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WO2025125352A1 - Procédé et appareil de fabrication d'un produit en verre - Google Patents

Procédé et appareil de fabrication d'un produit en verre Download PDF

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Publication number
WO2025125352A1
WO2025125352A1 PCT/EP2024/085726 EP2024085726W WO2025125352A1 WO 2025125352 A1 WO2025125352 A1 WO 2025125352A1 EP 2024085726 W EP2024085726 W EP 2024085726W WO 2025125352 A1 WO2025125352 A1 WO 2025125352A1
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WO
WIPO (PCT)
Prior art keywords
electrodes
glass
current
heating
melting vessel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/EP2024/085726
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English (en)
Inventor
Alexander Uwe Strobel
Michael Hahn
Sebastian Wolf
Günter Weidmann
Wolfgang Schmidbauer
Moritz Hauf
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Schott AG
Original Assignee
Schott AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from EP23215757.8A external-priority patent/EP4570764A1/fr
Priority claimed from EP23215752.9A external-priority patent/EP4570763A1/fr
Application filed by Schott AG filed Critical Schott AG
Priority to PCT/EP2024/085726 priority Critical patent/WO2025125352A1/fr
Publication of WO2025125352A1 publication Critical patent/WO2025125352A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
    • C03B5/02—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture in electric furnaces, e.g. by dielectric heating
    • C03B5/027—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture in electric furnaces, e.g. by dielectric heating by passing an electric current between electrodes immersed in the glass bath, i.e. by direct resistance heating
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
    • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
    • C03B5/18—Stirring devices; Homogenisation
    • C03B5/183—Stirring devices; Homogenisation using thermal means, e.g. for creating convection currents
    • C03B5/185—Electric means

Definitions

  • the present invention relates to a method and apparatus for making a glass product wherein an excellent glass quality is achieved by means of a direct electrical heating using multiple inverterbased heating circuits which may be independently adjusted in amplitude and/or phase shift.
  • the glassmaker has a number of options for heating a glass melt, e.g. gas burners, electric resistance heating, or inductive heating. As of today, gas is the predominant heat source used in glass melting.
  • the production of glass has a quite high carbon footprint due to the amount of energy required for the melting and fining processes. This is particularly the case for heating by gas burners which use natural gas.
  • a reduction of the carbon footprint is possible if, instead, an electric resistance heating is used which is provided with power from renewable energy sources like wind power, waterpower, or solar panels.
  • the same power sources may also be used to produce hydrogen by electrolysis which then can be used to feed the gas burners. While the latter requires less changes to an existing glass production facility with a gas burner heating, the intermediate step of electrolysis is of course associated with a considerable energy loss. Hence, a direct use of the electrical power is more desirable.
  • glass compositions There are various kinds of glass compositions. Some glass compositions are relatively easy to manufacture in good quality, others require sophisticated equipment and/or extremely well-balanced production processes. Generally, the glass compositions used to make drinking glasses and bottles, ordinary windowpanes and other construction glass products (e.g. glass wool used for insulation) are of the former type. One reason is that the glass used for these products has rather low melting temperatures and a steep viscosity-temperature curve; in addition, quality criteria of the manufactured products are not very stringent. For example, drinking glasses and construction glass products may contain an occasional bubble, and variations in shape and dimension are tolerable. These glass products may contain impurities to a certain extent without a problem because their use does not require defined light transmission properties, or stringent purity regulations.
  • the types of glass compositions used for many mass products have low melting temperatures because of significant amounts of alkali metal oxides and alkaline earth metal oxides.
  • the respective glass melting facilities achieve very high throughput, often more than 200 tons of glass per day, or even 400 tons per day. Of course, the amount of energy needed for making 200 tons of low melting glass is significantly lower than for a higher melting glass.
  • the quality required for a given product depends on its intended use.
  • Some high-quality glasses are used to make products that do not entertain the occasional bubble and must meet stringent criteria in terms of shape, dimensional variations, and purity (both chemical and optical). Many of these glasses are rather difficult to manufacture not only because of the stringent criteria but also because of high melting temperatures. High melting temperatures may be necessary to achieve melt viscosities sufficient for homogenization and removal of bubbles from the melt. Examples of high-quality glass products include pharmaceutical containers and glass tubes used for making such containers.
  • the first reason is obviously the requirement to replace the electrodes at certain intervals. This not only increases the operation costs for the facility but also has an impact on the carbon footprint since for the production of the electrodes a considerable amount of energy is required. Depending on the type of metal used, very high temperatures for melting have to be achieved and the further shaping and handling steps again consume energy. Hence, a frequent exchange of the electrodes significantly increases the carbon footprint of the glass production method. In addition to this, the glass production process has to be stopped for maintenance because it is not possible to simply pull single electrodes out of the melting tank for replacement while the facility continues operation.
  • the second reason is the just mentioned glass quality.
  • the dissolved metal of the electrodes may cause severe discolorations of the glass melt in different colors depending on the type of metal and glass composition used. While this may be tolerable to a certain extent for cheaper glass products which are dark colored anyway, it is already intolerable for cheaper glass products which are to be completely colorless or to have a certain defined color. For high-quality expensive glass products, this discoloration is an absolute showstopper which has to be avoided by all means.
  • a contamination of the glass products with metal of the electrodes is also critical where a certain light transmittance, especially in the UV region, is needed.
  • glass products for medical packaging and semiconductor industries have specified limits of metal particles allowed in their products.
  • Prior art melting vessels employing a current frequency of 50 Hz or 60 Hz are generally controlling the power within the heating circuits by means of thyristor controllers with a phase cutting, also known as phase-fired control (PFC), in combination with the transformers.
  • phase cutting also known as phase-fired control (PFC)
  • PFC phase-fired control
  • Components of the glass melt may react with the electrodes and/or platinum parts of the melting vessel, like pipes or stirrers, and the reaction products may end up in the glass product where they may cause discolorations, particles, and striae. As a consequence, the lifetime of the electrodes is reduced, and the glass quality is decreased.
  • this process should in particular work for glass types having a good electric conductivity. To this end, the process should provide an excellent performance regarding the efficiency of the transfer of the provided energy into the melt, i.e. , lowest possible losses, on the one hand and minimized electro corrosion of the electrodes on the other hand.
  • the state of the art still requires improvements regarding the efficiency of the heating when referring to the percentage of applied electrical energy which is actually used for heating the glass melt, regarding the options for influencing the melt flow and consequently the residence time and its spread, regarding the degree of electrode corrosion, and regarding the versatility of the glass types which can be melted.
  • this disclosure relates to a method of making a glass product, comprising the steps of
  • At least one heating circuit comprises an inverter providing a current (AC) to its heating circuit and adjusting the amplitude and/or phase angle of this current independently of the amplitudes and/or phase angles of the currents of the other heating circuits and applying a phase angle shift to its current relative to at least one other heating circuit; and
  • AC current
  • a common controller controls the amplitudes and/or phase angles of the currents in the heating circuits via the transformers and/or the at least one inverter, wherein the electrodes are operated at a current frequency of at most 25,000 Hz.
  • this disclosure relates to a method of making a glass product, comprising the steps of
  • heating circuits each comprising a transformer and at least two electrodes, the electrodes comprising an electrode material
  • a common controller controls the amplitudes and/or phases of the currents in the heating circuits via the transformers and/or the inverters, wherein the electrodes are operated at a current frequency of at most 25,000 Hz.
  • this disclosure relates to a method of making a glass product, comprising the steps of melting a batch of raw materials to form a glass melt in a melting vessel, heating the batch and/or the glass melt in the melting vessel using two or more heating circuits, each comprising a transformer and at least two electrodes, the electrodes comprising an electrode material,
  • At least one heating circuit comprises an inverter providing a current (AC) to its heating circuit and adjusting the amplitude and/or phase angle of this current independently of the amplitudes and/or phase angles of the currents of the other heating circuits and applying a phase angle shift to its current relative to at least one other heating circuit; and
  • AC current
  • a common controller controls the amplitudes and/or phase angles of the currents in the heating circuits via the transformers and/or the at least one inverter, wherein the electrodes are operated at a current frequency of at most 25,000 Hz; and/or wherein a common controller acts as a clock generator generating a clock signal for the inverters and controls a shift of the phase angle of the current provided by them to the heating circuits by independently applying a delay At > 0 ps to the clock signal; and/or wherein in each heating circuit a phase detector is installed between the transformers and the electrodes which measures the actual current signal at the electrodes and the common controller detects a phase shift by comparing this actual current signal with the clock signal provided to the inverters and adjusts the clock signal and/or applies a delay At > 0 ps to the clock signal in order to compensate for an undesired shift along the current flow from the inverter to the electrodes.
