Electrical equipment for glassmaking furnaces

Abstract

To provide an at least partially electric glass furnace suitable for melting vitrifiable materials. [Solution] The present invention relates to an at least partially electric glass furnace (1), comprising a melting tank (2) made of refractory material suitable for containing a bath (3) of molten vitrifiable material, and a plurality of electrodes (An, Bn, Cn, Dn) supplied with alternating current by an electrical installation (4) for heating the bath (3), the electrical installation (4) comprising at least one transformer (6) adapted to generate a plurality of single-phase output groups having a phase difference between each output group, each output being connected to at least one of the electrodes (An, Bn, Cn, Dn) by a single-phase conductor (7) for generating a first magnetic field (B1), and including a device arranged in the first magnetic field capable of generating a counter magnetic field.

Description

[Technical Field]

[0001] The present invention belongs to the general field of glass production. The invention more particularly relates to an at least partially electric glass furnace suitable for melting vitrifiable material. The invention also relates to a method for melting vitrifiable material to enable glass to be produced. Particularly advantageous applications of the invention are found in, but are not limited to, the production of glass wool, rock wool, textile glass yarns and / or flat or hollow glass. [Background technology]

[0002] As used herein, "vitrifiable materials" or "raw materials" refers to all materials, natural or synthetic, and materials derived from recycling, such as cullet, that can be added to the composition fed to a glass furnace. This includes silica sand, but also all additives (sodium carbonate, limestone, dolomite, alumina, etc.), waste materials (including inorganic fibers) that may be produced from fiber manufacturing or construction 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 sized inorganic fibers with binders (such as those used for thermal or acoustic insulation or for reinforcing plastics), glazing laminated with sheets of polyvinyl butyral polymer, such as windshields, glass bottles (household cullet), or any type of "composite" material combining glass and plastic materials, such as certain bottles. Also recyclable are "glass-metal composites or metal compounds," such as functionalized glazing with a metal-containing coating. As used herein, "bath of vitrifiable material" or "glass bath" refers to the molten product of these raw materials.

[0003] Similarly, "glass" is understood to be meant to encompass glass in the broad sense, i.e., any material having a vitreous, glass-ceramic, or ceramic matrix.

[0004] In addition, the term "manufacturing" includes the essential step of melting the vitrifiable material and, if necessary, all subsequent steps of refining / conditioning the molten glass for its final shaping, in particular in the form of flat glass (glazing), hollow glass (bottles, jars), mineral wool (in particular rock wool or glass wool) used for its thermal or sound insulating properties, or even glass in the form of textile yarns used for reinforcement.

[0005] Various examples of electric furnace designs are known from the state of the art, in which the electric current is conducted through heating electrodes in a bath of vitrifiable material. Such electrodes may be of the "submerged" type, either vertically arranged from the hearth into the bath or horizontally arranged through the side walls of the furnace, and / or of the "top entry" type, immersed from the free surface of the bath.

[0006] The electrodes are supplied with alternating current by an electrical installation comprising at least one transformer adapted to generate a plurality of single-phase output groups with a phase difference between each output group, each output being connected to at least one of said electrodes by a single-phase conductor.

[0007] Surprisingly, the inventors, glass furnace designers, have observed a phenomenon of heating of certain metallic structures located in the vicinity of these single-phase conductors, which is theoretically harmless in small electric furnaces, but which they have found to be problematic in large furnaces, where the bath of molten vitrifiable material is 25 m 2 Larger, preferably 49m 2They have a larger surface area and preferentially have a distance between two opposing walls of the tank of more than 5 m, preferentially more than 7 m. Considering the power required to supply these large furnaces, single-phase conductors carry currents whose intensities exceed 1000 A, preferentially exceed 4000 A, preferentially exceed 6000 A. At these levels of electrical intensity, the heating of the metal structures located in the vicinity of these single-phase conductors becomes much more significant and can even lead to the deterioration of the metal structures. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to remedy some or all of the drawbacks of the prior art, in particular the drawbacks mentioned above. [Means for solving the problem]

