Water electrolysis system

Abstract

SOLUTION: A water electrolysis system 10 comprises a water electrolysis stack 20 for electrolyzing water to generate oxygen gas and hydrogen gas, a gas-liquid separator 30 for separating hydrogen gas and water, a hydrogen pressurization stack 40 for pressurizing hydrogen gas, a gas tank 70 for storing inert gas and connected to a hydrogen flow path 110 connecting the water electrolysis stack 20 and the hydrogen pressurization stack 40, a feed valve 124 for feeding the inert gas to the hydrogen flow path 110 when opened, and a feed controller 162 for opening the feed valve 124, when the concentration of the oxygen gas flowing into the hydrogen flow path 110 exceeds a predetermined oxygen concentration threshold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a water electrolysis system. [Background technology]

[0002] In recent years, research and development into fuel cells has been conducted to contribute to energy efficiency in order to ensure more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Patent Document 1 discloses a hydrogen and oxygen production system. The oxygen gas and hydrogen gas produced by the hydrogen and oxygen production system can be supplied to a tank for a fuel cell, etc. The hydrogen and oxygen production system includes a water electrolysis device. In the water electrolysis device, water is electrolyzed by passing an electric current through an anode and a cathode provided on both sides of an electrolyte membrane. Hydrogen gas is produced at the cathode, and high-pressure oxygen gas is produced at the anode. Oxygen gas is less likely to permeate the electrolyte membrane than hydrogen gas. Because the oxygen gas is at high pressure, the occurrence of crossover, in which hydrogen permeates the electrolyte membrane, is suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2022-83098 Summary of the Invention [Problem to be solved by the invention]

[0005] Recently, there has been a demand for improved safety in the event of an abnormality occurring in a water electrolysis system.

[0006] The present invention aims to solve the above-mentioned problems, and ultimately contributes to energy efficiency. [Means for solving the problem]

[0007] An aspect of the present disclosure is a water electrolysis system comprising: a water electrolysis stack having a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and which electrolyzes water to produce oxygen gas and hydrogen gas; a gas-liquid separator that separates the hydrogen gas produced by the water electrolysis stack from water that was not electrolyzed by the water electrolysis stack; a hydrogen booster stack having a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and which pressurizes the hydrogen gas separated by the gas-liquid separator; a gas tank that stores an inert gas and is connected to a hydrogen flow path that connects the water electrolysis stack and the hydrogen booster stack via the gas-liquid separator; a supply valve that, when opened, supplies the inert gas stored in the gas tank to the hydrogen flow path; and a supply controller that opens the supply valve when an oxygen concentration, which is the concentration of oxygen gas flowing into the hydrogen flow path, exceeds a predetermined oxygen concentration threshold. [Effects of the Invention]

[0008] According to the present invention, safety in the event of an abnormality in a water electrolysis system can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a water electrolysis system according to one embodiment. [Figure 2] FIG. 2 is a flowchart showing an example of the operation of the control device. [Figure 3] FIG. 3 is a diagram illustrating the configuration of a water electrolysis system according to a modified example. [Figure 4] FIG. 4 is a flowchart showing an example of the operation of the control device. DETAILED DESCRIPTION OF THE INVENTION

[0010] A water electrolysis system according to one embodiment will be described with reference to the drawings. Fig. 1 is a diagram illustrating the configuration 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.

[0011] The water electrolysis stack 20 electrolyzes water to produce oxygen gas and hydrogen gas. The water is supplied from the gas-liquid separator 30. The gas-liquid separator 30 separates the hydrogen gas produced by the water electrolysis stack 20 from the water that was not electrolyzed by the water electrolysis stack 20. The gas-liquid separator 30 stores the separated water. The hydrogen booster stack 40 pressurizes the hydrogen gas separated by the gas-liquid separator 30. The oxygen tank 50 stores the oxygen gas produced by the water electrolysis stack 20. The hydrogen tank 60 stores the hydrogen gas pressurized by the hydrogen booster stack 40.

[0012] The oxygen gas stored in the oxygen tank 50 and the hydrogen gas stored in the hydrogen tank 60 are used in a component separate from the water electrolysis system 10. The separate component may be, for example, a fuel cell. A portion of the oxygen gas produced by the water electrolysis stack 20 may be supplied to the fuel cell without being stored. A portion of the hydrogen gas boosted by the hydrogen booster stack 40 may be supplied to the fuel cell without being stored. The gas tank 70 stores an inert gas. The inert gas is, for example, nitrogen gas or a noble gas. The control device 80 controls each component constituting the water electrolysis system 10. Details of the control by the control device 80 will be described later.

