Fuel cell system

Abstract

To provide a fuel cell system in which unreacted hydrogen gas recovered from hydrogen off-gas can be supplied to a fuel cell without using a pump.SOLUTION: A fuel cell system 1 comprises a fuel cell 2, a hydrogen supply flow path 40 for supplying hydrogen gas to the fuel cell 2, a variable regulator 43 provided in the hydrogen supply flow path 40, a gas-liquid separator 52 that stores recovered hydrogen gas obtained from hydrogen off-gas discharged from the fuel cell 2 in a buffer tank 520b, a relief valve 51 provided on the pre-stage of the gas-liquid separator 52, a circulation flow path 50 extending from the fuel cell 2 to a downstream flow path 402 of the hydrogen supply flow path 40, and a control device 6 that controls the variable regulator 43 and the relief valve 51. The control device 6 closes the relief valve 51 and controls the variable regulator 43 to set the pressure of the downstream flow path 402 to a level equal to or lower than the pressure of the buffer tank 520b, thereby allowing the recovered hydrogen gas in the buffer tank 520b to return to the downstream flow path 402.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system that generates electricity by supplying hydrogen gas to a fuel cell. [Background technology]

[0002] BACKGROUND ART Conventionally, fuel cell vehicles have been developed in which hydrogen gas is supplied from a hydrogen tank to a fuel cell, and the resulting electricity is supplied to an electric motor, which is used as a drive source to run the vehicle (see, for example, Patent Documents 1 and 2).

[0003] The fuel cell systems described in Patent Documents 1 and 2 are configured to recover unreacted hydrogen gas from the moisture-containing hydrogen off-gas discharged from the fuel cell using a gas-liquid separator, and then supply the recovered hydrogen gas back to the fuel cell using a pump. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-8089 [Patent Document 2] Patent Publication No. 2021-77481 Summary of the Invention [Problem to be solved by the invention]

[0005] In the fuel cell systems described in Patent Documents 1 and 2, a portion of the power generated by the fuel cell must be used to operate the pump, and the operation of the pump reduces power efficiency.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fuel cell system that is capable of supplying unreacted hydrogen gas recovered from hydrogen off-gas to a fuel cell without using a pump. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a fuel cell that generates electricity by an electrochemical reaction between hydrogen gas and oxygen gas and discharges hydrogen off-gas containing unreacted hydrogen gas and moisture, a hydrogen supply flow path that supplies hydrogen gas from a hydrogen supply source to the fuel cell, a hydrogen gas supply valve provided midway through the hydrogen supply flow path, a gas-liquid separator that separates moisture from the hydrogen off-gas to obtain recovered hydrogen gas and stores the recovered hydrogen gas in a buffer tank, a relief valve provided between the gas-liquid separator and the fuel cell, and a check valve provided between the gas-liquid separator and the hydrogen supply flow path. a valve, a circulation flow path connected from an outlet of the fuel cell through the relief valve, the gas-liquid separator, and the check valve to a downstream flow path in the hydrogen supply flow path between the hydrogen gas supply valve and the fuel cell, and a control device that controls the hydrogen gas supply valve and the relief valve, wherein when the recovered hydrogen gas stored in the buffer tank is returned to the downstream flow path, the control device closes the relief valve and controls the hydrogen gas supply valve to make the pressure in the downstream flow path equal to or lower than the pressure of the buffer tank. [Effects of the Invention]

[0008] According to the fuel cell system of the present invention, it is possible to supply unreacted hydrogen gas recovered from hydrogen off-gas to the fuel cell without using a pump. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing an example of the configuration of a fuel cell system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram illustrating an example of the configuration of a gas-liquid separator together with the configuration of its surroundings. [Figure 3] 10 is a flowchart illustrating an example of a procedure of a process executed by a control device. [Figure 4] 6 is a graph showing an example of changes in detected values ​​of a pressure sensor and a downstream pressure sensor in a normal mode and a circulation mode, together with changes in the open / closed state of a relief valve. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment Mode] 1 is a schematic diagram showing an example of the configuration of a fuel cell system 1 according to an embodiment of the present invention. This fuel cell system 1 is mounted on, for example, a fuel cell vehicle having an electric motor as a drive source, and generates electric power to be supplied to the electric motor.

