METHOD FOR HEATING A GLASS MELT

Description

[0001] The invention relates to a method for heating a flowing molten glass in a feeder channel enclosed by side walls and a ceiling, into which a plurality of fuel lances and oxidizing agent lances arranged at intervals from one another in the flow direction of the molten glass open above the molten glass, through which fuel or oxidizing agent is supplied and brought to react with each other in the feeder channel.

[0002] Feeders are used in glass production, primarily to transport molten gas from a melting furnace to further processing. The molten glass (glass melt) passing through the feeder channel is, for example, formed into droplets at the end of the feeder in the feeder head by cooled blades. These droplets are then processed into the finished glass product in subsequent steps or used in other ways for further processing.

[0003] To ensure high-quality glass production, the temperature conditions in the feeder must be precisely controlled. The feeder channel is therefore typically divided into several zones, arranged sequentially in the direction of glass flow, each with its own temperature control loop. Heating of the glass molten glass in the feeder channel is usually achieved either electrically using heating resistors or chemically, using burners or lances through which a fuel and an oxidizer are introduced into the feeder channel and reacted.

[0004] In the context of the present invention, a "burner" is understood to be a device in which fuel and oxidizing agent are introduced together—either via separate feeds within a burner head or as a mixture via a common feed connected to the fuel and oxidizing agent feed lines—into a treatment chamber, in particular a feed channel. In contrast, a "lance" is defined as a device with a usually tubular feed line by means of which only one medium—in the context of the present invention, fuel or oxidizing agent—is introduced into a treatment chamber (feed channel).

[0005] Currently, burners are most commonly used to heat a feeder. These burners, spaced apart from one another in the side walls or ceiling of the feeder channel (viewed in the direction of glass flow), are typically fuel-air burners or fuel-oxygen burners. They generally have either parallel feeds for fuel and oxidizer, which open together into the feeder channel at a single burner end, or the fuel and oxidizer are mixed within the burner or even before reaching it, and the resulting mixture is fed into the feeder channel via a common feed. In all cases, a flame forms immediately in front of the burner's outlet, and its heat radiation warms the surface of the molten glass.The burners are usually arranged in the side walls of the feed channel such that the flames emanating from them are essentially parallel to the surface of the molten glass and perpendicular to its flow direction. Arrangements of this type are described, for example, in US 3,523,781 A1, US 5,417,732 B1, US 5,814,121 B1, and WO 2015 048,405 A1.

[0006] To ensure that the glass melted in the furnace flows smoothly through the feeder, high temperatures of approximately 1100°C to 1400°C are required. A homogeneous temperature distribution within the feeder channel is crucial for the quality of the glass produced. To prevent localized overheating, feeders using fuel-air burner technology require a relatively large number of burners arranged lengthwise along the feeder channel, which, however, represents a significant cost factor.

[0007] Due to their improved heat transfer, based primarily on more intense thermal radiation resulting from a lower proportion of ballasts such as nitrogen in the furnace atmosphere, oxyfuel burners enable more uniform heating of the material in the feeder compared to air-fuel burners, thus improving temperature homogeneity in the glass melt. The elimination of nitrogen ballast in the exhaust gas significantly reduces fuel consumption, typically by more than half. At the same time, the number of burners per unit of feeder duct can be reduced. However, the number of burners per unit of duct cannot be reduced arbitrarily, as this would lead to inhomogeneities in the temperature distribution. Consequently, the use of a larger number of relatively small oxyfuel burners is necessary; these are expensive to purchase and also tend to generate undesirable turbulent flows in the flame.Local overheating cannot be ruled out when using fuel-oxygen burners, especially with narrow feeder channels and / or in the area of ​​the burner mouth.

[0008] In contrast, WO 9406723 A1 discloses a feeder channel in which lances are used to supply fuel and oxidizer, respectively. These lances are arranged alternately in the side walls of the feeder channel, viewed in the direction of glass flow. The lances are offset from one another in the two side walls, so that each fuel lance faces an oxidizer lance. Longitudinally, the lances are spaced far enough apart that the media flows do not mix in the immediate vicinity of the side walls, and thus no combustion occurs there. Instead, the media flows exiting the lances meet in the center of the feeder channel, forming a turbulent flame cloud that is intended to heat the glass melt in the feeder channel uniformly.

