Glass furnace

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

GLASS FURNACEFIELD 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 fingerprint.

[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. In particular, the use of oxy-combustion technology (oxygen as comburant and fuel as combustible) is known to reduce energy consumption and also to reduce exhaust gas emissions.

[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. In the glass art, it is known to call a full-electrical melter as a "cold-top melter", by opposition to classical combustion melter called "hot-top furnaces" (or "warm-top"). Indeed, in such an all-electrical melter, the glass batch is distributed over the glass melting surface forming an insulating batch "blanket" causing the temperature to drop from ~1400°C in the glass melt to < 500°C (and possibly down to 50°C) at the blanket and above.

[0007] All-electrical melters / furnaces offer significant advantages. First, the use of electricity at the melting step 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 over time and territorially, thereby avoiding unpredictability and variability of the glass manufacturing process using such fuels. Finally, heat losses in allelectrical melters are much lower as the melting energy is transferred essentially into the glass (e.g. thanks to electrodes allowing an electric current to pass through and heat the bath of molten glass from its bulk), which makes them energy-efficient furnaces, e.g. compared to hot-top combustion melter where there is a significant heat loss occurring from the superstructure of the furnace and in the residual waste gases, even if heat recovery system is used.

[0008] A lot of configurations and designs of glass furnaces with a cold-top melter have been proposed these last years in order to reduce energy consumption and CO2 fingerprint of glass manufacturing.

[0009] For example, it has been proposed in the art several segmented glass furnace designs, in which the melting zone and the fining zone are separated by a neck or a throat. Such segmented furnaces are known as advantageous on some various aspects. In particular, a segmented design allows, in general and amongst other :- to cut off heat radiation from flames in the fining tank (using combustion means to refine) towards melting tank, in order to confine efficiently combustion energy in the zone where high temperatures are needed (namely, the fining zone);to optionally separate atmospheres between the melting and the fining tanks, thereby limiting reflux of corrosive fumes from the fining tank to the melting tank ; to generate a restriction of the global molten glass flow that advantageously reduces the strength of glass convection in the melting tank and reduces the glass velocity, and thereby decreasing bottom refractory wear and corrosion; and to completely dissociate the dimensioning (lengths, widths and crown heights) and refractories nature of the melting and the fining tanks, and therefore to optimize each tank taking into account energy efficiency, glass quality and mechanical / structural / other constraints.

[0010] Nevertheless, such a segmented configuration has a serious drawback if one wants to consider using a "cold-top" melter. Indeed, when the melt / molten glass leaves the melting tank and flows to the fining tank through the neck, its temperature is very high (~1400°C). This generates two main issues coming from the contact of this very hot melt with the bottom of the fining tank at its upstream extremity:(i) refractories damages and thereby, a negative impact on furnace lifetime, and(ii) quality issues due to the creation of bubbles at the bottom refractories / melt interface.

[0011] Those issues have been solved in the glass art so far by cooling the upstream part of the fining tank and / or the neck, either by air blowing and / or by reducing the level of insulation at that location. But, obviously, this solution is not in favour of energy consumption of the furnace as a part of energy / heat of the melt is dissipated and lost at that stage, and afterwards / downstream, the melt must be re-heated (e.g. by burners) in order to be refined.

[0012] Hence, 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 specifically-designed segmented glass furnace with its above-cited advantages, which shows a decreased energy consumption and CO2 emissions, with an increased lifetime and while keeping a good glass quality.OBJECTIVE OF THE INVENTION

[0013] 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.

[0014] 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).

[0015] It is a further objective of the present invention to provide a glass furnace which shows a decreased energy consumption, thereby being more energy effective.

[0016] It is a further objective of the present invention to provide a design which allows to increase the lifetime if the glass furnace and, in particular, of the fining tank.

[0017] It is a further objective of the present invention to provide a glass furnace which allows to produce glass with a good quality.DESCRIPTION OF THE INVENTION

[0018] The present invention relates to a furnace for manufacturing glass, comprising• a melting tank equipped with a plurality of electrodes and configured to provide a melt;• a fining tank equipped with heating means and configured to provide a refined melt;• a neck separating said melting tank and said fining tank and configured to flow the melt from the melting tank to the fining tank ;• at least one glass batch charger located at the melting tank ;• at least one glass batch charger located at the fining tank, preferably in its upstream part ;• a working zone;• outlet means located downstream of the fining tank and configured to flow the refined melt from the fining tank to the working zone.

