GB2092285A

GB2092285A - Refractory Fibre Lining for Elevated Temperatures

Info

Publication number: GB2092285A
Application number: GB8200414A
Authority: GB
Original assignee: Isomax Ingenior OG Handelsaktieselskab
Current assignee: Isomax Ingenior OG Handelsaktieselskab
Priority date: 1981-01-09
Filing date: 1982-01-07
Publication date: 1982-08-11
Also published as: DE3200423A1; DK7182A; FR2497792A1; GB2092285B; FR2497792B1

Abstract

A furnace lining consisting of strips (4) of refractory fibre piled with the flat sides to one another, the strips are compressed to such a degree that the fibres are in intimate contact with one another. The edge (8) of the strips facing the furnace interior is provided with slits (9) spaced at 5 cm to 15 cm intervals and with a depth of 1 cm to 8 cm. Oxides may be introduced between the fibres close to the furnace interior to increase resistance to chemical and thermal exposures. <IMAGE>

Description

SPECIFICATION Refractory Fibre Lining for Elevated Temperatures This invention relates to a refractory fibre furnace lining of the kind described in U.S. Patent No. 4.222.337.

The furnace lining described in U.S. Patent No.

4.222.337 comprises strips cut from fibre blankets such that the fibres are mainly oriented transversally of the length of the strips, and so that the fibres are mainly oriented perpendicular to the furnace wall. In this way the tendency of the lining to break up is reduced. Furthermore it is suggested that the rim of the strips facing the furnace interior, the hot face, be cut at certain invervals to avoid random shrinkage cracks. The fibre strips are kept elastic compressed into engagement with the anchor devices placed in the lining away from the hot face.

As stated in U.S. Patent No. 4.222.337 the compression may be increased for strips close to the furnace interior over that of those close to the cold face by using more layers of strips in the pile close to the furnace interior, the hot face pile. The use of high temperature fibres for the hot face pile, and less temperature resistant (and so cheaper) fibres for the layers close to the cold face is also suggested.

Furnace linings built in this way can without extensive risk be used for furnace temperatures very close to the rated temperature of the fibre installed, e.g. 1112000 C, at even higher temperatures the fibres are transformed from amorphous to crystalline structure, which transformation leads to a considerable reduction in volume and also destroys the fibre lining, leading significantly to excessive shrinkage cracks and peeling.

In order to compensate for the shrinkage of the insulation material, and as stated in the German Publication No. 2.838.588 it is possible to build the lining of sheets of which the flat sides have been cut with slits varying from 2 mm to 10 mm in width and spaced at 5 cm to 20 cm intervals.

The maximum depth of the slits is suggested to be 2/3 of the sheet thickness. These sheets are intended to be fixed to the furnace wall by a cement, and the slits are designed to prevent the sheets breaking into pieces.

According to the invention we provide a furnace lining consisting of refractory fibre blankets or strips which are piled with their flat sides to one another, wherein the blankets or strips are compressed to such a degree that intimate contact is achieved between the individual fibres, and that the edge of the blankets or strips facing the furnace interior is provided with a number of slits spaced at 5 cm to 15 cm intervals, and with a depth of 1 cm to 8 cm.

According to the invention the particular part of the lining which is exposed to the furnace interior, the hot face part is exposed to such a degree that intimate contact between the individual refractory fibres is created, and this hot face of the lining is provided with slits spaced at 5 cm to 15 cm intervals with a depth of 1 cm to 8 cm.

As mentioned above it is known to compress the fibre strips to obtain an elastic pre-strain so that the individual strips or blankets can keep one another in position without introducing strings, rods or needling. This compression is not sufficient to protect the lining from destruction if the temperature exceeds the nominal temperature, the temperature at which a specific refractory fibre will work according to the conventional "wall papering" or stack bonded lining systems.

According to the invention the compression must be considerably higher.

It is not necessary to apply this increased, high compression over the entire lining thickness. The compression may gradually decrease from the hot face to the cold face. This may be achieved through several methods. For the construction of the lining one may e.g. use specially manufactured blankets or strips with a considerable thickness variation across the width, or one may simply along the hot face place extra strips of a lesser width than the final lining thickness in between the other strips. At the compression of the strips to a regular lining block or module the intended variation across the lining thickness of the degree of compression is so achieved.

The intimate contact between the individual fibres achieved by the compression leads to a gradually increased vitrification at temperatures above the recrystallisation limit without damaging shrinkage, which prevents peeling-off, and at the same time increases the resistance of the lining to aggressive furnace atmospheres.

Furthermore the invention has the advantage to open up for a possible upgrading of the fibre in the hot face part of the lining by introducing oxides between the individual fibres either directly in the form of powder or by impregnation with a suspension of oxides or with a solvent of chemical compounds which at heating up undergo such transformations that one or more oxides are deposited.

