AU3829499A

AU3829499A - Melting furnace, in particular for glass, and use thereof

Info

Publication number: AU3829499A
Application number: AU38294/99A
Authority: AU
Inventors: Alain Arnaud; Didier Jacques; Dominica Lizarazu; Tanguy Massart; Stephane Maugendre
Original assignee: Saint Gobain Isover SA France
Current assignee: Saint Gobain Isover SA France
Priority date: 1998-05-19
Filing date: 1999-05-18
Publication date: 1999-12-06
Also published as: ZA200000145B; NO20000240D0; SK492000A3; BR9906464A; JP2002515396A; WO1999059926A1; KR20010014390A; CA2296754A1; PL338081A1; HUP0003124A3; CN1272097A; HUP0003124A2; AR016039A1; FR2778910A1; EP1007483A1; NO20000240L

Description

FURNACE, ESPECIALLY A GLASS FURNACE, USE AND PROCESS USING THE FURNACE 5 The present invention relates to the technology of melting high-melting-point thermoplastic materials, such as glass. It relates more particularly to a furnace intended for melting such materials, and to its use. 10 Such a furnace, which melts materials such as glass, must be designed in such a way that its walls suitably insulate the molten bath from the outside so as to guarantee good thermal efficiency, while preventing any migration of the molten glass to the 15 outside. In this regard, a typical construction of a furnace wall has, on the external side, a sufficient thickness of insulating material and, on the internal side, surfaces made of refractory material resistant to 20 glass-induced corrosion. These refractory materials are installed in the furnace in the form of slabs or blocks, placed side by side, between which sealed joints must be made in order to prevent penetration by the glass. 25 With regard to the floor of the furnace, the slabs of refractory material, which have a high thermal conductivity, rest on blocks of insulating material via an unfashioned layer which provides a base having a perfectly horizontal level. This is generally a 30 concrete based on a hydraulic binder, deposited cold on the blocks of insulation. In principle, the temperature profile in the furnace during operation is such that the temperature below the refractory is close to the crystallization 35 temperature of the glass, or at least is such that the Viscosity of the glass becomes very high, so that if glass penetrates the thickness of refractory it freezes or crystallizes (devitrification) at the upper level of the insulation and its migration is therefore stopped.

