Fuel cell module

A fuel cell module includes in a casing: a fuel cell stack that is formed by stacking a plurality of unit cell; an oxidant gas distributing member that is disposed at a side surface, that extends in a stack direction of the unit cells, of the fuel cell stack that extends in a direction from one end to another end of each of the unit cells, and that supplies the oxidant gas to the another end of each unit cell after supplying the oxidant gas through the oxidant gas distributing member from the one end to the another end; a reformer disposed at the one end; and a combustion portion that is disposed between the one end and the reformer. The oxidant gas distributing member has a higher thermal conductivity at the one end side of the unit cells than at the another end side of the unit cells.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel cell module.

2. Description of the Related Art

The fuel cell generates electric energy, generally, by using hydrogen and oxygen as fuels. The fuel cell is environment-friendly and is able to achieve high energy efficiency, so that fuel cells are being widely researched and developed as a future energy supply source.

Generally, a fuel cell has a fuel cell stack that is constructed by stacking a plurality of unit cells, and therefore generates large electric power. Japanese Patent Application Publication No. 2007-59377 (JP-A-2007-59377) describes a reformer-integrated type fuel cell in which a reformer is disposed on an upper portion of a fuel cell stack. In this technology, oxidant gas flows in a reactant gas distributing member, and is thereby supplied to a lower end of each unit cell.

In a fuel cell module having a construction in which the fuel off-gas that is left unused for electricity generation is burned at one end of the unit cells as in the technology according to Japanese Patent Application Publication No. 2007-59377 (JP-A-2007-59377), sometimes there occurs temperature difference within the fuel cell module, that is, sometimes the temperature is relatively high at the one end of unit cells, and relatively low at another end of the unit cells. Furthermore, in a fuel cell module having a construction in which the oxidant gas for use for the electricity generation of the unit cells is supplied to the another end of the unit cells, there is risk of decline in the temperature at the another end of the unit cells and increase in the temperature difference within the unit cells in the vertical direction.

SUMMARY OF THE INVENTION

The invention provides a fuel cell module capable of reducing the temperature difference within a unit cell.

A first aspect of the present invention is related to a fuel cell module that includes in a casing: a fuel cell stack that is formed by stacking a plurality of unit cells that generate electricity using an oxidant gas and a fuel gas, an oxidant gas distributing member that is disposed at a side surface, that extends in a stack direction of the unit cells, of the fuel cell stack that extends in a direction from one end to another end of each of the unit cells, and that supplies the oxidant gas for use for electricity generation of the unit cells to the another end of each unit cell after supplying the oxidant gas through the oxidant gas distributing member in the direction of the unit cells from the one end to the another end; a reformer disposed at the one end; and a combustion portion that is disposed between the one end and the reformer, and that burns a fuel off-gas that is left unused in the electricity generation of the unit cells using an oxidant off-gas that is left unused in the electricity generation of the unit cells. The oxidant gas distributing member has a higher thermal conductivity at the one end side of the unit cells than at the another end of the unit cells.

According to the above aspect, it is possible to accelerate the heat exchange between each of the one end of the unit cells and the oxidant gas that flows in the oxidant gas distributing member. Due to this effect, the oxidant gas that flows in the oxidant gas distributing member can be efficiently heated by the heat at the each of the one end of the unit cells. This makes it possible to increase the temperature of the unit cells at the other end by the heated oxidant gas supplied to the other end of the unit cells. Besides, since the oxidant gas distributing member at the one end of the unit cells has a higher thermal conductivity than the another end of the unit cells, that is, since the thermal conductivity at the another end of the unit cells is lower in than the thermal conductivity at the one end of the unit cells, it is possible at the another end of the unit cells to restrain the heat exchange between the unit cells and the oxidant gas that flows in the oxidant gas distributing member.

In the above aspect, the oxidant gas distributing member may have, at the one end side of the unit cells, at least one of: a fin; a partition member that partitions a channel of the oxidant gas distributing member into a plurality of paths; and a dimple.

