Glass melting furnace

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

GLASS MELTING 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 "cold-top melter".

[0007] It is also known in the art to combine, in a "hybrid furnace", combustion heating means (burners) and electrical heating means (electrodes) in one 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] 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.

[0009] A lot of configurations and designs of hybrid glass furnaces have been proposed these last years in order to reduce energy consumption and CO2 fingerprint of glass manufacturing.

[0010] Nevertheless, most of the proposed designs show serious disadvantages. First, those designs require generally high investments either in order to adapt an existing furnace (one talks generally about "retrofitting" or "revamping") or, worse, because it is needed to build a new installation. Next to that drawback, the described designs have often a low flexibility in terms of energy used or, in other words, the chosen design of the furnace generally sets the nature and proportions of energies used (either full gas / fuel or full electricity or hybrid with, as explained above, a limitation as to the range of electrical input fraction allowable). Finally, some of the described glass furnaces designed to reduce energy consumption and improve carbon fingerprint have a negative impact on glass quality.

[0011] 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-designedglass furnace which shows a decreased CO2 emissions by using more electricity globally, showing an increased flexibility as to the energy and reducing significantly investments needed for its implementation, while keeping a good glass quality.OBJECTIVE OF THE INVENTION

[0012] 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.

[0013] 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).

[0014] 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.

[0015] It is a further objective of the present invention to provide a design that requires significantly less investments for its implementation compared to solutions proposed in the prior art, especially by allowing an easy and limited retrofitting / revamping of existing installations.

[0016] 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

[0017] The present invention relates to a furnace for manufacturing glass, comprising a main tank having end walls and side-walls and having (i) a melting zone configured to provide a melt and (ii) a fining zone configured to provide a refined melt; said furnace comprising further :• a plurality of burners and / or thermal plasma torches in said melting zone and located at said side-walls;• at least one batch charger located at upstream end wall of said melting zone;• a working zone;• outlet means located downstream of the fining zone and configured to flow the refined melt from the fining zone to the working zone; and,• at least one secondary melting tank equipped with a plurality of electrodes and configured to provide a secondary melt;• at least a top batch charger located at said at least one secondary melting tank;• at least one neck separating the at least secondary melting tank and said melting zone, said neck being located at a side-wall of said melting zone and configured to flow the secondary melt from said at least secondary melting tank to said melting zone.

[0018] Hence, the invention is based on a novel and inventive approach. In particular, the inventors have found that combining a standard furnace / melter configuration or "hot-top" furnace (main tank with combustion / plasma melting and fining zones, with upstream batch feeding) with an additional melter in the form of a full-electric "cold-top" melter with its own batch feeding and flowing towards the melting zone of the main standard tank, it is possible to reach the above-cited objectives, that-is-to-say to provide a glass furnace (i) showing a higher global electrical input fraction (thus a decreased CO2 emissions) compared to classical (combustion / plasma) glass furnaces, (ii) being very flexible as to the energy used, (iii) reducing significantly investments needed compared to designs proposed in the prior art, (iv) improving energy efficiency, (v) while keeping a good glass quality.

[0019] The design of the invention gives a furnace that allows to melt a part of the glass batch in a "cold-top" all-electrical melter, and the other part in the standard melter (using burners or plasma torches), and to refine all the melt (coming from electrical and standard melters) in order to reach glass quality specifications (for example, float glass specifications).

[0020] It is to be noted that, even if the use of thermal plasma torches in the standard melter results in an electrification of the process compared to the use of combustion heating, it is anyway significantly less energy-efficient than a direct heating by electrodes in the glass melt, like in a cold-top melter, because in such a cold-top melter energy dissipates directly in the glass and no energy is required to generate / process the working fluid.

[0021] More specifically:

[0022] As to the reduced investments : the design of the invention is particularly of interest because, next to its other advantages (CO2 emission, energy consumption, energy flexibility and), it can be implemented through the revamping of an existing furnace installation, like a standard combustion glass furnace, in an easy and limited way, thereby reducing significantly investments. For example, in the case of a revamping of an existing standard air-fuel furnace,the furnace can be converted into oxy-fuel furnace and the area where regenerators were located (not needed anymore) can then be used to install one or two cold-top melter(s).

