Water electrolysis system

Abstract

The invention provides a water electrolysis system. A water electrolysis system (10) is provided with: a water electrolysis stack (20) for electrolyzing water to generate oxygen gas and hydrogen gas; a gas-liquid separator (30); a hydrogen booster stack (40); a gas storage tank (70); the gas-liquid separator is used for separating hydrogen and water; the hydrogen boosting reactor is used for boosting hydrogen; a gas storage tank (110) that stores inert gas and is connected to a hydrogen flow path (110) that connects the water electrolysis stack (20) and the hydrogen booster stack (40); the supply valve supplies inert gas to the hydrogen flow channel (110) when the valve is opened. The supply control unit opens the supply valve (124) when the concentration of the oxygen gas flowing into the hydrogen flow path (110) exceeds a predetermined oxygen concentration threshold value. Therefore, the safety when the water electrolysis system is abnormal can be improved.

Description

Technical Field

[0001] The present invention relates to a water electrolysis system. Background Art

[0002] In recent years, research and development of fuel cells that contribute to improved energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy.

[0003] Japanese Patent Application Publication No. 2022-83098 discloses a hydrogen-oxygen production system. The oxygen and hydrogen generated by the hydrogen-oxygen production system can be supplied to a fuel cell tank, etc. The hydrogen-oxygen production system includes a water electrolysis device. In the water electrolysis device, water is electrolyzed by flowing current through an anode and a cathode provided on both sides of an electrolyte membrane. Hydrogen is generated at the cathode, and high-pressure oxygen is generated at the anode. Oxygen is more difficult to pass through the electrolyte membrane than hydrogen. Since the oxygen is at high pressure, crossover caused by hydrogen passing through the electrolyte membrane is suppressed. Summary of the Invention

[0004] Recently, there has been a demand for improving the safety of water electrolysis systems when abnormalities occur.

[0005] The purpose of the present invention is to solve the above-mentioned technical problems and thereby contribute to energy utilization efficiency.

[0006] The present invention is directed to a water electrolysis system comprising a water electrolysis stack, a gas-liquid separator, a hydrogen booster stack, a gas storage tank, a supply valve, and a supply control unit, wherein the water electrolysis stack comprises a membrane electrode structure (MES) in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and is used to electrolyze water to generate oxygen and hydrogen; the gas-liquid separator is used to separate the hydrogen generated by the water electrolysis stack from the water not electrolyzed by the water electrolysis stack; the hydrogen booster stack comprises a MES in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and is used to pressurize the hydrogen separated by the gas-liquid separator; the gas storage tank stores an inert gas and is connected to a hydrogen flow channel, which connects the water electrolysis stack and the hydrogen booster stack through (via) the gas-liquid separator; the supply valve supplies the inert gas stored in the gas storage tank to the hydrogen flow channel when the valve is opened; and the supply control unit opens the supply valve when the concentration of oxygen flowing into the hydrogen flow channel, i.e., the oxygen concentration, exceeds a predetermined oxygen concentration threshold.

[0007] According to the present invention, the safety of a water electrolysis system when an abnormality occurs can be improved.

[0008] The above-mentioned objects, features and advantages will be easily understood through the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a diagram illustrating the structure of a water electrolysis system according to one embodiment.

[0010] Figure 2 This is a flowchart showing an example of the operation of the control device.

[0011] Figure 3 A diagram illustrating the configuration of a water electrolysis system according to a modified example.

[0012] Figure 4 This is a flowchart showing an example of the operation of the control device. DETAILED DESCRIPTION

[0013] A water electrolysis system according to one embodiment will be described using the drawings. Figure 1 1 is a diagram illustrating the structure of a water electrolysis system 10 according to this embodiment. The water electrolysis system 10 includes a water electrolysis stack 20 , a gas-liquid separator 30 , a hydrogen booster stack 40 , an oxygen tank 50 , a hydrogen tank 60 , a gas tank 70 , and a control device 80 .

[0014] The water electrolysis stack 20 is used to electrolyze water to produce oxygen and hydrogen. This water is supplied from the gas-liquid separator 30. The gas-liquid separator 30 is used to separate the hydrogen generated by the water electrolysis stack 20 from the water not electrolyzed by the water electrolysis stack 20. The gas-liquid separator 30 stores the separated water. The hydrogen booster stack 40 is used to boost the pressure of the hydrogen separated by the gas-liquid separator 30. The oxygen storage tank 50 stores the oxygen generated by the water electrolysis stack 20. The hydrogen storage tank 60 stores the hydrogen pressurized by the hydrogen booster stack 40.

