Regenerative fuel cell system

Abstract

To suppress a decrease in durability of a fuel cell even when alkaline water is contained in a product gas.SOLUTION: A regenerative fuel cell system 10 includes a water electrolysis device 22 that electrolyzes alkaline water, a fuel cell 12 that generates electricity using the product gas generated by the electrolysis, a storage container 202 that stores the product water generated by the electricity generation, and a gas flow path 200 that guides the product gas through the product water stored in the storage container 202 to the fuel cell 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to regenerative fuel cell systems. [Background technology]

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

[0003] Patent Document 1 listed below discloses a regenerative fuel cell system including a water electrolysis device and a fuel cell. In this regenerative fuel cell system, the water electrolysis device electrolyzes water to produce gas. The fuel cell generates electricity using the gas produced by electrolysis in the water electrolysis device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2023-117525 Summary of the Invention [Problem to be solved by the invention]

[0005] In some cases, alkaline water is supplied to a water electrolysis device. In this case, the alkaline water is contained in the gas produced by electrolysis in the water electrolysis device. Supplying alkaline water to a fuel cell can cause a problem of reduced durability of the fuel cell.

[0006] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0007] An aspect of the present disclosure is a regenerative fuel cell system comprising a water electrolysis device that electrolyzes alkaline water, a fuel cell that generates electricity using a product gas that is gas generated by the electrolysis, a storage container that stores the product water that is water generated by the electricity generation, and a gas flow path that guides the product gas to the fuel cell through the product water stored in the storage container. [Effects of the Invention]

[0008] This allows the generated gas to neutralize alkaline water stored in the storage container, thereby preventing a decrease in the durability of the fuel cell. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a regenerative fuel cell system according to a first embodiment. [Figure 2] FIG. 2 is a block diagram of the control device. [Figure 3] FIG. 3 is a flowchart showing the procedure for controlling the operation of the water electrolysis apparatus to stop. [Figure 4] FIG. 4 is a diagram showing a storage container. [Figure 5] FIG. 5 is a schematic diagram showing a regenerative fuel cell system according to the second embodiment. [Figure 6] FIG. 6 is a flowchart showing the procedure of density control. DETAILED DESCRIPTION OF THE INVENTION

[0010] (First embodiment) 1 is a schematic diagram showing a regenerative fuel cell system 10 according to a first embodiment. The regenerative fuel cell system 10 includes a fuel cell 12, a gas generator 14, a supply mechanism 16, and a controller 18.

[0011] The fuel cell 12 generates electricity through an electrochemical reaction between oxygen gas and hydrogen gas. The fuel cell 12 has a plurality of electrochemical cells. Each electrochemical cell includes an electrolyte membrane and a pair of electrodes provided on both sides of the electrolyte membrane in the thickness direction. The electrolyte membrane used in the fuel cell 12 is a proton exchange membrane. One of the pair of electrodes is an anode electrode, and the other of the pair of electrodes is a cathode electrode. The fuel cell 12 supplies hydrogen gas to the anode electrode of each electrochemical cell. The fuel cell 12 supplies oxygen gas to the cathode electrode of each electrochemical cell. The fuel cell 12 collects electricity generated in each electrochemical cell by the electrochemical reaction between oxygen gas and hydrogen gas, and stores it in the battery 20.

[0012] The fuel cell 12 collects excess oxygen gas that has not undergone electrochemical reaction and discharges an oxygen-containing exhaust gas containing this oxygen gas. Most of the oxygen-containing exhaust gas is circulated back to the fuel cell 12 for reuse. The fuel cell 12 also collects excess hydrogen gas that has not undergone electrochemical reaction and discharges a hydrogen-containing exhaust gas containing this hydrogen gas. Most of the hydrogen-containing exhaust gas is circulated back to the fuel cell 12 for reuse.

[0013] The gas generator 14 is a device that generates either oxygen gas or hydrogen gas, and includes a water electrolysis device 22 and a hydrogen booster 24.

[0014] The water electrolysis device 22 is a gas generator 14 that electrolyzes water to generate oxygen gas and hydrogen gas. Water is supplied from a gas-liquid separator 26 via a water supply channel 28. The water supplied to the water electrolysis device 22 is alkaline water. For example, the water supplied to the water electrolysis device 22 is water containing potassium hydroxide. The water supply channel 28 connects the gas-liquid separator 26 and the water electrolysis device 22. A water supply pump 31 is provided in the water supply channel 28 at a position between the gas-liquid separator 26 and the water electrolysis device 22. The water supply pump 31 supplies water stored in the gas-liquid separator 26 to the water electrolysis device 22.

[0015] Refill water is supplied to the gas-liquid separator 26 from a water tank 30 via a refill water passage 29. The refill water is water that is replenished to the water (alkaline water) supplied to the water electrolysis device 22. A water supply pump 33 is provided in the refill water passage 29. The refill water is supplied to the gas-liquid separator 26 by the water supply pump 33.

[0016] The water electrolysis device 22 has a plurality of electrochemical cells. Each electrochemical cell includes an electrolyte membrane and a pair of electrodes provided on both sides of the electrolyte membrane in the thickness direction. The electrolyte membrane used in the water electrolysis device 22 is an anion exchange membrane. One of the pair of electrodes is an anode electrode, and the other of the pair of electrodes is a cathode electrode. A power supply device 23 is connected to the anode electrode and the cathode electrode. The power supply device 23 is configured to be able to change the voltage value applied to the anode electrode and the cathode electrode. The power supply device 23 may obtain the power for the voltage applied between the anode electrode and the cathode electrode from the battery 20.

[0017] The water electrolysis device 22 supplies water flowing in from the water supply channel 28 to the cathode electrode of each electrochemical cell. Each electrochemical cell electrolyzes water based on a voltage applied by the power supply device 23. As a result, oxygen gas is produced at the anode electrode, and hydrogen gas is produced at the cathode electrode. The oxygen gas produced in the water electrolysis device 22 is compressed to a high pressure. For example, the oxygen gas is compressed to a pressure in the range of 1 to 100 MPa.

