Abstract:
A method of forming a synthesis gas utilizing a reformer is disclosed. The method utilizes a reformer that includes a plasma zone to receive a pre-heated mixture of reactants and ionize the reactants by applying an electrical potential thereto. A first thermally conductive surface surrounds the plasma zone and is configured to transfer heat from an external heat source into the plasma zone. The reformer further includes a reaction zone to chemically transform the ionized reactants into synthesis gas comprising hydrogen and carbon monoxide. A second thermally conductive surface surrounds the reaction zone and is configured to transfer heat from the external heat source into the reaction zone. The first thermally conductive surface and second thermally conductive surface are both directly exposed to the external heat source. A corresponding apparatus and system are also disclosed herein.

Description:
RELATED APPLICATIONS 
       [0001]    This patent application is a divisional application of and claims priority to U.S. patent application Ser. No. 12/537,953, filed Aug. 7, 2009, which claims priority to U.S. Provisional Patent Application No. 61/087,549, filed Aug. 8, 2008, and which is a continuation-in-part of U.S. patent application Ser. No. 11/745,942, filed May 8, 2007, which claims priority to U.S. Provisional Patent Application No. 60/798,863, filed May 8, 2006. These applications are incorporated by reference. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    At least part of the technology disclosed in this patent application may have been funded by the United States Government under the following contracts: Department of Energy DE-FG-02-07ER84663, Department of Defense (Army) W56-HZV-07-C-0577 and Department of Defense (Navy) N00014-07-M-0450. The United States Government may have certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to liquid fuel reformation and more particularly to systems and methods for reforming liquid fuels for use in fuel cell systems. 
       DESCRIPTION OF THE RELATED ART 
       [0004]    As a society, we often take for granted the mobility (power and range) afforded by the energy storage density of common transportation fuels such as gasoline, aviation kerosene, and diesel fuel. The legacy investment in the refueling infrastructure alone makes it apparent that fuel cell technology capable of utilizing these existing fuels may have a distinct advantage over those restricted to high purity hydrogen or other less widely available fuels. The ability to utilize reformate produced from these existing transportation fuels, as well as from emerging non-petroleum based fuels such as bio-diesel, and synthetic (Fischer-Tropsch) liquids, without the need for extensive cleanup is one of the greatest advantages of solid oxide fuel cells (SOFCs). 
         [0005]    The higher efficiency of fuel cells compared to conventional engines is one of the main characteristics motivating the development and eventual commercialization of fuel cells. In stationary applications, utilizing natural gas fuel, this efficiency advantage is well established. However, where liquid fuels are used, a fuel processor used to reform liquid fuel exacts a heavy efficiency penalty on a fuel cell system. Historically, the sulfur and aromatic content of transportation fuels has made them impossible to reform using the catalytic steam reforming process used with natural gas systems, due to problems with “poisoning” the catalyst and carbon buildup. Instead, partial oxidation processes (e.g., POX, CPOX, ATR, etc.) have been employed, with varying degrees of practicality. 
         [0006]    Although reformate produced by partial oxidation typically represents about 80% of the energy content of the fuel as measured by heating value, the use of any partial oxidation process coupled to any type of fuel cell results in a loss in the range of 30 to 40% of the electric power generation potential of the fuel. This is primarily due to the fact that a fuel cell is not a heat engine. Rather, a fuel cell may be considered a Faradaic engine, and the Faradaic (current producing) potential of any fuel cell is reduced by 4 Coulombs for each mole of O 2  introduced in the partial oxidation process. Although steam reforming does not suffer from such an effect, no suitable catalysts are known for high-sulfur, hydrogen-lean transportation fuels. 
         [0007]    In view of the foregoing, what is needed is an improved system and method for generating reformate from various fuels that improves the Faradaic efficiency of fuel cells, such as solid oxide fuel cells (SOFCs), molten-carbonate fuel cells (MCFCs), or phosphoric acid fuel cells (PAFCs). Ideally, such a system and method would be capable of reforming fuels with high sulfur content (e.g., 10,000 ppm) without requiring sulfur pre-removal, while avoiding problems such as “poisoning” the catalyst or carbon buildup. Further needed is system and method for utilizing the heat generated by fuel cells such as SOFCs and MCFCs to improve the overall efficiency of fuel reformation and electricity production. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention has been developed in response to the present state of the art and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available apparatus and methods. Accordingly, the invention has been developed to provide a plasma-catalyzed, thermally integrated reformer for fuel cell systems. The features and advantages of the invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter. 
         [0009]    Consistent with the foregoing, an improved reformer is disclosed herein. In one embodiment, such a reformer may include a plasma zone to receive a pre-heated mixture of reactants and ionize the reactants by applying an electrical potential thereto. The ionized species are strongly accelerated to the oppositely charged electrode. In the process they undergo collisions which create free radicals, as well as species having excess translational, vibrational and electronic energy states compared to the equilibrium distributions predicted by kinetic theory. Species having any of these activated states are more reactive, and also change the reactions pathway. For convenience in describing this effect, and since the process starts with ionization, the collection of activated species will be referred to as ionized reactants. A first thermally conductive surface surrounds the plasma zone and is configured to transfer heat from an external heat source into the plasma zone. The reformer further includes a reaction zone to chemically transform the ionized reactants into synthesis gas comprising hydrogen and carbon monoxide. A second thermally conductive surface surrounds the reaction zone and is configured to transfer heat from the external heat source into the reaction zone. The first thermally conductive surface and second thermally conductive surface may both be directly exposed to the external heat source. 
