Abstract:
A solid oxide fuel cell apparatus includes: a startup temperature raiser configured to mix the fuel and the air, burn a mixture of the fuel and the air using a burner to obtain combustion gas, and introduce the combustion gas to the air electrode to increase a temperature of the fuel cell stack in startup of the apparatus. The startup temperature raiser includes: a combustion cylinder through which the combustion gas passes; a cooling cylinder configured to cover an outer periphery of the combustion cylinder; and a bypass air line configured to introduce a part of the air to an air area formed between the combustion cylinder and the cooling cylinder so as to cool the combustion cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2015-249645 filed in Japan on Dec. 22, 2015. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The disclosure relates to a fuel cell apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    The operation temperature of a high-temperature type fuel cell such as a solid oxide fuel cell is about 600° C. to 1000° C. Thus, the temperature of the high-temperature type fuel cell is lowered to a room temperature once the operation is stopped, and the fuel cell needs to be heated to a high temperature again when the operation is restarted. In this case, it takes time to heat the fuel cell to a high-temperature state and, consequently, it takes time to start the fuel cell. 
         [0006]    For this reason, in Japanese Patent Application Laid-open No. 2005-317232, a startup burner is arranged in an air introduction tube, so that fuel gas is introduced from a fuel gas introduction tube for burners and burned to heat air passing the air introduction tube, reducing time for startup. 
       SUMMARY 
       [0007]    However, when the temperature of the fuel cell stack is increased from a room temperature to a high temperature of about 600 to 1000° C. using a burner, the adjustment of combustion of fuel and air is difficult, and a dynamic range allowing stable combustion temperature adjustment is small. The combustion gas temperature is determined based on a ratio (air ratio) between a fuel amount and an air amount. For example, when the temperature of combustion gas is controlled to 300 to 650° C., and is lowered to 300° C., the air ratio becomes high, which deteriorates combustibility using a burner and causes a large amount of unburned gas and carbon monoxide. With the use of a burner, the combustion temperature is increased sharply. When the temperature of the fuel cell stack is increased sharply by combustion gas, condensation occurs easily in the fuel cell stack having delay in rise of a temperature. 
         [0008]    In view of the foregoing, it is desirable to provide a fuel cell apparatus allowing easy temperature adjustment of combustion gas when the temperature of a fuel cell stack is increased for short time using a burner in startup of the apparatus. 
         [0009]    According to one aspect of the present disclosure, there is provided a solid oxide fuel cell apparatus including: a fuel cell stack including a fuel electrode to which fuel is supplied and an air electrode to which air is supplied; a startup temperature raiser configured to mix the fuel and the air, burn a mixture of the fuel and the air using a burner to obtain combustion gas, and introduce the combustion gas to the air electrode to increase a temperature of the fuel cell stack in startup of the apparatus. The startup temperature raiser includes: a combustion cylinder through which the combustion gas passes; a cooling cylinder configured to cover an outer periphery of the combustion cylinder; and a bypass air line configured to introduce a part of the air to an air area formed between the combustion cylinder and the cooling cylinder so as to cool the combustion cylinder. The startup temperature raiser is configured to introduce to the air electrode by mixing the combustion gas that has been burned in the combustion cylinder and has passed through the combustion cylinder with the air introduced to the air area. 
