Process for producing a soda-lime-silica glass bath and installation for its implementation

Abstract

Method for producing a bath of soda-lime-silica glass and installation for its implementation This method comprises a step of reductive melting in submerged combustion (SCM) of said basic vitrifiable mixture with, where appropriate, added cullet, said reductive melting being obtained by a stoichiometric excess relative to the dioxygen oxidant of a gaseous fuel chosen from hydrogen and decarbonated gases, and / or by an addition of at least one solid reducing agent, in order to reduce the sulfate to sulfide, giving a glass called "sulfide glass" or "reduced glass"; and a second step of oxidative melting by radiative heating according to which said "sulfide glass" in the molten state is mixed with a cullet melting product called "sulfate glass" or "oxidized glass", to lead to a release of SO2 capable of entraining the bubbles present in the resulting glass in order to refine it. Figure to be published: Figure 1

Description

Title of the invention: Method for producing a soda-lime-silica glass bath and installation for its implementation

[0001] The present invention relates to a method for producing a bath of soda-lime-silica glass for the manufacture of both flat glass, for buildings and automobiles, by the "float" process, and hollow glass, from a vitrifiable base mixture comprising: - silica sand; - sodium carbonate or sodium sulfate; - a refining agent consisting of sodium sulfate; and - limestone and / or dolomite.

[0002] The soda-lime-silica glass bath that we aim to obtain has in particular the following composition: - 68 to 74% by mass of SiO2; - 11 to 15% by mass of Na2O + K2O; - 9 to 15% by mass of CaO + MgO; and - less than 5% by mass of other oxides, such as BaO, Al2O3, Fe2O3, SO3,

[0003] and can be obtained, according to the present invention, from a basic vitrifiable mixture, of composition: - 57 to 63% by mass of silica sand; - 17 to 23% by mass of sodium carbonate; - 15 to 20% by mass of limestone or dolomite; - less than 5% by mass of other constituents, such as feldspar, sulfate of soda and colorants,

[0004] or from a vitrifiable base mixture, of composition: - 52 to 59% by mass of silica sand; - 22 to 27% by mass of sodium sulfate; - 15 to 19% by mass of limestone or dolomite; - less than 5% by mass of other constituents, such as feldspar and colorants.

[0005] The present invention also relates to an installation for implementing this method.

[0006] For the melting of vitrifiable mixtures, flame furnaces with transverse or loop burners have been known for a long time, the fuel being natural gas, air or pure oxygen. The vitrifiable mixture is charged into these flame furnaces at one end of the furnace, with the molten glass exiting at the other end. The mixtures Vitrifiables here consist of silica sand, sodium carbonate, alkaline earth carbonates, sodium sulfate as a refining agent and recycled glass called cullet.

[0007] Heat transfer is provided mainly by radiation. The flame is above the glass bath and the hot fumes are used to heat the combustion air in installations called alternating-operation regenerators, which comprise stacks of refractory bricks.

[0008] In such flame furnaces, melting and refining are carried out in the same basin. Refining consists of eliminating bubbles using sodium sulfate, introduced in small quantities, which decomposes into SO2 at the hot point of the furnace, i.e. around 1550°C.

[0009] As an example of a flame furnace, we can mention the “float” glass furnace, which produces more than 600 tons of glass per day.

[0010] Recently introduced, submerged combustion melting (SCM) is based on the principle of developing the flame no longer above but in the glass bath.

[0011] The fuel gas (natural gas) and the oxidant (air or oxygen) are injected into the hearth by suitable burners. Heat transfer is ensured by convection and radiation of the flame in direct contact with the molten bath, which leads to very high productivity, namely a very high molten tonnage per unit of time and hearth surface. The regime is highly turbulent. The orientation of the furnace is mainly vertical, and production is currently limited to less than 200t / d per furnace.

[0012] The raw materials - identical to those of the conventional furnace - are injected laterally by an endless screw, below the level of the glass to limit dust. The fumes exit from the top. The melting temperature does not exceed 1350°C, which limits the wear of the refractories despite the strong convection.

[0013] The SCM furnace has also demonstrated its ability to use solid fuels, loaded with the vitrifiable mixture and consisting of biomass and various combustible waste, which are burned using natural gas or oxygen injected into the hearth.

