Fuel processor dewar and methods

Described herein is a fuel processor that produces hydrogen from a fuel source. The fuel processor comprises a reformer and burner. The reformer includes a catalyst that facilitates the production of hydrogen from the fuel source. Voluminous reformer chamber designs are provided that increase the amount of catalyst that can be used in a reformer and increase hydrogen output for a given fuel processor size. The burner provides heat to the reformer. One or more burners may be configured to surround a reformer on multiple sides to increase thermal transfer to the reformer. Dewars are also described that increase thermal management of a fuel processor and increase burner efficiency. A dewar includes one or more dewar chambers that receive inlet process gas or liquid before a burner receives the process gas or liquid. The dewar is arranged such that process gas or liquid passing through the dewar chamber intercepts heat generated in the burner before the heat escapes the fuel processor.

BACKGROUND OF THE INVENTION

The present invention relates to fuel cell technology. In particular, the invention relates to fuel processors that generate hydrogen and are suitable for use in portable applications.

A fuel cell electrochemically combines hydrogen and oxygen to produce electricity. The ambient air readily supplies oxygen. Hydrogen provision, however, calls for a working supply. Gaseous hydrogen has a low energy density that reduces its practicality as a portable fuel. Liquid hydrogen, which has a suitable energy density, must be stored at extremely low temperatures and high pressures, making storing and transporting liquid hydrogen burdensome.

A reformed hydrogen supply processes a fuel source to produce hydrogen. The fuel source acts as a hydrogen carrier. Currently available hydrocarbon fuel sources include methanol, ethanol, gasoline, propane and natural gas. Liquid hydrocarbon fuel sources offer high energy densities and the ability to be readily stored and transported. A fuel processor reforms the hydrocarbon fuel source and to produce hydrogen.

Fuel cell evolution so far has concentrated on large-scale applications such as industrial size generators for electrical power back-up. Consumer electronics devices and other portable electrical power applications currently rely on lithium ion and similar battery technologies. Fuel processors for portable applications such as electronics would be desirable but are not yet commercially available. In addition, techniques that reduce fuel processor size or increase fuel processor efficiency would be highly beneficial.

SUMMARY OF THE INVENTION

The present invention relates to a fuel processor that produces hydrogen from a fuel source. The fuel processor comprises a reformer and burner. The reformer includes a catalyst that facilitates the production of hydrogen from the fuel source. Voluminous reformer chamber designs are provided that increase the amount of catalyst that can be used in a reformer and increase hydrogen output for a given fuel processor size. The burner provides heat to the reformer. One or more burners may be configured to surround a reformer on multiple sides to increase thermal transfer to the reformer.

Dewars are also described that improve thermal management of a fuel processor by reducing heat loss and increasing burner efficiency. A dewar includes one or more dewar chambers that receive inlet process gases or liquids before a reactor receives them. The dewar is arranged such that inlet process gases or liquids passing through the dewar chamber intercepts heat generated in the burner before the heat escapes the fuel processor. Passing inlet process gases or liquids through a dewar chamber in this manner performs three functions: a) active cooling of dissipation of heat generated in burner before is reaches outer portions of the fuel processor, and b) heating of the air before receipt by the burner, and c) absorbing and recycling heat back into the burner increasing burner efficiency. When the burner relies on catalytic combustion to produce heat, heat generated in the burner warms cool process gases or liquids in the burner according to the temperature of the process gases or liquids. This steals heat from the reformer, reduces heating efficiency of a burner and typically results in greater consumption of the fuel source. The dewar thus pre-heats the incoming process gases or liquids before burner arrival so the burner passes less heat to the process gases or liquids that would otherwise transfer to the reformer.

In one aspect, the present invention relates to a fuel processor for producing hydrogen from a fuel source. The fuel processor comprises a reformer configured to receive the fuel source, configured to output hydrogen, and including a catalyst that facilitates the production of hydrogen. The fuel processor also comprises a boiler configured to heat the fuel source before the reformer receives the fuel source. The fuel processor further comprises at least one burner configured to provide heat to the reformer and disposed annularly about the reformer. The fuel processor may also comprise a boiler that heats the burner liquid fuel feed.

In another aspect, the present invention relates to a fuel processor for producing hydrogen from a fuel source. The fuel processor comprises a reformer configured to receive the fuel source, configured to output hydrogen, including a catalyst that facilitates the production of hydrogen. The reformer also includes a reformer chamber having a volume greater than about 0.1 cubic centimeters and less than about 50 cubic centimeters and is characterized by a cross sectional width and a cross sectional height that is greater than one-third the cross sectional width. The fuel processor also comprises a boiler configured to heat the fuel source before the reformer receives the fuel source. The fuel processor further comprises at least one burner configured to provide heat to the reformer.

In yet another aspect, the present invention relates to a fuel processor for producing hydrogen from a fuel source. The fuel processor comprises a reformer configured to receive the hydrogen fuel source, configured to output hydrogen, and including a catalyst that facilitates the production of hydrogen. The fuel processor also comprises a burner that is configured to provide heat to the reformer. The fuel processor further comprises a dewar that at least partially contains the reformer and the burner and includes a set of dewar walls that form a dewar chamber that is configured to receive an inlet process gas or liquid before the burner receives the inlet process gas or liquid. The fuel processor additionally comprises a housing including a set of housing walls that at least partially contain the dewar and provide external mechanical protection for the reformer and the burner.

In still another aspect, the present invention relates to a method for managing heat in a fuel processor. The fuel processor comprises a burner, a reformer and a dewar that at least partially contains the burner. The method comprises generating heat in the burner. The method also comprises passing an inlet process gas or liquid through a dewar chamber. The method further comprises heating the inlet process gas or liquid in the dewar chamber using heat generated in the burner.

In another aspect, the present invention relates to a method for generating hydrogen in a fuel processor. The fuel processor comprises a burner, a reformer and a dewar that at least partially contains the burner and reformer. The method comprises generating heat in the burner. The method also comprises passing an inlet process gas or liquid through a dewar chamber. The method further comprises heating the inlet process gas or liquid in the dewar chamber using heat generated in the burner. The method additionally comprises supplying the inlet process gas or liquid to the burner after it has been heated in the dewar chamber. The method also comprises transferring heat generated in the burner to the reformer. The method further comprises reforming a fuel source to produce hydrogen.

These and other features and advantages of the present invention will be described in the following description of the invention and associated figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1Aillustrates a fuel cell system10for producing electrical energy in accordance with one embodiment of the present invention. Fuel cell system10comprises storage device16, fuel processor15and fuel cell20.

A ‘reformed’ hydrogen supply processes a fuel source to produce hydrogen. As shown, the reformed hydrogen supply comprises a fuel processor15and a fuel source storage device16. Storage device16stores fuel source17, and may include a portable and/or disposable fuel cartridge. A disposable cartridge offers instant recharging to a consumer. In one embodiment, the cartridge includes a collapsible bladder within a hard plastic dispenser case. A separate fuel pump typically controls fuel source17flow from storage device16. If system10is load following, then a control system meters fuel source17to deliver fuel source17to processor15at a flow rate determined by the required power level output of fuel cell20.

Fuel source17acts as a carrier for hydrogen and can be processed to separate hydrogen. Fuel source17may include any hydrogen bearing fuel stream, hydrocarbon fuel or other hydrogen fuel source such as ammonia. Currently available hydrocarbon fuel sources17suitable for use with the present invention include gasoline, C1to C4hydrocarbons, their oxygenated analogues and/or their combinations, for example. Several hydrocarbon and ammonia products may also produce a suitable fuel source17. Liquid fuel sources17offer high energy densities and the ability to be readily stored and shipped. Storage device16may contain a fuel mixture. When the fuel processor15comprises a steam reformer, storage device16may contain a fuel mixture of a hydrocarbon fuel source and water. Hydrocarbon fuel source/water fuel mixtures are frequently represented as a percentage fuel source in water. In one embodiment, fuel source17comprises methanol or ethanol concentrations in water in the range of 1%-99.9%. Other liquid fuels such as butane, propane, gasoline, military grade “JP8” etc. may also be contained in storage device16with concentrations in water from 5-100%. In a specific embodiment, fuel source17comprises 67% methanol by volume.

