WO2002008128A1

WO2002008128A1 - Furnace crown and method for its construction

Info

Publication number: WO2002008128A1
Application number: PCT/BG2000/000017
Authority: WO
Inventors: Stoyan Stefanov Lyutskanov
Original assignee: Stoyan Stefanov Lyutskanov
Priority date: 2000-07-21
Filing date: 2000-07-21
Publication date: 2002-01-31
Also published as: AU2000257989A1

Abstract

The invention relates to the crown of a glass melting furnace built of tapered silica bricks, having a hermetic sealing layer above the brickwork, preventing the leakage of hot gases, fumes and agressive vapours. This hermetic sealing layer, according to the invention, comprises one or several layers of flat or profiled silica bricks, bonded between themselves and with the crown with a refractory silicate glue, being compatible with the silica bricks. The refractory silicate glue is having a strong and durable adhesive bond with the silica bricks up to 1600 oC, and a coefficient of expansion equal or very close to the coefficient of the silica bricks. This invention will find application for reducing or eliminating the condensation corrosion in the silica crowns, by reducing the chances of 'rat hole' formation in the loose joints between the silica bricks of the crown. It will prolong the service life of furnaces melting soda-lime, borosilicate, lead and sodium-silicate glasses. It will be especially suitable for solving the 'rat-hole' corrosion problems in oxy-fuel fired glass furnace silica crowns. The invention will also find wide application for hot repair of 'rat-holes' of heavily corroded old glass furnaces, by elimination of the corrosion problems and prolonging of the service life.

Description

FURNACE CROWN AND METHOD FOR ITS CONSTRUCTION

REGION OF TECHNIQUE

The present invention relates to the crown of a furnace and more specifically to a silica crown of a furnace and can find application is processes where a good hermetic sealing of the crown is required. In particular the invention can find application in the glass industry for preventing the alkaline corrosion of the melting furnaces both with oxy-fuel and air-fuel fired furnaces, melting borosilicate, lead, opal, sodium-silicate and other type of glasses, where aggressive vapours are available.

PREVIOUS STATUS OF TECHNIQUE

It is specially important for the continuous exploitation of the crown of a melting furnace, more specifically for the silica crown of a melting furnace in the glass industry, the provision of good hermetically, to hinder the formation of corrosion holes, the so called "rat holes", to prevent the ingress of hot gases containing batch dust, which may corrode the crown brickwork. Furthermore, in order to increase the efficiency of the furnace it is very important the heat losses to be minimum and the outside temperature of the silica crown brickwork to be above the condensation point of the vapours inside the furnace. It is accepted in the practice and it is very often used that the silica crowns of the melting furnaces have an external insulating layer for reduction of the heat losses and/or a hermetic lining preventing the leakage of the hot gases and vapours outside the crown.

The quality of the hermetic sealing contributes for obtaining of a more efficient thermal insulation, leading to reduction of the fuel consumption.

. It is known from W.Brandt et all., "Glass Furnace Insulation Practices", Glass Industry, August 1981 (from now on called Brandt), that a crown built out of tapered silica bricks covered outside with an insulating layer of light porous silica bricks, which may be covered with a second insulating layer finds application in the practice. The thermal insulation of this crown is sufficient, but in spite of that the fumes saturated with aggressive substances are passing easily through the joints of the brickwork to the insulating layer, where they easily attack the porous insulating bricks, which is a set back. This leads to condensation corrosion taking place, "rat holes" are opened and as a result the life of the furnace between two repairs is reduced.

It is known for instance from Brantd, as well from T.Clayton, "Crown Design and Performance in Oxygen Fired Furnaces", Glass Industry, September 1998 (from now on called as Clayton), that as a additional measure for avoiding the condensation corrosion a hermetic lining preventing the passing of gases is applied between the bricks of the crown and the insulating layer. This hermetic sealing is a homogeneous one, and it is a patch based on zircon silicate or fused silica grains. These crowns, however, are also not reliable, because of the differences between the coefficient of expansion of the sealing patches and the silica crown bricks. For example, the zirconium silicate patch has a coefficient of expansion about 35.10-7 cm/cm.oC, the fused silica patch - under 10.10-7 cm/cm.oC, whereas the thermal expansion of the silica crown bricks is 128.10-7 cm/cm.oC. The big difference in the coefficients of expansion brings as a result the cracking of such hermetic sealing layers, and also to a breach of the adhesive bond between the silica bricks and the sealing patch and to the formation of a clearance between them, leading to deterioration of the hermetic sealing.

TECHNICAL GROUNDS OF THE INVENTION

The basic problem, being solved with the present invention is, that the furnace crown becomes reliable and has a prolonged service life, becoming safe against the leakage of hot gases and fumes saturated with batch dust and alkalis leading to corrosion.

