JP2008234888A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent lowering of a fuel cell function and deterioration in a fuel electrode by making wetting status in a fuel electrode side uniform in each part of the fuel cell, preventing condensation of moisture in fuel flow paths, suppressing pooling of the moisture in the fuel flow path and assuring ejection of the pooled moisture. <P>SOLUTION: A fuel cell system is provided with; a fuel cell assembly to which a plurality of fuels cells holding electrolyte layers with fuel electrodes and oxygen electrodes are electrically connected through separators in which fuel flow paths are formed along the fuel electrodes and oxidant flow paths are formed along oxygen electrodes, fuel ejecting tube paths ejecting fuel gas from the fuel flow paths; and a side end holding part installed on a fuel gas ejecting side of the fuel cell assembly. A bottom end of a part formed inside a side end holding part in the fuel ejecting tube paths is lower than a bottom end of a part nearest to the fuel ejecting tube path side in the fuel flow paths and at the same time, the bottom ends of the part formed on the side end holding part in the fuel ejecting tube paths are connected to bottom ends of the fuel flow paths on an inclined surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  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 an alkaline aqueous solution (AFC), phosphoric acid (PAFC), molten carbonate (MCFC), solid oxide (SOFC), direct methanol (DMFC), etc. 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.

  In the polymer electrolyte fuel cell, moisture generated by the electrochemical reaction moves as proton-entrained water from the fuel electrode side to the oxygen electrode side, and reverses from the oxygen electrode side to the fuel electrode side. Move as diffusion water. Thereby, both sides of the solid polymer electrolyte membrane are maintained in a wet state. However, when the amount of moisture increases, the hydrogen gas flow path is locally blocked by moisture on the fuel electrode side, and the performance of the fuel cell deteriorates or the fuel electrode deteriorates. It is known.

Therefore, a step is formed at the connection portion between the outlet of the hydrogen gas flow path and the fuel discharge manifold connected to the outlet so that the position of the lower surface of the fuel discharge manifold is lower than the lower surface of the outlet of the hydrogen gas flow path. Thus, there has been proposed a technique for facilitating the outflow of moisture from the hydrogen gas flow path to the fuel discharge manifold to prevent the moisture from being retained and to make the current density uniform (see, for example, Patent Document 1).
JP 2004-327059 A

  However, in the conventional fuel cell system, since a step is formed at the connection portion between the outlet of the hydrogen gas passage and the fuel discharge manifold, the water in the hydrogen gas passage cannot be sufficiently discharged. It was. That is, even if the position of the lower surface of the fuel discharge manifold is lower than the lower surface of the outlet of the hydrogen gas flow path, the surface tension of the water acts because there is a corner in the step, so that the moisture is blocked at the corner. Stopped and stopped flowing smoothly. For this reason, the retention of moisture generated in the hydrogen gas channel cannot be sufficiently prevented.

  The present invention solves the problems of the conventional fuel cell system, and the fuel lower end of the fuel discharge pipe formed in the side end holding portion on the fuel gas discharge side is located on the most downstream side in the fuel cell stack. It is positioned lower than the lower end of the flow path and is connected by an inclined surface to make the wet state on the fuel electrode side uniform in each part of the fuel cell, prevent condensation of water in the fuel flow path, An object of the present invention is to provide a fuel cell system capable of suppressing the retention of moisture in the flow path, discharging the retained moisture reliably, and reliably preventing the performance degradation of the fuel cell and the deterioration of the fuel electrode. And

  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 flow path formed along the fuel electrode, and an oxidant flow path along the oxygen electrode. A plurality of electrically connected fuel cell assemblies through separators formed with fuel, a fuel discharge conduit for discharging fuel gas from the fuel flow path, and a fuel gas discharge side of the fuel cell assembly A lower end of a portion formed in the side end holding portion of the fuel discharge pipe is lower than a lower end of a portion of the fuel flow path closest to the fuel discharge pipe. And is connected to the lower end of the fuel flow path at an inclined surface.

  In another fuel cell system of the present invention, the fuel cell system further includes control means for controlling the discharge of the fuel gas, and the control means executes a discharge process for discharging the fuel gas from the fuel flow path at a predetermined timing. To do.

  In yet another fuel cell system of the present invention, the fuel cell system further includes a water retention sensor that detects that moisture has accumulated in the fuel flow path, and the control means includes a water retention sensor in the fuel flow path. When it is detected that moisture has accumulated, the discharging process is executed.

  In still another fuel cell system of the present invention, the control means executes the discharge process when a stop process for stopping the operation of the fuel cell system is executed.

  According to the configuration of the first aspect, it is possible to prevent the water discharged from the fuel flow path to the fuel discharge pipe from flowing back to the fuel flow path. In addition, since the lower end of the fuel flow path and the lower end of the fuel discharge pipe are connected by an inclined surface, moisture is not blocked by the action of surface tension, and smoothly flows from the fuel flow path to the fuel discharge pipe. To leak. Therefore, it is possible to prevent the performance of the fuel cell from being lowered and the fuel electrode from being deteriorated.

  According to the configuration of the second aspect, the water staying in the fuel flow path can be appropriately discharged, and the performance of the fuel cell can be prevented from being lowered and the fuel electrode can be prevented from being deteriorated.

  According to the structure of Claim 3, it can detect reliably that the water | moisture content remains in a fuel flow path.

