Electric 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 batch materials and a plurality of immersion heating electrodes (An, Bn, Cn, Dn), which are immersed from the free surface of said bath (3) and supplied with electric current by an electrical facility (4). The electrical facility (4) is configured to generate a two-phase alternating current. This makes it possible to heat larger furnaces / reduce the number of electrodes.

Description

Electric 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 the design of electric furnaces are known from the prior art, and in particular from patent EP0671116B1, in which the current is conducted into the bath of vitrifiable materials by so-called "dipping" electrodes, which are immersed from the free surface of the bath. This type of dipping electrode is distinguished in particular from so-called "immersed" electrodes, which are arranged vertically in the bath from the bottom of the furnace or horizontally, passing through the side walls of the furnace. Compared with the latter, dipping electrodes have a number of advantages.First of all, they obviously avoid the difficulties linked to the passage of the immersed electrodes through the refractory of the hearth or side walls, and also the problems of replacing these electrodes when worn, as well as the problems of sealing the melting tank or even wear of the refractories, in particular due to a high temperature which encourages the attack of the refractory and to powerful convection currents which develop near the electrodes during operation.

[0006] Usually, these immersion electrodes are supplied with three-phase current. Three-phase current has many advantages, the first of which is the fact that it is the so-called "industrial" current that is commonly distributed to factories by energy suppliers, hence the resulting adaptation of the machines. Three-phase current also delivers instantaneous power without a pulsed component, unlike, for example, single-phase current. Note, 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.While such a geometric constraint does not appear 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 more than 25 m², preferably more than 40 m², or even more than 100 m² and in which the edge-to-edge width of the glass bath is 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.

[0007] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

[0008] 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 immersible heating electrodes, which are immersed from the free surface of said bath and supplied with electric current by an electrical installation, said furnace being characterized in that said electrical installation is adapted to generate a two-phase alternating current.

[0009] For the purposes of the invention, the expression “two-phase alternating current” designates a system with two phases of the same frequency and the same amplitude which are in quadrature, that is to say phase-shifted by 90° or π / 2 radians.

[0010] In a contemporary context where current is distributed by energy suppliers in three-phase form, the implementation of an electrical installation adapted to transform this three-phase current into a two-phase current involves a priori unnecessary technical complexity and a significant increase in the initial cost of this technical installation.

[0011] Despite these a priori prohibitive drawbacks and in the specific context of supplying immersion electrodes of glass furnaces, the inventors have noted that such a two-phase system allows a glass furnace designer to free himself from certain geometric constraints specific to three-phase systems and the technical drawbacks linked to them, including the large number of electrodes to be implemented and the inhomogeneous distribution of the electric current within the bath of vitrifiable materials.

[0012] In contrast, a two-phase system offers a glass furnace designer the possibility of further separating the electrodes supplied by the same phase, for example by positioning them 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 with the distance traveled by the current within it – is greater, which implies a reduction in the electrical intensity to be delivered. It is then possible to distribute this intensity between a reduced number of electrodes and / or to limit the intensity delivered to each electrode, which increases their lifespan.

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

[0014] For the purposes of the invention, the expression "output group" designates a set of outputs of the two-phase transformer which are in phase matching. Conventionally, and as illustrated in the and in the description for a particular embodiment of the invention, an output group comprises only a single output which is connected to a plurality of pairs of electrodes (three in the embodiment illustrated in the), which it supplies with single-phase alternating current.

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

[0016] Connecting an output group to a beam, or in other words, to a plurality of pairs of electrodes, allows the current intensity to be distributed between them, and thus limits the wear and tear of each of them over time. Conversely, the implementation of a single pair of electrodes powered by a group of outputs allows the initial cost of the installation to be limited.

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

[0018] According to this alternative embodiment illustrated in particular in the, an output group comprises several outputs, mounted for example in parallel, each output being connected to one or more pairs of electrodes. In all cases, the single-phase current delivered to each of these electrodes is in phase adequacy.

[0019] According to a particular embodiment, each beam of electrodes is arranged in the bath of molten vitrifiable materials so as to respect a central symmetry according to a theoretical horizontal plane.

[0020] Maintaining such axial symmetry allows for a more homogeneous distribution of current between the electrodes, and therefore limits the probability of one of these electrodes wearing out more quickly 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 suitable for two-phase operation, in which the distance between electrodes connected to the two terminals of the same group of outputs can be increased without the risk of seeing electrodes arranged near the same wall exchanging with each other.

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

[0024] This advantageous geometric arrangement of the electrode pairs is particularly suited to two-phase operation and allows for balancing of currents. Such a quadrilateral arrangement contrasts in particular with the triangular or hexagonal arrangements, which are specific to three-phase systems.

