JPS63218166A - Operation of fuel cell - Google Patents

Abstract

PURPOSE:To recover moisture from exhaust gas even in a state of relatively high temperature for recycling the moisture for cell reaction by performing absorption of the moisture contained in the oxidizer gas while using absorbent. CONSTITUTION:The laminated cell body 1 of a methanol fuel cell, an anolyte tank 2 and a water absorber 3 mainly compose a generation set. Exhaust gas from the oxidizer pole of the fuel cell is made to make contact with a water absorbent through a water absorber 3 for making the water absorbent to absorb steam contained in the exhaust gas. That is, the exhaust gas is made to make contact with the water absorbent maintained at a temperature lower than the temperature of this exhaust gas for raising the temperature of this absorbent with heat generated from the fuel cell 1 to raise steam pressure of the moisture contained in the water absorbent in order to separate the moisture from the absorbent followed by supplying the separated moisture to a fuel pole. Thereby, water recovery and water recycling can be performed without requiring any other cooling source.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of operating a fuel cell, and in particular, to a method of operating a fuel cell, in particular, recovering water from the oxidizer electrode exhaust gas of a fuel cell, recycling this water to a fuel electrode, and recycling it again. This invention relates to a method of operating a fuel cell that participates in a reaction.

[Conventional technology]

Fuel cells extract the reaction energy of fuel and oxidizer directly as electrical energy, and are expected to be a new power generation method because they have high power generation efficiency, little noise and vibration, and normal exhaust gas.

In particular, acid electrolyte methanol fuel cells (hereinafter referred to as methanol fuel cells), which use methanol as fuel and sulfuric acid or the like as an electrolyte, operate at room temperature and relatively low temperature (approximately 60°C), and can be easily miniaturized. Therefore, it is expected to have a wide range of applications as a small to medium capacity power source.

In this methanol fuel cell, a first-order reaction occurs.

At the fuel electrode (methanol electrode), CHa OH+ H20→COz+6)(+ +6 e
-...(1) At the oxidizer electrode (air electrode), 6H++-02+ 6 e --) 3 Hz○
-(2) Such a reaction occurs, and formula (1) and (2)
) Putting the equations together.

CHa○H+ H20+ -02→CO2+3H20・
...(3) The power generation reaction is performed. That is, methanol fuel cells require methanol and water as reaction raw materials. The quantitative relationship between methanol and water is that in actual batteries, water that does not participate in the reaction and is discharged outside the system,
There is water produced by direct combustion of methanol, which must be determined by actual measurement. According to the studies conducted by the present inventors, this quantitative relationship depends on the operating conditions and battery structure, but is as shown below by Ohji.

CH30H+4. lH2O+1.502-)C○2+6
, I I(20...' (4) In other words, theoretically, the same number of moles of water as methanol is required, but the actual amount of water required is about four times the theoretical amount. There is.

Methanol fuel cells are used as small to medium capacity power sources such as portable power sources, and although replenishment of methanol is not that important, it is necessary to prepare and replenish several times the amount of water. Distilled water is preferable as this water in order to facilitate the electrode reaction, and without replenishment of water, the battery reaction will not proceed, resulting in a significant disadvantage in terms of battery performance.

In order to solve these problems, Japanese Patent Laid-Open No. 56-93268 discloses that water is recovered from the exhaust gas generated on the anolite side and reused.

This prior art discloses cooling exhaust gas to recover water and using air as a coolant.

[Problem that the invention seeks to solve]

However, while it would be advantageous to be able to recover water using these prior art methods, some types of fuel cells, particularly methanol fuel cells, may not always be operated under conditions that allow water recovery. do not have. For example, (4) above
Considering the relationship in the equation, under operating conditions where the temperature is 60°C and the air supply amount to the air electrode is 5 m Q /min per 1 c++f of air electrode, the humidity of the exhaust gas is 0.13 kgH207
kg dry air) J, based on (4), this 4.1
/6.1 To recover water, reduce the exhaust gas temperature to approximately 0,
It is necessary to lower it to 0.04 kgH2o/kg dry air. As a result, it becomes necessary to cool the exhaust gas to about 38°C. In other words, when the battery is operated under environmental conditions of 38°C or higher, it is not possible to recover all the necessary water, and when attempting to recover water simply by air cooling,
It becomes necessary to prepare another source of cooling and heat. However, a cooling source other than air cooling, such as cooling water, cannot be easily prepared. Especially in methanol fuel cells.

