MXPA99008787A - Method and device for melting and refining materials capable of being vitrified - Google Patents

Abstract

The invention concerns a method for melting and refining materials capable of being vitrified, such that part of or all the heat energy required for melting said materials capable of being vitrified is supplied by combustion of fossil fuel (s) with at least one oxidant gas, said fuel(s)/gas(es) or the gas products derived from combustion are injected beneath the mass of the materialscapable of being vitrified (7). The refining of materials capable of being vitrified after fusion is carried at out at least partially in"thin layer"form. The invention also concerns the device for implementing said method and its applications.

Description

METHOD AND DEVICE FOR MELTING AND REFINING VITRIFICARY MATERIALS DESCRIPTION OF THE INVENTION The invention relates to a process for melting and refining vitrifiable materials for the purpose of continuously feeding glass forming plants with molten glass. More particularly, there are plants for forming flat glass, such as flotation or rolling plants, but also plants for forming glass articles of the bottle or container type, plants for forming glass fibers of the wool-type material for thermal insulation or acoustic or textile fiber fibers called reinforcing fibers. A great research work has been carried out in these processes, which schematically comprise a first stage of fusion followed by a refining stage designed to thermally and chemically condition the molten glass and remove from it any batch stone, bubbles or any reason for defect that appears after training. In the fusion interval, it has been seen, for example, to accelerate the fusion process or improve its energy efficiency. Mention should be made of the process of rapidly heating the vitrifiable materials in a homogeneous and controlled manner and at the same time carrying out intense mechanical agitation which allows the still solid vitrifiable materials to come into intimate contact with the already liquid phase. This process is detailed in particular in patents FR-2, 423, 452, FR-2, 281, 902, FR-2, 340, 11 and FR-2, 551, 746 and generally uses an electrical heating means of the type of submerged electrode. Another type of fusion process has been developed, for example of the type described in patents US-3, 627, 504, US-3,260,587 or US-4,539,034 which consists in using, as a heating medium, submerged burners, ie , burners fed with gas and air, these are generally placed so that they are in the same plane of the hearth so that the flame develops within the mass of vitrifiable materials during the liquefaction. In any of the cases, although it is possible in reality to significantly reduce the residence time of the vitrifiable materials in the melting chamber and increase the production efficiency considerably compared to the "conventional" melting operations, the molten glass it must be melted, on the one hand, in the form of a foam which is difficult to refine - especially it is difficult to guarantee the quality of the final glass, especially optical glass.

Research has also been carried out in the field of refining. Thus, a centrifugal refining process is known, for example, from the patent FR-2, 132, 028, this process uses a device whose internal walls define a cylindrical chamber which has a vertical axis and rotates. The molten glass feeds the device in the upper part and is distributed in the chamber, defining a paraboidal cavity which is established naturally due to the effect of the centrifugal force. The object of the invention therefore is to improve the melting and refining process, directed especially for use in plants which are more compact and / or have a greater flexibility of operation and / or higher production efficiency and / or to manufacture glass that until now has been difficult to melt or refine and / or with a low cost of energy, etc., without these industrial advantages being obtained, damaging the quality of the glass produced. The object of the invention is first of all a process for melting and refining vitrifiable materials, which is characterized by the combination of two characteristics: on the one hand, all or part of the thermal energy necessary to melt the vitrifiable materials is supplied by fuel or fossil fuel combustion with at least one oxidizing gas, fuels / gas or gaseous products resulting from combustion are injected below the level of the mass of vitrifiable materials, on the other hand, the refining of the vitrifiable materials after melting takes place at least partially in the form of a "thin layer". In the context of the invention, it should be understood that the "thin layer" of refining means a refining in which molten vitrifiable materials are driven to flow at a very thin depth / thickness - to be more specific, at most 15 cm and even a maximum of 10 cm, for example - and this is obtained by various means. The molten materials can be specially driven to flow between two nearby physical walls, the distance that separates them defines the depth / thickness of the thin layer (the flow is obtained by centrifugal force or simply by gravity, for example). These thin-film characteristics can also be obtained by other means, especially by the choice of the dimensions of the refining compartment or compartments, the choice of means for feeding them as an inlet or for extracting them as an outlet. Some of these media will be explained later. In fact, the main advantage of this way imposing a small thickness on the stream of vitrifiable materials that are refined is that in this way it is possible to considerably reduce the trajectory generated by the bubbles contained in these molten materials towards the free surface of the latter. or the walls so that they are forced to rub, and this makes it easier for these bubbles to be blown up and removed. In fact, it has been shown that it is extremely advantageous to establish a synergy from an industrial point of view between the use of the melt named below "melted by submerged burners" for simplicity purposes and refining by "thin layer" as previously defined. However, since this combination is far from being imposed as evidence, it can be expected that all the advantages mentioned above will be obtained only at the expense of mediocre glass quality, which has not been the case. This is because, in the invention, a very particular refining is used when changing a size parameter, instead of feeding the refining zone with "conventional" molten glass to be refined, the feeding here is in fact with a glass that is obtained by melting the submerged burners, that is, with glass that has very special characteristics in the sense in which it is completely foamy, with a relatively low density compared to that of the standard glass that is going to be refined. Nothing would suggest that a relatively sparkling initial glass could be refined in a thin layer. Surprisingly, it has been shown that it is possible as it has been discovered that this foamed glass resulting from melting by submerged burners, also has the characteristics of containing relatively large bubbles; and it is actually in the form of a kind of foam which remains to be refined, and it is possible to control the size of the bubbles which it contains and, especially in certain preferred configurations and for certain compositions of vitrifiable materials, remove almost all of the the smallest bubbles, that is, those that have a diameter of approximately less than 100 μm and even smaller than 200 μm, when carrying out, in this glass while it is still melted, a kind of "micro refining" before the actual refining after melting, this micro refining facilitates the coalescence of the bubbles and the disappearance of the smaller bubbles in favor of the larger ones and is promoted by the addition in the vitrifiable materials of refining promoters of the coke or sulphate type. In addition, the glass that leaves the melting chamber generally has a relatively low residual amount of batch stone: the combination of "large" bubbles and small batch stones allows the use of thin-layer refining, which greatly facilitates the refined, at least part of which has been carried out, de facto, during the melting. "Large" bubbles have a higher rate of ascension, coalesce more quickly and are finally removed more quickly. It should also be noted that, in general, glass melted by submerged burners only contains little sulfate, the residual amount of which before refining is less than 600 ppm, especially less than 200 or 100 ppm, or even less than 50 ppm, expressed in weight of S03, whatever the type of vitrifiable material, which may or may not contain unintentional sulfates or which may even have sulphates added to it. This would be explained by the partial water pressure generated by the submerged combustion. It should also be noted that desulphated glass provides less volatile compound problems in the float, less risk of tin sulphide formation and therefore, ultimately, less risks of a tin defect in the glass sheet. This decreases the amount of sulfides (or even completely eliminates them) in the case of reduced glasses, especially iron sulfides which provide undesirable yellow / amber residual colors or nickel sulfide inclusions which can cause the glass to break during the cooling-type heat treatments. Therefore, the invention optionally makes it possible to generate glasses which are very low in sulfates even before the refining operation, and therefore glasses which are at least as low after refining, this is done without having to purify / select vitrifiable materials so that they are low in sulphates. on the contrary, it is even possible to add sulphate at the beginning.

