Combustor with alternating modes for flexible operation

Abstract

A burner includes a central conduit; a first annular pipe; and a nozzle plate across an outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending through the nozzle plate; and a second annular conduit leading to a downstream space wherein the central conduit and the first annular conduit are controllably connected to a first reactant and the second annular conduit is controllably connected to a source of a second reactant wherein one of the first reactant and the second reactant comprises a fuel, and the other of the first reactant and the second reactant includes oxygen. The combustion device comprises a plurality of such combustors, preferably arranged in two planes, where each plane contains at least one such combustor. A fuel-rich flame may be emitted in one of the planes and a fuel-lean flame may be emitted in the other plane. The rich and lean fuel properties of the flames emitted in the respective planes may periodically alternate.

Description

Technical Field

[0001] The present invention relates to combustion in industrial furnaces, such as furnaces used in the production of glass. Background Art

[0002] The manufacture of glass products generally involves melting a mixture of glassmaking ingredients in a glass melting furnace to produce molten glass, which is then processed and formed into a desired glass product. Typical glassmaking ingredients (which may also be used in the practice of the present invention) include oxides, hydroxides, silicates and sulfates of sodium and potassium, and mixtures thereof, as well as crushed and broken glass sheets. The heat for melting the glassmaking ingredients in the furnace is generally provided by the combustion of a fuel in the furnace, generally at a burner located in one or more walls of the furnace, which produces a flame extending from the burner to the interior of the furnace.

[0003] Unfortunately, this type of melting operation is known to result in the formation of a layer of bubbles, commonly referred to as foam, on the surface of the molten glass. Such foam is undesirable because it prevents effective heat exchange from the flame to the glassmaking ingredients and to the molten glass bath in the furnace. Foam can also reduce the quality of the molten glass.

[0004] The present invention provides the useful ability to minimize or prevent the formation of foam on the surface of a pool of molten glass. The present invention also provides for reducing the formation of undesirable combustion byproducts such as nitrogen oxides ("NOx").

[0005] Burners used in furnaces such as, but not limited to, glass melting furnaces may also suffer from fouling or plugging of ports in the furnace wall through which the combustion reactants are desired to be fed. The present invention also provides an effective ability to limit or avoid such fouling and plugging. Summary of the invention

[0006] One aspect of the present invention is a burner comprising:

[0007] a central conduit having a central axis and terminating in a central outlet opening into a downstream space;

[0008] a first annular duct surrounding the central duct, the first annular duct and the central duct being separated by an annular wall, wherein the first annular duct terminates in an outlet to the downstream space, wherein the first annular duct includes a nozzle plate spanning the outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the first annular duct through the nozzle plate to the downstream space;

[0009] wherein the central conduit and the first annular conduit are each connected to a source of a first reactant by a mechanism by which the flow of the first reactant from its source into the central conduit and the flow of the first reactant from its source into the first annular conduit can be controlled; and

[0010] a second annular conduit surrounding the first annular conduit and terminating in a second annular outlet opening into the downstream space, wherein the second annular conduit is connected to a source of a second reactant by means of a mechanism by which the flow of the second reactant from its source into the second annular conduit can be controlled;

[0011] One of the first reactant and the second reactant includes a fuel, and the other of the first reactant and the second reactant is an oxidant including oxygen.

[0012] Another aspect of the present invention is a combustion device, the combustion device comprising:

[0013] A first burner comprises:

[0014] a first central conduit having a central axis and terminating in a first central outlet opening into a first downstream space;

[0015] a first annular duct surrounding the first central duct, the first annular duct and the first central duct being separated by an annular wall, wherein the first annular duct terminates in an outlet to the first downstream space, wherein the first annular duct includes a nozzle plate spanning the outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the first annular duct through the nozzle plate to the first downstream space;

[0016] wherein the first central conduit and the first annular conduit are each connected to a source of a first reactant by a mechanism by which the flow of the first reactant from its source into the first central conduit and the flow of the first reactant from its source into the first annular conduit can be controlled; and

[0017] a second annular conduit surrounding the first annular conduit and terminating in a second annular outlet opening into the first downstream space, wherein the second annular conduit is connected to a source of a second reactant by means of a mechanism by which the flow of the second reactant from its source into the second annular conduit can be controlled;

[0018] and a second burner comprising

[0019] a second central conduit having a central axis and terminating in a second central outlet opening into a second downstream space;

[0020] a third annular duct surrounding the second central duct, the third annular duct and the second central duct being separated by an annular wall, wherein the third annular duct terminates in an outlet to the second downstream space, wherein the third annular duct includes a nozzle plate spanning the outlet of the third annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the third annular duct through the nozzle plate to the second downstream space;

[0021] wherein the second central conduit and the third annular conduit are connected to a source of the first reactant by a mechanism, by which the flow of the first reactant from its source into the second central conduit and the flow of the first reactant from its source into the third annular conduit can be controlled; and

[0022] a fourth annular conduit surrounding the third annular conduit and terminating in a fourth annular outlet leading to the second downstream space, wherein the fourth annular conduit is connected to a source of the second reactant by means of a mechanism by which the flow of the second reactant from its source into the fourth annular conduit can be controlled;

[0023] wherein the central axis of the first central conduit is above the central axis of the second central conduit;

[0024] One of the first reactant and the second reactant includes a fuel, and the other of the first reactant and the second reactant is an oxidant including oxygen.

[0025] Another aspect of the invention is a method of combustion in a furnace, the method comprising:

[0026] Providing the above-mentioned combustion device;

[0027] feeding fuel from a first central outlet of the first burner and a first annular duct nozzle plate into a first downstream space within the furnace;

[0028] feeding an oxidant from a second annular outlet of the first burner into the first downstream space, and

[0029] Combusting the fuel fed from the first central outlet and from the first annular duct nozzle plate with the oxidant fed from the second annular outlet to produce a mixture of the products of the combustion in the first downstream space; and

[0030] feeding fuel from a second central outlet of the second burner and a third annular duct nozzle plate into a second downstream space within the furnace;

[0031] feeding an oxidant from a fourth annular outlet of the second burner into the second downstream space, and

[0032] combusting said fuel fed from the second central outlet and from the third annular duct nozzle plate with said oxidant fed from the fourth annular outlet to produce a mixture of products of said combustion in said second downstream space;

[0033] The first downstream space is located above the second downstream space.

