Regenerative Fuel Cell System

Abstract

To provide a regenerative fuel cell system that can increase the accuracy of depressurization control of a flow control valve, prevent dissipation of gas to the outside, and simplify an opening and closing operation.SOLUTION: In executing depressurizing processing on a hydrogen boosting device and a water electrolysis device, on-off valves (47, 48, 49, 50) are kept opened, and the set pressure of supply pressure reducing valves (51, 52) is adjusted to be a lower value than the set pressure of bypass pressure reducing valves (56, 58). Consequently, gas remaining in gas depressurization areas (81, 82) can be supplied to a fuel cell (22) through the bypass pressure reducing valves (56, 58).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a regenerative fuel cell system. [Background technology]

[0002] In recent years, research and development into fuel cells has been conducted to contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy. Patent Document 1 discloses a regenerative fuel cell system 110 shown in FIG.

[0003] This regenerative fuel cell system 110 is basically composed of a fuel cell 112, a water tank (water supply device) 126, a water electrolysis device 122, a hydrogen booster device 124, an oxygen tank 142A, a hydrogen tank 142B, a gas-liquid separator 130, and a control device 118 that controls these.

[0004] In the regenerative fuel cell system 110, the water electrolysis device 122 and the hydrogen booster device 124 are normally operated with the power generation of the fuel cell 112 stopped, and a predetermined amount of gas is filled into the oxygen tank 142A and the hydrogen tank 142B.

[0005] During operation, the water electrolysis device 122 electrolyzes water supplied from the water tank 126 through the gas-liquid separator 130 to produce high-pressure oxygen and low-pressure hydrogen.

[0006] The high-pressure oxygen generated by the water electrolysis device 122 passes through the branching section BP and the gas-liquid separator 164A and is stored in the oxygen tank 142A.

[0007] The low-pressure hydrogen produced by the water electrolysis device 122 is supplied to the hydrogen pressure booster device 124 through a gas-liquid separator 130 .

[0008] During operation, the hydrogen pressure booster 124 boosts low-pressure hydrogen to high-pressure hydrogen. The boosted high-pressure hydrogen passes through the branching section BP and the gas-liquid separator 164B and is stored in the hydrogen tank 142B.

[0009] When the oxygen tank 142A and the hydrogen tank 142B are filled with a predetermined amount of gas by the operation of the water electrolysis device 122 and the hydrogen booster device 124, the water electrolysis device 122 and the hydrogen booster device 124 are depressurized.

[0010] In this depressurization process, high-pressure oxygen remaining in the water electrolysis device 122 and high-pressure hydrogen remaining in the hydrogen booster device 124 are supplied to the fuel cell 112 .

[0011] The fuel cell 112 consumes the supplied oxygen and hydrogen through an electrochemical reaction, and uses the generated power to charge the battery 120. In this way, the depressurization process (pressure reduction process) of the water electrolysis device 122 and the hydrogen booster device 124 is performed. After the depressurization process is performed, the operation of the water electrolysis device 122 and the hydrogen booster device 124 is stopped.

[0012] Thereafter, the fuel cell 112 can continue to generate electricity through an electrochemical reaction between oxygen supplied from the oxygen tank 142A and hydrogen supplied from the hydrogen tank 142B.

[0013] If the water electrolysis process by the water electrolysis device 122 and the pressure boosting process by the hydrogen pressure booster 124 are stopped without performing the depressurization process described above, high-pressure hydrogen generated in the hydrogen pressure booster 124 will cross-leak within the hydrogen pressure booster 124 and flow back into the gas-liquid separator 130, causing the hydrogen pressure in the gas-liquid separator 130 to increase.

[0014] When the pressure of hydrogen in the gas-liquid separator 130 rises above a threshold pressure, a relief valve (not shown) provided in the gas-liquid separator 130 opens, causing the hydrogen, which is the circulating medium, to be discharged to the outside.

[0015] Furthermore, if the water electrolysis process by the water electrolysis device 122 and the pressure boosting process by the hydrogen pressure boosting device 124 are stopped without performing the depressurization process, high-pressure oxygen generated by the water electrolysis device 122 will cross-leak within the water electrolysis device 122 and flow back into the gas-liquid separator 130, causing an increase in the oxygen pressure within the gas-liquid separator 130.

[0016] When the pressure of oxygen in the gas-liquid separator 130 rises above a threshold pressure, a relief valve (not shown) provided in the gas-liquid separator 130 opens, causing the hydrogen and oxygen circulating media to be discharged to the outside. Therefore, the regenerative fuel cell system 110 requires depressurization processing.

[0017] In order to perform an appropriate depressurization process, the regenerative fuel cell system 110 disclosed in Patent Document 1 is provided with flow control valves 160A and 160B.

[0018] During the depressurization process, the control device 118 measures the amount of pressure reduction (pressure reduction rate) per unit time of the pressure sensors 162A and 162B, and performs depressurization by controlling the flow rates of the flow control valves 160A and 160B so that the difference between the measured pressure reduction rate and the target pressure reduction rate becomes small.

[0019] In addition, in the regenerative fuel cell system 110 disclosed in Patent Document 1, the opening and closing of the first on-off valves 146A, 146B and the second on-off valves 148A, 148B is precisely controlled to eliminate the difference in timing between the completion of decompression of high-pressure oxygen and high-pressure hydrogen.

[0020] By supplying the oxygen or hydrogen that has been depressurized earlier from the oxygen tank 142A or the hydrogen tank 142B to the fuel cell 22, power generation in the fuel cell 112 continues, and control is performed to consume the gas that has been depressurized later (paragraphs

[0078] to

[0082] of Patent Document 1). [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Patent No. 7393450 Summary of the Invention [Problem to be solved by the invention]

[0022] However, the above-mentioned conventional depressurization process (depressurization method) has the following first to third problems.

[0023] [First issue] In depressurization control, which uses flow control valves 160A and 160B to control the flow rate, the flow rate cannot be accurately controlled because the primary and secondary pressures of flow control valves 160A and 160B fluctuate. Therefore, it is difficult to precisely control the actual depressurization speed so that it matches the target depressurization speed.

[0024] [Second issue] During depressurization, when a pressure difference occurs between the stacks of the water electrolysis device 122 and the hydrogen booster device 124, gas cross-leak occurs from the high-pressure side to the low-pressure side of the stack through the electrolyte membrane. This cross-leak increases the pressure on the low-pressure side of the stack, causing the pressure inside the gas-liquid separator 130 to increase, and a relief valve (not shown) provided in the gas-liquid separator 130 opens, discharging the gas to the outside and resulting in gas loss.

[0025] [Third issue] The timing difference between the completion of depressurization of oxygen and hydrogen is addressed by controlling the opening and closing of the first opening and closing valves 146A, 146B and the second opening and closing valves 148A, 148B, but this opening and closing control becomes extremely complicated.