[0014] However, the molten glass coming out of this furnace is only raw glass, loaded with bubbles, or even unmelted silica. It can only be used as is for the production of fibers (mineral wools) for which bubbles are not a problem.

[0015] For noble applications such as flat glass or hollow glass, this process is not used today.

[0016] The present invention aims at the total decarbonization of the production of soda-lime-silica glass, whether flat glass or hollow glass. It also aims to reduce the cost of raw materials.

[0017] For the production of low-carbon glass, the process according to the present invention is based on the principle of two-stage process operation, namely - a first stage consisting of a coarse reducing fusion in submerged combustion with a fuel chosen from hydrogen and decarbonized gases; and - a second stage consisting of an oxidative refining fusion by radiative heating, either at atmospheric pressure in a radiative enclosure of the same type as the refining zone of the current conventional furnace, or under reduced or slightly reduced pressure to accelerate degassing and reduce the size of the furnace, with, in both cases, the particularity that the refining is based on an original chemistry mixing two glasses of different nature, namely: - on the one hand, a normal, oxidized sulfated glass, which may include additional sulfate, originating exclusively from cullet which is introduced directly into the refining zone, or originating from the oxidizing fusion in submerged combustion of a vitrifiable mixture comprising all of the cullet in the refining zone; and - on the other hand, a glass from the first stage, produced from a starting vitrifiable mixture containing sodium sulfate, already present or added, but in which the sulfate is partially reduced to sulfide by a reducing agent.

[0018] When the two glasses meet, the following reaction occurs, also called hereinafter the “refining equation”:

[0019] 3Na2SO4 + Na2S = 4SO2 + 4Na2O

[0020] (sulfur +6 + sulfur -2 = sulfur +4)

[0021] where Na2SO4 is the sodium sulfate of the oxidized glass and Na2S is the sodium sulfide of the reduced glass,

[0022] this reaction leading to a powerful release of SO2.

[0023] It is this release of SO2 which, as in the case of all sulfate refining, will cause the other bubbles present in the glass, but here the reaction is more efficient than in conventional refining where the decomposition of the sulfate is a thermal decomposition. The sulfate will, according to the invention, decompose at a lower temperature and there will therefore be less need for heating to obtain the same quality of refining.

[0024] It is therefore necessary to ensure that the two reagents of this reaction which occurs at the time of mixing of the glasses in the oxidizing fusion zone are in sufficient quantity to ensure the reaction, the theoretical proportion being that there is 5.5 times more sulfate, expressed as Na2SO4 than sulfide, expressed as Na2S.

[0025] Indeed, if Qi is the flow rate of sulfate glass, in t / d, Ci is the % by mass of Na2SO4 in this glass, Q2 is the flow rate of sulfide glass, in t / d, and C2 is the % by mass of Na2S in this glass, we must have:

[0026] Qj x Ci = 5.5 Q2 * C2

[0027] In other words, the oxide-reducing conditions of each source of molten glass must be adjusted as best as possible, which determine Ci and C2 as a function of their flow rate values ​​respectively Qi and Q2. In other words, the sulfate and sulfide contents in the two glass streams must be adjusted by a carefully chosen introduction of reducing agent and, where appropriate, sulfate into the sulfide glass.

[0028] As a result, the furnace intended for refining can be of reduced size compared to that of a conventional float furnace.

[0029] To reduce the cost of raw materials, the present invention offers the possibility of replacing the sodium carbonate in the starting vitrifiable mixture with sodium sulfate, using the SCM process, the SO2 emitted by the latter through the fumes being able to advantageously be converted into desulfogypsum and pure, captureable CO2.

[0030] The present invention therefore firstly relates to a process for obtaining a refined soda-lime-silica glass bath from: • a basic vitrifiable mixture comprising: • silica sand; • sodium carbonate with sodium sulfate as a refining agent, or sodium sulfate; • limestone and / or dolomite; and • where appropriate at least one colorant, and • added cullet, which also contains sulfate ions,

[0031] characterized by the fact that it comprises the following two successive stages: 1. a submerged combustion reductive melting (SCM) of said basic vitrifiable mixture with, where appropriate, added cullet, said reductive melting being obtained by a stoichiometric excess relative to the dioxygen oxidant of a gaseous fuel chosen from hydrogen and decarbonated gases, and / or by the addition of at least one solid reducing agent, in order to reduce the sulfate to sulfide, giving a glass called “sulfide glass” or “reduced glass”; 2. oxidative melting by radiative heating whereby said “sulfide glass” in the molten state is mixed with a cullet melting product called “sulfate glass” or “oxidized glass”, to lead to the release of SO2 capable of entraining the bubbles present in the resulting glass with a view to refining it.

