OXYGEN FOR COMBUSTION IN FOREHEARTHS

Abstract

Efficiency of the combustion that is carried out in the forehearth of a glass manufacturing facility is improved by replacing air-fuel burners with a smaller number of air-fuel injectors and oxygen injectors.

Claims

1. A method comprising: from a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, wherein the molten glass in the channels is maintained in the molten state by heat of combustion provided directly to the top surface of the molten glass by combustion in a combustion zone above the molten glass in the forehearth system that has at least 2 air-fuel burners at which air and fuel fed to the air-fuel burners are combusted to provide the heat of combustion, removing at least 50% of said air-fuel burners and replacing them with one or more air-fuel injectors each of which opens at its own refractory port in a side wall of the channel and each of which is capable of injecting a premixed mixture of air and fuel into the space in the channel over the molten glass, and with one or more oxygen injectors each of which opens at its own refractory port in a side wall of the channel and each of which is capable of injecting gaseous oxidant into the space in the channel over the molten glass, wherein the sum of the number of said air-fuel injectors plus the number of said oxygen injectors, which replace said air-fuel burners, is less than the number of air-fuel burners that are removed, and then injecting from each air-fuel injector into the space above the molten glass in the channel a premixed mixture of air and fuel at a velocity greater than 50 ft/sec in which the amount of air in the mixture injected from the injector is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the mixture injected from the same injector, and injecting from each oxygen injector into the space above the molten glass in the channel gaseous oxidant containing at least 80 vol. % oxygen at a velocity less than 50 ft/sec and at a rate that provides sufficient oxygen, taken together with the oxygen content of the mixture of air and fuel that is injected from the air-fuel injectors, to completely combust the fuel that is injected from the fuel injectors, wherein there is no physical barrier between the molten glass and the space into which the mixture of air and fuel, and the gaseous oxidant, are injected, and in the space above the molten glass combusting the fuel injected from the air-fuel injectors with the oxygen in the air and with the oxygen injected from the oxygen injectors so as to generate excess oxygen in the flue gas.

2. A method according to claim 1 wherein all of said air-fuel burners are removed and replaced with one or more of said air-fuel injectors.

3.-5. (canceled)

6. A method according to claim 1 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass.

7. A method comprising: in a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, maintaining the molten glass in the channels in the molten state by heat of combustion which is provided to the space above the molten glass, by: injecting into the space above the molten glass, from one or more air-fuel injectors each of which opens at its own refractory port in a side wall of the channel, a premixed mixture of air and fuel at a velocity greater than 50 ft/sec in which the amount of air in the mixture injected from each air-fuel injector is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the mixture injected from the same injector, and injecting into the space above the molten glass, from one or more oxygen injectors each of which opens at its own refractory port in a side wall of the channel, gaseous oxidant containing at least 80 vol. % oxygen at a velocity less than 50 ft/sec and at a rate that provides sufficient oxygen, taken together with the oxygen content of the mixture of air and fuel that is injected from the air-fuel injectors, to completely combust the fuel that is injected from the fuel injectors, wherein there is no physical barrier between the molten glass and the space into which the mixture of air and fuel, and the gaseous oxidant, are injected, and in the space above the molten glass combusting the fuel injected from the air-fuel injectors with the oxygen in the air and with the oxygen injected from the oxygen injectors so as to generate excess oxygen in the flue gas.

8.-10. (canceled)

11. A method according to claim 7 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass.

12. A method comprising: from a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, wherein the molten glass in the channels is maintained in the molten state by heat of combustion provided directly to the top surface of the molten glass by combustion in a combustion zone above the molten glass in the forehearth system that contains at least 2 air-fuel burners at which air and fuel fed to the air-fuel burners are combusted to provide the heat of combustion, removing at least 50% of said air-fuel burners and replacing them with one or more hybrid burners including a central gaseous oxidant injector pipe and an annular passage for a premixed mixture of air and fuel wherein each hybrid burner opens at its own refractory burner port in a side wall of the channel and is recessed from the hot surface of the side wall, and each hybrid burner is capable of injecting a combustible gas mixture of gaseous oxidant and a premixed mixture of air and fuel into the space in the channel over the molten glass, wherein said gaseous oxidant contains at least 80 vol. % oxygen and the amount of air in the premixed mixture is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the premixed mixture and said air-fuel burners are replaced with hybrid burners at a ratio of one hybrid burner for each two to twelve air-fuel burners, that are replaced, wherein said gaseous oxidant is injected at a velocity greater than 100 ft/sec, in which the total amount of oxygen in the combustible gas mixture injected from the hybrid burner is sufficient for complete combustion of the fuel injected from the same burner and the flame length is less than the width of the channel, wherein there is no physical barrier between the molten glass and the space into which the mixture of oxidant and fuel is injected, and combusting the fuel injected from the hybrid burners in the space above the molten glass with excess oxygen in flue gas.

