JP2006156283A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute circulation of a fuel without using power generated by a fuel cell. <P>SOLUTION: This fuel cell system is provided with the fuel cell 3 for generating power by a fuel gas and an oxidizer gas and has a circulation passage 8 for supplying a fuel exhaust gas exhausted from the fuel cell 3 to the fuel cell 3 again. In the circulation passage 8, the fuel exhaust gas is circulated by using an oxidizer exhaust gas exhausted from the fuel cell 3 as a power source. As a concrete structure for circulating the fuel exhaust gas, a circulation device 20 is installed in the circulation passage 8. The circulation device 20 is composed of an expansion machine 22 for regenerating energy of the oxidizer exhaust gas and a compressor 21 for circulating the fuel exhaust gas by the regenerated energy, and the compressor 21 is driven by shaft power from the expansion machine 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system including a fuel cell that generates power by supplying a fuel gas and an oxidant gas, and more particularly to an improvement in a fuel cell system that circulates and reuses fuel exhaust gas through a circulation path.

  Fuel cell technologies that enable clean exhaust and high energy efficiency are attracting attention as countermeasures against environmental problems in recent years, in particular, air pollution caused by exhaust gas from automobiles, global warming due to carbon dioxide, and the like. The fuel cell system is an energy conversion system that supplies a fuel gas and an oxidant gas to a fuel electrode and an oxidant electrode of a fuel cell to cause an electrochemical reaction and convert chemical energy into electric energy. In the fuel cell system, only water is generated by the electrochemical reaction, and exhaust gas and carbon dioxide containing harmful substances are not discharged.

  In such a fuel cell system, not all of the supplied fuel gas (hydrogen gas) is used in the fuel cell, and as a device for improving the utilization efficiency of the fuel gas, it has not been used in the fuel cell. A fuel gas circulation type fuel cell system in which used fuel gas is circulated again to the fuel cell and reused is known (see, for example, Patent Document 1 and Patent Document 2).

  For example, in Patent Document 1, a fuel cell that is supplied with a fuel gas and an oxidant gas to generate power, a fuel supply channel for supplying the fuel gas to the fuel cell, and a fuel cell that is discharged from the fuel cell. A fuel circulation passage for circulating the fuel gas by joining the unreacted fuel gas to any position of the fuel supply passage, a fuel pump for taking in and sending out the unreacted fuel gas, and the fuel A fuel circulation fuel cell system including an ejector that sucks the unreacted fuel gas using a negative pressure generated when the gas flows and joins the unreacted fuel gas is disclosed. According to the invention described in Patent Document 1, the size of the fuel pump can be reduced by using the ejector together, and the power consumption of the fuel pump can be suppressed.

On the other hand, in Patent Document 2, for example, in claim 11, in a fuel cell system in which the supply source of hydrogen gas is a high-pressure vessel, the hydrogen gas flowing in the hydrogen supply path from the high-pressure vessel to the fuel cell is decompressed and expanded. An expander to be rotated, a rotation output shaft that outputs expansion energy of hydrogen gas expanded by the expander as rotational energy, and unreacted hydrogen gas discharged from the fuel cell to the hydrogen supply path of the fuel cell A circulation path; a hydrogen pump provided in the circulation path for circulating hydrogen gas; and an electric motor for driving the hydrogen pump, wherein the rotary output shaft, the hydrogen pump, and the electric motor are mechanically connected. A fuel cell system is disclosed. For example, as described in the seventh embodiment described below in paragraph No. 0059 and the like, in the invention described in Patent Document 2, when hydrogen gas is supplied from a high-pressure hydrogen tank to the fuel cell, hydrogen is expanded by an expander. The gas expansion energy is recovered, and the recovered expansion energy is taken out as mechanical energy and used as driving energy for the hydrogen circulation pump. Therefore, the energy of the hydrogen circulation pump generator can be reduced.
JP 2003-151588 A JP 2003-217461 A

  However, in the circulation system using the ejector as in the invention described in Patent Document 1, the circulation flow rate of the high-density gas cannot be secured due to the characteristics of the ejector, so that there is a problem that the power consumption of the pump for compensating this is large. is there.