[0013] The water electrolysis system 10 includes a water supply flow path 100 and a pump 102. The water supply flow path 100 is a flow path connecting the gas-liquid separator 30 and the water electrolysis stack 20. The pump 102 sucks water stored in the gas-liquid separator 30 and discharges it to the water supply flow path 100. The water discharged by the pump 102 flows through the water supply flow path 100 and is supplied to the water electrolysis stack 20.

[0014] The water electrolysis stack 20 has a plurality of unit cells 20u stacked on top of one another. Each unit cell 20u electrolyzes water. Each unit cell 20u has 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. Hydroxide ions OH, which will be described later, are ion-exchanged. - can be conducted through the anion exchange membrane.

[0015] A voltage is applied to the anode electrode 20a and the cathode electrode 20c from a power supply. A potential difference is generated between the anode electrode 20a and the cathode electrode 20c. 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 also generates hydroxide ions OH - occurs.

[0016] Hydroxide ions OH generated at the cathode electrode 20c - is conducted to the anode electrode 20a by the electrolyte membrane 20m in accordance with the potential difference between the two electrodes. An oxidation reaction occurs at the anode electrode 20a. The oxidation reaction generates hydroxide ions OH - The electrons are released to the anode electrode 20a, resulting in the generation of oxygen gas (O2) and water (H2O) at the anode electrode 20a.

[0017] The water electrolysis system 10 includes an oxygen supply flow path 104, a backpressure valve 106, and a pressure adjustment valve 108. The oxygen supply flow path 104 includes a flow path connecting the water electrolysis stack 20 and the oxygen tank 50, and a flow path connecting the water electrolysis stack 20 and the fuel cell. The backpressure valve 106 is provided in the flow path connecting the water electrolysis stack 20 and the oxygen tank 50. The pressure adjustment valve 108 is provided in the flow path connecting the water electrolysis stack 20 and the fuel cell.

[0018] Oxygen gas generated at the anode electrode 20a by the water electrolysis stack 20 flows through the oxygen supply flow path 104 and can be supplied to the oxygen tank 50 and the fuel cell. The back pressure valve 106 maintains the pressure of the oxygen gas flowing between the anode electrode 20a and the back pressure valve 106 and the pressure of the oxygen gas flowing between the anode electrode 20a and the pressure adjustment valve 108 higher than the pressure of the hydrogen gas generated at the cathode electrode 20c. This generates a pressure difference across the electrolyte membrane 20m.

[0019] Due to the pressure difference occurring across the electrolyte membrane 20m, water (water molecules) produced at the anode electrode 20a diffuses inside the electrolyte membrane 20m and moves to the cathode electrode 20c. The water that has moved to the cathode electrode 20c is used in the reduction reaction at the cathode electrode 20c. Due to the pressure difference occurring across the electrolyte membrane 20m, crosstalk, in which hydrogen gas produced at the cathode electrode 20c moves to the anode electrode 20a, is reduced.

[0020] The water electrolysis system 10 is provided with a hydrogen flow path 110. The hydrogen flow path 110 is a flow path that connects the water electrolysis stack 20 and the hydrogen booster stack 40 via the gas-liquid separator 30. As shown in Fig. 1 , the hydrogen flow path 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.

[0021] Hydrogen gas generated at the cathode electrode 20c by the water electrolysis stack 20 and water not electrolyzed by the water electrolysis stack 20 flow through the section 110a of the hydrogen flow path 110 and are separated by the gas-liquid separator 30. Water contained in the reaction off-gas discharged from the fuel cell described above also flows into the gas-liquid separator 30. The water separated by the gas-liquid separator 30 is stored upward from the bottom 30b of the gas-liquid separator 30 due to the action of gravity. The hydrogen gas is located above the stored water.

[0022] 1 shows a storable water level Lm of the gas-liquid separator 30 at a position at a height h from the bottom 30b of the gas-liquid separator 30. The level of the water stored in the gas-liquid separator 30 is maintained at or below the storable water level Lm. As described above, the water stored in the gas-liquid separator 30 flows through the water supply channel 100 and can be supplied to the water electrolysis stack 20.

