Fuel cell device and method for operating fuel cell device

A fuel cell single unit including: a fuel cell element in which an anode layer and a cathode layer are formed so as to sandwich an electrolyte layer; a reducing gas supply path for supplying a gas containing hydrogen to the anode layer; an oxidizing gas supply path for supplying a gas containing oxygen to the cathode layer; and an internal reforming catalyst layer, which has a reforming catalyst for steam-reforming a fuel gas, in at least a part of the reducing gas supply path is provided. An external reformer, which has a reforming catalyst for steam-reforming the fuel gas, is provided upstream of the reducing gas supply path, and the fuel gas partially reformed by the external reformer is supplied to the reducing gas supply path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of International Application No. PCT/JP2019/014223 filed Mar. 29, 2019, and claims priority to Japanese Patent Application No. 2018-070211 filed Mar. 30, 2018, the disclosures of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a fuel cell device including: a fuel cell element in which an anode layer and a cathode layer are formed so as to sandwich an electrolyte layer; a reducing gas supply path for supplying a gas containing hydrogen to the anode layer; and an oxidizing gas supply path for supplying a gas containing oxygen to the cathode layer.

Description of Related Art

The fuel cell element generates power as a single unit by supplying required gases (a reducing gas and an oxidizing gas) to the anode layer and the cathode layer. In the present specification, a unit configured to include the fuel cell element, the reducing gas supply path, and the oxidizing gas supply path is referred to as a “fuel cell single unit”. Furthermore, a plurality of these fuel cell single units are stacked in a predetermined direction to construct a fuel cell module according to the present invention. The fuel cell module is a core of a fuel cell device according to the present invention.

As the background art related to this type of fuel cell, techniques described in JP-A-2017-208232, JP-A-2016-195029, and JP-A-2017-183177 can be mentioned.

The object of the technique disclosed in JP-A-2017-208232 is to provide a fuel cell capable of preventing both an excessively high temperature and temperature unevenness during power generation without sacrificing a power generation performance, and the fuel cell includes a fuel supply flow path (corresponding to the “reducing gas supply path” of the present invention) (210and125) which is a flow path for supplying a fuel gas (corresponding to the “gas containing hydrogen” of the present invention) to a fuel electrode (corresponding to the “anode layer” of the present invention)112. Furthermore, in the fuel supply flow path, a reforming catalyst unit PR1for causing a steam reforming reaction is provided on a surface which is spaced from the fuel electrode112and faces the fuel electrode112.

In the technique disclosed in JP-A-2017-208232, a reformed gas reformed by the reforming catalyst unit PR1is introduced into the fuel electrode. Moreover, the reformed gas is consumed at the fuel electrode, and discharged from an outlet of the fuel supply flow path. In the technique, temperature rise of the fuel cell element is prevented by utilizing the fact that the steam reforming reaction is an endothermic reaction (heat supply is required). Here, a site where the reforming catalyst unit PR1is provided is a site on an upstream side of fuel gas supply with respect to the fuel electrode, and an exhaust gas which has undergone a cell reaction is discharged from an exhaust gas flow path different from the flow path in which the reforming catalyst unit PB1is provided (seeFIG.19(c)).

Furthermore, based on judgment from the drawings and the like, in terms of the structure, the fuel cell disclosed in JP-A-2017-208232 is a so-called anode electrode support-type fuel cell.

On the other hand, in JP-A-2016-195029 and JP-A-2017-183177, the inventors propose that the fuel cell element is provided in a thin layer shape on one surface of a metal support.

In the technique disclosed in JP-A-2016-195029, an electrochemical element is formed in a flat plate shape, and in the technique disclosed in JP-A-2017-183177, an electrochemical element is formed in a disc shape.

The techniques disclosed in these patent literatures relate to the electrochemical element, an electrochemical module, and an electrochemical device, but when the electrochemical element receives supply of a gas containing hydrogen and a gas containing oxygen to generate power, the electrochemical element serves as a fuel cell element, the electrochemical module serves as a fuel cell module, and the electrochemical device serves as a fuel cell device.

In the techniques disclosed in JP-A-2016-195029 and JP-A-2017-183177, by supporting the fuel cell element by the metal support, each layer (at least the anode layer, the electrolyte layer, and the cathode layer) forming the fuel cell element formed on one surface of the metal support can also be an extremely thin layer of micron order to several tens of micron order. Needless to say, the layer may have a thickness of about several millimeters.

In the conventional anode support-type fuel cell disclosed in JP-A-2017-208232, the anode layer is thick (generally, several millimeter order), and an internal reforming reaction also proceeds at once at an inlet portion where the fuel gas is introduced. For this reason, an inlet temperature of the fuel cell is lowered, and conversely, a temperature of an exhaust gas side is maintained at an original temperature of the fuel cell element. Therefore, a side where the reforming catalyst unit is provided is likely to have a low temperature, and a temperature difference between an inlet side and an outlet side is likely to occur.

Furthermore, steam is generated in a fuel cell reaction, but an exhaust gas, which has undergone a cell reaction, is discharged from the exhaust gas flow path without passing through the reforming catalyst unit, and thus the steam is not usefully utilized for the internal reforming reaction.

In the techniques disclosed in JP-A-2016-195029 and JP-A-2017-183177, since in a metal support-type fuel cell, the anode layer formed on the metal support is as thin as several tens of micron order, effects of the internal reforming reaction are less likely to be obtained compared to the anode support-type fuel cell disclosed in JP-A-2017-208232, and high power generation efficiency as in the anode support-type fuel cell is difficult to realize.

In any case, a technique of suitably using a fuel cell configured to include an internal reforming catalyst layer in the fuel cell single unit has not yet been established.

SUMMARY OF THE INVENTION

In consideration of such a circumstance, a main object of the present invention is to obtain a high-efficiency fuel cell capable of reasonably and effectively utilizing an internal reforming reaction.

Solution to Problem

A first feature configuration of the present invention is that a fuel cell single unit including: a fuel cell element in which an anode layer and a cathode layer are formed so as to sandwich an electrolyte layer; a reducing gas supply path for supplying a gas containing hydrogen to the anode layer; an oxidizing gas supply path for supplying a gas containing oxygen to the cathode layer; and an internal reforming catalyst layer, which has a reforming catalyst for reforming a raw fuel gas, in at least a part of the reducing gas supply path is provided, an external reformer, which has a reforming catalyst for reforming the raw fuel gas, is provided upstream of the reducing gas supply path, and the raw fuel gas at least partially reformed in the external reformer is supplied to the reducing gas supply path.

According to this feature configuration, at least hydrogen is supplied to the anode layer forming the fuel cell element through the reducing gas supply path. On the other hand, at least oxygen is supplied to the cathode layer through the oxidizing gas supply path. As a result, by supplying these gases, a power generation reaction can be favorably caused.

Incidentally, in an operation of the fuel cell configured in this way, according to a composition of the fuel cell element, it is necessary to maintain a temperature range (for example, as will be described later, when the fuel cell is SOFC, an operating temperature thereof is about 700° C.) required for a cell reaction. Since the cell reaction itself is an exothermic reaction, the cell can continue to operate by appropriate heat removal in a state where the temperature reaches a predetermined temperature range.

In addition, in the fuel cell single unit according to the present invention, the internal reforming catalyst layer is provided.

As a result, by supplying a gas (for example, the raw fuel gas in the present invention), which can be steam-reformed, to the internal reforming catalyst layer, internal reforming of the gas can be caused. Moreover, by leading hydrogen, which is generated in this way, to the anode layer of the fuel cell element, the hydrogen can be provided for power generation. At this time, heat generated by the exothermic reaction produced by the cell can be favorably utilized.

In other words, in the fuel cell device having this configuration, even when a reforming conversion rate in the external reformer is suppressed to a relatively low level, the reforming conversion rate can be supplemented by internal reforming in the fuel cell single unit, and as a result, stable power generation can be performed.

As will be described later, in the fuel cell device having this configuration, power generation efficiency can be improved compared to a fuel cell device including only the external reformer without including the internal reforming catalyst layer. In particular, improvement in a region of a low steam/carbon ratio (low S/C ratio) is remarkable. Moreover, since a difference in the hydrogen partial pressures between an inlet and an outlet of the reducing gas supply path for supplying the gas containing hydrogen to the anode layer can be reduced, an effect of suppressing deterioration of the fuel cell element, which likely to be caused under a low hydrogen partial pressure, can also be obtained.

Furthermore, in a case where the internal reforming is performed, by reducing the difference (concentration difference) in the hydrogen partial pressure between the outlet and the inlet of the fuel cell single unit, (the reducing gas supply path), uneven distribution of power generation amounts in the cell is reduced, a temperature difference is also reduced, and thus durability or reliability is improved by relaxing thermal stress of the fuel cell element.

Here, the hydrogen partial pressure has been described for easier understanding, but as will be described later, carbon monoxide may be generated together with hydrogen in the steam reforming, and both are used together for power generation. Hereinafter, a gas (hydrogen and carbon monoxide) which reacts with an oxygen ion moving to the anode layer in the fuel cell element is referred to as a “fuel gas for power generation”.

With the configuration of the present invention, by performing external reforming, and internal reforming caused in the fuel cell single unit, a fuel cell device having high energy efficiency can be obtained.

A second feature configuration of the present invention is that the anode layer of the fuel cell element is formed in a thin layer shape.

In a case where this feature configuration is adopted, a function of the fuel cell element, such as the power generation, can be performed only by forming the anode layer into a thin layer shape, and the problem that the efficiency is not increased when the fuel cell element is formed to be relatively thin, as described above, can be solved by performing both the external reforming and the internal reforming. Moreover, a used amount of an expensive material for the anode layer can be reduced, and cost reduction of the fuel cell device can be realized.

A third feature configuration of the present invention is that a steam supply path for supplying steam generated in the fuel cell element to the reducing gas supply path is provided.

By providing this feature configuration, steam generated by power generation can be supplied to the reducing gas supply path (the internal reforming catalyst layer provided in at least a part thereof) through the steam supply path. Moreover, when a gas (the raw fuel gas of the present invention) to be steam-reformed is supplied to the site, the internal reforming occurs at the site, at least hydrogen and carbon monoxide obtained by the reforming is supplied to the anode layer, and thus power generation can be performed.

A reaction and an effect thereof in a vicinity of the internal reforming catalyst layer will be briefly described. For example, as also shown by internal reforming reaction formulae inFIG.6, each reaction formula is formed such that a left side includes a raw fuel gas (CH4) and steam (H2O) and a right side includes hydrogen (H2) and carbon monoxide (CO), but these reactions are in a so-called “phase equilibrium state”, and thus the more steam is supplied to the reaction region and the more hydrogen or carbon monoxide is deprived from the reaction region, the more the steam reforming reaction proceeds. Furthermore, in the present invention, by providing the steam supply path, the supply of the steam to the internal reforming catalyst layer is promoted, and by supplying the hydrogen to the anode layer through the reducing gas supply path, the steam reforming can be favorably caused in the fuel cell single unit to perform efficient power generation.

A fourth feature configuration of the present invention is that the fuel cell single unit is configured to include one fuel cell element formed in a thin layer shape on a metal support, the reducing gas supply path, the oxidizing gas supply path, an internal reforming catalyst layer for generating at least hydrogen from the raw fuel gas by a steam reforming reaction is included in the fuel cell single unit, and an internal reformed fuel supply path for discharging steam generated by a power generation reaction from the anode layer to lead the steam to the internal reforming catalyst layer, and leading at least hydrogen generated in the internal reforming catalyst layer to the anode layer is provided.

According to this feature configuration, since the fuel cell element is supported by a strong metal support separate from the cell, it is not necessary to thicken the anode layer, for example, in order to maintain a strength of the fuel cell element, and it is also possible to make the fuel cell element as thin as a thickness of, for example, several tens of microns to several hundreds of microns. Accordingly, a used amount of an expensive ceramic material used for the fuel cell can be reduced, and a compact and high-performance fuel cell device can be obtained at a low cost.

