Electric apparatus for a glass-making furnace

Abstract

The invention relates to an at least partially electric glass-making furnace (1), comprising a melting tank (2) made of refractory materials that is suitable for containing a bath (3) of molten vitrifiable materials and a plurality of electrodes (An, Bn, Cn, Dn) for heating said bath (3), said electrodes being supplied with alternating electric current by an electric apparatus (4) comprising at least one transformer (6) suitable for generating a plurality of output groups in a phase with a phase difference between each output group, each output being connected to at least one of said electrodes (An, Bn, Cn, Dn) by a conductor in a phase (7) generating a first magnetic field (B1). The device comprises a device installed in the first electromagnetic field, able to generate a magnetic counter-field.

Description

Electrical installation of glass furnace

[0001] The present invention belongs to the general field of glass production. It relates more particularly to an at least partly electric glass furnace suitable for melting vitrifiable materials. It also relates to a method for melting vitrifiable materials so as to be able to manufacture glass. The invention finds a particularly advantageous, although in no way limiting, application in the production of glass wool, rock wool, textile glass yarns and / or flat or hollow glass.

[0002] In this description, the term “vitrifiable materials” or “raw materials” means all materials, natural ores or synthesized products, materials from recycling such as cullet, etc., which may be included in the composition used to feed a glass furnace. This includes silica sand, but also all additives (sodium carbonate, limestone, dolomite, alumina, etc.), waste (including mineral fibers) which may come from the production of said fibers or from construction sites (construction or deconstruction), all possible liquid or solid fuels (plastic, composite material or not, organic materials, coals), and any type of cullet.Also included are recyclable materials containing combustible (organic) elements such as, for example, sized mineral fibers with binder (of the type used in thermal or acoustic insulation or those used in the reinforcement of plastic materials), laminated glazing with polymer sheets of the polyvinyl butyral type 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 coatings containing metals. In the description, “bath of vitrifiable materials” or “glass bath” refers to the product of the melting of these raw materials.

[0003] Similarly, "glass" means glass in the broad sense, that is to say, encompassing any material with a vitreous, vitroceramic or ceramic matrix.

[0004] Furthermore, the term "manufacture" includes the essential melting stage of the vitrifiable materials and, where applicable, all subsequent / complementary stages aimed at refining / conditioning the molten glass with a view to its final shaping, in particular in the form of flat glass (glazing), hollow glass (flasks, bottles), glass in the form of mineral wool (in particular rock wool or glass wool) used for its thermal or sound insulation properties, or even possibly glass in the form of so-called textile threads used in reinforcement.

[0005] Various examples of electric furnace designs are known from the state of the art, in which the current is conducted into the bath of vitrifiable materials by heating electrodes. Such electrodes may be of the so-called "immersed" type - being arranged vertically in the bath from the bottom of the furnace or horizontally, passing through the side walls of the furnace - and / or be of the "plunging" type, being immersed from the free surface of the bath.

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

[0007] Surprisingly, the inventors, designers of glass furnaces, observed a heating phenomenon of certain metal structures positioned near these single-phase conductors. This phenomenon, a priori harmless in the case of small electric furnaces, turns out to be problematic in the case of large furnaces, in which the bath of molten vitrifiable materials has a surface area greater than 25 m², preferably greater than 49 m², and preferably has a distance between two opposite walls of said tank greater than 5 m, preferably greater than 7 m. Given the electrical power required to supply these large furnaces, the single-phase conductors carry a current whose intensity is greater than 1000 A, preferably greater than 4000 A, preferably greater than 6000 A.At these electrical intensity levels, the heating of said metal structures positioned near these conductors in one phase is much more significant, to the point that it can lead to the degradation of said metal structures.

[0008] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

[0009] To this end, and according to a first aspect, the invention relates to an at least partly electric glass furnace, comprising a melting tank made of refractory materials adapted to contain a bath of molten vitrifiable materials and a plurality of electrodes for heating said bath supplied with alternating electric current by an electrical installation comprising at least one transformer adapted to generate a plurality of output groups in one phase with a phase difference between each output group, each output being connected to at least one of said electrodes by a conductor of a phase generating a first magnetic field, said glass furnace being characterized in that it comprises at least one feedback device, preferably a plurality, arranged in said first magnetic field and adapted to generate a counter-magnetic field.