[0023] The hydrogen gas stored in the gas-liquid separator 30 flows through the section 110b of the hydrogen flow path 110 and can be supplied to the hydrogen booster stack 40. The water electrolysis system 10 is provided with a pump 112. The pump 112 sucks in the hydrogen gas separated by the gas-liquid separator 30 and discharges it into the section 110b of the hydrogen flow path 110. The hydrogen gas discharged by the pump 112 flows through the section 110b of the hydrogen flow path 110 and is supplied to the hydrogen booster stack 40.

[0024] The water flowing from the fuel cell into the gas-liquid separator 30 may be contaminated with some of the reaction off-gas discharged from the fuel cell. The reaction off-gas may contain oxygen gas. Therefore, the oxygen gas may be mixed with the hydrogen gas in the hydrogen flow path 110. The water electrolysis system 10 is provided with an oxygen remover 114. The oxygen remover 114 is provided with a catalyst such as palladium. The catalyst is disposed in section 110b of the hydrogen flow path 110 and removes the oxygen gas in the hydrogen flow path 110.

[0025] The hydrogen booster stack 40 has a plurality of unit cells 40u stacked on top of each other. Each unit cell 40u boosts the pressure of hydrogen gas. Each unit cell 40u has 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. Hydrogen ions H + Protons, a type of electrolyte, can be conducted through a proton exchange membrane.

[0026] A voltage is applied to the anode electrode 40a and the cathode electrode 40c from a power source. 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. This causes protons to be generated at the anode electrode 40a. The protons generated at the anode electrode 40a are conducted to the cathode electrode 40c by the electrolyte membrane 40m in accordance with the potential difference between the two electrodes. The protons (H + ) receives electrons from the cathode electrode 40c, thereby generating high-pressure compressed hydrogen gas (H2) at the cathode electrode 40c.

[0027] The water electrolysis system 10 is provided with a hydrogen supply flow path 116 and a back pressure valve 118. The hydrogen supply flow path 116 is a flow path that connects the hydrogen booster stack 40 and the hydrogen tank 60. The back pressure valve 118 is provided in the hydrogen supply flow path 116. Hydrogen gas generated at the cathode electrode 40c by the hydrogen booster stack 40 flows through the hydrogen supply flow path 116 and can be supplied to the hydrogen tank 60.

[0028] As described above, the hydrogen gas generated at the cathode electrode 40c is at high pressure. The back pressure valve 118 maintains the pressure of the hydrogen gas flowing between the cathode electrode 40c and the back pressure valve 118 at a pressure higher than the pressure of the hydrogen gas supplied to the anode electrode 40a. The hydrogen gas that is not pressurized by the hydrogen pressurization stack 40 flows through the section 110c of the hydrogen flow path 110 and returns to the gas-liquid separator 30.

[0029] As described above, in the water electrolysis stack 20, the oxygen gas produced at the anode electrode 20a is maintained at a higher pressure than the hydrogen gas produced at the cathode electrode 20c. That is, the internal pressure of the hydrogen flow channel 110 is lower than the pressure of the oxygen gas flowing between the anode electrode 20a and the backpressure valve 106 or the pressure regulating valve 108.

[0030] Suppose that an abnormality occurs in the water electrolysis stack 20, causing damage to the electrolyte membrane 20m in one or more unit cells 20u of the water electrolysis stack 20. In this case, a large amount of high-pressure oxygen gas may flow into the low-pressure hydrogen flow path 110. If a large amount of oxygen gas flows into the hydrogen flow path 110, the oxygen remover 114 may not be able to remove all of the oxygen gas, and the oxygen gas may reach the hydrogen booster stack 40.

[0031] Since a voltage is applied to the multiple unit cells 40u of the hydrogen booster stack 40, safety may be compromised if not only hydrogen gas but also oxygen gas is supplied to the hydrogen booster stack 40. Furthermore, in the oxygen removal device 114, heat may be generated when a large amount of oxygen gas comes into contact with the catalyst. Heat generation may also compromise safety.

[0032] To improve safety, the water electrolysis system 10 according to this embodiment determines the oxygen concentration, which is the concentration of oxygen gas that has flowed into the hydrogen flow path 110. If the oxygen concentration exceeds a predetermined oxygen concentration threshold, the hydrogen flow path 110 is purged with an inert gas. The purging process can reduce the oxygen concentration. This can improve safety in the event of an abnormality in the water electrolysis system 10.

