JP5380107B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly, to a technology for miniaturizing components of a fuel cell system and cooling means such as a radiator for cooling the components.

  As a fuel cell, a laminated body in which separators are laminated on both sides of a flat membrane electrode assembly (MEA) is used as a unit cell, and a plurality of unit cells, for example, several hundred layers are laminated to form a fuel cell stack. A fuel cell configured as is known. The membrane electrode structure has a three-layer structure in which an electrolyte membrane made of an ion exchange resin or the like is sandwiched between a pair of electrodes constituting a positive electrode (air electrode, cathode) and a negative electrode (fuel electrode, anode). According to such a fuel cell, for example, when a fuel gas is caused to flow through a gas passage facing the gas diffusion electrode on the fuel electrode side and an oxidant gas is caused to flow through a gas passage facing the gas diffusion electrode on the air electrode side, A chemical reaction occurs, generating electricity.

  Here, in order to stabilize the electrochemical reaction as described above, it is desirable that the membrane electrode structure is wet. For example, Patent Document 1 discloses that a power generation product water is added to a fuel gas in the fuel gas passage as a steam, so that the used fuel off-gas whose steam partial pressure has increased is used as a humidified gas, and an unused fuel gas is used as a fuel gas. A humidifying fuel cell system is disclosed.

  By the way, in recent years, the membrane electrode structure tends to become thinner as the performance of the fuel cell becomes higher, and the phenomenon that the water generated by the electrochemical reaction and coming out to the air electrode side moves to the fuel electrode side seems to occur. It has become. For this reason, when the fuel gas is humidified, a wet state of the fuel electrode becomes excessive, and a phenomenon called flooding occurs in which contact between the fuel and the fuel electrode is hindered. On the other hand, on the air electrode side, it is known that there are cases in which the electrochemical reaction is not so hindered even when the degree of wetting is excessive. Therefore, recently, a technique for humidifying the oxidant gas rather than humidifying the fuel gas has been emphasized.

  As a conventional fuel cell system for humidifying oxidant gas, for example, the one shown in FIG. 2 is known. A fuel cell system A shown in this figure is schematically configured by connecting a fuel cell stack 1 in which a large number of unit cells of a fuel cell are stacked, a heat exchanger 2, a compressor 3, and a humidifier 4 in series. . A radiator 5 is connected to the fuel cell system A, and a cooling medium circulates between the radiator 5, the fuel cell stack 1, the heat exchanger 2, and the compressor 3.

  In the fuel cell system A configured as described above, air is first supplied to the humidifier 4 and humidified, and then supplied to the compressor 2 and pressurized. Since the temperature of the air rises due to the pressurization at that time, the air is cooled to the operating temperature of the fuel cell by the heat exchanger 2 and supplied to the fuel cell stack 1. On the other hand, fuel gas such as hydrogen is supplied to the fuel cell stack 1 by a supply means (not shown), and electric power is generated by causing an electrochemical reaction between the fuel gas and air. The air (air off gas) that has been used in the fuel cell is supplied to the humidifier 4, the water vapor contained in the air off gas is exchanged with the supply air, and the supply air is humidified.

Japanese Utility Model Publication No. 61-3671

  However, in the fuel cell system as described above, the cooling medium is supplied from the radiator 5 to the fuel cell stack 1, the heat exchanger 2, and the compressor 3 for cooling, so that the radiator is enlarged and the cooling medium is circulated. For example, when it is applied to a fuel cell system for a vehicle, there is a problem that a layout design in the engine room is restricted. There has also been a strong demand to downsize the fuel cell system.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and it is possible to reduce the size of the radiator and the system components, and to reduce the number of piping for circulating the cooling medium, thereby reducing the layout design. It aims at providing the fuel cell system which can raise a freedom degree.

