Abstract:
A fuel cell system includes a fuel reformer configured to react a raw fuel and oxygen to produce a reformed fuel. The fuel cell system further includes a fuel cell configured to generate electricity by reacting oxygen at a first electrode and reformed fuel at a second electrode. The fuel cell system further includes a plate member at least partially defining an air chamber wall, an air chamber inlet, and an air chamber outlet. The air chamber is configured to route air to at least one of the fuel reformer and the first electrode of the fuel cell stack.

Description:
GOVERNMENT INTERESTS 
       [0001]    This invention was made with government support under contract number 2008*1177616*000, awarded by the U.S. Department of Defense. The government has certain rights in this invention. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention is related to air flow management in solid oxide fuel cell systems. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Fuel cells can generate electricity be reacting a fuel and an oxidant on opposite electrodes of an electrochemical cell. Portable fuel cell systems can operate utilizing a raw fuel contained onboard. Raw fuel requires further processing prior to utilization by the electrochemical cell. Raw fuel can be refined through a process that includes filtering the raw fuel through a filter and reforming the raw fuel by reacting the raw fuel with an oxidant at an onboard reformer to partially oxidize the fuel. Once the raw fuel is processed, the fuel is suitable for use as a fuel cell fuel, that is, a fuel which can be utilized by the electrochemical cell. 
         [0005]    Several components are utilized to process raw fuel to fuel cell fuel. Exemplary components include various pumps, blowers, fans, filters, reformers, and sensors, each of which can significantly increase the volume, weight, and overall cost of the fuel cell system. For example, there is significant volume, weight, and costs associated with components that deliver and control air flow to the anode and to the cathode of the fuel cell. The anode air flow stream is supplied to the onboard reformer and the anode air flow stream flow rate is controlled to control an air-to-fuel ratio to reform fuel by partial oxidation. To achieve the desired air-to-fuel ratio, the fuel cell systems includes anode air processing components including an air filter, controllable actuators, feedback control sensors, and various air delivery components. Further, fuel cell systems include fuel processing components including a fuel filter, controllable actuators, feedback control sensors, regulators, heating elements and expansion chambers and various fuel delivery components to deliver fuel to a proper locations within the fuel cell system where the fuel can mix with the anode air flow stream prior to delivery to the onboard reformer. The fuel cell system further includes components to direct reformed fuel from the onboard reformer to the fuel cell anode, thereby providing fuel for electrochemical fuel cell reactions. 
         [0006]    Further, fuel cell systems can include components to provide other desirable operating characteristics. For example, the fuel cell system can include heat and energy management systems and can include components to dampen vibrational forces or mechanically isolated portions of the fuel cell system from vibration and shock. Design features that manage heat and energy and that provide robustness can further add to the overall weight, volume, and cost of the fuel cell system. 
         [0007]    Therefore, there is a need for robust fuel cell systems with onboard reforming that is easy to manufacture, low cost, and that a have high power to volume ratio and a high power to weight ratio. 
       SUMMARY 
       [0008]    Disclosed herein in accordance with exemplary embodiments is a fuel cell system including a fuel reformer configured to react a raw fuel and oxygen to produce a reformed fuel. The fuel cell system further includes a fuel cell configured to generate electricity by reacting oxygen at a first electrode and reformed fuel at a second electrode. The fuel cell system further includes a plate member at least partially defining an air chamber wall, an air chamber inlet, and an air chamber outlet. The air chamber is configured to route air to at least one of the fuel reformer and the first electrode of the fuel cell stack. The first air actuator is configured to motivate air flow from the inner chamber to at least one of the fuel reformer and the first electrode of the fuel cell stack. 
     
    
     
       FIGURES 
         [0009]      FIGS. 1 and 2  are prospective views of a fuel cell system in accordance with an exemplary embodiment of the present disclosure; 
           [0010]      FIG. 3  is an exploded view of the fuel cell system of  FIG. 1 ; 
           [0011]      FIG. 4  is a cutaway prospective view of the fuel cell system of  FIG. 1 ; and 
           [0012]      FIG. 5  is a prospective view of a lower plate member of an integrated plate member of the fuel cell system of  FIG. 1 ; 
       
    
    
       [0013]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the solid oxide fuel cell as disclosed here, including, for example, specific dimensions of the catalytic substrate will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others for visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity of illustration. All references to direction and position, unless otherwise indicated, refer to the orientation of the solid state electrochemical device illustrated in the drawings. 
       DESCRIPTION 
       [0014]    Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,  FIGS. 1 and 2  depict differing prospective views an exemplary fuel cell system  10 . As will be discussed in further detail, the exemplary fuel cell system  10  has advanced integrated features providing substantial cost, weight and volume reduction over previous fuel cell system designs. 
