JP4767532B2 - Horizontally striped solid oxide fuel cell - Google Patents

Description

  The present invention relates to a horizontal oxide solid oxide fuel cell. More specifically, the present invention relates to a plurality of solid oxide fuel cells arranged on the outer surface of a porous insulating support base having a fuel flow path therein. The present invention relates to a horizontal stripe type solid oxide fuel cell arranged in a shape.

  A solid oxide fuel cell (SOFC (= Solid Oxide Fuel Cell), hereinafter abbreviated as SOFC as appropriate) generally has an operating temperature as high as about 800 to 1000 ° C. Those with operating temperatures in the range of 800-650 ° C are also being developed. The SOFC has an anode and a cathode arranged with an electrolyte material in between, and is composed of a three-layer unit of anode / electrolyte / cathode.

  During SOFC operation, both electrodes are connected to an external load through fuel on the anode side and oxidant gas (air, oxygen-enriched air, oxygen, etc., hereinafter referred to as air as appropriate) through the cathode side. Electric power can be obtained. However, since a single cell can only obtain a voltage of about 0.7 to 0.8 V at most, it is necessary to electrically connect a plurality of single cells (cells) in series in order to obtain practical power. is there. Interconnectors and cells are stacked alternately for the purpose of properly distributing, supplying, and discharging fuel and air to and from the anode and cathode respectively at the same time that adjacent cells are electrically connected in series. .

  The SOFC as described above is a type in which a plurality of cells are stacked. However, instead of this, it is considered that the arrangement of the cells is a horizontal stripe method. The horizontal stripe method includes a cylindrical type and a hollow flat type, and a cell comprising an anode, an electrolyte (usually an electrolyte made of a solid oxide), and a cathode on the outer surface of a porous insulating support substrate having a fuel flow path inside. Are arranged in a horizontal stripe pattern. FIG. 7 is a diagram showing a configuration example of a cylindrical type disclosed in JP-A-10-3932. 7A is an overall view, FIG. 7B is an enlarged view of a cross section of an X portion of FIG. 7A, and FIG. 7C is an enlarged view of a cross section of a Y portion of FIG. 7A. It is a figure shown.

JP-A-10-3932

  As shown in FIGS. 7A to 7C, a plurality of cells 25 formed by sequentially stacking an anode 22, an electrolyte 23, and a cathode 24 on the outer peripheral surface of a porous cylindrical substrate tube 21 are formed on the substrate tube 21. It is formed at intervals in the longitudinal direction. 26 is an interconnector for electrically connecting adjacent cells, and 33 is a current collecting ring. As a constituent material of the porous cylindrical substrate tube 21, calcia stabilized zirconia (CSZ) or the like is used.

  Although there is no explicit description of the operation in the publication, it is assumed that the vehicle is operated as follows. Air is flowed to the cathode 24 side of the outer periphery of the cylindrical substrate tube 21, and fuel is introduced from the collector ring 33 side into a supply tube (not shown in FIG. 7) in the cylindrical substrate tube 21, and at the tip thereof. The discharge is folded back and flows toward the anode 22 on the inner periphery of the cylindrical base tube 21. The anode off-gas released from the collector ring 33 side of the cylindrical base tube 21, that is, the unused fuel in the used fuel, is burned by the cathode off-gas, that is, oxygen in the used air. The heat generated by the combustion is used for preheating the supply air and maintaining the temperature of the cell stack.

  By the way, in the horizontal-striped solid oxide fuel cell, the discharge end of the spent fuel is usually an open system, and the unused fuel in the spent fuel and the spent air are near the outside of the discharge end. Unused oxygen is mixed and burned at a high temperature. As a result, it is possible to ensure safety by exhausting the combustible gas, which is an unused fuel in the used fuel, as an incombustible gas, and to supply heat necessary for operating the fuel cell. It becomes.

  However, if the distance between the discharge end of the spent fuel and the cell on the most discharge end side (the cell closest to the discharge end) or a cell in the vicinity thereof is short or the diameter of the discharge end is large, Although it diffuses back into the fuel flow path from the discharge end of the used fuel, the power generation output of the solid oxide fuel cell is reduced. Nothing has been found to prevent performance degradation due to back diffusion of air.

  The present invention has been made in order to solve such problems in a horizontal stripe type solid oxide fuel cell. In the horizontal stripe type solid oxide fuel cell, the fuel flow is started from the discharge end of the spent fuel. An object of the present invention is to provide a horizontal-stripe type solid oxide fuel cell that restricts the inflow of used air flowing back into the cell after being reverse-diffused into the road and prevents the output of the solid oxide fuel cell from decreasing. It is what.