An advantageous effect obtained by the combination according to the invention is related to the energy cost of the process: the fusion by submerged burners makes it possible to avoid using the electric melt of the submerged electrode type, the cost of which can be very significant depending on the country. In addition, and this is the most important point, melting by submerged burners generates connective agitation within the vitrifiable materials during liquefaction, as explained in detail in the following. This very strong mixing between materials not yet liquefied and those which are already melted is extremely effective and makes it possible to obtain, for vitrifiable materials of the same chemical composition, a melt at a lower temperature and / or melting which is much faster than in a conventional heating means. The temperatures found in the melt can be lower at all times than those of the usual processes, which is economically very advantageous, simply in terms of energy cost, but also by the selection of refractory-type materials used in the manufacture of plants-materials which are less corroded by heat, or they do so more slowly. The residence times in the melting and refining zones are significantly reduced and compatible, this obviously has a very positive effect on the production efficiency and on the performance of the plant as a whole. At the same time, the invention makes it possible to obtain plants which are very compact -this is because melting by submerged burners, again due to the very strong mixing that this causes, allows the size of the melting chamber to be considerably reduced. In addition, thin layer refining has the same consequences on the size of the compartments when this operation is carried out. Therefore, by reducing the depth of the glass during refining, the bubbles are removed more quickly and therefore it is possible to considerably reduce the "length" (in the glass flow direction) of the refining compartment or compartments. In general, the plant is therefore very compact, with clear advantages in terms of construction costs, simplification of operation, reduction in the wear of structural materials, etc. With respect to the melting operation, the chosen oxidant can be based, according to the invention, in air, in air enriched with oxygen or even substantially based on oxygen. A high concentration of oxygen in the oxidant is actually advantageous for several reasons: the volume of combustion smoke is reduced in this way, this is favorable from the point of view of energy, and avoids any risk of excessive fluidization of the vitrifiable materials which can cause them to splash on the roof structures of the fusion chamber. In addition, "the flames" that are obtained are shorter and more emissive, which allows a faster transfer of energy to vitrifiable materials and secondly it makes it possible to reduce, if desired, the depth of the "bath" of materials vitrifiable that liquefy. We speak here of "flame", but these are not necessarily flames in the usual sense of the term. We can talk, more generally, as is done in the rest of the "combustion regions" document. In addition, any emission of contaminating N0X gas is thus reduced to a minimum. With respect to fuel selection, it may or may not be of the gaseous fossil fuel type, such as natural gas, propane, fuel oil or any other hydrocarbon fuel. It can also be hydrogen. The melting process by submerged burners according to the invention is therefore an advantageous means to use hydrogen which is, moreover, difficult to use with "higher" burners not submerged, given the low emissivity character of the flames obtained by the H2 / 02 combustion. Combining the use, in the melting by submerged burners, of an oxygen oxidizer and a hydrogen fuel is a good means of ensuring an effective transfer of heat from the energy of the burners to the molten glass, which also leads to a completely "clean" process, that is, without the emission of oxides of nitrogen, NOx, or greenhouse gases of the Cox type, which could otherwise arise from the decarbonisation of the batch materials. Advantageously, the melting is carried out according to the invention in at least one melting chamber which is equipped with burners which are placed in such a way that their combustion regions or the combustion gases developed in the mass of vitrifiable materials during the melting. In this way, they are passed through their side walls and / or the screed and / or are suspended from the top, fastening them to the roof or to any other suitable superstructure. These burners can be such that the gas supply pipes are in the same plane as the wall through which they pass. It may be preferable that these tubes "enter" at least partially into the mass of vitrifiable materials in a manner that prevents the flames from being too large near the walls and does not cause premature wear of the refractory materials. It is also possible to choose to inject only the combustion gases, and the combustion regions are produced outside the appropriate melting chamber. As mentioned above, it has been observed that this heating method causes intense convective stirring of the vitrifiable materials - therefore convection cycles are formed on each side of the combustion or "flame" regions or combustion gas streams, which They permanently mix the molten and not yet molten materials, very effectively.

This therefore results in a highly favorable characteristic of "stirred" melt without making use of a mechanical agitation means which is not very reliable and / or is subject to rapid wear. Preferably, the height of the mass of the vitrifiable materials in the melting chamber and the height at which the combustion regions develop or the gases resulting from the combustion are adjusted so that these combustion / gas regions remain within the mass of vitrifiable materials - the objective is therefore to allow convective circulation cycles to be established in the material during liquefaction. In general, this type of fusion makes it possible to considerably reduce the emission of any type of dust in the melting chamber and any NOx type gas since the exchange of heat takes place very quickly, so that temperature peaks are avoided that are probably drivers of the formation of these gases. The emission of COx-type gases is also considerably reduced, the total energy consumption of the plant is lower than with conventional apparatuses that use incineration furnaces, for example those operating in the down-drawn mode. Optionally, the melting operation can be preceded by a preheating step of the vitrifiable materials at a temperature which, however, is notably less than that necessary to liquefy them, for example, at most 900 ° C. In order to carry out this preheating operation, the thermal energy of the furnace can advantageously be recovered. In this way, when extracting the heat from the furnace, the general consumption of specific energy of the plant can be reduced. The vitrifiable materials may comprise materials in batches, but also pieces of fractured glass or even fragments designed to be vitrified. It can also comprise fuel elements (organic matter): it is therefore possible to recycle, for example, mineral fibers which have been sized with binder (of the type used in thermal or acoustic insulation or those used in the reinforcement of plastics), glass or Laminated window loaves with polymer sheets of the polyvinyl butyral type, such as windshields, or any type of "composite" material which combines glasses with plastics, such as certain bottles. Therefore, it is possible to recycle "glass / metal or composite metal composite" such as glass functionalized with coatings containing metal, these, until now have been difficult to recycle as they would run the risk of gradually enriching the melting chamber with metals which would accumulate on the surface of the hearth. However, the agitation caused by the melt according to the invention avoids this sedimentation and therefore allows, for example, that the window glasses coated with enamel layer, with metal layers and / or various connection elements be recycled . The object of the invention is also to recycle all these composite elements that contain glass because they are melted by submerged burners in a glass oven. In particular, furnaces with submerged burners can be provided, the essential function of which is the manufacture of fractured glass pieces from these various materials that are to be recycled, where the particular fragmented pieces of glass can then serve, and possibly combined with standard fractured glass fragments, such as batch materials for conventional glass ovens. Advantageously, provision can be made to introduce all or part of the vitrifiable materials in the melting chamber below the level of the mass of vitrifiable materials to be melted. Some of these materials can be conventionally introduced from the top of the mass that is liquefied and the rest from below, for example, by means of supply of the type of feed screw. The materials can thus be introduced directly into the mass that is liquefied, at a single point or at various points distributed over the walls of the melting chamber. Such an introduction directly into the mass of materials that is liquefied (hereinafter referred to as the "melt") is advantageous for more than one reason: first, it substantially reduces any risk of the batch materials flying above the melt, and therefore it reduces the amount of solid powder emitted by the oven to a minimum. Therefore, it allows a better control of the minimum residence time of the materials before they are extracted in the refining zone and allows them to be selectively introduced at the point where the convective agitation is stronger, depending on the arrangement of the submerged burners. This or these insertion points in the melt in this manner may be close to the surface or deeper in the melt, for example at a melt height of between 1/5 and 4/5 of the total melt height above the melting point. level of the hearth, or in addition between 1/3 and 2/3 of the height. It has been observed that the process according to the invention makes it possible to recycle plastics in the form of composite products combined more particularly with glass, and therefore these plastics serve as part of the fuel. It is also possible, and advantageous, to introduce all or part of the fuel necessary for melting by submerged burners in the form of a solid fuel (organic materials of polymer or carbon type) or even a liquid fuel, this fuel is a partial substitute for at least the liquid (especially fossil) or gaseous fuels that feed the burners. In general, the term "vitrifiable materials" or "batch materials" used in this text is intended to cover the materials necessary to obtain a vitreous (or ceramic or vitreous-ceramic) matrix, but also the additives (refining additives, etc.), all liquid or solid optional fuels (plastic of composite material or non-composite material, organic matter, coal, etc.), and any type of fractured piece of glass. It is also possible to recycle laminated window panes with polymer sheets of the polyvinyl butyral type, such as windshields with which the vehicles are equipped, or other types of composite materials which combine glass with plastics, such as certain bottles, for example. It is also possible to recycle functionalized window panes with metal-containing coatings, which until now have been difficult to recycle since they run the risk of gradually enriching the melting chamber with metals that can accumulate on the surface of the hearth. However, the agitation caused by the melt according to the invention avoids this sedimentation and therefore allows, for example, that the window panes coated with enamel layers, with metal layers of various connecting elements, be recycled. The process according to the invention can operate with a high level of pieces of fractured glass.

