METHOD AND APPARATUS FOR MELTING AND REFINING GLASS, GLASS CERAMIC, AND GLASS CERAMIFIABLE TO GLASS CERAMIC

Abstract

A method and an apparatus for melting and refining glass, glass ceramic, or ceramizable to form glass ceramic are provided. The method and apparatus refine the materials such that less than 1 bubble/kg is included in the molten and refined material and the direct CO.sub.2 emissions amount to less than 100 kg per ton of molten material during the melting and refining.

Claims

1. A method for melting and refining glass, glass ceramic, glass ceramizable to form glass ceramic, comprising: controlling a melting and refining process so that molten and refined glass is provided that has less than 1 bubble/kg; and controlling the melting and refining process so that direct CO.sub.2 emissions during the melting and refining process amount to less than 100 kg per ton of the molten and refined glass.

2. The method of claim 1, wherein the melting and refining process comprises melting and refining in an all-electric tank using electrical energy that has at least a neutral CO.sub.2balance.

3. The method of claim 1, wherein the melting and refining process comprises radio frequency refining.

4. The method of claim 1, wherein the melting and refining process comprises using a skull crucible and high-load electrodes.

5. The method of claim 1, wherein the melting and refining process comprises heating to a temperature from 1700° C. to 2400° C. least in some zones of the molten and refined glass.

6. The method of claim 1, wherein the melting and refining process comprises heating to a temperature from 1700° C. to 2000° C. least in some zones of the molten and refined glass.

7. The method of claim 1, wherein the melting and refining process further comprises additionally heating the molten and refined glass using an additional heating unit.

8. The method of claim 7, wherein the additional heating unit comprises electric radiant heating.

9. The method of claim 7, wherein the additional heating unit heats using an energy source that is free of electrical energy.

10. The method of claim 9, wherein the additional heating unit comprises a burner burning a fuel selected from a group consisting of H.sub.2, synthetic methane, fossil methane, biogas, biofuel, and combinations thereof.

11. The method of claim 10, wherein the additional heating unit generates plasma flames.

12. The method of claim 1, wherein the melting and refining process has a throughput of the molten and refined glass of more than 10 tons per day.

13. The method of claim 1, wherein the melting and refining process has a throughput of the molten and refined glass of more than 200 tons per day.

14. The method of claim 1, further comprising ceramicizing the molten and refined glass.

15. An apparatus for melting and refining glass, glass ceramic, or glass that is ceramizable to form glass ceramic, comprising: a melting and refining system controllable to produce molten and refined glass with less than 1 bubble/kg, wherein the melting and refining system produces direct CO.sub.2 emissions of less than 100 kg per ton of the molten and refined glass.

16. The apparatus of claim 15, wherein the melting and refining system comprises an all-electric tank and a high-temperature refining device, wherein the melting and refining system has cold walls during the refining, and wherein the melting and refining system is configured to use electrical energy that has at least a neutral CO.sub.2balance.

17. The apparatus of claim 16, wherein the melting and refining system comprises an RF refining device.

18. The apparatus of claim 16, wherein the high-temperature refining includes device further comprises an auxiliary heating device with a burner that burns a fuel selected from a group consisting of H.sub.2, synthetic methane, fossil methane, biogas, biofuel, and combinations thereof.

19. The apparatus of claim 15, wherein the melting and refining system comprises a skull crucible with high-load electrodes.