[0025] According to a particular embodiment, the minimum distance between each electrode and the wall of the nearest tank 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.

[0026] For the purposes of the invention, such a minimum distance is measured along the normal to the wall of the tank closest to the electrode, and which passes through the latter. Note that the convection movements of the glass bath generated near each electrode tend to corrode the adjoining wall of the tank. The distance of the electrode from the tank therefore makes it possible to limit this premature wear of the tank wall.

[0027] According to a particular embodiment, each of said electrodes comprises a horizontal projection arm, preferably of square section, the horizontal extent of which is 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.

[0028] The use of a square-section electrode arm gives the latter better resistance to bending. This is all the more useful the longer the electrode arm. A long electrode arm in particular allows the electrode to be further away from the adjoining tank wall, in order to limit wear on the latter. This distance of the electrode from the tank wall is all the more interesting when the furnace power is increased. Indeed, the power depends on the voltage and the current, these two parameters are then adjusted with increasing values ​​with the increase in power. This results in an intensification of the convection movements of the glass bath generated near each electrode which tend to corrode the adjoining wall of the tank. The distance of the electrode from the tank wall makes it possible to limit this premature wear of the tank wall.

[0029] According to a particular embodiment, said electrical installation is adapted so that all the pairs of electrodes connected to the same output group of said two-phase transformer are supplied with an electric current of the same voltage.

[0030] According to a particular embodiment, the glass furnace is completely electric, and preferably comprises a cold vault (5).

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

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

[0033] The implementation of a plurality of two-phase transformers is particularly suitable for the electricity supply of large furnaces, for which the implementation of a two-phase system is particularly advantageous.

[0034] 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.

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

[0036] The production of these so-called large electric ovens usually encounters technical obstacles for those skilled in the art.

[0037] The first obstacle is the need for higher electrical power for the melting of vitrifiable materials. This higher electrical power leads to an increase in current and voltage values ​​at the electrodes and an intensification of the convection movements of the glass bath generated near each electrode which tend to corrode the adjoining wall of the tank.

[0038] The second obstacle is that if the area of ​​these furnaces is large, the result is a basin with a greater length and width. It is therefore necessary to be able to supply the heating energy to all points, including the center of the furnace, the area furthest from the wall.

[0039] The present invention solves these obstacles by synergistically combining the use of a two-phase system with arms whose horizontal extent is 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 a two-phase system allows, at a given power, to have less current at the electrodes than a three-phase system. It is then understood that it is possible to obtain, for an identical current, a higher power. This possibility of having a higher power or even a higher current is associated with arms having a greater horizontal extent.These arms, having a greater horizontal extension, allow the electrodes to be moved away from the walls, which reduces the risk of corrosion of the tank walls while allowing the heating of distant areas. In addition, the use of a two-phase system allows the number of electrodes to be reduced and therefore the cost of the installation to be reduced. The number of electrodes per square meter (m. 2 ) is between 0.1 and 0.45, preferably between 0.15 and 0.4 and even more preferably between 0.2 and 0.35.

[0040] According to a particular embodiment, these so-called large-size furnaces are obtained by adding several elementary modules. It is then considered that an elementary module is the equivalent of a furnace whose tank has a length and a width of a defined value, this elementary module comprising a series of heating electrodes having a defined arrangement. Preferably, the elementary module has a square shape. A so-called large-size furnace then comprises at least two elementary modules arranged contiguously, that is to say it comprises a tank whose dimensions in length and width are multiples of the defined value of the elementary module. It is then possible to simply obtain a so-called large-size furnace, this furnace being able to have various shapes such as a rectangular, square, L-shaped or T-shaped shape.

[0041] According to a particular embodiment, said two-phase transformer 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.

[0042] 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.

[0043] 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.

[0044] 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, and by application within said bath of a two-phase alternating current.

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

[0046] 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.

[0047] 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:

[0048] schematically represents, in profile, an electric glass furnace;

[0049] schematically represents, in a top view, the glass bath and the immersing electrodes of an electric furnace according to a particular embodiment of the invention;

[0050] schematically represents, in a top view, the glass bath and the immersing electrodes of an electric furnace according to an alternative embodiment of the invention;

[0051] is a flow diagram illustrating the successive steps of a manufacturing process according to a particular embodiment of the invention.

[0052] The diagrammatically 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 immersion heating electrodes (An, Bn, Cn, Dn) (only one is illustrated in the diagram, for the sake of simplification), the arms of which are of square section, and which are immersed from the free surface of said bath 3 and supplied with electric current by an electrical installation 4. In a known manner, the part of the electrode in contact with the glass bath is composed of molybdenum. A glass furnace 1 according to the invention is in particular characterized in that said electrical installation 4 is adapted to generate a two-phase alternating current.

