Devices with extended area structures for mass transfer processing of fluids Number:7,520,917 from the United States Patent and Trademark Office (PTO) owispatent A microchannel device includes several mass transfer microchannels to receive a fluid media for processing at least one heat transfer microchannel in fluid communication with a heat transfer fluid defined by a thermally conductive wall, and at several thermally conductive fins each connected to the wall and extending therefrom to separate the mass transfer microchannels from one another. In one form, the device may optionally include another heat transfer microchannel and corresponding wall that is positioned opposite the first wall and has the fins and the mass transfer microchannels extending therebetween.<H processing, structures, Devices, with, ex, 7520917.html, Patent, pto, 7520917

Title: Devices with extended area structures for mass transfer processing of fluids

Abstract: A microchannel device includes several mass transfer microchannels to receive a fluid media for processing at least one heat transfer microchannel in fluid communication with a heat transfer fluid defined by a thermally conductive wall, and at several thermally conductive fins each connected to the wall and extending therefrom to separate the mass transfer microchannels from one another. In one form, the device may optionally include another heat transfer microchannel and corresponding wall that is positioned opposite the first wall and has the fins and the mass transfer microchannels extending therebetween.

Patent Number: 7,520,917 Issued on 04/21/2009 to TeGrotenhuis, et al.

Inventors: TeGrotenhuis; Ward E. (Kennewick, WA), Wegeng; Robert S. (Richland, WA), Whyatt; Greg A. (West Richland, WA), King; David L. (Richland, WA), Brooks; Kriston P. (Kennewick, WA), Stenkamp; Victoria S. (Richland, WA)
Assignee: Battelle Memorial Institute (Richland, WA)

Appl. No.: 11/061,237

Filed: February 18, 2005

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60573160	May., 2004
60599718	Aug., 2004
60546114	Feb., 2004

Current U.S. Class: 95/210 ; 165/272; 165/276; 203/21; 203/89; 422/190; 422/198; 422/211; 48/197R; 95/241

Current International Class: B01D 53/14 (20060101)

Field of Search: 422/198,190,211 436/139,140,141,142,143 48/197R 165/165

References Cited [Referenced By]

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Foreign Patent Documents


WO 03/033983	Apr., 2003	WO
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Primary Examiner: Caldarola; Glenn A
Assistant Examiner: Oladapo; Taiwo
Attorney, Agent or Firm: Maughan; Derek H.

Government Interests

GOVERNMENT RIGHTS

This invention was made with Government support under Contract DE-AC0676RLO1830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.

Parent Case Text

REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Application No. 60/546,114 filed Feb. 18, 2004, U.S. Provisional Application No. 60/573,160 filed May 21, 2004, and U.S. Provisional Application No. 60/599,718 filed Aug. 5, 2004, all of which are hereby incorporated by reference. The present application is related to International Patent Application No. PCT/US2004/015402 filed May 17, 2004 (International Publication No. WO 2004/104140), U.S. patent application Ser. No. 10/385,831 filed Mar. 11, 2003 (Publication No. U.S. 2003/0180216), U.S. patent application Ser. No. 10/011,386 filed Dec. 5, 2001 (Publication No. U.S. 2002/0144600), U.S. patent application Ser. No. 10,717,608 filed on Nov. 21, 2003, U.S. patent application Ser. No. 09/640,903 filed Aug. 16, 2000 (now U.S. Pat. No. 6,680,044), and U.S. patent application Ser. No. 09/588,871 filed Jun. 6, 2000 (Now U.S. Pat. No. 6,666,909), all of which are hereby incorporated by reference.

Claims

What is claimed is:

1. A method, comprising: operating a device including a number of mass transfer microchannels, a heat transfer channel with a boundary defined by a thermally conductive wall, and several thermally conductive fins connected to the wall, the fins each corresponding to a mass transfer surface area along a respective one of the mass transfer microchannels; directing movement of a liquid through each of the mass transfer microchannels; performing a mass transfer process at an interface between the liquid and a gas in each of the mass transfer microchannels; and flowing a heat transfer fluid through the heat transfer channel to regulate the mass transfer process.

2. The method of claim 1, wherein the device includes a number of capillary structures each in a respective one of the mass transfer microchannels to convey the liquid.

3. The method of claim 1, wherein the directing includes flowing a film of the liquid down a surface based on gravitational force.

4. The method of claim 1, wherein the mass transfer process includes collecting the liquid in a reservoir.

5. The method of claim 1, wherein the mass transfer process includes at least one of distillation, condensation, gas absorption, and gas desorption.

6. The method of claim 1, wherein the mass transfer process is reactive.

7. The method of claim 1, wherein the device includes another heat transfer channels connected to each of the fins to transfer heat relative to the mass transfer microchannels.

8. A method, comprising: operating a device including a number of mass transfer microchannels, a plurality of thermally conductive fins, a first heat transfer channel with a boundary defined by a first thermally conductive wall, and a second heat transfer channel with a boundary defined by a second thermally conductive wall, the fins each being connected to the first wall and the second wall to transfer heat by conduction and the fins extending therebetween to separate the mass transfer microchannels from one another; providing a fluid media to the microchannels; performing a mass transfer process with the fluid media in each of the microchannels between the fins; and flowing a heat transfer fluid through the first heat transfer channel and the second heat transfer channel to regulate temperature of the mass transfer process.

9. The method of claim 8, which includes conveying a liquid in the mass transfer microchannels to perform the mass transfer process at an interface between the liquid and a gas.