When heating the fibres to recrystallisation temperature the oxides introduced will form mixed crystals together with the oxides of which the refractory fibres are composed.

By introduction of aluminium oxide before or after the installation of the fibre lining in such quantity that the combined fibre/oxide At203 content in this part of the lining will reach 73 per cent, ideal conditions are created for the formation of a large quantity of mullite crystals which are highly resistant to both temperature and aggressive furnace atmospheres. Introduction of chromiumoxide or zircon will likewise form highly resistant mixed crystals.

To mix various oxides into fibre blankets as a binder is not a new feature, but the upgrading described is achieved by heating to temperatures above the nominal rated temperatures or the recrystallisation limit for the specific fibre.

In this relation one observes that it is not possible to manufacture fibres by blowing or spinning with higher aluminium oxide content than approximately 62 per cent due to a considerable increase of the viscosity.

A furnace lining built according to the invention, and for which fibres consisting of approximately 50 per cent AL203 and 50 per cent SiO2 is used, and for which the highest dependable working temperature is approximately 11 000C, will be able to withstand continuous working temperatures up to approximately 1 4500C without destruction.

In the following a furnace lining built embodying the invention is described with reference to the accompanying drawings in which: Figure 1 shows a part of furnace wall with pertinent lining from which a part is cut out to show the anchor device, and Figure 2 shows a block or module of compressed layers of refractory fibres.

As can be seen from Figure 1 a lining 1 is built from strips 4 of refractory fibres with the flat sides into contact with one another. The strips 4 may be specially manufactured for the purpose, they may be cut from fibre blankets, or they may be individual layers of folded fibre blanket as shown at the Figure 2.

Behind the primary lining 1 a back-up installation layer 2 is piled along the furnace casing edge on edge. The primary lining 1 is as shown anchored to the furnace casing 5 by means of evenly distributed anchors 7 consisting of a plate with triangular teeth, and fastened to the furnace casing by means of steel rod. The back-up insulation 2 may consist of a cheap material e.g. mineral wool, and it is separated from the primary lining 1 by a blanket 3 of refractory fibre.

Before the anchors 7 are placed the fibre strips underneath are compressed in such a way that at least the part of them that faces the furnace interior obtains a density of 220 Kg to 280 Kg per cubic metre.

The hot face 8 of the primary lining 1 is provided with a number of slits 9. The spacing between the slits is 6 cm to 8 cm and their depth is 3 cm to 5 cm.

The hot face of the primary lining 1 may before or after the installation be impregnated with a suspension of aluminium oxide, or a solvent of chemical compounds which on heating deposits one or more oxides as indicated smith the dots 1 2. Upon heating of the furnace to 13-1 4000C recrystallisation of fibres and a vitrification of the fibres and the oxide takes place, and a iining is created of which the hot face part 8 is significantly more resistant to chemical and thermal exposure than is the case for linings installed according to conventional methods.

Figure 2 shows a precompressed lining module manufactured by folding of a fibre blanket. As shown the compression is maintained by needling 10 of the layers. To prevent the strings 10 cutting down into the fibre layers, strips 11 of carton are placed along the upper and lower faces of the module.

Claims

1. A furnace lining consisting of refractory fibre blankets or strips which are piled with their flat sides to one another, wherein the blankets or strips are compressed to such a degree that intimate contact is achieved between the individual fibres, and that the edge of the blankets or strips facing the furnace interior is provided with a number of slits spaced at 5 cm to 1 5 cm intervals, and with a depth of 1 cm to 8 cm.

2. A furnace lining according to Claim 1, wherein the blankets or strips are compressed to a density of 1 60 Kg to 500 Kg per cubic metre.

3. A furnace lining according to Claim 1 or 2, wherein the compression of the blankets or strips is the higher along the edge facing the furnace interior.

4. A furnace lining according to any one of Claims 1,2 and 3, wherein one or more oxides are introduced into at least the part of the fibres close to the furnace interior.

5. A furnace lining according to Claim 4, wherein at least one of said one or more oxides is aluminium oxide.

6. A furnace lining according to Claim 4, wherein at least one of said one or more oxides is chromiumoxide.

7. A furnace lining according to Claim 4, wherein at least one of said one or more oxides is zircon.

8. A furnace lining according to any one of Claims 4 to 7, wherein the lining density is of 1 60 Kg to 500 Kg per cubic metre.

9. A method of making a furnace lining in accordance with Claim 3, in which, between the blankets or strips, and along hot face a number of further strips of less width than the first mentioned strips are placed, where upon the pile of blankets or strips is compressed.

10. A method of making a furnace lining in accordance with Claim 4, in which the oxides are introduced between the fibres by impregnation before or after installation with a suspension of oxides or with a solvent of chemical compounds which upon heating undergo such transformation that one or more oxides are deposited.

11. A furnace lining substantially as herein described with reference to the accompanying drawings.

12. A method of making a furnace lining according to Clairn 9 and substantially as herein described.