Multi-stream microchannel devices

Description of equivalent WO 2004016347 A2

MULTI-STREAM MICROCHANNEL DEVICE

0002CROSS-REFERENCE TO RELATED APPLICATIONS The present application is related to the following commonly-assigned applications filed concurrently herewith on August 15, 2002: "Integrated Combustion Reactors and Methods of Conducting Simultaneous Endothermic and Exothermic Reactions", Attorney Docket No. 02-052 and "Process for Cooling a Product, in a Heat Exchanger Employing Microchannels for the Flow of Refrigerant and Product", Attorney Docket No. 01-002 which applications are incoφorated herein by reference.

0003FIELD OF THE INVENTION This invention relates to microchannel devices and processes for multi-stream heat exchange and particularly to multi-stream heat exchange in combination with chemical reaction and more particularly to multi-stream heat exchange in combination with endothermic chemical reactions such as reforming and more particularly to endothermic reactions coupled with exothermic reactions such as combustion.

BACKGROUND OF THE INVENTION

0005Heat exchangers are critical components in virtually all unit operations involving fluid (gas or liquid) streams. They become even more critical when it is desired to add heat or thermal energy or take away heat or thermal energy from a chemical reaction. For example, endothermic reactions often require, or benefit from, the addition of heat energy. Exothermic reactions, on the other hand, often require, or benefit from, the removal of heat energy. Owing to the economic importance of many such chemical reactions, there is a continual quest for improved performance, both in terms of conversion of reactants to products and in terms of selectivity to desired products relative to undesired products. MicroChannel Technology (MCT) has been demonstrated to provide many such benefits and recent years have seen a significant increase in the application of MCT to many unit operations. See, e.g., A. A. Rostami et al., Flow and Heat Transfer for Gas Flowing In Microchannels: A Review, 38 Heat and Mass Transfer 359-67 (2002) (applications in medicine biotechnology, avionics, consumer electronics, telecommunications, metrology, and many others) and R. S. Wegeng et al., Compact Fuel Processors for Fuel Cell Powered Automobiles Based on MicroChannel Technology, Fuel Cells Bulletin No. 28 (2002) (compact hydrogen generators for fuel cells). MCT utilizes microchannel devices for carrying out processes that had previously been constrained to far larger equipment; often three to 1,000 times as large for comparable total throughput. MCT devices, which contain features of at least one internal dimension of width or height of less than about 2 mm and preferably less than about 1 mm, have the potential to change unit operations in ways analogous to the changes that miniaturization has brought to computing technology. MCT can be used to advantage in small-scale operations, such as in vehicles or personal (portable) devices. Importantly, too, MCT systems that can be economically mass-produced and connected together to accomplish large-scale operations are very desirable.

0006More particularly, heat exchangers have become smaller and smaller with more heat energy transferred per unit volume due to the additional area of smaller channels in heat exchangers. Earlier technology includes so-called compact heat exchangers. See, e.g., V. V. Wadekar, a ChE's Guide to CHEs, Chemical Engineering Progress, Dec. 2000, 30-49. Compact heat exchangers provide heat energy transfer rate densities, or heat energy transfer rate per unit volume (thermal power density) (where the volume is the total core volume as defined herein below), only up to about 0.4 W/cc for gas-phase exchangers. MCT heat exchangers, by comparison, provide heat energy transfer rate densities (thermal power density) of about 1 W/cc to 40 W/cc. Compact heat exchangers also have low interstream planar heat transfer percents, typically less than 10 percent. MCT heat exchangers, by comparison, have much higher interstream planar heat transfer percents, typically greater than 10 percent, preferably greater than 20 percent, more preferably greater than 40 percent, and even more preferably greater than 50 percent. In addition, MCT heat exchangers can rely on smaller average approach temperatures when producing the higher thermal power densities.

0007The above disadvantages of compact heat exchangers can be overcome by the use of MCT heat exchangers. There are problems, however, even with existing MCT heat exchangers. For example, MCT heat exchangers have not been designed which can process more than two separate streams in a single integral device. Processing three or more streams in a heat exchanger can, for example, enable unequal heat gain and loss between the three or more streams. Thus, when it is desirable to transfer heat energy between three or more streams, a compact heat exchanger must be employed or multiple two-stream MCT heat exchangers must be employed. Even multiple two-stream MCT heat exchangers, however, allow significantly more heat transfer to the ambient and the necessary stream transfer piping can cause higher pressure drops to redistribute flows or dead zones and eddies which can cause extended residence times. These extended residence times can^" cause fouling, corrosion, erosion, decomposition, formation of undesirable byproducts, and, for example, coke can be deposited when processing carbon-containing streams at elevated temperatures. Furthermore, for MCT heat exchangers to realize their full potential, they must be combined in significant numbers to be scaled up to economic large-scale operations. Thus, owing to having a large number of small MCT heat exchangers in close proximity and the close proximity of one channel to another, manifolding the streams entering and exiting an MCT heat exchanger (or any MCT device) becomes a problem.

0008The manifold design objective is to provide for acceptably uniform flow through a device with an acceptable manifold geometry and stream mechanical energy losses. See, W.M. Kays and A.L. London, Compact Heat Exchangers, 3d ed., at 41 (1984). Restated, manifold design requires tradeoffs among device performance factors ^"as affected by flow uniformity, overall pressure drop, and manifold size and complexity. For example, device performance could be heat transfer performance in the case of endothermic reactions coupled with exothermic reactions within and MCT device. As will be appreciated by those skilled in the art, the manifold design for any given stream is readily approached through application of fluid dynamics. Kays at 41-43.

0009When manifolding multiple streams in MCT devices, the design problem becomes even greater than designing a two-stream manifold. Having more streams present in a device means proportionally less of the external surface area of that device is available for accessing each stream. The compactness of an MCT device works against the geometric spacing requirements needed to seal manifolds to prevent stream-to-stream leakage. The manifold design must, therefore, address both the design objective stated herein above, as well as the limited external surface area. Heat exchangers are not the only unit operation to benefit from the push toward miniaturization. Closely related, reactors, too, have begun to shrink in size substantially and with excellent results. Wegneg at 9-12 (vaporizers, reforming reactors, and steam reforming). There remain, however, special problems involving MCT reactors and the need for heat transfer. For example, thermal stresses pose significant problems. MCT devices are manufactured and assembled to much higher tolerances than comparable conventional large- scale devices and multiple MCT devices must be closely-packed to economically match the throughput of comparable to large-scale devices. (An MCT device, while producing high output per core unit volume of the device, typically must be combined in very high numbers to provide comparable throughput.) Thus, temperature differentials that could be easily tolerated by a conventional device of greater dimensions can produce unacceptable thermal stresses in an MCT device which is smaller and thus experiences a much higher temperature gradient. Illustratively, an MCT reactor that is overly constrained geometrically either by multiple integral heat exchangers or integrally-combined multiple integral MCT heat exchanger/reactor units can be subjected to potentially destructive thermal stresses. In general, as a result of the increased efficiency of MCT heat exchangers, they exhibit high temperature gradients with corresponding high thermal stresses. To solve this problem, heat exchangers have been "de-coupled" from the reactors to allow for thermal expansion. In doing so, however, separate piping or tubing is required. As a result, as with multiple two- stream MCT heat exchangers, there can be significant heat loss between multiple units to the ambient and through associated piping or tubing. As noted herein above, such piping connections can become sites for fouling and coke-formation problems. Alternatively, more expensive metals that can tolerate the thermal stresses or inexpensive throwaway devices must be employed.

