JPH0782868B2 - Molten carbonate fuel cell and operating method thereof - Google Patents

Description

The present invention relates to a fuel cell of a type using molten carbonate as an electrolyte, and a molten carbonate type fuel cell suitable for improving the performance of the fuel cell at times. And its operating method.

[Conventional technology]

A fuel cell of a type using molten carbonate as an electrolyte uses a hydrogen-enriched gas on the anode side and a mixed gas of air and carbon dioxide gas on the cathode side as reaction gases. The hydrogen-rich gas is, for example, a gas obtained by steam reforming of natural gas or a gas obtained by gasification of coal. The molten carbonate fuel cell is generally operated at a temperature around 650 ° C., and the cell voltage during operation is around 0.8V. Therefore, in an actual battery, a plurality of cells are stacked in series to obtain a predetermined voltage. In the fuel cell, the temperature rises mainly due to the generation of Juule heat. Therefore, in order to keep the temperature of the fuel cell constant, it is necessary to cool the cell, and a cooling plate is provided for every few cells.

This molten carbonate fuel cell has a major problem that it takes a long time from the start of power generation until the rated output is reached, and the performance of the fuel cell deteriorates when operating for a long time. is there.

From the viewpoint of extending the life of the fuel cell, the pressure of the fuel gas and the oxidant gas is increased when the load increases, and the pressure of each gas to be supplied is reduced when the load decreases to keep the voltage below the voltage at which electrochemical deterioration does not occur. By doing so, a method of extending the service life (Japanese Patent Laid-Open No. 60-10566), a method of performing the power generation method in which the positive and negative electrodes of the fuel cell are replaced with each other, and the positive and negative electrodes of the cell are converted once or more JP-A-60-189177),
There is a method of suppressing evaporation / diffusion of the electrolyte by making the gas supplied to the cathode or the anode contain the electrolyte (JP-A-61-24166).

[Problems to be solved by the invention]

Further, conventionally, in order to improve the performance of the molten carbonate fuel cell, a method of raising the cell temperature or raising the reaction gas pressure has been generally used. But,
Increasing battery temperature accelerates material corrosion and electrolyte evaporation, which shortens battery life.
There was a problem such as. On the other hand, increasing the pressure of the reaction gas improves the cell performance, but the gas pressure must be controlled so that a differential pressure is not applied to the operating method of the cell, that is, the anode and the cathode, and care must be taken in sealing the gas. There was a problem that I had to do it. It should be noted that these methods do not fundamentally improve the battery performance, but enhance the performance by an external factor, and if these methods are removed, the original performance is restored.

The object of the present invention is to eliminate the drawbacks of the prior art, to improve the performance of the fuel cell, to recover the deteriorated performance to the original high performance, and further to extend the life, To provide a driving method.

[Means for solving problems]

In order to achieve the above object, it is important to ensure a sufficient reaction field in the electrode. In order to form a reaction field, it is important to make the place where the gas and the electrolyte contact each other in the electrode wider, that is, to appropriately wet the electrode with the electrolyte. Generally, in electroosmosis, the electrolytic solution can be moved by changing the potential of the electrode. In a cell stack such as a fuel cell, it is difficult to keep individual electrodes at a constant potential. When the method of changing the potential was examined, it was found that the potential of the electrode suddenly changed when a part of the reaction gas was cut off or the concentration was reduced and a load was connected to the battery. It was also found that the larger the current value at that time, the better. That is, the hydrogen-rich gas supplied to the anode is shut off or the supply flow rate is reduced to reduce the concentration, and the supply gas amount is substantially suppressed to supply the nitrogen gas instead. Either the carbon dioxide gas or the air supplied to the battery is cut off or the supply flow rate is reduced to reduce the concentration, and a current is supplied by connecting a load circuit to the battery. That is,
The content of the present invention is to improve the performance of a battery by applying an external force to a battery having low performance or a battery having poor performance to move an electrolyte.

