METHOD AND HYBRID OVEN FOR THE PRODUCTION OF GLASS WITH AN ELECTRIC MELTING ZONE

Description

Technical field of the invention

[0001] The invention relates to a process and a hybrid furnace for the manufacture of glass comprising an electrical melting zone.

[0002] The invention relates more particularly to a hybrid glass manufacturing furnace further comprising an electric melting zone with a cold vault for melting a vitrifiable mixture to which is associated a refining and homogenizing zone with a hot vault comprising two glass convection belts in order to obtain high quality glass.

[0003] The invention also relates to a method for manufacturing glass in such a hybrid furnace for glassmaking.

[0004] The process and hybrid furnace for glassmaking according to the invention delivers high-quality glass which is particularly suitable for supplying glass to a glass flotation unit on a molten metal bath intended for the manufacture of flat glass. Technical background

[0005] We know of the state of the art various examples of furnace design for glass manufacturing which depend in particular on the product to be manufactured, i.e. the final shaping of the glass.

[0006] Thus, different furnace designs are distinguished depending on whether the production envisaged concerns glass fibers, industrial forming of hollow glass or that of flat glass.

[0007] One of the industrial challenges in the design of glass furnaces is to be able to obtain glass whose quality requirements depend on the product; in this respect, the production of flat glass is comparatively one of the most demanding.

[0008] Produced in very large quantities, flat glass is used in many applications due to its versatility, notably widely used in the electronics sector (flat screens) or in the construction and automotive sectors where this glass can be transformed using a wide variety of techniques (bending, tempering, etc.), thus constituting a basic glass for a whole range of glass products.

[0009] In proportion to the challenges of both quality and quantity, the present invention is therefore particularly aimed at the manufacture of glass for the industrial forming of such flat glass, which glass is conventionally obtained by means of a glass flotation unit on a bath of molten metal, generally tin, which is why such flat glass is also called float glass or "float" according to the English term.

[0010] For the manufacture of flat glass, it is expected that the flotation unit or "float" can be supplied with high-quality glass, i.e., glass containing the fewest unmelted particles and bubbles possible, generally glass with less than 0.5 bubbles per liter.

[0011] Indeed, the quality of glass is determined, in particular but not exclusively, by the number of bubbles present in the glass, expressed in "bubbles per liter." Thus, the quality of a glass is considered higher the lower, or even the more minute, the number of bubbles per liter it contains.

[0012] Furthermore, it is recalled that the presence of bubbles (or gaseous defects) in glass is inherent to the glass manufacturing process in which three successive stages or phases are generally distinguished: melting, refining and homogenization, and thermal conditioning of the glass.

[0013] The presence of bubbles in glass results from the melting stage, during which a glassable mixture, also called a "composition," is melted. This glassable mixture consists of raw materials, such as a mixture of sand, limestone (calcium carbonate), sodium carbonate, and dolomite for the production of soda-lime glass (the most commonly used type of glass for flat glass). Cullet (also called grout), made up of glass fragments, is advantageously added to facilitate melting.

[0014] The vitrifiable mixture is transformed into a liquid mass in which even the least miscible particles dissolve, i.e. those richest in silicon dioxide or silica (SiO2) and poor in sodium oxide (Na2O).

[0015] Sodium carbonate (Na₂CO₃) begins to react with sand grains at temperatures above 775°C, releasing carbon dioxide (CO₂) bubbles in a liquid that becomes increasingly viscous as the carbonate transforms into silicate. Similarly, the transformation of limestone grains into lime and the decomposition of dolomite also release carbon dioxide (CO₂).

[0016] The melting stage is complete when there are no more solid particles in the molten glass liquid which has become very viscous but which, at this stage of the manufacturing process, is then filled with air and gas bubbles.

[0017] The refining and homogenization stage then allows the elimination of these bubbles present in the molten glass. It is well known that "refining agents" are advantageously used during this stage; these are substances in low concentrations which, by decomposing at the melting temperature of the bath, provide gases that cause the bubbles to inflate, thus accelerating their rise to the surface of the glass.

[0018] The thermal conditioning stage of the manufacturing process then makes it possible to lower the temperature of the glass since, at the beginning of the shaping operation, the viscosity of the glass generally has to be at least ten times higher than during refining.

[0019] There is obviously a correspondence between each of the glassmaking stages that have just been described and the structure of a furnace intended for their implementation.

[0020] Generally, such a glassmaking furnace thus includes successively a melting zone in which the transformation by melting of the vitrifiable mixture into a glass bath takes place, then a refining and homogenizing zone to eliminate bubbles from the glass, and finally a thermal conditioning zone used to cool the glass to bring it to the forming temperature, which is much lower than the temperatures experienced by the glass during its production.

[0021] One key point to remember from the glassmaking process just mentioned is that the melting stage is accompanied by the emission of carbon dioxide (CO2), one of the main greenhouse gases involved in climate change.

[0022] Apart from the manufacture of high-quality glass, as well as the industrial challenges of high productivity with the lowest possible cost of building and operating furnaces, one of the other major challenges that the glass industry must face is currently ecological, namely the need to find solutions to reduce the carbon footprint (in English "CO2 footprint") linked to the glass manufacturing process.

[0023] To achieve a carbon neutrality objective, a comprehensive approach to the process is preferred, seeking to act on multiple levers to reduce both direct emissions during manufacturing and indirect emissions, as well as emissions upstream and downstream in the value chain, for example those related to the transport of materials upstream and then the product downstream.

[0024] Therefore, the multiple levers include product design and material composition, improving the energy efficiency of industrial processes, using renewable and decarbonized energy, collaborating with raw material suppliers and transporters to reduce their emissions, and finally, exploring technologies for capturing and sequestration residual emissions.

