Patent Publication Number: US-2012028157-A1

Title: Solid oxide fuel cell stack

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0072364, filed on Jul. 27, 2010, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments according to the present invention relate to a stack of fuel cells, and more particularly, to a solid oxide fuel cell stack. 
     2. Description of the Related Art 
     In a solid oxide fuel cell, a plurality of unit cells is connected to a manifold to form a bundle portion. Further, a plurality of bundle portions is connected to a separate fuel supply unit to form a stack. 
     However, the bundle portions are simultaneously connected to one fuel supply unit to receive fuel supplied from the fuel supply unit. In this instance, a fuel supply tube is separately provided to each of the bundle portions. Therefore, in a case where a specific one of the plurality of bundle portions has a defect, it is generally not possible to selectively block the fuel supply to the defective bundle portion without blocking the entire fuel supply to the other bundle portions as well. 
     Accordingly, the fuel is continuously supplied to the defective bundle portion and its unit cells. Therefore, the defective bundle portion may explode, and the performance of the other bundle portions may be degraded. 
     SUMMARY 
     In one embodiment, there is provided a solid oxide fuel cell stack for selectively blocking only the fuel supply to a specific bundle portion in a case where the use of the specific bundle portion is impossible due to a defect. 
     According to an exemplary embodiment of the present invention, a fuel cell stack is provided. The fuel cell stack includes a bundle portion, a fuel supply portion, and a fuel-blocking unit. The bundle portion includes a plurality of unit cells and a manifold having the plurality of unit cells connected thereto. Each of the unit cells has a stacked structure of a first electrode, an electrolytic layer, and a second electrode. The fuel supply portion is connected to the manifold of the bundle portion through a fuel supply tube provided at one side thereof. The fuel-blocking unit is connected to the fuel supply tube. The fuel-blocking unit is configured to block the fuel supply tube. 
     The bundle portion may include a plurality of bundle portions. The bundle portions may be electrically connected to one another. 
     The fuel supply tube may include a plurality of fuel supply tubes. The fuel-blocking unit may include a plurality of fuel-blocking units. The fuel supply tubes may be connected to respective ones of the bundle portions. The fuel-blocking units may be connected to respective ones of the fuel supply tubes. 
     The fuel-blocking unit may include an accommodating portion that accommodates a fuel-blocking member. The fuel-blocking unit may include a connection tube to communicate with the interior of the fuel supply tube. 
     The fuel-blocking member may include slurry. 
     The fuel-blocking member may include a ceramic material having a plastic deforming temperature of about 800° C. or higher. 
     The fuel-blocking member may be plastically deformed near a driving temperature of the fuel cell stack. 
     The fuel-blocking member may have a porosity of less than 10% in its plastic deformation. 
     The fuel supply tube may be formed in a shape of a curved flow path so that the fuel-blocking member is configured to inject into the curved flow path. 
     The connection tube may be connected to a curved portion of the fuel supply tube. 
     The fuel-blocking unit may include a straight-line guide tube of which one end is connected to the fuel supply tube. The fuel-blocking member may be configured to move through the guide tube. 
     The fuel-blocking member may be formed in a shape of a block that is installed and configured to move in the guide tube. 
     The fuel-blocking unit may further include a driving portion connected to the fuel-blocking member to move the fuel-blocking member. 
     The fuel-blocking member may be configured to be circumscribed in the fuel supply tube. 
     The fuel cell stack may be a solid oxide fuel cell stack. 
     As described above, according to an embodiment of the present invention, only the fuel supply to a specific bundle portion with a defect is selectively blocked in a fuel cell stack, so that it is possible to prevent the risk of explosion due to fuel leakage that may occur in the defective bundle portion. In addition, the fuel supply to a specific bundle portion is selectively blocked, so that it is possible to prevent the degradation of the performance of the other bundle portions or unit cells, thereby stably driving the fuel cell stack. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain aspects and/or principles of the present invention. 
         FIG. 1  is a schematic view showing the structure of a related fuel cell stack. 
         FIG. 2  is a schematic view showing the fuel supply structure of a solid oxide fuel cell stack according to an embodiment of the present invention. 
         FIG. 3  is an enlarged schematic view showing the structure of each bundle portion in the stack of  FIG. 2 . 
         FIG. 4  is a schematic view of a fuel-blocking unit according to a first embodiment of the present invention. 
         FIG. 5  is a schematic view showing a fuel supply tube that is blocked by a fuel-blocking member in the fuel-blocking unit of  FIG. 4 . 