13. A method according to claim 12 wherein all of said air-fuel burners are removed and replaced with one or more of said hybrid burners.

14.-18. (canceled)

19. A method according to claim 12 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass.

20. A method comprising: in a forehearth system in which molten glass from a glassmelting furnace flows through a channel having refractory side walls, maintaining the molten glass in the channel in the molten state by heat of combustion which is provided directly to the top surface of the molten glass, by: injecting a combustible gas mixture into the space above the molten glass from one or more hybrid burners each including a central gaseous oxidant injector pipe and an annular passage for a premixed mixture of air and fuel wherein each hybrid burner opens at its own refractory burner port in a side wall of the channel and is recessed from the hot surface of the side wall, and each hybrid burner is capable of injecting a combustible gas mixture of gaseous oxidant and a premixed mixture of air and fuel into the space in the channel over the molten glass, wherein said gaseous oxidant contains at least 80 vol. % oxygen and the amount of air in the premixed mixture is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the premixed mixture, wherein said gaseous oxidant is injected at a velocity greater than 100 ft/sec, in which the total amount of oxygen in the combustible gas mixture injected from the hybrid burner is sufficient for complete combustion of the fuel injected from the same burner and the flame length is less than the width of the channel, wherein there is no physical barrier between the molten glass and the space into which the mixture of oxidant and fuel is injected, and combusting the fuel injected from the hybrid burners in the space above the molten glass with excess oxygen in flue gas.

21.-24. (canceled)

25. A method according to claim 20 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass.

26. A method comprising: from a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, wherein the forehearth system includes a physical barrier above the molten glass, and wherein the molten glass in the channels is maintained in the molten state by indirect transfer to the molten glass of heat of combustion carried out in the region above the physical barrier, wherein the forehearth system contains a combustion zone above the barrier with at least 2 air-fuel burners at which air and fuel fed to the air-fuel burners are combusted to provide the heat of combustion, removing at least 50% of said air-fuel burners and replacing them with one or more air-fuel injectors each of which opens at its own refractory port in a side wall of the channel and each of which is capable of injecting a premixed mixture of air and fuel into a region above the physical barrier over the molten glass, and with one or more oxygen injectors each of which opens at its own refractory port in a side wall of the channel and each of which is capable of injecting gaseous oxidant into a region above the physical barrier over the molten glass, wherein the sum of the number of said air-fuel injectors plus the number of said oxygen injectors, which replace said air-fuel burners, is less than the number of air-fuel burners that are removed, and then injecting from each air-fuel injector into the region above the physical barrier in the channel a premixed mixture of air and fuel at a velocity greater than 50 ft/sec in which the amount of air in the mixture injected from the injector is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the mixture injected from the same injector, and injecting from each oxygen injector into the region above the physical barrier in the channel gaseous oxidant containing at least 80 vol. % oxygen at a velocity less than 50 ft/sec and at a rate that provides sufficient oxygen, taken together with the oxygen content of the mixture of air and fuel that is injected from the air-fuel injectors, to completely combust the fuel that is injected from the fuel injectors, and in the region above the barrier combusting the fuel injected from the air-fuel injectors with the oxygen in the air and with the oxygen injected from the oxygen injectors so as to generate excess oxygen in flue gas.

27. A method according to claim 26 wherein all of said air-fuel burners are removed and replaced with one or more of said air-fuel injectors.

28.-30. (canceled)

31. A method according to claim 26 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass or into the region above the physical barrier.

