U.S. patent application number 12/315860 was filed with the patent office on 2009-07-16 for processing apparatus with an electromagnetic launch.
Invention is credited to Marc A. Portnoff, David A. Purta.
Application Number | 20090179028 12/315860 |
Document ID | / |
Family ID | 39774912 |
Filed Date | 2009-07-16 |
United States Patent
Application |
20090179028 |
Kind Code |
A1 |
Purta; David A. ; et
al. |
July 16, 2009 |
Processing apparatus with an electromagnetic launch
Abstract
A processing apparatus, such as a microwave-based processing
apparatus. The apparatus includes a vessel having an inner surface
defining a chamber configured to hold a reaction mixture, a guide,
and a launch coupled to the guide. The guide can be at least
partially disposed in the vessel, and is configured to propagate
electromagnetic energy. The launch is configured to couple at least
a portion of the electromagnetic energy from the guide to the
reaction mixture. Example launches include a dielectric window and
a projection. Example projections include a metallic projection and
a dielectric projection.
Inventors: |
Purta; David A.; (Gibsonia,
PA) ; Portnoff; Marc A.; (Pittsburgh, PA) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Family ID: |
39774912 |
Appl. No.: |
12/315860 |
Filed: |
December 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11686586 |
Mar 15, 2007 |
7518092 |
|
|
12315860 |
|
|
|
|
Current U.S.
Class: |
219/695 |
Current CPC
Class: |
B01J 2219/1272 20130101;
B01J 2219/1227 20130101; B01J 2219/1215 20130101; B01J 2219/1239
20130101; B01J 2219/126 20130101; B01J 2219/1266 20130101; B01J
2219/1254 20130101; B01J 8/0257 20130101; B01J 2219/1296 20130101;
B01J 19/126 20130101; B01J 2219/1269 20130101 |
Class at
Publication: |
219/695 |
International
Class: |
H05B 6/70 20060101
H05B006/70 |
Claims
1-18. (canceled)
19. A radio frequency (RF) reactor system comprising: a vessel
including an inner surface defining a chamber configured to hold a
reaction mixture; a RF generator; a first dielectric-filled
waveguide and a second dielectric-filled waveguide coupled to the
RF generator and at least partially disposed within the vessel,
each of the first dielectric-filled waveguide and the second
dielectric-filled waveguide being configured to propagate RF
energy; a first launch and a second launch coupled to the first
dielectric-filled waveguide, each of the first launch and the
second launch being configured to launch a portion of the RF energy
propagated by the first dielectric-filled waveguide; and a third
launch and a fourth launch coupled to the second dielectric-filled
waveguide, each of the third launch and the fourth launch being
configured to launch a portion of the RF energy propagated by the
second waveguide.
20. The apparatus of claim 19, wherein the vessel further includes
a port configured to introduce at least one reactant with or
without at least one catalyst to the chamber and to release at
least one product with or without at least one catalyst from the
chamber.
21. The apparatus of claim 19, wherein the first launch includes a
window.
22. The apparatus of claim 19, wherein the first launch includes a
projection.
23. The apparatus of claim 19, wherein the first launch includes a
metallic projection.
24. The apparatus of claim 23, wherein the projection further
includes a dielectric material at least partially surrounding the
metallic projection.
25. The apparatus of claim 19, wherein the first launch includes a
dielectric projection.
26. The apparatus of claim 19, wherein the first dielectric-filled
waveguide includes a filling comprising at least one of quartz,
alumina, silica, boron nitride, aluminum nitride, Teflon, and
partially evacuated vacuum.
27. The apparatus of claim 19, wherein the first dielectric-filled
waveguide includes a RF transparent gaseous dielectric filling.
28. The apparatus of claim 19, wherein the RF generator comprises a
first RF generator and a second RF generator, wherein the first
dielectric-filled waveguide is coupled to the first RF generator,
and wherein the second dielectric-filled waveguide is coupled to
the second RF generator.
29-51. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/686,586 filed Mar. 15, 2007, the content of
which is incorporated herein by reference in its entirety.
BACKGROUND
[0002] The invention relates to processing apparatuses with one or
more electromagnetic launches. More specifically, the invention
relates to the launching of electromagnetic energy, such as
microwave energy, into a reaction mixture, for example, which may
include one or more reactants and may include a catalyst, in order
to enhance a chemical process.
[0003] Electromagnetic and radio frequency (RF) energy, such as
microwave energy, can be used in a variety of processes to enhance
physical or chemical reactions. For example, RF energy (i.e.,
energy propagating at about 3 kHz to about 300 GHz) can be used
with a catalyst to enhance the chemical reaction of a plurality of
reactants. When using microwaves, the process is typically referred
to as microwave-assisted or microwave-enhanced chemistry.
[0004] One of the challenges of utilizing RF energy, particularly
microwave energy, in such processes is to efficiently couple the
electromagnetic energy into the reaction mixture being processed.
It is typically preferable that the electromagnetic energy be
launched in such a way as to avoid or control hot spots in the
reaction mixture and to adequately distribute the electromagnetic
energy into the reaction mixture so that dead zones can be reduced
or controlled.
SUMMARY
[0005] One way to promote the efficient transfer of energy is
through the matching of the impedances of the source, load, and
transmission means. For example, if a complex impedance of the
microwave source is 50 ohms, and similarly a complex impedance of a
transmission line and the load are 50 ohms, then in theory, the
microwave energy will be nearly 100% transmitted from the source
into the load. In the case that the impedance of the transmission
line is matched to the impedance of the source, then there will be
no reflected energy from the transmission line back to the source.
Similarly, in the case that the impedance of the load is matched to
the impedance of the source, then there will be no reflected energy
from the load back to the source. In other words, when all
impedances are matched, power is transmitted efficiently, without
reflections, from the source to the load.
[0006] In at least one construction, the invention matches a
complex impedance of a reactor load with a complex impedance of a
microwave generator. In at least another construction, the
invention provides an efficient distribution of microwave energy
throughout the reactor volume (i.e., the load). In yet at least
another construction, the invention provides a means for expanding
the distribution of the microwave energy throughout any volume
(e.g. modular and scalable).
[0007] In one embodiment, the invention provides a processing
apparatus having a vessel including an inner surface defining a
chamber configured to hold a reaction mixture, a guide at least
partially disposed within the vessel, and a launch coupled to the
guide and disposed at least partially within the vessel. The guide
is configured to propagate electromagnetic energy, and the launch
being configured to launch at least a portion of the
electromagnetic energy from the guide into the reaction
mixture.
[0008] In another embodiment, the invention provides a processing
apparatus having a vessel including an inner surface defining a
chamber configured to hold a reaction mixture, a guide configured
to propagate electromagnetic energy, and a first launch and a
second launch coupled to the guide and at least partially disposed
within the vessel. Each of the first launch and the second launch
are configured to couple a portion of the electromagnetic energy
from the guide into the reaction mixture.
[0009] In another embodiment, the invention provides a processing
apparatus having a vessel including an inner surface defining a
chamber configured to hold a reaction mixture, a guide configured
to propagate electromagnetic energy, and a first dielectric
projection and a second dielectric projection coupled to the guide
and at least partially disposed within the vessel. Each of the
first dielectric projection and the second dielectric projection is
configured to couple a portion of the electromagnetic energy from
the guide into the reaction mixture.
[0010] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram of a RF or microwave-based
processing apparatus incorporating the invention.
[0012] FIG. 2 is a schematic, sectional view (which is not to
scale) of a RF or microwave reactor capable of being used in the
processing apparatus of FIG. 1.
[0013] FIG. 3 is a schematic, sectional view of a launch capable of
being used in the RF or microwave reactor of FIG. 1.
[0014] FIG. 4 is a schematic, sectional view of a launch capable of
being used in the RF or microwave reactor of FIG. 1.
[0015] FIG. 5 is a perspective view of a launch capable of being
used in FIG. 2.
[0016] FIG. 6 is a perspective view of a launch capable of being
used in the RF or microwave reactor of FIG. 1.
[0017] FIG. 7 is a schematic, sectional view (which is not to
scale) of a RF or microwave reactor capable of being used in the
microwave processing apparatus of FIG. 1.
[0018] FIG. 8 is a schematic, sectional view (which is not to
scale) of a second RF or microwave reactor capable of being used in
the microwave processing apparatus of FIG. 1.
[0019] FIG. 9 is a partial section view (along line 9-9 of FIG. 10)
of a waveguide capable of being used in the RF or microwave
processing apparatus of FIG. 8.
[0020] FIG. 10 is a partial section view (along line 10-10 of FIG.
9) of a waveguide capable of being used in the RF or microwave
reactor of FIG. 8.
[0021] FIG. 11 is a partial sectional view of a microwave reactor
capable of being used in the RF or microwave processing apparatus
of FIG. 1.
