JP2023170866A - fuel cell system - Google Patents

Abstract

To provide a technology that returns the residual oxygen discharged from an FC stack to the FC stack without using electric power.SOLUTION: An FC system disclosed in the present specification comprises an FC stack, an oxygen source that supplies oxygen to the FC stack, and an ejector that sends the oxygen to the FC stack. The ejector is a device that draws in a second gas of lower pressure than the pressure of a first gas as the pressure occurring in the surrounding of a nozzle lowers when the first gas is sprayed from the nozzle and sprays it together with the first gas. The ejector can draw in and spray the second gas without using electric power. In the FC system disclosed in the present specification, the oxygen from the oxygen source is supplied as the first gas to the ejector, and the residual gas discharged from the FC stack is supplied as the second gas to the ejector. The gas sprayed by the ejector is sent to the FC stack. By adopting the ejector, it is made possible to return the residual oxygen discharged from the FC stack to the FC stack without using electric power.SELECTED DRAWING: Figure 1

Description

The technology disclosed herein relates to a fuel cell system.

A fuel cell system generates electricity by reacting hydrogen and oxygen in a fuel cell stack. Hydrogen is supplied from a hydrogen tank. Fuel cell systems often use oxygen in the air, but may also use oxygen tanks (for example, Patent Document 1). In order to reuse unreacted oxygen (residual oxygen) in the fuel cell stack, in the system of Patent Document 1, unreacted residual oxygen discharged from the fuel cell stack is returned to the oxygen supply pipe using a circulation blower (pump).

Note that, hereinafter, for convenience of explanation, "fuel cell" may be referred to as "FC". A "fuel cell system" may be written as a "FC system," and a "fuel cell stack" may be written as an "FC stack."

Japanese Patent Application Publication No. 2018-147622

The reason why the circulation blower is used in the technique of Patent Document 1 is to force residual oxygen into the flow of high-pressure oxygen toward the FC stack. Electricity is required to drive the circulation blower (pump). This specification provides a technique for returning residual oxygen to the FC stack without using electrical power.

The FC system (fuel cell system) disclosed herein uses an ejector to return residual oxygen to the FC stack. An ejector is a device that sucks in a second gas whose pressure is lower than the pressure of the first gas due to the pressure drop that occurs around the nozzle when the first gas is injected from the nozzle, and injects it together with the first gas. The ejector can suck in the second gas, mix it with the first gas, and inject it without using electricity.

The FC system disclosed herein includes an FC stack, an oxygen source that supplies oxygen to the FC stack, and an ejector that delivers oxygen to the FC stack. In the FC system disclosed in this specification, oxygen as an oxygen source is supplied to the ejector as a first gas, and residual oxygen discharged from the FC stack is supplied to the ejector as a second gas. The ejector mixes the remaining oxygen with oxygen sent from the oxygen source and injects it into the FC stack. This FC system can return residual oxygen exhausted from the FC stack to the FC stack without using electricity.

The oxygen source may be a compressor that compresses atmospheric air, but is preferably an oxygen tank that stores compressed oxygen. By using an oxygen tank, electricity is not required to generate high-pressure oxygen gas.

Details and further improvements of the technology disclosed in this specification will be explained in the following "Detailed Description of the Invention".

FIG. 1 is a block diagram of an FC system according to an embodiment. FIG. 3 is a structural diagram of an ejector.

An FC system 2 (fuel cell system 2) according to an embodiment will be described with reference to the drawings. FIG. 1 shows a block diagram of the FC system 2. The FC system 2 includes an FC stack 3 (fuel cell stack 3) and a fuel tank 11. The fuel tank 11 stores fuel gas (hydrogen gas). As is well known, the FC stack 3 generates electricity by reacting hydrogen and oxygen. Many FC systems use oxygen in the air, but the FC system 2 of the embodiment includes an oxygen tank 21, and generates electric power by causing the oxygen in the oxygen tank 21 to react with the fuel gas in the fuel tank 11. The gas stored in the oxygen tank 21 may be a mixed gas of oxygen and other molecules. For example, the oxygen tank 21 may be a tank that stores a mixed gas (ie, air) containing 78% nitrogen, 21% oxygen, and 1% other components.

