BE1022547B1 - FUSION OF VITRIFIABLE MATERIALS - Google Patents

Abstract

A submerged burner melting furnace has a melting chamber which may be cylindrical and include at least five submerged burners.

Description

Fusion of vitrifiable materials

The present invention relates to a process and a batch melting furnace, especially a submerged combustion melting furnace, more particularly intended for the production of mineral fibers and especially of mineral wool for thermal insulation, for example of rock wool or glass wool.

In the production of mineral fibers, a mixture of raw materials comprising, for example, silicates, basalt, lime, sodium hydroxide and other minor constituents is generally used. The raw materials are loaded into a melting furnace and melted to form a viscous bath at temperatures in the range of 1250 to 1500 ° C. The molten bath is then sent to forming steps, such as flat glass formation, hollow glass formation, continuous fiber formation, glass wool or rock formation etc. The chemical composition of the molten bath is of course chosen according to the desired use and the forming steps downstream of the furnace.

Conventional melting furnaces used in glass production heat the molten bath by means of burners which generate a flame in the space between the surface of the molten bath and the furnace cupola. The raw materials are fed on the surface of the molten bath, the heat is transmitted to these freshly fed materials which are then absorbed in the bath.

Some types of furnaces include electrodes arranged in the melt. These may be the only source of heat or combined with other heating means.

Another type of furnace comprises one or more burners arranged in the melt so that the flame and the combustion products pass through said melt. These are submerged combustion burners.

In the case of rock wool production, Cupola kilns have traditionally been used.

Melting furnaces are described in US3592151A, US2008 / 256981A1, US3260587A, DE10029983A1 and WO2009 / 091558A1.

According to a first aspect, the invention relates to a submerged combustion burner glass furnace according to claim 1. According to another aspect, the invention relates to a process for melting vitrifiable materials.

By "vertical central axis of the furnace" is meant the vertical or substantially vertical axis of symmetry of the melting chamber. This may have a circular horizontal section; it can be cylindrical. Alternatively, it may have a polygonal horizontal section, such as a regular polygon, which may have six, seven, eight, nine or more sides. Each of these forms has a central axis of symmetry well defined. The horizontal section may however also have an elliptical or oval shape; in this case or similar cases, the vertical central axis of the furnace is the axis passing through the center of a circle in which is inscribed the shape of horizontal section.

The nozzles of the submerged burners can all be arranged at the same vertical distance, in the melting chamber, that is to say in the same horizontal plane. Alternatively, they can be arranged at different heights. The burner nozzle positioning plane is defined as being arranged at a weighted average distance from each of the nozzles; that is, the average distance is weighted on the number of burners.

By "weighted distance between the central axis of burner and the circumferential wall of the furnace" is meant the weighted distance between the central axis of the burner and the inner face of the circumferential wall of the melting chamber. When the central axis of the burner is parallel to this inner face, it is the distance between the central axis of the burner and the inner face. In other cases, the "weighted distance between the central burner axis and the circumferential wall of the furnace" is the arithmetic mean distance over the height of the melting chamber between the central axis of the burner and the nearest part of the inner face of the circumferential wall.

The melt can reach temperatures, especially at the outlet of the melting chamber, of at least 1100 ° C., at least 1200 ° C. or at least 1250 ° C. and which can not exceed 16 ° C., or 1500 ° C. or 1450 * C. The composition of the melt generated may include:

Such melting furnaces have an effective configuration for the melting of batch materials with reduced energy consumption and low investment costs, they make it possible to obtain the desired characteristics of the molten bath, including homogeneity at the level of temperature distribution and bath composition, to arrive at a final product of improved quality. They also make it possible to melt a multitude of vitrifiable materials while ensuring high flexibility in the control of the operating parameters.

In the preferred configurations, such melting furnaces improve the absorption in the melt of freshly charged raw materials, as well as the efficiency of the heat transfer to said raw materials, avoiding or at least greatly reducing the shortage. circuiting of the melting chamber by freshly charged raw materials. As a result, the size of the furnaces can be reduced for a given flow rate, while improving the homogeneity of the melt.