  On the other hand, the invention described in Patent Document 2 is configured to use the energy of high-pressure hydrogen, and therefore does not use high-pressure fuel gas such as a fuel cell system that obtains hydrogen by reforming liquid fuel or a direct fuel cell system. In the fuel cell system, there is a problem that energy for driving the circulation pump cannot be obtained.

  The present invention has been proposed for the purpose of overcoming such drawbacks of the prior art. That is, the present invention provides a fuel cell system capable of obtaining a driving force for circulating fuel regardless of the type of fuel and capable of circulating the fuel without using the power generated by the fuel cell. The purpose is to do.

  The fuel cell system according to the present invention is a fuel cell system that includes a fuel cell that generates power using fuel gas and oxidant gas, and has a circulation path for supplying the fuel exhaust gas discharged from the fuel cell to the fuel cell again. In the circulation path, the fuel exhaust gas is circulated using the oxidant exhaust gas discharged from the fuel cell as a power source.

  According to the fuel cell system of the present invention, it is possible to circulate fuel without using the electric power generated by the fuel cell, and the energy efficiency of the entire system can be greatly improved. Further, in the fuel cell system according to the present invention, the energy for circulating the fuel exhaust gas is obtained by using the energy of the oxidant exhaust gas. Therefore, the fuel does not need to be high-pressure fuel gas, and the liquid fuel is improved. Even in a fuel cell system that does not use high-pressure fuel gas, such as a fuel cell system that obtains hydrogen by quality or a direct fuel cell system, it is possible to obtain energy for the circulation.

  Hereinafter, embodiments of a fuel cell system to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 shows the configuration of the fuel cell system of this embodiment. As shown in FIG. 1, the fuel cell system of this embodiment mainly includes a fuel supply source 1 that supplies a fuel gas such as hydrogen gas, an oxidant gas supply device 2 that supplies air as an oxidant gas, and power generation. The fuel cell 3 which performs is comprised.

  In the fuel cell 3, an anode 4 to which a fuel gas (hydrogen gas) is supplied and a cathode 5 to which an oxidant gas (air) is supplied are overlapped with an electrolyte / electrode catalyst composite interposed therebetween to constitute a power generation cell. At the same time, it usually has a structure in which a plurality of power generation cells are stacked in multiple stages, and converts chemical energy into electrical energy by an electrochemical reaction. In the anode 4, when hydrogen is supplied, it is dissociated into hydrogen ions and electrons, the hydrogen ions pass through the electrolyte, the electrons pass through an external circuit, generate electric power, and move to the cathode 5. At the cathode 5, oxygen in the supplied air reacts with the hydrogen ions and electrons to generate water, which is discharged to the outside.

  For example, a solid polymer electrolyte membrane is used as the electrolyte of the fuel cell 3 in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte membrane is made of an ion (proton) conductive polymer membrane such as a fluororesin ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water.

  In the fuel cell 3, it is necessary to supply fuel gas and oxidant gas to the anode 4 and cathode 5, and the mechanism for this is fuel gas supply means and oxidant gas supply means.

  Here, the fuel gas supply means will be described. The fuel gas supply means includes, for example, a fuel gas supply valve for adjusting the flow rate, pressure and the like of the supplied fuel gas in addition to the fuel supply source 1 such as the hydrogen tank described above. A hydrogen pressure regulating valve is provided, and the fuel gas is supplied to the fuel cell 3 through the fuel gas supply line 6. That is, the fuel gas supplied from the fuel supply source 1 is supplied to the anode 4 of the fuel cell 3 through the fuel gas supply line 6 after the pressure and flow rate are adjusted by the fuel gas supply valve and the hydrogen pressure regulating valve. .

  The fuel cell 3 does not consume all the supplied fuel gas, and the remaining fuel gas (fuel exhaust gas discharged from the anode 4 of the fuel cell 3) is circulated and supplied to the fuel cell 3 again. Therefore, at the outlet of the anode 4 of the fuel cell 3, in addition to the fuel exhaust gas exhaust pipe 7, a circulation path 8 that leads the fuel exhaust gas to the fuel gas supply line 6 is provided, and the fuel discharged from the anode 4 of the fuel cell 3 The exhaust gas is circulated through the fuel exhaust gas exhaust pipe 7 and the circulation path 8, mixed with the fuel gas newly supplied from the fuel supply source 1, and supplied again to the anode 4 of the fuel cell 3.

