JP2000208160A - Fuel cell system and water collection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system allowing effective collection of pure water required in the system. SOLUTION: This fuel cell system has a fuel cell 3, a hydrogen supply system 1 for supplying a hydrogen-containing gas to the fuel cell 3, an oxygen supply system 7 for supplying an oxygen-containing gas to the fuel cell 3, a condenser 5 provided in an exhaust passage from the fuel cell 3, water tank 8 for storing water to be supplied in the system, a sensor 9 and a controller 10. The sensor 9 detects a changing amount of water stored in the water tank 8. When the change amount of the stored water detected by the sensor 9 becomes within a prescribed range, the controller 10 outputs a signal for increasing a pressure of the water-containing gas fed to the condenser 5.

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 capable of efficiently recovering pure water required in the system according to a water level.

[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, and comprises a fuel gas containing hydrogen at an anode of a pair of electrodes provided with an electrolyte membrane interposed therebetween. And a fuel gas containing oxygen is supplied to the other cathode, and electric energy is extracted from the electrodes by utilizing the following electrochemical reaction occurring on the surface of the pair of electrodes on the electrolyte membrane side ( For example, see JP-A-8-106914).

[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. After cooling the compressed air from the compressor with an aftercooler, the compressed air is supplied to the cathode (air electrode) of the fuel cell, while methanol is sent from the fuel tank to the reformer,
The hydrogen-containing gas reformed by the reformer is supplied to the anode (fuel electrode) of the fuel cell.

[0004]

In such a fuel cell system, first, it is necessary to supply water together with methanol in order to generate hydrogen in the reformer. Second, in order to wet the electrolyte membrane of the fuel cell, it is necessary to humidify at least one of the air and the reformed gas supplied to the fuel cell, and thus water is required. In order to circulate (supply) water consumed by these fuel cell systems in the system without supplying them from the outside, water is collected by condensing exhaust air of the fuel cell containing a large amount of water.

On the other hand, in order to increase the efficiency of the entire fuel cell system while maintaining the same output, it is necessary to reduce the power consumption of the compressor that supplies air. There are two methods for reducing the air flow rate and reducing the discharge pressure of the compressor, but the amount of oxygen required for the electrochemical reaction for extracting electricity in the fuel cell is determined. It cannot be reduced below the flow rate determined by the output of the fuel cell. Therefore, a method of improving the efficiency of the fuel cell system by reducing the discharge pressure of the compressor as much as possible is adopted.

However, when the discharge pressure of the compressor is reduced as described above, the air pressure applied to the condenser provided in the exhaust air flow path of the fuel cell also decreases, and the amount of condensed water decreases because the amount of saturated steam increases. I do. For this reason, in a fuel cell system that performs low-pressure operation, if the temperature of the cooling water supplied to the condenser is not sufficiently low, the amount of water that can be recovered by the condenser is smaller than the amount of water consumed in the system, There was a problem that pure water was insufficient.

[0007] The present invention has been made in view of such problems of the prior art, and has as its object to provide a fuel cell system capable of efficiently recovering pure water required in the system. Aim.

[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; A fuel cell comprising: an oxygen supply system for supplying an oxygen-containing gas to a fuel cell; a condenser provided in an exhaust passage from the fuel cell; and a water tank containing water for supply into the system. In the ground system, a sensor for detecting a fluctuation value of the water volume in the water tank, and a pressure of the moisture-containing gas sent to the condenser when the fluctuation value of the water volume detected by the sensor is within a predetermined range. And control means for outputting a signal for increasing the number.

When the discharge pressure of the compressor is reduced in order to increase the efficiency of the fuel cell system while maintaining a constant output, the amount of water that can be recovered by condensation decreases because the amount of saturated steam of the water-containing gas increases. . However, according to the first aspect of the present invention, the fluctuation value of the water volume in the water tank is detected by the sensor, and when the water recovery becomes necessary, the pressure of the water-containing gas sent to the condenser is increased. The amount of saturated water vapor decreases, thereby increasing the amount of water recovered. By providing such an operation mode for increasing the water recovery amount, the efficiency of the fuel cell system can usually be increased, and the water recovery amount can be increased and the water can be supplied in the system only when necessary. .

In the first aspect of the present invention, the moisture-containing gas includes an oxygen-containing gas (for example, air) and a hydrogen-containing gas (for example, reformed gas or hydrogen gas) discharged from a fuel cell. It may be.

The fluctuation value of the water volume in the water tank is
The purpose is to include a wide range of characteristic values relating to the remaining amount of water, such as the volume of water contained in the water tank itself and the amount of decrease in water volume per unit time.

