Abstract:
Process and apparatus are disclosed for delivering molten thermoplastic material from one chamber to another through a throat in a refractory wall separating said chambers. A refractory metal conduit is positioned within said refractory throat below the level of the floor of said chambers, and standpipes at each end of said conduit extending above the level of said floors, create stagnant thermoplastic material about the conduit so as to prevent corrosion products from flowing away from about the conduit and thereby also preventing fresh thermoplastic from replacing it. The stagnant material becomes enriched with corrosion products, which with the absence of flow retards further corrosion of the refractory about the conduit.

Description:
This application is based upon the provisional application Serial No. 60/076,969, filed Mar. 5, 1998, which we claim as the priority date of this application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the delivery of molten glass from one portion of a glass melting furnace of another portion thereof, and more particularly to an improved method and apparatus for delivering molten glass through a submerged throat within a glass melting tank while inhibiting the corrosion of refractory surrounding the submerged throat. 
     BACKGROUND OF THE INVENTION 
     The conventional method of conveying glass through a refractory wall within a glass melting tank is to incorporate the use of a channel made of refractory block. The channel or throat is generally located at the bottom of a bridgewall of the furnace, and is utilized to flow the molten glass from a melting chamber into an adjacent refining chamber, or for flowing the glass out of the furnace to be cooled in a forehearth. When there is molten glass on both sides of the wall dividing the various chambers, the throat or channel could be as simple as a hole in the wall. However, the action of the flowing molten glass tends to corrode the roof of the refractory channel, and typically the first part of the furnace to wear out is the throat area. 
     Thus, the effective life of glass melting furnaces is limited by the corrosion of the throats connecting the melting and fining zones or chambers, and those throats connecting the fining and refiner zones or chambers. The fining zone may be operated at temperatures above 1500° C., so the walls and throats associated therewith suffer severe corrosion. The roof of the throats suffers the greatest corrosion, and even fused zirconia block is corroded away over time until the refractory is so thin that a glass leak can occur. 
     Refractory metal pipes, such as molybdenum pipes, have been used in the past to convey some glasses from the bottom of a tank through a sidewall thereof into a distribution channel, such as shown in U.S. Pat. No. 4,029,887 to Spremulli. The flow of certain molten glasses through the moly pipe results in very small corrosion to the pipe per se. However, where the pipe passes through the sidewall, the corrosion of the surrounding refractory can be significant. The mechanism creating such high corrosion is known in the industry as upward drilling. That is, whenever there is a horizontal refractory surface with glass flowing therebeneath, bubbles in the glass will rise up until they hit the surface. The bubbles then tend to enhance corrosion due to a surface tension gradient on the bubbles, and the bubbles then in effect drill a hole into the refractory. 
     The dense corrosion products formed between the flowing glass and the corroded refractory then flow away, and fresh glass enters the area between the pipe and the refractory to repeat the corrosion process. When a molybdenum pipe is passed through a hole in the sidewall of a glass tank to flow molten glass from the tank, such as in the Spremulli patent, the refractory above the pipe will continue to corrode away even though the glass flows through the pipe. The corrosion of the refractory continues because there is nothing to prevent the dense corrosion products from flowing away. Eventually, there is very little refractory separating the glass from a water cooled outer rim of a refractory metal flange surrounding the pipe, and the process must be shut down before a glass leak occurs. 
     U.S. Pat. No. 4,365,987 to Boettner discloses the use of water cooled molybdenum flanges to prevent leaks between adjacent portions of a glass delivery system. However, the Boettner patent is primarily directed to a refractory metal glass delivery system of molybdenum for controlling the flow of glass from a furnace to a forehearth by means of a flow control device incorporated therein. The inlet to the flow control system is at a level above the bottom of the furnace, and no means are provided for inhibiting or virtually eliminating the corrosion of the refractory block about the inlet end of the delivery tube. Accordingly, the corrosion of the refractory wall through which the pipe passes limits the life of the delivery system. 
     Over the years attempts have been made to install throats within glass furnaces protected by refractory metal conduits such as molybdenum. However, such attempts have not been completely successful since no effort had been made to protect the refractory material surrounding the conduit from the corrosive effects of the glass on the outside of the conduit adjacent the surrounding refractory material. The use of a water-cooled flange about the conduit has helped to prevent complete flow through of the molten glass along the length of the conduit, but has not succeeded in preventing the corrosion of the refractory material adjacent the inlet and outlet ends and along the upper surface of the conduit. The present invention is directed to overcoming these deficiencies. 