A second aspect of the present invention is related to a fuel cell module that includes in a casing: a fuel cell stack that is formed by stacking a plurality of unit cells that generate electricity using an oxidant gas and a fuel gas; an oxidant gas distributing member that is disposed at a side surface, that extends in a stack direction of the unit cells, of the fuel cell stack that extends in a direction from one end to another end of each of the unit cells, and that supplies the oxidant gas for use for electricity generation of the unit cells to the another end of each unit cell after supplying the oxidant gas through the oxidant gas distributing member in the direction of the unit cells from the one end to the another end; a reformer disposed at the one end; a combustion portion that is disposed between the one end and the reformer, and that burns a fuel off-gas that is left unused in the electricity generation of the unit cells using an oxidant off-gas that is left unused in the electricity generation of the unit cells; and internal thermal insulation members that are disposed at two side surfaces of the fuel cell stack which extend in a stack direction of the unit cells. At least one of the internal thermal insulation members has a higher thermal conductivity at the one end side of the unit cells than at the another end of the unit cells.

According to the above aspect, it is possible to accelerate the heat exchange between each of the one end of the unit cells and the oxidant gas that flows in the oxidant gas distributing member. Due to this effect, the oxidant gas that flows in the oxidant gas distributing member can be efficiently heated by the heat at the each of the one end of the unit cells. This makes it possible to increase the temperature of the unit cells at the other end by the heated oxidant gas supplied to the other end of the unit cells. Besides, since the internal thermal insulation members of the oxidant gas distributing member side has a higher thermal conductivity at the one end of the unit cells than at the another end of the unit cells, that is, since the thermal conductivity at the another end of the unit cells is lower in than the thermal conductivity at the one end of the unit cells, it is possible at the another end of the unit cells to restrain the heat exchange between the unit cells and the oxidant gas that flows in the oxidant gas distributing member. Since the efficiently heated oxidant gas is supplied to the another end of the unit cells and the temperature decline in the another end of the unit cells is restrained, it possible to reduce the temperature difference within the unit cells in the direction from the one end to the another end.

In the above aspect, the internal thermal insulation members may be constructed so that the thermal conductivity increases gradually from the another end side of the unit cells to the one end side of the unit cells.

In the above aspect, the internal thermal insulation members may be constructed so that thermal conductivity increases stepwise from the another end side of the unit cells to the one end side of the unit cells.

In the above aspect, the oxidant gas distributing member may supply the oxidant gas in the order of the reformer, the combustion portion, and to the another end after supplying the oxidant gas from the one end to the another end. The oxidant gas distributing member may include a protruded portion that is protruded toward the side surface of the fuel cell stack.

According to the above aspect, since the protruded portion that is protruded toward the side surface of the fuel cell stack is provided on the oxidant gas distributing member, it is possible to accelerate the heat exchange at the protruding portion between the fuel cell stack and the oxidant gas that flows in the oxidant gas distributing member. Due to this effect, oxidant gas that flows in the oxidant gas distributing member can be heated by the heat of the fuel cell stack. Since the temperature of the oxidant gas that flows in the oxidant gas distributing member increases, it possible to reduce the temperature difference of the fuel cell stack within the unit cells in the direction from the one end to the another end.

In the above aspect, the protruded portion may include a rectifying member that brings the oxidant gas in the oxidant gas distributing member closer to the fuel cell stack than when there is no rectifying member formed.

In the above aspect, the another end side of the protruded portion may extend beyond the another end of the unit cellstowards the reformer side.

According to the above aspects, it possible to provide the fuel cell module that reduce the temperature difference within the unit cells.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments of the invention will be described below.

Firstly, a fuel cell module in accordance with a first embodiment of the invention will be described.FIG. 1is a partial perspective view of a unit cell10which includes a cross-sectional view of the unit cell10. As shown inFIG. 1, the unit cell10has a flattened column shape as a whole. Within an electroconductive support11having gas permeability, there are formed a plurality of fuel gas passageways12extending through the unit cell10in the direction of an axis thereof. A fuel electrode13, a solid electrolyte14and an oxygen electrode15are stacked in that order on one of two side surfaces of an outer periphery of the electroconductive support11. On the other side surface that opposes the oxygen electrode15, there is provided an interconnector17underneath which a joining layer16lies. A p-type semiconductor layer18is provided on top of the interconnector17.

