Patent Publication Number: US-6986797-B1

Title: Auxiliary reactor for a hydrocarbon reforming system

Description:
RELATED REFERENCES 
     The present invention claims priority of U.S. Provisional Patent Application Nos. 60/132,184 and 60/132,259, both filed on May 3, 1999. 
    
    
     GOVERNMENT RIGHTS 
     The United States Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of DE-FC02-97EE50472 awarded by the Department of Energy (DOE). 
    
    
     TECHNICAL FIELD 
     The present invention is generally related to an integrated hydrocarbon fuel reforming system for reforming a gaseous or liquid hydrocarbon fuel to produce a hydrogen-rich product stream used in, among other things, hydrogen fuel cells. More particularly, the invention is directed to an improved integrated hydrocarbon reforming system, including, an autothermal reformer having distinct zones for partial oxidation reforming and steam reforming, and also having an integrated shift bed for reducing carbon monoxide in the product stream, a preferential oxidation reactor, and an auxiliary reactor. 
     BACKGROUND OF THE INVENTION 
     Reforming of hydrocarbon fuels to make hydrogen is well known in the art. Conventionally, hydrocarbons are reformed predominately in large-scale industrial facilities providing hydrogen for bulk storage and redistribution, or producing hydrogen as an on-line, upstream reagent for another large-scale chemical process. For the most part, these prior processes operate continuously and at steady-state conditions. 
     More recently, however, a strong interest has developed in providing hydrocarbon-reforming reactors integrated with an end use of the hydrogen. Also, there is a strong interest to develop a low-cost, small-scale source for hydrogen that can replace the need for storing hydrogen gas on site or on board. More particularly, a great interest has developed in providing reactors for producing hydrogen, which can be integrated with a fuel cell which uses hydrogen as a fuel source to generate electricity. Such hydrogen generator/fuel cell systems are being pursued for stationary uses such as providing electrical power to a stationary facility (home or business), for portable electric power uses, and for transportation. 
     The use of fuel cells, such as polymer electrolyte membrane fuel cells (PEM-FC), has been proposed for many applications, specifically including electrical vehicular power plants used to replace internal combustion engines. Electrochemical fuel cells convert fuel and oxidant to electricity and reaction product. Hydrogen is most commonly used as the fuel and is supplied to the fuel cell&#39;s anode. Oxygen (commonly as air) is the cell&#39;s oxidant and is supplied to the cell&#39;s cathode. The reaction product is water. 
     Efficiency and low emissions are two benefits of fuel cell systems. A system running near 40% efficiency will offer the opportunity to significantly reduce fuel consumption and CO 2  production compared to conventional gasoline internal combustion engines. Perhaps more importantly, it has been shown that fuel cell systems, even when running with an onboard fuel processor, offer an opportunity to greatly reduce emissions of NO x , carbon monoxide, and hydrocarbons in automotive applications. 
     There are many technical requirements for reactors used in such applications, which are not required of traditional large or small-scale hydrogen generating reactors. For example, it is of particular interest to have such a system where the fuel cell can provide “power on demand.” Hence, hydrogen must be produced at required variable levels on demand. In other words, the hydrogen producing reactors must be sufficiently dynamic to follow the load. It is also of interest that such systems perform well upon start-up and shutdown cycling. In particular, it is desirable to have these integrated systems be stable through repeated on-off cycling including being ready to come back on-line in a relatively short time. 
     Another marked difference between proposed integrated systems and traditional reactors is that there must be sufficient processing in the integrated system itself, of the hydrocarbon feed stock so as to not only give a yield of hydrogen sufficient to meet the demand, but also to minimize byproducts of reaction including contaminants. In large-scale reactor systems, which produce enormous volumes and run continuously; space, weight, and cost of auxiliary systems is not so critical as in the integrated, smaller-scale reformers, especially those proposed for portable power or transportation applications. For example, carbon monoxide may be considered an undesirable reaction product on board a fuel cell powered automobile. However, in a steady state conventional process, the carbon monoxide can easily be handled by auxiliary separation systems, and may in fact be welcomed for its use in a synthesis gas to make acetic acid, dimethyl ether, and alcohols. 
     In short, the challenge for the smaller-scale, dynamic, integrated processors is the idea that what goes in the reformer, must come out at the same end as the desired hydrogen gas. Accordingly, processing has to be more complete and efficient, while it must also be cost effective, lightweight, and durable. The processing must be sufficient to reduce or eliminate species in the product gas which are harmful to the end use (for example, fuel cells) or other down stream components. 
     Another challenge exists for the proposed integrated systems with respect to the hydrocarbon feed stock. To be of maximum benefit, the proposed integrated systems should be able to use existing infrastructure fuels such as gasoline or diesel fuels. These fuels were not designed as a feed stock for generating hydrogen. Because of this, integrated systems are challenged to be able to handle the wide variety of hydrocarbons in the feed stock. For example, certain reforming byproducts such as olefins, benzene, methyl amide, and higher molecular weight aromatics can cause harm to catalysts used in reforming or purifying steps and may harm the fuel cell itself. Impurities in these fuels such as sulfur and chlorine can also be harmful to reactor catalysts and to the fuel cell. 
     It is also important to note, that a natural byproduct of hydrocarbon reforming is carbon monoxide. Carbon monoxide can poison proton exchange membrane fuel cells, even at very low concentrations of, for example, less than 100 ppm. Typical carbon monoxide levels exiting a fuel processing assembly (“FPA”) are about 2,000 to 5,000 ppm. This poses a problem for an integrated reactor system that is not faced by traditional reforming processes where significant carbon monoxide concentrations are either a useful co-product, or can be separated from the product gas without undue burden on the system economics as a whole. 
     Also, as noted above, integrated systems proposed to date are expected to transfer the total of the reformate to a fuel cell. Accordingly, techniques which separate carbon monoxide from hydrogen, such as pressure swing adsorption (“PSA”) or hydrogen permeable membrane separation, have the deficit of having to provide an alternate means for disposal or storage of the carbon monoxide. Both of the aforementioned techniques also suffer in efficiency as neither converts the carbon monoxide (in the presence of water) to maximize hydrogen production. PSA also suffers from high cost and space requirements, and presents a likely unacceptable parasitic power burden for portable power or transportation applications. At the same time, hydrogen permeable membranes are expensive, sensitive to fouling from impurities in the reformate, and reduce the total volume of hydrogen in the reformate stream. 
     One known method of reforming gaseous or liquid hydrocarbon fuels is by catalytic steam reforming. In this process a mixture of steam and the hydrocarbon fuel is exposed to a suitable catalyst at a high temperature. The catalyst used is typically nickel and the temperature is usually between about 700° C. and about 1000° C. In the case of methane, or natural gas, hydrogen is liberated in a catalytic steam reforming process according to the following overall reaction:
 
CH 4 +H 2 O→CO+3H 2   (1)
 
     This reaction is highly endothermic and requires an external source of heat and a source for steam. Commercial steam reformers typically comprise externally heated, catalyst filled tubes and rarely have thermal efficiencies greater than about 60%. 
     Another conventional method of reforming a gaseous or liquid hydrocarbon fuel is partial oxidation (POx) reforming. In these processes a mixture of the hydrocarbon fuel and an oxygen containing gas are brought together within a POx chamber and subjected to an elevated temperature, preferably in the presence of a catalyst. The catalyst used is normally a noble metal or nickel and the high temperature is normally between about 700° C. and about 1200° C. for catalyzed reactions, and about 1200° C. to about 1700° C. for non-catalyzed reactions. In the case of methane, or natural gas, hydrogen is liberated in a POx chamber according to the following overall reaction:
 
CH 4 +½O 2 →CO+2H 2   (2)
 
     This reaction is highly exothermic and once started generates sufficient heat to be self sustaining. That is, no external heat supply or steam supply is required. The catalytic partial oxidation reforming technique is simpler than the catalytic steam reforming technique, but is not as thermally efficient as catalytic steam reforming. 
     An additional known method of reforming a hydrocarbon fuel is by autothermal reforming, or “ATR”. An autothermal reformer uses a combination of steam reforming and partial oxidation reforming. Waste heat from the partial oxidation reforming reaction is used to heat the thermally steam reforming reaction. An autothermal reformer may in many cases be more efficient than either a catalytic steam reformer or a catalytic partial oxidation reformer. Again, using methane, or natural gas, as the hydrocarbon fuel, hydrogen is liberated according to the following overall reaction:
 
CH 4   +y H 2 O+(1 −y /2)O 2  →CO 2 +(2 +y )H 2 , where 0 &lt;y &lt;2  (3)
 
     Consideration of the standard enthalpies of formation shows that autothermal operation is theoretically achieved when y=1.115. 
     In addition to the reforming reactions discussed above it is usually necessary to consider the effects of another reaction occurring, the so called “water gas shift reaction.” Because the equilibrium of this reversible reaction is temperature (T) dependent, and at high temperatures carbon monoxide and water tend to be produced, the effects warrant consideration. In the water gas shift reaction the following overall reaction occurs:
 
CO+H 2 O (g) →CO 2 +H 2   (4)
 
     More favorably, however, is that given equilibrium conversion at low temperatures carbon dioxide and hydrogen tend to be produced. 
     Typical reformers produce carbon dioxide and hydrogen, and consequently some carbon dioxide and hydrogen react to produce concentrations of carbon monoxide and water due to the reverse water gas shift reaction occurring in the reforming chamber. As mentioned previously, this is undesirable because the concentration of carbon monoxide must be either completely removed or at least reduced to a low concentration—i.e., less than about 100 ppm after the shift reaction—to avoid poisoning the anode of the PEM-FC. Carbon monoxide concentrations of more than 20 ppm reaching the PEM-FC can quickly poison the catalyst of the fuel cell &#39;s anode. In a shift reactor, water (i.e., steam) is added to the hydrocarbon reformate/effluent exiting the reformer, in the presence of a suitable catalyst, to lower its temperature, and increase the steam to carbon ratio therein. The higher steam to carbon ratio serves to lower the carbon monoxide content of the reformate to less than 100 ppm according to the shift reaction (4) above. Ideally, the carbon monoxide concentration can be maintained below 1 ppm with the right shift catalyst, but the temperature required for this, about 100° C.–125° C., is too low for operation of current shift catalysts. 
     Advantageously, it is possible to recover some hydrogen at the same time by passing the product gases leaving the reformer, after cooling, into a shift reactor where a suitable catalyst promotes the carbon monoxide and water/steam to react to produce carbon dioxide and hydrogen. The shift reactor provides a convenient method of reducing the carbon monoxide concentration of the reformer product gases, while simultaneously improving the yield of hydrogen. 
     However, some carbon monoxide still survives the shift reaction. Depending upon such factors as reformate flow rate and steam injection rate, the carbon monoxide content of the gas exiting the shift reactor can be as low as 0.5 mol percent. Any residual hydrocarbon fuel is easily converted to carbon dioxide and hydrogen in the shift reactor. Hence, shift reactor effluent comprises not only hydrogen and carbon dioxide, but also water and some carbon monoxide. 
     The shift reaction is typically not enough to sufficiently reduce the carbon monoxide content of the reformate (i.e., below about 100 ppm). Therefore, it is necessary to further remove carbon monoxide from the hydrogen-rich reformate stream exiting the shift reactor, prior to supplying it to the fuel cell. It is known to further reduce the carbon monoxide content of hydrogen-rich reformate exiting a shift reactor by a so-called preferential oxidation (“PrOx”) reaction (also known as “selective oxidation”) effected in a suitable PrOx reactor. A PrOx reactor usually comprises a catalyst bed which promotes the preferential oxidation of carbon monoxide to carbon dioxide by air in the presence of the diatomic hydrogen, but without oxidizing substantial quantities of the H 2  itself. The preferential oxidation reaction is as follows:
 
CO+½O 2 →CO 2   (5)
 