[0034] Another embodiment of the combustion in the furnace according to the invention comprises:

[0035] A combustion device is provided, the combustion device comprising

[0036] a plurality of first burners, the plurality of first burners comprising

[0037] a first central conduit having a central axis and terminating in a first central outlet opening into a first downstream space;

[0038] a first annular duct surrounding the first central duct, the first annular duct and the first central duct being separated by an annular wall, wherein the first annular duct terminates in an outlet to the first downstream space, wherein the first annular duct includes a nozzle plate spanning the outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the first annular duct through the nozzle plate to the first downstream space;

[0039] wherein the first central conduit and the first annular conduit are each connected to a source of a first reactant by a mechanism by which the flow of the first reactant from its source into the first central conduit and the flow of the first reactant from its source into the first annular conduit can be controlled; and

[0040] a second annular conduit surrounding the first annular conduit and terminating in a second annular outlet opening into the first downstream space, wherein the second annular conduit is connected to a source of a second reactant by means of a mechanism by which the flow of the second reactant from its source into the second annular conduit can be controlled;

[0041] and a plurality of second burners, the plurality of second burners comprising

[0042] a second central conduit having a central axis and terminating in a second central outlet opening into a second downstream space;

[0043] a third annular duct surrounding the second central duct, the third annular duct and the second central duct being separated by an annular wall, wherein the third annular duct terminates in an outlet to the second downstream space, wherein the third annular duct includes a nozzle plate spanning the outlet of the third annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the third annular duct through the nozzle plate to the second downstream space;

[0044] wherein the second central conduit and the third annular conduit are connected to a source of the first reactant by a mechanism, by which the flow of the first reactant from its source into the second central conduit and the flow of the first reactant from its source into the third annular conduit can be controlled; and

[0045] a fourth annular conduit surrounding the third annular conduit and terminating in a fourth annular outlet leading to the second downstream space, wherein the fourth annular conduit is connected to a source of the second reactant by means of a mechanism by which the flow of the second reactant from its source into the fourth annular conduit can be controlled;

[0046] wherein the central axes of all the first burners are above the central axes of all the second burners;

[0047] wherein one of the first reactant and the second reactant comprises a fuel and the other of the first reactant and the second reactant is an oxidant comprising oxygen;

[0048] feeding fuel from a first central outlet and a first annular duct nozzle plate of each of the first burners into a first downstream space within the furnace;

[0049] feeding an oxidant from a second annular outlet of each of the first burners into the first downstream space, and

[0050] combusting the fuel fed from the first central outlet and from the first annular duct nozzle plate with the oxidant fed from the second annular outlet to produce a mixture of the products of the combustion which is introduced into the first downstream space; and

[0051] feeding fuel from a second central outlet of each of the second burners and a third annular duct nozzle plate into a second downstream space within the furnace;

[0052] feeding an oxidant from a fourth annular outlet of each of the second burners into the second downstream space, and

[0053] The fuel fed from the second central outlet and from the third annular duct nozzle plate is combusted with the oxidant fed from the fourth annular outlet to produce a mixture of products of the combustion that is passed into the second downstream space.

[0054] In another embodiment of the present invention, the mixture of combustion products introduced into one of the first downstream space and the second downstream space is fuel-rich, while the mixture of combustion products introduced into the other of the first downstream space and the second downstream space is fuel-lean.

[0055] In a preferred application of this embodiment, alternately, (A) the mixture of combustion products introduced into the first downstream space is fuel-rich, while the mixture of combustion products introduced into the second downstream space is fuel-lean, and (B) the mixture of combustion products introduced into the first downstream space is fuel-lean, while the mixture of combustion products introduced into the second downstream space is fuel-rich.

[0056] A preferred aspect of the present invention is a method of operating the above-described combustion apparatus to heat the interior of a furnace and to heat the contents of the furnace (such as a glass melting furnace to heat a bath containing molten glass), the method comprising alternately performing steps (A) and (B):

[0057] (A) feeding fuel from a first central outlet and from a first annular duct nozzle plate into the first downstream space;

[0058] feeding an oxidant from a second annular outlet into said first downstream space in an amount including an amount of oxygen insufficient to completely combust with all of said fuel fed from said first central outlet and from said first annular duct nozzle plate; and

[0059] causing incomplete combustion of the fuel fed from the first central outlet and from the first annular duct nozzle plate with the oxidant fed from the second annular outlet to produce a fuel-rich mixture of the products of the combustion in the first downstream space; and

[0060] feeding fuel from the second central outlet and from the third annular duct nozzle plate into the second downstream space;

[0061] feeding an oxidant from the fourth annular nozzle into the second downstream space in an amount including an amount of oxygen in excess of that necessary for complete combustion of all of said fuel fed from said second central outlet and from said third annular duct nozzle plate; and

[0062] combusting fuel fed from the second central outlet and from the third annular duct nozzle plate with said oxidant fed from the fourth annular outlet to produce a fuel-lean mixture of products of said combustion in said second downstream space;

[0063] wherein the first downstream space is located above the second downstream space; and

[0064] feeding the fuel-rich mixture from the first downstream space into the space above the surface of the molten pool, and feeding the fuel-lean mixture into the space above the surface of the molten pool between the fuel-rich mixture and the surface of the molten pool; and

[0065] (B) feeding fuel from the first central outlet and from the first annular duct nozzle plate into the first downstream space;

[0066] feeding an oxidant from a second annular outlet into said first downstream space in an amount including an amount of oxygen in excess of that necessary for complete combustion of all of said fuel fed from said first central outlet and from said first annular duct nozzle plate; and

[0067] Combusting the fuel fed from the first central outlet and from the first annular duct nozzle plate with the oxidant fed from the second annular duct to produce a fuel-lean mixture of the products of the combustion in the first downstream space, while

[0068] feeding fuel from the second central outlet and from the third annular duct nozzle plate into the second downstream space;

[0069] feeding an oxidant from the fourth annular duct into the second downstream space in an amount including an amount of oxygen insufficient to completely combust with all of the fuel fed from the second central outlet and from the third annular duct nozzle plate; and

[0070] causing incomplete combustion of the fuel fed from the second central outlet and from the third annular duct nozzle plate with the oxidant fed from the fourth annular duct to produce a fuel-rich mixture of products of the combustion in the second downstream space; and

[0071] The lean fuel mixture is fed from the first downstream space into the space above the surface of the molten pool, and the rich fuel mixture is fed between the lean fuel mixture and the surface of the molten pool into the space above the surface of the molten pool.

