Water electrolysis device

Abstract

To provide a water electrolysis apparatus capable of preventing ions from being included in water supplied to a water electrolysis stack more securely.SOLUTION: An apparatus performs water electrolysis of supplying water and adding a voltage to a water electrolysis cell to obtain hydrogen and oxygen, and has: a water electrolysis stack in which water electrolysis cells are stacked; a water supply side path having a pipe which supplies water to the water electrolysis stack; a hydrogen side path having a pipe which recovers hydrogen generated from the water electrolysis stack; and a water recirculation path having a pipe which returns water from the hydrogen side path to the water supply side path, where the water supply side path and the water recirculation path are equipped with a conductivity meter which measures the conductivity of water flowing through the pipe, a valve which drains water from the pipe, and a controller, and the controller performs control of draining water from the valve on the basis of a measured value of the conductivity meter.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a water electrolysis device.

Background Art

[0002] In a water electrolysis device that electrolyzes water to generate hydrogen and oxygen, if the water supplied to the water electrolysis cell where water electrolysis is performed contains ions, the deterioration of the water electrolysis cell may be accelerated, so it is desirable to remove these ions.

[0003] Patent Document 1 discloses that when the electrolysis of water by an electrolysis cell is stopped, the oxygen side treatment unit is controlled to supply the oxygen in the oxygen storage unit to the water supply flow path.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology of Patent Document 1, since ions remain in the system, there is a risk that the conductivity will increase over time.

[0006] In view of the prior art, an object of the present disclosure is to provide a water electrolysis device capable of more reliably suppressing the inclusion of ions in the water supplied to the water electrolysis stack.

Means for Solving the Problems

[0007] Water electrolysis devices often use metal piping, such as stainless steel. In oxygen and hydrogen atmospheres, these metals can dissolve as metal ions into the water flowing through the piping, potentially increasing the conductivity of the water. When such highly conductive water is supplied to a water electrolysis cell, there is a risk of decreased water electrolysis efficiency due to electrode adsorption of ions and electrode degradation due to oxidation. This dissolution of metal ions is particularly pronounced in a hydrogen atmosphere, and the inventors have found that the dissolution rate is four times higher in a hydrogen atmosphere compared to an oxygen atmosphere.

[0008] The present invention discloses a water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell and applying voltage, comprising: a water electrolysis stack in which water electrolysis cells are stacked; a water supply side path having piping for supplying water to the water electrolysis stack; a hydrogen side path having piping for recovering hydrogen produced from the water electrolysis stack; and a water return path having piping for returning water from the hydrogen side path to the water supply side path. The water supply side path and the water return path are equipped with a conductivity meter for measuring the conductivity of the water flowing through the piping, a valve for draining water from the piping, and a controller, the controller controlling the drainage from the valve based on the measurement value of the conductivity meter.

[0009] The controller may be configured to control the water electrolysis apparatus using a conductivity meter and valve located in the water supply path when water electrolysis is not performed in the water electrolysis stack, and to control the apparatus using a conductivity meter and valve located in the water return path when water electrolysis is performed in the water electrolysis stack.

[0010] During operation in a water electrolysis stack, the controller may be configured to obtain the water consumption flow rate due to water electrolysis, calculate the amount of accompanying water to the hydrogen side path, and determine the amount of wastewater based on the amount of accompanying water. [Effects of the Invention]

[0011] According to this disclosure, it is possible to more reliably prevent water containing a high concentration of ions from being supplied to the water electrolysis stack. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a conceptual diagram illustrating the configuration of the water electrolysis device 10. [Figure 2] Figure 2 is a cross-sectional view illustrating the layer structure of the water electrolysis cell 11. [Figure 3] Figure 3 is a conceptual diagram illustrating the configuration of the controller 30. [Figure 4] Figure 4 illustrates the control S10 of the water electrolysis apparatus. [Figure 5] Figure 5 illustrates the control S20 of the water electrolysis device. [Modes for carrying out the invention]

[0013] 1. Configuration of the water electrolysis device Figure 1 conceptually represents the configuration of a water electrolysis apparatus 10 in one form. The basic principles and concepts regarding the generation of hydrogen and oxygen by water electrolysis performed in the water electrolysis apparatus 10 can be based on known standards. In this embodiment, the water electrolysis apparatus 10 has a water electrolysis stack 20 in which a plurality of water electrolysis cells 11 are stacked and sandwiched at both ends by end plates, a water supply side path (oxygen side path) on one side of the water electrolysis stack 20, a hydrogen side path on the other side, and a water recirculation path that returns water from the hydrogen side path to the water supply side path. In the water electrolysis device 10, water is supplied from the water supply side path to the water electrolysis cell 11 provided in the water electrolysis stack 20, and power is supplied by the power supply 19 to decompose the water into hydrogen and oxygen. The obtained hydrogen is discharged into the hydrogen side path, recovered, and stored. Some of the water permeates the water electrolysis cell 11 as associated water and reaches the hydrogen side path from the water supply side path, where it is separated into hydrogen and water, and the separated water is returned to the water supply side path via the water recirculation path. The following provides further explanation of each component.

