Fuel cell module

A fuel cell module includes a fuel cell stack, a partial oxidation reformer, and a heat exchanger. The heat exchanger is provided on one side of the fuel cell stack, and the partial oxidation reformer and the exhaust gas combustor are provided on the other side of the fuel cell stack. The partial oxidation reformer is provided around the exhaust gas combustor. The fuel cell module includes a first thermoelectric converter and a second thermoelectric converter for performing thermoelectric conversion based on a temperature difference between the combustion gas and the oxygen-containing gas.

TECHNICAL FIELD

The present invention relates to a fuel cell module including a fuel cell stack for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas.

BACKGROUND ART

Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte of ion-conductive oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.

As the fuel gas supplied to the fuel cell, normally, a hydrogen gas produced from hydrocarbon raw material by a reformer is used. In general, in the reformer, a hydrocarbon raw fuel of a fossil fuel or the like, such as methane or LNG undergoes partial oxidation reforming or steam reforming to produce a reformed gas (fuel gas).

In this case, since the partial oxidation reformer induces exothermic reaction, reaction can be started at relatively low temperature and operation can be started efficiently, and the follow up performance is good. In contrast, the steam reformer has good reforming efficiency.

For example, a fuel cell system disclosed in Japanese Laid-Open Patent Publication No. 2010-218888 (hereinafter referred to as the conventional technique 1) is known. In the fuel cell system, as shown inFIG. 9, a fuel processing system1ais provided. The fuel processing system1ahas a reformer2aand a burner combustor3a.

In the fuel cell system, an air supply apparatus5ais controlled based on an indicator value of a flow rate meter4a. When the air is not supplied by the air supply apparatus5a, the indicator value of the flow rate meter4ais corrected to a value indicating that the flow rate is zero. According to the disclosure, in the structure, since the indicator value of the flow rate meter4aindicates the flow rate of the actual supplied air, the flow rate of the air supplied by the air supply apparatus5acan be regulated with a high degree of accuracy.

Further, in a partial oxidation reformer disclosed in Japanese Laid-Open Patent Re-publication No. WO 01/047800 (PCT) (hereinafter referred to as the conventional technique 2), as shown inFIG. 10, a reformer1bhas dual wall structure including a housing2b, and partition walls3bprovided in the housing2b. A reforming reaction unit4bis provided between the partition walls3b, and a space between the housing2band the partition walls3bis used as a raw material gas passage5baround the reforming reaction unit4b.

Heat insulation of the reforming reaction unit4bis performed by the raw material gas passage5bto reduce non-uniformity in the temperature inside the reforming reaction unit4b. The raw material gas in the raw material gas passage5bis heated beforehand by the reaction heat in the reforming reaction unit4b. Thus, the heat efficiency in the reformer1bis improved by self-heat collection, and a preheater for heating the raw material gas beforehand is formed integrally between the raw material gas passage5band the reforming reaction unit4b.

According to the disclosure, in the structure, in the reforming reaction unit4b, in the case where a hydrogen rich reforming gas is produced by reaction including partial oxidation from the raw material gas, non-uniformity in the temperature inside the reforming reaction unit4bis reduced, improvement in the heat efficiency is achieved, and the reformer has simple and compact structure.

SUMMARY OF INVENTION

However, in the conventional technique 1, the flow rate of the fluid is corrected, and correction based on the temperature is not considered. Thus, if the volume varies depending on the temperature range, the supplied fluid may exceed the fluid control range undesirably. Further, in the conventional technique 1, since a solid polymer electrolyte fuel cell stack is used, it is required to cool the reformed gas discharged from the reformer2a. Therefore, a large loss in heat energy occurs, and the heat energy cannot be utilized efficiently.

Further, in the conventional technique 2, since heat exchange occurs between the raw material gas and the reformed gas, the temperature of the reforming gas is decreased. Further, since the reformer for solid polymer electrolyte fuel cells is adopted, at the time of passing the reformed gas to a CO remover, it is required to decrease the temperature of the reformed gas, and the heat energy cannot be utilized efficiently.

The present invention has been made to solve the problems of this type, and an object of the present invention is to provide a fuel cell module which makes it possible to suppress the loss of heat energy, facilitate thermally self-sustaining operation, achieve reduction in cost and size, and improve the power generation efficiency.

The present invention relates to a fuel cell module including a fuel cell stack for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas, a partial oxidation reformer for reforming a mixed gas of an oxygen-containing gas and a raw fuel chiefly containing hydrocarbon to produce the fuel gas, and supplying the fuel gas to the fuel cell stack, an exhaust gas combustor for combusting the fuel gas discharged from the fuel cell stack as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack as an oxygen-containing exhaust gas to produce a combustion gas, and a heat exchanger for raising a temperature of the oxygen-containing gas by heat exchange with the combustion gas, and supplying the oxygen-containing gas to the fuel cell stack.

In the fuel cell module, the heat exchanger is provided on one side of the fuel cell stack, and the partial oxidation reformer and the exhaust gas combustor are provided on the other side of the fuel cell stack. The partial oxidation reformer is provided around the exhaust gas combustor. The fuel cell module includes a thermoelectric converter for performing thermoelectric conversion based on a temperature difference between the combustion gas and the oxygen-containing gas.