         FIG. 6  is a schematic view of a fuel-blocking unit according to a second embodiment of the present invention. 
         FIG. 7  is a schematic view of a fuel-blocking unit according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. In addition, when an element is referred to as being “on” another element, it can be directly on the other element or be indirectly on the other element with one or more intervening elements interposed therebetween. In addition, when an element is referred to as being “connected to” another element, it can be directly connected to the other element or be indirectly connected to the other element with one or more intervening elements interposed therebetween. Hereinafter, like reference numerals refer to like elements. In the drawings, the thickness or size of layers may be exaggerated for clarity and are not necessarily drawn to scale. 
       FIG. 1  is a schematic view showing the structure of a related fuel cell stack  1000 . In  FIG. 1 , a plurality of unit cells  10  that generate electricity are connected to a manifold  20  to form a bundle unit (or bundle portion)  100 . Further, a plurality of bundle portions  100  is connected to a separate fuel supply unit  200  to form a stack  1000 . 
     In this instance, the respective bundle portions  100  are simultaneously and separately connected to the fuel supply unit  200  through fuel supply tubes  220  to receive fuel supplied from the fuel supply unit  200 . As the fuel supply tubes  220  are individually provided to the respective bundle portions  100 , the respective bundle portions  100  receive the fuel supplied through independent fuel supply paths. In addition, a separate fuel discharge unit may be provided together with the fuel supply unit  200  in the fuel cell stack  1000 . The fuel discharge unit may have various structures. Therefore, the fuel discharge unit is not separately shown in  FIG. 1 . 
     In the fuel cell stack  1000  of  FIG. 1 , the fuel is distributed to the respective bundle portions  100  through the fuel supply tubes  220 . Then, the fuel supplied to each of the bundle portions  100  is again distributed in the manifold  20  of each of the bundle portions  100 , and the distributed fuel is supplied to each of the unit cells  10 . 
     However, in a stack  1000  having such a fuel supply structure, the respective bundle portions  100  are simply connected to the fuel supply unit  200  through the fuel supply tubes  220 . Therefore, the fuel supply cannot be individually controlled (e.g., stopped) for a particular bundle portion  100  unless the driving of the entire stack  1000  is controlled (e.g., stopped). That is, although the driving of a specific one of the bundle portions  100  may be impossible due to a defect of the one specific bundle portion  100 , it is not possible to block the fuel supply to the one specific bundle portion  100  without also blocking the entire fuel supply to the other bundle portions. 
     As a result, in order to continue driving a fuel cell stack  1000  that includes a defective bundle portion  100 , the fuel is continuously supplied to the defective bundle portion  100  as well as to any defective unit cells  10  included in the defective bundle portion  100 . For example, a defective unit cell  10  may have cracks, thus causing fuel to leak. In a case where the fuel is continuously supplied to such a defective unit cell  10 , the defective unit cell  10  may explode because of the external current collecting process between the unit cells  10 , and the performance of the other unit cells  10  may be degraded. As the fuel is unnecessarily supplied to the defective unit cell  10  (for which driving is impossible), the fuel is wasted. 
       FIG. 2  is a schematic view showing the fuel supply structure of a solid oxide fuel cell stack according to an embodiment of the present invention.  FIG. 3  is an enlarged schematic view showing the structure of each bundle portion  100  in the stack of  FIG. 2 . As shown in  FIG. 2 , the fuel cell stack generally includes bundle portions  100 , a fuel supply unit  200 , and fuel-blocking units  300 . 
     In the solid oxide fuel cell stack of  FIG. 2 , the bundle portion  100  is a portion in which electricity is generated and collected. As shown in  FIGS. 2 and 3 , the bundle portion  100  includes unit cells  10  and a manifold  20 . 
     The unit cell  10  is a portion that substantially generates electricity in the bundle portion. As shown in the inset of  FIG. 3 , the unit cell  10  has a multiple layer structure in which a first electrode  12  corresponding to an anode, an electrolytic layer  14 , and a second electrode  16  corresponding to a cathode are sequentially stacked. Although not shown in  FIGS. 2 and 3 , current collecting bodies for internal and external current collections may be formed on the inner and outer circumferential surfaces of the unit cell  10 . 
     Since the current collection efficiency of only one unit cell  10  is insufficient, a plurality of unit cells  10  are connected to one manifold  20  to form one bundle portion  100 . In this instance, the manifold  20  functions to connect the unit cells  10  and to distribute fuel supplied from the fuel supply unit  200 , which will be described later, to the unit cells  10 . 
