JP2006339112A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove water in a gas passage in a fuel cell while maintaining a water content of a solid electrolyte membrane. <P>SOLUTION: A controller 15 performs first purge processing purging the fuel gas flow passage and an oxidation gas flow passage in the fuel cell 1 with high humidity gas by controlling a hydrogen humidification means 4 and an air humidification means 10 after stopping power generation of the fuel cell 1 and performs a second purge processing purging the fuel gas flow passage and the oxidation gas flow passage which are purged with the high humidity gas with low humidity gas after performing the first purge processing. The controller 15 controls the hydrogen humidification means 4 and the air humidification means 10 during the second purge processing so that the amount of water taken out from the fuel cell 1 with the low humidity gas becomes larger than the amount of water carried into the fuel cell 1 with the high humidity gas by the first purge processing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell that generates power by sandwiching a solid electrolyte membrane between a fuel electrode and an oxidant electrode and receiving fuel gas and oxidant gas respectively supplied to the fuel electrode and the oxidant electrode.

  In general, when water generated by power generation is not properly removed from the inside of the fuel cell, water remains in the gas flow path and the gas diffusion layer inside the fuel cell, thereby inhibiting the diffusion of the reaction gas inside the fuel cell. End up. Such a phenomenon is generally called a flooding phenomenon. When the flooding phenomenon occurs, the reaction gas is prevented from reaching the catalyst by diffusion, and the power generation performance of the fuel cell is lowered. For this reason, the conventional fuel cell system improves the performance of removing water from the fuel cell by changing the operating conditions, such as increasing the temperature of the reaction gas or increasing the flow rate of the reaction gas. Occurrence is suppressed.

  However, since a large amount of energy is required for increasing the temperature of the reaction gas and increasing the flow rate, the system efficiency decreases when the occurrence of the flooding phenomenon is suppressed as described above. Also, if the temperature of the reaction gas decreases from the reaction gas inlet side to the reaction gas outlet side of the fuel cell, or if there is a part where the flow rate of the reaction gas is low inside the fuel cell, water will condense and form as a result. End up. In addition, when the outside air temperature of the system is as low as the freezing temperature, the saturated water vapor pressure becomes extremely low and the water is frozen, so that it is difficult to remove water by the reaction gas.

Against this background, when the fuel cell power generation is stopped in recent years, residual water in the gas flow path is removed by supplying a humidified reaction gas (humidified gas) at a higher flow rate than when idling. Then, a fuel cell system has been proposed in which residual water in the electrode is removed by supplying a dry reaction gas (non-humidified gas) that is not humidified to the fuel cell at a flow rate lower than that of the humidified reaction gas. (For example, refer to Patent Document 1). And according to such a fuel cell system, while suppressing the deterioration of the solid electrolyte membrane which comprises a fuel cell, while removing the residual water inside a fuel cell, a fuel cell can be restarted rapidly.
JP 2004-152600 A

  However, according to the conventional fuel cell system as described above, since the supply amount of the non-humidified gas is small, the water inside the fuel cell cannot be sufficiently removed, and the fuel cell is at a low temperature such as a sub-freezing temperature. It may be difficult to restart the fuel cell due to freezing of water remaining inside.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel capable of eliminating water in the gas flow path inside the fuel cell while maintaining the moisture content of the solid electrolyte membrane. It is to provide a battery system.

  In order to solve the above-described problem, a fuel cell system according to the present invention performs a first purge process for purging a reaction gas channel with a high-humidity gas after power generation of the fuel cell is stopped, and after the first purge process is performed. The second purge process for purging the reaction gas flow path purged with the high-humidity gas with the low-humidity gas is executed, and the amount of water taken out from the fuel cell by the low-humidity gas when the second purge process is executed is the first purge process. Is controlled so as to be more than the amount of water brought into the fuel cell by the high humidity gas.