         [0010]    A corresponding method and system are also disclosed and claimed herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    In order to describe the manner in which the above-recited features and advantages of the present invention are obtained, a more particular description of apparatus and methods in accordance with the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the present invention and are not, therefore, to be considered as limiting the scope of the invention, apparatus and methods in accordance with the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0012]      FIG. 1  is a high-level block diagram of one prior art system for generating synthesis gas for a fuel cell; 
           [0013]      FIG. 2  is high-level block diagram of one embodiment of a system in accordance with the invention, providing improved synthesis gas production; 
           [0014]      FIG. 3  is a high-level block diagram of one embodiment of a reformer in accordance with the invention, integrated with a fuel cell; 
           [0015]      FIG. 4  is a high-level block diagram of one embodiment of a reformer in accordance with the invention; 
           [0016]      FIGS. 5A through 5C  are several schematic profile views of an embodiment of a gliding arc plasma generator; 
           [0017]      FIG. 6  is a high-level block diagram of a thermally integrated reformer and fuel cell; 
           [0018]      FIG. 7  is a cutaway schematic view of one embodiment of a reformer in accordance with the invention; 
           [0019]      FIGS. 8A through 8C  are several perspective views of various components of a reformer in accordance with the invention; 
           [0020]      FIGS. 9A and 9B  are perspective views of other components of a reformer in accordance with the invention; 
           [0021]      FIG. 10  is a high-level block diagram of one embodiment of a reformer integrated with a Fischer-Tropsch process and used to generate synthetic fuel; 
           [0022]      FIG. 11  is a graph showing the fuel equivalence ratio operating range for a multi-mode reformer; 
           [0023]      FIGS. 12A through 12D  are side views of various different alternative shapes for the reformer; 
           [0024]      FIG. 13  is a perspective cutaway view of one embodiment of a reformer having the shape illustrated in  FIG. 12A ; 
           [0025]      FIG. 14  is a perspective view of one embodiment of a thermally integrated reformer and fuel cell, wherein the reformer has a shape similar to that illustrated in  FIG. 13 ; and 
           [0026]      FIG. 15  is a perspective view of an alternative embodiment of the gliding arc plasma generator illustrated in  FIGS. 5A through 5C . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of apparatus and methods in accordance with the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
         [0028]    Referring to  FIG. 1 , in general, a prior art system  100  for producing electricity using a feedstock fuel  106  as an input may include a reformer  102 , or fuel processor  102 , and a fuel cell  104 . The reformer  102  may receive and process a hydrocarbon feedstock fuel  106  to produce synthesis gas  112  containing a mixture of carbon monoxide and hydrogen gas. This synthesis gas  112  in addition to oxygen  114  may be used by the fuel cell  104  to produce electricity  116 . In certain embodiments, the fuel cell  104  may generate CO 2 +H 2 O  118  and heat  120  as a byproduct. 
         [0029]    Where natural gas or methane is used as the feedstock fuel  106 , a reformer  102  may utilize a process such as steam methane reforming (SMR) to produce synthesis gas  112 . This process generally involves reacting the methane with steam in the presence of a metal-based catalyst to produce the desired synthesis gas  112 . SMR and similar processes, however, are unable to reform liquid transportation fuels such as conventional diesel, heavy fuel oil, or jet fuel (e.g., JP-8, JP-10, Jet-A, etc.). This is because the sulfur and aromatic content of transportation fuels makes them difficult or impossible to reform using SMR, at least in part because of problems with “poisoning” the catalyst and carbon buildup. Instead, partial oxidation processes (e.g., POX, CPOX, ATR, etc.) are normally employed to reform transportation fuels. 
         [0030]    In general, a partial oxidation process may include partially combusting a sub stoichiometric mixture of fuel  106  (which may include chains of CH 2  groups) and oxygen  108 . The combustion reaction is exothermic and provides heat  110  necessary to reform the remaining fuel  106  to generate synthesis gas  112 , the reformation reaction of which is endothermic. The heat of reformation is on the order of 30 percent of the heat generated by completely combusting the fuel  106 , which can be obtained by partially combusting the fuel. Where fuels  106  are high in sulfur content, partial oxidation reactors may employ non-catalytic partial oxidation of the feed stream  106  with oxygen  108  in the presence of steam at temperatures exceeding 1200° C. 
         [0031]    The stoichiometric reformation reaction occurring at the reformer  102  and using oxygen  108  as the oxidant may be represented generally as follows: 
         [0000]      CH 2 +(½)O 2 →CO+H 2  
 
         [0032]    At the fuel cell  104 , the synthesis gas  112  and oxygen  114  is converted to electricity  116 , carbon dioxide  118 , and steam  118  in accordance with the following equation: 
         [0000]      CO+H 2 +O 2 →CO 2 +H 2 O+4 e   − 
 
         [0033]    As can be observed from the above equations, each CH 2  group generates about 4e −  (4 electrons) of electricity using a conventional partial oxidation reformer. 
         [0034]    Although effective, partial oxidation techniques exact a heavy efficiency penalty on the fuel cell  104 . The use of partial oxidation techniques coupled to a fuel cell  104  results in a loss in the range of 30 to 40 percent of the electric power generation potential of the fuel  106 . More specifically, the Faradaic (current producing) potential of a fuel cell  104  is reduced by 4 coulombs for each mole of oxygen  108  introduced in the partial oxidation process. Although steam reforming does not suffer from this effect, no suitable catalysts are known for high-sulfur, hydrogen-lean transportation fuels. 
