GB2048445A - A water cooled cover for an industrial furnace - Google Patents

Abstract

A water-cooled cover for an industrial furnace comprises a substantially rigid, wheel shaped structure defined by an outer supporting ring 10 and an inner supporting ring 12 which are interconnected by means of radial pipes 14. Cooling elements 18 are superimposed on the open sectors 16 of the structure, and are free to undergo thermal deformation relative to the structure. A central portion 24 of refractory material is positioned within the inner supporting ring 12 and is surrounded by a cooling rim 22. Cooling water is introduced into the outer supporting ring 10 and then passes through the radial pipes 14 into the inner supporting ring 12. From there the cooling water passes through the cooling elements 18 and the cooling rim 22 to an annular discharge ring 36. <IMAGE>

Description

SPECIFICATION A water cooled cover for an industrial furnace The invention relates to a water-cooled cover for industrial furnaces, particularly electric arc furnaces, in which the cooling is effected in separate zones in order to adapt it to thermal loadings which differ from one place to another.

Cooling systems are known to be used for the covers of industrial furnaces, particularly electric arc furnaces, in order to ensure that the said covers will last for a longer time. This cooling is usually carried out with water and not only increases the service life of the cover construction, as mentioned, but also enables the latter to recover energy from the heated waste water. This cooling of the cover is also known to be carried out in separate zones in order to adapt it to locally varying thermal loadings, i.e. the surface of the cover is subdivided into zones which can be cooled separately and individually according to the particular amount of heat to which they are subjected.

Zonal cooling of this kind has become known, for example, through German published patent application No 2546142. The system thereby proposed resides in the main in the subdivision of a double-floored cover by means of radial ribs into segments of a circle or of an annular ring, producing individual water chambers. These are supplied with water in approximately serpentine configuration by means of crosspieces. As is known, this method of guiding the cooling water is also applied to types of cooling boxes for cooling the walls of industrial furnaces, such as blast furnaces or electric furnaces, and also suffers from their drawbacks.These latter reside in the fact that breaks in the flow cross sections and hydraulically unsatisfactory systems of guiding the water not only cause the formation of eddies, with the resulting high resistance to flow, but also lead to the existence of clearance spaces, in which the speed of the water decreases considerably or even falls to zero, again detracting from the cooling effect and furthering the formation of deposits. If such deposits form in the course of time, practically no more cooling takes place at these points, the material of which the cover is made being thus subjected to excessive heat.

A further known drawback of this cooling box system resides in the fact that for reasons connected with the manufacturing technique, the crosspieces by which the cooling water is guided along a serpentine course are only welded to the upper or lower base of the cover at certain isolated points, leaving more or less sizeable gaps between the narrow sides of these guide bars and the bases of the cover, this providing a path for vagabond streams and consequently reducing the cooling efficiency. The cross section of these gaps is increased still further, with corresponding unfavourable consequences, if the bases, as is inclined to occur with covers of this design, develop a bulge as a result of the heat to which they are exposed. Needless to say, bulging of this kind mainly occurs on the lower base, facing towards the hot interior of the furnace.

Other deformations, caused by the hydrostatic pressure in the water chambers, may become superimposed on the aforementioned thermal deformations of the bases. The said water chambers, with their extensive flat boundary walls, are therefore unsuitable, for static reasons and on account of their insufficient strength, for a cooling system involving high water pressures, and as the flow conditions fall short of the optimum it is also only within limits that they are suitable for a cooling system involving high flow velocities.

Further disadvantages of this known construction for the cover result from the fact that the cooling chambers are an integral part of the cover. Where its strength is concerned, therefore, the cover has to be designed not only in the light of the weight which it is called upon to support, but also in the light of thermal stresses, which are difficult to estimate, owing to the fact that the cooling effect of this cooling system is only defined on approximate lines. Furthermore, since the cooling chambers are integrated into the cover structure, the entire cover has to be manipulated for repair purposes, if not actually removed and replaced, if a leak happens to occur.