Fuel processor15processes the hydrocarbon fuel source17and outputs hydrogen. A hydrocarbon fuel processor15heats and processes a hydrocarbon fuel source17in the presence of a catalyst to produce hydrogen. Fuel processor15comprises a reformer, which is a catalytic device that converts a liquid or gaseous hydrocarbon fuel source17into hydrogen and carbon dioxide. As the term is used herein, reforming refers to the process of producing hydrogen from a fuel source. Fuel processor15may output either pure hydrogen or a hydrogen bearing gas stream. Fuel processor15is described in further detail below.

Fuel cell20electrochemically converts hydrogen and oxygen to water, generating electricity and heat in the process. Ambient air commonly supplies oxygen for fuel cell20. A pure or direct oxygen source may also be used for oxygen supply. The water often forms as a vapor, depending on the temperature of fuel cell20components. The electrochemical reaction also produces carbon dioxide as a byproduct for many fuel cells.

In one embodiment, fuel cell20is a low volume polymer electrolyte membrane (PEM) fuel cell suitable for use with portable applications such as consumer electronics. A polymer electrolyte membrane fuel cell comprises a membrane electrode assembly40that carries out the electrical energy generating electrochemical reaction. The membrane electrode assembly40includes a hydrogen catalyst, an oxygen catalyst and an ion conductive membrane that a) selectively conducts protons and b) electrically isolates the hydrogen catalyst from the oxygen catalyst. A hydrogen gas distribution layer contains the hydrogen catalyst and allows the diffusion of hydrogen therethrough. An oxygen gas distribution layer contains the oxygen catalyst and allows the diffusion of oxygen and hydrogen protons therethrough. The ion conductive membrane separates the hydrogen and oxygen gas distribution layers. In chemical terms, the anode comprises the hydrogen gas distribution layer and hydrogen catalyst, while the cathode comprises the oxygen gas distribution layer and oxygen catalyst.

A PEM fuel cell often includes a fuel cell stack having a set of bi-polar plates. A membrane electrode assembly is disposed between two bi-polar plates. Hydrogen distribution43occurs via a channel field on one plate while oxygen distribution45occurs via a channel field on a second facing plate. Specifically, a first channel field distributes hydrogen to the hydrogen gas distribution layer, while a second channel field distributes oxygen to the oxygen gas distribution layer. The ‘term ‘bi-polar’ refers electrically to a bi-polar plate (whether comprised of one plate or two plates) sandwiched between two membrane electrode assembly layers. In this case, the bi-polar plate acts as both a negative terminal for one adjacent membrane electrode assembly and a positive terminal for a second adjacent membrane electrode assembly arranged on the opposite face of the bi-polar plate.

In electrical terms, the anode includes the hydrogen gas distribution layer, hydrogen catalyst and bi-polar plate. The anode acts as the negative electrode for fuel cell20and conducts electrons that are freed from hydrogen molecules so that they can be used externally, e.g., to power an external circuit. In a fuel cell stack, the bi-polar plates are connected in series to add the potential gained in each layer of the stack. In electrical terms, the cathode includes the oxygen gas distribution layer, oxygen catalyst and bi-polar plate. The cathode represents the positive electrode for fuel cell20and conducts the electrons back from the external electrical circuit to the oxygen catalyst, where they can recombine with hydrogen ions and oxygen to form water.

The hydrogen catalyst separates the hydrogen into protons and electrons. The ion conductive membrane blocks the electrons, and electrically isolates the chemical anode (hydrogen gas distribution layer and hydrogen catalyst) from the chemical cathode. The ion conductive membrane also selectively conducts positively charged ions. Electrically, the anode conducts electrons to a load (electricity is produced) or battery (energy is stored). Meanwhile, protons move through the ion conductive membrane, to combine with oxygen. The protons and used electrons subsequently meet on the cathode side, and combine with oxygen to form water. The oxygen catalyst in the oxygen gas distribution layer facilitates this reaction. One common oxygen catalyst comprises platinum powder very thinly coated onto a carbon paper or cloth. Many designs employ a rough and porous catalyst to increase surface area of the platinum exposed to the hydrogen and oxygen.

In one embodiment, fuel cell20comprises a set of bi-polar plates that each includes channel fields on opposite faces that distribute the hydrogen and oxygen. One channel field distributes hydrogen while a channel field on the opposite face distributes oxygen. Multiple bi-polar plates can be stacked to produce a ‘fuel cell stack’ in which a membrane electrode assembly is disposed between each pair of adjacent bi-polar plates. Since the electrical generation process in fuel cell20is exothermic, fuel cell20may implement a thermal management system to dissipate heat from the fuel cell. Fuel cell20may also employ a number of humidification plates (HP) to manage moisture levels in the fuel cell. Further description of a fuel cell suitable for use with the present invention is included in commonly owned co-pending patent application entitled “Micro Fuel Cell Architecture” naming Ian Kaye as inventor and filed on the same day as this patent application. This application is incorporated by reference for all purposes

While the present invention will mainly be discussed with respect to PEM fuel cells, it is understood that the present invention may be practiced with other fuel cell architectures. The main difference between fuel cell architectures is the type of ion conductive membrane used. In one embodiment, fuel cell20is phosphoric acid fuel cell that employs liquid phosphoric acid for ion exchange. Solid oxide fuel cells employ a hard, non-porous ceramic compound for ion exchange and may be suitable for use with the present invention. Generally, any fuel cell architecture may benefit from fuel processor improvements described herein. Other such fuel cell architectures include direct methanol, alkaline and molten carbonate fuel cells.

Fuel cell20generates dc voltage that may be used in a wide variety of applications. For example, electricity generated by fuel cell20may be used to power a motor or light. In one embodiment, the present invention provides ‘small’ fuel cells that are designed to output less than 200 watts of power (net or total). Fuel cells of this size are commonly referred to as ‘micro fuel cells’ and are well suited for use with portable electronics. In one embodiment, fuel cell20is configured to generate from about 1 milliwatt to about 200 watts. In another embodiment, fuel cell20generates from about 3 W to about 20 W. Fuel cell20may also be a stand-alone fuel cell, which is a single unit that produces power as long as it has an a) oxygen and b) hydrogen or a hydrocarbon fuel supply. A fuel cell20that outputs from about 40 W to about 100 W is well suited to power a laptop computer.

FIG. 1Billustrates schematic operation for fuel cell system10in accordance with a specific embodiment of the present invention. As shown, fuel cell system10comprises fuel container16, hydrogen fuel source17, fuel processor15, fuel cell20, multiple pumps21and fans35, fuel lines and gas lines, and one or more valves23. While the present invention will now primarily be described with respect to methanol as fuel source17, it is understood that the present invention may employ another fuel source17such as one provided above.

Fuel container16stores methanol as a hydrogen fuel source17. An outlet26of fuel container16provides methanol17into hydrogen fuel source line25. As shown, line25divides into two lines: a first line27that transports methanol17to a burner30for fuel processor15and a second line29that transports methanol17to reformer32in fuel processor15. Lines25,27and29may comprise plastic tubing, for example. Separate pumps21aand21bare provided for lines27and29, respectively, to pressurize the lines and transmit the fuel source at independent rates if desired. A model P625 pump as provided by Instech of Plymouth Meeting, Pa. is suitable to transmit liquid methanol for system10is suitable in this embodiment. A flow sensor or valve23situated on line29between storage device16and fuel processor18detects and communicates the amount of methanol17transfer between storage device16and reformer32. In conjunction with the sensor or valve23and suitable control, such as digital control applied by a processor that implements instructions from stored software, pump21bregulates methanol17provision from storage device16to reformer32.

Fan35adelivers oxygen and air from the ambient room through line31to regenerator36of fuel processor15. Fan35bdelivers oxygen and air from the ambient room through line33to regenerator36of fuel processor15. In this embodiment, a model AD2005DX-K70 fan as provided by Adda USA of California is suitable to transmit oxygen and air for fuel cell system10. A fan37blows cooling air over fuel cell20and its heat transfer appendages46.

