FUEL CELL SYSTEM

To restrain the leakage of an exhaust gas from inside of a fuel cell module to the outside of a fuel cell system. A simplified airtight housing 4 constituting a SOFC system accommodates a fuel cell module 1, an exhaust gas processing unit 2, and a heat exchanger 3. A SOFC package 7 accommodates the housing and defines and forms an auxiliary machinery compartment 8 around the housing. The housing has an intake hole 41. A blower 17a disposed in the housing draws in air from the inside of the housing and supplies the air to air electrodes of fuel battery cells in the module through a cathode air supply passage 17. The suction of the air from the inside of the housing by the blower maintains the inside of the housing at a pressure that is lower than the pressure in the area surrounding the housing (the compartment).

TECHNICAL FIELD

The present invention relates to a fuel cell system.

BACKGROUND ART

Fuel cell systems have been actively developed as power generating systems with high energy use efficiency. In particular, a solid oxide fuel cell system (hereinafter referred to as the “SOFC system”) has been attracting attention as a next-generation fixed power supply with low CO2emissions because of its high power generation efficiency.

The system is generally constituted by including fuel cells adapted to cause a hydrogen-containing fuel and air to react, thereby to generate electricity, and a casing that surrounds the fuel cells and maintains the fuel cells at a high temperature by burning therein a surplus hydrogen-containing fuel. These are the major parts of the system, and the combination of the major parts is referred to as a fuel cell module.

A hot exhaust gas is produced by combustion in the casing.

Hitherto, in a fuel cell module, to process the connection (join) with piping or wiring that penetrates the casing of the fuel cell module, a gasket (e.g., a gasket made of expanded graphite) having airtightness and resistance to high temperature has been used to secure airtightness by the fuel cell module itself. Securing the airtightness as described above makes it possible to restrain the exhaust gas from leaking from the inside of the casing to the outside when the system is operated.

Furthermore, in a step in which an outermost cover of the casing is closed after components are installed in the casing, the foregoing gasket made of expanded graphite has been used, or the cover has been welded, so as to secure the airtightness. The secured airtightness makes it possible to restrain the leakage of the exhaust gas from the inside of the casing to the outside when the system is operated.

As the techniques regarding the restraint of the leakage of an exhaust gas, the techniques described in Patent documents 1 and 2 are known.

Patent document 1 describes the use of a heat-resistant gasket made of graphite to close a cover (a metal plate).

Patent document 2 describes a fuel cell system provided with an exhaust gas suction device. The suction device draws in the exhaust gas from the inside of the casing and leads the air into a heat exchanger.

REFERENCE DOCUMENT LIST

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, if the welding process as described above is carried out to secure the airtightness of the fuel cell module, then it is required to inspect each welded place for airtightness in the fabrication of the fuel cell module. In the inspection, the number of places to be inspected increases as the number of welded places increases, possibly leading to increased time and effort required for the inspection. This may result in an increase in the manufacturing cost.

Furthermore, if the gasket made of the expanded graphite is used to secure the airtightness of the fuel cell module as described above, then, the manufacturing cost will be inevitably higher, because the gasket made of expanded graphite is relatively costly.

Furthermore, the suction device described in Patent document 2 may draw in a large amount of water vapor contained in the exhaust gas, so that the water vapor may adversely affect the mechanical life of the suction device. As a countermeasure, if, for example, an additional device for reducing water vapor were installed, then it would add to the manufacturing cost or make the fuel cell system substantially larger.

In view of the facts described above, an object of the present invention is to restrain the leakage of an exhaust gas from a fuel cell module to the outside of the system while restraining an increase in manufacturing cost and an undue increase in the size of the system.

Means for Solving the Problems

To this end, a fuel cell system according to the present invention is constituted by including: a fuel cell module that includes fuel cells that cause a hydrogen-containing fuel and air to react, thereby to generate electricity, and a casing that surrounds the fuel cells and maintains the fuel cells in a high temperature state by burning therein a surplus hydrogen-containing fuel of the fuel cells; a first housing that accommodates the fuel cell module; and a suction device that draws in air from the inside of the first housing so as to maintain the inside of the first housing in a negative pressure state.

Effects of the Invention

According to the present invention, the suction device draws in air from the inside of the first housing so as to maintain the inside of the first housing in a negative pressure state. Thus, the pressure in the first housing is maintained to be lower than the pressure in the area surrounding the first housing, so that even if a small amount of an exhaust gas were to leak from the fuel cell module into the first housing, it is possible to restrain the small amount of the exhaust gas from flowing out of the first housing. Furthermore, an air layer is formed between the outer surface of the fuel cell module and the inner surface of the first housing, so that the surface temperature of the first housing is lower than the temperature of the outer surface of the fuel cell module. Hence, in place of the foregoing gasket made of expanded graphite, a member (e.g., a rubber grommet) that is less expensive and has lower heat resistance than the gasket can be used for the connection with the piping or wiring that penetrate the first housing.

Furthermore, according to the present invention, the suction device draws in the air from the inside of the first housing. Thus, the suction device primarily draws out relatively dry air in the first housing, making it possible to obtain a relatively favorable mechanical service life.

Therefore, the present invention permits the use of a relatively inexpensive member for the aforesaid connection and enables the suction device to have a relatively favorable mechanical service life, thus making it possible to restrain the leakage of an exhaust gas from the fuel cell module to the outside of the system while controlling a manufacturing cost at the same time.

Furthermore, according to the present invention, the suction device primarily draws in relatively dry air in the first housing, obviating the need for installing an additional device to reduce water vapor as described above to extend the life of the suction device. This makes it possible to restrain an undue increase in the size of a fuel cell system.

MODE FOR CARRYING OUT THE INVENTION

FIG. 1illustrates the schematic configuration of a SOFC system in a first embodiment of the present invention.FIG. 2illustrates the schematic configuration of a fuel cell module.

