PROCESS AND APPARATUS FOR GLASS MANUFACTURE

Abstract

An apparatus for manufacturing glass includes a furnace. A doghouse of the furnace receives and melts solid-glass forming material using one or more submerged combustion burners. An elongated tank positioned downstream of the doghouse includes a melting chamber, a refining chamber, and a thermal conditioning. The melting chamber has in inlet through which molten glass is received from the doghouse. The refining chamber is positioned downstream of the melting chamber and receives molten glass from the melting chamber. The thermal conditioning chamber is positioned downstream of the refining chamber and receives molten glass from the refining chamber. Additionally, the thermal conditioning chamber delivers molten glass to a glass forming machine.

Claims

1. An apparatus for manufacturing glass including: a doghouse portion of a furnace that receives and melts solid glass-forming materials by application of heat from one or more submerged combustion burners; and an elongated tank downstream of the doghouse including: a melting chamber at an upstream end of the tank having an inlet through which molten glass is received from the doghouse, a refining chamber downstream of the melting chamber that receives molten glass from the melting chamber, and a thermal conditioning chamber downstream of the refining chamber that receives molten glass from the refining chamber and delivers the molten glass to a glass forming machine.

2. The apparatus set forth in claim 1, wherein the solid glass-forming materials are received in the doghouse via a submerged inlet located below a free surface of the molten glass already in the doghouse.

3. The apparatus set forth in claim 1, wherein the doghouse includes a floor, a roof, and a sidewall connecting the floor and the roof, and wherein the floor, roof, and sidewall of the doghouse are liquid-cooled such that a solid layer of glass forms on an interior surface thereof during operation of the apparatus.

4. The apparatus set forth in claim 3, wherein the floor, roof, and sidewall of the doghouse include a water-jacket defining a cooling channel through which a liquid coolant can flow over an exterior surface of the floor, roof, and sidewall of the doghouse to transfer heat away from the interior surface thereof.

5. The apparatus set forth in claim 1, wherein the doghouse is offset from the tank such that molten glass flowing from an upstream end to a downstream end of the doghouse flows in a direction transverse to the flow of molten glass in the tank.

6. The apparatus set forth in claim 1, wherein the doghouse does not include overhead combustion burners.

7. The apparatus set forth in claim 1, wherein the one or more submerged combustion burners are mounted in the floor of the doghouse.

8. An apparatus for manufacturing glass including: a doghouse configured to receive a mixture of solid glass-forming materials and including one or more submerged combustion burners, the doghouse defining a flow direction; and an elongated tank downstream of the doghouse that defines a flow direction oriented transverse to the flow direction of the doghouse, the elongated tank including: a melting chamber having an inlet in communication with the doghouse; a refining chamber downstream of, and in communication with, the melting chamber, wherein the melting chamber and the refining chamber are separated by a throat; and a thermal conditioning chamber downstream of, and in communication with, the refining chamber, wherein the refining chamber and the thermal conditioning chamber are separated by a waist.

9. The apparatus set forth in claim 8, further comprising: a second doghouse configured to receive a mixture of solid glass-forming materials and including one or more submerged combustion burners, the second doghouse defining a flow direction that is also transverse to the flow direction defined by the elongated tank.

10. The apparatus set forth in claim 9, wherein the doghouse and the second doghouse are positioned on opposite sides of the elongated tank.

11. The apparatus set forth in claim 10, wherein the doghouse and the second doghouse are opposed on opposite sides of the elongated tank such that the flow direction defined by the doghouse and the flow direction defined by the second doghouse are aligned.

12. The apparatus set forth in claim 8, wherein the doghouse includes a floor, a roof, and a sidewall, and wherein the one or more submerged combustion burners are mounted in the floor.

