Patent Publication Number: US-6221117-B1

Title: Hydrogen producing fuel processing system

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 08/951,091, which was filed on Oct. 15, 1997, is entitled Steam Reformer With Internal Hydrogen Purification, is now U.S. Pat. No. 5,997,594, which is a continuation-in-part application of U.S. patent application Ser. No. 08/741,057, filed Oct. 30, 1996, which is now U.S. Pat. No. 5,861,137, and the disclosure of which is hereby incorporated by reference. This application also is a continuation-in-part of and claims priority to co-pending U.S. patent application Ser. No. 09/190,917, which was filed on Nov. 12, 1998, is entitled Integrated Fuel-Cell System, and the disclosure of which is also hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to energy conversion, and particularly to a process and apparatus for production of purified hydrogen by steam reforming. 
     Purified hydrogen is an important fuel source for many energy conversion devices. For example, fuel cells use purified hydrogen and an oxidant to produce an electrical potential. A process known as steam reforming produces by chemical reaction hydrogen and certain byproducts or impurities. A subsequent purification process removes the undesirable impurities to provide hydrogen sufficiently purified for application to a fuel cell. 
     Under steam reforming, one reacts steam and alcohol, (methanol or ethanol) or a hydrocarbon (such as methane or gasoline or propane), over a catalyst. Steam reforming requires elevated temperature, e.g., between 250 degrees centigrade and 800 degrees centigrade, and produces primarily hydrogen and carbon dioxide. Some trace quantities of unreacted reactants and trace quantities of byproducts such as carbon monoxide also result from steam reforming. 
     Trace quantities of carbon monoxide, certain concentrations of carbon dioxide, and in some cases unsaturated hydrocarbons and alcohols will poison a fuel cell. Carbon monoxide adsorbs onto the platinum catalyst of the fuel cell and inhibits operation of the fuel cell, i.e., reduces the power output of the fuel cell. To a lesser degree, carbon dioxide and other unsaturated hydrocarbons and alcohols have the same result. All impurities to some extent reduce by dilution the partial pressure of hydrogen in the fuel cell and increase the mass transfer resistance for hydrogen to diffuse to the platinum catalyst, and thereby reduce power output of the fuel cell. Thus, fuel cells require an appropriate fuel input, i.e., purified hydrogen with no additional elements contributing to a loss in fuel cell efficiency. 
     Traditionally, hydrogen purification attempts to always maximize harvest of hydrogen from the reforming process. To maximize the amount of hydrogen obtained, a relatively expensive device, e.g., a thick and high quality palladium membrane, serves as a hydrogen-permeable and hydrogen-selective membrane [Ledjeff-Hey, K., V. Formanski, Th. Kalk, and J. Roes, “Compact Hydrogen Production Systems for Solid Polymer Fuel Cells” presented at the Fifth Grove Fuel Cell Symposium, Sep. 22-25, 1997]. Such thick, high quality palladium alloy membranes support maximum harvest of hydrogen with minimal, i.e., acceptable, impurities for use in a fuel cell. Such high level of purification, however, requires significant investment in the thick, high quality palladium membrane. 
     Traditionally, the process of steam reforming and the subsequent process of hydrogen purification occur in separate apparatus. The advantages of combining steam reforming and hydrogen purification in a single device are known [Oertel, M., et al, “Steam Reforming of Natural Gas with Integrated Hydrogen Separation for Hydrogen Production”,  Chem. Eng. Technol  10 (1987) 248-255; Marianowski, L. G., and D. K. Fleming, “Hydrogen Forming Reaction Process” U.S. Pat. No. 4,810,485, Mar. 7, 1989]. An integrated steam reforming and hydrogen purification device should provide a more compact device operating at lower temperatures not limited by the normal equilibrium limitations. Unfortunately, such a device has yet to be reduced to practical design. Where theory in this art recognizes the advantage of combining steam reformation and hydrogen purification in a single device, the art has yet to present a practical, i.e., economical, design. 
     Thus, a practical integrated steam reforming and hydrogen purification device has not yet become available. The subject matter of the present invention provides a practical combined steam reforming and hydrogen purification device. 
     SUMMARY OF THE INVENTION 
     A process for producing hydrogen containing concentrations of carbon monoxide and carbon dioxide below a given level begins by reacting an alcohol vapor (such as methanol) or a hydrocarbon vapor (such as propane) and steam to produce product hydrogen, carbon monoxide, and carbon dioxide. The reacting step occurs in the vicinity of, or immediately preceding, a hydrogen-permeable and hydrogen-selective membrane and the product hydrogen permeates the membrane. A methanation catalyst bed lies at the permeate side of the membrane and converts any carbon monoxide and carbon dioxide which passes through the membrane to methane, thereby yielding a product hydrogen stream with concentrations of carbon monoxide and carbon dioxide that are below acceptable thresholds. Optionally, reforming catalyst may also lie at the permeate side of the membrane along with the methanation catalyst to convert to product hydrogen any unreacted alcohol or hydrocarbon feed that passes through the membrane. Product hydrogen is then withdrawn from the methanation catalyst bed. 
     A steam reformer, also referred to as a fuel processor, according to the present invention includes a reforming bed that receives and reacts a mixture of alcohol or hydrocarbon vapor and steam to produce hydrogen and by product gases. The gases are then passed through a hydrogen-permeable and hydrogen selective membrane. On the permeate side of the membrane, a methanation catalyst converts carbon monoxide and carbon dioxide to methane. 
     Many other features of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying drawings in which preferred embodiments incorporating the principles of this invention are disclosed as illustrative examples only. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
     FIG. 1 illustrates generally an energy conversion system including a fuel cell and a steam reformer with internal hydrogen purification according to one form of the present invention. 
     FIG. 2 illustrates schematically a concentric, cylindrical architecture for the steam reformer with internal hydrogen purification of FIG.  1 . 
     FIG. 3 illustrates in cross section the steam reformer with internal hydrogen purification of FIG.  1 . 
     FIG. 4 illustrates schematically an alternate architecture for the steam reformer under the present invention nesting multiple reformer tubes within a common combustion region. 
     FIG. 5 illustrates schematically and partially in cross section a steam reformer with internal hydrogen purification according to the present invention including a modified combustion system distributed within the reformation region. 
     FIG. 6 illustrates schematically and partially in cross section another embodiment of a steam reformer with internal hydrogen purification according to the present invention including an isolated vaporization chamber. 
     FIG. 7 illustrates schematically a combustion system applicable to the present invention and providing along its length a generally uniform temperature gradient. 
     FIG. 8 illustrates the temperature gradient of the combustion system of FIG. 7 as compared to a conventional temperature gradient. 
     FIG. 9 illustrates another form of steam reformer with internal hydrogen purification under the present invention using plate membrane elements. 
     FIG. 10 illustrates in exploded view a plate membrane module of the steam reformer of FIG. 9 including membrane envelope plates. 
     FIG. 11 illustrates in exploded view a membrane envelope plate of FIG.  10 . 
     FIGS. 12-17 show membrane components for a tubular metal membrane module and assembly steps in the production of a tubular membrane module using manufacturing steps according to the present invention. 
     FIG. 18 illustrates in perspective, and partially broken away, another embodiment of a steam reformer according to the present invention including an isolated vaporization chamber and a plate-form membrane module. 
     FIG. 19 illustrates the steam reformer of FIG. 18 in section. 
     FIGS. 20 and 21 show components of the membrane module for the steam reformer of FIGS. 18 and 19. 
     FIG. 22 illustrates a component stack for the membrane module of the steam reformer of FIGS. 18 and 19 providing a series feed gas flow arrangement. 
     FIG. 23 illustrates a component stack for the membrane module of the steam reformer of FIGS. 18 and 19 providing a parallel feed gas flow arrangement. 
     FIG. 24 illustrates a component stack for the membrane module of the steam reformer of FIGS. 18 and 19 incorporating an exhaust plate for internal heating of the membrane module. 
     FIG. 25 illustrates in cross section another embodiment of a steam reformer according to the present invention. 
     FIG. 26 illustrates in cross section a variation of the reformer of FIG.  25 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an energy conversion system  10  employing a steam reformer with internal hydrogen purification (reformer)  12  according to a preferred form of the present invention. Reformer  12  provides at its outlet  14  purified hydrogen to a PEM fuel cell  16 . Fuel cell  16  receives at its inlet  18  an oxidant from oxidant source  20 . Fuel cell  16  produces an electrical potential  22  for application to an electrical load  24 , e.g., an electrical motor. Fuel cell  16  also includes outlets  26  and  28  serving as fuel and oxidant outlets, respectively. 
     For purposes of describing operation of reformer  12 , the liquid feedstock will be methanol (MeOH) and water, although other alcohols or hydrocarbons may be used in place of methanol. Reformer  12  receives at its fuel inlet  30  pressurized liquid methanol and water from a pressurized methanol/water source  32 . As described more fully hereafter, the pressurized mix of liquid methanol and water vaporizes within reformer  12  and reacts with a reforming catalyst to produce a hydrogen stream and a byproduct stream. A hydrogen-selective membrane separates the hydrogen stream from the byproduct stream. The hydrogen stream passes, by pressure differential, through the membrane and subsequently through a polishing catalyst to appear at the outlet  14  of reformer  12 . 
     While traditional reforming technology allows a high percentage of hydrogen produced to be taken across a selective membrane, the process and apparatus of the present invention takes less than a maximum available amount of hydrogen across the selective membrane. The present invention thereby allows use of a lesser-grade and, therefore, less expensive selective membrane. In addition, because less than the maximum amount of hydrogen is separated as a product stream, the required membrane area is reduced under this aspect of the present invention. The remaining portion of hydrogen enters the byproduct stream, mixes with air provided at inlet  34  by air blower  36 , and reacts with a combustion catalyst within reformer  12  to support elevated temperatures needed for steam reforming within reformer  12 . Reformer  12  thereby uses the byproduct stream, including a selected amount of hydrogen remaining therein, as a fuel source for its combustion process. No additional fuel source is applied to reformer  12  to support combustion. Reformer  12  also includes a plurality of combustion exhaust ports  38  releasing combustion byproducts. 
     The optimum amount of hydrogen to recover as a product stream is calculated from the heating value (enthalpy of combustion) of hydrogen. Sufficient hydrogen must be supplied in the byproduct stream to the catalytic combustion region so that the heat of combustion exceeds the total heat requirement of the reformer. The total heat requirement of the reformer (ΔH total ) is given by 
     
       
         ΔH total =ΔH rxn +ΔH vap +ΔH cp +ΔH loss   
       
     
     where ΔH rxn  is the enthalpy of the reforming reactions; ΔH vap  is the enthalpy of vaporization of the liquid feed stock; ΔH cp  is the enthalpy required to heat the vaporized feed stock to the reforming temperature; and ΔH loss  is the heat lost to the surrounding environment. Heat loss from the reformer is minimized (and reduced to a negligible degree) with adequate insulation. 
     In the case of steam reforming methanol according to the following reaction stoichiometry 
     
