolysis methods. Alkaline water electrolysis uses an alkaline aqueous solution (alkaline water) in which alkaline salts are dissolved as the electrolyte, and electrolyzes water to generate hydrogen gas from the cathode and oxygen gas from the anode.

For example, Patent Document 1 discloses a solid polymer membrane type water electrolysis device that has improved electrolysis efficiency by comprising a water electrolysis cell partitioned into an anode chamber and a cathode chamber by a solid polymer electrolyte membrane, a water supply tank that both supplies electrolyzed water and separates oxygen, and a water supply tank provided above the water electrolysis cell that both supplies circulating water and separates hydrogen.

JP 2002-285368 A

However, conventional water electrolysis systems have had difficulty circulating the electrolyte stably in response to fluctuating input power, making them inadequate for producing high-purity hydrogen.

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

In other words, the present invention is as follows.

An alkaline water electrolysis system according to one embodiment includes: a rectifier connected to a fluctuating power source and converting AC power into DC power;
a bipolar electrolytic cell that generates hydrogen and oxygen by electrolysis of water using an electrolyte based on a predetermined DC voltage supplied from the rectifier;
a gas-liquid separation tank provided at an upper portion of the bipolar electrolytic cell, which separates the hydrogen and the oxygen from the electrolytic solution and stores the electrolytic solution;
a heat exchanger provided inside the gas-liquid separation tank and configured to cool the electrolytic solution;
The present invention is characterized by comprising:
The alkaline water electrolysis system according to one embodiment further comprises: a flowmeter that measures a flow rate of the electrolytic solution;
A control device that controls an amount of heat exchanged by the heat exchanger based on a measurement result obtained by the flow meter;
The present invention is characterized by further comprising:
The alkaline water electrolysis system according to one embodiment further comprises a circulation pump that circulates the electrolytic solution,
The control device includes:
The circulation pump is controlled based on the measurement result obtained by the flow meter.
Furthermore, in the alkaline water electrolysis system according to one embodiment, the bipolar electrolytic cell comprises:
It is characterized by having a baffle plate that adjusts the gas-liquid ratio.

According to one embodiment, there is provided an operating method for an alkaline water electrolysis system, comprising the steps of: converting AC power into DC power by a rectifier connected to a fluctuating power source;
A step in which the bipolar electrolytic cell generates hydrogen and oxygen by electrolysis of water using an electrolyte based on a predetermined DC voltage supplied from the rectifier;
a gas-liquid separation tank provided at an upper portion of the bipolar electrolytic cell separating the hydrogen and the oxygen from the electrolytic solution and storing the electrolytic solution;
A heat exchanger provided inside the gas-liquid separation tank cools the electrolytic solution;
The present invention is characterized in that it includes:

The present invention provides an alkaline water electrolysis system capable of producing high-purity hydrogen, and a method for operating an alkaline water electrolysis system.

FIG. 1 is a diagram illustrating an example of the configuration of an alkaline water electrolysis system according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of the configuration of a bipolar electrolytic cell according to the present embodiment. FIG. 1 is a diagram showing an example of the configuration of an electrolysis cell according to an embodiment of the present invention. FIG. 1 is a diagram showing an example of the configuration of an electrolysis cell according to an embodiment of the present invention. 1 is a flowchart illustrating an example of a method for operating the alkaline water electrolysis system according to the present embodiment.

One embodiment of the present invention will now be described in detail with reference to the drawings. In principle, identical components will be given the same reference numbers and duplicate explanations will be omitted. For ease of explanation, the aspect ratio of each component in each drawing is exaggerated from the actual ratio.

In the following description, "vertical" means a direction parallel to the Z axis of the coordinate axis display depicted in the drawing, "up" means a positive direction on the Z axis, and "down" means a negative direction on the Z axis. "Horizontal" means a direction parallel to the XY plane of the coordinate axis display depicted in the drawing. "Diagonal" means a direction that forms a certain angle (excluding 0°, 90°, 180°, and 270°) with respect to the XY plane of the coordinate axis display depicted in the drawing. "Left" means a negative direction on the X axis of the coordinate axis display depicted in the drawing, and "right" means a positive direction on the X axis of the coordinate axis display depicted in the drawing. However, "vertical", "horizontal", "diagonal", "up", "down", "right", and "left" are merely defined for convenience and should not be interpreted in a restrictive manner.

<Configuration of alkaline water electrolysis system>
An example of the configuration of an alkaline water electrolysis system 70 according to the present embodiment will be described with reference to FIGS. 1 to 3B .

The alkaline water electrolysis system 70 comprises a rectifier 74, a bipolar electrolytic cell 50, a gas-liquid separation tank 72, a heat exchanger 79, a control device 30, a flow meter 77, a pressure gauge 78, a pressure regulating valve 80, and a circulation pump 71.

〔rectifier〕
The rectifier 74 is electrically connected to the bipolar electrolytic cell 50. The rectifier 74 is also electrically connected to the control device 30.

The rectifier 74 is connected to a fluctuating power source and converts AC power into DC power when fluctuating power (e.g., renewable energy) is supplied from outside the alkaline water electrolysis system 70. Renewable energy is energy obtained from at least one of wind power, solar power, hydroelectric power, tidal power, wave power, ocean currents, and geothermal power. Since renewable energy is prone to power fluctuations, power is randomly supplied to the alkaline water electrolysis system 70 over a wide range, from low current density to high current density.

The rectifier 74 applies a predetermined DC voltage between the anode terminal and the cathode terminal of the bipolar electrolytic cell 50. The predetermined DC voltage is determined by the control device 30. The rectifier 74 applies the predetermined DC voltage determined by the control device 30 between the anode terminal and the cathode terminal of the bipolar electrolytic cell 50, thereby controlling the operation or stop of the bipolar electrolytic cell 50.

[Bipolar electrolytic cell]
The bipolar electrolytic cell 50 is provided at the bottom of the gas-liquid separation tank 72, and is electrically connected to the rectifier 74. The bipolar electrolytic cell 50 generates oxygen from the anode side and hydrogen from the cathode side by electrolysis of water using an electrolyte based on a predetermined DC voltage supplied from the rectifier 74. The bipolar electrolytic cell 50 includes a plurality of electrolytic cells 65 (see FIG. 2). Details of the configurations of the bipolar electrolytic cell 50 and the electrolytic cells 65 will be described later.