[0026] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0027] An aspect of the present disclosure is a regenerative fuel cell system having a fuel cell that generates electricity through an electrochemical reaction between oxygen gas and hydrogen gas, the system comprising a pressure booster (a pair of a hydrogen pressure booster and a water electrolysis device) that generates either the pressurized oxygen gas or the pressurized hydrogen gas, two supply mechanisms for supplying the gas to the fuel cell, and a control device, the supply mechanism comprising a gas supply path that supplies the gas from the pressure booster to the fuel cell, a tank that is provided on the gas supply path and that stores the gas pressurized by the pressure booster, and a storage tank between the pressure booster and the tank. a bypass passage branching from a branching portion of the gas supply passage and joining a joining portion of the gas supply passage between the tank and the fuel cell, a supply pressure reducing valve provided in the gas supply passage between the tank and the joining portion, a bypass pressure reducing valve provided in the bypass passage, and an on-off valve that enables the gas to be supplied to the fuel cell, and when a pressure boosting stop operation by the pressure boosting device is started, the control device stops the supply of the gas to the tank and opens the on-off valve, and when in the open state, lowers the set pressure of the supply pressure reducing valve below the set pressure of the bypass pressure reducing valve. The oxygen gas remaining in the oxygen decompression region of one of the pressure boosting devices that pressurizes the oxygen gas and the hydrogen gas remaining in the hydrogen decompression region of the other pressure boosting device that pressurizes the hydrogen gas are supplied to the fuel cell to generate power, whereby the oxygen gas remaining in the oxygen decompression region and the hydrogen gas remaining in the hydrogen decompression region are supplied to the fuel cell to generate power. This is a regenerative fuel cell system that performs depressurization processing. [Effects of the Invention]

[0028] According to the above aspect, when performing the depressurization process of the booster device, fuel cell The on-off valve for supplying gas to the pressure booster is in an open state, and the set pressure of the supply pressure reducing valve is lower than the set pressure of the bypass pressure reducing valve. Therefore, the gas remaining in the gas decompression region of the pressure booster is released through the bypass pressure reducing valve. The aforementioned The gas can be supplied to a fuel cell, which consumes the gas through an electrochemical reaction to generate electricity. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram showing a regenerative fuel cell system according to an embodiment. [Figure 2] FIG. 2 is a time chart relating to the depressurization process. [Figure 3] FIG. 3 is an explanatory diagram of the oxygen decompression region and the hydrogen decompression region. [Figure 4] FIG. 4 is an explanatory diagram of the operation of converting oxygen and hydrogen that cross-leak from the high-pressure side to the low-pressure side during depressurization treatment into water using an oxygen removal catalyst. [Figure 5] FIG. 5 is an explanatory diagram of the set pressure of the pressure reducing valve in the first half of the depressurization process. [Figure 6] FIG. 6 is an explanatory diagram of the set pressure of the pressure reducing valve in the latter half of the depressurization process. [Figure 7] FIG. 7 is a schematic diagram showing a conventional regenerative fuel cell system for explaining the problems with conventional methods. DETAILED DESCRIPTION OF THE INVENTION

[0030] 1 is a schematic diagram showing a regenerative fuel cell system (RFC) 10 according to an embodiment. The regenerative fuel cell system 10 is used in a vacuum space such as outer space or the surface of the moon. It can also be used in the atmosphere.

[0031] [Overall explanation of regenerative fuel cell system 10] The regenerative fuel cell system 10 basically comprises a water electrolysis device 12, a gas-liquid separator (hydrogen gas-liquid separator) 14, a gas-liquid separator (oxygen gas-liquid separator) 15, an oxygen tank 16, a hydrogen pressure booster 18, a hydrogen tank 20, a water tank 21, a fuel cell 22, a battery 23, a gas-liquid separator (oxygen exhaust gas gas-liquid separator) 24, a gas-liquid separator (hydrogen exhaust gas gas-liquid separator) 26, and a control device 28. A controller 28 controls all components of the regenerative fuel cell system 10 .

[0032] In this embodiment, the water electrolysis apparatus 12 is a high differential pressure water electrolysis stack apparatus (hereinafter abbreviated as EC) that generates electrochemically compressed high-pressure oxygen gas and unpressurized hydrogen gas (low-pressure hydrogen gas) by water electrolysis.

[0033] Water for water electrolysis is supplied from a water tank 21 via a water supply line 29 , a gas-liquid separator 14 and a water supply line 30 to the water electrolysis device 12 .

[0034] The water supply path 29 connects the water tank 21 and the gas-liquid separator 14. A pump 25 is provided in the water supply path 29. The pump 25 is on / off controlled by the control device 28. When the pump 25 is turned on, it imparts flow energy to the water stored in the water tank 21 and supplies water from the water tank 21 to the gas-liquid separator 14. When the pump 25 is turned off, it stops supplying water. All the other pumps described below similarly impart flow energy to the fluid when turned on and stop the flow of the fluid when turned off.

[0035] The water electrolysis device 12 has one or more unit cells. Each unit cell includes a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode. The electrolyte membrane used in the water electrolysis device 12 is an anion exchange membrane in this embodiment, but may also be a proton exchange membrane.

[0036] The water electrolysis device 12 supplies water from the gas-liquid separator 14 to the cathode electrode of each unit cell. The unit cells perform water electrolysis based on a voltage applied to the anode electrode and the cathode electrode from the power supply 13. In this case, pressurized high-pressure (for example, in the range of 1 to 100 MPa) oxygen gas is produced at the anode electrode, and unpressurized hydrogen gas is produced at the cathode electrode.

[0037] The control device 28 can vary the voltage applied between the anode electrode and the cathode electrode by the power supply 13. The power of the power supply 13 may be power from a battery 23.

[0038] The water electrolysis device 12 collects high-pressure oxygen gas generated in each unit cell and outputs a release gas containing the oxygen gas to the oxygen supply mechanism 17A through the oxygen supply path 43. The release gas contains water vapor vaporized by the heat of the water electrolysis device 12 or the like.

[0039] At the same time, the water electrolysis device 12 collects hydrogen gas produced in each unit cell and excess water that has not been electrolyzed (unreacted water), and outputs a discharge fluid containing the hydrogen gas and unreacted water to the hydrogen supply channel 32. The discharge fluid also contains water vapor vaporized by the heat of the water electrolysis device 12, etc.

[0040] The discharge fluid (hydrogen gas and unreacted water) output from the water electrolysis device 12 to the hydrogen supply channel 32 flows into the gas-liquid separator 14. The gas-liquid separator 14 separates the discharge fluid into a gas component (hydrogen gas and water vapor) and a liquid component (liquid water). The gas component is supplied to the hydrogen pressure booster 18 by turning on a pump 34 of the hydrogen supply channel 32 provided on the outlet side of the gas-liquid separator 14.

