Patent Publication Number: US-2022223890-A1

Title: Fuel cell system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of International Application PCT/JP2020/044500 filed on Nov. 30, 2020, which claims priority from a Japanese Patent Application No. 2019-234466 filed on Dec. 25, 2019, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to a fuel cell system. 
     Background Art 
     Recently, the development of solid oxide fuel cells (SOFCs) is progressing. An SOFC is a power generation mechanism in which electrical energy is generated by causing oxide ions generated by an air electrode to pass through an electrolyte and move to a fuel electrode, such that the oxide ions react with hydrogen or carbon monoxide at the fuel electrode. SOFCs have the characteristics of having the highest operating temperatures for power generation (for example, from 900° C. to 1000° C.) and also the highest power-generating efficiency among currently known classes of fuel cells. 
     Patent Literature 1 discloses a solid oxide fuel cell that controls a water supplying apparatus such that water evaporation continues even after fuel supply is stopped, thereby inhibiting a pressure drop on the fuel electrode side of the fuel cell stacks. In this solid oxide fuel cell, the execution of a shutdown stop is attained while also sufficiently inhibiting oxidation of the fuel cells. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Laid-Open No. 2013-225484 
     SUMMARY OF INVENTION 
     However, in the solid oxide fuel cell described in Patent Literature 1, the water supplying apparatus is controlled even after the fuel supply is stopped. Consequently, the technology of Patent Literature 1 is expected to be controllable even after shutdown, and does not anticipate a blackout situation caused by a loss of a control power source or a loss of control by a control device. Moreover, the technology of Patent Literature 1 prevents a loss of pressure at the fuel electrode, but in the case of a high fuel cell temperature, the reaction inside the solid oxide fuel cell will progress and the fuel electrode will be degraded by oxidation, and consequently it is necessary to cool the solid oxide fuel cell. 
     An object of the present invention, which has been made in the light of such points, is to provide a fuel cell system that can prevent degradation in a solid oxide fuel cell, even in the case where a blackout occurs. 
     In one aspect, a fuel cell system according to the embodiments comprises a fuel cell module including a solid oxide fuel cell stack that generates electricity through an electrochemical reaction between a fuel gas and an oxidant gas, a control unit that controls the fuel cell module; 
     a detection unit for detecting a loss of control by the control unit, and an opening and closing apparatus configured to maintain gases inside the fuel cell module, and upon the detection unit detecting a loss of control of the control unit, release the gases from inside to outside the fuel cell module. 
     According to the present invention, it is possible to provide a fuel cell system that can prevent degradation in a solid oxide fuel cell, even in the case where a blackout occurs. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a fuel cell system according to a first embodiment. 
         FIG. 2  is a block diagram illustrating a fuel cell system according to a second embodiment. 
         FIG. 3  is a block diagram illustrating a fuel cell system according to a third embodiment. 
         FIG. 4  is a block diagram illustrating a fuel cell system according to a fourth embodiment. 
         FIG. 5  is a block diagram illustrating a fuel cell system according to a fifth embodiment. 
         FIG. 6  is a block diagram illustrating a fuel cell system according to a sixth embodiment. 
         FIG. 7  is a block diagram illustrating a fuel cell system according to a seventh embodiment. 
         FIG. 8  is a block diagram illustrating a fuel cell system according to an eighth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, a fuel cell system  100  according to the present embodiment will be described in detail with reference to the accompanying drawings.  FIG. 1  is a block diagram illustrating the fuel cell system  100  according to the first embodiment. For convenience, only the components related to the present invention are illustrated in  FIG. 1 . In  FIG. 1 , the flow channels of fluids such as a fuel gas and an oxidant gas are illustrated by solid lines, and signal lines of control signals in the fuel cell system  100  are illustrated by dashed lines. Note that the flow channels of fluids inside an SOFC  10  are illustrated by chain lines for convenience. 
     As illustrated in  FIG. 1 , the fuel cell system  100  includes a solid oxide fuel cell module (SOFC module)  10 . The SOFC module (hereinafter simply referred to as the “SOFC”)  10  includes a cell stack configured as a layering or a collection of a plurality of cells. Each cell has a basic configuration in which an electrolyte is disposed between an air electrode and a fuel electrode. The cells of the cell stacks are electrically connected in series. The SOFC  10  includes a power generation mechanism in which electrical energy is generated by causing oxide ions generated by an air electrode to pass through an electrolyte and move to a fuel electrode, such that the oxide ions react with hydrogen or carbon monoxide at the fuel electrode. 