The electrolyte is an alkaline aqueous solution in which an alkaline salt is dissolved, such as an aqueous NaOH solution or an aqueous KOH solution. The concentration of the alkaline salt is preferably 20% to 50% by mass, and more preferably 25% to 40% by mass. Considering ionic conductivity, kinetic viscosity, freezing at low temperatures, etc., it is particularly preferable that the electrolyte is an aqueous KOH solution in which the concentration of the alkaline salt is 25% to 40% by mass.

[Gas-liquid separation tank]
The gas-liquid separation tank 72 is provided above the bipolar electrolytic cell 50 and is connected to the bipolar electrolytic cell 50. The gas-liquid separation tank 72 separates the generated gases (hydrogen, oxygen) from the electrolytic solution, and stores the electrolytic solution that flows in from the bipolar electrolytic cell 50. The gas-liquid separation tank 72 includes an oxygen separation tank 72o and a hydrogen separation tank 72h.

The oxygen separation tank 72o separates the oxygen from the mixture of oxygen and electrolyte that flows in from the bipolar electrolytic cell 50 into an upper gas phase and a lower liquid phase. The separated oxygen is discharged from an outlet provided above the oxygen separation tank 72o. The separated electrolyte is stored inside the oxygen separation tank 72o, flows out from an outlet provided below the oxygen separation tank 72o, and flows back into the bipolar electrolytic cell 50.

The hydrogen separation tank 72h separates the mixture of hydrogen and electrolyte from the bipolar electrolytic cell 50, separating the hydrogen into an upper gas phase and the electrolyte into a lower liquid phase. The separated hydrogen is discharged from an outlet provided above the hydrogen separation tank 72h. The separated electrolyte is stored inside the hydrogen separation tank 72h, flows out from an outlet provided below the hydrogen separation tank 72h, and flows back into the bipolar electrolytic cell 50.

The oxygen or hydrogen discharged from the outlet of the gas-liquid separation tank 72 contains alkaline mist. Therefore, it is preferable that the gas-liquid separation tank 72 is provided with a device, such as a mist separator or a cooler, downstream of the outlet, that can liquefy the excess mist and return it to the gas-liquid separation tank 72.

The degree of gas-liquid separation of the gas-liquid separation tank 72 is determined by the flux of the electrolyte stored therein, the floating speed of the gas bubbles, the gas residence time, etc. If the degree of gas-liquid separation is appropriately determined, it is possible to avoid problems such as a decrease in gas purity due to mixing of oxygen and hydrogen when electrolyte flows from the bipolar electrolytic cell 50 into the gas-liquid separation tank 72.

Considering the installation volume, it is preferable that the gas-liquid separation tank 72 has a small capacity, but if the volume is too small, the liquid level of the electrolyte stored inside the gas-liquid separation tank 72 will fluctuate greatly due to changes in pressure or current. Therefore, it is preferable that the capacity of the gas-liquid separation tank 72 is designed taking into account the fluctuations in the liquid level of the electrolyte. The gas-liquid separation tank 72 may further include a level gauge that measures the height of the liquid level of the electrolyte stored inside.

The gas-liquid separation tank 72 may have any shape that can store the electrolyte therein, such as a cylindrical shape. The gas-liquid separation tank 72 is preferably made of an alkali-resistant metal material, such as nickel or SUS.

It is preferable that the gas-liquid separation tank 72 has a resin lining layer on its inner surface. If the gas-liquid separation tank 72 has a resin lining layer on its inner surface, it is preferable that the outer surface be covered with a heat-insulating material.

The resin lining layer preferably has a thickness of 0.5 mm to 4.0 mm, and more preferably 1.0 mm to 2.0 mm. If it is thinner than 0.5 mm, the inner surface of the gas-liquid separation tank 72 is likely to deteriorate due to gas and electrolyte, and if it is thicker than 4.0 mm, residual stress is released by high temperature and alkali, increasing the possibility of deformation or peeling. By ensuring that the thickness of the resin lining layer falls within this range, the durability of the gas-liquid separation tank 72 can be improved.

The resin lining layer preferably has a standard deviation of thickness of 1.0 mm or less, and more preferably 0.5 mm or less. By suppressing the variation in the thickness of the resin lining layer, the durability of the gas-liquid separation tank 72 can be improved. The variation in the thickness of the resin lining layer can be suppressed by appropriately adjusting the conditions of the blasting treatment performed on the surface of the gas-liquid separation tank 72 before forming the resin lining layer.

It is preferable that the resin lining layer is formed of two or more layers. The resin lining layer can be formed by known methods. Examples of such methods include a rotary baking method, a powder coating method, a liquid coating method, and a spraying method. Before forming the resin lining layer, the inner surface of the gas-liquid separation tank 72 may be subjected to one or more of the following treatments: degreasing, blasting with sand, primer treatment, etc.

The resin lining layer is preferably formed of a fluororesin material. Examples of the fluororesin material include at least one selected from the group consisting of polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). By forming the resin lining layer from a fluororesin material, the durability of the gas-liquid separation tank 72 against the electrode solution can be improved.

The heat-insulating material may be a known insulating material, such as glass wool, foam, etc. The inner surface of the gas-liquid separation tank 72 is susceptible to deterioration due to gas and electrolyte, particularly under high temperature conditions, but by covering the outer surface of the gas-liquid separation tank 72 with a heat-insulating material, such deterioration can be suppressed.

As described above, the gas-liquid separation tank 72 is provided above the bipolar electrolytic cell 50. This allows the liquid with high density to be guided to the lower side and the gas with low density to be guided to the upper side, so that even if fluctuating power is input to the alkaline water electrolysis system 70, the electrolyte can be circulated stably and self-circulation can be promoted. In addition, when the bipolar electrolytic cell 50 is stopped, the inside of the bipolar electrolytic cell 50 can be filled with the electrolyte held in the gas-liquid separation tank 72 due to the density difference between the gas-liquid separation tank 72 and the bipolar electrolytic cell 50, so that the diffusion of gas through the diaphragm can be suppressed. In addition, the problem of impurity gases being mixed between the oxygen separation tank 72o and the hydrogen separation tank 72h through the bipolar electrolytic cell 50 can be avoided. Furthermore, when the bipolar electrolytic cell 50 is located at the top of the gas-liquid separation tank 72, maintenance of the bipolar electrolytic cell 50 requires hoisting the bipolar electrolytic cell 50 to the top of the gas-liquid separation tank 72 using a crane or the like, which makes the maintenance complicated. However, when the bipolar electrolytic cell 50 is provided at the bottom of the gas-liquid separation tank 72, there is no need to hoist the bipolar electrolytic cell 50 using a crane or the like, which makes maintenance smoother.