0010In addition, the goal of combining multiple heat exchanger/reactor devices to provide economically high total throughput has proved to be elusive. See, e.g., O. Woerz, Microreactors as Tools in Chemical Research, in Microreaction Technology, IMRET 5: Procedings of the Fifth International Conference on Microreaction Technology at 385 (Michael Matlosz et al. eds. October 2001) ("In principle, [it is conceivable that microreactors can also be used for production]. However, serious problems would be encountered."). In the petroleum processing industry, for example, even minimally-sized specialty units, for, for example, hydrogen production, typically have a capacity of at least one million standard cubic feet per day (scfd) of hydrogen up to about 100 million scfd of hydrogen. A single-stream MCT device, in contrast, produces, at most, 1,000 to 10,000 scfd of hydrogen. Therefore, to provide comparable throughput, a system must comprise from 100 to up to 100,000 closely-integrated arrays of microchannel units.

0011The present invention overcomes the drawbacks of the prior art of having to provide multiple two-stream heat exchangers with the necessary inter-unit piping, the inability of integrating an MCT heat exchanger with an MCT reactor, and combining a plurality of integrated MCT heat exchanger/reactor devices to form an MCT system to gain the benefits of large-scale operation, that is, high throughput to equal large-scale operations. In doing so, significant thermal power density with multiple streams is achieved, heat loss to the ambient is reduced, corrosion, erosion, decomposition, and coke formation are reduced or eliminated, and higher throughput per unit volume is attained. In addition, thermal stresses are reduced by operating devices with a monotonically increasing temperature profile.

0012BRIEF DESCRIPTION OF THE INVENTION The present invention is a process and device for exchanging heat energy between three or more streams in an MCT heat exchanger, integrating the MCT heat exchanger with an MCT reactor to form an integrated MCT processing unit, combining a plurality of integrated MCT processing units into an integrated MCT processing system, and finally combining a plurality of integrated MCT systems into an MCT processing stack to provide the benefits of large-scale operation. Particularly, the MCT heat exchange process and device enables flexible heat transfer between multiple streams and total heat transfer rates of about 1 Watt (W) or more per core unit volume (cubic centimeters (cc)) (W/cc), pressure drop on the order of about 0.25 psi per in. or less, stream Reynolds Numbers in the transition or laminar zones, and interstream planar heat transfer percents of greater than about 30 percent. In some embodiments, the integrated MCT heat exchanger and MCT reactor exhibits a monotonically increasing temperature profile and, thus, thermal stresses are minimized.

0013BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 a is a perspective view of a heat exchanger according to the present invention. FIG. lb is a perspective section view at section lb — lb of the perspective heat exchanger shown in FIG. la.

0014FIG. lc is a plan view of the heat exchanger shown in FIG la. FIG. Id is a schematic perspective view of the heat exchanger shown in FIG. la illustrating counter-/co-flow operation.

0015FIG. 2a is a perspective view of a cross-flow heat exchanger according to a further embodiment of the present invention. FIG. 2b is a perspective section view of the cross-flow heat exchanger shown in FIG.

00162a at section 2b — 2b.

0017FIG. 2c is a schematic perspective view of the cross-flow heat exchanger shown in FIG. 2a illustrating co-/cross-flow operation.

0018FIG. 3 a is a cross-section view of an MCT device having a heat exchange portion and a reaction portion in combination according to the present invention.

0019FIG. 3b is a cross-section view of an MCT device having a heat exchange portion and a reaction portion in combination having a reverse orientation of the MCT device illustrated in FIG. 3a.

0020FIG. 4 is a cross-section view of an MCT device having a heat exchange portion and a reaction portion in combination according to a further embodiment of the present invention. FIG. 5 is a cross-section view of an MCT processing system having a heat exchange portion and a reaction portion in combination according to the present invention.

0021FIG. 6a is an exploded perspective view of an MCT processing complex according to the present invention. FIG. 6b is an exploded perspective view of an MCT processing complex reaction portion according to a further embodiment of the present invention.

0022FIG. 6c is an exploded perspective view of an MCT processing complex combustion portion according to a fiirther embodiment of the present invention.

0023FIG. 7a is a modified negative cutaway perspective view of the MCT processing complex shown in FIG. 6a where channels are shown as solid regions.

0024FIG. 7b is a rotated modified negative cutaway perspective view of the MCT processing complex shown in FIG. 7a.

0025FIG. 8 a is a perspective view an MCT processing stack according to a further embodiment of the present invention. FIG. 8b is a rotated perspective view of the MCT processing stack shown in FIG. 8a.

0026FIG. 9 is a perspective view of the MCT processing stack shown in FIG. 8a illustrating stream headers and stream flows. FIG. 10 is a plan view of the heat exchanger described in Example 1. FIG. 11a is a perspective view of a first end of the heat exchanger described in Example 1.

0027FIG. 1 lb is a perspective view of a second end of the heat exchanger described in Example 1.

0028FIG. 12 shows the Volumetric Flowrates, Outlet Pressures, and Fluid Compositions for Example 1.

0029FIG. 13 shows the Inlet Temperatures for Example 1. FIG. 14 shows the Outlet Temperatures for Example 1. FIG. 15 shows the Pressure Drops for Example 1.

0030FIG. 16 shows a comparison of a heat exchanger according to the present invention with a computer simulation.

0031FIG. 17 shows the relationship of hydraulic diameter to heat transfer coefficient. FIG. 18 shows an arrangement of channels exchanging heat wherein one fluid flows through a channel with heat enhancement fins.

0032FIG. 19 shows an arrangement of microchannels exchanging heat with no heat enhancement fins.

