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 a regenerative fuel cell system.

Background Art

[0002] In recent years, in order for more people to have access to affordable, reliable, sustainable, and advanced energy, research and development on fuel cells that contribute to energy efficiency has been carried out.

[0003] The following Patent Document 1 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 generate gas. The fuel cell generates electricity using the gas generated by the electrolysis of the water electrolysis device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The water electrolysis device may be supplied with alkaline water. In this case, alkaline water is contained in the gas generated by the electrolysis of the water electrolysis device. When alkaline water is supplied to the fuel cell, there may arise a problem that the durability of the fuel cell is reduced.

[0006] An object of the present invention is to solve the above-described problems.

Means for Solving the Problems

[0007] An aspect of this disclosure is a regenerative fuel cell system comprising: a water electrolysis device for electrolyzing alkaline water; a fuel cell for generating electricity using a product gas, which is a gas produced by the electrolysis; a storage container for storing the product water, which is water produced by the power generation; and a gas channel for guiding the product gas to the fuel cell through the product water stored in the storage container. [Effects of the Invention]

[0008] This allows alkaline water to be neutralized by the generated water stored in the storage container, even if it is present in the generated gas. As a result, the reduction in the durability of the fuel cell can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing a regenerative fuel cell system according to the first embodiment. [Figure 2] Figure 2 is a block diagram of the control device. [Figure 3] Figure 3 is a flowchart showing the procedure for controlling the shutdown of a water electrolysis device. [Figure 4] Figure 4 shows a storage container. [Figure 5] Figure 5 is a schematic diagram showing a regenerative fuel cell system according to the second embodiment. [Figure 6] Figure 6 is a flowchart showing the procedure for concentration control. [Modes for carrying out the invention]

[0010] (First Embodiment) Figure 1 is a schematic diagram showing a regenerative fuel cell system 10 according to the first embodiment. The regenerative fuel cell system 10 includes a fuel cell 12, a gas generator 14, a supply mechanism 16, and a control device 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 the anode electrode, and the other is the 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 the 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 did not undergo electrochemical reaction and discharges oxygen-containing exhaust gas containing this oxygen gas. Most of the oxygen-containing exhaust gas is recycled back into the fuel cell 12 and reused. The fuel cell 12 also collects excess hydrogen gas that did not undergo electrochemical reaction and discharges hydrogen-containing exhaust gas containing this hydrogen gas. Most of the hydrogen-containing exhaust gas is recycled back into the fuel cell 12 and reused.

[0013] The gas generator 14 is a device that generates either oxygen gas or hydrogen gas. The gas generator 14 is equipped with a water electrolysis device 22 and a hydrogen pressurizer 24.

[0014] The water electrolysis device 22 is a gas generator 14 that produces oxygen gas and hydrogen gas by electrolyzing water. Water is supplied from the 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 contains 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 installed in the water supply channel 28 between the gas-liquid separator 26 and the water electrolysis device 22. The water supply pump 31 supplies the water stored in the gas-liquid separator 26 to the water electrolysis device 22.

[0015] Makeup water is supplied from the water tank 30 to the gas-liquid separator 26 via the makeup water passage 29. The makeup water is the water that replenishes the water (alkaline water) supplied to the water electrolysis device 22. A water supply pump 33 is provided in the makeup water passage 29. The makeup 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 in the thickness direction of the electrolyte membrane. 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 of the voltage 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 the water flowing in from the water supply passage 28 to the cathode electrode of each electrochemical cell. Each electrochemical cell electrolyzes water based on the voltage applied by the power supply device 23. As a result, oxygen gas is generated at the anode electrode, and hydrogen gas is generated at the cathode electrode. The oxygen gas generated by the water electrolysis device 22 is compressed to a high pressure. For example, the oxygen gas is compressed in the range of 1 to 100 MPa.

[0018] The water electrolysis device 22 collects the oxygen gas generated in each electrochemical cell and outputs the exhaust gas containing the oxygen gas to the supply mechanism 16. The exhaust gas contains water vapor vaporized by the heat of the water electrolysis device 22 or the like. On the other hand, the water electrolysis device 22 collects the hydrogen gas generated in each electrochemical cell and the surplus water (unreacted water) in which electrolysis was not performed, and drains the discharge fluid containing the hydrogen gas and the unreacted water to the hydrogen supply passage 32. The discharge fluid also contains water vapor vaporized by the heat of the water electrolysis device 22 or the like.