     Desirably, the O 2  required for the PrOx reaction will be no more than about two times the stoichiometric amount required to react the CO in the reformate. If the amount of O 2  exceeds about two times the stoichiometric amount needed, excessive consumption of H 2  results. On the other hand, if the amount of O 2  is substantially less than about two times the stoichiometric amount needed, insufficient CO oxidation will occur. The PrOx process is described in a paper entitled “Preferential Oxidation of CO over Pt/ÿ-Al 2 O 3  and Au/ÿ—Fe 2 O 3 : Reactor Design Calculations and Experimental Results” by M. J. Kahlich, et al. published in the  Journal of New Materials for Electrochemical Systems,  1988 (pp. 39–46), and in U.S. Pat. No. 5,316,747 to Pow et al. 
     PrOx reactions may be either (1) adiabatic (i.e., where the temperature of the reformate (syngas) and the catalyst are allowed to rise during oxidation of the CO), or (2) isothermal (i.e., where the temperature of the reformate (syngas) and the catalyst are maintained substantially constant during oxidation of the CO). The adiabatic PrOx process is typically effected via a number of sequential stages which progressively reduce the CO content. Temperature control is important in both systems, because if the temperature rises too much, methanation, hydrogen oxidation, or a reverse shift reaction can occur. This reverse shift reaction produces more undesirable CO, while methanation and hydrogen oxidation negatively impact system efficiencies. 
     In either case, a controlled amount of O 2  (e.g., as air) is mixed with the reformate exiting the shift reactor, and the mixture is passed through a suitable catalyst bed known to those skilled in the art. To control the air input, the CO concentration in the gas exiting the shift reactor is measured, and based thereon, the O 2  concentration needed for the PrOx reaction is adjusted. However, effective real time CO sensors are not available and accordingly system response to CO concentration measurements is slow. 
     For the PrOx process to be most efficient in a dynamic system (i.e., where the flow rate and CO content of the hydrogen-rich reformate vary continuously in response to variations in the power demands on the fuel cell system), the amount of O 2  (e.g., as air) supplied to the PrOx reactor must also vary on a real time basis in order to continuously maintain the desired oxygen-to-carbon monoxide concentration ratio for reaction (5) above. 
     Another challenge for dynamic operation is that the reformate at start-up contains too much carbon monoxide for conversion in the PrOx reactor and, therefore, is not suitable for use in a PEM-FC. One approach to this problem is to discharge this unsuitable reformate without benefit, and potentially to the detriment of the environment. The partially reformed material may contain unacceptable levels of hydrocarbons, carbon monoxide, sulfur, noxious oxides, and the like. It would be an advantage to provide a process which utilizes the waste reformate to assist in the preheating of unreformed fuel before its entry into the reforming chamber, while simultaneously converting the harmful constituents of the waste reformate to acceptable emissions. 
     A PEM-FC typically does not make use of 100% of the incoming hydrogen from the reformer/reactor. Therefore, anode gases—mostly unused hydrogen—are discharged from the fuel cell simultaneous with the input of hydrogen. It would be an advantage in the industry to make use of this combustible material to assist the preheating of unreformed hydrocarbon fuel or for steam generation. Systems already proposed employ so called “tail gas combusters” to burn off such fuel cell exhaust gases. 
     The present invention addresses the above problems and challenges and provides other advantages as will be understood by those in the art in view of the following specification and claims. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the present invention an auxiliary reactor for use in conjunction with a reformer reactor for converting hydrocarbons to hydrogen gas, the reformer reactor having at least one reaction zone, is disclosed. The auxiliary reactor comprises a first burner for burning a first fuel and creating a heated auxiliary reactor gas stream, and a first heat exchanger for transferring heat from at least the auxiliary reactor gas stream and a heat transfer medium to be transferred to the reformer reaction zone for additional heat exchange with said reformer reactor zone. 
     In another embodiment the auxiliary reactor comprises a first cylindrical wall defining a first chamber for burning a first fuel and creating a heated auxiliary reactor gas stream, the chamber having a diameter, an inlet end, and an opposed outlet end, a second cylindrical wall surrounding the first wall and providing a second annular chamber there between, and the reactor configured so that heated auxiliary reactor gas flows out of the outlet end of the of the first chamber and into and through the second annular chamber, and a first conduit disposed in the second annular chamber, the conduit adapted to carry a first heat transfer medium, and the first conduit being connectable to the reformer reaction zone for additional heat exchange with said reformer reactor zone. 
     It is an aspect of the invention to provide an auxiliary reactor wherein the heat transfer medium is water. It is also an aspect of the invention to provide an auxiliary reactor wherein the heat transfer medium is two-phase water. 
     These and other aspects of the present invention set forth in the appended claims may be realized in accordance with the following disclosure with particular reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions of the present invention are discussed with particular reference to the appended drawings of which: 
         FIG. 1  is a schematic view of one embodiment of a system of the present invention showing the relationship of selected sub-systems to one another; 
         FIG. 2  is a schematic view of another embodiment of the system of the present invention showing fluid transport and flow between sub-systems; 
         FIG. 3  is a side view of one embodiment of a reformer reactor sub-system of the present invention; 
         FIG. 4  is an exploded view of a pressure vessel shell of the reformer reactor of  FIG. 3 ; 
         FIG. 5  is an exploded view of an inner protective shell of the reformer reactor of  FIG. 3 ; 
         FIG. 6  is a side cross-sectional view of the reformer reactor shown in  FIG. 3 ; 
         FIG. 7  is an exploded view of an autothermal reforming vessel of the reformer reactor shown in  FIG. 6 ; 
         FIG. 8  is an exploded view of a POx chamber of the reformer shown in  FIG. 6 ; 
         FIG. 9  is a top view of a steam ring of the reformer shown in  FIG. 6 ; 
         FIG. 10  is a top cross-sectional view of an air inlet section of the POx chamber shown in  FIG. 8 ; 
         FIG. 11  is a cross-sectional view of a pre-mixing manifold shown in  FIG. 6 ; 
         FIG. 12  is a side view of one embodiment of the PrOx reactor of the present invention; 
         FIG. 13  is a side cross-sectional view of the PrOx reactor shown in  FIG. 12 ; 
         FIG. 14  is a top cross-sectional view of the PrOx reactor shown in  FIG. 12 ; 
         FIG. 15  is a diagrammatic illustration of a two stage PrOx reactor embodiment of the present invention; 
         FIG. 16  is a side view of one embodiment of a second stage PrOx reactor, as shown in  FIG. 15 ; 
         FIG. 17  is a side cross-sectional view of the embodiment of the second stage PrOx reactor shown in  FIG. 16 ; 
         FIG. 18  is a diagrammatic illustration of an alternative PrOx reactor system design having a two catalyst beds configured in parallel; 
         FIG. 19  is a diagrammatic illustration of a two-stage PrOx arrangement having a chiller condenser in line; 
         FIG. 20  is a side cross-sectional view of one embodiment of an auxiliary reactor of the present invention; 
         FIG. 21  is a side cross-sectional view of an alternative embodiment of an auxiliary reactor of the present invention; 
         FIG. 22  is a side cross-sectional view of another alternative embodiment of an auxiliary reactor of the present invention; 
         FIG. 23  is a diagrammatic illustration of a water/steam loop and water/steam controls of the present invention; 
         FIG. 24  is a diagrammatic illustration of one embodiment of the present invention showing operational control points; 
         FIG. 25  is a diagrammatic illustration of a reformate flow through a system according to the present invention; 
         FIG. 26  is a diagrammatic illustration of a sample start-up procedure for the reformer, PrOx and auxiliary reactors of the system of  FIG. 2 ; 
         FIG. 27  is a diagrammatic illustration of a sample steady-state operation for the fuel cell system of the present invention; and 
         FIG. 28  is a diagrammatic illustration of control points for a reformer, an auxiliary reactor, and a steam separator in one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     While the present invention is susceptible of embodiment in many different forms, this disclosure will described in detail, preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments discussed or illustrated. 
     I. System and Sub-System Structure 
     Referring generally to the appended  FIGS. 1–28 , the hydrocarbon reforming process and apparatus of the present invention can be more readily understood. The disclosed hydrocarbon reforming system architecture is generally referenced by the number “ 10 ” in the following disclosure and drawings. Other specific components, such as the reforming chambers, catalyst beds, auxiliary reactors (e.g., PrOx reactors, tail gas combusters, etc.), and their respective parts, are similarly and consistently numbered throughout this disclosure. While the present hydrocarbon reforming system  10  is disclosed in combination with a PEM-fuel cell, such as those used for transportation systems and the like, the systems and components according to the invention may be employed in other applications calling for a supply of hydrogen-rich syngas. More particularly, the disclosed systems and subcomponents thereof will be preferred in applications where size, weight, portability, and energy efficiency are desired. Examples of such uses include portable power units, transportation, on demand merchant hydrogen, and small power plant (e.g., household backup or primary power systems). 
     As shown in  FIG. 1 , the integrated hydrocarbon reforming system  10  (“system,” “reforming system,” and like variations) is comprised of a reformer reactor  12 , a preferential oxidation reactor  13  (PrOx), an auxiliary reactor  14 , an associated fuel cell  15 , and a network of fluid transport structure  16 . In general, the reformer reactor  12  is downstream of the auxiliary reactor  14  and is in fluid communication therewith via fuel line  17 . The reformer reactor  12  is in turn upstream of the PrOx reactor  13  and is in fluid communication therewith via conduit  20 . 
     In this embodiment, the auxiliary reactor  14  can be used with liquid hydrocarbon fuels to preheat, desulfurize, and/or to vaporize the fuel before transfer through fuel line  17  to the reformer reactor  12 . This preheating may be used only for a temporary period such as during reformer start-up, as exemplified in  FIG. 2 . In that embodiment, the fuel preheat/vaporization task (and the hydrocarbon fuel source) is transferred to heat exchangers within a shift catalyst bed in the reformer  12  after the shift bed has risen to a desired temperature after start-up. The auxiliary reactor  14  can also be used to desulfurize liquid hydrocarbon feed stocks. In a preferred method, the desulfurization is carried out catalytically. The hydrocarbon fuel is transported from a hydrocarbon fuel source  18  to the auxiliary reactor  14  via fuel line  17 . The auxiliary reactor  14  may also be used to heat or preheat water to make steam used in the reformer  12  as a reactant and/or a heat transfer medium. The auxiliary reactor  14  can also be used to react excess hydrogen and other gases exhausted from the anode of the fuel cell  15 . Any heat from this reaction may be synergistically used in the aforementioned preheating or desulfurization processes. The auxiliary reactor  14  may also be used to combust reformate from the reformer  12  as desired. For example, upon start up or other circumstances when the reformate may not be of desired quality to transfer to the PrOx reactor  13  or the fuel cell  15 , then it can be optionally routed to the auxiliary reactor  14  via a valve  28  in conduit  16 . Again, any heat from this reaction may be synergistically used in the aforementioned preheating or desulfurization processes. Details of various embodiments of auxiliary reactor  14  are disclosed in detail below. With each embodiment, a preferred fuel or system support function is disclosed. 
     In the system  10 , water is first introduced from a reservoir to the auxiliary reactor  14 . Depending on the desired heating, the water is transferred as heated water, steam or two phase water-steam. Of course the level of heating is a matter of particular design relative to the particular system goals as exemplified by the preferred embodiments below. The water/steam/steam-water is synergistically transferred to the reformer  12 . Depending on system goals and design, the water/steam/water-steam can be routed through heat exchangers in shift catalyst beds (see for example,  FIG. 6  and reformer  12  with heat exchangers  39 , or boiler tubes, embedded in a low temperature shift (“LTS”) catalyst bed  36 ). The water/steam/water-steam may also be directed to heat exchangers in the PrOx reactor  13  for additional heat exchange with reformate during the exothermic reactions proceeding therein. 
     In alternate embodiments, an alternate source of vaporized fuel may also be supplied to the reformer  12  directly by such as supply line  19  disclosed in  FIGS. 1 and 2 . In this embodiment, the auxiliary reactor  14  is used to provide vaporized fuel to the reformer  12  during start-up. Upon reaching a desired temperature in a high temperature shift (“HTS”) bed  37 , hydrocarbon feed stock is then fed directly into heat exchangers  39  in the HTS  37  to preheat/vaporize the fuel before reaction. The fuel supply from the auxiliary reactor  14  can then be terminated. 