0033NUMERALS 10 MCT heat exchanger 11a First wall 1 lb Second wall 12a First microchannel 12b Second microchannel 12c Third microchannel 14 Length

003415a Height of microchannel 12a 15b Width of microchannel 12a 16a Height of microchannel 12b 16b Width of microchannel 12b 17a Height of microchannel 12c 17b Width of microchannel 12c 18 Height of first wall 11 a Width of second wall 1 lb

0035Height

0036Width

0037First fluid stream

0038Second fluid stream

0039Third fluid stream

0040MCT heat exchanger a First microchannel b Second microchannel c Third microchannel

0041Rib

0042First side

0043Second side

0044Third side

0045Fourth side

0046First fluid stream

0047Second fluid stream

0048Third fluid stream

0049MCT processing unit

0050Reactor microchannel

0051First reactor heat exchange microchannel

0052Reaction microchannel

0053Second reactor heat exchange microchannel

0054Reaction catalyst

0055Combustor microchannel

0056First combustor heat exchange microchannel

0057Combustion microchannel

0058Second combustor heat exchange microchannel 0 Combustion catalyst 2 Oxidizer microchannel 4 Aperture 5 Reactants stream 76 Products stream

005977 Fuel stream

006078 Oxidizer stream

006179 Exhaust stream 80 MCT processing unit

006282 Reactor microchannel

006384 First reactor heat exchange microchannel

006486 Reaction microchannel

006588 Second reactor heat exchange microchannel 90 Reaction catalyst

006692 Combustor microchannel

006794 First combustor heat exchange microchannel

006896 Combustion microchannel

006998 Second combustor heat exchange microchannel 100 Combustion catalyst

0070102 Oxidizer microchannel

0071104 Aperture

0072110 MCT processing system

0073111 MCT processing unit 112 First reactor microchannel

0074113 Second reactor microchannel

0075114 First reactor heat exchange microchannel

0076115 Second reactor heat exchange microchannel

0077116 First reaction microchannel 117 Second reaction microchannel

0078118 Third reactor heat exchange microchannel

0079120 Reaction catalyst

0080122 First combustor microchannel

0081123 Second combustor microchannel 124 First combustor heat exchange microchannel

0082125 S econd combustor heat exchange microchannel

0083126 First combustion microchannel 127 Second combustion microchannel

0084128 Third combustor heat exchange microchannel 130 Combustion catalyst

0085132 First oxidizer microchannel 133 Second oxidizer microchannel

0086134 Aperture

0087136 First termination microchannel

0088138 Second termination microchannel

0089140 Reactor microchannel tongue 142 Combustor microchannel tongue

0090210 MCT processing complex

0091212 First reactants manifold

0092213 First reactants manifold stub 213a Reactants flue 214 Second reactants manifold

0093215 Second reactants manifold stub

0094216 Products manifold

0095217 Products manifold stub 217a Products flue 218 First fuel manifold

0096219 First fuel manifold stub 219a Fuel flue

0097220 Second fuel manifold

0098221 S econd fuel manifold stub 222 First oxidizer manifold

0099223 First oxidizer manifold stub

0100223 a Oxidizer flue

0101224 Second oxidizer manifold

0102225 Second oxidizer manifold stub 310 MCT processing stack

0103312 Reactants header

0104314 Products header 316 Fuel header 318 Oxidizer header 320 Exhaust header

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE

0106The term "millichannel" refers to a channel having at least one internal dimension of width or height of up to about 10 mm.

0107The term "microchannel" refers to a channel having at least one internal dimension of width or height of up to about 2 mm, and in one embodiment from about 0.1 mm to about 2 mm, and in one embodiment from about 0.1 mm to about 1 mm. The length may be up to about 5 meters (m) or more. Preferably, the length is about 1 m or less. More preferably the length is about 0.5 m or less. A microchannel is also a millichannel.

0108A millichannel may be used in an apparatus in conjunction with microchannels for both heat exchanger apphcations and for combined heat exchange and reactor applications. The milli-channel offers the advantage of reduced pressure drop, but the disadvantage of lower heat transfer coefficients and surface area, including EPHTAP-type area. There are examples of when a process is advantaged by the inclusion of a milli-channel with microchannels for multiple fluid processing streams. As one example, if a relatively large fraction of heat greater than 70 percent were desired to be transferred from Fluid A to Fluid B and a much smaller fraction of heat from Fluid A to Fluid C in a single apparatus, then the Fluid C channels may be made in the milli-channel range. Combined exchanger and reactor applications may be advantaged by the inclusion of one or fluid milli-channel. As an example, in the limit of a very low pressure drop constraint on one or more fluids, such as combustion air, this channel may be designed in the milli-channel range. A very low pressure drop requirement for one fluid in a heat exchanger application may necessitate the use of a milli-channel. As one example, a process that utilized natural gas to provide home heating or power would be required to not exceed the allowable back pressure on the feed line, typically a few psi. Another advantage of a combined milli-channel and microchannel process is the combined application of homogeneous combustion with additional heat exchangers to preheat and recover heat. Heat recovery from combustion may take the form of heating water for portable or stationary applications. Homogeneous combustion is challenging in a microchannel for many hydrocarbon fuels, as the critical hydrocarbon quench diameter is often larger than a microchannel but well below the limits of a millichannel. As an example, the quench diameter of methane exceeds 2 mm at room temperature and would not ignite in a microchannel. As the critical dimension increases from the microchannel range out to the broader milli-channel range, the overall size of the device may grow larger. For some applications, this is not disadvantageous if there are no space limitations. It will be appreciated by one skilled in the art, that many applications could be advantaged through the combinations of microchannels and milli-channels to tailor the performance of a process to meet desired specifications. The term "microchannel" or "MCT" when applied to a device, process, system, or the like, means that such device, process, or system includes at least one microchannel.

0109The term "MCT processing unit" refers to a microchannel device having at least one reactor section and at least one heat exchanger section in combination.

0110The term "MCT processing system" refers to a plurality of MCT processing units in combination.

0111The term "MCT processing complex" refers to a plurality of MCT processing systems in combination.

0112The term "MCT processing stack" refers to a plurality of MCT processing complexes in combination. The term "total core volume V" refers to the sum total volume of microchannels plus the volume of walls separating the microchannels, but specifically excluding any volume defined by any manifolds or headers. Thus, outside walls which define the outer dimensions of the device, are not included. Referring to FIGs la and lb, by way of example only, the total core volume V of the device shown would be computed as follows: V = [(height 15a)*(width 15b)+(height 16a)*(width

011316b)+(height 17a)*(width 17b)+(height 18)*(width 17b)+(height 15a)*(width 19)]*[length 14] As will be understood by those skilled in the art, the total core volume V will be calculated based upon generally accepted principles of solid geometry and different configurations may be approached in different manners.

