JP2004363027A - Humidifying method of fuel cell and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the dew point supplied to the pole of a fuel cell nearly equal to the operating temperature of the fuel cell with a high energy efficiency. <P>SOLUTION: This is a humidifying method of a fuel cell which contains a first humidifying step in which a gas supplied to a pole of a fuel cell 4 is humidified by making it contact with a gas at the exit of the fuel cell through a vapor permeation membrane, and a second humidifying step in which the humidified gas is humidified by making it contact with the cooling water of the fuel cell through the vapor permeation membrane. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a humidification method for a fuel cell and a fuel cell system capable of realizing the humidification method. More specifically, the present invention relates to a method for humidifying a gas supplied to a pole of a fuel cell to improve the performance and energy efficiency of the fuel cell, and to a fuel cell system realizing the method.
[0002]
[Prior art]
A fuel cell uses a cell in which an air electrode serving as a cathode is disposed on one side of an electrolyte membrane made of a solid polymer, and a fuel electrode serving as an anode is disposed on the other side, and an oxidizing gas such as air is supplied to the cathode. A hydrogen-rich fuel gas is supplied to the anode, and an electromotive force is obtained by the following battery reaction for obtaining water from hydrogen and oxygen.
[0003]
H ₂ → 2H ⁺ + 2e ⁻ (Anode reaction)
2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (cathode reaction)
[0004]
This battery reaction involves hydrogen supplied to the anode becoming hydrogen ions, and the hydrogen ions move inside the electrolyte membrane from the anode side to the cathode side. Here, hydrogen ions move in the presence of moisture present in the electrolyte membrane, so that crossover of oxygen molecules and hydrogen molecules is unlikely to occur. However, the electrolyte membrane dries as the fuel cell operates. When the electrolyte membrane is dried, not only does the ionic conductivity decrease and the power generation efficiency decreases, but also the electrolyte membrane is easily damaged and deteriorated, which is a problem in the durability of the fuel cell. Therefore, it is necessary to keep the electrolyte membrane wet during the operation of the fuel cell, and a technique for appropriately maintaining the water content in the electrolyte membrane of the fuel cell has been developed.
[0005]
As one of techniques for appropriately maintaining the water content of the electrolyte membrane of such a fuel cell, a method of humidifying a dry fuel gas or air supplied to a pole of the fuel cell and a humidifying device therefor are used. I have been.
[0006]
Patent Literature 1 discloses that a reaction gas humidifier that supplies a reaction gas (air) before supplying an off-gas from a battery to a humidification gas chamber of a water vapor permeable membrane and a reaction gas before supplying the gas to a humidification target gas chamber is provided. A method for humidifying air by the method is disclosed. In this method, the inlet air is humidified by mass transfer due to the difference in partial pressure of water vapor between the moisture-saturated air at the outlet of the fuel cell and the dry air at the inlet. However, in this case, due to the fluid resistance of the fuel cell itself, the pressure of the fuel cell inlet air is higher than that of the fuel cell outlet air, and humidification can be performed only until a predetermined amount of water vapor based on such pressure balance is reached. Was a problem. Further, there is another problem that the humidifier cannot be increased in size in the use of a fuel cell system that requires compactness. Therefore, the humidification of the air supplied to the fuel cell was not sufficient, and the dew point of the air supplied to the fuel cell was about 58 to 60 ° C. Operating the fuel cell using such low humidified air causes drying of the polymer membrane, cross-leak occurs, and reduces the durability of the cell.
[0007]
Patent Literature 2 discloses that air is obtained by introducing hot water after cooling a fuel cell into a humidifier to humidify the reaction gas, and operating the thermal energy of the hot water supplied to the humidifier so as to match the latent heat of vaporization. Is disclosed. Such a method is humidification by mass transfer between dry air and hot water after cooling the fuel cell. For example, if it is attempted to humidify the dry air supplied to the fuel cell to a saturation state at 80 ° C. The latent heat of evaporation required to evaporate hot water is about 1.5 times the amount of power generated by the battery. Since the power generation / heat ratio of the fuel cell is approximately 1.0, it is necessary to heat the hot water in order to compensate for the amount of latent heat of evaporation that cannot be covered by the heat generated by the fuel cell. A heater equivalent to .5 times is required. For example, a fuel cell for 1.3 kW DC power generation requires a heater of about 0.5 kW. In such a method, auxiliary power for the heater increases, and power generation efficiency decreases.
