PATENT DOCUMENT

Publication Number: US-9945613-B2
Application Number: US-201213623645-A
Country: US
Kind Code: B2

Title: Heat exchangers in sapphire processing

Abstract:
Systems and methods are presented for efficient heating during production of corundum. One embodiment takes the form of a system for processing corundum including a first furnace and a second furnace. The first and second furnaces are sequentially arranged and heat from the first furnace is subsequently used to heat the second furnace.

Claims:
What is claimed is: 
     
       1. A system for processing corundum, comprising:
 a sapphire growth apparatus, comprising:
 a first furnace configured to grow a sapphire crystal from a seed material; 
 a crucible positioned within the first furnace and configured to maintain an orientation of the seed material during a growth of the sapphire crystal; and 
 an extraction assembly configured to remove the sapphire crystal from the crucible; 
 
 a second furnace configured to anneal the sapphire crystal grown by the first furnace by heating the sapphire material to an annealing temperature that is distinct from an operational temperature for the first furnace, the second furnace in communication with, and separated from, the first furnace via an insulated network of piping and comprising a heating element; 
 a heat battery configured for heat storage; and 
 a heat exchanger configured for transfer of energy between at least one of:
 from the first furnace to the heat battery; or 
 from the heat battery to the second furnace; 
 
 wherein the second furnace is configured to: 
 receive heat from the first furnace via the heat exchanger and the heat battery to preheat the second furnace; and 
 use the heating element to achieve the annealing temperature. 
 
     
     
       2. The system of  claim 1  further comprising at least one cooling system, wherein energy extracted from the cooling system is used in at least one of the first or second furnaces. 
     
     
       3. The system of  claim 1  wherein:
 the heat exchanger is a first heat exchanger configured for transfer of energy between the first furnace and the heat battery; and 
 the system further comprises a second heat exchanger configured for transfer of energy between the second furnace and the heat battery. 
 
     
     
       4. The system of  claim 1 , wherein the heat exchanger is configured to transfer energy between both of:
 from the first furnace to the heat battery; and 
 from the heat battery to the second furnace. 
 
     
     
       5. The system of  claim 1 , wherein heat from at least one of the first and second furnaces is provided to an additional heat exchanger to heat water or air for heating and ventilation systems. 
     
     
       6. The system of  claim 1 , further comprising a central heater configured to provide heat to at least one of the first furnace or second furnace to supplement the heat provided by the first and second furnace. 
     
     
       7. A method of operating multiple furnaces in sapphire processing, the method comprising:
 growing a sapphire crystal using a sapphire growth apparatus, the growing including:
 maintaining an orientation of a seed material within a crucible; and 
 heating the crucible using a first furnace operating at a first operational temperature; 
 growing a sapphire material having a crystal orientation that corresponds to the orientation of the seed material; 
 
 transferring heat from the first furnace to a heat battery; 
 transferring heat from the heat battery to a second furnace; and 
 annealing the sapphire crystal grown by the sapphire growth apparatus using the second furnace operating at a second operational temperature that is distinct from the first operational temperature. 
 
     
     
       8. The method of  claim 7 , wherein the heat from the first furnace is routed to second furnace in the form of a thermal fluid. 
     
     
       9. The method of  claim 8 , wherein the thermal fluid comprises one of water, pressurized steam, alcohol, a solution or molten salts. 
     
     
       10. The method of  claim 7 , further comprising:
 operating a central heat source; and 
 routing heat from the central heat source to at least one of the first and second furnaces. 
 
     
     
       11. The method of  claim 7 , wherein the heat from the central heat source is used in preliminary heating of at least one of the first and second furnaces. 
     
     
       12. A heating system for sapphire production, comprising:
 a heat battery configured for heat storage; 
 a plurality of furnaces, a first and a second furnace of the plurality of furnaces configured to sequentially process a sapphire material, each furnace comprising a heat exchanger; 
 a crucible positioned within one of the plurality of furnaces and configured to maintain an orientation of a seed material during a growth of a sapphire crystal; 
 an extraction assembly operative to extract the sapphire crystal from the crucible for subsequent processing; and 
 an insulated network of piping in communication with the heat battery and each of the plurality of furnaces, wherein heat is transferred via the heat exchangers between the heat battery and the plurality of furnaces using the insulated network of piping, wherein: 
 heat from the first furnace of the plurality of furnaces is used to preheat the second furnace subsequent to the first furnace being heated to and operating at a first operational temperature for the first furnace; and 
 the second furnace, subsequent to the preheat, is configured to anneal the sapphire crystal formed by the sapphire growth apparatus at a second operational temperature that is distinct from the first operational temperature. 
 