The present invention is a solid oxide retardant ponds multi-segment type comprising a porous insulating support a plurality of the solid oxide fuel cell to the outer surface of the substrate having a fuel flow path therein arranged in horizontal stripes there are, for the support substrate, the oxygen inverse diffusing the length of the fuel discharge end to a position of the cell Le of the most fuel discharge end as 20 / 1.5 or more lengths for pore diameter of the fuel flow path to prevent with frequency, the solid oxide fuel horizontal stripes method characterized by comprising so as to restrict the flow of the used oxidizing agent gas despreading the fuel flow path of the fuel discharge end or al supporting lifting body It is a battery.

  According to the present invention, the support base in the horizontal stripe type solid oxide fuel cell is configured to restrict the inflow of the used oxidant gas flowing back-diffused from the discharge end of the used fuel into the fuel flow path. It is possible to prevent a decrease in power generation output due to the inflow, and to prevent a decrease in battery performance as a whole solid oxide fuel cell.

The present invention is a solid oxide retardant ponds multi-segment type comprising a porous insulating support a plurality of the solid oxide fuel cell to the outer surface of the substrate having a fuel flow path therein arranged in horizontal stripes is there. Then, the said supporting lifting body, oxygen inverse diffusing the length from the fuel discharge end to a position of the cell Le of the most fuel discharge end as 20 / 1.5 or more lengths for pore diameter of the fuel flow path with prevention area, characterized by comprising so as to limit the flow of the used oxidizing agent gas despreading the fuel flow path of the fuel discharge end or al supporting lifting body.

  Here, in the present invention, it is important that the length (that is, the interval) of the support base extending from the fuel discharge end to the cell position on the most fuel discharge end side is at least 20 mm. Among them, it is particularly preferable that the length (that is, the interval) extending from the fuel discharge end to the cell position on the most fuel discharge end side is in the range of 30 mm to 50 mm. In the present invention, the fuel flow path provided inside the support base may be one or a plurality of fuel flow paths. The shape of the fuel flow path is configured to have a rectangular cross section, a square cross section, a circular cross section, an elliptical cross section, and other appropriate shapes. Hereinafter, the present invention will be described in more detail with reference to the drawings.

  FIG. 1 is a diagram for explaining a configuration example of an SOFC targeted in the present invention. 1A is a plan view, FIG. 1B is a back view, and FIG. 1C is a cross-sectional view taken along line AA in FIG. 1A. 1 (d) is a cross-sectional view taken along line BB in FIG. 1 (b), and FIG. 1 (e) is a side view of FIGS. 1 (a) to 1 (b) [FIGS. 1 (a) to (b). In the figure seen from the right side], each is enlarged. In FIG. 1, reference numeral 2 denotes a hollow strip-like (hollow flat) porous insulating support base, and the hollow portion 3 serves as a fuel flow path 3. Although FIG. 1 shows an example in which nine fuel flow paths 3 are provided, one or more fuel flow paths 3 are provided. The support base 2 has a fuel introduction opening 4 at one end and a spent fuel discharge opening 5 at the other end. The opening 5 becomes the discharge end of the used fuel including the unused fuel.

  A plurality of cells 6 are arranged in a horizontal stripe pattern on both the front and back surfaces of the support base 2. FIG. 1 shows an example of the support base 2 having a rectangular shape with a rounded cross section at both the left and right ends. The FIG. 1 shows an example in which nine cells are arranged on the front and back surfaces, respectively, but two or more cells are arranged on each. In this way, the horizontal stripe SOFC 1 is configured. That is, the SOFC 1 includes a plurality of porous insulating support bases 2 each having a fuel flow path 3 through which fuel flows from the fuel introduction opening 4 side to the spent fuel discharge opening 5 side. A cell 6 is provided.

  In the horizontal stripe type SOFC configured as described above, power is generated by flowing fuel through the fuel flow path and flowing air to the cathode side. FIG. 2A is a diagram for explaining the mode. As shown in FIG. 2A, the air circulation mechanism 8 is provided on the upper and lower surfaces of the SOFC, that is, on the cathode side. Air is introduced from the introduction pipe 7. And it discharge | releases and distributes from the some hole 9 of the air distribution mechanism 8, contributes to electric power generation, flowing through the cathode side, and is discharged | emitted as used air from the right end in FIG. 2 (a).

