Abstract:
A reaction vessel that integrates and balances an endothermic process with at least one exothermic process of the fuel cell system. Preferably the exothermic process is conducted in stages to provide more uniform and/or controllable heat generation and exchange, and to produce a uniform and/or controllable temperature profile in the endothermic reaction process. The invention allows for the elimination of the working fluid loop of prior art systems that had unsatisfactory response times at startup, and during transient conditions, and also added to the overall mass and volume of the fuel cell system.

Description:
“This is a division of application Ser. No. 09/669969 filed on Sep. 26, 2000 now U.S. Pat. No. 7,081,312.” 
    
    
     TECHNICAL FIELD 
     This invention relates to fuel cell systems and components, and more particularly to a fuel cell system that combines exothermic and endothermic processes in one reaction vessel. 
     BACKGROUND OF THE INVENTION 
     Alexander Grove invented the first fuel cell in 1839. Since then most of the fuel cell development has been primarily limited to applications supported by the government, such as the United States National Aeronautics and Space Administration (NASA), or to utility plants applications. However, recent developments in materials of construction and processing techniques have brought fuel cell development closer to significant commercial applications. A primary advantage of fuel cells is that fuel cells can convert stored energy to electricity with about 60-70 percent efficiency, with higher efficiencies theoretically possible. Further, fuel cells produce virtually no pollution. These advantages make fuel cells particularly suitable for vehicle propulsion applications and to replace the internal combustion engine which operates at less than 30 percent efficiency and can produce undesirable emissions. 
     Although fuel cells are desirable for vehicle propulsion applications, the fuel cell must be incorporated into a complicated on-board system that includes a fuel cell stack and auxiliary equipment. The following brief discussion of the operation and purpose of the fuel cell stack and its auxiliary equipment will be helpful in understanding the advantages and desirability of the present invention. 
     Fuel Cell Operation 
     A fuel cell principally operates by oxidizing an element, compound or molecule (that is, chemically combining with oxygen) to release electrical and thermal energy. Thus, fuel cells operate by the simple chemical reaction between two materials such as a fuel and an oxidant. Today, there are a variety of fuel cell operating designs that use many different fuel and oxidant combinations. However, the most common fuel/oxidant combination is hydrogen and oxygen. 
     In a typical fuel cell, hydrogen is consumed by reacting the hydrogen with oxygen from air to produce water, electrical energy and heat. This is accomplished by feeding the hydrogen over a first electrode (anode), and feeding the oxygen over a second electrode (cathode). The two electrodes are separated by an electrolyte which is a material that allows charged molecules or “ions” to move through the electrolyte. There are several different types of electrolytes that can be utilized including the acid-type, alkaline-type, molten-carbonate-type and solid-oxide-type. The so-called PAM (proton exchange membrane) electrolytes (also known as a solid polymer electrolyte) are of the acid-type, and potentially have high-power and low-voltage, and thus are desirable for vehicle applications. 
       FIG. 1  shows a fuel cell that has been simplified for purposes of illustrating the operation of a fuel cell. In the proton exchange membrane based fuel cell  10  shown, a hydrogen gas stream  12  is fed into a first sealed chamber or manifold (in the case of a fuel cell stack)  14  and over a first electrode (anode)  24  and on to a first face  16  (the anode side) of a proton exchange membrane assembly  18 . The proton exchange membrane assembly  18  typically includes the electrolyte membrane  19  having two faces, and on each face there is a catalyst, usually a noble metal such as platinum, and an electrically conductive diffusion media (such as a carbon fiber mat) overlying the catalyst. The catalyst and diffusion media are not shown in  FIG. 1 . The catalyst on the anode face of the assembly promotes the dissociation of hydrogen molecules and the catalyst on the cathode face of the assembly promotes the dissociation of oxygen molecules and a reaction of oxygen with hydrogen protons to produce water. The electrolyte membrane  19  allows the diffusion of hydrogen ions  26  from one electrode  24  to another electrode  34 .  FIG. 1  is a simple illustration attempting to depict the diffusion of these hydrogen ions  26  from the anode to the cathode side of the electrolyte membrane. However, the electrolyte membrane  19  does not include channels as shown in  FIG. 1 . 