[0019] The hydrogen supply path 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 through 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 booster device 24 is a gas generation device 14 that generates high-pressure hydrogen gas. The hydrogen booster device 24 boosts the hydrogen gas flowing in from the hydrogen supply path 32. The hydrogen gas flowing in from the hydrogen supply path 32 is the hydrogen gas generated by the water electrolysis device 22.

[0022] The hydrogen booster device 24 has a plurality of electrochemical cells. Each electrochemical cell includes an electrolyte membrane and a pair of electrodes provided on both sides in the thickness direction of the electrolyte membrane. The electrolyte membrane used in the hydrogen booster device 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 device 25 is connected to the anode electrode and the cathode electrode. The power supply device 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 device 25 may obtain the power of the voltage applied between the anode electrode and the cathode electrode from the battery 20.

[0023] The hydrogen blaster 24 supplies hydrogen gas flowing in from the hydrogen supply passage 32 to the anode electrode. The hydrogen blaster 24 ionizes the hydrogen gas based on the voltage applied by the power supply unit 25. The protons obtained by the ionization of hydrogen gas return to hydrogen gas by reaching the cathode electrode via an electrolyte membrane (proton exchange membrane). The hydrogen blaster 24 can compress the hydrogen gas by moving protons from the anode electrode into a closed space including the cathode electrode. For example, the hydrogen gas can be compressed in the range of 1 to 100 MPa. Thus, the hydrogen blaster 24 is an electrochemical hydrogen compressor (EHC) that can compress hydrogen gas electrochemically.

[0024] The hydrogen blasting unit 24 outputs exhaust gas containing pressurized hydrogen gas to the supply mechanism 16. The exhaust gas also contains water vapor vaporized by the heat of the hydrogen blasting unit 24. On the other hand, the hydrogen blasting unit 24 discharges any excess hydrogen gas that has not been ionized into the hydrogen discharge passage 35. The hydrogen discharge passage 35 connects the hydrogen blasting unit 24 to the gas-liquid separator 26.

[0025] The supply mechanism 16, which is a mechanism for supplying gas to the fuel cell 12, is equipped with 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 produced by the water electrolysis device 22 to the fuel cell 12. The hydrogen supply mechanism 38 is a supply mechanism 16 for supplying hydrogen gas produced by the hydrogen booster device 24 to the fuel cell 12.

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

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

[0028] However, please note that if "supply mechanism 16" refers to the oxygen supply mechanism 36, then "gas" refers to oxygen gas and not hydrogen gas. Also, please note that if "supply mechanism 16" refers to the oxygen supply mechanism 36, then "gas generator 14" refers to the water electrolysis device 22 and not the hydrogen blasting device 24. Similarly, please note that if "supply mechanism 16" refers to the hydrogen supply mechanism 38, then "gas" refers to hydrogen gas and not oxygen gas. Also, please note that if "supply mechanism 16" refers to the hydrogen supply mechanism 38, then "gas generator 14" refers to the hydrogen blasting device 24 and not the water electrolysis device 22.

[0029] The supply mechanism 16 includes a gas supply passage 40, a pressure vessel 42, a bypass passage 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 control valve 60, a pressure sensor 62, and a gas-liquid separator 64.

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

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

[0032] The bypass 44 is a route for supplying the gas produced by the gas generator 14 to the fuel cell 12 without going through the pressure vessel 42. The bypass 44 differs between the oxygen supply mechanism 36 and the hydrogen supply mechanism 38. The bypass 44 of the oxygen supply mechanism 36 connects the flow path section 40A1 of the first supply path 40A to the gas-liquid separator 68. The bypass 44 of the hydrogen supply mechanism 38 connects the flow path section 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 according to the control of the control device 18. The first on-off valve 46 may also be a shut-off valve. If an abnormality is detected, the shut-off valve will shut off the bypass path 44 independently of the control of the control device 18.