Since it is expected that the device will be used as a portable power source, the restriction of providing such a cooling and heat source will reduce the characteristics of the device as a portable power source.

In order to solve this problem, the present invention recovers water from the air electrode exhaust gas of a fuel cell without requiring a cold heat source even when the battery operating temperature is high, and reuses the water. The purpose of the present invention is to provide a method for operating a fuel cell that can secure the amount of water necessary for its operation.

[Means for solving problems]

The present invention brings exhaust gas from an oxidizer electrode of a fuel cell into contact with a water absorbent, absorbs water vapor contained in the exhaust gas into the water absorbent, and then supplies the absorbed water to the fuel electrode. This is a method of operating a fuel cell characterized by the following.

[Effect]

According to the present invention, the absorbent absorbs the moisture contained in the exhaust gas from the oxidizer electrode and supplies this moisture to the anode necessary for battery operation, so there is no need for any other cooling source. , water recovery and water reuse can be achieved.

〔Example〕

Next, an embodiment of the method of operating a fuel cell according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of a power generation device for carrying out one embodiment of the invention.

In FIG. 1, the apparatus of this embodiment mainly consists of a stacked cell main body 1 of a methanol fuel cell, an anolyte tank 2, and a water absorber 3. The anolyte tank 2 stores a mixed solution of sulfuric acid and methanol. An anolite circulation line 6 is connected from the anolite tank 2 to the fuel electrode of the battery main body 1, so that the anolite is supplied to the fuel electrode. On the other hand, an air line 8 to which air is supplied by a fan 41 is provided on the air electrode side of the fuel cell main body 1 . This air line 8 is connected within the water absorber 3. From water absorber 3.

An exhaust gas line 10 is provided for exhausting air from the absorber 3 to the outside.

The water absorber 3 is connected to an absorbent cooler 4 via an absorbent circulation line 9. A cooling air supply line 42 is connected to the absorbent cooler 4 .

The water absorber 3 is connected to an absorbent regenerator 5 via an absorbent circulation line 43. The absorbent regenerator 5 is connected to the absorbent cooler 4 via an absorbent circulation line 60 having a pump 44 . A cooling air line 61 is connected to the absorbent regenerator 5 for supplying cooling air.

An anolyte line 7 is connected to the anolyte tank 2 . This anolyte line 7 passes through the absorbent regenerator 5 and returns to the anolyte tank 2.

A water recovery line 11 is connected to the absorbent regenerator 5, and this line 11 is connected to the anolyte tank 2.

Next, the operation of this embodiment will be explained. Anolyte is supplied to the fuel cell main body 1 from the anolyte tank 2 by driving the pump 47 . The supply of this anorite is
The anolyte circulates through the anolyte circulation line 7. On the other hand, air is supplied to the air electrode via the air line 8 by driving the fan 41. By supplying anorite to the fuel electrode and air to the air electrode,
The methanol fuel cell generates electricity.

Air discharged from the fuel cell main body 1 is supplied to a water recovery device 3. In this absorber 3, the water absorbent supplied through the absorbent circulation line 9 and the exhaust gas from the air electrode come into contact. Here, water generated by power generation in the exhaust gas is absorbed by the water absorbent. The exhaust gas in which water has been absorbed, that is, the dehumidified exhaust gas, is discharged to the outside of the system as exhaust gas through the exhaust gas discharge line 10.

The water absorbent present in the water absorber 3 contains sulfuric acid.

