Glass furnace with decreased co 2 emissions, process thereof

Abstract

The present invention concerns an advantageous furnace for melting vitrifiable materials, comprising (i) a melting tank providing a melt; (ii) a fining tank with combustion heating means alimented with oxygen and hydrogen and providing a refined melt and water steam; (iii) at least one neck separating the melting and fining tanks; (iv) inlet means; (v) outlet means; said furnace further comprising (vi) a steam electrolysis unit to electrolyse water steam into a hydrogen flow and an oxygen flow, and (vii) a circuit to conduct hydrogen flow from steam electrolysis unit towards combustion heating means at the fining tank.

Description

GLASS FURNACE WITH DECREASED CO2EMISSIONS, PROCESS THEREOFFIELD OF THE INVENTION

[0001] The present invention relates to a glass furnace / process 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 / process that provides a lot of advantages, especially in terms of CO2emissions.

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

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

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

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

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

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

[0008] Finally, one of the proposed solution in the glass art in order to reduce carbon footprint of a glass manufacturing process is the use of greener sources of energy like hydrogen, H2, in the combustion heating means in the furnace, for melting and / or refining. This solution brings obviously great advantages in term of environment / energy consumption / CC>2 emissions, as in such a solution, hydrogen reacts / burns with oxygen (from air or injected as such) in an exothermic reaction to form only water steam / vapor.

[0009] Nevertheless, serious limitations have prevented their extensive use in the glass industry so far. Especially, hydrogen is still very expensive to produce and this makes its use non-economically viable as such as main energy source to melt / refine glass in a furnace.

[0010] Today, hydrogen is mainly produced by steam reforming, at temperatures 800-900°C, of carbon-containing feedstocks such as natural gas. It is also known to produce hydrogen by electrolysis of water, preferably using electricity from renewable energy sources. Carrying out this electrolysis with steam (i.e. water in vapor phase) allows to be more energetically effective (and then more economical) than electrolysis with liquid water (e.g. at room temperature), notably because a part of the energy required for the process is given by the heat. Moreover, the higher the steam temperature, the more energetically effective the electrolysis is. The process for producing hydrogen by electrolysis of water at high temperature is described, for example, in EP3967654A1.

[0011] In that context, it has been proposed recently, in W02021 / 008729A1, a process for operating a combustion glass melting furnace with an arrangement including an electrolysis device, using waste heat from flue gas of said furnace for forming a water steam stream. This water steam stream is then subjected to a high temperature electrolysis to form a hydrogenand an oxygen stream, with at least a part of the hydrogen stream being used as the fuel in the combustion.

[0012] Next to that, WO2023213543A2 describes a process for producing hydrogen from the exhaust gas from a hydrogen-operated glass melting furnace by high-temperature electrolysis, wherein a) water vapor is produced from hydrogen as fuel, b) the steam generated in step (a) is introduced as a reactant into a high-temperature electrolysis to produce an electrolysis product comprising hydrogen and oxygen, and c) hydrogen is separated from the steam obtained in step (a) and from the electrolysis product obtained in step (b).

[0013] However, it is also known that electrolysis of water in general requires a high purity of said water (steam) in order to be effective. Tough, when using the exhaust / flue gas from a melting tank, next to the water steam, there are also dust and other gases in significant amounts and coming especially from the decomposition of certain raw materials. Hence, exhaust gas evolving from the melting of a glass batch will comprise especially CO2 (coming from carbonate raw materials) but also SOX(coming from sulfate / sulfite raw materials) and NOX(coming from nitrate / nitrite raw materials). Therefore, in such a case, either the electrolysis process is not fully effective due to significant contamination of the treated water steam or the process requires a step of purification / separation of the water steam from its contaminants before operating the electrolysis, then detrimental to the overall process (time, energy, yield and / or costs, etc.).

[0014] However, in the context of global warming that puts pressure on glass manufacturers as well as the energy prices and CO2 taxes that could become soon a severe threat on competitiveness in the glass business, there is still a need to provide a glass furnace / process which shows decreased CO2 emissions, while being financially viable.OBJECTIVE OF THE INVENTION

[0015] 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.

[0016] In particular, it is a further objective of the present invention to provide a glass furnace / process which shows decreased CO2 emissions by using hydrogen as a fuel.