20. A glass or glass ceramic, comprising: a panel having less than 1 bubble/kg, the panel being configured for a use selected from a group consisting of cookware, fireplace window glass, a cooking surface, a grilling surface, a frying surface, fire protection glazing, oven window glass, a pyrolysis oven window glass, a lighting cover, safety glass, a laminated composite safety glass, a support panel, an oven lining, wherein the panel has a property selected from a group consisting of a thickness between 2.5 mm and 6 mm, a light transmittance between 5% and 80%, and a dimple pattern provided on at least one surface at least in sections thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The invention will now be described in more detail by way of several embodiments and with reference to the accompanying drawings, wherein:

[0073] FIG. 1 is a top plan view of a first exemplary embodiment (MT1), with the top or covers omitted for the sake of better comprehension, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a radio frequency refining tank (RF RT);

[0074] FIG. 2 is a cross-sectional view of the first exemplary embodiment (MT1), with the sectional plane cutting vertically approximately through the middle of the melting system, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a radio frequency refining tank (RF RT);

[0075] FIG. 3 is a top plan view of a second exemplary embodiment (MT2), with the top or covers omitted for the sake of better comprehension, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a refining tank with a skull crucible and high-load electrodes;

[0076] FIG. 4 is a cross-sectional view of the second exemplary embodiment (MT2), with the sectional plane cutting vertically approximately through the middle of the melting system, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a refining tank which includes a skull crucible and high-load electrodes;

[0077] FIG. 5 is a top plan view of a third exemplary embodiment (MT3), with the top or covers omitted for the sake of better comprehension, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a platinum refining tank;

[0078] FIG. 6 is a cross-sectional view of the third exemplary embodiment (MT3), with the sectional plane cutting vertically approximately through the middle of the melting system, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a platinum refining tank;

[0079] FIG. 7 is a top plan view of a fourth exemplary embodiment (MT4), with the top or covers omitted for the sake of better comprehension, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a vacuum refining tank;

[0080] FIG. 8 is a cross-sectional view of the fourth exemplary embodiment (MT4), with the sectional plane cutting vertically approximately through the middle of the melting system, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a vacuum refining tank;

[0081] FIG. 9 is a top plan view of a fifth exemplary embodiment (MT5), with the top or covers omitted for the sake of better comprehension, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a boost EAH refining tank;

[0082] FIG. 10 is a cross-sectional view of the fifth exemplary embodiment (MT5), with the sectional plane cutting vertically approximately through the middle of the melting system, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a boost EAH refining tank;

[0083] FIG. 11 is a top plan view of a sixth exemplary embodiment (MT6), with the top or covers omitted for the sake of better comprehension, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a high electric current refining tank; and

[0084] FIG. 12 is a cross-sectional view of the sixth exemplary embodiment (MT6), with the sectional plane cutting vertically approximately through the middle of the melting system, the melting tank having a throughput of more than 10 up to 200 t/d, and comprising an AE tank and a high electric current refining tank.

DETAILED DESCRIPTION

[0085] In the following description of the preferred embodiments, the same reference numerals denote the same or equivalent components or assemblies in the respective discussed embodiments. For the sake of clarity and better comprehension only, the figures are not drawn to scale.

[0086] In the context of the present disclosure, as already stated in the introductory part, direct CO.sub.2 emissions refer to those CO.sub.2 emissions that arise in the vicinity of the tank itself, i.e. which are caused by the heating of the tank with the glass to be melted contained therein or with of the glass ceramic contained therein, and by the refining. In the context of the present disclosure, glass ceramic also refers to glasses which do not yet have any crystalline fractions, but which can later be transformed into glass ceramics by appropriate time-dependent heat application.

[0087] In the present context, the term of glass ceramic shall in particular also encompass glass ceramic material in the batch, which is melted and refined by the presently disclosed method and which can be added to the batch for recycling purposes, for example, and can form part thereof.

[0088] However, the term glass ceramic is also intended to disclose the respective glasses that can be converted into glass ceramic, in particular ceramizable and/or crystallizable glasses, and is thus intended to express that it comes within the scope of the present disclosure for these glasses that can be further processed into glass ceramics, after the refining, to perform a respective ceramization or to cause crystallization processes, as is known to persons skilled in the art.

[0089] Such corresponding ceramization processes which are known to those skilled in the art, or the causing of corresponding crystallization processes also form part of the presently disclosed method for glasses which can be converted into glass ceramics.