[0009] A similar arrangement with an alternating sequence of fuel and oxidizer lances in a feeder channel is shown in EP 3 517 509 A1. The reactants exiting the lances mix in the feeder channel to form a cloud of an ignitable gas mixture, which, upon ignition, causes uniform heating.

[0010] Compared to installing burners, these two items are far more cost-effective; however, a disadvantage is that the concentrated combustion in the center of the feeder duct locally reduces the density of the furnace atmosphere. The resulting thermal lift drives the hot exhaust gases, as well as the flame cloud itself, towards the top of the feeder duct, thereby reducing the heat transfer to the molten glass and causing heat losses, while simultaneously subjecting the duct ceiling material to considerable thermal stress.

[0011] The invention is therefore based on the objective of providing a method for heating molten glass in a feeder channel that avoids the disadvantages of the prior art.

[0012] This problem is solved in a process of the type and purpose mentioned above by generating a fuel jet entering the feeder channel in a substantially laminar manner at each fuel lance for the combustion of the fuel with the oxidizing agent, and reacting with the oxidizing agent present in the feeder channel, forming flames.

[0013] According to the invention, the fuel is introduced from the fuel lances into the feeder channel with a flow that is as laminar as possible, where it forms a largely laminar fuel jet that prevents premature turbulent mixing of the fuel and oxidizer. During combustion, this results in slender, straight flames of high stability, each originating at a distance from the nozzle of a fuel lance and extending deep into the feeder channel, preferably without touching each other or the opposite wall of the feeder channel. In this way, the material of the walls and ceiling of the feeder channel is protected, and the formation of a turbulent flame cloud in the feeder channel, and the associated disadvantages, are avoided.The individual flames that form in front of the fuel lances lead to efficient and uniform heating of the glass flow in the feeder while simultaneously resulting in low NO x emissions.

[0014] Similar to the subject matter of WO 9406723 A1, the present invention also employs lances for fuel and oxidizer, which are arranged at intervals from one another in the side walls of the feeder channel – viewed in the direction of glass flow. However, according to the invention, a flame cloud is not formed. Similar to articles in which burners are used to heat the feeder channel, heating is achieved by means of individual, spaced-apart flames. The structure of the flames differs fundamentally from those formed by burners, however, since the oxygen required for combustion is not introduced into the flame core simultaneously with the fuel, but rather originates from oxidizer lances spaced apart from the fuel lances and thus diffuses into the fuel jet exiting the fuel lances from the surrounding area.Combustion therefore only occurs in a comparatively thin shear zone at the edge of the flame. The flame volume is thus generally substoichiometric and consists predominantly of fuel in its interior – although this proportion decreases along the length of the flame. Only in the region of the flame tip are the fuel and oxidizer mixed so intensively that complete combustion of the remaining fuel occurs.

[0015] The shape of the flames is primarily influenced by the cross-sectional area of ​​the fuel lance outlets and the fuel flow velocity. A comparatively high exit velocity and a relatively small cross-sectional area of ​​the fuel lance outlets should be selected to generate the narrowest possible flames and to prevent combustion from starting too close to the feeder channel walls, which would cause excessive thermal stress on the feeder walls. Preferably, the fuel flow exiting the fuel lance, i.e., at the fuel lance outlet, has a Reynolds number (Re) of < 10,000, preferably Re < 2,300. In addition to the fuel, the oxidizer should preferably also be introduced into the feeder channel with a laminar flow, which likewise has a Reynolds number of < 10,000, preferably Re < 2,300.However, the Reynolds number should not be less than Re = 500 for either the fuel or the oxidizer, otherwise the comparatively slow flow of the escaping gas and the flames that form will rise to the feeder ceiling, leading to a reduction in process efficiency and increased thermal stress on the wall material.

[0016] A funnel-shaped widening of the fuel lance outlets is disadvantageous; instead, according to the invention, cylindrical fuel lances are preferred, or those whose flow cross-section tapers towards the outlet. A particularly advantageous embodiment provides fuel lances with a substantially circular or oval outlet, the cross-sectional area of ​​which is less than 100 mm², preferably between 0.1 and 25 mm². Such fuel lances are particularly suitable for installation in existing systems where a feeder channel is already equipped with openings for installing burners, but which, for the purposes of the present invention, are fitted with fuel or oxidizer lances. The oxygen lances preferably have an outlet with a cross-sectional area of ​​less than 200 mm², preferably between 0.2 and 50 mm².

