Abstract:
An improved electrically-heated contact vaporizer (EHCV) for a catalytic hydrocarbon reformer. The EHCV has an electrically-heated vaporization surface and a helical-wound flow director. Preferably the EHCV includes a port and internal passages to permit controlled entry of an oxygen-containing gas, preferably air, into a flowing stream of vaporized fuel near the exit of the EHCV to mix with the vaporized fuel and spontaneously combust, forming hot gases for heating the reforming catalyst. A third wall may be provided to surround the outer wall of the air passage to provide further thermal insulation against heat loss.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to hydrocarbon reformers; more particularly, to apparatus for vaporizing fuel entering a hydrocarbon reformer; and most particularly, to an electrically heated contact fuel vaporizer (EHCV) for a reformer wherein a flow director extends into the vaporizing space to direct the flow of vapor and wherein, in one aspect of the invention, air may be introduced at start-up to cause spontaneous fuel combustion for warm-up of the reformer. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the art of catalytic reforming of hydrocarbons to generate hydrogen, it is known to provide an EHCV apparatus ahead of the reforming catalyst to vaporize fuel for reforming. Subsequent to vaporization, the fuel typically is mixed with a controlled amount of air to provide an optimum fuel/air mixture for reforming, which mixture ratio is below the Lower Explosive Limit (LEL) for the particular fuel being used. 
         [0003]    Especially upon startup of a reformer, a high thermal load is required to vaporize liquid fuel entering the reformer at ambient temperature. It is known to provide a vaporizer having a designated surface for vaporization of the fuel upon which the liquid fuel is impinged during operation of the reformer. Upon start-up, the surface must be heated by separate means, typically by an electrically-powered heater such as a glow plug or cartridge rod which is de-energized when a sufficient temperature increase is achieved. At equilibrium reformer operating temperatures, the surface typically receives sufficient waste heat to achieve reliable vaporization without further supplemental heating. 
         [0004]    In the prior art, ECHVs for vaporizing diesel fuel have used different methods to add heat to the fuel, typically a metering device that flows fuel to an open ended heating chamber consisting of a thin wall tube with the cartridge rod heater centered inside. The tube and heater forms an annulus about 1.0 mm in radial size extending the length of the working portion of the rod heater. The open end (outlet end) delivers the heated fuel in vapor form to a mixing chamber of the reforming device where air is mixed with the fuel vapor for reforming. 
         [0005]    Some disadvantages of such a prior art system are: 
         [0006]    a) the EHCV is mounted by means of a dual ferrule fitting, welded to the high thermal mass end plate of the mixing chamber of the reformer. This mounting system creates a seal between the EHCV and the chamber but does not thermally isolate the two and creates an undesirably large contact area between the EHCV and the reformer. The thermal mass of the end plate creates a heat sink which cools the vapor, reducing the efficiency of the device; 
         [0007]    b) the 1.0 mm annulus is too large even for the maximum required fuel flow of the application, which has the effect of minimizing surface contact between the liquid fuel and the rod heater and creates a thicker fluid film layer requiring longer residence time; the overly-large annulus also causes hot spots on the heater which are not being cooled by fuel or vapor, which impacts durability of the heater; 
         [0008]    c) fuel vapor enters the mixing chamber at low velocity, adversely impacting air/fuel mixing; 
         [0009]    d) the outer walls of the EHCV are exposed to cold reformer inlet air in the mixing chamber; 
         [0010]    e) outer fuel heating chamber walls are cooled by convection, thereby wasting energy; cooled chamber walls condense vapor by conduction, and condensed vapor droplets cause the prior art EHCV to sputter liquid fuel; 
         [0011]    f) because of the large annulus and multiple sources of heat loss, power requirement is high, typically about 400 W, and vaporized fuel output is relatively inefficient. 
         [0012]    At startup of a reformer, the reforming catalyst must be heated to achieve catalyzing temperature, typically to about 500° C. It is known in the prior art to provide a spark or other igniter mechanism extending through a wall of the reformer into a combustion chamber between the prior art EHCV and the reforming catalyst. For a short period, a combustible fuel/air mixture is formed in the combustion chamber and ignited by the igniter, the hot combustion gases then passing through the reforming catalyst. When catalyzing temperature is reached, ignition is suspended and the fuel/air ratio is adjusted for reforming. 
         [0013]    Providing an igniter in the hot zone of a reformer presents significant engineering and materials challenges. A standard automotive spark plug is not suitable as the continuously hot environment causes corrosion and failure, thus expensive or exotic materials of construction are required; a spark-ignition device is easily fouled by carbon deposits, leading to ignition failure; the igniter mounting requires additional bosses on the reformer housing, which are additionally expensive and undesirable; the igniter requires power to operate in addition to the power required for the EHCV; and the igniter itself adds to the cost and complexity of the reformer. 