         [0015]    The fuel cell system  10  includes a fuel cell stack  12  and a balance of plant subsystem  14 . The fuel cell stack  12  comprises the power generating component of the fuel cell system  10 . The balance of plant subsystem  14  includes fuel and air management components of the fuel cell system  10 , which deliver fuel and air to desired locations of the fuel cell stack  12  and can remove exhaust fluid from the fuel cell stack  12 . 
         [0016]    The balance of plant subsystem  14  includes an integrated air handling plate  20 , a rechargeable battery  19 , power electronics system  25 , an exhaust blower  26 , anode air/fuel delivery system  30 , a user interface (not shown), heat management systems, environmentally sealed air, power and lines with wall passthroughs (not shown). 
         [0017]    The rechargeable battery  19  can be any battery suitable for hybridization with the fuel cell stack  12  through the power electronics system  25 . The rechargeable battery  19  can comprise any of several rechargeable battery technologies including, for example, nickel-cadmium, nickel-metal hydride, lithium-ion, and lithium-sulfur technologies. In alternative embodiments, other reversibly energy storage technologies such as ultra-capacitors can be utilized in addition to or instead of the rechargeable battery  19 . Further in alternate embodiments, multiple energy storage devices can be utilized within a fuel cell system  10 . 
         [0018]    The power electronics system  25  includes an electrically conductive network configured to route power between the fuel cell stack  12  and the battery  19  and from the energy conversion devices (fuel cell stack  12  and the battery  19 ) to the face plate (not shown). Power levels within the power electronics  25  can be controlled utilizing power conversion members (not shown) controlled by a control system  16  ( FIG. 3 ) 
         [0019]    The exhaust blower  26  is configured to drive exhaust gases away from the fuel cell stack  12  in an exhaust flow path direction. In an exemplary embodiment the exhaust blower  26  is further configured to draw heat away from the integrated air handling plate  20 . In an alternate embodiment, the integrated air handling plate  20  is positioned to intersect the exhaust flow path substantially perpendicular to the exhaust flow path direction such that the exhaust gases provide preheating to air within the integrated air handling plate  20 . The anode air blower  28  is configured to motivate anode air at controlled flow rates to the fuel cell stack  12 . The anode air/fuel delivery system  30  includes a fuel valve  21  (which is integrated into the plate member integrated air handling plate  200  and an air fuel mixing point  19 . Fuel is delivered at controlled flow rates to the anode air/fuel delivery system  30  and is mixed with controlled amounts of air such that desired amounts of fuel along with a desired ratio of air to fuel is delivered to onboard reformers  100  ( FIG. 5 ) of the fuel cell stack  12 . The fuel level is controlled utilizing a fuel flow sensor and feedback control to actuate a fuel valve (not shown) to desired positions. Although the exemplary balance subsystem  14  is described having various exemplary actuators for motivating gases throughout the fuel cell system  10 , it is to be understood that other types of actuators (for example, pumps, fans, and blowers) can be utilized to motivate gasses. 
         [0020]    Referring to  FIG. 3 , a lower plate member  22  of the integrated plate member  20  includes a base plate  21  and elevated portions defining an anode air chamber  24  and a cathode air chamber  26 . The elevated portions are cut from metal plates and attached to the base plate  21 . The lower plate member  22  includes openings through the base plate  21  defining an anode blower opening  42 , a cathode air filter opening  36 , an anode air filter opening  54 , and an anode blower opening  64 . 
         [0021]    The cathode air chamber  26  includes the cathode air filter opening  36 , a first cathode air reservoir  28 , an air pinch point portion  31 , a second cathode air reservoir  32 , and a cathode blower opening  42 . The integrated air handling plate  20  further includes a first pressure sensor  38  and a second pressure sensor  40  coupled thereto. During operating, air is routed through the filter opening  36  to the cathode air reservoir  28  and is further routed downstream through the pinch point portion  31 , through the reservoir  32  and out the blower opening  42 . The pressure sensor  40  monitors a first pressure level indicative of air pressure within the cathode air reservoir  28 . The pressure sensor  38  monitors a second pressure level indicative of air pressure at the pinch point portion  31 . 
         [0022]    A control system  16  can determine a flow rate through the pitch point portion  31  and therefore can determine a flow rate of air passing through the cathode air chamber  26  based on the first pressure level signal, the second pressure level signal, and the known cross-sectional area of the first cathode air reservoir  28  perpendicular to air flux and the cross-sectional area of the pinch point portion  31  perpendicular to air flux through the cathode air chamber  26 . Specifically, the control system  16  utilizes the first and second pressure levels in the Bernoulli Equation along with specific calibrations to compensate for the compressibility of air. Utilizing pressure sensors at locations having differing cross-sectional areas provides significant cost reduction advantages (on the order of one tenth the cost) of traditional flow sensors to measure fluid flow within fuel cell systems. 
