JP2007194031A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of thoroughly exhausting impure gas accumulated in the fuel cell when starting it, reducing waste of fuel gas caused by exhaust of the impurity gas. <P>SOLUTION: When starting the fuel cell 1 obtaining power by electrochemical reaction of fuel gas and oxidant gas, suction of the gas in the fuel cell 1 from a gas exhaust port at anode side of the fuel cell 1 is started in a state that supply of the fuel gas to the fuel cell 1 is stopped by a gas suction means 3, and the supply of the fuel gas to the fuel cell 1 is started after starting the suction of the gas and prescribed conditions are satisfied while continuing the suction of the gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system having a fuel cell that obtains electric power by an electrochemical reaction between a fuel gas and an oxidizing gas.

  A fuel cell system supplies a fuel gas to an anode (fuel) electrode of a fuel cell, supplies an oxidizing gas to a cathode (oxygen) electrode, and causes an electrochemical reaction via an electrolyte of the fuel cell to produce electric energy. Is what you get. The fuel cell system needs to be able to generate power by spreading a sufficient amount of reaction gas to the cathode and anode during startup.

  However, in a state where the power generation of the fuel cell is stopped, nitrogen in the air supplied to the cathode electrode is accumulated on the anode electrode side due to air permeation through an electrolyte or the like. When the nitrogen concentration at the anode electrode is high and the hydrogen concentration is low, it is difficult to perform power generation processing, and therefore, the nitrogen accumulated on the anode side may be discharged when the fuel cell is started.

  For example, Patent Document 1 describes a fuel cell system that sucks gas on the anode side of a fuel cell from an anode off-gas passage through which off-gas at the anode electrode of the fuel cell passes after the supply of fuel gas is started. According to this fuel cell system, nitrogen accumulated on the anode side of the fuel cell can be discharged through the anode off gas passage.

As another fuel cell system, there is one that discharges nitrogen accumulated in the anode electrode before starting the supply of fuel gas to the fuel cell at the time of starting the fuel cell (see, for example, Patent Documents 2 and 3). ).
JP 2003-317766 A JP 2004-178902 A JP-A-8-124588

  However, since the fuel cell system described in Patent Document 1 performs gas suction at the time of start of supply of fuel gas to the fuel cell, the supplied fuel gas may be sucked and the fuel gas may be discharged wastefully. is there.

  On the other hand, since the fuel cell systems described in Patent Documents 2 and 3 suck nitrogen in a state where supply of fuel gas is stopped, it is possible to reduce wasteful discharge of hydrogen gas. However, if the gas is sucked in the state where the supply of the fuel gas is stopped, the anode side becomes a low pressure as the gas is sucked. Therefore, there is a limit to the amount of gas sucked in the fuel cell system, and there is a risk that impurity gas such as nitrogen cannot be sucked sufficiently.

  The present invention has been made in view of the above-described various problems. In a fuel cell system that discharges impurity gas accumulated on the anode side of a fuel cell at the time of starting the fuel cell, the fuel gas is discharged by the discharge of impurity gas. It is a technical problem to provide a fuel cell system that can sufficiently discharge impurity gas while reducing waste.

The present invention relates to a fuel cell that obtains electric power through an electrochemical reaction between a fuel gas and an oxidizing gas, fuel supply means for supplying the fuel gas to the fuel cell, and a fuel cell from a gas outlet on the anode side of the fuel cell. A gas suction means for sucking the gas in the fuel cell, and at the time of starting the fuel cell, the gas suction means starts sucking the gas in the fuel cell in a state where supply of the fuel gas by the fuel supply means is stopped, A fuel cell system comprising: control means for starting the supply of fuel gas by the fuel supply means while starting the gas suction and continuing the gas suction after a predetermined condition is satisfied. .

  The gas suction means sucks impurity gas such as nitrogen that has permeated and accumulated from the cathode side of the fuel cell to the anode side in order to suck the gas in the fuel cell from the gas discharge port on the anode side of the fuel cell. Can do.

