JP7622659B2 - Fuel Cell Systems - Google Patents

Description

The technology disclosed in this specification relates to a fuel cell system.

The fuel cell system is equipped with a main stop valve and an injector between the fuel cell stack and the fuel tank. For convenience of explanation, the gas flow path between the main stop valve and the injector is referred to as the high-pressure system flow path. Patent Document 1 discloses a technology for checking the quality of the main stop valve. In this specification, a defective main stop valve means that the main stop valve does not close completely even when a command to close the main stop valve is sent, causing fuel gas to leak from the fuel tank to the high-pressure system flow path.

The main stop valve check process disclosed in Patent Document 1 is as follows: Close the injector and open the main stop valve. When the gas pressure in the high-pressure line reaches a predetermined first pressure, close the main stop valve. Next, open the injector. When the gas pressure in the high-pressure line drops to a second pressure, close the injector. Wait for a fixed period of time with both the injector and the main stop valve closed. If the gas pressure in the high-pressure line exceeds "second pressure + allowable differential pressure" after the fixed period of time, it is determined that the main stop valve is not completely closed.

For ease of explanation, below, checking whether the main stop valve closes completely will be referred to as a main stop valve inspection. Also, for ease of explanation, "fuel cell" may be written as "FC." "Fuel cell system" may be written as "FC system," and "fuel cell stack" may be written as "FC stack."

JP 2019-149321 A

When checking the quality of the main stop valve, the injector is opened, causing fuel gas to flow into the FC stack before startup. As the scale of the FC system increases, the volume of the high-pressure flow passage also increases. If the volume of the high-pressure flow passage is large, a large amount of fuel gas flows into the FC stack during the quality check. If a large amount of fuel gas flows into the FC stack before startup, the following problems may occur: (1) The internal pressure of the FC stack becomes excessively high. (2) In the FC stack before startup, a large amount of fuel gas leaks from the fuel electrode to the air electrode. This specification provides a technology that prevents a large amount of fuel gas from remaining in the FC stack during a main stop valve inspection.

The FC system disclosed in this specification comprises a fuel tank, an FC stack, a main stop valve, an injector, a fuel pipe, a compressor, an exhaust pipe, an exhaust valve, and a controller. The main stop valve stops the outflow of fuel gas from the fuel tank. The injector adjusts the flow rate of fuel gas supplied to the FC stack. The fuel pipe connects the main stop valve to the injector. The compressor sends air to the FC stack. The exhaust pipe mixes the fuel gas in the FC stack with air and releases it. The exhaust valve closes the exhaust pipe. The controller controls the main stop valve, the injector, the compressor, and the exhaust valve. The controller performs a main stop valve inspection (opening and closing the main stop valve, then opening and closing the injector, and determining whether the main stop valve is good or bad based on the pressure change in the fuel pipe). While performing the main stop valve inspection, the controller opens the exhaust gas valve when the internal pressure of the FC stack reaches a predetermined threshold pressure, and drives the compressor so that the concentration of fuel released from the exhaust gas pipe is below a predetermined upper limit concentration.

The fuel cell system disclosed in this specification prevents a large amount of fuel gas from accumulating in the FC stack during main stop valve inspection. In addition, the controller controls the compressor so that the fuel concentration in the exhaust gas does not exceed the upper limit concentration. Gas containing a high concentration of fuel is not released.

The FC system disclosed in this specification is also preferably equipped with a bypass flow path that sends air from the compressor to the exhaust gas pipe, bypassing the FC stack. The controller may use the bypass flow path to send air from the compressor to the exhaust gas pipe while performing a main stop valve inspection. This can prevent the inside of the FC stack from drying out excessively before startup.

An example of the procedure for inspecting the main stop valve is as follows: The controller closes the injector and opens the main stop valve to raise the internal pressure of the fuel pipe to a first pressure, then closes the main stop valve and opens the injector to lower the internal pressure. The controller determines the amount of fuel gas injected by the injector while the internal pressure of the fuel pipe is lowering. If the amount of fuel gas injected exceeds a predetermined injection amount threshold before the internal pressure of the fuel pipe drops to a second pressure, the controller determines that the main stop valve is defective.