Specifically, it has an anode electrode and a cathode electrode, uses molten carbonate as an electrolyte, and supplies hydrogen-enriched gas to the anode electrode side as a reaction gas and a mixed gas of air and carbon dioxide gas to the cathode electrode side to generate electricity. In a molten carbonate fuel cell that supplies electric power generated to the main load of the plant or to another load, a means for switching the supplied electric power to the main load or another load, and fuel cell characteristics At the time of the decrease, a means for changing the pressure of the reaction gas in the fuel cell by suppressing the supply amount of at least one kind of the reaction gas supplied to the fuel cell for a predetermined time, and the pressure of the reaction gas are changed. And a means for switching the supply of electric power from the main load to the other load and forcibly flowing an electric current to the other load by means of the switching means, and when the characteristic is deteriorated, the switching is performed. Means for switching the power supply from the main load to another load to change the potential of the electrode of the fuel cell to move the electrolyte, and when the degraded characteristics are restored, switch the power supply from the other load to the main load. It is characterized by that.

[Operation] For example, if the hydrogen-rich gas is shut off or the supply flow rate is reduced to reduce the concentration, and instead, nitrogen gas is supplied to the anode and the load circuit is connected, the resistance on the anode side decreases and polarization also occurs. Get smaller. On the other hand, if hydrogen-rich gas is supplied to the anode and the carbon dioxide gas supplied to the cathode is shut off or the supply flow rate is reduced to reduce the concentration and a load circuit is connected, the resistance on the cathode side decreases and the polarization Also becomes smaller. This tendency is the same when air is cut off, but the effect is smaller than when carbon dioxide is cut off. It is not clear why the polarization of the anode and cathode is reduced by blocking a part of the reaction gas or decreasing the supply flow rate to reduce the concentration and connecting a load, but the potential change is not clear. Therefore, it is considered that the electrolyte migrates to form a reaction field. In addition to this, it is also considered that a part of the electrode is dissolved or reduced to increase the number of active sites.

An example of the schematic system of the present invention is shown in FIG. In FIG. 1, the fuel cell 1 is divided into three blocks. This is only an example of dividing into 3 blocks, and in the present invention, it may be divided into a stack or an arbitrary block. 2 detects the voltage of each block,
It is a voltage detection unit that serves to compare with a predetermined value. Reference numeral 3 is a controller that controls switching of anode gas and cathode gas and opening / closing of a load circuit. The voltage of each block is detected by the voltage detector 2, and the controller 3 switches the anode gas or the cathode gas based on the instruction from the voltage detector 2.
And the cathode gas switching device 5. At the same time, the load circuit switch 6 is connected to switch the circuit to the load 8, and the main load switch 7 is opened. Reference numeral 9 is an inverter that converts direct current generated by the fuel cell into alternating current generally used. For example, when one of the block voltages becomes lower than the set value, the anode gas switching device operates according to the instruction of the controller 3, the hydrogen-enriched gas is switched to nitrogen, and the main load switch 7 is disconnected. , The switch 6 of the load circuit is inserted. As the set value, for example, 90% of the rated output is selected. By this operation,
Fuel cells generate electricity when hydrogen gas is deficient. This state is maintained for an arbitrary time of about 1 to 15 minutes, and then the anode gas selector 4 is operated to send the hydrogen-rich gas to the fuel cell 1. When the performance of the fuel cell 1 is restored, the load circuit switch 6 is disconnected and the main load switch 7 is turned on. On the other side, when one of the block voltages of the fuel cell 1 becomes smaller than the set value, the controller 3 instructs the cathode gas switching device 5 to supply only carbon dioxide gas to the fuel cell. Then, the same operation as described above is performed, and the same operation as above is performed except that only air is supplied to the fuel cell instead of carbon dioxide gas. If any one of these three methods is used, the performance of the fuel cell is significantly improved, and the performance of the power generation device is maintained again. In addition, this 3
Which of the seeds is to be operated can be determined by a computer incorporated in the controller 3 by comparing the difference between the block voltage and the set value. In the above description, the battery is divided into blocks and a part of the reaction gas is shut off. However, the same effect can be obtained by reducing the supply concentration of a part of the reaction gas. Further, it is possible to detect the internal resistance of the laminated battery or the cell or the output of the battery instead of the voltage, and to issue an instruction from the controller when the value deviates from the predetermined index value range.

The means for changing the pressure of the reaction gas is, for example, the controller 3, the anode gas switching device 4 and the cathode gas switching device 5 controlled by the controller 3.
The means for forcibly passing current is constituted by, for example, the controller 3 and the load circuit switch 6 switched by the controller 3.

〔Example〕

 Examples of the present invention will be described below.