[0022] FIG. 12 is partial perspective view of the dielectric-filled
waveguides of FIG. 8.
[0023] FIG. 13 is a sectional view of the second RF or microwave
reactor taken along line 13-13 of FIG. 12.
[0024] FIG. 14 is a partial section view (along line 15-15 of FIG.
14) of a waveguide capable of being used in the RF or microwave
processing apparatus of FIG. 8.
[0025] FIG. 15 is a partial section view (along line 14-14 of FIG.
14) of a waveguide capable of being used in the RF or microwave
reactor of FIG. 8.
[0026] FIGS. 16-22 are schematic, sectional views of launches
capable of being used in the RF or microwave reactor of FIG. 1.
[0027] FIG. 23 is a schematic, sectional view showing a projection
having an electromagnetic power density penetration depth.
[0028] FIG. 24 is a schematic, sectional view showing a plurality
of projections having an electromagnetic power density penetration
depth.
[0029] FIG. 25 is a schematic, sectional view (which is not to
scale) of another RF or microwave reactor capable of being used in
the RF or microwave processing apparatus of FIG. 1.
[0030] FIG. 26 is a partial cutaway view of the wave the waveguides
of FIG. 12 disposed in a chamber of a RF or microwave reactor.
[0031] FIG. 27 is a partial side view of a waveguide used in the
reactor of FIG. 26.
[0032] FIG. 28 is a partial side view of the waveguide of FIG. 27
with portions of spheres representing a RF or microwave power
penetration depth at the 1/e level.
[0033] FIG. 29 is a plot of the S11 reflection coefficient versus
the launch probe length
DETAILED DESCRIPTION
[0034] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. Unless specified or limited otherwise,
the terms "mounted," "connected," "supported," and "coupled" and
variations thereof encompass both direct and indirect mountings,
connections, supports, and couplings. Further, "connected" and
"coupled" are not restricted to physical or mechanical connections
or couplings.
[0035] FIG. 1 represents a processing apparatus incorporating the
invention. Generally speaking, the processing apparatus receives
one or more reactants and produces one or more products using the
one or more reactants. The process is facilitated by energy being
provided to the reactants by the processing apparatus and may
further be facilitated by one or more catalysts. The mixture being
processed by the processing apparatus is referred to herein as a
reaction mixture.
[0036] It should be understood that the reaction mixture may
include any one of one or more reactants, one or more products, and
one or more catalysts depending on the status of the processing
apparatus. For example, prior to processing, the reaction mixture
may include a reactant and a catalyst; during processing, the
reaction mixture may include a reactant, a catalyst, and a product;
and at the end of the process, the reaction mixture may include a
catalyst and a product. Another example could include a process
where the apparatus has a vessel containing a fixed bed of
heterogeneous catalyst. In this case, reactants enter the catalyst
bed where a reaction mixture is formed and RF or microwave energy
is coupled into the reaction mixture, and products form and exit
the vessel. It should also be understood that the reaction mixture
may be a one-phase mixture, a two-phase mixture, or a three-phase
mixture.
[0037] The processing apparatus shown in FIG. 1 is a RF or
microwave-based processing apparatus 100, which provides RF or
microwave energy to facilitate the processing of the reactants.
While this description may focus on microwave-based apparatuses,
the invention is not limited as such. Rather, other electromagnetic
frequency energies may be used to facilitate the processing of the
reactants.
[0038] FIG. 1 schematically illustrates a microwave source 105 that
produces and transmits microwaves to a reactor (discussed further
below). The microwave source 105 includes a microwave generator 110
and a guide-distribution system 115. An example microwave generator
110 capable of being used in the processing apparatus 100 is a 30
to 100 kW, 915 MHZ microwave generator available from Microdry
Inc., having a web site address of http://www.microdry.com. The
guide-distribution system 115 is coupled to the microwave generator
110 to receive microwave energy from the generator. While FIG. 1
shows only one microwave generator 110 and one guide-distribution
system 115, it is envisioned that the processing apparatus 100 may
include multiple generators 110 and/or multiple guide-distributions
systems 115.
[0039] The guide-distribution system 115 includes one or more
interconnected guides (primary guide 125 and secondary guides 130,
135, and 140 are schematically represented in FIG. 1) for
propagating the microwave energy from the microwave generator 100
to the reactor. The term "guide" is broadly defined herein as a
material or device capable of propagating a form of electromagnetic
energy from one location to another. For example, the guide can
include a co-axial cable, a clad fiber, a dielectric-filled (e.g.,
filled with at least one of quartz, alumina, silica, boron nitride,
Teflon, or other microwave transparent or translucent material,
including gaseous filled or vacuum reduced dielectrics) waveguide,
or a similar transmission line capable of propagating
electromagnetic energy. Furthermore, the guide-distribution system
115 can include multiple guides of differing types. For example,
the primary guide 125 can be a gaseous-filled waveguide and the
secondary guides 130, 135, and 140 can be coaxial cables.
[0040] The guide-distribution system 115 can further include one or
more distributors/dividers (distributor 145 is schematically
represented in FIG. 1). The distributor 145 distributes the
microwave radiation received from the primary guide 125 to
secondary guides 130, 135, and 140. Of course, the number of guides
connected to a distributor 145 can vary. Additionally, a
distributor 145 is not required in all constructions of the
guide-distribution system 115.
[0041] The guide-distribution system 115 can further include one or
more transition devices (transition device 150 is schematically
represented in FIG. 1). The transition device 150 allows the
microwave to propagate from a first guide type (e.g., a
dielectric-filled waveguide) to a second guide type (e.g., a
coaxial cable) while reducing impedance matching losses. Similar to
the distributor 145, the transition device 150 is not required in
all constructions of the guide-distribution system 115. Other
waveguide or coaxial components, known to those skilled in the
arts, such as isolators, circulators, water loads, bends, couplers,
waveguide or coaxial transitions and flanges, may also be included
in the processing apparatus or into the distribution system.
[0042] The guide-distribution system 115 can further include one or
more tuners (tuners 152 are schematically represented in FIG. 1).
The tuners 152 improve impedance matching and allow for looser
tolerances in differing elements, such as from nodes 130 and 140 to
launches 180.
[0043] Various constructions of the microwave source 105 include:
A) a single generator, a guide, and a single launch (which is
discussed further below); B) a single generator, a
guide-distribution system including a distributor, and a plurality
of launches; and C) a plurality of generators, a guide-distribution
system associated with each generator, and one or more launches
associated with each generator. As will be discussed below, the
launches can be "internal" or "external" to a reactor.
[0044] During operation, the guide-distribution system 115
propagates the electromagnetic energy (e.g., the microwave energy)
from an electromagnetic wave generator (e.g., the microwave
generator 110) to the reactor (discussed further below). The design
of the guide-distribution system 115 can vary depending on, among
other things, the design of the reactor and the means used to
launch the electromagnetic energy into the reactor. It is typically
preferable for the complex impedances of each node in the guide
distribution system to match for efficient transmission of
electromagnetic energy. For example, the impedances at node 125
into node 145, at node 145 into nodes 130 and 135, at node 135 into
node 150, and at node 150 into node 140. It is also typically
preferable for the impedance of the guide distribution system 115
to match the generator 110 (e.g., at node 110 into node 125) and
for the impedance of each launch to match the coupled node (e.g.,
at nodes 130 and 140 into respective launches).
[0045] A schematic sectional view of a microwave reactor 160
capable of being used in the microwave-based processing apparatus
100 is shown in FIG. 2. In at least one construction, the reactor
is a vessel providing a means of access for reactant(s) and exit
for product(s) along with the required operating conditions, such
as temperature, pressure, and residence time to achieve process
objectives. Process objectives could be physical such as mixing or
separation of reactant species or chemical such as the combining of
two reactants molecules to create a new product molecule.
[0046] Referring to FIG. 2, the microwave-reactor 160 includes a
vessel 165, such as a metal (e.g., steel) vessel. The vessel 165
has an inner surface 170 defining a chamber 175. The microwave
reactor 160 includes one or more launches (e.g., launches 180 are
schematically shown in FIGS. 1 and 2 and described in connection
with FIG. 5) coupled to the guide-distribution system 115 (a
portion of which is shown in FIG. 2) and supported by the vessel
165. The launches 180 launch energy (schematically represented in
FIG. 3 as fields 185) from the guide-distribution system 115 into
the chamber 175.