  On the other hand, the fuel is introduced from the fuel inlet 4 at the left end in FIG. 2A, contributes to power generation while flowing through the fuel flow path 3, and is discharged from the spent fuel outlet 5 at the right end. The right end of the fuel discharge port 5 is the discharge end of the spent fuel. At that time, the fuel is gradually consumed along the flow direction and contributes to power generation. As a result, the amount of gas components (hydrogen and carbon monoxide) contributing to power generation gradually decreases toward the downstream side. To go. However, the SOFC cannot use all of the gas components that contribute to power generation, and the supplied fuel is usually used in about 70 to 80%, and the remaining 30 to 20% is unused and externally used. To be discharged.

  As described above, in the horizontal stripe type SOFC, the used fuel discharge end is usually an open system, and the used fuel and the used air are mixed in the vicinity of the outside of the end portion of the SOFC, so The fuel used and oxygen in the spent air burn at high temperatures. 2A, the spent fuel discharged from the right end, that is, the fuel discharge end, is mixed with the spent air and burned in the region of the right end face of the SOFC. As a result, unused fuel (hydrogen, carbon monoxide), which is a flammable gas, is changed to non-flammable gas (water vapor or carbon dioxide) to ensure safety and to generate heat necessary for operating the SOFC. It becomes possible to supply.

  However, when the present inventors actually operated the SOFC configured as described above and observed the combustion state in detail, (a) is the distance between the discharge end of the spent fuel and the cell near the discharge end short? Or (b) When the open diameter of the cell is large, the used air (including unused oxygen) diffuses and flows in the reverse direction from the discharge end of the used fuel into the fuel channel 3 and flows into the fuel channel. It was found that it burns with spent fuel and reduces the power generation output of SOFC. In particular, it was observed that (a) when the distance between the discharge end of the spent fuel and the cell in the vicinity of the discharge end is short, the output reduction is greatly affected. FIG. 2B is a diagram for explaining this phenomenon and fact, and shows an enlarged portion including the four cells on the right side of the SOFC shown in FIG.

  As shown as “oxygen reverse diffusion” in FIG. 2B, the used air flows back from the fuel discharge end into the fuel flow path. Here, cells are sequentially arranged in horizontal stripes from the fuel introduction side to the fuel discharge side on both the front and back surfaces of the support base having the fuel flow passage inside, and during the operation, the cells flow through the fuel flow passage. Electricity is generated by consuming fuel. However, when used air is back-diffused into the fuel flow path, oxygen is present at least on the anode side of the cell Z on the most fuel discharge end side, not fuel that contributes to power generation. Power generation is not performed at least in the cell Z on the most fuel discharge end side. As a result, the power generation output of the SOFC is lowered and the performance is lowered.

Therefore, in the present invention, the supporting substrate having a fuel flow channel, by its fuel discharge end by a predetermined distance extending from the position of the highest fuel discharge end cell Z "oxygen inverse diffusion prevention region", Fuel This restricts the inflow of used air that reversely diffuses into the fuel flow path from the discharge end side. That is, speaking of this from the side of the cell Z on the most fuel discharge end side, a range in which used air (including unused oxygen) flows backward from the discharge end of the used fuel in the fuel flow path of the cell Z. It arrange | positions with the above predetermined length (interval). Due to the interval, the inflow of used air that flows back and diffuses from the fuel discharge end to the cell Z on the most fuel discharge end side is restricted, and the influence of oxygen in the used air on the cell Z is avoided, This is to prevent a decrease in the power generation output of the SOFC.

FIGS. 3A to 3C are diagrams for explaining the mode. Figure 3 as (a), the supporting substrate, the position (i.e., the fuel discharge end side of the width of the cell Z) preventing region from toward the fuel discharge end "oxygen inverse diffusion cell Z of the outermost fuel discharge end ". The length of the "oxygen inverse diffusion prevention region", the length extending from the position of the cell Z (i.e., distance from the position of the cell Z to the fuel discharge end) and at least 20mm or more. As a result, the inflow of used air that is going to be back-diffused from the fuel discharge end to the cell Z on the most fuel discharge end side is restricted, that is, the influence of oxygen in the used air on the cell Z is avoided. In this way, it is possible to effectively prevent a decrease in the power generation output of the SOFC. Of these, the particularly preferred length is in the range of 30 mm to 50 mm. FIG. 3B shows a case where the length is 20 mm, and FIG. 3C shows a case where the length is 30 mm.