         [0035]    It will be appreciated by those of skill in the art that at least one reactant may be obtained as a product of the fuel cell reaction. For example, in one embodiment, CO 2  from the fuel cell may be introduced as the reactant for the plasma reformer. In another embodiment, steam from the fuel cell may be introduced as the reactant for the plasma reformer. 
         [0036]    Referring to  FIG. 2 , in general, to overcome the efficiency penalty of the above-mentioned reformers, an improved system  200  in accordance with the invention may include a sulfur-tolerant reformer  202  capable of reforming feedstock fuels  204  with high sulfur content (e.g., greater than 50 ppm sulfur content) to generate synthesis gas  206 . This synthesis gas  206  may be utilized by a synthesis gas consuming process  208 , such as a fuel cell  104  or other device or process which consumes synthesis gas  206 , which also generates heat  210  as a byproduct. The heat  210  from the consuming process  208  may be transferred to the reformer  202  where it may be used to drive the synthesis gas generating reaction, improving the yield of synthesis gas  206  from the reformer  202  and the overall efficiency of the system  200 . 
         [0037]    Referring to  FIG. 3 , one embodiment of a system  300  functioning in accordance with the system  200  described in  FIG. 2  may include a plasma reformer  302  and a fuel cell  304  generating heat  306  as a byproduct. In selected embodiments, the fuel cell  304  is a solid oxide fuel cell, molten carbonate fuel cell, or other fuel cell which operates at high temperatures (e.g., greater than 600° C.). As will be explained in more detail hereafter, the plasma reformer  302  may be used to reform fuels  308  with high sulfur content without the problems associated with catalyst poisoning or carbon buildup. Thus, the plasma reformer  302  may be suitable to reform high-sulfur, liquid transportation fuels such as diesel, heavy fuel oil, or jet fuel. 
         [0038]    Heat  306  generated by the fuel cell  304  may be transferred to the reformer  302  to provide heat of reformation to the reactants  308 ,  310 . This may reduce or eliminate the need to combust a portion of the fuel  308  to provide heat of reformation since it is provided by the fuel cell  304 . Consequently, the amount of oxygen  108  used as the oxidant (as described in  FIG. 1 ) and used to combust the fuel  308 , may be reduced or mostly eliminated and replaced with steam  310 . The substitution of steam  310  makes the reaction endothermic, but produces an additional H 2  or CO molecule which provides additional fuel to the fuel cell  304 . 
         [0039]    To illustrate this effect, the stoichiometric reaction occurring at the reformer  302  and using steam  310  as an oxidant may be represented generally as follows: 
         [0000]      CH 2 +H 2 O→CO+2H 2  
 
         [0040]    At the fuel cell  304 , the synthesis gas  312  is converted to electricity, carbon dioxide, and water in accordance with the following equation: 
         [0000]      CO+2H 2 +( 3/2)O 2 →CO 2 +2H 2 O+6 e   − 
 
         [0041]    As can be observed from the above equations, each CH 2  group generates 6e −  of electricity, which constitutes a 50 percent increase over the 4e −  generated by the partial oxidation process described in  FIG. 1 . The result is an improvement in efficiency comparable to that achievable with steam methane reforming, but novel in that it is able to use a high-sulfur, hydrogen-lean feedstock fuel  308  as the input. A similar efficiency benefit can also be achieved by using CO 2  as the reactant to replace a portion or all of the steam necessary for the reformation reaction. The mixture of steam and CO 2  may be obtained from the reaction product of the fuel cell. 
         [0042]    In general, a solid oxide fuel cell converts about 50 percent of the heating value of the synthesis gas  312  to electricity and the other 50 percent to heat. Because only about 30 percent of the heating value is needed to reform the feedstock fuel  308  to synthesis gas  312 , a solid oxide fuel cell produces sufficient heat  306  to provide the necessary heat of reformation to the reformer  302 . Nevertheless, even where the heat  306  generated by a fuel cell  304  is insufficient to provide the required heat of reformation, the heat  306  may be supplemented by other sources (e.g., by partially combusting the feedstock fuel or using other sources of waste heat) until it is sufficient. In this way, any significant amount of heat  306  generated by the fuel cell  304  may be recycled, rather than wasted, to improve the efficiency of the reformer  302 . 
         [0043]    Referring to  FIG. 4 , in selected embodiments, a plasma reformer  302  in accordance with the invention may include a preheat zone  400 , a plasma generator  402 , and a post plasma reaction zone  404 . The preheat zone  400  may be used to preheat the reactants  308  to the required reforming temperature range. Because the reformation reaction is highly endothermic, the reactants  308 ,  310  need to be heated significantly in order to generate the desired synthesis gas  312 . The thermodynamics of the reaction are such that synthesis gas production starts to increase at about 400° C. and maximizes at about 800° C. Thus, the reactants are ideally heated to a temperature at or around 800° C. to maximize synthesis gas production. The reactants  308 ,  310  are ideally preheated somewhere near this temperature when they pass through the plasma generator  402 , which acts as a catalyst to initiate the reformation reaction. In selected embodiments, only the steam  310  (as well as air, oxygen, or CO 2  mixed with the steam) is preheated. The feedstock fuel  308  may be mixed with the steam  310  just prior to passing through the plasma generator  402  (as indicated by the dotted line  406 ). This may prevent the feedstock fuel  308  from becoming too hot, thermally decomposing, and clogging up the system. 
