JPH0652660B2 - Molten carbonate fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel cell, and more particularly to a laminated molten carbonate fuel cell suitable for sealing and electrolyte replenishment.

[Conventional technology]

Fuel cells have high power generation efficiency because they can directly convert the chemical energy of fuel into electrical energy, and they also produce less harmful gas or liquid and have low noise, which is excellent in environmental harmony. Its development is active as a power source. Among them, the molten carbonate fuel cell has a particularly high power generation efficiency and can diversify the fuel from LNG to coal, and its early commercialization is desired.

The molten carbonate fuel cell comprises a pair of gas-diffusing porous electrodes of a cathode and an anode, an electrolyte body which holds a molten electrolyte of an alkali metal carbonate disposed between the electrodes, and the pair of gas diffusions. A unit cell is constituted by a chamber through which an oxidant can flow to supply one of the porous porous electrodes and a chamber through which a fuel can flow to supply the fuel to the other of the pair of gas-diffusing porous electrodes. ing.

Further, in a practical-scale molten carbonate fuel cell power generation plant, a large current can be obtained by increasing the battery voltage by stacking the unit cells in multiple stages in series and increasing the size of the battery to widen the electrode effective area. This is taken out to increase the capacity of the battery output, and is generally constructed as shown in FIG.

The unit cell is composed of an electrolyte body 1 which is a molten carbonate electrolyte holder, a cathode 2 and an anode 3 which are gas diffusive electrodes arranged on both sides of the electrolyte body 1, and a plurality of electrodes arranged outside these. A unit cell including a fuel flow chamber 8 and a separator 5 having an oxidant flow chamber 6 is sequentially stacked and configured. Further, a collector (current collector, not shown) is provided between each cathode 2 and each oxidant flow chamber 6.
Are often provided.

The electrolyte body 1 is a mixed carbonate (lithium carbonate) which is an electrolyte on a substrate having a porosity of 45 to 50%, which uses γ-lithium aluminate powder and fibers (powder / fiber = 80/20, weight ratio) as an electrolyte holding material. / Potassium carbonate = 62/38, molar ratio) is used after impregnation after battery assembly. Its shape is similar to that of the separator 5. The cathode 2 and the anode 3 are gas-diffusing porous sintered bodies made of Ni-oxide-based and Ni-based materials, respectively, and have a separator 5 shape.
The area is smaller by about 20% and is accommodated in the frame of the internal manifold 12 in the separator 5. Battery operating temperature is 650 ℃
Is. Cathode 2 (oxygen electrode), anode 3 (hydrogen electrode)
The battery reaction that occurs in the whole reaction formula is H ₂ + 1 / 2O ₂ → H ₂ O + 57.8 (kca
(l / mol) is an exothermic reaction as a whole. Therefore, in a practical battery, it is necessary to cool the battery body, so that the reaction gas is introduced at a temperature lower than the operating temperature and the heat balance is controlled.

However, in the molten carbonate fuel cell having such a structure, there is a possibility that the reaction gas may leak to the outside of the cell. In particular, the possibility is large at the peripheral end portion 9 of the electrolyte holding body where the electrolyte body 1 and the separator 5 are in contact with each other. As a gas sealing method in the molten carbonate fuel cell having such a structure, a method generally called a wet sealing method is adopted. That is, a molten electrolyte liquid film is formed on the contact surface between the electrolyte body 1 and the separator 5 to prevent the reaction gas from leaking to the outside of the battery.

Further, as another method, there is a method called a dry seal method. In this method, an insulating gasket, for example, a dense ceramic plate, is provided at the end portion 9 around the electrolyte holder between the separators 5 to prevent the reaction gas and the electrolyte from leaking out of the battery. For example, JP-A-58-19902
See Publication No. 3.

When a fuel cell is operated for a long period of time, the amount of carbonate retained in the electrolyte body decreases as the electrolyte disappears due to the electrolyte flowing out of the cell, leakage, evaporation, corrosion of components, etc. Battery performance will also decrease. In such a case, supplementing the electrolyte will restore the performance. As a method of replenishing the electrolyte, in JP-A-58-161266, by providing a frame body in which a plurality of cell windows are cut out, a cell unit is formed by accommodating and holding a unit battery for each cell window. A high-capacity fuel cell is formed without increasing the electrode area of the cell, and an electrolyte reservoir groove for supplying electrolyte to the matrix is formed on the upper surface of the lower frame that constitutes the frame body. A carbonate fuel cell is disclosed. Further, in JP-A-58-103785, by providing a groove for an electrolyte reservoir on the same surface as the gas flow path provided in the separator and providing a hole communicating the groove and the matrix, moisture absorption, A method of compensating for changes in the electrolytic mass in the matrix due to evaporation and maintaining a certain amount of electrolyte in the matrix is disclosed.

