Abstract:
A fuel cell unit includes an array of solid oxide fuel cell tube sheets having porous metallic exterior surfaces, interior fuel cell layers, and interior surfaces, and at least one header in operable communication with the array of solid oxide fuel cell tube sheets for directing a first reactive gas into contact with the porous metallic exterior surfaces and for directing a second reactive gas into contact with the interior surfaces, the header further comprising at least one busbar selected from the group consisting of an exterior busbar disposed in electrical contact with the porous metallic exterior surfaces and an interior busbar disposed in electrical contact with the interior surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Specifically referenced is U.S. patent application Ser. No. 11/103,333 entitled “Stack Configurations for Tubular Solid Oxide Fuel Cells”, filed on Apr. 11, 2005, the entire disclosure of which is incorporated herein by reference. 
     
    
       [0002]     The United States Government has rights in this invention pursuant to contract no. DE-AC05-00OR22725 between the United States Department of Energy and UT-Battelle, LLC. 
     
    
     FIELD OF THE INVENTION  
       [0003]     The present invention relates to stack configurations for solid oxide fuel cells (SOFC), and more particularly to stack configurations for SOFC having metallic support tube sheets with interior fuel cell membranes.  
       BACKGROUND OF THE INVENTION  
       [0004]     Devices commonly known as fuel cells comprise plates or tubes that directly convert to electricity the energy released by oxidation of hydrogen. Fuel cells offer the potential for a clean, quiet, and efficient power source for portable electric generation. Solid oxide fuel cells (SOFC), particularly tubular solid oxide fuel cells (TSOFC), are particularly attractive candidates for applications in distributed or centralized power applications.  
         [0005]     SOFC technology has the potential for providing high power densities, long, stable performance lifetimes, the ability to utilize a broad source of fuels without expensive reforming or gas cleanup, and provide high system efficiencies for a wide range of power generation for transportation.  
         [0006]     Critical limitations of the current state of SOFC technology such as long start-up times (generally many minutes to hours) and high cost of materials manufacture have significantly impacted consideration thereof for automotive applications.  
         [0007]     OBJECTS OF THE INVENTION  
         [0008]     Accordingly, objects of the present invention include: provision of SOFC configurations that minimize the use of costly materials, minimize manufacturing costs, minimize startup times, and maximize power generation efficiency. Further and other objects of the present invention will become apparent from the description contained herein.  
         [0009]     SUMMARY OF THE INVENTION  
         [0010]     In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a fuel cell unit that includes an array of solid oxide fuel cell tube sheets having porous metallic exterior surfaces, interior fuel cell layers, and interior surfaces, and at least one header in operable communication with the array of solid oxide fuel cell tube sheets for directing a first reactive gas into contact with the porous metallic exterior surfaces and for directing a second reactive gas into contact with the interior surfaces, the header further comprising at least one busbar selected from the group consisting of an exterior busbar disposed in electrical contact with the porous metallic exterior surfaces and an interior busbar disposed in electrical contact with the interior surfaces. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is an oblique, not-to-scale view of a portion of a fuel cell tube sheet in accordance with an embodiment of the present invention.  
         [0012]      FIG. 2  is an oblique, not-to-scale view of a portion of a fluted fuel cell tube sheet in accordance with an embodiment of the present invention.  
         [0013]      FIG. 3   a  is a schematic end view of a fuel cell tube sheet assembly in accordance with an embodiment of the present invention.  
         [0014]      FIG. 3   b  is a schematic end view of a fuel cell tube sheet assembly in accordance with an embodiment of the present invention.  
         [0015]      FIG. 3   c  is a schematic end view of a fuel cell tube sheet assembly in accordance with an embodiment of the present invention.  
         [0016]      FIG. 3   d  is a schematic end view of a fuel cell tube sheet assembly in accordance with an embodiment of the present invention.  
         [0017]      FIG. 4   a  is an oblique, exploded view of a fuel cell assembly in accordance with an embodiment of the present invention.  
         [0018]      FIG. 4   b  is a magnification of part of the fuel cell assembly shown in  FIG. 4   a.    
         [0019]      FIG. 5  is an oblique view of a fuel cell assembly in accordance with an embodiment of the present invention.  
         [0020]      FIG. 6  is an oblique, exploded, partial view of a fuel cell assembly in accordance with an embodiment of the present invention wherein the tube sheets are connected in parallel.  
         [0021]      FIG. 7  is an oblique, cutaway, partial view of the fuel cell assembly shown in  FIG. 6 .  
