Fuel cell module

A fuel cell module includes a fuel cell stack and fuel cell peripheral equipment. The fuel cell module includes a first area where an exhaust gas combustor and a start-up combustor are provided, a second area where a reformer and an evaporator are provided, and a third area where a heat exchanger is provided. The fuel cell module further includes a condensed water recovery mechanism for recovering condensed water produced through condensation of water vapor contained in a combustion gas, by flowing the condensed water through the third area, the second area, and the first area in that order.

TECHNICAL FIELD

The present invention relates to a fuel cell module including a fuel cell stack formed by stacking a plurality of fuel cells 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 solid oxide such as stabilized zirconia. The solid electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (hereinafter also referred to as MEA). The electrolyte electrode assembly is sandwiched 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 a system including this type of fuel cell stack, for example, a fuel cell battery disclosed in Japanese Laid-Open Patent Publication No. 2001-236980 (hereinafter referred to as the conventional technique1) is known. As shown inFIG. 10, the fuel cell battery includes a fuel cell stack1a, and a heat insulating sleeve2ais provided at one end of the fuel cell stack1a. A reaction device4ais provided in the heat insulating sleeve2a. The reaction device4aincludes a heat exchanger3a.

In the reaction device4a, as a treatment of liquid fuel, partial oxidation reforming which does not use water is performed. After the liquid fuel is evaporated by an exhaust gas, the liquid fuel passes through a feeding point5awhich is part of the heat exchanger3a. The fuel contacts an oxygen carrier gas heated by the exhaust gas thereby to induce partial oxidation reforming, and then, the fuel is supplied to the fuel cell stack1a.

Further, as shown inFIG. 11, a solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2010-504607 (PCT) (hereinafter referred to as the conventional technique2) has a heat exchanger2bincluding a cell core1b. The heat exchanger2bheats the cathode air utilizing waste heat.

Further, as shown inFIG. 12, a fuel cell system disclosed in Japanese Laid-Open Patent Publication No. 2004-288434 (hereinafter referred to as the conventional technique3) includes a first area1chaving a circular cylindrical shape extending vertically, and an annular second area2caround the first area1c, an annular third area3caround the second area2c, and an annular fourth area4caround the third area3c.

A burner5cis provided in the first area1c, and a reforming pipe6cis provided in the second area2c. A water evaporator7cis provided in the third area3c, and a CO shift converter8cis provided in the fourth area4c.

SUMMARY OF INVENTION

In the conventional technique1, at the time of reforming by partial oxidation in the reaction device4a, heat of the exhaust gas is used for heating the liquid fuel and the oxygen carrier gas. Therefore, the quantity of heat for raising the temperature of the oxygen-containing gas supplied to the fuel cell stack1atends to be inefficient, and the efficiency is low.

Further, the temperature of the exhaust gas progressively decreases toward the outer side of the reaction device4a. Thus, water vapor contained in the exhaust gas is cooled, and condensed water tends to be easily generated. Therefore, the condensed water stagnates in the reaction device4a, resulting in degradation of the components.

Further, in the conventional technique2, in order to increase heat efficiency, long flow channels are adopted to have a sufficient heat transmission area. Therefore, considerably high pressure losses tend to occur. Further, the disposal of condensed water is difficult, and the condensed water tends to easily stagnate in the apparatus. Thus, the components are deteriorated by the condensed water.

Further, in the conventional technique3, radiation of the heat from the central area having the highest temperature is suppressed using heat insulation material (partition wall). Therefore, heat cannot be recovered, and the efficiency is low. Further, the disposal of condensed water is difficult, and the condensed water tends to easily stagnate in the apparatus. Thus, the components are deteriorated by the condensed water.

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 having simple and compact structure in which it is possible to achieve improvement in the heat efficiency and facilitation of thermally self-sustaining operation and also it is possible to recover condensed water reliably.

The present invention relates to a fuel cell module including a fuel cell stack formed by stacking a plurality of fuel cells for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas, a reformer for reforming a mixed gas of water vapor and a raw fuel chiefly containing hydrocarbon to produce the fuel gas supplied to the fuel cell stack, an evaporator for evaporating water, and supplying the water vapor to the reformer, a heat exchanger for raising the temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing 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 the combustion gas, and a start-up combustor for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas.

The fuel cell module includes a first area where the exhaust gas combustor and the start-up combustor are provided, an annular second area around the first area and where the reformer and the evaporator are provided, an annular third area around the second area and where the heat exchanger is provided, and a condensed water recovery mechanism for recovering condensed water produced through condensation of water vapor contained in the combustion gas, by flowing the condensed water through the third area, the second area, and the first area in that order.

In the present invention, the first area including the exhaust gas combustor and the start-up combustor is centrally-located. The annular second area is successively provided around the first area, and the annular third area is then provided around the second area. The reformer and the evaporator are provided in the second area, and the heat exchanger is provided in the third area.

In the structure, heat waste and heat radiation are suppressed suitably. Thus, improvement in the heat efficiency is achieved, and thermally self-sustaining operation is facilitated. Further, simple and compact structure is achieved in the entire fuel cell module. The thermally self-sustaining operation herein means operation where the operating temperature of the fuel cell is maintained using only heat energy generated by the fuel cell itself, without supplying additional heat from the outside.