[0015] The oxygen stored in the oxygen storage tank 50 and the hydrogen stored in the hydrogen storage tank 60 are used by components different from the water electrolysis system 10. Different components refer to, for example, fuel cells. A portion of the oxygen generated by the water electrolysis stack 20 can be supplied to the fuel cell without being stored. A portion of the hydrogen boosted by the hydrogen booster stack 40 can be supplied to the fuel cell without being stored. The gas storage tank 70 is used to store an inert gas. An inert gas is, for example, nitrogen or a rare gas. The control device 80 controls the various components that constitute the water electrolysis system 10. The details of the control by the control device 80 will be described later.

[0016] The water electrolysis system 10 includes a water supply channel 100 and a pump 102. The water supply channel 100 connects the gas-liquid separator 30 to the water electrolysis stack 20. The pump 102 draws water stored in the gas-liquid separator 30 and discharges it into the water supply channel 100. The water discharged by the pump 102 flows through the water supply channel 100 and is supplied to the water electrolysis stack 20.

[0017] A plurality of single cells 20u are stacked on the water electrolysis stack 20. Each single cell 20u electrolyzes water. The single cell 20u includes a membrane electrode assembly MEA1. The membrane electrode assembly MEA1 includes an electrolyte membrane 20m, an anode electrode 20a, and a cathode electrode 20c. The electrolyte membrane 20m is sandwiched between the anode electrode 20a and the cathode electrode 20c. The electrolyte membrane 20m is, for example, an anion exchange membrane. The hydroxide ions OH described later - Able to conduct in anion exchange membranes.

[0018] A voltage is applied from a power source to the anode electrode 20a and the cathode electrode 20c. A potential difference is generated between the anode electrode 20a and the cathode electrode 20c. The water supplied to the water electrolysis system 10 receives electrons from the cathode electrode 20c. In other words, a reduction reaction occurs. This reduction reaction generates hydrogen gas (H2) at the cathode electrode 20c, and hydroxide ions OH are also generated. - .

[0019] The hydroxide ions OH generated at the cathode electrode 20c - According to the potential difference between the two electrodes, the hydroxide ions OH are conducted to the anode electrode 20a through the electrolyte membrane 20m. Oxidation reaction occurs at the anode electrode 20a. - Electrons are released toward the anode electrode 20a, and as a result, oxygen gas (O2) and water (H2O) are generated at the anode electrode 20a.

[0020] The water electrolysis system 10 includes an oxygen supply channel 104, a backpressure valve 106, and a pressure regulating valve 108. The oxygen supply channel 104 includes a channel connecting the water electrolysis stack 20 to the oxygen storage tank 50 and a channel connecting the water electrolysis stack 20 to the fuel cell. The backpressure valve 106 is provided in the channel connecting the water electrolysis stack 20 to the oxygen storage tank 50. The pressure regulating valve 108 is provided in the channel connecting the water electrolysis stack 20 to the fuel cell.

[0021] Oxygen gas generated at the anode electrode 20a of the water electrolysis stack 20 can flow through the oxygen supply flow path 104 and be supplied to the oxygen storage tank 50 and the fuel cell. The backpressure valve 106 maintains the pressure of the oxygen gas flowing between the anode electrode 20a and the backpressure valve 106, and the pressure of the oxygen gas flowing between the anode electrode 20a and the pressure regulating valve 108, higher than the pressure of the hydrogen gas generated at the cathode electrode 20c. This creates a pressure differential across the electrolyte membrane 20m.

[0022] By creating a pressure differential across the electrolyte membrane 20m, water (water molecules) generated at the anode electrode 20a diffuses within the electrolyte membrane 20m and moves toward the cathode electrode 20c. The water moving toward the cathode electrode 20c is used in the reduction reaction at the cathode electrode 20c described above. Creating a pressure differential across the electrolyte membrane 20m reduces crosstalk from hydrogen generated at the cathode electrode 20c to the anode electrode 20a.

[0023] The water electrolysis system 10 has a hydrogen flow channel 110. The hydrogen flow channel 110 is a flow channel that connects the water electrolysis stack 20 and the hydrogen booster stack 40 through the gas-liquid separator 30. Figure 1 As shown, the hydrogen flow channel 110 includes a section 110a between the water electrolysis stack 20 and the gas-liquid separator 30, a section 110b between the gas-liquid separator 30 and the hydrogen booster stack 40, and a section 110c between the gas-liquid separator 30 and the hydrogen booster stack 40 that is different from the section 110b.

[0024] Hydrogen generated at cathode electrode 20c by water electrolysis stack 20 and water not electrolyzed by water electrolysis stack 20 flow through section 110a of hydrogen flow channel 110 and are separated by gas-liquid separator 30. Water contained in the reaction exhaust gas discharged from the fuel cell also flows into gas-liquid separator 30. The water separated by gas-liquid separator 30 is accumulated upward from bottom 30b of gas-liquid separator 30 by gravity. The hydrogen is located above the accumulated water.

[0025] exist Figure 1 , the storable water level Lm of the gas-liquid separator 30 is shown at a height h from the bottom 30b of the gas-liquid separator 30. The water level stored in the gas-liquid separator 30 is maintained below the storable water level Lm. As described above, the water stored in the gas-liquid separator 30 can flow through the water supply channel 100 and be supplied to the water electrolysis stack 20.