[0032] The decarbonized gas(es) used in the reductive fusion step may be chosen from CH4, biogas, gaseous fuels from biological processes such as electrofuels (e-fuels), and mixtures thereof.

[0033] The solid reducer(s) used in the reductive melting step may be chosen from coke, biomass coke, biomass, materials capable of giving a coke residue after pyrolysis, such as plastic residues, and mixtures thereof.

[0034] According to a first embodiment of the present invention, the oxidative melting step is carried out by radiative heating under atmospheric pressure, the cullet being introduced into the oxidative melting zone in the cold state and / or in the hot state, being in the latter case derived from a melt, in particular from an oxidative melt in submerged combustion.

[0035] The radiative heating in the oxidative melting zone at atmospheric pressure can advantageously be carried out electrically and / or by H2 / O2 burners and / or using at least one fuel chosen from hydrogen and decarbonized gases, the decarbonized gases being chosen in particular from CH4, in particular, biogas, and gaseous fuels, in particular from biological processes such as electrofuels, and mixtures thereof.

[0036] According to a second embodiment of the present invention, the oxidative melting is carried out by radiative heating under reduced pressure, the cullet being introduced into the oxidative melting zone in the cold state and / or in the hot state, being in the latter case derived from a melting, in particular from an oxidative melting in submerged combustion.

[0037] The reduced pressure is advantageously from 0.1 to 1 bar absolute, in particular from 0.3 to 1 bar absolute, in particular from 0.5 to 1 bar absolute.

[0038] Radiative heating in the oxidative melting zone under reduced pressure can be carried out electrically and / or by H2 / O2 burners.

[0039] Low pressure refining is a known way to obtain very good quality glass, whether it is of flame fusion, electric fusion or submerged combustion origin. The depression causes the bubbles to enlarge and rise. This vacuum refining process - generally from 0.1 to 0.3 bar absolute - is currently used industrially for special glasses but not for commodity glasses, due to the use of platinum required by the glass inputs / outputs under very low pressures.

[0040] Considering the power of the refining motor according to the present invention, which is induced by the torque S+6 / S-2, it is estimated that such a very low pressure is not necessary and that it is possible to operate between 0.5 and 1 bar absolute. As a result, the construction of the refining furnace is greatly facilitated, without a plate or almost without platinum, and also that its size can be reduced compared to a conventional thermal refining furnace.

[0041] According to a particular characteristic of the process according to the present invention, additional sulfate can be added to the vitrifiable mixture subjected to submerged combustion melting intended to constitute the cullet to be combined with the sulfide glass in the oxidizing melting zone, in order to have a sufficiently high sodium sulfate level in the molten cullet to satisfy the refining equation.

[0042] In accordance with another particular characteristic of the process according to the present invention, the starting point is a vitrifiable starting mixture comprising sodium sulfate, and the SO2-rich fumes from the reductive melting zone are converted by reaction with limestone to give desulfogypsum and pure, captureable CO2, or with decarbonized limestone to give desulfogypsum, the SO2 released during the oxidative melting also being able to be subjected to the above-mentioned conversion.

[0043] The reductive melting may be carried out at a temperature of 1250-1400°C, in particular 1300-1350°C, and the oxidative melting may be carried out at a temperature equal to or at least 100°C higher than that of the reductive melting.

[0044] The difference between the redox value of the “sulfide glass” or “reduced glass” and the redox value of the “sulfate glass” or “oxidized glass” may be at least 0.2, in particular at least 0.4, the redox values ​​being defined by the ratio of ferrous iron FeO to the total iron expressed as Fe2O3 in the glass considered.

[0045] This technology opens the way to the circular economy of the production of two major basic products of sustainable construction, glass and plaster, the emissions of one being used in the production of the raw materials of the other.

