U.S. patent application number 15/242090 was filed with the patent office on 2016-12-08 for dual vessel chemical modification and heating of wood with optional vapor containment.
The applicant listed for this patent is Eastman Chemical Company. Invention is credited to David Carl Attride, Jarvey Eugene Felty, JR., Timothy Lee Guinn, Andrew C. Hiester, Harold Dail Kimrey, JR., Tyler Littrell, Jared Moore, John Peter Mykytka, James S. Nelson, Brad William Overturf, Mark Robert Shelton.
Application Number | 20160354948 15/242090 |
Document ID | / |
Family ID | 46315430 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160354948 |
Kind Code |
A1 |
Felty, JR.; Jarvey Eugene ;
et al. |
December 8, 2016 |
DUAL VESSEL CHEMICAL MODIFICATION AND HEATING OF WOOD WITH OPTIONAL
VAPOR CONTAINMENT
Abstract
A commercial scale system and process for chemically modifying
wood and then heating the chemically-modified wood. The
system/process separates the chemical modification step from the
heating step by utilizing two different vessels for the
modification and heating steps. The system and process can, in
certain situations, include a containment room for preventing
escape of vapors from a chemical wood modification reactor, a wood
heater, and/or a chemically-modified bundle of wood as the bundle
is transported from the wood modification reactor to the wood
heater.
Inventors: |
Felty, JR.; Jarvey Eugene;
(Gray, TN) ; Attride; David Carl; (Jonesborough,
TN) ; Overturf; Brad William; (Kingsport, TN)
; Hiester; Andrew C.; (Kingsport, TN) ; Littrell;
Tyler; (Lexington, AL) ; Moore; Jared;
(Kingsport, TN) ; Nelson; James S.; (Kingsport,
TN) ; Shelton; Mark Robert; (Kingsport, TN) ;
Kimrey, JR.; Harold Dail; (Knoxville, TN) ; Mykytka;
John Peter; (Kingsport, TN) ; Guinn; Timothy Lee;
(Bluff City, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Eastman Chemical Company |
Kingsport |
TN |
US |
|
|
Family ID: |
46315430 |
Appl. No.: |
15/242090 |
Filed: |
August 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13323184 |
Dec 12, 2011 |
9456473 |
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15242090 |
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61427030 |
Dec 23, 2010 |
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61427042 |
Dec 23, 2010 |
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61427053 |
Dec 23, 2010 |
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61427056 |
Dec 23, 2010 |
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61427064 |
Dec 23, 2010 |
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61427067 |
Dec 23, 2010 |
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61427070 |
Dec 23, 2010 |
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61427072 |
Dec 23, 2010 |
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61427075 |
Dec 23, 2010 |
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61427076 |
Dec 23, 2010 |
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61427079 |
Dec 23, 2010 |
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61427080 |
Dec 23, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B27K 5/0055 20130101;
F26B 2210/16 20130101; F26B 5/048 20130101; Y02P 20/124 20151101;
H05B 6/763 20130101; H05B 2206/046 20130101; H05B 6/80 20130101;
B27K 3/346 20130101; H05B 6/707 20130101; Y02P 20/10 20151101; F26B
3/347 20130101; C08H 8/00 20130101 |
International
Class: |
B27K 5/00 20060101
B27K005/00; H05B 6/70 20060101 H05B006/70; B27K 3/34 20060101
B27K003/34; F26B 5/04 20060101 F26B005/04; C08H 8/00 20060101
C08H008/00; H05B 6/80 20060101 H05B006/80; H05B 6/76 20060101
H05B006/76 |
Claims
1. A commercial-scale process for producing chemically-modified
wood, said process comprising: (a) loading a quantity of wood into
a chemical modification reactor, wherein said quantity of wood
weighs at least 500 pounds when loaded into said reactor and
wherein said chemical modification reactor defines an internal
reactor volume of at least 100 cubic feet; (b) chemically modifying
at least a portion of said quantity of wood to thereby provide a
chemical-wet quantity of wood, wherein said chemical-wet quantity
of wood comprises at least one heat-removable chemical component
resulting from said chemically modifying; (c) transporting at least
a portion of said chemical-wet quantity of wood out of said
chemical modification reactor and into a microwave heater; (d)
generating microwave energy with at least one microwave generator;
(e) passing at least a portion of said microwave energy from said
at least one microwave generator, through a microwave distribution
system, and into said microwave heater, wherein said microwave
distribution system comprises-- at least one waveguide for
transporting said microwave energy from said microwave generator to
said microwave heater, at least one microwave launcher for
discharging said microwave energy into the interior of said
microwave heater through at least one uncovered launch opening, and
at least one barrier assembly entirely disposed outside of said
microwave heater between said microwave generator and said
microwave launcher, wherein said barrier assembly fluidly isolates
said microwave heater from an external environment outside said
microwave heater while still permitting passage of said microwave
energy therethrough, wherein said barrier assembly is configured to
minimize arcing therein when said microwave energy passes
therethrough at a rate of at least 30 kW and when said pressure
within said microwave heater is not more than 350 torr, wherein
said at least one waveguide includes at least a first waveguide
segment and a second waveguide segment, wherein said first
waveguide segment is positioned between said microwave generator
and said barrier assembly and is configured to propagate microwave
energy from said microwave generator to said barrier assembly, and
wherein said second waveguide segment is positioned between said
barrier assembly and said microwave launcher and is configured to
propagate microwave energy from said barrier assembly to said
microwave launcher, wherein said first waveguide segment is
entirely disposed outside of said microwave heater and wherein said
second waveguide is at least partially disposed outside of said
microwave heater; and (f) heating at least a portion of said
chemical-wet quantity of wood in said microwave heater under a
pressure of not more than 350 torr to thereby vaporize at least a
portion of said at least one heat-removable chemical component in
said microwave heater to thereby provide a dried quantity of
chemically-modified wood.
2. The process of claim 1, wherein said chemically modifying of
step (a) comprises acetylating said at least a portion of said
quantity of wood.
3. The process of claim 1, wherein said at least one heat-removable
chemical component comprises acetic acid.
4. The process of claim 1, wherein said chemically modifying of
step (a) comprises a heat-initiated chemical reaction, wherein said
heat-initiated chemical reaction is not initiated by microwave
heating.
5. The process of claim 4, wherein said heat-initiated chemical
reaction is initiated by injecting hot vapors into said chemical
modification reactor to thereby heat at least a portion of said
quantity of wood, wherein at least a portion of said hot vapors
injected into said chemical modification reactor condense on at
least a portion of said quantity of wood.
6. The process of claim 1, wherein during said transporting of step
(b) vapors from said chemical modification reactor, from said
microwave heater, and/or from said chemical-wet quantity of wood
are reduced from escaping into an external environment by a
containment room coupled to said chemical modification reactor and
said microwave heater, further comprising, during said transporting
of step (b), drawing gases and vapors out of said containment room
using a ventilation system.
7. The process of claim 1, wherein said chemical modification
reactor and said microwave heater are spaced from one another by at
least 2 feet and not more than 50 feet, wherein said chemical
modification reactor and said microwave heater each have an
internal volume of at least 500 cubic feet.
8. The process of claim 1, wherein said heating of step (e)
includes introducing microwave energy into said microwave heater at
a rate of at least 50 kW.
9. The process of claim 1, wherein said quantity of wood is in the
form of a bundle having a total volume of at least 250 cubic feet,
wherein said quantity of wood weighs at least 1,000 pounds when
said quantity of wood is loaded into said reactor, wherein said
chemical-wet quantity of wood comprises at least 8 weight percent
of said at least one heat-removable chemical component prior to
step (d), wherein said dried quantity of chemically-modified wood
comprises not more than 3 weight percent of said at least one
heat-removable chemical component after step (d), wherein said
process dries said chemical-wet quantity of wood to produce said
dried quantity of chemically-modified wood in a time period of not
more than 8 hours.
10. The process of claim 1, wherein said process is has an annual
production capacity of at least about 500,000 board feet.
11. A commercial-scale process for producing chemically-modified
wood, said process comprising: (a) chemically modifying at least a
portion of a bundle of wood in a chemical modification reactor to
thereby provide a chemical-wet bundle of wood, wherein said
chemical-wet bundle of wood comprises at least one heat-removable
chemical component resulting from said chemically modifying; (b)
transporting at least a portion of said chemical-wet bundle of wood
from said chemical modification reactor, through a containment
room, and into a microwave heater, wherein each of said chemical
modification reactor and said microwave heater has an internal
volume of at least 100 cubic feet; (c) drawing gases and vapor out
of said containment room while said chemical-wet bundle of wood is
contained therein; (d) generating microwave energy using at least
one microwave generator; (e) directing said microwave energy from
said at least one microwave generator, through a microwave
distribution system, and into said microwave heater, wherein said
microwave energy is provided to said microwave heater at a rate of
at least 30 kW, wherein said microwave distribution system
comprises at least one barrier assembly for fluidly isolating said
heater from an external environment outside said heater while still
permitting passage of said microwave energy therethrough, wherein
said barrier assembly is positioned between said microwave
generator and said microwave heater and outside of said microwave
heater; and (f) heating at least a portion of said chemical-wet
bundle of wood with at least a portion of said microwave energy in
said microwave heater to thereby vaporize at least a portion of
said heat-removable chemical component and thereby provide a dried
bundle of chemically-modified wood, wherein said heating is carried
out at a pressure of not more than 350 torr.
12. The process of claim 11, wherein said containment room is
maintained at a pressure below atmospheric pressure during said
transporting.
13. The process of claim 11, wherein drawing of said gases and
vapor out of said containment room is carried out at a rate of a
least 2 exchanges per hour.
14. The process of claim 11, further comprising, subsequent to said
chemically modifying and prior to said heating, drawing vapors and
gases out of said chemical modification reactor and into said
containment room while drawing air from an external environment
into said chemical modification reactor.
15. The process of claim 11, further comprising, subsequent to said
chemically modifying and prior to said heating, drawing vapors and
gases out of said heater and into said containment room while
drawing air from an external environment into said heater.
16. The process of claim 11, further comprising transporting said
dried bundle of chemically-modified wood out of said heater and
into and/or under a product vapor removal structure, further
comprising drawing gases and vapors in though said product vapor
removal structure using a ventilation system, further comprising
using said ventilation system to draw gases and vapors out of said
containment room during said transporting from said chemical
modification reactor to said heater, further comprising using a
flow diverter to adjust how the total ventilation capacity of said
ventilation system is allocated between said containment room and
said product vapor removal structure.
17. The process of claim 11, wherein said chemical modification
reactor is an acetylation reactor and said chemically modifying
comprises acetylating, wherein said heater is a microwave heater
and said heating comprises application of microwave energy.
18. The process of claim 11, wherein said chemical-wet bundle of
wood comprises at least 8 weight percent of said heat-removable
chemical component prior to said heating of step (c), wherein said
dried bundle of chemically-modified wood comprises not more than 3
weight percent of said heat-removable chemical component subsequent
to said heating of step (c), wherein said heater dries said
chemical-wet bundle of wood to said dried bundle of wood in not
more than 12 hours.
19. The process of claim 11, wherein said microwave distribution
system further comprises at least one waveguide for transporting
said microwave energy from said microwave generator to said heater
and wherein said microwave distribution system further comprises at
least one microwave launcher comprising at least one uncovered
launch opening for discharging said microwave energy into the
interior of said heater.
20. The process of claim 19, wherein said at least one waveguide
includes at least a first waveguide segment and a second waveguide
segment, wherein said first waveguide segment is positioned between
said microwave generator and said barrier assembly and is
configured to propagate microwave energy from said microwave
generator to said barrier assembly, and wherein said second
waveguide segment is positioned between said barrier assembly and
said microwave launcher and is configured to propagate microwave
energy from said barrier assembly to said microwave launcher,
wherein said first waveguide segment is entirely disposed outside
of said heater and wherein said second waveguide is at least
partially disposed outside of said heater.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 13/323,184, filed on Dec. 12, 2011, which
claims priority to U.S. Provisional Patent Application Nos.
61/427,030; 61/427,042; 61/427,053; 61/427,056; 61/427,064;
61/427,067; 61/427,070; 61/427,072; 61/427,075; 61/427,076;
61/427,079; and 61/427,080, filed Dec. 23, 2010.
FIELD OF THE INVENTION
[0002] This invention generally relates to systems for chemically
modifying wood.
BACKGROUND
[0003] Electromagnetic radiation, such as microwave radiation, is a
known mechanism for delivering energy to an object. The ability of
electromagnetic radiation to penetrate and heat an object both
rapidly and effectively has proven advantageous in many chemical
and industrial processes. Further, because the use of microwave
energy as a heat source is generally non-invasive, microwave
heating is particularly useful in processing `sensitive` dielectric
materials, such as food and pharmaceuticals, and can even be useful
for heating materials having a relatively poor thermal
conductivity, such as wood. However, the complexities and nuances
of safely and effectively applying microwave energy, especially on
a commercial scale, have severely limited its application in
several types of industrial processes.
[0004] Because of its wide suitability for a variety of
applications, its renewable nature, and its relatively low cost,
wood is one of the most widely used building materials in
existence. However, because wood is a natural product, its physical
and structural properties can vary substantially, not only amongst
different species, but also amongst different trees, or even
different locations within the same piece of wood. Further, wood is
generally hygroscopic, which affects its dimensional stability, and
its biochemical composition makes it susceptible to attack by
insects and fungi. As a result, several types of wood treatment
processes have been developed to increase the stability of wood
through modification of its chemical, physical, and/or structural
properties. Examples of treatment processes include treatments,
coating treatments, thermal modification, and chemical
modification. The latter two treatment processes generally alter
the properties of wood to a more drastic degree than the others
and, consequently, these types of processes typically involve more
complex schemes and systems. For example, many chemical and thermal
treatment processes can be carried out under vacuum and/or in the
presence of one or more treatment chemicals. As a result,
commercialization of these types of technologies has been limited,
and multiple challenges remain to be overcome in order for these
processes to be industrialized on a wide scale.
[0005] Thus, a need exists for a more efficient and cost effective
commercial-scale system suitable for chemically or thermally
treating wood. A need also exists for an efficient and cost
effective industrial-scale microwave heating system suitable for
use in a wide variety of processes and applications, including the
treatment of wood.
SUMMARY OF THE INVENTION
[0006] One embodiment of the present invention concerns a system
for producing chemically-modified wood, the system comprising a
chemical modification reactor for producing a chemical-wet bundle
of wood, wherein the chemical modification reactor comprises a
first reactor door and defines an internal reactor volume of at
least 100 cubic feet; and a microwave heater for removing at least
a portion of one or more heat-removable chemicals from the
chemical-wet bundle of wood, wherein the microwave heater comprises
a first heater door and defines an internal heater volume of at
least 100 cubic feet. The internal reactor volume and the internal
heater volume are locationally distinct.
[0007] Another embodiment of the present invention concerns a
system for producing chemically-modified wood, the system
comprising a wood acetylation reactor for producing an acetylated,
chemical-wet bundle of wood, wherein the acetylation reactor
comprises a first reactor door and defines an internal reactor
volume of at least 100 cubic feet; and a heater for removing at
least a portion of one or more heat-removable chemicals from the
acetylated, chemical-wet bundle of wood, wherein the heater
comprises a first heater door and defines an internal heater volume
of at least 100 cubic feet. The internal reactor volume and the
internal heater volume are locationally distinct.
[0008] Still another embodiment of the present invention concerns a
system for producing chemically-modified wood, the system
comprising a chemical modification reactor comprising a first
reactor door for discharging the bundle of wood from the chemical
modification reactor after chemical modification; a heater
comprising a first heater door for receiving the bundle of wood
after discharge from the chemical modification reactor; and a
containment room defining a transfer region through which the
bundle of wood passes during transport from the first reactor door
to the first heater door. The containment room is coupled to the
chemical modification reactor and the heater and is operable to
substantially isolate an external environment from the transfer
region during transport of the bundle of wood from the chemical
modification reactor to the heater.
[0009] Yet another embodiment of the present invention concerns a
process for producing chemically-modified wood, the process
comprising: (a) loading a quantity of wood into a chemical
modification reactor, wherein the quantity of wood weighs at least
500 pounds when loaded into the reactor; (b) chemically modifying
at least a portion of the quantity of wood to thereby provide a
chemical-wet quantity of wood, wherein the chemical-wet quantity of
wood comprises at least one heat-removable chemical component
resulting from the chemically modifying; (c) transporting at least
a portion of the chemical-wet quantity of wood out of the chemical
modification reactor and into a microwave heater; and (d) heating
at least a portion of the chemical-wet quantity of wood in the
microwave heater to thereby vaporize at least a portion of the at
least one heat-removable chemical component in the microwave heater
to thereby provide a dried quantity of chemically-modified
wood.
[0010] Still another embodiment of the present invention concerns a
process for producing chemically-modified wood, the process
comprising: (a) chemically modifying at least a portion of a bundle
of wood in a chemical modification reactor to thereby provide a
chemical-wet bundle of wood, wherein the chemical-wet bundle of
wood comprises at least one heat-removable chemical component
resulting from the chemically modifying; (b) transporting at least
a portion of the chemical-wet bundle of wood from the chemical
modification reactor, through a containment room, and into a
heater, wherein during the transporting the containment room
reduces leakage of the vapors present in the chemical modification
reactor, emitted from the chemical-wet bundle of wood, and present
in the heater from being discharged into an environment external to
the chemical modification reactor and the heater; and (c) heating
at least a portion of the chemical-wet bundle of wood in the heater
to vaporize at least a portion of the heat-removable chemical
component and thereby provide a dried bundle of chemically-modified
wood.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a top view of a wood treatment system configured
in accordance with one embodiment of the present invention,
particularly illustrating a rail system for transporting bundles of
wood to and from a chemical modification reactor and a wood
heater;
[0012] FIG. 2 is a top view of a wood treatment system configured
in accordance with an alternative embodiment of the present
invention, particularly illustrating a turntable system for
transporting bundles of wood to and from a plurality of chemical
modification reactors and a plurality of wood heaters;
[0013] FIG. 3 is a top view of a wood treatment system configured
in accordance with an alternative embodiment of the present
invention, particularly illustrating a roller system for
transporting bundles of wood to and from a plurality of chemical
modification reactors and a plurality of wood heaters;
[0014] FIG. 4a is a top view of a pass-through wood treatment
system suitable for use in producing chemically-modified wood and
configured in accordance with one embodiment of the present
invention, particularly illustrating a chemical modification
reactor and a wood heater that comprise separate, axially-aligned,
two-door vessels and include a vapor containment room located
between the reactor and heater vessels;
[0015] FIG. 4b is an isometric view of the pass-through wood
treatment system of FIG. 4a, particularly illustrating an exemplary
blast panel/wall of the vapor containment room;
[0016] FIG. 4c is a sectional view of the vapor containment room
depicted in FIGS. 4a and 4b, particularly illustrating an exemplary
pair of one-way vents for allowing fluid (e.g., air) from the
external environment to flow into the vapor containment room;
[0017] FIG. 4d is a side view of the pass-through wood treatment
system of FIG. 4a, but also illustrating a ventilation system for
drawing vapors and gasses in through the vapor containment room and
in through a product vapor removal structure located at the outlet
of the heater;
[0018] FIG. 5 is a schematic view of a microwave heating system
configured in accordance with one embodiment of the present
invention, particularly illustrating a microwave heater that is
equipped with a vacuum system and receives microwave energy from a
microwave generator via a microwave distribution system;
[0019] FIG. 6 is an isometric view of a two-door, pass-through
vessel suitable for use as a chemical modification reactor and/or
microwave heater in accordance with various embodiments of the
present invention, particularly illustrating the shape and
dimensional proportions of the vessel;
[0020] FIG. 7a is a partial sectional view of the junction of a
door flange and a vessel flange of a microwave heater configured in
accordance with one embodiment of the present invention, particular
illustrating a microwave choke cooperatively formed by the door and
vessel flanges and having two chambers that extend parallel to and
alongside one another;
[0021] FIG. 7b is a partial sectional view of a microwave choke
similar the choke depicted in FIG. 7a, but having choke cavities
that extend at an acute angle relative to one another;
[0022] FIG. 7c is a cut-away isometric view of the door flange of a
microwave heater equipped with the microwave choke configuration
depicted in FIG. 7a, particularly illustrating a plurality of
circumferentially-spaced, open-ended slots or gaps formed in a
guidewall of the choke;
[0023] FIG. 7d is a side view of an open door on a microwave heater
equipped with a microwave choke having a removable portion
configured in accordance with one embodiment of the present
invention, particularly illustrating that the removable portion of
the microwave choke comprises a plurality of individually removable
and replaceable choke segments;
[0024] FIG. 7e is a sectional view of a "G"-shaped removable choke
portion previously depicted in FIG. 7d;
[0025] FIG. 7f is a sectional view of a "J"- or "U"-shaped
removable choke portion configured in accordance with a first
alternative embodiment of the present invention;
[0026] FIG. 7g is a sectional view of an "L"-shaped removable choke
portion configured in accordance with a second alternative
embodiment of the present invention;
[0027] FIG. 7h is a sectional view of an "I"-shaped removable choke
portion configured in accordance with a third alternative
embodiment of the present invention;
[0028] FIG. 8a is a cut-away isometric view of a microwave heater
configured in accordance with one embodiment of the present
invention, particularly illustrating the heater as being equipped
with an elongated waveguide launcher having staggered launch
openings on opposite sides of the launcher;
[0029] FIG. 8b is an enlarged partial view of the waveguide
launcher depicted in FIG. 8a, particularly illustrating the
configuration of the launch openings and the thickness of the
sidewalls defining the launch openings;
[0030] FIG. 9a is a side view of a microwave heating system
configured in accordance with one embodiment of the present
invention, particularly illustrating a microwave distribution
system for delivering microwave energy to the microwave heater;
[0031] FIG. 9b is a top cut-away view of the microwave heater
depicted in FIG. 9a, particularly illustrating the microwave
distribution system as including one pair of TM.sub.ab launchers on
one side of the microwave heater and a second pair of the TM.sub.ab
launchers on the opposite side of the microwave heater;
[0032] FIG. 9c is a diagram illustrating what is meant by the terms
"opposite side" and "same side";
[0033] FIG. 9d is a diagram illustrating what is meant by the term
"axially aligned";
[0034] FIG. 9e is a partial cut-away isometric view of a microwave
launching and reflecting or dispersing system configured in
accordance with one embodiment of the present invention,
particularly illustrating a launch system similar to that depicted
in FIG. 9b but also including a movable reflector associated with
each microwave launcher;
[0035] FIG. 9f is an isometric view of one embodiment of a
reflector suitable for use in a microwave heating system as
described herein, particularly illustrating the reflector as having
a non-planar reflecting surface with a concavity of a first
configuration;
[0036] FIG. 9g is an isometric view of another embodiment of a
reflector suitable for use in a microwave heating system described
herein, particularly illustrating the reflector as having a
non-planar reflecting surface with a concavity of a second
configuration;
[0037] FIG. 9h is a side elevation view of one embodiment of a
reflector suitable for use in a microwave heating system described
herein, particularly illustrating the curvature of the reflector
surface;
[0038] FIG. 9i is an enlarged, cut-away, isometric view of a
microwave launcher and reflector pair previously depicted in FIG.
9e, particularly illustrating an actuator system for providing
oscillating movement of the reflector;
[0039] FIG. 10a is a side view of a microwave heating system
configured in accordance with one embodiment of the present
invention, particularly illustrating a microwave distribution
system equipped with a plurality of TM.sub.ab barrier
assemblies;
[0040] FIG. 10b is an axial sectional view of one of the TM.sub.ab
barrier assemblies depicted in FIG. 10a, particularly illustrating
the barrier assembly as having two floating, sealed windows and
impedance transforming diameter step-changes near the junction of
the barrier assembly and the waveguides between which the barrier
assembly is coupled;
[0041] FIG. 10c is an end view of the microwave heating system
depicted in FIG. 10a with a bundle of wood being received in the
interior of the microwave heater, particularly illustrating the
microwave heater as being equipped with split microwave launchers
on opposite sides of the heater and movable reflectors for
rastering microwave energy emitted from the split launchers;
[0042] FIG. 10d is an enlarged side view of one of the split
launchers depicted in FIG. 10c, particularly illustrating the
launch angle for the two separate microwave energy fractions
emitted from the split launcher;
[0043] FIG. 10e is an enlarged view of one embodiment of a system
for moving a reflector, particularly illustrating an actuator used
to cause oscillation of the reflector and a bellows for inhibiting
fluid leakage at the location where the actuator penetrates the
wall of the microwave heater;
[0044] FIG. 11a is a schematic top view of a microwave heating
system configured in accordance with one embodiment of the present
invention, particularly illustrating the heating system as
including a plurality of microwave switches for routing microwave
energy to different microwave launchers in an alternating
fashion;
[0045] FIG. 11b is a schematic view of a microwave heating system
configured in accordance with an alternative embodiment of the
present invention, particularly illustrating the heating system as
including a plurality of microwave switches for routing microwave
energy to different microwave launchers in an alternating
fashion;
[0046] FIG. 12 is a schematic representation of a bundle of wood,
particularly illustrating the configuration utilized when
determining interior surface temperatures as described in Example
2;
[0047] FIG. 13 is a cumulative frequency histogram incorporating
thermal data obtained from surfaces B' through D' of the composite
bundle shown in FIG. 12; and
[0048] FIG. 14 is a cumulative frequency histogram illustrating a
predicted temperature distribution resulting from extrapolated
thermal data for a bundle of acetylated wood as described in
Example 3.
DETAILED DESCRIPTION
[0049] In accordance with one embodiment of the present invention,
a heating system is provided. Heating systems configured according
to various embodiments of the present invention can comprise a heat
source, a heating vessel (e.g., a heater), and an optional vacuum
system. Typically, heating systems configured according to one
embodiment of the present invention can be suitable for use as
stand-alone heating units, or can be employed as, or in conjunction
with, chemical reactors in a variety of processes. Heating systems
configured according to several embodiments of the present
invention will now be described in detail below, with reference to
the Figures.
