TWI444343B - Furnace and process for controlling the oxidative state of molten materials - Google Patents

Description

Furnace and method for controlling oxidation state of molten material

This invention relates to a method useful for oxy-fuel combustion in a furnace containing a molten material.

Certain aspects of the present invention relate to segmented flat flame combustion in a furnace containing a molten material such as glass that will be affected by the heat generated by combustion. This combustion is also used to affect the oxidation state of iron in the molten glass in the refining or refining section of the glass furnace.

In many industrial heating processes that ignite with fuels and oxidants, the fuel combustion products in the melt end of the furnace may interact or react with the molten material and often cause undesirable effects. For example, a fuel-rich flame that is known to invade a molten glass in a glass furnace causes a change in color of the glass product due to redox changes in the glass melt exposed to the fuel-rich flame.

Nitrogen oxides (NOx) may be contaminants produced during combustion and are intended to reduce the amount of production that occurs during combustion. It is known that the use of pure oxygen or oxygen-enriched air as an oxidant in the process can reduce the amount of NOx produced for combustion because it reduces the amount of nitrogen supplied to the combustion reaction on an equivalent oxygen basis. However, the use of an oxidant having a higher oxygen concentration than air causes the combustion reaction to proceed at a higher temperature, and this higher temperature is kinetic as to form NOx. Segmented combustion is used to reduce NOx production. U.S. Pat.

Among other industries, glass for the solar glass industry is expected to be relatively intermediate or clear and very transparent to visible light (e.g., at least 75% transmittance, or even better at least 80% transmission). One way to achieve such a glass is to use a very pure base glass material (e.g., substantially free of tin-like coloring agents). However, base materials with high purity are expensive and therefore not necessarily desirable and/or convenient. In other words, for example, removing iron from glass frits has some practical and/or economic limitations. Other methods of making "clear" glass are to add a foreign batch that aids in oxidation.

Control of the oxidation state of the glass is useful in the manufacture of "clear" or bright glass. In some cases, we desire iron having a very low FeO (ferrous state) content (for example, as discussed in US 20060581784; herein incorporated by reference). This may be advantageous because ferrous iron (Fe ²⁺ ; FeO) is a much stronger coloring agent than iron ions (Fe ³⁺ ; Fe ₂ O ₃ ). What is needed in this art is a furnace and method for controlling the oxidation state of a transition metal in a molten material.

The present invention addresses the problems associated with conventional methods that utilize, for example, flat flame, segmented combustion techniques to obtain a molten material to affect the oxidation state of the transition metal ions associated with the molten material. Affecting the oxidized state can impact the chemical and physical properties of the molten material (for example, oxidizing iron ions to Fe(III)) in order to improve the quality of the molten material (for example, improving floating glass such as solar glass) The clarity of the).

One aspect of the present invention is directed to a segmented flat flame combustion process in which a fuel and an oxidant are contacted in a combustion reaction having a streamlined flow in the segmented flat flame burner, and the molten glass is contacted with the combustion reaction to enhance The amount of Fe(II) in the molten glass, or contact with the oxygen of the segment to increase the amount of Fe(III) in the molten glass while still ensuring effectiveness from the combustion reaction to the molten glass Heat transfer.

Another aspect of the present invention relates to a refined zone (sometimes referred to as a refining zone) for manipulating a glass furnace in a manner that affects the oxidation state (eg, the burner increases the amount of Fe(III) in the molten glass) A flat flame burner in the domain) controls the oxidation state of the transition metal ions.

Another aspect of the present invention is directed to a glass furnace comprising a melt zone and a refined zone, wherein the refined zone comprises a segmented flat flame burner. Orienting the burner, the fully combusted product or the fully combusted product and the segmented oxygen in a manner associated with the surface of the molten glass to affect the oxidation state of the transition metal in the molten glass (eg, iron)

One aspect of the present invention is directed to a method of varying the oxidation state of a transition metal ion species in a furnace, wherein: (i) the furnace is set to a continuous operation profile comprising a packing end, a discharge end, adjacent the packing end a melting zone and a refining zone in fluid contact with the discharge end; (ii) introducing a glass forming component into the melting zone, traveling along a path from the melting zone to the refining zone, and from the refining zone The domain is taken in the form of molten glass And (iii) the furnace has a combustion energy requirement in the combustion space above the melting zone and the refining zone; the method comprises the steps of: (A) above the molten glass, away from the filler end The flat flame configuration and a stoichiometric ratio of not less than about 50 percent of the stoichiometric amount inject fuel and primary oxidant into the combustion space, the primary oxidant being a fluid comprising at least 21 mole percent oxygen, the fuel and the primary The oxidant is injected into the combustion space at a rate of about 1000 Torr per second or less; (B) burning the fuel in the combustion space and the primary oxidant to generate heat and including unreacted oxygen and unburned fuel. Combustion reaction product; (C) at a rate of about 2000 standard Torr or less per second, spraying a secondary oxidant into the combustion space in a flat configuration below the injection point of the fuel and the primary oxidant, and causing the secondary oxidant Sprayed between the molten glass and the injection point of the fuel and the primary oxidant, the secondary oxidant being a fluid comprising at least about 21 mole percent oxygen; (D) being enriched in the vicinity of the molten glass Oxygen layer, The oxygen-rich oxygen layer has a higher oxygen concentration than the molten glass; (E) transports oxygen from the oxygen-rich gas layer into the molten glass, and thereby drives at least one transition in the molten glass A redox reaction of a metal ion species to oxidize the transition metal ion species; and (F) combusting the secondary oxidant with unburned fuel to provide additional heat and combustion reaction products within the furnace.

Another aspect of the invention relates to a reduction of molten glass in a furnace A method of transitioning a metal ion species, wherein: (i) the furnace is set to a continuous operation mode comprising a packing end, a discharge end, a melting zone adjacent to the packing end, and a refining zone adjacent to the discharge end; (ii) introducing a glass forming component into the melting zone, traveling along a path from the melting zone to the refining zone, and taking out from the refining zone in the form of molten glass; and (iii) the furnace is in the furnace The combustion space above the melt zone and the refining zone has a combustion energy requirement; the method comprises the steps of: above the molten glass, away from the filler end in a segmented flat flame configuration and not exceeding a stoichiometric percentage The stoichiometric ratio of 70 injects fuel and a primary oxidant into the combustion space, the primary oxidant being a fluid comprising at least 21 mole percent oxygen, both the fuel and the primary oxidant at a rate of about 1000 Torr per second or less. Sprayed into the combustion space; (B) combusting fuel and primary oxidant in the combustion space to generate heat and combustion reaction products including unburned fuel; (C) at a rate of about 2000 standard Torr or less per second, The burning And spraying a secondary oxidant into the combustion space in a flat configuration above the injection point of the primary oxidant, and placing the injection point of the fuel and the primary oxidant between the molten glass and the injection point of the secondary oxidant, The secondary oxidant is a fluid comprising at least about 21 mole percent oxygen; (D) establishing a fuel-rich oxygen layer in the vicinity of the molten glass, a fuel-rich oxygen layer having a lower oxygen concentration than the molten glass; (E) transporting oxygen from the molten glass to the oxygen-rich gas layer, and thereby driving at least one transition metal in the molten glass The redox reaction of the ionic species to reduce the transition metal ion species; and (F) burning the secondary oxidant with the unburned fuel to provide additional heat and combustion reaction products within the furnace.

