METHOD AND APPARATUS FOR INTRODUCING SCRAP GLASS INTO A GLASS-MELTING FURNACE

Abstract: A method of melting glass includes introducing a glass batch material (16) into a glass-melting furnace (10) containing molten glass (12), and depositing the glass batch material in a batch-depositing zone (38) on top of the molten glass contained within the furnace. Scrap fibrous glass (62) containing organic coatings is deposited on top of the glass batch material within the batch-depositing zone. The scrap fibrous glass is melted and the organic coatings volatilized. The glass batch material is then melted.

Description: METHOD AND APPARATUS FOR INTRODUCING SCRAP GLASS INTO A GLASS-MELTING FURNACE TECHNICAL FIELD This invention relates to a method of preparing molten glass. More particularly, this invention relates to introducing scrap fibrous glass into a glass-melting furnace. BACKGROUND OF THE INVENTION Molten glass is prepared by heating glass batch material in a furnace. Glass manufacture involves the mixing of various batch ingredients, generally including silica sand, dry powders, granular oxides, carbonates, borates, and other raw materials (depending on the desired glass type) and heating them to a temperature of about 2730°F (1500°C), where they become molten and acquire a homogeneous nature. Scrap fibrous glass can be added to the molten glass. Scrap fibrous glass can contain binder and other organic material. Substantial quantities of heat are required for the melting process, generally supplied by combustion of fossil fuels. In a typical glass melting furnace, the heat supplied to the melt is provided predominantly by natural gas mixed with preheated combustion air or natural gas mixed with oxygen. The resultant flame fires over the melt and heat transfer to the melt is by radiation from the flame and the furnace enclosure, and by convection currents. Frequently, glass batch material includes cullet. Cullet is broken pieces of glass that are added to the other batch ingredients and charged to the melting furnace. A certain minimum proportion of the total batch, generally in the range of about 10-20 percent by weight, is preferred to be cullet in order to provide proper melting characteristics. The manufacture of glass fiber insulation products creates waste, including scrap fibrous glass. An environmentally responsible waste management policy includes reducing the need to dispose of scrap fibrous glass in landfills. Thus, there are efforts to reuse scrap fibrous glass by returning it to the glass-melting furnace. It would be helpful to create better ways of returning scrap fibrous glass to the glass melting furnace, such as the way described in this application. SUMMARY OF THE INVENTION The above objects as well as other objects not specifically enumerated are achieved by a method of melting glass which comprises introducing a glass batch material into a glass-melting furnace containing molten glass, and depositing the glass batch material in a batch-depositing zone on top of the molten glass contained within the furnace. Scrap fibrous glass containing organic coatings is deposited on top of the glass batch material within the batch-depositing zone. The scrap fibrous glass is melted and the organic coatings volatilized. The glass batch material is then melted. According to this invention, there is also provided a method of melting glass which comprises introducing a glass batch material into a glass-melting furnace containing molten glass. The glass batch material is deposited on top of the molten glass contained within the furnace. Scrap fibrous glass containing organic coatings is deposited on top of the glass batch material in a generally uniform layer. The scrap fibrous glass is melted and the organic coatings volatilized. The glass batch material is then melted. According to this invention, there is also provided a method of melting glass which comprises introducing a glass batch material into a glass-melting furnace containing molten glass. The glass batch material is heated to create anhydrous borates. The glass batch material is deposited on top of the molten glass contained within the furnace. Scrap fibrous glass is deposited on top of the glass batch material. Scrap fibrous glass is melted to bind the anhydrous borate. The borate compounds are melted to form molten glass. According to this invention, there is also provided an apparatus for melting glass which comprises a glass-melting furnace for containing molten glass. A batch port is positioned above a batch-depositing zone so that glass batch material is deposited in the batch-depositing zone. A scrap fibrous glass conduit is positioned for depositing scrap fibrous glass on top of the glass batch material within the batch-depositing zone. Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view in elevation of a glass melting furnace according to the invention. Fig. 2 is a plan view of the furnace shown in Fig. 1. Fig. 3 is a detailed section view in elevation of a batch-depositing zone of the furnace, taken along line 3-3 of Fig. 2. Fig. 4 is a plan view of batch-depositing zone of Fig. 3, taken along line 4-4. Fig. 5 is a detailed view in elevation of batch-depositing zone taken along 5-5 of Fig. 4. DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION As shown in Figs. 1 and 2, a furnace 10 for melting glass is a receptacle for containing molten glass 12 up to a glass line 14 and glass batch material 16 above at least a portion of that glass line 14. The furnace 10 includes a tank portion 18 including a bottom wall 20, side walls 22 and 24, rear end wall 26, and front end wall 28. The side walls 22, 24 support an arch roof or refractory crown 30 above the tank portion 18 and the glass line 14 to enclose a space 32 above the molten glass 12. The furnace 10 includes a plurality of burners 44 distributed over the furnace 10 in a suitable manner for providing a means to heat the furnace 10. In the preferred embodiment, the burners 44 use a mixture of oxygen and natural gas to heat the furnace 10. Glass batch material 16 comprising raw materials is introduced into the furnace 10 near the rear end wall 26 through batch ports 48 and 50 located in the side walls 22 and 24, respectively, by using respective batch screw feeders 52 and 54 having an elevation such that the batch material is introduced slightly above the glass line 14, typically about 1 to 2 inches (2.54 to 5.08 centimeters) above the glass line 14. For protection from the heat of the furnace 10, the batch screw feeders 52 and 54 are preferably positioned in alcoves 68 that are recessed into the side walls 22 and 24, respectively. The alcoves are located in approximately the rear one-third of the furnace. The alcoves are useful in practicing the invention for a number of reasons. The alcoves are recessed from the hotter portions of the furnace and are thus somewhat cooler and are somewhat protected from turbulent air flows. The cooler temperature allows for a longer life of the scrap fibrous glass feeding equipment and glass batch material screw feeders 52, 54. The lessened turbulent air flows prevent the scrap fibrous glass and glass batch material from becoming airborne instead of melting. The glass batch material 16 is fed near the rear end wall 26 of the furnace 10 at such a rate as to form and maintain a blanket of glass batch material 16 covering a portion of the surface of the molten glass 12. The scrap fibrous glass 62 falls on top of the glass batch material 16 in the batch-depositing zones 38 and 40 that are roughly coincident with the alcoves 68. Glass currents in the molten glass 12 and the progressive advance of the glass batch material 16 from the batch screw feeders 52, 54 develop a flow of unmelted glass batch material 16 moving in the direction from near the rear end wall 26 to the front end wall 28 of the furnace 10. The molten glass 12 flows under the front end wall 28 through a throat 56 in the front end wall 28, and passes along channel 58 to a forehearth (not shown) from which the molted glass is used in forming the desired product, such as fiberglass insulation. As shown in Figs. 3, 4, and 5, the batch port 50 in the side wall 24 is located slightly above the glass line 14. Glass batch material 16 is pushed out of a batch port 50 by a batch screw feeder 54. A heat protecting wall 60 is located slightly above the batch port 50. Scrap fibrous glass 62 is pushed through a scrap fibrous glass conduit 72 out of the scrap port 64 by a scrap screw feeder 70 from behind the heat protecting wall 60 and into a scrap introduction chamber 76. The scrap fibrous glass 62 falls from the scrap introduction chamber 76 onto the glass batch material 16 emerging from the batch port 50. The distance that the scrap fibrous glass 62 drops (the distance from the bottom of the fibrous glass port 64 to the bottom of the batch port 50) is the scrap drop height indicated at 74. Preferably, the center line of the scrap port 64 for