Glass furnace

Abstract

The invention concerns a glass manufacturing furnace comprising (i) a first tank (2) with electrodes (5), (ii) a second tank (6), (iii) a horizontal central batch charger (10) at first tank (2), (iv) a lateral batch charger (11,11',11'') located at first tank (2), (v) a neck (12) with a width WN and separating first tank (2) and second tank (6) and (vi) outlet means (13); wherein the central batch charger (10) has a charging width WC equal to or lower than 11*WN and an axis A passing through (i) the middle of WC and (ii) the middle of WN forms an angle α with WN between 80 and 100°.

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. In particular, the glass furnace is a hybrid furnace allowing an increased electric power for melting glass while keeping good glass quality and relative low energy consumption.

[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.

[0003] The invention also relates to a glass manufacturing process, notably using such an advantageous furnace.BACKGROUND OF THE INVENTION

[0004] 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.

[0005] 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).

[0006] 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 generallyelectrodes 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.

[0007] 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 an all-electrical melter as "cold-top melter", by opposition to classical combustion melter called "hot-top furnaces". Indeed, in such an all-electrical melter, the glass batch is distributed over the whole surface of the tank thereby forming an insulating batch "blanket", cutting heat exchange between the melt and the tank superstructure, thereby causing the temperature to drop from ~1400°C in the glass melt to < 500°C (and possibly down to 50°C) at the top of the blanket and above.

[0008] It is known that the charging of all-electric cold-top melting tanks is more difficult than combustion-heated tanks since complete coverage of the melting surface must be achieved. Generally, such a complete coverage is carried out using a "top batch charger" located above the glass melt and below the crown of the melting tank, with which the batch is distributed on top of the glass melt by a conveyor / distributor arm (also called "boom"), on one or both side(s) of the tank, e.g. being able to move backward and forward as well as sideways so that its successive discharging points effectively cover the whole surface. Such mobile top batch chargers are completely different than "horizontal batch chargers" used in conventional combustion / hot-top melter. Those last ones are located generally at the upstream end-wall of the melting tank and the glass batch is commonly laid down on the glass melt and then, is pushed by pushing means or a "pusher" in a more or less horizontal direction further / downstream in the tank. Those horizontal batch charger are also sometimes called "backwall batch chargers" due to their location in the tank, or "fixed position batch chargers", by opposition to the top batch chargers which are mobile above the melt.

[0009] Unfortunately, "top batch chargers" have severe drawbacks, especially for large glass furnaces like in float installations. First, they are currently limited to lengths of 7-8 meters and it is difficult to evenly cover the complete surface over large melter areas with such top batch chargers. Moreover, the existing large furnaces are generally equipped with standard "horizontal batch chargers" so that their revamping in hybrid / electric melting furnace needs consequent and expensive adaptations related to batch charging. Moreover, such top batch chargers involve an open atmosphere in the melting tank, generating disadvantages like highdilution by air, dust emissions around the tank and heat losses. Finally, they cannot be used in warm-top or hot-top conditions (namely, in combination with burners, that could be considered in order to have more flexibility regarding energy or increase furnace pull

[0010] Some attempts were made to use exclusively a fixed position batch charger located at the upstream end-wall (or backwall) of a full-electric melter, to get "semi-cold" conditions. Nevertheless, these conditions were seldom realized and only when the melter is near its maximum pull rate, leaving low to almost no freedom for adjusting the pull rate upon needs while keeping cold-top conditions. Moreover, this generates a "differential melting" along the length of the tank, which could be tackle partially by strong convection currents to achieve mixing and homogenization of the glass.

[0011] 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 for large flat glass furnaces. "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 start-up, maintenance, hot repair, culleting, ...).

[0012] In general, the use of electricity at the melting step (either in all-electric or in hybrid furnace) is very 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.

[0013] 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.

[0014] 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. One example of adaptation relates to the batch chargers, as discussed above.

[0015] 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).

[0016] Finally, some of the described glass furnaces designed to reduce energy consumption and improve carbon footprint have a negative impact on glass quality.

[0017] 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 glass furnace which shows a decreased CO2 emissions by using more electricity globally, showing an increased flexibility as to the energy, reducing investments needed for its implementation, avoiding as much as possible drawbacks linked to "top batch chargers", while keeping a good glass quality.OBJECTIVE OF THE INVENTION

[0018] 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.

[0019] 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).

[0020] 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.

[0021] It is a further objective of the present invention to provide a glass furnace which allows to produce glass with a good quality and with some flexibility as to energy.

[0022] It is a further objective of the present invention to provide a glass furnace which provides a "cold-top" melter while using horizontal glass batch charger(s).