In the present invention, the heat exchanger is provided on one side of the fuel cell stack, and the partial oxidation reformer and the exhaust gas combustor are provided on the other side of the fuel cell stack. Thus, heat radiation from the fuel cell stack is minimized, and variation in the temperature distribution in the fuel cell stack is reduced. Accordingly, the heat energy losses can be suppressed, and thermally self-sustaining operation is facilitated easily.

Thermally self-sustaining operation herein means operation where the entire heat quantity required for operation of the fuel cell system is supplied within the fuel cell system, and where the operating temperature of the fuel cell system is maintained using only heat energy generated in the fuel cell system, without supplying additional heat from the outside.

Further, the partial oxidation reformer is provided around the exhaust gas combustor. In the structure, in the state where the self-ignition temperature is maintained, the fuel exhaust gas and the oxygen-containing exhaust gas discharged from the fuel cell stack can be supplied into the exhaust gas combustor. Accordingly, in the exhaust gas combustor, stability in combustion is improved suitably, and thermally self-sustaining operation is facilitated easily.

Moreover, as a reformer, only the partial oxidation reformer is provided without requiring any steam reformer. Thus, since the water supply system for supplying water vapor is not provided, reduction in the number of parts is achieved, and reduction in the cost and size of the entire fuel cell module is achieved.

Further, the fuel cell module includes the thermoelectric converter for performing thermoelectric conversion based on the temperature difference between the combustion gas and the oxygen-containing gas. Thus, the temperature difference between the combustion gas and the oxygen-containing gas, i.e., the heat energy can be collected as electrical energy. In particular, it becomes possible to improve the power generation efficiency without any losses in the start-up time. Further, since the temperature of the combustion gas is decreased, generation of waste heat is suppressed. Moreover, since the temperature of the oxygen-containing gas is increased, thermally self-sustaining operation is facilitated.

The combustion gas herein is a gas generated by the exhaust gas combustor. The combustion gas is a heating medium which can provide heat by performing heat exchange with a fluid to be heated (e.g., another gas). After heat energy is released from the combustion gas, the combustion gas is referred to as the exhaust gas.

DESCRIPTION OF EMBODIMENTS

A fuel cell system10shown inFIG. 1includes a fuel cell module12according to a first embodiment of the present invention, and the fuel cell system10is used in various applications, including stationary and mobile applications. For example, the fuel cell system10is mounted on a vehicle.

The fuel cell system10includes the fuel cell module (SOFC module)12for generating electrical energy in power generation by electrochemical reactions of a fuel gas (a gas produced by mixing a hydrogen gas, methane, and carbon monoxide) and an oxygen-containing gas (air), a raw fuel supply apparatus (including a fuel gas pump)14for supplying a raw fuel (e.g., city gas) chiefly containing hydrocarbon to the fuel cell module12, an oxygen-containing gas supply apparatus (including an air pump)16for supplying the oxygen-containing gas to the fuel cell module12, and a control device18for controlling the amount of electrical energy generated in the fuel cell module12.

The fuel cell module12includes a fuel cell stack22formed by stacking a plurality of solid oxide fuel cells20in a vertical direction indicated by an arrow A. For example, the fuel cell20includes an electrolyte electrode assembly30(MEA). The electrolyte electrode assembly30includes a cathode26, an anode28, and an electrolyte24interposed between the cathode26and the anode28. For example, the electrolyte24is made of ion-conductive solid oxide such as stabilized zirconia.

A cathode side separator32and an anode side separator34are provided on both sides of the electrolyte electrode assembly30. An oxygen-containing gas flow field36for supplying an oxygen-containing gas to the cathode26is formed in the cathode side separator32, and a fuel gas flow field38for supplying a fuel gas to the anode28is formed in the anode side separator34. As the fuel cell20, various types of conventional SOFC can be adopted.

An oxygen-containing gas supply passage40a, an oxygen-containing gas discharge passage40b, a fuel gas supply passage42a, and a fuel gas discharge passage42bextend through the fuel cell stack22. The oxygen-containing gas supply passage40ais connected to an inlet of each oxygen-containing gas flow field36, the oxygen-containing gas discharge passage40bis connected to an outlet of each oxygen-containing gas flow field36, the fuel gas supply passage42ais connected to an inlet of each fuel gas flow field38, and the fuel gas discharge passage42bis connected to an outlet of each fuel gas flow field38.

The fuel cell module12includes a partial oxidation reformer (POX)44for reforming a mixed gas of a raw fuel chiefly containing hydrocarbon and the oxygen-containing gas, an exhaust gas combustor46for combusting the fuel gas discharged from the fuel cell stack22as a fuel exhaust gas, and combusting the oxygen-containing gas discharged from the fuel cell stack22as an oxygen-containing exhaust gas to produce a combustion gas, and a heat exchanger48for raising the temperature of the oxygen-containing gas by heat exchange with the combustion gas, and supplying the oxygen-containing gas to the fuel cell stack22.