[0019] Hence, the invention is based on a novel and inventive approach. In particular, the inventors have found that, by combining a segmented furnace configuration (melter / neck / refiner) with the melter being a "cold-top" type and a feeding of a part of the glass batch in the refiner, it brings a lot of advantages, next to those of the segmentation and the cold-top melter in themselves. In particular, it allows :1) charging a part of the glass batch into the fining tank, esp. at an upstream part. This plays the role of reducing the temperature of the glass melt in contact with the bottom refractories of the fining tank, instead of using air blowing and / or a reducing of insulation, thereby reducing refractory wear and bubble generation. This way of "cooling" is far more energy-efficient because it allows to transfer the glass melt heat to the glass batch fed in the fining tank (that needs to be melt) and the heat / energy of the melt coming from the melter will not be lost by dissipation anymore but instead valorized inside the melter ;2) charging a glass batch with a higher cullet ratio in the fining tank compared to the glass batch fed in the melting tank, even up to 100% cullet in the fining tank. This allows :- a higher energy efficiency of the furnace. Indeed, this allows consequently to maximize the amount of virgin raw materials, including carbonated raw materials (limestone, dolomite,...), fed in the cold-top melter. This is advantageous because heating / melting carbonated materials in the "cold-top" melter releases CO2 that passes through a "cold" glass batch layer (supplied from the top) and is therefore exhausted at relatively cold temperatures (between 100 and 250°C) compared to a standard combustion furnace; and- to achieve a higher average cullet ratio for the whole furnace. Indeed, in the glass art, cold top melters are operated at a cullet ratio up to 80% and generally, rather below 70% and even below 60%. Charging a part of the cullet in the fining tank, for example up to 100% cullet, allows to decrease cullet ratio charged in the cold top melter while reaching higher average cullet ratio for the whole furnace, in favour of sustainability and CO2 emissions.

[0020] It is also to be noted that, next to all the above cited advantages, the furnace of the invention, with its special design, allows also to increase the glass melting capacity (or "pull") compared a standard installation, thanks to the combination of melting capacity of the cold- top melter and that of the fining tank.

[0021] The invention also relates to a process for manufacturing glass in a furnace comprising a melting tank, a fining tank and a neck separating said melting tank and aid fining tank, said process comprising :a) a first charging step of a first glass batch in the melting tank through at least one glass batch charger; b) a first melting step said first glass batch in said melting tank by heating with a plurality of electrodes, thereby providing a melt; c) a second charging step of a second glass batch in the fining tank through at least one glass batch charger; d) a second melting step of said second glass batch in said fining tank; e) a flowing step of the melt from the melting tank to the fining tank through said neck: f) a fining step of the melt in the fining tank by heating with heating means, thereby providing a refined melt; and g) flowing the refined melt from the fining tank to a working zone through outlet means.

[0022] Finally, the invention also relates to the use of a furnace according to the invention in a flat glass manufacturing process.

[0023] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments and figures. The sole function of reference signs in present specification and claims is to make the invention clearer and easier to understand. In particular, reference signs are not to be construed as limiting the extent of the matter protected.

[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 plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.

[0026] 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 main flow direction of the glass in the melting tank (2) and in the fining tank (4) and are to be understood with their common sense, namely herein as meaning along the averaged moving direction of the glass batch / the glass melt(defined herein as "glass stream"), from the batch charger located at the melting zone 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 FIGS. 1 and 2. By "width" in the invention, it is meant, unless otherwise specified, the dimension (in average) perpendicular to the glass stream.

[0027] The furnace (1) of the invention comprises a melting tank (2) equipped with a plurality of electrodes (3) and configured to provide a melt.

[0028] According to the invention and as commonly adopted in the glass art, by "melting tank", it is meant a zone / tank where the glass batch are charged / fed and melted by heating, and which comprises, when the furnace is in operation, a melt and a "blanket" of unmelted glass batch that floats on the melt and is progressively melted. For example, the surface area of the melting tank (2) in the invention may range from 25 to 400 m2.

[0029] According to an embodiment of the invention, the plurality of electrodes (3) in the melting tank (2) are "bottom electrodes", namely electrodes located at the bottom of said tank (2), as immersed electrodes.