     Air is supplied to the system  10  at various points including at the fuel inlet to the HTS bed  37 , and at the conduit between the LTS bed  36  and the PrOx reactor  13 . Greater detail on these operations are found later in this specification (see section below,  System and Sub - System Control and Operation ). The reformate flow is illustrated separately in  FIG. 26 . 
     A. Reformer Reactor 
     One reformer  12  preferred for the present system  10  ( FIG. 1 ) is disclosed in  FIGS. 3–11 . In overview, in accordance with aspects of the invention, an autothermal fuel reformer is uniquely spatially and thermally integrated. Also, the autothermal reformer is housed and integrated spatially and thermally with water-gas shift reactors. Also spatially and thermally integrated into the reformer  12  are unique heat exchangers  39  for preheating air and fuel, generation of steam, and active cooling of various reaction zones. Advantageously, steam generated in shift catalyst beds of reformer  12  provide a rapidly-deliverable supply of steam for combustion upon increased demand on the system  10 . 
     The reformer shell shown in  FIGS. 4 and 5 , is generally comprised of a pressure containing cylinder  21 , thermal insulation rings  29 ,  29 ′, and an inner protective sleeve  30 . As disclosed in  FIG. 6 , these components are coaxially nested and closed at axially opposed ends,  22  and  23 , of cylinder  21  by end plates  26  and  28 , respectively. As such, the cylinder  21  provides pressure containment, the insulation rings  29 ,  29 ′ isolate the cylinder  24  from reaction temperatures, and the sleeve  30  prevents erosion or contamination of the insulating rings  29 ,  29 ′. 
     The outer cylinder  24  has a peripheral flange  25  along its lower peripheral edge, and is preferably manufactured from a high grade stainless steel, or an equally strong and flexible metal or alloy. It is desirable that the cylinder  24  be capable of withstanding internal pressures (e.g., one preferred method of operation maintains reformer pressures at about three atmospheres). The top plate  26  sits within a seat  27  defined in a circumferential top edge of the cylinder  24 . This, with suitable gasketing forms a seal at one end of the reformer  12 . 
       FIG. 5  discloses that the inner protective sleeve  30  preferably includes an integral flange  32 . As shown in  FIG. 6 , the flange  32  is sized to have a diameter sufficient to under lap flange  25  of the outer cylinder  24 . Bottom plate  28  attaches to the opposite axial end of the cylinder  24 . The flange  32  passes beneath the insulation sleeves  30  to the pressure cylinder  24  where it is sandwiched between the outer cylinder flange  25  and the bottom plate  28 . Several bolts are used to secure the three layers tightly together. Gasketing material may also be utilized to effect or assist sealing. This provides a secure seal against reformate infiltrating into the space between the sleeve  30  and the cylinder  24  and maintains the integrity of the thermal insulation  29 . 
     The protective sleeve  30 , as employed with reformer  12 , has two sections of different diameters. As shown in  FIGS. 5 and 6 , a top portion of the protective sleeve  30  has a larger diameter than the bottom portion. The purpose of this smaller diameter portion is to provide a greater space between the inner protective sleeve  30  and the pressure containing cylinder  21  so that additional insulation  29  can be accommodated adjacent the HTS bed  37  of the reformer  12 . 
     The bottom flange  32 , is preferably configured to extend radially outwardly ( FIG. 5 ), but may be configured to extend radially inwardly (not shown). A suitable seal may also be formed by a channel (not shown) defined in the plate  26 . The flange  32  of sleeve  30  preferably forms a complete ring about the protective shell ( FIG. 5 ), but may be discontinuous for some applications (not shown). The purpose is to provide a structurally sound connection and a seal against fluid flow. 
     The thermal insulation rings  29 ,  29 ′ facilitate retention of heat within the reformer  12  during operation. The rings  29 ,  29 ′ may be comprised of any suitable insulative material known to those skilled in the art, and may be provided in a pre-formed shape as disclosed in  FIG. 5 , such as a foam, rolled sheet. However, pellets or granules, fiber blanket, or other desired form may be suitable. 
     All of the necessary inlets and outlets—each of which will be discussed below—are provided for within the top plate  26  and bottom plate  28 , as shown in  FIGS. 3–6 . 
     Located within the inner protective sleeve  30  of reformer reactor  12  (as disclosed in  FIGS. 2 and 6 ), are structures to provided four distinct reaction zones or chambers: a partial oxidation (“POx”) zone or chamber  34 , a steam reforming zone  35 , a low temperature shift (LTS) bed or zone  36  (filled with catalyst), and a high temperature shift (HTS) bed or zone  37  (filled with catalyst). A helical preheat tube  38  for steam/fuel, a helical water/steam tube  39 , and a helical oxygen/air tube  40  are disposed within the LTS and HTS beds,  36  and  37 , respectively. A fuel inlet  41  on plate  28  is provided to communicate with fuel conduit  17 , for transferring heated fuel from the auxiliary reactor  14  to the helical fuel tube  38 . An inlet  42  disposed in the bottom plate  28  of the reformer reactor  12  delivers a supply of oxygen-containing gas to the helical oxygen/air tube  40  from an oxygen gas source  43 . A water/steam line  44  delivers a supply of two-phase water to water inlet  45 , which in turn transfers the fluid to the water/steam helical tube  39 . Finally, disposed in the top plate  26  of the reformer reactor  12  is a reformate outlet which discharges the reformate through a reformate conduit  20 , preferably into a preferential oxidation reactor  13 , as illustrated by  FIG. 25 . 
     The POx chamber  34  and steam reforming zone  35  together define an autothermal reforming vessel  46 . The autothermal reforming vessel  46  is shown in an exploded view in  FIG. 7 . The outermost bounds of the autothermal reforming vessel  46  are defined by a second closed cylindrical chamber  47  having a sidewall  51  closed at its axial top end by a top plate  52  welded thereon. The sidewall  51  of the second cylindrical chamber  47  is preferably skirted, as shown in  FIG. 7 . A second insulation layer  48  surrounds the chamber  47  and may be made of any conventional insulative material known to those skilled in the art. 
     A third cylindrical wall  49  is provided around the second insulation layer  48 . The third cylindrical wall  49  is closed at its upper axial end by a top plate  50 . Several bolt cylinders  53  are attached to the top plate  50  to permit attachment to the top plate  26  of the cylinder  24 . 
     The POx chamber  34  of the autothermal reforming vessel  46  may be charged with a catalyst and operated to perform catalytic POx reactions. It is preferably operated without a catalyst to conduct gas-phase flame-type partial oxidation reactions. Referring back to  FIG. 6 , it can be seen that the POx chamber  34  is also generally defined by a cylindrical tube  54  which acts to separate the two reforming zones while providing radiant heat transfer from the POx chamber  34  to the steam reforming zone  35  through the metal walls of cylinder tube  54 . The cylindrical tube  54  has a central axis preferably coincident with the longitudinal axis (x) of the reformer reactor  12 . 
     Referring to  FIG. 8 , the POx chamber  34  is seen in exploded view as three annular sections: a base section  55 , an inlet section  56 , and the cylindrical tube  54 . The tube  54  has a first end  57  where preheated fuel mixture enters via an inlet  58  disposed within the inlet section  56 , and a closed ventilated end  59  having a plurality of apertures  60  to allow the partially reformed gas to flow radially into a the first end of the steam reforming zone  35 . 
     The steam reforming zone  35  is also cylindrical and disposed annularly about the POx chamber  34  and extending substantially the entire length of the POx chamber  34 . The steam reforming zone  35  in the present embodiment is packed with a nickel containing catalyst, but may include cobalt, platinum, palladium, rhodium, ruthenium, iridium, and a support such as magnesia, magnesium aluminate, alumina, silica, zirconia, singly or in combination. Alternatively, the steam reforming catalyst can be a single metal, such as nickel, or a noble metal supported on a refractory carrier like magnesia, magnesium aluminate, alumina, silica, or zirconia, singly or in combination, promoted by an alkali metal like potassium. At a second end of the steam reforming zone  35 , where the reformate stream is discharged to a transition compartment  61 , a screen  62  is provided to support the catalyst bed. Within the transition compartment  61  a steam ring  63  is disposed. The steam ring  63 , an alternate embodiment of which is shown in  FIG. 9 , is annularly disposed about the base section  55  of the POx chamber  34 . A plurality of interspersed orifices  64  are disposed about the steam ring  63  for discharging steam into the reformate stream. The steam ring  63  is preferably triangular in cross section. Advantageously, this configuration permits the ring  63  to share a side with the base section  55 . The exposed side  65  of the ring  63  also advantageously deflects the reformate flow outward from the longitudinal axis (x) of the reformer  12 . The shared side of the triangular steam ring  63  facilitates secure attachment to the base section  55  of the POx chamber  34 . However, a rectangular or square cross section may provide similar results, and a circular or oval cross section might also be suitable, albeit more difficult to attach without the benefit of a shared side. The steam ring  63  is preferably coupled to a steam delivery tube which in turn is attached to a steam source such as a steam generator or steam separator (not shown). 
     The inlet assembly  56  of the POx chamber  34  is preferably replaceable and is seated on the base section  55  supporting the cylindrical tube  54  of the POx chamber  34  within the reforming chamber  46 . Referring to  FIG. 10 , the inlet section  56  is generally a disk-like structure having a substantially centered opening  67  defined by a cylindrical inner wall  68  which aligns with the inner wall of the POx chamber  34  when assembled. The outer circumference of the inlet section  56  in the preferred embodiment is squared on one side and rounded on the opposite side. A bore  69  through the inlet section  56  can be seen in  FIG. 10 . The bore  69  extends from the squared side of the inlet section  56  proximate a corner thereof and then inward to intersect the cylindrical inner wall  68  tangentially. Referring to  FIG. 11 , inserted within the bore  69  is an inlet tube  70 . The inlet tube is oriented perpendicular to the surface of the squared side. One end of the inlet tube  70  may be affixed within the bore  69  and an opposite end is coupled to a mixing manifold  71 . This provides a secure attachment of the inlet tube  70  as opposed to prior art delivery tubes which may attempt to directly attach to the cylindrical wall of the POx chamber. The exact shaping of the end of the delivery tube is rendered unnecessary since the bore  69  of the present invention is unitary to the replaceable inlet section. A replaceable, less-expensive, easier-to-construct tangential delivery port to the POx chamber  34  is thus established by this configuration. 
     As illustrated in  FIG. 6 , disposed annularly about the reforming chamber  46  is the shift reaction zone  72 , including two shift reaction beds, the HTS bed  37  and the LTS bed  36 . Optionally, a desulfurizing bed catalyst may be added as well. The HTS bed  37 , as shown in  FIG. 6 , spans approximately one-half the length of the shift reaction zone  72 . An input side  73  of the HTS bed  37  is disposed adjacent the transition compartment  61  for receiving the reformate stream. An outlet side  74  of the HTS bed  37  is abutted to an inlet end  36   a  of the LTS bed  36  for discharging shift-reacted constituents from the HTS bed  37 . The HTS bed  37  is preferably packed with a conventional high-temperature shift catalyst, including transition metal oxides, such as ferric oxide (Fe2O3) and chromic oxide (Cr203). Other types of high temperature shift catalysts include iron oxide and chromium oxide promoted with copper, iron silicide, supported platinum, supported palladium, and other supported platinum group metals, singly and in combination. These catalysts may be provided in several of the forms mentioned previously. 
     According to one aspect of the invention, the HTS catalyst bed is actively cooled. This active cooling is provided to prevent temperatures from rising in the zone to the point of damaging the catalyst. Cooling is advantageously accomplished by heat exchange with reactants flowing through tubes placed in the HTS zone. To effect good heat transfer, the catalyst is preferably in the form of granules, beads, etc., so as to pack closely to the heat transfer tubes. However, one or more monolithic catalyst could also be employed in the HTS zone if appropriately configured to coexist with a heat exchanger. 
     The heat transfer tubes are configured through the annular HTS zone as shown in  FIG. 6 . The helical fuel tube  38  forms a part of fuel line  17 . The plurality of coils of the cooling/fuel preheat tube  38  are arranged co-axially, centered substantially about the longitudinal axis (x) of the reformer reactor  12 . Heated fuel (or a fuel and steam mixture) is carried through the HTS bed  37  within the inner helical coils (A) of fuel tube  38  and then reaching one end reverses back through the HTS bed  37  within the outer helical coils (B) until it arrives at a mixing chamber  76  of the mixing manifold  71  ( FIG. 11 ). 
     A secondary preheated fuel line  77  is preferably connected directly to the mixing manifold  71  for start-up conditions. This direct preheated fuel feed can be disrupted as soon as the primary fuel source is properly heated and desulfurized, if necessary. 