The SOFC system includes a fuel cell module1constituting a major part (power generating part) thereof, an exhaust gas processing unit2, a heat exchanger3, a simplified airtight housing4, a power conditioner (hereinafter referred to as “the PCS”)5, a control unit6, and a SOFC package7. The exhaust gas processing unit2purifies the exhaust gas emitted from the fuel cell module1. The heat exchanger3collects the heat of the exhaust gas, which has been purified by the exhaust gas processing unit2, to obtain hot water. The simplified airtight housing4accommodates the fuel cell module1, the exhaust gas processing unit2, and the heat exchanger3. The simplified airtight housing4corresponds to the first housing in the present invention. The PCS5takes out the electric power generated by the fuel cell module1. The SOFC package7accommodates the simplified airtight housing4, the PCS5, and the control unit6. The SOFC package7corresponds to a second housing in the present invention. The compartment defined and formed by the inner surface of the SOFC package7and the outer surface of the simplified airtight housing4will be referred to as an auxiliary machinery compartment8. Thus, the PCS5and the control unit6are disposed in the auxiliary machinery compartment8.

The simplified airtight housing4is shaped like a box and is formed of a metal.

The simplified airtight housing4has two communication holes (an intake hole41and an exhaust hole42) formed to provide communication between the inside of the simplified airtight housing4and the outside thereof. The intake hole41corresponds to an intake portion of the simplified airtight housing4in the present invention. The intake hole41has a function to lead air outside the simplified airtight housing4into the simplified airtight housing4.

The SOFC package7is shaped like a box.

The SOFC package7has two communication holes (an intake hole71and an exhaust hole72) formed to provide communication between the inside of the SOFC package7and the outside thereof.

One end of an intake pipe43is connected in an airtight and liquid-tight manner to the intake hole41of the simplified airtight housing4. A middle portion of the intake pipe43penetrates the intake hole71of the SOFC package7. The other end of the intake pipe43juts out from the outer surface of the SOFC package7. In other words, the intake pipe43is a communication pipe that penetrates the SOFC package7to provide communication between the inside of the simplified airtight housing4and the outside of the SOFC package7. The intake pipe43also has a function for leading outside air into the simplified airtight housing4. One end of the intake pipe43may be connected to the intake hole41of the simplified airtight housing4, while the other end thereof may be connected to the intake hole71of the SOFC package7. A sealing member for the connection (join) between the simplified airtight housing4and the intake pipe43uses, for example, a rubber grommet G.

An exhaust pipe44is provided such that the exhaust pipe44penetrates the exhaust hole42of the simplified airtight housing4and the exhaust hole72of the SOFC package7.

One end of the exhaust pipe44is connected to an exhaust port31of the heat exchanger3in the simplified airtight housing4. A middle portion of the exhaust pipe44penetrates the exhaust hole42of the simplified airtight housing4in an airtight and liquid-tight manner and further passes through the exhaust hole72of the SOFC package7. The other end of the exhaust pipe44juts out of the outer surface of the SOFC package7. Hence, the inside (an exhaust gas passage) of the heat exchanger3is in communication with the outside of the SOFC package7through the exhaust pipe44. One end of the exhaust pipe44may be connected to the exhaust port31of the heat exchanger3in the simplified airtight housing4, the middle portion thereof may penetrate the exhaust hole42of the simplified airtight housing4, and the other end thereof may be connected to the exhaust hole72of the SOFC package7. For the penetrated portion (join) of the exhaust pipe44in the simplified airtight housing4, a rubber grommet G, for example, is used as the sealing member.

The SOFC package7is provided with a ventilation fan73that leads outside air into the auxiliary machinery compartment8. The SOFC package7also has a ventilation hole74formed to exhaust air from the auxiliary machinery compartment8. When the ventilation fan73is actuated to introduce outside air into the SOFC package7, the outside air cools the PCS5, auxiliary machines and the like (e.g., pumps15a,16aand the like, which will be discussed hereinafter) in the auxiliary machinery compartment8and then the outside air is exhausted to the outside through the ventilation hole74.

The simplified airtight housing4is provided with a pressure difference sensor4aas a pressure difference measuring unit that measures a difference in pressure ΔP between the internal pressure of the simplified airtight housing4and an external pressure (i.e. the internal pressure of the auxiliary machinery compartment8). A pressure difference measurement signal from the pressure difference sensor4a(a signal corresponding to the difference in pressure ΔP) is transmitted to the control unit6through a signal line, which is not illustrated. In the present embodiment, the difference in pressure ΔP means the difference between the internal pressure of the auxiliary machinery compartment8and the internal pressure of the simplified airtight housing4(i.e., ΔP=(Internal pressure of the auxiliary machinery compartment8)—(Internal pressure of the simplified airtight housing4)). Furthermore, in the present embodiment, the pressure difference sensor4ais used as the pressure difference measuring unit that measures the difference in pressure ΔP; however, the construction of the pressure difference measuring unit is not limited thereto. For example, a pressure sensor that measures the internal pressure of the simplified airtight housing4and a pressure sensor that measures the internal pressure of the auxiliary machinery compartment8may be separately installed and the difference in pressure ΔP may be calculated based on the measured pressure values of these pressure sensors, thereby implementing the function as the pressure difference measuring unit.

The fuel cell module1in the simplified airtight housing4has a reformer11, a fuel cell stack12(an assembly of multiple fuel battery cells13), and an offgas combustion portion14, which are disposed in a casing10, as illustrated inFIG. 2. In other words, the casing10surrounds the reformer11, the fuel cell stack12, and the offgas combustion portion14. The fuel cell stack12and the fuel battery cells13correspond to the fuel cells in the present invention.

The casing10is a box-shaped outer frame member formed of a heat-resistant metal. The casing10is preferably composed such that the inner surface thereof is lined with a heat insulating material. Furthermore, the casing10is disposed apart from the inner wall of the simplified airtight housing4to restrain heat transfer to the simplified airtight housing4. In other words, the casing10is installed such that an air layer is formed between the simplified airtight housing4and the fuel cell module1. The technique for the installation is, for example, a technique in which the casing10is installed through the intermediary of legs or a technique in which the casing10is installed through the intermediary of the heat exchanger3, which has a temperature that is lower than that of the casing10.

As illustrated inFIG. 1andFIG. 2, a raw fuel (a hydrocarbon-based fuel or the like) supply passage15, which extends from outside the SOFC package7into the casing10, is provided.