  A purge valve 9 is provided in the middle of the circulation path 8. The purge valve 9 has a function of releasing the fuel exhaust gas from the anode 4 of the fuel cell 3 to the outside. By opening and closing the purge valve 9, the fuel exhaust gas is released from the circulation path 8 to the outside. . When a fuel gas such as hydrogen is circulated, impurities such as nitrogen and CO accumulate in the circulation path 8 over time, and the hydrogen partial pressure decreases. Therefore, the problem that the efficiency of the fuel cell 3 falls arises. Therefore, when the impurity concentration becomes high or when the fuel cell system is started, the purge valve 9 is opened to purge the gas in the circulation path 8. Thereby, impurities can be removed from the circulation path 8.

  On the other hand, the oxidant gas supply means includes an oxidant gas supply device 2 including a compressor 10 and a motor 11 for sucking outside air and pumping air, which is an oxidant gas, to the cathode 5 of the fuel cell 3. An oxidant gas supply pipe 12 that guides the oxidant gas fed from the fuel cell 3 to the cathode 5 of the fuel cell 3, and an oxidant exhaust gas exhaust pipe 13 for discharging the oxidant exhaust gas from the cathode 5 of the fuel cell 3. Has been. Oxidant gas (air) is sent to the oxidant gas supply pipe 12 by the compressor 10 and the motor 11, and is humidified by a humidifier or the like as necessary, and then supplied to the cathode 5 of the fuel cell 3. Oxygen not consumed in the fuel cell 3 and other components in the air are discharged from the oxidant exhaust gas exhaust pipe 13. The oxidant exhaust gas exhaust pipe 13 is provided with a pressure adjusting valve 14.

  The above is the basic configuration of the fuel cell system. The fuel cell system having the above configuration uses the fuel supplied from the fuel supply source 1 and the oxidant gas supplied from the compressor 10 as described above. In the fuel cell 3 that generates electric power, the fuel unused at the anode 4 has a circulation path 8 so that it is mixed with the supplied fuel and circulated again. The pressure of the anode 4 is controlled by the amount of fuel supplied, and purging is performed by opening and closing the purge valve 9 so that the concentration of impurity gas accumulated in the anode 4 is kept below a certain level. The pressure of the cathode 5 is controlled by a compressor 10 driven by a motor 11 and a valve 14 provided downstream.

  In the fuel cell system having the above configuration, means for circulating the fuel gas is necessary. However, if a normal pump or the like is used as the circulation means, it is necessary to use a part of the electric power generated by the fuel cell 3 for driving, which is not efficient. Therefore, in this embodiment, the energy of the oxidant exhaust gas is used as a power source for circulating the fuel gas. Specifically, a circulation device 20 including a compressor 21 and an expander 22 is installed in the circulation path 8, and the energy of the oxidant exhaust gas discharged from the cathode 5 is taken out as axial power by the expander 22 and compressed. This is used for rotationally driving the machine 21.

  As the structure of the circulation device 20, for example, as shown in FIG. 2A, a compressor 21 and an expander 22 are provided, and these may be mechanically connected. In the case of this example, the rotating shaft 21a of the compressor 21 and the rotating shaft 22a of the expander 22 are mechanically connected by the coupling 23, and the rotation of the rotating shaft 22a of the expander 22 is the rotating shaft of the compressor 21. 21a is transmitted.

  In the circulation device 20 having the above structure, since the molecular weight of hydrogen as a fuel is small and shaft sealing is difficult, in order to prevent hydrogen leakage to the outside, as shown in FIG. The expander 22 is preferably integrated. Further, in order to avoid adverse effects such as a decrease in power generation efficiency due to the oxidant exhaust gas leaking from the expander 22 entering the compressor 21, the low pressure portion of the compressor 21 and the high pressure portion of the expander 22 are separated from each other. It is good to arrange so that a high pressure part and the low pressure part of expander 22 may approach. Specifically, as shown in FIG. 2A, in the compressor 21, the fuel exhaust gas discharged from the anode is introduced to a position near the expander 22 of the compressor 21, and the position away from the expander 22. To be discharged from. In the expander 22, the oxidant exhaust gas discharged from the cathode 5 is introduced to a position away from the compressor 21 of the expander 22 and discharged from a position close to the compressor 21.