       
         CH 3 OH+H 2 O=CO 2 +3H 2   
       
     
     where 8.4 gmole methanol and 8.4 gmole water are required to yield sufficient hydrogen (21 std. ft 3 ) to generate about 1 kW e . Assuming no heat loss and no heat exchange (between discharged hot streams and the relatively cold feed stock stream) ΔH total  is 300 kcal. Since the heat of combustion for hydrogen is 57.8 kcal/gmole, approximately 5.2 gmoles of hydrogen (4.3 std. ft 3 ) must be combusted to provide the required 300 kcal of heat for steam reforming sufficient methanol to generate 1 kW e . So, 70% to 80% of the hydrogen produced in the reformer is recovered as a product stream and the remaining 20% to 30% of the hydrogen is passed to the catalytic combustor in the byproduct stream to provide a fuel stream with sufficient heating value to meet the heating requirements (ΔH total ) of the reformer. 
     FIG. 2 illustrates schematically the concentric cylindrical architecture of steam reformer  12 . In FIG. 2, reformer  12  includes in concentric relation an outermost metal tube  50 , an inner metal tube  52 , a hydrogen-selective membrane tube  54 , and an innermost metal tube  56 . Tubes  50 ,  52 ,  54 , and  56  are of successively smaller diameter and arranged in concentric relation to one another. An annular combustion region  60  exists in the space within tube  50  but external of tube  52 . An annular reforming region  62  exists within tube  52  but external of membrane tube  54 . An annular hydrogen transport region  64  exists within membrane tube  54 , but external of tube  56 . A cylindrical polishing region  66  resides within the metal tube  56 . 
     FIG. 3 illustrates in cross section the steam reformer  12 . In FIG. 3, outermost metal tube  50 , a generally closed-end tubular structure, receives at one end via inlet  34  an air supply and releases at combustion ports  38  combustion byproducts. Within combustion region  60 , a combustion catalyst  100  resides near air inlet  34 . Alternatively, combustion catalyst  100  may be arranged as a plurality of bands spaced at intervals within combustion region  60 . Suitable combustion catalyst materials include platinum supported on alumina or other inert and thermally-stable ceramic. Inlet  30 , carrying the pressurized mix of methanol and water, passes through the end wall  50   a  of tube  50  and forms a coil  30   a  wrapping about the innermost metal tube  56  within the combustion region  60 , although metal tube  56  need not necessarily pass through the axis of coil  30   a . The distal end of coil  30   a  passes through the closed end  52   a  of tube  52  and opens into the reforming region  62 . The pressurized mix of liquid methanol and water entering coil  30   a  vaporizes at the elevated temperatures of combustion region  60  and enters the reforming region  62  as vapor. 
     Within reforming region  62  a reforming catalyst  102  (e.g., BASF catalyst K3-110 or ICI catalyst 52-8) reacts with the vaporized mix of methanol and water to produce hydrogen in the vicinity of the membrane tube  54 . Membrane tube  54  is composed of one of a variety of hydrogen-permeable and hydrogen-selective materials including ceramics, carbon, and metals. Especially preferred materials for fabricating said membrane tube  54  are hydrogen-permeable palladium alloys, e.g., palladium alloyed with 35-45 wt % silver. Each end of membrane tube  54  is sealed by a metal cap  104 . A metal gauze  106  within the reforming region  62  surrounds each cap  104  and maintains the catalyst  102  within region  62  and in the vicinity of membrane tube  54 . A hydrogen stream  103  migrates by pressure differential through membrane tube  54  and into hydrogen transport region  64 . A thin membrane tube  54  requires support against deformation under the pressure differential between reforming region  62  and hydrogen transport region  64 . For this purpose, a tension spring  101  supports membrane tube  54  from within while allowing hydrogen stream  103  to pass by, into and along transport region  64 . 
     Because a thin palladium alloy membrane may be used under the present invention, special construction methods have been developed under the present invention to make use of a delicate structure such as thin membrane tube  54 . Under conventional practice, a thick palladium alloy membrane can be brazed because it can withstand the high temperatures and liquid phase aspects of brazing. A thin palladium alloy membrane, as proposed herein however, cannot be brazed under conventional methods because the elevated temperature and liquid brazing alloy destroy such thin palladium material. A thin membrane tube  54  could, under conventional practice for example, attach to end caps  104  and establish a gas-tight seal by use of gaskets and suitable support structures. As discussed more fully hereafter, under the present invention a thin palladium alloy membrane, e.g., tube  54 , attaches to end caps  104  by first attaching a foil (not shown in FIG.  3 ), e.g., a copper or nickel foil, to the ends of tube  54  by ultrasonic welding and then brazing the foil-wrapped ends of tube  54  to end caps  104 . 
     Hydrogen stream  103  travels within transport region  64  toward and into the open end  56   a  of tube  56 . Hydrogen stream  103  includes some impurities, e.g., carbon monoxide, carbon dioxide and unreacted methanol and water vapor, also traveling along transport region  64  and into innermost tube  56  at its open end  56   a . All of hydrogen stream  103  enters the open end  56   a  of innermost tube  56 . 
     Within tube  56  a polishing catalyst  110  reacts with impurities in the hydrogen stream  103  passing therethrough. Metal gauze  112  downstream from catalyst  110  holds catalyst  110  within tube  56 . Polishing catalyst  110  (e.g., BASF catalyst G1-80 or ICI catalyst 23-1) reacts with certain impurities remaining in hydrogen stream  103 , e.g., as much as 1% of carbon monoxide and carbon dioxide, and converts such impurities to innocuous byproducts, e.g., methane. Stream  103  of purified hydrogen and, now innocuous, byproducts passes through metal gauze  112  and exits reformer  12  at the outlet  14 , i.e., at the opposite end  56   b  of tube  56 . 
     Polishing catalyst  110  may be several separate catalysts within tube  56 . In order to deal with carbon monoxide and carbon dioxide impurities, one uses a methanation catalyst. The process of methanation, i.e., reacting carbon monoxide or carbon dioxide with hydrogen to yield methane as shown below, is well known. 
     
       
         CO 2 +4H 2 =CH 4 +2H 2 O 
       
     
     
       
         CO+3H 2 =CH 4 +H 2 O 
       
     
     Methanation provides an acceptable polishing step because methane is considered relatively inert or innocuous to the fuel cell  16  (FIG. 1) whereas carbon dioxide and carbon monoxide are poisonous to the fuel cell. 
     If reformer  12  uses methanol in the steam reforming step, and leaks in the membrane tube  54  allow carbon monoxide and carbon dioxide to pass into the hydrogen stream  103 , some unreacted methanol and water vapor may exist in the hydrogen stream  103 . To convert such unreacted methanol into a harmless byproduct prior to entering the fuel cell  16  (FIG.  1 ), a reforming catalyst which is a low temperature copper/zinc shift catalyst, is placed through a portion (e.g., one-fourth to one-third) of the polishing catalyst bed, i.e., innermost tube  56 , followed downstream by a methanation catalyst. 
     The predominant chemical reaction for steam reforming methanol is shown below. 
     