  • controlling the amplitude and/or phase of a current independently of the amplitudes and/or phase angles of the currents of other heating circuits means that the one or more inverters can provide currents of different amplitudes and/or phase angles, i.e. the amplitude and/or phase angle of the current provided by one inverter is not affecting the amplitudes and/or phase angles of currents provided by other inverters in other heating circuits. It does not exclude that two or more inverters operate at different amplitudes and/or phase angles in a predetermined relationship, e.g. controlled by a common controller.
  • the feature of "independently applying a delay At” means that the various inverters can be operated with different time delays applied to the clock signal, i.e. the inverters work with differently timewise modified clock signals by keeping the frequency constant resulting in a different phase angle of the supplied current. It does neither exclude that two or more inverters operate with different timewise modified clock signals in a predetermined relationship nor that two or more inverters operate with identically timewise modified clock signals.
  • the phases of II and I in a certain heating circuit at the electrodes are preferably in phase.
  • this disclosure relates to an apparatus for glass melting comprising
  • the melting vessel further having two or more heating circuits, each comprising a transformer and at least two electrodes immersible into the glass melt, wherein at least one heating circuit comprises an inverter providing a current to its heating circuit and adjusting the amplitude and/or phase angle of this current independently of amplitude and/or phase angle of the currents of the other heating circuits; and
  • this disclosure relates to an apparatus for glass melting comprising
  • a melting vessel having walls and a bottom, and optionally a superstructure, for holding a glass melt
  • the melting vessel further having two or more heating circuits, each comprising a transformer, at least two electrodes immersible into the glass melt, and an inverter providing a current to its heating circuit and adjusting the amplitude and/or phase angle of this current independently of amplitude and/or phase angle of the currents of the other heating circuits; and
  • the common controller controls the amplitudes and/or phase angles of the currents in the heating circuits via the transformers and/or the inverters; and wherein electrodes are set to provide a current frequency of at most 25,000 Hz.
  • this disclosure relates to an apparatus for glass melting comprising
  • a melting vessel having walls and a bottom, and optionally a superstructure, for holding a glass melt
  • the common controller controls the amplitudes and/or phase angles of the currents in the heating circuits via the transformers and/or the at least one inverter; and wherein electrodes are set to provide a current frequency of at most 25,000 Hz; and/or wherein a common controller acts as a clock generator generating a clock signal for the inverters and controls a shift of the phase angle of the current provided by them to the heating circuits by independently applying a delay At > 0 ps to the clock signal; and/or wherein in each heating circuit a phase detector is installed between the transformers and the electrodes for measuring the actual current signal at the electrodes and the common controller is configured to detect a phase angle shift by comparing this actual current signal with the clock signal provided to the inverters including any applied delay At and to adjust the clock signal and/or the delay At in order to compensate for an undesired shift along the current flow from the inverter to the electrodes.
  • this disclosure relates to a glass product, optionally obtainable or obtained according to the method disclosed herein, comprising a glass composition having a fining agent and electrode material, wherein the fining agent is present in an amount of at least 300 ppm and the electrode material is present as an oxide in an amount of less than 15 ppm, the glass product comprising less than 2 bubbles per 10 g of glass, wherein optionally the glass composition has a total carbon content of less than 310 ppm, based on the weight of the carbon atoms with respect to the weight of the glass product.
  • a "glass melt” is a volume of a batch of glass raw materials that has a viscosity of less than 10 76 dPas. Such a viscosity can be measured using the fiber elongation method, e.g. as described in DIN ISO 7884-6:1998-02, where the elongation speed of a fiber with a defined diameter is determined with different weights at different temperatures.
  • the temperature at which the glass melt has a viscosity of 10 2 dPas is herein called “temperature T2".
  • the temperature at which the glass melt has a viscosity of 10 4 dPas is herein called “temperature T4".
  • Temperature T2 is less than 1,500 °C for glass compositions with high contents of alkali metal oxides or alkaline earth metal oxides, such as soda lime glass and other glass compositions. These viscosities can be measured using a rotational viscosimeter, e.g. as described in DIN ISO 7884-2:1998-2.
  • the dependence of viscosity on temperature is determined according to the VFT equation (Vogel-Fulcher-Tammann). The VFT equation is shown below.
  • t is the temperature under consideration.
  • A, B and to are the so-called VFT constants that are specific for each glass composition.
  • This disclosure relates to methods which allow for the electric heating of all types of glass with multiple heating circuits at least one or some or all of which can be influenced independently of each other in amplitude and/or phase of the current supplied to the electrodes.
  • the method is suitable for all types of melting vessels whose geometries allow for the installation of multiple heating circuits, such as melting tanks, platinum pipes, fining tanks, and flow ducts. It is not limited to rectangular geometries but also works with polygonal or circular geometries. This allows for the creation of highly complex flow profiles in the melt for improving the important parameters for glass quality of the residence time and the sand grain dissolution.
  • a continuous glass melting without fossil fuels is possible as the method may not only be used as an electrical additional heating but also as a fully electric heating, in a full-electric glass melter such as a so-called “Cold Top Melter”.
  • phase or phase angle In the context of electrical circuits, the expression “phase” or “phase angle” often used to describe the relationship between voltage and current in one AC (alternating current) circuit. If not otherwise specified, according to the present invention, “phase” or “phase angle” or “phase shift” or “phase angle shift” is defined as the phase difference of one specific physical quantity in one heating circuit (measured preferably near the electrodes of the heating circuit) relative to the same physical quantity in one or more other heating circuits, e.g. the phase angle of the current in one heating circuit is compared to the phase angle of the current in the other heating circuits and the difference is defined as the phase shift or phase angle or delay.
  • a “common controller” as used herein takes on several tasks and/or functions. First of all, the common controller collects some or all measurement data that are generated in some or preferably all heating circuits and optionally other parts of the melting vessel. Secondly, the common controller utilizes the collected measurement data to compare the actual values to the stored or set target values and sends out control signals to the control units such as e.g. thyristor power controllers, inverters and/or delay generators.
  • the control units such as e.g. thyristor power controllers, inverters and/or delay generators.
  • the common controller furthermore comprises or is connected to a clock generator or global clock generating a global clock signal.
  • the global clock acts as a frequency control unit which provides an external time base for all inverters. It is used to provide a global clock signal to the delay generators providing an individual shift of the phase angle of the current provided by each inverter.
  • the global clock is synchronized to the power grid frequency and phase. “A heating circuit using power grid frequency and phase” means that such heating circuit does not comprise a rectification device such as e.g. inverter.
  • All tasks and/or functions of the common controller can be concentrated in a single central common controller device; it is also possible that certain tasks and/or functions of the common controller are handled decentrally by further controllers or specialized devices such as e.g. a delay generator.
  • One or more controlling tasks and/or functions of the common controller can also be executed by qualified workers.
  • the common controller can be a part of a distributed control system (DCS).
  • DCS distributed control system
  • the amplitudes and/or phases at least one electrode of each heating circuit and therefore the power of each inverter is controlled.
  • the amplitudes can also be manipulated individually at each inverter.
  • an “inverter” or “frequency changer” is a power electronic component which converts one alternating current of one frequency and/or phase to an alternating current of another frequency and/or phase, in particular an alternating current the frequency and/or phase of which is different from the frequency and/or phase of the grid.
  • an inverter may comprise of (a) a rectifier transforming alternating current (AC) into DC, followed by (b) an intermediate circuit e.g. comprising a capacitor and (c) an inverted rectifier transforming DC into an alternating current.
