WOOD HEATER WITH ALTERNATING MICROWAVE LAUNCH LOCATIONS AND ENHANCED HEATING CYCLES
An optimized system and process for heating wood using a microwave heater. The optimized system/process directs microwave energy towards different regions of the wood at different times during heating. In certain situations, microwave energy is introduced into the heater using microwave launchers and the system includes one or more microwave switches that control distribution of microwave energy to the microwave launchers so that two adjacent and/or opposing microwave launchers do not simultaneously introduce microwave energy into the heater. The optimized heating process also includes heating wood using a plurality of sequential heating cycles carried out at different conditions. For example, at least one of the heating cycles can be carried out at a lower input rate of microwave energy and/or at a lower pressure than one of the previous heating cycles.
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This application 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 INVENTIONThis invention generally relates to microwave heating systems suitable for heating wood.
BACKGROUNDElectromagnetic 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.
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 impregnation 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.
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 INVENTIONOne embodiment of the present invention concerns a system for producing chemically-modified, dried, and/or thermally-modified wood, the system comprising a microwave heater for receiving a bundle of wood; at least one microwave generator for generating microwave energy; and a microwave distribution system for directing at least a portion of the microwave energy from the at least one microwave generator to the microwave heater. The microwave distribution system comprises a first microwave switch, a first microwave launcher, and a second microwave launcher, wherein the first and second microwave launchers are operable to emit microwave energy into the interior of the microwave heater at respective first and second spaced launch locations. The first microwave switch is selectively switchable between a first discharge phase and a second discharge phase. When the first microwave switch is in the first discharge phase, the first microwave switch is configured to route microwave energy predominantly to the first microwave launcher and not predominantly to the second microwave launcher. When the first microwave switch is in the second discharge phase, the first microwave switch is configured to route microwave energy predominantly to the second microwave launcher and not predominantly to the first microwave launcher.
Another embodiment of the present invention concerns a process for producing chemically-modified, dried, and/or thermally-modified wood, the process comprising heating a bundle of wood with microwave energy in a microwave heater to thereby provide a heated bundle of wood, wherein the heating comprises switching from a first heating phase to a second heating phase. During the first heating phase microwave energy is predominantly emitted into the microwave heater from one set of one or more microwave launchers and not predominantly emitted into the microwave heater from another set of one or more microwave launchers. During the second heating phase microwave energy is predominantly emitted into the microwave heater from the another set of one or more microwave launchers and not predominantly emitted into the microwave heater from the one set of one or more microwave launchers.
Still another embodiment of the present invention concerns a process for producing chemically-modified, dried, and/or thermally-modified wood, the process comprising heating at least a portion of a bundle of wood with microwave energy in a microwave heater to thereby provided a heated bundle of wood, the heating comprises sequential first and second heating cycles, wherein the second heating cycle is carried out at 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.
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.
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.
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.
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 “2×4” can have actual dimensions of 1.5 inches by 3.5 inches, but the nominal dimensions of “2×4” are still used. It should be understood that the dimensions referred to herein are generally nominal dimensions, unless otherwise noted.
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.
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.
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.
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.
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.
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.
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.
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.
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° C., no more than about 40° C., or no more than about 30° 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.
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° C., at least about 65° C., at least about 80° C. and/or to no more than about 175° C., no more than about 150° C., or no more than about 120° 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.
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.
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 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.
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°, at least about 55° C., or at least about 65° C. and/or not more than about 115° C., not more than about 105° C., or not more than about 95° 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.
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.
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
Referring now to
In operation, one or more bundles of wood can be removed from raw material storage area 60a via transport segment 42a. Although illustrated in
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
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 (10−3 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.
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
Turning now to
Referring now to
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.
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.
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.
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.
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
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
According to one embodiment shown in
Vapor containment room 360 can be configured in any manner suitable manner. In one embodiment depicted in
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
As depicted in
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.
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.
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.