10. The method of claim 9, wherein the device includes a number of capillary structures each in a respective one of the mass transfer microchannels to convey the liquid.

11. The method of claim 9, which includes collecting the liquid in a reservoir.

12. The method of claim 8, wherein the mass transfer process includes a catalytic chemical reaction.

13. The method of claim 8,wherein a cross section of the device taken perpendicular to the flow path of the fluid media through the mass transfer microchannels defines a microchannel gap height along the cross section and a microchannel gap width along the cross section for each of the mass transfer microchannels, and a ratio of the microchannel gap height to the microchannel gap width is at least three for each of the mass transfer microchannels.

14. A method, comprising: operating a device including a number of mass transfer microchannels, a heat transfer channel with a boundary defined by a thermally conductive wall, and a plurality of thermally conductive fins connected to the wall, the fins each corresponding to a mass transfer surface area along a respective one of the mass transfer microchannels; providing a fluid media through each of the mass transfer microchannels; transferring one or more components of one of a liquid and a gas to another of the liquid and the gas by performing a mass transfer process at a liquid-gas interface in each of the microchannels; and flowing a heat transfer fluid through the heat transfer channel to regulate the mass transfer process by conductively transferring heat through the fins.

15. The method of claim 14, wherein the device includes a number of capillary structures each in a respective one of the mass transfer microchannels to convey the liquid.

16. The method of claim 14, wherein the mass transfer process includes at least one of distillation, condensation, gas absorption, and gas desorption.

17. The method of claim 14, wherein the heat transfer channel is one of two heat transfer channels, the two heat transfer channels being connected to each of the fins opposite one another with the mass transfer microchannels positioned therebetween.

18. The method of claim 14, wherein a cross section of the device taken perpendicular to the flow path of the fluid media through the mass transfer microchannels defines a microchannel gap height along the cross section and a microchannel gap width along the cross section for each of the mass transfer microchannels, and a ratio of the microchannel gap height to the microchannel gap width is at least three for each of the mass transfer microchannels.

19. The method of claim 18, wherein the ratio is at least five for each of the mass transfer microchannels.

20. The method of claim 18, where the ratio is at least ten for each of the mass transfer microchannels.

Description

BACKGROUND

The present invention is directed to fluid processing techniques. More particularly, but not exclusively, the present invention is directed to microchannel processing of fluids with heat exchange.

The use of microchannel devices to enhance various chemical processes has increasingly become a topic of interest. In some instances, microchannels to process fluid and microchannels to transfer heat are integrated together in the same device. Frequently, these two channel types are coextensive along a separating wall. One drawback of this arrangement is that mass transfer and heat transfer characteristics become dependent on one another to a greater extent than may be desired. The efficiency of certain chemical reactions and chemical separations can be limited by such dependence.

Alternatively or additionally, for certain highly endothermic or exothermic reactions, separate cooling stages may be desired to provide a specific reaction temperature profile. Unfortunately, current schemes can hamper efficiency and/or reactor size reduction. Thus, there is an ongoing need for further contributions in these areas.

SUMMARY

One embodiment of the present invention includes a unique fluid processing technique. Other embodiments include unique systems, methods, devices, and apparatus to perform fluid processing with heat exchange. Further embodiments, forms, features, aspects, benefits, objects, and advantages shall become apparent from the detailed description and figures provided herewith.

BRIEF DESCRIPTION OF THE VIEWS OF THE FIGURES

FIG. 1 is a diagrammatic view of a fuel processing system.

FIG. 2 is a partial, diagrammatic view of a steam reforming device included in FIG. 1.

FIGS. 3 and 4 are partial, diagrammatic views of a reactor/vaporizer subsystem in a start-up configuration and in a sustained operation configuration following start-up, respectively.

FIG. 5 is a graph of an ideal temperature profile for a Water-Gas Shift (WGS) reaction.

FIG. 6 is a perspective, partial sectional view of one half of a WGS reactor of FIG. 1, the other half being a mirror image about the sectional plane.

FIG. 7 is a partial diagrammatic, sectional view of a portion of the reactor of FIG. 6.

FIG. 8 is a perspective, diagrammatic assembly view of a Preferred Oxidation Reaction (PROX) reactor of FIG. 1.

FIG. 9 is a partial, diagrammatic and sectional view of a microchannel device for performing a mass transfer between two media.

FIG. 10 is a partial, diagrammatic and sectional view of a microchannel device for performing a mass transfer process at a liquid-gas interface.

FIG. 11 is a flowchart of a device design procedure performed with a computer.

FIG. 12 is a predicted temperature profile for a two-section WGS reactor corresponding to the reactor of FIGS. 6 and 7.

FIGS. 13-16 are graphs of experimental results.

FIG. 17 is a partial cutaway, diagrammatic side view of the reactor shown in FIG. 8.

FIG. 18 is partial sectional, diagrammatic view of a distillation device.

FIG. 19 is a sectional view of the distillation device taken along the section line 19-19 shown in FIG. 18.

FIG. 20 is a sectional view of the distillation device taken along section line 20-20 shown in FIG. 19.

FIG. 21 is a sectional view of the distillation device taken along section line 21-21 shown in FIG. 19.

FIG. 22 is a sectional view of the distillation device taken along section line 22-22 shown in FIG. 19.

DESCRIPTION OF EMBODIMENTS

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.

A "microchannel" refers to a channel with at least one dimension less than about 1 cm, preferably less than about 1 mm, and more preferably less than about 0.5 mm. Other dimensions of a microchannel may be any magnitude. A microchannel includes any channels having a dimension between 1 mm and 1 cm that are sometimes called mesochannels.