As also described above, in addition to hydrogen, carbon monoxide is also generated in the steam reforming reaction of the raw fuel gas, but these gases are provided, as a fuel gas for power generation, for power generation in the anode layer.

A fifth feature configuration of the present invention is that in the metal support, the internal reforming catalyst layer is provided on a surface different from a surface on which the fuel cell element is formed.

According to this feature configuration, a specific surface, which is on the metal support and is different from a surface on which the fuel cell element is provided, can be utilized to be provided for internal reforming. Moreover, the internal reforming catalyst layer can be formed on the specific surface on the metal support, and provided for internal reforming, and thus a compact and high-performance fuel cell device can be obtained at a low cost.

A sixth feature configuration of the present invention is that a plurality of through-holes penetrating the metal support are provided, the anode layer is provided on one surface of the metal support, the reducing gas supply path is provided along the other surface, the internal reforming catalyst layer is provided on at least a part of the other surface, and each of the through-holes works in a flow direction in the reducing gas supply path to serve as the internal reformed fuel supply path.

According to this feature configuration, by supplying a gas (for example, the raw fuel gas in the present invention), which can be steam-reformed, to the internal reforming catalyst layer, the steam generated by the power generation reaction can be used to cause internal reforming of the gas. Moreover, by leading a fuel gas for power generation, which is generated in this way, to the anode layer of the fuel cell element, the fuel gas for power generation can be provided for power generation.

That is, the internal reformed fuel supply path in the present invention has a structure which serves both as a discharge unit of steam released from the anode layer, and as a supply unit for re-leading a fuel gas for power generation generated by steam reforming to the anode layer.

Furthermore, an area of an opening part of a through-hole on a surface of the metal support on which the anode layer is provided is preferably smaller than an area of an opening part of a through-hole on the other surface. This is because the supply of the fuel gas for power generation to the anode layer becomes easier by setting the area as described above.

A seventh feature configuration of the present invention is that the internal reforming catalyst layer is provided inside the through-hole.

According to this feature configuration, the through-hole provided in the metal support can be utilized to be provided for internal reforming. Moreover, the internal reforming catalyst layer can be formed in the through-hole, and provided for internal reforming, and thus a compact and high-performance fuel cell device can be obtained at a low cost.

An eighth feature configuration of the present invention is that at least one metal separator for partitioning the reducing gas supply path and the oxidizing gas supply path is provided in the fuel cell single unit, and the internal reforming catalyst layer is provided on at least a part of the metal separator on a side of the reducing gas supply path.

According to this feature configuration, a specific surface of the metal separator on which the reducing gas supply path is formed can be utilized to be provided for internal reforming. Moreover, the internal reforming catalyst layer can be formed on at least a part of the metal separator on the side of the reducing gas supply path, and provided for internal reforming, and thus a compact and high-performance fuel cell device can be obtained at a low cost.

A ninth feature configuration of the present invention is that the reforming catalyst contained in the internal reforming catalyst layer is at least a catalyst in which a metal is supported on a support.

According to this feature configuration, by using the catalyst in which the metal is supported on the support, a high-performance internal reforming catalyst layer can be obtained despite reduction in a used amount of a metal used for a catalyst, and thus a high-performance fuel cell device can be obtained at a low cost.

A tenth feature configuration of the present invention is that the reforming catalyst contained in the internal reforming catalyst layer is a catalyst containing Ni.

According to this feature configuration, by using Ni which is a relatively easily available and inexpensive metal, steam reforming can be caused in the internal reforming catalyst layer.

An eleventh feature configuration of the present invention is that a turbulence promotion component for disturbing flow in the reducing gas supply path is provided in the reducing gas supply path.

Flow of a gas flowing in the reducing gas supply path is likely to become laminar flow due to a configuration of the flow path, but by inserting the turbulence promotion component into the flow path, the flow is disturbed, and a direction (for example, flow orthogonal to main flow formed in the reducing gas supply path), which is different from a direction of the main flow, can be formed. As a result, the gas containing hydrogen can be efficiently supplied to the anode layer. Furthermore, the mixing and the release of the predetermined gas (a raw fuel gas or steam before reforming) to the internal reforming catalyst layer, which are described above, can be promoted, and the internal reforming by the internal reforming catalyst layer can be further promoted.

A twelfth feature configuration of the present invention is that the fuel cell element is a solid oxide fuel cell.

According to this feature configuration, power generation can be performed by directly supplying a reformed gas reformed by the external reformer to the solid oxide fuel cell without going through additional reforming steps such as removal of carbon monoxide in the reformed gas, and thus a fuel cell device having a simple configuration can be obtained.

Furthermore, the solid oxide fuel cell can be used in a high-temperature range in which a power generation operating temperature thereof is 650° C. or higher, but highly efficient power generation can be realized while effectively utilizing heat in the temperature range for the internal reforming reaction.

A thirteenth feature configuration of the present invention is that in a method for operating the fuel cell device described above, a steam/carbon ratio (S/C ratio) at an inlet of the external reformer is controlled to be within a range of 1.5 to 3.0.

As will be described in detail later, by performing external reforming by the external reformer and internal reforming in the fuel cell single unit as steam reforming, an amount of steam supplied to the external reformer can be reduced, high power generation efficiency can be obtained in a S/C ratio range wider than before, and thus the above range is preferable. Moreover, controlling the S/C ratio at the inlet of the external reformer to be within a range of 1.5 to 2.5 is more preferable because an effect of improving the power generation efficiency can be further obtained by this configuration. Furthermore, for example, in a specific investigation example by the inventor, a quantity of heat required for the external reformer can be reduced by 60%, a quantity of heat transfer required for steam generation can be reduced by 20%, and as a result, direct-current power generation efficiency can be improved by 3.6%.

In other words, under the same electric power load, a steam/carbon ratio (a S/C ratio) at the inlet of the external reformer is controlled to be lower than a steam/carbon ratio (a S/C ratio) set when the reforming of the fuel gas is performed only by the external reformer without providing the internal reforming catalyst layer, and thus the power generation efficiency can be improved.

A fourteenth feature configuration of the present invention is that in a method for operating the fuel cell device described above, a reforming temperature in the external reformer is controlled to be lower than a temperature in the internal reforming catalyst layer provided in the reducing gas supply path.

With this configuration, the internal reforming of the raw fuel gas is possible, hydrogen or carbon monoxide (fuel gas for power generation) generated in this way can be provided for power generation, and thus power generation corresponding to the electric power load can be realized without any hindrance. By lowering the temperature of the external reformer in this way, heat (energy) required when the steam reforming is performed by the external reformer in the related art can be greatly reduced.

When performing internal reforming, a partial pressure of the fuel gas for power generation near an inlet part of the fuel cell single unit, (the reducing gas supply path) is decreased by lowering the temperature of the external reformer, but an internal reforming reaction rapidly proceeds in the fuel cell element due to the generated steam, and thus it is possible to sequentially generate fuel gases for power generation in the fuel cell element, suppress an extreme decrease in the partial pressure of the fuel gas for power generation, and prevent the deterioration of the fuel cell element. Moreover, an extreme decrease in the partial pressure of the fuel gas for power generation near an outlet part can be suppressed. When off-gas combustion is performed as in a second embodiment described later, an increase in the partial pressure of the fuel gas for power generation at the outlet of the fuel cell element is advantageous for stabilizing the off-gas combustion.

A fifteenth feature configuration of the present invention is that in a method for operating the fuel cell device described above, the operation is performed so that a partial pressure of a fuel gas for power generation at an inlet of the reducing gas supply path is 50% or less of a total gas pressure.

With this configuration, the internal reforming of the fuel gas is possible, and thus a fuel gas for power generation generated in the fuel cell single unit can be provided for power generation. Therefore, even when a partial pressure of the fuel gas for power generation near the inlet part of the fuel cell single unit, (the reducing gas supply path) is lowered, power generation corresponding to the electric power load can be realized without any hindrance.

In other words, even when the reforming conversion rate in the external reformer is set to be lower than that in the related art under the same electric power load, and the partial pressure of the fuel gas for power generation at the inlet of the reducing gas supply path is set to 50% or less, an extreme decrease in the hydrogen partial pressure in the fuel cell element can be suppressed by the internal reforming reaction in the internal reforming catalyst layer, and the deterioration of the fuel cell element can be prevented. Moreover, setting the partial pressure of the fuel gas for power generation at the inlet of the reducing gas supply path to 43% or less is more preferable because, in addition to the above effects, a reforming load in the external reformer can be suppressed, and the effect of improving the power generation efficiency of the fuel cell device can be further enhanced.

A sixteenth feature configuration of the present invention is that in a method for operating the fuel cell device described above, the operation is performed so that a difference between an inlet proportion and an outlet proportion, which are expressed in a percentage, is maintained within 40%, where a proportion of a partial pressure of a fuel gas for power generation at an inlet of the reducing gas supply path to a total gas pressure at the inlet is defined as the inlet proportion, and a proportion of a partial pressure of a fuel gas for power generation at an outlet of the reducing gas supply path to a total gas pressure at the outlet is defined as an outlet proportion.

With this configuration, the internal reforming of the raw fuel gas is possible, and thus a fuel gas for power generation generated in the fuel cell single unit can be provided for power generation. Therefore, even when a partial pressure of the fuel gas for power generation near the inlet part of the fuel cell single unit, (the reducing gas supply path) is lowered, the difference in the partial pressures of the fuel gas for power generation between the inlet and the outlet of the reducing gas supply path can be made smaller than that in the related art. Accordingly, the extreme decrease in the hydrogen partial pressure in the fuel cell element can be suppressed, and the deterioration of the fuel cell element can be suppressed.

A seventeenth feature configuration of the present invention is that in a method for operating the fuel cell device described above, a reforming conversion rate of the raw fuel gas reformed by the external reformer is set to 30% to 60%.

Depending on a configuration of a facility, by setting the reforming conversion rate of the raw fuel gas reformed by the external reformer to 30% to 60%, a balance between the external reforming by the external reformer and the internal reforming is favorable, and the power generation efficiency of the fuel cell device can be further improved compared to the related art. Moreover, since the balance between the external reforming and the internal reforming is more favorable, 35% or greater is more preferable and 40% or greater is still more preferable. Furthermore, since the effect of improving the power generation efficiency of the fuel cell device is more likely to be obtained, 55% or less is more preferable and 50% or less is still more preferable. When the reforming conversion rate is less than 30%, an internal reforming load becomes too high. On the other hand, when the reforming conversion rate is greater than 60%, the effect of improving the power generation efficiency of the fuel cell device is less likely to be obtained.

An eighteenth feature configuration of the present invention is that in a method for operating the fuel cell device described above, desulfurization is performed so that a concentration of sulfur contained in the raw fuel gas is 1 vol. ppb or less (more preferably, 0.1 vol. ppb or less), and the raw fuel gas is supplied to the external reformer.

By adopting this configuration, adverse effects such as poisoning of the reforming catalyst or the like by a sulfur content contained in the raw fuel gas can be greatly reduced, and a stable operation can be ensured for a long period of time. By setting the concentration of the sulfur to 0.1 vol. ppb or less, the reliability and the durability of the fuel cell device can be further improved.

DESCRIPTION OF THE INVENTION

Hereinafter, as the embodiments of the present invention, a first embodiment, a second embodiment, and a third embodiment will be presented. In the description, for each embodiment, the entirety of a fuel cell device Y adopting each embodiment will be described, and then a fuel cell module M included in the fuel cell device Y and a fuel cell single unit U for constructing the fuel cell module M in a stacked state will be described.

A feature of the first embodiment is in that a fuel cell module M has a disc shape, and the fuel cell module M itself receives supply of a reducing gas and an oxidizing gas to operate as a cell, whereas the second embodiment has a feature in which a fuel cell module M has a substantially rectangular parallelepiped shape, and the fuel cell module M is housed in a housing10which houses an external reformer34and a vaporizer33to operate as a cell. In the third embodiment, a structure basically follows the structure of the first embodiment, and the fuel cell module M, which has a disc shape in the first embodiment, has a square shape. Fuel cell elements R according to the first embodiment and the third embodiment can be very thinly manufactured. On the other hand, a fuel cell element R according to the second embodiment can also be made thicker than the fuel cell element R according to the first embodiment. Needless to say, the fuel cell element R according to the second embodiment may be made relatively thin.