The raw fuel supply passage15is composed of a pipe that penetrates through holes (not illustrated), which are formed beforehand in the SOFC package7, the simplified airtight housing4and the casing10, respectively. A sealing member, such as the rubber grommet G, is used for the penetrated portion (join) between the pipe and the simplified airtight housing4. Furthermore, the penetrated portion (join) between the pipe and the casing10uses, for example, a metal pipe or a ceramic pipe (not illustrated).

As illustrated inFIG. 1, the raw fuel supply passage15in the auxiliary machinery compartment8is provided with a desulfurizer18and the pump15a, serving as a controller for supplying an appropriate amount, in this order from an upstream side toward a downstream side. The desulfurizer18removes a sulfur compound from a raw fuel. A for-reforming-air supply passage (not illustrated) is connected between the pump15aand the simplified airtight housing4in the raw fuel supply passage15. The for-reforming-air supply passage is provided with a blower (not illustrated), serving as a controller for supplying an appropriate amount.

As illustrated inFIG. 1andFIG. 2, a supply passage16of water for steam reforming (for-reforming water), which extends from a water tank34, which will be described hereinafter, in the auxiliary machinery compartment8into the casing10, is provided. The for-reforming-water supply passage16in the auxiliary machinery compartment8is provided with the pump16a, serving as the controller for supplying an appropriate amount.

The for-reforming-water supply passage16is composed of a pipe that penetrates through holes (not illustrated), which are formed beforehand in the simplified airtight housing4and the casing10, respectively. A sealing member, such as the rubber grommet G, is used for the penetrated portion (join) between the pipe and the simplified airtight housing4. Furthermore, the penetrated portion (join) between the pipe and the casing10uses, for example, a metal pipe or a ceramic pipe (not illustrated).

A cathode air supply passage17, which extends from the outside of the casing10to the inside thereof, is provided in the simplified airtight housing4. One end (an inlet17c) of the cathode air supply passage17is positioned in the simplified airtight housing4. Furthermore, the other end of the cathode air supply passage17faces the air electrodes (cathodes) of the fuel battery cells13. The cathode air supply passage17is provided with a blower17a, which is an air supply device, as a controller for supplying an appropriate amount. Furthermore, a filter17b, which removes foreign matter from air, is provided on the upstream side of the blower17ain the cathode air supply passage17.

The cathode air supply passage17is composed of a pipe that penetrates a through hole (not illustrated) formed in the casing10beforehand. The penetrated portion (join) between the pipe and the casing10uses, for example, a metal pipe or a ceramic pipe (not illustrated).

The reformer11illustrated inFIG. 2is formed by filling a chamber in a case, which is made of a heat-resistant metal, with a reforming catalyst. The supply passages15and16of a raw fuel and for-reforming water, respectively, are connected to the reformer11. Thus, the reformer11reforms a raw fuel by steam reforming reaction under the presence of the steam obtained by vaporizing water and generates a hydrogen-rich fuel gas (reformed gas). The reformed gas corresponds to the hydrogen-containing fuel in the present invention. In place of the steam reforming reaction, a technique publicly known as a hydrogen generation technique, including partial oxidation reaction, autothermal reforming reaction or the like, or a combination of these reforming reactions may be used to generate the reformed gas.

The fuel cell stack12is an assembly composed of the multiple solid oxide type fuel battery cells13connected in series. Each of the cells13is formed by arranging a fuel electrode (anode) and an air electrode (cathode) in layers on opposite surfaces of a solid oxide electrolyte. The reformed gas is supplied to the fuel electrode through a reformed gas supply passage19from an outlet of the reformer11. Air is supplied to the air electrode through the cathode air supply passage17.

Hence, in each of the fuel battery cells13, an electrode reaction denoted by Expression (1) given below takes place at the air electrode, while an electrode reaction denoted by Expression (2) given below takes place at the fuel electrode, thus generating electric power.

The fuel battery cells13are provided with a temperature sensor (not illustrated) that measures a temperature T thereof. A temperature measurement signal from the temperature sensor (a signal corresponding to the cell temperature T) is transmitted to the control unit6through a signal line, which is not illustrated.

The offgas combustion portion14is provided in the casing10. In the offgas combustion portion14, a surplus reformed gas (anode offgas) in the fuel cell stack12is burned in the presence of surplus air. The casing10maintains the reformer11and the fuel cell stack12in high temperature states by the combustion heat generated in the offgas combustion portion14. Hence, the inside of the casing10reaches a high temperature of, for example, about 600 to about 1000° C. during a power generating operation due to the power generation by the fuel cell stack12and the combustion of the surplus reformed gas.

Connected to the casing10is the exhaust gas processing unit2, which purifies a hot exhaust gas generated by the combustion therein.

The exhaust gas processing unit2is composed by, for example, filling a chamber in a metal case with a combustion catalyst. The exhaust gas processing unit2purifies, by the combustion catalyst, components such as carbon monoxide or hydrogen contained in the exhaust gas.

As illustrated inFIG. 1, the heat exchanger3, which carries out heat exchange between the exhaust gas that has been processed by the exhaust gas processing unit2and water, is connected to the exhaust gas processing unit2.

The heat exchanger3collects the waste heat of the fuel cell module1(the heat of the exhaust gas that contains the heat generated by the fuel cell stack12) to obtain hot water.

The heat exchanger3is connected to a hot-water storage tank of a hot-water supply unit (a package separate from the SOFC package7), which is not illustrated, by a heat medium circulation passage20. The heat medium circulation passage20in the auxiliary machinery compartment8is provided with a pump20a, serving as a controller for supplying an appropriate amount.

The heat medium circulation passage20is composed of a pipe that penetrates a through hole (not illustrated) formed beforehand in the simplified airtight housing4. The penetrated portion (join) between the pipe and the simplified airtight housing4uses, for example, the rubber grommet G, as the sealing member.

The moisture in the exhaust gas is condensed in the exhaust gas passage in the heat exchanger3by the heat exchange with the heat medium circulation passage20. Hence, a condensed water recovering passage32that extends from the exhaust gas passage in the heat exchanger3to the outside of the simplified airtight housing4(into the auxiliary machinery compartment8) is provided.

The condensed water recovering passage32is composed of a pipe that penetrates a through hole (not illustrated) formed beforehand in the simplified airtight housing4. The penetrated portion (join) between the pipe and the simplified airtight housing4uses, for example, the rubber grommet G, as the sealing member.