- 2 Such glass penetration may happen especially when a block of refractory cracks due to the effect of thermal expansion stresses, or when a joint between two blocks have been poorly sealed. It may also happen when 5 the glass introduced in the solid state into the furnace contains metallic residues. This is because the corrosion of refractory materials is accelerated when a drop of molten metal is present at the interface between the refractory and the glass, and veins may 10 form, via which the glass rapidly insinuates itself towards the insulating material. Despite all the precautions that may be taken, incidents still sometimes occur which throw the sealing of the furnace into question, where it seems that glass 15 has been able to reach an insulating block, with a temperature high enough not to freeze, and to damage the insulation. In particular, penetration of metal entrained by the glass into the blocks of insulation causes serious damage since the metal attacks the 20 insulation and creates pockets that the glass hollows out and/or fills. It is therefore important to prevent glass from penetrating through the surfaces forming the internal walls of the furnace since the risks of glass 25 penetrating through the walls of the furnace are liable to affect both the production capacity of the furnace and its safe operation. The object of the invention is to reduce these risks and to provide furnace walls having improved 30 glass-tightness, in particular when metallic residues are introduced into the bath of glass. This object, as well as others which will appear later, has been achieved according to the invention by endowing at least part of the internal 35 surfaces of the furnace, during its construction, with a lining which contains grit of refractory material. The expression "grit of refractory material" should be understood in the present application to mean, in the usual manner, a refractory material in - 3 particulate or granular form, which may especially be obtained by grinding or crushing. In this regard, the subject of the invention is a furnace for melting a high-melting-point material, 5 such as glass, this furnace comprising a floor and side walls which define a bath of molten material and being characterized in that at least part of the surface of the floor, and optionally of the side walls, which is in contact with the molten material initially consists 10 of at least one layer comprising grit of refractory material. The term "initially" should be understood to mean that the said surface or the said part of the surface has the constitution indicated right from the 15 beginning of the operation of the furnace (before or just after heat-up). The subject of the invention in this regard is a process for the manufacture of a furnace, which will be defined below. It seems, surprisingly, that a wall surface 20 produced from a particulate material, such as refractory grit, exhibits superior glass-tightness compared with a surface consisting of the juxtaposition of preformed articles, such as slabs. Hereafter, the text refers mainly to a bath of 25 glass as the molten mineral material in the furnace; unless indicated otherwise, this expression refers in general to any natural or artificial fusible mineral material, especially glass but also rock. One problem associated with conventional 30 construction of the internal surfaces of walls using superposed slabs on a base layer of a different kind is the cracking due to thermal expansion stresses. This is because, since the layers have different thermal expansion coefficients, the differential movements of 35 one with respect to another take place with friction, which subjects the slabs to tensile forces and which may cause them to crack or even to fracture. Contrary to this, the use according to the invention of a particulate material makes it possible to form a - 4 continuous surface layer, without any joints, which exhibits excellent resistance to the thermal expansion stresses in the furnace. Consequently, the risk of cracking is reduced and the glass-tightness is 5 improved. In general, the refractory material may advantageously be of any type resistant to glass-induced corrosion (it being possible for the degree of resistance to be relatively high) especially 10 of the type based on chromium oxide or based on zirconium, silicon and/or aluminium oxide (AZS type) . The grit which can be used according to the invention may be derived from reclaimed refractory material. The particle size of the grit can vary and may 15 advantageously be less than 50 mm, for example about 1 mm to 50 mm. Particle sizes of greater than 50 mm may nevertheless also be useful. In order to be more specific, the following terms will be used here: "fine" referring to grit having a particle size of less than 20 approximately 5 mm, "medium" referring to grit having a particle size of about 5 to 30 mm, "coarse" referring to grit having a particle size of about 30 to 50 mm and "very coarse" referring to grit having a particle size of greater than 50 mm. These particle sizes should be 25 understood to mean the smallest mesh size of a screen used for screening the particulate material. In