JP2009152013A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the humidifying performance of a humidifier in a fuel cell system. <P>SOLUTION: A fuel cell system includes a fuel cell 20 which generates power by the electrochemical reaction of reaction gases; a humidifier 34 for humidifying reaction gases by circulating reaction gases supplying to the fuel cell and reaction offgas exhausted from the fuel cell and exchanging moisture between the reaction gas and the reaction offgas; and a cooling device 36 for cooling the reaction offgas made to circulate to the humidifier. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell, and more particularly to a humidification mechanism for adjusting the water content of a reaction gas supplied to the fuel cell.

  A fuel cell generates electric power by an electrochemical reaction between a fuel gas typified by hydrogen gas and an oxidizing gas typified by air, and simultaneously generates moisture. A polymer electrolyte fuel cell, which is a type of fuel cell, has a structure in which a solid polymer electrolyte membrane is sandwiched between a hydrogen electrode (also referred to as an anode) and an oxygen electrode (also referred to as a cathode). In this type of fuel cell, the electrolyte membrane is responsible for proton conduction in the reaction between the fuel gas and oxygen gas. Therefore, in order to maintain the power generation reaction efficiently, it is necessary to control the moisture in the electrolyte membrane to an appropriate state. is there. Therefore, the fuel cell system is provided with a humidifier for humidifying the gas supplied to the fuel cell.

  Inside the humidifier is a hollow fiber membrane module (exchange resin) for exchanging moisture between the used gas exhausted from the fuel cell and the dry gas (humidified gas) supplied to the fuel cell. Is provided. The hollow fiber membrane module is a bundle of many hollow fiber membranes. Normally, the gas exhausted from the fuel cell is in a wet state including moisture generated during power generation, so this gas (humidified gas) is circulated inside (or outside) the hollow fiber membrane module. By allowing the humidified gas to flow outside (or inside) the module, the moisture contained in the humidified gas is absorbed by the hollow fiber membrane, and this moisture is given to the humidified gas.

  The amount of water vapor exchange in such a humidifier varies depending on conditions such as relative humidity and temperature between the humidified gas and the humidified gas. Therefore, a gas region where the humidification amount is insufficient may be partially generated, which is not preferable. This is because gas that is not sufficiently humidified is supplied to the fuel cell.

As a related technique, Patent Document 1 discloses that the moisture of the humidifier is controlled by controlling the pressure on the exhaust gas outlet side of the humidifier in order to sufficiently exert the humidifying performance of the humidifier regardless of the operation state of the fuel cell. A fuel cell system for controlling the exchange rate is disclosed. Patent Document 2 discloses a fuel cell system that separates high-pressure fuel gas into low-temperature gas and high-temperature gas, and uses the low-temperature gas for cooling the stack.
However, a system that can reliably improve the performance of the humidifier with a simpler configuration is desired.
JP 2005-322508 A JP 2005-268141 A

  Then, this invention aims at improving the humidification performance of a humidifier in a fuel cell system.

  In order to achieve the above object, a fuel cell system according to one aspect of the present invention includes a fuel cell that generates electric power by an electrochemical reaction of a reaction gas, a reaction gas supplied to the fuel cell, and an exhaust gas from the fuel cell. A humidifier that humidifies the reaction gas by circulating the reaction off-gas and exchanging moisture between the reaction gas and the reaction off-gas, and a cooling unit that cools the reaction off-gas flowing through the humidifier.

  When the substantially saturated reaction off-gas discharged from the fuel cell is cooled, it becomes supersaturated. When such a reaction off gas is introduced into the humidifier, the amount of humidification by the reaction off gas sharply increases, and the humidification performance is greatly improved. Further, even if the reaction off gas is not in a supersaturated state, the humidity of the gas is increased by cooling, so that the humidification amount can be increased.

  Here, as the cooling means, any method may be adopted as long as the gas can be cooled. For example, it may be a cooler that cools the reaction off gas using a cooling medium such as gas or liquid, or may be a flow path that is formed so as to adiabatically expand the reaction off gas introduced into the humidifier. .