The condensed water recovering passage32in the auxiliary machinery compartment8is provided with a recovered water processing unit33. The recovered water processing unit33includes, for example, an ion exchange resin. Furthermore, the downstream end of the condensed water recovering passage32in the auxiliary machinery compartment8is connected to the water tank34.

The condensed water generated by the heat exchange in the heat exchanger3is passed through the condensed water recovering passage32, processed by the recovered water processing unit33, and stored in the water tank34.

The water stored in the water tank34is drawn out by the foregoing pump16a, passed through the for-reforming-water supply passage16and supplied to the reformer11.

The PCS5is adapted to take out DC power generated by the fuel cell stack12of the fuel cell module1. The PCS5has an inverter to convert DC power to AC power and supplies the AC power to a household load (electric appliance), which is not illustrated. If the power generated by the fuel cell stack12does not satisfy the demand power of the household load, then grid power from a grid power source, which is not illustrated, is supplied to the household load to cover the shortage.

The control unit6is adapted to mainly control the power generated by the fuel cell stack12and the operation of the pump20afor circulating the heat medium used for the heat exchange. The control unit6includes a microcomputer. The microcomputer includes a CPU, a ROM, a RAM, an input/output interface and the like.

The control unit6controls the power to be generated by controlling the amounts of the raw fuel, the for-reforming water and the for-reforming air to be supplied to the reformer11through the intermediary of the pumps15a,16aand the like, by controlling the amount of the reformed gas (an anode gas) supplied to the fuel cell stack12, and by controlling the amount of air (a cathode gas) supplied to the fuel cell stack12through the intermediary of the blower17a.

Hence, the control unit6sets a target value of the power to be generated by the fuel cell stack12within the range of a rated maximum power to be generated according to the demand power of the household load and controls the amounts of the fuel, water and air to be supplied according to the set target values (so as to obtain the target value of the power to be generated), thereby controlling the power to be generated by the fuel cell stack12.

The control unit6also controls the PCS5. Specifically, the current to be taken out of the fuel cell stack12is set and controlled based on the target value of the power to be generated by the fuel cell stack12. More specifically, the target value of the power to be generated by the fuel cell stack12is divided by an output voltage (instantaneous value) of the fuel cell stack12to set the target value of current, and the current to be taken out from the fuel cell stack12is controlled according to the set target value of current.

When the blower17ais actuated, the blower17adraws in air from the inside of the simplified airtight housing4and supplies the air to the fuel cell stack12(the air electrodes of the fuel battery cells13) in the fuel cell module1through the cathode air supply passage17. This maintains the pressure inside the simplified airtight housing4to be lower than the pressure in the area around the simplified airtight housing4(the auxiliary machinery compartment8). In other words, the blower17afunctions as the suction device in the present invention and is capable of maintaining the inside of the simplified airtight housing4in the negative pressure state. Thus, even if a small amount of an exhaust gas leaks into the simplified airtight housing4from the fuel cell module1, it is possible to restrain the small amount of the exhaust gas from flowing out of the simplified airtight housing4(the auxiliary machinery compartment8) through the intake hole41or the gap between the grommet G and piping. Furthermore, the small amount of the exhaust gas that leaked into the simplified airtight housing4is drawn in together with air by the blower17aand led into the fuel cell module1, and the components, such as carbon monoxide and hydrogen in the exhaust gas are purified by the exhaust gas processing unit2. Hence, it is possible to restrain the components, such as carbon monoxide and hydrogen, in the small amount of the exhaust gas that has leaked into the simplified airtight housing4from being released out of the SOFC package7through the exhaust pipe44.

In the present embodiment, in order to further securely restrain the exhaust gas components from being released out of the SOFC package7, the negative pressure state in the simplified airtight housing4is monitored and the operation of the system is controlled according to the negative pressure state. The control unit6functions as the control unit in the present invention and controls the operation of the SOFC system based on the difference in pressure ΔP obtained by the pressure difference sensor4a,

FIG. 3is a flowchart illustrating the determination of the negative pressure state in the simplified airtight housing4that is carried out by the control unit6.

The negative pressure state determination in the flowchart ofFIG. 3is carried out at predetermined time intervals while the system is in operation.

In step S1, the difference in pressure ΔP obtained by the foregoing pressure difference sensor4aand a first predetermined difference in pressure P1 are compared. The first predetermined difference in pressure P1 denotes a threshold value for determining whether the negative pressure state in the simplified airtight housing4is normal or not, and is set beforehand.

If ΔP>(greater than) P1, then the control unit6determines that the negative pressure state in the simplified airtight housing4is maintained normal and proceeds to step S2to continue a normal operation of the system. Specifically, as described above, the control unit6carries out the control of the power to be generated by the fuel cell stack12and the control of the PCS5according to the demand power of the household load.

On the other hand, if ΔP≦(less than or equal to) P1, then the control unit6determines that the negative pressure state in the simplified airtight housing4is abnormal and proceeds to step S3.

In step S3, the difference in pressure ΔP obtained by the foregoing pressure difference sensor4aand a second predetermined difference in pressure P2 are compared. The second predetermined difference in pressure P2 denotes a threshold value for determining whether the anomaly of the negative pressure state in the simplified airtight housing4is minor or not, and is set beforehand. The first predetermined difference in pressure P1 and the second predetermined difference in pressure P2 are set beforehand such that a relationship denoted by 0<(less than) P2<(less than) P1 is satisfied.

If ΔP>(greater than) P2, then the control unit6determines that the negative pressure state in the simplified airtight housing4is abnormal but the anomaly is minor and proceeds to step S4to reduce an operation output of the system. Specifically, the target value of the power to be generated by the foregoing fuel cell stack12is reduced by a predetermined amount, or the maximum value thereof is limited in carrying out the control of the power generated by the fuel cell stack12and the control of the PCS5.

On the other hand, if ΔP≦(less than or equal to) P2, then the control unit6determines that the anomaly of the negative pressure state in the simplified airtight housing4is not minor and proceeds to step S5.

Alternatively, the control unit6may determine that the anomaly of the negative pressure state in the simplified airtight housing4is not minor and proceed to step S5if the state in which ΔP>(greater than) P2 lasts for a predetermined time or longer after the operation output of the system is reduced in step S4.