[0018] The water electrolysis device 22 collects oxygen gas produced in each electrochemical cell and outputs exhaust gas containing the oxygen gas to the supply mechanism 16. The exhaust gas contains water vapor vaporized by heat or the like from the water electrolysis device 22. Meanwhile, the water electrolysis device 22 collects hydrogen gas produced in each electrochemical cell and excess water (unreacted water) that was not electrolyzed, and discharges a discharge fluid containing the hydrogen gas and unreacted water into the hydrogen supply channel 32. The discharge fluid also contains water vapor vaporized by heat or the like from the water electrolysis device 22.

[0019] The hydrogen supply channel 32 includes a first partial flow path 32A, a second partial flow path 32B, and a third partial flow path 32C. The first partial flow path 32A connects the water electrolysis device 22 and the gas-liquid separator 26. The second partial flow path 32B connects the gas-liquid separator 26 and the water tank 30. The third partial flow path 32C connects the water tank 30 and the hydrogen booster device 24. A gas supply pump 34 is provided in the third partial flow path 32C.

[0020] The discharge fluid output from the water electrolysis device 22 flows into the gas-liquid separator 26 via the first partial flow path 32A. The gas-liquid separator 26 separates the discharge fluid into a liquid component (liquid water) and a gas component (hydrogen gas). The liquid water is supplied to the water electrolysis device 22 by the water supply pump 31. The hydrogen gas is supplied to the hydrogen booster device 24 by the gas supply pump 34.

[0021] The hydrogen pressure booster 24 is the gas generator 14 that generates high-pressure hydrogen gas. The hydrogen pressure booster 24 boosts the pressure of the hydrogen gas that flows in from the hydrogen supply channel 32. The hydrogen gas that flows in from the hydrogen supply channel 32 is hydrogen gas that is generated by the water electrolysis device 22.

[0022] The hydrogen booster 24 has a plurality of electrochemical cells. Each electrochemical cell includes an electrolyte membrane and a pair of electrodes provided on both sides of the electrolyte membrane in the thickness direction. The electrolyte membrane used in the hydrogen booster 24 is a proton exchange membrane. One of the pair of electrodes is an anode electrode, and the other of the pair of electrodes is a cathode electrode. A power supply 25 is connected to the anode electrode and the cathode electrode. The power supply 25 is configured to be able to change the voltage value of the voltage applied between the anode electrode and the cathode electrode. The power supply 25 may obtain the power for the voltage applied between the anode electrode and the cathode electrode from the battery 20.

[0023] The hydrogen booster 24 supplies hydrogen gas flowing in from the hydrogen supply channel 32 to the anode electrode. The hydrogen booster 24 ionizes the hydrogen gas based on a voltage applied by the power supply 25. Protons obtained by the ionization of the hydrogen gas reach the cathode electrode through an electrolyte membrane (proton exchange membrane) and return to hydrogen gas. The hydrogen booster 24 can compress the hydrogen gas by transferring the protons from the anode electrode to a closed space including the cathode electrode. For example, the hydrogen gas is compressed to a pressure range of 1 to 100 MPa. In this way, the hydrogen booster 24 is an electrochemical hydrogen compressor (EHC) that can electrochemically compress hydrogen gas.

[0024] The hydrogen booster 24 outputs exhaust gas containing pressurized hydrogen gas to the supply mechanism 16. The exhaust gas contains water vapor vaporized by the heat of the hydrogen booster 24. Meanwhile, the hydrogen booster 24 discharges excess hydrogen gas that has not been ionized to a hydrogen discharge path 35. The hydrogen discharge path 35 connects the hydrogen booster 24 and the gas-liquid separator 26.

[0025] The supply mechanism 16 is a mechanism for supplying gas to the fuel cell 12 and includes an oxygen supply mechanism 36 and a hydrogen supply mechanism 38. The oxygen supply mechanism 36 is a supply mechanism 16 for supplying oxygen gas generated in the water electrolysis device 22 to the fuel cell 12. The hydrogen supply mechanism 38 is a supply mechanism 16 for supplying hydrogen gas generated in the hydrogen booster device 24 to the fuel cell 12.

[0026] The oxygen supply mechanism 36 and the hydrogen supply mechanism 38 have basically the same configuration. Therefore, unless otherwise specified, the supply mechanism 16 common to the oxygen supply mechanism 36 and the hydrogen supply mechanism 38 will be described.

[0027] In the following description, the term "supply mechanism 16" refers to either the oxygen supply mechanism 36 or the hydrogen supply mechanism 38. Similarly, the term "gas" refers to either oxygen gas or hydrogen gas. Similarly, the term "gas generator 14" refers to either the water electrolysis device 22 or the hydrogen booster device 24.

[0028] However, it should be noted that when "supply mechanism 16" refers to the oxygen supply mechanism 36, "gas" refers to oxygen gas, not hydrogen gas. Also, when "supply mechanism 16" refers to the oxygen supply mechanism 36, "gas generator 14" refers to the water electrolysis apparatus 22, not the hydrogen booster apparatus 24. Similarly, when "supply mechanism 16" refers to the hydrogen supply mechanism 38, "gas" refers to hydrogen gas, not oxygen gas. Also, when "supply mechanism 16" refers to the hydrogen supply mechanism 38, "gas generator 14" refers to the hydrogen booster apparatus 24, not the water electrolysis apparatus 22.

[0029] The supply mechanism 16 includes a gas supply path 40, a pressure vessel 42, a bypass path 44, a first on-off valve 46, a second on-off valve 48, a first pressure regulating valve 50, a second pressure regulating valve 52, a first check valve 54, a second check valve 56, a pressure control valve 58, a flow rate regulating valve 60, a pressure sensor 62, and a gas-liquid separator 64.