  Alternatively, the fuel cell system further includes a vortex tube that separates a gas having a temperature lower than a predetermined temperature from a reaction off gas derived from the humidifier, and the cooling unit includes the low-temperature gas separated by the vortex tube. The reaction off gas may be cooled using as a cooling medium. The vortex tube can separate the compressed gas into a high-temperature side gas and a low-temperature side gas without requiring a power source, a refrigerant, or the like, and is relatively inexpensive, small and lightweight. Therefore, by using the low-temperature side gas separated by the vortex tube as a cooling medium, it is possible to suppress the equipment cost and the operating cost and to reduce the installation space.

  According to the present invention, in the fuel cell system, since the reaction off gas discharged from the fuel cell is cooled and then introduced into the humidifier, the humidification performance can be improved. Therefore, the reaction gas supplied to the fuel cell can be sufficiently humidified without unevenness.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a system diagram showing a configuration of a fuel cell system 1 according to a first embodiment of the present invention. The fuel cell system 1 is used as an in-vehicle power generation system for fuel cell vehicles, a power generation system for any moving body such as a ship, an aircraft, a train, or a walking robot, and also as a power generation facility for buildings (housing, buildings, etc.). It can be applied to stationary power generation systems. In this embodiment, it is for automobiles.

  The fuel cell system 1 includes a fuel cell 20, an oxidizing gas piping system 30 that supplies air as oxidizing gas to the fuel cell 20, and a fuel gas piping system 40 that supplies hydrogen gas as fuel gas to the fuel cell 20. Prepare.

  The fuel cell 20 is, for example, a solid polymer electrolyte type, and has a stacked structure in which a plurality of cells 21 including an electrolyte and electrode layers (anode and cathode) disposed on both sides thereof are stacked. The fuel cell 20 generates electric power by an electrochemical reaction between an oxidizing gas and a fuel gas (also referred to as a reaction gas).

  The oxidizing gas piping system 30 includes an oxidizing gas supply pipe 31 that supplies an oxidizing gas to the fuel cell 20 and an oxidizing off gas discharge pipe 32 that discharges a used oxidizing gas (oxidized off gas) discharged from the fuel cell 20. . The oxidizing gas supply pipe 31 is provided with an air compressor 33, a humidifier 34, and an on-off valve 35. On the other hand, the oxidizing off gas discharge pipe 32 is provided with a cooler 36, and a flow path of the oxidizing off gas discharge pipe 32 is formed so that the oxidizing off gas that has passed through the cooler 36 is discharged through the humidifier 34. ing.

  As the cooler 36, any cooling method may be adopted as long as the gas can be cooled. For example, any of an air cooling type using a gas as a cooling medium and a water cooling type using a cooling liquid (cooling water) may be used.

  An air cleaner for cleaning the outside air may be further provided upstream of the air compressor 33. Alternatively, a diluter or a muffler may be further provided downstream of the humidifier 34 in the oxidizing off gas discharge pipe 32.

The humidifier 34 humidifies the oxidant gas taken in from the outside using the high-humidity oxidant off-gas containing moisture generated during the electrochemical reaction in the fuel cell 20.
FIG. 2 is a diagram showing the internal structure of the humidifier 34. The casing 300 of the humidifier 34 has an oxidizing gas inlet (dry side inlet) 301 and an outlet (dry side outlet) 302, and an oxidizing off gas inlet (wet side inlet) 303 and an outlet (wet side outlet) 304. Is provided. Further, inside the humidifier 34, a hollow fiber membrane bundle (hollow fiber membrane module) 305 in which a plurality of hollow fiber membranes that preferably allow only water vapor to permeate is bundled is disposed. Further, the inside of the humidifier 34 is partitioned by a partition member 306 into an oxidizing gas channel (dry side channel) 307 and an oxidizing off gas channel (wet side channel) 308. Inside the humidifier 34, the oxidizing off gas is circulated inside the hollow fiber membrane module 305, and the oxidizing gas is circulated outside the hollow fiber membrane module 305. Then, the moisture of the oxidizing off gas is absorbed by the hollow fiber membrane, the moisture is given to the oxidizing gas, and as a result, the oxidizing gas is humidified.