[0033] In parallel with the purging process, the water electrolysis stack 20 is shut down, thereby reducing the amount of oxygen gas flowing into the hydrogen flow path 110. Furthermore, in parallel with the purging process, the hydrogen booster stack 40 is shut down, thereby stopping the application of voltage to the plurality of unit cells 40u. This can further improve safety. A configuration for realizing the purging process inside the hydrogen flow path 110 with an inert gas will be described with reference to FIG. 1.

[0034] The gas tank 70 stores a high-pressure inert gas. The water electrolysis system 10 is provided with a gas supply flow path 122 for the inert gas and an inert gas supply valve 124. The gas supply flow path 122 connects the gas tank 70 with the section 110b of the hydrogen flow path 110. The gas supply flow path 122 is connected to the hydrogen flow path 110 between the pump 112 and the oxygen remover 114. That is, the gas tank 70 is connected to the section 110b of the hydrogen flow path 110 upstream of the oxygen remover 114.

[0035] The supply valve 124 is provided in the gas supply flow path 122. When the supply valve 124 is opened, it supplies high-pressure inert gas stored in the gas tank 70 to the section 110b of the hydrogen flow path 110. As a result, the inert gas supplied to the hydrogen flow path 110 can reduce the oxygen concentration in the hydrogen flow path 110. The inert gas supplied to the hydrogen flow path 110 further flows into the oxygen remover 114 and the hydrogen booster stack 40, and also reduces the oxygen concentrations in the oxygen remover 114 and the hydrogen booster stack 40.

[0036] The high-pressure inert gas flows into the hydrogen flow path 110 in section 110b downstream of the gas-liquid separator 30, and also flows into the oxygen remover 114 and the hydrogen booster stack 40, which can rapidly reduce the oxygen concentration. The inert gas then flows through section 110c of the hydrogen flow path 110 and into the gas-liquid separator 30.

[0037] The inert gas that has flowed into the gas-liquid separator 30 is introduced into a space 30r located above the water level Ws of the water stored in the gas-liquid separator 30. The space 30r contains an inert gas, oxygen gas, hydrogen gas, and the like. The gas-liquid separator 30 has an opening 30p. The opening 30p is provided in a portion of the gas-liquid separator 30 that is above the storable water level Lm. The portion of the gas-liquid separator 30 that is above the storable water level Lm is, for example, an area of ​​the side surface 30s of the gas-liquid separator 30 that is above the storable water level Lm, or a top surface 30t of the gas-liquid separator 30. In the example shown in FIG. 1 , the opening 30p is provided on the top surface 30t of the gas-liquid separator 30. This prevents the opening 30p from being submerged by the water stored in the gas-liquid separator 30.

[0038] The water electrolysis system 10 is equipped with a discharge flow path 126 and a discharge valve 128. One end of the discharge flow path 126 is connected to the opening 30p of the gas-liquid separator 30. That is, the discharge flow path 126 is connected to a space 30r located above the water surface Ws in the gas-liquid separator 30 via the opening 30p. The other end of the discharge flow path 126 is connected to the outside.

[0039] The discharge valve 128 is provided in the discharge flow path 126. When the discharge valve 128 is opened, the discharge flow path 126 communicates with the outside. In this case, gas present in the space 30r in the gas-liquid separator 30 can be discharged to the outside. In this manner, the hydrogen flow path 110 is purged with the inert gas. That is, oxygen gas in the hydrogen flow path 110 can be discharged to the outside together with the inert gas. Therefore, the oxygen concentration in the hydrogen flow path 110 is sufficiently reduced, and the safety of the water electrolysis system 10 can be further improved.

[0040] As described above, the hydrogen flow path 110 is purged with an inert gas when the oxygen concentration exceeds a predetermined oxygen concentration threshold. Therefore, the water electrolysis system 10 is provided with a concentration sensor 130 that measures the oxygen concentration in the hydrogen flow path 110. Oxygen concentration information, which is information on the oxygen concentration measured by the concentration sensor 130, is supplied to the control device 80.

[0041] As described above, the control device 80 controls the components constituting the water electrolysis system 10. The control device 80 includes a calculation unit 150 and a storage unit 152. The calculation unit 150 includes a processor such as a central processing unit (CPU) or a graphics processing unit (GPU). In other words, the calculation unit 150 includes processing circuitry.

[0042] The storage unit 152 is a computer-readable recording medium. The storage unit 152 includes a volatile memory such as a random access memory (RAM) and a non-volatile memory such as a read-only memory (ROM) or a flash memory. The volatile memory is used as a working memory for the processor. The non-volatile memory stores programs executed by the processor and other necessary data. The programs stored in the storage unit 152 are executed to control the components constituting the water electrolysis system 10.

