Abstract:
A fuel reformer includes a feedstream delivery unit and a catalytic reactor. The feedstream delivery unit is configured to receive reactants and to provide the reactants to the catalytic reactor. The reformer further includes a flame arrestor disposed between the feedstream delivery unit and the catalytic reactor, and at least one spacer disposed between the feedstream delivery unit and the catalytic reactor, wherein the spacer is configured to allow the reactants to flow therethrough while inhibiting thermal radiation therethrough. In a further aspect, the surfaces of the feedstream delivery unit that come into contact with the reactants in use include coatings that eliminate catalytic reactions of the feedstream within the feedstream delivery unit.

Description:
[0001]    This invention was made with government support under contract DE-EE0000478 awarded by the Department of Energy. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a reformer assembly for generating hydrogen-containing reformate from hydrocarbons. In such an assembly, a feedstream comprising air and hydrocarbon fuel is converted by a catalyst into a hydrogen-rich reformate stream. In a typical reforming process, the hydrocarbon fuel is percolated with oxygen through a catalyst bed or beds contained within one or more reactor tubes mounted in a reformer vessel. The catalytic conversion process is typically carried out at elevated catalyst temperatures in the range of about 700° C. to 1100° C. It may be necessary to provide heat to the catalyst to achieve and maintain the required catalyst temperature. 
         [0003]    Because the feedstream includes a volatile mixture of fuel and oxygen, it may be prone to unwanted chemical reactions before reaching the catalyst in the reactor. It is desirable in the art to provide a reformer assembly that inhibits premature chemical reactions of the feedstream. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    A reformer assembly may experience unwanted chemical reactions of the feedstream before the feedstream reaches the catalyst. For example, hot surfaces in the reformer may promote precombustion by nature of their elevated temperatures. Structural materials in the reformer may have surfaces that exhibit catalytic properties at operating temperatures of the reformer, further promoting undesirable chemical reactions of the feedstream. Long residence time and/or poor mixing of reactants in the feedstream may trigger unwanted chemical reactions. Such chemical reactions may result in damage to the reformer. It is desirable to prevent chemical reactions of the feedstream from occurring before the feedstream reaches the catalyst. 
         [0005]    In accordance with an aspect of the invention, a fuel reformer includes a feedstream delivery unit and a catalytic reactor. The feedstream delivery unit is configured to receive reactants and to provide the reactants to the catalytic reactor. The reformer further includes a flame arrestor disposed between the feedstream delivery unit and the catalytic reactor, and at least one spacer disposed between the feedstream delivery unit and the catalytic reactor, wherein the spacer is configured to allow the reactants to flow therethrough while inhibiting thermal radiation therethrough. 
         [0006]    In a further aspect of the invention, the surfaces of the feedstream delivery unit that come into contact with the feedstream include coatings that eliminate catalytic reactions of the feedstream within the feedstream delivery unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  is a schematic longitudinal cross-sectional view of a catalytic hydrocarbon reformer assembly that incorporates aspects of the invention; 
           [0009]      FIG. 2  is a view of components in the reformer assembly of  FIG. 1 ; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    In a catalytic reformer, a feedstream containing fuel and oxygen is passed over a catalyst, thereby promoting chemical reactions producing hydrogen gas as well as other constituents. An exemplary reformer assembly that incorporates aspects of the invention is depicted in  FIG. 1 . A similar reformer assembly is described in commonly owned U.S. patent application Ser. No. 13/363,760, the disclosure of which is incorporated by reference in its entirety. 
         [0011]    Referring to  FIG. 1 , a catalytic reformer assembly  10  having a longitudinal axis  12  comprises walls that define two separate and distinct flow paths. A first flow path  50  is indicated by open arrows for a first medium, and a second flow path  52  indicated by solid arrows for a second medium. The first medium may be a hot fluid stream used to maintain a desired temperature, and the second medium may be a feedstream comprising fuel and oxygen that is to be heated by heat transfer from the first medium. The first medium flow path  50  includes a central flow channel  80  configured to direct flow in a first axial direction  6 . The first medium flow path  50  further includes a first annular flow channel  82  radially surrounding at least a portion of the central flow channel  80  and configured to direct flow from the exit of the central flow channel  80  (at endcap  28 ) in a second axial direction  8  opposite the first axial direction  6 . The first medium flow path  50  further includes a second annular flow channel  84  radially surrounding at least a portion of the first annular flow channel  82  and configured to direct flow from the exit of the first annular flow channel  82  in the first axial direction  6 . The first medium is discharged from the reformer assembly through outlet port  46 . 
         [0012]    Still referring to  FIG. 1 , the second medium flow path  52  comprises a third annular flow channel  86  and a fourth annular flow channel  88  each disposed radially between the first annular flow channel  82  and the second annular flow channel  84 , with the third annular flow channel  86  configured to direct flow in the second axial direction  8  and the fourth annular flow channel  88  configured to direct flow in the first axial direction  6 . The second medium is discharged from the reformer assembly  10  through outlet port  48 . 
         [0013]    As shown in  FIG. 1 , the second medium flow path may include an inner catalyst  62  disposed within the third annular flow channel  86  and/or an outer catalyst  64  disposed within the fourth annular flow channel  88 . The first medium flow path  50  is fluidly isolated from the second medium flow path  52  within the catalytic reformer assembly  10 , but the arrangement of the flow channels in  FIG. 1  allows the first medium flow path  50  to be thermally coupled to the second medium flow path  52  so as to influence the temperature at the catalyst  62 ,  64 . 