Fuel processor15receives methanol17from storage device16and outputs hydrogen. Fuel processor15comprises burner30, reformer32, boiler34and dewar150. Burner30includes an inlet that receives methanol17from line27and a catalyst that generates heat with methanol presence. In one embodiment, burner30includes an outlet that exhausts heated gases to a line41, which transmits the heated gases over heat transfer appendages46of fuel cell20to pre-heat the fuel cell and expedite warm-up time needed when initially turning on fuel cell20. An outlet of burner30may also exhaust heated gases into the ambient room.

Boiler34includes an inlet that receives methanol17from line29. The structure of boiler34permits heat produced in burner30to heat methanol17in boiler34before reformer32receives the methanol17. Boiler34includes an outlet that provides heated methanol17to reformer32.

Reformer32includes an inlet that receives heated methanol17from boiler34. A catalyst in reformer32reacts with the methanol17and produces hydrogen and carbon dioxide. This reaction is slightly endothermic and draws heat from burner30. A hydrogen outlet of reformer32outputs hydrogen to line39. In one embodiment, fuel processor15also includes a preferential oxidizer that intercepts reformer32hydrogen exhaust and decreases the amount of carbon monoxide in the exhaust. The preferential oxidizer employs oxygen from an air inlet to the preferential oxidizer and a catalyst based on, for example ruthenium or platinum, that is preferential to carbon monoxide over carbon dioxide.

Dewar150pre-heats a process gas or liquid before the air enters burner30. Dewar150also reduces heat loss from fuel cell15by heating the incoming process liquids or gases before the heat escapes fuel processor15. In one sense, dewar150acts as a regenerator that uses waste heat in fuel processor15to improve thermal management and thermal efficiency of the fuel processor. Specifically, waste heat from burner30may be used to pre-heat incoming air provided to burner30to reduce heat transfer to the air in the burner so more heat transfers to reformer32. Dewar150is described in further detail below.

Line39transports hydrogen from fuel processor15to fuel cell20. Gaseous delivery lines31,33and39may comprise polymeric or metallic tubing, for example. A hydrogen flow sensor (not shown) may also be added on line39to detect and communicate the amount of hydrogen being delivered to fuel cell20. In conjunction with the hydrogen flow sensor and suitable control, such as digital control applied by a processor that implements instructions from stored software, fuel processor15regulates hydrogen gas provision to fuel cell20.

Fuel cell20includes an hydrogen inlet port that receives hydrogen from line39and delivers it to a hydrogen intake manifold for delivery to one or more bi-polar plates and their hydrogen distribution channels. An oxygen inlet port of fuel cell20receives oxygen from line33and delivers it to an oxygen intake manifold for delivery to one or more bi-polar plates and their oxygen distribution channels. An anode exhaust manifold collects gases from the hydrogen distribution channels and delivers them to an anode exhaust port, which outlets the exhaust gases into the ambient room. A cathode exhaust manifold collects gases from the oxygen distribution channels and delivers them to a cathode exhaust port.

The schematic operation for fuel cell system10shown inFIG. 1Bis exemplary and other variations on fuel cell system design, such as reactant and byproduct plumbing, are contemplated. In addition to the components shown in shown inFIG. 1B, system10may also include other elements such as electronic controls, additional pumps and valves, added system sensors, manifolds, heat exchangers and electrical interconnects useful for carrying out functionality of system10that are known to one of skill in the art and omitted herein for sake of brevity.

FIG. 1Cillustrates an embodiment of fuel system10that routes unused hydrogen from fuel cell20back to burner30. Burner30includes a catalyst that reacts with the unused hydrogen to produce heat. Since hydrogen consumption within fuel cell20is often incomplete and the anode exhaust often includes unused hydrogen, re-routing the anode exhaust to burner30allows fuel cell system10to capitalize on unused hydrogen in fuel cell20and increase hydrogen usage and efficiency in system10. As the term is used herein, unused hydrogen generally refers to hydrogen output from a fuel cell.

Line51is configured to transmit unused hydrogen from fuel cell20to burner30of fuel processor15. ForFIG. 1C, burner30includes two inlets: an inlet55configured to receive the hydrogen fuel source17and an inlet53configured to receive the hydrogen from line51. Anode gas collection channels, which distribute hydrogen from fuel processor15to each membrane electrode assembly layer, collect and exhaust the unused hydrogen. An inlet fan pressurizes line39that delivers the hydrogen from an outlet of fuel processor15to an anode inlet of fuel cell20. The inlet fan also pressurizes the anode gas collection channels for distribution of hydrogen within fuel cell20. In one embodiment, gaseous delivery in line51back to fuel processor15relies on pressure at the exhaust of the anode gas distribution channels, e.g., in the anode exhaust manifold. In another embodiment, an extra fan is added to line51to pressurize line51and return unused hydrogen back to fuel processor15.

Burner30also includes an inlet59configured to receive oxygen from an oxygen exhaust included in fuel cell20. Cathode gas collection channels, which distribute oxygen and air from the ambient room to each membrane electrode assembly layer, collect and exhaust the unused oxygen. Line61delivers unused oxygen from an exhaust manifold, which collects oxygen from each cathode gas collection channel, to inlet59. Burner30thus includes two oxygen inlets: inlet59and an inlet57configured to receive oxygen from the ambient room after delivery though dewar150. Since oxygen consumption within fuel cell20is often incomplete and the cathode exhaust includes unused oxygen, re-routing the cathode exhaust to burner30allows fuel cell system10to capitalize on unused oxygen in fuel cell20and increase oxygen usage and efficiency in system10.

In one embodiment, fuel processor15is a steam reformer that only needs steam to produce hydrogen. Several types of reformers suitable for use in fuel cell system10include steam reformers, auto thermal reformers (ATR) or catalytic partial oxidizers (CPOX). ATR and CPOX reformers mix air with the fuel and steam mix. ATR and CPOX systems reform fuels such as methanol, diesel, regular unleaded gasoline and other hydrocarbons. In a specific embodiment, storage device16provides methanol17to fuel processor15, which reforms the methanol at about 250° C. or less and allows fuel cell system10use in applications where temperature is to be minimized.

FIG. 2Aillustrates a cross-sectional side view of fuel processor15in accordance with one embodiment of the present invention.FIG. 2Billustrates a cross-sectional front view of fuel processor15taken through a mid-plane of processor15that also shows features of end plate82. Fuel processor15reforms methanol to produce hydrogen. Fuel processor15comprises monolithic structure100, end plates82and84, reformer32, burner30, boiler34, boiler108, dewar150and housing152. Although the present invention will now be described with respect to methanol consumption for hydrogen production, it is understood that fuel processors of the present invention may consume another fuel source, as one of skill in the art will appreciate.

As the term is used herein, ‘monolithic’ refers to a single and integrated structure that includes at least portions of multiple components used in fuel processor15. As shown, monolithic structure100includes reformer32, burner30, boiler34and boiler108. Monolithic structure100may also include associated plumbing inlets and outlets for reformer32, burner30and boiler34. Monolithic structure100comprises a common material141that constitutes the structure. Common material141is included in walls that define the reformer32, burner32and boilers34and108. Specifically, walls111,119,120,122,130,132,134and136all comprise common material141. Common material141may comprise a metal, such as copper, silicon, stainless steel, inconel and other metal/alloys displaying favorable thermal conducting properties. The monolithic structure100and common material141simplify manufacture of fuel processor15. For example, using a metal for common material141allows monolithic structure100to be formed by extrusion or casting. In some cases, monolithic structure100is consistent in cross sectional dimensions between end plates82and84and solely comprises copper formed in a single extrusion. Common material141may also include a ceramic, for example. A ceramic monolithic structure100may be formed by sintering.