A fuel gas containing hydrogen is supplied to the fuel gas passageways12, so that hydrogen is supplied to the fuel electrode13. On the other hand, an oxidant gas containing oxygen is supplied to the surroundings of the unit cell10. Electricity is generated by the following electrode reactions occurring at the oxygen electrode15and the fuel electrode13. The electricity generating reaction takes place at a temperature, for example, 600° C. to 1000° C.
1/2 O2+2e—→O2−(solid electrolyte)  Oxygen electrode
O2−(solid electrolyte)+H2→H2O+2e—Fuel electrode

A material of the oxygen electrode15has oxidation resistance, and is porous so that gaseous oxygen will reach an interface between the oxygen electrode15and the solid electrolyte14. The solid electrolyte14has a function of migrating oxygen ion O2−from the oxygen electrode15to the fuel electrode13. The solid electrolyte14is composed of an oxygen ion-conductive oxide. Besides, the solid electrolyte14is stable in an oxidative atmosphere and also in a reductive atmosphere, and is composed of a compact material, in order to physically separate the fuel gas and the oxidant gas. The fuel electrode13is formed from a porous material that is stable in the reductive atmosphere and has affinity to hydrogen. The interconnector17is provided in order to electrically connect the unit cells10to each other in series, and is composed of a compact material so as to physically separate the fuel gas and the oxygen-containing gas.

For example, the oxygen electrode15is formed from a lanthanum cobaltite-base perovskite-type composite oxide, and the like, that is highly conductive for both electrons and positive ions. The solid electrolyte14is formed from, for example, a zirconia (ZrO2) containing Y2O3(YSZ) which is high in ion conductivity, and the like. The fuel electrode13is formed from, for example, a mixture of Y2O3-containing ZrO2(YSZ) and Ni, which is high in electron conductivity. The interconnector17is formed from, for example, a solid solution of LaCrO3with an alkaline earth oxide. As for these materials, materials that are similar to each other in thermal expansion coefficient are used.

FIG. 2Ais a perspective view in which a portion of a fuel cell stack20is shown in order to illustrate the fuel cell stack20. In the fuel cell stack20, a plurality of unit cells10are stacked in a row. In this case, the unit cells10are stacked so that the oxygen electrode15side of the unit cell10faces the interconnector17side of the adjacent unit cell10.

Current collectors30are disposed between the unit cells10. The current collectors30electrically connect adjacent unit cells10in series.FIG. 2Bis a plan view showing an example of the current collector30. The current collector30includes as a basic components: a first current collector piece31that contacts the oxygen electrode15of one of the two adjacent unit cells10; a second current collector piece32that extends diagonally from the one of the unit cell10to the other one of the two adjacent unit cells10; a third current collector piece33that contacts the interconnector17of the other one of the unit cell10; and a fourth current collector piece34that extends diagonally from the other one of the unit cell10to the one of the unit cell10. One of two opposite ends of the second current collector piece32is connected to the first current collector piece31, and the other end of the second current collector piece32is connected to the third current collector piece33. One of two opposite ends of the fourth current collector piece34is connected to the third current collector piece33, and the other end of the fourth current collector piece34is connected to the first current collector piece31. A plurality of such basic components are linked together in the axial direction of the unit cells10so as to form the current collector30.

The second current collector piece32and the fourth current collector piece34each have bent portions (two bent portions in the first embodiment). Due to the bent portions, the second current collector piece32and the fourth current collector piece34performs a function as springs. Due to the spring structure, the current collectors30have a characteristic of closely attaching to the unit cells10and a characteristic of following deformation of the unit cells10. Besides, due to spring structure, a space is formed between the first current collector piece31and the third current collector piece33, the current collectors30have a ventilation characteristic.

FIG. 3AandFIG. 3Bare perspective views for describing a reformer40, a manifold50to which fuel cell stacks20are fixed, and terminals. Two fuel cell stacks20are disposed on the manifold50, and the reformer40is disposed over (above) the fuel cell stacks20.

The two fuel cell stacks20are disposed side by side so that the stack direction of the unit cells10of the two fuel cell stacks20are substantially parallel to each other. Incidentally, the number of fuel cell stacks20fixed to the manifold50is not limited. The reformer40extends over (above) one of the two fuel cell stacks20in the stack direction of the unit cells10, extends over the other fuel cell stack20in the stack direction of the unit cells10, and the two extended ends are interconnected to form substantially a U-shape. As shown inFIG. 3B, an outlet opening of the reformer40and an inlet opening of the manifold50are interconnected by a fuel gas piping60.

As shown inFIG. 3A, a first terminal70is disposed on a positive end portion of one of the two fuel cell stacks20in the stack direction of the unit cells10. A second terminal71is disposed on a negative end portion of the other fuel cell stack20in the stack direction of the unit cells10. As shown inFIG. 3B, the negative end portion of the one fuel cell stack20and the positive end portion of the other fuel cell stack20are electrically connected in series by a third terminal72. When a load is electrically connected to the first terminal70and the second terminal71, the load can be supplied with electric power that is generated by the fuel cell stacks20.