     It thus has been an object of the present invention to provide method and apparatus for virtually eliminating or inhibiting the corrosion of refractory material about a refractory metal delivery system within a glass melting furnace. 
     SUMMARY OF THE INVENTION 
     The present invention sets forth method and apparatus for delivering molten glass from one zone or chamber of a glass melting furnace into another zone or chamber, through a submerged throat while inhibiting and virtually eliminating detrimental corrosion of refractory material forming a portion of the throat structure. A refractory metal pipe or conduit is positioned within the throat at a level below the level of the furnace floors on both sides of a dividing wall between the adjacent chambers. A closed bottom vertical pipe or conduit, hereinafter referred to as a standpipe, is positioned at each end of the refractory metal conduit, each of which has an upper end projecting above the floor of the furnace, such that the molten glass enters and exits the submerged throat at a point above the floor of the furnace by reason of the upper extent of the standpipes. 
     Accordingly, the glass between the refractory metal parts of the delivery system and the surrounding refractory becomes stagnant, and will eventually become enriched in corrosion products. Due to the enrichment of the glass with the corrosion products adjacent the delivery system, and the fact that such products are in a stagnant condition, there is no flowing away of the corrosion products which would allow fresh glass to replace it and therefore cause further corrosion. It is this enrichment and absence of flow that retards or virtually eliminates further corrosion of the adjacent refractory. Accordingly, a key factor of the invention is to prevent the corrosion products, which are dense, from flowing away from adjacent the conduit and thereby preventing fresh glass from replacing it. It is the use of the standpipes at the ends of a conduit, whose upper extent is below the level of the furnace floor, which create stagnation of the corrosion products in situ, and prevent additional glass from flowing into the area to cause additional corrosion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a somewhat schematic elevational view in section illustrating a preferred embodiment of the submerged throat delivery system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing, a portion of a glass melting furnace  10  is shown having two zones or chambers  12 ,  14 , separated by a bridgewall  16  having a submerged throat  18  communicating between the adjacent chambers  12  and  14 . Both the upper surface defined by the bottom of cover blocks  26 , and the lower surface  20  of the submerged throat  18  are below the level of the floor  22  of both chambers  12  and  14 . The submerged throat  18  is formed in the bridgewall  16  and is surrounded by refractory sidewall blocks (not shown) bottom blocks  24 , and cover blocks  26 . 
     A refractory metal pipe or conduit  28  is positioned within the submerged throat  18 , and first and second refractory metal vertically oriented pipes or conduits with closed bottoms, again referred to as standpipes  30   a  and  30   b , respectively are positioned within recesses  32  formed in the floors of chambers  12  and  14  adjacent ends of the submerged throat  18 . Each of the standpipes  30   a  and  30   b  has a flanged portion  34  secured to reduced end portions  36  of the refractory metal conduit or pipe  28 , making a leak proof seal. The upper end  38  of the refractory metal standpipes  30   a  and  30   b  extends above the level of the floor  22  of chambers  12  and  14 , and an open sidewall portion  40  of the standpipes  30   a  and  30   b , sealed by flanges  34  to the conduit  28 , provides open communication between the interior of conduit  28  and the standpipes  30   a  and  30   b  at the inlet end and outlet end, respectively, of the conduit. 
     A flange  42  of the refractory metal material is attached to the outer circumference of the conduit  28  with a leak tight joint. The purpose of the flange is to prevent molten glass from flowing around the outside of the conduit, since such flowing of glass would corrode the refractory blocks  24  and  26 . The outside edge of the flange  42  is protected from oxidation by a water cooled ring  44 . If desired, an inert gas can be blown into the ring  44  to help prevent air from entering. A plurality of purge gas tubes  46  are provided within the throat  18  and the recesses  32  below the pipe  28  and standpipes  30   a  and  30   b  to protect the refractory metal conduit  28  and standpipes  30   a  and  30   b  from oxidation until molten glass has an opportunity to surround the refractory metal parts. 