As mentioned in the above, the raffinate according to the invention is therefore carried out in molten vitrifiable materials of the glass type in a relatively foamy state. Typically, this "foam" has a density of about 0.5 to 2 g / cm3, especially 1 to 2, for example (to be compared with a density of approximately 2.3 or 2.4 in the case of non-foamed glass), it may have a sulphate content of at most 600 or even at most 100 ppm, expressed by weight of S03 and, above all, may contain a maximum of bubbles having a diameter of at least 100 or 200 μm. In order to improve the operating characteristics of the refining operation, various refining promoters are preferably added to the vitrifiable materials, the objective is especially to remove from the glass any bubble having a diameter less than 100, even less than 200 μm of the fusion stage, as mentioned before. This can reduce additives such as coke (which also allows the redox process of the glass to adjust). In this case, it is advantageous to select coke powder which has an average particle size of less than 200 μm. There may also be sulfates. Other refining promoters will be more effective during the appropriate refining stage, after the melting step. They allow the foam to be "destabilized": for example, they can be fluorine or a compound of fluorine or chlorine, more generally halides, or in addition a nitrate of the NaN03 type; Fluorine (halogen) seems to decrease the viscosity of the glass and therefore helps to drain the films which are formed between the bubbles, draining which promotes the collapse of the foam. It also decreases the surface tension of the glass. Advantageously, the process according to the invention makes it possible to carry out the melting at temperatures not exceeding 1400 ° C, especially at 1380 or I350 ° C, and refining at temperatures not exceeding 1500 ° C. According to a first variant, the refining according to the invention can be carried out in at least one static compartment (one which does not move during the operation) downstream of the melting chamber, of the flow type- channel, and which is provided with one or more means for propelling molten vitrifiable materials to be refined in a thin layer, especially at a depth of maximum 15 cm or, at the most, 10 cm. One or more means can also advantageously help to prevent the formation of the return glass stream in the mass of molten vitrifiable materials flowing in the compartment or compartments. The "return flow" refers to the convective recirculation cycles found within the vitrifiable materials in most conventional refining compartments. For more details regarding a non-limiting way of eliminating this return current and with respect to the advantages which are related, reference may advantageously be made, for example, to EP-616,983. In fact, it has been found that a great advantage associated with thin-layer flow is that any return flow can be eliminated, and at the same time there is a flow in the refining compartment of the plug-flow type. In the plug flow, the molten materials no longer have a downward velocity component and the bubbles, which tend to rise to the surface of the glass, are no longer driven to "submerge" back into the bath by entrainment due to the convective recirculation currents, which is eliminated in this way. According to a second variant, thin layer refining is carried out either in the melt chamber itself or in at least one static compartment located downstream thereof, by providing the vitrifiable materials melted by gravity, a downward trajectory between at least two adjacent walls, these are essentially mutually parallel, at least partially immersed in the melt and inclined with respect to the plane of the hearth of the fused chamber or compartment (or in other words) walls which are inclined in substantially mutually parallel inclined planes with respect to the longitudinal axis of the fusion chamber or the downstream compartment in question). Advantageously, these walls can be incorporated in one or more structural elements such as tubular elements, which especially have an approximately rectangular cross section, which is divided longitudinally (by a plurality of divisions): the refining that is obtained in this way when forming a plurality of thin layers of glass to be refined which flow along "lamellas" consisting of the walls mentioned above, the method of operation of this refining is explained in detail in the following, with the help of the figures . According to a third variant, refining is carried out downstream of the melting chamber, but in a compartment capable of rotating so as to ensure centrifugal refining, this compartment is further provided with one or more means for driving the vitrifiable materials melts to be refined in a thin layer at a "relative thickness" Rl / RO of at least 0.8 o, in absolute values, up to an "absolute thickness" of, at most, 10 cm. Within the context of the invention, the ratio Rl / RO should be understood as follows: RO is the average radius of the approximately cylindrical cavity defined by the compartment, through the cavity which flows the molten material, Rl is the radius Average of the dividing medium introduced into the cavity in order to propel the molten materials to follow a path between the internal walls of the cavity and the dividing medium.