         [0010]    The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a block diagram illustrating a whole configuration of a fuel cell apparatus according to an embodiment of the disclosure; 
           [0012]      FIG. 2  is a diagram illustrating a detailed configuration of a startup temperature raiser; 
           [0013]      FIG. 3  is a section view illustrating a modification of the startup temperature raiser; 
           [0014]      FIG. 4  is a section view along an A-A line illustrated in  FIG. 3 ; 
           [0015]      FIG. 5  is a flowchart illustrating the procedure of startup temperature rise control processing by a controller; 
           [0016]      FIG. 6  is a flowchart illustrating the detailed processing procedure of temperature rise processing by the startup temperature raiser illustrated in  FIG. 5 ; 
           [0017]      FIG. 7  is a diagram illustrating a processing flow according to a first concrete example of the startup temperature rise control processing; 
           [0018]      FIG. 8  is a diagram illustrating the relation among a surface temperature, a saturated air moisture amount, outside air take-in maximum moisture amount, combustion gas possible moisture amount, and a combustion gas setting temperature according to the first concrete example of the startup temperature rise control processing; 
           [0019]      FIG. 9  is a diagram illustrating a processing flow according to a second concrete example of the startup temperature rise control processing; 
           [0020]      FIG. 10  is a diagram illustrating the relation among a surface temperature, a saturated air moisture amount of a fuel cell stack, a saturated air moisture amount of outside air, combustion gas possible moisture amount, and a combustion gas setting temperature according to the second concrete example of the startup temperature rise control processing; 
           [0021]      FIG. 11  is a block diagram illustrating a configuration of a first modification of the fuel cell apparatus in which a position of a heater in  FIG. 1  is changed. 
           [0022]      FIG. 12  is a block diagram illustrating a configuration of a second modification of the fuel cell apparatus in which a position of a heater in  FIG. 1  is changed. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The following will describe an embodiment of the disclosure with reference to the enclosed drawings. 
         [0024]    (Whole Configuration) 
         [0025]      FIG. 1  is a block diagram illustrating the whole configuration of a fuel cell apparatus  1  according to an embodiment of the disclosure. The fuel cell apparatus  1  includes a fuel cell module  2 . The fuel cell module  2  includes a fuel cell stack  3  provided in a heat insulating housing. The fuel cell stack  3  is a cell stack with a plurality of power generation cells that generate power by reaction of fuel introduced from a fuel supply line L 25  with air introduced from an air supply line L 34 . 
         [0026]    The fuel cell stack  3  may have a known configuration such as a configuration in which a plurality of cylindrical power generation cells are gathered or a configuration in which a plurality of rectangular plate shaped power generation cells are stacked, for example. The fuel cell stack  3  of the embodiment uses a solid oxide fuel cell (SOFC) in which ion conductive ceramics are interposed as an electrolyte between a fuel electrode (anode)  3   a  and an air electrode (cathode)  3   b.    
         [0027]    Sulfur components in raw fuel (e.g., methane gas, town gas, etc.) from a fuel supply line L 21  are removed by a desulfurizer  22  connected through a fuel blower  21  and a fuel supply line L 22 . Furthermore, the fuel in which the sulfur components have been removed is reformed to reformed fuel containing hydrogen by a reformer  23  connected through a fuel supply line L 23 , a valve V 1 , and a fuel supply line L 24 , and the reformed fuel is introduced to the anode  3   a  via a fuel supply line L 25 . A reforming water evaporator  24  evaporates water introduced via a supply line L 26 , and introduces the evaporated water to the reformer  23  via a supply line L 27 . The reformer  23  generates reformed fuel in which raw fuel has been steam reformed. Note that when the cell stack has the function of the reformer  23 , the reformer  23  can be omitted. 
         [0028]    Meanwhile, air from an air supply line L 31  is introduced to the cathode  3   b  through an air blower  31 , an air supply line L 32 , a startup temperature raiser  10 , an air supply line L 33 , a heater  32 , and an air supply line L 34  including a valve V 3 . Fuel is introduced to the startup temperature raiser  10  through a fuel supply line L 11  diverging from the fuel supply line L 23  and a valve V 2 . The valve V 2  serving as a burner fuel controller only in startup is opened, so that the fuel and air supplied from the air supply line L 32  are mixed and burned using a burner. Then, the combustion gas is drawn to the air supply line L 33 . The temperature of the fuel cell stack  3  increases by introducing the combustion gas to the cathode  3   b . Note that the startup temperature raiser  10  is connected to the air supply lines L 32 , L 33 , and when a burner is not burning in normal operation, air introduced from the air supply line L 32  is drawn as it is to the air supply line L 33 . In the embodiment, the air blower  31  serves as an air boosting blower that supplies air or combustion gas to the fuel cell stack  3  and an air boosting blower that supplies air to the startup temperature raiser  10 . This can simplify the system and downsize the apparatus. 
