Abstract:
A glass melting plant refiner for thermal post-treatment of a glass melt containing bubbles, in particular for the production of fiberglass. To reduce the glass melt bubble content produced by submerged combustion burners, a refiner forms a glass melt tank, the glass melt flowing through the tank in a transport direction. The tank has a floor, side walls and a superstructure. A barrier, forming a raised floor part, runs essentially in the transport direction. The barrier forms, at each lateral side, a channel-shaped constriction with the side walls, a width of each constriction transverse to the transport direction being at most 0.45 times the tank width. At least one first fossil fuel heater heats the glass melt from above. At least one second electrical heating device, in each side wall and/or in the floor of the tank in the region of each constriction, extends into the glass melt.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the German patent application No. 10 2016 103 755.9 filed on Feb. 3, 2016, the entire disclosures of which are incorporated herein by way of reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a glass melting plant, in particular for the production of fiberglass, having a melt crucible, raw materials being supplied to the melt crucible by a supply device, and melted there. 
         [0003]    Glass melting plants can be heated by submerged combustion heaters. The advantage of such a glass melting plant is that a high melting performance is achieved in a small space. 
         [0004]    Such a glass melting plant has already been described in U.S. Pat. No. 3,260,587. This glass melting plant has a melt chamber having submerged combustion heaters into which the raw material is delivered via a supply device. The submerged combustion heaters are situated completely within the liquid glass. Connected to the outlet of the melt chamber is a refiner segment, and a weir (raised part) extends over the entire width of the melt chamber in the area of the outlet. 
         [0005]    In such melting plants having submerged combustion heaters, the problem frequently arises that the glass melt contains a high portion of gas bubbles. Here there is the theory that the bubble content arises from a reaction of the fossil fuel and the oxidant of the submerged combustion heater. The exothermic reaction of the two gaseous materials takes place inside the glass melt, and as reaction product from the fuel and the oxidant (as a rule, oxygen) there result carbon dioxide and water vapor. These reaction products form fine bubbles having a diameter of from 0.1 mm to 1 mm, and the bubbles reduce the quality of the glass melt. A gas portion in the glass melt of up to 30 vol. % has been reported. 
         [0006]    In the use of conventional melting technology, depending on the product, the requirement with regard to bubble content is described by the measurement quantity number of bubbles per weight of the sample. Required quality levels of the glass product are between 0.1 bubble/1000 g glass and 100 bubbles/100 g glass. Frequently, the size of the bubbles also has to be within a specified range. In glass melting plants that are heated by submerged combustion heaters, such quality requirements often cannot be met. Therefore, this melting technology is frequently limited to the production of fiberglass, or glass and stone wool. These products are used for the production of insulating mats in which the bubble content of the fibers does not have a disadvantageous effect. 
         [0007]    In order to make it possible to use the melting technology that is advantageous with regard to space requirements and melting performance for further applications as well, or to increase the quality of the produced glass, it is desirable to reduce the bubble content of the glass melt. For this purpose, in the glass melting plant known from U.S. Pat. No. 3,606,825, a refiner zone is provided in order to remove or release bubbles or other gaseous inclusions from the glass melt. The glass melting plant having submerged combustion heaters described in US 2004/0224833 A1 also has a refiner region connected to the glass melting tank. The glass melt heated by the submerged combustion heaters is, however, produced only in a side stream, and is supplied to the main stream glass melt, in particular, in the area of a feeder that is provided with mechanical homogenizing units for mixing the glass flowing out from the main stream and flowing together in the side stream. 
         [0008]    In order to reduce the portion of foam or bubbles in the glass melt, US 2015/0197440 A1 proposes that, in a tank following the melt crucible, and having a floor, a roof, and a side wall structure that connects the floor and the roof, the glass melt permeated with the foam and bubbles be heated in order to maintain or raise the temperature of the glass melt and in addition to control the composition of the gas above the glass melt in the tank, e.g., its water saturation, and/or to agitate the surface of the glass melt using a liquid or solid composition, for example, using drops of water. 
