JP2007250216A - Fuel cell system and method of operating same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of stably operating for a long time without decreasing the performance of a fuel cell and surely preventing generation of flooding by raising the temperature of a fuel cell stack when the temperature of the fuel cell stack is lowered to flooding generation temperature or less during operation in a state that a load of a prescribed value or more is applied. <P>SOLUTION: The system includes a temperature detecting device 56 detecting the temperature of the fuel cell stack 20; a heating means heating the fuel cell stack 20; and a control means raising the temperature of the fuel cell stack 20 to the flooding generation temperature or more by operating the heating means when a load applied to the fuel cell stack 20 is a prescribed value or more and the temperature of the fuel cell stack 20 is the flooding generation temperature or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system and an operation method thereof.

  Conventionally, since fuel cells have high power generation efficiency and do not emit harmful substances, they have been put into practical use as power generators for industrial and household use, or as power sources for artificial satellites and spacecrafts. Development is progressing as a power source for vehicles such as buses, trucks, passenger carts, and luggage carts. The fuel cell may be of an alkaline aqueous solution type (AFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), solid oxide type (SOFC), direct methanol (DMFC), or the like. Although good, a polymer electrolyte fuel cell (PEMFC) is common.

  In this case, the solid polymer electrolyte membrane is sandwiched between two gas diffusion electrodes and integrated to join. When one of the gas diffusion electrodes is used as a fuel electrode (anode electrode) and hydrogen gas as fuel is supplied to the surface thereof, hydrogen is decomposed into hydrogen ions (protons) and electrons, and the hydrogen ions are converted into a solid polymer electrolyte. Permeates the membrane. Further, when the other of the gas diffusion electrodes is an oxygen electrode (cathode electrode) and air as an oxidant is supplied to the surface, oxygen in the air is combined with the hydrogen ions and electrons to generate water. The An electromotive force is generated by such an electrochemical reaction.

The fuel cell can efficiently generate power in a predetermined temperature range. For this reason, a fuel cell system that heats the fuel cell by self-heating of the fuel cell during cold weather or the like has been proposed (see, for example, Patent Document 1).
JP 2002-313388 A

  However, in the conventional fuel cell system, there is no measure for preventing the occurrence of flooding in which the amount of generated water increases on the oxygen electrode side and the air flow path is blocked by moisture. Not given. As a result, flooding occurs and the performance of the fuel cell decreases, and the fuel cell system cannot be stably operated.

  The present invention solves the problems of the conventional fuel cell system, and when the temperature of the fuel cell stack falls below the flooding temperature during operation with a load of a predetermined value or more applied, the temperature of the fuel cell stack is reduced. By raising the fuel cell system, it is possible to reliably prevent flooding, and the fuel cell system can be stably operated over a long period of time without deteriorating the performance of the fuel cell, and its operation It aims to provide a method.

  Therefore, in the fuel cell system of the present invention, a fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode has a fuel gas flow path formed along the fuel electrode, and an air flow along the oxygen electrode. Fuel cell stacks stacked with a separator having a path formed therebetween, a temperature detector for detecting the temperature of the fuel cell stack, a heating means for heating the fuel cell stack, and a load applied to the fuel cell stack Control means for operating the heating means to raise the temperature of the fuel cell stack until it becomes higher than the flooding temperature when the temperature of the fuel cell stack is not more than a flooding temperature. Have.

  In another fuel cell system of the present invention, the heating means is a heater.

  In still another fuel cell system of the present invention, the heating means is an air circulation duct that circulates part of the air discharged from the fuel cell stack back to the air flow path.

  In still another fuel cell system of the present invention, the control means is a control device that controls the temperature of the fuel cell stack to be higher than about 38 [° C.].

