KR100671680B1 - Fuel cell system recoverying unreacted fuel - Google Patents

Abstract

The present invention relates to a fuel cell system, comprising: a main flow passage supplied with hydrogen-containing fuel from a fuel mixing section to a stack for generating electricity by an electrochemical reaction between hydrogen and an oxidant; A first flow passage through which the first fuel discharged from the stack flows into the fuel mixing unit; A second flow passage provided with second driving means for supplying a second fuel containing hydrogen to the fuel mixing portion; A supply line through which an oxidant is supplied to the stack from an oxidant supply unit; A concentration sensor and a temperature sensor for measuring the concentration and temperature of the fuel flowing along the flow path at the same location, respectively; And a BOP in which a drive control circuit for controlling the operation of the second driving means is controlled based on the sensed values provided from the concentration sensor and the temperature sensor. The power generation efficiency of the battery system can be maintained stably.

Pump, valve, drive control circuit, concentration sensor, temperature sensor

Description

FUEL CELL SYSTEM RECOVERYING UNREACTED FUEL}

1 is a block diagram showing a fuel cell system for recovering unreacted fuel according to the present invention;

2a to 2d is a configuration diagram in which the installation position of the sensor for detecting the concentration and temperature of the unreacted fuel in accordance with the present invention;

3 is a graph showing the correlation between the concentration of methanol fuel and temperature;

<Description of Symbols for Major Parts of Drawings>

10: stack

20: fuel storage unit

30: air supply

40: recovery tank

50: mixing tank

S1, S2: Sensor

The present invention relates to a fuel cell system that generates electricity by an electrochemical reaction of an oxidant such as hydrogen and oxygen, and more particularly to a fuel while recycling hydrogen-containing fuel, that is, unreacted fuel, which is not oxidized in a stack and is discharged. The present invention relates to a fuel cell system capable of maintaining a constant concentration of hydrogen-containing fuel supplied to a stack so as to stably maintain a power generation efficiency of a battery system.

Interest in fuel cells that generate electricity by electrochemically reacting hydrogen obtained from the oxidation of hydrogen-containing fuels such as natural gas, hydrogen-containing fuels such as methanol and oxygen in the air as a solution to environmental or resource problems. This has been concentrated. Such fuel cells may include phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), and solid oxide fuel cells (SOFCs), depending on the type of electrolyte used. ), Polymer electrolyte membrane fuel cells (PEMFC), alkaline fuel cells (AFC), and the like. The fuel cell may be applied to various applications such as mobile power, transportation, distributed generation, etc. according to the operating temperature, output range, etc. together with the fuel of the fuel used according to the type thereof.

Among the fuel cells described above, the polymer electrolyte fuel cell has excellent output characteristics, low operating temperature, fast start-up and response characteristics, and a unit cell which generates electricity by electrochemical reaction of hydrogen and oxygen. A built-in stack, a reformer for supplying the stack with hydrogen gas produced by reforming a hydrocarbon-based hydrogen-containing fuel such as methanol, ethanol or natural gas, and a hydrogen-containing fuel by pump operation And a fuel supply unit for supplying air to the reformer, and an air supply unit for supplying air to the stack.

On the other hand, direct methanol fuel cells (DMFCs) using hydrogen-containing fuels for direct power generation without the use of reformers to obtain hydrogen gas have the advantages of miniaturization as well as low operating temperatures and fast response characteristics. It is being researched and developed. The direct methanol fuel cell includes a stack containing unit cells that generate electricity through an electrochemical reaction between hydrogen and oxygen, a fuel supply unit supplying hydrogen-containing fuel to the stack by a pump operation, and air in the stack. It includes an air supply for supplying.

In a stack of a direct methanol fuel cell, hydrogen ions are produced by oxidizing hydrogen-containing fuel. Hydrogen-containing fuel that does not participate in this oxidation reaction, that is, unreacted fuel, is discharged from the stack together with carbon dioxide (CO ₂ ) and water (H ₂ O) generated as a result of the electrochemical reaction in the stack. This results in lower fuel efficiency in the system.

Therefore, in order to improve the use efficiency of hydrogen-containing fuel in a direct methanol type fuel cell, a technique of resupplying unreacted fuel to a stack has been disclosed. However, in this prior art, the concentration of hydrogen-containing fuel flowing into the stack could not be kept constant, and as a result, there was a problem in that the power generation efficiency of the fuel cell system could not be stably maintained.