[0026] The hydrogen stored in the gas-liquid separator 30 can flow through the section 110b of the hydrogen flow channel 110 and be supplied to the hydrogen booster stack 40. The water electrolysis system 10 includes a pump 112. The pump 112 draws the hydrogen separated by the gas-liquid separator 30 and discharges it into the section 110b of the hydrogen flow channel 110. The hydrogen discharged by the pump 112 flows through the section 110b of the hydrogen flow channel 110 and is supplied to the hydrogen booster stack 40.

[0027] The water flowing from the fuel cell into the gas-liquid separator 30 may sometimes be mixed with a portion of the reaction waste gas discharged from the fuel cell. This reaction waste gas may contain oxygen. Consequently, oxygen may be present mixed with hydrogen in the hydrogen flow channel 110. The water electrolysis system 10 includes an oxygen removal device 114. Oxygen removal device 114 includes a catalyst such as palladium. This catalyst is located in section 110b of the hydrogen flow channel 110 and is used to remove oxygen from the hydrogen flow channel 110.

[0028] A plurality of cells 40u are stacked on the hydrogen booster stack 40. Each cell 40u boosts the pressure of hydrogen gas. The cell 40u includes a membrane electrode assembly MEA2. The membrane electrode assembly MEA2 includes an electrolyte membrane 40m, an anode electrode 40a, and a cathode electrode 40c. The electrolyte membrane 40m is sandwiched between the anode electrode 40a and the cathode electrode 40c. The electrolyte membrane 40m is, for example, a proton exchange membrane. As hydrogen ions H + A type of proton can be conducted in the proton exchange membrane.

[0029] A voltage is applied from a power supply to the anode electrode 40a and the cathode electrode 40c. A potential difference is generated between the anode electrode 40a and the cathode electrode 40c. The hydrogen gas supplied to the hydrogen booster stack 40 releases electrons at the anode electrode 40a. As a result, protons are generated at the anode electrode 40a. The protons generated at the anode electrode 40a are conducted to the cathode electrode 40c through the electrolyte membrane 40m according to the potential difference between the two electrodes. The protons (H + ) receives electrons from the cathode electrode 40c. Accordingly, high-pressure compressed hydrogen gas (H2) is generated at the cathode electrode 40c.

[0030] The water electrolysis system 10 includes a hydrogen supply channel 116 and a backpressure valve 118. The hydrogen supply channel 116 connects the hydrogen booster stack 40 to the hydrogen tank 60. The backpressure valve 118 is provided in the hydrogen supply channel 116. Hydrogen gas generated at the cathode electrode 40c of the hydrogen booster stack 40 can flow through the hydrogen supply channel 116 and be supplied to the hydrogen tank 60.

[0031] As described above, the hydrogen gas generated at the cathode electrode 40c is at a high pressure. The backpressure valve 118 maintains the pressure of the hydrogen gas flowing between the cathode electrode 40c and the backpressure valve 118 at a higher pressure than the pressure of the hydrogen gas supplied to the anode electrode 40a. Hydrogen gas not pressurized by the hydrogen booster stack 40 flows through the section 110c of the hydrogen flow channel 110 and returns to the gas-liquid separator 30.

[0032] As described above, in the water electrolysis stack 20, the oxygen gas generated at the anode electrode 20a is maintained at a higher pressure than the hydrogen gas generated at the cathode electrode 20c. Specifically, the internal pressure of the hydrogen flow channel 110 is lower than the pressure of the oxygen gas flowing from the anode electrode 20a to the back pressure valve 106 or the pressure regulating valve 108.

[0033] Assume that some abnormality occurs within the water electrolysis stack 20, damaging the electrolyte membrane 20m in one or more cells 20u of the water electrolysis stack 20. In this case, a large amount of high-pressure oxygen gas would flow into the low-pressure hydrogen flow channel 110. When a large amount of oxygen gas flows into the hydrogen flow channel 110, the oxygen removal device 114 cannot completely remove the oxygen gas, and the oxygen gas may reach the hydrogen booster stack 40.

[0034] Since voltage is applied to the multiple cells 40u of the hydrogen booster stack 40, not only hydrogen but also oxygen is supplied to the hydrogen booster stack 40, potentially compromising safety. Furthermore, in the oxygen removal device 114, a large amount of oxygen may contact the catalyst, potentially generating heat. This heat may also compromise safety.

[0035] To improve safety, the water electrolysis system 10 of this embodiment determines the concentration of oxygen flowing into the hydrogen flow channel 110, i.e., the oxygen concentration. If the oxygen concentration exceeds a predetermined oxygen concentration threshold, a purge process using an inert gas is performed within the hydrogen flow channel 110. This purge process can reduce the oxygen concentration. This improves safety in the event of an abnormality in the water electrolysis system 10.