         [0044]    The preheat zone  400  may also be used to vaporize (i.e., convert to gas or mist) the reactants  308 ,  310  prior to routing them through the plasma generator  402 . Reactants  308 ,  310  in a solid or liquid form may provide clusters of condensed matter which may act as nucleation sites. This may cause solid carbon nucleation which, although unavoidable, may be reduced by vaporizing the reactants  308 ,  310 . In some cases, however, the reformer  302  may be used to process a feedstock fuel having a greater solid fraction. For example, a feedstock fuel such as a coal water slurry (i.e., coal dust entrained in water) or coal dust suspended in gas, which may have an energy content similar to jet fuel, may be vaporized as much as possible prior to being passed to the plasma generator  402 . Nevertheless, feedstock fuels in pure gas form (e.g., natural gas, biogas, etc.) may be preferable to avoid carbon formation. 
         [0045]    Once preheated, the reactants  308 ,  310  may be passed to the plasma generator  402  to ionize or break apart one or more of the reactants  308 ,  310  to create reactive elements. As will be explained in more detail hereafter, in selected embodiments, the plasma generator  402  may ionize the reactants  308 ,  310  with a gliding electrical arc. This gliding arc may provide the function of a physical catalyst by activating and initiating the reformation reaction. However, the gliding arc continually renews the active species whereas a physical catalyst relies on surface energy that can be “poisoned” by absorption of sulfur or buildup of carbon on the surface. The energy used to generate the gliding electric arc may be on the order of 1 or 2 percent of the heating value of the fuel  308  being processed. If a fuel cell  304  is 50 percent efficient (i.e., converts 50 percent of the fuel&#39;s electrical potential to electricity), then only 4 percent of the fuel cell&#39;s electricity is needed to operate the plasma generator  402 . This represents an efficiency improvement over partial oxidation techniques, which may consume 30 percent or more of the fuel&#39;s electrical potential when the fuel is partially combusted. 
         [0046]    After ionization, the reactants may be passed to a reaction zone  404  to absorb additional heat of reformation and complete the endothermic reactions. As vaporized reactants and products of the reactants leave the plasma generator  402 , some packets of gas may be oxygen rich while others may be oxygen lean. To further complete the reaction, the reactants may be physically mixed or homogenized by passing them through a chemical buffering compound, such as a solid state oxygen storage compound. Here, the storage compound may absorb oxygen from oxygen-rich packets while releasing oxygen to oxygen-lean packets. This provides both spatial and temporal mixing of the reactants to help the reaction continue to completion. 
         [0047]    In other embodiments, the reaction zone  404  may contain catalysts suitable for promoting equilibration of gas species at temperatures different than the reforming reaction. That is, the temperature of the synthesis gas produced in the reaction zone  404  may be reduced and other reactions may be initiated. For example, the synthesis gas may be used to produce methane within the reaction zone  404 . Similarly, the synthesis gas may be “shifted” to produce more hydrogen at the expense of carbon monoxide. This may be performed, for example, by passing the synthesis gas over an iron catalyst at temperatures below 400° C. In other embodiments, the reaction zone  404  may also be used to cool reaction products leaving the reformer  302 . 
         [0048]    Referring to  FIGS. 5A through 5C , in selected embodiments, a plasma generator  402  in accordance with the invention may include a pair of electrodes  500   a ,  500   b  having a large potential difference there between (e.g., 6 kV to 12 kV typical). A preheated vapor stream containing the reactants  308 ,  310  may be directed between the electrodes  500   a ,  500   b  in the direction  502 . The high voltage ionizes the gas which allows current to flow, creating an arc  504   a , as shown in  FIG. 5A . Because the ions are in an electric field having a high potential gradient, the ions begin to accelerate toward one electrode  500   a  or the other  500   b  depending on their charge. This provides tremendous kinetic energy for initiating the reformation reaction in addition to providing means for ionizing the reactants or simply breaking the reactants into radicals to create more reactive species. 
         [0049]    Under the influence of the flowing gas, the ionized particles are swept downstream in the direction  502 , with the ionized particles forming the least resistive path for the current to flow. As a result, the arc  504   a  moves downstream and spreads out as it follows the contour of the electrodes  500   a ,  500   b , as shown in  FIG. 5B . Eventually, the gap becomes wide enough that the current ceases to flow. The ionized particles, however, continue to move downstream. Once the current stops flowing, the potential builds up on the electrodes  500   a ,  500   b  until it once again ionizes the gas flowing there between. This creates a new arc  504   b  at a narrower region between the electrodes  500   a ,  500   b , as shown in  FIG. 5C . This process then repeats itself. Most of the endothermic reformation reaction may actually occur in the plasma area (i.e., the area between the electrodes  500   a ,  500   b ) or immediately downstream from the plasma area. 
         [0050]    Referring to  FIG. 6 , in order to provide heat of reformation to the reformer  302 , a design is needed to provide adequate heat transfer to the preheat zone  400 , plasma generator  402 , and reaction zone  404  of the reformer  302 . In selected embodiments, the reformer  302  and a fuel cell  304  may be placed inside a furnace  600  or other insulated enclosure  600  in order to retain heat and effectively transfer heat between the two components  302 ,  304 . In this embodiment, heat generated by the fuel cell  304 , which may include heat generated through electrical resistance as well as heat generated electrochemically, may be transferred to the reformer  302  through radiation, convection, or a combination thereof. 