[0023] It is a further objective of the present invention to provide a glass furnace which provides a melter which may operate cold-top or warm-top, upon needs.

[0024] 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.DESCRIPTION OF THE INVENTION

[0025] The present invention relates to a furnace for manufacturing glass from a glass batch, comprising :- at least a first tank having end-walls and side-walls, said tank being equipped with a plurality of electrodes;- a second tank having end-walls and side-walls, said tank being equipped with a plurality of burners and / or thermal plasma torches;- at least a central glass batch charger located at upstream end-wall of said at least first tank and comprising pushing means, with a glass batch charged with said at least a central glass batch charger forming, when the furnace is in operation, a central glass batch ribbon;- at least a lateral glass batch charger located at said at least a first tank;- a neck having a neck width WN and connecting downstream end-wall of said at least a first tank and upstream end-wall of said second tank;- outlet means located at downstream end-wall of said second tank; wherein:- said at least a central glass batch charger has a charging width Wc which is equal to or lower than 1.1*WN ; and- an axis A passing through (i) the middle Me of the charging width Wcand (ii) the middle MN of the neck width WN forms an angle a with the neck width WN ranging between 80 and 100°.

[0026] Hence, the invention is based on a novel and inventive approach. In particular, the inventors have found that a segmented furnace with a neck separating an electrically-heated melting tank and a flame-heated tank (at least for fining) with the combination of a central "standard" horizontal batch charger and lateral batch charger(s) together with a very specific configuration between the central batch charger and the neck (aligned and sized specifically), makes 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 glass furnaces,(ii) improving energy efficiency,(iii) being flexible as to the energy used (electrical / combustion),(iv) allowing to keep the existing standard horizontal batch chargers, with the advantages this brings regarding investment, no limitation in furnace size / width and closed atmosphere,(v) allowing to operate cold-top or warm-top during melting stage, upon needs, and(vi) keeping a good glass quality.

[0027] The specific central horizontal batch charger aligned and sized specifically in view of the neck allows to push the batch, in continuous ribbon or consecutive logs, in the melter / first tank towards the neck while ensuring smooth conveying of the batch logs / ribbon in the neck, and preventing batch deviation and / or conglomeration upstream or inside the neck. Next, the lateral glass batch charger(s) brings glass batch in order to achieve complete coverage of the melting area, to create the "cold-top" conditions and its above-cited advantages.

[0028] Moreover, advantageously, the charging with the central glass batch charger, facing / aligned with the neck, allows to adjust the total pull of the furnace by conducting a part of the batch towards the neck (and even the second tank), thereby ensuring that the first tank is always fully covered by a batch blanket. The possible melting of the batch in the neck / the second tank acts as a buffer for pull variations and this allows more flexibility for temperature management in the first tank. Indeed, pull can be managed independently from the glass temperature in the first tank (which is not the case in cold top furnaces where the glass temperature determines the achievable pull).

[0029] Next, the furnace of the invention allows also to have a furnace total length, i.e. comprising the lengths of said first tank, neck and second tank equivalent to the length of an existing conventional fuel-fired furnace, while maintaining the same pull capacity and glass quality, therefore also keeping the position of the existing batch conveyors and feeding installations unchanged in the case of revamping / conversion of an existing fuel-fired furnace to the described segmented hybrid furnace.

[0030] As to energy flexibility : the design of the invention gives a furnace showing more flexibility in the amount of electricity use in the first (melting) tank that (i) can operate in cold- top (full electric) or in warm-top (if a burners / plasma torches / radiative electrical heaters are added) conditions and (ii) with lower temperatures (and less electrical power) if one wants to melt a bigger part of the batch by combustion in the second tank.

[0031] As to furnace temperatures and lifetime: as explained above, the glass tank temperatures in the first (melting) tank could be lowered in order to decrease wear of therefractories. Moreover, the presence of batch in the neck and potentially in the upstream area of the second tank allows to decrease its bottom temperatures.

[0032] As to furnace atmosphere: the use of horizontal batch charger(s) in the first (melting) tank allows having an improved air sealing and therefore a better control of its atmosphere, avoiding high dilution by air and / or avoiding dust emissions around the first tank and heat losses, and possibly also allows easier CO2 capture from said melting tank, upon needs.

[0033] It is also to be noted that, next to all the above cited advantages, the furnace of the invention, with its segmentation, brings also the intrinsic advantages linked to the segmentation / presence of the neck.

