EP0773909A1

EP0773909A1 - Process and device for the parallel processing of molten and fritted glass in glass wool manufacture

Info

Publication number: EP0773909A1
Application number: EP96920760A
Authority: EP
Inventors: Fotis Christodoulopoulos
Original assignee: Afc Industrial & Business Consulting Ov Ltd
Current assignee: Afc Industrial & Business Consulting Ov Ltd
Priority date: 1995-06-02
Filing date: 1996-05-31
Publication date: 1997-05-21
Also published as: WO1996038390A1; PL318372A1; WO1996038392A1

Abstract

A glass manufacturing process has the following steps: molten glass is generated in the melting end of a glass melting furnace (10), the molten glass is drawn into fibres in a first fibre production device (12), batches of fritted glass are intermittently withdrawn through the outlet of the melting end and inductively molten in a melting device (16), and the molten glass produced in the melting device is drawn into fibres in a second (18) or in the first fibre production device (12). The fritted glass is introduced into a melting container that can be inductively heated and is made of a non-metallic, high temperature-resistant and good conductive material, is heated up to a temperature above its softening temperature and is transferred into a second melting container made of a non-conductive refractory material. The disclosed device has a melting container (18) made of graphite and partially surrounded by an induction coil (22).

Description

Device and method for parallel processing of molten glass and glass frits in glass wool production.

The invention relates to a device and a method for inductive melting of glass frits and a method for glass production.

In large-scale technical plants for the production of glass wool, the feedstocks are melted in a melting furnace of a glass melting furnace to a homogeneous amount of glass and then fiberized and processed in a fiberizing device. Glass wool production is a continuous process that begins with the addition of raw materials to the glass melting furnace and ends with an end product that can already be packaged and labeled. There is a mixing device upstream of the melting furnace, in which raw materials for the glass melt (sand, borax, soda, etc.) are either mixed with one another automatically using scales and metering valves or by hand in special containers in prescribed quantities. The premixed raw material is then automatically or manually fed into the glass melting furnace. At temperatures around 1300 ° to 1450 ° C, which are generated by burning heavy oil or gas or by an electric heating device, the various substances are transformed into a glass melt.

The glass melting furnaces are made of special high-temperature resistant materials that have to be heated up very slowly to the working temperature so that they do not get any cracks or other damage. The same precautions must be taken when the high temperature resistant materials are allowed to cool. For this reason, glass melting furnaces must be in a continuous

ERSÄΓZBLÄΓT (RULE 26) Operating mode, their total life is usually in the range of about three to four years and is limited by the life of the high temperature resistant material. The quality of the glass produced and the lifespan of the furnace also depend heavily on the continuous charging of the glass melting furnace.

The liquid glass leaving the glass melting furnace is passed through a duct made of refractory material, called feeder, so that it is cooled in a controlled manner to the temperature required for the defibration process. This temperature is around 1000 ° C. After the fiberglass is defibrated, which creates glass fleece or glass wool, the product obtained is processed in a dryer at temperatures around 200 to 300 ° C in order to gain sufficient mechanical stability, edge trimmed and possibly also divided into plates of a given length and packed.

In the event of a production failure, the glass that flows from a supply line in the direction of the fiberizing device is not fed into the fiberizing machine, but cooled and collected in order to be added to the raw materials in the glass melting furnace in a predetermined proportion. In the same way, recycled glass or defective glass for other applications can be added to the raw materials. The glass removed from the supply line to the defibration device in the event of a production failure breaks down into individual pieces of glass, which are usually referred to as glass frits, by cooling.

By returning the glass frits back to the glass melting furnace, the amount of usable glass delivered is reduced despite the continuous operation of the glass melting furnace, with typical values in industry for the so-called time efficiency of a glass wool plant being between 85 and 99%. The time efficiency indicates what proportion of the total time of the glass melting furnace operation the glass delivered by the glass melting furnace for the production of

SPARE BLADE (RULE 26) End product is used, and is not transformed into glass frits. The overall efficiency of a glass wool factory is defined as the product of the time efficiency (actual production time in relation to the theoretically possible production time) and the quantity efficiency (quantity actually produced in relation to the production quantity theoretically possible in the actual production time).

