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.-15. (canceled)

16. A method to reduce the amount of volatile boron compounds entrained into an effluent gas when producing boron-containing glass by melting mineral compositions including boron, where the boron content of the glass expressed as B.sub.2O.sub.3 is comprised between 2 and 15 wt. %, and wherein the mineral composition including boron is melted in a submerged combustion melter.

17. The method of claim 16, wherein no elimination of volatile boron compounds takes place upstream of heat recovery or heat transfer equipment.

18. The method of claim 16, wherein a glass melt is withdrawn from the submerged combustion melter and led to a refining step and subsequent glass forming step for the formation of flat glass, glass containers, glass fibers or continuous glass fibers.

19. The method of claim 16, wherein a glass melt is withdrawn from the submerged combustion melter and transferred to a glass fiber production unit, without any intermediate refining step, for production of glass wool fibers or stone wool fibers.

20. The method of claim 16, 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.

21. The method of claim 16, wherein the submerged combustion melter (10) comprises a melting chamber (11) equipped with at least five 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 submerged combustion burners of about 250-1250 mm and controlled in such a way that flames do not merge, and at a distance of about 250-500 mm from the side wall of the said melting chamber, and said submerged combustion burners having a central burner axis (31,32,33,34,35,36) oriented in an substantially vertical upright or slightly outwardly oriented burner orientation.

22. The method of claim 16, wherein the submerged combustion melter comprises a melting chamber (11) having a substantially cylindrical cross section.

23. The method of claim 16, wherein the submerged combustion melter comprises a melting chamber (11) equipped with submerged combustion burners (21,22,23,24,25,26) and containing a glass melt, and wherein said submerged combustion burners inject high pressure jets of combustion products into the melt, with the combustion gases having a velocity in the range of about 60 to 300 m/s.

24. The method of claim 16, wherein the submerged combustion melter comprises a melting chamber having melting chamber walls which comprise double steel walls separated by circulating cooling liquid comprising water, the internal face of the melter wall being optionally equipped with tabs or pastilles projecting towards the inside of the melter.

25. The method of claim 16, wherein heat is recovered from flue gases in a heat exchanger without prior reduction in the boron content of the flue gases.

26. The method of claim 16, wherein heat is recovered from flue gases and the recovery of heat from the flue gases comprises transferring heat energy from the flue gases to a heat exchanger fluid.

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.