Patent Publication Number: US-2023148040-A1

Title: Apparatus and method for melting glass with thermal plasma

Description:
This Application claims priority under 35 USC § 119(e) from U.S. Provisional Patent Application Ser. No. 63/022,001 filed on May 8, 2020, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to melting raw batch materials into molten glass and more specifically to melting raw batch materials into molten glass using thermal plasma. 
     BACKGROUND 
     In the production of glass articles, such as glass sheets for display applications, including televisions and hand-held devices, such as telephones and tablets, mostly solid raw batch materials are typically melted into molten glass in a melting vessel. In order to heat the area above the molten glass, melting vessels often employ one or more combustion burners, wherein a hydrocarbon containing fuel source, such as natural gas, reacts with oxygen in order to generate a hot flame above the surface of the molten glass. 
     Such combustion-based heating can, however, involve several potential drawbacks. For example, combustion of hydrocarbons results in the production of carbon-containing gasses, such as carbon dioxide and carbon monoxide, which emissions are widely recognized as contributors to climate change and increasingly subject to regulation and/or taxation in jurisdictions around the world. Combustion of hydrocarbons also typically results in the production of other emissions considered environmentally harmful, such as oxides of nitrogen (NOx), which may require the use of pollution control equipment to reduce emissions to an acceptable level. In addition, the cost and/or composition of hydrocarbon-containing fuels, such as natural gas, can vary substantially over time and/or in certain parts of the world, leading to unpredictability and/or undesirable variability in not only cost but also energy output of combustion. Accordingly, it would be desirable to heat a melting vessel in a manner that minimizes one or more of these drawbacks. 
     SUMMARY 
     Embodiments disclosed herein include an apparatus for melting raw batch materials into molten glass. The apparatus includes a chamber configured to confine molten glass up to a predetermined level within the chamber. The apparatus also includes a feed port configured to feed raw batch materials into the chamber. In addition, the apparatus includes a plurality of thermal plasma torches positioned above the predetermined level, each plasma torch configured to thermally decompose a working fluid fed therein and emit a plasma flame into the chamber. 
     Embodiments disclosed herein also include a method for melting raw batch materials into molten glass. The method includes feeding raw batch materials into a chamber through a feed port. The method also includes heating the chamber with a plurality of plasma torches positioned above a predetermined level in the chamber, each plasma torch thermally decomposing a working fluid fed therein and emitting a plasma flame into the chamber. In addition, the method includes melting the raw batch materials into molten glass up to the predetermined level. 
     Additional features and advantages of the embodiments disclosed herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the disclosed embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description present embodiments intended to provide an overview or framework for understanding the nature and character of the claimed embodiments. The accompanying drawings are included to provide further understanding and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure, and together with the description serve to explain the principles and operations thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of an example fusion down draw glass making apparatus and process; 
         FIG.  2    is a schematic side cutaway view of an example glass melting vessel in accordance with embodiments disclosed herein; 
         FIG.  3    is schematic top cutaway view of the example glass melting vessel of  FIG.  2   ; 
         FIG.  4    is schematic end cutaway view of the example glass melting vessel of  FIGS.  2  and  3   ; and 
         FIG.  5    is a schematic side cutaway view of an example plasma torch in accordance with embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present preferred embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. However, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, for example by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Directional terms as used herein—for example up, down, right, left, front, back, top, bottom—are made only with reference to the figures as drawn and are not intended to imply absolute orientation. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. 
     As used herein, the term “raw batch materials” refers to mostly solid materials, such as solid metal oxides, that are fed into a chamber of a melting furnace to be melted into molten glass. 
     As used herein, the term “molten glass” refers to a glass composition that is at or above its liquidous temperature (the temperature above which no crystalline phase can coexist in equilibrium with the glass). 
     As used herein, the term “thermal plasma torch” refers to a device that directs a flow of plasma generated from a working fluid that is fed into the thermal plasma torch and is thermally decomposed upon subjection to an energy source within the thermal plasma torch. Exemplary thermal plasma torches include those that employ direct current (DC), alternating current (AC), and radio frequency (RF) to thermally decompose the working fluid and generate the flow of plasma. 
