Regenerative fuel cell system

Abstract

The invention relates to a regenerative fuel cell system. When pressure relief processing of the hydrogen pressure increasing device (18) and the water electrolysis device (12) is performed, on-off valves (47, 48, 49, 50) for supplying hydrogen gas or oxygen gas to the fuel cell (22) are set in an open state, and the set pressure of the supply pressure reducing valves (51, 52) is adjusted to a value lower than the set pressure of the bypass pressure reducing valves (56, 58). Gas remaining in the gas pressure relief regions (81, 82) is supplied to the fuel cell (22) via bypass pressure relief valves (56, 58).

Description

Technical Field

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

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

[0003] Patent Document 1 (hereinafter referred to as prior art publication) discloses Figure 7 A regenerative fuel cell system 110 is shown.

[0004] The 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 124, an oxygen tank 142A, a hydrogen tank 142B, a gas-liquid separator 130, and a control device 118 that controls them.

[0005] In the regenerative fuel cell system 110 , normally, the water electrolysis device 122 and the hydrogen pressure booster 124 are operated while the power generation of the fuel cell 112 is stopped, so that the oxygen tank 142A and the hydrogen tank 142B are filled with a predetermined amount of gas.

[0006] During operation, the water electrolysis device 122 electrolyzes water supplied from the water tank 126 through the gas-liquid separator 130 to generate high-pressure oxygen and low-pressure hydrogen.

[0007] The high-pressure oxygen generated by the water electrolysis device 122 passes through the branch portion BP and the gas-liquid separator 164A and is stored in the oxygen tank 142A.

[0008] The low-pressure hydrogen generated by the water electrolysis device 122 is supplied to the hydrogen pressure boosting device 124 through the gas-liquid separator 130 .

[0009] The hydrogen pressure boosting device 124 boosts the pressure of low-pressure hydrogen to high-pressure hydrogen during operation. The boosted high-pressure hydrogen passes through the branch portion BP and the gas-liquid separator 164B and is stored in the hydrogen tank 142B.

[0010] When the water electrolysis device 122 and the hydrogen pressure boosting device 124 are operated and a predetermined amount of gas is filled in the oxygen tank 142A and the hydrogen tank 142B, a pressure relief process is performed on the water electrolysis device 122 and the hydrogen pressure boosting device 124 .

[0011] In this pressure relief process, high-pressure oxygen remaining at the outlet of the water electrolysis device 122 and its communication path and high-pressure hydrogen remaining at the outlet of the hydrogen pressure boosting device 124 and its communication path are supplied to the fuel cell 112 .

[0012] The fuel cell 112 consumes the supplied oxygen and hydrogen through electrochemical reactions, and uses the generated power to charge the battery 120. In this way, the water electrolysis device 122 and the hydrogen pressure boosting device 124 are depressurized (depressurized).

[0013] After the pressure relief process is performed, the operations of the water electrolysis device 122 and the hydrogen pressure boosting device 124 are stopped.

[0014] Thereafter, the fuel cell 112 can continue to generate electricity due to the electrochemical reaction between the oxygen supplied from the oxygen tank 142A and the hydrogen supplied from the hydrogen tank 142B.

[0015] When the water electrolysis process in the water electrolysis device 122 and the pressure increase process in the hydrogen pressure increase device 124 are stopped without performing the pressure relief process described above, the high-pressure hydrogen generated in the hydrogen pressure increase device 124 cross-permeates within the hydrogen pressure increase device 124. The cross-permeated hydrogen flows back to the gas-liquid separator 130, thereby increasing the pressure of the hydrogen in the gas-liquid separator 130.

[0016] When the pressure of hydrogen in the gas-liquid separator 130 rises to or above a threshold pressure, a relief valve (not shown) provided in the gas-liquid separator 130 opens, and hydrogen as the circulating medium is discharged to the outside.

[0017] Furthermore, when the water electrolysis process in the water electrolysis device 122 and the pressure boosting process in the hydrogen pressure boosting device 124 are stopped without performing the pressure relief process, the high-pressure oxygen generated in the water electrolysis device 122 cross-permeates within the water electrolysis device 122. The cross-permeated oxygen flows back into the gas-liquid separator 130, thereby increasing the oxygen pressure within the gas-liquid separator 130.

[0018] When the pressure of oxygen in the gas-liquid separator 130 rises to or above a threshold pressure, a relief valve (not shown) provided in the gas-liquid separator 130 opens, and the circulating medium, ie, hydrogen and oxygen, is discharged to the outside.

[0019] Therefore, the regenerative fuel cell system 110 requires a pressure relief process.

[0020] In order to perform appropriate pressure relief processing, the regenerative fuel cell system 110 disclosed in a conventional publication is provided with flow control valves 160A and 160B.

[0021] During the pressure relief process, the control device 118 calculates the pressure reduction amount per unit time (pressure reduction rate) of the pressure detected by the pressure sensors 162A and 162B. The control device 118 controls the flow rates of the flow control valves 160A and 160B to perform pressure relief so that the difference between the measured pressure reduction rate and the target pressure reduction rate is reduced.

[0022] Furthermore, in the regenerative fuel cell system 110 disclosed in the prior art, the first on-off valves 146A, 146B and the second on-off valves 148A, 148B are precisely controlled to open and close in order to eliminate the timing difference in the completion of the decompression of the high-pressure oxygen and high-pressure hydrogen.

[0023] Oxygen or hydrogen that is depressurized earlier is supplied from oxygen tank 142A or hydrogen tank 142B to fuel cell 22, thereby continuing power generation in fuel cell 112 and controlling gas consumption on the side that is depressurized later (paragraphs 0078 to 0082 of the previous publication).

[0024] Prior art literature

[0025] Patent Literature

[0026] Patent Document 1: Japanese Patent No. 7393450 Summary of the Invention

[0027] Problems to be solved by the invention

[0028] However, the above-mentioned conventional pressure relief treatment (pressure relief method) has the first to third problems described below.

[0029] [First question]

[0030] In pressure relief control using flow control valves 160A and 160B to control the flow rate, the primary and secondary pressures of the flow control valves 160A and 160B fluctuate, making it difficult to accurately control the flow rate. Consequently, it is difficult to accurately control the actual pressure reduction rate to match the target pressure reduction rate.