     A compressed air stream  22  is supplied to a second chamber or manifold (for a fuel cell stack)  15  in a manner so that the compressed air flows over a second electrode (cathode)  34  and on to a second face  20  of the proton exchange membrane assembly  18 . The proton exchange membrane assembly  18  is selective and allows only the hydrogen protons  26  to pass through the membrane assembly  18  rejecting larger diatomic hydrogen molecules  28 . When a single hydrogen proton (or its equivalent)  26  passes through the membrane, it leaves behind an electron  30 . The electrons  30  that are left behind can be collected in the electrode (conductor)  24 . Typically fuel cell systems include a stack of single cells (fuel cell stack) with adjacent cells sharing a common electrode. In that case, the electrodes  24 ,  34  would be bipolar. Preferably each electrode  24 ,  34  includes channels  25  formed therein through which either hydrogen or oxygen flows. 
     The concentrated electrons in the electrode  24  causes a potential negative voltage on the electrode  24  due to the excess of electrons (because the electrons are negatively charged). When the oxygen molecules are directed to the second face  20  of the proton exchange membrane assembly  18 , the oxygen meets the hydrogen proton  26  as the proton passes through the membrane. The chemical reaction of the hydrogen proton  26  and the oxygen on the cathode side of the cell requires electrons and therefore a shortage of electrons is created. The needed electrons can be supplied by a second electrode  34  (that is, the cathode electrode). The oxygen and the hydrogen proton  26 , in the presence of the electrons  30  from the second electrode  34 , easily combined to produce water  32 . The reactions at the electrodes are as follows:
 
Anode 2H 2 →4H + +4 e   − 
 
Cathode O 2 +4 e   − +4H + →2H 2 O.
 
     With two electrodes  24 ,  34  in the fuel cell system (the anode and the cathode) an electrical potential exist between the two electrodes. That is, the hydrogen electrode  24  has an excess of electrons and the oxygen electrode  34  needs electrons. The electrical potential can be utilized by placing an electrical load, such as electrical motor  36  (to propel a vehicle) between the anode  24  and the cathode  34 . Since electrical energy is used as it goes around the loop, the only by-products of this fuel system are water vapor and the heat loss through inefficiency of the cell itself (or about 30 percent of the power). With 70 percent efficiency, this process is significantly more attractive for extracting stored energy than an internal combustion engine that typically extracts only 20-30 percent of stored fuel energy. 
     Both hydrogen and oxygen are each supplied to the fuel cell in excess to provide the greatest rate of reaction possible. The hydrogen gas stream will be under pressure of about 3 bars if it is produced from a fuel reformation reaction and therefore the oxygen stream  22  must be pumped up to the same pressure to avoid damage to the proton exchange membrane and the catalyst of the assembly  18 . Any water produced or remaining on either side of the fuel cell is removed and is discharged or may be sent through a water/vapor stream line  38  to a water reservoir (such as the holding tank  46  shown in  FIG. 2 ) for use in other components or for use in the fuel cell at startup. The effluent or tail gas exhaust stream  40 ,  42  from both sides of the fuel cell are discharged to the atmosphere or preferably are supplied to a combustor for burning and producing heat needed for other operations such as the fuel reformation process described hereafter. Since the reactants are supplied to the fuel cell in excess, tail gas exhaust stream  40  from the anode side contains hydrogen and the tail gas exhaust stream  42  from the cathode side contains oxygen. Both of the fuel cell tail gas streams  40 ,  42  may be combusted in a catalytic combustor to provide heat for other components in the fuel cell system. 
     Preferably the fuel cell is maintained at a temperature of about 80 degrees Celsius or greater. Maintaining this temperature may require heat to be added or removed from the fuel cell stack. Often heat must be supplied to the fuel cell at startup. This heat can be supplied by a catalytic or flame combustor. However, during post startup or normal operation of the fuel cell, heat is generated by the fuel cell and the generated heat can be removed by any of a variety of heat exchange methods but preferably is removed using a liquid coolant. 
     Auxiliary Equipment 
     As will be appreciated from the forgoing, fuel cell systems require a variety of auxiliary equipment such as pumps, heat exchangers, fuel processors, combustors, water separation and collection equipment, hydrogen cleanup or purification systems and so on to support the operation of the fuel cell itself. Auxiliary equipment that is of interest with respect to this invention is discussed below. 