Providing an internal reforming catalyst layer D in the fuel cell single unit U and providing the external reformer34, which are the features of the present invention, are common to all the embodiment.

First Embodiment

FIG.1shows a configuration of the fuel cell device Y according to this embodiment.

The fuel cell device Y is a so-called “cogeneration system”, which is capable of generating and supplying both electric power and heat. The electric power is output via an inverter38, and as the heat, heat held by an exhaust gas can be recovered as warm water and utilized by a heat exchanger36. The inverter38converts, for example, a direct current of the fuel cell module M into electric power having the same voltage and the same frequency as those of electric power received from a commercial system (not shown), and outputs the electric power. A control unit39appropriately controls the inverter38, and also controls operations of respective machines configuring the fuel cell device Y.

The fuel cell device Y includes a boost pump30, a desulfurizer31, a reforming water tank32, the vaporizer33, and the external reformer34, as a main machine for supplying a reducing gas to the fuel cell module M, which is responsible for power generation. A main machine for supplying an oxidizing gas is a blower35, and the blower35is capable of sucking an air to supply an oxidizing gas containing oxygen.

A supply system (this system serves as a fuel supply unit in the fuel cell device) of the reducing gas will be further described. A hydrocarbon-based raw fuel gas such as a city gas (a gas which contains methane as a main component, and also contains ethane, propane, butane, and the like) is sucked and boosted by the boost pump30, and sent to the fuel cell module M. Since the city gas contains a sulfur compound component, it is necessary to remove (desulfurize) the sulfur compound component in the desulfurizer31. A copper-zinc-based desulfurizing agent is stored in the desulfurizer31, and a sulfur component contained in the raw fuel gas is reduced so that a content of the sulfur is 1 vol. ppb or less (more preferably 0.1 vol. ppb or less). As this type of copper-zinc-based desulfurizing agent, a desulfurizing agent obtained by hydrogen reduction of a copper oxide-zinc oxide mixture prepared by a coprecipitation method using a copper compound (for example, copper nitrate, copper acetate, or the like) and a zinc compound (for example, zinc nitrate, zinc acetate, or the like), or a desulfurizing agent obtained by hydrogen reduction of a copper oxide-zinc oxide-aluminum oxide mixture prepared by a coprecipitation method using a copper compound, a zinc compound, and an aluminum compound (for example, aluminum nitrate, sodium aluminate, or the like) can be typically used.

The desulfurized raw fuel gas is mixed with reforming water supplied from the reforming water tank32on a latter stage side of the vaporizer33, and water becomes steam in the vaporizer33. The raw fuel gas and the steam are sent to the external reformer34, and the raw fuel gas is steam-reformed. The steam reforming reaction is a reaction by a reforming catalyst stored in the reformer, and similarly to an internal reforming reaction described later, a part of a hydrocarbon-based raw fuel gas (for example, methane) is reformed, and gas (reformed gas) containing at least hydrogen is generated and provided for power generation.

The reforming by the external reformer34does not reform the entire raw fuel gas, but reforms the raw fuel gas at an appropriate ratio. Therefore, in the present invention, a gas, which is sent to an anode layer A configuring the fuel cell element R included in the fuel cell module M, is a mixed gas of the raw fuel gas (the gas which is not yet reformed) and the reformed gas. The reformed gas contains hydrogen and carbon monoxide, which are the fuel gases for power generation described above. The mixed gas is supplied to a reducing gas supply path L1included in the fuel cell single unit U.

More specifically, as shown inFIGS.3and4, the reducing gas supply path L1for supplying a gas containing hydrogen for power generation to the anode layer A is provided, the mixed gas (containing the raw fuel gas (the gas which is not yet reformed) and the reformed gas) is supplied to the reducing gas supply path L1, and at least hydrogen contained in the mixed gas is used in the fuel cell reaction in the fuel cell element R. An exhaust gas containing residual hydrogen, which has not been used in the reaction, is discharged from the fuel cell single unit U.

As described above, the heat exchanger36exchanges heat between the exhaust gas from the fuel cell module M and the supplied cold water to generate warm water. The heat exchanger36serves as an exhaust heat utilization unit of the fuel cell device Y. Instead of the exhaust heat utilization form, a form in which the exhaust gas discharged from the fuel cell module M is utilized for heat generation may be used. That is, the exhaust gas contains residual hydrogen and carbon monoxide, which have not been used in the reaction in the fuel cell single unit U, and raw fuel gas, and thus heat generated by combustion of these combustible gases can be utilized. In the second embodiment described later, residual combustion components are utilized, as a fuel, for heating the external reformer34and the vaporizer33.

FIGS.2and3show a top view and a cross-sectional view of the fuel cell single unit U according to the present embodiment.

The fuel cell single unit U is configured to include the fuel cell element R formed on a metal support1, and a metal separator (current-collector plate3with projections) bonded to a side opposite to the fuel cell element R. The metal support1in the present embodiment has a disc shape, the fuel cell element R is configured to include at least the anode layer A, an electrolyte layer B, and a cathode layer C, and is formed and disposed on a front side1eof the metal support1, and the electrolyte layer B is sandwiched between the anode layer A and the cathode layer C. When the fuel cell element R is formed on the front side1eof the metal support1, the metal separator3is positioned on a rear side1fof the metal support1. That is, the fuel cell element R and the metal separator3are positioned so as to sandwich the metal support1.

When the fuel cell single unit U includes the fuel cell element R and metal separator3formed on the metal support1as described above, a gas containing at least hydrogen is supplied to the anode layer A through the reducing gas supply path L1, a gas containing oxygen is supplied to the cathode layer C through an oxidizing gas supply path L2, and thus power can be generated. Moreover, as a structural feature of the fuel cell single unit U, a metal oxide layer x is provided on the front side1eof the metal support1, an intermediate layer y is provided on a surface (including an interface between the anode layer A and the electrolyte layer B covering the anode layer A) of the anode layer A, and a reaction preventing layer z is provided on a surface (including an interface between the electrolyte layer B and the cathode layer C covering the electrolyte layer B) of the electrolyte layer B. The metal oxide layer x, the intermediate layer y, and the reaction preventing layer z are layers provided for suppressing diffusion of constituent materials between material layers sandwiching these layers x, y, and z, and are shown inFIG.6for easier understanding.

The metal support1is a flat plate which is made of a metal and has a disc shape.

As is also clear fromFIGS.2and3, an opening part1bconcentric with the metal support1is formed in a center of the metal support1. In the metal support1, a plurality of through-holes1apenetrating the front side1eand the rear side1fare formed. A gas can flow between the front side1eand the rear side1fof the metal support1through the through-hole1a. The gas flowing through the through-hole1ais specifically the reformed gas (containing hydrogen H2) described above, and steam H2O generated by the power generation reaction in the fuel cell element R (seeFIG.6).

As a material for the metal support1, a material having excellent electron conductivity, heat resistance, oxidation resistance, and corrosion resistance is used. For example, ferritic stainless alloy, austenitic stainless alloy, a nickel-based alloy, or the like is used. In particular, an alloy containing chromium is suitably used. In the present embodiment, a Fe—Cr-based alloy containing 18% by mass to 25% by mass of Cr is used for the metal support1, but a Fe—Cr-based alloy containing 0.05% by mass or greater of Mn, a Fe—Cr-based alloy containing 0.15% by mass to 1.0% by mass of Ti, a Fe—Cr-based alloy containing 0.15% by mass to 1.0% by mass of Zr, a Fe—Cr-based alloy containing Ti and Zr and having a total content of Ti and Zr of 0.15% by mass to 1.0% by mass, and a Fe—Cr-based alloy containing 0.10% by mass to 1.0% by mass of Cu are particularly suitable.

The metal support1has a plate shape as a whole. Moreover, in the metal support1, a surface on which the anode layer A is provided is the front side1e, and the plurality of through-holes1apenetrating from the front side1eto the rear side1fare provided. The through-hole1ahas a function of allowing a gas to permeate from the rear side1fto the front side1eof the metal support1. Furthermore, by bending the plate-shaped metal support1, for example, the plate-shaped metal support1can also be deformed in a shape such as a box shape and a cylindrical shape and used.

The metal oxide layer x as a diffusion suppressing layer is provided on the surface of the metal support1(seeFIG.6). That is, the diffusion suppressing layer is formed between the metal support1and the anode layer A described later. The metal oxide layer x is provided not only on the surface of the metal support1which is exposed to the outside but also on a contact surface (interface) with the anode layer A. Moreover, the metal oxide layer x can also be provided on an inner surface of the through-hole1a. Element interdiffusion between the metal support1and the anode layer A can be suppressed by the metal oxide layer x. For example, when ferritic stainless containing chromium is used for the metal support1, the metal oxide layer x mainly contains a chromium oxide. Furthermore, diffusion of an chromium atom or the like of the metal support1into the anode layer A or the electrolyte layer B is suppressed by the metal oxide layer x which contains a chromium oxide as a main component. The thickness of the metal oxide layer x may be any thickness as long as both a high diffusion preventing performance and low electric resistance are achieved.

The metal oxide layer x can be form by various methods, but a method for oxidizing the surface of the metal support1to form a metal oxide is suitably utilized. Moreover, on the surface of the metal support1, the metal oxide layer x may be formed by a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method such as a sputtering method and a PLD method, a CVD method, or the like, and may be formed by plating and an oxidation treatment. Furthermore, the metal oxide layer x may contain a spinel phase having high conductivity.

When a ferritic stainless material is used for the metal support1, a thermal expansion coefficient of the metal support1is close to that of yttria-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC, also referred to as CGO) used as a material for the anode layer A or the electrolyte layer B. Therefore, even when a temperature cycle of a low temperature and a high temperature is repeated, the fuel cell element R is less likely to be damaged. Accordingly, a fuel cell element R having excellent long-term durability can be obtained, which is preferable.

As also described above, the metal support1has the plurality of the through-holes1aprovided so as to penetrate the front side1eand the rear side1f. Furthermore, for example, the through-hole1acan be provided in the metal support1by mechanical, chemical, or optical boring processing. As also shown in (b) ofFIG.3, the through-hole1asubstantially has a tapered shape in which the front side1eof the metal support1is narrow. The through-hole1ahas a function of allowing a gas to permeate from both the front and rear sides of the metal support1. In order to impart gas permeability to the metal support1, it is also possible to use a porous metal. For example, for the metal support1, a sintered metal, a foamed metal, or the like can also be used.

As also described above, the fuel cell element R is configured to have: the anode layer (anode electrode layer) A; the electrolyte layer B; the cathode layer (cathode electrode layer) C; and the intermediate layer y and the reaction preventing layer z, which are appropriately provided between these layers. The fuel cell element R is a solid oxide fuel cell SOFC. As described above, the fuel cell element R shown as the embodiment includes the intermediate layer y and the reaction preventing layer z, and thus the electrolyte layer B is indirectly sandwiched between the anode layer A and the cathode layer C. From the viewpoint that only cell power generation is caused, power can be generated by forming the anode layer A on one surface of the electrolyte layer B, and forming the cathode layer C on the other surface.

As shown inFIGS.3and6or the like, the anode layer A can be provided as a thin layer in a region which is on the front side1eof the metal support1and is larger than a region where the through-holes1aare provided. In a case of being provided as a thin layer, a thickness thereof can be, for example, about 1 μm to 100 μm and preferably 5 μm to 50 μm. When the thickness is set as described above, a sufficient electrode performance can be ensured while reducing a cost by reducing a used amount of an expensive material for the electrode layer. The entire region where the through-holes1aare provided is covered with the anode layer A. That is, the through-hole1ais formed inside a region of the metal support1where the anode layer A is formed. In other words, all the through-holes1aare provided so as to face the anode layer A.

