Glass furnace equipped with plasma torches in the fining zone

Abstract

The present invention concerns a furnace for melting vitrifiable materials, comprising (i) a melting tank with heating means configured to melt vitrifiable materials; (ii) a fining tank with heating means configured to refine the melt; (iii) a neck separating the melting tank and the fining tank; (iv) inlet means located at the melting tank to charge the vitrifiable materials; (v) outlet means at the fining tank to flow the refined melt to a working zone; wherein the heating means in the fining tank comprises a plurality of thermal plasma torches configured to emit from a working fluid a plasma flame above the melt.

Description

GLASS FURNACE EQUIPPED WITH PLASMA TORCHES IN THE FINING ZONEFIELD OF THE INVENTION

[0001] The present invention relates to a glass furnace aimed at continuously supplying molten glass to glass forming installations such as float or rolling installations, to produce glass products. In particular, the present invention relates to a glass furnace that provides a lot of advantages, especially in terms of CO2 emissions.

[0002] The invention is more particularly related, but not limited, to glass furnaces for manufacturing flat glass involving large production capacities, i.e. up to 1000 tons / day or more, and power demand up to 60 MW.BACKGROUND OF THE INVENTION

[0003] In the state of the art, vitrifiable materials or glass raw materials are melted in a glass furnace that commonly comprises :- a tank containing a melt when the furnace is in use;- inlet means located upstream of the furnace, for charging it with the glass raw materials / batch to be heated / melted;- heating means located in the tank for (i) melting the glass raw materials and (ii) downstream, for fining the melt, and finally,- an outlet for the melt to reach a processing zone or a working end.

[0004] In such glass furnaces, the melting and fining steps are commonly operated by heating through combustion (thanks to burners) or through electricity (thanks to electrodes).

[0005] In a combustion-type heating, a fuel source reacts with oxidizer (air or oxygen) in order to generate a flame above the surface of the molten glass. Fuel may be, for example, fossil fuel, natural gas, biogas or hydrogen. Flames coming from combustion / burners are provided above the bath of molten glass / raw materials and heat it from the top, while generally electrodes are generally immersed in said bath.

[0006] In an electrical heating, electrodes are commonly immersed (partially / totally) and often located at the bottom of the tank, and allow an electric current / power to pass through and heat the bath from its bulk.

[0007] It is also known to combine, in a "hybrid furnace", combustion heating means (burners) and electrical heating means (electrodes) in the furnace tank. In such known "electro-boosted combustion furnaces", the electrical input fraction is commonly limited to 10-15% of the total energy input. "Electrical input fraction" is commonly the part of electricity in the total energy input of the furnace for both the melting and fining, namely electricity / (fuel+electricity), the total energy input being that of the furnace in standard / normal production mode, i.e. at its standard pull range (excluding periods of startup, maintenance, hot repair, culleting, ...).

[0008] Finally, it is also known from WO2021225925A1 to melt glass raw materials in a tank equipped with plasma torches and electrodes, rendering the melting step operated fully with electricity. However, this document does not comment on the reason for having those two heating means : plasma torches and electrodes.

[0009] The use of electricity at the melting step, as presented in WO2021225925A1, is advantageous as it allows to reduce globally CO2 emissions, widely recognized as contributors to climate change and increasingly subject to regulation / taxation, as well as to reduce other emissions considered environmentally harmful such as NOx gas. Moreover, using electricity allows furthermore to avoid the variations of cost and / or composition of fossil fuels overtime and territorially, thereby avoiding unpredictability and variability of the glass manufacturing process using such fuels.

[0010] This document also proposes to recycle the working fluid fed in the plasma torches (e.g. at least 90% and up to 99% is recycled and re-injected in the torches). This is known in the art to be required for the plasma heating in a manufacturing process in general to be financially viable.

[0011] However, the melting step of glass raw materials occurring in a tank generates in a general manner large volumes of fumes / exhaust gas (for example, occurring from the decarbonization of carbonate raw materials) as well as a lot of dust and corrosive gas. Those exhaust gas are clearly detrimental for a recycling process of the working fluid implemented in a melting tank using plasma torches. Indeed, they renders the recycling process more complicated (i) due to dilution of the working fluid with the fumes and due the various nature of contaminants (solid, gas,...) and (ii) due to higher gas volumes to treat, thereby rendering plasma heating not interesting / viable from an economical point of view.

