PROCESS FOR PRODUCING MOLTEN. GLASS

TECHNICAL FIELD This invention relates to the melting of inorganic materials to produce molten glass.

BACKGROUND ART Conventional glass furnaces include a melting zone into which the raw batch material is charged. Air fuel .burner flames are projected into the melting zone to melt the raw-material v/hich then flows through a throat in the front wall. Conventionally, glass melting furnaces burn either natural gas or oil.

U.S. Patent 3,856,496, issued December 24, 1974, discloses one modification to the conventional glass melting furnace. Pairs of adjacent burners are mounted in the rear wall of the furnace for melting raw batch material. The angle between the adjacent burners of each pair can be adjusted to increase mixing of fuel and air to ensure complete combustion. The burners also rr.ay be adjusted to maximize the area of raw batch covered by the burner flames. The burners produce a flame anc create a circulation of hot effluent gases in the interior of the glass tank in a clockwise or counter clockwise pattern.

DISCLOSURE OF INVENTION We have discovered that by providing a flame of high energy heat and impinging it directly upon the surface of molten glass, procuction may be substantially increased and a reduction in the amount of energy employed per ton of

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- finished glass may be achieved. This invention is readily adaptable for use with oxygen-enriched burners. The burners actually in service use oxygen and natural gas. In one embodiment the flame is directed at the surface of molten glass open to exposure at the rows of bubbles in the glass melting furnace. In another embodiment, opposed oxygen-enriched burners are located in opposite furnace sidewalls facing each other. The burners are adjusted to maximize the area of molten glass covered by the burner flames. Creating a localized hot- spot on the surface of the molten glass is believed to be the critical feature of this process.

The very strong and v ery localized heat brought to the surface of the molten glass at a given location increases the temperature of the molten glass to such an extent that the throughput of the furnace can be increased with a reduction in the amount of fuel per ton used. This invention satisfies the time/temperature relationship required in melting batch. The high temperature burner is preferred because it increases the temperature of the molten glass without increasing the temperature of the whole melting tank. Merely increasing the energy in conventional burners may not be satisfactory as this tends to make the temperature of the furnaces too high. Also, increasing glass throughput by conventional methods is not always possible without abnormally increasing total fuel usage. This is uneconomical and often harmful to refractory structure. Conventional heat input would produce so much volume of combustion products that the fl mes would iir.pinge the refractory and cause its rapid destruction.

BRIEF DESCRIPTION CF THE DRAWINGS FIG. 1 is a side view of a glass melting furnace employed to carry out this invention. FIG. 2 is a rear view of a glass melting furnace employed to carry out this invention.

FIG. 3 shows a water cooled nozzle which feeds oxygen directly into the fuel jets.

BEST MODE OF CARRYING OUT INVENTION This invention may be used to produce conventional wool glass for insulation and ceiling board and to produce conventional textiles and reinforcements such as those made from E glass.

Preferably, this invention relates to a method and apparatus for processing heat-softenabl e minerals into materials such as glass and, more especially, to a method and apparatus for carrying on processing of mineral or inorganic materials from a batch stage through melting and delivering streams of the material, attenuating the streams to filaments and packaging the filaments. Textile filaments have been produced by attenuating streams of glass from a feeder to filaments by winding the filaments upon a collector or tube in package form.

While only a single oxygen-enriched burner or a pair of such burners is employed in the disclosed embodiment, multiple oxygen-enriched burners are well within the scope σf this invention.

FIG. 1 s a side view of a glass melting furnace employed to carry out this invention. Furnace 10 is formed of sidewall 12 and another sidewall , rear wall, front wall, roof and bottcrr structures (not shown). The front wall 14 contains a port or throat which permits the molten glass to leave the furnace. A row of conventional burners 16 is shown. A number of conventional bubblers 18 also is shown. Water cooled, oxygen gas burner 11 also is shown in position.

The chamber of melting furnace 10 is adapted to be fired or heated by fuel gas or other suitable fuel mixed with air which is preheated in the recuperator to a temperature not exceeding that at which the air may be safely mixed with the fuel gas at the regions of delivery of the fuel gas and air into the fuel chamber at lengthwise spaced regions above the level of the glass in the chamber.

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As shown in FIG. 1, a row or battery of combustion burners 16 mounted in burner blocks is arranged at each siαe of the furnace.

Arranged at opposite sides of furnace 10 adjacent the stack or rear end of furnace 10 are batch charging stations including batch feed openings provided with batch chargers or batch feeders not shown. Disposed above each of the batch chargers is a hopper, each hopper being provided with a control valve for regulating the delivery of raw batch into each charger.

The raw materials usually consist of sand, limestone, soda ash, and a borate such as colemanite or ulexite. The batch make-up depends on the type of glass being made and need not contain all of the above materials. Various other materials may be present in small amounts.

The glass also may be flux free glasses, i.e. , glasses that contain little or no fluxing agents such as boron or fl uorine.

The heat necessary for melting the raw materials and for maintaining the molten batch at a desired temperature is provided by two rows of conventional burners 16. The burners are designed to burn a suitable liquid fuel such as oil, or a fuel gas such as natural gas. The type of fuel used depends on what is available commercially, the economy of the fuel , and its suitability for glass melting. The burner pairs are positioned in the sidewall 12 and the opposite siαewall not shown. As previously discussed, FIG. 1 shows oxygen-enriched burner 11 positioned at the rear row of bubblers 18.