0114The term "total thermal power density" refers to the amount of heat gained by the cold stream(s) divided by the total core volume V. The term "interstream planar heat transfer area percent" (IPHTAP) relates to the highest effective heat transfer and refers to the surface area that separates two fluids exchanging heat in a channel device excluding ribs, fins, and surface area enhancers as a percent of the total interior surface area of a channel that also includes ribs, fins, and surface area enhancers. That is, the ratio of the area through which heat is transferred to neighboring channels with a different fluid flowing to the total surface area of the channel. Referring to FIG. 18, an arrangement of channels is shown exchanging heat; there are three fluids, Fluid A, Fluid B, and Fluid C. Fluid A exchanges heat with Fluid B and with Fluid C. Channel A comprises heat enhancement fins (N/in.) as shown in FIG. 18. IPHTAP is calculated as [2a/(2a+2b+2c)]*100. In a typical compact heat exchanger, where a = 2.0 in., b = 0.5 in., and N = 20 fins/in., IPHTAP equals 16 percent. A geometry with IPHTAP = 100 percent would signify that all available area is utilized for exchanging heat with neighboring different streams. This example assumes that heat exchange at both long edges of the channel. If the channel is an end channel and exchanges heat at only one edge, IPHTAP = 8 percent. In a microchannel, in contrast (FIG. 19), where a = 2.0 in., b = 0.025 in., d = 0.040 in. and e = 0.98 in., IPHTAP would be: Channel with Fluid A = [2a/(2a+2b)]*100 = 49 percent; Channel with Fluid B - [8c/(8c+8b)]*100 = 95 percent; Channel with Fluid C = [2e/(4e+4b)]*100 = 49 percent.

0115When used in this Specification, the terms "reactor", "reaction", "combustor", "combustion", "oxidizer", and the like, when referring to microchannels and streams, are nominal only. It is to be understood that, within the scope and spirit of the present invention, no reaction or any reaction and no combustion or any similar combustion or exothermic reaction may take place within such named microchannels. By way of example only, reactions may include catalytic processes such as acetylation, addition reactions, alkylation, dealkylation, hydrodealkylation, reductive alkylation, amination, aromatization, arylation, autothermal reforming, carbonylation, decarbonylation, reductive carbonylation, carboxylation, reductive carboxylation, reductive coupling, condensation, cracking, hydrocracking, cyclization, cyclooligomerization, dehalogenation, dimerization, epoxidation, esterification, exchange, Fischer-Tropsch, halogenation, hydrohalogenation, homologation, hydration, dehydration, hydrogenation, dehydrogenation, hydrocarboxylation, hydroformylation, hydrogenolysis, hydrometallation, hydrosilation, hydrolysis, hydrotreating, hydrodesulferization/hydrodenitrogenation (HDS HDN), isomerization, methanation, methanol synthesis, methylation, demethylation, metathesis, nitration, oxidation, partial oxidation, polymerization, reduction, Sabatier reaction, steam and carbon dioxide reforming, sulfonation, telomerization, transesterification, trimerization, water gas shift (WGS), and reverse water gas shift (RWGS). By further example, phase changes such as condensation and evaporation are also within the contemplation of the present invention, as are operations such as absorption and adsorption.

0116Referring initially to FIGs la-Id, the MCT heat exchanger 10 of the present invention has a total core volume V and comprises a first microchannel 12a, a second microchannel 12b, and at least a third microchannel 12c. In operation, a first stream 20, a second stream 22, and at least a third stream 24 flow through the first microchannel 12a, the second microchannel 12b, and the at least third microchannel 12c, respectively. While FIG. Id illustrates a single-pass, parallel counter/co-current flow pattern, it will be understood by those skilled in the art that the flow pattern may be any of suitable design. Multiple pass flows as well as co-current and cross-current flow patterns (shown in FIGs 2a-2c) are possible. Importantly, the total thermal power densities of such devices can be from about one (1) W/cc to 40 W/cc or more, the total pressure drop can be 0.25 psi per in. or less, and the interstream planar heat transfer area percent greater than 10 percent. Particular attention is drawn to the shapes, sizes, and separations of the first microchannel 12a, the second microchannel 12b, and the at least third microchannel 12c. By varying the dimensions and overall design format of the microchannel layout and the walls separating the microchannels, the flow of heat energy between streams can be varied virtually infinitely. It is also possible to provide a higher heat transfer rate per unit volume, less metal between microchannels is required, and a higher heat transfer coefficient per hydraulic diameter. Thus, h ~ f(D ), where ϊl is the heat transfer coefficient, Dfr is the hydraulic diameter, and

0117Dh = 4A/P, where A is the cross-sectional area and P is the wetted perimeter.

0118As is shown, for example, in FIG. 16, heat transfer coefficients, h, increase as the hydraulic

0119diameter, Dtø, decreases.

0120Consider, first, the overall size of the device; the width, length, and height. A larger overall size leads to higher total heat capacities and less relative heat loss (Qi_oss/Q_totai) but also leads to difficulties in manifolding and flow distribution, h a counter-current flow heat exchanger, a larger heat exchanger length gives a smaller average approach temperature between the hot and cold streams. That is, T ot-exit-mean ^_ T_coid-i_nι_et-me_an- However, a smaller approach temperature also indicates lower transversal heat flux between the streams. Consider, next, the thermal properties of the device; including the thermal conductivity, specific heat, and density. A higher thermal conductivity gives a higher ^"transversal heat transfer rate but also higher longitudinal heat conduction. The former will enhance the heat transfer between the streams in adjacent channels. The latter is undesirable because it degrades the heat exchange performance due to larger approach temperatures. An optimal thermal conductivity for a given structure and dimensions for microchannel heat exchangers can be determined. See, e.g., T. Stief et al., Numerical Investigations on Optimal Heat Conductivity in Micro Heat Exchangers, AIChE 2000 Spring Meeting (March 2-9, 2000). Larger specific heats and densities lead to higher thermal inertia and, therefore, a slow transition of operation statuses, for example start-up and shut-down. Consider, next, the total flow rate, or capacity, of an individual stream. The increase in flow rate generally leads to a smaller temperature drop of a hot stream (or to a smaller increase in temperature of a cold stream) throughout the exchanger. This also means that the overall approach temperature of all the streams will increase. If the flow rates of other streams remain unchanged, the local heat flux will increase by increasing the flow rate of one stream. A decrease in the microchannel dimension leads to an increase in the heat transfer coefficient and, in turn, the heat flux between the fluid in the microchannel and the microchannel wall. For a cold stream, its exit temperature becomes higher, for the same mass flux, than it was before reducing the size of the microchannel dimension. The overall thermal effectiveness is increased because the amount of heat transferred from or to the other streams also increases. However, the increase in the amount of heat transferred from or to the other streams is generally smaller than that of the stream whose microchannel dimension is reduced. There is, however, a practical lower limit since the lower the microchannel dimension, the higher the pressure drop. In the present invention, a microchannel having a rectangular cross-section is preferred as this geometry gives higher heat transfer coefficients and less solid material is required than with a square or round channel. Particularly, very wide microchannels with a very small microchannels can nearly isolate a particular stream from thermal communication with other streams. A spacer or rib in, or between streams, may function as a fin to improve the heat transfer between the stream and the solid wall and, in turn, improve the heat transfer to other streams. This effect is also found in ribs, webs, and spacers between different streams at temperatures lower than local wall temperatures. However, one of the effects of increasing the dimensions of webs, ribs, spacers, and perimeter metal is to increase the unwanted metal cross-sectional area and, in turn, the axial conduction. Another effect of increasing dimensions of webs between different streams is to increase the resistance of transverse heat conduction when heat transfer between the two streams is desired. These two effects decrease the transverse heat flux between different streams and, therefore, degrade the heat exchange performance. As will be appreciated by those skilled in the art, the choice of microchannel cross- section is not limited to rectangular; other polygonal and even circular or elliptical cross- sections can be used vvάthin the scope of the present invention.