32. A method comprising: in a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, wherein the forehearth system includes a physical barrier above the molten glass, maintaining the molten glass in the channels in the molten state by indirect transfer to the molten glass of heat of combustion carried out in the region above the physical barrier, by: injecting into the region above the physical barrier, from one or more air-fuel injectors each of which opens at its own refractory port in a side wall of the channel, a premixed mixture of air and fuel at a velocity greater than 50 ft/sec in which the amount of air in the mixture injected from the air-fuel injector is between 25% to 60%, of the stoichiometric air required for complete combustion of the fuel in the mixture injected from the same injector, and injecting into the region above the physical barrier, from one or more oxygen injectors each of which opens at its own refractory port in a side wall of the channel, gaseous oxidant containing at least 80 vol. % oxygen at a velocity less than 50 ft/sec and at a rate that provides sufficient oxygen, taken together with the oxygen content of the mixture of air and fuel that is injected from the air-fuel injectors, to completely combust the fuel that is injected from the fuel injectors, and in the region above the barrier, combusting the fuel injected from the air-fuel injectors with the oxygen in the air and with the oxygen injected from the oxygen injectors so as to generate excess oxygen in the flue gas.

33.-35. (canceled)

36. A method according to claim 32 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass or into the region above the physical barrier.

37. A method comprising: from a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, wherein the forehearth system includes a physical barrier above the molten glass, wherein the molten glass in the channels is maintained in the molten state by indirect transfer to the molten glass of heat of combustion carried out in the region above the physical barrier by combustion, and wherein the forehearth system includes a combustion zone including at least 2 air-fuel burners at which air and fuel fed to the air-fuel burners are combusted to provide the heat of combustion, removing at least 50% of said air-fuel burners and replacing them with one or more hybrid burners including a central gaseous oxidant injector pipe and an annular passage for a premixed mixture of air and fuel wherein each hybrid burner opens at its own refractory burner port in a side wall of the channel and is recessed from the hot surface of the side wall, and each hybrid burner is capable of injecting a combustible gas mixture of gaseous oxidant and a premixed mixture of air and fuel into the space in the channel over the molten glass, wherein said gaseous oxidant contains at least 80 vol. % oxygen and the amount of air in the premixed mixture is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the premixed mixture and said air-fuel burners are replaced with hybrid burners at a ratio of one hybrid burner for each two to twelve air-fuel burners that are replaced, wherein said gaseous oxidant is injected at a velocity greater than 100 ft/sec, in which the total amount of oxygen in the combustible gas mixture injected from the hybrid burner is sufficient for complete combustion of the fuel injected from the same burner and the flame length is less than the width of the channel, and combusting the fuel injected from the hybrid burners with excess oxygen in the flue gas in the region above the physical barrier.

38. A method according to claim 37 wherein all of said air-fuel burners are removed and replaced with one or more of said hybrid burners.

39.-43. (canceled)

44. A method according to claim 37 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass or into the region above the physical barrier.

45. A method comprising: in a forehearth system in which molten glass from a glassmelting furnace flows through one or more channels having refractory side walls, wherein the forehearth system includes a physical barrier above the molten glass, maintaining the molten glass in the channels in the molten state by indirect transfer to the molten glass of heat of combustion which is carried out in the region above the physical barrier, by: injecting a combustible gas mixture into the space above the molten glass from one or more hybrid burners each including a central gaseous oxidant injector pipe and an annular passage for a premixed mixture of air and fuel wherein each hybrid burner opens at its own refractory burner port in a side wall of the channel and is recessed from the hot surface of the side wall, and each hybrid burner is capable of injecting a combustible gas mixture of gaseous oxidant and a premixed mixture of air and fuel into the space in the channel over the molten glass, wherein said gaseous oxidant contains at least 80 vol. % oxygen and the amount of air in the premixed mixture is between 25% to 60% of the stoichiometric air required for complete combustion of the fuel in the premixed mixture, wherein said gaseous oxidant is injected at a velocity greater than 100 ft/sec, in which the total amount of oxygen in the combustible gas mixture injected from the hybrid burner is sufficient for complete combustion of the fuel injected from the same burner and the flame length is less than the width of the channel, and combusting the fuel injected from the hybrid burners in the space above the molten glass with excess oxygen in the flue gas.

46.-49. (canceled)

50. A method according to claim 45 further comprising injecting a gas that is oxidizing, reducing, or neither oxidizing nor reducing, through at least one side wall into the space above the molten glass or into the region above the physical barrier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG. 1 is a flowchart showing an overview of a glass manufacturing facility.

[0063] FIGS. 2A and 2B are cutaway views, in perspective and in cross-section respectively, of a portion of a forehearth without a cover.

[0064] FIGS. 3A and 3B are cutaway views, in perspective and in cross-section respectively, of a portion of a forehearth with a cover.