Basically, the fuel cell module12is made up of the fuel cell stack22and FC (fuel cell) peripheral equipment50. The FC peripheral equipment50includes the partial oxidation reformer44, the exhaust gas combustor46, and the heat exchanger48. The partial oxidation reformer44is provided around the exhaust gas combustor46. The exhaust gas combustor46has a columnar (or square pillar) outer shape. The partial oxidation reformer44has a ring shape (or square pillar shape) containing the exhaust gas combustor46.

The raw fuel supply apparatus14has a raw fuel channel51for supplying the raw fuel to the partial oxidation reformer44. The oxygen-containing gas supply apparatus16has an oxygen-containing gas channel53for supplying the oxygen-containing gas from the heat exchanger48to the fuel cell stack22.

The heat exchanger48is provided on one side of the fuel cell stack22, more preferably, on one side (upper side) of the fuel cells20in the stacking direction indicated by the arrow A, and the partial oxidation reformer44and the exhaust gas combustor46are provided on the other side of the fuel cell stack22, more preferably, on the other side (lower side) of the fuel cells20in the stacking direction indicated by the arrow A.

The direction in which the fuel cells20are stacked is the same as the direction of gravity. Stated otherwise, the heat exchanger48is provided above the fuel cell stack22in the direction of gravity, and the partial oxidation reformer44and the exhaust gas combustor46are provided below the fuel cell stack22in the direction of gravity.

The partial oxidation reformer44is a preliminary reformer for reforming higher hydrocarbon (C2+) such as ethane (C2H6), propane (C3H8), and butane (C4H10) in the city gas (raw fuel) to produce the fuel gas chiefly containing hydrogen and CO by partial oxidation reforming. The operating temperature of the partial oxidation reformer44is several hundred ° C.

The operating temperature of the fuel cell20is high, at several hundred ° C. Methane in the fuel gas is reformed at the anode28to obtain hydrogen and CO, and the hydrogen and CO are supplied to the portion of the electrolyte24adjacent to the anode28.

Partial oxidation catalyst (not shown) fills the inside of the partial oxidation reformer44. An ignition device (not shown) such as an igniter or a glow for ignition at the time of starting operation is provided at the partial oxidation reformer44. The partial oxidation reformer44has a mixed gas inlet port52aand a fuel gas outlet port52b. A raw fuel after desulfurization is supplied into the partial oxidation reformer44through the mixed gas inlet port52a, and the reformed gas (fuel gas) after partial oxidation reforming of the raw fuel is discharged from the partial oxidation reformer44through the fuel gas outlet port52b.

A combustion chamber54is provided in the exhaust gas combustor46. An oxygen-containing exhaust gas inlet port56, a fuel exhaust gas inlet port58, and exhaust gas outlet port60are connected to the combustion chamber54. At the combustion chamber54, an ignition device (not shown) such as an igniter or a glow for ignition of the mixed gas of the reduction gas (fuel gas) and the oxygen-containing gas at the time of starting operation is provided.

A heating space containing a plurality of oxygen-containing gas pipes (not shown) is formed in the heat exchanger48, and the oxygen-containing gas flowing through the oxygen-containing gas pipes is heated by the hot combustion gas supplied to the heating space. The heat exchanger48has an oxygen-containing gas supply port62aand an oxygen-containing gas discharge port62bconnected to the inlets and the outlets of the oxygen-containing gas pipes, and a combustion gas supply port64aand a combustion gas discharge port64bconnected to the heating space.

The fuel gas supply passage42aof the fuel cell stack22and the fuel gas outlet port52bof the partial oxidation reformer44are connected through a fuel gas channel66. The oxygen-containing gas discharge passage40bof the fuel cell stack22and the oxygen-containing exhaust gas inlet port56of the exhaust gas combustor46are connected through an oxygen-containing exhaust gas channel68. The fuel gas discharge passage42bof the fuel cell stack22and the fuel exhaust gas inlet port58of the exhaust gas combustor46are connected through a fuel exhaust gas channel70. The oxygen-containing gas supply passage40aof the fuel cell stack22and the oxygen-containing gas discharge port62bof the heat exchanger48are connected through an oxygen-containing gas channel72.

One end of a combustion gas channel74ais connected to the exhaust gas outlet port60of the exhaust gas combustor46, and the other end of the combustion gas channel74ais connected to the fuel cell stack22. One end of a combustion gas channel74bfor discharging the combustion gas is connected to the fuel cell stack22, and the other end of the combustion gas channel74bis connected to the combustion gas supply port64aof the heat exchanger48. One end of a combustion gas channel74cis connected to the combustion gas discharge port64bof the heat exchanger48, and the other end of the combustion gas channel74cis connected in series to a first thermoelectric converter76aand a second thermoelectric converter76b.

The first thermoelectric converter76ais placed in a first oxygen-containing gas supply channel53aof the oxygen-containing gas channel53, and the second thermoelectric converter76bis placed in a second oxygen-containing gas supply channel53bof the oxygen-containing gas channel53. The oxygen-containing gas is distributed to the first oxygen-containing gas supply channel53aand the second oxygen-containing gas supply channel53bthrough an oxygen-containing gas regulator valve78provided in the oxygen-containing gas channel53.