[0008]
In addition, a method of humidifying a gas supplied to a pole of a fuel cell by bubbling is known. However, such a method also involves a problem that it is difficult to reduce the size of the device.
[0009]
[Patent Document 1]
Japanese Patent No. 3111697
[Patent Document 2]
JP-A-9-55218
[0010]
[Problems to be solved by the invention]
A method for humidifying a gas supplied to a pole of a fuel cell to a dew point close to the operating temperature of the fuel cell, and a highly durable and efficient fuel cell system for performing high humidification. I do.
[0011]
[Means for Solving the Problems]
The present invention has been made to solve the above problems. That is, the present invention is a method for humidifying a fuel cell, wherein a gas supplied to a pole of the fuel cell is humidified by bringing the gas into contact with a gas at a fuel cell outlet through a water vapor permeable membrane. A second humidification step of humidifying the humidified gas by contacting the humidified gas with cooling water of a fuel cell through a water vapor permeable membrane. It is preferable that the gas supplied to the electrode of the fuel cell is at least one of a gas supplied to the air electrode and a gas supplied to the fuel electrode.
[0012]
Preferably, the water vapor permeable membrane is a hollow fiber membrane. By incorporating a humidifying module using a hollow fiber membrane into a humidifier, the entire system can be reduced in size and mass transfer can be generated with high efficiency.
[0013]
It is preferable that the difference between the dew point of the gas supplied to the electrode of the fuel cell through the first humidification step and the second humidification step and the operating temperature of the fuel cell is within five. By generating such a highly humidified gas, drying of the electrolyte membrane of the fuel cell can be prevented.
[0014]
In another aspect, the present invention relates to a fuel cell system, comprising: a fuel cell having an anode on one surface of an electrolyte membrane and an air electrode on the other surface; A first humidifier that humidifies the gas supplied to the electrode of the fuel cell by contacting the gas supplied to the electrode of the fuel cell with the gas at the outlet of the fuel cell through a water vapor permeable membrane; A second humidifier that humidifies the humidified gas by contacting the humidified gas with cooling water of the fuel cell through a water vapor permeable membrane; and Means for circulating the cooling water to be supplied to the humidifier.
[0015]
Preferably, the water vapor permeable membrane is a hollow fiber membrane. By incorporating a humidifying module using a hollow fiber membrane into a humidifier, a fuel cell system that is downsized can be provided.
[0016]
The first humidifier and the second humidifier are provided on at least one of a gas supply path supplied to a fuel electrode of a fuel cell and a gas supply path supplied to an air electrode of the fuel cell. Is preferred. With such a system, the gas supplied only to the air electrode side or only the fuel electrode side can be selectively humidified according to the properties of the supplied gas, or both can be humidified to form an electrolyte membrane. Can be kept moist.
[0017]
ADVANTAGE OF THE INVENTION According to the humidification method of a fuel cell and the fuel cell system according to the present invention, the gas supplied to the pole of the fuel cell using the gas discharged from the fuel cell and the cooling water of the fuel cell is used as the operating temperature of the fuel cell. Humidification can be performed with high efficiency up to the dew point at. A fuel cell system that can operate a fuel cell using the humidified gas has excellent durability and overall energy efficiency of the fuel cell.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. The following description is intended to illustrate, but not limit, the invention.
[0019]
FIG. 1 is a block diagram showing a fuel cell system for implementing a method for humidifying a fuel cell according to one embodiment of the present invention. The fuel cell system 1 includes a fuel cell 4, a first humidifier 2 for humidifying a gas supplied to an air electrode 41 of the fuel cell 4 by an outlet gas of the fuel cell 4, and a humidified gas. A second humidifier for further humidifying the cooling water of the fuel cell; and a cooling water circulation pump for circulating the cooling water of the fuel cell so as to pass through the second humidifier. .
[0020]
Here, in the following description of the embodiment, the gas supplied to the air electrode 41 of the fuel cell 4 is referred to as supply air. However, the gas supplied to the air electrode 41 of the fuel cell 4 is not limited to air, but may be any gas containing oxygen used for the cell reaction. In addition, the outlet gas of the fuel cell 4 refers to a gas whose oxygen is consumed by a cell reaction in the fuel cell, and which has been heated to a high temperature by being saturated with water vapor by generation of water in the cell reaction.