         [0014]    For convenience of fabrication, the reformer assembly  10  may comprise subassemblies including a combustor assembly, a reactor assembly, and a feedstream delivery unit (FDU) assembly, as described in U.S. patent application Ser. No. 13/363,760.  FIG. 2  depicts portions of an FDU assembly that incorporate aspects of the invention. 
         [0015]    Referring to  FIG. 1  and  FIG. 2 , the feedstream delivery unit (FDU) assembly  94  comprises a tubular FDU wall  36  and an FDU endcap portion  38  that fluid tightly closes off a first end  40  of the FDU wall  36 , the FDU wall  36  and the FDU endcap portion  38  defining an FDU inlet chamber  108 . An FDU inlet port  60  is defined by an opening in the FDU endcap portion  38  or in the FDU wall  36 . FDU assembly  94  is shown bearing a plurality of inner catalyst portions  62  disposed within the FDU wall  36  and a plurality of outer catalyst portions  64  disposed along the exterior of FDU wall  36 . Each inner catalyst portion  62  and outer catalyst portion  64  comprises a substrate having a catalyst disposed on its surface, the substrate having sufficient porosity to allow fluid flow therethrough. The FDU wall  36  and the FDU endcap portion  38  are each preferably made of metal. It will be appreciated that features depicted as discrete elements of the FDU, such as the FDU wall  36  and the FDU endcap portion  38 , may be further integrated with each other, or alternatively may be further divided into other combinations of components, without departing from the scope of the invention. 
         [0016]    Continuing to refer to  FIG. 1  and  FIG. 2 , the exemplary reformer assembly  10  also includes a flame arrestor  110 , at least one radiation shield  112 , and a POx catalyst substrate  114 , the functions of which will be described further below. In the exemplary embodiment of  FIG. 1  and  FIG. 2 , a wrap  116  is used to locate and secure the flame arrestor  110 , the radiation shield  112 , and the POx catalyst substrate  114  within the tubular FDU wall  36 . 
         [0017]    The POx catalyst substrate  114  supports a POx catalyst  115  that is used to promote a catalytic partial oxidation (POx) reaction of the feedstream to produce hydrogen gas for use in a solid oxide fuel cell. As used herein, the term POx catalyst is defined as a catalyst formulated so as to promote a reaction between a hydrocarbon fuel and oxygen at the POx catalyst  115 , where the reaction is of the form: 
         [0000]      C n H m +( n /2)O 2   →n CO+( m/ 2)H 2    
         [0018]    The hydrogen gas produced in this partial oxidation reaction is desirable for use in a fuel cell, while the carbon monoxide may be further reacted with water within a fuel reformer to produce additional hydrogen in a reaction of the form: 
         [0000]      CO+H 2 O→CO 2 +H 2  
 
         [0019]    The partial oxidation reaction at the POx catalyst  115  is exothermic, resulting in elevated temperature at the POx catalyst  115  and/or at the POx catalyst substrate  114 . Exposure to the hot surface of the POx catalyst  115  can promote premature combustion of the feedstream in the FDU. 
         [0020]    In an advantageous embodiment the flame arrestor  110  comprises a plurality of channels each having a length in the axial direction that is greater than a width in a direction perpendicular to the axial direction. The dimensions and aspect ratio of the channels defined in the flame arrestor are chosen to allow flow of the feedstream through the reactor (in the direction of the arrows  52 ) while maintaining velocities in the channels sufficient to inhibit propagation of a flame front in a direction opposite the direction of the arrows  52  into the FDU inlet chamber  108 . 
         [0021]    Similarly, in an advantageous embodiment the POx catalyst substrate  114  comprises a plurality of channels each having a length in the axial direction that is greater than a width in a direction perpendicular to the axial direction. The dimensions and aspect ratio of the channels defined in the POx catalyst substrate  114  are chosen to allow flow of the feedstream through the reactor (in the direction of the arrows  52 ) while maintaining velocities in the channels sufficient to inhibit propagation of a flame front in a direction opposite the direction of the arrows  52  into the FDU inlet chamber  108 . 
         [0022]    In addition to the flame arrestor  110 , the exemplary reformer  10  also includes one or more spacers  112  located between the inlet port  60  of the FDU and the POx catalyst substrate  114 . The spacers  112  preferably comprise ceramic paper or ceramic cloth. As used herein, ceramic paper is understood to mean a sheet material comprising ceramic fibers oriented randomly, and ceramic cloth is understood to mean a sheet material comprising ceramic fibers arranged in a woven orientation. The spacers  112  are porous enough to allow flow of the feedstream therethrough while inhibiting thermal radiation from the POx catalyst substrate  114  and/or the POx catalyst  115  from reaching the FDU inlet chamber  108 . 
         [0023]    The inventors have recognized that at elevated temperatures that may be found in the inlet chamber  108 , the materials used in the construction of the FDU assembly  94  may contribute to fostering unwanted chemical reactions in the FDU assembly  94 . Metal alloys may assume catalytic tendencies or promote deposition of carbon which can act as a hot spot to initiate premature combustion of the fuel/oxygen mixture. Several alternatives are available to be used, either alone or in combination, to mitigate the promotion of undesirable chemical reactions in the FDU. In one aspect of the invention, metallic structural components in the FDU comprise Alloy 625, an industry standard nickel-chromium based alloy. In another aspect of the invention, metallic structural components in the FDU comprise aluminized stainless steel. In another aspect of the invention, structural components in the FDU are coated with a coating material, for example yttria-stabilized zirconia, to create a thermal barrier. 
         [0024]    While the invention has been described in terms of specific embodiments, the present invention can be further modified within the spirit and scope of this disclosure. This application is intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the claims which follow.