[0014] 1.1. Water electrolysis stack As described above, the water electrolysis stack 20 is configured by stacking multiple water electrolysis cells 11 and sandwiching them between end plates located at each end.

[0015] Figure 2 shows a partial cross-section of the site where water electrolysis is performed in one water electrolysis cell 11. As can be seen from Figure 2, the water electrolysis cell 11 has a laminated structure composed of multiple layers. The layer configuration is as known in the art and is not particularly limited. For example, as shown in Figure 2, on one side of the electrolyte membrane 12, a hydrogen electrode catalyst layer 13, a hydrogen electrode diffusion layer 15, and a hydrogen electrode separator 17 are laminated, and on the other side of the electrolyte membrane 12, an oxygen electrode catalyst layer 14, an oxygen electrode diffusion layer 16, and an oxygen electrode separator 18 are laminated. The hydrogen electrode separator 17 is wavy in the cross-section, forming a groove-shaped hydrogen electrode flow path 17a between it and the hydrogen electrode diffusion layer 15. Hydrogen and accompanying water flow through this hydrogen electrode flow path 17a and are discharged to the hydrogen side path. On the other hand, the oxygen electrode separator 18 is also wavy in the cross-section and forms a groove-shaped oxygen electrode flow path 18a between it and the oxygen electrode diffusion layer 16. Water is supplied from the water supply side path to the oxygen electrode flow path 18a, and oxygen and the remaining water are discharged from the oxygen electrode flow path 18a to the water supply side path.

[0016] A power source 19 is connected between the two electrodes of the water electrolysis stack 2 via a power line. When a voltage is applied from this power source 19 to the water electrolysis stack 20, water electrolysis is performed in the water electrolysis cell 11. Here, the power source 19 is as known in the art, and a normal power source used for water electrolysis can be applied.

[0017] 1.2. Water supply side path (oxygen side path) In the water supply side path (oxygen side path), tap water is made into pure water by passing it through an ion exchanger etc. and stored in a tank 21, and there is a path for supplying water to the water electrolysis stack 20 through a cooler 23 and an ion exchanger 24 by a pump 22. The oxygen and water coming out of the water electrolysis stack 20 are returned to a gas-liquid separator 25 where the gas and liquid are separated. The gas (oxygen) is discharged, and the liquid (water) is returned to the tank 21 because it is reused for water electrolysis. These components are connected by pipes and are configured such that water and oxygen can flow through the necessary paths.

[0018] In this embodiment, the water supply side path includes a pipe 26 that connects a pipe for supplying water to the water electrolysis stack 20 and a pipe for draining the wastewater from the water electrolysis stack 20, and a valve 27. By means of this pipe 26, water can be circulated in the water supply side path without supplying water to the water electrolysis stack 20. By opening the valve 27, water can flow through the pipe 26, and by closing the valve 27, the flow of water through the pipe 26 is restricted.

[0019] Also, in this embodiment, in the pipe between the gas-liquid separator 25 and the tank 21 in the water supply side path, a conductivity meter 28 for measuring the conductivity of the water flowing in the pipe and a valve 29 are provided. Although a known conductivity meter 28 can be used, from the viewpoint of obtaining the conductivity, which is one of the pieces of information for adjusting the opening and closing of the valve 29 as described later, it is communicably connected to the controller 30 and is configured to be able to transmit the obtained conductivity information to the controller 30. The valve 29 is configured such that when it is opened, the water flowing in the pipe is drained from the water supply side path. When the valve is closed, the drainage is restricted so that water flows from the gas-liquid separator 25 to the tank 21. The form of such a valve 29 is not particularly limited, but it can be an electromagnetic valve so that its opening and closing can be controlled by the controller 30. <

[0020] Furthermore, a controller 30 is provided in the water supply side path. The controller 30 is a controller for controlling the water electrolysis apparatus 10 of this embodiment. More specifically, in this embodiment, it is a controller that controls the opening and closing of the valve 29 based at least on the conductivity information from the conductivity meter 28. However, it does not have to be a controller only for this purpose and can have other functions for controlling the water electrolysis apparatus 10. The form of the controller 30 is not particularly limited, but typically it can be configured by a computer. Fig. 3 conceptually shows a configuration example of the computer 30 as the controller 30.