[0047] The launch 180 is an example of an electromagnetic launch
capable of being used with the invention. As used herein, an
"electromagnetic launch" is broadly defined as a device or
apparatus capable of launching (e.g., propagating or radiating)
electromagnetic energy from the guide into a reaction mixture. One
may also refer to the electromagnetic launch as an "electromagnetic
injector" because electromagnetic energy is being injected into the
chamber as viewed from the chamber 175. The electromagnetic launch
can include a window (e.g., a dielectric window) or a projection
capable of launching electromagnetic energy from the guide into the
chamber. The projection can include a metallic-based projection
(e.g., a projection including a metallic pin, rod, spike, wire,
sphere, etc.) or a dielectric-based projection (e.g., a projection
including a dielectric pin, rod spike, fiber, sphere, etc.). The
metallic-based projection and the dielectric-based projection will
also be referred to herein as a "metallic antenna" and a
"dielectric antenna," respectively, because the projections act
like an antenna as viewed from the chamber 175.
[0048] A schematic, sectional view of a simple launch 250 is shown
in FIG. 3. The launch 250 includes a metallic projection rod 255, a
dielectric insulator 260, and a conductor wall, which can be the
vessel shell or a waveguide wall (waveguide wall 265 is shown for
FIG. 3). The use of the projection rod 255 with the dielectric
insulator 260, which is integrally coupled with waveguide wall 265,
creates an antenna (e.g., a quarter-wave antenna). A portion of the
electromagnetic energy propagating through the waveguide, on
impedance side A, conducts through the projection rod 255. With the
electromagnetic energy conducting through the projection rod 255,
the projection rod 255 launches an electromagnetic field on
impedance side B, which is inside the chamber 175.
[0049] Therefore, the projection rod 255 operates as an antenna and
can couple an electromagnetic field into the reaction mixture. The
reaction mixture has a complex impedance, which may or may not
cause the reaction mixture to change in temperature. The
temperature change is dependent upon whether the reaction exhibits
an endothermic, exothermic, or a neutral net change of energy
during the chemical reaction. The energy coupled is dependent upon
the specific bulk loss tangent of the combined species in the
mixture within the reactor. The energy coupled into any one species
in the mixture is dependent upon its specific loss tangent.
Generally a mixture or species with the higher loss tangent
exhibits a greater absorption of electromagnetic energy with a
faster decay of electromagnetic field intensity into that mixture
or species relative to another mixture or species. In some
embodiments, the reaction mixture is a substantially lossless
dielectric reaction mixture with a loss tangent less than 0.1.
[0050] A schematic, sectional view of a launch 300 is shown in FIG.
4. The launch 300 includes a metallic projection rod 303, which is
part of the center conductor 305 of a coaxial cable connector 310.
The coaxial cable connector 310 includes an outer conductor 315
(e.g., a braided conductor), a dielectric insulator 320, and the
center conductor 305. The coaxial cable connector 310 is supported
by a wall such as the vessel shell 165. The center conductor 305
extends beyond the dielectric insulator 320 and the conductor 315,
such that the projection rod 303 acts like the projection rod 255
discussed above. The coaxial cable connector 310 propagates
electromagnetic energy through the connector 310, resulting in the
projection rod 303 radiating or coupling electromagnetic energy to
impedance side B.
[0051] Therefore, the projection rod 303 operates as an antenna and
can couple or radiate an electromagnetic field into the reaction
mixture. As was discussed for FIG. 4, the reaction mixture has a
complex impedance, which determines the degree of energy coupled
into the reaction mixture. The coupling of energy into the reaction
mixture promotes the process.
[0052] It is envisioned that in other constructions of the
projection, the metallic antenna can take other forms, including
but not limited to, a pin, a spike, a coiled wire, and/or a sphere.
It is also envisioned that the projection can consist of or include
other materials, including a dielectric material.
[0053] FIG. 5 shows a perspective view of the launch 180 capable of
being used with the microwave reactor 160 (FIG. 2). The launch 180
includes a terminal that couples to a coaxial cable. More
specifically, the launch 180 includes threads 355 that interconnect
with corresponding threads of a coaxial cable. Similar to the
launch 300, the launch 180 includes a dielectric 365 and a
projection rod 360. The launch 180 also includes a flange 375
having apertures 382 used for securing the launch 180 to the vessel
165 (FIG. 2) with fasteners 383 (e.g., bolts, rivets, etc.). The
vessel 165 includes apertures 384 that receive the projection 385,
including rod 360. A launch 180 capable of being used with the
microwave reactor is available from CeramTec North America having a
web site address of http://www.ceramaseal.com.
[0054] FIG. 6 shows a perspective view of a launch 380 capable of
being used with the microwave reactor 160. The launch 380 is
similar to the launch 180, except the launch 380 does not include
the flange 375 for receiving a bolt, rivet, or similar fastener.
Instead, the launch 380 is secured to the vessel 165 by inserting
projection 385 into an aperture of the vessel 165, and welding
flange 390 to the vessel wall. That is, the fastener for coupling
the launch 380 to the vessel is a weld. However, other fasteners,
such as glues and chemical bonds, can be used in place of a weld.
Also, other fasteners, such as compression fasteners, can be used
for fastening the electromagnetic launches to the vessel 165.
Additionally, the sealing means can also incorporate means to
prevent the leakage of the electromagnetic energy, such as
incorporating an electromagnetic absorber into the O-ring or
gasket.
[0055] While FIGS. 5 and 6 include threads for interconnecting a
coaxial cable to the launches 180 and 380, other flanges known to
those skilled in the art and fasteners (e.g., welds, glues,
chemical bonds, compression fasteners, etc.) can be used. Also, it
is envisioned that other types of guides (e.g., dielectric-filled
waveguides) can couple to the launches 180 and 380 for propagating
the electromagnetic energy to the launches 180 and 380.
[0056] The commercial market for glass to metal seal feed-throughs
is primarily for analytical equipment where tests are performed
separately under high vacuum, high pressure, and high temperature.
The manufacturers of these products report the operating
temperature and pressure ranges, but it is commonly known that they
do not test the feed-throughs at both their upper operating high
temperature limit and at their upper operating pressure limit at
the same time. For example, the launch shown in FIG. 6 typically
has specifications listed as follows:
[0057] Pressure at 20.degree. C.: 320 psig
[0058] Temperature Minimum: -269.degree. C.
[0059] Temperature Maximum: 450.degree. C.
The manufacturer has not tested the unit to determine the maximum
pressure at its maximum operating temperature. The lack of having
microwave products able to operate at both elevated temperature and
pressures has limited microwave energy in its use on commercial
scale chemical processes.
[0060] It should be noted, that windows, made of microwave
transparent materials, like quartz or sapphire, have been used to
launch microwaves into test chambers. These windows can withstand
elevated temperatures greater that 450.degree. C. if the proper
sealing materials are used. The problem with the commercial
implementation of these windows is the cost to make these windows
able to operate at elevated temperatures and pressures. As the
window diameter increases, the window thickness increases
proportionally, and the increased window dimensions dramatically
increases the cost of the window. Thus, a window designed for a 915
MHz source would have a larger diameter, and would be significantly
more expensive than for a window designed for a 2.45 GHz source.
The coax feed through design is smaller in diameter and will be
more cost effective to implement if it can be shown to operate at
elevated pressure and temperature conditions.
[0061] Tests were performed with the launch shown in FIG. 6 welded
into a stainless steel chamber. The chamber was instrumented with
temperature and pressure sensors and capable of being heated up to
500.degree. C. and at pressures up to 300 psig. Over the course of
a month, the launch was subjected to temperatures ranging from
200-475.degree. C. and pressures up to 300 psig. Once the test
chamber temperature was established, the test chamber would be
pressurized and allowed to stand for at least overnight to
determine if any leaks developed in the launch. The chamber
pressure would then be cycled from ambient to test pressure and
allowed to stand at the test pressure to again measure for leaks.
Rapid and slow pressure cycling tests were performed. Pressure
temperature combinations included: [0062] 150.degree. C. 200 psig
[0063] 250.degree. C. 200 psig [0064] 350.degree. C. 200 psig
[0065] 400.degree. C. 260 psig [0066] 425.degree. C. 260 psig
[0067] 450.degree. C. 260 psig [0068] 450.degree. C. 300 psig
[0069] 475.degree. C. 300 psig Leaks were not observed until the
chamber reached 475.degree. C. at 300 psig. Upon lowering the
temperature below 450.degree. C. leaks were no longer observed.
[0070] Referring now to FIG. 7, the figure is a schematic,
sectional view of a stirred-bed microwave reactor 160 capable of
being used in the microwave-based processing apparatus 100. FIG. 7
also shows a portion of a guide-distribution system. The
microwave-reactor 160 includes the vessel 165 having the inner
surface 170 defining the chamber 175. The chamber 175 receives one
or more reactants through one or more inlets (or ports) of one or
more feed tubes. For example, FIG. 7 shows a first inlet 190 to
allow a first reactant (e.g., a hydrocarbon) to enter the vessel
165, and a second inlet 195 to allow a second reactant (e.g.,
H.sub.2 gas) to enter the vessel 165. Of course, the reactants can
enter through a single inlet or by other means.
