JP2940108B2 - Internal reforming fuel cell - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an internal reforming fuel cell, and more particularly, to a structure of a reforming reaction region thereof.

[Prior Art] FIG. 4 is a perspective view showing a part of an embodiment of a conventional internal reforming fuel cell disclosed in, for example, JP-A-60-3255. In the figure, (1) is an electrolyte layer, (2) is a fuel gas electrode, (3) is an oxidizing gas electrode, and the fuel gas electrode (2) and the oxidizing gas electrode (3) are interposed through the electrolyte layer (1). And are arranged so as to face each other, and these constitute a unit cell. (4) is a fuel gas flow path provided facing the fuel gas electrode (2), (5) is an oxidizing gas flow path provided facing the oxidizing gas electrode (3), and (6) is a fuel gas flow path. Fuel gas side flow path forming material for forming flow path (4), (7)
Is an oxidizing gas side channel forming material for forming the oxidizing gas channel (5). (8) is a separator plate serving to separate the fuel gas flow path (4) and the oxidizing gas flow path (5) when stacking a plurality of cells and electrically connect the plurality of cells in series. is there. (9) is a reforming catalyst held inside the fuel gas flow path (4).

Next, the operation will be described. When a fuel such as a hydrocarbon and steam are supplied to the fuel gas flow path (4), the hydrocarbon reacts with the steam by a contact reaction with the reforming catalyst (9) to form hydrogen, carbon monoxide, and carbon dioxide gas. Is converted. When the hydrocarbon is methane, this reaction is represented by Formula-1.

CH ₄ + H ₂ O → CO + 3H ₂ (Equation-1) The generated hydrogen and carbon monoxide pass through the holes provided in the fuel gas side flow path forming material (6) and pass through the porous fuel gas electrode (2). Diffuse the pores. On the other hand, the oxidizing gas flow path (5)
Is supplied with a mixed gas of air and carbon dioxide gas, and diffuses through the pores of the porous oxidizing gas electrode (3). Electrolyte layer (1)
At about 650 ° C, the operating temperature, which is in a molten state, reacts by an electrochemical reaction between the electrodes (2) and (3) and the above-mentioned reaction gas containing hydrogen and oxygen as main components. Gas consumed and current collector (not shown)
An electric potential is generated between them, and electric power is taken out to the outside. The reforming reaction occurring on the reforming catalyst (9) is an endothermic reaction, and the amount of heat required to maintain this reaction is supplied from the heat generated by the electrochemical reaction.

For steady operation of the fuel cell, it is essential to balance heat between the heat absorbed by the reforming reaction and the heat generated by the battery reaction, and the reforming reaction proceeds to match the heat generated by the battery reaction. Need to be done. Here, the reaction rate of the reforming reaction depends on the partial pressure of methane and the activity / amount of the reforming catalyst, and the reaction rate generally increases as the partial pressure of methane increases, and as the activity / amount of the reforming catalyst increases. large. In a typical example, the methane reforming reaction rate is proportional to the product of the partial pressure of methane, the activity of the reforming catalyst, and the amount of the reforming catalyst, as shown in Equation-2.

Methane reforming reaction rate = k * Partial pressure of methane * Catalytic activity * Contact amount (Equation-2) (k: proportional constant) Therefore, when the reforming catalyst is held uniformly over the entire combustion gas flow path At the fuel gas inlet, the reforming reaction speed increases, and the reforming reaction proceeds abruptly, thereby disturbing the heat balance and making it impossible to perform a steady operation of the fuel cell. In the conventional example, the cross-sectional area perpendicular to the flow direction of the fuel gas in the fuel gas flow path (4) is changed in the flow direction of the fuel gas, and the distribution of the filling amount of the reforming catalyst (9) is appropriately adjusted. We are trying to optimize the reforming reaction distribution to achieve a thermal balance and a uniform temperature distribution. Such a method works well if the activity of the reforming catalyst is constant, and a uniform temperature distribution as set can be obtained. However, the activity of the reforming catalyst is usually not constant but changes with time. As an example, an example of the change with time of the activity of the reforming catalyst is shown in FIG.
Shown in the figure. In the figure, the vertical axis indicates the catalyst activity, and the horizontal axis indicates the operation time. The reforming catalyst usually has a fine active metal retained on a ceramic carrier having a pore structure, and some decrease in activity based on sintering of the material or the like is inevitable in the long term. In this conventional example, since the reforming reaction rate on the reforming catalyst itself is controlled to control the reforming reaction amount, when the activity of the reforming catalyst decreases, the decrease in the reforming reaction rate due to the decrease in the activity of the reforming catalyst remains unchanged. As a result, it is impossible to obtain a stable and stable distribution of the reforming reaction over a long period of time. Therefore, in such a design, a temporal change in the distribution of the reforming reaction amount is inevitable in the long term, and it is difficult to obtain a stable and uniform temperature distribution over a long term. In addition, the adverse effect of the decrease in the amount of reforming reaction accompanying the decrease in catalytic activity is particularly remarkable at the fuel gas inlet, and a decrease in the hydrogen concentration in this portion causes a decrease in cell characteristics and induces oxidation of the active metal of the reforming catalyst. This leads to a further decrease in catalytic activity.