[0072] Advantageously, the method alternates between (A) and (B) in response to a detected characteristic of said pool of molten glass.

[0073] Preferred embodiments of these combustion methods include continuously combusting the fuel fed from a nozzle plate spanning the outlets of the first and third annular ducts.

[0074] As used herein, a "fuel-rich" stream or mixture contains one or more substances selected from the group consisting of a fuel combustible with oxygen and products formed by incomplete combustion of the fuel and oxygen, and does not contain oxygen or contains oxygen but in an amount insufficient to completely combust the fuel and the products of incomplete combustion present.

[0075] As used herein, a "fuel-lean" stream or mixture contains oxygen and one or more substances selected from the group consisting of fuels combustible with oxygen and products formed by incomplete combustion of the fuel and oxygen, wherein the amount of oxygen present is equal to or greater than the amount required to completely combust all of the substances.

[0076] As used herein, "complete combustion" of a fuel means reacting all of the hydrogen in the fuel (as H2 and as a bond to carbon in hydrocarbons) with oxygen to form H2O and reacting all of the carbon (if any) in the fuel (as elemental C or as a bond to hydrocarbons) to CO2.

[0077] As used herein, a first plane being "below" or "above" a second plane means that there is a space between the two planes and that a single horizontal line cannot pass through the two planes; and an axis of a pipe being "above" or "below" the axis of another pipe means that there is a space between the axes and that a single horizontal line cannot pass through the two axes; and a space being "below" or "above" another space means that a single horizontal line cannot pass through both of the spaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 is a cross-sectional view of a combustion device including two burners according to the present invention.

[0079] Figure 2 is a perspective view of the end of a burner according to the invention.

[0080] Figure 3 is a top plan view of a burner assembly according to the present invention.

[0081] Figure 4 is a side perspective view of a burner assembly according to the present invention.

[0082] Figure 5 is a perspective view of a burner block in which the present invention may be practiced.

[0083] Figure 6 is a top cross-sectional view of a burner block including a burner arrangement according to the present invention. DETAILED DESCRIPTION

[0084] The present invention can be used in furnaces of the type that include an enclosed space in which combustion occurs to heat material present in the enclosed space. The heating can be used to melt or fuse materials (such as by glass melting furnaces and cement kilns), or to incinerate materials (such as by incinerators). As described below, one preferred application is a glass melting furnace, especially a glass melting furnace that melts materials that, when melted, tend to emit substances that can condense onto surfaces of the burner (such as its associated outlets and ports).

[0085] The present invention may be implemented in a furnace wherein fuel and gaseous oxidant are fed toward the interior of the furnace through openings, referred to herein as outlets or ports.

[0086] First reference Figure 1 and Figure 2 , which shows burners 1 and 2 of the type that can be used in the present invention.

[0087] Figure 1 A cross-sectional view of two burners 1 and 2 positioned within a burner block 10 is shown as seen from the side in a vertical plane. In this view, the arrow pointing to "B" indicates the position of the melt pool of molten glassmaking material (referred to herein as the "melt pool") relative to the two burners 1, and the arrow pointing to "C" indicates the position of the furnace crown (roof) relative to the two burners 1. Figure 1 In the embodiment, the burner 1 opening into the space 14 is closer to the furnace crown and is above another burner 1 opening into the space 27 and closer to the molten pool.

[0088] like Figure 1 As shown, the burner 1 comprises a central duct 11 having a central axis 12. The central duct 11 terminates at one end (its downstream end) in a central outlet 13, which opens into a downstream space 14, which is outside and downstream of the outlet 13. A first annular duct 15 surrounds the central duct 11, wherein the first annular duct 15 and the central duct 11 are separated by an annular wall 16. The first annular duct 15 terminates at one end in an outlet 17, which opens into said downstream space 14. The downstream space 14 may be the interior of the furnace, but is preferably a port recessed into the burner block 10 relative to the interior 100 of the furnace (i.e., such that the respective outlets 13 and 17 are further away from the furnace interior 100 than the surface 10A of the burner block 10 facing the furnace interior 100).

[0089] like Figure 1 and Figure 2 As shown, the nozzle plate 18 is placed across the outlet 17 of the first annular duct 15, but does not cover the outlet 13. The face 18A on the downstream side of the nozzle plate 18 is preferably coplanar with the central outlet 13. The downstream end of the annular wall 16 is preferably located at the inner (upstream) face of the nozzle plate 18, but the annular wall 16 can extend into the downstream space 14. The nozzle plate 18 includes a plurality of orifices 19 that pass through the nozzle plate 18 from within the interior of the first annular duct 15 to the downstream space 14. The nozzle plate 18 is sealed to what would otherwise be the open outlet 17, so that any gas flowing within the first annular duct 15 can leave the first annular duct 15 through the orifices 19.

[0090] The number of orifices 19 in the nozzle plate 18 and the cross-sectional diameter of the orifices 19 should be effective to cause the gas flowing in the first annular duct 15 to be discharged from the orifices 19 at a higher velocity than the velocity of the gas in the first annular duct 15. A useful feature would be that the ratio of the sum of the cross-sectional areas of all orifices 19 in a given nozzle plate to the total area of ​​the surface of the nozzle plate in contact with the gas in the first annular duct 15 is up to 1:2, and preferably up to 1:10 or even 1:100. There are preferably 1 to 50 orifices 19 in each nozzle plate 18, more preferably 2, 3 or 4 up to 10 or 20. These features apply to each nozzle plate employed in the apparatus of the present invention.

[0091] See again Figure 1 The second annular duct 21 surrounds the first annular duct 15 and terminates in a second annular outlet 22 leading to the downstream space 14. The outer wall of the second annular duct 21 may be a surface of an opening passing through the burner block 10, such as Figure 1 As shown, or it may be a separate annular component, such as a metal cylinder.

[0092] like Figure 1 As shown, there is a second burner 2, which includes a central duct 23 having a central axis 24. The central duct 23 terminates at one end (its downstream end) in a central outlet 25, which opens into a downstream space 27, which is outside and downstream of the outlet 25. A third annular duct 28 surrounds the central duct 23, wherein the third annular duct 28 and the central duct 23 are separated by an annular wall 26. The third annular duct 28 terminates at one end in an outlet 29, which opens into the downstream space 27. The downstream space 27 can be the interior of the furnace, but is preferably a port recessed in the burner block 10 relative to the interior 100 of the furnace (i.e., such that the respective outlets 25 and 29 are further away from the furnace interior 100 than the surface 10A of the burner block 10 facing the furnace interior 100).