[0031] [Second question]

[0032] During the depressurization process, when a pressure differential develops between the stacks of the water electrolyzer 122 and the hydrogen pressure booster 124, gas cross-permeation occurs from the high-pressure side of the stack to the low-pressure side through the electrolyte membrane. This cross-permeation causes the pressure on the low-pressure side of the stack to rise, resulting in a pressure increase within the gas-liquid separator 130. This causes the relief valve (not shown) installed in the gas-liquid separator 130 to open, discharging the gas to the outside, causing the gas to disappear.

[0033] [Third Question]

[0034] Since the timings of completing the decompression of oxygen and hydrogen differ, the first on-off valves 146A and 146B and the second on-off valves 148A and 148B are controlled to cope with the difference. However, this on-off control becomes extremely complicated.

[0035] The object of the present invention is to solve the above-mentioned problems.

[0036] Solutions for solving problems

[0037] An aspect of the present disclosure relates to a regenerative fuel cell system having a fuel cell that generates electricity through an electrochemical reaction between oxygen and hydrogen, wherein the regenerative fuel cell system comprises: a boosting device (a pair of a hydrogen boosting device and a water electrolysis device) that generates a gas of either the boosted oxygen or the boosted hydrogen; a supply mechanism (two) for supplying the gas to the fuel cell; and a control device, wherein the supply mechanism comprises: a gas supply path that supplies the gas from the boosting device to the fuel cell; a tank that is provided on the gas supply path and stores the gas boosted by the boosting device; and a bypass path that connects the boosting device and the tank. The gas supply path branches off at a branch portion between the two branches and merges at a confluence portion of the gas supply path between the tank and the fuel cell; a supply pressure reducing valve, which is provided between the tank and the confluence portion in the gas supply path; a bypass pressure reducing valve, which is provided in the bypass path; and an on-off valve, which can supply the gas to the fuel cell. When the boost stop action of the boosting device starts, the control device stops supplying the gas to the tank and sets the on-off valve to an open valve state. The control device makes the set pressure of the supply pressure reducing valve in the open valve state lower than the set pressure of the bypass pressure reducing valve to perform the pressure relief processing of the boosting device.

[0038] Effects of the Invention

[0039] According to the above aspect, when the booster device performs pressure relief processing, the on-off valve for supplying gas to the fuel cell is opened, and the set pressure of the supply pressure reducing valve is lower than the set pressure of the bypass pressure reducing valve. Therefore, gas remaining in the gas pressure relief region of the booster device can be supplied to the fuel cell via the bypass pressure reducing valve. The fuel cell consumes gas through an electrochemical reaction to generate electricity.

[0040] The above-mentioned objects, features, and advantages will be easily understood from the following description of the embodiments described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram showing a regenerative fuel cell system according to an embodiment.

[0042] Figure 2 This is a timing diagram involved in the pressure relief process.

[0043] Figure 3 It is an explanatory diagram of the oxygen decompression area and the hydrogen decompression area.

[0044] Figure 4This is an explanatory diagram of the operation of converting oxygen and hydrogen that cross-permeate from the high-pressure side to the low-pressure side during the pressure relief treatment into water using an oxygen removal catalyst.

[0045] Figure 5 This diagram illustrates the setting pressure of the pressure reducing valve in the first half of the pressure relief process.

[0046] Figure 6 This diagram illustrates the set pressure of the pressure reducing valve in the second half of the pressure relief process.

[0047] Figure 7 This is a schematic diagram showing a conventional regenerative fuel cell system for explaining problems of the conventional method. DETAILED DESCRIPTION

[0048] Figure 1 This 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 vacuum spaces such as outer space and the lunar surface, and can also be used in the atmosphere.

[0049] [Overall Description of the Regenerative Fuel Cell System 10]

[0050] The regenerative fuel cell system 10 basically includes 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 booster 18, a hydrogen tank 20, a water tank 21, a fuel cell 22, a battery 23, a gas-liquid separator (oxygen exhaust gas-liquid separator) 24, a gas-liquid separator (hydrogen exhaust gas-liquid separator) 26 and a control device 28.

[0051] The control device 28 controls all components of the regenerative fuel cell system 10 .

[0052] In this embodiment, the water electrolysis device 12 is a high differential pressure water electrolysis stack apparatus (EC) that generates electrochemically compressed high-pressure oxygen and unpressurized hydrogen (low-pressure hydrogen) by electrolyzing water.

[0053] Water for water electrolysis is supplied from the water tank 21 to the water electrolysis device 12 via the water supply path 29 , the gas-liquid separator 14 , and the water supply path 30 .

[0054] A water supply passage 29 connects the water tank 21 and the gas-liquid separator 14. A pump 25 is provided in the water supply passage 29. Pump 25 is controlled on and off by a controller 28. When turned on, pump 25 imparts mechanical energy to the water stored in the water tank 21, causing water to be supplied from the water tank 21 to the gas-liquid separator 14. When turned off, pump 25 stops the water supply. Similarly, all other pumps described below impart mechanical energy to the fluid when turned on and stop the flow of the fluid when turned off.

[0055] The water electrolysis device 12 has one or more cells. Each cell includes a membrane electrode assembly (MEA) formed by sandwiching an electrolyte membrane 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.

[0056] The water electrolysis device 12 supplies water supplied from the gas-liquid separator 14 to the cathode electrode of each cell. The cell electrolyzes the water based on the voltage applied to the anode and cathode electrodes from the power supply 13. In this case, the anode electrode generates high-pressure oxygen gas (e.g., in the range of 1 MPa to 100 MPa), while the cathode electrode generates unpressurized hydrogen gas.

[0057] The control device 28 can change the voltage of the power source 13 applied between the anode electrode and the cathode electrode. The power of the power source 13 can also use the power of the battery 23.

[0058] The water electrolysis device 12 collects high-pressure oxygen generated in each cell and outputs the released gas containing the oxygen to the oxygen supply mechanism 17A through the oxygen supply path 43. The released gas contains water vapor vaporized by the heat of the water electrolysis device 12 or the like.

[0059] At the same time, the water electrolysis device 12 collects the hydrogen gas generated in each cell and the remaining water (unreacted water) that has not been electrolyzed, and outputs the discharged fluid containing the hydrogen gas and unreacted water to the hydrogen supply path 32. The discharged fluid also contains water vapor that has been vaporized by the heat of the water electrolysis device 12.