In step S5, the control for stopping the operation of the system illustrated inFIG. 4is carried out.

FIG. 4is the flowchart illustrating the control for stopping the operation of the system carried out by the control unit6.

In step S11, it is determined whether there is a request for an emergency stop of the system or not. The term “emergency stop” used herein means to stop the operation by carrying out a stop control that omits at least some steps of a normal operation stop control. The emergency stop is requested in the case of, for example, an emergency operation stop of the blower17a.

If it is determined that there is an emergency stop request, then the control unit6proceeds to step S12to carry out the control for an emergency stop of the system. In the emergency stop control, the system is stopped by, for example, immediately and simultaneously stopping current sweep, the supply of the raw fuel and the for-reforming water to the reformer11, and the supply of air for the cathode to the fuel cell stack12. At the time of the emergency stop control, the generation of the reformed gas is immediately stopped by the immediate stop of the supply of the raw fuel to the reformer11. Furthermore, the simultaneous stop described above causes the temperature in the fuel cell module1to promptly start going down, so that the volume of the gas in the fuel cell module1decreases accordingly. Thus, the air around the fuel cell module1(the air in the simplified airtight housing4) will move in a direction to be drawn into the fuel cell module1. This makes it possible to restrain the gas remaining in the fuel cell module1(e.g., the reformed gas or the anode offgas) from flowing back out through the cathode air supply passage17into the simplified airtight housing4.

On the other hand, if it is determined that there is no request for an emergency stop in step S11, then the control unit6proceeds to step S13to start a normal operation stop control.

In step S13, the current sweep is immediately stopped. Specifically, an instruction is given to the PCS5to stop the current sweep. The fuel cell stack12is disconnected from the household load. Stopping the generation of power will stop the heat generation in the fuel battery cells13themselves.

Furthermore, in step S13, the amounts of the raw fuel and the for-reforming water supplied to the reformer11and the amount of the cathode air supplied to the fuel cell stack12are reduced.

In step S14, the cell temperature T measured by the foregoing temperature sensor and a predetermined temperature Ts are compared. The predetermined temperature Ts is a temperature at which it is possible to restrain the heat deterioration attributable to the oxidation of the cell supports (not illustrated) or the like of the fuel battery cells13even when the fuel supply is stopped (even when a reducing atmosphere is lost), and is set beforehand.

If T>(greater than) Ts, then the control unit6returns to step S14after a predetermined time elapses and continues to measure the cell temperature T and to compare the cell temperature T and the predetermined temperature Ts. At the moment when T≦(less than or equal to) Ts, the control unit6proceeds to step S15.

In step S15, the supply of the raw fuel and the for-reforming water to the reformer11is stopped.

Thereafter, the monitoring of the cell temperature T is continued, and when the cell temperature T reaches room temperature, the supply of the cathode air to the fuel cell stack12is stopped (step S16) and the system is stopped.

Patent document 1 describes that the cover of the casing is provided with a cooling pipe for cooling the gasket. Cooling the gasket by using such a cooling pipe may cause a low-temperature region to be formed in the vicinity of the fuel cells, possibly leading to a disturbed heat balance of the fuel cells.

In this respect, according to the present embodiment, no low-temperature region will be formed in the vicinity of the fuel cell stack12. Hence, a relatively favorable heat balance of the fuel cell stack12can be maintained.

According to the present embodiment, the SOFC system (the fuel cell system) is constituted by including: the fuel cell module1, which includes the fuel cell stack12(fuel cells), which causes the reformed gas (hydrogen-containing fuel) and air to react, thereby to generate power, and the casing10, which surrounds the fuel cell stack12and burns therein a surplus reformed gas of the fuel cell stack12to maintain the fuel cell stack12in a high temperature state; the simplified airtight housing4(the first housing), which accommodates the fuel cell module1; and the blower17a(the air supply device and the suction device), which draws in air from the inside of the simplified airtight housing4to maintain the inside of the simplified airtight housing4in the negative pressure state. Thus, the inside of the simplified airtight housing4is maintained at a pressure which is lower than that in the surrounding of the simplified airtight housing4(the auxiliary machinery compartment8), so that even if a small amount of an exhaust gas leaks from the fuel cell module1into the simplified airtight housing4, it is possible to restrain the small amount of the exhaust gas from flowing out of the simplified airtight housing4(into the auxiliary machinery compartment8). Thus, the airtightness of the fuel cell module1can be eased within a range in which the power generating performance of the fuel cell stack12is not affected. Furthermore, the airtightness of the simplified airtight housing4can be eased within a range in which the inside of the simplified airtight housing4is maintained at a pressure that is lower than that in the surrounding of the simplified airtight housing4(the auxiliary machinery compartment8).

Furthermore, according to the present embodiment, an air layer is formed between the outer surface of the fuel cell module1and the inner surface of the simplified airtight housing4, so that the surface temperature of the simplified airtight housing4is lower than the outer surface temperature of the fuel cell module1. Therefore, in place of the foregoing gasket made of expanded graphite, a member that is less costly and has lower heat resistance (e.g., the rubber grommet G) than the foregoing gasket is used to join the piping or the wiring that penetrate the simplified airtight housing4.

Furthermore, according to the present embodiment, the blower17adraws in air from the inside of the simplified airtight housing4. Thus, the blower17amainly draws in the relatively dry air from the inside of the simplified airtight housing4, so that a relatively favorable mechanical life of the blower17acan be obtained, as compared with the suction device described in Patent document 2.

Furthermore, according to the present embodiment, the SOFC system is constituted by further including the exhaust gas processing unit2, which purifies the exhaust gas emitted from the fuel cell module1, and the simplified airtight housing4further accommodates the exhaust gas processing unit2. With this arrangement, the components, such as carbon monoxide and hydrogen, contained in the exhaust gas from the fuel cell module1are subjected to the purification processing in the simplified airtight housing4, thus permitting the restraint of the components from flowing out of the simplified airtight housing4(into the auxiliary machinery compartment8).