     Also coiled within the HTS bed  37  is the helical oxygen/air tube  40 . The oxygen/air tube  40  is comprised of a plurality of coils beginning with a first coil attached to oxygen/air inlet  42 . The coils are arranged such that a first outer set (C) run upward through the HTS bed  37  before transitioning into an inner set of coils (D) which run downward through the HTS bed  37 . Variations of this, as well as other coil arrangements, too numerous to discuss in this disclosure, are certainly possible without departing from the intended scope of the present invention. The oxygen/air tube  40  and the helical fuel tube  38  converge just prior to the mixing chamber  76 , as shown in  FIG. 11 , of the mixing manifold  71 . The two converged tubes are preferably coaxial as shown. This coaxial configuration allows the fluid with the higher flow velocity to assist the fluid flow of the lower flow velocity. The mixing chamber  76  then directs the fluids of the converged lines as a homogenous mixture into the inlet tube  70  toward the POx chamber  34 . 
     The LTS bed  36  begins at its inlet end  36   a  proximate the outlet side of the HTS bed  37 . The LTS bed  36  comprises the remainder of the shift reaction zone  72 . A suitable low-temperature shift catalyst, such as Cu/ZnO 2 , is packed, preferably as granules, beads, or the like, within the LTS bed  36 . A helical two-phase water tube  39  is disposed within the LTS bed  36  in a heat transfer relationship (see  System and Sub - System Control and Operation  below) and comprises a plurality of coiled sections. The plurality of coils of the helical water tube  39  are preferably co-axial with one another about the longitudinal axis (x) of the reformer reactor  12 .  FIG. 6  illustrates a preferred dispersed arrangement of the helical coils of water tube  39  within the LTS bed  36  having four columns of coils. Water enters the water tube  39  at inlet  45  which itself is connected to a water source. The flow travels through the bed within coils (E), then a “U” turn directs the flow into coils (F) moving through the LTS bed  36 . The flow then connects to coils (G) for a return through the bed  36  before finally another “U” turn directs the flow into coils (H) to travel back through the bed  36  a final time. The flow is discharged from the reformer reactor  12  through water/steam outlet  79 . 
     Steam is generated by transfer of heat to the water tube  39 . Preferably the tubes  39  are maintained at a sufficient pressure to accommodate a two-phase water/steam mixture. The two-phase water/steam is eventually discharged to a steam separator where it may be separated into liquid and gaseous (steam) portions and made available for use by other components of the system  10 . 
     A screen  80  is positioned at the discharge end of the LTS bed  36 . The screen  80  provides a barrier for the catalyst while still permitting reformate to flow into the open collection chamber  81  of the reformer reactor  12 . A single reformate outlet  82  is positioned at the approximate center of the reactor top surface  22  providing fluid communication with a transfer conduit  20 . The transfer conduit  20  directs the reformate flow into the PrOx reactor  13 . 
     B. PrOx Reactor 
     Referring to the drawings of  FIGS. 12–19 , a reactor for preferentially oxidizing carbon monoxide to carbon dioxide in a hydrogen-rich reformate stream, designated generally as reactor  13 , is shown. The reactor  13  is designed to direct a radial flow of hydrogen-rich reformate through a catalyst bed. The reactor  13 , as shown in  FIG. 12 , includes an outer body  83  having protective covering, preferably formed of stainless steel. At one end of the body  83  is a reformate inlet  84 , and at the other end is a reformate outlet  85 . Additionally, a steam/water inlet  86  and a steam/water outlet  87  are provided for heat exchange purposes (see  System and Sub - System Control and Operation  below). Optionally, air inlets (not shown) may be provided to permit reaction air to be diffused within critical areas of the reactor  13 . The steam coil allows for substantial isothermal PrOx quality. 
     Within the reactor  13  of the present embodiment, shown in  FIG. 13 , a flow diffuser  88  is immediately in-line with the reformate inlet  84 . The flow diffuser  88  is comprised of a collection chamber  89  having a discharge end  90  proximate a central manifold  91 . The discharge end  90  of the flow diffuser  88  has a plurality of apertures for the discharge of reformate into the central manifold  91 . Numerous alternate embodiments of the flow diffuser are possible without departing from the intended scope of the present invention. 
     The central manifold  91 , which may be referred to as a first zone, of the reactor  13  is defined by a first cylindrical wall  92 , preferably of a screen design having multiple openings disposed about the circumference and length of the wall  92 , closed off at one end  93  opposite the flow diffuser  88 . Annularly arranged about the central manifold  91  is a second zone packed with a suitable catalyst in the proper form. The second zone  94 , as shown in the top cross-sectional view of  FIG. 14 , is also preferably cylindrical, but may be of any shape complementary to the shape of the central manifold  91 . The second zone  94 , in the present embodiment, is packed with a suitable catalyst—either loosely or tightly—to form a catalyst bed  95 . By “suitable” it is meant a catalyst which selectively oxidizes carbon monoxide to carbon dioxide over diatomic hydrogen, though some oxidation of the hydrogen is inevitably acceptable. The catalyst may be prepared by any of the methods known to those skilled in the relevant art. While several catalyst exist which may be used with the present reactor  13 , a couple of preferred suitable catalyst include Pt/γ—Al 2 O 3  and Au/α—Fe 2 O 3 . 
     A second cylindrical wall  96 , also preferably of a screen design having multiple openings disposed about the circumference and length of the wall  96 , defines an outer edge of the catalyst bed  95 . The two cylindrical walls,  92  and  96 , may also be spherical or hemispherical in shape as alternate embodiments. A helical steam/water or boiler tube  97  is arranged within the catalyst bed  95  to substantially traverse the bed  95  and provide a heat transfer relationship with the catalyst material. In accordance with this relationship, the packed catalyst preferably maintains contact with the boiler tube  97 . Beginning at a steam/water inlet  86  the helical tube  97  progresses in a first direction (arrow A) through the catalyst bed  95  of the second zone  94  and, upon reaching the closed end  93 , retreats in a second opposite direction (arrow B) through the catalyst bed  95  to the steam outlet  87 . 
     An annular discharge channel  99  is defined between the second cylindrical wall  96  and an inside surface of the body  83  of the reactor  13 . The discharge channel  99  opens into a discharge area  100  at an end of the reactor  13  proximate the reformate outlet  85 . 
     In another embodiment of the present invention, the preferential oxidation of carbon monoxide to carbon dioxide is accomplished in at least a two stage process. That is, after discharge from the PrOx reactor  13 , the hydrogen-rich reformate stream may be further subjected to a second PrOx reactor  101 ′, as illustrated in  FIG. 15 . The second reactor  101  has proven to be an advantageous component in “turn-down.” “Turn-down” refers to the condition whereby the system operates at less than the maximum rated power. For instance, a system rated at 50 kW operating at only 25 kW is in a turn-down condition. While the second reactor  101 ′ may be designed similar to first reactor  13 , in the preferred embodiment, reactor  101 ′ is adiabatic. This is possible because the concentration of carbon monoxide is sufficiently low that oxidation will not overheat the catalyst bed to promote undesirable reactions (2) and (3) above. 
     Referring to  FIGS. 16 and 17 , one embodiment of the second PrOx  101 ′ is shown in a side view. The second PrOx  101 ′ is preferably a cylindrical vessel having an inlet  108 ′, an outer wall  106 ′, and an outlet  109 ′. Along the vessel wall is preferably positioned three thermocouples, or other known sensor devices. 
     A cross-section of the second reactor  101 ′, shown in  FIG. 17 , includes a monolithic catalyst  103  advantageously positioned within a single reaction zone  104 ′. A distinguishing aspect of the second PrOx reactor  101 ′ over the first PrOx reactor  13  is the absence of cooling coils in the reaction zone  104 ′. The incoming reformate stream, with air mixture as discussed above, encounters the catalyst and begins the oxidation as shown in reaction (1) above. The resulting reformate at discharge has a concentration of carbon monoxide preferably less than 10 ppm. The second reactor  101 ′ typically operates within the temperature range of from about 250° F. to about 500° F. 
     In another alternative preferred embodiment of the PrOx reactor stage of the system  10 , a chiller condenser  105  may be integrated in-line between the first reactor  13  and the second reactor  101 ′, as shown in  FIG. 19 . The chiller condenser  105  is preferably a fan used to significantly lower the temperature of the reformate stream after it exits the first reactor  13 . The cooling of the reformate at this point avoids undesirable side reactions in the reformate, such as the reverse water-gas shift reaction. However, such cooling may also have an adverse effect on the operation of the PrOx reactor due to an increase in the relative humidity of the stream. These competing interests should be considered in the overall integrated system design. 
     C. Auxiliary Reactor 
     The auxiliary reactor  14 , as illustrated in  FIG. 1 , is used in combination with the reformer reactor  12  and the fuel cell  15 . A primary function of the preferred auxiliary reactor  14  is to operate as a tail gas combustor burning the anode exhaust gases, comprised mostly of hydrogen, discharged from the fuel cell  15 . However, in conjunction with the combustion of anode gases, a unique structure of the auxiliary reactor  12  takes advantage of the excess heat created by the combustion to preheat and desulfurize unreformed fuel and steam for use in other parts of the hydrogen forming system  10 , such as the reformer reactor  12 . 
     Referring to  FIG. 20 , the reactor  14  is preferably a cylindrical vessel having a first annular wall  106  defining a first chamber  107 . The first chamber  107  has a diameter (D 1 ), an inlet end  108  and an opposed outlet end  109 . Disposed within the first chamber  107  is a suitable catalyst  110 , preferably a platinum (Pt) catalyst in monolith form. The function of the catalyst  110  within the first chamber  107  is discussed in further detail below. 
     A second annular wall  111  surrounds the first wall  106  and provides a second chamber  112  which is annularly disposed about the first chamber  107  and has a diameter (D 3 ). The auxiliary reactor  14  further includes a third annular wall  113  disposed between the second annular wall  111  and the first annular wall  106 , the third annular wall  113  extending substantially the length of the second annular chamber  112  and effectively dividing the second annular chamber  112  into first and second annular sub-chambers  114  and  115 , respectively. The first annular sub-chamber  114  being disposed between the first chamber  107  and the third annular wall  113 ; the second annular sub-chamber being disposed between the third annular wall  113  and the second annular wall  112 . 
     As seen in  FIG. 20 , the third annular wall  113  is of a double-wall construction defining third annular chamber  116 . Located within the third annular chamber is fourth annular wall  117 , extending substantially the length of the third annular chamber and effectively dividing the third annular chamber into third and fourth annular sub-chambers,  118  and  119 , respectively, the third annular sub-chamber  118  being disposed between the first annular sub-chamber  114  and the fourth annular wall  117 ; the fourth annular sub-chamber  119  being disposed between the fourth annular wall  117  and the second annular sub-chamber  115 . The third and fourth annular sub-chambers,  118  and  119 , respectively, define a U-shaped conduit  120  for the flow of unreformed fuel, as further explained below. 
     The reactor  14  additionally includes a flame-type burner assembly  121  upstream of the catalyst  110  in the first chamber  107 . The burner assembly  121  is defined by a burner chamber  122 , which includes a burner inlet  123  and a burner outlet  124 , the burner outlet  124  being connectable to the inlet end  108  of the first chamber  107 . The burner chamber  122  is generally cylindrical and is concentric with the first annular wall  106  but has a larger diameter (D 2 ) than the diameter (D 1 ) of the first chamber  107 . The larger diameter (D 2 ) thus restricts the flow of partially burned, heated gases from the burner chamber  122  into the first chamber  107 . An ignitor  125 , preferably a spark plug, is provided within the burner chamber  122  for creating a spark which ignites a fuel to create a flame at start-up. 
     The burner assembly  121  is provided in the present embodiment for mixing and burning a heated gas stream within the burner chamber  122 . An auxiliary first fuel, for example natural gas, may be directed to the burner chamber  122  through the burner inlet  123  to form a heated gas stream. The heated gas stream is then further directed to the catalyst  110  in the first chamber  107  through the outlet  124 . To improve combustion characteristics during steady-state operation, air in air conduit  127  is preheated by passing between an outer annular shell  126  and the burner chamber  122 . The inlet end  128  of the air conduit  127  is connected to a source of oxygen-containing gas (not shown). The air conduit  127  directs a stream of oxygen-containing gas to the burner inlet  123  of the burner assembly  121  for combustion within the burner chamber  122 . The burner inlet  123  is designed to allow for tangential delivery of the oxygen-containing gas and the auxiliary first fuel into the burner chamber  122 . 
     The auxiliary reactor  14  further includes an inlet tube  130  that passes through the burner chamber  122  and extends directly into the first chamber  107 . Preferably, the inlet tube  130  is an elongate tube which extends through the burner chamber  122  for heat exchange with the gases therein and the fuel cell exhaust gases flowing within the inlet tube  130 . 