[Problems to be solved by the invention]

In the molten carbonate fuel cell which is the main object of the present invention, the operating temperature is a high temperature of about 650 ° C., and the electrolyte applied is a highly corrosive alkali metal carbonate,
At present, it is difficult to find a suitable material that can withstand such an environment, including the above-mentioned sealing material. Therefore, there is no choice but to apply the so-called dry seal method using the wet seal method or the dense ceramic plate as described above.

However, the wet sealing method is not very reliable.
Further, in the molten carbonate fuel cell having the above structure, there is a high possibility that the electrolyte solution will flow out of the cell. That is, it is expected that the electrolyte solution retained in the electrolyte body gradually flows out of the battery by continuing the operation of the battery at a high temperature of about 650 ° C. for a long time. If such a state progresses, the reliability of the gas sealing property by the wet sealing method will decrease, and it is also considered that corrosion of the separator material by the outflowing electrolyte progresses. In addition, the electrolyte mass in the electrolyte body is insufficient, pinholes and cracks are generated in the electrolyte body, crossover phenomenon of oxidant, fuel or generated gas occurs, which may cause deterioration of battery performance and further increase safety. It can also cause problems.

On the other hand, the dry seal method also has the following problems. In this method, a dense ceramic plate, which is close to a rigid body, is used, and the load deformation is small.Therefore, it is necessary to strictly control the dimensional accuracy of these battery components and insulating gaskets based on the physical properties of the electrolyte and electrodes. In addition, unless the sealing surface of the separator or the insulating gasket is devised, the sealing characteristics cannot be improved unless tightened at a considerably high pressure. Even if the tightening pressure is increased to improve the sealing characteristics,
The contact state between the electrode and the electrolyte body or collector is not optimized, and the battery performance is affected by compressive creep deformation of the electrode, excessive movement of the electrolyte to the electrode due to compressive deformation of the electrolyte, and the electrode falling into the collector opening. There is a risk that secondary problems such as not being able to maintain the optimal state of

Also, in the long-term operation of the battery, a path through which the electrolyte oozes out the battery end, a path through which the electrolyte disappears due to a corrosion reaction with the constituent materials inside and / or outside the battery, and the electrolyte is evaporated into the fuel gas or the oxidizer. A route that disappears is being considered. Regarding the loss of the electrolyte except for the evaporation into the reaction gas and the consumption due to the internal corrosion of the battery, it is necessary to develop a highly reliable sealing technology to reduce the loss of the electrolyte. In the prior art, no consideration is given to the fact that the electrolyte retained in the electrolyte body disappears through the above-mentioned path, and the amount of impregnated carbonate in the electrolyte body is insufficient, and the reaction gas facing each other on both sides of the electrolyte body is insufficient. The airtightness of the comrades is reduced and gas crossover occurs. In this case, it may cause deterioration of battery performance.
In addition, there may be a problem in terms of safety. To prevent these problems, the battery performance is restored by replenishing the electrolyte, but any of the various electrolyte replenishment methods that have been proposed so far have a complicated structure and are problematic in practice.

An object of the present invention is to provide a molten carbonate fuel cell capable of preventing the electrolyte of the electrolyte body from leaking to the outside and easily replenishing the electrolyte.

[Means for solving problems]

In order to achieve such an object, the present invention comprises a plurality of unit cells formed by sandwiching an electrolyte holder that holds a molten carbonate electrolyte between a gas-diffusing cathode and a node, with a separator interposed between the electrolyte holder and the electrolyte holder. A through hole that forms a part of the oxidant supply / discharge internal manifold and a through hole that forms a part of the fuel supply / discharge internal manifold are provided around the body,
The cathode and the anode are arranged in a frame of the internal manifold, and the separator surrounds a through hole forming a part of the oxidant supply / discharge internal manifold and a through hole forming a part of the fuel supply / discharge internal manifold. A fuel supply / discharge internal manifold having a flow path communicating with the oxidant supply / discharge internal manifold on the side facing the cathode and supplying / discharging the oxidant to / from the cathode. In a molten carbonate fuel cell having a flow path communicating with the anode for supplying and discharging fuel to and from the anode, an average pore diameter is provided in at least a part of a portion outside a through hole forming a part of the internal manifold of the separator. Is provided with an electrolyte holding groove filled with a porous body having a larger average pore size than the electrolyte holding body and holding an electrolyte for replenishing the electrolyte holding body. , A peripheral end portion of the electrolyte holding body including the electrolyte holding groove that penetrates the electrolyte holding groove further outside the electrolyte holding groove is cooled to a temperature equal to or lower than the melting point of the electrolyte, and the separator holds the electrolyte holding portion. It is characterized in that a coolant channel for flowing a coolant for solidifying an electrolyte to form a seal is provided at a peripheral end portion of the body.

