JPH0240862A - Internal reforming type fuel cell - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel cell structure, and particularly to an internal reforming fuel cell that generates power while reforming fuel such as hydrocarbon within the cell.

[Conventional technology]

The conventional internal reforming fuel cell is disclosed in Japanese Patent Application Laid-Open No. 60-32255.
As described in the above issue, the amount of fuel reforming catalyst filled in the fuel passage is increased in the direction of fuel flow, so the amount of catalyst is small near the entrance of the fuel passage where the reforming reaction rate is high. The reforming reaction is suppressed, and conversely, near the exit where the reaction rate is low, the amount of catalyst is large, so the 1 reaction rate is accelerated.
As a result, the reforming reaction is made uniform in the direction of fuel flow as a whole, and the amount of heat absorbed is also made uniform, so it is possible to make the hot coal distribution inside the cell uniform.

Furthermore, according to the description in JP-A No. 61-58174, it is discussed that the activity of the catalyst is changed at different positions along the length direction between the inlet end and the outlet end of the passage. In this method, the catalyst concentration in the catalyst carrier is adjusted during the catalyst manufacturing process.

[Problem to be solved by the invention]

In the former of the above conventional techniques, in order to change the amount of catalyst along the flow, the width and depth of the fuel passage must be changed in the flow direction.

The fuel passage becomes structurally complex, which is disadvantageous in terms of manufacturing cost. Moreover, with this structure, the catalyst fills the fuel passage, which causes a large pressure loss between the inlet and outlet of the cell, reducing efficiency and making it difficult to control the differential pressure with the oxidizing gas side. However, there were problems with reliability and battery operation. Further, this technique cannot be applied to a method other than a filling method, for example, a method in which a plate-shaped catalyst is disposed in a passage. Furthermore, since the catalyst and the fuel electrode are close to each other, deterioration of catalyst activity due to molten salt also poses a problem in terms of battery life.

Further, in the latter of the above-mentioned conventional techniques, since the catalyst activity changes depending on the position, the method of adjusting the catalyst concentration in the carrier also complicates the manufacturing method of the reforming catalyst, which poses problems in terms of reliability and cost.

The purpose of the present invention is to provide an internal modification that can control fuel reforming reactions with a simple configuration and extremely low manufacturing cost, and as a result, can make the temperature distribution inside the battery uniform. The objective is to provide a high quality fuel cell.

[Means to solve the problem]

The above purpose is between the fuel inlet end and the outlet end.

In order to change the contact area between the fuel and the catalyst per unit electrode area along the flow direction, a perforated plate is provided between the fuel passage and the catalyst, and the opening ratio of the pores is changed from the inlet to the outlet. By making it bigger.

achieved.

Therefore, the internal reforming fuel cell of the present invention includes a unit cell in which a fuel electrode and an oxidizer electrode are arranged to face each other with an electrolyte plate interposed therebetween, a fuel passage corresponding to the fuel electrode, and a fuel passage installed in the fuel passage. In an internal reforming fuel cell, the fuel cell has an oxidizer passage corresponding to the oxidizer electrode and a fuel reforming catalyst, and generates power while reforming the fuel by supplying fuel and oxidizer to the passage respectively, The contact area between the fuel and the catalyst is expanded in the flow direction of the fuel, and more specifically, a perforated plate is interposed at least partially between the fuel passage and the catalyst, and the perforated plate is Direct contact between the fuel and the catalyst at the intervening location is allowed only through the pores of the perforated plate, and the opening ratio of the pores of the perforated plate is expanded from the inlet to the outlet in the fuel flow direction of the fuel passage. It is characterized by the fact that

[Effect]

The reforming reaction of methane, which is a fuel, is expressed by the following equation.

CH4+ Hz0 # CO+ 3 Hz
-(1)G O+ 3 Hz? :' COz+H
z - (2) In particular, equation (1) is the rate-determining step of the reforming reaction rate, and this reaction generates a large endothermic effect.

