Process for capture of co2 integrated into melting of glass

Abstract

To provide a glass melting method that further reduces CO2 emissions from the glass melting process without resorting to an expensive process and plant.SOLUTION: This invention relates to a glass melting process, including: introducing a vitrifiable solid charge into a furnace (1) to thereby heat and melt the charge (11) in the furnace (1) to obtain molten glass (17); discharging a molten glass from the furnace and discharging a CO2-containing exhaust gas (20) from the furnace, wherein the charge contains at least one carbonate salt that releases CO2 gas (18) in a dissociation reaction when the charge is heated and melted; and using the exhaust gas discharged from the furnace (1), to produce at least one additive (33) in a form of an alkali metal or alkaline earth metal by carbonation with CO2 present in the exhaust gas, at least a portion thereof being incorporated into the charge introduced into the furnace.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the manufacture of glass. [Background technology]

[0002] Greenhouse gas emissions contribute greatly to global warming. One of these gases is CO2.

[0003] Therefore, it is important to reduce CO2 emissions into the atmosphere from industrial sites as much as possible.

[0004] Industrial plants that emit CO2 include glass furnaces.

[0005] For the production of glass, a vitrifiable solid charge having a controlled and appropriate composition for the properties of the glass to be produced is introduced into a furnace and melted therein. The molten glass thus obtained is discharged from the furnace and shaped according to the desired end product / end use, e.g., flat glass, hollow glass, optical glass, etc. Exhaust gases are also discharged from the furnace.

[0006] Melting glass is energy intensive.

[0007] In most cases, at least a portion of the required energy is provided by burning a carbon-based fuel such as natural gas, fuel oil, coal, etc. The combustion of a carbon-based fuel produces combustion gases that contain CO2 (due to the carbon atoms present in the fuel) and water vapor (due to the hydrogen atoms in the fuel), which form part of the flue gases discharged from the furnace.

[0008] For the future of the planet, it is important to reduce harmful emissions of greenhouse gases such as CO2 and industrial waste.

[0009] Various processes have been developed that make it possible to capture the CO2 present in exhaust gases, in particular industrial exhaust gases, by physical processes (e.g. cryogenic separation) and / or chemical processes (e.g. chemical looping).

[0010] However, most of the currently available industrial CO2 capture processes are cost-effective only for treating high flows of flue gas, such as those generated at large industrial sites.

[0011] The volumes of flue gas generated by glass melting furnaces, including large continuous furnaces such as float furnaces (furnaces used to make float glass), are not sufficient with current technology to enable such cost-effective CO2 capture.

[0012] Because CO2 emissions contribute to greenhouse gas impacts, it is desirable to be able to reduce CO2 emissions from glass melting plants where CO2 capture by known CCUS processes is not cost-effective.

[0013] A CO2 capture process suitable for a glass melting furnace is described in JP 2012-001392 A. As shown in JP 2012-001392 A, in glass production, it is known to heat and melt raw materials by burning natural gas, heavy oil, natural gas reformed hydrocarbons, biomass-derived fuels, petroleum-based fuels (gasoline, diesel, etc.), oil sands, etc. This combustion generates combustion gas containing carbon dioxide.

[0014] In such a method, in order to suppress carbon dioxide emissions without reducing the quality or efficiency of glass production, JP 2012-001392 A proposes contacting the CO2-containing combustion gas discharged from the glass furnace with an aqueous solution of an alkali hydroxide to obtain an alkali carbonate, and then using the alkali salt as a raw material for a glass melting furnace.

[0015] JP 2011-037706 A discloses a method for producing molten glass in a glass melting furnace comprising a melting zone and a fining zone. The melting zone is heated by a ceiling-mounted oxygen-fuel burner with its flame directed downwards. A mixture of powdered starting materials is introduced into the melting zone through the oxygen-fuel burner. A ceiling-mounted auxiliary oxygen-fuel burner with its flame directed downwards is attached to the fining zone to heat the fining zone. According to one embodiment of the glass melting process, the exhaust gases discharged from the furnace are dedusted in a dust collector. As described in JP 2012-001392 A, all or part of the dedusted exhaust gases are introduced into a column filled with lime (calcium oxide) to obtain calcium carbonate. The calcium carbonate thus obtained forms part of the powdered starting material mixture introduced into the melting zone through the oxygen-fuel burner.

[0016] All-electric glass melting furnaces are also known, in which the heat supply to the furnace is provided solely by electrical energy via electrodes, rather than by the combustion of fossil energy.

[0017] In the case of glass melting furnaces that are heated at least in part by the combustion of a fuel, apart from the combustion gases, the exhaust gas from the furnace contains compounds released by the furnace charge, including CO2.

[0018] This is due to the fact that the vitrifiable solid charge is also a source of CO2 emissions. In addition to silicon oxide (SiO2), the charge typically also contains functional additives such as fluxes, also called fluxes, stabilizers, colorants, etc.