adding scrap fibrous glass is directly above the center line of the batch port 50 for adding glass batch material to the molten glass, as shown in Fig. 3. The alcove 68 is an inlet in the side wall 24. The Glass batch material 16 is pushed out of the batch port 50 by the batch screw feeder 54. Scrap fibrous glass 62 is likewise introduced near the rear end wall 26 of the furnace 10 through batch ports 48 and 50 located in the side walls 22 and 24, respectively. The scrap fibrous glass 62 and glass batch material 16 fall together in the batch-depositing zone 38. As shown in Fig. 5, the heat protecting wall 60 does not obstruct the flow of glass batch material 16 from the batch port 50. Rather, the heat protecting wall 60 shields the scrap fibrous glass 62, flowing from the scrap port 64 into the scrap introduction chamber 76, from the intense heat and turbulence of the main tank portion 18 of the furnace. After the scrap fibrous glass 62 is pushed from the scrap port 64, the scrap fibrous glass 62 falls on top of the glass batch material 16 and molten glass 12 at about the glass line 14 from the scrap drop height 74. The scrap drop height 74 is preferably in the range of about one-half meter to one meter (1.64 to 3.28 feet) and more preferably at a height of about one-half meter (1.64 feet). The scrap drop height 74 should be close enough to the glass line 14 that airborne scrap fibrous glass 62 is minimized. The problem with airborne scrap fibrous glass is that the airborne fibers collect on the walls and other surfaces of the furnace, then melt to become a flux that attacks the brick lining of the furnace. The heat protecting wall 60 and scrap introduction chamber 76 decrease the tendency of these materials to become airborne. The scrap fibrous glass 62 and glass batch material 16 are deposited together in the batch-depositing zone 38. The batch-depositing zone 38 has a preferred area of less than about one square meter (10.76 square feet). The batch screw feeder 54 pushes both glass batch material and scrap fibrous glass out of the alcove 68 into hotter portions of the furnace 10. The glass batch material 16 in the batch-depositing zone 38 is substantially unmelted when the scrap fibrous glass 62 is deposited on top of the glass batch material 16. When glass batch material 16 is added to the molten glass 12, a snake-like flow or current 36 is produced in the molten glass 12. The snake-like current 36 moves in the general direction from the rear end wall 26 to the front end wall 28 of the furnace 10. The continuous stream of glass batch material 16 prevents piling of the scrap fibrous glass 62. The continuous stream of glass batch material 16 also serves as a vehicle to transport the scrap fibrous glass 62 out of the batch-depositing zone 38 and into hotter portions of the furnace. In one embodiment of this invention, the scrap fibrous glass 62 is milled or ground to a consistency of between about 8 mesh and 200 mesh. When the scrap fibrous glass 62 is insufficiently milled so that the fibers are too long, the scrap fibrous glass 62 has sufficient insulation properties that it does not melt well into the molten glass, but instead clumps together. This clumping together of the scrap fibrous glass 62 can result in clogging the scrap introduction chamber 76 and blocking the alcove 68. At a consistency of finer than about 200 mesh, the scrap fibrous glass 62 also is not easily pushed through the scrap fibrous glass conduit 72 out of the scrap port 64 by the scrap screw feeder 70. Also, at a consistency of greater than 200 mesh, the scrap fibrous glass 62 is too easily made airborne and does not drop onto, or cover as well, the glass batch material 16. A preferred size is about 60 mesh. An important advantage of applying the scrap fibrous glass 62 generally uniformly over the glass batch material 16 is that the scrap fibrous glass 62 encapsulates the borate compounds in the glass batch material 16. Shortly after their introduction into the furnace, the borate compounds are decrepitating as they explosively release chemically- combined water. The decrepitation occurs at temperatures with the range from about 110°C (230°F) to about 500°C (932°F), and results in anhydrous borate compounds. This typically occurs within the alcoves 68 where the temperature is significantly lower than the temperature (typically about 1300°C (2372°F)) in the tank portion 18 of the furnace. The encapsulation promotes better glass homogeneity by preventing the