     As shown in  FIG. 3 , the manifold  20  has coupling ports  22  through which end portions of the respective unit cells  10  are coupled to the manifold  20  at one side of the manifold  20 . The manifold  20  also has a terminal portion (not shown) for collecting current between the coupled unit cells  10 . The coupling ports  22  are connected to a fuel distribution chamber  24  formed at one side thereof. As such, a plurality of unit cells  10  are connected to one manifold  20  to form one bundle portion  100 , and a plurality of such bundle portions  100  are connected to the fuel supply unit  200  to form one stack. 
     For convenience of illustration, the bundle portions  100  are divided into first, second, third, and fourth bundle portions  100   a,    100   b,    100   c,  and  100   d  as shown in  FIG. 2 . However, the number of bundle portions  100  may be increased or decreased in consideration of the entire capacity of the fuel cell stack. 
     The fuel supply unit  200  functions to distribute hydrogen gas fuel generated through a fuel reformer (not shown) and an oxidation reactor (not shown) to the bundle portions  100   a,    100   b,    100   c,  and  100   d.  The fuel supply unit  200  includes a fuel distribution portion  210 . 
     The fuel distribution portion  210  functions to distribute hydrogen fuel discharged from a selective oxidation reactor to each fuel path. Fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  connected to the fuel distribution portion  210  serve as fuel supply paths between the fuel distribution portion  210  and the respective bundle portions  100   a,    100   b,    100   c,  and  100   d.  The fuel supply tubes are formed in a simple tube shape. End portions of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  are connected to respective fuel discharge ports of the fuel distribution portion  210 , and other end portions of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  are connected to the respective fuel distribution chambers  24  of the manifolds  20  in the bundle portions  100   a,    100   b,    100   c,  and  100   d.    
     For reference, the number of fuel supply tubes  220  shown in  FIG. 2  is four, namely, first, second, third, and fourth fuel supply tubes  220   a,    220   b,    220   c,  and  220   d,  to correspond to the number of the bundle portions  100 . However, the number of fuel supply tubes  220  may be modified depending on the number of bundle portions  100 . 
     As the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  are separately connected to the respective bundle portions  100   a,    100   b,    100   c,  and  100   d,  the hydrogen fuel discharged from the fuel distribution portion  210  is supplied to the bundle portions  100   a,    100   b,    100   c,  and  100   d  along individual paths through the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d,  respectively. 
     In addition to the above-described structure of the fuel cell stack, a fuel-blocking unit  300  is further provided to the fuel cell stack as shown in  FIG. 2 . The fuel-blocking unit  300  is used to selectively block only the fuel supply to a specific bundle portion in a case where a defect of the specific bundle portion occurs. Embodiments of the fuel-blocking unit  300  of  FIG. 2  are shown in detail in  FIGS. 4 to 7 . 
     In the embodiments depicted in  FIGS. 4-6 , the fuel-blocking unit includes an accommodating portion  312  provided with a fuel-blocking member  320  and a connection tube  314  for transferring the fuel-blocking member  320  in the accommodating portion  312  to each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d.  That is, the accommodating portion  312  functions to accommodate the fuel-blocking member  320 , and the connection tube  314  serves as a moving path of the fuel-blocking member  320 . The fuel-blocking member  320  is an element that substantially blocks the fuel supply to each of the bundle portions  100 . 
     The fuel-blocking unit  300  may be implemented in different forms for different exemplary embodiments. Therefore, three embodiments of the fuel-blocking unit  300  of  FIG. 2  will be described below with reference to  FIGS. 4-7 . 
     First Embodiment 
       FIG. 4  is a schematic view showing a fuel-blocking unit according a first embodiment of the present invention.  FIG. 5  is a schematic view showing a fuel supply tube  220   a  that is blocked by a fuel-blocking member  320  in the fuel-blocking unit of  FIG. 4 . The fuel-blocking unit in this embodiment includes an accommodating portion  312  (having a fuel-blocking member  320  accommodated therein) and a connection tube  314 . 
     The accommodating portion  312  is a portion in which the fuel-blocking member  320 , which will be described later, is initially stored. The accommodating portion  312  has a general storage tank structure in which an accommodating space  312   a  is formed in the accommodating portion  312 , and a discharge port  312   b  for the fuel-blocking member  320  is formed at one side of the accommodating portion  312 . The accommodating portion  312  is positioned at one side of each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d.    