Housing152provides mechanical protection for internal components of fuel processor15such as burner30and reformer32. Housing152also provides separation from the environment external to processor15and includes inlet and outlet ports for gaseous and liquid communication in and out of fuel processor15. Housing152includes a set of housing walls161that at least partially contain a dewar150and provide external mechanical protection for components in fuel processor15. Walls161may comprises a suitably stiff material such as a metal or a rigid polymer, for example. Dewar150improves thermal heat management for fuel processor15and will be discussed in further detail with respect toFIG. 4A.

Referring toFIG. 2B, boiler34heats methanol before reformer32receives the methanol. Boiler34receives the methanol via fuel source inlet81, which couples to the methanol supply line27ofFIG. 1B. Since methanol reforming and hydrogen production via a catalyst102in reformer32often requires elevated methanol temperatures, fuel processor15pre-heats the methanol before receipt by reformer32via boiler34. Boiler34is disposed in proximity to burner30to receive heat generated in burner30. The heat transfers via conduction through monolithic structure from burner30to boiler34and via convection from boiler34walls to the methanol passing therethrough. In one embodiment, boiler34is configured to vaporize liquid methanol. Boiler34then passes the gaseous methanol to reformer32for gaseous interaction with catalyst102.

Reformer32is configured to receive methanol from boiler34. Walls111in monolithic structure100(see cross section inFIG. 3A) and end walls113(FIG. 2B) on end plates82and84define dimensions for a reformer chamber103. In one embodiment, end plate82and/or end plate84includes also channels95(FIG. 2A) that route heated methanol exhausted from boiler34into reformer32. The heated methanol then enters the reformer chamber103at one end of monolithic structure100and passes to the other end where the reformer exhaust is disposed. In another embodiment, a hole disposed in a reformer32wall receives inlet heated methanol from a line or other supply. The inlet hole or port may be disposed on a suitable wall111or113of reformer32.

Reformer32includes a catalyst102that facilitates the production of hydrogen. Catalyst102reacts with methanol17and facilitates the production of hydrogen gas and carbon dioxide. In one embodiment, catalyst102comprises pellets packed to form a porous bed or otherwise suitably filled into the volume of reformer chamber103. In one embodiment, pellet sizes are designed to maximize the amount of surface area exposure to the incoming methanol. Pellet diameters ranging from about 50 microns to about 1.5 millimeters are suitable for many applications. Pellet diameters ranging from about 350 microns to about 1500 microns are suitable for use with reformer chamber103. Pellet sizes and packing may also be varied to control the pressure drop that occurs through reformer chamber103. In one embodiment, pressure drops from about 0.2 to about 5 psi gauge are suitable between the inlet and outlet of reformer chamber103. Pellet sizes may be varied relative to the cross sectional size of reformer chamber103, e.g., as reformer chamber103increases in size so may catalyst102pellet diameters. In one embodiment, the ratio of pellet diameter (d) to cross sectional height117(D) may range from about 0.0125 to about 1. A D/d ratio from about 5 to about 20 is also suitable for many applications. A packing density may also characterize packing of catalyst102in reformer chamber103. For a copper zinc catalyst102, packing densities from about 0.3 grams/milliliter to about 2 grams/milliliter are suitable. Packing densities from about 0.9 grams/milliliter to about 1.4 grams/milliliter are appropriate for the embodiment shown inFIG. 3A.

One suitable catalyst102may include CuZn on alumina pellets when methanol is used as a hydrocarbon fuel source17. Other materials suitable for catalyst102may be based on nickel, platinum, palladium, or other precious metal catalysts either alone or in combination, for example. Catalyst102pellets are commercially available from a number of vendors known to those of skill in the art. Pellet catalysts may also be disposed within a baffling system disposed in the reformer chamber103. The baffling system includes a set of walls that guide the fuel source along a non-linear path. The baffling slows and controls flow of gaseous methanol in chamber103to improve interaction between the gaseous methanol and pellet catalyst102. Catalyst102may alternatively comprise catalyst materials listed above coated onto a metal sponge or metal foam. A wash coat of the desired metal catalyst material onto the walls of reformer chamber103may also be used for reformer32.

Reformer32is configured to output hydrogen and includes an outlet port87that communicates hydrogen formed in reformer32outside of fuel processor15. In fuel cell system10, port87communicates hydrogen to line39for provision to hydrogen distribution43in fuel cell20. Port87is disposed on a wall of end plate82and includes a hole that passes through the wall (seeFIG. 2B). The outlet hole port may be disposed on any suitable wall111or113.

Hydrogen production in reformer32is slightly endothermic and draws heat from burner30. Burner30generates heat and is configured to provide heat to reformer32. Burner30is disposed annularly about reformer32, as will be discussed in further detail below. As shown inFIG. 2B, burner30comprises two burners (or burner sections)30aand30band their respective burner chambers105aand105bthat surround reformer32. Burner30includes an inlet that receives methanol17from boiler108via a channel in one of end plates82or84. In one embodiment, the burner inlet opens into burner chamber105a. The methanol then travels the length142of burner chamber105ato channels disposed in end plate82that route methanol from burner chamber105ato burner chamber105b. The methanol then travels the back through the length142of burner chamber105bto burner exhaust89. In another embodiment, the burner inlet opens into both chambers105aand105b. The methanol then travels the length142of both chambers105aand105bto burner exhaust89.

In one embodiment, burner30employs catalytic combustion to produce heat. A catalyst104disposed in each burner chamber105helps a burner fuel passed through the chamber generate heat. In one embodiment, methanol produces heat in burner30and catalyst104facilitates the methanol production of heat. In another embodiment, waste hydrogen from fuel cell20produces heat in the presence of catalyst104. Suitable burner catalysts104may include platinum or palladium coated onto a suitable support or alumina pellets for example. Other materials suitable for catalyst104include iron, tin oxide, other noble-metal catalysts, reducible oxides, and mixtures thereof. The catalyst104is commercially available from a number of vendors known to those of skill in the art as small pellets. The pellets that may be packed into burner chamber105to form a porous bed or otherwise suitably filled into the burner chamber volume. Catalyst104pellet sizes may be varied relative to the cross sectional size of burner chamber105. Catalyst104may also comprise catalyst materials listed above coated onto a metal sponge or metal foam or wash coated onto the walls of burner chamber105. A burner outlet port89(FIG. 2A) communicates exhaust formed in burner30outside of fuel processor15.

Some fuel sources generate additional heat in burner30, or generate heat more efficiently, with elevated temperatures. Fuel processor15includes a boiler108that heats methanol before burner30receives the fuel source. In this case, boiler108receives the methanol via fuel source inlet85. Boiler108is disposed in proximity to burner30to receive heat generated in burner30. The heat transfers via conduction through monolithic structure from burner30to boiler108and via convection from boiler108walls to the methanol passing therethrough.

Air including oxygen enters fuel processor15via air inlet port91. Burner30uses the oxygen for catalytic combustion of methanol. As will be discussed in further detail below with respect toFIGS. 4A and 4B, air first passes along the outside of dewar150before passing through apertures in the dewar and along the inside of dewar150. This heats the air before receipt by air inlet port93of burner30.

FIG. 3Aillustrates a cross-sectional front view of monolithic structure100as taken through a mid-plane121in accordance with one embodiment of the present invention. Monolithic structure100extends from end plate82to end plate84. The cross section of monolithic structure100shown inFIG. 3Aextends from one end of structure100at end plate82to the other end of structure100at end plate84. Monolithic structure100includes reformer32, burner30, boiler34and boiler108between end plates82and84.

Reformer32includes a reformer chamber103, which is a voluminous space in fuel processor15that includes the reforming catalyst102, opens to the fuel source inlet (from boiler34for fuel processor15), and opens to hydrogen outlet87. Side walls111define a non-planar cross-sectional shape for reformer32and its reformer chamber103. Walls113on end plates82and84close the reformer chamber103on either end of the chamber103and include the inlet and outlet ports to the chamber103.

