FR2778910A1 - Melting furnace especially for melting recycled glass containing metallic residues to recover glass and optionally metal - Google Patents

Abstract

A melting furnace has melt-contacting surfaces initially consisting of one or more layers (12, 13) containing refractory material grains (14, 16). Independent claims are also included for the following: (i) a furnace production process comprising applying one or more layers (12, 13) as described above onto the hearth and optionally side wall surfaces, raising the furnace temperature and introducing the material to be melted; and (ii) a method of recovering metal from recycled glass by melting in the above furnace, the hearth layer (13) of which has a refractory material grain particle size allowing permeation of metal (18). Preferred Features: The refractory material grains (14, 16) consist of a material resistant to glass corrosion, especially a material based on chromium oxide or on zirconium, silicon and/or aluminum oxides, and may be contained in a mineral binder (15, 17) and.

Description

OVEN, ESPECIALLY GLASS, USE AND

PROCESS USING THE OVEN

  The present invention relates to techniques for melting thermoplastic materials with a high melting point, such as glass. It concerns more

  particularly an oven for melting such materials, and its use.

  Such an oven performing the melting of materials such as glass must be designed so that its walls adequately isolate the molten bath from the outside so as to guarantee good thermal efficiency, avoiding any

  migration of molten glass to the outside.

  In this respect, a typical oven wall construction provides, on the outside a sufficient thickness of insulating material, and on the inside of the

  surfaces of refractory material resistant to corrosion by glass.

  These refractory materials are installed in the furnace in the form of slabs or blocks, placed side by side, between which it is advisable to

  make watertight seals to avoid penetration of the glass.

  At the bottom of the oven, the refractory material slabs which have a high thermal conductivity rest on blocks of insulating material by means of a layer of special concrete, which makes it possible to provide a base

  having a perfectly horizontal level.

  In principle, the temperature profile is such that the temperature at the level of the concrete is close to the crystallization temperature of the glass, or at least is such that the viscosity of the glass becomes very high, so that if glass passes through the glass. 'refractory thickness, it freezes or crystallizes (devitrification) on contact with concrete and its migration is then stopped. This can happen in particular when the refractory block cracks under the effect of expansion stresses

  thermal, or when a joint between two blocks has been badly closed.

  This can also happen when the glass introduced in the solid state into the furnace contains metallic residues. In fact, corrosion of refractory materials is accelerated when a drop of molten metal is

  present at the interface between the refractory and the glass.

  It was observed that the concrete layer was not really waterproof, especially to glass but also to metal. However, the penetration of metal into the insulation blocks causes serious damage because the metal attacks the insulation and

  creates pockets that the glass comes to dig and / or fill.

  The risk of glass penetrating through the walls of the oven can affect both the production capacity of the oven and the safety of

its implementation.

  The object of the invention is to reduce these risks and to provide oven walls having improved glass tightness, in particular when introducing

  metal residue in the glass bath.

  This object, as well as others which will appear subsequently, has been achieved according to the invention by providing at least part of the interior surfaces of the oven with a

  coating comprising shot of refractory material.

  In this regard, the subject of the invention is an oven for melting a material with a high melting point, such as glass, this oven comprising a hearth and side walls delimiting a bath of molten material, and being characterized in that at least part of the surface of the hearth, and possibly of the side walls, which is in contact with the molten material consists of at least one

  layer comprising shot of refractory material.

  It has surprisingly appeared that a wall surface made from a particulate material such as refractory shot has an improved glass seal compared to a surface made up of the juxtaposition of preformed articles such as slabs Un Another problem linked to the production of interior wall surfaces with juxtaposed tiles is cracking under the effect of thermal expansion stresses, in particular at the joints. The use according to the invention of a particulate material makes it possible to constitute a surface layer

  which has excellent resistance to thermal expansion constraints.

  Consequently, the risk of cracking is reduced, and the glass seal is improved. In a particular embodiment, the surface in contact with the glass can consist essentially of shot. The particle size thereof can be advantageously chosen, depending on the nature of the glass present in the bath, in particular its viscosity at the temperature of the wall and its surface tension, so that the shot is not or very little wettable by the glass of the bath and therefore that the progression of the glass in the interstices between the particles of shot is prevented. In general, in this embodiment, a shot is all the more advantageous the finer its particle size. In another particular embodiment, which may be preferred in certain aspects, the layer or at least one of the layers of the surface in contact with the glass contains, in addition to the shot, a mineral binder formed from oxide (s ) melted (s) or glassy material (s). In this embodiment, the interstices between the particles of shot are at least partially filled

  of said binder, to constitute a composite material.