         [0051]    Accordingly, instead of insulating the reformer  302  to retain heat, the reformer  302  may be designed to conduct heat through an exterior wall where it may be transferred to internal components and fluids. In certain embodiments, residual synthesis gas or other fuel in the exhaust of the fuel cell  304  may be burned to provide additional heat to the reformer  302 . In other contemplated embodiments, heat may be transferred to the reformer  302  using a heat exchanger, such as a counter current heat exchanger. This may be used, for example, to preheat steam used by the reformer  302  with steam generated by the fuel cell  304 . 
         [0052]    In selected embodiments, the reformer  302  and fuel cell  304  may include a “cold” or reduced temperature region  602   a ,  602   b . This enables pipes or wires, which must often be welded to join them together or cut to disassemble, to be connected to the reformer  302  or fuel cell  304  in a region of reduced temperature. Accordingly, channels for conveying the feedstock fuel, air and steam, synthesis gas, and the like, as well as wires for conducting electricity may be connected to the reformer  302  and fuel cell  304  in the reduced temperature regions  602   a ,  602   b.    
         [0053]    Referring to  FIG. 7 , in one embodiment, a reformer  302  providing adequate heat transfer to the reactants may include an outer shell  700  to absorb heat radiated or otherwise conveyed from a fuel cell  304  or other external heat source. The outer shell  700  may be made of stainless steel or other materials having sufficient strength and stability at temperatures exceeding 800° C. In addition to providing a heat transfer mechanism to conduct heat to the reactants  308 ,  310 , the outer shell  700  provides a gas containment envelope that keeps the reactants  308 ,  310  as well as the products of the reactants (e.g., synthesis gas) isolated from the external environment. 
         [0054]    A first channel  702  may be used to convey a mixture of air and steam  310  into the reformer  302 . In certain embodiments, the channel  702  may originate in a low temperature region  602   a  of the reformer  302  and travel through a hot region  704  to preheat and further vaporize the air and steam  310 . In selected embodiments, the channel  702  may be coupled to a coil  706  to provide additional surface area to further preheat and vaporize the air and steam  310 . The coil  706  may be coupled to a channel  708  to convey the preheated air and steam  310  into an electrically insulated region, such as the inside of a non-conductive tube  710 . The non-conductive tube  710  may be made of a material such as an alumina ceramic and may prevent electricity from discharging from the plasma generator  402  to the conductive outer shell  700 , channels  702 ,  708 , or other conductive surfaces. 
         [0055]    Once the air and steam  310  are preheated, it may be mixed with a feedstock fuel conveyed through a feed channel  712 . In selected embodiments, this may occur within a mixing manifold  718  inside the non-conductive tube  710 . Where the feedstock fuel is a liquid or solid, the air and steam  310  is ideally preheated sufficiently to vaporize the feedstock fuel  308  as it mixes with the air and steam  310 . This preheated mixture is then introduced at some velocity between the electrodes  500   a ,  500   b  of the plasma generator  402  where it is ionized or broken into radicals to create more reactive species and thereby initiate the reformation reaction. The electrodes  500   a ,  500   b  may be connected to current-carrying conductors  720   a ,  720   b  connected to a voltage source outside of the reformer  302 . In the plasma area and the area immediately thereafter, most of the reactants may be converted to synthesis gas. 
         [0056]    The synthesis gas and any residual reactants may then be conveyed through the non-conductive tube  710  and into an annular reaction zone  404 , where residual reactants may absorb additional heat of reformation and continue to react to form synthesis gas or other desired products. Here, the reactants may be homogenized by passing them through a pack bed of chemical buffering compounds, such as the solid state oxygen storage compound previously mentioned, to promote further reaction. The pack bed may also serve to physically mix the reactants. In selected embodiments, the reactants and the products of the reactants may also be passed over catalysts suitable for promoting equilibration of gas species at temperatures different than the reforming reaction. 
         [0057]    The resulting products of reaction (e.g., synthesis gas) and any residual reactants (e.g., hydrocarbons, steam, oxygen, etc.) as well as nitrogen from the air may be collected through a port, such as a ring-shaped collection manifold  714  or other suitable collection device disposed within the annular reaction zone  404 . This fuel mixture may then be conveyed through a channel  716  where it may be transmitted to a fuel cell  304  for use as fuel. In selected embodiments, the annular region beneath the collection manifold  714  may be filled with an insulating material to maintain a temperature differential between the low temperature zone  602   a  and the hot zone  704 . 
         [0058]      FIGS. 8A through 8C  show several perspective and cutaway perspective views of one embodiment of a reformer  302  working in accordance with the principles described in association with  FIG. 7 .  FIG. 8A  shows one embodiment of an outer shell  700  having a flange  800  mountable to a furnace or other surface. A second flange  802  may be attached to many of the reformer&#39;s internal components, allowing them to be removed from the outer shell  700  without removing or detaching the outer shell  700 . Channels  702 ,  716  may be used to convey reactants and the products of reactants to and from the reformer  302 . 
         [0059]      FIG. 8B  shows a cutaway view of the outer shell  700 , the inner non-conductive tube  710 , and the coil  706 . Also shown is a channel  708  to convey preheated air and steam through a wall of the non-conductive tube  710  into the insulated core of the tube  710 . Also shown is a ring-shaped collection manifold  714  to collect synthesis gas and other residual materials from the annular reaction zone  404 .  FIG. 8C  shows various internal components of the reformer  302  with the outer shell  700  removed, including the non-conductive tube  710 , the coil  706 , the channels  702 ,  708 , and the collection manifold  714 . 