[0041] A pressure sensor 60 is provided on the hydrogen supply line 32 near the outlet of the gas-liquid separator 14, and an oxygen remover 33 is further provided between the outlet of the gas-liquid separator 14 and the inlet of the pump .

[0042] The oxygen remover 33 reacts the oxygen gas discharged from the water electrolysis device 12 to the gas-liquid separator 14 during the depressurization process with the hydrogen gas discharged from the hydrogen booster device 18 to the gas-liquid separator 14 using an oxygen removal catalyst to generate water.

[0043] More specifically, during depressurization, oxygen gas cross-leaks from the high-pressure side of the water electrolysis device 12 through the electrolyte membrane to the low-pressure side. The cross-leaked oxygen gas is discharged to the gas-liquid separator 14 through the hydrogen supply channel 32. During depressurization, hydrogen gas cross-leaks from the high-pressure side of the hydrogen booster device 18 through the electrolyte membrane to the low-pressure side. The cross-leaked hydrogen gas is discharged to the gas-liquid separator 14 through the hydrogen discharge channel 35. The control device 28 turns on the pump 34. When the pump 34 is turned on and the cross-leaked oxygen gas and the cross-leaked hydrogen gas flow through the hydrogen supply channel 32, the oxygen remover 33 reacts the oxygen gas and the hydrogen gas with an oxygen removal catalyst to generate water.

[0044] The hydrogen booster 18 has a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode. The electrolyte membrane used in the hydrogen booster 18 is a proton exchange membrane. A power source 19 is connected to the anode electrode and the cathode electrode.

[0045] The control device 28 can vary the voltage applied between the anode electrode and the cathode electrode by the power supply 19. The power of the power supply 19 may be powered by the battery 23.

[0046] The hydrogen booster 18 supplies hydrogen gas flowing in from the hydrogen supply channel 32 to the anode electrode. The hydrogen booster 18 ionizes the hydrogen gas based on a voltage applied from a power source 19. Protons obtained by the ionization of the hydrogen gas reach the cathode electrode via an electrolyte membrane (proton exchange membrane). The protons that reach the cathode electrode combine with electrons (electrons generated during the ionization) supplied from the power source 19 and return to hydrogen gas.

[0047] The hydrogen pressure booster 18 generates pressurized hydrogen gas by transferring protons from the anode electrode to the cathode electrode. For example, the hydrogen gas is compressed to a pressure range of 1 to 100 MPa. In this way, the hydrogen pressure booster 18 is an electrochemical hydrogen compressor (EHC) that electrochemically compresses hydrogen gas.

[0048] The hydrogen booster 18 outputs excess hydrogen gas that has not been ionized to the hydrogen discharge path 35. The hydrogen discharge path 35 is a flow path (pipe) for discharging hydrogen gas from the hydrogen booster 18 to the gas-liquid separator 14.

[0049] The hydrogen pressure booster 18 outputs a release gas containing pressurized hydrogen gas to the hydrogen supply mechanism 17 B. The release gas contains water vapor vaporized by the heat of the hydrogen pressure booster 18 or the like.

[0050] The oxygen supply mechanism 17A and the hydrogen supply mechanism 17B constitute the gas supply mechanism 17. The gas supply mechanism 17 is a mechanism for supplying the fuel cell 22 with reactant gases (hydrogen gas and oxygen gas).

[0051] The oxygen supply mechanism 17A supplies the oxygen gas produced in the water electrolysis device 12 to the fuel cell 22. The hydrogen supply mechanism 17B supplies the hydrogen gas produced in the hydrogen booster device 18 to the fuel cell 22.

[0052] [Explanation of oxygen supply mechanism 17A] The oxygen supply mechanism 17A has an oxygen supply path 43, an oxygen tank 16, a bypass path 45, an on-off valve 47, an on-off valve 49, a pressure reducing valve (supply pressure reducing valve) 51, a pressure reducing valve 53, a pressure reducing valve (bypass pressure reducing valve) 58, a back pressure valve 57, a pressure sensor 61, a temperature sensor 63, and a gas-liquid separator 15.

[0053] The oxygen supply channel 43 is a flow path for supplying high-pressure oxygen gas generated in the water electrolysis device 12 to the fuel cell 22 via the oxygen tank 16. One end of the oxygen supply channel 43 is connected to the water electrolysis device 12, and the other end of the oxygen supply channel 43 is connected to the fuel cell 22 via a pressure reducing valve 53.

[0054] The oxygen tank 16 is provided on the oxygen supply line 43. The oxygen tank 16 stores high-pressure oxygen gas generated by the water electrolysis device 12.

[0055] The bypass path 45 branches off from a branch point Bpo (BP) of the oxygen supply path 43 between the back pressure valve 57 and the gas-liquid separator 15, and joins at a joining point Mpo (MP) of the oxygen supply path 43 between the oxygen tank 16 and the fuel cell 22.

[0056] The on-off valve 47 is provided in the bypass path 45. The on-off valve 49 is provided in the oxygen supply path 43 between the junction Mpo and the oxygen tank 16.

[0057] The on-off valves 47 and 49 are solenoid valves, and are shut-off valves that are opened and closed by on-off control of the control device 28.

[0058] The pressure reducing valve 51 is provided in the oxygen supply path 43 between the confluence part Mpo and the oxygen tank 16. The pressure reducing valve 51 reduces the pressure of the oxygen gas supplied from the oxygen tank 16 to a predetermined pressure.

[0059] The pressure reducing valve 53 is provided in the oxygen supply channel 43 between the confluence point Mpo and the fuel cell 22. The pressure reducing valve 53 reduces the pressure of the oxygen gas supplied from the pressure reducing valve 51 or the bypass channel 45 to a predetermined pressure.

[0060] The back pressure valve 57 is provided in the oxygen supply channel 43 between the branch point Bpo and the oxygen tank 16. The back pressure valve 57 applies pressure (back pressure) to the water electrolysis device 12 through the gas space in the gas-liquid separator 15. This increases the pressure of oxygen gas generated at the anode electrode of each unit cell of the water electrolysis device 12, and makes it higher than the pressure of hydrogen gas generated at the cathode electrode.

[0061] The water electrolysis device 12 generates oxygen gas at the anode electrode, which has a higher pressure than hydrogen gas generated at the cathode electrode. This can suppress cross-leakage, in which hydrogen gas permeates through the electrolyte membrane from the cathode electrode to the anode electrode. As a result, a decrease in the amount of hydrogen gas supplied from the water electrolysis device 12 to the hydrogen booster device 18 can be prevented.

[0062] The pressure sensor 61 is provided in the oxygen supply channel 43 between the water electrolysis device 12 and the branch point Bpo. The pressure sensor 61 detects the pressure of oxygen gas supplied from the water electrolysis device 12 to the oxygen supply channel 43. The pressure sensor 61 outputs a signal indicative of the detected pressure to the control device 28.

