FLOAT GLASS PRODUCTION PROCESS AND INSTALLATION

Abstract

Glass production process whereby at least part of a reducing gas composition (100) introduced into a float chamber (4) receiving molten glass (3) from a melting chamber heated by combustion of fuel (27) with oxidant (28), is preheated by heat exchange with fumes (25) evacuated from a melting furnace (2) before said part of the reducing gas composition (100) is introduced in the float chamber (4) and installation for use in said glass production process.

Claims

1.-15. (canceled)

16. A process for the production of glass, comprising the steps of: producing molten glass in a melting furnace that is heated by combustion of a fuel with at an oxidant, said combustion generating heat and fumes, said fumes being evacuated from the melting furnace at a temperature between 900 C. and 1550 C., preferably of at least 1000 C.; continuously pouring the molten glass into a float chamber so as to form a glass ribbon floating on a molten tin bath inside the float chamber, whereafter said glass ribbon is continuously evacuated from the float chamber by conveyor rollers; introducing a gas composition into the float chamber so as to maintain a reducing atmosphere above the tin bath and the glass ribbon, said gas composition comprising of 99.9% vol to 100% vol of an inert gas and a reducing gas; during said step of introducing, continuously or intermittently evacuating the introduced gas composition from the float chamber (4) such that the evacuated gas composition is replaced with amounts of the introduced gas composition composition; and preheating a gas component, corresponding to at least part of the gas composition, by heat exchange with the evacuated fumes before the gas component is introduced in the float chamber as part of the gas composition.

17. The process of claim 16, wherein the gas component to be preheated is preheated by indirect heat exchange with the evacuated fumes.

18. The process of claim 16, further comprising the step of heating an intermediate gas by direct heat exchange with the evacuated fumes to produce a heated intermediate gas, wherein the heated intermediate gas is used to preheat said gas component by direct heat exchange with the heated intermediate gas.

19. The process of claim 18, wherein the heated intermediate gas is also used to preheat at least one combustion reactant selected from the oxidant and the fuel by direct heat exchange with the heated intermediate gas.

20. The process of claim 18, whereby the intermediate gas circulates in a closed loop.

21. The process of claim 16, wherein the gas component to be preheated is preheated by direct heat exchange with the evacuated fumes.

22. The process of claim 21, wherein, after having been preheated by direct heat exchange with the evacuated fumes and before being introduced into the float chamber as part of the gas composition, the preheated gas component is used to preheat at least one combustion reactant selected from the oxidant and the fuel by direct heat exchange.

23. The process of claim 16, whereby the gas component to be preheated essentially consists of inert gas.

24. The process of claim 23, wherein the inert gas is nitrogen.

25. The process of claim 16, wherein: the float chamber has a roof above the molten tin bath and heating elements are installed in or adjacent the roof; and said process further comprises the steps of determining the temperature with which the gas composition is introduced into the float chamber and regulating the heat generated by the heating elements as a function of the determined temperature.

26. The process of claim 16, wherein said fumes are evacuated from the melting furnace at a temperature between 1000 C. and 1550 C.

27. The process of claim 16, wherein said inert gas is nitrogen and said reducing gas is hydrogen.

28. A glass production installation, comprising: a glass melting furnace comprising a fumes outlet, a molten-glass outlet, and one or more burners for heating the furnace; a float chamber downstream of the molten-glass outlet comprising a basin for containing a molten tin bath, a roof above the basin, a molten-glass inlet, conveyor rolls for evacuating a glass ribbon from the float chamber via a glass outlet, one or more gas inlets for introducing a reducing gas composition into the float chamber, and a gas outlet for evacuating said reducing gas composition from the float chamber; and a heat recovery unit downstream of the fumes outlet of the melting furnace that is adapted for recovering heat from fumes evacuated from the melting furnace via said fumes outlet, wherein: said one or more gas inlets are located in or adjacent the roof; the heat recovery unit is connected to a source of a gas component selected from the group consisting of an inert gas, a reducing gas, and a gas composition comprising 99% vol to 100% vol of an inert gas and a reducing gas; said heat recovery unit is adapted for heating said gas component by direct or indirect heat exchange with fumes evacuated from the melting furnace via the fumes outlet; and the heat recovery unit includes a gas-component outlet that is in fluid connection with at least one gas inlet of the furnace thereby introducing the gas component, after said preheating, into the float chamber.

29. The installation of claim 28, wherein the heat recovery unit comprises: a primary heat exchanger adapted to heat an intermediate gas by direct heat exchange with fumes evacuated from the melting furnace via the fumes outlet, and a secondary heat exchanger adapted for heating the gas component by direct heat exchange with the intermediate gas heated in the primary heat exchanger.

30. The installation of claim 29, wherein the primary heat exchanger and the secondary heat exchanger are integrated in a closed circulation loop of the intermediate gas.

31. The installation of claim 29, whereby the heat-recovery unit further comprises a further heat exchanger adapted to preheat a combustion reactant by direct heat exchange with the heated intermediate gas from the primary heat exchanger, said further heat exchanger being fluidly connected to a source of combustion reactant and also to at least one burner of the melting furnace so as to supply the heated combustion reactant to said at least one burner, the combustion reactant being selected from fuel and oxidant.