A "fluid" refers to any substance that conforms to the shape of its container, including a liquid, a gas, a combination of two or more gases, a combination of two or more liquids, a combination of one or more gases and one or more liquids. A fluid can optionally include one or more types of solid particles carried therewith.

A "catalyst material" refers to any matrix, fiber, porous solid, or other solid state structure that is coated with, combined with, carries or otherwise includes one or more catalysts.

A "capture structure" is a structure disposed (at least partly) within a microchannel that assists or directs movement of a liquid.

"We" is a unit abbreviation of Watts electric power output by a corresponding fuel cell.

"Microchannel Volume" refers to the collective volume of all microchannels in a device including any catalyst, catalyst material, catalyst matrix, catalyzing structure, catalyst support material, capture structure, liquid conveying structure, liquid directing structure, or other processing structure included in one or more of the microchannels.

"Total volume" of a device refers to the volume of all microchannels, chambers, headers, or other spaces in the device and all structure forming the device.

In one embodiment, unique microchannel structures are utilized to perform mass transfer processing of fluids flowing through mass transfer microchannels and regulate temperature of this process with a heat transfer fluid flowing through heat transfer microchannels. Such processing can include separation of one or more constituents from a fluid mixture (such as adsorption, absorption, desorption, distillation, or condensation processes), catalytic chemical reactions, or noncatalytic reactions, just to name a few.

In another embodiment, unique microchannel structures are used to extract hydrogen from hydrocarbon-based vehicle fuel to facilitate fuel cell powered vehicles. These fuels can be provided with the existing petroleum fuel infrastructure. In one form, a series of reactors employ microchannel structures to provide heat to a highly endothermic steam reforming reaction to maintain high conversions, control the temperature profile for an exothermic WGS reaction, and provide for a PROX reaction to reduce CO concentration in a hydrogen gas stream directed to the fuel cell.

Referring to FIG. 1, yet a further embodiment is illustrated as fuel processing system 20. System 20 includes liquid hydrocarbon fuel source 22 and water source 24 to supply fuel and water, respectively, to vaporizer 30. Vaporizer 30 provides a fluid mixture of vaporized fuel (C.sub.xH.sub.y) and water (H.sub.2O) as reactants to steam reforming reactor 40. Steam reforming reactor 40 generates a fluid including molecular hydrogen, carbon monoxide, carbon dioxide, and water to Water-Gas Shift (WGS) reactor 100 in accordance with reaction (1) as follows: C.sub.xH.sub.y+H.sub.2O.fwdarw.H.sub.2+CO+CO.sub.2 (1) Because steam reforming based on reaction (1) is endothermic, combustor 50 is utilized to provide heat to steam reforming reactor 40 in an amount sufficient to maintain a desired conversion rate. Combustor 50 is fueled by molecular hydrogen that is output as anode exhaust by fuel cell 60, and also provides heat to operate vaporizer 30.

It has been discovered that the high surface area per unit volume and short heat transfer distances realized with microchannel processing provide a way to efficiently add heat to reaction (1) and maintain relatively high conversion. Furthermore, small mass transfer distances generally reduce diffusion resistance and allow the reaction to be maintained near its kinetic limit. As diagrammatically depicted in FIG. 2, steam reforming reactor 40 includes at least one microchannel device 42. Microchannel device 42 receives a heat exchange fluid in the form of hot air from combustor 50 in heat exchange microchannels 44 in the direction indicated by arrows 44a. The reformate gas travels through reaction microchannels 45 that are defined by a thermally conductive material, such as metal. This material is convectively heated by heat exchange fluid passing through microchannels 44. Travel of the reformate gas through microchannels 45 is crossflow relative to the heat exchange fluid such that it travels in a direction that is perpendicular to the view plane of FIG. 2 and arrows 44a. Microchannels 44 are interleaved with microchannels 45. The length of travel of heat exchange fluid through heat exchange microchannels 44 is considerably shorter relative to the length of travel of reformate gas through reaction microchannels 45. In typical applications, the quantity of interleaved microchannels 44 and 45 would be more numerous than that depicted, but are not shown in FIG. 2 to preserve clarity.

Reaction microchannels 45 each contain felt coated with a standard precious metal catalyst (not shown) of a type suitable to perform reaction (1) at a desired rate. In one experimental embodiment, device 42 was sized and shaped as a panel approximately 80 cm.sup.3 in volume (including headers) and was designed for 500 We operation with a pressure drop of approximately 1 inch H.sub.2O across the combustion gas side. It was discovered that this arrangement provides a desirably high heat transfer, low pressure drop, and also minimizes overheating with the hot combustion gases. The relatively short diffusion length within each of microchannels 44 provides high heat transfer, and this short distance provides for low pressure drop. By using the interleaved approach, where each combustion channel is directly next to two reaction channels, heat need only transfer through the thermally conductive material separating one heat exchange microchannel 44 from the two bordering reaction microchannels 45. Height h2 of microchannels 45 is much less than height h1 of microchannels 44, which typically results in a convection coefficient for the reformate that is higher than the heat exchange (air) side. Correspondingly, the metal temperature of reactor 40 can be held near reforming temperature and facilitates a relatively higher gas inlet temperature. Furthermore, a relatively thin device in the direction of arrow 44a tends to increase conduction from front to back to reduce metal temperature gradient, allowing higher gas temperature without excessively high metal temperature.