one embodiment, the surface in contact with the glass may essentially consist of grit. The particle size of the latter may be chosen advantageously 30 depending on the nature of the glass present in the bath, particularly its viscosity at the wall temperature and its surface tension, in order for the grit not to be able to be wetted by the glass of the bath, or to be wetted only very slightly, and therefore 35 in order for the glass to be prevented from getting into the interstices between the grit particles. In general in this embodiment, it is more advantageous for the grit to contain particles of fine particle size since the layer thus formed is more compact. The grit - 5 may advantageously comprise a mixture of particles of different particle sizes, this being suitable for obtaining maximum or optimized layer compactness or filling-in in order to form an impermeable layer. 5 In another embodiment, which may be preferred in some aspects, the layer, or at least one of the layers, of the surface in contact with the glass contains, in addition to the grit, a mineral binder compatible with the bath of molten glass, which may be 10 of the chemical or ceramic setting type, especially a mineral binder formed from one or more molten oxides or vitreous materials. In this embodiment of the layer, the interstices between the grit particles are at least partially filled in with the said binder, in order to 15 form a composite material. Preferably, the binder is initially mixed with the grit in particulate form, at least in one of the said layers. The composite material based on refractory grit and binder is quite a coherent material which allows 20 little or no molten material, such as glass, to pass between the grit particles. It is also a material with a low rate of glass-induced corrosion and which therefore has an improved lifetime. The particle size of the grit is less critical 25 in this embodiment since the particles are retained by the binder. However, the use of relatively fine grit remains advantageous since it makes it possible to create a compact layer with a high contact area between the particles and the binder, the composite layer 30 acting as a highly impermeable barrier to glass and to other residues possibly present in the molten bath. In one particular embodiment, the surface of the floor (or at least part of it) and, optionally, of the walls, comprises only a single layer containing 35 refractory grit. The particle size of the latter is preferably less than 50 mm, especially less than 30 mm and particularly less than 20 mm. The grit may advantageously comprise a mixture of particles of different particle sizes, this being suitable for - 6 obtaining maximum or optimized layer compactness or filling-in in order to form an impermeable layer. In some applications however, it is preferable for the grit not to be too fine so as to prevent any 5 risk of the grit being entrained into the bath of molten glass as a result of vigorous stirring at the surface of the floor and of the walls, which risk would be prejudicial to the quality of the molten glass. In one particularly preferred embodiment, a 10 first layer, called a "contact layer", comprising a first grit is placed in this way in contact with the molten bath and placed beneath the said contact layer is at least one other layer, called a "lower" layer, comprising another grit, the particle size of the grit 15 of the contact layer being greater than that of the grit or of the grit mixture of the or each lower layer. The grit of the contact layer is advantageously such that it cannot be entrained by the stirring of the bath and it protects the lower layer from this 20 stirring. In this case, the layer in contact with the molten bath preferably comprises grit having a particle size of greater than 10 mm, especially about 10 to 50 mm and particularly about 20 to 50 mm, and the or 25 each lower layer preferably comprises grit having a particle size of less than 20 mm or 10 mm, depending on the case, especially about 1 to 10 mm and very advantageously less than 5 mm, if necessary a mixture of particle sizes. 30 According to one particular embodiment, the or at least one lower layer contain a mineral binder, as mentioned above, while the contact layer essentially consists of the relatively coarse grit. When a surface lining layer comprises a binder 35 ensuring cohesion between the grit particles, this binder may be formed from various mineral materials, especially from oxides or from vitreous materials, such as glass, optionally partially devitrified, or of rock, such as basalt. The glass may or may not be the same as - 7 the glass present in the bath. It may in particular be at least partly a reclaimed glass (cullet) or else, advantageously, a dense glass that absorbs radiation in the infrared range. 5 The binder may advantageously be chosen, especially depending on its viscosity at the wall temperature and on its surface tension, so as to be able to close off (plug), at least partially, the interstitial spaces between the grit particles. 