  According to the fuel cell system of the present invention, the amount of water taken out from the fuel cell by the low-humidity gas when the second purge process is performed is equal to or greater than the amount of water brought into the fuel cell by the high-humidity gas in the first purge process. Thus, the water in the gas flow path inside the fuel cell can be eliminated while maintaining the moisture content of the solid electrolyte membrane. As a result, it is possible to suppress the difficulty in restarting the fuel cell due to water freezing at low temperatures.

  Hereinafter, the configuration and operation of the fuel cell system according to the first and second embodiments of the present invention will be described with reference to the drawings.

[Configuration of fuel cell system]
As shown in FIG. 1, the fuel cell system according to the first embodiment of the present invention generates power by receiving supply of hydrogen and air as fuel gas and oxidant gas to the fuel electrode 1a and the oxidant electrode 1b, respectively. A fuel cell 1 is provided. In this embodiment, the fuel cell 1 is constituted by a solid oxide fuel cell in which a polymer solid electrolyte membrane having hydrogen ion conductivity is sandwiched between a fuel electrode 1a and an oxidant electrode 1b. Moreover, the electrochemical reaction in the fuel electrode 1a and the oxidant 1b and the electrochemical reaction in the fuel cell 1 as a whole are based on the following formulas (1) to (3).

[Fuel electrode] H ₂ → 2H ⁺ + 2e ⁻ (1)
[Oxidant electrode] 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
[Overall] H ₂ +1/2 O ₂ → H ₂ O (3)
[Configuration of hydrogen system]
The fuel cell system includes a hydrogen flow rate control means 2 that adjusts the flow rate of hydrogen supplied from a hydrogen supply device (not shown), and humidifies the hydrogen supplied from the hydrogen flow rate control means 2 via the hydrogen supply flow path 3. Hydrogen humidifying means 4 for supplying fuel electrode 1a of fuel cell 1 is provided. Unused hydrogen in the fuel electrode 1 a is discharged out of the system through the hydrogen discharge channel 5. Further, valves 6a and 6b are provided on the upstream side and the downstream side of the hydrogen humidifying means 4, and the hydrogen supplied from the hydrogen flow rate control means 2 is adjusted by adjusting the opening degree of the valves 6a and 6b. The fuel electrode 1a can be directly supplied to the fuel electrode 1a via the bypass channel 7 without passing through (without humidification) 4.

[Air system configuration]
The fuel cell system includes an air flow rate control means 8 that adjusts the flow rate of air supplied from an air supply device (not shown), and humidifies the air supplied from the air flow rate control means 8 to fuel through an air supply flow path 9. Air humidifying means 10 for supplying the oxidant electrode 1b of the battery 1 is provided. Unused air at the oxidizer electrode 1 b is discharged out of the system through the air discharge channel 11. Valves 12a and 12b are provided on the upstream side and downstream side of the air humidifying means 10, and the air supplied from the air flow rate control means 8 is adjusted by adjusting the opening degree of the valves 12a and 12b. The oxidant electrode 1b can be directly supplied via the bypass channel 13 without going through 10 (without humidification).

[Control system configuration]
The fuel cell system includes a timer 14 for measuring time and a controller 15 for controlling the operation of the entire fuel cell system. The fuel cell system having such a configuration maintains the moisture content of the polymer solid electrolyte membrane constituting the fuel cell 1 by executing the following purge process when the fuel cell 1 stops generating power. Meanwhile, water in the gas flow path inside the fuel cell 1 is eliminated. The operation of the fuel cell system when performing the purge process will be described below with reference to the flowchart shown in FIG.

[Purge process]
The flowchart shown in FIG. 2 starts when the extraction of the generated current of the fuel cell 1 stops, and the purge process proceeds to step S1.

