JPH0622152B2 - Electrolyte replenishment method for molten carbonate fuel cell power generator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a fuel cell power generator having a mechanism for automatically detecting and replenishing an electrolytic mass that decreases during operation.

[Background of the Invention]

The molten carbonate fuel cell is a second-generation fuel cell for electric power following the phosphoric acid fuel cell, has high power generation efficiency, can use a wide range of fuels from LNG to coal, and does not use platinum as an electrode material. In order to have the advantage, domestic and foreign R & D is strongly promoted. As its name implies, the molten carbonate fuel cell uses a strong alkaline carbonate that melts at high temperature (498 ° C.) as an electrolyte and operates at a temperature of about 650 ° C.

The biggest problem in this type of fuel cell power generator is the escape and disappearance of the electrolyte from the electrolyte plate. As a result, the internal resistance of the battery increases and a “crossover” phenomenon occurs in which the fuel gas and the oxidizing gas flow through the electrolyte plate matrix, causing rapid deterioration of the battery characteristics and making power generation impossible. Becomes

The electrolyte outflow to the outside of the battery and the absorption by the electrodes that cause this "crossover" are due to the lack of holding power of the electrolyte plate, and improvement of the electrolyte plate matrix is desired, but the mechanical strength is high. In addition, the porosity must be high and the holding power must be large. In other words, the electrolyte plate is required to have contradictory conditions. Considering productivity, the holding power of the electrolyte plate is dramatically improved. Difficult to do. Further, the evaporation of the electrolyte into the reaction gas (exhaust gas) and the atmosphere outside the battery is a phenomenon that occurs regardless of the holding power of the electrolyte plate, and a method for preventing this has not yet been found. As described above, it is difficult to solve the loss of the electrolyte, and it can be said that this greatly hinders the practical use of this power generation device.

A method for resolving this problem is to replenish the electrolyte. It would be convenient if the battery could be disassembled and replenished, but this type of fuel cell cannot be disassembled at an operating temperature as high as 650 ° C. At the workable temperature, the electrolyte becomes a solid and adheres together with the separator. Therefore, it cannot be dismantled so that it can be re-operated. A possible solution is to replenish the electrolyte during the work. That is, the document US Department of Energy (No.AC03), US DEPARTMENT OF ENEGY
-77 ET11319 April 1980, p.p3-77 to 3-79, a method of storing a liquid state by filling a storage tank and a supply pipe with a matrix having the same pore size distribution as that of the electrolyte plate. Is. The matrix is also filled in the storage tank and the supply pipe in order to keep the amount of electrolyte in equilibrium inside and outside the battery body. When the electrolyte in the electrolyte plate partially disappears during the operation of the battery, the molten electrolyte in the storage tank is replenished to the electrolyte plate side to maintain equilibrium.

However, in this device, when the pores inside the main body are too small, the electrode becomes too wet, gas diffusion of the electrode deteriorates, and the three-phase interface decreases, so that the performance deteriorates. If the pores outside the body are too small, the storage electrolyte will not be supplemented in the electrolyte plate inside the body, but will also be contaminated, resulting in the opposite of the intended purpose.

As described above, it is difficult to store the electrolyte as a liquid. Furthermore, since the electrolyte of the present fuel cell is a strong alkali, it is necessary to select a material having excellent corrosion resistance in terms of materials for the storage tank and the supply pipe.

[Object of the Invention]

An object of the present invention is to appropriately supply an electrolyte to a fuel cell main body, thereby preventing deterioration of cell performance due to lack of electrolyte to prolong the life of the cell main body, and to ensure stable long-term operation of a molten carbonate fuel cell power generator. Is to enable.

[Outline of Invention]

The present invention detects the electrolytic mass of the electrolyte plate of a battery body composed of a fuel electrode, an air electrode, and an electrolyte plate holding a mixed molten carbonate electrolyte of Li ₂ CO ₃ and K ₂ CO ₃ , and detects the electrolytic mass by the detection signal. In an electrolyte replenishing method of a molten carbonate fuel cell power generator for replenishing an electrolyte of an electrolyte storage tank to the electrolyte plate, LiOH and KOH are stored in a solid state in the electrolyte storage tank, and the electrolyte storage tank is stored according to the detection signal. LiOH and KOH in the interior are heated to a melting point or higher, and LiOH and KOH heated to a temperature higher than the melting point are supplied to a reaction tank to produce CO ₂
It is characterized in that it is contacted with Li ₂ CO ₃ and K ₂ CO ₃ and then replenished to the electrolyte plate.

LiOH and KOH are stored in a solid state in an electrolyte storage tank, and are contacted with CO ₂ at the time of replenishing the electrolyte to convert it into a carbonate, so that the storage tank is stored in the form of Li ₂ CO ₃ and K ₂ CO _3. Corrosion can be suppressed to a minimum.

Also, according to the present invention, LiOH and K in the electrolyte storage tank
OH is heated to a liquid state, and Li ₂
It can be converted to CO ₃ and K ₂ CO ₃ to replenish the battery with electrolyte. As a result, the following effects (a) and (b) can be obtained.