[0012] Though, in the context of global warming that puts pressure on glass manufacturers as well as the energy prices and CO2 taxes that could become soon a severe threat on competitiveness in the glass business, there is still a need to provide a glass furnace which shows a decreased CO2 emissions by using more electricity globally (thus with an increased electrical input fraction), while being financially viable as well.

[0013] It is to be noted that WO2021225925A1 discloses that the glass melt may undergo a fining downstream of the melting, but without giving any operational indication regarding heating means at said fining step.OBJECTIVE OF THE INVENTION

[0014] It is an objective of the present invention to overcome the disadvantages described above with respect to the state of the art and resolving the technical problem.

[0015] In particular, it is a further objective of the present invention to provide a glass furnace which shows a decreased CO2 emissions by using more electricity globally (thus with an increased global electrical input fraction).

[0016] It is a further objective of the present invention to provide a glass furnace which shows a decreased CO2 emissions by using more electricity globally, while being financially viable.DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a furnace for melting vitrifiable materials, comprising : a melting tank equipped with heating means configured to melt vitrifiable materials and thereby to provide a melt; a fining tank equipped with heating means configured to refine the melt and thereby to provide a refined melt; at least one neck separating the melting tank and the fining tank; inlet means located at the melting tank, configured to feed the vitrifiable materials in said melting tank; and outlet means located downstream of the fining tank configured to flow the refined melt from the fining tank to a working zone; wherein the fining tank comprises, as heating means, a plurality of thermal plasma torches, each torch being configured to emit from a working fluid a plasma flame above the melt.

[0018] Hence, the invention is based on a novel and inventive approach. In particular, the inventors have found that, by using thermal plasma heating means in a fining tank / step while separating the melting tank / step and the fining tank / step with a neck, it is possible to reach the above-cited objectives, that-is-to-say to obtain a glass melting furnace showing a higher global electrical input fraction, compared to classical combustion glass furnaces, while being economically viable, especially while allowing an effective and easier recycling process of the working fluid fed in the plasma torches.

[0019] Moreover, it has been discovered that using thermal plasma torches in a fining step not only allows to «electrify» the fining but also to reach a fining as effective as with commonly used combustion burners. It is known that the temperature required to refine a glass melt must be >1400°C min, preferably higher than 1450°C, while the bottom temperature in the tank must be kept at a lower level (i.e. < 1400°C, preferably, <1350°C) to limit refractory corrosion. Moreover, the production of high-quality flat glass requires an area where flow of glass melt is laminar and stratified and with free surface in order to let bubbles escape from the glass melt. These two conditions are effectively and easily fulfilled by heating this free surface of glass melt from the top with plasma flames which allow to reach high temperature while generating stratified and laminar glass flow.

[0020] By implementing all the features of the invention, the furnace of the invention shows a lowered CO2 fingerprint when operating and it is economically viable especially as it allows an effective and easier recycling process of the working fluid fed in the plasma torches due to the neck separating the melting tank and the fining tank.

[0021] The invention also relates to a process for melting vitrifiable materials, comprising the steps of :(a) charging vitrifiable materials in a melting tank through inlet means;(b) melting the vitrifiable materials in the melting tank by heating with heating means, thereby providing a melt;(c) flowing the melt to the fining tank through a neck separating the melting tank and the fining tank;(d) fining the melt in the fining tank, thereby providing a refined melt;(e) flowing the refined melt to a working zone through outlet means;wherein the step (d) of fining the melt is carried out by heating the melt with a plurality of thermal plasma torches, each plasma torch being fed with a working fluid and emitting a plasma flame above the melt.

[0022] By implementing all the features of the invention, the process of the invention shows a lowered CO2 fingerprint and it is economically viable especially as it allows an effective and easier recycling process of the working fluid fed in the plasma torches due to the neck separating the melting tank and the fining tank.