〔Heat exchanger〕
The heat exchanger 79 is provided inside the gas-liquid separation tank 72. The amount of heat exchanged by the heat exchanger 79 is controlled by the control device 30, and the heat exchanger 79 adjusts the temperature of the electrolytic solution stored inside the gas-liquid separation tank 72. At this time, the heat exchanger 79 may be controlled by the control device 30 based on the flow rate of the electrolytic solution measured by the flow meter 77.

The heat exchanger 79o is provided inside the oxygen separation tank 72o and adjusts the temperature of the electrolyte stored inside the oxygen separation tank 72o. For example, when the bipolar electrolytic cell 50 is operated, the temperature of the electrolyte rises in the bipolar electrolytic cell 50. In such a case, the heat exchanger 79o cools the electrolyte stored inside the oxygen separation tank 72o. The heat exchanger 79o efficiently cools the electrolyte stored inside the oxygen separation tank 72o at the appropriate timing, thereby promoting self-circulation.

The heat exchanger 79h is provided inside the hydrogen separation tank 72h and adjusts the temperature of the electrolyte stored inside the hydrogen separation tank 72h. For example, when the bipolar electrolytic cell 50 is operated, the temperature of the electrolyte rises in the bipolar electrolytic cell 50, and in such a case, the heat exchanger 79h cools the electrolyte stored inside the hydrogen separation tank 72h. By efficiently cooling the electrolyte stored inside the hydrogen separation tank 72h at the appropriate time, the heat exchanger 79h can promote self-circulation.

As described above, the heat exchanger 79 is provided inside the gas-liquid separation tank 72, so that the electrolyte stored inside the gas-liquid separation tank 72 can be efficiently cooled. In addition, a density difference is generated between the gas-liquid separation tank 72 and the bipolar electrolytic cell 50, and self-circulation is accelerated in the alkaline water electrolysis system 70, so that highly efficient operation can be performed. In addition, the area occupied by the entire system can be reduced. In addition, the heat exchanger 79 is provided inside the gas-liquid separation tank 72, so that the high-temperature electrolyte can be cooled in the gas-liquid separation tank 72, and the amount of gas accompanying hydrogen and oxygen gas as steam can be suppressed. In addition, the heat exchanger 79 is provided inside the gas-liquid separation tank 72, so that the self-circulation of the electrolyte inside the gas-liquid separation tank 72 can be promoted, the temperature distribution inside the gas-liquid separation tank 72 can be suppressed, and local corrosion inside the gas-liquid separation tank 72 can be suppressed. Furthermore, since the heat exchanger 79 is provided inside the gas-liquid separation tank 72, there is no need to specially provide the heat exchanger 79 in the piping section outside the gas-liquid separation tank 72, which has the effect of reducing the installation area and suppressing piping pressure loss.

Although the use of the circulation pump 71 allows the electrolyte to be circulated stably, problems such as increased power consumption of the entire system and promotion of mixing of hydrogen and oxygen inside the bipolar electrolytic cell 50 occur. However, as described above, in the alkaline water electrolysis system 70 according to this embodiment, the gas-liquid separation tank 72 is provided on the upper part of the bipolar electrolytic cell 50, and the heat exchanger 79 provided inside the gas-liquid separation tank 72 appropriately cools the electrolyte. In other words, in the alkaline water electrolysis system 70, the density difference between the bipolar electrolytic cell 50 and the gas-liquid separation tank 72 is changed according to the amount of gas generated by the bipolar electrolytic cell 50, so that the bipolar electrolytic cell 50 can operate within a stable flow rate range. In addition, in the alkaline water electrolysis system 70, the electrolyte stored inside the gas-liquid separation tank 72 can be efficiently cooled and self-circulation can be accelerated. As a result, an alkaline water electrolysis system 70 can be realized that stably circulates the electrolyte according to the fluctuating input power and produces high-purity hydrogen.

〔Control device〕
The control device 30 may be any computer capable of performing predetermined processes according to a program, and may be, for example, a notebook personal computer (PC) used by an operator, a mobile phone such as a smartphone, a tablet terminal, etc. The control device 30 controls each component of the alkaline water electrolysis system 70.

The control device 30 includes a control unit and a memory unit. The control unit may be configured with dedicated hardware, or may be configured with a general-purpose processor or a processor specialized for a specific process. The memory unit includes one or more memories, and may include, for example, a semiconductor memory, a magnetic memory, an optical memory, etc. Each memory included in the memory unit may function, for example, as a main memory device, an auxiliary memory device, or a cache memory. Each memory does not necessarily need to be included inside the control device 30, and may be configured to be included outside the control device 30.

The control device 30 generates a control signal for controlling the operation or stop of the bipolar electrolytic cell 50 and outputs it to the rectifier 74. For example, the control device 30 outputs a control signal for operating the bipolar electrolytic cell 50 to the rectifier 74. For example, the control device 30 outputs a control signal for stopping the bipolar electrolytic cell 50 to the rectifier 74. In this way, the control device 30 appropriately determines a predetermined DC voltage to be supplied to the bipolar electrolytic cell 50, thereby controlling the operation or stop of the bipolar electrolytic cell 50.

The control device 30 generates a control signal for controlling the amount of heat exchanged by the heat exchanger 79 and outputs it to the heat exchanger 79. For example, the control device 30 controls the amount of heat exchanged by the heat exchanger 79o provided inside the oxygen separation tank 72o based on the flow rate of the electrolyte measured by the flow meter 77o. As a result, the electrolyte stored inside the oxygen separation tank 72o is cooled. For example, the control device 30 controls the amount of heat exchanged by the heat exchanger 79h provided inside the hydrogen separation tank 72h based on the flow rate of the electrolyte measured by the flow meter 77h. As a result, the electrolyte stored inside the hydrogen separation tank 72h is cooled.

The control device 30 generates a control signal for controlling the pressure regulating valve 80 and outputs it to the pressure regulating valve 80. For example, the control device 30 controls the pressure regulating valve 80o connected to the oxygen separation tank 72o based on the measurement result of the pressure gauge 78o that measures the pressure inside the oxygen separation tank 72o. As a result, the pressure inside the oxygen separation tank 72o is adjusted to an appropriate pressure (e.g., 100 kPa). For example, the control device 30 controls the pressure regulating valve 80h connected to the hydrogen separation tank 72h based on the measurement result of the pressure gauge 78h that measures the pressure inside the hydrogen separation tank 72h. As a result, the pressure inside the hydrogen separation tank 72h is adjusted to an appropriate pressure (e.g., 100 kPa).