[0010] For the purposes of the invention, a counter-field designates a magnetic field in the opposite direction, which therefore cancels out a first magnetic field.

[0011] The invention is based firstly on the surprising observation made by the inventors, designers of glass furnaces, of a phenomenon of heating of certain metallic structures positioned near the conductors in a phase of supplying current to the electrodes, then on the understanding of this phenomenon, and finally on the implementation of a counter-reaction device making it possible to overcome this unwanted heating of these metallic structures.

[0012] More precisely, it appeared to the inventors that this heating phenomenon was linked to the generation, within these metallic structures, of a current induced by the first magnetic field, that is to say by the magnetic field generated by the current flowing in the conductor in one phase. Not only does this induced current increase the risks of electrocution, but it also causes the heating of the metallic structures by the Joule effect.

[0013] In response, the invention is based on the new and inventive concept of implementing a feedback device arranged in said first magnetic field and adapted to generate a magnetic counter-field, thus reducing the risks of generating an induced current, and consequently the risks of heating and electrocution linked thereto.

[0014] According to a particular embodiment, such a glass furnace comprises a single feedback device arranged in said first magnetic field of each conductor in one phase and adapted to generate a magnetic counter-field.

[0015] According to a particular embodiment, such a feedback device comprises a closed loop of which at least one portion is composed of a conductive metallic material chosen from the group comprising copper, aluminum and iron, said portion being arranged in said first magnetic field and adapted to generate said magnetic counter-field.

[0016] Concretely, and according to the principles set out by Faraday's and Lenz's laws, when a conductive material is placed in a variable magnetic field, an electric field appears in it which in turn generates circular induced currents, called "eddy currents". The induced currents in turn generate a counter-magnetic field which opposes the flux modifications which gave rise to them, thus attenuating the latter.

[0017] According to a particular embodiment, said portion of the closed loop is in the form of a cable, a metal bar, or a box.

[0018] According to a particular embodiment, said closed loop is grounded at a single point.

[0019] According to a particular embodiment, a check of the voltage difference between said closed loop and said transformer is carried out, so as to detect voltage increases linked to a possible fault in this earthing.

[0020] According to a particular embodiment, said closed loop comprises a current control system, with a threshold value for cutting off said closed loop.

[0021] Such a safety device helps prevent the risk of excessive heating of the closed loop, and therefore the risk of fire.

[0022] According to a particular embodiment, said portion of the closed loop is arranged less than 1.0 meter, preferably less than 0.5 meter, preferably less than 0.3 meter from said single-phase conductor (7).

[0023] Positioning said portion of the closed loop in the immediate vicinity of the conductor in one phase makes it possible to capture a greater part of the magnetic field emitted by the latter, and thus to attenuate it better.

[0024] According to a particular embodiment, said portion of the closed loop is arranged more than 0.1 meter, preferably more than 0.2 meter from said single-phase conductor, and / or in that said single-phase conductor is coated with an electrical insulator, preferably plastic.

[0025] Maintaining a minimum distance between the closed loop and the conductor in one phase and / or the latter's electrical insulation prevents the risk of direct contact, particularly following the formation of an electric arc. This risk is particularly high during the ignition phase of the electrical installation, which is then traversed by a very high voltage current, known as magnetizing voltage.

[0026] According to a particular embodiment, said melting tank is sized so that said bath of molten vitrifiable materials has a surface area greater than 25 m², preferably greater than 40 m², preferably greater than 60 m², preferably greater than 100 m², and preferably has a distance greater than 5 m, preferably greater than 6.5 m, between two opposite walls of said tank.

[0027] Such dimensions refer to so-called large electric furnaces, for which the implementation of a two-phase system is particularly advantageous.

[0028] According to a particular embodiment, said electrical installation is adapted to generate a two-phase or three-phase alternating current.