[0017] Advantageously, the fuel and oxidizer lances are arranged alternately and offset from each other in each wall, so that fuel lances and oxidizer lances are always opposite each other in the feeder channel. This largely prevents the flames projecting into the feeder channel from both side walls from overlapping. Furthermore, the flame tips are intensively supplied with oxidizer, thus promoting efficient and complete combustion of the fuel.

[0018] Air, oxygen-enriched air with an oxygen content above 21 vol.% or oxygen with a preferred purity of above 90 vol.% is preferably used as the oxidizing agent, and a gaseous or liquid fuel, for example natural gas or hydrogen, is preferably used as the fuel.

[0019] A device suitable for carrying out the method according to the invention comprises a feed channel with an inlet region and an outlet region, through which molten glass is transported during operation of the device, thereby defining a flow direction. The feed channel is heated by the separate supply of fuel and oxidizer via fuel and oxidizer lances, respectively. These lances are arranged at intervals from one another in a side wall, both side walls, and / or the ceiling of the feed channel in the direction of flow of the molten glass.At least the fuel lances, and preferably also the oxidizer lances, are designed as cylindrical tubes with a round, elliptical, or oval inner cross-section, wherein the fuel lances have a cross-sectional area preferably less than 100 mm², particularly preferably between 0.1 and 25 mm², and the oxygen lances have a cross-sectional area preferably less than 200 mm², particularly preferably between 0.2 and 50 mm². Furthermore, the fuel lances and / or the oxygen lances are preferably operatively connected to a control system that allows regulation of the flow rate and velocity of the fuel or oxidizer exiting each fuel lance and, in particular, enables the formation of a largely laminar fuel jet penetrating the interior of the feeder channel, which is not, or only minimally, disturbed by turbulent flows in its surrounding area.

[0020] The drawings will be used to explain an embodiment of the invention in more detail. The schematic views show: Fig. 1: A device for carrying out the method according to the invention in a cross-section perpendicular to the flow direction of the molten glass, Fig. 2: The device made of Fig. 1 in a sectional view along plane II-II in Fig. 1 and Fig. 3: A fuel lance of the device made of Fig. 1 and 2 in longitudinal section.

[0021] Device 1 is a feeder, shown here only in part, for transporting and heating molten glass. For example, it is the segment of a feeder in which molten glass at a temperature of, say, 1100°C to 1600°C is conveyed from a melting furnace (not shown here) to a feeder head (also not shown here), where the glass molten in the furnace is cut into drops and fed to a further processing stage.

[0022] The segment of the device 1 shown here comprises a feeder channel 2, which is enclosed by a base 3, side walls 4, 5 and a cover 6 made of a refractory material. The feeder channel 2 serves to transport molten glass 7, which flows through the feeder channel 2 towards the [unclear] in the Fig. 2 The arrow 8 shown leads from an input area 9 to an output area 10 of the feeder channel 2.

[0023] Feed channel 2 is heated by the combustion of a fuel, for example natural gas or hydrogen, with an oxidizer, for example air or oxygen with a purity of 90% by volume or more. The fuel is supplied from a source not shown here via feed lines 11, 12, which are connected to a plurality of fuel lances 13a, 13b, 13c, 13d, 13e, 13f. The oxidizer is supplied from a source also not shown here, for example an oxygen tank, via feed lines 14, 15, which are connected to oxidizer lances 16a, 16b, 16c, 16d, 16e, 16f.The essentially cylindrical lances 13a, 13b, 13c, 13d, 13e, 13f; 16a, 16b, 16c, 16d, 16e, 16f open into the feeder channel 2 in the embodiment shown here essentially perpendicular to the flow direction of the molten glass 7 (arrow 8), but can also be inclined, in particular towards the melt and / or in or against the flow direction 8 of the molten glass 7. The fuel lances 13a, 13b, 13c, 13d, 13e, 13f and the oxidizing agent lances 16a, 16b, 16c, 16d, 16e, 16f are arranged alternately in each of the side walls 4, 5, i.e. in the flow direction of the glass melt 7, fuel lances 13a, 13b, 13c, 13d, 13e, 13f and oxidizing agent lances 16a, 16b, 16c, 16d, 16e, 16f alternate with each other.The fuel lances 13a, 13b, 13c and the oxidizing agent lances 16a, 16b, 16c are arranged in the side wall 4 offset from the fuel lances 13d, 13e, 13f and the oxidizing agent lances 16d, 16e, 16f in the side wall 5 such that one fuel lance 13a, 13b, 13c, 13d, 13e, 13f and one oxidizing agent lance 16a, 16b, 16c, 16d, 16e, 16f open opposite each other into the feeder channel 2.