A third variant consists of combining the two previous ones, especially by using for refining, a first static compartment and after a second rotary compartment. (In the context of the invention, the terms "upstream" and "downstream" refer to the flow direction of the gas through the plant from the point where the vitrifiable materials are supplied into the melting chamber to the point at which the refined gas is extracted ). The melting / refining process according to the invention allows glasses of very varied compositions and properties to be manufactured. In addition, it makes it possible, due to its low inertia, to change from one composition to another with very short transition times. It allows the refined molten gas to be fed into the plants to form a flat glass, hollow glassware, glass wool or fiberglass for reinforcement. Therefore it allows relatively small glasses to be manufactured, especially those that have a redox of more than or equal to 0.3. (Redox is defined as the proportion of FeO content, ferrous iron, as a percentage by weight, with respect to the total iron content by weight of the composition, expressed as Fe203). It also allows glasses to be manufactured having a high Si02 content, for example of at least 72 or even at least 75% by weight, these glasses are generally difficult to melt but advantageous, especially in terms of material cost of batch, because they have low density and are very compatible with plastics. It also makes it possible to manufacture very special glasses having a high alkaline earth oxide content, for example containing at least 18% by weight of CaO, glasses which, however, are very corrosive using the conventional melting process at a higher temperature. higher than in the invention, as well as glasses having a low sodium oxide content of, at most, 11% by weight, for example, or having a very low sulfate content, for example, of, at most, 600 ppm. Glasses containing iron, with a high but low redox content in sulphate also allow to obtain glasses which have a residual blue color which is particularly attractive and is sought in the field of flat glass for motor vehicles and for buildings , for example. Highly selective sun protection glasses can be obtained in this way in which solar protection layers can be deposited in order to improve the thermal performance characteristics thereof, for example TIN-type layers, these are described especially in the patents EP-638,527 and EP-511, 901.

The object of the invention is also a melting and refining apparatus which is especially suitable for implementing the process described above and which comprises: at least one melting chamber equipped with burners which are fed with fossil fuels of the gas type (natural) and with oxidants of the air or oxygen type, the burners are placed in such a way that they inject these gases or gases resulting from combustion, below the level of the mass of vitrifiable materials introduced into the melting chamber, a means for reinforcing the molten vitrifiable materials to be refined in the form of a "thin layer", the medium is included within the same melting chamber or in at least one refining compartment downstream of this chamber. Advantageously, as mentioned previously, the melting chamber can be equipped with at least one means for introducing vitrifiable materials below the melting level, especially at least two of them, preferably in the form of an opening (or openings) in the associated wall or walls, with a supply means of the type of feed screw. In this way, the risks of dust that is blown and eliminated are minimized, and at the same time optionally allows the introduction, above the melt, of vitrifiable materials such as silica, on which the preheating operation can be carried out without the risk of them settling and solidifying. Independently also from the refining operation, the invention also depends on design improvements with respect to the walls of the melting chamber which are designed to be in contact with the melt. They are possible to various variants. In certain cases, the known oxide-based refractory materials can simply be used, such as alumina, zirconia, chromium oxide and what are referred to as refractory AZS (alumina-zirconia-silica). It is generally preferred to combine them with a cooling system that involves the circulation of a water-type fluid (water jacket). The water jacket can be placed on the outside, the refractories are then placed in direct contact with the glass, or inside, the water jacket then has the function of creating a cooler glass stream near the refractories, and these are stressed particularly in this context as the melt is generated by the submerged burners causing strong convective currents against the walls. Another variant consists of using, in the molten zone, non-refractory only the water jacket mentioned above. Another variant consists of using refractory materials (optionally combined with a cooling system of the water jacket type and coating them with a coating made of a highly refractory metal such as molybdenum (or an alloy of Mo). distance (for example from 1 to a few millimeters) of the walls of the refractories and may be present in the melt with a continuous contact surface (solid plate or plates made of Mo) or a discontinuous contact surface (plate or plates of Mo). drilled with holes.) This coating has the purpose of mechanically avoiding the direct convection of the glass on the refractories by generating a "fixed" layer of glass along the refractories, or even avoiding any contact of the glass with the latter. melting chamber, all or part of the submerged burners are preferably designed in such a way that Inject, within the melt, a fluid which does not participate in combustion by (temporarily) replacing the oxidant and / or fuel. This fluid can be an inert gas of type N2 or a coolant or a type of liquid-water which vaporizes immediately in the melt. The fact of temporarily stopping combustion in this way, while continuing to inject a fluid into the burner, generally has two objectives: either to obtain the operation of the burner and more generally, for example, of the melting chamber in its In total, the injection of the N2 type inert gas allows the chamber to become safe in the region of the burners, or if you want to change the burner while the other burners are in operation and while there is still a presence of glass melting . In this case, as explained in detail in the following, the proper spraying of water through the burner allows the glass above the burner to freeze temporarily, which generates a kind of "bell" which allows a long enough to carry out the change without vitrifying the burner. According to the first variant mentioned above, the refining complement is static. It includes a flow channel that includes a channel and a roof. The means to propel the molten vitrifiable materials to be refined in the channel is a thin layer, especially at a depth of less than 15 cm, thus creating a plug-type flow which, for example, are of the kind structural and include properly selecting the ratio of average height to average channel width, proportion which is less than 1 and even less than 0.5. This channel may comprise, together with or as an alternative to the previous means, a means for driving the vitrifiable materials to be refined as a thin layer in the form of a means for controlling / regulating the flow of material at the entrance and / or the exit of the channel, or just upstream of the latter.

This channel may comprise, together with or as an alternative to the above means, another means for obtaining the flow of thin layer refining plug. In fact, this means generally consists of taking into consideration the flow of material through the refining compartment and the surface area developed by the bath of molten materials in the melt compartment, so as to determine the depth which is what sufficiently shallow to obtain a thin layer of plug flow. In addition, the channel can be equipped with a heating means, especially of the type having conventional burners placed above the vitrifiable materials, preferably oxygen burners. The channel can also be provided with a means for homogenizing the vitrifiable materials, for example, of the mechanical agitator type. According to the second variant, the melting chamber of the refining compartment downstream of the latter comprises at least one structural means for thin film refining in the form of at least two adjacent approximately parallel walls which are designed to be submerged at least partially in the dough to be refined and inclined with respect to the hearth of the chamber or compartment. Preferably, these walls are incorporated in one or more of the tubular elements described above.

Advantageously, they are placed in the actual fusion chamber and fused within the discharge opening downstream of the chamber. According to a third variant, the refining compartment includes at least one device capable of rotating in order to ensure centrifugal refining, the internal walls of the device substantially define the shape of a hollow vertical cylinder, at least in its central part . In order to drive the vitrifiable materials to flow as a thin layer through its centrifugal device, the cavity in the latter can advantageously be equipped with one or more divisions, at least over part of its height, driving the materials fused to flow between the internal walls of the device and these divisions, the average distance between the walls and the divisions define the "thickness" of the thin layer. In fact, according to the invention, the parabolic profile naturally adopted by the molten glass is prevented from forming when it is "freely" centrifuged, that is, only contained by cylindrical external walls. In contrast, according to the invention, the glass is forced to rub against the walls of the device and the divisions installed in the centrifuge body, to a relatively constant thickness over the height of the centrifuge, and at a much smaller depth than if allowed that the paraboidal profile mentioned above will be formed.