  In the fuel cell system, first, when the fuel cell is started, impurity gas such as nitrogen accumulated on the anode side is sucked by the gas supply means in a state where supply of the fuel gas by the fuel supply means is stopped. Then, after the gas suction is started and after a predetermined condition is established, the supply of the fuel gas to the fuel cell is started together with the gas suction.

  The predetermined condition is a condition for determining whether or not the suction of the impurity gas on the anode side of the fuel cell is completed to some extent. Whether or not the predetermined condition is satisfied can be determined by an elapsed time after starting the gas suction by the gas suction means, a gas pressure of a path through which the anode off gas of the fuel cell system passes, or the like.

  In the present invention, after the predetermined condition is satisfied, supply of the fuel gas by the gas supply means is started together with the suction of the impurity gas by the gas suction means. Thereby, the limit of the amount of impurity gas to be sucked by the pressure drop on the anode side of the fuel cell is eliminated, and a sufficient amount of impurity gas can be discharged from the fuel cell.

  That is, the present invention has the following excellent effects as compared with the conventional fuel cell system. In the present invention, impurity gas such as nitrogen can be sufficiently sucked from the fuel cell as compared with gas suction in a state where the supply of fuel gas is stopped. Further, as compared with gas suction after starting the supply of fuel gas, the amount of fuel gas sucked in with the suction of impurity gas is reduced, and waste of fuel gas can be reduced.

  As described above, according to the fuel cell system of the present invention, impurity gas such as nitrogen accumulated in the fuel cell can be discharged when the fuel cell is started, and fuel gas is wasted due to the discharge of the impurity gas. A sufficient amount of impurity gas can be discharged while reducing the above.

  The gas suction means may be any means as long as it can guide the impurity gas accumulated on the anode side in the fuel cell to the outside of the fuel cell. For example, the circulation system for supplying the fuel gas contained in the anode off-gas to the fuel cell again. In this fuel cell system, a gas pump used for supplying fuel gas, an ejector used as oxidizing gas supply means for supplying oxidizing gas to the cathode side of the fuel cell, and the like can be applied.

  The fuel cell system according to the present invention preferably further comprises suction gas supply means for supplying the gas sucked by the gas suction means to the cathode side of the fuel cell.

The gas accumulated on the anode side of the fuel cell sucked by the gas suction means includes not only the impurity gas such as nitrogen permeated from the cathode side to the anode side through the electrolyte membrane when power generation of the fuel cell is stopped, but also the fuel cell The fuel gas supplied to is included. When this sucked gas is discharged out of the system, high-concentration fuel gas is discharged. Accordingly, it is desirable to further include the suction gas supply means, and the fuel gas contained in the gas sucked by the suction gas supply means is processed on the cathode side of the fuel cell to further reduce the concentration of the fuel gas. it can.

  According to the fuel cell system of the present invention, at the time of starting the fuel cell, after the suction of the gas in the fuel cell is started and after the predetermined condition is satisfied, the gas accumulated on the anode side of the fuel cell is being suctioned. Since the supply of the fuel gas is started, the impurity gas accumulated on the anode side of the fuel cell can be sufficiently discharged, and wasteful discharge of the fuel gas accompanying the discharge of the impurity gas can be reduced.

  Embodiments of a fuel cell system according to the present invention will be described in detail with reference to the drawings. A fuel cell system 10 according to the present embodiment is an embodiment applied to a drive power source of a fuel cell vehicle, and includes a solid polymer electrolyte fuel cell frequently used in a fuel cell vehicle. Needless to say, the fuel cell system 10 according to the present invention can be applied to other fuel cell vehicles.