[0046] The present invention also relates to an installation for implementing the method as defined above, characterized in that it comprises: - at least one submerged combustion melting furnace for the reductive melting of the starting vitrifiable mixture; - a thermal refining furnace, in particular a flame furnace, intended to be supplied by the outlet of the submerged combustion melting furnace(s) and capable of operating at atmospheric pressure or at subatmospheric pressure; - a device for introducing cullet into said thermal refining furnace, said cullet introduction device consisting of at least one cold cullet charging niche at the head of said thermal refining furnace and / or at least one submerged combustion melting furnace for melting cullet for introduction into said thermal refining furnace; - a device for supplying the output of said thermal refining furnace to a float glass or hollow glass forming station; and - advantageously, a device for treating fumes rich in SO2 released during reductive fusion, by reaction with limestone or decarbonized limestone to obtain desulfogypsum and pure, captureable CO2, or limestone to obtain desulfogypsum. Examples

[0047] The following Examples illustrate the present invention without, however, limiting its scope.

[0048] In these Examples, the aim was to obtain a soda-lime-silica glass with a composition in % by mass:

[0049] SiO2.............................................71.7

[0050] Na2O............................................ 13.4

[0051] CaO........................................11.7

[0052] Miscellaneous*..................................3.1 (including 0.5 to 0.8% SO3)

[0053] * BaO, A12O3, Fe2O3, SO3,. . .

[0054] To this end, we left • a basic vitrifiable mixture called “in conventional sodium carbonate mode” (MV1) or a basic vitrifiable mixture called “in sodium sulfate mode” (MV2), the compositions of which (in % by mass) are given in the Table below; and of a flat glass cullet C, the quantity of which in relation to the basic vitrifiable mixture is indicated in each example. Composition (%) MV1 MV2 Silica sand 60.1 55.8 Sodium carbonate 19.6 0 Sodium sulfate 1 24.3 Limestone 17.6 17.2 Miscellaneous** 2.6 2.5

[0055] ** Feldspar, dyes,. . .

[0056] In the classic mode (MV1 Mix), CO2 emissions are limited to raw materials.

[0057] In the “sodium sulfate” mode (MV2 Mixture), there are no CO2 emissions from the soda.

[0058] Glass colorants, when present, are preferably added with the cullet to avoid possible interaction with reducing agents, such as Fe2O3.

[0059] The cullet used has a composition identical or substantially identical to that of the glass that one seeks to produce.

[0060] The installations used for the implementation of these Examples are shown schematically in Figures 1 to 4. “SCM” furnace designates a submerged combustion melting furnace.

[0061] [Fig.l] shows an installation comprising two identical SCM furnaces 1 and 2 which receive a vitrifiable mixture MV1 or MV2 and whose outlet feeds a conventional thermal refining flame furnace or float furnace 3, shown in a top view. The flames produced by hydrogen burners 4 are above the bath and heat mainly by radiation. Furnace 3, which receives cold cullet C, produces a glass which in a known manner flows through a corset 5 into an ember 6 and which feeds through a channel 7 a float glass forming station to produce a flat glass. Furnace 3 operates at atmospheric pressure.

[0062] [Fig.2] shows an installation which differs from that of [Fig.l] in that the cullet C is introduced hot into the furnace 3, coming from a SCM calcine furnace 8. The same reference numbers as those of [Fig.l] are used to designate the common elements.

[0063] [Fig. 3] shows an installation which differs from that of [Fig. 2] in that furnace 3' operates at subatmospheric pressure, the flames above the radiation heating bath being produced by H2 / O2 burners 4'. The same reference numbers as those in [Fig. 2] are used to designate the common elements. The outlets of the three SCM furnaces 1, 2 and 8 open into a horizontal channel 9 for supplying the molten vitrifiable mixture MV1 or MV2 with the cullet C to furnace 3'. The latter is lined with refractories placed entirely in a sealed metal casing.

[0064] As can be seen in [Fig.4] which schematically shows the furnace 3' in vertical section, the molten mixture MV1 or MV2 with the cullet C flows into the horizontal channel 9 to fall into the furnace 3' via a vertical channel or chute 10 which opens in a sealed and tightly clamped manner into an opening made at one end of the upper wall of the metal enclosure under reduced pressure of the furnace 3'. The molten mixture MV 1 or MV2 with C leaves through an opening 11 made in the bottom of the furnace 3' at its other end, to be directed towards the float glass forming station. At this other end, in the upper part of the furnace 3', another opening is made from which a pipe 12 connected to a vacuum pump and a fume condenser leaves.

