WO2020167472A1

WO2020167472A1 - Conduit heating apparatus and method with improved corrosion resistance

Info

Publication number: WO2020167472A1
Application number: PCT/US2020/015644
Authority: WO
Inventors: Martin Herbert Goller; Nicholas Scott Ryan; George Kristian SCHWENKE
Original assignee: Corning Incorporated
Priority date: 2019-02-14
Filing date: 2020-01-29
Publication date: 2020-08-20
Also published as: TW202035312A; JP2022521379A; KR20210119534A; CN113544100A

Abstract

A conduit heating apparatus and a method of heating a conduit. The conduit heating apparatus includes an annular heating element circumferentially surrounding at least a portion of the conduit. The annular heating element includes an annular channel and the method includes flowing a cooling fluid therethrough. The annular heating element also includes an interface region extending between the annular channel and a refractory ceramic material contained in an atmosphere. A temperature at a boundary between the interface region the refractory ceramic material is above the dew point of the atmosphere.

Description

CONDUIT HEATING APPARATUS AND METHOD WITH IMPROVED CORROSION

RESISTANCE

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 62/805,332 filed on February 14, 2019, the content of which is relied upon and incorporated herein by reference in its entirety.

Field

[0002] The present disclosure relates generally to the heating of conduits, such as metal conduits used in glass melting systems, and more particularly to the heating of conduits with improved corrosion resistance.

Background

[0003] In the production of glass articles, such as glass sheets for display applications, including televisions and hand held devices, such as telephones and tablets, molten material is typically transported through one or more conduits, such as conduits comprised of a precious metal, such as platinum. Such conduits can be directly heated, for example, by an electrically powered flange comprising a metallic material that circumferentially surrounds the conduit. A water cooled channel can help manage the temperature of the flange.

[0004] In such systems, the conduit is typically encased in a refractory material, such as a refractory ceramic material that may be further contained in an atmosphere controlled capsule. The atmosphere controlled capsule is typically a relatively humid environment having a dew point substantially higher the temperature of the fluid cooled channel. When the exterior of the channel is in direct contact with the refractory material, water condenses along the interface of the channel and the refractory material, which can significantly accelerate corrosion of the channel material, thereby shortening the useful life of not only the channel but also the flange. It would be desirable to find a solution to this problem that does not substantially adversely affect system operational parameters or capacity.

SUMMARY

[0005] Embodiments disclosed herein include a conduit heating apparatus. The conduit heating apparatus includes an annular heating element circumferentially surrounding at least a portion of the conduit. The annular heating element includes an annular channel configured to flow a cooling fluid therethrough. The annular heating element is at least partially surrounded by a refractory ceramic material contained in an atmosphere. A dew point of the atmosphere is above a temperature of the cooling fluid. The heating element includes an interface region comprising a metal or metal alloy. The interface region extends between the annular channel and the refractory ceramic material. A temperature of the interface region at a boundary between the interface region and the refractory ceramic material is above the dew point of the atmosphere.

[0006] Embodiments disclosed herein also include a method of heating a conduit. The method includes circumferentially surrounding at least a portion of the conduit with an annular heating element. The annular heating element includes an annular channel and a cooling fluid flowing therethrough. The annular heating element is at least partially surrounded by a refractory ceramic material contained in an atmosphere. A dew point of the atmosphere is above a temperature of the cooling fluid. The heating element includes an interface region comprising a metal or metal alloy. The interface region extends between the annular channel and the refractory ceramic material. A temperature of the interface region at a boundary between the interface region and the refractory ceramic material is above the dew point of the atmosphere.

[0007] 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.

[0008] 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

[0009] FIG. l is a schematic view of an example fusion down draw glass making apparatus and process;

[0010] FIG. 2 is a perspective view of an annular heating element circumferentially surrounding a portion of a conduit;

[0011] FIG. 3 is a schematic front cutaway view of an annular heating element

circumferentially surrounding a conduit and surrounded by a refractory ceramic material contained in an atmosphere;

[0012] FIG. 4 is a schematic side cutaway view of a portion of an annular heating element that includes an annular cooling fluid channel;

[0013] FIG. 5 is a schematic side cutaway view of a portion of an annular heating element that includes an annular shell surrounding an annular cooling fluid channel and a fluid gap extending between the annular cooling fluid channel and the annular shell;

[0014] FIG. 6 is a schematic side cutaway view of a portion of an annular heating element that includes an annular shell surrounding an alternatively configured annular cooling fluid channel and a fluid gap extending between the annular cooling fluid channel and the annular shell;