  FIG. 1 is a configuration diagram of a fuel cell system 10 according to an embodiment. The fuel cell system 10 includes a fuel cell 1 that obtains electric energy by an electrochemical reaction between hydrogen gas and an oxidizing gas, and the cathode side of the fuel cell 1 is connected to the cathode electrode of the fuel cell 1. An air supply passage 20 for supplying air (oxygen), a cathode offgas passage 21 through which the cathode offgas discharged from the fuel cell 1 passes, and air supply means provided in the most upstream portion of the air supply passage 20 An air pump 2 and an ejector 3 serving as a gas suction means that operates by using the energy of the air flowing through the air supply passage 20 as a power source and sucks a fluid in a gas suction passage, which will be described later, are provided.

  Further, in the anode side path of the fuel cell 1, a hydrogen supply path 30 that supplies hydrogen gas as a fuel gas to the anode electrode of the fuel cell 1, and an anode offgas path 31 through which the anode offgas discharged from the fuel cell 1 passes. And an anode off-gas tank 4 provided on the anode off-gas passage 31 for temporarily storing the anode off-gas discharged from the fuel cell 1 and the anode off-gas tank 4. The anode 3 of the fuel cell 1 is connected to the anode off-gas tank 4 by the ejector 3. A gas suction passage 32 through which the gas sucked from the side passes, a hydrogen tank 5 as a fuel supply means provided at the most upstream portion of the hydrogen supply passage 30, and a hydrogen supply passage 30 provided on the hydrogen supply passage 30. And a hydrogen supply valve 6 for opening and closing.

  A diluter 7 for diluting the off gas is provided downstream of the anode off gas passage 31 and the cathode off gas passage 21, and the off gas discharged from the fuel cell 1 is diluted and discharged outside the fuel cell system 10. The

  An anode off-gas on / off valve 8 for opening and closing the anode off-gas passage 31 is provided downstream of the anode off-gas tank 4 in the anode off-gas passage 31, and a suction gas opening and closing for opening and closing the gas suction passage 32 is provided in the gas suction passage 32. A valve 9 is provided. The anode off gas stored in the anode off gas tank 4 is guided to the anode off gas passage 31 or the gas suction passage 32 by opening and closing the anode off gas on / off valve 8 and the suction gas on / off valve 9.

  The anode off-gas passage 31 includes an off-gas circulation passage 33 that guides the anode off-gas to the cathode side of the fuel cell 1 and an off-gas discharge passage 34 that guides the anode off-gas to the diluter downstream of the anode off-gas on-off valve 8. The off gas circulation passage 33 is provided with a circulation gas on / off valve 11 that opens and closes the off gas circulation passage 33.

  By opening and closing the circulating gas on-off valve 11, the anode off-gas introduced from the anode off-gas tank 4 to the anode off-gas passage 31 is discharged out of the system through the diluter 7, or the fuel cell 1 through the ejector 3. To the cathode side. In the fuel cell startup control described below, the circulating gas on-off valve 11 is closed in order to introduce the anode off gas to the diluter 7 or the ejector 3.

  The fuel cell system 10 also includes an electronic control unit (ECU) 12 that controls various devices and a hydrogen concentration sensor 13 that detects the hydrogen concentration in the anode off-gas tank. The hydrogen concentration detected by the hydrogen concentration sensor 13 is input to the ECU 12. The ECU 12 performs various controls such as starting and stopping of the fuel cell 1 based on the input values and the operating conditions of various devices.

  Next, start-up control of the fuel cell 1 in the fuel cell system 10 configured as described above will be described in detail. The start control of the fuel cell is executed by the ECU 12. FIG. 2 is a flowchart of start control of the fuel cell.

  When the ECU 12 receives the activation of the fuel cell 1, the ECU 12 activates the air pump 2 to supply air to the fuel cell 1 (step 101). Next, the ECU 12 detects the concentration of hydrogen gas in the anode offgas tank 4 by the hydrogen concentration sensor 13 (step 102). The anode off-gas tank 4 is provided downstream of the anode-side discharge port of the fuel cell 1, and the hydrogen gas concentration in the fuel cell 1 is estimated by detecting the hydrogen gas concentration in the anode off-gas tank 4. can do.