In the embodiment depicted in
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
As shown in
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 ⅓X is provided to vapor containment room 360, ⅓X is provided to ventilation hood 404, and ⅓X 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 ⅔X is provided to vapor containment room 360, ⅙X is provided to ventilation hood 404, and ⅙X is provided to ventilation room 406.
One embodiment of the operation of wood treatment facility 416 will now be described in detail, with respect to
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.
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.
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.
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 SystemsAccording 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.
Turning now to
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.
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.
Turning now to
Microwave heater 530 can have an overall maximum internal dimension or length, L, and a maximum inner diameter, D, as shown in
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.
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
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
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/cm2), no more than about 25 mW/cm2, no more than about 10 mW/cm2, no more than about 5 mW/cm2, or no more than about 2 mW/cm2 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).
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 (10−3 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.
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 (10−3 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.
Referring now to
According to one embodiment shown in
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
As illustrated in
Referring now to
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.
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
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.
Microwave heater 530, generically represented in
Turning back to microwave heating system 420 illustrated in
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.
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 TExy 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 TMab 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 “TMab” or “TExy” 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.
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 TExy waveguides having a generally rectangular cross-section, while, in another embodiment, at least a portion of waveguides 442 can comprise TMab 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.
As schematically illustrated in
Turning again to
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
Turning now to
Turning now to
Turning now to
As shown in
Referring now to
As illustrated in
As shown in
Launch openings 767a-e can be arranged according to any suitable configuration or arrangement along elongated waveguide launcher 760. In one embodiment illustrated in
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
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.
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
Another embodiment of a microwave heating system 820 is provided in
Turning
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.
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° to about 180°. The “angle of radial alignment (β),” 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,
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
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, β, in the range of from at least or equal to 0° to about 90°. Exemplary launchers 845 and 846b in
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
As illustrated in
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
The microwave energy propagated by waveguide segments 842a-d can be in any suitable mode, including, for example, a TMab mode and/or a TExy mode, wherein a, b, x, and y have values as previously defined. In one embodiment, waveguide segments 842a-d each comprise TExy 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
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, TExy mode energy produced by the microwave generator (not shown in
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 TExy 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 TMab mode. In one embodiment, waveguide segments 842a-d can comprise TExy waveguide segments operable to transmit microwave energy from the generator to heater 830 in a TExy mode. In one embodiment, at least a portion of TExy waveguide segments 842a-d can be integrated into launchers 844a-d as depicted shown in
According to another embodiment depicted in
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
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.
Movable reflectors 890a-d can be movably coupled to microwave heater 830 according to any suitable method. For example, in one embodiment illustrated in
Yet another embodiment of a microwave heating system 920 is shown in
As shown in
According to one embodiment, microwave energy produced by a microwave generator (not shown) can be transmitted in a TExy mode through waveguide segments 942a-d prior to passing through external TExy-to-TMab mode converters 950a-d, which convert the energy passing therethrough to a TMab mode. The resulting TMab mode microwave energy can then exit mode converters 950a-d via respective waveguide segments 942e-h, as illustrated in
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.
Turning now to
As shown in
As illustrated in
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
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
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 10−2 torr liters/sec, no more than about 10−4 torr liters/sec, or no more than about 10−8 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.
Turning now to
As shown in
Further, in one embodiment illustrated in
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.
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 TMab 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 λ/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.
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.
For example, in one embodiment depicted in
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
According to one embodiment illustrated in
One embodiment of a split launcher 944 is depicted in
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
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, Θ, as shown in
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
In one embodiment shown in
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
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
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.
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
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.
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
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.
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
Turning now to
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
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 TExy switches, while, in another embodiment, microwave switches 1046a-d can comprise TMab 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
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.
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
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
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).
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° C., within about 105° C., within about 100° C., within about 90° C., within about 75° C., or within about 50° C. of each other. In various embodiments, the upper threshold temperature can be at least about 190° C., at least about 200° C., or at least about 220° C. and/or no more than about 275° C., no more than about 260° C., no more than about 250° C., or no more than about 225° C. In another embodiment, the lower threshold temperature can be at least about 115° C., at least about 120° C., at least about 125° C., at least about 130° C. and/or no more than about 150° C., no more than about 145° C., or no more than about 135° C.
