Abstract:
Systems for heat treating materials are presented. The systems typically involve a fluidized bed that contains granulated heat treating material. In some embodiments a fluid, such as an inert gas, is flowed through the granulated heat treating medium, which homogenizes the temperature of the heat treating medium. In some embodiments the fluid may be heated in a heating vessel and flowed into the process chamber where the fluid is then flowed through the granulated heat treating medium. In some embodiments the heat treating material may be liquid or granulated heat treating material and the heat treating material may be circulated through a heating vessel into a process chamber where the heat treating material contacts the material to be heat treated. Microwave energy may be used to provide the source of heat for heat treating systems.

Description:
GOVERNMENT RIGHTS 
     The U.S. Government has rights to this invention pursuant to contract number DE-AC05-00OR22800 between the U.S. Department of Energy and Babcock &amp; Wilcox Technical Services Y-12, LLC. 
    
    
     FIELD 
     This disclosure relates to the field of heat treatment of materials. More particularly, this disclosure relates to heat treatment of materials using fluidized bed systems. 
     BACKGROUND 
     Heat treating systems for materials typically involve energy-intensive processes. In addition to high energy consumption during a heat treatment operation, considerable energy is typically wasted either while maintaining a heat treatment system in operational standby mode (e.g., while awaiting the arrival of parts to be heat treated), or while heating a heat treatment system to take it from a shut-down mode to an operational mode. In addition, many heat treatment systems utilize heat treating media that require a long time to heat to operational temperature. What are needed therefore are improved systems for heat treating that are more energy efficient and that may be started up more rapidly. 
     SUMMARY 
     The present disclosure provides a system for heat treating material. A typical embodiment includes a process vessel having a wall enclosing a process chamber for containing microwave energy. A perforated separator is generally provided in the process chamber and granulated heat treating material is disposed in the process chamber in contact with the material to be heat treated. In this embodiment the granulated heat treating material comprises microwave susceptor granulated material. There is a fluid injection system for flowing a fluid into the process chamber and through the perforated separator and through the granulated heat treating material. Generally an exhaust port is for ejecting the fluid from the process chamber after the fluid has flowed through the granulated heat treating material. This embodiment also employs a microwave guide extending substantially through the entire wall of the process vessel. The microwave guide directs microwave energy into the process chamber where the microwave energy couples with at least a portion of the microwave susceptor granulated heat treating material. 
     In a further embodiment of a system for heat treating material there is a heating chamber. A heat transfer material is disposed in the heating chamber. A heat source is provided for heating the heat transfer material. There is a process chamber and granulated heat treating material is disposed in the process chamber in contact with the material to be heat treated. In this embodiment a fluid circulation system conveys a fluid from the heating chamber to the process chamber and back to the heating chamber, such that the fluid absorbs heat from the heat transfer material and transfers at least a portion of the heat to the granulated heat treating material. 
     Further embodiments provide a system for heat treating material that includes a heating chamber with a first portion of a heat treating material disposed in the heating chamber. Also provided is a process chamber with a second portion of the heat treating material disposed in the process chamber in contact with the material to be heat treated. There is a heat source for heating the first portion of the heat treating material. Also provided is a heat treating material circulation system for conveying at least a portion of the first portion of heat treating material from the heating chamber into the process chamber and for conveying at least a portion of the second portion of the heat treating material from the process chamber into the heating chamber to form a circulating heat treating material. The circulating heat treating material contacts the material to be heat treated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various advantages are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
         FIGS. 1 ,  2 ,  3 , and  4  are somewhat schematic cross sectional elevation views of four heat treatment systems. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration the practice of specific embodiments of heat treatment systems. It is to be understood that other embodiments may be utilized, and that structural changes may be made and processes may vary in other embodiments. 