(A) The responsiveness of electrolyte replenishment can be enhanced and the electrolyte can be replenished quickly compared to the case of replenishing after storing Li ₂ CO ₃ and K ₂ CO _{3 in} the electrolyte storage tank.

The melting points of LiOH and KOH are respectively 4 for LiOH.
77 ℃, KOH is 404 ℃, the mixture (LiOH: K
The melting point of OH = 62: 38) is 259 ° C.

In addition, mixtures of other compositions (LiOH: KOH = 40: 60 or 82: 1)
The melting point of 8) is 310 ° C.

On the other hand, the melting point of Li ₂ CO ₃ is 618 ° C., the melting point of K ₂ CO ₃ is 891 ° C., and its mixture (Li ₂ CO ₃ : K ₂ CO ₃ = 6).
The melting point of 2:38) is 498 ° C.

Thus, since the melting points of LiOH and KOH are remarkably lower than those of Li ₂ CO ₃ and K ₂ CO ₃ , less heat energy is required for melting and the time required for melting can be shortened. Will be able to replenish.

(B) LiOH and KO rather than Li ₂ CO ₃ and K ₂ CO ₃ forms
The H form has a smaller volume change between the solid and the liquid and is less affected by the stress applied to the electrolyte storage container due to the solid and liquid transformation. Therefore, deterioration and destruction of the container are prevented, and the life of the container is prolonged. It is possible.

That is, the electrolyte raw material in the electrolyte storage tank is heated and cooled every time the electrolyte is replenished, and the volume change is repeated. According to the present invention, the electrolyte raw material is stored in the form of Li ₂ CO ₃ and K ₂ CO _3. In comparison, fatigue, deterioration and destruction of the electrolyte storage tank due to the repeated volume change can be suppressed.

As a typical method to detect the lack of electrolyte, first,
There is a method to measure the internal resistance (liquid resistance) of the battery body. The internal resistance (liquid resistance) of the battery body varies depending on the amount of electrolyte retained in the electrolyte plate. If the electrolyte is well retained,
Since the carbonate ions (CO ₃ ² −) move easily, the liquid resistance also has a low value, but the resistance value increases as the retained amount decreases. From this, it is possible to continuously measure the internal resistance (liquid resistance) of the battery main body and detect the electrolyte shortage by the increase of the value.

The other method is a method of detecting a cross gas generated by crossover with an oxygen sensor and a hydrogen sensor (including a gas chromatography device). The cause of the crossover phenomenon is that gas crossing occurs through the pores generated by the disappearance of the electrolyte in the electrolyte plate, or through cracks caused by the cracking of the electrolyte plate.

If the latter is the cause, there is a risk of supplying extra electrolyte, but cracking of the electrolyte plate is rather fatal in terms of battery life, and in this case the operation must be stopped.
The cracks can be eliminated by improving the strength of the electrolyte plate by improving the electrolyte manufacturing method. In the future, the only cause of the crossover phenomenon will be the lack of electrolytes,
By detecting the crossed gas, it can be used as a signal source for electrolyte replenishment.

〔Example〕

FIG. 1 is a comparative example and is a schematic view of an electrolyte replenishing system for supplying an electrolyte directly from an electrolyte storage tank to a battery. L
This is a fuel cell power generator in which a mixed salt of i ₂ CO ₃ and K ₂ CO ₃ is stored in a solid state in the electrolyte storage tank 2, liquefied if necessary, and supplied to the cell body. Reference numeral 6 in the figure is a fuel cell main body for generating electricity by using a mixed molten salt of Li ₂ CO ₃ and K ₂ CO ₃ as an electrolyte, supplying hydrogen to the fuel electrode and supplying a mixed gas of air and carbon dioxide to the air electrode. Is.

A detector 4 for detecting electrolyte shortage due to long-term operation in the fuel cell is provided, and a relay switch 3 is activated by a signal of the detector to cause the Li ₂ CO ₃ and K ₂ C in the electrolyte storage tank 2 to operate.
O ₃ and liquefied are heated and supplied to the fuel cell main body 1 through the electrolyte supply pipe 5.

When the electrolyte is sufficiently replenished, the detector 4 causes the relay switch 3 to operate again, and the heating of the electrolyte raw material is stopped.

FIG. 2 shows an embodiment of the present invention.

Reference numeral 6 in the figure is a fuel cell main body for generating electricity by using a mixed molten salt of Li ₂ CO ₃ and K ₂ CO ₃ as an electrolyte, supplying hydrogen to the fuel electrode and supplying a mixed gas of air and carbon dioxide to the air electrode. Is.

In the electrolyte storage tank 7, LiOH and KOH are stored in a solid state.

A detector 9 for detecting the electrolyte shortage of the fuel cell main body is provided, and the relay switch 8 is actuated by the signal of the detector, and the high temperature fluid serving as a heat source for electrolyte liquefaction is stored in the electrolyte storage tank 7
The outside is circulated along the arrow, and the electrolyte is heated and liquefied.