[0060] The discharged fluid (hydrogen gas and unreacted water) output from the water electrolysis device 12 to the hydrogen supply line 32 flows into the gas-liquid separator 14. The gas-liquid separator 14 separates the discharged fluid into a gas component (hydrogen gas and water vapor) and a liquid component (liquid water). By turning on the pump 34 of the hydrogen supply line 32, which is located at the outlet of the gas-liquid separator 14, the gas component is supplied to the hydrogen pressure booster 18.

[0061] A pressure sensor 60 is provided on the hydrogen supply path 32 near the outlet of the gas-liquid separator 14 , and an oxygen remover 33 is provided between the outlet of the gas-liquid separator 14 and the inlet of the pump 34 .

[0062] The oxygen remover 33 reacts oxygen gas discharged from the water electrolysis device 12 to the gas-liquid separator 14 during the pressure relief process with hydrogen gas discharged from the hydrogen pressure increasing device 18 to the gas-liquid separator 14 using an oxygen removal catalyst to produce water.

[0063] More specifically, during the pressure relief process, oxygen cross-permeates from the high-pressure side of the water electrolysis device 12 to the low-pressure side through the electrolyte membrane. The cross-permeated oxygen is discharged to the gas-liquid separator 14 via the hydrogen supply path 32. During the pressure relief process, hydrogen cross-permeates from the high-pressure side of the hydrogen booster 18 to the low-pressure side through the electrolyte membrane. The cross-permeated hydrogen is discharged to the gas-liquid separator 14 via the hydrogen discharge path 35. The control device 28 turns on the pump 34. When the pump 34 is turned on and the cross-permeated oxygen and cross-permeated hydrogen flow through the hydrogen supply path 32, the oxygen remover 33 uses an oxygen removal catalyst to react the oxygen with the hydrogen to form water.

[0064] The hydrogen pressure booster 18 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 hydrogen pressure booster 18 is a proton exchange membrane. A power supply 19 is connected to the anode electrode and the cathode electrode.

[0065] The control device 28 can change the voltage of the power source 19 applied between the anode electrode and the cathode electrode. The power of the power source 19 can also use the power of the battery 23.

[0066] The hydrogen booster 18 supplies hydrogen gas flowing from the hydrogen supply path 32 to the anode electrode. The hydrogen booster 18 ionizes the hydrogen gas based on the voltage applied from the power supply 19. Protons generated by the ionized hydrogen gas reach the cathode electrode via the electrolyte membrane (proton exchange membrane). The protons reaching the cathode electrode combine with electrons supplied from the power supply 19 (electrons generated during the ionization) and return to hydrogen gas.

[0067] The hydrogen booster 18 generates pressurized hydrogen gas by transferring protons from the anode electrode to the cathode electrode. For example, the hydrogen gas is compressed within a range of 1 MPa to 100 MPa. Thus, the hydrogen booster 18 is an electrochemical hydrogen compressor (EHC) that electrochemically compresses hydrogen gas.

[0068] The hydrogen pressure booster 18 outputs the remaining hydrogen gas that has not been ionized to the hydrogen discharge path 35 . The hydrogen discharge path 35 is a flow path (pipeline) for discharging the hydrogen gas from the hydrogen pressure booster 18 to the gas-liquid separator 14 .

[0069] The hydrogen pressure boosting device 18 outputs the discharged gas including the pressurized hydrogen gas to the hydrogen supply mechanism 17B. The discharged gas contains water vapor vaporized by heat from the hydrogen pressure boosting device 18 or the like.

[0070] The oxygen supply mechanism 17A and the hydrogen supply mechanism 17B constitute a gas supply mechanism 17 . The gas supply mechanism 17 is a mechanism for supplying reaction gases (hydrogen and oxygen) to the fuel cell 22 .

[0071] The oxygen supply mechanism 17A supplies the oxygen gas generated in the water electrolysis device 12 to the fuel cell 22. The hydrogen supply mechanism 17B supplies the hydrogen gas generated in the hydrogen pressure boosting device 18 to the fuel cell 22.

[0072] [Description of Oxygen Supply Mechanism 17A]

[0073] The oxygen supply mechanism 17A includes 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 (pressure reducing valve for supply) 51, a pressure reducing valve 53, a pressure reducing valve (pressure reducing valve for bypass) 58, a back pressure valve 57, a pressure sensor 61, a temperature sensor 63, and a gas-liquid separator 15.

[0074] Oxygen supply path 43 is a flow path for supplying high-pressure oxygen generated in water electrolysis device 12 to fuel cell 22 via oxygen tank 16. One end of oxygen supply path 43 is connected to water electrolysis device 12, and the other end of oxygen supply path 43 is connected to fuel cell 22 via pressure reducing valve 53.

[0075] The oxygen tank 16 is provided on the oxygen supply path 43. The oxygen tank 16 stores high-pressure oxygen gas generated by the water electrolysis device 12.

[0076] The bypass passage 45 branches from a branch portion Bpo (BP) of the oxygen supply passage 43 between the back pressure valve 57 and the gas-liquid separator 15 , and merges at a confluence portion Mpo (MP) of the oxygen supply passage 43 between the oxygen tank 16 and the fuel cell 22 .

[0077] The on-off valve 47 is provided in the bypass passage 45 . The on-off valve 49 is provided between the confluence portion Mpo in the oxygen supply passage 43 and the oxygen tank 16 .

[0078] The on-off valves 47 and 49 are solenoid valves, respectively, and are cutoff valves that are opened and closed by the on-off control of the control device 28 .

[0079] The pressure reducing valve 51 is provided between the confluence portion Mpo in the oxygen supply path 43 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.

[0080] The pressure reducing valve 53 is provided between the confluence portion Mpo in the oxygen supply path 43 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 path 45 to a predetermined pressure.

[0081] The back pressure valve 57 is provided between the branch portion Bpo in the oxygen supply path 43 and the oxygen tank 16. The back pressure valve 57 applies pressure (back pressure) to the water electrolysis device 12 through the gas space of the gas-liquid separator 15. As a result, the pressure of the oxygen gas generated at the anode electrode of each cell of the water electrolysis device 12 increases, becoming higher than the pressure of the hydrogen gas generated at the cathode electrode.

[0082] The water electrolysis device 12 generates oxygen gas at a higher pressure at the anode electrode than the hydrogen gas generated at the cathode electrode. This suppresses cross-permeation of hydrogen gas from the cathode electrode to the anode electrode through the electrolyte membrane. Consequently, a decrease in the amount of hydrogen gas supplied from the water electrolysis device 12 to the hydrogen pressure booster 18 can be prevented.