[0023] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments and figures, given by way of simple illustrative and non-restrictive examples.

[0024] FIG. 1 is a schematic plan view (horizontal cross-section) of an embodiment of a furnace according to the invention.

[0025] FIG. 2 is a schematic perspective view of the embodiment of FIG. 1.

[0026] FIG. 3 is a schematic plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.

[0027] FIG. 4 is a schematic plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.

[0028] FIG. 5 is a flowchart of an embodiment of a process according to the invention.

[0029] In present specification and claims, it is well understood by the person skilled in the art that, as used herein the terms "a", "an" or "the" means at least "one" and should not be limited to "only one" unless explicitly indicated to the contrary. Also, when a range is indicated, the extremities are included. In addition, all the integral and subdomain values in the numerical range are expressly included as if explicitly written. Finally, the terms "upstream" and "downstream" refer to the flow direction of the glass and are to be understood with their common sense, namely as meaning along the averaged moving direction of the vitrifiable materials / the glass melt (defined herein as "glass stream"), from the inlet mean(s) to the outlet mean(s), when operating the furnace according to the invention, that is to say along the direction going from the left to the right in FIG. 1 for example. By "width" in the invention, it is meant, unless otherwise specified, the dimension (in average) perpendicular to the glass stream.

[0030] The furnace (1) of the invention comprises a melting tank (2) equipped with heating means configured to melt vitrifiable materials and thereby to provide a melt.

[0031] According to the invention and as commonly adopted in the glass art, by "vitrifiable materials", it is meant the mixture of starting materials fed in the furnace of the invention. Vitrifiable materials according to the invention may comprise glass raw materials and / or cullet. In one embodiment, the vitrifiable materials comprise raw materials and cullet, the amount of cullet being at least 10% in weight of the total amount of vitrifiable materials, preferably at least 20% in weight of the total amount of vitrifiable materials. More preferably, the amount of cullet is at least 30% in weight of the total amount of vitrifiable materials, or even, very preferred, at least 40% in weight. This is advantageous as it allows to reduce the CO2 production / emission of the furnace of the invention when operating (due to a reducing of the emission occurring from the decarbonization of the carbonate raw materials).

[0032] According to the invention and as commonly adopted in the glass art, by "melting tank", it is meant a tank defining a zone where the vitrifiable materials are charged and melt by heating, and comprising, when the furnace is in process, a melt and a "blanket" of unmelted vitrifiable materials that floats on the melt and is progressively melted and therefore reduced from upstream to downstream of the melting tank. For example, the surface area of the melting tank (2) in the invention may range from 25 to 400 m2.

[0033] According to the invention, the heating means (3;3') in the melting tank (2) may be any suitable heating means. According to an embodiment, the heating means (3;3') in the melting tank (2) is comprised of a plurality of electrodes and / or a plurality of burners and / or a plurality of thermal plasma torches. This means that said heating means (3;3') may be comprised of the three precited types of heating, or two of them or only one type of them.

[0034] FIG.1-3 illustrate a furnace according to an embodiment of the invention where the heating means in the melting tank (2) are comprised of a plurality of electrodes (3), in particular electrodes located at the bottom of said melting tank (2). FIG. 2 shows also with the broken lines an illustrative bath / melt level in the furnace.

[0035] FIG.4 illustrates a furnace according to an embodiment of the invention where the heating means in the melting tank (2) are comprised of a plurality of electrodes (3), in particular located at the bottom of said melting tank (2), and a plurality of burners (3'), in particular arranged along the side walls of the tank on each side thereof and in the downstream portion of the tank. The plurality of burners, if any, are configured to emit a combustion flame and may be supplied with fuel and air, or fuel and oxygen, or fuel and a gasthat is enriched in oxygen. Fuel may be fossil fuel, natural gas, biogas, hydrogen or mixture thereof.

[0036] Preferably, the heating means (3;3') in the melting tank (2) are comprised of a plurality of electrodes and / or a plurality of thermal plasma torches. This means that said heating means may be comprised of both precited types of heating, or only one type of them, thereby excluding burners. This is advantageous, notably in view of CO2 emissions, as this results in a fully-electrical melting tank / step. This allows globally to reach a higher electrical input fraction, e.g. of at least 70%.

