JP4636301B2 - Fuel tank and fuel cell system using the same - Google Patents

Description

  The present invention relates to a fuel tank for storing and supplying methanol (liquid fuel) as a fuel in a direct methanol fuel cell system, for example, and further to a fuel cell system provided with such a fuel tank.

  A fuel cell is a power generation device that generates power by electrochemically reacting a fuel fluid such as hydrogen gas or methanol with an oxidizing fluid (oxygen contained in air). For example, in the case of a solid polymer type fuel cell, each power generator portion has a structure in which an electrolyte membrane made of a solid polymer is sandwiched between an oxygen side electrode and a fuel side electrode. Air is supplied to supply the fuel, fuel fluid is supplied to the fuel side electrode, and power generation is performed by the electrochemical reaction.

  During power generation, in a polymer electrolyte fuel cell, ions (protons) move through an electrolyte membrane that is an ion exchange membrane and functions as a proton conductor membrane, and reacts with oxygen on the oxygen side electrode to generate a current. At the same time, water is generated at the oxygen side electrode. The power generation part of a fuel cell is called an electrolyte membrane / electrode assembly or MEA (Membrane and Electrode Assembly), and this electrolyte membrane / electrode assembly is a separator in which a fuel fluid channel and an air channel are formed. A fuel cell having a stacked structure (stacked structure) is configured by stacking a plurality of power generation cells as a power generation cell.

  The above-described fuel cell has been attracting attention in recent years as a clean power source in which the product generated by power generation is water and does not pollute the environment. For example, in a large system such as an electric vehicle or a residential power system While it is expected to be put to practical use, taking advantage of the small size and light weight of the polymer electrolyte fuel cell, its application as a power source for portable electronic devices such as notebook personal computers is also being studied.

  By the way, in a fuel cell used for such a portable electronic device or the like, a direct methanol fuel cell system using methanol as a fuel, which is easier to handle than hydrogen gas, is considered advantageous. In this direct methanol fuel cell system, the fuel tank attached to the electronic device is removed to replenish methanol as the fuel, the fuel tank filled with methanol is attached to the electronic device, and the methanol in the fuel tank is used as fuel. Electric power is generated by supplying the battery.

  In this case, in order to supply the methanol in the fuel tank to the fuel cell, it is necessary to push the methanol in the fuel tank to the outside. It is used. However, when such a method is adopted, there is a problem that driving power for driving the liquid feeding pump is required, and the energy efficiency of the fuel cell is lowered.

Thus, as a structure for supplying methanol without requiring driving power of the fuel cell, for example, a fuel tank having a structure in which methanol inside is mechanically pushed out has been proposed (see, for example, Patent Document 1). In the technique described in Patent Document 1, the fuel tank has a cylinder structure, and a spring is installed and pressed by a plunger (intermediate wall) to push out the internal fuel (methanol). Or the fuel tank etc. of the structure which isolate | separates the inside of a fuel tank into two phases by a partition, and extrudes methanol inside with an elastic membrane are proposed (for example, refer patent document 2 etc.). In Patent Document 2, a flexible elastic membrane that can be stretched and contracted is set in a container, and the liquid fuel is stored in the membrane, so that the liquid fuel can be used without using other energy by utilizing the tension of the elastic membrane. A fuel tank for discharging is disclosed. By adopting these techniques, fuel can be supplied without installing a pump or the like for sucking the liquid fuel in the fuel tank on the fuel cell system side.
Japanese Patent Laid-Open No. 4-223058 JP 2000-314376 A

  However, in the method using the elastic force of a spring or an elastic body, it is difficult to apply a uniform pressure, and in particular, methanol cannot be pushed out of the fuel tank at a constant pressure. For example, the applied pressure is greatly different between a state where the spring is fully compressed or a state where the elastic body is fully extended and a state where compression or extension is restored to some extent. In a fuel cell, in order to generate electric power stably, it is desired that liquid fuel is supplied at a constant pressure, and fluctuations in the fuel supply pressure hinder stable operation. In addition, when the amount of liquid fuel in the fuel tank becomes small, there is a problem that the elastic force is almost lost and it is difficult to take out the liquid fuel completely.