[0030] The plurality of electrodes (3) are advantageously arranged according to a specific pattern (e.g., checkerboard), in order to facilitate connection to transformers and electric current balance. For example, in the case of immersed electrodes, their height is between 0.3 and 0.8 times glass melt height. Alternatively, the electrodes (3) extend from the top of the melting tank (2) (for example, maintained commonly by a water-cooled holder) and are immersed. These "top electrodes" may be advantageously located along the edge of the melting tank (2) and / or at the corner(s).

[0031] Advantageously, a counter-reaction device may be arranged in the melting tank (2), said device being configured to generate a magnetic counter-field, thereby reducing the risks of induced current generation and consequently, the associated risks of overheating and electrocution.

[0032] The number of electrodes (3) in the invention is for example designed in order to limit maximum power for each electrode to 400kW, by respecting a maximum current density of 1.5A / cm2at the electrode surface.

[0033] Advantageously, the melting tank (2) according to the invention does not comprise any burner and / or any thermal plasma torch, or in other words, is exclusively alimented with heat by said plurality of electrodes (3). This allows to get a so-called "cold-top" melter and itsabove-cited advantages, as such and in the invention in particular. For the sake of clarity, this embodiment does not exclude the possibility to arrange one or several temporary burner(s) for an exceptional event in the manufacturing process (e.g., heating-up or electrical shutdown). Those temporary burners are commonly removed in normal / standard operations.

[0034] The furnace (1) of the invention comprises further a fining tank (4) equipped with heating means (5) and configured to provide a refined melt.

[0035] According to the invention and as commonly adopted in the glass art, by "fining tank", it is meant a zone / tank 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. It is equipped with heating means, for example said heating means in the fining tank (4) are comprised of a plurality of burners and / or thermal plasma torches.

[0036] According to an embodiment, the fining tank (4) comprises, as heating means, a plurality of burners. FIG.l illustrates a furnace according to this embodiment of the invention where the fining tank (4) comprises of a plurality of burners (5), in particular arranged along the side-walls on each side thereof. At FIG. 1, four burners are presented, two on each side of the tank (4) but depending on the design / size / power etc., the number may be adapted. The plurality of burners are configured to emit a combustion flame and may be supplied with fuel and air, or fuel and oxygen, or fuel and a gas that is enriched in oxygen. Fuel may be fossil fuel, natural gas, biogas, hydrogen or mixture thereof. In an embodiment, the plurality of burners (5) in the invention are supplied with fuel and oxygen (also commonly called "oxyfuel" combustion burners).

[0037] According to another embodiment, the fining tank (4) comprises, as heating means, a plurality of thermal plasma torches, configured to emit from a working fluid a plasma flame above the bath / melt in the fining tank (when the furnace is operating). As commonly adopted in the 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,...). Also as commonly adopted in the 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 is configured to emit a plasma flame above the melt, preferably in a direction essentially parallel to the melt surface. This embodiment is advantageous as it allows to increase further electrification of the whole furnace (or, in other words, to increase its electrical input fraction).

[0038] According to still another embodiment, the fining tank (4) comprises, as heating means, a plurality of burners and a plurality of thermal plasma torches.

[0039] Generally and as commonly known in the art, the fining tank (4) may comprise an immersed wall (or damwall), in order to reduce the flow of relatively cold glass coming back from the working-end to the fining tank (good for energy consumption), and to stabilize the glass convection pattern in the melt (good for process stability).

[0040] The furnace (1) of the invention comprises further a neck (6) separating said melting tank (2) and said fining tank (4) and configured to flow the melt from the melting tank (2) to the fining tank (4). According to the invention and as commonly accepted in the art, by a "neck" separating the melting tank (2) and the fining tank (4), it is meant : (i) a narrowing in width and in (crown) height compared to the melting tank (2) and to the fining tank (4), 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.

[0041] The base (or bottom) of the neck (6) in the invention may be located essentially at the level of the bottom of the melting tank (2), or above said level or below said level. Moreover, the base of the neck (6) may be located essentially at the level of the bottom of the fining tank (4), or above said level or below said level. Preferably, the base of the neck (6) in the invention is located above the level of the bottom of the melting tank (2). Preferably also, the base of the neck (6) in the invention is located above the level of the bottom of the fining tank (4).

[0042] According to an embodiment, there may be more than one neck (6) separating the melting and the fining tanks, for example two, even if it is not a preferred embodiment in the invention.