[0043] The calculation 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 calculation unit 150 executes the programs stored in the storage unit 152 to realize 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.

[0044] At least some of the hydrogen boosting 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 realized 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.

[0045] 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 oxygen concentration, which is the concentration of oxygen gas flowing into the hydrogen flow path 110, has exceeded a predetermined oxygen concentration threshold. The oxygen concentration threshold is determined in advance by experiment or the like and stored in the memory unit 152.

[0046] The water electrolysis stack control unit 168 starts the startup process of the water electrolysis stack 20. The hydrogen booster stack control unit 160 starts the startup process of the hydrogen booster stack 40. When the startup process of the water electrolysis system 10 starts in this manner, 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 in the hydrogen flow path 110 has exceeded the oxygen concentration threshold value.

[0047] If the determination unit 166 determines that the oxygen concentration exceeds the oxygen concentration threshold, the supply control unit 162, the discharge control unit 164, the water electrolysis stack control unit 168, and the hydrogen booster stack control unit 160 each perform the following controls. That is, the supply control unit 162 controls the supply valve 124 to open it. The discharge control unit 164 controls the discharge valve 128 to open it. The water electrolysis stack control unit 168 controls the water electrolysis stack 20 to start processing to shut down the water electrolysis stack 20. This suppresses the generation of oxygen gas, thereby further improving the safety of the water electrolysis system 10.

[0048] The hydrogen booster stack control unit 160 controls the hydrogen booster stack 40 to initiate processing to shut down the hydrogen booster stack 40. This reduces the possibility of reaction between the hydrogen gas supplied to the hydrogen booster stack 40 and the oxygen gas, thereby further improving the safety of the water electrolysis system 10.

[0049] The water electrolysis stack control unit 168 monitors the operating state of the water electrolysis stack 20 and determines whether or not the operation shutdown process for the water electrolysis stack 20 has been completed. The hydrogen booster stack control unit 160 monitors the operating state of the hydrogen booster stack 40 and determines whether or not the operation shutdown process for the hydrogen booster stack 40 has been completed.

[0050] When the water electrolysis stack control unit 168 determines that the operation shutdown process of the water electrolysis stack 20 has been completed and the hydrogen booster stack control unit 160 determines that the operation shutdown process of the hydrogen booster stack 40 has been completed, the discharge control unit 164 and the supply control unit 162 each perform the following controls. That is, the discharge control unit 164 controls the discharge valve 128 to close it. Furthermore, the supply control unit 162 controls the supply valve 124 to close it.

[0051] Completion of the shutdown process for the water electrolysis stack 20 causes the production of oxygen gas to stop. Stopping the production of oxygen gas can further improve the safety of the water electrolysis system 10. Furthermore, completion of the shutdown process for the hydrogen booster stack 40 causes the boosting of hydrogen gas to stop. Stopping the boosting of hydrogen gas can further improve the safety of the water electrolysis system 10.

[0052] While the water electrolysis stack 20 is being shut down, oxygen gas and hydrogen gas continue to be produced, but the amounts of oxygen gas and hydrogen gas produced decrease. If the amounts of these gases are suddenly reduced, 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 a sudden decrease in pressure inside the water electrolysis system 10. This may cause further damage to the electrolyte membrane 20m of the water electrolysis stack 20 or the electrolyte membrane 40m of the hydrogen booster stack 40.

[0053] To prevent such damage, it is necessary to control the rate of pressure reduction inside the water electrolysis system 10. Therefore, it is preferable to continue supplying the inert gas to the hydrogen flow path 110. Therefore, the supply control unit 162 does not close the supply valve 124 until the operation of both the water electrolysis stack 20 and the hydrogen booster stack 40 has stopped. In other words, the supply valve 124 remains open. This keeps the oxygen concentration in the hydrogen flow path 110 low.

[0054] Therefore, the oxygen concentration in the hydrogen flow path 110 can be kept low, and the operation of the water electrolysis stack 20 and the hydrogen booster stack 40 can be shut down while preventing further damage to the electrolyte membrane 20m of the water electrolysis stack 20 or the electrolyte membrane 40m of the hydrogen booster stack 40. This further improves the safety of the water electrolysis system 10.