         [0060]      FIGS. 9A and 9B  show several perspective views of embodiments of the mixing manifold  718 , collection manifold  714 , channels  702 ,  708 , and flanges  800 ,  802 , with the outer shell  700  and non-conductive tube  710  removed. As shown, in one embodiment, the mixing manifold  718  may be sustained by several support bars  900  connected to a bottom mounting plate  902 . The bottom mounting plate  902  may also be provided with apertures  904  to accommodate the current-carrying conductors  720   a ,  720   b  illustrated in  FIG. 7 . 
         [0061]    In addition to carrying current, the conductors  720   a ,  720   b  may act as supports for the electrodes  500   a ,  500   b . These conductors  720   a ,  720   b  may pass through cutout regions  906  of the mixing manifold  718 , without touching the manifold  718 , to support the electrodes  500   a ,  500   b  at a position above the manifold  718 . In the apertures  904 , the conductors  720   a ,  720   b  may be surrounded by high voltage insulators which prevent electricity from discharging to the mounting plate  902 , while allowing the conductors  720   a ,  720   b  to pass through the plate  902 . 
         [0062]    In selected embodiments, the mounting plate  902  may be removed from the flanges  800 ,  802  to remove the mixing manifold  718  and electrodes  500   a ,  500   b  from the reformer assembly  302  while leaving the rest of the reformer  302  in place. In selected embodiments, one or more notches  908  may be formed in the mounting plate  902  to ensure proper alignment, for example, of the mixing manifold  718  with the channel  708 . 
         [0063]    Referring to  FIG. 10 , although particular reference has been made to fuel cells  104  herein, a reformer  302  in accordance with the invention may be used to improve the efficiency of other devices, systems, or processes that generate heat as a byproduct. For example, the reformer  302  may be used in conjunction with a Fischer-Tropsch process  1000  to create synthetic fuel  1002  using synthesis gas  312  as an input. As was described in association with  FIG. 3 , using steam as an oxidant (in place of oxygen) may produce synthesis gas with a hydrogen to carbon monoxide ratio of roughly two to one. This ratio provides an ideal synthesis gas input to a Fischer-Tropsch process  1000 . It will be appreciated that the oxidant as a reactant may include oxygen or oxygen containing compounds such as steam, CO 2  or other compounds. 
         [0064]    A Fischer-Tropsch process  1000  may include chemically reacting synthesis gas (i.e., carbon monoxide and hydrogen) in the presence of a catalyst to produce various types of liquid hydrocarbons. After extracting the liquid hydrocarbons, a tail gas may remain which may include a mixture of water vapor, carbon dioxide, methane, nitrogen, unreacted synthesis gas, as well as residual vapor hydrocarbon products. The tail gas may be recycled back to a gasification unit or to a Fischer-Tropsch reactor inlet or may be burned as fuel. 
         [0065]    In selected embodiments, the tail gas may be burned to provide heat  1004  to a plasma reformer  302  in accordance with the invention. As previously described, this may allow steam to be used as the oxidant and may increase synthesis gas  312  production without requiring additional fuel  1006  at the reformer input. Furthermore, this provides synthesis gas with an improved hydrogen to carbon monoxide ratio (e.g., 2:1) for synthetic fuel production. Thus, a plasma reformer  302  in accordance with the invention may be used to improve synthetic fuel production when integrated with a Fischer-Tropsch process  1000 . 
         [0066]    Referring to  FIG. 11 , as described herein, the object of the reformer  302  is to break hydrocarbon molecules into hydrogen and carbon monoxide that can be used as fuel for the fuel cell  304 . Each carbon atom in the hydrocarbon backbone must be joined with an oxygen atom, supplied either from free oxygen in air or from bound oxygen in steam or carbon dioxide, in order to cap the severed C—C and C—H bonds of the hydrocarbon. As a result, the atom ratio of oxygen to carbon (O/C) in the feed is important. At a minimum, the value of O/C should be greater than 1 to yield as much CO as possible and avoid the formation of solid carbon. However, only free oxygen that will support partial combustion is considered in the fuel equivalence ratio φ that we are trying to maximize (and thereby minimize use of free oxygen) in order to increase system efficiency. 
         [0067]      FIG. 11  is a graph  1100  showing an example of the fuel equivalence ratio operating range of the reformer  302 . As shown in the graph  1100 , the reformer  302  may be configured to operate in multiple modes—partial oxidation (POX) mode and steam reforming mode, as well as transition modes there between. Values of φ less than 3.5 correspond to operation in partial oxidation mode, while values of φ greater than 4.5 correspond to operation in plasma-catalyzed steam reforming mode. The middle range, 3&lt;φ&lt;5, corresponds to the multi-mode transition from the purely POX operating mode to endothermic steam reforming mode. As can be seen from the graph  1100 , the amount of hydrogen produced by the reformer  302  roughly doubles when the reformer  302  transitions from partial oxidation mode to steam-reforming mode. This provides additional fuel to a fuel cell  304  or other consuming device without requiring an increase in the amount of feedstock fuel input to the reformer  302 . 
         [0068]    To push the reformer  302  to operating modes with higher values of φ, apparatus and methods are needed to more efficiently transfer heat into the plasma and reaction zones  402 ,  404 . This will allow more of the heat of reformation to be provided from external sources (e.g., fuel cells  304 , etc.) rather than from the partial oxidation process. Ideally, the reformer  302  will be designed such that it can transfer between about two and thirty percent of the heating value of the feedstock fuel present in the reformer into the plasma and reaction zones  402 ,  404  in order to provide part or all of the necessary heat of reformation. This will allow more of the oxygen needed to reform the feedstock fuel to be provided from steam or CO 2  as opposed to air. 