The control device 30 generates a control signal for controlling the circulation pump 71 and outputs it to the circulation pump 71. For example, the control device 30 controls the operation or stop of the circulation pump 71. For example, the control device 30 controls the rotation speed of the circulation pump 71 based on the flow rate of the electrolyte measured by the flow meter 77. This allows the flow rate of the electrolyte circulating through the alkaline water electrolysis system 70 to match the target flow rate determined by the control device 30, and the flow rate of the electrolyte circulating through the alkaline water electrolysis system 70 is adjusted to an appropriate flow rate.

The control device 30 controls the above-mentioned bipolar electrolytic cell 50, rectifier 74, heat exchanger 79, pressure regulating valve 80, circulation pump 71, and other components of the alkaline water electrolysis system 70.

[Circulation pump]
The circulation pump 71 is provided in a pipeline laid between the bipolar electrolytic cell 50 and the gas-liquid separation tank 72, and circulates the electrolyte. The circulation pump 71 is capable of rotating in both forward and reverse directions.

When the circulation pump 71 rotates in the normal direction, the electrolyte stored inside the gas-liquid separation tank 72 is transferred to the bipolar electrolytic cell 50 via a pipeline, and the electrolyte in the bipolar electrolytic cell 50 is transferred to the gas-liquid separation tank 72 via a pipeline. In this way, when the circulation pump 71 rotates in the normal direction, the electrolyte circulates between the bipolar electrolytic cell 50 and the gas-liquid separation tank 72.

When the circulation pump 71 reverses, the electrolyte in the bipolar electrolytic cell 50 is transferred to the gas-liquid separation tank 72 through the pipeline, and the electrolyte stored in the gas-liquid separation tank 72 is transferred to the bipolar electrolytic cell 50 through the pipeline. When the circulation pump 71 continues to reverse, the electrolyte is continuously transferred to the gas-liquid separation tank 72, and the electrolyte stored in the gas-liquid separation tank 72 and the electrolyte transferred to the gas-liquid separation tank 72 are drained. In this way, when the circulation pump 71 reverses, the electrolyte circulating between the bipolar electrolytic cell 50 and the gas-liquid separation tank 72 is drained, and the bipolar electrolytic cell 50 and the gas-liquid separation tank 72 are filled with new electrolyte. As a result, the circulating electrolyte is replaced with the new electrolyte.

The configuration of the circulation pump 71 is not particularly limited, and may be, for example, a rotary pump, a gear pump, a tube pump, etc. Using a tube pump as the circulation pump 71 improves chemical resistance and enables the alkaline water electrolysis system 100 to be made smaller.

〔Flowmeter〕
The flow meter 77 is provided below the bipolar electrolytic cell 50 and is connected to the bipolar electrolytic cell 50. The flow meter 77 measures the flow rate of the electrolyte circulating through the bipolar electrolytic cell 50, and outputs the measurement result to the control device 30.

The flow meter 77o measures the flow rate of the electrolyte circulating through the bipolar electrolytic cell 50 and outputs the measurement result to the control device 30. Based on the measurement result, the control device 30 controls the amount of heat exchanged by the heat exchanger 79o, thereby cooling the electrolyte stored inside the oxygen separation tank 72o. In addition, based on the measurement result, the control device 30 controls the circulation pump 71, thereby making it possible to match the flow rate of the electrolyte circulating through the alkaline water electrolysis system 70 with the target flow rate determined by the control device 30.

The flow meter 77h measures the flow rate of the electrolyte circulating through the bipolar electrolytic cell 50 and outputs the measurement result to the control device 30. Based on the measurement result, the control device 30 controls the amount of heat exchanged by the heat exchanger 79h, thereby cooling the electrolyte stored inside the hydrogen separation tank 72h. In addition, based on the measurement result, the control device 30 controls the circulation pump 71, thereby making the flow rate of the electrolyte circulating through the alkaline water electrolysis system 70 equal to the target flow rate determined by the control device 30.

The flowmeter 77 outputs the measurement results to the control device 30 as appropriate, and the control device 30 cools the electrolyte or appropriately controls the circulation pump 71 based on the measurement results, thereby stably circulating the electrolyte and promoting self-circulation even when fluctuating power is input to the alkaline water electrolysis system 70. This enables highly efficient operation and realizes an alkaline water electrolysis system 70 capable of producing high-purity hydrogen.

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

[Pressure Regulating Valve]
The pressure regulating valve 80 is controlled by the control device 30. The pressure regulating valve 80 is provided on the upper part of the gas-liquid separation tank 72 and connected to the gas-liquid separation tank 72. For example, the pressure regulating valve 80o is connected to the oxygen separation tank 72o and is controlled by the control device 30 based on the internal pressure of the oxygen separation tank 72o measured by a pressure gauge 78o to adjust the internal pressure of the oxygen separation tank 72o. For example, the pressure regulating valve 80h is connected to the hydrogen separation tank 72h and is controlled by the control device 30 based on the internal pressure of the hydrogen separation tank 72h measured by a pressure gauge 78h to adjust the internal pressure of the hydrogen separation tank 72h.

By appropriately adjusting the pressure regulating valve 80 by the control device 30, it is possible to suppress an excessive increase or decrease in the pressure inside the gas-liquid separation tank 72, and to maintain the pressure inside the gas-liquid separation tank 72 at an appropriate pressure. In addition, even if the pressure inside the gas-liquid separation tank 72 exceeds the design pressure due to gas generated by the electrolysis of water, it is possible to safely reduce the pressure.

[Other configurations]
In addition to the above-mentioned components, the alkaline water electrolysis system 70 may include a water supply device 73, an oxygen concentration meter 75, a hydrogen concentration meter 76, a temperature control valve, a detector, etc. As known components can be used as these components, detailed description thereof will be omitted.

The alkaline water electrolysis system 70 according to this embodiment has the above-mentioned configuration, and thus can stably circulate the electrolyte in accordance with the fluctuating input power. This makes it possible to realize an alkaline water electrolysis system 70 capable of producing high-purity hydrogen.

<Configuration of bipolar electrolytic cell>
Next, an example of the configuration of the bipolar electrolytic cell 50 according to this embodiment will be described in detail with reference to Figs. 2, 3A and 3B.