[0017] It is a further objective of the present invention to provide a glass furnace / process which shows decreased CO2 emissions by using hydrogen as a fuel, while being financially viable.DESCRIPTION OF THE INVENTION

[0018] The present invention relates to a furnace for melting vitrifiable materials, comprising :(i) a melting tank equipped with heating means configured to melt vitrifiable materials and thereby to provide a melt;(ii) a fining tank equipped with combustion heating means alimented with oxygen as an oxidizer and hydrogen as a fuel, said heating means being configured to emit a plurality of combustion flames and thereby to provide a refined melt and water steam as a combustion product;(iii) at least one neck separating the melting tank and the fining tank;(iv) inlet means located at the melting tank, configured to feed the vitrifiable materials in said melting tank; and(v) outlet means located downstream of the fining tank configured to flow the refined melt from the fining tank to a working zone; said furnace further comprising : a steam electrolysis unit, configured to electrolyze at least a part of said water steam into an electrolysis product flow comprising a hydrogen flow and an oxygen flow, and a circuit configured to conduct at least a part of said hydrogen flow from said steam electrolysis unit towards said combustion heating means at the fining tank.

[0019] Hence, the invention is based on a novel and inventive approach. In particular, the inventors have found that, in a glass melting furnace, by using the combination of (i) a H2 / O2 combustion in the fining tank; (ii) a steam electrolysis unit linked to the fining tank to treat the exhaust gas from said fining tank and (iii) a segmented design (namely with the melting zone separated from the fining zone by a neck), it is possible to reach the above-cited objectives, that-is-to-say to obtain a glass melting furnace / process showing decreased CO2 emissions due to the use of hydrogen as a fuel while being economically viable, especially while allowing an effective water steam electrolysis process, without the need to purify the water steam flow beforehand. Indeed, in the invention, the neck separating the melting tank and the fining tank allows to reduce greatly "contamination" of the exhaust gas in the fining zone with components coming from the melting zone, especially CO2 (but also NOx, SOx,dust,...), thereby providing an exhaust gas in the fining zone which is pure or almost pure water (coming from the combustion of H2 and O2).

[0020] The invention also relates to a process for melting vitrifiable materials, comprising the steps of :(a) charging vitrifiable materials in a melting tank through inlet means;(b) melting the vitrifiable materials in the melting tank by heating with heating means, thereby providing a melt;(c) flowing the melt to the fining tank through a neck separating the melting tank and the fining tank;(d) fining the melt in the fining tank by heating with a plurality of combustion flames emitted by combustion heating means alimented with oxygen as an oxidizer and hydrogen as a fuel, thereby providing a refined melt and a water steam;(e) flowing the refined melt to a working zone through outlet means; said process further comprising the steps of:(f) electrolysis of at least a part of said water steam, thereby producing an electrolysis product flow comprising a hydrogen flow and an oxygen flow, and(g) conducting at least a part of said hydrogen flow towards said combustion heating means at the fining tank, for it to be used as said fuel.

[0021] By implementing all the features of the invention, the process of the invention shows a lowered CO2 fingerprint and it is economically viable especially as it allows an effective water steam electrolysis process.

[0022] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments, given by way of simple illustrative and non- restrictive examples.

[0023] 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. By "width" in the invention, it is meant, unless otherwise specified, the dimension (in average) perpendicular to the glass stream. Finally, the terms "upstream" and "downstream" refer to the main flow direction of the glass in the melting tank and in the fining tank and are to be understood with theircommon sense, namely herein as meaning along the averaged moving direction of the glass batch / the glass melt (defined herein as "glass stream"), from the inlet means located at the melting tank to the outlet means, when operating the furnace according to the invention.

[0024] The furnace of the invention comprises a melting tank equipped with heating means configured to melt vitrifiable materials and thereby to provide a melt.