The present invention, fuel gas and a fuel cell oxidant gas is supplied for power generation by electrochemical reactions of the fuel gas and the oxidizing gas, the fuel moisture contained in the discharged oxidizing gas from the fuel cell Humidification means for transferring to the oxidant gas supplied to the battery, a compressor for compressing the oxidant gas and sending it to the fuel cell, and heat for cooling the oxidant gas supplied to the fuel cell after passing through the compressor In a fuel cell system comprising an exchange means and a condensation means for condensing the fuel gas discharged from the fuel cell and storing it as condensed water, the oxidant gas discharged from the fuel cell is circulated to the heat exchange means after heating by, is circulated as a humidification source to the humidifying means, the condensed water is supplied to the oxidant gas discharged from the fuel cell, the heat exchange of the oxidizing agent gas After heating by circulation to the means, it is characterized by circulating the humidifying source to the humidifying means.

  In the fuel cell system configured as described above, the reaction gas discharged from the fuel cell is heated by circulating it through the heat exchanging means. Therefore, the condensed water accompanying the reaction gas evaporates as the temperature of the reaction gas rises. The water vapor partial pressure in the reaction gas increases. Then, the latent heat of evaporation at this time is compressed by the compressor to cool the reaction gas that has become high temperature. Therefore, it is not necessary to supply a cooling medium from the radiator to the heat exchanging means, so that the cooling means can be reduced in size and piping between the cooling means and the heat exchanging means becomes unnecessary. Further, since the reaction gas having an increased water vapor partial pressure flows as a humidification source to the humidification means, the humidification efficiency in the humidification means is improved. Therefore, the humidifying means can be reduced in size.

In the present invention, since the moisture contained in the exhaust oxidant gas and the exhaust fuel gas can be used as a humidification source without wasting, the humidifier can be further downsized.

  According to the present invention, it is possible to reduce the size of the radiator and the humidifying means, and to obtain an effect that the degree of freedom in layout design can be increased by reducing piping for circulating the cooling medium.

1 is a system diagram showing a fuel cell system according to an embodiment of the present invention. It is a systematic diagram showing a conventional fuel cell system. It is a graph which shows the parameter of the air off gas in each place of the fuel cell system of embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a fuel cell system B according to an embodiment. In FIG. 1, reference numeral 10 denotes a fuel cell stack, and the fuel cell stack 10 is configured by stacking a large number of unit cells of a fuel cell. A heat exchanger (heat exchange means) 20 is connected to the fuel cell stack 10, and a compressor 30 is connected to the heat exchanger 20. Further, a humidifier (humidifying means) 40 is connected to the compressor 30.

  The fuel cell stack 10, the heat exchanger 20, the compressor 30, and the humidifier 40 are connected in series by the first pipe 21. Air is supplied to the first pipe 21, and this air is supplied to the high-temperature medium flow path of the heat exchanger 20. The fuel cell stack 10, the heat exchanger 20, and the humidifier 40 are connected in series by the second pipe 22. The cathode exhaust gas discharged from the fuel cell stack 10 is discharged to the second pipe 22, and this cathode exhaust gas is supplied to the cooling medium flow path of the heat exchanger 20.

  Here, the humidifier 40 includes a housing 41 in which a plurality of hollow fiber membranes for exchanging water are bundled in parallel. The hollow fiber membrane is a hollow thin yarn membrane that has the property of preventing the permeation of gas but allowing the permeation of moisture, that is, water molecules. In this case, moisture permeates through the hollow fiber membrane from the direction of high water vapor partial pressure to the low direction. Therefore, when a gas with a low relative humidity is circulated inside the hollow fiber membrane and a gas with a high relative humidity is circulated outside, the moisture permeates from the outside to the inside of the hollow fiber membrane and diffuses into the gas with a low relative humidity. And increase its humidity. The same effect can be obtained even if a gas having a high relative humidity is circulated inside the hollow fiber membrane and a gas having a low relative humidity is circulated outside.

