JPH0582028B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a high temperature operating type fuel cell device that uses hydrogen, carbon monoxide, etc. as fuel, oxygen, air, carbon dioxide gas, etc. as an oxidizing agent, and molten salt as an electrolyte. High-temperature operating fuel cell devices attempt to obtain high current densities by taking advantage of the high rate of chemical reactions at high temperatures. Conventional Structures and Problems Generally, high-temperature operating fuel cells use a molten salt that allows ion movement even at high temperatures, such as a carbonate having CO ₃ ^2- conductivity, as an electrolyte. Using hydrogen as a fuel and a mixture of oxygen and carbon dioxide in the air as an oxidizing agent, a molten salt fuel cell is constructed in which the following reaction is carried out.

[Chemical formula] As is clear from the above reaction formula, hydrogen reacts with the electrolyte CO ₃ ^2- on the fuel electrode side and is consumed, producing water and carbon dioxide as reaction products. On the other hand, on the oxidizer electrode side (hereinafter referred to as the air electrode side), oxygen and carbon dioxide gas are consumed in the electrolyte in the form of CO ₃ ^2- . Here, the carbon dioxide generated at the fuel electrode is supplied to the air electrode and consumed, so the overall reaction is H ₂ + 1/2O ₂ →H ₂ O
Water is produced from hydrogen and oxygen. In the electrolyte, only CO ₃ ^2- ions move, and carbon dioxide gas does not participate in mass balance. Therefore,
It is important that the electrolyte containing CO ₃ ^2- does not change during normal power generation or during shutdown. This type of fuel cell uses a molten salt as an electrolyte, and a holder containing this electrolyte is sandwiched between an air electrode and a fuel electrode from both sides, and a mixed gas of carbon dioxide and air is supplied from a gas chamber on the air electrode side to the fuel electrode side. The configuration is such that hydrogen is supplied to each of the gas chambers. Further, a current collector is provided in each gas chamber to facilitate the collection of electricity between the two electrodes. On the other hand, the supplied mixture of air and carbon dioxide undergoes an electrochemical reaction and is discharged outside the system, and in the same way, a flow path is provided in which hydrogen is discharged as carbon dioxide and water. Moreover, when generating electricity at a pressure close to normal pressure, a special high-pressure vessel is not required. One attempt to improve performance is to place the fuel cell body inside a high-pressure container and generate electricity in a somewhat high-pressure atmosphere. With this configuration, when power is generated at a high temperature, even if there is moisture in the fuel supplied from outside or in the air, the temperature will be high during power generation, so it will be discharged as water vapor and will react with the electrolyte. There's nothing to do. However, there are cases where the power generation of the fuel cell is stopped for reasons such as maintenance, and this operation is necessary from a practical management perspective. At this time, if the temperature of the fuel cell is regenerated and raised before the temperature drops to near room temperature, there will be no major effect, but if the fuel cell is stopped for a relatively long time, the temperature will naturally drop to room temperature. When the temperature of the fuel cell drops, the air around the fuel cell body or moisture contained in the replacement gas (inert gas) reacts with the electrolyte, causing the electrolyte (especially carbonate) to deliquesce. , it changes in quality. The deliquescent electrolyte becomes dissolved and partially creeps from the electrolyte holder and leaks to the outside of the battery.
This causes a short circuit phenomenon, and furthermore, the amount of electrolyte decreases, increasing the electrical resistance of the electrolyte holder, leading to a decrease in battery performance. OBJECTS OF THE INVENTION In view of the above-mentioned problems, the present invention has been devised by using a moisture adsorbent to maintain the electricity in a dry gas atmosphere when stopping power generation in a high-temperature operation type molten salt fuel cell device using carbonate as an electrolyte. The purpose of the present invention is to regenerate the moisture adsorbent using heat generated by the fuel cell. Structure of the Invention The present invention utilizes a molten salt fuel cell that uses a reducing gas (H ₂ , CO, etc.) as a fuel and an oxidizing gas (O ₂ , CO ₂ , air, etc.) as an oxidant to generate electricity, and can be regenerated by heat. and a dryer containing a built-in moisture adsorbent are disposed in a common sealable container, and the dryer has a ventilation structure that allows the built-in moisture adsorbent to come into contact with the atmosphere inside the container. This is a molten salt fuel cell device. Furthermore, the present invention uses inorganic porous materials, such as zeolite, alumina, molecular sieve, Ca,
Using chlorides and oxides such as Mg, when the fuel cell stops power generation and maintains it at room temperature, these moisture adsorbents absorb and remove moisture inside the fuel cell container to keep the cell dry and generate electricity. This molten salt fuel cell device is characterized in that when restarting, the fuel cell is regenerated using heat generated by the fuel cell or heat from an auxiliary heat source. DESCRIPTION OF EMBODIMENTS The details of the molten salt fuel cell device according to the present invention will be explained below with reference to the embodiment shown in FIG. The basic structure consists of a fuel cell main body 2 and a dryer 4 built in a sealable container 1. It has a ventilation structure, that is, a perforated plate 4' that allows contact with the atmosphere. This example is an example of normal pressure operation, and an inorganic porous material is used as a moisture adsorbent that can be regenerated by heat, and a perforated stainless steel plate is used as the ventilation structure of the dryer. The characteristic action of this device is that during fuel cell power generation, the water adsorbent is regenerated or kept in an active state using the heat generated by the fuel cell, and when the fuel cell is stopped and kept at around room temperature, Another method is to keep the inside of the container dry using a moisture absorbent. The configuration and operation will be explained in detail below. In the sealable container 1, the dryer 4 is installed under a pedestal 25 of the battery body 2, and a portion of the pedestal 25 is provided with a number of holes to facilitate ventilation. The battery body 2 has an air chamber 7 having an air electrode 6 on both sides with an electrolyte holder 5 in between, and a fuel chamber 9 having a fuel electrode 8. On the air chamber 7 side, an inlet pipe 10 for supplying an oxidizing agent and a discharge pipe 11 are connected through a joint 12. Reference numerals 13 and 14 indicate valves on the inlet side and the outlet side, which are used to supply and stop the oxidizing gas. An inlet pipe 15 for supplying fuel and a discharge pipe 16 are connected to the fuel chamber side 9 through a joint 17. Reference numerals 18 and 19 are valves on the inlet side and the outlet side, which perform fuel gas supply and stop operations. The entire device can be tightened to the bottom plate 20 with bolts 21 to seal the inside of the container. First, the temperature of the fuel cell was raised using the auxiliary heater 22, etc., and power was generated at a temperature of 500 to 650°C, including the amount of heat generated by the fuel cell itself. In the power generation state, the oxidant supply/discharge valves 13 and 14 and the joint 12
is open. Similarly, fuel supply/discharge valve 1
8, 19 and joint 17 are also open. When the battery is in operation, the battery temperature is 650℃.
Because there is a front and back, the temperature of the dryer placed inside the container also becomes high. In this embodiment, the temperature of the dryer during battery operation is maintained at around 370° C. by reducing the amount of heat insulating material covering the battery body on the side facing the dryer. Generally, at this temperature, the inorganic porous material can release adsorbed water and maintain its regenerated and active state. The valve 24 of the exhaust gas outlet 23 inside the container is used to prevent moisture desorbed from the moisture adsorbent inside the container, or combustible gas (not adopted in this embodiment) from remaining in the container, and to prevent corrosion of metal materials. It is in an open state to discharge a small amount of inert gas, etc. that is being circulated. When power generation is stopped, directly connect each valve 13, 1.
4, 18, 19, 24, or replace each valve 13, 1 with hydrogen gas by passing inert gas.
Close 4, 18, 19, 24. When the temperature inside the container drops to near room temperature, moisture contained in the atmosphere inside the container is absorbed and removed by the moisture adsorbent 3 in the dryer. As time passes, almost no moisture exists in the container, resulting in a dry atmosphere. The moisture absorbed by the moisture adsorbent 3 is regenerated by discharging the moisture from the discharge outlet 23 with the heat of the temperature (500 to 650 DEG C.) during power generation by the fuel cell. Next, the effects of the present invention were tested using the following method. The molten salt fuel cell itself was prototyped using a known method. The air electrode is a sintered nickel composite oxide containing lithium, the fuel electrode is a sintered porous nickel material, and the electrolyte is a mixture of 60wt% potassium carbonate and 40wt% lithium aluminate powder. It was manufactured by hot pressing at a temperature of 500℃. Fuel cells using zeolite as an inorganic porous material
Approximately 300 to 500g was used per 100W. First, several times the theoretical amount of air containing hydrogen gas as a fuel and carbon dioxide gas as an oxidizing agent is supplied, and the operating temperature is 650℃ and the current density is
After generating power at 100 mA/cm ² for 300 hours, power generation was stopped, the temperature was lowered to room temperature, and after being left for about 5 and 10 days, the performance was examined when power was generated again at the specified temperature and current density. Conventional example that does not use a dryer,
The following table shows the performance of the embodiments of the present invention excluding moisture in the container. The degree of decrease compared to the initial performance is expressed as a percentage.