[0037] The furnace (1) of the invention comprises further a fining tank (4) equipped with heating means configured to refine the melt and thereby to provide a refined melt.

[0038] According to the invention and as commonly adopted in the glass art, by "fining tank", it is meant a tank defining a zone where there is no more "blanket" of unmelted vitrifiable materials that floats on the melt and where the glass melt is heated at temperatures higher than melting tank temperatures (generally above 1400°C or even above 1450°C), in order to refine the glass (mainly by eliminating major part of bubbles). This fining tank is also commonly called "clarification tank" in the art. For example, the surface area of the fining tank (4) in the invention may range from 25 to 400 m2.

[0039] According to the invention, the fining tank comprises, as heating means, a plurality of thermal plasma torches (8). Each torch (8) in the invention is configured to emit from a working fluid (9) a plasma flame (10) above the melt (when the furnace is operating). An illustrative bath / melt level is shown at FIG.2 (broken lines). For clarity reason, in FIG.2, the representation of the plurality of thermal plasma torches (8) are simplified and the plasma flames (10) are omitted.

[0040] According to the invention and as commonly adopted in the glass art, by "thermal plasma torch" , it is meant a device that generates a flow of plasma (or plasma flame) from a working fluid that is fed into said torch and that is thermally decomposed / ionized upon subjection to an energy source within the torch. The thermal plasma torches of the invention may be of the type that uses electricity as an energy source to generate the plasma, said source being arc-driven source with various current waveforms (DC, AC, pulse DC,...) or electromagnetic (EM) wave-driven source with various EM wave generation (microwaves, induction,...).

[0041] According to the invention and as commonly adopted in the glass art, by "plasma flame", it is meant the flow of plasma that projects out of the thermal plasma torches of the invention. According to the invention, each thermal plasma torch (8) is configured to emit a plasma flame (10) above the melt, preferably in a direction essentially parallel to the melt surface. This last embodiment is advantageous as it allows a better heat transfer from the plasma flames to the melt in order to refine it.

[0042] For example, the plurality of thermal plasma torches (8) in the invention are advantageously arranged along the side walls of the fining tank (4) on each side thereof, e.g. in rows, to spread the plasma flames (10) over practically the entire width of said tank, and spaced from one another in such a way so as to distribute the heat over a major portion of the length (or the whole length) of the fining tank (4).

[0043] According to an embodiment of the invention, the working fluid (9) comprises hydrogen, helium, air, oxygen, neon, argon, nitrogen, carbon monoxide, carbon dioxide, water or a mixture thereof

[0044] According to still an embodiment of the invention, the working fluid (9) consists in hydrogen, helium, air, oxygen, neon, argon, nitrogen, carbon monoxide, carbon dioxide, water or a mixture thereof. The expression "consists in" in the present context means that the working fluid (9) may also include possible impurities present in the above-cited fluids.

[0045] Preferably, the working fluid (9) comprises nitrogen. More preferably, it comprises more than 80% in volume of nitrogen, or even it consists in nitrogen. Alternatively and preferably also, the working fluid (9) comprises nitrogen and argon, in various proportions.

[0046] According to an embodiment, the fining tank comprises further, as heating means and in addition to the plurality of thermal plasma torches, a plurality of electrodes. According to this embodiment, the plurality of electrodes are advantageously located in the upstream part of the fining tank (4), e.g. in the first third of the fining tank (4) taken in its length.

[0047] Preferably, the fining tank (4) in the invention does not comprise any burner.

[0048] More preferably, the heating means in the fining tank (4) consist in a plurality of thermal plasma torches (and therefore exclusively electrical heating means). This is advantageous for CO2 fingerprint of the furnace in working, especially when the electricity comes from "green(er)" sources / processes (renewable, e.g. wind power, or nuclear), and for the recycling of the working fluid from the fining tank towards the thermal plasma torches.

[0049] The furnace (1) of the invention comprises further at least one neck (5) separating the melting tank (2) and the fining tank (4).