In order to avoid these drawbacks of the prior art, the purpose of the invention is to propose a water-cooled furnace cover in which an optimum planned cooling effect can be ensured.

In accordance with the present invention, there is provided a water cooled cover for an industrial furnace, in which separate zones of the cover are cooled to relieve local thermal loadings, said cover comprising a central section of refractory material surrounded by a cooling rim which is adapted to allow cooling water to pass therethrough, a relatively rigid supporting structure of pipes adapted to allow cooling water to circulate through the structure, and a series of cooling elements adapted to allow cooling water to pass therethrough and which are free to undergo thermal deformation relative to the supporting structure.

Advantageously the cooling elements and the cooling rim each consist of a series of pipes arranged in side by side relationship, said pipes being welded together.

The supporting structure preferably consists of an outer supporting ring and an inner supporting ring, which rings are intercon nected by radial pipes, the inner ring being displaced out of the plane of the outer ring so as to define a supporting structure of substantially conical configuration. In such an arrangement, the cooling elements may be superimposed on the open sectors of the supporting structure defined by the inner and outer supporting rings and the radial pipes, and the cooling rim may be secured to the inner supporting ring by means of a clamping wedge system. In order to enhance the cooling effect of the cooling elements, at least one of the cooling elements may be subdivided into a number of portions.

Conveniently an annular cooling water discharge ring is provided adjacent the outer supporting ring. It order to prevent thermal stress arising between the discharge ring and the outer supporting ring the larger diameter of the annular cooling water discharge ring may be of approximately the same diameter as that of the outer supporting ring and the annular cooling ring may rest on the outer supporting ring.

In the just-described arrangement, there is preferably provided a number of flexible conduits communicating with the outer supporting ring through which cooling water is fed into the outer supporting ring from where the water flows through the radial pipes into the inner supporting ring, and there is provided a number of tubes connecting the cooling rim and each cooling element to the inner supporting ring, there being provided a number of discharge tubes connecting the outlets of the cooling elements and the cooling rim to the discharge ring, from where the cooling water is evacuated via likewise flexible conduits. In order to relieve any build-up of stresses in the structure, the connecting tubes may be flexible. Advantageously regulating valves may be provided in the pipes and tubes.In the case where it is desired to provide one or more openings in the cover, for example, to allow the discharge of waste gases, the openings in the furnace cover may be delimited by annular tubes which carry cooling water and which are provided on the radial pipes.

In a preferred embodiment, the cooling rim is of substantially frusto-conical shape and serves as a lining frame for the central portion. The cooling elements are secured in position by means of brackets attached to the supporting structure, the brackets being adapted to allow the cooling elements to undergo thermal deformation and the elements may be,sealed to the supporting structure by providing heat resisting material inside the securing brackets. The overall structure may then be provided with a sheet metal covering in order to prevent dustkdeposits forming on the cooling elements and thereby hampering the cooling efficiency of the elements.

According to this invention high velocities and pressures for the coolant, accompanied by maximum efficiency, are obtainable in finely subdivided cooling zones, while the supporting structure of the cover is not subjected to any thermal stresses emanating from the cooling system, and only certain separate parts of the cooling system have to be changed or replaced for maintenance and repair purposes.

The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying Figures wherein like reference numerals refer to like elements in the Figures in which: Figure 1 is a diametrical section through a first embodiment of a water-cooled furnace cover; Figure 2 is a plan view of the cover shown in Fig. 1; Figure 3 is a diametrical section through a second embodiment of a water-cooled furnace cover; Figure 4 is a plan view of the cover shown in Fig. 3; Figures 5a and 5b are examples of the system by which cooling systems are tightly affixed to the supporting structure of the furnace.

A first example of a water-cooled furnace cover of the type suggested will be described by direct reference to Figs. 1 and 2.