     The SOFC  10  includes an oxidant gas flow channel (cathode gas flow channel)  12  and a fuel gas flow channel (anode gas flow channel)  14 . The oxidant gas (air) and other gases brought in by a reaction air blower (oxidant gas supplier)  20  are supplied to an inlet  12 A of the oxidant gas flow channel  12 , and oxidant off-gas is discharged from an outlet  12 B of the oxidant gas flow channel  12 . The oxidant gas (air) is supplied to the inlet  12 A of the oxidant gas flow channel  12  through an oxidant gas supply line  21  that connects an outlet  20 A of the reaction air blower  20  to the inlet  12 A of the oxidant gas flow channel  12 . Additionally, the oxidant off-gas is discharged from the outlet  12 B of the oxidant gas flow channel  12  through an oxidant gas discharge line  22  connected to the outlet  12 B of the oxidant gas flow channel  12 . Note that the oxidant off-gas may also be referred to as the cathode off-gas. The oxidant gas flow channel  12  is illustrated by a straight line (chain line) inside the SOFC  10 , but the flow channel may be set in accordance with the shape of the cell stack. 
     A fuel gas (fuel) is supplied to an inlet  14 A of the fuel gas flow channel  14  from a fuel gas supplier (not illustrated) through a fuel gas supply line  23 , and in addition, reforming water and other gases are supplied from a reforming water supplier (not illustrated) through a reforming water supply line  24 . Fuel off-gas is discharged from an outlet  14 B of the fuel gas flow channel  14 . Note that the fuel off-gas may also be referred to as the anode off-gas. A reformed fuel (fuel gas) is generated on the basis of the fuel gas (fuel) supplied from the fuel gas supplier (not illustrated) and the reforming water supplied from the reforming water supplier (not illustrated). Additionally, a direct current (electricity) is generated by inducing an electrochemical reaction between the oxidant gas supplied to the oxidant gas flow channel  12  and the fuel gas supplied to the fuel gas flow channel  14  and generated. Note that a reformer for generating the reformed fuel (fuel gas) based on the fuel gas (fuel) and the reforming water may also be provided outside the SOFC  10 . 
     In the case where a blackout due to a loss of a control power source (hereinafter also simply referred to as a “blackout”) occurs, the supply of the fuel gas (fuel) from the fuel gas supplier (not illustrated) through the fuel gas supply line  23  stops, and in addition, the supply of the reforming water from the reforming water supplier (not illustrated) through the reforming water supply line  24  stops. Similarly, in the case where a blackout occurs, the supply of the air (oxidant gas) from the reaction air blower  20  through the oxidant gas supply line  21  stops. Immediately after a blackout, the SOFC  10  is at a high temperature and highly reactive, and consequently the hydrogen at the fuel electrode and the oxygen at the air electrode inside the SOFC  10  react, and all of the fuel gas (hydrogen) is consumed. However, because the oxidant gas supply line  21  side is not particularly sealed, as the temperature inside the SOFC  10  falls and the volume of gas decreases, outside air flows into the SOFC  10 . As a result, the inflowing air reacts with the fuel electrode, causing the fuel electrode to oxidize and become degraded. 
     The fuel cell system  100  includes a control unit  40  and a detection unit  41 . For example, the fuel cell system  100  may include a computing device such as a central processing unit (CPU), and a non-transitory computer-readable storage medium such as a read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. The storage medium contains program instructions stored therein, execution of which by the computing device causes the fuel cell system to provide the functions of the control unit  40  and the detection unit  41 . 
     Specifically, the control unit  40  controls the fuel cell system  100  including the SOFC  10 . The detection unit  41  detects a loss of control by the control unit  40 . The detection unit  41  includes a programmable logic controller (PLC) for example, and can detect whether or not the control by the control unit  40  has been lost by determining whether or not a controller signal transmitted from the control unit  40  on a fixed interval has been received. The detection unit  41  is connected to an uninterruptible power supply (UPS) and can detect a loss of control by the control unit  40  even in the case where a blackout occurs. 