  The composite material based on refractory shot and the binder is a fairly coherent material which does not allow the passage of a molten material such as glass between the particles of shot. It is also a material whose

  corrosion by glass is slow and therefore has an improved lifespan.

  By refractory material shot is meant in the present application a refractory material in particulate or granular form which can be obtained

  especially by grinding or crushing.

  The refractory material may advantageously be of any type resistant to corrosion by glass, in particular of the type based on chromium oxide or based

  zirconium oxide, silicon and / or aluminum (AZS type).

  The granulometry of the shot is variable and can advantageously be less than 50 mm, for example of the order of 1 mm to 50 mm. To fix the ideas, we will qualify as "fine" a shot whose particle size is less than about 5 mm, "medium" a shot whose particle size is of the order of 5 to 20 mm, and "coarse" a shot with a grain size of the order

from 20 to 50 mm.

  In certain applications, it is preferable that the shot is not too fine so as to avoid any risk of entrainment of the shot in the bath

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  of molten glass as a result of heavy mixing on the surface of the sole and

  walls, a risk which would be detrimental to the quality of the molten glass.

  The use of relatively fine shot is nevertheless advantageous since it makes it possible to create, possibly in association with a binder in the form of a composite layer, a barrier which is very tight against glass and other residues.

  possibly present in the molten bath.

  In a particularly preferred embodiment, a first layer, called "contact layer" comprising shot, is placed in contact with the molten bath and, under said contact layer, another layer called "lower layer" comprising shot, the granulometry of the shot of the contact layer being greater than that of the shot of the lower layer. The shot of the contact layer is advantageously such that it cannot be entrained by stirring the bath and protects the bottom layer from this

brewing.

  In this case, the layer in contact with the molten bath preferably comprises shot having a particle size of the order of 20 to 50 mm, and the lower layer preferably comprises shot of particle size less than

  mm, in particular of the order of 1 to 10 mm.

  When a layer of the surface coating comprises a binder ensuring cohesion between the particles of shot, this binder can be formed from various mineral materials, in particular from oxides or from vitreous materials such as glass, possibly partially devitrified, or rock such as basalt. The glass can be identical or different from the glass present in the bath. It may in particular be at least partially a recovery glass (cullet) or advantageously a dense glass absorbing the

  radiation in the infrared domain.

  The binder is advantageously chosen, in particular as a function of its viscosity at the temperature of the wall and of its surface tension, so as to seal at

  at least partially the interstitial spaces between the particles of shot.

  The composite layer can be produced in various ways: one can spread on the surface a mixture of refractory shot and mineral material and heat this mixture, for example when starting the furnace, to form the composite, or else one can arrange all first a layer of shot then a layer of mineral material which is melted to impregnate

the shot.

  On contact with particles of refractory material, the molten mineral material (glass or other binder material) is gradually loaded with oxide elements contained in said material. It seems that the cohesion of the layer thus formed is linked to the progressive modification of the chemical composition of the binder, which would lead to an increase in viscosity and / or devitrification of the latter at the temperature of the sole or of the wall, preventing the glass of the bath

  molten to infiltrate between the refractory particles.

  This enrichment of the interstitial glass (or other material) is generally all the more pronounced when the surface of exchange with the refractory material is

  high, that is to say that the granulometry of the shot is fine.

  We will adjust the choice of particle size and type of binder glass by

  depending on the properties of the material intended to be melted in the oven.

  The structure of the sole and / or of the walls can be adapted as required, in particular by choosing from the following variants: - the layer or layers comprising refractory shot can be applied to slabs or blocks of refractory material usually used to make the contact surface with the molten bath; the layer or layers comprising refractory shot can be applied in place of a traditional block or slab material, either on a

  leveling concrete layer, either directly on the insulating blocks.

  The layer or layers comprising shot can also be used on the interior walls of the furnace in well-defined zones, in particular as a function of the temperature prevailing in the bath or above the bath in the zones considered, or as a function of the quality of the material in the molten bath

level of the zones considered.

  In general, the refractory shot-based composite can be used in all types of ovens. Its use can nevertheless vary

depending on the type of oven.

  Thus, at the level of the sole, the layer comprising shot can be used over the entire surface of the sole in an electric oven, in particular of the plunging electrode type, whereas it may only be used in the area of charging in a burner oven, in which the downstream area can

  use conventional slabs in contact with the molten material.

  It is generally advantageous for the hearth to have a layer comprising refractory shot at least in an area of the furnace where the material to be melted is fed. Thus, when said material contains fusible residues, in particular metallic residues, which tend to deposit at the bottom of the bath in the furnace supply zone, the surface coating according to the invention is perfectly adapted to receive these residues. It can in particular make it possible to prevent the progression of these residues towards the structural levels

  walls, such as insulation blocks.