[0036] By performing the water electrolysis stack 20 shutdown process in parallel with the purification process, the amount of oxygen flowing into the hydrogen flow channel 110 can be reduced. In addition, by performing the hydrogen boost stack 40 shutdown process in parallel with the purification process, the voltage application to the plurality of single cells 40u is stopped. This can further improve safety. Figure 1 The structure for performing purification processing in the hydrogen flow channel 110 using an inert gas will be described.

[0037] Gas storage tank 70 stores high-pressure inert gas. Water electrolysis system 10 includes an inert gas supply passage 122 and an inert gas supply valve 124. Gas supply passage 122 connects gas storage tank 70 to section 110b of hydrogen flow passage 110. Gas supply passage 122 is connected to hydrogen flow passage 110 between pump 112 and oxygen removal device 114. Specifically, gas storage tank 70 is connected to section 110b of hydrogen flow passage 110 upstream of oxygen removal device 114.

[0038] Supply valve 124 is provided in gas supply passage 122. When opened, supply valve 124 supplies high-pressure inert gas stored in gas storage tank 70 to section 110b of hydrogen passage 110. This inert gas supplied to hydrogen passage 110 reduces the oxygen concentration within hydrogen passage 110. The inert gas supplied to hydrogen passage 110 further flows into oxygen removal device 114 and hydrogen booster stack 40, thereby reducing the oxygen concentration within both oxygen removal device 114 and hydrogen booster stack 40.

[0039] The high-pressure inert gas flows into the hydrogen flow channel 110 in section 110b downstream of the gas-liquid separator 30 and also flows into the oxygen removal device 114 and the hydrogen booster stack 40, thereby rapidly reducing the oxygen concentration. The inert gas then flows through section 110c of the hydrogen flow channel 110 and into the gas-liquid separator 30.

[0040] The inert gas flowing into the gas-liquid separator 30 is introduced into a space 30r located above the water surface Ws of the water stored in the gas-liquid separator 30. Inert gas, oxygen, hydrogen, etc. exist in the space 30r. An opening 30p is provided in the gas-liquid separator 30. The opening 30p is provided at a position above the storable water level Lm of the gas-liquid separator 30. The position above the storable water level Lm of the gas-liquid separator 30 refers to, for example, an area above the storable water level Lm in the side surface 30s of the gas-liquid separator 30 or the upper surface 30t of the gas-liquid separator 30. In Figure 1 In the illustrated example, the opening 30p is provided on the upper surface 30t of the gas-liquid separator 30. This prevents the opening 30p from being flooded by the water stored in the gas-liquid separator 30.

[0041] The water electrolysis system 10 includes a discharge channel 126 and a discharge valve 128. One end of the discharge channel 126 communicates with an opening 30p of the gas-liquid separator 30. Specifically, the discharge channel 126 communicates with a space 30r above the water surface Ws within the gas-liquid separator 30 through the opening 30p. The other end of the discharge channel 126 communicates with the outside.

[0042] A discharge valve 128 is provided in the discharge flow channel 126. When the discharge valve 128 is opened, the discharge flow channel 126 is connected to the outside. In this case, the gas in the space 30r within the gas-liquid separator 30 can be discharged to the outside. In this way, the hydrogen flow channel 110 is purified using an inert gas. In other words, the oxygen in the hydrogen flow channel 110 can be discharged to the outside along with the inert gas. As a result, the oxygen concentration in the hydrogen flow channel 110 is substantially reduced, further improving the safety of the water electrolysis system 10.

[0043] As described above, the purge process within the hydrogen flow channel 110 using an inert gas is performed when the oxygen concentration exceeds a predetermined oxygen concentration threshold. Therefore, the water electrolysis system 10 includes a concentration sensor 130 for measuring the oxygen concentration within the hydrogen flow channel 110. The oxygen concentration information measured by the concentration sensor 130 is supplied to the control device 80.

[0044] As described above, the control device 80 controls the various components that make up the water electrolysis system 10. The control device 80 includes a computing unit 150 and a storage unit 152. The computing unit 150 includes a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). Specifically, the computing unit 150 includes processing circuitry.

[0045] The storage unit 152 is a computer-readable recording medium. It includes volatile memory such as RAM (Random Access Memory) and nonvolatile memory such as ROM (Read Only Memory) or flash memory. The volatile memory serves as the processor's working memory. The nonvolatile memory stores programs executed by the processor and other necessary data. The execution of the programs stored in the storage unit 152 controls the various components that make up the water electrolysis system 10.

[0046] The computing unit 150 includes a hydrogen booster stack control unit 160, a supply control unit 162, a discharge control unit 164, a determination unit 166, and a water electrolysis stack control unit 168. The computing unit 150 executes a program stored in the storage unit 152 to implement the hydrogen booster stack control unit 160, the supply control unit 162, the discharge control unit 164, the determination unit 166, and the water electrolysis stack control unit 168.

