Patent Publication Number: US-2013236802-A1

Title: Power generation system and method of operating the same

Description:
TECHNICAL FIELD 
     The present invention relates to a power generation system configured to supply heat and electricity and a method of operating the power generation system, and particularly to the method of operating the power generation system. 
     BACKGROUND ART 
     A cogeneration system supplies generated electric power to users for electric power loads and recovers and stores exhaust heat for hot water supply loads of the users, the exhaust heat being generated by the electric power generation. Known as this type of cogeneration system is a cogeneration system configured such that a fuel cell and a water heater operate by the same fuel (see PTL 1, for example). A cogeneration system disclosed in PTL 1 includes: a fuel cell; a heat exchanger configured to recover heat generated by the operation of the fuel cell; a hot water tank configured to store water having flowed through the heat exchanger to be heated; and a water heater configured to heat the water flowing out from the hot water tank up to a predetermined temperature, and is configured such that the fuel cell and the water heater operate by the same fuel. 
     Moreover, a fuel cell power generation apparatus provided inside a building is known, which is configured for the purpose of improving an exhaust performance of the fuel cell power generation apparatus (see PTL 2, for example). A power generation apparatus disclosed in PTL 2 is a fuel cell power generation apparatus provided and used in a building including an intake port and includes an air introducing port through which air in the building is introduced to the inside of the fuel cell power generation apparatus, an air discharging pipe through which the air in the fuel cell power generation apparatus is discharged to the outside of the building, and a ventilation unit. The ventilation unit introduces the air from the outside of the building through the intake port to the inside of the building, further introduces the air through the air introducing port to the inside of the fuel cell power generation apparatus, and discharges the air through the air discharging pipe to the outside of the building. 
     Further, a power generation apparatus including a duct extending in a vertical direction is known, which is configured for the purpose of improving the exhaust performance of an exhaust gas generated by a fuel cell provided inside a building (see PTL 3, for example). In a power generation apparatus disclosed in PTL 3, a duct extending inside a building in a vertical direction and having an upper end portion located outside the building is a double pipe, and a ventilating pipe and an exhaust pipe are coupled to the duct such that an exhaust gas or air flows through the inside or outside of the duct. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Laid-Open Patent Application Publication No. 2007-248009 
         PTL 2: Japanese Laid-Open Patent Application Publication No. 2006-73446 
         PTL 3: Japanese Laid-Open Patent Application Publication No. 2008-210631 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Here, in the case of providing the cogeneration system disclosed in PTL 1 in a building, the below-described configuration may be adopted in reference to the power generation apparatus disclosed in PTL 2 or 3. To be specific, the configuration is that: a cogeneration unit and a hot water supply unit are separately provided, the cogeneration unit including a ventilation fan, a fuel cell, and a hydrogen generating unit configured to supply a fuel gas to the fuel cell, the hot water supply unit including a water heater; and an exhaust passage causing the cogeneration unit and the water heater to communicate with each other is formed. 
     In this configuration, for example, in a case where the water heater is activated and the ventilation fan is not activated, the exhaust gas discharged from the water heater may flow through the exhaust passage into the cogeneration unit. Then, one problem is that if the cogeneration unit is activated in a state where the exhaust gas has flowed into the cogeneration unit, the exhaust gas having a low oxygen concentration is supplied to the combustor provided in the cogeneration unit, and an ignition failure of the combustor of the fuel cell system easily occurs. 
     An object of the present invention is to provide a power generation system capable of suppressing the ignition failure of a combustor of a fuel cell system and having high reliability in the case of providing an exhaust passage causing the fuel cell system and a combustion device to communicate with each other as above, and a method of operating the power generation system. 
     Solution to Problem 
     To solve the above conventional problems, a power generation system according to the present invention includes: a fuel cell system including a fuel cell configured to generate electric power using a fuel gas and an oxidizing gas, a case configured to house the fuel cell, a reformer configured to generate the fuel gas from a raw material and steam, and a combustor configured to heat the reformer; a ventilator; a controller; a combustion device; and a discharge passage formed to cause the case and an exhaust port of the combustion device to communicate with each other and configured to discharge an exhaust gas from the fuel cell system and an exhaust gas from the combustion device to an atmosphere through an opening of the discharge passage, the opening being open to the atmosphere, wherein: the ventilator is configured to discharge a gas in the case to the discharge passage to ventilate an inside of the case; and the controller causes the combustion device to operate when the ventilator is in a stop state and then causes the ventilator to operate when the fuel cell system is activated. 
     Here, the expression “when the fuel cell system is activated” denotes “when the fuel cell system starts the activation”. Specifically, for example, the expression “when the fuel cell system is activated” may denote “when a signal is input to the controller such that the activation of the fuel cell system is started” or “when the controller outputs a signal to devices constituting the fuel cell system such that the activation of the fuel cell system is started”. In other words, the expression “when the fuel cell system is activated” denotes a period from when the signal is input to the controller such that the activation operation of the fuel cell system is started until when the devices constituting the fuel cell system starts operating. 
     With this, even if the exhaust gas discharged from the combustion device flows into the case by operating the combustion device when the ventilator is in a stop state, the exhaust gas in the case can be discharged to the outside of the case by operating the ventilator when the fuel cell system is activated. Therefore, the decrease in the oxygen concentration in the case can be suppressed. On this account, the ignition failure of the combustor of the fuel cell system can be suppressed, and the reliability of the power generation system can be improved. 
     In the power generation system according to the present invention, the controller may cause the combustor to operate after the controller causes the ventilator to operate. 
     In the power generation system according to the present invention, the controller may cause the ventilator to discharge a gas having a volume equal to or larger than a volume of the case to the discharge passage when the fuel cell system is activated. 
     The power generation system according to the present invention may further include an oxidizing gas supply unit configured to supply the oxidizing gas to the fuel cell, wherein the controller may cause the oxidizing gas supply unit to supply the oxidizing gas to the fuel cell after the controller causes the ventilator to operate. 
     In the power generation system according to the present invention, the combustion device may include a combustion air supply unit configured to supply combustion air, and when the combustion device is operating, the controller may control the ventilator such that an air flow rate of the ventilator becomes equal to or higher than a predetermined first air flow rate. 