     Included within the second annular sub-chamber  115  is a helical tube  131  that extends the length of the second annular sub-chamber  115 . The helical tube  131  is configured to allow for the flow of water, as discussed in more detail below. The helical tube  131  is connected to the water/steam line of the reformer  12  via conduit  132  to provide the water/steam needed for the LTS bed  36  of the reformer  12  (see  FIG. 23 ). Where a more compact reactor design is required, a plurality of fins  133 , preferably comprised of copper, are spaced in predefined intervals throughout the length of the helical tube  131 . The fins  133  radially extend from the circumference of the helical tube  131  to enhance the exchange of heat between the heated exhaust gas stream and the water within the helical tube  131 . 
     A second preferred embodiment of the auxiliary reactor, as shown in  FIG. 21 , is used preferably for reformers designed to reform a liquid hydrocarbon fuel, such as gasoline or ethanol, as opposed to natural gas or propane. The reactor  200  is preferably a cylindrical vessel having a first annular wall  206  defining a first chamber  207 . The first chamber  207  has a diameter (D 4 ), an inlet end  208  and an opposed outlet end  209 . Disposed within the first chamber  207  is a catalyst  210 , preferably a platinum (Pt) catalyst in monolith form, for burning fuel cell exhaust to create a heated auxiliary reactor gas stream. The catalyst  210  within the first chamber  207  is discussed in further detail below. 
     A second annular outer wall  211  surrounds the first wall  206  and provides a second annular chamber  212  having a diameter (D 5 ). Located within the second annular chamber  212  is a first helical coil  231  extending approximately the length of the second annular chamber  212 . Additionally, a second helical coil  232  is located within the first annular chamber upstream of the platinum (PT) catalyst monolith  210 . Both the first and second helical coils  231  and  232  are adapted to allow for the flow of a two-phase water/steam mixture therethrough. 
     The reactor  200  additionally includes a flame-type burner assembly  221  upstream of the catalyst  210  in the first chamber  207 . The burner assembly  221  is defined by a burner chamber  222  at one end of the first chamber  207 . Fuel and air are supplied to the burner chamber  222  via burner inlet  223  and air conduit  227 , respectively. An ignitor  225 , preferably a spark plug, is provided within the burner chamber  222  for creating a spark to ignite the fuel and create a flame at start-up. 
     The burner assembly  221  is designed for mixing and burning a heated gas stream within the burner chamber  222 . An auxiliary first fuel, in this instance gasoline, may be directed to the burner chamber  222  through inlet  223  to form a heated gas stream and the heated gas stream is then further directed to the catalyst  210  in the first chamber  207 . The inlet end  228  of the air conduit  227  is connected to a source of oxygen-containing gas (see  FIG. 2  for example). The air conduit  227  directs a stream of oxygen-containing gas to the burner inlet  223  of the burner assembly  221  for combustion within the burner chamber  222 . The burner inlet  223  is designed to allow for tangential delivery of the oxygen-containing gas and the auxiliary first fuel into the burner chamber  222 . 
     The auxiliary reactor  200  further includes an inlet tube  230  that passes through the burner chamber  222  and extends to the exit of the burner  222 . Preferably, the inlet tube  230  is an elongate tube which extends through the burner chamber  222  for heat exchange between the gases therein and the fuel cell exhaust gases flowing within the inlet tube  230 . 
     A third preferred embodiment of the auxiliary reactor, as shown in  FIG. 22 , is used mainly for reformers designed to reform, for instance, natural gas. The reactor  300  is preferably a cylindrical vessel having a first annular wall  306  defining a first chamber  307 . The first chamber  307  has a diameter (D 6 ), an inlet end  308  and an opposed outlet end  309 . A reaction zone  310  is provided within the first chamber  307 . 
     A second annular outer wall  311  surrounds the first wall  306  and provides a second annular chamber  312  having a diameter (D 7 ). Located within the second annular chamber  312  is a helical coil  331  extending approximately the length of the second annular chamber  312 . The helical coil  331  is adapted to allow for the flow of a two-phase water/steam mixture therethrough. 
     The reactor  300  additionally includes a flame-type burner assembly  321  upstream of the reaction zone in the first chamber  307 . The burner assembly  321  is defined by a burner chamber  322  at one end of the first chamber  307 . Fuel and air are supplied to the burner chamber  322  via burner inlet  323  and air conduit  327 , respectively. An ignitor  325 , preferably a spark plug, is provided within the burner chamber  322  for creating a spark to ignite the fuel and create a flame under start-up conditions. 
     The burner assembly  321  is designed for mixing and burning a heated gas stream within the burner chamber  322 . An auxiliary first fuel, natural gas, is directed to the burner chamber  322  through inlet  323  to form a heated gas stream and the heated gas stream is then further directed to the reaction chamber  310  in first chamber  307 . The inlet end  328  of the air conduit  327  is connected to a source of oxygen-containing gas (see  FIG. 2 , for example). The air conduit  327  directs a stream of oxygen-containing gas to the burner inlet  323  of the burner assembly  321  for combustion within the burner chamber  322 . The burner inlet  323  is designed to allow for tangential delivery of the oxygen-containing gas and the auxiliary first fuel into the burner chamber  322 . 
     The auxiliary reactor  300  may further include an inlet tube (not shown) that extends directly into the first chamber  307 . Preferably, the inlet tube is an elongate tube which extends through the burner chamber  322  for heat exchange between the gases therein and the fuel cell exhaust gases flowing within the inlet tube. 
     II. System and Sub-System Control and Operation 
     While some of the system controls and operations have been alluded to in the preceding disclosure, this section of the disclosure is specifically directed to explaining the preferred operation and means for such control. The control hardware for each subsystem, i.e., the reformer  12 , the PrOx reactor  13 , and the auxiliary reactor  14 , is discussed, including start-up, steady state, and transient conditions. Modifications to the specific controls may be necessary based upon the characteristics of the actual hydrogen forming system and its operation. 
     A. Water/Steam Loop 
     With reference to  FIG. 23 , the important water/steam cooling loop can be more readily understood. A reservoir (R) supplies water to the system  10  through a pump (P). The water is heated at heat exchanger (H) to produce two-phase water/steam mixture at point “W”. The pressure at point “W” of the loop is preferably maintained at about 150 psi with an initial temperature of about 100° C. 
     The loop runs through a heat exchange section of the auxiliary burner assembly (FPA) to provide cooled exhaust gases. A second pass is made through the anode gas burn section of the auxiliary reactor  14  in order to bring the temperature of the water/steam mixture to about 185° C. at point “X” in steady state operation. The loop is then routed to the fuel reformer  12 . 
     The water/steam mixture enters a low temperature shift catalyst bed  36  of the fuel reformer  12  first. Heat exchange with the catalyst is carried out as previously discussed to control the temperature of the bed. Optionally, the loop may pass through the desulfurizing bed (DS) between passes through the LTS bed  36 , as shown in  FIG. 23 . 
     Leaving the LTS bed  36  the water/steam mixture at point “Y” is usually about 185° C. and about 100–150 psi. The loop enters a first PrOx reactor  13  as an active cooling means for the catalyst bed  102 . Exiting the PrOx reactor  13  the water/steam mixture is preferably maintained at 185° C. at point “Z.” The water/steam mixture enters a steam separator (SS) before returning water to the water reservoir (R) and steam to reformer  12 . 
     Alternatively, the FPA and PrOx steam loop positions may be switched, depending on which bed is more important to heat quickly during start-up. Generally, the FPA is first, as shown in  FIG. 23 . 
     B. Control Points 
       FIG. 24  illustrates various control points for an exemplary embodiment of the present invention (double prime notation is used for each of the discussed points). Additionally, the system pressure is also used to co-regulate several of the disclosed processes, such as the water/steam loop. 
     A fuel valve  1 ″ is used for the primary fuel control. The fuel valve  1 ″ allows control of the fuel rate as one means of providing hydrogen on demand. A water/steam valve  2 ″ and an air valve  3 ″ are used at the reformer  12  to control the ratios of steam, air, and fuel. This helps to maintain the reformer chamber temperature for proper reformation. It is possible to provide two inlet streams (e.g., air/fuel to the POx chamber, or water/fuel to the steam reformer chamber) if necessary. 
     A steam control  4 ″ is used to provide enough steam to complete the water gas shift, as previously discussed. Another air valve  5 ″ is positioned prior to the inlet of the first PrOx reactor  13 . This valve  5 ″ provides control over the theoretical/calculated air delivered to oxidize carbon monoxide in the reformate stream to carbon dioxide. A third air valve  6 ″ is positioned prior to the inlet of the second PrOx reactor  101 ′. As will be further explained, regulation of air at this point provides additional air to the PrOx chamber to complete the oxidation of carbon monoxide during such conditions as start-up, shut-down, and transients. 
     A routing valve  7 ″ is used to divert reformate having an excess of carbon monoxide to the auxiliary reactor  14  where it can be burned off. This is typical at start-up. As soon as the carbon monoxide concentration reaches acceptable levels the reformate can be routed by the valve  7 ″ to the fuel cell  15 . Another start-up control point is control  8 ″. Control  8 ″ is used to provide a secondary fuel to the system on initial warm-up, usually with excess air as well. The secondary fuel is run through the auxiliary reactor  14  before routing to the reformer  12 . 
     The final control point is valve  9 ″ which is used to route a portion of the cathode exhaust to the auxiliary reactor. The remaining portion of the cathode exhaust is fed to an exhaust outlet or conduit. 
     Each of the disclosed control points is operated by a central processing system (not shown). The system operates via a program capable of adjusting the operating parameters of the fuel cell system through periodic or continuous feedback data from sensors mechanisms or the like. The data is processed and the system operates the appropriate control point in response to the rapidly changing conditions experienced during and transitioning through start-up, steady-state, transients, and shut-down. 
     C. Fuel Preheat 
     Referring to  FIG. 26 , at start-up, or under conditions similar to start-up conditions, all components of the present system  10  are generally “cold,” including the water and fuel sources. The term “cold” is intended not to refer to a specific temperature or range of temperatures at which the components may operate, but rather to indicate a threshold temperature at which the components operate at an acceptable level with respect to efficiency. Naturally, the temperature for each component will vary widely, and the temperature for any one component may vary widely from application to application. 
     With respect to liquid fuels it is necessary to vaporize the fuel so that it will burn in the POx chamber  34 . This task is preferably performed by the auxiliary reactor  14 , or a separate heat source, if available. Additionally, because sulfur can be a poison to reforming systems, certain fuels require desulfurization before entering the POx chamber  34 , as well. The auxiliary reactor can be provided with a desulfurizing bed (as described above) to perform this function. To the extent these functions can be accomplished by other integrated system components after start-up (i.e., when they have achieved a sufficient temperature), the auxiliary reactor  14  may be discontinue operation in this manner at that time. 
     D. Reformer 
     As illustrated by  FIG. 26  and detailed in  FIG. 6 , preheated fuel (or a fuel/steam mixture) enters the reformer reactor  12  at start-up via secondary fuel inlet  77  connected directly to the mixing chamber  76  of the mixing manifold  71 . Within the mixing chamber  76  the heated fuel is mixed with a supply of oxygen delivered to the mixing chamber  76  via the helical oxygen/air tube  40 . The homogeneous mixture is directed tangentially, via the inlet tube  70  and the bore  69  of the inlet section  56 , into the POx chamber  34 . The tangential delivery directs the hydrocarbon fuel flow immediately along the inside of the cylindrical wall  54  to effect a rising helical flow within the POx chamber  34 . 
     At start-up a conventional ignition device  135 , such as a spark plug, located within the hollow of base section  55 , is provided to ignite the fuel/steam/oxygen mixture within the POx chamber  34 . The POx chamber  34  may or may not contain a reforming catalyst. If used, the POx catalyst for the present invention may be any known catalyst used by those skilled in the art, but is preferably either a zirconium oxide (ZrO 2 ) catalyst (See co-pending U.S. patent application Ser. No. 09/562,789, filed May 2, 2000, now U.S. Pat. No. 6,524,550, and hereby incorporated by reference) supported on a noble metal (e.g., platinum (Pt), palladium (Pd), nickel (Ni)) in monolith form. The hydrocarbon fuel is ignited, and in the case of methane, hydrogen is liberated in the POx chamber  34  according to the following overall reactions:
 