[0025] According to the invention and as commonly adopted in the glass art, by "vitrifiable materials", it is meant the mixture of starting materials fed in the furnace of the invention. Vitrifiable materials according to the invention may comprise glass raw materials and / or cullet. In one embodiment, the vitrifiable materials comprise raw materials and cullet, the amount of cullet being at least 10% in weight of the total amount of vitrifiable materials, preferably at least 20% in weight of the total amount of vitrifiable materials. More preferably, the amount of cullet is at least 30% in weight of the total amount of vitrifiable materials, or even, very preferred, at least 40% in weight. This is advantageous as it allows to reduce the CO2 production / emission of the furnace of the invention when operating (due to a reducing of the emission occurring from the decarbonization of the carbonate raw materials).

[0026] According to the invention and as commonly adopted in the glass art, by "melting tank", it is meant a tank defining a zone where the vitrifiable materials are charged and melt by heating, and comprising, when the furnace is in process, a melt and a "blanket" of unmelted vitrifiable materials that floats on the melt and is progressively melted and therefore reduced from upstream to downstream of the melting tank. For example, the surface area of the melting tank in the invention may range from 25 to 400 m2.

[0027] According to the invention, the heating means in the melting tank may be any suitable heating means. According to an embodiment, the heating means in the melting tank is comprised of a plurality of electrodes and / or a plurality of combustion heating means and / or a plurality of plasma torches. This means that said heating means may be comprised of the three aforementioned types of heating, or two of them or only one type of them.

[0028] In the embodiment where the heating means in the melting tank are comprised of a plurality of electrodes, they may be located at the bottom of said melting tank as immersed electrodes or "bottom electrodes". Said plurality of electrodes may be advantageously arranged according to a specific pattern (e.g., checkerboard), in order to facilitate connection to transformers and electric current balance. For example, in the case of immersed electrodes, their height is between 0.3 and 0.8 times glass melt height. Alternatively, the plurality ofelectrodes, if any, may extend from the top of the melting tank (for example, maintained commonly by a water-cooled holder) and are immersed. These "top electrodes" may be advantageously located along the edge of the tank and / or at the corner(s). The number of electrodes may be 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.

[0029] In the embodiment where the heating means in the melting tank are comprised of a plurality of combustion heating means (or burners), they are configured to emit a plurality of combustion flames, esp. above the melt. They may 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, methane, hydrocarbons, biogas, hydrogen or mixture thereof. They may be arranged along the side walls of the melting tank on each side thereof, e.g. in rows, to spread the plurality of combustion flames over practically the entire width of said tank, and spaced from one another in such a way so as to distribute the heat over a major portion of the length (or the whole length) of the melting tank.

[0030] In the embodiment where the heating means in the melting tank are comprised of a plurality of plasma torches, they are configured, each, to emit from a working fluid a plasma above the melt, preferably in a direction essentially parallel to the melt surface. They may be of the type that uses electricity as an energy source to generate the plasma, said source being arc-driven source with various current waveforms (DC, AC, pulse DC,...) or electromagnetic (EM) wave-driven source with various EM wave generation (microwaves, induction,...). Preferably, the working fluid may comprise, or consist of, hydrogen, helium, air, oxygen, neon, argon, nitrogen, carbon monoxide, carbon dioxide, water or a mixture thereof

[0031] The furnace of the invention comprises further a fining tank equipped with combustion heating means alimented with oxygen as an oxidizer and hydrogen as a fuel, said heating means being configured to emit a plurality of combustion flames, esp. above the melt.

[0032] According to the invention and as commonly adopted in the glass art, by "fining tank", it is meant a tank defining a zone where there is no more "blanket" of unmelted vitrifiable materials that floats on the melt and where the glass melt is heated at temperatures higher than melting tank temperatures (generally above 1400°C or even above 1450°C), in order to refine the glass (mainly by eliminating major part of bubbles). This fining tank is also commonly called "clarification tank" in the art. For example, the surface area of the fining tank in the invention may range from 25 to 400 m2.

[0033] According to the invention, the fining tank comprises combustion heating means (or burners), configured to emit a plurality of combustion flames, esp. above the melt. They are alimented with oxygen as an oxidizer and hydrogen as a fuel. They may be arranged along the side-walls of the fining tank on each side thereof, e.g. in rows, to spread the combustion flames over practically the entire width of said tank, and spaced from one another in such a way so as to distribute the heat over a major portion of the length (or the whole length) of the fining tank.