[0015] FIG. 7 is a is a schematic side cutaway view of a portion of an annular heating element that includes an annular shell surrounding an alternatively configured annular cooling fluid channel and a fluid gap extending between the annular cooling fluid channel and the annular shell;

[0016] FIG. 8 is a schematic side cutaway view of a portion of an annular heating element that includes an annular ring between at least a portion of an annular cooling fluid channel and a refractory ceramic material;

[0017] FIGS. 9A and 9B are exploded side cutaway views of a portion of an annular heating element that include, respectively, an annular shell or an annular ring;

[0018] FIGS. 10A and 10B are schematic side cutaway and exploded side cutaway views of a portion of an annular heating element that includes an alternative embodiment of an annular ring between at least a portion of an annular cooling fluid channel and a refractory ceramic material; and

[0019] FIG. 11 is a schematic front cutaway view of an annular heating element circumferentially surrounding a conduit and surrounded by a refractory ceramic material, wherein the center of the annular heating element is offset from the center of the conduit. DETAILED DESCRIPTION

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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. [0025] 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 can optionally include one or more additional components such as heating elements (e.g., combustion burners or electrodes) 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.

[0026] 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.

[0027] 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.

[0028] 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

[0029] 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 materials 24 that can be fed into melting vessel 14 of glass melting furnace 12, as indicated by arrow 26. Raw 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 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 materials 24 at a controlled rate based on a level of molten glass sensed downstream from melting vessel 14. Raw materials 24 within melting vessel 14 can thereafter be heated to form molten glass 28.

[0030] 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.

[0031] 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.

[0032] Bubbles may be removed from molten glass 28 within fining vessel 34 by various techniques. For example, raw 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.

[0033] 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.

[0034] 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.

[0035] 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 in examples, 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.

[0036] FIG. 2 shows a perspective view of an annular heating element 100

circumferentially surrounding a portion of a conduit, which, in FIG. 2, is shown as a connecting conduit 38, although it is to be understood that one or more annular heating elements 100 may circumferentially surround any of the conduits illustrated in FIG. 1. In certain exemplary embodiments, annular heating element 100 may comprise the same or similar materials as connecting conduit 38. For example, when connecting conduit comprises platinum, annular heating element 100 may also comprise platinum. Annular heating element 100 may also comprise other materials, for example, at least one of nickel, copper, and alloys comprising at least one of nickel, copper, rhodium, palladium, and platinum. In addition, annular heating element 100 may be connected to a power source (not shown), such as an electrical power source, as known to persons having ordinary skill in the art. This can, in turn, cause resistive heating of annular heating element 100, which can, in turn, heat connecting conduit 38 as well as molten material, such as molten glass 28, flowing through connecting conduit 38 to a desired temperature.

[0037] FIG. 3 shows a schematic front cutaway view of an annular heating element 100 circumferentially surrounding a conduit (i.e., connecting conduit 38) and surrounded by a refractory ceramic material 200 contained in an atmosphere 300. Annular heating element 100 includes a relatively thin region 102 circumferentially surrounded by a relatively thick region 104 that is, in turn, circumferentially surrounded an annular channel 106 configured to flow a cooling fluid therethrough.

[0038] Relatively thin region 102, relatively thick region 104, and annular channel 106 may comprise the same or different materials relative to each other. For example, in certain embodiments, relatively thin region 102, relatively thick region 104, and annular channel 106 each comprise at least one of nickel, copper, and alloys comprising at least one of nickel, copper, rhodium, palladium, and platinum.

[0039] Refractory ceramic material 200, while not limited to any particular material, may, for example, comprise at least one of alumina, zircon, calcium aluminate, zirconia, and oxide ceramics comprising at least one of calcium, magnesium, aluminum, silicon, and zirconium. For example, embodiments disclosed herein include those in which refractory ceramic material 200 is included within a system that includes a cradle shell comprising, for example, fused zirconia, and at least one castable refractory material in the shell and surrounding the conduit as, for example, disclosed in W02009/058330, the entire disclosure of which is incorporated herein by reference.

[0040] Atmosphere 300 can be included and maintained within a system that controls the environment around at least a portion of the glass manufacturing apparatus 30, including conduit (i.e., connecting conduit 38) and refractory ceramic material 200. The system, for example, can include a control system and a capsule that are used to control the level of hydrogen around at least a portion of the glass manufacturing apparatus 30 so as to suppress the formation of gaseous inclusions and surface blisters in individual glass sheets 62. The system can also be used to help cool molten glass 28 while the molten glass 28 travels between vessels in the glass manufacturing apparatus 30. The system can also be used to maintain atmosphere 300 to include minimal oxygen around the vessels so as to reduce the oxidation of precious metals on the vessels. An exemplary system is shown and described in WO 2006/115972, the entire disclosure of which is incorporated herein by reference.