       
         CH 3 OH+H 2 O=CO 2 +3H 2   
       
     
     Returning to reforming region  62 , steam reforming byproduct stream  105  moves toward closed end  52   b  of tube  52  and through critical orifice  120  serving as an outlet for tube  52  and discharging near air inlet  34 . Optionally, deflector  57  directs the flow of byproduct stream  105  and air from inlet  34  toward combustion catalyst  100 . Byproduct stream  105  thereby encounters and mixes with the air inflow  107  of air at inlet  34 . Air inflow  107  may be preheated to enhance the catalytic ignition within combustion region  60 . For example, an air heater  37  (FIG. 1) may be provided in series along the inlet  34  to reformer  12 . Alternatively, inlet  34  may be routed through combustion region  60  as shown schematically in FIG.  3 . The resulting mixture travels toward and through combustion catalyst  100  and ignites thereat. The combustion byproducts then travel through combustion region  60  and eventually, after heating coil  30   a  and thermally supporting the steam reforming process within region  62 , exit reformer  12  at the combustion exhaust ports  38 . 
     Reformer  12  operates at a relatively lower temperature than conventional steam reforming devices. Because reformer  12  continually purifies hydrogen as it is produced, the steam reforming reaction may be conducted well away from its equilibrium limitation. Although equilibrium limitations are generally not important in the case of steam reforming methanol, they are very important in the case of steam reforming methane (natural gas). Unreacted reactants in the relatively lower temperature reforming process tend to be eventually reacted due to the continuous siphoning of hydrogen from the process. Under the present invention, the steam reforming process may be operated at approximately 250 to 600 degrees Celsius. For methanol reforming the operating temperature of the reformer would be approximately 250 to 300 degrees Celsius. 
     To create an appropriate pressure differential at membrane tube  54 , the liquid methanol and water should be pumped, i.e., provided by source  32 , at approximately 6 to 20 atmospheres. The polishing step should be conducted at approximately one to three atmospheres within polishing region  66 . The pressure within hydrogen transport region  64  is essentially equal to the pressure within polishing region  66 . The reforming process should be operated at 6 to 20 atmospheres to provide a substantial pressure differential across membrane tube  54 . Critical flow orifice  120  can be sized to provide a pressure drop from the reforming region  62  (6 to 20 atmospheres) to one atmosphere within the combustion region  60 . The byproduct stream  105  thereby enters the combustion region  60  at approximately one atmosphere. This allows operation of the air supply at inlet  34  at approximately one atmosphere, and thereby allows use of an inexpensive air blower  36 . 
     Dimensions for reformer  12  sufficient to feed a typical fuel cell  16  are relatively small. Ten liters per minute (21 cubic feet per hour) of hydrogen is sufficient to generate one kilowatt of electrical energy in fuel cell  16 . A steam reformer  12  under the present invention sufficient to support a one kilowatt fuel cell  16  would be roughly three inches in diameter by 15 to 16 inches in length. To increase volumetric production, the length of reformer  12  could be increased or the diameter of reformer  12  could be increased. The volumetric production rate for reformer  12  is limited primarily by the area of membrane  56  exposed to the reforming process. Increasing the length of reformer  12  or the diameter of reformer  12  increases the exposed area of membrane tube  54  and thereby increases hydrogen output for reformer  12 . However, multiple standard-sized reformers  12  may be employed in parallel within a common combustion zone. 
     FIG. 4 illustrates schematically the architecture of an alternate reformer  12 ′ with an enlarged outermost metal tube  50 ′ defining a common combustion region  60 ′. Within the relatively larger combustion region  60 ′, a plurality of reformer tubes  51 , i.e., each a combination of a tube  52 , a tube  54 , and a tube  56 , are arranged in spaced relation. While not shown in FIG. 4 for purposes of clarity, reformer  12 ′ would include a feedstock inlet, a product hydrogen outlet, and a combustion gas outlet. A common air inlet  34  supplies air to the common combustion region  60 ′. As may be appreciated, each of reformer tubes  51  provides a byproduct stream  105  (not shown in FIG. 4) to the common combustion region  60 ′. 
     Returning to FIG. 3, reformer  12  must be initiated to operate. Generally, the reforming region  62  must be elevated to approximately 150 to 200 degrees Celsius if methanol is the feedstock, or 300 to 500 degrees Celsius if hydrocarbons are the feedstock. Once the reforming process begins, the byproduct stream  105 , including by design a given amount of hydrogen as combustion fuel, enters the combustion region  60 , encounters combustion catalyst  100 , and combusts to thermally support the steam reforming process. The combustion catalyst only needs hydrogen present (mixed with air) to ignite the byproduct stream  105 . The goal in starting reformer  12 , therefore, is to elevate the reforming region  62  to approximately 150 to 200 degrees Celsius (in the case of methanol reforming). 
     A simple cartridge-type electric resistance heater  140 , either inserted into the reforming catalyst  102  or, as illustrated in FIG. 3, into the center of tube  56  initiates operation of reformer  12 . Alternatively, a resistance heater may be used to heat the methanol and water feed provided at inlet  30 . In either event, once the reforming catalyst  102  reaches a sufficiently high temperature (150 to 200 degrees Celsius) the reforming reaction begins and the combustion catalyst  100  reacts with hydrogen present in byproduct stream  105 . At this point, the electrical resistance heater  140  can be shut down. A 50 to 100 watt resistance heater  140  should be adequate, based on conventional thermal mass calculations, to sufficiently heat the reforming region  62  in a matter of minutes. 
     FIG. 5 illustrates, partially and in cross section, an alternate form of the present invention with its combustion system distributed through the reformation region to improve heat transfer from the combustion process to the reformation process. In FIG. 5, reformer  212  is a steam reformer with internal hydrogen purification receiving at its inlet  230  a feed stock, e.g., methanol and water, and providing at its outlet  214  purified hydrogen for application to, for example, a fuel cell (not shown in FIG.  5 ). As with earlier embodiments of the present invention, reformer  212  leaves a selected portion of hydrogen in its byproduct stream to support the combustion process. Combustion byproducts exit at the exhaust port  238 . 
     Reformer  212  includes an outer metal tube  252  sealed at each end by end plates  253 , individually  253   a  and  253   b  and gaskets  255 , individually  255   a  and  255   b . Bolts  257  secure end plates  253  against the shoulders  252 , individually,  252   a  and  252   b , at each end of tube  252 . A hydrogen purification module lies within and generally concentric to tube  252  and includes a thin palladium alloy membrane tube  254  sealed by end caps  304   a  and  304   b . Alternatively, membrane tube  254  may be comprised of hydrogen-selective and hydrogen-permeable materials other than palladium alloys, including porous carbon, porous ceramics, hydrogen-permeable metals other than palladium porous metals, and metal-coated porous carbon and porous ceramics and porous metals. As may be appreciated, tube  254  and caps  304  may be supported in some fashion (not shown) within tube  252 . End cap  304   b  communicates with outlet  214  through plate  253   b  and the product hydrogen stream  303  emerges from outlet port  214 . A polishing catalyst bed, preferably a methanation catalyst, is located at the permeate side of membrane tube  254  (not shown ) as discussed earlier and shown in FIG.  3 . 
     Inlet  230  passes through wall  253   a  and couples to a vaporization coil  230   a . Outlet  231  of coil  230   a  feeds directly into the reformation region  262  defined as being within tube  252  but external of tube  254 . Also located within and distributed throughout the reformation region  262  is a combustion coil  250 . In the particular embodiment illustrated, coil  250  surrounds in spiral fashion membrane tube  254  and extends substantially throughout the entire reformation region  262 . A combustion catalyst  302  lies within and either along the length of coil  250  or localized within coil  250  at or near end  250   a . End  250   a  of coil  250  receives a fuel stock, as described more fully hereafter, and combustion occurs within coil  250  as the fuel stock travels along coil  250  and encounters the combustion catalyst  302  therein. Because coil  250  extends uniformly throughout the reformation region  262  and because coil  250  provides significant surface area, rapid and well distributed heat transfer occurs from the combustion process occurring within coil  250  to the surrounding reformation region  262 . 
     Reformation region  262  couples through wall  253   b  at its outlet  220  to a conduit  221 . Conduit  221  carries the byproduct stream  205 , i.e., the byproduct of hydrogen reformation including a selected amount of hydrogen intentionally not taken across the membrane tube  254 , to the combustion process. Conduit  221  delivers byproduct stream  205  to a pressure let down valve  223 . Byproduct stream  205  then continues, at lowered pressure, into an intake manifold  207 . Manifold  207  includes an air inlet  209 , e.g., coupled to an air blower or to discharged air from the cathode component of the fuel cell (not shown in FIG.  5 ), and air passage way  211  carrying combustion air to a mixing region  213  at or near the inlet  250   a  of combustion coil  250 . The combustion fuel stock as provided by the byproduct stream  205 , thereby mixes with the incoming combustion air in mixing region  213  and enters end  250   a  of combustion coil  250 . Combustion catalyst  302  within coil  250  ignites the fuel stream  205  and heat transfers efficiently and rapidly in well distributed fashion into and throughout the reformation region  262 . 
     While a coil or spiral form of combustion system has been illustrated, i.e., the coil  250 , other shapes may be employed as a combustion system within the reformation region  262 . For example, generally tubular structures may assume a variety of forms for distribution throughout reformation region  262 . As discussed more fully hereafter, a counter-current combustion system as illustrated in FIG. 7 establishes improved, i.e., uniform, heat distribution throughout reformation region  262 . Thus, the advantage of distributing a combustion system throughout the reformation region  262  may be achieved in a variety of specific configurations. 
     In steam reformer  12  (FIG.  3 ), the combustion process occurred in a region surrounding the reformation region, i.e., externally of the tube  52  (FIG. 3) thereby requiring heat transfer into and across metal tube  52 . From the inner surface of tube  52 , heat transfer then occurred by migration across the reformation region. In steam reformer  212 , however, heat generated within and distributed throughout the reformation region  262 , i.e., within the coil  250 , better transfers more rapidly throughout the reformation region  262 . In essence, the combustion process has been brought into and distributed throughout the reformation region  262 . Heat transfer improves because the flow of reformation gasses passes directly over and around coil  250 . Generally, coil  250  provides significantly greater surface area for heat transfer between combustion and reformation as compared to the surface area provided by tube  52  in reformer  12 . Heat energy need not transfer into and migrate across the reformation region, but rather generates within the reformation region and radiates outward throughout the reformation region. 
     FIG. 6 illustrates another embodiment of the present invention, also distributing combustion heat energy throughout the reformation region, but further providing the advantage of isolating the vaporization process from the reformation process. Generally, a preferred temperature for vaporization of the feed stock, e.g., 400-650 degrees Centigrade, is greater than a preferred temperature, e.g., 250-500 degrees Centigrade, for hydrogen reformation In FIG. 6, steam reformer  312  includes an outer metal tube  352  defining therein a reformation region  362 . Tube  352  includes shoulders  352  at each end, individually  352   a  and  352   b . A vaporization module  340  attaches to shoulders  352   a  of tube  352 . Module  340  defines a vaporization chamber  342  isolated relative to reformation region  362 . More particularly, module  340  includes a generally cylindrical barrel  344  having an open end  344   a  and a closed end  344   b . An end plate  346  and gasket  348  seal vaporization chamber  342 , i.e., close the otherwise open end  344   a  of barrel  344 . The closed end  344   b  of barrel  344  couples to shoulders  352   a  of tube  352 . In this manner, closed end  344   b  together with a gasket  350  seal the end of tube  352  and, thereby, seal reformation chamber  362 . By isolating vaporization chamber  342  and reformation chamber  362 , vaporization occurs at preferred, i.e., significantly higher, temperatures than temperatures preferred for reformation chamber  362 . 
     Inlet  330  passes through end plate  346  and feeds into coil  230   a  as located within vaporization chamber  342 . The distal end of coil  230   a  then pass through closed end  344   b  of barrel  344  and feeds into reformation chamber  362 . In this manner, vaporized feed stock, i.e., methanol and water vapor, enter region  362  and chemically interact with reformation catalyst  400  distributed throughout reformation region  362 . 
     Vaporization chamber  342  includes outlets passing combustion exhaust along corresponding conduits  370  extending through combustion region  362 . In this manner, the heat energy of the combustion exhaust transfers through conduits  370  and into the reformation region  362 . Again, distributing heat energy throughout and within the reformation region improves heat transfer distribution and rate. For example, vaporization chamber  342  includes outlets  342   a  and  342   b  passing combustion gas into corresponding conduits  370   a  and  370   b . The combustion exhaust remains isolated relative to the combustion region  362 , but the heat energy of the combustion exhaust migrates through conduits  370  and into the combustion region  362 . Conduits  370  pass through an end plate  353   b , secured to shoulders  352   b , and the combustion exhaust releases to atmosphere. Heat transfer can be improved, and the degree of resistance to flow and turbulence along the exterior conduits  370  can be controlled by use of baffles  371 . 
     As in previously described embodiments, reformation occurring in reformation region  362  supports migration of hydrogen across a tubular palladium alloy membrane  354 . Other hydrogen-permeable and hydrogen-selective compositions tat may be used in place of palladium alloys for membrane  354  include porous carbon, porous ceramic, hydrogen-permeable metals, porous metals, and metal-coated porous ceramics and porous carbon and porous metal. Tubular membrane  354 , sealed at each end by means of end caps  304 , feeds the product hydrogen stream  303  at the outlet  314  of reformer  312 . A polishing catalyst bed (not shown) is located at the permeate side of membrane  354  as shown in FIG. 3. A preferred polishing catalyst is a nation catalyst. 
     By intentionally not recovering all hydrogen available in the reformation region  362 , the remaining hydrogen sweeps away in the byproduct stream  305  and provides a fuel stock for the vaporization module  340 . More particularly, reformation region  362  couples to a conduit  321  passing through end plate  353   b . Conduit  321  carries the byproduct stream  305 , including a selected amount of hydrogen remaining therein as fuel stock. Conduit  321  passes through a pressure let down valve  323  and provides the reduced-pressure fuel stock flow  305 ′ to an inlet manifold  307 . Inlet manifold  307  operates in similar fashion to the inlet manifold  207  of FIG. 5, i.e., receiving combustion air and promoting mixing of the combustion air and reduced-pressure byproduct stream  305 ′. As the combined combustion air and steam  305 ′ intermix at the mixing region  313 , an igniter  319  triggers combustion thereof. Igniter  319  may be a variety of devices, e.g., glow plug, spark plug, catalyst, and the like. In the preferred form of the reformer  312 , however, a high voltage spark ignition or possibly a glow plug is considered preferred as igniter  319  for long term reliability and ease of replacement. 
     In addition to isolation of vaporization, reformer  312  also provides the advantage of a preferred low pressure drop between the initiation of combustion and exhaust from the combustion region. The architecture of reformer  312  provides a lower pressure combustion process because conduits  370  are generally straight conduits offering reduced and controlled resistance to the flow of combustion exhaust gasses. With a lower pressure combustion process, combustion air, e.g., such as is provided at inlet  309  of intake manifold is  307 , may be provided by a relatively lower pressure and relatively less expensive air blower (not shown in FIG.  6 ). 
     FIG. 7 illustrates schematically an alternate combustion system applicable to the various embodiments of the present invention. In FIG. 7, a double-walled counter current combustor  450  includes an inlet manifold  452  receiving a byproduct stream  421  and an air stream  423 . Byproduct  421  is taken from a reformation process as a byproduct but includes a selected amount of hydrogen intentionally left therein as a fuel stock for combustion Byproduct stream  421  travels along an inner conduit  425  and exits conduit  425  in a mixing region  413 . Air stream  423  travels along manifold  452 , generally surrounding and parallel to inner conduit  425  and encounters byproduct stream  421  in mixing region  413 . Mixing region  413  comprises an inner tube  430  carrying therealong the mixture of combustion air, i.e., air stream  423  and fuel gas, i.e., byproduct stream  421 . Tube  430  is closed at one end, i.e., end  430   a  forming a portion of manifold  452 . The open end  430   b  of tube  430 , however, releases mixed fuel gas and combustion air into an outer mixing region  415 . Outer mixing region  415  is defined by an outer tube  432 . Tube  432  is closed at each of its ends  432   a  and  432   b  with manifold  452  passing through end  432   a . A combustion catalyst  440  is distributed throughout regions  413  and  415 . Alternately, combustion catalyst  440  may be localized within tube  430  at or near mixing region  413 . 