13. The apparatus set forth in claim 8, wherein the floor, roof, and sidewall of the doghouse are liquid-cooled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The disclosure, together with additional objects, features, advantages and aspects thereof, will be best understood from the following description, the appended claims and the accompanying drawing(s), in which:

[0010] FIG. 1 is a top view of an apparatus for manufacturing glass, in accordance with an illustrative embodiment of the present disclosure, including an elongated tank and a doghouse located upstream of the tank in which glass-forming materials are melted by application of heat from floor-mounted submerged combustion burners;

[0011] FIG. 2 is a top view of an apparatus for manufacturing glass, in accordance with another illustrative embodiment of the present disclosure, including an elongated tank and a pair of doghouses disposed on opposite sides of an upstream end of the tank;

[0012] FIG. 3 is a side sectional view of the doghouse of FIG. 1; and

[0013] FIG. 4 is a side view of the apparatus of FIG. 1 and a temperature profile of the apparatus.

DETAILED DESCRIPTION

[0014] The presently disclosed apparatus and process for manufacturing glass uses submerged combustion burners to rapidly melt a mixture of solid glass-forming materials known as a glass batch in a doghouse upstream of an elongated tank of a conventional glass furnace. The elongated tank includes a melting chamber, a refining chamber, and a conditioning chamber known as a forehearth. The glass batch may include a combination of solid raw materials, e.g. silica (SiO.sub.2), soda ash (Na.sub.2CO.sub.3), and limestone (CaCO.sub.3), as well as one or more pre-processed or recycled materials, e.g., cullet. In some cases, the glass batch may consist essentially of solid raw materials, without addition of any pre-processed or recycled materials. The glass batch also includes one or more refining agents, i.e., materials that release refining gases when heated above a certain temperature known as a refining-onset temperature. In some embodiments, the glass batch may include other minor ingredients, such as colorants and redox agents in amounts less than 5 wt. % of the glass batch.

[0015] The glass batch is melted in the doghouse by application of heat from the submerged combustion burners to produce molten glass. In the doghouse, the glass batch is heated to a temperature at or above the refining-onset temperature(s) of the one or more refining agents in the glass batch so that a major amount of the refining gas is released into the molten glass in the doghouse. The resulting molten glass is relatively foamy and contains a relatively high number of gas bubbles, as compared to molten glass that has been produced in a conventional commercial glass manufacturing furnace by application of heat from one or more overhead burners. The relatively high gas bubble content of the foamy molten glass may result from the additional gas bubbles introduced into the molten glass along with the by-products of combustion of the fuel and oxidant mixture supplied to the submerged combustion burners and/or the turbulent action caused within the molten glass by the submerged combustion burners. For example, the foamy molten glass produced in the doghouse by application of heat from the submerged combustion burners may comprise about 30 vol. % gas bubbles. On the other hand, molten glass produced in a conventional commercial glass manufacturing furnace by application of heat from overhead burners generally comprises, by volume, about 5% to about 20% gas bubbles.

[0016] However, unlike other glass melting operations, carbon dioxide (CO.sub.2) is not the primary constituent of the gas bubbles initially present in the resulting foamy molten glass. Because the glass batch is initially heated by the submerged combustion burners at or above the fining-onset temperature of the one or more refining agents in the glass batch, the gas bubbles in the resulting foamy molten glass comprise significant amounts of sulfur dioxide (SO.sub.2) and oxygen (O.sub.2) in addition to CO.sub.2. This means that the partial pressure of CO.sub.2 in the gas bubbles is relatively low, which increases the amount of CO.sub.2 released from the molten glass during the initial melting step and also decreases the amount of dissolved gases in the resulting molten glass. As a result, the efficiency of the subsequent refining process is increased due to the increase in the volume of gas bubbles in the molten glass that can be reabsorbed by the molten glass.

[0017] In addition, because the molten glass is heated to a relatively high temperature, i.e., to a temperature at or above the fining-onset temperature, at a relatively early stage of the manufacturing process, i.e., prior to entering the tank of the furnace, the resulting molten glass can be effectively refined in the tank in a relatively short amount of time and at a relatively low temperature, as compared to the times and temperatures typically required to refine molten glass produced at a lower temperature in a conventional continuously operated glass furnace. Further, contrary to conventional wisdom, the benefits of submerged combustion can now be realized in combination with continuous commercial glass manufacturing operations while also decreasing the total amount of time required to melt the solid glass-forming materials and to refine the resulting foamy molten glass.