It is the problem (object) of the invention to provide a method and an apparatus which, with the same trough capacity and using an approximately equal or lower melting energy, allow a larger amount of mineral wool, such as glass fleece, glass wool or rock wool, to be produced.

This object is achieved by a method for glass production with the features of claim 1 and a method for inductive melting of glass frits with the features of claim 3. The device for inductive melting of glass frits is characterized by the features of claim 8.

The idea on which the invention is based is to provide a method for glass production and a method and a device for inductive melting of glass frits, which allow a discontinuous removal of glass frits from the outlet of the feeder, the melting trough and an inductive melting of these glass frits in a separate melting device .

The removal of glass frits from the outlet of the melting tank is a common measure in the art; however, since these glass frits in the prior art are returned to the melting tank after a possible intermediate storage, the above-defined time efficiency of the glass melting furnace and thereby also the overall efficiency of the production decrease, so that the glass melting furnace would have to be larger in order to obtain the same total production quantity. In addition is

ERSÄΓZBLÄTT (REGEL26) the repeated melting of the glass frits in the glass melting furnace is energetically unfavorable and should therefore be avoided. However, further processing of the glass frits by remelting and subsequent defibering cannot be carried out in a conventional glass melting furnace because, as described above, this has to be operated continuously.

For this reason, a device for inductive melting of glass frits has been developed, which allows direct processing of the resulting glass frits in an energetically very favorable manner, without the increased overall efficiency having to be bought through a disproportionately increased energy expenditure.

Preferred embodiments of the invention are characterized by the remaining claims.

According to a preferred embodiment, the glass frits are heated and / or dried before being introduced into the melting device for inductive melting of the glass frits. The glass frits are heated and / or dried before being introduced into the inductive melting tank by means of internal heat exchange within the device for inductive melting of glass frits according to the invention. The induction coil is preferably liquid-cooled, the heat removed being able to be used for preheating and / or drying the glass frits.

According to a preferred embodiment, an essentially oxygen-free atmosphere is generated and maintained in the inductively heatable graphite melting container. This has the advantage that the service life of the inductively heatable melting container made of high-temperature resistant, highly conductive, non-metallic material, such as e.g. Graphite is increased because the graphite cannot burn off.

According to an advantageous embodiment, the inductively heatable melting container, e.g. made of graphite, inside with

ERSAΓZBLÄΓT (RULE 26) Platinum coated. This will make the

Frictional resistance between the glass and the graphite is reduced and the graphite surface is additionally protected.

The molten glass preferably flows out of the second melting container in a targeted manner. This allows the second melting tank to be connected directly to a downstream fiberizing device.

The two-stage process for inductive melting of glass frits with an inductively heatable melting container made of high-temperature-resistant, highly conductive, non-metallic material, such as graphite, and a second melting container made of non-conductive, high-temperature-resistant material allows the melting of glass with a very low energy input. The main physical effect, which is specifically used here, is that the glass becomes electrically conductive at a certain temperature depending on the composition. As a result, the glass can be brought inductively to the desired melting temperature in a second melting container made of non-conductive material. The first inductively heatable melting tank is preferably made of graphite because this is a very cheap material compared to the noble metals or high-temperature-resistant metal alloys used in the prior art, which is easy to process and is also a very good electrical conductor . This is why high temperatures can be reached very quickly through inductive heating in graphite. In addition, graphite has a high heat capacity and high thermal conductivity, which enables the heat to be released quickly to the glass. Finally, a graphite container can be used to melt highly corrosive glass compositions because the graphite container can be replaced more often due to the low cost and increased wear.

The melting container is preferably designed to be rotationally symmetrical. This has the advantage that the melting tank

SPARE BLADE (RULE 26) on the one hand is inexpensive to manufacture and on the other hand the arrangement of an induction coil around the melting tank can be easily achieved, with the use of a ring-shaped induction coil the same distance between the induction coil and the melting tank can be achieved.