         [0029]    The heater  32  increases a temperature of air supplied from the air supply line L 33 . The heater  32  is used in startup of the apparatus and in normal operation. 
         [0030]    Air offgas drawn from the cathode  3   b  is subjected to heat exchange by an air preheater  33 , and then introduced to a combustor  41  via an offgas line L 41 . Meanwhile, fuel offgas drawn from the anode  3   a  is introduced to the combustor  41  via an offgas line L 42  connected to the offgas line L 41 . Note that the fuel reforming reaction by the reformer  23  is an endoergic reaction, and thus a heat exchanger may be provided at the previous stage of the reformer  23  to preheat fuel using fuel offgas, for example. The air preheater  33  includes an air supply line L 35  passing the air preheater  33  to preheat air in normal operation. When the air supply line L 35  is used, the valve V 3  is closed, and a valve V 4  is open. Note that the valves V 3 , V 4  function as switching units that switch supply of air or combustion gas to the air electrode  3   b.    
         [0031]    The combustor  41  burns the introduced fuel offgas and air offgas with a catalyst. The combustion gas is exhausted to the atmosphere through an offgas line L 43 , a heat exchanger  42 , and an offgas line L 44 . The heat exchanger  42  is a heat exchanger for exhaust heat recovery, and generates warm water with an exhaust heat recovery line L 45  connected thereto. 
         [0032]    (Detailed Configuration of Startup Temperature Raiser) 
         [0033]      FIG. 2  is a diagram illustrating a detailed configuration of the startup temperature raiser  10 . As illustrated in  FIG. 2 , the startup temperature raiser  10  includes a mixing unit  11 , a burner unit  12 , a combustion cylinder  13 , a cooling cylinder  14 , and a bypass air line L 12 . The mixing unit  11  mixes fuel introduced from the fuel supply line L 11  and air introduced from the air supply line L 32 . The burner unit  12  starts to burn the mixed gas flowing in from the mixing unit  11  using a burner. The combustion cylinder  13  burns the mixed gas in the cylinder as a combustion area. The bypass air line L 12  introduces air diverging from the air supply line L 32  to a base end side (side of the burner unit  12 ) of the cooling cylinder  14 . The cooling cylinder  14  covers the outer periphery of the combustion cylinder  13 . An air area E 1  is formed between the cooling cylinder  14  and the combustion cylinder  13 . That is, the combustion cylinder  13  and the cooling cylinder  14  form a double tube structure. The combustion gas that has been burned in the combustion cylinder  13  and has passed through the combustion cylinder  13  is mixed with air introduced to the air area E 1  and is introduced to the air electrode  3   b  of the fuel cell stack  3 . 
         [0034]    Air is introduced to the air area E 1  via the bypass air line L 12 . Thus, it is possible to cool a combustion temperature in the combustion cylinder  13  and suppress an ambient temperature of the cooling cylinder  14  to be low. With the combustion cylinder  13  formed of punching metal, combustion gas and air in the air area E 1  are mixed through a plurality of holes on the combustion cylinder  13  without any influence on the combustion state, further cooling the combustion gas. Therefore, when the temperature of combustion gas is controlled to 300 to 650° C., and is lowered to 300° C., for example, it can be lowered without increasing an air ratio at the combustion unit. That is, it is possible to lower the combustion gas temperature while stabilizing combustibility using a burner. As a result, the combustion gas temperature can be adjusted stably in a large dynamic range. 
         [0035]    Note that an orifice  15  is provided on the bypass air line L 12  so that air diverges at a predetermined flow ratio to the bypass air line L 12  and the air supply line L 32 . The orifice  15  is provided to set an air flow ratio because it allows a simplified structure. An opening of the orifice  15  is determined based on a result of preliminary adjustment of combustion gas temperature. Thus, a variable flow valve may be provided instead of the orifice  15 . 
         [0036]    As illustrated in  FIG. 3  and  FIG. 4 , a spiral passage LL may be formed in the air area E 1  to expand a contact area of air flowing in the air area E 1  with the combustion cylinder  13  and enhance the cooling effect. 