[0050] In one embodiment, a heating system of the present invention
can be used to heat lignocellulosic materials. Lignocellulosic
materials can include any material comprising cellulose and lignin
and, optionally, other materials such as hemicelluloses. Examples
of lignocellulosic materials can include, but are not limited, to
wood, bark, kenaf, hemp, sisal, jute, crop straws, nutshells,
coconut husks, grass and grain husks and stalks, corn stover,
bagasse, conifer and hardwood barks, corn cobs, and other crop
residuals, and any combination thereof.
[0051] In one embodiment, the lignocellulosic material can be wood.
The wood can be a softwood or a hardwood. Examples of suitable wood
species can include, but are not limited to, pine, fir, spruce,
poplar, oak, maple, and beech. In one embodiment, wood can comprise
red oak, red maple, German beech, or Pacific albus. In another
embodiment, the wood can comprise a pine species including, for
example, Radiata pine, Scots pine, Loblolly pine, Longleaf pine,
Shortleaf pine, or Slash pine, the latter four of which can be
collectively referred to as "Southern Yellow Pine." The wood
processed by heating systems according to one embodiment of the
present invention can be in any suitable form. Non-limiting
examples of suitable forms of wood can include, but are not limited
to, shredded wood, wood fibers, wood flour, wood chips, wood
particles, wood flakes, wood strands, and wood excelsior. In one
embodiment, the wood processed in one or more heating systems of
the present invention can comprise sawn timber, debarked tree
trunks or limbs, boards, planks, veneers, beams, profiles, squared
timber, or any other cut of lumber.
[0052] Typically, the size of the wood can be defined by two or
more dimensions. The dimensions can be actual "measured" dimensions
or can be nominal dimensions. As used herein, the term "nominal
dimension" refers to the dimensions calculated using the size
designation for the wood. The nominal size can be larger than the
measured dimensions. For example, a dried "2.times.4" can have
actual dimensions of 1.5 inches by 3.5 inches, but the nominal
dimensions of "2.times.4" are still used. It should be understood
that the dimensions referred to herein are generally nominal
dimensions, unless otherwise noted.
[0053] In one embodiment, the wood can have three dimensions: a
length, or longest dimension; a width, or second longest dimension;
and a thickness, or shortest dimension. Each of the dimensions can
be substantially the same, or, one or more of the dimensions can be
different from one or more of the other dimensions. According to
one embodiment, the length of the wood can be at least about 6
inches, at least about 1 foot, at least about 3 feet, at least
about 4 feet, at least about 6 feet, or at least about 10 feet. In
another embodiment, the width of the wood can be at least about 0.5
inches, at least about 1 inch, at least about 2 inches, at least
about 4 inches, at least about 8 inches, at least about 12 inches,
or at least about 24 inches and/or no more than about 10 feet, no
more than about 8 feet, no more than about 6 feet, no more than
about 4 feet, no more than about 3 feet, no more than about 2 feet,
no more than about 1 foot, or no more than about 6 inches. In yet
another embodiment, the thickness of the wood can be at least about
0.25 inches, at least about 0.5 inches, at least about 0.75 inches,
at least about 1 foot, at least about 1.5 feet, or at least about 2
feet and/or no more than about 4 feet, no more than about 3 feet,
no more than about 2 feet, no more than about 1 foot, and/or no
more than about 6 inches.
[0054] According to one embodiment, the wood can comprise one or
more pieces of solid wood, engineered solid wood, or a combination
thereof. As used herein, the term "solid wood" refers to wood that
measures at least about 10 centimeters in at least one dimensions
but that is otherwise of any dimension (e.g., lumber having
dimensions as described previously). As used herein, the term
"engineered solid wood" refers to a wooden body having the minimum
dimensions of solid wood (e.g., at least one dimension of at least
about 10 cm), but that is formed of smaller bodies of wood and at
least one binder. The smaller bodies of wood in engineered solid
wood may or may not have one or more of the dimensions described
previously with respect to solid wood. Non-limiting examples of
engineered solid wood can include wood laminates, fiberboard,
oriented strand board, plywood, wafer board, particle board, and
laminated veneer lumber.
[0055] In one embodiment, the wood can be grouped in a bundle. As
used herein, the term "bundle" refers to two or more pieces of wood
stacked, placed, and/or fastened together in any suitable fashion.
According to one embodiment, a bundle can comprise a plurality of
boards stacked and coupled to one another via a belt, strap, or
other suitable device. In one embodiment, the two or more pieces of
wood can be in direct contact or, in another embodiment, the wood
pieces can be at least partially spaced using at least one spacer
or "sticker" disposed therebetween.
[0056] In one embodiment, the bundle can have any suitable
dimensions and/or shape. In one embodiment, the bundle can have a
total length, or longest dimension, of a least about 2 feet, at
least about 4 feet, at least about 8 feet, at least about 10 feet,
at least about 12 feet, at least about 16 feet, or at least about
20 feet and/or no more than about 60 feet, no more than about 40
feet, or no more than about 25 feet. The bundle can have a height,
or second longest dimension, of at least about 1 foot, at least
about 2 feet, at least about 4 feet, at least about 6 feet, at
least about 8 feet, and/or no more than about 16 feet, no more than
about 12 feet, no more than about 10 feet, no more than about 8
feet, no more than about 6 feet, or no more than about 4 feet. In
one embodiment, the bundle can have a width, or shortest dimension,
of at least about least about 1 foot, at least about 2 feet, at
least about 4 feet, at least about 6 feet, and/or no more than
about 20 feet, no more than about 16 feet, no more than about 12
feet, no more than about 10 feet, no more than about 8 feet, or no
more than about 6 feet. The total volume of the bundle, including
the spaces between the boards, if any, can be at least about 50
cubic feet, at least about 100 cubic feet, at least about 250 cubic
feet, at least about 375 cubic feet, or at least about 500 cubic
feet. According to one embodiment, the weight of the bundle of wood
(or cumulative weight of one or more objects, articles, or loads to
be treated) introduced into the reactor and/or heater of one or
more heating systems of the present invention (e.g., prior to
heating or treatment) can be at least about 100 pounds, at least
about 500 pounds, at least about 1,000 pounds, or at least about
5,000 pounds. In one embodiment, the bundle can be cubical or
cuboidal in shape.
[0057] In another embodiment, one or more heating systems of the
present invention can be used to chemically modify, dry, and/or
thermally modify wood, thereby producing chemically-modified,
dried, and/or thermally-modified wood. Wood that has been dried
and/or thermally-modified wood may referred to as
"thermally-treated" wood, such that the term "thermally-treated
wood" refers to wood that has been heated, dried, and/or
thermally-modified. As used herein, the term "thermally modify"
means to at least partially modify the chemical structure of at
least a portion of one or more pieces of wood in the absence of an
exogenous treating agent. In one embodiment, a heating system,
specific configurations of which will be described in detail
shortly, can be used to heat and/or dry wood in a thermal
modification process to thereby provide a bundle of
thermally-modified wood. According to one embodiment, thermal
modification can occur simultaneously with heating and/or drying of
wood in a wood heater and/or dryer, while, in another embodiment,
wood can be heated and/or dried in a wood heater or dryer without
being thermally modified. As used herein, the term "dry" means to
cause or accelerate vaporization of or to otherwise remove at least
a portion of one or more liquid or otherwise heat-removable
components from the wood via the addition of heat or other suitable
form of energy. Thermal modification processes can include a step
of contacting wood with one or more heat transfer agents such as,
for example, steam, heated inert vapors like nitrogen or air, or
even liquid heat transfer media such as heated oils. In another
embodiment, a radiant heat source may be used during thermal
modification. Thermally-modified wood can have a substantially
lower moisture content than untreated wood and can have enhanced
physical and/or mechanical properties such as, for example,
increased flexibility, higher resistance to decay and biological
attacks, and increased dimensional stability.
[0058] In yet another embodiment, heating systems configured
according to various embodiments of the present invention can be
used to chemically modify wood. As used herein, the term
"chemically modify" means to at least partially modify the chemical
structure of at least a portion of one or more pieces of wood in
the presence of one or more exogenous treating agents. Specific
types of chemical modification processes can include, but are not
limited to, acetylation and other types of esterification,
epoxidation, etherification, furfurlyation, methylation, and/or
melamine treatment. Non-limiting examples of suitable treatment
agents can include anhydrides (e.g., acetic, phthalic, succinic,
maleic, propionic, or butyric); acid chlorides; ketenes; carboxylic
acids; isocyanates; aldehydes (e.g., formaldehyde, acetyldehyde, or
difunctional aldehydes); chloral; dimethyl sulfate; alkyl
chlorides; beta-propiolacetone; acrylonitrile; epoxides (e.g.,
ethylene oxide, propylene oxide, or butylenes oxides); difunctional
epoxides; borates; acrylates; silicates; and combinations
thereof.
[0059] Processes for chemically modifying wood can include a
chemical modification step followed by a heating step. During the
chemical modification or reaction step, which can be carried out in
a chemical modification reactor, wood can be exposed to one or more
of the exogenous treatment agents described previously, which can
react with at least a portion of the functional groups (e.g.,
hydroxyl groups) of the untreated wood to thereby provide
chemically-modified wood. During the chemical modification step,
one or more heat-initiated chemical reactions can take place, which
may or may not be initiated by an external source of energy (e.g.,
thermal energy or electromagnetic energy, including, for example,
microwave energy.) Specific details of chemical modification
processes vary amongst the many types of chemical modification, but
most chemically-modified wood can have enhanced structural,
chemical, and/or mechanical properties including lower moisture
sorption, higher dimensional stability, more biological and pest
resistance, increased decay resistance, and/or higher weather
resistance as compared to untreated wood.
[0060] In one embodiment, wood can be acetylated in a wood
acetylation reactor. Acetylation can include replacement of surface
or near-surface hydroxyl groups with acetyl groups. In one
embodiment, the treatment agent utilized during acetylation can
comprise acetic anhydride in a concentration of at least about 50
weight percent, at least about 60 weight percent, at least about 70
weight percent, at least about 80 weight percent, at least about 90
weight percent, at least about 98 weight percent, or about 100
weight percent, with the balance, if any, comprising acetic acid
and/or one or more diluents or optional acetylation catalysts. In
one embodiment, the treatment agent for acetylation can comprise
mixtures of acetic acid and acetic anhydride having an
anhydride-to-acid weight ratio of at least about 80:20, at least
about 85:15, at least about 90:10, or at least about 95:5.
[0061] Prior to acetylation, the wood can be dried to reduce its
moisture (e.g., water) content to no more than about 25 weight
percent, no more than about 20 weight percent, no more than about
15 weight percent, no more than about 12 weight percent, no more
than about 9 weight percent, or no more than about 6 weight percent
using kiln drying, vacuum degassing, or other suitable methods.
During acetylation, the wood can be contacted with the treatment
agent via any suitable method. Examples of suitable contact methods
can include, but are not limited to, vapor contacting, spraying,
liquid immersion, or combinations thereof. In one embodiment, the
temperature of the treatment vessel can be no more than about
50.degree. C., no more than about 40.degree. C., or no more than
about 30.degree. C., while the pressure can be at least about 25
psig, at least about 50 psig, at least about 75 psig and/or no more
than about 500 psig, no more than about 250 psig, or no more than
about 150 psig during the time the wood is contacted with the
treatment agent.
[0062] Once the contacting step is complete, at least a portion of
the liquid treatment agent, if present, can optionally be drained
from the reactor and heat can be added to initiate and/or catalyze
the reaction. In one embodiment, microwave energy, thermal energy,
or combinations thereof can be introduced into the vessel in order
to increase the temperature of the wood to at least about
50.degree. C., at least about 65.degree. C., at least about
80.degree. C. and/or to no more than about 175.degree. C., no more
than about 150.degree. C., or no more than about 120.degree. C.,
while maintaining a pressure in the reactor of at least about 750
torr, at least about 1,000 torr, at least about 1,200 torr, or at
least about 2,000 torr and/or no more than about 7,700 torr, no
more than about 5,000 torr, no more than about 3,500 torr, or no
more than about 2,500 torr. According to one embodiment, least a
portion of the heat added to the reactor can be transferred to the
wood from a non-microwave source, such as, for example, a hot vapor
stream comprising at least about 50, at least about 75, at least
about 90, or at least about 95 weight percent acetic acid, with the
balance comprising acetic anhydride and/or diluents. In one
embodiment, the hot vapor, a portion of which can condense on at
least a portion of the bundle of wood being treated, is introduced
into the reaction vessel for at least about 20 minutes, at least
about 35 minutes or, at least about 45 minutes and/or no more than
about 180 minutes, no more than about 150 minutes, or no more than
about 120 minutes.
[0063] After the reaction step, the "chemically-wet"
chemically-modified wood can comprise at least one chemical
component capable of being removed by heat and/or vaporization. As
used throughout this application, the terms "chemically-wet" or
"chemical-wet" refers to wood containing one or more chemicals
present at least partially in a liquid phase as a result of a
chemical treatment or modification. A "chemically-wet" bundle of
wood can refer to a bundle of wood of which at least a portion is
at least partially chemically-wet. Some examples of the one or more
chemicals can include reactants, impregnants, reaction products, or
the like. For example, when wood is acetylated, at least a portion
of the residual acetic acid and/or anhydride can be removed by
vaporization. As used herein, the term "acid-wet" refers to wood
containing residual acetic acid and/or anhydride. An "acid-wet"
bundle of wood refers to a bundle of wood of which at least a
portion is at least partially acid-wet. According to one embodiment
of the present invention, the chemical-wet or acid-wet wood can
comprise at least about 20 weight percent, at least about 30 weight
percent, at least about 40 weight percent, or at least about 45
weight percent and/or no more than about 75 weight percent, no more
than about 60 weight percent, or no more than about 50 weight
percent of one or more heat-removable or vaporizable chemicals,
such as, for example, acetic acid and/or anhydride. As used herein,
the term "heat-removable" or "vaporizable" chemical component
refers to a component that can be removed by heat and/or
vaporization. In one embodiment, the vaporizable or heat-removable
component or chemical can comprise acetic acid.
[0064] At least a portion of one or more heat-removable chemicals
can then be removed via flash vaporization from the chemical-wet
wood. In one embodiment, the flash vaporization step can be
accomplished by reducing the pressure in the reactor from a
pressure of at least about 1,000 torr, at least about 1,200 torr,
at least about 1,800 torr, or at least about 2,000 torr and/or no
more than about 7,700 torr, no more than about 5,000 torr, no more
than about 3,500 torr, no more than about 2,500 torr, or no more
than about 2,000 torr to atmospheric pressure. In another
embodiment, the flash vaporization step can be accomplished by
reducing the pressure of the reactor from an elevated pressure, as
described above, or atmospheric pressure, to a pressure of no more
than about 100 torr, no more than about 75 torr, no more than about
50 torr, or no more than about 35 torr. According to one
embodiment, the amount of one or more heat-removable chemical
components (e.g., the chemical content) remaining in the
chemical-wet wood after the flash vaporization step can be at least
about 6 weight percent, at least about 8 weight percent, at least
about 10 weight percent, at least about 12 weight percent, or at
least about 15 weight percent and/or no more than about 60 weight
percent, no more than about 40 weight percent, no more than about
30 weight percent, no more than about 25 weight percent, no more
than about 20 weight percent, or no more than about 15 weight
percent.
[0065] According to one embodiment, a heating step can be carried
out subsequent to the chemical modification step to further heat
and/or dry the chemically-modified (or chemical-wet) wood to
thereby provide a heated and/or dried bundle of chemically-modified
wood. As used herein, a bundle or other article or material is
referred to as "heated" simply as a convenience to indicate that a
temperature of at least a portion of the bundle has been elevated
above ambient temperature. Similarly, as used throughout this
application, a bundle or other article or material is referred to
as "dried" simply as a convenience to indicate that at least some
heat-removable chemicals have been removed from at least a portion
of the bundle by, in some embodiments, heating. In one embodiment,
the heating step can be operable to further reduce the level of one
or more heat-removable chemical components present in the wood. The
energy source utilized during the heating step can be any source of
radiative, conductive, and/or convective energy suitable for
heating and/or drying wood. In one embodiment, the heater can be a
microwave heater employing a microwave energy. In another
embodiment, another heat source can be utilized to directly or
indirectly (via, for example, a hot gas injection, a jacketed or
heat-traced vessel, or other means) heat at least a portion of the
vessel, such as, for example, one or more side walls. In this
embodiment, the side walls can be heated to a temperature of at
least about 45.degree., at least about 55.degree. C., or at least
about 65.degree. C. and/or not more than about 115.degree. C., not
more than about 105.degree. C., or not more than about 95.degree.
C. The heating step can be carried out under any suitable
conditions, including pressures above, at, or near atmospheric
pressure. Specific embodiments of various heating systems suitable
for use in producing chemically-modified and/or thermally-modified
wood will be discussed in detail shortly.
[0066] The heating step can be carried out such that at least about
50 percent, at least about 65 percent, at least about 75 percent,
or at least about 95 percent of the total amount of the one or more
heat-removable chemical components remaining in the chemical-wet
wood is removed. In one embodiment, this can correspond to at least
about 100 pounds, at least about 250 pounds, at least about 500
pounds, or at least about 1,000 pounds of total liquid removed. As
a result of the heating step, in one embodiment, the heated or
dried chemically-modified wood can comprise no more than about 5
weight percent, no more than about 4 weight percent, no more than
about 3 weight percent, no more than about 2 weight percent, or no
more than about 1 percent, based on the initial (pre-heated) weight
of the bundle, of the one or more heat-removable chemicals (e.g.,
acetic acid). In addition, the heated or dried chemically-modified
wood can have a water content of no more than about 6 weight
percent, no more than about 5 weight percent, no more than about 3
weight percent, no more than about 2 weight percent, or no more
than about 1 weight percent, or no more than about 0.5 weight
percent based on the initial (pre-heated) weight of the wood. In
one embodiment, the wood can have a water content of approximately
0 percent subsequent to the heating step.
[0067] In one embodiment, the chemical modification step and the
heating step can take place in a single vessel. In another
embodiment, the chemical modification step and the heating step can
be carried out in separate vessels, such that the internal volumes
of the chemical modification reactor and the heater are
locationally distinct. As used herein, the "internal volume" of a
vessel refers to the entirety of the space encompassed by the
vessel, including any volume defined by or within the door or doors
of the vessel when closed. As used herein, the term "locationally
distinct" means that the internal volumes are not overlapping. When
the chemical modification reactor and heater comprise separate
vessels, various types of wood transportation systems can be
utilized in order to transport the wood between the two vessels. In
one embodiment, the transportation system can comprise rails (as
illustrated in FIG. 1), tracks, belts, hooks, rollers (as
illustrated in FIG. 3), bands, carts, motorized vehicles, fork
trucks, pulleys, turntables (as illustrated in FIG. 2), and any
combination thereof. Various embodiments of wood treatment
facilities capable of producing chemically-modified and/or
thermally-modified wood will now be discussed in detail, with
respect to FIGS. 1-3.
[0068] Referring now to FIG. 1, one embodiment of a wood treatment
facility 10 is illustrated as comprising a chemical modification
system 20, a heating system 30, a transportation system 40, and raw
and finished material storage areas 60a,b. Chemical modification
system 20 comprises a chemical modification reactor 22, a reactor
heating system 24, and an optional reactor
pressurization/depressurization system 26. Heating system 30
comprises a heater 32, an energy source 34, and an optional heater
pressurization/depressurization system 36. Transportation system 40
comprises a plurality of transport segments 42a-e for transporting
wood between storage areas 60a,b, reactor 22, and heater 32, as
described in detail below.
[0069] In operation, one or more bundles of wood can be removed
from raw material storage area 60a via transport segment 42a.
Although illustrated in FIG. 1 as comprising tracks or rails, it
should be understood that transport segment 42a can comprise any
type of transportation mechanism suitable for moving wood between
storage area 60a and reactor 22. As shown in FIG. 1, the wood can
then be introduced or loaded into reactor 22 via an open reactor
entrance door 28. Thereafter, first reactor entrance door 28 can be
closed in order to allow the wood disposed within reactor 22 to be
chemically-modified according to one or more processes described
above.
[0070] Once the reaction is complete, the chemical-wet wood can be
withdrawn from reactor 22 and be transported to heater 32.
According to one embodiment, the chemical-wet wood can be removed
from reactor 22 via reactor entrance door 28 and transported to
heater 32 via transport segment 42b. In another embodiment, the
wood can be removed via an optional reactor exit door 29 and
transported to heater 32 via transport segment 42c, as shown in
FIG. 1. The chemical-wet wood can then be introduced or loaded into
heater 32 via an open heater entrance door 38, which can then be
closed to thereby form a fluid seal between heater entrance door 38
and the body of heater 32 prior to initiating the heating of the
wood. When optional reactor and heater exit doors 29, 39, are
present, exit doors 29, 39 can be located on generally opposite
ends of reactor 22 and heater 32 than respective reactor and heater
entrance doors 28, 38.
[0071] In various embodiments, during the heating of the wood
within heater 32, pressurization system 36 can be used to maintain
a pressure within heater 32 of no more than about 550 torr, no more
than about 450 torr, no more than about 350 torr, no more than
about 250 torr, no more than about 200 torr, no more than about 150
torr, no more than about 100 torr, or no more than about 75 torr.
In one embodiment, the vacuum system can be operable to reduce the
pressure in heater 32 to no more than about 10 millitorr (10.sup.-3
torr), no more than about 5 millitorr, no more than about 2
millitorr, no more than about 1 millitorr, no more than about 0.5
millitorr, or no more than about 0.1 millitorr. In addition, when
heater 32 comprises a microwave heater, one or more features
described in detail shortly, including for example, an optional
microwave choke, one or more microwave launchers, and the like can
be used to introduce energy into the interior of heater 32, thereby
heating and/or drying at least a portion of the bundle of wood
contained therein.
[0072] According to one embodiment, the wood treatment facility 10
can comprise multiple reactors and/or heaters. Any number of
reactors and/or heaters can be employed, and the reactors and/or
heaters can be arranged in any suitable configuration. For example,
wood treatment facility 10 can utilize at least 1, at least 2, at
least 3, at least 5 and/or no more than 10, no more than 8, or no
more than 6 reactors and/or heaters. When multiple reactors and/or
heaters are employed, the vessels can be paired in any suitable
combination or ratio. For example, the ratio of reactors to heaters
can be 1:1, 1:2, 2:1, 1:3, 3:1, 2:3, 3:2, 1:4, 4:1, 4:2, 2:4, 3:4,
4:3 or any feasible combination. According to one embodiment, one
or more of reactors and/or heaters can comprise separate entrance
and exit doors, while, in another embodiment, one or more of the
reactors and/or heaters can comprise a single door for loading and
unloading wood. In one embodiment, the heated and/or dried wood can
be removed from heater 34 via heater entrance door 38, and
transported to storage area 60b via transport segment 42d.
Alternatively, the wood can be withdrawn via an optional heater
exit door 39, if present, and transported via segment 42e to
storage area 60b, as illustrated in FIG. 1. Various configurations
of wood treatment facilities employing multiple reactors and
heaters configured according to several embodiments of the present
invention will be described briefly with respect to FIGS. 2 and
3.
[0073] Turning now to FIG. 2, a wood treatment facility 110
configured according to one embodiment of the present invention is
illustrated. Wood treatment facility 110 comprises a plurality of
reactors illustrated as 122a, 122b, 122n and plurality of heaters
illustrated as 132a, 132b, 132n. According to one embodiment, each
of the reactors 122a, 122b, 122n and each of the heaters 132a,
132b, 132n comprise a single door 128a, 128b, 128n, 138a, 138b,
138n, for selectively permitting the passage of wood into and out
of each vessel. In addition, wood treatment facility 110 can
comprise a rotatable platform (illustrated as a turntable 140)
operable to position a bundle of wood 102 such that it can be
transported between reactors 122a, 122b, 122n, heaters 132, 132b,
132n, and a storage area 160, in various directions generally
indicated by arrows 190a-c.
[0074] Referring now to FIG. 3, another embodiment of a wood
treatment facility 210 is shown as comprising a plurality of
chemical modification reactors illustrated as 222a, 222n and a
plurality of heaters illustrated as 232a, 232b, 232n. As shown in
FIG. 3, each of the reactors comprises a respective reactor
entrance door 228a, 228n and an optional reactor exit door 229a,
229n. Similarly, each of the heaters 232a, 232b, 232n comprises a
heater entrance door 238a, 238b, 238n and an optional heater exit
door 239a, 239b, 239n. Transportation system 240 shown in FIG. 3
comprises a plurality of segments 242a-j and 244a-e operable to
transport wood to, from, and between reactors 222a, 222n and
heaters 232a, 232b, 232n. Although illustrated as comprising
continuous belt segments, transportation system 240 can comprise
one or more segments comprising any suitable transportation
mechanism, as discussed in detail previously.
[0075] According to one embodiment, in operation, wood loaded into
first reactor 222a via transport segment 242a can be introduced
through reactor entrance door 228a. Once the chemical modification
process is complete, chemical-wet wood can be removed from reactor
222a via reactor entrance door 228a and can subsequently be
transported to one of heaters 232a, 232b, or 232n via respective
transport segments 242e, 242f, 242g. In an alternative embodiment,
wood removed from reactor 222a can be removed through reactor exit
door 229a via transport segment 244a prior to being transported to
heater 232a, 232b, or 232n as described previously. In addition,
wood treated in reactor 222n can be loaded, chemically-modified,
and transported to one of heaters 232a, 232b, 232n, in a similar
manner as previously described.
[0076] Thereafter, the bundle or bundles of chemically-wet wood
transported to heaters 232a, 232b, and 232n can be heated and/or
dried according to one or more methods described herein. In one
embodiment, at least one of heaters 232a, 232b, and 232n can
comprise a microwave heater. Once the heating step is completed,
heated and/or dried bundles can be withdrawn from heaters 232a,
232b, and 232n via respective entrance doors 238a, 238b, 238n, or,
optionally, from respective exit doors 239a, 239b, 239n, when
present. Subsequently, the modified bundles can be transported to
subsequent processing and/or or storage via transport segments
242h,i,j or 244c,d,e, depending on whether the bundles were removed
from heater entrance doors 238a, 238b, 238n or heater exit doors
239a, 239b, 239n.