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

[0035] The first pressure regulating valve 50 is located in the bypass passage 44 of the oxygen supply mechanism 36. The first pressure regulating valve 50 is not located 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 part where the bypass passage 44 branches off from the first supply passage 40A.

[0036] The second pressure regulating valve 52 is installed in the section of the second supply passage 40B between the second on-off valve 48 and the fuel cell 12. The second pressure regulating valve 52 reduces the gas pressure.

[0037] The first check valve 54 is installed in the section between the branch BP of the first supply passage 40A and the gas-liquid separator 64. The second check valve 56 is installed in the bypass passage 44 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 passage 40A. The pressure control valve 58 narrows the flow path portion 40A2. As a result, if the gas generator 14 is a water electrolysis device 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] In other words, in the water electrolysis device 22, the pressure on the anode side of the electrolyte membrane is higher than the pressure on the cathode electrode side of the electrolyte membrane. Therefore, it is possible to suppress the crossover of hydrogen gas generated at the cathode electrode permeating the electrolyte membrane toward the anode electrode. As a result, it is possible to suppress a reduction in the amount of hydrogen gas supplied from the water electrolysis device 22 to the hydrogen blast pressurizer 24.

[0040] The flow control valve 60 is installed in the second supply line 40B. The flow control valve 60 is configured to adjust the flow rate of gas flowing to the fuel cell 12. The flow control valve 60 adjusts the flow rate according to the control of the control device 18.

[0041] The pressure sensor 62 detects the pressure of the gas supplied to the gas supply line 40. The pressure sensor 62 outputs a signal indicating the detected pressure to the control device 18. Preferably, the pressure sensor 62 is installed in the gas supply line 40 near the gas generator 14. For example, the pressure sensor 62 is installed in the first supply line 40A between the gas generator 14 and the branching section BP.

[0042] The gas-liquid separator 64 is installed on the gas supply passage 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 passage 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 gaseous component (gas). The gas separated by the gas-liquid separator 64 is supplied to the pressure vessel 42. Therefore, it is possible to suppress 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 an excessively rust-resistant structure.

[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 passage 65. The liquid water supply passage 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 passage 65 to the gas-liquid separator 26, which stores the water supplied to the water electrolysis device 22. Therefore, the amount of water used in the water electrolysis device 22 can be saved.

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

[0045] The gas-liquid separator 68 and the circulation pump 70 are installed 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 gaseous component (oxygen gas and water vapor) and a liquid component (liquid water). The gaseous component is supplied back to the fuel cell 12 by the circulation pump 70. Meanwhile, the liquid component is supplied to the water tank 30 via the water supply channel 71. The water supply channel 71 connects the gas-liquid separator 68 and the water tank 30.

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

[0047] The gas-liquid separator 74 and the circulation pump 76 are installed 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 gaseous component (hydrogen gas and water vapor) and a liquid component (liquid water). The gaseous component is supplied back to the fuel cell 12 by the circulation pump 76. The liquid component, on the other hand, is supplied to the water tank 30 via the water supply channel 77. The water supply channel 77 connects the gas-liquid separator 74 and the water tank 30.

[0048] Figure 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 consist of volatile memory and non-volatile memory. Examples of processors 100 include CPUs and GPUs. Examples of volatile memory include RAM. Examples of non-volatile memory include ROMs and flash memory.

[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. Alternatively, 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 configured by an electronic circuit including discrete devices.

[0050] The water electrolysis control unit 110 is capable of controlling the operation of the water electrolysis device 22 and controlling the 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 current flows between the cathode electrode and the anode electrode of the water electrolysis device 22.

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

[0053] For example, if 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 switches from controlling the operation of the water electrolysis device 22 to controlling the shutdown of the water electrolysis device 22. The shutdown control of the water electrolysis device 22 will be described later.

[0054] The hydrogen pressurization control unit 112 is capable of controlling the operation of the hydrogen pressurization device 24 and controlling the operation of the hydrogen pressurization device 24. For example, when the supply of hydrogen gas to the third sub-flow channel 32C of the hydrogen supply line 32 is confirmed, the hydrogen pressurization control unit 112 executes operation control of the hydrogen pressurization device 24. The supply of hydrogen gas to the third sub-flow channel 32C is confirmed, for example, based on a flow sensor installed in the third sub-flow channel 32C near the hydrogen pressurization device 24.