The supporting structure of the furnace cover 8 consists of an outer supporting tube 10, bent in the form of a circle, and of an inner supporting tube 12, likewise bent in the form of a circle, these tubes being interconnected by means of tubes 14 taking the radial direction. This supporting structure therefore presents the shape of a wheel, when viewed from above (Fig. 2), with an outer rim 10, a "hub" 1 2 and "spokes" 14. The open zones 1 6 between the outer rim 10, the hub 1 2 and the spokes 14 are provided with cooling elements 1 8 welded in "tube-to-tube" configuration, i.e. in side by side relationship, in which the cooling water is guided over a serpentine traject. The outer rim 10, when the cover is closed, simply rests on the side wall 20 of the furnace.

The cooling water is fed into the outer rim 10, e.g. at two diametrically opposite points (not shown). From the outer rim the water passes through the spokes 14 into the inner rim (hub) 12, which functions as a cooling water divider, inasmuch as it is from this point that the cooling elements 18 on the one hand and also advantageously conical cooling rim 22 on the other hand are supplied with cooling water. The cooling elements 1 8 are with advantage subdivided into a number of portions, in order to intensify the cooling effect, those of the example illustrated being subdivided into the two portions 1 8a and 1 8b, which are supplied separately with cooling water from the inner ring 1 2. This is done through a supply pipe 28 for the inner portion 1 8a and through a supply pipe 30 for the outer portion 18b.The outlet for the cooling water is provided by pipes 32 and 34, through which it enters a peripheral waste water discharge ring 36, which in the example shown takes its course outside the supporting tube 10 but which itself has no supporting function. The various supply and discharge pipes, such as the pipes 28, 30, 32 and 34, can with advantage be made of a flexible material.

The separation of the cooling water circuits into two portions 1 8a and 1 8b is effected by a partition wall 38 in one of the cooling tubes of a cooling element 1 8. On this partition wall the circulation terminates in the portion 18a, and the water emerges through the pipe 32, while the circulation of the portion 1 8b commences behind this partition wall, inasmuch as cooling water is fed in through the pipe 30.

From the waste water discharge ring 36 the cooling water is conveyed through one or more flexible tubes (not shown) of a cooling water processing installation (likewise not shown) in which, if necessary, part of the thermal energy of the heated waste water can be recovered.

If a certain space is to remain vacant in a zone 16, as is necessary, for example, for the discharge of the waste gases of the furnace into a waste gas pipe 40 (Fig. 1) or for other purposes, it is of advantage to provide further spokes 42 and 44, taking the form of a ring conduit 46 and 48 around the opening to be provided. In this case a separate cooling element 50, 52, 54 and 56 is provided on each side of the spokes 42 and 44, in place of a cooling element 1 8 radially subdivided into two portions 1 8a and 18b. The cooling water then passes through pipes 58, 60, 62 and 64 into the cooling elements 50, 52, 54 and 56, leaving them via pipes 66, 68, 70 and 72.

The central piece 24 of the furnace cover with the apertures 26 for the electrodes (not shown) consist of a refractory substance and undergoes particularly effective cooling, inasmuch as the conical rim 22, consisting of a tube-to-tube structure of tubes welded together, functions direct as a lining frame for the fire-proof substance of this central piece 24. This conical cooling rim 22 rests on the inner supporting ring 1 2 and can be affixed to the latter by causing straps 74 on the rim 22 to engage bolts 76 on the supporting ring 1 2.

Transverse clamping wedges 78 enable this connection to be secured and released without loss of time. The cooling water is likewise supplied to the cooling rim 22 from the inner supporting tube 12, the waste water being fed into the waste water discharge ring 36 (not shown).

Suspension points 80 on the outer supporting ring 10 enable the cover to be lifted when the furnace is to be charged.

Figs. 3 and 4 show a variant of a watercooled furnace cover. The waste water discharge ring 36' is in this case not situated radially outwards from the outer supporting ring 10', as in Figs. 1 and 2, but rests on the said ring. The advantage of this arrangement resides in the fact that if the two rings are of the same diameter, no stresses can arise between them. A further difference results in the method adopted for the cooling of the space in the zone of the two furnaces cover openings defined by the spoke rings 46', 48'. In this case the said space can be cooled by three cooling segments 82, 84, 86, while in the version shown in Figs. 1 and 2 this operation necessitates four elements 50, 52, 54 and 56.