         [0023]    The anode air chamber  24  includes the anode air filter opening  54 , a first anode air reservoir  56 , an air pinch point portion  70 , a second anode air reservoir  62  and an anode blower opening  64 . The integrated air handling plate  20  further includes a third pressure sensor  58  and a fourth pressure sensor  60  disposed within the anode air chamber  24 . During operating, air is routed through the anode air filter opening  54  to the first anode air reservoir  56  and is further routed downstream through the pinch point portion  70 , through the second anode reservoir  62  and out the anode blower opening  64 . The third pressure sensor  58  monitors a third pressure level indicative of air pressure within the anode air reservoir  56 . The fourth pressure sensor  60  monitors a fourth pressure level indicative of air pressure at the pinch point portion  70 . 
         [0024]    A control system  16  can determine a flow rate through the pinch point  70  and therefore can determine a flow rate of air passing through the cathode air chamber  24  based on the first pressure level signal, the second pressure level signal, and the known cross-sectional areas for fluid flow at the cathode air reservoir  56  and the pinch point portion  70 . 
         [0025]    Alternate designs can incorporate other flow sensor designs, including, for example, various mechanical and electromagnetic flow sensors, temperature-based flow sensors, ultrasonic flow sensors, and coriolis flow sensors can be utilized to measure air and fuel flow rates. 
         [0026]      FIG. 4  depicts an exploded view of the integrated plate member  20  including a cathode blower assembly  80 , an anode air filter  84 , a cathode air filter  86 , the lower plate portion  22 , and upper plate portions  90 . 
         [0027]    During operation air enters an outer housing (not shown) of the fuel cell system  10  into a housing chamber wherein the air then travels through the anode air filter  84  and the cathode air filter  86 . Air filtered through the anode air filter  84  is routed to the anode air chamber  24 , and air filtered through the cathode air filter  86  is routed to the cathode air chamber  26 . The anode and cathode air filter can comprise filters generally capable with removing particulates or other potentially substances from the air flow stream prior to utilization as an oxidant within the fuel cell system  10 . 
         [0028]    The cathode air blower assembly  80  includes a blower housing (not shown), a cathode air blower impeller  81  powered by an electric motor (not shown). The cathode air blower impeller  81  is mounted on a side of the lower plate portion  22  opposite the second cathode air reservoir  32  of the lower plate portion  22 . The cathode air blower housing comprises a cut metal member coupled to the side of the lower plate member  22  thereby integrating the cathode air blower impeller  81  and blower impellers housing within the integrated air handling plate  20 . The cathode air blower assembly  80  motivates the cathode air from the cathode blower chamber  32  through a resilient boot member  88  to the fuel cell stack  12 . The integration of the cathode air blower assembly  80  within the integrated air handling plate  20  provides advantages in that cathode air blower assembly  80  provides cost advantages by utilizing sheet metal components and shared components with the lower plate member. In alternate embodiments portions of the integrated air handling plated can be formed from alternate materials such as polymer based materials and be formed through alternate processing, for example, injection molding and/or stamping. The integrated design reduces part count, decreasing assembly and manufacturing times and increasing manufacturing quality to reduce costs. The integration of the cathode air blower assembly within the integrated air handling plate  20  provides weight and size advantages when compared with non-integrated designs. Further, the integration of the cathode blower assembly  80  provides high mechanical strengths and high resistance to vibrational forces and ability to integrate active cooling to electrical components, to seal components and to integrate active cooling of electrical components. 
         [0029]    The upper plate portions  90  comprises cut metal components that are fastened to lower plate portion  22  to enclose the anode air chamber  24  and cathode air chamber  26 . Portions of the power electronics system  25  are mounted to the upper plate portions  90  proximate the anode chamber  24  and the cathode chamber  26 . By mounting the power electronics proximate the air flow passageways, heat can be transferred away from the power electronics system and to the air in the anode air chamber  24  and the cathode air chamber  26  thereby providing benefits of removing heat form the power electronics system  25  and preheating the anode air stream and cathode air stream prior to providing the anode air flow stream and the cathode air flow streams to the fuel cell stack  12 . 
         [0030]    The balance of plant subsystem  14  is mechanically isolated from the fuel cell stack  12 . The balance of plant subsystem  14  for each of anode air blowers are coupled to the fuel cell stack utilizing resilient members  98 . 