An aqueous salt solution having high solubility in water, such as LiBr, Ca(lltz, Ca(NOx)z), can be used.

The absorbent that has absorbed water from the exhaust gas is supplied to the absorbent regenerator 5. On the other hand, the anolyte circulating in the anolyte line 7 passes through the absorbent regenerator 5. This anorite is heated to near battery operating temperature (usually about 60° C.). Since the anolyte line 7 circulates through the absorbent storage portion in the absorbent regenerator 5, heat exchange is performed between the anolyte and the absorbent. That is, by heating the absorbent, the temperature of the absorbent increases and the vapor pressure of water in the absorbent increases. As a result, water vapor evaporates from the absorbent.

On the other hand, this water vapor becomes condensed water through heat exchange with the air flowing in the cooling air line 43. This condensed water is
It is refluxed to the anolyte tank 2 through the line 11 and subjected to the battery reaction again.

The anolyte flowing through the anolyte line 7 is a heating means for the absorbent. Thus, as a heating means for evaporating water from the absorbent, in addition to the anolyte heated to the operating temperature, heat from other heat sources can also be used. for example.

Waste heat from other plants can also be used.

In the embodiment described above, an absorbent cooler 4 is provided to cool the absorbent supplied from the absorbent regenerator 5 to the water absorber 3. This is to restore the ability to supply water in the exhaust gas by cooling the absorbent.

The absorbent concentrated in the absorbent regenerator 5 is cooled by air in the absorbent cooler 4 to recover its absorption capacity, and is supplied to the water absorber 3 again.

According to this embodiment, water can be recovered from the air electrode exhaust gas even at a relatively high temperature, which is the operating temperature of the battery, without requiring a special cooling source. moreover,
The water absorbent can be regenerated using the heat generated by the battery. Condensed water can be obtained at a higher temperature than when battery exhaust gas is directly cooled and recovered. In this way, this embodiment does not require a special cooling source and does not impair its effectiveness as a portable battery.

Next, specific examples will be described.

0,13 kgHzo/kg dry air 0,04
kgHz.

/kg of dry air, only cooling the exhaust gas, i.e., when using other cooling sources, 38
It was necessary to cool the exhaust gas to ℃.

However, when 26% sulfuric acid is used as the absorbent, water can be recovered from the exhaust gas by heating the absorbent to 45°C. When 60% sulfuric acid is used as an absorbent, water can be absorbed from the exhaust gas by heating the absorbent to 60°C.

This 60°C is the operating temperature of a methanol fuel cell, so it not only does not require a special cold source, but also shows that water can be recovered from the absorbent even at relatively high cell operating temperatures. has been done. Further, when a 23% LiBr aqueous solution is used as the absorbent, water can be recovered by heating the absorbent to 45°C. Next, when the temperature of the absorbent is raised to 60°C, which is the typical operating temperature of a methanol fuel cell, the water vapor pressure of the 26% sulfuric acid aqueous solution rises to 122 IHzO, and when it is cooled at 45°C, it increases to 45°C. It can be easily recovered based on the difference between the saturated water vapor pressure at 72IIllH20.

For a 23% LiBr aqueous solution, the water vapor pressure at 60°C is approximately 121 mIHzO, and similarly at 45°C.
Water can be easily recovered.

In the embodiments described above, the recovery temperature at which water is recovered from the absorbent can be selected by selecting the absorbent and the concentration of the absorbent.

In the above embodiment, a methanol fuel cell has been described, but the present invention is not limited to a methanol fuel cell, and can be applied to other types of fuel cells.

Next, a second embodiment of the present invention will be described.

FIG. 2 shows the configuration of an apparatus for carrying out this embodiment. The embodiment shown in FIG. 2 differs from FIG. 1 in that the anolyte itself is used as the absorbent. This is because the configuration of the apparatus shown in FIG. 2 differs from that shown in FIG. 1 in the following points. The anorite tank has an absorbent circulation line 9.
is connected.