  According to the configuration of claim 4, the water staying in the fuel flow path can be properly discharged, and the fuel gas can be replaced smoothly when the fuel cell system is started next time. It is possible to prevent deterioration of the battery performance and deterioration of the fuel electrode.

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

  FIG. 2 is a plan view showing the configuration of the fuel cell stack according to the first embodiment of the present invention, and FIG. 3 is a diagram showing the configuration of the fuel cell system according to the first embodiment of the present invention.

  In the figure, 20 is a fuel cell stack as a fuel cell assembly composed of a plurality of fuel cells (FC), and is used as a power source for vehicles such as passenger cars, buses, trucks, passenger carts, luggage carts, etc. Is done. Here, the vehicle is equipped with a large number of auxiliary equipment that consumes electricity, such as lighting devices, radios, and power windows. Since the output range is extremely wide, it is desirable to use the fuel cell stack 20 as a power source in combination with a battery, a secondary battery such as a lithium ion battery, and a power storage means including a capacitor.

  The fuel cell may be an alkaline aqueous solution type, phosphoric acid type, molten carbonate type, solid oxide type, direct type methanol, or the like, but is preferably a solid polymer type fuel cell.

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

  In this case, the solid polymer electrolyte membrane is sandwiched between two gas diffusion electrodes and integrated to join. Then, when one of the gas diffusion electrodes is used as a fuel electrode, and hydrogen gas as a fuel gas is supplied to the fuel electrode via a fuel flow path 13 described later that is in contact with the surface of the fuel electrode, hydrogen is converted into hydrogen ions (protons). It is decomposed into electrons and hydrogen ions permeate the solid polymer electrolyte membrane. Further, when the other of the gas diffusion electrodes is an oxygen electrode, and air as an oxidant is supplied to the oxygen electrode via an air channel as an oxidant channel in contact with the surface of the oxygen electrode, oxygen in the air, the hydrogen Ions and electrons combine to produce water. An electromotive force is generated by such an electrochemical reaction.

  For example, in the present embodiment, as an example, a PEM type fuel cell is used, for example, a stack in which 100 cells are connected in series is used. Although hydrogen gas, which is fuel taken out by reforming methanol, gasoline, etc. with a reformer, can be directly supplied to the fuel cell, a sufficient amount of hydrogen can be stably supplied even during high-load operation of the vehicle. It is desirable to supply the hydrogen gas stored in the fuel storage means 73 so that the fuel can be supplied.

  Here, the fuel storage means 73 is preferably a container storing a hydrogen storage alloy, but is a container storing a hydrogen storage liquid such as decalin, a container storing hydrogen gas such as a hydrogen gas cylinder, or the like. May be. Thereby, hydrogen gas is always sufficiently supplied at a substantially constant pressure, so that the fuel cell can follow the fluctuation of the load of the vehicle and supply a necessary current.

  In the present embodiment, the fuel cell stack 20 includes a plurality of cell modules 21 as shown in FIG. In addition, the arrow in FIG. 2 has shown the flow of the hydrogen gas as fuel gas. The cell module 21 is a fuel in which a unit cell (MEA) 11 as a fuel cell, which will be described later, and the unit cells 11 are electrically connected to each other and hydrogen gas introduced into the unit cell 11 circulates. The separator 12 which separates the flow path 13 and the air flow path through which air flows, and the unit cell 11 and the separator 12 are set as one set, and a plurality of sets are stacked in the thickness direction. In the cell module 21, the unit cells 11 and the separators 12 are stacked in multiple stages so that the unit cells are arranged with a predetermined gap (gap) therebetween.

  The unit cell 11 includes an air electrode as an oxygen electrode provided on the solid polymer electrolyte membrane side as an electrolyte layer and a fuel electrode provided on the other side. The air electrode and the fuel electrode include an electrode diffusion layer made of a conductive material that permeates while diffusing the reaction gas, and a catalyst layer formed on the electrode diffusion layer and supported in contact with the solid polymer electrolyte membrane. Consists of. In addition, an air electrode side collector as a current collector that collects electricity by contacting the electrode diffusion layer on the air electrode side of the unit cell 11 and a current collector that collects electricity by contacting the electrode diffusion layer on the fuel electrode side of the unit cell 11. And a fuel electrode side collector as an electric body.

  In the unit cell 11, water moves. In this case, when fuel gas, that is, hydrogen gas as an anode gas is supplied into the fuel flow path 13 in contact with the surface of the fuel electrode, hydrogen is decomposed into hydrogen ions and electrons, and the hydrogen ions are accompanied by proton-entrained water. Permeates the solid polymer electrolyte membrane. Further, when the air electrode is used as a cathode electrode and an oxidant, that is, air as a cathode gas is supplied into an air flow path, oxygen in the air is combined with the hydrogen ions and electrons to generate water. The Moisture permeates through the solid polymer electrolyte membrane as back-diffused water and moves into the fuel flow path 13 in contact with the fuel electrode surface. Here, the reverse diffusion water means that water generated in the air flow path diffuses into the solid polymer electrolyte membrane and permeates through the solid polymer electrolyte membrane in the direction opposite to the hydrogen ions to the fuel electrode. It has penetrated.