Here therefore there is a considerable gain in efficiency, the bubbles are exploded under the centripetal force much more quickly in the divisions, the trajectory of the bubbles is much shorter. As in the static variant, the flow can be referred to as plug flow. This allows the height of the centrifuge to be reduced, with its size retaining the same performance characteristics. Preferably, the distance between the divisions and the walls is a maximum of a few centimeters or is defined by the ratio Rl / RO of at least 0.8, the proportion is explained in the foregoing. According to a preferred design, the device is fed in the upper part with molten vitrifiable materials by a static supply means of the flow channel type. This delivery means may comprise at least one compartment under reduced pressure in order to allow the device to be powered and / or to allow the first refining operation to be carried out. The device can advantageously be provided with a means for trapping solid particles having a density greater than that of the glass, this means is especially located in its lower zone and is in the form of notches / grooves made in the internal walls. Preferably, the rotation speed of the device is selected to be between 100 and 1500 revolutions per minute.

The device can also be provided with a mechanical means which is stationary and which follows its rotation, and is capable of cutting the foam and pushing it down into the lower zone of the device from which the refined glass is extracted. This means is especially in the form of perforated detractors, or fins placed in the upper zone of the device. The invention will be explained in detail in the following, with the aid of three non-limiting modes, illustrated by the following figures: Figure 1: a diagrammatic melting / refining plant using a static refining apparatus; Figure 2: a diagrammatic melting / refining plant using a centrifugal refining apparatus; Figure 3: an enlarged view of the refining apparatus of the plant according to Figure 2; Figure 4: scheme of a melting / refining plant that uses refining by lamellas in the current melting chamber; Y Figure 5: schematic cross-sectional view of a submerged burner placed inside the melting chamber of the plants shown in the preceding figures. These figures are not necessarily scale and for clarity purposes they have been greatly simplified. The apparatus described below is designed to melt and refine glasses of very varied compositions, in this case glasses designed to feed a flotation plant to produce flat glass. But this request is not limited to this. These glasses can also be fed, for example, for equipment for forming hollow glass articles or fiber-forming equipment of the internal-centrifugal device type. Furthermore, of course, all standard glasses of the silica-soda-lime type and various types of special glasses are particularly advantageous to manufacture using the apparatus according to the invention, especially those which hitherto were considered difficult to melt: glasses which they have a low content of Na20 and a relatively high alkaline earth oxide, especially a CaO content, which is advantageous from an economic point of view in terms of the cost of batch materials, but also glasses which are very corrosive at conventional temperatures of fusion and which are relatively difficult to melt using standard processes. These can be glass compositions described, for example, in patent FR 97/08261 of July 1, 1997, such as (in% by weight): SiO, 72 - 74.3% A1203 0 - 1.6% Na20 11.1 - 13.3% K20 0 - 1.5% CaO 7.5 - 10% MgO 3.5 - 4.5% Fe, 0, 0.1 - 1% or in addition to type composition (expressed in percentages by weight): SiO, 66-72, especially 68-70% A1203 0-2% Fe203 0-1% CaO 15-22% MgO 0-6, especially 3-6% Na20 4-9, especially 5-6% K20 0-2 , especially 0 - 1% S03 traces.

Another example that illustrates this family of compositions is as follows: sio2 69% A1203 1% Fe203 0.1% CaO 18.9% MgO 5% Na20 5.6%? 2o 0.3% SO, trace.

This glass has a lower annealing temperature, also called stress point temperature, of 590 ° C (temperature at which the glass has a viscosity of 1014.5 poises). It also has a liquid temperature of 1225 ° C, a temperature T? = log2 of 1431 ° C and a temperature T? = log3.5 of 1140 ° C (T? = log2 and T? = log 3 5 correspond to the temperatures at which the glass is found when it reaches a viscosity, in poises, of log 2 and log3.5, respectively). It has fire-resistant glass properties, resulting from a high softening point (greater than 800 ° C) and suitable properties to be applied in palm meshes due to its high "stress point". glasses having a high content of silica, these are also advantageous from the economic point of view, and have a relatively low density, the composition ranges of which, again expressed in percentages by weight are as follows: Si02 72 to 80% CaO + MgO + BaO 0. 3 to 14% Na20 11 to 17% alkaline oxides 11 to 18. 5% A1203 0. 2 to 2% B203 O to 2% Fe203 O A 3% S03 optionally traces coke 0-600 ppm and optionally coloring oxides, for example the oxides of Ni, Cr, Co, etc. (These glasses have the characteristics of 'being particularly viscous). An example illustrating this family of compositions is as follows: Si02 76.4% Fe203 0.1% A1203 0.1% CaO 7.6% MgO 5% Na20 10% K, 0 0.3% It has a relative density of approximately 2.46 (compared to relative densities of 2.52 for the standard glass of silica-soda-lime of the "Planilux" type sold by Saint-Gobain Vitrage).

It is also observed in the foregoing that the process according to the invention can be used to obtain reduced glasses, the high redox, the iron content and the very low content of sulfates from which it allows obtaining glasses with a residual blue color. . Use of the process according to the invention, which is also possible to manufacture glasses having a zero or almost zero content of alkali metal oxide of the Na20 type, especially for the purpose of applications of glass laying with fire resistance or for substrates used for the electronics industry. For such compositions, reference may be made in particular to EP-526,272 and EP-576,362. Other glasses, especially those having a low MgO content, of the type described in EP-688,741 and WO 96/00194 can also be manufactured by using the process of the invention. A first implementation method is therefore shown in Figure 1: a channel 1 simultaneously allows part of the vitrifiable materials to be introduced into the melt chamber 2 via the roof 3 and to remove the combustion smoke. This smoke will preheat the vitrifiable materials, and therefore its thermal energy is recovered. The materials in batches capable of being introduced in this way above the melt 7 especially comprise silica, which can be preheated without hardening in a solid mass. The rest of the batch materials are injected at least at a point 1"located below the level of the melt 7, especially by means of an open supply path of feed screw Only one injection point has been shown here, this In addition, it is placed rather high with respect to the total height B of the melt, at approximately 2/3 of its height and on the front wall of the chamber.In fact, several injection points can be provided on the walls (front walls or side walls) which may or may not be at the same height, especially in the upper half or in the lower half of this height B, for example between 1/3 and 2/3 of this height. the melt makes it possible to greatly reduce the amount of material that is flying by eliminating itself above the melt (emission of solid particles of dust) and, based on its configuration, makes it possible to direct the materials to the point or wherein the convective agitation is stronger and / or takes this into consideration in order that these materials remain for at least the minimum period of time in chamber 2 before passing into the refining zone. The solder 4 of the chamber is equipped with rows of burners 5 which pass through and penetrate into the melting chamber over a small height. The burners 5 are preferably provided with a cooling medium, not shown, of the water jacket type. The burners 5, when functioning, develop regions of combustion in zones 6, creating near them convective currents within the vitrifiable material that is liquefied. This convective stirring generates a foam which will transfer the thermal energy through the melt 7. The melt is preferably carried out at about 1350 ° C, for example in the case of a standard glass of the family of silica-soda-lime glasses. The walls of the chamber 2 which are in contact with the melt 7 here are made of cooled refractory materials, from the outside, by a cooling system of the water jacket type (not shown). A variant consists in that this cooling system, with the metallic walls, leans against the refractory parts but not inside and therefore is in contact with the melt. These two variants make it possible to slow down the wear rate of the refractories by superficially cooling the glass near the walls of the refractories. The operation of the burners 5 has been adapted to submerged melting in the manner shown very diagrammatically in Figure 5. Figure 5a shows a longitudinal section of a burner 5 and Figure 5b shows a cross section, in the plane AA 'indicated in Figure 5a of the latter. The burner is coated with a cooling system 60 of the water jacket type and has a central tube 61 around which a plurality of tubes 62 are concentrically placed, all these tubes of cylindrical section are fused in the nozzle of the burner 63. In normal operation (operation [a]), the tube 61 is fed with a combustible gas of the natural gas type (or other edible gas or fuel oil) and the tubes 62 are fed with oxidant, in this case oxygen, for example, the CH4 / 02 interaction generates a combustion region in the melt. When it operates safely (operation [b]), that is, when it is desired to stop combustion in the burner without the risk of full vitrification, nitrogen is injected through the tube 61 and / or through the tubes 62. In operation designed to allow the burner to be exchanged for another (operation [c]), water is injected through tube 61, water which instantly vaporizes in the burner even in, or shortly after leaving the burner, steam generates a class of glass roof cooled above the burner; any operation of the burner then stops and there is sufficient time to carry out the exchange before the "roof" collapses. The injected water is collected at least partially in the burner by the tubes 62 (the papers of the tubes 61 and 62 in this mode of operation can also be inverted). Any other refrigerant is therefore liable to freeze the glass and can also be used as a substitute.