[0011] The fuel cell system 1 includes a fuel cell 2, an air supply system 3 that supplies air containing oxygen gas to the fuel cell 2, a hydrogen supply system 4 that supplies hydrogen gas as fuel to the fuel cell 2, a hydrogen circulation system 5 that recovers unreacted hydrogen gas discharged from the fuel cell 2 and returns it to the air supply system 3, and a control device 6. The power generated by the fuel cell 2 is converted by a PCU (Power Control Unit) 7 that includes a capacitor, a DC-DC converter, and an inverter, and is supplied to an electric motor 8, which is the drive source of the vehicle, etc.

[0012] The fuel cell 2 has a stack structure in which a plurality of unit cells 22 are stacked inside a case 21. In Fig. 1, a portion of the case 21 is cut away to show the interior. Each unit cell 22 includes a flat electrolyte membrane 221, a fuel electrode (anode) 222 provided on one side of the electrolyte membrane 221 in the stacking direction, an air electrode (cathode) 223 provided on the other side of the electrolyte membrane 221 in the stacking direction, and a pair of separators 224 arranged opposite each other with the fuel electrode 222 and the air electrode 223 sandwiched between them.

[0013] In each unit cell 22 constituting the fuel cell 2, hydrogen gas as fuel gas is supplied to the fuel electrode 222, and oxygen gas is supplied to the air electrode 223, whereby electricity is generated by an electrochemical reaction between the hydrogen gas and the oxygen gas. The fuel cell 2 also discharges from the outlet 20 unreacted hydrogen gas that did not electrochemically react with the oxygen gas, and hydrogen off-gas containing moisture generated during electricity generation in the fuel cell 2.

[0014] The air supply system 3 includes an air supply flow path 30 through which air supplied to the fuel cell 2 flows, and a compressor 31 provided in the air supply flow path 30. Oxygen off-gas discharged from the fuel cell 2 is discharged from the air exhaust flow path 10.

[0015] The hydrogen supply system 4 includes a hydrogen tank 41 as a hydrogen supply source, a main stop valve 42 which is an electromagnetic on-off valve that blocks or allows the supply of hydrogen gas from the hydrogen tank 41, a variable regulator 43 as a hydrogen gas supply valve that adjusts the pressure of the hydrogen gas supplied to the fuel cell 2, a hydrogen supply flow path 40 that is connected from the hydrogen tank 41 to the fuel cell 2 via the main stop valve 42 and the variable regulator 43, and an upstream pressure sensor 44 and a downstream pressure sensor 45 that detect the pressure in the hydrogen supply flow path 40 on the upstream and downstream sides of the variable regulator 43. The variable regulator 43 is provided midway along the hydrogen supply flow path 40 between the main stop valve 42 and the fuel cell 2. A pressure reducing valve may be provided between the main stop valve 42 and the variable regulator 43.

[0016] The hydrogen supply flow path 40 includes an upstream flow path 401 between the main stop valve 42 and the variable regulator 43, and a downstream flow path 402 between the variable regulator 43 and the fuel cell 2, and supplies hydrogen gas from the hydrogen tank 41 to the fuel cell 2. The upstream pressure sensor 44 detects the pressure in the upstream flow path 401 and outputs a detection signal indicating the detected pressure value to the control device 6. The downstream pressure sensor 45 detects the pressure in the downstream flow path 402 and outputs a detection signal indicating the detected pressure value to the control device 6.

[0017] Based on the detection values ​​of the upstream pressure sensor 44 and the downstream pressure sensor 45, the control device 6 controls the variable regulator 43 so that an amount of hydrogen gas corresponding to the amount of power generation required by the fuel cell 2 is supplied to the fuel cell 2. The variable regulator 43 is capable of adjusting the pressure of hydrogen gas in the downstream flow path 402 between predetermined upper and lower limit values. In addition, while power generation is being performed by the fuel cell 2, the control device 6 constantly supplies current to the main stop valve 42 to maintain it in an open state.