10 In an advantageous embodiment, the binder may be chosen in such a way that its density (especially at the floor temperature) is greater than the density of the glass present in the furnace. This thus produces effective physical separation between the binder glass 15 and the molten glass produced in the furnace. Also advantageously, the binder may be chosen in such a way that its viscosity is greater than the viscosity of the glass present in the furnace. The binder glass thus has a viscosity at the floor 20 temperature which is high enough to properly retain the grit particles and the difference in viscosity prevents the binder from mixing with the molten glass produced in the furnace. It may, in particular, be advantageous to use a 25 devitrified glass as the binder. Also advantageously, the binder may be chosen in such a way that its thermal conductivity is less than that of the molten glass produced in the furnace. Thus, by ensuring that the temperature beneath the grit 30 layer is quite low, it is possible to reduce the rate of glass-induced corrosion of the materials of which the furnace is composed. Depending especially on the nature of the refractory grit material which is used, the mineral 35 binder may exhibit greater or less chemical inertness with respect to the grit. This is because it may happen that the binder (glass or other binder material) reacts with the refractory grit material, corroding the latter with - 8 oxide elements passing from the refractory material into the binder phase. This enrichment of the binder with refractory oxide elements generally has the effect of modifying the devitrification characteristics and/or 5 the viscosity of the interstitial mineral binder. It would seem that the cohesion of the layer thus formed is at least partly due to the gradual modification of the chemical composition of the binder, which would lead to an increase in the viscosity and/or 10 the devitrification of the latter at the floor or wall temperature, preventing the glass of the molten bath from insinuating between the particles of refractory. This enrichment of the interstitial glass (or other material) generally becomes more pronounced the 15 higher the surface area for exchange with the refractory material, i.e. the finer the particle size of the grit. In the case of the so-called "contact" layer, which is directly exposed to the glass of the bath, it 20 may be preferred for the refractory grit material to be relatively resistant or insensitive to corrosive attack by the glass. Preferably, the refractory material is resistant both to the binder glass and to the glass of the bath. The contact layer thus formed then undergoes 25 very little or no transformation throughout the operation of the furnace, thus guaranteeing, in particular, a high level of quality of the glass produced, this quality being constant over time. Advantageously, the refractory grit used for 30 this contact layer contains chromium oxide, preferably in an amount of at least 10% and especially at least 30% by weight, for example at least 60%. Moreover, in the case of the so-called "lower" layer, a refractory material may be preferred which is 35 at least partially corrodible by the interstitial binder, most particularly a material containing alumina. It is then possible to combine two effects: firstly, the glass (or other binder) enriched with refractory oxides is less corrosive towards the lower - 9 structural levels and, secondly, the glass (or other binder) enriched with refractory oxides is more viscous and less subject to convective motion. The grit used for this layer may advantageously 5 be chosen from AZS-type materials, especially those that are recycled, to which a small amount of chromium oxide may optionally be added. It is also possible to adjust the choice of binder glass specifically for each layer, depending in 10 particular on its oxide composition and on its viscosity, in order to interact suitably with the grit of each of the layers. The choice of particle size and of the type of binder glass will be adjusted depending on the 15 properties of the material to be melted in the furnace. The composite layer may be produced in various ways: a mixture of refractory grit and of mineral material may especially be spread out over the surface and this mixture heated, for example during start-up of 20 the furnace, in order to form the composite, or else a layer of grit may firstly be placed followed by a layer of mineral material which is melted in order to impregnate the grit. In this regard, the subject of the invention is 25 also a process for manufacturing a furnace, such as a glass furnace, in which a floor and side walls intended to delimit a bath of molten material are produced, characterized in that it comprises the steps consisting in: 30 - applying at least one layer, comprising grit of refractory material and intended to be in contact with the bath, on at least one part of the surface of the floor, and optionally of the side walls, and then - raising the temperature of the furnace and 35 introducing a high-melting-point material, such as glass, so as to form the bath of molten material. In the first step, a mineral binder may be applied as a mixture with the grit of at least one layer, or as a layer on top of a grit layer.

