METHOD FOR HEATING MOLTEN GLASS

Abstract

The invention relates to a method for heating flowable molten glass in a feed channel which is enclosed by lateral walls and a cover and into which a plurality of fuel lances and oxidizing agent lances that are mutually spaced in the flow direction of the molten glass open above the molten glass, fuel or an oxidizing agent being supplied through said lances and being brought into reaction with each other in the feed channel. The invention is characterized in that in order to combust the fuel with the oxidizing agent, a flame is produced in front of the opening of each fuel lance, said flame being designed such that adjacent or opposite flames do not contact one another.

Claims

1. A method for heating a flowing glass melt in a feeder channel encased by side walls and a ceiling, where a plurality of fuel lances, arranged with spacing from one another in the flow direction of the glass melt, and oxidant lances open into said channel above the glass melt, where fuel and oxidant, respectively, are supplied through said lances and reacted with one another in the feeder channel, wherein for the combustion of the fuel with the oxidant, at each fuel lance a fuel material jet is generated which enters the feeder channel substantially laminarly and is reacted with oxidant present in the feeder channel to form respectively a flame.

2. The method as claimed in claim 1, wherein for the generation of the flame, the flow of the fuel and/or of the oxidant on emergence from the fuel lance has a Reynolds number Re of Re<10000, preferably Re<2300.

3. The method as claimed in claim 1, wherein for the generation of the flame, the flow of the fuel and/or of the oxidant on emergence from the fuel lance has a Reynolds number Re of Re>500.

4. The method as claimed in claim 1, wherein the fuel lances have a substantially circular, elliptical or oval opening aperture whose cross-sectional area is less than 100 mm.sup.2, preferably between 0.1 and 25 mm.sup.2.

5. The method as claimed in claim 1, wherein the oxidant lances have a substantially circular, elliptical or oval opening aperture whose cross-sectional area is less than 200 mm.sup.2, preferably between 0.2 and 50 mm.sup.2.

6. The method as claimed in claim 1, wherein fuel lances and oxidant lances are arranged in each side wall of the feeder channel in a row in alternation with one another and the rows in both side walls are arranged with offsetting from one another.

7. The method as claimed in claim 1, wherein the oxidant employed comprises air, oxygen-enriched air or oxygen.

8. An apparatus for implementing the method as claimed in claim 1, having a feeder channel encased by side walls and a ceiling, where a plurality of fuel lances, arranged with spacing from one another in the flow direction of the glass melt (7), and oxidant lances open into said channel, where fuel and oxidant, respectively, are supplied through said lances and reacted with one another in the feeder channel, wherein the fuel lances are embodied as cylindrical pipes having a round, elliptical or oval internal cross section with an internal cross-sectional area of less than 100 mm.sup.2, preferably between 0.1 mm.sup.2 and 25 mm.sup.2.

9. The apparatus as claimed in claim 8, wherein the oxidant lances are embodied as cylindrical pipes having a round, elliptical or oval cross section with an internal cross-sectional area of less than 200 mm.sup.2, preferably between 0.2 and 50 mm.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An exemplary embodiment of the invention is elucidated in more detail with the drawings. In schematic views,

[0021] FIG. 1: shows an apparatus for implementing the method of the invention in a cross section perpendicular to the flow direction of the glass melt,

[0022] FIG. 2: shows the apparatus from FIG. 1 in a sectional view along the plane II-II in FIG. 1, and

[0023] FIG. 3: shows a fuel lance of the apparatus from FIGS. 1 and 2 in longitudinal section.

DETAILED DESCRIPTION

[0024] The apparatus 1 is a feeder, represented here only in a detail, for transporting and heating a glass melt. The detail concerned is, for example, the segment of a feeder in which molten glass with a temperature of 1100° C. to 1600° C., for example, is passed from a melting furnace, not represented here, to a feeder head, again not represented here, at which the glass melted in the melting furnace is chopped into droplets and supplied for further processing.