     As used herein, the term “plasma flame” refers to the flow of plasma that projects out of a thermal plasma torch. 
     As used herein, the term “combustion burner” refers to a device that primarily generates heat from combustion of a fuel, the term “combustion” referring to exothermic redox chemical reaction(s) between the fuel, such as natural gas, and an oxidant, such as oxygen from air. 
     Shown in  FIG.  1    is an exemplary glass manufacturing apparatus  10 . In some examples, the glass manufacturing apparatus  10  can comprise a glass melting furnace  12  that can include a melting vessel  14 . In addition to melting vessel  14 , glass melting furnace  12  includes one or more additional components, such as heating elements (as will be described in more detail herein) that heat raw materials and convert the raw materials into molten glass. In further examples, glass melting furnace  12  may include thermal management devices (e.g., insulation components) that reduce heat lost from a vicinity of the melting vessel. In still further examples, glass melting furnace  12  may include electronic devices and/or electromechanical devices that facilitate melting of the raw materials into a glass melt. Still further, glass melting furnace  12  may include support structures (e.g., support chassis, support member, etc.) or other components. 
     Glass melting vessel  14  is typically comprised of refractory material, such as a refractory ceramic material, for example a refractory ceramic material comprising alumina or zirconia. In some examples glass melting vessel  14  may be constructed from refractory ceramic bricks. Specific embodiments of glass melting vessel  14  will be described in more detail below. 
     In some examples, the glass melting furnace may be incorporated as a component of a glass manufacturing apparatus to fabricate a glass substrate, for example a glass ribbon of a continuous length. In some examples, the glass melting furnace of the disclosure may be incorporated as a component of a glass manufacturing apparatus comprising a slot draw apparatus, a float bath apparatus, a down-draw apparatus such as a fusion process, an up-draw apparatus, a press-rolling apparatus, a tube drawing apparatus or any other glass manufacturing apparatus that would benefit from the aspects disclosed herein. By way of example,  FIG.  1    schematically illustrates glass melting furnace  12  as a component of a fusion down-draw glass manufacturing apparatus  10  for fusion drawing a glass ribbon for subsequent processing into individual glass sheets. 
     The glass manufacturing apparatus  10  (e.g., fusion down-draw apparatus  10 ) can optionally include an upstream glass manufacturing apparatus  16  that is positioned upstream relative to glass melting vessel  14 . In some examples, a portion of, or the entire upstream glass manufacturing apparatus  16 , may be incorporated as part of the glass melting furnace  12 . 
     As shown in the illustrated example, the upstream glass manufacturing apparatus  16  can include a storage bin  18 , a raw material delivery device  20  and a motor  22  connected to the raw material delivery device. Storage bin  18  may be configured to store a quantity of raw batch materials  24  that can be fed into melting vessel  14  of glass melting furnace  12 , as indicated by arrow  26 . Raw batch materials  24  typically comprise one or more glass forming metal oxides and one or more modifying agents. In some examples, raw material delivery device  20  can be powered by motor  22  such that raw material delivery device  20  delivers a predetermined amount of raw batch materials  24  from the storage bin  18  to melting vessel  14 . In further examples, motor  22  can power raw material delivery device  20  to introduce raw batch materials  24  at a controlled rate based on a level of molten glass sensed downstream from melting vessel  14 . Raw batch materials  24  within melting vessel  14  can thereafter be heated to form molten glass  28 . 