[0090] Typical glass ceramics include the glass ceramics marketed by Schott AG under the trade names Ceran® and Robax®, for example.

[0091] The glasses presently disclosed for producing glass articles include the groups of borosilicate (BS), aluminosilicate (AS), and boroaluminosilicate glasses, and lithium aluminum silicate glass ceramics (LAS), which are mentioned here by way of example, without losing the claim of generality.

[0092] In particular a glass with an Li.sub.2O content from 4.6 wt % to 5.4 wt % and an Na.sub.2O content from 8.1 wt % to 9.7 wt % and an Al.sub.2O.sub.3 content from 16 wt % to 20 wt % can be used as an Li—Al—Si glass.

[0093] For example, a Li—Al—Si glass with a composition comprising 3.0-4.2 of Li.sub.2O, 19-23% of Al.sub.2O.sub.3, 60-69 wt % of SiO.sub.2, as well as TiO.sub.2 and ZrO.sub.2 can be used as a glass that is ceramizable to form a glass ceramic, also known as a green glass.

[0094] Furthermore, a glass or a glass that is ceramizable to form a glass ceramic with an Li.sub.2O content of less than 3 wt % can also be used.

[0095] A glass containing the following components (in wt %) can be used as a borosilicate glass:

TABLE-US-00001 SiO.sub.2 70-87 B.sub.2O.sub.3  7-25 Na.sub.2O + K.sub.2O 0.5-9.sup.  Al.sub.2O.sub.3 0-7 CaO  0-3.

[0096] A glass in particular with the following composition can also be used as a borosilicate glass:

TABLE-US-00002 SiO.sub.2 70-86 wt % Al.sub.2O.sub.3 0-5 wt % B.sub.2O.sub.3 9.0-25 wt % Na.sub.2O 0.5-5.0 wt % K.sub.2O 0-1.0 wt % Li.sub.2O 0-1.0 wt %;

[0097] or else a glass, in particular an alkali borosilicate glass, which contains:

TABLE-US-00003 SiO.sub.2 78.3-81.0 wt % B.sub.2O.sub.3 9.0-13.0 wt % Al.sub.2O.sub.3 3.5-5.3 wt % Na.sub.2O 3.5-6.5 wt % K.sub.2O 0.3-2.0 wt % CaO 0.0-2.0 wt %.

[0098] A pharmaceutical glass can also be used, for example a glass marketed by Schott AG under the trade name Fiolax® (e.g. Fiolax® Pro, Fiolax® clear).

[0099] In one example, a glass such as a borosilicate glass can be used, which contains:

TABLE-US-00004 SiO.sub.2 71-77 wt % B.sub.2O.sub.3 9-12 wt % Al.sub.2O.sub.3 4.5-8 wt % Na.sub.2O 6-8 wt % K.sub.2O 0-3 wt % CaO 0-2 wt % BaO 0-1.5 wt %.

[0100] Emissions of CO.sub.2 as generated by the provision of electrical energy are not referred to as direct CO.sub.2 emissions in the context of the present disclosure, however, as already mentioned above, it is advantageous to accordingly reduce such emissions as well, in particular to at least ensure a neutral CO.sub.2 balance.

[0101] Each of the accompanying figures illustrates a device 1 for melting and a device 2 for refining glass and/or glass ceramic, which together are in particular also referred to as a melting system.

[0102] The melting device 1 is an all-electric tank, i.e. a tank that is fully and solely heated using electrical energy. This tank is also referred to as an AE tank or all-electric meltdown tank, the latter term usually being employed to express that a batch is melted and not a previously molten and resolidified glass.

[0103] Current-carrying rod electrodes 3 protrude into the melt 3a which is covered by a batch 6 that is fed onto and resupplied to the melt 3a by feeding machines to produce a batch cover that is caused to melt down inside the device.