  In the fuel cell stack 20 shown in FIG. 2, a plurality of cell modules 21 are stacked in the horizontal direction in the figure and are sandwiched by side end holding portions 40 from both left and right ends. In the example shown in FIG. 2, ten unit cells 11 and separators 12 are stacked to form one cell module 21, and ten cell modules 21 are stacked to form one fuel cell stack 20. Is forming. Since the separators 112 are always arranged on both sides of the unit cell 11, the number of the separators 12 in one cell module 21 is eleven.

  In this case, the fuel cell stack 20 has a flattened rectangular parallelepiped shape as a whole, and the air flow inside is the direction of gravity as a direction perpendicular to the drawing in FIG. It is straight. Further, as indicated by arrows in FIG. 2, the flow of hydrogen gas is in a serpentine shape that is folded for each cell module 21 in a horizontal plane that is substantially orthogonal to the direction of gravity, that is, in a meandering shape. The second fuel supply pipe 33 for supplying hydrogen gas is connected to one side end holding part 40, and the first fuel discharge pipe 31 for discharging hydrogen gas is connected to the other side end holding part 40. Yes.

  Each cell module 21 includes a fuel through-hole 35 serving as a fuel gas passage formed at both ends so as to penetrate the cell module 21 in the thickness direction. The second fuel supply pipe 33 is connected to the fuel through hole 35 of the cell module 21 located on the most upstream side with respect to the hydrogen gas flow, and the first fuel discharge pipe 31 is connected to the hydrogen gas flow. Is connected to the fuel through hole 35 of the cell module 21 located on the most downstream side. The first fuel discharge pipe 31 is a cell located on the most downstream side via a side end through hole 37 and a fuel gas outlet side manifold 44 as a fuel gas flow path formed in the side end holding portion 40. The module 21 is connected to the fuel through hole 35.

  In the present embodiment, the fuel cell system has a system for supplying hydrogen gas to the fuel cell stack 20, as shown in FIG. The hydrogen gas is supplied from the fuel storage means 73 to a first fuel supply line 32 as a fuel supply line, and a second fuel supply line as a fuel supply line connected to the first fuel supply line 32. Through 33, the fuel gas is supplied to the inlet of the fuel gas flow path of the fuel cell stack 20. The first fuel supply pipe 32 is provided with a fuel supply electromagnetic valve 26 as a hydrogen supply electromagnetic valve. The second fuel supply line 33 is provided with a pressure sensor 78 as pressure detecting means for detecting the pressure in the fuel gas flow path. The fuel storage means 73 has a sufficiently large capacity and always has a capability of supplying hydrogen gas at a sufficiently high pressure. In addition, the said fuel storage means 73 may be single, may be plural, and may be any number in the case of plural.

  The hydrogen gas discharged as an unreacted component from the outlet of the fuel flow path 13 of the fuel cell stack 20 is discharged to the outside of the fuel cell stack 20 through the first fuel discharge pipe 31 as a fuel discharge pipe. The The first fuel discharge pipe 31 is provided with a water recovery drain tank 60 as a recovery container. The water recovery drain tank 60 is connected with a second fuel discharge pipe 30 as a fuel discharge pipe for discharging water and separated hydrogen gas, and the second fuel discharge pipe 30 has a hydrogen circulation line. A suction circulation pump 36 as a pump is provided. Further, a hydrogen circulation electromagnetic valve 34 as a hydrogen circulation switching electromagnetic valve is disposed in the second fuel discharge pipe 30. The water recovery drain tank 60 and the opposite end of the second fuel discharge pipe 30 are connected to the second fuel supply pipe 33. Thereby, the hydrogen gas led out of the fuel cell stack 20 can be recovered and supplied to the fuel gas flow path of the fuel cell stack 20 for reuse.

  The water recovery drain tank 60 also functions as a suction tank for storing hydrogen gas discharged from the fuel gas passage when the operation of the fuel cell system is stopped. Therefore, the capacity of the water recovery drain tank 60 is such that when air as a replacement gas is introduced into the fuel gas flow path and hydrogen gas as the fuel gas is purged, the capacity of the water recovery drain tank 60 is increased. The remaining hydrogen gas is rapidly driven into the water recovery drain tank 60, and is set so as to be large enough not to remain in the fuel gas flow path. That is, even when the air is introduced into the fuel cell stack 20, the hydrogen gas remaining in the fuel gas flow path is rapidly removed even if the fuel gas flow path of the fuel cell stack 20 is not evacuated. The water recovery drain tank 60 has a sufficiently large capacity so that it does not move into the water recovery drain tank 60 and become mixed with oxygen in the air introduced in the fuel cell stack 20. Is.

  Further, a third fuel discharge pipe 56 as a fuel discharge pipe is connected between the suction circulation pump 36 and the hydrogen circulation solenoid valve 34 in the second fuel discharge pipe 30, and the third fuel discharge pipe The passage 56 is provided with a hydrogen start / stop solenoid valve 56a as a hydrogen exhaust solenoid valve. Thereby, hydrogen gas can be discharged at the end of the operation of the fuel cell stack 20.

  Further, the second fuel supply line 33 is connected to an outside air introduction line 28 as a purge means. The outside air introduction conduit 28 is provided with an outside air introduction solenoid valve 28a and an air filter 28b as air introduction solenoid valves, and the outside air, that is, the air as the replacement gas when the operation of the fuel cell stack 20 is completed. The hydrogen gas as the fuel gas can be purged by being introduced into the fuel gas flow path.