[Problems to be Solved by the Invention] Since the conventional internal reforming fuel cell is configured as described above, it is difficult to obtain a stable and uniform temperature distribution over a long period of time, and the activity of the reforming catalyst is high. This leads to a problem that the reduction in the battery performance directly leads to a reduction in the battery characteristics, and further induces a further reduction in the activity of the reforming catalyst.

The present invention has been made in order to solve the above problems, and the distribution of the reaction amount of the reforming reaction hardly changes in response to the change in the activity of the reforming catalyst, and as a result, the reaction is stable for a long time. It is an object of the present invention to obtain an internal active fuel cell which can obtain a uniform temperature distribution and stable activity and cell characteristics of the reforming catalyst.

[Means for Solving the Problems] An internal reforming fuel cell according to the present invention comprises a plurality of reforming reaction sections in which a reforming reaction region is provided in series in a fuel gas flow direction inside a fuel gas flow path. Further, the reforming reaction portion is divided into a reforming reaction small portion in which the reforming reaction proceeds and a non-reforming reaction small portion in which the reforming reaction does not proceed. The amount of the reforming reaction in each reforming reaction section is controlled by individually adjusting the flow rate ratio of the fuel gas supplied to the section, and the reforming reaction amount in the fuel gas flow direction in the reforming reaction region as a whole is Are controlled so as to control the distribution.

[Action] The reforming reaction portion in the present invention has a reforming catalyst sufficient to allow the reforming reaction to proceed to near the equilibrium state. It is determined by the flow rate, composition, and operating conditions of the fuel gas supplied to the catalyst, and is almost independent of the catalytic activity. The distribution of the amount of reforming reaction in the direction of fuel gas flow in the reforming reaction region can be obtained by setting the amount of reforming reaction in each reforming reaction portion. In the reaction portion, the distribution ratio of the fuel gas to the reforming reaction small portion and the non-reforming reaction small portion is determined by setting the distribution ratio by the pressure adjusting means. Therefore, the reforming reaction distribution set in this way is insensitive to a change in the activity of the reforming catalyst, a uniform temperature distribution can be obtained stably over a long period of time, and the stable activity of the reforming catalyst and the battery Properties can be obtained.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, (1) is an electrolyte layer, (2) is a fuel gas electrode, (3) is an oxidizing gas electrode, (4) is a fuel gas channel, (8) is a separator plate, and (9) as in the conventional example. Is a reforming catalyst. Reference numeral (10) denotes a reforming reaction region provided inside the fuel gas flow path (4), which is located upstream from the fuel gas flow direction.
(11a), (11b), (11c), (11d), and (11e). (12) is a reforming reaction small part which has the ability to reform the hydrocarbons in the fuel gas while holding the reforming catalyst (9), and a part of each of the reforming reaction parts (11a) to (11e). Make. (13) is a non-reforming reaction small portion which does not have a reforming catalyst and thus has no ability to advance a reforming reaction, and constitutes the remaining other portion of the reforming reaction portions (11a) to (11e). (1
4) is the reforming reaction small part (12) and the non-reforming reaction small part (13)
And a separator for separating the above. (15) is a pressure loss adjusting means for adjusting a gas distribution ratio when the fuel gas is distributed and supplied to the reforming reaction small part (12) and the non-reforming reaction part small part (13). In the present embodiment, non-catalyst-filled particles having no catalytic function for the reforming reaction are employed in the pressure-loss adjusting means (15), and the non-catalyst-filled particles (15) are appropriately added to the non-reforming reaction small portion (13). The gas distribution ratio is adjusted by filling.