[0034] The invention also relates to a process for manufacturing glass products from a glass batch in a furnace comprising (i) at least a first tank having end-walls and side-walls and (ii) a second tank having end-walls and side-walls, said process comprising the steps of, from upstream to downstream :(a) charging a first portion of said glass batch in said at least first tank through at least a central glass batch charger located at upstream end-wall of said first tank and comprising pushing means, thereby forming a central glass batch ribbon;(b) charging a second portion said glass batch in said at least first tank through at least a lateral glass batch charger located at said first tank, to cover the surface of said tank which is not covered by said central glass batch ribbon;(c) melting at least a part of the glass batch in said first tank by heating with a plurality of electrodes, thereby providing a glass melt;(d) flowing the glass melt and the remaining part of the glass batch through a neck having a width WN and connecting downstream end-wall of said first tank and upstream endwall of said second tank;(e) melting at least a part of said remaining part of the glass batch in said neck;(f) flowing the glass melt to said second tank;(g) fining the glass melt in said second tank by heating with a plurality of burners and / or thermal plasma torches, thereby providing a refined glass melt; and(h) flowing the refined melt through outlet means from said second tank to a working zone; wherein :said at least a central glass batch charger has a charging width Wc which is equal to or lower than 1.1*WN ; and an axis A passing through (i) the middle Me of the charging width Wc and (ii) the middle MN of the neck width WN forms an angle a with the neck width WN ranging between 80 and 100°.

[0035] Finally, the invention also relates to the use of a furnace according to the invention in a flat glass manufacturing process.

[0036] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments and following figures:FIG. 1 is a schematic plan view (horizontal cross-section) of an embodiment of a furnace according to the invention.FIG. 2 is a schematic plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.FIG. 3 is a schematic plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.FIG. 4 is a schematic plan view (horizontal cross-section) of another embodiment of a furnace according to the invention.

[0037] 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.

[0038] 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 tanks (2) and (6) 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 " main glass stream"), from the upstream end-walls of the first tank (2) 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 (as indicated by an arrow). By "width" in the invention, it is meant,unless otherwise specified, the dimension or the segment taken perpendicularly to the main glass stream.

[0039] By the expression "manufacturing glass" and as commonly adopted in the art, it is intended a process that allows manufacturing glass articles like glass sheets, esp. float glass sheets, or glass containers, at least through melting of a glass batch in a furnace followed by a fining.

[0040] By the term "glass batch", it is intended herein the meaning given commonly in the related glass field, 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 in the invention 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 emission occurring 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.

[0041] In the furnace of the invention, the at least a first tank (2) has end-walls (3,3') and sidewalls (4,4'). The first tank (2) of the invention is used to melt at least a part of the charged glass batch and acts as a "melter". For example, the surface area of the tank (2) in the invention may range from 25 to 400 m2.

[0042] In an embodiment, the crown of said at least a first tank (2) is a suspended flat crown. This allows to better control temperature variations in case of cut-off of batch charging (like in a standard cold-top melter), for example following a production incident or in the case of a temporary stop of the production.

[0043] Generally, a glass (melting) tank has, in horizontal cross-section, a rectangular or square shape (90° angle between two contiguous walls, an end-wall and a side-wall). In an embodiment of the invention, the at least a first tank (2) may have a form, in horizontal crosssection, which deviates from a rectangular or square shape. For example, it may have atrapezoidal shape, with the angle between its downstream end-wall (3') and each of its sidewalls (4;4') being lower than 90°, preferably lower than 85°. This is advantageous as it allows to guide said central glass batch ribbon towards said neck (12).

[0044] In an advantageous embodiment, the at least a first tank (2) comprises guiding means configured to float on a glass melt when the furnace is in operation and to guide the central glass batch ribbon from the at least a central glass batch charger (10) towards the neck (12). For example, such guiding means may take the form of at least two parallel bars, e.g. made of graphite, spaced apart from a distance lower than but close to the neck width WN.

[0045] According to the invention, said at least a first tank (2) is equipped with a plurality of electrodes (5). The electrodes (5) are immersed and possibly located at the bottom of the at least a first tank (2).

[0046] The "bottom electrodes" are advantageously arranged according to a specific pattern (e.g., checkerboard), in order to facilitate connection to transformers and electric current balance. For example, their height is between 0.3 and 0.8 times glass melt height.

[0047] Alternatively, the electrodes (5) according to the invention extends from the top of the first tank (2) (for example, maintained commonly by a water-cooled holder) and are immersed. These "top electrodes" are advantageously located along the edge of the tank and / or at the corner(s).

[0048] The number of electrodes 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.

[0049] In an embodiment, a counter-reaction device may be arranged in the at least a first 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.

[0050] According to an embodiment, next to the plurality of electrodes (5), said at least a first tank (2) may comprise further at least a burner and / or at least a plasma torch and / or at least a radiative electrical heater. Such an embodiment is advantageous to create a "warm-top" melter / tank, in orderto increase the melting rate if desired. Such an embodiment include also the possibility to arrange one or several temporary burner(s) and / or plasma torch(es) 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.