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° C., at least about 145° C., at least about 150° C., or at least about 160° C. and/or no more than about 250° C., no more than about 240° C., no more than about 225° C., no more than about 210° C., or no more than about 200° 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.
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 Use of Sequential Heating Cycles Utilizing Different Levels of Microwave EnergyThis 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.
A microwave heating system similar to the system illustrated in
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 2a and 2b, below.
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 3, below, summarizes the results of runs A-H, including the average and maximum peak temperatures achieved during heating and the number of scorched boards.
As shown in Table 3, 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 2 Effect of Reduced Energy Heating Cycles on Bundle Temperature DistributionsThis 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.
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™ 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 4, below.
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° C.). The results for Simulations A-E are tabulated below in Table 4.
Although the total amount of energy 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.
Example 3 Determination of Energy Distribution Profile within a BundleThis 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 4, to predict chemical moisture profiles of wood heated on a commercial scale.
A horizontally-elongated microwave heater similar to the heater illustrated in
The microwave heater also included four movable reflectors similar to those illustrated in
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
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
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 6 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 6 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.
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
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™ 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
As shown in
This prophetic example uses the experimental energy distribution data obtained in Example 3 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 3.
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.
During heating of the bundle, microwave energy is introduced into the microwave heater in a similar manner as previously described in Example 3. 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 3. The predicted temperature distribution resulting from the cumulative thermal data is provided in
As shown in
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 7, 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° 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 5 Effect of Movable Reflectors in a Microwave Heater Utilizing Split LaunchersThis example illustrates the impact of utilizing movable reflectors in a microwave heater employing a plurality of split launchers on the surface temperature distribution of the heated bundle of wood. A microwave heater similar to the heater described in Example 3, including two pairs of oppositely-disposed split launchers and four movable reflectors positioned near the outlets of each launcher, was modeled using HFSS™ software (available from Ansys in Canonsburg, Pa.). Two simulations were conducted. During the first simulation (Simulation A), the reflectors were modeled as being stationary at a reflector position of −4° (i.e., nearest the wall). During Simulation B, the each reflector was modeled as following the reflector motion profile as previously described in Table 6 of Example 3. The resulting predicted temperature distributions for each simulation are provided below in
As shown in
This example illustrates the effect of utilizing movable reflectors on the final temperature distribution of a bundle of acetylated wood heated and/or dried in a microwave heater. As illustrated herein, the movable reflectors helped disperse the microwave energy in a more even manner within the interior of the heater and, as a result, the surface temperature distribution of a bundle of wood heated in the presence of one or more movable reflectors is narrower and has a higher peak temperature.
A microwave heating system similar to the system illustrated in
Two experimental runs, Run L and Run M, were conducted to determine the impact of dispersing the microwave energy within the heater using a set of movable reflectors. A stickered, water-damp bundle of acetylated Radiata pine having nominal dimensions of 36 inches wide by 38 inches tall by 8 feet long, was assembled. The bundle included a centrally-located, six-broad row of planks that were each equipped with fiber optic temperature sensors placed into a hold drilled near the center of the board. The sensors were used to monitor and record the peak average temperature during the heating step. During Run L, no movable reflectors were used and, during Run M, four movable reflectors, each positioned near the discharge opening of one of the four microwave launchers (as generally shown in
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.
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.
Claims
1. A system for producing chemically-modified, dried, and/or thermally-modified wood, said system comprising:
- a microwave heater for receiving a bundle of wood;
- at least one microwave generator for generating microwave energy; and
- a microwave distribution system for directing at least a portion of said microwave energy from said at least one microwave generator to said microwave heater,
- wherein said microwave distribution system comprises a first microwave switch, a first microwave launcher, and a second microwave launcher,
- wherein said first and second microwave launchers are operable to emit microwave energy into the interior of said microwave heater at respective first and second spaced launch locations,
- wherein said first microwave switch is selectively switchable between a first discharge phase and a second discharge phase,
- wherein, when said first microwave switch is in said first discharge phase, said first microwave switch is configured to route microwave energy predominantly to said first microwave launcher and not predominantly to said second microwave launcher,
- wherein, when said first microwave switch is in said second discharge phase, said first microwave switch is configured to route microwave energy predominantly to said second microwave launcher and not predominantly to said first microwave launcher.
