FR2775683A1 - Vitrifiable materials melting and refining - Google Patents

Abstract

All or part of the thermal energy required for melting the materials is supplied by the combustion of fossil fuel(s) with at least one combustive gas. The fuel/gas or the gaseous products derived from combustion are injected beneath the mass of vitrifiable materials. Refining of melted materials incorporates at least one step of pressurization at sub-atmospheric pressure. An Independent claim is included for apparatus used to implement the method of melting and refining vitrifiable materials.

Description

MELTING AND REFINING PROCESS
VITRIFIABLE MATERIALS
The invention relates to a process for melting and refining vitrifiable materials with a view to feeding continuously molten glass to glass forming installations.

 More particularly targeted are flat glass forming installations such as float or laminating installations, but also hollow glass forming installations of the bottle, flask type, of glass fibers of the mineral wool type for thermal or sound insulation or else of glass fiber yarn called reinforcement.

 Many research studies have focused on these processes, schematically comprising a first melting step, followed by refining intended to thermally and chemically condition the molten glass, to remove the unfounded, the bubbles, any cause of defects appearing after forming.

In the field of fusion, efforts have been made, for example, to accelerate fusion, or to improve energy efficiency. Mention may thus be made of the process consisting in rapidly heating, in a homogeneous and controlled manner, the vitrifiable materials, by carrying out an intense mechanical stirring making it possible to intimately bring the still solid vitrifiable materials into contact with the already liquid phase. This process is detailed in particular in patents FR-2 423 452,
FR-2 281 902, FR-2 340 911, FR-2 551 746, and generally uses electrical heating means of the immersed electrode type.

 Another type of melting 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, consisting in using immersed burners as heating means, that is to say burners supplied with gas and air, generally arranged so as to be flush with the level of the hearth so that the flame develops within the mass of the vitrifiable materials in the course of liquefaction.

 In one case as in the other, if one succeeds in reducing very significantly the residence time of the vitrifiable materials in the melting chamber, in considerably increasing the production yield compared to conventional fusions, on the other hand, the molten glass is in the form of a foam which is difficult to refine: it is in particular difficult to guarantee the same quality for the final glass, in particular optical glass.

 Research has also been done in the field of maturing.

Thus, it is for example known from patent EP-775,671 and from patent US-4,919,697 to operate at least part of the refining under reduced pressure, which has made it possible for example to obtain glasses very poor in sulfates, with strong redox.

However, such refining causes intense foaming, which can be difficult to control and eliminate.

 The object of the invention is therefore to improve melting and refining processes, aiming in particular to use more compact installations and / or to be more flexible in operation, and / or with greater production yield, etc. ., without these industrial advantages being obtained at the expense of the quality of the glass produced.

 The invention firstly relates to 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 for the fusion of vitrifiable matter is provided by the combustion of fossil fuel (s) with at least one oxidizing gas, said fuels / gases or gaseous products resulting from combustion being injected below the level of the mass of vitrifiable matters, + other On the other hand, the refining of the vitrifiable materials after fusion comprises at least one step of bringing it to sub-atmospheric pressure.

 It turned out that there was in fact an extremely advantageous synergy on the industrial level between the use of a fusion called hereinafter by submerged burners for simplicity and that of refining at reduced pressure.

 However, this combination was far from self-evident, and one would have expected that all these advantages detailed below will only be obtained at the cost of a mediocre quality of glass, which n was not the case.

Indeed, if the principle of refining at reduced pressure was known in its generality, it remained difficult to use, and it was not sure to obtain the same tolerable residual rate of bubbles / unfounded as with conventional refining . However, in the invention, this very specific refinement is used by changing a size parameter, namely that instead of supplying the refining zone with conventional molten glass to be refined, it is here supplied in fact with a glass. obtained by fusion by submerged burners, that is to say glass with very specific characteristics in the sense that it is generally sparkling, with a relatively low density compared to that of a standard glass. There was nothing to suggest that a relatively frothy glass could be refined at reduced pressure at the start.

 Surprisingly, this turned out to be possible because it was discovered that this sparkling glass resulting from a fusion by submerged burners also had the characteristic of containing only extremely little sulphates, whether or not one had any. departure. There is in fact generally less than 600 and even less than 100 ppm of sulphate expressed by weight as SO 3 in the glass leaving the melting chamber, and this without having to control, reducing the level of sulphate usually contained in the raw materials used , unintentionally, or even by voluntarily adding sulfates to the batch materials. And it is this low level of sulphate which makes it possible to refine effectively under reduced pressure without problem. Otherwise, a high or simply standard sulphate content in the glass to be refined would have caused, during the refining at reduced pressure, a very strong expansion of the foam by desulphation, an expansion which would have been quite difficult to control. , to master.