[0018] FIG. 1 illustrates an apparatus 10 for manufacturing glass, in accordance with an embodiment of the present disclosure. The apparatus 10 includes a glass batch charger 12, a doghouse 14, and an elongated tank 16. Glass batch materials are charged or introduced into an upstream end of the doghouse 14 via the glass batch charger 12 and melted in the doghouse 14 by application of heat from one or more submerged combustion burners 18.

[0019] The glass batch materials introduced into the doghouse 14 may comprise, by weight, less than 20% of at least one fining agent, including all ranges and subranges therebetween. Some examples of suitable fining agents include sulfates, e.g., sodium sulfate (Na.sub.2SO.sub.4), which decomposes at temperatures in the range of 1100 C. to 1500 C. releasing gases of sulfur dioxide (SO.sub.2) and/or oxygen (O.sub.2). When the at least one fining agent in the glass batch comprises sodium sulfate (Na.sub.2SO.sub.4), the sodium sulfate may be present in the glass batch in an amount ranging between 5-15 wt. % of the glass batch. The resulting molten glass is relatively foamy and may comprise between 25 vol. % and 35 vol. % gas bubbles, including all ranges and subranges therebetween. The gas bubbles in the molten glass may comprise 5-20 vol. % sulfur dioxide (SO.sub.2) and 5-20 vol. % carbon dioxide (CO.sub.2), including all ranges and subranges between these ranges.

[0020] The molten glass produced in the doghouse 14 is directed from the doghouse 14 into an upstream end of the tank 16. A weir or dam 20 may be positioned at a downstream end of the doghouse 14 to prevent un-melted glass-forming materials from entering the tank 16. Bubbles of a fining gas may be introduced into the molten glass flowing out of the doghouse 14 into the tank 16 by one or more submerged bubblers. In such case, the molten glass may have a temperature in the range of 1450 degrees Celsius to 1550 degrees Celsius as it exits the doghouse 14, including all ranges and subranges therebetween. The fining gas introduced into the molten glass may comprise sulfur dioxide (SO.sub.2) and may be introduced into the molten glass in a sufficient amount to reduce the partial pressure of carbon dioxide (CO.sub.2) in the gas bubbles.

[0021] The tank 16 includes a melting chamber 22, a refining chamber 24, and a conditioning chamber typically referred to as a forehearth 26. The melting chamber 22 and the refining chamber 24 may be separated by a throat 28, and the refining chamber 24 and the forehearth 26 may be separated by a waist 30.

[0022] The total duration, from charging of the glass batch in the doghouse 14 to discharging of the molten glass from the forehearth 26 may be less than 9 hours.

[0023] Molten glass produced within the doghouse 14 is received in the melting chamber 22 and flows from an upstream end to a downstream end thereof, toward the throat 28. Heat may be applied to the molten glass in the melting chamber 22, for example, by one or more additional combustion burners 46 (FIG. 4) located above a free surface S (FIGS. 3 and 4) of the glass and directed slightly above or onto the free surface S. Any remaining un-melted components of the glass batch may be melted in the melting chamber 22, such as any remaining sand grains. Gas bubbles are released from the molten glass in the melting chamber 22 as part of a primary fining process, wherein gas bubbles having diameters of greater than about 0.5 mm ascend within the body of molten glass to a free surface thereof and escape. Gas bubbles having diameters of greater than 0.4 mm may be referred to as blisters, gas bubbles having diameters in the range of 0.1-0.4 mm are oftentimes referred to as seeds, and gas bubbles having diameters of less than 0.1 mm may be referred to as micro-seeds.

[0024] The rate at which the gas bubbles are released from the molten glass may be increased by use of one or more additional refining techniques. Such techniques may include: creating a subatmospheric pressure environment above the free surface of the body of molten glass, use of a sonic horn to produce ultrasonic vibrations within the molten glass, bubbling an inert gas through the body of molten glass, and stirring the molten glass.