     One embodiment of a heat treatment system  10  is illustrated in  FIG. 1 . The heat treatment system  10  is configured to heat treat various pieces of material  12 . The heat treatment system  10  includes a process vessel  14  that has a process chamber  16  that is configured to contain microwave energy. There is a perforated separator  18  in the process vessel  14 , and the process chamber  16  is configured with granulated heat treating material  20  that contacts the material  12  to be heat treated. In the embodiment of  FIG. 1 , the granulated heat treating material  20  includes microwave susceptor granulated material  22 , such as granular silicon carbide. 
     There is a fluid injection system  24  that flows a fluid  26  into a chamber  28  and from there into the process chamber  16 . The fluid  26  is usually a gas and is typically an inert gas such as argon or nitrogen, but in some embodiments the fluid  26  may be a liquid. A combination of the size of the perforations in the perforated separator  18  and the pressure of the fluid in the chamber  28  may be used to prevent the granulated heat treating material  20  from flowing through the perforated separator  18  into the chamber  28 . The fluid  26  flows from the chamber  28  through the perforated separator  18  and into the granulated heat treating material  20 . There is an exhaust port  32  where the fluid  26  exits the process chamber  16  after percolating through the granulated heat treating material  20 . In most embodiments the fluid  26  that exits the process chamber  16  through the exhaust port  32  is recycled through the fluid injection system  24  back into the process chamber  16 . 
     Continuing with  FIG. 1 , there is a microwave waveguide  34  that is configured to direct microwave energy  36  into the process chamber  16  through a third opening  38 . The waveguide  34  passes substantially all the way through the wall  40  of the process vessel. The microwave energy  36  couples with and heats the microwave susceptor granulated material  22 . In some embodiments the granulated heat treating material  20  includes microwave transparent granulated material, such as aluminum oxide. Such material is typically less dense than the microwave susceptor granulated material  22  and the microwave transparent granulated material facilitates mixing and percolation of the fluid  26  through the granulated heat treating material  20 . The heated microwave susceptor granulated material  22  heats other non-suscepting components (if any) of the granulated heat treating material  20  by means of heat conduction, convection, and radiation effects. The heated granulated heat treating material  20  contacts and heat treats the material  12  to be heat treated. 
     A baffle  42  is designed with openings  44  that permit the microwave energy  36  to pass through openings  44  into the process chamber  16 . The baffle  42  is configured to prevent the granulated heat treating material  20  from flowing into the microwave waveguide  34 . The flow of the fluid  26  tends to homogenize the temperature of the granulated heat treating material  20  in the process chamber  16 . Typically the microwave waveguide  34  is sealed off from atmosphere so that the fluid  26  does not continuously leak out of the process chamber  16  through the baffle  42 . 
     The fluid injection system  24  and the exhaust port  32  are designed with waveguide-beyond-cutoff dimensions so that the microwave energy  36  does not leak from the process chamber  16  through the fluid injection system  24  or the exit port  32 . 
     In the embodiment of  FIG. 1  the microwave energy  36  directly couples with at least a portion of the microwave susceptor granulated heat treating material  22  without passing through any unavoidable intermediary material, even material that may be substantially microwave transmissive. That is, the microwave energy  36  encounters only air (which is typically present in the microwave guide  34 ) and the baffle  42  before entering the process chamber  16 . This configuration may improve the efficiency of the heat treating system  10  because any extraneous material, even material that is substantially microwave transparent, may absorb or reflect some of the microwave energy  36  before it reaches the microwave susceptor granulated heat treating material  22 . 