Further, this absorbent circulation line 9 is connected to a water absorber 3, and through the water absorber 3, the absorbent circulation line 9 passes through the fuel electrode of the fuel cell main body, and is connected to the anorite circulation line 6. . This anorite circulation line 6 is connected to the anorite 1-tank 2. In addition, in this example,
A water absorber 3 and an exhaust gas purifier 12 are connected via an exhaust gas line 10.

A part of the anorite is used as an absorbent in the absorbent circulation line 9
The water is supplied to the water absorber 3 by The anolyte guided to the absorbent 3 forms a shower on the upper surface of the absorbent 3, expanding the absorption area. Here, in the water absorber 3, the anorite comes into contact with the cathode exhaust gas supplied via the air line 8, and dehumidification (water recovery) takes place. The anolyte in which water has been absorbed is supplied to the battery body 1 through an absorbent circulation line 9. Since the anorite contains water before being supplied to the battery body 1, the water required for the electrochemical reaction is compensated for here. The water-absorbed anorite is reused for battery reactions. The anorite that has passed through the battery body 1 is
It is returned to the anolyte tank 2 via the anolyte circulation line 6. Immediately after leaving the battery body 1, the anolite is used because the water contained in the anolite is used for battery reactions.

The concentration is high. This highly concentrated anolyte is returned to the anolyte tank 2, and this highly concentrated anolyte is further circulated to the water absorber 3, so that the water absorption capacity is high.

The supply speed of the anolyte can be adjusted by the driving force of the pump 47. Pump 4 to absorb water with anolite
By adjusting the driving force of 7, the anolyte flow rate can be adjusted.

The exhaust gas discharged from the water absorber 3 to the outside of the system contains methanol at a vapor pressure corresponding to the methanol concentration contained in the anolite. Therefore, in case it is difficult to directly release this exhaust gas into the atmosphere, an exhaust gas purifier 12 is provided, and if the exhaust gas is purified by this purifier 12, the problem of air pollution will be eliminated. As this exhaust gas purifier 12, a methanol catalytic combustor, an absorbent tank, etc. are used.

As described above, according to this example, since the anolite is directly used as a water absorbent, there is no need to use a special absorbent, and the water in the exhaust gas emitted from the oxidizing agent moves directly into the anolite. , the separation of water from the absorbent becomes unnecessary. Therefore, the system configuration of the device becomes very simple.

Note that in this embodiment, it is not necessary to specifically air-cool the anorite supplied from the absorbent circulation line 9 to the water absorber 3.

This is because since it is concentrated sulfuric acid, it has absorption ability even at the battery operating temperature of 60°C.

However, this does not prevent the provision of a cooling source to cool the anorite.

FIG. 3 shows a modification of the embodiment shown in FIG. 2. Third
The embodiment shown in the figure differs from the embodiment shown in FIG. 2 in that the circulation order of the anolite is different from that shown in FIG. That is, the anolite leaving the anolite tank 2 is supplied to the water absorber 3 via the fuel electrode of the fuel cell main body 1. This is the point where the anolyte that has absorbed water from the air electrode exhaust gas in the water absorber 3 is returned to the anolyte tank 2.

According to this embodiment, as the anolyte passes through the current body 1, the sulfuric acid concentration is increased. Therefore, the water absorption capacity of the water absorber 3 is increased, and the water recovery efficiency is improved. The sulfuric acid, ie, the anolyte, whose concentration has been reduced by recovering the water, is refluxed to the acylite tank 2 and used as an anolite for the next battery reaction.

In this example, the amount of circulation of the anolite is reduced, and the pump 4
The power consumption required for the circulation of No. 7 can be reduced. Furthermore, as a result of the improved dehumidification ability of the anolyte, the ability to remove methanol from the air electrode exhaust gas is improved, and the methanol concentration in the exhaust gas discharged to the outside of the system can be reduced. Therefore, the exhaust gas purifier 12 becomes unnecessary, or at least the capacity of the purifier can be reduced.