  In this embodiment, the 1st piping 21 is connected inside the hollow fiber membrane. Specifically, the first pipe 21 is connected to a humidified gas supply port 42 provided on the upstream end face of the bundle of hollow fiber membranes. Therefore, air with low relative humidity that is not humidified is supplied to the inside of the hollow fiber membrane. A compressor 30 is connected to the humidified gas outlet 43 provided on the downstream end face of the bundle of hollow fiber membranes.

  A cathode exhaust gas supply port 44 and a cathode exhaust gas discharge port 45 are provided on the outer peripheral side of the bundle of hollow fiber membranes, and the second pipe 22 is connected to the cathode exhaust gas supply port 44. Although illustration is omitted, a cooling medium cooled by a cooling means such as a radiator is circulated and cooled in the fuel cell stack 10 and the compressor 30.

  An ejector 50 is connected to the fuel cell stack 10, and a fuel tank 60 filled with a fuel gas such as hydrogen is connected to the ejector 50. Further, the fuel cell stack 10 is connected with a condensing means 70. The condensing means 70 is preferably a catch tank configured to store condensed water, but may be a pipe. The condensing means 70 gas-liquid separates the moisture and gas generated in the fuel cell, and the ejector 50 forms a negative pressure by the flow of fuel gas from the fuel tank 60 to the fuel cell stack 10. The gas separated from the condensed water by the condensing means 70 is sucked in by this negative pressure and mixed with the fuel gas supplied from the fuel tank 60 to obtain a predetermined fuel gas concentration, which is supplied to the fuel cell stack 10.

  A relay box 80 is connected to the fuel cell stack 10 via a pipe 23. The condensed water separated from the anode exhaust gas in the condensing means 70 and the fuel gas not sucked into the ejector 50 are supplied to the relay box 80 through the third pipe 23. The condensed water and fuel gas are supplied to the second pipe 22 between the fuel cell stack 10 and the heat exchanger 20.

  Next, the operation of the fuel cell system B configured as described above will be described. When power is generated by operating the fuel cell system B, air is supplied to the fuel cell stack 10 through the humidifier 40, the compressor 30, and the heat exchanger 20 in order. On the other hand, fuel gas is supplied to the fuel cell stack 10 from the fuel tank 60 via the ejector 50, and electric power is generated by causing an electrochemical reaction between the fuel gas and air. The fuel gas after use becomes anode discharge gas and is sucked into the condensing means 70 where it is gas-liquid separated. The gas component including the fuel gas separated in the condensing means 70 is sucked into the ejector 50, mixed with the fuel gas supplied from the fuel tank 60, and supplied to the fuel cell stack 10. Further, the condensed water separated in the condensing means 70 is stored, and flows through the third pipe 23 together with the fuel gas that has not been sucked into the ejector 50 and is supplied to the relay box 80.

  The condensed water and fuel gas supplied to the relay box 80 are supplied to the second pipe 22 between the fuel cell stack 10 and the heat exchanger 20 and mixed with the cathode exhaust gas discharged from the fuel cell stack 10. Then, these discharged flow components are supplied to the cooling medium flow path of the heat exchanger 20. On the other hand, air that has been pressurized by the compressor 30 to a high temperature is fed into the high-temperature medium flow path of the heat exchanger. For this reason, the temperature of the discharged stream rises, the condensed water contained in the discharged stream evaporates as the temperature rises, and the water vapor partial pressure of the discharged stream increases. The latent heat of evaporation at this time is compressed by the compressor 30 to cool the exhausted stream.

  FIG. 3 is a graph showing parameters of the discharged flow at various points in the fuel cell system B. 3A shows the parameters of the cathode exhaust gas immediately after being discharged from the fuel cell stack 10, and FIG. 3B shows the condensed water and fuel gas supplied from the relay box 80 to the cathode exhaust gas. The parameter after mixing is shown. From these figures, there is no change in any of the parameters other than the increase in condensed water. However, after the exhaust stream is exhausted from the heat exchanger 20, as shown in FIG. 3C, the temperature and dew point rise due to heating. On the other hand, the amount of water vapor has increased while the condensed water has decreased due to evaporation. Therefore, if the amount of condensed water is sufficient, the relative humidity of the discharged stream can be increased to 100%.