       FIG. 2  depicts an embodiment of a heat treating system  50  that is configured for heat treating various pieces of material  12 . There is a heating vessel  54  that includes a heating chamber  56  that is configured to heat granulated heat transfer material  60 . Referring to  FIG. 4 , which depicts an embodiment similar to the embodiment of  FIG. 2 , in some embodiments a porous block of heat transfer material  61  may be used instead of the granulated heat transfer material  60 . In the embodiment of  FIG. 2  the heating is accomplished by microwave energy  62  but in other embodiments the granulated heat transfer material  60  may be heated by thermal combustion, electrical resistance, induction, or other heating methods. In the embodiment of  FIG. 2  the granulated heat transfer material  60  includes microwave susceptor granulated material  64 , such as granular silicon carbide. It is understood herein that references to microwave susceptor material includes material that is only partially suscepting (and therefore partially transparent and/or partially reflective) of microwave energy. In embodiments that employ a porous block of heat transfer material (and that use microwave energy to heat the heat transfer material), the porous block includes microwave susceptor material. 
     In the embodiment of  FIG. 2  a microwave waveguide  68  is configured to direct the microwave energy  62  into the heating chamber  56  through a first heating chamber opening  70 . A waveguide baffle  72  is provided and in this embodiment the waveguide baffle is configured with openings  74  that permit the microwave energy  62  to pass through the openings  74  into the heating chamber  56  while preventing the granulated heat transfer material  60  from flowing into the microwave waveguide  68 . In other embodiments the waveguide baffle  72  may be fabricated from a solid substantially microwave transparent material such as aluminum oxide. The microwave energy  62  couples with and heats the microwave susceptor granulated material  64 . In the embodiment of  FIG. 2  the waveguide  68  passes through a wall  78  of the heating vessel  54 , but in other embodiments the wall  78  of the heating vessel  54  may be substantially transparent to microwave energy and in such configurations the waveguide  68  may not extend into the wall  78 , and instead the waveguide  68  may direct the microwave energy  62  through the microwave-transparent wall  78  of the heating vessel  54 . 
     The granulated heat transfer material  60  may include microwave transparent heat transfer granulated material. The heated microwave susceptor granulated material  64  may heat other non-suscepting components (if any) of the granulated heat transfer material  60  by means of heat conduction, convection, and/or radiation effects. 
     The heat treating system  50  also includes a process vessel  84  having a process chamber  86  that is spaced apart from the heating chamber  56  and configured with granulated heat treating material  96  that contacts the material  12  that is to be heat treated. The material  12  that is to be heat treated is typically supported by a porous basket  98 . The granulated heat treating material  96  may comprise one or more ceramic materials, salts, metals, or other heat treating media. There is a fluid circulation system  100  that employs a fan  102  (or a pump in the cases where a liquid fluid is used) to circulate a fluid  104  from the heating chamber  56  to the process chamber  86  and back to the heating chamber  56 . The fluid  104  is usually a gas and is typically an inert gas such as argon or nitrogen. In embodiments that include microwave transparent heat transfer granulated material, such material is typically less dense than the microwave susceptor granulated material  64 , and the microwave transparent heat transfer granulated material facilitates the flow of the fluid  104  through the granulated heat transfer material  60 . In embodiments that utilize a porous block of heat transfer material, the porous block of heat transfer material may include material that is substantially microwave transparent, such as aluminum oxide, which may improve the porosity of the block of heat transfer material. In the embodiment of  FIG. 2 , the fluid  104  absorbs heat from the granulated heat transfer material  60  and conveys heat to the granulated heat treatment material  96 . The granulated heat treating material  96  contacts and heat treats the material  12  to be heat treated. 
     Typically the waveguide  68  is sealed off from atmosphere so that the fluid  104  does not continuously leak out of the heating chamber  56  through the waveguide baffle  72 . Heating chamber baffles  110  prevent the granulated heat transfer material  60  from flowing out of the heating chamber  56 . The heating chamber baffles  110  are also configured with waveguide-beyond-cutoff dimensions to prevent the microwave energy  62  from leaking out of the heating chamber  56  into the fluid circulation system  100 . A first process chamber baffle  120  and a second process chamber baffle  122  are provided to prevent the granulated heat treatment material  96  from flowing out of the process chamber  86 . The first process chamber baffle  120  may also be configured as a diffuser to help distribute the flow of the fluid  104  throughout the granulated heat treatment material  96 . 