In some applications, such as fuel-cell based vehicles, a relatively rapid start-up of reactor 40 typically would be desired. Referring to FIGS. 3 and 4, one arrangement including steam reformer reactor 40 is diagrammatically shown that includes multiple devices 42 with baffles 43a and dampers 43b to direct heat exchange fluid flow. Heat exchange fluid is pressurized by start-up blower 45a or sustaining blower 45b as further explained hereinafter. Also included is start-up combustor 46, recuperative heat exchanger 47, vaporizer 30, blower damper 43c, and blower damper 43d. Heat exchange fluid flows along arrows 44b and 44c in FIGS. 3 and 4, respectively, and reformate flows perpendicular to the view plane of FIGS. 3 and 4.

More specifically, FIG. 3 depicts start-up configuration 41a in which dampers 43b are positioned in cooperation with baffles 43a to direct heat exchange fluid from top plenum 48a to bottom plenum 48b and through each device 42 in a parallel fashion. For this arrangement, blower damper 43c is closed and blower damper 43d is open. With configuration 41a, hydrocarbon fuel is burned with air using start-up combustor 46 and a relatively high flow rate generated with start-up blower 45a. This high-flow combustion gas passes through devices 42 in parallel and then to vaporizer 30 and combustion air recuperative heat exchanger 47. Once the reaction temperature is reached, blower damper 43c is opened, blower damper 43d is closed, and dampers 43b are repositioned relative to baffles 43a to force a smaller quantity of air through devices 42 in series for sustained operation as shown in configuration 41b of FIG. 4. In this case, blower 45b is utilized to provide a relatively lower flow compared to start-up blower 45a to improve efficiency during sustained operation at temperature. Incremental additions of hydrogen gas between devices 42 can be utilized to maintain temperature, as desired. Nonetheless, in other embodiments, more or fewer devices 42 may be used, reactor 40 or device 42 may be configured differently, vaporizer 30 may operate independent of reactor heat exchange fluid, different pressurization/blower arrangements may be used, and/or a different heat source may be employed for start-up or sustained operation.

Referring back to FIG. 1, reformate products are supplied from steam reformer reactor 40 to WGS reactor 100. While the steam reforming reaction typically is operated at more than 650.degree. C. and is endothermic, the water-gas shift reaction typically operates at less than 400.degree. C. and is mildly exothermic. The WGS reaction is provided as reaction (2) as follows: CO+H.sub.2O H.sub.2+CO.sub.2 (2) This reaction is controlled to increase the hydrogen content of the product stream for steam reforming and to decrease the CO concentration. Reaction (2) is equilibrium limited, and operation below 270.degree. C. is typically desirable for vehicle fuel-cell applications. As a result, the reaction kinetics are generally slower than desired.

Typically, the ideal temperature profile along the flow path of reactants through a WGS reactor is shown in FIG. 5. This profile seeks to maximize reaction rate as the reaction proceeds by balancing reaction kinetics which are faster at higher temperatures and equilibrium which is favored at lower temperatures. Therefore, there exists an optimal temperature for maximum reaction rate at a given fluid composition. In conventional schemes, a two-stage adiabatic reactor with a heat exchanger has been utilized to approximate this profile with most of the conversion, approximately 82%, occurring in the first third of the reactor, and the remaining approximately 8% of conversion occurring along the remaining two-thirds of the reactor. It should be appreciated that the ideal temperature profile of FIG. 5 indicates are relatively rapid decrease in temperature--from 665.degree. C. at the inlet to 400.degree. C. at eight percent of the reactor catalyst. The corresponding reactor zone is also where two-thirds of the heat of reaction is being generated, adding to the unbalanced heat load at the inlet end of the reactor. Consequently, it is no surprise that standard reactor configurations have fallen short of the ideal profile.

WGS reactor 100 includes microchannel device 102. Compared to standard WGS reactors, microchannel device 102 more effectively removes heat to balance equilibrium conversion and kinetics, while reducing size of the reactor and operating desirably without a separate heat exchanger. As illustrated in FIG. 6, microchannel device 102 includes different zones 104 relative to the reactant/product flow path through device 102, as directionally indicated by arrow 106. These zones 104 are implemented with adiabatic section 108a at the front end portion 110a of device 102 and temperature differential section 108b at the back end portion 110b of device 102. In one implementation of device 102, the exothermic reaction in adiabatic section 108a heats the feed gas from about 340 to about 410.degree. C.; and this feed gas stream then enters differential temperature section 108b where it is cooled from approximately 410.degree. C. down to about 275.degree. C. as the reaction progresses.

Reactants are supplied to adiabatic section 108a through inlet 112 of device 102. Adiabatic section 108a includes catalyst monoliths 109 in the form of metal foams coated with catalyst material. From adiabatic section 108a, the reaction gas continues along the flow path in the direction indicated by arrows 106 into differential section 108b. Arrows 106 are parallel to flow axis F-F. Product from device 102 exits through outlet 114. Referring additionally to FIG. 7, a schematic cross section 101 of a portion of differential section 108b is shown that is taken along the flow path such that the view plane of FIG. 7 is perpendicular to the reactant flow path along arrows 106. Within differential section 108b, the reaction gas is distributed through a number of reaction microchannels 120 extending along flow axis F-F. Each microchannel 120 is lined on opposite sides 121a and 121b with catalyst material 122. This catalyst material 122 may be a pure catalyzing agent or provided on or in a matrix that is neutral with respect to performance of reaction (2). Microchannels 120 are each separated from one another by a respective one of a number of thermally conductive fins 124 extending between thermally conductive walls 126a and 126b. Walls 126a and 126b define boundaries or margins 128 of each microchannel 120 at opposing microchannel ends 127a and 127b. Fins 124 are connected to walls 126a and 126b to provide a low resistance to heat exchange, and typically are integrally formed together from a metal with suitable thermal properties. It should be appreciated that not all like features in FIGS. 6 and 7 are specifically designated by reference numbers to preserve clarity.