2. The system of claim 1, wherein said first and second microwave launchers are located on generally opposite sides of said microwave heater.
3. The system of claim 2, wherein said first and second microwave launchers are axially aligned with one another.
4. The system of claim 1, wherein said first and second microwave launchers are located on generally the same side of said microwave heater.
5. The system of claim 4, wherein said first and second microwave launchers are axially adjacent to one another.
6. The system of claim 1, wherein said microwave distribution system further comprises an automatic control system programmed to control the switching of said first microwave switch between said first and second discharge phases based on one or more of a predetermined set of parameters.
7. The system of claim 1, wherein said microwave distribution system further comprises a second microwave switch, a third microwave launcher, and a fourth microwave launcher, wherein said third and fourth microwave launchers are operable to emit microwave energy into the interior of said microwave heater at respective third and fourth spaced launch locations, wherein said second microwave switch is selectively switchable between a third discharge phase and a fourth discharge phase, wherein, when said second microwave switch is in said third discharge phase, said second microwave switch is configured to route microwave energy predominantly to said third microwave launcher and not predominantly to said fourth microwave launcher, wherein, when said second microwave switch is in said fourth discharge phase, said second microwave switch is configured to route microwave energy predominantly to said fourth microwave launcher and not predominantly to said third microwave launcher.
8. The system of claim 7, wherein said first and second microwave launchers are located on generally opposite sides of said microwave heater, wherein said third and fourth microwave launchers are located on generally opposite sides of said microwave heater, wherein said first and fourth microwave launchers are located on a first side of said microwave heater, wherein said second and third microwave launchers are located on a second side of said microwave heater.
9. The system of claim 8, wherein said first and fourth microwave launchers are axially adjacent to one another, wherein said second and third microwave launchers are axially adjacent to one another, wherein said first and second microwave launchers are axially aligned with one another, wherein said third and fourth microwave launchers are axially aligned with one another.
10. The system of claim 9, wherein said microwave distribution system further comprises an automatic control system programmed to control the switching of said first microwave switch between said first and second discharge phases and the switching of said second microwave switch between said third and fourth discharge phases, wherein said automatic control system is programmed to cause simultaneous operation in said first and third phases and simultaneous operation in said second and fourth phases.
11. The system of claim 10, wherein said automatic control system is programmed to prevent simultaneously operation in said first and fourth phases and simultaneous operation in said second and third phases.
12. The system of claim 7, wherein said first and second microwave launchers are located on a first same side of said microwave heater, wherein said third and fourth microwave launchers are located on a second same side of said microwave heater, wherein said first and third microwave launchers are located on generally opposite sides of said microwave heater, wherein said second and fourth microwave launchers are located on generally opposite sides of said microwave heater.
13. The system of claim 12, wherein said first and second microwave launchers are axially adjacent to one another, wherein said third and fourth microwave launchers are axially adjacent to one another, wherein said first and third microwave launchers are axially aligned with one another, wherein said second and fourth microwave launchers are axially aligned with one another.
14. The system of claim 13, wherein said microwave distribution system comprises an automatic control system programmed to control the switching of said first microwave switch between said first and second discharge phases and the switching of said second microwave switch between said third and fourth phases, wherein said automatic control system is programmed to cause simultaneous operation in said first and fourth phases and simultaneous operation in said second and third phases.
15. The system of claim 14, wherein said automatic control system is programmed to prevent simultaneous operation in said first and third phases and simultaneous operation in said second and fourth phases.