  In the operation method of the fuel cell system of the present invention, the fuel cell system is configured to supply air to an air flow path of a fuel cell stack mounted on a vehicle and to supply fuel gas to the fuel gas flow path of the fuel cell stack. When the load applied to the fuel cell stack is equal to or higher than a predetermined value and the temperature of the fuel cell stack is equal to or lower than the flooding generation temperature, the fuel cell stack is heated to become higher than the flooding generation temperature. The temperature of the fuel cell stack is raised until

  According to the present invention, in the fuel cell system, the fuel cell in which the electrolyte layer is sandwiched between the fuel electrode and the oxygen electrode has a fuel gas flow path formed along the fuel electrode, and an air flow along the oxygen electrode. Fuel cell stacks stacked with a separator having a path formed therebetween, a temperature detector for detecting the temperature of the fuel cell stack, a heating means for heating the fuel cell stack, and a load applied to the fuel cell stack Control means for operating the heating means to raise the temperature of the fuel cell stack until it becomes higher than the flooding temperature when the temperature of the fuel cell stack is not more than a flooding temperature. Have.

  Further, in the operation method of the fuel cell system, the operation of the fuel cell system that supplies air to the air flow path of the fuel cell stack mounted on the vehicle and supplies the fuel gas to the fuel gas flow path of the fuel cell stack. In the method, when a load applied to the fuel cell stack is equal to or higher than a predetermined value and the temperature of the fuel cell stack is equal to or lower than a flooding occurrence temperature, the fuel cell stack is heated to become higher than the flooding occurrence temperature. The temperature of the fuel cell stack is increased.

  In this case, the occurrence of flooding can be reliably prevented, and the fuel cell can be stably operated over a long period of time without being deteriorated.

  In another fuel cell system, the heating means is a heater.

  In this case, since the temperature of the fuel cell stack can be raised rapidly, the occurrence of flooding can be reliably prevented.

  In still another fuel cell system, the heating means is an air circulation duct that circulates a part of the air discharged from the fuel cell stack back to the air flow path.

  In this case, power consumption can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  2 is a diagram showing the configuration of the fuel cell stack according to the first embodiment of the present invention, FIG. 3 is a diagram showing the configuration of the cell module of the fuel cell according to the first embodiment of the present invention, and FIG. It is a schematic cross section which shows the structure of the unit cell of the fuel cell in the 1st Embodiment of invention.

  In FIG. 2, a fuel cell stack 20 as a fuel cell (FC) is used as a power source for vehicles such as passenger cars, buses, trucks, passenger carts, and luggage carts. Here, the vehicle is equipped with a large number of auxiliary devices that consume electricity, such as lighting devices, radios, and power windows, which are used even when the vehicle is stopped. Since the output range is extremely wide, it is desirable to use a fuel cell stack 20 as a power source in combination with a secondary battery or capacitor as a power storage means (not shown).

  The fuel cell stack 20 is of an alkaline aqueous solution type (AFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), solid oxide type (SOFC), direct methanol (DMFC), or the like. However, a polymer electrolyte fuel cell (PEMFC) is desirable.

  More preferably, PEMFC (Proton Exchange Membrane Fuel Cell) type fuel cell or PEM (Proton Exchange Membrane) using hydrogen gas as fuel gas, that is, anode gas, and oxygen or air as oxidant, that is, cathode gas. ) Type fuel cell. Here, the PEM fuel cell is generally a fuel cell in which a catalyst, an electrode, and a separator are combined on both sides of a solid polymer electrolyte membrane as an electrolyte layer that transmits ions such as protons. Are composed of a plurality of stacks connected in series.

  In the present embodiment, the fuel cell stack 20 includes a plurality of cell modules 10 as shown in FIG. In addition, the arrow in FIG. 2 has shown the flow of the hydrogen gas as fuel gas. As shown in FIG. 3, the cell module 10 is electrically connected to a unit cell (MEA) 10A as a fuel cell and the unit cells 10A, and is introduced into the unit cell 10A. The separator 10B that separates the flow path of hydrogen gas as the fuel and the flow path of air as the oxidant, the unit cell 10A and the separator 10B as one set, and a plurality of sets are stacked in the thickness direction. In the cell module 10, the unit cells 10A and the separators 10B are stacked in multiple stages so that the unit cells 10A are arranged with a predetermined gap.

  The unit cell 10A includes an air electrode 12 as an oxygen electrode provided on the solid polymer electrolyte membrane 11 side as an electrolyte layer and a fuel electrode 13 provided on the other side. The air electrode 12 includes a diffusion layer made of a conductive material that permeates while diffusing the reaction gas, and a catalyst layer that is formed on the diffusion layer and supported in contact with the solid polymer electrolyte membrane 11. Further, the air electrode side as a net-like current collector in which a large number of openings that allow the mixed flow of air and water to pass through is collected in contact with the electrode diffusion layer on the air electrode 12 side of the unit cell 10A. It has a collector 14 and a fuel electrode side collector 15 as a net-like current collector for contacting the electrode diffusion layer on the fuel electrode 13 side of the unit cell 10 </ b> A and leading out current similarly.