Since the energy transfer from the coil to the melting tank does not take place by convection or radiation, a suitable temperature-insulating layer can be applied between the coil and the melting tank, so that the smallest possible proportion of the energy of the melting tank can escape to the outside.

According to a preferred embodiment, the induction coil is liquid-cooled. The advantage of a liquid-cooled induction coil is that the heating of the melting container made of graphite is achieved only by the induction effect, but not by heat conduction or heat radiation between the heated, current-carrying induction coil and the jacket of the graphite container. Furthermore, as has already been explained above, the heat generated by the induction coil can be used sensibly for preheating and / or drying the glass frits before introduction into the inductively heatable melting container.

The invention is described below purely by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of the process flow for glass production.

2 shows the schematic structure of a preferred embodiment of the device according to the invention for inductive melting of glass frits; and

Fig. 3 illustrates the melting tank in more detail.

1 shows the sequence of the method for glass production according to the invention, as is particularly suitable for the production of glass wool. The entire device consists of a glass melting furnace 10, which is operated continuously. As already described above, the glass melting furnace is made of a refractory material such as firebrick. Compared to the production of glass fleece, the production of glass wool is only economical in much larger plants. Therefore, the production of glass wool is usually very large glass melting furnaces. However, the device according to the invention and the method can be used both for glass wool production, glass fleece production and also rock wool production.

As has already been described above, the heating and cooling of the glass melting furnace is a very lengthy process, so that in the event of a production failure of a downstream processing stage, the glass melting furnace must continue to be operated continuously. During the correct operation of the glass melting furnace, the amount of liquid glass produced is fed to a defibration device 12, which works according to one of the known methods and produces a nonwoven which can be further processed in a downstream finishing stage up to packaging and labeling.

If a production malfunction occurs in the defibering device or one of the subsequent systems, or if one of these systems has to be taken out of operation for a short time for maintenance purposes, liquid glass still emerges continuously from the glass melting furnace and is removed before entering the defibering device 12, the glass melt froze again. The resulting pieces of glass are referred to as frits and are stored in a suitable manner in a frit rack 14.

In the devices in the prior art, the frits from the frit tray 14 together with the minerals used are metered back into the glass melting furnace 10. As a result, the proportion of fries that

SPARE BLADE (RULE 26) Large systems in the prior art can amount to up to 15% of the glass outflow from the glass melting furnace, melted twice or, if the frits are returned several times, also melted several times in the glass melting furnace. This means that although the amount of liquid glass emerging from the glass melting furnace is kept constant, the amount of minerals processed does not correspond to the optimum throughput of the glass melting furnace.

For this reason, according to the present invention, the frits in the frit rack 14 are fed to a batch melting device 16, in which the frits are melted again to liquid glass. While a glass melting furnace must be of sufficient size to compensate for fluctuations in the amount of minerals used due to the large volume of the glass melting furnace, the frits are inherently homogeneous and the batch melting device 16 can therefore be made significantly smaller than the glass melting furnace. The molten glass that emerges from the batch melting device 16 arrives in a second fiberizing device 18, which produces the glass wool fleece parallel to the fiberizing device 12. Alternatively, it is also possible to supply the molten glass quantity from the batch melting device 16 to the defibration device 12 in addition to the molten glass quantity coming from the trough. This additional amount of glass wool fleece produced by the defibration device 18 or 12 is not critical for the overall process, because the amount of glass collected in the frit tray 14 can only be returned to the manufacturing process gradually and over a longer period of time.

Fig. 2 shows schematically the structure of the device according to the invention for inductive melting of glass frits. The melting device 16 can be divided into four different zones, which are designated in the schematic representation in FIG. 2 with the numbers I. to IV.

SPARE BLADE (RULE 26) Zone I denotes the area in which frits are fed to the melting tanks and essentially serves to meter the inflow of frits.

