Abstract:
A system for removal of H 2 S from sulfur-containing reformate comprising a permanent canister assembly having fittings for flow of reformate therethrough and a replaceable cartridge assembly containing an H 2 S adsorber element and fittings for convenient, simple, and reliable mating and sealing with the permanent canister assembly. The cartridge assembly comprises a housing that may be optionally a full cylinder or a semi-cylinder. The cartridge assembly may be easily reloaded off-line for re-use of the cartridge components with a fresh adsorber element. Preferably, the adsorber element is also renewable off-line for re-use.

Description:
RELATIONSHIP TO GOVERNMENT CONTRACTS 
     The present invention was supported in part by a U.S. Government Contract, No. DE-FC36-04G014319. The United States Government may have rights in the present invention. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a mechanism for selective gas adsorption; more particularly, to a mechanism for selectively removing hydrogen sulfide (H 2 S) from a stream of mixed gases; and most particularly, to a convenient replaceable cartridge system for removing H 2 S from reformate generated by a hydrocarbon reformer. 
     BACKGROUND OF THE INVENTION 
     In the fuel cell arts of hydrogen-oxygen fuel cells, it is known to provide gaseous hydrogen-containing fuel to a fuel cell stack by reforming hydrocarbon materials; for example, gasoline, diesel fuel, natural gas, or methane. A device for producing such hydrogen-containing fuel is known as a “reformer”, and the fuel itself is known in the arts as “reformate”. 
     Naturally occurring hydrocarbon starting materials typically contain small amounts of sulfur which can be present as H 2 S in reformate. A fuel cell stack such as a solid oxide fuel cell stack contains elements that are disabled, or “poisoned”, by small amounts of H 2 S in the reformate. Such a fuel cell stack suffers loss of power if the reformate fuel stream contains more than about 10 parts per billion (ppb) of sulfur; however, typical hydrocarbon sources can contain up to 2 parts per million (ppm) of sulfur, i.e., 200 times the desirable upper limit. Thus, from a practical standpoint, it is necessary to provide a device in the reformate stream between the reformer and the fuel cell stack to selectively remove a high percentage of the H 2 S from the reformate stream. 
     Efficient selective H 2 S adsorbers are known in the art, for example, nickel/alumina/rare earth compositions. Such materials can be highly efficient but have finite capacity and therefore must be regenerated or replaced periodically during operation of a fuel cell system. Removal and replacement of the adsorber material is the preferred procedure rather than in situ renewal. Such removal and replacement can be cumbersome. Moreover, since the adsorber operates in a hot zone environment where temperatures can exceed 750° C., a cool-down period is needed to return the temperature of the adsorber below a temperature suitable for handling of the adsorber, before removal and replacement of the adsorber can be completed, making such an exchange time-consuming. 
     What is needed in the art is an improved system for removal of H 2 S from a reformate stream requiring a minimum number of replacement parts and minimum operator training, and causing minimal fuel cell system downtime for replacement of an H 2 S adsorber. 
     It is a principal object of the present invention to simplify removal and replacement of an H 2 S adsorber in the hot zone of a fuel cell system. 