[0077] The chemical modification process previously discussed can
be carried out at any suitable scale. For example, the
above-described wood treatment facilities can comprise lab-scale,
pilot plant-scale, or commercial-scale wood treatment facilities.
In one embodiment, the wood treatment facility used to produce
chemically-modified and/or thermally-modified wood can be a
commercial-scale facility having an annual production capacity of
at least about 500,000 board feet, at least about 1 million board
feet, at least about 2.5 million board feet, or at least about 5
million board feet. As used herein, the term "board feet" refers to
a volume of wood expressed in units measuring 144 cubic inches. For
example, a board having dimensions of 2 inches by 4 inches by 36
inches has a total volume of 288 cubic inches, or 2 board feet. In
various embodiments, the internal volume of a single chemical
modification reactor (i.e., the "internal reactor volume") and/or
the internal volume of a single heater (i.e., the "internal heater
volume") can be at least about 100 cubic feet, at least about 500
cubic feet, at least about 1,000 cubic feet, at least about 2,500
cubic feet, at least about 5,000 cubic feet, or at least about
10,000 cubic feet in order to accommodate commercial-scale
operation.
[0078] Even when carried out on a commercial scale, chemical and/or
thermal modification processes as described herein can be carried
out with relatively short overall cycle times. For example,
according to one embodiment, the total cycle time of the chemical
and/or thermal modification processes carried out using one or more
systems of the present invention, measured from the time the
modification step is initiated to the time the heating step is
completed, can be no more than about 48 hours, no more than about
36 hours, no more than about 24 hours, or no more than about 12
hours, no more than about 10 hours, no more than about 8 hours, or
no more than about 6 hours. This is in contrast to many
conventional wood treatment processes, which can have overall cycle
times that last several days or even weeks.
[0079] In accordance with one embodiment of the present invention,
wood treatment facilities of the present invention can comprise one
or more vapor containment rooms and/or ventilation structures for
substantially isolating the external environment (i.e., the
environment immediately outside the chemical modification reactor
and the heater) from the chemically-wet chemically-modified wood
during transport of the wood. The vapor containment rooms and/or
ventilation structures can be connected to a ventilation system
that removes at least a portion of the gaseous environment out of
the containment/ventilation area, thereby minimizing leakage one or
more undesirable vapor-phase chemicals into the external
environment. Additional details and one embodiment of a wood
treatment facility employing vapor containment rooms and/or
ventilation structures will now be described in greater detail with
respect to FIGS. 4a-d.
[0080] FIG. 4a is a top view of a vapor containment room 360
coupled to a chemical modification reactor 322 and a heater 332.
Vapor containment room 360 can be operable to partially, or almost
completely, isolate the external environment from a
chemically-modified bundle of wood as the wood is transported from
chemical modification reactor 322 to heater 332 via a transfer
region 361 located between reactor 322 and heater 332. As used
herein, the term "isolate" refers to the inhibition of fluid
communication between one or more areas, zones, or regions.
According to one embodiment, vapor containment room 360 can be
coupled to a ventilation system (not shown in FIG. 4a) operable to
remove at least a portion of the vapor and gases from the interior
of vapor containment room 360, thereby reducing, minimizing, or
preventing leakage of one or more heat-removable chemical
components contained within the interior of reactor 322, within the
interior of heater 332, and/or from the chemically-modified bundle
of wood to the external environment.
[0081] In one embodiment, chemical modification reactor 322 can
comprise a reactor entrance door 328 for receiving a bundle of wood
from an external environment and a reactor exit door 329 for
discharging the bundle of wood from chemical modification reactor
322 after chemical modification. In addition, heater 332 can
comprise a heater entrance door 328 for receiving the bundle of
chemically-modified, chemical-wet wood discharged from chemical
modification reactor 322. According to one embodiment, heater 332
can also include a heater exit door 339 separate from heater
entrance door 338 for discharging a bundle of wood from heater 332.
In one embodiment, respective reactor and heater entrance doors
328, 338 and reactor or heater exit doors 329, 339, when present,
can be positioned on a generally opposite end of reactor 322 or
heater 332 such that the respective central axes of elongation of
reactor 322 and heater 332, represented as axes 370a,b in FIG. 4b,
can extend through respective entrance 328, 338 and exit 329, 339
doors. In one embodiment, reactor 322 and heater 332 are axially
aligned with one another such that the central axes of elongation
370a,b in FIG. 4b, are substantially aligned with one another,
while, in other one embodiment, axes 370a,b can be parallel to each
other. As used herein, the term "substantially aligned" refers to
two or more vessels configured such that the maximum acute angle
formed between the intersection of their respective central axes of
elongation is not more than about 20.degree.. In some embodiments,
the maximum acute angle between the intersection of the two axes of
elongation of substantially aligned vessels can be not more than
about 10.degree., not more than about 5.degree., not more than
about 2.degree., or not more than about 1.degree.. In some
embodiments, reactor 322 and heater 332 can be arranged in a
side-by-side configuration (not shown).
[0082] According to one embodiment shown in FIG. 4a, vapor
containment room 360 can be sealingly coupled to reactor 322 and
heater 332 such that the external environment is substantially
isolated from transfer region 361 during transport of the bundle of
wood from reactor 322 to heater 332. As used herein, the term
"sealingly coupled" refers to two or more objects attached,
fastened, or otherwise associated such that leakage of fluid is
substantially reduced or nearly prevented from the junction of such
objects. In one embodiment, reactor entrance door 328 and/or heater
exit door 339, when present, can open to the external environment,
while reactor exit door 329 and/or heater entrance door 338 can
open to the interior of vapor containment room 360, thereby
isolating the external environment from vapor or gases from
chemical reactor 322, heater 332, and/or the bundle of chemical-wet
wood during transport between reactor 322 and heater 332 via
transfer region 361.
[0083] Vapor containment room 360 can be configured in any manner
suitable manner. In one embodiment depicted in FIGS. 4a and 4b,
vapor containment room 360 comprises four generally upright walls
342a-d coupled to a ceiling structure 344 and a floor (not shown).
Although illustrated in FIGS. 4a and 4b as being generally attached
to ceiling structure 344, a vapor outlet conduit 349 for removing
vapors and gases from the interior of vapor containment room 360
could alternatively be attached to one of walls 342a-d or to the
floor. Additional details regarding the removal of vapors and gases
from vapor containment room 360 will be described in more detail
shortly.
[0084] In one embodiment of the present invention, at least one of
walls 342a-d can comprise at least one blast panel or blast wall
343 for controlling the direction of a pressure release in the
event of an explosion or rapid pressurization within vapor
containment room 360. In one embodiment, blast panel 343 can be
attached to the ceiling 344 and/or floor (not shown) of vapor
containment room 360. Blast panel or wall 343 can be hinged,
tethered, or otherwise fastened to another structure of vapor
containment room 360 in order to prevent or reduce the likelihood
that blast panel or wall 343 will be freely projected at an
undesirable velocity away from vapor containment room 360 by an
explosion. Blast panel or wall 343 can have a substantially solid
surface, as shown in FIG. 4b, or can comprise a plurality of slats
or slots (not shown). Typically, the sections of walls 342a-d that
are not blast panels/walls 343 are construction of a high-strength
materials such as, for example, precast concrete panels, concrete
blocks, or steel panels. Although illustrated herein as having four
walls, it should be understood that vapor containment rooms having
various other shapes can also be employed.
[0085] As depicted in FIG. 4c, vapor containment room 360 can be
equipped with one or more vents 370a,b for selectively permitting
fluid flow from the external environment into the interior of vapor
containment room 360. In one embodiment, vents 370a,b are one-way
vents that permit fluid flow from the external environment into
vapor containment room 360, as indicated by arrows 380a,b in FIG.
4c, but reduce, inhibit, or substantially prevent fluid flow from
the interior of vapor containment room 360 out into the external
environment. Examples of external fluids that can flow into vapor
containment room 360 via vents 370a,b include ambient air or one or
more inert gases such as nitrogen.
[0086] In one embodiment, vents 370a,b, can be configured to
maintain a predetermined pressure difference between the interior
of vapor containment room 360 and the external environment. By
maintaining a predetermined pressure difference between the
interior of vapor containment room 360 and the external
environment, vents 370a,b can control the rate at which a fluid
from the external environment is drawn into vapor containment room
360. To maintain a relatively constant pressure difference between
the interior of vapor containment room 360 and the external
environment, vents 370a,b can be equipped with a control mechanism
(e.g., an electronic actuator, a hydraulic actuator, a pneumatic
actuator, or a mechanical spring) for varying the degree of
openness of vents 370a,b based on the pressure difference across
vents 370a,b. When the pressure difference between the external
environment and the interior of the vapor containment room 360 is
too high, vents 370a,b open wider, and, analogously, when the
pressure difference is too low, vents 370a,b move towards a closed
position. In one embodiment, vents 370a,b, can be spring loaded and
biased towards the closed position, so that when the pressure
difference between the vapor containment room 360 and the external
environment is below a threshold value, vents 370a,b are closed,
but when the pressure in vapor containment room 360 is lower than
the pressure of the external environment by an amount exceeding the
threshold pressure difference value, vents 370a,b open to allow an
external fluid to be drawn into vapor containment room 360.
[0087] Further, when vents 370a,b are spring loaded, the vents help
maintain a substantially constant pressure difference between the
interior of vapor containment room 360 and the external environment
by automatically opening wider when the pressure difference is high
and automatically moving towards the closed position when the
pressure difference is low. In one embodiment, vapor containment
room 360 is maintained at a sub-atmospheric pressure during
transport and can be maintained at a vacuum of at least about 0.05
inches of water, at least about 0.1 inches of water, or at least
about 0.15 inches of water and/or no more than about 10 inches of
water, no more than about 1 inch of water, or no more than about
0.5 inches of water. In one embodiment, vents 370a,b, are
configured to permit fluid from the external environment (e.g.,
ambient air) to be drawn into vapor containment room 360 at a rate
that causes at least about 2, at least about 4, or at least about 5
exchanges per hour to be drawn out of vapor containment room 360,
where one exchange is equal to one volume of vapor containment room
360. As used herein, the term "exchanges per hour" refers to the
total number of times per hour that the total volume of fluid in
the system is replaced, calculated by dividing the volumetric flow
rate of vapor removed from the system by the total system
volume.
[0088] In one embodiment, the size of vapor containment room 360
can be such that the reactor and heater 322, 332 (e.g., positioning
the internal volumes of the reactor and heater) are spaced apart
from each other by a distance that is at least about 2 feet, at
least about 4 feet, or at least about 6 feet and/or no more than
about 50 feet, no more than about 30 feet, or no more than about 20
feet. In one embodiment, the length of the vapor containment room
can be the same as, or substantially the same as, the distance
between reactor 322 and heater 332. According to one embodiment,
the ratio of the length of vapor containment room 360 to the total
length of reactor 322 and/or the total length of heater 332 can be
at least about 0.1:1, at least about 0.2:1, or at least about 0.3:1
and/or no more than about 1:1, no more than about 0.6:1, or no more
than about 0.5:1. When the space between reactor 322 and heater 332
is minimized, reactor exit door 329 and heater entrance door 338
may be capable of contacting one another during opening. In such an
embodiment, reactor exit door 329 and heater entrance door 338 can
be configured to nest/overlap with one another (but not contact one
another) when they are both fully opened.
[0089] FIG. 4d is a side view of a wood treatment facility 416
comprising a reactor 322, a heater 332, and a vapor containment
room 360 disposed therebetween. FIG. 4d additionally depicts an
embodiment that employs a product vapor removal system or structure
400 located near exit door 339 of heater 332. Product vapor removal
system 400 can be configured to transport vapors out of and away
from the area near exit door 339 of heater 332 (e.g. the recovery
room). This configuration can substantially reduce and, in some
embodiments can nearly prevent escape of vapors from the
chemically-treated bundle of wood exiting heater 332 and/or from
vapors exiting reactor 322 and/or heater 332 to the external
environment. As shown in FIG. 4d, both vapor containment room 360
and product vapor removal system 400 can be connected or otherwise
operably coupled to a common ventilation system 402. Ventilation
system 402 is used to draw vapors and gases out of vapor
containment room 360 and/or through product vapor removal system
400. Although FIG. 4d illustrates one common ventilation system 402
being used for both vapor containment room 360 and product vapor
removal system 400, it is possible to use individual ventilation
systems for each containment/ventilation area of the wood treatment
facility.
[0090] In the embodiment depicted in FIG. 4d, product vapor removal
system 400 comprises a ventilation hood 404 and a ventilation room
406 disposed between ventilation hood 404 and heater 332.
Ventilation hood 404 and ventilation room 406 can be connected to
ventilation system 402, which draws vapor out of ventilation hood
404 and/or ventilation room 406. Ventilation room 406 can be
configured to receive a bundle of chemically-modified wood through
heater exit door 339, which opens into ventilation room 406.
[0091] Ventilation room 406 can be equipped with a ventilation room
exit 408 through which the chemically-modified wood passes to a
cooling location below ventilation hood 404. In one embodiment,
ventilation room exit 408 can be equipped with a door 409 that,
when closed, substantially isolates the external environment from
the interior of ventilation room 406. When ventilation room is
equipped with such a door, ventilation room may also be equipped
with vents (not shown) similar to vents 370a,b of vapor containment
room 360, described previously with reference to FIG. 4c. However,
in another embodiment, ventilation room exit 408 is configured to
constantly permit passage of fluid from the external environment
into the interior of ventilation room 406. In such an embodiment,
ventilation room exit 408 can be entirely open so as to permit free
flow of fluid therethrough. Alternatively, ventilation room exit
408 can be partially covered with a flexible material (e.g., a
hanging VISQUEEN sheet or strips of VISQUEEN) that permits passage
of the bundle of chemically-treated wood therethrough, but that at
least partially inhibits free flow of fluid therethrough. In one
embodiment of the present invention, ventilation room 406 can be
entirely eliminated and ventilation hood 404 can be positioned
adjacent exit door 339 of heater 332.
[0092] As shown in FIG. 4d, ventilation system 402 can include one
or more vacuum generators 410, a treatment device 412, a flow
diverter 414, and a plurality of vapor outlet conduits 349a-c.
Vacuum generator 410 can be operable to draw vapor out of vapor
containment room 360, ventilation hood 404, and/or ventilation room
406 via outlet conduits 349a,b,c, respectively. Treatment device
412 can be operable to remove or to change the composition of at
least a portion of one or more components from the vapors drawn out
of vapor containment room 360, ventilation hood 404, and/or
ventilation room 406 via vacuum generator 410. Examples of suitable
treatment devices can include, but are not limited to, scrubbers,
thermal oxidizers, catalytic oxidizers or other catalytic
processes, and/or precipitators.
[0093] According to one embodiment, flow diverter 414 can be
operable adjust the total ventilation capacity of vacuum generator
410 by, for example, directing the vapor flow amongst vapor outlet
conduits 349a,b,c thereby distributing the total ventilation
capacity of ventilation system 402 between vapor containment room
360, and product vapor removal structure (e.g., ventilation hood
404, and/or ventilation room 406). As used herein, the term "total
ventilation capacity" refers to the maximum volume of vapors
removable from the system via a vacuum generator or other source,
expressed as a time-based rate. Distribution of the total
ventilation capacity amongst vapor containment room 360,
ventilation hood 404, and/or ventilation room 406 may be
advantageous, for example, to accommodate the various steps of a
chemical modification treatment. In one embodiment, flow diverter
414 can be operable to evenly distribute the total ventilation
capacity, represented generically as "X", such that 1/3X is
provided to vapor containment room 360, 1/3X is provided to
ventilation hood 404, and 1/3X is provided to ventilation room 406.
In another exemplary embodiment, flow diverter 414 can allocate
more ventilation capacity to one of the three areas, such as, for
example vapor containment room 360, so that 2/3X is provided to
vapor containment room 360, 1/6X is provided to ventilation hood
404, and 1/6X is provided to ventilation room 406.
[0094] One embodiment of the operation of wood treatment facility
416 will now be described in detail, with respect to FIG. 4d. A
first bundle of wood, represented herein by the letter "C," can be
loaded into chemical modification reactor 322 via reactor entrance
door 328 and chemically treated. Simultaneously, a second bundle of
wood, represented here by the letter "B," can be introduced into
heater 332 via heater entrance door 338 and heated and/or dried.
While bundles C and B are being chemically-modified and
heated/dried in chemical modification reactor 322 and heater 332,
respectively, a third bundle of wood, represented herein with the
letter "A", can be removed from ventilation room 406 and positioned
under ventilation hood 404, as generally shown in FIG. 4d.
[0095] Once bundle A has been sufficiently dried, it can be removed
from ventilation hood 404 and transported to a storage area (not
shown). Then, the allocation of the total ventilation capacity of
ventilation system 402 can be adjusted using flow diverter 414 such
that amount of ventilation capacity allocated to vapor containment
room 360 is increased, while the amount of ventilation capacity
allocated to ventilation hood 404 is decreased. Next, after
completion of the heating of bundle "B", heater entrance and exit
doors 338, 339 can be opened consecutively and any residual vapor
or gas present in the interior of heater 332 can be removed and
passed through vapor containment room 360 before entering
ventilation system 402. In one embodiment, this evacuation of
heater 332 can also comprise drawing an external fluid (e.g.,
ambient air or other inert gas) into the system through ventilation
hood 404 and ventilation room 406, when present. The external fluid
can then enter heater 332 via heater exit door 339 and pass through
the interior of heater 332, before exiting heater 332 via heater
entrance door 338 and passing into vapor containment room 360. Once
in vapor containment room 360, the external fluid, along with any
residual vapor or gas removed from the interior of heater 332, can
be withdrawn from vapor containment room 360 by way of ventilation
system 402 at a rate of at least about 2 exchanges per hour, at
least about 4 exchanges per hour, or at least about 6 exchanges per
hour. For example, if the ventilation system had a total volume of
100 cubic meters and the rate of vapor removal was 200 cubic meters
per hour, the exchanges per hour would be (200 cubic meters per
hour)/(100 cubic meters) or 2 exchanges per hour.
[0096] Once the external fluid and residual vapor/gas has been
removed from vapor containment room 360, bundle B can be removed
from heater 332 via heater exit door 339, passed through
ventilation room 406 (if present), and positioned under ventilation
hood 404 to cool and/or further dry bundle B, as discussed in
detail previously. Heater exit door 339 can then be closed before
reactor exit door 329 and reactor entrance door 328 are
sequentially opened. Thereafter, ventilation system 402 can be used
to evacuate residual vapor or gas from the interior of chemical
modification reactor 322. In one embodiment, an external fluid
(e.g., ambient air or other inert gas) can be drawn into reactor
322 via reactor entrance door 328 and pass through the interior of
reactor 322 before exiting into vapor containment room 360 via
reactor exit door 329. As described above, the external fluid and
any residual vapors or gases can then be withdrawn from vapor
containment room 360 via vapor outlet conduit 349a at a rate of at
least about 2 exchanges per hour, at least about 4 exchanges per
hour, or at least about 6 exchanges per hour.
[0097] Thereafter, bundle C can be removed from chemical
modification reactor 322 via reactor exit door 329 and passed
through vapor containment room 360 along a transport path 399. In
one embodiment, product ventilation system 402 can be used to draw
gases and vapors from vapor containment room 360 during the
transportation of the bundle between reactor 322 and heater 332.
Chemically-wet bundle C can then be introduced into the interior of
heater 332 via heater entrance door 338, prior to initiating
heating of bundle C. Next, a fourth bundle (not shown) can be
loaded into the interior of chemical modification reactor 322
before closing, in sequence, reactor entrance door 328, reactor
exit door 329, and heater entrance door 338. The allocation of
total ventilation capacity to vapor containment room 360 can be
decreased, while increasing the allocation to ventilation hood 404,
to thereby cool and/or further dry bundle B. A fifth bundle (not
shown) can be assembled, either in a loading area (not shown) or
near reactor entrance door 328 before repeating the
above-referenced steps to process a new sequence of wood
bundles.
[0098] It should be understood that, in the above-described
operational sequence, some steps can preferably be carried out in
the order described, while some steps can be carried out
simultaneously and/or the order of some steps can be switched. The
above sequence of steps is included simply to describe one
exemplary method of operating wood treatment system 416.
Microwave Heating Systems
[0099] According to one embodiment, one or more of the heating
systems described above can comprise microwave heating systems that
utilize microwave energy to heat one or more objects or items. In
addition to one embodiment of the wood treatment facilities
described above, microwave heating systems configured according to
one embodiment of the present invention have wide applicability to
a variety of other processes. It should be understood that, while
predominantly described herein with respect to processes for
heating "wood" or a "bundle of wood," the processes and systems
described herein are equally applicable to applications wherein one
or more articles, objects, or loads are heated. Examples of other
types of application that can utilize microwave heating systems as
described herein can include, but are not limited to, high
temperature vacuum ceramic and metal sintering, melting, brazing,
and heat treating of various materials. In one embodiment, the
microwave heating system can include a vacuum system (e.g., a
microwave vacuum heater) and can be utilized for vacuum drying of
materials such as minerals and semiconductors, vacuum drying of
foodstuffs such as fruits and vegetables, vacuum drying of ceramic
and fibrous molds, as well as vacuum drying of chemical
solutions.
[0100] Turning now to FIG. 5, a microwave heating system 420
configured according to one embodiment of the present invention is
illustrated as comprising at least one microwave generator 422, a
microwave heater 430, a microwave distribution system 440, and an
optional vacuum system 450. Microwave energy produced by microwave
generator 422 can be directed to microwave heater 430 via one or
more components of microwave distribution system 440. Additional
details regarding components and operation of microwave
distribution system 440 will be discussed in detail shortly. When
present, vacuum system 450 can be operable to reduce the pressure
in microwave heater 430 to no more than about 550 torr, no more
than about 450 torr, no more than about 350 torr, no more than
about 250 torr, no more than about 200 torr, no more than about 150
torr, no more than about 100 torr, or no more than about 75 torr.
In one embodiment, the vacuum system can be operable to reduce the
pressure in microwave heater 430 to no more than about 10 millitorr
(10.sup.-3 torr), no more than about 5 millitorr, no more than
about 2 millitorr, no more than about 1 millitorr, no more than
about 0.5 millitorr, or no more than about 0.1 millitorr. Each of
the components of microwave heating system 420 will now be
discussed in detail below.
[0101] Microwave generator 422 can be any device capable of
producing or generating microwave energy. As used herein, the term
"microwave energy" refers to electromagnetic energy having a
frequency between 300 MHz and 30 GHz. As used herein the term
"between" used in a range is intended to include the recited
endpoints. For example, a number "between x and y" can be x, y, or
any value from x to y. In one embodiment, various configurations of
microwave heating system 420 can utilize microwave energy having a
frequency of about 915 MHz or a frequency of about 2.45 GHz, both
of which have been generally designated as industrial microwave
frequencies. Examples of suitable types of microwave generators can
include, but are not limited to, magnetrons, klystrons, traveling
wave tubes, and gyrotrons. In various embodiments, one or more
microwave generators 422 can be capable of delivering (e.g., have a
maximum output of) at least about 5 kW, at least about 30 kW, at
least about 50 kW, at least about 60 kW, at least about 65 kW, at
least about 75 kW, at least about 100 kW, at least about 150 kW, at
least about 200 kW, at least about 250 kW, at least about 350 kW,
at least about 400 kW, at least about 500 kW, at least about 600
kW, at least about 750 kW, or at least about 1,000 kW and/or not
more than about 2,500 kW, not more than about 1,500 kW, or not more
than about 1,000 kW. Although illustrated as comprising one
microwave generator 422, microwave heating system 420 can comprise
two or more microwave generators configured to operate in a similar
manner.
[0102] Microwave heater 430 can be any device capable of receiving
and heating one or more articles, including, for example, bundles
of wood or lumber, using microwave energy. In one embodiment, at
least about 75 percent, at least about 85 percent, at least about
95 percent, or substantially all of the heat or energy provided by
microwave heater 430 can be provided by microwave energy. Microwave
heater 430 can also be used as a microwave dryer, which can be
further operable to dry one or more items disposed therein using
microwave energy as described herein.
[0103] Turning now to FIG. 6, one embodiment of a microwave heater
530 is illustrated as comprising a vessel body 532 and a door 534
for selectively permitting and blocking the access to or passage of
one or more objects (not shown) into and out of the interior 536 of
microwave heater 530. In one embodiment, vessel body 532 of
microwave heater 530 can be elongated along a central axis of
elongation 535, which can be oriented in a substantially horizontal
direction, as illustrated in FIG. 6. Vessel body 532 can have a
cross-section of any suitable shape or size. In one embodiment, the
cross-section of vessel 532 can be substantially circular or round,
while, in another embodiment, the cross-section can be elliptical.
According to one embodiment, the size and/or shape of the
cross-section of vessel body 532 can change along the direction of
elongation, while, in another embodiment, the shape and/or size of
its cross-section can remain substantially the same. In the
embodiment depicted in FIG. 6, vessel body 532 of microwave heater
530 comprises a horizontally elongated, cylindrical vessel body
having a circular cross-section.
[0104] Microwave heater 530 can have an overall maximum internal
dimension or length, L, and a maximum inner diameter, D, as shown
in FIG. 6. In one embodiment, L can be at least about 8 feet, at
least about 10 feet, at least about 16 feet, at least about 20
feet, at least about 30 feet, at least about 50 feet, at least
about 75 feet, at least about 100 feet and/or no more than about
500 feet, no more than about 350 feet, no more than about 250 feet.
In another embodiment, D can be at least about 3 feet, at least
about 5 feet, at least about 10 feet, at least about 12 feet, at
least about 18 feet, at least about 20 feet, at least about 25
feet, or at least about 30 feet and/or no more than about 25 feet,
no more than about 20 feet, or no more than about 15 feet. In one
embodiment, the ratio (L:D) of the length of microwave heater 530
to its inner diameter (L:D) can be at least about 1:1, at least
about 2:1, at least about 3:1, at least about 4:1, at least about
6:1, at least about 8:1, at least about 10:1 and/or no more than
about 50:1, no more than about 40:1, or no more than about
25:1.