  In the process of step S1, the controller 15 controls the valves 6a, 6b, 12a, 12b, the hydrogen humidifying means 4, and the air humidifying means 10 to generate hydrogen and air having a relative humidity of 100% (high humidity). The fuel electrode 1a and the oxidant electrode 1b are respectively supplied (first purge process). More specifically, the controller 15 determines the relative amount of hydrogen and air on the inlet side of the fuel cell 1 so that the amount of water supplied to the fuel cell 1 is larger than the amount of water discharged from the fuel cell 1. Control humidity. Simultaneously with the supply of high-humidity hydrogen and air, the controller 15 starts time measurement by turning on the timer 14. According to such processing, the amount of water remaining inside the fuel cell 1 increases with the passage of time T as shown in FIG. Thereby, the process of step S1 is completed and the purge process proceeds to the process of step S2.

  In the process of step S2, the controller 15 refers to the time measured by the timer 14 and determines whether or not a predetermined time T1 has elapsed since the execution of the process of step S1 was started. Then, as the predetermined time T1 elapses after the execution of the process in step S1, the controller 15 turns off the timer 14, and then advances the purge process to the process in step S3. The predetermined time T1 is a time from when the supply of high-humidity hydrogen and air is started until the amount of water in the fuel cell 1 reaches a predetermined amount. This value is obtained in advance by experiments by providing a sensor or the like.

  In the process of step S3, the controller 15 adjusts the opening degree of the valves 6a, 6b, 12a, 12b, and passes the hydrogen and air to the fuel electrode 1a and the oxidant without passing through the hydrogen humidifying means 4 and the air humidifying means 10, respectively. By supplying the electrode 1b, dry (low humidity) hydrogen and air are supplied to the fuel electrode 1a and the oxidant electrode 1b, respectively (second purge process). Further, the controller 15 controls the hydrogen flow rate control means 2 and the air flow rate control means 8 to increase the flow rates of hydrogen and air supplied to the fuel electrode 1a and the oxidant electrode 1b as compared with the first purge process. At the same time, the time measurement is started by turning on the timer 14 simultaneously with the supply of the dry hydrogen and air. According to such processing, the amount of water remaining in the fuel cell 1 decreases with the passage of time T as shown in FIG. Thereby, the process of step S3 is completed, and the purge process proceeds to the process of step S4.

  In the process of step S4, the controller 15 refers to the time measured by the timer 14 and determines whether or not a predetermined time T2 has elapsed since the execution of the process of step S3 was started. Here, the predetermined time T2 is a time when the amount of water remaining in the fuel cell 1 becomes negative after the supply of dry hydrogen and air is started, and is longer than the predetermined time T1, It is a value obtained in advance by an experiment by providing a moisture sensor inside. In addition, by setting the predetermined time T2 to the time when the amount of water remaining in the fuel cell 1 becomes negative after the supply of dry hydrogen and air is started, a part of the water in the polymer solid electrolyte membrane is The amount of water discharged outside the fuel cell 1 and remaining in the fuel cell 1 after the second purge process is smaller than before the first purge process is performed. Then, as the predetermined time T2 elapses after the execution of the process of step S3 is started, the controller 15 finishes a series of purge processes, and the fuel cell system is brought into a stopped state.

  As is apparent from the above description, according to the fuel cell system according to the first embodiment of the present invention, the controller 15 controls the hydrogen humidifying means 4 and the air humidifying means 10 after the power generation of the fuel cell 1 is stopped. Thus, the first purge process for purging the fuel gas flow path and the oxidant gas flow path inside the fuel cell 1 with the high humidity gas is performed, and after the first purge process is performed, the fuel gas flow purged with the high humidity gas is performed. A second purge process for purging the channel and the oxidant gas channel with the low humidity gas is executed. Further, the controller 15 causes the amount of water taken out from the fuel cell 1 by the low-humidity gas to be equal to or greater than the amount of water brought into the fuel cell 1 by the high-humidity gas in the first purge processing when the second purge process is executed. The hydrogen humidifying means 4 and the air humidifying means 10 are controlled.