[0019] Some of these additives, particularly the alkali metal and / or alkaline earth metal carbonates, dissociate in the furnace, thereby releasing CO2 into the atmosphere above the charge in the furnace. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] JP 2012-001392 A [Patent Document 2] JP 2011-037706 A Summary of the Invention [Problem to be solved by the invention]

[0021] It is an object of the present invention to further reduce CO2 emissions from glass melting processes without resorting to expensive processes and plants. [Means for solving the problem]

[0022] The invention proposes a glass melting process comprising the steps of introducing a vitrifiable solid charge into a furnace (called step a.), heating and melting the charge in the furnace to obtain molten glass (called step b.), discharging the molten glass from the furnace (called step c.) and discharging off-gases from the furnace (called step d.).

[0023] The charge introduced into the furnace in step a. comprises at least one carbonate of an alkali metal or an alkaline earth metal.

[0024] In step b., the at least one carbonate undergoes a dissociation reaction, after which CO2 gas is released.

[0025] The off-gas exhausted from the furnace during step d. comprises CO2. The CO2 in the off-gas comprises CO2 gas released as a result of dissociation of carbonates in the charge as described above, but may also include CO2 gas of other origins, for example CO2 generated when carbon-based fuels are burned to heat the furnace.

[0026] The method also includes a step e., in which the exhaust gas discharged from the furnace during step d. is used to produce at least one additive in the form of an alkali metal or alkaline earth metal carbonate by carbonation with the CO2 present in the exhaust gas, at least a portion of the additive thus produced being incorporated in the charge introduced into the furnace in step a.

[0027] As a result, at least a portion of the CO2 in the exhaust gas discharged from the furnace is captured by the carbonation reaction and recycled to the furnace without being released into the atmosphere.

[0028] In the glass melting method of the present invention, the heating of the charge in step b. is performed by: By electrical heating, or by combustion of a non-carbonaceous fuel (12) with an oxidizer (13), or by combustion of a non-carbon-based fuel (12) with an oxidizer (13) in combination with electrical heating, or by both the combustion of a non-carbon-based fuel (12) with an oxidizer (13) and the combustion of a carbon-based fuel with an oxidizer, or by both the combustion of a non-carbon-based fuel (12) with an oxidizer (13) in combination with electrical heating, and the combustion of a carbon-based fuel with an oxidizer, It will be held. [Brief description of the drawings]

[0029] [Figure 1] FIG. 2 is a diagram representing a process according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram representing a process according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In the present specification, "functional additives" are understood to mean components of the solid charge other than sand (SiO2) and cullet. These functional additives are added to the charge to improve the melting and / or refining and / or shaping of the glass (for example in the case of glass fibers) or to modify the properties of the obtained solid glass product (for example refractive index, thermal shock resistance, Young's modulus, etc.). Thus, the charge can be supplemented with: Sodium carbonate (where appropriate, in combination with potassium carbonate as a flux), Calcium carbonate (where appropriate, in combination with magnesium carbonate as a stabilizer), Aluminum oxide (to increase hydrolysis resistance), Lead oxide (to increase the density, refractive index and brightness of the glass), Boron oxide (as a network former, providing greater thermal stability), Metal oxides of the transition elements and / or certain lanthanides (as colouring or decolourising agents), and · Redox additives (such as carbon and sodium sulfate).

[0031] In the context of this application, the terms "oxidant" and "oxidizer" are synonymous and are used interchangeably.

[0032] As used herein, a "carbon-based fuel" is a fuel that contains carbon atoms. Combustion of Carbon-Based Fuels During this process, the carbon atoms are reacted with each other to form carbon oxides.

[0033] Carbon-based fuels that can be used in the context of the present invention include natural gas and biogas.

[0034] As used herein, a "non-carbon based fuel" is a fuel that does not contain carbon atoms. A non-carbon based fuel does not generate carbon oxides during the combustion of the fuel. Non-carbon based fuels that can be used in the context of the present invention include hydrogen and ammonia. In order to limit the overall carbon footprint, the use of blue or green hydrogen is preferred. A distinction is made between grey, green and blue hydrogen. The production of grey hydrogen exhibits a CO2 emission intensity of up to 9.3 kg CO2 / kg H2 during hydrogen production. For example, grey hydrogen can be produced by steam methane reforming without CCUS (Carbon Capture and Utilisation or Sequestration). The production of blue hydrogen exhibits a CO2 emission intensity of up to 0.97 kg CO2 / kg H2. For example, blue hydrogen can be produced by steam methane reforming with CCUS. The production of green hydrogen does not emit CO2. Green hydrogen can, for example, be produced by the electrolysis of water using renewable energy (see van Cappellen, L., Croezen, H. and Rooijers, F, Feasibility Study into Blue Hydrogen, CE Delft, 2018).