0121Referring now to FIGs 2a-2c, in another embodiment of the present invention, an MCT heat exchanger has at least four surfaces 34, 36 (indicated but not shown), 38, and 40 (indicated but not shown), and comprises a first microchannel 32a, a second microchannel 32b, and at least a third microchannel 32c. In operation, a first stream 42, a second stream 44, and at least a third stream 46 flow through the first microchannel 32a, the second microchannel 32b, and the at least third microchannel 32c, respectively. Illustratively, the third microchannel 32c may further comprise a plurality of interior walls or ribs 33. As will be appreciated by those skilled in the art, the ribs 33 introduce significant design flexibility and allow a virtually limitless combination of hydraulic diameters. In addition, the ribs 33 can, in appropriate circumstances, help provide additional structural support when dealing with pressure differentials across the walls separating one microchannel from another. While FIGs. 2a-2c illustrate a single-pass flow pattern, it will be understood by those skilled in the art that the flow pattern may be of any suitable design. In addition, one skilled in the art will appreciate that the angles between the faces need not be exact right angles as shown; many other angles will be effective depending upon the application. Importantly, however, the total thermal power density of such devices can be about 21 W/cc to 40 W/cc or more.

0122As will be further appreciated by those skilled in the art, the usefulness of the present invention is not limited to the specific configurations illustrated in FIGs la- Id and 2a-2c. By way of example only, the various microchannels may vary in number, size, and complexity. The relative positions of one microchannel to other microchannels may also be varied as may the thickness as well as the inherent thermal conductivity of the walls separating one microchannel from the other microchannels. See discussion herein above.

0123Example 1 Referring now to FIGs 10-15, a heat exchanger was specifically designed to simulate a heat exchanger according to one embodiment of the present invention. The heat exchanger used five distinct fluids, denoted in FIGs 10-15 as Fluids A, B, C, D, and E. Fluids C and D were split into two streams each with each stream flowing through separate microchannels; fluids A, B, and E each flowed through separate microchannels (as Streams A, B, and E, respectively), making a total of seven microchannels in the heat exchanger. As shown in FIG. 10, Fluid C flowed through two microchannels as Stream Cl and Stream C2. Similarly, Fluid D flowed through two microchannels as Stream Dl and D2. The experimental results show the performance of the heat exchanger and the results as compared to numerical simulations from a computer program. Referring again to FIG. 10, the heat exchanger consisted of seven rectangular microchannels, each ten inches (in.) long. The height of each microchannel where Streams A and B flowed was 0.020 in. The height of the microchannel where Stream E flowed was 0.040 in. The height of each microchannel where Stream Dl and Stream D2 flowed was 0.020 in., and the heights of the microchannels where Streams Cl and C2 flowed were 0.030 in. and 0.020 in., respectively. The order of the seven streams in the heat exchanger was Cl, Dl, A, B, E, C2, and D2 (shown in FIG. 10). (For clarity and consistency, the heat exchanger microchannels are referred to by the name of the stream flowing through them. Thus, Stream Cl flows through microchannel Cl.)

0124The heat exchanger was constructed of Inconnel 625 and the microchannels were made by "popping" a 0.030-in. diameter hole with an electrode in the places where the rectangular microchannels were needed. After the holes were made, microchannels were made by using wire ElectroDischarge Machining (EDM). If the microchannel width was less than 0.030 in., the edge portions of the original round hole still existed around the outside of the microchannel; the portions of the original hole were purposely, alternatingly, offset to the top and bottom of the microchannels. If the microchannel width was equal to or greater than 0.030 in., no portions of the round hole remained. Referring to FIGs. 11a and lib, manifolding for the inlet of MicroChannel C2 was accomplished by sending Stream C2 directly into the device while manifolding for the outlet of MicroChannel Cl was accomplished by exiting Stream Cl directly out from the device; the other microchannels were blocked off by welding the microchannels closed on the front and back faces. The inlet to MicroChannel Cl was manifolded by drilling in through the side of the heat exchanger. The outlet from MicroChannel Cl came directly out of the heat exchanger similar to MicroChannel C2. MicroChannel D2 on the edge of the heat exchanger was also manifolded in and out of the side of the heat exchanger. The other microchannels in the center of the heat exchanger were manifolded in the top and bottom of the heat exchanger. The diameter of the inlet and outlet holes was equal to or smaller than the width of the channel, i.e., 0.020 in. to 0.040 in. Generally, three or four holes that served as the inlet or exit were drilled into each such microchannel.

0125The exact composition and flowrates of each of the streams for each test are shown in FIG. 12. Experiments were performed with flowrates corresponding to six conditions. The first two conditions were nearly equivalent except that the reactant and product streams entered the heat exchanger at approximately one-half the expected pressure.

0126Experiments were performed at the temperatures and pressures shown in FIGs 12 and 13. The directions of the streams are shown in FIGs 11a and lib. Streams A, Cl, C2 flow in the same direction and counter-current to the flow of Streams B, Dl, D2, and E. There were three sets of experimental tests performed for the heat exchanger; Tests X,

0127Y, and Z as shown in FIGs 12-15. The pressure drops of some of the streams are shown in FIG. 15; all pressure drops were measured before and after the fluid entered and exited the microchannel, therefore contraction and expansion losses are included in the measured pressure losses. The pressure losses of the individual streams were measured with differential pressure gauges, most of which measured a maximum differential pressure of 5.4 psi and a resolution of 0.1 psi. The stream labeled Dl was measured with a meter capable of measuring 9.0 psi and a resolution of 0.2 psi.

0128The five-stream heat exchanger demonstrated that a multi-stream microchannel heat exchanger could successfully heat and cool multiple streams in a single device. There was reasonable agreement with a numerical simulation that was constructed. The comparison between the experimental values and the results from the numerical simulation are shown in FIG. 16. The inlet temperatures were fixed and the outlet temperatures calculated. An approach temperature was also calculated:

0129∑T m C_Pi =!