[0105] Microwave heater 530 can be constructed out of any suitable
material. In one embodiment, microwave heater 530 can comprise at
least one electrically conductive and/or highly reflective
material. Examples of suitable materials can include, but are not
limited to, selected carbon steels, stainless steels, nickel
alloys, aluminum alloys, and copper alloys. Microwave heater 530
can be almost completely constructed out of a single material, or
multiple materials can be used to construct various portions of
microwave heater 530. For example, in one embodiment, microwave
heater 530 can be constructed of a first material and can then be
coated or layered with a second material on at least a portion of
its interior and/or exterior surface. In one embodiment, the
coating or layer can comprise one or more of the metals or alloys
listed above, while, in another embodiment, the coating or layer
can comprise glass, polymer, or other dielectric material.
[0106] Microwave heater 530 can define one or more spaces suitable
for receiving a load. For example, in one embodiment, microwave
heater 530 can define a bundle-receiving space configured to
receive and hold one or more bundles of wood (not shown in FIG. 6).
The load (e.g., wood) can be positioned within interior 536 of
microwave heater 530 in a static or dynamic manner. For example, in
one embodiment wherein the load is statically positioned in
microwave heater 530, the load can be relatively motionless during
heating and may be held in place using static positioning devices
(not shown) such as, for example, a shelf, a platform, a parked
cart, a stopped belt, or the like. In another embodiment wherein
the load is dynamically positioned within microwave heater 530, the
load can be in motion during at least a portion of heating using
one or more dynamic positioning devices (not shown) during heating.
Examples of dynamic positioning devices can include, but are not
limited to, continuous moving belts, rollers, horizontally and/or
vertically oscillating platforms, and rotating platforms. In one
embodiment, one or more dynamic positioning devices may be used in
a generally continuous process, while one or more static
positioning devices may be employed in a batch or semi-batch
process.
[0107] According to one embodiment of the present invention,
microwave heater 530 can also comprise one or more sealing
mechanisms to reduce, inhibit, minimize, or substantially prevent
the leakage of fluids and/or microwave energy into or out of the
vessel interior 536 during treatment. As illustrated in FIG. 6,
vessel body 532 and door 534 can each present respective body-side
and door-side sealing surfaces 531, 533. In one embodiment,
body-side and door-side sealing surfaces 531, 533 can directly or
indirectly form a fluid seal between door 534 and vessel body 532
when door 534 is closed. A direct seal can be formed when at least
a portion of body-side and door-side sealing surfaces 531, 533 make
direct physical contact with one another. An indirect seal can be
formed between door 534 and vessel body 532 when one or more
resilient sealing members for fluidly isolating the interior of
microwave heater 530 from an external environment (not shown in
FIG. 6) are at least partially compressed against door-side and/or
body-side sealing surfaces 533, 531 when door 534 is closed.
Examples of resilient sealing members can include, but are not
limited to, o-rings, spiral wound gaskets, sheet gaskets, and the
like. According to one embodiment, the direct or indirect seal
formed between vessel body 532 and door 534 can be such that
microwave heater 530 can have a fluid leak rate of no more than
about 10.sup.-2 torr liters/sec, no more than about 10.sup.-4 torr
liters/sec, or no more than about 10.sup.-8 torr liters/sec at or
near the junction of body 532 and door 534, when subjected to a
helium leak test conducted according to procedure B1 entitled
"Spraying Testing" described in the document entitled "Helium Leak
Detection Techniques" published by Alcatel Vacuum Technology using
a Varian Model No. 938-41 detector. In one embodiment, fluid seal
can be particularly useful when the environment inside microwave
heater 530 comprises a sub-atmospheric and otherwise challenging
process environment.
[0108] Microwave heaters configured according to one embodiment of
the present invention can also comprise a microwave choke for
inhibiting or substantially preventing microwave energy leakage
between door 534 and vessel body 532 of microwave heater 530 when
door 534 is closed (e.g., at or near the junction of door 534 and
vessel body 532). As used herein, the term "choke" refers to any
device or component of a microwave vessel operable to reduce the
amount of energy leaking from or escaping the vessel during the
application of microwave energy. In one embodiment, the choke can
be any device operable to reduce the amount of microwave leakage
from the vessel by at least about 25 percent, at least about 50
percent, at least about 75 percent, or at least about 90 percent as
compared to when a choke is not employed. In one embodiment of the
present invention, the microwave choke can be operable to allow no
more than about 50 milliwatts per square centimeter (mW/cm.sup.2),
no more than about 25 mW/cm.sup.2, no more than about 10
mW/cm.sup.2, no more than about 5 mW/cm.sup.2, or no more than
about 2 mW/cm.sup.2 of microwave energy to leak out of the heater
through the choke when measured 5 cm from the vessel with a Narda
Microline Model 8300 broad band isotropic radiation monitor (300
MHz to 18 GHz).
[0109] Further, in contrast to conventional microwave chokes, which
often fail when subjected to sub-atmospheric pressures, microwave
chokes configured according to one embodiment of the present
invention can be operable to substantially inhibit microwave energy
leakage, even under deep vacuum conditions. For example, in one
embodiment, a microwave choke as described herein can inhibit
microwave energy leakage from the heater to the extent described
above when the pressure in the microwave heater is no more than
about 550 torr, no more than about 450 torr, no more than about 350
torr, no more than about 250 torr, no more than about 200 torr, no
more than about 100 torr, or no more than about 75 torr. In one
embodiment, a microwave choke as described herein can inhibit
microwave energy leakage from the heater to the extent as described
above when the pressure in the microwave heater is no more than
about 10 millitorr (10.sup.-3 torr), no more than about 5
millitorr, no more than about 2 millitorr, no more than about 1
millitorr, no more than about 0.5 millitorr, or no more than about
0.1 millitorr. Further, a microwave choke according to one
embodiment of the present invention can maintain its level of
leakage prevention on large-scale units, such as, for example,
microwave heaters having a microwave energy input rate of at least
about 5 kW, at least about 30 kW, at least about 50 kW, at least
about 60 kW, at least about 65 kW, at least about 75 kW, at least
about 100 kW, at least about 150 kW, at least about 200 kW, at
least about 250 kW, at least about 350 kW, at least about 400 kW,
at least about 500 kW, at least about 600 kW, at least about 750
kW, or at least about 1,000 kW and/or not more than about 2,500 kW,
not more than about 1,500 kW, or not more than about 1,000 kW.
[0110] In one embodiment, substantially no arcing can occur near
the choke 650 while microwave energy is introduced into the vessel
(e.g., during the heating step), even at the levels of microwave
energy and vacuum pressure described above. As used herein, the
term "arcing", refers to undesired, uncontrolled electrical
discharge, at least partially caused by ionization of a surrounding
fluid. Arcing, which can damage equipment and materials and poses a
substantial fire or explosion hazard, has a lower threshold at
lower pressures, especially sub-atmospheric (e.g., vacuum)
pressures. Typically, conventional systems limit rate of energy
input in order to minimize or avoid arcing. In contrast to
conventional systems, however, microwave heaters configured
according to embodiments of the present invention can be operable
to receive microwave energy at a rate of at least about 5 kW, at
least about 30 kW, at least about 50 kW, at least about 60 kW, at
least about 65 kW, at least about 75 kW, at least about 100 kW, at
least about 150 kW, at least about 200 kW, at least about 250 kW,
at least about 350 kW, at least about 400 kW, at least about 500
kW, at least about 600 kW, at least about 750 kW, or at least about
1,000 kW and/or not more than about 2,500 kW, not more than about
1,500 kW, or not more than about 1,000 kW can be introduced into a
microwave heater (optionally referred to as a vacuum microwave
heater or a vacuum microwave dryer) when the pressure is no more
than about 550 torr, no more than about 450 torr, no more than
about 350 torr, no more than about 250 torr, no more than about 200
torr, no more than about 100 torr, no more than about 75 torr, no
more than about 10 millitorr (10.sup.-3 torr), no more than about 5
millitorr, no more than about 2 millitorr, no more than about 1
millitorr, no more than about 0.5 millitorr, or no more than about
0.1 millitorr and/or at least about 50 torr or at least about 75
torr with substantially no arcing at or near the choke.
[0111] Referring now to FIG. 7a, a cross-sectional segment of one
embodiment of a microwave choke 650 for substantially inhibiting
microwave energy leakage between a door 634 and a vessel body 632
of a microwave heater when door 634 is closed is provided. As shown
in FIG. 7a, at least a portion of microwave choke 650 is
cooperatively defined or formed between door 634 and vessel body
632 when door 634 is closed and respective door-side 633 and
body-side 631 sealing surfaces are in direct or indirect contact
with one another. In one embodiment, an optional fluid sealing
member 660 can also be present to inhibit, minimize, or
substantially prevent leakage of fluid into or out of the microwave
heater, as discussed previously. Fluid sealing member 660, when
present, can be coupled to vessel body 632 or, as shown in FIG. 7a,
to door 634.
[0112] According to one embodiment shown in FIG. 7a, microwave
choke 650 defines a first radially-extending choke cavity 652, a
second-radially extending choke cavity 654, and a
radially-extending choke guidewall 656 disposed at least partly
between first and second choke cavities 652, 654 when the door 634
of the microwave heater is closed. In one embodiment illustrated in
FIG. 7a, first choke cavity 652 is defined between vessel body 632
and choke guidewall 656 when door 634 is closed, while second choke
cavity 654 is at least partially disposed between door 634 and
choke guidewall 656, such that choke guidewall 656 is substantially
coupled to door 634. First choke cavity 652 can be open to the
interior of the microwave heater and can be radially positioned
between the interior of the microwave heater and the fluid seal
created by sealing member 660, when present. In another embodiment
of the present invention (not shown in FIG. 7a), second choke
cavity 654 can be at least partially defined by vessel body 632,
such that second choke cavity 654 can be positioned between vessel
body 632 and choke guidewall 656 when door 634 is closed, such that
choke guidewall 656 is substantially coupled to vessel body
632.
[0113] In one embodiment, at least a portion of second choke cavity
654 can extend alongside at least a portion of first choke cavity
652 when door 634 is closed. In one embodiment, at least about 40
percent, at least about 60 percent, at least about 80 percent, or
at least about 90 percent of the total length of second choke
cavity 654 can extend alongside first choke cavity 654 when door
634 is closed. The total length of first and/or second choke
cavities 652, 654, designated with the letter "L" in FIG. 7a, can
be at least about 1/16 times, at least about 1/8 times, at least
about 1/4 times and/or no more than about 1 times, no more than
about 3/4 times, or no more than about 1/2 times the length of the
predominant wavelength of the microwave energy in the interior of
the microwave heater. The length, L, of first and/or second choke
cavities 652, 654 can be at least about 1 inch, at least about 1.5
inches, at least about 2 inches, or at least about 2.5 inches
and/or no more than about 8 inches, no more than about 6 inches, or
no more than about 5 inches.
[0114] As illustrated in FIG. 7b, a relative extension angle,
.phi., can be defined between the direction of extension of first
choke cavity 652, designated by line 690, and the direction of
extension of second choke cavity 654, designated by line 692. In
various embodiments, the relative extension angle, .phi., can be no
more than about 60.degree., no more than about 45.degree., no more
than about 30.degree., or no more than about 15.degree.. In some
embodiments, the direction of extension of second choke cavity 654
can be substantially parallel to the direction of extension of
first choke cavity 652, as depicted in FIG. 7a.
[0115] Referring now to FIG. 7c, a partial isometric
cross-sectional portion of a microwave choke is provided. As shown
in FIG. 7c, choke guidewall 656 can be integrally formed into door
634. According to one embodiment, guidewall 656 can comprise a
plurality of spaced open-ended gaps 670 disposed circumferentially
along guidewall 656. In one embodiment, the spacing between the
centerline of each of the gaps can be at least about 0.5 inches, at
least about 1 inch, at least about 2 inches, or at least about 2.5
inches and/or no more than about 8 inches, no more than about 6
inches, or no more than about 5 inches.
[0116] According to another embodiment of the present invention, at
least a portion of choke 650 can comprise a removable portion 651
removably coupled to vessel body 632 or door 634. In one
embodiment, removable portion 651 can be removably coupled to door
634. As used herein, the term "removably coupled" means attached in
a manner such that a portion of the choke can be removed without
substantial damage to or destruction of the vessel body, the choke,
and/or the door. In one embodiment, removable choke portion 651 can
comprise at least a portion or all of guidewall 656. FIG. 7d
illustrates a microwave choke having at least one removable portion
651. In one embodiment depicted in FIG. 7d, guidewall 656 can be
coupled to removable choke portion 651. Removable choke portion 651
can comprise a plurality of removable choke segments 653a-e that
are each removably coupled to door 634 or vessel body 632
(embodiment not shown). In one embodiment, removable choke portion
651 can comprise at least 2, at least 3, at least 4, at least 6, at
least 8 and/or no more than 16, no more than 12, no more than 10,
or no more than 8 removable choke segments 653. According to one
embodiment wherein removable choke portion 651 has a generally
ring-shaped diameter, individually removable choke segments 653a-e
can have a generally arcuate shape, as shown in FIG. 7d.
[0117] Removable choke portion 651 can be fastened to door 634 or
vessel body 632 according to any known method including, for
example, bolts, screws, or any other type of suitable removable
fastening device. In one embodiment, removable choke portion 651
can be magnetically fastened to door 634 or vessel body 632.
Depending, in part, on the desired method of fastening, removable
choke portion 651 can have a variety of cross-sectional shapes. For
example, as illustrated in FIGS. 7e-h, removable choke portion 651
can define a cross-section which is generally G-shaped (as shown in
FIG. 7e), generally J-shaped or U-shaped (as shown in FIG. 70,
generally L-shaped (as shown in FIG. 7g), or generally I-shaped (as
shown in FIG. 7h).
[0118] In operation, removable choke portion 651 can be attached,
removed, and/or subsequently replaced without removing portions of
or substantially re-machining vessel body 632 and/or door 634 in
order to resume normal operation of the microwave heater. For
example, in one embodiment, a plurality of individually removable
choke segments 653a-e can be separately and individually attached
to door 634 and/or vessel body 632. Subsequently, when one or more
portions of the microwave choke become damaged or otherwise require
replacement, one or more individually removable choke segments 653
and/or the entire removable choke portion 651 can be separately and
individually detached or removed from vessel body 632 or door 634
and replaced with one or more new (e.g., replacement) removable
choke segments 653 and/or a new removable choke portion 651. In one
embodiment, the number of removable choke segment or segments 653a,
b, c, d, and/or e detached from and then reattached to (e.g.,
removed from and replaced onto) vessel body 632 or door 634 can be
not more than or no more than the total number of choke segments
653a-e of removable portion 651.
[0119] Microwave heater 530, generically represented in FIG. 6, can
be classified as a single mode cavity, a multi-mode cavity, or a
quasi-optical cavity depending on how the microwave energy therein
behaves. As used herein, the term "single mode cavity" refers to a
cavity designed and operated to maintain the microwave energy
therein a single, specific mode pattern. Oftentimes, the design and
properties of a single mode cavity can limit the size of the vessel
and/or how a load can be positioned within the chamber. As a
result, in one embodiment, microwave heater 530 can comprise a
multimode or a quasi-optical mode cavity. As used herein, the term
"multimode cavity" refers to a cavity or chamber wherein the
microwave energy is excited into a plurality of standing wave
patterns in a semi-random or undirected manner. As used herein, the
term "quasi-optical mode cavity" refers to a cavity or chamber
wherein most, but not all, of the energy is directed toward a
particular area in a controlled manner. In one embodiment, a
multimode cavity has a higher energy density near the center of the
vessel than a quasi-optical cavity, while quasi-optical cavities
can leverage the quasi-optical properties of microwave energy to
more closely control and direct the emission of energy into the
cavity interior.
[0120] Turning back to microwave heating system 420 illustrated in
FIG. 5, microwave distribution system 440 is operable to transmit
or direct at least a portion of the microwave energy produced by
microwave generator 422 into microwave heater 430, as discussed
briefly above. As shown schematically in FIG. 5, microwave
distribution system 440 can include at least one waveguide 442
operably coupled to one or more microwave launchers, illustrated as
launchers 444a-c. Optionally, microwave distribution system 440 can
comprise one or more microwave mode converters 446 for changing the
mode of the microwave energy passing therethrough and/or one or
more microwave switches (not shown) for selectively routing
microwave energy to one or more of microwave launchers 444a-c.
Additional details regarding specific components and various
embodiments of microwave distributions system 440 will now be
discussed in detail below.
[0121] Waveguides 442 can be operable to transport microwave energy
from microwave generator 422 to one or more of microwave launchers
444a-c. As used herein, the term "waveguide" refers to any device
or material capable of directing electromagnetic energy from one
location to another. Examples of suitable waveguides can include,
but are not limited to, co-axial cables, clad fibers,
dielectric-filled waveguides, or any other type of transmission
line. In one embodiment, waveguides 442 can comprise one or more
dielectric-filled waveguide segments for transporting microwave
energy from microwave generator 422 to one or more of launchers
444a-c.
[0122] Waveguides 442 can be designed and constructed to propagate
microwave energy in a specific predominant mode. As used herein,
the term "mode" refers to a generally fixed cross-sectional field
pattern of microwave energy. In one embodiment of the present
invention, waveguides 442 can be configured to propagate microwave
energy in a TE.sub.xy mode, wherein x is an integer in the range of
from 1 to 5 and y is 0. In another embodiment of the present
invention, waveguides 442 can be configured to propagate microwave
energy in a TM.sub.ab mode, wherein a is 0 and b is an integer in
the range of from 1 to 5. It should be understood that, as used
herein, the above-defined ranges of a, b, x, and y values as used
to describe a mode of microwave propagation are applicable
throughout this description. Further, in some embodiments, when two
or more components of a system are described as being "TM.sub.ab"
or "TE.sub.xy" components, the values for a, b, x, and/or y can be
the same or different for each component. In one embodiment, the
values for a, b, x, and/or y are same for each component of a given
system.
[0123] The shape and dimensions of waveguides 442 can depend, at
least in part, on the desired mode of the microwave energy to be
passed therethrough. For example, in one embodiment, at least a
portion of waveguides 442 can comprise TE.sub.xy waveguides having
a generally rectangular cross-section, while, in another
embodiment, at least a portion of waveguides 442 can comprise
TM.sub.ab waveguides having generally circular cross-sections.
According to one embodiment of the present invention, circular
cross-section waveguides can have a diameter of at least about 8
inches, at least about 10 inches, at least about 12 inches, at
least about 24 inches, at least about 36 inches, or at least about
40 inches. In another embodiment, rectangular cross-section
waveguides can have a short dimension of at least about 1 inch, at
least about 2 inches, at least about 3 inches and/or no more than
about 6 inches, no more than about 5 inches, or no more than about
4 inches, while the long dimension can be at least about 6 inches,
at least about 10 inches, at least about 12 inches, at least about
18 inches and/or no more than about 50 inches, no more than about
35 inches, or no more than about 24 inches.
[0124] As schematically illustrated in FIG. 5, microwave
distribution system 440 can comprise one or more mode conversion
segments 446 operable to change the mode of the microwave energy
passing therethrough. For example, mode converter 446 can comprise
a TM.sub.ab-to-TE.sub.xy mode converter for changing the mode of at
least a portion of the microwave energy from a TM.sub.ab to a
TE.sub.xy mode. In another embodiment, mode conversion segment 446
can comprise a TE.sub.xy-to-TM.sub.ab mode converter for receiving
TN.sub.ab mode energy and converting and discharging microwave
energy in a TE.sub.xy mode. The values for a, b, x, and y can be
within the ranges described previously. Microwave distribution
system 440 can comprise any number of mode converters 446 and, in
one embodiment, can include at least 1, at least 2, at least 3, or
at least 4 mode converters positioned at various locations within
microwave distribution system 440.
[0125] Turning again to FIG. 5, microwave distribution system 440
can comprise one or more microwave launchers 444 for receiving
microwave energy from generator 422 via waveguides 442 and emitting
or discharging at least a portion of the microwave energy into the
interior of microwave heater 430. As used herein, the terms
"microwave launcher" or "launcher" refers to any device capable of
emitting microwave energy into the interior of a microwave heater.
The microwave distribution systems according to various embodiments
of the present invention can employ at least 1, at least 2, at
least 3, at least 4, at least 5, at least 6, at least 8, at least
10, and/or no more than 100, no more than 50, or no more than 25
microwave launchers. Microwave launchers can be any suitable shape
and/or size and can be constructed of any materials, including, for
example, selected carbon steels, stainless steels, nickel alloys,
aluminum alloys, and copper alloys. In one embodiment wherein
microwave distribution system 440 comprises two or more microwave
launchers, each launcher can be made of the same material, while,
in another embodiment, two or more launchers can be made of
different materials.
[0126] In operation, microwave energy generated by one or more
microwave generators 422 can be optionally routed or directed to
one or mode converters 446 (if present) via waveguides 442.
Thereafter, the microwave energy in waveguides 442 can be
optionally split into two or more separate microwave portions
(e.g., at least three portions as shown in FIG. 5) before being
directed to one or more microwave launchers, illustrated as
launchers 444a-c in FIG. 5. Microwave launchers 444a-c can be
partially or entirely disposed within microwave heater 430 and can
be operable to introduce or emit at least a portion of the
microwave energy passed thereto into the interior of heater 430 via
one or more spaced launch locations, thereby heating and/or drying
the objects, articles, or load disposed therein, including, for
example, one or more bundles of wood. Specific configurations and
details regarding various embodiments of microwave heating systems
will now be discussed in detail below.
[0127] Turning now to FIGS. 8-10, several embodiments of microwave
heating systems configured according to the present invention are
provided. Although described as being configured to receive and
heat a bundle of wood, it should be understood that the microwave
heating systems described below can be suitable for use in any of
the other processes and systems described previously, as well as
any system or process wherein microwave heating is used. Further,
it should be understood that, although described with reference to
a particular figure or embodiment, all elements and components
described below may be suitable for use in any microwave heating
system configured according to one or more embodiments of the
present invention.
[0128] Turning now to FIGS. 8a and 8b, one embodiment of a
microwave heating system 720 is illustrated as comprising a
microwave heater 730 and a microwave distribution system 740 for
delivering microwave energy from a microwave generator (not shown)
to heater 730. An optional vacuum system (not shown) can be
operable in various embodiments to reduce the pressure in the
interior of microwave heater 730 to, for example, no more than
about 550 torr, no more than about 450 torr, no more than about 350
torr, no more than about 300 torr, no more than about 250 torr, no
more than about 200 torr, no more than about 150 torr, no more than
about 100 torr, no more than about 75 torr and/or no more than
about 10 millitorr (10.sup.-3 torr), no more than about 5
millitorr, no more than about 2 millitorr, no more than about 1
millitorr, no more than about 0.5 millitorr, or no more than about
0.1 millitorr. Several features of one or more embodiments of
microwave heating system 720 will be discussed in detail below.
[0129] Turning now to FIG. 8a, microwave distribution system 740 is
illustrated as comprising an elongated waveguide launcher 760 that
is at least partially, and may be entirely, disposed within the
interior of microwave heater 730. As shown in FIG. 8a, elongated
waveguide launcher 760 can extend substantially horizontally within
the interior of microwave heater 730. As used herein, the term
"substantially horizontally" means within about 10.degree. of
horizontal. In one embodiment, the ratio of the length of elongated
waveguide launcher 760 to the total length of the interior space of
microwave heater 730 can be, for example, at least about 0.3:1, at
least about 0.5:1, at least about 0.75:1, or at least about 0.90:1.
In one embodiment, elongated waveguide launcher that extends
substantially horizontally 760 can be located toward the upper or
lower half of the interior volume of microwave heater 730 and may
be at least partially or entirely vertically disposed above the
heater entrance door 738 and an optional heater exit door (not
shown) that, when present, is disposed on a generally opposite end
of microwave heater 730. As used herein, the terms "upper" and
"lower" volume refer to regions located in the upper vertical or
lower vertical portion of the internal volume of the vessel. In one
embodiment, elongated waveguide launcher 760 can be, for example
entirely disposed within the uppermost one-third, one-fourth, or
one-fifth of the interior volume of microwave heater 730, while, in
another embodiment, elongated waveguide launcher 760 can be, for
example disposed within the lowermost one-third, one-fourth, or
one-fifth of the total interior volume of microwave heater 730. To
measure the "uppermost" or "lowermost" fractional portions of the
total interior volume described above, the portion of the vessel
cross-section extending from the respective uppermost or lowermost
wall of the vessel toward the central axis of elongation for the
desired portion (e.g., one-third, one-fourth, or one-fifth) of the
cross-section can be extended along the central axis of elongation
to thereby define the "uppermost" or "lowermost" fractional volumes
of the internal vessel space.
[0130] As shown in FIG. 8a, microwave heater 730, which can be
configured to receive and heat a bundle of wood, comprises a heater
entrance door 738, which can optionally comprise a choke (not
shown), configured to allow a bundle of wood 702 to be introduced
into a bundle receiving space 739. Although illustrated as being in
direct contact, it should be understood that bundle 702 can also
comprise one or more spacers or "stickers" disposed between the
boards. In one embodiment (not shown), microwave heater 730 can
also comprise an optional heater exit door 739 positioned on the
opposite end of microwave heater 730 from heater entrance door 738.
When microwave heater 730 comprises a separate heater exit door
739, bundle 702 can optionally be loaded via entrance door 738,
passed through microwave heater 730 and unloaded via the exit door
739, rather than being both loaded and unloaded through heater
entrance door 738. The reference to "entrance" and "exit" doors in
this embodiment is not limiting, and bundle 702 can optionally be
loaded via door 739, passed through microwave heater 730 and
unloaded via door 738. Further, in another embodiment, bundle 702
can be both loaded (inserted) and unloaded (removed) from entrance
door 738 when, for example, optional exit door 739 is not present.
In one embodiment, elongated waveguide launcher 760 can be
positioned in microwave heater 730 substantially below (not shown)
or above bundle 702 such that, as bundle 702 is passed into, out
of, and/or through the interior of heater 730, elongated launcher
does not have to be moved, removed, retracted, or otherwise
repositioned.