CH 4 +½O 2 →CO+2H 2   (2)
 
and
 
CO+H 2 O CO 2 +H 2   (4)
 
The exothermic reaction (2) is self-sustaining and maintains an operating temperature range of from about 700° to about 1200° C. for one specific embodiment of a catalyzed POx chamber, or from about 1200° to about 1700° C. for one specific embodiment of a non-catalyzed POx. The generated heat preferably radiates by design outward to the steam reforming zone  35 .
 
     The reforming stream optimally travels in a helical path through the POx chamber  34  toward the ventilated end  59  of the cylindrical wall  54 . At the plurality of apertures  60  the partially reformed fuel/oxygen/steam mixture travels outward into the steam reforming zone  35 . The steam reforming zone  35  is preferably packed with a nickel catalyst which is supported at the discharge end of the zone by a metal screen  62 . Within the steam reforming catalyst the remaining fuel undergoes the following steam reforming reactions to liberate hydrogen:
 
CH 4 +H 2 O→CO+3H 2   (1)
 
and
 
CO+H 2 O CO 2 +H 2   (4)
 
     The steam reforming reaction (1) is endothermic, requiring a great deal of heat energy to form hydrogen. The reaction draws heat through the cylindrical wall  59  of the POx chamber  34  to maintain an operation temperature of about 700° to about 1000° C. The reformate stream passes through the support screen  62  into the transition compartment  61 . 
     Within the transition compartment  61  the reformate travels optimally radially outward and is provided a supply of steam from steam ring  63 . The steam supply here serves two purposes. First, it helps to cool the reformate for the water-gas shift reaction. Higher temperatures favor the production of water and carbon monoxide (the “reverse shift reaction”). Second, the water is a necessary component to react with the carbon monoxide to produce hydrogen and carbon dioxide. Too little water added will result in poor performance of the HTS and LTS shift beds. 
     The reformate/steam mixture moves axially from the transition compartment  61  into the first bed of the shift reaction zone  72 , the HTS bed  37 . The purpose of the HTS bed  37  is to reduce the concentration of carbon monoxide in the reformate stream. The temperature of the HTS bed  37  increases as the carbon monoxide concentration is reduced. The activity of the catalyst increases with the temperature. However, the rising temperature is, of course, detrimental to the purpose because, as stated previously, the higher temperature favors the reverse shift reaction—i.e., production of water and carbon monoxide. To cool the stream, some of the heat produced in the HTS bed  37  is transferred to the fuel and oxygen/air supply through the helical tubes  38  and  40 , respectively. Still, the operating temperature range of the HTS bed  37  is from about 550° C. at the inlet end to about 350° C. at the discharge end. The concentration of carbon monoxide within the reformate stream is reduced in the HTS bed  37  to about 2.0%. 
     Optionally, a desulfurizing bed (not shown) may be disposed adjacent the HTS bed  37 . The desulfurizing bed would be comprised of a suitable catalyst such as zinc oxide (ZnO 2 ) in granule or bead form. As the reformate passes through and contacts the zinc catalyst poisoning sulfur and sulfur compounds would be removed from the stream. 
     A second shift bed is also provided in the present invention. The LTS bed  36 , similar to the HTS bed  37 , provides further reduction of the carbon monoxide concentration in the reformate stream. However, the LTS bed  36  is continuously cooled to provide an isothermal bed. In the present embodiment, the LTS bed  36  includes four rows of helical windings (E, F, G, and H) of the water tube  39  in a heat exchange relationship with the bed catalyst. The windings may be reversed if desired—i.e., the water inlet feeding winding (H) and finally ending with the discharge of steam at the outlet of winding (E). The discharged steam is preferably directed to a steam separator as discussed previously. The cooled shift bed permits greater reduction of the carbon monoxide concentration in the reformate stream. 
     The reformate exits the LTS bed  36  through a screen  80  before entering into the open discharging chamber  81  of the reformer reactor  12 . The reformate collecting in the discharging chamber  81  is eventually directed to an outlet  82  positioned at the approximate center of the reactor top surface  22 . From the outlet a transfer conduit  20  directs the reformate flow into the PrOx reactor  13 . 
     With respect to process controls, four major flows into the reformer  12  need to be properly controlled: air, fuel, POx steam and the HTS bed steam through steam ring  63 . The air flow may be controlled using an air flow sensor that feeds back to a valve  136 , as illustrated in  FIG. 25 . Fuel may be controlled using a fuel injector with or without a conventional fuel sensor (not shown). If the fuel flow is choked across the injector and the supply pressure is constant, the flow should be constant for a given duty cycle, regardless of variations in downstream pressure. Alternatively, differential pressure across the injector may be controlled to maintain a constant flow for a given duty cycle. Periodic calibration may be necessary to eliminate the need for a fuel sensor. The POx steam flow may be controlled using a motor actuated or solenoid valve  140 , as illustrated in  FIG. 28 , and an orifice plate  139  can be used to measure the steam flow. Control of the HTS bed steam may also be accomplished with a pressure actuated or control valve  155  to control the flow rate and the pressure in the system. The pressure setpoint on the regulator  155  is typically changed manually, or may be controlled remotely. For transient steam control (see System and Sub- System Control and Operation  below) to the HTS bed  37  it may be desirable to vary the pressure setpoint to protect the overall steam-to-carbon ratio from a drastic drop. Creating such a variable pressure setpoint using a control valve that has feedback from a pressure transducer is one alternative. 
     In addition to the flow controls discussed, several pressure transducers and numerous thermocouples may be necessary to monitor and control the pressure and temperature of the reformer  12 . 
     E. PrOx Reactor 
     Beginning with the PrOx inlet  13 , it is typically connected downstream of the reformer reactor  12  (as shown in  FIG. 1 ) where a hydrocarbon material is reformed with steam to produce a hydrogen-rich reformate having a small, but undesirable, concentration of carbon monoxide (typically&lt;1%). In addition to hydrogen and carbon monoxide, the reformate includes carbon dioxide, water, and other carbon containing compounds (typically only a few percent or less). 
     As the reformate enters the reactor  13  at the inlet  84 , referring to  FIG. 13 , it is directed into the central manifold first zone  91  through a diffuser  88 . Optionally, the diffuser  88  may be eliminated from the reactor. 
     In operation, the reformate stream is initially delivered to the inlet at a first pressure (P 1 ) and temperature (T 1 ), but immediately experiences a pressure drop (ΔP) to a second pressure (P 2 ) upon entering the first zone  91  through the diffuser  88 . The temperature of the reformate at this point is initially unaffected. However, the pressure is sufficient to force the reformate stream through the first wall  92  of the first zone  91 , which has a temperature typically within the range of from about 200° F. to about 500° F. As the reformate travels radially from the first zone  91  in a plurality of flow paths it enters the catalyst bed  95  of the second zone  94  within the reactor  13  adjacent the first zone  91 . 
     As the reformate stream encounters the catalyst bed  95 , continuing in the same general diverging directions through the second zone  94 , the carbon monoxide of the stream is oxidized to carbon dioxide by the following reaction:
 
CO+½O 2 →CO 2   (5)
 
The oxygen necessary for sufficient oxidation to occur may be provided as a mixture with the incoming reformate or introduced to the reactor  13  via an incoming air line  141 , as shown in  FIG. 15 . Additionally, as it becomes necessary to replenish the oxygen for reaction with the carbon monoxide, secondary air inlets may be provided to direct the desired quantity of air into the reactor  13 . These inlets would help to ensure that the reformate throughout the catalyst bed  95  has a sufficient supply of oxygen.
 