[0050] For the sake of clarity, according to the invention and as commonly accepted in the art, by a "neck" separating the melting tank and the fining tank, it is meant : (i) a narrowing in width and in (crown) height compared to the melting tank and the fining tank, together with (ii) an opening (of the neck) being only partially under the glass melt / batch blanket free surface, then leaving a free opening above the glass melt / batch blanket. This definition excludes therefore a "throat", which has its "opening" completely under the glass melt / blanket free surface (thereby leaving no free space above the glass melt / batch blanket), as commonly accepted in the art.

[0051] The base of the neck (5) in the invention may be located essentially at the level of the floor / bottom of the melting tank (2), or above said level or below said level. Moreover, the base of the neck (5) may be located essentially at the level of the floor / bottom of the fining tank (4), or above said level or below said level.

[0052] Such a neck (5) separating the melting tank (2) and the fining tank (4) in the invention is advantageous because it stabilizes the blanket of raw materials and avoid unmelted particles flowing directly towards the fining tank. This point can advantageously improve glass quality. Moreover, it also allows a wider opening (than a common throat) and therefore lower glass velocities leading to lower refractory corrosion and wear. This point can advantageously improve furnace lifetime. Moreover, the presence of the neck (5) in the invention allows to deal with / treat independently exhaust gas from melting tank (2) independently from exhaust gas from fining tank (4). Above all, in the context of the invention using thermal plasma torches, it allows to avoid or greatly reduce "contamination" (in volume and components) of exhaust gas in fining tank (4) by exhaust gas from melting tank (2), thereby allowing an easier and more effective recycling of working fluid (9) from the fining tank (4). Finally, the use of neck is compatible with glass furnaces with large production capacities (> 400 tons / d and up to 100 tons / d.).

[0053] According to an embodiment of the invention, the furnace comprises two necks (5) separating the melting tank (2) and the fining tank (4) and arranged in the width of the melting and fining tanks. According to still an embodiment of the invention, the furnace comprises two melting tanks and two necks, each neck separating a melting tank and the fining tank.

[0054] The furnace (1) of the invention comprises further inlet means (6) located at the melting tank (2), configure to fed the vitrifiable materials in said melting tank (2).

[0055] Preferably, and as known in the art, the inlet means (6) are either located upstream of the melting tank (2) and / or located at the top of the melting tank (2).

[0056] In an embodiment, the inlet means (6) are located upstream of the melting tank (2), either in the width of said tank (as shown in FIG. 1, 2, 4) or laterally in its length. In an alternative embodiment, the inlet means (6) are located at the top of the melting tank (2) ("top batch charger"), which allow advantageously to charge the vitrifiable materials directly on the top of glass melt, especially over the entire surface of the melting tank (2). It may advantageously be of the type "rotating batch charger" or "linear X-Y-batch charger" (e.g., in the form of a distributor arm that can move in both X-Y directions, namely in the length and width of the melting tank), located above the glass melt and below the crown of the melting tank. A top batch charger is illustrated in FIG. 3. Preferably, a top batch charger may be considered when the melting tank does not comprise any burner.

[0057] In an advantageous embodiment of the invention, the furnace comprises a melting tank (2) enlarged laterally and equipped with at least two inlet means, located on both sides of the melting tank (2) based on the location of the neck (5), either at the lateral sides or as top batch chargers.

[0058] The furnace (1) of the invention comprises further outlet means (7) located downstream of the fining tank (2) configured to flow the refined melt from the fining tank (2) to a working zone (11). According to an embodiment and as illustrated in Figs. 1-3, the outlet means (7) are composed of at least an outlet neck or, alternatively, at least an outlet throat, in order to lead the melt towards a working zone (11).

[0059] The working zone (11) is also commonly called in the art "working end" or also "braise" or also "conditioning zone". The working zone (11) according to the invention may comprise, for example, a conditioning zone in which thermal conditioning by controlled cooling is carried out prior to glass melt leaving said zone through an outlet to a forming zone. Such a forming zone may comprise, for example, a float installation and / or a rolling installation, with the aim to manufacture flat glass products.