The raw fuel supply apparatus14includes a desulfurizer80for removing sulfur compounds in the city gas (raw fuel). The desulfurizer80is provided in a middle of the raw fuel channel51. The raw fuel channel51is connected to the mixed gas inlet port52aof the partial oxidation reformer44.

The oxygen-containing gas supply apparatus16includes the oxygen-containing gas regulator valve78for distributing the oxygen-containing gas from the oxygen-containing gas channel53to the heat exchanger48and the partial oxidation reformer44, i.e., the first oxygen-containing gas supply channel53aand the second oxygen-containing gas supply channel53b. The first oxygen-containing gas supply channel53ais connected to the oxygen-containing gas supply port62aof the heat exchanger48. The second oxygen-containing gas supply channel53bis connected to the raw fuel channel51at a position between the desulfurizer80and the partial oxidation reformer44.

As shown inFIG. 2, the first thermoelectric converter76aincludes a first channel member82as a passage of the oxygen-containing gas as a medium to be heated, a second channel member84as a passage of the combustion gas as a heating medium, and a plurality of thermoelectric conversion elements86a,86b, and86ceach having a different thermoelectric conversion temperature. The thermoelectric conversion elements86a,86b, and86care provided between the first channel member82and the second channel member84.

The first channel member82has a box shape, and includes a serpentine oxygen-containing gas channel82cextending in a serpentine pattern between an oxygen-containing gas inlet82aand an oxygen-containing gas outlet82b. The serpentine oxygen-containing gas channel82cis formed by partition plates82dprovided alternately in a zigzag pattern in the first channel member82.

The second channel member84has a box shape, and includes a serpentine combustion gas channel84cextending in a serpentine pattern between a combustion gas inlet84aand a combustion gas outlet84b. The serpentine combustion gas channel84cis formed by partition plates84dprovided alternately in a zigzag pattern in the second channel member84. The combustion gas in the serpentine combustion gas channel84cand the oxygen-containing gas in the serpentine oxygen-containing gas channel82cflow in parallel to each other.

Both ends of the thermoelectric conversion elements86a,86b, and86care sandwiched between the first channel member82and the second channel member84, and the thermoelectric conversion elements86a,86b, and86care capable of generating an electromotive force by the temperature between these ends. A plurality of the thermoelectric conversion elements86a(though three thermoelectric conversion elements86aare provided inFIG. 2, the number of the thermoelectric conversion elements86acan be determined arbitrarily. Likewise, the number of the thermoelectric conversion elements86band the thermoelectric conversion elements86ccan be determined arbitrarily.) are provided on the upstream side of the serpentine oxygen-containing gas channel82cand the serpentine combustion gas channel84c. The thermoelectric conversion elements86aare hot temperature type thermoelectric conversion elements having a high thermoelectric conversion temperature.

The thermoelectric conversion elements86bprovided in the mid-portions of the serpentine oxygen-containing gas channel82cand the serpentine combustion gas channel84care intermediate temperature type thermoelectric conversion elements having an intermediate thermoelectric conversion temperature. The thermoelectric conversion elements86cprovided on the downstream side of the serpentine oxygen-containing gas channel82cand the serpentine combustion gas channel84care low temperature thermoelectric conversion elements having a low thermoelectric conversion temperature.

The second thermoelectric converter76bhas structure identical to the first thermoelectric converter76a. The constituent elements of the second thermoelectric converter76bthat are identical to those of the first thermoelectric converter76aare labeled with the same reference numeral, and description thereof will be omitted.

Next, operation of the fuel cell system10will be described below with reference to a flow chart shown inFIG. 3.

Firstly, at the time of starting operation of the fuel cell system10, the opening angle of the oxygen-containing gas regulator valve78is determined. Specifically, the raw fuel supply apparatus14is operated, and the opening angle of the oxygen-containing gas regulator valve78is adjusted such that the air (oxygen-containing gas) and the raw fuel such as the city gas (containing CH4, C2H6, C3H8, C4H10) required for partial oxidation reforming are supplied (step S1). The control of the partial oxidation reforming is performed based on the air fuel ratio (O2/C) (the number of oxygen moles in the supplied air/the number of carbon moles in the supplied raw fuel). The air and raw fuel are supplied to the partial oxidation reformer44at the optimal air-fuel ratios.

In the raw fuel supply apparatus14, sulfur is removed from the raw fuel supplied to the raw fuel channel51by the desulfurizer80, and thereafter the raw fuel is supplied to the mixed gas inlet port52aof the partial oxidation reformer44. In the oxygen-containing gas supply apparatus16, after the air is supplied to the oxygen-containing gas channel53, a predetermined amount of the air is distributed to the first oxygen-containing gas supply channel53a, and a predetermined amount of the air is distributed to the second oxygen-containing gas supply channel53b, through the oxygen-containing gas regulator valve78. The air distributed to the second oxygen-containing gas supply channel53bis mixed with the raw fuel in the raw fuel channel51, and the air is supplied to the mixed gas inlet port52aof the partial oxidation reformer44.