     The highest temperature combustion occurs when the mixture of fuel gas and combustion air first encounter catalyst  440 , i.e., at the outlet of manifold  452 . As the gas mixture continues along tube  430  and encounters catalyst  440  therealong, continued combustion occurs but generally at progressively lower temperatures. As the gas mixture continues out of tube  430 , at its open end  430   b , it reverses direction and travels back along tube  432  and encounters more catalyst  400 . As a result, beat energy is produced along the length of tubes  430  and  432  and exhaust gasses exit at the exhaust port  435 . 
     Generally, a significant temperature gradient exists along a combustion catalyst bed, the hottest potion being where the fuel gas and combustion air first encounter the combustion catalyst or igniter device. Such significant temperature gradient can be undesirable, especially when applying the heat energy to a reformation process most desirably conducted at uniform the throughout Under the present invention, combustor  450  provides a more uniform temperature gradient along its length as compared to a conventional combustion bed. The hottest gasses within combustor  450 , i.e., near manifold  452 , release heat energy through tube  430  and into the coolest gasses within combustor  450 , i.e., near exhaust port  435 . By thermally coupling the hottest portion of the gasses with the coolest portion of the gasses a more uniform overall temperature gradient exists along combustor  450 . 
     FIG. 8 illustrates a relationship between the length L of a combustion bed (x axis) and temperature Therealong (y axis). Curve  460  in FIG. 8 illustrates substantially higher temperatures at the beginning of a conventional combustion bed and a significant drop in temperature throughout the conventional combustion bed. Curve  462 , however, illustrates the more uniform, i.e., more flat, temperature gradient obtained by use of combustor device  450 . More particularly, a shallow and fairly level curve  462  indicates a uniform temperature along the length of combustor  450 . Accordingly, combustor  450  provides a more uniform dispersal of heat energy into a reformation region. 
     While illustrated as a generally straight device in FIG. 7, it will be understood that the double-walled architecture of the combustion device  450  may be formed in alternate shapes, e.g., spiral, and applied to the various embodiments of the present invention as a combustion system. 
     In addition to alternate combustion and vaporization features, alternative methods of hydrogen purification may be employed in a steam reformer under the present invention. In addition to tubular and concentric-tubular architectures, planar membrane structures may also be employed in a steam reformer with internal hydrogen purification. 
     FIG. 9 illustrates schematically a further embodiment of a steam reformer with internal hydrogen purification according to the present invention and using planar membrane structures. In FIG. 9, reformer  512  includes an outer metal tube  550  having shoulders  550   a  and  550   b  at each open end thereof. Within tube  550 , a metal reforming catalyst tube  552  and a metal polishing catalyst tube  556  lie in generally parallel relation along the length of tube  550 . As may be appreciated, however, a variety of geometric configurations and relationships between tubes  552  and  556  may be employed. Reforming catalyst tube  552  contains a reforming catalyst  502  and establishes a reformation region  562 . Similarly, polishing catalyst tube  556  contains a polishing catalyst  504  and establishes a polishing region  564 . An end plate  590  and gasket  592  couple to shoulder  550   a  and seal tube  550 . Inlet port  530  carries a liquid feed stock, e.g., methanol and water, through end plate  590  and into vaporization coil  530   a . In the particular embodiment illustrated, coil  530  wraps about one end of tube  552  and sits near the combustion exhaust port  538  provided in end plate  590 . Vaporization coil  530   a  couples to end  552   a  of tube  552  whereby vaporized feed stock exits coil  530   a  and enters reformation region  562 . 
     A plate membrane module  554  couples to shoulder  550   b  and seals end  550   b  of tube  550  to complete a combustion region  560  within tube  550 , but external of tubes  552  and  556 . Plate membrane module  554  couples to tube  552  to receive a reformate-rich gas flow  501 , couples to conduit  529  to provide a product or hydrogen stream  503 , and couples to conduit  521  to provide a byproduct stream  505  as fuel stock to support combustion in region  560 . More than one tube  552  may be used. Byproduct stream  505 , as in earlier-described embodiments of the present invention, intentionally includes a given amount of hydrogen not taken from the reformation process and applied to the combustion process. Conduit  521  carries byproduct steam  505  from plate membrane module  554  through a pressure let down valve  523  and into combustion region  560  at the inlet port  525  thereof. Adjacent fuel inlet port  525 , an air inlet port  528  admits air, e.g., forced by blower (not shown), into combustion region  560 . Alternatively, a manifold, as in earlier-described embodiments of the present invention, may be used to admit air and byproduct stream  505  into combustion region  560 . As the byproduct stream  505  enters region  560 , and intermixes with the combustion air at port  528 , it continues past an igniter  575 . Igniter  575  initiates combustion of the mixture of byproduct stream  505  and combustion air thereby supporting a combustion process within combustion region  560 . As may be appreciated, heat developed in this combustion process support vaporization of feed stock in the vaporization coil  530   a  and thereby provides vaporized gasses to the reformation region  562 . Heat from combustion in region  560  also serves to directly heat the reforming region  562  and to heat the polishing region  564 . 
     Conduit  529  carries the product (hydrogen) stream  503  into end  556   b  of polishing catalyst tube  556 . More than one conduit  529  and more than one tube  556  may be used. Product stream  503  passes through the polishing region  564 , where undesirable elements are neutralized, and the final purified hydrogen product passes from the end  556   a  of tube  556  and out the outlet port  514 . For example, when the polishing catalyst  504  is a methanation catalyst, carbon monoxide and carbon dioxide present in product steam  503  are converted to methane as described previously. 
     FIG. 10 illustrates in exploded view the plate membrane module  554  and its relationship to tube  552  and to conduits  521  and  529 . Plate membrane module  554  includes end plates  554   a  and  554   b . A series of membrane envelope plates  590  stack between end plates  554 . In the particular embodiment of the invention illustrated in FIG. 10, three such membrane envelope plates  590 , individually  590   a - 590   c , stack between end plates  554 . End plates  554   a  and  554   b  and membrane envelope plates  590  are all generally rectangular and have corresponding dimensions. Other geometries, such as circular, may be used rather than the rectangular geometry shown. In other words, plates  554   a - 554   b  and  590   a - 590   c  stack like a deck of cards and couple together, e.g. by brazing, to form module  554 . End plate  554   b  is a solid planar structure. End plate  554   a , however, includes inlet and outlet ports for coupling to other portions of reformer  512  (shown in FIG.  9 ). In particular, reformation catalyst tube  552  couples to a reformate-rich inlet port  592   a  to receive the products of reformation, i.e., to receive the reformate rich flow  501 . Conduit  521  couples to a reformate-depleted outlet port  594   a  to take from module  554  the byproduct stream  505 . In the particular embodiment illustrated, module  554  has two product outlet ports, individually  596   a  and  598   a , providing product stream  503 . However, only one product outlet port may be used in some embodiments. Conduit  529 , shown twice in FIG. 10, couples to ports  596   a  and  598   a  to collect the product stream  503  therefrom All of the ports  592   a ,  594   a ,  596   a , and  598   a , need not be located on end plate  554   a . Rather, one or more of the ports may be located on end plate  554   b  as desired or necessary in a planar configuration. 
     Each membrane envelope plate  590  includes ports positioned in locations corresponding to ports  592   a ,  594   a ,  596   a , and  598   a  of end plate  554   a . When stacked and operating as the plate membrane module  554 , these various ports align and provide conduits to and from the filtration process executed by module  554 . Each of plates  590   a - 590   c  include a product port  598 , individually  598   b - 598   d . Ports  598   a - 598   d  align and cooperate to provide a conduit for product stream  503  out of module  554  and into conduit  529 . As will be explained more fully hereafter, the product, i.e., hydrogen, enters ports  598   b - 598   d  laterally within the corresponding membrane envelope plate  590 . Each of membrane envelope plates  590   a - 590   c  include also a port  596 , individually  596   b - 596   d , aligned with outlet port  596   a  of end plate  554   a . Ports  596   a - 596   d  also carry product stream  503  away from plate membrane envelopes  590  and into conduit  529 . As with ports  598   b - 598   d , ports  596   b - 596   d  receive the hydrogen stream  503  laterally from within the corresponding membrane envelope plate  590 . 
     Ports  592   b - 592   d  align with port  592   a  of end plate  554  and hereby provide a conduit for introduction of the hydrogen-rich reformate flow  501  from tube  552  and into membrane envelope plates  590 . Each of plates  590   a - 590   c  include a byproduct port  594   b - 594   d . Ports  594   b - 594   d  align with port  594   a  of end plate  554   a  to provide a conduit for the byproduct stream  505  away from membrane envelope plates  590 . Forcing the hydrogen-rich reformate flow  501  into port  592   a  produces the byproduct flow  505  at port  594   a  for application to the comb on process within combustion region  560  and produces the product stream  503  for application to the polishing region  564 . 
     Each of the membrane envelope plates  590  itself includes a stack of individual plate elements. FIG. 11 illustrates in exploded view the set of plate elements found in each of the membrane envelope plates  590 . In FIG. 11, each of the plate elements include ports establishing communication through the membrane envelope  590  as described above in connection with FIG.  10 . Some of these ports, however, are “open” laterally into the corresponding plate element and thereby provide lateral access to portions of module  554 . 
     Each membrane envelope plate  590  includes a left spacer plate  600  and right spacer plate  602  as the outer most plates in the stack. Generally, each of spacer plates  600  and  602  are “frame” sutures defining an inner open region  604 . Each inner open region  604  couples laterally to ports  592  and  594 . Port  592  thereby admits flow  501  into open region  604  and port  594  thereby carries byproduct stream  505  out of open region  604 . Ports  596  and  598 , however, are closed relative to open region  604  thereby isolating the product stream  503 . 
     Each membrane envelope plate  590  also includes a left membrane plate  606  and a right membrane plate  608 , each adjacent and interior to a corresponding one of plates  600  and  602 . Membrane plates  606  and  608  each include as a central portion thereof a palladium alloy membrane  610  secured to an outer metal frame  607 . In plates  606  and  608 , all of the ports  592 ,  594 ,  596 , and  598  are closed relative to the palladium alloy membrane  610 . Each palladium alloy membrane  610  lies adjacent to a corresponding one of open regions  604 , i.e., adjacent to the hydrogen-rich reformate flow  501  arriving by way of port  592 . This provides unity for hydrogen to pass through the palladium alloy membrane  610  of the adjacent membrane plate  606 . The remaining gasses, i.e., the byproduct stream  505 , leave open region  604  through port  594 . 
     A screen plate  609  lies intermediate membrane plates  606  and  608 , i.e., on the interior or permeate side of each of membranes  610 . Screen plate  609  includes an outer frame  611  and carries in a central region thereof a screen  612 . Ports  592  and  594  are closed relative to the central region of screen plate  609 , thereby isolating the byproduct stream  505  and the reformate-rich flow  501  from the product stream  503 . Ports  596  and  598  are open to the interior region of plate screen  609  carrying screen  612 . Hydrogen, having passed through the adjoining membranes  610 , travels along and through screen  612  to the ports  596  and  598  and eventually to conduit  529  as the product stream  503 . 
     As the hydrogen-rich reformate flow  501  enters port  592   a  and forces its flow against membranes  610 , hydrogen passes therethrough as the product stream  503  and along ports  596  and  598 . The byproduct steam  505  diverts at the membranes  610  and travels along port  594  to conduit  521 . 
     A variety of methods, including brazing, gasketing, and welding, may be used, individually or in combination, to achieve gas-tight seals between plates  600 ,  602 ,  606 ,  608 , and  609 , as well as between membrane envelopes  590   a-c.    
     Screen  612  not only provides a flow path for the product flow  503 , but also bears the pressure differential applied to membranes  610  to force hydrogen, i.e., product stream  503 , across membranes  610 . While illustrated only as a screen structure in FIG. 11, it will be understood with a variety of structures may be used within an open region of screen plate  609  to provide the support function against pressure applied to membranes  610  and to provide a flow for product stream  503 . To the extent that palladium alloy membranes  610  are better supped by an appropriate structure, e.g., screen  612 , thinner and less expensive palladium alloy membranes  610  may be employed. Alterative materials to screen  612  include porous ceramics, porous carbon, porous metal, ceramic foam carbon foam, and metal foam. 
     As discussed throughout this specification, use of thin, less expensive palladium alloy membranes significantly reduces the cost of a steam reformer under the present invention. While it is recognized that use of such thin palladium alloy membranes will result in some contaminants passing into the product stream  503 , subsequent purification steps may be taken, e.g., such as illustrated in several embodiments of the present invention. 
     Manufacturing steps taken in manipulation of the thin palladium alloy membranes, particularly in establishing a gas-tight seal relative to such membranes, must take into account the delicate nature of such thin palladium alloy membranes. In particular, conventional welding or brazing manufacturing steps, i.e., steps including a liquid-phase, cannot by applied to extremely thin (typically &lt;50 microns) palladium alloy membranes. In particular, when liquid phase material contacts the thin palladium alloy membrane it dissolves and melts the membrane and, due to the extremely thin nature of the membrane, cannot serve as an acceptable manufacturing step. There are a variety of ways to establish a gas-tight seal relative to a thin palladium alloy membrane, however, the subject matter of the present invention proposes a particular method of manufacturing to achieve a gas tight seal of a thin palladium alloy membrane without causing significant damage to, i.e., leaks in, the palladium alloy membrane. 
     Under the present invention, a palladium alloy membrane may be attached and form a gas tight seal relative to an adjoining structure by means of an intermediate foil attached by ultrasonic welding. The method of manufacture proposed herein may be applied to the tubular form of membrane modules, e.g., such as shown in FIG. 3, or to plate form membrane structures such as shown in FIG.  11 . Membrane tube  54  may then be coupled by brazing the foil to end caps  304 . In the plate membrane form of the present invention, membranes  610  carrying a foil may be attached by brazing the foil to the surrounding frame  607  of plates  606  and  608 . When applied to joining metals, ultrasonic welding strips away and cleans the metal surfaces to such extent that contact between such ultra-clean metals results in joining by solid state intermetallic diffusion. The ultrasonic action scrubbing the mating surfaces of the materials may be done under pressure such as 20 to 60 psi. Once these materials contact, the metal atoms diffuse together and thereby establish a gas tight seal. Important to note, ultrasonic welding does not require a liquid phase and when properly executed does not present opportunity for deterioration of a thin palladium alloy membrane. Because of the relatively low temperature requirements of ultrasonic welding, very little warping of material occurs. Accordingly, ultrasonic welding is particularly well suited for establishing a gas tight seal relative to an ultra thin palladium alloy membrane. 
     Under the disclosed embodiment of the present invention, ultrasonic welding is used to attach a copper or nickel alloy foil to the surface of the thin palladium alloy membrane. Once this additional copper or nickel alloy layer has been ached it is brazed or welded to an adjoining material e.g., end caps  304  or frames  607 . 
     FIGS. 12-16 show the components and manufacturing steps used in constructing a membrane module, e.g., such as illustrated in FIGS. 1,  5 , and  6  generally described as a tubular palladium alloy structure supported with end caps. FIGS. 12 and 13 illustrate a palladium alloy foil  702  and a copper or nickel frame  706  joined, respectively, in preparation for joining by ultrasonic welding as illustrated in FIG.  14 . FIG. 15 shows the combined palladium alloy foil and copper or nickel frame assembly  720  rolled into a tubular structure and again joined by ultrasonic welding to maintain the tubular structure. In this configuration, the end portion of the tubular assembly bears exposed sections of copper or nickel material. The end caps are then brazed directly to this exposed portion of copper or nickel frame to complete the gas-tight structure. 
     With reference to FIGS. 12-16, a tubular hydrogen-permeable metal membrane  700  (FIG. 17) was prepared by the following general method of construction. Both Pd-40Cu and Pd-25Ag foil (nominally 25 micron thick) were used as the hydrogen-permeable membrane  702  (shown individually in FIG.  12 ). A tension spring  704  (FIGS.  15 - 17 ), composed of either carbon steel or stainless steel, was used as support within the tubular membrane structure  700 . 
     The first step was to join the palladium-alloy foil  702  to the copper foil frame  706  (nominally 50 microns to 125 microns thick) as shown in FIG.  14 . The palladium-alloy foil  702  was typically 8.9 cm wide by 26.4 cm long, and the copper foil frame  706  was typically 10.2 cm wide by 27.9 cm long with a cut out center, equally spaced from all four sides, approximately 7.6 cm wide by 24.1 cm long. This provided a 0.6 cm overlap  710  (FIG. 14) between the palladium-alloy foil  702  and the copper foil frame  706  as foil  702  occupied the cut out center of frame  706 . 