As a constituent material of the supporting substrate, a mixture of MgO and MgAl ₂ O ₄ , a zirconia-based oxide, a mixture of zirconia-based oxide and MgO and MgAl ₂ O ₄ , or the like can be used, but is not limited thereto. Among them, a mixture of MgO and MgAl ₂ O ₄ is preferably a mixture of MgO contained 20～70Vol% of the total amount of MgO and MgAl ₂ O _4. These preferably contain Ni (NiO). Examples of zirconia-based oxides include yttria-stabilized zirconia [YSZ: (Y ₂ O ₃ ) _X (ZrO ₂ ) _1-X (where x = 0.03 to 0.12)]. It is done. These preferably contain a catalytic metal such as Ni.

As a constituent material of the anode, for example, a material containing Ni as a main component, a ceramic material containing a metal, or the like is used, but is not limited thereto. Among the ceramic materials containing metals, examples of the ceramic material include yttria-stabilized zirconia [YSZ: (Y ₂ O ₃ ) _X (ZrO ₂ ) _1-X (where x = 0.05 to 0.15)]. As the metal, at least one metal selected from Ni, Cu, Fe, Ru, and Pd, that is, one or more of these metals is used.

Among these metal-containing ceramic materials, Ni-containing YSZ (Ni—YSZ cermet), that is, Ni and [(Y ₂ O ₃ ) _X (ZrO ₂ ) _1-X (where x = 0.05-0. 15)] is a preferable anode material in the present invention, and it is particularly preferable that Ni in the mixture is dispersed in an amount of 40 vol% or more.

The constituent material of the electrolyte may be a solid electrolyte having ionic conductivity, and examples thereof include the following materials (1) to (4), but are not limited to these exemplified materials.
(1) Yttria-stabilized zirconia [YSZ: (Y ₂ O ₃ ) _X (ZrO ₂ ) _1-X (where x = 0.05 to 0.15)].
(2) Scandia-stabilized zirconia [(Sc ₂ O ₃ ) _X (ZrO ₂ ) _1-X (where x = 0.05 to 0.15)].
(3) Yttria-doped ceria [(Y ₂ O ₃ ) _X (CeO ₂ ) _1-X (where x = 0.02 to 0.4)].
(4) Gadria-doped ceria [(Gd ₂ O ₃ ) _X (CeO ₂ ) _1-X (where x = 0.02 to 0.4)].

Hereinafter, the present invention will be described in more detail based on examples. For the supporting base, the length from the position of the cell Z of the outermost fuel discharge end side to the fuel discharge end is different, namely to produce a SOFC of each multi-segment type different widths for "oxygen inverse diffusion prevention region", performance for each The test was conducted.

  FIG. 4 is a diagram showing each produced SOFC. 4A is a plan view, FIG. 4B is a left side view, and FIG. 4C is a right side view. FIG.4 (d) is the sectional view on the AA line in Fig.4 (a), and has shown the surface side among them. 4E is an enlarged view of a portion including three cells on the right side of the cross section taken along the line BB in FIG. 4A. FIG. 4A and FIG. In the figure, descriptions of the interconnectors 13 and 14 are omitted. As shown in FIGS. 4A to 4E, the support base 2 has nine fuel flow paths 3, and has nine cells 6 on both the front and back surfaces. Moreover, the numerical value shown as a width | variety in each location is a dimension of the mm unit in the said location. Although not shown, the inner diameters (inner diameters) of the nine fuel flow paths 3 are both 1.5 mm.

In FIG. 4D, 2 is a support substrate, 3 is a fuel flow path, 10 is an anode, 11 is an electrolyte, 12 is a cathode, and 13 is an interconnector. A mixture of NiO and YSZ (weight mixing ratio = 1: 4) is used as the material of the support base 2, a mixture of NiO and YSZ (weight mixing ratio = 2: 3) is used as the anode material, and YSZ is used as the material of the electrolyte 11. (La _0.6 Sr _0.4 ) Co _0.2 Fe _0.8 O ₃ , which is a perovskite oxide, and La (Ti _0.8 Nb _0.2 ) O ₃ as the material of the interconnector 13. Reference numeral 14 denotes a member for connecting the interconnector 13 and the cathode 12, which is also an interconnector, and Ag is used as the material thereof.

Then, with them in common, of the support substrate 2, 4 (a) and (e) in the length of the portion indicated as "oxygen inverse diffusion prevention region", or "the position of the highest fuel discharge end cell" A plurality of the same SOFCs were produced except that the length of the support base from the “fuel release end” to the “fuel discharge end” was varied. The length (interval) is indicated as “← X →” in FIG.