[0009] To this end, and according to a first aspect, the present invention relates to an at least partially electric glass furnace, comprising a melting tank made of refractory material suitable for containing a bath of molten vitrifiable material, and a plurality of electrodes for heating said bath supplied with alternating current by an electrical installation comprising at least one transformer adapted to generate a plurality of single-phase output groups with a phase difference between each output group, each output being connected to at least one of said electrodes by a single-phase conductor generating a first magnetic field, characterized in that said glass furnace comprises at least one, preferably a plurality of, counter-reaction devices arranged in said first magnetic field and configured to generate a counter-magnetic field. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows a schematic side view of an electric glass furnace. [Figure 2] FIG. 2 shows a schematic top view of a glass bath and electrodes of an electric furnace according to a specific embodiment of the present invention. [Figure 3]FIG. 3 shows a schematic diagram of the electrical installation and counter-reactor of a glass furnace according to a particular embodiment of the invention. [Figure 4] FIG. 4 shows a schematic representation of details of a counter-reactor for a glass furnace according to a particular embodiment of the invention. [Figure 5] FIG. 5 is a flow chart illustrating the sequence of steps in a manufacturing method according to a particular embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] For the purposes of the present invention, a counter magnetic field means a magnetic field that is in the opposite direction and therefore cancels out a first magnetic field.

[0012] The invention is based firstly on the fact that the inventors, designers of glass furnaces, have surprisingly observed the phenomenon of heating of certain metal structures placed close to single-phase conductors supplying current to the electrodes, then on the understanding of this phenomenon, and finally on the implementation of a counter-reaction device which makes it possible to mitigate this undesired heating of these metal structures.

[0013] More precisely, we believe that this heating phenomenon is related to the generation of currents in these metallic structures induced by a first magnetic field, i.e., the magnetic field generated by the current flowing in the single-phase conductor. These induced currents not only increase the risk of electric shock, but also heat the metallic structures due to the Joule effect.

[0014] In contrast to this, the present invention is based on the novel inventive idea of ​​implementing a counter-reaction device arranged in said first magnetic field and adapted to generate a counter-magnetic field, thereby reducing the risk of generating induced currents and, consequently, the associated risks of overheating and electric shock.

[0015] According to a particular embodiment, such a glass furnace comprises a single counter-reactor arranged within the above-mentioned first magnetic field of each single-phase conductor and adapted to generate a counter-magnetic field.

[0016] According to certain embodiments, such a counter-reaction device comprises a closed loop, at least one portion of which is made of a conductive metallic material selected from the group including copper, aluminum and iron, said portion being positioned within said first magnetic field and adapted to generate a counter-magnetic field.

[0017] Specifically, according to the principles of Faraday and Lenz's law, when a conductive material is placed in a varying magnetic field, an electric field is generated within it, which in turn generates circular induced currents known as "eddy currents." The induced currents then generate magnetic fields that oppose the changing magnetic flux that gave rise to them, thus causing their decay.

[0018] According to a particular embodiment, said portion of the closed loop is in the form of a cable, a metal bar or a box.

[0019] According to a particular embodiment, the closed loop is connected to ground at a single point.

[0020] According to certain embodiments, the voltage difference between the closed loop and the transformer is monitored to detect voltage rises associated with possible ground faults.

[0021] According to a particular embodiment, the closed loop comprises a current control system having a cut-off threshold for the closed loop.

[0022] Such a safety device prevents the risk of closed loop overheating and therefore the risk of fire.

[0023] According to a particular embodiment, said portion of the closed loop is located less than 1.0 meter, preferably less than 0.5 meter, preferably less than 0.3 meter from said single phase conductor (7).

[0024] By placing this portion of the closed loop in close proximity to the single-phase conductor, it is possible to capture a larger proportion of the magnetic field emitted by the single-phase conductor and therefore to better attenuate it.

[0025] According to a particular embodiment, said portion of the closed loop is located more than 0.1 meters, preferably more than 0.2 meters, from said single-phase conductor and / or said single-phase conductor is coated with an electrical insulator, preferably plastic.

[0026] Maintaining a minimum distance between the closed loop and the single-phase conductors and / or electrically insulating the latter prevents the risk of direct contact, especially after the formation of an electric arc. This risk is particularly high during the switched-on state of the electrical installation, when a current with a very high voltage, known as the magnetizing voltage, flows through the system.