[0051] According to the invention, said second tank (6) has end-walls (7,7') and side-walls (8,8'), said tank being equipped with a plurality of burners (9) and / or thermal plasma torches located, preferably located at said side-walls (8,8'). For example, the surface area of said second tank (6) in the invention may range from 25 to 400 m2.

[0052] In the furnace of the invention, the second tank (6) is used at least to refine the melt / molten glass that has been melted in the first tank (2) and in the neck (12), in order to reach glass quality specifications, esp. for float glass. As commonly adopted in the glass art, by "fining", it is meant a step during which there is no more glass batch left and the glass melt is heated at temperatures higher than melting 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 step is also commonly called "clarification tank" in the art. In an embodiment, the second tank (6) may comprise bubblers (not illustrated in FIGS), commonly arranged in the width of said tank, roughly in line(s), as commonly used in a fining step of a glass melt.

[0053] Next to the fining, optionally, said second tank (6) may, in some cases and in its upstream part, be used to melt the part of glass batch that has been melted neither in the first tank (2) nor in the neck (12).

[0054] According to an embodiment, said second tank (6) is equipped with a plurality of burners (9), as illustrated in FIGS. 1-4, preferably located at said side-walls (8,8'), in particular arranged along said side-walls (8,8') on each side thereof. The plurality of burners according to the invention 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).

[0055] According to another embodiment, said second tank (6) is equipped with a plurality of thermal plasma torches, configured to emit from a working fluid a plasma flame above the bath / melt in the 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,...) orelectromagnetic (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).

[0056] According to still another embodiment, said second tank (6) is equipped with a plurality of burners (9) and a plurality of thermal plasma torches.

[0057] Advantageously, said second tank (6) 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, the electrodes according to this embodiment are located at the bottom of the second tank (6).

[0058] Generally and as commonly known in the art, the second tank (6) may comprise an immersed wall (or damwall) (not illustrated in FIGS), in order to reduce the flow of relatively cold glass coming back from the working-end to said tank (good for energy consumption), and to stabilize the glass convection pattern in the melt (good for process stability).

[0059] The furnace of the invention comprises a neck (12), having a width WN, connecting downstream end-wall (3') of said at least a first tank (2) and upstream end-wall (7) of said second tank (6) or, in other words, separating the at least first tank (2) and said second tank (6). According to the invention, by a "neck" connecting downstream end-wall (3') of said at least a first tank (2) and upstream end-wall (7) of said second tank (6), it is meant :- a narrowing in width compared to the first tank (2);- a narrowing in width compared to the second tank (6); and- 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.

[0060] Preferably, the crown height of the neck (12) is at the same level as or lower than the crown height of said first tank (2). Preferably also, the crown height of the neck (12) is lower than the crown height of said second tank (6).

[0061] The neck (12) in the invention provides a furnace design with a segmentation of the first tank(s) (melting) and the second tank (fining), which brings a lot of advantages in favour of energy consumption / CCh emissions and in favour of mechanical stability / lifetime of thefurnace. Moreover, advantageously, this furnace with its specific segmented design allows to deal with flue gas from first tank and flue gas from second tank independently, if desired.

[0062] The base (or floor) of the neck (12) in the invention may be located essentially at the level of the floor / bottom of the first tank (2), or above said level or below said level. Moreover, the base of the neck (12) may be located essentially at the level of the floor / bottom of the second tank (6), or above said level or below said level. Preferably, the base of the neck (12) in the invention is located above the level of the floor / bottom of the first tank (2). Preferably also, the base of the neck (12) in the invention is located above the level of the floor / bottom of the second tank (6). Very preferably, the base of the neck (12) is located above the level of the floor / bottom of the first tank (2) and of the second tank (6). This is advantageous in order to reduce the intensity of the glass flowing back from the second tank to the neck.

[0063] According to the invention, the furnace comprises at least a central glass batch charger (10) located at upstream end-wall (3) of said at least first tank (2), said at least a central glass batch charger (10) comprising pushing mean.

[0064] Due to its location and the existence of a "pusher", as explained above, this means that such a batch charger (10) is of the type "horizontal batch charger". Generally, upstream of such a batch charger, there is a charging hopper / silo: the glass batch is (i) discharged from the hopper by gravity to an intermediate / smaller batch hopper and / or a batch table that acts to lay down the batch which is then pushed, by pushing means, in a more or less horizontal direction further / downstream in the first tank (2) on the glass melt. The pushing means according to the invention is, for example, a spade, a paddle or a pushing bar, notably water- cooled.