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

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

[0057] For example, if the supply of hydrogen gas to the third sub-flow channel 32C is no longer detected, the hydrogen booster control unit 112 switches from controlling the operation of the hydrogen booster 24 to controlling the shutdown of the hydrogen booster 24. The shutdown control of the hydrogen booster 24 will be described later.

[0058] The power generation control unit 114 is capable of controlling the operation of the fuel cell 12 and controlling the shutdown of the fuel cell 12. For example, when the amount of electricity stored in the battery 20 falls below a lower limit, 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. Furthermore, the power generation control unit 114 controls at least one of the second pressure regulating valve 52 and the flow rate regulating 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 channel 40B of the oxygen supply mechanism 36. The oxygen gas that did not undergo an electrochemical reaction in the fuel cell 12 flows into the second supply channel 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 channel 40B of the hydrogen supply mechanism 38. The hydrogen gas that does not undergo an electrochemical reaction in the fuel cell 12 flows into the second supply channel 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, if the amount of electricity stored in the battery 20 exceeds the upper limit, the power generation control unit 114 switches from controlling the operation of the fuel cell 12 to controlling the shutdown 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. Furthermore, the power generation control unit 114 stops the control of the second pressure regulating valve 52 and the flow rate regulating valve 60.

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

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

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

[0067] In addition, during the depressurization process, the water electrolysis control unit 110 adjusts the opening of the first pressure regulating valve 50 to achieve the target depressurization rate based on the pressure detected by the pressure sensor 62. This suppresses a rapid drop in gas pressure, and as a result, prevents the formation of blisters and the like on the electrolyte membrane of the water electrolysis device 22.

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

[0069] In addition, during the depressurization process for the shutdown control of the hydrogen pressurizer 24, the hydrogen pressurization control unit 112 adjusts the opening degree of the second pressure regulating valve 52. When the above-mentioned depressurization process is started, the shutdown control of the water electrolyzer 22 moves 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 comparing 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 operation stop control 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 controlling the power supply unit 23 and stops the electrochemical reaction (water electrolysis reaction) in the water electrolysis device 22. The water electrolysis control unit 110 also fixes the opening of the flow control valve 60 to a predetermined opening. Once the depressurization process is complete, the operation stop control 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 water supply pump 31. This completes the operation stop control of the water electrolysis device 22.

[0073] As shown in Figure 1, when the first on-off valve 46 is opened during operation stop control, the oxygen gas produced in the water electrolyzer 22 flows from the branch BP of the gas supply line 40 into the bypass line 44. The oxygen gas that flows into the bypass line 44 is supplied to the fuel cell 12. The oxygen gas produced in the water electrolyzer 22 contains water vapor from alkaline water that has been supplied to the water electrolyzer 22 and moved from the cathode electrode to the anode electrode along with hydroxide ions, as described above. When the depressurization process of operation stop control begins, the differential pressure 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 differential pressure decreases. As a result, more water vapor from alkaline water is generated at the anode electrode compared to during operation control. In other words, the effects of the present invention can be more fully demonstrated in operation stop control of a differential pressure type water electrolyzer, where there is not much water vapor during operation control, but a lot of water vapor can be generated during operation stop control.

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

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

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

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

[0078] The upper part of the side wall 214 is penetrated by the upstream portion of the oxygen exhaust gas flow path 66, called the flow path 66A. The downstream end of the upstream portion of the flow path 66A is located above the generated water stored in the internal space 216. As shown in Figure 1, the upstream end of the upstream portion of the flow path 66A is connected to the fuel cell 12.