Further, since the condensed water recovery mechanism is provided, condensed water produced through condensation of water vapor contained in the combustion gas can flow through the third area, the second area, and the first area in that order, i.e., from the low temperature side to the high temperature side. Thus, rechange of the condensed water into vapor state is facilitated, and accordingly the condensed water does not stagnate in the FC peripheral equipment. Therefore, condensed water is prevented from affecting the durability of the FC peripheral equipment as much as possible, and the recovered condensed water can be utilized as water vapor for reforming.

DESCRIPTION OF EMBODIMENTS

As shown inFIG. 1, a fuel cell system10includes 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) 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, a water supply apparatus (including a water pump)18for supplying water to the fuel cell module12, and a control device20for controlling the amount of electrical energy generated in the fuel cell module12.

The fuel cell module12includes a solid oxide fuel cell stack24formed by stacking a plurality of solid oxide fuel cells22in a vertical direction (or horizontal direction). The fuel cell22includes an electrolyte electrode assembly (MEA)32. The electrolyte electrode assembly32includes a cathode28, an anode30, and an electrolyte26interposed between the cathode28and the anode30. For example, the electrolyte26is made of ion-conductive solid oxide such as stabilized zirconia.

A cathode side separator34and an anode side separator36are provided on both sides of the electrolyte electrode assembly32. An oxygen-containing gas flow field38for supplying the oxygen-containing gas to the cathode28is formed in the cathode side separator34, and a fuel gas flow field40for supplying the fuel gas to the anode30is formed in the anode side separator36. As the fuel cell22, various types of conventional SOFCs can be adopted.

The operating temperature of the fuel cell22is high, that is, several hundred ° C. Methane in the fuel gas is reformed at the anode30to obtain hydrogen and CO, and the hydrogen and CO are supplied to a portion of the electrolyte26adjacent to the anode30.

An oxygen-containing gas supply passage42a, an oxygen-containing gas discharge passage42b, a fuel gas supply passage44a, and a fuel gas discharge passage44bextend through the fuel cell stack24. The oxygen-containing gas supply passage42ais connected to an inlet of each oxygen-containing gas flow field38, the oxygen-containing gas discharge passage42bis connected to an outlet of each oxygen-containing gas flow field38, the fuel gas supply passage44ais connected to an inlet of each fuel gas flow field40, and the fuel gas discharge passage44bis connected to an outlet of each fuel gas flow field40.

The fuel cell module12includes a reformer46for reforming a mixed gas of a raw fuel chiefly containing hydrocarbon (e.g., city gas) and water vapor to produce a fuel gas supplied to the fuel cell stack24, an evaporator48for evaporating water and supplying the water vapor to the reformer46, a heat exchanger50for raising the temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack24, an exhaust gas combustor52for combusting the fuel gas discharged from the fuel cell stack24as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack24as an oxygen-containing exhaust gas to produce the combustion gas, and a start-up combustor54for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas.

Basically, the fuel cell module12is made up of the fuel cell stack24and FC (fuel cell) peripheral equipment (BOP)56(seeFIGS. 1 and 2). The FC peripheral equipment56includes the reformer46, the evaporator48, the heat exchanger50, the exhaust gas combustor52, and the start-up combustor54.

As shown inFIGS. 3 to 5, the FC peripheral equipment56includes a first area R1where the exhaust gas combustor52and the start-up combustor54are provided, an annular second area R2formed around the first area R1and where the reformer46and the evaporator48are provided, an annular third area R3formed around the second area R2and where the heat exchanger50is provided. A cylindrical outer member55constituting an outer wall is provided on the outer peripheral side of the third area R3.

The start-up combustor54includes an air supply pipe57and a raw fuel supply pipe58. The start-up combustor54has an ejector function, and generates negative pressure in the raw fuel supply pipe58by the flow of the air supplied from the air supply pipe57for sucking the raw fuel. An end-side combustion portion of the start-up combustor54is surrounded by a tubular member59.

The exhaust gas combustor52is spaced away from the start-up combustor54, and includes a combustion cup60formed in a shape of a cylinder having a bottom. A plurality of holes (e.g., circular holes or rectangular holes)60aare formed along the outer circumference of the marginal end of the combustion cup60on the bottom side. A stack attachment plate62is engaged with the other end of the combustion cup60on the opening side. The fuel cell stack24is attached to the stack attachment plate62.

One end of an oxygen-containing exhaust gas channel63aand one end of a fuel exhaust gas channel63bare provided at the combustion cup60. The combustion gas is produced inside the combustion cup60by combustion reaction of the fuel gas (more specifically, fuel exhaust gas) and the oxygen-containing gas (more specifically, oxygen-containing exhaust gas).

As shown inFIG. 1, the other end of the oxygen-containing exhaust gas channel63ais connected to the oxygen-containing gas discharge passage42bof the fuel cell stack24, and the other end of the fuel exhaust gas channel63bis connected to the fuel gas discharge passage44bof the fuel cell stack24.