[0083] The pressure sensor 61 is provided between the water electrolysis device 12 and the branch portion Bpo in the oxygen supply path 43. The pressure sensor 61 detects the pressure of oxygen supplied from the water electrolysis device 12 to the oxygen supply path 43. The pressure sensor 61 outputs a signal indicating the detected pressure to the control device 28.

[0084] Temperature sensor 63 is provided in oxygen supply path 43 between water electrolysis device 12 and gas-liquid separator 15. Temperature sensor 63 detects the temperature of oxygen supplied from water electrolysis device 12 to oxygen supply path 43. Temperature sensor 63 outputs a signal indicating the detected temperature to control device 28.

[0085] The gas-liquid separator 15 is provided in the oxygen supply path 43 between the water electrolysis device 12 and the branch portion Bpo.

[0086] The oxygen gas released from the water electrolysis device 12 to the oxygen supply path 43 contains water vapor in addition to oxygen gas. The gas-liquid separator 15 cools the water vapor in the released gas to produce liquid water, and then supplies the oxygen gas, from which the water has been removed, to the oxygen tank 16. This prevents the oxygen tank 16 from becoming wet. As a result, the durability of the oxygen tank 16 can be improved without excessive rust prevention treatment.

[0087] 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 (communication path) for supplying liquid water stored in the gas-liquid separator 15 to the gas-liquid separator 14. The liquid water supply path 65 is provided with a drain valve 64 which is an on-off valve.

[0088] Liquid water obtained from the water vapor in the oxygen released by 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 line 65. This saves water used in the water electrolysis device 12. The gas-liquid separator 14 stores water to be supplied to the water electrolysis device 12. A water supply line 30 is provided between the gas-liquid separator 14 and the water electrolysis device 12. A pump 31 is provided on the water supply line 30.

[0089] [Description of Hydrogen Supply Mechanism 17B]

[0090] 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 (pressure reducing valve for supply) 52, a pressure reducing valve 54, a pressure reducing valve (pressure reducing valve for bypass) 56, a back pressure valve 59, a pressure sensor 62 and a temperature sensor 69.

[0091] The hydrogen supply path 44 is a flow path for supplying hydrogen gas pressurized by the hydrogen pressurizing device 18 to the fuel cell 22 via the hydrogen tank 20 . One end of the hydrogen supply path 44 is connected to the hydrogen pressurizing device 18 , and the other end is connected to the fuel cell 22 via a pressure reducing valve 54 .

[0092] The hydrogen tank 20 is provided on the hydrogen supply path 44. The hydrogen tank 20 stores high-pressure hydrogen gas whose pressure is increased by the hydrogen pressure increasing device 18.

[0093] The bypass passage 46 branches off from a branch portion Bph (BP) of the hydrogen supply passage 44 between the hydrogen pressure boosting device 18 and the hydrogen tank 20 , and merges at a confluence portion Mph (MP) of the hydrogen supply passage 44 between the hydrogen tank 20 and the fuel cell 22 .

[0094] The on-off valve 48 is provided in the bypass passage 46 . The on-off valve 50 is provided between the merging portion Mph in the hydrogen supply passage 44 and the hydrogen tank 20 .

[0095] The on-off valves 48 and 50 are solenoid valves, respectively, and are cut-off valves that are opened and closed by the on-off control of the control device 28 .

[0096] The pressure reducing valve 52 is provided between the confluence portion Mph in the hydrogen supply path 44 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.

[0097] The pressure reducing valve 54 is provided between the junction Mph in the hydrogen supply path 44 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 path 46 to a predetermined pressure.

[0098] The back-pressure valve 59 is provided between the branch portion Bph in the hydrogen supply path 44 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 cell of the hydrogen booster 18, making it higher than the pressure of the hydrogen gas supplied to the anode electrode.

[0099] The pressure sensor 62 is provided between the hydrogen pressure boosting device 18 and the branch portion Bph in the hydrogen supply path 44. 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.

[0100] The temperature sensor 69 is provided between the hydrogen pressure booster 18 and the branch portion Bph in the hydrogen supply path 44. The temperature sensor 69 detects the temperature of the hydrogen gas supplied from the hydrogen pressure booster 18 to the hydrogen supply path 44. The temperature sensor 69 outputs a signal indicating the detected temperature to the control device 28.

[0101] [Description of the Fuel Cell 22]

[0102] The oxygen supply mechanism 17A further includes an oxygen exhaust passage 76 , a gas-liquid separator 24 , a circulation pump 70 , and a drain valve 72 .

[0103] The hydrogen supply mechanism 17B further includes a hydrogen exhaust passage 77 , a gas-liquid separator 26 , a circulation pump 71 , and a drain valve 73 .

[0104] The fuel cell 22 has a stack formed of a plurality of cells electrically connected in series. Each cell includes a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between an anode electrode and a cathode electrode.

[0105] The fuel cell 22 supplies oxygen gas supplied from the oxygen tank 16 via the pressure reducing valves 51 and 53 to the cathode electrodes of the cells. The fuel cell 22 supplies hydrogen gas supplied from the hydrogen tank 20 via the pressure reducing valves 52 and 54 to the anode electrodes of the cells.

[0106] Each cell of the fuel cell 22 generates electricity through an electrochemical reaction between oxygen and hydrogen.

[0107] The power generated by the fuel cell 22 is supplied to a load (main load) (not shown) and to auxiliary equipment loads including the control device 28. The remainder of the generated power is charged to the battery 23. The generated current Ifc of the fuel cell 22 is detected by the current sensor 27 and obtained by the control device 28. Furthermore, the stored voltage of the battery 23 and the generated voltage of the fuel cell 22 are detected by voltage sensors (not shown) and obtained by the control device 28.

[0108] Oxygen-containing exhaust gas including unreacted oxygen in each cell of the fuel cell 22 is supplied to the oxygen supply path 43 via the oxygen circulation path 66. The oxygen circulation path 66 is a flow path for returning the oxygen-containing exhaust gas discharged from the fuel cell 22 to the oxygen supply path 43.

[0109] 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 path 76 into a gas component (oxygen and water vapor) and a liquid component (liquid water). The gas component is supplied back to the fuel cell 22 by the circulation pump 70. On the other hand, the liquid component is supplied to the water tank 21 via the on-off valve, namely the drain valve 72.