[0025] In direct emissions, in addition to those inherent in the glass manufacturing process mentioned previously, the type of energy used, particularly for the high-temperature melting stage (over 1500°C), represents the largest share of the carbon footprint of the glass manufacturing process, since it is generally a fossil fuel, most often natural gas, or even petroleum products such as fuel oil.

[0026] Therefore, the search for new furnace designs must not only meet industrial challenges related to glass quality but also reduce the carbon footprint of the glassmaking process, both direct and indirect emissions of carbon dioxide (CO2), and this by reducing in particular the use of fossil energy(s).

[0027] Glassmaking is carried out in furnaces which have constantly evolved from the first pot (or crucible) furnaces to the Siemens furnace which is usually considered the ancestor of today's large continuous casting glass furnaces, such as transverse burner furnaces capable of producing up to 1200 tons of float glass per day.

[0028] The choice of energy used for melting thus leads to distinguishing mainly two major designs of furnace for glassmaking, respectively flame furnaces and electric furnaces.

[0029] According to the first design, flame furnaces generally use fossil fuels, including natural gas for the burners, with thermal energy thus transferred to the glass by heat exchange between the flames and the surface of the glass bath.

[0030] The aforementioned transverse burner furnaces are an example of a furnace according to this first design and are widely used to supply molten glass to a flotation or "float" unit intended for the manufacture of flat glass.

[0031] According to the second conception, electric furnaces are furnaces in which thermal energy is produced by Joule effect in the mass of molten glass.

[0032] Indeed, glass, an insulating substance at room temperature, becomes electrically conductive at high temperatures, so that it is possible to consider using the Joule effect within the glass molten glass itself to heat it.

[0033] However, electric furnaces are used, for example, for the production of special glasses such as fluoride opal glass or lead crystal, or are commonly used for the manufacture of glass fibers for thermal insulation.

[0034] Indeed, it is commonly accepted by those skilled in the art that such electric furnaces are not able to supply, either in quantity or especially in quality of glass (remember less than 0.5 bubbles per liter), a glass flotation unit on a molten metal bath intended for the manufacture of flat glass.

[0035] This is why flame furnaces (such as transverse burner furnaces) remain today the only furnaces capable of supplying such a glass flotation unit.

[0036] However, flame furnaces rely on the use of fossil fuels, mainly natural gas for fuel, so their carbon balance is not very compatible with the objectives of reducing carbon dioxide (CO2) emissions, i.e. the carbon footprint of the glassmaking process.

[0037] To complete the presentation of furnace designs for glass manufacturing according to the state of the art, we will mention a "third design" or evolution of furnace, which has recently undergone developments to address in particular the ecological challenge of reducing carbon dioxide (CO2) emissions.

[0038] This third furnace design is based on a flame furnace but uses an auxiliary electric heater, notably to temporarily increase furnace production or to improve glass quality.

[0039] Therefore, such ovens are still called "flame ovens with an electric backup".

[0040] Ovens according to this third design thus combine several energy sources, respectively fossil and electrical, and are for this reason also called "hybrid" ovens.

[0041] Adding supplementary electric heating improves the melting capacity of flame furnaces, which is limited by the heat transfer occurring between the flame and the surface of the glass bath.

[0042] Nevertheless, the operation of such a hybrid furnace still relies primarily on the use of a fossil fuel, typically gas, so the final impact on improving the carbon footprint of the glassmaking process remains limited.

[0043] Indeed, electricity is only used as a supplement here, so its impact is proportional. Moreover, to effectively improve the carbon footprint, the electricity used must be so-called "green" electricity, that is, electricity produced from renewable and decarbonized energy sources.

[0044] Document FR 2614614 describes a glass melting furnace having a melting compartment, for example equipped with electrodes, a refining compartment with heating means such as burners, and a glass conditioning tank. Documents US4809294 and US2017197859 describe electric melting furnaces with immersion electrodes. Documents US4001001, FR2261233, US5426663, and WO2020229559 describe glass melting furnaces using electrodes and burners.

[0045] The aim of the invention is in particular to propose a new design of furnace for the manufacture of glass, as well as a manufacturing process, capable of delivering high quality glass to supply in particular a glass flotation unit intended to manufacture flat glass and this while having an energy consumption which allows a significant reduction of carbon dioxide (CO2) emissions related to the glass manufacturing process. Summary of the invention

[0046] To this end, the invention proposes a hybrid oven according to claim 1.

[0047] Advantageously, the hybrid furnace is designed to supply high-quality glass to a forming area consisting of a glass flotation unit on a molten metal bath.

[0048] The oven according to the invention is called "hybrid" by analogy with the third oven design described previously; the term "hybrid" is thus used to describe it because of the use of two different energy sources, namely electrical energy and fuel energy.

[0049] However, the analogy with the present invention does not go further since electrical energy is the only source of energy used in the manufacture of glass to obtain the melting of the glass and that combustible energy, of fossil type or equivalent, is therefore only used in the furnace for the refining and homogenization of the glass.

[0050] Advantageously, the hybrid furnace according to the invention combines on the one hand an electric melting zone with a cold vault and, on the other hand, a refining zone for homogenizing glass with flames, i.e. by combustion.

[0051] Thanks to such a combination, the hybrid furnace according to the invention makes it possible to obtain high quality glass, i.e. having less than 0.1 bubbles per liter, so that this glass is advantageously capable of supplying a glass flotation or "float" unit intended for the manufacture of flat glass.

[0052] The present invention therefore goes against the prejudices of the man skilled in the art, for whom an electric melting furnace cannot, moreover, make it possible to obtain such high-quality glass.

[0053] In the present invention, a high-quality glass is thus obtained through the refining and homogenization step which is implemented after the electrical melting step.

[0054] Advantageously, there is no return of molten glass from the refining and homogenizing zone to the melting zone in a hybrid furnace according to the invention.