     The power generation system according to the present invention may further include an air intake passage formed to cause the case and the combustion device to communicate with each other and configured to supply air to the fuel cell system and the combustion device through an opening of the air intake passage, the opening being open to the atmosphere, wherein the air intake passage may be formed so as to be heat-exchangeable with the exhaust passage. 
     The power generation system according to the present invention may further include an operation detector configured to detect that the combustion device has operated. 
     In the power generation system according to the present invention, in a case where the operation detector detects that the combustion device has operated when the ventilator is in a stop state, the controller may cause the ventilator to operate when the fuel cell system is activated. 
     Further, in the power generation system according to the present invention, the operation detector may be at least one of a temperature detector, a pressure detector, a gas concentration detector, and a sound detector. 
     A method of operating the power generation system according to the present invention is a method of operating a power generation system, the power generation system including: a fuel cell system including a fuel cell configured to generate electric power using a fuel gas and an oxidizing gas, a case configured to house the fuel cell, and a ventilator; a combustion device; and a discharge passage formed to cause the case and an exhaust port of the combustion device to communicate with each other and configured to discharge an exhaust gas from the fuel cell system and an exhaust gas from the combustion device to an atmosphere through an opening of the discharge passage, the opening being open to the atmosphere, wherein: the ventilator is configured to discharge a gas in the case to the discharge passage to ventilate an inside of the case; and the combustion device operates when the ventilator is in a stop state, and then, the ventilator operates when the fuel cell system is activated. 
     With this, even if the exhaust gas discharged from the combustion device flows into the case by operating the combustion device when the ventilator is in a stop state, the exhaust gas in the case can be discharged to the outside of the case by operating the ventilator when the fuel cell system is activated. Therefore, the decrease in the oxygen concentration in the case can be suppressed. On this account, the ignition failure of the combustor of the fuel cell system can be suppressed, and the reliability of the power generation system can be improved. 
     Advantageous Effects of Invention 
     According to the power generation system of the present invention and the method of operating the power generation system, even if the exhaust gas discharged from the combustion device flows into the case by operating the combustion device when the ventilator is in a stop state, the exhaust gas in the case can be discharged to the outside of the case by operating the ventilator when the fuel cell system is activated. Therefore, the ignition failure of the combustor of the fuel cell system can be suppressed, and the reliability of the power generation system can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing the schematic configuration of a power generation system according to Embodiment 1 of the present invention. 
         FIG. 2  is a flow chart schematically showing an activation operation of a fuel cell system of the power generation system according to Embodiment 1. 
         FIG. 3  is a schematic diagram showing an example in which a temperature detector is used as an operation detector in the power generation system shown in  FIG. 1 . 
         FIG. 4  is a schematic diagram showing an example in which a pressure detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
         FIG. 5  is a schematic diagram showing an example in which a gas concentration detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
         FIG. 6  is a schematic diagram showing an example in which a sound detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
         FIG. 7  is a schematic diagram showing the schematic configuration of the power generation system of Modification Example of Embodiment 1. 
         FIG. 8  is a flow chart schematically showing the activation operation of the fuel cell system of the power generation system according to Embodiment 2. 
         FIG. 9  is a schematic diagram showing the schematic configuration of the power generation system according to Embodiment 3 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be explained in reference to the drawings. In the drawings, the same reference signs are used for the same or corresponding components, and a repetition of the same explanation is avoided. Moreover, in the drawings, only components necessary to explain the present invention are shown, and the other components are not shown. Further, the present invention is not limited to the following embodiments. 
     Embodiment 1 
     A power generation system according to Embodiment 1 of the present invention includes: a fuel cell system including a fuel cell, a case, a reformer, and a combustor; a ventilator; a combustion device; a discharge passage; and a controller, and the controller causes the combustion device to operate when the ventilator is in a stop state and then causes the ventilator to operate when the fuel cell system is activated. 
     Here, the expression “when the fuel cell system is activated” denotes “when the fuel cell system starts the activation”. Specifically, for example, the expression “when the fuel cell system is activated” may denote “when a signal is input to the controller such that the activation of the fuel cell system is started” or “when the controller outputs a signal to devices constituting the fuel cell system such that the activation of the fuel cell system is started”. In other words, the expression “when the fuel cell system is activated” denotes a period from when the signal is input to the controller such that the activation operation of the fuel cell system is started until when the controller causes the devices (for example, the combustor) constituting the fuel cell system to start operating. Therefore, the expression “when the fuel cell system is activated” includes a case where the devices (for example, the combustor) constituting the fuel cell system start operating. 
     Moreover, for example, in a case where the fuel cell system performs a DSS operation, the expression “when the fuel cell system is activated” may denote an operation start time of the fuel cell system, the operation start time being preset in the controller. Here, the DSS (Daily Start and Stop) operation denotes an operation in which the fuel cell system repeatedly starts and stops everyday, and the fuel cell system starts operating at a predetermined time and stops at a predetermined time or stops after a predetermined time from the operation start time. 
     Configuration of Power Generation System 
       FIG. 1  is a schematic diagram showing the schematic configuration of the power generation system according to Embodiment 1 of the present invention. 
     As shown in  FIG. 1 , a power generation system  100  according to Embodiment 1 of the present invention is provided in a building  200 . The power generation system  100  includes a fuel cell system  101 , a ventilation fan  13 , a controller  102 , a combustion device  103 , and a discharge passage  70 . The fuel cell system  101  includes a fuel cell  11 , a case  12 , a reformer  14   a , and a combustor  14   b . The discharge passage  70  is formed so as to cause the case  12  of the fuel cell system  101  and an exhaust port  103 A of the combustion device  103  to communicate with each other. Then, the controller  102  causes the combustion device  103  to operate when the ventilation fan  13  is in a stop state and then causes the ventilation fan  13  to operate when the fuel cell system  101  is activated. 
     In Embodiment 1, the power generation system  100  is provided in the building  200 . However, the present embodiment is not limited to this. The power generation system  100  may be provided outside the building  200  as long as the discharge passage  70  is formed so as to cause the case  12  of the fuel cell system  101  and the exhaust port  103 A of the combustion device  103  to communicate with each other. 