In the bipolar electrolytic cell 50, multiple 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. The anode terminal element 51a is electrically connected to the anode 2a located at the leftmost end, and the cathode terminal element 51c is electrically connected to the cathode 2c located at the rightmost end. Current flows from the anode terminal element 51a through the cathode 2c and anode 2a included in the multiple bipolar elements 60 toward the cathode terminal element 51c.

The bipolar electrolytic cell 50 is arranged in the following order from left to right: fast head 51g1, insulating plate 51i1, anode terminal element 51a, anode side gasket part 7a, diaphragm 4, cathode side gasket part 7c, multiple bipolar elements 60, anode side gasket part 7a, diaphragm 4, cathode side gasket part 7c, cathode terminal element 51c, insulating plate 51i2, and loose head 51g2. The multiple bipolar elements 60 are arranged so that the cathode 2c faces the anode terminal element 51a side and the anode 2a faces the cathode terminal element 51c side. The bipolar electrolytic cell 50 is integrated by being tightened with the tie rod system 51r as a whole. A hydraulic cylinder or the like may be used as the tightening mechanism. The bipolar electrolytic cell 50 can be arbitrarily arranged from either the anode side or the cathode side, and is not limited to the above order.

Compared to a monopolar electrolytic cell, the bipolar electrolytic cell 50 can reduce the current of the power supply and can mass-produce compounds and specified substances in a short period of time. Therefore, from an industrial perspective, it is possible to reduce costs by using a bipolar electrolytic cell rather than a monopolar electrolytic cell.

[Multi-pole element]
The bipolar element 60 includes an anode 2a, a cathode 2c, a partition wall 1 that separates the anode 2a and the cathode 2c, and an outer frame 3 that borders the partition wall 1. One surface of the bipolar element 60 serves as the anode 2a, and the other surface serves as the cathode 2c.

The number of pairs of the bipolar element 60 is not particularly limited, and it is sufficient that they are repeatedly arranged in the number of pairs required for the designed production volume, but it is preferable that there are 50 to 500 pairs, more preferably 70 to 300 pairs, and particularly preferably 100 to 200 pairs.

When the number of pairs of the bipolar element 60 is small, the adverse effect of leakage current on gas purity is mitigated. Also, when the number of pairs of the bipolar element 60 is large, it becomes difficult to distribute the electrolyte evenly to each electrolytic cell 65. Also, when the number of pairs of the bipolar element 60 is too large, it becomes difficult to manufacture the bipolar electrolytic cell 50. When a large number of bipolar elements 60 with poor manufacturing accuracy are stacked, the sealing surface pressure becomes uneven in the bipolar electrolytic cell 50, and electrolyte leakage and gas leakage are likely to occur. Therefore, by having the number of pairs of the bipolar element 60 satisfy the above-mentioned range, it is possible to reduce self-discharge that occurs when the power supply is stopped and to stabilize the electrical control system. Also, it is possible to reduce the pump power and the leakage current, and to store electricity with high efficiency.

[Electrolytic cell]
The electrolytic cell 65 includes a partition wall 1, an anode chamber 5a, and an anode 2a included in one adjacent bipolar element 60, and a cathode 2c, a cathode chamber 5c, and a partition wall 1 included in the other 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 elastic body 2e, and a current plate 6. The electrolytic cell 65 may include a baffle plate 8.

The temperature of the electrolyte inside the electrolytic cell 65 is preferably 40°C or higher, and more preferably 80°C or higher. The temperature of the electrolyte inside the electrolytic cell 65 is preferably 110°C or lower, and more preferably 95°C or lower. By ensuring that the temperature of the electrolyte inside the electrolytic cell 65 is within this range, it is possible to effectively prevent the various components of the alkaline water electrolysis system 70 from being deteriorated by heat while maintaining high electrolysis efficiency.

The electrolytic cell 65 has a lower limit of an applied current density of preferably 1 kA/m ² or more, and more preferably 8 kA/m ² or more. The electrolytic cell 65 has an upper limit of an applied current density of preferably 15 kA/m ² or less, and more preferably 10 kA/m ² or less. In particular, when a variable power supply is used as in the alkaline water electrolysis system 70, it is preferable that the upper limit of the current density be in the above range.

The internal pressure of the electrolytic cell 65 is preferably between 3 kPa and 1000 kPa, and more preferably between 3 kPa and 300 kPa.

-Bulkhead-
The partition wall 1 separates the anode 2a from the cathode 2c. The partition wall 1 is electrically connected to the current collector 2r via a current plate 6.

The partition 1 is preferably formed of a conductive material. Examples of conductive materials include nickel, nickel alloys, mild steel, and nickel alloys plated with nickel. By forming the partition 1 from a conductive material, a uniform supply of power can be achieved. It is particularly preferable that the material of the partition 1 that comes into contact with the electrolyte is formed from nickel. This can improve alkali resistance, heat resistance, and the like.

The shape of the partition wall 1 is not particularly limited, but it is preferable that the partition wall 1 is a plate having a predetermined thickness. In addition, the partition wall 1 may have a planar shape of, for example, a rectangular shape, a circular shape, or an elliptical shape, and if the partition wall 1 is rectangular, the corners may be rounded.

-electrode-
The anode 2a is provided in the anode chamber 5a, and the cathode 2c is provided in the cathode chamber 5c. The anode 2a and the cathode 2c belonging to one electrolytic cell 65 are electrically connected to each other. The cathode 2c is electrically connected to a current collector 2r via a conductive elastic body 2e.

Electrode 2 is preferably a porous body in order to increase the surface area available for water electrolysis and to efficiently remove gas generated by water electrolysis from the surface of electrode 2. Examples of porous bodies include plain woven mesh, punched metal, expanded metal, and metal foam.

Electrode 2 may be the substrate itself, but it is preferable for it to have a highly reactive catalytic layer on the surface of the substrate.

The substrate is preferably formed from a material such as mild steel, stainless steel, nickel, or a nickel-based alloy, in terms of its resistance to the usage environment.

The catalytic layer of the anode 2a is preferably formed of a material with high oxygen generation ability and good durability, such as nickel, cobalt, iron, or platinum group elements. In addition, materials for achieving the desired catalytic activity, durability, etc. include, for example, metal elements such as palladium, iridium, platinum, gold, ruthenium, rhodium, cerium, nickel, cobalt, tungsten, iron, molybdenum, silver, copper, zirconium, titanium, hafnium, and lanthanoids, compounds such as oxides, composite oxides or alloys made of multiple metal elements, or mixtures thereof, and carbon materials such as graphene.