  According to the fuel cell system of the present embodiment having the above-described configuration, the energy of the oxidant exhaust gas from the cathode 5 is used as a power source and converted into shaft power by the expander 22 to drive the circulation device 20. Therefore, even in a fuel cell system that does not use high-pressure fuel gas, the circulation device 20 can be driven without using the power generated by the fuel cell. In addition, by integrating the compressor 21 and the expander 22 in the circulation device 20, the driving force of the expander 22 can be supplied to the compressor without causing hydrogen gas (fuel gas), which is difficult to seal, to flow out. 21 can be used. Furthermore, in the circulation device 20, the high-pressure portion of the expander 22 and the low-pressure portion of the compressor 21 are designed not to be close to each other, so that the fuel exhaust gas may be mixed into the oxidant exhaust gas, It is not mixed in the fuel exhaust gas, and it is possible to prevent a decrease in power generation efficiency and deterioration of the fuel cell.

  The configuration of the fuel cell system of this embodiment is shown in FIG. Since the basic configuration of the fuel cell system is the same as that of the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

  In the fuel cell system of this embodiment, as shown in FIG. 3, in the circulation device 20, a purge path 24 is provided between the compressor 21 and the expander 22, and the purge valve 9 is installed in the purge path 24. ing. Therefore, when the purge valve 9 is opened, the fuel exhaust gas in the compressor 21 is introduced into the expander 22 and discharged together with the oxidant exhaust gas.

  In the fuel cell system according to this embodiment, the fuel exhaust gas discharged from the anode 4 as described above is intentionally released into the oxidant exhaust gas discharged from the cathode 5 so that the fuel exhaust gas is expanded inside the expander 22 or expanded. In the turbulent flow just after, it is possible to sufficiently diffuse and dilute with oxidant exhaust gas. As a result, the fuel exhaust gas can be discharged into the atmosphere at a concentration below the flammable limit.

  The configuration of the fuel cell system of this embodiment is shown in FIG. In the fuel cell system of the present embodiment, the basic configuration is the same as that of the first embodiment, so the same components are denoted by the same reference numerals, and description thereof is omitted here. .

  In the fuel cell system of this embodiment, as shown in FIG. 4, an auxiliary motor 25 is provided in the vicinity of the expander 22 constituting the circulation device 20. The auxiliary motor 25 is installed, for example, between the compressor 21 and the expander 22 or at a position outside the expander 22.

  The auxiliary motor 25 plays a role of supplementing the power for driving the compressor 21 under the operating conditions of the fuel cell 3 such that the regenerative power of the expander 22 is insufficient. In addition, under operating conditions in which the regenerative power of the expander 22 is excessive, energy can be recovered by generating power with the auxiliary motor 25.

  As described above, according to the fuel cell system of the present embodiment, the fuel exhaust gas can be smoothly circulated in the circulation path 8 regardless of the operating conditions. Moreover, when excessive regenerative energy generate | occur | produces, this can be collect | recovered and it can achieve further efficiency improvement.

  The configuration of the fuel cell system of this embodiment is shown in FIG. Also in the fuel cell system of the present embodiment, the basic configuration is the same as in the case of the first embodiment. Therefore, the same components are denoted by the same reference numerals, and description thereof is omitted here.

  In the fuel cell system of this embodiment, an auxiliary pump 26 is installed in parallel with the circulation device 20 between the fuel exhaust gas exhaust pipe 7 and the circulation path 8 of the fuel cell 3. The auxiliary pump 26 can be connected in series with the circulation device 20. The auxiliary pump 26 has a function of compensating for an insufficient circulating flow rate under the operating conditions of the fuel cell 3 such that the regenerative power of the expander 22 is insufficient.

  According to the fuel cell system of the present embodiment, the insufficient circulation flow rate can be compensated for in the operating conditions of the fuel cell 3 where the regenerative power of the expander 22 is insufficient, and the fuel exhaust gas is circulated regardless of the operating conditions. 8 can smoothly circulate.

  The configuration of the fuel cell system of this embodiment is shown in FIG. Also in the fuel cell system of the present embodiment, the basic configuration is the same as in the case of the first embodiment. Therefore, the same components are denoted by the same reference numerals, and description thereof is omitted here.