In the main stop valve inspection method of Patent Document 1 mentioned above, the internal pressure of the fuel pipe is lowered to the second pressure, and then a fixed time is waited for. If the pressure has dropped after the fixed time has elapsed, it is determined that the main stop valve is defective. With this method, it takes time to determine whether the main stop valve is good or bad. In the FC system disclosed in this specification, the quality of the main stop valve is determined based on the amount of fuel ejected from the injector and the pressure change in the fuel pipe. This makes it possible to shorten the time required for main stop valve inspection.

Details and further improvements of the technology disclosed in this specification are explained in the "Description of Embodiments" below.

FIG. 1 is a block diagram of an FC system according to an embodiment. 4 is a flowchart of a main stop valve inspection process. 4 is a flowchart of the main stop valve inspection process (continuation of FIG. 2 ). 4 is a flowchart of an FC stack internal pressure monitoring process.

An FC 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 comprises an FC stack 3, multiple fuel tanks 4a, 4b, and a compressor 9. Fuel (hydrogen) is stored in the fuel tanks 4a, 4b. The FC system 2 generates electricity by reacting the fuel in the fuel tanks 4a, 4b with oxygen in the air. Gaseous fuel (i.e., fuel gas) is sent from the fuel tanks 4a, 4b to the FC stack 3, and the compressor 9 supplies air to the FC stack 3.

The FC stack 3 is connected to each of the multiple fuel tanks 4a, 4b via a fuel pipe 7. The fuel pipe 7 is equipped with main stop valves 5a, 5b and an injector 6. The main stop valves 5a, 5b are located on the upstream side of the fuel pipe 7 (the side closest to the fuel tanks 4a, 4b) and stop the outflow of fuel gas from the fuel tanks 4a, 4b. When the FC stack 3 is stopped, the main stop valves 5a, 5b are closed, ensuring the safety of the FC system 2.

The injector 6 is located downstream of the fuel pipe 7 (closest to the FC stack 3) and adjusts the flow rate of fuel gas supplied to the FC stack 3. Note that a gas regulator may be installed between the injector 6 and the main stop valves 5a, 5b. In that case, the flow rate of fuel gas supplied to the FC stack 3 is adjusted by the injector 6 and the gas regulator. However, it is the injector 6 that ultimately adjusts the flow rate of fuel gas supplied to the FC stack 3.

The fuel pipe 7 connects the fuel tanks 4a, 4b to the FC stack 3, but for ease of explanation, the portion of the fuel pipe 7 that connects the main stop valves 5a, 5b to the injector 6 is referred to as the high-pressure fuel pipe 7a, and the portion that connects the FC stack 3 to the injector 6 is referred to as the low-pressure fuel pipe 7b.

A gas-liquid separator 15 is connected to the fuel gas outlet of the FC stack 3. The gas-liquid separator 15 separates unreacted fuel gas from the gas discharged from the fuel gas outlet. The separated fuel gas is returned to the low-pressure fuel pipe 7b via the return path 16 and is reused. The return path 16 is equipped with a pump 14, which forcibly returns the unreacted fuel gas to the low-pressure fuel pipe 7b.

An exhaust gas pipe 17 is connected to the gas outlet of the gas-liquid separator 15, and a muffler 20 is attached to the middle of the exhaust gas pipe 17. The impurities separated by the gas-liquid separator 15 are discharged to the outside through the exhaust gas pipe 17 and the muffler 20. Air is also sent from the compressor 9 through an exhaust air pipe 19 to the muffler 20. A small amount of fuel gas remains in the impurities separated by the gas-liquid separator 15. The controller 10 estimates the concentration of fuel in the exhaust gas discharged to the outside from the muffler 20, and air is sent from the compressor 9 so that the estimated concentration value of the fuel contained in the exhaust gas is equal to or lower than a predetermined upper limit concentration. Since the concentration can be estimated using conventional technology, a description of the concentration estimation will be omitted. The concentration may be measured by a concentration sensor. Hereinafter, the estimated concentration value of the fuel contained in the exhaust gas is simply referred to as the "fuel concentration".

An exhaust gas valve 18 is installed midway through the exhaust gas pipe 17. The exhaust gas valve 18 closes the exhaust gas pipe 17, stopping exhaust gas from escaping to the outside.