[0053] According to the particular embodiment illustrated in, the oven 1 is completely electric and is equipped with a cold vault 5.

[0054] According to a particular embodiment, and as illustrated by the, said 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, 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 single-phase alternating current. The bundles of electrodes are arranged in the bath 3 in a substantially 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.

[0055] According to this alternative embodiment illustrated in, the first output group comprises several outputs (AB, A'-B') connected in parallel, the first output AB being connected to a bundle of two pairs of electrodes ((An; Bn); (Cn; Dn) with n=1,2), while the second output A'-B' is connected to a single pair of electrodes (A3; B3). In all cases, the single-phase current delivered to each of these electrodes is in phase adequacy.

[0056] 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.

[0057] According to the embodiments illustrated in Figures 2 and 3, the electrical installation comprises only a two-phase transformer 6 which supplies a “block” of electrodes (An, Bn, Cn, Dn). According to alternative embodiments not illustrated, relating in particular to large electric furnaces, the electrical installation comprises a plurality of two-phase transformers which respectively supply a plurality of blocks of electrodes covering the surface of the glass bath 3.

[0058] 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 immersion heating electrodes (An, Bn, Cn, Dn), which are immersed from the free surface of said bath (3) and supplied with electric current by an electrical installation (4), said furnace (1) being characterized in that said electrical installation (4) is adapted to generate a two-phase alternating current. Glass furnace (1) according to claim 1, characterized in that said electrical installation comprises at least one 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), each output group (AB, CD) supplying at least one pair ((An; Bn); (Cn; Dn)) of said electrodes. Glass furnace (1) according to claim 2, characterized in that at least one output group (AB, CD) of said 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)). Glass furnace (1) according to one of claims 2 and 3, characterized in that at least one output group (AB, CD) of said at least one two-phase transformer (6) comprises one or more outputs. Glass furnace (1) according to one of claims 3 and 4, characterized in that each bundle of electrodes ((An; Bn); (Cn; Dn)) is arranged in the bath (3) of molten vitrifiable materials so as to respect a central symmetry according to a theoretical horizontal plane. Glass furnace (1) according to one of claims 2 to 5, characterized in that the electrodes of the same output group (AB, CD) are arranged near opposite walls of the tank (2). Glass furnace (1) according to one of claims 2 to 6, characterized in that said pairs ((An; Bn); (Cn; Dn)) of electrodes supplied by the same two-phase transformer (6) are arranged in a quadrilateral according to a theoretical horizontal plane, preferably in a rectangle, preferably in a square, in the bath (3) of molten vitrifiable materials. Glass furnace (1) according to one of claims 1 to 7, characterized in that the minimum distance (dmin) between each electrode (An, Bn, Cn, Dn) and the nearest wall of the tank (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. Glass furnace (1) according to one of claims 1 to 8, characterized in that each of said electrodes (An, Bn, Cn, Dn) comprises a horizontal projection arm, preferably of square section, the horizontal extent of which is 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. Glass furnace (1) according to one of claims 2 to 9, characterized in that said electrical installation (4) is adapted so that all the pairs of electrodes connected to the same output group (AB, CD) of said two-phase transformer (6) are supplied with an electric current of the same voltage. Glass furnace (1) according to one of claims 1 to 10, characterized in that it is fully electric, and preferably comprises a cold vault (5). Glass furnace (1) according to one of claims 2 to 11, characterized in that it comprises a plurality of said two-phase transformers (6), preferably three. Glass furnace (1) according to one of claims 1 to 12, 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 2 to 13, characterized in that said two-phase transformer (6) 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 2 to 13, characterized in that the number of electrodes per square meter is between 0.1 and 0.45, preferably between 0.15 and 0.4 and even more preferably between 0.2 and 0.

35. Method for melting vitrifiable materials implemented by means of a glass furnace (1) according to one of claims 1 to 15, characterized in that it comprises at least one step of electrically heating said bath (3) of molten vitrifiable materials by means of said plurality of electrodes (An, Bn, Cn, Dn), and by applying within said bath (3) a two-phase alternating current. Method for melting vitrifiable materials according to claim 16 implemented by means of a glass furnace (1) according to claim 10, characterized in that all the pairs ((An; Bn); (Cn; Dn)) of electrodes connected to the same output group (AB, CD) of said two-phase transformer (6) are supplied with an electric current of the same voltage. 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 16 and 17.

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