[0029] Three-phase current has many advantages, the first of which is that it is the so-called "industrial" current that is commonly distributed to factories by energy suppliers, hence the resulting adaptation of machines. Three-phase current also delivers instantaneous power without a pulsed component, unlike, for example, single-phase current. It should be noted, however, that the principle of phase balance tends to implement a triangular or hexagonal arrangement of the electrodes on the surface of the glass bath.If such a geometric constraint does not seem a priori to pose a prohibitive problem in the context of a small electric furnace, it does, however, pose one in the context of a large electric furnace, the glass bath of which extends over an area greater than 25 m², preferably greater than 40 m², preferably greater than 60 m², preferably greater than 100 m², and preferably has between two opposite walls of said tank (2) a distance greater than 5 m, preferably greater than 6.5 m. In such a configuration and in view of the aforementioned geometric constraints, the current tends to concentrate between the electrodes of the same tank edge and / or adjacent edges, thus reducing the distance traveled by the current within the glass bath and therefore the resistance of the glass bath to the passage of this current.For a predetermined electrical power corresponding to the energy required to melt the vitrifiable materials, and in the context of a glass bath offering only reduced resistance, it is therefore necessary to increase the intensity of the current delivered. However, the wear of the electrodes and refractories constituting the tank increases with the intensity of the current delivered per electrode. In order to overcome this wear problem, the natural solution is to distribute the current delivered between a greater number of electrodes, which however has the disadvantage of increasing the operating costs of these electrodes – the latter being more numerous – without resolving certain problems of inhomogeneity of distribution of the electric current within the glass bath.

[0030] According to a particular embodiment, at least one heating electrode, preferably all the heating electrodes, is immersed from the surface of said bath of molten vitrifiable materials.

[0031] Compared to so-called "immersed" electrodes, immersion electrodes have a number of advantages. First of all, they avoid the difficulties associated with passing the immersed electrodes through the refractory, and also the problems of replacing these electrodes when worn, problems with sealing the melting tank or even wear of the refractories, particularly due to a high temperature which promotes attack of the refractory and to powerful convection currents which develop near the electrodes during operation.

[0032] According to a particular embodiment, said transformer is two-phase and supplies a number of electrodes less than or equal to 16, preferably less than or equal to 12, preferably less than or equal to 8.

[0033] Depending on whether each output group supplies two times four electrodes, two times three electrodes or two times two electrodes, the total number of electrodes supplied by the same two-phase transformer thus varies respectively between 16, 12 and 8 electrodes.

[0034] Compared to a three-phase system and for a glass bath module of equivalent surface area - and therefore equivalent electrical power - the two-phase system offers the possibility of reducing the number of electrodes used in the furnace.

[0035] According to a particular embodiment, said transformer is adapted to generate at each output group an alternating current in one phase with an intensity value greater than 1000A, preferably greater than 4000A, preferably greater than 6000A.

[0036] According to a particular embodiment, the invention relates to a method for melting vitrifiable materials implemented by means of such a glass furnace, characterized in that it comprises at least one step of electrical heating of said bath of molten vitrifiable materials by means of said plurality of electrodes supplied with alternating current by said electrical installation.

[0037] According to a particular embodiment, the intensity value of said alternating electric current is greater than 1000A, preferably greater than 4000A, preferably greater than 6000A.

[0038] According to a particular embodiment, the invention relates to a method for manufacturing glass wool, rock wool, textile glass yarns and / or flat or hollow glass, characterized in that it implements such a melting method.

[0039] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting character. In the figures:

[0040] schematically represents, in profile, an electric glass furnace;

[0041] schematically represents, in a top view, the glass bath and the electrodes of an electric furnace according to a particular embodiment of the invention;

[0042] schematically represents an electrical installation as well as a feedback device of a glass furnace according to a particular embodiment of the invention;

[0043] schematically represents the detail of a feedback device of a glass furnace according to a particular embodiment of the invention;

[0044] is a flow diagram illustrating the successive steps of a manufacturing process according to a particular embodiment of the invention.