  Here, the fuel supply solenoid valve 26, the outside air introduction solenoid valve 28a, the hydrogen circulation solenoid valve 34, and the hydrogen start / stop solenoid valve 56a are so-called on-off type, such as an electric motor, a pulse motor, and an electromagnet. Actuated by an actuator consisting of 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. The air filter 28b removes dust, impurities, harmful gases and the like contained in the air.

  On the other hand, air as an oxidant is supplied to an air flow path of the fuel cell stack 20 from an oxidant supply source such as an air supply fan, an air cylinder, and an air tank (not shown) through an intake manifold and the like. 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 an exhaust manifold, a condenser, etc. which are not shown in figure.

  The intake manifold is provided with a water supply nozzle for spraying water to maintain the oxygen electrode (cathode electrode) of the fuel cell stack 20 in a wet state. Further, the oxygen electrode and the fuel electrode can be cooled by the sprayed water. Further, the condenser is for condensing and removing moisture contained in the air discharged from the fuel cell stack 20, and the water condensed by the condenser is collected in a water tank (not shown) Supplied to the supply nozzle.

  The secondary battery as the power storage means is a so-called battery (storage battery), and a lead storage battery, a nickel cadmium battery, a nickel hydrogen battery, a lithium ion battery, a sodium sulfur battery, and the like are common. The power storage means does not necessarily have to be a battery, and electrically stores and discharges energy, such as a capacitor (capacitor) such as an electric double layer capacitor, a flywheel, a superconducting coil, and a pressure accumulator. Any form may be used as long as it has a function. Furthermore, any of these may be used alone, or a plurality of them may be used in combination.

  The fuel cell stack 20 is connected to a load (not shown) and supplies the generated current to the load. Here, the load is generally an inverter device that is a drive control device, and converts a direct current from the fuel cell stack 20 or the power storage means into an alternating current to rotate a vehicle wheel. To supply. Here, the drive motor also functions as a generator, and generates a so-called regenerative current when the vehicle is decelerated. In this case, since the drive motor is rotated by the wheel to generate electric power, the wheel is braked, that is, functions as a vehicle braking device (brake). Then, the regenerative current is supplied to the power storage means, and the power storage means is charged.

  In the present embodiment, the fuel cell system has control means (not shown). The control means includes arithmetic means such as a CPU and MPU, storage means such as a magnetic disk and semiconductor memory, an input / output interface and the like, and is supplied from various sensors to the fuel flow path 13 and the air flow path of the fuel cell stack 20. The flow rate of hydrogen, oxygen, air, etc., temperature, output voltage, etc. are detected and the oxidant supply source, fuel supply solenoid valve 26, outside air introduction solenoid valve 28a, hydrogen circulation solenoid valve 34, suction circulation pump 36, The operation of the hydrogen start / stop solenoid valve 56a and the like is controlled. The control means also includes a timer for measuring the elapsed time since the supply of hydrogen gas to the fuel gas flow path of the fuel cell stack 20 is stopped. Then, the control means selectively executes a standby mode or a stop mode, as will be described later. Furthermore, the control means controls the operation of all devices that supply fuel and oxidant to the fuel cell stack 20 in cooperation with other sensors and other control devices.

  Next, the configuration of the connecting portion between the fuel through hole 35 of the cell module 21 located on the most downstream side in the fuel cell stack 20 and the side end through hole 37 of the side end holding portion 40 will be described in detail.

  FIG. 1 is a cross-sectional view showing a configuration of a connecting portion between a fuel through hole and a side end through hole of the fuel cell stack according to the first embodiment of the present invention, and is a cross-sectional view taken along line AA in FIG. is there. 1A shows a comparative example, and FIG. 1B shows the first embodiment of the present invention.

  As shown in the drawing, the side end holding portion 40 disposed adjacent to the cell module 21 located on the most downstream side with respect to the flow of hydrogen gas in the fuel cell stack 20 is made of a conductive material such as metal, A terminal 41 that contacts the separator 12 located on the most downstream side and functions as an electrode terminal of the fuel cell stack 20, an insulator 42 made of an electrically insulating material that contacts the terminal 41, a contact with the insulator 42, and a fuel cell An end plate 43 for sandwiching and tightening the stack 20 and a fuel gas outlet side manifold 44 connected to the outside of the end plate 43 are provided. In the example shown in the drawing, the fuel gas outlet side manifold 44 is formed separately from the end plate 43 and connected to the outside of the end plate 43, but is formed integrally with the end plate 43. Also good.

  The side end holding portion 40 penetrates the terminal 41, the insulator 42 and the end plate 43 in the thickness direction, and is a side end through hole which is a part of a fuel discharge conduit communicating with the inside of the fuel gas outlet side manifold 44. The side end through hole 37 is a part of the fuel flow path 13 and is connected to a fuel through hole 35 formed so as to penetrate the cell module 21 in the thickness direction.

  Further, as shown in the figure, a fuel flow path 13 is formed on the side of each separator 12 in contact with the fuel electrode of the unit cell 11, and in each cell module 21, hydrogen gas flows through the fuel flow path 13. And flows into the fuel through hole 35.

  As described in “Background Art”, the hydrogen gas in the fuel flow path 13 includes moisture that has moved as back-diffused water from the oxygen electrode side toward the fuel electrode side. When the partial pressure increases, it condenses into condensed water. And if there is much quantity of the water to condense, the fuel flow path 13 will be locally blocked by the water | moisture content, the performance of the unit cell 11 will fall, or the fuel electrode of the unit cell 11 will deteriorate. .