[0065] The level of the molten mixture MV 1 or MV2 with C is marked in [Fig.4] both in channel 9 (level n) and in furnace 3' (level n'). The flow rate of the molten mixture MV1 or MV2 with C falling into furnace 3' is regulated by a punch, symbolized by the arrow F, necessary to maintain the level n' The height H of the mixture at the outlet of furnace 3' depends on the reduced pressure which prevails in the latter, so that the glass can flow out. For example, if P = 0.75 bar absolute, the height h will be at least 1 m - 1 bar absolute of pressure representing approximately 4 m of glass height.

[0066] The radiative heating of the furnace 3' can be provided electrically or by H 2 / O2 burners. In this case, as the combustion product is only water, a flue gas + water condensation trap is installed before the vacuum pump.

[0067] Example 1: Production of a glass bath for flat glass

[0068] The aim is to produce a glass bath for flat glass at a rate of 600 t / d, with a quality of refined glass resulting in less than one gas bubble per liter, of a size less than 200 pm. Raw materials

[0069] - MV1: 66% by mass of molten glass compared to the total output of 600 t / d, or 400 t / d - C: 33% by mass compared to the total output of 600 t / d, i.e. 200 t / d, introduced cold into the oxidizing melting zone for refining. Refining equation

[0070] Q1 = 200 t / d

[0071] Q2 = 400 t / d

[0072] Cl = 0.8% by mass of Na2SO4

[0073] C2 = 0.1% by mass of Na2S

[0074] The C2 value is obtained here by the sole fuel H2 which is a reducing agent and by the stoichiometric adjustment of the flame. Sodium sulfate is also added in the MV1 composition. Facility

[0075] That of [Fig. 1]: - identical SCM 1 and 2 furnaces, supplied with MV 1 vitrifiable mixture: each of furnaces 1 and 2 consists of a vertical cylindrical tank with an internal diameter of 3m and a height of 3m, lined with alumina zirconia concrete refractories with a thickness of 100 mm in a metal casing, and is equipped with H2 / O2 burners in the hearth with a total power of 10 MW; - refining furnace 3, with a melting surface of 150 to 200 m2, radiatively heated by air / hydrogen or H2 / O2 burners or any other carbon-neutral gas and operating at a power of approximately 14 MW; - two symmetrical niches for loading the cullet at the head of kiln 3.

[0076] We can note the reduced size of furnace 3 compared to the refining part - post-hot point part - of a classic float furnace with 400m2 of melting surface.

[0077] Reductive fusion in submerged combustion: at a temperature of 1300 / 1350°C

[0078] Melting in the refining zone: carried out at approximately 1500°C. Adjusting the refining equation

[0079] The cullet is introduced at a rate of 100 t / day into each kiln niche. Q1 = 200 t / day

[0080] Each of the SCM 1 and 2 furnaces, supplied with MV1, has a draw of 200 t / day. Q2 = 400 t / day

[0081] A final redox in the glass produced of approximately 0.2 to 0.5 is targeted.

[0082] The refining equation Qix Ci= 5.5 Q2x C2 provides C2 = 0.07% by mass of Na2S, a value close to 0.1% by mass, which is the value of C2 to aim for in practice.

[0083] The target value C2 is assured: • on the one hand, by adding sodium sulfate to the MV1 composition, an addition which must be adjusted taking into account melting losses; and • on the other hand, by the addition of a reducer, which here is the hydrogen fuel itself provided that the flame is adjusted to sub-stoichiometry.

[0084] The following conditions are then met: - MV1 with the introduction of 0.3-0.5% by mass of sodium sulfate so that at the outlet, we have C2 = 0.1% by mass; - H2 / O2 flame regulated as reducing, i.e. with an H2 / O2 ratio of approximately 102% H2 compared to the stoichiometric value.

[0085] Example 2: Production of a glass bath for flat glass

[0086] This example differs from Example 1 in that the value of C2 is obtained by an additional reducing agent which is the carbon resulting from the introduction of biomass into the raw materials.

[0087] Target production - Raw materials - Refining equation - Installation

[0088] As in Example 1 Adjusting the refining equation

[0089] The procedure is as in Example 1 except that the hydrogen reducer in the melting / refining phase is replaced by the carbon reducer.