[0041] FIG. 4 shows a schematic side cutaway view of a portion of an annular heating element 100 that includes an annular cooling fluid channel 106. As with the embodiment illustrated in FIG. 3, annular heating element 100 includes a relatively thin region 102 circumferentially surrounded by a relatively thick region 104 that is, in turn, circumferentially surrounded the annular channel 106 configured to flow a cooling fluid 150 therethrough. Annular heating element 100, including annular channel 106, is surrounded by refractory ceramic material 200.

[0042] In certain exemplary embodiments, cooling fluid 150 can comprise a liquid, such as, for example, water. Cooling fluid 150 may also comprise oil and/or a corrosion resistant additive. Cooling fluid 150 may also comprise a gas, such as, for example, at least one gas selected from air, nitrogen, oxygen, helium, hydrogen, and neon.

[0043] The temperature of cooling fluid 150, while not limited to any particular value, in certain exemplary embodiments can be less than or equal to about 60°C, such as from about 0°C to about 60°C, and further such as from about 10°C to about 50°C, and yet further such as from about 20°C to about 40°C, and still yet further such as from about 25°C to about 35°C.

[0044] Embodiments disclosed herein include those in which a dew point of the

atmosphere 300 is above the temperature of the cooling fluid 150. The dew point of the atmosphere 300, while not limited to any particular value, in certain exemplary embodiments can be at least about 60°C, such as at least about 65°C, and further such as at least about 70°C, such as from about 60°C to about 100°C, and further such as from about 65°C to about 95°C, and yet further such as from about 70°C to about 90°C.

[0045] In certain exemplary embodiments, the dew point of the atmosphere 300 is at least about 5°C, such as at least about 10°C, and further such as at least about 15°C, and yet further such as at least about 20°C, and still yet further such as at least about 25°C, and even still yet further such as at least about 30°C, including from about 5°C to about 70°C, such as from about 10°C to about 60°C, and further such as from about 15°C to about 50°C, and yet further such as from about 20°C to about 40°C above the temperature of the cooling fluid 150.

[0046] FIG. 5 shows a schematic side cutaway view of a portion of an annular heating element 100 that includes an annular shell 108 surrounding an annular channel 106 configured to flow a cooling fluid 150 therethrough and a fluid gap 160 extending between the annular cooling fluid channel 106 and the annular shell 108. Annular heating element 100, including annular shell 108, is surrounded by refractory ceramic material 200. Annular shell 108 and fluid gap 160 comprise an interface region (shown as I in FIG. 9A) extending between the annular channel 106 and the refractory ceramic material 200.

[0047] FIG. 6 shows a schematic side cutaway view of a portion of an annular heating element 100 that includes an annular shell 108 surrounding an alternatively configured annular channel 106 having a greater degree of contact with relatively thick region 104 and configured to flow a cooling fluid 150 therethrough and a fluid gap 160 extending between the annular cooling fluid channel 106 and the annular shell 108. Annular heating element 100, including annular shell 108, is surrounded by refractory ceramic material 200. Annular shell 108 and fluid gap 160 comprise an interface region (shown as I in FIG. 9A) extending between the annular channel 106 and the refractory ceramic material 200.

[0048] FIG. 7 shows a schematic side cutaway view of a portion of an annular heating element 100 that includes an annular shell 108 surrounding an alternatively configured annular channel 106 having D-shaped cross-section and configured to flow a cooling fluid 150 therethrough and a fluid gap 160 extending between the annular cooling fluid channel 106 and the annular shell 108. Annular heating element 100, including annular shell 108, is surrounded by refractory ceramic material 200. Annular shell 108 and fluid gap 160 comprise an interface region (shown as I in FIG. 9A) extending between the annular channel 106 and the refractory ceramic material 200.

[0049] FIG. 8 shows a schematic side cutaway view of a portion of an annular heating element 100 that includes an annular ring 110 between at least a portion of an annular channel 106 configured to flow a cooling fluid 150 therethrough and a refractory ceramic material 200. Annular heating element 100, including annular ring 110, is surrounded by refractory ceramic material 200. Annular ring 110 comprises an interface region (shown as I in FIG. 9B) extending between the annular channel 106 and the refractory ceramic material 200. In certain exemplary embodiments, annular ring 110 can comprise at least one of nickel, copper, and alloys comprising at least one of nickel, copper, rhodium, palladium, and platinum.

