Abstract:
An auto-thermal reformer assembly is provided having a plurality of self-contained reformer modules positioned within a pressure vessel. The reformer modules each contain catalyst for inducing reforming reactions to produce hydrogen rich gas. At least one heat exhanger is provided for transferring heat from the hydrogen rich gas to the reactants entering or inside of the pressure vessel.

Description:
This invention was conceived under government contract NSWC:N000167-98-C-0056. The United States&#39; government may retain certain rights to this invention. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of fuel processors and in particular to a new and useful auto-thermal reformer for reforming hydrocarbon-based fuels to make hydrogen rich gas. 
     Fuel cell systems that generate electricity from hydrogen rich gas to provide stationary, decentralized energy supplies, or for use as an energy source for electric vehicles, are the subject of research activity throughout the world. At present, economic and practical aspects dictate that only universally available and generally accepted fuels can be considered for hydrogen rich gas generation. Natural gas is particularly attractive for stationary applications, whereas use of liquid hydrocarbon fuels is more likely in the mobile sector. 
     Reforming is a term of art used to describe the process of generating hydrogen rich gas for use in fuel cells. Reformers that generate hydrogen rich gas on an industrial scale have been known for decades; however, these industrial scale reformers cannot be efficiently scaled down for decentralized and/or mobile applications in the range of several tens or hundreds of kilowatts (kW). Steam-reforming and Auto-thermal reforming (ATR) are specific methods of reforming. 
     SUMMARY OF THE INVENTION 
     In ATR, fuel is partially reacted by adding air to the fuel and steam mixture in the reformer to heat it to the appropriate reaction temperatures. ATR is advantageous because it has lower steam requirements (e.g. a molar steam to carbon ratio of about 2.5 to 3.5) than steam reforming and it improves efficiency in comparison to steam-reforming. ATR relies on flameless oxidation of oxygen from the air, thereby resulting in combustion of about 20 to 33% of the fuel and a release of the heat needed to drive the ATR reforming reactions. 
     The unoxidized fuel endothermically reacts with steam to create a mixture of hydrogen, carbon monoxide and carbon dioxide. An ATR reformer quickly adapts to new operating conditions because of its direct coupling and dynamic ability to respond to changing loads. Furthermore, ATR does not require additional external burners (and their attendant power supplies), making the system less complex and less expensive. 
     It is an object of the present invention to provide an auto-thermal reformer system for converting liquid fuels into hydrogen rich gas for further possible use in a fuel cell power system. 
     Accordingly, an auto-thermal reformer is provided having a plurality of reformer modules housed within a pressure vessel, and including an integrated steam superheater which uses the hydrogen rich gas to beat the incoming steam mixture. The individual modules also contain catalyst beds and a heat exchanger for converting hot, atomized and vaporized liquid fuel into hydrogen rich gas. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a cross-sectional side view of the auto-thermal reformer of the present invention; and 
     FIG. 2 is a front perspective view of the internal components of the reformer of FIG.  1 . 
     FIG. 3 is a diagrammatic representation of the internal components of the reformer of FIG. 1 taken along the line A—A. 
     FIG. 4 is a diagrammatic representation of the internal components of the reformer of FIG. 1 taken along the line B—B. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, in which like reference numerals are used to refer to the same or similar elements, FIG. 1 shows an auto-thermal reformer (ATR) assembly  10  having tubular reforming modules  50  and other equipment housed within pressure vessel  20 . The liquid fuel is fed into the ATR assembly  10  through an inlet pipe  25  at the bottom of the vessel  20 . Notably, inlet pipe  25  may be encased in protective shield tube  75  to prevent over heating of the liquid fuel feed. The incoming liquid fuel is then introduced into mixing chamber  70  of vessel  20  via atomizer  26 . 
     Ideally, the assembly will have 8 modules, as implied by FIGS. 1 and 2, although this may be altered without departing from the principles of this invention. For the sake of clarity, the assembly shown in FIGS. 3 and 4 has 4 modules. 
     Air enters the top of vessel  20  via air distribution means  30 . Distribution means  30  divides the airflow among the reforming modules  50 . Air may be introduced directly into the top of modules  50  via nozzles  45 , or other known means. 