  And in unit cell 10A, as FIG. 4 shows, water moves. In FIG. 4, 48 is a fuel chamber as a fuel gas flow path, and 49 is an oxygen chamber as an air flow path. In this case, when a fuel gas, that is, hydrogen gas as an anode gas is supplied into the fuel chamber 48 of the fuel electrode side collector 15, hydrogen is decomposed into hydrogen ions (protons) and electrons, and the hydrogen ions are converted into proton-entrained water. Along with this, it passes through the solid polymer electrolyte membrane 11. Further, when the air electrode 12 is a cathode electrode and an oxidant, that is, air as a cathode gas is supplied into the oxygen chamber 49, oxygen in the air is combined with the hydrogen ions and electrons to generate water. Is done. Moisture permeates through the solid polymer electrolyte membrane 11 as reverse diffusion water and moves into the fuel chamber 48 of the fuel electrode side collector 15.

  Next, the overall configuration of the fuel cell system will be described.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention.

  In the figure, an apparatus for supplying hydrogen gas as a fuel gas to the fuel cell stack 20 and an apparatus for supplying air as an oxidant are shown. Although hydrogen gas, which is fuel taken out by reforming methanol, gasoline, or the like by a reformer (not shown), can be directly supplied to the fuel cell stack 20, it is stable and sufficient even during high-load operation of the vehicle. In order to be able to supply an amount of hydrogen gas, it is desirable to supply the hydrogen gas stored in the fuel storage means 21. Thereby, the hydrogen gas is always sufficiently supplied at a substantially constant pressure, so that the fuel cell stack 20 can follow the fluctuation of the load of the vehicle and supply a necessary current. . In this case, the output impedance of the fuel cell stack 20 is extremely low and can be approximated to zero.

  The fuel cell stack 20 includes a first heater 41 as a heating unit. In the example shown in the figure, the first heater 41 is attached so as to surround the periphery of the fuel cell stack 20, but if the temperature can be raised by heating the fuel cell stack 20, the fuel It may be attached to any part of the battery stack 20 in any way.

  Hydrogen gas is stored in a container containing a hydrogen storage alloy, a container containing a hydrogen storage liquid such as decalin, a fuel storage means 21 such as a hydrogen gas cylinder, a first fuel supply line 22 as a fuel supply line, and The fuel is supplied to an inlet of a fuel gas flow path of the fuel cell stack 20 through a second fuel supply pipe 33 as a fuel supply pipe connected to the first fuel supply pipe 22. The first fuel supply line 22 includes a fuel storage means former opening / closing valve 23, a first pressure sensor 27a, a second pressure sensor 27b, a third pressure sensor 27c, a first fuel pressure adjusting valve 25a, and a second fuel. A pressure regulating valve 25b, a first fuel supply electromagnetic valve 26a, and a second fuel supply electromagnetic valve 26b are provided. In this case, the fuel storage means 21 has a sufficiently large capacity and is capable of always supplying sufficiently high pressure hydrogen gas.

  The hydrogen gas discharged as an unreacted component from the outlet of the fuel gas flow path of the fuel cell stack 20 is discharged to the outside of the fuel cell stack 20 through the fuel discharge pipe 31. A water recovery drain tank 35 as a recovery container is disposed in the fuel discharge line 31. The water recovery drain tank 35 is connected with a fuel discharge line 30 for discharging water and the separated hydrogen gas. The fuel discharge line 30 is provided with a suction circulation pump 36 as a pump. Yes. A hydrogen circulation electromagnetic valve 34 is disposed in the fuel discharge line 30. The end of the fuel discharge line 30 opposite to the water recovery drain tank 35 is connected to the second fuel supply line 33. Thereby, the hydrogen gas discharged to the outside of the fuel cell stack 20 can be recovered, supplied to the fuel gas flow path of the fuel cell stack 20, and reused.