  • AC rectifier transforming alternating current
  • an intermediate circuit e.g. comprising a capacitor
  • an inverted rectifier transforming DC into an alternating current e.g. the inverted rectifier transforming DC into an alternating current.
  • a ’’thyristor controller” or “thyristor power controller” controls the power and/or voltage supplied within the grid frequency to a heating circuit.
  • a “transformer” transfers electrical energy from one electrical circuit to another circuit thereby allowing for a change of the voltage level of one alternating current e.g. the grid to the desired voltage level.
  • a transformer provides galvanic isolation of the heating circuits.
  • Power grid frequency or utility frequency or power line frequency or mains frequency is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user.
  • AC alternating current
  • the power grid frequency is 50 Hz or 60 Hz.
  • a ’’heating circuit as used herein is meant to comprise a power source and at least two electrodes immersible into the glass melt (and of course the electric lines required for connecting them).
  • the two electrodes are the minimum requirement for being able to initiate a current flow in the glass melt when provided with a current from the power source.
  • this does not exclude that one or more of the electrodes of one heating circuit are also part of another heating circuit, i.e. , one electrode may be connected to two different power sources.
  • the total number of (physical) electrodes in a melting vessel may be less than the sum of the (logical) electrodes in the defined heating circuits in the melting vessel.
  • a “melting vessel” is a vessel used for holding a glass melt.
  • the vessel defines a volume that can contain a glass melt.
  • the melting vessel may have a substantially rectangular base, or bottom plate. It may have walls to keep the melt within the vessel. According to one embodiment, a melting vessel will not be filled to the rim. However, according to other embodiments, a melting vessel can be completely filled with molten glass, e.g. if the melting vessel is a pipe or duct.
  • a melting vessel may have a superstructure above the glass melt surface ("covered melting vessel”). The superstructure may be vaulted.
  • the "melting vessel” may be a part of a larger melting facility.
  • the term “melting vessel” as used herein is meant as an umbrella term for all containers containing a glass melt which may comprise parts such as a melting tank, a refining tank or refining area, or pipes or ducts connecting the same.
  • a “bubble” is a gaseous inclusion within the glass or the glass melt, optionally having a diameter of at least 10 pm.
  • the “diameter” means the largest diameter of the gaseous inclusion.
  • Residence time is the time that a given portion of the glass melt spends in the melting vessel before being withdrawn from the melting vessel. Residence time can be measured using so- called tracers, i.e. components that are added to the glass melt so that they can be detected in the product, allowing conclusions as to the time spent in the melting vessel. Examples of tracer compounds are Ca, Sr and Y.
  • the "average residence time” is defined as: melting vessel volume [m 3 ] m ⁇ melting vessel throughput [— ]
  • the "minimum residence time” or "shortest residence time” is referring to the shortest time a portion of the glass melt will spend in the vessel. In an ideal scenario, every portion of the glass melt will spend exactly the same amount of time in the vessel. This will create uniform melt properties and, hence, the best glass quality. However, due to a complex flow pattern, turbulences, "short-circuit flows", and dead zones in a real vessel, there is a spread of the amount of time around the average residence time. Melt portions in a dead zone or turbulences will spend more time in the vessel while those in a short-circuit flow which refers to a fast stream directly from the entry to the exit of the vessel will exit faster.
  • the glass maker consequently aims at a spread of the residence time as small as possible and in particular tries to shift the minimum residence time towards the average residence time because the fast-exiting portions have a high risk of insufficiently melted batch materials or an insufficiently homogenized melt.
  • One option for achieving this goal is to influence the temperature zones in the melt and therewith the flow patterns.
  • the present disclosure uses a different approach to be able to minimize the electro corrosion potential and, additionally, to independently adjust the single heating circuits for the creation of optimized complex flow profiles of the melt. Both objects are achieved by using inverters before transformers in the at least one or more or all of the heating circuits which are jointly controlled by a common controller.
  • the glass product can be a sheet, wafer, plate, tube, rod, ingot, strip, or block.
  • the disclosed method and apparatus can achieve several advantages over those of prior art. In particular, they achieve a high electric efficiency while keeping the electro corrosion of the electrodes low. Furthermore, they achieve an optimal current distribution in the glass melt based on desired patterns. They allow for the creation of different zones in the glass melt by targeted current and power distribution in the glass melt. They can create high minimal residence times of the glass melt within the melting vessel and avoid short circuit flows. This flexibility is not fixed by construction measures but can be controlled and adjusted as necessary during the melting process. Finally, they achieve an optimal melting of a glass batch in the melting vessel.
  • inverter-based electric heating circuits may be operated in a range from about 20 Hz to 25,000 Hz, i.e., from below the standard line frequency up to the medium frequency range, which allows for the selection of the frequency best suited to the posed melting problem.
  • the residence time of the glass melt in the melting vessel and its spread are an important factor for the quality of the glass product produced from this glass melt.
  • the residence time and its spread are improved by locally applying heating power to the glass melt for creating hotspots and by installing different heating zones in the melting vessel.
  • the standard line frequency of 50 Hz 160 Hz is used.
  • the different heating zones have to be created by constructional aspects of the melting vessel, varying the spatial density of the installed electrodes, different wiring patterns of the electrodes, and/or influencing the current path by means of phase and power differences.
  • the phase angle shift between different heating circuits is freely adjustable in a range of 0° to 360°and can be changed and adapted flexibly - timewise and/or phase wise - during the glass production process.
  • the desired heating profiles can be established and controlled, e.g. certain asymmetric heating profiles or optimized symmetric heating profiles. Even a heating in coordinated levels is possible.
  • Such a flexibility in the heating patterns also enables a flexible usage of a full electric heating tank which e.g. for different throughputs or even without having to change construction measures such as the electrode positioning and wiring in the melting vessel.
  • Controlling and adjusting the phase angle of the current relative to the phase angle of the current in other heating circuits is a valuable and powerful option.
  • the present invention can also be used for phase angle correction of the current in one heating circuit relative to the phase of the voltage within the same heating circuit.
  • the phase angle of the voltage may shift relative to the phase angle of the current along the path from the inverter to the electrodes in particular when operated at higher frequencies and also vary during operation
  • a correction of this phase shift of the voltage relative from the phase of the current is particularly advantageous in two aspects.
  • a detector which is installed at the electrodes can detect and measure the phase angle shift of the voltage relative to the current. Since the present method and apparatus allow for the free adjustment of the phase angle of the current, this detected shift can be corrected. To assure the maximum power at the electrodes, the phases of current and voltage of a heating circuit should be in phase.
  • the detection of the phase angle between the phases of current and voltage allows for a correct assessment of the actual heating power distribution in the glass melt and optimized power in the melt.
  • a correction is useful in a first aspect for the correct establishment of the intended heating profile and hotspot creation for influencing the flow pattern of the glass melt.
  • this can also be an important factor for minimizing the occurrence of parasitic currents and the power loss associated with them in a melting vessel which is operated with parallel heating circuits having a phase angle difference of 0° like the standard heating circuits used in prior art. This way, the electrical efficiency may be improved when operating at higher frequencies and, consequently, either energy can be saved, or the operation frequency may be increased for lowering the electro corrosion further.
  • Another important effect which can be achieved by the present method and apparatus is a maximization of the effective electrode surface.
  • the present disclosure will allow for values of even beyond 95 % in specially arranged electrodes which are operated with suitable phase angle shifts. This will of course drastically reduce the electrode material particles in the melt and increase the lifetime of the electrodes.
  • a further advantage of the present method and apparatus is that the power grid is loaded completely symmetrically, since when using inverters, the electrical current is first rectified before the flexible output frequency is generated.
  • the present method and apparatus consider some adaptations for achieving an optimal efficiency.
  • the voltage should be adapted according to the conductivity in the melting vessel and the desired power. This can be done with transformers which are specifically adapted to the frequency of the inverters. Furthermore, as a consequence of the inductance of these transformers, the phase angle between the current and the voltage has to be corrected. In an ideal case, current and voltage are in phase. This is the case at the point of origin of the power. Due to unwanted complex resistances (capacitances, inductances) along the current path caused by cable coverings, transformer, etc., current and voltage typically are no longer in phase. Due to this phase angle shift, part of the generated electrical power is not released in the glass melt (reactive power).