  Therefore, in the present embodiment, during the steady operation of the fuel cell system, the hydrogen gas is discharged at a predetermined timing, and the suction circulation pump 36 is operated to suck the hydrogen gas in the fuel flow path 13. By discharging from the fuel cell stack 20, the flow rate of the hydrogen gas in the fuel flow path 13 is increased, and the water remaining in the fuel flow path 13 is blown away and discharged. As a result, the fuel electrode is not covered with moisture, and the performance of the unit cell 11 can be prevented from being deteriorated and the fuel electrode can be prevented from deteriorating. The discharge process may be executed every predetermined cycle, may be executed every predetermined driving time, or executed every time the travel distance of the vehicle reaches a predetermined value. Alternatively, it may be executed at any time when stagnation of running moisture is detected.

  Even when the operation of the fuel cell system is stopped, when the hydrogen gas in the fuel channel 13 is sucked by the suction circulation pump 36 and discharged into the atmosphere, the flow rate of the hydrogen gas in the fuel channel 13 is reduced. It becomes higher and the water staying in the fuel flow path 13 is blown off and discharged. As a result, the fuel electrode is not covered with moisture, and the performance of the unit cell 11 can be prevented from being deteriorated and the fuel electrode can be prevented from deteriorating.

  By the way, in the normal fuel cell stack 20, the connection part between the fuel through hole 35 of the cell module 21 and the side end through hole 37 of the side end holding part 40 has a structure as shown in FIG. I have. That is, the lower end of the fuel through hole 35, that is, the position of the bottom surface, and the lower end of the side end through hole 37, that is, the position of the bottom surface are the same. Therefore, moisture can flow not only from the fuel through hole 35 toward the side end through hole 37, but also from the side end through hole 37 toward the fuel through hole 35. Therefore, for example, the flow rate of the hydrogen gas when the hydrogen gas is discharged into the atmosphere is not sufficient, and moisture remains in the side end through-hole 37 indicated by B in the figure, or the discharge of the hydrogen gas is stopped. When water in the first fuel discharge pipe 31 flows back to the side end through-hole 37 due to a decrease in the flow rate of hydrogen gas in the fuel flow path 13 at that time, the discharged water is used for the fuel of the cell module 21. It may flow back to the through hole 35 and further flow back into the fuel flow path 13 due to a capillary phenomenon or the like.

  Therefore, in the present embodiment, as shown in FIG. 1B, the position of the bottom surface as the lower end of the side end through hole 37 is lower than the position of the bottom surface as the lower end of the fuel through hole 35. In addition, the bottom surface of the fuel through-hole 35 and the bottom surface of the side end through-hole 37 are connected by an inclined surface 38. In the example shown in the figure, the entire range of the side end through hole 37 in the terminal 41 is an inclined surface 38, but the inclined surface 38 is only in a part of the side end through hole 37 in the terminal 41. It may be formed, or may be formed so as to cover not only the terminal 41 but also the range including the insulator 42 and the end plate 43. Further, the inclination angle of the inclined surface 38 can be arbitrarily set.

  Thus, since the position of the bottom surface of the side end through-hole 37 is lower than the position of the bottom surface of the fuel through-hole 35, the discharged water indicated by B in the figure is the fuel through-hole of the cell module 21. There is no back flow up to the hole 35, and therefore no back flow into the fuel flow path 13. In addition, since the bottom surface of the fuel through hole 35 and the bottom surface of the side end through hole 37 are connected by the inclined surface 38, the water smoothly flows out from the fuel through hole 35 to the side end through hole 37. That is, if the bottom surface of the fuel through-hole 35 and the bottom surface of the side end through-hole 37 are connected by a step, the surface tension of water acts, so that the upper corner of the step, that is, the fuel The water surface may be maintained in an arc shape at a corner on the through hole 35 side, and the flow may be blocked. However, in the present embodiment, the flow is not blocked by the surface tension of the water because it is connected not by the step but by the inclined surface 38.

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

  During steady operation in the fuel cell system according to the present embodiment, the hydrogen gas flowing out from the outlet of the fuel storage unit 73 is adjusted after the pressure of the hydrogen gas flowing out from the outlet of the fuel storage unit 73 is set to a predetermined pressure. The pressure is not adjusted during the operation of the fuel cell system, and is maintained as it is. An oxidant supply source (not shown) always operates so as to supply a constant amount of air to the air flow path of the fuel cell stack 20. 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 11 of the fuel cell stack 20, and the reverse diffusion water passes through the solid polymer electrolyte membrane and reaches the fuel flow path 13. It permeates and humidifies the fuel electrode side of the solid polymer electrolyte membrane. As a result, the fuel electrode side of the solid polymer electrolyte membrane becomes wet, and hydrogen ions generated from hydrogen by the electrochemical reaction can move smoothly in the solid polymer electrolyte membrane.