[0104] The refining device 2 comprises a radio frequency, in particular inductively heated refining tank, also referred to as an RF refining tank, or a tank heated by high-load electrodes 12 which cause electric current to flow through the material to be refined.

[0105] The devices 1 and 2 are made of or are lined with refractory material 5 in their wall areas, in particular the wall areas in contact with the melt 3a.

[0106] These devices 1 and 2 of the presently disclosed embodiments permit to implement a method in which the molten and refined glass 3a, 3b or the molten and refined glass ceramic 3a, 3b includes less than 1 bubble/kg after the melting and refining, and in which direct CO.sub.2 emissions especially from fossil fuels amount to less than 100 kg per ton of molten glass 3a, 3b during the melting and refining.

[0107] Here, the specification of the number of bubbles/kg after the melting and refining also correspond to the number of bubbles/kg in a later, optionally additionally hot-formed product, for example also in a hot-formed glass ceramic product.

[0108] Device 2 is a device for high-temperature refining, in particular a device which has cold walls during the refining, i.e. which forms a respective skull crucible 11 that is distinguished by its cold walls consisting of the melted and resolidified glass 3a.

[0109] As a result, very efficient refining can be performed, in particular due to the respective very high temperatures reaching temperatures between 1700° C. and 2400° C. in the method presently disclosed, at least in some zones of the glass to be refined or the glass ceramic to be refined, and for glass ceramics, i.e. for glasses to be further processed into glass ceramics, temperatures from 1700° C. to 2000° C. should preferably be achieved.

[0110] By way of example, FIG. 1 shows a top plan view of a first embodiment, with the top or covers omitted for the sake of better comprehension, in which the melting tank of the device 1 for melting glass or glass ceramic is an AE melting tank and has a throughput of more than 10 up to 200 t/d, and in which the device 2 for refining glass or glass ceramic comprises a radio frequency refining tank, RF RT.

[0111] FIG. 2 shows a cross-sectional view of this first exemplary embodiment, with the sectional plane cutting vertically approximately through the middle of the melting system, i.e. through the middle of the device 1 for melting glass or glass ceramic and of the device 2 for refining glass or glass ceramic.

[0112] The device 1 for melting glass or glass ceramic comprises rod electrodes 3 arranged therein for heating the melt, while the device 2 for refining glass or glass ceramic comprises one or more induction coils 10 which provide radio frequency heating for the glass inside the skull crucible 11, and moreover comprises auxiliary heating means in the form of gas burners 4.

[0113] This auxiliary heating with gas burners 4 may involve any of one or more H.sub.2 burners, burners for synthetically obtained or produced methane (CH.sub.4), plasma flames, biogas and/or biofuel burners.

[0114] The molten glass 3a exiting the device 1 following the melting preferably enters the device 2 for being refined through a distributor 9 and leaves it for further use through channel 16, for example in order to be fed to a downstream hot forming process.

[0115] FIG. 3 shows a top plan view of a second exemplary embodiment, with the top or covers omitted for the sake of better comprehension, in which the melting tank of the device 1 for melting glass or glass ceramic has a throughput of more than 10 up to 200 t/d and comprises an AE melting tank which is also heated by rod electrodes 3 through which electric current is passed, and in which the device 2 for refining glass or glass ceramic comprises a refining tank with a skull crucible 11 and high-load electrodes 12 for heating the latter.

[0116] Again in this exemplary embodiment, burners 4 are provided for additional heating. For the sake of clarity, the burners 4 are each represented by round black circles in the figures, however without each being denoted by an own reference numeral.

[0117] As with the first exemplary embodiment, the glass surface 8 of the molten glass 3a or of the molten glass ceramic 3a and the glass surface 8 of the molten and refined glass 3b or of the molten and refined glass ceramic 3b is only slightly inclined in the flow direction.

[0118] FIG. 4 shows a cross-sectional view of the second exemplary embodiment, with the sectional plane cutting vertically approximately through the middle of the melting system.