  In particular, the wall surface coating according to the invention has a remarkable advantage when the material to be melted contains metallic residues, in the sense that it withstands corrosion much better than a conventional contact refractory material. melted at a temperature

near its melting point.

  In fact, in a glass oven, the bottom surface of which is formed by a usual refractory slab, the presence of liquid metal on the bottom surface causes a level of the triple point molten glass-liquid metal-refractory

  very severe corrosion of the refractory.

  We then quickly see a degradation of the constituent elements of

  the wall by metal infiltration.

  This drawback does not arise or is considerably reduced when a wall surface is produced according to the invention. In this regard, the invention also relates to the use of an oven as described above for melting recovery glass. containing

metallic residues.

  The recovery glass can come from various sources, in particular from mirrors, heated glazing for motor vehicles, in particular rear glasses, or tinned or enamelled glass, in particular for automobile glazing. The metals present in the form of metal residues in these recovery glasses can be in particular silver, copper, tin or others. It was surprising to note that, depending on the granulometry of the shot used (for a given vitreous binder), the liquid metal resulting from the melting of the recovery glass could or not penetrate into the surface layer (s). The critical size of the particles of shot depends on the nature of the metal in particular on its viscosity in the molten state at the temperature of the sole, as well as on the

  glassy binder and molten glass in this bath.

  Thus, the surface of an oven wall can be adapted to recover the

  metal separated from the glass by fusion, this surface being permeable to said metal.

  In this regard, the subject of the invention is also a process for the separation of metal present in recovery glass, this process comprising a step consisting in melting the recovery glass in an oven as described above, in which the shot included in the surface layer of the sole which is in contact with the glass has a particle size suitable for making said

layer permeable to said metal.

  In a first embodiment, there can be provided, immediately under said layer, a space for recovering the liquid metal flowing through said layer. Optionally, a perforated element such as a grid can be placed in the upper part of this space, serving as a support for the contact layer. In another embodiment, there can be placed, immediately under said layer, a second so-called "lower" layer comprising shot having a particle size suitable for making said lower layer

impermeable to liquid metal.

  The metal is then trapped at the border between the two shot-based layers and gradually stored during a campaign to use the furnace. After one or more campaigns of use, it suffices to deposit the surface coating of the sole, from which the recovered metal can be easily extracted. This method allows, in the same device, to recycle the glass of

  recovery while the metal is recovered separately.

  Other characteristics and advantages of the invention will become apparent from the

  detailed description which will follow made with reference to the appended drawings, on

which:

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  - Figure 1 shows a schematic view in partial longitudinal section of an oven according to the invention;

  - Figure 2 shows an enlarged detail of the hearth of the oven of Figure 1.

  In FIG. 1, only the elements necessary for understanding the invention have been shown, without respecting the scale of the device. In FIG. 2, only the orders of magnitude of the respective elements have

been respected.

  The oven 1 shown in Figure 1 consists essentially of a hearth 2, side walls 3 and a roof 4, defining a bath 5 of a molten material such as glass. It further comprises supply means 6, such as a conveyor, for melting material 7 and a channel 8 for flow of the molten material. The means for melting the material 7 are not shown. The material may consist of recovery glass (cullet) and / or a

powdery oxide composition.

  The sole 2 essentially consists, from the outside towards the inside, of a wall made of insulating blocks 9 arranged in one or more rows (only one row being shown), of a layer 10 of refractory concrete on which are optionally laid slabs 11 of refractory material, then a first layer 12 and a second layer 13 continuous of material-based

refractory.

  The detail of layers 12 and 13 is visible on the enlargement of FIG. 2. The first layer 12, or lower layer, comprises shot 14 of refractory material, in particular of AZS or chromium oxide type, of a relatively granulometry. fine, embedded in or surrounded by a binder 15 formed at

  from a glassy material such as glass.

  The second layer 13, or contact layer, comprises another shot 16 of refractory material, of composition identical or different from that of shot 14, but of grain size greater than that of said first shot 14, the particles of shot 16 being surrounded of a mineral binder 17, of identical or different composition to that of the layer of

contact 12.

  These layers can be produced on the surface of the slabs 11

in various ways.

  In a preferred manufacturing method, a lower layer of the relatively fine shot 14 is deposited on the slabs 11, then an upper layer of the relatively large shot 16 is deposited on the lower layer. The whole is then covered with a thickness of fusible cullet of vitreous material, in particular glass, and the oven is started: the fusion of cullet allows the impregnation of the layers of shot and the progressive coating of the particles of shot 14 and 16 to finally produce layers 12 and 13 in which

  the molten cullet acts as a binder and ensures the cohesion of the whole.