     Although compressed or liquefied hydrogen could be used to operate a fuel cell in a vehicle, to date this is not practical. The use of compressed or liquefied hydrogen ignores the extensive infrastructure currently being used to supplying gasoline for internal combustion engine automobiles and trucks. Consequently, it is more desirable to utilize a fuel such as methanol, gasoline, diesel, methane and the like to provide a hydrogen source for the fuel cell. However, the methanol, gasoline, diesel, methane and the like must be reformed to provide a hydrogen gas source. This is accomplished by using methanol or gasoline fuel processing or reforming equipment, and hydrogen cleanup or purification equipment. 
     Fuel cell systems often include a fuel processing section which reforms the fuel such as methanol, gasoline, diesel, methane and the like to produce hydrogen and a variety of other byproducts. However, these reforming (reformation) processes are endothermic and require energy input to drive the reformation reaction. 
     Typically, a catalytic or flame combustor is utilized to provide heat for the reforming process. Most often, this is accomplished by utilizing a working fluid (liquid or gas) loop that transfers heat from the combustion process to the reforming process. However, the response time for heat transfer needed during startup and transient conditions of the fuel cell are less than optimal when the system uses a fluid to transfer heat between the combustor and the reformer vessel. Further, the working fluid loop, associated heat exchangers and piping add to the overall mass and volume of the fuel cell system. 
     Thus it would be desirable to provide a low-cost, low-weight system for supplying heat to a fuel cell reforming process and wherein the system is responsive to the heat load fluctuations of the reforming process. The present invention overcomes some of the inefficiencies of the prior art 
     SUMMARY OF INVENTION 
     The invention includes a reaction vessel that integrates and balances an endothermic process with at least one exothermic process of a fuel cell system. Preferably the exothermic process is conducted in stages to provide more uniform and/or controllable heat generation and exchange, and to produce a uniform, and/or controllable temperature profile in the endothermic reaction process, if desired (depending on the fuel used). The invention eliminates the working fluid heat exchange loop of prior art fuel reforming sections that had unsatisfactory response times at startup, and during transient conditions, and also added to the overall mass and volume of the fuel cell system. 
     One embodiment of the invention includes a reaction vessel having an outer shell and catalyst carried in the shell for promoting an endothermic reaction. The reaction vessel is constructed and arranged to charge an endothermic reactant(s) into the shell. A plurality of heat exchanger devices are also provided having portions separately positioned and carried within the shell. Each heat exchanger device is independently controlled from the other heat exchanger devices so that heat transferred by the heat exchanger devices to the catalyst, and the temperature of the catalyst in the shell, may be varied at different locations within the reaction vessel. Preferably the reaction vessel is constructed and arranged so that exothermic reactants may be charged into each heat exchanger device and combusted to generate heat for driving the endothermic reaction occurring in another portion of the reaction vessel. The exothermic reactants may include anode and cathode exhaust streams from a fuel cell stack. 
     Another embodiment of the present invention includes a reaction vessel having a plurality of endothermic reaction sections and a plurality of heat transfer devices. Each heat transfer device is associated with an endothermic reaction section so that sufficient heat may be transferred to the endothermic reaction section and so as to control the temperature profile of the endothermic reaction section within a predetermined range. The endothermic reaction sections may be spaced apart from each other and so that a heat transfer device is positioned between adjacent spaced apart endothermic reaction sections. 
     Another embodiment of the present invention includes a combination reaction vessel having multiple staged catalytic combustion chambers and a plurality of endothermic reaction chambers. Each endothermic reaction chamber has a combustion chamber adjacent thereto so that heat generated in the combustion chamber is transferred to the adjacent endothermic reaction chamber. Each catalytic combustion chamber may have a plurality of reactant charge openings for supplying at least one reactant to the catalytic combustion chamber. The charge openings may be positioned within the catalytic combustion chamber to provide a substantially uniform temperature along the length of the catalytic combustion chamber. 
