WO2003054464A1

WO2003054464A1 - A method and an arrangement relating to furnace insulation.

Info

Publication number: WO2003054464A1
Application number: PCT/SE2002/002257
Authority: WO
Inventors: Lars Göran Johansson
Original assignee: Sandvik Ab
Priority date: 2001-12-12
Filing date: 2002-12-06
Publication date: 2003-07-03
Also published as: SE0104171L; SE520632C2; SE0104171D0; AU2002366937A1

Abstract

The invention relates to a method of insulating a furnace with the aid of free-standing elements of insulating material whose volume decreases at high temperatures. The invention is characterised in that the insulating elements are wedge-shaped and placed so that the wedges point inwards towards the heated volume of the furnace. The insulating elements are caused to move in the direction of the wedges as the volume of the insulating elements decreases, such as to cause said elements to approach each other in a direction at right angles to the direction of movement of said elements, therewith maintaining the imperviousness of the furnace insulation during the heating process. The invention also relates to an arrangement.

Description

A METHOD AND AN ARRANGEMENT RELATING TO FURNACE

INSULATION

In the case of furnaces that operate at very high temperatures, high demands are placed on the material used to insulate the volume heated in the furnace. Because the insulating material surrounds the whole of the volume heated in the furnace, the insulating material also becomes very hot.

One known problem in respect of such furnaces is that there is a scarcity of known materials that are able to manage the high thermal stresses to which the insulating material is subjected over a sufficiently long period of time so as to be useful. A common feature of known materials in this regard is that they shrink or contract at high temperatures, which causes sealing problems in furnaces using these materials, since permeabilities arise due to the fact that the volume of isolation material decreases so that gaps and cracks are formed.

Typical conditions for a given type of electric furnace involve operation at temperatures up to 1700°C over a period of several hours. High-grade aluminium oxide (Al₂O₃) brick is an example of the insulating material used. Although this material is highly tolerable to heat, it shrinks or contracts at high temperatures, thereby resulting in the above permeability problems.

Because the temperature gradient of such furnaces is highly significant at said temperatures, the heat losses will also be significant should the heated volume insulation become permeable. It is therefore desirable to provide a method that retains the impermeability of furnace insulation even when the temperature is increased.

The present invention provides a method to this end, and also an arrangement for carrying out the method.

Accordingly, the present invention relates to a method of insulating a furnace with the aid of free-standing insulating elements whose volume decreases at high temperatures, wherein the method is characterised in that the insulating elements are wedge-shaped and placed so that the wedges point inwardly towards the heated volume of the furnace; in that the insulating elements are caused to move in the direction of the wedges when the volume of the insulating elements decreases; in that the insulating elements are caused to approach each other in a direction at right angles to the direction of movement of said elements; and in that the impermeability of the furnace insulation is thereby retained in the heating process.

The invention also relates to an arrangement of the kind that comprises essentially the features set forth in Claim 6.

The invention will now be described in more detail partly with reference to an exemplifying embodiment thereof shown in the accompanying drawings.

Fig. 1 is a radial cross-sectional view of a preferred embodiment of the invention.

Fig. 2 is a side view of a preferred embodiment of the invention.

Figs. 1 and 2 are different perspective views of a furnace according to one and the same embodiment of the invention. The furnace is constructed so that the heated volume 1 has the form of an upstanding cylinder whose surfaces are covered with insulating material 2. The insulating material is disposed in free-standing insulating elements 3, which are placed side-by-side along the longitudinal axis of the cylinder.

The insulating material consists conveniently of aluminium oxide or some other corresponding appropriate material. One material is aluminium-oxide brick with a back- insulation of ceramic fibreboard.

The individual insulating elements are also divided longitudinally into several freestanding blocks 4, where each of the blocks is stacked vertically to form a complete insulating element.

When heating the insulating elements 3, permeability occurs in two ways as a result of material shrinkage. The insulation blocks 4 shrink, or contract, in an axial direction which causes cracks to appear between the individual blocks. The insulating elements 3 also shrink, or contract, radially and therewith give rise to cracks between the elements. The first type of permeability is rectified with the aid of the gravitational force 5 by means of which the insulating blocks are caused to move down and into mutual contact. Although the second type of permeability presents a greater problem, this problem is solved by means of the present invention.

When heating the heated volume 1, the insulating elements 3 will shrink and form cracks 6 between said elements. Because the insulating elements are disposed in a manner which enables them to move freely in a radial direction, the cracks 6 can be sealed by moving the insulating elements 3 radially in towards the heated volume. The furnace insulation is sealed entirely in this way, therewith minimising heat losses.