[0023] As to glass quality the melt produced in the cold-top melter(s) flows into the standard melter, upstream of the hotspot, and this glass flow is then carried upstream by natural convection streams. This increases significantly "residence time" of the melt from cold-top melter(s), leading to (i) the dissolution of potential unmolten particles that could remain and flow out from cold-top melter(s) and (ii) more time for small bubbles to grow, rise and escape from the glass melt, in favour of glass quality.

[0024] As to energy efficiency : compared to standard furnace (without additional cold-top melter according to the invention), the design of the invention helps to increase energy efficiency because the molten glass flowing from energy-efficient cold-top melter will bring more heat into the standard melter and help the melting of batch fed into the standard melter.

[0025] As to flexibility : the design of the invention gives a furnace enabling to control the amount / flow rate of glass batch to be melted in the standard melter (theoretically, from 0 to 100%, but e.g., from 25% to 100%) and in the additional cold-top melter(s) (the remainder) leading to flexibility in the use of electricity and fuel / plasma working fluid. It gives also the possibility to fed different batch amounts and / or nature in the standard melter and in the additional cold-top melter(s).

[0026] 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 standard melter and that of the additional cold-top melter(s) (as an illustration, for a standard furnace generally operating at a maximum pull of 600 t / d, the invention allows to set the pull of the standard main melter at 300t / d and that of the cold-top melter(s) at 500t / d, leading to a, increased total pull of 800 t / d) ; and a cold repair of the cold-top melter(s), while keeping standard main furnace in operation (cold-top melter(s) can indeed be easily partitioned / isolated). This is advantageous as a cold-top melter are known to have shorter lifetime compared to a standard melter.

[0027] The invention also relates to a process for manufacturing glass in a furnace comprising a main tank having end walls and side-walls and having a melting zone and a fining zone, comprising the steps of : a) charging a first glass batch in the melting zone through at least one batch charger located at upstream end wall of said melting zone; b) melting said first glass batch in said melting zone by heating with a plurality of burners and / or plasma torches located at the side-walls; c) charging a second glass batch through at least one top batch charger in least one secondary melting tank; d) melting said second glass batch in said at least secondary melting tank by heating with a plurality of electrodes, thereby providing a secondary melt; e) flowing said secondary melt to the melting zone through at least one neck separating the at least one secondary melting tank and the melting zone and located at a sidewall of said melting zone; f) fining, in the fining zone, the melt flowing from the melting zone, thereby providing a refined melt; and g) flowing the refined melt from the fining zone to a working zone through outlet means.

[0028] The invention also relates to a process of revamping a combustion glass furnace, comprising the steps of : providing an existing glass furnace comprising (i) a main tank having end walls and side-walls and having a melting zone and a fining zone; (ii) a plurality of burners and / or thermal plasma torches in said melting zone, (iii) at least one batch charger located at upstream end wall of said melting zone; a working zone and outlet means located downstream of the fining zone; building at least one secondary melting tank equipped with a plurality of electrodes and with at least a top batch charger and connected to said melting tank through at least one neck located at a side-wall of said melting zone.

[0029] Finally, the invention also relates to the use of a furnace according to the invention in a flat glass manufacturing process.

[0030] 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 referencesigns 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.

[0031] FIG. 1 is a schematic plan view (horizontal cross-section) of an embodiment of a furnace according to the invention.

[0032] FIG. 2 is a schematic plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.

[0033] 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 main tank (2) 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 FIG. 1. By "width" in the invention, it is meant, unless otherwise specified, the dimension (in average) perpendicular to the glass stream.

[0034] The furnace (1) of the invention comprises a main tank (2) having end walls (3; 3') and side-walls (4, 4') and having a melting zone (5) and a fining zone (6).

[0035] According to the invention and as commonly adopted in the glass art, by "melting zone", it is meant a zone 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 and therefore reduced from upstream to downstream of the melting zone. For example, the surface area of the melting zone (2) in the invention may range from 25 to 400 m2.

[0036] According to the invention and as commonly adopted in the glass art, by "fining zone", it is meant 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 zone (6) in the invention may range from 25 to 400 m2. It is advantageously equipped with heating means, for example burners, in a common way. It may also be equipped with thermal plasma torches, in addition to or in replacement of burners.

[0037] Generally and as commonly known in the art, the fining zone (6) may comprise an immersed wall (or damwall) (7), in order to reduce the flow of relatively cold glass coming back from the working-end to the melting zone (good for energy consumption), and to stabilize the glass convection pattern in the melt (good for process stability).