[0110] Meanwhile, hydrogen-containing exhaust gas including unreacted hydrogen in each cell of the fuel cell 22 is supplied to the hydrogen supply path 44 via the 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.

[0111] 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 path 77 into a gas component (hydrogen gas and water vapor) and a liquid component (liquid water). The gas component is supplied back to the fuel cell 22 by the circulation pump 71. On the other hand, the liquid component is supplied to the water tank 21 via the on-off valve, namely the drain valve 73.

[0112] [Description of Control Device 28]

[0113] The control device 28 comprehensively controls all components of the regenerative fuel cell system 10 to execute the operation of the regenerative fuel cell system 10 .

[0114] 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 can be composed of volatile memory and non-volatile memory. Examples of processors include a CPU (Central Processing Unit) and an MCU (Micro Controller Unit). Examples of volatile memory include RAM (Random Access Memory). Examples of non-volatile memory include ROM (Read Only Memory) and flash memory.

[0115] The control device 28 turns on the power supply 13 of the water electrolysis device 12 to apply voltage to the anode and cathode electrodes of the cells and turns on the pump 31 to supply water from the gas-liquid separator 14 to the water electrolysis device 12 .

[0116] As a result, the water electrolysis device 12 enters the operating state (pressure boosting state, water electrolysis state), and performs electrolysis of water (water electrolysis).

[0117] When the control device 28 stops the application of voltage from the power supply 13 to the cells and stops 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).

[0118] The controller 28 also turns on the power supply 19 of the hydrogen pressure booster 18 to apply voltage to the anode and cathode electrodes of the cell and turns on the pump 34 to supply hydrogen gas from the gas-liquid separator 14 to the hydrogen pressure booster 18 .

[0119] As a result, the hydrogen pressure booster 18 enters an operating state (pressurization state) and increases the pressure of hydrogen gas. When the control device 28 stops the application of voltage from the power supply 19 to the cell and stops the supply of hydrogen gas to the hydrogen pressure booster 18, the hydrogen pressure booster 18 enters a non-operating state (after a depressurization state, it enters a stopped state).

[0120] [Description of Operation of Regenerative Fuel Cell System 10]

[0121] Basically, refer to Figure 2 The operation of the regenerative fuel cell system 10 configured as described above will be described below with reference to a timing chart (operation sequence).

[0122] Figure 2 In the figure, EC 12 represents a water electrolysis device 12 , EHC 18 represents a hydrogen booster device 18 , FC 22 represents a fuel cell 22 , and RFC 10 represents a regenerative fuel cell system 10 .

[0123] The regenerative fuel cell system 10 according to this embodiment executes a characteristic pressure relief process (processing between time point t2 and time point t3 ) described in detail below.

[0124] To facilitate understanding of the pressure reduction process, the oxygen pressure increase (water electrolysis) process and the hydrogen pressure increase process from time point t0 to time point t2 will be described first.

[0125] At a point in time immediately before time t0, the fuel cell 22, the water electrolyzer 12, and the hydrogen pressure booster 18 are stopped, and the regenerative fuel cell system 10 is stopped. While the regenerative fuel cell system 10 is stopped, the shutoff valves for supplying oxygen and hydrogen to the fuel cell 22, namely, the on-off valve 47, the on-off valve 48, the on-off valve 49, and the on-off valve 50, are closed.

[0126] At time t0, operation of the regenerative fuel cell system 10 begins. First, the controller 28 turns on the pumps 25 and 31, supplying water stored in the water tank 21 to the cathode electrodes of each cell of the water electrolysis device 12 via the water supply line 29, the gas-liquid separator 14, and the water supply line 30.

[0127] Then, the control device 28 causes the power supply 13 to supply a predetermined current to the cathode electrode and the anode electrode of each cell of the water electrolysis device 12 , thereby starting a voltage boosting operation of the water electrolysis device 12 .

[0128] In this case, oxygen gas with a pressure boost is generated at the anode electrode due to the electrolysis of water, and the 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.

[0129] The reaction formula on the anode electrode side of the water electrolysis device 12 is shown below.

[0130] 2OH - →(1 / 2)O2+H2O+2e -

[0131] When the water electrolysis device 12 starts the pressure boosting operation, hydrogen gas is generated at the cathode electrode due to water electrolysis. This hydrogen gas is released from the water electrolysis device 12 and supplied to the anode electrode of each cell of the hydrogen pressure boosting device 18 via the connected pump 34 and hydrogen supply path 32 .

[0132] The reaction formula on the cathode electrode side of the water electrolysis device 12 is shown below.

[0133] 2H2O+2e - →H2+2OH -

[0134] The control device 28 checks the supply of hydrogen gas to the hydrogen supply path 32 based on the pressure detected by the pressure sensor 60 provided in the hydrogen supply path 32 .

[0135] Upon confirming the supply of hydrogen to the hydrogen supply path 32, at time t1, the control device 28 controls the power supply 19 to cause the hydrogen pressure boosting device 18 to perform a pressure boosting operation. When the hydrogen pressure boosting device 18 begins the pressure boosting operation, hydrogen gas, which is pressurized by ionization, is generated at the cathode electrode. This pressurized hydrogen gas is supplied to the hydrogen tank 20 via the hydrogen supply path 44 of the hydrogen supply mechanism 17B.

[0136] The reaction formula on the cathode electrode side of the hydrogen pressure boosting device 18 is shown below.

[0137] 2H + +2e - →H2

[0138] The reaction formula on the anode electrode side of the hydrogen pressure boosting device 18 is shown below.

[0139] H2→2H + +2e -

[0140] By the water electrolysis process and hydrogen pressure increase process from time point t1 to time point t2, when the hydrogen tank 20 and the oxygen tank 16 store predetermined amounts of hydrogen and oxygen, respectively, at time point t2, the control device 28 starts the pressure reduction process at time point t2.

[0141] [Detailed description of pressure relief treatment]

[0142] Figure 3 1 and 2 are explanatory diagrams schematically showing regions where decompression treatment should be performed (gas decompression regions surrounded by dotted lines, namely, an oxygen decompression region 81 and a hydrogen decompression region 82 ).