[0093] See again Figure 1 The fourth annular duct 30 surrounds the third annular duct 28 and terminates in a fourth annular outlet 31 leading to the downstream space 27. The outer wall of the fourth annular duct 30 may be a surface of an opening passing through the burner block 10, such as Figure 1 As shown, or it may be a separate annular component, such as a metal cylinder.

[0094] The burners 1 and 2 described above are preferably positioned in a burner block 10, as further described below. The burner block should be constructed of a material capable of withstanding high temperatures in excess of 1500F, up to 3500F, without melting or decomposing. Materials suitable for this use are well known in the art of high temperature furnaces and include refractory inorganic materials such as AZS. Each of the central ducts 11 and 23 and the first annular duct 15 and the third annular duct 28 are preferably made of a material that withstands the above-mentioned high temperatures.

[0095] The central pipes 11 and 23, the first annular pipe 15 and the third annular pipe 28 are each connected to a source 35 of the first reactant via a mechanism represented by 36, which is capable of controlling the flow of the first reactant from the source 35 into the central pipes 11 and 23 via a feed line represented by 37, and is capable of controlling the flow of the first reactant from its source 35 into each of the first annular pipe 15 and the third annular pipe 28 via a feed line represented by 38.

[0096] The second annular conduit 21 and the fourth annular conduit 30 are connected to a source 40 of the second reactant by means indicated at 41 which is capable of controlling the flow of the second reactant from the source 40 via feed lines indicated at 42 into each of the second and fourth annular conduits.

[0097] One of the above-mentioned first reactant and the second reactant includes fuel, and the other of the first reactant and the second reactant is a gaseous oxidant including oxygen. Suitable fuel preferably includes hydrogen, any combustible hydrocarbons that are gaseous at 25 ℃, a mixture of combustible hydrocarbons that are gaseous at 25 ℃, and a mixture of hydrogen and one or more combustible hydrocarbons that are gaseous at 25 ℃. The example of suitable fuel includes hydrogen, natural gas, methane, ethane, propane and butane and their mixture. Suitable gaseous oxidant includes air or any gaseous mixture, and its oxygen concentration is at least 21 volume %, preferably at least 70 volume % oxygen, more preferably at least 90 volume % oxygen. In the preferred operating mode of the present invention, the first reactant is preferably fuel, and the second reactant is preferably a gaseous oxidant. The fuel source (35 or 40 according to this specification) can be a storage tank containing fuel. The oxidant source (35 or 40 according to the present specification) can be a tank containing the oxidant in gaseous, liquid or as a mixture of gas and liquid, which tank may include a vaporizer to convert the liquid oxidant to a gaseous state when discharged from the source into an associated feed pipeline.

[0098] The mechanism indicated as 36 is capable of controlling the flow rate of the first reactant into each of the central ducts 11 and 23 and into each of the first annular ducts 15 and the third annular duct 28. In order to properly implement the present invention, it is important to be able to control the relative proportion of the amount of the first reactant fed to each central duct 11 and each first annular duct 15 in the burner 1 closer to the crown of the furnace relative to the amount of the first reactant fed to each central duct 23 and each third annular duct 28 in the burner 2 closer to the molten glass bath (i.e., farther from the crown) relative to the total amount of the first reactant fed to all the central ducts 11 and to all the first annular ducts 15. These respective aspects of the control provided by the mechanism indicated as 36 may be provided by a single mechanism or by several different mechanisms operating together, such as a three-way ball valve or a plurality of valves connected in series, for example.

[0099] The mechanism indicated as 40 is capable of controlling the flow rate of the second reactant into each second annular duct 21 and each fourth annular duct 30. In order to properly implement the present invention, it is important to be able to control the relative proportion of the amount of second reactant fed to each second annular duct 21 in the burner 1 closer to the crown of the furnace relative to the amount of second reactant fed to each fourth annular duct 30 in the burner 2 closer to the molten glass bath (i.e., farther from the crown) relative to the total amount of second reactant fed to all second annular ducts 21. These respective aspects of the control provided by the mechanism indicated as 40 may be provided by a single mechanism or preferably by a plurality of valves operating together.

[0100] A mechanism for controlling the flow of fuel and oxidant may be provided so that each flow in its own conduit is individually controlled. Alternatively, a mechanism for maintaining a desired ratio of fuel to oxidant may be provided so that when the combustion mode of a group of burners (such as the burners in each given plane, as described herein) changes from fuel rich to fuel lean or from fuel lean to fuel rich, the conduits and orifices through which the fuel and oxidant flow may change, but the ratio of the positive flows may be maintained unchanged. In other words, when the flow to the first downstream space is fuel-rich (because the ratio of fuel to oxidant flowing therein is a particular value that is considered fuel-rich), and the flow to the second downstream space is fuel-lean (because the ratio of fuel to oxidant flowing therein is a particular value that is considered fuel-lean), and (as described herein) it is thereafter desired to change the flow into the first downstream space to fuel-lean and the flow into the second downstream space to fuel-rich, the control mechanism may be configured such that the flow rates of the fuel and oxidant that conform to the particular values ​​of the fuel-rich flow and the fuel-lean flow remain the same, but the respective conduits into which the fuel-rich flow and the fuel-lean flow are directed are changed (i.e., reversed) such that the fuel / oxidant flow that had been delivered to the first downstream space now flows to the second downstream space and the fuel / oxidant flow that had been delivered to the second downstream space now flows to the first downstream space. This arrangement enables an operator to change the characteristics of the flows to two respective spaces in the furnace without having to adjust and readjust the individual flow rates of the fuel and oxidant.

[0101] Figure 1 The view in FIG. 1 shows two burners 1 and 2 in cross section, but the description also applies to a burner arrangement comprising two or more burners 1 and comprising two or more burners 2. Additional burners 1 and 2 are provided in FIG. Figure 3 and Figure 4 are better seen in Figure 1 was blocked as in.

[0102] The burner arrangement as another aspect of the present invention utilizes a plurality of burners 1 and 2 positioned in any desired array, which provide combustion heat from the combustion occurring at the outlet of the burners to the interior 100 of the furnace. Most preferably, the burners 1 and 2 are arranged in two planes, one above the other, i.e., one plane closer to the crown of the furnace (i.e., farther from the surface of the molten pool) and one plane closer to the surface of the molten pool.