This virtual absence of sulphate in the glass leaving the melting chamber can in particular be explained by the partial pressure of water generated by combustion by burners immersed in the vitrifiable materials.

 Another very advantageous characteristic of the glass leaving the melting chamber according to the invention should also be noted: if it is actually in the form of a kind of foam which remains to be refined, it is possible to control the size of the bubbles that it contains, and in particular in certain cases, eliminates almost all the smallest bubbles, that is to say with a diameter of approximately less than 200 μm, by effecting on this glass during its melting a kind of prior micro-refining true refining following fusion, micro-refining facilitating the coalescence of the bubbles, the disappearance of the smallest bubbles in favor of the larger ones and favored by the addition of coke-type refining agents in the batch materials or sulfates. In addition, this glass at the outlet of the melting chamber generally has a particularly low residual level of unfused, which again, like the size of the bubbles, facilitates the refining operation following the melting.

 The invention therefore makes it possible to have glasses very poor in sulphate even before the refining operation, therefore glasses at least as poor, or even depleted in sulphate after refining, and this without having to purify / select vitrifiable materials. so that they have little sulfate. On the contrary, one can even add sulfate at the start, which is quite surprising and advantageous.

 An advantageous effect obtained by the combination according to the invention relates to the energy cost of the process: fusion by submerged burners makes it possible not to have recourse to electric fusion 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, fusion by submerged burners creates a convective mixing within the vitrifiable materials during liquefaction, as detailed below. This very strong mixture between materials which are not yet liquefied and those which are already in fusion is extremely effective, and makes it possible to obtain a fusion, with vitrifiable materials of identical chemical composition, at a lower temperature and / or much faster than with traditional means of heating. And refining under reduced pressure also makes it possible to refine the glass at a lower temperature, and much faster. In fact, by lowering the pressure during the refining, an increase in the molar volume of the gases contained in the vitrifiable materials in fusion is caused, hence an increase in the volume of the bubbles which they contain and consequently an increase in their rates of ascent to the surface of the bath and their evacuation.

By refining at reduced pressure, we can allow ourselves to work at a lower temperature than in conventional refinings, precisely in the lower temperatures used with the technique of fusion by submerged burners,
The temperatures encountered in both the melting and the refining according to the invention are therefore entirely compatible and adapted to one another, and generally lower than in usual methods, which is very advantageous economically, simply in terms of energy cost, but also by the choice of refractory type materials used in the manufacture of installations: less hot, they corrode less quickly.

The residence times in the melting zone and in that of refining are also very significantly reduced and compatible, which is obviously very positive on the production yield, on the output of the installation as a whole. At the same time, the invention makes it possible to obtain very compact installations: in fact, melting by submerged burners, still thanks to the very strong stirring which it causes, makes it possible to considerably reduce the size of the melting chamber. And refining under reduced pressure has the same consequences on the size of the compartment or compartments where this operation is carried out: overall,
The installation can therefore be very compact, with clear gains in terms of construction cost, simplification of operation, reduction of wear of construction materials,
With regard to the melting operation, the oxidant chosen can be, according to the invention, based on air, air enriched in oxygen or even substantially based on oxygen. A high oxygen concentration in the oxidizer is in fact advantageous for various reasons: the volume of combustion fumes is thus reduced, which is favorable from an energy point of view and which avoids any risk of excessive fluidization of the batch materials which can cause projections on the superstructures, vaults of the melting chamber. In addition, the flames obtained are shorter, more emissive, which allows a faster transfer of their energy to the batch materials, and incidentally to reduce if desired the depth of the batch of batch materials during liquefaction. We are talking about flames here, but they are not necessarily flames in the usual sense of the term. We can speak more generally, as in the rest of the text, of combustions. In addition, any possible emission of polluting NOX gas is thus reduced to a minimum.

 As regards the choice of fuel, this may be of the gaseous or non-gaseous fossil fuel type such as natural gas, fuel oil or any other hydrocarbon fuel. It can also be hydrogen. The melting process by submerged burners according to the invention is then an advantageous means of using hydrogen, which is moreover difficult to use with overhead burners, not submerged, given the low emissivity of the flames obtained by combustion between H2 and 02.

 Combining the use of an oxygen oxidizer and that of a hydrogen fuel in a submerged burner fusion is a good way of ensuring an efficient thermal transfer of energy from the burners to the molten glass, which also leads to a process completely clean, that is to say without emission of nitrogen oxide NOx, or greenhouse gases of the COx type other than that which may come from the decarbonation of raw materials.