Another aspect of the present invention relates to a furnace comprising: a filler for making glass, a melting zone, a molten filler, and a refining zone, wherein the refining zone comprises a molten filler Segmented flat flame burner.

Another aspect of the present invention is directed to a method of modifying an oxidation state of a transition metal ion species in a molten glass in a furnace, comprising the steps of: injecting a fuel and a primary oxidant in a flat flame configuration above the molten glass, the primary The oxidant comprises at least about 21 mole percent oxygen in an amount to provide at least about 50 percent of the stoichiometric oxygen demand of the fuel and no more than about 186 percent; and the melt of the secondary oxidant sprayed into the furnace in a flat configuration Between the glass and the injection point of the fuel and the primary oxidant, thereby establishing an oxygen-rich gas layer adjacent to the molten glass, the secondary oxidant comprising at least 21 mole percent oxygen, when combined with the primary oxidant, The amount can provide at least about 200 percent of the stoichiometric oxygen demand of the fuel.

Another aspect of the present invention is directed to a method of reducing a transition metal ion species in a molten glass in a furnace, comprising the steps of: Spraying a fuel and a primary oxidant in a flat flame configuration above the molten glass, the primary oxidant comprising at least about 21 mole percent oxygen, the amount providing a stoichiometric oxygen demand of the fuel of at least about 18 percent and no more than about 70 percent And spraying the secondary oxidant into the furnace in a flat configuration such that the injection point of the fuel and the primary oxidant is between the molten glass and the injection point of the secondary oxidant, thereby establishing adjacent to the melting An oxygen-rich gas layer of glass, the secondary oxidant comprising at least 21 mole percent oxygen, when combined with the primary oxidant, provides an amount of at least about 80 percent of the stoichiometric oxygen demand of the fuel.

Another aspect of the present invention is directed to a method of modifying an oxidation state of a transition metal ion species in a molten glass in a furnace, the method comprising: providing two burners on opposite walls of the longitudinal direction of the furnace; Spraying a fuel and a primary oxidant in a flat flame configuration above the molten glass within the furnace, the primary oxidant comprising at least about 21 mole percent oxygen, the amount providing a stoichiometric oxygen demand of the fuel of at least about 18 percent without exceeding Approximately 186 percent; the secondary oxidant is sprayed through the burners into a flat flame configuration adjacent to the fuel and the flame formed by the primary oxidant, thereby establishing a fuel-rich gas on the molten glass a layer and an oxygen-rich gas layer, the secondary oxidant comprising at least 21 mole percent of oxygen; wherein the primary oxidant is when the burner is positioned such that the fuel-rich gas layer is adjacent to the molten glass And the total oxygen provided by the secondary oxidant does not exceed 95% of the stoichiometric oxygen demand of the fuel; Wherein the burners are positioned such that the oxygen-rich gas layer is adjacent to the molten glass, the primary oxidant and the secondary oxidant provide a total oxygen content of at least 110 percent of the stoichiometric oxygen demand of the fuel.

As used herein, the phrase "flat flame" means a visible flame in which the longest dimension of the flame section taken perpendicular to the surface of the molten material is parallel to the molten surface.

The phrase "completely combusted product" as used herein means one or more of carbon dioxide and water vapor.

As used herein, the phrase "incompletely combusted product" means one or more of carbon monoxide, hydrogen, carbon, and partially combusted hydrocarbons.

As used herein, the phrase "unburned fuel" means a material comprising one or more of a fuel that has not been combusted, an incompletely combusted product of the fuel, and mixtures thereof.

The phrase "segmented" as used herein is intended to mean a segment as defined in U.S. Patent No. 5,611,682, the disclosure of which is incorporated herein by reference.

As used herein, the phrase "stoichiometric" means the ratio of oxygen to fuel for combustion purposes. A stoichiometric ratio of less than about one hundred percent means that there is less oxygen present (i.e., fuel rich) than is required for complete combustion of the fuel present. A stoichiometric ratio above about one hundred percent means that there is more oxygen present than is required to completely burn the fuel (i.e., in the presence of excess oxygen or oxygen).

As used herein, the phrase "refining" or "refining zone" means a portion of the glass furnace that does not belong to the melt zone and is located between the end of the melt zone of the furnace and the discharge end.

As used herein, the phrase "hot spring zone" means a zone within the glass furnace in which two convection rings cause the molten glass to rush upward. According to the design and conditions in the glass furnace, in addition to other blocks, the hot spring zone may be located in the melting zone and the refined zone.

One or more zones of any industrial furnace or industrial furnace heated by one or more burners may be used in the practice of the invention. An example of such a furnace includes a glass furnace.

The heat generated in the combustion reaction is radiated to the glass frit or filler to heat the molten glass. This heat is radiated directly or indirectly from the combustion reaction to the molten glass by interaction with complex radiation from surrounding furnace gases and walls. A relatively small amount of heat is passed from the combustion reaction to the packing by convection in a high temperature furnace.

The present invention is broadly directed to a method and furnace for melting a glass forming component. In a typical glass furnace, or as it is often referred to as a glass tank, the glass-making material, referred to as a batch, is filled into the melt zone of the furnace. In addition to the initial start of the furnace, the glass furnace is continuously operated and, therefore, there is a current molten glass bath, referred to as a melt, in the melt zone where the material is placed. The molten glass and the molten batch are collectively referred to as "fillers." The unprocessed or unmelted batch can be filled into the kiln by well known mechanical filling means. In a typical embodiment, the batch floats on the surface of the bath to form a semi-immersion layer containing an unmelted solid known as a batch cover (batch overlay). The cover layer sometimes breaks down Separate batch piles or batch islands (also known as floating tables or materials). For the purposes of the present invention, a furnace section containing substantially unmelted batch solids floating on the surface of a molten glass bath is defined as the "melting zone". For example, the unmelted batch solids are visible floating on the surface of the furnace portion. The glass then enters the refined zone where the bubbles are released, and in the refined zone, the glass is homogenized and repelled, such as bubbles or "seeds". The glass is continuously taken out from the refining zone. The melting zone and refining zone of the glass cell kiln may be present in a single tank or the glass tank kiln may consist of two or more connected and individual tanks.