  • the apparatus of the present disclosure optionally uses a power factor correction in combination with the transformer for compensating this reactive power.
  • These two adaptations may be implemented at any point between the inverter and the melting vessel. In optional embodiments, these adaptations are implemented in close proximity to the electrodes.
  • the melting vessel comprises at least two heating circuits each comprising a transformer and an electrical connection to at least two electrodes, the electrodes comprising an electrode material.
  • the number of heating circuits in a melting vessel is not particularly limited. Depending on the size and form of the melting vessel, the melting vessel may comprise at least 2 or at least 3 or at least 5 or at least 8 heating circuits or at least 10 or at least 20 and/or up to 10 or up to 20 or up to 50 heating circuits. In future highly electrified glass melting vessels, also higher numbers of heating circuits of e.g. up to 100 heating circuits can be implemented.
  • Each heating circuit is electrically connected to at least two electrodes immersible into the glass melt.
  • one or more heating circuits each comprise two electrodes.
  • one or more heating circuits can also share electrodes, for example, four electrodes can be shared by up to three or four heating circuits.
  • At least one electrode of the at least two electrodes immersible into the glass melt comprised by a first heating circuit may also be comprised by a second heating circuit, and the electrodes of the first and second heating circuits are arranged such that when provided with a current, the path of current through the glass melt between the electrodes of the first heating circuit is identical with the overlapping region with the path of current through the glass melt between the electrodes of the second heating circuit.
  • the two heating circuits have one electrode in common. Consequently, the number of electrodes in the melting vessel will be one less than in the two heating circuits, for example three instead of four for a setup with two heating circuits with two electrodes, each.
  • the heating circuits are then arranged such that the path of current of first heating circuit lies completely within the path of current of second heating circuit so that the overlapping region is identical with the former.
  • At least one heating circuit comprises an inverter.
  • Other heating circuits may not comprise an inverter which are comparatively expensive components.
  • the operating current frequency is not changed from the grid frequency, it is advantageous from an economical point of view to realize the power supply of at least one heating circuit by using e.g. a thyristor power controller and/or a regulating transformer.
  • Such heating circuits without inverters can particularly be used in parts of the melting vessel where specifically tailored heat distribution profiles in the glass melt are not essential and/or the available frequencies from the primary transformers are sufficient and a phase angle shift for these heating circuits is not required.
  • Heating circuits in parts of the melting vessel in which specific heat distribution profiles are essential are preferably equipped with inverters and thus the phase angle adjustment possibility of this invention in order to optimize the flow pattern and/or dwell time of the glass melt as described above.
  • the common controller is preferably also connected to one or more heating circuits without inverters, can thus detect the phase angle of such heating circuits and can generate a clock signal relative to these heating circuits.
  • the delay generators of the heating circuits with inverters can thus provide a shift of the phase angle of the current by applying a delay At > 0 ps to the clock signal of the common controller (8).
  • At Ah or At2
  • the phase angle shift between the heating circuits with inverters is freely adjustable in a range of 0° to 360° relative to other heating circuits.
  • a phase detector may be installed between the transformers and the electrodes which measures the actual current signal at the electrodes and the common controller detects a phase angle shift by comparing this actual current signal with the clock signal provided to the inverters including any applied delay At and adjusts the clock signal and/or the delay At in order to compensate for an undesired shift along the current flow from the inverter to the electrodes.
  • the glass melting system of the present disclosure can be seen as a complex meshed network.
  • Each inverter can initially feed into the glass melt with different power, current, voltage, and phase. Due to a typical resistivity of the glass melt in a range of from 0,3 Q cm to 200 Q cm at a temperature of 1,600 °C, the inverters as sources of power are not independent from each other but electrically coupled via the glass melt. A change in a parameter at one inverter may cause a change in all other inverters being part of the same network. All heating circuits are to be operated with the same frequency in the range of from 20 Hz to 25,000 Hz and to have a defined phase relative to each other. These two conditions are achieved by a clock generator in a common controller which provides an external time base for all inverters connected to that common controller.
  • a second mode of operation where a shift in the phase angle of a certain inverter is desired, a respective delay At in the clock signal supplied to this inverter will be applied. This can be done individually and independently from each other for all inverters.
  • the delay in the trigger signals may be implemented either by means of separate delay generators installed between the common controller (i.e. decentrally) and the respective inverters or by delay generators integrated within the common controller (i.e. centrally).
  • the system works like in the first mode of operation.
  • a phase detector which is installed at or in proximity of the electrode, it is possible to measure the actual signal curve of the current at the electrode and compare it to the signal of the clock generator in the common controller (including any applied delay At) for determining the phase angle shift of each electrode or heating circuit, respectively.
  • This information can be used for varying the applied delay time At to precisely set a desired phase angle shift at an electrode or to readjust the electrode to be in phase with the others if no shift in phase angle is intended.
  • the electrodes are operated at a current frequency of at least 20 Hz and at most 25,000 Hz, optionally of at least 50 Hz and at most 25,000 Hz, optionally of at least 50 Hz and at most 15,000 Hz, optionally of at least 50 Hz and at most 10,000 Hz, optionally of at least 100 Hz and at most 10,000 Hz, optionally of at least 1 ,000 Hz and at most 5,000 Hz, optionally of at least 1 ,000 Hz and at most 3,000 Hz.
  • the electrodes may be operated at a current frequency of less than 25,000 Hz, less than 15,000 Hz, less than 12,500 Hz, less than 10,000 Hz, less than 7,500 Hz, less than 5,000 Hz, less than 4,500 Hz, less than 4,000 Hz, less than 3,500 Hz, or less than 3,000 Hz.
  • the electrodes may be operated at a current frequency of less than 3,000 Hz.
  • the electrode may be operated at a current frequency of at least 20 Hz, at least 50 Hz, at least 100 Hz, at least 1 ,000 Hz, at least 1 ,500 Hz, at least 2,000 Hz, or at least 2,500 Hz.
  • a lower limit of 100 Hz ascertains that the electrode corrosion is sufficiently low at the required current density and the formation of bubbles is adequately suppressed.
  • An upper limit of 5,000 Hz ascertains that the power loss due to emission and induction remains at an acceptable level.
  • a flow profile and/or the residence time of the glass melt in the melting vessel are adjusted by setting the amplitude and/or the phase angle of the current of each individual heating circuit such that desired thermal zones are created within the glass melt.
  • the common controller may synchronize its clock signal with an external clock signal e.g. the phase of the power grid.
  • the global clock e.g. within the common controller may synchronize to the external clock signal which is equivalent to a frequency by detecting the zero crossings of the external frequency signal and adjusting its own zero crossings of the clock signal with them.
  • the frequencies may in this case be identical, but they do not have to be identical. In the latter case, the zero crossings of the lower frequency first signal may be matched with the n th zero crossing of the higher frequency second signal wherein n is dependent on the frequency difference.
  • Such an external clock signal synchronization may be advantageous for adapting to the continuously slightly changing power grid frequency of neighboring components in a melting facility which is operated at the power grid frequency of 50/60 Hz.
  • the melting vessel is selected from a melting tank, a platinum pipe, a fining tank, a horizontal flow duct, and a vertical duct.
  • the disclosed method is equally suitable for all of these types of melting vessels.
  • One or more or all of the electrodes may be rod-shaped and/or plate-shaped and/or domeshaped and/or tube-shaped and/or block-shaped. While in some cases the electrodes may also be plate-shaped and then in particular be designed as a part of the walls or bottom of the melting vessel, in most cases rod-shaped electrodes are chosen.
  • the rod-shaped electrodes are more versatile in arranging and easier to replace. Moreover, since the rod-shaped electrodes are spot-like sources of current, the zones of input of energy into the melt are easier to design to the desired layout. In some applications, also dome-shaped, tube-shaped, or block-shaped electrodes may be used in place of the rod-shaped electrodes.