[0050] FIGS. 9 A and 9B show exploded side cutaway views of a portion of an annular heating element 100 that include, respectively, an annular shell 108 (FIG. 9 A) or an annular ring 110 (FIG. 9B). A temperature of the interface region, I, at a boundary, B, between the interface region, I, and the refractory ceramic material 200 is above the dew point of the atmosphere (shown as 300 in FIG. 3). [0051] FIGS. 10A and 10B show, respectively, a schematic side cutaway view and an exploded side cutaway view of a portion of an annular heating element 100 that includes an alternative embodiment of an annular ring 110 between at least a portion of an annular channel 106 configured to flow a cooling fluid 150 therethrough and a refractory ceramic material 200. Annular heating element 100, including annular ring 110, is surrounded by refractory ceramic material 200. Annular ring 110 comprises an interface region (shown as I in FIG. 10B) extending between the annular channel 106 and the refractory ceramic material 200. A temperature of the interface region, I, at a boundary, B, between the interface region,

I, and the refractory ceramic material 200 is above the dew point of the atmosphere (shown as 300 in FIG. 3). In certain exemplary embodiments, annular ring 110 can comprise at least one of nickel, copper, and alloys comprising at least one of nickel, copper, rhodium, palladium, and platinum.

[0052] Accordingly, embodiments disclosed herein include those in which the temperature of the interface region, I, at the boundary, B, between the interface region, I, and the refractory ceramic material 200 is above the dew point of the atmosphere 300 and the dew point of the atmosphere 300 is above the temperature of the cooling fluid 150 flowing through annular channel 106. For example, in certain embodiments, the temperature of the interface region, I, at the boundary, B, between the interface region, I, and the refractory ceramic material 200 is at least about 5°C, such as at least about 10°C, and further such as at least about 15°C, including from about 5°C to about 100°C, such as from about 10°C to about 50°C, above the dew point of the atmosphere 300 and the dew point of the atmosphere 300 is at least about 5°C, such as at least about 10°C, and further such as at least about 15°C, and yet further such as at least about 20°C, and still yet further such as at least about 25°C, and even still yet further such as at least about 30°C, including from about 5°C to about 70°C, such as from about 10°C to about 60°C, and further such as from about 15°C to about 50°C, and yet further such as from about 20°C to about 40°C above the temperature of the cooling fluid 150 flowing through annular channel 106.

[0053] In certain exemplary embodiments, the temperature of the interface region, I, at the boundary, B, between the interface region, I, and the refractory ceramic material 200 is at least about 65 °C, such as at least about 75 °C, and further such as at least about 85°C, such as from about 65°C to about 200°C, including from about 75°C to about 150°C, and further including from about 85°C to about 125°C. Meanwhile, the temperature of the interface region, I, at the boundary, B, between the interface region, I, and the refractory ceramic material 200 is above the dew point of the atmosphere 300 and the dew point of the atmosphere 300 is above the temperature of cooling fluid 150, wherein the temperature of cooling fluid 150 is than or equal to about 60°C, such as from about 0°C to about 60°C, and further such as from about 10°C to about 50°C, and yet further such as from about 20°C to about 40°C, and still yet further such as from about 25°C to about 35°C.

[0054] In certain exemplary embodiments the dew point of the atmosphere 300 is at least about 60°C, such as at least about 65°C, and further such as at least about 70°C, such as from about 60°C to about 100°C, and further such as from about 65°C to about 95°C, and yet further such as from about 70°C to about 90°C. Meanwhile, the temperature of the interface region, I, at the boundary, B, between the interface region, I, and the refractory ceramic material 200 is above the dew point of the atmosphere 300 and the dew point of the atmosphere 300 is above the temperature of cooling fluid 150.

[0055] When interface region, I, comprises a fluid gap 160, such as, for example, as shown in FIGS. 5-7, and 9A, fluid gap 160 can, for example, comprise a gas, such as, for example, air. In addition, a temperature and dew point of a gas in the fluid gap 160 can be controlled to be within a predetermined temperature and dew point range. For example, the temperature of the gas in fluid gap 160 can controlled to be above the dew point of the atmosphere 300.

In addition, the dew point of the gas in the fluid gap 160 controlled to be below the temperature of the cooling fluid 150 flowing through annular channel 106.