     For example, the detection unit  41  can detect that the control unit  40  has lost control and a blackout has occurred if the detection unit  41  has not received the controller signal even after a certain time elapses. Additionally, the detection unit  41  may also directly detect the supply of power to the control unit  40 . In this case, the detection unit  41  can detect that the control unit  40  has lost control and a blackout has occurred if the supply of power to the control unit  40  has stopped. The control unit  40  as above may constitute means for controlling the fuel cell system  100  including the SOFC  10 . Furthermore, the detection unit  41  may constitute means for detecting a loss of control by the control unit  40 . 
     The SOFC  10  is surrounded by a heat-insulating material  50  that keeps the SOFC  10  warm. An opening  60  is provided in the upper vertical end of the SOFC  10 . An open line (release line)  62  closed off by a valve  61  is connected to the opening  60 . In addition, an opening  70  is provided on the lower vertical end of the SOFC  10 . An open line (release line)  72  closed off by a valve  71  is connected to the opening  70 . The diameter by which the valve  61  is opened may be approximately the same as the diameter of the oxidant gas discharge line  22 . Similarly, the diameter by which the valve  71  is opened may be approximately the same as the diameter of the oxidant gas supply line  21 . 
     The valves  61  and  71  are normally open solenoid valves that maintain a closed state while energized by the control unit  40 . Conversely, the valves  61  and  71  open when not energized by the control unit  40 , which occurs when the detection unit  41  detects a loss of control by the control unit  40  and a blackout or the like occurs due to a situation such as a loss of power. For this reason, under normal conditions in which a blackout has not occurred, the energized state of the valves  61  and  71  is maintained by the control unit  40 , and the closed state of the valves  61  and  71  is also maintained. Consequently, under normal conditions, the hot gas inside the SOFC  10  is not discharged into the atmosphere through the open lines  62  and  72 . In contrast, in the case where a blackout occurs due to a loss of power or the like and the control by the control unit  40  is lost, the valves  61  and  71  are no longer energized by the control unit  40 , and the valves  61  and  71  open. Consequently, when a blackout occurs, the hot gas inside the SOFC  10  is discharged into the atmosphere through the open lines  62  and  72 . 
     The valve  61 , the valve  71 , the open line  62 , and the open line  72  as above constitute an opening and closing apparatus that opens the SOFC  10 . The present embodiment describes a case in which the valves  61  and  71  and the open lines  62  and  72  are included as two valves and corresponding open lines. 
     In this way, when a blackout occurs in the fuel cell system  100  according to the first embodiment, the valve  61  and the valve  71  are opened. The open line  62  and the open line  72  connected to the valve  61  and the valve  71  are disposed at respectively different heights in the vertical direction of the SOFC  10 . Consequently, the hot gas inside the SOFC  10  moves upward and is discharged into the atmosphere through the open line  62  connected to the opening  60  disposed in the top of the SOFC  10 . Additionally, atmospheric gas (air) of a volume equal to the gas discharged from inside the SOFC  10  is supplied into the SOFC  10  through the open line  72  connected to the opening  70  disposed in the bottom of the SOFC  10 . Immediately after a blackout, the SOFC  10  has an extremely high internal temperature from 700° C. to 900° C., and therefore it is fully possible to cool the SOFC  10  even with room temperature atmospheric gas (air) supplied into the SOFC  10 . 
     Consequently, the fuel cell system  100  according to the first embodiment can discharge the hot gas from inside the SOFC  10 , supply atmospheric gas (air), and rapidly lower the temperature of the SOFC  10 . As a result, degradation of the SOFC  10  can be prevented, even in the case where a blackout occurs. 
     Also, in the first embodiment, the open line  62  and the open line  72  penetrate the heat-insulating material  50  surrounding the SOFC  10  to connect to the SOFC  10 . For this reason, when a blackout occurs, the hot gas inside the SOFC  10  is discharged into the atmosphere directly through the open line  62 , without going through the heat-insulating material  50 . Additionally, the SOFC  10  can be cooled by supplying the atmospheric gas (air) directly to the SOFC  10  through the open line  72 , without going through the heat-insulating material  50 . With this arrangement, even if a blackout occurs, the temperature of the SOFC  10  can be lowered rapidly without having to consider the heat-insulating effect provided by the heat-insulating material  50 . As a result, degradation of the SOFC  10  can be prevented. 