  The water recovery drain tank 35 is connected to a starting fuel discharge line 38. The starting fuel discharge line 38 is provided with a hydrogen starting exhaust electromagnetic valve 37, and when the fuel cell stack 20 is started. The hydrogen gas discharged from the fuel gas channel can be discharged into the atmosphere. The outlet end of the starting fuel discharge line 38 is connected to the exhaust manifold 46. In addition, a hydrogen combustor may be provided in the startup fuel discharge line 38 as necessary. The hydrogen gas discharged by the hydrogen combustor can be combusted to form water, and then discharged into the atmosphere.

  Here, the first fuel pressure regulating valve 25a and the second fuel pressure regulating valve 25b are those of a butterfly valve, a regulator valve, a diaphragm type valve, a mass flow controller, a sequence valve, etc., but the first fuel pressure regulating valve Any type of hydrogen gas may be used as long as the pressure of the hydrogen gas flowing out from the outlets of 25a and the second fuel pressure regulating valve 25b can be adjusted to a preset pressure. The pressure adjustment may be performed manually, but is preferably performed by an actuator including an electric motor, a pulse motor, an electromagnet, or the like.

  The first fuel supply solenoid valve 26a, the second fuel supply solenoid valve 26b, the hydrogen circulation solenoid valve 34, and the hydrogen start exhaust solenoid valve 37 are so-called on-off types, and include an electric motor, a pulse motor, The actuator is operated by an electromagnet or the like. The fuel storage means original opening / closing valve 23 is operated manually or automatically using an electromagnetic valve. Further, the suction circulation pump 36 may be of any type as long as it can forcibly discharge the reverse diffusion water together with the hydrogen gas and can bring the inside of the fuel gas passage into a negative pressure state. Good.

  On the other hand, the air as the oxidant passes through the supply filter 53 and is sucked into the air supply fan 51 as the oxidant supply source, and passes through the air supply line 52 and the intake manifold 44 from the air supply fan 51. The fuel cell stack 20 is supplied to an oxygen chamber, that is, an air flow path. In this case, the pressure of the supplied air is a normal pressure of about atmospheric pressure. The air supply fan 51 may be of any type as long as it can suck and discharge air. Further, the supply filter 53 may be of any type as long as it removes dust (dust), impurities, etc. contained in the air. Note that oxygen can be used as the oxidizing agent instead of air. And the air discharged | emitted from an air flow path is discharged | emitted in air | atmosphere through the exhaust manifold 46 and the exhaust filter 47 as a manifold. The exhaust manifold 46 is provided with a temperature detector 56 that detects the temperature of the air immediately after being discharged from the fuel cell stack 20.

  A second heater 42 is disposed in the air supply pipe 52 as a heating means for heating the air supplied to the fuel cell stack 20 and increasing the temperature of the fuel cell stack 20. Note that the second heater 42 may be disposed in a portion other than the air supply conduit 52 as long as the air supplied to the fuel cell stack 20 can be heated.

  Further, an inverter device 61 as a drive control device as a load and a capacitor unit 63 as a power storage unit are connected in parallel to an electric terminal (not shown) of the fuel cell stack 20. The capacitor unit 63 includes a capacitor (capacitor) such as an electric double layer capacitor. In addition, the said electrical storage means does not necessarily need to be a capacitor, and secondary batteries, such as a lead storage battery, a nickel cadmium battery, a nickel hydride battery, a lithium ion battery, and a sodium sulfur battery, may be what is called a battery (storage battery). Any form may be used as long as it has a function of electrically storing and discharging energy, such as a flywheel, a superconducting coil, and a pressure accumulator. Furthermore, any of these may be used alone, or a plurality of them may be used in combination.

  Further, the inverter device 61 converts a direct current from the fuel cell stack 20 or the capacitor unit 63 into an alternating current and supplies the alternating current to an unillustrated alternating current motor that is a driving source for rotating the wheels of the vehicle. Here, in the fuel cell system, since the fuel cell stack 20 or the capacitor unit 63 is connected in parallel to supply current to the inverter device 61, for example, when the vehicle is stopped, the fuel cell stack When the stack 20 is stopped, or when the current from the fuel cell stack 20 is less than the required current during high load operation such as on a slope, the current is automatically supplied from the capacitor unit 63 to the inverter device 63. The

  Reference numeral 62 denotes an IGBT unit including an IGBT (insulated gate bipolar transistor) which is a high-speed switching element as a charging switching element, and is a control circuit that controls charging of the capacitor unit 63.