[0090] The following conditions are then met: - Neutral flame stoichiometry; - MV 1 with introduction of biomass coke or direct non-pyrolyzed biomass, at a rate of 1 to 2% by mass of coke or carbon, value to be adjusted to obtain the value of C2 = 0.1% by mass at the outlet of SCM 1 and 2 furnaces.

[0091] Example 3: Production of a glass bath for flat glass

[0092] This example differs from Example 1 in that the cullet is previously melted in an SCM furnace and poured molten into the oxidative melting zone for refining, which leads to an additional introduction of sodium sulfate into this SCM to obtain the Cl value of 0.8% by mass. Facility

[0093] That of [Fig.2]: • identical SCM 1 and 2 furnaces supplied with MV1 vitrifiable mixture, which are as described in Example 1; • SCM 8 furnace, supplied with cullet. SCM 8 furnace is centrally located to ensure a rational mix of feeds in furnace 3. SCM 8 furnace has the same constituent characteristics as SCM 1 and 2 furnaces, except that it has a reduced installed power of 6 MW. • refining furnace 3 with characteristics identical to those of furnace 3 of the installation in [Fig.l], but with a melting surface reduced in size to approximately 100 to 150m2, because all the glass it receives is already melted, and operates at a power of 8 MW; • all temperatures corresponding to submerged combustion are identical, 1300 / 1350°C, except for the SCM supplied with cullet where it can be only 1300°C. Melting in the refining zone is carried out at a temperature of 1500 / 1550°C. Adjusting the refining equation

[0094] The three SCM furnaces each fire 200 t / d. The side SCM furnaces are fed with the MV1 vitrifiable mixture.

[0095] For this purpose, 1% by mass of sodium sulfate is added to the cullet introduced into the SCM8 furnace because the latter eliminates more sulfate than the radiative heating of furnace 3. Thus, 1% by mass of sodium sulfate is added relative to MV1 to aim for C2 = 0.8% by mass at the outlet.

[0096] Example 4: Production of a glass bath for flat glass

[0097] This Example differs from Example 3 in that the oxidizing fusion zone for refining works under reduced pressure.

[0098] Target production - Raw materials - Refining equation

[0099] As in Example 1 Facility

[0100] That of Figures 3 and 4: • SCM ovens 1, 2 and 8 as defined in Example 3; • 3' oven identical to oven 3 but operating under reduced pressure - here P = 7.599 x 106Pa (0.75 atmosphere) - and with a surface area reduced to 50m2 considering that the refining is accelerated by the reduced pressure. The heating is a H2 / O2 flame radiative heater and can even be an electric radiant heater, the installed power in this part is reduced to 6MW; • the temperatures corresponding to submerged combustion are unchanged but the temperature in refining under reduced pressure can be lowered compared to atmospheric refining, namely 1400-1450°C. Adjusting the refining equation

[0101] As in Example 3.

[0102] The residence time of the glass in Examples 1, 2 and especially 3 and 4 is considerably reduced compared to a conventional float furnace, in particular by more than 50%.

[0103] The economic consequence is therefore significant for ovens that have to change color frequently: for example, a conventional oven losing more than 50 days of color transition per year will see these losses fall to less than 25 days.

[0104] Example 5 - Production of a glass bath for flat glass

[0105] This Example differs from Example 1 in that the MV2 mixture (i.e. with sodium sulfate) is used instead of the MV1 mixture.

[0106] The reducing agent which is necessary to treat the sulfated raw materials is here the hydrogen fuel: we therefore adjust the stoichiometry of the SCM flame to have an excess of H2.

[0107] Target production - Installation - Refining equation

[0108] As in Example 1. Raw materials

[0109] - MV2: 66% by mass of molten glass compared to the total output of 600 t / d, or 400 t / d - C: flat glass cullet at a rate of 33% by mass compared to the total output of 600 t / d, i.e. 200 t / d. Adjusting the refining equation

[0110] The procedure is as in Example 1, except that the vitrifiable mixture which feeds the two SCM furnaces 1 and 2 is the MV2 mixture and that the power installed on these two furnaces is higher, by 20%, to take into account the higher enthalpy, of the order of 10%, of the desulfation reaction.