Another problem, being solved with the present invention, is that the corrosion resistance of the crown is improved.

A third problem, being solved with the present invention is, that the use of a more efficient thermal insulation becomes possible, without any influence leading to shortening the service life of the crown. These and other problems are solved with a crown constructed with dense tapered silica bricks and a hermetic sealing over the brickwork , hindering the leakage of fumes and alkaline substances.

The hermetic sealing lining incorporates at least one layer of dense silica bricks adhesive bonded between themselves and towards the main brickwork of the crown with a refractory silicate glue, chemically compatible and having a coefficient of expansion equal or very close, with a difference of +/- 5% towards the material of the bricks of the main brickwork and the hermetic sealing lining. The refractory silicate glue is bonded with the main brickwork of the crown with a first sealing layer, and over the bricks of the hermetic sealing lining there is a second sealing layer of the same refractory silicate glue. The refractory adhesive silicate glue furthermore, must keep its adhesive properties up to temperatures of 1600 oC. The hermetic sealing lining constructed according to the invention allows a labyrinth type laying of the refractory silicate glue used for sealing, which creates a very serious barrier for the flue gases. In such a case, even if a small crack is formed in the first sealing layer, it could not be spread to the whole thickness of the hermetic sealing lining, because it will face as a barrier the dense silica bricks, laid very close to each other, impervious for the flue gases.

In one version of the invention the bricks of the hermetic sealing lining are rectangular and can have a standard size 64 x 115 x 223 mm.

In another version of the invention the hermetic lining is constructed with two layer of silica bricks with "IT'-shaped profile, laid down in a way that the edges of the two nearby sides of two bricks are entering in the middle side of a brick of the other row. In this case the hermetic sealing lining has a more clearly expressed labyrinth type applied sealing refractory silicate glue, contributing for the additional increase of the hermetic sealing.

In another version of the invention the refractory silicate glue keeps its adhesive bond with the silica up to 1600 oC and has a coefficient of expansion with a difference of not more than +/- 5% towards the expansion of the silica bricks of the main brickwork and the hermetic sealing lining.

The method of building of the crown incorporates the construction of the main brickwork with dense tapered silica bricks, covering it with the first sealing layer of refractory silicate glue on top, and placing over this layer at least one layer of dense silica bricks, with refractory silicate glue between them. The dense silica bricks are covered with a second sealing layer of refractory silicate glue. After drying and hardening of the refractory silicate glue, it is possible to apply a thermal insulation according to some of the known methods. According to one variant of application of the invention the thickness of the sealing layers of refractory silicate glue is about 20 mm, and that between the bricks of the hermetic sealing layer is about 1 mm.

DESCRIPTION OF THE ATTACHED FIGURES

The present invention is illustrated with the attached figures, as follows:

Figure 1 is showing a cross section of a crown with a hermetic sealing lining comprising one layer of dense silica bricks;

Figure 2 is showing a cross section of a crown with a hermetic sealing lining comprising two layers in chess-board order flat dense silica bricks;

Figure 3 is showing a cross section of a crown with a hermetic sealing lining comprising two layers entering in one another in chess-board order "II"- profile dense silica bricks.

EXAMPLES OF IMPLEMENTATION

Fig. 1 is showing an example of implementation of the present invention, representing a crown of a glass melting furnace, in this case built with brickwork 1 of dense tapered silica bricks. The crown is covered with an insulating layer 2 for thermal insulation, built according to the known methods. Over the main brickwork 1 under the insulating layer 2 there is an internal hermetic sealing lining 3 for preventing the leakage of flue gases and vapours containing alkalis and other corroding substances. The hermetic sealing lining 3 in this example is comprising of one layer dense silica bricks 4, for instance having sizes 64 x 115 x 223 mm, laid face to face, bonded together with the refractory adhesive composition (silicate glue) 5. The refractory adhesive composition is chosen in a way to be chemically compatible and to have an equal or very close coefficient of thermal expansion with the material of the bricks of the main brickwork 1 and of the hermetic sealing layer 3, for example about 128.10-7 cm/cm.oC. Furthermore, the refractory adhesive composition (silicate glue) is chosen in such a way to keep its adhesive properties at temperatures up to 1600 oC.

Fig. 2 is showing a crown where the hermetic sealing lining 3 is built out of two courses flat dense silica bricks 4 laid in chess-board order.

Fig 3 is showing another version of implementation. In this case the hermetic sealing layer 3 is built with two courses of dense silica bricks with a "II"- shaped profile 6 placed in such a way, that the edges of two neighbouring shoulders of bricks from one raw are entering the middle space of one brick from the other raw. The method of building the crown can be illustrated with the following examples.