Reformer chamber103includes a non-planar volume. As the term is used herein, a non-planar reformer chamber103refers to a shape in cross section that is substantially non-flat or non-linear. A cross section refers to a planar slice that cuts through the fuel processor or component. For cross sections that include multiple fuel processor components (e.g., both burner30and reformer32), the cross section includes both components. For the vertical and front cross section121shown inFIG. 3A, the cross section dimensions shown are consistent for monolithic structure100from end plate82to end plate84, and are consistent at each cross section121(FIG. 2A).

Reformer32and its reformer chamber103may employ a quadrilateral or non-quadrilateral cross-sectional shape. Four sides define a quadrilateral reformer chamber103in cross section. Four substantially orthogonal sides define rectangular and square quadrilateral reformers32. A non-quadrilateral reformer32may employ cross-sectional geometries with more or less sides, an elliptical shape (seeFIG. 3B), and more complex cross-sectional shapes. As shown inFIG. 3A, reformer32includes a six-sided cross-sectional ‘P-shape’ with chamfered corners. One corner section of reformer32is removed from monolithic structure100to allow for boiler34proximity to burner30.

Reformer chamber103is characterized by a cross-sectional width115and a cross-sectional height117. A maximum linear distance between inner walls111of chamber103in a direction spanning a cross section of reformer chamber103quantifies cross-sectional width155. A maximum linear distance between inner walls111of chamber103orthogonal to the width115quantifies cross-sectional height117. As shown, cross-sectional height117is greater than one-third the cross-sectional width115. This height/width relationship increases the volume of reformer chamber103for a given fuel processor15. In one embodiment, cross-sectional height117is greater than one-half cross-sectional width115. In another embodiment, cross-sectional height117is greater than the cross-sectional width115.

Referring back toFIG. 2A, reformer chamber103includes a length142(orthogonal to the width115and height117) that extends from one end of monolithic structure100at end plate82to the other end of structure100at end plate84. In one embodiment, reformer chamber103has a length142to width115ratio less than 20:1. In a less elongated design, reformer chamber103has a length142to width115ratio less than 10:1.

Reformer32provides a voluminous reformer chamber103. This three dimensional configuration for reformer chamber103contrasts micro fuel processor designs where the reformer chamber is etched as micro channels onto a planar substrate. The non-planar dimensions of reformer chamber103permit greater volumes for reformer32and permit more catalyst102for a given size of fuel processor15. This increases the amount of methanol that can be processed and increases hydrogen output for a particular fuel processor15size. Reformer32thus improves fuel processor's15suitability and performance in portable applications where fuel processor size is important or limited. In other words, since the size of inlet and outlet plumbing and ports varies little while increasing the reformer chamber103volume, this allows fuel processor15to increase hydrogen output and increase power density for portable applications while maintaining size and weight of the associated plumbing relatively constant. In one embodiment, reformer chamber103comprises a volume greater than about 0.1 cubic centimeters and less than about 50 cubic centimeters. In some embodiments, reformer32volumes between about 0.5 cubic centimeters and about 2.5 cubic centimeters are suitable for laptop computer applications.

Fuel processor includes at least one burner30. Each burner30includes a burner chamber105. For a catalytic burner30, the burner chamber105is a voluminous space in fuel processor15that includes catalyst104. For communication or burner reactants and products to and from the burner chamber105, the burner chamber105may directly or indirectly open to a fuel source inlet (from boiler108for fuel processor15), open to an air inlet93, and open to a burner exhaust89.

The number of burners30and burner chambers105may vary with design. Monolithic structure100ofFIG. 3Aincludes a dual burner30aand30bdesign having two burner chambers105aand105b, respectively, forming non-continuous chambers that substantially surround reformer32in cross section. Burner30acomprises side walls119a(FIG. 3A) included in monolithic structure100and end walls113on end plates82and84(FIG. 2B) that define burner chamber105a. Similarly, burner30bincludes side walls119b(FIG. 3A) included in monolithic structure100and end walls113on end plates82and84(FIG. 2B) that define burner chamber105b. Monolithic structure100ofFIG. 3Cincludes a single burner30cwith a single burner chamber105cthat fully surrounds reformer32. Tubular arrangement ofFIG. 3Bincludes over forty burners204that fully surround reformer202. Monolithic structure452ofFIG. 4Fincludes a single burner divided into 104 burner chambers that fully surround reformer32.

Referring toFIG. 2B, each burner30is configured relative to reformer32such that heat generated in a burner30transfers to reformer32. In one embodiment, the one or more burners30are annularly disposed about reformer32. As the term is used herein, annular configuration of at least one burner30relative to reformer32refers to the burner30having, made up of, or formed by, continuous or non-continuous segments or chambers105that surround reformer32. The annular relationship is apparent in cross section. For burner and reformer arrangements, surrounding refers to a burner30bordering or neighboring the perimeter of reformer32such that heat may travel from a burner30to the reformer32. Burners30aand30bmay surround reformer32about the perimeter of reformer32to varying degrees based on design. At the least, one or more burners30surround greater than 50 percent of the reformer32cross-sectional perimeter. This differentiates fuel processor15from planar and plate designs where the burner and reformer are co-planar and of similar dimensions, and by geometric logic, the burner neighbors less than 50 percent of the reformer perimeter. In one embodiment, one or more burners30surround greater than 75 percent of the reformer32cross-sectional perimeter. Increasing the extent to which burner30surrounds reformer32perimeter in cross section increases the surface area of reformer32that can be used to heat the reformer volume via heat generated in the burner. For some fuel processor15designs, one or more burners30may surround greater than 90 percent of the reformer32cross-sectional perimeter. For the embodiment shown inFIG. 3B, burner30surrounds the entire reformer32cross-sectional perimeter.

Although the present invention will now be described with respect to burner30annularly disposed about reformer32, it is understood that monolithic structure100may comprise the reverse configuration. That is, reformer32may be annularly disposed about burner30. In this case, reformer32may comprise one or more continuous or non-continuous segments or chambers103that surround burner30.

Each burner30thus bilaterally borders reformer32. N-lateral bordering in this sense refers to the number of sides, N, of reformer32that a burner30(and its burner chamber105) borders in cross section. Thus, burner30bborders the right and bottom sides of reformer32, while burner30aborders the top and left sides of reformer32. A ‘U-shaped’ burner30may be employed to trilaterally border reformer32on three sides. Together, burners30aand30bquadrilaterally border reformer32on all four orthogonal reformer32sides. The reformer32used in the configuration ofFIG. 3Bincludes multiple tubular burners that quadrilaterally border reformer32.FIG. 3Cillustrates a cross-sectional front view of monolithic structure100that comprises a single burner30chaving an ‘O-shape’ that completely surrounds reformer chamber103in accordance with one embodiment of the present invention. Burner30cis a continuous chamber about the perimeter of reformer32and quadrilaterally borders reformer32.

Heat generated in burner30transfers directly and/or indirectly to reformer32. For the monolithic structure100ofFIG. 3A, each burner30and reformer32share common walls120and122and heat generated in each burner30transfers directly to reformer32via conductive heat transfer through common walls120and122. Wall120forms a boundary wall for burner30band a boundary wall for reformer32. As shown, one side of wall120opens to burner chamber105bwhile another portion of the wall opens to reformer chamber103. Wall120thus permits direct conductive heat transfer between burner30band reformer32. Similarly, wall122forms a boundary wall for burner30aand a boundary wall for reformer32, opens to burner chamber105a, opens to reformer chamber103, and permits direct conductive heat transfer between burner30aand reformer32. Walls120and122are both non-planar in cross section and border multiple sides of reformer chamber103that are neighbored by burners30band30a. Wall120thus provides direct conductive heat transfer in multiple orthogonal directions128and129from burner30ato reformer32. Wall122similarly provides direct conductive heat transfer in directions opposite to128and129from burner30bto reformer32.

Boiler34comprises cylindrical walls143included in monolithic structure100and end walls113on end plates82and84(seeFIG. 2B) that define boiler chamber147. Circular walls143in cross section form a cylindrical shape for boiler34that extends from routing end82to routing end84. Boiler34is disposed in proximity to burners30aand30bto receive heat generated in each burner30. For monolithic structure100, boiler34shares a common wall130with burner30aand a common wall132with burner30b. Common walls130and132permit direct conductive heat transfer from each burner30to boiler34. Boiler34is also disposed between burners30and reformer32to intercept thermal conduction consistently moving from the high temperature and heat generating burners30to the endothermic reformer32.

