Electric glass manufacturing furnace

Abstract

The invention relates to an at least partially electrical glass manufacturing furnace (1) comprising a melting tank (2) made of a refractory material adapted to contain a bath (3) of a molten batch of material and a plurality of immersion heating electrodes (An, Bn, Cn, Dn) immersed from a free surface of the bath (3) and supplied with electrical current by an electrical facility (4), the electrical installation (4) is configured to generate a two-phase alternating current. This makes it possible to heat a larger furnace / reduce the number of electrodes.

Description

[0001] The present invention belongs to the general field of glass production. The present invention more particularly relates to at least partially electric glass furnaces suitable for melting vitrifiable materials. The present invention also relates to a method for melting vitrifiable materials in order to be able to manufacture glass. The present invention has particularly advantageous applications in the production of glass wool, rock wool, textile glass yarn, and / or flat or hollow glass, but is in no way limited thereto.

[0002] In the present specification, "vitrifiable material" or "raw material" is understood to mean all materials, natural ores or synthetic products that can enter the composition fed to the glass furnace, materials derived from recycling such as cullet, etc. This includes silica sand, but also all additives (sodium carbonate, limestone, dolomite, alumina, etc.), waste materials (including mineral fibers) that can be generated from the production of said fibers or from construction sites or demolition sites, all possible liquid or solid fuels (composite or non-composite plastics, organic materials, coal), and any type of cullet. Also included are recyclable materials containing combustible (organic) elements, such as, for example, sized mineral fibers with adhesives (of the type used for thermal insulation or sound insulation or for reinforcing plastic materials), laminated assembly glass (such as windshields) with sheets of polyvinyl butyral polymer, glass bottles (household cullet), or any type of "composite" material combining glass and plastic materials, such as certain bottles. Also recyclable are "glass-metal composite materials or metal compounds", such as functionalized assembly glass with a metal-containing coating. In the specification, a "bath of vitrifiable materials" or a "glass bath" means the molten product of these raw materials.

[0003] Likewise, "glass" is understood to mean glass in a broad sense, i.e., covering any material having a vitreous, glass-ceramic or ceramic matrix.

[0004] Furthermore, the term "manufacture" includes the indispensable step of melting the vitrifiable materials, and, if necessary, all subsequent steps of refining / conditioning the molten glass for its final shaping, particularly in the form of flat glass (assembly glass), hollow glass (bottles, jars), glass in the form of mineral wool (particularly rock wool or glass wool) used for its thermal insulation or sound insulation properties, or even optionally glass in the form of textile yarns used for reinforcing materials.

[0005] Various examples of electric furnace designs are known from the prior art and in particular from patent EP0671116B1, in which an electric current is conducted in a bath of vitrifiable material through so-called "top-entry" electrodes that are immersed from the free surface of the bath. This type of top-entry electrode is particularly different from the so-called "submerged" electrodes, which are arranged vertically in the bath from the furnace floor or horizontally through the side walls of the furnace. Compared with the latter, the top-entry electrodes offer a number of advantages. First of all, they avoid the difficulties associated with the immersed electrodes passing through the bottom or side wall refractories, as well as the problems of replacing these electrodes when worn, and the problems associated with the sealing of the melting bath or refractory wear, especially due to the high temperatures that favor refractory erosion and due to the strong convection currents generated near the electrodes during operation.