 Advantageously, the melting takes place according to the invention in at least one melting chamber which is fitted with burners arranged so that their combustion or combustion gases develop in the mass of the batch materials in the course of melting. They can thus be made to cross its side walls, the floor and / or hang them from above, by hanging them on the vault or on any suitable superstructure. These burners can be such that their gas supply conduits are flush with the wall they pass through. It may be preferable for these conduits to enter at least partially into the mass of the batch materials, so as to prevent the flames from being too close to the walls and causing premature wear of the refractory materials. It is also possible to choose to inject only the combustion gases, the combustions being carried out outside the melting chamber proper.

 As mentioned above, it turned out that this heating mode caused by convection an intense mixing of the vitrifiable materials of the convection loops thus form on either side of the combustions or flames or streams of combustion gases, mixing in permanently melted and not yet melted very efficiently. We thus find the very favorable characteristics of a stirred fusion, without having recourse to unreliable mechanical stirring means and / or susceptible to rapid wear.

 Preferably, the height of the mass of vitrifiable materials in the melting chamber is adjusted as well as that on which the combustions or gases resulting from combustion develop so that these combustions / gases remain in the mass of said vitrifiable materials: the aim is to allow the convective circulation loops to settle in the material being liquefied.

 In general, this type of fusion makes it possible to considerably reduce the emission of all types of dust at the level of the melting chamber, and of NOX type gases because the heat exchanges take place very quickly, avoiding the temperature peaks liable to favor the formation of these gases.

 It also considerably reduces the emission of COx type gases.

 Optionally, provision can be made to precede the melting by a step of preheating the batch materials, at a temperature however markedly lower than that necessary for liquefying them, for example at most 900 "C. To carry out this preheating, it is advantageous to recover the thermal energy of the fumes. By exhausting them thermally, we can globally reduce the specific energy consumption of the installation.

 Vitrifiable materials can include raw materials, but also cullet, or even waste intended to be vitrified. They can also include combustible (organic) elements: it is thus possible to recycle, for example, sized mineral fibers, with binder, laminated glazing with sheets of polymer of the polyvinyl butyral type such as windshields, or any type of composite material combining glass and plastic materials such as certain bottles.

 The process according to the invention can operate with a high level of cullet.

 As mentioned above, the refining according to the invention is therefore carried out on melting vitrifiable materials of the glass type in the foamy state. Typically, this foam has a density of about 1 to 2 for example (to be compared to a density of the order of 2.4 for non-sparkling glass), preferably a sulfate content of at most 600 or even d '' at most 100 ppm expressed by weight of SO 3 and a majority of bubbles with a diameter of at least 200 µm.

 To improve the performance of the refining, additives to the vitrifiable materials are preferably added various refining aid additives, the aim was in particular to make the bubbles of diameter less than 200 μm disappear from the glass at the melting stage. , as mentioned above. They can be reducing additives, such as coke (which also makes it possible to adjust the redox of the glass). In this case, it is advantageous to select coke powder with an average particle size of less than 200 μm. They can also be sulfates. Refining under reduced pressure causes the bubbles to grow, the aim being that this growth takes place quickly, and that the bubbles can be removed and burst on the surface of the glass bath easily. Other refining aid additives will be rather effective during the actual refining stage, after that of the melting. They allow in particular to destabilize the foam: it is for example fluorine or fluorinated compound, or nitrate of the NaNO3 type: fluorine seems to lower the viscosity of the glass, it would thus facilitate drainage of the films which form between bubbles, drainage favoring the collapse of the foam. It also lowers the surface tension of the glass.

 Another factor influencing the way bubbles grow during refining under reduced pressure is the nature of the gases above the molten material. You can of course simply choose a partial air pressure.

It is also possible to choose to enrich the atmosphere with inert gas of nitrogen type, or even to choose a partial pressure only in inert gas of nitrogen type. It has indeed been observed that choosing a residual pressure of inert gas of the nitrogen type is favorable to the bursting of the bubbles at the surface during the refining. In fact, it is the too high concentration of oxidizing gas type 2 which seems unfavorably tend to slow down this bursting.

Advantageously, the sub-atmospheric pressure in which at least part of the refining takes place is less than or equal to 0.5 atmosphere (0.5.105
Pa), in particular of the order of 0.3 to 0.01 atmosphere (approximately 3.104 to 0.1.103 Pa).