(2) In the first aspect of the present invention, the method of increasing the pressure of the water-containing gas sent to the condenser is not particularly limited, and examples thereof include the methods described in the second to fourth aspects.

That is, in the fuel cell system according to the second aspect, the control means outputs a signal for increasing the pressure of the oxygen-containing gas to a compressor for supplying the oxygen-containing gas to the fuel cell. And

In the fuel cell system according to the present invention, since the pressure of the oxygen-containing gas sent from the compressor to the fuel cell is increased, the pressure of the exhausted oxygen-containing gas passing through the condenser is also increased, and the saturated steam As the volume decreases, the amount of water recovered increases.

In the fuel cell system according to a third aspect of the present invention, the control means controls a flow control valve provided at an outlet of the condenser to increase a pressure of the moisture-containing gas passing through the condenser. Is output.

In the fuel cell system according to the third aspect of the present invention, the pressure of the moisture-containing gas passing through the condenser is controlled by controlling the flow control valve at the outlet of the condenser (specifically, by reducing the valve opening). As the amount increases, the amount of saturated steam decreases, and the amount of recovered water increases. This method can be employed alone or in combination with the method described in claim 2.

According to a fourth aspect of the present invention, in the fuel cell system, the control means outputs a signal to the fuel cell to reduce its output and decrease the flow rate of the oxygen-containing gas.

In the fuel cell system according to the fourth aspect of the present invention, the output of the fuel cell is temporarily reduced to thereby reduce the flow rate of the oxygen-containing gas up to that time. As a result, the pressure of the oxygen-containing gas increases, and the pressure of the exhausted oxygen-containing gas passing through the condenser also increases, so that the amount of saturated steam decreases, and the amount of recovered water increases. According to the present invention, the compressor and its drive motor can be made highly efficient in accordance with the low-pressure and high-efficiency operation of the fuel cell system, and the efficiency of the entire system can be improved.

(3) In order to achieve the above object, a water recovery method in a fuel cell system according to claim 5 according to another aspect of the present invention passes through a condenser according to a water storage fluctuation amount in the system. It is characterized in that the pressure of the moisture-containing gas is controlled.

By controlling the pressure of the moisture-containing gas passing through the condenser, the amount of saturated water vapor of the gas changes, whereby the amount of condensation can be controlled.

In particular, when recovering water as in the method for recovering water in a fuel cell system according to claim 6, it is preferable to increase the pressure of the water-containing gas passing through the condenser. Since the saturated steam amount of the moisture-containing gas is almost inversely proportional to the pressure, increasing the pressure of the moisture-containing gas decreases the saturated steam amount, and as a result, increases the amount of water repair.

The term "water storage fluctuation amount" is intended to include a wide range of characteristic values relating to the remaining amount of water, such as the volume of water stored in a water tank itself and the amount of reduction in water volume per unit time.

[0023]

According to the first to sixth aspects of the present invention, a water recovery mode operation is performed in which the pressure of the moisture-containing gas passing through the condenser is increased when the remaining amount of water is low. When the fuel cell system is not needed, the low pressure mode operation is performed, so that pure water can be supplied in the fuel cell system while increasing the efficiency of the entire fuel cell system.

Further, by increasing the efficiency of the entire system, the capacity of the water tank itself and the capacity of the secondary battery can be reduced, and the system can be reduced in size and cost.

In addition, according to the fourth aspect of the invention, the compressor and its drive motor can be made highly efficient in accordance with the low-pressure and high-efficiency operation of the fuel cell system. Can be further improved.

[0026]

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 FIGS. 2 and 3 are flowcharts showing a control procedure of this embodiment.

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

The compressor 7 takes in outside air or the like, compresses the compressed air to about 0.5 to ² kg / cm ² according to the load of the system, and supplies the compressed air to the fuel cell 3. 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 3 is 80 to 85
C. is desirable, but the air compressed by the compressor 7 is usually 150 ° C. or higher, so that an aftercooler is provided between the compressor 7 and the fuel cell 3 in order to cool it to the above temperature range. It is desirable to provide such. As this type of aftercooler, any of a water-cooled type and an air-cooled type can be used.

On the other hand, the reformer 1 includes, for example, a fuel tank 1
Is a fuel gas containing a large amount of hydrogen by steam reforming the methanol contained in 2 and receives the supply of methanol and water to perform a decomposition reaction of methanol and a denaturation reaction of carbon monoxide represented by the following formula. 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 and water from the fuel tank 12 to the reformer 1 is performed by a pump 13.