[0006] Generally, these top-entry electrodes are supplied with three-phase current. The three-phase current offers a number of advantages, especially the fact that the three-phase current is the so-called "industrial" current that is usually distributed by energy suppliers to factories, thus resulting in the adjustment of the machine. For example, unlike single-phase current, the three-phase current also delivers instantaneous power without a pulsating component. However, it should be noted that the principle of phase balance tends to a triangular or hexagonal arrangement of the electrodes on the surface of the glass bath. While such a geometric constraint does not seem a priori to pose a problem in the case of small electric furnaces, it does pose a problem in the case of large electric furnaces (where the glass bath extends over 25 m 2 , preferably over 40 m 2 , or even over 100 m 2 , and where the side-to-side width of the glass bath is greater than 5 m, preferably greater than 6.5 m). In such a configuration and taking into account the above geometric constraints, the current tends to concentrate between the electrodes at the same bath edge and / or adjacent bath edges, thereby reducing the distance covered by the current within the glass bath and thus reducing the resistance of the glass bath to the passage of this current. For a predetermined electric power corresponding to the energy required to melt the vitrifiable material and in the case of a glass bath that only offers a reduced resistance, it is therefore necessary to increase the intensity of the current delivered. However, the wear of the electrodes and the refractories constituting the bath increases with the intensity of the current passed through the electrodes. To overcome this wear problem, the natural solution is to distribute the current delivered between a larger number of electrodes, but this has the disadvantage of increasing the operating cost of these electrodes - because there are more electrodes - without solving certain problems of non-uniform current distribution within the glass bath.

[0007] The object of the present invention is to overcome some or all of the disadvantages of the prior art, especially those set out above.

[0008] To this end, and according to a first aspect, the present invention relates to an at least partially electrical glass melting furnace comprising a melting tank made of refractory material adapted to contain a bath of molten vitrifiable material and a plurality of top-entry heating electrodes which dip into the free surface of the bath and are supplied with current by electrical equipment, the furnace being characterized in that the electrical equipment is configured to generate two-phase alternating current.

[0009] For the purposes of the present invention, the term "two-phase alternating current" refers to a system of two phases having the same frequency and amplitude, the two phases being orthogonal, i.e. phase-shifted from each other by 90° or π / 2 radians.

[0010] In the current situation where the current is distributed in three-phase form by the energy supplier, implementing electrical equipment adapted to convert such three-phase current into two-phase current implies a priori unnecessary technical complexity and a non-negligible increase in the initial cost of such technical equipment.

[0011] Despite these a priori disadvantages, and in the specific case of powering the top-entry electrodes of a glass melting furnace, the inventors have found that such a two-phase system enables the glass melting furnace designer to get rid of certain geometric constraints and associated technical drawbacks specific to three-phase systems, including the large number of electrodes to be used and the non-uniform distribution of current within the bath of vitrifiable material.

[0012] In contrast, the two-phase system offers the glass melting furnace designer the possibility of further spacing apart the electrodes fed by the same phase, for example by positioning the electrodes near opposite edges of the melting tank. Compared to a three-phase system, and for a given electrical power, the resistance generated by the glass bath - which increases as the distance covered by the current within the glass bath increases - is greater, meaning that the current to be delivered is reduced. The intensity can then be distributed between a reduced number of electrodes and / or the intensity delivered to each electrode can be limited, thereby increasing their service life.

[0013] According to a particular embodiment, the electrical equipment comprises at least one two-phase transformer adapted to generate two single-phase output sets with a 90° phase difference between each output set, each output set supplying at least one pair of said electrodes.

[0014] For the purposes of the present invention, the term "output set" refers to a set of phase-aligned outputs of a two-phase transformer. Conventionally, and as shown in Figure 2 and the description of the particular embodiments of the present invention, an output set only comprises a single output connected to a plurality of electrode pairs (three in the embodiment shown in Figure 2 ) which supplies single-phase alternating current.

[0015] According to a particular embodiment, at least one output group of the at least one two-phase transformer feeds at least two pairs of electrodes, preferably three pairs of electrodes.

[0016] Connecting the output group to the bundle, or in other words, to a plurality of pairs of electrodes, enables the current intensity to be distributed therebetween, thereby limiting the wear over time of each of them. Conversely, using a single pair of electrodes fed by a group of outputs limits the initial cost of the device.

[0017] According to a particular embodiment, at least one output group of the at least one two-phase transformer includes one or more outputs.

[0018] According to this alternative embodiment, shown particularly in Figure 3 , the output group includes, for example, a plurality of outputs mounted in parallel, each output being connected to one or more pairs of electrodes. In all cases, the single-phase currents delivered to each of these electrodes are phase-aligned.

[0019] According to a particular embodiment, each bundle of electrodes is arranged in a bath of vitrifiable material in a molten state in such a way as to follow central symmetry along a theoretical horizontal plane.