[0043] According to another embodiment of the invention, the furnace may comprise a removable wall located at the neck (6) (e.g. a skimbar coming from the side wall of the neck),in order to (i) possibly stop unmelted vitrifiable materials that could arrive at the end of the melting tank (2) and thereby avoid their passing through the neck towards the fining tank (4) and (ii) control the intensity of or annihilate the backward flow of the glass melt from the fining tank towards the melting tank.

[0044] In the invention, the furnace (1) comprises at least one glass batch charger (7) located at the melting tank (2), preferably at least one top glass batch charger.

[0045] By "top glass batch charger" and as commonly adopted in the glass art, it is meant a batch charger which allows to charge the glass batch directly on the top of the glass melt, especially over the entire surface of the melting tank. In the invention, it may for example 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 tank (2)), located above the glass melt and below the crown of the tank (2). Such a linear X-Y top glass batch charger (7) is illustrated at FIG. 1.

[0046] The furnace may comprise more than one top glass batch charger (7), for example, two.

[0047] In an embodiment of the invention, illustrated at FIG.2, the furnace (1) comprises a melting tank (2) that is enlarged laterally and equipped with a glass batch charger located at each lateral side, so that the melting tank (2) comprises two upstream zones with two opposed glass streams (when the furnace is operating) converging through a central downstream zone facing the neck (6). This embodiment, illustrated in FIG.2, therefore shows two glass batch chargers (7), especially two top glass batch chargers.

[0048] By "glass batch" in the invention, it is meant the common and known sense given in the glass art, namely a mixture of starting materials including glass raw materials and / or cullet. For example, when glass to manufacture is a soda-lime glass, a glass batch comprises silica source(s) (commonly sand) and source(s) of alkalis and alkaline earths (often sodium carbonate / soda ash, limestone and dolomite and / ortheir decarbonated products), but it may also comprise other materials like cullet, potash, salt cake (or sodium sulfate), feldspar, coloring agents (cobalt oxide, chromium oxide,...), clarifying agents (cerium oxide,..), oxidizers (sodium nitrate,...), reducing agents (graphite, coke, pyrite,...), decolorizing agents (selenium, cobalt,...), etc. Preferably, the glass batch comprises glass raw materials and cullet. Use of cullet is advantageous as it allows (i) raw materials sustainability and (ii) reducing of the CO2 production / emission of the furnace when operating (due to a reducing of the emissionoccurring from the decarbonization of the carbonate raw materials used otherwise). Preferably, the total glass batch in the invention comprises more than 20% in weight, or preferably more than 30% and up to 95% in weight of cullet, even up to 100%.

[0049] The at least one glass batch charger (7) located at the melting tank (2) according to the invention is configured to feed the melting tank (2) with a first glass batch.

[0050] In the invention, the furnace (1) comprises also at least one glass batch charger (8) located at the fining tank (4), preferably in its upstream part.

[0051] Said at least one glass batch charger (8) located at the fining tank (4) according to the invention is configured to feed the fining tank (4) with a second glass batch. The heating means in the fining tank (4) are therefore of interest for fining the glass melt but also for melting said second glass batch.

[0052] Any type of appropriate glass batch charger may be considered in the invention for the glass batch charger (8) located at the fining tank (4). Commonly, it may be a device usually located below a charging hopper. In such a case, the batch is discharged from the hopper by gravity. The alternative movement of a paddle then pushes the batch into the fining tank. Another example of appropriate glass batch charger (8) is an endless screw charger.

[0053] According to an advantageous embodiment, said at least one glass batch charger (8) located at the fining tank (4) according to the invention is located at a side wall of said fining tank. In such a case, it may be a so-called doghouse which correspond commonly to a tank extension where the melt is covered with the glass batch as it flows in the fining tank.

[0054] According to an embodiment, said at least one glass batch charger (8) located at the fining tank (4) is located in the first upstream half of said fining tank (4) (namely the first half of the fining tank (2) along the glass stream or in its length), preferably, in the first upstream third of said fining tank (4). This is advantageous as the "cold" glass batch fed at that location plays the role of reducing the temperature of the hot glass melt, coming from the melting tank and in contact with the bottom refractories of the fining tank, instead of using air blowing and / or a reducing of insulation, thereby reducing refractory wear and bubble generation while valorizing heat of the melt.

[0055] Preferably, the furnace (1) comprises at least two glass batch chargers located at the fining tank (4), preferably each being located on either side wall of said fining tank (4), as illustrated in FIGS. 1-2. In FIGS. 1-2, the glass batch chargers (8) are schematized as arrow for sake of clarity.