[0038] Generally and as known in the art, the transition between the melting zone (5) and the fining zone (6) in the main tank (2) is done with bubblers (8), commonly arranged in the width of said tank, roughly in line(s).

[0039] According to the invention, the furnace comprises a plurality of burners and / or thermal plasma torches in the melting zone (5). According to the invention, the plurality of burners and / or plasma torches are located in the melting zone (5) at the side-walls (4;4') of the main tank (2).

[0040] According to an embodiment, the furnace comprises a plurality of burners (9). FIG.l illustrates a furnace according to this embodiment of the invention where the melting zone (5) comprises of a plurality of burners (9), in particular arranged along the side-walls (4, 4') on each side thereof. 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. Preferably, the plurality of burners (9) in the invention are supplied with fuel and oxygen (also commonly called "oxy-fuel" combustion burners).

[0041] According to another embodiment, the furnace comprises a plurality of thermal plasma torches, configured to emit from a working fluid a plasma flame above the bath / melt in the melting zone (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). For example, for the melting, after having maximized the electrification thanks to the use of the at least one secondary melting tank, one could take it further by using thermal plasma torches (in total or partial replacement of burners) in the melting zone (5). This embodiment may thus be advantageously combined with the embodiment where the fining zone (6) is equipped with thermal plasma torches as heating means (in total or partial replacement of standard burners). According to still another embodiment, the furnace comprises a plurality of burners and a plurality of thermal plasma torches.

[0042] Advantageously, the melting zone (5) may be equipped, next to the plurality of burners and / or thermal plasma torches, with a plurality of electrodes, preferably in its upstream part. Preferably also, the electrodes are located at the bottom of the melting zone (5), as immersed electrodes.

[0043] In the invention, the furnace comprises at least one batch charger (10) located at upstream end wall (3') of the melting zone (5). Said batch charger (10) according to the invention is configured to feed the melting zone (5), at its upstream part, with a first glass batch.

[0044] 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.

[0045] Any type of appropriate batch charger may be considered in the invention. Commonly, a batch charger is a device usually located below a charging hopper. The batch is discharged from the hopper by gravity and evenly spread on a batch charger table. The alternative movement of a paddle then pushes the batch evenly into the furnace and creates batch piles.

[0046] The furnace (1) of the invention comprises at least one secondary melting tank (11) equipped with a plurality of electrodes (12) and configured to provide a secondary melt. The at least one secondary melting tank (11) may be advantageously located on a side of one of the side-walls (4; 4'), as illustrated in FIG.l. In the case of a revamping of an existing standard air-fuel furnace, the furnace can be converted into an oxy-fuel furnace (with "oxy-fuel burners") and the at least one secondary melting tank (11) of the invention may be mounted in the area where the regenerators were located (not needed anymore). This means that the invention requires low investments for its implementation compared to solutions proposed in the prior art, by allowing an easy and limited retrofitting / revamping of the existing installation.

[0047] Advantageously, the furnace (1) of the invention comprise two secondary melting tanks (11), preferably each being located on either side of the side-walls (4;4'). This embodiment is illustrated at FIG. 2. This embodiment is advantageous as it provides a symmetry for the fluxes in general and also as it gives the possibility to partition one of the two melting tanks (11), upon need (e.g., cold repair) and keep the other one in operation, thereby keeping the main advantages of the furnace design of the invention.

[0048] Preferably, the plurality of electrodes (12) in the at least one secondary melting tank (11) are "bottom electrodes", namely electrodes located at the bottom of the secondary melting tank (11), as immersed electrodes.

[0049] The plurality of electrodes (11) 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 (12) extend from the top of the secondary melting tank (11) (for example, maintained commonly by a water-cooled holder)and are immersed. These "top electrodes" may be advantageously located along the edge of the secondary melting tank (11) and / or at the corner(s).

[0050] Advantageously, a counter-reaction device may be arranged in the at least one secondary melting tank (11), said device being configured to generate a magnetic counterfield, thereby reducing the risks of induced current generation and consequently, the associated risks of overheating and electrocution.

[0051] The number of electrodes (12) 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.

[0052] Advantageously, the at least one secondary melting tank according to the invention does not comprise any burner, or in other words, is exclusively alimented with heating by said plurality of electrodes (12). This allows to get a so-called "cold-top" melter and its above-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.