As a material for the anode layer A, for example, a composite material such as NiO-GDC, Ni-GDC, NiO-YSZ, Ni-YSZ, CuO—CeO2, and Cu—CeO2can be used. In these examples, GDC, YSZ, and CeO2can be referred to as a composite aggregate.

In addition, the anode layer A is preferably formed by a low-temperature calcination method (for example, a wet method using a calcination treatment in a low-temperature range without performing a calcination treatment in a high-temperature range of higher than 1,100° C.), a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. By these processes which can be used in a low-temperature range, a favorable anode layer A can be obtained without using calcination in a high-temperature range of higher than 1,100° C., for example. For the reason, the element interdiffusion between the metal support1and the anode layer A can be suppressed without damaging the metal support1, and an electrochemical element having excellent durability can be obtained, which is preferable. Moreover, using the low-temperature calcination method is more preferable because handling of raw materials becomes easy.

Furthermore, an amount of Ni contained in the anode layer A can be in a range of 35% by mass to 85% by mass. Moreover, the amount of Ni contained in the anode layer A is more preferably greater than 40% by mass and still more preferably greater than 45% by mass because a power generation performance can be further enhanced. On the other hand, the amount of Ni is more preferably 80% by mass or less because a cost is easily reduced.

The anode layer A has a plurality of pores (not shown) inside and on the surface thereof so as to have gas permeability. That is, the anode layer A is formed as a porous layer. The anode layer A is formed, for example, so that the denseness is 30% or greater and less than 80%. As a size of the pore, a size suitable for allowing an electrochemical reaction to smoothly proceed during the reaction can be appropriately selected. Moreover, the denseness is a proportion of a material constituting a layer to a space, can be expressed as (1−porosity), and is equivalent to a relative density.

As shown inFIG.6, the intermediate layer y can be formed as a thin layer on the anode layer A in a state of covering the anode layer A. In a case of being provided as a thin layer, a thickness thereof can be, for example, about 1 μm to 100 μm, preferably about 2 μm to 50 μm, and more preferably about 4 μm to 25 μm. When the thickness is set as described above, a sufficient performance can be ensured while reducing a cost by reducing a used amount of an expensive material for the intermediate layer. As a material for the intermediate layer y, for example, yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), gadolinium-doped ceria (GDC), yttrium-doped ceria (YDC), samarium-doped ceria (SDC), or the like can be used. In particular, ceria-based ceramics are suitably used.

The intermediate layer y is preferably formed by a low-temperature calcination method (for example, a wet method using a calcination treatment in a low-temperature range without performing a calcination treatment in a high-temperature range of higher than 1,100° C.), a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. By these film formation processes which can be used in a low-temperature range, the intermediate layer y can be obtained without using calcination in a high-temperature range of higher than 1,100° C., for example. For the reason, the element interdiffusion between the metal support1and the anode layer A can be suppressed without damaging the metal support1, and a fuel cell element R having excellent durability can be obtained. Moreover, using the low-temperature calcination method is more preferable because handling of raw materials becomes easy.

The intermediate layer y has oxygen ion (oxide ion) conductivity. Moreover, the intermediate layer y more preferably has mixed conductivity of an oxygen ion (oxide ion) and an electron. The intermediate layer y having these properties is suitable for application to the fuel cell element R.

The electrolyte layer B is formed as a thin layer on the intermediate layer y in a state of covering the anode layer A and the intermediate layer y. Moreover, the electrolyte layer can also be formed as a thin layer having a thickness of 10 μm or less. Specifically, as shown inFIGS.3and6or the like, the electrolyte layer B is provided over (straddling) the intermediate layer y and the metal support1. With such a configuration, by bonding the electrolyte layer B to the metal support1, the electrochemical element as a whole can have excellent fastness properties.

In addition, the electrolyte layer B is provided in a region which is on the front side1eof the metal support1and is larger than a region where the through-holes1aare provided. That is, the through-hole1ais formed inside a region of the metal support1where the electrolyte layer B is formed.

Furthermore, at the periphery of the electrolyte layer B, gas leakage from the anode layer A and the intermediate layer y can be suppressed. Specifically, during power generation, gas is supplied to the anode layer A from the rear side of the metal support1through the through-hole1a. At a site where the electrolyte layer B is in contact with the metal support1, gas leakage can be suppressed without providing a separate member such as a gasket. Moreover, in the present embodiment, the electrolyte layer B covers the entire periphery of the anode layer A, but a configuration in which the electrolyte layer B is provided on an upper part of the anode layer A and the intermediate layer y, and a gasket or the like is provided at the periphery may be adopted.

As a material for the electrolyte layer B, yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), gadolinium-doped ceria (GDC), yttrium-doped ceria (YDC), samarium-doped ceria (SDC), strontium- and magnesium-doped lanthanum gallate (LSGM), or the like can be used. In particular, zirconia-based ceramics are suitably used. When the electrolyte layer B is made of the zirconia-based ceramics, an operating temperature of SOFC using the fuel cell element R can be made higher than that in a case of ceria-based ceramics. When SOFC is used, and a system configuration in which a material, such as YSZ, which can exhibit a high electrolyte performance even in a high-temperature range of about 650° C. or higher is used as the material for the electrolyte layer B, a hydrocarbon-based raw fuel such as a city gas and LPG is used as a raw fuel of the system, and the raw fuel is steam-reformed to become a reducing gas of SOFC is adopted, it is possible to construct a high-efficiency SOFC system in which heat generated in a cell stack of SOFC is used for reforming the raw fuel gas.

The electrolyte layer B is preferably formed by a low-temperature calcination method (for example, a wet method using a calcination treatment in a low-temperature range without performing a calcination treatment in a high-temperature range of higher than 1,100° C.), a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. By these film formation processes which can be used in a low-temperature range, an electrolyte layer B which is dense and has high gastightness and gas barrier properties can be obtained without using calcination in a high-temperature range of higher than 1,100° C., for example. For the reason, the damage of the metal support1can be suppressed, the element interdiffusion between the metal support1and the anode layer A can be suppressed, and the fuel cell element R which is excellent in a performance and durability can be obtained. In particular, using a low-temperature calcination method, a spray coating method, or the like is preferable because a low-cost element can be obtained. Furthermore, using the spray coating method is more preferable because the electrolyte layer which is dense and has high gastightness and gas barrier properties can be easily obtained in a low-temperature range.

The electrolyte layer B is densely configured so as to shield a gas such as a reducing gas or an oxidizing gas from being leaked and exhibit high ionic conductivity. A denseness of the electrolyte layer B is preferably 90% or greater, more preferably 95% or greater, and still more preferably 98% or greater. When the electrolyte layer B is a uniform layer, the denseness thereof is preferably 95% or greater and more preferably 98% or greater. Moreover, when the electrolyte layer B is formed in a form of a plurality of layers, at least some of these layers preferably include a layer (dense electrolyte layer) having a denseness of 98% or greater, and more preferably include a layer (dense electrolyte layer) having a denseness of 99% or greater. This is because when such a dense electrolyte layer is included in a part of the electrolyte layer, the electrolyte layer which is dense and has high gastightness and gas barrier properties can be easily formed even in a case where the electrolyte layer is formed in a form of a plurality of layers.

The reaction preventing layer z can be formed as a thin layer on the electrolyte layer B. In a case of being provided as a thin layer, a thickness thereof can be, for example, about 1 μm to 100 μm, preferably about 2 μm to 50 μm, and more preferably about 3 μm to 15 μm. When the thickness is set as described above, a sufficient performance can be ensured while reducing a cost by reducing a used amount of an expensive material for the reaction preventing layer. A material for the reaction preventing layer z may be any material as long as the material can prevent a reaction between the components of the electrolyte layer B and the components of the cathode layer C, but for example, a ceria-based material or the like is used. Moreover, as the material for the reaction preventing layer z, a material containing at least one element selected from the group consisting of Sm, Gd, and Y is suitably used. Furthermore, the material may contain at least one element selected from the group consisting of Sm, Gd, and Y, and a total content ratio of these elements may be 1.0% by mass to 10% by mass. By introducing the reaction preventing layer z between the electrolyte layer B and the cathode layer C, a reaction between the constituent materials of the cathode layer C and the constituent materials of the electrolyte layer B can be effectively suppressed (diffusion suppression), and long-term stability of the performance of the fuel cell element R can be improved. Forming the reaction preventing layer z by appropriately using a method in which the reaction preventing layer z can be formed at a treatment temperature of 1,100° C. or lower is preferable because the damage of the metal support1can be suppressed, the element interdiffusion between the metal support1and the anode layer A can be suppressed, and the fuel cell element R which is excellent in a performance and durability can be obtained. For example, the formation can be performed by appropriately using a low-temperature calcination method (for example, a wet method using a calcination treatment in a low-temperature range without performing a calcination treatment in a high-temperature range of higher than 1,100° C.), a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. In particular, using a low-temperature calcination method, a spray coating method, or the like is preferable because a low-cost element can be obtained. Moreover, using the low-temperature calcination method is more preferable because handling of raw materials becomes easy.

The cathode layer C can be formed as a thin layer on the electrolyte layer B or the reaction preventing layer z. In a case of being provided as a thin layer, a thickness thereof can be, for example, about 1 μm to 100 μm and preferably 5 μm to 50 μm. When the thickness is set as described above, a sufficient electrode performance can be ensured while reducing a cost by reducing a used amount of an expensive material for the cathode layer. As a material for the cathode layer C, for example, a complex oxide such as LSCF and LSM, a ceria-based oxide, and a mixture thereof can be used. In particular, the cathode layer C preferably contains a perovskite-type oxide containing two or more elements selected from the group consisting of La, Sr, Sm, Mn, Co, and Fe. The cathode layer C formed of the above materials functions as a cathode.

In addition, forming the cathode layer C by appropriately using a method in which the cathode layer C can be formed at a treatment temperature of 1,100° C. or lower is preferable because the damage of the metal support1can be suppressed, the element interdiffusion between the metal support1and the anode layer A can be suppressed, and the fuel cell element R which is excellent in a performance and durability can be obtained. For example, the formation can be performed by appropriately using a low-temperature calcination method (for example, a wet method using a calcination treatment in a low-temperature range without performing a calcination treatment in a high-temperature range of higher than 1,100° C.), a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. In particular, using a low-temperature calcination method, a spray coating method, or the like is preferable because a low-cost element can be obtained. Moreover, using the low-temperature calcination method is more preferable because handling of raw materials becomes easy.

In the fuel cell single unit U, electrical conduction properties between the metal support1and the anode layer A are ensured. Moreover, an insulating coating film may be formed on a required portion of the surface of the metal support1, as needed.

<Power Generation in Fuel Cell Element>

The fuel cell element R receives supply of both a reducing gas containing hydrogen and an oxidizing gas containing oxygen to generate power. As described above, by supplying both the gases to respective electrode layers (the anode layer A and the cathode layer C) of the fuel cell element R, as shown inFIG.6, in the cathode layer C, an oxygen molecule O2reacts with an electron e−to generate an oxygen ion O2−. The oxygen ion O2−moves to the anode layer A through the electrolyte layer B. In the anode layer A, each of (hydrogen H2and carbon monoxide CO), which are the fuel gas for power generation, reacts with an oxygen ion O2−to generate steam H2O, carbon dioxide CO2, and an electron e−. By the above reaction, an electromotive force is generated between the anode layer A and the cathode layer C to perform power generation. The power generation principle is the same also in the second embodiment (seeFIG.11).

Hereinafter, a structure for supplying the reducing gas and the oxidizing gas will be described, and a configuration relating to internal reforming unique to the present invention will be described.