  When the AC motor functions as a power generator during vehicle deceleration operation and generates a so-called regenerative current, the regenerative current is supplied to the capacitor unit 63 during the vehicle deceleration operation, and the capacitor unit 63 Recharged. Further, even when the regenerative current is not supplied, when the capacitor unit 63 is discharged and the terminal voltage decreases, the current generated by the fuel cell stack 20 is automatically supplied to the capacitor unit 63.

  As described above, in the fuel cell system, when the capacitor unit 63 is always charged and the current from the fuel cell stack 20 does not satisfy the required current, the current is supplied from the capacitor unit 63 to the inverter device 63. Since the vehicle is automatically supplied, the vehicle can travel stably in various travel modes.

  In the present embodiment, the fuel cell system has an FC control ECU (Electronic Control Unit) (not shown) as a control device. The control device includes a calculation means such as a CPU and MPU, a storage means such as a magnetic disk and a semiconductor memory, an input / output interface, and the like. From various sensors including a hydrogen concentration detector, a fuel gas flow path of the fuel cell stack 20 and The air supply fan 51, the first fuel supply electromagnetic valve 26a, the second fuel supply electromagnetic valve 26b, the hydrogen circulation are detected by detecting the flow rate, temperature, output voltage, etc. of hydrogen, oxygen, air, etc. supplied to the air flow path. The operations of the solenoid valve 34 and the hydrogen start exhaust solenoid valve 37 are controlled. Further, the FC control ECU cooperates with other sensors provided in the vehicle and an EV (Electric Vehicle) control ECU (not shown) as a vehicle control means to supply fuel and oxidant to the fuel cell stack 20. Centrally control the operation of all equipment supplied. When the FC control ECU determines, based on the output of the temperature detector 56, that the temperature of the fuel cell stack 20 has become equal to or lower than the flooding occurrence temperature during operation while receiving a load of a predetermined value or more, the first heater 41 and the second heater 42 are energized to raise the temperature of the fuel cell stack 20, thereby preventing flooding.

  Next, changes in the single cell voltage when flooding occurs in the fuel cell system having the above-described configuration will be described.

  FIG. 5 is a graph showing a single cell voltage when flooding occurs in the first embodiment of the present invention.

  In the fuel cell stack 20, in the oxygen chamber 49 of each unit cell 10A, water generated by combining oxygen in the air, hydrogen ions, and electrons, that is, generated water is generated. When viewed finely, the distribution of moisture in the gas phase and the liquid phase in the oxygen chamber 49 is not necessarily uniform, and the amount of moisture, the flow rate, and the like vary locally. For this reason, a large amount of moisture is concentrated locally, and flooding that inhibits the flow of air in the oxygen chamber 49 may occur. In particular, flooding is highly likely to occur in a low current density region where the flow rates of the reaction gas, that is, hydrogen gas and air are small. Although flooding may occur in the fuel chamber 48, in the present embodiment, only the case where it occurs in the oxygen chamber 49 will be described for convenience of explanation.

  When flooding occurs, the air electrode 12 is covered with moisture and cannot come into contact with the air, and the cell voltage of the unit cell 10A that has caused flooding, that is, the single cell voltage is reduced. It is possible to detect that flooding has occurred by monitoring.

  And when the inventor of this invention measured the change of the voltage of each unit cell 10A contained in the fuel cell stack 20, the result as shown in FIG. 5 was able to be obtained. In FIG. 5, the vertical axis represents the single cell voltage [V] and the fuel cell stack outlet temperature [° C.], and the horizontal axis represents the time [second]. The fuel cell stack outlet temperature is the temperature of air immediately after being discharged from the fuel cell stack 20 detected by the temperature detector 56, and is the temperature of the fuel cell stack 20. Here, it can be said that the temperature of the fuel cell stack 20 is the same as the temperature of the unit cell 10 </ b> A included in the fuel cell stack 20.