As shown inFIGS. 3 to 5, the reformer46is 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 methane (CH4), hydrogen, and CO by steam reforming. The operating temperature of the reformer46is set at several hundred ° C.

The reformer46includes a plurality of reforming pipes (heat transmission pipes)66provided around the exhaust gas combustor52and the start-up combustor54. Each of the reforming pipes66is filled with reforming catalyst pellets (not shown). Each of the reforming pipes66has one end (lower end) fixed to a first lower ring member68a, and the other end (upper end) fixed to a first upper ring member68b.

The outer circumferential portions of the first lower ring member68aand the first upper ring member68bare fixed to the inner circumferential portion of a cylindrical partition plate70by welding or the like. The inner circumferential portions of the first lower ring member68aand the first upper ring member68bare fixed to the outer circumferential portion of the combustion cup60of the exhaust gas combustor52and the outer circumferential portion of the tubular member59of the start-up combustor54by welding or the like. The partition plate70extends in an axial direction indicated by an arrow L, and an end of the partition plate70adjacent to the fuel cell stack24is fixed to the stack attachment plate62. A plurality of openings72are formed in the outer circumference of the partition plate70in a circumferential direction at predetermined height positions.

The evaporator48has evaporation pipes (heat transmission pipes)74provided adjacent to, and outside the reforming pipes66of the reformer46. As shown inFIG. 6, the reforming pipes66are arranged at equal intervals on a virtual circle, concentrically around the first area R1. The evaporation pipes74are arranged at equal intervals on a virtual circle, concentrically around the first area R1. The number of the evaporation pipes74is half of the number of the reforming pipes66. The evaporation pipes74are positioned on the back side of every other position of the reforming pipe66(i.e., at positions spaced away from the center of the first area R1).

As shown inFIGS. 3 and 4, each of the evaporation pipes74has one end (lower end) which is fixed to a second lower ring member76aby welding or the like, and the other end (upper end) which is fixed to a second upper ring member76bby welding or the like. The outer circumferential portions of the second lower ring member76aand the second upper ring member76bare fixed to the inner circumferential portion of the partition plate70by welding or the like. The inner circumferential portions of the second lower ring member76aand the second upper ring member76bare fixed to the outer circumferential portion of the combustion cup60of the exhaust gas combustor52and the outer circumferential portion of the tubular member59of the start-up combustor54by welding or the like.

The second lower ring member76ais positioned below the first lower ring member68a(i.e., outside the first lower ring member68ain the axial direction), and the second upper ring member76bis positioned above the first upper ring member68b(i.e., outside the first upper ring member68bin the axial direction).

An annular mixed gas supply chamber78ais formed between the first lower ring member68aand the second lower ring member76a, and a mixed gas of raw fuel and water vapor is supplied to the mixed gas supply chamber78a. Further, an annular fuel gas discharge chamber78bis formed between the first upper ring member68band the second upper ring member76b, and the produced fuel gas (reformed gas) is discharged to the fuel gas discharge chamber78b. Both ends of each of the reforming pipes66are opened to the mixed gas supply chamber78aand the fuel gas discharge chamber78b.

A ring shaped end ring member80is fixed to an end of the partition plate70on the start-up combustor54side by welding or the like. An annular water supply chamber82ais formed between the end ring member80and the second lower ring member76a, and water is supplied to the water supply chamber82a. An annular water vapor discharge chamber82bis formed between the second upper ring member76band the stack attachment plate62, and water vapor is discharged to the water vapor discharge chamber82b. Both ends of each of the evaporation pipes74are opened to the water supply chamber82aand the water vapor discharge chamber82b.

The fuel gas discharge chamber78band the water vapor discharge chamber82bare provided in a double deck manner, and the fuel gas discharge chamber78bis provided on the inner side with respect to the water vapor discharge chamber82b(i.e., below the water vapor discharge chamber82b). The mixed gas supply chamber78aand the water supply chamber82aare provided in a double deck manner, and the mixed gas supply chamber78ais provided on the inner side with respect to the water supply chamber82a(i.e., above the water supply chamber82a).

A raw fuel supply channel84is opened to the mixed gas supply chamber78a, and an evaporation return pipe90described later is connected to a position in the middle of the raw fuel supply channel84(seeFIG. 1). The raw fuel supply channel84has an ejector function, and generates negative pressure by the flow of the raw fuel for sucking the water vapor.

The raw fuel supply channel84is fixed to the second lower ring member76aand the end ring member80by welding or the like. One end of a fuel gas channel86is connected to the fuel gas discharge chamber78b, and the other end of the fuel gas channel86is connected to the fuel gas supply passage44aof the fuel cell stack24(seeFIG. 1). The fuel gas channel86is fixed to the second upper ring member76bby welding or the like, and extends through the stack attachment plate62(seeFIG. 2).

A water channel88is connected to the water supply chamber82a. The water channel88is fixed to the end ring member80by welding or the like. One end of the evaporation return pipe90formed by at least one evaporation pipe74is provided in the water vapor discharge chamber82b, and the other end of the evaporation return pipe90is connected to a position in the middle of the raw fuel supply channel84(seeFIG. 1).