As shown inFIG.3, the fuel cell single unit U is configured to include the current-collector plate3with projections as a metal separator. As shown in (a) ofFIG.4, the current-collector plate3with projections is a plate which is made of a metal and has a disc shape, has a concave-convex structure site3aincluding one or more concave portions or convex portions, is disposed so as to face the rear side1fof the metal support1, and is bonded to the metal support1via a bonding site W. The concave-convex structure site3ais connected to the cathode layer C of another fuel cell single unit U when the plurality of the fuel cell single units U are stacked. Therefore, the current-collector plate3with projections is electrically connected to the metal support1, and further to the anode layer A. In the current-collector plate3with projections, a gas does not flow between front and back thereof. As will be described later, a metal support1side (in other words, an anode layer A side) of the current-collector plate3with projections can be the reducing gas supply path L1described above, and a rear side (a side spaced from the metal support1) thereof can be the oxidizing gas supply path L2described above.

The supply and the discharge of these gases will be described below.

The fuel cell single unit U includes a gas supply pipe2.

The gas supply pipe2separately supplies the reducing gas and the oxidizing gas to spaces (each serving as a supply path through which a gas flows outward in a radial direction) formed above and below the current-collector plate3with projections. The gas supply pipe2is a member which is made of a metal and has a cylindrical shape, and is inserted into the opening part1bof the metal support1in a state where a central axis Z of the gas supply pipe2is aligned with a central axis Z of the metal support1and fixed by welding. Moreover, the metal support1may be biased against the gas supply pipe2with a seal material sandwiched therebetween. As a material for the gas supply pipe2, the same material as that for the metal support1described above can be used. Furthermore, forming a diffusion preventive layer, which is the same as that for the metal support1, on a surface of the gas supply pipe2is suitable because Cr scattering can be suppressed.

In addition, the gas supply pipe2may have a sufficient strength for configuring the fuel cell single unit U and the fuel cell module M described later. Moreover, a sintered metal, a foamed metal, or the like can also be used for the gas supply pipe2, but in this case, a treatment such as surface coating may be applied in order to prevent gas permeation.

The gas supply pipe2has a partition wall2awhich is disposed inside thereof in parallel with the central axis Z, and is partitioned into a first flow path2band a second flow path2c. The first flow path2band the second flow path2chave a form in which a gas does not flow between both flow paths so that different gases can flow through the respective flow paths.

A first flow hole2dand a second flow hole2e, which penetrate the inside and the outside, are formed in the gas supply pipe2. The first flow hole2dconnects a space (serving as the reducing gas supply path L1of the present invention) between the metal support1and the current-collector plate3with projections to the first flow path2bso that a gas can flow between the both. The second flow hole2econnects a space (serving as the oxidizing gas supply path L2of the present invention) on a side opposite to the metal support1with respect to the current-collector plate3with projections to the second flow path2cso that a gas can flow between the both. The first flow hole2dand the second flow hole2eare formed at different positions in a direction along the central axis Z of the gas supply pipe2, and are formed on both sides of the current-collector plate3with projections sandwiched therebetween.

Therefore, in the present embodiment, the first flow path2bis connected to the reducing gas supply path L1formed on an upper side of the current-collector plate3with projections, and the second flow path2cis connected to the oxidizing gas supply path L2formed on a lower side of the current-collector plate3with projections.

As shown inFIG.4, in the current-collector plate3with projections, a plurality of the concave-convex structure sites3aare formed so as to project in a vertical direction from a disc surface of the current-collector plate3with projections. The concave-convex structure site3ahas a vertex having a gentle conical shape.

As shown inFIG.3, the current-collector plate3with projections is disposed so as to face the rear side1fof the metal support1, and is bonded to the metal support1via the bonding site W. For example, the current-collector plate3with projections can be directly biased against and bonded to the metal support1, but in this case, a portion where the vertex of the concave-convex structure site3aand the metal support1contact each other serves as the bonding site W. Moreover, the current-collector plate3with projections can be biased against and bonded to the metal support1with the bonding site W which is formed by applying a ceramic paste or the like having excellent conductivity to the vertex of the concave-convex structure site3a, or the current-collector plate3with projections can be biased against and bonded to the metal support1with a metal felt or the like which is sandwiched between the current-collector plate3with projections and the metal support1. Alternatively, the current-collector plate3with projections and the metal support1can be boned to each other while forming the bonding site W by brazing a part or the whole of the vertex of the concave-convex structure site3a. In addition, the current-collector plate3with projections is disposed so that the gas supply pipe2passes through an opening part3b. The current-collector plate3with projections and the gas supply pipe2are bonded to each other by welding at the periphery of the opening part3b. Furthermore, the current-collector plate3with projections may be biased against the gas supply pipe2with a seal material sandwiched therebetween.

As a material for the current-collector plate3with projections, the same material as that for the metal support1described above can be used. Moreover, forming a diffusion preventive layer, which is the same as that for the metal support1, on a surface of the current-collector plate3with projections is suitable because Cr scattering can be suppressed. The current-collector plate3with projections configured as described above can be manufactured at a low cost by press molding or the like. Furthermore, the current-collector plate3with projections is made of a material, which does not allow a gas to permeate, so that a gas cannot flow between the front side1eand the rear side1f.

With this structure, the current-collector plate3with projections as the metal separator is electrically connected to the anode layer A, which configures the fuel cell element R, via metal support1. As will be described later, in a state where the fuel cell single units U are stacked to form the fuel cell module M, the current-collector plate3with projections is also electrically connected to the cathode layer C.

The current-collector plate3with projections may have a sufficient strength for configuring the fuel cell single unit U and the fuel cell module M described later, and the current-collector plate3with projections having a thickness of, for example, about 0.1 mm to 2 mm, preferably about 0.1 mm to 1 mm, and more preferably about 0.1 mm to 0.5 mm can be used. Moreover, in addition to the metal plate, a sintered metal, a foamed metal, or the like can also be used for the current-collector plate3with projections, but in this case, a treatment such as surface coating may be applied in order to prevent gas permeation.

As described above, the current-collector plate3with projections has the concave-convex structure site3a, and the vertex of the concave-convex structure site3ais bonded to the rear side1fof the metal support1. In the structure, a disc-shaped (doughnut-shaped) space (the reducing gas supply path L1) which is axisymmetric with respect to the central axis Z is formed between the metal support1and the current-collector plate3with projections. A reducing gas is supplied to the supply path L1from the first flow path2bthrough the first flow hole2dof the gas supply pipe2. As a result, the reducing gas is supplied to the through-hole1aof the metal support1and then to the anode layer A.

Similarly, by bonding the vertex of the concave-convex structure site3aof the current-collector plate3with projections to the cathode layer C of the fuel cell single unit U positioned on the lower side, a space (the oxidizing gas supply path L2) in which a gas can be supplied to the cathode layer C through the second flow hole2eof the gas supply pipe2is formed.

Hereinbefore, the basic configuration of the fuel cell according to the present invention has been described, but hereinafter, the feature configurations of the present invention will be described mainly with reference toFIGS.5and6.

As also described above, in the present embodiment, the reducing gas supply path L1for supplying a gas containing hydrogen to the anode layer A is formed between the current-collector plate3with projections and the metal support1. Moreover, as also indicated by an arrow inFIG.5, the gas flowing through the supply path L1is directed in one direction from the side of the gas supply pipe2positioned on a center side of the disc to a radially outward side. Furthermore, hydrogen for a power generation reaction can be supplied to the anode layer A through the through-hole1a, which is provided so as to penetrate the front and rear of the metal support1.

Here, the power generation reaction in the fuel cell element R is as described above, but due to the reaction, steam H2O is released from the anode layer A to the through-hole1aand the reducing gas supply path L1. As a result, the reducing gas supply path L1of the present invention serves as a supply unit for supplying a gas containing hydrogen H2to the anode layer A, and also serves as a discharge destination of steam H2O.

Therefore, in the present invention, as shown inFIGS.5and6, the internal reforming catalyst layer D is provided on the surface (the surface on the metal support1side) of the current-collector plate3with projections on the side of the reducing gas supply path L1.

As also described above, in addition to hydrogen H2obtained by external reforming, a raw fuel gas (the gas which is not yet reformed: in the illustrated example, methane CH4) to be reformed flows through the reducing gas supply path L1, but by returning steam H2O generated in the anode layer A to the reducing gas supply path L1, the steam H2O can flow into the supply path L1to reform a fuel gas CH4. Needless to say, the generated hydrogen H2or carbon monoxide CO can be supplied to the anode layer A through the through-hole1aon a downstream side, and provided for power generation.

As a material for the internal reforming catalyst layer D, for example, a large number of ceramic-made porous granular materials holding a reforming catalyst such as nickel, ruthenium, and platinum can be formed in an air-permeable state.

In addition, when the internal reforming catalyst layer D contains Ni, a content of Ni can be in a range of 0.1% by mass to 50% by mass. Moreover, the content of Ni when the internal reforming catalyst layer D contains Ni is more preferably 1% by mass or greater and still more preferably 5% by mass or greater. This is because a higher internal reforming performance can be obtained by setting the content as described above. On the other hand, the content of Ni when the internal reforming catalyst layer D contains Ni is more preferably 45% by mass or less and still more preferably 40% by mass or less. This is because the cost of the fuel cell device can be further reduced by setting the content as described above. Moreover, it is also preferable to carry Ni on a support.

Furthermore, the internal reforming catalyst layer D is preferably formed by a low-temperature calcination method (for example, a wet method using a calcination treatment in a low-temperature range without performing a calcination treatment in a high-temperature range of higher than 1,100° C.), a spray coating method (a method such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, and a cold spraying method), a PVD method (a sputtering method, a pulsed laser deposition method, or the like), a CVD method, or the like. This is because by these processes which can be used in a low-temperature range, a favorable internal reforming catalyst layer D can be obtained while suppressing damage due to high-temperature heating of the reducing gas supply path L1(for example, the metal support1and the current-collector plate3with projections) provided with the internal reforming catalyst layer D, and the fuel cell single unit U having excellent durability can be obtained. Moreover, forming the internal reforming catalyst layer D after the diffusion suppressing layer x is formed on the surface of the metal support1or the current-collector plate3with projections is preferable because scattering of Cr from the metal support1or the current-collector plate3with projections can be suppressed.

For example, a thickness of such an internal reforming catalyst layer D is preferably 1 μm or greater, more preferably 2 μm or greater, and still more preferably 5 μm or greater. This is because by setting the thickness as described above, a contact area with a fuel gas or steam is increased and thus an internal reforming conversion rate can be increased. Moreover, for example, the thickness is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 100 μm or less. This is because by setting the thickness as described above, a used amount of an expensive material for the internal reforming catalyst can be reduced to reduce a cost.

Returning toFIG.6again, the steam reforming reaction in the internal reforming catalyst layer D will be briefly described. As shown in the same drawing, by providing the internal reforming catalyst layer D in the fuel cell single unit U, the raw fuel gas CH4supplied to the reducing gas supply path L1can be reformed as follows to generate hydrogren H2and carbon monoxide CO which serve as a fuel gas for power generation. The reforming reaction is the same also in the embodiment shown inFIG.11.
CH4+H2O→CO+3H2[Chem. 1]
CO+H2O→CO2+H2[Chem. 2]
CH4+2H2O→CO2+4H2[Chem. 3]

A temperature of the reducing gas supply path L1(the internal reforming catalyst layer D) is practically 600° C. to 900° C., which is the operating temperature of the fuel cell element R. A structure which schematically shows the functional configuration of the fuel cell single unit U, as a fuel cell, according to the first embodiment described above is a structure shown inFIG.19(a).

In the above description, the outline of the fuel cell module M in the first embodiment is described. The structure of the fuel cell module M in this embodiment will be specifically described.

As shown inFIG.5, the fuel cell module M according to the first embodiment is configured by stacking the plurality of the fuel cell single units U. That is, the fuel cell module M is configured by stacking the plurality of the fuel cell single units U with a gasket6sandwiched therebetween. The gasket6is disposed between the gas supply pipe2of one fuel cell single unit U and the gas supply pipe2of another fuel cell single unit U. Moreover, the gasket6electrically insulates the metal support1, the gas supply pipe2, and the current-collector plate3with projections of one fuel cell single unit U from the metal support1, the gas supply pipe2, and the current-collector plate3of another fuel cell single unit U. Furthermore, the gasket6airtightly maintains a connection site (a connection site of the gas supply pipe2) of the fuel cell single unit U so that a gas flowing through the first flow path2band the second flow path2cof the gas supply pipe2is not leaked or mixed. The gasket6is formed, for example, by using vermiculite, mica, alumina, or the like as a material so that the electrical insulation and the airtight maintenance are possible.