     Second Embodiment 
     A fuel cell system  200  according to a second embodiment differs from the first embodiment in that the open line  62  and the open line  72  are connected to the SOFC  10  through the heat-insulating material  50  surrounding the SOFC  10 .  FIG. 2  is a block diagram illustrating the fuel cell system  200  according to the second embodiment. Note that in the embodiment described hereinafter, components that are the same as the first embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     The SOFC  10  is surrounded by a heat-insulating material  50  that keeps the SOFC  10  warm. An opening  60  is provided in the upper end of the heat-insulating material  50  on the top of the SOFC  10 . An open line  62  closed off by a valve  61  is connected to the opening  60 . In addition, an opening  70  is provided in the lower end of the heat-insulating material  50  on the bottom of the SOFC  10 . An open line  72  closed off by a valve  71  is connected to the opening  70 . In other words, in the fuel cell system  200  according to the second embodiment, the open line  62  and the open line  72  are connected to the SOFC  10  through the heat-insulating material  50 , without penetrating the heat-insulating material  50 . 
     When a blackout occurs in the fuel cell system  200  according to the second embodiment, the valve  61  and the valve  71  are opened. Additionally, the hot gas inside the SOFC  10  moves upward through the SOFC  10  and the heat-insulating material  50  and is discharged into the atmosphere through the open line  62  connected to the opening  60  disposed in the heat-insulating material  50  on the top of the SOFC  10 . Additionally, atmospheric gas (air) of a volume equal to the gas discharged from inside the SOFC  10  is supplied into the SOFC  10  through the open line  72  connected to the opening  70  disposed in the heat-insulating material  50  on the bottom of the SOFC  10 . Immediately after a blackout, the SOFC  10  has an extremely high internal temperature from 700° C. to 900° C., and therefore it is fully possible to cool the SOFC  10  even with room temperature atmospheric gas (air) supplied to the SOFC  10  through the heat-insulating material  50 . 
     Consequently, the fuel cell system  200  according to the second embodiment can discharge the hot gas from inside the SOFC  10  and supply atmospheric gas (air) through the heat-insulating material  50 , and rapidly lower the temperature of the SOFC  10 . As a result, degradation of the SOFC  10  can be prevented, even in the case where a blackout occurs. 
     Also, in the second embodiment, the open line  62  and the open line  72  are connected to the SOFC  10  through the heat-insulating material  50  without penetrating the heat-insulating material  50  surrounding the SOFC  10 . For this reason, when a blackout occurs, the hot gas inside the SOFC  10  is discharged into the atmosphere through the open line  62  and the heat-insulating material  50 . Additionally, the SOFC  10  can be cooled by supplying the atmospheric gas (air) to the SOFC  10  through the open line  72  and the heat-insulating material  50 . With this arrangement, the temperature of the SOFC  10  can be lowered rapidly when a blackout occurs. As a result, degradation of the SOFC  10  can be prevented. Furthermore, it is not necessary to modify existing equipment such as the heat-insulating material  50 , thereby conserving the heat-insulating effect provided by the heat-insulating material  50  and suppressing a reduction in the power-generating efficiency of the fuel cell system  200 . 
     Third Embodiment 
     A fuel cell system  300  according to a third embodiment differs from the first embodiment in that the valve  61  and the valve  71  are connected to the oxidant gas supply line  21  and the oxidant gas discharge line  22 , respectively.  FIG. 3  is a block diagram illustrating the fuel cell system  300  according to the third embodiment. Note that in the embodiment described hereinafter, components that are the same as the first embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     In the fuel cell system  300  according to the third embodiment, the valve  61  is directly connected to the oxidant gas discharge line  22 . Also, in the fuel cell system  300  according to the third embodiment, the open line  72  closed off by the valve  71  is connected to the oxidant gas supply line  21 . The oxidant gas supply line  21  and the valve  71  are connected via a T-shaped pipe  80 , for example. 
     Consequently, in the third embodiment, during a blackout, the hot gas inside the SOFC  10  can be discharged through the valve  61  connected to the oxidant gas discharge line  22 . In addition, atmospheric gas (air) can be supplied through the valve  71  connected to the oxidant gas supply line  21 . With this arrangement, the temperature of the SOFC  10  can be lowered rapidly. As a result, degradation of the SOFC  10  can be prevented, even in the case where a blackout occurs. The oxidant gas supply line  21  as above constitutes an oxidant gas supplying unit that supplies the oxidant gas to the SOFC  10 . Also, the oxidant gas discharge line  22  constitutes an oxidant gas discharging unit that discharges the oxidant gas from the SOFC  10 . 