[0021] The computer 30 includes a CPU (Central Processing Unit) 31 which is a processor, RAM (Random Access Memory) 32 which functions as a work area, ROM (Read-Only Memory) 33 as a storage medium, a receiving unit 34 which is an interface for receiving information into the computer 30 whether wired or wireless, and an output unit 35 which is an interface for sending information from the computer 30 to the outside whether wired or wireless. A conductivity meter 28 is connected to the receiving unit 34 in a communication manner, and is configured to receive conductivity information via signals. Meanwhile, a valve 29 is connected to the output unit 35 in a communication manner, and is configured to control the opening and closing of the valve 29.

[0022] Computer 30 stores computer programs that define each process for control performed in the water electrolysis apparatus 10 of this embodiment as specific commands and execute these commands. In computer 30, the CPU 31, RAM 32, and ROM 33, which are hardware resources, work together with the computer programs. Specifically, the CPU 31 realizes the function by executing the computer program recorded in ROM 33 in RAM 32, which functions as a work area, based on conductivity information from the conductivity meter 28 acquired via the receiving unit 34. The information acquired or generated by the CPU 31 is stored in RAM 32. Then, based on the obtained results, commands are sent to the valve 29 via the output unit 35 as needed. The specific details of the control performed by the water electrolysis device 10 will be explained later.

[0023] 1.3. Hydrogen-side pathway In the hydrogen-side path, as can be seen in Figure 1, hydrogen and associated water from the water electrolysis stack 20 are collected in the gas-liquid separator 40, where the gas and liquid are separated. The gas (hydrogen) is stored in the hydrogen tank 41 via a dehumidifier and the like. Meanwhile, the water (associated water) separated in the gas-liquid separator 40 is returned to the tank 21 in the water supply-side path via the water recirculation path. These components are also connected by piping, and the system is configured so that water and hydrogen can flow through the necessary paths.

[0024] 1.4. Water Circulation Pathways In the water recirculation path, the water separated by the gas-liquid separator 40 in the hydrogen-side path is sent by the pump 51 to the tank 21 in the water supply-side path. The water recirculation path is equipped with the pump 51, a conductivity meter 52, and a valve 53, and these components are connected by piping to allow water to flow through the necessary paths. While a known conductivity meter 52 can be used, as described later, from the viewpoint of obtaining conductivity, which is one of the pieces of information for operating the valve 53, it is configured to be communicatively connected to the controller 30 and to transmit the obtained conductivity information to the controller 30. Valve 53 is configured to drain water flowing through the piping from the water return path when it is open. When the valve is closed, drainage is restricted so that water flows from the gas-liquid separator 40 to the tank 21. The form of such valve 53 is not particularly limited, but it can be a solenoid valve so that its opening and closing can be controlled by the controller 30. Alternatively, valve 53 can be a control valve so that the amount of drainage can be adjusted. If it is a control valve, the operation of that valve can also be controlled by the controller 30. Although a controller is also provided in the water return path, it can be considered in the same way as the controller 30 described above, and the controller 30 can be used for both. Accordingly, as shown in Figure 3, the conductivity meter 52 is connected to the receiving unit 34 of the controller 30 in a communication manner, and the valve 53 is connected to the output unit 35 of the controller 30 in a communication manner.

[0025] 2. Control of the water electrolysis device As described above, in water electrolysis devices, the water supplied to the water electrolysis stack may contain ions, and if such water is supplied to the water electrolysis cell, it may cause malfunctions. Therefore, in this embodiment, control is implemented to suppress the supply of water containing a large amount of ions to the water electrolysis stack, thereby more reliably preventing the occurrence of malfunctions.

[0026] The water electrolysis apparatus 10 has several preparation steps between the stopped state and normal water electrolysis operation, specifically including pipe flushing, stack flushing, and stack aging. In this embodiment, each of these preparation steps, as well as the normal operation of water electrolysis, is controlled by the controller 30. This will be explained below.