[0031]

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 Although not shown in detail, the reformer 1 is provided with a combustor having a burner for heating the reaction section in the reforming section and the shift section described above. , Reformer 1
A part of the fuel gas generated by itself and the exhaust gas from the fuel cell 3 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 is supplied to the combustor as combustion air.

In the fuel cell 3, 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. As a result, electric energy is taken out to the secondary battery 4.

[0033]

Embedded anode ^{_{reaction: H 2 → 2H + + 2e}} - cathodic ^{reaction: 2H + + 2e - + (} 1/2) O 2 → H
₂ O At this time, pure water contained in the water tank 8 is supplied to the cathode side of the fuel cell 3 through the humidifier 2 for humidifying compressed air. The pure water generated on the cathode side in the above reaction and the excess exhaust air on the cathode side are sent to the condenser 5 (corresponding to the condenser of the present invention).

Cooling water for condensing exhaust air passing therethrough is sent to the condenser 5, and the cooling water is cooled by a radiator 6. The condensed water generated in the condenser 5 is collected in the water tank 8 and sent to the reformer 1 and the humidifier 2 by the pump 13 again. A flow control valve 11 is provided at an outlet pipe of the condenser 5, and its opening is controlled by a command signal from the control device 10.

The water tank 8 is provided with a water level sensor 9 for detecting the remaining amount of pure water stored in the water tank 8, and a detection signal from the water level sensor 9 is sent to the control device 10. The controller 10 takes in the remaining amount of pure water sent from the water level sensor 9, calculates the amount of change in the remaining amount of pure water, and determines whether or not to perform the water recovery mode operation.
The compressor 7, the secondary battery 4 and the flow control valve 11 are controlled.

Next, the operation will be described. As shown in FIGS. 2 and 3, when the operation of the fuel cell system is started and an output request command is input from an external device (steps 1 to 3).
2) The compressor 7 takes in the outside air, compresses it appropriately to 0.5 to ² kg / cm ² (temperature is 150 ° C. or more) according to the load of the system, and 80 to 8 kg through an aftercooler.
After a suitable temperature of 5 ° C., the compressed air is supplied to the cathode side of the fuel cell 3. On the other hand, the methanol (environmental temperature) contained in the fuel tank 12 is supplied to the reformer 1 as methanol + water by the pump 13, and the hydrogen-containing gas at 300 to 400 ° C. generated by the reformer 1 Battery 3
To the anode side. Then, electric power is extracted from the fuel cell 3 to the secondary battery 4 by an electrochemical reaction between these oxygen and hydrogen. At this time, from the water tank 8 to the fuel cell 3
Pure water is supplied via the humidifier 2 to the cathode side of.

The exhaust air on the cathode side of the fuel cell 3 is guided to the condenser 5 and cooled by the cooling water circulating through the radiator 6 to be collected as condensed water in the water tank 8. Further, pure water generated by the above-described electrochemical reaction is also included in this.

At this time, in this embodiment, first, the water level of the water tank 8 is measured by the water level sensor 9 (Steps 3 to 3).
6). The measurement of the water level is obtained by the amount of change in the water level (step 6) during a predetermined time (step 4). It is determined whether or not the operation in the water recovery mode is necessary based on the amount of increase or decrease of the water in the water tank 8 (step 7).

The amount of water recovered by the condenser 5 is obtained by adding the amount of water in the atmosphere, the amount of water for humidification, and the amount of water generated by the reaction of the fuel cell. It will be reduced. Among these, the amount of moisture in the atmosphere varies depending on the environmental state of the system operation, the amount of moisture for humidification is the amount of water determined by the operating state of the fuel cell 3, and the amount of moisture generated in the fuel cell 3 is It is determined by the output current of the fuel cell. Further, since the amount of water contained in the exhaust gas at the outlet of the condenser is determined by the temperature of the air cooled by the condenser 5 and the air pressure supplied to the condenser 5, the temperature of the cooling fluid (cooling water temperature) supplied to the condenser 5 and the air pressure It fluctuates by

Therefore, when the amount of water in the atmosphere is large,
When the output of the fuel cell 3 is large, when the cooling water temperature of the condenser 5 is low, and when the air pressure is high, the amount of recovered moisture increases, and in the opposite case, decreases. Therefore, if the output (or current) of the fuel cell 3, the cooling water temperature of the radiator 6, the inlet pressure of the fuel cell 3, and the amount of change in water in the water tank 8 are measured (step 10), The amount of water can be calculated backward, and if this is obtained, the amount of increase in the amount of recovered water due to the increase in air pressure can be calculated (steps 11 to 12). FIG. 6 shows an example of the relationship between the inlet water pressure of the fuel cell 3 and the recovered water amount thus obtained.