[0131] Referring now to FIG. 8b, a partial detailed isometric view
of elongated waveguide launcher 760 is provided. In one embodiment,
elongated waveguide launcher 760 can be substantially hollow and
comprise one or more sidewalls. The one or more sidewalls can be
configured in a variety of ways such that elongated waveguide
launcher 760 can have a variety of cross-sectional shapes. For
example, in one embodiment, elongated waveguide launcher 760 can
have a single sidewall defining a substantially circular or
elliptical cross-sectional shape. In another embodiment, as shown
in FIG. 8b, elongated waveguide launcher 760 can comprise four
substantially planar side walls 764a-d arranged to give launcher
760 a generally rectangular transverse (or, in another embodiment,
square) cross-sectional configuration. Elongated waveguide launcher
760 can be configured to propagate and/or emit microwave energy in
any suitable mode, including TE.sub.xy and/or TM.sub.ab modes, as
discussed in detail previously. According to one embodiment,
elongated waveguide launcher 760 can comprise a elongated TE.sub.xy
launcher and, in one embodiment, can be implemented with
commercially available rectangular waveguide sizes, such as WR284,
WR430, or WR340. The specific dimensions of elongated waveguide
launcher 760 can be any suitable dimensions and, in one embodiment,
may be custom fabricated according to the description provided in
U.S. application Ser. Nos. 11/524,239 and 11/254,261, each
incorporated herein by reference to the extent not inconsistent
with the present disclosure.
[0132] As illustrated in FIG. 8b, the one or more sidewalls of
elongated waveguide launcher 760 can define a plurality of launch
openings for discharging or emitting microwave energy into the
interior of microwave heater 730. Although depicted in FIG. 8b as
defining a plurality of elongated slots 767a-e having a generally
rectangular shape with rounded ends, launch openings 767a-e can be
of any suitable shape. Each of elongated slots 767a-e can define a
length, designated as "L" in FIG. 8b, and a width, designated as
"W" in FIG. 8b. In one embodiment, the length-to-width (L:W) ratio
of elongated slots 767a-e can be, for example, at least about 2:1,
at least about 3:1, at least about 4:1, or at least about 5:1. In
addition, as shown in FIG. 8b, elongated slots 767a-e can be
oriented at various angles with respect to the horizontal. In one
embodiment, elongated slots 767a-e can extend at an angle relative
to the horizontal of, for example, at least about 10.degree., at
least about 20.degree., at least about 30.degree. and/or, for
example, no more than about 80.degree., no more than about
70.degree., or no more than about 60.degree.. In one embodiment,
each of elongated slots 767a-e can have equal shapes, sizes, and/or
orientations. In one embodiment, the shapes, sizes, and/or
orientations of individual elongated slots 767a-e can differ.
Changes to the shape, size, and/or orientation of elongated slots
767a-e can impact the distribution of energy emitted from elongated
waveguide launcher 760. Although shown as being uncovered in the
embodiment illustrated in FIG. 8b, one or more launch openings 767
can be substantially covered by one or more covering structures
(not shown) adjacent to the launch openings that are operable to
prevent the flow of fluids into and out of openings 767, but that
allow the discharge of microwave energy therefrom.
[0133] As shown in FIG. 8b, one or more of launch openings 767a-e
can be at least partially, or entirely, defined by one or more
sidewalls 764a-d of elongated waveguide launcher 760. In one
embodiment, at least about 50 percent, at least about 75 percent,
at least about 85 percent, or at least about 90 percent, for
example, of the thickness of launch openings 767a-e can be defined
by one or more sidewalls 764a-d. According to the embodiment
illustrated in FIG. 8b, launch openings 767a-e can be at least
partially, or entirely, defined by two substantially upright
sidewalls 764a,c. As used herein, the term "substantially upright"
means within 30.degree. of vertical. Sidewalls 764a-d of elongated
launcher 760 can be relatively thick in one embodiment, while, in
other one embodiment, sidewalls 764a-d can be relatively thin. For
example, the average thickness, designated as x in FIG. 8b, of
sidewalls 764a-d can be at least about 1/32 (0.03125) inches, at
least about 1/8 (0.125) inches, at least about 3/16 (0.1875) inches
and/or, for example, no more than about 1/2 (0.5) inches, no more
than about 1/4 (0.25) inches, no more than about 3/16 (0.1875)
inches, or no more than about 1/8 (0.125) inches. According to one
embodiment wherein one or more side walls of elongated waveguide
launcher 760 are relatively thin, elongated waveguide launcher 760
can emit microwave energy into the interior of microwave heater 730
with a microwave launch efficiency of at least about 50 percent, at
least about 75 percent, at least about 85 percent, at least about
90 percent, or at least about 95 percent. As used herein, the term
"microwave launch efficiency" can be defined by converting the
result of the following equation to a percentage: (total energy
introduced into the launcher-total energy discharged from all of
the openings of the launcher)/(total energy introduced into the
launcher).
[0134] Launch openings 767a-e can be arranged according to any
suitable configuration or arrangement along elongated waveguide
launcher 760. In one embodiment illustrated in FIG. 8b, launch
openings 767a-e can include a first set of launch openings (e.g.,
launch openings 767a,b) disposed on one side of launcher 760 and a
second set of launch openings (e.g., launch openings 767c-e)
disposed on another, generally opposite side of elongated waveguide
launcher 760. According to one embodiment, first and second sets of
launch openings can be axially staggered from each other, such that
corresponding openings (e.g., openings 767a,c, shown as launch pair
or opening pair 780a, and openings 767b,d, shown as launch or
opening pair 780b) are not axially aligned with one another.
Although illustrated in FIG. 8b as having only two launch opening
pairs 780a,b, it should be understood that any desired number of
launch opening pairs can be utilized.
[0135] According to one embodiment, each launch pair 780a,b
includes one launch opening disposed on one side of elongated
waveguide launcher 760 (e.g., opening 767a of pair 780a and opening
767b of pair 780b both disposed on side wall 764a) and another
launch opening disposed on the opposite side of launcher 760 (e.g.,
opening 767c of pair 780a and opening 767d of pair 780b both
disposed on side wall 764c in FIG. 8b). In one embodiment, the
openings 767a,c and 767b,d disposed on opposite sides of elongated
waveguide launcher 760 can be axially aligned, while, in another
embodiment, the oppositely-spaced openings 767a,c and 767b,d can
form a plurality of "near neighbor" pairs (e.g., launch pairs
780a,b comprise "near neighbor" openings 767a,c and 767b,d,
respectively). In one embodiment, for example, when an odd number
of launch openings is used, one or more single launch openings may
stand alone without forming a pair with any other opening. In one
embodiment, the stand-alone opening may be an end opening, such as
end opening 767e shown in FIG. 8b.
[0136] According to one embodiment wherein pairs 780a,b comprise
near neighbor pairs of openings, at least one of the launch
openings 767a-d of launch opening pairs 780a,b can be configured so
as to cancel at least a portion of the microwave energy reflected
back into the interior space of waveguide 760 as generated by one
or more of the other launch openings 767a-d of the near-neighbor
pairs 780a,b. For example, microwave energy reflections caused by
opening 767a of pair 780a can be at least partially, substantially,
or nearly entirely cancelled by the configuration of the other
opening 767b of pair 780a. In a similar manner, the microwave
energy reflections caused by opening 767c of pair 780b can be at
least partially, substantially, or nearly entirely cancelled by the
configuration of the other opening 767d of pair 780b.
[0137] Furthermore, in one embodiment when launch openings 767a-d
are arranged in near neighbor pairs, the total amount of energy
transferred from each of launch opening 767a-d of opening pairs
780a,b into the interior of microwave heater 730 can be equal to a
fraction of the total amount of microwave energy introduced into
launcher 760. For example, in one embodiment wherein the launcher
comprises N paired launch openings and a single end opening, the
fraction of microwave energy emitted from each pair of launch
openings (and/or the unpaired or single end opening) can be
expressed by the following formula: 1/(N+1). Thus, according to one
embodiment illustrated in FIG. 8b wherein N=2, the total amount of
energy emitted by each of pairs 780a,b can be equal to 1/(2+1) or
1/3 of the total energy introduced into elongated waveguide
launcher 760. Similarly, in such embodiment the energy emitted from
an unpaired launch opening (e.g., single end opening 767e in FIG.
8b) can be expressed by the formula 1/(N+1). Thus, in the
embodiment shown in FIG. 8b, launch opening 767e can also emit
approximately 1/3 of the total energy introduced into elongated
waveguide launcher 760.
[0138] Another embodiment of a microwave heating system 820 is
provided in FIGS. 9a-h. As shown in FIG. 9a, microwave heating
system 820 comprises a microwave heater 820 and a microwave
distribution system 840 operable to transport microwave energy from
a microwave generator (not shown) to heater 820. In one embodiment,
microwave heating system 820 can also comprise a vacuum system (not
shown) for reducing the pressure in microwave heater 830 below
atmospheric pressure. As shown in FIG. 9a, microwave heater 830 can
include a heater entrance door 838 for introducing a bundle of wood
(or other load) into the interior of heater 830. Optionally,
microwave heater 830 can comprise a heater exit door (not shown in
FIG. 9a) disposed on the generally opposite end of heater 830 from
heater entrance door 838. In addition, microwave heater 830 can
comprise a plurality of spaced launch openings, such as those
illustrated as 841a,b in FIG. 9a, located at various positions
along one or more external side walls 831 of microwave heater 830.
Launch openings 841a,b can be operable to accommodate one or more
components of microwave distribution system 840, thereby
facilitating the transmission of microwave energy into microwave
heater 830. Additional details regarding microwave distribution
system 840 will now be discussed in further detail with regard to
FIGS. 9b-h.
[0139] Turning FIG. 9b, a top partial cutaway view of microwave
heater 830 is provided, particularly illustrating a plurality of
microwave launchers 844a-d directly or indirectly coupled to
opposite sidewalls 831a,b of microwave heater 830. As used herein,
the term "indirectly coupled" refers to one or more intermediate
pieces of equipment used to at least partially connect one or more
launchers to the vessel. Launchers 844a-d can be operable to emit
microwave energy into the interior of microwave heater 830 via one
or more open outlets 845a-d, as shown in FIG. 9b. Although
illustrated in FIG. 9b as comprising four launchers 844a-d, it
should be understood that microwave heater 830 can comprise any
desired number of launchers. In one embodiment (not shown),
microwave heater 830 can comprise two additional launchers axially
positioned to the left of launchers 844a,b in FIG. 9b and/or to the
right of launchers 844c,d. The additional launchers (not shown) can
be facing in the same direction and/or in different directions. For
example, in one embodiment shown in FIG. 9b, launchers 844a-d are
shown as facing in opposite directions. Further, in one embodiment
(not shown), microwave heater 830 can comprise four additional
launchers, arranged in an analogous manner as launchers 844a-d,
illustrated in FIG. 9b, as described further below.
[0140] Microwave launchers 844 can be positioned along, within, or
proximate microwave heater 830 according to any suitable
configuration. In one embodiment, microwave launchers 844 can be
configured to comprise two pairs of launchers. The individual
launchers within the pair can be located on generally the same side
(e.g., the pair comprising launchers 844a and 844d and the other
pair comprising launcher 844b and 844c) or on generally opposite
sides (e.g., the pair comprising microwave launchers 844a and 844b
and the other pair comprising 844c and 844d) of microwave heater
830.
[0141] As used herein, the term "generally opposite sides" or
"opposite sides" refers to two launchers positioned such that the
angle of radial alignment defined therebetween is in the range of
from at least about 90.degree. to about 180.degree.. The "angle of
radial alignment (.beta.)," is defined as the angle formed between
two straight lines drawn from the center of each launcher to the
central axis of elongation of the vessel. For example, FIG. 9c
shows exemplary launchers 845 and 846a, defining an angle of radial
alignment, .beta..sub.1, therebetween. The angle of radial
alignment between two launchers positioned on generally opposite
sides of a vessel can be at least about 120.degree., at least about
150.degree., at least about 165.degree. and/or no more than about
180.degree. or approximately 180.degree.. In one embodiment, two
launchers can be positioned on generally opposite sidewalls, as
generally depicted in FIG. 9b, while, in another embodiment, two
oppositely disposed launchers can be positioned at or near the
vertical top and bottom of the heater (not shown).
[0142] In one embodiment wherein one or more pairs launchers
include individual launchers located on generally opposite sides of
a microwave heater (e.g., launchers 844b and 844a or launchers 844c
and 844d in FIG. 9b), the individual launchers within the pairs can
also be axially aligned with one another. As used herein, the term
"axially aligned" refers to two launchers defining an angle of
axial alignment therebetween in the range of from 0.degree. to
45.degree.. As used herein, the "angle of axial alignment" can be
defined by the angle formed between the shortest straight lines
drawn between the centers of each launcher (that also intersects
the axis of elongation of the vessel) and a line drawn
perpendicular to the axis of elongation. In FIG. 9d, the angle of
axial alignment, a, is formed between line 850, which is drawn
between the centers of exemplary launchers 845 and 846, and line
852, which is perpendicular to the axis of elongation 835a. In one
embodiment, axially aligned launchers can define an angle of axial
alignment of at least about 0.degree. and/or, for example, no more
than about 30.degree. or no more than about 15.degree..
[0143] In another embodiment, individual launchers within a pair
can be located on generally the same side of a microwave heater. As
used herein, the term "generally the same side" or "same side"
refers to two launchers having an angle of radial alignment,
.beta., in the range of from at least or equal to 0.degree. to
about 90.degree.. Exemplary launchers 845 and 846b in FIG. 9c are
located on generally the same side of the microwave heater, as the
angle of radial alignment defined therebetween (e.g., 112) is no
more than about 90.degree.. In one embodiment, two launchers
disposed on the same side of a microwave heater can define an angle
of radial alignment of at least about 0.degree. and/or no more than
about 60.degree., no more than about 30.degree., and no more than
about 15.degree., or approximately 0.degree..
[0144] In one embodiment wherein one or more pairs of launchers
include individual launchers located on generally the same side of
a microwave heater (e.g., launchers 844a and 844d or launchers 844b
and 844c in FIG. 9b), the individual launchers within the pairs can
also be axially adjacent to one another. As used herein, the term
"axially adjacent" refers to two or more launchers positioned on
the same side of a microwave heater such that no other launchers on
that side are disposed between the axially adjacent launchers.
According to one embodiment wherein a microwave distribution system
comprises two or more pairs of oppositely positioned microwave
launchers, one launcher from the first pair is disposed on
generally the same side as one launcher from the second pair,
thereby creating an axially adjacent pair of launchers.
[0145] As illustrated in FIG. 9b, each of microwave launchers
844a-d can define a respective open outlet 845a-d for emitting
microwave energy into the interior of microwave heater 830. Open
outlets can be positioned to emit energy into the interior of
microwave heater 830 in any suitable pattern or direction. For
example, in one embodiment shown in FIG. 9b, open outlets of
axially adjacent launchers (e.g., outlets 845a,d of launchers
844a,d and outlets 845b,c of launchers 844b,c) can be oriented to
face each other in a direction substantially parallel to the
external sidewall to which the launchers are coupled (e.g.,
sidewall 831a for launchers 844a,d and sidewall 831b for launchers
844b,c), thereby discharging microwave energy in that general
direction. As used herein, the term "substantially parallel" means
within about 10.degree. of parallel. In one embodiment, at least
one of open outlets 845a-d can be oriented to discharge energy
substantially parallel to the axis of elongation of microwave
heater 830, designated as line 835 in FIG. 9b. According to one
embodiment, at least one of open outlets 845a-d can be oriented
toward an axial midpoint of heater 830. As used herein, the "axial
midpoint" of a vessel is defined by a plane that is orthogonal to
axis of elongation 835 and intersects the midpoint 839 of the axis
of elongation 835 as shown in FIG. 9b. In one embodiment, each of
open outlets 845a-d are oriented toward the axial mid-point of
heater 830 such that the open outlet 845a,b of front-side launchers
844a,b substantially face towards open outlets 845c,d of back-side
launchers 844c,d, as depicted in FIG. 9b.
[0146] According to one embodiment, in operation, microwave energy
produced by one or more microwave generators (not shown) can be
transported via waveguides 842a-d to launchers 844a-d, which emit
the energy into the interior of microwave heater 830. Although not
illustrated in FIG. 9b, any number or configuration of microwave
generators can be used to produce microwave energy for use in
microwave heating system 820. In one embodiment, a single generator
can be used to supply energy to heater 830 via waveguides 842a-d
and launchers 844, while, in another embodiment, heating system 820
can include two or more generators. According to another
embodiment, a network of one or more microwave generators can be
utilized such that microwave energy is emitted from at least one,
at least two, at least three, or all four of microwave launchers
844a-d at substantially the same time. In one embodiment, one or
more launchers 844a-d can be coupled to a single generator and the
energy from the generator can be allocated amongst the launchers
using one or more microwave switches. In another embodiment, one or
more of launchers 844a-d can have a singly-dedicated generator,
such that at least about 75 percent, at least about 90 percent, or
substantially all of the microwave energy produced by that
generator is routed to a single launcher. Additional details
regarding specific embodiments of microwave generators, waveguides,
and launchers and the operation thereof are provided shortly, with
respect to FIGS. 11a and 11b.
[0147] The microwave energy propagated by waveguide segments 842a-d
can be in any suitable mode, including, for example, a TM.sub.ab
mode and/or a TE.sub.xy mode, wherein a, b, x, and y have values as
previously defined. In one embodiment, waveguide segments 842a-d
each comprise TE.sub.xy waveguide segments, with segments 842a and
842d configured to penetrate sidewall 831a and segments 842b and
842c configured to penetrate sidewall 831b and extend radially into
the interior of microwave heater 830, toward the axis of elongation
835, as shown in FIG. 9b.
[0148] According to one embodiment of the present invention, the
mode of the microwave energy propagated through waveguide segments
842a-d can be changed prior to (or simultaneously with) being
emitted into the interior of microwave heater 830. For example, in
one embodiment, TE.sub.xy mode energy produced by the microwave
generator (not shown in FIG. 9b) can be emitted into microwave
energy as TM.sub.ab mode energy after passing through one or more
mode converting segments, represented in FIG. 9b as mode converters
850a-d. Mode converters can be of any suitable size and shape and
any suitable number of mode converters can be used in microwave
distribution system 840. In one embodiment, one or more mode
converters 850a-d can be disposed outside of the interior space
(volume) of microwave heater 830, while, in another embodiment,
mode converters 850a-d can be partially, or entirely, disposed
within the interior of microwave heater 830. Mode converters 850a-d
can be located in or near sidewalls 831a,b or, as illustrated in
FIG. 9b, can be spaced from external sidewalls 831a,b of microwave
heater 830.
[0149] According to one embodiment wherein mode converters 850a-d
are partially or entirely disposed within heater 830, the microwave
energy can initially enter the microwave heater in a TE.sub.xy mode
and, subsequently, at least a portion of the energy can be
converted such that at least a portion of the energy emitted from
launchers 844a-d into the interior of microwave heater 830 can be
in a TM.sub.ab mode. In one embodiment, waveguide segments 842a-d
can comprise TE.sub.xy waveguide segments operable to transmit
microwave energy from the generator to heater 830 in a TE.sub.xy
mode. In one embodiment, at least a portion of TE.sub.xy waveguide
segments 842a-d can be integrated into launchers 844a-d as depicted
shown in FIG. 9b. As the energy passes from waveguide segments
842a-d through mode converters 850a-d, the energy is converted to a
TM.sub.ab mode. Subsequently, the TM.sub.ab mode energy exiting
mode converters 850a-d can then pass through a respective TM.sub.ab
waveguide segment 843a-d, illustrated in FIG. 9b as being entirely
disposed within the interior of microwave heater 830 and spaced
from the sidewalls 833 thereof, before being discharged into heater
830 via TM.sub.ab open outlets 845a-d.
[0150] According to another embodiment depicted in FIG. 9e,
microwave heating system 820 can comprise one or more reflectors
890a-d positioned near the open outlets 845a-d and operable to
reflect or disperse microwave energy emitted from launchers 844a-d
into microwave heater 830. In one embodiment, the reflectors can be
fixed or stationary reflectors, such that energy is reflected or
dispersed while the position of the reflector does not change. In
another embodiment illustrated in FIG. 9e, one or more of
reflectors 890 can be a movable reflector operable to change
position in order to reflect or disperse microwave energy into
microwave heater 830. Each movable reflector 890a-d in FIG. 9e
presents a respective reflecting surface 891a-d for reflecting or
dispersing energy emitted from microwave launchers 844a-d. As shown
in FIG. 9e, each reflecting surface can be spaced from external
side walls 831a,b and can be positioned such that one or more of
the respective launch openings 845a-d of launchers 844a-d face
toward their respective reflective surfaces 891a-d which, in turn,
are positioned to contact, direct, or reflect at least a portion of
the microwave energy from launch openings 845a-d. In one
embodiment, at least a portion of, or substantially all of, the
microwave energy emitted from microwave launchers 844a-d can at
least partially contact and can be least partially reflected or
dispersed by respective reflector surfaces 891a-d. In one
embodiment, one or more of reflecting surfaces 891a-d can be
oriented to face a direction that is substantially parallel the
direction of elongation of external side walls 831a,b.
[0151] In one embodiment, reflector surfaces 891a-d can be
substantially planar, while, in other embodiment, one or more
reflector surfaces 891a-d can be non-planar. For example, in one
embodiment, one or more non-planar reflector surfaces 891a-d can
define a curvature as illustrated by embodiment depicted in FIG.
9h. Reflector surfaces 891a-d can be smooth or can one or more
convexities. As used herein, the term "convexity" refers to a
region of a reflector that is surface operable to disperse, rather
than reflect, energy therefrom. In one embodiment, a convexity can
have a generally convex shape, as illustrated by the examples of
convexities 893a,b shown in FIGS. 9f and 9g. In another embodiment,
a convexity can have a generally concave shape, such as, for
example, a dimple or other similar indentation.
[0152] According to one embodiment of the present invention, one or
more reflectors 890a-d can be movable reflectors. Movable
reflectors can be any reflectors operable to change position. In
one embodiment, movable reflectors 890a-b can be oscillating
reflectors capable of moving in a designated pattern, such as, for
example, a generally up-and-down pattern or a pattern of rotation
about an axis. In one embodiment, movable reflectors can be
randomly movable reflectors operable to move in any of a variety of
random and/or unplanned movements.
[0153] Movable reflectors 890a-d can be movably coupled to
microwave heater 830 according to any suitable method. For example,
in one embodiment illustrated in FIG. 9i, microwave heater 830 can
comprise a reflector driver system (or actuator) 899 for movable
reflector 890 within the interior space of heater 830. As shown in
FIG. 9i, reflector driver system 899 can comprise one or more
support arms 892, which fastenably couple reflector 890 to an
oscillating shaft 893. In order to cause shaft 893 to rotate and
thereby move reflector 890 in an in-an-out pattern, as generally
indicated by arrow 880, a motor 898 can turn a wheel 896 to which a
linear shaft 895 can be coupled in a generally off-center manner.
As indicated by arrow 881, shaft 895 can move in a generally
up-and-down manner as wheel 896 turns, thereby causing a lever arm
894 to rotate shaft 893 about pivot axis 897, as generally
indicated by arrow 882. As a result, reflector 890 can move as
generally indicated by arrow 880 and can be operable to reflect or
to disperse at least a portion of the microwave energy emitted from
discharge opening 845 of microwave reflector 844 in a pattern
determined, at least in part, by the movement of reflector 890.
[0154] Yet another embodiment of a microwave heating system 920 is
shown in FIGS. 10a-f. As illustrated in one embodiment FIG. 10a, a
microwave heater 930 comprises a heater entrance door 938 for
loading a bundle of wood 902 into the interior of heater 930 and a
heater exit door 939 for removing bundle 902 from microwave heater
930. Although illustrated in FIG. 10a as including separate
entrance and exit doors 938, 939, it should be understood that
microwave heater 930 can, in another embodiment, include only a
single door for both loading and unloading bundle of wood 902 from
the interior of microwave heater 930. In the embodiment shown in
FIG. 10a, heater entrance and exit doors 938, 939 can be located on
generally opposite ends of microwave heater 930 such that bundle
902 can be generally passed through heater 930 via a transport
mechanism, such as, for example, a cart (not shown). In addition,
microwave heating system 920 can comprise an optional vacuum system
(not shown) for controlling the pressure in heater 930.
[0155] As shown in FIG. 10a, microwave heating system 920 can
include a microwave distribution system 940 comprising a plurality
of spaced launch openings 941a-d defined in an external sidewall
931 of microwave heater 930. Each launch opening 941 can be
operable to receive a microwave launcher (not shown) for emitting
energy into the interior of microwave heater 930. Microwave
launchers can be at least partly, or entirely, disposed within the
interior of microwave heater 930. Specific embodiments of one or
more types of microwave launchers will be discussed in more detail
shortly.
[0156] According to one embodiment, microwave energy produced by a
microwave generator (not shown) can be transmitted in a TE.sub.xy
mode through waveguide segments 942a-d prior to passing through
external TE.sub.xy-to-TM.sub.ab mode converters 950a-d, which
convert the energy passing therethrough to a TM.sub.ab mode. The
resulting TM.sub.ab mode microwave energy can then exit mode
converters 950a-d via respective waveguide segments 942e-h, as
illustrated in FIG. 10a. Thereafter, at least a portion of the
microwave energy in TM.sub.ab waveguide segments 942e-h can be
passed through respective barrier assemblies 970a-d prior to
entering microwave heater 930 via TM.sub.ab waveguide segments
942i-l. As used herein, the term "barrier assembly" can refer to
any device operable to fluidly isolating the microwave heater from
an external environment, while still permitting the passage of
microwave energy therethough. For example, in one embodiment shown
in FIG. 10a, respective barrier assemblies 970a-d can each comprise
at least one sealed window member 972a-d, which can be permeable to
microwave energy, but provides a desired degree fluid isolation
between each upstream 942e-h TM.sub.ab waveguide segment and each
of downstream 942i-l TM.sub.ab waveguide segments. As used herein,
the term "sealed window member" refers to a window member
configured in a manner that it will provide sufficient fluid
isolation between the two spaces on either side of the window
member to allow maintaining a pressure differential across such
window member. Additional details regarding specific embodiments of
barrier assemblies 970a-d will now be discussed in detail, with
respect to FIG. 10b.