0130∑m C_Pi ι^'=l

0131where T_m is the mean temperature of the hot streams at a first end of the heat exchanger and is also used to calculate the mean temperature of the cold streams at the first end, the mean temperature of the hot streams at the second end, and the mean temperature of the cold streams at the second end. Tj is the -^'th hot stream, m, is the mass flow rate (kg/s) of the rth hot stream, Cpj is the heat capacity of the -th hot stream. The mean temperature of the hot streams at the first end was 857 deg. C and at the second end 250 deg. C. The mean temperature of cold streams at the first end 730 deg. C and at the second end 161 deg. C. The mean approach temperatures are: 126 deg. C at the first end and 89 deg. C at the second end.

0132Referring now to FIG. 3 a, in another embodiment of the present invention, an MCT processing unit 50 has a total core volume V (not shown) and comprises a reactor microchannel 52, a combustor microchannel 62, and an oxidizer microchannel 72. The reactor microchannel 52 comprises a first reactor heat exchange microchannel 54, a reaction microchannel 56, and a second reactor heat exchange microchannel 58. Alternatively, only one reactor heat exchange microchannel may be present. Also, as will be understood by those skilled in the art, the precise point where the reactor microchannel 52 is no longer primarily exchanging heat and is functioning primarily as a reactor can be difficult to determine and can be somewhat arbitrary. For example, the reactor microchannel 52 may be in thermal communication with one or more other microchannels in the same unit. The reaction microchannel 56 may further include a reaction catalyst 60. The reaction catalyst 60 may contain any suitable metal or semi-metal and/or their oxides comprising one or more elements from Groups -HA, IVA, VA, VIIA, VIIIA, IB, IIB, IIB, IVB, Ce, Pr, Sm, Tb, Th or their oxides and combinations thereof. The reaction catalyst 60 may also contain promoters which enhance the chemical or physical properties of the reaction catalyst 60, and may contain any suitable metal, semi-metal or non-metal, and/or their oxides, comprising one or more elements from the previous list and/or Group IA, IIA, VB, VIB and combinations thereof. The reaction catalyst 60 may also be supported on any suitable support material, such as silica, alumina, zirconia, titania, magnesia, yttria, ceria, lanthana, carbon or combinations of these, which supply either sufficient surface area or chemical interaction to benefit the action of the active constituent. The reaction catalyst 60, by way of example only, may be applied to an engineered substrate such as a felt, foam, fin, mesh, gauze, or foil and the substrate inserted into a cutout (not shown) in a wall of the reaction microchannel 56 to act as a flow-by catalyst, may be inserted into the reaction microchannel 56 to act as a flow- through catalyst, or may be applied to a wall or walls of the reaction microchannel 56 as a washcoat. Thus, the reaction catalyst 60 may be present in the form of a powder or small pellet, a monolith, a wall coating or combinations of these forms. In the case of powders and monoliths, the reaction catalyst 60 may be comprised of a skeletal, or Raney type, metal. In the case of a monolith, the reaction catalyst 60 may be present as a slurry or wash coating on a foam, felt, screen, mesh, gauze or similar substrate. In the case of a wall coating, the reaction catalyst 60 may be applied as by slurry coating or direct wash coating, preferably with prior treatment of the wall in such a way as to maximize adhesion and/or surface area. In some cases, constituents of the reaction catalyst 60 may be comprised wholly or partially from native materials present in the wall or monolith alloys. The reaction catalyst 60 may also include two or more different catalyst types in different regions of the reaction microchannel 56. Alternatively, depending upon the desired reaction, the reaction microchannel 56 may include no reaction catalyst 60. Finally, there may be no reaction in reaction microchannel 56, for example, when vaporizing a liquid stream.

0133The combustor microchannel 62 comprises a first combustor heat exchange microchannel 62, a combustion microchannel 66, and a second combustor heat exchange microchannel 68. As with the reactor microchannel 52, alternatively, only one combustor heat exchange microchannel may be present. Also, as with the reactor microchannel 52, as will be understood by those skilled in the art, the precise point where the combustor microchannel 62 is no longer primarily exchanging heat and is functioning primarily as a combustor can be difficult to determine and somewhat arbitrary. And, in fact, combustion and significant heat exchange can, and does, occur in the same region of the combustor microchannel 62. For example, the combustor microchannel 62 may be in thermal communication with one or more other microchannels in the same device. The combustion microchannel 66 may also include a combustion catalyst 70. To provide further flexibility, the first combustor heat exchange microchannel 64 and the second heat exchange microchannel 68 may also include a combustion catalyst 70 to provide pre- and post- oxidation reactions. The combustion catalyst may contain any suitable active metal and/or metal oxide, preferably comprising one or more elements from Groups MA, VIIIA or IB, Ce, Pr, Sm or their oxides and combination thereof, or more preferably comprising one or more of the elements Pt, Pd, Y, La, Ce, Pr or their oxides, and combinations thereof. The combustion catalyst 70 may also be supported on any suitable support material, such as silica, alumina, zirconia, titania, magnesia, yttria, ceria, lanthana, carbon or combinations thereof, which supply either sufficient surface area or chemical interaction to benefit the action of the active constituent. The combustion catalyst 70 may be present in the form of a powder or small pellet, a monolith, a wall coating or combinations of these forms. In the case of powders and monoliths, the combustion catalyst 70 may be comprised of a skeletal, or Raney type, metal. In the case of a monolith, the combustion catalyst 70 may be present as a slurry or wash coating on a foam, felt, screen, mesh, gauze or similar substrate. In the case of a wall coating, the combustion catalyst 70 may be applied as by slurry coating or direct wash coating, preferably with prior treatment of the wall in such a way as to maximize adhesion and or surface area. In some cases, constituents of the combustion catalyst 70 may be comprised wholly or partially of native materials present in the wall or monolith alloys. Alternatively, depending upon the desired combustion, the combustion microchannel 66, the first combustor heat exchange microchannel 64, and the second combustor heat exchange microchannel 68 may include no combustion catalyst 70. As will be appreciated by those skilled in the art, combustion may be replaced with any number of exothermic reactions. By way of example only, acetylation, alkylation, hydrodealkylation, epoxidation, Fischer- Tropsch, hydration, dehydration, hydrogenation, oxidative dehydrogenation, hydrolysis, methanation, methanol synthesis, metathesis, oxidation, polymerization, and water-gas shift (WGS).

0134The oxidizer microchannel 72 comprises one or more apertures 74 through which the oxidizer microchannel 72 is in fluid communication with the combustor microchannel 62. As with the combustor microchannel 62, the oxidizer microchannel 72 may provide for the introduction of other reactants to an exothermic reaction.

