JP2000208159A - Fuel cell system - Google Patents

Abstract

(57) [Problem] To provide a fuel cell system that efficiently recovers pure water required in a system and has excellent fuel controllability to a reformer. A fuel cell, a hydrogen supply system for supplying a hydrogen-containing gas to the fuel cell, an oxygen supply system for supplying an oxygen-containing gas to the fuel cell, and pure water for humidification in the fuel cell. A fuel electric field system comprising a humidifying pure water supply system 2 for supplying water, and heat exchange between the exhaust gas from the cathode of the fuel cell and the fuel contained in the fuel tank of the hydrogen supply system to be included in the exhaust gas A condenser 4 is provided for condensing the collected water and supplying the condensed water to a humidifying pure water supply system 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system, and more particularly to a fuel cell system that efficiently recovers pure water required in the system and has excellent fuel controllability to a reformer.

[0002]

2. Description of the Related Art A fuel cell system of this type is a device for directly converting the energy of fuel into electric energy. A fuel gas containing hydrogen is supplied to an anode of a pair of electrodes provided with an electrolyte therebetween. While supplying the fuel gas, the fuel gas containing oxygen is supplied to the other cathode, and electric energy is extracted from the electrodes by utilizing the following electrochemical reaction generated on the surface of the pair of electrodes on the electrolyte side.

[0003]

## STR1 ## anode ^{_{reaction: H 2 → 2H + + 2e}} - cathodic ^{reaction: 2H + + 2e - + (} 1/2) O 2 → H
₂ O As a device for generating a fuel gas supplied to a pair of electrodes, as a device for generating a fuel gas containing hydrogen, a reformer for converting methanol into steam to produce a fuel gas containing a large amount of hydrogen is used. 2. Description of the Related Art As an apparatus for generating a fuel gas containing oxygen, a compressor that takes in air to generate compressed air is known. Then, as shown in FIG. 4, for example, the compressed air from the compressor 7 is cooled by an aftercooler 8 and then supplied to the cathode (air electrode) of the fuel cell 1 while the methanol is supplied from the fuel tank 14 to the reformer 3. And the reformer 3
Is supplied to the anode (fuel electrode) of the fuel cell 1.

[0004]

In such a fuel cell system, pure water generated at the cathode (air electrode) is led to the water separation tank 2 together with the exhaust air, where it is separated into gas and liquid. While the water is guided to the reformer 3 and subjected to combustion or the like, the pure water separated in the water separation tank 2 is used for humidifying the fuel cell 1.

The pure water for humidification supplied to the fuel cell 1 from the water separation tank 2 is subjected to humidification, and then included in the exhaust air from the air electrode in the form of steam, which is returned to the water separation tank 2 again. It is.

However, in the conventional fuel cell system, the pure water for humidification returned to the water separation tank 2 cannot be condensed here, and is contained in the exhaust air to the reformer 3 as it is. Will be discharged outside. Therefore, the amount of pure water for humidification is insufficient with pure water separated and recovered by the water separation tank 2, and a separate pure water supply system is required.

The present invention has been made in view of such problems of the prior art, and efficiently recovers pure water required in a system and has excellent fuel controllability to a reformer. To provide a fuel cell system.

[0008]

According to a first aspect of the present invention, there is provided a fuel cell system comprising: a fuel cell; a hydrogen supply system for supplying a hydrogen-containing gas to the fuel cell; In a fuel cell system including an oxygen supply system that supplies an oxygen-containing gas to a fuel cell, and a humidification pure water supply system that supplies humidification pure water to the fuel cell, exhaust gas from the cathode of the fuel cell is provided. A condenser that supplies heat to the fuel contained in the fuel tank of the hydrogen supply system to condense water contained in the exhaust gas and supplies the condensed water to the pure water supply system for humidification. Features.

When the fuel cell is humidified by the humidifying pure water supply system, the pure water after the humidification is discharged from the fuel cell in a state of being contained in the exhaust gas as water vapor.
In the described invention, the exhaust containing water vapor is cooled by the fuel contained in the fuel tank to condense the water vapor, and this condensed water, that is, pure water is supplied to the pure water supply system for humidification. Pure water is not taken out of the system, and pure water can be supplied in the fuel cell system. As a result, a separate pure water supply system can be omitted, and the fuel cell system is excellent in cost and simplification of the system configuration.

(2) Although not particularly limited in the invention described in claim 1, the fuel cell system according to claim 2 includes a heat exchanger that heats the fuel that has passed through the condenser. And

In the fuel cell system according to the first aspect of the present invention, when the exhaust from the cathode of the fuel cell is cooled by the fuel, the fuel is heated to be in a gas-liquid mixed state (gas-liquid two-layer state). When the fuel in the gas-liquid mixed state is supplied to the reformer, it becomes relatively more difficult to control the fuel supply amount and the fuel pressure as compared with the state, but in the invention according to claim 2, the fuel passes through the condenser. The fuel in the mixed gas-liquid state is vaporized by being heated by the heat exchanger, so that the controllability of the fuel is improved.