The present invention can be used to control or alter the charge of materials (e.g., used to make glass) that readily change the oxidation state when exposed to combustion conditions within the furnace. Examples of materials that readily change the oxidation state include a molten filler containing a cation (e.g., a transition metal cation) capable of taking multiple oxidation states, including transition metal oxides. A specific example in which the oxidation state is easily changed is a filler containing an iron cation (for example, iron oxide in a form containing one or more of FeO, Fe ₃ O ₄ (or a similar mixed oxidation state) or Fe ₂ O ₃ ). The form of iron oxide is typically present in the filler from which the glass is made.

A molten glass body is held in the furnace in the continuous glass furnace and an unprocessed glass batch is fed to the surface of the molten glass cell through an inlet at one end of the furnace. The batch forms an unmelted layer or a "cover layer" on the surface of the molten glass cell, which may extend a considerable distance into the furnace until it becomes melted into the molten glass cell. . The heat that melts the batch is provided to the furnace by a burner above the height of the molten glass, sometimes assisted by an immersion electric heater. On the furnace side opposite to the inlet end, the molten glass is taken out from the molten glass pool through the discharge opening Glass. (For example, as described in U.S. Patent No. 4,536,205, incorporated herein by reference).

Without wishing to be bound by theory or description, the combustion space affects the glass melt and glass flow in the glass furnace, and more specifically the oxidation state of the transition metal ions in the "hot spring zone" (eg , as described by Trier (W. Trier, Glass Furnaces: design construction and operation, p 144, translated by KLLoewenstein, Society of Glass Technology, 2000).

The effect of heating from above, the heat loss from the kiln and the process of melting and refining can cause a difference in density in the molten glass bath, which causes a flow difference.

For the purposes of this disclosure, a furnace section containing substantially unmelted batch solids floating on the surface of a molten glass bath is defined as the "melting zone", however the "refining zone" or "refining zone" It is defined as a furnace section that does not contain significant unmelted batch solids floating on the surface of the molten glass bath. Foam or slag may be present on the surface of the molten glass bath in the refined zone or may be clear on the surface of the molten glass bath, referred to as "mirror" glass (for example, as described in U.S. Patent No. 6,519,973; Incorporated herein by reference).

The batch cover at the inlet end of the furnace is relatively cold and acts as a heat sink and also shields the lower portion of the molten glass cell from the radiant heat of the top combustion. On the other hand, the area of the molten glass pool just downstream of the melting point of the batch cover tends to be the hottest area in the molten glass pool. These temperature conditions establish two counter-rotating cycles in the molten glass cell. In this area, just beyond the hot glass trend of the batch cover layer The tendency of the cooler glass near the sinking inlet end establishes a cyclic pattern below the batch blanket, wherein the glass in the upper portion of the pool below the blanket flows toward the inlet end (ie, in the upstream direction) And the glass in the lower portion of the cell below the batch cover flows to the outlet end (i.e., downstream direction). The cyclic pattern between the end of the batch cover layer and the outlet end of the furnace is in the opposite direction, the surface portion of the glass flowing in the downstream direction and the glass in the vicinity of the bottom of the pool flowing in the upstream direction. The strong convection of the molten glass at the junction of these convection rings, and thus the area is known as the "hot spring zone". The molten glass near the surface of the hot spring zone is often the hottest part of the molten glass in the furnace and, therefore, it is desirable for the treated glass to flow through this area to ensure the melting and refining of the glass. . (For example, as described in U.S. Patent No. 4,536,205, incorporated herein by reference).

The highest temperature zone on the top of the furnace is known as the "hot spot." Typically, the hot spot temperature of the roof is at least about 20K hotter than the top temperature on the adjacent burner ports (or at least 1% hotter in absolute units such as Kelvin), and more often than adjacent combustion. The top temperature on the mouth is about 40K hotter (or at least 2 percent more in absolute units such as Kjelda). This hot spot temperature results in a melted glass density gradient that creates the aforementioned natural convection in a region of the glass melt near the hot spot in the combustion space. Typically, the location of the hot spring zone is within about 20% of the length of the furnace relative to the hot spot, and more typically within about 10% of the length of the furnace. The hot spring zone assists in homogenizing the glass and prevents unreacted batch material from entering the refining zone to reduce the number of defects in the final glass product (e.g., Trier, pp 144 to 156). Typically the hot spot temperature (in absolute order As indicated by Kjeldahl), it has a temperature 15% higher than the surface temperature of the glass of the hot spring zone, and more generally about 10% higher. Where there is no significant temperature difference between the hot spot and the remainder of the furnace in the furnace, it may also be applied to the hot spring zone, for example by using a foamer or electrode.

Iron in the ferrous (Fe ²⁺ ; FeO) state is a cyan colorant, and iron in the ferric state (Fe ³⁺ ) is a yellow-green colorant. The ferrous (Fe ²⁺ ; FeO) cyan colorant is particularly important when looking for a relatively clear or intermediate color glass, which will add significant color to the glass because it is a strong colorant. Although iron in the ferric state (Fe ³⁺ ; Fe ₂ O ₃ ) is also a coloring agent, iron in the ferric state is less important when it is sought to achieve a relatively clear color glass because it is trivalent. Iron in the iron state tends to be a weaker coloring agent than its ferrous state counterpart. (U.S. Patent No. 7,557,053; herein incorporated by reference). That is to say, the oxidation state of the transition metal ions affects the transmittance, gloss and color of the finally produced glass.

Or iron in the ferrous state may be used in some glass products, such as container glass, where a ferrous iron-green colorant may be desired.