  The present invention has been proposed to solve such problems of the prior art, and liquid fuel can always be pushed out at a constant pressure, without using electric energy such as a liquid feed pump, It is an object of the present invention to provide a fuel tank and a fuel cell system capable of stably operating the fuel cell. It is another object of the present invention to provide a fuel tank and a fuel cell system that can discharge the liquid fuel therein to the end and can increase the operation time per filling.

In order to achieve the above-described object, the fuel tank of the present invention has two spaces partitioned by a partition wall, in which liquid fuel is accommodated in one space and a low boiling point solvent is enclosed in the other space. The partition wall is movable so that the liquid fuel and the low-boiling point solvent are not mixed with each other and can be moved in a state where pressure balance is maintained. The low-boiling point solvent is a mixed solvent of dimethyl ether and diethyl ether. Yes, the amount of dimethyl ether added is an amount that does not remain as a liquid when the space in which the low-boiling point solvent is sealed becomes maximum, and the partition wall is pressed by the vapor pressure of the low-boiling point solvent, and the liquid fuel is pushed out. It is characterized by.
The fuel cell system of the present invention, a fuel cell, the fuel cell system including a fuel tank for supplying liquid fuel is a fuel to the fuel cell, fuel tanks, the two spaces partitioned by the partition The liquid fuel is accommodated in one space, the low boiling point solvent is sealed in the other space, and the partition wall has a sealing property and a pressure balance so that the liquid fuel and the low boiling point solvent are not mixed. It has mobility that can be moved in a maintained state, and the low boiling point solvent is a mixed solvent of dimethyl ether and diethyl ether, and the amount of dimethyl ether added is the maximum when the space in which the low boiling point solvent is enclosed becomes maximum. It is an amount that does not remain as a liquid, and is characterized in that the partition wall is pressed by the vapor pressure of the low boiling point solvent and the liquid fuel is pushed out.

In the fuel tank having the above configuration, liquid fuel is pushed out by using the vapor pressure of a low boiling point solvent that is a mixed solvent of dimethyl ether and diethyl ether, so there is no need to use a liquid feed pump or the like, and the drive No power is required. Further, in the fuel tank having the above configuration, the vapor pressure of the low boiling point solvent that is always enclosed is applied to the partition wall, and the vapor pressure is constant if the operating condition (for example, the operating environment temperature) is constant, and is always constant. Liquid fuel is pushed out at a pressure of. The extrusion by the vapor pressure of the low boiling point solvent is kept constant even when the remaining amount of the liquid fuel decreases, and therefore the liquid fuel in the fuel tank is pushed out quickly to the end.

In the fuel tank and the fuel cell system of the present invention, a partition wall having sealing properties and mobility for liquid fuel and a low boiling point solvent is provided, and the vapor pressure of the low boiling point solvent which is a mixed solvent of dimethyl ether and diethyl ether is used. Since liquid fuel is pushed out and supplied, liquid fuel can always be pushed out at a constant pressure, and the fuel cell can be stably operated without using electric energy such as a liquid feed pump. . In addition, since the pressurization by the vapor pressure of the low boiling point solvent is continued without changing the remaining amount of the liquid fuel, it is possible to discharge the liquid fuel in the whole to the end, and it is possible to fill up per one filling. It is possible to extend the operation time of the fuel cell. Furthermore, since the amount of dimethyl ether added is such that it does not remain as a liquid when the space in which the low-boiling solvent is enclosed is maximized, an appropriate pressure can be applied to the partition wall over a wide operating temperature range. it can.

  Hereinafter, embodiments of a fuel tank and a fuel cell system to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 shows an example of a fuel tank to which the present invention is applied. The fuel tank 1 of the present embodiment is a so-called plunger-type pressurized fuel tank, and the interior of the outer container 2 is partitioned by a partition wall (plunger) 3. Each space partitioned by the partition walls 3 is a space A (in this example, the space on the left side in the figure) containing liquid fuel (for example, methanol), and a space B (in the figure, in which a low boiling point solvent is enclosed). Right space).