         [0009]    In US 2009/0235695 A1, in contrast, for the homogenization of the glass melt it is proposed to provide, in the glass melt tank above a submerged combustion heater, a burner situated in the superstructure whose flame in the region of the glass melt impinges on the surface of the melt, in which region the bubbles produced by the submerged combustion heater reach the surface of the glass melt. 
         [0010]    A glass melting plant having a refining region for the reduction of the portion of bubbles is also described in U.S. Pat. No. 8,402,787 B2, where a movable refiner tank has at its input a shaft that is made such that the transfer of the molten glass to the refiner region takes place with a minimal loss of heat. 
         [0011]    In US 2015/0315057, it is further proposed, for the removal of foam and bubbles from the glass melt, to use acoustic waves or particle radiation, for example, using compounds containing sulfur, glass shards, ground glass, particles having a composition that can be integrated into the molten glass, frozen CO2, solid organic materials, or combinations or mixtures thereof. In addition, it is proposed to remove the foam or the bubbles through continuous or intermittent agitation with material woven in the manner of a sieve, or non-woven material. 
         [0012]    The solutions described above are however complex and cost-intensive, or change the composition of the glass melt. In addition, the desired improvement of quality is frequently still not achieved. 
       SUMMARY OF THE INVENTION 
       [0013]    An object of the present invention is therefore to provide a device that brings about an effective reduction of the bubble content of the glass melt using simple and low-cost means. In addition, the object is to indicate a corresponding low-cost method. 
         [0014]    The object indicated above is achieved by a refiner. In particular, the refiner has a tank for accommodating the glass melt, which flows through the tank in a direction of transport between the front end and an outlet situated at the rear end, the tank having a floor, two side walls preferably extending parallel to the direction of transport, and a superstructure situated above the side walls and terminating the tank upwardly, a barrier running essentially in the direction of transport being situated on the floor of the tank in the form of a floor raised part, the barrier forming a channel-shaped constriction (narrowing) of the tank at least in a front region, in the direction of transport, at each side directly above the floor of the tank, the width of each constriction transverse to the direction of transport being at most 0.45 times the width of the tank, particularly preferably at most 0.4 times the width of the tank, at least one first fossil fuel heating device being provided that is situated in the superstructure and/or in the side wall and that heats the glass melt from above, and at least one second electrical heating device being situated in each side wall and/or in the floor of the tank in the region of each constriction, which heating device extends into the glass melt and also heats it. Here, the refiner is formed as a further vessel connected directly to the outlet of the melt crucible, in which at least one submerged combustion heater heats the initial materials in order to bring them to the melting point. 
         [0015]    The present invention is based on the recognition that the bubble content of the glass melt can be reduced by increasing the buoyancy of the bubbles. The bubbles can be brought to the surface of the glass melt solely through their buoyancy. Stokes&#39; Law describes the relation between the viscosity of the glass melt, the difference in density between the glass melt and the gas bubbles, and the radius of the gas bubbles. Because the gas melt has a high viscosity, the speed of the rise of the gas bubbles is low. As a result, for the thermal post-treatment of a glass melt containing bubbles a second vessel (refiner) is required through which the glass melt is guided. The size of the second vessel (refiner), and thus the dwell time of the glass melt in this vessel, as well as the temperature control or heating, determine the extent to which the bubble content of the glass melt can be reduced. 
