Abstract:
A startup burner for rapidly heating a catalyst in a reformer, as well as related methods and modules, is disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Under 35 U.S.C. § 119, this application claims priority to U.S. Provisional Application Ser. No. 60/571,910, filed May 17, 2004, the contents of which are incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This invention was made with Government support under Contract No. DE-FC02-99EE50580 awarded by the U.S. Department of Energy. The Government has certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The present invention relates to startup burners, as well as related methods and modules. 
     BACKGROUND 
     It is possible, with contemporary compact designs, to make fuel reformers with sufficient energy density to be suitable for automotive use. However, compactness does not necessarily provide rapid startup. One of the limiting factors in starting up a cold reformer is heating the catalyst contained therein to a desired light off temperature. 
     SUMMARY 
     The present invention relates to a startup burner for use in connection with a reformer. Generally speaking, the burner includes a burner chamber, fuel and air inlets, an igniter, and at least a first and second mixing zone. The burner produces a hot gas emission suitable for heating a catalyst (e.g., a catalyst used in an autothermal reforming (ATR)) to a desired temperature (e.g., the light-off temperature of the catalyst). Preferably the catalyst achieves the desired temperature in about three minutes or less, or more generally in about one-quarter or less of the time required to heat the catalyst without the burner. 
     In one aspect, the present invention features a method that includes the following four steps: (1) mixing a first oxygenated flow (e.g., air) and a fuel to create a rich fuel/air mixture; (2) igniting the rich fuel/air mixture to produce a partially oxidized mixture; (3) reacting the partially oxidized mixture with a second oxygenated flow (e.g., air) to produce a final gas; and (4) heating a reforming catalyst by flowing the final gas through the catalyst. The first and second oxygenated flows can be from the same source. 
     In some embodiments, the heating step can include heating the catalyst to a desired temperature (e.g., a light-off temperature) in at most about 3 minutes (e.g., at most 2 minutes or at most about 1 minute). The desired temperature can be at most 400° C. (e.g., at most about 350° C., at most about 300° C., or at most about 250° C.). After heating the catalyst to the desired temperature, the supply of the first oxygenated flow can be terminated and then water either as a liquid or as a gas can be mixed with the fuel to create a humidified fluid. The humidified fluid can be subsequently mixed with the second oxygenated flow to form a reactant mixture for use in a reforming reaction. Water can also be mixed with the fuel after heating the catalyst to the desired temperature, but before terminating the supply of the first oxygenated fluid. 
     In another aspect, the present invention features a startup burner for heating a catalyst in a reformer. The startup burner includes a burner chamber; a first mixing zone in fluid communication with and upstream of the burner chamber, in which a first oxygenated flow and a fuel flow are mixed within the first mixing zone to form a mixture; an igniter proximate to the first mixing zone for igniting the mixture to produce a partially oxidized mixture within the burner chamber; and a second mixing zone in fluid communication with and downstream of the burner chamber, wherein the partially oxidized mixture further reacts with a second oxygenated flow to produce a final gas, which is directed to flow through the catalyst. The first and second oxygenated flows and the fuel flow can respectively have a heat exchange relationship with an exhaust stream from an auxiliary burner. The startup burner can be removably detachable to the reformer (i.e., can be readily connected with the reformer and removed from the reformer). The startup burner can be constructed and operated such that the final gas passing through the catalyst bed is produced by a clean lean combustion. 
     In still another aspect, the present invention features a module that includes a reformer (e.g., an autothermal reformer) containing a catalyst and a startup burner in fluid communication with and upstream of the reformer. The startup burner is adapted to burn a fuel/air mixture to produce a first region of combustion in which the combustion is rich, followed by a second region of combustion in which the product of the first region of combustion further reacts with air to produce a lean exhaust; which is directed to flow through the catalyst to heat the catalyst to a desired temperature. The module can further contains an auxiliary burner adapted to burn either or both of a fuel and a fuel cell anode exhaust to produce heat for warming fluids in the module. 
     These and other aspects of the invention will be more readily understood by those skilled in the art from the following detailed description of a preferred invention and the appended drawing figures. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The present invention may be more readily understood with frequent reference being made to the appended drawings where: 
         FIG. 1  is a schematic illustrating generally the flows of one embodiment of the reformer system; 
         FIG. 2  is a cross section of a specific embodiment of the invention; 
         FIG. 3  is a graphical illustration of a calculated startup time reduction; 
         FIG. 4  is a graphical illustration of catalyst bed temperatures versus time for a modeled run; and 
         FIG. 5  is a graphical illustration of catalyst bed temperatures versus time in actual operation. 