[0018] The hydrogen circulation system 5 has a circulation flow path 50 that runs from the outlet 20 of the fuel cell 2 to the downstream flow path 402 of the hydrogen supply flow path 40, a relief valve 51, a gas-liquid separator 52, a check valve 53, and a pressure sensor 54 that are provided along the circulation flow path 50. The relief valve 51 is provided between the outlet 20 of the fuel cell 2 and the gas-liquid separator 52, and its open / close state is controlled by the control device 6. The check valve 53 is provided between the gas-liquid separator 52 and the downstream flow path 402, and blocks the flow of hydrogen gas from the downstream flow path 402 side to the gas-liquid separator 52 side. The circulation flow path 50 runs from the outlet 20 of the fuel cell 2 through the relief valve 51, the gas-liquid separator 52, and the check valve 53, and is connected to the downstream flow path 402.

[0019] 2 is a schematic diagram showing an example of the configuration of gas-liquid separator 52 together with the configuration of its surrounding area. Gas-liquid separator 52 separates moisture from hydrogen off-gas to obtain hydrogen gas. Hereinafter, the hydrogen gas obtained from hydrogen off-gas will be referred to as recovered hydrogen gas. Gas-liquid separator 52 has a case 520 provided with an inlet 521, an outlet 522, and a drainage channel 523. Inside case 520, a water storage section 520a for storing moisture separated from the hydrogen off-gas and a buffer tank 520b for storing recovered hydrogen gas are formed.

[0020] Hydrogen off-gas flows in through inlet 521, and is separated into hydrogen gas and water within case 520. The relatively heavy water falls and accumulates in water reservoir 520a at the bottom of case 520, while the relatively light recovered hydrogen gas is stored in buffer tank 520b at the top of case 520. The water accumulated in water reservoir 520a is drained when drain valve 12 provided in drainage channel 11 is opened. Outlet 522 is provided at the top of case 520, and when check valve 53 is opened, the recovered hydrogen gas stored in buffer tank 520b flows out from outlet 522 to downstream flow path 402 of hydrogen supply flow path 40.

[0021] In this embodiment, a part of the gas-liquid separator 52 is the buffer tank 520b, but this is not limiting, and a buffer tank for storing the recovered hydrogen gas may be provided separately from the gas-liquid separator 52 on the downstream side (check valve 53 side) of the gas-liquid separator 52. In this case, the volume of the case 520 of the gas-liquid separator 52 can be reduced.

[0022] The pressure sensor 54 is provided in the circulation flow path 50 between the gas-liquid separator 52 and the check valve 53, and detects the pressure in the buffer tank 520b. A detection signal indicating the detected value of the pressure in the buffer tank 520b is input to the control device 6. The control device 6 controls the relief valve 51 and the variable regulator 43 based on the detected value of the pressure sensor 54, and introduces the recovered hydrogen gas stored in the buffer tank 520b into the fuel cell 2. Next, the control operation performed by the control device 6 will be described.

[0023] The control device 6 alternately executes control in a normal mode in which hydrogen gas from the hydrogen tank 41 is supplied to the fuel cell 2, and control in a circulation mode in which recovered hydrogen gas stored in the buffer tank 520b is introduced into the fuel cell 2. In the normal mode, the opening of the variable regulator 43 is controlled while the check valve 53 is closed, and an amount of hydrogen gas corresponding to the opening is supplied to the fuel cell 2. In the circulation mode, the opening of the variable regulator 43 is reduced, and the check valve 53 is opened by the pressure of the recovered hydrogen gas stored in the buffer tank 520b, and the recovered hydrogen gas stored in the buffer tank 520b is introduced into the fuel cell 2 via the downstream flow path 402 of the hydrogen supply flow path 40.

[0024] When the control device 6 shifts from the normal mode to the circulation mode and returns the recovered hydrogen gas stored in the buffer tank 520b to the downstream flow path 402 of the hydrogen supply flow path 40, it closes the relief valve 51 and controls the variable regulator 43 to make the pressure of the hydrogen gas in the downstream flow path 402 equal to or lower than the pressure of the buffer tank 520b. Furthermore, when the detection value of the pressure sensor 54 reaches or exceeds a predetermined value, the control device 6 shifts from the normal mode to the circulation mode and returns the recovered hydrogen gas stored in the buffer tank 520b to the downstream flow path 402. When the detection value of the pressure sensor 54 is below the predetermined value, the control device 6 intermittently opens and closes the relief valve 51 to gradually increase the pressure in the buffer tank 520b.

