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.