     The connection tube  314  connects the accommodating portion  312  to each of the fuel supply tubes  220  of the fuel supply unit  200  to serve as a moving path of the fuel-blocking member  320 . The connection tube  314  may, for example, have the form of a tube structure. One end of the connection tube  314  is connected to the discharge port  312   b  of the accommodating portion  312 , and the other end of the connection tube  314  is connected to the fuel supply tube  220 . In this embodiment, a valve (not shown) or the like may be provided near the connection point with the accommodating portion  312  or near the connection point with each of the fuel supply tubes  220   a,    200   b,    220   c,  and  220   d  to control the supply of the fuel-blocking member  320 . 
     The fuel-blocking member  320  that constitutes the fuel-blocking unit of  FIGS. 4-5  together with the accommodating portion  312  and the connection tube  314  is an element that substantially blocks the fuel supply to each of the bundle portions  100  as described above. In this embodiment, the fuel-blocking member  320  may be made of a ceramic material in a slurry state. For instance, a ceramic material that is plastically deformable at the driving temperature of a solid oxide fuel cell may be used as the fuel-blocking member  320 . That is, in a case where the ceramic material is used for the fuel-blocking member  320  to a solid oxide fuel cell system, the ceramic material may plastically deform at about 800° C., which corresponds to a driving temperature of the system, to have a porosity of about 10% or lower, preferably a porosity of about 5% or lower. In a case where the porosity is greater than 10%, the substantial effect of blocking the fuel may be reduced. Although the driving temperature of the solid oxide fuel cell is about 800° C., a material having plastic deformation at a temperature of about 500° C. to 1000° C. may be used. 
     The fuel-blocking unit of  FIGS. 4-5  is provided to each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  to be individually operated. Although not shown in  FIGS. 4-5 , a separate pump or the like may be provided to the accommodating portion  312 , if necessary, so that the fuel-blocking member  320  is discharged from the accommodating portion  312  by a pumping pressure. 
     Hereinafter, the operation and effect of the embodiment shown in  FIGS. 4-5  will be described. First, as shown in  FIG. 2 , the hydrogen fuel distributed in the fuel distribution portion  210  of the fuel supply unit  200  is individually supplied to the bundle portions  100   a,    100   b,    100   c,  and  100   d  through the respective fuel supply tubes  220   a,    220   b,    220   c,  and  220   d,  and the supplied fuel is finally supplied to the unit cells  10  through the manifolds  20  of the respective bundle portions  100   a,    100   b,    100   c,  and  100   d.    
     Then, internal current collection is performed by the reaction between hydrogen and oxygen in each of the unit cells  10  to which the fuel is supplied, and electricity generated from each of the unit cells  10  is collected at the exterior through the manifold  20 . In such a manner, the electricity is separately generated in each of the bundle portions  100   a,    100   b,    100   c,  and  100   d.  Since the bundle portions  100   a,    100   b,    100   c,  and  100   d  are electrically connected to one another through an electric wire or the like, the electricity generated from each of the bundle portions  100   a,    100   b,    100   c,  and  100   d  is finally collected by the connection among the bundle portions  100   a,    100   b,    100   c,  and  100   d.    
     In the driving process of the fuel cell, the normal driving of the fuel cell may be impossible because cracks (or other defects) occur in one of the unit cells  10  of, for example, the first bundle portion  100   a.  In this case, if the fuel-blocking unit of  FIGS. 4-5  is operated, the fuel-blocking member  320  is discharged from the accommodating portion  312  by the operation of a discharge unit (not shown) such as a pump, moved along the connection tube  314  and then accumulated in the first fuel supply tube  220   a,  as shown in  FIG. 5 . 
     The fuel-blocking member  320  accumulated in the first fuel supply tube  220   a  is plastically deformed by the driving temperature of the fuel cell, and a partial section in the first fuel supply tube  220   a  is completely blocked. Therefore, the fuel supply to the first bundle portion  100   a  is blocked. 
     As the fuel supply to a bundle portion  100  having a defect is selectively blocked, it is possible to prevent the fuel from leaking in the defective bundle portion  100 , thereby preventing the risk of explosion due to the fuel leakage in the defective bundle portion  100 . In addition, the fuel unnecessarily supplied to a defective (e.g., leaking) unit cell  10  (for which driving is impossible) is blocked, thereby preventing waste of the fuel. 
     For reference, since the bundle portions  100   a,    100   b,    100   c,  and  100   d  are electrically connected to one another as described above, the first bundle portion  100   a  of which fuel supply is blocked loses the function of generating electricity but continues to serve as an electrical connection (for example, via an electric wire) among the bundle portions  100   a,    100   b,    100   c,  and  100   d.    