In the partial oxidation reformer44, ignition is performed by an ignition device (not shown). Thus, partial oxidation reforming by the partial oxidation reformer44is started. For example, if O2/C=0.5, partial oxidation reaction (2CH4+O2→4H2+2CO) occurs. The partial oxidation reaction is exothermic reaction, and a hot reduction gas (fuel gas at about 600° C.) is produced by the partial oxidation reformer44.

The hot reduction gas is supplied to the fuel gas supply passage42aof the fuel cell stack22through the fuel gas channel66. In the fuel cell stack22, after the hot reduction gas flows through the fuel gas flow field38, the hot reduction gas is discharged from the fuel gas discharge passage42binto the fuel exhaust gas channel70. The reduction gas flows into the combustion chamber54of the exhaust gas combustor46from the fuel exhaust gas inlet port58connected to the fuel exhaust gas channel70.

In the oxygen-containing gas supply apparatus16, the air supplied to the first oxygen-containing gas supply channel53aflows from the oxygen-containing gas supply port62ato the heat exchanger48. While the air is moving through the oxygen-containing gas pipes, heat exchange between the air and the combustion gas (described later) supplied into the heating space occurs, and the air is heated. The heated air is supplied to the oxygen-containing gas supply passage40aof the fuel cell stack22through the oxygen-containing gas channel72.

In the fuel cell stack22, after the heated air flows through the oxygen-containing gas flow field36, the air is discharged from the oxygen-containing gas discharge passage40binto the oxygen-containing exhaust gas channel68. The oxygen-containing exhaust gas channel68is opened to the combustion chamber54of the exhaust gas combustor46, and the air flows into the combustion chamber54. Therefore, the fuel exhaust gas and the oxygen-containing exhaust gas flow into the combustion chamber54. When the temperature in the combustion chamber54exceeds the self-ignition temperature of the fuel gas, combustion by the air and the fuel gas is started in the combustion chamber54. If the temperature in the combustion chamber54does not exceed the self-ignition temperature, ignition is performed by an ignition device (not shown) (step S2).

The combustion gas produced in the combustion chamber54flows from the exhaust gas outlet port60, and the combustion gas is supplied to the fuel cell stack22through the combustion gas channel74ato raise the temperature of the fuel cell stack22. Further, the combustion gas flows through the combustion gas channel74binto the combustion gas supply port64aof the heat exchanger48.

Thus, the combustion gas is supplied into the heating space in the heat exchanger48, and heats the oxygen-containing gas flowing through the oxygen-containing gas pipes. Then, the combustion gas flows from the combustion gas discharge port64bthrough the combustion gas channel74c, and then, the combustion gas is supplied into the first thermoelectric converter76aand the second thermoelectric converter76bsuccessively.

As shown inFIG. 2, in the first thermoelectric converter76aand the second thermoelectric converter76b, the oxygen-containing gas as the external air is supplied from the oxygen-containing gas inlet82aof the first channel member82to the serpentine oxygen-containing gas channel82c, and the combustion gas is supplied from the combustion gas inlet84aof the second channel member84into the serpentine combustion gas channel84c. Thus, temperature differences occur between both ends of the thermoelectric conversion elements86a,86b, and86cbetween the serpentine oxygen-containing gas channel82cand the serpentine combustion gas channel84c, and the heat energy is collected as electrical energy.

As described above, since the heated air, the heated fuel gas, and the combustion gas flow through the fuel cell stack22, the temperature of the fuel cell stack22is increased. In the meanwhile, the partial oxidation reformer44is heated by the exhaust gas combustor46. It is determined whether or not the partial oxidation reformer44is in a predetermined state where operation of the fuel cell stack22can be performed (step S3).

Specifically, as shown inFIG. 4, a high efficiency operation range where highly efficient reaction occurs is determined as a map based on the temperature and the air/fuel ratio of the partial oxidation reformer44. In the case where the temperature T1of the partial oxidation reformer44is in the range of 700° C.≦T1≦900° C., and the air/fuel ratio is in the range of 0.45≦O2/C≦0.55, it is determined that the reforming state of the partial oxidation reformer44is OK.

If it is determined that reforming state of the partial oxidation reformer44is OK (YES in step S3), the process proceeds to step S4. In step S4, it is determined whether or not the temperature of the fuel cell stack22(stack temperature) is T2(e.g., 650° C.) or more. If it is determined that the stack temperature is T2or more (YES in step S4), the process proceeds to step S5.

In step S5, it is determined whether or not power generation can be performed in the fuel cell stack22. Specifically, OCV (open-circuit voltage) of the fuel cell20is measured, and when the OCV reaches a predetermined value, it is determined that power generation can be performed in the fuel cell stack22(YES in step S5). Thus, power generation is started in the fuel cell stack22(step S6).

During power generation of the fuel cell stack22, in the same manner as in the case of the start-up operation, the air flows through the oxygen-containing gas flow field36, and the fuel gas flows through the fuel gas flow field38. Therefore, the air is supplied to the cathode26of each fuel cell20, and the fuel gas is supplied to the anode28of each fuel cell20to induce chemical reactions at the cathode26and the anode28for generating electricity.