[0065] In the invention, a glass batch charged with said at least a central glass batch charger (10) forms, when the furnace is in operation, a central glass batch ribbon. Such a central glass batch ribbon according to the invention may be a continuous glass batch ribbon and / or in the form of consecutive glass batch logs, contiguous or spaced apart. The central glass batch ribbon is illustrated at FIGS. 3 and 4, in the form of contiguous and spaced apart glass batch logs (14).

[0066] According to the invention, the at least a central glass batch charger (10) is configured / designed so that :- it has a charging width Wc which is equal to or lower than 1.1*WN., preferably equal to or lower than 1.05*WN; and- an axis A passing through (i) the middle Me of the charging width Wc and (ii) the middle MN of the neck width WN forms an angle a with the width WN ranging between 80 and 100°, preferably between 85 and 95° and, more preferably, between 87 and 93°.

[0067] The middle M of a width W herein will be easily understood and means the middle of the segment corresponding to the width W. As well, to assess the angle a, one takes the angle between the axis A and the segment corresponding to the width WN. The elements WN, MN, Wc, Me, A, a are illustrated for different embodiments of the invention in FIGS. 1-4. In each FIG., the angle a is roughly equal to 90°.

[0068] The two above conditions allow :(i) that the central glass batch ribbon, in the form a continuous ribbon or consecutive logs, has a width when arriving at the neck (12) which is lower than the neck width WN (and lower than the maximum width of the central glass batch ribbon due to progressive meting and size decreasing); and(j) that the batch charging is almost or fully aligned with the neck (12).

[0069] Hence, the central glass batch ribbon can advantageously enterthe neck (12) smoothly, without deviation and / or conglomeration upstream or inside said neck.

[0070] In the invention, the neck (12) therefore receives a part of the charged glass batch, which means that melting still occurs in the neck (12). For such reason, advantageously, said neck (12) may comprise at least a burner and / or at least a plasma torch and / or at least a radiative electrical heater.

[0071] In the invention, by the "charging width, Wc" of the at least a central glass batch charger (10), it is meant the width over which the glass batch is charged inside the first tank (2) and roughly the maximum width of the central glass batch ribbon. This width is, for example, in case the glass batch is discharged on a table, the width of the table delimited by its two lateral and vertical walls / plates.

[0072] According to an embodiment, the furnace may comprise more than one central glass batch charger (10), for example, two, three, four or more, preferably contiguous. In such a case, the charging width Wc according to the invention corresponds to the sum of the individual charging width Wcx of each central glass batch charger (Wc = Wei + Wc2 + Wc3 + ...).

[0073] FIGS. 1-3 illustrate the embodiment where there is one central glass batch charger (10) and FIG. 4 illustrates the embodiment where there are two central glass batch chargers (10).

[0074] In an embodiment, said neck (12) comprises means for slowing down the central glass batch ribbon. This is advantageous especially when the central glass batch ribbon is in the form of individual and consecutive logs, because slowing down those logs will allow to tighten them in case too much spacing occurs, to ensure keeping full coverage of the surface of the first tank (2) (for cold-top conditions). Such means may be, for example, a barrier or curtain, notably in refractory material or in water cooled steel, placed in the neck above the surface of the glass melt level, so as to slow down the batch logs moving downstream in the neck, but still allowing them to pass through. An alternative option is to use a mobile barrier that cyclically moves vertically. The vertical position of the mobile barrier and / or the frequency of vertical movements can be adapted in order to control the coverage in the first tank (2).

[0075] According to the invention, the furnace comprises at least a lateral glass batch charger (11, 11', 11”) located at said at least a first tank (2). By "lateral glass batch charger" in the invention, it is meant a batch charger able to charge glass batch to cover the surface of the first tank (2) which is not covered by the central glass batch ribbon (produced by said central glass batch charger(s)).

[0076] The at least a lateral glass batch charger in the invention may be :- either at least a lateral top glass batch charger (11”);- or at least two lateral glass batch chargers (11, 11') located at upstream end-wall (3) of said at least a first tank (2), each comprising pushing means and being located on each side of said at least a central glass batch charger (10).

[0077] FIGS. 1,3-4 illustrate the embodiment where the furnace comprises two lateral glass batch chargers (11, 11') located at upstream end-wall (3) of said at least a first tank (2). FIG. 2 illustrate the embodiment where the furnace comprises a top batch charger (11”).

[0078] In the embodiment wherein the at least a lateral glass batch charger is at least two lateral glass batch chargers (11, 11') located at upstream end-wall (3) of said at least a first tank (2): Due to their location and the existence of a "pusher", this means that they are of the type "horizontal batch charger", as described above.