[0027] According to a particular embodiment, the melting tank has a bath of molten vitrification raw material of 25 m 2 Larger surface area, preferentially 40m 2 Larger, preferably 60m 2 Larger, preferably 100m 2 It has a larger surface area and is preferentially dimensioned so that the distance between two opposing walls of the tank is greater than 5 m, preferably greater than 6.5 m.

[0028] Such dimensions relate to so-called large electric furnaces, for which the use of a two-phase system is particularly advantageous.

[0029] According to a particular embodiment, the electrical installation is adapted to generate two-phase or three-phase alternating current.

[0030] Three-phase current offers many advantages, particularly in that it is the so-called "industrial" current that is customarily distributed to factories by energy suppliers, and therefore offers advantages in terms of equipment compatibility. Furthermore, three-phase current also provides instantaneous power without pulse components, unlike, for example, single-phase current. However, it should be noted that the principle of phase balance tends towards a triangular or hexagonal arrangement of electrodes on the surface of the glass bath. While such geometric constraints do not seem to pose a theoretical challenge in the context of small electric furnaces, they do pose challenges in the context of large electric furnaces, in the case of large electric furnaces, where the glass bath is typically 25 m 2 Ultra, preferentially 40m 2 Ultra, 60m as a priority 2 Over, preferentially 100m 2 The tank (2) extends over an area of ​​more than 1000 m, and the distance between the two opposing walls of the tank (2) is greater than 5 m, preferentially greater than 6.5 m. In such a configuration, taking into account the aforementioned geometric constraints, the current tends to concentrate between the electrodes at the same and / or adjacent tank ends, thus reducing the distance covered by the current in the glass bath and, therefore, the resistance of the glass bath to the passage of this current. For a given power corresponding to the energy required to melt the vitrifiable material, and in the context of a glass bath that offers only reduced resistance, it becomes necessary to increase the intensity of the current being sent. However, with the intensity of the current being sent per electrode, wear on the electrodes and refractories that make up the tank increases. To overcome this wear problem, a natural solution is to distribute the current being sent among a greater number of electrodes. However, this has the drawback of increasing the operating costs of these electrodes, since there are more of them, and does not solve the specific problem of non-uniformity in the current distribution in the glass bath.

[0031] According to a particular embodiment, at least one heating electrode, and preferentially all heating electrodes, are immersed below the surface of said bath of molten vitrifiable material.

[0032] Compared with so-called "immersed" electrodes, top-entry electrodes offer a number of advantages: firstly, they avoid the difficulties associated with the passage of immersed electrodes through the refractory, and also the problems of replacing these electrodes when worn, sealing the melt tank, or even wear of the refractory, especially due to the high temperatures and strong convection currents that arise in the vicinity of the electrodes during operation, which favor refractory attack.

[0033] According to a particular embodiment, said transformer is two-phase and supplies a number of electrodes equal to or less than 16, preferably equal to or less than 12, preferably equal to or less than 8.

[0034] Depending on whether each output group supplies four electrodes twice, three electrodes twice, or two electrodes twice, the total number of electrodes supplied from a single two-phase transformer varies between 16, 12, and 8, respectively.

[0035] Compared to three-phase systems, for glass bath modules of equivalent surface area (and therefore equivalent power), two-phase systems offer the possibility of reducing the number of electrodes used in the furnace.

[0036] According to a particular embodiment, the transformer is adapted to generate, in each output group, a single-phase alternating current having a current value greater than 1000 A, preferentially greater than 4000 A, preferentially greater than 6000 A.

[0037] According to a particular embodiment, the invention relates to a method for melting vitrifiable material carried out by such a glass furnace, characterized in that the method comprises at least one step of electrically heating a bath of molten vitrifiable material by means of said plurality of electrodes supplied with alternating current by said electrical installation.

[0038] According to a particular embodiment, the current value of said alternating current is greater than 1000A, preferably greater than 4000A, preferably greater than 6000A.

[0039] According to a particular embodiment, the present invention relates to a method for producing glass wool, rock wool, glass textile yarns and / or flat or hollow glass, characterized in that such a melting method is carried out.