[0157] Barrier assemblies configured according to one embodiment of
the present invention minimize or eliminate arcing, even at high
energy throughputs and/or low operating pressures. According to one
embodiment of the present invention, each barrier assembly 970a-d
can permit energy passage at a rate of at least about 5 kW, at
least about 30 kW, at least about 50 kW, at least about 60 kW, at
least about 65 kW, at least about 75 kW, at least about 100 kW, at
least about 150 kW, at least about 200 kW, at least about 250 kW,
at least about 350 kW, at least about 400 kW, at least about 500
kW, at least about 600 kW, at least about 750 kW, or at least about
1,000 kW and/or not more than about 2,500 kW, not more than about
1,500 kW, or not more than about 1,000 kW through its respective
window member 972a-d, while the pressure in microwave heater 930
can be no more than about 550 torr, no more than about 450 torr, no
more than about 350 torr, no more than about 250 torr, no more than
about 200 torr, no more than about 150 torr, no more than about 100
torr, or no more than about 75 torr. In one embodiment, the
pressure in microwave heater can be no more than about 10
millitorr, no more than about 5 millitorr, no more than about 2
millitorr, no more than about 1 millitorr, no more than about 0.5
millitorr, or no more than about 0.1 millitorr. In one embodiment,
the microwave energy passed through barrier assemblies 970a-d can
be introduced such that the electromagnetic field is maintained
lower than the threshold of arcing to thereby prevent or minimize
arcing in barrier assemblies 970a-d.
[0158] Turning now to FIG. 10b, an axial cross-sectional view of a
barrier assembly 970 is provided. Barrier assembly 970 comprises a
first sealed window member 972a and an optional second sealed
window member 972b disposed within a barrier housing 973. When
present, second sealed window member 972b can be operable to
cooperate with first sealed window member 972a to provide a desired
level of fluid isolation between the upstream (e.g., entry) and
downstream (e.g., exit) TM.sub.ab waveguide segments 975a,b while
permitting the passage of at least a portion of the microwave
energy from first TM.sub.ab waveguide segment 975a to second
TM.sub.ab waveguide segment 975b. According to one embodiment,
first and second TM.sub.ab waveguide segments 975a,b can have
circularly cylindrical cross-sections. In one embodiment, waveguide
segments 975a,b can be two ends of a single continuous waveguide,
in which barrier assembly 970 can be disposed, while, in another
embodiment, waveguide segments can be two separate waveguide
portions or components suitably fastened or coupled to either side
of barrier assembly 970.
[0159] As shown in FIG. 10b, barrier housing 973 can comprise a
first or entry section 973a, an optional second or intermediate
section 973b, and third or exit section 973c, with first sealed
window member 972a disposed between first and second sections
973a,b and second sealed window member 972b disposed between second
and third sections 973b,c. According to one embodiment, the
pressure of each of first, second, and third segments 973a,b,c can
be different. For example, in one embodiment, the pressure of first
segment 973a can be greater than the pressure of second segment
973b, which can be greater than the pressure of third segment 973c.
Each of first, second, and third sections 973a-c of barrier housing
973 can be held together by any suitable fastening device (not
shown), such as, for example screws, bolts, and the like. Further,
barrier assemblies 970a-d can also comprise one or more impedance
transformers, which alter the impedance of the microwave radiation.
An example is illustrated as impedance transforming diameter step
changes 974a,b in the embodiment shown in FIG. 10b, for maximizing
energy transfer from the microwave generator (not shown) to the
load in the microwave heater (not shown). In one embodiment,
impedance transforming diameter step changes 974a,b can be located
near at least one of sealed window members 972,b, while, in another
embodiment, step changes 974a,b can be located near or at least
partially defined by the entry and/or exit TM.sub.ab waveguides
975a,b.
[0160] As illustrated in FIGS. 10a and 10b, sealed window members
972a,b can comprise one or more discs. Each disc can be constructed
of any material with a suitable degree of corrosion resistance,
strength, impermeability to fluids, and permeability to microwave
energy. Examples of suitable materials can include, but are not
limited to, aluminum oxide, magnesium oxide, silicon dioxide,
beryllium oxide, boron nitride, mullite, and/or polymeric compounds
such as TEFLON. According to one embodiment, the loss tangent of
the disc can be no more than about 2.times.10.sup.-4, no more than
about 1.times.10.sup.-4, no more than about 7.5.times.10.sup.-5, or
no more than about 5.times.10.sup.-5.
[0161] The discs can have any suitable cross-section. In one
embodiments discs can have a cross-section compatible with the
cross-section of the adjoining waveguides 975a,b. In one
embodiment, the discs can have a substantially circular
cross-section and can have a thickness, designated in FIG. 10b as
"x", equal to at least about 1/8, at least about 1/4, at least
about 1/2 and/or no more than about 1, no more than about 3/4, or
no more than about 1/2 of the length of the predominant wavelength
of the microwave energy passing through barrier assembly 970. The
diameter of the discs can be at least about 50 percent, at least
about 60 percent, at least about 75 percent, at least about 90
percent and/or no more than about 95 percent, no more than about 85
percent, no more than about 70 percent, or no more than about 60
percent of the diameter of one or more adjoining waveguides
975a,b.
[0162] Each disc of sealed window members 972a-d can be operably
coupled to respective barrier assembly 970a-d in any suitable
fashion. In one embodiment, each of sealed window members 972a-d
can comprise one or more sealing devices flexibly coupled to
barrier housing 973 and/or sealed window members 972a,b. As used
herein, the term "flexibly coupled" means fastened, attached, or
otherwise arranged such that the members are held in place without
directly contacting one or more rigid structures. For example, in
one embodiment shown in FIG. 10b, barrier assembly 970 can comprise
a plurality of resilient rings 982a,b and 984a,b compressed between
various segments 973a-c of and operable to flexibly couple sealed
window members 972a,b into barrier housing 973.
[0163] According to one embodiment, each respective upstream 982a,b
and downstream 984a,b resilient rings can be operable to adequately
prevent or limit fluid flow between first and second 973a,b and/or
second and third 973b,c sections of barrier assembly 970. For
example, when subjected to a helium leak test according to
procedure B1 entitled "Spraying Testing" described in the document
entitled "Helium Leak Detection Techniques" published by Alcatel
Vacuum Technology using a Varian Model No. 938-41 detector, the
fluid leak rate of sealed window members 972a-d and/or barrier
assemblies 970a-d can be no more than about 10.sup.-2 torr
liters/sec, no more than about 10.sup.-4 torr liters/sec, or no
more than about 10.sup.-8 torr liters/sec. In addition, each of
sealed window members 972a,b can individually be operable to
maintain or withstand a pressure differential across sealed window
members 972a,b and/or barrier assembly 970 in amounts such as at
least about 0.25 atm, at least about 0.5 atm, at least about 0.75
atm, at least about 0.90 atm, at least about 1 atm, or at least
about 1.5 atm without out breaking, cracking, shattering, or
otherwise failing.
[0164] Turning now to FIG. 10c, a cross-sectional microwave heating
system 920 is provided. The microwave heating system depicted in
FIG. 10c includes a microwave distribution system 940 comprising at
least one pair of microwave launchers (e.g., launchers 944a and
944h) disposed on generally opposite sides of a microwave heater
930. Although shown as including a single pair of launchers in FIG.
10c, it should be understood that microwave distribution system 940
can further comprise one or more additional pairs of similarly (or
somewhat differently) configured microwave launchers having, in
some embodiments, one launcher from each pair disposed on generally
opposite sides of microwave heater 930. Further, in another
embodiment (not shown in FIG. 10c), microwave distribution system
940 may comprise two or more rows vertically-spaced microwave
launchers positioned on the generally same side of microwave heater
930. In one embodiment, each side of microwave heater 930 can
include two or more vertically-spaced rows of launchers, such that
one launcher from each oppositely-disposed pair may be located at a
higher vertical elevation than one launcher from another
oppositely-disposed pair. For example, in one embodiment, launchers
944a and/or 944h could be positioned at a slightly higher vertical
elevation than depicted in FIG. 10c and another launcher pair could
be positioned such that one of the two launchers would be
positioned on the same side of microwave heater 930, but at a
generally lower vertical elevation than launcher 944a, and the
other launcher would be positioned on the same side of microwave
heater 930, but at a generally lower vertical elevation than
launcher 944h. Furthermore, although shown as split launchers
944a,h, the vertically-spaced launchers, in one embodiment, could
be any type (or any combination of types) of microwave launchers
described herein.
[0165] As shown in FIG. 10c, microwave distribution system 940
comprises a plurality of waveguide segments 942 coupled to at least
one pair of microwave launchers 944a,h. For example, as shown in
the embodiment in FIG. 10c, launcher 944a can be coupled to
waveguide segments 942a, 942e, and 942i, while launcher 944h can be
coupled to waveguide segments 942x, 942y, and 942z operable to
deliver microwave energy from one or more microwave generators (not
shown in FIG. 10c) to the interior of microwave heater 930. In one
embodiment, microwave distribution system 940 can include one or
more mode converters 947a-d, as shown in FIG. 10c, coupled to one
or more of waveguide segments 942. According to one embodiment,
mode converters 947a-d can be operable to change the transmission
mode of the microwave energy passing therethrough from a TE.sub.xy
mode to a TM.sub.ab mode (i.e., a TE.sub.xy-to-TM.sub.ab mode
converter) or from a TM.sub.ab mode to a TE.sub.xy mode (i.e., a
TM.sub.ab-to-TE.sub.xy mode converter). For example, as shown in
FIG. 10c, mode converters 947a and 947c can each be operable to
convert the microwave energy transmitted through waveguides 942a
and 942x from a TE.sub.xy mode to a TM.sub.ab mode as it passes
into waveguides 942e and 942y. As discussed previously, the values
of a, b, x, and y can be the same or different and can have the
values provided above. Optionally, mode converters 947b and 947d
can be operable to convert the microwave energy transmitted through
waveguides 942e and 942i as well as the energy transmitted through
942y and 942z from a TM.sub.ab mode to a TE.sub.xy mode.
[0166] Further, in one embodiment illustrated in FIG. 10c, at least
one of mode converters 947a-d can comprise a mode converter
splitter operable both to change the mode of the microwave energy
passing therethrough and to split it into two or more separate
streams of microwave energy for discharge into the interior space
of the microwave heater. According to one embodiment, second mode
converters 947b and 947d can each comprise mode converting
splitters at least partially disposed within the interior of
microwave heater 930. In another embodiment, second mode converting
splitters 947b and 947d can be entirely disposed within the
interior of microwave heater 930 and can each be a part of a split
launcher 944a and 944h, respectively, as illustrated in FIG. 10c.
Additional details regarding split launchers 944a,h will be
discussed shortly.
[0167] According to one embodiment of the present invention wherein
the microwave distribution system 940 comprises two or more mode
converters in one or more waveguide segments, the total electrical
length between the first and second mode converters, extending
through and including the electrical length of any barrier assembly
(if present) can be equal to a value that is a non-integral number
of half-wavelengths of the competing mode of microwave energy
passing therethrough. As used herein, the term "electrical length"
refers to the electrical path of transmission of the microwave
energy, expressed as the number of wavelengths of the microwave
energy required to propagate along a given path. In one embodiment
wherein the physical transmission path includes one or more
different type of transmission media having two or more different
dielectric constants, the physical length of the transmission path
can be shorter than the electrical length. Thus, electrical length
depends on a number of factors including, for example, the specific
wavelength of microwave energy, the thickness and type (e.g.,
dielectric constant) of the transmission medium or media.
[0168] According to one embodiment, the total electrical length
between the first mode converter 947a,c and the second mode
converter 947b,d extending through and including the total
electrical length of the TM.sub.ab barrier assembly 970a,h can be
equal to a non-integral number of half-wavelengths of the competing
mode of microwave energy. As used herein, the term "non-integral"
refers to any number that is not a whole number. A non-integral
half-wavelength, then, may correspond to a distance of n times
.lamda./2, wherein n is any non-integral number. For example, the
number "2" is a whole number, while the number "2.05" is a
non-integral number. Thus, an electrical length corresponding to
2.05 times the half-wavelength of the competing mode of microwave
energy would be a non-integral number of half-wavelengths of that
competing mode.
[0169] As used herein, the term "competing mode of microwave
energy" refers to any mode of microwave energy propagating along a
given path other than the desired or target mode of microwave
energy intended for propagation along that path. The competing mode
may include a single, most prevalent mode (i.e., the predominant
competing mode) or a plurality of different, non-prevalent
competing modes. When multiple competing modes are present, the
total electric length between the first and second mode converters,
extending through and including the electrical length of any
barrier assembly (if present), can be equal to a value that is a
non-integral number of half-wavelengths of at least one of the
multiple competing modes and, in one embodiment, can be equal to a
value that is a non-integral number of half-wavelengths of the
predominant competing mode.
[0170] For example, in one embodiment depicted in FIG. 10c, first
mode converters 947a,c comprise TM.sub.ab mode converters operable
to convert at least a portion of the microwave energy in respective
waveguide segments 942a and 942d from a TE.sub.xy mode into a
TM.sub.ab mode in waveguide segments 942b and 942e. However, in
practice, at least a portion of the microwave energy may be
converted into a mode other than the desired mode. Any mode other
than the desired mode is generally referred to herein as the
"competing mode" of microwave energy. In one embodiment of the
present invention wherein the desired mode of microwave energy is a
TM.sub.ab mode, the competing mode of microwave energy may be a
TE.sub.mn mode, wherein n is 1 and m is an integer between 1 and 5.
Thus, in one embodiment, the total electrical length of the
TM.sub.ab waveguides 942e and 942i between first and second mode
convertors 947a and 947b, extending through and including the
electrical length of barrier assembly 970a, can be equal to a
non-integral number of half-wavelengths of the TE.sub.mn mode,
wherein n is 1 and m is an integer between 1 and 5. In another
embodiment, m can be 2 or 3.
[0171] In one embodiment, selecting physical lengths and properties
of waveguide segments 942, mode converters 947a-d, and/or barrier
assemblies 970a,h can minimize energy concentration within barrier
assemblies 970a,h. For example, according to one embodiment, while
at least about 5 kW, at least about 30 kW, at least about 50 kW, at
least about 60 kW, at least about 65 kW, at least about 75 kW, at
least about 100 kW, at least about 150 kW, at least about 200 kW,
at least about 250 kW, at least about 350 kW, at least about 400
kW, at least about 500 kW, at least about 600 kW, at least about
750 kW, or at least about 1,000 kW and/or not more than about 2,500
kW, not more than about 1,500 kW, or not more than about 1,000 kW
of energy can be passed through barrier assemblies 970a,h, the
temperature of at least a portion of at least one sealed window
member within barrier assemblies 970a,h (not shown in FIG. 10c) can
change by no more than about 10.degree. C., no more than about
5.degree. C., no more than about 2.degree. C. or no more than about
1.degree. C. In another embodiment, the pressure differential
across the at least one sealed window member and/or the pressure
within microwave heater 930 can be maintained as described above
with similar results.
[0172] According to one embodiment illustrated in FIG. 10c, at
least one of the individual microwave launchers 944a,h located on
generally opposite sides of and at least partially disposed within
the interior of microwave heater 930 can comprise a split launcher
defining at least two discharge openings for emitting microwave
energy into the interior of microwave heater 930. Although
illustrated as comprising a single pair (e.g., a first split
launcher 944a and a second split launcher 944h) of launchers in
FIG. 10c, it should be understood that microwave heater 930 can
comprise any suitable number of launchers or pairs of launchers, as
described herein.
[0173] One embodiment of a split launcher 944 is depicted in FIG.
10d. Split launcher 944 can comprise a single inlet or openings 951
for receiving microwave energy and a single (not shown) or two or
more discharge openings, or outlets, 945a,b for emitting microwave
energy therefrom. In one embodiment, the ratio of microwave energy
inlets to discharge outlets for a single split launcher can be 1:1,
at least 1:2, at least 1:3, or at least 1:4. According to one
embodiment, the mode of the microwave energy introduced into inlet
951 can be the same as the mode of the microwave energy emitted via
discharge openings 945a,b, while, in another embodiment, the modes
can be different. For example, in one embodiment wherein split
launcher 944 comprises a mode converting splitter 949, the
microwave energy introduced into a single inlet of a first sidewall
of a microwave heater can undergo a mode conversion and be divided
into at least two separate microwave energy portions, which can
subsequently be emitted into the interior of the heater, optionally
in a different mode. For example, in one embodiment shown in FIG.
10d, split launcher 944 can comprise a TM.sub.ab waveguide segment
942, one or two or more TE.sub.xy waveguide segments 943a,b and a
TM.sub.ab to TE.sub.xy mode converting splitter 949 disposed
therebetween. In operation, microwave energy in a TM.sub.ab mode
introduced via waveguide segment 942 passes through mode converting
splitter 949 before being discharged, simultaneously or nearly
simultaneously, in one or two or more separate fractions of
microwave energy from respective outlets 945a,b of waveguides
943a,b in a TE.sub.xy mode.
[0174] When launcher 944 comprises a single discharge opening, mode
converting splitter 949 can simply be a mode converter 949 (not a
splitter) for changing the mode of the microwave energy passing
therethrough. For example, in one embodiment wherein launcher 944
comprises a single discharge opening (not shown in FIG. 10d),
launcher 944 can comprise a single TM.sub.ab waveguide segment, a
single TE.sub.xy waveguide segment, and a TM.sub.ab-to-TE.sub.xy
mode converter 949 disposed therebetween. The mode converter can be
located outside, partially inside, or completely inside the
interior of the microwave heater. In operation, microwave energy in
a TM.sub.ab mode introduced via the inlet waveguide segment can
pass through mode converter 949 before being discharged in a
TE.sub.xy mode. The discharge opening of the single-opening
launcher can be oriented at any suitable angle with respect to the
horizontal or can be substantially parallel to the horizontal. In
one embodiment, the energy discharged from the single-opening
launcher can be oriented from the horizontal by an angle of at
least about 20.degree., at least about 30.degree., at least about
45.degree., or at least about 60.degree. and/or not more than about
100.degree., not more than about 90.degree., or not more than about
80.degree..
[0175] When multiple discharge openings are present, each of
discharge openings 945a,b of split launcher 944 can be oriented
from each other such that the paths of microwave energy discharged
therefrom define a relative angle of discharge, .crclbar., as shown
in FIG. 10d. In one embodiment, the relative angle of discharge
between the paths of microwave energy discharge openings 945a,b can
be at least about 5.degree., at least about 15.degree., at least
about 30.degree., at least about 45.degree., at least about
60.degree., at least about 90.degree., at least about 115.degree.,
at least about 135.degree., at least about 140.degree. and/or no
more than about 180.degree., no more than about 170.degree., no
more than about 165.degree., no more than about 160.degree., no
more than about 140.degree., no more than about 120.degree., no
more than about 100.degree., or no more than about 90.degree.. In
one embodiment, the orientation of discharge openings 945a,b can
also be described with respect to the orientation of the paths of
the microwave energy discharged therefrom relative to the axis of
extension 948 of TM.sub.ab waveguide segment 942. In one
embodiment, each of discharge openings 945a,b can be configured to
discharge microwave energy at respective first and second discharge
angles (.phi..sub.1 and .phi..sub.2) from the axis of extension 948
of TM.sub.ab waveguide segment 942. In one embodiment, .phi..sub.1
and .phi..sub.2, can be approximately equal, as generally depicted
in FIG. 10d, or, in another embodiment, one of the two angles can
be larger than the other. In various embodiments, .phi..sub.1
and/or .phi..sub.2 can be at least about 5.degree., at least about
10.degree., at least about 15.degree., at least about 30.degree.,
at least about 35.degree., at least about 55.degree., at least
about 65.degree., at least about 70.degree. and/or no more than
about 110.degree., no more than about 100.degree., no more than
about 95.degree., no more than about 80.degree., no more than about
70.degree., no more than about 60.degree., or no more than about
40.degree..
[0176] In one embodiment, split launcher 944 can be a
vertically-oriented split launcher such launcher 944 comprises at
least one upward-oriented discharge opening (e.g., 945a) configured
to emit microwave energy at an upward angle from the horizontal and
at least one downward-oriented discharge opening (e.g., 945b)
configured to emit microwave energy at a downward angle from the
horizontal. Although depicted in FIG. 10c as comprising
vertically-oriented split launchers 944a,h configured to discharge
energy at angles relative to the horizontal, in another embodiment,
one or more of split launchers 944a,h of microwave heater 930 can
be horizontally-oriented, such that the split launcher, as
described above, has been are rotated by 90.degree.. In another
embodiment, one or more split launchers 944a,h can be rotated by an
angle between 0.degree. and 90.degree.. In one embodiment (not
shown), a microwave heater can include two or more
vertically-spaced rows of horizontally-oriented split launchers
located on one side of the heater and two or more vertically-spaced
rows of horizontally-oriented split launchers on the other,
generally opposite side of the same heater. According to this
embodiment, the vertically-spaced rows of launchers can comprise
single-opening launchers, horizontally-oriented split launchers,
vertically-oriented split launchers, or any combination
thereof.
[0177] In one embodiment shown in FIG. 10c, microwave heater 930
can comprise one or more (or at least two) movable reflectors
990a-d positioned at various locations within microwave heater 930
and configured to raster microwave energy emitted from one or more
discharge openings 945a-d of one or more microwave launchers 944a,h
into the interior of microwave heater 930. Reflectors 990a-d can
have any suitable configuration, such as, for example,
configurations including one or more of the features previously
described with respect to FIGS. 9f-h. Further, although generally
illustrated as comprising four movable reflectors 990a-d, it should
be understood that microwave heater 930 can comprise any suitable
number of movable reflectors. In one embodiment, a microwave heater
comprising n split launchers can comprise at least 2n movable
reflectors. In another embodiment, a microwave heater can employ a
total of four movable reflectors, each defining a reflector surface
that extends substantially along the length of microwave heater
930, such that two or more axially adjacent launchers "share" one
or more reflectors or reflecting surfaces.
[0178] Regardless of the specific number of reflectors employed,
each reflector 990a-d can be operable to raster at least a portion
of the microwave energy exiting launchers 944a,h via discharge
openings 945a-d into microwave heater 930 to thereby heat and/or
dry at least a portion of the bundle or other object, article, or
load. As used herein, the term "raster" means to direct, project,
or concentrate energy over a certain area. In contrast to
conventional reflecting or dispersing energy, rastering energy
involves a greater degree of intentional directing or
concentrating, which can be accomplished by utilizing the
quasi-optical properties of microwave energy. In contrast to
conventional means, rastering does not include use of stationary
reflection surfaces or conventional mode stirring devices, such as
fans. In one embodiment, the microwave heater can comprise a
plurality of split launcher pairs (e.g., two or more pairs of
launchers), wherein each pair comprises two launchers having
substantially similar configurations (as described above). In one
embodiment, one launcher of each pair can be positioned on
generally opposite sides or on the same side of the microwave
heater, as discussed in detail previously, with respect to FIGS. 9c
and 9d. According to one embodiment, one or more movable reflectors
990a-d can be positioned near (and/or positioned to face) one or
more discharge openings of each of microwave launchers 944. In one
embodiment wherein first and second launchers 944a and 944h each
comprise split microwave launchers defining respective
upward-oriented discharge openings 945a and 945c and respective
downward-oriented discharge openings 945b and 945d, at least one
movable reflector can be positioned near one or more of discharge
openings 945a-d to raster at least a portion of the microwave
energy discharged from split launchers 944a,h (e.g., two or more
separate TE.sub.xy mode microwave portions) into the interior of
microwave heater 930. In one embodiment illustrated in FIG. 10c,
microwave heater 930 can comprise at least four movable reflectors,
each defining a respective reflecting surface and positioned near
respective discharge openings 945a-d of split launchers 944a,h. As
illustrated in FIG. 10c, movable reflectors 990a-d can be located
in the bottom left quadrant (e.g., reflector 990a), the top left
quadrant (e.g., reflector 990b), the top right quadrant (e.g.,
reflector 990c), and the bottom right quadrant (e.g., reflector
990d) of microwave heater 930. Two or more of reflectors 990a-d can
also be present when launchers 944a,h are horizontally-oriented
split launchers or single-opening launchers, as described in detail
previously.
[0179] Movable reflectors 990a-d can be configured in two
vertically-spaced pairs (e.g., reflector 990a paired with reflector
990b and reflector 990c paired with reflector 990d) and/or in two
horizontally-spaced pairs (e.g., reflector 990b paired with
reflector 990c and reflector 990a paired with reflector 990d). As
illustrated in FIG. 10c, pairs of vertically-spaced reflectors
(e.g., reflector pair 990a,b and 990c,d) can be positioned near
split launchers 944a,h such that one movable reflector is
positioned near each of discharge openings 945a-d of launchers
944a,h (e.g., discharge openings 945a-d face towards respective
movable reflectors 990a-d). As depicted in FIG. 10c, movable
reflectors 990b and 990c can be positioned at a higher vertical
elevation than respective movable reflectors 990a and 990d, such
that split launchers 944a,h can be vertically positioned between
vertically-spaced pairs of launchers (e.g., launcher 944a
vertically positioned between vertically-spaced pair of reflectors
990a,b and launcher 944h vertically positioned between
vertically-spaced pair of reflectors 990c,d). In one embodiment,
movable reflector 990 is positioned such that reflector surface 991
faces toward an open outlet of its corresponding microwave launcher
(not shown). In another embodiment, one or more movable reflectors
990a-d can be positioned in alignment with or positioned to face
the central axis of elongation of microwave heater 930 (not shown
in FIG. 10c).
[0180] Movable reflectors 990a-d can be directly or indirectly
coupled to one or more side walls of a microwave heater and can be
moved or actuated in any suitable fashion. One or more of the
reflectors 990a-d can move along a pre-programmed (planned) path,
or one or more can be caused to move in a random or non-repeating
pattern. When multiple reflectors 990a-d are present, two or more
reflectors 990a-d can have the same or similar pattern of movement,
in one embodiment, while, in the same or another embodiment, two or
more reflectors 990a-d can have different patterns of movement.