Zone II denotes inductive heat generation in the graphite melting tank. As shown schematically in FIG. 2, this second zone consists of a graphite ring 20 which is surrounded by an induction coil 22. The current-carrying induction coil 22 generates an induction current in the graphite jacket of the melting tank 20, which leads to a heating of the graphite jacket. Due to the high heat capacity of graphite, which is comparable to the heat capacity of glass and at the same time the high thermal conductivity of graphite, the heat in the graphite ring can be given off by heat conduction to the glass frits to be melted. In addition, heat is also transported through heat radiation. Due to the fact that glass, depending on its composition, has only a low electrical conductivity in the temperature range below approx. 900 ° C, the glass frits cannot be heated directly by induction, but only by using or interposing a suitable heatable container.

Materials used in the prior art for the production of inductive melting devices are, in addition to platinum, stainless steels, such as alloys of iron and carbon, nickel and / or chromium, molybdenum or palladium. While palladium-rhodium alloys have a higher electrical conductivity than graphite and most stainless steels suffer a significant deterioration in their mechanical properties at temperatures above 1200 ° C, graphite has the advantage that it is much cheaper than high-temperature resistant metal alloys, which means that the ratio between Contact area of the container to glass mass can be increased without high costs and on the other hand graphite is a very good electrical conductor. As a result, high temperatures can be reached very quickly by inductive heating in the graphite. Another major advantage of graphite is that this material is also more corrosive for melting

REPLACEMENT SHEET (RULE 26) Glass compositions are suitable and easy to work with. Another advantage of graphite is that because of its low cost, corrosive glass compositions can also be melted, with a correspondingly more frequent replacement of the graphite container

The disadvantage of the graphite material for use as a melting container is that it can be subject to wear by "burning off". For this reason, around the melt, i.e. around the melting tank 20, a nitrogen atmosphere or an atmosphere of another, oxygen-free gas is generated so that no oxidation processes can take place on the graphite surface. The interior of the melting tank 20 may have a thin platinum coating. This platinum layer minimizes the frictional resistance between the glass mass and the graphite surface

The melting container 20 has a relatively large contact area in relation to the glass mass to be heated therein and is preferably manufactured in a cylindrical shape with a ratio between the cylinder height and the cylinder diameter of approximately 8 to 10.

In the melting container 20, the glass frits are heated until they are above the softening temperature but still below the temperature of approximately 900 ° C. to 1200 ° C. in the area in which the glass becomes conductive.

The induction coil 22 is preferably cooled in a water bath or with the aid of suitable cooling elements, such as cooling hoses, and the heated water is used, by suitable heat exchange, to dry and / or preheat the glass frits before they are introduced into the melting device. After crossing Zone II i.e. of the melting vessel made of graphite, depending on the melting temperature of the glass composition, the glass, which is already liquid or is still solid, is conveyed into zone III, in which, on the one hand, glass calms down and, on the other hand, inductive heat generation takes place in the glass.

REPLACEMENT SHEET (RULE 26) As described above, depending on the chemical composition, the glass becomes electrically conductive in the range of approx. 900 ° C. This means that the glass can be heated inductively and / or dielectrically above this temperature. The advantage of direct inductive heating of the glass is that, on the one hand, there is no or only a very slight temperature gradient within the container and, on the other hand, the temperature control of the melting temperature of the glass can be carried out in a very direct and therefore simple manner, because the long period between a change in the induction current through the induction coil, a subsequent heating of the inductively and / or dielectrically heated container and the subsequent heat conduction in the glass can be significantly reduced by the direct induction heating of the glass.

Through the direct energy transfer into the glass, a much more uniform distribution of this energy in the glass can be achieved, whereby the glass can calm down in a relatively short time, so that it can then be directly defibrated.

The second melting tank 24 consists of a non-conductive, high temperature-resistant material and is also surrounded by an induction coil 26, which can be regulated separately from the induction coil 22. The second melting tank 24 is preferably made of a non-conductive ceramic material, so that the current induced by the induction coil 26 flows exclusively or almost exclusively in the glass melt.

Finally, the glass melt in zone IV is conducted out of the inductive melter 16 and from there to the fiberizing device 18, which is indicated schematically in FIG. 1. A nozzle 26 is preferably used here to regulate the outlet of the molten glass.