 Next, the operation will be described.

 First, the progress of the reforming reaction is as follows.

The fuel gas containing hydrocarbons or alcohols as main components introduced into the fuel gas flow path (4) has a small reforming reaction portion (12) and a small non-reforming reaction portion (13) according to a predetermined ratio. And distributed. In the reforming reaction portion (12), there is sufficient reforming catalyst (9) to improve hydrocarbons and alcohols contained in the supplied fuel gas to near equilibrium.
Is maintained, and the reforming reaction proceeds. On the other hand, the non-reforming reaction small portion (13) does not hold the reforming catalyst, and the reforming reaction hardly proceeds. Reforming reaction small part (12)
And a non-reforming reaction portion (13)
The reforming reaction amount in a) to (11e) is a small part of the reforming reaction (1
The reforming reaction amount is equal to the reforming reaction amount in 2), and the reforming reaction amount is substantially determined by the composition and flow rate of the fuel gas supplied to the reforming reaction small portion (12). Now, the reforming reaction part (11
Assuming that the fuel gas composition in a) to (11e) is constant, by adjusting the distribution ratio of the fuel gas to the reforming reaction small part (12) and the non-reforming reaction small part (13), The amount of reforming reaction in the reforming reaction portions (11a) to (11e) can be adjusted.

In the present embodiment, the distribution ratio of the fuel gas is adjusted by using the pressure loss adjusting means (15) to adjust the flow resistance of each of the reforming reaction small portion (12) and the specific reforming reaction small portion (13). It is achieved by doing.

The fuel gas in which part of the hydrocarbons or alcohols has been reformed in the upstream reforming reaction section (11a) is sequentially supplied to the downstream reforming reaction section (11e), and the downstream reforming reaction small section. Hydrocarbons or alcohols are further reformed by the action of the reforming catalyst (9) of (12).

 Next, the progress of the battery reaction is as follows.

Hydrogen or carbon monoxide generated as a result of the reforming reaction by the action of the reforming catalyst (9) held in the reforming reaction small portion (12) is subjected to an electrochemical reaction at the fuel gas electrode (2). . In FIG. 1, the reforming reaction sub-portion (12) is spatially separated from the adjacent fuel gas electrode (2) by a separator (14). Therefore, there is a small part of the reforming reaction (12)
The hydrogen or carbon monoxide produced as a result of the reforming reaction flows further down the specific reforming reaction portion (13) of the reforming reaction portion (11) further downstream, where it is subjected to an electrochemical reaction. You. The reforming catalyst (9) is connected to the adjacent fuel gas electrode (2).
Although not necessarily required to be kept in a space isolated from the fuel gas, the reforming catalyst generally tends to be poisoned by the electrolyte vapor evaporated or scattered from the fuel gas electrode (2). Therefore, in order to aim for stable operation for a long period, it is preferable to keep the reforming catalyst spatially separated from the adjacent fuel gas electrode (2).

Here, in the internal reforming fuel cell according to the present invention, the distribution of the reforming reaction rate of the fuel gas in the fuel gas flow path is determined as follows. As an example, the fuel gas is methane, steam carbon ratio is 2.0, 650 ℃, atmospheric pressure operation,
It is assumed that there is a load. FIG. 2 schematically shows a reforming reaction rate distribution according to an example of the examination result. In FIG. 2, the change of the reforming reaction rate in each reforming reaction portion is shown by approximation with a straight line. Actually, in each reforming reaction portion, the reforming reaction rate asymptotically changes from the inlet to the outlet.

First, the first reforming reaction section (11a) will be described.
Small reforming reaction part (12) in first reforming reaction part (11a) to prevent rapid progress of reforming reaction at fuel gas inlet
The distribution ratio of fuel gas to fuel is 1/8. Further, since the fuel gas flowing through the non-reforming reaction small portion (13) in the first reforming reaction portion (11a) hardly contains hydrogen, the fuel gas electrode (2) facing this portion has an electric power. Chemical reactions do not proceed very actively. Therefore, the first reforming reaction part (11
It is desirable to set a) as small as possible. Usually, the outer peripheral portion of the peripheral portion of the cell, which extends over a width of, for example, 10 to 30 mm, is called a wet seal portion, and is not considered to be an effective electrode portion. Therefore, if the first reforming reaction portion (11a) is provided in the wet seal portion at the fuel gas inlet portion, the fuel gas can be reformed without adversely affecting the battery characteristics.