  In the fuel cell system of this embodiment, as shown in FIG. 6, a bypass passage 27 that bypasses the expander 22 of the circulation device 20 is provided in the oxidant exhaust gas exhaust pipe 13, and a valve is provided in the bypass passage 27. 28 is provided. The bypass flow path 27 and the valve 28 control the circulation flow rate of the fuel exhaust gas and the pressure of the cathode 5. For example, basically, since the circulation flow rate of the fuel exhaust gas is determined according to the energy of the oxidant exhaust gas discharged from the cathode 5, when the energy of the oxidant exhaust gas is excessive with respect to the required circulation flow rate, By controlling the degree of opening and closing of the valve 28 and exhausting part of the oxidant exhaust gas without passing through the expander 22, it is possible to match the required circulation amount.

  According to the fuel cell system of the present embodiment, since the bypass flow path 27 that bypasses the expander 22 is provided, it is possible to prevent generation of an excessive circulation flow rate, and the motor 11 and the expander 22 of the oxidant gas supply device 2. Can prevent over-rotation. Further, if the opening degree of the valve 28 is controlled in the bypass flow path 27, it is possible to control the circulation flow rate to an appropriate level.

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

It is a figure showing a schematic structure of a fuel cell system of a 1st embodiment. An example of a circulation apparatus is shown, (a) is a figure which shows schematic structure of a circulation apparatus, (b) is a figure which shows the state made into integral structure. It is a figure which shows schematic structure of the fuel cell system of 2nd Embodiment. It is a figure which shows schematic structure of the fuel cell system of 3rd Embodiment. It is a figure which shows schematic structure of the fuel cell system of 4th Embodiment. It is a figure which shows schematic structure of the fuel cell system of 5th Embodiment.

Explanation of symbols

1: fuel supply source 2: oxidant gas supply device 3: fuel cell 4: anode 5: cathode 6: fuel gas supply line 7: fuel exhaust gas exhaust pipe 8: circulation path 9: purge valve 10: compressor 11: motor 12: Oxidant gas supply pipe 13: Oxidant exhaust gas exhaust pipe 14: Valve 20: Circulator 21: Compressor 22: Expander 23: Coupling 24: Purge path 25: Auxiliary motor 26: Auxiliary pump 27: Bypass path 28: Valve

Claims (11)

A fuel cell system comprising a fuel cell that generates power by receiving supply of fuel gas and oxidant gas, and having a circulation path for supplying fuel exhaust gas discharged from the fuel cell to the fuel cell again,
In the circulation path, the fuel exhaust gas is circulated using oxidant exhaust gas discharged from the fuel cell as a power source. The fuel cell system according to claim 1,
A circulation device is installed in the circulation path;
The circulation device includes an expander that regenerates the energy of the oxidant exhaust gas and a compressor that circulates the fuel exhaust gas using the regenerated energy, and the compressor is driven by shaft power from the expander. A fuel cell system. The fuel cell system according to claim 2, wherein
The fuel cell includes an oxidant gas exhaust pipe for discharging oxidant exhaust gas, the oxidant gas exhaust pipe is connected to the circulation device, and the oxidant exhaust gas is introduced into the expander. Battery system. The fuel cell system according to claim 2, wherein
The fuel cell system according to claim 1, wherein the circulation device has a structure in which the low-pressure part of the expander and the high-pressure part of the compressor are not close to each other. The fuel cell system according to claim 4, wherein
In the expander, the oxidant exhaust gas is introduced from a position away from the compressor and discharged from a position close to the compressor. In the compressor, the fuel exhaust gas is introduced from a position close to the expander, and from the expander. A fuel cell system which is discharged from a distant position. The fuel cell system according to claim 2, wherein
The fuel cell system, wherein the expander and the compressor are integrated. The fuel cell system according to claim 2, wherein
A fuel cell system comprising a purge path for purging fuel exhaust gas discharged from the compressor. The fuel cell system according to claim 7, wherein
The purge path is connected to the expander, and a part of the fuel exhaust gas discharged from the compressor is introduced into the expander and diluted. The fuel cell system according to claim 2, wherein
The fuel cell system, wherein the circulation device includes an auxiliary motor. The fuel cell system according to claim 2, wherein
A fuel cell system, wherein an auxiliary pump is installed in the circulation path. The fuel cell system according to claim 3,
The fuel cell system, wherein the oxidant gas exhaust pipe has a bypass flow path that bypasses the expander.

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