Preferably, most of the molten bath mixture is in the central zone of fusion which may be substantially cylindrical and may have a diameter of at least 25 cm, at least 30 cm, at least 40 cm, at least 50 cm. cm, at least 60 cm or at least 70 cm and / or not more than 200 cm, not more than 180 cm or not more than 160 cm.

The furnace or at least the melting chamber can be cooled with a liquid, preferably water. It may comprise a double wall comprising an inner wall which constitutes in particular the circumferential wall of the furnace, and an outer wall arranged at a distance from the inner wall so as to release a space traversed by a cooling liquid, in particular water. It is thus possible to advantageously omit the use of refractory materials.

According to a preferred embodiment, the furnace of the invention makes it possible to generate a toroidal circulation in the molten bath, having an upward circulation close to the central axes of the burners, converging on the surface of the molten bath in the direction of the vertical central axis of the furnace and descending near said vertical central axis of the furnace, in a substantially cylindrical space having as a base the central melting zone.

The oven can be equipped with 5 to 10 submerged burners, preferably 6 - 8 burners, depending on the dimensions of the melting chamber, burner dimensions, operating pressure and other design parameters. In the case of a furnace intended for the production of a molten bath for the manufacture of glass fibers, glass wool or rock wool, the melting chamber may be cylindrical and have an internal diameter of 1.5. at 3 m, preferably from 1.75 to 2.5 meters.

The distance between two adjacent burners is chosen according to burner dimensions, operating pressure and other parameters. Too low a distance can cause a melting of the flames of various burners, a phenomenon to avoid. The distance between two adjacent burners is preferably about 1.5 to 2.5, more preferably about 1.75 to 2.25, most preferably about 2 times the distance between the central axis of the burner and the circumferential wall.

Two adjacent burners are advantageously arranged at a distance of about 250-1200mm, preferably about 500-900mm, more preferably about 600-800, most preferably about 650-750mm.

According to a preferred embodiment, the burners are arranged at a distance between their central axis and the circumferential wall which promotes the circulation of the melt described above and avoids the attraction of the flames towards the wall. The distance between the central burner axis and the circumferential wall is advantageously of the order of 250 to 750 mm. Too low a distance can cause damage to the circumferential wall and / or unnecessarily solicit and / or reduce the heat transfer efficiency. Some melted bath flow between the burner and the circumferential wall may be desirable but too great a distance between the central axis of the burner and the circumferential wall tends to allow unwanted melt flows to be generated and to create dead zones which are unfavorable to the proper mixing of the molten bath, it can result in a loss of homogeneity thereof. The distance between the central axis of the burners and the circumferential wall is advantageously chosen so that a bath layer with a thickness of between about 2 and 20 mm stiffens on the circumferential wall. Such a layer serves to protect the wall and facilitates the operation of the oven without the use of refractory material coating, especially when the wall is cooled by a liquid.

A combustible gas, in particular a gas comprising hydrocarbons, for example natural gas, and a gas comprising oxygen, in particular oxygen, technical oxygen (for example having, for example, an oxygen content of at least 95 % by weight) or oxygen-enriched air are fed to the burners. These gases are preferably fed separately and mixed in the burner and / or in the nozzles thereof.

According to a preferred embodiment of the invention, a toroidal circulation is generated in the melt; that is, the velocity vectors of the moving material fill sections of a substantially horizontal toroid whose axis of revolution corresponds substantially to the central vertical axis of the furnace and whose outer diameter essentially corresponds to the circumference defined by the axes of the burners, the molten bath flowing from the outside to the inside of the surface of the molten bath. This circulation entrains fresh raw material deep into the molten bath near the vertical central axis of the furnace, in a substantially cylindrical space having as a base the central melting zone, and improves the efficiency of the heat transfer to the raw material. and thus the homogeneity of the melt.

In the central melting zone, the molten bath and / or the raw materials entrained can reach speeds> 0.1 m / s,> 0.2 m / s,> 0.3 m / s or * 0.5 m / s and / or s2.5 m / s, <2 m / s, s1.8 m / s or <1.5 m / s.

It also results from the furnace arrangement of the invention that the raw materials can be loaded over the surface of the melt. They are then trained and quickly incorporated into the melt.