[0079] The upper wall 210 is penetrated by the downstream portion of the oxygen exhaust gas flow path 66, called the flow path 66B. The upstream end of the downstream portion of the flow path 66B is located above the water level of the generated water stored in the internal space 216. As shown in Figure 1, the downstream end of the downstream portion of the 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 penetrates the upper wall 210 and extends below the water surface of the generated water. The tubular member 218 may be the downstream end of the bypass passage 44. Alternatively, the tubular member 218 may be a separate member from the bypass passage 44. In this case, the upper end of the tubular member 218 and the downstream end of the bypass passage 44 are joined. The lower end of the tubular member 218 is located below the water surface of the generated water stored in the internal space 216. The lower end of the tubular member 218 is spaced apart from the lower wall 212.

[0081] Oxygen gas that flows into the bypass passage 44 when the first on-off valve 46 is opened during operation stop control reaches the tubular member 218. The oxygen gas that reaches the tubular member 218 is released into the generated water from the lower end of the tubular member 218. The oxygen gas released into the generated water becomes bubbles and moves above the water surface of the generated water. At this time, the water containing oxygen gas (alkaline water vapor) is neutralized by the generated water. The oxygen gas that has moved above the water surface of the generated water flows into the downstream portion of the oxygen exhaust gas passage 66, the passage 66B, and is supplied to the fuel cell 12 via the second supply passage 40B.

[0082] In this manner, the gas flow path 200 guides the oxygen gas produced at the anode electrode of the water electrolyzer 22 to the fuel cell 12 through the generated water stored in the storage container 202. This allows the oxygen gas to neutralize alkaline water with the generated water stored in the storage container 202, even if alkaline water is present in it. This effect can be particularly pronounced by supplying the gas used for operation shutdown control, which can generate water vapor from vaporized alkaline water, to the storage container 202. Therefore, alkaline water does not reach the fuel cell 12, and deterioration of sealing members, electrolyte membranes, etc., provided in the fuel cell 12 by such alkaline water can be suppressed. As a result, a reduction 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 produced in the water electrolysis device 22 to the hydrogen booster device 24 through replenishment 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 in the diagram, the downstream end of the second partial flow path 32B of the hydrogen supply passage 32 is provided in the water tank 30 as a component corresponding to the tubular member 218 described above. The downstream end of the second partial flow path 32B penetrates the upper wall of the water tank 30 and extends below the water surface of the replenishment water stored inside the water tank 30. The replenishment water is acidic because it is liquid water (generated water) stored in the storage container 202.

[0085] As described above, the hydrogen gas separated by the gas-liquid separator 26 is the hydrogen gas produced by the water electrolysis device 22. Therefore, the hydrogen gas flowing from the gas-liquid separator 26 into the second sub-flow channel 32B contains water vapor from vaporized alkaline water. The hydrogen gas flowing into the second sub-flow channel 32B is released into the replenishment water from the lower end of the second sub-flow channel 32B. The hydrogen gas released into the replenishment water becomes bubbles and moves above the water surface of the replenishment water. At this time, the water containing hydrogen gas (alkaline water vapor) is neutralized by the replenishment water. The hydrogen gas that has moved above the water surface of the replenishment water flows into the third sub-flow channel 32C and is supplied to the hydrogen booster 24.

[0086] In this manner, the hydrogen supply line 32 guides the hydrogen gas produced in the water electrolyzer 22 to the hydrogen booster 24 through the replenishment water stored in the water tank 30. As a result, even if alkaline water is present in the hydrogen gas, it can be neutralized by the replenishment water stored in the water tank 30. Therefore, alkaline water does not reach the fuel cell 12, and deterioration of the sealing members, electrolyte membranes, etc., provided in the fuel cell 12 by such alkaline water can be suppressed. Consequently, a reduction 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 the second embodiment. In Figure 5, components equivalent to those described in the first embodiment are denoted by the same reference numerals. In the second embodiment, explanations that overlap with those of the first embodiment are omitted.

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

[0089] The concentration meter 220 is installed in the storage container 202. The concentration meter 220 measures the hydrogen ion concentration of the generated water stored in the storage container 202. The concentration meter 220 may also be a pH meter.

[0090] The water supply channel 222 connects the gas-liquid separator 64 and the storage container 202. The water supply channel 222 is equipped with a water supply pump 224 and a check valve 226. The water supply pump 224 supplies 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 the concentration control unit 228.