Now, when the fuel undergoes a reforming reaction while in contact with the catalyst layer,
When passing through a fuel passage of a certain arbitrary length, the conversion rate of methane at the outlet is expressed by the following formula, assuming that formula (1) is a first-order reversible reaction.

22, XAOO is the equilibrium conversion rate determined by the gas composition, temperature, and pressure at the inlet of any channel section, and IAI represents the methane conversion rate at the inlet of the channel section. Also XAO
is the methane conversion rate at the outlet of the section. The methane conversion rate refers to the proportion of methane used to generate hydrogen through the reforming reaction out of the supplied methane. A conversion rate of 100% means that all of the supplied methane has been used to generate hydrogen. show. - is the reforming reaction rate constant, and Sv is the space velocity.

(Volume flow rate of fuel) / (Spatial volume of flow path in contact with catalyst)
It is expressed as

Therefore, the larger the XAO, which is the methane conversion rate at the outlet, the faster the reforming reaction rate within that section. In conventional methods, attempts have been made to vary the reforming reaction rate constant.

In the present invention, the reaction rate is controlled by changing Sv while leaving kffl unchanged.

For example, by reducing the contact area between the fuel and the catalyst per unit electrode area, the residence time of the fuel in contact with the catalyst per unit electrode area becomes shorter, which is equivalent to increasing the space velocity Sv. Become.

Therefore, by introducing a perforated plate whose opening area ratio increases sequentially from the fuel side inlet end to the outlet end between the fuel passage and the catalyst, the Sv on the inlet side increases and the outlet side ° increases. Sv becomes smaller.

As a result, the reforming reaction at the inlet end is suppressed and, conversely, the reforming reaction at the outlet end is promoted. Overall, the reforming reaction is made uniform in the direction of fuel flow, resulting in a uniform temperature distribution inside the cell. can be achieved.

〔Example〕

FIG. 1 is a perspective view showing an internal reforming fuel cell according to an embodiment of the present invention. In the figure, the structure of a unit cell composed of an electrolyte plate 1, a fuel electrode 2, an oxidizer electrode 3, and an oxidizer passage 4 for supplying an oxidizer is the same as the conventional one.

A plate-shaped reforming catalyst layer 6 is installed on the fuel side of the fuel and oxidizer separation plate 5.

Further, on the fuel passage 7 side of the reforming catalyst layer 6, an extremely thin sheet metal 8 of conductive metal covers the catalyst layer 6. FIG. 2 shows a plan view of this sheet metal. The sheet metal is provided with perforations 9 along the flow of fuel 10 at the inlet end
1 to the outlet end 12, the aperture ratio of the perforations increases. The fuel passage 7 flows through a space formed by the sheet metal 8 and the fuel electrode 2. The fuel passage 7 is provided with a perforated corrugated plate 13 to support the fuel electrode 2, and a portion of the reformed fuel passes through the small holes of the perforated plate and reaches the surface of the fuel electrode.

Next, the operation will be explained. As in the conventional case, when hydrocarbons such as methane and steam are supplied to the fuel passage 7, when hydrogen, carbon oxide and carbon dioxide gas are generated by contact with the reforming catalyst layer, in the present invention, Since the contact area between the fuel and the catalyst increases along the flow direction of the fuel depending on the number of perforations, the contact time with the catalyst layer per unit electrode area can be increased at any position in the flow direction. different.

To be more precise, compared to the case where the contact area is uniform over the entire surface, the contact time is shorter near the entrance, and conversely, the contact time is longer near the exit.

Therefore, since the contact time is short near the entrance of the fuel passage 7 where the reaction rate of the reforming reaction is high, the amount of fuel reformed during that time tends to decrease.

On the other hand, near the exit where the reforming reaction rate is low, the contact time becomes longer, so the amount of reformed fuel tends to increase. Since the amount of heat absorbed is proportional to the flow rate of the reformed fuel, the amount of reformed fuel becomes uniform in the flow direction of the fuel, and therefore the amount of heat absorbed also becomes uniform.