[0071] The vessel 165 can also receive a catalyst. The catalyst can
also enter the vessel by an inlet or can be placed in the vessel by
some other means. For example, the vessel 165 can open to allow a
heterogeneous catalyst to be placed in the vessel 165. The
heterogeneous catalyst can be held between support screens 197. The
type of catalyst used can vary depending on the reactor 160 and/or
the desired process. For example, the catalyst can be a
heterogeneous catalyst or a homogeneous catalyst.
[0072] For the reactor shown in FIG. 7, a motor 200 rotates a
stirrer 205 housed in a draft tube 210 causing the reaction
mixture, excluding the catalyst, to flow down through the draft
tube 210. The reaction mixture moves through energy fields,
schematically represented by fields 185, resulting in a processed
product. The processed product is released from the chamber 175 by
an outlet (or port) 220.
[0073] Therefore, the draft tube 210 can serve the purpose of
creating turbulence with the reaction mixture and/or the feeds to
result in mixing. The draft tube 210 can also be used to reflect
microwave energy from the launch to provide a desired result (e.g.,
promoting a uniform microwave field). Further, the draft tube 210
can minimize interactions from other launches, thereby minimizing
mutual coupling. It is also envisioned that the reactor can include
other tubes or structure for reflecting microwave energy and for
minimizing mutual couplings.
[0074] In other constructions, other means can be used to move the
reaction mixture through the chamber 175. For example, the reactor
160 can include one or more inlets and one or more outlets, with
the heating resulting from the energy fields, to cause the reaction
mixture to move without the draft tube 210 and stirrer 205. The
removal and introduction of products and reactants, respectively,
with the microwave energy coupled into the reaction mixture causes,
in some reactions, sufficient movement of the reaction mixture in
the chamber 175.
[0075] Industrial applications for the reactor 160 shown in FIG. 7
would be the hydroprocessing of a fossil fuel or the processing of
a biofuel. For example, U.S. Patent Publication Nos. 2004/0074759
and 2004/0074760, the contents of which are incorporated herein by
reference, disclose two methods of performing microwave-assisted
chemistry. In the instance of hydroprocessing a fossil fuel, the
fossil fuel and hydrogen would be preheated and mixed to a
temperature below the point of undesirable reactions taking place,
such as coking. The fossil fuel-hydrogen mixture would be fed into
the microwave reactor's catalyst bed whereby the combination of
process conditions (e.g. temperature, pressure, liquid hourly space
velocity (LHSV), microwave power, and modulation) and catalyst
activity would promote the desired hydroprocess (e.g.
hydrogenation, hydrocracking, hydrodesulfurization,
hydrodenitrogenation, hydrodemetalization, etc.).
[0076] Referring again to FIG. 7, the microwave reactor 160
includes one or more launches (e.g., launch 180 is schematically
shown in FIG. 7) coupled to the guide-distribution system (a
portion of which is shown in FIG. 7) and supported by the vessel
165. The launches 180 launch microwave energy (schematically
represented in FIG. 7 as fields 185) from the guide-distribution
system 115 to the chamber 175. The microwave energy is coupled into
the reaction mixture based upon the reaction mixtures complex
impedance. The coupling of energy into the reaction mixture
promotes the desired chemistry of the process. For example, an
application where localized temperature rise is important to the
process, the microwave energy is coupled so as to cause a rapid
temperature rise that can speed the reaction occurring in the
vessel 165. Microwave energy transfer utilizes the dielectric
energy transfer mechanism of the reaction mixture to create a
temperature profile that contrasts, potentially significantly, to
conventional heat conduction mechanisms. One possible result of the
microwave heating is to significantly improve the selectivity and
speed of chemical reactions. Another possible result is a shorter
reaction time that minimizes undesirable side reactions that would
minimize product decomposition and maximize product yield.
Therefore, the type and/or location, as well as other
characteristics (e.g., number), of the launches can affect the
reaction time and quality of the microwave-assisted chemistry.
[0077] For FIG. 7, the guide-distribution system includes a
plurality of waveguides 130 and a plurality of coaxial cables 140.
The plurality of launches 180 are coupled to the waveguides 130 and
coaxial cables 140. For simplicity, only a portion of the
guide-distribution system is shown in FIG. 7; however, other
portions of the guide-distributions system 115 of FIG. 1 may or may
not be present. Further, while FIG. 7 shows waveguides 130 and
cables 140, both types of transmission lines are not required.
[0078] FIG. 25 shows another construction of a stirred-bed
microwave reactor 160A capable of being used in the microwave-based
processing apparatus 100. For FIG. 25, the guide distribution
system includes a first transition 150 from a coaxial cable 135 to
a waveguide 140, and a second transition 150A from a first
waveguide 135A to a second waveguide 140A. The launches 180 are
then coupled to the waveguides 140 and 140A. Similar to FIG. 7,
other portions of the guide-distributions system 115 of FIG. 1 may
or may not be present, and other arrangements for the
guide-distribution system 115 are envisioned.
[0079] It should be apparent from FIG. 7 that the microwave reactor
160 can be scalable. For example, the microwave reactor 160 shown
in FIG. 7 can have eighteen (six are shown) launches 180 divided
into three levels of six launches 180. In another construction, the
vessel 165 can be lengthened along the Y-axis such that a fourth
level of six launches can be added to the microwave reactor 160.
Therefore, the microwave reactor 160 is scalable along the Y-axis.
Other microwave reactors 160 can be scalable depending on the
design of the vessel 165, the means for introducing the microwave
energy to the reaction mixture, and the expected impedance of the
reaction mixture.
[0080] FIG. 8 is a schematic, sectional view of another microwave
reactor 430 capable of being used with the processing apparatus
100. The reactor 430 includes a vessel 435 having an inner surface
440 defining a chamber 445. An inlet 455 introduces the reaction
mixture to the chamber 445 from a feed tube 460. The reactor may
utilize homogeneous catalysts, heterogeneous catalysts or a
combination of the two. The feed tube 460 includes two ports: a
first port 465 to receive one or more reactants and a second port
470 to optionally receive one or more catalysts. The reactor 430
launches electromagnetic energy (i.e., microwave energy for the
processing apparatus 100) into the reaction mixture to promote a
physical or chemical reaction, resulting in one or more products.
The one or more products are released from the chamber 445 by an
outlet 475. As discussed above, the means for introducing the
reactants and/or catalysts, moving the reactant mixture, and
releasing the products may vary. It is also contemplated that the
one or more reactants and the one or more catalysts can be heated
prior to introducing them into the chamber 445 and/or the microwave
reactor 430 can include a heater (schematically represented as 480)
for heating the reaction mixture in the chamber 445, such as a
steam or oil jacket. Further, it is envisioned that the microwave
reactor 430 can include a preheater (schematically represented as
485) for preheating the temperature of the reaction mixture in the
chamber 445.
[0081] The vessel 435 includes a port 488 (a plurality of ports is
shown in FIG. 8) that couples a dielectric-filled waveguide 490 to
the microwave source 105 (FIG. 1). More specifically, the waveguide
490 can be coupled to another waveguide 130 (FIG. 1) or a
distributor 145 (FIG. 1). The waveguide 490 receives microwave
energy from the microwave source 105 via the port 488 and
propagates the microwave energy through the waveguide. For the
construction shown in FIG. 8, the waveguide 490 terminates in the
chamber 445. However, the waveguide 490 can extend through the
vessel 435.
[0082] FIG. 9 is a partial sectional view of a waveguide 490A along
line 9-9 of FIG. 10, and FIG. 10 is a sectional view of the
waveguide 490A along line 10-10 of FIG. 9. The waveguide 490A can
be used in the reactor 430 of FIG. 8. The waveguide 490A includes
launches (launch 250 is shown in FIGS. 9 and 10) for launching
microwave energy from the waveguide 490A into the chamber 445. The
launches 250 shown in FIGS. 9 and 10 are similar to the launches
250 shown in FIG. 3. That is, the launches 250 used in the
waveguide 490A of FIG. 9 include a projection rod 255 (FIG. 3)
supported by a dielectric insulator 260 (FIG. 3), which is integral
with the waveguide wall 265. As was discussed with FIG. 3, the
launches 250 act as antennas and couples or radiates
electromagnetic energy into the chamber 275. The microwave energy
coupled into the chamber has a microwave penetration depth
(typically referred as 1/e) for active E&M fields. The
penetration depth, is the distance by which the power density has
decreased to about 37% of its initial value, and is represented in
FIGS. 9 and 10 by spheres (sphere 500 is shown in FIGS. 9 and 10),
although the decay shape is technically exponential.