  • One or more or all of the electrodes may be arranged horizontally extending from a wall of the melting vessel or vertically extending from a bottom of the melting vessel or from a surface of the glass melt.
  • the method is a continuous process or batch process.
  • the method is particularly suitable for a continuous process because its strength lies in the specific shaping of the flow of the glass melt which is of course more relevant for the continuous process.
  • the method is also advantageous for a batch process, where the distribution of the electrical heating power can be changed by this invention from one melting phase to the other.
  • additional heating is provided by a fuel burner, or no fuel burner is used for additional heating.
  • no fuel burner is used for additional heating.
  • This burner may then be fueled by a "green gas", i.e. hydrogen produced from renewable energies.
  • a fuel burner also an electrical additional heating means can be used.
  • the method is a continuous process having a throughput of at least
  • the throughput may be at least 1 t/d m 2 or at least
  • the throughput may be at most 10 t/d m 2 or at most 9 t/d m 2 or at most 8 t/d m 2 .
  • the throughput may be 1 t/d m 2 to 10 t/d m 2 or 2 t/d m 2 to
  • Such a throughput may aid in reducing the content of the electrode material in the resulting glass product.
  • the increased flow of the glass melt shortens the residence time of the melt in the melting vessel and consequently the time during which the melt may be contaminated with the dissolved electrode material. Meanwhile, the corrosion rate of the electrodes remains essentially constant since the main factors of influence are the composition of the glass melt, the electrode material, and the current density.
  • a temperature of the glass melt, a withdrawal rate of glass melt from the melting vessel, and an electrical operation frequency of the electrodes is such that the corrosion rate of one or more or all of the electrodes is less than 2.5 mm/a with a current density of 0.5 A/cm 2 and a glass melt temperature of 1,550 °C.
  • the corrosion rate of the electrodes is less than 2.5 mm per year for optimal results.
  • the corrosion rate may be less than 2.5 mm/a, less than 2.25 mm/a, less than 2.0 mm/a, less than 1.75 mm/a, or less than 1.5 mm/a.
  • the corrosion rate may be at least 0.05 mm/a, at least 0.1 mm/a, at least 0.15 mm/a, at least 0.2 mm/a, at least 0.25 mm/a, or at least 0.3 mm/a.
  • the electrode material of one or more or all of the electrodes is selected from Pt, Rh, Ir, Pd, alloys of these noble metals, Ta, Mo, MoSi2, MoZrCh, W, SnC>2, C, and combinations thereof.
  • the current density used at one or more or all of the electrodes is 0.2 A/cm 2 - 2.0 A/cm 2 .
  • This range provides good balance between power input into the melt and corrosion as well as a possible reduction of the number of electrodes.
  • the current density may be 0.2 A/cm 2 - 2.0 A/cm 2 or 0.3 A/cm 2 - 1.8 A/cm 2 or 0.4 A/cm 2 - 1.65 A/cm 2 or 0.5 A/cm 2 - 1.5 A/cm 2 .
  • the current density may be at least 0.2 A/cm 2 or at least 0.3 A/cm 2 or at least 0.4 A/cm 2 or at least 0.5 A/cm 2 .
  • the current density may be at most 2.0 A/cm 2 or at most
  • a ratio of the current frequency to the electric conductivity of the melt at a temperature of 1,600 °C is 0.001 kHz Q m to 50 kHz Q m. It has been found by the inventors that by means of this ratio range, the current frequency may be set to provide a low carbon footprint for a given glass composition to be melted having a certain electric conductivity.
  • the ratio may be at least 0.001 kHz Q m, at least 0.01 kHz Q m, at least 0.1 kHz Q m, at least 0.5 kHz Q m, at least 1 kHz Q m, at least 2 kHz Q m 3 kHz Q m, at least 5 kHz Q m, at least 7 kHz Q m, at least 10 kHz Q m, at least 15 kHz Q m, at least 20 kHz Q m, or at least
  • the ratio may be at most 50 kHz Q m, at most 49 kHz Q m, at most 48 kHz Q m, at most 47 kHz Q m, at most 46 kHz Q m, at most 45 kHz Q m, at most 44 kHz Q m, at most
  • the ratio may be 0.001 kHz Q m - 50 kHz Q m, 0.01 kHz Q m - 49 kHz Q m, 0.1 kHz Q m - 48 kHz Q m, 0.5 kHz Q m - 47 kHz Q m, 1 kHz Q m - 46 kHz Q m, 2 kHz Q m - 45 kHz Q m, 3 kHz Q m - 44 kHz Q m, 5 kHz Q m - 43 kHz Q m, 7 kHz Q m - 42 kHz Q m, 10 kHz Q m - 41 kHz Q m, 15 kHz Q m - 40 kHz Q m,
  • the electric conductivity of the melt at a temperature of 1 ,600 °C is at least 0.5 S/m.
  • the current method is particularly useful for glass compositions which form a melt having a high electric conductivity because the problem of an increased carbon footprint is very pronounced in these types of glass and not yet satisfactorily solved in the state of the art. Hence, these compositions will profit most of the possibility of a fully electric heating.
  • the application of the disclosed method is of course not limited to them.
  • the electric conductivity may be at least 0.5 S/m, at least 0.75 S/m, at least 1 S/m, at least 2 S/m, at least 3 S/m, at least 4 S/m, at least 5 S/m, at least 10 S/m, at least 15 S/m, at least 20 S/m, at least 25 S/m, or at least 30 S/m.
  • the electric conductivity may be at most 50 S/m, at most 48 S/m, at most 47 S/m, at most 46 S/m, at most 45 S/m, at most 44 S/m, at most 43 S/m, at most 42 S/m, at most 41 S/m, at most 40 S/m, at most 38 S/m, or at most 36 S/m.
  • the electric conductivity may be 0.5 S/m - 50 S/m, 0.75 S/m - 48 S/m, 1 S/m - 47 S/m, 2 S/m - 46 S/m, 3 S/m - 45 S/m, 4 S/m - 44 S/m, 5 S/m - 43 S/m, 10 S/m - 42 S/m, 15 S/m - 41 S/m, 20 S/m - 40 S/m, 25 S/m - 38 S/m, or 30 S/m - 36 S/m.
  • the electric conductivity may be 0.8 S/m, 1.7 S/m, 2.7 S/m, 3.7 S/m, 11.2 S/m, 13.2 S/m, 32.8 S/m, or 42.8 S/m.
  • the signal lines of the apparatus may be a direct or indirect connection by wire or wireless technique.
  • the inverters are set to provide a current frequency of at least 20 Hz and at most 25,000 Hz, optionally of at least 50 Hz and at most 25,000 Hz, optionally of at least 50 Hz and at most 10,000 Hz, optionally of at least 100 Hz and at most 10,000 Hz or of at least 1 ,000 Hz and at most 5,000 Hz.
  • the common controller may be configured to apply the delay At > 0 ps to each clock signal internally and/or delay generators may be installed in the signal lines connecting the inverters with the common controller.
  • a phase detector may be installed between the transformers and the electrodes for measuring the actual current signal at the electrodes and the common controller may be configured to detect a phase angle shift by comparing this actual current signal with the clock signal provided to the inverters including any applied delay At and to adjust the clock signal and/or the delay At in order to compensate for an undesired shift along the current flow from the inverter to the electrodes.
  • one or more or all of the electrodes may be located partially or completely in or on a wall of the melting vessel and/or in or on the bottom of the melting vessel and/or in the super-structure of the melting vessel (6) and/or constitute a wall section and/or a bottom section and/or a superstructure section of the melting vessel.
  • One or more electrodes may be located partially or completely in or on a wall of the melting vessel.
  • One or more electrodes may be located partially or completely in or on a bottom plate of the melting vessel.
  • one or more electrodes constitute a wall section and/or a bottom plate section of the melting vessel.
  • one or more of the electrodes may be extending upwardly from the bottom of the melting vessel up to at least 20 % glass melt depth, at least 30 %, at least 40 %, at least 50 %, at least 60 %, at least 70 % or at least 80 % of the glass melt depth.