     The fuel cell  11 , the ventilation fan  13 , a fuel gas supply unit  14 , and an oxidizing gas supply unit  15  are provided in the case  12  of the fuel cell system  101 . The controller  102  is also provided in the case  12 . In Embodiment 1, the controller  102  is provided in the case  12  of the fuel cell system  101 . However, the present embodiment is not limited to this. The controller  102  may be provided in the combustion device  103  or may be provided separately from the case  12  and the combustion device  103 . 
     A hole  16  penetrating a wall constituting the case  12  in a thickness direction of the wall is formed at an appropriate position of the wall. A pipe constituting the discharge passage  70  is inserted through the hole  16  such that a gap is formed between the hole  16  and the discharge passage  70 . The gap between the hole  16  and the discharge passage  70  constitutes an air supply port  16 . With this, the air outside the power generation system  100  is supplied through the air supply port  16  to the inside of the case  12 . 
     In Embodiment 1, the hole through which the pipe constituting the discharge passage  70  is inserted and the hole constituting the air supply port  16  are constituted by one hole  16 . However, the present embodiment is not limited to this. The hole through which the pipe constituting the discharge passage  70  is inserted and the hole constituting the air supply port  16  may be separately formed on the case  12 . The air supply port  16  may be constituted by one hole on the case  12  or may be constituted by a plurality of holes on the case  12 . 
     The fuel gas supply unit  14  is configured to supply the fuel gas (hydrogen gas) to the fuel cell  11  while adjusting the flow rate of the fuel gas. Used as the fuel gas supply unit  14  is a hydrogen generator including the reformer  14   a  configured to generate the fuel gas from a hydrocarbon gas that is a raw material and steam and the combustor  14   b  configured to heat the reformer  14   a . The combustor  14   b  is constituted by a burner, a combustion catalyst, or the like. 
     In Embodiment 1, the fuel cell  11  (to be precise, an inlet of a fuel gas channel  11 A of the fuel cell  11 ) is connected to the fuel gas supply unit  14  through a fuel gas supply passage  71 . 
     The oxidizing gas supply unit  15  may have any configuration as long as it can supply an oxidizing gas (air) to the fuel cell  11  while adjusting the flow rate of the oxidizing gas. The oxidizing gas supply unit  15  may be constituted by a fan, a blower, or the like. The fuel cell  11  (to be precise, an inlet of an oxidizing gas channel  11 B of the fuel cell  11 ) is connected to the oxidizing gas supply unit  15  through an oxidizing gas supply passage  72 . 
     The fuel cell  11  includes an anode and a cathode (both not shown). In the fuel cell  11 , the fuel gas supplied to the fuel gas channel  11 A is supplied to the anode while the fuel gas is flowing through the fuel gas channel  11 A. The oxidizing gas supplied to the oxidizing gas channel  11 B is supplied to the cathode while the oxidizing gas is flowing through the oxidizing gas channel  11 B. The fuel gas supplied to the anode and the oxidizing gas supplied to the cathode react with each other to generate electricity and heat. 
     The generated electricity is supplied to an external electric power load (for example, a home electrical apparatus) by an electric power conditioner, not shown. The generated heat is recovered by a heat medium flowing through a heat medium channel, not shown. The heat recovered by the heat medium can be used to, for example, heat water. 
     In Embodiment 1, each of various fuel cells, such as a polymer electrolyte fuel cell, a direct internal reforming type solid-oxide fuel cell, and an indirect internal reforming type solid-oxide fuel cell, may be used as the fuel cell  11 . In Embodiment 1, the fuel cell  11  and the fuel gas supply unit  14  are configured separately. However, the present embodiment is not limited to this. Like a solid-oxide fuel cell, the fuel gas supply unit  14  and the fuel cell  11  may be configured integrally. In this case, the fuel cell  11  and the fuel gas supply unit  14  are configured as one unit covered with a common heat insulating material, and the combustor  14   b  can heat not only the reformer  14   a  but also the fuel cell  11 . In the direct internal reforming type solid-oxide fuel cell, since the anode of the fuel cell  11  has the function of the reformer  14   a , the anode of the fuel cell  11  and the reformer  14   a  may be configured integrally. Further, since the configuration of the fuel cell  11  is similar to that of a typical fuel cell, a detailed explanation thereof is omitted. 
     An upstream end of an off fuel gas passage  73  is connected to an outlet of the fuel gas channel  11 A. A downstream end of the off fuel gas passage  73  is connected to the discharge passage  70 . An upstream end of an off oxidizing gas passage  74  is connected to an outlet of the oxidizing gas channel  11 B. A downstream end of the off oxidizing gas passage  74  is connected to the discharge passage  70 . 
     With this, the fuel gas unconsumed in the fuel cell  11  (hereinafter referred to as an “off fuel gas”) is discharged from the outlet of the fuel gas channel  11 A through the off fuel gas passage  73  to the discharge passage  70 . The oxidizing gas unconsumed in the fuel cell  11  (hereinafter referred to as an “off oxidizing gas”) is discharged from the outlet of the oxidizing gas channel  11 B through the off oxidizing gas passage  74  to the discharge passage  70 . The off fuel gas discharged to the discharge passage  70  is diluted by the off oxidizing gas to be discharged to the outside of the building  200 . 
     The ventilation fan  13  is connected to the discharge passage  70  through a ventilation passage  75 . The ventilation fan  13  may have any configuration as long as it can ventilate the inside of the case  12 . With this, the air outside the power generation system  100  is supplied through the air supply port  16  to the inside of the case  12 , and the gas (mainly, air) in the case  12  is discharged through the ventilation passage  75  and the discharge passage  70  to the outside of the building  200  by activating the ventilation fan  13 . Thus, the inside of the case  12  is ventilated. 
     In Embodiment 1, the fan is used as a ventilator. However, the present embodiment is not limited to this. A blower may be used as the ventilator. The ventilation fan  13  is provided in the case  12 . However, the present embodiment is not limited to this. The ventilation fan  13  may be provided in the discharge passage  70 . In this case, it is preferable that the ventilation fan  13  be provided upstream of a branch portion of the discharge passage  70 . 
     The combustion device  103  includes a combustor  17  and a combustion fan (combustion air supply unit)  18 . The combustor  17  and the combustion fan  18  are connected to each other through a combustion air supply passage  76 . The combustion fan  18  may have any configuration as long as it can supply combustion air to the combustor  17 . The combustion fan  18  may be constituted by a fan, a blower, or the like. 