[0079] In this embodiment, each of the two lateral glass batch charger (11, 11') is able to charge glass batch to coverthe surface of the first tank (2) which is not covered by said central glass batch ribbon, one for the left side, the other one for the right side of said ribbon.

[0080] According to this embodiment, there may be more than two lateral glass batch chargers located at upstream end-wall (3) of said at least a first tank (2) and comprising apushing means. For example, there may be two (or more) such lateral glass batch chargers on the left side of the central glass batch charger(s) (10) and two (or more) such lateral glass batch chargers on the right side of the central glass batch charger(s).

[0081] In the embodiment wherein the at least a lateral glass batch charger is at least a lateral top glass batch charger (11"):

[0082] By "top glass batch charger" and as commonly adopted in the glass art, it is meant a batch charger located above the glass melt and below the crown of the tank and allowing to charge the batch directly on the top of glass melt. In the invention, it may for example be of the type "rotating batch charger" or "linear X-Y-batch charger", preferably a "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)). In this embodiment, the furnace may comprise only one lateral top glass batch charger (11”), able to charge glass batch to cover the surface of the tank (2) which is not covered by said central glass batch ribbon (the left and the right sides of said ribbon). Still in this embodiment, alternatively, the furnace may comprise two lateral top glass batch chargers (11”), each being able to charge glass batch to cover the surface of the first tank (2) which is not covered by said central glass batch ribbon, one for the left side, the other one for the right side of said ribbon. When the furnace comprises lateral top glass batch charger(s), then it can be advantageous as it allows to use "top electrodes" in the first tank (2), with reduced risk for bottom wear and leakages in such a case. Moreover, such lateral top glass batch charger(s) allows better control of batch coverage on each side of the central glass batch ribbon, ensuring the desired full coverage for cold-top conditions. Nevertheless, as already exposed above, such top glass batch chargers in general are more expensive, generates an open furnace atmosphere and prevent from any possibility of warm- top conditions (if burner and / or plasma torch at the first tank).

[0083] The furnace (1) of the invention comprises outlet means (13) located at downstream end-wall (7') of said second tank (6). These outlet means are preferably configured to flow the (refined) melt from the tank (6) to a working zone (not illustrated in FIGS). According to an embodiment and as illustrated in FIGS. 1-4, the outlet means are composed of an outlet neck or, alternatively, an outlet throat, in order to lead the melt towards said working zone.

[0084] According to an embodiment of the invention, the furnace comprise two first tanks (2). In such a case, each tank (2) comprises at least a central glass batch charger (10), at leasta lateral glass batch charger (11, 11', 11”) and a neck (12). In this embodiment, the two first tanks (2), the two necks (12), the central glass batch chargers (10) and the lateral glass batch chargers (11, 11', 11”) are in accordance with the invention and they may be the same or different, in their dimensions and / or design, between one first tank and the other one.

[0085] According to another embodiment, the at least a first tank (2) may comprise means for assessing a thickness of a batch blanket present on the surface of a glass melt, for example means for observing and / or measuring a thickness of a batch blanket. Preferably, such means are installed in the downstream half of the at least a first tank (2). This is advantageous in order to adjust the glass batch charging rates, notably at the at least a lateral glass batch charger (11, 11', 11”), in order to ensure that a batch blanket covers the whole surface of said first tank (2). For example, a laser or a thermographic camera may be used as such means for assessing a thickness.

[0086] The process of the invention is for manufacturing glass products, for example glass sheets, from a glass batch in a furnace (1) comprising (i) at least a first tank (2) having endwalls (3,3') and side-walls (4,4') and (ii) a second tank (6) having end-walls (7,7') and sidewalls (8,8').

[0087] The process comprises the steps of, from upstream to downstream :(a) charging a first portion of said glass batch in said at least first tank (2) through at least a central glass batch charger (10) located at upstream end-wall (3) of said first tank (2) and comprising pushing means, thereby forming a central glass batch ribbon;(b) charging a second portion said glass batch in said at least first tank (2) through at least a lateral glass batch charger (11, 11', 11”) located at said first tank (2), to cover the surface of said tank (2) which is not covered by said central glass batch ribbon;(c) melting at least a part of the glass batch in said first tank (4) by heating with a plurality of electrodes (5), thereby providing a glass melt;(d) flowing the glass melt and the remaining part of the glass batch through a neck (12) having a width WN and connecting downstream end-wall (3') of said first tank (2) and upstream end-wall (7) of said second tank (6);(e) melting at least a part of said remaining part of the glass batch in said neck (12);(f) flowing the glass melt to said second tank (6);(g) fining the glass melt in said second tank (6) by heating with a plurality of burners (9) and / or thermal plasma torches, thereby providing a refined glass melt; and(h) flowing the refined melt through outlet means (13) from said second tank (6) to a working zone.