[0111] As for Example 1, a

[0112] reducing effect theoretically equivalent to 4.2% by mass of pure carbon relative to the weight of sulfate, following the reaction:

[0113] Na2SO4 + ' / 2 C + SiO2 = Na2SiO3 + / 2 CO2 + SO2

[0114] or its hydrogen equivalent:

[0115] Na2SO4 + H2 + SiO2 = Na2SiO3 + H2O + SO2

[0116] We must therefore add 1.4% by mass of H2 relative to the weight of sulfate? therefore adjust the stoichiometry accordingly by transferring this hydrogen to the burners, i.e. approximately 672 kg H2 / day to be adjusted in excess relative to the flame stoichiometry, i.e. less than 10% of the stoichiometric H2 consumption.

[0117] Example 6: Production of a glass bath for flat glass

[0118] This example differs from Example 5 in that coke is used as a reducing agent, the origin of which is biomass introduced with the MV2 mixture into the SCMs. Target production - Raw materials

[0119] As in Example 5 Facility

[0120] That of [Fig. 1] Adjusting the refining equation

[0121] The procedure is as in Example 5, except that the reducing agent is biomass coke. 4.2 to 4.5% by weight of coke relative to the weight of sulfate is added to the MV2 composition, so as to obtain 0.1% of sulfide at the outlet.

[0122] The SO2 will be emitted at a rate of 70 t / d and converted into 92 t / d of desulfogypsum (DSG) in an installation away from the glass line, with an input of 68 t / d of limestone CaCO3 or its decarbonized equivalent, according to the diagram in [Fig.5].

[0123] Example 7: Production of a glass bath for hollow glass

[0124] The target is a production of 450 t / d from the refining furnace. Raw materials

[0125] - MV1: 33% by mass of molten glass compared to the total draw - C: 66% by mass compared to the total draw.

[0126] The temperatures are the same as in the case of flat glass, but with refining at a temperature of 1500°C or a temperature close to 1500°C. Refining equation

[0127] Q1 = 300 t / d

[0128] Q2 = 150 t / d

[0129] Cl = 0.8% by mass of Na2SO4

[0130] C2 = 0.3% by mass of Na2S Facility

[0131] That of [Fig.l] but with a single SCM oven: - a single SCM furnace (1 or 2) with a diameter of 2.5 m, supplied with MV 1 vitrifiable mixture; - oven 3; and - two symmetrical niches for placing cullet Adjusting the refining equation

[0132] The only SCM furnace (1 or 2) is fired at 150 t / d, MV1 being melted using H2 / O2 burners aiming for a sulphide content equal to:

[0133] (300*0.8) / (5.5* 150) = 0.29%, or in practice 0.3%

[0134] This sulfide content is obtained either by hydrogen, or by the introduction of biomass, or by a contribution of both.

[0135] The remainder of the cullet is melted in furnace 3, which therefore sees its melting surface reduced by at least 30%.

[0136] Example 8 - Production of a glass bath for hollow glass

[0137] The aim is to produce 450 t / d of hollow glass from the refining furnace. Raw materials

[0138] - MV 1: 10% by mass compared to the total draw - C: 90% by mass compared to the total draw. Refining equation

[0139] Q1 = 405 t / d

[0140] Q2 = 45 t / d

[0141] Cl = 0.8% by mass of Na2SO4

[0142] C2 = 1.3% by mass of Na2S Facility

[0143] That of Example 7 Adjusting the refining equation

[0144] The proportion of raw materials is low in this case, and leads to a C2 value of 1.3% Na2S which can be difficult to achieve, either by hydrogen or by biomass.

[0145] Cullet can then be introduced into the SCM with the raw materials.

[0146] Thus we can return to example 7 by adding for example 105 t / d of cullet.

Claims

Claims

1. - Process for obtaining a refined soda-lime-silica glass bath from: • a basic vitrifiable mixture comprising: • silica sand; • sodium carbonate with sodium sulfate as a refining agent, or sodium sulfate; • limestone and / or dolomite; and • where appropriate at least one colorant, and • added cullet, which also contains sulfate ions, characterized in that it comprises the following two successive stages:

1. a submerged combustion reductive melting (SCM) of said basic vitrifiable mixture with where appropriate added cullet, said reductive melting being obtained by a stoichiometric excess relative to the dioxygen oxidant of a gaseous fuel chosen from hydrogen and decarbonated gases, and / or by an addition of at least one solid reducing agent, in order to reduce the sulfate to sulfide, giving a glass called "sulfide glass" or "reduced glass"; 2.an oxidative fusion by radiative heating according to which said “sulfide glass” in the molten state is brought to mix with a cullet fusion product called “sulfate glass” or “oxidized glass”, to lead to a release of SO2 capable of entraining the bubbles present in the resulting glass with a view to refining it.

