JP5178044B2 - Fuel cell - Google Patents

Description

  The present invention relates to a cylindrical fuel cell having a cylindrical shape, a flat cylindrical shape, an elliptical shape, or the like. The present invention is suitable for a solid oxide fuel cell (SOFC) having a solid oxide electrolyte or a solid polymer fuel cell (PEFC) having a solid polymer electrolyte.

  The fuel cell includes a cell composed of an anode (fuel electrode), an electrolyte, and a cathode (air electrode), supplies fuel gas to the anode side of the cell, supplies oxidant gas to the cathode side, and supplies fuel via the electrolyte. It is a power generator that generates electricity by electrochemically reacting an oxidant.

  A solid oxide fuel cell (SOFC), which is one type of fuel cell, has high power generation efficiency and is operated at a high temperature of 600 to 1000 ° C., so that a fuel reforming reaction can be performed in the cell. For this reason, the diversification of fuel can be achieved, the battery system structure is simplified, and there is a potential for cost reduction compared to other fuel cells. Naturally, the exhaust heat is also high in temperature, so that it is easy to use, and not only a combined heat / electric system but also a hybrid system with other systems such as a gas turbine can be easily formed.

  SOFCs are roughly divided into cylindrical and flat plate shapes depending on the shape of the solid electrolyte. The cylindrical shape is more resistant to thermal stress than the flat plate shape, and is a great advantage for SOFCs operating at high temperatures.

  As an example of a cylindrical SOFC, Patent Document 1 includes a cell in which a fuel electrode, an electrolyte, and an air electrode are stacked in this order on the outer wall of a cylindrical porous substrate tube, and a spiral groove is formed on the inner wall of the substrate tube. It is described that the flow of fuel gas is disturbed to efficiently remove water vapor from the inner surface of the base tube, thereby improving the efficiency of the fuel cell.

JP 2006-100212 A (summary)

By the way, in the cylindrical SOFC, the power generation performance of the fuel electrode located on the downstream side tends to be lower than the power generation performance of the fuel electrode located on the upstream side of the fuel flow. Patent Document 1 described above is not intended to address this problem, nor gives a hint to solve this problem.

  An object of the present invention is to provide a cylindrical fuel cell in which the power generation performance of a fuel electrode located on the downstream side of the fuel flow can be enhanced.

The present invention comprises a cylindrical cell having a cathode inside having anode and the collector electrode to the outside of the electrolyte, with the fuel flow path along the anode, cylindrical with an oxidizing agent passage along the cathode in fuel fuel cell a plurality are connected in series or parallel cell, the concentration ratio of the fuel gas to the fuel flow path to the total gas amount Ru flow to enhance the side of the anode of the fuel flow path, flowing through the fuel flow path Gas swirling means for swirling gas is provided , each cylindrical fuel cell further includes a cell container for storing the cell, and a space between the cell container and the anode is a fuel flow path .

  According to the present invention, the cell reaction becomes active even on the downstream side of the fuel flow path, and the power generation performance can be improved.

  The present invention proposes to increase the fuel concentration in the vicinity of the anode in order to activate the cell reaction downstream of the fuel flow path. It is also proposed to install a selective fuel permeable membrane in the fuel flow path to increase the downstream fuel concentration. Furthermore, it is proposed to install a fuel recycle line and to provide a selective fuel permeable membrane in the line.

  As a means for increasing the fuel concentration in the vicinity of the anode, a method of applying a turning force to the gas flowing through the fuel flow path is effective, and can be applied to a cylindrical fuel cell having an anode outside the electrolyte.

  By applying a swirling force to the fuel flow, a centrifugal force acts on the gas, and water vapor or carbon dioxide having a larger mass number than hydrogen, which is a fuel, is directed toward the outer periphery having a large radius by the centrifugal force. Thereby, the fuel concentration on the inner peripheral side where the cell reaction occurs can be increased. The increase in fuel concentration in the vicinity of the anode due to gas swirling appears more strongly on the downstream side of the fuel flow path, and can activate the cell reaction on the downstream side of the fuel gas flow.