[0091] The concentration control unit 228 operates when the processor 100 (Figure 2) executes a program. The concentration control unit 228 may be implemented by an integrated circuit such as an ASIC or FPGA. Alternatively, the concentration control unit 228 may be composed of an electronic circuit including discrete devices. The concentration control unit 228 is capable of performing concentration control to adjust the concentration of the generated water stored in the storage container 202 based on the hydrogen ion concentration measured by the concentration meter 220.

[0092] Figure 6 is a flowchart showing the concentration control procedure. Concentration control is performed, for example, during the operation period of the regenerative fuel cell system 10.

[0093] In step S11, the concentration control unit 228 compares the hydrogen ion concentration measured by the concentration meter 220 with a threshold. The threshold is set to a hydrogen ion concentration corresponding to a hydrogen concentration index selected from the range of pH 6 to pH 7, for example. If the hydrogen ion concentration measured by the concentration meter 220 is on the neutral side of the threshold, the concentration control unit 228 continues to compare the hydrogen ion concentration measured by the concentration meter 220 with the threshold. On the other hand, if the hydrogen ion concentration measured by the concentration meter 220 is on the acidic side of the threshold, the concentration control proceeds to step S12.

[0094] In step S12, the concentration control unit 228 determines whether the water electrolysis device 22 is stopped or not. If the water electrolysis control unit 110 (Figure 2) is performing operation control or operation stop control, the concentration control unit 228 determines that the water electrolysis device 22 is 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 (Figure 2) is not performing operation control or operation stop control, the concentration control unit 228 determines that the water electrolysis device 22 is 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. Once 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 meter 220 with a threshold. If the hydrogen ion concentration measured by the concentration meter 220 is on the acidic side of the threshold, 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 meter 220 is on the neutral side of the threshold, the concentration control proceeds to step S15.

[0097] In step S15, the concentration control unit 228 stops the water supply pump 224. Once 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 supplied to the storage container 202 is greater than the amount of water (alkaline water) supplied to the storage container 202 when the operation of the water electrolysis device 22 is controlled to stop. Therefore, the acidity of the generated water stored in the storage container 202 tends to increase (become more acidic).

[0099] In this embodiment, if the hydrogen ion concentration measured by the concentration meter 220 is on the acidic side of the threshold, the concentration control unit 228 drives the water supply pump 224. This prevents the acidity of the generated water stored in the storage container 202 from increasing (becoming 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 prevents the alkalinity of the generated water stored in the storage container 202 from increasing (becoming stronger).

[0101] The following additional information is disclosed regarding the above embodiment.

[0102] (Note 1) The regenerative fuel cell system (10) of this disclosure comprises a water electrolyzer (22) for electrolyzing alkaline water, a fuel cell (12) for generating electricity using the product gas generated by the electrolysis, a storage container (202) for storing the product water generated by the power generation, and a gas channel (200) for guiding the product gas to the fuel cell through the product water stored in the storage container.

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

[0104] (Note 3) The regenerative fuel cell system described in Appendix 2 may include a tubular member (218) that penetrates the upper wall (210) of the storage container and extends below the water surface of the generated water.

[0105] (Note 4) The regenerative fuel cell system described in Appendix 2 comprises an on-off valve (46) provided in the first flow channel and a water electrolysis control unit (110) that controls the water electrolysis device, wherein the water electrolysis control unit may close the on-off valve while the water electrolysis device is being operated and open the on-off valve when the operation stop control of the water electrolysis device is initiated.

[0106] (Note 5) The regenerative fuel cell system described in Appendix 1 comprises a concentration meter (220) for measuring the hydrogen ion concentration of the generated water stored in the storage container, a water supply pump (224) for supplying the alkaline water to the storage container, and a concentration control unit (228) for adjusting the hydrogen ion concentration of the generated water, wherein if the hydrogen ion concentration measured by the concentration meter is on the acidic side of a threshold, the concentration control unit may drive the water supply pump.

[0107] (Note 6) The regenerative fuel cell system described in Appendix 5, wherein the concentration control unit may drive the water supply pump when the water electrolysis device is stopped.