[0103] One such array comprises a first plurality of burners 1, typically 2 to 10 or 20 burners, and preferably such as Figure 3Three burners are shown, which are positioned side by side in one plane; and a second group of a further plurality of burners 2, typically 2 to 10 or 20 burners, and preferably such as three burners, which are positioned side by side in another plane (not shown because it is obscured by the three burners 1 shown), which is below the plane in which the first group of burners is arranged. Figure 3 , which is a top view looking down at the burner in such a plane, it can be seen that the burner 1 extends from a housing 101, which can include controls 36 and 41, which control the flow of the first reactant and the second reactant in the feed line, and can include a feed line through which the first reactant and the second reactant are fed to each burner (i.e., to the central conduit and to the first annular conduit and the second annular conduit, as described herein). The burners located in a given plane can be arranged so that their respective central axes 12 are parallel to each other, or so that the axes 12 of adjacent burners 1 are at an angle A greater than zero degrees up to 10 degrees, 20 degrees, or even 30 degrees.

[0104] See also Figure 4 , two groups of burners are shown, one group 51 burners 1 in one plane, and another group 52 burners 2 in another plane below the plane of the first group 51 burners (i.e., closer to the molten glass bath). The planes in which the two groups of burners are located can be parallel to each other, or the planes can be at an angle H greater than zero up to 15, 30, 45 or even 60 degrees relative to each other.

[0105] Figure 5 Depicted is the exterior of a representative burner block 500 with which the burner of the present invention may be used to form a burner arrangement as one aspect of the present invention. The burner block 500 includes a front surface 501 that will face the interior 100 of the furnace. The burner block 500 also includes side surfaces 502, a top surface 503, and a bottom surface 504. The passages within the burner block 500 terminate at an opening 505 in the front surface 501. Figure 4 The array of burners 1 and 2 depicted in will be located within burner block 500. Figure 4 Each of the central axes of each of the six burners appearing in will be aligned with one of the openings 505 .

[0106] Figure 6is a cross-sectional view from above looking down into a burner block 500 of an array of burners 1 all arranged in one plane. Each burner is located in its own channel 506 within the burner block 500. The central duct 11 and the first annular duct 15 and the second annular duct 21 are shown, each of which is located between the outer wall of the first annular duct 15 and the inner surface 507 of the channel 506. The aforementioned downstream region 14 is outside the outlet 13, inside the channel 506. Each downstream region 14 communicates with the channel 506 ending at the opening 505. Preferably, the diameter of each channel 506 from its associated outlet 13 downstream to its opening 505 presents a converging-diverging shape, wherein the diameter of the channel 506 seen in the direction from the downstream region 14 to the opening 505 decreases, then becomes constant, and then increases to the opening 505.

[0107] operate

[0108] In operation, the burner device is operated so that the fuel and oxygen burn, resulting in flames formed at the ends of the burners 1 and 2, and the flames extend into the corresponding downstream spaces 14 and 27, and into the interior 100 of the burner, which is fuel-rich or fuel-lean as required; and preferably the fuel entering the downstream spaces 14 and 27 through the orifices 19 in the nozzle plate 18 is burned continuously with the oxygen fed into the corresponding downstream spaces 14 and 27 (this provides the desired benefits described below).

[0109] The burner arrangement can be operated so that all flames extending from the ends of burners 1 and 2 toward space 100 and into the space are fuel-rich; or so that all flames extending from the ends of burners 1 and 2 toward space 100 and into the space are fuel-lean; or so that all flames extending from the ends of burners in one plane are fuel-rich, and all flames extending from the ends of burners in another plane (i.e., another plane in a preferred arrangement in which two planes of burners are present) are fuel-lean. The flames in the set extend from the burners in a given plane and are formed by a combination of flames from each of these burners. The flames in the set can be fuel-rich or fuel-lean. In a given plane, the fuel-rich flames in the set can be formed by flames from individual burners in the plane, wherein the flames from each burner in the plane are fuel-rich, or the fuel-rich flames in the set can be formed by flames extending from the burners, wherein one or more of the flames are fuel-rich and one or more of the flames are fuel-lean, provided that the overall characteristics of the set flames are fuel-rich. Similarly, in a given plane, a fuel-lean flame in a collection can be formed by flames from individual burners in the plane, wherein the flames from each burner in the plane are fuel-lean, or a fuel-lean flame in a collection can be formed by flames extending from the burners, wherein one or more of the flames are fuel-lean and one or more of the flames are fuel-rich, provided that the overall characteristic of the collection flame is fuel-lean. In the preferred operating mode described below, the fuel-rich and fuel-lean characteristics of the flames from the burners or from the respective planes in which the burners are located are periodically switched.

[0110] In order to produce a fuel-rich flame from a particular burner, the fuel and oxidant are fed into the burner from their respective sources at relative rates such that there is a stoichiometric excess of fuel relative to the amount of oxygen fed to the burner. That is, the amount of oxygen present in the oxidant fed to the burner will be less than the amount of oxygen required for complete combustion (i.e., complete conversion to H2O, and if the fuel contains carbon, to CO2) of all of the fuel fed to the burner. The appropriate stoichiometric ratio can be readily met based on knowledge of the oxygen content of the oxidant stream and the flow rates of the oxidant and fuel streams.

[0111] In order to produce a fuel-lean flame from a particular burner, the fuel and oxidant are fed into the burner from their respective sources at relative rates such that there is a stoichiometric excess of oxygen relative to the amount of fuel fed to the burner. That is, the amount of oxygen present in the oxidant fed to the burner will be greater than the amount of oxygen required for complete combustion (i.e., complete conversion to H2O, and if the fuel contains carbon, to CO2) of all the fuel fed to the burner. The appropriate stoichiometric ratio can be readily met based on knowledge of the oxygen content of the oxidant stream and the flow rates of the oxidant and fuel streams.