[0030] The gas supply path 40 is a path for supplying gas from the gas generator 14 to the fuel cell 12. The gas supply path 40 includes a first supply path 40A and a second supply path 40B. The first supply path 40A is a flow path that guides gas from the gas generator 14 to the pressure vessel 42. The first supply path 40A includes a flow path portion 40A1 that connects the gas generator 14 and the gas-liquid separator 64, and a flow path portion 40A2 that connects the gas-liquid separator 64 and the pressure vessel 42. The second supply path 40B is a flow path that guides gas from the pressure vessel 42 to the fuel cell 12.

[0031] The pressure vessel 42 is provided on the gas supply path 40. The pressure vessel 42 stores the gas generated by the gas generator 14. The gas stored in the pressure vessel 42 is compressed.

[0032] The bypass path 44 is a path for supplying the gas generated in the gas generator 14 to the fuel cell 12 without passing through the pressure vessel 42. The bypass path 44 is different for the oxygen supply mechanism 36 and the hydrogen supply mechanism 38. The bypass path 44 of the oxygen supply mechanism 36 connects the flow path portion 40A1 of the first supply path 40A to the gas-liquid separator 68. The bypass path 44 of the hydrogen supply mechanism 38 connects the flow path portion 40A1 of the first supply path 40A to the second supply path 40B.

[0033] The first on-off valve 46 is provided in the bypass path 44. The first on-off valve 46 is configured to be openable and closable. The first on-off valve 46 opens and closes under the control of the control device 18. The first on-off valve 46 may be a shut-off valve. When an abnormality is detected, the shut-off valve shuts off the bypass path 44 without being controlled by the control device 18.

[0034] The second on-off valve 48 is provided in the second supply path 40B. The second on-off valve 48 is configured to be openable and closable. The second on-off valve 48 opens and closes under the control of the control device 18. The second on-off valve 48 may be a shut-off valve.

[0035] The first pressure regulating valve 50 is provided in the bypass passage 44 of the oxygen supply mechanism 36. The first pressure regulating valve 50 is not provided in the bypass passage 44 of the hydrogen supply mechanism 38. The first pressure regulating valve 50 is located between the branching portion BP of the bypass passage 44 of the oxygen supply mechanism 36 and the first on-off valve 46. The branching portion BP is the portion where the bypass passage 44 branches off from the first supply passage 40A.

[0036] The second pressure regulation valve 52 is provided in a portion of the second supply path 40B between the second on-off valve 48 and the fuel cell 12. The second pressure regulation valve 52 reduces the pressure of the gas.

[0037] The first check valve 54 is provided in a portion of the first supply path 40A between the branch portion BP and the gas-liquid separator 64. The second check valve 56 is provided in the bypass path 44 at a portion downstream of the first on-off valve 46.

[0038] The pressure control valve 58 is provided in the flow path portion 40A2 of the first supply path 40A. The pressure control valve 58 narrows the flow path portion 40A2. As a result, when the gas generator 14 is a water electrolysis apparatus 22, the pressure of the oxygen gas generated at the anode electrode of each electrochemical cell increases and becomes higher than the pressure of the hydrogen gas generated at the cathode electrode of each electrochemical cell. The pressure control valve 58 may be a solenoid valve with an adjustable opening. Alternatively, the pressure control valve 58 may be a back pressure valve.

[0039] That is, in the water electrolysis device 22, the pressure on the anode side of the electrolyte membrane is higher than the pressure on the cathode side of the electrolyte membrane. This prevents crossover, in which hydrogen gas generated at the cathode permeates through the electrolyte membrane toward the anode. As a result, a decrease in the amount of hydrogen gas supplied from the water electrolysis device 22 to the hydrogen booster device 24 can be prevented.

[0040] The flow rate adjustment valve 60 is provided in the second supply path 40B. The flow rate adjustment valve 60 is configured to be able to adjust the flow rate of the gas flowing to the fuel cell 12. The flow rate adjustment valve 60 adjusts the flow rate in accordance with the control of the control device .

[0041] Pressure sensor 62 detects the pressure of the gas supplied to gas supply line 40. Pressure sensor 62 outputs a signal indicating the detected pressure to control device 18. Pressure sensor 62 is preferably provided in gas supply line 40 near gas generator 14. For example, pressure sensor 62 is provided in first supply line 40A at a location between gas generator 14 and branch portion BP.

[0042] The gas-liquid separator 64 is provided on the gas supply line 40 between the pressure control valve 58 and the first check valve 54. As described above, the exhaust gas discharged from the gas generator 14 to the gas supply line 40 contains water vapor in addition to gas. The gas-liquid separator 64 separates the exhaust gas into a liquid component (liquid water) and a gas component (gas). The gas separated by the gas-liquid separator 64 is supplied to the pressure vessel 42. This prevents the pressure vessel 42 from becoming wet. As a result, the durability of the pressure vessel 42 can be improved without making the pressure vessel 42 excessively rust-resistant.

[0043] Meanwhile, the liquid water separated by the gas-liquid separator 64 is supplied to the gas-liquid separator 26 via the liquid water supply channel 65. The liquid water supply channel 65 connects the gas-liquid separator 64 and the gas-liquid separator 26. The liquid water obtained from the water vapor in the exhaust gas discharged from the water electrolysis device 22 is supplied via the liquid water supply channel 65 to the gas-liquid separator 26, which stores the water to be supplied to the water electrolysis device 22. This allows for saving the water used in the water electrolysis device 22.