     Ultrasonic welding was used to establish peripheral gas-tight seals  712  between the palladium-alloy foil  702  and the copper foil frame  706  at all four edges of the palladium-alloy foil  702 . An Amtech (Shelton, Conn.) Ultraseam Model 40 welder was used. This welder operates at 40 kHz and delivers up to about 750 W of power to the ultrasonic transducer. Both the horn (connected to the ultrasonic transducer) and the anvil rotate at a rate selected by the operator during normal operation of the welder. Welding is accomplished by placing metal between the horn and anvil and applying power to the ultrasonic transducer. 
     The horn and anvil for the ultrasonic welder are circular, 7.0 cm diameter, with a bearing surface strip about 0.2 cm wide and finished to a surface roughness equivalent to an EDM #3 finish. The horn and anvil were hard coated with titanium nitride. Typical welding parameters are: 40% full power to the transducer, 40 psig applied pressure between the horn and the anvil, 4 rpm rotation rate for the horn and anvil, and the horn “floating” on the foil pieces to be welded (i.e., no preset separation between the horn and anvil). To ensure that the metals are bonded during the welding process, the adjoining metal surfaces should be cleaned of residues such as oxidation, grease and oils, dirt etc. It is also considered beneficial if the palladium-alloy membrane foil  702  and the copper foil frame  706  are annealed prior to welding, since soft metals are more reliably joined by ultrasonic welding than are hard metals. 
     After welding the palladium-alloy foil  702  to the copper foil frame  706  to establish the membrane assembly  720  as shown in FIG. 14, the welded seals  712  were examined for leaks by a standard dye penetration test. If no leaks were found, membrane assembly  720  was cleaned of excess dye and then wrapped, as illustrated in FIG. 15, lengthwise around a 2.8 cm (outside diameter) tension spring  704 , 27.9 cm long and made from either stainless steel or carbon steel wire nominally 0.25 cm diameter. The overlap  722  of opposite edges of assembly  720  was then joined by ultrasonic welding to form lap seal  724  along the length of the now tubular structure. Lap seal  724  was established by using the ultrasonic welding parameters specified above. Lap seal  724  was then folded over against the membrane tube to conform to a cylindrical shape. Copper end caps  730  (FIG. 16) were then fitted to the membrane tube ends and brazed in place at joints  731  (FIG. 17) using standard copper/phosphorous or copper/silver/phosphorous brazing alloys and a hydrogen/air or hydrocarbon/air (e.g., methane, propane, or acetylene) torch. The brazing alloy is applied only to copper end caps  730  and copper foil frame  706 . Important to note, establishing braze joints  731  coupling end caps  730  to the cylindrical form of assembly  720  does not expose the delicate palladium alloy membrane foil  702  to liquid phase material, i.e., does not destroy the delicate, thin foil  702 . Because the various ultrasonic welds  712  and  724  establish a gas-tight seal and the braze joints  731  also establish a gas-tight seal, hydrogen passes from a reformation process external of tube  700  only through foil  702 . At least one end cap  730  was fitted with a port  732  and outlet  734  to collect the permeate hydrogen from the inside, or bore, of the membrane tube. Within tube  700 , a methanation catalyst  740  may be employed whereby purified hydrogen may be taken from membrane tube  700  as described herein-above. Thus, membranes  700  so constructed are suitable for the high pressure feed gas to be passed over the external surface of the membrane tube, with the permeate collected at the interior surface of the membrane. 
     FIG. 18 illustrates in perspective and partially broken away, a steam reformer  812  according to another embodiment of the present invention. Reformer  812  employs an isolated vaporization chamber  820  similar to that of reformer  312  (FIG.  6 ). More particularly, reformer  812  receives at input conduit  830  a feed stock and conduit  830  delivers this mixture into vaporization chamber  820  at the vaporization coil  830   a . Elevated temperatures within chamber  820  vaporize the feed stock provided at input conduit  830 . Coil  830   a  passes into and opens into reformation chamber  862 . Vaporized fuel thereby enters the reformation chamber  862 . Chamber  862  is filled with a reformation catalyst  863  and steam reformation occurs within steam reformation region  862 . A reformation product stream  801  exits reformation region  862  at the outlet conduit  852 . Conduit  852  delivers product stream  801  to membrane module  854 . Module  854  separates stream  801  into a byproduct stream  805  and a hydrogen-rich stream  803 . 
     The hydrogen-depleted reformate byproduct stream  805  travels along conduit  821  from membrane module  854  to a pressure let down valve  823  (schematically illustrated in FIG. 19) and then to a manifold  807 . Manifold  807  operates in similar fashion to manifold  207  of reformer  212  (FIG.  5 ). More particularly, manifold  807  introduces an air supply taken from inlet  809 , e.g., from a forced air supply, and intermixes it with stream  805  at a mixing region  813 . An igniter  819  ignites the intermixed air and stream  805  and the resulting combustion elevates temperatures within the vaporization chamber  820 . As in earlier described embodiments of the present invention, stream  805  includes by design a certain amount of hydrogen not taken across the palladium alloy membranes of module  854 . Stream  805  thereby serves as a fuel source for combustion within vaporization chamber  820 . 
     Exhaust ports  842  carry the combustion byproducts from chamber  820  through combustion conduits  843  and out exhaust ports  838 , shown more clearly in FIG.  19 . Conduits  843 , however, pass through the reformation chamber  842  and thereby distribute heat throughout reformation region  862  in support of the reformation process therein. Exhaust conduits  843  may take a variety of forms, including finned tubes and spirals, to provide substantial surface area and desirable uniform distribution of heat throughout reformation region  862 . 
     Still referring to FIG. 19, product stream  803  emerging from membrane module  854  travels through a conduit  856  having therein a methanation catalyst  804 . Conduit  856  passes through the reformation region  862  and through the vaporization chamber  820  and thereby collects heat energy therefrom in support of the methanation process occurring in conduit  856 . The distal end  814  of conduit  856  provides a product outlet, i.e., provides hydrogen in sufficiently purified form for application to, for example, PEM fuel cell  16  (FIG.  1 ). 
     FIGS. 20 and 21 illustrate a membrane frame and permeate frame, respectively, employed in the membrane module  854  of FIGS. 18 and 19. In FIG. 20, the membrane frame  870  includes a circular copper or nickel frame  870   a  with a rectangular center cut out  870   b . A rectangular palladium alloy membrane  870   c , oversized relative to center cut out  870   b , is joined at seals  870   d  to the frame  870   a . By using ultrasonic welding to establish seals  870   d  about the periphery of palladium alloy membrane  870   c , a gas-tight seal results between membrane  870   c  and frame  870   a . Finally, membrane frame  870  includes a feed manifold aperture  872  and a permeate manifold aperture  874 . 
     In FIG. 21, a permeate frame  876  includes a central cut out  876   a . Cut out  876   a  includes a first portion generally rectangular and corresponding generally in dimension to membrane  870   c . This portion of cut out  876   a  is occupied by a wire mesh spacer  876   b . Other materials that may be used in place of wire mesh spacer  876   b  include porous and foamed ceramic, porous and foamed carbon, and porous and foamed metal. A second portion of cut out  876   a  extends peripherally outward to define a permeate manifold  884  and containing therein a wire mesh insert  876   c . Frame  876  may be recessed to accommodate face-to-face contact with frame  870 , i.e., to accommodate membrane  870   c  as attached to the face of frame  870   b . Finally, permeate frame  876  includes a feed manifold aperture  882 . 
     As may be appreciated, frame  870  and frame  876  correspond in outer dimensions and certain portions align when stacked. For example, feed manifold  872  aligns with feed manifold  882 . Also, permeate manifold  874  may be aligned with the substantially larger permeate manifold  884 . Thus, when appropriately stacked with other components, described more fully hereafter, a membrane module  854  may be established to separate stream  801  into streams  803  and  805  as described herein-above. 
     FIG. 22 illustrates use of frames  870  and  876  stacked to form a series flow arrangement for module  854 . In FIG. 22, permeate frame  876  occupies a central position with a membrane frame  870  on each side, i.e., above and below as illustrated in FIG.  22 . Feed manifold  882  of frame  876  aligns with feed manifolds  872  of frames  870 . Permeate manifold  884  of frame  876  aligns with permeate manifolds  874  of frames  870 . Feed frames  880  are located at the outward side of each of frames  870 , i.e., above and below frames  870  as illustrated in FIG.  22 . Each frame  880  is of circular shape corresponding to that of frames  870  and  876 . Each frame  880  includes an open central region extending laterally outward to correspond with, i.e., to fluidly couple with, aligned apertures  872  and  882  of frames  870  and  876 . Each frame  880  also includes a permeate manifold aperture  887  isolated relative to the center cut out portion. 
     Thus, the arrangement illustrated in FIG. 22 offers a series flow configuration directing the feed gas sequentially across successive membranes  870   c . For example, consider a feed gas traveling upward through the component stack illustrated in FIG.  22 . As the feed gas enters the center open region of the lowest frame  880 , hydrogen has opportunity to pass through the membrane  870   c  of the lowest membrane frame  870 . As may be appreciated, any such hydrogen which does cross the lowest membrane frame  870  migrates into the open region of permeate frame  876  and can then migrate by way of permeate manifolds  884 ,  874  and  887  out of the component stack for harvest. The series flow arrangement of FIG. 22 offers a second opportunity for feed gas to pass through a membrane  870   c . More particularly, feed gas travels from the open center region of the lowest frame  880  into the feed manifold  872  of the lowest frame  870 , through the feed manifold  882  of the permeate frame  876 , through the feed manifold  872  of the upper frame  870 , and into the central open region of the upper most feed frame  880 . In this open central region, the feed gas is exposed to a second palladium alloy membrane. More particularly, hydrogen remaining in the feed gas as it enters the open region of the upper frame  880  is exposed to the membrane  870   c  of the upper membrane frame  870 . Any such hydrogen crossing this upper membrane  870   c  enters the central open region of permeate frame  876  and may then travel along manifolds  884 ,  874  and  887  for harvest. 
     As may be appreciated, additional similar components may be stacked in the arrangement illustrated in FIG. 22 to provide successive opportunity for feed gas exposure to palladium alloy membranes in series fashion. An actual implementation would include end plates and necessary outlet and inlet ports for harvesting hydrogen gas and forcing feed gas into the component stack as described earlier in connection with the plate form membrane module  554 . 
     In such series flow arrangement as illustrated in FIG. 22, the feed gas stream is directed to flow over a first membrane surface, then a second membrane surface, and so on as desired. Such series flow arrangement encourages mixing of the feed gas stream components after passage over each membrane in the membrane module component stack. 
     FIG. 23 illustrates a second arrangement for membrane module components providing a parallel flow configuration, i.e., where the feed stock stream divides and has one opportunity for exposure to a palladium alloy membrane. In FIG. 23, permeate frames  870 ′ correspond generally to the previously described permeate frames  870 , but include also a raffinate manifold  875 . Similarly, permeate frame  876 ′ corresponds to the previously described permeate frame  876 , but includes also a raffinate manifold  885 . Raffinate manifolds  885  and  875  align for fluid communication therebetween when frames  870 ′ and  876 ′ stack as illustrated in FIG.  23 . 
     The arrangement illustrated in FIG. 23 establishes a parallel flow of feed gas across the palladium alloy membranes  870   c . More particularly, consider a feed gas entering the open central region of the lower feed frame  880 . Such feed gas is exposed to the membrane  870   c  of the lower frame  870 ′. Concurrently, some of the feed gas may divert across the lower membrane  870   c  and then travel along the raffinate channels established by apertures  875  and  885 , or along the apertures  872  and  882  and eventually enter the open region of the upper feed frame  880 . At this point, the feed gas is exposed to the membrane  870   c  of the upper frame  870 ′. Accordingly, hydrogen present therein may migrate across membrane  870   c  and into the center open region of permeate frame  876 ′. Thereafter, such hydrogen would pass along manifolds  884  of frame  876 ′ and  874  of frames  870 ′ and eventually through apertures  887  for harvest. In such parallel flow configuration, all of the feed channels over the membrane surfaces are fed from a common feed supply manifold. This favors low pressure drop for the flowing feed gas stream. 
     The arrangement of membrane component stacking as illustrated in FIGS. 22 and 23 allows series or parallel, respectively, flow of the feed gas through the membrane module. Because the feed frames  880  are compatible, it is possible to combine series flow and parallel flow stacking arrangements in a single membrane module. More particularly, an arrangement such as illustrated in FIG. 22 may be stacked adjacent to an arrangement as illustrated in FIG.  23 . Multiple combinations of such arrangements may be provided in a single membrane module as desired to establish a given first-stage of the hydrogen purifier as illustrated in the present invention. 
     FIG. 24 illustrates an additional frame component which may be incorporated into a membrane module. In FIG. 24, exhaust frame  890  includes a feed manifold aperture  892 , a permeate manifold  894 , and a raffinate manifold  895 . As may be appreciated, stacking exhaust frame  890  in a membrane module such as illustrated in FIGS. 22 and 23 allows passage of feed gas through aperture  892 , hydrogen product through aperture  894 , and passage of raffinate through aperture  895  without otherwise affecting operation of the membrane modules as described herein above. Exhaust frame  890  includes also an exhaust manifold  897  providing a lateral passage for hot combustion exhaust gas through frame  890 . As may be appreciated, exhaust manifold  897  is isolated relative to apertures  892 ,  894 , and  895 . Hot exhaust gas passing through exhaust frame  890  elevates the temperature of a membrane module including frame  890  and thereby speeds heating of the membrane module during start up. Exhaust frame  890  may be incorporated into the stacked component structure of a membrane module along with the other frame members by conventional brazing, gasketing, or welding techniques as described herein. 
     Stacking and construction of the planar-type components as illustrated herein may be executed by use of conventional brazing, gasketing, or welding methods to create a stacked component membrane module. To establish seals between the stacked components of the modules, i.e., the membrane assemblies, permeate and feed frames, exhaust frame members, and end plates, brazing, gasketing, or welding methods are appropriate and may be used without deterioration of the delicate palladium alloy membranes  870   c . For example, brazing alloy may be applied between adjoining frame elements and the entire assembly heated to achieve a brazed joint within a controlled-atmosphere brazing furnace. Alternatively, the module may be assembled then welded from the exterior, for example, by using an orbital pipe-welding machine. In yet another proposed method of manufacture of a sealed membrane module, the components are stacked and sufficient pressure applied to the stack such that all joining surfaces are in intimate pressurized contact. Then, heating the entire assembly to between 500 and 800 degrees Celsius for two hours to eight hours results in intermetallic diffusion between the adjoining surfaces to create a sealed joint. Yet another method for achieving gas-tight seals is to use conventional flexible (compressible) graphite gaskets or composite graphite-metal gaskets. 
     Thus, a variety of embodiments, configurations and alternatives have been shown for implementing steam reformation under the present invention. Various experiments and testing procedures have been conducted to prove the viability of steam reformation under the present invention and will be described in general terms as follows. 
     As disclosed earlier in the preferred embodiments of the present invention, the hydrogen-rich reformate stream is purified by means of a two-stage hydrogen purifier that is also the subject of this invention. The two-stage hydrogen purifier utilizes a membrane for the first stage to accomplish a bulk separation of hydrogen from the reformate stream. Then, the permeate hydrogen from the first-stage membrane is subjected to a polishing step (the second stage) to further reduce the concentration of selected impurities, such as CO and CO 2 , to acceptably low levels as required for the hydrogen to serve as the fuel for PEM fuel cells. For instance, a typical PEM fuel cell using a standard platinum electrocatalyst requires hydrogen containing &lt;10 ppm CO and, preferably, &lt;100 ppm CO 2  to achieve maximum power output from the fuel cell. 
     The membrane used in the first stage of the purifier is selected from hydrogen-permeable and hydrogen-selective high-temperature membranes. Thermally-stable membranes allow the purifier to be thermally integrated with the reformer, eliminating the requirement for cooling the hydrogen-rich reformate prior to purification, thereby simplifying the overall system and reducing the cost of the system. 
     Preferred membranes are microporous ceramic, microporous carbon, microporous metallic, and dense metallic membranes. Especially preferred are thin membranes composed of hydrogen-permeable and hydrogen-selective metals including palladium and palladium alloys, nickel and nickel alloys, and the Group 4 and Group 5 metals and their alloys. Thin membranes composed of Pd-40Cu are especially preferred for high hydrogen permeability and durability. In particular, the Pd-40Cu alloy exhibits highest hydrogen permeability and, therefore, most favorable economics, if the Pd-40Cu alloy contains low concentrations of carbon and oxygen. The following table demonstrates the correlation between high hydrogen permeability (represented as hydrogen flux through the 25 micron thick membrane at 100 psig hydrogen, 400 degrees Celsius) and low carbon content. 
     