As shown inFIG. 7, the evaporation return pipe90has dual pipe structure92in a portion thereof passing through the mixed gas supply chamber78aand the water supply chamber82a. The dual pipe structure92includes an outer pipe94. The outer pipe94surrounds the evaporation return pipe90, and the outer pipe94is positioned coaxially with the evaporation return pipe90. The outer pipe94is fixed to the first lower ring member68a, the second lower ring member76a, and the end ring member80by welding or the like, and extends in the direction indicated by an arrow L. A gap is provided between the outer circumference of the evaporation return pipe90and the inner circumference of the outer pipe94. This gap may not be provided.

The evaporation return pipe90may have dual pipe structure92ain a portion thereof passing through the fuel gas discharge chamber78b. The dual pipe structure92aincludes an outer pipe94a. The outer pipe94asurrounds the evaporation return pipe90, and the outer pipe94ais positioned coaxially with the evaporation return pipe90. The outer pipe94ais fixed to the first upper ring member68band the second upper ring member76bby welding or the like, and extends in the direction indicated by the arrow L. A gap is formed between the outer circumference of the evaporation return pipe90and the inner circumference of the outer pipe94aas necessary. The lower end of the outer pipe94ais not welded to the first upper ring member68b.

As shown inFIGS. 3 and 4, the heat exchanger50includes a plurality of heat exchange pipes (heat transmission pipes)96which are provided along and around the outer circumference of the partition plate70. Each of the heat exchange pipes96has one end (lower end) fixed to a lower ring member98a, and the other end (upper end) fixed to an upper ring member98b.

A lower end ring member100ais provided below the lower ring member98a, and an upper end ring member100bis provided above the upper ring member98b. The lower end ring member100aand the upper end ring member100bare fixed to the outer circumference of the partition plate70and the inner circumference of the outer member55by welding or the like.

An annular oxygen-containing gas supply chamber102ato which the oxygen-containing gas is supplied is formed between the lower ring member98aand the lower end ring member100a. An annular oxygen-containing gas discharge chamber102bis formed between the upper ring member98band the upper end ring member100b. The heated oxygen-containing gas is discharged to the oxygen-containing gas discharge chamber102b. Both ends of each of the heat exchange pipes96are fixed to the lower ring member98aand the upper ring member98bby welding or the like, and opened to the oxygen-containing gas supply chamber102aand the oxygen-containing gas discharge chamber102b.

The mixed gas supply chamber78aand the water supply chamber82aare placed on the radially inward side relative to the inner circumference of the oxygen-containing gas supply chamber102a. The oxygen-containing gas discharge chamber102bis provided outside the fuel gas discharge chamber78bat a position offset downward from the fuel gas discharge chamber78b.

A cylindrical cover member104is provided on the outer circumferential portion of the outer member55. The center position of the cylindrical cover member104is shifted downward. Both of upper and lower ends (both of axial ends) of the cover member104are fixed to the outer member55by welding or the like, and a heat recovery area (chamber)106is formed between the cover member104and the outer circumferential portion of the outer member55.

A plurality of holes108are formed circumferentially in a lower marginal end portion of the outer member55of the oxygen-containing gas supply chamber102a, and the oxygen-containing gas supply chamber102acommunicates with the heat recovery area106through the holes108. An oxygen-containing gas supply pipe110communicating with the heat recovery area106is connected to the cover member104. An exhaust gas pipe112communicating with the third area R3is connected to an upper portion of the outer member55.

For example, one end of each of two oxygen-containing gas pipes114is provided in the oxygen-containing gas discharge chamber102b. Each of the oxygen-containing gas pipes114has a stretchable member such as a bellows114abetween the upper end ring member100band the stack attachment plate62. The other end of each of the oxygen-containing gas pipes114extends through the stack attachment plate62, and is connected to the oxygen-containing gas supply passage42aof the fuel cell stack24(seeFIG. 1).

As shown inFIG. 3, a first combustion gas channel116aas a passage of the combustion gas is formed in the first area R1, and a second combustion gas channel116bas a passage of the combustion gas that has passed through the holes60ais formed in the second area R2. A third combustion gas channel116cas a passage of the combustion gas that has passed through the openings72is formed in the third area R3. Further, a fourth combustion gas channel116dis formed as a passage after the exhaust gas pipe112. The second combustion gas channel116bforms the reformer46and the evaporator48, and the third combustion gas channel116cforms the heat exchanger50.

As shown inFIGS. 3, 4, and 7, the FC peripheral equipment56includes a condensed water recovery mechanism117for recovering condensed water produced through condensation of water vapor contained in the combustion gas, by flowing the condensed water through the third area R3, the second area R2, and the first area R1in that order.

The condensed water recovery mechanism117includes a first inner ring surface68asof the first lower ring member68aforming the bottom portion of the second area R2, and a second inner ring surface98asof the lower ring member98aforming the bottom portion of the third area R3. As shown inFIG. 7, the height of the bottom portion formed by the second inner ring surface98asis a dimension h higher than the height of the bottom portion formed by the first inner ring surface68as.