(3) The heat exchanger according to the second aspect of the present invention is not particularly limited, but in the fuel cell system according to the third aspect, the heat exchanger is a reformer for the hydrogen supply system. The fuel cell system further includes a first heat exchanger that exchanges heat between the generated hydrogen-containing gas and the fuel.

Further, in the fuel cell system according to the present invention, the heat exchanger includes a second heat exchanger for exchanging heat between the oxygen-containing gas compressed by the compressor of the oxygen supply system and the fuel. It is characterized by including.

Further, in the fuel cell system according to the present invention, the heat exchanger includes a third heat exchanger that exchanges heat between the fuel and cooling water of a cooling system for cooling the fuel cell. Features.

According to a third aspect of the present invention, the temperature of the hydrogen-containing gas generated in the reformer is 300 ° C. to 400 ° C. when methanol is used as a fuel. Although the temperature of the oxygen-containing gas compressed by the method depends on the supply amount of the oxygen-containing gas to the fuel cell and the suction temperature, generally, 150 ° C. or more can be expected. In the invention according to claim 6, the temperature of the cooling water in the cooling system is 80 ° C to 85 ° C, which is the control temperature of the fuel cell. Therefore, for example, if the fuel is methanol (boiling point is 64.7 ° C.)
In this case, it is possible to completely vaporize using at least one of the first to third heat exchangers.

(4) When the fuel cell system is started, the heat exchanger often has a relatively low temperature, and in addition to the amount of heat for vaporizing the fuel, the amount of heat taken by the equipment is required. Become. For this reason, in the fuel cell system according to the fifth aspect, the compressor has means for decreasing the compression efficiency and increasing the discharge temperature of the oxygen-containing gas.

For example, a communication pipe is provided between the suction port and the discharge port of the compressor, and at the time of starting the system, the communication pipe is opened to reduce the efficiency of the compressor. This allows
The temperature of the oxygen-containing gas discharged from the compressor increases.
As another means, the amount of heat can be increased by, for example, increasing the rotation speed of the compressor higher than in a steady state and increasing the air flow rate.

[0018]

According to the first aspect of the present invention, pure water for humidification is not taken out of the system, and pure water can be supplied in the fuel cell system. Can be omitted, and the fuel cell system is excellent in cost and simplification of the system configuration.

In addition, according to the second aspect of the invention, the fuel in the gas-liquid mixed state passing through the condenser is vaporized by being heated by the heat exchanger, so that the fuel supply amount and the fuel pressure , Etc., will be improved. As a result, it can be expected that the vaporizer included in the reformer is omitted or reduced in capacity.

According to the third, fourth and sixth aspects of the present invention, the fuel in the gas-liquid mixed state is vaporized by utilizing the amount of heat in the fuel cell system. There is no need to provide a separate dedicated heating device.

According to the fifth aspect of the present invention, the fuel can be completely vaporized even at the time of starting the fuel cell system, and the fuel controllability at the time of starting is further improved.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a block diagram showing an embodiment of a fuel cell system according to the present invention, and FIG. 3 is a graph showing the amount of saturated steam of air with respect to pressure for each temperature.

First, the fuel cell system according to the present embodiment
A fuel cell 1 provided with a counter electrode with an electrolyte interposed therebetween;
Compressed air (oxygen-containing gas of the present invention) from the compressor 7 is supplied to the cathode side of the fuel cell 1, and hydrogen-containing gas from the reformer 3 is supplied to the anode side.

The compressor 7 takes in outside air or the like, compresses it to about 0.5 to ² kg / cm ² according to the load of the system, and supplies it to the fuel cell 1. The type of the compressor is not particularly limited. A piston type compressor, a scroll type compressor, a turbo type compressor or the like can be used.

The air supplied to the fuel cell 1 is 80 to 85
C. is desirable, but since the air compressed by the compressor 7 is usually 150 ° C. or higher, the after-cooling is performed between the compressor 7 and the fuel cell 1 in order to cool it to the above temperature range. A cooler 8 is provided. As the aftercooler 8, any of a water-cooled type and an air-cooled type can be used.

On the other hand, the reformer 3 includes, for example, a fuel tank 1
The fuel contained in the fuel gas is converted into a fuel gas containing a large amount of hydrogen by steam reforming the methanol contained in the fuel gas. Simultaneously proceeding, a reforming section that generates a reformed gas containing hydrogen and carbon dioxide, and unreacted carbon monoxide and water in the reformed gas obtained in this reforming section are subjected to the same reforming reaction. And a shift unit that is modified into hydrogen and carbon dioxide to generate a fuel gas having a high hydrogen content. The supply of methanol from the fuel tank 14 to the reformer 3 is performed by the fuel pump 11.