[0055] In a hybrid furnace according to the invention, no convection belt or glass recirculation loop extends from the refining and homogenizing zone to the melting zone.

[0056] In the invention, the glass refining and homogenization step is carried out on glass advantageously containing little or no unmelted material thanks in particular to the separation device which increases the residence time of the glass in the melting zone which is also configured to include a low convection buffer zone.

[0057] Advantageously, the hybrid furnace according to the invention relies on electrical energy for the melting of the vitrifiable mixture and takes advantage of the increasing availability of "green" electricity, for example obtained from wind, solar, etc. energy and not from fossil fuels such as coal or oil.

[0058] Advantageously, the fuel energy used in the burners of the refining and homogenizing zone is not a fossil fuel such as natural gas but another equivalent fuel energy, preferably hydrogen, as a variant of bio-methane.

[0059] The hybrid furnace according to the invention is therefore able to meet not only the challenge of the high quality of glass required to supply a flotation or "float" unit but also the ecological challenge in order to allow a reduction of the carbon footprint of the manufacturing process.

[0060] According to other characteristics of the oven according to the invention: -- The hybrid furnace includes a loading zone in which a loading device is arranged to introduce the vitrifiable mixture into the electric melting zone; -- the loading device is configured to deposit the vitrifiable mixture over the entire surface of the glass bath so as to form an insulating layer between the glass bath and the roof of the melting zone; the immersion electrodes extend vertically; -- the hybrid furnace includes immersion electrodes Andrising electrodes; the buffer zone depth is greater than 800 mm; the electrical melting zone and the glass refining and homogenizing zone are connected by a corset; -- the electrical melting zone and the glass refining and homogenizing zone are connected by a groove; the hybrid furnace includes a separation device between the electrical melting zone and the refining and homogenizing zone which is particularly suitable for preventing the return of molten glass from the refining and homogenizing zone to said melting zone; the separation device is positioned at the level of the corset, preferably at the upstream end of the corset; the separation device includes a barrier which is partially immersed in the glass bath;The dam is mounted vertically to allow adjustment of its immersion depth in the glass bath, so that the cross-section of the molten glass passage can vary depending on the dam's depth setting; the dam is removable, i.e., demountable, in particular to allow for its replacement in case of wear and to facilitate furnace maintenance; the separation device includes a means of separation to separate the atmosphere of the cold-roofed electric melting zone from the atmosphere of the hot-roofed refining and homogenizing zone; the first convection belt and the second convection belt are separated by a belt reversal zone determined by a hot spot or source corresponding to the hottest point of the glass; the refining and homogenizing zone includes at least one burner which is arranged to obtain said hot spot determining said belt reversal zone;The hybrid furnace includes a wall which is arranged in said belt reversal zone; the hybrid furnace includes a variation in the depth of the hearth relative to a glass surface in the refining and homogenizing zone, preferably at least one elevation, or even a difference in level, said variation in depth being located in the part comprising the first convection belt and / or in the part comprising the second convection belt; the hybrid furnace includes modulation means such as electric boosting and / or bubbling devices which, arranged in the refining and homogenizing zone, are capable of modulating the convection of said belts in order to facilitate the glassmaking process; the conditioning basin of the cooling zone includes, from upstream to downstream, a corset and then a brazier;-- in any vertical plane transverse to the longitudinal axis of the conditioning basin, there are points in the glass having a longitudinal velocity component going from downstream to upstream; -- after the conditioning basin, no return current occurs in the flow channel intended to supply high-quality glass to a forming zone, in other words, the flow of the glass in the channel is a "piston" type flow; the hybrid furnace is capable of delivering high-quality glass with less than 0.1 bubbles per liter, preferably less than 0.05 bubbles per liter; -- said hybrid glass-making furnace supplies a glass flotation unit on a molten metal bath.

[0061] To this end, the invention also proposes a method for manufacturing glass in a hybrid furnace of the type described above, said manufacturing method successively comprising the steps of: (a) - melt a vitrifiable mixture in a cold-roofed electric melting zone to obtain molten glass; (b) - refine and homogenize said molten glass in a hot-roofed refining and homogenizing zone comprising a first convection belt and a second convection belt; (c) - cool the glass in a cooling zone which, formed by a conditioning basin, is traversed by the second convection belt.

[0062] Advantageously, the process includes an adjustment step (d) consisting of adjusting the depth of a movable dam which, immersed in the glass, is arranged in a corset connecting the electrical melting zone to the refining and homogenizing zone, to control the flow of molten glass taken from the melting zone.

[0063] Preferably, after the cooling step (c) in the conditioning basin, the glass flows into a flow channel to supply high-quality glass to a glass flotation unit. Brief description of the figures

[0064] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which: there figure 1 is a side view representing a glassmaking furnace according to an embodiment of the invention and illustrating a cold-roofed electrical melting zone associated with a hot-roofed refining and homogenizing zone comprising a first convection belt and a second convection belt, and finally a cooling zone through which said second convection belt passes; the figure 2 is a top view that represents the oven according to the figure 1 and which illustrates the electrical melting zone connected to the refining and homogenizing zone by a corset in which is arranged a vertically mounted mobile dam and the cooling zone formed by a conditioning basin comprising a corset and an ember. Detailed description of the invention

[0065] In the following description, we will adopt, without limitation, the longitudinal, vertical, and transverse orientations with reference to the trihedron (L, V, T) represented on the figures 1 and 2 .

[0066] We will also conventionally use the terms "upstream" and "downstream" with reference to longitudinal orientation, as well as "upper" and "lower" or "top" and "bottom" with reference to vertical orientation, and finally "left" and "right" with reference to transverse orientation.

[0067] In this description, the terms "upstream" and "downstream" refer to the direction of glass flow in the furnace, with the glass flowing from upstream to downstream along a median longitudinal axis AA' of the hybrid furnace (upstream at A, downstream at A') shown on the figure 2 .