FIG. 3 shows a view of the melting container and the feed area of frits into the first melting container 20 made of graphite. The glass frits are conveyed in the direction of arrow A into a feed chute 30, at the exit of which a suitable one

ERSÄΓZBLÄ! T (RULE 26) Conveyor 32, in the present example, a screw conveyor is arranged. The shaft of the screw conveyor 34 is connected to the belt pulley of a suitable drive element 40, for example an electric motor, via a pulley 36 connected in a rotationally rigid manner thereto and a belt 38. By operating the electric motor 40, the glass frits added to the metering device in the direction of arrow A are transported by the screw conveyor device and reach the graphite melting tank 20.

In addition, the feed chute 30 can be preheated using the heat generated during the cooling of the induction coil 22. This is indicated schematically in FIG. 3 with the pipe coil 42 around the feed chute 30.

The melting tank 20 consists of graphite and is produced in one piece from this material. In this case, the graphite material also already forms a conically tapering region which tapers in the direction of the outlet 44 of the melting container 20. As described above, the melting container 20 is surrounded by an induction coil 22, which, not shown in FIG. 3, is preferably liquid-cooled. Likewise, the connected supply and control devices, which can also contain suitable temperature sensors inside the melting tank, are not shown in FIG. 3.

The melting container 20 has rings 46 and 48 made of a refractory material both at the glass inlet and at the glass outlet. The gas outlet 44 forms an outlet nozzle, the regulation of the flow rate regulating the residence time of the glass in the melting tank 22. The glass emerging from the outlet nozzle at outlet 44 is then introduced into the subsequent melting container made of high-temperature-resistant material, this subsequent melting container also being surrounded by an induction coil.

SPARE BLADE (RULE 26)

Claims

Expectations

1. Process for glass production, in particular for the production of mineral wool> comprising the following steps:

Generating a glass melt in the melting furnace

Glass melting furnace;

Defibrating the glass melt in a first

Defibration device; discontinuous removal of glass frits from the

Outlet of the melting tank; inductive melting of the glass frits in one

Melter; and

Shredding those produced in the melter

Glass melt in a second or in the first

Defibration device.

2. The method for manufacturing glass according to claim 1, further comprising:

Heating and / or drying the glass frits before introduction into the melting device for inductive melting of the glass frits.

3. A method for inductive melting of glass frits comprising the following steps:

Introducing glass frits into an inductively heatable

Melting tank made of a non-metallic, high temperature resistant, highly conductive material;

Heat the glass frit to above the

Softening temperature of the glass;

Convey the heated glass frits into a second

Melting container made of non-conductive, refractory

Material; and further heating and melting the heated

Glass frits using an induction coil around the second melting tank.

ERSÄΓZBLÄTT (REGEL26)

4. The method according to claim 3, characterized in that the inductively heatable melting container is made of graphite.

5. The method of claim 3 or 4, further comprising:

Preheat and / or dry the glass frit before inserting it into the inductively heatable melting container.

6. The method of claim 3, 4 or 5, further comprising:

Generation and maintenance of an essentially oxygen-free atmosphere in the inductively heatable melting tank.

7. The method according to any one of claims 3 to 6, characterized in that the inside of the inductively heatable melting container is coated with precious metal.

8. The method according to any one of the preceding claims, further comprising: targeted outflow of the molten glass from the second melting tank.

9. Use of a graphite container for inductive melting of lumpy glass.

10. Apparatus for inductive melting of glass frits, comprising: a melting container made of graphite, which is partially surrounded by an induction coil.

11. Device for inductive melting of glass frits according to claim 10, characterized in that the melting container is rotationally symmetrical and has a ratio between cylinder height and cylinder diameter of approximately 8 to 10.

ERSAΓZBLAΓT (RULE 26)

12. Device for inductive melting of glass frits according to claim 10 or 11, characterized in that the induction coil is liquid-cooled.

13. The device for inductive melting of glass frits according to one or more of the preceding claims 10 to 12, further comprising: a second melting container made of a non-conductive, heat-resistant material, which is surrounded by a second induction coil.

ERSÄΓZBLAΓT (RULE 26)