In addition, as described above, the current-collector plate3with projections electrically connects the metal support1of one fuel cell single unit U to the cathode layer C. Therefore, in the fuel cell single unit U according to the present embodiment, the fuel cell elements R of respective fuel cell single units U are electrically connected in series.

The gas flow in the fuel cell module M has already been described.

A configuration form of the reducing gas supply path L1may be the current-collector plate3with projections having a shape shown in (a) ofFIG.4, or may be as shown in (b) ofFIG.4or (c) ofFIG.4. In these configurations, a common technical element may be a configuration in which a reducing gas (specifically, a mixed gas of a gas, which is not yet reformed, and a reformed gas) containing hydrogen and an oxidizing gas (specifically, an air) which is a gas containing oxygen move to an outer diameter side and are exhausted as an exhaust gas.

In the present invention, the reducing gas supply path L1flows from the supply side of the mixed gas to the discharge side, and a gas containing hydrogen H2flows to the anode layer A through the plurality (a large number) of the through-holes1aprovided therebetween. Moreover, by returning steam H2O generated in the anode layer A to the internal reforming catalyst layer D, the steam reforming is performed to generate hydrogen and carbon monoxide which are fuel gases for power generation, the fuel gas for power generation containing hydrogen H2is supplied to the anode layer A from the through-hole1apositioned on the downstream side, and thus power generation can be performed. Therefore, such a gas path is referred to as an internal reformed fuel supply path L3, a discharge side of the generated steam H2O is referred to as a discharge unit L3a, and a supply side of hydrogen H2subjected to internal reforming is referred to as a supply unit L3b. The discharge unit L3ais also the steam supply path of the present invention. Furthermore, the discharge unit L3acan also simultaneously function as the supply unit L3b, and the supply unit L3bcan also simultaneously function as the discharge unit L3a.

Second Embodiment

Hereinafter, a fuel cell device Y, a fuel cell module M, and a fuel cell single unit U according to the second embodiment will be described with reference to the drawings.

FIG.7shows an outline of the fuel cell device Y.

The fuel cell device Y is also configured to include the fuel cell module M, and a power generation operation is performed by a reducing gas containing hydrogen and an oxidizing gas containing oxygen, which are supplied to the fuel cell module M.

As shown inFIGS.7,8(a), and8(b), the fuel cell module M is formed in a form of a substantially rectangular parallelepiped, and the fuel cell module M, an external reformer34, a vaporizer33, and the like are included in one housing10. Functions of respective machines (a boost pump30, a desulfurizer31, a reforming water tank32, the vaporizer33, and the external reformer34) included in a supply system of the reducing gas are the same as those in the first embodiment described above. However, since the external reformer34and the vaporizer33are positioned in the housing10housing the fuel cell module M, heat of the fuel cell module M is effectively utilized.

The fuel cell module M according to the second embodiment is provided with a combustion unit101for an exhaust gas containing hydrogen on an upper part thereof, residual combustion components (specifically, hydrogen, carbon monoxide, and methane) contained in the exhaust gas of the fuel cell can be combusted at the site101, and heat of the combustion can be utilized for steam reforming and vaporization.

Functions of an inverter38, a control unit39, and a heat exchanger36are the same as those in the previous embodiment.

Therefore, also in the second embodiment, the fuel cell device Y is a so-called “cogeneration system”, which is capable of generating and supplying both electric power and heat.

Incidentally, the supply of the reducing gas containing hydrogen and the supply of the oxidizing gas containing oxygen with respect to respective electrode layers (an anode layer A and a cathode layer C) included in the fuel cell single unit U or the fuel cell element R have a configuration unique to this embodiment.

The outline thereof will be described with reference toFIGS.7and11. A gas manifold102is provided on the downstream side of the external reformer34, a gas (a raw fuel gas), which is not yet reformed, and a reformed gas are distributed and supplied to the reducing gas supply path L1included in the fuel cell single unit U, and the reducing gas containing hydrogen is supplied to the anode layer A from the supply path L1.

On the other hand, in the supply of the oxygen to an oxidizing gas supply path L2, an air is sucked by a blower35into the housing10, and the sucked oxidizing gas containing oxygen is supplied to the cathode layer C through the oxidizing gas supply paths L2respectively provided in the fuel cell single unit U and a current-collector plate CP. In this embodiment, the combustion unit101is provided between the fuel cell module M and the external reformer34, but the air sucked by the blower35is also utilized for combustion of the residual fuel in the combustion unit101.

As described above, the exhaust gas generated by the predetermined cell reaction and combustion reaction is sent to the heat exchanger36, and is provided for a predetermined heat utilization. Here, a machine103aprovided at an exhaust port103of the housing10is a machine for treating an exhaust gas.

Next, the fuel cell module M will be described with reference toFIGS.8(a) and8(b).

FIG.8(a)shows a side view of the fuel cell module M, andFIG.8(b)shows a cross-sectional view (VIII-VIII cross section ofFIG.8(a)) thereof.

In this embodiment, the fuel cell module M is configured by stacking a plurality of the fuel cell single units U in a lateral direction (a right-left direction ofFIGS.8(a) and8(b)). Specifically, each of the fuel cell single units U can be installed upright on the gas manifold102described above. That is, the fuel cell module M is constructed by erecting the metal support1supporting the fuel cell element R on the gas manifold102.

In the second embodiment, the metal support1is configured to include the reducing gas supply path L1extending in a vertical direction in an erected state, and is formed in a tubular shape. On the other hand, since the current-collector plate CP having a concave-convex shape is provided so as to be electrically connected to the metal support1, and the current-collector plate CP has air permeability, an oxidizing gas (specifically, an air) sucked to a peripheral part of the fuel cell module M is allowed to reach the cathode layer C of the fuel cell element R (seeFIG.11).

As shown inFIGS.8(a) and8(b), the fuel cell module M is configured to include the plurality of the fuel cell single units U, the gas manifold102, the current-collector plate CP, a terminal member104, and a current drawing unit105.

The fuel cell single unit U is configured to include the fuel cell element R on one surface of the metal support1which is a hollow tube, and has a long flat plate shape or a flat bar shape as a whole. Moreover, one end part of the fuel cell single unit U in a longitudinal direction is fixed to a gas manifold102with an adhesive member such as a glass seal material. The metal support1is electrically insulated from the gas manifold102.

The fuel cell element R is configured in a form of a thin film or layer (in the present invention, a form including the both is referred to as a “thin layer shape”) as a whole. There is no difference in that also in this embodiment, the fuel cell element R is configured to include the anode layer A, an electrolyte layer B, and the cathode layer C. The matter in which a metal oxide layer x, an intermediate layer y, and a reaction preventing layer z described above are provided is also the same. The metal oxide layer x, the intermediate layer y, and the reaction preventing layer z are shown inFIG.11.

In the second embodiment, the plurality of the fuel cell single units U are stacked in a state where a back surface of the metal support1of one fuel cell single unit U is in contact with the current-collector plate CP of another fuel cell single unit U, and thus a predetermined electrical output can be taken out.

For the current-collector plate CP, a member having conductivity, gas permeability, and elasticity in a direction of stacking and parallel arrangement of the fuel cell single units U is used. For example, an expanded metal using a metal foil, a metal mesh, or a felt-like member is used for the current-collector plate CP. Therefore, the air supplied from the blower35can permeate or flow through the current-collector plate CP to be supplied to the cathode layer C of the fuel cell element R. In the present invention, a flow path which configures the fuel cell single unit U and passes through the current-collector plate CP and through which a gas containing oxygen flows is referred to as the oxidizing gas supply path L2(seeFIG.11).

In addition, since the current-collector plate CP has elasticity in a direction of parallel arrangement of the fuel cell single units U, the metal support1cantilevered by the gas manifold102can also be displaced in the direction of the parallel arrangement, and robustness of the fuel cell module M against disturbances such as vibration and temperature change is enhanced.

The plurality of the fuel cell single units U arranged in parallel are sandwiched between a pair of the terminal members104. The terminal member104is a member which has conductivity and is elastically deformable, and a lower end thereof is fixed to the gas manifold102. The current drawing unit105extending outward in the direction of the parallel arrangement of the fuel cell single unit U is connected to the terminal member104. The current drawing unit105is connected to the in the inverter38, and sends a current generated by the power generation of the fuel cell element R to the inverter38.

<Fuel Cell Single Unit U>

FIGS.9and10(a)-10(c) show a schematic configuration of the fuel cell single unit U according to the second embodiment.

FIG.9is a perspective view of the fuel cell single unit U, andFIGS.10(a)-10(c)shows a forming procedure of the unit U.

As also described above, the fuel cell single unit U is configured to include the metal support1having conductivity and the fuel cell element R, and the fuel cell element R is configured to have the anode layer A and the cathode layer C which are formed so as to sandwich the electrolyte layer B.

The metal support1is configured to include a rectangular flat plate member72, a U-shaped member73of which cross section orthogonal to a longitudinal direction has a U shape, and a lid part74. A long side of the flat plate member72and a long side of the U-shaped member73(sides corresponding to two U-shaped vertexes) are bonded to each other, and one end part (in the drawing, an upper end side) is closed by the lid part74. Therefore, the metal support1which has a flat plate shape or a flat bar shape as a whole and has a space inside is formed. The flat plate member72is disposed parallel to the central axis of the metal support1.

An internal space of the metal support1serves as the reducing gas supply path L1described above. The lid part74is provided with an exhaust gas discharge port77for discharging a gas flowing through the reducing gas supply path L1to the outside of the metal support1. A discharge side (an upper side) of the exhaust gas discharge port77serves as the combustion unit101described above. An end part on a side (which is a lower side, and a site connected to the gas manifold102described above) opposite to the end part where the lid part74is provided is opened, and thus serves as the inlet of the reducing gas supply path L1.

As materials for the flat plate member72, the U-shaped member73, and the lid part74, materials having excellent conductivity, heat resistance, oxidation resistance, and corrosion resistance are used. For example, ferritic stainless steel, austenitic stainless steel, a nickel-based alloy, or the like is used. That is, the metal support1is robustly configured. In particular, ferritic stainless steel is suitably used.

When the ferritic stainless steel is used as the material for the metal support1, a thermal expansion coefficient of the metal support1is close to that of yttria-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC, also referred to as CGO) used as a material in the fuel cell element R. Therefore, even when a temperature cycle of a low temperature and a high temperature is repeated, the fuel cell single unit U is less likely to be damaged. Accordingly, a fuel cell element R having excellent long-term durability can be obtained, which is preferable.

In addition, as the material for the metal support1, a material having a thermal conductivity of greater than 3 Wm−1K−1is preferably used, and a material having a thermal conductivity of greater than 10 Wm−1K−1is more preferable. For example, since stainless steel has a thermal conductivity of about 15 to 30 Wm−1K−1, the stainless steel is suitable as the material for the metal support1.

Furthermore, as the material for the metal support1, a high toughness material which does not cause brittle fracture is more desirable. A metal material has high toughness compared to a ceramic material or the like, and is suitable as the metal support1.

As is also clear fromFIGS.10(a)-10(c), the flat plate member72is provided with a plurality of through-holes78penetrating the front surface and the rear surface of the flat plate member72. A gas can flow between the inside and the outside of the metal support1through the through-hole78. On the other hand, in a region of the flat plate member72or the U-shaped member73where the through-holes78are not provided, a gas cannot flow between the inside and the outside of the metal support1.

Hereinbefore, the basic configuration of the fuel cell according to the present invention has been described, but hereinafter, the feature configurations of the present invention will be described mainly with reference toFIGS.10(a)-10(c)and11.