 Advantageously, the method according to the invention allows the melting and / or refining to be carried out at temperatures not exceeding 1400 "C., in particular at most 1380 or 13500C.

 The refining according to the invention, according to a first variant, can be done in at least one static compartment (stationary in operation) downstream of the melting chamber and of which at least one zone is put under reduced pressure.

 According to a second variant, the refining is always carried out downstream of the melting chamber, but in a compartment capable of being rotated in order to ensure refining by centrifugation, with at least one zone of said compartment, in particular the most upstream, reduced pressure.

 A third variant consists in combining the two preceding ones, in particular by using for refining a first static compartment with a zone under reduced pressure, then a second in rotation also comprising a zone under reduced pressure, preferably more reduced than in the static compartment .

 According to a preferred embodiment, the method according to the invention provides for treating the flow of vitrifiable materials in fusion, between the melting phase and the refining phase or at the start of the refining phase, by at least one means. jet divider. This means, for example an element pierced with orifices by which the flow of molten glass is forced to pass, makes it possible to divide this flow into a large number of small diameter threads. The size of the orifices is advantageously chosen so as to be close to the size of the bubbles which it is sought to eliminate.

Thus, if the jet divider means is placed just downstream of the sub-atmospheric pressure zone of the refining compartment, the action of the reduced pressure will be exerted very quickly on the threads generated by the divider means. jet, and allow rapid refining, even with high glass flow rates.

The glass supply to be refined from the refining compartment can thus become in a way analogous to that obtained by a die which would open into a chamber at reduced pressure.

 (In the context of the invention, the terms upstream and downstream refer to the direction of flow of the glass in the installation from the charging of the vitrifiable materials into the melting chamber until the extraction of the refined glass ).

 The melting / refining process according to the invention makes it possible to manufacture glasses of very varied compositions and properties. Due to its low inertia, it also makes it possible to pass from one composition to another with very short transition times.

 It thus makes it possible to manufacture relatively reduced glasses, in particular having a redox greater than or equal to 0.3. (Redox is defined as the ratio of the percentage content by weight of ferrous iron FeO to the total iron content by weight of the composition expressed as Fe2O3).

 It also makes it possible to manufacture glasses with a high SiO2 content, for example at least 72 or even at least 75% by weight, glasses generally difficult to melt, but advantageous, in particular in terms of cost of raw materials, because 'They are of low density, and they have a very good compatibility with plastic materials. It also makes it possible to manufacture fairly specific glasses, with a high level of alkaline earth oxide, for example containing at least 18% by weight of CaO, yet fairly corrosive with traditional melting processes at higher temperature than in l he invention, as well as glasses with a low level of sodium oxide, of at most 11% by weight for example, or with a very low level of sulfates, of at most 100 ppm for example. Glasses containing iron, of high redox but with a low sulphate content also make it possible to obtain glasses with residual color in blueprints, particularly aesthetic and sought after in the field of flat glass for the automobile and for building for example. One can thus obtain very selective anti-sun glasses, on which one can deposit anti-solar layers to reinforce their thermal performances, of the TiN type for example, layers described in particular in patents EP-638 527 and EP-511 901 .

 The invention also relates to a melting and refining device, in particular suitable for implementing the method described above, and which comprises: * at least one melting chamber equipped with burners supplied with fossil fuel (s) of the gas type (natural) and of oxidizer (s) of the air or oxygen type, said burners being arranged so as to inject these gases or the gases resulting from combustion below the level of the mass of vitrifiable materials introduced into said melting chamber , * at least one refining compartment downstream of the melting chamber and comprising at least one zone capable of being put under subatmospheric pressure.

 Advantageously, as mentioned above, it is possible to provide the device according to the invention with at least one jet dividing means between the melting chamber and the refining compartment, in particular just at the entrance to the refining compartment. or in its most upstream part. It may be an element pierced with orifices of appropriate size.

 Furthermore, it should be noted that using such a jet dividing means can also be envisaged independently of the suitable melting mode: such a dividing means makes it possible to refine more quickly, with high glass flow rates, whatever the way glass has been obtained, for example by conventional means of the overhead burner type (not submerged) and / or by electrical melting by immersed electrodes.

 Similarly, it may be advantageous to use it even if the refining is carried out at atmospheric pressure.

 However, it is particularly advantageous to use it in a context of melting by submerged burners which tends to generate a foam with very high bubble rate, and / or in a context of refining under reduced pressure, because it considerably increases l which is already particularly high.