[0055] After both the operation of the water electrolysis stack 20 and the operation of the hydrogen booster stack 40 are stopped, the discharge valve 128 is closed. Closing the discharge valve 128 can prevent damage to the water electrolysis system 10 due to a pressure drop inside the water electrolysis system 10, even when the external atmospheric pressure is low or there is no air outside. Furthermore, closing the supply valve 124 can prevent damage to the water electrolysis system 10 due to a pressure increase inside the water electrolysis system 10 and can prevent the inert gas stored in the gas tank 70 from being wasted.

[0056] Fig. 2 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, the safety control process procedure for the water electrolysis system 10 shown in Fig. 2 is started. This process procedure is performed by the calculation unit 150 of the control device 80 executing a program stored in the memory unit 152.

[0057] When this processing procedure starts, in step S1, the determination unit 166 acquires oxygen concentration information from the concentration sensor 130. In step S2, the determination unit 166 determines whether the oxygen concentration in the hydrogen flow path 110 indicated by the oxygen concentration information acquired in step S1 is higher than the oxygen concentration threshold value stored in the memory unit 152. If the result in step S2 is YES, the processing procedure proceeds to step S3. If the result in step S2 is NO, the processing procedure returns to step S1.

[0058] In step S3, the determination unit 166 determines that the oxygen concentration in the hydrogen flow path 110 has exceeded 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.

[0059] In step S6, the water electrolysis stack control unit 168 starts the process of shutting down the water electrolysis stack 20. In step S7, the hydrogen booster stack control unit 160 starts the process of shutting down the hydrogen booster stack 40. In step S8, the water electrolysis stack control unit 168 determines whether the process of shutting down the water electrolysis stack 20 has been completed. If the result in step S8 is YES, the process proceeds to step S9. If the result in step S8 is NO, the process in step S8 is repeated.

[0060] In step S9, the hydrogen booster stack control unit 160 determines whether the operation shutdown process of the hydrogen booster stack 40 has been completed. If the result of step S9 is YES, the process proceeds to step S10. If the result of step S9 is NO, the process of step S9 is repeated. 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 of step S11 is completed, the process ends.

[0061] If the operation of the water electrolysis stack 20 is stopped, high-pressure oxygen gas will not be generated. In this case, sufficient safety can be ensured. Therefore, the process of shutting down the operation of the hydrogen booster stack 40 is not necessarily performed.

[0062] The above-described embodiment may be modified as follows: In the following modifications, explanations that overlap with the above-described embodiment will be omitted.

[0063] (Variation) In the above-described embodiment, the water electrolysis system 10 is provided with the concentration sensor 130 that measures the oxygen concentration in the hydrogen flow path 110. However, instead of measuring the oxygen concentration with the concentration sensor 130, the catalyst temperature, which is the temperature of a catalyst provided in the oxygen remover 114, may be measured. FIG. 3 is a diagram illustrating the configuration of the water electrolysis system 10 according to this modification. The water electrolysis system 10 shown in FIG. 3 is provided with a temperature sensor 180 that measures the catalyst temperature. Catalyst temperature information, which is information about the catalyst temperature measured by the temperature sensor 180, is supplied to the control device 80.

[0064] When the oxygen concentration in the hydrogen flow path 110 increases, a large amount of oxygen gas may come into contact with the catalyst in the oxygen remover 114, which may generate heat. Therefore, based on the catalyst temperature measured by the temperature sensor 180 and the correspondence relationship between the oxygen concentration and the catalyst temperature, the determination unit 166 may determine that the oxygen concentration in the hydrogen flow path 110 has exceeded the oxygen concentration threshold value.

[0065] That is, when the catalyst temperature exceeds a predetermined catalyst temperature threshold, it is determined that the oxygen concentration in the hydrogen flow path 110 has exceeded the oxygen concentration threshold. The correspondence relationship between the oxygen concentration and the catalyst temperature is determined in advance by experiment or the like, and is stored in the storage unit 152. Furthermore, based on this correspondence relationship, a catalyst temperature threshold is determined in advance in correspondence with the above-mentioned oxygen concentration threshold, and is stored in the storage unit 152.

[0066] When the start-up process of the water electrolysis system 10 is initiated, 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 in the hydrogen flow path 110 has exceeded the oxygen concentration threshold. When the oxygen concentration increases, the catalyst temperature rises rapidly. Therefore, it becomes easier to detect that the oxygen concentration in the hydrogen flow path 110 has exceeded the oxygen concentration threshold.