       
         
           
               
               
               
            
               
                   
                   
               
               
                   
                 Hydrogen Flux 
                 Concentration, ppm 
               
            
           
           
               
               
               
               
               
            
               
                   
                 std. ft 3 /f 2  • hr 
                 Carbon 
                 Oxygen 
                 Silicon 
               
               
                   
                   
               
               
                   
                 240 
                  40 
                 25 
                 10 
               
               
                   
                 125 
                  56 
                 29 
                 39 
               
               
                   
                 115 
                 146 
                 25 
                 15 
               
               
                   
                  56 
                 219 
                 25 
                 27 
               
               
                   
                   
               
            
           
         
       
     
     The hydrogen-permeable membrane does not have to exhibit an exceptionally high selectivity for hydrogen over other gases, since the second stage of the hydrogen purifier serves to further reduce the concentration of selected impurities that remain in the permeate hydrogen after passing through the membrane. Selectivity is defined as the ratio of the permeation rate of hydrogen divided by the permeation rate of an impurity. The selectivity for hydrogen exhibited by the membrane is at least 20, and preferably at least 50. 
     Use of such membranes with relatively low selectivity will not yield a permeate hydrogen stream that is of acceptable purity for use in a PEM fuel cell. For example, steam reforming methanol yields a hydrogen-rich reformate stream containing about 25% combined CO and CO 2 . A membrane with a hydrogen selectivity of 50 will produce a permeate hydrogen stream containing 25%/50=0.5% combined CO and CO 2 . However, this level of impurities is readily treated with the polishing step (the second stage). Thus, the two-stage hydrogen purifier allows the use of membranes that, due to imperfections or otherwise, have relatively low selectivity for hydrogen over other gases. Such membranes are much less expensive than are membranes that have substantially higher hydrogen selectivity (e.g., hydrogen selectivity &gt;1000). 
     To obtain a very thin metal hydrogen-permeable membrane without sacrificing mechanical strength of the membrane, the thin hydrogen-permeable membrane is supported by a support layer. The support layer must be thermally and chemically stable under the operating condition of the membrane, and the support layer is preferably porous or containing sufficient voids to allow hydrogen that permeates the thin membrane to pass substantially unimpeded through the support layer. Examples of support layer materials include metal, carbon, and ceramic foam, porous and microporous ceramics, porous and microporous metals, metal mesh, perforated metal, and slotted metal. Especially preferred support layers are woven metal mesh (also known as screen) and tubular metal tension springs. 
     In the event that the membrane is a thin hydrogen-permeable metal (e.g., palladium alloys) and the support layer is composed of a metal, the metal used for the support layer is preferably selected from a corrosion-resistant alloy, such as stainless steels and non-ferrous corrosion-resistant alloys comprised of one or more of the following metals: chromium, nickel, titanium, niobium, vanadium, zirconium, tantalum, molybdenum, tungsten, silicon, and aluminum. These corrosion-resistant alloys have a native surface oxide layer that is chemically and physically very stable and serves to significantly retard the rate of intermetallic diffusion between the thin metal membrane and the metal support layer. Such intermetallic diffusion, if it were to occur, often results in significant degradation of the hydrogen permeability of the membrane and is undesirable [see Edlund, D. J., and J. McCarthy, “The Relationship Between Intermetallic is Diffusion and Flux Decline in Composite-Metal Membranes: Implications for Achieving Long Membrane Lifetimes” J. Membrane., 107 (1995) 147-153]. 
     The rate of intermetallic diffusion between the thin metal membrane and the metal support layer may also be retarded by applying certain non-porous coatings to the metal support. Suitable coating materials include aluminum oxide; aluminum nitride; silicon oxide; tungsten carbide; tungsten nitride; oxides, nitrides, and carbides of the Group 4 and Group 5 metals; boron nitride; and boron carbide. Many of these coating are employed as hard coatings on tools and dies, and as release agents. 
     The second stage of the hydrogen purifier is designed to further reduce the concentration of impurities that adversely affect the power output and operation of the PEM fuel cell. Particularly, the second-stage polishing step is designed to remove CO and, to a lesser degree, CO 2  from the hydrogen that has permeated the first-stage membrane. Furthermore, the second-stage polishing step is conducted at or near the operating temperature of the first-stage membrane and the reformer, thereby eliminating the need to substantially heat or cool the hydrogen stream before passage through the polishing step. By thermally integrating the polishing step, the need for heat exchangers is eliminated and the overall operation of the system is simplified and the cost of the system is reduced. 
     Suitable chemical operations for the second-stage polishing step include preferential oxidation of CO, a widely practiced method for removing CO from hydrogen fuel streams for PEM fuel cells [Swathirajan, S., and H. Fronk, “Proton-Exchange-Membrane Fuel Cell for Transportation” Proceedings of the Fuel Cells &#39;94 Contractors Review Meeting, DOE/METC-94/1010, Aug. 17-19(1994)105-108]. However, selective oxidation only removes CO from the hydrogen stream, it does not reduce the CO 2  content. In fact, selective oxidation increases the CO 2  content of the hydrogen. A preferred chemical operation for the polishing step is methanation, which removes both CO and CO 2  from the hydrogen stream, as represented by the following chemical reactions: 
      CO+3H 2 =CH 4 +H 2 O 
     