Without wishing to be bound by any theory or explanation, the formation of iron oxide (FeO or Fe ²⁺ ) in the ferrous state in the glass manufacturing process may depend on the mass transfer of oxygen. Fe ions typically enter the furnace as impurities in the untreated filler. Fe ₂ O ₃ and FeO, with oxygen, form a reduction-oxidation (redox) pair:

When the temperature is raised to the melting point of the glass, the reaction is faster and usually equilibrated. However, the equilibrium constant, K, depends on the temperature,

Wherein the equilibrium constant of the redox pair, K, can be defined as

Moreover, [FeO], for example, represents the concentration of FeO. Because the Gibbs energy of this reaction, G, is a grade of 80,000 J/mol (according to the reaction network of http://www.crct.polymtl.ca/reacweb.htm ), the reaction will be shifted with sufficient temperature increase. To the right. That is, the value of K will increase as the temperature increases. For example, when the equilibrium constant at the surface temperature of the glass in the hot spring zone at about 1450 ° C is compared with the equilibrium constant at the surface temperature of the glass in the refined zone of about 1375 ° C (for example, Trier, Figure 6.78 p155), the equilibrium constant in the hot spring zone will be approximately 2.76 times greater than the equilibrium constant in the refined zone. As a result, the concentrations of FeO and O ₂ typically reach a maximum in the middle of the furnace, especially in the hot spring zone and around, where the temperature is highest. In a typical glass furnace, the oxygen concentration in the combustion space is very low because the maximum fuel efficiency is obtained by operating a ratio of fuel to oxidant that is very close to the stoichiometric ratio required for complete combustion. As a result of the low oxygen concentration in the combustion space above the glass melt, the oxygen in the glass melt tends to diffuse out of the glass, and as the glass cools while moving from the hot spring zone of the furnace FeO could not be converted back to Fe ₂ O ₃ during the refining stage. The result is the formation of FeO, and thus the color in the resulting glass. In the case of, for example, solar glass, less FeO is desired in the resulting glass. In some cases of container glass, more FeO is desired in the resulting glass.

Without wishing to be bound by any theory or explanation, it is believed that the loss of oxygen from the glass melt to the combustion space depends on several factors, including the oxygen concentration gradient, diffusivity, and the solubility of oxygen in the glass melt. First, the highest oxygen concentration gradient in the periphery of the hot spring band, not only because of the high temperature to promote the formation of FeO and the like to balance O ₂ as discussed above, and because the glass convective upward flow of oxygen from the surface and enhance the overall concentration moved Boundary layer.

Secondly, the diffusivity of oxygen in the glass melt, D, also increases with temperature.

Wherein the soda lime-silicate glass has an A _d = 3 x 10 ^-3 m ² /s, and E _d = 26585 K (for example, as described by Pigeonneau et al., "Shrinkage of an oxygen bubble rising in a molten glass," Chemical Engineering Science (2010), 65(10), 3158 to 3168). This implies that the diffusivity is also highest near the hot spring zone. For example, when the oxygen diffusivity at the surface temperature of the glass in the hot spring zone at about 1450 ° C is compared with the oxygen diffusivity at the average surface temperature in the refined zone of about 1375 ° C, the hot spring The diffusivity in the band will be about 2 times greater than the diffusivity in the refined band. The combination of the high oxygen concentration gradient and the thermal active oxygen diffusivity in the glass melt indicates that maximum oxygen loss from the glass melt to the combustion space above the glass melt will occur in the vicinity of the hot spring zone.

With regard to the case where Fe ³⁺ is desired in the final glass product, additional oxygen input, via an oxygen burner (eg, the burner of FIG. 3) or an oxygen lance, is used to prevent the melt from the glass to the refined zone. Preferably, the hot spot is adjacent to or in proximity to the hot spot, and better access to the combustion space in the hot spring zone will be most efficient. The additional oxygen input creates a region of high oxygen concentration in the combustion space of the glass adjacent the refined zone (and more preferably the zone), which in turn creates a resulting void from the combustion space to the molten glass The oxygen concentration gradient within the oxygen transport.

Regarding the case where Fe ²⁺ is desired in the final glass product, substoichiometric (fuel-rich, or oxygen-depleted) combustion is used to enhance oxygen loss from the glass melt to the combustion space in the refined zone. The most efficient, preferably close to the hot spring zone (e.g., rotating the burner shown in Figure 3 by 180 degrees to place the fuel-rich zone of Figure 2 adjacent to the molten glass surface). This creates a region of low oxygen concentration (reduction conditions) in the combustion space of the glass adjacent to the refined zone (and more preferably the hot spring zone), which in turn creates a result from the molten glass to the combustion The oxygen concentration gradient of oxygen transport in the space.

Third, the solubility of oxygen in the glass melt, L, also increases with temperature.

Wherein the alkali lime-silicate glass A _L = 1.37x10 ^-4 mol m ^-3 Pa ^-1 , and E _L = 6633K (for example, as described by Pigeonneau et al., "Shrinkage of an oxygen bubble rising in a molten Glass, "Chemical Engineering Science (2010), 65(10), 3158 to 3168). This suggests that the solubility of the O ₂ is also highest near the hot spring zone. For example, when the oxygen solubility at the surface temperature of the glass in the hot spring zone at about 1450 ° C is compared with the oxygen solubility at the average surface temperature in the refined zone of about 1375 ° C, the hot spring zone The solubility in the solution will be about 1.2 times greater than the solubility in the refined band. It is believed that although the oxygen concentration in the melt increases at higher temperatures, the increment is not of the same order of magnitude as the diffusion, D, increment, or equilibrium constant, K, as described above. However, in the case where Fe ^{3+ is} the desired final oxidation state of the iron ions in the glass, when oxygen is supplied at a higher concentration to the adjacent refined zone (and more preferably the hot spring zone) Increased solubility plus higher diffusivity is advantageous in the combustion space of the glass because the glass has an increased capacity for dissolved oxygen. This will oxidize Fe ²⁺ to Fe ³⁺ after subsequent use of oxygen dissolved in the glass melt as the glass cools while moving from the hot spring zone of the furnace to the refining zone.

Referring now to Figure 1, Figure 1 is a schematic top plan view of a glass furnace including a flat flame burner located in the refined zone. The batch is filled into one end of the furnace and melted through the refiner or refining zone wherein the oxidized state of the molten glass is at least partially altered and the glass is subsequently discharged from the furnace.

In order to establish a condition in the furnace sufficient to affect the oxidation state of the molten glass, the fuel and the main oxidant are introduced into the refined zone of the furnace (for example, the hot spring zone) through the burner above the molten glass. The fuel and primary oxidant can be injected into the furnace separately or in a premixed state. The fuel and primary oxidant are supplied to the furnace through a plurality of burners. Any suitable oxy-fuel burner can be used to practice the invention. Examples of suitable oxy-fuel burners for carrying out the invention are the segments disclosed in U.S. Patent Nos. 5,611, 682, 6, 524, 097, 7, 390, 189, and U.S. Patent Application Serial No. 12/688,115, filed on Jan. Flat flame burner; the disclosure of which is incorporated herein by reference. Suitable oxy-fuel burners in business It is commercially available from Air Products and Chemicals, Inc. (Abbott, Pennsylvania) under the trade name HR or HriTM burners. If necessary, in addition to other techniques for introducing oxygen into the furnace environment and molten glass, the concentration of oxygen in the refined zone can be achieved by applying techniques well known in the art (e.g., oxygen blowing, in the melt) The oxygen bubbler in the molten glass is further improved.