The burner and its various modes of operation described above, from one embodiment of the invention, independently of the melting and general refining operation involved in the glass plant. The molten foamed glass resulting from the melting by submerged burners is then removed at the bottom by a channel 8 which is optionally provided with a means for adjusting plug type flow (not shown). In this way, the flow of foamed glass entering the static refining compartment can be controlled. This compartment is in the form of a channel 9 defined by a slide guide 10 and a roof 11. It is equipped with oxygen burners 12. The vitrifiable materials flow through the channel, without a return flow, over a height H of about 5 to 10 cm. This height is adjusted so that it has the desired plug flow in channel 9, taking into consideration the densities of the molten materials in the melt chamber 2 and channel 9, as well as the heights 11 and 12 of the melts in these two zones. In order to obtain the desired thin layer, it is necessary here to increase the level of channel 10 of channel 9 with respect to that of hearth 4 of chamber 2. On the outlet side of channel 9, a submerged dam 13 emerges at a adjustable depth in the melt which allows the output flow to be adjusted; the refined glass is poured out at the end of the channel 9 in order to feed a formation plant, in this case the chamber of a floating bath, for example. Therefore, the refining is carried out in a shallow glass layer, which makes the trajectory of the bubbles towards the surface shorter (their ascension rate is further facilitated when they are already predominantly at least 200 μm). ) and, due to the plug flow that is obtained, prevents them from sinking again in the course of the rise in the melt. Figures 2 and 3 show a second embodiment. The main difference compared to Figure 1 is in the manner in which the walls of the refractories of the chamber 2 are protected. Here, submerged in the melt 7, is a refractory material coating consisting of a thin wall of molybdenum. which matches the shape of the melting chamber cavity and holds it in place at a distance of 1 to a few millimeters from the walls of the refractories by means of suitable spacers and / or by being suspended in the melt from the walls of the refractories located above the melt or from the ceiling. This sheet 40 is perforated with holes, firstly in its horizontal area that covers the base 4, so that it is capable of being penetrated by the burners 5, as well as in all the other walls, with a homogeneous distribution in the holes: therefore, this perforation does not prevent contact between the refractories and the molten glass, however mechanically decomposes the convection movements of the glass near the refractories and therefore reduces its rate of wear. The holes 41 in the walls of the lining 40, in addition to the lining of the sill, are preferably cylindrical and of variable dimensions, those which are found in the wall on the side of the sill have at least two constituent holes 42 whose size is sufficient to allow the burners 5 to pass through them. The liner 40 should also be extensively perforated (with the number 43) on its wall lining the transverse wall downstream of the chamber so that the glass can be removed by means of the channel 20a. The same is true for zone 1 ', for introducing the batch materials: there is necessarily a complementarity between the holes made in the walls made of refractories and in the molybdenum cladding. This coating of Mo is itself an invention, which is particularly suitable in combination with a chamber for melting by submerged burners, regardless of the manner in which any subsequent refining is carried out (the same applies to cooling, on the outer side of the glass side of the refractories, illustrated in the previous figure). The other difference with Figure 1 resides in the manner in which the glass is removed from the melting chamber. In the case of Figure 2, the glass is extracted slightly "upper", with a supply tube 20 divided into a first horizontal part 20 (a) and a second vertical part 20 (b), and a third part 20 (c) ) horizontally feeding the centrifuge apparatus 21. Another variant is that the molten glass is extracted from the melting chamber at the top, for example by means of a submerged channel, as is well known to those familiar in the field of glass processing Figure 3 is concentrated in the horizontal zone 20 (c) of the channel 20 for supplying the molten foamed glass 20, extracted from the melting chamber 2, which feeds the body of the centrifuge 21 by means of a tube 20 '. The centrifuge 21 has an upper part 22 which is located between the neck 35 fed with glass to be refined and the metal plate 24, and a lower part 30 which is located below the metal plate 24. Means (not shown) designed to control the flow of glass entering the centrifuge can be provided. The glass descends through the neck 35 into the centrifuge and stops in its fall through the metal plate 24 which, in combination with the upper part of the division 34 described above, generates a kind of "basket" collector. Due to the centrifugal force, the glass tends to ascend in zone 26 and then to pass over division 34; in this way it flows from the zone 26 into the interior of the zone 30 in the form of a thin layer contained by the internal wall 33 of the centrifuge 21 on the one hand, and by the division 34 placed in the cavity of the centrifuge on the other hand. The inner wall 33 is approximately in the form of a cylinder of radius RO and the division 34 has a cylindrical zone 34 (a) of radius Rl, this zone is closed in the lower part in the zone 34 (b). The division 34 is provided with a centering means (not shown), similar to plate 24. In dashed lines the parabolic shape acquired by the glass due to the centrifugal effect is diagrammatically shown if division 34 did not exist. Division 34 and the plate 24, which can be made of molybdenum, at least for the parts which are completely submerged in the glass. the outer cover of the inner wall 33 of the body of the centrifuge 21 may consist of electrovaceated refractory pieces 32 comprising an incorporated thermal insulator 31 so that the latter is not crushed by the centrifugal force. A notch or slot 28 is also provided which is located around the inner wall of part 30 (or is discontinuous), thereby allowing all of the solid particles of higher density than glass, of the inclusion type refractory, get trapped. During centrifugal refining, solid particles denser than glass are dragged against the walls and trapped in the slots 28 from which they can no longer exit. On the other hand, the bubbles explode under the centripetal action, towards the inside of the centrifuge body against the division 34. Finally, in the lower part of the part 30, the refined glass is extracted by means of a channel by a head 29 receiver approximately funnel-shaped. Under standard operating conditions, it is not necessary to provide a glass heating means, and the rotation speed can be about 700 revolutions per minute and the height h of the centrifuge can be, for example, from 1 to 3 meters. In Figure 4 a third embodiment is shown, which shows a fusion chamber 2 identical to that of Figure 1, which is also systematic and contains a system for refining in multiple thin layers. Here, the melting and refining are therefore carried out in the same melting chamber, the glass is extracted in the lower part by means of the discharge orifice 8 'inside a channel 8 in order to feed the machines of training directly, especially machines for making wool mineral fibers or for forming jars and containers (this refining system can also be placed in a downstream compartment). The principle of such refining is as follows: tubular elements 50 made of molybdenum (or platinum) whose rectangular cross-section is shown in Figure 4d are used. These tubes are longitudinally divided by walls 51 and thus form "lamellas" 52 open at the ends of the tube (for example 5 to 30 lamellae). These tubes 50 are immersed in the bath of vitrifiable materials that are melted (hereinafter referred to as the "melt") as shown in Figure 4a (a longitudinal sectional view of the melting chamber) and in Figure 4b (an elevation). from the same camera). The two tubes 50 are fastened on the side walls of the chamber, for example they are fixed to the walls when resting on ramps of refractory material, so that they are inclined at an angle with respect to the plane of the hearth 4, or in addition to the Y axes that converge on the longitudinal X axis of the furnace at angle a. In this way, these two tubes 50 are positioned in the manner in which they can be easily fixed to the walls of the oven and are at a significant distance from the burners. These settings allow molybdenum to be protected from the intense heating that occurs near the burners. Similarly, it is preferable that these tubes are completely submerged in order to prevent them from oxidizing in the air, otherwise the alternative would be to provide a non-oxidizing atmosphere above the melt (especially an N2 atmosphere). The two tubes 50 arise in a collection tube 55 which feeds into the discharge orifice 8 of the chamber. The refining is carried out in the following manner: the gas to be refined enters the section of the tubes in the upper part 53 and then flows into the lamellas 52 in a downward trajectory simply by gravity, as shown in FIG. Figure 4c illustrating typical flakes 52. The speed of the glass in these lamellas 52 is maximum in the center of the lamellas and much smaller in the walls 53, 53 'which contain them. With respect to the bubbles 60, these reach, quickly, by ascent, the upper wall 53 of the lamellas 52, and in this way separate from the downward flow of glass formed by the arrow in figure 4c. Again, by ascension, they go towards the entrance 66 of the tube 50, as a countercurrent to the flow of glass while the purified glass of the bubbles reaches the lower part 56 of the lamellas 52 and is removed directly from the collector 55 of the melting chamber . The entire system is more effective the lower the height h of each lamella 52 and the greater its surface area. This is particularly appropriate in the context of submerged burner melt which tends to generate bubbles that have a relatively large diameter and therefore can be removed quickly. It is possible to calculate the number, height and active surface area of these lamellae based on the size of the bubbles that are to be removed, at the outlet of the melting chamber and on the basis of the viscosity of the glass, in a special way but also by properly choosing its length and angle of inclination according to the length of the fusion chamber (or the compartment downstream where they are located). By way of example, in the case of a melt chamber that produces 200 tons of glass per day, in order to remove all bubbles having a diameter greater than 250 micrometers, the tubes 50 may have dimensions of 400 x 520 x 6550 mm3 and each one can contain 20 lamellas, for an oven length of approximately 6000 mm. A variant of this mode consists of fixing elements with similar lamellae in a downstream compartment. In all cases (static or centrifugal refiner) it is evident that the size of the melting / refining apparatus currently available can be greatly reduced. It has also been advantageous to add refining promoters of vitrifiable materials, especially coke having a small particle size, sulfate, nitrate, fluorine or chlorine, the function of these promoters has been described above. (Both in the melt compartment and in the refining compartment, it is possible to replace molybdenum with platinum). It is important to emphasize that, although the combination of melting by submerged burners with a refining step using reduced pressurization is remarkably advantageous, the invention also relates to these two aspects taken separately. Thus, it may be advantageous to use the melting method by submerged burners with a standard refining step and, conversely, to use a refining step with reduced pressurization subsequent to a melting step using a conventional heating means and at the same time remain within the scope of the invention, even if the synergy indicated above is not obtained. It should also be noted that it may be advantageous to use the melting method by submerged burners without having to make additional use of refining in the usual sense of the term. This may be the case in the field of fiber processing, in which it is possible to consider feeding the internal centrifugal fiber processing machines directly with foamed glass obtained using the melt by submerged burners., the centrifugation is necessarily carried out by this fiber-making technique that is de facto obtained from refining the glass. It is also possible to consider the direct treatment of the foamed glass that comes from the melting operation, for the purpose of manufacturing glass with foam used as an insulator, for example in the construction industry. It is also possible to apply this melt method for recycling glass / metal or glass / plastic composite products, as mentioned above, either to produce a usable glass or to produce pieces of fractured glass to feed a conventional glass-making oven ( in base, in particular in the proportion of these composite products with respect to the rest of the other conventional vitrifiable materials).