     A combustible gas, such as a natural gas, and a combustion fuel, such as a liquid fuel, are supplied to the combustor  17  from a combustion fuel supply unit, not shown. One example of the liquid fuel is kerosene. The combustor  17  combusts the combustion air supplied from the combustion fan  18  and the combustion fuel supplied from the combustion fuel supply unit to generate heat and a flue gas. The generated heat can be used to heat water. To be specific, the combustion device  103  may be used as a boiler. 
     An upstream end of an exhaust gas passage  77  is connected to the combustor  17 , and a downstream end of the exhaust gas passage  77  is connected to the discharge passage  70 . With this, the flue gas generated in the combustor  17  is discharged through the exhaust gas passage  77  to the discharge passage  70 . To be specific, the flue gas generated in the combustor  17  is discharged to the discharge passage  70  as the exhaust gas discharged from the combustion device  103 . The flue gas discharged to the discharge passage  70  flows through the discharge passage  70  to be discharged to the outside of the building  200 . 
     A hole  19  penetrating a wall constituting the combustion device  103  in a thickness direction of the wall is formed at an appropriate position of the wall. A pipe constituting the discharge passage  70  is inserted through the hole  19  such that a gap is formed between the hole  19  and the discharge passage  70 . The gap between the hole  19  and the discharge passage  70  constitutes an air supply port  19 . With this, the air outside the power generation system  100  is supplied through the air supply port  19  to the inside of the combustion device  103 . 
     To be specific, the discharge passage  70  branches, and two upstream ends thereof are respectively connected to the hole  16  and the hole  19 . The discharge passage  70  is formed to extend up to the outside of the building  200 , and a downstream end (opening) thereof is open to the atmosphere. With this, the discharge passage  70  causes the case  12  and the exhaust port  103 A of the combustion device  103  to communicate with each other. 
     In Embodiment 1, the hole through which the pipe constituting the discharge passage  70  is inserted and the hole constituting the air supply port  19  are constituted by one hole  19 . However, the present embodiment is not limited to this. The hole through which the pipe constituting the discharge passage  70  is inserted (the hole to which the pipe constituting the discharge passage  70  is connected) and the hole constituting the air supply port  19  may be separately formed on the combustion device  103 . The air supply port  19  may be constituted by one hole on the combustion device  103  or may be constituted by a plurality of holes on the combustion device  103 . 
     The controller  102  may be any device as long as it controls respective devices constituting the power generation system  100 . The controller  102  includes a calculation processing portion, such as a microprocessor or a CPU, and a storage portion, such as a memory, configured to store programs for executing respective control operations. In the controller  102 , the calculation processing portion reads out and executes a predetermined control program stored in the storage portion. Thus, the controller  102  processes the information and performs various control operations, such as the above control operations, regarding the power generation system  100 . 
     The controller  102  may be constituted by a single controller or may be constituted by a group of a plurality of controllers which cooperate to execute control operations of the power generation system  100 . For example, the controller  102  may be configured to control the ventilation fan  13 , and the other controllers may be configured to control the devices of the power generation system  100  except for the ventilation fan  13 . The controller  102  may be constituted by a microcontroller or may be constituted by a MPU, a PLC (Programmable Logic Controller), a logic circuit, or the like. 
     Operations of Power Generation System 
     Next, the operations of the power generation system  100  according to Embodiment 1 will be explained in reference to  FIGS. 1 and 2 . Since the electric power generating operation of the fuel cell system  101  of the power generation system  100  is performed in the same manner as the electric power generating operation of a typical fuel cell system, a detailed explanation thereof is omitted. Embodiment 1 is explained on the basis that the controller  102  is constituted by one controller and the controller controls respective devices constituting the power generation system  100 . 
       FIG. 2  is a flow chart schematically showing the activation operation of the fuel cell system of the power generation system according to Embodiment 1. 
     As shown in  FIG. 2 , the controller  102  confirms whether or not an activation command of the fuel cell system  101  is input (Step S 101 ). Here, examples of a case where the activation command of the fuel cell system  101  is input are a case where a user of the power generation system  100  operates a remote controller, not shown, to instruct the activation of the fuel cell system  101  and a case where a preset operation start time of the fuel cell system  101  has come. 
     In a case where the activation command of the fuel cell system  101  is not input (No in Step S 101 ), the controller  102  repeats Step S 101  until the activation command of the fuel cell system  101  is input. In contrast, in a case where the activation command of the fuel cell system  101  is input (Yes in Step S 101 ), the controller  102  proceeds to Step S 102 . 
     In Step S 102 , the controller  102  determines whether or not the combustion device  103  has operated when the ventilation fan  13  is in a stop state. Specifically, for example, based on whether or not a storage portion, not shown, stores information that the activation command of the combustion device  103  has been output after a stop command of the ventilation fan  13  has been output, the controller  102  can determine whether or not the combustion device  103  has operated when the ventilation fan  13  is in a stop state. Whether or not the operation of the combustion device  103  is continuing while the present program is being executed does not matter. 
     In a case where the combustion device  103  has not operated when the ventilation fan  13  is in a stop state (No in Step S 102 ), the controller  102  can consider that the exhaust gas from the combustion device  103  has not flowed into the case  12 . Therefore, the present program is terminated. In contrast, in a case where the combustion device  103  has operated when the ventilation fan  13  is in a stop state (Yes in Step S 102 ), the controller  102  proceeds to Step S 103 . 
     In Step S 103 , the controller  102  activates the ventilation fan  13 . With this, the gas in the case  12  flows through the ventilation passage  75  and the discharge passage  70  to be discharged to the outside of the building  200 . In addition, the air outside the case  12  flows through the air supply port  16  into the case  12 . 
     It is preferable that when the combustion device  103  is operating, the controller  102  control an operation amount of the ventilation fan  13  such that the gas in the case  12  is discharged to the discharge passage  70 . Specifically, the controller  102  controls the operation amount of the ventilation fan  13  such that an air flow rate of the ventilation fan  13  becomes equal to or higher than a predetermined first air flow rate. Here, the first air flow rate is obtained in advance by experiments or the like and may be, for example, the highest air flow rate of the combustion fan  18  or the flow rate of the exhaust gas at the time of a steady operation of the combustion device  103 . 