[0035] The oxidant may be air, oxygen-enriched air or industrial oxygen. In the present specification, the term "industrial oxygen" is understood to mean a gas having an oxygen content of 90-100% by volume, preferably 95-100% by volume. The oxidant may be fed to the furnace as such or after mixing with other gases. This is particularly true when the furnace is fed with "artificial air" consisting of a mixture of industrial oxygen and an essentially inert gas such as recycled exhaust gas. The use of such a mixture may in particular allow better coverage of the charge by the flame in the furnace. In the process of the invention, different oxidants may be combined. For example, different burners may be operated with different oxidants, as in the case of the implementation often referred to as "oxygen boost", or different oxidants may be fed separately into the furnace.

[0036] All or part of the heat for heating the charge in step b. can be provided by electrical heating, for example by electrodes immersed in the molten charge.

[0037] Such electrical heating may be the sole heat source of the furnace or may be combined with other heat sources, such as the combustion of a fuel, especially a non-carbon-based fuel, and an oxidizer.

[0038] According to some embodiments of the present invention, the heat for heating the charge in step b. is generated by burning a non-carbon-based fuel, optionally in combination with electrical heating.

[0039] In that case, the generation of CO2 due to fuel combustion is avoided. Virtually all of the CO2 in the exhaust gas from the furnace is CO2 released by the charge in the furnace, but in the case of air ingress to the furnace, generally negligible amounts of CO2 may also enter the furnace as part of the ingress air.

[0040] Typically, some of the CO2 from the functional additive remains in the molten glass and is not released to the furnace atmosphere, and furthermore, because not all of the CO2 in the exhaust gas is typically captured by the carbonation reaction of step c., in such embodiments the amount of carbon captured from the exhaust gas to produce the additive in step e. may be less than the amount of carbon in the carbonate added to the charge in step a.

[0041] The same applies if, in step b., the furnace is heated exclusively by electrical heating. circle.

[0042] According to another embodiment of the invention, the heat for heating the charge in step b. is generated by burning a combination of carbon-based and non-carbon-based fuels, again optionally with additional electrical heating. In this case, the exhaust gas from the furnace contains both the CO2 released by the charge during step b. and the CO2 generated by the combustion of the carbon-based fuel fraction during said step b. In this case, there is more CO2 in the exhaust gas, available for the production of additives by carbonation in step e. of the process, but less CO2 is generated in the furnace by the combustion of fuels, all other factors being equal, compared to the heat generated in the furnace by the combustion of only carbon-based fuels. It is therefore possible to optimize the amount of CO2 present in the exhaust gas by burning a combination of non-carbon-based and carbon-based fuels during step b.

[0043] Thus, the heating means / heat source used to heat the charge in the furnace has a large influence on the composition of the off-gas discharged from the furnace in step d.

[0044] If in step b. a carbon-based fuel is also burned to heat the charge, the exhaust gas discharged will contain CO2 produced by the combustion of the carbon-based fraction of the fuel in addition to the CO2 released by the charge.

[0045] When fuel is combusted with air as an oxidant, the exhaust gases discharged contain significant amounts of nitrogen, which by its nature does not contribute to the combustion of the fuel; nitrogen is the major component of the air used as the oxidant.

[0046] When fuel is combusted with oxygen as the oxidant, the exhaust gases discharged contain much less nitrogen (N2) (e.g., due to ingress of charge and / or ambient air into the furnace) and are practically nitrogen-free.

[0047] If the fuel is burned with oxygen-enriched air, or if the furnace uses both air and oxygen as oxidizers (e.g., in separate burners, or if the furnace contains an "aero" burner in combination with an oxygen lance (also known as "oxygen boost")), the nitrogen content in the discharged flue gas will be between these two extremes.

[0048] If the fuel combusted in step b. is exclusively a non-carbon-based fuel, this combustion does not produce CO2. This is especially the case when the fuel is hydrogen or ammonia.

[0049] Combustion of hydrogen (2H2 + O2 → 2H2O) produces water vapor, which is found in the exhaust gas emitted in step d. Combustion of ammonia (4NH3 + 3O2 → 6H2O + 2N2) produces water vapor and nitrogen, which is found in the exhaust gas emitted.

[0050] Electric heating does not produce combustion gases inside the furnace.

[0051] Therefore, when electrical heating and / or combustion of non-carbon-based fuels is used as the sole heat source in the furnace, the CO2 present in the exhaust gases exiting the furnace is essentially limited to the CO2 released into the furnace atmosphere by the charge.

[0052] When the combustion of a non-carbonaceous fuel is combined with the combustion of a carbonaceous fuel, all other factors being equal (such as the nature of the oxidant, the amount of heat provided by the combustion, the composition and feed rate of the charge, etc.), the amount of CO2 in the exhaust gas will be greater than if only a non-hydrocarbonaceous fuel were burned in step b., but less than if only a carbonaceous fuel were burned in the furnace.