[0047] At least a portion of the hydrogen booster stack control unit 160, the supply control unit 162, the discharge control unit 164, the determination unit 166, and the water electrolysis stack control unit 168 may be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), or an electronic circuit including discrete devices.

[0048] The hydrogen booster stack control unit 160 controls the operation of the hydrogen booster stack 40. The water electrolysis stack control unit 168 controls the operation of the water electrolysis stack 20. The supply control unit 162 controls the inert gas supply valve 124. The discharge control unit 164 controls the discharge valve 128 provided in the discharge flow path 126. The determination unit 166 determines whether the concentration of oxygen flowing into the hydrogen flow path 110, i.e., the oxygen concentration, exceeds a predetermined oxygen concentration threshold. The oxygen concentration threshold is determined in advance through experiments and other means and is stored in the storage unit 152.

[0049] The water electrolysis stack control unit 168 starts the startup process for the water electrolysis stack 20. The hydrogen booster stack control unit 160 starts the startup process for the hydrogen booster stack 40. As the startup process for the water electrolysis system 10 begins, the determination unit 166 repeatedly acquires oxygen concentration information from the concentration sensor 130. Based on the acquired oxygen concentration information, the determination unit 166 determines whether the oxygen concentration within the hydrogen flow channel 110 exceeds the oxygen concentration threshold.

[0050] If the determination unit 166 determines that the oxygen concentration exceeds the oxygen concentration threshold, the supply control unit 162, discharge control unit 164, water electrolysis stack control unit 168, and hydrogen booster stack control unit 160 each perform the following control operations. Specifically, the supply control unit 162 controls the supply valve 124 to open. The discharge control unit 164 controls the discharge valve 128 to open. The water electrolysis stack control unit 168 controls the water electrolysis stack 20 to initiate a shutdown process for the water electrolysis stack 20. This suppresses the generation of oxygen, further improving the safety of the water electrolysis system 10.

[0051] The hydrogen booster stack control unit 160 controls the hydrogen booster stack 40 to start the shutdown process of the hydrogen booster stack 40. This reduces the possibility of the hydrogen gas supplied to the hydrogen booster stack 40 reacting with oxygen, thereby further improving the safety of the water electrolysis system 10.

[0052] The water electrolysis stack control unit 168 monitors the operating state of the water electrolysis stack 20 and determines whether the shutdown process of the water electrolysis stack 20 is complete. The hydrogen booster stack control unit 160 monitors the operating state of the hydrogen booster stack 40 and determines whether the shutdown process of the hydrogen booster stack 40 is complete.

[0053] When the water electrolysis stack control unit 168 determines that the shutdown process for the water electrolysis stack 20 is complete and the hydrogen booster stack control unit 160 determines that the shutdown process for the hydrogen booster stack 40 is complete, the discharge control unit 164 and the supply control unit 162 each perform the following control. Specifically, the discharge control unit 164 controls the discharge valve 128 to close the discharge valve 128. Furthermore, the supply control unit 162 controls the supply valve 124 to close the supply valve 124.

[0054] The shutdown of the water electrolysis stack 20 completes, and oxygen generation ceases. This cessation of oxygen generation further enhances the safety of the water electrolysis system 10. Furthermore, the shutdown of the hydrogen booster stack 40 completes, and hydrogen pressure boosting ceases. This cessation of hydrogen pressure boosting further enhances the safety of the water electrolysis system 10.

[0055] Furthermore, while the water electrolysis stack 20 is shut down, oxygen and hydrogen continue to be generated, but the amount of oxygen and hydrogen generated decreases. If these amounts suddenly decrease, the electrolyte membrane 20m of the water electrolysis stack 20 and the electrolyte membrane 40m of the hydrogen booster stack 40 may expand due to the rapid decompression within the water electrolysis system 10. This could further damage the electrolyte membrane 20m of the water electrolysis stack 20 or the electrolyte membrane 40m of the hydrogen booster stack 40.

[0056] To prevent this damage, it is necessary to control the decompression rate within the water electrolysis system 10. Therefore, it is preferable to continuously supply inert gas to the hydrogen flow channel 110. Therefore, until both the water electrolysis stack 20 and the hydrogen booster stack 40 cease operation, the supply control unit 162 does not close the supply valve 124. In other words, the supply valve 124 remains open. This keeps the oxygen concentration within the hydrogen flow channel 110 low.

[0057] Therefore, while the oxygen concentration in the hydrogen flow channel 110 is kept low, further damage to the electrolyte membrane 20m of the water electrolysis stack 20 or the electrolyte membrane 40m of the hydrogen booster stack 40 can be prevented, and the water electrolysis stack 20 and the hydrogen booster stack 40 can be shut down. Consequently, the safety of the water electrolysis system 10 can be further improved.