  • the one or more electrodes may extend up to 100 %, up to 95 % or up to 90 % of the glass melt depth from the bottom of the melting vessel.
  • the one or more electrodes may extend from 50 % to 100 %, from 60 % to 95 %, or from 70 % to 90 % of the glass melt depth from the bottom of the melting vessel.
  • the one or more or all of electrodes may be rod-shaped, dome-shaped, plate-shaped, tube-shaped, or block-shaped.
  • the rod-shaped electrodes are more versatile in arranging and easier to replace. Moreover, since the rod-shaped electrodes are spot-like sources of current, the zones of input of energy into the melt are easier to design to the desired layout. In some applications, also dome-shaped, tube-shaped, or block-shaped electrodes may be used in place of the rod-shaped electrodes.
  • the electrode material may be selected from Pt, Rh, Ir, Pd, alloys of these noble metals, Ta, Mo, MoSi2, MoZrC>2, W, SnC>2, C, and combinations thereof.
  • the melting vessel is selected from a melting tank, a platinum pipe, a fining tank, a horizontal flow duct, and a vertical duct.
  • the melting vessel may be any part of a larger melting facility containing a glass melt which may comprise parts such as a melting tank, a refining tank or refining area, or pipes or ducts connecting the same. In general, those pipes are made of platinum.
  • the ducts may also be made of platinum or of refractory ceramics. The only prerequisite regarding the melting vessel and its shape and size is that it will allow for the installation of two or more heating circuits, i.e., there has to be enough space for at least two pairs of electrodes within the vessel.
  • the melting vessel has a cross-sectional shape of a circle, an oval, or a polygon having 3 to 64 corners.
  • the cross-sectional shape may be a circle or oval, which mainly concerns pipes or ducts, or a polygon having 3 to 64 corners, which is particularly of interest for melting tanks and fining tanks.
  • the polygon may optionally have 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 20, 24, 30, 32, 36, 42, 48, 54, 60, or 64 corners. In certain useful embodiments the polygon has 4, 5, 8, 10, 12, 24, 36, 48, 60, or 64 corners.
  • the fining agent may be present in the glass product in an amount of at least 300 ppm or at least 400 ppm or at least 500 ppm or at least 600 ppm or at least 700 ppm or at least 800 ppm or at least 900 ppm or at least 1 ,000 ppm or at least 2,000 ppm or at least 3,000 ppm or at least 4,000 ppm or at least 5,000 ppm or at least 10,000 ppm or at least 15,000 ppm.
  • the fining agent may be present in an amount of at most 30,000 ppm or at most 28,000 ppm or at most 26,000 ppm or at most 24,000 ppm or at most 22,000 ppm or at most 20,000 ppm or at most 10,000 ppm or at most 1 ,000 ppm or at most 900 ppm or at most 800 ppm or at most 700 ppm or at most 600 ppm or at most 500 ppm or at most 400 ppm or at most 300 ppm.
  • the fining agent may be present in an amount of 300 ppm to 30,000 ppm or 400 ppm to 28,000 ppm or 500 ppm to 26,000 ppm or 600 ppm to 24,000 ppm or 700 ppm to 22,000 ppm or 800 ppm to 20,000 ppm or 900 ppm to 15,000 ppm or 1 ,000 ppm to 10,000 ppm.
  • the electrode material may be present in the glass product as an oxide in an amount of less than 15 ppm or less than 10 ppm or less than 5 ppm or less than 4.5 ppm or less than 4 ppm or less than 3.5 ppm or less than 3 ppm or less than 2.5 ppm or less than 2 ppm.
  • the electrode material may be present as an oxide in an amount of more than 0.1 ppm or more than 0.2 ppm or more than 0.3 ppm or more than 0.4 ppm or more than 0.5 ppm or more than 0.75 ppm or more than 1 ppm.
  • the total carbon content in the glass product may be of less than 310 ppm or of less than 300 ppm or of less than 290 ppm or of less than 280 ppm or of less than 270 ppm or of less than 260 ppm or of less than 250 ppm.
  • the glass product may comprise a glass composition having an amount of an electrode material in the form of an oxide of from 0.1 ppm to 10 ppm, wherein optionally the electrode material is selected from Pt, Rh, Ir, Pd, alloys of these noble metals, Ta, Mo, MoSi2, MoZrCh, W, SnC>2, C, and combinations thereof.
  • the electrode material may be present in the glass product as an oxide in an amount of from 0.1 ppm to 10 ppm, from 0.1 ppm to 5 ppm, from 0.2 ppm to 4.5 ppm, from 0.3 ppm to 4 ppm, from 0.4 ppm to 3.5 ppm, from 0.5 ppm to 3 ppm, from 0.75 ppm to 2.5 ppm, or from 1 ppm to 2.5 ppm.
  • the electrode material may be present as an oxide in an amount of less than 10 ppm or less than 5 ppm or less than 4.5 ppm or less than 4 ppm or less than 3.5 ppm or less than 3 ppm or less than 2.5 ppm or less than 2 ppm.
  • the electrode material may be present as an oxide in an amount of more than 0.1 ppm or more than 0.2 ppm or more than 0.3 ppm or more than 0.4 ppm or more than 0.5 ppm or more than 0.75 ppm or more than 1 ppm.
  • the glass product may comprise a glass composition which contains alkali metal oxides in amounts of less than 20 % by weight, less than 15 % by weight, less than 12 % by weight, less than 10 % by weight or less than 5 % by weight.
  • the glass composition may be free of alkali metal oxides.
  • the amount of alkali metal oxides in the glass composition may be at least 1 % by weight or at least 2 % by weight.
  • the amount of alkali metal oxides in the glass composition may be > 1 % by weight and ⁇ 20 % by weight or > 2 % by weight ⁇ 10 % by weight.
  • the glass composition may be a borosilicate, alumino-borosilicate, or aluminosilicate glass.
  • the glass composition may contain alkaline earth metal oxides in amounts of less than 20 % by weight, less than 15 % by weight, less than 12 % by weight, less than 10 % by weight, or less than 5 % by weight.
  • the glass composition may be free of alkaline earth metal oxides.
  • the amount of alkaline earth metal oxides in the glass composition may be at least 1 % by weight or at least 2 % by weight.
  • the amount of alkaline earth metal oxides in the glass composition may be > 1 % by weight and ⁇ 20 % by weight or > 2 % by weight ⁇ 10 % by weight.
  • Optional glass compositions include AI2O3 in an amount of at least 1.5 % by weight or at least 5.0 % by weight or even at least 10.0 % by weight.
  • the amount of AI2O3 may be up to 23.0 % by weight, up to 20.0 % by weight or up to 18.0 % by weight. In certain embodiments, the amount of AI2O3 may range from 1.5 % to 23.0 % by weight, from 5.0 % to 20.0 % by weight or from 10.0 % to 18.0 % by weight.
  • the glass composition may include B2O3 in an amount of at least 0.0 % by weight or at least 8.0 % by weight or even at least 10.0 % by weight.
  • the amount of B2O3 may be up to 22.0 % by weight, up to 20.0 % by weight, up to 16.0 % by weight or up to 14.0 % by weight.
  • the amount of B2O3 may range from 0.0 % to 22.0 % by weight, from 0.0 % to 20.0 % by weight, from 8.0 % to 16.0 % by weight or from 10.0 % to 14.0 % by weight.
  • the glass compositions used in this invention have a total content of SiO2, AI2O3 and B 2 O 3 of at least 75.0 % by weight, at least 78.0 % by weight or even at least 85.0 % by weight.
  • the total amount of SiO2, AI2O3 and B2O3 may be limited to not more than 97.0 % by weight, up to 93.5 % by weight or up to 90.0 % by weight.
  • the amount of SiO2, AI2O3 and B2O3 may range from 75.0 % to 95.0 % by weight, from 78.0 % to 92.5 % by weight or from 85.0 % to 90.0 % by weight.