     As the secondary air enters the second zone  94 , it naturally diffuses throughout the catalyst bed  95  where it reacts with carbon monoxide adsorbed by the selective catalyst according to the reaction above. 
     The oxidation of carbon monoxide is further promoted by maintaining the temperature of the catalyst bed within a desired range, preferably about 20° C. to about 170° C. Higher temperatures result in faster reaction rates, permitting the use of a smaller volume reactor, but also promoting the undesired side reactions (2) and (3) above. The present reactor  13  is preferably isothermal. 
     The PrOx reactor  13  of the preferred system comprises a means for actively cooling the catalyst within the second zone  94 . A preferred means is shown in  FIG. 13 . Water/steam tube  97 , double-helically configured throughout the catalyst bed  95 , provides a continuous heat exchange with the catalyst bed  95 . That is, a flow of water from a convenient source is pumped continuously into the tube  97  through the water inlet  86  of the PrOx reactor  13 . The cooling fluid flows through the water/steam tube  97  drawing heat from the catalyst bed  95 , which is in contact with the water/steam tube  97 , and discharging from the reactor  13  at the water outlet  87 . The water/steam tube  97  is preferably made from a very good conductive, but non-reactive metal, such as  304  SS, to further assist in the heat exchange. It should be understood that several other boiler tube arrangements would be suitable for actively cooling the catalyst bed including, but not limited to, single-helical, longitudinal, and any other configuration which results in the boiler tubes being interspersed throughout the second zone  94  or catalyst bed  95 . It should also be understood that the water/steam tube  97  may be extended into the first zone  91  to actively cool the reformate before it enters the second zone  94 . 
     The discharging heated water/steam from the water outlet  87  of the active cooling means may be used elsewhere in the system  10 . For instance, additional tubing may connect the water outlet  87  to a heat exchanger used in a shift reaction zone  72  (see  FIG. 6 ). In such a use, the heat from the heated water/steam may be dissipated within the shift reaction zone  72  to help raise and maintain the temperature of the reactor  12  to within a desired high temperature range. 
     In any event, after the reformate stream has passed through the second zone  94  it enters a discharge flow passing through a second metal (stainless steel) screen wall  96  which defines the outer extent of the second zone  94 . Referring again to  FIG. 13 , the reformate then enters an annular discharge channel  99  where it is directed toward the reformate outlet  85 . The concentration of carbon monoxide in the reformate stream at this time should be no more than about 500 ppm. Preferably it is lower, for the composition of the reformate, however, also includes hydrogen, carbon dioxide, water, and nitrogen. 
     The system configuration, in order to deal with flow variations of the reformate made in response to changing power requirements, may include a PrOx reactor  13  (including a second PrOx reactor  13 ′, as shown in  FIG. 12 ) having dynamic control of the oxygen used to oxidize the carbon monoxide concentration. As discussed previously, the oxygen to carbon monoxide ratio must be maintained within a stochiometrically balanced range based on reaction ( 1 ) above. Preferably between about 1:4 to about 1:1, but most preferably about 1:2, oxygen to carbon monoxide. 
     To maintain the proper mix ratio, the reactors may include means for determining the relative amount of carbon monoxide in the stream. The means can be provided by an infrared carbon monoxide sensor  142 . The carbon monoxide sensor  142 , as shown in  FIG. 19 , may be placed in-line after a chiller condenser  105 . This position is preferable because: (1) water in the reformate stream may interfere with the infrared sensor; (2) the temperature of the stream has been cooled at this point by the chiller condenser and is, therefore, more suitable for the placement of the sensor; and (3) the carbon monoxide concentration is not too low, which makes a good quality signal to noise ratio a better possibility. 
     The sensor  142 , if used, could be read periodically to determine the carbon monoxide concentration exiting the PrOx reactor  13 . A control scheme can be utilized to control a means for adding an amount of oxygen to the reformate stream to produce the desired ratio of oxygen to carbon monoxide as it enters the PrOx reactor  13 , or alternatively, as it enters the second PrOx reactor  13 ′. 
     Additionally, the sensor  142  allows for the utilization of means for automatically adjusting the amount of oxygen containing gas being added to the stream based upon carbon monoxide concentration fluctuations. 
     Alternatively, instead of (or in addition to) monitoring the concentration of carbon monoxide directly, means for determining the concentration may be indirect. For instance, means may be provided for monitoring at least a first parameter which may give an indication of the relative concentration of carbon monoxide. This includes calculating the desired amount of oxygen based upon normally expected amounts of carbon monoxide to be produced by the source and adjusting oxygen flow based on these calculated expectations. Possible methods for determining carbon monoxide concentrations include determining a change in pressure within the preferentially oxidizing reactor or reformer reactor, determining a change in temperature within the preferentially oxidizing reactor or reformer reactor, and measuring time from an event known to cause carbon monoxide fluctuation. 
     Another alternative embodiment of the present system handles the fluctuating demand in a different manner. Such an embodiment, as shown in  FIG. 18 , includes a PrOx reactor  13 ″ having a first catalyst bed  95   a  having a catalyst for oxidation of carbon monoxide in preference to diatomic hydrogen, and a second catalyst bed  95   b  having a catalyst for oxidation of carbon monoxide in preference to diatomic hydrogen. During operation, a first manifold  91 ″ within the reformate conduit  20 ″ connects both the first and second catalyst beds,  95   a  and  95   b , in parallel to the reformate source (i.e., the reactor  12 ) for optionally directing the flow through one or the other of the first or second beds,  95   a  or  95   b , both in the case of an increase in the reformate source flow so as to accommodate the added flow. 
     Preferably, the dynamic reformate flow is detected by means for monitoring flow of the reformate from the source, such as a suitably positioned flow meter. The manifold is then designed to be responsive to the means for monitoring so as to direct the flow of reformate through either one or both of the catalyst beds in response to a fluctuation of reformate flow. 
     A signal is emanated from the flow meter in connection with the source and indicating a change in operational parameters of the source which will cause a corresponding change in flow of the reformate from the source. The operational parameters of interest may include increased demand, decreased demand, acceleration, deceleration, start-up, shut down, change of fuels, thermal fluctuations of the source, fuel input, steam input, and the like. 
     With respect to either a single or double-stage PrOx, the reformate as it exits either PrOx reactor stage of the system, if suitable, may be directed to the PEM-fuel cell  15 , as illustrated in  FIG. 2 , for use in the generation of electricity, as is known in the art. Alternatively, where the reformate is not yet suitable for use in a fuel cell, the stream may be either further “cleaned” of compounds which may affect the operation of the fuel cell or, in the case of reformate formed at start up, it may be combusted in an auxiliary reactor until the quality of the product stream reaches acceptable levels. 
     Combustion is permitted, referring again to  FIG. 2 , by a discharge line  143  connecting the PrOx reactor  13 ′ (or  13 , in the case of a single PrOx reactor) to the PEM-fuel cell  15 , but also having a branched conduit  144  controlled by a valve  145  and connected to the auxiliary reactor  14 . At start up, the valve  145  directs the product stream from the PrOx reactor  13  into the conduit  144  for eventual discharge into the auxiliary reactor  14  where it can be completely burned off. Burning off oxidized reformate immediately after start up minimizes poisoning of the PEM-fuel cell  15 . This process is used because at start up the steam reforming chamber  35  and the shift beds,  36  and  37 , of the reformer  12  and the catalyst bed  95  of the PrOx reactor  13  have not achieved the necessary temperatures to reform, shift, or oxidize the hydrocarbon/reformate stream completely. The result is a reformate having a high concentration of carbon monoxide or other fuel cell poisons. 
     The preferred PrOx has two air flows, a water flow, and a fan that must be controlled for proper operation. The air flow control is preferably a closed-loop system which measures the air flow rate using a mass air flow sensor and controls the flow using a proportional solenoid valve ( FIG. 24 ). 
     The temperature of the PrOx reactor catalyst bed  95  may be controlled by a conventional pool boiler design, known by those skilled in the art. The water level in the pool boiler can be maintained by measuring the water column height with a differential pressure transducer and controlling water flow with a solenoid valve. The steam produced in the PrOx should preferably go to the HTS bed  37 , if possible. 
     The inlet temperature of a second PrOx reactor  101  (see  FIG. 15 ) can be controlled by varying the air flow over a cross flow heat exchanger  147  ( FIG. 19 ). The temperature can be measured with a thermocouple located in the reformate line just before the second PrOx reactor  101 , as discussed above. The air flow can be provided by at least one fan, and preferably two fans, with a conventional speed control PWM drive (not shown). 
     F. Auxiliary Reactor 
     In operation of the first preferred embodiment of  FIG. 20 , exhaust anode gases from the fuel cell  15  are directed into the inlet tube  130 , preheated within the burner chamber  122  of the burner assembly  121  and directed into the first chamber  107  upstream of the catalyst  110  where the gases mix with air. 
     As the fuel cell exhaust gases pass through the first chamber, the combination of the heated fuel stream and the platinum (Pt) catalyst  110  causes catalytic oxidation of the exhaust gases. The remaining exhaust gases are then directed through the outlet end  109  of the first chamber  107  and into the second annular chamber  112 , referring to  FIG. 20 . The design of second annular chamber  112  directs the stream of burned exhaust gases downwardly through the first annular sub-chamber  114 , in counter-flow fashion to the direction of the flow of the exhaust gases in the first chamber  107 . At the end of the first annular sub-chamber  114 , the stream is redirected upwardly through the second annular sub-chamber  115  in counter-flow fashion with the direction of the flow of gases within the first annular sub-chamber  114 . Located at the opposed end of the second annular sub-chamber  115  is an exhaust outlet  152 , which allows the remaining exhaust gases to be released into the atmosphere. 
     Included within the second annular sub-chamber  115  is a helical tube  131  that extends the length of the second annular sub-chamber  115 . The helical tube  131  is configured to allow for the flow of water. The fuel cell exhaust stream flowing upwardly through the second annular sub-chamber  115  exchanges heat with the water found within the helical tube to assist in the formation of a two-phase water/steam mixture. The helical tube  131  is connected to the water/steam line  39  ( FIG. 2 ) of the reformer  12  via the conduit  132  to provide the water/steam needed for the LTS bed  36  of the reformer  12  ( FIG. 6 ). Where a more compact reactor design is required, a plurality of fins  133 , preferably comprised of copper, are spaced in predefined intervals throughout the length of the helical coil  131 . The fins  133  radially extend from the circumference of the helical coil to enhance the exchange of heat between the heated exhaust gas stream and the water within the helical coil  131 . 
     Located at the end of the reactor  14  opposite the burner assembly  121  is unreformed fuel inlet  150 , which allows for the introduction of unreformed fuel into the reactor  14 . The unreformed fuel is directed through U-shaped conduit  120 , defined within the third annular wall  113 , in constant heat exchange relationship with the stream of fuel cell exhaust gases though the first and second annular sub-chambers,  114  and  115 , respectively. The flow of the unreformed fuel through the first half of the U-shaped conduit  120 , i.e., the third annular sub-chamber  118 , parallels the flow of the fuel cell exhaust gas through the first annular sub-chamber  114 , and the flow of the unreformed fuel through the second half of the U-shaped conduit  120 , i.e, the fourth annular sub-chamber  119 , parallels the flow of the fuel cell exhaust gases through the second annular sub-chamber  115 . The resultant exchange of heat from the exhaust gases to the unreformed fuel preheats the unreformed fuel for introduction into the reformer  12  via fuel line  17 . Preferably, a zinc-containing catalyst is placed within either of both halves of the U-shaped conduit  120 , i.e., the third annular sub-chamber  118  or the fourth annular sub-chamber  119 , for desulfurizing the unreformed hydrocarbon fuel flowing therethrough. 
     The auxiliary reactor  14  is used to combust exhaust from the PrOx not consumed in the fuel cell  15 . This allows the emissions to be maintained at near zero. The excess heat is used to generate steam. The overall goal of the control strategy, therefore, is to keep the catalyst  110  at a temperature high enough to burn the combustibles in the anode exhaust, maximize steam production, and keep emissions low. To accomplish this it is necessary to ensure that the auxiliary reactor  14  is operating lean and at a temperature range of about 1000° F. (approx. 550° C.) to about 1470° F. (approx. 800° C.). One method of doing this is to set a desired temperature and excess oxygen level for the auxiliary reactor  14 . The oxidant flow rate can be adjusted based on the temperature in the catalyst  110  to maintain the desired temperature. As changes are made in the system operation, an oxygen sensor will detect these changes and also adjust the oxidant flow rate to ensure lean operation. 
     In operation of the second preferred embodiment, as seen in  FIG. 21 , exhaust anode gases from the fuel cell  15  are directed into the inlet tube  230 , preheated within the burner chamber  222  and directed into the first chamber  207  upstream of the platinum (Pt) catalyst  210 . As the fuel cell exhaust gases pass through the first chamber  207 , the combination of the heated fuel stream and the platinum (Pt) catalyst  210  causes catalytic oxidation of the exhaust gases. The remaining exhaust gases are then directed through the outlet end  209  of the first chamber  207  and into the second annular chamber  212 , as shown in  FIG. 21 . The design of second annular chamber  212  redirects the stream of burned exhaust gases upwardly in counterflow fashion to the direction of the stream within the first chamber  207 . Located at the opposed end of the second annular chamber  212  is an exhaust outlet  252 , which allows the remaining exhaust gases to be released into the atmosphere. 
     The fuel cell exhaust stream flowing upwardly through the second annular chamber  212  exchanges heat with the water/steam found within the first helical tube  231  to assist in the formation of a two-phase water/steam mixture. The two-phase water/steam mixture in the first helical tube  231  is then directed to the second helical coil  232  via conduit  233 , external to the reactor  14 . The additional heat within the first chamber  207  is furthered transferred to the two-phase water/steam mixture within the second helical coil  232  to further promote the formation of steam. The second helical tube  232  is connected to the water/steam line  39  ( FIG. 2 ) of the reformer  12  to provide the steam needed for the LTS bed  36  ( FIG. 6 ). 
     The third preferred embodiment, as seen in  FIG. 22 , directs exhaust anode gases from the fuel cell  15  into the inlet tube  327 , preheats the anode exhaust gases within the burner chamber  322  and directs the exhaust gases into the first chamber  307  upstream of the platinum (Pt) catalyst  310 . As the fuel cell exhaust gases pass through the first chamber, the combination of the heated fuel stream and the platinum (Pt) catalyst  310  causes catalytic oxidation of the exhaust gases. The remaining exhaust gases are then directed through the outlet end  309  of the first chamber  307  and into the second annular chamber  312 , as shown in  FIG. 22 . The design of second annular chamber  312  redirects the stream of burned exhaust gases upwardly in counterflow fashion to the direction of the stream within the first chamber  307 . Located at the opposite end of the second annular chamber is an exhaust outlet  330 , which allows the remaining exhaust gases to be released into the atmosphere. 
     The fuel cell exhaust stream flowing upwardly through the second annular chamber  312  exchanges heat with the water/steam found within helical tube  331  to assist in the formation of a two-phase water/steam mixture. Helical tube  331  is connected to the water/steam line  39  ( FIG. 2 ) of the reformer  12  to provide the steam needed for the LTS bed  36  ( FIG. 6 ). 
     G. Steady-State Control 