  The outer container 2 is formed of a rigid material, for example, a metal, a resin such as polyethylene or polypropylene. The outer container 2 is not limited to this, and can be formed of any material. However, the outer container 2 needs to be a pressure-resistant container that can withstand the vapor pressure of the low boiling point solvent enclosed in the space B. It is preferable to use a metal container.

  The partition wall 3 has a sealing property such that the liquid fuel accommodated in the space A and the low boiling point solvent sealed in the space B do not mix, and can be operated in a state where pressure equilibrium is maintained. It is a partition of a formula. The movable partition 3 moves in the left-right direction in the figure in the exterior container 2 by increasing or decreasing the liquid fuel. For example, when the liquid fuel is refilled in the fuel tank 1, the partition wall 3 slides in the right direction in the drawing as the liquid fuel is filled. When the partition wall 3 reaches the inner wall surface at the right end of the outer container 2, the fuel tank 1 becomes full. When the liquid fuel in the fuel tank 1 is supplied to the fuel cell, the partition wall 3 is slid leftward in the drawing by being pushed by the vapor pressure of the low boiling point solvent in the space B. Along with this, the liquid fuel in the space A is pushed out from the discharge port 2a.

  In order to supply the liquid fuel by the above-described operation, it is necessary to enclose a low boiling point solvent having an appropriate vapor pressure in the space B. Hereinafter, this low boiling point solvent will be described.

  As shown in FIG. 2, the movable partition 3 moves due to the balance between the pressure in the space A and the pressure in the space B. If the pressure in the space B is larger than the pressure in the space A, the partition wall 3 moves to the left in the figure, and the liquid fuel in the space A is pushed out. Here, since the space A is opened to the atmosphere when the fuel is supplied, the inside pressure becomes atmospheric pressure. Therefore, the low boiling point solvent only needs to have a vapor pressure exceeding the atmospheric pressure in the operating temperature range.

However, if the vapor pressure of the low boiling point solvent is too high, there is a disadvantage caused by sudden pressure application, so it is preferable that the vapor pressure is not too high. Ideally, the vapor pressure of the low boiling point solvent slightly exceeds the atmospheric pressure, and a differential pressure of about 0.1 atm is always applied to the partition wall 3. From this point of view, the low-boiling vapor pressure _{P A} in the solvent is preferably from 1 atm _{<P A} ≦ 1.5 atm, and more preferably 1 atm _{<P A} ≦ 1.2 atm.

    Any low boiling point solvent can be used as long as it satisfies the above-mentioned conditions of vapor pressure. However, in consideration of actual use, the metal outer container 2 is corroded. It is necessary to consider that there is no absence, low toxicity, and low cost. Examples of the low boiling point solvent that satisfies these conditions include dimethyl ether and diethyl ether.

  As shown in FIG. 3, dimethyl ether has a high vapor pressure even at room temperature, and is suitable for applying pressure to the partition walls 3 particularly when used in a low temperature range. However, the vapor pressure becomes too high when the operating temperature is high. On the other hand, as shown in FIG. 4, the vapor pressure of diethyl ether does not exceed the atmospheric pressure up to about 38 ° C. and pressure cannot be applied to the partition wall 3. Appropriate pressure can be applied to the partition 3.

  Considering these facts, it can be said that it is preferable to use a mixed solvent in which dimethyl ether and diethyl ether are mixed. By using these mixed solvents, an appropriate pressure can be applied to the partition walls over a wide use temperature range. In this case, if the amount of dimethyl ether is too large, the pressure may increase excessively in the high temperature range, so that it is preferable to set the amount of each low-boiling solvent used in consideration of this. Specifically, the amount may be such that dimethyl ether does not remain as a liquid when the space B in which the low-boiling point solvent is enclosed is maximized.