[0027]

Embedded image Methanol reaction: CH ₃ OH → CO + 2H
_{2 -21.7kcal} / mol modification _{reaction: CO + H 2 O → CO} 2 + H 2 +
9.8 kcal / mol Total reaction: CH ₃ OH + H ₂ O → CO ₂ +
3H ₂ -11.9 kcal / mol Further, the reformer 3 is provided with a combustor having a burner for heating the reaction section in the reforming section and the shift section described above. A part of the generated fuel gas and the exhaust gas from the fuel cell 1 are fed, and the unreacted hydrogen gas in the exhaust gas is burned here.

In addition to the hydrogen gas, air from the compressor 7 (exhaust air introduced from the fuel cell 1 through the water separation tank 2 in this embodiment) is also supplied to the combustor as combustion air. Supplied.

In the fuel cell 1, the compressed air introduced into the cathode (air electrode) and the hydrogen-containing gas introduced into the anode (fuel electrode) undergo the following electrochemical reaction on the electrode surface with the electrolyte interposed therebetween. Extracts electric energy.

[0030]

Embedded anode ^{_{reaction: H 2 → 2H + + 2e}} - cathodic ^{reaction: 2H + + 2e - + (} 1/2) O 2 → H
₂ O At this time, pure water stored in the water separation tank 2 is supplied to the fuel cell 1 for humidifying the compressed air. Further, in the above reaction, pure water generated on the cathode side and excess exhaust air on the cathode side are sent to the water separation tank 2.

At this time, in the present embodiment, a condenser (condenser) 4 is provided between the fuel cell 1 and the water separation tank 2, and the methanol sent from the fuel tank 14 is passed through the condenser 4. From water cathode to water separation tank 2
The exhaust air sent to is supercooled and condensed. In the water separation tank 2, the condensed water (pure water) condensed by the condenser 4 and the exhaust air are separated, and the exhaust air is guided to the reformer 3.

Further, between the condenser 4 and the reformer 3, the condenser 4 absorbs heat from the exhaust air to heat the methanol in a gas-liquid mixed state.
Two heat exchangers 5, 6 are provided.

One heat exchanger 5 (corresponding to a first heat exchanger of the present invention) exchanges heat between the hydrogen-containing gas reformed by the reformer 3 and methanol in a gas-liquid mixed state. The hydrogen-containing gas supplied from the reformer 3 to the fuel cell 1 is 300 to 4 when methanol is used as fuel.
The temperature is as high as 00 ° C.

The other heat exchanger 6 (corresponding to a second heat exchanger of the present invention) exchanges heat between air compressed by the compressor 7 and methanol in a gas-liquid mixed state. The compressed air discharged from the compressor is usually 150 ° C. or higher, depending on the load of the system (in other words, the air supply pressure to the fuel cell 1) and the temperature of the intake air.

Since the methanol heated by these two heat exchangers 5 and 6 has a boiling point of 64.7 ° C., it is completely vaporized and supplied to the reformer 3 in a vaporized state. .

Next, the operation will be described. The compressor 7 takes in the outside air, and divides it by 0.5 to 2 depending on the load of the system.
After compressing to kg / cm ² (temperature is 150 ° C. or higher), and after adjusting to an appropriate temperature of 80 to 85 ° C. through an after cooler 8,
This compressed air is supplied to the cathode side of the fuel cell 1. A temperature sensor 10 is provided at the inlet of the fuel cell 1 to measure the temperature of the compressed air, and cooling water supplied to the aftercooler 8 based on the measured value (a cooling system is not shown).
It is desirable to control the amount of

On the other hand, the methanol (environmental temperature) stored in the fuel tank 14 is supplied to the reformer 3 by the fuel pump 11, and 300 to 400 ° C. generated in the reformer 3.
Is supplied to the anode side of the fuel cell 1.
Then, electric power is extracted from the fuel cell 1 by an electrochemical reaction between these oxygen and hydrogen. At this time, pure water for humidification is supplied from the water separation tank 2 to the fuel cell 1.

Here, pure water is generated on the cathode side of the fuel cell 1 by the above-described electrochemical reaction. In order to recover the pure water, the pure water is guided to the water separation tank 2 together with the compressed air supplied to the cathode side. In the condenser 4 provided on the way, the condenser 4 is cooled by methanol at ambient temperature. FIG. 3 shows the amount of saturated water vapor of the air with respect to the air pressure for each temperature. At the outlet of the fuel cell 1, the discharged air is 80 to 85 ° C., which is cooled with methanol having a boiling point of 64.7 ° C. Then, condensed water is obtained by the pure water condensed amount shown in FIG.