  As a means for giving a turning force to the gas, it is effective to install a rectifying plate having a nozzle attached obliquely upward at the gas inlet portion of the fuel flow path. By supplying the fuel gas to the fuel flow path through the nozzle, a turning force can be applied to the fuel gas. It is also effective to divide the collector electrode into a plurality and arrange them obliquely upward. A swirl force is applied to the gas when the gas passes between the divided collector electrodes. It is preferable to combine the rectifying plate with nozzle and the division of the collector electrode.

  In addition, as the gas swirling means, it is effective to provide a spiral groove on the inner surface of the cell container, or to provide a spiral filler on the inner surface of the cell container or the outer surface of the anode.

  The method of providing the selective fuel permeation means in the fuel flow path or the fuel recycle line can be applied to either a cell having an anode outside the electrolyte or a cell having a cathode outside the electrolyte. Hydrogen gas is generally used as the fuel gas for SOFC and PEFC, and hydrogen permeable membranes are well known. Therefore, implementation is easy.

  A fuel cell system is constructed by connecting a plurality of cylindrical fuel cells described above in series or in parallel.

  The cylindrical fuel cell of the present invention includes a cell having a cylindrical shape, a flat cylindrical shape, an elliptical shape, or the like. Including these, the present invention is referred to as a cylindrical fuel cell.

  Hereinafter, embodiments of the present invention will be described by taking an example in which the outside of the cylindrical cell is an anode and the inside is a cathode, but the present invention is not limited to this.

  FIG. 1 shows a three-dimensional view and a longitudinal sectional view of a cylindrical cell according to an embodiment of the present invention. (A) is a three-dimensional view, (b) is a longitudinal sectional view. In the cell, an anode 2 (fuel electrode) is formed on the outer periphery of the solid electrolyte 1, a cathode 3 (air electrode) is formed on the inner periphery, and a collecting electrode 5 for taking out current is divided into a plurality of parts on the outer surface of the anode 2 It consists of what was formed. The overall shape is bag-shaped. These are accommodated in the cell container 15, and the fuel flow path 6 is formed with the inner surface of the cell container 15 and the outer surface of the anode 2 as flow path walls. An air introduction pipe 4 for supplying air as an oxidant is provided at the center of the cell, and an air flow path 7 is formed. Although not shown in FIG. 1, the fuel is supplied obliquely upward using a rectifying plate with a nozzle or the like to form a swirling flow.

  The cell current flows from the collector electrode 5 through the anode 2 and the solid electrolyte 1 to the cathode 3. The fuel flows like a fuel flow 8 indicated by an arrow while turning in the circumferential direction of the fuel flow path 6.

  The solid electrolyte 1 has a cylindrical bag shape, and yttrium-stabilized zirconia (YSZ) or the like is used as a material. The anode 2 is made of a porous cermet made of nickel and YSZ. Nickel acts as a reforming catalyst. As the material of the cathode 3, lanthanum manganate or the like is used.

  Here, the battery reaction is shown. First, a method for reforming a hydrocarbon fuel to generate a reformed gas containing hydrogen will be described taking methane as an example of the hydrocarbon fuel. On the reforming catalyst, methane and steam react (reformation reaction) mainly by the reaction of the formula (1) to generate hydrogen. In addition to the nickel-based reforming catalyst, a ruthenium-based catalyst can also be used.

CH ₄ + H ₂ O = CO + 3H ₂ (1) Formula At the same time, CO reacted by the formula (1) is reacted with H ₂ O represented by the following formula (2) (CO conversion reaction). Furthermore, it is converted to hydrogen and used as fuel.

CO + H ₂ O = CO ₂ + H ₂ (2) Formula The reaction for generating hydrogen from a hydrocarbon-based fuel is an endothermic reaction, and heat must be supplied to continue this reaction. It is necessary to maintain the reforming catalyst at about 400 to 800 ° C.

  The battery reaction (power generation reaction) occurs at the anode 2 and is expressed by the following formulas (3) and (4) and is an exothermic reaction.

H ₂ + 1 / 2O ₂ = H ₂ O (3) Formula CO + 1 / 2O ₂ = CO ₂ (4) Accordingly, when the cell reaction proceeds, water vapor and carbon dioxide are generated, and in the fuel flow path 6 Will increase the concentration of water vapor and carbon dioxide. On the other hand, hydrogen and carbon monoxide, which are fuels, are consumed in the cell reaction, and the concentration of fuel decreases as it goes downstream. As a result, the concentration of the fuel gas in the total gas amount (fuel gas amount + cell reaction product amount) in the fuel flow path decreases as it goes downstream.