The present invention is proposed to solve the conventional problems as described above, while maintaining the concentration of the hydrogen-containing fuel supplied to the stack to stabilize the power generation efficiency while not participating in the oxidation reaction in the stack and discharged unreacted The object is to provide a fuel cell system that can be fed back into the stack and recycled.

In order to achieve the above object, according to the present invention, a fuel cell system includes a main flow passage through which a hydrogen-containing fuel is supplied from a fuel mixing section to a stack for generating electricity by an electrochemical reaction between hydrogen and an oxidant; A first flow passage through which the first fuel discharged from the stack flows into the fuel mixing unit; A second flow passage provided with second driving means for supplying a second fuel containing hydrogen to the fuel mixing portion; A supply line through which an oxidant is supplied to the stack from an oxidant supply unit; A concentration sensor and a temperature sensor for measuring the concentration and temperature of the fuel flowing along the flow path at the same location, respectively; And a BOP in which a drive control circuit for controlling the operation of the second driving means is built by the sensed values provided from the concentration sensor and the temperature sensor.

Preferably, the first flow passage is provided with a recovery tank for storing the first fuel discharged from the stack or a first driving means for supplying the first fuel, wherein the concentration sensor and the temperature sensor are located at the rear end of the recovery tank or It is installed at the rear end of the first driving means.

In addition, the concentration sensor and the temperature sensor is installed at the front end of the fuel mixing unit, inside the fuel mixing unit or after the fuel mixing unit.

The drive means is a pump or a valve.

Preferably, the oxidant is oxygen.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In this case, the terms used in the description of the present invention are defined for convenience of description, and the terms used herein may vary according to the intention or custom of the person skilled in the art, but the technical components of the present invention. It should not be understood in a limiting sense.

For example, the term 'unreacted fuel' refers to a fuel discharged with water (H ₂ O) produced as a result of an electrochemical reaction in a stack of fuel cell systems, and the term 'high concentration fuel' refers to ethanol, methanol and natural It means a fuel of high purity selected from a hydrocarbon-based fuel group consisting of gas and not mixed with water, and the term 'hydrogen fuel' means a fuel supplied to a stack.

First, the fuel cell system according to the present invention is made for a direct methanol fuel cell (DMFC) that generates electricity by directly supplying a hydrogen-containing fuel such as ethanol, methanol or a hydrocarbon-based fuel such as natural gas to a stack. The present invention is not limited thereto, and may be employed in a polymer electrolyte fuel cell including a reformer for reforming a hydrogen-containing fuel to obtain hydrogen gas.

As illustrated in FIG. 1, a direct methanol fuel cell includes a stack 10 generating electricity by an electrochemical reaction between hydrogen and oxygen, and a fuel storage in which a high concentration fuel to be supplied to the stack 10 is stored. The unit 20, the air supply unit 30 for forcibly supplying an oxidant such as oxygen in the air to the stack 10, and a recovery tank 40 for recovering and storing unreacted fuel discharged from the stack 10. a recycle tank and a mixing tank 50 for supplying the stack 20 with hydrogen containing fuel mixed with the unreacted fuel discharged from the recovery tank 40 and the high concentration fuel discharged from the fuel storage unit 20. .

The stack 10 is provided with a plurality of unit cells including a polymer membrane 4 and an electrode membrane assembly (MEA) including cathode and anode electrodes 2 and 6 provided on both sides of the polymer membrane 4. . The anode 6 oxidizes the hydrogen-containing fuel supplied from the mixing tank 50 to generate hydrogen ions (H ⁺ ) and electrons (e ⁻ ). The cathode electrode 2 converts oxygen in the air supplied from the air supply unit 30 into oxygen ions and electrons. The polymer membrane 4 is a conductive polymer electrolyte membrane having a function of ion exchange of hydrogen ions generated from the anode electrode 6 to the cathode electrode 2 and preventing permeation of hydrogen-containing fuel. It has a thickness on the order of μm.

The electricity generated as a result of the electrochemical reaction of hydrogen and oxygen in the unit cell is output to an external circuit through an output terminal (not shown) provided to the stack 10, the hydrogen-containing fuel that does not participate in the oxidation reaction in the stack 10 That is, the unreacted fuel is discharged to the recovery tank 40 through the discharge unit together with carbon dioxide (CO ₂ ) and water (H ₂ O). Carbon dioxide contained in the unreacted fuel is discharged to the recovery tank 40 to the outside.