[0083] FIG. 11 is a partial sectional view of the reactor 430A
having six waveguides 490B, each of which includes three launches
250 in the sectional view. Accordingly, the sectional view of FIG.
11 shows eighteen launches 250. FIG. 12 is a partial perspective
view of six waveguides 490 (of FIG. 8) with portions of spheres 505
representing the microwave penetration depths for the launches 250.
Unlike FIG. 9, the eighteen launches 250 shown in FIG. 11 are
offset to create a helical or spiral effect for the portions of
spheres 505, for example as shown in FIG. 28. FIG. 13 is a top view
of FIG. 12 along line 13-13. As shown in FIGS. 12 and 13, the
placement of the waveguides 490 and the launches 250 promote a
controlled electromagnetic field pattern in the chamber 445. FIG.
26 is a partial cutaway view of the seven waveguides of FIG. 12
disposed in the vessel 435. FIG. 27 is a partial side view of a
waveguide 490 used in the reactor 430 of FIG. 26. The waveguide 490
of FIG. 27 includes multiple launches placed in a spiral pattern
across and around the surface of the waveguide. FIG. 28 is a
partial side view of the waveguide 490 of FIG. 27 with portions of
spheres 505.
[0084] As will be discussed in more detail below, it is envisioned
that one can vary the number and locations of the waveguides 490,
the number and locations of the launches 250, the properties (e.g.,
shape, type, dielectric filling, etc.) of the waveguide 490, the
properties of the launches 250 (e.g., shape, type, composition,
etc.), and/or the intensity of the electromagnetic field to result
in a desired electromagnetic field pattern in the chamber. For
example, the desired electromagnetic field pattern can be a
substantially uniform distribution pattern. It also should be
apparent from FIGS. 11-13 that the microwave reactor can be
scalable. For example, the microwave reactor vessel shown in FIG.
12 has six waveguides with a set length. In another construction,
the number of waveguides and the length of the waveguides, for
example, can vary to allow for a larger or smaller processing
vessel.
[0085] For FIGS. 8, 12, 13, and 26-28, the microwave guide 490
assists the conveyance of microwave energy to the launch 250 and is
at least partially located inside the reactor 430. The guide 490 is
generally a loss-less means of conveying microwave energy to the
launch 250. With this internal distribution, the portion of the
guide 490 that is within the reactor 430 also functions as a
distributor of the microwave energy to one or more launches 250.
Generally this use of the distributor's function is to distribute
or to divide the microwave energy between and into the one or more
launches 250. Generally the distribution is of even or equal
proportions, however for specific requirements, the fraction of
distribution can be readily controlled. This type of distributor
can be comprised of nearly any means known to those skilled in the
art to convey or to transfer microwave energy, but attention
typically should be given to the generally elevated temperatures of
the materials within the reactor 430 and to seals and material
compatibility properties so that the components will not
degrade.
[0086] A particularly suitable type of guide to use for
distribution of microwave energy within the reactor is a circular
or rectangular metallic waveguide (a circular waveguide 490 is
shown in FIGS. 8-13 and 26-28). The metallic waveguide may either
be hollow or filled with a dielectric such as air, nitrogen, or
other gasses or other materials that are transparent or
semitransparent to microwaves such as ceramics, Teflon, and
plastics. The use of a microwave or RF transparent or
semi-transparent filler within the guide distribution system has
the added advantage that the diameter (or other measures comprising
the internal dimensions) of the waveguide 490 may be constructed
using a differing dimension, generally smaller, (compared to air or
vacuum filled) for a given frequency of microwave or RF energy and
which is dependent upon the filler material's dielectric constant.
Additionally, if the dielectric constant of the material within the
distribution guide is suitably selected with respect to the
dielectric constant of the average bulk dielectric constant's
constituents within the reactor, then the spacing of multiple
launches (onto the outer surface of the distributing guide) can be
made fairly easily at nearly any desirable location by one skilled
in the art. The dielectric constant of the material inside the
distributing waveguide would be chosen by one skilled in the art to
control or to nearly match the wavelength of the propagating
electromagnetic fields inside the (generally loss-less)
distributing guide to control or to match the wavelength of the
decaying electromagnetic fields within the (lossy) reactor
volume.
[0087] An example of a single distributing waveguide with multiple
launches can be seen in FIG. 27. The launches 250 can be placed in
a spiral pattern across and around the surface of the distributing
waveguide, or can be placed in many different patterns which may be
symmetrical or random in location upon the surface of the
distributing waveguide. The locations of the launches are generally
selected to suitably fill the volume of the reactor with a pattern
of electromagnetic fields into which the distributing waveguide is
placed. A three-dimensional hexagonal-packing pattern is a very
efficient packing density when using a spherical 1/e field model
representation for the electromagnetic field decay emanating from
each launch. FIG. 28 shows a partial side view of the single
waveguide of FIG. 27 with potential 1/e electromagnetic field
spherical distributions around the distributing waveguide and
emanating from the location of each launch. Multiple distributing
waveguides 490 can be placed into a cylindrical reactor 430 to
achieve nearly any desired reactor volume. This is depicted
schematically in FIGS. 8 and 26 which illustrates the multiple
launches 250 and in FIG. 12 where the electromagnetic field
distributions 505 are emanating from the location of each launch
from the surface of the distributing waveguide.
[0088] For the simplest operation the RF or microwave source(s) can
be operated in a continuous wave (CW) mode. Additionally,
modulation of one or more microwave generators 110 can be used. For
example, proper modulation techniques known to those skilled in the
art allow the electromagnetic power fields to be swept through the
reactor 430, similar to phased-array or aperture controlled radar.
Controlling the phase and power of an array of smaller antennas
into the applicator and suitably sweeping the amplitude and/or
phase can create a constructive, additive, wavefront that sweeps
through the space volume. Time averaging or other modulation
techniques can also be used to achieve a more uniform microwave
coupling of RF energy over time throughout the applicator volume
and throughout the catalyst bed.
[0089] Referring now to FIGS. 14 and 15, FIG. 14 is a partial,
sectional view of a waveguide 490C along line 14-14 of FIG. 15, and
FIG. 15 is a sectional view of the waveguide 490C along line 15-15
of FIG. 14. The waveguide 490C can be used in the reactor 430 of
FIG. 8. The waveguide 490C includes a gaseous or non-gaseous (e.g.,
quartz, alumina, silica, boron nitride, Teflon, or other microwave
transparent or translucent material) dielectric 550 disposed in a
conductive wall 555 of the waveguide 490C. The waveguide 490C
further includes a plurality of launches integrally coupled with
the wall. The launches take the form of windows (window 560 is
shown in FIGS. 14 and 15) that allow the microwave energy to
propagate through the windows 560 and launch into the reaction
mixture. It is also envisioned that the waveguides 490C can use
projections (e.g., metallic or dielectric antennas) in place of or
in addition to the windows 560 for launching the microwave energy
into the chamber 445.
[0090] In yet another envisioned construction, the microwave
reactor can include guides and launches disposed at least partially
within the chamber for launching microwave energy into the chamber,
and further can include launches supported by the vessel wall for
launching additional microwave energy into the chamber.
[0091] As has been disclosed above, the launches launch
electromagnetic energy from a guide into a chamber's reaction
mixture. The electromagnetic energy coupled or radiated into the
chamber has a penetration depth (typically referred as 1/e) for
active E&M fields. The penetration depth is represented in
various above-discussed figures by spheres. It has also been
disclosed above, that the properties of the launches (e.g., shape,
type, composition, etc.), among other things, affect the radiation
pattern (including depth) for the active E&M fields. Various
constructions of the launches will be discussed in further detail
below.
[0092] Referring back to FIG. 4, a schematic, sectional view of the
launch 300 is shown in FIG. 4. The launch 300 includes the metallic
projection rod 303, which may be part of the center conductor 305
of a coaxial cable or waveguide connector. Optionally the metallic
projection rod 303 can be suitably attached for example by a screw
thread to the center conductor 305. The coaxial cable conductor
includes the conductor 315 (e.g., a braided conductor), the
dielectric insulator 320, and the center conductor 305. The
metallic projection rod 303 extends beyond the dielectric insulator
320 and the conductor 315, such that the projection rod 303 acts
like the projection rod 255 discussed above.
[0093] FIG. 16 is a schematic, sectional view of the launch 300A.
For FIG. 16, the conductor 315 and the dielectric insulator 320
extend past the wall 165. One reason for extending the conductor
315 and the dielectric insulator 320 is to promote the sealing of
the launch 300A with the wall 165. Another reason is to promote
field shaping of the active E&M fields. As can be seen in FIG.
16, projection rod 303 is displaced from the wall 165, as compared
to the projection rod 303 of FIG. 4, thereby creating differing
effects for the E&M fields of FIGS. 4 and 16, such as
controlling dead zones.