       
         CO 2 +4H 2 =CH 4 +2H 2 O 
       
     
     Methanation occurs rapidly at &gt;300° C. in the presence of a catalyst, such as nickel, palladium, ruthenium, rhodium, and platinum. Preferably, methanation is conducted at 400° C. to 600° C. in the presence of a commercial supported nickel reforming or methanation catalyst such as R1-10 and G1-80 manufactured and sold by BASF. 
     As the embodiments described earlier have shown, the first stage and second stage of the hydrogen purifier can be integrated so that they are in close proximity, thereby minimizing heat loss as well as reducing the size, weight, and cost of the hydrogen purifier. For example, if a tubular membrane is used as the first stage, the second-stage polishing step may be located within the bore of the membrane tube at the permeate side of the membrane. If a plate-type membrane is selected, the polishing step may be located at the permeate side of the membrane between membrane plates, or it may be located in a tube or other shape that is directly connected to the plate-type membrane at the permeate-hydrogen discharge port. Furthermore, if the membrane is supported for strength, and if the polishing step is methanation, the methanation catalyst may be incorporated within the support for the membrane. For instance, the membrane support may comprise a nickel or other metal mesh with a high nickel surface area. 
     While previously disclosed embodiments of the invention have shown the two-stage hydrogen purifier as an integral part of the fuel processor, it will be appreciated that the two-stage hydrogen purifier may function external to a conventional process for hydrogen manufacture (e.g., steam reformer, partial-oxidation reactor, or autothermal reformer). 
     Concerns over safety call for use of non-flammable fuel feedstocks for use to produce hydrogen by the steam-reforming process. The advantages of using non-flammable fuel feedstocks include elimination of fire or explosion danger due to vapors from the fuel feedstock accumulating in enclosed environments and, for military applications, elimination of fire or explosion risk from hot metal fragments striking and penetrating fuel storage tanks. 
     Non-flammable fuel feedstocks for generating hydrogen by steam reforming and as disclosed in this invention include polyhydroxy alcohols and polyethers that are miscible with water. As used herein, non-flammable means that combustion in normal air at about 1 atm. pressure is not self-sustaining. Preferred fuels include ethylene glycol, propylene glycol, and the glycol ethers of ethylene glycol and propylene glycol (e.g., diethylene glycol). These fuels are collectively called glycols. When mixed with a stoichiometric amount of water for steam reforming (e.g., two molar equivalents water to one molar equivalent ethylene glycol; and four molar equivalents water to one molar equivalent propylene glycol), these fuel feedstocks are not flammable even when subjected to a propane/air flame from a torch. The flame merely heats the glycol/water mixture until the water in the mixture boils. Provided substantial water is still present in the glycol/water mixture, combustion is not supported. 
     The non-flammable nature of the glycol/water mixtures is due to the very low vapor pressure of the glycol component (e.g., ethylene glycol and propylene glycol). For instance, the vapor pressure of ethylene glycol is only 20 torr at 100° C. Furthermore, the water component of these mixtures, in addition to being a necessary reactant for steam reforming, serves two functions that contribute to the non-flammable nature of these glycol/water mixtures. First, water in the mixture serves, by evaporative cooling, to reduce the maximum temperature to which the mixture can be heated thereby limiting the maximum vapor pressure of the glycol. Second, as water evaporates at the surface of the mixture, the water vapor dilutes oxygen (from air) at the surface of the glycol/water mixture. Since oxygen is necessary for combustion, and combustion is generally favored by high oxygen concentrations, substantial dilution of oxygen from air by evaporating water serves to reduce the flammability of the glycol/water mixture. 
     Thus, certain feedstock mixtures are non-flammable. Simply stated, to be non-flammable the vapor pressure of the combustible component, i.e., organic component, of the fuel feedstock must remain below the lower flammability limit at 100° C.; the approximate temperature at which water in the mixture will boil. Generally, this requires that the organic component have a vapor pressure &lt;100 torr at 100° C. 
     In addition to being non-flammable, glycol/water mixtures, best known for their use as heat exchange fluids in internal combustion engines, are converted to a hydrogen-rich reformate stream in the presence of nickel-based steam-reforming catalysts at temperatures in the range of 400° C. to 700° C. Glycol/water mixtures also offer the advantage of forming stable solutions over a wide range of water concentration, so that the proper water to glycol steam reforming ratio can be obtained by appropriately mixing the glycol/water fuel feedstock and then dispensing this fuel feedstock into a supply tank (or reservoir) from which the fuel feedstock is delivered at the proper rate to the reformer. Yet another advantage of the glycol/water mixtures is that they remain liquid over a large temperature range, and they are generally viscous liquids. Glycol/water mixtures, sold commercially as antifreeze coolants, remain liquid even at temperatures well below 0° C. and at temperatures greater than 100° C. Being liquid, glycol/water mixtures are efficiently pumped to elevated pressure for delivery to the reformer so that steam reforming can be conducted at elevated pressure (up to  500  psig, but preferably  100  psig to 300 psig). The high viscosity of glycol/water mixtures leads to greater pumping efficiency, particularly if a gear pump, piston pump, or centrifugal pump is used to deliver the high-pressure fuel feedstock to the reformer. The high viscosity reduces slippage past the wetted surfaces of the pump, which often limits the maximum pressure differential at which a pump may be used. 
     To demonstrate the integrated fuel processor of this invention, the fuel processor depicted generally in FIG. 5 was constructed and operated. The tubular metal membrane (first stage of the hydrogen purifier) was made using the method generally described in connection with FIGS. 12-17. The hydrogen-permeable metal foil  702  consisted of Pd-40Cu nominally 25 microns thick, and the membrane was about 15 cm long (2.8 cm outside diameter). The second stage of the hydrogen purifier, a catalytic methanizer, was contained in a copper tube, 1.8 cm outside diameter, that was inserted inside the bore of the tubular membrane  700 . One end of the copper methanation tube was sealed to one of the tubular-membrane end caps  730 . The other end of the copper methanation tube was terminated about 0.3 cm from the end of the membrane tube whereby hydrogen permeating to the inside of the membrane tube  700  would freely flow into the open end of the methanation tube such as shown generally in FIG.  3 . The methanation tube was filled with catalyst G1-80 (BASF), a supported nickel composition that is active for methanation of CO and CO 2 . 
     The reforming region of the fuel processor was filled with catalyst K3-110, a copper/zinc supported catalyst sold by BASF generally for conducting the water-gas shift reaction at &lt;350° C. The shell of the fuel processor, the spiral combustion tube, and the end plates were all constructed from stainless steel. Insulation was placed around the exterior of the shell and end plates to reduce heat loss. 
     The fuel processor was operated using methanol/water mix as the feed. The methanol/water solution was prepared by mixing 405 mL methanol (histological grade, Fisher Scientific) with 180 mL deionized water. The fuel processor was heated to 200° C. to 300° C. using an externally placed electric resistance heater. Once the fuel processor was hot, the electric heaters were turned off and methanol/water solution was pumped into the fuel processor at 200 psig. The methanol/water feed was first vaporized then the vapors passed over the K3-110 reforming catalyst to produce hydrogen-rich reformate. The two-stage hydrogen purifier then extracted product hydrogen at ambient pressure from the hydrogen-rich reformate. The hydrogen-depleted raffinate was directed to the combustor as described above. Combustion of this raffinate gas inside the fuel processor heated the fuel processor to 300° C. to 350° C. and provided all required heat once operation of the fuel processor commenced. 
     The purity of the product hydrogen was determined by gas chromatography and the flow rate of the product hydrogen was measured using a calibrated gas flow meter. Analysis of the product hydrogen confirmed &lt;10 ppm CO and &lt;10 ppm CO 2 . The flow rate of product hydrogen was 2 L/min. The reformer was operated in this mode, without any external source of heating, for 6 hours at which time the experiment was concluded. 
     According to a second example, tubular Pd-25Ag membranes with a 2.2 cm outside diameter were made using the general method described in connection with FIGS. 12-17. The Pd-25Ag foil was 25 micron thick and 7.0 cm wide by 16 cm long and the copper foil frame was 125 micron thick and 8.3 cm wide by 17.8 cm long. The dimensions of the center cut out in the copper foil frame was 5.7 cm wide by 14 cm long. The welding equipment and methods described in connection with FIGS. 12-17 were used to join the palladium-alloy foil to the copper foil frame. The support for the membrane was a carbon steel tension spring, 2.2 cm outside diameter. The spring was made using wire nominally 0.25 cm diameter. End caps were brazed to the ends of the membrane tube using the method given above or, in some cases, end caps were sealed to the ends of the membrane tube using graphite seals. The graphite seals were achieved using flexible graphite tape (1.3 cm wide) wrapped around the membrane tube and then compressed against the membrane in a standard compression fitting. 
     In another example, plate-type membrane modules were made using the following general method. Hydrogen-permeable Pd-40Cu foil, nominally 25 micron thick and 5.1 cm by 5.1 cm square, were welded to a copper foil frame (nominally 125 micron thick) using the ultrasonic welder and welding parameters discussed above. The copper foil frame was circular in shape (8.9 cm diameter) with cut outs for feed and permeate as shown in FIG.  20 . After welding the Pd-40Cu membrane to the copper foil frame to make the membrane assembly, the weld was checked for leaks by a standard dye penetration test. 
     The copper permeate plate (FIG. 21) was 0.3 cm thick and 8.9 cm diameter. A recessed was machined in the permeate plate to accept the support layer for the membrane. This recess, as shown in FIG. 21, was of the same dimensions as the membrane and connected to the permeate manifold channel. The support layer consisted of a first layer of stainless steel screen (70×70 mesh), placed against the permeate plate, then a second layer of stainless steel screen (200×200 mesh) that the thin Pd-40Cu foil rested against. This combination of coarse mesh and fine mesh was determined to both adequately support the thin membrane without excessively damaging the membrane, and provide acceptably low resistance to the lateral flow of permeate hydrogen. 
     The stainless steel screen was fixed to the permeate plate with a single drop of cyanoacrylate glue, and the glue allowed to dry. Then, two membrane assemblies were brazed to a single permeate plate, one membrane assembly at each major surface of the permeate plate. Brazing was achieved using a standard brazing alloy (nominally 80% copper, 15% silver, and 5% phosphorous) in either ribbon form or as a paste (powdered brazing alloy mixed with a paste binder). This brazing alloy was purchased from Lucas-Milhaupt, Inc. (Cudahy, Wis.). To prevent unwanted creep of the brazing alloy over the surface of the Pd-40Cu membrane, Nicrobraz Red Stop-Off Type II (Wall Colmonoy Corp., Madison Hts., Mich.) was applied around the edge of the Pd-40Cu membrane. This assembly was then placed on a flat surface beneath a steel weight (approximately 1.5 kg) and heated to 750° C. in a brazing furnace. A coating of boron nitride, a release agent, was applied to the steel surfaces in contact with the membrane assembly during brazing to prevent sticking between the membrane assembly and the steel surfaces. Brazing was done under vacuum, a nitrogen atmosphere, or a nitrogen stream containing a low concentration of methanol or hydrogen to serve as a reducing gas (to prevent oxidation). The brazing temperature of 750° C. was held for 15 minutes prior to cooling. 
     To demonstrate the non-flammability of ethylene glycol/water mixtures, the following experiment was conducted. Ethylene glycol (1.0 mL) was mixed with two molar equivalents water (0.65 mL). The resulting homogeneous solution is of the proper stoichiometry for steam reforming, as shown by the following ideal reaction equation: 
     
       
         HOCH 2 CH 2 OH+2H 2 O=2CO 2 +5H 2   
       
     
     This solution of ethylene glycol and water was directly exposed to the flame from a propane/air torch. The ethylene glycol/water solution did not burn or support combustion. 
     In yet another example, a 2:1 molar ratio of water-to-ethylene glycol was prepared by mixing 65 mL deionized water and 100 mL purified reagent grade (Fisher Scientific) to form a homogeneous solution. This ethylene glycol/water solution was reformed to produce hydrogen in a laboratory-scale packed-bed catalytic reactor as described below. 
     The catalytic reactor consisted of a cylindrical stainless steel shell 2.5 cm inside diameter and 22.9 cm long. The reactor contained a fixed bed of the commercial catalyst G1-80 (BASF), which is a supported nickel steam reforming catalyst. A length of stainless steel tubing (0.3 cm diameter by about 25 cm long) was coiled around one end of the catalytic reactor to serve as a preheater and vaporizer for the ethylene glycol/water feed. One end of this vaporization coil was connected to the inlet of the catalytic reactor, the other end of the coil was connected to a reservoir containing the ethylene glycol/water feed. The temperature within the catalytic reactor was measured and controlled via a thermocouple inserted within the catalyst bed. 
     The catalytic reactor was heated to 500° C. by means of an external electric furnace. The G1-80 catalyst was then reduced in situ by first flowing ethylene glycol/water feed into the catalytic reactor at a rate of 2.5 mL/min (liquid flow rate) for 2 hrs, then flowing pure hydrogen at ambient pressure through the catalytic reactor for another 4 hrs. Following reduction of the steam reforming catalyst, ethylene glycol/water feed was admitted into the catalytic reactor at ambient pressure. The temperature of the catalytic reactor was varied between 400° C. and 500° C. The product gas was shown to be predominantly CO 2  and H 2  by gas chromatography analysis, unreacted ethylene glycol/water was collected in a cold trap and quantified by gravimetric analysis, and the product flow rate was measured using a calibrated gas flow meter to determine the degree of conversion to products. The results of these experiments are summarized in the following table. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Temperature 
                   
                   
               
               
                 (° C.) 
                 Product Flow Rate (L/min) 
                 Conversion to Products (%) 
               