[0021]
As the fuel cell 4, a polymer electrolyte fuel cell can be used. FIG. 1 conceptually shows a part of such a fuel cell 4 which is extracted and conceptually shown. FIG. 3 shows a conceptual view of a fuel cell and a fuel cell obtained by stacking the fuel cells. explain. The fuel cell 4 shown in FIG. 3 includes a fuel cell 40 including a fuel electrode 42 on one side of an electrolyte membrane 44 and an air electrode 41 on the other side, and a cooling unit 43 forming a flow path of cooling water. Through a plurality. The cooling unit 43 has a structure in which the fuel electrode 42 of one fuel cell 40 and the air electrode 41 of another fuel cell are separated by a separator (not shown), and cooling is performed by flowing cooling water inside the separator bonding part. Has become. By flowing the cooling water through the cooling unit 43, the fuel electrode 42 of a certain fuel cell 40 and the air electrode 41 of an adjacent fuel cell can be cooled.
[0022]
The first humidifier 2 is a device capable of humidifying the supply air by bringing the supply air into contact with the fuel cell 4 outlet gas having a high moisture content. In such a humidifier 1, the flow path of the supply air and the flow path of the outlet gas of the fuel cell 4 are defined by a water vapor permeable film, and the air supplied to the air electrode 41 through the water vapor permeable film. Any material that can cause mass transfer with the outlet gas of the fuel cell 4 may be used.
[0023]
Humidifiers using such a water vapor permeable membrane are known to those skilled in the art, and the water vapor permeable membrane humidifies to a predetermined degree depending on the output of the fuel cell 4 and the size of the entire fuel cell system 1. Can be used. It is particularly preferable that the water vapor permeable membrane has a large specific surface area and a pore size through which water vapor passes is 0.1 μm or less.
[0024]
Further, as the humidifier 2, it is preferable to use a humidifying module using a hollow fiber membrane as a water vapor permeable membrane. This is because the humidifying module using the hollow fiber membrane has an advantage that the humidifier 2 can be reduced in size and has high strength because the surface area of the water vapor permeable membrane can be increased. When such a hollow fiber membrane is used for the first humidifier 2, a flow path for supply air to be humidified is formed inside the hollow fiber, and a fuel cell outlet gas saturated with water vapor is formed outside the hollow fiber. A channel may be formed. Alternatively, a flow path for a fuel cell outlet gas saturated with water vapor may be formed inside the hollow fiber, and a flow path for humidified supply air may be formed outside the hollow fiber.
[0025]
The amount of supply air supplied to the humidifier 2 and the amount of gas at the outlet of the fuel cell vary depending on the size of the humidifier 2, but the membrane surface area is 1 m. ² 10 to 200 L / min, preferably 20 to 80 L / min.
[0026]
The second humidifier 3 humidifies the supply air humidified and heated by the first humidifier 2 by contact with the cooling water of the fuel cell. Therefore, the second humidifier 3 is provided downstream of the first humidifier 2 along the flow of the supply air. In such a humidifier 3, the flow path of the supply air and the flow path of the cooling water of the fuel cell 4 are defined by a water vapor permeable film, and the supply air and the cooling of the fuel cell 4 are separated through the water vapor permeable film. Any material that can cause mass transfer with water may be used.
[0027]
As such a second humidifier 3, the same as the above-described first humidifier 2 can be used. Therefore, the same thing can be selected as a water vapor permeable membrane. The structure of the second humidifier 3 may be the same as that of the first humidifier, or may be a structure in which air and cooling water are in direct contact with each other, such as bubbling or a wet wall method. . The size and length of the humidifier can be changed according to the required amount of water vapor transmission. When a hollow fiber membrane is used for the second humidifier 3, a flow path for supply air to be humidified is formed inside the hollow fiber, and a flow path for cooling water for the fuel cell is formed outside the hollow fiber. May be. Alternatively, the flow path of the cooling water of the fuel cell may be formed inside the hollow fiber, and the flow path of the supply air to be humidified may be formed outside the hollow fiber.
[0028]
Although the cooling water of the fuel cell 4 is supplied to the second humidifier 3, the system may be such that cooling water at the outlet of the fuel cell 4 is supplied. The cooling water may be supplied to the system. The positional relationship between the second humidifier 3 and the cooling unit 43 of the fuel cell 4 in the system for circulating cooling water including the cooling water circulation pump 6 can be appropriately determined by those skilled in the art.