[0063] The temperature sensor 63 is provided in the oxygen supply channel 43 between the water electrolysis device 12 and the gas-liquid separator 15. The temperature sensor 63 detects the temperature of the oxygen gas supplied from the water electrolysis device 12 to the oxygen supply channel 43. The temperature sensor 63 outputs a signal indicating the detected temperature to the control device 28. The gas-liquid separator 15 is provided on the oxygen supply channel 43 between the water electrolysis device 12 and the branch point Bpo.

[0064] The oxygen gas released from the water electrolysis device 12 to the oxygen supply channel 43 contains water vapor in addition to the oxygen gas. The gas-liquid separator 15 cools the water vapor in the released gas to generate liquid water, and supplies the oxygen gas from which the moisture has been removed to the oxygen tank 16. This can prevent the oxygen tank 16 from becoming wet. As a result, the durability of the oxygen tank 16 can be improved without applying excessive rust-resistant treatment to the oxygen tank 16.

[0065] The gas-liquid separator 15 is connected to the gas-liquid separator 14 via a liquid water supply path 65. The liquid water supply path 65 is a flow path (communicating path) for supplying the liquid water stored in the gas-liquid separator 15 to the gas-liquid separator 14. A drain valve 64, which is an on-off valve, is provided on the liquid water supply path 65.

[0066] Liquid water obtained from water vapor in the oxygen gas released from the water electrolysis device 12 is supplied from the gas-liquid separator 15 to the gas-liquid separator 14 via the drain valve 64 and the liquid-water supply channel 65. This makes it possible to conserve water used in the water electrolysis device 12. The gas-liquid separator 14 stores the water to be supplied to the water electrolysis device 12. A water supply channel 30 is provided between the gas-liquid separator 14 and the water electrolysis device 12. A pump 31 is provided on the water supply channel 30.

[0067] [Explanation of hydrogen supply mechanism 17B] The hydrogen supply mechanism 17B has a hydrogen supply path 44, a hydrogen tank 20, a bypass path 46, an on-off valve 48, an on-off valve 50, a pressure reducing valve (supply pressure reducing valve) 52, a pressure reducing valve 54, a pressure reducing valve (bypass pressure reducing valve) 56, a back pressure valve 59, a pressure sensor 62, and a temperature sensor 69.

[0068] The hydrogen supply path 44 is a flow path for supplying hydrogen gas pressurized by the hydrogen pressure booster 18 to the fuel cell 22 via the hydrogen tank 20. One end of the hydrogen supply path 44 is connected to the hydrogen pressure booster 18, and the other end of the hydrogen supply path 44 is connected to the fuel cell 22 via a pressure reducing valve 54.

[0069] The hydrogen tank 20 is provided on the hydrogen supply line 44. The hydrogen tank 20 stores high-pressure hydrogen gas that has been pressurized by the hydrogen pressure booster 18.

[0070] The bypass path 46 branches off from a branch point Bph (BP) of the hydrogen supply path 44 between the hydrogen booster 18 and the hydrogen tank 20, and merges with the hydrogen supply path 44 at a merge point Mph (MP) between the hydrogen tank 20 and the fuel cell 22.

[0071] The on-off valve 48 is provided in the bypass passage 46. The on-off valve 50 is provided in the hydrogen supply passage 44 between the junction Mph and the hydrogen tank 20.

[0072] The on-off valves 48 and 50 are solenoid valves, and are shut-off valves that are opened and closed by the on-off control of the control device 28.

[0073] The pressure reducing valve 52 is provided in the hydrogen supply passage 44 between the junction Mph and the hydrogen tank 20. The pressure reducing valve 52 reduces the pressure of the hydrogen gas supplied from the hydrogen tank 20 to a predetermined pressure.

[0074] The pressure reducing valve 54 is provided in the hydrogen supply channel 44 between the confluence point Mph and the fuel cell 22. The pressure reducing valve 54 reduces the pressure of the hydrogen gas supplied from the pressure reducing valve 52 or the bypass channel 46 to a predetermined pressure.

[0075] The back pressure valve 59 is provided in the hydrogen supply path 44 between the branch point Bph and the hydrogen tank 20. The back pressure valve 59 applies pressure (back pressure) to the hydrogen booster 18. This increases the pressure of the hydrogen gas generated at the cathode electrode of each unit cell of the hydrogen booster 18, and makes it higher than the pressure of the hydrogen gas supplied to the anode electrode.

[0076] The pressure sensor 62 is provided in the hydrogen supply path 44 between the hydrogen pressurizer 18 and the branch point Bph. The pressure sensor 62 detects the pressure of the hydrogen gas supplied to the hydrogen supply path 44. The pressure sensor 62 outputs a signal indicating the detected pressure to the control device 28.

[0077] The temperature sensor 69 is provided in the hydrogen supply line 44 between the hydrogen booster 18 and the branch point Bph. hydrogen The temperature sensor 69 detects the temperature of the gas and outputs a signal indicating the detected temperature to the control device 28.

[0078] [Explanation of Fuel Cell 22] The oxygen supply mechanism 17A further includes an oxygen exhaust gas passage 76, a gas-liquid separator 24, a circulation pump 70, and a drain valve 72.

[0079] The hydrogen supply mechanism 17B further includes a hydrogen exhaust gas passage 77, a gas-liquid separator 26, a circulation pump 71, and a drain valve 73.

[0080] The fuel cell 22 has a stack of unit cells electrically connected in series. Each unit cell includes a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode.

[0081] The fuel cell 22 supplies oxygen gas, which is supplied from the oxygen tank 16 via pressure reducing valves 51 and 53, to the cathode electrode of each unit cell. The fuel cell 22 supplies hydrogen gas, which is supplied from the hydrogen tank 20 via pressure reducing valves 52 and 54, to the anode electrode of each unit cell. Each unit cell of the fuel cell 22 generates electricity through an electrochemical reaction between oxygen gas and hydrogen gas.

[0082] The power generated by the fuel cell 22 is supplied to a load (main load) not shown, and also to auxiliary loads including the control device 28. Excess generated power is charged into the battery 23. The generated current Ifc of the fuel cell 22 is detected by a current sensor 27 and acquired by the control device 28. The stored voltage of the battery 23 and the generated voltage of the fuel cell 22 are each detected by a voltage sensor not shown and acquired by the control device 28.

[0083] The oxygen-containing exhaust gas containing unreacted oxygen gas in each unit cell of the fuel cell 22 is supplied to the oxygen supply channel 43 via the oxygen circulation channel 66. The oxygen circulation channel 66 is a flow path for returning the oxygen-containing exhaust gas discharged from the fuel cell 22 to the oxygen supply channel 43.