Claims (37)

1. A process for melting and refining vitrifiable materials, characterized in that all or part of the thermal energy necessary to melt the vitrifiable materials is supplied by the combustion of fuel or fuels with at least one oxidizing gas, fuel or fuel / gas or gaseous products resulting from combustion are injected below the level of the mass of vitrifiable materials and further the refining of the vitrifiable materials after melting is carried out at least partially in the form of a "thin layer".

2. The process according to claim 1, characterized in that oxidant is based on air, air enriched with oxygen or oxygen.

3. The process according to one of the preceding claims, characterized in that the melting of the vitrifiable materials takes place in at least one melting chamber, which is equipped with burners that pass through its side walls and / or pass through of the hearth and / or are suspended from the roof or from superstructures, so that their combustion regions or combustion gases are developed in the mass of vitrifiable materials, melt.

4. The process according to one of the preceding claims, characterized in that the combustion regions created by the combustion of the fossil fuel with the oxidizing gas or gases and / or the gases resulting from the combustion convectively agitate the vitrifiable materials.

5. The process according to claim 3 to claim 4, characterized in that the height of the mass of the vitrifiable materials in the melting chamber and the height at which the combustion / gas regions resulting from combustion develop, adjust so that fuel / combustion gases remain within the mass of the vitrifiable materials.

- - The process according to one of the preceding claims, characterized in that the melting is preceded by a step of preheating the vitrifiable materials to a maximum of 900 ° C.

7. The process according to one of the preceding claims, characterized in that the vitrifiable materials comprise batch materials and / or pieces of vitrifiable fractured and / or scraped glass and / or fuel elements, especially "glass-plastic composites, composite materials of glass-metal, organic materials or coal.

8. The process according to one of the preceding claims, characterized in that the refining operation is carried out in vitrifiable molten materials of the glass type in the foamed state, which have a density of approximately 0.5 to 2 g / cm3 in particular.