Correspondingly, walls 126a and 126b collectively bound heat exchange microchannels 130. Microchannels 130 are oriented for co-current or counter-current flow of a heat exchange fluid relative to the direction of flow through microchannels 120 along axis F-F. As shown in FIG. 6 for co-current flow, heat exchange fluid enters device 102 through inlets 116a and exits though outlets 116b. Microchannels 120 each have a sectional height dimension hg that represents a microchannel gap height along cross section 101 of FIG. 7. This gap height dimension is parallel to and oriented in the same direction as axis S1-S1, is alternatively designated L.sub.m, and is generally the same as the height of each fin 124 for the depicted arrangement.

Microchannels 120 each have a sectional width dimension w.sub.g that represents a microchannel gap width between corresponding fins 124. Accordingly, this microchannel gap width includes catalyst material 122 and/or any other structure positioned in microchannel 120 between the spaced apart fins defining such microchannel. In contrast, catalyst material width w.sub.c and flow channel width w.sub.f represent the width of catalyst material 122 in microchannel 120 and the width of the open flow channel slot in microchannel 120, respectively, such that w.sub.g=2w.sub.c+w.sub.f. The microchannel gap width dimension w.sub.g is parallel to and oriented in the same direction as axis S2-S2.

Each microchannel 120 is separated from microchannel 130 by wall 126a and/or 126b with a thickness of t.sub.w in a direction parallel to axis S1-S1. Microchannels 130 each have a maximum width dimension w.sub.h along cross section 101 parallel to axis S2-S2 and a maximum height dimension h.sub.x along cross section 101 parallel to axis S1-S1. Fin thickness is indicated as t.sub.f along a direction parallel to axis S2-S2. Notably axes F-F, S1-S1, and S2-S2 are orthogonal relative to one another.

It has been found that the co-current flow of microchannels 120 and 130 relative to one another and heat transfer characteristics of this structure can be used to provide an asymptotic temperature profile that approaches the ideal profile of FIG. 5. Device 102 further provides structures to provide a greater volume of catalyst than other reactor arrangements for WGS reactions. In one example, the catalyst accounted for more than half (52%) of the total volume of device 102.

Referring back to FIG. 1, system 20 utilizes Preferential Oxidation (PROX) reactor 200 to further reduce CO content provided to fuel cell 60. In this reaction, a near stoichiometric amount of air is added to the WGS reactor synthesis gas and the CO is oxidized while the larger concentration of H.sub.2 is not oxidized, as represented by reaction (3) that follows: CO+1/2O.sub.2.fwdarw.CO.sub.2 (3) In this reaction the molecular hydrogen and CO compete for oxidation with temperature impacting the relative balance. The optimal reaction temperature depends on the catalyst utilized, among other things.

For the application of system 20 to a fuel cell based vehicle, one embodiment generates about a 1% CO product from the WGS reaction and produces an outlet CO concentration of less than 10 ppm using an O.sub.2:CO ratio of 1:1 or less from PROX reactor 200. This fluid stream can then be used to feed a standard Proton Exchange Membrane (PEM) of fuel cell 60 without appreciably degrading it. For this transportation application, it also can be desirable to reduce the size and weight of reactor 200. Appropriate temperature control of this highly exothermic reaction is generally desired for this and many other applications, although in still others it may not be of concern. Reactor 200 controls temperature of reaction (3) by applying microchannel heat exchangers.

Referring additionally to FIGS. 8 and 17, reactor 200 is illustrated; however, not all like features are designated by reference numerals to preserve clarity. FIG. 8 shows reactor 200 in a perspective, partially diagrammatic assembly view. Reactor 200 includes opposing end plates 202a and 202b with stack 203 positioned therebetween to provide a multistage reaction device 205. Device 205 processes fluid flowing in the direction indicated by arrow 204 therethrough. Device 205 receives reactant fluid through an inlet aperture 205a through end plate 202a, which is schematically represented. This fluid reactant stream first encounters microchannel heat exchanger 218a at front end 206a of the process to provide a desired reactant temperature.

Heat exchanger 218a includes a number of process microchannels 219a through which the reactant stream flows during operation of reactor 200 in the direction indicated by arrow 204 (See FIG. 17). Heat exchanger 218a also includes a number of heat transfer microchannels 219b that are thermally coupled to process microchannels 219a with a low thermal resistance to facilitate thermal conduction therebetween. Microchannels 219b receive a heat transfer fluid therethrough to regulate temperature of the reactant through this coupling. A heat transfer fluid source 230 is schematically shown in FIG. 17 for heat exchanger 218a. Microchannels 219a and 219b are also collectively designated heat exchange microchannels 219.

From heat exchanger 218a of front end 206a, initial processing stage 206b is encountered which includes reactor housing 210a that defines reaction chamber 211a. Catalyzing structure 214a is positioned within chamber 211a. Housing 211a surrounds structure 214a to contain/confine fluid being processed therewith. Catalyzing structure 214a includes catalyst material 214 to enhance the PROX reaction performed with the reactant fluid from heat exchanger 218a. Catalyst material 214 includes support material 215 that defines a number of microchannel fluid processing passageways 216 therethrough. Support material 215 carries one or more PROX-enhancing catalysts.