[0025] The segment of the apparatus 1 that is represented here comprises a feeder channel 2, which is encased by a floor 3, side walls 4, 5 and a ceiling 6 composed of a refractory material. The purpose of the feeder channel 2 is to transport a glass melt 7, which is routed by the feeder channel 2 in the direction of the arrow 8 shown in FIG. 2 from an inlet region 9 to an outlet region 10 of the feeder channel 2.

[0026] The feeder channel 2 is heated by combustion of a fuel, such as natural gas or hydrogen, with an oxidant, such as air or oxygen with a purity of 90 vol % or more, for example. The fuel is supplied from a source—not shown here—via supply lines 11, 12, which are in fluidic communication with a plurality of fuel lances 13a, 13b, 13c, 13d, 13e, 13f. The oxidant is supplied from a source—likewise not shown here—such as an oxygen tank, for example, via supply lines 14, 15, which are in fluidic communication with oxidant lances 16a, 16b, 16c, 16d, 16e, 16f. The substantially cylindrical lances 13a, 13b, 13c, 13d, 13e, 13f; 16a, 16b, 16c, 16d, 16e, 16f in the exemplary embodiment shown here open substantially perpendicularly to the flow direction of the glass melt 7 (arrow 8) into the feeder channel 2, but may also be inclined, having more particularly an arrangement inclined in the direction of the melt and/or in or against the flow direction 8 of the glass melt 7. The fuel lances 13a, 13b, 13c, 13d, 13e, 13f and the oxidant lances 16a, 16b, 16c, 16d, 16e, 16f are arranged in alternation in each of the side walls 4, 5; in other words, in the flow direction of the glass melt 7, fuel lances 13a, 13b, 13c, 13d, 13e, 13f and oxidant lances 16a, 16b, 16c, 16d, 16e, 16f alternate with one another.

[0027] The fuel lances 13a, 13b, 13c and the oxidant lances 16a, 16b, 16c here are arranged in the side wall 4 with offsetting from the fuel lances 13d, 13e, 13f and the oxidant lances 16d, 16e, 16f in the side wall 5 in a manner such that in each case one fuel lance 13a, 13b, 13c, 13d, 13e, 13f and one oxidant lance 16a, 16b, 16c, 16d, 16e, 16f open out oppositely into the feeder channel 2.

[0028] In the operation of the apparatus 1, fuel is introduced via the fuel lances 13a, 13b, 13c, 13d, 13e, 13f and oxidant via the oxidant lances 16a, 16b, 16c, 16d, 16e, 16f into the feeder channel 2 in a stoichiometric ratio to one another. Here it is ensured that at least the fuel flow at the opening aperture of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f flows into the feeder channel 2 as a very largely laminar free jet. To generate the laminar flow, the fuel is carried into the feeder channel 2 preferably with a Reynolds number of Re<10000, preferably between Re=500 and Re=2300. As a result of the laminar flow of the fuel, there is only slight mixing with the oxidant supplied from the oxidant lances 16a, 16b, 16c, 16d, 16e, 16f; significant mixing takes place only in a shear region around a free jet consisting of at least virtually pure fuel, this jet forming in front of the opening aperture of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f.

[0029] In order to set the combustion in train, the atmosphere in the interior of the feeder channel 2, before the introduction of the fuel and/or of the oxidant, is brought to a temperature which is above the ignition temperature of the mixture of fuel and oxidant, for example. The largely laminar flow of the fuel emerging from the fuel lances 13a, 13b, 13c, 13d, 13e, 13f leads to combustion only within the stated shear region. This results in slim, stable flames 17 which begin with a spacing in front of the opening apertures of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f, project deeply into the interior of the feeder channel 2, and at a flame tip 18—shown here, for reasons of clarity, only at the flame 17 in front of the opening of the fuel lance 13d—at which the oxidant has completely penetrated the fuel jet and consequently there is complete combustion of the remaining fuel. Because of their narrow, elongated shape, adjacent flames 17 make no contact or only minimal contact with one another.