According to one embodiment, at least one of reflectors 990a-d can
move in a generally arcuate-shaped path and can pass through
various segments or "regions" of the overall path with a certain
speed and/or residence time. The size and number of regions, as
well as the speed with which the reflector moves through each
region or the reflector residence time in each region depend on a
variety of factors, such as for example, the size and type of the
bundle, the type of wood, and the preliminary and desired
characteristics of the initial and final bundle.
[0181] In one embodiment, each of reflectors 990a-d can be
individually driven or actuated according to one or more
embodiments described herein, while, in another embodiment, two or
more reflectors can be connected to a common drive mechanism (e.g.,
rotating shaft to be actuated at the same time. One example of a
drive mechanism for moving a reflector 990 using an actuator 960 is
shown in FIG. 10e. Actuator 960 can be a linear actuator having a
fixed portion 961 coupled to a sidewall 933 of the microwave heater
and an extensible portion 963 connected to a movable reflector 990.
According to one embodiment illustrated in FIG. 10e, at least part
of fixed portion 961 can extend through external side wall 933 and
into a bellows structure 964, thereby sealingly coupling actuator
960 to side wall 933. In one embodiment, bellows structure 964 can
be operable to reduce, minimize, or nearly prevent fluid flow into
or out of the location where actuator 960 extends through side wall
933. As shown in FIG. 10e, movable reflector 990 further comprises
a support arm 980 pivotally coupled to side wall 933 of the
microwave heater. As used herein, the term "pivotally coupled"
refers to two or more objects attached, fastened, or otherwise
associated such that at least one of the objects can generally move
or pivot about a fixed point. In operation, a driver 970 moves
extensible portion 963 of linear actuator 960 in an in-and-out type
motion, as indicated by arrow 971. Extensible portion 963 of linear
actuator 960 allows movable reflector 990 to move in a generally
arcuate pattern, as indicated by arrow 973. Driver 970 can be
controlled in any suitable manner, including, for example, using
one or more programmable automatic control systems (not shown).
[0182] According to one embodiment of the present invention, it may
be advantageous to minimize the amount of unoccupied, unobstructed,
or open volume defined within the interior of a microwave heater.
As used herein, the term "total open volume" refers to the total
volume of space within the interior of the vessel not occupied by
physical obstructions when a bundle of wood is not disposed in the
vessel. In one embodiment of the present invention, the ratio of
the total volume of the bundle of wood (including spaces between
individual pieces of wood) to the total open volume of the
microwave heater can be at least about 0.20, at least about 0.25,
at least about 0.30, at least about 0.35. In some of the foregoing
embodiments, the ratio is also no more than about 0.75, no more
than about 0.70, or no more than about 0.65.
[0183] In one embodiment, the microwave heater can define an
unobstructed bundle-receiving space for receiving a bundle of wood.
The unobstructed bundle receiving space can also be configured to
receive at least a portion of the microwave energy emitted to heat
and/or dry one or more objects (or bundles) therein. Unobstructed
bundle-receiving space of microwave heater 930 is denoted as 951 in
FIG. 10c. As used herein, the term "unobstructed bundle-receiving
space" refers to a space defined within the interior of a microwave
heater that is capable of receiving and holding a bundle of wood.
In one embodiment, the unobstructed bundle receiving space can
define a volume of a similar shape and within about 10 percent of
the volume occupied by the largest size bundle of wood able to be
loaded and/or processed within microwave heater 930. For example,
if the largest bundle size able to be accommodated by microwave
heater was 1,000 cubic feet, the unoccupied bundle receiving space
would have a volume, in one embodiment of about 1,100 cubic feet
and a similar shape (e.g., cuboidal) as the bundle processed within
heater 930.
[0184] The bundle receiving space may be "unobstructed" because it
may not include any physical obstructions (e.g., waveguides,
launchers, reflectors, etc.) disposed therein on a permanent basis.
In one embodiment of the present invention, the microwave heater
can comprise a circular cross-sectional shape, while unobstructed
bundle-receiving space 951 can define a cuboidal volume and/or be
configured to receive a bundle of wood having a cuboidal shape. In
one embodiment, the ratio of the total open volume of microwave
heater 930 to the volume of the unobstructed bundle-receiving space
can be at least about 0.20, at least about 0.25, at least about
0.30, at least about 0.35. In some of the foregoing embodiments,
the ratio is also no more than about 0.75, no more than about 0.70,
or no more than about 0.65.
[0185] According to one embodiment, at least a portion of the
unobstructed bundle receiving space 951 can be defined between two
or more "obstructions," including, for example, two or more
launchers, reflectors, waveguides, or other objects located on the
same or generally opposite sides of microwave heater 930 that take
up physical space within the interior volume of the heater. In one
embodiment wherein microwave heater 930 comprises two
oppositely-disposed doors (e.g., an entrance door 928 and an exit
door disposed on generally opposite ends of microwave heater 930),
at least a portion of unobstructed bundle receiving space 951 can
be defined between the two oppositely-disposed doors. In one
embodiment illustrated in FIG. 10c, none of launchers 944a,h or
movable reflectors 990a-d, which are examples of obstructions, are
disposed within unobstructed bundle space 951. In one embodiment
wherein at least a portion of the unobstructed bundle receiving
space is defined between two or more obstructions (e.g.,
waveguides, launchers, reflectors, etc.), the minimum clearance
between the outermost edges of one or more obstructions and the
unobstructed bundle-receiving space (and/or the bundle, when
present) can be at least about 0.5 inches, at least about 1 inch,
at least about 2 inches, at least about 6 inches, at least about 8
inches and/or no more than about 18 inches, no more than about 10
inches, or no more than about 8 inches. In one embodiment, one of
the obstructions do not physically contact the bundle when loaded
into heater 930.
[0186] One or more embodiments of the operation of a microwave
heating system according to the present invention will now be
described, with general reference to a process for heating a bundle
of wood. However, it should be understood that one or more elements
of the heating processes described herein can also be suitable for
use in processes for heating other items, as, for example, those
processes described previously. Furthermore, it should be
understood that one or more of the above-described embodiments of
microwave heating systems, including those discussed with respect
to FIGS. 8-10 and variations thereof, can be operated using at
least some, or all, of the operational steps, methods, and/or
processes described in detail below.
[0187] To initiate heating of a bundle of wood, the wood can first
be loaded into a microwave heater, which can be configured
according to one or more embodiments of the present invention
previously described. In one embodiment, the bundle can have an
overall initial weight (e.g., prior to heating) of at least about
100 pounds, at least about 250 pounds, at least about 375 pounds,
or at least 500 pounds prior to heating and/or drying. Once loaded,
the vacuum system, if present, can then be used to reduce the
pressure of the heater to no more than about 550 torr, no more than
about 450 torr, no more than about 350 torr, no more than about 300
torr, no more than about 250 torr, no more than about 200 torr, no
more than about 150 torr, no more than about 100 torr, or no more
than about 75 torr.
[0188] While maintaining the sub-atmospheric pressure in the
microwave heater, one or more microwave generators can then be
operated to begin introducing microwave energy into the interior of
the vessel to thereby heat and/or dry at least a portion of the
bundle. During the introduction of microwave energy into the
interior of the microwave heater, the pressure within the vessel
can be above, nearly at, or below atmospheric pressure. According
to one embodiment, the pressure of the interior of the microwave
heater during the heating step can be at least 350 torr, at least
about 450 torr, at least about 650 torr, at least about 750 torr,
at least about 900 torr, or at least about 1,200 torr, while, in
another embodiment, the pressure in microwave heater can be no more
than about 350 torr, no more than about 250 torr, no more than
about 200 torr, no more than about 150 torr, no more than about 100
torr, or no more than about 75 torr. The total generator capacity
or the rate of energy introduced into the interior of the microwave
heater during the heating and/or drying of the wood can be at least
about 5 kW, at least about 30 kW, at least about 50 kW, at least
about 60 kW, at least about 65 kW, at least about 75 kW, at least
about 100 kW, at least about 150 kW, at least about 200 kW, at
least about 250 kW, at least about 350 kW, at least about 400 kW,
at least about 500 kW, at least about 600 kW, at least about 750
kW, or at least about 1,000 kW and/or not more than about 2,500 kW,
not more than about 1,500 kW, or not more than about 1,000 kW.
[0189] According to one embodiment, the process of heating a bundle
of wood can comprise a plurality of individual sequential heating
cycles. The overall heating process can comprise at least 2, at
least 3, at least 4, at least 5, at least 6 and/or no more than 20,
no more than 15, no more than 12, or no more than 10 individual
sequential heating cycles. Each heating cycle can include the
introduction of microwave energy, optionally at sub-atmospheric
pressure. In one embodiment, microwave energy can be introduced
into the microwave heater under a pressure of not more than about
350 torr, while, in other one embodiment, the pressure in the
microwave heater can be at least about 350 torr.
[0190] According to one embodiment, each of the one or more
individual heating cycles can be carried out for (e.g., have a
duration of) at least about 2 minutes, at least about 5 minutes, at
least about 10 minutes, at least about 20 minutes, at least about
30 minutes and/or no more than about 180 minutes, no more than
about 120 minutes, or no more than about 90 minutes. Overall, the
entire length of the heating process (e.g., overall cycle time) can
be at least about 0.5 hours, at least about 2 hours, at least about
5 hours, or at least about 8 hours and/or no more than about 36
hours, no more than about 30 hours, no more than about 24 hours, no
more than about 18 hours, no more than about 16 hours, no more than
about 12 hours, no more than about 10 hours, no more than about 8
hours, or no more than 6 hours.
[0191] In one embodiment, wherein the overall heating process
comprises two or more individual heating cycles, one or more
subsequent individual heating cycles can be carried out with a
different input rate of microwave energy and/or at a different
pressure than the previous cycle. For example, in one embodiment,
the subsequent individual heating cycles can be carried out at a
lower input rate of microwave energy and/or at a lower pressure
than the previous cycle. In another embodiment, one or more
subsequent individual heating cycles can be carried out at a higher
input rate of microwave energy and/or at a higher pressure than the
previous cycle. In yet another embodiment, one or more subsequent
cycles can be carried out at a lower input rate of microwave energy
and a higher pressure or a higher input rate of microwave energy
and a lower pressure than one or more previous individual heating
cycles. When the overall heating process includes two or more
individual heating cycles, one or more of the second (or later)
cycles may be carried out as described above, according to some
embodiments. In other embodiments, two or more cycles can be
carried out at the same or nearly the same pressure and/or input
rate of microwave energy.
[0192] According to one embodiment, the overall heating process can
include a first sequential heating cycle followed by a second
heating cycle, wherein the second heating cycle is carried out with
a lower input rate of microwave energy than the first heating
cycle, a lower pressure than the first heating cycle, or both a
lower input rate of microwave energy and a lower pressure than the
first heating cycle. Further, in one embodiment when the overall
cycle comprises three or more heating cycles, the input rate of
microwave energy and/or pressure of each subsequent cycle (other
than the first) can be lower than the input rate of microwave
energy and/or pressure of the previous cycle. For example, in one
embodiment, the nth individual heating cycle can be carried out at
a lower input rate of microwave energy, a lower pressure, or both a
lower input rate of microwave energy and a lower pressure than the
(n-1)th individual heating cycle.
[0193] During the first individual heating cycle, a first maximum
input rate of microwave energy can be introduced into the microwave
heater. As used herein, the term "maximum input rate of microwave
energy" refers to the highest rate at which microwave energy is
introduced into the heater during a heating cycle. In various
embodiments, the maximum input rate of microwave energy introduced
during the first individual heating cycle (e.g., the first maximum
input rate of microwave energy) can be, for example at least about
5 kW, at least about 30 kW, at least about 50 kW, at least about 60
kW, at least about 65 kW, at least about 75 kW, at least about 100
kW, at least about 150 kW, at least about 200 kW, at least about
250 kW, at least about 350 kW, at least about 400 kW, at least
about 500 kW, at least about 600 kW, at least about 750 kW, or at
least about 1,000 kW and/or, for example, not more than about 2,500
kW, not more than about 1,500 kW, not more than about 1,000 kW, or
not more than 500 kW.
[0194] Subsequently, a second individual heating cycle can be
carried out such that the second maximum input rate at which
microwave energy is introduced into the microwave heater during the
second individual heating cycle (e.g., the second maximum input
rate of microwave energy) can, in some embodiments, be, for
example, at least about 25 percent, at least about 50 percent, at
least about 70 percent and/or, for example, no more than about 98
percent, no more than about 94 percent, or no more than about 90
percent of the maximum input rate achieved during the first heating
cycle. Similarly, when the heating process comprises three or more
individual heating cycles, the maximum input rate of microwave
energy of the nth individual heating cycle (e.g., third or fourth
cycle) in one embodiment can be, for example, at least about 25
percent, at least about 50 percent, at least about 70 percent
and/or, for example no more than about 98 percent, no more than
about 94 percent, no more than about 90 percent, or no more than
about 85 percent of the maximum input rate during the (n-1)th
(e.g., previous) individual heating cycle.
[0195] In one embodiment, the second (or subsequent) individual
heating cycle can be carried out at a lower pressure than the first
(or previous) individual heating cycle. For example, in one
embodiment wherein sub-atmospheric or vacuum pressure is utilized
during the heating cycle, the lowest pressure reached during the
first heating cycle can be at least about 250 torr. Subsequently, a
second individual heating cycle can be carried out such that the
lowest pressure reached (e.g., highest level of vacuum pressure
achieved) during the second cycle can, in one embodiment, for
example, be at least about 25 percent, at least about 50 percent,
at least about 70 percent, at least about 75 percent, at least 80
percent and/or in one embodiment, for example, no more than about
98 percent, no more than about 94 percent, or no more than about 90
percent of the lowest pressure reached during the first heating
cycle. Similarly, when the heating process comprises three or more
individual heating cycles, the pressure of the nth individual
heating cycle in one embodiment, for example, can be at least about
25 percent, at least about 50 percent, at least about 70 percent,
at least about 75 percent, at least 80 percent and/or no more than
about 98 percent, no more than about 94 percent, no more than about
90 percent of the lowest pressure reached, or no more than 85
percent of the lowest pressure reached during the (n-1)th
individual heating cycle.
[0196] Table 1, below, summarizes broad, intermediate, and narrow
ranges for the microwave energy rate, expressed as a percent of
maximum generator output, and the pressure, expressed in torr, for
consecutive first, second, third, and nth individual heating
cycles, according to one embodiment of the present invention. As
used herein, the term "maximum generator output" refers to the
maximum combined over the entire array cumulatively generated by
all of the microwave generators within a heating system. In one
embodiment, the maximum input rate of microwave energy for one or
more heating cycles can also be expressed as a percentage of
maximum generator output, as shown in Table 1.
TABLE-US-00001 TABLE 1 Microwave Energy Rate and Pressures for
Individual Heating Cycles Rate of Microwave Energy, Individual % of
Max Pressure, torr Cycle No. Broad Intermediate Narrow Broad
Intermediate Narrow 1 60-100% 70-100% 80-100% <250 <200
20-100 2 40-100% 50-95% 60-90% <250 <200 20-100 3 20-80%
25-75% 30-70% <250 <150 20-100 n 5-60% 10-50% 15-40% <150
<100 10-75
[0197] According to one embodiment of the present invention, each
of the one or more individual heating cycles can comprise a heating
period (e.g., a first, second, or nth heating period), wherein
microwave energy is introduced into the heater, and an optional
resting period (e.g., a first, second, or nth resting period)
wherein a reduced amount or substantially no microwave energy is
introduced into the heater. For example, during the heating period,
microwave energy can be introduced into the microwave heater at an
input rate sufficient to heat and/or at least partially dry at
least a portion of the wet or chemical-wet bundle of wood, while,
during the resting period, the input rate of microwave energy
introduced into microwave heater can, in one embodiment, be no more
than about 25 percent, no more than about 10 percent, no more than
about 5 percent, or no more than about 1 percent of the maximum
input rate of microwave energy introduced during the heating
period. In one embodiment wherein multiple individual heating
cycles are employed, each cycle can include one or more heating
periods and one or more rest periods. For example, when two
individual sequential heating cycles are utilized, the first
individual heating cycle can include at least a first heating
period and a first resting period, while the second individual
heating cycle can include at least a second heating period and a
second resting period. Alternatively, the second heating period can
follow the first heating period with no interim resting period.
[0198] In one embodiment, each of the heating periods can have, for
example, a duration of at least about 5 minutes, at least about 10
minutes, at least about 15 minutes, at least about 30 minutes
and/or, for example, no more than about 60 minutes, no more than
about 40 minutes, no more than about 30 minutes, or no more than
about 20 minutes. In one embodiment, the resting period can have a
duration of, for example, at least about 5 minutes, at least about
10 minutes, or at least about 20 minutes and/or, for example, no
more than about 90 minutes, no more than about 60 minutes, or no
more than about 40 minutes. In one embodiment, the ratio of the
length of the heating period to the length of the resting period of
an individual heating cycle can be for example, at least about
0.5:1, at least about 1:1, at least about 1.25:1, or at least 2:1
and/or, for example, no more than about 5:1, no more than about
3:1, no more than about 2.5:1, or no more than about 1.5:1.
[0199] Microwave energy can be introduced into the microwave heater
during each of the heating periods in any suitable manner. For
example, in one embodiment, microwave energy can be emitted from
one or more launchers in a substantially continuous manner
throughout the entire duration of the heating period. In one
embodiment, energy can be emitted from one single launcher at a
time, while, in another embodiment, energy can be emitted from two
or more launchers simultaneously. The amount, timing, duration,
coordination, and synchronization of microwave energy discharged
from each of the launchers can be controlled using an automatic
control system. When the discharge of energy into the microwave
heater includes switching between two or more launchers, the
switching can also be controlled by the control system, as
discussed in detail shortly.
[0200] According to one embodiment, energy can be introduced into
the microwave heater such that each heating period can include two
or more different heating modes (also called discharge modes,
discharge phases, or heating phases). In one embodiment, different
rates of microwave energy can be emitted from one or more launchers
during each heating phase. For example, in one embodiment, during a
first heating phase, energy can be emitted from a first launcher at
a higher rate than is emitted from a second launcher, while, during
a second heating phase, energy can be emitted from the second
launcher at a higher rate than from the first launcher. According
to one embodiment, one or more launchers can emit microwave energy
into the microwave heater, while one or more launchers can emit
substantially no energy into the microwave heater, thereby focusing
energy onto different locations of the bundle of wood (or other
object). Each separate heating phase can be carried out for a
period (i.e, have a duration) of, for example at least about 2
minutes, at least about 5 minutes, at least about 12 minutes, at
least about 15 minutes and/or, for example, no more than about 90
minutes, no more than about 60 minutes, no more than about 45
minutes or no more than about 30 minutes. An optional resting
period of at least about 2 minutes, at least about 4 minutes, or at
least about 6 minutes and/or no more than about 15 minutes, no more
than about 12 minutes, or no more than about 10 minutes can follow
one or both separate heating phases.
[0201] When the microwave heater comprises four or more launchers,
the microwave distribution system can be configured such that each
launcher emits microwave energy into the microwave heater in a
separate heating or discharge phase, depending on the position of
one or more microwave switches. For example, in one embodiment
wherein the microwave heater comprises a first, second, third, and
fourth microwave launcher, two or more microwave switches (e.g., a
first and a second microwave switch) can be configured such that
microwave energy can be predominantly emitted from each launcher in
a respective first, second, third, and fourth heating phase. In one
embodiment, two or more discharge phases can be carried out at
substantially the same time, while two or more discharge phases can
be prevented from being carried out substantially the same time.
Additional details regarding operation of microwave heaters
utilizing heating periods that include alternating discharge phases
will now be discussed in detail below, with reference to FIGS. 11a
and 11b.
[0202] Turning now to FIGS. 11a and 11b, schematic top views of a
microwave heating system 1020 configured according to one
embodiment of the present invention are provided. Microwave heating
system 1020 is illustrated as comprising at least four microwave
generators 1022a-d for producing microwave energy and a microwave
distribution system 1040 for directing at least a portion of the
microwave energy into a microwave heater 1030. Microwave
distribution system 1040 also comprises a plurality of spaced
microwave launchers 1044a-h (which, in one embodiment, can comprise
one or more split launchers) operable to emit at least a portion of
microwave energy into the interior of microwave heater 1040. Each
of microwave launchers 1044a-h can be operably coupled to one or
more of a plurality of (in this figure, a first through fourth)
microwave switches 1046a-d, as shown in FIGS. 11a and 11b.
Microwave switches 1046a-d can be operable to route microwave
energy to one or more of launchers 1044a-h in any suitable mode
including, for example, a TM.sub.ab mode and/or a TE.sub.xy mode,
as discussed in detail previously. In one embodiment, the energy
propagated through microwave distribution system 1040 can change
modes at least once prior to being discharged into microwave heater
1030. Various configurations and methods of operating microwave
heating system 1020 according to one or more embodiments of the
present invention will now be described in detail below, with
reference to FIGS. 11a and 11b.
[0203] Each of microwave switches 1046a-d can be operable to
direct, control, or allocate the flow of microwave energy to each
of two or more microwave launchers 1044a-h positioned on generally
the same side or generally opposite sides of microwave heater 1030.
For example, in one embodiment depicted in FIG. 11a, each of
microwave switches 1046a-d can be coupled to a pair of axially
adjacent microwave launchers (e.g., launchers 1044a and 1044b,
launchers 1044c and 1044d, launchers 1044e and 1044f, and launchers
1044g and 1044h), represented as launcher pairs 1050a-d. In another
embodiment illustrated in FIG. 11b, each of microwave switches
1046a-d can be coupled to a pair of axially aligned microwave
launchers (e.g., launchers 1044a and 1044h, launchers 1044b and
1044g, launchers 1044c and 1044f, and launchers 1044d and 1044e),
shown as launcher pairs 1050e-h.
[0204] Microwave switches 1046a-d can be any suitable type of
microwave switch and, in one embodiment, can be a rotary microwave
switch. A rotary microwave switch can include an outer housing, an
internal routing element disposed therein, and an actuator for
moving the internal routing element within the housing. In one
embodiment, the internal routing element can be rotatably coupled
to the outer housing and the actuator can be operable to
selectively rotate the internal routing element, relative to the
outer housing, to thereby switch or direct the direction of flow of
the microwave energy passing therethrough. Other types of suitable
microwave switches can also be employed. In one embodiment,
microwave switches 1046a-d can comprise TE.sub.xy switches, while,
in another embodiment, microwave switches 1046a-d can comprise
TM.sub.ab switches. Any additional suitable components, such as one
or more mode converters, barrier assemblies, or components
discussed elsewhere in this application but not shown in FIGS. 11a
and 11b, can be located upstream or downstream microwave switches
1046a-d.
[0205] In operation, microwave switches 1046a-d can be selectively
switchable between a first heating (or discharge) phase and a
second heating (or discharge) phase. During the first heating
phase, more energy can be emitted or discharged from one or more
microwave launchers, while less energy is emitted from one or more
other microwave launchers. Similarly, during the second heating
phase, more energy can be emitted or discharged from one or more
other microwave launchers, while less energy can be emitted or
discharged from one or more microwave launchers.
[0206] In one embodiment, during the first heating phase, each of
microwave switches 1046a-d can be configured to route microwave
energy predominantly to one or more launchers within a first set of
microwave launchers (labeled as set of "A" launchers in FIGS. 11a
and 11b) and not predominantly to one or more launchers of a second
set of microwave launchers (labeled as a set of "B" launchers in
FIGS. 11a and 11b). During the second discharge phase, each of
microwave switches 1046a-d can be configured to route microwave
energy predominantly to one or more launchers of the second set
(e.g., the "B" launchers) and not predominantly to one or more
launchers of the first set (e.g., the "A" launchers) in each of
respective pairs of launchers 1050a-d and 1050e-h, in FIGS. 11a and
11b. As used herein, references to routing microwave energy
"predominantly" to launcher X and "not predominantly" to launcher Y
means that at least about 50 percent of the microwave energy
received by a switch is routed to launcher X, while no more than
about 50 percent of the microwave energy received by the switch is
routed to launcher Y. In one embodiment, for example at least about
75 percent, at least about 90 percent, at least about 95 percent,
substantially all of the energy can be predominantly routed to
launcher X, while, for example no more than about 25 percent, no
more than about 10 percent, no more than about 5 percent or
substantially none of the energy can be routed to launcher Y.
[0207] In one embodiment, microwave heating system 1030 can further
comprise a control system 1060 for controlling the action and
configuration of microwave switches 1046a-d. In one embodiment,
control system 1060 can be operable to configure each of switches
1046a-d to be in the first discharge phase, such that all "A"
launchers (e.g., launchers 1044a,c,e,g) emit microwave energy into
microwave heater 1030, while all "B" launchers (e.g., launchers
1044b,d,f,h) emit a smaller amount of, or substantially no
microwave energy into the interior of microwave heater 1030, as
illustrated by the respective shaded and un-shaded regions of
microwave heater 1030 in FIGS. 11a and 11b. Subsequently, control
system 1060 can then be operable to configure each of switches
1046a-d to be in the second discharge phase, such that all "A"
launchers (e.g., launchers 1044a,c,e,g) emit a smaller amount of,
or substantially no microwave energy into the interior of microwave
heater 1030, while all "B" launchers (e.g., launchers 1044b,d,f,h)
emit microwave energy into the interior of microwave heater 1030
(not represented in FIGS. 11a and 11b).
[0208] According to one embodiment, control system 1060 can also be
operable to control the switching of microwave switches 1046a-d
between the first and second discharge phases based on a set of
predetermined parameters including, for example, cycle time, total
energy discharged, and the like. For example, in one embodiment,
control system 1060 can be operable to configure each of microwave
switches 1046a-d into the first discharge phase substantially
simultaneously, such that microwave energy can be emitted from each
of the "A" launchers 1044a,c,e,g simultaneous for a period of time.