The air supply unit 30 is provided with a driving pump P for supplying air to the cathode electrode 2 of the stack 10, and mixes unreacted fuel between the recovery tank 40 and the mixing tank 50. First driving means for supplying to the tank 50 side, for example, a first flow passage in which the first pump P1 is provided is formed, and a high concentration fuel is provided between the fuel storage unit 20 and the mixing tank 50. The second flow path is provided with a second drive means, for example, the second pump (P2) for supplying to the mixing tank 50 side. Hydrogen-containing fuel generated by mixing unreacted fuel and high concentration fuel, respectively, supplied through the first channel and the second channel in the mixing tank 50 is supplied to the anode electrode 6 of the stack 10.

In addition, the fuel cell system controls the operation of driving means such as a driving pump P of the air supply unit 30, a first pump P1 of the first channel, a second pump P2 of the second channel, and the like. It includes a balance of plant (BOP) including a drive control circuit for. By the control operation of the drive control circuit, the operation of the driving means such as the driving pump P, the first pump P1, the second pump P2, and the like is controlled, whereby unreacted fuel flowing into the mixing tank 50 and The flow rate of the high concentration fuel is controlled so that the concentration of the hydrogen-containing fuel flowing into the anode electrode 6 of the stack 10 is kept constant, and the amount of air flowing into the cathode electrode 2 is controlled.

In the driving means, the first pump P1 and the second pump P2 may be replaced by a valve. Therefore, a first valve may be installed in the first channel instead of the first pump P1 and a second valve may be installed in the second channel instead of the second pump P2.

According to the present invention, in the first flow path, the effective fuel in the unreacted fuel discharged from the recovery tank 40 by the operation of the first pump (P1) between the recovery tank 40 and the first pump (P1). A concentration sensor S1 and a temperature sensor S2 are provided for sensing the concentration and temperature of the component, ie, the fuel component that can participate in the oxidation reaction in the stack. Preferably, the concentration sensor S1 and the temperature sensor S2 are located at the same point in the first flow path to sense the concentration and temperature of the unreacted fuel at the same location.

2A to 2D, the concentration sensor S1 and the temperature sensor S2 may include the rear end of the first pump P1, the front end of the mixing tank 50, the inside of the mixing tank 50, or the mixing tank 50. It may be installed in the same position at each rear end of the). Therefore, the concentration sensor S1 and the temperature sensor S2 detect the concentration and temperature of the active fuel component contained in the hydrogen-containing fuel as well as the unreacted fuel.

The concentration and temperature of the effective fuel component are detected as analog values by the concentration sensor (S1) and temperature sensor (S2), and these analog values are converted into digital values through an A / D converter (not shown) and then embedded in the BOP. Received by a digital signal processor (DSP).

In the BOP, the detected concentration of the effective fuel component from the digital value received by the DSP is compared with a reference concentration calculated by referring to a graph showing a correlation with temperature, and the driving control circuit is driven by the comparison result. The operation of the second driving means is controlled.

For example, referring to FIG. 3, which shows a correlation between methanol concentration and temperature, if the detection temperature of methanol is 40 ° C., the reference concentration of methanol corresponds to 1.0 M, and the detection temperature of methanol is 100 ° C. The corresponding methanol concentration is 4.0M.

Therefore, in the fuel cell system, when the temperature of the effective fuel component is detected by the temperature sensor S2, the reference concentration corresponding to the detected temperature is calculated with reference to the graph. The calculated reference concentration is compared with the detected concentration of the effective fuel component detected by the concentration sensor (S1). As a result of the comparison, the driving control circuit controls the operation of the driving means.

Referring to FIG. 1 again, in the state where the operation of the first pump P1 or the opening degree of the first valve is kept constant, the detected concentration of the effective fuel component contained in the unreacted fuel discharged from the recovery tank 40 By the comparison result of the reference concentration, the drive control circuit adjusts the supply amount of the high concentration fuel supplied to the mixing tank 50 by adjusting the operation of the second pump P2 or the opening degree of the second valve.