Furthermore, according to the present embodiment, the blower17ais an air supply device that supplies the air drawn from the inside of the simplified airtight housing4to the fuel cell module1. Therefore, even if a small amount of the exhaust gas leaks from the fuel cell module1into the simplified airtight housing4, the small amount of the exhaust gas is led into the fuel cell module1together with the air in the simplified airtight housing4. This means that there is no need to separately provide equipment, such as piping, for safely discharging the exhaust gas out of the simplified airtight housing4and also out of the auxiliary machinery compartment8while maintaining the simplified airtight housing4in the negative pressure state, thus making it possible to restrain the exhaust gas from leaking out of the simplified airtight housing4(the auxiliary machinery compartment8) without causing the system to become unduly larger.

Furthermore, according to the present embodiment, the blower17ais an air supply device that supplies the air drawn from the inside of the simplified airtight housing4to the air electrodes of the fuel battery cells13in the casing10. This obviates the need for providing an exclusive blower for maintaining the simplified airtight housing4in the negative pressure state, so that the inside of the simplified airtight housing4can be maintained in the negative pressure state by using the cathode air supply blower17awithout causing an undue increase in the size of the system, thus allowing the system to have a relatively simple construction.

Furthermore, according to the present embodiment, the SOFC system is constituted by further including the SOFC package7(the second housing), which accommodates the simplified airtight housing4. With this arrangement, the auxiliary machinery compartment8can be defined and formed around the simplified airtight housing4, allowing auxiliary machinery to be gathered in the auxiliary machinery compartment8.

Furthermore, according to the present embodiment, the SOFC system is constituted by further including the intake pipe43(communication pipe), which penetrates the SOFC package7to provide communication between the inside of the simplified airtight housing4and the outside of the SOFC package7, and the blower17ais disposed inside the simplified airtight housing4. With this arrangement, the air outside the SOFC package7can be smoothly introduced into the simplified airtight housing4through the intake pipe43, making it possible to restrain undue heat generation of the blower17ain the simplified airtight housing4.

Furthermore, according to the present embodiment, the SOFC system is constituted by further including: the pressure difference sensor4a(the pressure difference measuring unit), which obtains the difference between the internal pressure of the simplified airtight housing4and the external pressure of the simplified airtight housing4(the difference in pressure ΔP); and the control unit6, which controls the operation of the SOFC system based on the difference in pressure ΔP obtained by the pressure difference sensor4a. With this arrangement, if, for example, the negative pressure in the simplified airtight housing4starts to decrease (i.e., if the internal pressure of the simplified airtight housing4starts to approach the internal pressure of the auxiliary machinery compartment8) due to the clogging of the filter17bor a failure of the blower17awhile the blower17ais in operation, then the change in the negative pressure state in the simplified airtight housing4can be promptly grasped and the operation of the system can be controlled accordingly, thus making it possible to control the operation of the system with higher safety while restraining the leakage of the exhaust gas from the simplified airtight housing4into the auxiliary machinery compartment8.

Furthermore, according to the present embodiment, if the difference in pressure ΔP is greater than the first predetermined difference in pressure P1 (ΔP>P1), then the target value of the power to be generated by the fuel cell stack12is set according to the demand power of the household load, and the power to be generated by the fuel cell stack12is controlled to reach the target value (refer to step S2inFIG. 3). On the other hand, if the difference in pressure ΔP is greater than the second predetermined difference in pressure P2, and less than or equal to the first predetermined difference in pressure P1 (P2<ΔP≦P1), then, for example, the target value of the power to be generated by the fuel cell stack12is reduced by a predetermined amount and the power to be generated by the fuel cell stack12is controlled to reach the reduced new target value (refer to step S4inFIG. 3). In other words, according to the present embodiment, the control unit6decreases the operation output of the SOFC system as the difference in pressure ΔP decreases. Thus, the amount of the exhaust gas produced in the fuel cell module1can be reduced when the negative pressure in the simplified airtight housing4decreases, so that the leakage of the exhaust gas from the fuel cell module1into the simplified airtight housing4can be restrained.

Furthermore, according to the present embodiment, if the difference in pressure ΔP decreases to the second predetermined difference in pressure P2 or less (the predetermined threshold value or less), then the control unit6stops the operation of the SOFC system (refer to step S5inFIG. 3, andFIG. 4). Thus, if the negative pressure in the simplified airtight housing4considerably decreases, then the control for stopping the operation of the system can be immediately started, so that the leakage of the exhaust gas from the inside of the simplified airtight housing4into the auxiliary machinery compartment8can be restrained.

In the present embodiment, the intake pipe43and the exhaust pipe44are constructed to be separate pipes; however, the constructions of the intake pipe and the exhaust pipe are not limited thereto. For example, the intake pipe and the exhaust pipe may be integrally constructed by using a pipelike member having a double-pipe structure composed of an outer pipe and an inner pipe. In this case, by using the space between the outer pipe and the inner pipe as an intake passage and using the space in the inner pipe as an exhaust passage, the pipelike member having the double-pipe structure is capable of restraining the heat of the exhaust gas from being directly transmitted to the outer surface of the pipelike member (the outer pipe).

FIG. 5illustrates the schematic configuration of a SOFC system in a second embodiment of the present invention.

The following will describe aspects that are different from the first embodiment illustrated inFIG. 1.

In the present embodiment, an air intake passage51extending from the inside of a simplified airtight housing4to an exhaust gas processing unit2is provided. One end (the inlet) of the air intake passage51is positioned in the simplified airtight housing4. The other end of the air intake passage51is connected to the exhaust gas processing unit2. The air intake passage51is provided with a blower51a, which is an air supply device, serving as a device for controlling an appropriate supply amount.

When the blower51ais actuated, the blower51adraws air from the inside of the simplified airtight housing4through the air intake passage51and supplies the air to the exhaust gas processing unit2. Thus, the pressure inside the simplified airtight housing4is maintained to be lower than the pressure in the surrounding of the simplified airtight housing4(an auxiliary machinery compartment8). This means that the blower51afunctions as the suction device in the present invention and is capable of maintaining the inside of the simplified airtight housing4in a negative pressure state. Therefore, even if a small amount of an exhaust gas leaks from a fuel cell module1into the simplified airtight housing4, it is possible to restrain the small amount of the exhaust gas from leaking out of the simplified airtight housing4(into the auxiliary machinery compartment8) through an intake hole41or a gap between a grommet G and the piping. Furthermore, the small amount of the exhaust gas leaked into the simplified airtight housing4is drawn in together with air by the blower51aand led into the exhaust gas processing unit2, and then the components, such as carbon monoxide and hydrogen, in the exhaust gas are subjected to purification processing. Hence, it is possible to restrain the components, such as carbon monoxide and hydrogen, in the small amount of the exhaust gas that has leaked into the simplified airtight housing4from being released out of a SOFC package7through an exhaust pipe44.

