JP2006164894A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel economy by storing a mixed gas including an inert gas discharged from a fuel cell and supplying the same to the fuel cell again. <P>SOLUTION: This fuel cell system comprises: a fuel cell 1; an oxidant supply passage 3 for supplying air required for a power generating reaction to an oxidant electrode of the fuel cell 1; and a gas supply passage 2 for supplying a reaction gas required for the power generating reaction to a fuel electrode of the fuel cell 1. The fuel cell system further comprises: a gas circulating system 5 for circulating a mixed gas to the supply passage after the power generating reaction of the fuel cell 1, the mixed gas being a mixture of the reaction gas unreacted that is discharged from the fuel electrode and the inert gas coming from the oxidant electrode; and a gas discharge means 4 for discharging the mixed gas from the gas circulating system 5. The fuel cell system further comprises a gas storage means 6 for storing the mixed gas discharged from the gas circulating system 5, and the mixed gas stored in the gas storage means 6 is supplied to the gas supply passage 2 again. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system that stores gas discharged from a fuel cell and reuses the stored gas.

Conventional fuel cell systems are known in which unreacted gas discharged from a fuel cell is caused to flow through a circulation passage and the gas is supplied again to the fuel cell. According to this, a sufficient amount of reaction gas is circulated and high efficiency is achieved by supplying a sufficient amount of reaction gas to the fuel cell regardless of the operating state of the fuel cell. (For example, see Patent Document 1)
JP 2003-151593 A

  In the fuel cell system provided with the circulation passage for reusing the unreacted gas discharged from the conventional fuel cell, a part or all of the unreacted gas existing in the circulation passage is discarded at a predetermined timing. There was a problem that fuel consumption deteriorated.

  In view of the above problems, an object of the present invention is to provide a fuel cell system that suppresses fuel consumption loss of the fuel cell.

  A fuel cell in which a fuel electrode and an oxidant electrode are arranged on both sides of the electrolyte membrane, an oxidant supply passage for supplying air required for a power generation reaction to the oxidant electrode of the fuel cell, and a fuel electrode of the fuel cell A gas supply passage for supplying a reaction gas required for the power generation reaction. After the power generation reaction of the fuel cell, a gas circulation system that circulates a mixed gas of an unreacted reaction gas discharged from the fuel electrode and an inert gas mixed from the oxidant electrode to the gas supply passage, and from the gas circulation system A gas discharge means for discharging the mixed gas; and a gas storage means for storing a part of the mixed gas that is recirculated to the gas circulation system, and the mixed gas stored in the gas storage means is again supplied to the gas supply passage. Supply.

  According to the present invention, when the mixed gas discharged from the fuel cell in the circulation path of the fuel cell is discharged, the mixed gas is stored in the storage means, and when the fuel cell is in a predetermined operation state, the stored gas is stored. Supply to fuel cell and reuse. This significantly improves the fuel efficiency of the fuel cell system.

  A schematic configuration of the fuel cell system used in the first embodiment is shown in FIG.

  In this embodiment, a fuel cell 1 that generates power using a reaction gas and an oxidant gas is provided. Hydrogen gas is used as the reaction gas, and air is used as the oxidant gas. The reaction gas is not limited to this, and for example, a hydrogen-containing gas reformed by a reformer can be used as the reaction gas.

  The fuel cell 1 consumes fuel gas and oxidant gas during a power generation reaction. At that time, the fuel gas is supplied to the fuel electrode of the fuel cell 1 in excess of the necessary amount for the power generation reaction. Further, in the oxidizer electrode, although the inert gas (nitrogen gas) contained in the oxidizer gas is in a trace amount, the oxidizer electrode cross-leaks from the oxidizer electrode to the fuel electrode via the electrolyte membrane of the fuel cell 1 to the fuel electrode. Mixed.

  Therefore, the fuel cell 1 discharges the mixed gas of the surplus fuel gas for the power generation reaction and the inert gas that cross leaks from the oxidant electrode to the fuel electrode.

  In order to perform a power generation reaction of the fuel cell 1, a fuel gas supply passage 2 that supplies fuel gas to a fuel cell 1 from a fuel gas tank (not shown) and an oxidant supply passage 3 that supplies air to the fuel cell 1 are provided. Further, an oxidant discharge passage 10 that discharges an oxidant gas that the fuel cell 1 has not used for the power generation reaction, and a fuel gas circulation that introduces the above-described mixed gas from the downstream of the fuel cell 1 to the upstream fuel gas supply passage 2. A passage 5 is provided. A connecting portion of the fuel gas circulation passage 5 to the fuel gas supply passage 2 is provided with an ejector 11 that sucks the mixed gas in the fuel gas circulation passage 5 using the fluid energy of the gas flowing through the fuel gas supply passage 2.