[0094] FIG. 17 is a schematic, sectional view of the launch 300C.
The launch 300C includes a metallic projection rod 303, which is
part of the center conductor 305 of a coaxial cable 310. The
coaxial cable connector 310 includes a conductor 315 (e.g., a
braided conductor), a dielectric insulator 320C, and the center
conductor 305. The coaxial cable connector 310 is supported by a
wall such as the vessel shell 165. The center conductor 305 extends
beyond the conductor 315, such that the projection rod 303 acts
like the projection rod 255 discussed above. However, unlike the
projection rods discussed thus far, the projection rod 303 is at
least partially surrounded by the dielectric insulator 320C (FIG.
17 shows the dielectric insulator completely surrounding the
projection rod 303). The coaxial cable connector 310 propagates
electromagnetic energy through the cable connector 310, resulting
in the projection rod 303 radiating an electromagnetic field on
impedance side B. Therefore, the projection of FIG. 17 can be
viewed as a metallic antenna with a dielectric at least partially
surrounding the metallic antenna.
[0095] One reason for surrounding the projection rod 303 with the
dielectric insulator 320C is to protect the projection rod 303 from
physical damage and/or chemical damage. Another reason for at least
partially surrounding the projection rod 303 with the dielectric
insulator 320C is to promote field shaping of the active E&M
fields. Adding the dielectric material around the projection rod
(as compared to FIG. 4), changes the properties of the antenna-like
effect of the projection rod 303, and therefore, changes the shape
of the active E&M fields. For example, the depth and
geometrical shape of the sphere 1/e change in response to the
addition of the dielectric material. Yet another reason for
surrounding the projection rod 303 with the dielectric insulator
320C is to limit hot spot formation by the projection rod 603. The
likelihood a hot spot surrounds the projection can decrease when a
dielectric insulator surrounds the projection rod 303 and extends
at least some of the electromagnetic energy and reduces the power
density. It is also envisioned that the dielectric insulator may be
used to at least partially heat the reaction mixture by
convectional heat if the dielectric is lossy or a partial absorber
of electromagnetic energy.
[0096] FIG. 18 is a schematic, sectional view of the launch 300D.
Similar to the launch 300C, the projection rod 303 of launch 300D
is at least partially surrounded by a dielectric material 600. In
one construction, the dielectric material 600 is different from the
dielectric insulator 320 and is microwave transparent. The coaxial
cable 300D propagates electromagnetic energy through the cable
connector 310, resulting in the projection rod 303 radiating an
electromagnetic field on impedance side B. Therefore, the launch
300D of FIG. 18 can be viewed as a metallic antenna with a
dielectric at least partially surrounding the metallic antenna.
[0097] Similar to FIG. 17, one reason for surrounding the
projection rod 303 with the dielectric material 600 is to protect
the projection rod 303 from physical damage and/or chemical damage.
Another reason for at least partially surrounding the projection
rod 303 with the dielectric material 600 is to promote field
shaping of the active E&M fields. Similar to FIG. 17, adding
the dielectric material 600 around the projection rod 303 changes
the properties of the antenna-like effect of the projection rod
303, and therefore, changes the shape of the active E&M fields.
For example, the depth and geometrical shape of the sphere 1/e
change in response to the addition of the dielectric material 600.
Moreover, varying the geometry (e.g., the shape) and the properties
(e.g., the loss tangent) of the dielectric material 600 further
shapes the active E&M fields. Yet another reason for
surrounding the projection rod 303 with the dielectric material 600
is to limit hot spot formation. The control of hot spot formation
also relates to the varying of the geometry and the properties of
the dielectric material 600. Example dielectric materials 600
include Teflon.RTM., quartz, glass, plastic, ceramic, and similar
substantially lossless materials having a loss tangent less than
0.1, with a preferable loss tangent less than 0.01. However,
dielectric materials with greater loss tangents may be used if the
projection is used for heating.
[0098] The dielectric parameter called the loss tangent is known by
those skilled in the art to measure the relative RF or microwave
energy that a particular material absorbs at a given frequency. The
loss tangent, also related to the loss factor, is the ratio of the
energy lost to the energy stored. A larger loss tangent for a
material means that more energy is absorbed relative to a material
with a lower loss tangent. The dielectric absorption of energy can
cause different materials to heat at substantially different rates
and to achieve considerably different temperatures within the same
RF or microwave field.
[0099] FIG. 19 is a schematic, sectional view of the launch 300E.
For FIG. 19, the launch 300E includes the projection rod 303, a
first dielectric material 600, and a second dielectric material
605. That is, the launch 300E includes a projection rod 303 and a
plurality of dielectric materials 600 and 605. The use of a
plurality of dielectric materials 600 and 605 and the geometrical
shape of the materials 600 and 605 further promote the shape of the
active E&M fields and limit hot spot formation.
[0100] FIG. 20 is a schematic, sectional view of the launch 300F.
For FIG. 20, the launch 300F includes a hybrid projection rod 303F
having a varying shape from previous projection rods, a first
dielectric material 600F, and a second dielectric material 605F.
FIG. 21 is a schematic, sectional view of the launch 300G. For FIG.
21, the launch 300G includes a projection rod 303, a first
dielectric material 600G having a first non-uniform shape, and a
second dielectric material 605G having a second non-uniform shape.
The use of differing geometrical shapes for the projection rod, the
use of one or more dielectric materials, and/or the use of
differing geometrical shapes and properties of the one or more
materials further promote the shaping of the active E&M fields
and the possible control of hot spot formation.
[0101] FIG. 22 is a schematic, sectional view of the launch 300H
being coupled to the vessel 165 by dielectric material 600H. In
addition to the already discussed possible benefits of using a
dielectric material to at least partially surround the projection
rod 303, the dielectric material 600H can be used to provide a
better seal between the coaxial cable 303 and the vessel 165. A
fastener can be used to secure the coaxial cable to the vessel
wall, and compress the dielectric material 600H. For example,
launch 300H can include a flange 610 having apertures 615 for
receiving a plurality of fasteners 615 (e.g., bolts) where the
flange 610 can compress the dielectric material 600H. Additionally,
RF seals or gaskets know to those skilled in the art can be added
to minimize any potential leakage of electromagnetic energy.
[0102] Before proceeding further, while the above launches
300A-300H were described based on the launch 300, the concepts can
also apply to launch 250. The portion of the projection rod 355 on
the reactor side can also be modified based on the concepts
disclosed in FIGS. 18-21. It is also envisioned that the projection
rods 255 and 303 can be at least partially surrounded by one or
more layers of a second metallic material, the projection rods 255
and 303 can be made of a dielectric materials, and other
combinations of metallic and dielectric layers can be used.
[0103] Method of Designing a Reactor
[0104] As discussed above, when a projection is inserted into a
waveguide and supplied with microwave energy, it generally acts as
an antenna, for example a quarter-wave antenna. The size, shape,
and composition of the projection determine its frequency,
bandwidth, and power-handling capability. The location and geometry
of the projection in relation to the surrounding dielectric media
and space-volume geometry help determine the energy transfer
efficiency. In order to obtain the desired energy transfer
efficiency and desired field distribution inside the microwave
reactor, one can design and optimize the projection geometry,
composition, and location, and design and optimize the geometry
(space-volume) of the reactor in relation to the projection and the
complex dielectric values of the materials within the reactor.
[0105] One representative method to design a reactor is provided
below. Other methods do not require all the steps below, can
include additional steps not described herein, and/or can vary the
order of the steps.
[0106] 1. Determine desired process-rate or flow rate, for example,
bbl/day or bbl/hour.
[0107] 2. Determine the acceptable space-velocity for the system
(catalyst and reactor configuration).
[0108] 3. Determine the required volume for the reactor.
[0109] 4. Determine any liquid or fluid-flow velocity constraints
& fix range of fluid velocity.
[0110] 5. Determine required microwave power/energy density (e.g.,
watts/cc) or electromagnetic field strength (e.g.,
volts/meter).
[0111] 6. Determine dielectric properties of all species
(reactants--at different conversions; catalyst--both fresh and
assorted ages). Dielectric properties usually vary as a function of
temperature, operating conditions, and the degree of completion for
the desired reaction, as well as for coking and general catalyst
ageing.
[0112] 7. Determine (approximate calculations and later modeling)
the microwave power penetration depth for the full range of
operating conditions.
[0113] 8. Determine desired or acceptable E&M field profile
& degree of required field uniformity.
[0114] 9. Determine frequency to be used.
[0115] 10. Determine E&M model distribution (fit the E&M
modes into the reactor volume by adjusting the dimensions; 1/e
power distribution guideline for field energy decay).