     Next, the controller  102  outputs an activation start command to each of devices constituting the fuel cell system  101  (Step S 104 ) and terminates the present program. With this, the activation operation of the fuel cell system  101  is started. Specifically, the combustion fuel (for example, a natural gas) and the combustion air are supplied to the combustor  14   a  of the fuel gas supply unit  14 . The combustor  14   a  combusts the combustion fuel and the combustion air to generate the flue gas. The reformer  14   a  is heated by heat transfer from the generated flue gas. Then, when the temperature of the reformer  14   a  reaches a temperature at which the raw material (for example, hydrocarbon, such as methane) can be reformed, the raw material and the steam are supplied to the reformer  14   a The reformer  14   a  causes a reforming reaction between the supplied raw material and steam to generate the fuel gas. The generated fuel gas is supplied through the fuel gas supply passage  71  to the fuel cell  11  (to be precise, the fuel gas channel  11 A). The oxidizing gas is supplied from the oxidizing gas supply unit  15  through the oxidizing gas supply passage  72  to the fuel cell  11  (to be precise, the oxidizing gas channel  11 B). 
     As above, in the power generation system  100  according to Embodiment 1, even if the exhaust gas from the combustion device  103  flows through the discharge passage  70  into the case  12  by operating the combustion device  103  when the ventilation fan  13  is in a stop state, the exhaust gas in the case  12  can be discharged to the outside of the case  12  by operating the ventilation fan  13  when the fuel cell system  101  is activated. 
     Therefore, in the power generation system  100  according to Embodiment 1, since the inside of the case  12  is ventilated, the decrease in the oxygen concentration in the case  12  and the ignition failure of the combustor  14   a  can be suppressed, and the reliability of the power generation system  100  can be improved. 
     Here, in a case where a desulfurizer configured to desulfurize a sulfur compound contained in a natural gas or the like is not provided in the combustion device  103 , SO X  is generated by the combustion operation of the combustion device  103 . Then, if the generated SO X  flows through the discharge passage  70  into the case  12  to be supplied to the reformer  14   a  of the fuel gas supply unit  14  together with the combustion air, the poisoning of the catalyst contained in the reformer  14   a  may be accelerated. 
     However, in the power generation system  100  according to Embodiment 1, as described above, the exhaust gas (containing SO X ) from the combustion device  103  is discharged to the outside of the case  12 . Therefore, the SO X  is prevented from being supplied to the reformer  14   a . On this account, the poisoning of the reformer  14   a  and the decrease in the efficiency of the reforming of the reformer  14   a  can be suppressed, and the durability of the power generation system  100  can be improved. 
     In Embodiment 1, the discharge passage  70 , the off fuel gas passage  73 , the off oxidizing gas passage  74 , and the exhaust gas passage  77  are explained as different passages. However, the present embodiment is not limited to this. These passages may be regarded as one discharge passage  70 . 
     In Embodiment 1, as a method of determining by the controller  102  whether or not the combustion device  103  has operated, the method of determining whether or not the combustion device  103  has operated by determining whether or not the information that the activation command of the combustion device  103  is output is stored is exemplified. However, the present embodiment is not limited to this. Examples of the method of determining whether or not the combustion device  103  has operated are a method of utilizing information (data or signal) output from the combustion device  103  and a method of utilizing information (data or signal) input to the combustion device  103 . 
     One example of the method of utilizing the output information is a method of utilizing information from an operation detector configured to detect that the combustion device  103  has operated. Hereinafter, cases where the operation detector is a temperature detector, the operation detector is a pressure detector, the operation detector is a gas concentration detector, and the operation detector is a sound detector will be explained in reference to  FIGS. 3 to 6 . 
       FIG. 3  is a schematic diagram showing an example in which the temperature detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
     As shown in  FIG. 3 , a temperature sensor  51  is provided on at least one of the discharge passage  70 , the off fuel gas passage  73 , the off oxidizing gas passage  74 , and the ventilation passage  75  (in  FIG. 3 , the temperature sensor  51  is provided on the discharge passage  70 ), and based on a temperature detected by the temperature sensor  51 , the controller  102  determines whether or not the combustion device  103  has operated. 
     Specifically, the temperature sensor  51  detects the temperature of the exhaust gas flowing through the passage (herein, the discharge passage  70 ) and outputs the detected temperature to the controller  102 . In a case where the input temperature is equal to or higher than a predetermined threshold temperature T 1  or in a case where a difference between the temperatures before and after a predetermined time is equal to or higher than a predetermined threshold temperature T 2 , the controller  102  determines that the combustion device  103  has operated. 
     Here, the predetermined threshold temperature T 1  is a temperature value obtained in advance by experiments or the like and is suitably set depending on the installation location of the temperature sensor  51 . Similarly, the predetermined threshold temperature T 2  is a temperature value obtained in advance by experiments or the like and is suitably set depending on the installation location of the temperature sensor  51 . 
       FIG. 4  is a schematic diagram showing an example in which the pressure detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
     As shown in  FIG. 4 , a pressure sensor  52  is provided on at least one of the discharge passage  70 , the off fuel gas passage  73 , the off oxidizing gas passage  74 , and the ventilation passage  75  (in  FIG. 4 , the pressure sensor  52  is provided on the discharge passage  70 ), and based on a pressure detected by the pressure sensor  52 , the controller  102  determines whether or not the combustion device  103  has operated. Specifically, the pressure sensor  52  detects the pressure in the passage (herein, the discharge passage  70 ) and outputs the detected pressure to the controller  102 . In a case where the input pressure is equal to or higher than a predetermined threshold pressure P 1  or in a case where a difference between the pressures before and after a predetermined time is equal to or higher than a predetermined threshold pressure P 2 , the controller  102  determines that the combustion device  103  has operated. 
     Here, the predetermined threshold pressure P 1  is a pressure value obtained in advance by experiments or the like and is suitably set depending on the installation location of the pressure sensor  52 . Similarly, the predetermined threshold pressure P 2  is a pressure value obtained in advance by experiments or the like and is suitably set depending on the installation location of the pressure sensor  52 . 