[0034] According to the invention, the plurality of combustion heating means in the fining tank provides (i) a refined melt and (ii) a water steam as a combustion product. Indeed, the heat generated by the plurality of the combustion flames allow the glass melt to be refined and the combustion / burning process of hydrogen and oxygen in said combustion heating means gives water in the form of steam (due to the high temperature in the fining tank).

[0035] According to an embodiment, the fining tank comprises further, in addition to the combustion heating means, a plurality of electrodes. According to this embodiment, the plurality of electrodes are advantageously located in the upstream part of the fining tank, e.g. in the first third of the fining tank taken in its length.

[0036] The furnace of the invention comprises further at least one neck separating the melting tank and the fining tank.

[0037] For the sake of clarity, according to the invention and as commonly accepted in the art, by a "neck" separating the melting tank and the fining tank, it is meant : (i) a narrowing in width and in (crown) height compared to the melting tank and the fining tank, together with (ii) an opening (of the neck) being only partially under the glass melt / batch blanket free surface, then leaving a free opening above the glass melt / batch blanket. This definition excludes therefore a "throat", which has its "opening" completely under the glass melt / blanket free surface (thereby leaving no free space above the glass melt / batch blanket), as commonly accepted in the art.

[0038] The base of the neck in the invention may be located essentially at the level of the floor / bottom of the melting tank, or above said level or below said level. Moreover, the base of the neck may be located essentially at the level of the floor / bottom of the fining tank, or above said level or below said level.

[0039] Such a neck separating the melting tank and the fining tank in the invention is advantageous because it stabilizes the blanket of raw materials and avoid unmelted particlesflowing directly towards the fining tank. This point can advantageously improve glass quality. Moreover, it also allows a wider opening (than a common throat) and therefore lower glass velocities leading to lower refractory corrosion and wear. This point can advantageously improve furnace lifetime. Moreover, the presence of the neck in the invention allows to deal with / treat independently exhaust gas from melting tank independently from exhaust gas from fining tank. Above all, in the context of the invention and as already explained, it allows to avoid or greatly reduce "contamination" of exhaust gas in fining tank by exhaust gas from melting tank, thereby allowing an easier and more effective water steam electrolysis.

[0040] According to an embodiment of the invention, the furnace comprises two necks separating the melting tank and the fining tank and arranged in the width of the melting and fining tanks. According to still an embodiment of the invention, the furnace comprises two melting tanks and two necks, each neck separating a melting tank and the fining tank.

[0041] The furnace of the invention comprises further inlet means located at the melting tank, configured to feed the vitrifiable materials in said melting tank.

[0042] Preferably, and as known in the art, the inlet means are either located upstream of the melting tank and / or located at the top of the melting tank.

[0043] In an embodiment, the inlet means (are located upstream of the melting tank, either in the width of said tank or laterally in its length. In an alternative embodiment, the inlet means are located at the top of the melting tank ("top batch charger"), which allow advantageously to charge the vitrifiable materials directly on the top of glass melt, especially over the entire surface of the melting tank. It may advantageously be of the type "rotating batch charger" or "linear X-Y-batch charger" (e.g., in the form of a distributor arm that can move in both X-Y directions, namely in the length and width of the melting tank), located above the glass melt and below the crown of the melting tank. Preferably, a top batch charger may be considered when the melting tank comprises electrodes as heating means.

[0044] In an advantageous embodiment of the invention, the furnace comprises a melting tank (enlarged laterally and equipped with at least two inlet means, located on both sides of the melting tank based on the location of the neck, either at the lateral sides or as top batch chargers.

[0045] The furnace of the invention comprises further outlet means located downstream of the fining tank, configured to flow the refined melt from the fining tank to a working zone.According to an embodiment, the outlet means are composed of at least an outlet neck or, alternatively, at least an outlet throat, in order to lead the melt towards a working zone.

[0046] The working zone according to the invention may comprise, for example, a conditioning zone in which thermal conditioning by controlled cooling is carried out prior to glass melt leaving said zone through an outlet to a forming zone. Such a forming zone may comprise, for example, a float installation and / or a rolling installation, with the aim to manufacture flat glass products.