     Another embodiment of the invention includes a charge manifold having a plurality of charge pipes extending therefrom. Each charge pipe extends into an exothermic reaction chamber. The charge pipes have charge holes provided along the length of each charge pipe so the fuel or oxidant may be charged into the combustion reaction chamber through the charge holes. Preferably valves are associated with each charge pipe and a controller is provided for selectively controlling the amount of fuel or oxidant charged to each exothermic reaction chamber. Each charge pipe may separate adjacent side-by-side exothermic reaction chambers. A directional flow header may be provided at the end of each exothermic reaction chamber for directing gases exiting one exothermic reaction chamber to the entrance of an adjacent side-by-side exothermic reaction chamber. 
     Another embodiment of present invention includes the incorporation of a fuel/water vaporizer into the combination reaction vessel. A fuel/water mixture is injected into a plurality of vaporization chambers and is vaporized by heat generated by the catalytic combustion of a fuel mixture charged into a plurality of exothermic reaction chambers. No catalyst is provided in the vaporization chambers. An oxidant and fuel are charged into the exothermic reaction chambers and catalytically combusted to produce heat to vaporize the fuel/water mixture. 
     Another embodiment of present invention includes a combination reaction vessel that incorporates an exothermic and endothermic reaction. The reaction vessel includes a plurality of endothermic reaction chamber sections that are spaced apart vertically and horizontally. A plurality of exothermic reaction chamber sections are also provided in a spaced apart fashion so that a partition section is provided between laterally spaced apart exothermic reaction chamber sections. The partition sections provide for staged adiabatic reforming of the fuel/water mixture. The catalyst loading in different portions of the endothermic reaction chamber sections may be varied as desired. 
     These and other objects, features and advantages of present invention will become apparent from the following brief description of drawings, detailed description of preferred embodiments, and appended claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a fuel cell useful in the present invention; 
         FIG. 2  is a schematic illustration of a fuel cell system useful in a present invention; 
         FIG. 3  is a sectional view of a combination reaction vessel for housing an endothermic and an exothermic reaction according to the present invention; 
         FIG. 4  is a sectional view of an alternative embodiment of a combination reaction vessel for housing an endothermic and an exothermic reaction according to the present invention; 
         FIG. 5  is a sectional view of an alternative embodiment of a combination reaction vessel for housing an endothermic and an exothermic reaction according to the present invention; 
         FIG. 6  is an exploded, prospective view, with portions broken away, of an alternative embodiment of a combination reaction vessel for housing an endothermic and an exothermic reaction according to the present invention; and 
         FIG. 7  is a sectional view of an alternative embodiment of a reaction vessel for housing a staged endothermic reaction according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 2 , the fuel cell system according to the present invention includes a fuel cell (or fuel cell stack)  10 . The system may also include the following auxiliary equipment to support the fuel cell stack  10 . Water is provided and held in a water reservoir or holding tank  46  which is connected to a vaporizer  48  by water line  44 . A fuel source is provided and held in a tank  52  that is also connected to the vaporizer  48  by line  50 . Preferably the fuel used is methanol, gasoline, diesel, methane and the like. The fuel and water may be vaporized by any method known to those skilled in the art, but preferably the heat for the vaporization step is supplied by a heat exchanger  39  in the vaporizer that catalytically combusts hydrogen  40 ′ and oxygen  42 ′ from the fuel cell stack  10  exhaust. Alternatively, the vaporizer may be included as an integral part of the reaction vessel  54  as will be described hereafter. The fuel and water are vaporized together (or may be vaporized separately) and a resultant vaporized fuel/water stream is delivered via line  58  to an endothermic reaction section of a combination reaction vessel  54 . Preferably a fuel reformation process is conducted in the endothermic reaction section. 
     The combination reaction vessel  54  also houses an exothermic reaction section. The exothermic reaction may be, for example, catalytic combustion of a fuel or preferential oxidation of the exhaust stream from the fuel reforming section. If the exothermic reaction process is catalytic combustion, preferably the anode exhaust stream  40  and cathode exhaust stream  42  from the fuel cell  10  are used as the catalytic combustion reactants. The exhaust from the exothermic reaction may be discharged to the atmosphere via line  43 . 