Thus, the amount of pure water contained in the exhaust air and exhausted to the outside of the system can be suppressed, and the efficiency of collecting pure water in the system can be improved.

The methanol that has passed through the condenser 4 is in a gas-liquid mixed state because the condenser 4 absorbs heat. The methanol in such a state is heated by the hydrogen-containing gas (300 to 400 ° C.) from the reformer 3 by passing through the heat exchanger 5, and further heated by the heat exchanger 6.
Through the compressed air from the compressor 7 (150 ° C.
Above). Since the boiling point of methanol is 64.7 degrees Celsius as described above, it passes through these two heat exchangers 5 and 6 to be completely vaporized.
It is desirable to provide a temperature sensor 9 at the inlet of the reformer 3 as shown in the figure, and to determine whether or not the gas is completely vaporized by measuring the temperature of methanol.

As a result, the controllability of the amount and pressure of methanol supplied to the reformer 3 is improved.

When the fuel cell system is started, for example, the heat exchanger 6 and other devices are also relatively low in temperature. Therefore, in addition to the amount of heat for vaporizing methanol, the amount of heat deprived by such devices is required. It is said. For this reason, for example, a communication pipe is provided between the suction port and the discharge port of the compressor 7, and the efficiency of the compressor is reduced by opening the communication pipe at the time of starting. As a result, the temperature of the compressed air discharged from the compressor 7 increases, and the above-described increase in the amount of heat can be covered. In addition to this, for example, the heat quantity can be increased by increasing the rotation speed of the compressor 7 to a value higher than the steady state and increasing the air flow rate.

Second Embodiment FIG. 2 is a block diagram showing another embodiment of the fuel cell system of the present invention, and the same reference numerals are given to the same components as those in the first embodiment.

The present embodiment is different from the above-described embodiment in that methanol in a gas-liquid mixed state is heated using cooling water of a cooling system of the fuel cell 1. That is, the cooling water from the cooling system of the fuel cell 1 including the radiator 12 and the water pump 13 passes through the heat exchanger 6.

This cooling water has a temperature of the fuel cell 1 of 80 to 80.
Since the temperature is 85 ° C., the temperature almost reaches the outlet side of the fuel cell 1. Therefore, methanol having a boiling point of 64.7 ° C. can be vaporized. Also, the fuel cell 1
When the cooling system is used, the cooling water is cooled by the vaporization of methanol, so that the capacity of the radiator 12 can be reduced.

FIG. 2 shows a configuration in which the cooling water that has passed through the radiator 12 and the water pump 13 is guided to the heat exchanger 6.
If the cooling water that has passed through the heat exchanger 6 is directly introduced into the heat exchanger 6, the heating effect is greater.

The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a fuel cell system of the present invention.

FIG. 2 is a block diagram showing another embodiment of the fuel cell system of the present invention.

FIG. 3 is a graph showing the amount of saturated water vapor of air with respect to pressure for each temperature.

FIG. 4 is a block diagram showing a conventional fuel cell system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Water separation tank 3 ... Reformer 4 ... Condenser 5 ... Heat exchanger 6 ... Heat exchanger 7 ... Compressor 8 ... Aftercooler 9, 10 ... Temperature sensor 11 ... Fuel pump 12 ... Radiator 13 ... Water pump 14 ... Fuel tank

Claims (6)

[Claims] 1. A fuel cell, a hydrogen supply system for supplying a hydrogen-containing gas to the fuel cell, an oxygen supply system for supplying an oxygen-containing gas to the fuel cell, and supplying pure water for humidification to the fuel cell. A fuel electric field system having a humidifying pure water supply system, wherein heat exchange is performed between exhaust gas from the cathode of the fuel cell and fuel contained in a fuel tank of the hydrogen supply system, and water contained in the exhaust gas. And a condenser for supplying the condensed water to the humidifying pure water supply system. 2. The fuel cell system according to claim 1, further comprising a heat exchanger that heats the fuel that has passed through the condenser. 3. The heat exchanger according to claim 2, wherein the heat exchanger includes a first heat exchanger for exchanging heat between the hydrogen-containing gas generated in the reformer of the hydrogen supply system and the fuel. The fuel cell system as described. 4. The heat exchanger according to claim 2, wherein the heat exchanger includes a second heat exchanger for exchanging heat between the oxygen-containing gas compressed by the compressor of the oxygen supply system and the fuel. 3
The fuel cell system as described. 5. The fuel cell system according to claim 4, wherein said compressor has means for lowering the compression efficiency and increasing the discharge temperature of the oxygen-containing gas. 6. The heat exchanger according to claim 2, wherein the heat exchanger includes a third heat exchanger for exchanging heat between the fuel and cooling water of a cooling system for cooling the fuel cell. The fuel cell system according to any one of the above.