[0053] When the combustion of non-carbon-based fuels and carbon-based fuels is combined, a mixture of non-carbon-based and carbon-based fuels can be burned. Alternatively, the non-carbon-based and carbon-based fuels can be injected separately through the same burner or through different injectors. The non-carbon-based and carbon-based fuels can be burned with the same oxidizer or with oxidizers of different compositions, etc.

[0054] According to an advantageous embodiment, when both non-carbon-based and carbon-based fuels are combusted to heat the furnace in step b., the ratio between the non-carbon-based and carbon-based fuels combusted in the furnace is controlled, preferably to a maximum of 252 kg CO2 / tonne of molten glass, more preferably to a maximum of 166 kg CO2 / tonne of molten glass, for example to a maximum of 85 kg CO2 / tonne of molten glass, such that a maximum of 269 kg CO2 is generated by the combustion of the carbon-based fuel per tonne of molten glass discharged from the furnace in step c.

[0055] For any given carbon-based fuel, the less carbon-based fuel that is burned in the furnace, the less CO2 is produced during the combustion process.

[0056] However, combining the combustion of a non-carbon-based fuel with the combustion of a carbon-based fuel in the method according to the invention also has certain advantages. For example, it makes it easier to carry out the method of the invention with equipment including burners and furnaces originally developed for methods based only on the combustion of fossil fuels, optionally in combination with electric heating, and makes it easier to reproduce known heating profiles in furnaces. It may therefore be useful for at least 10%, for example at least 25% or at least 50% of the heat generated by combustion during step b. of the process to be generated by the combustion of a carbon-based fuel.

[0057] The reactor in which the carbonation of step e. takes place is called the "carbonator". Carbonation is advantageously carried out by direct contact of the exhaust gases leaving the furnace with the carbonates formed in the carbonator, the oxides and / or hydroxides of alkali metals or alkaline earth metals.

[0058] Thus, carbonation can be carried out by direct contact between the exhaust gas and an alkali metal or alkaline earth metal oxide of the carbonate, by direct contact between the exhaust gas and an alkali metal or alkaline earth metal hydroxide of the carbonate, or by direct contact between the effluent and a mixture of an alkali metal or alkaline earth metal oxide and hydroxide of the carbonate.

[0059] For example, as an additive, calcium carbonate can be produced by contacting a CO2-containing tail gas with CaO and / or Ca(OH)2.

[0060] If it is envisaged during step e. to produce carbonates of several alkali metals and / or alkaline earth metals, these carbonates can be produced in separate carbonators or the CO2-containing tail gas can be contacted with oxides and / or hydroxides of several alkali metals and / or alkaline earth metals in the same carbonator.

[0061] The carbonator may be a batch carbonator, a fluidized bed carbonator, or an entrained bed carbonator.

[0062] To promote carbonation, it is necessary to maximize the contact surface between the exhaust gas and the CO2 it contains on the one hand, and the alkali or alkaline earth metal oxides / hydroxides on the other hand. This is because two phases are distinguished in the carbonation reaction: a first phase, which reacts very fast at the contact interface between the gaseous CO2 and the solid oxides / hydroxides, and a second phase, which reacts slower, the rate of which is controlled by the diffusion of CO2 into the solid phase.

[0063] It is therefore appropriate to use oxides / hydroxides with small particle sizes, for example less than 1 mm, preferably between 100 μm and 200 μm. Porous oxides, for example at least 0.078 cm 3 It is also possible to improve the contact between the exhaust gas and the oxide by using an oxide with a porosity of 0.01 / Å / g. Oxides with a specific surface area (BET) greater than 17 are advantageously used.

[0064] Carbonation / decarbonation are equilibrium chemical reactions (reversible reactions). It is therefore desirable to choose reaction conditions in the carbonator that favor carbonation over decarbonation. An important parameter in this context is the temperature in the carbonator. The temperature in the carbonator is kept below the temperature that favors decarbonation. Carbonation in the carbonator is generally carried out at temperatures below 1050°C, preferably below 950°C. It has been found to be advantageous to carry out carbonation in the carbonator at temperatures between 500°C and 950°C, preferably between 550°C and 800°C, more preferably between 550°C and 700°C. This temperature can also be chosen as a function of the alkali metal or alkaline earth metal of the carbonate to be produced and as a function of the use of the oxide or hydroxide of said metal as starting material for the carbonation.

[0065] The temperature in the carbonator is determined to a large extent by the temperature at which the exhaust gas is introduced into the carbonator. The temperature at which the exhaust gas is introduced into the carbonator is advantageously between 600°C and 1000°C, preferably between 650°C and 950°C, more preferably between 700°C and 900°C.

[0066] The temperature of the exhaust gas at the outlet of the furnace is generally such that it promotes decarbonation rather than carbonation.

[0067] According to one embodiment of the present invention, the exhaust gas is cooled to a predetermined temperature or temperature range before being introduced into the carbonator, which, as described above, is advantageously between 600°C and 1000°C, preferably between 650°C and 950°C, and more preferably between 700°C and 900°C.