         [0069]    Referring to  FIG. 12A , in certain embodiments, the shape of the reformer  302  may be modified to allow more heat to be transferred into the plasma and reaction zones  402 ,  404 . For example,  FIG. 12A  shows a side view  1204  and a top view  1206  of one example of an M-shaped reformer  302 . In this example, the plasma zone  402  is located in the center portion  1200  of the M-shape and two post-plasma reaction zones  404   a ,  404   b  are provided in the two branches  1202   a ,  1202   b  of the M-shape. Consequently, a feedstock fuel and oxidant may flow through the center portion  1200  of the reformer  302  and split into two streams flowing into the branches  1202   a ,  1202   b . One notable difference between the M-shaped reformer  302  and the reformer  302  illustrated in  FIG. 7  is that the plasma and reaction zones  402 ,  404  are not co-axial but include distinct thermally conductive surfaces that are each exposed to an external heat source. The will ideally provide better heat transfer into the plasma and reaction zones  402 ,  404 . 
         [0070]    As can be seen from the top view  1206 , the reformer  302  may be characterized by a length  1208  and a width  1210 . In this embodiment, the length  1208  is significantly longer than the width  1210 , giving the reformer  302  a length-to-width aspect ratio that is significantly greater than 1:1. This aspect ratio increases the reformer&#39;s surface area relative to its cross-sectional area to provide greater heat transfer into the reformer  302 . In selected embodiments, the aspect ratio of the reformer (from the top view  1206 ) is greater than 1.5 to 1 to provide desired heat transfer into the reformer  302 . In certain embodiments, the aspect ratio is selected to provide a surface area sufficient to transfer between about two and thirty percent of the heating value of the feedstock fuel in the reformer  302  into the plasma and reaction zones  402 ,  404 . 
         [0071]      FIG. 12B  shows a side view  1204  and a top view  1206  of another embodiment of a reformer  302 , in this example a U-shaped reformer  302 . In this example, the plasma zone  402  is located in a first side portion  1212  and the reaction zone  404  is located in the other side portion  1214 . Like the M-shaped reformer  302 , the plasma and reaction zones  402 ,  404  of the U-shaped reformer  302  include distinct thermally conductive surfaces that are exposed to the heat source. As is further evident from the top view  1206 , the aspect ratio of the reformer  302  is significantly greater than 1:1, providing improved heat transfer into the reformer  302 . 
         [0072]      FIG. 12C  shows a side view  1204  and top view  1206  of another embodiment of a reformer  302 , in this example a serpentine-shaped reformer  302 . In this embodiment, the plasma zone  402  may be located in a first portion  1220  of the serpentine shape and the reaction zone  404  may be located in a second portion  1222  of the serpentine shape. Like the reformers of  FIGS. 12A and 12B , the plasma and reaction zones  402 ,  404  of the serpentine-shaped reformer  302  include thermally conductive surfaces that are both exposed to an external heat source. The aspect ratio of the reformer  302  is also significantly greater than 1:1, providing improved heat transfer into the reformer  302 . 
         [0073]      FIG. 12D  shows yet another embodiment of a reformer  302 , in this example a rectangular-shaped reformer  302 . It will be appreciated by those of skill in the art that various configuration may be utilized and that a rectangular-shaped reformer  302  may be made of tubes in an arrangement the projects a rectangular outline. In this example, the plasma zone  402  is located in a first portion  1230  of the reformer  302  and the reaction zone  404  is located in a second portion  1236  of the reformer  302 . In this embodiment, the reaction zone  404  includes one or more channels  1232  extending between a pair of headers  1234   a ,  1234   b . This configuration is similar to the structure of a conventional steam radiator for heating a building, although the heat would be absorbed rather than emitted. The channel and header design significantly increases the surface area of the reformer  302 , thereby increasing the heat transfer into the reformer  302 . Like the reformers of  FIGS. 12A through 12C , the plasma and reaction zones  402 ,  404  of the reformer  302  include distinct thermally conductive surfaces that are each directly exposed to the external heat source. Similarly, the aspect ratio of the reformer  302  is also significantly greater than 1:1. 
         [0074]    The reformers  302  illustrated in  FIGS. 12A through 12D  are simply examples of different shapes that may be used to provide additional heat transfer into the plasma and reaction zones  402 ,  404 . Other shapes are possible and within the scope of the invention. In general, any reformer  302  having plasma and reaction zones  402 ,  404  with distinct exposed thermally conductive surfaces is deemed to fall within the scope of the invention. Furthermore, any reformer  302  having an aspect ratio (as seen from the top view  1206 ) that is greater than 1:1, or in other embodiments greater than 1.5:1, is also deemed to fall within the scope of the invention. In other embodiments, any reformer  302  having a surface area sufficient to transfer between about two and thirty percent of the heating value of the feedstock fuel presently in the reformer  302  into the plasma and reaction zones  402 ,  404  is deemed to fall within the scope of the invention. 