     
    
    
     DETAILED DESCRIPTION 
     While the present invention is susceptible of embodiment in many different forms, this disclosure will describe in detail at least one preferred embodiment, and possible alternative embodiments, with the understanding that the present disclosure is to be considered merely as an exemplification of the principles and is not intended to limit the broad aspect of the invention to the specific embodiments illustrated. 
     In general, fuel reformers of the ATR-type, or related reformer types such as a partial oxidation reformers, generate the heat required for the endothermic steam reforming reaction by oxidizing part of the fuel to be reformed in the reforming catalyst bed, or in a special cavity at its entrance. The other major type of fuel reformer is a steam reformer, in which no oxygen and therefore no combustion occurs in the reforming catalyst bed, and all heat is supplied to the reaction across a wall encasing the bed, or by a similarly indirect route. While steam reforming has certain advantages over ATR, particularly in producing a reformate with a higher hydrogen concentration, heating a steam reformer through the walls of the catalyst chamber is inherently slow. An ATR reactor can be heated more rapidly to high temperatures by the ATR reaction itself, but first the ATR catalyst must be heated to its light-off temperature, at which it becomes catalytically effective so that the reaction becomes highly exthotherrnic and catalyst temperature starts to rise rapidly. A startup burner can be used for this startup process, i.e., to accelerate the heating of the catalyst to its light-off temperature. 
       FIG. 1  shows a preferred topology of the flows in the system during startup. At the upper right is an autothermal reformer  10  having an outlet to downstream systems  12 , a catalyst section  18  and an inlet section  15  with a first inlet  20  of an oxygenated flow, preferably air (“ATR air”), and a second inlet  30  through which is admitted a second flow, which at startup comprises a mixture of an oxygenated gas, preferably air, and fuel passing through startup burner  32 . The burner  32  typically includes an igniter  34 . The fuel is gasoline in this example, but can be any hydrocarbon or alcohol suitable for use in a reformer to produce hydrogen for a fuel cell. 
     The fuel/air mixture for the startup burner is made from regulated sources of fuel and of air, the air line  42  branching from a general air supply  44 . Fuel and air are mixed and are preheated in a first heat exchanger  38  (“HX3”) by heat exchange with the exhaust  62  of an system auxiliary burner, or “tail gas combustor” (TGC)  50 . The exhaust is generally emitted after this heat exchange step. The TGC  50 , having igniter  52 , is supplied at startup by regulated sources of air flow  54  and of fuel flow  56  which are often mixed before entering the TGC  50 . Provisions may be made for pre-vaporization of the fuel flow  56  if required. Note that after startup, TGC  50  typically is not supplied with fuel, but is used for converting waste hydrogen from a fuel cell (e.g., a fuel cell anode exhaust) into heat, usually used for preheating various fluids in the system. 
     The TGC exhaust  58  enters a second heat exchanger  60  (“HXI”) and leaves it via line  62 , passing to the first heat exchanger  38  and then being exhausted from the system. “ATR air”, i.e., air supplied to the autothermal reformer via the route through which air is added for the autothermal reforming reaction in normal use, is supplied via line  48  to second heat exchanger  60  and then via line  20  into the inlet section  15  of the reformer. The volume of air required in the startup operation will typically, although not necessarily, be significantly less than the amount needed in full operation. 
     The system typically has an inlet for water, steam, or a combination of the two which will substitute for air inlet  42  when the system is moved from start-up conditions to regular operation. The fuel  40  and the steam or water will preferably be mixed before entering the first heat exchanger  38 , especially if the fuel is liquid and needs to be vaporized. 
     It may appear that having two burners (i.e., a TGC and a startup burner), as opposed to just one, in the system is inefficient. However, it can actually be an advantage. This is because a suitably designed system can have all components sized properly for efficiency in normal operation, while allowing conversion from a start-up procedure to a normal running procedure simply by changing an air feed to the startup burner during startup to a steam feed during normal operation. The execution of this arrangement, which is preferred, but not rigidly required, will be more evident after the layout of a preferred mechanical system is described. 