The liquefied hydroxide in the electrolyte storage tank 7 is taken out to the reaction tank 13 by the feeder 12 and heated to CO ₂
It is converted into the above-mentioned carbonate by contacting with and is supplied to the fuel cell main body 6 through the electrolyte supply pipe 10.

When the electrolyte is sufficiently replenished, the detector 9 causes the relay switch 8 to operate again, and the liquefaction of the electrolyte raw material and the contact with CO ₂ are stopped.

According to the present invention, LiOH and KOH in the electrolyte storage tank are heated into a liquid state, and Li ₂ and KOH are added in an amount necessary for supplying the electrolyte.
It can be converted into CO ₃ and K ₂ CO ₃ and supplied to the battery.

In addition, it is desirable that an antioxidant gas such as carbon dioxide gas, pure nitrogen gas, or argon is supplied to the space portion of the storage layer.

It is desirable to use a liquid resistance measuring device as the detector for detecting the electrolyte shortage in the battery body. The detector preferably activates the relay switch 8 when the liquid resistance value exceeds a certain value.

In addition, it is desirable to use the exhaust gas of the battery main body or the external reformer as the high temperature fluid from the viewpoint of effective utilization of exhaust heat.

Further, when heating the electrolyte, in addition to the above means,
A heater may be provided in the storage tank or the like and a part of the generated power may be used to operate the heater.

The electrolyte supply pipe may be a SUS pipe, but is preferably an α-Al ₂ O ₃ pipe.

The following reactions proceed inside the reaction tank 13.

2LiOH + CO ₂ → Li ₂ CO ₃ + H ₂ O ₃ (1) 2KOH + CO ₂ → K ₂ CO ₃ + H ₂ O (2) The hydroxides of the formulas (1) and (2) are heated and supplied with carbon dioxide gas. It becomes a carbonate. The mixing ratio of the carbonate is determined by the molar ratio of the hydroxide supplied as the raw material. For example, the desired mixing ratio of carbonate is Li ₂ CO ₃ : K ₂ CO ₃ = 62: 38.
If so, the hydroxide may be supplied as LiOH: KOH = 62: 38.

Further, the steam generated when the hydroxide is brought into contact with CO ₂ in the reaction tank 13 to form a carbonate may be mixed with the reaction gas of the anode in order to prevent carbon deposition due to the shift reaction of the anode. It is possible.

FIG. 3 shows the change over time in the performance of the fuel cell power generator shown in the examples. In the case of a power generator that is not replenished with electrolyte, the performance (battery voltage E) decreases as indicated by the broken line after more than 2000 hours, but in the power generator of the embodiment of the present invention in which electrolyte is replenished, the performance of 6000 hours or more Lifespan was recorded.

〔The invention's effect〕

According to the present invention, the electrolyte plate in the fuel cell body can be quickly replenished with an appropriate amount of electrolyte when necessary, so that the life of the cell body can be extended and the molten carbonate fuel cell can be stably operated for a long period of time. Become.

[Brief description of drawings]

FIG. 1 is a comparative example, and is a schematic diagram of an electrolyte replenishing system for supplying a carbonate electrolyte directly from an electrolyte storage tank to a battery, and FIG. 2 is a schematic diagram of an electrolyte replenishing system of one embodiment of the present invention, and FIG. FIG. 3 is a diagram showing a change with time of the present invention. 1,6 ... Fuel cell body, 2,7 ... electrolyte storage tank,
3, 8 ... Relay switch, 4, 9 ... Detector, 5, 1
0 ... Electrolyte supply pipe, 11 ... Carbon dioxide line, 12 ...
... Feeder, 13 ... Reaction tank.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Okada, 4026 Kushimachi, Hitachi City, Hitachi, Ibaraki Prefecture, Hitachi Research Institute, Ltd. (72) Masato Takeuchi, 4026, Kushimachi, Hitachi City, Ibaraki, Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Hiroki Tamura 4026 Kushimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (56) Reference JP 60-264055 (JP, A) JP 60-264054 (JP) JP, A) JP-A-61-214367 (JP, A)

Claims (1)

[Claims] 1. A fuel electrode, an air electrode, and Li ₂ CO ₃ and K ₂ CO ₃
A molten carbonate fuel cell power generation for detecting the electrolytic mass of the electrolyte plate of a battery main body composed of an electrolyte plate holding a mixed molten carbonate electrolyte, and supplying the electrolyte in the electrolyte storage tank to the electrolyte plate by the detection signal. In the electrolyte replenishing method of the apparatus, LiOH and KOH are stored in the electrolyte storage tank in a solid state, and LiOH and KOH in the electrolyte storage tank are heated to a melting point or higher by the detection signal and heated to the melting point or higher. Supplying LiOH and KOH to the reaction tank, CO
_A method for replenishing electrolyte in a molten carbonate fuel cell power generator, comprising replenishing the electrolyte plate after contacting with ₂ to form Li ₂ CO ₃ and K ₂ CO ₃ .