[0044] The oxygen supply mechanism 36 has an oxygen exhaust gas flow path 66, a gas-liquid separator 68, and a circulation pump 70 in addition to the configuration of the supply mechanism 16 described above. The oxygen exhaust gas flow path 66 is a path for returning oxygen-containing exhaust gas discharged from the fuel cell 12 to the fuel cell 12. The oxygen exhaust gas flow path 66 has an upstream partial flow path 66A and a downstream partial flow path 66B. The upstream partial flow path 66A connects the fuel cell 12 and the gas-liquid separator 68. The downstream partial flow path 66B connects the gas-liquid separator 68 to a portion of the second supply path 40B between the flow rate adjustment valve 60 and the fuel cell 12.

[0045] The gas-liquid separator 68 and the circulation pump 70 are provided on the oxygen exhaust gas flow path 66. The gas-liquid separator 68 separates the oxygen-containing exhaust gas discharged from the fuel cell 12 into the oxygen exhaust gas flow path 66 into a gas component (oxygen gas and water vapor) and a liquid component (liquid water). The gas component is supplied again to the fuel cell 12 by the circulation pump 70. Meanwhile, the liquid component is supplied to the water tank 30 via a water supply path 71. The water supply path 71 connects the gas-liquid separator 68 and the water tank 30.

[0046] The hydrogen supply mechanism 38 has a hydrogen exhaust gas flow path 72, a gas-liquid separator 74, and a circulation pump 76 in addition to the configuration of the supply mechanism 16 described above. The hydrogen exhaust gas flow path 72 is a path for returning hydrogen-containing exhaust gas discharged from the fuel cell 12 to the fuel cell 12. The hydrogen exhaust gas flow path 72 has an upstream partial flow path 72A and a downstream partial flow path 72B. The upstream partial flow path 72A connects the fuel cell 12 and the gas-liquid separator 74. The downstream partial flow path 72B connects the gas-liquid separator 74 to a portion of the second supply path 40B between the flow rate adjustment valve 60 and the fuel cell 12.

[0047] The gas-liquid separator 74 and the circulation pump 76 are provided on the hydrogen exhaust gas flow path 72. The gas-liquid separator 74 separates the hydrogen-containing exhaust gas discharged from the fuel cell 12 into the hydrogen exhaust gas flow path 72 into a gas component (hydrogen gas and water vapor) and a liquid component (liquid water). The gas component is supplied again to the fuel cell 12 by the circulation pump 76. Meanwhile, the liquid component is supplied to the water tank 30 via a water supply path 77. The water supply path 77 connects the gas-liquid separator 74 and the water tank 30.

[0048] 2 is a block diagram of the control device 18. The control device 18 includes one or more processors 100 and one or more storage media 102. The storage media 102 may be configured with volatile memory and non-volatile memory. Examples of the processor 100 include a CPU, a GPU, etc. Examples of the volatile memory include a RAM, etc. Examples of the non-volatile memory include a ROM, a flash memory, etc.

[0049] The processor 100 includes a water electrolysis control unit 110, a hydrogen boost control unit 112, and a power generation control unit 114. When the processor 100 executes a program stored in the storage medium 102, the processor 100 operates as the water electrolysis control unit 110, the hydrogen boost control unit 112, and the power generation control unit 114. At least one of the water electrolysis control unit 110, the hydrogen boost control unit 112, and the power generation control unit 114 may be implemented by an integrated circuit such as an ASIC or FPGA. At least one of the water electrolysis control unit 110, the hydrogen boost control unit 112, and the power generation control unit 114 may be implemented by an electronic circuit including a discrete device.

[0050] The water electrolysis control unit 110 can control the operation and shutdown of the water electrolysis device 22. For example, when the processor 100 receives a command to start operation of the regenerative fuel cell system 10, the water electrolysis control unit 110 starts controlling the operation of the water electrolysis device 22.

[0051] In controlling the operation of the water electrolysis device 22, the water electrolysis control unit 110 drives the water supply pump 31 to supply water to the water electrolysis device 22. In controlling the operation of the water electrolysis device 22, the water electrolysis control unit 110 controls the power supply device 23 so that a predetermined value of current flows between the cathode and anode electrodes of the water electrolysis device 22.

[0052] When the operation control of the water electrolysis device 22 is executed, oxygen gas produced in the water electrolysis device 22 is supplied to the pressure vessel 42 of the oxygen supply mechanism 36 via the gas supply path 40 of the oxygen supply mechanism 36. Meanwhile, hydrogen gas produced in the water electrolysis device 22 is supplied to the hydrogen booster device 24 via the hydrogen supply path 32.

[0053] For example, when the amount of gas supplied to the pressure vessel 42 of the oxygen supply mechanism 36 exceeds a predetermined amount, the water electrolysis control unit 110 shifts from operation control of the water electrolysis device 22 to operation shutdown control of the water electrolysis device 22. The operation shutdown control of the water electrolysis device 22 will be described later.

[0054] The hydrogen boost control unit 112 can control the operation of the hydrogen booster device 24 and the stoppage of the operation of the hydrogen booster device 24. For example, when it is confirmed that hydrogen gas is being supplied to the third partial flow path 32C of the hydrogen supply path 32, the hydrogen boost control unit 112 controls the operation of the hydrogen booster device 24. The supply of hydrogen gas to the third partial flow path 32C is confirmed, for example, based on a flow rate sensor or the like installed in the third partial flow path 32C near the hydrogen booster device 24.

[0055] In controlling the operation of the hydrogen booster 24, the hydrogen booster control unit 112 drives the gas supply pump 34 to supply hydrogen gas to the hydrogen booster 24. In controlling the operation of the hydrogen booster 24, the hydrogen booster control unit 112 controls the power supply 25 so that a predetermined value of current flows between the cathode and anode electrodes of the hydrogen booster 24.

[0056] When the operation control of the hydrogen booster 24 is executed, the hydrogen gas generated in the hydrogen booster 24 is supplied to the pressure vessel 42 of the hydrogen supply mechanism 38 via the gas supply path 40 of the hydrogen supply mechanism 38 .