The fuel incorporated into the furnace can be any gas or other fluid containing combustibles that can form a combustion zone in the furnace. Among these fuels, natural gas, coke oven gas, propane, methane, and oil (for example, No. 2 fuel or No. 6 fuel) can be cited.

The primary oxidant comprises a fluid having an oxygen concentration of at least about 50 volume percent oxygen, and often at least 90 volume percent oxygen (eg, in addition to other systems for storing and supplying oxygen, by PSA, VSA, liquid oxygen tank, cryogenic air) The oxygen supplied by the separator element). The primary oxidant can be a commercially available pure oxygen having an oxygen concentration of 99.5 percent or greater.

In one aspect of the invention, it is directed to reducing the oxidation state of one or more cations in the glass, providing the fuel and the primary oxidant to the furnace at a plurality of flow rates such that the ratio of the primary oxygen to fuel is low It is about 95 percent stoichiometric and often ranges from about 18 percent to about 95 percent of the stoichiometric amount.

In another aspect of the invention, the oxidation state of one or more cations in the glass is oxidized, and the fuel and the primary oxidant are supplied to the furnace at a plurality of flow rates such that the ratio of the primary oxygen to the fuel is About 18 percent above stoichiometric, and often about 18 percent of stoichiometric Up to about 110 percent.

In another aspect of the invention, both the fuel and the primary oxidant are injected into the furnace at a rate of about 330 standard Torr per second (sfps = volumetric flow scfs/area) or less. The fuel is typically provided at a rate of from about 26 to about 330 sfps. After the pre-combustor of the combustor (e.g., as shown in more detail in Figure 3, wherein oxygen introduced into the combustor surrounds the natural gas and is used to segment/supply additional oxygen), the velocity It will increase from about 1.5 to about 3 times the inlet speed, which can be about 990 fps or less. In one aspect of the invention, the fuel is provided at a rate of from about 39 to about 990 fps.

In one aspect of the invention, the primary oxidant is provided at a rate of from about 6.5 to about 200 sfps. After being accelerated through the burner's pre-combustor (eg, as shown in more detail in FIG. 3), the speed is increased to about 1.5 to about 3 times the inlet speed, which may be between about 9.75 and about 600 fps. between.

Another aspect of the present invention is directed to the use of a segmented flat flame burner that includes a segmented valve, a primary helium, and a fuel helium (e.g., for supplying natural gas NG). This burner can be used to supply an oxidizing or reducing gas layer in the vicinity of the molten glass in the refined zone. When the valve is fully open segment, the O ₂ about 23% of the total flow passing through the main port. If necessary, the burner can be operated at an O ₂ :NG molar flow ratio of about 1:1, or sometimes about 1.6:1, with a stoichiometric ratio of 2:1 for complete combustion. When the burner is operated at a stoichiometric ratio of 1.6:1, the most reductive gas layer in the main crucible will have a stoichiometric ratio of about 1.6*0.23 = 0.368. This means that a complete combustion in this main crucible requires a stoichiometric ratio of about 18.4%. In order to obtain the most reductive gas layer through the primary helium, the remaining oxygen is passed through the section and at the desired overall stoichiometric ratio. In order to supply the most reductive gas layer in the vicinity of the glass, the burner is engaged in a position close to the main crucible of the glass, and the segment valve is opened to direct the maximum amount of oxidant to the segment.

If necessary, the burner can be operated at an O ₂ :NG molar flow ratio of about 6:1, or sometimes about 4:1, with a stoichiometric ratio of 2:1 for complete combustion. When the valve is fully closed segment, about 93% of the total flow rate of O ₂ passing through the main port. Therefore, the most non-reducing gas layer of the main crucible will have a stoichiometric ratio of about 4*0.93=3.72. This means that a complete combustion in this main crucible requires a stoichiometric ratio of about 186%. In order to obtain the most non-reducing gas layer (the most oxidizing gas layer) through the main crucible, the remaining oxygen is passed through the section and at the desired overall stoichiometric ratio. In order to supply the most oxidizing gas layer in the vicinity of the glass, the burner cooperates with a section 埠 near the glass, and the segment valve opens to direct the maximum amount of oxidant to the segment 埠, And directing the maximum amount of oxidant to the vicinity of the glass.

When this inventive method relates to the reduction of the oxidation state of the transition metal cations in the glass, the combustion reaction product may comprise a fully combusted product. However, due to the defined substoichiometric primary oxygen to fuel ratio, it also includes unburned fuel. The incomplete combustion of the fuel with the primary oxidant allows the fuel and primary oxidant to be combusted at a lower temperature than in other cases, thus reducing the tendency for NOx formation. Due to incomplete mixing and short residence times during the combustion reaction, the combustion reaction products may also be packaged Some residual oxygen is included, but the oxygen concentration within the combustion reaction will tend to be close to the thermodynamic equilibrium.

When this inventive method is concerned with the oxidation state of the transition metal cations in the glass, the combustion reaction product may include a fully combusted product. However, due to the defined superstoichiometric primary oxygen to fuel ratio, some of the remaining oxygen. Incomplete combustion of all of the primary oxidant allows the fuel and primary oxidant to be combusted at substantially lower temperatures than in other cases, thus reducing the tendency for NOx formation. Due to incomplete mixing and short residence times during the combustion reaction, the combustion reaction products may also include unburned fuel, but the unburned fuel concentration within the combustion reaction products is close to the thermodynamic equilibrium.

In an aspect of the invention, in order to establish a reducing gas layer on the surface of the molten glass, a secondary oxidant is supplied to the furnace through a section 埠 above the main crucible (for example, the burner orientation shown in FIG. 3 is oriented) Rotate 180 degrees). Typically, in this view, the secondary oxidant is injected into the furnace at a location further away from the upper surface of the molten glass. The secondary oxidant may be supplied to the furnace from above the fuel and primary oxidant, or from an angle offset from the vertical, for example by an angle of up to 45 degrees.

In another aspect of the invention, in order to establish an oxidizing gas layer on the surface of the molten glass, the secondary oxidant is supplied to the furnace through a section 埠 below the main crucible (for example, the orientation of the burner is consistent with FIG. 2 ). Typically, in this view, the secondary oxidant is injected into the furnace at a point between the upper surface of the molten glass and the primary crucible. The secondary oxidant may be from a vertical below the fuel and the primary oxidant, or from a deviation from the vertical plane (eg, For example, an angle typically offset by up to 45 degrees is provided into the furnace.