     Second Embodiment 
       FIG. 6  is a schematic view showing a fuel-blocking unit according to a second embodiment of the present invention. In this embodiment, the configuration is similar to that of the embodiment illustrated in  FIGS. 4-5 . However, this embodiment is different in that S-shaped curved flow paths  222   a  and  222   b  are formed near the connection point of each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  with the manifold  20 , and the connection tube  314  of the fuel-blocking unit of  FIG. 6  is connected to the curved flow paths  222   a  and  222   b.    
     As shown in  FIG. 6 , in a normal operating configuration, S-shaped curved flow path  222   b  is lower than the curved flow path  222   a.  As such, the fuel-blocking member  320  discharged from the fuel-blocking unit of  FIG. 6  is naturally accumulated at a lower position (that is, curved flow path  222   b ) than that of the curved flow path  222   a.    
     Therefore, if the first bundle portion  100   a  has a defect, the fuel-blocking member  320  is discharged from the accommodating portion  312  and then injected into the first fuel supply tube  220   a  as described in the embodiment shown in  FIGS. 4-5 . The injected fuel-blocking member  320  is accumulated in a recessed section (e.g., in the curved flow path  222   b ) by its own weight in the process of passing through the curved flow paths  222   a  and  222   b.  In this state, the fuel-blocking member  320  is plastically deformed to block the fuel supply path. In this embodiment, the recessed section refers to a portion designated by reference numeral  222   b  in the curved flow paths. 
     As the fuel-blocking member  320  is accumulated in the curved flow paths  222   a  and  222   b  of each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d,  it is not easily swept by the flow of the fuel but instead accumulates in the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  as compared with the embodiment of  FIGS. 4-5 , in which the fuel-blocking member  320  is accumulated in the straight-line flow path. Accordingly, the blocking efficiency in the fuel supply path can be increased in this embodiment. 
     Third Embodiment 
       FIG. 7  is a schematic view showing a fuel-blocking unit according to a third embodiment of the present invention. The basic configuration of this embodiment is similar to the earlier embodiments (of  FIGS. 4-6 ) discussed above. However, this embodiment is slightly different from those embodiments in that the structure of the fuel-blocking unit of  FIG. 7  and the blocking method of the fuel supply path are mechanically implemented. 
     Specifically, in this embodiment, the fuel-blocking member  320  is formed as a block-shaped barrier. A separate driving portion  340  allows the block-shaped fuel-blocking member  320  to be pushed into each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  through a straight-line guide tube  310 . The guide tube  310  is connected to each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d  while serving as a transfer path of the block-shaped fuel-blocking member  320  in the interior thereof. 
     The fuel-blocking member  320  is formed in the shape of a block having the same width as the inside diameter of each of the fuel supply tubes  220   a,    220   b,    220   c,  and  220   d.  That is, the fuel-blocking member  320  is necessarily circumscribed in the fuel supply tube to have a sealing effect. 
     The fuel-blocking member  320  may be separately connected to the driving portion  340  having the type of a cylinder rod or jig to be moved by the driving force of the driving portion  340 . Alternatively, the driving portion  340  may have the type of an air compression device or the like so that the fuel-blocking member  320  is pushed and moved by the air pressure obtained by supplying compressed air into the guide tube  310 . 
     A ceramic material may be used as the fuel-blocking member  320 . In addition, the fuel-blocking member  320  can be any material and structure that have a sufficient sealing property in each of the fuel supply tubes  220   a,    220   b,    220   c,    220   d.    
     In this embodiment, the flow of fuel is blocked by simply moving the fuel-blocking member  320  toward each of the fuel supply tubes  220   a,    220   b,    220   c,    220   d  and blocking each of the fuel supply tubes  220   a,    220   b,    220   c,    220   d.  As the fuel-blocking structure is entirely implemented using a simple mechanical method, this embodiment is advantageous in that the fuel-blocking process can be rapidly and simply performed as compared with the earlier embodiments of  FIGS. 4-6  in which the flow path is blocked by passing through a plastic deforming process after slurry is accumulated. 
     As described above, the fuel supply to a bundle portion  100  with a defect is selectively blocked through the fuel-blocking unit, so that it is possible to continue the driving operation of the stack while reducing or preventing the risk of explosion due to fuel leakage or the like and while reducing or preventing the degradation of the performance of the entire stack. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.