  According to such a configuration, water remaining in the gas channel can be eliminated while maintaining the moisture content of the polymer solid electrolyte membrane constituting the fuel cell 1, so that it remains in the gas channel at a low temperature. It can suppress that the water which was doing freezes and the electric power generation of the fuel cell 1 is inhibited. In this embodiment, the high-humidity gas and the low-humidity gas are supplied to both the fuel gas channel and the oxidant gas channel, but the high-humidity gas and the oxidant gas channel are only supplied to one of the fuel gas channel and the oxidant gas channel. A low humidity gas may be supplied.

  Further, according to the fuel cell system according to the first embodiment of the present invention, the controller 15 controls the flow rate of the low humidity gas in the second purge process to be equal to or higher than the flow rate of the high humidity gas in the first purge process. Therefore, even if the water brought into the fuel cell 1 in the first purge process remains, the water remaining in the fuel cell 1 in the second purge process is discharged, and the remaining water Thus, it is possible to avoid freezing of the gas flow path.

  Further, according to the fuel cell system of the first embodiment of the present invention, the controller 15 discharges from the fuel cell 1 the amount of water supplied to the fuel cell 1 by the high humidity gas when the first purge process is executed. Since the relative humidity of the high-humidity gas on the reaction gas inlet side of the fuel cell 1 is controlled so as to be equal to or greater than the amount of water to be produced, even if the state when the fuel cell 1 is stopped tends to dry, the polymer The solid electrolyte membrane can be sufficiently humidified.

  In the fuel cell system according to the first embodiment of the present invention, the controller 15 executes the first purge process for a predetermined time T1, and then executes the second purge process for a predetermined time T2. That is, since the controller 15 controls the purge process executed according to time, the first purge process and the second purge process can be executed without using a device for detecting the humidified state inside the fuel cell 1.

  Further, according to the fuel cell system according to the first embodiment of the present invention, the predetermined time T2 is set longer than the predetermined time T1, so that excessive water is generated inside the fuel cell 1 by the first purge process. Even if it remains, it is possible to discharge the water remaining inside the fuel cell 1 by the second purge process and to avoid the gas flow path being frozen by the remaining water.

[Configuration of fuel cell system]
As shown in FIG. 4, the fuel cell system according to the second embodiment of the present invention is a fuel cell stored in the coolant tank 21 in addition to the configuration of the fuel cell system according to the first embodiment. A coolant pump 23 for pumping a coolant for cooling 1 to the fuel cell 1 via the coolant circulation channel 22, and a radiator for cooling the coolant discharged from the coolant channel 24 inside the fuel cell 1. 25 and a radiator fan 26 that adjusts the cooling capacity of the radiator 25 by sending air to the radiator 25. In the fuel cell system having such a configuration, when extraction of the generated current of the fuel cell 1 is stopped, a purge process shown below is performed, so that the water content of the polymer solid electrolyte membrane constituting the fuel cell 1 is increased. Water in the gas flow path inside the fuel cell 1 is excluded while maintaining the rate. Hereinafter, the operation of the fuel cell system when performing the purge process will be described with reference to the flowchart shown in FIG.

[Purge process]
The flowchart shown in FIG. 5 starts when the extraction of the generated current of the fuel cell 1 stops, and the purge process proceeds to step S11.

  In the process of step S11, the controller 15 controls the valves 6a, 6b, 12a, 12b, the hydrogen humidifying unit 4, and the air humidifying unit 10 to generate hydrogen and air having a relative humidity of 100 [%] (high humidity). The fuel electrode 1a and the oxidant electrode 1b are respectively supplied (first purge process). Further, the controller 15 increases the flow rate of the coolant flowing through the coolant flow path 24 by increasing the number of rotations of the coolant pump 23 and increases the cooling capacity of the radiator 25 by increasing the number of rotations of the radiator fan 26. Increase. Simultaneously with the supply of high-humidity hydrogen and air, the controller 15 starts time measurement by turning on the timer 14. According to such processing, the amount of water remaining inside the fuel cell 1 increases with the elapse of time T. In addition, the internal temperature of the fuel cell 1 decreases faster than the case where it is naturally cooled by the coolant, and water tends to remain inside the fuel cell 1. Thereby, the process of step S11 is completed, and the purge process proceeds to the process of step S12. Since the processing content after step S12 is the same as the processing content after step S2, description thereof will be omitted below.