 According to a first variant mentioned above, the refining compartment is static and in elevation (that is to say a height significantly greater than its dimensions on the ground). This compartment comprises a substantially vertical internal partition which delimits, in combination with the internal walls of the compartment, at least two channels. It is successively a first channel imposing an ascending path on the vitrifiable materials then a second channel imposing a descending path on the said vitrifiable materials, the first channel preferably being that which is put under subatmospheric pressure. This creates a sort of siphon for the glass to be refined. This compartment is advantageously equipped with means for adjusting / regulating the pressure drop of the vitrifiable materials in fusion at the entrance to the refining compartment. Likewise, provision is made to adjust the height of the refining compartment as a function of various criteria, in particular as a function of the level of depression chosen in the zone under reduced pressure.

According to a second variant, the refining compartment comprises at least one device capable of being rotated to ensure refining by centrifugation, the internal walls of said device substantially delimiting the shape of a vertical hollow cylinder at least in its part median. Advantageously,
The device comprises a so-called upper zone at sub-atmospheric pressure and a so-called lower zone left at ambient pressure, and separated from one another by one or more mechanical means of the metal plate type pierced with orifice (s).

 According to a preferred design, the apparatus is supplied at the top with molten vitrifiable materials for a static supply means of the flow channel type. These supply means may include at least one compartment put under reduced pressure to allow the supply of the device and / or operate a first refining.

 It is necessary to provide sealing means ensuring the junction between the end of this channel / these supply means and the device, means of the dynamic joint or rotary joint type, as detailed later. The device is advantageously provided with means for trapping solid particles with a density greater than that of glass, means in particular located in its lower zone and in the form of notches / grooves formed in its internal walls. Preferably, the speed of rotation of the device is selected between 100 and 1500 revolutions per minute.

 The apparatus can also be provided with fixed mechanical means or according to its rotation, and capable of shearing the foam and of entraining it from the top to the bottom, towards the lower zone of the apparatus from which the refined glass is withdrawn.

 These means are in particular in the form of drilled deflectors, fins, arranged in the upper zone of said device.

 This type of centrifugal refining with passage through a reduced pressure zone is particularly effective. In fact, the reduced pressure will make it possible to ensure the strongest possible growth of the bubbles before the actual refining by centrifugation: the bubbles are eliminated all the more quickly in the apparatus as their diameter is important. The reduced pressure will also make it possible to further decrease the residual sulfate content of the glass produced.

Note that a desulfated glass (this remark also applies to the first variant where the refining is done in static), gives less problems of volatile compounds in the float bath, less risk of formation of tin sulfide and therefore ultimately less risk of tin defect on the glass sheet. This also guarantees the absence of sulphides in the case of reduced glasses, in particular iron sulphides giving undesired yellow / amber residual colors or inclusions of nickel sulphide, which can cause the glass to break during heat treatments of the type quenching.

 Centrifugal refining comprising a reduced pressure phase is particularly indicated in the case of refining relatively sparkling glass.

The invention will be detailed below using two non-limiting embodiments, illustrated by the following figures
Ci figure 1: a schematic installation of fusion / refining using a static refining device,
LI Figure 2: a schematic melting / refining installation using a centrifugal refining device.

O Figure 3: an enlarged view of a device for refining the installation of the type shown in FIG. 2,
O Figure 4: an enlarged schematic view of the jet divider used in the device of Figure 2.

 These figures are not necessarily to scale and for clarity are extremely simplified.

 The devices described below are suitable for melting and refining glasses of very varied compositions, here glasses intended to supply a float installation for producing flat glass. But this application is not limiting.

In addition to, of course, all the standard glasses of the soda-lime-silica type, various types of special glasses are particularly advantageous to manufacture with the devices according to the invention, in particular those considered hitherto difficult to melt: * glasses with low Na2O level and relatively high level of alkaline earth oxide, in particular CaO, advantageous economically in terms of cost of raw materials, but fairly corrosive to conventional melting temperatures and relatively hard to melt by conventional methods. It can be glass compositions for example described in the patent
FR97 / 08261 of July 1, 1997, such as (weight%)
SiO2 72-74.3%
Al203 0-1.6%
Na2O 11.1-13.3%
K20 0-1.5%
7.5-10% CaO
MgO 3.5-4.5% Fe2O3 0.1-1% or of compositions of the type (expressed in weight percentages):
SiO2 66-72, especially 68-70%
Al203 0- 2%
Fe2O3 0-1%
CaO 15-22%
MgO 0-6, especially 3-6%
Na2O 4-9, especially 5-6%
K20 0-2, especially 0-1%
SO3 traces
An example illustrating this family of compositions is as follows:
SiO2 69%
Al203 1%
Fe2O3 0.1%
CaO 18.9%
MgO 5%
Na2O 5.6%
K20 0.3%
SO3 traces
This glass has a lower annealing temperature also called strain point of 590 C (temperature at which the glass has a viscosity of 10145 poises). It also has a liquidus temperature of 1225 C, a temperature T (log2) of 1431 C and a temperature T (log3.5) of 1140 C [T log (2) and T log (3.5) correspond to the temperatures that the glass has respectively when it reaches in poise a viscosity of log2 or log3.5].