[0057] For example, when it is no longer confirmed that hydrogen gas is being supplied to the third partial flow path 32C, the hydrogen boost control unit 112 shifts from controlling the operation of the hydrogen booster device 24 to controlling the shutdown of the hydrogen booster device 24. The shutdown control of the hydrogen booster device 24 will be described later.

[0058] The power generation control unit 114 can control the operation of the fuel cell 12 and stop the operation of the fuel cell 12. For example, when the amount of power stored in the battery 20 falls below a lower limit value, the power generation control unit 114 starts controlling the operation of the fuel cell 12.

[0059] In controlling the operation of the fuel cell 12, the power generation control unit 114 opens the second on-off valve 48 of the oxygen supply mechanism 36 and drives the circulation pump 70 of the oxygen supply mechanism 36. The power generation control unit 114 also opens the second on-off valve 48 of the hydrogen supply mechanism 38 and drives the circulation pump 76 of the hydrogen supply mechanism 38. The power generation control unit 114 also controls at least one of the second pressure regulation valve 52 and the flow rate regulation valve 60 based on the target power generation amount, etc.

[0060] When the operation control of the fuel cell 12 is executed, the oxygen gas stored in the pressure vessel 42 of the oxygen supply mechanism 36 is supplied to the fuel cell 12 via the second supply path 40B of the oxygen supply mechanism 36. The oxygen gas that has not undergone the electrochemical reaction in the fuel cell 12 flows into the second supply path 40B of the oxygen supply mechanism 36 via the oxygen exhaust gas flow path 66 and is supplied to the fuel cell 12 again.

[0061] Meanwhile, the hydrogen gas stored in the pressure vessel 42 of the hydrogen supply mechanism 38 is supplied to the fuel cell 12 via the second supply path 40B of the hydrogen supply mechanism 38. The hydrogen gas that has not undergone an electrochemical reaction in the fuel cell 12 flows into the second supply path 40B of the hydrogen supply mechanism 38 via the hydrogen exhaust gas flow path 72 and is supplied to the fuel cell 12 again.

[0062] For example, when the amount of power stored in the battery 20 exceeds an upper limit, the power generation control unit 114 shifts from controlling the operation of the fuel cell 12 to controlling the operation of the fuel cell 12 to stop the operation of the fuel cell 12.

[0063] In controlling the shutdown of the fuel cell 12, the power generation control unit 114 closes the second on-off valve 48 of the oxygen supply mechanism 36 and stops the circulation pump 70 of the oxygen supply mechanism 36. The power generation control unit 114 also closes the second on-off valve 48 of the hydrogen supply mechanism 38 and stops the circulation pump 76 of the hydrogen supply mechanism 38. The power generation control unit 114 also stops control of the second pressure adjustment valve 52 and the flow rate adjustment valve 60.

[0064] Next, the operation shutdown control of the gas generator 14 will be described. The operation shutdown control of the water electrolysis apparatus 22 and the operation shutdown control of the hydrogen booster apparatus 24 are basically the same. Therefore, only the operation shutdown control of the water electrolysis apparatus 22 will be described here, unless otherwise specified. Figure 3 is a flowchart showing the procedure for the operation shutdown control of the water electrolysis apparatus 22.

[0065] In step S1, the water electrolysis control unit 110 opens the first on-off valve 46 of the oxygen supply mechanism 36. Once the first on-off valve 46 is opened, the control for stopping the operation of the water electrolysis apparatus 22 proceeds to step S2.

[0066] In step S2, the water electrolysis control unit 110 starts depressurization treatment. During the depressurization treatment, the water electrolysis control unit 110 controls the power supply device 23 so that the current flowing between the electrodes of each electrochemical cell of the water electrolysis device 22 gradually decreases.

[0067] Additionally, during the depressurization process, the water electrolysis control unit 110 adjusts the aperture of the first pressure regulating valve 50 to achieve the target depressurization rate, based on the pressure detected by the pressure sensor 62. This prevents a sudden decrease in gas pressure, thereby preventing blisters and other defects from occurring on the electrolyte membrane of the water electrolysis device 22.

[0068] The aperture of the first pressure regulating valve 50 is adjusted, for example, as follows: The water electrolysis control unit 110 measures the depressurization rate per unit time based on the pressure detected by the pressure sensor 62, and calculates the difference between this depressurization rate and a target depressurization rate. The target depressurization rate is a target value for the depressurization rate to suppress the occurrence of blisters, etc., and is stored in the storage medium 102. The water electrolysis control unit 110 sets the aperture of the first pressure regulating valve 50 so that the difference from the target depressurization rate becomes smaller. The aperture of the first pressure regulating valve 50 is set smaller as the difference from the target depressurization rate becomes larger.

[0069] In the depressurization process of the operation shutdown control of the hydrogen booster device 24, the hydrogen booster control unit 112 adjusts the aperture of the second pressure regulating valve 52. When the depressurization process is started, the operation shutdown control of the water electrolysis device 22 proceeds to step S3.

[0070] In step S3, the water electrolysis control unit 110 compares the pressure detected by the pressure sensor 62 with a predetermined pressure. If the pressure detected by the pressure sensor 62 is equal to or greater than the predetermined pressure, the water electrolysis control unit 110 continues to compare the pressure detected by the pressure sensor 62 with the predetermined pressure. On the other hand, if the pressure detected by the pressure sensor 62 is less than the predetermined pressure, the control for stopping the operation of the water electrolysis device 22 proceeds to step S4.

[0071] In step S4, the water electrolysis control unit 110 terminates the depressurization process. That is, the water electrolysis control unit 110 stops control of the power supply device 23 to stop the electrochemical reaction (water electrolysis reaction) in the water electrolysis device 22. The water electrolysis control unit 110 also fixes the aperture of the flow rate adjustment valve 60 to a predetermined aperture. When the depressurization process is completed, the control for stopping the operation of the water electrolysis device 22 proceeds to step S5.