     In other words, in the third embodiment, the existing equipment configuration can be utilized without provided a separate configuration such as the opening  60  and the opening  70  like in the first embodiment, and when a blackout occurs, the SOFC  10  can be cooled rapidly to prevent degradation of the SOFC  10 . With this arrangement, a reduction in cost can be attained. Furthermore, it is not necessary to modify existing equipment such as the heat-insulating material  50 , thereby conserving the heat-insulating effect provided by the heat-insulating material  50  and suppressing a reduction in the power-generating efficiency of the fuel cell system  300 . 
     Fourth Embodiment 
     A fuel cell system  400  according to a fourth embodiment differs from the third embodiment in that a control loss fuel supply line  110  and a control loss reforming water supply line  111  are disposed.  FIG. 4  is a block diagram illustrating the fuel cell system  400  according to the fourth embodiment. Note that in the embodiment described hereinafter, components that are the same as the third embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     The control loss fuel supply line  110  is closed off by a valve  120 , and connects a fuel cylinder (not illustrated) to the inlet  14 A of the fuel gas flow channel  14 . Also, the control loss reforming water supply line  111  is closed off by a valve  121 , and connects a reforming water cylinder (not illustrated) to the inlet  14 A of the fuel gas flow channel  14 . 
     The valves  120  and  121  are normally open solenoid valves that maintain a closed state while energized by the control unit  40 . Conversely, the valves  120  and  121  open when not energized by the control unit  40 , which occurs when the detection unit  41  detects a loss of control by the control unit  40  and a blackout or the like occurs due to a situation such as a loss of power. For this reason, under normal conditions in which a blackout has not occurred, the energized state of the valves  120  and  121  is maintained by the control unit  40 , and the closed state of the valves  120  and  121  is also maintained. Consequently, under normal conditions, the fuel gas and the reforming water are not supplied to the SOFC  10  from the fuel cylinder (not illustrated) and the reforming water cylinder (not illustrated) through the control loss fuel supply line  110  and the control loss reforming water supply line  111 . In contrast, in the case where a blackout occurs due to a loss of power or the like and the control by the control unit  40  is lost, the valves  120  and  121  are no longer energized by the control unit  40 , and the valves  120  and  121  open. For this reason, in the case where a blackout occurs, the fuel gas is supplied from the fuel cylinder (not illustrated) to the SOFC  10  through the control loss fuel supply line  110 . Similarly, the reforming water is supplied from the reforming water cylinder (not illustrated) to the SOFC  10  through the control loss reforming water supply line  111 . 
     Note that the flow rate of the fuel gas supplied from the fuel cylinder (not illustrated) through the control loss fuel supply line  110  may be lower than the flow rate of the fuel gas supplied through the fuel gas supply line  23  when a blackout has not occurred, and may be approximately 1/10 if the temperature is lowered sufficiently. Similarly, the flow rate of the reforming water supplied from the reforming water cylinder (not illustrated) through the control loss reforming water supply line  111  may be lower than the flow rate of the reforming water supplied through the reforming water supply line  24  under normal conditions while a blackout has not occurred, and may be approximately 1/10 if the temperature is lowered sufficiently. The control loss fuel supply line  110  as above constitutes a control loss fuel supplying unit that supplies the fuel gas to the SOFC  10  in the case where the detection unit  41  detects a loss of control by the control unit  40 . Also, the control loss reforming water supply line  111  constitutes a control loss reforming water supplying unit that supplies the reforming water to the SOFC  10  in the case where the detection unit  41  detects a loss of control by the control unit  40 . 
     In the fourth embodiment, even in the case where a blackout occurs and the supply of the fuel gas (fuel) through the fuel gas supply line  23  is stopped, the fuel gas is supplied from the fuel cylinder (not illustrated) to the SOFC  10  through the control loss fuel supply line  110 . Similarly, even in the case where a blackout occurs and the supply of the reforming water through the reforming water supply line  24  is stopped, the reforming water is supplied from the reforming water cylinder (not illustrated) to the SOFC  10  through the control loss reforming water supply line  111 . With this arrangement, reduction gas is generated by a reforming reaction, and consequently a reduction state can be achieved inside the SOFC  10  and degradation caused by the oxidation of the fuel electrode of the SOFC  10  can be deterred. Furthermore, since the reforming reaction is an endothermic reaction, the cooling of the SOFC  10  can be promoted by the achievement of the reduction state. 