[0029]
Here, one mode of a humidifier that can be used in the present embodiment is shown in FIG. The device shown in FIG. 2 is a device manufactured such that the first humidifier 2 and the second humidifier 3 are integrated, and the first humidifier 2 uses a hollow fiber membrane 25. A humidification module is provided, and includes a sweep inlet 21 to which supply air is supplied, a fuel cell outlet gas inlet 23, and a fuel cell outlet gas outlet 24. The sweep outlet of the first humidifier 2 (not shown) is connected to the sweep inlet of the second humidifier 3 (not shown), and the supply air passing through the first humidifier 2 is directly supplied to the second humidifier 2. The humidifier 3 is supplied. The second humidifier 3 is provided with a humidifying module using a hollow fiber membrane 35, and is provided with a sweep outlet 32 from which supply air is discharged, a cooling water inlet 33, and a cooling water outlet 34. As described above, the device manufactured such that the first humidifier 2 and the second humidifier 3 are integrated not only can omit piping and joints, but also can be compared with a case where the devices are separately installed. There is an advantage that the size can be significantly reduced. However, the first humidifier 2 and the second humidifier 3 used in the present invention are not limited to such a form.
[0030]
The cooling water circulation pump 6 that circulates the cooling water of the fuel cell may be any pump that can circulate the cooling water so as to pass through both the cooling unit 43 of the fuel cell 4 and the second humidifier 3. . The amount of cooling water to be circulated depends on the output of the battery, but can be 1 to 10 L / min when the output of the fuel cell is 1300 W. Further, the system can be configured such that the entire amount of the cooling water supplied to the cooling unit 43 of the fuel cell is supplied to the second humidifier 3.
[0031]
The hot water recovery heat exchanger 7 is for cooling heat generated at the time of power generation in the fuel cell by using circulating cooling water from a hot water recovery facility (not shown). This is a heat exchanger for heat exchange and recovery as hot water.
[0032]
The above-described fuel cell system 1 shown in FIG. 1 has the humidifiers 2 and 3 provided in the flow path of the supply air supplied to the air electrode 41 of the fuel cell 4. The fuel cell system in which the humidifiers 2 and 3 are provided in the flow path of the fuel gas supplied to the fuel electrode 42 may be provided, and the fuel cell system further includes the humidifiers 2 and 3 in the flow paths of both gases. May be. In the system in which the humidifiers 2 and 3 are provided in the flow path of the fuel gas supplied to the fuel electrode 42 of the fuel cell 4, the first gas as described above is provided after the fuel gas reformer 8 shown in FIG. The humidifier 2, the second humidifier 3, and the cooling water circulation pump 6 can be installed. Alternatively, the same can be applied to a fuel cell system in which fuel gas is supplied without using a reformer.
[0033]
Next, a method for humidifying a fuel cell using the above-described fuel cell system 1 will be described. Such a humidification method for a fuel cell includes a first humidification step of humidifying the gas supplied to the electrode of the fuel cell 4, and a second humidification step of further humidifying the humidified gas.
[0034]
Air can be used as the gas supplied to the air electrode 41 of the fuel cell. However, such a gas is not limited to air only, and may be any gas containing oxygen used in a battery reaction. In the following description, the gas supplied to the air electrode of the fuel cell is referred to as supply air. At the stage where the supply air is supplied to the cathode of the fuel cell, Always The temperature may be 25-30 ° C., and the absolute humidity is 0.027 kg · H ₂ It may be about O / kg dry air. Since the initial humidity of the supply air has almost no effect on the humidification method according to the present embodiment, air of any humidity can be used as the supply air.
[0035]
In the first humidification step, the supply air is humidified by coming into contact with the gas at the outlet of the fuel cell through the water vapor permeable membrane. The fuel cell outlet gas used to perform such humidification is preferably at about 60 to 80 ° C. and 1 to 10 kPa. By bringing the gas under such temperature and pressure conditions into contact with the supply air through the water vapor permeable membrane, mass transfer of water vapor can be caused by the water vapor pressure difference. For example, when the fuel cell outlet gas is 72 ° C. and 5 kPa, as a result of mass transfer of water vapor, the supply air is 62 ° C. and the absolute humidity is 0.171 kg · H. ₂ It can be O / kg dry air.
[0036]
In the first humidification step, the supply air is preferably provided with 40-80% of the required steam. The amount of water vapor to be supplied does not substantially depend on the initial humidity of the supply air.