# glasses with a high silica content, which are also interesting from an economic point of view, and with a relatively low density, the range of compositions, always expressed in percentages by weight, is as follows:
SiO2 72 to 80%
CaO + MgO + BaO 0.3 to 14% Na2O 11 to 17% alkaline oxides 11 to 18.5%
Al203 0.2 to 2%
B2O3 0 to 2% Fe2O3 0 to 3% 503 traces possibly coke 0 - 600 ppm and possibly oxides of coloring oxide of Ni, Cr, Co, ..) (These glasses have the characteristic to be particularly viscous).

An example illustrating this family of compositions is as follows
SiO2 76.4%
Fe203 0.1%
Al203 0.1%
CaO 7.6%
MgO 5% Na2O 10%
K20 0.3%
It has a density of approximately 2.46 (to be compared to the densities of 2.52 of the standard silica-soda-lime glass of the Planilux type sold by Saint-Gobain
Glazing).

 + We have also seen above that it was possible to obtain with the process according to the invention reduced glasses, whose strong redox, iron content, and very low sulphate content make it possible to obtain glasses of residual color. blue.

 + With the process according to the invention, it is also possible to manufacture glasses with a zero or almost zero rate of alkaline oxides of the Na2O type, in particular for applications for fire-resistant glazing or for substrates used in the electronic industry. . For such compositions, reference may be made in particular to patents EP-526,272 and EP-576,362.

 Other glasses, in particular with a low level of MgO of the type of those described in patents EP-688 741 and WO96 / 00194 can also be produced by the process of the invention.

 A first embodiment is therefore shown in FIG. 1: a channel 1 makes it possible both to introduce the vitrifiable materials into the melting chamber 2 through the vault 3 and to evacuate the combustion fumes. These fumes will preheat the batch materials, thereby recovering their thermal energy. The bottom 4 of the chamber is equipped with rows of burners 5 which pass through it and enter the melting chamber over a reduced height. The burners 5 are preferably provided with cooling means, not shown, of the water box type. The burners 5 in operation develop combustions in zones 6, creating near them convection currents within the vitrifiable material during liquefaction. This convective stirring creates a foam which will transfer the thermal energy throughout the bath 7. The fusion is preferably carried out around 13500C, for example for a standard glass of the family of soda-lime-silica glasses. The molten sparkling glass is then withdrawn at the bottom by a channel 8 provided with a pressure drop adjustment means of the punch type not shown. This controls the pressure drop of the sparkling glass entering the static refining compartment 9. This compartment has side walls 10, a bottom wall 11 at the same level as the bottom of the melting chamber, and an upper wall 12 delimiting a substantially parallelepiped interior volume. There is also a partition 13 fixed to the bottom wall 11 but leaving a passage in the upper part. This assembly also defines a channel 14 imposing an upward path on the glass, then a channel 15 imposing a downward path on the glass. In the highest part 16, a level of glass H is formed.

 The refined glass is then withdrawn through a channel 17 coming to supply a compartment 18 bringing the glass to the forming installation of the float type, not shown.

 In the refining compartment, the zone of the channel 14 is placed under reduced pressure, for example 0.3 atmosphere. The sparkling glass coming from channel 8 will then rise in this channel, the possible residual unfunds being gradually digested and the bubbles increasing in size as they rise in the channel. The foam expansion rate remains very moderate, however, thanks to the fact that the foam from the melting chamber 3 has a very low residual sulfate rate. In zone 16, the bubbles burst on the surface H, the foam disappears quickly, and the generally refined glass then descends along the channel 15. If necessary, one can provide in this zone 16 auxiliary heating means, of the burner type. conventional or electrical resistances attached to the wall 12, and possibly mechanical means, not shown, intended to facilitate the bursting of bubbles of the dam type.

 To give an order of magnitude, it can be provided that the height h of the refining compartment is of the order of a few meters, for example 3 meters for the pressure reduced by 0.3 atm. chosen.

 Figures 2 and 3 show the second embodiment. For simplicity, the melting chamber 2 will not be described again, which is of the same design as that shown in FIG. 1.