[0056] For example, the temperature of the gas in fluid gap 160 can be controlled to help enable the temperature of the interface region, I, at the boundary, B, between the interface region, I, and the refractory ceramic material 200 to be above the dew point of the atmosphere 300. In certain exemplary embodiments, the temperature of the gas in fluid gap 160 can be at least about 60°C, such as from about 60°C to about 120°C, including from about 70° to about 100°C. Meanwhile, the dew point of the gas in fluid gap 160 can, for example, be less than about 25°C, and further such as less than about 15°C, such as from about -25°C to about 25°C, including from about -15°C to about 15°C.

[0057] In certain exemplary embodiments, fluid gap 160 may also comprise a liquid, such as, for example, a hydrophobic liquid, such as an oil. Fluid gap may also comprise a hydrophilic liquid, such as an aqueous liquid comprising a corrosion resistant additive.

[0058] FIG. 11 shows a schematic front cutaway view of an annular heating element 100 circumferentially surrounding a conduit 38 and surrounded by a refractory ceramic material 200, wherein the center X of the annular heating element 100 is offset from the center Y of the conduit 38. As with the embodiment shown in FIG. 3, annular heating element 100 includes a relatively thin region 102 circumferentially surrounded by a relatively thick region 104 that is, in turn, circumferentially surrounded an annular channel 106 configured to flow a cooling fluid therethrough. Offsetting the annular heating element 100 from the conduit 38, can, in some embodiments, enable more evenly distributed current flow through conduit material.

[0059] 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.

[0060] 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.

Claims

What is claimed is:

1. A conduit heating apparatus comprising:

an annular heating element circumferentially surrounding at least a portion of the conduit, the annular heating element comprising an annular channel configured to flow a cooling fluid therethrough;

wherein:

the annular heating element is at least partially surrounded by a refractory ceramic material contained in an atmosphere;

a dew point of the atmosphere is above a temperature of the cooling fluid; and

the heating element comprises an interface region comprising a metal or metal alloy, the interface region extending between the annular channel and the refractory ceramic material, wherein a temperature of the interface region at a boundary between the interface region and the refractory ceramic material is above the dew point of the atmosphere.

2. The apparatus of claim 1, wherein the interface region comprises an annular shell surrounding the annular channel and a fluid gap extending between the annular channel and the annular shell.

3. The apparatus of claim 2, wherein the fluid gap comprises air.

4. The apparatus of claim 2, wherein the fluid gap comprises a gas and a

temperature and dew point of the gas is controlled to be within a predetermined temperature and dew point range.

5. The apparatus of claim 4, wherein the temperature of the gas is controlled to be above the dew point of the atmosphere and the dew point of the gas is controlled to be below the temperature of the cooling fluid.

6. The apparatus of claim 1, wherein the interface region comprises an annular ring between at least a portion of the annular channel and the refractory ceramic material.

7. The apparatus of claim 1, wherein the metal or metal alloy is selected from nickel, copper, palladium, or platinum or an alloy thereof.

8. The apparatus of claim 1, wherein the cooling fluid comprises a liquid.

9. The apparatus of claim 8, wherein the liquid comprises water.

10. The method of claim 1, wherein the cooling fluid comprises at least one gas selected from air, nitrogen, oxygen, helium, hydrogen, and neon.

11. A method of heating a conduit comprising:

circumferentially surrounding at least a portion of the conduit with an annular heating element, the annular heating element comprising an annular channel and a cooling fluid flowing therethrough; wherein:

a dew point of the atmosphere is above a temperature of the cooling fluid; and

12. The method of claim 11, wherein the interface region comprises an annular shell surrounding the annular channel and a fluid gap extending between the annular channel and the annular shell.

13. The method of claim 12, wherein the fluid gap comprises air.

14. The method of claim 12, wherein the fluid gap comprises a gas and a

15. The method of claim 14, wherein the temperature of the gas is controlled to be above the dew point of the atmosphere and the dew point of the gas is controlled to be below the temperature of the cooling fluid.

16. The method of claim 11, wherein the interface region comprises an annular ring between at least a portion of the annular channel and the refractory ceramic material.

17. The method of claim 11, wherein the metal or metal alloy is selected from nickel, copper, palladium, or platinum or an alloy thereof.

18. The method of claim 11, wherein the cooling fluid comprises a liquid.

19. The method of claim 18, wherein the liquid comprises water.

20. The method of claim 11, wherein the cooling fluid comprises at least one gas selected from air, nitrogen, oxygen, helium, hydrogen, and neon.