borate compounds from agglomerating and forming corrosive surface pools. The scrap fibrous glass 62 will also help hold glass batch material 16 in current paths produced by the flow of glass batch material 16 being pushed into the alcove 68. As the batch screw feeder pushes the resulting stream of both glass batch material 16 and scrap fibrous glass 62 out into the hot furnace, flames consume the organic compounds in the scrap fibrous glass 62. This is possible because the scrap fibrous glass is on top of the glass batch material 16 and is thus exposed to oxygen, preheated air or both. The process promotes the melting of scrap fibrous glass 62 because the heat source oxidizes or volatilizes the binders and organic material in the scrap fibrous glass 62. For purposes of this invention, the binders and organic material may be either burned, vaporized or both. The melting of the scrap fibrous glass 62 causes the encapsulation of the glass batch material, thereby preventing the borates in the glass batch material 16 from pooling and attacking the glass line refractory. It will also help reduce airborne particulate borate compounds normally formed during the loss of water by the borate materials. Also, by distributing the scrap fibrous glass 62 uniformly, rather than non- uniformly, the glass batch material 16 will melt more quickly. The term "generally uniform layer" means a layer of about one-half inch (1.27 centimeters) to about 3 inches (7.62 centimeters) thick. When using a batch screw feeder 54 to introduce the glass batch material 16 into the furnace, the flow of glass batch material 16 and the generally uniform layer of scrap fibrous glass 62 will be about 12 inches (30 centimeters) wide. The use of screw feeders helps ensure a generally uniform thickness for the deposited scrap fibrous glass 62 because the glass batch material is continuously advanced into the furnace. The embodiment of the invention disclosed in Figs. 1 through 5 shows the screw type feeder for introducing glass batch material into the furnace. The invention may also be practiced in glass-melting furnaces of both the "pusher" and "table" varieties. A pusher type glass-melting furnace (not shown) functions by mechanically pushing glass batch material from a shelf near or at the rear of the furnace onto the previously deposited glass batch material below. Depositing a generally uniform layer of scrap fibrous glass onto the glass batch material while the glass batch material is either on the shelf or on the molten glass according to the present invention would likely reduce explosions of and corrosion by borate compounds in the furnace. The batch-depositing zone of a pusher glass-melting furnace is about at the area where glass batch material is being pushed from the shelf. In a manner similar to that shown with respect to the first embodiment, a scrap introduction chamber and heat protecting wall could be installed in a pusher glass-melting furnace at about the area where glass batch material is being pushed from the shelf. A table type glass-melting furnace (not shown) functions by depositing glass batch material from a movable table near the rear of the furnace onto the molten glass below. Depositing a generally uniform layer of scrap fibrous glass onto the glass batch material while the glass batch material is either on the table or on the molten glass would reduce explosions of and corrosion by borate compounds in the furnace. The batch-depositing zone of a table glass-melting furnace is about at the area where glass batch material is being deposited from the movable table. Likewise, a scrap introduction chamber and heat protecting wall could be installed in a table glass-melting furnace at about the area where glass batch material is being deposited from the movable table. As described above, in one aspect of the invention, the glass batch material is deposited into the batch-depositing zone and scrap fibrous glass is added on top, still within the batch-depositing zone. The scrap fibers are dropped only a short drop height distance. In contrast, typical procedures for adding scrap fibrous glass involve blowing or injecting the scrap fibrous glass in an airborne manner. One of the advantages of more quietly depositing the scrap fibrous glass is that the quantity of lofted or airborne fibers is minimized. The principle and mode of operation of this invention have been described in its prefeπed embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope.