[Action]

According to the above configuration, the wet seal is formed at the peripheral end portion of the electrolyte holder by melting the electrolyte at the ambient temperature of the battery operating temperature. That is, the seal layer is formed by the melt liquid film having the electrolyte. As a result, the airtightness of the peripheral edge of the electrolyte holder is improved, and it is possible to prevent the reaction gas of fuel and air and the generated gas from them from leaking outside the cell. Further, by cooling the wet seal portion to a temperature not higher than the melting point of the electrolyte to solidify the electrolyte and forming a seal layer with the solidified salt, a more precise sealing function can be obtained. Then, the seal layer is permanently maintained during the battery operation by being cooled by the refrigerant flowing through the cooling flow path provided in the peripheral portion of the battery.

Further, by shutting off the refrigerant flowing through the cooling channel or gradually reducing the flow rate to melt the salt, the melted electrolyte is absorbed and moved from the electrolyte holding groove to the electrolyte body by the capillary phenomenon, so it is necessary when necessary. The electrolyte can be replenished to the electrolyte body in an appropriate amount.

〔Example〕

 Hereinafter, the present invention will be described based on embodiments shown in the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention, which has a structure in which the internal chamber 19 is incorporated in the separator 5, that is, an internal chamber structure. This internal chamber 19
A large number of layers are stacked to form one cooling flow path. The separator 5 is provided with an electrolyte holding groove 21 which is an electrolyte replenishing mechanism. The electrolyte holding groove 21 is filled with LiAlO ₂ as a holding material in an amount that exceeds 100% of the electrolytic mass that can be held in the electrolyte body 1 during battery assembly. After the battery is assembled, first, the electrolyte body 1 is sufficiently impregnated with the carbonate by keeping it at 650 ° C. for several hours without performing any cooling treatment. During this holding time, the electrolyte is sufficiently impregnated even at the end portion, and the end portion 9 around the electrolyte holder (the portion indicated by the diagonal lines in FIG. 1) which is required to be airtight is wet by its own liquid film. A seal is formed. At this time, the excess amount of electrolyte melts temporarily, but
Held in 21. Then, a coolant is introduced into the chamber 19 to form a dry seal portion on the peripheral end portion 9 of the electrolyte holder. That is, the temperature of the refrigerant is adjusted so that the peripheral end portion 9 of the electrolyte holder is cooled to the melting point (488 ° C.) or lower of the mixed carbonate,
It is considered that if the flow rate is optimally controlled, the state will shift to a fine dry seal state and the airtightness will be greatly improved as compared with the wet seal state. Once the transfer to the dry seal is performed, the battery is operated while constantly maintaining the refrigerant introduction condition and the operating condition to further prevent the electrolyte from seeping out from the electrolyte holder peripheral end portion 9 and the internal manifold opening 12a. It has the effect of suppressing the corrosion of the peripheral portion.

Although the above-mentioned seal has not been experimentally verified, a suitable result was obtained when a simulation was performed by calculation for the temperature distribution on the unit cell plane during operation. The cooling temperature of the end portion 9 around the electrolyte holder is 400
When the heat balance was calculated by setting the inlet temperature of the fuel gas and the oxidizing agent to 600 ° C, the temperature distribution on the separator 5 as shown in Fig. 3 was obtained. That is, the end portion 9 around the electrolyte holder, which is the seal portion, is kept at the melting point (488 ° C.) or less of the electrolyte, suggesting that the operation is technically possible while keeping the solidified state. If this state is maintained, a sufficient effect can be expected regarding the end seal.

However, if the operation is continued for a longer time, the electrodes 2, 3
Dispersion of the electrolyte occurs due to transpiration and the like. This is an unavoidable problem in improving the seal. In this way, when the electrolytic mass in the electrolyte body 1 is decreased and the battery performance is deteriorated, the carbonate in the electrolyte holding groove 21 is melted and replenished. The detailed method is described below. The peripheral edge portion 9 of the electrolyte holder, which has become a dry seal portion by cooling, is held below the melting point of carbonate. At this time, the refrigerant is shut off or the flow rate is reduced to gradually melt the salt. However, the electrolyte holding groove 21 is filled with a carbonate-resistant porous sintered body such as a LiAlO ₂ sintered body to hold the electrolyte. The average pore diameter is defined as electrode member> holding body in electrolyte holding groove> electrolyte body. The melted electrolyte is absorbed and moved from the electrolyte holding groove 21 to the electrolyte body 1 by the capillary phenomenon. When the carbonate absorption in the electrolyte body 1 is saturated, the refrigerant is introduced again to form the dry seal part.