     Glass manufacturing apparatus  10  can also optionally include a downstream glass manufacturing apparatus  30  positioned downstream relative to glass melting furnace  12 . In some examples, a portion of downstream glass manufacturing apparatus  30  may be incorporated as part of glass melting furnace  12 . In some instances, first connecting conduit  32  discussed below, or other portions of the downstream glass manufacturing apparatus  30 , may be incorporated as part of glass melting furnace  12 . Elements of the downstream glass manufacturing apparatus, including first connecting conduit  32 , may be formed from a precious metal. Suitable precious metals include platinum group metals selected from the group of metals consisting of platinum, iridium, rhodium, osmium, ruthenium and palladium, or alloys thereof. For example, downstream components of the glass manufacturing apparatus may be formed from a platinum-rhodium alloy including from about 70 to about 90% by weight platinum and about 10% to about 30% by weight rhodium. However, other suitable metals can include molybdenum, palladium, rhenium, tantalum, titanium, tungsten and alloys thereof. 
     Downstream glass manufacturing apparatus  30  can include a first conditioning (i.e., processing) vessel, such as fining vessel  34 , located downstream from melting vessel  14  and coupled to melting vessel  14  by way of the above-referenced first connecting conduit  32 . In some examples, molten glass  28  may be gravity fed from melting vessel  14  to fining vessel  34  by way of first connecting conduit  32 . For instance, gravity may cause molten glass  28  to pass through an interior pathway of first connecting conduit  32  from melting vessel  14  to fining vessel  34 . It should be understood, however, that other conditioning vessels may be positioned downstream of melting vessel  14 , for example between melting vessel  14  and fining vessel  34 . In some embodiments, a conditioning vessel may be employed between the melting vessel and the fining vessel wherein molten glass from a primary melting vessel is further heated to continue the melting process or cooled to a temperature lower than the temperature of the molten glass in the melting vessel before entering the fining vessel. 
     Bubbles may be removed from molten glass  28  within fining vessel  34  by various techniques. For example, raw batch materials  24  may include multivalent compounds (i.e. fining agents) such as tin oxide that, when heated, undergo a chemical reduction reaction and release oxygen. Other suitable fining agents include without limitation arsenic, antimony, iron and cerium. Fining vessel  34  is heated to a temperature greater than the melting vessel temperature, thereby heating the molten glass and the fining agent. Oxygen bubbles produced by the temperature-induced chemical reduction of the fining agent(s) rise through the molten glass within the fining vessel, wherein gases in the molten glass produced in the melting furnace can diffuse or coalesce into the oxygen bubbles produced by the fining agent. The enlarged gas bubbles can then rise to a free surface of the molten glass in the fining vessel and thereafter be vented out of the fining vessel. The oxygen bubbles can further induce mechanical mixing of the molten glass in the fining vessel. 
     Downstream glass manufacturing apparatus  30  can further include another conditioning vessel such as a mixing vessel  36  for mixing the molten glass. Mixing vessel  36  may be located downstream from the fining vessel  34 . Mixing vessel  36  can be used to provide a homogenous glass melt composition, thereby reducing cords of chemical or thermal inhomogeneity that may otherwise exist within the fined molten glass exiting the fining vessel. As shown, fining vessel  34  may be coupled to mixing vessel  36  by way of a second connecting conduit  38 . In some examples, molten glass  28  may be gravity fed from the fining vessel  34  to mixing vessel  36  by way of second connecting conduit  38 . For instance, gravity may cause molten glass  28  to pass through an interior pathway of second connecting conduit  38  from fining vessel  34  to mixing vessel  36 . It should be noted that while mixing vessel  36  is shown downstream of fining vessel  34 , mixing vessel  36  may be positioned upstream from fining vessel  34 . In some embodiments, downstream glass manufacturing apparatus  30  may include multiple mixing vessels, for example a mixing vessel upstream from fining vessel  34  and a mixing vessel downstream from fining vessel  34 . These multiple mixing vessels may be of the same design, or they may be of different designs. 