In the first reforming reaction section (11a), according to the set distribution ratio, 1/8 of the supplied fuel gas flows through the reforming reaction small section (12), and the remaining 7/8 of the supplied fuel gas flows. A flow of fuel gas flows through the non-reforming reaction subsection (13). Here, the reforming reaction small portion (12) holds a reforming catalyst (9) sufficient to reform the supplied fuel gas to near the equilibrium state. The required amount of reforming catalyst is calculated by a conventional reaction engineering technique. Under such a reaction condition that the fuel gas is reformed to near the equilibrium state, the reforming reaction amount in the reforming reaction portion (12) is insensitive to the change in the activity of the reforming catalyst (9). And is determined mainly by the flow rate of the supplied combustion gas. FIG. 3 shows an example of the result of study on how the methane reforming rate, that is, the reforming reaction amount, changes with the change in the activity. As shown in FIG. 3, even if the activity of the reforming catalyst is reduced to, for example, 1/10 of the initial value, the reforming reaction amount is reduced to only about 60% of the initial value. It can be seen that the amount is very stable with respect to the catalytic activity. The reason for this is that, in the present invention, the reforming reaction is designed to proceed to near the equilibrium state in each reforming reaction small portion (12). Does not significantly affect the amount of reforming reaction in each reforming reaction subportion (12). The degree of stability of the reforming reaction amount depends on the design conditions of the reforming reaction portion (12), and as is apparent from FIG.
The closer the gas composition at the outlet is to the equilibrium state, the greater the stability.
Actually, the design conditions of the reforming reaction portion (12), for example, the filling amount of the reforming catalyst (9) are determined by the tendency of the activity of the reforming catalyst (9) to decrease and the space volume of the reforming reaction portion (12). Determined by taking into account. On the other hand, the non-reforming reaction small portion (13) does not hold the reforming catalyst, and the reforming reaction hardly proceeds. Therefore, the reforming reaction amount as the reforming reaction portions (11a) to (11e) is equal to the reforming reaction amount in the reforming reaction small portion (12).

As described above, the reforming reaction amounts of the reforming reaction portions (11a) to (11e) can be adjusted by appropriately setting the gas distribution ratio of the fuel gas to the reforming reaction small portion (12). Furthermore, the reforming reaction amount set in this manner is insensitive to a change in the catalytic activity of the reforming catalyst (9), and a stable reforming reaction amount can be obtained over a long period of time.

In the present investigation example, the gas distribution ratio in the second reforming reaction section (11b) was reduced to 1/4 and the gas distribution ratio in the third reforming reaction section (11c) was reduced to 1/3. The distribution ratio of the gas in the reforming reaction section (11d) was set to 1/2, so that a substantially uniform distribution of the reforming reaction in the fuel gas flow direction was obtained as shown in FIG. In order to obtain a uniform temperature distribution in a plane, the reforming reaction needs to proceed according to the amount of heat generated by the battery reaction. Such a preferable distribution of the reforming reaction amount is determined separately experimentally or by a technique of reaction engineering. Such a distribution of the reforming reaction amount is determined by the method according to the present invention.
It can be obtained by appropriately adjusting the number of reforming reaction portions to be set, the size of each reforming portion, the gas distribution ratio in each reforming reaction portion, and the like.

In the present study example, the fifth reforming reaction part (11e) was composed of only the reforming reaction small part (12). As the downstream side of the fuel gas flow path decreases, the residual methane concentration decreases, and (Equation 2)
As is clear from the above, the reforming reaction rate is reduced. Under such conditions, the necessity of the non-reforming reaction small portion (13) to suppress the progress of the speed of the reforming reaction becomes relatively small. The fuel gas discharged from the fifth reforming reaction part (11e) is used for an electrochemical reaction at a fuel gas electrode (2) located further downstream.