As also described above, in the present embodiment, the reducing gas supply path L1for supplying a gas containing hydrogen to the anode layer A is formed in the metal support1. Moreover, as also indicated by an alternate long and short dash line arrow inFIG.9, the gas in the supply path L1is directed in one direction from an axial opening side (a lower side) of the metal support1to an axial lid part side (an upper side). Hydrogen H2for a power generation reaction can be supplied to the anode layer A through the through-hole78, which is provided so as to penetrate the front and rear of the flat plate member72. Here, the power generation reaction in the fuel cell element R is as described above, but due to the reaction, steam H2O is released from the anode layer A to the through-hole78. As a result, a part of the through-hole78and the reducing gas supply path L1of the present embodiment serves as a supply unit L3bfor supplying a gas containing hydrogen H2, and also serves as a discharge unit L3aof steam H2O.

Accordingly, as shown inFIGS.10(a)-10(c)and11, the internal reforming catalyst layer D is provided on a rear surface of72bof the flat plate member72and an inner surface73bof the metal support1.

As also described above, in addition to hydrogen obtained by external reforming, a gas (which is a raw fuel gas, and in the illustrated example, methane CH4), which is not yet reformed, to be reformed flows through the reducing gas supply path L1, but by returning steam H2O generated in the anode layer A to the internal reforming catalyst layer D, steam reforming is performed, hydrogen H2is supplied to the anode layer A from the through-hole78positioned on the downstream side (in a case ofFIG.11, a rear side of the paper), and thus power generation can be performed. Therefore, the matter in which the internal reformed fuel supply path L3according to the present invention includes the discharge unit L3aof the generated steam H2O and the supply unit L3bof hydrogen H2subjected to internal reforming is the same as in the first embodiment. Furthermore, the discharge unit L3acan also simultaneously function as the supply unit L3b, and the supply unit L3bcan also simultaneously function as the discharge unit L3a. The discharge unit L3aserves as the steam supply path.

A material for the internal reforming catalyst layer D, a thickness thereof, and the like are the same as described above.

By adopting such a structure, in the metal support1, steam H2O discharged from the anode layer A is utilized to cause steam reforming, and hydrogen H2and carbon monoxide CO obtained by the reforming can be supplied to and utilized for the anode layer A as the fuel gas for power generation.

The fuel cell single unit according to the second embodiment practically has a structure shown inFIG.19(a).

Third Embodiment

Hereinafter, a fuel cell device Y, a fuel cell module M, and a fuel cell single unit U according to the third embodiment will be described with reference to the drawings.

FIG.12is a schematic diagram showing the entire configuration of the fuel cell device Y, and shows a fuel gas supply system FL, an oxidizing gas supply system AL, and an anode off-gas circulation system RL which are connected to the fuel cell module M, which is a fuel cell main body.

In the fuel cell module M, one of a plurality of the fuel cell single units U which are stacked to configure the fuel cell module M is schematically shown. As also described above, the fuel cell single unit U includes the fuel cell element R. The fuel cell single unit U, the fuel cell element R, and the like will be described in relation to the first embodiment described above. In the first embodiment, the metal support1is formed in a disc shape, whereas in the third embodiment, a metal support1is formed in a basic square shape, and in a longitudinal direction thereof, the fuel cell element R, a reducing gas supply path L1, and an oxidizing gas supply path L2are formed.

Features of the third embodiment are the following two points.

1. In a steady operation state where activation of the fuel cell is completed and power generation is performed according to an electric power load, steam circulated through the anode off-gas circulation system RL is used for reforming.

2. An internal reforming catalyst layer D and a turbulence promotion component E are provided in the reducing gas supply path L1provided in the fuel cell single unit U.

Also in this embodiment, the fuel cell device Y is configured as a so-called cogeneration system (heat and electric power supply system), and includes a heat exchanger36as an exhaust heat utilization unit which utilizes heat discharged from the fuel cell device Y, and an inverter38as an output conversion unit for outputting electric power generated in the fuel cell device Y.

A control unit39controls operations of the entire fuel cell device Y according to the electric power load required for the fuel cell device Y. Each machine to be controlled will be described in the description of the machine. Input information to the control unit39is information on activation start and activation stop of the fuel cell device Y and the electric power load required for the device Y.

The fuel cell device Y is configured to include the fuel cell module M, the fuel gas supply system FL, the oxidizing gas supply system AL, and the anode off-gas circulation system RL. The fuel gas supply system FL corresponds to the fuel supply path of the present invention.

The fuel gas supply system FL includes a raw fuel gas supply system FLa which is provided with a boost pump30and a desulfurizer31, and a steam supply system FLb which is provided with a reforming water tank32, a reforming water pump32p, and a vaporizer33.

The raw fuel gas supply system FLa and the steam supply system FLb adopt a form of being merged into the anode off-gas circulation system RL, and supply a raw fuel gas and steam to an external reformer34provided on a downstream side. The external reformer34is connected, on a downstream side, to the reducing gas supply path L1formed in the fuel cell single unit U configuring the fuel cell module M.

The boost pump30boosts a hydrocarbon-based gas, such as a city gas, which is an example of the raw fuel gas, and supplies the gas to the fuel cell device Y. In the supply form, an amount of the raw fuel gas commensurate with the electric power load required for the fuel cell device Y is supplied in accordance with an instruction from the control unit39.

The desulfurizer31removes (desulfurizes) a sulfur compound component contained in a city gas or the like.

The reforming water tank32stores reforming water (basically pure water) in order to supply steam required for steam reforming in the external reformer34. In the supply form, the raw fuel gas is supplied in an amount in accordance with an instruction from the control unit39in order to obtain the fuel gas commensurate with the electric power load required for the fuel cell device Y. However, as also will be described later, in the fuel cell device Y according to this embodiment, in the normal steady operation state, steam contained in the anode off-gas can cover the steam required for steam reforming, and thus supply of reforming water from the reforming water tank32and vaporization in the vaporizer33are fulfilled mainly at the time of activation of the fuel cell device Y.

The vaporizer33converts the reforming water supplied from the reforming water tank32into steam. The external reformer34steam-reforms a raw fuel gas desulfurized in the desulfurizer31using the steam generated in the vaporizer33to form a reformed gas which is a gas containing hydrogen. However, since the internal reforming catalyst layer D is included in the fuel cell single unit U according to the present invention, reforming of the raw fuel gas is performed also in the unit U. As a result, in the external reformer34, a part of the raw fuel gas is reformed, and the remainder is supplied, as it is, to the reducing gas supply path L1of the fuel cell single unit U.

A steam reforming catalyst is stored in the external reformer34, but examples of this type of catalyst include a ruthenium-based catalyst and a nickel-based catalyst. Moreover, specifically, a Ru/Al2O3catalyst obtained by carrying a ruthenium component on an alumina support, a Ni/Al2O3catalyst obtained by carrying a nickel component on an alumina support, or the like can be used.

Incidentally, an operation in the steady operation state where the fuel cell device Y continuously generates power according to the electric power load will be described below.

Since the fuel cell is of an oxide ion conduction type, steam is contained in an exhaust gas (an anode off-gas) discharged from the reducing gas supply path L1provided in the fuel cell single unit U. Therefore, an operation form in which excessive moisture is condensed and removed while cooling the gas, and the anode off-gas whose steam partial pressure is adjusted is returned to the external reformer34and provided for steam reforming is adopted.

That is, the fuel cell device Y includes the anode off-gas circulation system RL, and the anode off-gas circulation system RL includes a cooler32afor cooling the anode off-gas flowing inside, a condenser32bfor further cooling the gas and extracting the condensed water to adjust a steam partial pressure of the anode off-gas flowing inside, and a heater32cfor raising a temperature of the anode off-gas returned to the external reformer34.

By adopting this structure, a circulation pump32dis caused to work, and the amount of the steam input to the external reformer34may depend on the gas circulated through the anode off-gas circulation system RL. By adjusting a condensation temperature in the condenser32bat a final stage, the partial pressure of the steam circulated through the anode off-gas circulation system RL can be adjusted, and a steam/carbon ratio (a S/C ratio) of the gas input to the external reformer34can be controlled.

In the circulation form, an amount of steam required when at least a part of the raw fuel gas is reformed in the external reformer34in accordance with the electric power load required for the fuel cell device Y is set so that an appropriate S/C ratio is obtained in the external reformer34, and the operation is performed in accordance with an instruction from the control unit39.

Objects to be controlled here are a circulation amount by the circulation pump32d, pressure setting, and setting and controlling of a condensation temperature (as a result, a steam partial pressure at an outlet) in the condenser32bwhich is a final stage of cooling.

The oxidizing gas supply system AL is provided with a blower35, and, on a downstream side, connected to the oxidizing gas supply path L2formed in the fuel cell single unit U configuring the fuel cell module M. An air suction amount by the blower35also ensures an air amount sufficient to cause a power generation reaction in the fuel cell in accordance with the electric power load, and the operation is performed in accordance with an instruction from the control unit39.

The above description is a contrivance mainly of the supply side of the reducing gas in the third embodiment, but as in the present invention, in a configuration in which the internal reforming catalyst layer D is included in the fuel cell single unit U and hydrogen or carbon monoxide obtained by internal reforming is used as a cell fuel, steam generated by power generation is consumed by steam reforming, and thus a load on the condenser32bto be provided for condensing steam contained in the anode off-gas described above is reduced. As a result, the fuel cell device Y according to the present invention is also advantageous in this respect.

Contrivance of Position where Internal Reforming Catalyst Layer is Provided

As shown inFIGS.13and14, the fuel cell single unit U according to the third embodiment is formed in a substantially square box shape when viewed from above, and flow directions of the reducing gas and the oxidizing gas are set to a specific one direction. InFIGS.13and14, the direction is upward to the right in the drawings.

Incidentally, the position where the internal reforming catalyst layer D is provided is as described above, but in this embodiment, as shown inFIG.14, the position of the internal reforming catalyst layer D is limited to a position which is the same as that of a through-hole1aon the most upstream side in the flow direction of the reducing gas, among through-holes1aprovided to supply the reducing gas to an anode layer A and discharge steam generated in the anode layer A to the reducing gas supply path L1, and a position on a downstream side of the position.

By providing the internal reforming catalyst layer D at such a position, the steam generated in the anode layer A can be effectively used according to the object of the present invention.

The fuel cell single unit U according to the third embodiment practically has a structure shown inFIG.19(b).

Contrivance to Provide Turbulence Promotion Component

As shown inFIGS.12,13, and14, the reducing gas supply path L1for supplying the fuel gas to the anode layer A is provided with the turbulence promotion component E (Ea) for disturbing the flow in the path.

More specifically, a net-like body Ea is provided on a surface of the through-hole1a, which is formed so as to penetrate the metal support1, on an inflow side of the reducing gas, which is a gas containing hydrogen, and opposite to a surface on which the fuel cell element R is formed. Specifically, the net-like body Ea is formed by sticking a lath metal or a metal wire mesh on the metal support1. As a result, the gas containing hydrogen flowing through the reducing gas supply path L1is disturbed by the net-like body Ea, and induces a flow direction component toward the through-hole1aand flow flowing out from the through-hole1a, and thus the supply of the fuel gas to the anode layer A and the leading of the steam from the anode layer A can be favorably caused.

The above description relates to the structure of the fuel cell in which the internal reforming (the steam reforming in the fuel cell element R) is performed by utilizing the steam H2O generated in the anode layer A of the fuel cell element R in the fuel cell single unit U according to the present invention.

Advantages in a case where the fuel cell is operated with the internal reforming of the present invention will be described below.

FIG.15shows a comparison of the power generation efficiency of the fuel cell between a case where internal reforming is performed and a case where the internal reforming is not performed, andFIGS.16and17show partial pressures of fuel gas for power generation, which contains hydrogen and carbon monoxide, at the inlet and the outlet (specifically, the inlet and the outlet of the reducing gas supply path L1) of the fuel cell element R in both the cases.FIG.18is a graph showing a difference in the partial pressures of the fuel gas for power generation between the same inlet and the same outlet.