     Control of the system  10  becomes easier once start-up is complete and the fuel cell  15  is brought on-line. A description of the control for each subsystem during steady-state operation is given below with particular reference to  FIG. 27 . At all times during operation, the values of critical process variables should be checked against upper and lower limits. If any value is out of these limits, an alarm can be triggered to notify the operator. 
     1. Reformer (FIGS.  1 – 11 ) 
     Once the reformer  12  has been brought up to the preferred operation temperature, it is controlled by maintaining the desired power, equivalence ratio, and steam to carbon ratio in both the POx chamber  34  and the HTS bed  37 . The temperature should be held at the desired setpoint by slightly adjusting the air flow and thus the equivalence ratio. To adjust the steam reformer exit temperature, the POx chamber temperature setpoint can be adjusted. The POx steam to carbon is maintained using a control valve  156  to control steam flow. The system is designed to produce the remaining steam needed internally and this excess is fed to the HTS bed  37  through a back-pressure regulator. 
     2. PrOx Reactor (FIGS.  12 – 19 ) 
     The oxygen to carbon monoxide ratio in the first PrOx reactor  13  should be a fixed number determined empirically from initial testing done conventionally to characterize the system  10 . Provided there is sufficient air, the design of the first PrOx reactor  13  should be such that the carbon monoxide output will be relatively constant with varying carbon monoxide at the reformate inlet  84 . In the event that there are no online analyzers for the system  10 , the oxygen to carbon monoxide ratio can be set to account for an upper limit of steady state inlet carbon monoxide. The oxygen to carbon monoxide ratio for the second PrOx reactor  13 ′ should be adjusted to maintain a fixed temperature rise through the catalyst bed  95  and outlet carbon monoxide concentrations less than 10 ppm. 
     3. Auxiliary Reactor (FIGS.  20 – 22 ) 
     The auxiliary reactor  14  is used to burn off anything not consumed in the fuel cell  15  during steady-state operation. This allows the emissions to be maintained at near zero. The excess heat is used to generate steam. The overall goal of the control strategy, therefore, is to keep the catalyst at a temperature high enough to burn the combustibles in the anode exhaust, maximize steam production, and keep emissions low. At the same time, the upper temperature limit on the catalyst must be avoided. To accomplish this it is necessary to ensure that the Auxiliary reactor  14  is operating lean and within a temperature range of about 1000° to about 1470° F. One method of doing this is to set a desired temperature and equivalence ratio for the Auxiliary reactor  14 . The oxidant flow rate can be adjusted based on the temperature in the catalyst to maintain the desired temperature. As changes are made in the system operation, the oxygen sensor  148  should detect these changes and the air flow rate will then be adjusted to ensure lean operation. It may be necessary to vary the equivalence ratio setpoint if the concentration of hydrogen in the anode exhaust varies significantly. 
     4. Water/Steam 
     At steady state, the pump speed and thus water flow rate are controlled based on the total steam being generated. In the present embodiment, the steam added to the POx chamber  34  and the HTS bed  37  are added together and multiplied by a factor of safety. This becomes the setpoint for the water flow rate, and thereby ensures that superheated conditions are avoided. If a superheated condition occurs, the factor of safety is automatically modified to add additional water until the steam temperature returns to the saturated temperature. An alternative approach determines the necessary water flow according to an operating map based on fuel input. 
     H. Transient Control 
     During transient conditions, the control of the reforming system  10  must be modified slightly to prevent excessive temperatures, high carbon monoxide concentration, and other emissions. The following disclosure contains a general description of control goals of each subsystem during transient conditions. 
     1. Steam Generation-Generally 
     In overview, according to the invention, the system  10  integrates elements of thermal control with elements of necessary steam generation. For example, temperature of shift beds are impacted by heat exchange with a steam generating system (or steam loop). Also, reformate temperature is impacted by addition of steam in connection with a high temperature shift reaction. Steam condensation and water separation from the reformate is integrated as cooling of reformate to the benefit of preferential oxidation. 
     Also, according to the invention, steam generation is integrated in a unique way in the system  10 , with processes and apparatus responsible for dynamic (e.g. transient) operation, such as following load demands, and rapid start-ups. Other advantages and aspects will be disclosed herein with respect to the system&#39;s overall thermal balance and dynamic response control. 
       FIG. 28  discloses the system  10  control scheme for dynamic control. This control design and process is applicable for the many uses where a load on the system is dynamic, that is, the demand for hydrogen-rich gas varies. For example, transportation fuel cell applications will require acceleration and deceleration of the vehicle, which will cause a dynamic response from the system if integrated into such a system. More importantly, the need for a quick response will be required, and according to the invention, the disclosed system can meet that need. 
     Generally, the process includes supplying a hydrocarbon fuel and oxygen at a first rate to reformer reactor  12  for steady state operation. Steam generated by the auxiliary reactor  14  and the heat exchange in the low temperature shift zone  36  is also supplied to the reactor  12  at a first rate for steady state performance. At steady state pressure on the steam loop  16  including auxiliary reactor  14 , the heat exchange tubes  39  in the low temperature shift bed  36  and the steam separator  105  is kept at a pressure of about 130 psi. Upon a change in demand, either for more or for less hydrogen, the system changes the rate of supply of each of the hydrocarbon fuel and the steam to a second supply rate. The change in steam demand causes an immediate change in loop steam pressure. According to the invention, the steam pressure is permitted to change within an acceptable range. Various aspects of the system design permits this as well as a rather rapid recovery of the loop  16  steam pressure. 
     Preferably the acceptable range within which the steam pressure is permitted to change is about 200 psi, but more preferably about 150 psi. In other words, the steam pressure for system  10  is permitted to vary between about 50 psi to about 200 psi during a transient operation. 
     For example, if the demand on system  10  increased, a control signal would be sent from the device, such as a fuel cell, depicted generically as a controller (C) in  FIG. 28 . Based upon that signal, a direct and proportional signal would be sent to air supply valve (AV 1 ) hydrocarbon fuel supply control valve (FV 1 ) to increase the rate of each. 
     Also in response to the control signal both steam valves (SV 1 ) and (SV 2 ) are respectively adjusted to increase supply of steam to the fuel steam mixture and to increase the supply of steam to the reformate before it enters the high temperature shift reaction. According to one aspect of the invention, the supply of both of these constituents can be, and preferably is kept at the steady state steam to carbon ratio of about 3 during the transient response. 
     Due to the fact that the system  10  employs two-phase pressurized steam, the delivery of extra steam from the steam separator  151  occurs within fractions of a second and can be delivered in a matter of one or more milliseconds. That is, upon a drop in pressure when valves (AV 1 ) and (FV 1 ) are adjusted to increase supply, the pressure drop causes the immediate production of steam from latent heat in the water of the two-phase mixture. The system response is also significantly aided, according to the invention, by the almost immediate (millisecond) creation of steam from the heat exchangers in the low temperature shift and PrOx catalyst beds. Not only is there latent heat in the water in those heat exchangers, there is a relatively large heat buffer provided by the catalysts and reactor masses. It is believed that steam from these heat exchangers is readied for supply within one or more milliseconds as well. 
     In response to the control signal, the valve (AV 2 ) is adjusted to increase air flow to the auxiliary reactor  14 . An oxygen sensor  148  senses the that the oxygen concentration is over a set point and triggers a control response of valve (FV 2 ) to increase the fuel to the auxiliary reactor  14 . The result is added steam generation. The oxygen sensor  148  will continue to attempt to keep the fuel supply to the auxiliary reactor  14  in limit. In the meantime, as the auxiliary reactor  14  and the heat exchangers in the reformer  12  and the PrOx  13  continue to generate steam, the pressure begins to return to the desired 130 psi. According to one aspect of the invention, synergistically, the higher output by the reformer and PrOx increases their contribution to the generation of steam. Once at the new power or burn rate, the system  10  temperatures also tend to better equilibrate due to the advanced amount of steam supply due to the added heat exchange presented by the design. 
     As disclosed in  FIG. 28 , the response of the air valve (AV 2 ) to the control signal (CS) is indirect. The control signal (CS) is first assessed and pursuant to predetermined values in a computer memory lookup table (LT), the appropriate auxiliary reactor burn rate is determined and a secondary control signal is sent to valve (AV 2 ). However, while the pressure is returning to the desired 130 psi, supplementary trim control signals (TS) are sent to air valve (AV 2 ) according to pressure values sensed by pressure gauge (PG) to adjust the air supply downward. Again, the oxygen sensor  148  will reduce the fuel according to the sensed reduction of air. 
     According to another aspect of the invention, this trimming process occurs independently of whether or not a control signal is sent from the controller (C). This trimming process helps maintain the system thermal equilibrium caused by other factors, such as changes in system efficiencies, and ambient temperature changes. 
     It should be noted, that thermal stability of the partial oxidation reaction is controlled by a POX trim signal (TS) generated in response to sensor (thermocouple)  149 . This trim signal causes the air flow to the POx to be adjusted based upon temperature of reactants in the partial oxidation reaction. Preferably this trim signal can be generated independently of a control signal from controller (C). 
     Also, according to another aspect of the invention, the sizing of the partial oxidation zone and downstream steam reforming zone can be such that high volumetric flow rates caused by either a very large increase in hydrogen demand or a high steady state demand, will cause a much higher mixing velocity and swirling of the gases to extend vigorously upward in the POx chamber which raises its efficiency and thermal output. At some higher flow levels, partial oxidation at significant levels will begin to be promoted by the steam reforming catalyst. 
     It is also useful to consider a decrease in demand to illustrate other aspects of the invention. Upon a downturn in hydrogen demand, a control signal is generated and sent as in the discussion above. All of the valves and controls respond exactly as above but to decrease air, fuel and steam supplied to the various components. The pressure is again permitted to rise, but preferably not to more than 200 psi in this embodiment. The system again comes back to equilibrium. However, the challenge faced with a decrease is what to do with the excess steam, and or thermal energy. The system  10  is designed and sized such that only a portion of the steam is generated by the reformer  12  and PrOx reactor  13  which may have significantly higher thermal mass than the auxiliary reactor and steam loop. In the preferred embodiment of system  10 , only about half of the thermal energy needed for steam generation is supplied by the auxiliary reactor  14 . In other embodiments, a different balance of thermal energy may be desired. Also, the fact that heat exchange is done with tube boilers coupled with an auxiliary steam generator, both permit the total water and steam mass to be smaller, versus for example a pool boiler. This permits reduction in the amount of excess steam generated after turn down. It is also this relatively low ratio of catalyst mass to the mass of water in each of: (1) the tube heat exchangers; and, (2) the system as a whole, that permits such a rapid response in steam generation in a turn-up scenario. 
     Another significant transient is start-up. According to one aspect of the invention provides that upon start up, the auxiliary reactor  14  is started to generate steam. This steam is routed through the catalyst beds  36  and  37  as discussed herein. This advantageously permits these reactors to address carbon monoxide production earlier after start up than otherwise would be the case. This permits an earlier delivery of an acceptable hydrogen-rich stream to a load, such as a fuel cell  15 . 
     2. Reformer 
     During transients, the goal for the reformer  12  is to change power as quickly as possible while maintaining the steam to fuel ratio in the POx chamber  34 , as well as the overall steam to fuel ratio and the temperature in the POx chamber  34 . This helps prevent any large spikes in the carbon monoxide concentration. One component of the control of the reformer  12  during transient conditions is for the flows of fuel, air, and steam to all follow each other. The time required for the air to reach a new steady-state point will directly affect the speed of the transients. When a request for a change in air is sent, the entire reformer  12  must wait for this change to occur. As the air flow is ramped up or down to the desired flow rate, the fuel flow rate must follow this change to maintain the set ratio (preferably, about 1.5 steam to carbon in the reformer  12  with another 1.5 added directly to the HTS bed  37 ). The steam flow rate to the POx follows the fuel flow rate to maintain the desired steam to carbon ratio. Once the transient condition is complete, the automatic control to maintain steam to carbon ratio in the POx chamber  34  can be resumed. 
     When increasing the power in the system  10 , the steam to carbon ratio in the HTS bed  37  will most likely drop (since the system will not immediately increase steam production) unless an adjustment is made in the steam system. If the overall steam to carbon ratio drops, the carbon monoxide will increase at the exit of the reformer  12 . To prevent this, it may be necessary to drop the pressure setpoint in the steam loop to allow extra steam into the HTS bed  37 . This adjustment can help to minimize any spike in carbon monoxide concentration exiting the reformer  12  and the extra air required by the PrOx reactor  13  during transient conditions. The pressure should then be gradually increased back to the nominal value as steam production increased at the new power and the overall steam to carbon ratio begins to rise again. Clearly adjusting the pressure in the steam loop is not the best solution if the system is going through frequent transient conditions. Such potentially could result in a loss of steam pressure and a drop in the catalyst bed temperatures. In this case, it may be necessary to re-light the auxiliary reactor burner chamber  122  and generate additional steam to maintain the steam loop pressure. 
     3. PrOx Reactor 
     If steam control is maintained in the reformer, PrOx air flow during transients should adjust to maintain to set oxygen to carbon monoxide ratios the reformate flow change. Where a loss of steam flow rate occurs and elevated carbon monoxide levels occurs, the oxygen to carbon monoxide ratio in the first PrOx reactor  13  can be mapped against time to give an elevated amount of air until the LTS bed exit carbon monoxide concentration level returns to its steady state value. Such a map can be used to determine empirically where an online analyzer will be available. The oxygen to carbon monoxide ratio for the second PrOx reactor  13 ′ need not be adjusted since the carbon monoxide outlet from the first PrOx  13  does not change during the transient. 
     4. Auxiliary Reactor 
     Control of the auxiliary reactor  14  during transient conditions is similar to control during steady state. As more or less anode exhaust reaches the auxiliary reactor  14 , the oxygen sensor  148  picks up on this change and adjust the air flow rate into the system  10 . If the concentration of hydrogen in the anode exhaust changes significantly, the equivalence ratio setpoint for the auxiliary reactor  14  will be adjusted accordingly to maintain the desired temperature. 
     5. Water/Steam 
     Since maintaining steam in the fuel processing system is so important to the performance of the system  10 , appropriate adjustments of the water flow rate into the system  10  are also extremely important. An increase/decrease in power will result in moreaess steam production and the water flow rate should be changed accordingly. The steam flow rate into the POx chamber  34  and HTS bed  37  will lag behind this change, however. Alternatively, it may be necessary to estimate what the water flow rate should be at different powers experimentally and use this information during transients instead of relying on the total flow rate of steam. 
     While specific embodiments have been illustrated and described, numerous modifications are possible without departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.