Passageways 216 each include inlet 216a to receive fluid for processing and outlet 216b to output fluid after processing. It should be appreciated that passageways 216 may intersect one another and may branch. Correspondingly, passageways 216 can be arranged such that each one only has one inlet 216a and one outlet 216b, can branch to have more inlets 216a than outlets 216b or more outlets 216b than inlets 216a, or a combination of these. Further passageways 216 can differ in size, length, orientation, shape, and the like. In one embodiment, passageways 216 are provided as a network of intersecting pores through a monolithic block that interconnect many different inlets 216a and outlets 216b. In one particular implementation, catalyst material 214 was provided in the form of a porous monolith with support material 215 being a block of copper foam.

Catalyzing structure 214a defines process fluid inlet face 212a that abuts outlet face 220a of microchannel heat exchanger 218a to form a low resistance thermal interface. Accordingly, heat exchanger 218a can also be used, at least in part, to regulate temperature of structure 214a. Face 212a of catalyzing structure 214a defines at least some of inlets 216a of passageways 216. Opposite face 212a, structure 214a defines fluid outlet face 212b, which in turn defines at least some of outlets 216b of passageways 216. Immediately downstream of catalyzing structure 214a is microchannel heat exchanger 218b, which is also included in stage 206b. Heat exchanger 218b defines inlet face 220b that abuts face 212b of structure 214a to form a thermal interface therewith and further regulate temperature. Heat exchanger 218b includes process microchannels 219a to receive fluid output by structure 214a, and heat transfer microchannels 219b each thermally coupled to one or more of microchannels 219a as described in connection with heat exchanger 218a. Heat exchanger 218b may be coupled to source 230 and/or a different heat transfer fluid source. Likewise, heat exchanger 218b defines an outlet face 220a opposite inlet face 220b.

Fluid flows along arrow 204 from stage 206b into intermediate processing stage 206c. Stage 206c includes reactor housing 210b defining reaction chamber 211b that houses catalyzing structure 214b. Catalyzing structure 214b is comprised of two blocks of catalyzing material 214, having approximately twice the volume of catalyzing structure 214a. Catalyst material 214 includes support material 215 defining a number of passageways 216 with corresponding inlets 216a and outlets 216b. At least a portion of inlets 216a are defined by process fluid inlet face 212a and at least a portion of outlets 216b are defined by process fluid outlet face 212b. Microchannel heat exchanger 218c concludes stage 206c, and includes inlet face 220b in low resistance thermal contact with face 212b of structure 214b and outlet face 220a opposite face 220b. Heat exchanger 218c includes process microchannels 219a and heat transfer microchannels 219b configured the same as heat exchangers 218a and 218b, and can use the same or a different heat transfer fluid source (not shown).

Process fluid is output from intermediate processing stage 206c to enter end stage 206d. Stage 206d includes reactor housing 210c that defines reaction chamber 211. Chamber 211c contains catalyzing structure 214c. catalyzing structure 214c is comprised of three blocks of catalyst material 214, which is about three times the volume of catalyst material in structure 214a, but is otherwise configured the same with support material 215, passageways 216, inlets 216a, outlets 216b, face 212a, and face 212b. Stage 206d ends with heat exchanger 218d configured the same as heat exchanger 218a-including outlet face 220a opposite inlet face 220b. Face 212a of structure 214c abuts face 220a of heat exchanger 218c and face 212b of structure 214c abuts face 220b of heat exchanger 218d. Heat exchanger 218d can utilize the same or a different heat transfer fluid source relative to heat exchangers 218a, 218b, 218c, and 218d.

From stage 206d, reaction product is output through aperture 205b of end plate 202b that results from the upstream catalytic processing in stages 206b, 206c, and 206d. For the PROX reaction, the product is a molecular hydrogen stream provided fuel cell 60 with a lower CO concentration than was input to device 205. Referring specifically to FIG. 17, heat exchanger 218b is further configured with one or more ports 242 in fluid communication with reactant source 240 to add reactant upstream of structure 214b. More particularly, heat exchanger 218b can be further configured as a fluid mixer. Furthermore, heat exchanger 218c includes at least one port 252 to receive product or otherwise divert a portion of the process fluid stream, routing it away from structure 214c and reactor 200. Port, 252 is in fluid communication with product stream conduit 250. Product separation can be performed by any standard process. Heat exchangers 218a, 218b, 218c, and 218b (collectively heat exchangers 218) can be of any type. Commonly owned International Patent Application No. PCT/US2004/015402 filed May 17, 2004 (International Publication No. WO 2004/104140) provides further background regarding microchannel heat exchangers and mixers.

In one arrangement, each block of catalyst material 214 is comprised of a catalyst coated copper foam material with 60 pores per inch. Because of the contact between the catalyst foam and the heat exchanger panel, heat generated by the strongly exothermic PROX reaction is transferred both by convection through the gases and conduction through the foam to the corresponding heat exchanger(s) 218. To further control the reaction and maintain an isothermal temperature profile, air is added in selected small quantities at each of the stages (corresponding to the arrangement of reactant source 240), rather than once at the beginning. It has been found that reactor 200 can have more than 50% of its total volume occupied by catalyst material while acceptably controlling reaction temperature. For one form of reactor 200 that was developed, the catalyst material accounted for nearly 70% of the reactor volume (excluding outside walls and headers).