The catalytic layer of the cathode 2c is preferably formed of a material with high hydrogen generation capacity, and examples of such materials include nickel or cobalt, iron, or platinum group elements. In addition, examples of materials for achieving the desired catalytic activity, durability, etc. include simple metals, compounds such as oxides, composite oxides or alloys of multiple metal elements, or mixtures thereof. Specifically, for example, Raney alloys consisting of a combination of multiple materials such as Raney nickel, nickel and aluminum, or nickel and tin, porous coatings produced by plasma spraying using nickel compounds or cobalt compounds as raw materials, alloys or composite compounds of nickel and elements selected from cobalt, iron, molybdenum, silver, copper, etc., metals or oxides of platinum group elements such as platinum or ruthenium having high hydrogen generation capacity, and mixtures of metals or oxides of these platinum group elements and 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. In order to achieve high catalytic activity, durability, etc., a plurality of catalyst layers made of the above materials may be laminated, or a plurality of materials may be mixed in the catalyst layer. In addition, in order to improve durability and adhesion to the substrate, an organic substance such as a polymer material may be contained in the material.

The electrolysis voltage depends heavily on the performance of the electrode 2. By reducing the electrolysis voltage, it is possible to reduce energy consumption in the alkaline water electrolysis system 70. The electrolysis voltage includes the theoretically required voltage for electrolysis of water, as well as the overvoltage of the anode reaction (oxygen generation), the overvoltage of the cathode reaction (hydrogen generation), and the voltage due to the electrode distance between the anode 2a and the cathode 2c. Here, overvoltage means a voltage that needs to be applied in excess, exceeding the theoretical decomposition potential, when passing a certain current. By lowering the overvoltage, it is possible to reduce the electrolysis voltage.

Electrode 2 preferably has properties such as high electrical conductivity, high oxygen generation capacity or hydrogen generation capacity, and high wettability of the electrolyte on the surface of electrode 2. When electrode 2 has such properties, the above-mentioned overvoltage can be reduced. In addition, electrode 2 preferably has properties that make it difficult for the substrate and catalyst layer to corrode, the catalyst layer to fall off, dissolution in the electrolyte, and adhesion of inclusions to membrane 4 to occur, even when unstable power such as renewable energy is supplied.

- Current collector -
The current collector 2r has the functions of transmitting electricity to the conductive elastic body 2e and the electrode 2, supporting the load received from the conductive elastic body 2e and the electrode 2, and allowing the gas generated from the electrode 2 to pass through to the partition wall 1 side without hindrance.

The current collector 2r preferably has a shape such as an expanded metal or a punched perforated plate. The opening ratio of the current collector 2r preferably satisfies a range in which hydrogen gas generated from the electrode 2 can be extracted to the partition wall 1 side without hindrance. If the opening ratio is too large, problems such as a decrease in the strength of the current collector 2r or a decrease in conductivity to the conductive elastic body 2e are likely to occur, and if the opening ratio is too small, gas escape becomes poor. For this reason, it is preferable that the opening ratio of the current collector 2r is appropriately set in consideration of these problems.

From the viewpoint of electrical conductivity and alkali resistance, the current collector 2r is preferably formed of a material such as nickel, a nickel alloy, stainless steel, or mild steel. From the viewpoint of corrosion resistance, the current collector 2r is preferably nickel-plated on nickel, mild steel, or stainless steel/nickel alloy.

-Conductive elastic body-
The conductive elastic body 2e is in contact with the current collector 2r and the electrode 2, and is provided between the current collector 2r and the cathode 2c. The conductive elastic body 2e has a function of bringing the diaphragm 4 and the electrode 2 into close contact with each other by evenly applying an appropriate pressure to the electrode 2 without damaging the diaphragm 4.

It is preferable that the conductive elastic body 2e is conductive to the electrode 2, but does not impede the diffusion of the gas generated from the electrode 2. If the conductive elastic body 2e impedes the diffusion of the gas, the electrical resistance increases and the area of the electrode 2 used for the electrolysis of water decreases, thereby reducing the efficiency of electrolysis.

The conductive elastic body 2e is not particularly limited in its configuration and may have a known configuration. The conductive elastic body 2e may be, for example, a cushion mat made of woven nickel wire with a wire diameter of about 0.05 mm to 0.5 mm that has been corrugated.

-Outer frame-
The outer frame 3 is provided along the outer edge of the partition wall 1 so as to surround the partition wall 1. The shape of the outer frame 3 is not particularly limited as long as it can surround the partition wall 1, but it is preferable that the outer frame 3 has an inner surface extending along the vertical direction with respect to the plane of the partition wall 1, over the periphery of the partition wall 1. The outer frame 3 is preferably set appropriately in accordance with the shape of the partition wall 1 in a plan view.

The outer frame 3 is preferably formed of a material having electrical conductivity, such as nickel, a nickel alloy, mild steel, a nickel alloy, etc. From the viewpoint of alkali resistance and heat resistance, the outer frame 3 is preferably formed of nickel, a nickel alloy, mild steel, or a nickel alloy, and nickel plating is applied thereon.

-diaphragm-
The diaphragm 4 separates an anode chamber 5a having an anode 2a from a cathode chamber 5c having a cathode 2c. The diaphragm 4 is provided between the anode terminal element 51a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51c. The diaphragm 4 is ion permeable and separates hydrogen gas from oxygen gas while conducting ions. The diaphragm 4 is composed of an ion exchange membrane having ion exchange ability, a porous membrane through which the electrolyte can permeate, or the like. The diaphragm 4 preferably has low gas permeability, high ionic conductivity, low electronic conductivity, and high strength.

--Porous membrane--
The porous membrane has a structure having a plurality of fine through holes and allowing the electrolyte to pass through. Examples of the porous membrane having such a structure include a polymer porous membrane, an inorganic porous membrane, a woven fabric, and a nonwoven fabric. These membranes are formed by applying a known technique.

The porous membrane preferably contains at least one polymer resin selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone. This makes it possible to maintain excellent ion permeability.

Since the porous membrane exhibits ionic conductivity when the electrolyte permeates it, it is preferable that the porous structure, such as the pore size, porosity, and hydrophilicity, be appropriately controlled. By appropriately controlling the porous structure of the porous membrane, it is possible to not only allow the electrolyte to pass through but also to improve the barrier properties against generated gas.

