JP2989332B2 - Fuel cell system - Google Patents

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 improving start-up performance.

[0002]

2. Description of the Related Art Conventionally, as a method of supplying fuel to a fuel cell body in the above fuel cell system, generally, hydrogen gas from a high-pressure hydrogen cylinder is supplied to a pressure reducing valve (hydrogen supplied from a high-pressure hydrogen cylinder at a predetermined pressure). Pressure has been reduced) through a hydrogen supply passage provided.

However, in the above-mentioned fuel cell system, the high-pressure hydrogen cylinder has a low filling amount of hydrogen gas per unit volume, so that the number of times of replacing the cylinder increases, and the handling of the cylinder is poor. Had a problem of decreasing. Therefore, the following fuel cell system has been proposed. A system in which alcohol or naphtha is used as a fuel, and a fuel reformer for reforming alcohol or the like into hydrogen gas is provided in a passage for supplying the fuel, and hydrogen gas is supplied to a battery body. A system in which a tank containing a hydrogen storage alloy is provided instead of a high-pressure hydrogen cylinder, and hydrogen gas is supplied from the hydrogen storage alloy.

[0004]

However, the above-described fuel cell system has the following problems. With this system, although the volume density of the fuel is improved, a large-scale device such as a fuel reformer is additionally required, which leads to an increase in the size and cost of the device. With this system, the hydrogen storage alloy undergoes an endothermic reaction when releasing hydrogen gas. Therefore, unless heat is supplied from the outside, the equilibrium hydrogen pressure decreases and the amount of released hydrogen gas fluctuates.

Therefore, as disclosed in Japanese Patent Publication No. 56-26113 and US Pat. No. 4,826,741, a system is proposed which supplies exhaust heat from a fuel cell body to a hydrogen storage alloy to prevent a decrease in hydrogen gas release pressure. Have been. However, this system has no problem when the operation is in a steady state, but when the exhaust heat temperature is low such as at the start of operation of the fuel cell system, the heat supply is insufficient and the equilibrium hydrogen pressure of the hydrogen storage alloy does not increase. As a result, there has been a problem that hydrogen gas cannot be supplied smoothly at the time of starting operation or the like.

In view of the above, it is conceivable to use a hydrogen storage alloy having a high equilibrium hydrogen pressure. But,
In this case, as the ambient temperature of the device rises, the temperature of the hydrogen storage alloy also rises, and the pressure of the hydrogen gas rapidly rises. As a result, it is necessary to improve the pressure resistance of the tank storing the hydrogen storage alloy, and thus there is a problem that the manufacturing cost of the fuel cell system increases.

The present invention has been made in view of the current situation, and can supply hydrogen gas to a fuel cell body smoothly even at a low exhaust heat temperature at the start of operation, and at a low cost. It aims to provide a fuel cell system that can be manufactured.

[0008]

In order to achieve the above object, the present invention provides a fuel cell body having an oxygen electrode and a hydrogen electrode, and a method for supplying hydrogen to the hydrogen electrode of the fuel cell body during normal operation. The hydrogen storage alloy is configured to have a higher equilibrium hydrogen pressure than the main hydrogen storage alloy at the same temperature,
A hydrogen gas is supplied to the hydrogen electrode of the fuel cell body until the equilibrium hydrogen pressure becomes equal to that of the main hydrogen storage alloy, and an auxiliary hydrogen storage alloy is supplied with hydrogen gas from the main hydrogen storage alloy during a steady operation. It is characterized by the following.

[0009]

With the above configuration, at the start of operation of the fuel cell system, the auxiliary hydrogen storage alloy and the main hydrogen storage alloy are at the same temperature and both are fully filled with hydrogen gas.
Hydrogen gas is supplied to the fuel cell main body from an auxiliary hydrogen storage alloy having a high equilibrium hydrogen pressure. Therefore, even at the start of operation, a decrease in the hydrogen gas release pressure is suppressed, so that the hydrogen gas can be smoothly supplied to the fuel cell body.

When the supplied exhaust heat temperature rises and the equilibrium hydrogen pressure of the main hydrogen storage alloy becomes higher than the equilibrium hydrogen pressure of the auxiliary hydrogen storage alloy (in this case, the auxiliary hydrogen storage alloy is exhausted). Heat is not supplied), and hydrogen gas is supplied from the main hydrogen storage alloy to the fuel cell main body, and steady operation is started. Then, at this time, a part of the hydrogen gas from the main hydrogen storage alloy is supplied to the auxiliary hydrogen storage alloy, so that the auxiliary hydrogen storage alloy becomes full again during the steady operation. Therefore, even when the operation is started again or the main hydrogen storage alloy is replaced, the hydrogen gas is supplied from the auxiliary hydrogen storage alloy to the fuel cell main body, so that the smooth power generation is maintained.