[0027] 2.1. Pipe flushing Pipe flushing is a preparatory step performed without applying voltage to the water electrolysis stack 20, and is a process of flushing the water supply side path. During pipe flushing, water is circulated by the pump 22 with valve 27 open. Therefore, water circulates through the pump 22, cooler 23, ion exchanger 24, valve 27 (pipe 26), gas-liquid separator 25, and tank 21, and does not circulate through the water electrolysis stack 20. In the piping flushing process, the controller 30 obtains conductivity from the conductivity meter 28 (S11), as shown in Figure 4 as S10, and determines whether the conductivity is above a predetermined threshold (e.g., 1 μS / m) (S12). If the conductivity is above the threshold in S12, it is determined to be Yes, the valve 29 is opened to drain the water (S13), and the process returns to S11. On the other hand, if the conductivity is below the threshold in S12, it is determined to be No, the valve 29 is closed (S14), and the process returns to S11. If the valve 29 is already closed, that closed state is maintained. This allows for the removal of highly conductive (ion-rich) water during pipe flushing.

[0028] 2.2. Stack Flushing Stack flushing is a preparatory step performed without applying voltage to the water electrolysis stack 20, and involves flushing the water supply path and the flow path on the water supply path side of the water electrolysis stack. In stack flushing, water is circulated by the pump 22 with valve 27 closed. Therefore, the water circulates through the pump 22, cooler 23, ion exchanger 24, water electrolysis stack 20, gas-liquid separator 25, and tank 21. In the stack flushing process, the controller 30 obtains conductivity from the conductivity meter 28 (S11), as shown in Figure 4 as S10, and determines whether the conductivity is above a predetermined threshold (e.g., 1 μS / m) (S12). If the conductivity is above the threshold in S12, it is determined to be Yes, the valve 29 is opened to drain (S13), and the process returns to S11. On the other hand, if the conductivity is below the threshold in S12, it is determined to be No, the valve 29 is closed (S14), and the process returns to S11. If the valve 29 is already closed, that closed state is maintained. This allows for the removal of ions by draining highly conductive (ion-rich) water during stack flushing.

[0029] 2.3. Stack Aging Stack aging is a preparatory step performed by applying voltage to the water electrolysis stack 20, and is a step that prepares the conditions so that the water electrolysis stack 20 can perform water electrolysis as a steady-state operation. During stack aging, a voltage is applied to the water electrolysis stack 20, and water is circulated by the pump 22 with the valve 27 closed in the water supply path. Therefore, water circulates through the pump 22, cooler 23, ion exchanger 24, water electrolysis stack 20, gas-liquid separator 25, and tank 21. In the hydrogen path, hydrogen and associated water discharged from the water electrolysis stack 20 reach the gas-liquid separator 40, where hydrogen and water (associated water) are separated. Meanwhile, in the water return path, water is returned from the gas-liquid separator 40 to the tank 21 by the pump 51. During the stack aging process, the controller 30 obtains conductivity from the conductivity meter 52 (S21), as shown in Figure 5 as S20, and determines whether the conductivity is above a predetermined threshold (e.g., 1 μS / m) (S22). If the conductivity is above the threshold in S22, it is determined to be Yes, the valve 53 is opened to drain (S23), and the process returns to S21. On the other hand, if the conductivity is below the threshold in S22, it is determined to be No, the valve 53 is closed (S24), and the process returns to S21. If the valve 53 is already closed, that closed state is maintained. This allows for the removal of highly conductive (ion-rich) water during stack aging, thereby eliminating ions.

[0030] Here, when the valve 53 can adjust its discharge flow rate, it can be adjusted to discharge an amount of water equivalent to the accompanying water volume. The accompanying water volume is calculated by the controller 30, for example, as follows. First, we calculate the water consumption rate. The water consumption rate [L / min] can be calculated using the following formula. Electrolytic current [q / s] ÷ Faraday constant 96500 [q / mol] × 0.5 × 18 [g / mol] × 10 -3 [L / mL] × Number of water electrolysis cells × 60 [seconds / minute] Next, multiply the obtained water consumption flow rate by four to obtain the associated water volume [L / min].