         [0037]    Note that as illustrated in  FIG. 1  and  FIG. 2 , a controller C obtains a surface temperature input from a surface temperature detector T 1  that detects a surface temperature of the fuel cell stack  3 , a combustion temperature input from a combustion temperature detector T 2  that detects a combustion temperature in the combustion cylinder  13 , an air temperature input from an air temperature detector T 3  that detects an air temperature of the air area E 1 , and a combustion gas temperature input from a combustion gas temperature detector T 4  arranged in the exit of the cooling cylinder  14  to detect a combustion gas temperature. The controller C controls an air supply amount by the air blower  31  based on a surface temperature, a combustion temperature, an air temperature, and a combustion gas temperature. The controller C may control a fuel supply amount by the fuel blower  21  or control both an air supply amount and a fuel supply amount. With the control of an air supply amount by the air blower  31 , the structure is simpler. Moreover, the air supply amount is larger, and thus when an air supply amount is controlled, the temperature can be adjusted finely. Note that the controller C controls air temperature rise by the heater  32  based on a surface temperature. Furthermore, the controller C controls opening and closing of the valves V 1  to V 4 . The controller C closes all of the valves V 1  to V 4  when operation of the apparatus is stopped. The controller C closes the valves V 1 , V 4  and opens the valves V 2 , V 3  in startup of the apparatus. The controller C opens the valves V 1 , V 4  and closes the valves V 2 , V 3  in normal operation. 
         [0038]    (Startup Temperature Rise Control Processing) 
         [0039]    The following will describe the procedure of startup temperature rise control processing by the controller C with reference to the flowcharts illustrated in  FIG. 5  and  FIG. 6 . First, the controller C controls all of the valves V 1  to V 4  to be closed when the operation of the apparatus is stopped. The controller C opens the valve V 3  in startup of the apparatus, and controls the heater  32  to increase a temperature of the air to increase a temperature of the fuel cell stack  3  (Step S 101 ). 
         [0040]    Thereafter, the controller C determines whether the surface temperature detected by the surface temperature detector T 1  has reached a predetermined surface temperature (Step S 102 ). When the surface temperature has not reached the predetermined surface temperature (No at Step S 102 ), the processing shifts to Step S 101  so that the heater  32  continues to increase the temperature. 
         [0041]    Meanwhile, when the surface temperature has reached the predetermined surface temperature (Yes at Step S 102 ), the controller C controls the heater  32  to stop heating operation, controls the startup temperature raiser  10  to perform temperature rise processing (Step S 103 ), and then finishes the processing. 
         [0042]    As illustrated in  FIG. 6 , in the temperature rise processing by the startup temperature raiser  10 , the valve V 1  is closed and the valve V 2  is opened first (Step S 201 ). This starts fuel supply to the startup temperature raiser  10  via the fuel supply line L 11 . Then, the controller C ignites a startup burner (Step S 202 ). Furthermore, the controller C determines whether the startup burner has been ignited (Step S 203 ). Whether the startup burner is ignited can be determined by detecting a combustion temperature, for example. When the startup burner has not been ignited (No at Step S 203 ), the processing shifts to Step S 202  again to ignite the startup burner. 
         [0043]    On the other hand, when the startup burner has been ignited (Yes at Step S 203 ), the controller C controls a combustion gas temperature by controlling, through the air blower  31 , an air flow so that a moisture generation amount of the combustion gas is less than a remaining air moisture amount obtained by subtracting an air moisture amount of air to be introduced to the startup temperature raiser  10  from a saturated air moisture amount corresponding to the surface temperature (Step S 204 ). This increases the temperature of the fuel cell stack  3  without condensation. 
         [0044]    Thereafter, the controller C determines whether the surface temperature has reached a target temperature, 600° C., for example (Step S 205 ). When the surface temperature has not reached the target temperature (No at Step S 205 ), the processing shifts to Step S 204  so that the startup temperature raiser  10  continues temperature rise control processing. 