  • glass compositions used in this invention may comprise (in % by weight, the composition summing up to 100 %):
  • P 2 O 5 0 - 2 optionally further comprising coloring oxides, such as Nd 2 O 3 , Fe 2 O 3 , CoO, NiO, V 2 Os, MnO 2 , TiO 2 , CuO, CeO 2 , Cr 2 O 3 ,
  • coloring oxides such as Nd 2 O 3 , Fe 2 O 3 , CoO, NiO, V 2 Os, MnO 2 , TiO 2 , CuO, CeO 2 , Cr 2 O 3 ,
  • fining agents such as As 2 O 3 , Sb 2 O 3 , SnO 2 , SO 3 , Cl, F and/or
  • rare earth metal oxides 0 - 5 % by weight rare earth metal oxides
  • the glass composition can - alternatively or additionally to the compositions described above - be described by the following composition ranges.
  • the glass composition can be a borosilicate glass which contains the following components in wt.-%:
  • the glass composition can be a borosilicate glass which contains the following components in wt.-%:
  • AI 2 O 3 0.0 to 8.0, or 0.0 to 5.0
  • the glass composition can be a borosilicate glass which contains the following components in wt.-%:
  • AI 2 O 3 3.0 to 8.0, or 3.5 to 8.0
  • the glass composition can be an alkali borosilicate glass which contains the following components in wt.-%:
  • the glass composition can be an alkali borosilicate glass which contains the following components in wt.-%:
  • the glass composition can contain the following components in wt.-%:
  • the glass composition can contain the following components in wt.-%:
  • the glass composition can contain the following components in wt.-%:
  • SiO 2 50.0 to 68.0, or 55.0 to 68.0
  • TiO 2 0.0 to 1.0, or substantially free from TiO 2
  • the glass product may comprise a glass composition having a conductivity for thermal radiation at 1 ,580 °C of at least 300 W/m K.
  • the conductivity for thermal radiation may be at least 300 W/m K, at least 310 W/m K, at least 320 W/m K, or at least 330 W/m K.
  • the conductivity for thermal radiation may be at most 800 W/m K, at most 700 W/m K, at most 600 W/m K, or at most 500 W/m K.
  • the glass product may comprise a glass composition having an electric conductivity of at least 0.5 S/m in the molten state at a temperature of 1 ,600 °C.
  • the electric conductivity may be at least 0.5 S/m, at least 0.75 S/m, at least 1 S/m, at least 2 S/m, at least
  • the electric conductivity may be at most 50 S/m, at most 48 S/m, at most 47 S/m, at most 46 S/m, at most 45 S/m, at most 44 S/m, at most 43 S/m, at most 42 S/m, at most 41 S/m, at most 40 S/m, at most 38 S/m, or at most 36 S/m.
  • the electric conductivity may be 0.5 S/m - 50 S/m, 0.75 S/m - 48 S/m, 1 S/m - 47 S/m, 2 S/m - 46 S/m, 3 S/m - 45 S/m,
  • the electric conductivity may be 0.8 S/m, 1.7 S/m, 2.7 S/m, 3.7 S/m, 11.2 S/m, 13.2 S/m, 32.8 S/m, or 42.8 S/m.
  • the glass product may comprise a glass composition having a T2 at 1 ,300 °C or higher, and/or a temperature T4 at 900 °C or higher.
  • the method of this invention is particularly useful for glass compositions with very high melting temperatures, such as glass compositions comprising only limited amounts of alkali and alkaline earth metal oxides.
  • the composition of the glass may, for example, be such that the melt has a viscosity of 100 dPas at temperatures above 1 ,550 °C. When heating the melt to a temperature sufficiently high that the viscosity is 10 2 5 dPas or less, a lot of energy is required. However, low viscosities and the corresponding high temperatures are desirable for bubbles to leave the melt.
  • the glass compositions used in this invention have T2 temperatures much higher than 1 ,300 °C.
  • the T2 temperature for the glass melt in the melting vessel during the method of this disclosure may be above 1 ,350 °C, above 1 ,400 °C, above 1 ,450 °C, above 1 ,500 °C, above 1 ,550 °C, or above 1 ,580 °C and preferably even above 1 ,600 °C or above 1 ,620 °C.
  • T2 temperature of the glass compositions may be less than 2,000 °C, less than 1 ,900 °C, less than 1 ,800 °C, less than 1 ,750 °C, or less than 1 ,700 °C. Glass compositions with very high T2 temperatures are very difficult to process and require a lot of energy for melting.
  • the T4 temperature of the glass composition in the melting vessel during the method of this disclosure may be above 900 °C or above 950 °C or above 1 ,000 °C and in particular above 1 ,050 °C or above 1 ,120 °C. In embodiments, T4 temperature of the glass compositions may be less than 1 ,500 °C, less than 1 ,450 °C, or less than 1 ,400 °C. Glass compositions with very high T4 temperatures are very difficult to process and require a lot of energy for melting.
  • the fining agent is selected from the group consisting of AS2O3, Sb2O3, CeO2, SnC>2, Fe2C>3, chloride, fluoride, sulfate, and combinations thereof.
  • Figure 1 is a scheme of a glass melting vessel with a single heating circuit using one pair of electrodes.
  • Figure 2 is a scheme of a glass melting vessel of an embodiment with three heating circuits each using one pair of electrodes and a centralized phase shift.
  • Figure 3 is a scheme of a glass melting vessel of an embodiment with three heating circuits each using one pair of electrodes and a decentralized phase shift.
  • Figure 4 is a scheme of a glass melting vessel of an embodiment with three heating circuits each one shifted in phase by 60°.
  • Figure 5 is a scheme of a glass melting vessel of a further embodiment with three heating circuits each one shifted in phase by Aqu and Aq>2, respectively.
  • Figure 1 shows a scheme of an exemplary glass melting vessel with a single heating circuit using one pair of electrodes. The purpose of this figure is to exemplify the constituents of a heating circuit as used within this application.
  • the upper left corner of the figure indicates the three conductors (Li , L2, L3) of a three-phase power line provided from the power grid. These are connected to an inverter (1) which converts the power grid frequency of 50/60 Hz to a medium range frequency of from 20 Hz to 25,000 Hz.
  • the inverter (1) is connected via the power factor correction (2) for keeping the phase difference between current and voltage minimal and a transformer (3).
  • a pair of electrodes (5) is arranged below the surface (4) of the glass melt such that the electrodes (5) coming from above are fully immersed in the glass melt.
  • Figure 2 depicts a scheme of a glass melting vessel of an embodiment with three heating circuits each using one pair of electrodes.
  • the three conductors or AC mains of the power grid (Li , L2, L3) providing power to the inverters (1) are not shown in this figure.
  • the layout of the single heating circuits is identical to the one shown in Figure 1 .
  • pairs are in this example arranged horizontally extending from the walls of the melting vessel
  • the three inverters (1) are connected by means of the signal lines (7) with the common controller (8).
  • the common controller (8) is responsible for the coordination of the inverters (1). It creates a clock signal for synchronizing the connected inverters (1) which each provide a current and control its amplitude. This allows to set specific heating profiles for the single heating circuits independently from each other for the purpose of shaping the flow of the glass melt within the melting vessel (6).
  • the optimized flow will be able to minimize or avoid dead zones and ascertain a homogeneously mixed glass melt which will in turn improve the glass quality.
  • the fining process can be improved by increasing the temperature in certain areas to decrease the viscosity of the melt for facilitating the surfacing of the bubbles.
  • the common controller (8) has integrated a delay generator which allows applying a delay Ati, At 2 , and At 3 to the trigger signals of the clock generator for the three inverters (1) of the three heating circuits. By applying a At 0, the phase angle of the current provided by the respective inverter (1) can be shifted. This is an example of a centralized implementation of the delay.
  • each of the delay generators (9) can provide an individual delay Ati , At 2 , and Ata to the trigger signal for its associated inverter (1) which can vary the power output independently from 0 % to 100 %.
  • the embodiment shown in Figure 4 is also an example of a decentrally affected phase angle shift.
  • the three conductors (Li, L 2 , L3) of a three-phase power line provided from the power grid are shown which are connected to the three inverters (1) which are able to vary the power output from 0 % to 100 % and convert the power grid frequency of 50/60 Hz to a medium range frequency of from 20 Hz to 25,000 Hz.