  In the fuel tank 1 having the above configuration, the partition wall 3 is pressed by the vapor pressure of the low boiling point solvent in the space B, the liquid fuel in the space A is pushed out, and supplied to the fuel cell system side through the discharge port 2a. At this time, a differential pressure between the vapor pressure of the low-boiling point solvent and the atmospheric pressure is always applied to the partition wall 3, and quantitative fuel supply at a constant pressure is realized. Further, the differential pressure is applied to the partition wall 3 without changing even if the liquid fuel in the space A decreases, so that the liquid fuel in the space A is pushed out to the end.

  The pressurized supply of the low boiling point solvent by the vapor pressure is applicable not only to a plunger type fuel tank but also to a balloon type fuel tank. FIG. 5 shows an application example to a balloon type fuel tank. A fuel tank 10 shown in FIG. 5 is composed of an outer container 11 and an inner container 12 and has a double structure. The outer container 11 is formed of a rigid material, such as a metal. The inner container 12 is formed of a stretchable soft material such as a balloon, swells by injecting liquid fuel, for example, methanol, expands to substantially coincide with the outer container 11, and stores methanol as liquid fuel.

  In the fuel tank 10, a connector 13 is attached in order to fill the interior container 12 with liquid fuel and take out the liquid fuel in the interior container 12 to the fuel cell system side. The connector 13 is connected to a connector on the fuel cell system side and constitutes a fuel flow path. Therefore, the liquid fuel in the interior container 12 is supplied to the fuel cell of the fuel cell system through the connector 13.

  Also in the fuel tank 10 having the above-described configuration, by sealing the low boiling point solvent in the space between the outer container 11 and the inner container 12, the inner container is utilized using the vapor pressure of the low boiling point solvent as in the previous embodiment. It is possible to extrude the liquid fuel in 12 at a constant pressure.

  The fuel tank having the above-described configuration can be incorporated in a fuel cell system as shown in FIG. Hereinafter, this fuel cell system will be described.

  The fuel cell system of this example includes a fuel cell stack 21 that generates power, an air supply system that supplies air to the fuel cell stack 21, a fuel supply system that supplies fuel, a water treatment mechanism, and a control controller 22 that controls them. A DC-DC converter 23 driven by the power generated by the fuel cell stack 21 and a load 24 are included.

  The air supply system includes an air supply pump 25, and the fuel supply system includes a methanol tank 26, a fuel mixer 27, and an aqueous fuel solution circulation pump 28. Use a tank. The water treatment mechanism includes a gas-liquid separator 29, a moisture reservoir 30, and a treatment device 31, and an electromagnetic valve 32, a carbon dioxide remover 33, and the like are provided along with these.

  In the fuel cell system having the above-described configuration, methanol is pushed out from the methanol tank 26 and supplied to the fuel mixer 27. The aqueous fuel solution circulation pump 28 supplies the aqueous fuel solution to the fuel cell stack 21 from a fuel mixer 27 that mixes methanol and moisture to produce an aqueous fuel solution. The aqueous fuel solution consumed in the fuel cell stack 21 is circulated to the fuel mixer 27 provided with the carbon dioxide remover 33 and supplied again to the fuel cell stack 21 by the aqueous fuel solution circulation pump 28. The fuel mixer 27 provided with the carbon dioxide remover 33 separates carbon dioxide from the discharged liquid discharged by the fuel cell stack 21 and sends the carbon dioxide to the processing device 31. The processing device 31 discharges the carbon dioxide into the atmosphere. In a fuel cell system using a liquid fuel such as methanol, the liquid fuel itself is a cooling medium for the fuel cell, and the fuel cell system does not require a separate cooling channel. In addition, the fuel cell system using liquid fuel has an advantage that a back pressure valve is not required as compared with the case of using gaseous fuel such as hydrogen gas because the liquid fuel itself is incompressible.