9. The process according to claim 8, characterized in that the refining is carried out in glass type molten vitrifiable materials in the foamed state, most of the bubbles are at least 100 and even at least 200 μm in size. diameter.

10. The process according to one of the preceding claims, characterized in that the vitrifiable materials contain refining promoters, especially coke-type reducing additives, which preferably have an average particle size of less than 200 μm, sulfates, or fluorine-based additives or chlorine, or nitrates of the NaN03 type.

11. The process according to one of the preceding claims, characterized in that the melting is carried out at a maximum of 1400 ° C, especially at a maximum of 1380 or 1350 ° C, and refining, at a maximum of 1500 ° C.

12. The process according to one of the preceding claims, characterized in that the refining is carried out in. at least one static compartment which is downstream of the melt chamber of the flow channel type, and which is provided with one or more means for urging the molten vitrifiable materials to be refined in a thin layer, especially to a depth of maximum 15 cm, preferably maximum 10 cm, which is a flow of the plug flow type.

13. The process according to claim 12, characterized in that one or more of the means prevent the formation of the return glass stream in the mass of molten vitrifiable materials flowing through the compartment or compartments.

14. The process according to one of claims 1 to 11, characterized in that the refining is carried out in the current melting chamber or in at least one compartment that is downstream of the latter, promoting the molten vitrifiable materials for that follow a gravity-descending path between at least two adjacent walls which in essence are mutually parallel and at least partly submerged in the mass of molten vitrifiable materials and are inclined with respect to the plane of the hearth of the melting chamber of the downstream compartment.

15. The process according to claim 14, characterized in that the walls are incorporated in at least one longitudinally divided tube of approximately rectangular section.

16. The process according to one of claims 1 to 11, characterized in that the refining is carried out in at least one compartment that is downstream of the melting chamber and that is capable of being rotated in order to ensure refining centrifugal, compartment which is provided with one or more means to propel the molten vitrifiable materials to be refined in a thin layer over a "thickness" Rl / RO of at least 0.8 or on an absolute thickness of, at most , 10 cm.

17. The process according to one of the preceding claims, characterized in that all or part of the vitrifiable materials are introduced into the melting chamber below the level of the mass of vitrifiable materials to be melted.

18. An apparatus for melting and refining vitrifiable materials, specially designed to implement the process according to one of the preceding claims, characterized in that it comprises: - at least one melting chamber equipped with burners which are fed with fossil fuels of the gas type natural and with oxidants of the air or oxygen type, the burners are placed in such a way that they inject the fuels / gases or the gases resulting from their combustion, below the level of the mass of vitrifiable materials introduced into the melting chamber, - means for refining the vitrifiable materials melted in the form of a "thin layer", in the current melting chamber or in at least one refining compartment downstream of the chamber.

19. The apparatus according to claim 18, characterized in that the refining compartment or compartments are static and have a flow channel comprising a channel and a roof, one or more means for driving the molten vitrifiable materials to be refined in the channel in a thin layer, with flow of the type of plug flow, especially on a depth of less than 15 cm, which is at least the selection of the ratio of average height to the average width of the channel, this proportion is lower of 1 and especially less than 0.5.

20. The apparatus according to claim 18 or 19, characterized in that the refining compartment or compartments are static and have a flow channel comprising a channel and a roof, one or more means for propelling the molten vitrifiable materials that are going to refining in the channel in a thin layer, especially over a depth of less than 15 cm, which is at least one or more means for adjusting / regulating the flow of molten vitrifiable materials at the entrance and / or exit of the compartment of refined.

21. The apparatus according to one of claims 18 to 20, characterized in that the flow channel is equipped with a heating means, especially of the type having oxygen burners, above the molten vitrifiable materials.

22. The apparatus according to one of claims 18 to 21, characterized in that the flow channel is provided with a means for homogenizing the vitrifiable materials.

23. The apparatus according to claim 18, characterized in that the melting chamber or a refining compartment downstream of the latter comprises at least one structural means for thin film refining, in the form of at least two adjacent walls which are approximately parallel to each other, designed to be submerged at least partially in the mass of molten vitrifiable materials and which are inclined with respect to the hearth of the chamber or compartment.

24. The apparatus according to claim 23, characterized in that these walls are incorporated in at least one longitudinally divided tubular element, which especially has an approximately rectangular section.

25. The apparatus according to claim 24, characterized in that this or these tubular elements are in the melting chamber and emerge in the discharge opening downstream of the chamber.

26. The apparatus according to claim 18, characterized in that the refining compartment includes at least one device capable of being rotated in order to ensure centrifugal refining, the internal walls of the device define approximately a cavity in the form of a hollow cylinder the which is vertical in its central part.

27. The apparatus according to claim 26, characterized in that the device capable of being rotated is provided in the cavity with divisions over at least part of its height, urging the molten vitrifiable materials to flow between the internal walls of the device and the divisions, the average distance between the walls and the divisions defines the "thickness" of the thin layer.

28. The apparatus according to claim 27, characterized in that the average distance between the walls and the divisions is defined by a ratio of their radii Rl / RO of at least 0.8.

29. The apparatus according to one of claims 26 to 28, characterized in that the walls of the device are coated with refractory pieces of the electro-casting type, these include a built-in thermal insulator so that it is prevented from being crushed by the centrifugal force.

30. The apparatus according to one of claims 26 to 29, characterized in that the device is provided with one or more means for trapping solid particles, this is located especially in its lower area and is in the form of notches / grooves made in its internal walls .

31. The apparatus according to one of claims 18 to 30, characterized in that the melting chamber is equipped with at least one means for introducing vitrifiable materials below the level of the mass of vitrifiable materials that are melted, especially at least two. of them, preferably in the form of one or more openings associated with a supply means of the screw feed type.

32. The apparatus according to one of claims 18 to 31, characterized in that the walls of the melting chamber, especially those designed to be in contact with the mass of vitrifiable materials to be melted, are based on refractory materials associated with a cooling system that uses a fluid of the water type.

33. The apparatus according to one of claims 18 to 32, characterized in that the walls of the melting chamber, especially those designed to be in contact with the mass of vitrifiable materials to be melted, are based on refractory materials coated with a metal coating of the molybdenum type.

34. The apparatus according to claim 33, characterized in that the coating is maintained at a distance from the walls, consisting of the refractory materials.

35. The apparatus according to claim 33 or 34, characterized in that the coating constitutes a surface for contact with the molten materials which is continuous or drilled with holes.

36. The apparatus according to one of claims 18 to 35, characterized in that at least part of the burners of the melting chamber are designed to also be capable of injecting, within the mass of vitrifiable materials, a fluid which does not participate in the combustion, as a substitute for the oxidant and / or the fuel, especially an inert gas of the N2 type and / or a water type coolant.

37. The application of the process according to one of claims 1 to 18 or of the apparatus according to one of claims 19 to 36 for the manufacture of flat glass, especially flat glass having a blue color. residual and a function of solar protection or fire resistance, for the electronic industry, for the manufacture of glasses for hollow products of the bottle or container type, or for the manufacture of glass wool or fiberglass for reinforcement.