In use, the secondary oxidant can be in the form of a fluid having an oxygen concentration of at least about 50 mole percent. The secondary oxidant can be commercially pure oxygen. When commercial pure oxygen is used, the secondary oxidant can be supplied to the furnace at a rate of about 400 sfps or less, and often at a rate of about 200 sfps or less. This speed will be provided at a higher speed if the oxygen purity is lower. In most cases, the secondary oxidant has a significantly higher oxygen concentration than air. With respect to a specified amount of fuel consumption, the total gas volume through the furnace is reduced as the oxygen concentration of the oxidant increases. This lower volumetric flux through the furnace, at the speed at which the segmented combustion embodiment of the present invention can be applied, results in a secondary oxidant gas layer near the filler having a different composition to the contents of the remainder of the furnace. (Oxidation or reductibility depending on the particular embodiment) can be established. The gas layer can be selected to achieve the desired oxidation state in the underlying molten surface.

Occasionally, the momentum ratio of the fuel and primary oxidant stream to the secondary oxidant stream can range from about 0.5 to about 5.5 or less.

The secondary oxidant gas layer has an oxygen concentration that exceeds the combustion reaction product in the combustion reaction zone. Although any suitable oxygen delivery system or lance can be used to administer the secondary oxidant into the furnace in the practice of the present invention, the gas lance disclosed in U.S. Patent Nos. 5,611,682 and 7,390,189 is incorporated herein by reference. An oxidant is injected into the furnace, which is incorporated herein by reference.

In the case where the target is to reduce the oxidation state of the transition metal oxide in the molten glass, the secondary oxidant is supplied to the furnace at a certain flow rate. Thus, when added to the primary oxidant, a stoichiometric amount of oxygen to fuel ratio of at least about 80 percent is established, and sometimes within a range of from about 90 percent to about 100 percent. When the ratio of the primary and secondary oxidants to the fuel is less than one hundred percent stoichiometric, the remaining oxygen required to achieve complete combustion of the fuel in the furnace can be provided by mixing the air.

In the case where the oxidation state of the transition metal oxide in the molten glass is targeted, the secondary oxidant is supplied to the furnace at a flow rate to establish a stoichiometric amount when added to the primary oxidant. About 100 percent oxygen to fuel ratio, and sometimes within about 100 percent to about 120 percent. When the ratio of the primary and secondary oxidants to the fuel is greater than one hundred percent stoichiometric, the remaining oxygen can be taken to achieve complete combustion throughout the combustion space of the furnace and exhaust venting through the furnace.

In the reduction viewpoint of the present invention, since the secondary oxidant is supplied to a position in the furnace (for example, above the main crucible), a reducing gas layer is formed which occurs in a uniform with the furnace atmosphere. The interaction interacts differently with the molten glass. In a specific embodiment of the oxidation of the present invention, since the secondary oxidant is supplied to a location within the furnace (e.g., below the primary crucible), an oxidizing gas layer is formed which will be uniform with the furnace atmosphere The interaction that takes place interacts differently with the molten glass.

Downstream of the combustion reaction, the secondary oxidant and the unburned fuel may be mixed, for example, in a region remote from the burner face in the furnace, thereby preventing: 1) the secondary oxidant and the present invention Restoration in a specific embodiment The oxidizable component of the molten glass directly interacts (reacts), or 2) the incompletely combusted product directly interacts (reacts) with the reducible component of the filler in the oxidized embodiment of the invention to complete The fuel is burned and provides additional heat and combustion reaction products in the furnace.

The combustion reaction products in the furnace are typically discharged through a flue. When the invention is used in a zone of a furnace having multiple zones, the combustion reaction products can be discharged to adjacent zones. The increase in the flue enthalpy also affects the degree of stratification of the furnace atmosphere. If necessary, the combustion reaction product in the furnace is discharged from the furnace from a point where the fuel and the main oxidant are supplied to the furnace.

While particular emphasis is placed on floating glass furnaces, the present invention can be used to control the oxidation state of a wide range of glasses (e.g., glass fibers, container glass, tableware, specialty glass, among other glass types).

Although particular emphasis is placed on affecting the oxidation state of iron, other metal ions in the molten glass may be oxidized or reduced in accordance with the present invention.

Although any suitable burner can be used to heat and melt the filler, a segmented flat flame burner can be used throughout the furnace, if necessary, for melting the filler and controlling the oxidation state in the refined zone. . The oxy-fuel burners may be disposed at multiple locations along the furnace, in addition to other locations suitable for supplying oxygen or reducing gases to the molten glass and affecting the oxidation state of at least one of the metal species, In the top of the furnace, adjacent to the hot spot, above the hot spring zone.

Although the present invention can be used in conjunction with a wide range of glass composition applications, in certain aspects of the invention, the glass has no more than about 0.1%, more preferably from about 0 (or 0.04) to 0.1%, and even more preferably. 0.01 (or 0.04) to 0.08%, and optimally about 0.03 (or 0.04) to 0.07% of total iron content (Fe ₂ O ₃ - equivalent).

The following examples are intended to illustrate certain aspects of the invention and are not intended to limit the scope of the appended claims.

Example

Computational Fluid Dynamics (CFD) simulations were performed to investigate the use of the oxy-fuel burner shown in Figure 3 to control the oxidation state of iron ions in the soda lime silicate glass melt. About this study using commercial software, Fluent (version 12.1). Compare with three examples:

Example 1: A basic example representing a conventional air-fired floating glass furnace having an ignition rate of 46.89 MW (160 MMBTU/hr) and a soda lime-silicate glass draw rate of 670 MTPD. Figure 4 shows the simulated temperature profile in the centerline plane of the furnace (the temperature in y-axis and the x-axis correspond to the length of the furnace). As shown, this temperature is the middle section of the furnace, the highest around 埠5 and 6. Due to this temperature distribution, natural convection is present in the glass melt, and as a result there is a hot spring zone just downstream of the crucible 6 (as illustrated in Figure 5, where the crucible corresponds to the glass melt above) Rectangular openings and numbered from left to right). Fe ₂ O ₃ (Fe ³⁺ ) entered the filler end at a mass ratio of about 0.03% (left hand side of Figures 4 to 7). When the temperature is increased, Fe ₂ O ₃ is reduced to FeO(Fe ²⁺ ) and O ₂ , and the highest concentrations of FeO and O ₂ are around 埠5 and 6. In this basic embodiment, when a small amount of oxygen is available in the environment, O ₂ in the glass melt diffuses out of the glass, further shifting the reduction, and increasing the concentration of FeO. Although the FeO will be oxidized during the downstream cooling process, the evanescent oxygen still causes FeO to be present at the exit of the glass from the furnace.