At the front end of device 205 in stage 206b, where most of the reaction is occurring and thus most of the heat is generated, less catalyst can be used and the heat exchangers can be closer together. Further downstream more catalyst can be used with fewer heat exchangers. In other embodiments directed to a PROX or non-PROX application, multiple devices 205 can be used; more or fewer stages can be utilized in the device; reactant(s) may be introduced between one or more processing stages; product(s) can be removed before the final processing stage; different catalyst types or amounts may be used with different stages, more or fewer heat exchangers; different heat exchanger types, and/or device 205 or its variants can be utilized to perform an endothermic reaction. Alternatively or additionally, one or more of structures 214a, 214b, and 214c can include one or more catalysts that are different from those of one or more other of the structures. In one particular embodiment, an additional stage was utilized and the first three stages used a different catalyst than the last stage.

As illustrated in FIG. 17, heat exchangers 218 each have a process flow path from face 220b to face 220a of distance d1. Structures 214a, 214b, and 214c have different process flow distances of d2, d3, and d4, respectively. It should be appreciated that d2 is preferably at least 50% greater than d1. More preferably, d2, d3, and d4 are greater than d1. Even more preferably d3 is greater than d2, and still more preferably d3 is greater than d4. This dimensional arrangement corresponds to more catalyzing surface area with each downstream stage to provide better conversion results as the relative reactant amount changes. The application of a relatively thin panel microchannel heat exchanger generally provides a lower pressure drop, and has a smaller volume subject to temperature control, relative to other types of heat exchangers. Nonetheless, in other forms, a different type of heat exchanger may be utilized.

The product from reactor 200 is provided to fuel cell 60 to generate electric power in a standard manner. From fuel cell 60, anode exhaust gas is provided to combustor 50 along with air to generate heat for vaporizer 30 and reactor 40, as previously described. Water from electric power generation with fuel cell 60 is condensed by condenser 70 which provides condensed water to vaporizer 30 and expels cathode exhaust gas as shown in FIG. 1.

It has been discovered that the microchannel structure of device 102 can be desired for other applications and reactor designs. For example, such structure provides unique techniques to perform mass transfer processes that occur at a liquid/gas interface, chemical separations, and other catalytic or noncatalytic reactions besides the WGS reaction. Referring to FIG. 9, microchannel device 300 is illustrated that has mass transfer microchannels 320 and heat transfer microchannels 330 similar to microchannels 120 and 130 of device 102 shown in FIGS. 6 and 7. In both devices 102 and 300, an extended surface area structure is utilized, as more specifically designated by reference numeral 304 in FIG. 9.

A fluid subject to mass transfer flows through mass transfer microchannels 320 perpendicular to the view plane of FIG. 9. This mass transfer fluid is provided from mass transfer fluid source 340, which is schematically represented in FIG. 9. A heat transfer fluid flows through heat transfer microchannels 330 co-current, counter-current, or cross-current to the flow of fluid through mass transfer microchannels 320. Heat transfer fluid is provided from heat transfer fluid source 350, which is schematically shown in FIG. 9.

Structure 304 includes thermally conductive fin 324 integrally connected to thermally conductive walls 326a and 326b. Correspondingly, fin 324 separates mass transfer microchannels 320 from one another, and walls 326a and 326b separate mass transfer microchannels 420 from heat transfer microchannels 430. Fin 324 and walls 326a and 326b are typically formed from metal.

Structure 304 addresses both mass transfer and heat transfer considerations pertinent to a variety of processes. The physical processes where such structure could be applied are broad, including chemical reactions and other mass transfer processes, such as chemical separations. More than one physical process can also be occurring in sequence or in parallel, such as with catalytic distillation. Fin 324 of structure 304 can be arranged to provide a lower resistance to heat transfer to or from the physical process relative to wall 326a and/or 326b, which can reduce occurrence of hot spots and cold spots for exothermic and endothermic reactions, respectively. Alternatively or additionally, with proper relative dimensioning of fin 324, heat collection or distribution can be increased relative to the physical process as compared to thermal conduction through wall 326a and/or 326b.

Fin 324 can also support extended area for mass transfer processes between different media 322a and 322b in microchannel 320 as illustrated in FIG. 9. Media 322a is in closer thermal contact with fin 324 than media 322b. In turn, fin 324 is thermally coupled to microchannels 330 by a low thermal resistance through walls 326a and 326b. Media 322a or 322b could be comprised of a solid, a liquid, a gas, or multiple phases, such as a fluid in a porous catalyst material. The mass transfer between media 322a and 322b could support a heterogeneous chemical reaction in one of the media. Other examples include chemical separations, such as gas absorption, adsorption, desorption, condensation, or distillation.

For a given microchannel 320, the primary area for heat transfer is proportional to L.sub.h, while the area for mass transfer is proportional to 2L.sub.m. Although the areas are geometrically related, structure 304 provides additional design variables that significantly decouple the heat transfer and mass transfer areas. Structure 304 can be repeated many times to provide a microchannel device with a desired mass transfer characteristic and desired heat transfer characteristic, a few of which are shown in cross section 101 of device 102 in FIG. 7. The geometric repetition of such structures is consistent with the layering of microchannels to achieve capacity desired for a given application, such as device 102.