     Steam also enters the top of vessel  20  through steam inlet  35 . It then flows, separate from the air, in a downward direction through vessel  20 , first being distributed into superheater  60  via air plenum  120 . After exiting superheater  60 , the superheated steam mixes with the liquid fuel in chamber  70 . This fuel/steam mix then is directed upwardly through or around the individual reforming modules  50  via annular jacket  40 . Preferably, the fuel/steam mix undergoes a heat exchange process with hydrogen rich gas exiting the module at this time. 
     After reaching the top of annular jacket  40 , the steam/fuel is mixed with air in the top of each reforming module  50 . While in the module  50 , the steam/fuel/air mix comes into contact with catalyst means, such as catalyst bed  72 , and subsequently undergoes reforming reactions well known to those skilled in the art. These catalyzed reactions produce, among other things, the desired hydrogen rich gas (also known as reformate or synthesis gas). 
     As further illustrated in FIG. 2, catalyst means  72  is preferably a fixed bed, which is contained in each of the tubular reforming modules  50 . Specifically, reforming catalyst is held in module  50  by any known catalyst support means, preferably catalyst pellets held in place by a mesh grid (or other support members) located in the upper part of the modules (not shown). Additionally or alternatively, the interior of the module  50  may be coated with catalyst and may contain catalyst coated members (not shown). 
     The reforming catalyst should be selected using considerations known to those skilled in the art. Preferably, the catalyst will contain a precious metal such as palladium, platinum, iridium, rhodium or the like. Other traditional reforming catalysts, such and iron-and nickel-based catalysts, could also be utilized. 
     After the reforming reactions take place, hot reformate flows downwardly through each module  50  and is then directed through a heat exchanger  55 . Preferably, each module  50  has a heat exchanger  55  integrated into its construction. These heat exchangers  55  heat the incoming fuel/steam mixture (as mentioned above) by utilizing the heat of the exiting reformate. Reformate exits module  50  and/or heat exchanger  55  through collection tubes  57 . These collection tubes  57  direct the reformate into common plenum  85 . Common plenum  85 , in turn, forces the reformate to undergo another heat exchange process, this time passing up through super heater  60 , located in the center of vessel  20  and just above chamber  70 . 
     Finally, reformate is collected at exhaust plenum  130  and then exits assembly  10  via main outlet  100 . Notably, main outlet  100  is preferably located at the top of vessel  20 . 
     FIG. 3 is a diagrammatic representation of a top sectional view of the assembly  10  taken along line A—A of FIG.  1 . Elements in close proximity to the plane defined by line A—A are drawn with broken lines. Notably, all of the elements present in close proximity to this plane may not necessarily be shown in FIG. 3 for the purposes of clarity. 
     As seen in FIG. 3, annular jackets  40  surround each module  50  and permit the fuel/steam mix to flow to the top of the module  50 , where the fuel/steam is then mixed with air which is delivered to distribution nozzles  45  via air distribution means  30 . The fuel/steam/air is then passed over catalyst means (not shown in FIG. 3) of module  50 , where the reforming reactions occur. 
     The steam is introduced to the assembly  10  through inlet  35 , which then redirects the steam flow downward via duct  31 . Duct  31  leads to a plenum which forces the steam into a superheater and then into a mixing chamber where it mixes with atomized fuel (not shown in FIG.  3 ). 
     Exhaust plenum  130  is also pictured. Reformate is collected in plenum  130  after passing through two heat exchangers (not shown in FIG.  3 ). Duct  131  then directs the reformate out of assembly  10  through outlet  100 . 
     The area between modules  50  may be filled with insulation means  90 . This insulation helps to enhance the thermal performance of the assembly and may add structural support for its elements. 
     FIG. 4 is a diagrammatic representation of a top sectional view of the assembly  10  taken along line B—B of FIG.  1 . Elements in close proximity to the plane defined by line B—B are drawn with broken lines. Notably, all of the elements present in close proximity to this plane may not necessarily be shown in FIG. 4 for the purposes of clarity. Also, superheater  60 , plenum  85 , and atomizer  26  shown in FIG. 4 are not drawn in the same scale as they are seen in FIG. 1, again for the purposes of clarity. 
     As seen in FIG. 4, modules  50  are in fluidic connection with heat exchangers  55 . Newly-produced hot reformate exits the catalyst bed (not shown in FIG. 4) of module  50 , passes downwardly through heat exchanger  55 , and then is directed via collection tubes  57  into plenum  85 . Plenum  85  forces the still hot reformate up through superheater  60  as described above. 