32. The installation of claim 28, whereby the heat-recovery unit comprises a first heat exchanger for heating the gas component by direct heat exchange with the fumes evacuated from the melting furnace via the fumes outlet.

33. The installation of claim 28, further comprising a further heat exchanger adapted to preheat a combustion reactant by direct heat exchange with the heated gas component from the first heat exchanger, said further heat exchanger being fluidly connected to a source of combustion reactant and to at least one burner of the furnace so as to supply the heated combustion reactant to said at least one burner, the of combustion reactant being selected from fuel and oxidant.

34. The installation of claim 28, further comprising: at least one heating element mounted in or adjacent the roof inside the float chamber; a temperature detector adapted to determine the temperature of the reducing gas composition at at least one gas inlet of the float chamber; and a control unit adapted to regulate the heat generation by the at least one heating element, wherein the control unit is connected to the temperature detector and is programmed to regulate the heat generated by the at least on heating element as a function of the temperature determined by the heat detector.

35. The installation of claim 28, wherein the inert gas is nitrogen and the reducing gas is hydrogen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0096] The present invention and its advantages are illustrated in the following examples, reference being made to FIGS. 1 to 3, whereby:

[0097] FIG. 1 is a schematic representation of a first embodiment of the invention;

[0098] FIG. 2 is a schematic representation of a second embodiment of the present invention; and

[0099] FIG. 3 is a schematic cross-section representation of a float chamber suitable for use in the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0100] In the following examples, the inert gas is nitrogen and the reducing gas is hydrogen.

[0101] As illustrated in FIGS. 1 and 2, solid glass-forming material 1, often referred to as batch, is introduced into a melting furnace 2.

[0102] In melting furnace 2, the glass-forming material 1 is heated and melted.

[0103] The molten glass 3 thus obtained is introduced into a float chamber 4, downstream of the melting furnace 2. As illustrated in FIG. 3, inside the float chamber 4, the molten glass 3 spreads across the surface of a bath 41 of molten tin. The molten glass 3 then progressively cools down as it travels through the float chamber 4 until a glass ribbon 5 is formed which can be evacuated from the float chamber 4 by means of conveyor rollers 42.

[0104] As also illustrated in FIG. 3, a gas composition 100 is introduced into one or more openings 43 in the roof 44 of the float chamber 4 (four such openings 43 are represented in FIG. 3), so as to maintain a reducing atmosphere above the tin bath and the glass ribbon. The outlet opening(s) through which the gas composition is regularly evacuated from float chamber 4 is/are not represented.

[0105] In addition, the float chamber 4 also comprises a number of heating elements 45, such as electrical heaters, which are used to maintain the desired temperature profile in the float chamber 4 so as to obtain the desired temperature profile of the glass5 as it travels through chamber 4. The number of heating elements 45 may run into the hundreds. In some cases, the float chamber 4 may also contain cooling elements (not shown) near the glass outlet of the chamber 4 and in the vicinity of the glass ribbon to further control the temperature of the glass ribbon 5 as it leaves chamber 4.

[0106] The melting furnace 2 is heated by means of at least one burner 21 (only a single burner 21 is represented in FIGS. 1 and 2).

[0107] The one or more burners 21 inject fuel 23 and combustion oxidant 24 into the melting furnace 2, where the fuel combusts with the combustion oxidant so as to generate heat for melting the glass-forming material 1. In the illustrated embodiments, the combustion oxidant is industrial oxygen with a purity of about 92% vol.

[0108] Other heating elements (not shown), such as electric loop electrodes, may also be present in the melting furnace 2.

[0109] The combustion of the fuel 23 generates fumes 25 which leave the melting furnace at a temperature of about 1450 C.

[0110] In the embodiment illustrated in FIG. 1, said hot fumes 25 are introduced into the heat exchanger 60, where the hot fumes 25 are used to directly preheat a gas component 101, which corresponds to the nitrogen fraction of the gas composition 100 which is injected into the float chamber 4. Following the heat exchange between the hot fumes 25 and the gas component 101, the fumes 26 are evacuated from heat exchanger 60 and preferably subjected to a pollutant removal process before being released into the atmosphere.

[0111] In the embodiment illustrated in FIG. 1, the gas component 102 which has been heated in heat exchanger 60 is first introduced into heat exchanger 80 in which the combustion oxidant 23 is preheated by direct heat exchange with heated gas component 102. The thus preheated combustion oxidant 27 is then supplied to the burner(s) 21 of furnace 2. From heat exchanger 80, the heated gas component 103 is sent to heat exchanger 90 in which the fuel 24 is preheated by direct heat exchange with the heated gas component 103. The thus preheated fuel 28 is equally supplied to burner(s) 21.

[0112] The heated gas component (nitrogen) 104 leaving heat exchanger 90 is then admixed with hydrogen 105 (and optionally with other gases present in the gas composition) so as to obtain gas composition 100 which is introduced into the float chamber 4 as described above.