     
     
       13. The heating system of  claim 12 , wherein at least one of the plurality of furnaces comprises an electrical furnace. 
     
     
       14. The heating system of  claim 12 , wherein the first furnace is dedicated to heating during a growth phase of sapphire. 
     
     
       15. The heating system of  claim 12 , wherein the second furnace is dedicated to heating during a sapphire annealing phase. 
     
     
       16. The system of  claim 1 , wherein the sapphire growth apparatus is configured to grow the sapphire crystal using one of the Kyropoulos process, the edge-defined film-fed growth process, or the vertical horizontal gradient freezing process.

Description:
TECHNICAL FIELD 
     The present application is directed to heat exchangers and, more particularly, to heat exchangers that may be implemented as part of a crystalline growth and/or annealing process. 
     BACKGROUND 
     Corundum is a crystalline form of aluminum oxide and is found in various different colors, all of which are generally commonly referred to as sapphire except for red corundum which is commonly known as ruby and pinkish-orange corundum which is known as padparadscha. Transparent forms of corundum are considered precious stones or gems. Generally, corundum is extraordinarily hard with pure corundum defined to have 9.0 Mohs and, as such, is capable of scratching nearly all other minerals. The terms “corundum” and “sapphire” are generally interchangeable as used herein. 
     As may be appreciated, due to certain characteristics of sapphire, including its hardness and transparent characteristics, among others, it may be useful in a variety of different applications. However, the same characteristics that are beneficial for particular applications commonly increase both the cost and difficulty in processing and preparing the sapphire for those applications. As such, beyond costs associated with it being a precious stone, the costs of preparing the corundum for particular uses is often prohibitive. For example, the sapphire&#39;s hardness makes cutting and polishing the material both difficult and time consuming when conventional processing techniques are implemented. Further, conventional processing tools such as cutters experience relatively rapid wear when used on corundum. 
     SUMMARY 
     Systems and methods are presented for efficient heating during production of corundum. One embodiment may take the form of a system for processing corundum including a first furnace and a second furnace. The first and second furnaces are sequentially arranged and heat from the first furnace is subsequently used to heat the second furnace. 
     Another embodiment may take the form of a method of operating multiple furnaces in sapphire processing. The method includes operating a first furnace and routing heat from the first furnace to a second furnace. The heat from the first furnace preheats the second furnace. The method also includes operating the second furnace subsequent to the operation of the first furnace. 
     Yet another embodiment may take the form of a heating system for sapphire production. The heating system includes a heat battery and a plurality of furnaces. Each furnace includes a heat exchanger. The heating system further includes an insulated network of piping in communication with the heat battery and each of the plurality of furnaces. Heat is transferred within the system between the heat battery and the plurality of furnaces via the network of piping and the heat exchangers. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following Detailed Description. As will be realized, the embodiments are capable of modifications in various aspects, all without departing from the spirit and scope of the embodiments. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a Kyropoulos process for sapphire growth. 
         FIG. 2  illustrates an EFG process for sapphire growth. 
         FIG. 3  illustrates a VHGF process for sapphire growth. 
         FIG. 4A  illustrates a system for recycling heat in sapphire processing by passing heat directly between two furnaces after heating phases for the furnaces. 
         FIG. 4B  illustrates an alternative system for recycling heat in sapphire processing by passing heat directly between two furnaces after heating phases for the furnaces wherein a single growth furnace supplies heat to two annealing furnaces. 
         FIG. 5  illustrates another alternative system for recycling heat in sapphire processing by implementing a heat battery. 
         FIG. 6  illustrates yet another alternative system for recycling heat in sapphire processing by implementing a central heater. 
         FIG. 7  illustrates still another system for recycling heat in sapphire processing by implementing a central heater to supply heat to a heat battery which receives and distributes heat to the furnaces. 
         FIG. 8  illustrates a further system for recycling heat in sapphire processing by implementing a central heater to preheat the furnaces and a heat battery to recycle heat from the furnaces. 
         FIG. 9  is a flow chart illustrating a sample method of operating a sapphire growth and annealing system. 
     