  Therefore, in the present invention, a turning force is applied to the fuel flow 8. As a result, centrifugal force acts on the gas, and water vapor or carbon dioxide with a mass number larger than that of hydrogen moves toward the outer periphery with a large radius due to the centrifugal force. At the anode on the small radius side where the cell reaction occurs, the fuel concentration with respect to the total gas amount The ratio becomes high. Therefore, it is possible to prevent the power generation performance from being lowered downstream of the anode.

  Here, the concentration factor (α-1) by centrifugal force can be expressed by the following equation (5).

α-1 = (Ma−Mb) V ² / 2RT (5) where α is a separation factor, Ma and Mb are mass numbers, V is a rotation speed, R is a gas constant, and T is a temperature.

  If the rotation speed V is set to 300 m / s, hydrogen is concentrated by about 21% compared to carbon dioxide and about 8% compared with water.

FIG. 2 is a cross-sectional view of the fuel flow path in the present embodiment, and schematically shows how the hydrogen concentration is high and low. Since a centrifugal force acts on the gas flowing through the fuel flow path 6, the fuel rich region 11 having a high H ₂ concentration or CO concentration is formed on the inner peripheral side near the anode 2, and H ₂ O or CO that is a cell reaction product. _The battery reaction product rich region 12 containing a large amount of ₂ is formed on the outer peripheral side far from the anode 2. Therefore, the ratio of the fuel to the total flow rate can be increased on the surface of the anode 2 even downstream of the fuel gas flow.

  FIGS. 3A and 3B show a three-dimensional view and a longitudinal sectional view of a cylindrical cell provided with means for applying a turning force to the fuel gas. In this embodiment, a rectifying plate 9 is provided at the bottom of the cylindrical cell and the bottom of the fuel flow path 6. The rectifying plate 9 is provided with a rectifying nozzle 10 for rectifying the flow. The rectifying nozzle 10 is installed obliquely upward to give a swirl flow to the fuel. The fuel flow 8 becomes a swirling flow and flows out upward of the cell. At this time, a concentration gradient as shown in FIG. 2 is formed.

  4A and 4B show a three-dimensional view and a longitudinal sectional view of a cylindrical cell in which the collector electrode 5 is disposed so as to be inclined upward and further includes a current plate 9. Thus, by providing the collector electrode 5 in a spiral shape, the turning force can be further increased.

  As the gas swirling means, there are a method of providing a filler spirally on the inner periphery of the cell container or the outer periphery of the anode, and a method of providing a spiral groove on the inner periphery of the cell container 15. These means are preferably used together with the rectifying nozzle 10 as shown in FIG.

For comparison, FIGS. 7A and 7B show an elevation view and a longitudinal sectional view of a cylindrical cell having no gas swirling means. Since the fuel flow 8 is a straight flow and does not become a swirl flow, the hydrogen concentration in the vicinity of the anode cannot be increased. For this reason, the cell reaction downstream of the fuel flow cannot be enhanced, and high power generation performance cannot be obtained .

[Reference Example 1]
Here, a reference example in which a hydrogen permeable membrane is provided in the middle of the fuel flow path 6 to increase the hydrogen gas concentration on the downstream side of the fuel flow will be described.

FIGS. 5A and 5B show a three-dimensional view and a longitudinal sectional view of a cylindrical cell according to this reference example. A hydrogen permeable membrane 13 is provided in the middle of the fuel flow path 6. Since only the hydrogen in the fuel gas permeates through the hydrogen permeable membrane 13, the hydrogen concentration toward the downstream is increased and the power generation performance is improved. The hydrogen permeation amount Q can be expressed by the following equation (6).

Q = ΦS (√P1−√P2) / d (6) where Φ is a transmission coefficient, S is a transmission area, P1 and P2 are upstream and downstream gas pressures, and d is a film thickness. .

For example, when the transmission coefficient Φ is 10 ⁻⁶ , when the transmission area S is 1 cm ² and the thickness is 2 μm, it is possible to flow hydrogen for a current of 10 A with a pressure difference of about 100 Pa. The installation position of the hydrogen permeable membrane 13 in FIG. 5 is preferably about 1/3 to 1/2 from the uppermost end in the axial direction of the cell. That is, it is preferable to install a hydrogen permeable membrane in a region where the hydrogen concentration in the fuel gas is low and a region where the reforming is completed .