[0047] According to the invention, the furnace further comprises a steam electrolysis unit, configured to electrolyze at least a part of said water steam into an electrolysis product flow comprising a hydrogen flow and an oxygen flow. The electrolysis unit according to the invention may be any suitable electrolysis unit described in the art, including electrodes, esp. suitable for carrying out "high temperature electrolysis", without the need to detail more in the present text.

[0048] According to the invention, the furnace further comprises a circuit configured to conduct at least a part of said hydrogen flow from said steam electrolysis unit towards said combustion heating means at the fining tank.

[0049] According to an advantageous embodiment, the furnace comprises further a separation means configured to separate said hydrogen flow and said oxygen flow from said electrolysis product flow.

[0050] According to another advantageous embodiment, the furnace comprises further a circuit configured to conduct at least a part of said oxygen flow from said steam electrolysis unit towards said combustion heating means at the fining tank.

[0051] The invention also relates to a process for melting vitrifiable materials, comprising the steps of :(a) charging vitrifiable materials in a melting tank through inlet means;(b) melting the vitrifiable materials in the melting tank by heating with heating means, thereby providing a melt;(c) flowing the melt to the fining tank through a neck separating the melting tank and the fining tank;(d) fining the melt in the fining tank by heating with a plurality of combustion flames emitted by combustion heating means alimented with oxygen as an oxidizer and hydrogen as a fuel, thereby providing a refined melt and water steam;(e) flowing the refined melt to a working zone through outlet means; said process further comprising the steps of:(f) electrolysis of at least a part of said water steam, thereby producing an electrolysis product flow comprising a hydrogen flow and an oxygen flow, and(g) conducting at least a part of said hydrogen flow, preferably the whole hydrogen flow, towards said combustion heating means at the fining tank, for it to be used as said fuel.

[0052] The process is advantageously carried out with operating the furnace of the invention.

[0053] Features and embodiments described above in relation with the furnace, for example for the melting tank, the fining tank, the neck, the inlet means, the outlet means, the combustion heating means, the electrolysis unit, the vitrifiable materials, are applicable to the process of the invention.

[0054] At the step (f) of electrolysis, the water steam provided by the combustion at the fining tank is split into an electrolysis product flow by supplying electricity (e.g. a direct current).

[0055] The step (f) of electrolysis of the invention corresponds to a so-called "high- temperature electrolysis" because the water steam treated at that step comes from the fining tank / step as an exhaust gas and show therefore a high temperature. In particular, according to an embodiment, the water steam, at step (f) of electrolysis, has a temperature higher than 100°C or 150°C, preferably higher than 200°C (or, in other words, the step of electrolysis is carried out at a temperature higher than 150°C, preferably higher than 200°C). More preferably, the water steam, at step (f) of electrolysis, has a temperature higher than 250°C, 300°C, 350°C, 400°C, 450°C or even 500°C. In another embodiment, the water steam, at step (f) of electrolysis, has a temperature up to 1200°C, 1100°C, 1000°C, 900°C or 850°C.

[0056] In an embodiment, next to said water steam, auxiliary components may be provided at the step (f) of electrolysis in a known manner, such as electrolytes or organic solvents.

[0057] The step (f) of electrolysis according to the invention (namely a "high-temperature electrolysis") is carried out in a known manner, as described in the art, without the need to detail more in the present text.

[0058] The process of the invention comprises a step of conducting at least a part of said hydrogen flow towards said combustion heating means at the fining tank, for it to be used as said fuel. Advantageously, the hydrogen flow from the step (f) of electrolysis and used as afuel at the fining tank has a high temperature, which is in favour of global energy consumption of the furnace.

[0059] Preferably, the hydrogen flow and the oxygen flow are produced at the step (f) of electrolysis as separate flows. If it is not the case, according to an embodiment, the process of the invention comprises further, after step (f) and before step (g), a step of separating said hydrogen flow and said oxygen flow from said electrolysis product flow.

[0060] According to another embodiment, the process of the invention comprises, after step (f), a step of conducting at least a part of said oxygen flow, preferably the whole oxygen flow, towards said combustion heating means at the fining tank, for it to be used as said oxidizer. According to this embodiment, advantageously, the oxygen flow from the step (f) of electrolysis and used as an oxidizer at the fining tank has a high temperature, which is in favour of global energy consumption of the furnace.