[0060] According to a particularly advantageous embodiment, the furnace (1) comprises further means for recycling the working fluid (9) from the fining tank (4) towards the plurality of thermal plasma torches (8). As already explained above, the recycling of the working fluid(9), with the furnace of the invention, is greatly facilitated and very effective. Indeed, the combination of plasma heating in the fining tank with a neck separating the melting tank and the fining tank allows to reduce "contamination" (in volume and components) of the working fluid.

[0061] According to another advantageous embodiment of the invention and as illustrated at FIG. 4, the furnace comprises further at least an extraction mean (12) of exhaust gas in the melting tank (2). Preferably, said extraction mean(s) (12) is / are located on side walls, on one side or, as illustrated at FIG. 4, both sides of the tank.

[0062] According to another advantageous embodiment of the invention, the furnace comprises further at least an extraction mean (13) of exhaust gas in the fining tank (5). Preferably, said extraction mean(s) is / are located on side walls, on one side or, as illustrated at FIG. 4, both sides of the fining tank (5), preferably in the upstream part of the fining tank (5).

[0063] The invention also relates to a process for melting vitrifiable materials, comprising the steps of :(a) charging vitrifiable materials in a melting tank through inlet means;(b) melting the vitrifiable materials in the melting tank by heating with heating means, thereby providing a melt;(c) flowing the melt to the fining tank through a neck separating the melting tank and the fining tank;(d) fining the melt in the fining tank, thereby providing a refined melt;(e) flowing the refined melt to a working zone through outlet means;

[0064] wherein the step (d) of fining the melt is carried out by heating the melt with a plurality of thermal plasma torches, each plasma torch being fed with a working fluid and emitting a plasma flame above the melt.

[0065] The process is advantageously carried out with operating the furnace of the invention.

[0066] FIG. 5 illustrates, as a flowchart, an embodiment of the process of the invention.

[0067] Features and embodiments described above in relation with the furnace, for example for the melting tank, the fining tank, the neck, the inlet means, the outlet means, the heating means, the working fluid and the vitrifiable materials, are applicable to the process of the invention.

[0068] The process according to the invention preferably has an electrical input fraction of at least 50%. More preferably, the process according to the invention has an electrical input fraction of at least 60%, or even at least 70%. Ideally, the process according to the invention has an electrical input fraction of 100% (in the case where no burner are present or used in the melting and the fining steps).

[0069] According to an embodiment of the process of the invention, at the charging step (a), when the vitrifiable materials comprise glass raw materials and cullet, both are preferably charged together in the melting tank (2), i.e. through same inlet mean(s). Alternatively, both are charged in the melting tank (2) independently, through different inlet mean(s) (for example, one inlet mean for the raw materials and one inlet mean for the cullet).

[0070] In an advantageous embodiment, the process of the invention comprises further a step of recycling the working fluid (9) from the fining tank (4) towards the plurality of thermal plasma torches (8). According to this embodiment, at the step of recycling, at least a part of the working fluid (9) fed in the plurality of thermal plasma torches (8) is recycled. Preferably, at least 50% in volume, more preferably, at least 60% in volume or even at least 70% in volume of the working fluid (9) fed in the plurality of thermal plasma torches (8) is recycled at the step of recycling. This allows the plasma heating to be more advantageous or even viable economically-speaking. Said step of recycling according to the invention includes advantageously steps of treating the working fluid (9), e.g. physically and / or chemically.

[0071] In an embodiment, the process of the invention comprises further a step of extracting exhaust gas from the fining tank (4) thanks to extracting means (13). Advantageously, the exhaust gas extracted at that step of extracting is directed, at least partially, towards said step of recycling.

[0072] In another embodiment of the process of the invention, the step (b) of melting the vitrifiable materials in the melting tank (2) is carried out by heating with a plurality of electrodes and / or a plurality of thermal plasma torches and / or a plurality of burners. This means that heating at the step (b) of melting may be carried out with the three precited types of heating, or two of them or only one type of them. Preferably, the step (b) of melting the vitrifiable materials in the melting tank is carried out by heating with a plurality of electrodes and / or a plurality of thermal plasma torches. This means that said heating at the step (b) of melting is carried out with both precited types of heating, or only one type of them, thereby combustion heating (with burners). This is advantageous for CO2 fingerprint of the process asthis results in a f u I ly-e lectrica I melting step, and for the recycling of the working fluid from the fining tank towards the thermal plasma torches.