       FIG. 5  is a schematic diagram showing an example in which the gas concentration detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
     As shown in  FIG. 5 , a gas concentration sensor  53  is provided on at least one of the discharge passage  70 , the off fuel gas passage  73 , the off oxidizing gas passage  74 , and the ventilation passage  75  (in  FIG. 5 , the gas concentration sensor  53  is provided on the discharge passage  70 ), and based on an exhaust gas (for example, CO 2  or SO X ) concentration detected by the gas concentration sensor  53 , the controller  102  determines whether or not the combustion device  103  has operated. Specifically, the gas concentration sensor  53  detects the concentration of the exhaust gas in the passage (herein, the discharge passage  70 ) and outputs the detected concentration of the exhaust gas to the controller  102 . In a case where the input concentration of the exhaust gas is equal to or higher than a predetermined threshold concentration C 1  or in a case where a difference between the concentrations before and after a predetermined time is equal to or higher than a predetermined threshold concentration C 2 , the controller  102  determines that the combustion device  103  has operated. 
     Here, the predetermined threshold concentration C 1  is a concentration value obtained in advance by experiments or the like and can be suitably calculated from, for example, the concentration of hydrocarbons contained in the combustion fuel supplied to the combustion device  103  and the number of carbons contained in the combustion fuel supplied to the combustion device  103  or the concentration of sulfur constituents contained in the combustion fuel supplied to the combustion device  103 . Similarly, the predetermined threshold concentration C 2  is a concentration value obtained in advance by experiments or the like and can be suitably calculated from, for example, the concentration of hydrocarbons contained in the combustion fuel supplied to the combustion device  103  and the number of carbons contained in the combustion fuel supplied to the combustion device  103  or the concentration of sulfur constituents contained in the combustion fuel supplied to the combustion device  103 . 
       FIG. 6  is a schematic diagram showing an example in which the sound detector is used as the operation detector in the power generation system shown in  FIG. 1 . 
     As shown in  FIG. 6 , one example is a method in which: a sound sensor  54  is provided on at least one of the discharge passage  70 , the off fuel gas passage  73 , the off oxidizing gas passage  74 , and the ventilation passage  75  (in  FIG. 6 , the sound sensor  54  is provided on the discharge passage  70 ); and based on a sound pressure detected by the sound sensor  54 , the controller  102  determines whether or not the combustion device  103  has operated. Specifically, when the ventilation fan  13  is in a stop state, the sound sensor  54  detects the sound pressure transmitting in the passage (herein, the discharge passage  70 ) and outputs the detected sound pressure to the controller  102 . In a case where the input sound pressure is equal to or higher than a predetermined threshold sound pressure SP 1  or in a case where a difference between the sound pressures before and after a predetermined time is equal to or higher than a predetermined threshold sound pressure SP 2 , the controller  102  determines that the combustion device  103  has operated. 
     Here, the predetermined threshold sound pressure SP 1  is a sound pressure value (pressure value) or sound pressure level obtained in advance by experiments or the like and is suitably set depending on the installation location of the sound sensor  54 . Similarly, the predetermined threshold sound pressure SP 2  is a sound pressure value (pressure value) or sound pressure level obtained in advance by experiments or the like and is suitably set depending on the installation location of the sound sensor  54 . 
     In contrast, one example of the method of utilizing the input information is a method in which: a flow rate detector (gas meter) configured to detect the flow rate of the combustion fuel (for example, a natural gas) supplied to the combustion device  103  is provided; and whether or not the combustion device  103  has operated is determined based on the flow rate detected by the flow rate detector. Specifically, the flow rate detector detects the flow rate of the combustion fuel supplied to the combustion device  103  and outputs the detected flow rate to the controller  102 . In a case where the input flow rate is equal to or higher than a predetermined threshold flow rate F 1  or in a case where a difference between the flow rates before and after a predetermined time is equal to or higher than a predetermined threshold flow rate F 2 , the controller  102  determines that the combustion device  103  has operated. 
     Another example is a method in which: an electric power detector (at least one of a voltage detector and a current detector) configured to detect electric power supplied to the combustion device  103  is provided; and whether or not the combustion device  103  has operated is determined based on an electric power value (a voltage value or a current value) detected by the electric power detector. Specifically, the electric power detector detects the electric power value that is the value of the electric power supplied to the combustion device  103  and outputs the detected electric power value to the controller  102 . In a case where the input electric power value is equal to or higher than a predetermined threshold electric power value E 1  or in a case where a difference between the electric power values before and after a predetermined time is equal to or higher than a predetermined threshold electric power value E 2 , the controller  102  determines that the combustion device  103  has operated. 
     Yet another example is a method in which in a case where a remote controller configured to command the operation of the combustion device  103  by a user is provided, the controller  102  determines whether or not the combustion device  103  has operated, based on information regarding whether or not the operation of the combustion device  103  is commanded from the remote controller. Specifically, in a case where the controller  102  obtains information that an operation command is output from the remote controller to the combustion device  103 , the controller  102  determines that the combustion device  103  has operated. 
     An example other than the above examples is a method in which in a case where the combustion device  103  is used as a boiler, a temperature sensor is provided on a water passage through which water heated by the combustion device  103  flows, and whether or not the combustion device  103  has operated is determined based on the temperature detected by the temperature sensor. Specifically, the temperature sensor detects the temperature of the water flowing through the water passage and outputs the detected temperature to the controller  102 . Specifically, in a case where the input temperature is equal to or higher than a predetermined threshold temperature T 3  or in a case where a difference between the temperatures before and after a predetermined time is equal to or higher than a predetermined threshold temperature T 4 , the controller  102  can determine that the heat is being supplied from the combustion device  103 . Thus, the controller  102  determines that the combustion device  103  has operated. 
     Modification Example 
     Next, Modification Example of the power generation system  100  according to Embodiment 1 will be explained. 
     The power generation system of Modification Example includes an air intake passage formed to cause the case and the combustion device to communicate with each other and configured to supply air to the fuel cell system and the combustion device from outside, and the air intake passage is formed so as to be heat-exchangeable with the exhaust passage. 