[0068] Furthermore, the terms "belt" and "loop" are synonymous here, these terms relating to the recirculation of glass in the furnace being well known to the person skilled in the art, just as are respectively the notions of "cold vault" and "hot vault" for a furnace intended for the manufacture of glass.

[0069] We have represented on the figures 1 and 2 , respectively in side and top views (which are not to scale), a hybrid furnace 10 for the manufacture of glass illustrating an embodiment of the present invention.

[0070] As previously indicated, by analogy with the third oven design described earlier, the term "hybrid" is used here to describe the oven according to the invention because of the use of two different energy sources, namely electrical energy and fuel energy.

[0071] However, the analogy with the present invention does not go further since, on the one hand, electrical energy (constituting the first source) is the only source of energy used to obtain the melting of the glass and, on the other hand, combustible energy (constituting the second source), of fossil or equivalent type, is used only for the refining and homogenization of the glass.

[0072] The hybrid furnace 10 according to the invention is in particular intended to supply a glass flotation unit on a bath of molten metal, generally tin, for the manufacture of flat glass.

[0073] As illustrated by the figures 1 and 2 , the hybrid furnace 10 comprises successively from upstream to downstream, along the said median longitudinal axis AA' of the furnace, at least one zone 100 for electric melting, one zone 200 for refining and homogenizing and one zone 300 for cooling the glass.

[0074] According to a first feature of the invention, the melting zone 100 of the hybrid furnace 10 is electrically powered.

[0075] Advantageously, the electrical fusion zone 100 is of the "cold vault" type.

[0076] Advantageously, the glass melting stage is achieved using only electrical energy during glass manufacturing, in comparison with state-of-the-art hybrid furnaces in which the melting stage is achieved using fuel energy and, as a supplement, electrical energy.

[0077] The electrical melting zone 100 includes electrodes 110 to melt a vitrifiable mixture (or "composition") which consists of raw materials and cullet (or "grit") in order to obtain a glass bath 130.

[0078] Cullet is known to consist of glass fragments obtained from glass recycling, which are crushed and cleaned before being added to raw materials to manufacture new glass.

[0079] Advantageously, the calcine promotes fusion, that is, the transformation by fusion of the vitrifiable mixture into glass.

[0080] Moreover, cullet allows us to valorize used glass by recycling it (glass being infinitely recyclable), the quantities of raw materials needed to manufacture glass are therefore reduced proportionally, which contributes to reducing the carbon footprint of the manufacturing process.

[0081] The hybrid furnace 10 comprises a loading zone 120 in which is arranged a loading device 12 (also called a loader) which is intended to introduce the vitrifiable mixture into the electrical melting zone 100, said loading device 12 being schematically illustrated by an arrow on the figure 1 .

[0082] Advantageously, the furnace loading device 12 is configured to deposit the vitrifiable mixture over the entire surface of the glass bath 130 so as to form an insulating layer 112 between the glass bath 130 and an arch 140 of the electrical melting zone 100, which is why the latter is called the "cold arch".

[0083] Preferably, the glass bath 130 is uniformly covered with a layer 112 made of vitrifiable mixture, for example 10 to 40 cm thick, below which take place the complex chemical reactions which, described in the preamble to the application, lead to the production of molten glass.

[0084] In the zone 100 of cold-arch electrical melting, the power dissipated around the electrodes 110 generates a zone 132 of strong convections including in particular very intense updrafts which bring the necessary heat to the boundary between the melt and the vitrifiable mixture forming said layer 112 of vitrifiable mixture.

[0085] In the state-of-the-art glassmaking process, in addition to carbon dioxide (CO2), the decomposition of raw materials and the use of fossil fuel as fuel for the melting stage also generate polluting emissions consisting mainly of nitrogen oxide (NOx), sulfur oxide (SOx), halogens and dust.

[0086] Advantageously, the absence of combustion (flames) in the cold vault electric melting zone 100 of the hybrid furnace 10 according to the invention results in the pollution rate of NOx and SOx being comparatively very low.

[0087] Furthermore, although permeable to carbon dioxide (CO2), the layer 112 of vitrifiable mixture present on the surface of the bath 130 advantageously traps by condensation or by chemical reactions the vapors, sometimes toxic depending on the composition, emitted by the molten glass.

[0088] According to the invention, the electrodes 110 are arranged on the surface so as to immerse in the glass bath 130, through the layer 112 covering the surface of the bath 130 as illustrated by the figure 1 .

[0089] Preferably, the 110 plunging electrodes extend vertically. Alternatively, the 110 plunging electrodes extend obliquely, that is, they are inclined at a given angle to the vertical orientation.

[0090] In an alternative (not part of the invention), the electrodes 110 are arranged through a sole 150 of the electrical melting zone 100 so as to be immersed in the bath 130, the rising electrodes (as opposed to the plunging electrodes) preferably extending vertically, alternatively obliquely.

[0091] Compared to electrodes arranged across the sole 150, the 110 plunge electrodes also allow easier control of their wear state and result in a dissipation of electrical energy which is advantageously closer to the fusion interface, of the 112 layer of vitrifiable mixture.

[0092] Advantageously, the 110 plunging electrodes, compared with rising electrodes, allow a 150 base of the 100 electrical fusion zone to be maintained which is free of any openings.

[0093] Preferably, the sole 150 of the electrical melting zone 100 is flat as illustrated by the figure 1 .

[0094] Alternatively, the sole 150 includes at least one variation in depth relative to the surface of the glass bath 130, said variation including at least one elevation and / or at least one leveling.

[0095] Preferably, the fusion electrodes 110 are evenly distributed in the bath 130. Furthermore, the number of nine electrodes 110 shown here on the figures 1 and 2 This is only an illustrative example and is therefore by no means exhaustive.