         [0045]    On the other hand, when the surface temperature has reached the target temperature (Yes at Step S 205 ), the valve V 1  is opened and the valve V 2  is closed to supply fuel to the side of the anode  3   a (Step S 206 ), while the valve V 3  is closed and the valve V 4  is opened to supply air to the cathode  3   b  through the air preheater  33 . Thus, the processing shifts to normal operation. Then, the processing returns to Step S 103 . 
         [0046]    (First Concrete Example of Startup Temperature Rise Control Processing) 
         [0047]    Next, the first concrete example of startup temperature rise control processing at Step S 204  will be described with reference to  FIG. 7  and  FIG. 8 . As illustrated in  FIG. 7 , the controller C first obtains a surface temperature D 1 . Note that the surface temperature D 1  is a lowest surface temperature of the fuel cell stack  3 . Then, the controller C calculates a saturated air moisture amount D 2  corresponding to the obtained surface temperature D 1 , based on a curved line LA indicating the saturated air moisture amount relative to the surface temperature. Note that the curved line LA is an approximation expression, and R is a correlation coefficient. 
         [0048]    Then, the controller C subtracts an outside air take-in maximum moisture amount D 3  predetermined in the product specifications from the saturated air moisture amount D 2  of the fuel cell stack  3  to calculate a remaining air moisture amount D 4  of the fuel cell stack  3 . The outside air take-in maximum moisture amount D 3  is a predetermined maximum air moisture amount, and is a moisture amount of 56.5 [g/m 3 ] in 40° C. and 85% RH, for example. 
         [0049]    Thereafter, the controller C calculates a combustion gas setting temperature D 5  based on a curved line LB indicating the relation of the combustion gas setting temperature (target temperature) relative to the combustion gas possible moisture amount enabling generation of a moisture amount of the remaining air moisture amount D 4  in combustion gas. Note that the remaining air moisture amount D 4  and the combustion gas possible moisture amount are the same value. Moreover, the curved line LB is an approximation expression, and R is a correlation coefficient. 
         [0050]    Then, the controller C performs combustion gas temperature control in which the combustion gas temperature is controlled to be lower than the combustion gas setting temperature D 5  so that the moisture generation amount of the combustion gas becomes less than the remaining air moisture amount D 4 . That is, the controller C performs temperature rise control of the fuel cell stack  3  while adjusting an air supply amount by controlling the air blower  31  so that the combustion gas temperature becomes lower than the combustion gas setting temperature D 5 . 
         [0051]    Note that when the combustion gas setting temperature D 5  is lower than 200° C., the temperature rise control by the startup temperature raiser  10  is difficult. Thus, as illustrated in  FIG. 8 , it is preferable that the heater  32  performs temperature rise control when the combustion gas setting temperature D 5  is lower than 200° C., while it is preferable that the startup temperature raiser  10  performs temperature rise control when the combustion gas setting temperature D 5  is equal to or higher than 200° C. To be more specific, the heater  32  performs the temperature rise control at least until the surface temperature D 1  is 40° C. 
         [0052]    In this case, the controller C preferably performs the temperature rise control through the startup temperature raiser  10  when the surface temperature reaches the surface temperature D 1  (predetermined surface temperature at Step S 102 ) at the combustion gas setting temperature D 5  of 200° C. 
         [0053]    Such combustion gas temperature control can prevent condensation of the fuel cell stack  3  and thus prolong the lifetime of the fuel cell stack. 
         [0054]    (Second Concrete Example of Startup Temperature Rise Control Processing) 
         [0055]    Next, the second concrete example of startup temperature rise control processing at Step S 204  will be described with reference to  FIG. 9  and  FIG. 10 . In the second concrete example, an outside air temperature detector and an outside air humidity detector that are not illustrated are provided to calculate a saturated air moisture amount D 33  each time based on a detected outside air temperature D 31  and outside air humidity D 32 , instead of the outside air take-in maximum moisture amount D 3  predetermined in the product specifications. 