16. The system of claim 1, wherein said first microwave switch comprises an outer housing, an internal routing element disposed in said housing, and an actuator for moving said internal routing element within said housing.
17. The system of claim 16, wherein said internal routing element is rotatably coupled to said outer housing, wherein said actuator is operable to selectively rotate said internal routing element relative to said housing to thereby switch between said first and second discharge phases.
18. The system of claim 1, wherein said first microwave switch is configured to receive and route microwave energy in a TExy mode, wherein x is an integer in the range of 1 to 5 and y is 0.
19. The system of claim 1, further comprising a vacuum system operable to reduce the pressure in said microwave heater to 350 torr or less, and said at least one microwave generator is capable of generating microwave energy at a rate of at least 100 kW, wherein said microwave heater has an internal volume of at least 100 cubic feet.
20. The system of claim 1, further comprising a chemical modification reactor separate from said microwave heater and operable to chemically modify said bundle of wood.
21. The system of claim 20, wherein said chemical modification reactor is an acetylation reactor operable to acetylate said bundle of wood.
22. A process for producing chemically-modified, dried, and/or thermally-modified wood, said process comprising:
- heating a bundle of wood with microwave energy in a microwave heater to thereby provide a heated bundle of wood,
- wherein said heating comprises switching from a first heating phase to a second heating phase,
- wherein during said first heating phase microwave energy is predominantly emitted into said microwave heater from one set of one or more microwave launchers and not predominantly emitted into said microwave heater from another set of one or more microwave launchers,
- wherein during said second heating phase microwave energy is predominantly emitted into said microwave heater from said another set of one or more microwave launchers and not predominantly emitted into said microwave heater from said one set of one or more microwave launchers.
23. The process of claim 22, wherein said one set of one or more microwave launchers comprises a first microwave launcher and said another set of one or more microwave launchers comprises a second microwave launcher, wherein said first and second microwave launchers are located on generally opposite sides of said microwave heater, wherein said first and second microwave launchers are axially aligned with one another.
24. The process of claim 22, wherein said one set of one or more microwave launchers comprises a first microwave launcher and said another set of one or more microwave launchers comprises a second microwave launcher, wherein said first and second microwave launchers are located on generally the same side of said microwave heater, wherein said first and second microwave launchers are axially adjacent to one another.
25. The process of claim 22, wherein said one set of one or more microwave launchers comprises a first microwave launcher and a third microwave launcher, wherein said another set of one or more microwave launchers comprises a second microwave launcher and a fourth microwave launcher, wherein said first and second microwave launchers are located on generally opposite sides of said microwave heater and said third and fourth microwave launchers are located on generally opposite sides of said microwave heater.
26. The process of claim 25, wherein said first and fourth microwave launchers are axially adjacent to one another, wherein said second and third microwave launchers are axially adjacent to one another, wherein said first and second microwave launchers are axially aligned with one another, wherein said third and fourth microwave launchers are axially aligned with one another.
27. The process of claim 26, wherein said switching is carried out using at least two microwave switches, wherein a first one of said at least two microwave switches routes microwave energy between said first and second microwave launchers, wherein a second one of said at least two microwave switches routes microwave energy between said third and fourth microwave launchers.
28. The process of claim 26, wherein said switching is carried out using at least two microwave switches, wherein a first one of said at least two microwave switches routes microwave energy between said first and fourth microwave launchers, wherein a second one of said at least two microwave switches routes microwave energy between said second and third microwave launchers.
29. The process of claim 22, wherein said heating comprises heating at least a portion of said bundle of wood via sequential first and second heating cycles, wherein each of said first and second heating cycles comprises said switching from said first heating phase to said second heating phase, wherein each of said first and second heating cycles comprises, in sequence, said first heating phase, said second heating phase, and a resting period, wherein during said resting period the rate of microwave energy emitted into said microwave heater is less than 25 percent of the maximum rate of microwave energy introduced into said microwave heater during said first and/or said second heating phases.
30. The process of claim 22, wherein at least a portion of said bundle of wood has been chemically modified prior to said heating.