[0096] Alternatively, the electrical fusion zone 100 could cumulatively include plunging and rising electrodes.

[0097] According to another arrangement variant (not part of the invention), the electrodes 110 pass through at least one lateral wall delimiting said electrical fusion zone 100, said electrodes 110 then extending horizontally and / or obliquely.

[0098] Advantageously, the electrodes 110 are made of molybdenum, this refractory metal which can withstand temperatures of 1700°C and is particularly suitable for achieving such a melting of glass using the Joule effect, the glass only becoming conductive at high temperature.

[0099] According to the invention, the electrical fusion zone 100 includes a low convection zone, called buffer zone 134, which is located between the free end of the plunging electrodes 110 and the sole 150.

[0100] The electrical fusion zone 100 is thus configured to present, below the plunging electrodes 110, a depth (P) determined so as to obtain such a buffer zone 134 of low convection.

[0101] The depth (P) between the free end of the plunging electrodes 110 and the sole 150 is greater than 600 mm, preferably greater than 800 mm.

[0102] Such a low convection buffer zone 134 is another reason to prefer plunging electrodes 110 over rising electrodes passing through the sole 150.

[0103] Advantageously, the presence of a low convection buffer zone 134 directly contributes to obtaining high-quality glass by promoting a longer residence time of the glass in the melting zone 100.

[0104] Preferably, the electric melting zone 100 and the glass refining and homogenization zone 200 are connected to each other by a corset 160, i.e., a zone of reduced width, as illustrated by the figure 2 .

[0105] The transition from the electrical melting zone 100 to the corset 160 is achieved by a sudden narrowing of the width and the cross-section of the passage of the glass, for example here by walls 162 and 163 forming an angle of 90° with the median longitudinal axis AA' of the furnace.

[0106] The passage from the corset 160 to the zone 200 for refining and homogenizing the glass is done by a sudden widening of the glass passage section, for example here by walls 262 and 263 forming an angle of 90° with the median longitudinal axis AA' of the furnace.

[0107] Alternatively, the angle at the entrance of the 160 corset could have a value greater than 90° so that the narrowing of the width is less abrupt, more gradual; similarly, the value of the angle at the exit of the 160 corset could be chosen so that the widening is also less abrupt, more gradual along the median longitudinal axis AA' of the furnace.

[0108] Advantageously, the molten glass flowing from upstream to downstream through the corset 160 is taken from the lower part of the electrical melting zone 100, i.e. from the bottom, the glass there being "colder" compared to the zone 132 of strong convections located between the electrodes 110.

[0109] Alternatively, the electrical melting zone 100 and the glass refining and homogenization zone 200 are connected by a groove (not shown) and not by a corset 160.

[0110] The hybrid furnace 10 preferentially features a 160 corset rather than a throat, which is particularly more susceptible to wear caused by the continuous flow of molten glass.

[0111] According to a second feature of the invention and in contrast to the cold vault electric melting zone 100, the refining and homogenizing zone 200 of the hybrid furnace 10 is of the "hot vault" type.

[0112] The 200 refining and homogenizing zone of the hybrid furnace 10 is configured to eliminate bubbles (or gaseous defects) present in the molten glass coming from the 100 electric melting zone in order to obtain high-quality glass and, in particular, suitable for supplying a glass flotation unit.

[0113] To do this, the refining and homogenizing zone 200 includes a first convection belt 210, called the upstream recirculation loop, and a second convection belt 220, called the downstream recirculation loop.

[0114] Preferably, the first convection belt 210, called the upstream recirculation loop, is longitudinally shorter than the second convection belt 220, as illustrated by the figure 1 .

[0115] Advantageously, the convection currents in the glass corresponding to the said belts 210, 220 operate a mixing which promotes the elimination of bubbles and increases the residence time of the glass in the refining and homogenization zone 200, which contributes to obtaining a high-quality glass.

[0116] The first convection belt 210 and the second convection belt 220 are separated by a zone 230 of reversal of the belts 210, 220 which is determined by a hot spot (also called "source point") which corresponds to the hottest point of the glass, generally at a temperature above 1500°C.

[0117] The refining and homogenizing zone 200 includes at least one burner 215, preferably here two overhead burners 215 which are arranged under a vault 240 to obtain said hot spot determining the zone 230 of reversal of said belts 210, 220.

[0118] In the refining and homogenizing zone 200, part of the thermal energy released by combustion is transmitted directly to the glass by radiation and convection, another part is transmitted by the vault 240 which returns it to the glass by radiation, and which for this reason is called the "hot vault".

[0119] Preferably, the burners 215 of the refining and homogenizing zone 200 are transverse burners, schematically represented on the figure 2 .

[0120] Thus, the heating of the glass in the refining and homogenizing zone 200 is achieved by the flames of the burners 215 which develop by combustion above the surface S of the glass.

[0121] In a hybrid furnace 10 according to the invention, after its commissioning for manufacturing, the glass melting step carried out in the melting zone 100 is obtained solely with electrical energy.

[0122] Advantageously, the surface heating of the glass carried out by combustion of a fossil energy or equivalent fuel in said zone 200 is therefore intended solely for the implementation of the refining and homogenization step of the glass taken from said melting zone 100.

[0123] In comparison in particular with a hybrid furnace according to the third design described above, the fossil or equivalent fuel energy used by the burners 215 for combustion does not participate in the melting stage so that this fuel energy is in the invention used as a "supplement" to the electrical energy used in addition for melting.

[0124] Therefore, a hybrid furnace 10 according to the invention makes it possible to significantly reduce the share of fuel energy compared to electrical energy in the glassmaking process, with electrical energy becoming the main energy and fuel energy secondary or auxiliary.