  By providing the ejector 11, the mixed gas discharged from the fuel cell 1 can be introduced into the fuel gas supply passage 2 more smoothly than in the case where only the differential pressure is used.

  A gas storage device 6 is provided in the middle of the gas discharge passage 4 branched from the fuel gas supply passage 2 upstream of the fuel cell 1 and downstream of the ejector 11. A valve 7 and a valve 8 are provided upstream and downstream of the gas storage device 6, respectively. By opening and closing these valves 7 and 8, the mixed gas discharged from the fuel cell 1 existing in the fuel gas circulation passage 5 is stored, or the mixed gas stored in the gas storage device 6 is supplied to the fuel cell 1 again. Here, the gas storage device 6 may be a space in which gas can be stored, and the piping itself also serves as the gas storage device 6.

  Further, a controller 9 is provided for controlling the electric power generated in the fuel cell 1 and the devices in the system, the valve 7, the valve 8, and the like.

  Next, the operation will be described.

  When the concentration of the inert gas in the mixed gas in the fuel gas circulation passage 5 is increased and the mixed gas is discharged from the fuel cell system, the fuel gas circulation passage 5 is opened by opening the valve 7 and the valve 8 by a signal from the controller 9. The mixed gas always passes through the gas storage device 6 and is discharged out of the system.

  The inert gas concentration in the mixed gas is estimated by the power control means 9 based on the operation time of the fuel cell 1 and the like.

  In order to stop the discharge of the mixed gas from the fuel gas circulation passage 5, the valve 7 and the valve 8 are closed. At that time, a part of the mixed gas discharged from the fuel cell 1 is stored in the gas storage device 6.

  When the gas mixture in the fuel gas circulation passage 5 is stored in the gas storage device 6, if the pressure in the fuel gas supply passage 2 or the fuel gas circulation passage 5 is higher than the pressure in the gas storage device 6, It becomes easy to store the mixed gas in the gas storage device 6.

  For this reason, it is preferable to store the mixed gas in the gas storage device 6 when the pressure of the fuel gas circulation passage 5 is high and the load of the fuel cell 1 is relatively high.

  The mixed gas stored in the gas storage device 6 contains a component of fuel gas. When the fuel cell 1 consumes less fuel gas, for example, when idling, the mixed gas is sufficiently supplied. Power generation is possible.

  Therefore, when the valve 7 is opened when the amount of fuel gas supplied to the fuel gas supply passage 2 is small and the pressure is low, such as when the fuel cell 1 is idling, the mixed gas stored in the gas storage device 6 becomes fuel. It is sent to the battery 1. In this case, since the mixed gas pressure of the gas storage device 6 is higher than the pressure of the fuel gas supply passage 2, even if the content of the fuel gas is small, it sufficiently penetrates into the fuel electrode and the power generation reaction efficiency in the fuel cell 1. Is well maintained.

  When the mixed gas in the gas storage device 6 is consumed in this way, the valve 7 is closed to prepare for the next mixed gas filling opportunity.

  The effect of this embodiment will be described.

  In the present embodiment, when the mixed gas in the fuel gas circulation passage 5 is discharged, a part of the gas is stored in the gas storage device 6 and the gas is re-supplied to the fuel cell 1. The mixed gas discharged out of the battery system can be reused, and the fuel efficiency of the fuel cell system can be significantly improved.

  Further, since the gas storage device 6 is connected downstream of the fuel gas supply passage 2 to which the fuel gas circulation passage 5 is connected, there is no special pressure adjusting means for storing and releasing the mixed gas in the gas storage device 6. However, the gas mixture can be stored in the gas storage device 6 at a relatively high pressure, and the gas mixture can be supplied to the fuel cell 1.

  By accumulating the mixed gas in the gas storage device 6 when the pressure of the mixed gas in the fuel gas circulation passage 5 is high, the mixed gas can be stored in a high pressure state, and the accumulated amount is also increased.

  In addition, by reusing the mixed gas stored in the gas storage device 6 when the operating load of the fuel cell 1 is small or idle, the fuel cell 1 can be effectively used even when the concentration of the fuel gas is low. Can contribute to power generation reaction.

  Next, the second embodiment will be described with reference to FIG. 2 for different portions from the first embodiment.