[0020] Following such an axis of symmetry ensures a more uniform distribution of the current between the electrodes and thus limits the possibility that one of these electrodes wears out faster than the others.

[0021] According to a particular embodiment, the electrodes of the same output group are arranged near opposite walls of the tank.

[0022] This advantageous geometric arrangement of the pairs of electrodes is particularly well suited to two-phase operation, in which the distance between the electrodes connected to the two terminals of the same output group can be increased without the risk of the electrodes arranged near the same wall exchanging with each other.

[0023] According to a particular embodiment, the pairs of electrodes powered by the same two-phase transformer are arranged in a quadrilateral, preferably in a rectangle, preferably in a square, along a theoretical horizontal plane in a bath of vitrifiable material in a molten state.

[0024] This advantageous geometric arrangement of the pairs of electrodes is particularly suitable for two-phase operation and enables the current to be balanced. Such a quadrilateral arrangement contrasts particularly with the triangular or hexagonal-shaped arrangements typical of three-phase systems.

[0025] According to a particular embodiment, the minimum distance between each electrode and the closest tank wall is greater than 450 mm, preferably greater than 600 mm, more preferably greater than 800 mm, preferably greater than 950 mm, preferably greater than 1075 mm.

[0026] For the purposes of the present invention, such a minimum distance is measured along the normal to the wall of the trough closest to and passing through the electrode. Note that the convective movement of the glass bath generated near each electrode tends to corrode the adjacent trough wall. Therefore, moving the electrode away from the trough limits such premature wear of the trough wall.

[0027] According to a particular embodiment, each of the electrodes comprises a horizontally projecting arm, preferably having a square cross-section, which extends horizontally by more than 2000 mm, preferably more than 2500 mm, preferably more than 3000 mm, preferably more than 3500 mm, preferably more than 3700 mm, preferably more than 3900 mm.

[0028] Using an electrode arm with a square cross-section gives the electrode arm greater resistance to bending. This is particularly useful when the electrode arm is long. In particular, a long electrode arm allows the electrode to be moved further away from the adjacent trough wall in order to limit wear on the adjacent trough wall. This distance between the electrode and the trough wall is all the more advantageous when the furnace power is increased. Since power depends on voltage and current, these two parameters are subsequently adjusted to higher values as the power increases. The result is an enhancement of the convective movement of the glass bath generated near each electrode, which tends to corrode the adjacent trough wall. Moving the electrode away from the trough wall limits such premature wear of the trough wall.

[0029] According to a particular embodiment, the electrical equipment is adapted such that all pairs of electrodes connected to the same output set of the two-phase transformer are supplied with current at the same voltage.

[0030] According to a particular embodiment, the glass furnace is fully electrical and preferably includes a cold crown (5).

[0031] For the purposes of the present invention, the furnace is said to be "fully electrical" in the sense that all of the heating energy supplied to the glass bath is of an electrical nature. Such a furnace thus lacks heating burners.

[0032] According to a particular embodiment, the glass furnace includes a plurality of, preferably three, of said two-phase transformers.

[0033] Using a plurality of two-phase transformers is particularly suitable for supplying power to large furnaces, where the use of a two-phase system is particularly advantageous.

[0034] According to a particular embodiment, the melting trough is dimensioned such that the bath of molten vitrifiable material has a length greater than 25 m 2 、preferably greater than 40 m 2 、preferably greater than 60 m 2 、preferably greater than 100 m 2surface area, and preferably has a distance between two opposite walls of the trough greater than 5 m, preferably greater than 6.5 m.

[0035] Such dimensions relate to so-called large electric furnaces, for which the use of a two-phase system is particularly advantageous.

[0036] For a person skilled in the art, constructing these so-called large electric furnaces usually encounters technical obstacles.

[0037] The first obstacle is that melting the vitrifiable material requires a large amount of electric power. This large amount of electric power results in higher current and voltage at the electrodes, enhancing the convective movement of the glass bath generated near each electrode, which tends to corrode the adjacent trough walls.

