JP2603916B2 - Heater panel for electrolyte plate production of molten carbonate fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a heater panel used for manufacturing an electrolyte plate of a molten carbonate fuel cell.

[Technical background of the invention]

Conventionally, fuel cells are widely known as high-efficiency energy conversion devices. Fuel cells are classified into phosphate type, molten carbonate type, and solid electrolyte type depending on the electrolyte used. Above all, the molten carbonate fuel cell has major features such as high operating temperature, electrode reaction easily occurring, no need for expensive noble metal catalyst, and high power generation thermal efficiency.

Such a molten carbonate fuel cell is usually made into a unit cell with a pair of porous electrode plates opposed to each other, i.e., an electrolyte layer containing an alkali carbonate as an electrolyte between an oxidant electrode and a fuel electrode. Usually, a plurality of the unit batteries are stacked via an interconnector. And, during operation, the above-mentioned alkali carbonate is added to 500 to 750.
In a molten state at a high temperature of ℃, the carbonate reacts with the oxidizing gas and the fuel gas respectively diffused in the respective electrode plates to obtain a DC power by an electrochemical process.

The electrolyte layer of such a molten carbonate fuel cell needs to satisfy the following conditions. (A) It has sufficient mechanical strength, especially compressive strength, at the operating temperature, as well as sufficient ability to retain the molten carbonate, and cross-mixing of gas due to cracking of the electrolyte layer in the fuel cell. (B) The contact with each electrode should be sufficient to reduce the internal resistance per unit battery, and it should be as thin as possible. (C) Large in order to increase the output per unit battery And high yield to ensure high mass productivity of fuel cells.

By the way, the electrolyte layer of the molten carbonate fuel cell, which is a so-called paste type, is prepared by mixing an aggregate for holding the electrolyte and a carbonate, and hot-mixing at 400 to 500 ° C. and 200 to 500 kg / cm ^2. It is used as a plate-like body called a so-called electrolyte tile obtained by pressing. In this electrolyte tile, several rod-shaped heating elements 2, 3, 4, 5 are embedded in a panel body 1 made of stainless steel as shown in FIG. 4 so as to be parallel to one side of the panel body 1. It is manufactured using a heated heater panel. In addition, these heating elements 2-5
Is applied with a voltage from a single power supply.

[Problems of background technology]

However, in the heater panel as shown in FIG. 4, a large temperature difference may be generated in the vertical direction or the horizontal direction in the central portion and the peripheral portion in the heating surface. When hopless is performed using a heater panel having such a non-uniform temperature distribution, non-uniform melting and non-uniform flow of carbonates occur during heating, resulting in non-uniform density distribution in the manufactured electrolyte plate, particularly at low temperatures. In some parts, the pore content was sometimes increased. For this reason, the electrolyte plate manufactured using the conventional heater panel has a reduced mechanical strength in a portion having a high porosity, and is easily broken even in ordinary handling when the size is increased. Therefore, attention must be paid to the incorporation of the electrolyte plate into the battery, and even after the incorporation, cracks are caused due to the thermal cycle of the battery, and cross-mixing of gases is likely to occur.

[Object of the invention]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and a heater for manufacturing an electrolyte plate of a molten carbonate fuel cell capable of forming an electrolyte plate having a uniform density and improving the mechanical strength of the electrolyte plate. It is intended to provide a panel.

[Summary of the Invention]

A heater panel for manufacturing an electrolyte plate of a molten carbonate fuel cell according to the present invention is characterized in that a heating element is divided into a plurality of parts and embedded in a panel body, and a mechanism for independently controlling each of the divided heating elements is provided. It is a feature.

According to such a heater panel, the temperature difference between the buried portion of the heating element and other portions is small, and non-uniform melting and non-uniform flow of the carbonate do not occur during heating, so that the relative density of the manufactured electrolyte plate is reduced. Can be made uniform.