  The exhaust stream whose relative humidity has been increased by the heat exchanger 20 is supplied to the humidifier 40. In the humidifier 40, an exhaust stream composed of cathode exhaust gas, condensed water, and fuel gas flows outside the hollow fiber membrane, and air supplied to the fuel cell stack 10 flows inside the hollow fiber membrane. And the water vapor | steam contained in a discharge | emission flow osmose | permeates a hollow fiber membrane, is absorbed by air, and air is humidified. In addition, although the fuel gas contained in the discharge | emission flow part is discharge | released from the humidifier 40, it is diluted to the nonflammable state by the dilution box.

  In the fuel cell system B configured as described above, since the cooling medium supplied to the heat exchanger 20 is an exhaust stream containing condensed water, it is not necessary to supply the cooling medium to the heat exchanger 20 from the radiator. Therefore, the radiator can be reduced in size, and piping between the radiator and the heat exchanger 20 becomes unnecessary. Further, since the reaction gas having an increased water vapor partial pressure flows through the humidifier 40 as a humidification source, the humidification efficiency in the humidifier 40 is improved. Therefore, the humidifier 40 can be reduced in size.

  In particular, in the above embodiment, the condensed water and the exhausted fuel gas supplied from the condensing means 70 are mixed with the cathode exhaust gas flowing through the second pipe 22 via the relay box 80, and thus were originally released to the atmosphere. Since the moisture contained in the anode exhaust gas is also supplied to the humidifier 40, the humidification efficiency of the discharged cathode exhaust gas can be further improved.

  In the above embodiment, the anode exhaust gas discharged from the fuel cell stack 10 is supplied to the condensing means 70, but the fuel cell stack 10 and the condensing means 70 are connected as shown by a two-dot chain line in FIG. By branching a pipe in the middle of the distribution route to be connected and connecting this pipe 24 to the relay box 80, condensed water dripped as a drain at the anode exhaust gas discharge port of the fuel cell stack 10 can be supplied to the relay box 80. it can. Further, the condensed water dripped as a drain at the cathode exhaust gas outlet of the fuel cell stack 10 can be supplied to the relay box 80 through the pipe 25. By comprising in this way, the humidification efficiency for a discharge | emission flow can be improved further.

  In the present invention, the radiator and the humidifying means can be reduced in size, and the degree of freedom in layout design can be increased by reducing piping for circulating the cooling medium. is there.

10 Fuel cell stack 20 Heat exchanger (heat exchange means)
30 Compressor 40 Humidifier (humidifying means)
50 Ejector 60 Fuel tank 70 Condensing means 80 Relay box

Claims (1)

A fuel cell that generates electricity through an electrochemical reaction of the fuel gas and the oxidizing gas is supplied fuel gas and oxidant gas,
A humidifying means for transferring the moisture contained in the oxidizing gas discharged from the fuel cell to the oxidant gas supplied to the fuel cell,
A compressor that compresses the oxidant gas and sends it to the fuel cell;
Heat exchange means for cooling the oxidant gas supplied to the fuel cell after flowing through the compressor;
Condensing means for condensing the fuel gas discharged from the fuel cell and storing it as condensed water;
In a fuel cell system comprising:
After the oxidant gas discharged from the fuel cell is circulated through the heat exchange means and heated, the oxidant gas is circulated as a humidification source to the humidification means, and the condensed water is supplied to the oxidant gas discharged from the fuel cell. The fuel cell system is characterized in that the oxidant gas is circulated through the heat exchanging means and heated, and then circulated as a humidification source through the humidifying means .

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