[0112] For the overall efficiency of furnace operation, the total amount of oxygen provided in the oxidant stream fed to all burners 1 and 2 (including the first annular duct and the third annular duct) should be sufficient to completely burn all the fuel fed thereto. Compared with the NOx formation produced by burning all the fuel only at the burner, the fuel fed to the burners is combusted in stages by only partially burning the fuel fed to burners 1 and 2 and passing the incompletely burned fuel into the furnace, and then more completely combusting the incompletely burned fuel with the oxygen entering the furnace, resulting in less NOx formation (which means nitrogen oxides and nitrogen oxide mixtures). For the purpose of staged combustion and reducing NOx formation, a portion of the oxygen (usually 50% to 100% by volume, and preferably 90% to 97% by volume) of the fuel fed to the furnace should be fed to the second annular duct or the fourth annular duct of the burner operating with lean fuel, and the remaining portion of the oxygen should be fed through the second duct or the fourth duct of the burner operating with rich fuel.

[0113] The amount of fuel fed into each downstream space 14 and 27 and combusted therein should be sufficient to maintain the temperature in the interior space 100 at a temperature of 1500F or higher, but not so high as to cause the solid materials forming the burner block 10 to melt or decompose.

[0114] The combustion fuel entering the spaces 14 and 27 from the orifice 19 provides an elevated temperature in the spaces 14 and 27. Such elevated temperatures at these locations provide significant advantages, i.e., reducing or eliminating the formation of solid deposits in the spaces 14 and 27 and on adjacent surfaces. In the absence of combustion at the outer surface 18A of the orifice plate 18, materials in the furnace atmosphere that are in a gaseous state or in a state of finely divided suspended particles may condense onto the surfaces in the spaces 14 and 27 and / or adjacent surfaces, because these surfaces may tend to be relatively cooler than the rest of the furnace atmosphere. Whether these condensed deposits are solid or liquid, the formation of deposits can lead to operational difficulties, such as narrowing and blocking of the opening, loss of uniformity of the flame, pressure changes, and deposit fragments falling into the molten glass in the molten pool and impairing the quality or uniformity of the molten glass. Preferably, the combustion at the orifice 19 in each space 14 and 27 is carried out continuously without interruption, regardless of whether the total combustion products in the spaces 14 and 27 are fuel-rich or fuel-lean.

[0115] The advantages of the present invention in reducing or eliminating the formation of such deposits are particularly valuable in the operation of glass melting furnaces because the glassmaking materials that are typically fed into glass melting furnaces and melted therein typically contain materials that, when heated to glass melting temperatures, form products including oxides, hydroxides and / or sulfates of sodium and / or potassium, or even fully reduced metallic sodium and / or metallic potassium. These products can enter the gas atmosphere in the furnace and can then condense to form the aforementioned deposits on furnace surfaces.

[0116] A particularly preferred application of the present invention is the operation of a glass melting furnace. Glassmaking materials (referred to as "batch"), which may include one or more of the oxides, hydroxides, silicates and carbonates of sodium and the oxides, hydroxides, silicates and carbonates of potassium and mixtures thereof, and / or broken glass pieces (referred to as "glass scrap") are fed into the furnace and melted by the heat of combustion of a fuel, wherein the combustion includes the combustion of a fuel and an oxidant in the manner described herein. The heat of combustion in the furnace 100 melts the glassmaking materials and forms a molten pool of molten glass, which is removed from the furnace 100 for further processing as indicated, which may include fining and other steps conventional in glassmaking.

[0117] In this preferred application, the burners in one plane are operated in one of the modes (A) or (B), and the burners in the other plane are operated in the other of the modes (A) or (B), and the mode in which each group of burners operates is periodically switched alternately between the two modes, i.e., from mode (A) to mode (B), back to mode (A), and back to mode (B), and similarly onwards. The switching of one plane of the burners from mode (A) to mode (B) can occur simultaneously with the switching of another plane of the burners from mode (B) to mode (A), or the first plane of the burners can be switched from one mode to another mode without switching the second plane, so that for a period of time both planes are in the same mode; and then the second plane is switched from its mode to another mode.

[0118] In a preferred embodiment of the present application, in mode (A), fuel is fed from the first central outlet and from the first annular duct nozzle into the first downstream space;

[0119] an oxidant is fed from the second annular outlet into the first downstream space in an amount insufficient to completely combust with all of the fuel fed from the first central outlet and from the first annular duct nozzle; and

[0120] The fuel fed from the first central outlet and from the first annular duct nozzle is incompletely combusted with the oxidant fed from the second annular outlet to produce a fuel-rich mixture of the products of said combustion in the first downstream space;

[0121] fuel is fed into the second downstream space from the second central outlet and from the third annular duct nozzle;

[0122] oxidant is fed from the fourth annular nozzle into the second downstream space in an amount exceeding that necessary for complete combustion with all of said fuel fed from said second central outlet and from said third annular duct nozzle; and

[0123] Fuel fed from the second central outlet and from the third annular duct nozzle is combusted with said oxidant fed from the fourth annular outlet to produce a fuel-lean mixture of products of said combustion in said second downstream space.

[0124] The corresponding fuel-rich mixture and the lean fuel mixture are fed into the interior 100 of the furnace from their corresponding downstream spaces. Since the first downstream space is located above the second downstream space, the lean fuel layer (which is chemically oxidizing) of the product caused by operating in mode (A) is closer to the surface of the molten pool than the rich fuel layer (which is chemically reducing). The rich fuel layer may also contain soot formed by the chemical cracking of the fuel components. When the surface of the molten pool of molten glass does not show the above-mentioned "foam", it is preferred to establish this arrangement of the lean fuel layer and the rich fuel layer. The radiant flame formed when the rich fuel flame layer and the lean fuel flame layer interact with each other in the furnace imparts heat to the molten pool.

[0125] exist Figure 4 and Figure 5 In mode (A), the fuel-rich flame layer is 53, and the fuel-lean flame layer is 54.