[0058] Furthermore, after both the water electrolysis stack 20 and the hydrogen booster stack 40 are stopped, the discharge valve 128 is closed. Closing the discharge valve 128 prevents damage to the water electrolysis system 10 due to a decrease in pressure within the water electrolysis system 10, even when the external atmospheric pressure is low or when no air is present. Furthermore, closing the supply valve 124 prevents damage to the water electrolysis system 10 due to an increase in pressure within the water electrolysis system 10, and prevents unnecessary consumption of the inert gas stored in the gas storage tank 70.

[0059] Figure 2 This is a flowchart showing an example of the operation of the control device 80. When the start-up process of the water electrolysis system 10 is started, Figure 2 The safety control process steps for the water electrolysis system 10 are shown. This process step is performed by the calculation unit 150 of the control device 80 executing a program stored in the storage unit 152.

[0060] When this process begins, in step S1, determination unit 166 acquires oxygen concentration information from concentration sensor 130. In step S2, determination unit 166 determines whether the oxygen concentration in hydrogen flow channel 110 indicated by the oxygen concentration information acquired in step S1 is higher than the oxygen concentration threshold stored in storage unit 152. If the answer is yes in step S2, the process proceeds to step S3. If the answer is no in step S2, the process returns to step S1.

[0061] In step S3, the determination unit 166 determines that the oxygen concentration in the hydrogen flow channel 110 exceeds the oxygen concentration threshold. In step S4, the supply control unit 162 opens the supply valve 124. In step S5, the discharge control unit 164 opens the discharge valve 128.

[0062] In step S6, the water electrolysis stack control unit 168 initiates shutdown processing for the water electrolysis stack 20. In step S7, the hydrogen booster stack control unit 160 initiates shutdown processing for the hydrogen booster stack 40. In step S8, the water electrolysis stack control unit 168 determines whether the shutdown processing for the water electrolysis stack 20 is complete. If the answer is yes in step S8, the process proceeds to step S9. If the answer is no in step S8, the process repeats step S8.

[0063] In step S9, the hydrogen booster stack control unit 160 determines whether the shutdown process for the hydrogen booster stack 40 is complete. If the answer is yes in step S9, the process proceeds to step S10. If the answer is no in step S9, the process repeats step S9. In step S10, the discharge control unit 164 closes the discharge valve 128. In step S11, the supply control unit 162 closes the supply valve 124. When the process in step S11 is complete, the process ends.

[0064] Furthermore, if the water electrolysis stack 20 is shut down, high-pressure oxygen will not be generated. In this case, sufficient safety can be ensured. Therefore, shutting down the hydrogen booster stack 40 is not necessarily necessary.

[0065] The above-mentioned embodiment can be modified as follows. In the following modifications, descriptions overlapping with those of the above-mentioned embodiment are omitted.

[0066] (Variation) In the above embodiment, the water electrolysis system 10 includes the concentration sensor 130 for measuring the oxygen concentration in the hydrogen flow channel 110. However, instead of measuring the oxygen concentration with the concentration sensor 130, the temperature of the catalyst provided in the oxygen removal device 114, that is, the catalyst temperature, may be measured. Figure 3 : is a diagram illustrating the structure of a water electrolysis system 10 according to this modification. Figure 3 The water electrolysis system 10 shown in the figure includes a temperature sensor 180 for measuring the catalyst temperature. Information on the catalyst temperature measured by the temperature sensor 180 , that is, catalyst temperature information, is supplied to the control device 80 .

[0067] When the oxygen concentration in hydrogen flow channel 110 increases, a large amount of oxygen may come into contact with the catalyst in oxygen removal device 114, potentially generating heat. Therefore, based on the relationship between the catalyst temperature measured by temperature sensor 180 and the oxygen concentration and catalyst temperature, determination unit 166 can determine that the oxygen concentration in hydrogen flow channel 110 exceeds the oxygen concentration threshold.

[0068] Specifically, when the catalyst temperature exceeds a predetermined catalyst temperature threshold, it is determined that the oxygen concentration within hydrogen flow path 110 exceeds the oxygen concentration threshold. The correspondence between oxygen concentration and catalyst temperature is determined in advance through experiments and the like and stored in storage unit 152. Furthermore, based on this correspondence, a catalyst temperature threshold is determined in advance in correspondence with the oxygen concentration threshold and stored in storage unit 152.

[0069] When the water electrolysis system 10 begins its startup process, the determination unit 166 repeatedly acquires catalyst temperature information from the temperature sensor 180. Based on the acquired catalyst temperature information, the determination unit 166 determines whether the oxygen concentration within the hydrogen flow channel 110 exceeds an oxygen concentration threshold. As the oxygen concentration increases, the catalyst temperature rises rapidly. Therefore, it is easy to detect when the oxygen concentration within the hydrogen flow channel 110 exceeds the oxygen concentration threshold.