According to this example, the anorite is at the battery operating temperature (7) 6
Even at 0℃, 0.13 kgHzo/kg dry air is
,04 kg H20/kg dry air can be dehumidified.

Next, other embodiments of the present invention will be described.

FIG. 4 shows a block diagram of an apparatus for carrying out this embodiment. This embodiment differs from the previous embodiments in that a membrane-based regenerator 14 is used to recover water from the absorbent. Namely.

In FIG. 4, an absorbent circulation line 51 coming out of the water absorber 3 passes through a membrane regenerator 14 and is connected to an absorbent circulation tank 13. An absorbent circulation line 9 is connected to the absorbent W-ring tank, and this line 9 is connected to the water absorber 3.

On the other hand, anorite line 7 coming out of anorite tank 2
passes through the membrane-based regenerator 14 and returns to the anolyte tank 2.

Next, the operation of this embodiment will be explained. The absorbent is sent from the absorbent circulation tank 13 to the water absorber 3 through the absorbent circulation line 9 by a driving means such as a pump. After absorbing moisture in the exhaust gas of the oxidant gas from the fuel cell main body 1, the absorbent is passed through the line 51 to the membrane regenerator 14.
In this paper, the absorbent is regenerated using a water selectively permeable membrane.

The absorbent and the anolite are brought into contact with each other through a membrane that has selective permeability to water and has almost no permeability to sulfuric acid and methanol in the absorbent or the anolite. Water in the absorbent is moved into the anorite based on the osmotic pressure difference to regenerate the absorbent.

In this embodiment, in order to regenerate the absorbent without causing a phase change, the temperature of the absorbent is raised in the regenerator as explained in the embodiment of FIG. No need for cooling temperature cycles.

〔Effect of the invention〕

As explained above, according to the present invention, since the moisture contained in the oxidant gas is absorbed using an absorbent, the operating temperature of the battery can be maintained without requiring a special cold source. Even at relatively high temperatures, water can be recovered from exhaust gas and reused for battery reactions.

[Brief explanation of the drawing]

FIGS. 1 to 4 are block diagrams of an embodiment of an apparatus for carrying out the method of operating a fuel cell according to the present invention. DESCRIPTION OF SYMBOLS 1...Fuel cell main body water absorber, 4...Anolyte tank, 3...Water absorber, 4...Absorbent cooler, 5...
...Absorbent regenerator, 6...Anolyte circulation line, 7
...Anorite line, 8...Air line, 9...
・Absorbent circulation line, 10...Exhaust gas line, 11・
...Water line, 12...Exhaust gas purifier.

Claims (1)

[Claims] 1. The exhaust gas from the oxidizer electrode of the fuel cell is brought into contact with a water absorbent, the water vapor contained in the exhaust gas is absorbed into the water absorbent, and then the absorbed moisture is used as fuel. A method of operating a fuel cell, characterized in that the fuel cell is supplied to an electrode. 2. In claim 1, the exhaust gas is brought into contact with the water absorbent maintained at a temperature lower than the temperature of the exhaust gas, and the temperature of the absorbent is raised by heat generated from the fuel cell to absorb the water. A method for operating a fuel cell, which comprises increasing the water vapor pressure of water contained in an absorbent to separate water from the absorbent, and then supplying the separated water to a fuel electrode. 3. The method of operating a fuel cell according to claim 1 or 2, wherein the water absorbent is concentrated sulfuric acid. 4. In claim 1, the water is separated from the absorbent by introducing the absorbent formed by absorbing moisture from the exhaust gas to a membrane separation device, and the separated moisture is supplied to the anorite. A method of operating a fuel cell characterized by: 5. In any one of claims 1 to 4, the fuel cell is an acidic electrolyte methanol fuel cell using sulfuric acid as an electrolyte, and uses an anolite as an absorbent to absorb water. 1. A method of operating a fuel cell, characterized by supplying the fuel to a fuel electrode.