[0113] Using the waste energy present in the fumes of the melting furnace 2, gas composition 100 can be injected into the float chamber 4 at a substantially higher temperature, for example at 400 C., thus reducing the additional heat requirement of the float chamber 4 and the energy consumption of heating elements 45.

[0114] Although it is preferred to incorporate the preheating of combustion oxidant 23 and fuel 24 in the process of the invention, the process can also be performed without such preheating, i.e. without heat exchanger 80 and 90 (in this case temperature at which the gas composition is injected into the float chamber 4 may be higher, for example about 650 C.).

[0115] In the embodiment illustrated in FIG. 2, the gas composition 100 circulates in a closed circuit. Such a closed circuit reduces the nitrogen and hydrogen consumption of the float chamber. In addition, recycling of the gas composition may be necessary for environmental or economic reasons, for example when the inert gas is or contains argon or helium or when the reducing gas is or contains carbon monoxide or ammonia.

[0116] Following the controlled evacuation of the gas composition from chamber 4, the evacuated gas composition 110. In such a closed circuit, the evacuated gas composition is typically cooled in a cooling unit 111.

[0117] Thereafter, humidity (H.sub.2O) 112 is removed from the gas composition in drying unit 113. In addition, other contaminants 114, such as H.sub.2S, are removed in one or more purification units 115.

[0118] The dried and purified gas composition 115 is then topped up with additional nitrogen 116 and hydrogen 117 (if necessary) and optionally also with other desired components of the gas composition.

[0119] In the embodiment illustrated in FIG. 2, the gas mixture 118 is then heated by indirect heat exchange with the hot fumes 25 from the melting furnace 2.

[0120] In heat exchanger 60, an intermediate fluid such as air, nitrogen, CO.sub.2, etc. is heated by direct heat exchange with the hot fumes. The thus heated intermediate fluid 201 is then introduced into heat exchanger 70 where the gas mixture 118 is heated by direct heat exchange with the heated intermediate fluid 201. The heated gas mixture is thereafter introduced into float chamber 4 as the gas composition 100.

[0121] The intermediate fluid may flow in an open circuit, in particular when the intermediate fluid is air. In the illustrated embodiment, however, the intermediate fluid flows back to heat exchanger 60 in a closed circuit. It is also possible to combine the heating of the gas composition with fuel and/or oxidant preheating. In the illustrated embodiment, the heated intermediate fluid leaving heat exchanger 70 is introduced into heat exchanger 80 in which the combustion oxidant 23 is preheated by direct heat exchange with the intermediate fluid 202 and thereafter into heat exchange 90 for preheating the fuel 24 by direct heat exchange with the heated intermediate fluid 203. Finally, the intermediate fluid is sent back to heat exchanger 60 to be heated by direct heat exchange with the hot fumes 25.

[0122] As mentioned before preheating of the oxidant 23 and the fuel 24 is not necessary, but preferred.

[0123] It will be appreciated that may variants may be envisaged.

[0124] For example, in the embodiment shown in FIG. 1, the order of heat exchangers 80 and 90 may be reversed or heat exchangers 80 and 90 may be in parallel with respect to the flow of heated gas component 102.

[0125] Likewise, in the embodiment of FIG. 2, a different order may be used for the succession of heat exchangers 70, 80 and 90. The topping up of dried purified gas composition 115 may also take place downstream of heat exchanger 70.

[0126] When the intermediate fluid 200 is nitrogen, i.e. the inert gas of the gas composition, heated nitrogen 201, 202 from the closed circuit may be used as top-up nitrogen 116 for the gas composition, after which additional (unheated) nitrogen 118 is added to the closed circuit (shown as an interrupted line and arrow in FIG. 2).

[0127] As further illustrated in FIG. 3, a control unit 300 may be used to regulate the operation of the heating elements 45 (and optionally also any cooling elements present) in the float chamber 4. This control unit regulates the operation of the heating (hand cooling) elements 45 so that the desired temperature profile of the float chamber 4 and the glass 3, 5.

[0128] In general, the control unit is programmed in a manner specifically adapted to the type of glass, ribbon thickness and any coating or other glass-treatment process taking place in the float chamber 2.

[0129] Control unit may also be connected to temperature detectors in the float chamber, so that the operation of the heating (and cooling) elements 45 may be adjusted as a function of the detected actual temperature (s) in the float chamber.

[0130] When, in accordance with the present invention, a gas component, corresponding to at least part of the gas composition, has been preheated by direct or indirect heat exchange with the fumes 25 evacuated from the melting furnace 2, so that the gas composition 100 is introduced into the float chamber 4 at a higher temperature, it is desirable to determine the temperature at which said gas composition 100 is fed to the float chamber 2, for example by means of temperature detector 301 which is connected to control unit 300. In this manner, the control unit can adjust the operation of the heating elements 45 in function of the temperature with which the gas composition 100 is introduced into the float chamber 4. This embodiment also permits to take into account any changes in the temperature to which the gas composition is heated, for example due to variations in the operation of the melting furnace 2 and the corresponding changes in the temperature and/or volume of the fumes evacuated from the furnace 2.

[0131] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0132] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0133] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of comprising. Comprising is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

[0134] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0135] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0136] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0137] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.