31. The process of claim 22, wherein at least a portion of said bundle of wood has been acetylated prior to said heating.
32. The process of claim 22, wherein during said first and second heating phases the pressure in said microwave heater is maintained below 350 torr, wherein during said first and second heating phases microwave energy is introduced into said microwave heater at a rate of at least 50 kW, wherein prior to said heating, said bundle of wood has an initial weight of at least 500 pounds.
33. A process for producing chemically-modified, dried, and/or thermally-modified wood, said process comprising:
- heating at least a portion of a bundle of wood with microwave energy in a microwave heater to thereby provided a heated bundle of wood,
- wherein said heating comprises sequential first and second heating cycles,
- wherein said second heating cycle is carried out at a lower input rate of microwave energy than said first heating cycle, a lower pressure than said first heating cycle, or both a lower input rate of microwave energy and a lower pressure than said first heating cycle.
34. The process of claim 33, wherein said second heating cycle is carried out at a lower input rate of microwave energy than said first heating cycle.
35. The process of claim 34, wherein during said second heating cycle the maximum input rate of microwave energy introduced into said microwave heater is not more than 98 percent of the maximum input rate of microwave energy introduced into said microwave heater during said first heating cycle, wherein during said first heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 50 kW.
36. The process of claim 33, wherein said second heating cycle is carried out at a lower pressure than said first heating cycle.
37. The process of claim 36, wherein during said second heating cycle the lowest pressure reached in said microwave heater is not more than 98 percent of the lowest pressure reached in said microwave heater during said first heating cycle, wherein during said second heating cycle the lowest pressure reached in said microwave heater is not more than 250 torr.
38. The process of claim 33, wherein said second heating cycle is carried out at both a lower input rate of microwave energy and a lower pressure than said first heating cycle.
39. The process of claim 38, wherein during said second heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 50 percent and not more than 94 percent of the maximum input rate of microwave energy introduced into said microwave heater during said first heating cycle, wherein during said second heating cycle the lowest pressure reached in said microwave heater is at least 50 percent and not more than 94 percent of the lowest pressure reached in said microwave heater during said first heating cycle.
40. The process of claim 39, wherein during said first heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 100 kW, wherein during said first heating cycle the lowest pressure reached in said microwave heater is not more than 350 torr.
41. The process of claim 33, wherein the duration of each of said first and second heating cycles is at least 10 minutes and not more than 180 minutes.
42. The process of claim 33, wherein said bundle of wood is a chemically-wet bundle of wood and said heating provides a dried bundle of wood, wherein said chemical-wet bundle of wood comprises at least 8 weight percent of one or more heat-removable chemical components prior to said heating, wherein said dried bundle of chemically-modified wood comprises not more than 3 weight percent of said one or more heat-removable chemical components subsequent to said heating, wherein said process at least partially dries said chemical-wet bundle of wood to produce said dried bundle of chemically-modified wood in a time period of not more than 8 hours, wherein said chemical-wet bundle of wood weighs at least 500 pounds prior to said heating.
43. The process of claim 42, wherein said first heating cycle comprises a first heating period and a first resting period, wherein during said first heating period microwave energy is introduced into said microwave heater at an input rate sufficient to heat at least a portion of said chemical-wet bundle of wood, wherein during said first resting period the input rate of microwave energy introduced into said microwave heater is not more that 25 percent of the maximum input rate of microwave energy introduced into microwave heater during said first heating period, wherein said second heating cycle comprises a second heating period and a second resting period, wherein during second heating period microwave energy is introduced into said microwave heater at an input rate sufficient to heat at least a portion of said chemical-wet bundle of wood, wherein during said second resting period the input rate of microwave energy introduced into said microwave heater is not more that 25 percent of the maximum input rate of microwave energy introduced into microwave heater during said second heating period.
44. The process of claim 43, wherein the duration of each of said first and second heating periods is at least 5 minutes and not more than 90 minutes, wherein the duration of each of said first and second resting periods is at least 5 minutes and not more than 90 minutes.