  In FIG. 5, 71 indicates the measurement result of the exhaust temperature of the fuel cell stack 20, and 72 indicates the measurement result of the single cell voltage. Since 72 is a measurement result of the voltage of each unit cell 10A included in the fuel cell stack 20, it is shown as a set of many lines. A range 73 indicates a single cell voltage that has decreased in response to the occurrence of flooding. An arrow 74 indicates the temperature range of the fuel cell stack 20 corresponding to the occurrence of flooding. The temperature range is about 25 to 38 [° C.]. An arrow 75 indicates a range where flooding occurs, and an arrow 76 indicates a range where flooding is eliminated.

  From FIG. 5, flooding occurs when the temperature of the fuel cell stack 20 is in the range of about 25 to 38 ° C., and the flooding is eliminated when the temperature of the fuel cell stack 20 exceeds about 38 ° C. I understand that I don't. That is, about 38 [° C.] is the flooding generation temperature in the fuel cell stack 20, and flooding occurs when the temperature of the fuel cell stack 20 is lower than the flooding generation temperature, and no flooding occurs when the temperature is higher than the flooding temperature. .

  When no load is applied to the fuel cell stack 20, no flooding occurs even if the temperature of the fuel cell stack 20 is equal to or lower than the flooding occurrence temperature. That is, flooding occurs when the temperature of the fuel cell stack 20 falls below the flooding generation temperature only when a load greater than a predetermined value is applied. Therefore, in the present embodiment, when the temperature of the fuel cell stack 20 detected by the temperature detector 56 falls below the flooding occurrence temperature, that is, about 38 ° C., the first heater 41 and the second heater 42 Energization is performed to increase the temperature of the fuel cell stack 20 until it exceeds the flooding occurrence temperature, thereby preventing flooding.

  Next, the operation of the fuel cell system having the above configuration will be described.

  FIG. 6 is a diagram showing a temperature change of the fuel cell stack according to the first embodiment of the present invention.

  During steady operation in the fuel cell system of the present embodiment, the pressure of hydrogen gas flowing out from the outlets of the first fuel pressure adjustment valve 25a and the second fuel pressure adjustment valve 25b is set in advance and adjusted to a constant pressure. The first fuel pressure adjustment valve 25a and the second fuel pressure adjustment valve 25b are not adjusted during operation of the fuel cell system, and are maintained as they are. Further, the fuel storage means 21 operates so that air set in advance according to the output current of the fuel cell stack 20 as a fuel cell is supplied. In this case, the amount of air supplied is an amount sufficiently larger than the amount of air necessary for the output of the fuel cell stack 20 to be maximized.

  When the fuel cell stack 20 starts operation, reverse diffusion water is generated in each unit cell 10A constituting the fuel cell stack 20, and the reverse diffusion water permeates the solid polymer electrolyte membrane 11 to flow the fuel gas. Then, the fuel electrode 13 side of the solid polymer electrolyte membrane 11 is humidified. Thereby, the fuel electrode 13 side of the solid polymer electrolyte membrane 11 is in a wet state, and hydrogen ions generated from hydrogen by an electrochemical reaction can move smoothly in the solid polymer electrolyte membrane 11.

  Further, the hydrogen gas as an unreacted component that is supplied to the fuel gas flow path and surplus is mixed with the back-diffused water that has permeated into the fuel gas flow path and becomes surplus, and a gas-liquid mixture Become. The hydrogen gas that has become the gas-liquid mixture is sucked by the suction circulation pump 36 and discharged to the outside of the fuel cell stack 20 through the fuel discharge pipe 31 connected to the fuel cell stack 20. The gas-liquid mixture passes through the fuel discharge pipe 31 and is introduced into the water recovery drain tank 35. Then, by staying in the water recovery drain tank 35 having a relatively wide space, heavy moisture falls downward due to gravity, and reverse diffusion water is separated from hydrogen gas. The hydrogen gas in a state where the reverse diffusion water is separated and dried is discharged out of the water recovery drain tank 35 from the fuel discharge line 30.

  In steady operation, the hydrogen gas discharged from the fuel discharge line 30 passes through the open hydrogen circulation electromagnetic valve 34, is introduced into the second fuel supply line 33, and again. Then, it is supplied to the fuel gas flow path of the fuel cell stack 20 and reused.