[0068] Before being introduced into the carbonator, the exhaust gases may in particular be cooled in one or more heat exchangers.

[0069] In this specification, the term "heat exchanger" is understood to mean a device in which thermal energy is transferred from a first fluid (called the heated fluid or the fluid to be cooled) to a second fluid (i.e. the fluid to be heated), the two fluids being separated from each other by one or more walls so that they do not mix, and the thermal energy is transferred through the walls from the first fluid to the second fluid.

[0070] According to one embodiment of the present invention, the thermal energy extracted from the exhaust gas during its cooling is recovered and used as an energy source, thus making it possible to use this thermal energy extracted from the exhaust gas to heat the oxidant and / or the fuel.

[0071] In this way, the oxidant and / or fuel can be heated in a heat exchanger used to cool the exhaust gas, the exhaust gas being the first fluid (i.e. the fluid carrying the heat) and the oxidant, respectively the fuel being the second fluid (i.e. the fluid to be heated).

[0072] The heat exchange between the exhaust gas and the oxidant / fuel may be direct heat exchange, where the exhaust gas, oxidant and fuel are on either side of and in direct contact with the wall through which thermal energy is transferred.

[0073] The heat exchange between the exhaust gas and the oxidant / fuel may be an indirect heat exchange involving an intermediate fluid, in which case the thermal energy is first transferred by direct heat exchange between the exhaust gas and the intermediate fluid, and the thermal energy thus transferred and absorbed is subsequently transferred by direct heat exchange from the intermediate fluid to the oxidant and fuel, respectively.

[0074] As noted above, it is known to heat the charge of a glassmelting furnace at least in part by heat generated by combustion of a fuel with an oxidizer.

[0075] When the thermal energy extracted from the exhaust gas is used as an energy source for heating the oxidant and / or fuel, the heated oxidant and / or fuel thus obtained are advantageously used to heat the charge in the furnace by combustion using the heated oxidant and / or heated fuel as combustion reactants. In this way, the energy efficiency of the process of the present invention is improved by recycling the thermal energy discharged from the furnace with the exhaust gas.

[0076] The method according to the invention is applicable to a variety of glass melting furnaces: the furnace may therefore be a batch furnace, a semi-batch furnace or a continuous furnace.

[0077] The additives produced in step e. of the process and introduced into the furnace with the charge in step a. are generally functional additives. In the furnace, alkali metal or alkaline earth metal carbonates react and bond with the sand (SiO2), typically from 800°C.

[0078] Thus, the carbonate salt produced in step e. may be sodium carbonate, calcium carbonate, potassium carbonate, magnesium carbonate, lithium carbonate, barium carbonate, or a mixture or combination of at least two of said carbonate salts.

[0079] For example, when sodium carbonate and calcium carbonate are added to the charge, the following reaction is observed: From -800°C: Na2CO3+CaCO3→Na2Ca(CO3)2 Na2Ca(CO3)2+2SiO2→Na2SiO3+CaSiO3+2CO2 From -1000°C: Na2CO3+SiO2→Na2SiO3+CO2 CaCO3+SiO2 →CaSiO3+CO2

[0080] The silicates formed participate in glass formation in the molten phase.

[0081] A large amount of CO2 is generated and partially dissolves in the molten glass. Another part of the generated CO2 becomes gas bubbles and escapes from the molten glass by moving upward, contributing to the refinement of the molten glass.

[0082] In glass production, sodium carbonate is used as a flux, which reduces the melting point of the charge. It is produced in step e. by carbonation of Na2O and / or NaOH: Na2O+CO2⇔Na2CO3 2NaOH+CO2⇔Na2CO3+H2O

[0083] Potassium carbonate is also a flux. In step e., potassium carbonate is produced by carbonation of KO and / or KOH: K2O+CO2⇔K2CO3 2KOH+CO2⇔K2CO3+H2O

[0084] Calcium carbonate is the main stabilizer of glass. It gives it chemical protection, especially against the effects of water. Calcium carbonate is produced in step e. by carbonation of CaO and / or Ca(OH)2: CaO+CO2⇔CaCO3 Ca(OH)2+CO2⇔CaCO3+2H2O

[0085] Magnesium carbonate makes it possible to increase the viscosity of the glass in the molten state and promotes its electrical resistance, thermal stability and acid resistance. It is produced in step e. by carbonation of MgO and / or Mg(OH)2: MgO+CO2⇔MgCO3 Mg(OH)2+CO2⇔MgCO3+2H2O

[0086] Lithium carbonate is also a flux that can lower the melting point. It can also reduce the thermal expansion coefficient of glass. Lithium carbonate is produced in step e. by carbonation of Li2O and / or LiOH: Li2O+CO2⇔Li2CO3 2LiOH+CO2⇔Li2CO3+H2O

[0087] Barium carbonate is another flux used in the manufacture of glass. It also acts as a matting agent, reducing the shine of the finished product. Barium carbonate is produced by the carbonation of BaO and / or Ba(OH)2 in step e.: BaO+CO2⇔BaCO3 Ba(OH)2+CO2⇔BaCO3+2H2O

[0088] During step e. of the method according to the invention, the CO2 present in the exhaust gas leaving the furnace can in particular be used to produce one or more of the following functional additives: sodium carbonate, calcium carbonate and potassium carbonate.