     Consequently, when a blackout occurs, the hot gas inside the SOFC  10  can be discharged through the valve  61  connected to the oxidant gas discharge line  22 , while in addition, atmospheric gas (air) can be supplied through the valve  71  connected to the oxidant gas supply line  21 . With this arrangement, in the fourth embodiment, the temperature of the SOFC  10  can be lowered rapidly. Furthermore, with the reduction state, degradation caused by the oxidation of the fuel electrode can be deterred. Moreover, the cooling of the SOFC  10  can be promoted by the endothermic reforming reaction. 
     Fifth Embodiment 
     A fuel cell system  500  according to a fifth embodiment differs from the fourth embodiment in that an off-delay timer  42  is provided.  FIG. 5  is a block diagram illustrating the fuel cell system  500  according to the fifth embodiment. Note that in the embodiment described hereinafter, components that are the same as the fourth embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     The control loss fuel supply line  110  according to the fifth embodiment is closed off by a valve  130 , and connects a fuel cylinder (not illustrated) to the inlet  14 A of the fuel gas flow channel  14 . Also, the control loss reforming water supply line  111  is closed off by a valve  131 , and connects a reforming water cylinder (not illustrated) to the inlet  14 A of the fuel gas flow channel  14 . 
     The control unit  40  and the off-delay timer  42  according to the fifth embodiment are connected to an uninterruptible power supply and can count a predetermined time even in the case where a blackout occurs. Also, the valves  130  and  131  are solenoid valves that maintain a closed state under normal conditions while a loss of control by the control unit  40  is not detected by the detection unit  41 . In contrast, the valves  130  and  131  open when the detection unit  41  detects a loss of control by the control unit  40  and a blackout or the like occurs due to a situation such as a loss of power. For example, under normal conditions in which a blackout has not occurred, the energized state of the valves  130  and  131  is maintained by the control unit  40 , and the closed state of the valves  130  and  131  is also maintained. Consequently, under normal conditions, the fuel gas and the reforming water are not supplied to the SOFC  10  from the fuel cylinder (not illustrated) and the reforming water cylinder (not illustrated) through the control loss fuel supply line  110  and the control loss reforming water supply line  111 . In contrast, in the case where a blackout occurs due to a loss of power or the like and the control by the control unit  40  is lost, the valves  130  and  131  are no longer energized by the control unit  40 , and the valves  130  and  131  open. For this reason, in the case where a blackout occurs, the fuel gas is supplied from the fuel cylinder (not illustrated) to the SOFC  10  through the control loss fuel supply line  110 . Similarly, the reforming water is supplied from the reforming water cylinder (not illustrated) to the SOFC  10  through the control loss reforming water supply line  111 . 
     The off-delay timer  42  starts a count when the detection unit  41  detects a loss of control by the control unit  40 . Thereafter, when a predetermined time has elapsed since the start of the count, the off-delay timer  42  cancels the energization of the valve  130  through the control unit  40  and stops the supply of the control loss fuel gas through the control loss fuel supply line  110 . Similarly, when a predetermined time has elapsed since the start of the count, the off-delay timer  42  cancels the energization of the valve  131  through the control unit  40  and stops the supply of the control loss reforming water through the control loss reforming water supply line  111 . A time long enough for the temperature of the SOFC  10  to drop can be set as the predetermined time, for example. The off-delay timer  42  as above constitutes a supply stopping unit that stops the supply of the fuel gas through the control loss fuel supply line  110  and/or the supply of the reforming water through the control loss reforming water supply line  111  in the case where the predetermined time has elapsed since the detection unit  41  detected a loss of control by the control unit  40 . 
     In the fifth embodiment, at a timing after enough time for the temperature of the SOFC  10  to drop has elapsed, for example, the supply of the control loss fuel gas through the control loss fuel supply line  110  and the supply of the control loss reforming water through the control loss reforming water supply line  111  are stopped. This arrangement makes it possible to conserve the quantity of the fuel supplied through the control loss fuel supply line  110  and the quantity of the reforming water supplied through the control loss reforming water supply line  111 . As a result, the number of installed fuel cylinders (not illustrated) and reforming water cylinders (not illustrated) can be decreased, the fuel cell system  500  can be scaled down, and cost savings can be attained. 
