Submerged glass delivery throat and delivery method

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.

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.degree. 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.

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 30a and
 30b, 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 30a and 30b 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 30a and
 30b extends above the level of the floor 22 of chambers 12 and 14, and an
 open sidewall portion 40 of the standpipes 30a and 30b, sealed by flanges
 34 to the conduit 28, provides open communication between the interior of
 conduit 28 and the standpipes 30a and 30b 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 30a and 30b to protect the refractory metal
 conduit 28 and standpipes 30a and 30b 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 30a and 30b, 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.degree. 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 30a and 30b 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.sub.2, 92% N.sub.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 30a
 and 30b. 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 30a and 30b, 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 30a,
 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 30b, 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 30a and 30b 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 30a and 30b and the
 adjacent refractory block, but more importantly stagnant glass is created
 in the area 50 between the upper walls of the standpipes 30a and 30b 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 30a and 30b 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 30a and 30b 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.