[0072] In step S5, the water electrolysis control unit 110 closes the first on-off valve 46 of the oxygen supply mechanism 36 and stops the feedwater pump 31. This terminates the control to shut down the operation of the water electrolysis apparatus 22.

[0073] As shown in FIG. 1 , when the first on-off valve 46 is opened during operation shutdown control, oxygen gas generated in the water electrolysis device 22 flows from the branch portion BP of the gas supply channel 40 into the bypass channel 44. The oxygen gas that flows into the bypass channel 44 is supplied to the fuel cell 12. As described above, the oxygen gas generated in the water electrolysis device 22 contains water vapor generated by vaporization of alkaline water that was supplied to the water electrolysis device 22 and moved from the cathode electrode to the anode electrode together with hydroxide ions. When the depressurization process during operation shutdown control begins, the pressure difference between the cathode electrode and the anode electrode decreases, and the amount of water pushed back from the anode electrode to the cathode electrode by the pressure difference decreases. As a result, more water vapor generated by vaporization of alkaline water is generated at the anode electrode than during operation control. In other words, the effects of the present application can be more effectively achieved during operation shutdown control of a differential pressure water electrolysis device in which not much water vapor is generated during operation control but a lot of water vapor is generated during operation shutdown control.

[0074] This regenerative fuel cell system 10 is provided with a gas flow path 200 for suppressing the supply of alkaline water to the fuel cell 12. The gas flow path 200 has a gas flow path 200A for introducing oxygen gas and a gas flow path 200B for introducing hydrogen gas.

[0075] The gas flow path 200A includes a first flow path portion (bypass path 44), a second flow path portion (downstream side flow path portion 66B), and the inside of a storage container 202 provided in the gas-liquid separator 68.

[0076] 4 is a diagram showing the storage container 202. The storage container 202 has an internal space 216 surrounded by an upper wall 210, a lower wall 212, and a side wall 214. The internal space 216 stores produced water. This produced water is liquid water that is generated by the power generation of the fuel cell 12 and separated by the gas-liquid separator 68. The liquid water that is generated by the power generation of the fuel cell 12 is acidic.

[0077] The water level of the produced water may be maintained within a predetermined range. For example, when the water level detected by a water level sensor provided in the storage container 202 falls below a lower limit water level, the power generation control unit 114 executes operation control of the fuel cell 12. When the water level detected by the water level sensor reaches an upper limit water level, the power generation control unit 114 shifts from operation control of the fuel cell 12 to control stop of operation of the fuel cell 12. Note that a portion of the produced water stored in the storage container 202 is supplied to the water tank 30 at any timing. In this case, the control device 18 opens an on-off valve (not shown) provided in the water supply line 71 to supply the produced water to the water tank 30.

[0078] An upstream partial flow path 66A of the oxygen exhaust gas flow path 66 penetrates an upper portion of the side wall 214. The downstream end of the upstream partial flow path 66A is located above the produced water stored in the internal space 216. As shown in FIG. 1 , the upstream end of the upstream partial flow path 66A is connected to the fuel cell 12.

[0079] A downstream partial flow path 66B of the oxygen exhaust gas flow path 66 penetrates the upper wall 210. The upstream end of the downstream partial flow path 66B is located above the water surface of the produced water stored in the internal space 216. As shown in FIG. 1, the downstream end of the downstream partial flow path 66B is connected to the second supply path 40B.

[0080] A tubular member 218 is provided in the storage container 202. The tubular member 218 passes through the upper wall 210 and extends below the surface of the produced water. The tubular member 218 may be the downstream end of the bypass path 44. Alternatively, the tubular member 218 may be a member separate from the bypass path 44. In this case, the upper end of the tubular member 218 and the downstream end of the bypass path 44 are joined. The lower end of the tubular member 218 is located below the surface of the produced water stored in the internal space 216. The lower end of the tubular member 218 is spaced apart from the lower wall 212.

[0081] When the first on-off valve 46 is opened during operation shutdown control, oxygen gas that flows into the bypass path 44 reaches the tubular member 218. The oxygen gas that reaches the tubular member 218 is released into the produced water from the lower end of the tubular member 218. The oxygen gas released into the produced water turns into bubbles and moves above the surface of the produced water. At that time, the water containing oxygen gas (alkaline water vapor) is neutralized by the produced water. The oxygen gas that moves above the surface of the produced water flows into the downstream partial flow path 66B of the oxygen exhaust gas flow path 66 and is supplied to the fuel cell 12 via the second supply path 40B.

[0082] In this way, the gas flow path 200 guides oxygen gas generated at the anode electrode of the water electrolysis device 22 to the fuel cell 12 through the produced water stored in the storage container 202. As a result, even if alkaline water is contained in the oxygen gas, the water can be neutralized by the produced water stored in the storage container 202. In particular, a more significant effect can be achieved by supplying a gas for operation shutdown control, which can generate water vapor produced by vaporizing a larger amount of alkaline water, to the storage container 202. Therefore, alkaline water does not reach the fuel cell 12, and deterioration of the sealing members, electrolyte membrane, and the like provided in the fuel cell 12 due to the alkaline water can be suppressed. As a result, a decrease in the durability of the fuel cell 12 can be suppressed.

[0083] The gas flow path 200B is a hydrogen supply path 32 that guides hydrogen gas generated in the water electrolysis device 22 to the hydrogen booster device 24 through makeup water stored in the water tank 30. The gas flow path 200B includes a first partial flow path 32A, a second partial flow path 32B, a part of the water tank 30, and a third partial flow path 32C.