- 10 Advantageously, in this first step, applied on a layer comprising a binder is another layer essentially comprising grit having a particle size greater than that of the lower layer. 5 The second step allows the binder to be melted and/or thermally activated so that at least one composite layer is formed. The structure of the floor and/or walls may be adapted depending on the requirements; in particular, 10 the layer or layers comprising the grit (14, 16) [sic] may be applied on a fashioned or unfashioned base layer made especially of slabs or blocks of refractory material or insulation. The term "fashioned" should be understood to mean a layer made of fashioned articles 15 which are fitted into the furnace as opposed to a layer obtained from a shapeless material deposited or spread in the the furnace. In particular, a choice may be made among the following alternative embodiments: - the layer or layers comprising the refractory 20 grit may be applied to slabs or blocks of refractory material which are normally used for producing the surface in contact with the molten bath; - the layer or layers comprising the refractory grit may be applied instead of a conventional material 25 in block or slab form, either on a layer of levelling concrete or directly on the blocks of insulation. The layer or layers comprising the grit may also be used on the internal walls of the furnace in well-defined regions chosen especially depending on the 30 termperature within the bath or above the bath in the regions in question, or depending on the quality of the material in the molten bath within the regions in question. When it is desired to apply a layer based on 35 refractory grit on a vertical wall of the furnace, suitable means for keeping the particulate material in place along a vertical wall element may be used, or else the particulate material may be deposited in order to make it slope freely, as long as the material has an - 11 angle of repose which is sufficiently small for the surface layer not to have too great an inclination. This second embodiment may prove to be particularly advantageous when the furnace has a low 5 bath height (especially of less than 800 mm, and in particular 500 mm) because, with a reasonable angle of repose, the inclined wall does not occupy a very large volume of the bath. In general, the composite based on refractory 10 grit may be used in all types of furnaces, advantageously in order to form the entire surface of the floor and optionally of the walls of the furnace. Nevertheless, its use may vary depending on the type of furnace. 15 Thus, on the floor, the layer comprising the grit may be used over the entire surface of the floor in an electric furnace, especially of the type with immersed electrodes, whereas it will only be able to be used in the charging region in a burner-type furnace in 20 which the downstream region may use conventional slabs in contact with the molten material. In general, it is advantageous for the floor to have a layer comprising refractory grit at least in a region of the furnace in which the material to be 25 melted is fed. Thus, when the said material contains fusible residues, particularly metallic residues, which have a tendency to be deposited on the bottom of the bath in the feed region of the furnace, the surface lining according to invention is perfectly suited for 30 accommodating these residues. It may especially make it possible to prevent these residues from advancing towards the lower structural levels of the walls, such as the blocks of insulation. In particular, the surface lining of the walls 35 according to the invention has a remarkable advantage when the material to be melted contains metallic residues, in the sense that it is more resistant than a conventional refractory contact material to corrosion - 12 by the molten material at a temperature close to its melting point. This is because, in a glass furnace in which the surface of the floor consists of the usual slab of 5 refractory, the presence of liquid metal on the surface of the floor induces, at the molten-glass/liquid metal/refractory triple point, very extensive corrosion of the refractory. Deterioration of the constituent elements of 10 the wall by infiltration of the metal is then rapidly observed. This drawback does not occur, or is significantly reduced, when a wall surface according to the invention is produced. 15 In this regard, the subject of the invention is also the use of a furnace as described above for melting reclaimed glass containing metallic residues. The reclaimed glass may come from various sources, especially mirrors, heated windows of motor 20 vehicles, particularly rear windows or tinned or enamelled glass, especially for car windows, or else recycled packaging. The metals present as metallic residues in this reclaimed glass may be especially silver, lead, copper, tin or other metals. 25 It was surprising to observe that the liquid metal arising from the melting of the reclaimed glass could or could not penetrate the surface layer or layers depending on the particle size of the grit employed (for a given mineral binder). The critical 30 size of the grit particles depends on the nature of the metal, in particular on its viscosity in the molten state at the floor temperature, as well as on the interstitial mineral binder and on the glass melted in the bath. 35 Thus, the surface of a furnace wall may be adapted in order to recover the metal separated from the glass by melting, this surface being permeable to the said metal.