  As is clear from the above description, according to the fuel cell system according to the second embodiment of the present invention, the controller 15 allows the rate of decrease in the internal temperature of the fuel cell 1 to be greater than the rate of decrease in the internal temperature due to natural cooling. Therefore, the amount of water remaining inside the fuel cell 1 can be increased, and the polymer solid electrolyte membrane can be further humidified.

  As mentioned above, although the embodiment to which the invention made by the present inventor is applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

1 is a block diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a flowchart figure which shows the flow of the purge process used as the 1st Embodiment of this invention. It is a figure which shows the change of the quantity of the water which remains in the fuel cell accompanying execution of the purge process which becomes the 1st Embodiment of this invention. It is a block diagram which shows the structure of the fuel cell system used as the 2nd Embodiment of this invention. It is a flowchart figure which shows the flow of the purge process used as the 2nd Embodiment of this invention.

Explanation of symbols

1: Fuel cell 1a: Fuel electrode 1b: Oxidant electrode 2: Hydrogen flow rate control means 3: Hydrogen supply flow path 4: Hydrogen humidification means 5: Hydrogen discharge flow paths 6a, 6b, 12a, 12b: Valves 7, 13: Bypass Flow path 8: Air flow rate control means 9: Air supply flow path 10: Air humidification means 11: Air discharge flow path 14: Timer 15: Controller

Claims (6)

A fuel cell system comprising a fuel cell that generates power by sandwiching a solid electrolyte membrane between a fuel electrode and an oxidant electrode and receiving fuel gas and oxidant gas supplied to the fuel electrode and the oxidant electrode, respectively,
Reactive gas humidifying means for humidifying the fuel gas and the oxidant gas, and supplying the humidified fuel gas and oxidant gas to the fuel electrode and the oxidant electrode, respectively;
A first purge process for purging at least one of the fuel gas flow path and the oxidant gas flow path with a high-humidity gas by controlling the reaction gas humidification means after stopping the power generation of the fuel cell. A purge means for performing a second purge process for purging the reaction gas flow path purged with the high humidity gas with the low humidity gas after the first purge process is performed,
The purge means is configured such that when the second purge process is executed, the amount of water taken out from the fuel cell by the low-humidity gas is greater than or equal to the amount of water brought into the fuel cell by the high-humidity gas in the first purge process. And controlling the reactive gas humidifying means. The fuel cell system according to claim 1,
The fuel cell system, wherein the purge means controls the flow rate of the low humidity gas in the second purge process to be equal to or higher than the flow rate of the high humidity gas in the first purge process. The fuel cell system according to claim 1 or 2, wherein
The purge means is configured so that when the first purge process is performed, the amount of water brought into the fuel cell by the high humidity gas is equal to or greater than the amount of water discharged from the fuel cell. A fuel cell system for controlling the relative humidity of the high-humidity gas in the fuel cell system. The fuel cell system according to claim 3, wherein
The fuel cell system according to claim 1, wherein the purge means controls the rate of decrease in the internal temperature of the fuel cell to be equal to or greater than the rate of decrease in the internal temperature due to natural cooling. The fuel cell system according to any one of claims 1 to 4, wherein
The fuel cell system, wherein the purge means performs the second purge process for a second predetermined time after performing the first purge process for a first predetermined time. The fuel cell system according to claim 5, wherein
The fuel cell system, wherein the purge means controls the second predetermined time to be equal to or longer than the first predetermined time.

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