[0088] Specifically, in the process of the invention:- the at least a central glass batch charger (10) has a charging width Wc which is equal to or lower than 1.1*WN., preferably equal to or lower than 1.05*WN; and- an axis A passing through (i) the middle Me of the charging width Wc and (ii) the middle MN of the neck width WN forms an angle a with the width WN ranging between 80 and 100°, preferably between 85 and 95° and, more preferably, between 87 and 93°.

[0089] The process is thus advantageously carried out with operating the furnace (1) of the invention.

[0090] Features and embodiments described above in relation with the furnace (1), for example for the at least first tank (2), the second tank (6), the neck (12), the central and lateral glass batch chargers, the outlet means (13), etc. are applicable to the process of the invention as well.

[0091] According to the process of the invention, melting occurs therefore in the at least a first tank (2) and also in the neck (12). Through adjustment of the total pull of the furnace, this ensures, combined with the other features of the furnace / process, esp. the lateral charging, a full coverage of the surface of the first tank (2) by glass batch, providing cold-top conditions. Moreover, the melting of a part of the batch in the neck acts as a buffer for pull variations and this allows more flexibility for temperature management in the first tank, as already explained above. Finally, the presence of batch in the neck allows to decrease / control its bottom temperatures.

[0092] In an embodiment, the step (e) of melting in said neck (12) is a step of melting all said remaining part of the glass batch. This means that at the end of the neck (12), all the charged glass batch is melted and that essentially no melting occurs in the second tank (6). Alternatively, in another embodiment, the process of the invention may comprise, after step (f) and before step (g), a step of melting at least a part of said remaining part of the glass batch in said second tank (6). According to this embodiment, this means that some glass batch exits the neck (12) and arrives in the second tank (6) where it is melted, and therefore, melting occurs in the first tank (2), in the neck (12) and also in the upstream part of the second tank (6). This is advantageous as, like for the neck, (i) it provides a buffer for pull variations and therefore more flexibility for temperature management in the first tank and (ii) the presenceof batch in the second tank (upstream part) allows to decrease / control its bottom temperatures.

[0093] In another embodiment, said melting step (c) in the process of the invention is carried out by heating further with at least a burner and / or at least a plasma torch and / or at least a radiative electrical heater. This is advantageous as it allows to create, upon needs, "warm- top" conditions in the first tank, in order to increase the melting rate if desired.

[0094] In the process of the invention, said first portion and said second portion of the glass batch may be the same or different, in their composition, nature and in their charging rate.

[0095] Advantageously, the process of the invention may further comprise a step of slowing down said central glass batch ribbon inside the neck (12). As explained above in relation with the furnace of the invention, this is advantageous especially when the central glass batch ribbon is in the form of individual logs, because slowing down those logs will ensure keeping full coverage of the surface of the first tank (2) by tightening them. This step of slowing down may be done by using, for example, a barrier or curtain, notably in refractory material or in water cooled steel, placed in the neck (12) above the surface of the glass melt level, so as to slow down the batch logs moving downstream in the neck, but still allowing them to pass through. An alternative option is to use a mobile barrier that cyclically moves vertically. The vertical position of the mobile barrier and / or the frequency of vertical movements can be adapted in order to control the coverage in the first tank (2).

[0096] Advantageously also, the process of the invention may further comprise a step of adjusting, independently, the batch charging rates at the at least a central glass batch charger and at the at least a lateral glass batch charger. This allows to better ensure full coverage of the surface of said first tank (2) by glass batch, to reach the cold-top conditions.

[0097] In an embodiment, the process of the invention further comprises a step of assessing a thickness of the glass batch at the surface of the glass melt in the at least a first tank (2). This step of assessing may comprise observing and / or measuring the thickness of the glass batch (batch blanket). This can be done by using for example, a thermographic camera and / or a laser. Preferably, this step is carried down in the downstream half of the at least a first tank (2). Such a step is advantageous as the data it provides allow to adjust the glass batch charging rates, notably at the at least a lateral glass batch charger, in order to ensure that a batch blanket covers the whole surface of the first tank (2).

[0098] Finally, the invention also relates to the use of a furnace (1) according the invention, in a flat glass manufacturing process, preferably in a float glass manufacturing process. In this last embodiment, downstream of the working zone, the furnace (1) comprises further a float installation, including notably and as known a tin bath.