  In order to store the mixed gas discharged from the fuel cell 1, a branch passage 19 is provided in parallel with the fuel gas circulation passage 5, and the gas storage device 6 is provided in the middle of the branch passage 19. A connecting portion for introducing the gas stored in the gas storage device 6 into the fuel gas circulation passage 5 is provided with an ejector 15, and a valve 13 is provided upstream of the ejector 15 and downstream of the gas storage device 6.

  Further, a gas discharge passage 4 for discharging the mixed gas to the outside of the present system is provided downstream of the fuel cell 1 through the valve 12 from the fuel gas circulation passage 5 downstream of the fuel cell 1.

  Here, the mixed gas discharged from the fuel cell 1 is discharged by opening and closing the valve 12, or the mixed gas is circulated in the system.

  Further, the mixed gas discharged from the fuel cell 1 is stored in the gas storage device 6 or the mixed gas stored in the gas storage device 6 is introduced into the fuel gas circulation passage 5 by opening and closing the valves 13 and 14.

  Next, the operation will be described.

  When the concentration of the inert gas in the mixed gas in the fuel gas circulation passage 5 increases and the mixed gas in the fuel cell system is discharged, the mixed gas circulating through the fuel gas circulation passage 5 by opening the valve 12 is opened. Is discharged out of the system. Further, the valve 12 is closed to stop the discharge of the mixed gas from the fuel gas circulation passage 5.

  Further, when the mixed gas in the fuel gas circulation passage 5 is stored in the gas storage device 6, the fuel gas circulation passage 5 and the gas storage device 6 are connected in parallel, so that no differential pressure is required. Therefore, a part of the mixed gas circulating in the fuel gas circulation passage 5 is stored in the gas storage device 6 by opening and closing the valves 13 and 14.

  For this reason, when the mixed gas discharged from the fuel cell 1 is stored, it is preferable that the output of the fuel cell 1 is relatively high, that is, the pressure in the system is high.

  When the pressure of the fuel gas supplied to the fuel cell 1 from the fuel gas circulation passage 5 is low, the mixed gas stored in the gas storage device 6 is introduced into the fuel gas circulation passage 5 via the ejector 15 when the valve 13 is opened. And sent to the fuel cell 1. In this case, since the output of the fuel cell 1 is lower and the pressure of the fuel gas circulation passage 5 is lower than when the mixed gas is stored in the gas storage device 6, the power generation reaction rate of the fuel cell 1 is maintained well, The mixed gas stored in the gas storage device 6 is also smoothly introduced into the fuel gas circulation passage 5.

  The effect of this embodiment will be described.

  In this embodiment, since the gas storage device 6 is provided in the branch circuit 19 downstream of the fuel cell 1 and in parallel with the fuel gas circulation passage 5, when the mixed gas in the fuel gas circulation passage 5 is stored in the gas storage device 6. , Pressure loss can be suppressed.

  By accumulating the mixed gas in the gas storage device 6 when the pressure of the mixed gas in the fuel gas circulation passage 5 is high, the mixed gas can be stored in a high pressure state, and the accumulated amount is also increased.

  Further, when the mixed gas stored in the gas storage device 6 is reused, the supply to the fuel cell 1 becomes smoother by passing the ejector 15 to the fuel gas circulation passage 5.

  Next, a third embodiment will be described with reference to FIG. 3 with a focus on differences from the second embodiment.

  A gas storage device 6 is provided in the middle of a branch circuit 19 parallel to the fuel gas circulation passage 5 for circulating the mixed gas discharged from the fuel cell 1.

  A valve 14 is provided upstream of the gas storage device 6 in the branch circuit 19. An ejector 15 is provided at a connection portion of the mixed gas discharged from the gas storage device 6 to the fuel gas supply passage 2. However, the ejector 15 is provided upstream of the ejector 11 provided at the connection portion of the fuel gas circulation passage 5.

  A valve 13 is provided downstream of the gas storage device 6 and upstream of the ejector 15. Further, the gas discharge passage 4 is branched from the upstream of the valve 13 downstream of the gas storage device 6 via the valve 12. Further, the gas storage device 6 is provided with an inert gas estimation means 18 for estimating the concentration of the inert gas in the stored mixed gas.

  Here, the inert gas estimation means 18 may estimate the concentration of the inert gas using a method for detecting or estimating the concentration of the fuel gas in the mixed gas discharged from the fuel cell 1, for example. The concentration of the fuel gas may be predicted based on the voltage in the battery 1, and the concentration of the inert gas may be estimated.