     Here, the expression “the air intake passage is formed so as to be heat-exchangeable with the discharge passage” denotes that the air intake passage and the discharge passage do not have to contact each other and may be spaced apart from each other to a level that the gas in the air intake passage and the gas in the exhaust passage are heat-exchangeable with each other. Therefore, the air intake passage and the discharge passage may be formed with a space therebetween. Or, one of the air intake passage and the discharge passage may be formed inside the other. To be specific, a pipe constituting the air intake passage and a pipe constituting the exhaust passage may be formed as a double pipe. 
     Configuration of Power Generation System 
       FIG. 7  is a schematic diagram showing the schematic configuration of the power generation system of Modification Example of Embodiment 1. In  FIG. 7 , the air intake passage is shown by hatching. 
     As shown in  FIG. 7 , the power generation system  100  of Modification Example is the same in basic configuration as the power generation system  100  according to Embodiment 1 but is different from the power generation system  100  according to Embodiment 1 in that an air intake passage  78  is formed. Specifically, the air intake passage  78  is formed so as to: cause the combustion device  103  and the case  12  of the fuel cell system  101  to communicate with each other: supply air to the combustion device  103  and the fuel cell system  101  from the outside (herein, the outside of the building  200 ); and surround an outer periphery of the discharge passage  70 . To be specific, the air intake passage  78  and the discharge passage  70  are constituted by a so-called double pipe. 
     More specifically, the air intake passage  78  branches, and two upstream ends thereof are respectively connected to the hole  16  and the hole  19 . The air intake passage  78  is formed to extend up to the outside of the building  200 , and a downstream end (opening) thereof is open to the atmosphere. With this, the air intake passage  78  causes the case  12  and the combustion device  103  to communicate with each other, and the air can be supplied from the outside of the power generation system  100  to the fuel cell system  101  and the combustion device  103 . 
     The power generation system  100  of Modification Example configured as above also has the same operational advantages as the power generation system  100  according to Embodiment 1. 
     Embodiment 2 
     In the power generation system according to Embodiment 2 of the present invention, when the fuel cell system is activated, the controller causes the ventilator to discharge to the discharge passage a gas having a volume equal to or larger than the volume of the case. 
     Since the configuration of the power generation system  100  according to Embodiment 2 of the present invention is the same as that of the power generation system  100  according to Embodiment 1, an explanation thereof is omitted. 
       FIG. 8  is a flow chart schematically showing the activation operation of the fuel cell system of the power generation system according to Embodiment 2. 
     As shown in  FIG. 8 , Steps S 201  to S 203  in the power generation system  100  according to Embodiment 2 are respectively the same as Steps S 101  to S 103  of the activation operation of the fuel cell system  101  of the power generation system  100  according to Embodiment 1. 
     When the ventilation fan  13  is activated in Step S 203 , the controller  102  obtains an operation time t of the ventilation fan  13  (Step S 204 ). Next, the controller  102  determines whether or not the operation time t obtained in Step S 204  is equal to or longer than a first time t 1  (Step S 205 ). Here, the first time t 1  is a time necessary to discharge the gas having a volume equal to or larger than the volume of the case  12  through the ventilation passage  75  and the discharge passage  70  to the outside of the building  200  and is suitably set depending on the operation amount of the ventilation fan  13 . 
     In a case where the operation time t obtained in Step S 204  is shorter than the first time t 1  (No in Step S 205 ), the controller  102  returns to Step S 204  and repeats Steps S 204  and S 205  until the operation time t becomes equal to or longer than the first time t 1 . In contrast, in a case where the operation time t obtained in Step S 204  is equal to or longer than the first time t 1  (Yes in Step S 205 ), the controller  102  proceeds to Step S 206 . 
     In Step S 206 , the controller  102  outputs the activation start command to each of the devices constituting the fuel cell system  101  and terminates the present program. With this, the activation operation of the fuel cell system  101  is started. 
     As above, in the power generation system  100  according to Embodiment 2, the controller  102  controls the ventilation fan  13  such that the gas having a volume equal to or larger than the volume of the case  12  is discharged to the discharge passage  70 . With this, the exhaust gas in the case  12  from the combustion device  103  can be discharged to the outside of the case  12  and therefore to the outside of the building  200 . Therefore, in the power generation system  100  according to Embodiment 2, the ignition failure of the reformer  14   a  of the fuel gas supply unit  14  can be suppressed, and the reliability of the power generation system  100  can be improved. 
     Embodiment 3 
     The power generation system according to Embodiment 3 of the present invention is configured such that the fuel cell system further includes a hydrogen generator including a reformer configured to generate a hydrogen-containing gas from a raw material and steam and a combustor configured to heat the reformer. 
     Configuration of Power Generation System 
       FIG. 9  is a schematic diagram showing the schematic configuration of the power generation system according to Embodiment 3 of the present invention. 
     As shown in  FIG. 9 , the power generation system  100  according to Embodiment 3 of the present invention is the same in basic configuration as the power generation system  100  according to Embodiment 1 but is different from the power generation system  100  according to Embodiment 1 in that: the fuel gas supply unit  14  is constituted by a hydrogen generator  14 ; and the off fuel gas passage  73  is connected to the combustor  14   b  of the hydrogen generator  14 . Specifically, the hydrogen generator  14  includes the reformer  14   a  and the combustor  14   b.    
     The downstream end of the off fuel gas passage  73  is connected to the combustor  14   b . The off fuel gas flows from the fuel cell  11  through the off fuel gas passage  73  to be supplied to the combustor  14   b  as the combustion fuel. A combustion fan  14   c  is connected to the combustor  14   b  through an air supply passage  79 . The combustion fan  14   c  may have any configuration as long as it can supply the combustion air to the combustor  14   b . For example, the combustion fan  14   c  may be constituted by a fan, a blower, or the like. 
     The combustor  14   b  combusts the supplied off fuel gas and combustion air to generate the flue gas and heat. The flue gas generated in the combustor  14   b  heats the reformer  14   a  and the like, and then, is discharged to a flue gas passage  80 . The flue gas discharged to the flue gas passage  80  flows through the flue gas passage  80  to be discharged to the discharge passage  70 . The flue gas discharged to the discharge passage  70  flows through the discharge passage  70  to be discharged to the outside of the power generation system  100  (the building  200 ). 
     A raw material supply unit and a steam supply unit (both not shown) are connected to the reformer  14   a , and the raw material and the steam are supplied to the reformer  14   a  Examples of the raw material are a natural gas containing methane as a major component and a LP gas containing propane as a major component. 