     SUMMARY OF THE INVENTION 
     Briefly described, a system for removal of H 2 S from sulfur-containing reformate comprises a permanent canister assembly located in a hot zone within the fuel cell unit having fittings for flow of reformate therethrough and a replaceable cartridge assembly containing an H 2 S adsorber element and fittings for convenient, simple, and reliable mating and sealing with the permanent canister assembly. In one aspect of the invention, the cartridge assembly is readily accessible for servicing through a removable plate located on an outside wall of the housing of the fuel cell unit. The cartridge assembly comprises a housing that may be optionally a full cylinder or a semi-cylinder. After its removal from the hot zone through the access plate, a fresh replacement cartridge may be re-installed immediately thereby significantly reducing fuel cell down-time. The removed cartridge assembly may be readily reloaded off-line for re-use of the cartridge components with a fresh adsorber element. The replenishable adsorber element may be of any form including, for example: powder; coated pellets; or a porous monolith element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which  FIG. 1  is an exploded isometric view of a permanent canister assembly; 
         FIG. 2  is an exploded isometric view of a replaceable H 2 S cartridge assembly of a first embodiment for use with the permanent canister assembly shown in  FIG. 1  in accordance with the present invention; 
         FIG. 3  is an isometric view of an exemplary fuel cell hot zone with the accessible replacement cartridge assembly shown, in accordance with the invention; and 
         FIG. 4  is an exploded isometric view of a replaceable H 2 S cartridge assembly of a second embodiment for use with the permanent canister assembly shown in  FIG. 1  in accordance with the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , an exemplary canister assembly  10  in accordance with the present invention comprises a cylindrical canister housing  12  coupled as by welding at a first end  14  to a first end cap  16 . An entry fitting assembly  18  includes a first fitting  20  for entry of sulfur-containing reformate  22  into an entry port in first end cap  16 . An exit fitting assembly  24  includes a second fitting  26  for exiting of reduced-sulfur reformate  28  from an exit port in first end cap  16 . A connector member such as, for example, connecting ring  30 , is attached as by welding to a second end  32  of housing  12 . Canister assembly  10  is fixedly mounted within a hot zone of an associated fuel cell unit with second end  32  proximate an outside wall of the unit as will be later described with reference to  FIG. 3 . Referring again to  FIG. 1 , connecting ring  30  comprises means for matably and sealably receiving a replaceable adsorption cartridge assembly  74 ,  74 ′, exemplarily shown in  FIGS. 2 and 4 , into permanent canister  10 . Such mating and sealing means may include, but is not limited to, ring seal  35 , threaded bores  36  and bolts  38  ( FIG. 2 ), circumferential threadings (not shown), or any other means without limit that can be readily disassembled and can reliably seal a replacement adsorption cartridge assembly into canister assembly  10 . 
     Referring now to  FIG. 2 , an exemplary adsorption cartridge assembly  74  in accordance with one aspect of the present invention comprises a cylindrical cartridge housing  40  for receiving an axial return tube  42  supported at first and second housing ends  44 , 46  by first and second “spiders”  48 , 50 , so known colloquially in the art because of their resemblance to webs of orb spiders. Preferably, second spider  50  is disposed and preferably is welded at a short distance  52  from second end  46  to create a headspace  54  within housing  40 . Return tube  42  is slidably received in first and second central apertures  56 , 58  in spiders  48 , 50 , respectively. A second end cap  60  is sealingly attached as by welding to second housing end  46  to complete headspace  54  and preferably is provided with an opening  62  and fitting  64  to permit purging of air from the system during startup. Fitting  64  is closed during normal operation. 
     The cartridge components thus far described are entirely re-usable. 
     In one aspect of the invention, for use in housing  40 , an H 2 S adsorption element  66  is formed as a cylindrical porous monolith having either open cells or longitudinal channels (neither shown) for longitudinal passage of reformate and selective adsorption of H 2 S in known fashion. The outer diameter  68  of element  66  selected to be close-fitting within housing  40 , and the inner diameter  70  of axial passage  72  is selected to be close-fitting around return tube  42 . 
     Referring now to  FIGS. 1 and 2 , in a first embodiment of a cartridge assembly  74  in accordance with the present invention, to replace a loaded element, element  66  is inserted into cartridge housing  40  via open end  44 . Return tube  42  is inserted into element passage  72  and thence into spider aperture  58 . Alternatively, return tube  42  is permanently attached to second spider  50  and element  66  is installed into housing  40  directly over return tube  42 . First spider  48  is installed into housing  40  against element  66  and onto return tube  42  and fixed in place, for example, by welding. If desired or necessary, first and/or second screens  76 , 78  may be installed adjacent spiders  48 , 50 . 