Example 2 represents an embodiment in which an oxy-fuel burner is positioned above the hot spring zone of the glass melt (as illustrated in Figure 6). The burner was operated at a stoichiometric ratio of 200%. Additional oxygen from the oxy-fuel burner provides an oxygen-rich environment above the hot spring zone and assists in preventing oxygen from escaping from the melt to the combustion space above the melt. As a result, the glass FeO concentration at the outlet of the furnace was reduced by about 35% when compared with the basic example (Example 1).

Example 3 represents a case in which the oxy-combustor was built on the batch (as illustrated in Figure 7). Because of the lower temperature in the batch region, iron is thermodynamically more stable in its Fe ³⁺ state (and as a result the oxygen concentration in the glass is lower), the reaction between Fe ³⁺ and Fe ²⁺ is slow, And O ₂ thermal activation diffuses into the glass melt very little. Thus the extra oxygen in the environment does not provide any significant benefit in controlling the oxidation of the glass. This simulation shows that the FeO concentration in the final product is not significantly changed relative to the embodiment without the oxy-fuel burner.

These examples show that the desired result in accordance with the present invention can be achieved by placing an oxy-fuel burner above the refining zone and, in particular, adjacent to or near the hot spring zone of the furnace.

Examples 4 and 5

Examples 4 and 5 illustrate the effect of the present invention as a function of iron impurity. The impurity of 0.01% Fe ₂ O ₃ in the raw material of Example 4 (Fig. 8) and Example 5 had an impurity of 0.1% Fe ₂ O ₃ (Fig. 9). By using the oxy-fuel burners according to Examples 1 to 4, two methods of introducing oxygen are used, one of which utilizes an oxy-fuel burner above the hot spring zone and the other on the batch. Figure 8 shows that when the purity is low (about 0.01% by weight), the oxygen concentration in the bulk melt is on the same order of magnitude as the oxygen concentration at the surface (for example, spraying oxygen onto the hot spring zone at a hot spot) The above will have a significant impact on the oxygen concentration). When the impurity is high (about 0.1% by weight), the oxygen concentration in the bulk melt is much higher than the oxygen at the surface. As a result, it is expected that the injection of additional oxygen does not have a significant impact on the oxygen transfer in Example 5/Fig.

The scope of the present invention is not limited by the specific aspects or embodiments disclosed in the embodiments, which are intended to be considered as illustrative of some aspects of the invention, and any functionally equivalent embodiments. All are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will be apparent to those skilled in the art and are intended to come within the scope of the appended claims.

11‧‧‧flat flame oxygen booster

12‧‧‧ heat accumulator

13‧‧‧ glass flow

14‧‧‧Refining machine

15‧‧‧Batch line

16‧‧‧Furn

17‧‧‧Batcher

21‧‧‧ Burning oxygen

22‧‧‧ natural gas

23‧‧‧ Sectional oxygen

24‧‧‧Flame-rich flame zone (on top surface)

25‧‧‧Highly oxidized flame zone (on the bottom)

26‧‧‧ glass

31‧‧‧ Pre-combustor or burner burner brick

32‧‧‧ natural gas

33‧‧‧Oxygen

34‧‧‧ Segmenting oxygen

1 is a schematic plan view of a glass furnace including a flat flame burner located in the refined zone.

2 is a schematic cross-sectional view of a glass furnace including a segmented flat flame burner for oxidizing transition metal cations.

3 is a flat flame burner including a segment of a pre-combustor or burner block that can be used in this inventive furnace or method.

Figure 4 is a schematic diagram illustrating the temperature distribution along the length of the furnace.

Figure 5 is a schematic diagram illustrating the temperature distribution along the length of the furnace.

Fig. 6 is a schematic view illustrating a temperature distribution along the length of the furnace.

Fig. 7 is a schematic view illustrating a temperature distribution along the length of the furnace.

Figure 8 is a graph showing the oxygen concentration as a function of the distance from the glass frit or packing end of the glass furnace.

Figure 9 is a graph showing the oxygen concentration as a function of the distance from the glass frit or packing end of the glass furnace.

Claims (25)