Boiler108is configured to receive heat from burner30to heat methanol before burner30receives the methanol. Boiler108also comprises a tubular shape having a circular cross section that extends through monolithic structure100from end plate82to end plate84. Boiler108is disposed in proximity to burners30aand30bto receive heat generated in each burner30, which is used to heat the methanol. Boiler108shares a common wall134with burner30aand a common wall136with burner30b. Common walls134and136permit direct conductive heat transfer from burners30aand30bto boiler108.

FIG. 3Dillustrates an outside view of end plate82in accordance with one embodiment of the present invention. End plate82includes fuel source inlet81, fuel source fuel source inlet85, hydrogen outlet port87and burner air inlet93. Fuel source inlet81includes a hole or port in end wall113of end plate82that communicates methanol (usually as a liquid) from an external methanol supply to boiler34for heating the methanol before receipt by reformer32. Methanol fuel source inlet85includes a hole or port in end wall113of end plate82that communicates methanol (usually as a liquid) from an external methanol supply to boiler108for heating the methanol before receipt by burner30. Burner air inlet93includes a hole or port in end wall113of end plate82that communicates air and oxygen from the ambient room after it has been preheated in dewar150. Hydrogen outlet port87communicates gaseous hydrogen from reforming chamber103outside fuel processor15.

Bolt holes153are disposed in wings145of monolithic structure100. Bolt holes153permit the passage of bolts therethrough and allow securing of structure100and end plates82and84.

FIG. 3Billustrates a cross-sectional layout of a tubular design200for use in fuel processor15in place of monolithic structure100in accordance with another embodiment of the present invention. Structure200includes a reformer202, burner204, boiler206and boiler208.

The cross-sectional design200shown inFIG. 3Bis consistent throughout a cylindrical length between end plates (not shown) that include inlet and outlet ports for supply and exhaust of gases to components of design200. The circular shape of reformer202, burner chambers212, boiler206and boiler208thus extends for the entire cylindrical length between the end plates. The end plates may also be responsible for routing gases between individual tubes, such as between tubular burners234.

Reformer202includes cylindrical walls203that define a substantially circular cross section. Reformer232thus resembles a hollow cylinder in three dimensions that defines a tubular reformer chamber210. In general, reformer202may include any elliptical shape (a circle represents an ellipse of about equal orthogonal dimensions) suitable for containing the catalyst102, for methanol flow through reformer chamber210, for hydrogen production in reformer chamber210, and for hydrogen flow in reformer chamber210. As shown, reformer chamber210is defined by a cross sectional width and a cross sectional height that are substantially equal and thus reformer202includes a 1:1 cross sectional aspect ratio.

Burner204comprises a set of cylindrical walls214that each defines a tubular burner chamber212. As shown, tubular design200includes over forty tubular burner chambers212that fully surround the cross sectional perimeter of reformer32. Each tubular burner chamber212includes a substantially circular cross-section defined by the cylindrical wall214. Each tubular burner chamber212includes catalyst104that facilitates heat generation from methanol. Burner204may comprise from about two to about two hundred cylindrical walls214and tubular burner chambers212. Some designs may include from about ten to about sixty tubular burner chambers212. In one embodiment, each cylindrical wall214comprises a metal and is extruded to its desired dimensions. In a specific embodiment, cylindrical wall214comprises nickel. The nickel wall214may be formed by electroplating nickel onto a suitable substrate such as zinc or aluminum that may subsequently etched out to leave the nickel tube. Other materials that a nickel wall214may be formed onto include zinc, tin, lead, wax or plastics. In addition to nickel, wall214may include gold, silver, copper, stainless steel, ceramics and materials that display suitable thermal properties without causing complications with burner catalyst104.

As shown, burner204fully annularly surrounds the cross-sectional perimeter of reformer202. In this case, burner204comprises three ring-like layers216,218and220of tubes214disposed circularly about reformer202and at three different radii. The tubes214in each layer216,218and220circumscribe reformer202. Heat generated in each tubular chamber212of burner30transfers directly or indirectly to reformer202via several paths: a) heat conduction through the tubes214in layer216to the walls of reformer202; b) heat conduction through the tubes214in outer layers218and220to tubes214in layer216and to the walls of reformer202; and/or c) heat radiation between tubes214in outer layers218and220and tubes214and then conduction inward to reformer202.

Boiler206is configured to heat methanol before reformer202receives the methanol. Boiler206receives heat from burner204and comprises a cylindrical wall207that defines a tubular shape for the boiler. Boiler206is disposed in proximity to burner tubes214to receive heat generated in each burner chamber212. Specifically, boiler206is disposed in the second ring-like layer218and receives heat from adjacent burner chambers212in layers216,218and220. Burner204provides heat to boiler206via conduction through the walls of each adjacent tube214and through wall207.

Boiler208is configured to heat methanol before burner204receives the methanol. Boiler208receives heat from burner204and also comprises a cylindrical wall209that defines a tubular shape for the boiler. Similar to boiler206, boiler208is disposed in the second ring-like layer218and receives heat from adjacent burner chambers212in layers216,218and220.

In one embodiment, a monolithic fuel processor15comprises multiple segments joined together in the direction of gas flow in reformer chamber103and joined at sectional lines121. Each segment has a common profile as shown inFIG. 3Aand may comprise metal or ceramic elements that are bonded or brazed perpendicular to the direction of gas flow. Alternatively, fuel processor15may comprise a single long monolithic piece that bounds all of reformer32, burner30, boiler34and boiler108except for areas bound by end pieces82and84.

In another embodiment, fuel processor15comprises multiple pieces joined together in cross section.FIG. 3Eillustrates a fuel processor15in accordance with another embodiment of the present invention. In this case, fuel processor15comprises three pieces: lower piece280, middle piece282and cap piece284. Lower piece280and middle piece282attach to form reformer32and two burner chambers30. Cap piece284and middle piece282attach to form boilers34and108. Each piece208,282and284comprises a common material and may be extruded or cast to suitable dimensions. Attachment between the pieces may comprise chemical bonding, for example.

FIG. 4Aillustrates a side cross-sectional view of fuel processor15and movement of air created by dewar150in accordance with one embodiment of the present invention.FIG. 4Billustrates a front cross-sectional view of fuel processor15and demonstrates thermal management benefits gained by dewar150. While thermal management techniques described herein will now be described as fuel processor components, those skilled in the art will recognize that the present invention encompasses methods of thermal management for general application.

A burner30in fuel processor15generates heat and typically operates at an elevated temperature. Burner30operating temperatures greater than 200 degrees Celsius are common. Standards for the manufacture of electronics devices typically dictate a maximum surface temperature for a device. Electronics devices such as laptop computers often include cooling, such as a fan or cooling pipe, to manage and dissipate internal heat. A fuel processor internal to an electronics device that loses heat into the device calls upon the device's cooling system to handle the lost heat.

In one embodiment, fuel processor15comprises a dewar150to improve thermal management for fuel processor15. Dewar150at least partially thermally isolates components internal to housing152—such as burner30—and contains heat within fuel processor15. Dewar150reduces heat loss from fuel processor15and helps manage the temperature gradient between burner30and outer surface of housing152. And as will be described below, dewar150also pre-heats air before it is received by burner30.

Dewar150at least partially contains burner30and reformer32, and includes a set of dewar walls154that help form a dewar chamber156and a chamber158. In some embodiments, dewar150fully surrounds burner30and reformer32in a cross sectional view and at both ends of burner30and reformer32. Less containment by dewar150is also suitable to provide thermal benefits described herein. The multipass dewar300ofFIG. 4Eonly partially encloses burner30and reformer32in cross section. In some cases, dewar150does not extends fully along the length of monolithic structure100and provides less than full containment.