    
    
     DETAILED DESCRIPTION 
     As mentioned above, certain properties of sapphire lead to significantly higher energy costs to produce a given part compared to alternative materials such as glass. Specifically, for example, the sapphire growth process and annealing process are two high energy consumption steps in the part production for sapphire where more efficient heating processes may help achieve high volume sapphire production in an economically efficient manner. 
     Sapphire growth occurs at temperatures around 2200 degrees Celsius and, depending on the growth technique employed and the output size, is a process that can take from eight hours to over a week in duration. Annealing is a secondary processing step (e.g., different from a post-growth annealing that is generally common to most growth methods) that occurs downstream after most part figuration is complete to eliminate residual stresses and “heal” processing defects that can lead to decreased mechanical reliability and strength. 
     The annealing step can last as long as 30 hours at temperatures as high as 1900 degrees Celsius. Glass on the other hand is formed rather quickly at around 1300 degrees Celsius and chemically strengthened (the high temperature post formation processing step analogous to sapphire annealing) in a bath for generally around 10 hours at approximately 400 degrees Celsius. Since such a large disparity exists in terms of energy requirements to fabricate a part from sapphire compared to glass, efficiencies in heating may contribute to sapphire processing becoming economically efficient and a viable alternative to glass in consumer electronic products as well as other applications. 
     One embodiment may include linking all heating and cooling systems of the growers and furnaces together so that much less heat is wasted and greater efficiencies could be realized. Specifically, furnaces (either or both annealing and growth furnaces) could have their heating and cooling systems linked to other systems through heat exchanges. By staggering the processing schedules among groups of machines, heat that is removed from one furnace could be fed directly into another furnace to reduce the energy input requirement of its heating step. This could be achieved using some thermal fluid (water/pressurized steam, alcohol, solutions, molten salts, and so on) and an insulated network of piping within a cell of linked machines. As used herein, the term “furnace” may generally refer to a heating system or device which facilitates achieving temperatures for either growth or annealing of sapphire. As such, the furnaces referred to herein may include heat sources (e.g., heating elements), insulation, crucibles, and so forth. 
     In another embodiment, furnaces could all be linked to a central heat “battery” instead of directly to each other, when a furnace needs to expel heat, such as during the cooling stage of an annealing furnace, or the solidification phase of crystal growth process, it would release the heat to the central heat mass and charge the battery. Conversely, during the initial heating of the furnaces, they would discharge the battery and pull heat in through a heat exchanger. 
     Yet another configuration may utilize a heat source that would be more efficient than the electrical heater utilized in the furnaces to generate heat to supply to a large number of furnaces thereby supplementing the electrical heating of the furnaces with more efficient energy input at the early, less sensitive heating stages. This may be used in conjunction with other methods, with the goal of reducing cost and environmental impacts of replacing glass with sapphire. 
     Generally, the process of growing sapphire starts with alumina powder that is subjected to a densification process to form densified alumina or fully formed sapphire (crackle). The alumina is melted and a seed crystal is inserted into the molten alumina. The molten alumina is then cooled with precisely controlled temperatures and the crystal is formed on the seed. Additional processing steps such as cutting and polishing the formed crystal may be performed, as well as annealing steps to help “heal” the crystalline structure that may have formed during growth or subsequent processing, as mentioned above. 
     Some common and distinct growth methods include Kyropoulos, Verneuil, Czochralski, flux, heat exchange method (“HEM”), hydrothermal, vertical horizontal gradient freezing (“VHGF”), Stepanov (i.e., edge-defined film-fed growth (“EFG”)), and Bridgman (i.e., horizontal moving growth). The Kryopoulos, Verneuil, Czochralski, flux, and hydrothermal processes generate a sapphire boule, whereas the EFG, VHGF and horizontal moving growth processes generate sapphire members having continuous cross-sections. It should be appreciated that although specific examples described herein may refer to a particular process for sapphire growth the examples are not intended to be limiting. As such, the present techniques, systems and methods may be used in conjunction with each of the various sapphire growth processes. 
     Turning to the drawings and referring initially to  FIG. 1 , a system  100  for performing the Kyropoulos process is illustrated in by a cross-sectional view of a crucible  102 . The crucible  102  holds the alumina melt  104  and a seed crystal  106  is inserted into the crucible  102  with a support rod  108 . Crystallization of the molten alumina  104  occurs on the seed crystal  106  following the orientation of the seed crystal. In some embodiments, the rod  108  may be configured to reorient the seed crystal to achieve a desired crystallographic orientation. 