[0126] Continuing in this preferred embodiment, in mode (B), fuel is fed from the first central outlet and from the first annular conduit nozzle into the first downstream space;

[0127] oxidant is fed from the second annular outlet into the first downstream space in an amount in excess of an amount sufficient to completely combust with all of the fuel fed from the first central outlet and from the first annular duct nozzle; and

[0128] causing the fuel fed from the first central outlet and from the first annular duct nozzle to combust with the oxidant fed from the second annular duct to produce a fuel-lean mixture of the products of the combustion in the first downstream space, while

[0129] fuel is fed into the second downstream space from the second central outlet and from the third annular duct nozzle;

[0130] an oxidant is fed from the fourth annular duct into the second downstream space in an amount insufficient to completely combust with all of the fuel fed from the second central outlet and from the nozzles of the third annular duct; and

[0131] causing incomplete combustion of the fuel fed from the second central outlet and from the nozzle of the third annular duct with the oxidant fed from the fourth annular duct to produce a fuel-rich mixture of the products of the combustion in the second downstream space;

[0132] The corresponding rich fuel mixture and lean fuel mixture are fed into the interior 100 of the furnace from their corresponding downstream spaces. Since the first downstream space is located above the second downstream space, the rich fuel layer (which is chemically reducing) of the product caused by operating in mode (B) is closer to the surface of the molten pool than the lean fuel layer (which is chemically oxidizing). The rich fuel layer may also contain soot formed by the chemical cracking of the fuel components when the fuel is fed into the downstream space. When the surface of the molten pool of molten glass exhibits the above-mentioned "foam", it is preferred to establish this arrangement of the lean fuel layer and the rich fuel layer. The chemical reduction characteristics of the rich fuel layer interact with the foam and remove some or all of the foam. When the rich fuel layer contains soot, this interaction is enhanced. The radiant flame formed when the rich fuel flame layer and the lean fuel flame layer interact with each other in the furnace imparts heat to the molten pool.

[0133] exist Figure 4 and Figure 5 In mode (B), the fuel-lean flame layer is 53, and the fuel-rich flame layer is 54.

[0134] Switching between modes (A) and (B), and indeed any change in any burner from forming a fuel-rich flame to a fuel-lean flame or from a fuel-lean flame to a fuel-rich flame, can be performed by adjusting the flow rates of the first reactant and the second reactant with the aforementioned controls 36 and 41. The switching and changing can be performed manually, that is, by an operator observing the conditions in the furnace and deciding when to change the conditions and the magnitude of the change. The switching and changing can be performed automatically by including a sensor, indicated as 39, which detects one or more characteristics in the furnace and signals controls 36 and 41 to change the rate and relative rate of the fuel and oxidant in response to the detected characteristics exhibiting a predetermined value, at which the feed characteristics of the fuel and oxidant will be changed or switched. Examples of characteristics that can be detected by sensor 39 and acted upon by controls 36 and 41 include the temperature of a surface in the furnace (such as surface 10A); the temperature of a bath of molten glass; the presence or vapor pressure of a component of the gas atmosphere in the furnace (such as H2O, O2, CO2, or SO2); or the reflectivity of the surface of the bath of molten glass.

[0135] The following table lists the preferred ranges of the amounts of fuel and oxygen fed to the respective pipes of the burner in the practice of the present invention. In this table, "upper flame layer" and "lower flame layer" refer to the ranges from the upper flame layer to the lower flame layer. Figure 4 The flames emitted by the burners arranged as shown. The "lower flame layer" refers to the flames produced by the burners 2 in plane 52, which is closer to the surface of the molten glass pool than the flames produced by the burners in plane 51, which is the "upper flame layer" and is farther away from the surface of the molten glass pool.

[0136] surface

[0137]

[0138]

Claims

1. A burner, comprising: a central conduit having a central axis and terminating in a central outlet opening into a downstream space; a first annular duct, the first annular duct surrounding the central duct, the first annular duct and the central duct being separated by an annular wall, wherein the first annular duct terminates in an outlet to the downstream space, wherein the first annular duct includes a nozzle plate spanning the outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the first annular duct through the nozzle plate to the downstream space; wherein the central conduit and the first annular conduit are each connected to a source of a first reactant by a mechanism, by means of which the flow of the first reactant from its source into the central conduit and the flow of the first reactant from its source into the first annular conduit can be controlled; as well as a second annular conduit surrounding the first annular conduit and terminating in a second annular outlet opening into the downstream space, wherein the second annular conduit is connected to a source of a second reactant by means of a mechanism by which the flow of the second reactant from its source into the second annular conduit can be controlled; One of the first reactant and the second reactant includes a fuel, and the other of the first reactant and the second reactant is an oxidant including oxygen. 2 . The burner of claim 1 , wherein the first reactant is a fuel and the second reactant comprises oxygen.

3. A combustion device, comprising: A first burner, comprising: a first central conduit having a central axis and terminating in a first central outlet opening into a first downstream space; a first annular duct, the first annular duct surrounding the first central duct, the first annular duct and the first central duct being separated by an annular wall, wherein the first annular duct terminates in an outlet to the first downstream space, wherein the first annular duct includes a nozzle plate spanning the outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the first annular duct through the nozzle plate to the first downstream space; wherein the first central conduit and the first annular conduit are each connected to a source of a first reactant by a mechanism, and the mechanism is capable of controlling the flow of the first reactant from its source into the first central conduit and the flow of the first reactant from its source into the first annular conduit; as well as a second annular conduit surrounding the first annular conduit and terminating in a second annular outlet leading to the first downstream space, wherein the second annular conduit is connected to a source of a second reactant by means of a mechanism by which the flow of the second reactant from its source into the second annular conduit can be controlled; and a second burner, the second burner comprising a second central conduit having a central axis and terminating in a second central outlet opening into a second downstream space; a third annular duct surrounding the second central duct, the third annular duct and the second central duct being separated by an annular wall, wherein the third annular duct terminates in an outlet to the second downstream space, wherein the third annular duct includes a nozzle plate spanning the outlet of the third annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the third annular duct through the nozzle plate to the second downstream space; wherein the second central conduit and the third annular conduit are connected to the source of the first reactant by a mechanism, and the mechanism is used to control the flow of the first reactant from its source into the second central conduit and the flow of the first reactant from its source into the third annular conduit; as well as a fourth annular conduit surrounding the third annular conduit and terminating in a fourth annular outlet leading to the second downstream space, wherein the fourth annular conduit is connected to a source of the second reactant by means of a mechanism by which the flow of the second reactant from the source thereof into the fourth annular conduit can be controlled; wherein the central axis of the first central conduit is above the central axis of the second central conduit; One of the first reactant and the second reactant includes a fuel, and the other of the first reactant and the second reactant is an oxidant including oxygen.

4. The combustion apparatus of claim 3, wherein the first reactant comprises fuel and the second reactant comprises oxygen. 5 . The combustion device according to claim 3 , comprising a plurality of the first burners, and further comprising a plurality of the second burners, wherein the central axes of all the first burners are above the central axes of all the second burners. 6 . The combustion device according to claim 5 , wherein all of the plurality of first burners are located in a first plane, and all of the plurality of second burners are located in a second plane that is not the first plane.