[0116] 11. Approximate or use more precise finite element modeling
of the system, and distribute and re-inject microwave power to
achieve total volume and E&M field profile requirements.
[0117] 12. Use symmetry wherever possible to simplify
scalability/expandability.
[0118] Method of Designing Projections
[0119] The design basis disclosed in this section is primarily
directed to projections. However, the design basis can also utilize
a transparent or RF/microwave-permeable window or aperture
concept.
[0120] The concept of "matching" is to efficiently couple or to
transfer power or energy from a source through one of several types
of transmission means or lines and finally into a load, the load
being the consumer of the power or energy. In order to achieve the
theoretically perfect coupling efficiency of 100%, the magnitude of
the complex electrical impedance of the power source typically
should first equal or match the magnitude of the complex electrical
impedance of the transmission line, which in turn typically should
equal or match the magnitude of the complex electrical impedance of
the load. One characteristic of a transmission line or means is
that it does not dissipate or lose appreciable energy. Similarly,
one characteristic of the load is that it efficiently utilizes or
absorbs all of the energy delivered to it.
[0121] It is also typically preferable to control the amount or
percentage of energy being coupled or transmitted, while at the
same time controlling or minimizing the reflected power. This is
particularly useful to control the distribution of energy through
or into several points or volumes. It may also be desirable to
control the mutual coupling between the launches to minimize or
control the reflected power. Mutual coupling, which is the
influence that one launch has on another, can be controlled by
several techniques, such as adjusting the spacing between launches,
adjusting launch or reactor geometry, or adjusting dielectric
properties.
[0122] Generally, these teachings show a systematic methodology to
match, or to efficiently couple, the energy of an RF or microwave
frequency source impedance (complex impedance) into nearly any
volume of reactor geometry, which may have its own unique complex
RF or microwave impedance. Additionally, the teachings generally
show a methodology or means to distribute or to divide the power
throughout the volume of the reactor, which comprises the load.
[0123] For an example, start with a 50 ohm RF or microwave source
if coaxial cable is used to convey power to the reactor. Similarly,
begin with the characteristic (complex) impedance of the dielectric
waveguide if a waveguide transmission line is utilized as the
transmission line and means into the reactor. The RF/microwave
source impedance to be matched is generally split into multiples
and configured into a repeatable, extendable, or scalable fashion
in order to distribute the microwave power into the reactor at the
desired power density throughout the desired reactor volume. One
method for designing the injectors for this example is discussed
below. Other suitable methods may not require all the steps below,
and can include additional steps not described herein, and/or can
vary the order of the steps.
[0124] 1. Determine frequency (fixed or range) to be used.
[0125] 2. Determine maximum power to be applied through each
projection point.
[0126] 3. Either (a) mathematically approximate or more precisely
(b) utilize finite element modeling of the system specifically from
the microwave transmission line/source, through or between the
reactor wall, and then into the reactor volume to optimize power
transfer. FIG. 23, for example, represents a single projection 620
having a targeted 1/e power density 622 into a vessel 625.
Calculate forward and reflected power of each projection; control
the geometry of the projection to govern and to control the
fraction of the desired transmitted forward power and to generally
minimize the reflected power including the mutual coupling. One
side of the projection's equivalent geometry should match the
impedance of transmission line/coax and the second side of the
projection's equivalent geometry can be designed to match the
impedance of the reactor load, for example comprising the reactants
and/or catalyst.
[0127] 4. Using one of a variety of conductive, dielectric,
insulating, or combinations of rod or projection geometries, a
coaxial transmission electromagnetic finite-element model can be
used (finite element modeling or approximated calculations) to
evaluate and to adjust rod geometries with respect to the relative
insulators, dielectrics, and conducting surfaces of the neighboring
and intersecting materials. Proper control of pin or projection
geometry parameters, such as lengths and one or more diameter
configurations, allows one skilled in the art to match the
RF/microwave complex impedance of the reactor volume geometry with
that of the transmission line/means, and similarly with the
source.
[0128] 5. Proper repetition of this projection design in
conjunction with considerations/modeling/adjustments of the
resulting internal E&M field structure, due to geometrical
placement of the projection in and around the reactor, results in
efficient distribution and coupling of the microwave power into the
reactor at the desired power density and with the acceptable field
uniformity and into the desired reactor volume.
[0129] In one embodiment, the invention allows the use of multiple
power injection points into the reactor or the re-injection of
microwave power to suitably distribute (in a controlled fashion and
designable power-density) the energy/power into the volume of the
reactor. It is typically preferable for the power distribution to
be as uniform as possible. Exceptions, such as to induce a high
thermal gradient(s) across the catalyst and reactor volume, are
also possible to suit the needs of the specific application.
[0130] The fit of the overlapping E&M fields, or modes, within
the reactor volume can be controlled by adjusting the dimensions of
the projection, reactor cavity, geometrical spacing, or other
component placements. For example, FIG. 24 represents a plurality
of projections 620 in a vessel 625, where the approximate targeted
1/e power density 622 provides a suitable filling of the active
E&M fields using a plurality of projections. The distribution
of the E&M fields can initially be approximated and then
controlled and fine-tuned by using a spherical shell or other
approximation for the 1/e field decay as a guideline for the volume
to overlap or to re-inject additional power into the
reactor/applicator. The penetration depth, 1/e, is used to denote
the depth at which the power density has decreased to 37% of its
initial value at the surface. Approximate or more precise finite
element modeling of the system can be used to distribute and
re-inject microwave power to achieve the total volume and E&M
field profile requirements.
[0131] Symmetrical projection placement within or around the
reactor volume can simplify and considerably extend the scalability
and expandability of the usable reactor volume. For example, in
FIGS. 14 and 15, a spherical packing density of overlapping E&M
microwave fields can be symmetrically arranged within the reactor
by arranging a spiral-wrapped configuration of projection/launches
around the internal transmission line distributor design.
[0132] Example of Microwave Reactor Design for a Biodiesel
Production Process
[0133] It is known that the transesterification processes is useful
for converting plant oils and/or animal fats into alkyl esters,
also known as biodiesel. In U.S. Patent Publication No.
2005/0274065, the content of which is incorporated herein by
reference, it is disclosed that the use of microwave energy is
beneficial to the transesterification process. The example herein
provides a method to design a microwave chemical reactor for the
production of biodiesel via a transesterification reaction. The
reactor can be designed as a fixed bed heterogeneous catalytic
process, a homogeneous process, or the combination of the two. The
reactor can also be designed to perform the esterification process
per U.S. Patent Publication No. 2005/0274065.
[0134] The design process takes into account both unique E&M
field properties developed by the reactants, product, and catalysts
used in the transesterification process, and process operating
parameters such as temperature, pressure, LHSV, microwave power
density, and desired production rates (e.g. liters/hr, bbl/day). To
design a reactor, one guiding principle is to determine E&M
fields that develop during this process and calculate a 1/e power
penetration depth for E&M field energy decay. For example, the
penetration depth can be determined graphically using finite
element modeling techniques or calculated by other means such as
shown in equation [e1]. This allows the reactor geometry to be
adjusted to fit the E&M modes into the reactor volume.
Penetration Depth=(.lamda..sub.o.times.(.di-elect
cons..sub.r').sup.1/2)/(2.times..pi..times..di-elect cons..sub.r'')
[e1] [0135] where [0136] .lamda..sub.o wavelength, measured in,
.lamda..sub.o=c/f [0137] f frequency, measured in Hz [0138]
.di-elect cons..sub.r' relative dielectric constant [0139]
.di-elect cons..sub.r'' relative dielectric loss [0140] c speed of
light [0141] tan .delta. loss tangent equal to .di-elect
cons..sub.r''/.di-elect cons..sub.r' [0142] .delta. dielectric loss
angle, measured in degrees
[0143] The fit of the overlapping E&M fields, or modes, within
the reactor volume can be controlled by several means including
adjusting the dimensions of the launch/injector, reactor cavity,
geometrical spacing, or other component placements. The
distribution of the E&M fields can initially be approximated,
and then controlled and fine-tuned by using the 1/e field decay or
penetration depth as a guideline for the important dimension to
overlap or to re-inject additional power into the reactor.
[0144] For this example, a finite element model (FEM) can be
employed to evaluate the geometry of the system and to distribute
and launch microwave power to fill the desired total reactor volume
and meet E&M field profile requirements. Reactor geometry
symmetry wherever possible, can be used to simplify scalability and
expandability. Other methods to achieve approximate or less precise
solutions exist.