[0125] Therefore, it will be understood that the design of the hybrid oven 10 according to the invention is particularly advantageous for reducing the carbon footprint when, on the one hand, the fuel energy is a fossil fuel such as gas and, on the other hand, the electrical energy is in whole or in part "green" electricity obtained from renewable and decarbonized energy sources.

[0126] The refining and homogenizing zone 200 may include more than two burners 215, in particular burners upstream and / or downstream of said inversion zone 230 which, also positioned above the surface S of the glass, are capable of heating said surface S of the glass in order to complete the refining and homogenizing of the glass by eliminating bubbles (or gaseous defects) present in the molten glass.

[0127] Indeed, by adjusting the power of the 215 burners, we can adjust the longitudinal distribution of temperatures and therefore the position of the hot spot, which is an important parameter in the operation of the oven.

[0128] The 215 burners produce a flame by combustion which can be obtained in a known way by combining different types of fuel and oxidizer but whose choice also has direct consequences in the carbon balance of glass manufacturing, i.e. the direct and indirect greenhouse gas emissions which are linked to the manufacture of the product, in particular carbon dioxide (CO2) emissions.

[0129] For combustion by the burners 215 of the refining and homogenizing zone 200, oxygen present in the air is generally used as an oxidant, which air can be enriched in oxygen in order to obtain superoxygenated air, or even almost pure oxygen is used in the particular case of oxycombustion.

[0130] Generally, the fuel used is natural gas. However, to further improve the carbon balance, a biofuel (in English "green-fuels") will be used advantageously, in particular "biogas", that is to say a gas composed essentially of methane and carbon dioxide which is produced by methanization, i.e. the fermentation of organic matter in the absence of oxygen, or even preferably "bio-methane" (CH4).

[0131] Hydrogen (H2) will be used even more preferentially as a fuel, which, compared to biogas, advantageously contains no carbon.

[0132] Advantageously, the hybrid glassmaking furnace 10 according to the invention can include regenerators made of refractory materials operating (for example in pairs and in inversion) or metallic air / fume exchangers (also called recuperators) which respectively use the heat contained in the fumes from manufacturing to preheat the gases and thus improve combustion.

[0133] In the embodiment illustrated by the figures 1 and 2 , the hybrid furnace 10 includes a separation device 170 between the electrical melting zone 100 and the refining and homogenization zone 200.

[0134] Advantageously, the separation device 170 is able to prevent a return of molten glass from the refining and homogenizing zone 200 to the electrical melting zone 100, that is to say a return from the first glass convection belt 210.

[0135] Advantageously, the 170 separation device increases the residence time of the glass in the 100 electrical fusion zone, which contributes to obtaining high-quality glass.

[0136] Advantageously, the separation device 170 is positioned at the level of the corset 160, preferably at the upstream end of said corset.

[0137] As illustrated on the figures 1 and 2 , the separation device 170 includes at least one barrier 172 which is partly immersed in the molten glass.

[0138] Advantageously, the separation device 170 ensures a delimitation of the layer 112 of vitrifiable mixture covering the glass bath 130 in the zone 100 of electric melting with cold vault from the zone 200 of refining and homogenization with hot vault.

[0139] Preferably, the delimitation of the vitrifiable mixture layer 112 is ensured by the barrier 172, which extends for this purpose above the surface of the glass bath 130, as illustrated by the figure 1 .

[0140] Preferably, the dam 172 is removable, that is to say demountable, so that said dam 172 is capable of being changed, or even repaired, in particular due to wear occurring in contact with the glass, and this makes the maintenance of the hybrid furnace 10 easier.

[0141] Dam 172 is for example made of non-refractory metal or metal alloy, said dam 172 then being suitable for cooling by a cooling circuit (not shown) with heat transfer fluid, in particular a circuit of the "water jacket" type according to the English terms used.

[0142] Alternatively, the 172 dam is made of refractory material, typically ceramic, for example an electrofused refractory "AZS" (acronym for Alumina-Zircon-Silica) or a refractory metal such as molybdenum.

[0143] Advantageously, the dam 172 is mounted vertically to allow adjustment of its immersion depth in the glass bath 130 so that the section of the passage of the molten glass, called the sampling (or drawing) zone 180, located above the sole 150, is likely to vary according to the adjustment of the depth of the dam 172.

[0144] The separation device 170 also includes a separation means 174 for separating the atmosphere of the melting zone 100 from the atmosphere of the refining and homogenization zone 200, which includes fumes.

[0145] Preferably, the separation means 174 is a curtain constituting an element added to the superstructure of the hybrid furnace 10.

[0146] The blocks in contact with the glass are conventionally called the "infrastructure" and the materials placed above the infrastructure are called the "superstructure".

[0147] The superstructure material, which comes above the infrastructure tank blocks and is not in contact with the glass but with the atmosphere inside the furnace, is generally of a different nature than that of the infrastructure tank blocks.

[0148] Even if the material used for the superstructure is identical to that of the infrastructure, for example in the case of a hot vault, these two parts of the structure of a furnace are generally distinguished.

[0149] Alternatively, the means of separation 174 consists of a part of the superstructure, for example a double partition in the shape of a "U" opening outwards.

[0150] Advantageously, the 172 barrier was then mounted between the two wings of the "U" of the partition, i.e. in the lower hollow portion connecting them.

[0151] Preferably, the barrier 172 and the atmospheric curtain 174 forming the separation device 170 are structurally distinct, independent elements.

[0152] Preferably, the curtain 174 is not in contact with the glass surface but with the barrier 172 to establish said separation, the curtain 174 being, for example, located behind it as illustrated in the figure 1 , that is, downstream of the dam.

[0153] Alternatively, curtain 174 is located in front of, either upstream of dam 172 or located in the same vertical plane.