[0056] The furnace (1) of the invention comprises further a working zone. A working zone is also commonly called in the art "working end" or also "braise" or also "conditioning zone". The working zone 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.

[0057] The furnace (1) of the invention comprises further outlet means (9) located downstream of the fining tank (4) and configured to flow the refined melt from the fining tank (4) to the said working zone. According to an embodiment and as illustrated in FIGS. 1-2, the outlet means (9) are composed of an outlet neck or, alternatively, an outlet throat, in order to lead the refined melt towards said working zone.

[0058] The invention also relates to a process for manufacturing glass in a furnace comprising a melting tank, a fining tank and a neck separating said melting tank and said fining tank, said process comprising : a) a first charging step of a first glass batch in the melting tank through at least one glass batch charger; b) a first melting step said first glass batch in said melting tank by heating with a plurality of electrodes, thereby providing a melt; c) a second charging step of a second glass batch in the fining tank through at least one glass batch charger; d) a second melting step of said second glass batch in said fining tank; e) a flowing step of the melt from the melting tank to the fining tank through said neck: f) a fining step of the melt in the fining tank by heating with heating means, thereby providing a refined melt; and g) a flowing step of the refined melt from the fining tank to a working zone through outlet means.

[0059] The process is advantageously carried out with operating the furnace of the invention.

[0060] Features and embodiments described above in relation with the furnace, for example for the melting tank, the fining tank, the neck, the batch chargers, the outlet means, theelectrodes, the heating means, the working zone, etc., are applicable to the process of the invention as well.

[0061] In the process of the invention, the first glass batch and the second glass batch may be the same or different, in their composition, nature and in their flow.

[0062] Preferably, said second glass batch comprises a cullet ratio higher than 80%, said cullet ratio being defined as the weight of cullet in second glass batch compared to the total weight of said second glass batch. More preferably, said second glass batch comprises a cullet ratio higher than 85%, or higher than 90% or 95% and even up to 100%. The cullet in the said first glass batch has advantageously a composition which is close to the glass melt coming from the melting tank. For example, it may be a cullet coming directly from production offcut flow.

[0063] Preferably, said first glass batch comprises a cullet ratio higher than 40%, said cullet ratio being defined as the weight of cullet in first glass batch compared to the total weight of said first glass batch. More preferably, said first glass batch comprises a cullet ratio higher than 50%, or higher than 60%, or higher than 70% or 80% and even up to 100%.

[0064] In particular, it is very advantageous in the process of the invention to feed as much cullet as possible (of the amount of cullet to be charged in total in the furnace) in the fining tank. Indeed, consequently, this allows to maximize the amount of virgin raw materials, including carbonated raw materials (limestone, dolomite,...), fed in the melting tank of the invention. This is advantageous because heating / melting carbonated materials in the "cold- top" melter releases CO2 that passes through a "cold" glass batch layer (supplied from the top) and is therefore exhausted at relatively cold temperatures (between 100 and 250°C), while it would have been exhausted at high temperatures if in a standard combustion melter (above 1300°C, or even higher than 1400°C or 1500°C). As an illustration, the corresponding energy demand reduction linked to the lowered temperature of CO2 exhaust is about 0.25 GJ per ton of molten virgin raw materials. This allows also to advantageous increase electrification of the melting process, and thereby reducing use of fossil fuels.

[0065] Preferably also, cullet ratio in said second glass batch divided by cullet ratio in said first glass batch is equal to or higher than 1.2, said cullet ratio in first glass batch being defined as the weight of cullet in first glass batch compared to the total weight of said first glass batch. More preferably, the cullet ratio in said second glass batch divided by the cullet ratio in said first glass batch is equal to or higher than 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and even higher than2.