[0089] According to one embodiment of the present invention, the method is used for the production of soda-lime or borosilicate glass.

[0090] In the case of soda-lime glass, step e. of the process is advantageously used to produce at least one carbonate selected from sodium carbonate, calcium carbonate and barium carbonate, preferably selected from sodium carbonate and calcium carbonate, at least a portion of the carbonate thus produced being added to the solid charge as a functional additive.

[0091] In the case of borosilicate glass, step e. of the process is advantageously used to produce at least one carbonate selected from sodium carbonate, potassium carbonate, calcium carbonate and magnesium carbonate, preferably at least one carbonate selected from sodium carbonate and potassium carbonate, at least a portion of the carbonate thus produced being added to the solid charge as functional additive.

[0092] The molten glass discharged from the furnace in step c. of the present process can be used to produce flat glass, such as glass for windows, hollow glass, such as glasses, bottles and flasks, or fiberglass, such as insulating fiberglass, reinforcing fiberglass and optical fiberglass, each product having a glass composition suitable for its application. The carbonate produced in step e. of the present process and added to the solid charge is advantageously selected in function of said composition.

[0093] The invention and its advantages are illustrated by the following examples, with reference to Figures 1 and 2, which are diagrammatic representations of two embodiments of a process according to the invention.

[0094] In order to comply with environmental standards for preventing global warming, industrial sites must reduce emissions of greenhouse gases such as CO2 into the atmosphere as much as possible.

[0095] CO2 emitting industries include glass furnaces.

[0096] As already mentioned above, the melting of glass most often involves the combustion of fossil carbon-based fuels such as natural gas, fuel oil or coal as the energy source for the melting and vitrification, which generates CO2.

[0097] As mentioned above, CO2 emissions from this process also result from the decarboxylation of one or more carbonates present in the starting material.

[0098] Therefore, the replacement of fossil fuels with non-carbon based fuels such as hydrogen and heating without combustion, especially electrical heating, makes it possible to reduce CO2 emissions from the glass melting process but not to eliminate them.

[0099] For hollow glass containing 11% CaO in its composition, the decomposition of CaCO3 produces 86.42 kg of CO2 per tonne of hollow flint glass produced. For an average 300 t / d glass furnace, 26 t / d of CO2 is generated from batches. For a flat glass furnace producing around 1,000 t / d, this corresponds to 65 t / d of CO2 emissions.

[0100] The need to reduce CO2 emissions from glass melting furnaces remains a hot topic.

[0101] At fixed industrial sites that emit large amounts of CO2, it is recommended to implement Carbon Capture and Sequestration (CCS). CCS is a process that involves capturing the CO2 present in the exhaust gases, liquefying the captured CO2, and sequestrating the liquefied CO2, for example in caverns that previously contained natural gas. It is generally accepted that CO2 sequestration is only a temporary solution before finding a permanent solution. An alternative to CCS is Carbon Capture and Storage (CCU). One such approach is Carbon Capture and Utilisation. CCU differs from CCS in that the liquefied carbon is not sequestered indefinitely, but is used in another industrial process, for example in the production of carbonated drinks. For industrial development, CCS and CCU require not only high flows of flue gas containing CO2, but also emissions in a composition such that the CO2 present in the emissions can be extracted and purified without being prohibitively costly.

[0102] Glass melting furnaces have relatively low CO2 emissions compared to electricity generating power plants, whether or not they burn fossil fuels. Furthermore, the exhaust gases from glass melting furnaces contain components, especially those originating from the charge, that make it difficult to capture the CO2 at the required purity. In these circumstances, the capital costs required to install CCS or CCU in glass melting furnaces are not cost-effective.

[0103] The present invention provides a more cost-effective means for reducing CO2 emissions from glass melting furnaces.

[0104] As shown in FIG. 1, a charge 11 containing vitrifiable material and / or cullet, as well as functional additives including, inter alia, the stabilizer CaCO 3 , is introduced into a melting furnace 1 . In the furnace 1, a charge 11 is melted to form a glass bath 15. Above the bath 15 there is a gas atmosphere 16. The molten glass contained in bath 15 exits furnace 1 as a stream of liquid glass 17 and is refined before being directed to a forming facility (not shown) for producing the final product.