In the present embodiment, the combined use of a blower17aand the blower51apermits an enhanced negative pressure in the simplified airtight housing4. Furthermore, the blower51acan be operated even if the operation of the blower17ais stopped. This makes it possible to maintain the inside of the simplified airtight housing4in the negative pressure state by the blower51awhen the operation of the blower17ais stopped.

According to the present embodiment, in particular, the blower51ais an air supply device that supplies the air drawn out of the simplified airtight housing4to the exhaust gas processing unit2. Hence, even if a small amount of the exhaust gas leaks from a fuel cell module1into the simplified airtight housing4, the small amount of the exhaust gas is led into the exhaust gas processing unit2together with the air in the simplified airtight housing4, thus making it possible to restrain the exhaust gas from leaking out of the simplified airtight housing4(into an auxiliary machinery compartment8) and to more effectively purify the small amount of the exhaust gas leaked into the simplified airtight housing4.

FIG. 6illustrates the schematic configuration of a SOFC system in a third embodiment of the present invention.

The following will describe aspects that are different from the first embodiment illustrated inFIG. 1.

In the present embodiment, intake holes41,71and an intake pipe43are provided in the vicinity of a blower17a. Furthermore, a cathode air supply passage17, the blower17a, and a filter17bare disposed such that air flowing from the outside of a SOFC package7into a simplified airtight housing4through the intake pipe43passes by the blower17aand the filter17band flows into one end (an inlet17c) of the cathode air supply passage17.

According to the present embodiment, in particular, the air directly flowing into the simplified airtight housing4through the intake pipe43from the outside of the SOFC package7passes by the blower17aand the filter17band is led into the inlet17cof the cathode air supply passage17(i.e., the inlet of the blower17a). Therefore, the air from the outside of the SOFC package7cools the blower17aand the filter17band then flows into the cathode air supply passage17, thus allowing the cathode air to be used for cooling the blower17aand the filter17b.

FIG. 7illustrates the schematic configuration of a SOFC system in a fourth embodiment of the present invention.

The following will describe aspects that are different from the first embodiment illustrated inFIG. 1.

In the present embodiment, a SOFC package7does not have the intake hole71. Furthermore, an intake pipe43′ is provided in place of the intake pipe43. One end of the intake pipe43′ is connected in an airtight and liquid-tight manner to an intake hole41of the simplified airtight housing4. The other end of the intake pipe43′ is positioned in an auxiliary machinery compartment8. The intake pipe43′ may be omitted and the air in the auxiliary machinery compartment8may be directly led into the simplified airtight housing4through the intake hole41.

In the present embodiment, an intermediate portion of a cathode air supply passage17, a blower17aand a filter17bare positioned in the auxiliary machinery compartment8. Hence, a portion of the cathode air supply passage17that is on the upstream side relative to the filter17band a portion thereof on the downstream side relative to the blower17aare respectively constituted of pipes that penetrate through holes (not illustrated) formed beforehand in the simplified airtight housing4. The penetrated portions (joins) between the pipes and the simplified airtight housing4use, for example, rubber grommets G as the sealing members. Among the pipes constituting the cathode air supply passage17, the pipe having one end (an inlet17c) thereof positioned in the simplified airtight housing4, the intermediate portion thereof penetrating the simplified airtight housing4, and the other end thereof connected to the intake end of the blower17athrough the intermediary of the filter17bis referred to as an intake pipe. The intake pipe has a function for leading the air in the simplified airtight housing4toward the blower17ain the auxiliary machinery compartment8. Furthermore, among the pipes constituting the cathode air supply passage17, the pipe having one end thereof connected to the discharge end of the blower17a, the intermediate portion thereof penetrating the simplified airtight housing4and the casing10, and the other end thereof facing the air electrodes of fuel battery cells13is referred to as an air supply pipe. The air supply pipe has a function for leading the air discharged from the blower17ato the air electrodes of the fuel battery cells13. The air supply pipe may alternatively be configured such that the intermediate portion thereof penetrates the simplified airtight housing4and the other end thereof is connected to an exhaust gas processing unit2instead of the intermediate portion thereof penetrating the simplified airtight housing4and the casing10and the other end thereof facing the air electrodes of the fuel battery cells13.

In the present embodiment, a heat exchanger3is disposed in the auxiliary machinery compartment8. Furthermore, an exhaust gas passage61is provided. One end of the exhaust gas passage61is connected to the exhaust gas processing unit2and the other end is connected to the heat exchanger3. The exhaust gas passage61is constituted of a pipe that penetrates a through hole (not illustrated) formed beforehand in the simplified airtight housing4. The penetrated portion (join) between the pipe and the simplified airtight housing4uses a high temperature gasket H as the sealing member.

An exhaust pipe44has one end thereof connected to an exhaust port31of the heat exchanger3in the auxiliary machinery compartment8. An intermediate portion of the exhaust pipe44passes through an exhaust hole72in the SOFC package7. The other end of the exhaust pipe44projects outward from the outer surface of the SOFC package7. The exhaust pipe44may alternatively have one end thereof connected to the exhaust port31of the heat exchanger3in the simplified airtight housing4and the other end thereof connected to the exhaust hole72of the SOFC package7.

According to the present embodiment in particular, one end of the intake pipe43′ is connected to the intake hole41of the simplified airtight housing4, while the other end thereof is positioned in the auxiliary machinery compartment8. Thus, the air in the auxiliary machinery compartment8that has been warmed by the heat generated by auxiliary machinery is preferentially taken into the simplified airtight housing4to supply the air to the air electrodes of the fuel battery cells13. As a result, the capture of outside air into the auxiliary machinery compartment8by a ventilation fan73is expedited, so that a temperature rise in the auxiliary machinery compartment8is restrained, permitting stabilized operations and prolonged life of auxiliary machinery. Furthermore, there is no need to form the intake hole71in the SOFC package7, so that the number of steps for processing the SOFC package7can be reduced.