0135In operation, by way of example only, a reactants stream 75, such as a mixture of steam and methane, is introduced into the reactor microchannel 52 at the first reactor heat exchange microchannel 54. A fuel stream 77, such as hydrogen or methane or other hydrocarbon, is introduced into the combustor microchannel 62 at the first combustor heat exchange microchannel 64, and an oxidizer stream 78, such as air, is introduced into the oxidizer microchannel 72. As the reactants stream 75 flows through the reaction microchannel 56 it is converted, for example, in a reforming reaction, to the products stream 58, such as a mixture of steam, methane, and hydrogen. A reaction catalyst 60 is used. As the fuel stream 77 flows through the first combustor heat exchange microchannel 64 and the combustion microchannel 66, it becomes combined with oxidizer 78 introduced into the oxidizer microchannel 72 and thus into the combustor microchannel 64 via the one or more apertures 74, and combusts to form the exhaust stream 79. A combustion catalyst 70 may be [is?] used. Note that pre-oxidation may occur in the first combustor heat exchange microchannel 64 to preheat the reactants stream 75. Likewise, oxidation may continue into the second combustor heat exchange microchannel 68 to provide additional heat energy downstream of the combustion microchannel 66. By further example only, the reaction converting the reactants stream 75 into the products stream 76 is an endothermic reaction such as steam methane reforming or hydrocarbon dehydrogenation, the fuel stream 77 is hydrogen or a combination of carbonaceous fuels, and the oxidizer stream 78 is air.

0136As will be appreciated by those skilled in the art, the present invention, embodiments of which are represented and described herein, may be useful for unit operations where there is only a single reaction. By way of example only, reactor microchannel 52 may serve as a vaporizer. Similarly, an MCT device may comprise a first combustor microchannel in thermal communication with a second combustor microchannel, the combustor microchannels supported by one or more oxidizer microchannels. And, as discussed herein above, oxidative combustion need not be one of the reactions involved. To further illustrate the flexibility of the present invention, FIG. 3b shows a modification of the MCT processing unit 50 of FIG. 3 a. All descriptions in FIG. 3 a are attributable to FIG. 3b but the flow is shown in a countercurrent pattern.

0137FIG. 4 shows another embodiment of the present invention. An MCT processing unit 80 has a total core volume V (not shown) and comprises a reactor microchannel 82, a combustor microchannel 92, and an oxidizer microchannel 102. The reactor microchannel 82 comprises a first reactor heat exchange microchannel 84, a reaction microchannel 86, and a second reactor heat exchange microchannel 88. Alternatively, only one reactor heat exchange microchannel may be present. Also, as will be understood by those skilled in the art, the precise point where the reactor microchannel 82 is functioning primarily as a reactor or not can be difficult to determine and can be somewhat arbitrary. For example, the reactor microchannel 82 may be in thermal communication with one or more other microchannels in the same device. The reaction microchannel 86 may further include a reaction catalyst 90. Alternatively, depending upon the desired reaction, the reaction microchannel 86 may include no reaction catalyst 90.

0138The combustor microchannel 92 comprises a first combustor heat exchange microchannel 92, a combustion microchannel 96, and a second combustor heat exchange microchannel 98. As with the reactor microchannel 82, alternatively, only one combustor heat exchange microchannel may be present. Also, as with the reactor microchannel 82, as will be understood by those skilled in the art, the precise point where the combustor microchannel 92 is no longer primarily exchanging heat and is functioning primarily as a combustor can be difficult to determine and somewhat arbitrary. For example, the combustor microchannel 92 may be in thermal communication with one or more other microchannels in the same device. The combustion microchannel 96 may also include a combustion catalyst 100. To provide further flexibility, the first combustor heat exchange microchannel 94 and the second heat exchange microchannel 98 may also include combustion catalyst 100. The combustion catalyst 100 may be [different types of catalysts and different methods of applying]. Alternatively, depending upon the desired combustion, the combustion microchannel 96, the first combustor heat exchange microchannel 94, and the second combustor heat exchange microchannel 98 may include no combustion catalyst 100.

0139The oxidizer microchannel 102 comprises one or more apertures 104 through which the oxidizer microchannel 102 is in fluid communication with the combustor microchannel 92.

0140Operation of the MCT processing unit 80, by way of example only, is analogous to that described herein above in reference to the MCT processing unit 50.

0141As will be appreciated by those skilled in the art, the apertures 74 (shown in FIGs 3 a and 3b) and the apertures 104 (shown in FIG. 4) add yet another dimension to the design flexibility of the present invention. By varying the placement, cross-section, shape, and size of a plurality of apertures 74 and of a plurality of apertures 104, significant flexibility can be achieved in combining two or more streams. Likewise, the thickness of the material through which the apertures 74 and the apertures 104 are created can add yet another dimension to the design flexibility. By changing these variables, the mixing or fluid communication between the two streams can be uniquely controlled. By way of example only, in a combustion application, the temperature profile and the heat transferred can be tailored to the particular application and reactor design. This is achieved because the oxidizer stream 78 acts as a limiting agent in a combustion reaction. Thus, the apertures 74 and apertures 104 function to introduce specific amounts of the oxidizer stream 78 to specific points so as to control the rate and extent of the combustion reaction along the entire length of the combustor microchannel 62 and combustor microchannel 92. Referring now to FIG. 5, an MCT processing system 110 has a total core volume V

0142(not shown) and comprises a plurality of MCT processing units 111, a first termination microchannel 136, and a second termination microchannel 138. As will be understood by those skilled in the art, the choice of termination modes may be varied according to the design requirements of the MCT processing system 110. As discussed herein above, to realize the advantages of MCT, multiple MCT processing units 111 must be combined into an integrated system to approach the total throughput of a large-scale operation. The MCT processing system 110 helps accomplish that by integrating a plurality of MCT processing units 111, the basic technology of which has been introduced herein above.

0143Each MCT processing unit 111 comprises a first reactor microchannel 112, a second reactor microchannel 113, a first combustor microchannel 122, a second combustor microchannel 123, a first oxidizer microchannel 132, and a second oxidizer microchannel 133. The first reactor microchannel 112 comprises a first reactor heat exchange microchannel 114, a first reaction microchannel 116, and a third reactor heat exchange microchannel 118. The second reactor microchannel 113 comprises a second reactor heat exchange microchannel 115 and a second reaction microchannel 117 and is in fluid communication with the third reactor heat exchange microchannel 118. The first reaction microchannel 116 may also include a reaction catalyst 120. The second reaction microchannel 117 may also include a reaction catalyst 120. Preferably, as shown in FIG. 5, a reactor microchannel tongue 140 is also included. The first combustor microchannel 122 comprises a first combustor heat exchange microchannel 124, a first combustion microchannel 126, and a third combustor heat exchange microchannel 128. The second combustor microchannel 123 comprises a second combustor heat exchange microchannel 125 and a second combustion microchannel 127 and is in fluid communication with the third combustor heat exchange microchannel 128. The first combustion microchannel 126 may also include a combustion catalyst 130. The second combustion microchannel 127 may also include a combustion catalyst 130. Preferably, as shown in FIG. 5, a combustor microchannel tongue 142 is also included. The reactor microchannel tongue 140 and the combustor microchannel tongue 142 provide flow stabilization and, if non-rigid, flow equalization to overcome minor variations in microchannel dimensions.