[0084] Although not shown, the downstream end of second partial flow path 32B of hydrogen supply channel 32 is provided in water tank 30 as a member corresponding to tubular member 218 described above. The downstream end of second partial flow path 32B penetrates the upper wall of water tank 30 and extends below the surface of make-up water stored inside water tank 30. The make-up water is liquid water (produced water) stored in storage container 202 and is therefore acidic.

[0085] As described above, the hydrogen gas separated by the gas-liquid separator 26 is hydrogen gas generated in the water electrolysis device 22. Therefore, the hydrogen gas that flows from the gas-liquid separator 26 into the second partial flow path 32B contains water vapor resulting from evaporation of alkaline water. The hydrogen gas that flows into the second partial flow path 32B is released into the make-up water from the lower end of the second partial flow path 32B. The hydrogen gas released into the make-up water becomes bubbles and moves above the surface of the make-up water. At that time, the water containing hydrogen gas (alkaline water vapor) is neutralized by the make-up water. The hydrogen gas that moves above the surface of the make-up water flows into the third partial flow path 32C and is supplied to the hydrogen booster device 24.

[0086] In this way, the hydrogen supply path 32 guides the hydrogen gas generated in the water electrolysis device 22 to the hydrogen booster device 24 through the make-up water stored in the water tank 30. As a result, even if alkaline water is contained in the hydrogen gas, the water can be neutralized by the make-up water stored in the water tank 30. Therefore, the alkaline water does not reach the fuel cell 12, and deterioration of the sealing members, electrolyte membrane, etc. provided in the fuel cell 12 due to the alkaline water can be suppressed. As a result, a decrease in the durability of the fuel cell 12 can be suppressed.

[0087] (Second embodiment) Figure 5 is a schematic diagram showing a regenerative fuel cell system 10 according to a second embodiment. In Figure 5, the same components as those described in the first embodiment are denoted by the same reference numerals. In the second embodiment, descriptions that overlap with those in the first embodiment will be omitted.

[0088] In the second embodiment, a concentration measuring device 220, a water supply passage 222, a water supply pump 224, a check valve 226, and a concentration control unit 228 are further provided.

[0089] The concentration measuring device 220 is provided in the storage container 202. The concentration measuring device 220 measures the hydrogen ion concentration of the produced water stored in the storage container 202. The concentration measuring device 220 may be a pH meter.

[0090] The water supply line 222 connects the gas-liquid separator 64 and the storage container 202. A water supply pump 224 and a check valve 226 are provided in the water supply line 222. The water supply pump 224 supplies the water stored in the gas-liquid separator 64 to the storage container 202. The water stored in the gas-liquid separator 64 is alkaline. The water supply pump 224 is driven by a concentration control unit 228.

[0091] The concentration control unit 228 operates when the processor 100 (FIG. 2) executes a program. The concentration control unit 228 may be realized by an integrated circuit such as an ASIC or an FPGA. The concentration control unit 228 may also be configured by an electronic circuit including discrete devices. The concentration control unit 228 can perform concentration control to adjust the concentration of the produced water stored in the storage container 202 based on the hydrogen ion concentration measured by the concentration measuring device 220.

[0092] 6 is a flowchart showing the procedure for concentration control. The concentration control is carried out, for example, while the regenerative fuel cell system 10 is in operation.

[0093] In step S11, the concentration control unit 228 compares the hydrogen ion concentration measured by the concentration measuring device 220 with a threshold value. The threshold value is set to a hydrogen ion concentration corresponding to a hydrogen concentration index selected from the range of pH6 to pH7, for example. If the hydrogen ion concentration measured by the concentration measuring device 220 is on the neutral side of the threshold value, the concentration control unit 228 continues to compare the hydrogen ion concentration measured by the concentration measuring device 220 with the threshold value. On the other hand, if the hydrogen ion concentration measured by the concentration measuring device 220 is on the acidic side of the threshold value, the concentration control proceeds to step S12.

[0094] In step S12, the concentration control unit 228 determines whether the water electrolysis device 22 has stopped. If the water electrolysis control unit 110 (FIG. 2) is executing operation control or operation shutdown control, the concentration control unit 228 determines that the water electrolysis device 22 has not stopped. In this case, the concentration control does not proceed to step S13. On the other hand, if the water electrolysis control unit 110 (FIG. 2) is not executing operation control or operation shutdown control, the concentration control unit 228 determines that the water electrolysis device 22 has stopped. In this case, the concentration control proceeds to step S13.

[0095] In step S13, the concentration control unit 228 drives the water supply pump 224. When the water supply pump 224 is driven, the concentration control proceeds to step S14.

[0096] In step S14, the concentration control unit 228 compares the hydrogen ion concentration measured by the concentration measuring device 220 with a threshold value. If the hydrogen ion concentration measured by the concentration measuring device 220 is on the acidic side of the threshold value, the concentration control unit 228 continues to drive the water supply pump 224. On the other hand, if the hydrogen ion concentration measured by the concentration measuring device 220 is on the neutral side of the threshold value, the concentration control proceeds to step S15.

[0097] In step S15, the concentration control unit 228 stops the water supply pump 224. When the water supply pump 224 is stopped, the concentration control proceeds to step S11.

[0098] The amount of water (acidic water) generated by the power generation of the fuel cell 12 and supplied to the storage container 202 is greater than the amount of water (alkaline water) supplied to the storage container 202 during control to stop the operation of the water electrolysis device 22. Therefore, the acidity of the produced water stored in the storage container 202 tends to be higher (stronger acidity).

[0099] In this embodiment, when the hydrogen ion concentration measured by the concentration measuring device 220 is on the acidic side of the threshold value, the concentration control unit 228 drives the water supply pump 224. This makes it possible to prevent the acidity of the produced water stored in the storage container 202 from becoming higher (stronger).

[0100] Furthermore, in this embodiment, the concentration control unit 228 drives the water supply pump 224 when the water electrolysis device 22 is stopped. This makes it possible to prevent the alkalinity of the produced water stored in the storage container 202 from becoming too high (strong).