The FC system 2 includes multiple valves (such as the fuel tank valve 19), multiple pressure sensors (not shown), multiple temperature sensors (not shown), and the like. All valves are controlled by controller 10. Measured values of all sensors are sent to the controller 10.

The fuel system of the FC system 2 will be explained. The fuel tank 11 and the FC stack 3 are connected by a fuel supply pipe 12. As is well known, the inside of the FC stack 3 is divided into an anode electrode 3a (fuel electrode) and a cathode electrode 3c (oxygen electrode). The fuel supply pipe 12 connects the fuel tank 11 and the anode 3a of the FC stack 3, and sends fuel gas from the fuel tank 11 to the anode 3a.

The fuel supply pipe 12 is equipped with a fuel tank valve 19, an injector 13, and a fuel stop valve 14. The fuel tank valve 19 is disposed at the most upstream position of the fuel supply pipe 12 (the position closest to the fuel tank 11), and stops the outflow of fuel gas from the fuel tank 11. The fuel stop valve 14 is arranged at the most downstream position of the fuel supply pipe 12 (the position closest to the FC stack 3). When the FC stack 3 is stopped, the fuel tank valve 19 is closed, and the safety of the FC system 2 is ensured. The fuel stop valve 14 is used to quickly stop the fuel supply to the FC stack 3 when some abnormality occurs during operation of the FC stack 3.

The injector 13 is arranged in the fuel supply pipe 12 between the fuel tank valve 19 and the fuel stop valve 14 . The injector 13 maintains the pressure of the fuel gas supplied to the FC stack 3 at an appropriate anode pressure.

A gas-liquid separator 17 is connected to the anode gas outlet 4 of the FC stack 3 . The gas-liquid separator 17 separates unreacted fuel gas and moisture (and impurities) from the gas discharged from the anode gas outlet 4. The separated fuel gas is returned to the fuel supply pipe 12 through the fuel return path 16 and reused. The fuel return path 16 is equipped with a pump 18 , and the pump 18 forcibly returns unreacted fuel gas to the fuel supply pipe 12 .

A first exhaust pipe 41 is connected to the gas outlet of the gas-liquid separator 17, and the first exhaust pipe 41 communicates with a muffler 45. Moisture and impurities separated by the gas-liquid separator 17 are discharged to the outside through the first exhaust pipe 41 and the muffler 45.

A fuel exhaust valve 42 is attached in the middle of the first exhaust pipe 41. The exhaust fuel valve 42 closes the first exhaust pipe 41 and stops exhaust gas containing impurities and residual fuel from exiting.

The oxygen system of the FC system 2 will be explained. The oxygen tank 21 and the cathode 3c (oxygen electrode) of the FC stack 3 are connected through an oxygen supply pipe 22. The oxygen supply pipe 22 sends oxygen from the oxygen tank 21 to the cathode 3c.

The oxygen supply pipe 22 is equipped with an oxygen tank valve 29, oxygen stop valves 23 and 24, an oxygen regulator 25, and an ejector 30. The oxygen tank valve 29 is disposed at the most upstream position of the oxygen supply pipe 22 (the position closest to the oxygen tank 21), and stops oxygen from flowing out from the oxygen tank 21. When the FC stack 3 is stopped, the oxygen tank valve 29 is closed, and wasteful outflow of oxygen is suppressed.

The oxygen stop valve 24 is arranged at the most downstream position of the oxygen supply pipe 22 (the position closest to the FC stack 3). The oxygen stop valve 24 is used to quickly stop the supply of oxygen to the FC stack 3 when some abnormality occurs during operation of the FC stack 3.