[0073] In another embodiment of the process of the invention, the step (d) of fining the melt in the fining tank is carried out by heating the melt exclusively with said plurality of thermal plasma torches.

[0074] In still another embodiment, the process of the invention comprises further a step of extracting exhaust gas from the melting tank (2) thanks to extracting means (12).

[0075] Finally, the invention also relates to the use of a furnace according the invention, in a flat glass manufacturing process, for example in a float glass manufacturing process. In this last embodiment, downstream of the working zone (11), the furnace comprises further a float installation, including notably and as known a tin bath.

[0076] The person skilled in the art realizes that the present invention is by no means limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It is further noted that the invention relates to all possible combinations of features, and preferred features, described herein and recited in the claims.

Claims

CLAIMS1. Furnace for melting vitrifiable materials, comprising :(i) a melting tank equipped with heating means configured to melt vitrifiable materials and thereby to provide a melt;(ii) a fining tank equipped with heating means configured to refine the melt and thereby to provide a refined melt;(iii) at least one neck separating the melting tank and the fining tank;(iv) inlet means located at the melting tank, configure to fed the vitrifiable materials in said melting tank; and(v) outlet means located downstream of the fining tank configured to flow the refined melt from the fining tank to a working zone; characterized in that the fining tank comprises, as heating means, a plurality of thermal plasma torches, each torch being configured to emit from a working fluid a plasma flame above the melt.

2. Furnace according to the preceding claim, characterized in that the heating means in the melting tank are comprised of a plurality of electrodes and / or a plurality of burners and / or a plurality of thermal plasma torches.

3. Furnace according to the preceding claim, characterized in that the heating means in the melting tank are comprised of a plurality of electrodes and / or a plurality of thermal plasma torches.

4. Furnace according to one of the preceding claims, characterized in that the working fluid comprises hydrogen, helium, air, oxygen, neon, argon, nitrogen, carbon monoxide, carbon dioxide, water or mixtures thereof.

5. Furnace according to the preceding claim, characterized in that the working fluid consists in nitrogen.

6. Furnace according to one of the preceding claims, characterized in that the fining tank does not comprise any burner.

7. Furnace according to one of the preceding claims, characterized in that each thermal plasma torch is configured to emit a plasma flame in a direction essentially parallel to the melt surface.

8. Furnace according to one of the preceding claims, characterized in that it comprises further means for recycling the working fluid from the fining tank towards the plurality of thermal plasma torches.

9. Process for melting vitrifiable materials, comprising the steps of :(a) charging vitrifiable materials in a melting tank through inlet means;(b) melting the vitrifiable materials in the melting tank by heating with heating means, thereby providing a melt;(c) flowing the melt to the fining tank through a neck separating the melting tank and the fining tank;(d) fining the melt in the fining tank, thereby providing a refined melt;(e) flowing the refined melt to a working zone through outlet means; characterized in that the step (d) of fining the melt is carried out by heating the melt with a plurality of thermal plasma torches, each plasma torch being fed with a working fluid and emitting a plasma flame above the melt.

10. Process according to the preceding claim, characterized in that it comprises further a step of recycling the working fluid from the fining tank towards the plurality of thermal plasma torches.

11. Process according to the preceding claim, characterized in that at least 50% in volume of the working fluid fed in the plurality of thermal plasma torches is recycled.

12. Process according to one of claims 9-11, characterized in that the step (b) of melting the vitrifiable materials in the melting tank is carried out by heating with a plurality of electrodes and / or a plurality of thermal plasma torches.

13. Process according to one of claims 9-12, characterized in that the step (d) of fining the melt in the fining tank is carried out by heating exclusively with said plurality of thermal plasma torches.

14. Use of a furnace according to claims 1-8, in a flat glass manufacturing process.

15. Use of a furnace according to preceding claim, in a float glass manufacturing process.

Images