[0084] The gas-liquid separator 24 and the circulation pump 70 are provided on the oxygen circulation path 66. The gas-liquid separator 24 separates the oxygen-containing exhaust gas discharged from the fuel cell 22 to the oxygen exhaust gas path 76 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 22 by the circulation pump 70. Meanwhile, the liquid component is supplied to the water tank 21 via a drain valve 72, which is an on-off valve.

[0085] On the other hand, hydrogen-containing exhaust gas containing unreacted hydrogen gas in each unit cell of the fuel cell 22 is supplied to the hydrogen supply path 44 via a hydrogen circulation path 67. The hydrogen circulation path 67 is a flow path for returning the hydrogen-containing exhaust gas discharged from the fuel cell 22 to the hydrogen supply path 44.

[0086] The gas-liquid separator 26 and the circulation pump 71 are provided on the hydrogen circulation path 67. The gas-liquid separator 26 separates the hydrogen-containing exhaust gas discharged from the fuel cell 22 to the hydrogen exhaust gas path 77 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 22 by the circulation pump 71. Meanwhile, the liquid component is supplied to the water tank 21 via a drain valve 73, which is an on-off valve.

[0087] [Explanation of the control device 28] The controller 28 controls all components of the regenerative fuel cell system 10 and executes the operation of the regenerative fuel cell system 10 .

[0088] The control device 28 is a computer that controls the regenerative fuel cell system 10. The control device 28 includes one or more processors and a storage medium. The storage medium may be composed of a volatile memory and a non-volatile memory. Examples of the processor include a CPU, an MCU, etc. Examples of the volatile memory include a RAM, etc. Examples of the non-volatile memory include a ROM, a flash memory, etc.

[0089] The control device 28 turns on the power supply 13 of the water electrolysis device 12 to apply a voltage to the anode and cathode electrodes of the unit cell. In addition, the control device 28 turns on the pump 31 to supply water from the gas-liquid separator 14 to the water electrolysis device 12.

[0090] As a result, the water electrolysis device 12 enters an operating state (pressure-boosting state, water electrolysis state) and performs water electrolysis (water electrolysis).

[0091] When the control device 28 stops the application of voltage from the power source 13 to the unit cells and the supply of water to the water electrolysis device 12, the water electrolysis device 12 enters a non-operating state (a depressurized state and then a stopped state).

[0092] The control device 28 also turns on the power supply 19 of the hydrogen pressure booster 18 to apply a voltage to the anode and cathode electrodes of the unit cell. In addition, the control device 28 turns on the pump 34 to supply hydrogen gas from the gas-liquid separator 14 to the hydrogen pressure booster 18.

[0093] This puts the hydrogen pressure booster 18 into an operating state (pressurizing state) and boosts the hydrogen gas. When the control device 28 stops the application of voltage from the power source 19 to the unit cell and the supply of hydrogen gas to the hydrogen pressure booster 18, the hydrogen pressure booster 18 goes into a non-operating state (a stopped state after passing through a depressurizing state).

[0094] [Operation of regenerative fuel cell system 10] The basic operation of the regenerative fuel cell system 10 configured as above will be explained below with reference to the time chart (operation sequence) of FIG.

[0095] In FIG. 2, EC 12 indicates the water electrolysis device 12, EHC 18 indicates the hydrogen booster device 18, FC 22 indicates the fuel cell 22, and RFC 10 indicates the regenerative fuel cell system 10.

[0096] The regenerative fuel cell system 10 according to this embodiment executes a characteristic depressurization process (processing between time t2 and time t3) which will be described in detail below.

[0097] For ease of understanding this depressurization process, first, the oxygen pressure increase (water electrolysis) process and the hydrogen pressure increase process from time t0 to time t2 will be described.

[0098] Immediately before time t0, the fuel cell 22, the water electrolysis device 12, and the hydrogen booster device 18 are stopped, and the regenerative fuel cell system 10 is stopped. When the regenerative fuel cell system 10 is stopped, the shut-off valves 47, 48, 49, and 50, which are the shut-off valves for supplying oxygen gas and hydrogen gas to the fuel cell 22, are closed.

[0099] At time t0, operation of the regenerative fuel cell system 10 is started. In this case, the control device 28 first turns on the pump 25 and the pump 31 to supply water stored in the water tank 21 to the cathode electrode of each unit cell of the water electrolysis device 12 through the water supply channel 29, the gas-liquid separator 14, and the water supply channel 30.

[0100] The control device 28 then supplies a predetermined current from the power source 13 to the cathode and anode electrodes of each unit cell of the water electrolysis device 12, causing the water electrolysis device 12 to start a voltage boosting operation.

[0101] In this case, oxygen gas pressurized by electrolysis of water is generated at the anode electrode, and this oxygen gas is supplied to the oxygen tank 16 of the oxygen supply mechanism 17A via the oxygen supply path 43 of the oxygen supply mechanism 17A. The reaction formula on the anode electrode side of the water electrolysis device 12 is shown below. 2OH -→(1 / 2)O2+H2O+2e -

[0102] When the water electrolysis device 12 starts the pressure boosting operation, hydrogen gas is produced at the cathode electrode by electrolysis of water. This hydrogen gas is released from the water electrolysis device 12 and supplied to the anode electrode of each unit cell of the hydrogen pressure boosting device 18 via the pump 34 and the hydrogen supply path 32 that have been turned on. The reaction formula on the cathode electrode side of the water electrolysis device 12 is shown below. 2H2O+2e - →H2+2OH -

[0103] The control device 28 confirms the supply of hydrogen gas to the hydrogen supply path 32 based on the pressure detected by a pressure sensor 60 provided in the hydrogen supply path 32 .

[0104] When the supply of hydrogen gas to the hydrogen supply path 32 is confirmed, at time t1, the control device 28 controls the power supply 19 to cause the hydrogen pressure booster 18 to perform a pressure boosting operation. When the hydrogen pressure booster 18 starts the pressure boosting operation, hydrogen gas is ionized and pressurized to produce hydrogen gas at the cathode. This pressurized, high-pressure hydrogen gas is supplied to the hydrogen tank 20 via the hydrogen supply path 44 of the hydrogen supply mechanism 17B. The reaction formula on the cathode electrode side of the hydrogen booster 18 is shown below. 2H + +2e - →H2 The reaction formula on the anode electrode side of the hydrogen boosting device 18 is shown below. H2→2H + +2e -

[0105] When predetermined amounts of hydrogen and oxygen are stored in the hydrogen tank 20 and the oxygen tank 16, respectively, at time t2 due to the water electrolysis process and hydrogen pressure boosting process performed between time t1 and time t2, the control device 28 starts the depressurization process at time t2.

[0106] [Detailed explanation of decompression treatment] FIG. 3 is an explanatory diagram that schematically shows the regions to be subjected to depressurization treatment (oxygen depressurization region 81 and hydrogen depressurization region 82, which are gas depressurization regions surrounded by dashed lines).