In a similar manner, as shown in FIGS. 2A to 2D, concentrations provided at the rear end of the first pump P1, the front end of the mixing tank 50, the inside of the mixing tank 50, or the rear end of the mixing tank 50, respectively. According to a result of comparing the detected concentration of the effective fuel component detected by the sensor S1 and the temperature sensor S2 and the reference concentration calculated from the detected temperature, the driving control circuit operates the second pump P2 or the second valve. By adjusting the opening degree of the high-concentration fuel supplied to the mixing tank 50 is adjusted.

That is, when the detected concentration of the effective fuel component is higher than the calculated reference concentration, the driving voltage of the second pump P2 is lowered or the opening degree of the second valve is kept small so that the high concentration of fuel supplied to the mixing tank 50 can be obtained. Reduce the supply On the contrary, if the detected concentration of the unreacted fuel is lower than the calculated reference concentration, the high concentration of the fuel supplied to the mixing tank 50 may be increased by increasing the driving voltage of the second pump P2 or keeping the opening of the second valve large. Increase the supply

As a result, while the unreacted fuel is supplied from the recovery tank 40 to the mixing tank 50 in a quantitative manner, the high concentration fuel whose feed amount is adjusted in proportion to the concentration of the effective fuel component is supplied to the mixing tank 50, so that the mixing tank ( The concentration of the hydrogen-containing fuel supplied from the 50 to the anode electrode 6 of the stack 10 can be kept constant so that the power generation efficiency of the fuel cell system can be stably maintained.

The foregoing is merely illustrative of preferred embodiments of the present invention and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. It must be recognized.

According to the present invention, by detecting the concentration and temperature of the unreacted raw material discharged without participating in the oxidation reaction in the stack, and by adjusting the supply of high concentration fuel based on the comparison result of the reference concentration and the detected concentration to the mixing tank By supplying, the concentration of hydrogen-containing fuel flowing from the mixing tank to the anode electrode of the stack can be kept constant, thereby recycling unreacted fuel and maintaining the power generation efficiency of the fuel cell system.

Claims (14)

A main flow passage through which a hydrogen-containing fuel is supplied from a fuel mixing section to a stack that generates electricity by an electrochemical reaction between hydrogen and an oxidant; A first flow passage through which the first fuel discharged from the stack flows into the fuel mixing unit; A second flow passage provided with second driving means for supplying a second fuel containing hydrogen to the fuel mixing portion; A supply line through which an oxidant is supplied to the stack from an oxidant supply unit; A concentration sensor and a temperature sensor for measuring the concentration and temperature of the fuel flowing along the flow path at the same location, respectively; And And a BOP in which a drive control circuit for controlling the operation of the second driving means is controlled by the sensed values provided from the concentration sensor and the temperature sensor. The method of claim 1, And a recovery tank for storing the first fuel discharged from the stack in the first flow passage. The method of claim 2, The concentration sensor and the temperature sensor are installed in the same position at the rear end of the recovery tank fuel cell system. The method of claim 2, And a first driving means for supplying a first fuel from the recovery tank to the fuel mixing section in the first flow passage. The method of claim 4, wherein The concentration sensor and the temperature sensor is installed in the same position at the rear end of the first driving means fuel cell system. The method of claim 1, The concentration sensor and the temperature sensor are installed in the same position in front of the fuel mixing unit fuel cell system. The method of claim 1, And the concentration sensor and the temperature sensor are installed at the same position within the fuel mixing unit. The method of claim 1, The concentration sensor and the temperature sensor is installed in the same position at the rear end of the fuel mixing unit fuel cell system. The method according to any one of claims 1 to 8, And the first driving means and the second driving means are pumps or valves. The method according to any one of claims 1 to 8, The fuel cell system, characterized in that the second fuel has a relatively high concentration compared to the first fuel. The method according to any one of claims 1 to 8, When the detected concentration of the fuel detected by the concentration sensor is lower than the reference concentration of the fuel calculated from the detected temperature detected by the temperature sensor, the supply amount of the second fuel supplied to the fuel supply unit is increased. Fuel cell system. The method of claim 11, And a supply amount of the first fuel supplied to the fuel mixing unit is kept constant. The method of claim 1, The oxidant is a fuel cell system, characterized in that oxygen. The method of claim 2, The recovery tank is provided with a discharge unit for discharging carbon dioxide contained in the first fuel discharged from the stack to the outside.

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