 The main difference is the way the glass is drawn from the melting chamber. In the case of FIG. 2, the glass is withdrawn a little higher, with a supply duct 20 decomposing into a first horizontal part 20 (a), a second vertical part 20 (b) and a third horizontal part 20 (c) opening into the apparatus of the centrifuge 21. To allow the glass to rise in the channel and thus supply the centrifuge, it is necessary to put at least the zone 20 (b) of the channel under moderate reduced pressure, by example under 0.5 atmosphere. Another variant consists in that the molten glass is withdrawn from the melting chamber in the upper part, for example using an immersed groove as is well known in the glassmaking field.

 FIG. 3 focuses on the horizontal zone 20 (c) of the supply channel for the molten sparkling glass 20 withdrawn from the melting chamber 2, which supplies the body of the centrifuge 21 with glass. The latter has an upper part 22 between the part 23 and the metal plate 24, and a lower part 30 located under the metal plate 24. The part 23 is hollow, it is a cylinder provided with lights making it possible to regulate the flow rate, the pressure drop of the glass entering the centrifuge 21. The glass also enters the upper part 22 where a partial vacuum of for example 0.1 bar or atmosphere is established. The question arises of the junction 25 between the static part of the channel 20 and the part set in rotation of the body 21.

 A first solution consists in adopting a dynamic joint. The sparkling glass leaving the hollow part 23 goes under the centrifugal force to tend to go up in the zone 26 and to come out spontaneously by the space left free at the junction 25: it is thus the glass itself, which, continuously ejected, seals. Provision may be made to limit, regulate the flow rate of the ejected glass by modulating the space between the mobile assembly 21 and the fixed assembly 20.

 Another solution consists in placing a so-called rotating joint of suitable composition in junction 25. It can in particular be a rotary ring with liquid ring, using a liquid with very low vapor pressure of the silicone oil type and the operating principle of which is the same as that of the liquid ring vacuum pumps: The ring liquid is centrifuged by rotation and pressurized opposing the vacuum existing within the centrifuge.

 The glass then flows through the orifices of the plate 24 into the zone 23 provided with a vent pipe 27. This plate, at least for the parts completely immersed in the glass, can advantageously be made of molybdenum . The external lining of the internal walls of the body of the centrifuge can consist of electrofused refractory pieces 32 comprising a thermal insulator 31 incorporated so that the latter is not crushed by centrifugal force. Also provided is a notch, groove 28 going around the internal wall of the part 30 (or discontinuous), which makes it possible to trap all the solid particles of density greater than that of glass, of the refractory inclusions type. Indeed, the flow from bottom to top of the glass in the centrifuge is done as follows: the plate 24 decomposes the centrifuge into two parts, authorizes centrifugation of the glass in a thin layer reducing the height of the device relative to that which would be necessary without it and without the application of reduced pressure. One of the conditions for the glass to flow correctly from bottom to top is that the pressure of the glass corresponding to the distance between the vertices of the two parabolas is greater than the sum of the pressure drops and the difference between the reduced pressure of the part 22 and the ambient pressure of part 23, which is achievable. The glass flowing through the plate 24 will therefore be pressed in a thin layer against the internal walls of the part 30, the solid particles more dense than the glass are then projected against the walls and trapped in the grooves 28 from where they can no longer stand out. The bubbles on the other hand grow and come by centripetal action to burst towards the inside of the body of the centrifuge. In the end, the glass refined by a channel, the head of which has an approximate shape of funnel 29, is withdrawn from the lowest part of part 30. In standard operating conditions, it is not necessary to provide means for reheating the glass, the speed of rotation can be of the order of 700 revolutions per minute and the height h of the centrifuge of for example 1 to 3 meters.

 FIG. 4 very simply shows an advantageous variant of the refiner according to FIGS. 2 and 3, concentrated on the junction zone 40 between the supply channel 20c at atmospheric pressure and the body of the centrifuge 21 under reduced pressure: There is a piston 41 capable of adjusting the pressure drop and the flow rate of entry of the glass to be refined into the centrifuge 21. A grid 43 of pierced molybdenum has been interposed in the flow orifice 42 of the channel 20c towards the centrifuge. regularly of preferably cylindrical orifices, which plays the role of a supply die for the centrifuge and which divides the glass jet at the inlet into a multiplicity of small glass nets, represented very schematically under the reference 44 and of diameter about 1 to a few millimeters for example. This grid 43 thus acts as a jet divider, the bubbles contained in each net 44 are eliminated much faster than if they were contained in a glass vein of much wider section. The combination of these small nets 44 with the use of reduced pressure makes it possible to burst the bubbles in the glass extremely quickly. The threads 44 from which the bubbles have been eliminated are found at the bottom of the centrifuge 21 in the form of droplets which coalesce on its internal walls due to the centrifugal force.