[0107] On the oxygen supply side, the oxygen depressurization region 81 includes the oxygen supply channel 43 up to the primary side of the back-pressure valve 57 that communicates with the anode electrode of the water electrolysis device 12, and the bypass channel 45 up to the primary side of the pressure reducing valve 58 that communicates with the anode electrode of the water electrolysis device 12. The oxygen depressurization region 81 is generally a region where high-pressure oxygen gas is present in the flow path (space) from the anode electrode of the water electrolysis device 12 to the junction Mpo when the water electrolysis device 12 stops its pressure boosting operation.

[0108] On the hydrogen supply side, the region of the hydrogen supply path 44 up to the primary side of the back pressure valve 59 communicating with the cathode electrode of the hydrogen pressure booster 18 and the region of the bypass path 46 up to the primary side of the pressure reducing valve 56 communicating with the cathode electrode of the hydrogen pressure booster 18 correspond to the hydrogen decompression region 82.

[0109] Below, the depressurization treatment (depressurization process) will be explained in the following order: A. First depressurization method (method for solving the first problem), B. Second depressurization method (method for solving the second problem), and C. Third depressurization method (method for solving the third problem).

[0110] A. First decompression method (solution to the first problem) In the above-mentioned [First Problem], it was difficult to control the target decompression speed (depressurization speed) of the oxygen gas and hydrogen gas to be depressurized.

[0111] In this first depressurization technique, the generated current Ifc is controlled by the control device 28 according to the following calculation: In this first depressurization technique, the depressurization rate can be controlled accurately and precisely by controlling the generated current Ifc, which is easy to control. The amount of hydrogen gas consumed by the fuel cell 22 can be calculated by the following formula (1).

[0112] Hydrogen gas consumption [mol / sec] = Ifc [A] / (2 ​​× F [C / mol]) …(1) where F is Faraday's constant = 9.65 x 10 4 [C / mol].

[0113] The hydrogen-side depressurization rate (hydrogen-side depressurization rate) [kpA / sec] corresponding to the target depressurization rate in the hydrogen depressurization region 82 can be calculated by the following formula (2): Here, the volume of the hydrogen depressurization region 82 (hydrogen-side volume [mL]) is known from design and actual measurement.

[0114] Hydrogen side decompression rate [kpA / sec] = Hydrogen gas consumption [mol / sec] × R × Gas temperature [K] × Z / Hydrogen side volume [mL] … (2) where R is the gas constant and Z is the compressibility factor. Regarding the compressibility factor Z, for an ideal gas, The volume of the child The existence of intermolecular attractive forces is ignored, but when the gas pressure is in a high pressure state (real gas), intermolecular attractive forces exist and the volume occupied by the molecules cannot be ignored. The compressibility coefficient is the sum of the intermolecular attractive forces and the molecular but The coefficient for correcting the effect of the volume occupied is defined as Z = PV / (nRT). The compressibility coefficient Z varies depending on parameters such as the type of gas, number of moles n, pressure P, temperature T, and volume V, so the compressibility coefficient Z is calculated in advance by changing these parameters.

[0115] The amount of oxygen gas consumed in the fuel cell 22 can be calculated by the following formula (3).

[0116] Oxygen gas consumption [mol / sec] = Ifc [A] / (4 × F [C / mol]) …(3)

[0117] The oxygen side decompression rate (oxygen side decompression rate) [kpA / sec] corresponding to the target decompression rate in the oxygen decompression region 81 can be calculated by the following equation (4): Here, the volume of the oxygen decompression region 81 (oxygen side volume [mL]) is known from design and actual measurement.

[0118] Oxygen side decompression rate [kpA / sec] = Oxygen gas consumption [mol / sec] × R × Gas temperature [K] × Z / Oxygen side volume [mL] … (4) Since the compressibility coefficient Z varies depending on parameters such as the type of gas, the number of moles n, the pressure P, the temperature T, and the volume V, the compressibility coefficient Z is determined in advance by changing these parameters.

[0119] In this case, the hydrogen-side pressure reduction rate or the oxygen-side pressure reduction rate is set so that the generated current Ifc calculated by substituting equation (2) into equation (1) is the same as the generated current Ifc calculated by substituting equation (4) into equation (3).

[0120] In actual depressurization processing, as shown in FIG. 2, after time t2, all of the on-off valves 47 to 50 are opened and the generated current Ifc is controlled by the control device 28, so the first problem can be easily solved.

[0121] Instead of the above calculation, the relationship between the generated current Ifc and the pressure reduction rate may be measured in advance and recorded as a relationship characteristic in a storage device (not shown) in the control device 28. The control device 28 may determine the generated current Ifc based on the pressure reduction rate by referring to the relationship characteristic.

[0122] In practice, it is preferable that the control device 28 calculates the pressure reduction rate of the pressure value detected by the pressure sensors 61, 62 (pressure reduction value per unit time: measured pressure reduction rate) and adjusts the power generation current Ifc by feedback control so that the difference from the target pressure reduction rate becomes small.

[0123] B. Second decompression method (method to solve the second problem) This will be explained with reference to the schematic diagram of FIG. During the depressurization process using the first depressurization method (method for solving the first problem), a pressure difference occurs between the electrolyte membranes of the stacks of the water electrolysis device 12 and the hydrogen booster device 18. As a result, gas cross-leakage (cross-leakage of oxygen permeating in the opposite direction through the electrolyte membrane and cross-leakage of hydrogen permeating in the opposite direction through the electrolyte membrane) occurs from the high-pressure side to the low-pressure side of each stack of the water electrolysis device 12 and the hydrogen booster device 18, as shown by the thick dashed lines in Fig. 4 . This cross-leaked oxygen and cross-leaked hydrogen must be depressurized (disposed of).

[0124] Regarding oxygen cross-leak in the water electrolysis apparatus 12, as shown in FIG. 4 , hydrogen remaining in the gas-liquid separator 14 and cross-leaked hydrogen supplied from the hydrogen booster 18 to the gas-liquid separator 14 through a hydrogen discharge channel 35 are reacted with cross-leaked oxygen supplied from the water electrolysis apparatus 12 to the gas-liquid separator 14 through a hydrogen supply channel 32 in an oxygen remover 33 equipped with an oxygen removal catalyst to produce water, thereby depressurizing the water.

[0125] When the reaction is carried out in the oxygen remover 33, the pump 34 is turned on to circulate the oxygen and hydrogen that have cross-leaked onto the hydrogen supply line 32.

[0126] Generally, oxygen cross-leakage and hydrogen cross-leakage are more prevalent for hydrogen, which has smaller molecules. Therefore, hydrogen remains on the primary side of the hydrogen booster 18, which is connected to the hydrogen discharge line 35, i.e., in the gas-liquid separator 14, and the pressure rises.