[0045] It schematically represents, in a side view, an electric glass furnace 1. Such a glass furnace 1 comprises a melting tank 2 made of refractory materials adapted to contain a bath 3 of molten vitrifiable materials and a plurality of heating electrodes (An, Bn) including a plunging electrode An and a so-called "immersed" electrode Bn, these two electrodes being supplied with electric current by an electrical installation 4 to which they are connected via conductors in one phase 7.

[0046] According to alternative embodiments of the invention, all of the electrodes are immersed, or all of the electrodes are dipping.

[0047] According to the particular embodiment illustrated in, the furnace 1 is entirely electric and is equipped with a cold vault 5. According to alternative embodiments, such a glass furnace is of the hybrid type and comprises, in addition to the electrodes, combustion heating means, preferably submerged and / or emerged burners, and a hot vault.

[0048] According to a particular embodiment, and as illustrated by the, said electrical installation comprises a two-phase transformer 6 adapted to generate two output groups (AB, CD) in one phase with a phase difference of 90° between each output group (AB, CD). According to this particular embodiment, an output group comprises only a single output (AB, CD) which is connected to a bundle of three pairs of electrodes ((An; Bn); (Cn; Dn) with n=1,2,3), which it supplies with alternating current in one phase. The bundles of electrodes are arranged in the bath 3 in a square shape and in such a way as to respect a central symmetry according to a theoretical horizontal plane, relative to a point O located at the center of the bath 3.

[0049] In practice, a first single-phase current is generated by the transformer 6 at the terminals of a first output group AB and passes through the glass bath between the electrodes A1, A2, A3 on the one hand, and the electrodes B1, B2, B3 on the other hand, thus heating the bath 3 of vitrifiable materials by the Joule effect. In parallel, a second single-phase current, of the same frequency and the same amplitude as the first current, but phase-shifted by 90° or π / 2 radians with respect to the latter, is generated by the transformer 6 at the terminals of a second output group CD and passes through the glass bath between the electrodes C1, C2, C3 on the one hand, and the electrodes D1, D2, D3 on the other hand, thus heating the bath 3 of vitrifiable materials by the Joule effect. Overall, the electrical installation 6 is thus adapted to generate a two-phase alternating current within the glass bath 3.

[0050] The diagrammatically represents an electrical installation 4 as well as a feedback device 8, the details of which are illustrated in the. Such a feedback device 8 is arranged in the first magnetic field B1 generated by a conductor 7 and is adapted to generate a magnetic counter-field B2.

[0051] More specifically, this feedback device 8 comprises a closed loop 9 of which at least a portion is in the form of a copper bar 10 which is positioned in the first field B1 and in return fulfills the function of generating the magnetic counter-field B2, thus reducing the risks of generating an induced current, and consequently the risks of heating and electrocution linked thereto. According to alternative embodiments, said portion 10 may take the form of a cable or a box, and be composed of a conductive material, such as aluminum or iron.

[0052] According to the embodiment illustrated in the, the closed loop 9 is grounded at a single point, in particular so as to limit the risks of electrocution. It also includes a system for controlling the current (not illustrated) flowing through the closed loop, in order to prevent the risks of excessive heating of the closed loop, and therefore the risks of fire.

[0053] It should be noted that even if not apparent in the figures, due to the lack of scale, the electric furnace considered is qualified as large, since it has a bath of molten vitrifiable materials whose surface area is greater than 40 m², and has a distance between the two opposite walls of said tank greater than 6.5 m. Taking into account the electrical power required to supply this furnace, the conductors in one phase carry a current whose intensity is between 7000 and 8000A.

[0054] This is a flow diagram illustrating the successive steps of a manufacturing method according to a particular embodiment of the invention, which comprises a first step S1 of melting vitrifiable materials by electrical heating of said bath 3 of vitrifiable materials by means of a two-phase alternating current, and a second step S2 of manufacturing glass wool, rock wool, textile glass yarns and / or flat or hollow glass.

