JP4381508B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly to a fuel cell system including a fuel cell body having a plurality of cells each having a fuel electrode and an oxygen electrode as a pair.
[0002]
[Prior art]
Known fuel cells include phosphoric acid fuel cells and solid polymer electrolyte fuel cells. These fuel cells supply hydrogen-rich gas as a reducing agent to the fuel electrode of the fuel cell body, introduce oxygen in the air as an oxidant to the oxygen electrode, and generate electricity based on an electrochemical reaction between the pair of electrodes. Is to do. The hydrogen-rich gas is produced by reacting raw fuel and water components in a reformer. This reformed gas is steam reformed using fossil fuels such as natural gas, butane, propane and naphtha as raw fuel, and steam reformed using alcohols such as methanol as raw fuel. The reformed gas contains several percent of CO in the gas. Since the platinum catalyst used as an electrode of the fuel cell is easily poisoned by this CO, it is necessary to reduce the CO concentration in the reformed gas.
[0003]
Therefore, in a phosphoric acid fuel cell that operates at about 190 ° C., when fossil fuel is used as the raw fuel, a carbon converter is connected to the rear stage of the reformer, and CO in the reformed gas is oxidized to CO ₂ . In the case of conversion and reducing the CO concentration to about 1% or using methanol as the raw fuel, it is known to reduce the CO concentration to about 1% by adjusting the operating temperature or the ratio of water vapor to fuel. .
[0004]
[Problems to be solved by the invention]
On the other hand, in a solid polymer electrolyte fuel cell operating at a low temperature of about 80 ° C., in order to prevent poisoning of the platinum catalyst, it is necessary to greatly reduce the CO concentration to several tens of ppm or less. Have been proposed (for example, JP-A-9-199154). In these methods, the CO concentration in the reformed gas can be maintained at several tens of ppm or less during steady operation, but it cannot be adequately dealt with when sudden load fluctuations occur during startup, etc. When the concentration of CO is high, the power generation capacity is reduced and the fuel cell system may be damaged.
[0005]
For this reason, it is necessary to take measures for the fuel cell system when the CO concentration in the reformed gas is detected and the CO concentration falls below a predetermined level. As the CO concentration detection device, semiconductor type, electrolytic type electric type, and optical type detection devices such as infrared are widely used. However, the above-mentioned semiconductor type and electric type detection devices have a level of several hundred ppm. It is difficult to detect CO, and the above-described optical detection device is unsuitable for practical use because the device becomes extremely large.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel cell that can easily detect the concentration of CO in the reformed gas even when a sudden load fluctuation occurs. To provide a system.
[0007]
Furthermore, another object of the present invention is to provide a fuel cell system in which the apparatus can be prevented from being damaged even if the CO concentration in the reformed gas becomes high.
[0008]
[Means for Solving the Problems]
A fuel cell system according to claim 1 of the present invention includes:
A reformer that reforms raw fuel to produce a reformed gas rich in hydrogen, and a plurality of cells each having a fuel electrode into which hydrogen in the reformed gas is introduced and an oxygen electrode into which oxygen is introduced. A fuel cell system comprising a fuel cell main body,
A cell in which the voltage of at least one of the cells decreases according to the CO concentration, and the cell includes a voltage detection device that detects the voltage of the cell ,
The voltage value detected by the voltage detection device has dropped below the voltage value necessary to shut off the supply of the raw fuel in order to prevent damage to the fuel cell system due to an increase in CO concentration in the reformed gas. In this case, a raw fuel cutoff means for performing the cutoff is provided .