[0119] FIG. 5 shows a top plan view of a third embodiment, with the top or covers omitted for the sake of better comprehension, in which the melting tank has a throughput of more than 10 up to 200 t/d and comprises an AE melting tank and a platinum refining tank with a platinum refining tube 13.

[0120] FIG. 6 shows a cross-sectional view of this third exemplary embodiment, with the sectional plane cutting vertically approximately through the middle of the melting system.

[0121] FIG. 7 discloses a top plan view of a fourth embodiment, with the top or covers omitted for the sake of better comprehension, in which the melting tank of the device 1 for melting glass or glass ceramic has a throughput of more than 10 up to 200 t/d and comprises an all-electric AE tank, for example, and in which the device 2 for refining glass or glass ceramic comprises a vacuum refining tank which includes a vacuum refining channel 15 made of platinum, which defines a negative pressure zone 14.

[0122] FIG. 8 shows a cross-sectional view of this fourth exemplary embodiment, which also indicates the respective locally prevailing pressure conditions.

[0123] In device 1, in channel or distributor 9, and in channel 16, a pressure P is adjusted which approximately corresponds to atmospheric pressure of about 1 bar. Due to the pressure P′ prevailing in negative pressure zone 14, which is much lower than atmospheric pressure, the molten glass 3a is raised during the refining, as can be clearly seen from the higher level of glass bath surface 8′, which allows for very efficient and energy-saving refining.

[0124] FIG. 9 shows a top plan view of a fifth exemplary embodiment, with the top or covers omitted for the sake of better comprehension, in which the melting tank has a throughput of more than 10 up to 200 t/d, and in which the device 1 comprises an AE tank and the device 2 comprises a boost EAH refining tank 17. The boost EAH refining tank 17A comprises a refining tank with electrical auxiliary heating such as disclosed in present Applicant's DE 10 304 973 A1, for example. The disclosure of this document is incorporated into the subject-matter of the present application by reference. Auxiliary heating is implemented by rod electrodes 3 in refining device 2 and is capable of providing more than 90% of the energy input required for heating. Nevertheless, the burners 4 described above can also be used in addition thereto.

[0125] FIG. 10 shows a cross-sectional view of this fifth exemplary embodiment, with the sectional plane cutting vertically approximately through the middle of device 1 and of device 2.

[0126] FIG. 11 discloses a top plan view of a sixth embodiment, with the top or covers omitted for the sake of better comprehension, in which the melting tank has a throughput of more than 10 up to 200 t/d, and in which device 1 comprises an AE tank and device 2 comprises a high electric current refining tank 18. Again, in this high electric current refining tank 18, electrical auxiliary heating can be employed using rod electrodes 3 which are capable of providing more than 90% of the electrical energy required for heating. Nevertheless, the burners 4 as described above can also be used in addition thereto.

[0127] The cross-sectional view of FIG. 12 of the sixth exemplary embodiment, with the sectional plane cutting vertically approximately through the middle of the melting system, shows a barrier 19 for narrowing the cross section of the flow of molten glass 3a, 3b, which barrier is effective to increase the current density flowing between the rod electrodes 3 preferably in the flow direction of the molten glass 3a, 3b, since the barrier 19 is made of non-conductive refractory material. This increase in electrical resistance in the area above the barrier 19 greatly increases the temperature of the molten glass 3a, 3b, which results in the refining becoming much more efficient in this area. The reduction in the height of the molten glass that is present above the barrier 19 also results in an acceleration of the release of bubbles during this refining.

[0128] The table below shows conventional embodiments of melting tanks MT and refining tanks RT, in which fossil fuels such as gas and oil are used in the burners.