  • the inverters (1) are again connected via a power factor correction (2) for keeping the phase difference between current and voltage minimal and a transformer (3) to the electrodes (5).
  • the round melting vessel (6) which is shown in a top view, three pairs of electrodes (5) are arranged extending horizontally from the wall. As indicated in the figure, in this example, the three heating circuits formed by the three pairs of electrodes (5) are shifted in their phase angle of the current by 60° each. As in the example of Figure 3, this is achieved decentrally by means of three delay generators (9) which are installed in the signal lines (7) between the common controller (8) and the inverters (1) and provide an individual delay Ati , At 2 , and Ata to the trigger signal for its associated inverter (1). In addition to this, in each heating circuit, in the electrical lines connecting the transformers (3) with the electrodes (5) a phase detector (10) is installed in close proximity to one of the electrodes (5).
  • phase detectors (10) measure the actual current signal at the electrodes (5) and provide this information via the further signal lines (7) to the common controller (8).
  • the common controller (8) detects the phase angle shift by comparing this information with the clock signal provided to the inverters (1) including any applied delay and can adjust the trigger signal or the delay Ati , At 2 , and Ata, respectively, in order to compensate for an undesired shift along the current flow from the inverter (1) to the electrodes (5) due to the cables and/or the transformers (3).
  • the embodiment shown in Figure 5 is a further example of a phase angle shift wherein not all heating circuits comprise an inverter.
  • the three conductors (Li , L 2 , L 3 ) of a three- phase power line provided from the power grid are shown which are connected to two inverters (1) and a thyristor power controller (11).
  • the thyristor power controller (11) also serves to vary the power output from 0 % to 100 % and is connected via a transformer (3) to electrodes (5).
  • This third heating circuit uses the phase of the power grid.
  • the inverters (1) serve to vary the power output from 0 % to 100 % and to impose a phase shift to their heating circuits relative to the other heating circuits.
  • the inverters (1) are connected via a power factor correction (2) for keeping the phase difference between current and voltage minimal and a transformer (3) to the electrodes (5).
  • the power grid frequency of 50 or 60 Hz is preferably used.
  • the common controller (8) is connected to the global clock and acts as a clock generator generating a clock signal for the two heating circuits comprising inverters (1) in a defined phase angle to the heating circuit with the thyristor power controller (11).
  • the two delay generators (9) installed in the signal lines (7) between the common controller (8) and the inverters (1) provide a shift of the phase angle of the current provided by them to the heating circuits by independently applying an individual delay Ati and At 2 to the trigger signal for its associated inverter (1).

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Glass Melting And Manufacturing (AREA)

Abstract

La présente invention concerne un procédé et un appareil de fabrication d'un produit en verre, une excellente qualité de verre étant obtenue au moyen d'un chauffage électrique direct à l'aide de multiples circuits de chauffage basés sur un onduleur qui peuvent être réglés indépendamment en termes d'amplitude et d'angle de phase.
PCT/EP2024/085726 2023-12-12 2024-12-11 Procédé et appareil de fabrication d'un produit en verre Pending WO2025125352A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2024/085726 WO2025125352A1 (fr) 2023-12-12 2024-12-11 Procédé et appareil de fabrication d'un produit en verre

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
EP23215757.8A EP4570764A1 (fr) 2023-12-12 2023-12-12 Procédé et appareil de fabrication d'un produit en verre
EP23215752.9A EP4570763A1 (fr) 2023-12-12 2023-12-12 Procédé et récipient pour le chauffage électrique d'un bain de verre
EP23215752.9 2023-12-12
EP23215757.8 2023-12-12
PCT/EP2024/085726 WO2025125352A1 (fr) 2023-12-12 2024-12-11 Procédé et appareil de fabrication d'un produit en verre

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WO2025125352A1 true WO2025125352A1 (fr) 2025-06-19

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Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3818112A (en) * 1973-04-30 1974-06-18 Corhart Refractories Co Electrical furnace for melting glass
US4211887A (en) 1978-10-25 1980-07-08 Owens-Corning Fiberglas Corporation Electrical furnace, zones balanced with a symmetrically tapped transformer
US4600426A (en) * 1984-10-01 1986-07-15 Ppg Industries, Inc. Metering device for molten glass and the like
EP0812809A2 (fr) * 1996-06-12 1997-12-17 Praxair Technology, Inc. Procédé de réduction d'émission toxique d'un four de verre par utilisation de l'eau pour le procédé d'affinage
US5922097A (en) * 1996-06-12 1999-07-13 Praxair Technology, Inc. Water enhanced fining process a method to reduce toxic emissions from glass melting furnaces
US20020131555A1 (en) * 2001-03-15 2002-09-19 Ray Fleming Apparatus for producing vacuum arc discharges
CZ24918U1 (cs) 2012-09-05 2013-02-11 Vysoká skola chemicko - technologická v Praze Sklářská tavící pec pro kontinuální tavení skel řízenou konvekcí skloviny
US20130279532A1 (en) * 2010-10-14 2013-10-24 Schott Ag Energy efficient high-temperature refining
WO2014036979A1 (fr) 2012-09-05 2014-03-13 Vysoká škola chemicko-technologická v Praze Procédé de fusion du verre continue sous convection contrôlée du bain de verre fondu et four de fusion de verre pour la production de ce dernier
JP5835691B2 (ja) * 2011-10-26 2015-12-24 高周波熱錬株式会社 通電加熱装置及び方法
JP2017214272A (ja) * 2016-04-25 2017-12-07 ショット アクチエンゲゼルシャフトＳｃｈｏｔｔ ＡＧ 気泡形成を回避しつつガラス溶融物からガラス製品を製造するための装置および方法
DE102018122017A1 (de) 2017-09-08 2019-03-14 Glass Service, A.S. Schmelzraum eines kontinuierlichen Glasschmelzofens und Verfahren zum Glasschmelzen in diesem Schmelzraum

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3818112A (en) * 1973-04-30 1974-06-18 Corhart Refractories Co Electrical furnace for melting glass
US4211887A (en) 1978-10-25 1980-07-08 Owens-Corning Fiberglas Corporation Electrical furnace, zones balanced with a symmetrically tapped transformer
US4600426A (en) * 1984-10-01 1986-07-15 Ppg Industries, Inc. Metering device for molten glass and the like
EP0812809A2 (fr) * 1996-06-12 1997-12-17 Praxair Technology, Inc. Procédé de réduction d'émission toxique d'un four de verre par utilisation de l'eau pour le procédé d'affinage
US5922097A (en) * 1996-06-12 1999-07-13 Praxair Technology, Inc. Water enhanced fining process a method to reduce toxic emissions from glass melting furnaces
US20020131555A1 (en) * 2001-03-15 2002-09-19 Ray Fleming Apparatus for producing vacuum arc discharges
US20130279532A1 (en) * 2010-10-14 2013-10-24 Schott Ag Energy efficient high-temperature refining
JP5835691B2 (ja) * 2011-10-26 2015-12-24 高周波熱錬株式会社 通電加熱装置及び方法
CZ24918U1 (cs) 2012-09-05 2013-02-11 Vysoká skola chemicko - technologická v Praze Sklářská tavící pec pro kontinuální tavení skel řízenou konvekcí skloviny
WO2014036979A1 (fr) 2012-09-05 2014-03-13 Vysoká škola chemicko-technologická v Praze Procédé de fusion du verre continue sous convection contrôlée du bain de verre fondu et four de fusion de verre pour la production de ce dernier
JP2017214272A (ja) * 2016-04-25 2017-12-07 ショット アクチエンゲゼルシャフトＳｃｈｏｔｔ ＡＧ 気泡形成を回避しつつガラス溶融物からガラス製品を製造するための装置および方法
DE102018122017A1 (de) 2017-09-08 2019-03-14 Glass Service, A.S. Schmelzraum eines kontinuierlichen Glasschmelzofens und Verfahren zum Glasschmelzen in diesem Schmelzraum

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