[0099] 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 from a glass batch, comprising :- at least a first tank (2) having end-walls (3,3') and side-walls (4,4'), said tank being equipped with a plurality of electrodes (5);- a second tank (6) having end-walls (7,7') and side-walls (8,8'), said tank being equipped with a plurality of burners (9) and / or thermal plasma torches;- at least a central glass batch charger (10) located at upstream end-wall (3) of said at least first tank (2) and comprising pushing means, with glass batch charged with said at least a central glass batch charger (10) forming, when the furnace is in operation, a central glass batch ribbon;- at least a lateral glass batch charger (11, 11', 11”) located at said at least a first tank (2);- a neck (12) having a neck width WN and connecting downstream end-wall (3') of said at least a first tank (2) and upstream end-wall (7) of said second tank (6);- outlet means (13) located at downstream end-wall (7') of said second tank (6); characterized in that : said at least a central glass batch charger (10) has a charging width Wc which is equal to or lower than 1.1*WN; and an axis A passing through (i) the middle Me of the charging width Wc and (ii) the middle MN of the neck width WN forms an angle a with the neck width WN ranging between 80 and 100°.

2. Furnace according to the preceding claim, characterized in that said axis A forms an angle a with the neck width WN ranging between 85 and 95°, preferably, between 87 and 93°.

3. Furnace according to one of the preceding claims, characterized in that said central glass batch ribbon is a continuous glass batch ribbon and / or is in the form of consecutive glass batch logs (14), contiguous or spaced apart.

4. Furnace according to one of the preceding claims, characterized in that said at least a lateral glass batch charger (11, 11', 11”) is :- either at least a lateral top glass batch charger (11”);- or at least two lateral glass batch chargers (11, 11') located at upstream end-wall (3) of said at least first tank (2), each comprising pushing means and being located on each side of said at least a central glass batch charger (10).

5. Furnace according to one of the preceding claims, characterized in that said neck (12) comprises means for slowing down said central glass batch ribbon.

6. Furnace according to one of the preceding claims, characterized in that said at least a first tank (2) comprises further at least a burner and / or at least a plasma torch and / or at least a radiative electrical heater.

7. Furnace according to one of the preceding claims, characterized in that said neck (12) comprises at least a burner and / or at least a plasma torch and / or at least a radiative electrical heater.

8. Furnace according to one of the preceding claims, characterized in that said at least a first tank (2) comprises guiding means configured to float on a glass melt when the furnace is in operation and to guide said central glass batch ribbon from the at least a central glass batch charger (10) towards the neck (12).

9. Process for manufacturing glass products from a glass batch in a furnace (1) comprising (i) at least a first tank (2) having end-walls (3,3') and side-walls (4,4') and (ii) a second tank (6) having end-walls (7,7') and side-walls (8,8'), said process comprising the steps of, from upstream to downstream :(a) charging a first portion of said glass batch in said at least first tank (2) through at least a central glass batch charger (10) located at upstream end-wall (3) of said first tank (2) and comprising pushing means, thereby forming a central glass batch ribbon;(b) charging a second portion said glass batch in said at least first tank (2) through at least a lateral glass batch charger (11, 11', 11'') located at said first tank (2), to cover the surface of said tank (2) which is not covered by said central glass batch ribbon;(c) melting at least a part of the glass batch in said first tank (4) by heating with a plurality of electrodes (5), thereby providing a glass melt;(d) flowing the glass melt and the remaining part of the glass batch through a neck (12) having a width WN and connecting downstream end-wall (3') of said first tank (2) and upstream end-wall (7) of said second tank (6);(e) melting at least a part of said remaining part of the glass batch in said neck (12);(f) flowing the glass melt to said second tank (6);(g) fining the glass melt in said second tank (6) by heating with a plurality of burners (9) and / or thermal plasma torches, thereby providing a refined glass melt; and(h) flowing the refined melt through outlet means (13) from said second tank (6) to a working zone; characterized in that : said at least a central glass batch charger (10) has a charging width Wc which is equal to or lower than 1.1*WN ; and an axis A passing through (i) the middle Me of the charging width Wc and (ii) the middle MN of the neck width WN forms an angle a with the neck width WN ranging between 80 and 100°.

10. Process according to preceding claim, characterized in that it further comprises, after step (f) and before step (g), a step of melting at least a part of said remaining part of the glass batch in said second tank (6).

11. Process according to one of claims 9-10, characterized in that said melting step (c) is carried out by heating further with at least a burner and / or at least a plasma torch and / or at least a radiative electrical heater.

12. Process according to one of claims 9-11, characterized in that it further comprises a step of slowing down said central glass batch ribbon inside the neck (12).

13. Process according to one of claims 9-12, characterized in that it further comprises a step of adjusting, independently, the batch charging rates at the at least a central glass batch charger and at the at least a lateral glass batch charger.

14. Process according to one of claims 9-13, characterized in that it further comprises a step of assessing a thickness of the glass batch at the surface of the glass melt in the at least a first tank (2).

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

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