Each burner or group of burners (eg opposed burners) can be individually controlled. Thus, one or more burners in the vicinity of the raw material feed can be set at different gas velocities or gas pressures of the adjacent burners, in order to improve the heat transfer. This different setting may be only temporary, namely until the incorporation of the raw material into the melt. It may further be advantageous to adjust the burners adjacent to the outlet at a lower gas velocity / pressure to allow adjustment of the withdrawn fraction. The central burner axis may be inclined with respect to the vertical, for example at an angle of 1 °, 3 ° or 5 and / or 30 °, preferably <15 °, more particularly <10 °. , especially towards the center of the melting chamber. Such an arrangement can improve the flow of molten bath and orient the latter towards the center of the melting chamber, away from the outlet

Furthermore, one or more of the burners may form a swirl angle of at least 1 "with respect to a plane perpendicular to the burner positioning plane which passes through the central vertical axis of the furnace and the position of the respective burner . The swirl angle can be> 1 °,> 2 ',> 3 °,> 5 ° and / or s 30 °, <20', s 15 ° or <10 °. Preferably, each burner has the same swirl angle. This arrangement of the burners is intended to print a velocity component tangential to the combustion gases and thus a vortex movement in the molten bath to further improve the mixing and thus the homogeneity.

The raw material can be fed with a feed device through an opening above the surface of the molten bath. The raw material can be fed continuously or batchwise. A load can vary between 20 and 50 kg. In the case of an oven having a capacity of about 70000 kg / day, the loading frequency can vary between 20 and 50 kg / min. Preferably, the raw material will be fed continuously or almost continuously in order to facilitate the control of the process, especially the temperature, and to improve the homogeneity of the molten bath.

Said opening is advantageously closable, for example by a piston or other control, in order to reduce the heat losses and the fumes emanations through the feed. Raw materials can be prepared properly. They are charged countercurrent fumes have seen their preheating.

The melt can be drawn continuously or discontinuously, for example at a point near the bottom of the furnace. If the raw material is loaded near the circumferential wall, the exit opening is preferably located opposite the feed. When the supply is discontinuous, the outlet opening is closable, for example by a ceramic piston.

The submerged burners can be concentric burners, injecting the combustion products under pressure into the melt so as to overcome the pressure of the melt and to force upward movement of the flame and the products of combustion. The velocity of the combustion gases, in particular at the outlet of the burner nozzles, may be 2 60 m / s, 2 100 m / s or 2 120 m / s and / or <350 m / s, <330 m / s, s 300 or s200 m / s, preferably of the order of 60 to 300 m / s, more particularly of 100 to 200 m / s, more particularly of 110 to 160 m / s. The internal face of the dconferential wall of the melting chamber may have a multitude of lugs which are intended to facilitate the attachment of the stiffened melt layer to said wall to act as a thermal insulating coating.

The melting furnace of the invention may be equipped with heat recovery devices. Thus, the hot fumes rising above the molten bath can be used to preheat the raw materials or their heat energy can be used for other purposes in equipment upstream or downstream in a production line, including products. insulators. Similarly, the heat energy contained in the coolant of the furnace walls can be recovered.

The described device and method are particularly suitable for melting all kinds of vitrifiable materials in an efficient manner, with low energy consumption and low maintenance costs. An oven according to the invention is particularly advantageous in a production line of products based on mineral fibers, for example glass fibers, glass wool and rock wool. The invention is described in more detail below, in support of the figures in which: - Figure 1 shows a horizontal section through a furnace according to the invention; - Figure 2 shows a vertical section through the oven of Figure 1; - Figure 3 is a schematic representation of the arrangement of the burners; and - Figure 4 is a schematic representation of the toroidal flow.

The glass furnace 10 shown in FIGS. 1, 2 and 3 comprises a melting chamber 11 for containing a melt 17 having, for example, a composition for the production of rock wool fibers, and the upper chamber 90.

The melting chamber shown is cylindrical and has a vertical central axis 7, a circumferential wall 12 defined by its internal boundary which has a diameter of about 2 m, a base or a bottom 13 and an open upper end qw * communicates with the chamber 90. This comprises: • a chimney 91 for the evacuation of gases from the melting chamber 11; • baffles 92, 93 which shield against any projections of the melt surface 14; and • a raw material loading device 15 arranged at the chamber 90, which allows the feed of raw material into the melt 10 at a loading position 101 above the bath surface 18, close to the circumferential wall 12 of the melting furnace.