Example (1): An electrode having Ni as a cathode and a porous plate of NiO as a cathode was used, and as an electrolyte plate, 20% by weight of Al ₂ O ₈ fibers was added to LiAlO ₂ fine powder.
The added matrix was impregnated with the mixed carbonate. The composition of the mixed carbonate is 62 mol of Li ₂ CO ₃ and K ₂ CO ₃ 38
It is a mixture of mol ratios. Effective area of electrode 100c
An internal manifold type fuel cell in which m ² and 15 cells were stacked was made. The fuel cell was divided into 5 cells in 5 blocks, and the voltage of each block was detected. The batteries were placed in a manifold and heated by a heater to 650 ° C before power generation. A reformed gas of natural gas was supplied to the anode, and a gas having a volume ratio of air and carbon dioxide of 7: 3 was supplied to the cathode. When the tightening pressure of the battery was set to 3 kg / cm ² and power was generated at a current density of 150 mA / cm ² , the value of each block was the second
As shown in the figure, it was about 2V. Power generation was continued for about 250 hours under these conditions, but the voltage rise was small. Therefore, the hydrogen-enriched gas being supplied to the anode was then switched to titanium, and the fuel cell was operated for about 10 minutes with the load circuit still on. At this time, the voltage of each block dropped significantly. The anode gas was then switched from titanium to hydrogen enriched gas.
The load remains on. The voltage of each block rapidly increased to about 4V. This is shown in FIG. In FIG. 2, the area marked with an arrow H ₁ indicates the point at which the above treatment was attempted. This operation caused the voltage to rise significantly, but continued to generate electricity, and the voltage gradually dropped again. Therefore, when the hydrogen-enriched gas was changed to titanium again and the same operation was performed again, the voltage increased and the performance could be recovered. This state is an arrow
It is shown in FIG. ₂ by H ₂ . Similarly, repeat the point again with arrow H ₃
It is shown in FIG. When the voltage of each block, that is, the performance of the fuel cell decreases, the anode gas is switched to an inactive gas and the power is forcibly generated to significantly improve the performance of the fuel cell. I knew that I could do it.

Example (2): The same fuel cell as that shown in Example (1) was manufactured, and electricity was generated at a current density of 150 mA / cm ² . As a result, the initial value of each block was about the same, about 2.2V. About 150 in this state
When the power generation was continued for an hour, the voltage rose to about 2.5V.
Therefore, next, of the gas supplied to the cathode side, that is, of the air and carbon dioxide gas, only carbon dioxide gas was cut off, and only air was supplied to the fuel cell to generate power for about 3 minutes. When the carbon dioxide gas was cut off, the voltage of each block dropped sharply, but power generation was continued. Next, when carbon dioxide was again supplied to the cathode, the voltage rose sharply. FIG. 3 shows the result. In FIG. 3, the arrow C ₁ indicates that the above operation has been performed. After that, when the power generation was continued again at a current density of 150 mA / cm ² , the voltage gradually decreased, so the carbon dioxide gas supplied to the cathode was cut off again for about 3 minutes, and the same operation was performed, the voltage increased again. Natsuta. This state is shown by an arrow C ₂ in FIG. The power generation was continued at a current density of 150 mA / cm ² , and the same operation was repeated, and the result is shown by an arrow C ₃ .

Example (3): The same fuel cell as shown in Example (1) was manufactured and power was generated at a current density of 150 mA / cm ² . As a result, the voltage of each block at the beginning was about 2.2V, which was almost the same. About 15 in this condition
After continuing power generation for 0 hours, the air supplied to the cathode was cut off, and only carbon dioxide gas was supplied to the cathode to continue power generation for about 3 minutes. When the air was cut off, the voltage of each block dropped sharply. When air was supplied to the cathode while power was being generated again, the voltage of each block rose to about 3.2V. This is shown in FIG. 4 by the arrow with the symbol O ₁ . The position of the arrow indicates that the above treatment has been performed. Next, power generation was continued at a current density of 150 mA / cm ² , and the same operation was repeated twice when the voltage of the block dropped. This point is indicated by arrows O ₂ and O ₃ in FIG. In each case, the voltage recovered and increased, but it increased to about 3.7V.

Then, as in the case of Example (2), the carbon dioxide gas supplied to the cathode was cut off, the power generation was continued for about 3 minutes, and the carbon dioxide gas was supplied again, as shown by an arrow C ₄ in FIG. As you can see, the voltage of the block has exceeded 4V.