     The reformation process effluent stream  56  may include hydrogen molecules (H 2 ), CO, CO 2 , N 2 , CH 4 . The reformation process effluent stream  56  may be delivered to a hydrogen purification section  59  to reduce the concentration of CO and hydrocarbons (or carbon based molecules). The hydrogen purification section  59  may include any of a variety of components for purifying the reformation process effluent stream  56  and may include high and low temperature reactors to shift the equilibrium of the stream  56  constituents (thus reducing the concentration of CO), preferential oxidation reactor(s), additional hydrocarbon reforming components, separators, absorbers and similar equipment. Eventually a hydrogen rich stream  60  is delivered to the anode side of the fuel cell  10 . 
     As indicated earlier, air  22  is pumped to the cathode side of the fuel cell  10 . The anode and cathode exhaust streams from the fuel cell stack carry water that can be condensed out using a separator/condenser as the stream exits fuel cell stack and the liquid water may be sent to reservoir  46 . Alternatively, the water may be condensed out after the stack effluent passes through exhaust tail gas combustors. 
       FIG. 3  illustrates a combination reaction vessel  54  for housing an endothermic and an exothermic reaction. The combination reaction vessel  54  includes an endothermic reaction chamber section  62  and an exothermic reaction chamber section  64  that share a common wall or substrate  66 . Each endothermic reaction chamber section  62  and exothermic reaction chamber section  64  includes an associated outside wall  68 ,  70  respectively. A catalyst  61  for promoting the reformation reaction of the fuel and water, is provided in the endothermic reaction chamber section  62 . As illustrated in  FIG. 3  the catalyst  61  may overlie at least one of the outside wall  68  and/or the substrate  66 . The catalyst  61  may be provided directly on the outside wall  68  or the substrate  66 , or intermediate layers (not shown) may be provided therebetween. The vaporized fuel and water mixture may enter the endothermic reaction chamber section  62  from one end  72  or may be selectively charged to the endothermic reaction chamber through charge lines  74  or openings  75  selectively positioned along the length of the endothermic reaction chamber section  62 . The term “endothermic reactants” as used herein means reactants of an endothermic reaction. In this case, for example, the endothermic reactants are the organic fuel and water. 
     The exothermic reaction chamber section  64  may be similarly constructed. As illustrated in  FIG. 3 , an exothermic catalyst  65  may overlie at least one of the outside wall  70  or substrate  66 . Similarly, the catalyst  65  may be provided directly on the outside wall  70  or the substrate  66 , or intermediate layers (not shown) may be provided therebetween. In one embodiment of the invention, a fuel combustion process may be conducted in the exothermic reaction chamber  64 . An oxidant such as oxygen (from air) may be charged into the chamber section  64  through one end  76  of the chamber and a fuel such as hydrogen or a hydrocarbon may be supplied to the chamber through one or more charge lines  74 ′ or through a charge openings  75 ′ that may be positioned along the length of the exothermic reaction chamber section  64 . Alternatively, the fuel may be charged through the open end  76  and the oxidant supplied through the charge lines  74 ′ or charge openings  75 ′. In another embodiment, an exothermic reaction such as a preferential oxidation reaction to reduce CO or hydrocarbons may be conducted in the exothermic reaction chamber section  64 . In any event, the heat generated by the exothermic reaction in the exothermic reaction chamber section  64  is transferred through the substrate  66  to warm the endothermic reaction chamber section  62 , catalyst  61  and reactants, and to drive (that is, to provide the heat necessary to complete the reaction) the endothermic reaction process. The term “exothermic reactants” as used herein means the reactants of an exothermic reaction. The exothermic reactants may include a fuel such as an organic fuel including, for example, hydrogen, methanol, gasoline, diesel, methane and the like; and an oxidant, such as oxygen in the form of air. 
       FIG. 4  illustrates an alternative embodiment of the present invention wherein either the endothermic or the exothermic catalyst may be provided on a solid porous substrate  78  or porous pellets  80  or any of a variety materials that would provide increased surface area for either of the catalysts. When the catalyst is on a high surface area material such as a porous block or porous pellets that are carried in the chamber, the catalyst is also considered to be overlying the substrate for purposes of this invention. 