[Table] As is clear from the table, the conventional example can be left unused for 5 days.
In contrast, the performance decreases by 30 to 40% and over 60% after being left for 10 days, whereas in the example of the present invention, the performance decrease is only a few percent, which is a performance improvement of more than 10 times compared to the conventional example. ing. In the conventional example, the electrolyte in the electrolyte holder absorbs moisture in the gas, causing a deliquescent phenomenon, and a portion of the electrolyte leaks to the outside, which is considered to be due to an increase in resistance due to deterioration of the electrolyte. This phenomenon has been confirmed through experiments. Effects of the Invention As described above, according to the present invention, the molten salt fuel cell device has almost no deterioration in performance even when power generation is stopped due to maintenance, and has stable performance.
Longer life can be achieved. Moreover, the fuel cell can generate electricity and regenerate the adsorbent at the same time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a molten salt fuel cell device according to an embodiment of the present invention. 1... Pressure resistant container, 2... Battery body, 3... Moisture adsorbent, 4... Dryer, 5... Electrolyte holder, 7
... Air chamber, 9 ... Fuel chamber, 10 ... Inlet side pipe for oxidizer supply, 15 ... Inlet side pipe for fuel supply, 22 ... Auxiliary heater, 25 ... Frame, 4' ...
...Perforated plate.

Claims (1)

[Claims] 1. A molten salt fuel cell body composed of a fuel electrode to which a reducing gas is supplied as a fuel and an air electrode to which an oxidizing gas is supplied as an oxidant, stacked with an electrolyte interposed, and a moisture adsorbent that is regenerated by heat. A molten salt fuel cell device characterized in that a dryer containing a built-in dryer is disposed in a common sealed container, and the dryer has a ventilation portion that brings the moisture adsorbent contained therein into contact with the atmosphere inside the container.