FIG. 4is a perspective view for describing details of the reformer40. The reformer40has a structure in which an input port member41, an evaporation portion42, a heating portion43, and a reforming portion44are connected in that order from the inlet opening side. The input port member41is supplied with a hydrocarbon-base fuel and a reforming water. The hydrocarbon-base fuel for use herein may be, for example, a coal gas (town gas). In the first embodiment, the input port member41has a double-pipe structure. The reforming water is introduced to the inner pipe of the input port member41, and the hydrocarbon-base fuel is introduced to the space between the inner pipe and the outer pipe.

The evaporation portion42is a space in which reforming water is evaporated by utilizing combustion heat of a fuel off-gas described below. In the first embodiment, the inner pipe of the input port member41extends to the evaporation portion42. The reforming water introduced to the input port member41flows out from a distal end of the inner pipe of the input port member41, and evaporates within the evaporation portion42. After that, reforming water (vapor) flows into the heating portion43. The hydrocarbon-base fuel introduced to the input port member41flows into the evaporation portion42, and then flows into the heating portion43.

The heating portion43is a space in which the reforming water and the hydrocarbon-base fuel are heated by combustion heat of the fuel off-gas. For example, ceramics balls are enclosed in the heating portion43. The reforming portion44is a space in which the steam-reforming reaction of the reforming water and the hydrocarbon-base fuel takes place. For example, ceramics balls to which a reforming catalyst, such as Ni, Ru, Rh, Pt, etc., is applied are enclosed in the reforming portion44.

FIG. 5is a sectional view for describing an overall construction of a fuel cell module200in accordance with the first embodiment. The fuel cell module200is disposed in a casing80having a double wall which forms a flow channel in which the oxidant gas flow. A lower thermal insulation member81disposed in a lower portion of the manifold50, and side thermal insulation members82disposed in the stack direction of the unit cells10define a space in which the fuel cell stack20, the reformer40, the manifold50, etc. shown inFIGS. 3A and 3Bare housed. Incidentally, in the first embodiment, first internal thermal insulation members83are disposed between an oxidant gas distributing member100described below and the unit cells10. Besides, second internal thermal insulation members84are disposed between the unit cells10and the side thermal insulation members82. In the first embodiment, the unit cells10at the reformer40side is defined as upward, and the unit cells10at the manifold50side is defined as downward.

An oxidant gas inlet opening of the casing80is provided at a bottom surface of the casing80. The oxidant gas enters an oxidant gas box, that is the bottom portion of the casing80, and flows through side flow channels formed at the casing80, and then flows above the fuel cell stacks20. After that, the oxidant gas flows down into the oxidant gas distributing member100disposed between the two fuel cell stacks20, and then is supplied to the fuel cell stacks20from their lower end. As described above with reference toFIGS. 3A and 3B, the fuel gas is supplied from the manifold50into the fuel gas passageways12of the unit cells10. Thus, electricity is generated in each unit cell10.

The fuel gas that has not been used for electricity generation (fuel off-gas) in the unit cells10, and the oxidant gas that has not been used for electricity generation (oxidant off-gas) in the unit cells10merges at an upper end of the unit cells10. Since the fuel off-gas contains combustibles, such as hydrogen and the like, that have not been used for electricity generation, the fuel off-gas can be burned by utilizing oxygen contained in the oxidant off-gas. In the first embodiment, the portions between the upper ends of the unit cells10and the reformer40are called combustion portions90. The combustion heat generated at the combustion portions90is utilized for the reforming reaction in the reformer40. Due to the combustion heat, the reforming reaction in the reformer40is accelerated.

After combusted in the combustion portions90, the fuel off-gas and the oxidant off-gas (hereinafter, referred to as “combustion off-gas”) flow into a combustion off-gas distributing channel. The combustion off-gas distributing channel includes first combustion off-gas distributing channels85formed between the oxidant gas distributing member100and the reformer40, and second combustion off-gas distributing channels86formed between the side thermal insulation members82and the reformer40. The combustion off-gas having passed through the first combustion off-gas distributing channels85is supplied to upper combustion off-gas channels87that are formed between an upper surface of an internal wall of the casing80and upper surfaces of the reformer40. After that, the combustion off-gas flows down through side combustion off-gas channels88that are formed between the side thermal insulation members82and the casing80. The combustion off-gas having passed through the second combustion off-gas distributing channels86flows into the side combustion off-gas channels88, and flows downward therethrough. After flown through the side combustion off-gas channels88, the combustion off-gas flows into an off-gas box that is formed between the lower thermal insulation member81and the oxidant gas box. After that, the off-gas is discharged from the fuel cell module200.