The air partially consumed in the reaction (containing unconsumed air) is discharged as oxygen-containing exhaust gas to the oxygen-containing exhaust gas channel68. Further, the fuel gas partially consumed in the reaction (containing unconsumed fuel gas) is discharged as the fuel exhaust gas to the fuel exhaust gas channel70. The oxygen-containing exhaust gas and the fuel exhaust gas are supplied to the exhaust gas combustor46, and combusted in the exhaust gas combustor46. In the exhaust gas combustor46, when the temperature of the fuel gas exceeds the self-ignition temperature of the fuel gas, combustion by the air and the fuel gas is started in the combustion chamber54.

In step S3, if the reforming state of the partial oxidation reformer44is NG (NO in step S3), the process proceeds to step S7. In step S7, the temperature of the partial oxidation reformer44is regulated, and the raw fuel and the air (O2/C) supplied to the partial oxidation reformer44are regulated.

Further, in step S4, if the stack temperature is less than T2(NO in step S4), the process proceeds to step S8. In step S8, it is determined whether the temperature of the exhaust gas combustor46is a predetermine temperature T3(e.g., 900° C.) or more. If it is determined that the temperature of the exhaust gas combustor46is the predetermined temperature T3or more (YES in step S8), the process returns to step S4. If it is determined that the temperature of the exhaust gas combustor46is less than the predetermined temperature T3(NO in step S8), the process returns to step S2.

In the first embodiment, the heat exchanger48is provided on one side of the fuel cell stack22, and the partial oxidation reformer44and the exhaust gas combustor46are provided on the other side of the fuel cell stack22. Thus, heat radiation from the fuel cell stack22is minimized, and variation in the temperature distribution in the fuel cell stack22is reduced. Accordingly, the heat energy losses can be suppressed, and thermally self-sustaining operation is facilitated easily.

The thermally self-sustaining operation herein means operation where the entire heat quantity required for operation of the fuel cell system10is supplied within the fuel cell system10, and where the operating temperature of the fuel cell system10can be maintained only using the heat generated by the fuel cell system10, without supplying additional heat from the outside.

Further, the partial oxidation reformer44is provided around the exhaust gas combustor46. In the structure, in the state where the self-ignition temperature is maintained, the fuel exhaust gas and the oxygen-containing exhaust gas discharged from the fuel cell stack22can be supplied into the exhaust gas combustor46. Accordingly, in the exhaust gas combustor46, stability in combustion is improved suitably, and thermally self-sustaining operation is facilitated easily.

Moreover, as a reformer, only the partial oxidation reformer44is provided without requiring any steam reformer. Thus, since the water supply system for supplying water vapor is not provided, reduction in the number of parts can be achieved, and reduction in the cost and size of the entire fuel cell module12is achieved.

Further, in the first embodiment, the fuel cell module12includes the first thermoelectric converter76aand the second thermoelectric converter76bfor performing thermoelectric conversion based on the temperature difference between the oxygen-containing gas and the combustion gas. As shown inFIG. 2, the first thermoelectric converter76aand the second thermoelectric converter76binclude the first channel member82as a passage of the oxygen-containing gas as a medium to be heated, the second channel member84as a passage of the combustion gas as a heating medium, and the plurality of thermoelectric conversion elements86a,86b, and86ceach having a different thermoelectric conversion temperature. The thermoelectric conversion elements86a,86b, and86care provided between the first channel member82and the second channel member84.

In the structure, the first thermoelectric converter76aand the second thermoelectric converter76bcan collect electrical energy based on the temperature difference between the combustion gas and the oxygen-containing gas. That is, the heat energy can be collected as electrical energy. In particular, it becomes possible to improve the power generation efficiency without any losses in the start-up time. Further, since the temperature of the combustion gas is decreased, generation of waste heat is suppressed. Moreover, since the temperature of the oxygen-containing gas is increased, thermally self-sustaining operation is facilitated. Instead of providing the first thermoelectric converter76aand the second thermoelectric converter76b, only one of the first thermoelectric converter76aand the second thermoelectric converter76bmay be provided.

The combustion gas herein is a gas produced by the exhaust gas combustor46. The combustion gas is a heating medium which can provide heat by performing heat exchange with a fluid to be heated (e.g., another gas). After heat energy is released from the combustion gas, the combustion gas is referred to as the exhaust gas.

Further, in the fuel cell module12, the combustion gas channels74ato74cfor supplying the combustion gas discharged from the exhaust gas combustor46successively to the fuel cell stack22and the heat exchanger48, and the oxygen-containing gas channel53for supplying the oxygen-containing gas to the heat exchanger48and the partial oxidation reformer44are provided. The first thermoelectric converter76aand the second thermoelectric converter76bare provided downstream of the heat exchanger48in the combustion gas channel74c, and provided upstream of the heat exchanger48and the partial oxidation reformer44in the oxygen-containing gas channel53.