[0037]
In the second humidification step, the supply air humidified in the first humidification step is humidified by contact with the cooling water of the fuel cell via the water vapor permeable membrane. Cooling water used to perform such humidification is brought into contact with supply air at 65-82 ° C.
[0038]
By bringing the cooling water at such a temperature into contact with the supply air through the water vapor permeable membrane, mass transfer of the water vapor can be caused. For example, when the supply air after humidification in the first humidification step is 5 kPa at 62 ° C., as a result of the mass transfer of steam in the second humidification step, the supply air is reduced to 69 ° C. , Absolute humidity 0.259kg ・ H ₂ It can be O / kg dry air.
[0039]
In the second humidification step, humidification is performed so that the dew point of the supply air humidified in the first humidification step is substantially equal to the operating temperature of the fuel cell. Therefore, in the second humidification step, it is preferable to supply the supply air with 20 to 60% of the required steam. As in the second humidification step, in order to cause mass transfer between a gas and a liquid, it is necessary to supplement the heat energy of the latent heat of evaporation of the cooling water. When the power is 0.3 kW, according to the present embodiment, the heat energy of 0.32 kW is obtained from the cooling water, and the difference between the dew point of the supply air and the operating temperature of the fuel cell can be kept within 5 ° C.
[0040]
The above-mentioned numerical values are described when the operating temperature of the fuel cell is set to 70 ° C. For example, when the operating temperature of the fuel cell is set to 80 ° C., in the first humidification step, the supply air temperature is set to 70 ℃, absolute humidity 0.276kg ・ H ₂ O / kg dry air, in the second humidification step, the temperature of the supply air is 78 ° C and the absolute humidity is 0.468 kg · H ₂ It can be O / kg dry air. At this time, in the first humidification step, water vapor of 59% of the required water vapor can be supplied to the supply air, and in the second humidification step, water vapor of 41% of the required water vapor can be supplied to the supply air. At this time, the energy required to supplement latent heat of vaporization in the second humidification step is 0.54 times the output of the fuel cell. When the operating temperature of the fuel cell is 80 ° C., the temperature of the supply air is 78 ° C. and the absolute humidity is 0.468 kg · H only in the second humidification step. ₂ In order to obtain O / kg dry air, the energy required to supplement latent heat of vaporization is 1.32 times the DC output of the fuel cell, resulting in a shortage of energy and an inability to supply a required amount of water vapor.
[0041]
In the present embodiment, the method for humidifying the supply air, which is the gas supplied to the air electrode of the fuel cell, has been specifically described. However, the same applies to the hydrogen-rich fuel gas supplied to the fuel electrode of the fuel cell. It can be humidified by using the method described above.
[0042]
According to the humidification method of the fuel cell according to the present embodiment, the dew point of the supply air, which is the gas supplied to the air electrode of the fuel cell, is efficiently utilized by using the energy source discharged from the fuel cell 4 itself. Humidification can be performed so as to be approximately equal to the operating temperature of the fuel cell. Specifically, the difference between the dew point of the supply air and the operating temperature of the fuel cell can be kept within 5 ° C. By making such a high humidification, the electrolyte membrane of the fuel cell is kept in a wet state, The durability of the fuel cell can be improved.
[0043]
【Example】
Next, the present invention will be described in more detail by way of examples. The following examples illustrate, but do not limit, the invention.
[0044]
Here, an embodiment in which the gas supplied to the fuel cell is humidified using the fuel cell system shown in FIG. 1 will be described. The fuel cell system 1 used in the embodiment is a fuel cell system 1 capable of humidifying gas supplied to an air electrode, and includes a fuel cell 4, a first humidifier 2, and a second humidifier 3. And a cooling water circulation pump 6.
[0045]
The fuel cell 4 used had a DC output of 1.3 kW and used an electrolyte membrane having an N112 membrane manufactured by DuPont and having a thickness of 50 μm. The humidification method adopted the external humidification method. In this embodiment, this fuel cell was operated at 70 ° C.