An oxygen regulator 25 and an oxygen stop valve 23 are arranged between the oxygen tank valve 29 and the oxygen stop valve 24. The oxygen regulator 25 adjusts the flow rate of oxygen supplied to the cathode 3c. The oxygen stop valve 23 is attached between the oxygen regulator 25 and the oxygen tank valve 29 of the oxygen supply pipe 22.

The oxygen tank valve 29 and the oxygen stop valves 23 and 24 are valves that can only be switched between fully open and fully closed. The oxygen regulator 25 is a valve that can continuously change the area of the flow path, and can adjust the flow rate of oxygen. By adjusting the flow rate of oxygen, the oxygen pressure on the downstream side of the oxygen regulator 25 can be lowered than the oxygen pressure on the upstream side.

When air is used as oxygen to be sent to the FC stack 3, a compressor is required to compress the air in order to increase the pressure of the air (oxygen) sent to the FC stack 3. However, the FC system 2 of the embodiment uses an oxygen tank 21 that stores high-pressure oxygen, so a compressor is not necessary. The pressure of oxygen in the oxygen tank 21 is higher than the proper pressure of oxygen (cathode proper pressure) used in the FC stack 3. The oxygen regulator 25 lowers the oxygen pressure (oxygen pressure in the oxygen tank 21) higher than the appropriate cathode pressure to the appropriate cathode pressure. Note that pressure sensors (not shown) are provided on the upstream and downstream sides of the oxygen regulator 25 and on the downstream side of the ejector 30, respectively. The controller 10 monitors the measured values of these pressure sensors and controls the oxygen regulator 25 so that the pressure of oxygen supplied to the FC stack 3 is maintained at the appropriate cathode pressure.

In other words, the oxygen regulator 25 and the oxygen stop valve 23 serve as an injector. When operating the FC stack 3, the controller 10 opens the oxygen stop valve 23 and controls the oxygen regulator 25 so that the pressure of oxygen supplied to the cathode 3c of the FC stack 3 is maintained at a predetermined appropriate cathode pressure. Control.

An ejector 30 is provided in the oxygen supply pipe 22 between the oxygen regulator 25 and the oxygen stop valve 24. A first fluid inlet 30a of the ejector 30 is connected to the oxygen regulator 25, and a second fluid inlet 30b is connected to a residual oxygen outlet 27a of a gas-liquid separator 27, which will be described later. The ejection port 30c of the ejector 30 is connected to the cathode 3c of the FC stack 3 through the oxygen stop valve 24. The operation of the ejector 30 will be described later.

A gas-liquid separator 27 is connected to the cathode gas outlet 5 of the FC stack 3 . The gas-liquid separator 27 separates unreacted oxygen (residual oxygen) and moisture from the gas discharged from the cathode gas outlet 5. Unreacted residual oxygen exits from the residual oxygen outlet 27a. The residual oxygen outlet 27a of the gas-liquid separator 27 is connected to the second fluid inlet 30b of the ejector 30 through the oxygen reflux path 26. The remaining oxygen separated by the gas-liquid separator 27 is returned to the ejector 30 through the oxygen reflux path 26 and reused. The oxygen reflux path 26 is equipped with a stop valve 28 . If there is no need to return residual oxygen to the ejector 30, the stop valve 28 is closed.

A second exhaust pipe 44 is connected to the gas outlet of the gas-liquid separator 27, and an exhaust oxygen valve 43 is attached to the middle of the second exhaust pipe 44. When it is necessary to discharge the moisture and impurities separated by the gas-liquid separator 27, the exhaust oxygen valve 43 is opened. When moisture and impurities are extremely small, there is no need to discharge them, so the exhaust oxygen valve 43 is closed. The moisture and impurities separated by the gas-liquid separator 27 are sent to the muffler 45, mixed with the moisture and impurities discharged from the gas-liquid separator 17 on the fuel side, and discharged to the outside.

The function of the ejector 30 will be explained. FIG. 2 shows a structural diagram of the ejector 30. The black arrow lines in FIG. 2 indicate the flow of gas. The ejector 30 includes a first fluid inlet 30a, a second fluid inlet 30b, a spout 30c, a body 31, a nozzle 32, and a diffuser 33. A nozzle 32 is arranged inside the body 31.