         [0022]      FIG. 8  is an oblique view of a header in accordance with an embodiment of the present invention wherein the tube sheets are connected in series.  
         [0023]      FIG. 9  is an oblique view of the other side of the header shown in  FIG. 8 .  
         [0024]      FIG. 10  is an oblique view of a header of the other end of a fuel cell assembly from the header shown in  FIG. 8 .  
         [0025]      FIG. 11  is an oblique view of the other side of the header shown in  FIG. 10 .  
         [0026]      FIG. 12  is an axial cutaway top view through an assembled tube sheet and header in accordance with an embodiment of the present invention. 
     
    
       [0027]     Equivalent elements in the figs. are identified with like numerals.  
         [0028]     For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The present invention improves SOFC by using a combination of an exterior, preferably metallic support structure and interior membranes in unique stack configurations. Referring to  FIG. 1 , an example of a SOFC tube sheet  10  defines an array of integral, generally cylindrical openings  18  having annular cross-sections. The tube sheet  10  can be comprised of any robust, porous, conductive material, preferably metallic. The tube sheet  10  can be made by any conventional means such as molding, extrusion, casting, forging, isostatic compression, etc. The tube sheet should be open on both ends; the openings  18  pass completely therethrough.  
         [0030]     Each generally cylindrical opening  18  defined by the tube sheet  10  is coated on the inside thereof with a porous anode  12  such as Ni—Ni Yttria stabilized zirconia (YSZ), for example. The anode  12  is coated on the inside with a dense electrolyte  13  such as Y 2 O 3 —ZrO 2 , for example. The dense electrolyte  13  is coated on the inside with a porous cathode  14  such as LaMnO3, for example. The compositions used to make the SOFC tube sheet are not critical to the present invention. Moreover, the anode and cathode layers can be interchanged.  
         [0031]     The cross-sectional shape of the tube sheet  10  and the openings  18  defined thereby are not critical to the invention, although some shapes will be found to be more beneficial, especially those shapes which promote contact of reactive gases with respective surfaces of the tube sheet  10 . Referring to  FIG. 2 , an example of a differently shaped SOFC tube sheet  20  shows that inner and/or outer surfaces  22 ,  24  can have wavy shape that increases surface area and promotes turbulence of reactive gases.  
         [0032]      FIG. 3   a  shows an embodiment of the invention wherein tube sheets  10  are arranged in a stack  120  having a staggered configuration, being separated by serpentine gaps  26  that promote turbulence of reactive gases flowing therethrough. A non-staggered arrangement may also be suitable. Although nonlinear gaps  26  are preferable, embodiments of the invention with linear gaps would also be operable.  
         [0033]     The shapes of the tube sheets and gaps therebetween are infinitely variable in accordance with the present invention. For example,  FIGS. 3   b,    3   c,  and  3   d  show, respectively, embodiments of the invention having tube sheets  30 ,  34 ,  38  having various shapes, thereby defining gaps  32 ,  36 ,  40  that are of different shapes.  
         [0034]     Referring to  FIGS. 4   a,    4   b,  and  5 , the tube sheets  10  can be arranged in a stack  120  in a SOFC unit  50 . The SOFC unit  50  comprises a housing (case)  52  and end caps  54 ,  56 . An intake end cap  54  has air intake openings  58  to admit air into the unit  50 , a fuel inlet  60 , and an electrical terminal port  62 , generally including a seal and/or electrical insulation. An exhaust end cap  56  has a fuel exhaust port  64  and air exhaust openings similar to the air intake openings  58 . The intake end cap  54  and exhaust end cap  56  can be identical except for accommodation of the interior electrical terminal port  62 , which can be located wherever it may be convenient, such as at either or both end caps  54 ,  56 . The tube sheets  10  are held in respective positions in the SOFC unit  50  by the components at each end thereof, which are described hereinbelow.  
         [0035]      FIGS. 4   a,    4   b,    5 ,  6 ,  7   a,  and  7   b  show embodiments of the invention wherein the tube sheets  10  are interconnected in parallel fashion. The stack  120  of tube sheets  10  is enclosed on each end by a support means that can include various functional components. The first such component is an exterior busbar  124  that is in electrical communication with the outer, metallic components of the tube sheets  10 . The exterior busbar  124  has slot-shaped openings  126  that fit and align with the tube sheets  10  for allowing air to enter the openings  18  therethrough. The exterior busbar  124  can have posts, wings, flanges, or other type of extensions  125  that are associated with the openings  126  and extend over the tube sheets  10  and contact the exterior surfaces thereof of to provide electrical communication therewith. The exterior busbar  124  can be brazed, welded, press-fit, or otherwise robustly attached onto each tube sheets  10  in order to hold the stack  120  together and/or provide dependable electrical connection. Other plates (not illustrated) similar in shape to the exterior busbar  124 , either conducting or non-conducting, can be used to support the tube sheets  10  between the ends thereof. The exterior busbar  124  can have an integral terminal  127  such as a tab, prong, or post, for example.  