In addition, since there is no need to increase the equilibrium hydrogen pressure of the main hydrogen storage alloy, it is possible to make the pressure-resistant container containing the main hydrogen storage alloy compact.

[0012]

【Example】

First Embodiment FIG. 1 is a schematic explanatory view showing a fuel cell system according to a first embodiment of the present invention, in which a fuel cell body 1, a main tank 2 containing a hydrogen storage alloy, and Are connected via a hydrogen gas supply passage 7. The hydrogen gas supply passage 7 is provided with a fuel valve 3a, a check valve 4, a sub-tank 5 containing a hydrogen storage alloy, and a fuel valve 3b in this order from the main tank 2 side.

The fuel cell body 1 has a structure in which many single cells each having a hydrogen electrode and an oxygen electrode are stacked, and the output thereof is 1 KW. The main tank 2 has a structure for supplying hydrogen to the fuel cell main body 1 during a steady operation of the fuel cell system. The main tank 2 contains a rare earth / nickel-based hydrogen storage alloy (equilibrium characteristic shown in FIG. 2A). Is filled in 10 kg.

The fuel valves 3a and 3b supply and stop hydrogen. The check valve 4 prevents the hydrogen gas in the sub tank 5 from being supplied to the main tank 2.
The sub-tank 5 has a structure for supplying hydrogen to the fuel cell main body 1 at the start of operation of the fuel cell system. The sub-tank 5 has a rare-earth / nickel-based hydrogen storage alloy (having an equilibrium characteristic shown in FIG. 2B). 500 g of the hydrogen storage alloy filled in the main tank 2 at the same temperature and higher in equilibrium hydrogen pressure).

In the figure, reference numeral 6 denotes a blower, which sends the exhaust heat of the battery to the main tank 2. Further, in this system, since a use temperature of 10 to 30 ° C. is assumed, a hydrogen storage alloy having the above-mentioned equilibrium characteristics is used. The operation of the fuel cell system having the above configuration will be described in detail below. When power is generated by the fuel cell, it is necessary to supply hydrogen gas and oxygen gas to the hydrogen electrode and the oxygen electrode in the fuel cell body 1. First,
To supply hydrogen gas to the hydrogen electrode, the fuel valves 3a and 3
b is opened. Then, due to the pressure difference between the fuel cell main body 1 and the sub tank 5,
Hydrogen gas is supplied from the sub tank 5 to the fuel cell body 1. At this time, the pressure of the main tank 2 is
Since it is lower, it is possible to prevent hydrogen gas from being supplied to the main tank 2 by the action of the reverse valve 4. On the other hand, on the oxygen electrode side, oxygen gas is dissolved in the electrolyte near the electrode, so that oxygen gas is supplied to the oxygen electrode. Accordingly, a reaction as shown in the following chemical reaction occurs in the fuel cell main body 1, and an electromotive force is generated although the output is low.

[0016]

Embedded image

Using the electric power thus generated, a blower (not shown) is operated to supply air continuously to the oxygen electrode. Then, when such an operation is started, the temperature of the hydrogen storage alloy in the sub-tank 5 decreases and the pressure in the sub-tank 5 decreases because the hydrogen storage alloy causes an endothermic reaction with the release of hydrogen gas. As a result, the hydrogen supply amount is slightly reduced, but since the equilibrium hydrogen pressure of the hydrogen storage alloy in the sub-tank 5 is high, there is no significant problem in the operation performance. Therefore, the operation is continued, and the temperature of the fuel cell main body 1 gradually increases due to the reaction.

Next, when the blower 6 is operated by the electromotive force, the exhaust heat of the fuel cell main body 1 is sent to the main tank 2, so that the temperature of the main tank 2 rises and the equilibrium hydrogen of the built-in hydrogen storage alloy is increased. The pressure gradually increases. Then, when the equilibrium hydrogen pressure of the main tank 2 becomes higher than the equilibrium hydrogen pressure of the sub tank 5, hydrogen gas is supplied from the main tank 2 to the fuel cell main body 1 via the check valve 4. Thereby, the steady operation is started.

Here, when the steady operation is started in this manner, the hydrogen gas from the main tank 2 is supplied to the sub tank 5
To the fuel cell body 1 through the sub-tank 5
Is gradually increased due to a hydrogen storage reaction or the like. Therefore, the same amount of hydrogen gas as the hydrogen gas released from the sub-tank 5 at the start of operation is stored in the hydrogen storage alloy of the sub-tank 5. That is, the hydrogen storage alloy in the sub-tank 5 has a feature that it releases hydrogen gas at the start of operation and stores the hydrogen storage alloy at the time of steady operation.
As a result, the hydrogen storage alloy in the sub tank 5 becomes full again, and the operation of the battery can be easily started at the next operation start.