         [0014]    What is needed in the art is an EHCV that provides high-efficiency high-volume vaporizing of diesel fuel and also eliminates the need for a separate igniter in a hydrocarbon reformer. 
         [0015]    It is a principal object of the present invention to vaporize fuel more efficiently. 
         [0016]    It is a further object of the present invention to eliminate the need for a separate igniter in a hydrocarbon reformer being supplied by an improved EHCV in accordance with the present invention. 
       SUMMARY OF THE INVENTION 
       [0017]    Briefly described, an improved EHCV for a catalytic hydrocarbon reformer includes an electrically-powered rod heater surrounded by a first tube defining a first annulus therebetween. In one aspect of the invention, the first annulus is about 0.2 mm in radial dimension and having an open end defining an exit from the EHCV. A spiral flow director is disposed in the first annulus to direct flow of fuel and vapor in a helical path around the rod heater through the EHCV. A tubular insulative housing surrounds the first tube, preferably comprising an outer housing tube and a thermal barrier tube disposed between the outer housing tube and the first tube. 
         [0018]    A first inlet port for introduction of liquid fuel at the inlet end of the EHCV extends through the insulative housing and the first tube into the first annulus to provide fuel to the heating rod for vaporization. 
         [0019]    In one aspect of the invention, the helical path for directing the flow of fuel through the EHCV may be formed as a channel in either the internal surface of the first tube, the outer surface of the rod heater, or partially in both. Further, multiple rod heaters may be chained in parallel with one or more cross-passages connecting the heaters, fluidically, to increase the heating capacity of the EHCV. 
         [0020]    In a second embodiment useful in reformers having no combustion igniter, a second inlet port and internal passages including a second annulus between the thermal barrier tube and the first tube permit controlled entry of oxygen, preferably in the form of air, into the first annulus near the exit end thereof to mix with hot, vaporized fuel exiting the vaporizer, thereby creating a fuel/air mixture above the LEL which spontaneously combusts to form hot gases for heating the reforming catalyst as in the prior art. When a sufficient temperature is achieved in the reformer, air flow into the EHCV is suspended, extinguishing combustion, and fuel flow rate is adjusted for reforming. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is a longitudinal cross-sectional view of a first embodiment of an improved EHCV in accordance with the present invention; 
           [0023]      FIG. 2  is a perspective cutaway view of a portion of a first embodiment similar to the embodiment shown in  FIG. 1 ; 
           [0024]      FIG. 3  is a sectioned view of a variation of the tubular housing shown in  FIG. 1  in accordance with the invention; 
           [0025]      FIG. 4  is a cross-sectional view of a second embodiment of an improved EHCV in accordance with the present invention; 
           [0026]      FIG. 5  is a perspective view, partially in cutaway, of the second embodiment shown in  FIG. 4 ; and 
           [0027]      FIG. 6  is simplified schematic drawing showing control and incorporation of the improved EHCV into a catalytic hydrocarbon reformer. 
       
    
    
       [0028]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Referring to  FIGS. 1 and 2 , a first embodiment 10 of an improved EHCV in accordance with the present invention comprises an electrically-powered heating element  12 , for example, a glow plug or rod heater, disposed in a tubular housing  14  and preferably connected thereto by mating threads  16 . A first port  18  in housing  14  contains a first nipple  20  for delivering liquid hydrocarbon fuel  22  for vaporization on surface  24  of element  12 . 
         [0030]    Fuel flows along heater surface  24 , confined by a concentric first tube  25  in a first annular flow space  27  and is discharged at exit  26  into a mixing chamber ahead of a catalytic hydrocarbon reformer. In radial dimension, an annulus of flow space  27  is less than 1.0 mm, and preferably is about 0.2 mm, in contrast to a typical prior art EHCV wherein this dimension is about 1.0 mm. The reduced annulus height of flow space  27  results in faster heating of a thinner layer of fuel. 
         [0031]    A flow director  28 , which may take the form of a helical wire or a raised helical rib on heating element  12  or on an ID of first tube  25 , is disposed in flow space  27  and causes fuel and fuel vapor to follow a helical path through flow space  27 , which path serves to prevent channeling as is known to occur in prior art EHCV devices, thus defining a longer contact path for fuel against surface  24  and distributing fuel and fuel vapor more evenly over surface  24 , thereby preventing formation of undesirable hot spots. Further, fuel vapor exits EHCV  10  with a swirling motion, thus improving mixing with introduced air in the mixing chamber. The spiral pattern of flow director  28  may be formed having a constant pitch as shown in  FIG. 2 , or having a varied pitch (not shown) to further optimize fuel vaporization. 