     While, in the present invention, a refractory metal such as molybdenum (moly) is preferred for use as the refractory metal pipe or conduit  28  and the refractory metal standpipes  30   a  and  30   b , other materials such as tungsten, tantalum, rhenium, columbium, steel or alloys thereof may be used. Also, noble metals, such as platinum and rhodium or alloys thereof may be used where appropriate. Since moly will oxidize rapidly above about 550° C., it must be protected from oxidation until it is completely surrounded by molten glass. The standard practice is to completely cover the floor of the furnace with cullet, so that the moly conduit  28  and the moly standpipes  30   a  and  30   b  are also covered with cullet. Then as the furnace heats up, the cullet will melt and seal off oxygen from above the conduit and standpipes. In addition, two purge tubes  46  beneath the conduit  28  supply an inert gas or forming gas (8% H 2 , 92% N 2 ) to the cavity around the conduit during startup. In addition purging gas tubes  46  supply inert gas to the recesses  32  about the moly standpipes  30   a  and  30   b . Currently at startup, the conduit and standpipes are covered with cullet as previously mentioned and inert gas is provided to flow about the conduit  28 , standpipes  30   a  and  30   b , and flange  42  to protect the moly surfaces from oxidation until such time as the cullet is melted and flows over the moly surfaces and seals off oxygen from attacking the moly. That is, once the molten glass flows around the conduit, standpipes and moly flange, the molten glass acts as a seal and will protect the moly from oxidation. Further, the molten glass will flow along the outside of the conduit until it contacts the steel ring  40  and the cooled ring solidifies the glass to prevent further flow. 
     In operation, as the thermoplastic material, such as molten glass, flows from chamber  12  to chamber  14 , it follows the direction of arrows a such that it flows over the top or upper edge  38  of a first standpipe  30   a , through an opening  40  in a sidewall thereof communicating with the inlet end of conduit  28 , and then out through a second opening  40  communicating with the outlet ends of the conduit into a second standpipe  30   b , and out over an upper edge  38  of such second standpipe into chamber  14 . The chamber  12  could be a melting zone and chamber  14  could be a fining zone, or in the alternative, chamber  12  could be a fining zone and chamber  14  could be a refiner, since the delivery system of the present invention can be utilized between either of these combinations. 
     The fact that the refractory metal conduit or pipe  28  is submerged below the level of the floor  22  of the chambers  12  and  14 , and the upper ends or openings  38  of the standpipes  30   a  and  30   b  are above the level of the floor  22  of the adjacent chambers  12  and  14 , creates stagnant glass about the inlet and outlet ends of the conduit  28 . That is, not only does stagnant glass  48  form in the wells  32  between the standpipes  30   a  and  30   b  and the adjacent refractory block, but more importantly stagnant glass is created in the area  50  between the upper walls of the standpipes  30   a  and  30   b  and the adjacent cover blocks  26 . Keeping the glass around outer walls of the conduit stagnant prevents corrosion products, which are dense, from flowing away from the conduit, which in turn prevents fresh glass from replacing it. Since the moly standpipes  30   a  and  30   b  convey the molten glass to a point above the level of the floors  22  of the furnace  10 , the glass between the molybdenum parts and the surrounding refractory is therefore stagnant and will eventually become enriched in corrosion products. The standpipes at each end of the conduit  28  do not allow the refractory corrosion products to be swept away by glass flowing through the pipe. In fact, the cavity around the pipe will tend to collect the corrosion products that then settle on the floor of the furnace. The enriched corrosion products between the conduit and the surrounding refractory, and the absence of flow therebetween will then retard further corrosion of the adjacent refractory block, since fresh glass which would cause further corrosion is prevented from entering the area. 
     In those situations wherein it is not feasible to line the bottom of the furnace with cullet at start up so as to cover and protect the molybdenum conduit and standpipes from oxidation, such as when it is necessary to fire in tamp, ramming mixture, or the like at a high temperature, a trough or gutter  52  may be formed across the width of the furnace  10  by means of a curb wall  54 . The trough  52 , formed between the curb wall  54  and the bridgewall  16 , has a floor  56  at the same level as the level of the floor  22 . At startup then, the trough is filled with cullet, and inert gases are supplied through the purged gas tubes  36 , so that when the cullet is melted there will be sufficient molten glass to cover the surfaces of the molybdenum conduit  28  and standpipes  30   a  and  30   b  so as protect the surfaces thereof from oxidation. 
     Although I have disclosed the now preferred embodiments of the invention it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit and scope thereof as defined in the appended claims.