       FIG. 5  illustrates an alternative embodiment of the present invention wherein a reactant charge pipe  82  extends into one of the reaction chambers  62 ,  64  and has a plurality of discharge holes  84  formed therein along the length of the reaction chamber to selectively discharge a reactant into the chamber at predetermined locations. Preferably, the charge pipe  82  delivers a fuel such as hydrogen to the combustion reaction chamber  64  which has an oxidant such as oxygen or air flowing therein. Alternatively, the charge pipe  82  may be used to introduce oxygen to allow for staged preferential oxidation. The use of the reactant charge pipe  82  with discharge holes  84  allows the fuel or oxidant to be supplied in relatively low concentrations so as to reduce the risk of autoignition and also to provide a more uniform heat generation profile along the length of the exothermic reaction chamber  64 . Of course, porous catalyst pellets or another suitable supported catalyst may be provided in the exothermic reaction chamber  64 . 
     The substrate  66  (shown in  FIGS. 3-5 ) may be made from a variety of materials having suitable heat transfer characteristics and may include any of several metals such as stainless-steel, copper, aluminum, or any of a variety of composites, ceramics, compounds or polymer base materials. 
     As described earlier, when the exothermic reaction produces heat, the heat is transferred through the substrate wall  66  separating an adjacent set of chambers  62 ,  64 . As such, the combination reaction vessel provides a staged exothermic reaction process (preferably combustion of a fuel) to provide a uniform temperature profile and heat transfer to drive an endothermic reaction (preferably a fuel reforming process) occurring in an adjacent chamber. 
     Referring now to  FIG. 6 , another embodiment of the present invention includes a combination reaction vessel  54  having a plurality of spaced apart, parallel endothermic reaction chambers  62 . In this case the endothermic reaction chambers  62  are vertically spaced apart and separated by an exothermic reaction chamber  64  that has a longitudinal axis and flow path running in a perpendicular direction to the longitudinal axis and flow path of the endothermic reaction chamber  62 . However, parallel co-flowing and counter flow configurations are contemplated as a part of the present invention. As described earlier, an endothermic reaction catalyst is provided in each of the endothermic reaction chambers  62  and the endothermic reactants, such as a methanol/water, gasoline/water vapor mixture, or other fuel/water mixture are supplied through one end  72  (see also  FIG. 3 ) of the endothermic reaction chamber and flow in the direction indicated by arrow shown entering the reaction chamber  62  in  FIG. 6 . 
     A plurality of spaced apart parallel exothermic reaction chambers  64  are provided so that each exothermic chamber  64  separates two endothermic reaction chambers  62  so as to provide a staged exothermic reaction process. The exothermic chambers  64  may also be arranged in a laterally adjacent side-by-side configuration. An inlet header  86  is provided having an inlet opening  88  formed therein through which at least one of the exothermic reactants is charged to the exothermic reaction chambers  64 . Preferably, exhaust gas (which contains oxygen) from the cathode side of the fuel cell is feed through the inlet opening  88 . The cathode exhaust gas flows down a first set of exothermic reaction chambers and is directed by a flow directing header  90  down a second set of exothermic reaction chambers, and so on in a serpentine fashion throughout the combination reaction vessel  54  and finally exits through an exhaust opening  92  formed in an outlet header  94 . 
     A second exothermic reaction reactant may be charged into the exothermic reaction chambers  64  utilizing a charge manifold  96 . In a preferred embodiment, the charge manifold  96  includes a plurality of charge pipes or lines  82 . A charge pipe  82  is received in one of each of the exothermic reaction chambers  64 . Preferably, the charge pipe  82  has a plurality of discharge holes  84  which are spaced apart along the length of the exothermic reaction chamber (as also shown in  FIG. 5 ). The combination reaction vessel  54  may be constructed and arranged so that the charge pipes  82  also function to separate laterally adjacent side-by-side exothermic reaction chambers. That is, the charge crepe  82  acts as a wall separating laterally adjacent exothermic reaction chambers. Because the exothermic reaction chambers  64  are staged in sections and at least one reactant is selectively and/or uniformly charged to each chamber along the length of the exothermic chamber, the heat generated throughout the exothermic reaction chamber may be controlled so that it is substantially uniform, or graduated if so desired. Consequently, the heat transferred to the endothermic reaction chamber, catalyst and reactants is such that the temperature profile in the endothermic reaction chamber is controlled to be substantially uniform, or graduated if so desired. Maintaining a controllable temperature profile in a fuel reforming process is important to avoid undesirable side effects such as catalyst degradation, or methane slip. At low power, the temperature profile may be such as to promote a high temperature reformation with a high temperature shift reaction at the exit of the reaction chamber. The temperature at the exit end of the reaction chamber should be high enough to suppress methane formation for a given catalyst. 