The temperature distribution inside the battery becomes uniform.

Figure 3 shows a case where the contact area with the catalyst layer per unit electrode area is uniform over the entire surface of the cell (indicated by a broken line), and a case where the area is divided into four sections along the fuel flow direction, starting from the inlet side. The temperature distribution from the fuel side inlet end to the outlet end at the center of the cell when the contact area is increased in the order of 1/4.1/2.3/4.4/4 (shown by the solid line) is shown below. The comparison results are shown below.

These temperature distributions are examples of calculation results obtained by battery temperature distribution analysis that combines electrochemical reaction, reforming reaction, and heat transfer models, but it is clear that the effect of temperature distribution improvement by this example is It can be seen that is expressed.

FIG. 4 is a perspective view of a part of an internal reforming fuel cell showing another embodiment. In the above embodiment, sheet metal was introduced, but the sheet metal was not used and the perforated corrugated plate 13 The purpose is to control the contact area of the catalyst with only The perforated corrugated plate 13 may or may not have holes on the side surface 15, but at least the corrugated convex portion 14 in contact with the fuel electrode 3
must have holes for gas diffusion to the electrodes.

As shown in the plan view of the corrugated plate 13 in FIG.
From there, the number of perforations increases toward the outlet end 12, and as a result, the opening area increases along the flow. Note that the contact area of the catalyst layer cannot be controlled in the fuel passage 7a, but in the other passage 7-b.

The contact area can be changed by the perforations 9, and as a whole, the contact area of the catalyst layer increases on the downstream side of the fuel, similar to the above embodiment. In this embodiment, members such as the metal sheet 8 as in the above-mentioned embodiments are unnecessary, and the cost can be further reduced.

〔Effect of the invention〕

As described above, according to the present invention, the contact area with the catalyst layer is increased in the fuel flow direction in the fuel passage.

The fuel reforming reaction can be made uniform throughout the cell, and as a result, an internal reforming fuel cell can be obtained that can make the temperature distribution inside the cell more uniform at a lower cost than in the past.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a part of an internal reforming fuel cell according to an embodiment of the present invention, FIG. 2 is a plan view of a sheet metal according to an embodiment of the present invention, and FIG. Analysis results of electrolyte plate temperature distribution showing the effect in the embodiment, Fig. 4 is a perspective view of a battery according to another embodiment of the present invention, and Fig. 5 is a plan view of a perforated corrugated plate according to another embodiment of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Electrolyte plate, 2... Fuel electrode, 3... Oxidizer electrode, 4... Oxidizer passage, 5... Branch plate, 6...
Reforming catalyst layer, 7...Fuel passage, 8...Metal sheet, 13...Porous wave A1-Topelo to/l size pulverization'-4
Distance Danjia 4 figure high S command! 10

Claims (1)

[Claims] 1. A unit cell in which a fuel electrode and an oxidizer electrode are arranged to face each other with an electrolyte plate interposed therebetween, a fuel passage corresponding to the fuel electrode, and a fuel reforming catalyst installed in the fuel passage. and an oxidizer passage corresponding to the oxidizer electrode, and an internal reforming fuel cell that generates electricity while reforming the fuel by supplying fuel and oxidizer to the passages respectively, wherein the fuel and the catalyst are connected to each other. An internal reforming fuel cell characterized in that the contact area of the fuel cell is increased in the direction of the flow of the fuel. 2. A perforated plate is interposed at least in part between the fuel passage and the catalyst, and direct contact between the fuel and the catalyst at the location where the perforated plate is interposed is allowed only through the pores of the perforated plate. The internal reforming fuel cell according to claim 1. 3. The internal reforming fuel cell according to claim 2, wherein the aperture ratio of the pores in the perforated plate is increased from the inlet to the outlet, which is the flow direction of the fuel in the fuel passage.