  Referring again to FIG. 1, the fuel gas piping system 40 includes a fuel gas supply pipe 41 that supplies fuel gas to the fuel cell 20, and a fuel that discharges used fuel gas (fuel offgas) discharged from the fuel gas. Off-gas discharge pipe 42. The fuel gas piping system 40 may further be provided with a high-pressure gas tank for storing fuel gas, a circulation pump for reusing fuel off-gas, and the like.

  When the operation of the fuel cell system 1 is started, outside air as an oxidizing gas is taken in and compressed by the air compressor 33. The oxidizing gas is humidified in the humidifier 34 and then introduced into the fuel cell 20 through the opened on-off valve 35. In the fuel cell 20, electric power is generated by an electrochemical reaction between the oxidizing gas and the fuel gas supplied from the fuel gas supply pipe 41, and moisture is generated at the same time. The oxidized off gas and the fuel off gas after the reaction are discharged from the fuel cell 20 through the oxidized off gas discharge pipe 32 and the fuel off gas discharge pipe 42, respectively. The oxidant off-gas is introduced into the humidifier 34 after being cooled in the cooler 36 and used to humidify the oxidant gas. Thereafter, the oxidizing off gas passes through the oxidizing off gas discharge pipe 32 and is discharged to the outside of the fuel cell system 1.

Here, in the present embodiment, the reason why the oxidizing off gas is cooled and then introduced into the humidifier 34 will be described.
FIG. 3 shows the humidification characteristics of a typical humidifier. Usually, the humidification performance depends on the relative humidity and temperature of the wet side gas (humidified gas) and the dry side gas (humidified gas). For example, when the relative humidity on the wet side is 100% (saturated water vapor state), humidification can be performed until the relative humidity on the dry side becomes about 20%. Such humidification characteristics change relatively slowly until the wet-side relative humidity reaches 100%. However, when the relative humidity on the wet side exceeds 100%, that is, in a supersaturated state (a state where saturated water vapor and droplets are mixed), the gradient of the humidification characteristic becomes steep, and the humidification ability is improved in each stage. This is because not only water vapor but also droplets greatly contribute to humidification on the dry side. For example, when the relative humidity on the wet side becomes 120%, the dry side can be humidified until the relative humidity becomes about 40%.

  When discharged from the fuel cell 20, the oxidizing off-gas is almost in a saturated water vapor state. Therefore, the supersaturation can be easily achieved by cooling the oxidizing off gas in the cooler 36. By introducing such an oxidizing off gas into the humidifier 34, the humidifying performance of the humidifier 34 can be improved, and the oxidizing gas can be sufficiently humidified without unevenness.

  Further, even if the oxidizing off gas is not in a saturated water vapor state at the time when it is discharged from the fuel cell 20, the relative humidity increases by cooling the oxidizing off gas, so that the humidifier 34 humidifies the oxidizing gas. Can be increased.

Next, a fuel cell system according to a second embodiment of the present invention will be described with reference to FIG.
The fuel cell system 2 shown in FIG. 4 includes a throttle 37 instead of the cooler 36 shown in FIG. The throttle 37 is provided in a part of the oxidizing off-gas discharge pipe 32 disposed between the fuel cell 20 and the humidifier 34. Other configurations are the same as those shown in FIG.

  The oxidizing off gas discharged from the fuel cell 20 once shrinks when passing through the throttle 37. At this time, since the pressure of the oxidizing off gas increases, the oxidizing off gas expands rapidly after passing through the throttle 37. Thereby, the oxidizing off gas is cooled and becomes supersaturated. By introducing such an oxidizing off gas into the humidifier 34, the humidifying performance of the humidifier 34 can be improved.