FIG. 6Ais an extracted perspective view of the oxidant gas distributing member100and the reformer40. In first embodiment, the oxidant gas distributing member100is disposed in the casing80so as to be sandwiched between a portion of the reformer40that is above one of the two fuel cell stacks20, and a portion of the reformer40that is above the other one of the two fuel cell stacks20. An upper end portion of the oxidant gas distributing member100is protruded upward from the reformer40, and is connected to a flow channel for supplying the oxidant gas to the upper portion of the casing80. A lower end of the oxidant gas distributing member100extends to the vicinity of the unit cells10.

FIG. 6Bis a perspective view of the oxidant gas distributing member100. The oxidant gas distributing member100has a flattened box shape and has a hollow space. The hollow space functions as a flow channel through which the oxidant gas flows. Hereinafter, the hollow space is called the oxidant gas distributing channel.

The upper end portion of the oxidant gas distributing member100has an opening portion through which the oxidant gas flows into the oxidant gas distributing member100. In the first embodiment, the opening portion at the upper end portion of the oxidant gas distributing member100extends entirely over the upper end portion of the oxidant gas distributing member100. The lower end portion of the oxidant gas distributing member100that faces the two fuel cell stack20side walls has a plurality of oxidant gas outlet openings101that are formed at predetermined intervals along the stack direction of the unit cells10. The oxidant gas discharged from the oxidant gas outlet openings101is supplied to the lower end portion of each unit cell10. Specifically, the oxidant gas channel of the oxidant gas distributing member100is a flow channel which supplies the oxidant gas along the reformer40, the combustion portion90, and an end (upper end) of the unit cells10to another end (lower end) of the unit cells10in that order, and the oxidant gas is then supplied to the lower end of each unit cell10.

The oxidant gas distributing member100includes a thermal conductive portion120that is provided at the one end (upper end) of the unit cells10and that has a higher thermal conductivity than the another end (lower end) of the unit cells10.FIG. 6Cis a sectional view of the thermal conductive portion120that is viewed from the upper end of the oxidant gas distributing member100. The thermal conductive portion120has a partition member121that separates the flow path of an oxidant gas distributing channel into a plurality of sections. That is, the thermal conductive portion120has a so-called micro-channel structure. In this case, the thermal conductive portion120has a larger thermal conduction area than other portions of the oxidant gas distributing member100. Due to this effect, the thermal conductive portion120has a higher thermal conductivity than the other portions of the oxidant gas distributing member100. Incidentally, the partition member121rectifies the flow of the oxidant gas in the oxidant gas distributing-channel.

According to the fuel cell module200in accordance with this embodiment, the oxidant gas can be heated by the heat exchange between the combustion portions90and upper end of the unit cells10, and the oxidant gas that flows in the oxidant gas distributing member100. This makes it possible to supply the heated oxidant gas to the lower end of each unit cell10, so that the temperature of the lower end of each unit cell10will increase. In consequence, it is possible to reduce the temperature difference within the unit cells10in the vertical direction. Besides, since the upper end of the oxidant gas distributing member100(the upper end of the unit cells10) has a higher thermal conductivity than the lower end of the oxidant gas distributing member100(the lower end of the unit cells10), that is, since the lower end of the oxidant gas distributing member100is lower in thermal conductivity than the upper end of the oxidant gas distributing member100, it is possible at the lower end of the unit cells10to restrain the heat exchange between the unit cells10and the oxidant gas that flows in the oxidant gas distributing member100. This makes it possible to restrain the temperature decline of the lower end of the unit cells10, so that the temperature difference in the unit cells10in the vertical direction can be reduced.

Incidentally, the thermal conductive portion120may also have a construction other than that formed by the partition member121as long as the oxidant gas distributing member100has a higher thermal conductivity than other portions of the oxidant gas distributing member100. For example, as shown inFIG. 6D, the thermal conductive portion120may have fins22as an alternative. Alternatively, the thermal conductive portion120may have dimples. For example, the dimples may be formed on internal surfaces of the oxidant gas distributing member100, that is, on the side walls at the fuel cell stack20side.