[0065] FIG. 4 is a top view of a portion of a forehearth without a cover.

[0066] FIG. 5 is a side cross-sectional view of an injector useful in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0067] The present invention is useful in improving the efficiency of glass manufacture.

[0068] Referring to FIG. 1, glass manufacture conventionally includes melting glassmaking components in a furnace which is represented as 1 in FIG. 1. Glassmaking materials are fed into furnace 1 where they are heated, typically by combustion within the furnace, to melt the materials thereby forming molten glass and to maintain the molten glass in the molten state. The resulting molten material, referred to as molten glass or glassmelt, passes from furnace 1 (or from a refining zone which for this description is considered to be part of furnace 1) into forehearth system 2 which comprises a distributor section 8 and a series of channels 3 in which the glassmelt flows to reach forming stations 10 in which the glassmelt is formed into the products or shapes that the operator desires. Molten glass is conditioned in the forehearth system so that it achieves a desired uniform temperature when the molten glass arrives at the forming stations 10. Typically, many small burners are used to provide temperature uniformity along the path taken by the molten glass. Each distributor section and each channel has one or more combustion zone(s) and each zone is fired with at least one burner.

[0069] Referring to FIGS. 2A and 2B, the channel 3 of the forehearth system includes side walls 5 and bottom 7, which are formed from refractory material that can withstand the high temperatures of the flowing glassmelt 4 (that is, temperatures which are typically on the order of 2200 F. to 2700 F.).

[0070] The forehearth system includes apparatus at which combustion occurs in combustion zone 9 which provides heat of combustion to the top surface 6 of the glassmelt 4. In the embodiment shown in FIGS. 2A, 2B and 4, in which heat is provided to the molten glass directly (as that term is defined herein), the apparatus includes burners or injectors 21 which are arrayed side by side in burner blocks 25 on each side of the channel 3. At these burners 21, combustion of fuel and oxidant (air) forms flames 22 which extend into the space above the top surface 6 of glassmelt 4. Above the burner blocks there are side walls (not shown) and a roof (not shown) to enclose the combustion zone 9. Preferably, the flames extend from each side wall 5 of the channel 3 approximately halfway across the surface 6. The burners 21 on each side of channel 3 can be directly across from each other, as shown in FIG. 4, or can be staggered so that a burner on one side of channel 3 projects toward the space between adjacent burners on the other side.

[0071] FIGS. 3A and 3B show an alternative structure of forehearth system, in which a cover or physical barrier 11 is located between the top surface 6 of the glassmelt 4 and the burners or injectors 21 and the flames 22 which emanate from the burners 21. Combustion of fuel and oxidant occurs in combustion zone 9 which is in the region above cover 11. In this alternate embodiment heat transfer to the molten glass is indirect, which may provide more uniform heating of the molten glass and may lessen the risk of adverse interaction between the flames and the top surface of the molten glass. The physical barriers 11 should be made of material that can withstand the aforementioned high temperatures, yet permit heat to reach the surface 6, such as by conduction or absorption and re-radiation toward the surface 6. Preferably the physical barrier extends the full width of the channel and prevents combustion gases to come in contact with the glassmelt.

[0072] Referring to FIG. 2B, optionally, a stream 23 (shown in dashed lines as being optional) of gas can be injected through one or both of side walls 5 into the space above surface 6. Referring to FIG. 3B, optional stream 23 can be injected into the space below the cover 11. In another embodiment, the gas stream 23 can optionally flow into the region above cover 11 where it may participate in the combustion in that region. This gas stream 23 can be an oxidizing composition, such as air or oxygen-enriched air, or a stream containing at least 80 vol. % oxygen; or it can be a reducing composition, comprising hydrogen and/or carbon monoxide and/or other reducing component(s); or it can be neither oxidizing nor reducing, such as nitrogen and/or argon.

[0073] In typical forehearth systems with which the present invention is applicable, the burners 21 are air-fuel burners, that is, premixed air and fuel are fed to each burner 21 and combusted to create heat of combustion (and flames 22). Selected numbers of these air-fuel burners are replaced with either a combination of air-fuel injectors and injectors which inject gaseous oxidant, or with hybrid fuel-oxygen burners described below with respect to FIG. 5.