  The air supply pump 25 takes in air as an oxidant from the atmosphere and supplies it to the fuel cell stack 21. The air used for power generation in the fuel cell stack 21 is separated from moisture by the gas-liquid separator 29 and discharged into the atmosphere via the processing device 31. The separated water is stored in the water reservoir 30 and then sent to the fuel mixer 27 to be used for generating the fuel aqueous solution. The electromagnetic valve 32 provided between the moisture reservoir 30 and the fuel mixer 27 adjusts the amount of water supplied from the moisture reservoir 30 to the fuel mixer 27.

  Further, the DC-DC converter 23 connected to the fuel cell stack 21 and the load 24 connected to the DC-DC converter 23 are driven by taking out power from the fuel cell stack 21. The controller 22 controls driving of each device constituting the fuel cell system.

  In the fuel cell system having the above configuration, the fuel tank described above is used as the methanol tank 26. The methanol accommodated in the space A partitioned by the partition wall 3 is pushed out by the partition wall 3 to which the vapor pressure of the low boiling point solvent is applied, and is discharged from the fuel tank (methanol tank 26). The discharged methanol is supplied to the fuel cell stack 21 and used for power generation. In such a fuel cell system, a methanol supply pump (liquid feed pump) for sucking up methanol in the methanol tank 26 is unnecessary, and the apparatus configuration can be simplified.

  As mentioned above, although specific embodiment of this invention was described, it cannot be overemphasized that this invention is not restricted to these embodiment, A various change is possible in the range which does not deviate from the summary of this invention. For example, each embodiment has been described with reference to the case where methanol is used as the fuel. However, the embodiments can be applied to all fuel tanks of fuel cell systems using liquid fuel such as hydrocarbon fuel.

It is a schematic sectional drawing which shows an example of the fuel tank to which this invention is applied. It is a schematic diagram which shows the mode of the vapor pressure added to a partition. It is a characteristic view which shows the vapor pressure curve of dimethyl ether with the vapor pressure curve of methanol. It is a characteristic view which shows the vapor pressure curve of diethyl ether with the vapor pressure curve of methanol. It is a schematic sectional drawing which shows the other example of a fuel tank. It is a block diagram which shows the structural example of a fuel cell system.

Explanation of symbols

1,10 Fuel tank 2 Outer container 2a Discharge port 3 Bulkhead 21 Fuel cell stack 26 Methanol tank

Claims (4)

It has two spaces partitioned by a partition wall, and liquid fuel is stored in one space, and a low boiling point solvent is sealed in the other space,
The partition wall is provided with a mobility capable of moving in a state in which a sealing property and a pressure equilibrium are maintained such that the liquid fuel and the low boiling point solvent are not mixed,
The low boiling point solvent is a mixed solvent of dimethyl ether and diethyl ether, and the addition amount of the dimethyl ether is an amount that does not remain as a liquid when the space in which the low boiling point solvent is enclosed is maximized,
Wherein said partition wall by the vapor pressure of the low boiling solvent is pressed, Ru said liquid fuel is pushed out
Fuel tank. The low boiling solvents, that have a vapor pressure exceeding the atmospheric pressure in the use temperature range,請 Motomeko 1 fuel tank according. The vapor pressure P _A of the low-boiling solvent, 1 atm <Ru P _A ≦ 1.5 atm der,請 Motomeko second fuel tank according. In a fuel cell system comprising a fuel cell and a fuel tank for supplying liquid fuel as fuel to the fuel cell,
The partition wall is provided with a mobility capable of moving in a state in which a sealing property and a pressure equilibrium are maintained such that the liquid fuel and the low boiling point solvent are not mixed,
The fuel tank has two spaces partitioned by a partition wall, and liquid fuel is accommodated in one space, and a low boiling point solvent is sealed in the other space, and the low boiling point solvent includes dimethyl ether and diethyl ether. The amount of the dimethyl ether added is an amount that does not remain as a liquid when the space in which the low-boiling-point solvent is enclosed is maximized,
Wherein the vapor pressure of the low boiling point solvent the partition is pressed, Ru said liquid fuel is pushed out
Fuel cell system.

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