JP7635728B2 - Fuel Cell Systems - Google Patents

Description

The technology disclosed in this specification relates to a fuel cell system that includes multiple fuel cell stacks.

Patent Documents 1 and 2 disclose fuel cell systems that generate electricity using multiple fuel cell stacks. In the fuel cell stack, fuel gas (hydrogen gas) reacts with oxygen (air) to generate electricity. The fuel gas remaining in the fuel cell stack (unreacted fuel gas) is sent to a diluter. In the diluter, the unreacted fuel gas is diluted with air to a predetermined allowable concentration before being released.

The fuel cell system in Patent Document 1 is equipped with a common air compressor and a common diluter for multiple fuel cell stacks. The fuel cell system in Patent Document 2 is equipped with an air compressor for each fuel cell stack.

JP 2006-155997 A JP 2020-57460 A

This specification relates to a fuel cell system equipped with multiple fuel cell stacks, and provides a technology for efficiently diluting unreacted fuel gas.

The fuel cell system disclosed in this specification includes a plurality of fuel cell stacks, a plurality of air compressors, a diluter, a bypass passage, an adjustment valve, and a controller. Each air compressor is connected to each fuel cell stack and sends air to the corresponding fuel cell stack. The diluter mixes unreacted fuel gas discharged from each fuel cell stack with air and discharges the mixture. The bypass passage connects the air compressors to the diluter and sends air from each air compressor to the diluter, bypassing the fuel cell stack. The adjustment valve connects each air compressor to the bypass passage and adjusts the flow rate of air sent from each air compressor to the bypass passage. The controller controls the air compressor and the adjustment valve so that the concentration of fuel gas contained in the gas discharged from the diluter is equal to or lower than a predetermined allowable concentration. The controller selects an air compressor with the smallest output or loss from among the plurality of air compressors, and controls the adjustment valve so that air is sent from the selected air compressor to the diluter through the bypass passage .

In the fuel cell system disclosed in this specification, an air compressor with minimal output or loss is used to dilute the unreacted fuel gas. Therefore, the fuel gas can be efficiently diluted.

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 a fuel cell system according to an embodiment.

The fuel cell system 2 of the embodiment will be described with reference to the drawings. In the following, for ease of explanation, "fuel cell" may be abbreviated as FC. FIG. 1 shows a block diagram of the FC system 2. The controller 6 and various devices (valves 31, 32, 33, 34, air compressor 12, gas sensor 16, boost converter 11, inverter 4, etc.) are connected by communication lines, but the communication lines are not shown in the figure.

The FC system 2 has two FC stacks (a first FC stack 10a and a second FC stack 10b), and each FC stack generates electricity. In the following, the first FC stack 10a and the second FC stack 10b may be referred to as FC stack 10 without distinction.

In addition, when there is no distinction between valves 31a and 31b, air pipes 22a and 22b, and air compressors 12a and 12b, they may be referred to as valve 31, air pipe 22, and air compressor 12.

Each FC stack 10 is associated with a boost converter 11. The boost converter 11 is connected to the power output terminal of the FC stack 10, and the output terminal of the boost converter 11 is connected to the DC terminal of the inverter 4. The boost converter 11 boosts the DC power generated by the FC stack 10 and supplies it to the inverter 4. The inverter 4 converts the boosted DC power into AC power. The system output terminal 5 is connected to the AC terminal of the inverter 4, and the power generated by the FC stack 10 is supplied to other devices from the system output terminal 5.

The FC stack 10 is supplied with fuel gas (hydrogen gas) from the fuel tank 3 through a fuel supply pipe 21. A fuel valve 31 is connected to the fuel supply pipe 21, and the flow rate of the fuel gas supplied to the FC stack 10 can be adjusted by adjusting the opening of the fuel valve 31. The fuel valve 31 is sometimes called an injector.

A pressure sensor (not shown) is connected downstream of the fuel valve 31, and the pressure measured by the pressure sensor is equal to the pressure inside the FC stack 10. The controller 6 controls the opening of the fuel valve 31 so that the measurement value of the pressure sensor is kept within an appropriate range (i.e., so that the internal pressure of the FC stack 10 is kept within an appropriate range) while the FC stack 10 is generating electricity. The first fuel valve 31a adjusts the flow rate of fuel gas supplied to the first FC stack 10a, and the second fuel valve 31b adjusts the flow rate of fuel gas supplied to the second FC stack 10b.

Air (oxygen) is supplied to the FC stack 10 through an air pipe 22. The air pipe 22 is equipped with an air compressor 12 and an air valve 32, and air is sent to the FC stack 10 by the air compressor 12. The amount of air (oxygen) supplied to the FC stack 10 is adjusted by the output of the air compressor 12 and the opening of the air valve 32. The controller 6 adjusts the amount of air supplied to the FC stack 10 according to the flow rate of fuel gas supplied to the FC stack 10.

The first FC stack 10a is connected to the first air compressor 12a by the first air pipe 22a, and the second FC stack 10b is connected to the second air compressor 12b by the second air pipe 22b. A first air valve 32a is attached to the first air pipe 22a, and a second air valve 32b is attached to the second air pipe 22b.

In the FC stack 10, fuel gas (hydrogen) reacts with air (oxygen) to generate electricity. The gas after the reaction (exhaust gas) is sent to the gas-liquid separator 14 via the exhaust gas pipe 23. The exhaust gas also contains a small amount of fuel gas (unreacted fuel gas) that was not used in the reaction in the FC stack 10. In the gas-liquid separator 14, the unreacted fuel gas is separated from the exhaust gas. The separated fuel gas is returned to the fuel supply pipe 21 via the return pipe 24.