[0046]
As shown in FIG. 2, the first humidifier 2 and the second humidifier 3 are connected in series and integrated, and each has a built-in hollow fiber membrane module 25 and 35 therein. Using. The hollow fiber membrane module 25 of the first humidifier 2 used a bundle of 2500 hollow fiber membranes having an outer diameter of 0.8 mm, an inner diameter of 0.65 mm, and a length of 180 mm. The pores of the hollow fiber membrane had a pore size of 0.04 μm. The hollow fiber membrane module 35 of the second humidifier 3 also used an outer diameter of 0.8 mm, an inner diameter of 0.65 mm, and a bundle of 2500 hollow fiber membranes having a length of 70 mm. The average pore diameter of the pores of the hollow fiber membrane was 0.04 μm.
[0047]
The cooling water circulation pump 6 was a centrifugal pump with a flow rate of 5 L / min and a head of 5 m.
[0048]
As air supplied to the air electrode 41 of the fuel cell 3, air in the atmosphere was taken and used. The supply air was supplied from the blower 5 at 25 ° C. and 75 NL / min. The supply air was introduced into the first humidifier 2 from the sweep inlet 21 of the first humidifier 2. The air at the inlet 21 of the first humidifier 2 has a temperature of 25 ° C. and an absolute humidity of 0.02 kg · H ₂ O / kg dry air. In the first humidifier 2, mass transfer was performed between the supply air and the fuel cell outlet gas through the hollow fiber membrane 25, and the supply air was humidified. Humidified supply air at the outlet of the first humidifier 2 has a temperature of 60 ° C. and an absolute humidity of 0.151 kg · H. ₂ O / kg dry air.
[0049]
The supply air from the first humidifier 2 was supplied to the second humidifier 3. Mass transfer was performed between the supply air and the cooling water of the fuel cell through the hollow fiber membrane 35, and the supply air was humidified. The supply air at the sweep outlet 32 of the second humidifier has a temperature of 69 ° C. and an absolute humidity of 0.259 kg · H. ₂ O / kg dry air. The humidified and steam-saturated supply air was supplied to the air electrode 41 of the fuel cell 4, and a part of the supply air was consumed by the following reaction.
[0050]
2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (cathode reaction)
[0051]
The remaining supply air not consumed in the cathode reaction was heated by the heat generated in the cathode reaction, humidified by the moisture generated by the reaction, and discharged from the outlet of the fuel cell 4 as a fuel cell outlet gas. The temperature of the fuel cell outlet gas at the outlet of the fuel cell 4 is 72 ° C., and the absolute humidity is 0.313 kg · H. ₂ O / kg dry air. The fuel cell outlet gas is introduced into the first humidifier 2 from the fuel cell outlet gas inlet 23 of the first humidifier 2, and is subjected to substance exchange with supply air supplied from the blower 5. The gas was discharged from the outlet gas outlet 24. The supply amount of the fuel cell outlet gas to the first humidifier 2 was 68.7 NL / min in dry air amount.
[0052]
The temperature of the fuel cell cooling water discharged from the fuel cell 4 flowing through the cooling unit 43 of the fuel cell 4 was 72 ° C. This cooling water was circulated by the cooling water circulation pump 6. The circulated cooling water was supplied from the cooling water inlet 33 of the second humidifier 3 to the second humidifier 3 at 70 ° C. at a supply rate of 5 L / min. In the second humidifier 3, the temperature of the cooling water that was mass-exchanged with the air humidified in the first humidifier 2 was 70 ° C. at the cooling water outlet 34 of the second humidifier 3. The cooling water discharged from the second humidifier 3 was again supplied to the fuel cell 4 and used for cooling the fuel cell.
[0053]
As a result of operating the fuel cell 4 at 70 ° C. while humidifying the air using the fuel cell system 1 of the present invention, the electrolyte membrane 44 maintains an appropriate amount of water even after continuous operation for 2000 hours. I was Further, in the course of the operation of the fuel cell 4, the supply air supplied to the air electrode 31 of the fuel cell 4 could be humidified at the beginning of the operation or during the operation.
[0054]
On the other hand, using the same fuel cell, introducing the supply air at 25 ° C. at a rate of 75 NL / min into the same humidifier as the first humidifier 2 described above, and humidifying the gas by contact with the outlet gas of the fuel cell. In the comparative example where only the operation was performed, the temperature of the supply air exiting the humidifier was 60 ° C., and the absolute humidity was 0.151 kg · H. ₂ O / kg dry air. In addition, the same operation was performed with the first humidifier having a shape in which the inner diameter, the outer diameter, and the number of the hollow fiber membranes were the same, and the length was increased from 180 mm to 360 mm. As a result, the length of the hollow fiber membrane was also increased. Nevertheless, the temperature and absolute humidity of the supply air leaving the humidifier did not change at all before the increase. This was presumed to be due to the fact that the humidification performance had already reached saturation from the difference in water vapor pressure. The outlet gas of the fuel cell used had a temperature of 72 ° C. and an absolute humidity of 0.313 kg · H. ₂ O / kg dry air.