[0066] In the embodiment where said second glass batch comprises a cullet ratio of 100% (in other words, where only cullet is charged as second glass batch in the fining tank (4)), the process may advantageously comprises further a step of cullet pre-heating, at least partially by recovering heat from flue gas coming from the fining tank (4), before charging said cullet in said fining tank (4) at the step (c) of second charging. This embodiment is very advantageous as it allows to reduce further energy consumption at the fining tank (4) and consequently, of the process of the invention. The step of cullet pre-heating according to this embodiment may be carried out in at least one cullet pre-heater, for example, of the type of one of those described in US5526580 or DE3716687. The furnace of the invention may then further comprise a cullet pre-heater. Advantageously, the at least one cullet pre-heater may be located at upstream part of the fining tank (4), either in the width of said tank or laterally in its length. Advantageously, the step of cullet pre-heating may be carried out in at least two cullet pre-heaters located, for example, at upstream part of the fining tank (4), in its width or laterally in its length on both sides. For example, the step of cullet pre-heating may be carried out in four cullet pre-heaters located at upstream part of the fining tank (4), distributed in its width or laterally in its length (for example, two on each side). Still according to this embodiment, advantageously, the flue gas are exhausted at the fining tank (4) at the upstream part of said fining tank (4), meaning that this is advantageously done close to the at least one batch charger (which is located at upstream end wall of said fining tank (4)). The temperature of the cullet at the step of cullet pre-heating in the invention is preferably and at maximum around 450°C. This allows to avoid clogging issues at the cullet-pre-heater.

[0067] In an embodiment of the process of the invention, said first melting step (b) is carried out exclusively with a plurality of electrodes in the melting tank.

[0068] In another embodiment of the process of the invention, the fining tank comprises, as heating means, a plurality of burners and / or a plurality of thermal plasma torches.

[0069] 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, the furnace comprises further a float installation, including notably and as known a tin bath.

[0070] 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 theinvention relates to all possible combinations of features, and preferred features, described herein and recited in the claims.

Claims

CLAIMS1. Furnace (1) for manufacturing glass, comprising :• a melting tank (2) equipped with a plurality of electrodes (3) and configured to provide a melt;• a fining tank (4) equipped with heating means and configured to provide a refined melt;• a neck (6) separating said melting tank (2) and said fining tank (4) and configured to flow the melt from the melting tank (2) to the fining tank (4) ;• at least one glass batch charger (7) located at the melting tank (2) ;• at least one glass batch charger (8) located at the fining tank (4), preferably in its upstream part ;• a working zone;• outlet means (9) located downstream of the fining tank (4) and configured to flow the refined melt from the fining tank (4) to the working zone.

2. Furnace according to the preceding claim, characterized in that said at least one glass batch charger (8) located at the fining tank (4) is located in the first upstream half of said fining tank (4).

3. Furnace according to the preceding claim, characterized in that said at least one glass batch charger (8) located at the fining tank (4) is located in the first upstream third of said fining tank (4).

4. Furnace according to one of the preceding claims, characterized in that said melting tank (2) does not comprise any burner and / or any thermal plasma torch.

5. Furnace according to one of the preceding claims, characterized in that the fining tank (4) comprises, as heating means, a plurality of burners (5) and / or a plurality of thermal plasma torches.

6. Furnace according to one of the preceding claims, characterized in that it comprises at least two glass batch chargers (8) located at the fining tank (4), each being located on either side of said fining tank (4).

7. Furnace according to one of the preceding claims, characterized in that the at least one glass batch charger (7) located at the melting tank (2) is a top batch charger.

8. Process for manufacturing glass in a furnace comprising a melting tank, a fining tank and a neck separating said melting tank and said fining tank, said process comprising :(a) a first charging step of a first glass batch in the melting tank through at least one glass batch charger;(b) a first melting step said first glass batch in said melting tank by heating with a plurality of electrodes, thereby providing a melt;(c) a second charging step of a second glass batch in the fining tank through at least one glass batch charger;(d) a second melting step of said second glass batch in said fining tank;(e) a flowing step of the melt from the melting tank to the fining tank through said neck:(f) a fining step of the melt in the fining tank by heating with heating means, thereby providing a refined melt; and(g) a flowing step of the refined melt from the fining tank to a working zone through outlet means.

9. Process according to the preceding claim, characterized in that said second glass batch comprises a cullet ratio higher than 80%, said cullet ratio being defined as the weight of cullet in second glass batch compared to the total weight of said second glass batch.

10. Process according to one of claims 8-9, characterized in that cullet ratio in said second glass batch divided by cullet ratio in said first glass batch is equal to or higher than 1.2, said cullet ratio in first glass batch being defined as the weight of cullet in first glass batch compared to the total weight of said first glass batch.

11. Process according to one of claims 8-10, characterized in that said first melting step (b) is carried out exclusively with a plurality of electrodes in the melting tank.

12. Process according to one of claims 8-11, characterized in that the fining tank (4) comprises, as heating means, a plurality of burners (5) and / or a plurality of thermal plasma torches.

13. Use of a furnace according to claims 1-7, in a flat glass manufacturing process, preferably in a float glass manufacturing process.