     The reformer  14   a  includes a reforming catalyst. The reforming catalyst may be any material as long as, for example, it can serve as a catalyst in a steam-reforming reaction by which the hydrogen-containing gas is generated from the raw material and the steam. Examples of the reforming catalyst are a ruthenium-based catalyst in which a catalyst carrier, such as alumina, supports ruthenium (Ru) and a nickel-based catalyst in which the same catalyst carrier as above supports nickel (Ni). A catalyst capable of performing an autothermal reforming reaction may be used as the reforming catalyst of the reformer  14   a.    
     In the reformer  14   a , the hydrogen-containing gas is generated by the reforming reaction between the supplied raw material and steam. The generated hydrogen-containing gas flows as the fuel gas through the fuel gas supply passage  71  to be supplied to the fuel gas channel  11 A of the fuel cell  11 . 
     Embodiment 3 is configured such that the hydrogen-containing gas generated in the reformer  14   a  is supplied as the fuel gas to the fuel cell  11 . However, the present embodiment is not limited to this. Embodiment 3 may be configured such that the hydrogen-containing gas flowed through a shift converter or carbon monoxide remover provided in the hydrogen generator  14  is supplied to the fuel cell  11 , the shift converter including a shift catalyst (such as a copper-zinc-based catalyst) for reducing carbon monoxide in the hydrogen-containing gas supplied from the reformer  14   a , the carbon monoxide remover including an oxidation catalyst (such as a ruthenium-based catalyst) or a methanation catalyst (such as a ruthenium-based catalyst). 
     The activation operation of the fuel cell system  101  of the power generation system  100  according to Embodiment 3 is performed in the same manner as the activation operation of the fuel cell system  101  of the power generation system  100  according to Embodiment 1. However, since the fuel gas supply unit  14  is constituted by a hydrogen generator, operations after the activation start command is output to each of the devices constituting the fuel cell system  101  in Step S 104  are as below. 
     To be specific, when the activation start command is output from the controller  102 , the combustion air is supplied from the combustion fan  14   c  to the combustor  14   b . In addition, the combustion fuel (for example, a material gas) is supplied from a material gas supply unit, not shown, to the combustor  14   b . Then, the combustor  14   b  combusts the combustion fuel and the combustion air to generate the flue gas. The flue gas generated in the combustor  14   b  heats the reformer  14   a  and the like and then flows through the flue gas passage  80  and the discharge passage  70  to be discharged to the outside of the building  200 . 
     Next, the raw material (for example, hydrocarbon of a natural gas) and the steam are supplied to the reformer  14   a , and the hydrogen-containing gas is generated by the steam-reforming reaction. The generated hydrogen-containing gas flows as the fuel gas through the fuel gas supply passage  71  to be supplied to the fuel gas channel  11 A of the fuel cell  11 . In addition, the oxidizing gas (air) is supplied from the oxidizing gas supply unit  15  through the oxidizing gas supply passage  72  to the oxidizing gas channel  11 B. In the fuel cell  11 , the supplied fuel gas and oxidizing gas electrochemically react with each other. Thus, electricity and heat are generated. 
     The fuel gas unconsumed in the fuel cell  11  flows through the off fuel gas passage  73  to be supplied to the combustor  14   b . The oxidizing gas unconsumed in the fuel cell  11  flows through the off fuel gas passage  73  and the discharge passage  70  to be discharged to the outside of the building  200 . 
     The power generation system  100  according to Embodiment 3 configured as above also has the same operational advantages as the power generation system  100  according to Embodiment 1. In addition, the inside of the case  12  is ventilated. Therefore, the decrease in the oxygen concentration in the case  12  and the ignition failure of the combustor  14   b  of the hydrogen generator  14  can be suppressed, and the reliability of the power generation system  100  can be improved. 
     In Embodiments 1 to 3 (including Modification Examples), the ventilation fan  13  is used as a ventilator. However, these embodiments are not limited to this. For example, the oxidizing gas supply unit  15  may be used instead of the ventilation fan  13 . In a case where the fuel gas supply unit  14  is constituted by a hydrogen generator and the hydrogen generator includes the combustor  14   b  and the combustion fan  14   c , the combustion fan  14   c  may be used as a ventilator instead of the ventilation fan  13 . 
     Further, as a ventilator, the ventilation fan  13  and the oxidizing gas supply unit  15  may be used at the same time, the ventilation fan  13  and the combustion fan  14   c  may be used at the same time, the combustion fan  14   c  and the oxidizing gas supply unit  15  may be used at the same time, or the ventilation fan  13 , the combustion fan  14   c , and the oxidizing gas supply unit  15  may be used at the same time. 
     From the foregoing explanation, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Therefore, the foregoing explanation should be interpreted only as an example and is provided for the purpose of teaching the best mode for carrying out the present invention to one skilled in the art. The structures and/or functional details may be substantially modified within the spirit of the present invention. In addition, various inventions can be made by suitable combinations of a plurality of components disclosed in the above embodiments. 
     INDUSTRIAL APPLICABILITY 
     According to the power generation system of the present invention and the method of operating the power generation system, the ignition failure of the combustor of the fuel cell system can be suppressed, and the reliability of the power generation system can be improved. Therefore, the power generation system of the present invention and the method of operating the power generation system are useful in the field of fuel cells. 
     REFERENCE SIGNS LIST 
     
         
         
           
               11  fuel cell 
               11 A fuel gas channel 
               11 B oxidizing gas channel 
               12  case 
               13  ventilation fan 
               14  fuel gas supply unit 
               14   a  reformer 
               14   b  combustor 
               14   c  combustion fan 
               15  oxidizing gas supply unit 
               16  air supply port 
               17  combustor 
               18  combustion fan 
               19  air supply port 
               70  discharge passage 
               71  fuel gas supply passage 
               72  oxidizing gas supply passage 
               73  off fuel gas passage 
               74  off oxidizing gas passage 
               75  ventilation passage 
               76  combustion air supply passage 
               77  exhaust gas passage 
               78  air intake passage 
               79  air supply passage 
               80  flue gas passage 
               100  power generation system 
               101  fuel cell system 
               102  controller 
               103  combustion device 
               103 A exhaust port 
               200  building