[0038] The second obstacle is that the larger the area of these furnaces, the greater the length and width of the basin. Therefore, it must be possible to supply heating energy to any point, including supplying heating energy to the center of the furnace - the area farthest from the walls.

[0039] The present invention solves these obstacles by a synergistic combination of the use of a two-phase system having arms with a horizontal extension greater than 2000 mm, preferably greater than 2500 mm, preferably greater than 3000 mm, preferably greater than 3500 mm, preferably greater than 3700 mm, preferably greater than 3900 mm. This synergy is based on the fact that for a given power level, the two-phase system allows for less current to be obtained at the electrodes than a three-phase system. This means that for the same current, a higher power output can be obtained. The possibility of having a greater power or even a greater current is associated with arms having a greater horizontal extension. These arms with their greater horizontal extension enable the electrodes to be further away from the walls, thereby reducing the risk of trough wall corrosion while being able to heat distant areas. In addition, the use of a two-phase system reduces the number of electrodes and thus reduces the cost of the equipment. The number of electrodes per square meter (m 2 ) is from 0.1 to 0.45, preferably from 0.15 to 0.4, and even more preferably from 0.2 to 0.35.

[0040] According to a specific embodiment, these so-called large furnaces are obtained by adding a plurality of basic modules. The basic modules are then considered to be equivalents of the furnaces, the troughs of which have a defined length and width, and the basic module includes a series of heating electrodes with a defined arrangement. Preferably, the basic module is square. The so-called large furnace then includes at least two consecutively arranged basic modules, that is, it includes a trough, the length and width dimensions of which are multiples of the defined values of the basic module. Then, the so-called large furnace can be simply obtained, which can have various shapes such as rectangular, square, L-shaped or T-shaped.

[0041] According to a particular embodiment, the two-phase transformer supplies power to a plurality of electrodes that is less than or equal to 16, preferably less than or equal to 12, and preferably less than or equal to 8.

[0042] Depending on whether each output group supplies power to two sets of four electrodes, two sets of three electrodes, or two sets of two electrodes, the total number of electrodes supplied by a single two-phase transformer varies between 16, 12, and 8 electrodes, respectively.

[0043] Compared to a three-phase system, and for a glass bath module with an equivalent surface area - and thus an equivalent electric power - the two-phase system offers the possibility of reducing the number of electrodes used in the furnace.

[0044] According to a particular embodiment, the present invention relates to a method for melting vitrifiable materials implemented by means of such a glass furnace, characterized in that the method comprises at least one step of electrically heating the bath of molten vitrifiable materials by means of the plurality of electrodes and by applying a two-phase alternating current in the bath.

[0045] According to a particular embodiment, all electrode pairs connected to the same output group of the two-phase transformer are supplied with current at the same voltage.

[0046] According to a particular embodiment, the present invention relates to a method for manufacturing glass wool, rock wool, glass textile yarn, and / or flat or hollow glass, characterized in that it implements such a melting method.

[0047] Other features and advantages of the present invention will become apparent from the non-limiting description given below with reference to the accompanying drawings, which show exemplary embodiments of the present invention. In the drawings:

[0048] Figure 1 Figure 1 shows a schematic cross-sectional view of an electric glass furnace;

[0049] Figure 2 Figure 2 shows a schematic top view of the glass bath and top-entry electrodes of an electric furnace according to a particular embodiment of the present invention;

[0050] Figure 3 Figure 3 shows a schematic top view of the glass bath and top-entry electrodes of an electric furnace according to an alternative embodiment of the present invention;

[0051] Figure 4 Figure 4 is a flowchart showing the successive steps of a manufacturing method according to a particular embodiment of the present invention. ​​​​​​​​

[0052] Figure 1 shows a schematic cross-sectional view of an electric glass melting furnace 1. Such a glass melting furnace 1 includes a melting trough 2 made of refractory material adapted to contain a bath 3 of molten vitrifiable material and a plurality of top-entry heating electrodes (An, Bn, Cn, Dn) (only one is shown in Figure 1 ), the arms of said heating electrodes having a square cross-section and being immersed from the free surface of said bath 3 and supplied with current by an electrical device 4. It is well known that the part of the electrode in contact with the glass bath is made of molybdenum. The glass melting furnace 1 according to the present invention is particularly characterized in that the electrical device 4 is adapted to generate two-phase alternating current.