       FIG. 3  depicts an embodiment of a heat treating system  150  that is configured for heat treating various pieces of material  12 . There is a heating vessel  154  that includes a heating chamber  156  that is configured to heat a first portion of a heat treating material  160 . In the embodiment of  FIG. 3  the heat treating material is a granulated material, but in other embodiments the heat treating material  160  may be a liquid heat treating material, such as a molten salt or a slurry such as a liquid/powder mixture. In the embodiment of  FIG. 3  the heating is accomplished by microwave energy  162  delivered into the heating chamber  156 . In other embodiments the first portion of heat treating material  160  may be heated by thermal combustion, electrical resistance, induction, or other heating methods. 
     In the embodiment of  FIG. 3  the first portion of heat treating material  160  includes microwave susceptor material  164 , such as granular silicon carbide. A waveguide baffle  172  is provided and in this embodiment the waveguide baffle  172  has openings  174  that permit the microwave energy  162  to pass through openings  174  into the heating chamber  156  while preventing the first portion of the heat treating material  160  from flowing into the microwave waveguide  168 . In other embodiments the waveguide baffle  172  may be fabricated from a solid substantially microwave transparent material such as aluminum oxide. The microwave energy  162  couples with and heats the microwave susceptor material  164 . The heated microwave susceptor material  164  heats other non-suscepting components (if any) of the first portion of heat treating material  160  by means of heat conduction, convection, and/or radiation effects. 
     In the embodiment of  FIG. 3  the waveguide  168  passes through a first heating chamber opening  170  through a wall  178  of the heating vessel  54 , but in other embodiments the wall  178  of the heating vessel  54  may be substantially transparent to microwave energy and in such configurations the waveguide  168  may not extend into the wall  178 , and instead the waveguide  168  may direct the microwave energy  162  through the microwave-transparent wall  178  of the heating vessel  154 . 
     Typically the microwave waveguide  168  is sealed off from atmosphere so that there is no significant loss of pressure through the waveguide baffle  172 . Heating chamber baffles  210  are provided and configured with waveguide-beyond-cutoff dimensions to prevent the microwave energy  162  from leaking out of the heating chamber  156  into the circulation system  200 . 
     The heat treating system  150  also includes a process vessel  184  having a process chamber  186  that is spaced apart from the heating chamber  156  and is configured with a second portion of the heat treating material  196  that contacts the material  12  that is to be heat treated. The material  12  that is to be heat treated is typically supported by a porous basket  98 . There is a heat treating material circulation system  200  that employs a fan  202  (or a pump in a liquid heat treating material system) to circulate at least a portion of the first portion of the heat treating material  160  from the heating chamber  156  to the process chamber  186  where it mixes with the second portion of the heat treating material  196 . The heat treating material circulation system  200  also circulates at least a portion of the second portion of the heat treating material  196  from the process chamber  186  into the heating chamber  156 , along with at least a portion of the portion of the first portion of the heat treating material that was conveyed by the heat treating material circulation system  200  from the heating chamber  156  to the process chamber  186 . As the heat treating material circulation system  200  operates at least a portion of the original first portion of the heat treating material  160  is transported into the process chamber  186  and mixes with the original second portion of the heat treating material  196 , and at least a portion of the original second portion of the heat treating material  196  is transported into the heating chamber  156  and mixes with the original first portion of the heat treating material  156 , such that the first portion of the heat treating material  160  and the second portion of the heat treating material become a circulating heat treating material  220 . The circulating heat treating material  220  contacts and heat treats the material  12  to be heat treated. 
     In summary, embodiments disclosed herein provide various systems for heat treating material. The foregoing descriptions of embodiments have been presented for purposes of illustration and exposition. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of principles and practical applications, and to thereby enable one of ordinary skill in the art to utilize the various embodiments as described and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.