FIG. 2 is a rear view of furnace 10 showing one example of the angle at which burners 11 are extended into the furnace. In addition, FIG. 2 shows roof 20 and bottom floor 22. FIG. 2 also shows throat 24 extending through front wal 1 14.

FIG. 3 shows the cetailed features of burner 11. A burner construction wherein the oxygen is injected directly into the fuel at the nozzle is shewn in FIG. 3.

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Burner 11 includes a cylindrical pipe 30 having a fuel inlet 32 which feeds the fuel to the burner. Pipe 30 terminates in a nozzle tip 34 from which the fuel jets are emitted. Oxygen is fed to tube 30 by means 36 so that the oxygen and fuel are emitted together from the nozzle tip 34. To prevent burner 11 from overheating, water a pooled jacket is employed. FIG. 3 shows water inlet 38 and water outlet 40. Burner 11 usually employs bronze rear casting 42 and oxygen quick-disconnect fitting 44.

The temperature of the flame may vary widely. Properly speaking, there is no preferred temperature range for the flame. The temperature generally depends upon the quality of the natural gas and the oxygen/gas ratio. In the following embodiment, the temperature of the oxygen flame is about 2780°C. This figure is substantially higher than the temperature of a conventional burner with air which is about 1950°C.

In one embodiment, the tεmp ^' erature of the flarne should be at least 2500°C. The oxygen/gas ratio is adjusted close to stoichiometric, v/hich is a ratio of 1.75:1. Actually, a ratio of 2:1 preferably is chosen for safety. It is extremely important not to fire a reducing gas flame as gas cracking occurs immediately.

In the conventional process of the following embodiment, the surface temperature of the molten glass in the absence of the oxygen flame of this invention usually is 1560 to 1600°C. Accordingly, the temperature of the oxygen flame is at least 10C0-ilC0°C higher than the surface temperature of the molten glass, compared to only a 350°C difference with regard to air fl mes of conventional burners .

The preferred burners to be employed in this invention use only natural gas and pure oxygen. That is, the burners do not employ an air/cxygen mixture with the fuel. It is within the scope of this invention, however, to employ burners where the use of an air/oxygen mixture may be possible as long as the temperature of the heat

source is sufficiently high to (1) increase the throughput of the furnace and (2) reduce the amount of fuel employed per ton of glass.

Exarr.pl ε To demonstrate that this invention achieves increased pul without increasing total fuel per ton usage, the following comparison was made. A conventional glass melting furnace was used as a standard. The fuel usage for the furnace is 17.2 million BTUs per ton of glass. The furnace had a front wall temperature of 1540°C.

With this invention, throughput increased about 26% and the gas consumed by the conventional burners and the oxygen burners equaled 14.4 million BTUs per ton of glass. Oxygen usage was 70 SCFK (standard cubic feet per minute) and the front wall temperature was 1555°C. The improvement in fuel usage was a reduction of about 18 of fuel for the same glass tonnage in the conventional furnace.

Exposed molten material ^' can be found in many regions of the melting chamber. Frequently, the floor of the chamber may be provided with orifices for delivering jets of gas into and upwardly through the molten material . Often, the orifices are arrangec in row ^' s transversely of the chamber. In one embodiment, the high intensity heat may be directed at exposed molten material in the region of the chamber near these orifices. In another embodiment, the high intensity heat may be directed at exposed molten material in the region near the row of orifices nearest the batch charging end of the chamber. Still other areas of exposed molten glass may occur in regions near electrodes if electric heating is employee to melt the batch. In still another embodiment the oxygen burners may be installed at the front end of the melter above front bubbl ers .

INDUSTRIAL APPLICABILITY

This invention can be used with a method and apparatus for processing heat- cftenabl e mineral materials

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such as glass and, more especially, to a method and apparatus for carrying on processing of mineral or inorganic material from a batch stage through melting, delivering streams of the material , attenuating the streams to filaments and packaging the filaments.

Textile filaments have been produced by attenuating streams of glass from a feeder to filaments by winding the filaments upon a collector or tube in package form.

The invention can be used with a method wherein a series of glass melting and processing facilities or units are employed, each unit provided with a plurality of forehearth sections oriented or arranged in aligned rows and the forehearth sections provided with large numbers of orificed feeders in combination with filament-attenuating and packaging units individual to each feeder or plurality of feeders arranged in an enclosure or chamber wherein the packaging units or devices are disposed in rows along each side of an aisle to facilitate supervision of the operations by a minimum number of operators.

The invention uses a melting and conditioning facility or unit for processing raw batch filament-forming material and conditioning the same suitable for forming textile filaments wherein a plurality of forehearths or forehearth sections are supplied with the material from the unit, the unit being of a size and character to promote a repeated circulation or recycling of the molten material in paths by agitation and convection whereby the material is fined and refined during its circulatory movements in the melting and conditioning unit so that the material is maintained in the unit for a period of time to assure substantially complete degas fi cati on of the material and the promotion of homogeneity thereof.

The invention uses a plurality of melting and furnaces or units wherein each unit is provided with a plurality of forehearths or forehearth sections each provided with a plurality of stream feeders or bushings

-Ci- arranged to discharge streams of glass wherein the feeders are aligned in rectilinear rows and the groups of ^' streams are processed to strands of filaments by winding machines disposed in rows beneath the feeders facilitating ^" operation with a minimum number of operators.

The melting units are particularly adaptable for conditioning glass or other mineral material for forming textile filaments wherein the amount of glass processed per unit of time is greatly increased and advantage taken of high melting rates and volume production of filaments to reduce the cost of textile filaments.

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