In the above embodiment, the non-reforming reaction small portion (13) is filled with non-catalyst-filled particles as the pressure loss adjusting means (15), and the pressure loss in the non-reforming reaction small portion (13) is adjusted. The example in which the gas distribution ratio is adjusted has been described. Alternatively, the gas distribution ratio can be adjusted by adjusting the ratio of the cross-sectional area of the flow passage between the reforming reaction small portion (12) and the non-reforming reaction small portion (13). To play.

Also, if a corrugated plate-like forming material such as the oxidizing gas-side flow path forming material (7) shown in FIG. 4 is used as the fuel gas-side flow path forming material (6), the flow path on one side is reformed. Small part (1
2) The remaining one-side channel can be set as the non-reforming reaction small portion (13), and this embodiment can be easily realized.

[Effects of the Invention] As described above, according to the present invention, the reforming reaction region includes a plurality of reforming reaction portions provided in series in the fuel gas flow direction inside the fuel gas, and further includes the reforming reaction region. The reaction portion is divided into a reforming reaction small portion where the reforming reaction proceeds and a non-reforming reaction small portion where the reforming reaction does not proceed, and
By controlling the ratio of the flow rate of the fuel gas supplied to both reaction small portions individually by the pressure adjusting means, the reaction amount of the reforming reaction in each reforming reaction portion is controlled, and the fuel gas in the reforming reaction region as a whole is controlled. An internal reforming fuel cell that is configured to control the distribution of the amount of reforming reaction in the flow direction, so that a stable and uniform temperature distribution is obtained over a long period of time, and that the activity and cell characteristics of the reforming catalyst are stable. Can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a main part of an internal reforming fuel cell according to an embodiment of the present invention, and FIG. FIG. 3 is a characteristic diagram showing the distribution of the reforming rate of the fuel gas in the fuel gas flow path, and FIG. 3 is a catalyst showing the amount of the reforming reaction in a small reforming reaction in the internal reforming fuel cell according to one embodiment of the present invention. FIG. 4 is a characteristic diagram showing activity dependency, FIG. 4 is a perspective view showing the structure of a conventional internal reforming fuel cell,
FIG. 5 is a characteristic diagram showing the change over time in the activity of the reforming catalyst. In the figure, (1) is an electrolyte layer, (2) is a fuel gas electrode, (3) is an oxidizing gas electrode, (4) is a fuel gas path,
(5) is an oxidizing gas flow path, (9) is a reforming catalyst, (11a) to
(11e) is the reforming reaction part, (12) is the reforming reaction small part, (1
3) is a small part of the non-reforming reaction, and (14) is a separator. In the drawings, the same reference numerals indicate the same or corresponding parts.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-140560 (JP, A) JP-A-61-58174 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 8/02 H01M 8/06

Claims (3)

(57) [Claims] 1. A unit cell in which a fuel gas electrode and an oxidizing gas electrode are arranged to face each other with an electrolyte layer interposed therebetween, and a reforming reaction proceeds by holding a reforming catalyst provided for the fuel gas electrode. A fuel gas flow path having a function of squeezing, and a fuel cell including an oxidizing gas flow path provided for the oxidizing gas electrode, wherein a reforming reaction small portion in which a reforming reaction proceeds while holding the reforming catalyst; A non-reforming reaction small portion in which the reforming reaction does not proceed without holding the reforming catalyst; and a pressure loss adjusting means for controlling a distribution ratio of the fuel gas to the reforming reaction small portion and the non-reforming reaction small portion. And a reforming reaction in which a part of the fuel gas is distributed and supplied to the small reforming reaction portion with a predetermined fuel gas distribution ratio, and the remainder of the fuel gas is distributed and supplied to the non-reforming reaction small portion. Part inside the fuel gas flow path A plurality of fuel gas distribution directions are provided in series along the flow direction of the fuel gas, and the distribution ratio of the fuel gas in each of the reforming reaction portions is adjusted so that a predetermined distribution of the reforming reaction amount in the fuel gas flow direction in the fuel gas flow path is obtained. The internal reforming fuel cell is characterized in that the fuel cell and the fuel cell are mutually adjusted. 2. The internal reforming fuel cell according to claim 1, wherein the pressure loss adjusting means is non-catalyst-filled particles that do not participate in the reforming reaction. 3. The internal reforming apparatus according to claim 1, wherein the pressure loss adjusting means adjusts a ratio of a cross-sectional area of the flow passage between the small reforming reaction portion and the small non-reforming reaction portion. Type fuel cell.