[0070] If the determination unit 166 determines that the oxygen concentration exceeds the oxygen concentration threshold, the supply control unit 162 controls the supply valve 124 to open it. Furthermore, the discharge control unit 164 controls the discharge valve 128 to open it. Furthermore, the water electrolysis stack control unit 168 controls the water electrolysis stack 20 to initiate shutdown processing. The hydrogen booster stack control unit 160 controls the hydrogen booster stack 40 to initiate shutdown processing.

[0071] Figure 4 This is a flowchart showing an example of the operation of the control device 80. When the start-up process of the water electrolysis system 10 is started, Figure 4 The safety control process steps for the water electrolysis system 10 are shown. The process steps are performed by the operation unit 150 of the control device 80 executing the program stored in the storage unit 152. Figure 2 The same steps as the above steps are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

[0072] When this process begins, in step S41, determination unit 166 acquires catalyst temperature information from temperature sensor 180. In step S42, determination unit 166 determines whether the catalyst temperature indicated by the catalyst temperature information acquired in step S41 is higher than the catalyst temperature threshold stored in storage unit 152. If the answer is yes in step S42, the process proceeds to step S3. If the answer is no in step S42, the process returns to step S41.

[0073] The following supplementary notes are further disclosed regarding the above-mentioned embodiment and modifications.

[0074] (Note 1) The water electrolysis system (10) of the present invention comprises a water electrolysis stack (20), a gas-liquid separator (30), a hydrogen booster stack (40), a gas storage tank (70), a supply valve (124) and a supply control unit (162), wherein the water electrolysis stack comprises a membrane electrode structure (MEA1) in which an electrolyte membrane (20m) is clamped by an anode electrode (20a) and a cathode electrode (20c), and is used to electrolyze water to generate oxygen and hydrogen; the gas-liquid separator is used to separate the hydrogen generated by the water electrolysis stack from the water not electrolyzed by the water electrolysis stack; the hydrogen booster stack comprises an anode electrode (40 a) and a cathode electrode (40c) sandwiching an electrolyte membrane (40m) between a membrane electrode assembly (MEA2) for boosting the pressure of hydrogen separated by the gas-liquid separator; the gas storage tank storing inert gas and connected to a hydrogen flow channel (110), the hydrogen flow channel connecting the water electrolysis stack and the hydrogen booster stack via the gas-liquid separator; the supply valve, when opened, supplies the inert gas stored in the gas storage tank to the hydrogen flow channel; the supply control unit opens the supply valve when the concentration of oxygen flowing into the hydrogen flow channel, i.e., the oxygen concentration, exceeds a predetermined oxygen concentration threshold. With this structure, the safety of the water electrolysis system can be improved when an abnormality occurs.

[0075] (Note 2) In the water electrolysis system described in Supplement 1, the gas storage tank may be connected to a section (110b) in the hydrogen flow channel between the gas-liquid separator and the hydrogen booster stack. With this configuration, the inert gas can reduce the oxygen concentration in the hydrogen flow channel, the oxygen removal device, and the hydrogen booster stack.

[0076] (Note 3) The water electrolysis system described in Supplementary Note 1 may further include a discharge flow channel (126), a discharge valve (128), and a discharge control unit (164), wherein the discharge flow channel is connected to an opening (30p) provided in the gas-liquid separator; the discharge valve connects the discharge flow channel to the outside when the valve is opened; and the discharge control unit opens the discharge valve when the oxygen concentration exceeds the oxygen concentration threshold. With such a structure, the oxygen concentration in the hydrogen flow channel is sufficiently reduced, and the safety of the water electrolysis system can be further improved.

[0077] (Note 4) In the water electrolysis system according to Supplementary Note 3, the opening may be provided at a position above the storable water level (Lm) of the gas-liquid separator. This configuration can prevent the opening from being submerged in water in the gas-liquid separator.

[0078] (Note 5) The water electrolysis system described in Supplementary Note 1 may further include a water electrolysis stack control unit (168) that controls the water electrolysis stack to start a process of stopping the operation of the water electrolysis stack when the oxygen concentration exceeds the oxygen concentration threshold. According to such a structure, since the generation of oxygen is suppressed, the safety of the water electrolysis system can be further improved.

[0079] (Note 6) In the water electrolysis system described in Supplementary Note 5, the supply valve may be kept open until the operation of the water electrolysis stack is stopped. With this configuration, since the generation of oxygen is stopped, the safety of the water electrolysis system can be further improved.

[0080] (Note 7) The water electrolysis system according to Supplementary Note 5 may further include a hydrogen booster stack control unit (160) which controls the hydrogen booster stack to start a shutdown process of the hydrogen booster stack when the oxygen concentration exceeds the oxygen concentration threshold. With such a configuration, the possibility of the hydrogen supplied to the hydrogen booster stack reacting with oxygen is reduced, thereby further improving the safety of the water electrolysis system.