         [0016]    Moreover, an extensive modeling study has shown that fossil fuel heating alone is not suitable to cause a sufficient number of the bubbles to rise. Only a barrier situated in the flow, which brings about a division and constriction of the flow, together with the additional electrical heating, results in a significant strengthening of the buoyancy, and correspondingly to a significant reduction in the bubble content. According to the present invention, the combination of the barrier extending in the direction of transport with the first, fossil fuel heating device, that supplies heat from above and the second, electrical heating device, that directly heats the glass melt, brings about a significant reduction of the number of bubbles in the glass melt. The buoyancy of the bubbles is promoted by the heating from all sides, because this reduces the viscosity of the glass melt. The barrier forming the channel-shaped constrictions brings about a division of the flow of the glass melt. The main flow paths here run along the barrier at the side thereof inside the channel-shaped constrictions with an increased flow speed that also promotes the buoyancy of the gas-filled bubbles. Inside the constriction, the glass melt has a height that corresponds to the height of the glass melt before the barrier. Above the barrier, the height of the glass melt is lower, corresponding to the height of the barrier. 
         [0017]    In a preferred exemplary embodiment, length l 1  of each constriction is from 0.2 to 0.8 times the length L 1  of the tank of the refiner, and/or the width b 1  of each constriction is at least 0.1 times the width W 1  of the tank of the refiner, particularly preferably at least 0.2 times the width W 1  of the tank of the refiner, and/or the height h 1  of the barrier is from 0.2 to 0.8 times the height H 1  of the melt surface in the refiner over the floor of the tank. A barrier having such dimensions particularly effectively removes the bubbles present in the glass melt and brings about an adequately large throughput of the refiner. 
         [0018]    Here it is to be explicitly noted that the barrier does not extend over the entire width of the tank, at least in the region of the channel-shaped constrictions. For example, the channel-shaped constriction is limited laterally on the one hand by the side wall of the barrier and on the other hand by the side wall of the tank. In the existing art, up to now only raised parts have been described that raise the glass melt over the entire width of the tank, so that the glass melt has a shallower depth over its entire width transverse to the direction of transport. The design of the barrier according to the present invention, in contrast, brings about a division and acceleration of the glass flow in order to promote the rise of the bubbles. 
         [0019]    In a development of the present invention, the at least one first fossil fuel heating device is situated in the superstructure and/or in the side wall in such a way that it heats the glass melt from above predominantly in a region that, in the direction of transport, is situated before, next to, and/or over the constriction formed by the barrier. Through such a heating, a reduction of viscosity is achieved, in particular, in the crucial region for the reduction of the bubble content. 
         [0020]    It is further advantageous if, in the region of each constriction, there are situated at least two second heating devices in the side wall and/or in the floor of the tank, preferably each lateral to the barrier. This achieves a still better heating of the refiner, so that the number of bubbles can be further reduced. 
         [0021]    It is further advantageous if the shape of the barrier in cross-section is made symmetrical relative to a mid-axis of the tank that runs parallel to the direction of transport. 
         [0022]    In a development of the present invention, an apex surface or an apex line of the barrier is situated below the melt surface of the glass melt, the apex line or apex surface preferably extending parallel or obliquely to the melt surface, and the apex surface or apex line particularly preferably climbing upward in the direction of transport. Here, the apex surface or apex line limits the barrier upwardly, i.e., at the side opposite the floor. An apex surface is formed if the barrier is shaped upwardly flat, comparable to a flat roof. An apex line results if the barrier forms at the top an edge running in the direction of transport, i.e., a shape comparable to a pitched or gabled roof, a hipped roof, or a mansard roof. In particular, given the realization of the barrier having an apex line, the flow of the glass melt can effectively be divided so that the bubble content can be further reduced. The rise of the bubbles is further promoted in that the apex surface or the apex line climbs upward in the direction of transport. 
         [0023]    For the same reason, it is advantageous if the cross-section of the barrier transverse to the direction of transport is trapezoidal or triangular at least in some segments. 
         [0024]    The barrier can have, in a front region or rear region in the direction of transport, a segment that runs to a point in the direction of the floor of the tank. 
         [0025]    It is further advantageous if the width of the channel-shaped constriction:
       becomes smaller in the direction of transport, or   remains constant in the direction of transport, or   becomes smaller in a first region and remains constant in a second region, in the direction of transport, the second region preferably being situated behind the first region in the direction of transport.       
 