[0030] The quantities and flow rates of the streams of fuel and oxidant emerging at the lances (13a, 13b, 13c, 13d, 13e, 13f; 16a, 16b, 16c, 16d, 16e, 16f) are continually monitored and regulated at adjustment valves 19, 20, 21, 22 by means of a control unit, not shown here, as a function of measured parameters, such as, for example, a temperature in the feeder channel 2 or in the glass melt 7 or the NOx content in the exhaust gas line 24. The regulation ought in particular to take place in such a way that the flame tips 18 of the flames 17 end with a spacing from the respectively opposite side wall 5, 4 and that the temperature range does not overshoot or undershoot a defined, specified temperature range in the feeder channel 2 or in the glass melt 7.

[0031] Instead of or in addition to the arrangement of the fuel lances 13a, 13b, 13c, 13d, 13e, 13f and the oxidant lances 16a, 16b, 16c, 16d, 16e, 16f in the side walls 4, 5, lances for fuel and oxidant—likewise in alternating order—may also be provided in the ceiling 6, as indicated by the lance 23. Within the realm of the invention it is also conceivable for the fuel lances 13a, 13b, 13c, 13d, 13e, 13f and the oxidant lances 16a, 16b, 16c, 16d, 16e, 16f to be arranged in the side walls 4, 5 and/or in the ceiling 6 in such a way that the streams of material emanating from them are directed at least with a directional component parallel or opposite to the flow direction 8 of the glass melt 7.

[0032] The structure of the front portion of a fuel lance 13a, 13b, 13c, 13d, 13e, 13f is shown using the example of the fuel lance 13a in FIG. 3. The fuel lance 13a takes the form of a cylindrical pipe having an internal cross section which is circular for example, is routed through a passage 25 in the side wall 4—of which only portions are shown here—and opens out at the end face with an opening aperture 26 which finishes approximately flush with the inner wall of the side wall 4. The fuel is conveyed in the direction of the arrow 27 through the fuel lance 13a. The cylindrical structure of the fuel lance 13a and its internal cross section of less than 100 mm.sup.2 in area allow it to be installed even in existing feeder channels which are equipped for passages 25 designed for small burners. The oxidant lances 16a, 16b, 16c, 16d, 16e, 16f may be embodied, similarly, as cylindrical pipes, in which case their internal cross section is preferably less than 200 mm.sup.2.

[0033] The apparatus 1 of the invention leads to a very uniform heating of the glass melt 7 in the feeder channel 2 and to very low NO.sub.x emissions. The development of a turbulent flame cloud in the channel center is avoided, so boosting the efficiency of the method. In comparison to the use of burners, such as oxyfuel burners, for example, there is a considerable cost saving in terms of the installed hardware, and also the thermal load on the side walls 4, 5 and the ceiling 6 of the feeder channel is considerably lower.

[0034] The invention, in any case, is not confined to the arrangement of lances installed in alternation and/or with offsetting from one another as shown in the exemplary embodiment, but instead also embraces other arrangements of lances for fuel and for oxidant, arranged with spacing from one another in the longitudinal direction of a feeder channel, and enabling the development in the feeder channel of flames which are separate from one another.

LIST OF REFERENCE SIGNS

[0035] 1 apparatus [0036] 2 channel [0037] 3 floor [0038] 4 side wall [0039] 5 side wall [0040] 6 ceiling [0041] 7 glass melt [0042] 8 arrow [0043] 9 inlet region [0044] 10 outlet region [0045] 11 supply line for fuel [0046] 12 supply line for fuel [0047] 13a-f fuel lance [0048] 14 supply line for oxidant [0049] 15 supply line for oxidant [0050] 16a-f oxidant lance [0051] 17 flame [0052] 18 flame tip [0053] 19 adjustment valve [0054] 20 adjustment valve [0055] 21 adjustment valve [0056] 22 adjustment valve [0057] 23 lance [0058] 24 exhaust gas line [0059] 25 passage [0060] 26 opening aperture (of the fuel lance) [0061] 27 arrow