7. The combustion device of claim 6, wherein one or both of the first plane and the second plane are horizontal.

8. The combustion device of claim 6, wherein the first plane and the second plane are both horizontal.

9. The combustion device of claim 6, wherein the first plane and the second plane intersect.

10. A method of burning in a furnace, the method comprising: Providing a combustion device according to claim 3; feeding fuel from the first central outlet of the first burner and a first annular duct nozzle plate into a first downstream space within the furnace; feeding an oxidant from the second annular outlet of the first burner into the first downstream space, and combusting the fuel fed from the first central outlet and from the first annular duct nozzle plate with the oxidant fed from the second annular outlet to produce a mixture of the products of the combustion in the first downstream space; and feeding fuel from the second central outlet of the second burner and a third annular duct nozzle plate into a second downstream space within the furnace; feeding an oxidant from the fourth annular outlet of the second burner into the second downstream space, and combusting the fuel fed from the second central outlet and from the third annular duct nozzle plate with the oxidant fed from the fourth annular outlet to produce a mixture of products of the combustion in the second downstream space; The first downstream space is located above the second downstream space. 11 . The method of claim 10 , further comprising continuously combusting the fuel fed from the nozzle plate across the outlets of the first and third annular ducts.

12. A method of burning in a furnace, the method comprising: A combustion device is provided, the combustion device comprising a plurality of first burners, the plurality of first burners comprising a first central conduit having a central axis and terminating in a first central outlet opening into a first downstream space; a first annular duct, the first annular duct surrounding the first central duct, the first annular duct and the first central duct being separated by an annular wall, wherein the first annular duct terminates in an outlet to the first downstream space, wherein the first annular duct includes a nozzle plate spanning the outlet of the first annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the first annular duct through the nozzle plate to the first downstream space; wherein the first central conduit and the first annular conduit are each connected to a source of a first reactant by a mechanism, and the mechanism is capable of controlling the flow of the first reactant from its source into the first central conduit and the flow of the first reactant from its source into the first annular conduit; as well as a second annular conduit surrounding the first annular conduit and terminating in a second annular outlet opening into the first downstream space, wherein the second annular conduit is connected to a source of a second reactant by means of a mechanism by which the flow of the second reactant from its source into the second annular conduit can be controlled; and a plurality of second burners, the plurality of second burners comprising a second central conduit having a central axis and terminating in a second central outlet opening into a second downstream space; a third annular duct surrounding the second central duct, the third annular duct and the second central duct being separated by an annular wall, wherein the third annular duct terminates in an outlet to the second downstream space, wherein the third annular duct includes a nozzle plate spanning the outlet of the third annular duct, wherein the nozzle plate includes a plurality of orifices extending from within the third annular duct through the nozzle plate to the second downstream space; wherein the second central conduit and the third annular conduit are connected to the source of the first reactant by a mechanism, and the mechanism is used to control the flow of the first reactant from its source into the second central conduit and the flow of the first reactant from its source into the third annular conduit; as well as a fourth annular conduit surrounding the third annular conduit and terminating in a fourth annular outlet leading to the second downstream space, wherein the fourth annular conduit is connected to a source of the second reactant by means of a mechanism by which the flow of the second reactant from the source thereof into the fourth annular conduit can be controlled; wherein the central axes of all the first burners are above the central axes of all the second burners; wherein one of the first reactant and the second reactant comprises a fuel, and the other of the first reactant and the second reactant is an oxidant comprising oxygen; feeding fuel from the first central outlet of each of the first burners and the first annular duct nozzle plate into a first downstream space within the furnace; feeding an oxidant from the second annular outlet of each of the first burners into the first downstream space, and combusting the fuel fed from the first central outlet and from the first annular duct nozzle plate with the oxidant fed from the second annular outlet to produce a mixture of the products of the combustion which is introduced into the first downstream space; and feeding fuel from the second central outlet of each of the second burners and the third annular duct nozzle plate into a second downstream space within the furnace; feeding an oxidant from the fourth annular outlet of each of the second burners into the second downstream space, and The fuel fed from the second central outlet and from the third annular duct nozzle plate is combusted with the oxidant fed from the fourth annular outlet to produce a mixture of the products of the combustion that is passed into the second downstream space. 13 . The method of claim 12 , further comprising continuously combusting the fuel fed from the nozzle plate across the outlet of each of the first and third annular ducts.

14. The method of claim 12, wherein all of the first plurality of burners are located in a first plane, and all of the second plurality of burners are located in a second plane that is not the first plane, and the first plane is above the second plane.

15. The method of claim 14, wherein one or both of the first plane and the second plane are horizontal. The method of claim 14 , wherein the first plane and the second plane are both horizontal. The method of claim 14 , wherein the first plane and the second plane intersect.

18. The method of claim 12, wherein the mixture of combustion products passed into one of the first downstream space and the second downstream space is fuel-rich, and the mixture of combustion products passed into the other of the first downstream space and the second downstream space is fuel-lean.

19. The method of claim 18, wherein the mixture of combustion products passed into the first downstream space is fuel-rich, and the combustion at each of the first combustors produces fuel-rich combustion products.

20. The method of claim 18, wherein the mixture of combustion products passed into the first downstream space is fuel lean, and the combustion at each of the first combustors produces fuel lean combustion products.

21. The method of claim 18, wherein the mixture of combustion products passed into the second downstream space is fuel-rich, and the combustion at each of the second combustors produces fuel-rich combustion products.

22. The method of claim 18, wherein the mixture of combustion products passed into the second downstream space is fuel-lean, and the combustion at each of the second combustors produces fuel-lean combustion products.

23. The method of claim 18, wherein alternately, (A) the mixture of combustion products introduced into the first downstream space is fuel-rich and the mixture of combustion products introduced into the second downstream space is fuel-lean, and (B) the mixture of combustion products introduced into the first downstream space is fuel-lean and the mixture of combustion products introduced into the second downstream space is fuel-rich.

24. The method of claim 12, wherein the furnace contains a bath of molten glass.

25. The method of claim 13, wherein the furnace contains a bath of molten glass.

26. The method of claim 14, wherein the furnace contains a bath of molten glass.

27. The method of claim 18, wherein the furnace contains a bath of molten glass.

28. The method of claim 23, wherein the furnace contains a bath of molten glass.

29. The method of claim 28, alternating between (A) and (B) in response to a detected characteristic of the pool of molten glass.

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