         [0029]    In addition, the above object is achieved, with the advantages explained above, by a glass melting plant that has a melt crucible and a refiner as described above, the raw materials being supplied to the melt crucible by a supply device and melted there, and an outlet of the melt crucible situated opposite the supply device being connected to an inlet of the refiner preferably situated in the superstructure of the front end of the refiner. The raw materials can also contain glass shards. The glass melting plant according to the present invention preferably additionally has a conditioning channel connected to the refiner in the direction of transport and a feeder channel situated behind the conditioning channel. 
         [0030]    With regard to the constructive size and the melt performance, it is advantageous if at least one submerged combustion heater, which heats the material, is situated in the melt crucible. 
         [0031]    The above object is also achieved, with the same advantages, by a method for thermal post-treatment of a glass melt containing bubbles, the glass melt being situated in a tank, the glass melt flowing through the tank in a direction of transport between a front end and an outlet situated at the rear end, the tank having a floor, two side walls extending preferably parallel to the direction of transport, and a superstructure situated above the side walls that terminates the tank upwardly, the glass melt being guided over a barrier, in the form of a raised part of the floor, that is situated on the floor of the tank and runs essentially in the direction of transport, the barrier forming, at least in a front region in the direction of transport, at each side directly above the floor of the tank, at least one channel-shaped constriction of the tank, the width of each constriction transverse to the direction of transport being at most 0.45 times the width of the tank, preferably at most 0.4 times the width of the tank, the glass melt being heated from above by at least one first fossil fuel heating device situated in the superstructure and/or in the side wall, and being directly heated by at least one second electrical heating device situated in each side wall and/or in the floor of the tank in the region of each constriction and extending into the glass melt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    In the following, the present invention is explained in more detail on the basis of exemplary embodiments shown in the Figures. Here, all features described and/or shown graphically, in themselves or in any combination, form the subject matter of the present invention, independent of their summarization in the claims or the relations of dependency among the claims. 
           [0033]      FIG. 1  schematically shows an exemplary embodiment of a glass melting plant according to the present invention, in the form of a flow schema, 
           [0034]      FIG. 2  schematically shows the melt crucible and the refiner of the glass melting plant according to  FIG. 1 , in a longitudinal section, 
           [0035]      FIG. 3  schematically shows details of the refiner shown in  FIG. 2  in a further longitudinal section, 
           [0036]      FIGS. 4 a  and 4 b    schematically show the refiner according to  FIG. 3  in further cross-sections along the line AB (see  FIG. 3 ) or CD ( FIG. 4 a   ), 
           [0037]      FIGS. 5, 6   a  and  6   b  schematically show the representations according to  FIGS. 3 and 4   a, b  with a marking that visualizes the movement of the bubbles in the melt, and 
           [0038]      FIGS. 7 and 8  schematically show further examples of barrier shapes and their configuration on the floor of the refiner, each in a perspective view from the side. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    The raw material mixture for the glass production, in particular for the production of fiberglass, is continuously fed to a melt crucible  2  in the region of an inlet  1 . As a rule, this takes place above a melt surface  4 , using a continuously operating supply device. Alternatively, the raw material mixture can also be supplied below the melt surface  4 . The melt crucible  2  is generally equipped with a water cooling unit and is made with a double-walled construction. The melt crucible  2  further has in its floor submerged combustion heaters  5  that melt the supplied raw material mixture. The submerged combustion heaters  5  are supplied with a fossil fuel  6  and with an oxidant. The gaseous reaction products of the fuel  6  with the oxidant (usually oxygen) of these submerged combustion heaters  5  partly remain in a glass melt  20  as bubbles. In part, however, they already rise in the melt crucible  2  and escape via an exhaust gas flue  3  of the melt crucible  2 . From an outlet opening  7  close to the floor of melt crucible  2 , the glass melt  20  is supplied to a refiner  8 . 
         [0040]    A supply opening  13  of the refiner  8  is situated at the front end of the refiner  8 , in the region of a transport direction T (see arrow in  FIGS. 2, 3, and 4   a ) of the glass melt  20 . In the refiner  8 , the gas bubbles contained in the glass melt rise to the surface. This is also referred to as refining. In the refiner  8  there arises a melt surface  9 , and the glass melt leaves the refiner  8  at its rear end in direction of the transport direction T, through an outlet  10 . 
         [0041]    From the refiner  8 , the glass melt now moves over a ramp  25 , which provides a shape that promotes flow and is situated before the outlet  10 , into a third vessel  30  in which the glass melt is cooled to a temperature required for processing. This process is also referred to as thermal conditioning. From the third vessel  30 , the glass melt is then conducted into a fourth vessel  40  that is equipped with a heating system. In this fourth vessel  40 , the glass melt is released in a controlled fashion from openings in the floor and is processed to form fibers. The fourth vessel is also referred to as the feeder channel. The openings from which the glass melt exits in order to produce the fibers are called bushings. 