  When the concentration of the inert gas in the mixed gas in the fuel gas circulation passage 5 increases and the concentration of the inert gas estimated by the inert gas estimation means 18 is higher than a predetermined value, the concentration of the fuel gas in the fuel cell system In order to recover, the valve 13 is closed and the valves 12 and 14 are opened. Thereby, the mixed gas in the fuel gas circulation passage 5 always passes through the gas storage device 6 and is discharged out of the system. To stop the discharge of the mixed gas from the fuel gas circulation passage 5, the valve 12 and the valve 14 are closed. At the same time, a part of the mixed gas discharged from the fuel cell 1 is stored in the gas storage device 6. Stopping the discharge of the mixed gas to the outside of the system is performed when the estimated value of the inert gas estimating means 18 is lower than a specified value.

  When the gas mixture in the fuel gas circulation passage 5 is stored in the gas storage device 6, the gas mixture in the fuel gas circulation passage 5 can be stored in the gas storage device 6 if the pressure of the gas mixture circulating in the system is high. It becomes easy.

  For this reason, it is preferable to store the mixed gas in the gas storage device 6 when the pressure of the fuel gas circulation passage 5 is high and the load of the fuel cell 1 is relatively high.

  The gas storage device 6 is provided with an inert gas estimation means 18 to estimate the concentration of the inert gas in the mixed gas stored in the gas storage device 6. Therefore, when the estimated concentration of the inert gas in the mixed gas stored in the gas storage device 6 is lower than a predetermined value, the valve 13 is opened and the mixed gas stored in the gas storage device 6 is returned to the fuel cell 1 again. Supply. Here, the predetermined value of the concentration of the inert gas is a value at which a target load of the fuel cell 1 can be sufficiently obtained from experiments and calculations.

  The effect of this embodiment will be described.

  The gas storage device 6 is provided with an inert gas estimation means 18, and the gas discharge passage 4 is provided downstream, thereby detecting the inert gas concentration of the mixed gas in the fuel gas circulation passage 5 that has passed through the gas storage device 6. Therefore, it can be determined whether or not it can be discharged, and wasteful gas mixture can be prevented from being discharged, leading to further improvement in fuel consumption.

  The fuel gas is contained by providing the fuel gas circulation passage 5 upstream of the portion where the mixed gas discharged from the gas storage device 6 is introduced into the fuel gas supply passage 2 in the fuel gas circulation passage 5. The circulation amount of the mixed gas increases, the pressure of the mixed gas circulated and supplied to the fuel cell 1 increases, and the output of the fuel cell 1 can be increased.

  Next, a fourth embodiment will be described with reference to FIG. 4 with a focus on differences from the third embodiment.

  A fuel gas circulation passage 5 for introducing the mixed gas discharged from the fuel cell 1 from the downstream of the fuel cell 1 to the upstream fuel gas supply passage 2 is provided, and a gas circulation pump 17 is provided in the middle of the fuel gas circulation passage 5. In the fuel gas circulation passage 5, a throttle valve 16 for adjusting the flow rate of the mixed gas discharged from the fuel cell 1 and adjusting the pressure of the fuel gas circulation passage 5 is provided upstream of the gas circulation pump 17.

  A branch circuit 19 is branched from the downstream side of the fuel cell 1 in parallel with the fuel gas circulation passage 5, and the gas storage device 6 is provided in the middle of the branch circuit 19 via a valve 14. Downstream of the gas storage device 6, the fuel gas circulation passage 5 is connected upstream of the gas circulation pump 17. Here, in this embodiment, although the connection part mentioned above was made upstream of the gas circulation pump 17, you may connect downstream. In addition, a valve 13 is provided upstream of the connecting portion and downstream of the gas storage device 6.

  On the other hand, the gas storage device 6 includes a gas discharge passage 4 through which a mixed gas stored in the gas storage device 6 is discharged via a valve 8.

  When the concentration of the inert gas in the mixed gas in the fuel gas circulation passage 5 is increased and the mixed gas is discharged from the fuel cell system, the mixed gas in the fuel gas circulation passage 5 is always gas when the valve 8 and the valve 14 are opened. It passes through the storage device 6 and is discharged out of the system. Further, the valve 8 and the valve 14 are closed to stop the discharge of the mixed gas from the fuel gas circulation passage 5.

  Next, when storing the mixed gas in the fuel gas circulation passage 5 in the gas storage device 6, the opening of the throttle valve 16 is reduced and the valves 13 and 14 are opened and closed. By adjusting the opening degree of the throttle valve 16 to temporarily increase the pressure in the fuel gas circulation passage 5, the mixed gas discharged from the fuel cell 1 can be easily stored in the gas storage device 6.