Besides, the partition member121, the fins122or the dimples of the thermal conductive portion120may also be provided on external surfaces of the oxidant gas distributing member100, that is, on the side walls at the fuel cell stack20side.

Next, a fuel cell module200ain accordance with a second embodiment of the invention will be described.FIG. 7is a sectional view for describing an overall construction of the fuel cell module200a. The fuel cell module200ais different from the fuel cell module200shown inFIG. 5in that the fuel cell module200ahas only one fuel cell stack20instead of two fuel cell stacks20, and in that the fuel cell module200ahas a reformer40ainstead of the reformer40, and in that the fuel cell module200adoes not have the second internal thermal insulation members84. The reformer40ahas a construction that corresponds to only one of two sections of the reformer40shown inFIG. 4which are correspondingly located above the two fuel cell stacks20.

In the fuel cell module200ain accordance with the second embodiment, the oxidant gas can be heated by the heat exchange between the combustion portion90and upper end of the unit cells10, and the oxidant gas that flows in the oxidant gas distributing member100. This makes it possible to supply the heated oxidant gas to the lower end of each unit cell10, so that the temperature of the lower end of each unit cell10will increase. In consequence, it is possible to reduce the temperature difference within the unit cells10in the vertical direction.

Incidentally, in the fuel cell module200a, it suffices that one of the two oxidant gas distributing members100has a thermal conductive portion120. However, the temperature difference within the unit cells10in the vertical direction can be further reduced if each of the two oxidant gas distributing members100has a thermal conductive portion120.

Next, a fuel cell module200bin accordance with a third embodiment of the invention will be described.FIG. 8is a sectional view for describing an overall construction of the fuel cell module200b. The fuel cell module200bis different from the fuel cell module200shown inFIG. 5in that the fuel cell module200bis provided with an oxidant gas distributing member100binstead of the oxidant gas distributing member100, and in that first internal thermal insulation members83bare provided instead of the first internal thermal insulation members83. The oxidant gas distributing member100bis different from the oxidant gas distributing member100in that the oxidant gas distributing member100bdoes not have a partition member121.

As for the first internal thermal insulation members83b, the thermal conductivity is higher at the lower end of the unit cells10than at the upper end thereof. In the third embodiment, the first internal thermal insulation members83bare constructed so that the thermal conductivity increases stepwise (or gradually) from the lower end to the upper end of the unit cells10. Concretely, each of the first internal thermal insulation members83bis divided into two sections in the vertical direction. The thermal conductivity of the upper-side first internal thermal insulation members83bis higher than that of the lower-side first internal thermal insulation members83b. In this case, the heat exchange between the oxidant gas that flowing in the oxidant gas distributing member100band the unit cells10occurs more efficiently at the one end (upper end) of the unit cells10than at the another end (lower end) of the unit cells10.

According to the fuel cell module200bin accordance with this embodiment, heat of the upper end side of the unit cells10can be efficiently transferred to the oxidant gas distributing member100bvia the thermal conductive portions (upper-side portion) of the first internal thermal insulation members83b. Besides, heat transferred to the oxidant gas distributing member100bcan be used to heat the oxidant gas that flows in the oxidant gas distributing member100b. This will make it possible to reduce the temperature difference within the unit cells10in the vertical direction.

Besides, since the thermal conductivity is lower at the lower end of the unit cells10than at the upper end of the unit cells10, heat exchange between the unit cells10and the oxidant gas that flows in the oxidant gas distributing member100bcan be restrained at the lower end of the unit cells10. Due to this effect, temperature decline at the lower end of the unit cells10can be restrained, so that the temperature difference within the unit cells10in the vertical direction can be reduced.

FIG. 9is a graph for describing effects of the fuel cell module200b. A fuel cell module300in accordance with a comparative example has a first internal thermal insulation members that have a uniform thermal conductivity. In comparison between the fuel cell module200band the fuel cell module300, the temperature at the lower end of the unit cells10is higher in the fuel cell module200bthan in the fuel cell module300, and the temperature at the upper end thereof is lower in the fuel cell module200b. In consequence, the temperature difference within the unit cells10in the vertical direction is reduced in the fuel cell module200b.