[0011]
The fuel cell system according to claim 2 of the present invention is the fuel cell system according to claim 1, wherein when the voltage value detected by the voltage detection device falls below a predetermined value, the load circuit of the fuel cell main body is It is provided with the interruption | blocking circuit which interrupts | blocks.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0015]
FIG. 1 shows an example of an embodiment of a fuel cell system according to the present invention. The fuel cell system of the present invention includes a reformer 1 and a fuel cell main body 2 having a plurality of cells 3. The reformer 1 performs a steam reforming reaction between raw fuel and water components to produce a reformed gas rich in hydrogen. Examples of the raw fuel include fossil fuels such as butane, propane, and naphtha, and alcohols such as methanol, but use a butane of a small gas cylinder that is generally available on a commercially available cassette stove or the like. Is preferred. The cell 3 has a solid polymer electrolyte membrane, one of the solid polymer electrolyte membranes has a fuel electrode, the other has an oxygen electrode, and the fuel electrode contains the reformed gas rich in hydrogen as a reducing agent. Then, oxygen in the air is introduced as an oxidant into the oxygen electrode, and power generation based on an electrochemical reaction is performed between the pair of electrodes. Upper Ki燃 charge battery body 2 are those having a plurality of these cells 3.
[0016]
In the present invention, at least one cell 3a among the cells 3 is provided with a voltage detection device 4 for detecting the voltage of the cell 3a. As shown in FIG. 6, the voltage of the cell 3 decreases according to the CO concentration. For example, when the CO concentration suddenly increases from 100 ppm to 100 ppm, the potential of the cell 3 decreases from 0.6 V (symbol c) to 0.55 V (symbol d) in 1 minute (between codes ab). Therefore, the CO concentration in the reformed gas can be detected by detecting the degree of voltage drop. In the present invention, since the cell 3a includes the voltage detection device 4, the concentration of CO in the reformed gas can be easily detected, so that it is possible to cope with a sudden load fluctuation.
[0017]
Next, the fuel cell system of the invention related to the present invention will be described. FIG. 2 shows an example of an embodiment of a fuel cell system according to the present invention.
Only differences from the fuel cell system will be described. In the present invention, as shown in FIG. 2, a cell 3b is installed separately from the fuel cell main body 2, and the cell 3b includes a voltage detection device 4 for detecting the voltage of the cell 3b. In order to detect the voltage of the cell 3b, the size of the cell 3 of the fuel cell main body 2 is not required. Therefore, the fuel cell system can be reduced in size by separating and installing the small cells 3b including the voltage detection device 4. Similarly to the above, in the present invention, since the cell 3b includes the voltage detection device 4, the concentration of CO in the reformed gas can be easily detected. As a result, it is possible to cope with a sudden load fluctuation.
[0018]
In the case of a sudden change in load, a warning buzzer, a warning lamp, or the like may be used to respond manually or automatically. Next, an example of automatically handling will be described.
FIG. 3 shows an example of an embodiment of the present invention. As shown in FIG. 3, the present invention includes a determination unit 5 that receives a signal from the voltage detection device 4 of the cell 3 a and, based on the signal from the determination unit 5, supplies the raw fuel to the raw fuel supply path 6. The raw fuel shutoff means 7 for shutting off the supply of fuel and the load circuit 8 of the fuel cell main body 2 are provided with a shutoff circuit 9 for shutting off the load circuit 8.
[0019]
The determination means 5 receives a signal from the voltage detection device 4, detects the voltage value of the cell 3a, and determines whether or not the voltage value has decreased below a predetermined value. If the voltage value of the cell 3a falls below a predetermined voltage value, the CO concentration in the reformed gas is contained above a predetermined value, so whether or not the CO concentration in the reformed gas has reached a predetermined value or more. It will be determined. As this predetermined voltage value, for example, a voltage with a CO concentration of 500 ppm or more may be set. Moreover, you may set in the range of 100-1000 ppm according to the performance of a fuel cell.
[0020]
An example of the raw fuel cutoff means 7 is a cutoff valve. The determination means 5 and the raw fuel cutoff means 7 are connected by an electric circuit 10, and when it is detected that the voltage value of the cell 3a has dropped below a predetermined value, a signal is transmitted from the determination means 5 and the raw fuel is Shut off the supply. Further, when it is detected that the voltage value of the cell 3a has dropped below a predetermined value, a signal is transmitted from the determination means 5 to the cutoff circuit 9 provided in the load circuit 8, and the cutoff circuit 9 is activated. The load circuit 8 is shut off.