[0025] Secondary fining of the molten glass, also known as refining takes place in the refining chamber 24 and to some extent the waist 30. Refining of the molten glass occurs after all of the relatively larger gas bubbles have been released from the molten glass and is accomplished by allowing the molten glass to cool to a temperature at which the remaining small gas bubbles, i.e., seeds, are absorbed by or dissolved into the molten glass. After the molten glass has been refined, the molten glass preferably contains less than 20 seeds per ounce of molten glass and does not include any gas bubbles having diameters greater than 0.3 mm. In some embodiments, the refined molten glass may contain less than 10 seeds per ounce of molten glass.

[0026] The refined molten glass is directed from the refining chamber 24 to the forehearth 26, where it is thermally conditioned by being cooled to a suitable temperature for forming.

[0027] Thereafter, the refined and thermally conditioned molten glass may be directed to one or more glass forming operations and used to produce glass articles. The composition of the glass articles may include: 65-80 wt. % SiO.sub.2, 12-15 wt. % Na.sub.2O, and 9-12 wt. % CaO, including all ranges and subranges between these ranges. Only about 0.1-5.0%, by weight, of the at least one fining agent in the glass batch may be retained in the final glass composition. For example, the amount of sulfur trioxide (SO.sub.3) retained in the glass may be in the range of 0.1 wt. % to 0.3 wt. %, including all ranges and subranges therebetween.

[0028] FIG. 2 illustrates an apparatus 110 for manufacturing glass, in accordance with another embodiment of the present disclosure. This embodiment is similar in many respects to the embodiment illustrated in FIG. 1, and like numerals among the embodiments generally designate like or corresponding elements. Accordingly, the descriptions of the embodiments are incorporated into one another, and description of subject matter common to the embodiments generally may not be repeated here.

[0029] In the embodiment illustrated in FIG. 2, two offset doghouses 114 are positioned on opposite sides of an upstream end of an elongated melting tank 116. Solid glass batch materials are introduced into an upstream end of each of the doghouses 114 via separate glass batch chargers 112 and melted by application of heat from submerged combustion burners 118. The flow of molten glass within the offset doghouses 114 is transverse to the flow direction of the molten glass flowing from the upstream end to the downstream end of the melting tank 116. Offsetting the doghouses 114 from the main melting tank 116 in this way allows the reactive chemistry of the foamy molten glass to calm down to a certain extent prior to entering the melting tank 116, which may help mitigate erosion of the refractory materials in the melting tank 116. The molten glass produced in the doghouse 114 is directed into a melting chamber 122 located at the upstream end of the melting tank 116. Thereafter, the molten glass is directed from the melting chamber 122, through a throat 128, into a refining chamber 124, a waist 130, and then a forehearth 126.

[0030] FIG. 3 illustrates a side sectional view of the doghouse 14 of FIG. 1. As shown, the doghouse 14 includes a floor 32, a roof 34, and a sidewall 36 connecting the floor 32 and the roof 34. The doghouse 14 receives glass batch materials from the glass batch charger 12, which may include a hopper 38 and a conveyor 40. The conveyor 40 may have an outlet above or below a free surface S of the molten glass already in the doghouse 14. The conveyor 40 may be a reciprocating pusher-type charger, a screw conveyor, or any other device suitable for charging glass batch materials into the doghouse 14 above or below the free surface S of the molten glass already in the doghouse 14.

[0031] The submerged combustion burners 18 are mounted in the floor 32 of the doghouse 14 and may be positioned such that the glass batch entering the doghouse 14 is immediately exposed to the high-intensity flame(s) and combustion products generated by the one or more submerged burners 18. This arrangement allows for relatively rapid dissolution of the solid glass batch materials in the molten glass, as compared to conventional commercial glass melting furnace, which typically rely solely on burners 46 positioned above the free surface S of the molten glass in the doghouse 14 and the melting tank 22 to melt the blanket of glass batch materials overlying the free surface S of the molten glass.