45. The process of claim 43, wherein each of said first and second heating periods comprise at least two different heating phases, wherein said different heating phases focus microwave energy on different locations of said chemical-wet bundle of wood during said heating to thereby heat at least a portion of said bundle of wood.
46. The process of claim 45, wherein said heating includes emitting microwave energy into said microwave heater using at least a first and a second spaced microwave launcher, wherein said at least two different heating phases includes a first heating phase and a second heating phase, wherein during said first heating phase more microwave energy is emitted from said first microwave launcher than from said second microwave launcher and during said second heating phase more microwave energy is emitted from said second microwave launcher than from said first microwave launcher.
47. The process of claim 46, wherein said first and second microwave launchers are located on generally opposite sides of said microwave heater.
48. The process of claim 46, wherein said first and second microwave launchers are located on a same side of said microwave launcher and are axially adjacent to one another.
49. The process of claim 46, wherein the duration of each of said first and second heating cycles is at least 10 minutes and not more than 180 minutes, wherein the duration of each of said first and second heating periods is at least 5 minutes and not more than 60 minutes, wherein the duration of each of said first and said second heating phases is at least 2 minutes and not more than 45 minutes and wherein the duration of each of said first and second resting periods is at least 5 minutes and not more than 90 minutes.
50. The process of claim 33, further comprising a third heating cycle following said second heating cycle, wherein said third heating cycle is carried out at a lower input rate of microwave energy than said second heating cycle, a lower pressure than said second heating cycle, or both a lower input rate of microwave energy and a lower pressure than said second heating cycle.
51. The process of claim 50, wherein during said second heating cycle the maximum input rate of microwave energy introduced into said microwave heater is not more than 98 percent of the maximum input rate of microwave energy introduced into said microwave heater during said first heating cycle, wherein during said third heating cycle the maximum input rate of microwave energy introduced into said microwave heater is not more than 85 percent of the maximum input rate of microwave energy introduced into said microwave heater during said second heating cycle, wherein during said first heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 50 kW.
52. The process of claim 50, wherein during said second heating cycle the lowest pressure reached in said microwave heater is not more than 98 percent of the lowest pressure reached in said microwave heater during said first heating cycle, wherein during said third heating cycle the lowest pressure reached in said microwave heater is not more than 98 percent of the lowest pressure reached in said microwave heater during said second heating cycle, wherein during said first heating cycle the lowest pressure reached in said microwave heater is not more than 350 torr.
53. The process of claim 50, wherein during said second heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 50 percent and not more than 94 percent of the maximum input rate of microwave energy introduced into said microwave heater during said first heating cycle, wherein during said third heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 50 percent and not more than 94 percent of the maximum input rate of microwave energy introduced into said microwave heater during said second heating cycle, wherein during said first heating cycle the maximum input rate of microwave energy introduced into said microwave heater is at least 100 kW.
54. The process of claim 50, further comprising a fourth heating cycle following said third heating cycle, wherein said fourth heating cycle is carried out at a lower input rate of microwave energy than said third heating cycle, a lower pressure than said third heating cycle, or both a lower input rate of microwave energy and a lower pressure than said third heating cycle.
55. The process of claim 33, wherein said bundle of wood weighs at least 500 pounds prior to said heating.
56. The process of claim 33, wherein at least a portion of said bundle of wood has been chemically modified prior to said heating to thereby produce 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 prior to said heating.
57. The process of claim 56, wherein said at least one heat-removable chemical component comprises acetic acid.
Type: Application
Filed: Dec 12, 2011
Publication Date: Jun 28, 2012
Applicant: EASTMAN CHEMICAL COMPANY (Kingsport, TN)
Inventors: Harold Dail Kimrey, JR. (Knoxville, TN), David Carl Attride (Jonesborough, TN), Brad William Overturf (Kingsport, TN), Mark Robert Shelton (Kingsport, TN)
Application Number: 13/323,194
International Classification: H05B 6/68 (20060101);