- 13 In this regard, the subject of the invention is also a process for separating metal present in reclaimed glass, this process comprising a step consisting in melting the reclaimed glass in a furnace 5 as described above, in which the grit contained in the surface layer of the floor which is in contact with the glass has a particle size suitable for making the said layer permeable to the said metal. In a first embodiment, a space may be provided, 10 immediately below the said layer, for recovering the liquid metal flowing through the said layer. Optionally, a perforated element such as a grid, serving as a support for the contact layer, may be placed at the top of this space. 15 In another embodiment, a second layer, called a "lower" layer, comprising grit having a particle size suitable for making the said lower layer impermeable to the liquid metal, may be placed immediately beneath the said contact layer. 20 The metal is then ultimately trapped between the two grit-based layers and gradually builds up over the course of an operating campaign of the furnace. After one or more operating campaigns, all that is required is to remove the surface lining of the floor, 25 from which the recovered metal may be easily extracted. This method makes it possible, using the same device, to recycle the reclaimed glass while the metal is recovered separately. Further characteristics and advantages of the 30 invention will appear in the detailed description which follows, given with regard to the appended drawings in which: - Figure 1 shows a diagrammatic view in partial longitudinal section of a furnace according to the 35 invention; - Figure 2 shows an enlarged detail of the floor of the furnace in Figure 1; - 14 - Figure 3 shows a diagrammatic view in longitudinal section of another furnace according to the invention. In Figures 1 and 3, only the elements necessary 5 for understanding the invention have been shown, without respecting the scale of the device. In Figure 2, only the orders of magnitude of the respective elements have been respected. The furnace 1 shown in Figure 1 essentially 10 consists of a floor 2, side walls 3 and a roof 4, which define a bath 5 of molten material such as glass. It furthermore comprises means 6 for feeding the material 7 to be melted, such as a conveyer, and a melt feeder 8. The means for melting the material 7 have not been 15 shown. The material may consist of reclaimed glass (cullet) and/or a pulverulent composition of oxides. The floor 2 essentially consists, from the outside inwards, of a wall made of insulating blocks 9 placed on one or more rows (only one row being shown) 20 of an optional refractory concrete layer 10 on which slabs 11 of refractory material are optionally laid, followed by a continuous first layer 12 and a continuous second layer 13 based on refractory material. 25 The details of the layers 12 and 13 may be seen in the enlargement of Figure 2. The first layer 12, or lower layer, comprises grit 14 of refractory material, especially of the AZS or chromium oxide type, having a relatively fine particle size, especially of less than 30 20 mm, advantageously 10 mm and particularly 5 mm, embedded in or surrounded by a binder 15 formed from oxides or from a vitreous material such as glass. The second layer 13, or contact layer, comprises another grit 16 of refractory material, which 35 may or may not have the same composition as the grit 14, especially of at least 10 mm, advantageously at least 20 mm, but which is greater than that of the said first grit 14, the grit particles 16 being surrounded - 15 by a mineral binder 17 which may or may not have the same composition as that of the contact layer 12. These layers on the surface of the slabs 11 may be produced in various ways. 5 In a first method of manufacture, a lower layer of the relatively fine grit 14 is deposited on the slabs 11 and then an upper layer of the relatively coarse grit 16 is deposited on the lower layer. Next, the entire assembly is covered with a thickness of 10 fusible cullet of vitreous material, especially glass, and the furnace is started up: the melting of the cullet makes it possible to impregnate the layers of grit and to gradually coat the grit particles 14 and 16 in order eventually to produce the layers 12 and 13 in 15 which the melted cullet acts as the binder and ensures cohesion of the assembly. As the molten glass from the cullet gradually flows between the grit particles, it interacts with the surface of the grit particles and picks up the oxide 20 element(s) of the refractory, for example Al, Zr, Si in the case of AZS grit, or Cr in the case of chromium grit. The glass enriched with refractory oxide elements becomes more viscous and may eventually end up devitrifying in the free interstitial spaces, the 25 devitrified viscous material preventing glass from the bath 5 from moving towards the lower layers. In an alternative embodiment, a separator element such as a grid or a screen made of refractory material could be placed between the two grit layers, 30 and optionally a similar element could be placed on the second layer so as to maintain the respective levels of the layers. The same technique using a retention grid could be used