     Sixth Embodiment 
     A fuel cell system  600  according to a sixth embodiment differs from the third embodiment in that the valves  61  and  71  are each disposed closer to the SOFC  10  side than a heat exchanger  90 .  FIG. 6  is a block diagram illustrating the fuel cell system  600  according to the sixth embodiment. Note that in the embodiment described hereinafter, components that are the same as the third embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     In the fuel cell system  600  according to the sixth embodiment, a heat exchanger  90  is connected to the oxidant gas supply line  21  and the oxidant gas discharge line  22 . The heat exchanger  90  transfers heat from the oxidant off-gas flowing through the oxidant gas discharge line  22  to the oxidant gas flowing through the oxidant gas supply line  21 . In the fuel cell system  600  according to the sixth embodiment, the open line  72  closed off by the valve  71  is disposed with respect to the oxidant gas supply line  21  closer to the SOFC  10  than the heat exchanger  90 . For example, the open line  72  closed off by the valve  71  is connected to the oxidant gas supply line  21  through the T-shaped pipe  80  closer to the SOFC  10  side than the heat exchanger  90 . Also, in the fuel cell system  600  according to the sixth embodiment, the open line  62  closed off by the valve  61  is disposed with respect to the oxidant gas discharge line  22  closer to the SOFC  10  side than the heat exchanger  90 . For example, the open line  62  closed off by the valve  61  is connected to the oxidant gas discharge line  22  through a T-shaped pipe  81  closer to the SOFC  10  side than the heat exchanger  90 . 
     Consequently, in the fuel cell system  600  according to the sixth embodiment, during a blackout, the hot gas inside the SOFC  10  can be discharged through the valve  61  disposed with respect to the oxidant gas discharge line  22  closer to the SOFC  10  side than the heat exchanger  90 . The open line  62  provided with the valve  61  is disposed with respect to the oxidant gas discharge line  22  closer to the SOFC  10  side than the heat exchanger  90 . With this arrangement, the discharge of the hot gas inside the SOFC  10  toward the heat exchanger  90  side can be deterred. Consequently, even if the oxidant gas (air) leaks in from the gaps or the like in the reaction air blower  20 , a rise in the temperature of the oxidant gas supplied from the oxidant gas supply line  21  through heat exchanger  90  due to the heat of the oxidant off-gas can be suppressed, and a rise in the temperature of the SOFC  10  can be suppressed. 
     Additionally, in the fuel cell system  600  according to the sixth embodiment, during a blackout, atmospheric gas (air) can be supplied into the SOFC  10  through the valve  71  disposed with respect to the oxidant gas supply line  21  closer to the SOFC  10  side than the heat exchanger  90 . The open line  72  provided with the valve  71  is disposed with respect to the oxidant gas supply line  21  closer to the SOFC  10  side than the heat exchanger  90 . Consequently, when a blackout occurs, atmospheric gas (air) at a normal temperature can be supplied directly into the SOFC  10  rather than the hot air (oxidant gas) that has absorbed heat in the heat exchanger  90 . Consequently, when a blackout occurs, the temperature of the SOFC  10  can be lowered rapidly and degradation of the SOFC  10  can be prevented. 
     Seventh Embodiment 
     A fuel cell system  700  according to a seventh embodiment differs from the first embodiment in that the valves  61  and  71  are disposed on the vertical sides of the SOFC  10 .  FIG. 7  is a block diagram illustrating the fuel cell system  700  according to the seventh embodiment. Note that in the embodiment described hereinafter, components that are the same as the first embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     In the fuel cell system  700  according to the seventh embodiment, the opening  60  is provided on an upper vertical side of the SOFC  10 . The open line  62  closed off by the valve  61  is connected to the opening  60  in the direction orthogonal to the vertical direction of the SOFC  10 , or in other words the horizontal direction. In addition, the opening  70  is provided on a lower vertical side of the SOFC  10 . The open line  72  closed off by the valve  71  is connected to the opening  70  in the direction orthogonal to the vertical direction of the SOFC  10 , or in other words the horizontal direction. 