On the basis of the calculation result, the condenser 5 with respect to the amount of water that can be recovered according to the current environment and conditions.
The target value of the pressure at the outlet of is determined (step 13),
The output of the compressor 7 and the opening of the flow control valve 11 are adjusted so as to satisfy this target value (steps 14 and 15). As a result of this adjustment, the inlet pressure of the fuel cell 3 and the outlet pressure of the condenser 5 are measured, and it is determined whether or not these are the target pressures (steps 16 to 18).

By doing so, the amount of water recovered by the condenser 5 increases, so that the water level in the water tank 8 rises (steps 19 and 20), and when the water level becomes sufficient (step 19). 7) Return from the water recovery mode operation to the normal low pressure operation to improve the efficiency of the entire system (step 8).

Second Embodiment FIG. 4 is a flowchart showing another embodiment of the fuel cell system according to the present invention. The configuration of steps 1 to 12 of the first embodiment is the same. The configuration of the fuel cell system is the same as that of the first embodiment shown in FIG.
The maximum output of the compressor 7 is the minimum pressure required for the fuel cell system to obtain the rated output.

In the water recovery mode operation, the pressure of the exhaust air passing through the condenser 5 is increased in order to obtain the pressure of the condenser 5 necessary for water recovery as in the first embodiment described above. When the fuel cell 3 is operating at an air flow rate at which the compressor 7 cannot satisfy the discharge pressure, the output of the fuel cell 3 is temporarily reduced, and the discharge pressure is increased by reducing the air flow rate.

That is, when the operation mode is switched to the water recovery mode operation (steps 9 to 12), the capacity of the secondary battery 4 is measured (step 121), and when the charged amount of the secondary battery 4 is larger than the set value, the fuel After reducing the output of the battery 3 (steps 122 to 123), the compressor 7 and the flow control valve 1
1 to increase the pressure passing through the condenser 5. If the charge amount of the secondary battery 4 is smaller than the set value in step 122, the output of the fuel cell 3 cannot be reduced as it is, so the process once proceeds to steps 124 and 125 to increase the output of the fuel cell 3 once. After the amount of charge to the secondary battery 4 is increased, the above-described processing is executed.

In the present embodiment, the water recovery mode operation is performed precisely while controlling the charge amount of the secondary battery 4, and the compressor 7 and its driving motor are set to the minimum required for the fuel cell system. Therefore, the efficiency of the fuel cell system as a whole is improved, and the water recovery rate is also improved.

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 flowchart showing a control procedure of the embodiment of the fuel cell system of the present invention.

FIG. 3 is a flowchart showing a control procedure of the embodiment of the fuel cell system of the present invention.

FIG. 4 is a flowchart showing another embodiment of the fuel cell system of the present invention.

FIG. 5 is a graph showing an increase / decrease of recovered water with respect to an air pressure at a fuel cell inlet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reformer 2 ... Humidifier 3 ... Fuel cell 4 ... Secondary battery 5 ... Condenser 6 ... Radiator 7 ... Compressor 8 ... Water tank 9 ... Water level sensor 10 ... Control device 11 ... Flow control valve 12 ... Fuel tank 13 …pump

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 an exhaust passage from the fuel cell. A condenser, and a fuel electric field system including a water tank containing water for supply into the system, a sensor for detecting a fluctuation value of the water volume in the water tank,
Control means for outputting a signal for increasing the pressure of the water-containing gas sent to the condenser when a fluctuation value of the water volume detected by the sensor falls within a predetermined range, the fuel comprising: Battery system. 2. The fuel cell system according to claim 1, wherein said control means outputs a signal for increasing the pressure of the oxygen-containing gas to a compressor for supplying the oxygen-containing gas to the fuel cell. . 3. The control means outputs a signal to a flow control valve provided at an outlet of the condenser to increase the pressure of the water-containing gas passing through the condenser. 3. The fuel cell system according to 1 or 2. 4. The fuel cell system according to claim 1, wherein said control means outputs a signal to said fuel cell to reduce its output and decrease the flow rate of oxygen-containing gas. 5. A method for recovering water in a fuel cell system, comprising controlling the pressure of a water-containing gas passing through a condenser according to the amount of fluctuation in water storage in the system. 6. The method for recovering water in a fuel cell system according to claim 5, wherein when recovering the water, the pressure of the water-containing gas passing through the condenser is increased.