[0055]
As described above, according to the humidification method using the fuel cell system 1 of the present embodiment, no breakage or deterioration of the electrolyte membrane 44 and no reduction in power generation efficiency due to these are recognized, and good power generation is performed in the fuel cell 4. We were able to.
[0056]
Further, from the viewpoint of the energy balance of the entire fuel cell system, the first humidifier 2 uses only the outlet gas of the fuel cell 4, so that no new energy is required. Since the latent heat of vaporization for evaporating the cooling water to cause mass transfer between the cooling water and the supply air for 20 to 60% of the required water vapor amount can be covered by the heat generated by the fuel cell 4, energy is newly added. do not need. In this fuel cell system, energy efficiency is greatly improved as compared with conventional humidification in which all cooling water is evaporated, for example, because a heater for heating the cooling water is not required.
[0057]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the humidification method of the fuel cell concerning this invention, the dew point of the air supplied to the air electrode of a fuel cell is made substantially equal to the operating temperature of a fuel cell using the gas and cooling water discharged from a fuel cell. Humidification operation is possible. In addition, since the humidification method can use the cooling water of the fuel cell, a high humidification operation can be performed even in the initial operation. Such humidification can prevent breakage and deterioration of the electrolyte membrane in the fuel cell, and can improve the performance and durability of the fuel cell.
Further, the fuel cell system of the present invention capable of implementing the humidifying method including the two humidifying steps according to the present invention has high energy efficiency and excellent durability as a whole system.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a fuel cell system according to the present invention.
FIG. 2 is a cross-sectional view illustrating an example of a humidifier using a hollow fiber membrane.
FIG. 3 is a conceptual diagram showing a configuration of a fuel cell included in a fuel cell system according to the present invention.
[Explanation of symbols]
1 fuel cell system
2 First humidifier
3 Second humidifier
4 Fuel cell
5 Blower
6 Cooling water circulation pump
7 Heat exchanger for hot water recovery
8 Reformer
21 Sweep entrance
23 Fuel cell outlet gas inlet
24 Fuel cell outlet gas outlet
25 hollow fiber membrane
32 sweep exit
33 Cooling water inlet
34 Cooling water outlet
35 hollow fiber membrane
40 fuel cell
41 air electrode
42 Fuel electrode
43 Cooling unit
44 Electrolyte membrane

Claims (7)

A first humidification step of humidifying the gas supplied to the electrode of the fuel cell by bringing the gas into contact with the gas at the fuel cell outlet through a water vapor permeable membrane,
A second humidification step of humidifying the humidified gas by contacting the humidified gas with cooling water of the fuel cell through a water vapor permeable membrane. The method according to claim 1, wherein a difference between a dew point of gas supplied to a pole of the fuel cell through the first humidification step and a second humidification step and an operation temperature of the fuel cell is within 5 ° C. 5. The method according to claim 1 or 2, wherein a hollow fiber membrane is used as the water vapor permeable membrane. The method according to any one of claims 1 to 3, wherein the gas supplied to the electrode of the fuel cell is at least one of a gas supplied to an air electrode and a gas supplied to a fuel electrode. A fuel cell in which a fuel electrode is provided on one surface of an electrolyte membrane, and a plurality of fuel cells having an air electrode on the other surface are stacked via a cooling unit forming a flow path of cooling water,
A first humidifier that humidifies the gas supplied to the electrode of the fuel cell by contacting the gas at the outlet of the fuel cell with the gas through the water vapor permeable membrane;
A second humidifier that humidifies the humidified gas by contacting the fuel cell cooling water with a water vapor permeable membrane,
A fuel cell system comprising: means for circulating the cooling water so that the cooling water of the fuel cell is supplied to the cooling unit of the fuel cell and the second humidifier. The fuel cell system according to claim 5, wherein the water vapor permeable membrane is a hollow fiber membrane. The first humidifier and the second humidifier are provided on at least one of a gas supply path supplied to a fuel electrode of a fuel cell and a gas supply path supplied to an air electrode of the fuel cell. The fuel cell system according to claim 5.

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