Regarding the description of the partial pressure of the fuel gas for power generation, a proportion (%) with respect to a total gas pressure is used.

Furthermore, the difference in the partial pressures of the fuel gas for power generation is as follows.

Proportion of partial pressure of fuel gas for power generation at inlet of reducing gas supply path: Rin
Rin=[partial pressure of fuel gas for power generation]/[total gas pressure]×100%

Proportion of partial pressure of fuel gas for power generation at outlet of reducing gas supply path: Rout
Rout=[partial pressure of fuel gas for power generation]/[total gas pressure]×100%
Difference in partial pressures of fuel gas for power generation=Rin−Rout [%]

In these drawings, a black square mark indicates a case where the internal reforming according to the present invention is performed, and a white rhombus mark corresponds to a case where the internal reforming is not performed.

In all the drawings, a horizontal axis represents a molar ratio (a S/C ratio) of steam (S) and carbon (C) introduced into the fuel cell. The S/C ratio is a S/C ratio of the gas (the mixed gas of the raw fuel gas and the steam) introduced into the external reformer34in the configurations of the fuel cell devices Y shown inFIGS.1,7, and12, and is an operating parameter which may be changed depending on operating conditions such as the electric power load of the fuel cell. The S/C ratio was changed from 1.5 to 3.0 at an interval of 0.5. The range is a range which may be normally changed in the operation of the fuel cell device Y.

In addition, conditions set for the investigation are shown.

Generated voltage of fuel cell single unit0.8VTemperature (=internal reforming temperature)700°C.of fuel cell elementTotal fuel utilization rate of fuel cell80%

The total fuel utilization rate of the fuel cell is a proportion of the fuel gas (H2+CO) for power generation consumed by the power generation reaction in the fuel cell device Y, and is expressed by the following expression.
[Number of moles of fuel gas for power generation consumed by power generation reaction]/[total of fuel gases for power generation which is supplied to fuel cell and generated by internal reforming]×100%

Equilibrium Temperature of External Reformer

case where internal reforming is performed700°C.case where internal reforming is not performed500°C.Process pressure120kPa

The process pressure is specifically a gas pressure in the external reformer34and the respective gas supply paths L1and L2.

Investigation Results

<Power Generation Efficiency or the Like>

As is also clear fromFIG.15, in a case where the internal reforming is performed, the fuel gas for power generation is increased due to fuel reforming by the steam generated inside the fuel cell, the power generation amount is increased under conditions of a constant fuel utilization rate, and thus efficiency is increased.

Since the equilibrium temperature of the external reformer34in a case where the internal reforming is performed can be suppressed as low as 500° C., even when the S/C ratio is low, thermal decomposition (caulking) of hydrocarbon is less likely to occur, and thus an advantage of enhancing reliability of a process or a system arises.

As a result, due to the design of the fuel cell device Y, lowering the temperature of the external reformer34and reducing the S/C ratio can supply steam reforming reaction heat and evaporation heat and reduce a heat transfer area of the condenser (the condenser32bwhich is included in the anode off-gas circulation system RL described in the third embodiment) for water self-sustaining (an operation form in which a fuel gas is obtained by performing steam reforming using only steam (water) generated by power generation in an operation state where power generation is performed according to the electric power load), which is also advantageous in terms of a cost. In this investigation, when the S/C ratio in a case where the internal reforming is not performed is set to 2.5, and the S/C ratio in a case where the internal reforming is performed is set to 2.0, due to the design of the fuel cell device Y, a quantity of heat required for the external reformer34is reduced by 60%, a quantity of heat transfer of the vaporizer33required for steam generation is reduced by 20%, and direct-current power generation efficiency is improved by 3.6%.

<Partial Pressure of Fuel Gas for Power Generation>

As is also clear fromFIG.16, there is a difference of 1.5 to 2 times in the partial pressures of the fuel gas for power generation at the inlet of the fuel cell element R depending on the presence or absence of the internal reforming, and a value in a case where the internal reforming is performed is a lower value. In a case where the internal reforming is not performed, the higher the S/C ratio, the lower the partial pressure. This is because an influence of an increase in the steam is greater than an influence of an increase in the generation amount of the hydrogen or the carbon monoxide.

In a case where the internal reforming is performed, even when the S/C ratio is changed, the partial pressure of the fuel gas for power generation is hardly changed. Since the temperature of the external reformer34is low, an increase in the fuel and an increase in the steam due to the high S/C ratio are almost balanced.

In addition, in a case where the internal reforming is performed, the partial pressure of the fuel gas for power generation at the inlet of the fuel cell can be reduced by lowering the temperature (500° C.) of the external reformer34, but the steam reforming reaction rapidly occurs due to the generated steam in the fuel cell (700° C.), and thus the partial pressure of the fuel gas for power generation at the outlet of the fuel cell is increased. The increase in the partial pressure at the outlet of the cell is advantageous for stabilizing off-gas combustion.

Furthermore, in a case where the internal reforming is performed, by reducing the difference (concentration difference) in the partial pressures of the fuel gas for power generation between the outlet and the inlet of the fuel cell, uneven distribution of power generation amounts in the fuel cell element R is reduced, a temperature difference is also reduced, and thus durability or reliability is improved by relaxing thermal stress of the fuel cell.

<Operation of Fuel Cell Device Y>

According to the investigation conducted by the inventors, the fuel cell device described above is preferably operated under the following conditions.

(1) The steam/carbon ratio (the S/C ratio) at the inlet of the external reformer34is controlled to be within a range of 1.5 to 3.0. The S/C ratio is more preferably controlled to be within a range of 1.5 to 2.5. In particular, when the external reformer34is operated at a relatively low S/C ratio (1.5 to 2.5) as described above, by setting the concentration of the sulfur contained in the raw fuel gas to 1 vol. ppb or less (more preferably, 0.1 vol. ppb or less), a stable operation can be ensured for a long period of time.

(2) The reforming temperature in the external reformer34is controlled to be lower than the temperature in the internal reforming catalyst layer D provided in the reducing gas supply path L1.

(3) The operation is performed so that the partial pressure of the fuel gas for power generation at the inlet of the reducing gas supply path L1is 50% or less of a total gas pressure.

That is, under the same electric power load, the partial pressure of the fuel gas for power generation at the inlet of the reducing gas supply path L1is controlled to be lower than the partial pressure of the fuel gas for power generation at the inlet of the reducing gas supply path L1, which is set when the reforming of the fuel gas is mainly performed in the external reformer34(for example, at the time of starting the fuel cell device Y).

(4) The operation is performed so that the difference between the proportions (the proportion of the partial pressure of the fuel gas for power generation with respect to the total gas pressure, which is expressed in a percentage) of the partial pressures of the fuel gas for power generation at the inlet and the outlet of the reducing gas supply path L1is maintained within 40%.

(5) The reforming conversion rate of the fuel gas reformed by the external reformer34is set to 30% to 60%.

(6) Under the same electric power load, the steam/carbon ratio (the S/C ratio) at the inlet of the external reformer34is controlled to be lower than the steam/carbon ratio (the S/C ratio) set when the reforming of the fuel gas is mainly performed in the external reformer34(for example, at the time of starting the fuel cell device Y).

Other Embodiments

(1) In the first embodiment, the anode layer A is disposed between the metal support1and the electrolyte layer B, and the cathode layer C is disposed on a side opposite to the metal support1when viewed from the electrolyte layer B. A configuration in which the anode layer A and the cathode layer C are disposed in reverse can also be adopted. That is, a configuration in which the cathode layer C is disposed between the metal support1and the electrolyte layer B, and the anode layer A is disposed on a side opposite to the metal support1when viewed from the electrolyte layer B can also be adopted. In this case, by reversing the positional relationship between the reducing gas supply path L1and the oxidizing gas supply path L2, and, as also described above, providing the internal reforming catalyst layer D on the side (in this case, the lower side of the metal separator7) of the reducing gas supply path L1, the object of the present invention can be achieved.

(2) In each of the above-described embodiments, one fuel cell element R is formed on the metal support1, but a plurality of the fuel cell elements R may be divided and arranged on the front side of the metal support1.

(3) In the embodiments described above, regarding the formation site of the internal reforming catalyst layer D, a case where the internal reforming catalyst layer D is formed on the rear side1fof the metal support1and the inner surface of the metal separator3or7on the side of the reducing gas supply path L1has been described, but when the internal reforming catalyst layer D is formed at a site where the steam generated in the anode layer A flows, the internal reforming catalyst layer D serves for the internal reforming, and thus may be provided on the inner surface of the through-hole1aprovided in the metal support1.

(4) Regarding the reforming in the external reformer34, the external reformer34performs the steam reforming, but in the present invention, the load on the external reformer34can be reduced, and thus a reformer which performs reforming other than the steam reforming, for example, partial combustion reforming or autothermal reforming can also be adopted.

The raw fuel gas used in the present invention is a so-called hydrocarbon-based fuel, which may be any fuel as long as at least hydrogen can be generated by reforming the raw fuel gas.

(6) In the above embodiments, the turbulence promotion component E is formed with the net-like body Ea and is stuck on the surface of the metal support1, but the turbulence promotion component E may have a function of directing the flow in the reducing gas supply path L1in the direction of the through-hole1a, and a large number of obstacle bodies Eb which disturb the flow of the reducing gas supply path L1may be arranged. The obstacle body Eb may have any shape such as a spherical shape, a triangular pyramid shape, and a columnar shape.FIG.20shows an example in which the obstacle body Eb has a spherical shape.

(7) In the above embodiment, the internal reforming catalyst layer D and the turbulence promotion component E are described as being independent from each other, but for example, the internal reforming catalyst layer D may be provided on at least a part of the surface of the net-like body Ea described above or at least a part of the obstacle body Eb. This example is shown inFIG.21.

That is, by providing the internal reforming catalyst layer D on at least a part (in the illustrated example, a surface) of the turbulence promotion component E, the turbulence promotion component E can be disposed to exhibit both functions of turbulent flow promotion and internal reforming.

(8) In the first embodiment and the second embodiment, the example in which the internal reforming catalyst layer D is provided in the reducing gas supply path L1has been shown. Also in these embodiments, the turbulence promotion component E may be provided in the reducing gas supply path L1.FIG.22shows a configuration example in a case of the second embodiment of the present invention. In this example, the mesh as the net-like body Ea (E) serving as the turbulence promotion component is disposed inside the fuel gas supply path as the reducing gas supply path L1formed in the tube, and the internal reforming catalyst layer D is also formed on the outer surface thereof.

(9) In the above embodiments, the example in which the hydrocarbon-based gas such as a city gas (a gas which contains methane as a main component, and also contains ethane, propane, butane, and the like) is used as the raw fuel gas has been shown, but as the raw fuel gas, hydrocarbons such as a natural gas, naphtha, and kerosene, alcohols such as methanol and ethanol, and ethers such as DME can be used.

(10) In the above embodiments, the case where the intermediate layer y is disposed between the anode layer A and the electrolyte layer B, and the reaction preventing layer z is disposed between the electrolyte layer B and the cathode layer C has been described, but a configuration in which interposed layers such as the intermediate layer y and the reaction preventing layer z, which are interposed between the electrode layer and the electrolyte layer, is not provided may be adopted, or only one of the interposed layers may be provided. Moreover, the number of the interposed layers can also be increased, as needed.

(11) In the above embodiments, the case where the metal oxide layer x as a diffusion suppressing layer is provided on the surface of the metal support1has been described, but as needed, a configuration in which the metal oxide layer x is not provided may be adopted, or a plurality of the metal oxide layers x may be provided. Moreover, a diffusion suppressing layer different from the metal oxide layer can also be provided.

Furthermore, the configurations disclosed in the above-described embodiments can be applied in combination with the configuration disclosed in another embodiment unless inconsistency occurs, and since the embodiments disclosed in the present specification are examples, the embodiments of the present invention are not limited thereto and can be appropriately modified within a range not departing from the object of the present invention.