The number of divisions of each first internal thermal insulation member83bis not particularly limited. Besides, the second internal thermal insulation members84may have the same construction as the first internal thermal insulation members83b.FIG. 10is a sectional view for describing an overall construction of a fuel cell module200bin accordance with a first modification of the third embodiment. The fuel cell module200bin accordance with this modification is different from the fuel cell module200bshown inFIG. 8in that each first internal thermal insulation member83bis divided into five sections so that the thermal conductivity thereof increases stepwise (gradually) from the lower end to the upper end of the fuel cell stacks20, and in that second internal thermal insulation members84bare provided instead of the second internal thermal insulation members84. The second internal thermal insulation members84b, similarly to the first internal thermal insulation members83b, are each divided into five sections so that the thermal conductivity thereof increases stepwise (gradually) from the lower end to the upper end of the unit cells10.

In the fuel cell module200bin accordance with this modification, heat of the upper end of the unit cells10can be efficiently transferred to the oxidant gas distributing member100bvia thermal conductive portions (upper-side portions) of the first internal thermal insulation members83b. This makes it possible to reduce the temperature difference within the unit cells10in the vertical direction.

Incidentally, in the fuel cell modules200bin accordance with the third embodiment and the first modification of the third embodiment, the first internal thermal insulation members83band the second internal thermal insulation members84bmay have a construction in which the thermal conductivity thereof gradually increases from the lower end to the upper end of the unit cells10.

In a second modification of the third embodiment, the side thermal insulation members82may also have a construction in which the thermal conductivity thereof increases stepwise or gradually from the lower end to the upper end of the unit cells10. Due to this construction, heat of the upper end of the unit cells10can be released to the outside via thermal conductive portions (upper-side portions) of the side thermal insulation members82. This makes it possible to reduce the temperature difference within the unit cells10in the vertical direction.

Incidentally, in the fuel cell modules200bin accordance with the third embodiment and first and second modifications of the third embodiment, the oxidant gas distributing member100in accordance with the first embodiment may be provided instead of the oxidant gas distributing member100b.

Next, a fuel cell module200cin accordance with a fourth embodiment of the invention will be described.FIG. 11is a sectional view for describing an overall construction of the fuel cell module200c. The fuel cell module200cis different from the fuel cell module200ashown inFIG. 7in that oxidant gas distributing members100bare provided instead of the oxidant gas distributing members100, and in that first internal thermal insulation members83bare provided instead of the first internal thermal insulation members83.

In the fuel cell module200cin accordance with this embodiment, heat of an upper end of the unit cells10can be efficiently transferred to the oxidant gas distributing members100bvia thermal conductive portions (upper-side portions) of the first internal thermal insulation members83b. Besides, heat transferred to the oxidant gas distributing member100bcan be used to heat the oxidant gas that flows in the oxidant gas distributing members100b, while at the lower end of the unit cells10, the heat exchange between the unit cells10and the oxidant gas that flows in the oxidant gas distributing members100bcan be restrained. Due to this effect, the temperature difference within the unit cells10in the vertical direction can be reduced.

Besides, the first internal thermal insulation members83bmay also have a construction in which the thermal conductivity thereof increases gradually from the lower end to the upper end of the unit cells10. Besides, the side thermal insulation members82may also have a construction in which the thermal conductivity thereof increases stepwise or gradually from the lower end to the upper end of the unit cells10. Besides, the fuel cell module200cmay be provided with oxidant gas distributing members100in accordance with the second embodiment instead of the oxidant gas distributing members100b.

Subsequently, a fuel cell module200din accordance with a fifth embodiment of the invention will be described.FIG. 12is a sectional view for describing an overall construction of the fuel cell module200d. The fuel cell module200dis different from the fuel cell module200shown inFIG. 5in that an oxidant gas distributing member100dis provided instead of the oxidant gas distributing member100. The oxidant gas distributing member100dis different from the oxidant gas distributing member100in that the oxidant gas distributing member100ddoes not have a partition member121, and in that the oxidant gas distributing channel has a protruded portion140that is protruded toward side surfaces of fuel cell stacks20which extend in the stack direction of the unit cells10.

FIG. 13Ais a perspective view of the oxidant gas distributing member100d. The protruded portion140is provided with rectifying members141.FIG. 13Bis a sectional view of the oxidant gas distributing member100dviewed in the stack direction of the unit cells10. The rectifying members141brings the flow of the oxidant gas in the oxidant gas distributing channel closer to the side walls of the protruded portion140at the fuel cell stack20side (hereinafter, termed the wall surfaces in the protruded portion140). As long as this function is secured, the rectifying members141are not particularly limited. In this embodiment, the rectifying members141are bar members whose axial direction coincides with the stack direction of the unit cell10. In this construction, the oxidant gas upstream of the bar members will flow close to the wall surfaces in the protruded portion140after striking the bar members. Incidentally, the material of the bar members is not particularly limited; for example, it may be a porous material.