     Downstream glass manufacturing apparatus  30  can further include another conditioning vessel such as delivery vessel  40  that may be located downstream from mixing vessel  36 . Delivery vessel  40  may condition molten glass  28  to be fed into a downstream forming device. For instance, delivery vessel  40  can act as an accumulator and/or flow controller to adjust and/or provide a consistent flow of molten glass  28  to forming body  42  by way of exit conduit  44 . As shown, mixing vessel  36  may be coupled to delivery vessel  40  by way of third connecting conduit  46 . In some examples, molten glass  28  may be gravity fed from mixing vessel  36  to delivery vessel  40  by way of third connecting conduit  46 . For instance, gravity may drive molten glass  28  through an interior pathway of third connecting conduit  46  from mixing vessel  36  to delivery vessel  40 . 
     Downstream glass manufacturing apparatus  30  can further include forming apparatus  48  comprising the above-referenced forming body  42  and inlet conduit  50 . Exit conduit  44  can be positioned to deliver molten glass  28  from delivery vessel  40  to inlet conduit  50  of forming apparatus  48 . For example, exit conduit  44  may be nested within and spaced apart from an inner surface of inlet conduit  50 , thereby providing a free surface of molten glass positioned between the outer surface of exit conduit  44  and the inner surface of inlet conduit  50 . Forming body  42  in a fusion down draw glass making apparatus can comprise a trough  52  positioned in an upper surface of the forming body and converging forming surfaces  54  that converge in a draw direction along a bottom edge  56  of the forming body. Molten glass delivered to the forming body trough via delivery vessel  40 , exit conduit  44  and inlet conduit  50  overflows side walls of the trough and descends along the converging forming surfaces  54  as separate flows of molten glass. The separate flows of molten glass join below and along bottom edge  56  to produce a single ribbon of glass  58  that is drawn in a draw or flow direction  60  from bottom edge  56  by applying tension to the glass ribbon, such as by gravity, edge rolls  72  and pulling rolls  82 , to control the dimensions of the glass ribbon as the glass cools and a viscosity of the glass increases. Accordingly, glass ribbon  58  goes through a visco-elastic transition and acquires mechanical properties that give the glass ribbon  58  stable dimensional characteristics. Glass ribbon  58  may, in some embodiments, be separated into individual glass sheets  62  by a glass separation apparatus  100  in an elastic region of the glass ribbon. A robot  64  may then transfer the individual glass sheets  62  to a conveyor system using gripping tool  65 , whereupon the individual glass sheets may be further processed. 
       FIG.  2    shows a schematic side cutaway view of an example glass melting vessel  14  in accordance with embodiments disclosed herein. Glass melting vessel  14  includes a chamber  114  wherein raw material delivery device  20  delivers a predetermined amount of raw batch materials  24  into the chamber  114  through feed port  116 . Glass melting vessel  14  also includes a plurality of electrodes  102  and a plurality of thermal plasma torches  104 . 
     In operation, plurality of electrodes  102  and plurality of thermal plasma torches  104  heat chamber  114  such that raw batch materials  24  are melted into molten glass  28  up to a predetermined level (L) within chamber  114 . As can be seen in  FIG.  2   , plurality of plasma torches  104  are positioned above the predetermined level (L) and plurality of electrodes  102  are positioned below the predetermined level (L). 
       FIGS.  3  and  4   , show, respectively, schematic top and end cutaway views of the example glass melting vessel  14  of  FIG.  2   . As can be seen in  FIGS.  3  and  4   , each plasma torch  104  emits a plasma flame  108  into the chamber  114 . In addition, as shown in  FIG.  3   , feed port  116  is positioned on a first wall  120  of the chamber  114  and the plurality of thermal plasma torches  104  are positioned on second and third walls  122 ,  124  of the chamber  114 , the second and third walls  122 ,  124  each extending in directions that are generally parallel to each other and generally perpendicular to the first wall  120 . Moreover, as shown in  FIG.  3   , raw batch materials  24  are fed into the chamber  114  without the raw batch materials  24  contacting the plasma flame  108  of any of the plurality of plasma torches  104 . For example, embodiments disclosed herein include those in which raw batch materials  24  are fed into the chamber  114  at a predetermined distance away from the nearest plasma flame  108 , such as a distance of at least about 1 meter away from the nearest plasma flame  108 , including a distance of from about 1 meter to about 10 meters away, such as from about 2 meters to about 5 meters away from the nearest plasma flame  108 . 