[0024] During operation of the device 1, fuel is introduced into the feed channel 2 via the fuel lances 13a, 13b, 13c, 13d, 13e, 13f, and oxidizer via the oxidizer lances 16a, 16b, 16c, 16d, 16e, 16f, in a stoichiometric ratio. Care is taken to ensure that at least the fuel flow at the outlet of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f enters the feed channel 2 as a free jet that is as laminar as possible. To generate the laminar flow, the fuel is preferably introduced into the feed channel 2 at a Reynolds number of Re < 10000, preferably between Re = 500 and Re = 2300.The laminar flow of the fuel results in only a slight mixing with the oxidizing agent supplied from the oxidizing agent lances 16a, 16b, 16c, 16d, 16e, 16f; significant mixing occurs only in a shear zone around a free jet consisting of at least nearly pure fuel, which forms in front of the nozzle opening of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f.

[0025] To initiate combustion, the atmosphere inside feeder channel 2 is heated to a temperature above the ignition temperature of the fuel-oxidizer mixture before the fuel and / or oxidizer is introduced. The largely laminar flow of the fuel exiting fuel lances 13a, 13b, 13c, 13d, 13e, 13f results in combustion only within the specified shear range. Slender, stable flames 17 are produced, which begin spaced apart in front of the openings of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f, extend deep into the interior of the feeder channel 2 and end at a flame tip 18 - shown here for clarity only at the flame 17 in front of the opening of the fuel lance 13d - at which the oxidizing agent has completely penetrated the fuel jet and consequently complete combustion of the remaining fuel takes place.Due to their elongated, narrow shape, adjacent flames 17 do not touch or only touch slightly.

[0026] The quantities and flow rates of the fuel and oxidizer streams exiting the lances (13a, 13b, 13c, 13d, 13e, 13f; 16a, 16b, 16c, 16d, 16e, 16f) are continuously monitored and controlled at control valves 19, 20, 21, 22 by means of a control unit (not shown here) as a function of measured parameters, such as the temperature in the feeder channel 2 or in the glass melt 7, or the NOx content in the exhaust pipe 24. In particular, the control should be such that the flames 17 terminate with their flame tips 18 at a distance from the respective opposite side wall 5, 4, and that a specific, predetermined temperature range in the feeder channel 2 or in the glass melt 7 is neither exceeded nor fallen below.

[0027] Instead of or in addition to the arrangement of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f and the oxidizing agent lances 16a, 16b, 16c, 16d, 16e, 16f in the side walls 4,5, lances for fuel and oxidizing agent - also in alternating order - can also be provided in the ceiling 6, as indicated by the lance 23. Likewise, within the scope of the invention, it is conceivable that the fuel lances 13a, 13b, 13c, 13d, 13e, 13f and the oxidizing agent lances 16a, 16b, 16c, 16d, 16e, 16f are arranged in the side walls 4, 5 and / or the ceiling 6 in such a way that the material flows emanating from them are directed at least with one directional component parallel or opposite to the flow direction 8 of the glass melt 7.