The compressor 9 and the FC stack 3 are connected by an air pipe 12. The air pipe 12 and the exhaust air pipe 19 are connected by a bypass flow path 11. An air supply valve 23 is attached to the air pipe 12, and an air exhaust valve 24 is attached to the exhaust air outlet of the FC stack 3. A bypass valve 13 is attached to the bypass flow path 11. When the bypass valve 13 is closed, the air supply valve 23 is opened, and the compressor 9 is driven, outside air is sent to the FC stack 3. When the FC stack 3 is driven, the air exhaust valve 24 is also opened. When the air supply valve 23 and the air exhaust valve 24 are closed, the bypass valve 13 is opened, and the compressor 9 is driven, outside air bypasses the FC stack 3 from the compressor 9 and is sent to the exhaust gas pipe 17 through the exhaust air pipe 19.

The flow path is equipped with pressure sensors 31a and 31b, and the FC stack 3 is equipped with a temperature sensor 32. The pressure sensor 31a measures the internal pressure of the high-pressure fuel pipe 7a. The pressure sensor 31b measures the internal pressure of the low-pressure fuel pipe 7b. The measured values of the pressure sensors 31a, 31b and the temperature sensor 32 are sent to the controller 10. The FC system 2 is equipped with several other pressure sensors and temperature sensors, but illustrations and descriptions of these are omitted.

The controller 10 controls the main stop valves 5a, 5b, the injector 6, various valves (main stop valves 5a, 5b, air supply valve 23, air exhaust valve 24, bypass valve 13, exhaust gas valve 18), the compressor 9, and the pump 14. Based on an output command from a higher-level controller (not shown), the controller 10 adjusts the flow rate of fuel gas and the flow rate of air supplied to the FC stack 3 so that the FC stack 3 outputs a specified amount of power. The controller 10 adjusts the flow rate of fuel gas supplied to the FC stack 3 by controlling the injector 6, and adjusts the amount of air supplied to the FC stack 3 by controlling the compressor 9.

In the FC system 2, the main stop valves 5a and 5b are checked for quality before starting the FC stack 3. Alternatively, the main stop valves 5a and 5b are checked for quality when the FC stack 3 is stopped. The main stop valves 5a and 5b are solenoid-type valves that open and close according to commands from the controller 10. When the main stop valves 5a and 5b are defective, it means that the main stop valves 5a and 5b do not close completely despite a command to close them being sent from the controller 10, and fuel gas in the fuel tanks 4a and 4b leaks through the main stop valves 5a and 5b into the high-pressure fuel pipe 7a.

As mentioned above, the process for determining whether the main stop valves 5a, 5b are in good condition is referred to as the main stop valve inspection process below. The main stop valve inspection process is outlined as follows. The controller 10 opens and closes the main stop valves 5a, 5b while keeping the injector 6 closed, and then opens and closes the injector 6 while keeping the main stop valves 5a, 5b closed. The controller 10 determines whether the main stop valves 5a, 5b are in good condition based on the change in internal pressure of the high-pressure fuel pipe 7a between the opening and closing of the injector 6 and the opening and closing of the main stop valves 5a, 5b. The specific steps of the main stop valve inspection process are explained using Figures 2-4.

Figures 2 and 3 are flowcharts of the main stop valve inspection process. Figure 4 is a flowchart of the FC stack internal pressure monitoring process, which is executed simultaneously and in parallel with the main stop valve inspection process.

First, the controller 10 starts the FC stack internal pressure monitoring process (step S2). The FC stack internal pressure monitoring process will be described later. Next, the controller 10 closes the injector 6 and opens the main stop valves 5a and 5b (step S3). When the main stop valves 5a and 5b are opened, fuel gas flows from the fuel tanks 4a and 4b into the high-pressure fuel pipe 7a. The controller 10 monitors the measurement value of the pressure sensor 31a (i.e., the internal pressure of the high-pressure fuel pipe 7a), and closes the main stop valves 5a and 5b when the internal pressure of the high-pressure fuel pipe 7a reaches a predetermined first pressure (steps S4: YES, S5).