The condensed water recovery mechanism117has condensed water passage holes117aformed in a lower portion (which is opposite to an upper portion where the fuel cell stack24is provided) of the partition plate70. As shown inFIG. 6, the condensed water recovery mechanism117has three or more condensed water passage holes117aarranged circumferentially. In the first embodiment, the three condensed water passage holes117aare arranged at equal angular intervals around the center of the FC peripheral equipment56.

Each of the condensed water passage holes117ahas an opening diameter (2 r) which is set to be 8 mm or more. As shown inFIG. 8, in order to flow the condensed water through the condensed water passage hole117a, it is necessary to satisfy an inequality P>T where P represents the total pressure generated in the opening area of the condensed water passage hole117a, and T represents a surface tension generated therein.

From the above inequality, the inequality of r×ρg×πr2>2πr×T is derived where r represents the opening radius, ρ represents the water density, g represents the acceleration of gravity, and T represents the surface tension of water. Then, the inequality of r>3.85 mm is obtained, that is 2r>7.7. Therefore, the opening diameter is set to be 8 mm or more.

In the partition plate70, the upper limit of the opening diameter should preferably be set such that the pressure loss at the condensed water passage hole117ais equal to or lower than, for example, 10% of the pressure loss at the opening72. The upper limit can be determined based on the ratio of the cross sectional area of the openings72to the cross sectional area of the condensed water passage holes117a, which is 10:1. The cross sectional areas are calculated from the number of the openings72and the opening diameter thereof, and the number of the condensed water passage holes117aand the opening diameter thereof.

As shown inFIGS. 3, 4, and 7, at a lower portion of the first area R1, a recovery pipe117bis provided adjacent to the start-up combustor54. By connecting the recovery pipe117b, for example, in the middle of the raw fuel supply channel84, it is possible to recover water vapor that is vaporized again by the exhaust gas of the first area R1and use the recovered water vapor for reforming.

As shown inFIG. 1, the raw fuel supply apparatus14includes a raw fuel channel118. The raw fuel channel118is branched into the raw fuel supply channel84and the raw fuel supply pipe58through a raw fuel regulator valve120. A desulfurizer122for removing sulfur compounds in the city gas (raw fuel) is provided in the raw fuel supply channel84.

The oxygen-containing gas supply apparatus16includes an oxygen-containing gas channel124. The oxygen-containing gas channel124is branched into the oxygen-containing gas supply pipe110and the air supply pipe57through an oxygen-containing gas regulator valve126. The water supply apparatus18is connected to the evaporator48through the water channel88.

Operation of the fuel cell system10will be described below.

At the time of starting operation of the fuel cell system10, the air (oxygen-containing gas) and the raw fuel are supplied to the start-up combustor54. More specifically, by operation of the air pump, the air is supplied to the oxygen-containing gas channel124. By adjusting the opening degree of the oxygen-containing gas regulator valve126, the air is supplied to the air supply pipe57.

In the meanwhile, in the raw fuel supply apparatus14, by operation of the fuel gas pump, for example, raw fuel such as the city gas (containing CH4, C2H6, C3H8, C4H10) is supplied to the raw fuel channel118. By regulating the opening degree of the raw fuel regulator valve120, the raw fuel is supplied into the raw fuel supply pipe58. The raw fuel is mixed with the air, and supplied into the start-up combustor54(seeFIGS. 3 and 4).

Thus, the mixed gas of the raw fuel and the air is supplied into the start-up combustor54, and the mixed gas is ignited to start combustion. Therefore, the combustion gas produced in combustion flows from the first area R1to the second area R2. Further, the combustion gas is supplied to the third area R3, and then, the combustion gas is discharged to the outside of the fuel cell module12through the exhaust gas pipe112.

As shown inFIGS. 3 and 4, the reformer46and the evaporator48are provided in the second area R2, and the heat exchanger50is provided in the third area R3. Thus, the combustion gas discharged from the first area R1first heats the reformer46, next heats the evaporator48, and then heats the heat exchanger50.

Then, after the temperature of the fuel cell module12is raised to a predetermined temperature, the air (oxygen-containing gas) is supplied to the heat exchanger50, and the mixed gas of the raw fuel and the water vapor is supplied to the reformer46.

More specifically, as shown inFIG. 1, the opening degree of the oxygen-containing gas regulator valve126is adjusted such that the flow rate of the air supplied to the oxygen-containing gas supply pipe110is increased, and the opening degree of the raw fuel regulator valve120is adjusted such that the flow rate of the raw fuel supplied to the raw fuel supply channel84is increased. Further, by operation of the water supply apparatus18, the water is supplied to the water channel88. The air is supplied from the oxygen-containing gas supply pipe110to the heat recovery area106of the outer member55. Thus, the air flows through the holes108into the oxygen-containing gas supply chamber102a.