[0081] (Note 8) In the water electrolysis system according to Supplementary Note 7, the supply valve may remain open until both the water electrolysis stack and the hydrogen booster stack are stopped. With this configuration, the safety of the water electrolysis system can be further improved.

[0082] (Note 9) The water electrolysis system according to any one of Supplementary Notes 1 to 8 may further include a catalyst and a determination unit (166), wherein the catalyst is arranged in the hydrogen flow channel and is used to remove oxygen in the hydrogen flow channel; when the temperature of the catalyst, i.e., the catalyst temperature, exceeds a catalyst temperature threshold value predetermined according to the correspondence between the oxygen concentration and the catalyst temperature and corresponding to the oxygen concentration threshold value, the determination unit determines that the oxygen concentration exceeds the oxygen concentration threshold value, and when the determination unit determines that the oxygen concentration exceeds the oxygen concentration threshold value, the supply control unit opens the supply valve. According to such a structure, it is easy to detect that the oxygen concentration in the hydrogen flow channel exceeds the oxygen concentration threshold value.

[0083] The present invention has been described in detail, but the present invention is not limited to the above-mentioned embodiments. These embodiments can be supplemented, replaced, changed, partially deleted, etc. in a variety of ways without departing from the scope of the present invention or the scope of the present invention derived from the contents recorded in the technical solution and its equivalents. In addition, these embodiments can also be implemented in combination. For example, in the above-mentioned embodiment, the steps of each action or the steps of each processing are shown as an example and are not limited to these. In addition, the same applies to the cases where numerical values or formulas are used in the description of the above-mentioned embodiment.

Claims

1. A water electrolysis system, characterized in that: It includes a water electrolysis stack, a gas-liquid separator, a hydrogen booster stack, a gas storage tank, a supply valve and a supply control unit, wherein: The water electrolysis stack comprises a membrane electrode structure (MES) in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and is used to electrolyze water to generate oxygen and hydrogen. The gas-liquid separator is used to separate the hydrogen generated by the water electrolysis stack and the water not electrolyzed by the water electrolysis stack; The hydrogen booster stack comprises a membrane electrode structure in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and is used to boost the pressure of the hydrogen separated by the gas-liquid separator; The gas storage tank stores inert gas and is connected to a hydrogen flow channel, and the hydrogen flow channel is connected to the water electrolysis stack and the hydrogen booster stack through the gas-liquid separator; The supply valve supplies the inert gas stored in the gas storage tank to the hydrogen flow channel when the valve is opened; The supply control unit opens the supply valve when the concentration of oxygen gas flowing into the hydrogen flow path, ie, the oxygen concentration, exceeds a predetermined oxygen concentration threshold value.

2. The water electrolysis system according to claim 1, characterized in that The gas storage tank is connected to a section of the hydrogen flow channel between the gas-liquid separator and the hydrogen booster stack.

3. The water electrolysis system according to claim 1, characterized in that It also has a discharge flow channel, a discharge valve and a discharge control unit, wherein The discharge flow channel is communicated with an opening provided in the gas-liquid separator; The discharge valve connects the discharge flow channel to the outside when the valve is opened; The discharge control unit opens the discharge valve when the oxygen concentration exceeds the oxygen concentration threshold value.

4. The water electrolysis system according to claim 3, characterized in that The opening is provided at a position above a storable water level of the gas-liquid separator.

5. The water electrolysis system according to claim 1, characterized in that The water electrolysis stack controller further includes a water electrolysis stack controller that controls the water electrolysis stack to start a process of stopping the operation of the water electrolysis stack when the oxygen concentration exceeds the oxygen concentration threshold.

6. The water electrolysis system according to claim 5, characterized in that The supply valve is kept open until the operation of the water electrolysis stack is stopped.

7. The water electrolysis system according to claim 5, characterized in that The method further includes a hydrogen boost stack control unit configured to control the hydrogen boost stack so as to start a process of stopping the operation of the hydrogen boost stack when the oxygen concentration exceeds the oxygen concentration threshold value.

8. The water electrolysis system according to claim 7, characterized in that: The open state of the supply valve continues until the operation of the water electrolysis stack and the operation of the hydrogen booster stack are both stopped.

9. The water electrolysis system according to any one of claims 1 to 8, characterized in that: It also includes a catalyst and a determination unit, wherein The catalyst is disposed in the hydrogen flow channel and is used to remove oxygen in the hydrogen flow channel; When the temperature of the catalyst, i.e., the catalyst temperature, exceeds a catalyst temperature threshold value predetermined according to the correspondence relationship between the oxygen concentration and the catalyst temperature and corresponding to the oxygen concentration threshold value, the determination unit determines that the oxygen concentration exceeds the oxygen concentration threshold value. The supply control unit opens the supply valve when the determination unit determines that the oxygen concentration exceeds the oxygen concentration threshold value.

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