Each SOFC manufactured in this way [that is, each SOFC in which the width (length) of the region in which the cell is not provided in the support base 2 is different as shown by the symbol “← X →” in FIG. 5 (a) to 5 (b), and an air flow mechanism (see FIG. 2 (a)) is attached to the cathode side and disposed in an electric furnace, and hydrogen is supplied to the fuel flow path as fuel. At the same time, a performance test was conducted by flowing air over the cathode surface. At that time, the operating temperature (operating temperature) was 750 ° C., the current density (I) was 0.2 A / cm ² , and the fuel utilization rate (Uf) was constant at 75%. FIG. 5A shows the arrangement relationship of the loader and the like, and the standard resistance and voltmeter V are for setting the loader so that the current density I = 0.2 A / cm ² . FIG. 5B is a view corresponding to FIG. 4D and shows the arrangement of the voltmeter V with respect to the “most fuel discharge end side cell”.

FIG. 6 is a diagram showing the results. The horizontal axis represents the voltage value of the length of the "oxygen inverse diffusion prevention region" X (mm), the vertical axis "uppermost fuel discharge end cell Z" in each SOFC. As shown in FIG. 6, first, a cell voltage of 0.22 V is obtained only with SOFC in which X is 14 mm. This indicates that the cell Z on the most fuel discharge end side is hardly involved in power generation. This is because used air is back-diffused and flows into the fuel flow path, and oxygen, not fuel, is present on the anode side of the cell Z on the most fuel discharge end side.

  Next, a cell voltage of 0.69 V is obtained in the SOFC in which X is 20 mm, which indicates that the cell Z on the most fuel discharge end side is effectively involved in power generation. This is because the oxygen back-diffusion prevention zone of that length limits the inflow of used air flowing back from the fuel discharge end to the cell Z on the most fuel discharge end side, and the influence of oxygen is almost prevented. It shows that. When X is 20 mm in length, there is some influence of oxygen due to the back-diffusion flow of used air into the fuel flow path, but the voltage value is close to the voltage value in cells other than the cell Z. I can say that.

  Further, the cell voltage in the cell Z on the most fuel discharge end side in the SOFC in which X is longer than 20 mm is further increased, 0.71 V in the SOFC with X = 30 mm, 0.74 V in the SOFC with X = 40 mm, A SOFC of 50 mm shows a value of 0.76 V, a SOFC of X = 55 mm shows a value of 0.8 V, and thereafter a value of about 0.8 V is shown.

The figure explaining the structural example of SOFC of the horizontal stripe system made into object by this invention The figure explaining the output reduction phenomenon and the fact by the back diffusion of oxygen from the fuel discharge end to the fuel flow path in the conventional horizontal stripe type SOFC The figure explaining the aspect of this invention Diagram showing each SOFC made for performance test The figure which shows the outline of the performance test equipment set for the performance test of each SOFC The figure which shows the result of the example Diagram showing prior art cell stack

Explanation of symbols

1 SOFC
DESCRIPTION OF SYMBOLS 2 Hollow strip-shaped (hollow flat shape) support base 3 Hollow part, fuel flow path 4 Fuel introduction opening 5 Fuel discharge opening 6 Each cell formed in the horizontal stripe shape in the support base 7 Air introduction pipe 8 Air distribution mechanism 9 A plurality of holes of the air distribution mechanism Z A cell on the most fuel discharge end side 10 Anode 11 Electrolyte 12 Cathode 13, 14 Interconnector 21 Porous cylindrical substrate tube 22 Anode 23 Electrolyte 24 Cathode 25 Cell 26 Interconnector 33 Current collecting ring

Claims (3)

The outer surface of the insulating supporting substrate porous having an internal fuel flow path a plurality of solid oxide fuel cell comprising a solid oxide retardant ponds multi-segment type formed by arranging a horizontal stripe, the for supporting substrate, it is oxygen inverse dispersion prevention area as 20 / 1.5 or more lengths for pore size of the length from the fuel discharge end to a position of the cell Le of the most fuel discharge end the fuel channel the solid oxide fuel cell of multi-segment type, characterized by comprising so as to limit the flow of the used oxidizing agent gas despreading the fuel flow path of the fuel discharge end or al supporting lifting body.   2. The horizontal stripe type solid oxide fuel cell according to claim 1, wherein the fuel flow path is one or a plurality of fuel flow paths.   3. The horizontal stripe type solid oxide fuel cell according to claim 1 or 2, wherein the fuel flow path is a fuel flow path having a rectangular cross section, a quadrangular cross section, a circular cross section, or an elliptical cross section. A solid oxide fuel cell of the horizontal stripe type.

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