[0040] 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 thereof. In the diagram: FIG. 1 shows a schematic side view of an electric glass furnace. FIG. 2 shows a schematic top view of a glass bath and electrodes of an electric furnace according to a specific embodiment of the present invention. FIG. 3 shows a schematic diagram of the electrical installation and counter-reactor of a glass furnace according to a particular embodiment of the invention. FIG. 4 shows a schematic representation of details of a counter-reactor for a glass furnace according to a particular embodiment of the invention. FIG. 5 is a flow chart illustrating the sequence of steps in a manufacturing method according to a particular embodiment of the present invention.

[0041] 1 shows a schematic side view of an electric glass furnace 1. Such a glass furnace 1 comprises a melting tank 2 made of a refractory material suitable for containing a bath 3 of molten vitrifiable material, and a number of heating electrodes (An, Bn), including top-entry electrodes An and so-called "immersion" electrodes Bn, which are supplied with electric current by an electrical installation 4 to which the electrodes are connected via a single-phase conductor 7.

[0042] According to alternative embodiments of the invention, all electrodes are immersed or all electrodes are top entry.

[0043] According to a particular embodiment shown in Figure 1, the furnace 1 is fully electric and comprises a cold crown 5. According to an alternative embodiment, such a glass furnace is of hybrid type and comprises, in addition to electrodes, combustion heating means, preferentially immersed and / or exposed burners, and a hot crown.

[0044] According to a particular embodiment, as shown in Figure 2, the electrical installation comprises a two-phase transformer 6 adapted to generate two single-phase output groups (AB, CD) with a phase difference of 90° between each output group (AB, CD). According to this particular embodiment, the output group includes only a single output (AB, CD) connected to a bundle of three electrode pairs ((An; Bn); (Cn; Dn) (n = 1, 2, 3) supplying a single-phase alternating current. The electrode bundle is arranged in the bath 3 in a square shape and with central symmetry along a theoretical horizontal plane with respect to a point O located at the center of the bath 3.

[0045] In practice, a first single-phase current is generated by the transformer 6 at the terminals of the first output group AB and passes through the glass bath between electrodes A1, A2, A3 on the one hand and electrodes B1, B2, B3 on the other hand, thereby heating the bath 3 of vitrifiable material by the Joule effect. In parallel, a second single-phase current of the same frequency and amplitude as the first current but phase-shifted by 90° or π / 2 radians with respect to the first current is generated by the transformer 6 at the terminals of the second output group CD and passes through the glass bath between electrodes C1, C2, C3 on the one hand and electrodes D1, D2, D3 on the other hand, thereby heating the bath 3 of vitrifiable material by the Joule effect. In this way, the electrical installation 6 as a whole is adapted to generate a two-phase alternating current in the glass bath 3.

[0046] Figure 3 shows schematically an electrical installation 4 and a counter-reaction device 8, the details of which are shown in Figure 4. Such a counter-reaction device 8 is arranged within a first magnetic field B1 generated by a conductor 7 and is adapted to generate a counter-magnetic field B2.

[0047] More precisely, this counter-reaction device 8 comprises a closed loop 9, at least part of which takes the form of a copper bar 10, which is placed in the first field B1 and which serves to generate a counter-magnetic field B2, thus reducing the risk of induced currents being generated and therefore the associated risks of overheating and electric shock. According to an alternative embodiment, said part 10 may take the form of a cable or a box and may be made of an electrically conductive material such as aluminium or iron.

[0048] According to the embodiment shown in Figure 3, the closed loop 9 is earthed at a single point, in particular to limit the risk of electric shock, and it also comprises a system for controlling the current (not shown) flowing through the closed loop, in order to prevent the risk of overheating of the closed loop and therefore the risk of fire.

[0049] Although it is not clear from the drawing, since there is no scale, the electric furnace in question has a surface area of ​​40 m 2 It should be noted that this furnace qualifies as large because it has a bath of molten vitrifiable material with a length exceeding 100 m and a distance between both opposing walls of the bath exceeding 6.5 m. Considering the power required to supply this furnace, a single-phase conductor carries a current with an intensity between 7000 and 8000 A.

[0050] FIG. 5 is a flow diagram showing the sequence of steps of a manufacturing method according to a particular embodiment of the invention, including a first step S1 of melting the vitrifiable material by electrically heating a bath 3 of vitrifiable material by means of a two-phase alternating current, and a second step S2 of producing glass wool, rock wool, glass textile yarns, and / or flat or hollow glass.