     A plurality of temperature or concentrations sensors  104  may be selectively placed in the combination reaction vessel, and valves  100  may be included in the charge manifold  96  to selectively control the amount of reactant being charged to the chamber and thus control the reaction as desired. Associated on-board computer controllers  102 , drivers and associated electrical equipment can be provided to control the above described components and processes in a manner known to those skilled in the art. 
     For example, in a methanol reformer, the charge manifold  96  may be constructed and arranged to controllably charge reactants so that a uniform temperature profile at full power is provided which would utilize the entire reactor volume. However, under turndown situations (for example, when the vehicle is stopped), less power is required, and thus only a portion of the reactor is required to reform fuel because of the lower power demand. In these turndown situations it may be desirable to control the exothermic reaction adjacent to each endothermic reaction chamber section so that only selected endothermic reaction chamber sections or portions of selected endothermic reaction chamber sections are provided with enough heat to reform fuel. The remaining endothermic reaction sections or portions thereof could be utilized to perform a water gas shift reaction to reduce the concentration of CO in the fuel reforming stream. For example, the temperature in the first two endothermic reaction sections could be controlled to provide relatively high temperature fuel reforming and the temperature in the remaining endothermic reaction sections (that is, in the rearward portion of the reaction vessel) could be controlled to be relatively low thereby reducing unwanted reformation byproducts and so that a maximum conversion is accomplished during the fuel reforming while minimizing methane slip. 
     In another embodiment, illustrated in  FIG. 7 , the vaporizer may be included in the front portion of the combination reaction vessel  54 . The combination reaction vessel shown in  FIG. 7  operates similarly to the vessel shown in  FIG. 2 , but with a few exceptions. In this embodiment, a fuel/water mixture may be charged through line  258  into a first section of the combination reaction vessel  54  to be vaporized in a first heat exchanger section  202 . The fuel/water mixture flows through a plurality of spaced apart chambers  262 ′ that do not include a fuel reforming catalyst. Thereafter, the endothermic reaction chambers  262  include a fuel reforming catalyst as previously discussed. 
     The fuel/water mixture entering the chambers  262 ′ is vaporized by heat generated by the catalytic combustion of a combustion fuel mixture charged into a plurality of exothermic reaction chambers  264 . An oxidant or fuel, preferably an oxidant such as oxygen from the fuel cell stack effluent, may be charged to the exothermic reaction chambers  264  through a charge line  242  and header  243 . An oxidant or fuel, preferably a fuel such as hydrogen from the fuel cell stack effluent, is charged to the exothermic reaction chambers  264  through charge line  282 . A combustion fuel mixture travels through the plurality of spaced apart exothermic reaction chambers  264  generating heat to vaporize the fuel/water mixture or reform the fuel/water mixture. Preferably one of the oxidant or fuel is charged to the exothermic reaction chambers  264  through charge lines  282  in a staged fashion as previously discussed. However, in this embodiment, the exothermic reaction chambers  264  to are spaced apart vertically and horizontally so that a partition section  299  is provided between laterally spaced apart exothermic reaction chambers  264 . The partition sections  299  provide for staged adiabatic reformation of the fuel/water mixture. If desired, the catalyst loading in different portions of the endothermic reaction chambers  262  may be varied as desired. That is, the catalyst loading may be graded throughout the reforming sections. The combination reaction vessel  54  may include flow directing headers  190  to directing the flow of exhaust exiting the first set of exothermic reaction chambers  264  so that it enters a second set of exothermic reaction chambers that are spaced a distance from the first set. The combustion reaction exhaust exits the vessel through line  245  in the reformation reaction exhaust exits the vessel through line  256 .