Thus, the temperature difference between the combustion gas and the oxygen-containing gas, i.e., the heat energy can be collected as electrical energy without hindering thermally self-sustaining operation, and it becomes possible to improve the power generation efficiency. Further, since the temperature of the combustion gas is decreased, generation of waste heat is suppressed. Moreover, since the temperature of the oxygen-containing gas is increased, thermally self-sustaining operation is facilitated.

Further, the oxygen-containing gas channel53is branched into the first oxygen-containing gas supply channel53afor supplying the oxygen-containing gas to the heat exchanger48and the second oxygen-containing gas supply channel53bfor supplying the oxygen-containing gas to the partial oxidation reformer44. The oxygen-containing gas regulator valve78for regulating distribution of the oxygen-containing gas is provided at the branch portion.

In the system, temperatures of the fuel cell stack22and the FC peripheral equipment (BOP)50including the heat exchanger48can be increased at the same time, and thus, reduction in the start-up time is achieved. Further, since reduction reaction can be induced on the anode side, the start-up time is reduced.

Further, at least one of the first thermoelectric converter76aand the second thermoelectric converter76bis provided in the first oxygen-containing gas supply channel53aor the second oxygen-containing gas supply channel53b, at a position downstream of the oxygen-containing gas regulator valve78. Thus, the temperature difference between the combustion gas and the oxygen-containing gas, i.e., the heat energy can be collected as electrical energy without hindering thermally self-sustaining operation, and it becomes possible to improve the power generation efficiency.

Further, since the temperature of the combustion gas is decreased, generation of waste heat is suppressed. Moreover, since the temperature of the oxygen-containing gas is increased, thermally self-sustaining operation is facilitated. Moreover, since the temperature of the oxygen-containing gas is increased on the downstream side of the oxygen-containing gas regulator valve78, durability of the oxygen-containing gas regulator valve78is not impaired. Further, as shown inFIG. 2, in the first thermoelectric converter76aand the second thermoelectric converter76b, the combustion gas flowing through the serpentine combustion gas channel84cand the oxygen-containing gas flowing through the serpentine oxygen-containing gas channel82cflow in parallel to each other, and the thermoelectric conversion elements86a,86b, and86ceach having a different thermoelectric conversion temperature are provided.

Therefore, for example, on the upstream side of the parallel flow, since the temperature difference between the combustion gas and the oxygen-containing gas is large, the hot temperature type thermoelectric conversion element86ais used. On the downstream side of the parallel flow, since the temperature difference is small, the low temperature type thermoelectric conversion element86cis used. In this manner, since the optimum thermoelectric conversion elements86a,86b, and86care used depending on the temperature difference, the efficient thermoelectric conversion can be performed reliably.

Further, in the fuel cell module12, the heat exchanger48is provided on one side of the fuel cell stack22in the stacking direction of the fuel cells20, and the partial oxidation reformer44and the exhaust gas combustor46are provided on the other side of the fuel cell stack22in the stacking direction of the fuel cells20. Thus, heat radiation from the fuel cell module12is minimized, and the heat energy losses can be suppressed. Stated otherwise, thermally self-sustaining operation is facilitated.

Further, the fuel cell module12is a solid oxide fuel cell module. Therefore, the fuel cell module12is most applicable to high temperature type fuel cells such as SOFC.

As shown inFIG. 5, a fuel cell system10aincludes a fuel cell module12aaccording to a second embodiment of the present invention. The constituent elements of the fuel cell module12aaccording to the second embodiment of the present invention that are identical to those of the fuel cell module12according to the first embodiment are labeled with the same reference numerals, and description thereof will be omitted.

The fuel cell module12aincludes a thermoelectric converter76, and the thermoelectric converter76is provided in the oxygen-containing gas channel53, at a position upstream of the oxygen-containing gas regulator valve78. The oxygen-containing gas is supplied to the thermoelectric converter76through the oxygen-containing gas channel53, and the combustion gas is supplied to the thermoelectric converter76through the combustion gas channel74c. The thermoelectric converter76has the same structure as the first thermoelectric converter76a(and the second thermoelectric converter76b) according to the first embodiment.

In the second embodiment, the same advantages as in the case of the first embodiment are obtained. For example, the temperature difference between the combustion gas and the oxygen-containing gas, i.e., the heat energy can be collected as electrical energy without hindering thermally self-sustaining operation, and it becomes possible to improve the power generation efficiency. Further, since the temperature of the combustion gas is decreased, generation of waste heat is suppressed. Moreover, since the temperature of the oxygen-containing gas is increased, thermally self-sustaining operation is facilitated.

Further, since the thermoelectric converter76is provided in the oxygen-containing gas channel53at a position upstream of the oxygen-containing gas regulator valve78, only the single thermoelectric converter76can be provided. Thus, structure is simplified economically and advantageously.

FIG. 6is an exploded perspective view showing main components of a thermoelectric converter100of a fuel cell module according to a third embodiment of the present invention.

The thermoelectric converter100may be used instead of at least any of the first thermoelectric converter76aand the second thermoelectric converter76b(thermoelectric converter76) according to the first and second embodiments of the present invention. Likewise, the thermoelectric converter as described later in fourth and fifth embodiments may be used instead of at least any of the first thermoelectric converter76aand the second thermoelectric converter76b(thermoelectric converter76) according to the first and second embodiments of the present invention.