[0053] According to Figure 1 the specific embodiment shown, the furnace 1 is entirely electric and equipped with a cold furnace top 5.

[0054] According to a specific embodiment and as shown in Figure 2 , the electrical device includes a two-phase transformer 6 adapted to generate two single-phase output groups (A - B, C - D) with a 90° phase difference between each output group (A - B, C - D). According to this specific embodiment, the output group includes only a single output (A - B, C - D) which is connected to a bundle of three pairs of electrodes ((An; Bn); (Cn; Dn), where n = 1, 2, 3), and said single output is supplied with single-phase alternating current. The bundle of electrodes is arranged in the bath 3 in a substantially square shape and in a manner that follows central symmetry along a theoretical horizontal plane with respect to a point O located at the center of the bath 3.

[0055] According to Figure 3 this alternative embodiment shown, the first output group includes a plurality of outputs (A - B, A' - B') mounted in parallel, the first output A - B being connected to a bundle of two pairs of electrodes ((An; Bn); (Cn; Dn), where n = 1, 2), and the second output A' - B being connected to a single pair of electrodes (A3; B3). In all cases, the single-phase current delivered to each of these electrodes is phase-aligned.

[0056] ​In practice, the first single-phase current is generated by the transformer 6 at the terminals of the first output group A - B and passes, on the one hand, through the glass bath between the electrodes A1, A2, A3 and, on the other hand, through the glass bath between the electrodes B1, B2, B3, thereby heating the bath 3 of the vitrifiable material by the Joule effect. In parallel, a second single-phase current is generated by the transformer 6 at the terminals of the second output group C - D, the second single-phase current having the same frequency and amplitude as the first current but being phase-shifted by 90° or π / 2 radians with respect to the first current, and passing, on the one hand, through the glass bath between the electrodes C1, C2, C3 and, on the other hand, through the glass bath between the electrodes D1, D2, D3, thereby heating the bath 3 of the vitrifiable material by the Joule effect. Overall, the electrical device 6 is thus adapted to generate a two-phase alternating current in the glass bath 3.

[0057] According to Figure 2 and 3 the embodiment shown, the electrical device comprises only the two-phase transformer 6, which supplies power to the electrode "blocks" (An, Bn, Cn, Dn). According to an alternative embodiment not shown, particularly relating to large electric melting furnaces, the electrical device comprises a plurality of two-phase transformers, which respectively supply power to a plurality of electrode blocks covering the surface of the glass bath 3.

[0058] Figure 4 is a flow chart showing the successive steps of a manufacturing method according to a particular embodiment of the invention, which comprises a first step S1 of melting the vitrifiable material by electrically heating the bath 3 of the vitrifiable material by means of a two-phase alternating current, and a second step S2 of manufacturing glass wool, rock wool, glass fabric filaments and / or flat or hollow glass.​

Claims

1. An at least partially electrical glass melting furnace (1), comprising a melting trough (2) made of refractory material adapted to accommodate a bath (3) of molten vitrifiable material and a plurality of top-entry heating electrodes (An, Bn, Cn, Dn), said top-entry heating electrodes (An, Bn, Cn, Dn) being immersed from the free surface of the bath (3) and being supplied with electric current by an electrical device (4), characterized in that the electrical device (4) is configured to generate two-phase alternating current.

2. The glass melting furnace (1) according to claim 1, characterized in that, The electrical device comprises at least one two-phase transformer (6), said two-phase transformer (6) being adapted to generate two single-phase output groups (A-B, C-D) having a phase difference of 90° between each output group (A-B, C-D), each output group (A-B, C-D) supplying at least one pair of said electrodes ((An; Bn); (Cn; Dn)).

3. The glass melting furnace (1) according to claim 2, characterized in that, At least one output group (A-B, C-D) of the at least one two-phase transformer (6) supplies a bundle of at least two electrode pairs ((An; Bn); (Cn; Dn)), preferably three electrode pairs ((An; Bn); (Cn; Dn)).