     Consequently, the open lines  62  and  72  of the fuel cell system  700  according to the seventh embodiment do not project out in the vertical direction of the SOFC  10 . For this reason, the vertical dimension (height dimension) of the fuel cell system  700  can be reduced. As a result, even in the case of loading the fuel cell system  700  onto a truck or the like for transport along a route with a height limit, for example, it is easy to keep the height dimension of the fuel cell system  700  within the limit. Moreover, even in the case of installing the fuel cell system  700  in an installation location with a height limit, the open line  62  closed off by the valve  61  and the open line  72  closed off by the valve  71  can be connected without worrying about the dimensions in the vertical direction. In addition, since there are no vertical projections underneath, the ground contact surface can be made flat and a stable installation environment can be provided. 
     Eighth Embodiment 
     A fuel cell system  800  according to an eighth embodiment differs from the first embodiment in that the SOFC  10  is disposed inside a housing  200  and the open lines  62  and  72  are connected to the SOFC  10  through the housing  200 .  FIG. 8  is a block diagram illustrating the fuel cell system  800  according to the eighth embodiment. Note that in the embodiment described hereinafter, components that are the same as the first embodiment already described will be denoted with the same reference signs, and duplicate description of such components will be omitted or simplified. 
     In the fuel cell system  800  according to the eighth embodiment, the SOFC  10  is surrounded by the housing  200 . The housing  200  protects the SOFC  10  from wind and rain, and also from the viewpoint of crime prevention. An inlet  201  and an outlet  202  are disposed in the housing  200 . The inlet  201  and the outlet  202  include a fan, for example. The inlet  201  introduces an outside gas (air) into the housing  200  under control by the control unit  40 . The outlet  202  discharges the gas (air) inside the housing  200  to the outside under control by the control unit  40 . However, in the case where there is a loss of power and a blackout occurs, the control by the control unit  40  is lost, the inlet  201  and the outlet  202  stop, and as a result, the temperature inside the housing  200  rises. 
     In contrast, in the eighth embodiment, the open line  62  and the open line  72  penetrate the housing  200  surrounding the SOFC  10  to connect to the SOFC  10 . Consequently, even in the case where a blackout occurs and the inlet  201  and the outlet  202  stop, the hot gas inside the SOFC  10  can be discharged through the open line  62  to the atmosphere outside of the housing  200 . Furthermore, atmospheric gas (air) on the outside of the housing  200  can be supplied directly through the open line  72  to cool the SOFC  10  directly. With this arrangement, even if a blackout occurs, the temperature of the SOFC  10  can be lowered rapidly without having to consider the heat-insulating effect provided by the housing  200 . As a result, degradation of the SOFC  10  can be prevented. 
     Note that the present invention is not limited to the embodiments described above, and various modifications are possible. In the embodiments described above, properties such as the sizes, shapes, and functions of the components illustrated in the accompanying drawings are not limited to what is illustrated, and such properties may be modified appropriately insofar as the effects of the present invention are still achieved. Otherwise, other appropriate modifications are possible without departing from the scope of the present invention. 
     The fuel cell system  100  according to the above embodiments describes a case where the control unit  40  losing control when a controller signal is no longer received after a certain time elapses is used as a detection unit configured to detect a loss of control by the control unit  40 . However, the configuration of the detection unit configured to detect a loss of control by the control unit  40  is not limited to the above and may be changed appropriately. 
     Also, in the fuel cell system  100  according to the above embodiments, two valves (the valve  61  and the valve  71 ) and two corresponding open lines (the open line  62  and the open line  72 ) are disposed as an opening and closing apparatus that opens the SOFC  10 . However, it is sufficient if there is at least one opening and closing apparatus that opens the SOFC  10 , and three or more opening and closing apparatuses may also be disposed. In this case, at least two or more opening and closing apparatuses are preferably disposed at different heights in the vertical direction of the SOFC  10 . 
     Also, in the fuel cell system  300  according to the above embodiments, the open line  62  and the open line  72  are connected to the oxidant gas supply line  21  and the oxidant gas discharge line  22 , respectively, but are not limited thereto. For example, at least one of the open line  62  or the open line  72  may be connected to the oxidant gas supply line  21  or the oxidant gas discharge line  22 . 
     INDUSTRIAL APPLICABILITY 
     The fuel cell system according to the present invention can prevent degradation in a solid oxide fuel cell even in the case where a blackout occurs for the solid oxide fuel cell, and is suitable for application to fuel cell systems for domestic use, commercial use, and all other industrial fields. 
     This application is based on Japanese Patent Application No. 2019-234466 filed on Dec. 25, 2019, the content of which is hereby incorporated in entirety.