[0108] (Note 7) The regenerative fuel cell system described in Appendix 1 comprises a water tank (30) for storing replenishment water, which is water to be added to the alkaline water; a hydrogen booster (24) for pressurizing hydrogen gas; and a hydrogen supply path (32) for guiding the hydrogen gas produced 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 oxygen gas produced by the water electrolysis device to the fuel cell through the generated water.

[0109] While this disclosure has been described in detail, it is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of this disclosure or from the intent of this disclosure derived from the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above. [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 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 line 40A...First supply line 40B...Second supply channel 42...Pressure vessel 44... Bypass road (first flow path section) 46... First shut-off valve (shut-off valve) 58... Pressure control valve 60... Flow control valve 110...Water electrolysis control unit 112...Hydrogen boosting control unit 114...Power generation control unit 200, 200A, 200B...Gas flow path 202...Storage container 220...Concentration meter 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 the product gas, which is the gas produced by the aforementioned electrolysis, A storage container for storing the generated water, which is water produced by the aforementioned power generation, A gas channel that guides the generated gas to the fuel cell through the generated water stored in the storage container, A pressure vessel for storing the high-pressure generated gas, A pressure control valve is provided in the first supply path that guides the generated gas from the water electrolysis apparatus to the pressure vessel, Equipped with, The aforementioned gas flow path is A first flow path section connecting the first supply path and the storage container, A second supply channel for guiding the generated gas from the pressure vessel to the fuel cell, and a second flow path section connecting the storage vessel, Includes, The first flow channel section includes a tubular member that penetrates the upper wall of the storage container and extends below the water surface of the generated water, in a regenerative fuel cell system.

2. A water electrolysis apparatus for electrolyzing alkaline water, A fuel cell that generates electricity using the product gas, which is the gas produced by the aforementioned electrolysis, A storage container for storing the generated water, which is water produced by the aforementioned power generation, A gas channel that guides the generated gas to the fuel cell through the generated water stored in the storage container, A pressure vessel for storing the high-pressure generated gas, A pressure control valve is provided in the first supply path that guides the generated gas from the water electrolysis apparatus to the pressure vessel, Equipped with, The aforementioned gas flow path is A first flow path section connecting the first supply path and the storage container, A second supply channel for guiding the generated gas from the pressure vessel to the fuel cell, and a second flow path section connecting the storage vessel, Includes, The on / off valve provided in the first flow path section, A water electrolysis control unit that controls the water electrolysis apparatus, Furthermore, The water electrolysis control unit closes the on-off valve while the water electrolysis device is being controlled, and opens the on-off valve when the control to stop the operation of the water electrolysis device is initiated, in a regenerative fuel cell system.

3. A water electrolysis apparatus for electrolyzing alkaline water, A fuel cell that generates electricity using the product gas, which is the gas produced by the aforementioned electrolysis, A storage container for storing the generated water, which is water produced by the aforementioned power generation, A gas channel that guides the generated gas to the fuel cell through the generated water stored in the storage container, A concentration measuring instrument for measuring the hydrogen ion concentration of the generated water stored in the storage container, A water supply pump that supplies the alkaline water to the storage container, A concentration control unit for adjusting the hydrogen ion concentration of the generated water, Equipped with, If the hydrogen ion concentration measured by the concentration measuring instrument is on the acidic side of the threshold, the concentration control unit drives the water supply pump in a regenerative fuel cell system.

4. A regenerative fuel cell system according to claim 3, The concentration control unit drives the water supply pump when the water electrolysis device stops, in a regenerative fuel cell system.

5. A water electrolysis apparatus for electrolyzing alkaline water, A fuel cell that generates electricity using the product gas, which is the gas produced by the aforementioned electrolysis, A storage container for storing the generated water, which is water produced by the aforementioned power generation, A gas channel that guides the generated gas to the fuel cell through the generated water stored in the storage container, A water tank for storing supplement water, which is water used to replenish the alkaline water, A hydrogen pressurizer that increases the pressure of hydrogen gas, A hydrogen supply path that guides the hydrogen gas generated in the water electrolysis device through the replenishment water stored in the water tank to the hydrogen booster, Equipped with, The gas flow path is a regenerative fuel cell system that guides oxygen gas produced by the water electrolysis device through the generated water to the fuel cell.

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