               
                   
               
             
            
               
                 500 +/− 50 
                 3-5 
                 90-95 
               
               
                 465 +/− 25 
                 4-5 
                 90-95 
               
               
                 400 +/− 25 
                 4-5 
                 93-98 
               
               
                   
               
            
           
         
       
     
     To demonstrate the utility of the two-stage hydrogen purifier when utilized as a stand-alone hydrogen purifier, the following experiment was conducted. 
     A tubular hydrogen-permeable metal membrane was made using the method described in FIGS. 12-17. The membrane consisted of Pd-25Ag foil nominally 25 micron thick and was 2.2 cm outside diameter by 15 cm long, the overall length of the membrane tube (including end caps) was approximately 21 cm. This tubular membrane serves as the first stage of the purifier. The second stage of the purifier, a catalytic methanizer, was contained in a copper tube, 1.58 cm outside diameter, that was inserted inside the bore of the tubular membrane. One end of the copper methanation tube was sealed to one of the tubular-membrane end caps. The other end of the copper methanation tube was terminated about 0.3 cm from the end of the membrane tube so that hydrogen permeating to the inside of the membrane tube would freely flow into the open end of the methanation tube (this arrangement is shown in FIG.  3 ). The methanation tube was filled with catalyst G1-80 (BASF), a supported nickel composition that is active for methanation of CO and CO 2 . 
     This two-stage hydrogen purifier was placed in a stainless steel shell equipped with electric resistance heaters. The hydrogen purifier was heated to 300° C. to 350° C., and methanol/water reformate (approximately 70-75% hydrogen, balance CO and CO 2 ) at 50 psig was passed into the stainless steel shell and over the exterior surface of the Pd-25Ag membrane tube. Product hydrogen at ambient pressure, after permeation through the Pd-25Ag membrane and then passage over the methanation catalyst, was collected and analyzed by gas chromatography. Analysis confirmed that the product hydrogen contained &lt;2 ppm CO and &lt;50 ppm CO 2 . 
     Thus, a steam reformer with internal hydrogen purification has been shown and described. The reformer of the present invention utilizes a single feed, e.g., a methanol and water or hydrocarbon and water mix, as both the chemical feed stock to support hydrogen reforming and also as a combustion fuel source to provide sufficient temperature to support steam reforming. The present invention recovers by design less than a maximum amount of hydrogen available in a reforming step to leave in the byproduct stream sufficient hydrogen as fuel to support the combustion process. The present invention uses two distinct hydrogen purification processes. First, a membrane produces a hydrogen stream as a bulk filtration step, but the product hydrogen stream may still contain some undesirable impurities. Second, a polishing process converts the undesirable impurities in the hydrogen stream to innocuous components not affecting operation of, for example, a fuel cell. Advantageously, this allows use of a relatively less expensive, thin palladium-alloy membrane in the steam reforming process. 
     In FIG. 25, another embodiment of the fuel processor, or reformer, is shown and generally indicated at  900 . Similar to the previously described embodiments, reformer  900  includes a shell  902  that houses steam reforming  904  and combustion  906  regions, as well as at least one steam reforming tube  908 . Three such tubes are shown in FIG. 25, and each contains steam reforming catalyst  910 . It should be understood that, like the rest of the reformers disclosed herein, reformer  900  may include as few as one tube and preferably includes multiple tubes. Between six and ten reforming tubes have proven effective, both in hydrogen production rate and compactness of the overall reformer. However, the number of tubes in any particular embodiment may vary, depending upon such factors as the size of the reformer&#39;s shell, the desired rate of hydrogen production, and the number of additional elements within the shell. For example, when a plate-type membrane module is used, there is more available space adjacent the side walls of the reforming tubes. 
     As shown in FIG. 25, a portion  911  of each reforming tube  908  extends external shell  902 . This enables the tubes (and the reforming catalyst contained therein) to be accessed without having to open the shell. In this configuration each end portion  911  includes a removable cap or other closure which may be selectively removed to permit access to the interior of the tube, and thereafter replaced. This configuration for the reforming tubes may be used with any of the other reformers disclosed herein, just as reformer  900  may include reforming tubes which are completely housed within shell  902 . 
     Tubes  908  are heated by hot combustion gasses passing from internal combustion manifold  912  to internal exhaust manifold  914 , and ultimately exiting reformer  900  through outlet  916 . In FIG. 25, a plurality of passages  918  are shown which permit the hot combustion gasses to pass between manifolds  912  and  914 , and thereby heat tubes  908  as the gasses flow around the tubes. 
     Hot combustion gasses are produced by burner  920 . Upon initial startup, burner  920  is ignited by a suitable ignition source, such as spark plug  922 , or any of the other ignition sources disclosed herein. Combustion air, preferably at or near ambient pressure, is brought into burner  920  through combustion port  924 . 
     Feedstock for the steam reforming process is admitted into the fuel processor through inlet tube  926  and passes into the hot combustion region  906  of fuel processor  900 , wherein the feedstock is vaporized. A single inlet tube  926  may be used to admit a feedstock comprising alcohol and water, or multiple separate inlet tubes may be used (such as disclosed herein) if the feedstock consists of separate streams of water and a hydrocarbon or alcohol. As shown in FIG. 25, inlet tube  926  forms a coil  927  that extends around tubes  908  multiple times before entering a distribution manifold  928 . Coil  927  should be of sufficient length that the feedstock is vaporized prior to reaching distribution manifold  928 . It should be understood that the circuitous path of coil  927  is shown in FIG. 25 for purposes of illustrating one possible path. The important concern is that the coil is of sufficient length that the feedstock passing there through is vaporized by heat transmitted to it as it travels to distribution manifold  928 . To aid with the vaporization of the feedstock, multiple coils of tubing may be used to effectively increase the heat transfer surface area of the tubing, and thereby aid in the vaporization of the feedstock. Vaporization of the feedstock may also be accomplished using plate-type vaporizers. 
     From distribution manifold  928 , the vaporized feedstock is distributed to steam reforming tubes  908 . When tubes  908  are of similar size or are adapted to process generally equal volumes of feeds, the feedstock is evenly distributed between the tubes by manifold  928 . However, the feedstock may be otherwise proportioned if the tubes are adapted to receive and process different flows of the feedstock. 
     Within reforming tubes  908 , the feedstock undergoes a catalytic reaction to yield a hydrogen-rich reformate gas stream which contains carbon monoxide and carbon dioxide in addition to hydrogen. To purify the produced hydrogen, fuel processor  900  includes a purification module (or membrane module)  930 , through which the reformate gas stream is passed. One or more hydrogen-selective inorganic membranes, such as any of the hydrogen-selective metal (and preferably palladium alloy) membranes disclosed herein, are contained within module  930 . Membrane module  930  may include any suitable configuration, including those previously described herein. The hydrogen that permeates the hydrogen-selective membranes passes from the module through an outlet port  932  and into a polishing catalyst bed  934 . Preferably, the polishing catalyst bed contains a methanation catalyst (not shown) to convert carbon monoxide and carbon dioxide in the permeate stream into methane. 
     As shown in FIG. 25, polishing catalyst bed  934  is located external shell  902 , where it is heated by radiant heat and thermal conduction from hot shell  902 . As shown, bed  934  lies against the exterior surface  936  of shell  902 . However, it is within the scope of the invention that bed  934  may be at least partially or completely spaced away from shell  902 , so long as it still receives sufficient heat for the polishing reaction. Polishing catalyst bed  934  is further heated by the hot hydrogen that flows into the bed from the methanation module  930 . Finally, purified hydrogen exits reformer  900  via tube  938 . By locating the polishing catalyst bed external shell  902 , reformer  900  may either include additional reforming tubes within its shell, or the shell may be smaller because it no longer needs to house the polishing catalyst bed. 
     It should be understood that as used herein, purified hydrogen refers to a stream that is at least substantially comprised of hydrogen gas. The stream may include other components, such as methane produced in the polishing catalyst bed, but the stream contains less than defined minimum amounts (i.e. trace concentrations) of impurities (such as carbon monoxide and carbon dioxide) which would harm or lessen the effectiveness of a fuel cell. 
     Waste gasses, including some of the produced hydrogen gas, that do not pass through the hydrogen-selective membrane within module  930  are used as fuel to heat fuel processor  900 . Therefore, the hydrogen-depleted raffinate stream (which exits module  930  through conduit  940 ) is directed into burner  920 . As discussed previously, the concentration of hydrogen within the raffinate stream may be selectively controlled so that there is sufficient fuel gas to maintain reformer  900  within desired temperature ranges. 
     FIG. 25 illustrates other non-essential elements that may be used within any of the reformers disclosed herein. For example, in FIG. 25, reformer  900  further includes a pressure gauge  942  for monitoring the pressure of the fuel gas in conduit  940 , a pressure relief valve  944 , and a vent valve  946 . Also illustrated are a valve  948 , which controls the flow of fuel gas in conduit  940  to the burner and applies back pressure on the reforming region, and a valve  949 , which controls the flow of start-up fuel gas (previously produced and stored or supplied from an external source), such as hydrogen, propane or natural gas, during a cold start-up of the reformer. 
     In FIG. 26, a variation of the reformer of FIG. 25 is shown and generally indicated at  950 . Unless otherwise indicated, reformers  900  and  950  contain the same components and subcomponents. To provide more space within shell  902 , and thereby permit additional reforming tubes  908  to be housed therein, reformer  950  includes vaporization coils  952  which are located external shell  902 . As shown, coils  952  are wrapped around the external surface  936  of shell  902  and are in contact therewith. Similar to the polishing catalyst bed described with respect to FIG. 25, coils  952  may be at least partially or completely spaced apart from shell  902 . In this case, the important factor is that sufficient heat is transmitted to the feedstock within the coils to vaporize the feedstock before it reaches distribution manifold  928 . In the position shown in FIG. 26, the coils are heated by radiation and thermal conduction from the hot surface of shell  902 . 
     The reformer shown in FIG. 26 also demonstrates structure for admitting immiscible feedstocks to the reformer. As shown, reformer  950  includes an inlet tube  954  through which a water feed is received and delivered to vaporization coils  952 . A hydrocarbon or alcohol feed is admitted through inlet tube  956 , and it is mixed with the hot steam before passing into the reformer through a reformer inlet tube  958 . The combined feedstock stream passes into one end of a mixing chamber  960 , which contains an optional static mixer or a packing (not shown) to promote turbulent flow and thereby encourage mixing of the vaporized feedstocks. The mixed, vaporized feedstock exit the mixing chamber and are delivered to distribution manifold  961 , which in turn distributes the feedstock to the reforming tubes. 
     To increase the energy efficiency and to increase the combustion chamber temperature within reformer  950 , reformer  950  includes a quenching chamber  962  adapted to partially quench the reformate gas stream prior to its entrance into membrane module  930 . As shown, the reformate gas stream must pass through chamber  962  after exiting reforming tubes  908  and prior to entering membrane module  930 . Chamber  962  includes a pair of ports  964  and  966  through which combustion air respectively enters and exits the chamber. The air is cooler than the reformate gas stream, and therefore cools tee reformate gas stream prior to its entry into the membrane module. During this exchange, the combustion air is heated prior to its entry to burner  920 . 
     The quenching chamber and external vaporization coils described with respect to reformer  950  may be used with any of the reformers (aka fuel processors) described herein. Similarly, the external polishing catalyst bed may be used with any of the reformers described herein, such as to increase the number of reforming tubes within the reformer&#39;s shells or to decrease the size of the shell. It should be understood that the reformers described herein have been shown and described to illustrate particular features of the invention, and that particular elements or configurations may be selectively used with any of the reformers described herein. 
     In many of the previously described embodiments, the end plates and/or membrane modules of the reformers (or fuel processors) are secured to the rest of the reformers with bolts and gaskets. It should be understood that any other suitable form of fastening mechanism and seal may be used so long as the shell is sealed against leaks and secured together so that it does not unintentionally open, such as during operation. Although welding and other more permanent fasteners are within the scope of suitable fastening mechanisms, fastening mechanisms which may be selectively removed and resecured, such as the bolts and nuts shown for example in FIGS. 25 and 26, are preferred. 
     While the invention has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. Applicants regard the subject matter of the invention to include all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. No single feature, function, element or property of the disclosed embodiments is essential. The following claims define certain combinations and subcombinations which are regarded as novel and non-obvious. Other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such claims, whether they are broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of applicants&#39; invention.