[0021]
The fuel cell system shown in FIG. 4 includes determination means 5 that receives a signal from the voltage detection device 4 of the cell 3b separated from the fuel cell main body 2, and supplies raw fuel based on the signal from the determination means 5. The path 6 is provided with a raw fuel cutoff means 7 for cutting off the supply of raw fuel, and a load circuit 8 of the fuel cell main body 2 with a cut-off circuit 9 for cutting off the load circuit 8. The determination means 5, the raw fuel cutoff means 7, and the cutoff circuit 9 have the same functions as the fuel cell system described above.
[0022]
FIG. 5 shows an example of an embodiment of the invention related to the present invention. As shown in FIG. 5, the present invention includes a CO reduction device 11 for reducing CO in the reformed gas between the reformer and the fuel cell body. Examples of the CO reduction device 11 include means for mixing air into the reformed gas. If about several percent of air is mixed in the reformed gas and brought into contact with the platinum catalyst and burned, CO is reduced. As the amount of air to be mixed, since the CO concentration of air is about 1%, if it is mixed about 5%, the CO concentration decreases, and even if it is excessive, mixing about 10% is sufficient. The CO reduction device 11 desirably has a function of adjusting the mixing ratio of the reformed gas and air. The determination means 5 and the CO reduction device 11 are connected by an electric circuit 12, and when it is detected that the voltage value of the cell 3a has dropped below a predetermined value, a signal is transmitted from the determination means 5 and the reformed gas Increase the amount of air mixed in.
[0023]
【The invention's effect】
In the fuel cell system according to claim 1 of the present invention, the voltage value of the cell is a voltage value that needs to cut off the supply of raw fuel in order to prevent damage to the fuel cell system due to an increase in the CO concentration in the reformed gas. Since the raw fuel supply means for cutting off the supply of the raw fuel when it is reduced below is provided, even if the CO concentration in the reformed gas becomes high, the apparatus can be prevented from being damaged.
[0026]
The fuel cell system according to claim 2 of the present invention, when the voltage value of cell Le drops below a predetermined value, so comprises means interrupting circuit for interrupting the load circuit of the fuel cell body, the reformed gas Even if the CO concentration increases, the apparatus can be prevented from being damaged.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an embodiment of the invention related to the present invention.
FIG. 2 is a schematic view showing another example of the embodiment of the invention related to the present invention.
FIG. 3 is a schematic diagram showing an example of an embodiment of the present invention.
FIG. 4 is a schematic view showing another example of the embodiment of the invention related to the present invention.
FIG. 5 is a schematic view showing another example of the embodiment of the invention related to the present invention.
FIG. 6 is an explanatory diagram showing cell voltage and CO concentration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reformer 2 Fuel cell main body 3, 3a, 3b Cell 4 Voltage detector 5 Determination means

Claims (2)

A reformer that reforms raw fuel to produce a reformed gas rich in hydrogen, and a plurality of cells each having a fuel electrode into which hydrogen in the reformed gas is introduced and an oxygen electrode into which oxygen is introduced. A fuel cell system comprising a fuel cell main body,
A cell in which the voltage of at least one of the cells decreases according to the CO concentration;
E Bei voltage detecting device in which the cell detects the voltage of the cell,
The voltage value detected by the voltage detection device has dropped below the voltage value necessary to shut off the supply of the raw fuel in order to prevent damage to the fuel cell system due to an increase in CO concentration in the reformed gas. when the fuel cell system characterized Rukoto comprises a raw fuel cutoff means for performing the blocking. When the voltage value detected by the voltage detection device has dropped below a predetermined value, the fuel cell system according to claim 1, characterized in that it comprises a blocking circuit for blocking the load circuit of the fuel cell body.

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