         [0075]    Referring to  FIG. 13 , a cutaway perspective view of one embodiment of an M-shaped reformer  302  is illustrated. As shown, the reformer  302  includes a plasma zone  402 , located in a center portion  1200  of the reformer  302 , and two post-plasma reaction zones  404   a ,  404   b , located in the two branches  1202   a ,  1202   b  of the reformer  302 . The plasma zone  402  includes a pair of electrodes  500   a ,  500   b  having a large potential difference there between. A preheated vapor stream containing a feedstock fuel and an oxidant (e.g., O 2 , H 2 O, CO 2 ) may be conveyed through a channel  1300  and directed between the electrodes  500   a ,  500   b . This will ionize the reactants and provide the kinetic energy necessary to initiate the reformation reaction. Where the reformer&#39;s outer housing is made of a conductive material, such as steel, the plasma zone  402  may be lined with a non-conductive material, such as an alumina ceramic, to prevent electricity from discharging from the electrodes  500   a ,  500   b  through the housing. 
         [0076]    Synthesis gas and residual reactants may be conveyed through the M-shaped housing into the reaction zones  404   a ,  404   b , where residual reactants may absorb additional heat of reformation and continue to react to form synthesis gas or other desired reaction products. In these zones  404   a ,  404   b , the reactants may be homogenized by passing them through a pack bed (not shown) of chemical buffering compounds, such as the solid state oxygen storage compound previously mentioned, to promote further reaction. The pack bed may also serve to physically mix and provide additional heat of reformation to the reactants. In selected embodiments, the reactants and the products of the reactants may also be passed over catalysts suitable for promoting equilibration of gas species at temperatures different than the reforming reactions. 
         [0077]    In certain embodiments, the pack bed may be placed in perforated metal baskets (not shown) that sit on top of slotted metal grates  1302   a ,  1302   b . Ports (not shown) may be placed immediately beneath the slotted grates  1302   a ,  1302   b  to remove the reformed fuel (i.e., the synthesis gas) from the reformer  302  and convey it to a fuel cell  304  or other fuel-consuming device. This allows the reformed fuel to be conveyed from the reformer  302  to the fuel cell  304  in the hot zone as opposed to piping the reformed fuel through a bottom flange  1304  of the reformer  302  and into a low-temperature zone (thereby undesirably cooling the fuel). This also keeps the flange  1304  cooler and makes it easier to change stacks  304  without cutting or welding pipe. In certain embodiments, the regions beneath the grates  1302   a ,  1302   b  may be filled with an insulating material to maintain a temperature differential between the low temperature zone and the hot zone. 
         [0078]    Referring to  FIG. 14 , a perspective view of one embodiment of a thermally integrated system  1400  comprising a pair of reformers  302  and a pair of fuel cells  304  is illustrated. In this embodiment, the reformers  302  and fuel cells  304  are housed inside an insulated enclosure  1402  (the form of which is indicated by the dotted lines) to retain heat within the enclosure  1402  and facilitate heat transfer between the components  302 ,  304 . More specifically, heat generated by the fuel cells  304 , which may include heat generated through electrical resistance and electrochemical reactions, may be transferred to the reformers  302  by way of radiation and/or convection. A heat exchanger  1404  may be provided within the enclosure  1402  to transfer heat from exhaust gases (which may include oxygen-depleted air as well as some CO 2  and water vapor) exiting the fuel cell stacks  304  to the incoming reactant streams (which may include the feedstock fuel, air, and steam) entering the reformers  302 . This may retain heat within the enclosure  1402  to provide additional heat of reformation to the reformers  302 , thereby improving efficiency. 
         [0079]    In the illustrated embodiment  1400 , the reformer  302  is an M-shaped reformer  302 , although any of the reformers  302  illustrated in  FIGS. 7 through 12D  may be used. One notable attribute of the reformers  302  illustrated in  FIGS. 12A through 12D  is that their elongated aspect ratio makes their integration with the fuel cell stacks  304  more compact. The elongated aspect ratio also facilitates easier connection of the reformers  302  to the fuel cell stacks  304  within the hot zone (i.e., the space inside the enclosure  1402 ). The elongated aspect ratios further increase surface area and enhance heat transfer into the plasma and reaction zones  402 ,  404  of the reformers  302 . 
         [0080]    In one embodiment, an integrated system  1400  such as that illustrated in  FIG. 14  may be used to reform JP-10 feedstock fuel using the plasma reformer  302 . An electric furnace was used to heat a U shape reformer similar to the embodiment illustrated in  FIG. 12B . The reformer operation was proven with repeated 200 hour runs on JP-10. The reformer operated with an exceptionally high fuel equivalence ratio (low O 2  addition) φ&gt;20 (O 2  was 4.8 percent of stoichiometric). An SOFC single cell embodiment of the present invention showed equivalent performance with both JP-10 reformate and H 2 . An SOFC stack embodiment of the present invention showed equivalent performance with both JP-10 reformate and H 2 . 
         [0081]    Referring to  FIG. 15 , one alternative embodiment of a plasma generator  402  is illustrated. As shown, the plasma generator  402  includes more electrodes  500  than the pair illustrated in  FIGS. 5A through 5C . In certain embodiments, the electrodes  500  may be arranged in a radial pattern although other patterns, such as linear arrays, are also possible. The additional electrodes  500  provide additional arcing and thus additional energy to ionize the reactants and initiate the reformation process. This will allow greater quantities of feedstock fuel to be processed by the plasma generator  402 . The illustrated plasma generator  402  may be used in larger reformers  302  or where additional reformer throughput is needed. 
         [0082]    The present invention may be embodied in other specific forms without departing from its essence or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes within the meaning and range of equivalency of the claims are to be embraced within their scope.