Claims

Glass furnace (1) at least partly electric, comprising a melting tank (2) made of refractory materials adapted to contain a bath (3) of molten vitrifiable materials and a plurality of electrodes (An, Bn, Cn, Dn) for heating said bath (3) supplied with alternating electric current by an electrical installation (4) comprising at least one transformer (6) adapted to generate a plurality of output groups in one phase with a phase difference between each output group, each output being connected to at least one of said electrodes (An, Bn, Cn, Dn) by a conductor of a phase (7) generating a first magnetic field (B1), said glass furnace (1) being characterized in that it comprises at least one feedback device (8), preferably a plurality, arranged in said first magnetic field (B1) and adapted to generate a counter-magnetic field (B2). Glass furnace (1) according to claim 1, characterized in that it comprises a single feedback device (8) arranged in said first magnetic field (B1) of each conductor in one phase (7) and adapted to generate a magnetic counter-field (B2). Glass furnace (1) according to one of claims 1 and 2, characterized in that said feedback device (8) comprises a closed loop (9) of which at least one portion (10) is composed of a conductive metallic material chosen from the group comprising copper, aluminum and iron, said portion (10) being arranged in said first magnetic field (B1) and adapted to generate said magnetic counter-field (B2) Glass furnace (1) according to claim 3, characterized in that said portion (10) of the closed loop (9) is in the form of a cable, a metal bar, or a box. Glass furnace (1) according to one of claims 3 and 4, characterized in that said closed loop (9) is earthed at a single point. Glass furnace (1) according to one of claims 3 to 5, characterized in that said closed loop (9) comprises a current control system, with a threshold value for cutting off said closed loop (9). Glass furnace (1) according to one of claims 3 to 6, characterized in that said portion (10) of the closed loop (9) is arranged less than 1.0 meter, preferably less than 0.5 meter, preferably less than 0.3 meter from said single-phase conductor (7). Glass furnace (1) according to one of claims 3 to 7, characterized in that said portion (10) of the closed loop (9) is arranged more than 0.1 meters, preferably more than 0.2 meters from said single-phase conductor (7), and / or in that said single-phase conductor (7) is coated with an electrical insulator, preferably plastic. Glass furnace (1) according to one of claims 1 to 8, characterized in that said melting tank (2) is dimensioned so that said bath (3) of molten vitrifiable materials has a surface area greater than 25 m², preferably greater than 40 m², preferably greater than 60 m², preferably greater than 100 m², and preferably has a distance greater than 5 m, preferably greater than 6.5 m, between two opposite walls of said tank (2). Glass furnace (1) according to one of claims 1 to 9, characterized in that said electrical installation (4) is adapted to generate a two-phase or three-phase alternating current. Glass furnace (1) according to one of claims 1 to 10, characterized in that at least one heating electrode (An, Bn, Cn, Dn), preferably all the heating electrodes (An, Bn, Cn, Dn), is immersed from the surface of said bath (3) of molten vitrifiable materials. Glass furnace (1) according to one of claims 10 and 11, characterized in that said transformer (6) is two-phase and supplies a number of electrodes less than or equal to 16, preferably less than or equal to 12, preferably less than or equal to 8. Glass furnace (1) according to one of claims 1 to 12, characterized in that said transformer (6) is adapted to generate at each output group an alternating current in one phase with an intensity value greater than 1000A, preferably greater than 4000A, preferably greater than 6000A. Method for melting vitrifiable materials implemented by means of a glass furnace (1) according to one of claims 1 to 13, characterized in that it comprises at least one step of electrical heating of said bath (3) of molten vitrifiable materials by means of said plurality of electrodes (An, Bn, Cn, Dn) supplied with alternating current by said electrical installation (4). Method for melting vitrifiable materials according to claim 14, implemented by means of a glass furnace (1) according to claim 13, characterized in that the intensity value of said alternating electric current is greater than 1000A, preferably greater than 4000A, preferably greater than 6000A. Process for manufacturing glass wool, rock wool, textile glass yarns and / or flat or hollow glass, characterized in that it implements a melting process according to one of claims 14 and 15.

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