         [0031]    The anode air/fuel delivery system  30  includes an air/fuel mixing portion (not shown) and an air/fuel blower assembly  96  fluidly coupled to the integrated plate member  20  by a resilient member  102 . The air/fuel blower assembly  96  includes an interface housing  104  and a blower housing  106 . During operation fuel is routed through integrated plate member  20 , through resilient member  102 , through the air fuel mixing point  19 , through the interface housing  104  and through the blower housing  106  and into the fuel cell stack  12 . The blower housing included a motor-powered impellers (not shown) therein to motivate the air and the fuel from the integrated plate member to the fuel cell stack  12 . 
         [0032]    The exemplary fuel cell system  10  provides several features contributing to the ability to mass manufacture the fuel cell and contributing to energy-to-mass and energy to volume ratios and to high manufacturability. For example, the fuel cell system includes a substantially flat, integrated plate member that is easy to manufacture in that the integrated plate member is formed by cutting plates and coupling the plates together. Further, the design geometry allows for injection molding which allows for low part costs at high volumes. 
         [0033]    The integrated plate member  20  includes a design that integrates several features of previous fuel cell systems. For example, the integrated plate member  20  includes channels for routing wherein previous designs included separate tubes and hoses to route fluid between system components. Further, the integrated plate member includes several mounting points for several subcomponents, wherein previous designs included separate brackets and housing portions for mounting. Further, the integrated plate has temperature management features that decreases stack volume over previous stack designs and requires less energy to manage temperature than previous stack designs. Still further, the integrated plate member requires fewer components and comprises low-cost, easy-to-manufacture sheet metal components (or alternate materials such as polymer-base material), which requires lower costs than previous system designs. 
         [0034]    Referring to  FIG. 5 , the fuel cell stack  12  includes a manifold member  91  a fuel feed tube  110 , an onboard fuel reformer  100 , fuel cell tubes  120 , tube support members  112 , an insulated body  114 , and recuperator  116 . 
         [0035]    The manifold member  91  is provided to receive air and fuel from the anode air/fuel delivery system  30  and to deliver the air and fuel mixture to each of the fuel feed tubes  110 . The manifold member  91  is connected to each of the fuel cell feed tubes  110  such that a substantially gas-tight seal is maintained between an inner chamber of each fuel feed tubes  110  and an inner chamber of the manifold member  91 . In one embodiment, the manifold member comprises a resilient member, for example, a flexible tube. The resilient member allows for movement of the plurality of fuel cell tubes connected to the manifold member relative to other fuel cell components. The resilient member can further dampen oscillations and reduce mechanical stresses on components of the fuel cell system due to movement of fuel cell components relative to each other. Movement of fuel cell components relative to each other can be caused by external forces on the fuel cell system (for example, vibrational movement), by thermal expansion mismatch between fuel cell system components and by fluid flow within the fuel cell system. 
         [0036]    The fuel feed tubes  110  are disposed partially within the fuel cell tubes  120 . The onboard fuel reformer  100  is positioned within each of the fuel cell tubes  120  proximate an electrochemically active area of the fuel cell tubes  120 . The anode air and unreformed fuel is routed through the fuel feed tube  110  to the onboard fuel reformer  100  where the fuel is reformed and the resulting reformed fuel is heated during the exothermic reformation reactions (for an exemplary fuel cell system having an internal onboard fuel reformer, see U.S. patent application Ser. No. 10/979,017 which is hereby incorporated by reference herein.) In alternate embodiments, the fuel can be reformed utilizing endothermic reaction and the fuel cell tubes can be heated to operating temperatures utilizing alternate heating devices such as an internal combustor or a resistance heating device. 
         [0037]    The fuel cell tubes  120  each comprise an anode layer, an electrolyte layer, and a cathode layer at the active portion that generates electromotive force at the active portion at operating temperatures in the range of 700 to 850 degrees Celsius. However, only the active portion of the fuel cell tube contains the anode layer, the electrolyte layer, and the cathode layer, and therefore, only a portion of the fuel cell tube requires high operating temperatures for generating electromotive force. 
         [0038]    The insulated body  114  comprises composite insulation material that can maintain the fuel cell stack  12  at the operating temperatures. The recuperator  116  is provided to transfer heat between the exhaust gases generated within the fuel cell stack  12  and the cathode air stream inlet to the fuel cell stack  12 . In an alternate embodiment, heat exchangers can be utilized to transfer heat between other fluid streams. 
         [0039]    From the foregoing disclosure and detailed description of certain embodiments, it will be apparent that various modifications, additions and other alternative embodiments are possible without departing from the true scope and spirit of the invention. The embodiments discussed were chosen and described to provide illustrations of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to use the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.