The thermoelectric converter100includes a first channel member102as a passage of the oxygen-containing gas, a second channel member104as a passage of the combustion gas, and a plurality of thermoelectric conversion elements106provided between the first channel member102and the second channel member104. The thermoelectric conversion elements106have a predetermined thermoelectric conversion temperature.

The first channel member102includes a serpentine oxygen-containing gas channel102cextending in a serpentine pattern between an oxygen-containing gas inlet102aand an oxygen-containing gas outlet102b. The serpentine oxygen-containing gas channel102cis formed by partition plates102dprovided alternately in a zigzag pattern in the first channel member102.

The second channel member104includes a serpentine combustion gas channel104cextending in a serpentine pattern between a combustion gas inlet104aand a combustion gas outlet104b. The serpentine combustion gas channel104cis formed by partition plates104dprovided alternately in a zigzag pattern in the second channel member104. The combustion gas in the serpentine combustion gas channel104cand the oxygen-containing gas in the serpentine oxygen-containing gas channel102cflow in a counterflow manner.

In the third embodiment having the above structure, in the thermoelectric converter100, the combustion gas and the oxygen-containing gas flow in a counterflow manner. The thermoelectric converter100includes the plurality of thermoelectric conversion elements106having a predetermined thermoelectric conversion temperature. In the structure, in the thermoelectric converter100, the thermoelectric conversion elements having the optimum thermoelectric conversion temperature can be used depending on the expected temperature difference. Thus, efficient thermoelectric conversion can be performed reliably.

FIG. 7is an exploded perspective view showing main components of a thermoelectric converter110of a fuel cell module according to a fourth embodiment of the present invention.

The thermoelectric converter110includes a first channel member112as a passage of the oxygen-containing gas, a second channel member114as a passage of the combustion gas, and a plurality of thermoelectric conversion elements116provided between the first channel member112and the second channel member114. The thermoelectric conversion elements116have a predetermined thermoelectric conversion temperature.

The first channel member112includes a serpentine oxygen-containing gas channel112cextending in a serpentine pattern between an oxygen-containing gas inlet112aand an oxygen-containing gas outlet112b. The serpentine oxygen-containing gas channel112cis formed by partition plates112dprovided alternately in a zigzag pattern in the first channel member112.

The second channel member114includes a serpentine combustion gas channel114cextending in a serpentine pattern between a combustion gas inlet114aand a combustion gas outlet114b. The serpentine combustion gas channel114cis formed by partition plates114dprovided alternately in a zigzag pattern in the second channel member114. The combustion gas in the serpentine combustion gas channel114cand the oxygen-containing gas in the serpentine oxygen-containing gas channel112cflow in a manner that the combustion gas and the oxygen-containing gas intersect with each other.

In the fourth embodiment having the above structure, in the thermoelectric converter110, the combustion gas and the oxygen-containing gas flow in a manner that the combustion gas and the oxygen-containing gas intersect with each other. The thermoelectric converter110includes the plurality of thermoelectric conversion elements116having a predetermined thermoelectric conversion temperature. In the structure, in the thermoelectric converter110, the thermoelectric conversion elements116having the optimum thermoelectric conversion temperature can be used depending on the expected temperature difference. Thus, efficient thermoelectric conversion can be performed reliably.

FIG. 8is an exploded perspective view showing main components of a thermoelectric converter120of a fuel cell module according to a fifth embodiment of the present invention.

The thermoelectric converter120includes a first channel member122as a passage of the oxygen-containing gas, a second channel member124as a passage of the combustion gas, and a plurality of thermoelectric conversion elements126provided between the first channel member122and the second channel member124. The thermoelectric conversion elements126have a predetermined thermoelectric conversion temperature.

The first channel member122includes a serpentine oxygen-containing gas channel122cextending in a serpentine pattern between an oxygen-containing gas inlet122aand an oxygen-containing gas outlet122b. The serpentine oxygen-containing gas channel122cis formed by partition plates122dprovided alternately in a zigzag pattern in the first channel member122.

The second channel member124includes a serpentine combustion gas channel124cextending in a serpentine pattern between a combustion gas inlet124aand a combustion gas outlet124b. The serpentine combustion gas channel124cis formed by partition plates124dprovided alternately in a zigzag pattern in the second channel member124. The combustion gas in the serpentine combustion gas channel124cand the oxygen-containing gas in the serpentine oxygen-containing gas channel122cflow symmetrically with each other.

In the fifth embodiment having the above structure, in the thermoelectric converter120, the combustion gas and the oxygen-containing gas flow symmetrically with each other. The thermoelectric converter120includes the plurality of thermoelectric conversion elements126having a predetermined thermoelectric conversion temperature. In the structure, in the thermoelectric converter120, the thermoelectric conversion elements126having the optimum thermoelectric conversion temperature can be used depending on the expected temperature difference. Thus, efficient thermoelectric conversion can be performed reliably.

Although certain embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made to the embodiments without departing from the scope of the invention as set forth in the appended claims.