In this and other reactions, mass transfer of reactants and products occurs between the two media, and heat is generated or consumed by exothermic or endothermic reactions, respectively. For the exothermic case, heat is transferred to fins, through the wall, and to a coolant flowing through the heat transfer channels. Heat flows through the opposite pathway for the endothermic case. In addition, the reactant fluid can be progressively heated or cooled as it flows through the mass transfer microchannels to establish a desired temperature profile. The flow direction of the reactant fluid relative to the flow direction of the heat exchange fluid can be counter-current, co-current, or cross-current. In the case of structure 304, microchannels 320 and 330 are layered orthogonal to one another.

The decoupling of mass transfer and primary heat transfer area facilitates design of an ratio of mass transfer area to primary heat transfer area that desirably differs from the standard 1:1 ratio common to existing layered configurations. With reference to device 102 of FIG. 7, the ratio of mass transfer area, A.sub.m, to primary heat transfer area, A.sub.m, is given by expression (1) as follows:

.times. ##EQU00001## By increasing the aspect ratio of the fins, A.sub.m/A.sub.h can be made arbitrarily greater than 1. The use of microchannels in conjunction with such fins provides acceptable fin heat transfer efficiency, and a ratio of mass to heat transfer ratio significantly greater than 1. The presence of four independent design variables in the area ratio expression above provides for flexibility in decoupling the mass transfer area from the heat transfer area in designing the device as described above. This concept is applicable for any number of configurations of the heat transfer channels. These channels may or may not be microchannels depending on the specific design. Additionally or alternatively, extended surface area structures, including fins, can be added in the heat transfer channels to provide a target ratio of less than one.

Pressure drop is another consideration in designing microchannel reactors. The flow area for the reactant fluid can be increased over the standard layered approach without increasing the hydraulic radius by increasing flow channel length, L.sub.m, without increasing flow channel width, w.sub.f. Thus, when desired, pressure drop can be controlled with or without control of heat and mass transfer characteristics. Alternatively or additionally, extended area structures, such as fins 324, can also be used as structural support members of the device.

In one example, structure 304 with extended surface area provided by fin 324 or the like is applicable to relatively narrow target ranges for reaction temperature, such as might be desired to obtain high conversion and/or good selectivity. Some catalysts for the PROX reaction can entail target temperature ranges of less than 10.degree. C. based on certain conditions. In another example, establishing a temperature profile down the length of a reactor can be aided by inclusion of structures with extended surface area--such as that previously described in connection with device 102.

Referring additionally to FIG. 10, applications directed to a mass transfer process between liquid and gas, for example at a liquid/gas interface, are further described in connection with the partial sectional view of device 400; where like reference numerals refer to like features previously described. Device 400 includes structure 304 implemented in the form of thermally conductive fin 424 integrally connected to thermally conductive walls 426a and 426b. Correspondingly, fin 424 separates mass transfer microchannels 420, and walls 426a and 426b separate mass transfer microchannels 420 from heat transfer microchannels 430. Fin 424 and walls 426a and 426b are typically formed from a metal. Mass transfer fluid is provided from mass transfer fluid source 440 (shown schematically) to flow through mass transfer microchannels 420 perpendicular to the view plane of FIG. 10. A heat transfer fluid is supplied from heat transfer fluid source 450 (shown schematically) to flow through heat transfer microchannels 430 co-current, counter-current, or cross-current to fluid flowing through mass transfer microchannels.

Device 400 further includes liquid 422a and gas 422b. Liquid 422a is conveyed with liquid conveying structure 435 included in each microchannel 420 in thermal contact with fin 424. Structure 435 can be a form of capture structure that retains liquid by capillary forces or interfacial tension, such as a wick 437, an arrangement of capillary tubes, a porous solid material, grooves, or the like. Liquid movement with structure 435 can be to or from liquid reservoir 460, which is schematically represented in FIG. 10. For the configuration of device 400, mass transfer occurs at a liquid/gas interface formed between liquid 422a carried with structure 435 and gas 422b in contact with such liquid. Such an arrangement may be desired to carry out distillation, gas absorption, gas desorption, reactive distillation, gas-liquid reactions, or another multiphasic chemical process. As in the case of device 102 and 300, the structure 304 of device 400 can be repeated as needed to form an array of interspersed mass transfer microchannels 420 and heat transfer microchannels 430.

Where structure 435 of device 400 is provided as wicking, the gas is provided as a vapor fluid, and mass exchange is occurring between the phases; heat generated or consumed at the gas-liquid interface per unit area is determined by the enthalpy change, .DELTA.H.sub.m, per unit mass exchange times the mass flux, j.sub.m. Further, given the extended area structure is designed with high fin efficiency and the thermal conductivity and thickness of the gas media is high enough so that the overall heat transfer resistance between the gas-liquid interface and the heat transfer media is dominated by the resistance from the wall to the heat transfer media, then expression (2) results as follows: U A.sub.w.apprxeq.h.sub.cA.sub.w (2) where U is the overall heat transfer coefficient, A.sub.w is the primary heat transfer area, and h.sub.c is the heat transfer coefficient between the wall and the heat transfer media.

Because the diffusivity in the gas phase is about five orders of magnitude higher than the diffusivity of the liquid phase and the width of gas and liquid media phases are comparable, the mass transfer resistance is typically dominated by the liquid phase mass transfer, which for mass transfer into the liquid phase is represented by expression (3) as follows:

.apprxeq..function. ##EQU00002## where k.sub.m is the mass transfer coefficient in the liquid phase, c.sub.l.sup.eq is liquid phase equilibrium concentration at the given bulk gas phase concentration and c.sub.l is the bulk liquid phase concentration. In order for mas