     As shown in  FIG.  4   , glass melting vessel  14  includes electrodes  106  extending from bottom of chamber  114 , wherein electrodes  106  are positioned below the predetermined level (L). As further shown in  FIG.  4   , plasma torches  104  emit plasma flames  108  in a direction that is generally parallel to predetermined level (L). 
     While  FIGS.  2 - 4   , show a glass melting vessel  14  that includes electrodes  102  extending from walls of chamber  114  and electrodes  106  extending from the bottom of chamber  114 , embodiments disclosed herein can include those in which only electrodes extending from walls of chamber  114 , only electrodes  106  extending from the bottom of chamber  114 , or neither type of electrode is included in glass melting vessel  14 . Each of the electrodes  102  and/or  106  can be connected to one or more power sources (not shown) according to methods known to persons having ordinary skill in the art. 
     Embodiments disclosed herein also include those in which glass melting vessel  14  does not include a combustion burner. 
       FIG.  5    shows a schematic side cutaway view of an example plasma torch  104  in accordance with embodiments disclosed herein. Plasma torch  104  shown in  FIG.  5    is a direct current (DC) plasma torch that includes cathode  126  and anode  128 , which when sourced with electrical power, ignites plasma arc  130  and energizes a working fluid  132  fed into the plasma torch  104  in order to generate plasma flame  108 . 
     While  FIG.  5    shows a DC plasma torch, embodiments disclosed herein include those in which plurality of plasma torches  104 , for example, comprise alternating current (AC), direct current (DC), or radio frequency (RF) plasma torches. Such plasma torches can, for example, include commercially available AC, DC, or RF plasma torches that can be incorporate or retrofitted to be incorporated into a glass melting vessel  14  in accordance with knowledge of persons having ordinary skill in the art. Exemplary commercially available plasma torches include but are not limited to DC industrial steam plasma torches available from Plazarium. 
     While not limited to any particular fluid, the working fluid  132  can, for example, be selected from water, hydrogen, helium, neon, and/or argon. Accordingly, exemplary embodiments include those in which each of the plurality of plasma torches  104  thermally decomposes a working fluid  132  selected from water, hydrogen, helium, neon, and/or argon. 
     In certain exemplary embodiments, the working fluid  132  is water. 
     In certain exemplary embodiments, plasma flame  108  generated by thermal decomposition of the working fluid  132  fed in plasma torch  104  can have a temperature of at least about 2000° C., such as at least about 2500° C., and further such as at least about 3000° C., including from about 2000° C. to about 30,000° C., such as from about 2500° C. to about 25,000° C., and further such as from about 3000° C. to about 20,000° C. 
     Embodiments disclosed herein include those in which at least a portion of working fluid  132  fed in each of the plurality of plasma torches  104  has been recycled into plasma torches  104  through melting vessel  14 . For example, as shown in  FIG.  5   , primary (unrecycled) working fluid  132   a  from a working fluid source and recycled working fluid  132   b  from melting vessel  14  are both fed into plasma torch  104  and mixed to generate working fluid  132 . In certain exemplary embodiments, at least about 90%, such as at least about 95%, including from about 90% to about 99%, and further from about 95% to about 99% of the working fluid  132  fed into each of the plurality of plasma torches  104  is recycled through melting vessel  14  (i.e., at least about 90%, such as at least about 95%, including from about 90% to about 99%, and further from about 95% to about 99% of the total working fluid  132  fed into each of the plurality of plasma torches  104  is recycled working fluid  132   b  as shown in  FIG.  5   ). 
     While the above embodiments have been described with reference to a fusion down draw process, it is to be understood that such embodiments are also applicable to other glass forming processes, such as float processes, slot draw processes, up-draw processes, tube drawing processes, and press-rolling processes. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to embodiment of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure cover such modifications and variations provided they come within the scope of the appended claims and their equivalents.