[0032] The floor 32, roof 34, and sidewall 36 of the doghouse 14 may be cooled such that a solid, frozen layer of glass forms on an interior surface 48 thereof during the glass manufacturing process. This solid layer of glass may help protect the floor 32, roof 34, and sidewall 36 from corrosion and wear or erosion, which may result from the formation of convection currents or turbulence within the molten glass in the doghouse 14. In the embodiment illustrated in FIG. 3, the floor 32, roof 34, and sidewall 36 are cooled using water jackets or panels 42 having a cooling water channel 44 formed therein through which cooling water or another liquid coolant can flow. In this arrangement, liquid coolant can flow through the cooling water channel 44 such that the liquid coolant contacts an exterior surface 50 of the doghouse 14 and transfers heat away from the interior surface 48 of the doghouse 14. Transferring heat away from the interior surface 48 of the doghouse 14 will effectively cool a layer of molten glass disposed along the interior surface 48 of the doghouse 14 and allow for the formation of a solid, frozen layer of glass on the interior surface 48 of the doghouse 14.

[0033] FIG. 4 illustrates a side view of the apparatus 10 of FIG. 1 and a temperature profile of the molten glass flowing through the apparatus 10. The glass batch materials are introduced into the doghouse 14 via the glass batch charger 12 and melted in the doghouse 14 by application of heat from the submerged combustion burners 18. The molten glass produced in the doghouse 14 is directed into the melting chamber 22 located at the upstream end of the tank 16. Thereafter, the molten glass is directed from the melting chamber 22, through the throat 28, into the refining chamber 24, the waist 30, and then the forehearth 26.

[0034] Unlike conventional commercial glass manufacturing operations, the molten glass within the doghouse 14 reaches a higher temperature than any region within the tank 16, and preferably is heated within the doghouse 14 to a temperature at or above the fining-onset temperature of the fining agent(s) within the glass batch. For example, the solid glass batch materials and the molten glass may be melted together in the doghouse 14 at a temperature, T1, in the range of 1350 degrees Celsius to 1550 degrees Celsius, including all ranges and subranges therebetween. In some embodiments, the solid glass batch materials and the molten glass may be melted together in the doghouse 14 at a temperature, T1, in the range of 1450 degrees Celsius to 1550 degrees Celsius, including all ranges and subranges therebetween. The temperatures reached in the doghouse 14 of the presently disclosed apparatus 10 are substantially higher than the temperatures reached in the doghouse of a conventional continuously operated glass furnace, which are typically less than 1200 degrees Celsius.

[0035] According to embodiments of the present disclosure, the temperature of the molten glass in the tank 16 may be at least 100 degrees Celsius lower than the melting temperatures achieved within the doghouse 14. For example, the molten glass flowing through the tank 16 may be maintained at a temperature less than or equal to 1400 degrees Celsius.

[0036] The molten glass may gradually cool as it flows through the melting chamber 22. By the time the molten glass reaches the refining chamber 24, the molten glass may have cooled down to a temperature, T2, in the range of 1200 degrees Celsius to 1300 degrees Celsius, including all ranges and subranges therebetween. The molten glass may continue to cool as it flows through the refining chamber 24, the waist 30, and the forehearth 26 until the molten glass reaches a suitable temperature for forming, T3, in the range of 1000 degrees Celsius to 1100 degrees Celsius, including all ranges and subranges therebetween.

[0037] Using submerged combustion burners 18 within the doghouse 14 allows the glass batch to be rapidly melted and also allows the resulting molten glass to be heated above the fining-onset temperature of the fining agent(s) in a relatively short period of time, and preferably before the resulting molten glass enters the melting chamber 22. When a glass batch is melted in a conventional continuously operated glass furnace, the resulting molten glass does not reach a maximum temperature until it reaches a relatively hot zone known as a spring zone within the tank 16, which is generally located within the melting chamber 22. The temperature of the spring zone within a melting tank of a conventional continuously operated glass furnace may be in the range of 1600 degrees Celsius to 1650 degrees Celsius.

[0038] There thus has been disclosed a glass manufacturing process, that fully satisfies one or more of the objects and aims previously set forth. The disclosure has been presented in conjunction with several illustrative embodiments, and additional modifications and variations have been discussed. Other modifications and variations readily will suggest themselves to persons of ordinary skill in the art in view of the foregoing discussion. For example, the subject matter of each of the embodiments is hereby incorporated by reference into each of the other embodiments, for expedience. The disclosure is intended to embrace all such modifications and variations as fall within the spirit and broad scope of the appended claims.