Claims

1. 1. An at least partially electric glass furnace (1), comprising: a melting tank (2) made of a refractory material suitable for containing a bath (3) of molten vitrifiable material; and a plurality of electrodes (An, Bn, Cn, Dn) supplied with alternating current by an electrical installation (4) for heating the bath (3), the electrical installation (4) comprising at least one transformer (6) adapted to generate a plurality of single-phase output groups with a phase difference between each output group, each output being connected to at least one of the electrodes (An, Bn, Cn, Dn) by a single-phase conductor (7) which generates a first magnetic field (B1), the glass furnace (1) comprising at least one, preferably a plurality of, counter-reaction devices (8) arranged in the first magnetic field (B1) and adapted to generate a counter-magnetic field (B2).

2. 2. A glass furnace (1) according to claim 1, characterized in that it comprises a single counter-reactor (8) arranged in the first magnetic field (B1) of each single-phase conductor (7) and adapted to generate a counter-magnetic field (B2).

3. 3. The glass furnace (1) according to claim 1 or 2, characterized in that the counter-reaction device (8) comprises a closed loop (9), at least one part (10) of which is made of an electrically conductive metallic material selected from the group comprising copper, aluminum and iron, said part (10) being arranged in the first magnetic field (B1) and adapted to generate the counter-magnetic field (B2).

4. 4. A glass furnace (1) according to claim 3, characterized in that said portion (10) of said closed loop (9) is in the form of a cable, a metal bar or a box.

5. 5. A glass furnace (1) according to claim 3 or 4, characterized in that the closed loop (9) is grounded at a single point.

6. Glass furnace (1) according to any one of claims 3 to 5, characterized in that the closed loop (9) comprises a current control system with a cut-off threshold for the closed loop (9).

7. 7. The glass furnace (1) according to any one of claims 3 to 6, characterized in that the portion (10) of the closed loop (9) is located less than 1.0 meter, preferably less than 0.5 meter, preferably less than 0.3 meter from the single-phase conductor (7).

8. 8. The glass furnace (1) according to any one of claims 3 to 7, characterized in that the portion (10) of the closed loop (9) is located more than 0.1 meters, preferably more than 0.2 meters, from the single-phase conductor (7) and / or the single-phase conductor (7) is covered with an electrical insulator, preferably plastic.

9. The melting tank (2) contains the bath (3) of molten vitrifiable material, the bath having a volume of 25 m ２ Larger, preferably 40m ２ Larger, preferably 60m ２ Larger, preferably 100m ２ 9. The glass furnace (1) according to any one of claims 1 to 8, which is dimensioned to have a larger surface area and preferably a distance between two opposite walls of the tank (2) greater than 5 m, preferentially greater than 6.5 m.

10. A glass furnace (1) according to any one of claims 1 to 9, characterized in that the electrical installation (4) is adapted to generate two-phase or three-phase alternating current.

11. 11. A glass furnace (1) according to any one of claims 1 to 10, characterized in that at least one heating electrode (An, Bn, Cn, Dn), preferably all heating electrodes (An, Bn, Cn, Dn), are immersed below the surface of the bath (3) of molten vitrifiable material.

12. 12. Glass furnace (1) according to claim 10 or 11, characterized in that the transformer (6) is two-phase and supplies a number of electrodes not exceeding 16, preferably not exceeding 12, preferably not exceeding 8.

13. 13. The glass furnace (1) according to any one of claims 1 to 12, characterized in that the transformer (6) is adapted to generate, in each output group, a single-phase alternating current having a current value greater than 1000 A, preferably greater than 4000 A, preferably greater than 6000 A.

14. 14. A method for melting vitrifiable material carried out by a glass furnace (1) according to any one of claims 1 to 13, characterized in that it comprises at least one step of electrically heating the bath (3) of molten vitrifiable material by means of the plurality of electrodes (An, Bn, Cn, Dn) supplied with alternating current by the electrical installation (4).

15. 15. A method for melting vitrifiable material according to claim 14, carried out by a glass furnace (1) according to claim 13, characterized in that the current value of the alternating current is greater than 1000 A, preferably greater than 4000 A, preferably greater than 6000 A.

16. 16. A method for producing glass wool, rock wool, textile glass yarns and / or flat or hollow glass, characterized in that the melting method according to claim 14 or 15 is carried out.

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