  Next, the ECU 12 determines whether or not the hydrogen concentration detected in step 102 is equal to or higher than a predetermined concentration (step 103). The predetermined concentration is a hydrogen concentration at which it is possible to determine that power generation processing is possible at a concentration equal to or higher than the concentration. As a result of the determination, if the hydrogen concentration detected in step 102 is equal to or higher than the predetermined concentration, it is assumed that hydrogen gas sufficient for power generation processing is present at the anode electrode of the fuel cell 1, and the hydrogen supply valve 6 is opened to supply hydrogen gas as fuel. The battery 1 is supplied (step 111), the power generation process is started (step 112), and the startup process of the fuel cell 1 is terminated.

  On the other hand, if the detected hydrogen concentration is less than the predetermined concentration as a result of the determination in step 103, it is assumed that an impurity gas such as nitrogen that has permeated from the cathode side stays on the anode side of the fuel cell 1, and the impurity gas Perform the suction process.

  In the impurity gas suction process, first, the anode off-gas flow path is switched to the suction process (step 104). Specifically, the suction gas on / off valve 9 in the gas suction passage 32 is opened, and the anode off gas on / off valve 8 in the anode off gas passage 31 is closed. As a result, the downstream flow path of the anode off-gas tank 4 becomes the gas suction passage 32.

  Next, the anode 3 impurity gas in the fuel cell 1 is sucked by the ejector 3 through the gas suction passage 32 (step 105). In the present embodiment, the ejected gas is guided to the air supply passage 20 by the ejector 3 and supplied to the cathode electrode of the fuel cell 1 through the air supply passage 20.

  The gas sucked by the ejector 3 contains hydrogen gas at a low concentration. By supplying hydrogen gas contained in the sucked gas to the cathode electrode, the hydrogen gas can be used for power generation processing. With this configuration, it is possible to effectively use hydrogen gas and reduce wasteful discharge of hydrogen gas.

  After a lapse of a predetermined time from the start of suction of the impurity gas in step 105 (step 106), the hydrogen supply valve 6 is opened and supply of hydrogen gas to the fuel cell 1 is started (step 107). The predetermined time is a time when it is determined that the suction of the gas on the anode side of the fuel cell 1 is completed to some extent by the ejector 3, and is set as appropriate based on the capacity of the anode off-gas tank, the suction capability of the ejector, and the like.

  In a state where hydrogen gas is not supplied to the fuel cell 1, the pressure on the anode side decreases as the gas is sucked, and it becomes difficult to suck the gas by the ejector 3. In the gas suction without supplying hydrogen gas, there is a limit to the amount of gas that can be sucked, and a sufficient amount of impurity gas may not be sucked. Therefore, it is desirable to start supplying hydrogen gas after a predetermined time has elapsed from the start of gas suction. With this configuration, there is no limit on the amount of gas to be sucked, and a sufficient amount of impurity gas can be sucked.

  Further, when the gas is sucked after the supply of the hydrogen gas is started, the amount of hydrogen gas discharged accompanying the suction of the impurity gas is increased, and the wasteful discharge of the hydrogen gas is increased. In this embodiment, the suction of the impurity gas is started in a state where the supply of the hydrogen gas is stopped, and the hydrogen gas is supplied after the impurity gas is sucked for a predetermined time. By comprising in this way, the amount of hydrogen gas discharged | emitted with the suction of impurity gas can be reduced, and the waste of hydrogen gas can be reduced.

  After the supply of the hydrogen gas is started, the hydrogen concentration in the anode off-gas tank 4 is detected by the hydrogen concentration sensor 13 (step 108). By detecting the hydrogen concentration, it is determined whether or not the suction of the impurity gas from the anode electrode is completed. The ECU 12 determines whether the detected hydrogen concentration is equal to or higher than the predetermined concentration (step 109). If the detected hydrogen concentration is lower than the predetermined concentration, the ECU 12 continues the gas suction and performs processing until it is determined that the hydrogen concentration is equal to or higher than the predetermined concentration. repeat.