4. The glass melting furnace (1) according to any one of claims 2 and 3, characterized in that, At least one output group (A-B, C-D) of the at least one two-phase transformer (6) comprises one or more outputs.

5. The glass melting furnace (1) according to any one of claims 3 and 4, characterized in that, Each electrode bundle ((An; Bn); (Cn; Dn)) is arranged in the bath (3) of molten vitrifiable material in such a way as to follow central symmetry along a theoretical horizontal plane.

6. The glass melting furnace (1) according to any one of claims 2 to 5, characterized in that The electrodes of the same output group (A-B, C-D) are arranged near opposite walls of the trough (2).

7. The glass melting furnace (1) according to any one of claims 2 to 6, characterized in that, The electrode pairs ((An; Bn); (Cn; Dn)) supplied by the same two-phase transformer (6) are arranged in a quadrilateral configuration, preferably in a rectangle, preferably in a square, along a theoretical horizontal plane in the bath (3) of molten vitrifiable material.

8. The glass melting furnace (1) according to any one of claims 1 to 7, characterized in that, The minimum distance (dmin) between each electrode (An, Bn, Cn, Dn) and the closest trough wall (2) is greater than 450 mm, preferably greater than 600 mm, preferably greater than 800 mm, preferably greater than 950 mm, preferably greater than 1075 mm.

9. The glass melting furnace (1) according to any one of claims 1 to 8, characterized in that, Each of the electrodes (An, Bn, Cn, Dn) comprises a horizontally projecting arm, preferably having a square cross-section, which extends horizontally by more than 2000 mm, preferably more than 2500 mm, preferably more than 3000 mm, preferably more than 3500 mm, preferably more than 3700 mm, preferably more than 3900 mm.

10. The glass melting furnace (1) according to any one of claims 2 to 9, characterized in that, The electrical device (4) is adapted such that all electrode pairs connected to the same output group (A-B, C-D) of the two-phase transformer (6) are supplied with current at the same voltage.

11. The glass melting furnace (1) according to any one of claims 1 to 10, characterized in that, It is fully electrical and preferably comprises a cold hearth roof (5).

12. The glass melting furnace (1) according to any one of claims 2 to 11, characterized in that, It comprises a plurality of, preferably three, said two-phase transformers (6).

13. The glass melting furnace (1) according to any one of claims 1 to 12, characterized in that, The melting tank (2) is dimensioned such that the bath (3) of the molten vitrifiable material has a surface area greater than 25 m 2 , preferably greater than 40 m 2 , preferably greater than 60 m 2 , preferably greater than 100 m 2 , and preferably has a distance between two opposite walls of the tank (2) greater than 5 m, preferably greater than 6.5 m.

14. The glass melting furnace (1) according to any one of claims 2 to 13, characterized in that, The two-phase transformer (6) supplies a plurality of electrodes less than or equal to 16, preferably less than or equal to 12, preferably less than or equal to 8.

15. The glass melting furnace (1) according to any one of claims 2 to 13, characterized in that, The number of electrodes per square meter is from 0.1 to 0.45, preferably from 0.15 to 0.4 and even more preferably from 0.2 to 0.

35.

16. A method for melting a vitrifiable material using a glass melting furnace (1) according to any one of claims 1 to 15, characterized in that, It includes at least one step of electrically heating the bath (3) of the fusible vitrifiable material by means of the plurality of electrodes (An, Bn, Cn, Dn) and by applying a two-phase alternating current within the bath (3).

17. A method for melting vitrifiable materials according to claim 16 by means of a glass melting furnace (1) according to claim 10, characterized in that, All electrode pairs ((An; Bn); (Cn; Dn)) connected to the same output group (A - B, C - D) of the two-phase transformer (6) are supplied with current at the same voltage.

18. A method for manufacturing glass wool, rock wool, glass fabric filaments, and / or flat or hollow glass, characterized in that, It implements the melting method according to any one of claims 16 and 17.

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