The exhaust gas and water remaining in the gas-liquid separator 14 are sent to the diluter 15 through the valve 34. Meanwhile, the air remaining in the reaction is sent from the FC stack 10 to the diluter 15 through the exhaust air pipe 25. A small amount of fuel gas remains in the exhaust gas sent to the diluter 15. The remaining fuel gas is mixed with the air remaining in the reaction in the diluter 15 and diluted. The diluter 15 is equipped with a gas sensor 16. The controller 6 monitors the fuel gas concentration in the diluter 15 using the gas sensor 16. A valve 34 is provided between the gas-liquid separator 14 and the diluter 15, and the controller 6 controls the valve 34 to adjust the flow rate of the exhaust gas sent to the diluter 15 so that the concentration of fuel gas contained in the gas discharged from the diluter 15 is equal to or lower than a predetermined allowable concentration. The fuel gas diluted to a level equal to or lower than the allowable concentration is released from the diluter 15 to the atmosphere.

When a relatively large amount of fuel gas must be released into the atmosphere, air is sent from the air compressor 12 to the diluter 15 through the bypass path 26. The bypass path 26 directly connects the air compressor 12 and the diluter 15. In other words, the bypass path 26 can send air from the air compressor 12 to the diluter 15 without passing through the FC stack 10. By providing the bypass path 26, additional air can be sent to the diluter 15 without changing the amount of air supplied to the FC stack 10.

The first air compressor 12a and the bypass passage 26 are connected by a first adjustment valve 33a, and the second air compressor 12b and the bypass passage 26 are connected by a second adjustment valve 33b. If the air discharged from the FC stack 10 is insufficient to dilute the fuel gas concentration in the exhaust gas to an allowable concentration or less, the controller 6 opens the adjustment valve 33a or 33b to make up for the lack of air, and sends air directly from the air compressor 12a or 12b to the diluter 15.

When sending air to the diluter 15 through the bypass path 26, the controller 6 selects, from among the multiple air compressors 12, the air compressor 12 with the smallest output or loss. The controller 6 increases the output of the selected air compressor 12, opens the regulating valve 33 connected to the selected air compressor 12, and sends air from the selected air compressor 12 to the diluter 15.

The FC system 2 includes multiple FC stacks 10, and the multiple FC stacks 10 may have different operating conditions. If the operating conditions are different, the amount of air sent to the FC stack 10 will also be different. In addition, each FC stack 10 needs to be periodically drained. When draining water from the FC stack 10, a large amount of air is supplied to the FC stack 10. In addition, when the FC stack 10 is stopped, the fuel gas remaining in the FC stack 10 needs to be discharged from the FC stack 10. At this time, a large amount of air is also sent to the FC stack 10. In this way, the amount of air required by the multiple FC stacks may differ. Since the amount of air required is different, the target output of the multiple air compressors 12 also differs.

When there is a shortage of air for dilution, the controller 6 selects the air compressor 12 with the smallest output or loss, and sends air from the selected air compressor 12 to the diluter 15. Since the air compressor with the smallest output or loss is used to send air directly to the diluter 15, the unreacted fuel gas can be efficiently diluted. For example, when the first air compressor 12a is operating at 200 [W] and the second air compressor 12b is operating at 100 [W], if there is a shortage of air in the diluter 15, the controller 6 selects the second air compressor 12b with the smallest output. The controller 6 increases the output of the selected second air compressor 12b and opens the second adjustment valve 33b corresponding to the second air compressor 12b.

The loss of the air compressor 12 depends on the rotation speed (or output). The controller 6 stores a correspondence table between the rotation speed (or output) and the loss, and refers to the table to select the air compressor 12 with the smallest loss. The controller 6 may select the air compressor 12 with the smallest output from among the multiple air compressors 12, or may select the air compressor 12 with the smallest loss.

Notes on the technology described in the embodiment are as follows. The FC system disclosed in this specification may have three or more FC stacks connected in parallel. Each FC stack is equipped with an air compressor 12. The exhaust gases from the three FC stacks are sent to the gas-liquid separator 14 through a common exhaust gas pipe 23. The exhaust gas remaining in the gas-liquid separator 14 is sent to the diluter 15. When the fuel gas concentration in the exhaust gas is high, the controller 6 selects the air compressor 12 with the smallest output or loss from among the three or more air compressors 12. The controller 6 increases the output of the selected air compressor 12, opens the adjustment valve 33 corresponding to the selected air compressor 12, and sends air directly to the diluter 15.

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: Fuel cell system 3: Fuel tank 4: Inverter 5: System output 6: Controller 10, 10a, 10b: FC stack 11: Boost converter 12, 12a, 12b: Air compressor 14: Gas-liquid separator 15: Diluter 16: Gas sensor 21: Fuel supply pipe 22, 22a, 22b: Air pipe 23: Exhaust gas pipe 24: Return pipe 25: Exhaust air pipe 26: Bypass 31, 32, 33, 34: Valve

Claims (1)

A plurality of fuel cell stacks;
a plurality of air compressors, each of which delivers air to a respective one of the fuel cell stacks;
a diluter that mixes unreacted fuel gas and air discharged from each of the fuel cell stacks and discharges the mixture;
a bypass passage for transmitting air from each of the air compressors to the diluter, bypassing the fuel cell stack;
an adjusting valve for adjusting the flow rate of air sent from each of the air compressors to the bypass;
a controller that controls the air compressor and the regulating valve so that the concentration of the fuel gas contained in the exhaust gas in the diluter is equal to or lower than a predetermined allowable concentration;
Equipped with
The controller selects the air compressor having the smallest output or loss from among the plurality of air compressors, and controls the regulating valve so as to send air from the selected air compressor through the bypass path to the diluter.
Fuel cell system.

Images