  When the impurity gas is sucked and the hydrogen concentration of the gas in the anode offgas tank 4 is determined to be equal to or higher than the predetermined concentration, the anode offgas flow path is switched to the power generation processing in order to start the power generation processing (step 110). . Specifically, the suction gas on / off valve of the gas suction passage 32 is closed, and the anode off gas on / off valve 8 of the anode off gas passage 31 is opened. Thereby, the downstream flow path of the anode off gas tank 4 becomes the anode off gas passage 31. The anode off gas flows into the diluter 7 through the anode off gas passage 31, is diluted by the diluter 7, and is discharged out of the system.

  After switching the anode off-gas flow path, the hydrogen supply valve 6 is opened, hydrogen gas is supplied to the anode electrode of the fuel cell 1 to start power generation processing (step 111), and power generation processing is started. (Step 112), the start-up control of the fuel cell 1 is terminated.

  As described above, according to the fuel cell system 10 according to the present embodiment, when the fuel cell 1 is started, an impurity gas such as nitrogen that permeates from the cathode side to the anode side and accumulates on the anode side is appropriately sucked. Thus, the power generation process can be performed.

  In the present embodiment, it is determined that the impurity gas suction is completed to some extent after a predetermined time has elapsed from the start of the impurity gas suction, but it is determined that the impurity gas suction is completed to some extent due to other conditions. May be. For example, the pressure downstream of the hydrogen supply valve 6 in the hydrogen supply passage 20 that discharges the impurity gas is detected, and if the pressure is less than a predetermined pressure, it is determined that the suction of the impurity gas has been completed to some extent. May be.

Further, in the present invention, the impurity gas is sucked by the ejector 3, but the impurity gas is not limited to the ejector 3 as long as the impurity gas staying on the anode side of the fuel cell can be sucked. .

  In addition, since the present invention uses the ejector 3 as the suction means, the air pump 2 is activated before starting the impurity gas suction processing. However, when the suction means that does not use air energy as a power source is used, When the impurity gas is sucked, it is not necessary to start the air pump. When the impurity gas suction process is completed and the supply of hydrogen gas is started, the air pump 3 is started to start the supply of air. It may be configured.

1 is a configuration diagram of a fuel cell system according to an embodiment. FIG. It is a flowchart which shows starting control of a fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Air pump 3 Ejector 4 Anode off gas tank 5 Hydrogen tank 6 Hydrogen supply valve 7 Diluter 8 Anode off gas on-off valve 9 Suction gas supply valve 10 Fuel cell system 11 Circulating gas on-off valve 12 ECU
13 Hydrogen concentration sensor 20 Air supply passage 21 Cathode off-gas passage 30 Hydrogen supply passage 31 Anode off-gas passage 32 Suction gas passage 33 Circulating gas passage 34 Off-gas discharge passage

Claims (4)

A fuel cell that obtains electric power by an electrochemical reaction between a fuel gas and an oxidizing gas;
Fuel supply means for supplying fuel gas to the fuel cell;
Gas suction means for sucking the gas in the fuel cell from the gas outlet on the anode side of the fuel cell;
At the start of the fuel cell, the gas suction means starts sucking the gas in the fuel cell in a state where the fuel gas supply is stopped, and after the gas suction is started, and a predetermined condition And a control means for starting the supply of the fuel gas by the fuel supply means while continuing the suction of the gas after the establishment of the fuel cell system.   The fuel cell system according to claim 1, further comprising suction gas supply means for supplying the gas sucked by the gas suction means to the cathode side of the fuel cell.   3. The fuel cell system according to claim 1, wherein the predetermined condition is that a gas pressure sucked by the gas suction unit is equal to or lower than a predetermined pressure.   3. The fuel cell system according to claim 1, wherein the predetermined condition is a lapse of a predetermined time from the start of gas suction by the gas suction means.

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