[0154] Alternatively, the dam 172 and the curtain 174 are made in one piece, thus ensuring a dual function: firstly, the function of separating the glass between the melting zone 100 and the refining and homogenizing zone 200, and secondly, a function of separating the atmosphere of the melting zone 100 with a cold vault 140 and the atmosphere of the refining and homogenizing zone 200 with a hot vault 240.

[0155] In the embodiment illustrated by the figures 1 and 2 , the hybrid oven 10 advantageously includes a wall 260 which is arranged in the said zone 230 of belt reversal.

[0156] Preferably, the wall 260 extends vertically from the floor 250 of the ripening and homogenization zone 200.

[0157] As illustrated by the figure 1, the wall 260 has a top part which, immersed below the surface S of the glass, determines the passage of the glass from the first convection belt 210, called the upstream recirculation loop, to the second convection belt 220, called the downstream recirculation loop.

[0158] Preferably, the hybrid furnace 10 includes modulation means (not shown) such as electrical "boosting" and / or bubblers which, arranged in the refining and homogenizing zone 200, are capable of modulating the convection of said belts 210, 220 in order to facilitate the conduct of glass manufacturing.

[0159] Advantageously, the modulation means therefore include, according to the English term, electrical "boosting", that is to say, auxiliary electric heating means including electrodes and / or bubblers, that is to say, a system for injecting at least one gas, such as air or nitrogen, at the level of the sole, the bubbles of which then create an upward movement of the glass.

[0160] Preferably, the hybrid furnace 10 includes at least a variation 270 of the depth, relative to the surface S of the glass, of a hearth 250 located in the refining and homogenizing zone 200.

[0161] The 270 depth variation is located in the part including the first 210 convection belt and / or in the part including the second 220 convection belt.

[0162] Advantageously, the variation 270 of the depth of the sole 250 is, for example, constituted by at least one elevation, or even here several elevations, which are illustrated by the figure 1 .

[0163] Alternatively, the variation 270 of the depth of the sole 250 is constituted by at least one difference in level.

[0164] The elevation forming the variation 270 of depth of the sole 250, i.e. here a reduction of the depth, is for example constituted by at least one step 272, or even two steps.

[0165] The variation 270 of depth can be carried out more or less gradually, for example by a straight portion 274 in the case of the two steps 272 located upstream of the wall 260 or alternatively by an inclined portion 276 as illustrated for example in the case of the step 322 located downstream of the wall 260, at the junction of the refining and homogenizing zone 200 and the glass cooling zone 300.

[0166] Preferably, the 300 cooling zone therefore also includes a 370 depth variation which is formed by an elevation.

[0167] As illustrated by the figure 1 , the 370 depth variation in the 300 cooling zone includes for example the step 322, located in the corset 320, to which leads from the sole 250 the inclined junction 276 and another step 332 which is located in the ember 330, downstream of the step 322.

[0168] Step 322 also connects progressively to the other step 332 by means of an inclined portion 376 which is located at the junction between the corset 320 and the ember 330.

[0169] Alternatively, the respective straight and inclined portions that have just been described with reference to the figure 1could be reversed between steps 272 on the one hand and steps 322, 332 on the other hand, or be of only one type, that is to say either straight or inclined.

[0170] As illustrated by the figure 1 and as just described with successive steps 322 and 332, the cooling zone 300 includes a floor 350 which is configured so that the depth relative to the glass surface S gradually decreases from upstream to downstream, from the wall 260.

[0171] According to a third feature of the invention, the hybrid furnace 10 comprises, downstream of the refining and homogenizing zone 200, said glass cooling zone 300 which is traversed by the second convection belt 220, called the downstream recirculation loop.

[0172] The cooling zone 300 is formed by a conditioning basin 310 which communicates with at least one flow channel 400 intended to supply high-quality glass to a forming zone (not shown) located downstream.

[0173] Advantageously, the conditioning basin 310 of the cooling zone 300 includes, from upstream to downstream, a corset 320 and then a braise 330.

[0174] Advantageously, the atmosphere of the refining and homogenizing zone 200 and the colder atmosphere of the cooling zone 300 are separated from each other by a thermal screen 360 such that a partition extends vertically from an arch 340 to the vicinity of the surface S of the glass, preferably without dipping into the glass.

[0175] Advantageously, in any vertical plane transverse to the median longitudinal axis AA' of the furnace, there exist in the conditioning basin 310 points in the glass having a longitudinal velocity component going from downstream to upstream.

[0176] After the conditioning basin 310, there is no return flow in the flow channel 400 intended to supply glass to the forming area, in other words the flow of glass in the channel 400 is a "piston" type flow.

[0177] Advantageously, the hybrid furnace 10 according to the invention is capable of delivering high-quality glass with less than 0.1 bubbles per liter, preferably less than 0.05 bubbles per liter, such high-quality glass being particularly suitable for supplying a glass flotation unit on a molten metal bath.

[0178] The hybrid glassmaking furnace 10 according to the invention preferentially feeds a glass flotation unit on a bath of molten metal, for example tin, intended for the manufacture of flat glass.

[0179] The invention further relates to a method for manufacturing glass in a hybrid furnace 10 of the type just described with reference to figures 1 and 2 .

[0180] Thus, the manufacturing process according to the invention comprises successive steps consisting of: (a) - melt a vitrifiable mixture in a cold-roofed electric melting zone to obtain molten glass; (b) - refine and homogenize said molten glass in a hot-roofed refining and homogenizing zone comprising a first convection belt (called the upstream recirculation loop) and a second convection belt (called the downstream recirculation loop); (c) - cool the glass in a cooling zone which, formed by a conditioning basin, is traversed by the second convection belt.

[0181] Advantageously, the process includes an adjustment step (d) consisting of adjusting the depth of the movable dam 172 which, immersed in the glass, is arranged in a corset 160 connecting the electrical melting zone 100 to the refining and homogenizing zone 200, to control the flow of molten glass taken from the melting zone 100.