[0143] On the oxygen supply side, the region of the oxygen supply path 43 extending to the primary side of the back pressure valve 57 communicating with the anode electrode of the water electrolysis device 12 and the region of the bypass path 45 extending to the primary side of the pressure reducing valve 58 communicating with the anode electrode of the water electrolysis device 12 correspond to the oxygen pressure relief region 81. The oxygen pressure relief region 81 is a region where high-pressure oxygen gas exists in the flow path (space) extending from the anode electrode of the water electrolysis device 12 to the confluence portion Mpo when the water electrolysis device 12 stops the pressure boost operation.

[0144] On the hydrogen supply side, the area 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 boosting device 18 and the area of ​​the bypass path 46 up to the primary side of the pressure reducing valve 56 communicating with the cathode electrode of the hydrogen boosting device 18 correspond to the hydrogen pressure relief area 82.

[0145] The pressure relief process (pressure relief step) will be described below in the order of A. first pressure relief method (solution to the first problem), B. second pressure relief method (solution to the second problem), and C. third pressure relief method (solution to the third problem).

[0146] A. First pressure relief method (solution to the first problem)

[0147] In the above-mentioned [first problem], it is difficult to control the target decompression rate (decompression rate) of the oxygen gas and hydrogen gas to be decompressed.

[0148] In the first pressure relief method, the control device 28 controls the generated current Ifc according to the following calculation. In the first pressure relief method, the pressure relief rate can be controlled accurately and precisely by easily controlling the generated current Ifc.

[0149] The amount of hydrogen consumed in the fuel cell 22 can be calculated by the following formula (1).

[0150] Hydrogen consumption [mol / sec] = Ifc [A] / (2 × F [C / mol])… (1)

[0151] Here, F is the Faraday constant = 9.65×10 4 [C / mol].

[0152] The hydrogen-side decompression rate (hydrogen-side decompression rate) [kpA / sec] corresponding to the target decompression rate in the hydrogen decompression region 82 can be calculated by the following formula (2). Here, the volume of the hydrogen decompression region 82 (hydrogen-side volume [mL]) is known through design and actual measurement.

[0153] Hydrogen side decompression rate [kpA / sec] = hydrogen consumption [mol / sec] × R × gas temperature [K] × Z / hydrogen side volume [mL] (2)

[0154] Here, R is the gas constant and Z is the compressibility factor.

[0155] Regarding the compressibility factor Z, while the molecular volume and intermolecular attraction are negligible in an ideal gas, when the gas pressure is high (as in real gases), intermolecular attraction exists, and the volume occupied by the molecules becomes non-negligible. The compressibility factor Z is defined as Z = PV / (nRT), and serves as a factor to correct for the effects of intermolecular attraction and the volume occupied by molecules. The compressibility factor 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. Therefore, the compressibility factor Z is calculated by varying these parameters in advance.

[0156] The oxygen consumption in the fuel cell 22 can be calculated by the following formula (3).

[0157] Oxygen consumption [mol / sec] = Ifc [A] / (4 × F [C / mol])… (3)

[0158] 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 formula (4). Here, the volume of the oxygen decompression region 81 (oxygen-side volume [mL]) is known through design and actual measurement.

[0159] Oxygen side decompression rate [kpA / sec] = oxygen consumption [mol / sec] × R × gas temperature [K] × Z / oxygen side volume [mL] (4)

[0160] The compression 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. Therefore, the compression coefficient Z is determined by changing these parameters in advance.

[0161] In this case, the hydrogen side decompression rate or the oxygen side decompression rate is set so that the generated current Ifc calculated by substituting equation (2) into equation (1) and the generated current Ifc calculated by substituting equation (4) into equation (3) are the same value.

[0162] In the actual pressure relief process, Figure 2 As shown, after the time point t2, all 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.

[0163] Furthermore, instead of the above calculation, the relationship between the generated current Ifc and the decompression rate may be measured in advance and recorded as a relationship characteristic in a storage device (not shown) within the control device 28. Alternatively, the control device 28 may determine the generated current Ifc based on the decompression rate while referring to the relationship characteristic.

[0164] In practice, the control device 28 preferably calculates the decompression rate of the pressure values ​​detected by the pressure sensors 61 and 62 (pressure decompression value per unit time: measured decompression rate) and adjusts the generated current Ifc by feedback control so as to reduce the difference from the target decompression rate.

[0165] B. Second pressure relief method (solution to the second problem)

[0166] Reference Figure 4 Schematic diagram for explanation.

[0167] In the pressure relief process of the first pressure relief method (solution to the first problem) described above, a pressure difference is generated between the electrolyte membranes of each stack of the water electrolysis device 12 and the hydrogen pressure boosting device 18. Therefore, a pressure difference occurs from the high pressure side to the low pressure side of each stack of the water electrolysis device 12 and the hydrogen pressure boosting device 18. Figure 4 The cross permeation of gases (cross permeation of oxygen that permeates the electrolyte membrane in the reverse direction and cross permeation of hydrogen that permeates the electrolyte membrane in the reverse direction) is shown by the thick dotted line in FIG.

[0168] The cross-permeated oxygen and hydrogen need to be depressurized (disposed of).

[0169] Regarding the cross permeation of oxygen in the water electrolysis device 12, as Figure 4 As shown, an oxygen remover 33 having an oxygen removal catalyst is used to react the hydrogen remaining in the gas-liquid separator 14 and the cross-permeated hydrogen supplied to the gas-liquid separator 14 from the hydrogen booster 18 through the hydrogen discharge path 35 with the cross-permeated oxygen supplied to the gas-liquid separator 14 from the water electrolysis device 12 through the hydrogen supply path 32 to form water, thereby releasing the pressure.

[0170] When the reaction is progressing in the oxygen remover 33 , the pump 34 is turned on to allow the cross-permeated oxygen and hydrogen to flow through the hydrogen supply path 32 .

[0171] Generally, in the cross permeation of oxygen and hydrogen, hydrogen with smaller molecules is more abundant. Therefore, hydrogen remains in the primary side of the hydrogen pressure booster 18 communicating with the hydrogen discharge path 35, that is, in the gas-liquid separator 14, causing the pressure to rise.

[0172] Therefore, in the pressure reduction control, the remaining hydrogen is pressurized by flowing current from the power supply 19 to the hydrogen pressure increasing device 18. The pressurized high-pressure hydrogen can be consumed by the third pressure reduction method described below.

[0173] In fact, it is also possible to determine the current flowing from the power supply 19 to the hydrogen boosting device 18 so that the deviation between the pressure value detected by the pressure sensor 60 (the pressure value of the gas-liquid separator 14) and the target pressure value (the allowable pressure value of the gas-liquid separator 14, i.e., the target pressure value) becomes zero.