The first fluid entering from the first fluid inlet 30a increases in flow velocity at the nozzle 32. As is well known, as the flow rate of a fluid increases, the pressure decreases. Therefore, the pressure decreases around the nozzle 32 (the space A between the inner wall of the body 31 and the outer surface of the nozzle 32) from which the accelerated first fluid is ejected.

Even if the second fluid entering from the second fluid inlet 30b has a low flow rate, it is sucked into the space A where the pressure is reduced around the nozzle 32 and heads toward the jet port 30c together with the first fluid (black in FIG. 2). (arrow lines indicate gas flow). A diffuser 33 is arranged downstream of the nozzle 32. The fluid whose speed has increased in the nozzle 32 is decelerated while passing through the diffuser 33, and its pressure is restored. By appropriately selecting the opening diameter at the tip of the diffuser 33, the pressure of the fluid ejected from the ejection port 30c can be returned to the same level as the pressure of the fluid entering from the first fluid inlet 30a. The ejector 30 can mix the second fluid entering from the second fluid inlet 30b with the first fluid entering from the first fluid inlet 30a and eject it from the ejection port 30c without using electric power (power). The pressure of the second fluid supplied to the second fluid inlet 30b may be lower than the pressure of the first gas supplied to the first fluid inlet 30a.

In the FC system 2, high-pressure oxygen supplied from the oxygen tank 21 is supplied to the ejector 30 as a first gas, and low-pressure residual oxygen separated by the gas-liquid separator 27 is supplied to the ejector 30 as a second gas. (Pressure of oxygen supplied from oxygen tank 21 > pressure of residual oxygen). The ejection port 30c of the ejector 30 is connected to the FC stack 3. The low-pressure residual oxygen discharged from the FC stack 3 is mixed with high-pressure oxygen in the oxygen tank 21 by the ejector 30 and returned to the FC stack 3. The FC system 2 of the embodiment can return residual oxygen to the FC stack and reuse it without using electric power (motive power).

The structure of the FC system 2 including the ejector 30 can also be expressed as follows. The FC system 2 includes an FC stack 3, an oxygen source (oxygen tank 21) that supplies oxygen to the FC stack 3, an oxygen supply pipe 22 that connects the oxygen tank 21 and the FC stack 3, and an ejector disposed in the oxygen supply pipe 22. 30, an oxygen reflux path 26 is provided for returning unreacted oxygen (residual oxygen) discharged from the FC stack 3 to the ejector 30.

The ejector 30 includes a first fluid inlet 30a for feeding the first fluid into the nozzle 32, a second fluid inlet 30b for introducing the second fluid around the nozzle 32, and a jet for ejecting a mixed fluid of the first fluid and the second fluid. It is equipped with an outlet 30c. The ejector 30 is provided in the oxygen supply pipe 22 so that the oxygen discharged from the oxygen tank 21 enters through the first fluid inlet 30a, and the oxygen discharged from the jet port 30c flows into the FC stack 3. The oxygen reflux path 26 is connected to the second fluid inlet 30b of the ejector 30.

The characteristics of the connection relationship of the ejector 30 can be expressed more simply as follows. The ejector 30 sucks in the second gas due to the pressure drop that occurs around the nozzle 32 when the first gas is injected from the nozzle 32, and injects the second gas into the FC stack 3 together with the first gas. Oxygen in the oxygen tank 21 (oxygen source) is supplied as the first gas, and residual oxygen discharged from the FC stack 3 is supplied as the second gas.

Some features of the example FC system are listed below. The FC system 2 includes an oxygen tank 21 that stores high-pressure oxygen as an oxygen source. By providing the oxygen tank 21, oxygen at a pressure higher than atmospheric pressure can be sent to the FC stack 3 without requiring a compressor. However, even in a FC system that does not have an oxygen tank and uses oxygen in the atmosphere, by adopting an ejector 30 like FC system 2, residual oxygen can be transferred to the FC stack 3 without using electric power (power). You can get the benefits of going back.