     A system  110  for growing sapphire according to the EFG process is illustrated with a cross-sectional view of crucible  112 . The crucible  112  holds alumina melt  114  or molten alumina. Heating elements  118  may surround and heat the crucible  112 . The heating elements  118  may take any suitable form and in some embodiments may take the form or electrical heating elements. 
     The molten alumina  114  is drawn up a melt supply slit of a die  116  which may take the form of two close, parallel plates which draw the molten alumina up through capillary action. The die  116  may extend to a die tip  117  at a boundary of the crucible. A seed crystal (not shown) may be brought into contact with the molten alumina at the die tip  117  which propagates crystalline growth and a sapphire ribbon  120  may be drawn upwardly out of the crucible  112 . The sapphire ribbon  120  is formed in the shape of the die tip  117  and the sapphire crystalline structure of the ribbon follows the existing orientation of the seed. 
     A system  122  for growing sapphire according to the VHGF process is illustrated in  FIG. 3 , with a cross-sectional view of a chamber  124 . The chamber  124  surrounds an alumina charged crucible  126  into which a seed crystal is positioned at the bottom of the crucible. A heat sink  128  and heater  130  are each coupled to crucible  126  and an insulator  132  is provided within the chamber around the heater and crucible. The heater  130  melts the alumina in the crucible and the melted alumina is subsequently cooled by the heat sink  128  to form crystal in the shape of the crucible and following the orientation of the seed crystal. The crucible  126  is cracked off the crystal once cooled. 
     A heat exchanger  140  may be included with each system  100 ,  110  and  122 , to transfer heat from or to the system as discussed herein. The heat exchanger  140  may be either a parallel-flow or counter-flow heat exchanger and may take any suitable form including but not limited to a shell and tube heat exchanger, a plate heat exchanger, a plate and shell heat exchanger, fluid heat exchanger, pillow plate heat exchanger, phase-change heat exchanger, direct contact heat exchanger, and so forth. 
       FIG. 4A  illustrates an example sapphire processing system  150  in accordance with an example embodiment. The system includes a growth furnace  152  and a corresponding heat exchanger  154 , and an annealing furnace  156  with a corresponding heat exchanger  158 . For the present purposes, the growth furnace  152  may be part of an EFG system for growing sapphire, such as the system  110 . The growth furnace  152  and the annealing furnace  156  may be configured to share heat. In particular, for example, the furnace  152  may initially operate to grow the sapphire crystal and reach temperatures around 2200 degrees Celsius. The annealing furnace  156  may operate at some time after the growth furnace  152  and heat from the growth furnace may be transferred to the annealing furnace to help initially heat the annealing furnace. As such, the furnaces are sequentially heated and the heat from one furnace is used to initially heat (or preheat) the other furnace). 
     The heat from the furnaces may be passed between the furnaces via an insulated network of piping  160 , conduits, or other suitable liquid or gas transport system. The sapphire grown in the growth furnace  152  may be passed to other processing steps  162  such as a cutting step before being placed in the annealing furnace  156 . In some embodiments, an annealing step may be performed shortly or immediately after growth and cooling of the sapphire. As such there may be multiple annealing steps in the processing of the sapphire and each annealing step may utilize recycled heat. Additionally, in some embodiments, heat may be shared between two or more growth furnaces and/or two or more annealing furnaces. 
     In some embodiments, upon completion of the annealing processes, heat from the annealing furnace  156  may be transferred back to the growth furnace  152 , or to another furnace or heating step in the processing of the sapphire. In other embodiments, the heat from one or both of the growth furnace  152  and annealing furnace  156  may be transferred to a system external to the sapphire processing system. For example, the heat may be used to heat water and/or be used for heating and ventilation purposes. As such, the heat generated from one or more furnaces in the system  150  may be conserved and recycled for multiple steps in the creation of sapphire and/or may be utilized for purposes external to the sapphire processing. 
     The recycling of heat or energy from the furnaces may result in significant savings, especially when the scale of sapphire production includes many furnaces. In large production environment tens, hundreds or even thousands of furnaces may be operating and the savings in both time and energy costs may be significant. In the large production systems, one growth furnace  152  may provide heat to multiple annealing furnaces  156   a ,  156   b , as shown in system  164  of  FIG. 4B . Alternatively, heat from multiple growth furnaces may be provided to a single annealing furnace and vice-versa. Additionally, in large production facilities, the furnaces may be coupled together in a cellular topology with each cell having multiple furnaces coupled together by the insulated piping so that multiple furnaces within a single cell may share heat or so that heat may be recycled within the cell. 