  Further, when the mixed gas stored by the gas storage device 6 is introduced into the fuel gas circulation passage 5, the pressure of the fuel gas circulation passage 5 is preferably lower than that of the gas storage device 6. Therefore, by opening the opening of the throttle valve 16 and opening the valve 13, the mixed gas stored in the gas storage device 6 can be easily introduced into the fuel gas circulation passage 5.

  By adjusting the output of the circulation pump 17 and the opening of the throttle valve 16, the pressure of the mixed gas in the fuel gas circulation passage 5 and the branch passage 19 is controlled, and the mixing of the fuel gas circulation passage 5 in the gas storage device 6 is controlled. The gas is stored, and the mixed gas stored in the gas storage device 6 is supplied to the fuel cell 1 again.

  The effect of this embodiment will be described.

  The fuel gas circulation passage 5 is provided with a throttle valve 16 and a gas circulation pump 17, and the pressure of the gas storage device 6 can be controlled by adjusting the opening of the throttle valve 16 and the output of the gas circulation pump 17. The discharged mixed gas can be stored in the gas storage device 6, or the mixed gas stored in the gas storage device 6 can be re-supplied to the fuel cell 1 regardless of the output of the fuel cell 1.

  Further, by providing the gas storage device 6 with the gas discharge passage 4 for discharging the mixed gas in the fuel gas circulation passage 5, it becomes easy to grasp the composition of the mixed gas discharged outside the system.

It is obvious that the present invention is not limited to the above-described embodiments, and includes various improvements and modifications that can be made by those skilled in the art within the scope of the technical idea of the invention described in the claims. .

It is a block diagram of the system of a 1st embodiment. It is a block diagram of the system of a 2nd embodiment. It is a block diagram of a system of a 3rd embodiment. It is a block diagram of the system of a 4th embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Gas supply path 3 Oxidant supply path 4 Gas discharge path (gas discharge means)
5 Fuel gas circulation passage (gas circulation system)
6 Gas storage device (gas storage means)
7 Valve 8 Valve 11 Ejector (first ejector)
15 Ejector (second ejector)
16 Throttle valve (pressure regulating valve)
17 Gas circulation pump 18 Inert gas estimation means (gas concentration measurement means)
19 Branch circuit

Claims (9)

A fuel cell in which a fuel electrode and an oxidant electrode are arranged on both sides of the electrolyte membrane;
An oxidant supply passage for supplying air required for power generation reaction to the oxidant electrode of the fuel cell;
A gas supply passage for supplying a reaction gas required for a power generation reaction to the fuel electrode of the fuel cell;
In a fuel cell system comprising:
A gas circulation system for circulating a mixed gas of unreacted reaction gas discharged from the fuel electrode and inert gas mixed from the oxidant electrode to the gas supply passage after the power generation reaction of the fuel cell;
Gas discharging means for discharging the mixed gas from the gas circulation system;
Comprising gas storage means for storing a part of the mixed gas refluxed to the gas circulation system;
The fuel cell system, wherein the mixed gas stored in the gas storage means is supplied again to the gas supply passage. The gas storage means includes a gas storage device for storing the mixed gas, and a valve disposed on each of the introduction and discharge sides of the mixed gas,
The fuel cell system according to claim 1, wherein the gas discharge unit includes a valve that controls discharge of the mixed gas. The gas storage means in the passage branched from the gas supply passage upstream of the fuel cell downstream from the connection portion of the gas circulation system of the gas supply passage, and the gas discharge means downstream thereof,
3. The fuel cell system according to claim 1, wherein a part of the mixed gas discharged from the gas discharging means is stored in the gas storage means. The gas storage means is provided in a branch passage parallel to the gas circulation system,
3. The fuel cell according to claim 1, wherein the mixed gas discharged from the fuel cell and stored in the gas storage means is introduced from the branch passage into a gas circulation system or a gas supply passage. system.   The fuel cell system according to claim 4, wherein the gas discharge means is provided in a passage branched from the upstream or downstream of the gas storage means.   The fuel cell system according to claim 4 or 5, wherein the gas circulation system includes a circulation pump that forcibly circulates the mixed gas and a pressure regulating valve that controls a circulation pressure of the mixed gas.   The fuel cell system according to any one of claims 1 to 6, wherein the gas circulation system or the gas storage unit includes a gas concentration measuring unit that estimates or detects an inert gas concentration in the mixed gas.   The fuel cell stem according to any one of claims 1 to 7, wherein a first ejector is provided at a connection portion from the gas circulation system to the gas supply passage.   The fuel cell system according to any one of claims 4 to 6, wherein a second ejector is provided at a connection portion from the branch passage to the gas circulation system or the gas supply passage.

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