[0031] 2.4. Normal operation in water electrolysis Normal operation in water electrolysis involves applying a voltage to the water electrolysis stack 20 to obtain hydrogen. In normal operation, a voltage is applied to the water electrolysis stack 20, and water is circulated by the pump 22 with the valve 27 closed in the water supply path. Therefore, water circulates through the pump 22, cooler 23, ion exchanger 24, water electrolysis stack 20, gas-liquid separator 25, and tank 21. In the hydrogen path, hydrogen and associated water discharged from the water electrolysis stack 20 reach the gas-liquid separator 40, where hydrogen and water (associated water) are separated. Meanwhile, in the water return path, water is returned from the gas-liquid separator 40 to the tank 21 by the pump 51. During the stack aging process, the controller 30 obtains conductivity from the conductivity meter 52 (S21), as shown in Figure 5 as S20, and determines whether the conductivity is above a predetermined threshold (e.g., 1 μS / m) (S22). If the conductivity is above the threshold in S22, it is determined to be Yes, the valve 53 is opened to drain (S23), and the process returns to S21. On the other hand, if the conductivity is below the threshold in S22, it is determined to be No, the valve 53 is closed (S24), and the process returns to S21. If the valve 53 is already closed, that closed state is maintained. This allows for the removal of highly conductive (ion-rich) water during stack aging, thereby eliminating ions.

[0032] Here, when the valve 53 can adjust its discharge flow rate, it can be adjusted to discharge an amount of water equivalent to the accompanying water volume. The accompanying water volume can be calculated by the controller 30, for example, as follows. First, we calculate the water consumption rate. The water consumption rate [L / min] can be calculated using the following formula. Electrolytic current [q / s] ÷ Faraday constant 96500 [q / mol] × 0.5 × 18 [g / mol] × 10 -3 [L / mL] × Number of water electrolysis cells × 60 [seconds / minute] Next, multiply the obtained water consumption flow rate by four to obtain the associated water volume [L / min].

[0033] 3. Effects, etc. According to this embodiment of the water electrolysis apparatus 10, the supply of ions to the water electrolysis stack 20 can be more reliably suppressed by control. In addition, since this embodiment makes it possible to remove ions without relying on an ion exchanger, it is possible to keep the capacity of the ion exchanger small and reduce the frequency of replacement and maintenance when installing one.

[0034] In addition to the configuration described above, the insulation resistance of the water electrolysis stack may be measured instead of the conductivity meter. Furthermore, the conductivity can be reduced by using a water level sensor to monitor the water level in the gas-liquid separator of the hydrogen-side path and draining the water from the hydrogen-side path within a range where the amount of water circulating in the water reduction path can be maintained.

[0035] Furthermore, when shutting down the water electrolysis system, to reduce the elution of metal ions into the water in the hydrogen-side pathway, the amount of water in the hydrogen-side pathway may be reduced while monitoring the water level gauge of the gas-liquid separator in the hydrogen-side pathway. This reduces the stack aging time when restarting the water electrolysis system. [Explanation of Symbols]

[0036] 10...Water electrolysis unit, 11...Water electrolysis cell, 20...Water electrolysis stack, 21...Tank, 22...Pump, 23...Cooler, 24...Ion exchanger, 25...Gas-liquid separator, 27...Valve, 28...Conductivity meter, 29...Valve, 30...Controller, 40...Gas-liquid separator, 41...Tank, 51...Pump, 52...Conductivity meter, 53...Valve

Claims

1. A water electrolysis apparatus that supplies water to a water electrolysis cell and applies voltage to obtain hydrogen and oxygen, A water electrolysis stack in which the aforementioned water electrolysis cells are stacked, A water supply side route having piping for supplying water to the water electrolysis stack, A hydrogen-side path having piping for recovering hydrogen generated from the water electrolysis stack, It has a water return path having a pipe that returns water from the hydrogen side path to the water supply side path, The water supply path includes a path for supplying water to the water electrolysis stack, a path for recovering oxygen generated from the water electrolysis stack, and a path having piping to return the water separated from the oxygen recovery path to the path for supplying water to the water electrolysis stack. The water return piping and the water return path are equipped with a conductivity meter for measuring the conductivity of the water flowing through the piping, a valve for draining water from the piping, and a controller. The controller controls the drainage from the valve based on the measurement value of the conductivity meter. Water electrolysis equipment.

2. The controller is, In the water electrolysis apparatus, when water electrolysis is not performed in the water electrolysis stack, control is performed using the conductivity meter and valve located in the water return piping; when water electrolysis is performed in the water electrolysis stack, control is performed using the conductivity meter and valve located in the water return path. The water electrolysis apparatus according to claim 1.

3. The water electrolysis apparatus according to claim 2, wherein, during operation in which water electrolysis is performed in the water electrolysis stack, the controller obtains the water consumption flow rate due to water electrolysis, calculates the amount of accompanying water to the hydrogen side path, and determines the amount of wastewater based on the amount of accompanying water.

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