 The use of such a jet divider is also of interest in the case where the refining is carried out in a static refiner like that shown in FIG. 1.

 In either case (static or centrifugal refiner), we see that we can dramatically compact the size of the melting / refining devices currently available. It should also be noted that it is advantageous for the partial vacuum, both in the case of the static refiner and of the centrifugal refiner, to be a nitrogen vacuum, facilitating the bursting of the bubbles and less damaging for the parts. like the part 24 of the centrifugal refiner. It is also advantageous to add to the vitrifiable materials ripening aid agents whose role has been described above, in particular coke with small particle size, sulphate, nitrate or fluorine.

 It is important to emphasize that, even if the combination of melting by submerged burners with refining using partial pressurization is extremely advantageous, the invention also relates to these two aspects taken separately. It is thus with advantage to use the melting mode by submerged burners with a standard refining, and conversely to use a refining with reduced pressurization following a melting by conventional heating means, while remaining within the scope of the invention, even if one no longer obtains the synergy outlined above.

 Note also that one can advantageously use the melting mode by submerged burners without having to resort to refining at all in the usual sense of the term. This can be the case in the field of fiber drawing, where it is possible to envisage feeding the fiber drawing machines by internal centrifugation directly in sparkling glass obtained by fusion by submerged burners, the centrifugation imposed by this fiber drawing technique realizing de facto l refining of glass. One can also consider directly treating the sparkling glass resulting from the merger, with a view to manufacturing foam glass used as an insulator in the building sector for example.

Claims (11)

 1. A method of melting and refining vitrifiable materials, characterized in that all or part of the thermal energy necessary for the fusion of said vitrifiable materials is provided by the combustion of fuel (s) with at least one oxidizing gas, the (s) said (s) fuel / gas or gaseous products of combustion being injected below the level of the mass of vitrifiable materials (7) and in that the refining of vitrifiable materials after melting comprises at least one step of put under atmospheric pressure.  2. Method according to claim 1, characterized in that the oxidant is based on air, air enriched in oxygen or oxygen.  3. Method according to one of the preceding claims, characterized in that the fuel is hydrocarbon, of the fuel oil or natural gas type, and / or is based on hydrogen.  4. Method according to one of the preceding claims, characterized in that the vitrifiable materials comprise raw materials and / or cullet and / or vitrifiable waste and / or combustible elements.  5. Method according to one of the preceding claims, characterized in that the flow of molten vitrifiable materials is treated between the melting phase and the refining phase by at least one jet divider means (43).  6. Device for melting and refining vitrifiable materials, in particular intended for implementing the method according to one of the preceding claims, characterized in that it comprises: * at least one melting chamber (2) equipped with burners (5) supplied with fuel (s) and with oxidant (s) of the air or oxygen type, said burners being arranged so as to inject said fuels / gases or gases resulting from their combustion below the level of the mass (7) of the materials vitrifiable materials introduced into said melting chamber, * at least one refining compartment (9, 21) downstream of the melting chamber (2) and comprising at least one zone at sub-atmospheric pressure.  7. Device according to claim 6, characterized in that it is provided with at least one jet divider means (43) between the melting chamber and the refining compartment or in the refining compartment preferably in its most upstream part.  8. Device according to claim 7, characterized in that the jet dividing means is an element pierced with orifices through which the flow of vitrifiable materials in fusion is forced to pass, in particular of the plate pierced with orifices type (43), preferably with a size of orifices close to that of the bubbles to be eliminated from the molten mass.  9. Device according to one of claims 6 to 8, characterized in that the refining compartment (9) is static, in elevation and in that it comprises an internal partition (13) substantially vertical delimiting with the walls of said compartment with at least two channels, one of which successively has a first channel (14) imposing an ascending path on the molten vitrifiable materials and a second channel (15) imposing a descending path on said molten vitrifiable materials.  10. Device according to one of claims 6 to 8, characterized in that the refining compartment comprises at least one device (21) capable of being rotated to ensure ripening by centrifugation, the internal walls of said device substantially delimiting the shape of a hollow cylinder, vertical in its middle part.  11. Device according to claim 10, characterized in that said apparatus comprises an upper zone (22) at sub-atmospheric pressure and a lower zone (30) at ambient pressure, separated from one another by one or more means mechanical type of metal plate pierced with orifice (s) (24).