According to the fuel cell module200din accordance with this embodiment, since the protruded portion140is provided, it is possible to accelerate the heat exchange between the unit cells10and the oxidant gas that flows in the oxidant gas distributing member100d. Due to this effect, since the heated oxidant gas can be supplied to the lower end of each unit cell10, the temperature difference within the unit cells10in the vertical direction can be reduced. Incidentally, the protruded portion140may be provided so that the protruded portion140is not located at the lower end of the unit cells10(is located above a lower end portion of the unit cells10). For example, the protruded portion140may be located above the oxidant gas outlet openings101. In this construction, the heat exchange between the unit cells10and the oxidant gas that flows in the oxidant gas distributing member100d(the protruded portion140) can be restrained at the lower-end side of the unit cells10. Due to this effect, the temperature difference within the unit cells10in the vertical direction can be reduced.

Besides, according to the fuel cell module200d, since the rectifying members141are provided, the flow of the oxidant gas in the protruded portion140can be brought closer to the fuel cell stacks20. Due to this effect, the heating of the oxidant gas can be accelerated.

Incidentally, as shown inFIG. 13B, the thickness of the walls of the protruded portion140at the fuel cell stack20sides is greater than the thickness of the oxidant gas distributing member100dat the fuel cell stack20side other than the protruded portion140. Due to this effect, it is possible to accelerate the transfer of heat in the portions of the protruded portion140, which has greater thickness, in the stack direction of the unit cells10. In consequence, in the oxidant gas flowing in the protruded portion140, the temperature difference within the stack direction of the unit cells10can be reduced. Due to this effect, the temperature difference within the fuel cell stacks20in the stack direction of the unit cells10can be reduced.

Incidentally, the first internal thermal insulation members83and the side thermal insulation members82of the fuel cell module200din accordance with this embodiment may also be constructed as in the third embodiment.

FIG. 14is a sectional view for describing an overall construction of a fuel cell module200din accordance with a first modification of the fifth embodiment. The fuel cell module200din accordance with this embodiment is different from the fuel cell module200dshown inFIG. 12in that the protruded portion140of the oxidant gas distributing member100dextends to an upper end of the oxidant gas distributing member100d.

According to the fuel cell module200din accordance with this modification, in a portion of the protruded portion140that extends near combustion portions90and a portion of the protruded portion140that extends near the first combustion off-gas distributing channels85, it is possible to accelerate the heat exchange between the combustion portions90and the oxidant gas that flows in the oxidant gas distributing member100d. Due to this effect, the oxidant gas that flows in the oxidant gas distributing member100dcan be further heated. In consequence, the oxidant gas having a further increased temperature can be supplied to the lower end of each unit cell10, so that the temperature difference within the unit cells10in the vertical direction can be further reduced.

Subsequently, a fuel cell module200ein accordance with a sixth embodiment of the invention will be described.FIG. 15is a sectional view for describing an overall construction of the fuel cell module200e. The fuel cell module200eis different from the fuel cell module200ashown inFIG. 7in that oxidant gas distributing members100dare provided instead of the oxidant gas distributing members100. Incidentally, in the sixth embodiment, the oxidant gas distributing members100deach have a protruded portion140that is protruded toward an adjacent side surface of a fuel cell stack20.

In the fuel cell module200ein accordance with the sixth embodiment, since the protruded portions140are provided, it is possible to accelerate the heat exchange between the fuel cell stack20and the oxidant gas that flows in the oxidant gas distributing members100d. Due to this effect, the heated oxidant gas can be supplied to the lower end of each unit cell10, so that the temperature difference within the unit cells10in the vertical direction can be reduced.

Incidentally, the protruded portion140of each oxidant gas distributing member100dmay extend to the upper end thereof as in the construction shown inFIG. 14. Besides, it is also permissible that only one of the two oxidant gas distributing members100dhave a protruded portion140. However, if each of the oxidant gas distributing members100dhas a protruded portion140, the temperature difference within the unit cells10in the vertical direction can be more reduced.

Besides, the first internal thermal insulation members83and the side thermal insulation members82of the fuel cell module200ein accordance with the sixth embodiment may be constructed as in the fourth embodiment.

While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.