In another embodiment, control system 1060 can be operable to
include a time delay or lag between configuring one or more
switches 1046a-d into the first discharge phase. As a result, the
microwave energy emitted from one or more "A" or "B" launchers may
be delayed or staggered, relative to the discharge of energy from
one or more other "A" or "B" launchers. In one embodiment, control
system 1060 may be configured to allow one or more switches 1046a-d
to be in the first discharge phase, while one or more other
switches 1046a-d are in the second discharge phase, such that
microwave energy can be emitted from one or more "A" launchers and
one or more "B" launchers simultaneously. In one embodiment of the
present invention, control system 1060 can also be operable to at
least partially prevent simultaneous energy discharge from directly
opposed pairs of launchers (e.g., pair 1044a and 1044h, pair 1044b
and 1044g, pair 1044c and 1044f, pair 1044d and 1044e) and/or
axially adjacent pairs (e.g., pair 1044a and 1044b, pair 1044c and
1044d, pair 1044e and 1044f, pair 1044g and 1044h).
[0209] Heating systems configured and/or operated according to one
embodiment of the present invention can be operable to heat an
object or load more efficiently than conventional heating systems.
In particular, heating systems configured according to various
embodiments of the present invention can be operable to process
large, commercial-scale loads. In one embodiment, heating systems
as described herein can heat a bundle of wood or other load having
a cumulative, pre-heating (or pre-treatment) weight of at least
about 100 pounds, at least about 500 pounds, at least about 1,000
pounds, at least about 5,000 pounds, or at least about 10,000
pounds. In various embodiments, a bundle of wood can be heated
and/or dried such that no more than, for example, about 20 percent,
no more than about 10 percent, no more than about 5 percent, and no
more than about 2 percent of the total volume of wood can reach a
temperature that does exceed an upper threshold temperature. In the
same or other embodiments, at least about 80 percent, at least
about 90 percent, at least about 95 percent, and at least about 98
percent, for example, of the total volume of wood can reach a
temperature that does exceed a lower threshold temperature. The
lower and upper threshold temperatures can be relatively close to
one another and can, for example, be within about 110.degree. C.,
within about 105.degree. C., within about 100.degree. C., within
about 90.degree. C., within about 75.degree. C., or within about
50.degree. C. of each other. In various embodiments, the upper
threshold temperature can be at least about 190.degree. C., at
least about 200.degree. C., or at least about 220.degree. C. and/or
no more than about 275.degree. C., no more than about 260.degree.
C., no more than about 250.degree. C., or no more than about
225.degree. C. In another embodiment, the lower threshold
temperature can be at least about 115.degree. C., at least about
120.degree. C., at least about 125.degree. C., at least about
130.degree. C. and/or no more than about 150.degree. C., no more
than about 145.degree. C., or no more than about 135.degree. C.
[0210] According to one embodiment, at least about 80 percent, at
least about 90 percent, at least about 95 percent, and at least
about 98 percent of the total volume of the wood can reach a
maximum temperature of at least about 130.degree. C., at least
about 145.degree. C., at least about 150.degree. C., or at least
about 160.degree. C. and/or no more than about 250.degree. C., no
more than about 240.degree. C., no more than about 225.degree. C.,
no more than about 210.degree. C., or no more than about
200.degree. C. As a result, a bundle of wood (optionally a
chemical-wet bundle of wood) having an initial (e.g., pre-heating
or pre-treatment) weight of at least about 100 pounds, at least
about 500 pounds, at least about 1,000 pounds, or at least about
5,000 pounds can be heated in no more than about 48 hours, no more
than about 36 hours, no more than about 24 hours, no more than
about 18 hours, no more than about 16 hours, no more than about 12
hours, no more than about 10 hours, no more than about 8 hours, or
no more than about 6 hours.
[0211] The various aspects of the present invention can be further
illustrated and described by the following Examples. It should be
understood, however, that these Examples are included merely for
purposes of illustration and are not intended to limit the scope of
the invention, unless otherwise specifically indicated.
EXAMPLES
Example 1
Acetylation of Wood in a Two-Vessel System
[0212] This example describes a pilot-scale experiment in which
wood is acetylated and heated in a dual vessel system. As shown
herein, utilizing separate vessels for the acetylation step and the
heating step allows for the production of dried, acetylated wood
within a short period of time.
[0213] A pilot-scale acetylation reactor having a diameter of 10
inches and a length of 9 feet was constructed. Several Southern
Yellow Pine boards, kiln dried to a moisture content between 6 and
8 weight percent, were loaded into the acetylation reactor and the
reactor door was closed and sealed. A vacuum system was used to
reduce the pressure in the acetylation reactor to between 40 and 70
torr and the vacuum was maintained for 20 to 45 minutes to remove
residual air and/or water from the wood. After the hold period, the
interior volume of the reactor was filled with acetic anhydride at
room temperature and the pressure in the reactor was increased to
between 80 and 90 psig to thereby maximize impregnation of the wood
with the acetic anhydride.
[0214] After about 40 minutes, the liquid was drained from the
reactor and the pressure was increased to 1,500 torr with warm
nitrogen. At the same time, the temperature was increased to about
140.degree. C. using the reactor steam jacket and, once all the
liquid was drained from the reactor, hot acetic acid vapors were
injected into the vessel to contact the wood, thereby catalyzing
the reaction. After about 60 minutes, the hot vapor injection was
stopped and acetylation was allowed to occur at the increased
reactor pressure for a period between 1.5 and 3 hours. Thereafter,
the pressure in the reactor was reduced to flash vaporize residual
acetic acid and/or anhydride thereby at least partially drying the
acetylated wood. The pressure in the reactor was then reduced
further to about 60 to 80 torr thereby drying the boards to a
chemical moisture content between 10 and 20 weight percent.
Nitrogen was injected to reduce the temperature in the reactor.
[0215] Once cooled, the acetylated boards were removed, wrapped in
plastic to minimize vapor emissions to the external environment,
and transported to a hood, where the boards were cut into 16 to 18
inch lengths prior to being introduced into a microwave heater. The
microwave heater, which had a diameter of 19 inches and a length of
43 inches, was a model .mu.WAVEVAC0350 vacuum microwave dryer
(commercially available from Pueschner Microwave Power Systems in
Schwanewede, Germany) that utilized a 3.5 kW, 2450 MHz microwave
generator. The exterior walls of the heater were electrically
warmed to prevent condensation of acetic acid and/or acetic
anhydride during the heating/drying cycle.
[0216] Prior to loading the microwave heater, a hole was drilled
near the center of each of the acetylated boards and a NEOPTIX
fiber optic temperature sensor was inserted into the hole to
monitor the temperature during heating. The boards were then placed
on a turntable located in the center of the microwave heater, which
also included a system for monitoring gravimetric data during
heating. The door on the heater was closed and sealed and the
chamber was purged with nitrogen. A mode stirrer positioned on the
upper wall of the chamber was turned on and a vacuum pump was used
to reduce the pressure within the interior of the heater to between
20 and 60 torr. The microwave generator was then turned on and set
to emit 400 W of energy into the heater. Within minutes, the
temperature of the boards increased to between 170.degree. C. and
190.degree. C.
[0217] During the duration of the heating process, gravimetric and
temperature data were monitored and a programmable logic controller
(PLC) was used to cycle the generator on and off until the target
board temperature was reached. The boards were maintained at the
target temperature for between 30 and 90 minutes and, after the
heating cycle was completed, the PLC stopped the vacuum pump, and
returned the chamber to atmospheric pressure. The door of the
microwave heater was then opened and the dried boards were removed.
The average final chemical moisture content of the dried,
acetylated boards was less than 5 weight percent.
Example 2
Determination of Energy Distribution Profile within a Bundle
[0218] This example provides actual data obtained from a
pilot-scale microwave heater used to heat and/or dry a bundle of
acetylated wood. Thermal images were used to construct an energy
distribution profile, which will then be correlated, in prophetic
Example 3, to predict chemical moisture profiles of wood heated on
a commercial scale.
[0219] A horizontally-elongated microwave heater similar to the
heater illustrated in FIGS. 10a, c, d, and e was constructed with
an outer diameter of 12 feet and an overall length of 16 feet. The
heater included an entrance door for loading and unloading the
bundle from the vessel. Four split microwave launchers similar to
those illustrated in FIGS. 10c and 10d were arranged in two
oppositely-disposed pairs and were connected to a FERRITE 75 kW 915
MHz microwave generator (commercially available from Ferrite
Microwave Technologies, Inc. in Nashua, N.H.) via a system of
TE.sub.10 waveguides. Three microwave switches were configured to
route energy from the generator to one of the two launchers of each
pair, as described in detail below.
[0220] The microwave heater also included four movable reflectors
similar to those illustrated in FIG. 10c. Each reflector defined a
continuous reflective surface extending substantially along the
length of the heater. Each of the four split launchers were
vertically positioned between a pair of movable reflectors such
that the energy emitted from the respective upward- and
downward-oriented discharge openings of each split launcher was
rastered into the interior of the microwave heater by the
reflective surfaces disposed in each of the four quadrants of the
internal volume of the heater. Each reflective surface was rotated
along a generally arcuate path via a shaft, which utilized an
external driver. Details regarding the motion of the movable
reflectors will be described in detail shortly.
[0221] Approximately 15,000 pounds of acetylated Radiata pine was
allowed to moisture-equilibrate in the ambient atmosphere such that
the average water content of the wood was about 2-3 weight percent.
The wood was then bundled into a composite bundle comprising four
individually-secured stacks (e.g., stacks A-D shown in FIG. 12).
The composite bundle, represented as bundle 1304 in FIG. 12, had
nominal dimensions of 4 feet wide by 8 feet tall by 16 feet long.
Each of stacks A-C had a width of 6 inches, while stack D had a
width of 2.5 feet. Composite bundle 1304 was introduced into the
microwave heater and the door was closed and secured prior to
initiating the heating cycle.
[0222] First, the microwave switches were configured such that the
energy from the generator would be routed to two diagonally
opposite (e.g., oppositely-disposed, axially-staggered) launchers
at the same time, while the remaining two diagonally opposite
launchers remained idle. The generator was then started and set to
deliver 75 kW to the first diagonally opposite pair of launchers,
in a manner similar to the one discussed previously with respect to
launcher set "A" of FIGS. 11a and 11b. Next, after about 10
minutes, the generator was stopped and the microwave switches were
reconfigured to route energy from the first active set of
diagonally opposite launchers to the idle set of diagonally
opposite launchers during the second heating mode. The generator
was then restarted at 75 kW and microwave energy was again
discharged into the heater. After another 10 minutes, the generator
was stopped so that the switches could be returned to the original
configuration, thereby re-routing energy back to the first pair of
diagonally opposite launchers. This sequence of alternatively
discharging energy from axially-staggered pairs of launchers
continued in 10-minute increments for a total of 80 minutes (e.g.,
100 kW-hr).
[0223] During each heating mode, the energy discharged from each of
the microwave launchers was rastered into the interior of the
microwave heater by controlling the motion and position of each of
the movable reflectors. A programmable logic controller (PLC) was
set to rotate each reflector, using a servo motor, through various
portions (or regions) of its total arcuate path at various speeds.
The top and bottom pairs of reflectors were programmed to move at
the same speed, but the movement of one reflector of each pair was
initiated before the other, thereby avoiding both reflectors of the
pair moving in synchronized tandem. Table 2 below, summarizes the
boundaries (e.g., starting and ending position) and total length of
each of the eight regions of motion, as well as the reflector speed
and time spent in each region (e.g., residence time) for each of
the top and bottom pairs of reflectors, expressed as a percentage
of the overall reflector cycle time. Note that Table 2 summarizes
only half of the profile for each reflector; once each pair of
reflectors moved through regions 1-8 as described below, each
reflector then traveled in a reverse pattern, beginning with region
8 and moving back to region 1.
TABLE-US-00002 TABLE 2 Profile for Movable Reflectors Top
Reflectors Bottom Reflectors Starting Ending Length Length
Residence Residence Position Position of Path of Path Speed Time
Speed Time Region (.degree.) (.degree.) (.degree.) (%) (.degree./s)
(% of Cycle) (.degree./s) (% of Cycle) 1 0.0 0.1 0.1 0.31% 0.07 0.9
0.05 1.0 2 0.1 4.0 3.9 12.19% 0.10 23.3 0.05 24 3 4.0 8.0 4.0
12.50% 1.82 1.0 1.82 1.3 4 8.0 12.0 4.0 12.50% 1.82 1.0 1.82 1.3 5
12.0 16.0 4.0 12.50% 1.82 1.0 1.82 1.3 6 16.0 24.0 8.0 25.00% 1.82
2.0 1.82 2.6 7 24.0 28.0 4.0 12.50% 0.25 7.5 0.26 9.5 8 28.0 32.0
4.0 12.50% 0.04 48.0 0.04 59.0
[0224] Once the overall heating cycle was complete, the generator
was turned off and the heated composite bundle was transported to a
holding zone wherein a MIKRON 7500 model camera with a wide angle
lens was positioned approximately 10 feet from one of the elongated
sides of the heated bundle. Stack A, the outermost stack of boards
shown in FIG. 12, was removed from the composite bundle to thereby
expose an interior surface of stack B, designated as B' in FIG. 12.
The camera recorded thermal images of surface B' at a rate of 1
image per every 5 seconds and, after about 20 seconds, stack B was
removed from the composite bundle. The camera then began recording
thermal images of an interior surface of stack C, designated as
surface C' in FIG. 12. After about 20 seconds, stack C was removed
from the bundle, thereby exposing the internal surface of stack D,
designated as surface D' in FIG. 12. The camera recorded thermal
images of surface D' for about 20 seconds and was then stopped.
[0225] To analyze the composite temperature distribution throughout
the volume of the bundle, pixel-by-pixel temperature data obtained
within a representative region of interest for each of surfaces B'
through D' was imported into a spreadsheet using MikroSpec.TM.
Professional thermal imaging software (version 4.0.5, available
from Metrum in Berkshire, UK). A cumulative frequency histogram,
incorporating thermal data obtained from all interior surfaces B'
through D' of the composite bundle is shown in FIG. 13.
[0226] As shown in FIG. 13, less than 20 percent of the volume of
the bundle had a temperature below 42.degree. C. or above
52.degree. C. When correlated to a bundle of dried, acetylated
wood, this type of energy distribution results in the predicted
chemical moisture content profile, described in prophetic Example
3.
Example 3
(Prophetic): Calculation of Chemical Moisture Content Profile
within an Acetylated Bundle
[0227] This prophetic example uses the experimental energy
distribution data obtained in Example 2 to predict the chemical
moisture profile (e.g., amount and distribution of one or more heat
removable chemicals within the total volume) of acetylated wood
heated and/or dried in a commercial-scale microwave heating system
configured similarly to the system described previously in Example
2.
[0228] A bundle of acetylated wood, having dimensions of
approximately 101 inches tall by 52 inches wide by 16 feet long is
loaded into a microwave heater having an internal diameter of 11
feet, 7 inches and a flange-to-flange length of 17 feet. The
pressurizable heater includes an oppositely-disposed entrance and
exit opening, each sealable with a full diameter dished door. The
total internal volume of the heater is 2605 cubic feet, and the
ratio of the total volume of the bundle of wood to the total open
(e.g., unoccupied) volume in the microwave heater is 0.29:1. Prior
to heating in the microwave heater, the bundle has a "chemical
moisture content" (i.e., an amount of one or more heat-vaporizable
chemicals including, for example, acetic acid, acetic anhydride,
and combinations thereof) of approximately 10-15 weight
percent.
[0229] During heating of the bundle, microwave energy is introduced
into the microwave heater in a similar manner as previously
described in Example 2. In addition, a vacuum system is used to
maintain the internal pressure of the heater at 60 torr. After 80
minutes, the microwave generator is turned off, the bundle is
removed, and thermal images of interior surfaces of the bundle are
taken in the manner previously described in Example 2. The
predicted temperature distribution resulting from the cumulative
thermal data is provided in FIG. 14.
[0230] As shown in FIG. 14, the projected temperature distribution
for the acetylated bundle of wood has a mean peak temperature of
165.degree. C., and less than 0.3 percent of the total volume of
the bundle has a temperature below 115.degree. C. or above
235.degree. C. According to previously-obtained empirical data
correlating wood temperature to chemical moisture content, the
temperature distribution in FIG. 14 predicts a chemical moisture
content profile as summarized in Table 3, for a dried bundle of
acetylated wood processed as described above.
TABLE-US-00003 TABLE 3 Projected Chemical Moisture Content Profile
for Dried Acetylated Wood Percent of Bundle Predicted Moisture
Temperature Volume Content T < 115.degree. C. 0.3% ~2 wt %
moisture 115.degree. C. < T < 135.degree. C. 2.2% ~1 wt %
moisture T > 235.degree. C. 0.3% Scorched 115.degree. C. < T
< 235.degree. C. 99.4% Dried 135.degree. C. < T <
235.degree. C. 97.2% Dried
[0231] The overall objective of heating and/or drying the
acetylated wood is to remove residual acetylation chemicals (e.g.,
by minimizing the chemical moisture content of the dried bundle),
while not over-drying or scorching the treated wood. As shown in
Table 3, less than 0.3 percent of the total volume of the
acetylated bundle is under-dried (e.g., has a moisture content of 2
weight percent or more) or subjected to scorching (e.g., has an
average temperature greater than 235.degree. C.). In addition, less
than 2.2 percent of the total volume of the bundle has a moisture
content of 1 percent or more. Thus, at least 97.2 (and up to 99.4)
percent of the total volume of the acetylated bundle is heated and
dried to a chemical moisture content of less than 1-2 weight
percent, while simultaneously minimizing the amount of scorched
wood.
Example 4
Use of Sequential Heating Cycles Utilizing Different Levels of
Microwave Energy
[0232] This example illustrates how the method of applying heat to
a bundle of wood affects the temperature distribution of the heated
wood. Several trials were conducted that included one or more
individual heating cycles having various durations, pressures,
and/or energy levels to determine the impact on the temperature of
the bundle, as well as the quantity of wood scorched, during the
heating cycle.
[0233] A microwave heating system similar to the system illustrated
in FIGS. 9a, 9b, and 9e was constructed and included a FERRITE 75
kW 915 MHz microwave generator (commercially available from Ferrite
Microwave Technologies, Inc. in Nashua, N.H.) coupled to a vacuum
microwave heater via a series of TE.sub.10 waveguides. Three rotary
microwave switches were configured to selectively route microwave
energy from the generator to one of four microwave launchers
located in the interior of the microwave heater. Each launcher was
designed to receive energy in a TE.sub.10 mode, but included a mode
converter disposed within the interior of the vessel for converting
the energy to a TM.sub.01 mode before being emitted into the
heater. The vacuum heater, which had a diameter of 6.5 feet and an
overall length of 8 feet, included a single door on one end for
loading and unloading the wood. The system also included a
mechanical, dry (e.g., non-oil sealed) vacuum pump (commercially
available from Edwards Limited in Tewksbury, Mass.) for controlling
the pressure within the heater as desired during the heating
step.
[0234] For each of trial Runs A-H, six planks of acetylated Radiata
pine having nominal dimensions of 1 inch by 6 inches by 8 feet were
equipped with fiber optic temperature sensors placed into holes
drilled at the center point of each board. The sensor-equipped
boards were placed in row 13 of a stickered bundle that included a
total of 156 boards of acetylated Radiata pine arranged in 26
layers. The bundle was then fastened together and loaded into the
vacuum heater. During each run A-H, the bundle was exposed to
different heating and/or pressure profiles. For each run, the peak
average and peak maximum fiber optic temperatures, the weight of
the bundle before and after heating (to calculate evaporative
loss), and the total energy input were measured for each cycle. Key
characteristics of each bundle and specifics of each heating
profile are summarized in Tables 4a and 4b, below.
TABLE-US-00004 TABLE 4a Bundle Properties and Individual Heating
Profiles for Runs A-H Bundle Properties Overall Cycle Data Avg. Dry
Total Power Energy Moisture Weight Pressure Input Density (kW/lb
Run Content (%) (lb) (torr) (kW-hr) dry wood) A 2.55 1553 350 26.2
0.0094 B 2.04 1833 350 30.7 0.0107 C 2.18 1528 350 26.0 0.0107 D
2.10 1800 350 30.7 0.0109 E 2.70 1630 200 37.0 0.0148 F 2.45 1592
200 36.0 0.0155 G 2.72 1566 300 32.0 0.0125 H 1.95 1836 350 41.3
0.0168
TABLE-US-00005 TABLE 4b Bundle Properties and Individual Heating
Profiles for Runs A-H (cont'd) First Second Third Fourth Heating
Cycle Heating Cycle Heating Cycle Heating Cycle Energy Time Rest
Energy Time Rest Energy Time Rest Energy Time Rest Run (kW) (min)
(min) (kW) (min) (min) (kW) (min) (min) (kW) (min) (min) A 25 63 --
-- -- -- -- -- -- B 25 40 30 2 20 14 22 20 -- -- -- -- C 25 55 50 2
10 -- -- -- -- -- -- -- D 25 40 30 2 20 9 22 20 -- -- -- -- E 22 60
16 8 50 -- -- -- -- -- -- -- F 18 40 20 8 40 28 12 45 -- -- -- -- G
20 40 20 0 34 20 12 36 -- -- -- -- H 25 40 35 0 40 40 16 8 42 12 20
--
[0235] Upon completion of each run, the bundle was removed and each
of the boards was visually inspected for signs of scorching, which
was defined as quarter-size or larger blackened or burned marks.
The evaporative (moisture) loss was calculated by comparing the
weight of the bundle before and after heating (and the known dry
weight of each board). The energy density (per pound of dry wood)
was calculated based on the total energy input and initial weight
and moisture content of the wood. Table 5, below, summarizes the
results of runs A-H, including the average and maximum peak
temperatures achieved during heating and the number of scorched
boards.
TABLE-US-00006 TABLE 5 Summary of Results for Runs A-H Results
Energy Density Average Peak Maximum Peak Scorched Run (kW/lb dry
wood) Temp (.degree. C.) Temp (.degree. C.) Boards (#) A 0.0094 116
159 0 B 0.0107 119 161 0 C 0.0107 139 184 7 D 0.0109 116 179 0 E
0.0148 136 154 19 F 0.0155 123 137 0 G 0.0125 113 193 0 H 0.0168
142 192 10
[0236] As shown in Table 5, for similar energy densities (e.g.,
Runs C and D and Runs E and F), runs employing more individual
cycles conducted at lower energy levels and/or for shorter
durations (e.g., Runs D and F) were more likely to avoid scorching
than runs employing less individual cycles conducted at higher
energy levels and/or for longer durations (e.g., Runs C and E).
Further, as illustrated by Run H, even runs conducted with multiple
cycles having reduced energy levels can result in scorching if the
energy level and/or duration of initial cycles are conducted at a
high energy level and/or for a long duration. Thus, it was
concluded that the number and duration of the individual cycles
within an overall heating cycle, as well as the level of energy
and/or pressure of each of the individual cycles, has an impact on
the average and maximum peak temperature of the wood, as well as
the number of boards scorched during the heating cycle.
Example 5
Effect of Reduced Energy Heating Cycles on Bundle Temperature
Distributions
[0237] This example provides simulated results illustrating the
impact of heating a bundle of wood using two or more individual
heating cycles, each carried out at a lower level of microwave
energy and/or a lower pressure.
[0238] The temperature profiles for a theoretical bundle of wood
having nominal dimensions of 52 inches by 101 inches by 129 inches
exposed to several different simulated heating profiles were
predicted using composite modeling data. Five simulations (e.g.,
Simulations A-E) were conducted using HFSS.TM. software (available
from Ansys in Canonsburg, Pa.) for predicting electromagnetic field
distributions under each heating profile and MATLAB software
(available from Mathworks in Natik, Mass.) for predicting the
temperature distribution within a central, vertical plane (e.g.,
the "central slice") of the bundle, on a one-inch grid. Details of
each of the simulated heating profiles for each of Simulations A-E
are summarized in Table 6, below.
TABLE-US-00007 TABLE 6 Heating Profiles Modeled in Simulations A-E
First Second Third Heating Cycle Heating Cycle Heating Cycle Energy
Time Rest Energy Time Rest Energy Time Rest Simulation (kW) (min)
(min) (kW) (min) (min) (kW) (min) (min) A 75 35 10 sec 75 35 end --
-- -- B 75 35 30 75 35 end -- -- -- C 75 40 30 56.25 40 end -- --
-- D 75 23 30 75 23 30 75 23 end E 75 40 30 37.5 40 30 18.75 40
end
[0239] The simulated temperature data was exported from MATLAB into
a spreadsheet and a statistical analysis was performed to determine
(1) the peak maximum temperature during the heating cycle and (2)
the percent of the total volume of the central "slice" that would
be scorched (i.e., would achieve a temperature above 240.degree.
C.). The results for Simulations A-E are tabulated below in Table
7.
TABLE-US-00008 TABLE 7 Peak Temperature and Bundle Volume Scorched
for Simulations A-E Peak Volume Temperature Scorched Simulation
(.degree. C.) (%) A 289 1.30 B 279 0.92 C 269 0.64 D 270 0.59 E 239
0.00
[0240] Although the total amount of power added during each overall
heating cycle was the same (e.g., 87.5 kW-hr), the timing, the
duration, and the level of energy applied to the load affected the
maximum peak temperature and level of scorching for each
simulation. For example, as evidenced by the peak temperatures and
scorched volumes of Simulations A and E, allowing the wood to
"rest" between two applications of energy (e.g., individual
sequential heating cycles) resulted in a lower overall peak
temperatures and less scorching than when no rest period was used.
When the maximum level of microwave energy utilized in a subsequent
cycle is less than the previous cycle, the peak temperature and
amount of scorching expected is also lower, as evidenced by the
comparison of Simulations B and C. Further, when three (or more)
subsequent cycles are utilized, each at a lower level of energy
than the previous, an even lower peak temperature and/or amount of
scorching is obtainable, as shown in Simulation D.
[0241] The preferred forms of the invention described above are to
be used as illustration only, and should not be used in a limiting
sense to interpret the scope of the present invention. Obvious
modifications to the exemplary one embodiment, set forth above,
could be readily made by those skilled in the art without departing
from the spirit of the present invention.
[0242] The inventors hereby state their intent to rely on the
Doctrine of Equivalents to determine and assess the reasonably fair
scope of the present invention as pertains to any apparatus not
materially departing from but outside the literal scope of the
invention as set forth in the following claims.
* * * * *