  As it flows between the particles of shot, the glass melted from the cullet interacts with the surface of the shot and becomes charged with element (s) of refractory oxide (s), for example AI , Zr, Si in the case of AZS shot, or Cr in the case of chrome shot. The glass ends up devitrifying in the free interstitial spaces, the devitrified material preventing the

  passage of glass from the bath 5.

  Alternatively, a separating element such as a grate or a refractory metal screen could be interposed between the two layers of shot, and possibly a similar element could be placed on the second layer of

  so as to maintain the respective levels of the layers.

  The same technique with a support grid could be used to

  apply one or more similar layers to the side walls 3.

  In FIG. 2, the difference in behavior of the two layers 12 and 13 with respect to a metal 18, present in the molten state in the bath, is also illustrated, in particular in the case where the material to be melted 7 is a recovery glass

  containing metallic residues.

  The granulometry of the shot 16 and the quality of the bonding glass 17 are such

  that the layer 13 is permeable to metal 18.

  On the contrary, the particle size of the shot 14 and the quality of the bonding glass

  are such that layer 12 is impermeable to metal 18.

  Thus, in operation, the metal 18 present in the molten state in the bath 5 flows by gravity to the bottom 2, penetrates through the layer 13 by making a passage between the particles of shot 16, and is blocked at the border between layers 13 and 12, where it accumulates in the form of drops whose size gradually increases. The thickness of the layer 13 is advantageously determined so that it provides a storage capacity for the metal, in the interstitial spaces between the shot, sufficient for a given duration of the campaign of use. The invention which has just been described in the particular case of a glass furnace whose hearth, of given structure, is equipped over its entire surface with two layers based on shot is not in any way limited to this embodiment. . The

  indications given in the detailed description can be extended to

  other embodiments in particular in the following cases: the sole has another structure (in particular the insulating blocks, the concrete and / or the slabs are absent); only one layer based on shot is used; the layer or layers are applied to the side walls; the layer (s) are only applied on

part of the sole.

  The other usual arrangements in glass type ovens

  are also suitable in the present invention.

Claims (11)

  1. Oven (1) for melting a material with a high melting point, such as glass, comprising a hearth (2) and side walls (3) delimiting a bath (5) of molten material, characterized in that at least part of the surface of the hearth (2), and possibly of the side walls (3), which is in contact with the molten material (5) consists of at least one layer (12,13)   comprising shot (14,16) of refractory material.   2. Oven according to claim 1, characterized in that the refractory shot material is a material resistant to corrosion by glass, in particular of the type based on chromium oxide or based on zirconium oxide, silicon and / or aluminum.   3. Oven according to claim 1 or 2, characterized in that the shot   (14,16) has a particle size less than 50 mm.   4. Oven according to any one of claims 1 to 3, characterized in   that said surface comprises a first layer (13) in contact with the molten material, beneath which is a lower layer (12) comprising shot (14) whose particle size is less than the particle size of the   shot (16) of the first layer (contact layer 13).   5. Oven according to claim 4, characterized in that the contact layer (13) comprises shot (16) having a particle size of the order of 20 to mm and the lower layer (12) comprises shot (14 ) having a   particle size less than 20 mm.   6. Oven according to any one of the preceding claims,   characterized in that said layer or at least one of said layers (12, 13) comprises, in addition to the shot (14.16), an inorganic binder (15,17) formed from oxide or a vitreous material such as glass, in particular recovery glass.   7. Oven according to any one of the preceding claims,   characterized in that the layer (s) (12,13) comprising shot   (14,16) are applied to slabs (11) or blocks of refractory material.   8. Oven according to any one of the preceding claims,   characterized in that the bottom surface has a layer comprising refractory shot at least in a portion of the oven where takes place   the supply of material to be melted.   9. Use of an oven according to any one of claims   above to melt recovery glass containing metal residues. 10. Method for recovering metal (18) present in recovery glass comprising a step consisting in melting the glass   recovery in an oven (1) according to any one of claims 1 to 8   wherein the shot (16) included in the layer (13) of the sole (2) which is in contact with the glass has a particle size suitable for rendering said layer (13) permeable to said metal (18).   11. Recovery method according to claim 10, characterized in that the oven (1) comprises, immediately under said surface layer (13), a lower layer (12) comprising shot (14) whose particle size is   adapted to make the lower layer (12) impermeable to said metal (18).