Each insulating element is in contact with an external pressure plate 7. The pressure plate 7 is adapted to apply an inwardly directed, radial pressure to the insulating element 3 with the aid of a series of bolts 8 which, when tightened, function to apply a pressure to the pressure plate 7 relative to a fixed longitudinally extending bar 9. A number of such bars 9 are disposed equidistantly around the furnace, wherewith each bar 9 is intended to displace an insulating element 6 in a radial direction. Each of the bars 9 is fixated in its position outside the pressure plate by an upper 10 and a lower 11 generally circular curb, when the furnace is generally circular. When the furnace has a shape other than circular, the curbs may have a shape corresponding to the shape of the furnace.

The bars 9 and the curbs 10, 11 are conveniently made of steel or aluminium.

Thus, the bolts 8 can be successively tightened by the furnace operator during the heating process, such as to move the insulating elements 3 radially inwards in relation to the furnace and thereby ensure that the impermeability of the insulation will be maintained throughout the entire heating procedure. This impermeability remains even when heating to the desired temperature, thereby guaranteeing that heat losses will be minimised.

Although the invention has been described with reference to an exemplifying embodiment thereof, the person skilled in this art will be aware that this embodiment can be varied while still achieving the advantages afforded by and the features characteristic of the present invention. The invention shall not therefore be considered to be limited to the aforedescribed exemplifying embodiment thereof, since variations can be made within the scope of the accompanying Claims.

Claims

1. A method of insulating a furnace with the aid of free-standing elements (3) of insulating material whose volume decreases at high temperatures, wherein the heated volume (1) of the furnace has the form of an upstanding cylinder, and wherein the insulating elements (3) are placed side-by-side around the barrel surface of the cylinder, and wherein each of said elements extends in the longitudinal direction of the cylinder, characterised in that the insulating elements (3) are wedge-shaped and disposed so that the wedge points inwards towards the heated volume (1) of the furnace; in that the insulating elements (3) are caused to move in the wedge direction as the volume of the insulating elements (3) decreases; in that the insulating elements (3) are caused to approach each other in a direction at right angles to the direction of movement of said elements, thereby retaining the imperviousness of the furnace insulation (2) during the heating process.

2. A method according to Claim 1, characterised in that each of the elements (3) of insulating mterial is comprised of at least two blocks (4) of insulating material; and in that the blocks (4) are stacked one upon the other, whereby the blocks are pressed together as a result of the gravitational force (5) acting thereon and thereby caused to seal the cracks that occur between the end surfaces of the blocks (4) as said blocks are heated and therewith shrink.

3. A method according to Claim 1 or 2, characterised by causing each element (3) to move successively in towards the heated volume (1) of the furnace, such as to seal the leaks that occur in the insulation (2) during the heating process.

4. A method according to Claim 1, 2 or 3, characterised by causing each element (3) of insulating material to be in contact with an external pressure plate (7), wherein said pressure plate is caused to exert pressure on said insulating element (3) in a direction towards the heated volume (1) of the furnace, by causing a bolt (8) to exert a similar inwardly directed pressure on the pressure plate (7) relative to a longitudinally extending beam (9) which is fixed by an upper (10) and a lower (11) curb, wherein the pressure on the insulating element (3) causes said element to move in a direction towards the heated volume (1) of the furnace until a desired seal is obtained.

5. An arrangement for insulating a furnace with the aid of free-standing elements (3) of insulating material whose volume decreases when heated, wherein the heated volume (1) of the furnace has the form of an upstanding cylinder, and wherein insulating elements (3) are disposed side-by-side around the perimeter of said cylinder, and wherein each of said elements extends in the longitudinal direction of the cylinder, characterised in that the insulating elements (3) are wedge-shaped and positioned so that the wedges point in towards the heated volume (1) of the furnace; in that the insulating elements (3) are able to move freely in a direction towards the heated volume (1) of the furnace; in that the distance between the individual elements (3) can be adjusted by moving said elements inwards or outwards relative to the heated volume (1) of the furnace; and in that the imperviousness of the furnace insulation (2) can thereby be retained during heating of the furnace.

6. An arrangement according to Claim 5, characterised in that each of the insulating elements (3) comprises at least two blocks (4) of insulating material; in that the blocks (4) are placed one on top of the other, wherein said blocks are pressed together as a result of the gravitational force (5) acting thereon, such as to seal the cracks that occur between the end surfaces of respective blocks (4) as they shrink or contract.

7. An arrangement according to Claim 5 or 6, characterised in that each element (3) can be moved successively in towards the heated volume (1) of the furnace during the furnace heating process, so as to seal the leaks occurring in the insulation (2) and thereby reduce heat losses in furnace operation.

8. An arrangement according to Claim 5, 6 or 7, characterised in that each element (3) of insulating material is in contact with an external pressure plate (7) which is adapted to exert pressure on said insulating element (3) in a direction towards the heated volume (1) of the furnace, by means of a bolt (8) which, in turn, functions to exert a similar inwardly acting pressure on the pressure plate (7) relative to a longitudinally extending bar (9) which is fixated by an upper (10) and a lower (11) curb, wherein the pressure on the insulating element (3) causes the element to move towards the heated volume (1) of the furnace until the desired imperviousness is achieved.