[0025] 3 is a flowchart showing an example of the procedure of the process executed by the control device 6. When power generation by the fuel cell 2 starts, the control device 6 opens the main stop valve 42 (step S1), supplies hydrogen gas from the variable regulator 43 to the fuel cell 2 (step S2), and intermittently opens and closes the relief valve 51 (step S3). The control device 6 also acquires the detection value of the pressure sensor 54 (step S4) and determines whether the detection value of the pressure sensor 54 is equal to or greater than a predetermined value (step S5). If the detection value of the pressure sensor 54 is not equal to or greater than the predetermined value (the determination result in step S5 is No), the process of steps S2 to S4 continues. The process of steps S2 to S5 is the process of the control device 6 in normal mode.

[0026] When the detection value of the pressure sensor 54 becomes equal to or greater than a predetermined value (the determination result in step S5 is Yes), the control device 6 fixes the relief valve 51 in a closed state (step S6) and controls the variable regulator 43 to reduce the pressure of the hydrogen gas in the downstream flow path 402 (step S7). As a result, when the pressure of the hydrogen gas in the downstream flow path 402 becomes lower than the pressure in the buffer tank 520b, the check valve 53 opens and the recovered hydrogen gas stored in the buffer tank 520b is introduced into the fuel cell 2 from the downstream flow path 402 of the hydrogen supply flow path 40.

[0027] Thereafter, the control device 6 acquires the detection value of the downstream pressure sensor 45 (step S8), and determines whether or not the detection value of the downstream pressure sensor 45 has reached the lower limit of the pressure that can be adjusted by the variable regulator 43 (step S9). When the detection value of the downstream pressure sensor 45 has reached the lower limit of the pressure that can be adjusted by the variable regulator 43 (the determination result of step S9 is Yes), the control device 6 returns the process to step S2. The processes of steps S6 to S9 are the processes of the control device 6 in the circulation mode.

[0028] 4 is a graph showing an example of the transition of the detected values ​​of the pressure sensor 54 and the downstream pressure sensor 45 in normal mode and circulation mode, along with the change in the open / close state of the relief valve 51. The horizontal axis of the graph is the time axis. On the vertical axis of the graph showing the detected values ​​of the pressure sensor 54 and the downstream pressure sensor 45, Pu and Pl represent the upper and lower limit values ​​of the pressure that can be adjusted by the variable regulator 43, and Pg represents the predetermined value of step S5 in the above flowchart. The predetermined value Pg is a value between the upper limit value Pu and the lower limit value Pl, and is set so that the recovered hydrogen gas can be efficiently stored and introduced into the fuel cell 2.

[0029] In the normal mode, the control device 6 opens the relief valve 51 at a predetermined time interval ΔT. When the relief valve 51 is open, recovered hydrogen gas, from which moisture has been separated from the hydrogen off-gas, accumulates in the buffer tank 520b, causing the pressure detected by the pressure sensor 54 to increase. The time interval ΔT is, for example, 20 to 30 seconds, but does not necessarily have to be constant.

[0030] When the detection value of pressure sensor 54 reaches predetermined value Pg, control device 6 transitions to circulation mode, fixes relief valve 51 in a closed state, and reduces the opening of variable regulator 43. As a result, hydrogen gas in downstream flow path 402 is consumed by fuel cell 2, and the pressure of downstream flow path 402 detected by downstream pressure sensor 45 gradually decreases. When the pressure of downstream flow path 402 decreases to predetermined value Pg, check valve 53 opens, and recovered hydrogen gas flows from buffer tank 520b into downstream flow path 402 and is consumed by fuel cell 2, and the detection values ​​of pressure sensor 54 and downstream pressure sensor 45 gradually decrease.