         [0056]    As illustrated in  FIG. 9 , the controller C first obtains the surface temperature D 1 . Note that the surface temperature D 1  is a lowest surface temperature of the fuel cell stack  3 . Then, the controller C calculates the saturated air moisture amount D 2  corresponding to the obtained surface temperature D 1 , based on the curved line LA indicating the saturated air moisture amount relative to the surface temperature. Note that the curved line LA is an approximation expression, and R is a correlation coefficient. 
         [0057]    Then, the controller C subtracts the saturated air moisture amount D 33  of air (outside air) calculated based on the outside air temperature D 31  and the outside air humidity D 32  from the saturated air moisture amount D 2  of the fuel cell stack  3  to calculate the remaining air moisture amount D 4  of the fuel cell stack  3 . The saturated air moisture amount D 33  is 2.83 [g/m3] when the outside air temperature D 31  is 10° C. and the outside air humidity D 32  is 30% RH, for example. 
         [0058]    Thereafter, the controller C calculates the combustion gas setting temperature D 5  based on the curved line LB indicating the relation of the combustion gas setting temperature (target temperature) relative to the combustion gas possible moisture amount enabling generation of a moisture amount of the remaining air moisture amount D 4  in combustion gas. Note that the remaining air moisture amount D 4  and the combustion gas possible moisture amount are the same value. Moreover, the curved line LB is an approximation expression, and R is a correlation coefficient. 
         [0059]    Then, the controller C performs combustion gas temperature control in which the combustion gas temperature is controlled to be lower than the combustion gas setting temperature D 5  so that the moisture generation amount of the combustion gas becomes less than the remaining air moisture amount D 4 . That is, the controller C performs temperature rise control of the fuel cell stack  3  while adjusting an air supply amount by controlling the air blower  31  so that the combustion gas temperature becomes lower than the combustion gas setting temperature D 5 . 
         [0060]    Note that when the combustion gas setting temperature D 5  is lower than 200° C., the temperature rise control by the startup temperature raiser  10  is difficult. Thus, as illustrated in  FIG. 10 , it is preferable that the heater  32  performs temperature rise control when the combustion gas setting temperature D 5  is lower than 200° C., while it is preferable that the startup temperature raiser  10  performs the temperature rise control when the combustion gas setting temperature D 5  is equal to or higher than 200° C. To be more specific, the heater  32  performs the temperature rise control when the surface temperature D 1  is 5° C. 
         [0061]    In this case, the controller C preferably performs the temperature rise control through the startup temperature raiser  10  when the surface temperature reaches the surface temperature D 1  (predetermined surface temperature at Step S 102 ) at the combustion gas setting temperature D 5  of 200° C. 
         [0062]    Such combustion gas temperature control can prevent condensation of the fuel cell stack  3  and thus prolong the lifetime of the fuel cell stack. 
         [0063]    In the above-described embodiment, the startup temperature raiser  10  is provided on the air supply line. However, the embodiment is not limited thereto, and the startup temperature raiser  10  may be provided on the fuel supply line L 11 . 
         [0064]    In the above-described embodiment, the heater  32  is provided at the previous stage of the air supply line L 34 . However, the embodiment is not limited thereto, and the heater may be provided on the air supply line L 34  passing the air preheater  33 , such as a heater  52  illustrated in  FIG. 11 . Here, when the heater  52  performs temperature rise control, the valve V 3  is closed and the valve V 4  is open. Furthermore, the heater ( 62 ) may be provided on a bypass line L 62  bypassing the air preheater  33 , such as a heater  62  illustrated in  FIG. 12 . Here, when the heater  62  performs temperature rise control, the valves V 3 , V 4  are closed and a valve V 62  is open. Note that when the heater  62  is not used, the valve V 62  is closed. Note that combustion gas does not pass the heater  62  unlike the heaters  32 ,  52 , and an apparatus having low heat resistance can be applied to the embodiment. 
         [0065]    As described above, the embodiments according to the disclosure can increase a temperature of the fuel cell stack for short time, expand a temperature adjustment range of combustion gas, and facilitate temperature adjustment. 
         [0066]    Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.