When the FC system 2 includes an oxygen tank 21 and an ejector 30, an oxygen regulator 25 may be provided between the oxygen tank 21 and the ejector 30 to adjust the flow rate of oxygen. By employing the oxygen regulator 25, the pressure of oxygen supplied to the ejector 30 can be adjusted so that the pressure of oxygen supplied to the FC stack 3 becomes an appropriate pressure.

Conventional FC systems use injectors to regulate the pressure of fuel delivered to the FC stack. A typical injector has the following structure. The injector includes a needle that closes the gas injection port and a solenoid that moves the needle. The needle is pressed against the gas injection port by a spring, and blocks the gas injection port when the solenoid is de-energized. When the solenoid is energized, the needle moves back and the gas injection port opens. When the solenoid is de-energized, the needle returns and closes the gas injection port. A tapping sound occurs when the needle hits the edge of the gas injection port. The injector must be turned on and off frequently to adjust the pressure of oxygen supplied to the FC stack. When the injector is turned on and off frequently, the needle frequently hits the edge of the gas injection port, creating a tapping noise.

In the case of an FC system equipped with an oxygen tank that stores oxygen to be supplied to the FC stack, it is conceivable to use an injector to adjust the pressure of oxygen. However, when an injector is used, tapping noise occurs as described above.

The FC system 2 of the embodiment includes an FC stack 3, an oxygen tank 21, an oxygen supply pipe 22 connecting the FC stack 3 and the oxygen tank 21, an oxygen regulator 25, and an oxygen stop valve 23. The oxygen regulator 25 is arranged in the oxygen supply pipe 22 and adjusts the flow rate of oxygen supplied from the oxygen tank 21 to the cathode electrode 3c of the FC stack. Oxygen stop valve 23 stops the flow of oxygen from oxygen tank 21 to oxygen regulator 25 . This FC system 2 uses an oxygen regulator 25 instead of an injector to adjust the pressure of oxygen supplied to the FC stack 3. The regulator is a valve that adjusts the flow rate by changing the area of the flow path. Regulators are quieter than injectors because they do not have a needle that moves back and forth using a solenoid like injectors do.

Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims as filed. Furthermore, the techniques illustrated in this specification or the drawings can achieve multiple objectives simultaneously, and achieving one of the objectives has technical utility in itself.

2: Fuel cell system (FC system) 3: Fuel cell stack (FC stack) 3a: Anode electrode 3c: Cathode electrode 4: Anode electrode gas outlet 5: Cathode electrode gas outlet 10: Controller 11: Fuel tank 12: Fuel supply pipe 13: Injector 14: Fuel stop valve 16: Fuel recirculation path 17, 27: Gas-liquid separator 18: Pump 19: Fuel tank valve 21: Oxygen tank 22: Oxygen supply pipe 23, 24: Oxygen stop valve 25: Oxygen regulator 26 : Oxygen reflux path 27a: Residual oxygen outlet 28: Stop valve 29: Oxygen tank valve 30: Ejector 30a: First fluid inlet 30b: Second fluid inlet 30c: Spout 31: Body 32: Nozzle 33: Diffuser 41: First Exhaust pipe 42: Exhaust fuel valve 43: Exhaust oxygen valve 44: Second exhaust pipe 45: Muffler

Claims (2)

fuel cell stack,
an oxygen source that supplies oxygen to the fuel cell stack;
The ejector sucks in a second gas by a pressure drop generated around the nozzle when the first gas is injected from the nozzle and sends it to the fuel cell stack together with the first gas, the ejector comprising: an ejector that is supplied as a gas and to which residual oxygen discharged from the fuel cell stack is supplied as the second gas;
Equipped with a fuel cell system. The fuel cell system according to claim 1, wherein the oxygen source is an oxygen tank.

Images