Furthermore, according to the present embodiment, the blower17aand the filter17bare disposed in the auxiliary machinery compartment8(i.e., outside the simplified airtight housing4). The temperature in the auxiliary machinery compartment8is lower than that in the simplified airtight housing4. Hence, the blower17aand the filter17bcan be favorably cooled, as compared with the case in which the blower17aand the filter17bare disposed in the simplified airtight housing4, so that the heat deterioration of the blower17aand the filter17bcan be restrained.

FIG. 8illustrates the schematic configuration of a SOFC system in a fifth embodiment of the present invention.

The following will describe aspects that are different from the first embodiment illustrated inFIG. 1.

In the present embodiment, a SOFC package7does not have the intake hole71. Furthermore, the intake pipe43is omitted. In the present embodiment, therefore, when a blower17ais operated, the air in an auxiliary machinery compartment8directly flows into a simplified airtight housing4through an intake hole41. Hence, in the present embodiment, the air in the auxiliary machinery compartment8that has been warmed by the heat generated by auxiliary machinery is preferentially taken into the simplified airtight housing4to supply the air to the air electrodes of fuel battery cells13. As a result, the capture of outside air into the auxiliary machinery compartment8by a ventilation fan73is expedited, so that a temperature rise in the auxiliary machinery compartment8is restrained, permitting stabilized operations and prolonged life of the auxiliary machinery. Furthermore, there is no need to form the intake hole71in the SOFC package7, so that the number of steps for processing the SOFC package7can be reduced.

FIG. 9illustrates the schematic configuration of a SOFC system in a sixth embodiment of the present invention.

The following will describe aspects that are different from the first embodiment illustrated inFIG. 1.

In the present embodiment, a heat medium circulation passage20is provided with a heat exchanger80at a portion thereof that is located in a simplified airtight housing4and on the downstream side relative to the inlet of a heat exchanger3. A position R1 and a position R2 of the heat medium circulation passage20illustrated inFIG. 9are connected by a pipe, which is not illustrated.

The heat exchanger80is positioned between an inlet17cand a filter17bin a cathode air supply passage17.

The heat exchanger80carries out heat exchange between a heat medium before flowing into the heat exchanger3(i.e., the heat medium before the heat is collected from an exhaust gas) and the cathode air before passing through the filter17b. The heat exchange cools the cathode air and as a result, the temperature of the cathode air approaches the temperature of the heat medium. In other words, the heat exchanger80functions as the cooling device in the present invention and cools the cathode air. Thus, it is possible to restrain the cathode air from exceeding the temperature limits of the filter17band the blower17a, even when a large amount of heat is radiated from a fuel cell module1and an exhaust gas processing unit2, and the air temperature in the simplified airtight housing4is high.

According to the present embodiment in particular, the SOFC system (fuel cell system) is constituted by further including the heat exchanger80(cooling device) that cools the air in the simplified airtight housing4(in the first housing) that is drawn in by the blower17a(suction device). This makes it possible to restrain the cathode air from exceeding the temperature limits of the filter17band the blower17a, thus permitting prolonged lives of the filter17band the blower17a.

In the present embodiment, the example in which the cathode air is cooled by the heat exchanger80(cooling device) using the heat medium, has been described; however, the method for cooling the cathode air is not limited thereto. For example, in addition to or in place of providing the heat medium circulation passage20with the heat exchanger80as described above, the heat exchanger80may be provided at a portion of the for-reforming-water supply passage16, which portion is positioned in the simplified airtight housing4. In this case, the cathode air can be cooled by the heat exchanger80, which carries out the heat exchange between the cathode air and the for-reforming water.

In the first, the second, the fifth, and the sixth embodiments described above, the blower17aand the filter17bare disposed in the simplified airtight housing4. However, in these embodiments, the blower17aand the filter17bmay be disposed outside the simplified airtight housing4, and the cathode air supply passage17may be constituted by the intake pipe and the air supply pipe described above, as with the foregoing fourth embodiment.

Furthermore, in the first to the third and the sixth embodiment described above, in place of the intake pipe43, the intake pipe43′, one end of which is connected in an airtight and liquid-tight manner to the intake hole41of the simplified airtight housing4and the other end of which is positioned in the auxiliary machinery compartment8, may be provided, as with the foregoing fourth embodiment.

Furthermore, in the second and the third embodiments described above, the SOFC package7may not be provided with the intake hole71and the intake pipe43may be omitted, so that the air in the auxiliary machinery compartment8flows directly into the simplified airtight housing4through the intake hole41when the blower17ais operated.

Furthermore, in the foregoing sixth embodiment, the cathode air is cooled by the heat exchanger80. However, this air cooling method may be applied to the second to the fifth embodiments described above to cool the cathode air.

Furthermore, in the first to the sixth embodiments, the descriptions have been given by using the hydrogen-rich fuel gas (reformed gas) generated by the reformer11as the hydrogen-containing fuel supplied to the fuel electrodes of the fuel battery cells13; however, the hydrogen-containing fuel is not limited thereto. For example, pure hydrogen may be used as the hydrogen-containing fuel. In this case, the SOFC system may be constructed by omitting the desulfurizer18illustrated inFIG. 1andFIG. 5toFIG. 9and the reformer11illustrated inFIG. 2such that the pure hydrogen is directly supplied to the fuel electrodes of the fuel battery cells13from outside the SOFC package7through the raw fuel supply passage15.

Furthermore, in the first to the sixth embodiments described above, the intake hole41has been illustrated as the intake part that leads the air outside the simplified airtight housing4into the simplified airtight housing4; however, the configuration of the intake part of the simplified airtight housing4is not limited thereto. For example, in the case in which the simplified airtight housing4is formed to be shaped like a box by assembling plate-like members, the gaps or the like formed among the plate-like members correspond to the intake part of the simplified airtight housing4and allow the air outside the simplified airtight housing4to be led into the simplified airtight housing4.

Furthermore, the illustrated embodiments are merely exemplary of the present invention, and various improvements and modifications made by one skilled in the art within the scope of the appended claims will be apparently embraced in the present invention in addition to those explicitly illustrated by the embodiments that have been described.

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