[0101] The following additional notes are further disclosed regarding the above embodiment.

[0102] (Appendix 1) The regenerative fuel cell system (10) of the present disclosure includes a water electrolysis device (22) that electrolyzes alkaline water, a fuel cell (12) that generates electricity using the product gas generated by the electrolysis, a storage container (202) that stores the product water generated by the electricity generation, and a gas flow path (200) that guides the product gas to the fuel cell through the product water stored in the storage container.

[0103] (Appendix 2) The regenerative fuel cell system according to Supplementary Note 1 may include a pressure vessel (42) that stores the high-pressure generated gas, and a pressure control valve (58) provided in a first supply path (40A) that guides the generated gas from the water electrolysis device to the pressure vessel, and the gas flow path may include a first flow path section (44) that connects the first supply path to the storage container, a second supply path (40B) that guides the generated gas from the pressure vessel to the fuel cell, and a second flow path section (66B) that connects the first supply path to the storage container.

[0104] (Appendix 3) In the regenerative fuel cell system described in Appendix 2, the first flow path portion may include a tubular member (218) that penetrates the upper wall (210) of the storage container and extends below the surface of the produced water.

[0105] (Appendix 4) The regenerative fuel cell system according to Supplementary Note 2 may further include an on-off valve (46) provided in the first flow path portion, and a water electrolysis control unit (110) that controls the water electrolysis device, wherein the water electrolysis control unit closes the on-off valve during operation control of the water electrolysis device, and opens the on-off valve when control to stop operation of the water electrolysis device is initiated.

[0106] (Appendix 5) The regenerative fuel cell system according to Supplementary Note 1 includes a concentration measuring device (220) that measures the hydrogen ion concentration of the produced water stored in the storage container, a water supply pump (224) that supplies the alkaline water to the storage container, and a concentration control unit (228) that adjusts the hydrogen ion concentration of the produced water, and when the hydrogen ion concentration measured by the concentration measuring device is on the acidic side of a threshold value, the concentration control unit may drive the water supply pump.

[0107] (Appendix 6) In the regenerative fuel cell system according to Supplementary Note 5, the concentration control unit may drive the water supply pump when the water electrolysis device is stopped.

[0108] (Appendix 7) The regenerative fuel cell system according to Supplementary Note 1 includes a water tank (30) for storing replenishment water, which is water to be replenished with the alkaline water; a hydrogen booster (24) for pressurizing hydrogen gas; and a hydrogen supply path (32) for guiding the hydrogen gas generated by the water electrolysis device to the hydrogen booster through the replenishment water stored in the water tank, wherein the gas flow path may also guide the oxygen gas generated by the water electrolysis device to the fuel cell through the produced water.

[0109] 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]

[0110] 10...Regenerative fuel cell system 12...Fuel cell 14...Gas generator 16...Supply mechanism 18...Control device 22...Water electrolysis device 24...Hydrogen pressure booster 26, 64, 68, 74...Gas-liquid separator 30...water tank 32...hydrogen supply line 36...Oxygen supply mechanism 38...Hydrogen supply mechanism 40...gas supply path 40A...first supply path 40B... Second supply passage 42... Pressure vessel 44... Bypass path (first flow path portion) 46... First on-off valve (on-off valve) 58...Pressure control valve 60...Flow adjustment valve 110...water electrolysis control unit 112...hydrogen boost control unit 114...power generation control unit 200, 200A, 200B...gas flow path 202...Storage container 220...Concentration measuring device 224...Water supply pump 228...Concentration control unit

Claims

1. a water electrolysis device that electrolyzes alkaline water; a fuel cell that generates electricity using a generated gas that is a gas generated by the electrolysis; a storage container for storing produced water that is water generated by the power generation; a gas flow path that guides the generated gas through the generated water stored in the storage container to the fuel cell; A regenerative fuel cell system comprising:

2. 10. The regenerative fuel cell system of claim 1, a pressure vessel for storing the high-pressure produced gas; a pressure control valve provided in a first supply path that guides the generated gas from the water electrolysis apparatus to the pressure vessel; Equipped with The gas flow path is a first flow path portion connecting the first supply path and the storage container; a second supply passage that guides the generated gas from the pressure vessel to the fuel cell, and a second flow passage that connects the storage vessel; A regenerative fuel cell system comprising:

3. 3. The regenerative fuel cell system according to claim 2, The first flow path portion includes a tubular member that penetrates an upper wall of the storage container and extends below the surface of the produced water.

4. 3. The regenerative fuel cell system according to claim 2, an on-off valve provided in the first flow path portion; a water electrolysis control unit that controls the water electrolysis device; Equipped with The water electrolysis control unit closes the on-off valve during operation control of the water electrolysis device, and opens the on-off valve when operation stop control of the water electrolysis device is started.

5. 10. The regenerative fuel cell system of claim 1, a concentration measuring device for measuring the hydrogen ion concentration of the produced water stored in the storage container; a water supply pump that supplies the alkaline water to the storage container; a concentration control unit that adjusts the hydrogen ion concentration of the generated water; Equipped with When the hydrogen ion concentration measured by the concentration measuring device is on the acidic side of a threshold value, the concentration control unit drives the water supply pump.

6. 6. The regenerative fuel cell system according to claim 5, The concentration control unit drives the water supply pump when the water electrolysis device is stopped.

7. 10. The regenerative fuel cell system of claim 1, a water tank for storing replenishment water to be replenished to the alkaline water; a hydrogen pressure booster that boosts the pressure of hydrogen gas; a hydrogen supply passage that guides the hydrogen gas generated by the water electrolysis device through the replenishment water stored in the water tank to the hydrogen booster device; Equipped with The gas flow path guides oxygen gas generated in the water electrolysis device through the generated water to the fuel cell.

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