As shown inFIG. 4B, dewar150annularly surrounds burner30in cross section. The set of walls154includes side walls154aand154cthat combine with top and bottom walls154band154dto form the rectangular cross section shown inFIG. 4B; and includes two end walls154eand154fthat combine with top and bottom walls154band154dto form the rectangular cross section shown inFIG. 4A. End wall154fincludes apertures that permit the passage of inlet and outlet ports85,87and89therethough.

Dewar chamber156is formed within dewar walls154and comprises all space within the dewar walls154not occupied by monolithic structure100. As shown inFIG. 4B, dewar chamber156surrounds monolithic structure100. As shown inFIG. 4B, chamber156comprises ducts between monolithic structure100and walls154on all four sides of dewar150. In addition, chamber156comprises air pockets between end walls of dewar150and outside surfaces of end plates82and84on both ends of monolithic structure100(FIG. 4A).

Chamber158is formed outside dewar walls154between dewar150and housing152. Chamber158comprises all space within housing152not occupied by dewar150. As shown inFIG. 4B, housing152encloses dewar150and the further internal monolithic structure100. Chamber158comprises ducts between walls154on all four sides of dewar150and housing152. In addition, chamber158comprises air pockets167between dewar150and housing152on both ends that prevent contact and conductive heat transfer between dewar150and housing152(FIG. 4A).

Dewar150is configured such that a process gas or liquid passing through dewar chamber156receives heat generated in burner30. The process gas or liquid may include any reactant used in fuel processor such as oxygen, air, or fuel source17, for example. Dewar150offers thus two functions for fuel processor15: a) it permits active cooling of components within fuel processor15before the heat reaches an outer portion of the fuel processor, and b) it pre-heats the air going to burner30. For the former, air moves through fuel processor15and across walls154of dewar150such that the cooler air absorbs heat from the warmer fuel processor15components.

As shown inFIG. 4A, housing152includes an air inlet port91or hole that permits the passage of air from outside housing152into air into chamber158. A fan usually provides the air directly to fuel processor15and pressurizes the air coming through port91. Top and bottom walls154band154dinclude air inlet ports or holes172that allow air to pass from chamber158to dewar chamber156. Air flow through fuel processor15then flows: in air inlet port91, through chamber158along the length of the dewar150, through holes172in walls154band154d, through chamber156back along the length of the dewar150in the opposite direction as in through chamber158, and into air inlet ports176that allow the air to enter burner30. In chamber158, the air a) moves across the outside surface of dewar walls154and absorbs heat convectively from dewar walls154, and b) moves across the inside surface of housing152and absorbs heat convectively from the housing152walls (when housing152is at a greater temperature than the air). In chamber156, the air a) moves across the outside surface of monolithic structure100and absorbs heat convectively from the walls of monolithic structure100, and b) moves across the inside surface of dewar150and absorbs heat convectively from dewar walls154.

Dewar150is thus configured such that air passing through the dewar receives heat generated in burner30via direct convective heat transfer from walls in monolithic structure100on the outside of burner30to air passing through dewar chamber156. Dewar150is also configured to such that air passing through chamber156receives heat indirectly from burner30. Indirectly in this sense refers to heat generated in burner30moving to another structure in fuel processor15before receipt by the air.

FIG. 4Cillustrates a thermal diagram of the heat path produced by a wall154of dewar150. Heat from burner30conducts through monolithic structure100to a surface of structure100that opens into dewar chamber156. From here, the heat a) conducts into the air passing through dewar chamber156, thereby heating the air; b) radiates to the inner wall155of dewar wall154, from which the heat convects into the air passing through dewar chamber156; c) radiates to the inner wall155of dewar wall154, conducts through wall154to the outer surface157of dewar wall154, from which the heat convects into the air passing through dewar chamber158, and d) radiates to the inner wall155of dewar wall154, conducts through wall154to the outer surface157of dewar wall154, radiates to a wall of housing152, from which the heat convects into the air passing through dewar chamber158.

Dewar150thus provides two streams of convective heat dissipation and active air-cooling in volumes156and158that prevent heat generated in burner30(or other internal parts of fuel processor15) from escaping the fuel processor.

Reflectance of heat back into chamber156decreases the amount of heat lost from fuel processor150and increases the heating of air passing through chamber156. To further improve the radiative reflectance back into chamber156, an inside surface of dewar wall154may include a radiative layer160to decrease radiative heat transfer into wall154(seeFIG. 4Bor4C). Radiative layer160is disposed on an inner surface155on one or more of walls154to increase radiative heat reflectance of the inner surface155. Generally, the material used in radiative layer160has a lower emissivity than the material used in walls154. Materials suitable for use with walls154of dewar150include nickel or a ceramic, for example. Radiative layer160may comprise gold, platinum, silver, palladium, nickel and the metal may be sputter coated onto the inner surface155. Radiative layer160may also include a low heat conductance. In this case, radiative layer160may comprise a ceramic, for example.

When dewar150fully encapsulates monolithic structure100, the dewar then bounds heat loss from the structure and decreases the amount of heat passing out of dewar150and housing152. Fuel processors15such as that shown inFIGS. 4A and 4Bare well suited to contain heat within housing152and manage heat transfer from the fuel processor. In one embodiment, burner operates at a temperature greater than about 200 degrees Celsius and the outer side of the housing remains less than about 50 degrees Celsius. In embodiments for portable applications where fuel processor15occupies a small volume, volumes156and158are relatively small and comprise narrow channels and ducts. In some cases, the height of channels in volumes156and158is less than 5 millimeters and a wall of burner30on monolithic structure is no greater than 10 millimeters from a wall of housing152.

The thermal benefits gained by use of dewar150also permit the use of higher temperature burning fuels as a fuel source for hydrogen production, such as ethanol and gasoline. In one embodiment, the thermal management benefits gained by use of dewar150permit reformer32to process methanol at temperatures well above 100 degrees Celsius and at temperatures high enough that carbon monoxide production in reformer32drops to an amount such that a preferential oxidizer is not needed.

As mentioned above, dewar150offers a second function for fuel processor15by pre-heating the air going to a burner. Burner30relies on catalytic combustion to produce heat. Oxygen in the air provided to burner30is consumed as part of the combustion process. Heat generated in the burner30will heat cool incoming air, depending on the temperature of the air. This heat loss to incoming cool air reduces the heating efficiency of burner30, and typically results in a greater consumption of methanol. To increase the heating efficiency of burner30, the present invention heats the incoming air so less heat generated in the burner passes into the incoming air. In other words, chambers and air flow formed by dewar150allow waste heat from the burner to pre-heat air before reaching the burner, thus acting as a regenerator for fuel cell15.

While fuel processor15ofFIGS. 4A and 4Bshows dewar150encapsulating monolithic structure100, the present invention may also employ other architectures for dewar150and relationships between burner30or reformer32and dewar150that carry out one or both of the dewar functions described above.FIG. 4Dillustrates a cross sectional view of a fuel processor15that elongates the convective path for cool air flow over a warmer dewar wall254in accordance with another embodiment of the present invention. Fuel processor15includes a tubular design for the burner30and reformer32.

Dewar250routes cool incoming air across an elongated heat transfer path. Dewar250includes a spiral wall254in cross section that surrounds burner30and reformer32. Spiral wall254defines a spiral dewar chamber256. Cool air enters dewar chamber256at a dewar entrance252. The innermost portion257of wall254attaches to an outer wall258of burner30. Heat from burner30conducts linearly through spiral wall254. Thus, inner portion257is the warmest portion of wall254, while wall254at entrance252is typically the coolest. Air progressively warms as it travels through dewar chamber256. As the air travels inward, temperature of wall254rises, as does the amount of heat available for transfer to the air. Depending on the transient temperature of the air, the amount of heat lost from wall154may also increase as the air progresses inward.

Spiral dewar250elongates convection interaction between the incoming cool air and a wall warmed by the burner. Dewar250also increases the number of walls and convective layers in a given radial direction from the fuel processor center. As shown inFIG. 4D, dewar250comprises 4-5 walls and convective layers in a given radial direction, depending on where the number is counted. The number of walls and convective in a radial direction may vary with design. In one embodiment, spiral dewar250is configured with from 1 layer to about 50 walls and convective layers in a given radial direction from the fuel processor center. Three layers to 20 layers are suitable for many applications. A channel width260defines the duct space between adjacent walls254. In one embodiment, channel width260ranges from about ¼ millimeters to about 5 millimeters.