in order to apply one or more similar layers to 35 the side walls 3. In another method of manufacture, grit particles 14 and 16, in an intimate mixture with the binder 15 and 17, respectively, are deposited as layers 12 and 13. When the temperature of the furnace 1 is - 17 - the lower layer 21 (similar to the lower layer 12 in the furnace 1) comprises a binder and relatively fine grit, for example having a particle size of about 0 to 5 mm, of a type which is relatively 5 corrodible by a glass-based binder, for example of the AZS type, it being possible for this optionally to contain a limited amount of chromium oxide. This layer is impermeable to the glass, especially because the fine grit is packed down in a 10 very compact manner and saturates the interstitial glass with refractory oxides because of the high exchange surface area; it furthermore is very corrosion resistant. In particular, it fulfils the role of a concrete, hence the optional character of the layer 10 15 of refractory concrete; - the middle layer 22 comprises a binder and a coarser grit than that of the layer 21, for example having a particle size of about 10 to 30 mm, and of a type which is relatively corrodible by a glass-based 20 binder, which may or may not be different from the type of the grit in layer 21. In one particular example, this grit may be of the AZS type and may contain up to 30% of chromium oxide. The function of the layer 22 is to enrich the 25 interstitial glass with refractory oxides in order to make it, on the one hand, less corrosive when it reaches the lower layer 21 and, on the other hand, more viscous in order to limit the convection and diffusion of the corrosive oxides; 30 - the upper layer 23 (which may be similar to the contact layer 13 in the furnace 1) comprises a relatively coarse grit, for example having a particle size of at least 50 mm, from which the fine particles have been carefully removed, of a type resistant to 35 glass-induced corrosion, for example one which is single-phase and rich in chromium oxide. Its function is essentially to stop convection on the lower layers; it is not carried away by the - 18 glass currents and does not create by [sic] defects on account of its high particle size. The grit particles of the layers 21, 22 and 23 may be recycling materials. 5 Each wall consists of a bottom part made from insulating blocks 9, laid, where required, on the optional layer 10 of refractory concrete. Resting on this bottom part is a top part made of blocks 3 of refractory material (such as those used for forming the 10 walls of the furnace 1). That surface of the walls facing towards the glass bath has a lining comprising refractory grit which is continuous with the upper layer 23. This lining is inclined to the vertical at an 15 angle corresponding to the angle of repose of the particulate material used to form the layer 23. It is intended to isolate the blocks 3 and 9 from the bath of glass. As a variant with respect to the first 20 embodiment, the grit-based layers 21, 22 may be produced by firstly preparing a mixture of the grit in question and of the corresponding glass-based binder in particulate form, especially cullet, and by spreading out, in succession: 25 - a compact horizontal layer of the mixture for the lower layer 21; - then a compact horizontal layer of the mixture for the middle layer 22. The upper layer 23 is produced by depositing a 30 horizontal layer of coarse grit which lies above the level separating a refractory block 3 from an insulating block 9 and, finally, by applying the coarse grit along the vertical walls in the form of a sloping bank. 35 Finally, the furnace begins to be heated, in order to melt the binder or binders and to form the layers 21 and 22, respectively. Next, a high-melting point material, such as glass or cullet, is introduced in order to start up the furnace; the grit in the layer - 19 23 is then wetted by the molten material which forms a binder. The chemical exchanges between binder glass and refractory glass may continue for a certain period of 5 time during the heat-up or start-up of the furnace before reaching a state ensuring the desired level of tightness. Because of the grit-based lining on the internal walls of the furnace, it is possible to reduce 10 the thickness of the refractory blocks 3 and to replace the lower refractory blocks 3 of the furnace 1 by less expensive insulating blocks 9, and to reduce the cost of the furnace significantly, without prejudicing to the thermal insulation or the corrosion resistance. 15 The invention that has just been described in the particular case of a glass furnace, the floor of which, of a given structure, is provided over its entire surface with at least two grit-based layers, is in no way limited to this embodiment. The information 20 given in the detailed description may be extended to other embodiments, especially to the following cases: the floor has another structure (in particular, the blocks of insulation, the concrete and/or the slabs are absent); only a single grit-based layer is used; the 25 layer or layers are applied to only one part of the floor. The other usual arrangements in glass-type furnaces are also appropriate in the present invention.