The panel body is made of a material that is chemically stable to carbonates, has better thermal conductivity than conventional stainless steel, and has a smaller coefficient of thermal expansion (boron carbide, silicon nitride, If aluminum nitride, silicon carbide or graphite is used, the uniformity of the temperature within the heating surface of the heater panel can be further improved, and the thickness of the electrolyte plate can be made uniform.

In addition, stress tends to concentrate at the center during hot press molding with a heater panel.To compensate for the low stress at the periphery, temperature control is performed so that the temperature in the periphery increases when no pressure is applied. It is desirable to do. The above-described temperature control is facilitated by burying the heating elements in, for example, a radial or concentric manner.

(Example of the invention)

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example 1 A commercially available dense graphite (C) was used, and as shown in FIG. 1, a heating element 12 extending diagonally into a panel body 11 of 360 × 360 × 30 mm and a central portion of each side of the panel body 11. A heater panel in which the heating elements 13 extending perpendicularly were radiated and embedded was produced. The heating state of these heating elements 12 and 13 can be independently controlled by a temperature controller (not shown).

The heater panel 11 was mounted on a hot press at a maximum operating temperature of 800 ° C. and a maximum allowable pressure of 100 t / cm ² , and the set temperature was set to 485 ° C. to start heating. First, 65% of the maximum output power is supplied to the heating element 12 to heat it up, and the temperature difference between the central part and the peripheral part is detected by a thermocouple (not shown) inserted into the heater panel 11. The output level of the heating element 13 was controlled so that the temperature distribution in the panel 11 became uniform. The temperature distribution of the heater panel operated in this manner was 483 to 485 ° C. as shown in FIG. 2, and the temperature difference was only 2 ° C.

Further, each powder of γ-LiAlO ₂ , Li ₂ CO ₃ and K ₂ CO ₃ was mixed at a weight ratio of 40:28:32, and 150 g of the mixed powder was filled in a mold for forming an electrolyte plate, and hot pressed. Equipment at 465 ° C, 3
Operating under the condition of 00 kg / cm ₂ , an electrolyte plate of about 2.34 mm was obtained.
The obtained electrolyte plate was cut out into small pieces of 15 × 15 mm, and the relative density (actual density with respect to the theoretical density when no pores existed) and the thickness were measured. Table 2 shows the relative density and standard deviation.

Example 2 Using a commercially available dense graphite (C), circular heating elements 22, 23 and 24 having different diameters are concentrically arranged in a panel body 21 of 360 × 360 × 30 mm as shown in FIG. A divided and buried heater panel was produced. These heating elements 22,
23 and 24 can independently control the heating state by a temperature controller (not shown).

The heater panel 21 was mounted on a hot press at a maximum operating temperature of 800 ° C. and a maximum allowable pressure of 100 t / cm ² , and the set temperature was set to 485 ° C. to start heating. First, a power of 65% of the maximum output is supplied to the heating elements 22 and 23 to heat up the temperature, and the temperature difference between the central part and the peripheral part is detected by a thermocouple (not shown) inserted into the heater panel 21. The output level of the heating element 24 was controlled so that the temperature distribution in the heater panel became uniform. The temperature distribution of the heater panel operated in such a manner was almost the same as that in Example 1.

Using this heater panel, an electrolyte plate was manufactured under the same conditions as in Example 1, and the obtained electrolyte plate was cut out into small pieces similar to those in Example 1, and the relative density and thickness were measured. Table 2 shows the relative density and standard deviation.

Comparative Example A heater panel was heated under the same conditions as in Example 1 by using a heater panel in which bar-shaped heating elements 2 were disposed in parallel and buried in a panel body 1 made of stainless steel as shown in FIG. As a result, as shown in FIG. 5, the temperature on the heating surface was 471 to 484 ° C., and the temperature difference was 13 ° C.

Using this heater plate, an electrolyte plate was manufactured under the same conditions as in Example 1. The obtained electrolyte plate was made into small pieces as in Example 1, and the relative density and thickness were measured. Table 2 shows the results.