0144The first oxidizer microchannel 132 comprises at least one aperture 134 through which the first oxidizer microchannel 132 is in fluid communication with the first combustor microchannel 126. The second oxidizer microchannel 133 comprises at least one aperture 134 through which the second oxidizer microchannel 133 is in fluid communication with the second combustor microchannel 123.

0145Operation of each MCT processing unit 111, by way of example only, is analogous to that described herein above in reference to the MCT processing unit 50 and the MCT processing unit 80.

0146Referring now to FIG. 6a, an MCT processing complex 210 has a total core volume V (not shown) and comprises a plurality of MCT processing systems 110 (best illustrated in FIG. 5), a first reactants manifold 212, a second reactants manifold 214, a products manifold 216, a first fuel manifold 218, and a second fuel manifold 220. As will be appreciated by those skilled in the art, the precise arrangement of each manifold is subject to various design considerations and it is within the scope and intent of the present invention to include other such arrangements. By way of example only, the first fuel manifold 218, the second fuel manifold 220, the first reactants manifold 212, and the second reactants manifold 214the first reactants manifold 212, and the second reactants manifold 214 all terminate on the same face of the MCT processing complex 210 but a different positions along an external face of the MCT processing complex 210. (Also seen in FIGs 8a and 8b.) As will further be appreciated by those skilled in the art, an exhaust manifold (not shown) could also be included to collect fluids exiting the third combustor heat exchange microchannels 128. By way of further illustration, FIGs 7a and 7b show a partial cutaway negative wireframe view of the microchannel arrangement shown in FIG. 6a. In addition to a plurality of MCT processing systems 110, it is preferable to repeat the MCT processing complex 210 to form an MCT processing stack 310 (illustrated in FIGs. 8 and 9) capable of high throughput.

0147FIGs 6b and 6c illustrate a further embodiment of the present invention for manifolding the various microchannels. For example, a reactants flue 213a provides fluid communication between a plurality of first reactor microchannels 116 and an outside surface of the MCT processing complex 210 via the first reactants manifold 212 and a first reactants manifold stub 213 and between a plurality of second reactants microchannels 117 and an outside surface of the MCT processing complex 210 via the second reactants manifold 214 and a second reactants manifold stub 215. Likewise, a products flue 217a provides analogous fluid communication for a plurality of third reactor heat exchange microchannels 118, a fuel flue 219a provides analogous fluid communication for a plurality of first combustor microchannels 122 and a plurality of second combustor microchannels 123, and the oxidizer flue 223 a provides analogous fluid communication for a plurality of first oxidizer microchannels 132 and a plurality of second oxidizer microchannels 133. As will be appreciated by those skilled in the art, an exhaust flue may provide fluid communication between a plurality of third combustor heat exchange microchannels 128, thus further illustrating the design flexibility of the present invention. In addition, by way of example only, the orientations of the first reactants manifold stub 213, the first reactants manifold 212, and the plurality of first reactor microchannels 116 relative to one another is virtually infinitely flexible. Thus, allowing even further design flexibility depending upon the specific application.

0148Referring now to FIGs 8a and 8b, an MCT processing stack 310 has a total core volume V (not shown) and comprises a plurality of MCT processing complexes 210. Shown in FIG. 8a are a plurality of first fuel manifolds 218 and second fuel manifolds 220 in substantial linear alignment, a plurality of first reactants manifolds 212 and second reactants manifolds 214 in substantial linear alignment, and a plurality of third combustion heat exchanger microchannels 128 in substantial linear alignment. Shown in FIG. 8b are a plurality of first oxidizer manifolds 222 and second oxidizer manifolds 224 in substantial linear alignment, and a plurality of products manifolds 216 in substantial linear alignment. While FIGs 8a and 8b illustrate a specific relational arrangement of manifolds and the plurality of third combustor heat exchange microchannels 128, it will be understood by one skilled in the art that other arrangements are possible. Referring now to FIG. 9, an MCT processing stack 310 comprises a plurality of MCT processing complexes 210, a reactants header 312, a products header 314, a fuel header 316, an oxidizer header 318, and an exhaust header 320. As will be appreciated by those skilled in the art, the precise arrangement of each manifold is subject to various design considerations and it is within the scope and intent of the present invention to include other such arrangements.

0149Fabrication of the MCT processing stack 310 is by know techniques. The MCT processing complexes 210 are made as first subassemblies. The headers 312, 314, 316, 318 are then conventionally welded onto the exterior of the subassemblies. The heating rate during welding must be closely momtored to ensure a high level of quality; hot spots may damage the subassemblies, including delamination. In addition to welding on the headers 312, 314, 316, 318, the subassemblies themselves may be welded into place on any form of infrastructure. This infrastructure, by way of example only, may serve as outer protection, fixing the device in space, safety containment, insulation, cooling jacket, and lifting points. In operation, by way of example only, a reactants stream 75 is introduced into the reactants header 312, a products stream 76 is discharged from the products header 314, a fuel stream 77 is introduced into the fuel header 316, an oxidizer stream 78 is introduced into the oxidizer header 318, and the exhaust stream 79 is discharged form the exhaust header 320. The embodiment shown in FIGs 8a-9 shows a plurality of integral heat exchanger and reactor combinations. There are five distinct fluid streams: The reactants stream 75, the products stream 76, the oxidizer stream 78, the fuel stream 77, and the exhaust stream 79. As shown in the accompanying figures, the exhaust stream 79 exits straight out of each MCT processing complex 210 via each third combustor heat exchange microchannel 128. Alternatively, any of the other streams could be headered straight off each MCT processing complex 210. The exhaust stream 79 was selected to minimize the overall pressure drop of the oxidizer stream 78-fuel stream 77-exhaust stream 79 system. The four remaining streams are headered on the sides of each MCT processing complex 210 and, thus, on the sides of the MCT processing stack 310. Each fluid stream enters or exits at different points along the length of each MCT processing complex 210. For multi-stream devices, therefore, fluids may enter or exit at different points of the MCT processing complex 210, thus allowing much design flexibility in the thermal profile. For example, streams that enter much warmer than other streams may be selected to be headered further down the length, or toward warmer sections of the device. Thus, advantage is taken of the monotonically increasing temperature profile feature of the device. The heights of the manifolds is selected to generally minimize overall pressure drop while still allowing for good flow distribution among the internal array of microchannels. Smaller heights may be utilized where higher pressure drops can be tolerated.

0150CLOSURE While the invention has been explained in relation to various detailed embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the Specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.