[0053] The furnace (1) of the invention also comprises at least a top batch charger (13) located at said at least one secondary melting tank (11). Said top batch charger (13) according to the invention is configured to feed the at least one secondary melting tank (11) with a second glass batch. By "top batch charger" and as commonly adopted in the glass art, it is meant a batch charger which allows to charge the batch directly on the top of 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 (11)), located above the glass melt and below the crown of the tank (11). Such a linear X-Y top batch charger is illustrated at FIGS. 1-2.

[0054] The furnace may comprise more than one top batch charger (13), for example, two. If the furnace (1) comprises two secondary melting tanks (11), each tank (11) comprises at least one top batch charger (13).

[0055] The furnace (1) of the invention comprises at least one neck (14) separating the at least secondary melting tank (11) and said melting zone (5), located at a side-wall (4; 4') of said melting zone (5) and configured to flow the secondary melt from said at least secondarymelting tank (11) to said melting zone (5). According to the invention and as commonly accepted in the art, by a "neck" separating the at least secondary melting tank (11) and said melting zone (5, it is meant : (i) a narrowing in width and in (crown) height compared to the melting tank (11) and to said melting zone (5), 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. The neck (14) may be combined with a throat portion connected to the at least one secondary melting tank (11), said neck being then connected directly to said melting zone (5) ("throat" as commonly adopted in the glass art means an open portion completely under the glass melt / blanket free surface, leaving no free space above the glass melt / batch blanket) .

[0056] Advantageously, said at least one neck (14) is located in the first upstream half of said main tank (2). This allows the secondary melt to flow to the melting zone (5) upstream of the melting zone hotspot, that will then consequently be carried upstream by natural convection, with the above-cited advantages.

[0057] The base (or floor) of the neck (14) in the invention may be located essentially at the level of the floor / bottom of the at least one secondary melting tank (11), or above said level or below said level. Moreover, the base of the neck (14) may be located essentially at the level of the floor / bottom of the melting zone (5), or above said level or below said level. Preferably, the base of the neck (14) in the invention is located above the level of the floor / bottom of the at least one secondary melting tank (11). Preferably also, the base of the neck (14) in the invention is located above the level of the floor / bottom of the melting zone (5).

[0058] According to an embodiment, there may be more than one neck (14) by secondary melting tank (11), for example two.

[0059] Forthe sake of clarity and as illustrated in FIG. 2, in the embodiment where the furnace (1) comprises two secondary melting tanks (11), each tank (11) comprises its own neck (14), one neck being located at a side-wall (4) and the other neck being located at the other sidewall (4'). Those two necks (14) may be the same or different, in their dimensions, design and / or position at the side wall.

[0060] The furnace (1) of the invention comprises a working zone (14). 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 inwhich 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.

[0061] The furnace (1) of the invention comprises further outlet means (15) located downstream of the fining zone (6) and configured to flow the refined melt from the fining zone (6) to the working zone (14). According to an embodiment and as illustrated in FIGS. 1- 2, the outlet means are composed of an outlet neck or, alternatively, an outlet throat, in order to lead the refined melt towards said working zone.

[0062] The invention also relates to a process for manufacturing glass in a furnace (1) comprising a main tank (2) having end walls (3;3') and side-walls (4;4') and having a melting zone (5) and a fining zone (6), comprising the steps of :(a) charging a first glass batch in the melting zone (5) through at least one batch charger (10) located at upstream end wall (3') of said melting zone (5);(b) melting said first glass batch in said melting zone (5) by heating with a plurality of burners (9) and / or thermal plasma torches located at the side-walls (4;4');(c) charging a second glass batch through at least one top batch charger (13) in at least one secondary melting tank (11);(d) melting said second glass batch in said secondary melting tank (11) by heating with a plurality of electrodes (12), thereby providing a secondary melt;(e) flowing said at least one secondary melt to the melting zone (5) through at least one neck (14) separating the at least one secondary melting tank (11) and the melting zone (5) and located at a side-wall (4;4') of said melting zone (5);(f) fining, in the fining zone (6), the melt flowing from the melting zone (5), thereby providing a refined melt; and(g) flowing the refined melt from the fining zone (5) to a working zone (14) through outlet means (15).

[0063] The process is advantageously carried out with operating the furnace (1) of the invention.