Therefore, as shown inFIGS. 3 and 4, the air flows into the heat exchanger50, and after the air is temporarily supplied to the oxygen-containing gas supply chamber102a, while the air is moving inside the heat exchange pipes96, the air is heated by heat exchange with the combustion gas supplied into the third area R3. After the heated air is temporarily supplied to the oxygen-containing gas discharge chamber102b, the air is supplied to the oxygen-containing gas supply passage42aof the fuel cell stack24through the oxygen-containing gas pipes114(seeFIG. 1). In the fuel cell stack24, the heated air flows along the oxygen-containing gas flow field38, and the air is supplied to the cathode28.

After the air flows through the oxygen-containing gas flow field38, the air is discharged from the oxygen-containing gas discharge passage42binto the oxygen-containing exhaust gas channel63a. The oxygen-containing exhaust gas channel63ais opened to the combustion cup60of the exhaust gas combustor52, and the oxygen-containing exhaust gas is supplied into the combustion cup60.

Further, as shown inFIG. 1, the water from the water supply apparatus18is supplied to the evaporator48. After the raw fuel is desulfurized in the desulfurizer122, the raw fuel flows through the raw fuel supply channel84, and moves toward the reformer46.

In the evaporator48, after the water is temporarily supplied to the water supply chamber82a, while water is moving inside the evaporation pipes74, the water is heated by the combustion gas flowing through the second area R2, and vaporized. After the water vapor flows into the water vapor discharge chamber82b, the water vapor is supplied to the evaporation return pipe90connected to the water vapor discharge chamber82b. Thus, the water vapor flows inside the evaporation return pipe90, and flows into the raw fuel supply channel84. Then, the water vapor is mixed with the raw fuel supplied by the raw fuel supply apparatus14to produce the mixed gas.

The mixed gas from the raw fuel supply channel84is temporarily supplied to the mixed gas supply chamber78aof the reformer46. The mixed gas moves inside the reforming pipes66. In the meanwhile, the mixed gas is heated by the combustion gas flowing through the second area R2, and is then steam-reformed. After removal (reforming) of hydrocarbon of C2+, a reformed gas chiefly containing methane is obtained.

After this reformed gas is heated, the reformed gas is temporarily supplied to the fuel gas discharge chamber78bas the fuel gas. Thereafter, the fuel gas is supplied to the fuel gas supply passage44aof the fuel cell stack24through the fuel gas channel86(seeFIG. 1). In the fuel cell stack24, the heated fuel gas flows along the fuel gas flow field40, and the fuel gas is supplied to the anode30. In the meanwhile, the air is supplied to the cathode28. Thus, electricity is generated in the electrolyte electrode assembly32.

After the fuel gas flows through the fuel gas flow field40, the fuel gas is discharged from the fuel gas discharge passage44bto the fuel exhaust gas channel63b. The fuel exhaust gas channel63bis opened to the inside of the combustion cup60of the exhaust gas combustor52, and the fuel exhaust gas is supplied into the combustion cup60.

Under the heating operation by the start-up combustor54, when the temperature of the fuel gas in the exhaust gas combustor52exceeds the self-ignition temperature, combustion of the oxygen-containing exhaust gas and the fuel exhaust gas is started inside the combustion cup60. In the meanwhile, combustion operation by the start-up combustor54is stopped.

The combustion cup60has the holes60a. Therefore, as shown inFIG. 3, the combustion gas supplied into the combustion cup60flows through the holes60afrom the first area R1into the second area R2. Then, after the combustion gas is supplied to the third area R3, the combustion gas is discharged to the outside of the fuel cell module12.

In the FC peripheral equipment56, the combustion gas flows through the first area R1, the second area R2, and the third area R3in that order, and exchanges heat with each area. Thereafter, the combustion gas is discharged to the outside. At that time, water vapor contained in the combustion gas is condensed due to decrease of the temperature of the combustion gas. The condensed water tends to stagnate, in particular, easily in the third area R3where the temperature is relatively low.

As shown inFIG. 7, the condensed water stagnating in the third area R3moves to the second area R2through the condensed water passage holes117aof the condensed water recovery mechanism117, which are formed in the lower portion of the partition plate70. Then, the condensed water moves to the first area R1, and is thereafter introduced into the tubular member59of the start-up combustor54. In the first area R1, hot exhaust gas has been produced, whereby the condensed water is evaporated to produce water vapor. The produced water vapor (including the condensed water) is recovered through the recovery pipe117b.

In the first embodiment, the FC peripheral equipment56includes the first area R1where the exhaust gas combustor52and the start-up combustor54are provided, the annular second area R2around the first area R1and where the reformer46and the evaporator48are provided, and the annular third area R3around the second area R2and where the heat exchanger50is provided.

That is, the first area R1is provided at the center, the annular second area R2is provided around the first area R1, and the annular third area R3is provided around the second area R2. Heat waste and heat radiation can be suppressed suitably. Thus, improvement in the heat efficiency is achieved, thermally self-sustaining operation is facilitated, and the structure of the entire fuel cell module12can be made simple and compact. Thermally self-sustaining operation herein means operation where the operating temperature of the fuel cell22is maintained using only heat energy generated in the fuel cell22itself, without supplying additional heat from the outside.