The feeder 15 comprises a screw or other horizontal conveying means which discharges the raw material into a hopper which can be opened and closed by a piston.

The glass furnace has a double steel wall 19 through which a cooling liquid, preferably water, is flowing at a sufficient speed to maintain the melting chamber and the coolant at the desired temperature "and in order to extracting energy from the inner circumferential wall 12 so as to at least partially stiffen the melt to form a protective layer.

Six submerged burners 21, 22, 23, 24, 25, 26 are arranged equidistantly along a circular burner line 27 which is concentric with the central vertical axis of the furnace 7 and has a diameter of the order of 1, 4 m. Each submerged burner has a central axis 31,32,33,34,35,36 and one or more nozzles 41,42,43,44,45,46 which are projected flames and / or combustion fluids in the molten bath 17. The burners are arranged at substantially the same distance 512, 523, 534, 545, 556, 561 with respect to each of the adjacent burner positions. The nozzles 41, 42, 43, 44, 45, 46 as shown extend slightly beyond the base 13 of the melting chamber, i.e. they are all in the same plane. positioning 14.

Each central burner axis 31,32,33,34,35,36 determines the center of a burner circle 71,72,73,74,75,76 which has a radius r1, r2, r3, r4, r5, r6 substantially equal to the distance between the central burner axis and the circumferential wall 12 of the combustion chamber. These burner circles determine a central zone 70 in the plane 14 which has a diameter of 250 mm.

The molten bath 17 can be withdrawn through the closable outlet opening 16 made in the circumferential wall 12 of the melting chamber, close to the bottom 13 of the melting chamber 12, substantially opposite the feed 15.

Submerged combustion burners 21,22,23,24,25,26 are concentric burners operating at gas velocities in the melt of the order of 100 to 200 m / s, preferably 110 to 160 m / s. s. The burners burn natural gas with air and / or oxygen in the melt. This combustion and the resulting gases generate a swirl and therefore intense mixing in the melt and a very efficient heat exchange before escaping into the upper chamber 90 and then into the chimney 91. The hot gases can be used to preheating the raw materials and / or the combustible gas and / or the oxidant (air and / or oxygen) upstream of the burners. The fumes are advantageously cooled, for example by mixing with ambient air, and / or filtered before release into the ambient environment.

Preferably, the arrangement according to the invention generates a toroidal flow in the molten bath, as represented in FIG. 4. The molten bath follows an upward movement near the central axes of the burners, returns to the vertical central axis 7 at the surface of the molten bath 18 and descends into a cylindrical portion which extends along the vertical central axis of the furnace from the central melting zone. Such a toroidal movement guarantees an intense mixing of the molten bath, a good incorporation of the raw materials in the melt and ensures a suitable residence time in the melting chamber, while avoiding a premature exit of insufficiently melted particles.

In order to further increase the mixing rate in the melt, one or more burners may impose a tangential component to the flue gases, thereby generating a vortex motion in the melt. To do this, one or more burners can form a swirl angle of at least 1 'relative to a plane perpendicular to the positioning plane of the burners 14, which passes through the vertical central axis 7 of the melting chamber and the position of the respective burner.

The oven may also be equipped with an auxiliary burner (not shown) especially for temporary use, such as preheating the oven before start, in case of non-operation of one or more submerged burners, or in other situations that temporarily require extra calories. This additional burner is advantageously mounted on a rail which makes it possible to bring it near an opening which is formed in the circumferential wall of the combustion chamber and which is closable when the auxiliary burner is not used.

The internal wall 12 of the combustion chamber advantageously comprises a multitude of lugs (not shown) which promote the formation and fixing of a stiffened melt layer on the wall 12, a stiffened layer which constitutes an insulating layer, it As a result, in the case of glass melting, it is melted in the glass and is not contaminated with residues of refractory material.

A melting furnace according to the invention is particularly suitable in a glass fiber, glass wool or rock production line, in view of the reduced energy consumption and its flexibility in the composition changes of raw materials. Low maintenance costs and low investment costs make it an excellent choice.