[0064] Features and embodiments described above in relation with the furnace (1), for example for the melting zone, the fining zone, the neck, the batch chargers, the outlet means, the heating means, the secondary melting tank, working zone, etc., are applicable to the process of the invention as well.

[0065] The secondary melt in the invention, when flowing from the at least one secondary melting tank (11) towards the working zone (14) may still comprise unmelted particles of batch, but generally in very low amounts.

[0066] In the process of the invention, the first batch and the second batch may be the same or different, in their composition, nature and in their flow.

[0067] Preferably, said first batch comprises a cullet ratio higher than 80%, said cullet ratio being defined as the weight of cullet in first batch compared to the total weight of said first batch. More preferably, said first batch comprises a cullet ratio higher than 85%, or higher than 90% or 95% and even up to 100%. 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 melting zone (5). Indeed, consequently, this allows to maximize the amount of virgin raw materials, including carbonated raw materials (limestone, dolomite,...), fed in the at least one secondary melting tank (11). 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.

[0068] Preferably also, the cullet ratio in first said batch divided by the cullet ratio in said second batch is higher than 1.2, said cullet ratio in second batch being defined as the weight of cullet in second batch compared to the total weight of said second batch. More preferably, the cullet ratio in first said batch divided by the cullet ratio in said second batch is higher than 1.5, 1.6, 1.7, 1.8, 1.9, and even higher than 2.

[0069] In an embodiment of the process of the invention, the batch flow rate at charging step (c) is equal to or higher than the batch flow rate at charging step (a). This is advantageous in term of energy efficiency but, above all, in term of direct CO2 emissions. Preferably, according to this embodiment, the batch flow rate at charging step (c) is 1.1 times higher than the batch flow rate at charging step (a), or even 1.2, 1.5, 1.7, 2 times and even 3 times higher than the batch flow rate at charging step (a). By "batch flow rate", it is meant herein the common andadopted meaning in the art, namely the weight (in tons) per day of glass batch (including raw materials and cullet) fed, herein either at charging step (a) or at charging step (c).

[0070] In an embodiment of the process of the invention, said melting step (b) is carried out further by heating with a plurality of electrodes.

[0071] In the embodiment where said first batch comprises a cullet ratio of 100% (in other words, where only cullet is charged as first batch in the melting zone (5)), the process may advantageously comprises further a step of cullet pre-heating, at least partially by recovering heat from flue gas coming from the melting tank (5), before charging said cullet in said melting tank (5) at the step (a) of charging. This embodiment is very advantageous as it allows to reduce further energy consumption at the melting tank (5) 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 melting tank (5), 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 preheaters located, for example, at upstream part of the melting tank (5), 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 melting tank (5), 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 melting (5) at the upstream part of said melting tank (5), meaning that this is advantageously done close to the at least one batch charger (which is located at upstream end wall of said melting zone (5)). 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.

[0072] In an embodiment of the process of the invention, said melting step (b) is carried out with a plurality of burners (9), especially oxy-fuel burners.

[0073] In another embodiment of the process of the invention, said melting step (d) is carried exclusively with a plurality of electrodes.

[0074] The invention also relates to a process of revamping a combustion glass furnace, comprising the steps of :providing an existing glass furnace comprising (i) a main tank having end walls and side-walls and having a melting zone and a fining zone; (ii) a plurality of burners and / or thermal plasma torches in said melting zone, (iii) at least one batch charger located at upstream end wall of said melting zone; a working zone and outlet means located downstream of the fining zone; building at least one secondary melting tank equipped with a plurality of electrodes and with at least a top batch charger and connected to said melting tank through at least one neck located at a side-wall of said melting zone.

[0075] In an advantageous embodiment of the process of revamping of the invention, said existing glass furnace comprises a plurality of burners alimented with air and fuel and at least a pair of regenerators located on either side of said side-walls (air-fuel standard combustion furnace); the process further comprising : a step of replacing said plurality of burners in the existing glass furnace so that they are alimented in oxygen and fuel (oxy-fuel burners), and a step of dismantling the at least a pair of regenerators; the at least one secondary melting tank being built at the place of dismantled regenerators.

[0076] Finally, the invention also relates to the use of a furnace (1) 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 (15), the furnace (1) comprises further a float installation, including notably and as known a tin bath.