         [0042]    The refiner  8 , shown in more detail in  FIGS. 3, 4   a , and  4   b , has a tank for accommodating the glass melt  20  having a floor  11 , side walls  21  running parallel to the direction of transport, and a superstructure  12  that upwardly terminates the tank. The superstructure  12  is situated above the side walls  21 . In superstructure  12 , at the front end of the tank, there is situated an opening  13  through which the glass melt moves from the melt vessel  2  into the refiner  8 . The tank of the refiner has a length L 1  and a width W 1 . The melt surface  9  has a height H 1  over the floor  11  (cf.  FIGS. 5 through 6   b ). 
         [0043]    Downstream from the opening  13 , in the superstructure  12  there are provided a multiplicity of openings  15  through which there extends, vertically or at an angle, a respective burner lance  16  as a fossil fuel heating device, into a space  14  over the glass melt  20 . Each burner lance  16  is supplied with fossil fuel and an oxidant (usually oxygen). The fossil fuel burners  16  heat the glass melt  20  from above, in a region before (in the direction of transport T) and over a barrier  18  on the floor  11  of the tank. 
         [0044]    Underneath the melt surface  9 , through each side wall  21 , four electrodes  17  extend into the glass melt  20 . The electrodes are mounted laterally relative to the barrier  18 , and directly heat the glass melt. 
         [0045]    The barrier  18  is a raised part situated in the center of the tank, having an approximate distance D 1  from the opening  13  in the direction of transport T. The barrier  18  has its longest dimension (length l 1 ) in the direction of transport T. The barrier  18  has a distance b 1  from each side wall  21 . Together with each side wall  21 , the barrier  18  forms a respective channel-shaped constriction  19  having a width b 1 , which forces the flow of the glass melt  20  to divide into partial streams that move along the constriction  19 . Within the constriction  19 , the glass melt  20  has a height H 1  that corresponds to the height H 1  of the glass melt  20  in front of the barrier  18 . Above the barrier  18 , a height H 2  of the glass melt is lower, corresponding to a height h 1  of barrier  18 . 
         [0046]    In cross-section, the barrier  18  has a trapezoidal shape over the greater part of its length (see  FIG. 4 b   ), the upper side of the trapezoid forming an apex surface  23  over the length of the barrier  18 . The apex surface  23  runs parallel to the melt surface  9 . In addition, electrodes  17  are configured such that their mid-axis runs parallel to the apex surface  23  and has a distance from the floor  11  of the refiner  8  that corresponds to the height h 1  of the barrier  18 . Only in the direction of transport T, at the beginning and at the end of the barrier  18 , does the barrier have a ramp-type segment  18   a  that runs to a point in the direction of the floor  11 , giving the barrier  18  a shape that better promotes flow. 
         [0047]      FIGS. 5 through 6   b  show, on the basis of the arrows in the glass melt  20 , the path of the bubbles in the glass melt. Underneath the opening  13 , the bubbles move in the direction of the floor  11 . Before the barrier  18 , the flow of the glass melt  20  is divided, by the centrically situated barrier  18 , into two partial streams that each move along the channel-shaped constrictions  19  and, in these, rise to the surface of the glass melt  20 . 
         [0048]    A model example, having a barrier analogous to the barrier  18  shown in  FIGS. 3 through 6   b:    
         [0049]    In a model, it was calculated that in the production of fiberglass (c-glass) in a glass melting plant having a throughput performance of 250 metric tons/day, the quantity of bubbles in the glass melt  20  transferred from the melt crucible  20  to the refiner  8  has a volume percent portion of 25%. The refiner  8  has a length L 1  of 8900 mm, a width W 1  of 2000 mm, and a height of the melt surface  9  over the floor  11  of 575 mm. The barrier  18  begins at a distance D 1  of 3750 mm from the point of transfer of the glass melt from the melt crucible  2 , the barrier being situated on the floor  11  of the refiner  8 . The barrier  18  has a length l 1  of 2600 mm and a height h 1  of 200 mm. The width of the barrier  18  is 650 mm. Consequently, a distance b 1  of the barrier from each side wall  21 , i.e., the width of the constriction  19 , is approximately 675 mm 
         [0050]    To the left and to the right of the barrier  18 , in each case four electrodes  17 , situated inside the wall  21 , extend into the glass melt  20 . The apex surface  23  of the barrier  18  is at the same height as the mid-axes of the electrodes  17 ; i.e., the electrodes extend into the glass melt  20  at a height of 200 mm over the floor  11 . In the superstructure  12  of the refiner  8 , there are situated four rows of three burner lances  16  each, oriented at an angle of 20° relative to the transport direction T of the glass melt  20 . 
         [0051]    The electrical power introduced via the electrodes  17  is a total of 200 kW. The heating power of the burner lances  16  is a total of about 300 kW. Upon its entry into the refiner  8 , the glass melt  20  has a temperature of about 1230° C. In the refiner  8 , the glass melt is heated to a temperature of about 1280° C. According to the model calculation, the number of bubbles along the refiner  8  is reduced to half through the combination of the measures described above. 
         [0052]    The table below provides, in addition to the model example explained above (designated as a case study in the table), further examples of glass melting plants where the barrier (raised part)  18  has, in each case, the shape shown in  FIGS. 3 through 6   b . Three different “regions” are distinguished, namely
       a region I having a daily throughput of between 80 t and 300 t,   a region II having a daily throughput of between 200 t and 250 t,   a region III having a daily throughput of between 150 t and 200 t.       
 