[0061] In another embodiment of the process of the invention, the step (b) of melting the vitrifiable materials in the melting tank is carried out by heating with a plurality of electrodes and / or a plurality of combustion heating means and / or a plurality of plasma torches. This means that said heating means may be comprised of the three aforementioned types of heating, or two of them or only one type of them. Preferably, the step (b) of melting the vitrifiable materials in the melting tank is carried out by heating with a plurality of electrodes and / or a plurality of plasma torches. This means that said heating at the step (b) of melting is carried out with both aforementioned types of heating, or only one type of them. This is advantageous for CO2 fingerprint of the process as this results in a fully-electrical melting step.

[0062] Finally, the invention also relates to the use of a furnace according the invention, in a flat glass manufacturing process, for example in a float glass manufacturing process. In this last embodiment, downstream of the working zone, the furnace comprises further a float installation, including notably and as known a tin bath.

[0063] The person skilled in the art realizes that the present invention is by no means limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It is further noted that the invention relates to all possible combinations of features, and preferred features, described herein and recited in the claims.

Claims

CLAIMS1. Furnace for melting vitrifiable materials, comprising :(i) a melting tank equipped with heating means configured to melt vitrifiable materials and thereby to provide a melt;(ii) a fining tank equipped with combustion heating means alimented with oxygen as an oxidizer and hydrogen as a fuel, said heating means being configured to emit a plurality of combustion flames and thereby to provide a refined melt and a water steam as a combustion product;(iii) at least one neck separating the melting tank and the fining tank;(iv) inlet means located at the melting tank, configured to feed the vitrifiable materials in said melting tank; and(v) outlet means located downstream of the fining tank configured to flow the refined melt from the fining tank to a working zone; said furnace further comprising : a steam electrolysis unit configured to electrolyse at least a part of said water steam into an electrolysis product flow comprising a hydrogen flow and an oxygen flow, and a circuit configured to conduct at least a part of said hydrogen flow from said steam electrolysis unit towards said combustion heating means at the fining tank.

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

3. Furnace according to one of the preceding claims, characterized in that the fining tank comprises further a plurality of electrodes.

4. Furnace according to one of the preceding claims, characterized in that it comprises further separation means configured to separate said hydrogen flow and said oxygen flow from said electrolysis product flow.

5. Furnace according to one of the preceding claims, characterized in that it comprises further a circuit configured to conduct at least a part of said oxygen flow from said steam electrolysis unit towards said combustion heating means at the fining tank.

6. Process for melting vitrifiable materials, comprising the steps of :(a) charging vitrifiable materials in a melting tank through inlet means;(b) melting the vitrifiable materials in the melting tank by heating with heating means, thereby providing a melt;(c) flowing the melt to the fining tank through a neck separating the melting tank and the fining tank;(d) fining the melt in the fining tank by heating with a plurality of combustion flames emitted by combustion heating means alimented with oxygen as an oxidizer and hydrogen as a fuel, thereby providing a refined melt and a water steam;(e) flowing the refined melt to a working zone through outlet means; said process further comprising the steps of:(f) electrolysis of at least a part of said water steam, thereby producing an electrolysis product flow comprising a hydrogen flow and an oxygen flow, and(g) conducting at least a part of said hydrogen flow towards said combustion heating means at the fining tank, for it to be used as said fuel.

7. Process according to the preceding claim, characterized in that it comprises further, after step (f) and before step (g), a step of separating said hydrogen flow and said oxygen flow from said electrolysis product flow.

8. Process according to one of claims 6-7, characterized in that it comprises further, after step (f), a step of conducting at least a part of said oxygen flow towards said combustion heating means at the fining tank, for it to be used as said oxidizer.

9. Process according to one of claims 6-8, characterized in that the water steam, at the step (f) of electrolysis, has a temperature higher than 150°C, preferably higher than 300°C.

10. Process according to one of claims 6-9, characterized in that the water steam, at step (f) of electrolysis, has a temperature up to 1200°C.

11. Process according to one of claims 6-10, characterized in that the step (b) of melting the vitrifiable materials in the melting tank is carried out by heating with a plurality of electrodes and / or a plurality of combustion heating means and / or a plurality of plasma torches.

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

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