     Alternately, cartridge housing  40  is formed as a semi-cylinder, as shown in  FIG. 2 , permitting element  66  to be inserted radially  80  into housing  40 , absent return tube  42 . The return tube and first spider are then installed as described above. 
     The removal of element  66  from the cartridge assembly is the reverse of assembly for either of the housing embodiments. 
     Referring to  FIG. 3 , canister assembly  10  is fixedly mounted within hot zone  90  of an associated fuel cell unit with second end  32  proximate an outside wall  92  of the unit. Outside wall  92  defines access opening  94  which is sized to permit removal and inserting of cartridge assembly through its opening. Mating cover plate  96  and seal (not shown) fit over access opening to seal the opening during normal operation of the fuel cell unit. Threaded bores  98  and bolts  99 , or any other means without limit, may be used to secure the seal and cover plate over the access opening. 
     For use, when cartridge assembly is ready for replacement, without the need for a lengthy cool-down step to allow the adsorber&#39;s temperature to reduce to a temperature substantially below its operating temperature, cover plate  96  may be first removed from outside wall  92  to access end cap  60 . Bolts  38  are then removed permitting end cap  60  of the cartridge assembly to be separated from canister assembly ring  30 . Loaded cartridge assembly  74  may then be removed through access opening  94  to be recharged, off-line. In reverse order, a fresh cartridge assembly  74  may then be inserted into canister assembly  10  via access opening  94  in outside wall  92 , and opening  82  in ring  36 . Second end cap  60  may be then be sealingly secured to ring  30  as described above. Note that an end  84  of return tube  42  protrudes from first spider  48  for engaging (not visible in  FIG. 1 ) exit fitting  26 . Thus, in accordance with the invention, a cool-down period in which the temperature of the adsorber drops substantially below its operating temperature before the adsorber is removed is not necessary. 
     In operation of an H 2 S removal system in accordance with the present invention, sulfur-containing reformate  22  from a catalytic hydrocarbon reformer  23  enters entry fitting assembly  18  and is directed to flow longitudinally in a first direction  86  through element  66  wherein H 2 S is selectively adsorbed onto element  66  and removed from reformate  22 , resulting in reduced-sulfur reformate  28  in headspace  54 . Reduced-sulfur reformate  28  flows from headspace  54  longitudinally in a second and opposite direction  88  through return tube  42  and exits the system via exit fitting assembly  24  for use in a fuel cell system  25  (not shown). 
     Referring now to  FIG. 4 , in accordance with another aspect of the present invention, an exemplary adsorption cartridge assembly  74 ′ in which adsorber material in the form of powder or coated pellets is used, is shown. In this embodiment, an enclosure is formed for receiving and containing the powder or pellets using many of the components of embodiment  74  for receiving a monolith element, including cartridge housing  40 , end cap  60 , spider  50 , screen  78  and return tube  42 . Housing  40  may be formed of a full cylinder or from two semi-cylinders as described above. The components may be assembled together in any convenient order, such as by welding, to form a cup-like enclosure for receiving adsorbent pellets or powder, the enclosure being bounded on three sides by housing  40 , tube  42  and, at a first end  41 , screen  78  supported by spider  50 . At a second end  43 , distal from the first end, third spider  51  is fixed in place, as example by welding, to provide a gapped recess  53  between third spider  51  and edge  55  of housing  40 . Thus, enclosure  57  is formed for receiving adsorbent pellets or powder. Adsorbent pellets or powder may then be loaded into enclosure space  39  through openings  59  in third spider  51 . Once the cartridge assembly  74 ′ is loaded in this manner, screen  76 ′ may be secured by first spider  48 ′ in recess  53  to contain the pellets/powder using, for example, screws  61 , fitted into threaded bores  63  in third spider  51 . Cartridge assembly  74 ′, like cartridge assembly  74 , is entirely re-usable. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.