[0182] Advantageously, the adjustment step (d) allows the quantity of molten glass passing from the electrical melting zone 100 to the refining and homogenization zone 200 to be varied, for example as a function of the draw.

[0183] Dam 172 also allows molten glass to be collected from the lower part of the cold-vault electric melting zone 100, in the vicinity of the sole 150.

[0184] The glass is thus extracted from the low convection buffer zone 134.

[0185] After the cooling step (c) in the conditioning basin 310, the glass flows into a flow channel 400 intended to supply high-quality glass to a glass flotation unit.

Claims

1. An hybrid furnace (10) for manufacturing glass, in particular for supplying a glass floating unit on a molten metal bath, said hybrid furnace (10) comprising from upstream to downstream: - an electric melting zone (100) with a cold-top (140) comprising electrodes (110) for melting a vitrifiable mixture to obtain a bath (130) of glass, said electrodes (110) being arranged on the surface so as to plunge into said vitrifiable mixture, said electric melting zone (100) comprising a zone of low convection, so-called buffer zone (134), situated between the free end of said plunging electrodes (110) and a hearth (150) of the melting zone (100), said melting zone (100) being configured to have, below the plunging electrodes (110), a depth (P) determined in such a way as to obtain said buffer zone (134) of low convection, said depth (P) between the free end of the plunging electrodes (110) and the hearth (150) being greater than 600 mm; - a refining and homogenization zone (200) with a hot-vault comprising a first convection belt (210) and a second convection belt (220); and - a glass cooling zone (300) formed by a conditioning tank (310) which, traversed by said second convection belt (220), communicates with at least one flow channel (400).

2. The furnace according to claim 1, characterized in that said plunging electrodes (110) extend vertically.

3. The furnace according to claim 1 or 2, characterized in that the depth (P) is greater than 800 mm.

4. The furnace according to any one of the preceding claims, characterized in that the electric melting zone (100) and the refining and homogenization zone (200) of the glass are connected by a neck (160).

5. The furnace according to any one of the preceding claims, characterized in that the hybrid furnace (10) comprises a device (170) for separating the electric melting zone (100) from the refining and homogenizing zone (200) which is in particular able to prevent a return of molten glass from the refining and homogenizing zone (200) to said melting zone (100).

6. The furnace according to claims 4 and 5 taken in combination, characterized in that the separating device (170) is positioned at the level of the neck (160), preferably at the upstream end of the neck (160).

7. The furnace according to claim 6, characterized in that the separation device (170) comprises a dam (172) which is partly immersed in the glass bath (130).

8. The furnace according to claim 7, characterized in that the dam (172) is mounted vertically movable to allow the depth of immersion in the glass bath (130) to be adjusted, so that the cross-section of the passage of the molten glass is likely to vary according to the adjustment of the depth of the dam (172).

9. The furnace according to one of claims 7 or 8, characterized in that the dam (172) is removable, i.e. dismountable, in order to allow it to be changed in case of wear and to facilitate maintenance of the furnace.

10. The furnace according to any one of claims 5 to 9, characterized in that the separation device (170) comprises a separation means (174) for separating the atmosphere from the cold-top electric melting zone (100) and the atmosphere from the hot-top refining and homogenizing zone (200).

11. The furnace according to any one of the preceding claims, characterized in that the first convection belt (210) and the second convection belt (220) are separated by an inversion zone (230) of the belts (210, 220) determined by a hot spot or source corresponding to the hottest point of the glass and in that the refining and homogenizing zone (200) comprises at least one burner (215) which is arranged to obtain said hot spot determining said inversion zone (230) of the belts.

12. The furnace according to claim 11, characterized in that the hybrid furnace (10) comprises a low wall (260) which is arranged in said inversion zone (230) of the belts.

13. The furnace according to any one of the preceding claims, characterized in that the hybrid furnace (10) comprises a variation (270, 370) of the depth of the hearth (250, 350) with respect to the surface (S) of the glass in the refining and homogenization zone (200), preferably at least an elevation (272, 322, 332) or even a difference in level, said depth variation (270, 370) being located in the portion comprising the first convection belt (210) and / or in the portion comprising the second convection belt (220).

14. The furnace according to any one of the preceding claims, characterized in that the hybrid furnace (10) comprises means of modulation such as electric "boosting" and / or bubblers which, arranged in the refining and homogenizing zone (200), are capable of modulating the convection of said belts (210, 220) in order to facilitate the conduct of the manufacture of glass.

15. The furnace according to any one of the preceding claims, characterized in that the conditioning tank (310) of the cooling zone (300) comprises, from upstream to downstream, a neck (320) and then a working end (330).

16. The furnace according to any one of the preceding claims, characterized in that the hybrid furnace (10) is able to deliver high-quality glass having less than 0.1 bubbles per litre, preferably less than 0.05 bubbles per litre.

17. A method for manufacturing glass in a hybrid furnace (10) according to any one of the preceding claims, said manufacturing method comprising successively the steps of: (a) - melting a vitrifiable mixture in electric melting zone (100) with a cold-top to obtain molten glass; (b) - refining and homogenizing said molten glass in refining and homogenizing zone (200) with a hot-top comprising a first convection belt (210) and a second convection belt (220); (c) - cooling the glass in a cooling zone (300) which, formed by a conditioning tank (310), is traversed by the second convection belt (220).

18. The method for manufacturing glass according to the preceding claim, characterized in that the method comprises a step (d) of adjustment consisting in adjusting the depth of a movable dam (172) which, immersed in the glass, is arranged in a neck (160) connecting the electric melting zone (100) to the refining and homogenizing zone (200), to control the flow rate of molten glass taken from the electric melting zone (100).