TABLE-US-00005 CO.sub.2 from Typical CO.sub.2 from fossil Total CO.sub.2 glass Type of Type of batch energy (fossil) quality glass tank kg/t glass kg/t glass kg/t glass bubbles/kg BS tank B 0 530 530 <0.5 BS tank A 0 440 440 <0.5 AS tank B 30 625 625 <1.0 LAS tank B 90 565 565 <1.0 LAS tank C 5 330 330 <0.2 LAS tank D 5 303 305 <0.2 LAS tank E 30 550 550 <0.2 BS tank F 20 187 187 <1.0 BS tank G 20 610 610 <1.0 BS tank H 20 1130 1130 <1.0

[0129] Exemplary implementations of the embodiments as disclosed above, in particular with regard to the method according to the invention and the apparatus according to the invention with respect to CO.sub.2 emissions from fossil fuels, in particular from melting tanks MT and refining tanks RT for the production of special glass, are listed in the table below.

TABLE-US-00006 CO.sub.2 CO.sub.2 from from CO.sub.2 fossil Glass fossil CO.sub.2 Glass Total from energy quality energy from quality CO.sub.2 Type Type batch MT downstream RT H.sub.2 or downstream fossil of of kg/t kg/t MT kg/t biofuel RT kg/t glass tank glass glass bubbles/kg glass RT bubbles/kg glass LAS MT1 5 0 <1000 50 <0.2 50 LAS MT1 5 0 <1000 0 X <0.2 0 LAS MT1 30 0 <1000 70 <0.2 70 LAS MT1 30 0 <1000 0 X <0.2 0 LAS MT1 90 0 <1000 70 <0.2 70 LAS MT1 90 0 <1000 0 X <1.0 0 AS MT2 30 0 <100 50 <1.0 50 AS MT2 30 0 <100 0 X <1.0 0 AS MT3 30 0 <100 10 <1.0 10 AS MT3 30 0 <100 0 X <1.0 0 BS MT5 0 0 <100 90 <0.5 90 BS MT5 0 0 <100 0 X <0.5 0 BS MT6 20 0 <500 90 <1.0 90 BS MT6 20 0 <500 0 X <1.0 0 BS MT2 20 0 <500 50 <1.0 50 BS MT2 20 0 <500 0 X <1.0 0

[0130] However, in all the examples in the table above regarding glass quality downstream of refining tank RT, in particular downstream of the refining tank RT according to the invention, even half the specified number of bubbles/kg is preferably achieved with the presently disclosed embodiments, and most preferably even a quarter of the specified number of bubbles/kg.

[0131] Generally, the tank types described above are designed for a throughput of less than 200 tons per day for special glass.

LIST OF REFERENCE NUMERALS

[0132] 1 Device for melting glass, glass ceramic or in particular glass ceramizable to form glass ceramics, e.g. AE meltdown tank or AE melting tank (MT),

[0133] 2 Device for refining glass or glass ceramic, e.g. all-electric radio frequency or RF refining tank (RT),

[0134] 3 Rod electrodes

[0135] 3a Melt of the molten glass or molten glass ceramic

[0136] 3b Melt of the molten and refined glass or the molten and refined glass ceramic

[0137] 4 Gas burners (synthetic or fossil CH.sub.4, H.sub.2, or biofuel in combustion with oxygen)

[0138] 5 Refractory material

[0139] 6 Batch, providing a batch cover and subsequently leading to meltdown

[0140] 7 Feeding machines

[0141] 8 Glass bath surface

[0142] 8′ Glass bath surface at a higher level as caused by negative pressure P′

[0143] 9 Distributor

[0144] 10 RF induction coil

[0145] 11 Skull crucible

[0146] 12 High-load electrodes

[0147] 13 Pt refining tube

[0148] 14 Negative pressure zone of vacuum refining channel 15, preferably having walls made of platinum

[0149] 15 Vacuum refining channel (Pt)

[0150] 16 Channel

[0151] 17 Boost EAH refining tank with more than 90% of electrical auxiliary heating (EAH)

[0152] 18 High electric current refining tank with more than 90% of electrical auxiliary heating (EAH)

[0153] 19 Barrier for narrowing the flow cross section