  As shown in FIG. 6, when the fuel cell stack 20 starts operation, the temperature of the fuel cell stack 20 is lower than about 25 [° C.], which is the lower limit of the temperature range in which flooding occurs. In FIG. 6, the vertical axis represents the fuel cell stack temperature, and the horizontal axis represents the power generation time. When the operation is continued, the temperature of the fuel cell stack 20 increases with the passage of the power generation time as indicated by the line 81 due to self-heating. However, since the temperature rise is slow, the time during which the temperature of the fuel cell stack 20 is in the temperature range where flooding occurs is long, and the probability that flooding will occur increases.

  Therefore, in the present embodiment, when the fuel cell stack 20 starts operation, the first heater 41 and the second heater 42 are energized to heat the fuel cell stack 20. As a result, the temperature of the fuel cell stack 20 rises rapidly as indicated by the line 82, and the time in the temperature range where flooding occurs is shortened. Therefore, the occurrence of flooding can be effectively prevented. The first heater 41 and the second heater 42 are energized within a range indicated by 83 in FIG. 6, that is, within a range where the temperature of the fuel cell stack 20 is about 38 [° C.] or less, which is a flooding occurrence temperature. When the temperature of the fuel cell stack 20 becomes higher than the flooding occurrence temperature, the energization to the first heater 41 and the second heater 42 is stopped.

  In addition, after the temperature of the fuel cell stack 20 becomes higher than the flooding generation temperature, when the temperature of the fuel cell stack 20 decreases to be equal to or lower than the flooding generation temperature, the first heater 41 and the second heater 42 again. And the temperature of the fuel cell stack 20 is raised until it becomes higher than the flooding occurrence temperature.

  As described above, in the present embodiment, when the temperature of the fuel cell stack 20 becomes equal to or lower than the flooding occurrence temperature during operation with a load of a predetermined value or more applied, the first heater 41 and the second heater 42 is energized and raised until the temperature of the fuel cell stack 20 becomes higher than the flooding temperature. Therefore, occurrence of flooding can be reliably prevented, and the performance of the fuel cell stack 20 does not deteriorate. Moreover, it can drive | operate stably over a long period of time. Furthermore, when the temperature of the fuel cell stack 20 rises to become higher than the flooding temperature, the power supply to the first heater 41 and the second heater 42 is stopped, so that power consumption can be suppressed.

  In the present embodiment, only the case where the first heater 41 and the second heater 42 are energized has been described. However, only either the first heater 41 or the second heater 42 may be energized. .

  Next, a second embodiment of the present invention will be described. In addition, about what has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol. The description of the same operation and the same effect as those of the first embodiment is also omitted.

  FIG. 7 is a diagram showing the configuration of the fuel cell system according to the second embodiment of the present invention.

  As shown in the figure, the fuel cell system in the present embodiment has an air circulation duct 43 as a circulation means for connecting the exhaust manifold 46 and the air supply pipe 52, and the air flow path of the fuel cell stack 20. Part of the air discharged from the air is returned to the air supply pipe 52 and circulated. As a result, air whose temperature has risen through the air flow path of the fuel cell stack 20 flows into the air flow path again, so that the temperature of the fuel cell stack 20 can be raised. In this case, the air circulation duct 43 functions as a heating unit that heats the air supplied to the fuel cell stack 20 and raises the temperature of the fuel cell stack 20.

  The air circulation duct 43 may be provided with a flow control valve as a control means to adjust the amount of air to be circulated. In addition, an on-off valve may be provided in the air circulation duct 43 to stop air circulation as necessary.

  Next, the operation of the fuel cell system in the present embodiment will be described.

  FIG. 8 is a diagram showing a temperature change of the fuel cell stack according to the second embodiment of the present invention.

  As shown in the figure, when the fuel cell stack 20 starts operation, the temperature of the fuel cell stack 20 is lower than about 25 [° C.] which is the lower limit of the temperature range in which flooding occurs. In the figure, the vertical axis represents the fuel cell stack temperature, and the horizontal axis represents the power generation time. If the air circulation duct 43 is not disposed, the temperature of the fuel cell stack 20 gradually rises with the lapse of power generation time as indicated by a line 81 due to self-heating when the operation is continued. The time during which the temperature of the fuel cell stack 20 is in the temperature range where flooding occurs is long, and the probability that flooding will occur increases.