The fuel cell system having the above structure is hereinafter referred to as (A) system. Comparative Example The configuration is the same as that of the above embodiment except that the sub tank 5 is not provided. The fuel cell system having such a structure is hereinafter referred to as (X) system. [Experiment] The relationship between battery output, hydrogen gas flow rate, line pressure, and time in the system (A) of the present invention and the system (X) of the comparative example was examined, and the results are shown in FIG.

As is clear from FIG. 3, the system (A) has less fluctuation in the line pressure (hydrogen gas pressure) and the hydrogen gas flow rate (hydrogen gas supply amount) at the start of operation than the system (X). Therefore, it is recognized that the time until the battery output reaches the rated output can be shortened. still,
In the above embodiment, the case where the ambient temperature is 10 to 30 ° C. has been described. However, when the system is used in a cold region, more remarkable effects can be obtained as compared with the conventional system. For example, the case of the above (A) system and (X) system will be described.

In the above-mentioned (A) system and (X) system, both having an equilibrium characteristic as shown by the line segment a in FIG. 2 are used as the hydrogen storage alloy of the main tank 2. In a hydrogen storage alloy having equilibrium characteristics, when the ambient temperature is 0 ° C. or lower, the equilibrium hydrogen pressure of the hydrogen storage alloy is lower than the atmospheric pressure, so that no hydrogen gas can be generated. Therefore, in the (X) system, unless the hydrogen storage alloy in the main tank 2 is heated,
It cannot be supplied to the fuel cell body 1 at all. On the other hand, in the case of the (A) system, the equilibrium hydrogen pressure of the hydrogen storage alloy in the sub-tank 5 is about 4 atm and is equal to or higher than the atmospheric pressure even when the ambient temperature becomes 0 ° C. or less. Therefore, it is possible to start the fuel cell system without heating.

Further, the fuel cell system of the present invention only needs to add a sub-tank and some of its associated parts to the conventional system, so that there is almost no increase in weight or volume. Further, as disclosed in Japanese Patent Application Laid-Open No. 56-26113, there is no need to employ a configuration in which fuel gas is burned to heat the hydrogen storage alloy, so that power generation efficiency may be reduced. Absent.

In addition, the present invention exhibits excellent effects even when the battery is operated continuously. This is as shown below. That is, in general, when the battery is operated continuously, there is no problem at all on the oxygen electrode side because air may be supplied by a blower or the like using a part of the generated electric power. It is necessary to replenish the consumed hydrogen gas in some way. Specifically, the operation of replacing the fuel tank is required. However, since such a fuel cell system assumes continuous operation, when replacing the fuel tank during power generation, the hydrogen gas supply stops and power generation stops unless the replacement work is performed quickly in the conventional system. Will stop. On the other hand, according to the system of the present invention, the hydrogen gas is supplied from the sub-tank 5 to the fuel cell main body 1 when the main tank 2 is replaced, so that there is an effect that the spare time of the main tank 2 can be spared. is there. [Other Matters] In the above embodiment, a rare earth / nickel-based hydrogen storage alloy is used as the hydrogen storage alloy.However, the present invention is not limited to this, and an iron-titanium or titanium-manganese alloy may be used. Needless to say, the same effects as in the above embodiment can be obtained.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to FIG. The members having the same functions as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. This is based on the following third embodiment,
The same applies to the fourth embodiment. As shown in FIG.
The structure is the same as that of the first embodiment except that the sub tank 5 is provided not in the hydrogen gas supply passage 7 but in a branch passage 10 branched from the hydrogen gas supply passage 7.

Experiments have confirmed that such a structure has the same effect as the first embodiment. Third Embodiment A third embodiment of the present invention will be described below with reference to FIG. As shown in FIG. 5, a hydrogen gas recirculation passage 12 for recirculating hydrogen gas from the sub tank 5 to the main tank 2 is provided.
2 has the same structure as that of the first embodiment except that a back pressure valve 11 is provided. Note that the specific operating pressure of the back pressure valve 11 must be set to be slightly lower than the withstand pressure of the container of the sub-tank 5, and is usually set to operate at about 10 to 30 atm. In the embodiment, the back pressure valve is set to 1
It is set to operate at 5 atm). Further, the back pressure valve 11 may be either a fixed pressure type or a variable type.