[0105] The furnace 1 is heated by combustion of a fuel 12 and an oxidant 13. Gas 14 generated by the combustion is discharged from the furnace 1 as an exhaust gas 20. The fuel 12 can be a combination of carbon-based and non-carbon-based fuels, however, in the illustrated embodiment, all of the fuel 12 is green hydrogen, thus reducing CO2 emissions per tonne of glass from the melter by avoiding the generation of CO2 from combustion. Despite this measure, CO2 is indeed present in the off-gas 20 exiting the furnace 1, more specifically due to the decarbonation of carbonates, in particular calcium carbonate, present in the charge 11 during melting of the charge 11 and during refining of the molten glass in the glass bath 15. This decarbonation produces gaseous CO2, at least a part 18 of which passes into the gaseous atmosphere 16 and is exhausted from the furnace 1 by the off-gas 20.

[0106] In order to further reduce the emission of CO2 into the atmosphere without resorting to expensive processes such as CCS or CCU, the flue gas 20 discharged from the furnace 1 is used to produce at least one additive in the form of an alkali metal or alkaline earth metal carbonate by carbonation with the CO2 present in the flue gas 20, at least a part of which is introduced into the furnace 1 together with the charge 11.

[0107] For this purpose, the CO2-containing flue gas 20 is introduced into a carbonator 30 and the flue gas 20 is contacted with CaO31 under conditions, in particular temperature and residence time conditions, such that at least 50%, preferably at least 60%, more preferably at least 70% of the CO2 present in the flue gas 20 reacts with CaO31 to form CaCO3.

[0108] In FIG. 1, a single carbonator 30 is shown. The use of several carbonators operating simultaneously or alternately is also possible, whereby "operation" refers to the chemical process of carbonation, i.e. the formation of carbonates. In the figure, the only carbonate formed by carbonation with the CO2 present in the exhaust gas 20 is CaCO3. The CO2 present in the exhaust gas 20 can likewise be used for the production of another alkali metal or alkaline earth metal carbonate that can be used as a functional additive in the glass melting furnace 1, and in fact can even be used for the production of a combination of such carbonates.

[0109] The CO2-depleted residue 32 of the exhaust gas leaves the carbonator 30, as does the carbonation product 33.

[0110] The conditions in the carbonator 30, in particular the temperature and residence time conditions, are selected so that at least 50%, preferably at least 60%, and more preferably at least 70% of the CO2 present in the exhaust gas 20 reacts with the ground CaO31 with the formation of CaCO3. The amount of CaO 31 introduced into the carbonator 30 and its surface area in contact with the flue gas 20 is selected to maximize the conversion of CaO to CaCO 3 . To increase this contact surface area, porous CaO in particulate form is advantageously chosen. Thus, in the embodiment shown in FIG. 3Porous CaO with a pore volume of more than 1 / Å / g, also called quicklime, is commercially available. This porous CaO is ground to a particle size of less than 1 mm, preferably about 137 μm, to obtain a specific surface area (BET) of more than 17. This ground CaO31 is then fed to a carbonator 30. The carbonator 30 is inserted into the In the embodiment shown in Fig. 1, the carbonator 30 is a batch carbonator. The contact time between the exhaust gas 20 and the pulverized CaO 31 is longer than 4 minutes. The temperature in the carbonator 30 is between 500°C and 650°C.

[0111] At least a portion of the carbonation product 33 discharged from the carbonator 30, together with a make-up 34 of CaCO3 if necessary, is incorporated in the charge 11 introduced into the furnace 1. In this way, a large part of the CO2 of the exhaust gas 20 is captured and the resulting CaCO3 is used as a feed for the furnace 1. To the extent that the carbonation of CaO is not complete and it is found necessary to limit the amount of unconverted CaO added to the charge 11 and / or the amount of carbonate formed in the carbonator 30 exceeds the amount added to the charge 11, a portion 35 of the carbonation product 33 is extracted for recycle and not added to the charge 11.

[0112] As mentioned above, the temperature in the carbonator 30 is selected to promote reaction of the CO2 and CaO present in the exhaust gas 20, and this temperature is, for example, between 500°C and 650°C. The exhaust gas 20 leaves the furnace 1 at a temperature (typically between 1400°C and 1550°C, and in practice higher), which promotes decarbonation rather than carbonation. The temperature within the carbonator 30 is largely determined by the temperature of the exhaust gas 20 at the inlet of the carbonator 30 .

[0113] In order to ensure an adequate temperature in the carbonator 30 , it is proposed to cool the exhaust gas 20 between the outlet from the furnace 1 and the inlet to the carbonator 30 .

[0114] 1, for this purpose the exhaust gas 20 passes through a heat exchanger 40 arranged in the flow path of the exhaust gas 20 between the furnace 1 and the carbonator 30. The operation of said heat exchanger 40 is adjusted so that the exhaust gas 20 enters the carbonator 30 at an appropriate temperature.