〔The invention's effect〕

According to the present invention, as shown in FIGS. 2 to 4, the performance of the fuel cell can be improved and at the same time, the deteriorated performance can be restored to the original high performance.
As described above, it is not clear why the performance of the fuel cell is improved by cutting off a part of the reaction gas supplied to the anode and the cathode, continuing the power generation for a short time, and then supplying the reaction gas again. It is conceivable that the wettability of the electrode by the electrolyte changes or that the reaction surface of the electrode can be activated. In any case, by using the present invention, the performance of the fuel cell can be significantly improved and at the same time, the performance of which has deteriorated can be restored to the original high performance. It is possible to extend the life of the.

[Brief description of drawings]

FIG. 1 is an example of a system diagram showing an outline of the present invention, and FIGS. 2, 3, and 4 are diagrams showing the performance of a fuel cell using the present invention. 1 ... Fuel cell main body, 2 ... Voltage detector, 3 ... Controller, 4 ... Anode gas selector, 5 ... Cathode gas selector, 6 ... Load circuit switch, 7 ... Main load switch, 8 …… Load, 9 …… Inverter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Iwamoto 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Manufacturing Co., Ltd.Hitachi Research Laboratories (72) Inventor Yoshio Iwase 4026 Kuji Town, Hitachi City Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Koichi Miyoshi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Inventor Yuichi Kamo 4026 Kuji Town, Hitachi City, Ibaraki Hitachi Research Institute, Ltd. (56) References JP-A-55-148370 (JP, A) JP-A-61-225773 (JP, A)

Claims (3)

[Claims] 1. An electric power generator having an anode electrode and a cathode electrode, using molten carbonate as an electrolyte, and supplying hydrogen enriched gas to the anode electrode side and mixed gas of air and carbon dioxide gas to the cathode electrode side as reaction gases. However, in a molten carbonate fuel cell that supplies electric power generated to the main load of the plant or other loads, means for switching the supply destination of the generated electric power to either the main load or another load, and deterioration of fuel cell characteristics Occasionally, means for changing the pressure of the reaction gas in the fuel cell by suppressing the supply amount of at least one kind of the reaction gas supplied to the fuel cell for a predetermined time, and when the pressure of the reaction gas is changing. And a means for switching the supply of electric power from the main load to the other load by the switching means and forcibly flowing a current to the other load. By switching the power supply from the main load to another load by changing means, the potential of the electrode of the fuel cell is changed to move the electrolyte, and when the deteriorated characteristics are restored, the power supply from the other load to the main load is restored. A molten carbonate fuel cell characterized by switching. 2. A type having an anode electrode and a cathode electrode, using molten carbonate as an electrolyte, and supplying a hydrogen-enriched gas to the anode electrode side as a reaction gas and a mixed gas of air and carbon dioxide gas to the cathode electrode side. Made by stacking multiple unit cells,
In the method of operating a molten carbonate fuel cell that supplies electric power to the main load of the plant or other loads, when the output of the fuel cell falls below the preset output from the rating, the reaction gas to be supplied to the fuel cell is The supply amount of at least one kind of gas is suppressed for a predetermined time to change the pressure of the reaction gas, and further, the power supply destination is switched from the main load to another load to force the current to flow to the other load. When the electric potential of the electrode of the fuel cell is changed to move the electrolyte and the output of the fuel cell is restored, the changed supply amount of the reaction gas is returned to the preset flow rate and the main load is applied from other loads. A method for operating a molten carbonate fuel cell, characterized in that the connection is changed over to continue power generation. 3. A type which has an anode electrode and a cathode electrode, uses molten carbonate as an electrolyte, and supplies a hydrogen-enriched gas to the anode electrode side as a reaction gas and a mixed gas of air and carbon dioxide gas to the cathode electrode side. Made by stacking multiple unit cells,
In a method of operating a molten carbonate fuel cell that supplies electric power to a main load or other loads of a plant, when the output of a block consisting of one unit cell or more drops from a rated value to a preset output or less, the power is supplied to the block. The supply amount of at least one kind of the reaction gas to be controlled is changed for a predetermined time to change the pressure of the reaction gas in the fuel cell, and the power supply destination is switched from the main load to another load and forced. A current to another load, the potential of the electrode is changed to move the electrolyte, and when the output of the block is restored, the changed supply amount of the reaction gas is returned to a preset flow rate. A method for operating a molten carbonate fuel cell, characterized in that connection is switched from another load to a main load to continue power generation.