[0174] C. The third pressure relief method (solution to the third problem)

[0175] (1) Figure 5 This is a schematic explanatory diagram for explaining the third decompression method (1) for causing the oxygen in the oxygen decompression region 81 and the hydrogen in the hydrogen decompression region 82 to be consumed preferentially in the fuel cell 22 .

[0176] In the third pressure relief 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 becomes a value lower than the set pressure Psd of the pressure reducing valve 58 on the oxygen pressure relief region 81 side (Psc <Psd)。

[0177] According to this setting, only the high-pressure oxygen remaining in the oxygen pressure relief area 81 is used as Figure 5 As shown by the thick dashed line in FIG, oxygen flows into the fuel cell 22 through the pressure reducing valve 58 and the bypass passage 45, while oxygen does not flow into the oxygen supply passage 43 provided with the pressure reducing valve 51. In other words, only the oxygen in the oxygen pressure relief region 81, which is the area requiring pressure relief, is consumed in the fuel cell 22. This eliminates the need for complex opening and closing control of the on-off valve 47 and the on-off valve 49 during pressure relief, as in conventional methods. Figure 2 As can be seen from the decompression processing period from the time point t2 to the time point t3, during this period, both the on-off valve 47 and the on-off valve 49 are maintained in the open state.

[0178] At the same time, in the third pressure relief method, the control device 28 adjusts the pressure reducing valve 52 and the pressure reducing valve 56 so that the set pressure Psa of the pressure reducing valve 52 becomes a value lower than the set pressure Psb of the pressure reducing valve 56 on the hydrogen pressure relief region 82 side (Psa <Psb)。

[0179] According to this setting, only the high-pressure hydrogen remaining in the hydrogen pressure relief region 82 is as follows Figure 5 As shown by the thick dashed line in FIG, hydrogen flows into the fuel cell 22 through the pressure reducing valve 56 and the bypass passage 46, and does not flow into the hydrogen supply passage 44 provided with the pressure reducing valve 52. In other words, only hydrogen in the hydrogen pressure relief region 82, which is the area requiring pressure relief, is consumed in the fuel cell 22. This eliminates the need for complex control of the on-off valve 48 and the on-off valve 50 as in the conventional method. Figure 2 As can be seen from the decompression processing period from the time point t2 to the time point t3, during this period, both the on-off valve 48 and the on-off valve 50 are maintained in the open state.

[0180] The control device 28 charges the battery 23 with the generated power generated by the oxygen and hydrogen consumed in the fuel cell 22 during the pressure relief process from the time point t2 to the time point t3 .

[0181] (2) Figure 6 This is a schematic explanatory diagram for explaining the third decompression method (2) in which the oxygen in the oxygen decompression region 81 and the hydrogen in the hydrogen decompression region 82 are preferentially consumed in the fuel cell 22 .

[0182] When the third decompression method (1) is executed, the hydrogen in the hydrogen decompression area 82 is completely consumed before the oxygen in the oxygen decompression area 81 because 2 [mol] of hydrogen is consumed relative to 1 [mol] of oxygen through the electrochemical reaction (2H2+O2→2H2O) of the fuel cell 22.

[0183] Therefore, in this case, the control device 28 adjusts the setting pressure of the pressure reducing valve 52 so that the setting pressure Psa of the pressure reducing valve 52 becomes the pressure measured by the pressure sensor 62 of the hydrogen pressure relief region 82 .

[0184] From this, as Figure 6 As shown by the thick dashed line in FIG, an amount of hydrogen corresponding to the hydrogen shortage in the hydrogen pressure relief region 82 can be supplied from the hydrogen tank 20 to the fuel cell 22 .

[0185] In this case, the electrochemical reaction of the fuel cell 22 continues, thereby being able to consume all the high-pressure oxygen in the oxygen pressure relief region 81 .

[0186] Furthermore, due to the volume ratio of oxygen pressure relief region 81 to hydrogen pressure relief region 82, and the pressure ratio of oxygen pressure relief region 81 to hydrogen pressure relief region 82, the oxygen in oxygen pressure relief region 81 will be completely consumed before the hydrogen in hydrogen pressure relief region 82. Even in this case, due to the same principle, the electrochemical reaction of fuel cell 22 continues, thereby completely consuming the high-pressure hydrogen in hydrogen pressure relief region 82. The above is a detailed description of the pressure relief process.

[0187] Moreover, if Figure 2 As shown, at time t3, the end point of the pressure relief process, the on-off valve 47 of the bypass passage 45 and the on-off valve 48 of the bypass passage 46 are closed. From time t3 to time t4, the fuel cell 22 generates electricity using the oxygen and hydrogen stored in the oxygen tank 16 and hydrogen tank 20. At time t4, the fuel cell 22 ceases generating electricity, and the operation of the regenerative fuel cell system 10 ends.

[0188] Regarding the above-mentioned embodiment, the following supplementary notes are also disclosed.

[0189] (Note 1)

[0190] The regenerative fuel cell system 10 disclosed in the present invention has a fuel cell 22 that generates electricity by an electrochemical reaction between oxygen and hydrogen. In the regenerative fuel cell system, there are: a boosting device 18, 12 that generates a gas of either the boosted oxygen or the boosted hydrogen; a supply mechanism 17, 17A, 17B that supplies the gas to the fuel cell; and a control device 28, wherein the supply mechanism has: a gas supply path 43, 44 that supplies the gas from the boosting device to the fuel cell; a tank 16, 20 that is provided on the gas supply path and stores the gas boosted by the boosting device; a bypass path 45, 46 that branches from the gas supply path between the boosting device and the tank. The branch BP branches and merges at the confluence MP of the gas supply path between the tank and the fuel cell; the supply pressure reducing valves 51 and 52 are arranged between the tank and the confluence in the gas supply path; the bypass pressure reducing valves 56 and 58 are arranged in the bypass path; and the on-off valves 47, 48, 49 and 50 are capable of supplying the gas to the fuel cell. When the boost stop action of the boosting device starts, the control device stops supplying the gas to the tank and sets the on-off valve to an open valve state. The control device makes the set pressure of the supply pressure reducing valves 51 and 52 in the open valve state lower than the set pressure of the bypass pressure reducing valves 56 and 58 to perform the pressure relief processing of the boosting device.