[0115] FIG. 2 shows an advantageous embodiment in which thermal energy extracted from the exhaust gas 20 in a heat exchanger 40 is used to preheat at least a portion of the fuel 12 and / or at least a portion of the oxidant 13 upstream of the furnace 1.

[0116] In order to regulate the delivery of the portion 12a of the fuel 12 and / or the portion 13a of the oxidant 13 to the heat exchanger, a distribution valve 52 is provided in the passage of the fuel 12 to the furnace 1, and / or a distribution valve 53 is provided in the passage of the oxidant 13 to the furnace 1. In this manner, the portion 12b of the fuel 12 and the portion 13b of the oxidant 13 that are not directed to the heat exchanger 40 are introduced into the furnace 1 without passing through the heat exchanger 40.

[0117] In this manner, by introducing a portion 12a of the fuel 12 and / or a portion 13a of the oxidant 13 into the heat exchanger 40, the cooling level of the exhaust gas 20 can be adjusted in the heat exchanger 40 while reusing the thermal energy extracted from the exhaust gas 20 in the glass melting furnace 1.

[0118] The distribution between the portions 12a and 12b and / or between the portions 13a and 13b can be adjusted automatically, for example, as a function of the temperature of the exhaust gas 20 at the outlet of the heat exchanger 40 or at the inlet of the carbonator 30.

[0119] Thus, for example, it is possible to preheat both the fuel 12a and the oxidant 13a in a single heat exchanger 40 or in two separate heat exchangers 40, or to preheat only the fuel 12a or only the oxidant 13a.

Claims

1. The following steps: a. Introduction of a vitrifiable solid charge (11) containing at least one type of carbonate into the furnace (1), b. At least one of the carbonates undergoes a dissociation reaction to CO ２ The process involves heating and melting the charge (11) in the furnace (1) to obtain molten glass (17) by releasing gas (18), c. Discharge of the molten glass (17) from the furnace (1), d. CO from the furnace (1) ２ Discharge of contained exhaust gas (20), and e. Using the exhaust gas (20) discharged from the furnace (1), the CO present in the exhaust gas (20) ２ Formation of at least one additive (33) in the form of an alkali metal or alkaline earth metal carbonate by carbonate chlorination, A glass melting method including, At least a portion of the additive (33) produced in step e is incorporated into the charge (11) introduced into the furnace (1) in step a. The heat required to heat the charge (11) in step b. is: By electric heating, - By combustion of a non-carbon fuel (12) with an oxidizer (13), optionally combined with electric heating, or - Combustion of a non-carbon fuel (12) with an oxidizer (13), and combustion of a carbon fuel with an oxidizer, optionally combined with electric heating, A glass melting method characterized by being provided.

2. The method according to claim 1, wherein at least a portion of the heat for heating the charge (11) in step b. is provided by the combustion of a non-carbon fuel (12) selected from hydrogen and ammonia.

3. The method according to claim 1 or 2, wherein at least a portion of the heat for heating the charge (11) in step b. is provided by combustion, and the oxidizing agent (13) is selected from air or oxygen-enriched air.

4. The method according to claim 1 or 2, wherein, for the purpose of carbonate production in step e, the exhaust gas (20) is brought into contact in a carbonater (30) with an alkali metal or alkaline earth metal oxide (31) and / or hydroxide corresponding to the carbonate produced in step e.

5. The method according to claim 4, wherein the carbonator (30) is a batch-type carbonator, a fluidized bed carbonator, or a jet-bed carbonator.

6. The method according to claim 4, wherein the carbonated oxidation is carried out in the carbonater (30) at a temperature between 500°C and 950°C.

7. The method according to claim 4, wherein the exhaust gas (20) is cooled to a temperature of 600°C to 1000°C before being introduced into the carbonator (30).

8. The method according to claim 4, wherein the exhaust gas (20) is cooled in one or more heat exchangers (40) before being introduced into the carbonator (30).

9. The method according to claim 8, wherein, during the cooling of the exhaust gas (20), thermal energy extracted from the exhaust gas (20) is used to heat an oxidizer (13) and / or a non-carbon fuel (12), at least a portion of the heat for heating the charge (11) in step b. is provided by combustion, and the oxidizer (13) and / or non-carbon fuel (12) heated during the cooling of the exhaust gas (20) is used as a combustion reactant for heating the charge (11) in the furnace (1).

10. The method according to claim 1 or claim 2, wherein the furnace (1) is a batch furnace, a semi-batch furnace, or a continuous furnace.

11. The method according to claim 1 or 2, wherein in step e, at least one of the additives (33) selected from sodium carbonate, calcium carbonate, potassium carbonate, magnesium carbonate, lithium carbonate, or barium carbonate is produced.

12. The method according to claim 11, wherein in step e, at least one of the additives (33) selected from sodium carbonate, calcium carbonate, and potassium carbonate is produced.

13. The method according to claim 1 or 2, wherein the method is used to produce soda-lime glass or borosilicate glass.

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