The thickness of the porous membrane is not particularly limited, but is preferably, for example, 200 μm or more and 700 μm or less. If the thickness of the porous membrane is 250 μm or more, it is possible to obtain even better gas barrier properties and further improve the strength of the porous membrane against impact. From this viewpoint, the lower limit of the thickness of the porous membrane 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, the ion permeability is less likely to be hindered by the resistance of the electrolyte contained in the pores during operation of the alkaline water electrolysis system 70, so that even better ion permeability can be maintained. From this viewpoint, the upper limit of the thickness of the porous membrane is more preferably 600 μm or less, more preferably 550 μm or less, and even more preferably 500 μm or less.

--Ion exchange membrane--
The ion exchange membrane may be either a cation exchange membrane that selectively allows cations to pass therethrough or an anion exchange membrane that selectively allows anions to pass therethrough.

The material of the ion exchange membrane is not particularly limited, and known materials can be used. The ion exchange membrane is preferably formed of, for example, a fluorine-containing resin or a modified resin of a polystyrene-divinylbenzene copolymer. From the viewpoint of excellent heat resistance and chemical resistance, it is particularly preferable that the ion exchange membrane is formed of a fluorine-containing resin.

- Electrode chamber -
The electrode chambers 5 allow the electrolyte to pass through and are defined by the partition wall 1, the outer frame 3, the diaphragm 4, etc. The range defined by the electrode chambers 5 varies depending on the structure of the outer frame 3 provided at the outer end of the partition wall 1. The electrode chambers 5 include, at the boundary with the outer frame 3, an electrolyte inlet for introducing the electrolyte into the electrode chambers 5 and an electrolyte outlet for discharging the electrolyte from the electrode chambers 5. For example, the anode chamber 5a includes an anolyte inlet for introducing the electrolyte into the anode chamber 5a and an anolyte outlet for discharging the electrolyte discharged from the anode chamber 5a. For example, the cathode chamber 5c includes a cathode electrolyte inlet for introducing the electrolyte into the cathode chamber 5c and a cathode electrolyte outlet for discharging the electrolyte discharged from the cathode chamber 5c.

The electrode chamber 5 may be provided with a baffle plate 8 for adjusting the gas-liquid ratio inside the bipolar electrolytic cell 50. The electrode chamber 5 may also be provided with an internal distributor for uniformly distributing the electrolyte on the electrode 2 surface inside the bipolar electrolytic cell 50. The electrode chamber 5 may also be provided with protrusions for creating Karman vortices inside the bipolar electrolytic cell 50 to uniformize the concentration and temperature of the electrolyte or to promote degassing of gas adhering to the electrode 2 and the diaphragm 4.

In addition, the current collector 2r may be provided not only in the cathode chamber 5c but also in the anode chamber 5a. The current collector 2r may be made of the same material and have the same configuration as the current collector provided in the cathode chamber 5c. It is also possible for the anode 2a itself to function as the current collector.

-rectifier-
The current plate 6 supports the anode 2a and is provided between the anode 2a and the partition wall 1. The current plate 6 supports the cathode 2c and the current collector 2r and is provided between the current collector 2r and the partition wall 1.

The straightening plate 6 is attached to one of the partition walls 1 of the adjacent electrolytic cell 65, and for example, in the anode chamber 5a, a structure in which the partition wall 1, the straightening plate 6, and the anode 2a are stacked in this order from left to right may be adopted. The partition wall 1, the straightening plate 6, and the anode 2a may be electrically connected and directly connected physically. Examples of methods for directly attaching these components to each other include welding. Of course, in the anode chamber 5a, a structure in which the partition wall 1, the straightening plate 6, the current collector 2r, the conductive elastic body 2e, and the anode 2a are stacked in this order from left to right may be adopted.

The current plate 6 is attached to the other partition wall 1 of the adjacent electrolytic cell 65. For example, in the cathode chamber 5c, a structure in which the cathode 2c, the conductive elastic body 2e, the current collector 2r, the current plate 6, and the partition wall 1 are stacked in this order from left to right may be adopted. The cathode 2c, the conductive elastic body 2e, the current collector 2r, the current plate 6, and the partition wall 1 may be electrically connected and may be directly physically connected. Methods for directly attaching each of these components to each other include welding.

By providing the current rectifier 6 in the electrolysis chamber 5, it becomes easier for current to flow from the partition 1 to the anode 2a, or from the cathode 2c to the partition 1. In addition, by providing the current rectifier 6 in the electrolysis chamber 5, it becomes possible to reduce convection that occurs inside the electrolysis chamber 5 due to turbulence in the gas-liquid flow inside the electrolysis chamber 5, thereby suppressing local increases in the temperature of the electrolyte.

The current plate 6 is preferably made of a conductive metal material. Examples of such materials include nickel-plated mild steel, stainless steel, and nickel.

It is preferable that at least a portion of the current rectifier plate 6 is conductive, and it is even more preferable that the entire current rectifier plate 6 is conductive. By making the current rectifier plate 6 conductive, it is possible to suppress an increase in the voltage of the electrolytic cell 65 caused by electrode deflection.

-gasket-
The gasket 7 is provided on the outer frame 3 that borders the partition wall 1. The gasket 7 has the function of preventing leakage of the electrolyte and generated gas to the outside of the bipolar electrolytic cell 50, and preventing gas mixing between the anode chamber 5a and the cathode chamber 5c.

The gasket 7 has a square or ring shape with the electrode 2 surface hollowed out to match the surface that contacts the outer frame 3. By sandwiching the diaphragm 4 between two gaskets, the diaphragm 4 can be stacked between adjacent bipolar elements 60.

The gasket 7 preferably has a slit portion capable of accommodating the diaphragm 4 so as to hold the diaphragm 4. The gasket 7 also preferably has an opening portion that allows the diaphragm 4 to be exposed on both surfaces of the gasket 7. By providing the opening portion in the gasket 7, it becomes possible to accommodate the edge of the diaphragm 4 within the slit portion and cover the end face at the edge of the diaphragm 4. This can reliably prevent the electrolyte and gas from leaking from the end face at the edge of the diaphragm 4.

The material of the gasket 7 is not particularly limited, and known rubber materials or resin materials having insulating properties can be selected. Specific examples of the rubber or resin material include natural rubber (NR), styrene butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated polyethylene rubber (CSM). Fluorine resin materials such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE), and resin materials such as polyphenylene sulfide (PPS), polyethylene, polyimide, and polyacetal can be used. Among these, it is particularly preferable to select ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) from the viewpoints of elastic modulus and alkali resistance.