[0077] 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 (1) for manufacturing glass, comprising a main tank (2) having end walls (3,3') and side-walls (4,4') and having (i) a melting zone (5) configured to provide a melt and (ii) a fining zone (6) configured to provide a refined melt; said furnace comprising further :• a plurality of burners (9) and / or thermal plasma torches in said melting zone (5) and located at said side-walls (4,4');• at least one batch charger (10) located at upstream end wall (3') of said melting zone (5);• a working zone (14);• outlet means (15) located downstream of the fining zone (6) and configured to flow the refined melt from the fining zone (6) to the working zone (14); characterized in that it comprises further:• at least one secondary melting tank (11) equipped with a plurality of electrodes (12) and configured to provide a secondary melt;• at least a top batch charger (13) located at said at least one secondary melting tank (11);• at least one neck (14) separating the at least secondary melting tank (11) and said melting zone (5), located at a side-wall (4,4') of said melting zone (5) and configured to flow the secondary melt from said at least secondary melting tank (11) to said melting zone (5).

2. Furnace according to the preceding claim, characterized in that said at least one neck (14) is located in the first upstream half of said main tank (5).

3. Furnace according to one of the preceding claims, characterized in that said at least one secondary melting tank (11) does not comprise any burner.

4. Furnace according to one of the preceding claims, characterized in that said melting zone (5) is further equipped with a plurality of electrodes, preferably in its upstream part.

5. Furnace according to one of the preceding claims, characterized in that it comprises two secondary melting tanks (11), preferably each being located on either side of the sidewalls (4,4').

6. Process for manufacturing glass in a furnace comprising a main tank (2) having end walls (3,3') and side-walls (4,4') and having a melting zone (5) and a fining zone (6), comprising the steps of :(a) charging a first glass batch in the melting zone (5) through at least one batch charger located at upstream end wall of said melting zone (5);(b) melting said first glass batch in said melting zone (5) by heating with a plurality of burners (9) and / or thermal plasma torches located at the side-walls (4,4');(c) charging a second glass batch through at least one top batch charger (13) in at least one secondary melting tank (11);(d) melting said second glass batch in said at least secondary melting tank (11) by heating with a plurality of electrodes (12), thereby providing a secondary melt;(e) flowing said secondary melt to the melting zone (5) through at least one neck (14) separating the at least one secondary melting tank (11) and the melting zone (5) and located at a side-wall (4, 4') of said melting zone;(f) fining, in the fining zone (6), the melt flowing from the melting zone (5), thereby providing a refined melt; and(g) flowing the refined melt from the fining zone (6) to a working zone (14) through outlet means (15).

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

8. Process according to one of claims 6-7, characterized in that cullet ratio in first said batch divided by cullet ratio in said second batch is higher than 1.2, said cullet ratio in second batch being defined as the weight of cullet in second batch compared to the total weight of said second batch.

9. Process according to one of claims 6-8, characterized in that the batch flow rate at charging step (c) is equal to or higher than the batch flow rate at charging step (a).

10. Process according to preceding claim, characterized in that the batch flow rate at charging step (c) is 50% higher than the batch flow rate at charging step (a).

11. Process according to one of claims 6-10, characterized in that said melting step (b) is carried out further by heating with a plurality of electrodes.

12. Process according to one of claims 6-11, characterized in that said melting step (d) is carried exclusively with a plurality of electrodes.

13. Process of revamping a combustion glass furnace, comprising the steps of : providing an existing glass furnace comprising (i) a main tank having end walls and side-walls and having a melting zone and a fining zone; (ii) a plurality of burners and / or thermal plasma torches in said melting zone, (iii) at least one batch charger located at upstream end wall of said melting zone; a working zone and outlet means located downstream of the fining zone; building at least one secondary melting tank equipped with a plurality of electrodes and with at least a top batch charger and connected to said melting tank through at least one neck located at a side-wall of said melting zone.

14. Process according to preceding claim, characterized in that : said existing glass furnace comprises a plurality of burners alimented with air and fuel and at least a pair of regenerators located on either side of said side-walls; the process further comprises : o a step of replacing said plurality of burners in the existing glass furnace so that they are alimented in oxygen and fuel, and o a step of dismantling the at least one regenerator; the at least one secondary melting tank being built at the place of dismantled regenerators.

15. Use of a furnace according to claims 1-5, in a flat glass manufacturing process, preferably in a float glass manufacturing process.