Claims

1. Furnace (1; 20) for melting a high-melting-point material, such as glass, comprising 5 a floor (2) and side walls (3) which define a bath (5) of molten material, characterized in that at least part of the surface of the floor (2), and optionally of the side walls (3), which is in contact with the molten material (5) initially consists of at least one layer 10 (12, 13; 21, 22, 23) comprising grit (14, 16) of refractory material.

2. Furnace according to Claim 1, characterized in that the refractory grit material (14, 16) is a material resistant to glass-induced corrosion, 15 especially of the type based on chromium oxide or based on zirconium, silicon and/or aluminium oxide.

3. Furnace according to Claim 1 or 2, characterized in that the said layer or at least one of the said layers (12, 13; 21, 22, 23) comprises, in 20 addition to the grit (14, 16), a mineral binder (15, 17) advantageously formed from an oxide or from a vitreous material, such as glass, especially reclaimed glass.

4. Furnace according to Claim 3, characterized in 25 that the said layer or at least one of the said layers (12, 13; 21, 22) is formed from grit and from a binder which are initially mixed in particulate form.

5. Furnace according to any one of the preceding claims, characterized in that the or each binder has a 30 density greater than that of the molten material contained in the bath (5).

6. Furnace according to any one of the preceding claims, characterized in that the or each binder has a viscosity greater than that of the molten material 35 contained in the bath (5).

7. Furnace according to any one of the preceding claims, characterized in that the or each binder has a thermal conductivity less than that of the molten material contained in the bath (5). - 21

8. Furnace according to any one of the preceding claims, characterized in that the said surface or part of the said surface comprises a single layer comprising grit, preferably with a particle size of less than 5 50 mm, especially less than 20 mm.

9. Furnace according to one of Claims 1 to 7, characterized in that the said surface or part of the said surface comprises a first layer (13; 23) comprising a first grit (16) in contact with the molten 10 material, beneath which there is at least one lower layer (12; 22, 21) comprising lower grit (14), the particle size of the first grit (16) being greater than the particle size of the lower grit (14).

10. Furnace according to Claim 9, characterized in 15 that the first layer (13; 23) comprises grit (16) having a particle size of at least 10 mm, especially ,about 20 to 50 mm, and the lower layer (12; 22, 21) comprises grit (14) having a particle size of less than 20 mm, especially about 1 to 10 mm. 20

11. Furnace according to either of Claims 9 and 10, characterized in that the grit of the first layer (23) in contact with the molten material is of a type resistant to glass-induced corrosion and the grit of the or each lower layer (21, 22) is of a type 25 relatively corrodible by the glass.

12. Furnace according to any one of the preceding claims, characterized in that the layer or layers (12, 13; 21, 22, 23) comprising grit (14, 16) are applied to a fashioned or unfashioned base layer, made especially 30 of slabs (11) or blocks of refractory or insulating material.

13. Furnace according to any one of the preceding claims, characterized in that the surface of at least one side wall (3) consists of a lining (23) which 35 comprises grit of refractory material and is inclined with respect to the vertical.

14. Furnace according to any one of the preceding claims, characterized in that the surface of the floor includes a layer comprising refractory grit at least in - 22 one portion of the furnace where feeding with material to be melted takes place.

15. Process for manufacturing a furnace (1), such as a glass furnace, in which a floor (2) and side walls 5 (3) intended to define a bath (5) of molten material are produced, characterized in that it comprises the steps consisting in: - applying at least one layer (12, 13; 21, 22, 23), comprising grit (14, 16) of refractory material 10 and intended to be in contact with the bath (5), on at least part of the surface of the floor (2) and optionally of the side walls (3), and then; - raising the temperature of the furnace (1) and introducing a high-melting-point material, such as 15 glass, so as to form the bath (5) of molten material.

16. Process for manufacturing a furnace according to Claim 15, characterized in that, in the first step, a mineral binder (15, 17) is applied as a mixture with the grit (14, 16) of at least one layer (21, 22), or as 20 a layer on top of a layer of grit (14, 16), and, in the second step, the binder (15, 17) is melted and/or thermally activated in order to form at least one composite layer (12, 13; 21, 22).

17. Process for manufacturing a furnace according 25 to Claim 16, characterized in that in the first step, applied on a layer (22) comprising a binder is another layer (23) essentially comprising grit having a particle size greater than that of the lower layer or layers. 30

18. Use of a furnace according to any one of the preceding claims for melting reclaimed glass containing metallic residues.

19. Process for recovering metal (18) present in reclaimed glass, comprising a step consisting in 35 melting the reclaimed glass in a furnace (1) according to one of Claims 1 to 15, in which the grit (16) contained in that layer (13) of the floor (2) which is in contact with the glass has a particle size suitable - 23 for making the said layer (13) permeable to the said metal (18)

20. Recovery process according to Claim 19, characterized in that the furnace (1) includes, 5 immediately below the said surface layer (13), a lower layer (12) comprising grit (14) whose particle size is suitable for making the lower layer (12) impermeable to the said metal (18).