       FIG. 2  shows a schematic drawing (relative part sizes, etc. not necessarily to scale) of a current embodiment of a system having the flow schematic of  FIG. 1 . The autothermal reformer, the startup burner and the heat exchangers are closely integrated into a module  100 . The module  100  has a first annular wall  110 , a second annular wall  112 , a third annular wall  114 , and a fourth annular wall  116  that surrounds the reformer catalyst  118 . It is the catalyst  118  that needs to be warmed to a light-off temperature to allow for operation of the reformer. The quicker the achievement of the catalyst light-off temperature, the quicker the startup operation. 
     The four walls define three annular zones: first zone  150 , second zone  152 , and third zone  154 . Each annular zone is a component of a heat exchanger, as explained below. In this embodiment, a spiral tube  120 , having an inlet (not illustrated) and an outlet  122 , runs through the first zone  150 . In alternative embodiments, not illustrated, the spiral tube  120  could be replaced by an additional shell and annular zone, could be located in a different annular zone than the one illustrated, or could be located in a different device other than the one illustrated (e.g., an independent TGC). 
     At the bottom of  FIG. 2 , tube  142  is the entrance into the startup burner  130  for fuel and air during startup, and is connected by a linkage (shown here as dotted line  135 ), to outlet  122  of spiral tube  120 . The tube  120  is the equivalent of the fuel/air side in the first heat exchanger  38  of  FIG. 1 , which equilibrates a fuel/air mixture with the burner exhaust. In  FIG. 2 , the TGC exhaust  158  flows in first annular zone  150 , passing through the zone along spiral tube  120  and thereby exchanging heat with the fuel/air mixture in spiral tube  120 . In this embodiment, the first heat exchanger consists largely of tube  120  and zone  150  (and its walls  110  and  112 ). The TGC exhaust  158  leaves the system after this exchange, for example at exit  159  while the heated fuel/air mixture is passed from exit  122  to burner entrance  142 . 
     While entering tube  142 , the fuel/air mixture is ignited by igniter  134 . The fuel/air mixture is caused to swirl by mixer  136 , or functionally equivalent means, and the swirling burning gas passes into burner cup  130  where it combusts. As previously noted, air is the preferred oxygen flow source. Where “air” is referenced, it is intended to represent any suitable oxygenated flow. 
     The fuel/air mixture is preferably rich, i.e., the fuel/air stoichiometry (phi) is preferably greater than 1, for example between about 1.6 and about 1.05 (e.g., about 1.2), because burning a rich (fuel excess) fuel/air mixture prevents excessive heating and NOx formation. The swirling action can be arranged to allow a stable flame to persist in cup  130 , so that igniter  134  need not be used continuously, but only to start the flame. The top of cup  130  may be connected to a stabilizer plate  137 , and may, as in the current embodiment, be further connected to annular shell  114 . 
     The swirling partially oxidized fuel/air mixture then leaves burner cup  130 , is diverted by diverter plate  126 , and enters mixing zone  128 . In this zone, the hot partially oxidized fuel mixes with excess air entering from third zone  154 , which is the entrance route for air normally used for the ATR reaction. 
     In  FIG. 1 , the ATR air passes through line  48  into second heat exchanger  60 , and then via line  20  into the autothermal reformer  10 . In  FIG. 2 , a physical embodiment of  FIG. 1 , ATR air enters the module  100  at entrance  144  which annularly surrounds burner cup  130 . The ATR air is typically from a source outside the system, and is typically controlled by a valve, not illustrated. The ATR air is preheated as it passes through passage  148 , around the outside wall  132  of burner cup  130 , and then enters the second zone  152 , where it is further heated by the TGC exhaust  158  flowing in zone  150 . At connection  160  (top of the reformer), second zone  152  connects to third zone  154 , which exchanges heat with catalyst  118  via fourth wall  116 . The ATR air leaves zone  154  at exit  156 , and reacts in mixing zone  128  with the partially oxidized fuel exiting burner cup  130 . Mixing zone  128  may have mixing vanes  124  or other aids to completely mix the ATR air and the partially oxidized fuel. The gas mixture, now having excess air (phi less than 1; “lean”), passes through porous diffuser plate  125  and into catalyst bed  118 , optionally via a mixing space  123 . In the presence of the extra air, conversion of the hydrocarbons in the partially oxidized fuel to carbon dioxide is completed at a relatively low temperature, thereby preventing NOx formation and damage to the catalyst. 
     The diluted gas then passes through and heats up the catalyst bed  118  ( 18  in  FIG. 1 ). After heating the catalyst bed or monolith  118 , the exhaust leaves the autothermal reformer zone through a fenestrated or open section  162  of reformer end plate  164 . 