[0074] In any of the embodiments of the present invention that employ fuels, the preferred fuels are gaseous hydrocarbons such as natural gas, methane, ethane, propane, butane, and mixtures thereof. In the embodiments of the present invention that employ separate air-fuel injectors and oxidant injectors, or that employ hybrid fuel-oxygen injectors, the preferred oxidants are gaseous compositions containing at least 80 vol. % oxygen.

[0075] In the embodiments of the present invention that replace air-fuel burners with separate injectors of air-fuel mixture and injectors of gaseous oxidant, the preferred characteristics are:

The flow rate of the air-fuel mixture is 20 to 400 scfh, preferably 40 to 200 scfh. (It will be understood by those skilled in this art that the firing rate and the air-fuel flow rate which are required in a given forehearth system depend on the size of the forehearth.)
The fuel-rich air-fuel mixture contains 25% to 60% (preferably 30% to 50%, more preferably 30 to 40%) of the oxygen needed to completely combust the fuel in the mixture.
The flow rate of gaseous oxidant with or without the aforementioned cover 11 being present is 10 to 50 scfh, preferably 15 to 40 scfh.
The velocity of the gaseous oxidant from oxidant injector with or without the aforementioned cover 11 being present is less than 50 ft/sec, preferably less than 20 ft/sec.

[0076] Preferably, in these aspects of the invention, the ports through which gaseous oxidant is injected are spaced from any port through which the air-fuel mixture is injected, by a distance measured between the points at which adjacent ports are closest to each other, of at least two times the diameter of the larger port.

[0077] In each of these aspects of the invention, it is preferred that the ratio of the momentum flux (which is defined as the mass flow rate of a gas stream times the velocity of the gas stream) of the gaseous oxidant stream from oxidant injector to the momentum flux of the premixed mixture stream of air and fuel from air-fuel injector is between 0.02 to 0.4, preferably 0.1 to 0.3, more preferably 0.1 to 0.2.

[0078] With this aspect of the invention, the air-fuel burners can be replaced at a ratio of 2 to 12 air-fuel burners, preferably 2 to 6, replaced by each one air-fuel injector plus each one gaseous oxidant injector. Replacement can be effected by physically removing a burner, and plugging the holes in side walls 5 that remain where a burner was removed and was not replaced at the same location with an air-fuel injector or with an oxidant injector.

[0079] In other embodiments of the present invention, 25% to 87.5% of existing air-fuel burners are removed and the remaining air-fuel burners are modified to become hybrid burners such as depicted in FIG. 5. Referring to FIG. 5, an air-fuel burner had included conduit 46 that is centrally positioned in cavity 41 and ends in opening 47 which is recessed from the port opening 21 of cavity 41 in side wall 5. Premixed fuel and air is fed through inlet 48 into conduit 46. This air-fuel burner can be modified in the practice of the present invention by inserting feed tube 43 into conduit 46, preferably to be coaxially aligned with the axis of conduit 46. Feed tube 43 ends at opening 44 which is recessed from the port opening 21 of cavity 41 in side wall 5. Gaseous oxidant is fed through inlet 45 into feed tube 43.

[0080] This embodiment of the present invention has the advantages that fewer ports need to be established than is the case with separate provision of air-fuel injectors and oxidant injectors. Also, retrofitting is eased because an existing air-fuel burner and burner port can be transformed, without having to create additional openings in side wall 5, simply by inserting feed tube 43 into the existing air-fuel burner body and cavity 41 which had been occupied by the air-fuel burner.

[0081] The end 44 of feed tube 43 is recessed from the port 21 in order to minimize the risk of deposit formation on the end due to coking of hydrocarbons or due to condensation of vapors of glassforming products or byproducts such as sodium hydroxide or sodium sulfate.

[0082] In the embodiments of the present invention that modify and replace air-fuel burners with a hybrid burner such as shown in FIG. 5, the preferred characteristics are:

The flow rate of the air-fuel mixture is 20 to 400 scfh, and preferably 40 to 200 scfh. (It will be understood by those skilled in this art that the firing rate and the air-fuel flow rate which are required in a given forehearth system depend on the size of the forehearth.)
The fuel-rich air-fuel mixture contains 25% to 60%, preferably 30% to 50%, more preferably 30 to 40%, of the oxygen needed to completely combust the fuel in the mixture. The velocity of gaseous oxidant from hybrid burner with or without cover 11 is greater than 100 ft/sec, preferably greater than 200 ft/sec, more preferably greater than 300 ft/sec.