Note that "closing the main stop valve" in step S5 of FIG. 2 means, more precisely, that the controller 10 sends a command to close the main stop valve. If the main stop valves 5a and 5b are normal, they will close completely in response to the command to close from the controller 10, and the fuel tanks 4a and 4b and the high-pressure fuel pipe 7a will be completely blocked. However, if the main stop valves 5a and/or 5b do not close completely even though the controller 10 has sent a command to close, fuel gas will continue to leak from the fuel tanks 4a and/or 4b to the high-pressure fuel pipe 7a. The process in FIGS. 2 and 3 is a process for detecting such a failure to close the main stop valves 5a and/or 5b.

Next, the controller 10 opens the injector 6 (FIG. 3, step S12). When the injector 6 is opened, the fuel gas in the high-pressure fuel pipe 7a flows to the low-pressure fuel pipe 7b. The controller 10 calculates the volume (injection amount) of the fuel gas injected by the injector 6 (step S13). The flow rate (volume of fuel gas injected per unit time) injected by the injector 6 depends on temperature and pressure. The relationship between flow rate and temperature/pressure is known. The measurement value of the temperature sensor 32 provided in the FC stack 3 can be used as an approximate temperature of the injected fuel gas. The gas pressure in the injector 6 is estimated from the measurement values of the pressure sensors 31a and 31b arranged upstream and downstream of the injector 6. The controller 10 obtains the gas pressure upstream of the injector 6 from the measurement value of the pressure sensor 31a attached to the high-pressure fuel pipe 7a, and obtains the gas pressure downstream of the injector 6 from the measurement value of the pressure sensor 31b attached to the low-pressure fuel pipe 7b. The controller 10 estimates the gas pressure that correlates with the flow rate of the injector 6 from the gas pressures upstream and downstream of the injector 6. A description of the estimation of the gas pressure is omitted. The flow rate of the injector 6 is obtained from the measurement values of the temperature sensor 32 and the pressure sensors 31a and 31b. Note that the sensor measurement values used to obtain the flow rate of the injector 6 are not limited to the above example. For example, if a flow rate sensor is provided upstream or downstream of the injector 6, the measurement value of the flow rate sensor can be used as the flow rate of the injector 6 as is.

The controller 10 repeatedly calculates the volume (injection amount) of fuel gas injected from the injector 6 while the injector 6 is open (steps S15, NO, S13). The injection amount is calculated from the time since the injector 6 was opened and the flow rate of the injector 6. If the injection amount exceeds a predetermined injection amount threshold before the internal pressure of the high-pressure fuel pipe 7a drops to the second pressure, the controller 10 determines that at least one of the main stop valves 5a, 5b is defective (step S14: NO). In other words, if the injection amount exceeds a predetermined injection amount threshold before the internal pressure of the high-pressure fuel pipe 7a drops to the second pressure, the controller 10 determines that at least one of the main stop valves 5a, 5b is defective.

The first pressure and the second pressure are determined in advance. The second pressure is set to a value lower than the first pressure. The injection amount threshold is set to a gas volume required to reduce the internal pressure of the high-pressure fuel pipe 7a from the first pressure to the second pressure. Therefore, if the internal pressure of the high-pressure fuel pipe 7a drops to the second pressure before the injection amount of the injector 6 exceeds the injection amount threshold, the controller 10 determines that the main stop valves 5a and 5b are normal (step S14: NO, S15: YES). In this case, the controller 10 notifies the upper controller (not shown) that the main stop valves 5a and 5b are normal (step S16). Then, the controller 10 closes the injector 6 (step S18), ends the FC stack internal pressure monitoring process (step S19), and ends the main stop valve inspection process.

On the other hand, when the injection amount of the injector 6 exceeds the injection amount threshold, it is found that at least one of the main stop valves 5a, 5b is not completely closed and fuel gas is leaking from the fuel tanks 4a, 4b to the high-pressure fuel pipe 7a. That is, the controller 10 determines that at least one of the main stop valves 5a, 5b is defective. In this case, the controller 10 notifies a higher-level controller (not shown) of the defect in the main stop valves 5a, 5b (step S17). If a defect in the main stop valve 5a or 5b is detected, the controller 10 closes the injector 6 even if the internal pressure does not drop to the second pressure (step S18). After closing the injector 6, the controller 10 ends the FC stack internal pressure monitoring process (step S19) and ends the main stop valve inspection process.