[0127] Therefore, regarding the remaining hydrogen, current is passed from power source 19 to hydrogen pressurization device 18 during depressurization control, and the remaining hydrogen is pressurized to a high pressure. The pressurized high-pressure hydrogen can be consumed by the third depressurization method described below.

[0128] In practice, the current flowing from the power source 19 to the hydrogen pressure booster 18 may be determined so that the deviation between the pressure value detected by the pressure sensor 60 (pressure value of the gas-liquid separator 14) and the target pressure value (target pressure value which is the allowable pressure value of the gas-liquid separator 14) becomes zero.

[0129] C. Third decompression method (solution to the third problem) (1) FIG. 5 is a schematic diagram illustrating a third depressurization technique (1) in which oxygen in the oxygen depressurization region 81 and hydrogen in the hydrogen depressurization region 82 are consumed preferentially by the fuel cell 22. In FIG.

[0130] In the third depressurization method (1), the control device 28 adjusts the pressure reducing valve 51 and the pressure reducing valve 58 so that the set pressure Psc of the pressure reducing valve 51 is lower than the set pressure Psd of the pressure reducing valve 58 on the oxygen depressurization region 81 side (Psc <Psd)。

[0131] With this setting, only the high-pressure oxygen remaining in the oxygen depressurization region 81 flows into the fuel cell 22 through the pressure reducing valve 58 and the bypass path 45, as shown by the thick dashed line in Figure 5, and oxygen does not flow through the oxygen supply path 43 in which the pressure reducing valve 51 is provided. In other words, only the oxygen in the oxygen depressurization region 81, which is the region that requires depressurization, is consumed by the fuel cell 22. This eliminates the need for complex opening and closing control of the on-off valves 47 and 49 during depressurization, as in the conventional method. As can be seen from the pressure reducing process period from time t2 to time t3 in Figure 2, both the on-off valves 47 and 49 are maintained in an open state during that period.

[0132] At the same time, in this third depressurization method, the control device 28 adjusts the pressure reducing valve 52 and the pressure reducing valve 56 on the hydrogen depressurization region 82 side so that the set pressure Psa of the pressure reducing valve 52 is lower than the set pressure Psb of the pressure reducing valve 56 (Psa <Psb)。

[0133] With this setting, only the high-pressure hydrogen remaining in the hydrogen depressurization region 82 flows into the fuel cell 22 through the pressure reducing valve 56 and the bypass path 46, as shown by the thick dashed line in Figure 5, and hydrogen does not flow into the hydrogen supply path 44 in which the pressure reducing valve 52 is provided. In other words, only the hydrogen in the hydrogen depressurization region 82, which is the region that requires depressurization treatment, is consumed by the fuel cell 22. This eliminates the need for complex control of the on-off valves 48 and 50 as in the conventional method. As can be seen from the pressure reducing treatment period from time t2 to time t3 in Figure 2, both the on-off valves 48 and 50 are maintained in an open state during that period. The control device 28 charges the battery 23 with the power generated from the oxygen and hydrogen consumed in the fuel cell 22 during the depressurization process from time t2 to time t3.

[0134] (2) FIG. 6 is a schematic diagram illustrating a third depressurization method (2) in which oxygen in the oxygen depressurization region 81 and hydrogen in the hydrogen depressurization region 82 are consumed preferentially by the fuel cell 22.

[0135] When the above-mentioned third decompression method (1) is performed, the hydrogen in the hydrogen decompression region 82 is completely consumed before the oxygen in the oxygen decompression region 81 due to the electrochemical reaction (2H2 + O2 → 2H2O) in the fuel cell 22 consuming 2 moles of hydrogen for every 1 mole of oxygen.

[0136] In this case, the control device 28 adjusts the set pressure Psa of the pressure reducing valve 52 so that the set pressure Psa of the pressure reducing valve 52 becomes the pressure measured by the pressure sensor 62 in the hydrogen depressurization region 82 .

[0137] As a result, as shown by the thick dashed line in FIG. 6, hydrogen that is insufficient in the hydrogen depressurization region 82 can be supplied from the hydrogen tank 20 to the fuel cell 22. In this case, the electrochemical reaction in the fuel cell 22 continues, and the high-pressure oxygen in the oxygen depressurization region 81 can be completely consumed. Depending on the ratio of the volumes of the oxygen depressurization region 81 and the hydrogen depressurization region 82 and the ratio of the pressures of the oxygen depressurization region 81 and the hydrogen depressurization region 82, the oxygen in the oxygen depressurization region 81 may be completely consumed before the hydrogen in the hydrogen depressurization region 82. Even in this case, the electrochemical reaction in the fuel cell 22 can continue based on the same principle, and all of the high-pressure hydrogen in the hydrogen depressurization region 82 can be consumed. This concludes the detailed explanation of the depressurization process.

[0138] 2, at time t3, which is the end time of the depressurization process, the on-off valve 47 of the bypass path 45 and the on-off valve 48 of the bypass path 46 are closed. Thereafter, between time t3 and time t4, the fuel cell 22 performs power generation using the oxygen gas and hydrogen gas stored in the oxygen tank 16 and the hydrogen tank 20. When the power generation operation of the fuel cell 22 is stopped at time t4, the operation of the regenerative fuel cell system 10 ends.

[0139] The following additional notes are further disclosed regarding the above embodiment.

[0140] (Appendix 1) The regenerative fuel cell system (10) of the present disclosure is a regenerative fuel cell system having a fuel cell (22) that generates electricity through an electrochemical reaction between oxygen gas and hydrogen gas, and includes a pressure booster (18, 12) that generates either pressurized oxygen gas or pressurized hydrogen gas, a supply mechanism (17, 17A, 17B) for supplying the gas to the fuel cell, and a control device (28). The supply mechanism includes a gas supply path (43, 44) that supplies the gas from the pressure booster to the fuel cell, a tank (16, 20) provided on the gas supply path and storing the gas pressurized by the pressure booster, and a branch (BP) of the gas supply path between the pressure booster and the tank. The gas supply system further comprises a bypass path (45, 46) that merges into a junction (MP) of the gas supply path between the tank and the fuel cell, a supply pressure reducing valve (51, 52) that is provided in the gas supply path between the tank and the junction, a bypass pressure reducing valve (56, 58) that is provided in the bypass path, and an on-off valve (47, 48, 49, 50) that enables the gas to be supplied to the fuel cell, and when the boost device starts a boost stop operation, the control device stops the supply of the gas to the tank and opens the on-off valve, and when in the open state, lowers the set pressure of the supply pressure reducing valve (51, 52) below the set pressure of the bypass pressure reducing valve (56, 58) to perform a depressurization process of the boost device.

[0141] In this way, when performing the depressurization process of the booster device, the gas remaining in the gas depressurization area can be supplied to the fuel cell via the bypass pressure reducing valve by the simple method of opening the on-off valve and setting the set pressure of the supply pressure reducing valve lower than the set pressure of the bypass pressure reducing valve.