[0191] In this way, when performing the pressure relief processing of the boosting device, the gas remaining in the gas pressure relief area can be supplied to the fuel cell via the bypass pressure relief valve by using a simple method such as opening the on-off valve and making the set pressure of the supply pressure relief valve lower than the set pressure of the bypass pressure relief valve.

[0192] (Note 2)

[0193] In the regenerative fuel cell system according to Supplementary Note 1, during execution of the pressure relief process, the control device may calculate a generated current of the fuel cell based on a gas consumption amount to control a pressure reduction rate during the pressure relief process.

[0194] In this case, the gas consumption can be controlled with high precision in the control of the generated current, and thus the pressure relief process can be performed at an accurate pressure relief speed (pressure relief speed).

[0195] (Note 3)

[0196] In the regenerative fuel cell system described in Note 1, during the execution of the pressure relief process, the control device may determine the power generation current by referring to the relationship characteristics between the power generation current of the fuel cell and the pressure reduction rate during the pressure relief process, which have been measured and stored in advance.

[0197] This makes it possible to more easily determine the generated current for controlling the pressure reduction rate.

[0198] (Note 4)

[0199] In the regenerative fuel cell system described in Note 1, pressure sensors 61 and 62 may be further provided between the boosting device and the branch portion. During the execution of the pressure relief process, the control device measures the pressure reduction rate by the pressure sensor to obtain a measured pressure reduction rate, and adjusts the generated current so that the difference between the measured pressure reduction rate and the target pressure reduction rate is reduced.

[0200] This makes it possible to easily adjust the generated current for controlling the pressure reduction rate.

[0201] (Note 5)

[0202] The regenerative fuel cell system described in Note 1 may also include: a gas-liquid separator 14, to which the gas that has not been pressurized by the boosting device and the water generated by the power generation of the fuel cell are supplied; and an oxygen remover 33, which is arranged between the gas-liquid separator and the boosting device. During the execution of the pressure relief process, the control device uses the oxygen remover to react the hydrogen that cross-penetrates from the boosting device to the gas-liquid separator with oxygen to form water.

[0203] Thus, during the pressure relief process, hydrogen gas that cross-permeates the electrolyte membrane of the pressure boosting device reacts with oxygen gas by a catalytic reaction to form water, so that the pressure relief process can be reliably performed.

[0204] (Note 6)

[0205] In the regenerative fuel cell system described in Supplementary Note 5, during the execution of the pressure relief process, the control device may cause current to flow through the pressure boosting device 18 to boost the pressure of the hydrogen gas corresponding to the cross-permeation.

[0206] This makes it possible to perform the pressure relief process more reliably.

[0207] (Note 7) In the regenerative fuel cell system described in Note 6, a pressure sensor 60 for detecting the pressure of the hydrogen gas in the gas-liquid separator may be further provided, and the control device may determine the current flowing in the boosting device based on feedback control that eliminates the deviation between the pressure value detected by the pressure sensor and the target pressure value.

[0208] This makes it possible to perform a more reliable pressure relief process on the residual gas in the gas-liquid separator.

[0209] The present disclosure has been described in detail, but the present disclosure is not limited to the above-mentioned embodiments. These embodiments can be subjected to various additions, replacements, changes, partial deletions, etc. without departing from the scope of the present disclosure, or without departing from the scope of the present disclosure described in the claims and the scope of the present disclosure derived from their equivalents. In addition, these embodiments can also be implemented in combination. For example, in the above-mentioned embodiments, the order of each action and the order of each processing are shown as an example and are not limited to this. In addition, the same applies to the case where numerical values ​​or mathematical formulas are used in the description of the above-mentioned embodiments.

Claims

1. A regenerative fuel cell system comprising a fuel cell that generates electricity through an electrochemical reaction between oxygen and hydrogen, wherein the regenerative fuel cell system comprises: a boosting device for generating a gas of either the boosted oxygen or the boosted hydrogen; a supply mechanism for supplying the gas to the fuel cell; and a control device, The supply mechanism comprises: a gas supply path for supplying the gas from the pressure boosting device to the fuel cell; a tank provided on the gas supply path and storing the gas pressurized by the pressurizing device; a bypass passage branching from a branch portion of the gas supply passage between the boosting device and the tank and merging at a merging portion of the gas supply passage between the tank and the fuel cell; a supply pressure reducing valve provided in the gas supply path between the tank and the confluence portion; a bypass pressure reducing valve, which is arranged in the bypass passage; as well as an on-off valve capable of supplying the gas to the fuel cell, When the pressure boosting device starts a pressure boosting stop operation, the control device stops supplying the gas to the tank and opens the on-off valve. The control device performs a pressure relief process on the pressure-increasing device by making the setting pressure of the supply pressure-reducing valve lower than the setting pressure of the bypass pressure-reducing valve in the valve-open state.

2. The regenerative fuel cell system according to claim 1, wherein: During the depressurization process, the control device calculates the power generation current of the fuel cell based on the gas consumption amount to control the depressurization speed during the depressurization process.

3. The regenerative fuel cell system according to claim 1, wherein: During the depressurization process, the control device determines the generated current by referring to previously measured and stored characteristics of the relationship between the generated current of the fuel cell and the depressurization rate during the depressurization process.

4. The regenerative fuel cell system according to claim 1, wherein: A pressure sensor is further provided between the boosting device and the branch portion. During the depressurization process, the control device measures a depressurization rate by the pressure sensor 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 is reduced.

5. The regenerative fuel cell system according to claim 1, wherein: Also features: a gas-liquid separator to which the gas not pressurized by the pressurizing device and water generated by power generation of the fuel cell are supplied; and an oxygen remover, which is arranged between the gas-liquid separator and the booster, During the pressure relief process, the control device causes the hydrogen gas that cross-permeates from the pressure increasing device to the gas-liquid separator to react with oxygen gas using the oxygen remover to generate water.

6. The regenerative fuel cell system according to claim 5, wherein: During the depressurization process, the control device causes current to flow through the pressure increasing device to increase the pressure of the hydrogen gas corresponding to the cross permeation.

7. The regenerative fuel cell system according to claim 6, wherein: A pressure sensor is also provided to detect the pressure of the hydrogen gas in the gas-liquid separator. The control device determines the current flowing through the pressure boosting device based on feedback control that eliminates a deviation between a pressure value detected by the pressure sensor and a target pressure value.

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