     In this embodiment, the various parts of the device for mixing the ATR air with the combusted fuel are parts of a single mixing assembly, comprising parts  124 ,  125 ,  126  and  128 , which are held together by a shell  127 , and optionally further carrying a ring  129  to create space  123  separating diffuser plate  125  from catalyst  118 . 
     As noted, while the ATR air is passing through the second zone  152 , the air is in heat exchange, across second wall  112 , with TGC exhaust  158 , which is running countercurrently in the first (outer) annular zone  150 . This pair of annular zones, and wall  112 , are the core of the second heat exchanger  60  of  FIG. 1 . It is clear from  FIG. 2  that in the embodiment described, the interaction of the exhaust  158  with the two heat exchangers is simultaneous rather than the sequential interaction implied by  FIG. 1 . 
     When the catalyst has reached a certain temperature (e.g., the light-off temperature), the system can be shifted to normal operation very simply. The flow of air into the startup burner  32  ( FIG. 1 ) from inlet  42  can be stopped, and steam, generated elsewhere in the system, can be mixed with the fuel coming from line  40  and the mixture flows into the first heat exchanger  38 . The steam/fuel mixture can also be sent to the first heat exchanger  38  without terminating the flow of air from inlet  42 . Turning to  FIG. 2 , it can be seen that the steam/air mixture for reforming then follows the path of the fuel/air mixture used in the startup process. It passes through helical tube  120  to exit  122 , burner entrance  142 , burner cup  130 , the mixing zone  128  to be mixed with a regulated amount of heated ATR air from entrance  156 , and into the hot catalyst  118 , where autothermal reforming now occurs, absorbing heat from the concurrent oxidation of part of the reforming fuel with the ATR air. In this stage of operation, heat flowing outward from the catalyst  118  is absorbed by the ATR air flowing through annular zones  154  and  152 , and thereby the escaping heat is returned to the reformer. 
     Turning to other components, the module  100  generally requires an igniter  134  and an electric source to allow the igniter  134  to spark to initiate the startup process. Elsewhere in the module  100 , devices for turning on and off an air flow to mix with fuel going into the reformer must be added. Devices for regulating steam to be mixed with that fuel, and to regulate ATR air volume in proportion to the fuel flow, must also be present in a normal ATR reformer. 
       FIG. 3  shows the modeling results predicting the increased speed of catalyst warming obtainable from the module  100 . The predicted startup time is decreased from 18 minutes to three minutes by use of the startup burner.  FIG. 4  shows the modeling results predicting the temperature profile in the catalyst bed as a function of time.  FIG. 5  shows actual temperature profile in the catalyst bed as a function of time, which validates the modeling results. The startup burner described above can significantly shorten startup time. 
     In one embodiment, an improved utility of a reformer equipped with a startup burner described above is its modularity and ease of assembly. For example, the mixing assembly (parts  124  through  129 ) can be made as one unit and then inserted into a single shell (shell  116 ) along with the catalyst  118 . Likewise, the entire startup burner can be made as an assembly (elements  142 ,  134 ,  130 ,  136 ,  137 ) and connected either by bonding, or simply by fit, with shell  114 . A heat exchange unit can comprise shells  10  and  112  with tube  120 . A module can then be assembled by combination of a reformer with these three assemblies, with suitable spacing elements in between, plus options such as base block  138 , which can serve to stabilize the burner cup  130  and its inlet tube  142 . 
     Another important aspect of the inventive module equipped with a separate startup burner is its efficiency. Heat released by the startup burner is directly transferred to the adjacent catalyst, while the temperature of the exhaust of the startup burner is controlled by reacting the combustion exhaust of a rich fuel/air mixture with a second oxygenated flow. At each stage of operation, both in the startup phase and in the normal operation phase, thin concentric heat exchangers serve to focus heat where it is needed while minimizing heat loss from the system. In particular, the two annular zones  152  and  154  convey heat from the TGC exhaust to warm the catalyst  118  during startup, and then help retain heat in the catalyst during normal operation. Likewise, the mixing assembly works efficiently both in the startup stage and in the normal operation stage. The “ATR air” is typically preheated by the startup burner during startup and by the TGC and the autothermal reformer during normal operation. This switching of heat exchange patterns is accomplished without valving of any hot fluids, except for the opening of a steam inlet valve. 
     Once in possession of this description of the invention, a variety of functionally equivalent burner/reformer combinations can be envisaged by a skilled artisan. While the invention has been shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.