Claims (14)

1 submerged combustion glass furnace (10) having a melting chamber (11) having a circumferential wall (12), a bottom (13), a vertical central axis of the melting chamber (7) and a positioning plane burners (14), the oven further comprising: a raw material feeder (15); a molten bath outlet opening (16); and at least five submerged combustion burners (21, 22, 23, 24, 25), each of the at least five burners (21, 22, 23, 24, 25) having a central axis (31, 32, 33, 34, 35) and one or more nozzles (41,42,43,44,45); the burner positioning plane being perpendicular to the vertical central axis of the furnace (7) and arranged at a weighted average distance from each of the nozzles (41,42,43,44,45); characterized in that each of the at least five submerged combustion burners (21,22,23,24,25) is arranged to extend from the respective burner position (51,52,53,54,55) defined by the intersection between the central burner axis (31, 32, 33, 34, 35) and the positioning plane of the burners (14); each burner position (51,52,53,54,55) is arranged at a burner distance (512,523,534,545,551) defined as the distance between a burner and each of the two adjacent adjacent burners (51,52,53,54, 55) and the difference between each burner distance and the arithmetic average of the burner distances is at most 20% of the arithmetic mean of the burner distance; each central burner axis (31, 32, 33, 34, 35) is associated with a burner ring (71, 72, 73, 74, 75) which extends around the central axis of said burner (31, 32 , 33, 34, 35) and has a radius (r1, r2, r3, r4, r5) which is equal to the weighted average distance between the central axis of the burner and the circumferential wall of the furnace; the difference between the radius of each burner circle (71,72,73,74,75) and the arithmetic mean radius of the burner rings (71,72,73,74,75) is at most 20% of this medium radius; and the furnace comprises a central zone (70) at the positioning plane (14) housed between the burner rings (71,72,73,74,75), having a diameter of at least 250 mm. 2 glass furnace according to claim 1 characterized in that it is equipped with 5 to 10 immersed combustion burners. 3 glass furnace according to one of the preceding claims characterized in that each central axis of the burner is arranged at an angle of less than 15 ° relative to the vertical. 4 glass furnace according to one of the preceding claims characterized in that for one or more burners, the central axis of the burner forms an angle of at least 1 ° relative to a plane which is perpendicular to the positioning plane of the burners , passes through the vertical central axis of the furnace and the position of the respective burner. Glass furnace according to one of the preceding claims, characterized in that the central burner axis of one or more of the submerged combustion burners consists of the central axis of the concentric tubes of a concentric tube burner. Glass furnace according to one of the preceding claims, characterized in that the melting chamber is substantially cylindrical. 7 glass furnace according to one of the preceding claims characterized in that the> melting chamber is substantially cylindrical and has an inner diameter of between 1.5 and 3.5 m. 8 glass furnace according to one of the preceding claims characterized in that the weighted mean distance between the central axis of each of the burners and the circumferential wall is between 5 cm and 80 cm. 9 glass furnace according to one of the preceding claims characterized in that the distance between adjacent burners in relation to each of the at least five submerged combustion burners is between 25 cm and 120 cm. Glass furnace according to one of the preceding claims, characterized in that the distance between each burner position in relation to each of the at least five immersed combustion burners and the vertical central axis of the furnace is between 50 cm and 150 cm. . 11 Production line of a glass product selected from glass fiber, glass wool and rock wool, comprising: a glass furnace according to one of the preceding claims; and a fibrising device for converting the molten bath of the oven into fibers. Process for preparing a melt of vitrifiable materials, comprising the following steps: loading of solid raw materials into a melting furnace; and melting the solid raw materials into the submerged combustion melting furnace to form a melt of vitrifiable materials in the furnace; a substantially toroidal flow being generated in the melt during the melting step, having flows converging towards the central vertical axis of the furnace at the surface of the melt, the axis of revolution of the toroid being substantially vertical. Process according to Claim 12, characterized in that the molten bath follows a downward movement in the center of the melting chamber near the axis of revolution and is recirculated in an upward movement towards the surface of the molten bath. Process according to Claim 12 or 13, characterized in that the melting furnace is a furnace according to one of Claims 1 to 11.