Next, a fuel cell system according to a third embodiment of the present invention will be described with reference to FIGS.
The fuel cell system 3 shown in FIG. 5 further includes a vortex tube 38 and a cooling gas communication pipe 39 that connects the vortex tube 38 and the cooler 36 in addition to the configuration shown in FIG. In the present embodiment, the gas supplied from the vortex tube 38 is used as the cooling medium of the cooler 36. Other configurations are the same as those shown in FIG.

FIG. 6 is a cross-sectional view showing the inside of the vortex tube 38.
The vortex tube 38 is an apparatus that separates the compressed gas into a gas lower in temperature than the inlet temperature (low temperature gas) and a high temperature gas (high temperature gas).

  The vortex tube 38 has a hollow tube structure 800, and a gas supply port 801 is provided near one end (near the right end in FIG. 6) of the side portions of the hollow tube structure 800. ing. The gas supply port 801 is connected to the humidifier 34 via the oxidizing off gas discharge pipe 32 (FIG. 5). Further, a low temperature gas discharge port 802 for discharging a low temperature gas is provided at the end portion (right end), and a high temperature gas discharge port 803 is provided at the other end portion (left end). Further, a nozzle 804 is provided in the vicinity of the gas supply port 801 inside the hollow tube structure 800, and a valve is provided inside the high temperature gas discharge port 803.

  Here, the gas flowing through the oxidizing gas piping system 30 is compressed to some extent by the air compressor 33. Therefore, when the oxidizing off gas discharged from the humidifier 34 is introduced into the hollow tube structure 800 through the gas supply port 801, a swirling gas flow is formed in the tube. In this swirling gas flow, heat flows from the center to the outside. As a result, the oxidizing off gas is separated into a swirling flow of the inner low temperature gas and a swirling flow of the outer high temperature gas.

  The separated low-temperature gas is introduced into the cooler 36 through the cooling gas communication pipe 39 connected to the low-temperature gas discharge port 802, and acts as a cooling medium for cooling the oxidation off-gas supplied to the humidifier 34. It is discharged from the cooler 36. On the other hand, the separated hot gas is discharged from the hot gas discharge port 803 through the valve 805 and guided to the exhaust system. Note that by adjusting the opening degree of the valve 805, the degree of separation between the low temperature gas and the high temperature gas, in other words, the temperature of each of the low temperature gas and the high temperature gas can be controlled.

  In the above first to third embodiments, the case where the oxidizing gas is humidified has been described. However, the humidifying performance can be improved in the same manner even when the fuel gas is humidified.

1 is a diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a figure which shows the internal structure of a humidifier. It is a figure which shows the humidification characteristic of a humidifier. It is a figure which shows the structure of the fuel cell system which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the fuel cell system which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the internal structure of a vortex tube.

Explanation of symbols

  1-3, Fuel cell system, 20 ... Fuel cell, 31 ... Oxidizing gas supply pipe, 32 ... Oxidizing off-gas discharge pipe, 34 ... Humidifier, 36 ... Cooler, 37 ... Throttle, 38 ... Vortex tube

Claims (5)

A fuel cell that generates electricity by an electrochemical reaction of the reaction gas; and
A humidifier that circulates the reaction gas supplied to the fuel cell and the reaction off gas discharged from the fuel cell, and humidifies the reaction gas by exchanging moisture between the reaction gas and the reaction off gas;
Cooling means for cooling the reaction off-gas flowing through the humidifier;
A fuel cell system comprising:   2. The fuel cell system according to claim 1, wherein the cooling unit brings a reaction off gas to be circulated through the humidifier into a supersaturated state.   The fuel cell system according to claim 1 or 2, wherein the cooling means is a cooler that cools the reaction off gas using a cooling medium.   The fuel cell system according to claim 1 or 2, wherein the cooling means is a flow path formed so as to adiabatically expand the reaction off gas introduced into the humidifier. Further comprising a vortex tube for separating a gas having a temperature lower than a predetermined temperature from a reaction off gas derived from the humidifier;
3. The fuel cell system according to claim 1, wherein the cooling unit cools the reaction off-gas using a low-temperature gas separated by the vortex tube as a cooling medium.