Further, the FC peripheral equipment56includes the condensed water recovery mechanism117. Thus, the condensed water produced through condensation of water vapor contained in the combustion gas can flow through the third area R3, the second area R2, and the first area R1in that order, i.e., from the low temperature side to the high temperature side.

Thus, rechange of the condensed water into vapor state is facilitated, and as a result, the condensed water does not stagnate in the FC peripheral equipment56. Therefore, the condensed water is prevented from affecting the durability of the FC peripheral equipment56as much as possible, and the recovered condensed water can be utilized as water vapor for reforming.

Further, in the first embodiment, as shown inFIG. 3, the reformer46includes the annular mixed gas supply chamber78a, the annular fuel gas discharge chamber78b, the reforming pipes66, and the second combustion gas channel116b. The mixed gas is supplied to the mixed gas supply chamber78a, and the produced fuel gas is discharged into the fuel gas discharge chamber78b. Each of the reforming pipes66has one end connected to the mixed gas supply chamber78a, and the other end connected to the fuel gas discharge chamber78b. The second combustion gas channel116bsupplies the combustion gas to the space between the reforming pipes66.

The evaporator48includes the annular water supply chamber82a, the annular water vapor discharge chamber82b, the evaporation pipes74, and the second combustion gas channel116b. The water is supplied to the water supply chamber82a, and the water vapor is discharged into the water vapor discharge chamber82b. Each of the evaporation pipes74has one end connected to the water supply chamber82a, and the other end connected to the water vapor discharge chamber82b. The second combustion gas channel116bsupplies the combustion gas to the space between the evaporation pipes74.

The heat exchanger50includes the annular oxygen-containing gas supply chamber102a, the annular oxygen-containing gas discharge chamber102b, the heat exchange pipes96, and the third combustion gas channel116c. The oxygen-containing gas is supplied to the oxygen-containing gas supply chamber102a, and the heated oxygen-containing gas is discharged into the oxygen-containing gas discharge chamber102b. Each of the heat exchange pipes96has one end connected to the oxygen-containing gas supply chamber102a, and the other end connected to the oxygen-containing gas discharge chamber102b. The third combustion gas channel116csupplies the combustion gas to the space between the heat exchange pipes96.

As described above, the annular supply chambers (mixed gas supply chamber78a, water supply chamber82a, and oxygen-containing gas supply chamber102a), the annular discharge chambers (fuel gas discharge chamber78b, water vapor discharge chamber82b, and oxygen-containing gas discharge chamber102b) and the pipes (reforming pipes66, evaporation pipes74, and heat exchange pipes96) are provided as basic structure. Thus, simple structure is achieved easily. Accordingly, the production cost of the fuel cell module12is reduced effectively. Further, by changing the volumes of the supply chambers and the discharge chambers, and the length, the diameter, and the number of the pipes, a suitable operation can be achieved depending on various operating conditions, and the design flexibility of the fuel cell module can be enhanced.

Further, the fuel gas discharge chamber78band the water vapor discharge chamber82bare provided in a double deck manner, and the fuel gas discharge chamber78bis provided on the inner side with respect to the water vapor discharge chamber82b. The mixed gas supply chamber78aand the water supply chamber82aare provided in a double deck manner, and the mixed gas supply chamber78ais provided on the inner side with respect to the water supply chamber82a. In the structure, in the second area R2, the reformer46and the evaporator48can be arranged compactly and efficiently. As a result, reduction in the overall size of the FC peripheral equipment56is achieved easily.

Further, the mixed gas supply chamber78ais formed between the first lower ring member (inner ring)68ainto which ends of the reforming pipes66are inserted and the second lower ring member (outer ring)76aspaced away from the first lower ring member68a. The fuel gas discharge chamber78bis formed between the first upper ring member (inner ring)68binto which the other ends of the reforming pipes66are inserted and the second upper ring member (outer ring)76bspaced away from the first upper ring member68b.

Further, the water supply chamber82ais formed between the second lower ring member (inner ring)76ainto which ends of the evaporation pipes74are inserted and the end ring member (outer ring)80spaced away from the second lower ring member76a. The water vapor discharge chamber82bis formed between the second upper ring member (inner ring)76binto which the other ends of the evaporation pipes74are inserted and the stack attachment plate (outer ring)62spaced away from the second upper ring member76b.

Likewise, the oxygen-containing gas supply chamber102ais formed between the lower ring member (inner ring)98ainto which ends of the heat exchange pipes96are inserted and the lower end ring member (outer ring)100aspaced away from the lower ring member98a. The oxygen-containing gas discharge chamber102bis formed between the upper ring member (inner ring)98binto which the other ends of the heat exchange pipes96are inserted and the upper end ring member (outer ring)100bspaced away from the upper ring member98b.

In the structure, each of the mixed gas supply chamber78a, the fuel gas discharge chamber78b, the water supply chamber82a, the water vapor discharge chamber82b, the oxygen-containing gas supply chamber102a, and the oxygen-containing gas discharge chamber102bis made of the inner ring and the outer ring, and the structure of these chambers is simplified effectively. Thus, the production cost is reduced effectively, and the size reduction is achieved easily.