A method of changing the oxidation state of a transition metal ion species in a furnace, wherein: (i) the furnace is set to a continuous operation type comprising a packing end, a discharge end, a melting zone adjacent to the packing end, and the unloading a refining zone in which the material end is in fluid contact; (ii) introducing a glass forming component into the melting zone, traveling along a path from the melting zone to the refining zone, and melting the glass from the refining zone And (iii) the furnace has a combustion energy requirement in a combustion space above both the melting zone and the refining zone; the method comprising the steps of: (A) above the molten glass, away from the filler end The flat flame configuration and a stoichiometric ratio of not less than about 50 percent of the stoichiometric amount inject fuel and primary oxidant into the combustion space, the primary oxidant being a fluid comprising at least 21 mole percent oxygen, the fuel and the primary The oxidant is injected into the combustion space at a rate of about 1000 Torr per second or less; (B) burning the fuel in the combustion space and the primary oxidant to generate heat and including unreacted oxygen and unburned fuel. Combustion reaction (C) at a rate of about 2000 standard Torr per second or lower, injecting a secondary oxidant into the combustion space in a flat configuration below the injection point of the fuel and the primary oxidant, and injecting the secondary oxidant Between the molten glass and the injection point of the fuel and the primary oxidant, the secondary oxidant is a fluid comprising at least about 21 mole percent oxygen; (D) establishing an oxygen-rich oxygen layer in the vicinity of the molten glass, the oxygen-rich oxygen layer having a higher oxygen concentration than the molten glass; (E) transporting oxygen from the oxygen-rich gas layer Into the molten glass, and thereby driving a redox reaction of at least one transition metal ion species in the molten glass to oxidize the transition metal ion species; and (F) burning the secondary oxidant and the unburned fuel To provide additional heat and combustion reaction products in the furnace. The method of claim 1, wherein the molar flow ratio of oxygen to fuel in the primary and secondary oxidants is higher than the molar flow ratio required for complete combustion. The method of claim 1, wherein the primary or secondary oxidant or both are fluids comprising at least 50 mole percent oxygen. A method for reducing a transition metal ion species in a molten glass in a furnace, wherein: (i) the furnace is set to a continuous operation type comprising a packing end, a discharge end, a melting zone adjacent to the packing end, and adjacent a refining zone of the discharge end; (ii) introducing a glass forming component into the melting zone, traveling along a path from the melting zone to the refining zone, and taking out the molten glass from the refining zone; And (iii) burning of the furnace above both the melting zone and the refining zone The space has a combustion energy requirement; the method comprises the steps of: (A) above the molten glass, away from the filler end, in a segmented flat flame configuration and a stoichiometric ratio of no more than about 70 percent of the stoichiometric amount to the combustion space a medium-injected fuel and a primary oxidant, the primary oxidant being a fluid comprising at least 21 mole percent oxygen, the fuel and the primary oxidant being injected into the combustion space at a rate of about 1000 Torr per second or less; (B) Burning the fuel and the primary oxidant in the combustion space to generate heat and a combustion reaction product comprising unburned fuel; (C) at a rate of about 2000 standard Torr or less per second, at the fuel and the primary oxidant Spraying a secondary oxidant into the combustion space in a flat configuration above the injection point, and placing the fuel and the primary oxidant injection point between the molten glass and the injection point of the secondary oxidant, the secondary oxidant a fluid comprising at least about 21 mole percent oxygen; (D) establishing a fuel-rich oxygen layer in the vicinity of the molten glass, the fuel-rich oxygen layer having a lower oxygen concentration than the molten glass; Causing oxygen from the molten glass to the oxygen-rich gas layer and thereby driving a redox reaction of at least one transition metal ion species in the molten glass to reduce the transition metal ion species; F) burning the secondary oxidant with unburned fuel to provide additional heat and combustion reaction products in the furnace. Such as the method of claim 4, wherein the primary and secondary oxidation The molar flow ratio of oxygen to fuel in the agent is lower than the molar flow ratio required for complete combustion. The method of claim 4, wherein the primary or secondary oxidant or both are fluids comprising at least 50 mole percent oxygen. A method of affecting the oxidation state of a transition metal ion species in a molten glass in a furnace having a hot spring zone at the intersection of two convection rings in the molten glass, the method comprising the steps of: above the melting At the glass, the fuel and the main oxidant are sprayed into the furnace, the fuel above the molten glass and the main oxidant are burned to generate heat and combustion reaction products, and the secondary oxidant is introduced into the furnace above the molten glass. Forming a fuel-rich gas layer and an oxygen-rich gas layer near the hot spring zone above the molten glass, and one of the gas layers is located between the molten glass and the gas layer Between the fuel-rich gas layer, the oxygen concentration is less than the molten glass, and the oxygen-rich gas layer has an oxygen concentration greater than the molten glass; and, one of the gas layers is exposed to the Melting the glass to transfer oxygen between the molten glass and one of the gas layers, thereby altering the oxidation state of at least one transition metal ion species in the molten glass. The method of claim 7, wherein the fuel-rich gas layer is one of the gas layers in the vicinity of the molten glass. The method of claim 7, wherein the oxygen-rich gas layer is one of the gas layers in the vicinity of the molten glass. The method of claim 7, wherein the transition metal ion species comprises an iron cation. The method of claim 9, wherein the furnace comprises a hot spring zone. The method of claim 11, wherein the hot spring zone is located within a range of 20% of the furnace length from the hot spot of the furnace. The method of claim 12, wherein the oxygen-rich gas layer is exposed to the molten glass in the hot spring zone. The method of claim 9, further comprising introducing an additional amount of oxygen into the refined zone using an oxygen blow. The method of claim 7, wherein the Fe ₂ O ₃ equivalent concentration in the batch or raw material used to obtain the molten glass is less than about 0.1% by weight. The method of claim 11, wherein the hot spring zone is located in the melting zone. The method of claim 11, wherein the hot spring zone is located within the refined zone. The method of claim 7, further comprising introducing additional oxygen through the oxygen blowing tube. The method of claim 7, wherein the furnace comprises: a filler for making glass, a melting zone, a molten filler, and a refining zone, wherein the refining zone comprises a segmented oxy-fuel burner. The method of claim 19, wherein the refined zone comprises a hot spring zone and the burner is located above the hot spring zone. The method of claim 1, wherein the furnace comprises a hot spring zone at an intersection of two convection rings in the molten glass; and wherein the oxygen-rich gas layer is established in the vicinity of the hot spring zone . The method of claim 4, wherein the furnace comprises a hot spring zone at the intersection of the two convection rings in the molten glass; and wherein the fuel-rich gas layer is located in the vicinity of the hot spring zone. A method of altering an oxidation state of a transition metal ion species in a molten glass in a furnace, comprising the steps of: injecting a fuel and a primary oxidant in a flat flame configuration above the molten glass, the primary oxidant comprising at least about 21 mole percent Oxygen in an amount that provides at least about 50 percent of the stoichiometric oxygen demand of the fuel and no more than about 186 percent; and molten glass that is sprayed into the furnace in a flat configuration with the secondary oxidant and the fuel and the primary oxidant Between the injection points, thereby establishing an oxygen-rich gas layer adjacent to the molten glass, the secondary oxidant comprising at least 21 mole percent of oxygen, when combined with the primary oxidant, the amount provides the chemistry of the fuel The metered oxygen demand is at least about 200 percent. A method of reducing a transition metal ion species in a molten glass in a furnace, comprising the steps of: injecting a fuel and a primary oxidant in a flat flame configuration above the molten glass, the primary oxidant comprising at least about 21 mole percent oxygen, The amount may provide a stoichiometric oxygen demand of the fuel of at least about 18 percent and no more than about 70 percent; and injecting the secondary oxidant into the furnace in a flat configuration such that the fuel and the primary oxidant injection point are located in the melt Between the molten glass and the injection point of the secondary oxidant, thereby establishing an oxygen-rich gas layer adjacent to the molten glass, the secondary oxidant comprising at least 21 mole percent of oxygen, when combined with the primary oxidant, The amount can provide at least about 80 percent of the stoichiometric oxygen demand of the fuel. A method for changing an oxidation state of a transition metal ion species in a molten glass in a furnace, the method comprising: providing two burners on opposite walls of the longitudinal direction of the furnace; and passing the burners, the molten glass in the furnace Spraying fuel and a primary oxidant in a flat flame configuration above, the primary oxidant comprising at least about 21 mole percent oxygen, the amount providing a stoichiometric oxygen demand of the fuel of at least about 18 percent and no more than about 186 percent; Spraying the secondary oxidant in a flat configuration into the furnace adjacent to the fuel and the flame formed by the primary oxidant, thereby establishing a fuel-rich gas layer and an oxygen-rich gas on the molten glass a layer, the secondary oxidant comprising at least 21 mole percent of oxygen; wherein each of the burners is positioned such that the fuel-rich gas layer is adjacent to the molten glass, the primary oxidant and the secondary oxidant provide a total The amount of oxygen does not exceed 95% of the stoichiometric oxygen demand of the fuel; and wherein each burner is positioned such that the oxygen-rich gas layer is adjacent to the molten glass It provided the primary oxidizer and the secondary oxidizer 110 for at least a percentage of the total oxygen amount stoichiometric oxygen requirement of the fuel.