     Atomizer  26  is also pictured. Atomizer  26  is fed by incoming fuel line (not shown in FIG. 4) and causes fuel to be atomized and then vaporized when it is mixed with superheated steam in a chamber (not shown in FIG. 4) located below the superheater  60 . This mixing occurs prior to the fuel/steam being introduced to the top of module  50 , as described above. 
     As above, the area between modules  50  may be filled with insulation means  90 . This insulation helps to enhance the thermal performance of the assembly and may add structural support for its elements. 
     The bypass reformate outlet  110  at the bottom of the vessel  20  allows control of the superheated steam temperature. Specifically, the temperature of the reactions in vessel  20  may be selectively controlled by utilizing bypass outlet  110  to reduce or increase the flow of hot reformate passing through superheater  60  (this controls the temperature of the fuel/steam mix provided to each module  50 ). Essentially, this control mechanism can be utilized to prevent overheating of the catalyst beds and to more generally operate the assembly  10  over a range of desired throughputs. 
     This bypass control represents an improvement over other known reforming methods and assemblies in that it permits a simple means of monitoring and controlling the reforming reactions through alteration of the heat exchange temperatures in superheater  60 . Alternatively or additionally, bypass outlet  110  can be connected to a holding tank which subsequently feeds back into main outlet  100 , thereby allowing the selective control of the quantity of reformate exiting assembly  10 . 
     The modules  50 , fuel atomizer  26 , and superheater  60  are contained within the pressured vessel  20 . This provides the advantage of having all of the atomized and vaporized fuel contained within a single pressure vessel  20 . Notably, the optimal operating pressurization of vessel  20  is in the range of 50 psig. Pressurization at any desired level will permit the assembly  10  to have a more compact construction. Ultimately, those skilled in the art will select a pressurization to suit the needs of a particular system. 
     Superheater  60  may be utilized as needed to heat the incoming reactants. Those skilled in the art will be able to adapt superheater  60  to heat the air, fuel, steam, and/or fuel/steam mix as required. Similarly, heat exchanger  55  may also be adapted to heat the air, fuel, steam, and/or fuel/steam mix as required. The construction described above and illustrated in the figures is merely the preferred arrangement for each of these elements. 
     Use of multiple, self-contained modules  50  enhances the overall operation of the assembly. Similar to the bypass control discussed above, the incoming reactants&#39; flowpath may be selectively controlled and directed into any number of desired modules(e.g., through the use of remotely controlled valves placed at the inlets  25 ,  30 ,  35  and/or at the nozzles  45 , annular jackets  40 , and collection tubes  57  or other known control means). Additionally or alternatively, the modules may be designed to have varying amounts of reactivity (by altering the catalyst content and/or quanitity present in each module). These sorts of selective controls, combined with the fact that each module operates independent of the other, would result in an ability to manipulate the quantity/quality of the reformate in real-time to suit the particular needs of the overall system. 
     Careful design of the vessel  20  could also permit easier service, replacement, and/or removal of modules without requiring extended periods of downtime. However, this advantage would be tempered by the increased complexity of the operational and construction requirements necessary to adapt pressurization vessel  20  for this purpose. 
     Another advantage to the present invention is better thermal integration, since all hot components are close together. Notably, high performance insulation  90  may be strategically placed to further enhance thermal integration. The insulation  90  may be of any type known to those skilled in the art, and the insulation  90  need not be hydrogen permeable. 
     In fact, unlike some prior art reformers (such as the one disclosed in U.S. Pat. No. 5,938,800, assigned to McDermott Technology Inc. and incorporated by reference herein), the present invention eliminates altogether the need for hydrogen membranes. Similarly, the present design does not rely upon the presence of excessively hot flue gas in order to have the invention function properly. 
     Still another advantage of the present invention in comparison to prior reformers is its ability to handle a wide range of incoming hydrocarbon fuels. Specifically, incoming fuel may be either liquid or gaseous, and the integrated bypass control would further permit adjustment of the system&#39;s performance based on the type of fuel being fed into the system. Additionally, those skilled in the art could specifically engineer each module  50  to efficiently process a particular type of incoming fuel (through judicious catalyst selection, beat exchanger performance, nozzle and annular jacket construction, etc.), so that the selective control of reactant flowpaths would direct the incoming fuel to the proper module  50 . 
     The capacity of each module  50  is preferably sufficient to supply hydrogen to a 50 kW fuel cell. Additional capacity, i.e. scaleup, is achieved with lower risk by adding more modules  50 , compared to increasing the size of an individual module  50 . 
     While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.