As described above, the present invention melts the electrolyte at ambient temperature around the battery operating temperature (650 ° C) to form a wet seal.
That is, the melt liquid film of the electrolyte itself forms a seal layer on the peripheral end portion 9 of the electrolyte holder. As a result, the airtightness is improved, and it is possible to prevent the reaction gas of fuel and air and the generated gas from them from leaking to the outside of the cell. Further, the seal layer is cooled to a temperature not higher than the melting point of the electrolyte and the electrolyte is solidified, and the solidified salt forms a seal layer in a dry seal state, so that a more precise sealing function is provided. As a result, the electrolyte does not flow out of the sealing layer to the outside, corrosion of the members is reduced, and long-term stability of the battery can be achieved.

Further, by shutting off the refrigerant flowing through the cooling channel or decreasing the flow rate to gradually melt the salt, the molten electrolyte is absorbed and moved from the electrolyte holding groove to the electrolyte body by the capillary phenomenon. Therefore, it becomes possible to replenish the electrolyte body with the electrolyte in a required amount when needed.

〔The invention's effect〕

As described above, according to the present invention, the leakage of the electrolyte to the outside of the battery is prevented, so that there is a remarkable effect in preventing the deterioration of the battery constituent materials and maintaining the battery performance. Further, it is possible to compensate for the shortage of the electrolyte in the electrolyte body, which is also very effective in extending the life of the battery.

[Brief description of drawings]

FIG. 1 is a perspective view showing the basic structure of a molten carbonate fuel cell, FIG. 2 is a cross-sectional view of a fuel cell according to an embodiment of the present invention, and FIG. 3 is a diagram showing simulated temperature distribution on a separator. Is. 1 ... Electrolyte body which is a molten carbonate electrolyte holder, 2, 3 ...
Gas diffusion electrode cathode and anode, 5 ... Separator, 6 ... Oxidant flow chamber, 8 ... Fuel flow chamber, 9 ... Electrolyte holder peripheral end, 12 ... Internal manifold, 21 ... Electrolyte holding as electrolyte replenishment mechanism groove.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Okada, 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture, Hitate Manufacturing Co., Ltd. (72) Inventor Yoshio Iwase, 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Nitate Manufacturing Co., Ltd. Hitachi Research Laboratory (72) Inventor Naruyoshi Kobayashi 502 Jinritsu-cho, Tsuchiura-shi, Ibaraki Hiritsu Seisakusho Co., Ltd. In-house (72) Inventor Koichi Miyoshi 4026, Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Co., Ltd. (56) References JP-A-60-246570 (JP, A) JP-A-61-248369 (JP, A) )

Claims (1)

[Claims] 1. A unit cell composed of an electrolyte holder for holding a molten carbonate electrolyte sandwiched between a gas-diffusing cathode and an anode, and a plurality of unit cells are laminated with a separator interposed therebetween, and the unit battery is oxidized around the electrolyte holder. The separator has a through hole forming a part of the agent supply / discharge internal manifold and a through hole forming a part of the fuel supply / discharge internal manifold, the cathode and the anode being arranged in a frame of the internal manifold, and the separator. Is a through hole forming a part of the internal manifold for supplying and discharging the oxidant and a through hole forming a part of the internal manifold for supplying and discharging the fuel, and the inside of the oxidizing agent supplying and discharging is on the side facing the cathode. The fuel supply / discharge internal manifold communicates with the manifold and has a flow path for supplying / discharging oxidant to / from the cathode, and communicates with the fuel supply / discharge internal manifold to supply fuel to the anode. In a molten carbonate fuel cell having a flow path for draining, in the separator, an average pore diameter is at least part of an outer side portion of a through hole forming a part of the internal manifold of the separator from an average pore diameter of the electrolyte holder. An electrolyte holding groove for holding an electrolyte for filling a large porous body and replenishing the electrolyte holding body is provided, and the electrolyte holding body is further penetrated through the electrolyte holding body and a separator at an outer side portion of the electrolyte holding groove. Coolant flow that cools the peripheral end of the electrolyte holding body including the groove to a temperature equal to or lower than the melting point of the electrolyte, and causes the refrigerant to flow to form a seal by solidifying the electrolyte to the peripheral end of the electrolyte holding body that the separator contacts. A molten carbonate fuel cell characterized in that a passage is provided.