When the main stop valve inspection process is completed via step S16, the upper controller executes the next normal process. If the main stop valve inspection process is performed before starting up the FC stack 3, and if the main stop valve is normal, the upper controller then executes the startup process for the FC stack 3. If the main stop valve inspection process is performed before stopping the FC stack, and if the main stop valve is normal, the upper controller then executes the process to stop the FC stack 3.

On the other hand, if the main stop valve inspection process is terminated via step S17, the upper controller executes a process corresponding to a main stop valve malfunction (abnormality response process). If a malfunction of the main stop valve 5a or 5b is detected, the upper controller displays a message indicating a main stop valve malfunction, for example, on the display device of the FC system 2. Alternatively, the upper controller turns on a warning lamp of the FC system 2.

The processing in Figures 2 and 3 checks whether the main stop valves 5a and 5b are completely closed in response to a closure command from the controller 10.

Next, the FC stack internal pressure monitoring process will be described with reference to FIG. 4. The process of FIG. 4 is repeatedly executed during the main stop valve inspection process. More precisely, the process of FIG. 4 is repeatedly executed while the injector 6 is open during the main stop valve inspection process.

The controller 10 acquires the internal pressure of the FC stack 3 (step S22). Since the low-pressure fuel pipe 7b is directly connected to the FC stack 3, the measurement value of the pressure sensor 31b that measures the internal pressure of the low-pressure fuel pipe 7b is used as the internal pressure of the FC stack 3.

The controller 10 compares the internal pressure of the FC stack 3 with a predetermined threshold pressure (step S23). The threshold pressure is set to the upper limit of the pressure range suitable for starting the FC stack 3. The internal pressure of the FC stack 3 starts to rise at the same time as the injector 6 is opened in step S12 of FIG. 3. When the internal pressure of the FC stack 3 reaches the threshold pressure (step S23: YES), the controller 10 executes the processes of steps S24 and S25. That is, the controller 10 opens the exhaust gas valve 18 (step S24) and drives the compressor 9 so that the concentration of fuel contained in the exhaust gas discharged to the outside air is equal to or lower than the upper limit concentration (step S25).

During the FC stack internal pressure monitoring process, the controller 10 closes the air supply valve 23 and air exhaust valve 24, and keeps the bypass valve 13 open. Because the bypass valve 13 is open, air is sent from the compressor 9 to the exhaust gas pipe 17 via the bypass flow path 11. A portion of the fuel gas from the FC stack 3 flows through the exhaust gas pipe 17 via the gas-liquid separator 15. The fuel gas exhausted from the FC stack 3 is mixed with air in the muffler 20 attached midway through the exhaust gas pipe 17, and is released to the outside air.

In step S25, the controller 10 drives the compressor 9 so that the fuel concentration contained in the exhaust gas released into the outside air is equal to or lower than a predetermined upper limit concentration. Increasing the output of the compressor 9 increases the amount of air supplied to the muffler 20, decreasing the fuel concentration. This control prevents exhaust gas containing fuel with a concentration exceeding a specified value (upper limit concentration) from being released.

If it is determined in step S23 that the internal pressure of the FC stack 3 does not exceed the threshold pressure, the controller 10 ends the process without opening the exhaust gas valve 18 or driving the compressor 9 (steps S23: NO, S26). As described above, the controller 10 repeatedly executes the process of FIG. 4.

The advantages of the main stop valve inspection in the FC system 2 of the embodiment will be described. During the main stop valve inspection process, the controller 10 opens the exhaust gas valve 18 when the internal pressure of the FC stack 3 reaches a threshold pressure. At the same time, the controller 10 drives the compressor 9 so that the concentration of fuel released from the exhaust gas pipe 17 is equal to or lower than the upper limit concentration. The former process prevents a large amount of fuel gas from remaining in the FC stack 3 during the main stop valve inspection. The latter process prevents exhaust gas containing a high concentration of fuel from being released to the outside during the main stop valve inspection.