[0067] When the determination unit 166 determines that the oxygen concentration has exceeded 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 start processing to shut down the water electrolysis stack 20. The hydrogen booster stack control unit 160 controls the hydrogen booster stack 40 to start processing to shut down the hydrogen booster stack 40.

[0068] Figure 4 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 initiated, the safety control process procedure for the water electrolysis system 10 shown in Figure 4 is initiated. This process procedure is performed by the calculation unit 150 of the control device 80 executing a program stored in the storage unit 152. Steps that are the same as those described above with reference to Figure 2 are given the same reference numerals, and descriptions thereof will be omitted where appropriate.

[0069] When this processing procedure starts, in step S41, the determination unit 166 acquires catalyst temperature information from the temperature sensor 180. In step S42, the determination unit 166 determines whether the catalyst temperature of the catalyst indicated by the catalyst temperature information acquired in step S1 is higher than the catalyst temperature threshold value stored in the memory unit 152. If the result in step S42 is YES, the processing procedure proceeds to step S3. If the result in step S42 is NO, the processing procedure returns to step S41.

[0070] The following additional notes are provided regarding the above-described embodiment and modifications.

[0071] (Appendix 1) The water electrolysis system (10) of the present disclosure includes a water electrolysis stack (20) that includes a membrane electrode assembly (MEA1) in which an electrolyte membrane (20m) is sandwiched between an anode electrode (20a) and a cathode electrode (20c) and that electrolyzes water to produce oxygen gas and hydrogen gas; a gas-liquid separator (30) that separates the hydrogen gas produced by the water electrolysis stack from water that has not been electrolyzed by the water electrolysis stack; and a membrane electrode assembly (MEA2) in which an electrolyte membrane (40m) is sandwiched between an anode electrode (40a) and a cathode electrode (40c), The water electrolysis system includes a hydrogen booster stack (40) that boosts the pressure of the hydrogen gas separated by the gas-liquid separator, a gas tank (70) that stores an inert gas and is connected to a hydrogen flow path (110) that connects the water electrolysis stack and the hydrogen booster stack via the gas-liquid separator, a supply valve (124) that, when opened, supplies the inert gas stored in the gas tank to the hydrogen flow path, and a supply control unit (162) that opens the supply valve when the oxygen concentration, which is the concentration of oxygen gas flowing into the hydrogen flow path, exceeds a predetermined oxygen concentration threshold. This configuration can improve safety in the event of an abnormality in the water electrolysis system.

[0072] (Appendix 2) In the water electrolysis system described in Appendix 1, the gas tank may be connected to a section (110b) in the hydrogen flow path between the gas-liquid separator and the hydrogen pressurization stack. With this configuration, the inert gas can reduce the oxygen concentration in the hydrogen flow path, the oxygen removal device, and the hydrogen pressurization stack.

[0073] (Appendix 3) The water electrolysis system described in Supplementary Note 1 may further include an exhaust flow path (126) in communication with an opening (30p) provided in the gas-liquid separator, an exhaust valve (128) that, when opened, connects the exhaust flow path to the outside, and an exhaust control unit (164) that opens the exhaust valve when the oxygen concentration exceeds the oxygen concentration threshold. With this configuration, the oxygen concentration in the hydrogen flow path is sufficiently reduced, and the safety of the water electrolysis system can be further improved.

[0074] (Appendix 4) In the water electrolysis system described in Supplementary Note 3, the opening may be provided at a position above a storable water level (Lm) of the gas-liquid separator. This configuration prevents the opening from being submerged in the water in the gas-liquid separator.

[0075] (Appendix 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 to shut down the water electrolysis stack when the oxygen concentration exceeds the oxygen concentration threshold. This configuration suppresses the generation of oxygen gas, thereby further improving the safety of the water electrolysis system.

[0076] (Appendix 6) In the water electrolysis system described in Supplementary Note 5, the supply valve may be kept open until operation of the water electrolysis stack is stopped. With this configuration, production of oxygen gas is stopped, thereby further improving the safety of the water electrolysis system.

[0077] (Appendix 7) The water electrolysis system described in Supplementary Note 5 may further include a hydrogen booster stack control unit (160) that controls the hydrogen booster stack to start a process for shutting down the hydrogen booster stack when the oxygen concentration exceeds the oxygen concentration threshold. Such a configuration reduces the possibility of a reaction between hydrogen gas and oxygen gas supplied to the hydrogen booster stack, thereby further improving the safety of the water electrolysis system.