Further, the fuel gas discharge chamber78b, the water vapor discharge chamber82b, and the oxygen-containing gas discharge chamber102bare provided at the side of one end adjacent to the fuel cell stack24, and the mixed gas supply chamber78a, the water supply chamber82a, and the oxygen-containing gas supply chamber102aare provided at the side of the other end distant from the fuel cell stack24.

In the structure, the reactant gas immediately after heating and the reactant gas immediately after reforming (fuel gas and oxygen-containing gas) can be supplied to the fuel cell stack24promptly. Further, the exhaust gas from the fuel cell stack24can be supplied to the exhaust gas combustor52, the reformer46, the evaporator48, and the heat exchanger50of the FC peripheral equipment56while decrease in the temperature of the exhaust gas from the fuel cell stack24due to heat radiation is suppressed as much as possible. Thus, improvement in the heat efficiency is achieved, and thermally self-sustaining operation is facilitated.

Further, the condensed water recovery mechanism117includes a first inner ring surface68asof the first lower ring member68aforming the bottom portion of the second area R2, and a second inner ring surface98asof the lower ring member98aforming the bottom portion of the third area R3. As shown inFIG. 7, the height of the bottom portion formed by the second inner ring surface98asis a dimension h higher than the height of the bottom portion formed by the first inner ring surface68as.

Thus, the condensed water can flow from the outer side (low temperature side) to the inner side (high temperature side) of the FC peripheral equipment56, and rechange of the condensed water into vapor state can be facilitated. Therefore, the condensed water does not stagnate in the FC peripheral equipment56, and it is possible to prevent the condensed water from affecting the durability of the FC peripheral equipment56and to utilize the recovered condensed water as water vapor for reforming.

The FC peripheral equipment56includes a partition plate70arranged vertically between the second area R2and the third area R3. The condensed water recovery mechanism117has the condensed water passage hole117aformed in the lower portion of the partition plate70which is opposite to the upper portion where the fuel cell stack24is provided.

In the structure, blow-through of the combustion gas can be suppressed suitably thereby to further improve the heat efficiency, whereby thermally self-sustaining operation can be facilitated reliably. Further, the condensed water can move from the outer side (low temperature side) to the inner side (high temperature side) of the FC peripheral equipment56through the condensed water passage holes117aof the partition plate70. Thus, rechange of the condensed water into vapor state is facilitated, and consequently the condensed water does not stagnate in the FC peripheral equipment56. Therefore, condensed water is prevented from affecting the durability of the FC peripheral equipment56as much as possible, and the recovered condensed water can be utilized as water vapor for reforming.

Further, as shown inFIG. 6, three or more condensed water passage holes117aare arranged circumferentially. Thus, even if the FC peripheral equipment56is inclined due to an installation condition or the like of the FC peripheral equipment56, the condensed water can be recovered reliably. Therefore, it is possible to prevent the condensed water from affecting the durability of the FC peripheral equipment56as much as possible.

Still further, the opening diameter of the condensed water passage hole117ais set to be 8 mm or more. Thus, the flow of the condensed water is not blocked by the surface tension of the condensed water, and accordingly it is possible to recover the condensed water reliably. Therefore, it is possible to prevent the condensed water from affecting the durability of the FC peripheral equipment56as much as possible.

Further, the fuel cell module12is a solid oxide fuel cell module. Therefore, the fuel cell module12is suitable for, in particular, high temperature type fuel cells such as SOFC.

FIG. 9is a partial sectional side view showing structure of FC peripheral equipment142of a fuel cell module140according to a second embodiment of the present invention. The constituent elements of the fuel cell module140according 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 numeral, and description thereof will be omitted.

The FC peripheral equipment142includes a condensed water recovery mechanism144. The condensed water recovery mechanism144includes a first inner ring surface146sof a first lower ring member146forming the bottom portion of the second area R2, and a second inner ring surface148sof a lower ring member148forming the bottom portion of the third area R3.

The first lower ring member146corresponds to the first lower ring member68ain the first embodiment, and the lower ring member148corresponds to the lower ring member98ain the first embodiment. The first lower ring member146and the lower ring member148are downwardly inclined toward the center of the first area R1. That is, each of the first inner ring surface146sand the second inner ring surface148sis downwardly inclined from the outer circumferential end portion to the inner circumferential end portion. Totally, the downwardly-inclined surface is formed from the second inner ring surface148sto the first inner ring surface146s.

In the second embodiment, the condensed water in the third area R3moves toward the partition plate70along the inclination of the second inner ring surface148s, and thereafter moves to the second area R2through the condensed water passage holes117a. Further, the condensed water moves to the first area R1along the inclination of the first inner ring surface146s, and is then introduced in the tubular member59. In the structure, the condensed water can be discharged more efficiently. Further, it is possible to obtain the same advantages as in the first embodiment, for example, that heat waste and heat radiation can be suppressed suitably thereby to improve the heat efficiency, whereby thermally self-sustaining operation is facilitated.

While the invention has been particularly shown and described with reference to preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the scope of the invention as defined by the appended claims.