[0145] One of the initial steps to take is to measure the
dielectric properties, i.e. the complex dielectric permittivity and
permeability, at process operating conditions, of the reactant
mixture (e.g. alcohol, plant oil, and catalyst (homogeneous or
heterogeneous), the product mixture (e.g. methyl esters, glycerin,
and alcohol), and a few data points relating to the mixtures
developed at different stages of the process (e.g. alcohol, plant
oil, methyl esters, glycerin, and catalyst). It is known to those
skilled in the art that dielectric parameters are generally
frequency and temperature dependent. Therefore, dielectric
properties of the reactant and product mixture, including any
catalysts, should be determined at or around the frequency of the
microwave or RF source to be used for the process and at or around
the process temperatures.
[0146] Commercial high power sources are available primarily at 915
MHz (e.g. above 30 kW). Lower and moderate power sources (e.g.
below 10 kW) are more commonly available in the 2.45 GHz frequency.
It is also known to those skilled in the art that the penetration
depth (1/e) changes as a function of wavelength. As a first order
approximation, at 915 MHz, the penetration depth would reduce by
more than 60% (e.g. 915/2450) if a 2.45 GHz microwave source was
used. Based on this consideration, the reactor sizing can be
designed to work with either a 2.45 GHz or a 915 MHz microwave
source. For this example the 915 MHz source was selected. Also to
be determined at this step is the maximum microwave power to be
applied through each launch based on the process microwave
chemistry requirements. The required microwave power density that
is sufficient to promote/effect the reaction or process can be
determined by experimental or other means. For example, in one
system, U.S. Patent Publication No. 2005/0274065, it was
experimentally determined that approximately one watt/cc was useful
to promote the biodiesel process. To achieve the targeted power
density calculate or use FEM methods to evaluate the required power
to be injected into each launch. For this example, it was
determined that a useful injected power was about 1000-1500 watt.
FEM evaluations used 1500 watts per launch to achieve the targeted
power density of one watt/cc.
[0147] A next step is to optimize the launch geometry at the
selected frequency to achieve the desired impedance (e.g. 50 ohms)
and to minimize the reflected power, characterized by the S11
parameter. S11 is the input port voltage reflection coefficient.
FIG. 29 shows a plot of the S11 reflection coefficient versus the
launch probe length. Plotted are various geometries where the
radius of the Teflon sleeve is changed to determine the optimum
metal probe and Teflon sleeve geometry. It can be seen that a
minimum S11 reflected power is achieved for this range of
geometries. This achieves at least 95% efficient coupling as shown,
for example, in FIG. 29.
[0148] The field structure around the launch was then modeled and
evaluated as shown in FIG. 23. With reference to FIG. 23, the
launch 620 includes a metal projection rod 640 surrounded by Teflon
sleeve 645. A portion of the rod 640 and sleeve 645 are disposed in
the chamber 625. The data from the plot determines the 1/e power
distribution as a function of distance away from the launch. The
1/e distance provides a guideline (e.g. spacing equals twice the
1/e spacing) for spacing multiple launches to maintain a desired
power density average or to maintain the power density equal to or
greater than a chosen value to be contained within the 1/e field
space. For biodiesel production, at 915 MHz, the 1/e distance
averages around 15.7 cm. At the entrance and exit of the
cylindrical reactor, improved performance can be obtained by
considering the reflection boundary condition between the metallic
wall and the launch. Specifically, it is useful to use the
following guideline to determine the distance from the launch to
the end of the reactor. Start by locating the launch one-quarter
wavelength away from the end of the reactor. Furthermore, one can
fine-tune the launch placement by minimizing S11. For the biodiesel
example, this distance was determined to be 5.33 cm.
[0149] Usually, process chemistry makes it desirable for the
microwave power distribution to be as uniform as possible or at
least greater than a functional minimum. Exceptions, such as to
induce a high thermal gradient(s) across the catalyst and reactor
volume, are also possible if required for a specific
application.
[0150] Because the operating temperatures and pressure conditions
are relatively mild for transesterification (e.g. under 150 psig,
150.degree. C.), a launch made with Teflon as the dielectric
insulator can be used. This lowers the cost compared to a
glass/ceramic dielectric insulator that can handle higher operating
temperatures. In one example, the launch probe diameter is 0.48 cm.
To provide mechanical support to the launch, as well as to provide
chemical protection, a Teflon sleeve was fitted over the
launch.
[0151] For this example, comprising a tube reactor (e.g. circular
geometry), the penetration depth guides the selection of the
diameter of the reactor. This is done such that the cross sectional
area contains the 1/e field space without significant voids. FIG.
24 shows the fields for multiple launches 620 so as to extend the
average field intensity, contained within the 1/e field space. By
using calculations or modeling, one can determine the mutual
coupling between launches and adjust the geometries as necessary. A
suitable tube diameter was determined to be about 12.2 cm. The
process rate conditions, LHSV, can be used to determine the reactor
tube length. For a desired LHSV of 80, and a desire process rate of
2270 liters/hr, a reactor volume of 28.4 liters is needed. Given
this reactor volume and a reactor diameter of 12.2 cm, the reactor
length is calculated to be approximately 2.43 m. A reactor built
according to this design is able to couple microwaves efficiently
into biodiesel reactants such as soybean oil and methanol and
biodiesel products, methyl esters and glycerin. Therefore, the
spacing of the launch design can be used as a means of controlling
the residence time (1/LHSV) of the reactor. The repetition of the
launch with a suitable spacing and field overlap is also a means of
maintaining controlled or uniform electromagnetic fields coupled
into the reactant mixture while controlling the process residence
time. Combining the teachings for intra-launch spacing and for
boundary condition launch spacing (at reactor ends) 18 launches
provides the optimum number of launches for the biodiesel reactor.
However if only the intra-launch spacing consideration is used, 16
launches are suitable. In the 16-launch solution, an additional
intra-launch spacing distance should be included on each end of the
reactor to allow the field to decay before it is reflected
internally from the end of the reactor and back to the launch.
[0152] Process sensitivity data can be used to further refine the
launch impedance and geometry, launch spacing, and reactor geometry
to accommodate variations in process conditions. For example, one
could study how reflected power and the mutual coupling parameters
change the required launch geometry and spacing as a function of
changes in reactant and product mixtures, and other process
parameters such as temperature. It is typically preferable to
design the distribution of the electromagnetic energy inside the
reactor to control a targeted average power or field strength and
to minimize or reduce the dead zones. One way to control this field
distribution is to suitably select the spacing between multiple
launches and to utilize appropriate phases for each launch
(relative to a common power source). Phase control can be one
important parameter to understand because the total electric and
magnetic fields inside the reactor are the superimposition of the
electric and magnetic fields from each of the individual excitation
sources.
[0153] As discussed previously, a general guideline for spacing
multiple launches is in the range of approximately from a single
1/e distance (one penetration depth's distance) to twice the 1/e
distance (two times the penetration depth) so as to achieve an
average field or power density higher than 1/e (37%) of the desired
field or power density. For cases that require greater average
field uniformity or higher average field density, the launch
spacing could be smaller than the 1/e distance, e.g. shorter than
one penetration depth. In the example case for a biodiesel reactor,
the complex permittivity for the catalyst and reactant mixture is
approximately .di-elect cons.'=5.5, .di-elect cons.''=0.79, with a
loss tangent=0.145. In this case, the target power density was 1
watt/cc. It was found that improved performance was obtained by
placing the second (neighboring) launch 83% of the 1/e distance
away, 13.1 cm, which is about one wavelength in the dielectric
media, and making the phases of the (neighboring) launch input
power 180 degree different from each other. For intra-launch
spacing, the field structure can be controlled or improved by
setting the phase angle of the S21 coupling coefficient to zero.
S21 is the high frequency electromagnetic coupling coefficient
between two nearby ports and can be thought of as a mutual coupling
factor. This suitably minimized the dead zones and achieved the
desired average power density. In this particular case, the
superposition of the 180.degree. phase difference positively
reinforced the electromagnetic fields between the two (neighboring)
launches. Another way to achieve the reinforcement of the
electromagnetic fields and to maintain a more standard zero degrees
phase shift between each launch's source power is by inserting the
second launch at the same spacing but from the bottom of the
reactor, e.g. 180 degrees around the circumference with respect to
the first "0" degree launch.
[0154] The reactor design is not limited to this one process but
can be used for many applications (e.g. oil/water separation,
fossil fuel cracking, fossil fuel hydroprocessing, petrochemical,
and pharmaceutical) by evaluating the different dielectric values
(e.g. reactants, products, catalysts), and adjusting the launch
geometry and spacing by using a suitable penetration depth and
field profile. It should be noted, that other process conditions
may need to be taken into consideration during the reactor design
process such as liquid or fluid-flow velocity constraints, system
thermal stability requirements and catalytic diffusion and kinetic
factors.
[0155] Accordingly, the invention provides a new and useful
processing apparatus with an electromagnetic launch. Various
features and advantages of the invention are set forth in the
following claims.
* * * * *
References