[0031] When the detection value of the downstream pressure sensor 45 drops to the lower limit value Pl, the control device 6 switches to normal mode, supplies hydrogen gas from the hydrogen tank 41 to the fuel cell 2 via the variable regulator 43, and opens the relief valve 51 at a predetermined time interval ΔT. Thereafter, while power is generated by the fuel cell 2, hydrogen gas is supplied to the fuel cell 2 while switching between the normal mode and the circulation mode.

[0032] (Effects of the embodiment) According to the present embodiment described above, the check valve 53 is opened by the pressure difference between the pressure of the recovered hydrogen gas stored in the buffer tank 520b and the pressure in the downstream flow path 402, so that the recovered hydrogen gas can be supplied to the fuel cell 2 without the need to use a pump to supply hydrogen gas obtained by separating moisture from hydrogen off-gas to the fuel cell 2. This eliminates the need to use electric power to operate the pump, and allows the electric power generated by the fuel cell 2 to be efficiently supplied to a load such as the electric motor 8. Furthermore, noise and vibrations associated with the operation of the pump are eliminated, making it possible to improve quietness inside the vehicle cabin.

[0033] In this embodiment, it is necessary to provide the relief valve 51 and the pressure sensor 54 in the hydrogen circulation system 5, but the power consumption thereof is smaller than the power consumption of a pump when hydrogen gas obtained by separating moisture from hydrogen off-gas using the pump is supplied to the fuel cell 2. In this case, the power consumption of the pump is, for example, 25.2 W, and the power consumption of the relief valve 51 and the pressure sensor 54 is, for example, 2.59 W. In this way, according to this embodiment, the power required to supply hydrogen gas obtained by separating moisture from hydrogen off-gas again to the fuel cell 2 can be reduced to about one-tenth.

[0034] (Addendum) Although the present invention has been described above based on the embodiments, the invention according to the claims is not limited to these embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention.

[0035] Furthermore, the present invention can be implemented by appropriately modifying it by omitting some components or adding or substituting components without departing from the spirit of the invention. For example, in the above embodiment, a case has been described in which variable regulator 43 is used as the hydrogen gas supply valve, but this is not limitative, and an injector, for example, may also be used as the hydrogen gas supply valve. Furthermore, the fuel cell system 1 is not limited to being installed in fuel cell vehicles, and the fuel cell system according to the present invention can also be installed in moving bodies other than vehicles, such as ships and aircraft. [Explanation of symbols]

[0036] 1...Fuel cell system 2...Fuel cell 40... Hydrogen supply passage 43... Variable regulator (hydrogen gas supply valve) 50... Circulation flow path 51... Relief valve 520b...Buffer tank 53...Check valve 54...Pressure sensor 6...Control device

Claims

1. a fuel cell that generates electricity through an electrochemical reaction between hydrogen gas and oxygen gas and discharges hydrogen off-gas containing unreacted hydrogen gas and moisture; a hydrogen supply passage for supplying the hydrogen gas from a hydrogen supply source to the fuel cell; a hydrogen gas supply valve provided midway along the hydrogen supply channel; a gas-liquid separator that separates moisture from the hydrogen off-gas to obtain recovered hydrogen gas and stores the recovered hydrogen gas in a buffer tank; a relief valve provided between the gas-liquid separator and the fuel cell; a check valve provided between the gas-liquid separator and the hydrogen supply channel; a circulation flow path connected from an outlet of the fuel cell through the relief valve, the gas-liquid separator, and the check valve to a downstream flow path in the hydrogen supply flow path between the hydrogen gas supply valve and the fuel cell; a control device that controls the hydrogen gas supply valve and the relief valve, when returning the recovered hydrogen gas stored in the buffer tank to the downstream flow path, the control device closes the relief valve and controls the hydrogen gas supply valve to make the pressure in the downstream flow path equal to or lower than the pressure of the buffer tank. Fuel cell system.

2. a pressure sensor for detecting the pressure of the buffer tank; the control device causes the recovered hydrogen gas stored in the buffer tank to return to the downstream flow path when the detected value of the pressure sensor becomes equal to or greater than a predetermined value. The fuel cell system according to claim 1 .

3. When the detected value of the pressure sensor is less than the predetermined value, the control device intermittently opens and closes the relief valve to gradually increase the pressure in the buffer tank. The fuel cell system according to claim 2 .

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