[Reference Example 2]
In this reference example, an example in which a fuel recycling line is provided and a hydrogen permeable membrane is provided in the middle of the line will be described.

FIG. 6 shows a longitudinal sectional view of a cylindrical cell device which is a reference example of the present invention. This is a case where the fuel remaining at the upper end of the cell is returned to the cell bottom and the recycling operation is performed. A hydrogen permeable membrane 13 is installed in the middle of the recycle line 14. Thereby, unnecessary battery reaction products and the like can be separated from the recycle line 14, and hydrogen can be selectively returned to the inlet portion of the fuel flow path.

  In the above embodiment, the bag tube is described as an example of a cylindrical shape, but an open cylindrical shape without a bottom does not impair the effect at all.

  Further, the cell shape is not limited to the cylindrical shape, but can be applied to cells such as a flat cylindrical shape and an elliptical shape, and the same effect can be obtained.

  In the fuel cell of this embodiment, since almost the entire area of the cylindrical cell contributes to the battery reaction, the power generation area can be increased, the power generation amount can be increased, and the overvoltage can be reduced to reduce the internal resistance, so that the energy efficiency Can be increased.

The solid view and longitudinal cross-sectional view of a cylindrical cell in the state which abbreviate | omitted the gas swirling means are shown. A cross-sectional view of a fuel flow path of a cylindrical cell is shown. The solid view and longitudinal cross-sectional view of the cylindrical cell which is an Example of this invention are shown. The solid view and longitudinal cross-sectional view of the cylindrical cell which are other Examples of this invention are shown. The solid figure and longitudinal cross-sectional view of the cylindrical cell which provided the hydrogen permeable membrane in the fuel flow path are shown. The longitudinal cross-sectional view of the cylindrical cell which provided the hydrogen permeable membrane in the fuel recycle line is shown. A three-dimensional view and a longitudinal sectional view showing a fuel flow of a conventional cylindrical cell having no gas swirling means and a hydrogen permeable membrane are shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte, 2 ... Anode (fuel electrode), 3 ... Cathode (air electrode), 4 ... Air introduction pipe, 5 ... Collector electrode, 6 ... Fuel flow path, 7 ... Air flow path, 8 ... Fuel flow, 9 DESCRIPTION OF SYMBOLS ... Rectification plate, 10 ... Rectification nozzle, 11 ... Fuel rich area | region, 12 ... Battery reaction product rich area | region, 13 ... Hydrogen permeable membrane, 14 ... Recycle line, 15 ... Cell container.

Claims (6)

A cylindrical fuel cell comprising a cylindrical cell having an anode and a collecting electrode outside the electrolyte and having a cathode inside, a fuel flow path along the anode, and an oxidant flow path along the cathode In a fuel cell in which a plurality of are connected in series or in parallel,
Gas swirling means for swirling the gas flowing in the fuel flow path so as to increase the concentration ratio of the fuel gas to the total gas amount flowing in the fuel flow path on the anode side of the fuel flow path ;
Each of the cylindrical fuel cells further comprises a cell container that houses the cell,
A fuel cell , wherein a space between the cell container and the anode is the fuel flow path . The fuel cell according to claim 1 , wherein the fuel gas is hydrogen gas. 2. The fuel cell according to claim 1 , wherein the gas swirling means includes a rectifying plate having a nozzle obliquely upward at a gas inlet portion of the fuel flow path of each of the cylindrical fuel cells. 2. The fuel cell according to claim 1 , wherein the collecting electrode of each of the cylindrical fuel cells is divided into a plurality of gas swirling means, and the divided collecting electrodes are installed obliquely upward. As the gas swirling means, a rectifying plate having a nozzle obliquely upward is provided at a gas inlet portion of the fuel flow path of each cylindrical fuel cell, and the collector electrode of each cylindrical fuel cell is divided into a plurality of parts. the fuel cell according to claim 1, characterized in that the divided collecting electrode was placed diagonally upward, respectively. 2. The fuel cell according to claim 1 , wherein a spiral groove is provided on an inner surface of the cell container of each of the cylindrical fuel cells as the gas swirling means.

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