  On the other hand, in the present embodiment, since the air circulation duct 43 connects the exhaust manifold 46 and the air supply conduit 52, a part of the air discharged from the air flow path of the fuel cell stack 20 circulates. The fuel cell stack 20 is heated. As a result, the temperature of the fuel cell stack 20 rises rapidly as indicated by the line 84, and the time in the temperature range where flooding occurs is shortened. Therefore, the occurrence of flooding can be effectively prevented. In the example shown in the figure, an open / close valve is provided in the air circulation duct 43, and within the range indicated by 85, that is, within the range where the temperature of the fuel cell stack 20 is 38 [° C.] or less, which is the flooding occurrence temperature. Only when the air is circulated and the temperature of the fuel cell stack 20 becomes higher than the flooding temperature, the on-off valve is closed to stop the air circulation.

  As described above, in the present embodiment, the fuel cell system connects the exhaust manifold 46 and the air supply conduit 52 by the air circulation duct 43, and a part of the air discharged from the air flow path of the fuel cell stack 20. Therefore, the temperature of the fuel cell stack 20 can be raised until it becomes higher than the flooding occurrence temperature. Therefore, occurrence of flooding can be reliably prevented, and the performance of the fuel cell stack 20 does not deteriorate. Moreover, it can drive | operate stably over a long period of time.

  Further, in the present embodiment, since it is not necessary to energize the first heater 41 and the second heater 42 as in the first embodiment, the temperature rise of the fuel cell stack 20 is the same as in the first embodiment. Although it is more gradual than the embodiment, the power consumption can be reduced.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

It is a figure which shows the structure of the fuel cell system in the 1st Embodiment of this invention. It is a figure which shows the structure of the fuel cell stack in the 1st Embodiment of this invention. It is a figure which shows the structure of the cell module of the fuel cell in the 1st Embodiment of this invention. It is a schematic cross section which shows the structure of the unit cell of the fuel cell in the 1st Embodiment of this invention. It is a graph which shows the single cell voltage when the flooding in the 1st Embodiment of this invention generate | occur | produces. It is a figure which shows the temperature change of the fuel cell stack in the 1st Embodiment of this invention. It is a figure which shows the structure of the fuel cell system in the 2nd Embodiment of this invention. It is a figure which shows the temperature change of the fuel cell stack in the 2nd Embodiment of this invention.

Explanation of symbols

10A Unit cell 10B Separator 11 Solid polymer electrolyte membrane 12 Air electrode 13 Fuel electrode 20 Fuel cell stack 41 First heater 42 Second heater 43 Air circulation duct 48 Fuel chamber 49 Oxygen chamber 56 Temperature detector 61 Inverter device

Claims (5)

A fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode is laminated with a separator having a fuel gas flow path formed along the fuel electrode and an air flow path formed along the oxygen electrode. A fuel cell stack,
A temperature detector for detecting the temperature of the fuel cell stack;
Heating means for heating the fuel cell stack;
When the load applied to the fuel cell stack is equal to or higher than a predetermined value and the temperature of the fuel cell stack is equal to or lower than a flooding temperature, the temperature of the fuel cell stack is increased until the heating means is activated to become higher than the flooding temperature. And a control means for raising the fuel cell system.   The fuel cell system according to claim 1, wherein the heating means is a heater.   2. The fuel cell system according to claim 1, wherein the heating unit is an air circulation duct that circulates a part of the air discharged from the fuel cell stack back to the air flow path. 3.   2. The fuel cell system according to claim 1, wherein the control unit is a control device that controls the temperature of the fuel cell stack to be higher than about 38 ° C. 3. A fuel cell system operating method for supplying air to an air flow path of a fuel cell stack mounted on a vehicle and supplying fuel gas to a fuel gas flow path of the fuel cell stack,
When the load applied to the fuel cell stack is equal to or higher than a predetermined value and the temperature of the fuel cell stack is equal to or lower than the flooding occurrence temperature, the fuel cell stack is heated until the temperature becomes higher than the flooding occurrence temperature. A method of operating a fuel cell system, characterized by raising a temperature.

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