As the scale of the FC system 2 increases (as the number of fuel tanks connected to the FC stack increases), the capacity of the high-pressure fuel pipe 7a increases. As the capacity of the high-pressure fuel pipe 7a increases, the amount of fuel gas that flows into the FC stack 3 during main stop valve inspection increases. The main stop valve inspection process in the FC system 2 of the embodiment is suitable for such large-scale FC systems.

In the main stop valve inspection process of the embodiment, the quality of the main stop valve is judged based on the internal pressure of the high-pressure fuel pipe 7a and the injection volume while the injector 6 is open. Since it is based on the injection volume of the injector 6, the quality of the main stop valve is judged in a short time. The process of the embodiment can judge the quality of the main stop valve in a short time.

In the FC system 2 of the embodiment, during the main stop valve inspection process, if the internal pressure of the FC stack 3 exceeds a threshold pressure, fuel gas is released. The internal pressure of the FC stack 3 is prevented from rising excessively. In addition, when the fuel gas remaining in the FC stack 3 is released, the controller 10 and compressor 9 work to dilute the fuel so that the fuel concentration is below the upper limit concentration. Furthermore, the air used to dilute the fuel is sent from the compressor 9 to the exhaust gas pipe 17, bypassing the FC stack 3. Since excessive air is not sent to the FC stack 3, the FC stack 3 can also be prevented from drying out.

Notes regarding the technology described in the embodiment are as follows. The high-pressure fuel pipe 7a corresponds to the fuel pipe connecting the main stop valves 5a, 5b to the injector 6. In the embodiment, the main stop valves 5a, 5b are opened and closed simultaneously. One main stop valve may be closed while the other main stop valve is closed to execute the processes of Figures 2 to 4, and then one main stop valve may be opened and closed while the other main stop valve is closed to execute the processes of Figures 2 to 4. The quality of multiple main stop valves can be determined individually. The number of fuel tanks (main stop valves) connected to the injector may be three or more. The FC system may also be configured to have one main stop valve for multiple fuel tanks.

Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exert technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful.

2: FC system 3: FC stack 4a, 4b: Fuel tank 5a, 5b: Main stop valve 6: Injector 7: Fuel pipe 7a: High pressure fuel pipe 7b: Low pressure fuel pipe 9: Compressor 10: Controller 11: Bypass flow path 12: Air pipe 13: Bypass valve 14: Pump 15: Gas-liquid separator 16: Return flow path 17: Exhaust gas pipe 18: Exhaust gas valve 19: Exhaust air pipe 20: Muffler 23: Air supply valve 24: Air exhaust valve 31a, 31b: Pressure sensor 32: Temperature sensor

Claims (3)

A fuel tank;
A fuel cell stack;
a main stop valve for stopping the outflow of fuel gas from the fuel tank;
an injector for adjusting a flow rate of the fuel gas supplied to the fuel cell stack;
a fuel pipe connecting the main stop valve and the injector;
a compressor for delivering air to the fuel cell stack;
an exhaust gas pipe that mixes the fuel gas in the fuel cell stack with the air and discharges the mixture;
an exhaust gas valve for closing the exhaust gas pipe;
a controller that controls the main stop valve, the injector, the compressor, and the exhaust gas valve;
Equipped with
The controller opens and closes the injector after opening and closing the main stop valve, and while performing a main stop valve inspection to determine whether the main stop valve is good or bad based on pressure changes in the fuel pipe, opens the exhaust gas valve when the internal pressure of the fuel cell stack reaches a predetermined threshold pressure, and drives the compressor so that the concentration of fuel released from the exhaust gas pipe is below a predetermined upper limit concentration. The controller, in the main stop valve inspection,
closing the injector and opening the main stop valve to raise the internal pressure of the fuel pipe to a first pressure, then closing the main stop valve and opening the injector, and if the amount of fuel gas injected by the injector exceeds a predetermined injection amount threshold before the internal pressure of the fuel pipe drops to a second pressure , it is determined that the main stop valve is defective.
The fuel cell system according to claim 1 . The fuel cell system according to claim 1 or 2, further comprising a bypass flow path that sends the air from the compressor to the exhaust gas pipe, bypassing the fuel cell stack, and the controller sends the air from the compressor to the exhaust gas pipe using the bypass flow path while performing the main stop valve inspection.

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