  In addition, surplus hydrogen gas supplied to the fuel flow path 13 mixes with the back diffusion water that has permeated into the fuel flow path 13 and becomes surplus to form a gas-liquid mixture. The hydrogen gas that has become the gas-liquid mixture is sucked by the suction circulation pump 36 and led out of the fuel cell stack 20 through the first fuel discharge pipe 31 connected to the fuel cell stack 20. The gas-liquid mixture passes through the first fuel discharge pipe 31 and is introduced into the water recovery drain tank 60. Then, by staying in the water recovery drain tank 60 having a relatively wide space, heavy moisture falls downward due to gravity, and the reverse diffusion water is separated from the hydrogen gas. The hydrogen gas in a state where the reverse diffusion water is separated and dried is discharged from the second fuel discharge pipe 30 to the outside of the water recovery drain tank 60.

  In steady operation, the hydrogen gas discharged from the second fuel discharge line 30 passes through the open hydrogen circulation electromagnetic valve 34 and is introduced into the second fuel supply line 33. Again, it is supplied to the fuel gas flow path of the fuel cell stack 20 and reused. Since the hydrogen start / stop solenoid valve 56a is in a closed state, the hydrogen gas discharged from the suction circulation pump 36 is not discharged into the atmosphere through the third fuel discharge pipe 56, 2 is introduced into the fuel supply line 33. Further, since the outside air introduction electromagnetic valve 28 a is also closed, the atmosphere is not introduced into the second fuel supply conduit 33.

  Here, since the second fuel discharge pipe 30 is connected to the side wall of the upper part of the water recovery drain tank 60, only the hydrogen gas in a state where the reverse diffusion water is separated and reduced in weight becomes the second fuel discharge. It is discharged from the conduit 30 and no moisture is discharged. Further, since the first fuel discharge pipe 31 and the second fuel discharge pipe 30 are connected to the side wall of the upper part of the water recovery drain tank 60 at a position away from each other, the water recovery from the first fuel discharge pipe 31 is performed. The gas / liquid mixture introduced into the drain tank 60 does not flow out of the second fuel discharge line 30 as it is. Thereby, it is possible to appropriately trap excess reverse diffusion water that has permeated into the fuel gas flow path, and it is possible to collect and reuse the excess hydrogen gas.

  On the other hand, the reverse diffusion water that has been separated from the gas-liquid mixture and dropped is stored as stored water in the lower portion of the water recovery drain tank 60. Since the capacity of the water recovery drain tank 60 is set to be large, the vehicle on which the fuel cell stack 20 is mounted once travels after filling the fuel storage means 73 with hydrogen gas as fuel. It is not necessary to discharge water from the water recovery drain tank 60 until the next time hydrogen gas is filled into the fuel storage means 73.

  Next, the operation when stopping the operation of the fuel cell system will be described.

  FIG. 4 is a flowchart showing the operation when stopping the operation of the fuel cell system according to the first embodiment of the present invention.

  First, when the driver of the vehicle operates the main switch or the like to stop the operation, an operation stop command is transmitted to the control means of the fuel cell system (step S1), and the operation of stopping the operation of the fuel cell system is performed. Be started. When the control means receives an operation stop command, it stops the supply of hydrogen gas to the fuel flow path 13 and executes a stop mode in which the hydrogen gas in the fuel flow path 13 is purged with air. First, the control means executes a hydrogen supply electromagnetic valve CLOSE (step S2), closes the fuel supply electromagnetic valve 26, and shuts off the supply of hydrogen gas from the fuel storage means 73. Subsequently, the control means executes the hydrogen circulation switching electromagnetic valve OFF (step S3), closes the hydrogen circulation electromagnetic valve 34, and stops the hydrogen gas circulation. Thereby, the supply of hydrogen gas to the fuel flow path 13 of the fuel cell stack 20 is interrupted.

  Subsequently, the control means executes the hydrogen exhaust solenoid valve OPEN (step S4), opens the hydrogen start / stop solenoid valve 56a, and causes the hydrogen gas in the fuel flow path 13 to pass through the third fuel discharge pipe 56 into the atmosphere. To discharge. In this case, since the suction circulation pump 36 is operating, pressure reduction is started, and the fuel cell stack 20, the water recovery drain tank 60, the second fuel supply line 33, the second fuel discharge line 30, and the first fuel discharge The hydrogen gas remaining in the pipe line 31 is sucked by the suction circulation pump 36 and discharged from the third fuel discharge pipe 56 to the atmosphere. And since the inside of the fuel flow path 13 becomes a negative pressure, the hydrogen gas is reliably removed from the fuel flow path 13 quickly and discharged. In addition, since the flow rate of the hydrogen gas in the fuel flow path 13 becomes high, the moisture staying in the fuel flow path 13 is blown off and discharged together with the hydrogen gas.

  The pressure of hydrogen gas in the fuel flow path 13 is detected by a pressure sensor 78. In this case, since the pressure of the hydrogen gas can be considered to be the same in the range from the fuel supply solenoid valve 26 to the suction circulation pump 36 in the path through which the hydrogen gas flows, the pressure sensor 78 is disposed within the range. Thus, the pressure detected by the pressure sensor 78 is equal to the pressure of the fuel flow path 13 of the fuel cell stack 20.

  Subsequently, the control means determines in this state whether or not the pressure of the hydrogen gas in the fuel flow path 13 has become less than a preset threshold value, for example, −70 [kPaG]. (Step S5). In this case, since the threshold value represents a considerable negative pressure, the state where the pressure is less than the threshold value is a state in which hydrogen gas does not substantially remain in the fuel passage in the fuel passage 13. In addition, the said control means repeats the said determination until the pressure of the hydrogen gas in the fuel flow path 13 becomes less than a threshold value.