         [0036]     The next component is an insulator  128  having openings  130  that align with the tube sheets  10  for allowing air to enter the openings  18  therethrough. The insulator  128  seals against the exterior busbar  124 .  
         [0037]     The next component is an interior busbar  132  having openings  134  that align with the tube sheets  10  for allowing air to enter the openings  18  therethrough. The interior busbar  132  seals against the insulator  128 , which prevents electrical contact between the exterior busbar  124  and the interior busbar  132 . The interior busbar  132  has posts, wings, flanges, or other type of extensions  136  that are associated with the openings  134  and extend into the openings  18  and contact the interior surfaces of the tube sheets  10  to provide electrical communication therewith. The interior busbar  132  can be brazed, welded, press-fit, or otherwise robustly attached into each tube sheet  10  in order to hold the stack  120  together and/or provide dependable electrical connection. The interior busbar  132  can have an integral terminal  137  such as a tab, prong, or post, for example.  
         [0038]     The next component is an end cap  54  which is either insulating or includes an insulating (i.e., electrically insulating) inner liner to prevent electrical contact and subsequent shorting of the busbars  124 ,  132 . The end cap  54  can have an insulating terminal support  62  to accommodate the terminals  127 ,  137 . The insulating terminal support  62  can be a grommet, an interlocking connector, or any other structure that provides at least one of ease of assembly, terminal support, insulation, reinforcement, and fastening. The end cap  54  can have a groove  55  or other means for sealable attachment to the housing  52 .  
         [0039]     The exterior busbar  124 , insulator  128 , and interior busbar  132  can be integrated into a single component having a plurality of layers. The insulator can serve as a support for the tube sheets  10 , and can have conductive (for example, metal) coatings on either side to serve as busbars  124 ,  132 .  
         [0040]      FIGS. 8-12  show an embodiment of the invention wherein the tube sheets  10  are interconnected in series fashion. Robust, insulating support plates  302 ,  352 , support the tube sheets  10  on either end of the stack. At least one of the insulating support plates further includes accommodation of an electrical terminal; a terminal tab  308  is used in the example shown. The insulating support plates  302 ,  352 , have holes  360 ,  362  respectively, that align with the openings  18  in the tube sheets  10  for allowing air to enter therethrough  
         [0041]     Exterior busbars  310  and interior busbars  312  are adherently disposed on respective sides of the support plates  302 ,  352  in patterns with insulated separation ribs  322  as shown that connect the tube sheets  10  in series and parallel as desired. The patterns shown connect the tube sheets  10  in parallel vertical stacks which are connected in series horizontally. The exterior busbars  310  and interior busbars  312  extend over respective sides of the terminal tab  308  to provide respective external electrical connections  314 ,  316  to a mating connector (not illustrated).  
         [0042]     The tube sheets  10  fit into slots  304  in the exterior and interior busbars  310  and abut the support plates  302 ,  352 . Solder joints  326  can be used to fasten the exterior busbars  310  to the exteriors of the tube sheets  10  and provide electrical connection thereto. Hollow pins such as rivets  320  can be used to pass through the holes  304  and provide electrical connection to the interiors of the tube sheets  10 . Solder joints  328  can be used to fasten the rivets  320  to the interior busbars  312 .  
         [0043]     The skilled artisan will recognize that fuel and air inlets described above are of a typical nature, and can be of any suitable size, shape, configuration, and/or location on the unit. Moreover, the skilled artisan will recognize that electrical terminals described in all of the embodiments above are of a typical, conventional nature, and can be of any suitable size, shape, configuration, and/or location on the unit. The terminals can be battery posts or can be incorporated into one or more electrical plugs, connectors, sockets, and/or the like. The terminals can be connected to the current collectors by any suitable conventional means, such as, for example, wires, plates, strips, and the like.  
         [0044]     Features of the present invention provide advantages of sealing as the metallic support allows for the use of brazes and welds.  
         [0045]     While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be prepared therein without departing from the scope of the inventions defined by the appended claims.