[0028] The construction of the front section of a fuel lance 13a, 13b, 13c, 13d, 13e, 13f is shown using the fuel lance 13a as an example in Fig. 3The fuel lance 13a is shown as a cylindrical tube with, for example, a circular inner cross-section, passing through a feedthrough 25 in the side wall 4 (shown here only in section) and terminates at its end with a nozzle opening 26 that is approximately flush with the inner wall of the side wall 4. The fuel is fed through the fuel lance 13a in the direction of arrow 27. The cylindrical design of the fuel lance 13a and its inner cross-section of less than 100 mm² allow it to be installed even in existing feed channels equipped with feedthroughs 25 designed for small burners. The oxidizer lances 16a, 16b, 16c, 16d, 16e, 16f can be similarly designed as cylindrical tubes, their inner cross-section preferably being less than 200 mm².

[0029] The device 1 results in very uniform heating of the glass melt 7 in the feeder channel 2 and very low NOₓ emissions. The formation of a turbulent flame cloud in the channel center is avoided, thereby increasing the efficiency of the process. Compared to the use of burners, such as oxyfuel burners, there is a significant cost saving with regard to the installed hardware; in addition, the thermal stress on the side walls 4, 5 and the ceiling 6 of the feeder channel is considerably lower.

[0030] Furthermore, the invention is not limited to the arrangement of lances installed alternately and / or offset from each other as shown in the exemplary embodiment, but also includes other arrangements of lances for fuel and for oxidizing agent spaced apart from each other in the longitudinal direction of a feeder channel, with which the formation of flames separate from each other in the feeder channel can be achieved. Reference symbol list

[0031] 1 Device 2 Channel 3 Bottom 4 Side wall 5 Side wall 6 Ceiling 7 Glass melt 8 Arrow 9 Inlet area 10 Outlet area 11 Fuel supply line 12 Fuel supply line 13a-f Fuel lance 14 Oxidizing agent supply line 15 Oxidizing agent supply line 16a-f Oxidizing agent lance 17 Flame 18 Flame tip 19 Control valve 20 Control valve 21 Control valve 22 Control valve 23 Lance 24 Exhaust pipe 25 Feedthrough 26 Nozzle opening (of the fuel lance) 27 Arrow

Claims

1. Method for heating a flowing glass melt in a feeder channel (2) encased by side walls (4, 5) and a ceiling (6), where a plurality of fuel lances (13a, 13b, 13c, 13d, 13e, 13f), arranged with spacing from one another in the flow direction of the glass melt (7), and oxidant lances (16a, 16b, 16c, 16d, 16e, 16f) open into said channel above the glass melt (7), where fuel and oxidant, respectively, are supplied through said lances and reacted with one another in the feeder channel (2), characterized in that for the combustion of the fuel with the oxidant, at each fuel lance (13a, 13b, 13c, 13d, 13e, 13f) a fuel material jet is generated which enters the feeder channel (2) substantially laminarly and is reacted with oxidant present in the feeder channel (2) to form respectively a flame (17).

2. Method according to Claim 1, characterized in that for the generation of the flame (17), the flow of the fuel and / or of the oxidant on emergence from the fuel lance (13a, 13b, 13c, 13d, 13e, 13f) has a Reynolds number Re of Re < 10000, preferably Re < 2300.

3. Method according to Claim 1 or 2, characterized in that for the generation of the flame (17), the flow of the fuel and / or of the oxidant on emergence from the fuel lance (13a, 13b, 13c, 13d, 13e, 13f) has a Reynolds number Re of Re > 500.

4. Method according to any of the preceding claims, characterized in that the fuel lances (13a, 13b, 13c, 13d, 13e, 13f) have a substantially circular, elliptical or oval opening aperture (26) whose cross-sectional area is less than 100 mm2, preferably between 0.1 and 25 mm2.

5. Method according to any of the preceding claims, characterized in that the oxidant lances (16a, 16b, 16c, 16d, 16e, 16f) have a substantially circular or oval opening aperture whose cross-sectional area is less than 200 mm2, preferably between 0.2 and 50 mm2.

6. Method according to any of the preceding claims, characterized in that fuel lances (13a, 13b, 13c, 13d, 13e, 13f) and oxidant lances (16a, 16b, 16c, 16d, 16e, 16f) are arranged in each side wall (4, 5) of the feeder channel (2) in a row in alternation with one another and the rows in both side walls (4, 5) are arranged with offsetting from one another.

7. Method according to any of the preceding claims, characterized in that the oxidant employed comprises air, oxygen-enriched air or oxygen.