         [0032]    In one aspect of the invention, tube  25  is formed, at least in part, of an insulative material to minimize heat losses from the heated fuel. 
         [0033]    Preferably, an outer tubular wall  31  defining a housing extension is swaged or otherwise attached to housing  14  and closes against first tubular wall  25  near the exit end thereof. Outer tubular wall  31  may be a low mass structural member for sealing the vaporizer while minimizing parasitic heat transfer it because of its low mass structure. 
         [0034]    A second tubular wall  38  may extend longitudinally from housing  14 , as for example, from a step  39  in housing  14  as shown in  FIG. 1 . In one aspect of the invention, wall  38  is also closed against first tubular wall  25  near the exit end thereof. Preferably, wall  38  is formed of an insulative material to reduce radiative heat loss from heater  12  and to act as an infrared energy reflector. Preferably, wall  38  is separated from both outer tubular wall  31  and first tubular wall  25 , defining first and second insulative captive air annuli  40 , 41 . 
         [0035]    Preferably, in mounting the EHCV to a reformer, the contact area between the EHCV and the reformer is reduced in comparison to prior art mountings to minimize heat loss from the EHCV. 
         [0036]    Referring to  FIG. 3 , housing  114  of a variation of the embodiment shown in  FIGS. 1 and 2  is disclosed. First and second glow plugs or rod heaters (not shown) are disposed in housing branches  114   a  and  114   b  similar to the singular rod heater shown in  FIGS. 1 and 2 . A first port  118  in housing  114  is provided for delivering liquid hydrocarbon fuel  22  to first housing branch  114   a  for vaporization. Helical flow channel  128   a , formed in the internal surface of branch  114   a  as shown, or in the outer surface of the rod heater (not shown) causes fuel and fuel vapor to follow a helical path through branch  114   a  in contact with the rod heater. The fuel and fuel vapor then passes through cross-passage  115 , and follows a second helical flow channel  128   b  in branch  114   b  for further vaporization, thereafter being discharged at exit  126  into a mixing chamber ahead of a catalytic hydrocarbon reformer. With respect to this variation, helical flow channels  128   a , 128   b  may be formed partially in the internal surfaces of the housing and partially in the outer surfaces of the rod heaters. 
         [0037]    Referring now to  FIGS. 3 and 4 , in a second embodiment 10′ of an EHCV improved in accordance with the present invention, a second port  32  in housing  14  contains a second nipple  34  for injecting a combustible gas  36 , such as an oxygen-containing gas such as for example, air, into the EHCV. Nipple  34  extends to air annulus  40 . A plurality of radial openings  42 , for example, six, are provided in first tubular wall  25  near the exit end thereof, connecting air annulus  40  with flow space  27  and thus permitting mixing of injected combustible gas  36  into the vaporized fuel just as the vapor exits the EHCV and further permitting the mixture to impinge on the end of heating element  12 . When a fuel/air ratio above the LEL is formed in the hot, vaporized fuel, spontaneous combustion of the fuel/air mixture occurs in the reformer mixing chamber, providing hot combustion gases for heating the reformer catalyst. 
         [0038]    Referring now to  FIG. 5 , operation of either EHCV  10  or EHCV  10 ′ is controlled by a control apparatus  50 , for example a programmable controller or a computer, referred to herein generically as “controller”. Controller  50  is programmed with a plurality of algorithms for sending signals controlling energizing and de-energizing of heating element  12 , flow of liquid fuel  22 , flow of combustible gas  36 , and flow of reforming air  52  (signals  54 , 56 , 58 , 60 , respectively). (Note that in use of first embodiment 10, combustible gas  36  may be metered directly into chamber  28  rather than into the EHCV as shown in  FIG. 5  for embodiment 10′). 
         [0039]    In operation of either EHCV  10  or EHCV  10 ′, whenever vaporized fuel is required and the temperature of surface  24  is below a predetermined lower limit, heating element  12  is energized to raise the temperature of surface  24 . When the ambient temperature in EHCV  10  or  10 ′ is sufficient to maintain vaporization of fuel, heating element is de-energized. 
         [0040]    In operation of EHCV  10 ′, when the temperature within reformer  30  is insufficient to cause reforming catalysis of vaporized fuel, combustible gas  36  is injected through openings  42 , forming a combustible fuel/air mixture that combusts spontaneously in chamber  62  to form hot gases that are passed through reformer  30 . When the reformer attains catalysis temperature, flow of combustible gas  36  is terminated, and flow of reforming air  52  is adjusted to provide an optimal fuel/air mixture for reforming. 
         [0041]    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.