  When the pressure of the hydrogen gas in the fuel flow path 13 becomes less than the threshold, the control means executes the air introduction solenoid valve ON (step S6), opens the outside air introduction solenoid valve 28a, and fuels the air. It introduces into the flow path 13. In this case, since the fuel supply electromagnetic valve 26 is in a closed state, the introduced air does not flow toward the fuel storage means 73. As a result, the fuel flow path 13 of the fuel cell stack 20 is filled with air. Since the air passes through the air filter 28b and is filtered, it does not contain dust, impurities, harmful gases, etc. present in the atmosphere. Therefore, a member such as a catalyst in the fuel flow path 13 is not contaminated or altered by the dust, impurities, harmful gas, or the like.

  In the present embodiment, since the water recovery drain tank 60 that also functions as a suction tank is connected to the fuel cell stack 20, when air is introduced into the fuel cell stack 20, the fuel flow of the fuel cell stack 20 is increased. The hydrogen gas remaining in the passage 13 is rapidly driven into the water recovery drain tank 60. Therefore, even when the air is introduced into the fuel cell stack 20, even if the fuel flow path 13 of the fuel cell stack 20 is not evacuated, the hydrogen gas remaining in the fuel flow path 13 is introduced. It will not be mixed with oxygen in the air. Therefore, no potential shift occurs in the unit cell 11, so that the catalyst particles are not eluted and the performance of the fuel cell stack 20 is not deteriorated. Further, the water staying in the fuel flow path 13 is also blown away by the hydrogen gas having a high flow rate and discharged from the fuel cell stack 20. Further, the moisture is blown away by the air introduced into the fuel flow path 13 and is discharged from the fuel cell stack 20.

  In this case, the larger the volume of the water recovery drain tank 60 is, the shorter the time required for the hydrogen gas remaining in the fuel cell stack 20 to move into the water recovery drain tank 60 is. If the value is too large, the entire fuel cell system will be enlarged. Before introducing air into the fuel flow path 13 of the fuel cell stack 20, the suction circulation pump 36 functions as a decompression pump, and sucks the hydrogen gas remaining in the fuel flow path 13 of the fuel cell stack 20. To do. In this case, since the suction circulation pump 36 also functions as a decompression pump, it is not necessary to provide the decompression pump independently, and the entire fuel cell system can be made compact.

  Subsequently, the control means determines whether or not the voltage output from the fuel cell stack 20 in this state has become a preset threshold, for example, 5 [V] or less (step S7). Here, the threshold value corresponds to an output corresponding to a state in which no hydrogen gas remains in the fuel flow path 13 and the air is filled, and there is substantially no potential difference between the fuel electrode and the oxygen electrode. This is the voltage value. In addition, the said control means repeats the said determination until the voltage which the fuel cell stack 20 outputs becomes less than a threshold value.

  When the output of the fuel cell stack 20 becomes equal to or lower than the predetermined voltage, the control means stops all the auxiliary machines (step S8) and ends the process. The control means stops the suction circulation pump 36, closes the outside air introduction electromagnetic valve 28a, and finally stops the oxidant supply source. As a result, the operation of the fuel cell stack 20 is stopped.

  Thus, in the present embodiment, the position of the bottom surface of the side end through hole 37 of the side end holding portion 40 is lower than the position of the bottom surface of the fuel through hole 35 of the cell module 21, and the fuel penetration The bottom surface of the hole 35 and the bottom surface of the side end through hole 37 are connected by an inclined surface 38. Thereby, it is possible to prevent the drained water from flowing back to the fuel through hole 35 of the cell module 21, and further to prevent the discharged water from flowing back into the fuel flow path 13. Further, since the bottom surface of the fuel through-hole 35 and the bottom surface of the side end through-hole 37 are connected by the inclined surface 38, moisture is not blocked by the action of surface tension, and the fuel through-hole 35 It flows smoothly into the side end through hole 37. Therefore, it is possible to prevent the performance of the unit cell 11 from deteriorating and the deterioration of the fuel electrode.

  Next, a second embodiment of the present invention will be described. In addition, about the thing which 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. 5 is an essential part enlarged view showing the configuration in the vicinity of the side end holding part of the fuel cell stack according to the second embodiment of the present invention. 5A is a perspective view, and FIG. 5B is a cross-sectional view showing a cross section along the plane C in FIG. 5A.

  In the present embodiment, as shown in FIG. 5, a water retention sensor 46 is provided in the fuel cell stack 20 to detect that moisture has accumulated in the fuel flow path 13. In addition, the flow of hydrogen gas is meandering as shown by the arrow in FIG.

  In the example shown in the figure, the water retention sensor 46 is attached to the side end holding part 40 on the most downstream side with respect to the flow of hydrogen gas, and the detection part 46a for detecting the presence of moisture is located on the most downstream side with respect to the flow of hydrogen gas. The cell module 21 is located on the opposite side of the fuel gas outlet side manifold 44, that is, on the lower side in the fuel through hole 35 on the inlet side. This part is considered to be the part where moisture is most likely to stay in the fuel flow path 13.