[0142] (Appendix 2) In the regenerative fuel cell system described in Supplementary Note 1, the control device may calculate the power generation current of the fuel cell based on the gas consumption amount while the depressurization process is being performed, and control the depressurization speed during the depressurization process.

[0143] In this case, the gas consumption amount can be controlled with high precision by controlling the generated current, and therefore the depressurization process can be performed at an accurate depressurization speed (depressurization speed).

[0144] (Appendix 3) In the regenerative fuel cell system described in Appendix 1, the control device may determine the power generation current during the depressurization process by referring to the relationship characteristics between the power generation current of the fuel cell that have been measured and stored in advance and the depressurization rate during the depressurization process. This makes it possible to more easily determine the generated current for controlling the pressure reduction rate.

[0145] (Appendix 4) In the regenerative fuel cell system described in Appendix 1, a pressure sensor (61, 62) may further be provided between the boost device and the branching section, and the control device may measure the pressure reduction rate of the pressure sensor during execution of the depressurization process to obtain a measured pressure reduction rate, and adjust the power generation current so that the difference between the measured pressure reduction rate and a target pressure reduction rate becomes small. This allows for easy adjustment of the generated current that controls the pressure reduction rate.

[0146] (Appendix 5) The regenerative fuel cell system described in Appendix 1 may further include a gas-liquid separator (14) to which gas that has not been pressurized by the pressure booster and water produced by power generation by the fuel cell are supplied, and an oxygen remover (33) disposed between the gas-liquid separator and the pressure booster, and the control device may react hydrogen gas and oxygen gas that cross-leak from the pressure booster to the gas-liquid separator in the oxygen remover to produce water during the depressurization process.

[0147] According to this, hydrogen gas and oxygen gas that cross-leak through the electrolyte membrane of the booster device during depressurization are reacted by a catalytic reaction to form water, so that depressurization can be carried out reliably.

[0148] (Appendix 6) In the regenerative fuel cell system described in Supplementary Note 5, the control device may apply a current to the pressure booster (18) during the depressurization process to boost the hydrogen gas by an amount corresponding to the cross-leak. This allows the pressure release process to be carried out more reliably.

[0149] (Appendix 7) The regenerative fuel cell system described in Appendix 6 may further include a pressure sensor (60) that detects the pressure of the hydrogen gas in the gas-liquid separator, and the control device may determine the current to be passed through the boost device based on feedback control that eliminates the deviation between the pressure value detected by the pressure sensor and a target pressure value. This allows the depressurization of the gas remaining in the gas-liquid separator to be carried out more reliably.

[0150] 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]

[0151] 10...Regenerative fuel cell system 12...Water electrolysis device 13, 19...power supply 14, 15, 24, 26...gas-liquid separator 16...Oxygen tank 17...Gas supply mechanism 17A: Oxygen supply mechanism 17B: Hydrogen supply mechanism 18...Hydrogen booster 20...Hydrogen tank 21...Water tank 22...Fuel cell 23...Battery 27...Current sensor 28...Control device 29, 30...Water supply lines 32...Hydrogen supply path 33...Oxygen remover 35...Hydrogen discharge passage 43...Oxygen supply passage 44...Hydrogen supply path 45, 46...Bypass paths 47~50...On-off valves 51~56, 58...Reducing valves 57, 59... Back pressure valve 60~62... Pressure sensor 63, 69...Temperature sensor 64, 72, 73...Drain valve 65...liquid water supply passage 81...oxygen depressurization area 82...Hydrogen decompression area

Claims

1. A regenerative fuel cell system having a fuel cell that generates electricity through an electrochemical reaction between oxygen gas and hydrogen gas, a pressure booster that generates one of the pressurized oxygen gas and the pressurized hydrogen gas, a supply mechanism that supplies the gas to the fuel cell, and a control device; The supply mechanism includes: a gas supply path that supplies the gas from the pressure booster to the fuel cell; a tank provided on the gas supply path and configured to store the gas pressurized by the pressure booster; a bypass path that branches off from a branching portion of the gas supply path between the pressure booster and the tank and joins a joining portion of the gas supply path between the tank and the fuel cell; a supply pressure reducing valve provided in the gas supply path between the tank and the junction; a bypass pressure reducing valve provided in the bypass passage; an on-off valve that allows the gas to be supplied to the fuel cell; The control device When the boosting device starts a boosting stop operation, the supply of the gas to the tank is stopped and the on-off valve is opened; the set pressure of the supply pressure reducing valve in the open state is set lower than the set pressure of the bypass pressure reducing valve, and the oxygen gas remaining in the oxygen depressurization region of one of the boosting devices that pressurizes the oxygen gas and the hydrogen gas remaining in the hydrogen depressurization region of the other boosting device that pressurizes the hydrogen gas are supplied to the fuel cell to generate power, thereby performing depressurization of the oxygen gas remaining in the oxygen depressurization region and the hydrogen gas remaining in the hydrogen depressurization region. Regenerative fuel cell system.

2. 2. The regenerative fuel cell system according to claim 1, The control device During the depressurization process, a power generation current of the fuel cell is calculated based on the gas consumption amount, and a depressurization speed during the depressurization process is controlled. Regenerative fuel cell system.

3. 2. The regenerative fuel cell system according to claim 1, The control device During the depressurization process, the generated current is determined by referring to a relationship characteristic between the generated current of the fuel cell, which has been measured and stored in advance, and the depressurization rate during the depressurization process. Regenerative fuel cell system.

4. 2. The regenerative fuel cell system according to claim 1, Furthermore, a pressure sensor is provided between the pressure booster and the branching portion, The control device During the depressurization process, the pressure sensor measures a depressurization rate to obtain a measured depressurization rate, and adjusts the power generation current of the fuel cell so that the difference between the measured depressurization rate and a target depressurization rate becomes small. Regenerative fuel cell system.

5. 2. The regenerative fuel cell system according to claim 1, a gas-liquid separator to which the gas not pressurized by the pressure booster and the water generated by the power generation of the fuel cell are supplied; an oxygen remover disposed between the gas-liquid separator and the pressure booster; The control device During the depressurization treatment, hydrogen gas and oxygen gas cross-leaking from the pressure booster to the gas-liquid separator are reacted in the oxygen remover to produce water. Regenerative fuel cell system.

6. 6. The regenerative fuel cell system according to claim 5, The control device During the depressurization process, a current is passed through the pressure booster to boost the hydrogen gas by an amount corresponding to the cross-leakage. Regenerative fuel cell system.

7. 7. The regenerative fuel cell system according to claim 6, Further, a pressure sensor is provided to detect the pressure of the hydrogen gas in the gas-liquid separator, The control device The current to be passed through the booster device is determined based on feedback control such that the deviation between the pressure value detected by the pressure sensor and a target pressure value is eliminated. Regenerative fuel cell system.

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