Spiral dewar250may be constructed by electroplating nickel onto a removable layer such as aluminum or zinc.FIG. 4Hillustrates spiral dewar250in an unrolled form during initial construction in accordance with another embodiment of the present invention. Initial aluminum or zinc layer262is added to control channel width260during rolling. The removable layer262is subsequently electroplated with the wall214choice of material, for example nickel. After which the aluminum or zinc layer is etched out employing an electroforming technique thus leaving a spiral dewar250.

The spiral dewar250shown inFIG. 4Halso employs an embossed or folded burner structure264that wraps around reformer32.FIGS. 4I and 4Jillustrate wash coatings266on a wall268of burner30in accordance with two embodiments of the present invention. For the folded burner structure264ofFIG. 4I, a wash coat266including the burner catalyst104is applied to both sides of wall268.

A flat wall270suitable for use in spiral dewar250is shown inFIG. 4J. Flat wall270includes channels272etched or otherwise disposed along its surface. A wash coat266including the burner catalyst104is then added over the surface of flat wall270and channels272.

Fuel processors15such as that shown inFIG. 4Dare very well suited to contain internally generated heat. In one embodiment, burner30operates at a temperature greater than about 350 degrees Celsius and the outer side of the housing remains less than about 75 degrees Celsius. This facilitates the use of higher temperature burning fuel sources within burner30such as ethanol and propane, for example.

Dewars as shown inFIGS. 4A and 4Dmay be considered ‘multipass’ since the incoming air passes over multiple surfaces for convective heat transfer between the warmer surfaces and cooler air. The embodiment inFIG. 4Aillustrates a two-pass system where the air passes through two dewar chambers, while the embodiment inFIG. 4Dillustrates an N-pass where N is the number of dewar walls in a given radial direction from the fuel processor center.

FIG. 4Eillustrates a cross sectional view of a multipass dewar300in accordance with another embodiment of the present invention. Dewar300comprises four dewar walls302a-dthat connect to a housing wall304. Dewar300partially contains monolithic structure100. Dewar wall302acooperates with housing wall304to enclose monolithic structure100, which includes burner30. Dewar wall302band housing wall304enclose dewar wall302aand burner30. Similarly, dewar wall302cand housing wall304enclose dewar wall302b, while dewar wall302dand housing wall304enclose dewar wall302c. Dewar walls302a-dform four volumes for incoming air to pass over warmer walls and receive heat. Air enters dewar inlet port310and flows through dewar chamber308aand into dewar chamber308bthrough port312after travelling through substantially the whole chamber308a. Air then serially passes into and through chambers308cand308dbefore entering burner inlet314.

FIGS. 4F and 4Gillustrate a cross section of a fuel processor15including a monolithic structure452and multipass dewar450in accordance with another embodiment of the present invention. Monolithic structure452includes multiple reformer chambers454that are disposed in a central portion of structure452. Multiple burner chambers456surround and quadrilaterally border the reformer chambers454. Reformer boiler458is arranged within the cross section of burner chambers456, while burner boiler460is arranged in external portion of the cross section.

Dewar462comprises four dewar walls462a-d. In the cross section shown inFIG. 4F, dewar wall462asurrounds monolithic structure452. Dewar wall462bsurrounds and encloses dewar wall462a. Dewar wall462csurrounds and encloses dewar wall462b, while dewar wall462dsurrounds and encloses dewar wall462c. Dewar walls462a-dform four dewar volumes for incoming air to pass through and receive heat. As shown inFIG. 4G, air enters dewar inlet port464and flows through dewar chamber468aand into dewar chamber468bafter traveling through substantially the whole chamber468aalong the length of monolithic structure452. Air then serially passes from chamber468bto chamber468cand chamber468dbefore entering burner inlet470.

FIG. 5illustrates a process flow500for generating hydrogen in a fuel processor in accordance with one embodiment of the present invention. The fuel processor comprises a burner, a reformer and a dewar that at least partially contains the burner and reformer. Although the present invention has so far discussed dewars with respect to annular reformer and burner designs described herein, it is also anticipated that dewars described herein are also useful to contain heat in other reformer and burner designs. Many architectures employ a planar reformer disposed on top or below to a planar burner. Micro-channel designs fabricated in silicon commonly employ such stacked planar architectures and would benefit from dewars described herein.

Process flow500begins by generating heat in the burner (502). Catalytic burner architectures may include those described above or a micro-channel design on silicon. Further description of a micro-channel fuel processor suitable for use with the present invention is included in commonly owned co-pending patent application entitled “Planar Micro Fuel Processor” naming Ian Kaye as inventor and filed on the same day as this patent application. This application is incorporated by reference for all purposes. A catalyst in the burner facilitates heat generation in the presence of the heating fuel. The burner may also employ an electric burner that includes an resistive heating element that produces heat in response to input current.

Air enters a port for the dewar and passes through a dewar chamber (504). For the dewar ofFIG. 4A, burner30and dewar150share a wall and the air passes through the dewar chamber156in a direction that at least partially counters a direction that the air passes through burner chamber105.

The air is then heated in the dewar chamber using heat generated in the burner (506). Heat travels from burner30to dewar chamber156via conductive heat transfer. Heat may also travel from a burner to a dewar chamber via convective and/or radiative heat transfer. Once in the dewar chamber, the air is typically heated via convective heat transfer from a wall of the dewar to the air. In one embodiment, the dewar shares a wall with the burner and air in the dewar chamber is heated using heat from the shared wall. Heat from the burner wall may also travel to other walls in the dewar and heat air in the dewar chamber after the heat transfers from the shared wall to another non-shared dewar wall. Heat traveling between the shared wall and non-shared dewar wall transfer by conduction between connected walls or radiation between facing walls.

Process flow500then supplies the warmed air to the burner after it has been heated in the dewar chamber (508). Typically, the fuel processor includes an exit to the dewar chamber and an inlet to the burner—along with any intermittent plumbing—that allow the heated air to pass therebetween. For the fuel processor shown inFIG. 2A, space between dewar150and burner30at the ends of the burner route the air from the dewar to the burner.

The air is then used in the burner for catalytic combustion to generate heat. The generated heat is then transferred from the burner to the reformer (510). In the reformer, the heat is then used in reforming a fuel source to produce hydrogen (512).

The first three elements (502,504, and506) of process flow500also form a method of managing heat in a fuel processor. In this case, heat generated in the burner (502) passes to air in the dewar (504). The dewar150at least partially thermally isolates components internal to the fuel processor housing—such as the burner—and contains heat within the fuel processor. The dewar thus reduces heat loss from the fuel processor and helps manage the temperature gradient between the burner and outer surfaces of the housing. The dewar may also contain extended and/or multiple dewar chambers through which the air passes and is heated by heat generated in the burner.FIG. 4Aillustrates a second dewar chamber158formed between the dewar and a housing for the fuel processor. Air passes first through chamber158then into dewar chamber156.FIG. 4Dillustrates a spiral dewar including an extended dewar chamber408. In this case, dewar250includes one wall that increasingly provides heat as incoming air nears the burner.FIG. 4Eillustrates a dewar300including four partially dewar chambers308where each dewar chamber heats incoming air in turn as it nears the burner.FIG. 4Fillustrates a dewar including four annular and concentric and rectangular dewar chambers408that each heat incoming air in turn as it travels to the burner.

While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents that fall within the scope of this invention which have been omitted for brevity's sake. For example, although reformer32includes chamfered corners as shown inFIG. 3A, the present invention may employ non-chamfered corners in reformer32. In addition, although the present invention has been described in terms of a monolithic structure100that forms the volumetric reformer32, the present invention is not limited to volumetric reformers disposed in monolithic structures. It is therefore intended that the scope of the invention should be determined with reference to the appended claims.