  The detection unit 46a is composed of two electrodes arranged on the upper and lower sides. When the water level rises and both electrodes come into contact with water, the electrical conductivity between the electrodes changes. As shown by B in the fuel through-hole 35, the presence of water remaining is detected. When the presence of moisture remaining in the fuel through-hole 35 is detected as indicated by B, it is determined that moisture has been retained in the fuel flow path 13. In addition, the site | part which arrange | positions the water retention sensor 46 and the site | part in which the detection part 46a is located can be changed suitably.

  When the water retention sensor 46 detects that water has accumulated during steady operation of the fuel cell system, hydrogen gas is discharged to discharge the hydrogen gas from the fuel flow path 13 of the fuel cell stack 20. Thus, the staying water is discharged from the fuel flow path 13 together with the hydrogen gas. Further, when it is detected by the water retention sensor 46 when the operation of the fuel cell system is stopped, the depressurization process and the air introduction process are repeated to remove the retained moisture from the fuel flow path 13. Let it drain.

  Since the configuration of other points is the same as that of the first embodiment, description thereof is omitted.

  Next, in this embodiment, the operation when it is detected that moisture has accumulated when the operation of the fuel cell system is stopped will be described.

  FIG. 6 is a flowchart showing the operation when stopping the operation of the fuel cell system according to the second embodiment of the present invention.

  First, when the driver of the vehicle operates the main switch or the like to stop the operation, an operation stop command is transmitted to the control means of the fuel cell system, and the operation of stopping the operation of the fuel cell system, that is, the stop process Is performed (step S11). The operation of the stop process is the same as that in the first embodiment, and a description thereof will be omitted.

  Subsequently, a decompression process and an air introduction process are performed (step S12), and after hydrogen gas in the fuel flow path 13 of the fuel cell stack 20 is discharged, air is introduced into the fuel flow path 13. Note that the operations of the decompression process and the air introduction process are the same as those in the first embodiment, and a description thereof will be omitted. Similarly to the first embodiment, the water remaining in the fuel flow path 13 is blown off and discharged from the fuel cell stack 20 by the operations of the decompression process and the air introduction process.

  Subsequently, sensing by the water retention sensor 46, that is, an operation for detecting that moisture is retained is performed, and it is determined whether or not moisture is retained (step S13). When the moisture is not retained, the process is terminated as it is, so that the operation of the fuel cell stack 20 is stopped.

  Further, when moisture remains, the decompression process and the air introduction process are performed again. As a result, the moisture remaining in the fuel flow path 13 is blown off and discharged from the fuel cell stack 20.

  Thus, in the present embodiment, the water retention sensor 46 that detects that moisture has accumulated in the fuel flow path 13 is provided. Then, when it is detected that moisture is retained during steady operation of the fuel cell system, the hydrogen gas is discharged to increase the flow rate of the hydrogen gas in the fuel flow path 13 of the fuel cell stack 20, The staying water is discharged from the fuel flow path 13 together with the hydrogen gas. Thereby, it is possible to reliably detect that the moisture has accumulated and to discharge the appropriately retained moisture, and thus it is possible to suppress the consumption of hydrogen gas.

  In addition, when it is detected that water is retained in the fuel flow path after the operation of the stop process, the retained water is discharged from the fuel flow path 13 by repeating the operations of the decompression process and the air introduction process. . Therefore, the retained water can be reliably discharged from the fuel flow path 13, so that the reaction gas can be replaced smoothly when the fuel cell system is started next time, and the unit cell 11 is deteriorated. Can be prevented.

  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 sectional drawing which shows the structure of the connection part of the fuel through-hole and side end through-hole of the fuel cell stack in the 1st Embodiment of this invention, Comprising: It is AA arrow sectional drawing of FIG. It is a top view 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 fuel cell system in the 1st Embodiment of this invention. It is a flowchart which shows the operation | movement at the time of stopping the driving | operation of the fuel cell system in the 1st Embodiment of this invention. It is a principal part enlarged view which shows the structure of the side end holding part vicinity of the fuel cell stack in the 2nd Embodiment of this invention. It is a flowchart which shows the operation | movement at the time of stopping the driving | operation of the fuel cell system in the 2nd Embodiment of this invention.

Explanation of symbols

11 Unit cell 12 Separator 13 Fuel flow path 20 Fuel cell stack 30 Second fuel discharge line 31 First fuel discharge line 38 Inclined surface 40 Side end holding part 46 Water retention sensor

Claims (4)

A fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode is electrically connected via a separator in which a fuel channel is formed along the fuel electrode and an oxidant channel is formed along the oxygen electrode. A connected fuel cell assembly;
A fuel discharge line for discharging fuel gas from the fuel flow path;
A fuel cell system having a side end holding portion disposed on a fuel gas discharge side of the fuel cell assembly,
The lower end of the portion formed in the side end holding portion in the fuel discharge conduit is lower than the lower end of the portion closest to the fuel discharge conduit in the fuel flow path, and is connected to the lower end of the fuel flow path at an inclined surface. A fuel cell system. Control means for controlling the discharge of the fuel gas;
2. The fuel cell system according to claim 1, wherein the control unit executes a discharge process of discharging fuel gas from the fuel flow path at a predetermined timing. A water retention sensor that detects that moisture has accumulated in the fuel flow path;
3. The fuel cell system according to claim 2, wherein the control unit executes the discharge process when the water retention sensor detects that water has accumulated in the fuel flow path.   The fuel cell system according to claim 2, wherein the control unit executes the discharge process when a stop process for stopping the operation of the fuel cell system is executed.

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