With this configuration, when the ambient temperature is 30
Even when the temperature is higher than or equal to ° C., it is possible to prevent a problem such as gas leak from occurring. This is for the following reason.
That is, if the ambient temperature is 30 ° C. or less, no problem occurs because the equilibrium hydrogen pressure of the hydrogen storage alloy in the sub tank 5 is as low as about 10 atm or less, as is apparent from FIG.
However, for example, when the fuel cell system is used in hot weather, the ambient temperature may increase to 50 ° C. or higher. When the ambient temperature becomes unexpectedly high as described above, the equilibrium hydrogen pressure rises, which causes problems such as hydrogen gas leakage. In such a case, a method is conceivable in which a relief valve is provided in the piping system, and when the hydrogen gas pressure exceeds a predetermined value, the hydrogen gas is released out of the system.

However, in this method, hydrogen gas (fuel) is used.
Since the fuel cell system is discarded, the economic efficiency of the fuel cell system decreases and the power generation efficiency decreases. further,
Since flammable gas is released, there is a problem in terms of safety. Therefore, when the sub tank 5 and the main tank 2 are connected via the hydrogen gas recirculation passage 12 provided with the back pressure valve 11 as in the third embodiment, the ambient temperature becomes 35%.
When the pressure in the sub tank 5 reaches 15 atm after the temperature rises to about ° C, the back pressure valve 11 is opened. At this time, since the gas pressure of the main tank 2 is about 3 atm and lower than that of the sub tank 5, hydrogen gas returns to the main tank 2. As a result, the pressure of the entire fuel cell system can be prevented from becoming equal to or higher than the set value without releasing the hydrogen gas to the outside of the fuel cell system. Therefore, it is possible to improve power generation efficiency and economy while improving safety of the fuel cell system.

Further, the fuel cell system of the present invention requires only a few additional components to the system shown in the first embodiment, so that there is almost no increase in weight and volume, and the production cost rises. Nor. (Fourth Embodiment) A fourth embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 6, a hydrogen gas recirculation passage 12 through which hydrogen gas can recirculate from the sub tank 5 to the main tank 2 is provided.
2, except that a back pressure valve 11 is provided in the second embodiment. Experiments have confirmed that such a structure has the same effect as the third embodiment.

[0031]

As described above, according to the present invention, at the start of operation of the fuel cell, the hydrogen gas is supplied to the fuel cell body from the auxiliary hydrogen storage alloy having a high equilibrium hydrogen pressure, so that the hydrogen gas is smoothly supplied. Can be supplied to the fuel cell body. Further, since it is not necessary to increase the equilibrium hydrogen pressure of the main hydrogen storage alloy, the pressure vessel for storing the main hydrogen storage alloy can be made compact. Therefore, the startability of the fuel cell system can be drastically improved without increasing the manufacturing cost.

In addition, when the steady operation is started, part of the hydrogen gas from the main hydrogen storage alloy is supplied to the auxiliary hydrogen storage alloy. Even when the operation is started again or when the main hydrogen storage alloy is replaced, an excellent effect that smooth power generation is maintained can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of a fuel cell system according to a first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between temperature and equilibrium hydrogen pressure in a hydrogen storage alloy in a main tank and a hydrogen storage alloy in a sub tank.

FIG. 3 is a graph showing the relationship between battery output, hydrogen gas flow rate, line pressure and time in the system (A) of the present invention and the system (X) of the comparative example.

FIG. 4 is a schematic explanatory view of a fuel cell system according to a second embodiment of the present invention.

FIG. 5 is a schematic explanatory view of a fuel cell system according to a third embodiment of the present invention.

FIG. 6 is a schematic explanatory view of a fuel cell system according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell main body 2 Main tank 5 Sub tank 7 Hydrogen gas supply passage 10 Branch passage 11 Back pressure valve 12 Hydrogen gas return passage

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Nasako 2-18 Keihanhondori, Moriguchi City Sanyo Electric Co., Ltd. (56) References JP-A-52-73345 (JP, A) JP-A-58- 121566 (JP, A) JP-A-60-68 (JP, A) JP-A-51-90637 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 8/00-8 /twenty four

Claims (1)

(57) [Claims] A fuel cell body having an oxygen electrode and a hydrogen electrode; a main hydrogen storage alloy for supplying hydrogen to a hydrogen electrode of the fuel cell body during a steady operation; A hydrogen gas is supplied to the hydrogen electrode of the fuel cell body until the equilibrium hydrogen pressure is equal to that of the main hydrogen storage alloy, and hydrogen is supplied from the main hydrogen storage alloy during the steady operation. A fuel cell system, comprising: an auxiliary hydrogen storage alloy to which a gas is supplied.