- Baffle plate -
The baffle plate 8 is a partition plate having a function of restricting the flow of the electrolyte inside the electrode chamber 5. The baffle plate 8 adjusts the ratio of the electrolyte to the gas inside the electrode chamber 5, and separates the electrolyte from the gas, for example, so that only the electrolyte flows on the back side and the electrolyte and the gas flow on the front side. In other words, the baffle plate 8 causes the gas to remain in a predetermined location, thereby circulating the electrolyte inside the electrode chamber 5 and making the concentration of the electrolyte more uniform.

The baffle plate 8 is provided, for example, inside the cathode chamber 5c. The baffle plate 8 is preferably provided between the cathode 2c and the partition wall 1 along the lateral direction of the cathode chamber 5c, diagonally or parallel to the partition wall 1. In the space near the cathode 2c separated by the baffle plate 8, as the electrolysis of water progresses, the concentration of the electrolyte decreases and hydrogen is generated. This may cause a difference in specific gravity between the gas and liquid, but by disposing the baffle plate 8 inside the cathode chamber 5c, the internal circulation of the electrolyte in the cathode chamber 5c can be promoted, and the concentration distribution of the electrolyte in the cathode chamber 5c can be made more uniform.

Although an example of the configuration of the bipolar electrolytic cell 50 has been described in detail above, the bipolar electrolytic cell 50 is not limited to the above-mentioned configuration. In addition to the above-mentioned components, the bipolar electrolytic cell 50 may also include, for example, a header for distributing or collecting the electrolyte.

<Method of operating alkaline water electrolysis system>
An example of a method for operating the alkaline water electrolysis system 70 according to this embodiment will be described with reference to FIG. 4 .

In step S101, when fluctuating power is supplied from outside the alkaline water electrolysis system 70, the rectifier 74 converts AC power into DC power. The rectifier 74 then applies a predetermined DC voltage between the anode terminal and the cathode terminal of the bipolar electrolytic cell 50.

In step S102, the bipolar electrolytic cell 50 generates oxygen from the anode side and hydrogen from the cathode side by electrolysis of water using the electrolyte based on a predetermined DC voltage applied from the rectifier 74.

In step S103, the oxygen separation tank 72o separates oxygen from the mixture of oxygen and electrolyte that has flowed in from the bipolar electrolytic cell 50. The separated oxygen is discharged from an outlet provided above the oxygen separation tank 72o. The separated electrolyte is stored inside the oxygen separation tank 72o. The hydrogen separation tank 72h separates hydrogen from the mixture of hydrogen and electrolyte that has flowed in from the bipolar electrolytic cell 50. The separated hydrogen is discharged from an outlet provided above the hydrogen separation tank 72h. The separated electrolyte is stored inside the hydrogen separation tank 72h.

In step S104, the heat exchanger 79o cools the electrolyte stored in the oxygen separation tank 72o. The heat exchanger 79h cools the electrolyte stored in the hydrogen separation tank 72h.

According to the operation method of the alkaline water electrolysis system 70 of this embodiment, the electrolyte can be circulated stably in response to the fluctuating input power. Therefore, by applying the operation method of the alkaline water electrolysis system 70 of this embodiment, it is possible to produce high-purity hydrogen.

Although the above-mentioned embodiment has been described as a representative example, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present disclosure. Therefore, the present invention should not be interpreted as being limited by the above-mentioned embodiment, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple configuration blocks shown in the configuration diagram of the embodiment into one, or to divide one configuration block. It is also possible to combine multiple steps shown in the flowchart of the embodiment into one, or to divide one step.

The present invention makes it possible to realize an alkaline water electrolysis system capable of producing high-purity hydrogen, which is particularly useful in fields such as petroleum refining, chemical synthesis, and metal refining, as well as in applications such as hydrogen stations for fuel cell vehicles, smart communities, and hydrogen power plants.

REFERENCE SIGNS LIST 1 Partition wall 2 Electrode 2a Anode 2c Cathode 2e Conductive elastic body 2r Current collector 3 Outer frame 4 Diaphragm 5 Electrode chamber 5a Anode chamber 5c Cathode chamber 6 Current rectifier 6a Anode current rectifier 6c Cathode current rectifier 7 Gasket 8 Baffle plate 30 Control device 50 Bipolar electrolytic cell 51g1 Fast head 51g2 Loose head 51i1 Insulating plate 51i2 Insulating plate 51a Anode terminal element 51c Cathode terminal element 51r Tie rod 60 Bipolar element 65 Electrolytic cell 70 Alkaline water electrolysis system 72 Gas-liquid separation tank 72o Oxygen separation tank 72h Hydrogen separation tank 73 Water supply device 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 78 Pressure gauge 78o Pressure gauge 78h Pressure gauge 79 Heat exchanger 79o Heat exchanger 79h Heat exchanger 80 Pressure regulating valve 80o Pressure regulating valve 80h Pressure regulating valve

Claims (4)

A rectifier that is connected to a fluctuating power source and converts AC power into DC power;
a bipolar electrolytic cell that generates hydrogen and oxygen by electrolysis of water using an electrolyte based on a predetermined DC voltage supplied from the rectifier;
a gas-liquid separation tank provided at an upper portion of the bipolar electrolytic cell, which separates the hydrogen and the oxygen from the electrolytic solution and stores the electrolytic solution;
a heat exchanger provided inside the gas-liquid separation tank and configured to cool the electrolytic solution;
A flowmeter that measures a flow rate of the electrolyte;
A control device that controls an amount of heat exchanged by the heat exchanger based on a measurement result obtained by the flow meter;
An alkaline water electrolysis system comprising: Further comprising a circulation pump for circulating the electrolyte,
The control device includes:
Controlling the circulating pump based on the measurement result measured by the flow meter.
The alkaline water electrolysis system according to claim 1 . The bipolar electrolytic cell is
Equipped with a baffle plate to adjust the gas-liquid ratio.
The alkaline water electrolysis system according to claim 1 or 2 . a rectifier coupled to a fluctuating power source converting AC power to DC power;
A step in which the bipolar electrolytic cell generates hydrogen and oxygen by electrolysis of water using an electrolyte based on a predetermined DC voltage supplied from the rectifier;
a gas-liquid separation tank provided at an upper portion of the bipolar electrolytic cell separating the hydrogen and the oxygen from the electrolytic solution and storing the electrolytic solution;
A heat exchanger provided inside the gas-liquid separation tank cools the electrolytic solution;
a flow meter measuring a flow rate of the electrolyte;
A control device controls an amount of heat exchanged by the heat exchanger based on a measurement result measured by the flow meter;
A method for operating an alkaline water electrolysis system, comprising:

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