As shown in Table 2, in Example 1, the relative density of the test piece was
It was distributed between 94.7 and 98.7% with an average value of 95.8% and a standard deviation of 0.81. The thickness variation was about 190 μm, the average value was 2.34 mm, and the standard deviation was 0.09. These values are almost the same in the second embodiment. That is, in Examples 1 and 2, the variation in both the relative density and the thickness is smaller than in the case where the conventional heater panel shown in FIG. 4 is used.

When the heater panel according to the present invention is used, the variation in the relative density is small because the heating element is divided and embedded in the panel body, and these are independently controlled, and the heat conduction of the panel body is reduced. This is considered to be because the temperature distribution became uniform in the heating surface due to the improvement in the property, and the non-uniform melting and non-uniform flow of the carbonate did not occur. As a result, even if the electrolyte plate to be manufactured is enlarged, the mechanical strength is improved and the handling is easy because the mechanical strength is improved, the crack is not generated even by the thermal cycle during operation, and the gas does not cross-mix.

When the heater panel according to the present invention is used, the variation in the thickness of the manufactured electrolyte plate is small because, in addition to the high thermal conductivity of the panel body, the coefficient of thermal expansion is small, It is considered that this is because the heater panel itself can maintain its smoothness. As a result, the adhesion between the electrolyte plate and each electrode plate in the early stage of operation of the fuel cell is also improved.

In addition, since the panel body of the heater panel according to the present invention is chemically stable against carbonate, no corrosion occurred on the panel surface even after long-term operation.

Furthermore, the heater panel according to the present invention has good thermal conductivity of the panel body, has a good temperature rise, has a small density, is lightweight, and has a small heat capacity, so that the power required during hot pressing can be reduced.

In the above embodiment, the case where graphite was used as the panel body of the heater panel was described, but not limited to this, boron carbide, silicon nitride,
Even if aluminum nitride, silicon carbide or the like is used, the same effect as that of the embodiment can be obtained.

〔The invention's effect〕

As described in detail above, according to the heater panel for manufacturing an electrolyte plate of a molten carbonate fuel cell of the present invention, the density of the manufactured electrolyte plate can be made uniform, the mechanical strength can be improved, and the thickness of the electrode plate can be made uniform. And a remarkable effect such as improvement in the adhesion to the substrate.

[Brief description of the drawings]

FIG. 1 is a plan view of a heater panel for manufacturing an electrolyte plate of a molten carbonate fuel cell in Example 1 of the present invention, FIG. 2 is an explanatory diagram showing a temperature distribution during operation of the heater panel, and FIG.
FIG. 4 is a plan view of a heater panel for manufacturing an electrolyte plate of a molten carbonate fuel cell in Example 2 of the present invention. FIG. 4 is a plan view of a heater panel for manufacturing an electrolyte plate of a conventional molten carbonate fuel cell. FIG. 4 is an explanatory diagram showing a temperature distribution during operation of the heater panel. 11, 21 ... Panel body, 12, 13, 22, 23, 24 ... Heating element.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihiko Tsuge 1 Kogamu Toshiba-cho, Saiwai-ku, Kawasaki City Inside Toshiba Research Institute, Inc. (56) References JP-A-54-97907 (JP, A) JP-A-57 JP-A-50-51910 (JP, A) JP-A-55-114500 (JP, A)

Claims (2)

(57) [Claims] 1. A heater panel for manufacturing an electrolyte plate of a molten carbonate fuel cell in which a heating element is buried in a panel body and hot pressing of an electrolyte powder is performed, wherein the heating element is divided into a plurality of radial or concentric circles in the panel body. A heater panel for manufacturing an electrolyte plate of a molten carbonate fuel cell, comprising a mechanism embedded in a shape and independently controlling each of the divided heating elements. 2. The heater panel according to claim 1, wherein the panel body is made of boron carbide, silicon nitride, aluminum nitride, silicon carbide, or graphite.