[0078] (Appendix 8) In the water electrolysis system described in Supplementary Note 7, the supply valve may be kept open until operation of both the water electrolysis stack and the hydrogen boosting stack is stopped. This configuration can further improve the safety of the water electrolysis system.

[0079] (Appendix 9) The water electrolysis system according to any one of Supplementary Notes 1 to 8 further includes a catalyst disposed in the hydrogen flow path to remove oxygen gas from the hydrogen flow path, and a determination unit (166) that determines, when a catalyst temperature of the catalyst exceeds a predetermined catalyst temperature threshold value corresponding to the oxygen concentration threshold value based on a correspondence relationship between the oxygen concentration and the catalyst temperature, that the oxygen concentration has exceeded the oxygen concentration threshold value, and the supply control unit may open the supply valve when the determination unit determines that the oxygen concentration has exceeded the oxygen concentration threshold value. This configuration makes it easier to detect that the oxygen concentration in the hydrogen flow path has exceeded the oxygen concentration threshold value.

[0080] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments. [Explanation of symbols]

[0081] 10...Water electrolysis system 20...Water electrolysis stack 30...Gas-liquid separator 40...Hydrogen booster stack 50...Oxygen tank 60...Hydrogen tank 70...Gas tank 80...Control device 100...water supply passage 102...pump 104...oxygen supply channel 106...back pressure valve 108... Pressure regulating valve 110... Hydrogen flow path 112... Pump 114... Oxygen removal device 116... Hydrogen supply passage 118... Back pressure valve 122...Gas supply passage 124...Supply valve 126...Discharge flow path 128...Discharge valve 130: concentration sensor 150: calculation unit 152...Memory unit 160...Hydrogen booster stack control unit 162...supply control unit 164...discharge control unit 166... ​​Determination unit 168... Water electrolysis stack control unit 180...Temperature sensor

Claims

1. a water electrolysis stack having a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and which electrolyzes water to produce oxygen gas and hydrogen gas; a gas-liquid separator that separates hydrogen gas generated by the water electrolysis stack from water that has not been electrolyzed by the water electrolysis stack; a hydrogen booster stack having a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, the hydrogen booster stack pressurizing the hydrogen gas separated by the gas-liquid separator; a gas tank that stores an inert gas and is connected to a hydrogen flow path that connects the water electrolysis stack and the hydrogen boosting stack via the gas-liquid separator; a supply valve that, when opened, supplies the inert gas stored in the gas tank to the hydrogen flow path; a supply control unit that opens the supply valve when an oxygen concentration, which is the concentration of the oxygen gas flowing into the hydrogen flow channel, exceeds a predetermined oxygen concentration threshold; A water electrolysis system comprising:

2. The water electrolysis system according to claim 1, a gas tank connected to a section of the hydrogen flow path between the gas-liquid separator and the hydrogen booster stack;

3. The water electrolysis system according to claim 1, a discharge flow path communicating with an opening provided in the gas-liquid separator; a discharge valve that, when opened, connects the discharge flow path to the outside; an exhaust control unit that opens the exhaust valve when the oxygen concentration exceeds the oxygen concentration threshold; The water electrolysis system further comprises:

4. The water electrolysis system according to claim 3, a water electrolysis system, wherein the opening is provided at a position above a water level that can be stored in the gas-liquid separator.

5. The water electrolysis system according to claim 1, a water electrolysis stack control unit that controls the water electrolysis stack to start a process to shut down the water electrolysis stack when the oxygen concentration exceeds the oxygen concentration threshold.

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

7. The water electrolysis system according to claim 5, a hydrogen booster stack control unit that controls the hydrogen booster stack to start a process for shutting down the hydrogen booster stack when the oxygen concentration exceeds the oxygen concentration threshold.

8. The water electrolysis system according to claim 7, the supply valve remains open until operation of both the water electrolysis stack and the hydrogen boosting stack is stopped.

9. The water electrolysis system according to any one of claims 1 to 8, a catalyst disposed in the hydrogen flow path to remove oxygen gas from the hydrogen flow path; a determination unit that determines that the oxygen concentration has exceeded the oxygen concentration threshold value when a catalyst temperature, which is a temperature of the catalyst, exceeds a catalyst temperature threshold value that is predetermined in accordance with the oxygen concentration threshold value based on a correspondence relationship between the oxygen concentration and the catalyst temperature; Furthermore, When the determination unit determines that the oxygen concentration exceeds the oxygen concentration threshold, the supply control unit opens the supply valve.

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