         [0056]    [note: t=metric tons] 
         [0057]    For the model example and the regions I through III, the table indicates the inner dimensions of the refiner and the measurements of the barrier (raised part)  18 . 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Refiner 
                   
                   
                 Case 
                   
                   
                   
               
               
                 dimension 
                   
                 Unit 
                 study 
                 Region 
                 Region II 
                 Region III 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Throughput 
                   
                 t/d 
                 250 
                 80-300 
                 200-250 
                 150-200 
               
               
                 Length 
                 L1 
                 m 
                 8.9 
                 4-15 
                  5-12 
                  4-10 
               
               
                 Width 
                 W1 
                 m 
                 2 
                 1-3  
                 1-3 
                 1-3 
               
               
                 Depth 
                 H1 
                 m 
                 0.575 
                 0.3-0.8  
                 0.3-0.8 
                 0.3-0.8 
               
               
                 Barrier 
               
               
                 Length 
                 l1 
                 m 
                 2.6 
                    0.2-0.8 × L1 
                    0.3-0.6 × L1 
                    0.3-0.6 × L1 
               
               
                 Width 
                 w1 
                 m 
                 1 
                      0.2-0.8 × W1 
                        0.3-0.6 × W1 
                        0.3-0.6 × W1 
               
               
                 Depth 
                 h1 
                 m 
                 0.35 
                      0.2-0.8 × H1 
                      0.3-0.6 × H1 
                      0.3-0.6 × H1 
               
               
                 Width of 
                 b1 
                 m 
                 0.5 
                        0.1-0.45 × W1 
                      0.15-0.4 × W1 
                        0.2-0.4 × W1 
               
               
                 constriction 
               
               
                 Specific 
                   
                 t/m2d 
                 14.0 
                 8-20 
                 10-16 
                 10-16 
               
               
                 load 
               
               
                   
               
             
          
         
       
     
         [0058]      FIGS. 7 and 8  show further variant shapes of the barrier  18 . The barrier  18  shown in  FIG. 7  has a triangular cross-sectional shape and forms on its upper side an apex line  23   a  that runs parallel to the melt surface  9  (not shown). In addition, the barrier shown in  FIG. 7 , compared to the barrier shown in  FIGS. 3 through 6   b , does not have the beginning and end segment  18   a  running to a point. 
         [0059]    In contrast, such a beginning segment, and possibly also end segment,  18   a  is provided in the barrier shown in  FIG. 8 . 
         [0060]    The barrier  18  shown in  FIG. 8  has at its beginning a trapezoidal cross-section. In the direction of transport T, the apex surface  23  tapers in such a way that it finally forms only an apex line  23   a , and the cross-sectional shape of the barrier  18  in this region forms a triangle. The apex surface  38  also climbs upward in the direction of transport T, so that the height h 1  of the barrier increases in the direction of transport T. 
         [0061]    All such barriers  18  bring about a significant reduction of the bubble content of the glass melt, and thus an improvement of the glass quality. 
         [0062]    As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art. 
       LIST OF REFERENCE CHARACTERS 
       [0000]    
       
           1  inlet 
           2  melt crucible 
           3  waste gas flue 
           5  submerged combustion burner 
           6  combustion gas 
           7  outlet opening 
           8  refiner 
           9  melt surface 
           10  outlet 
           11  floor 
           12  superstructure 
           13  opening 
           14  space above glass melt  20   
           15  opening 
           16  burner lance 
           17  electrode 
           18  barrier 
           18   a  segment 
           19  channel-shaped constriction 
           20  glass melt 
           21  side wall 
           23  apex surface 
           23   a  apex line 
           25  ramp 
           30  third vessel 
           40  fourth vessel 
         T direction of transport