SUBMERGED COMBUSTION MELTING OF VITRIFIABLE MATERIAL

Abstract

The present invention relates to a process for producing a boron containing glass, comprising melting raw materials including boron compounds in a submerged combustion melter (11), withdrawing flue gases from said melter and recovering heat from said flue gases in appropriate heat recovery equipment prior to release into the environment.

Claims

1. A process for producing a boron containing glass, comprising melting raw materials including boron compounds in a submerged combustion melter (10), withdrawing flue gases from said melter and recovering heat from said flue gases in heat recovery equipment prior to release into the environment.

2. The process of claim 1 wherein the boron content of the glass expressed as B.sub.2O.sub.3 is comprised between 2 and 15 w %.

3. The process of claim 1 wherein the glass melt is withdrawn from the submerged combustion melter and led to a refining step and subsequent glass forming step, said glass forming step comprising the formation of flat glass, glass containers, glass fibers or continuous glass fibers.

4. The process of claim 1 wherein the glass melt is withdrawn from the submerged combustion melter and transferred to a glass fiber production unit, without any intermediate refining step, for production of mineral wool fibers selected from glass wool fibers and stone wool fibers.

5. The process of claim 1 wherein the submerged combustion melter (10) comprises a melting chamber (11) equipped with submerged combustion burners (21,22,23,24,25,26), a raw material feeder (15) and a melt outlet (16), the submerged combustion burners being arranged in a substantially annular burner zone, on a substantially circular burner line (27), through the bottom (13) of the said melting chamber, at a distance between adjacent burners and controlled in such a way that flames do not merge, and said burners having a central burner axis (31,32,33,34,35,36) oriented in an substantially vertical upright or slightly outwardly oriented burner orientation.

6. The process of claim 5 wherein adjacent melter burners (21, 22, 23, 24, 25, 26) are arranged at a distance of about 250-1250 mm, or about 500-900 mm, or about 600-800 mm, or about 650-750 mm.

7. The process of claim 5 wherein the burners (21, 22, 23, 24, 25, 26) are arranged at a distance of about 250-500 mm from the side wall of said melting chamber.

8. The process of claim 5 wherein the burner circle diameter (27) is comprised between about 1200 and 2000 mm.

9. The process of claim 5 wherein at least 5 burners (21, 22, 23, 24, 25, 26), or 6 to 10 burners, or 6 to 8 burners are arranged within the burner zone.

10. The process of claim 5 wherein the cross section of the melting chamber (11) is selected from a substantially cylindrical cross section, an elliptical cross section and a polygonal cross section having more than 4 sides, or more than 5 sides.

11. The process of claim 1 wherein the submerged burners (21, 22, 23, 24, 25, 26) inject high pressure jets of the combustion products into the melt, with the combustion gases having a velocity in the range of about 60 to 300 m/s, about 100 to 200 m/s, or about 110 to 160 m/s.

12. The process of claim 5 wherein the melting chamber walls comprise double steel walls separated by circulating cooling liquid, the internal face of the melter wall being optionally equipped with tabs or pastilles or other small elements projecting towards the inside of the melter.

13. The process of claim 1 wherein heat is recovered from the flue gases in a heat exchanger without prior reduction in the boron content of the flue gases.

14. The process of claim 1 wherein recovery of heat from the flue gases comprises transferring heat energy from the flue gases to a heat exchanger fluid.

15. A method of recovering energy from flue gases produced when melting a boron containing glass, comprising withdrawing flue gases from a submerged combustion melter and recovering heat from said flue gases.

Description

[0028] An embodiment of the present invention will be described in more details below, with reference to the appended drawings of which:

[0029] FIG. 1 is a schematic representation of a toroidal flow pattern;

[0030] FIG. 2 shows a vertical section through a melter; and

[0031] FIG. 3 is a schematic representation of a burner layout.

[0032] A melter 10 comprises: a cylindrical melting chamber 11 having a bottom 13 and a diameter of about 2.0 m which contains a melt; an upper chamber 90; and a chimney 91 for evacuation of fumes. The upper chamber 90 is equipped with baffles 92, 93 that prevent melt projections thrown from a surface of the melt being entrained into the fumes. A raw material feeder 15 is arranged at the level of the upper chamber 90 and is designed to load fresh raw material into the melter 10 at a point 101 located above the melt surface 18 and close to the side wall of the melter. The feeder 15 comprises a horizontal feeding means, for example a feed screw (not shown), which transports the raw material mix to a hopper fastened to the melter 10, the bottom of which may be opened by a vertical piston as required by the control of the melter operation. The bottom of the melting chamber 11 comprises submerged burners 21,22,23,24,25,26, each having a central burner axis 31,32,33,34,35,36 and nozzles 41,42,43,44,45,46, arranged on a circular burner line 27 concentric with the melter axis of symmetry 7 and having a diameter of about 1.4 m. The burner layout is schematically represented in FIG. 3. For the sake of clarity, the design represented in the figures has a preferred layout with six submerged burners distributed over the burner line 27. Different layouts are possible depending on the dimensions of the melter, the viscosity of the melt 17 and the characteristics of the burners. It is preferred that the flames do not merge and that the arrangement generates a toroidal melt flow as defined above. The melt may be withdrawn from the melting chamber through a controllable outlet opening 16 located in the melting chamber side wall, close to the melter bottom, substantially opposite the feeding device 15.

[0033] The melting chamber wall is a double steel wall cooled by a cooling liquid, preferably water. Cooling water connections provided at the external melter wall allow a flow sufficient to withdraw energy from the inside wall such that melt can solidify on the internal wall and the cooling liquid, here water, does not boil.

[0034] The melter represented in the figures is substantially cylindrical. Submerged combustion may generate high stress components that act on the melter walls and/or heavy vibrations. These may be significantly reduced in the case of a cylindrical melting chamber. If so desired, the melter may further be mounted on dampers which are designed to absorb most of the vibrational movements.

[0035] The submerged burners are operated at gas flow or speed of 100 to 200 m/s, preferably 110 to 160 m/s and generate combustion of fuel gas and air and/or oxygen within the melt. The combustion and combustion gases then generate flows within the melt before they escape into the upper chamber and then through the chimney. These hot gases incorporate a high level of thermal energy at least a portion of which, preferably at least 15%, 20%, 25% 30% 40% or 50%, is recovered notably in a heat exchanger. The fumes are generally filtered prior to release to the environment to remove particulates but do not require treatment to remove boron compounds.

[0036] The burners generate an ascending movement of melt in their proximity and a convective circulation within the melt. The arrangement of the burners in an annular burner zone, preferably on a circular burner line 27, in the bottom of the melting chamber 11, is capable of generating the toroidal movement explained above.