2. - Method according to claim 1, characterized in that the decarbonized gas(es) used in the reductive fusion step are chosen from CH4, biogas, gaseous fuels from biological processes such as electrofuels, and mixtures thereof.

3. - Method according to one of claims 1 and 2, characterized in that the solid reducing agent(s) used in the reductive melting step are chosen from coke, biomass coke, biomass, materials capable of giving a coke residue after pyrolysis, and mixtures thereof.

4. - Method according to one of claims 1 to 3, characterized in that the oxidative melting step is carried out by radiative heating under atmospheric pressure, the cullet being introduced into the oxidative melting zone in the cold state and / or in the hot state, being in the latter case derived from a melt, in particular from an oxidative melt in submerged combustion.

5. - Method according to claim 4, characterized in that the radiative heating is carried out in the oxidative melting zone at atmospheric pressure electrically and / or by H2 / O2 burners and / or using at least one fuel chosen from hydrogen and decarbonized gases, the decarbonized gases being chosen in particular from CH4, in particular biogas, and gaseous fuels, in particular from biological processes such as electrofuels, and mixtures thereof.

6. - Method according to one of claims 1 to 3, characterized in that the oxidative melting is carried out by radiative heating under reduced pressure, the cullet being introduced into the oxidative melting zone in the cold state and / or in the hot state, being in the latter case derived from a melting, in particular from an oxidative melting in submerged combustion.

7. - Method according to claim 6, characterized in that the reduced pressure is from 0.1 to 1 bar absolute (0.1*105 Pa to 105 Pa), in particular from 0.3 to 1 bar absolute (0.3* 105 Pa to 105 Pa), in particular from 0.5 to 1 bar absolute (0.5* 105 Pa to 105 Pa).

8. - Method according to one of claims 6 and 7, characterized in that the radiative heating is carried out in the oxidizing melting zone under reduced pressure electrically and / or by h2 / o2 burners.

9. - Method according to one of claims 3 to 7, characterized in that additional sulfate is added to the vitrifiable mixture subjected to submerged combustion melting intended to constitute the cullet to be combined with the sulfide glass in the oxidizing melting zone.

10. - Method according to one of claims 1 to 9, characterized in that one starts from a vitrifiable starting mixture comprising sodium sulfate, and that the SO2-rich fumes from the reducing melting zone are converted by reaction with limestone to to give desulfogypsum and pure, captureable CO2, or with decarbonized limestone to give desulfogypsum, the SO2 released during oxidative fusion can also be subjected to the above-mentioned conversion.

11. - Method according to one of claims 1 to 10, characterized in that the reductive melting is carried out at a temperature of 1250-1400°C, in particular 1300-1350°C, and the oxidative melting is carried out at a temperature equal to or at least 100°C higher than that of the reductive melting.

12. - Method according to one of claims 1 to 11, characterized in that the difference between the redox value of the "sulfide glass" or "reduced glass" and the redox value of the "sulfate glass" or "oxidized glass" is at least 0.2, in particular at least 0.4, the redox values ​​being defined by the ratio of ferrous iron FeO to the total iron expressed as Fe2O3 in the glass in question.

13. - Installation for implementing the method as defined in one of claims 1 to 12, characterized in that it comprises: - at least one submerged combustion melting furnace for the reductive melting of the starting vitrifiable mixture; - a thermal refining furnace, in particular a flame furnace, intended to be fed by the outlet of the submerged combustion melting furnace(s) and capable of operating at atmospheric pressure or at subatmospheric pressure; - a device for introducing cullet into said thermal refining furnace, said cullet introduction device consisting of at least one cold cullet charging niche at the head of said thermal refining furnace and / or at least one submerged combustion melting furnace for melting cullet for introduction into said thermal refining furnace;- a device for supplying the output of said thermal refining furnace to a float glass or hollow glass forming station; and - advantageously, a device for treating the SO2-rich fumes released during the reductive melting, by reaction with limestone or decarbonized limestone for; obtain desulfogypsum and pure, capturable CO2, or limestone to obtain desulfogypsum.

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