Claims: WHAT IS CLAIMED IS: 1. A method of melting glass comprising : introducing a glass batch material (16) into a glass-melting furnace (10) containing molten glass; depositing the glass batch material in a batch-depositing zone (38) on top of the molten glass contained within the furnace; depositing scrap fibrous glass (62) containing organic coatings on top of the glass batch material within the batch-depositing zone; melting the scrap fibrous glass and volatilizing the organic coatings; and melting the glass batch material. 2. The method of claim 1, wherein the step of depositing the scrap fibrous glass (62) creates a generally uniform layer of scrap fibrous glass on top of the glass batch material (16) in the batch-depositing zone (38). 3. The method of claim 1, in which the batch-depositing zone (38) has an area of less than about one square meter (10.76 square feet). 4. The method of claim 1, wherein the scrap fibrous glass (62) is introduced by passing it through a wall (24) of the furnace (10) through a scrap fibrous glass conduit (72) and out of a scrap port (64). 5. The method of claim 4, wherein the scrap fibrous glass (62) is introduced from behind a heat protecting wall (60). 6. The method of claim 4, wherein the scrap fibrous glass (62) is introduced into a scrap introduction chamber (76). 7. The method of claim 1 , wherein the glass batch material (16) in the batch- depositing zone (38) is substantially unmelted when the scrap fibrous glass (62) is deposited on top of the glass batch material. 8. The method of claim 1, wherein the scrap fibrous glass (62) is deposited by discharging it from a scrap fibrous glass conduit (72) at a height (74) of less than about one meter (3.28 feet) above the batch material (16) in the batch-depositing zone (38). 9. The method of claim 1, wherein the batch-depositing zone (38) is positioned in a recessed area (68) in a wall (24) of the furnace (10). 10. The method of claim 1, wherein the glass batch material (16) is deposited in the batch-depositing zone (38) using one or more of a screw feeder (54), a blanket feeder, and a batch pusher. 11. The method of claim 1 , wherein the step of depositing the scrap fibrous glass (62) is done by using a continuous stream of glass batch material (16) as a vehicle of transport to prevent piling of the scrap fibrous glass. 12. A method of melting glass comprising: introducing a glass batch material (16) into a glass-melting furnace (10) containing molten glass; depositing the glass batch material on top of the molten glass (12) contained within the furnace; depositing scrap fibrous glass (62) containing organic coatings on top of the glass batch material in a generally uniform layer (36); melting the scrap fibrous glass and volatilizing the organic coatings; and melting the glass batch material. 13. The method of claim 12, wherein the batch material in the batch-depositing zone (38) is substantially unmelted when the scrap fibrous glass (62) is deposited on top of the glass batch material (16). 14. The method of claim 12, wherein scrap fibrous glass (62) is deposited by discharging it at a height (74) of less than about one meter (3.28 feet) above the glass batch material (16) in the batch-depositing zone (38) from a scrap fibrous glass conduit (72). 15. A method of melting glass in a glass furnace (10) comprising: introducing a glass batch material (16) into a glass-melting furnace containing molten glass (12); heating the glass batch material to create anhydrous borates; depositing the glass batch material on top of the molten glass contained within the furnace; depositing scrap fibrous glass (62) on top of the glass batch material; melting the scrap fibrous glass to bind the anhydrous borate; and melting the glass batch material to form molten glass. 16. The method of claim 15, wherein the step of depositing a layer of scrap fibrous glass (62) on top of the glass batch material (16) is done with a generally uniform layer (36) of the scrap fibrous glass. 17. The method of claim 15, wherein the glass batch material (16) in the batch- depositing zone (38) is substantially unmelted when the scrap fibrous glass (62) is deposited on top of the glass batch material. 18. An apparatus for melting glass, comprising: a glass-melting furnace (10) for containing molten glass (12); a batch port (50) positioned above a batch-depositing zone (38) so that glass batch material (16) is deposited in the batch-depositing zone; and a scrap fibrous glass conduit (72) for depositing scrap fibrous glass (62) on top of the glass batch material within the batch-depositing zone. 19. The apparatus of claim 18, including a heat protecting wall (60) that protects the scrap fibrous glass (62) from heat from the furnace (10). 20. The apparatus of claim 18, in which the scrap fibrous glass conduit (72) has a discharge port (64) positioned at a scrap drop height (74) of less than about one meter (3.28 feet) above the batch material (16) in the batch-depositing zone (38).

Inventors: PLOETZ LAWRENCE J, PLOETZ, LAWRENCE, J.
Applicants: OWENS CORNING FIBERGLASS CORP, PLOETZ LAWRENCE J, OWENS CORNING, PLOETZ, LAWRENCE, J.
Application year: 2001
Main classification: C03B
IPC codes: C03B3