     Turning to  FIG. 5 , an alternative system  170  for heat conservation in sapphire production is illustrated. Generally, the system  170  includes the furnaces  152 ,  154  and the heat exchangers  154 ,  158 . Additionally, the system  170  includes a heat battery  172 . The heat battery  172  is created for storage and distribution of heat within the system  170 . As such, heat from the furnaces  152 ,  156  is routed to the heat battery  172  at the completion of a heating phase to “charge” the battery. When it is time to preheat a furnace, heat is dispersed to the furnaces from the heat battery  172 . This configuration may be particularly beneficial in large cell topologies (e.g., multiple growth furnaces and/or multiple annealing furnaces) where it may be difficult to have each furnace coupled to every other furnace. Thus, the heat battery  172  helps to efficiently retrieve and redistribute heat within the system. 
     The heat battery  172  may take any suitable form of a storage volume for collection and distribution of a thermal fluid. The heat battery  172  may include valves that coordinate with valves of heat exchanges associated with various furnaces so that the thermal fluid may be passed between the heat battery and the furnaces. The heat battery  172  may be well insulated to prevent heat loss. Additionally, in some embodiments, the heat battery  172  may include a heater to help maintain the thermal fluid at a desired temperature and/or to heat the thermal fluid. 
       FIG. 6  illustrates yet another alternative system  180  in which a central heater  182  may be coupled to the furnaces and supply heat to the furnaces. In particular, the heater  182  may utilize a cheaper heating fuel and/or technique than the furnaces and may generally operate at lower temperatures. For example, the heater may utilize natural gas or other combustible fuel. The central heater  182  generally may not operate at a high level of precision as it may be purposed for preheating, while the furnaces may utilize a precisely controlled electrical heater or other type of heating. Additionally, the heater  182  may operate at relatively low temperatures as compared to the furnaces used for crystal growth and annealing of the sapphire. 
       FIGS. 7 and 8  illustrate still further alternative systems  184 ,  190  utilizing the heat battery  172  and the central heater  182 . In the system  184  of  FIG. 7 , the central heater  182  may feed directly into the heat battery  172  and the heat battery may then distribute the heat. Alternatively, in the system  190  of  FIG. 8 , the central heater  182  may directly heat the furnaces. The furnaces may additionally be heated by the heat battery  172  and supply heat to the battery upon completion of a heating step. 
       FIG. 9  is a flow chart illustrating an example method  200  of operating a sapphire growth and annealing system in accordance with an example embodiment. Initially, the method  200  includes operating a first furnace (Block  202 ). Upon completion of the first heating step, heat from the first furnace may be supplied to either a second furnace to preheat the second furnace (Block  204 ) or it may be provided to a heat battery (Block  206 ). If the heat is provided to the heat battery, the heat may be stored in the battery until it is eventually provided to the second furnace (Block  204 ) to preheat the second furnace. Once the second furnace is preheated, the second furnace may operate (Block  208 ) to further raise the temperature of the second furnace. Upon completion of the second furnace&#39;s operation, heat may be transferred out of the second furnace to either the first furnace (Block  210 ) to preheat the first furnace or back to the heat battery (Block  212 ) and the first furnace may be operated again (Block  202 ). It should be appreciated that in some embodiments, heat may be transferred out of the furnaces during prior to completion of a heating step to help maintain the temperature of the furnace at a desired level. The heat may be transferred to the battery or to another furnace. 
     The heat from may be transferred between the furnaces (and to or from the heat battery) in any suitable manner. In some embodiments, a thermal fluid may be used. For example, water, pressurized steam, alcohol, a solution or molten salts may be used. Additionally, it should be appreciated that a central heater may be utilized to either preheat one or more furnace or to charge the heat battery. 
     Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the embodiments. For example, heat extracted during a cooling phase may be recycled as well as the heat from heating stages. As such, the heat exchangers may be utilized in both heating and cooling stages to help conserve and recycle the heat of the system. Accordingly, the specific embodiments described herein should be understood as examples and not limiting the scope thereof.

Metadata:
Filing Date: 20120920
Publication Date: 20180417
Grant Date: 20180417
Priority Date: 20120920
Inventors: PREST, CHRISTOPHER D.
MEMERING, DALE N.
Assignee: APPLE INC
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Family ID: 50274833