EXAMPLE 1.

After building the main brickwork 1 according to the known methods, a layer of about 20 mm refractory silicate glue 5 is laid over it. At least one layer of dense silica bricks 4 or 6 are placed over it, close to each other. A layer of refractory silicate glue 5 is applied between the bricks with a thickness of about 1 mm, and then another layer of refractory silicate glue 5 is applied in thickness of 20 mm over it. The refractory silicate glue 5 is hardening at room temperature for about 24 hours. A thermal insulation layer 2 is applied over the hardened hermetic sealing lining 3 using any of the known methods.

EXAMPLE 2.

After the building of the main brickwork 1, a temporary thermal insulation with a known composition, for example ceramic fibres, is applied over it. After that the crown is heated up slowly following a smooth regime of increasing the temperature of the furnace, until the maximum temperature of about 1600 oC is reached. After that the temporary insulation is dismantled and a layer of about 20 mm refractory silicate glue 5 is applied over the main brickwork 1, and at least one layer of dense silica bricks 4 or 6 is applied on over it, connected with 1 mm silicate glue 5, and finally a layer of 20 mm refractory silicate glue 5 is applied on top. The thermal insulation 2 is built according to the known methods.

EXAMPLE 3

The same as example 2, but the temporary insulation is dismantled before reaching the maximum working temperature, for example, at 800 oC furnace temperature.

EXAMPLE 4

This example describes a working furnace having initial signs of corrosion.

The old thermal insulation of the crown is dismantled, and if some holes are available with flames coming out, the so called "rat holes", the same are filled up according to the known methods for hot repair. After that, a layer of at least 20 mm is applied, for example 20-30 mm refractory silicate glue 5 is applied, and over it more than one layer dense silica bricks are laid, for example two layers of "IP-profile dense silica bricks 6, and over then a second layer of 20-30 mm refractory silicate glue 5 is applied. In this way the corrosion process if the crown is delayed, and the life of the crown is prolonged to a great extent. EXAMPLE 5

A silica crown of a working furnace with no signs of corrosion is worked out and upgraded in the following way.

The old thermal insulation and all other linings are dismantled. The main brickwork 1 is cleaned from dust with a wet broom, in order to moisten lightly the surface. On top of this surface a layer of 20-30 mm refractory silicate glue 5 is applied by spreading with a trowel. Immediately after that one or several layer of flat or profiled dense silica bricks 4 or 6 are applied, before the glue is getting hard. On top of these bricks a new 20-30 mm layer of refractory silicate glue 5 is applied, and after that a thermal insulation 2 is built according to any of the known methods.

The above examples of implementation are serving only as an illustration and do not limit the invention idea, being limited only by the attached claims.

Claims

PATENT CLAIMS

1. A furnace crown comprising a main brickwork built out of dense tapered silica bricks and a hermetic sealing lining over the main brickwork for hampering the leakage of alkali fumes, characterised that the hermetic sealing lining (3) incorporates at least one layer dense silica bricks (4,6) adhesive bonded between themselves and with the main brickwork (1) by a refractory silicate glue (5) chemically compatible and having equal or very close coefficient of thermal expansion with the material of the bricks of the main brickwork (1) and the hermetic sealing lining (3), so that no cracking takes place.

2. A furnace crown according to claim 1, characterised that the refractory silicate glue (5) keeps its adhesive ability up to a temperature of 1600 oC.

3. A furnace crown according to claims 1 and 2, characterised that the bricks (4) of the hermetic sealing layer (3) are rectangular.

4. A furnace crown according to claim 3, characterised that the bricks (4) of the hermetic sealing layer (3) are arranged in two layers in chess-board order.

5. A furnace crown according to claims 1 or 2, characterised that the hermetic sealing layer (3) is built of two layers bricks with "LT'-shaped profile, laid in a way that the edges of two nearby shoulders of two bricks are entering the middle side of a brick from the other row.

6. A method for building of a silica crown according to any of the claims 1-5, comprising the building of the main brickwork with dense tapered bricks and laying of a hermetic sealing layer (3) over the main brickwork, characterised that the hermetic sealing layer (3) is built over the main brickwork (1) by the application of a first sealing layer of a refractory silicate glue (5), on top of which at least one layer of dense silica bricks (4,6) are laid down with the refractory silicate glue (5) between them, whereby the dense silica bricks are covered with a second layer of the refractory silicate glue (5).

7. A method for building the crown according to claim 6, characterised that the thickness of the sealing layers of refractory silicate glue (5) is between 10 and 30 mm, and between the bricks (4,6) of the hermetic sealing layer (3) is about 1 mm.