As the arrangement of the waste water discharge tube 36' on the supporting ring 10' forms a peripheral edge which might make it easier for dust deposits to form behind the pipe 36' and render it more difficult to remove these deposits, a sheet covering 88 may be provided as an optional measure, from which covering any such deposits can be easily removed.

In the design of the new furnace cover particular care was taken to ensure that any thermal stresses between the individual components of the cover would be largely eliminated. As has just been described, such stresses between the tubes 10 and ring 36, for example, are avoided by positioning the ring 36' in such a way that it rests on the tube 10'. Similarly, the thermal deformations in the zone of the central piece of the furnace can be kept under control thanks to the possibility of providing intensive cooling by means of a cooling rim 22.

A further measure taken for this purpose is the arrangement of the cooling elements 18, 50, 52, 54, 56, 82, 84 and 86 in such a way that they rest loosely on the adjacent members of the supporting structure 10, 1 2 and 14, thus having the necessary clearance for a possibly different thermal expansion in relation to these members. To enable the cooling elements to be reliably held in position without impeding this freedom of movement and also in order to render the cover hermetic towards the outside a mounting system such as shown in Figs. 5a and 5b is suggested.This consists of brackets 90 and 92 which are screwed to the spokes 1 4 and the supporting tubes 1 2 (not shown) and 10 and which secure the cooling elements 1 8 in position but without impeding thermal deformations. The spaces inside the securing brackets are filled with asbestos 94 or a similar substance in order to prevent gases and dust from emerging from the interior of the furnace.

In order not to expose the cover to more than the unavoidable minimum of heat a fireproof layer is provided, by a spraying process, over the entire system of tubing on the lower side of the cover.

In order to optimize the entire cover cooling system the various cooling water supply and/ or discharge pipes can be provided with regulating valves by which the temperature of the cooling water derived from the separate cooling zones can be regulated individually.

Claims (18)

1. A water cooled cover for an industrial furnace, in which separate zones of the cover are cooled to relieve local thermal loading, said cover comprising a central section of refractory material surrounded by a cooling rim which is adapted to allow cooling water to pass therethrough, a relatively rigid supporting structure of pipes adapted to allow cooling water to circulate through the structure, and a series of cooling elements adapted to allow cooling water to pass therethrough and which are free to undergo thermal deformation relative to the supporting structure.

2. A cover according to claim 1, wherein the cooling elements and the cooling rim each consist of a series of pipes arranged in side by side relationship, said pipes being welded together.

3. A cover according to claim 1 or claim 2, wherein the supporting structure consists of an outer supporting ring and an inner supporting ring, which rings are interconnected by radial pipes, the inner ring being displaced out of the plane of the outer ring so as to define a supporting structure of substantially conical configuration.

4. A cover according to claim 3, wherein the cooling elements are superimposed on the open sectors of the supporting structure defined by the inner and outer supporting rings and the radial pipes.

5. A cover according to claim 4, wherein at least one of the cooling elements is subdivided into a number of portions.

6. A cover according to any of claims 3 to 5, wherein the cooling rim is secured to the inner supporting ring by means of a clamping wedge system.

7. A cover according to any of claims 3 to 6, further comprising an annular cooling water discharge ring adjacent the outer supporting ring.

8. A cover according to claim 7, wherein the larger diameter of the annular cooling water discharge ring is of approximately the same diameter as that of the outer supporting ring and the annular cooling ring rests on the outer supporting ring.

9. A cover according to claim 7 or claim 8, wherein there is provided a number of flexible conduits communicating with the outer supporting ring through which cooling water is fed into the outer supporting ring from where the water flows through the radial pipes into the inner supporting ring, and there is provided a number of tubes connecting the cooling rim and each cooling element to the inner supporting ring, there being provided a number of discharge tubes connecting the outlets of the cooling elements and the cooling rim to the discharge ring, from where the cooling water is evacuated via likewise flexible conduits

10. A cover according to claim 8, wherein all or some of the tubes are flexible.

11. A cover according to claim 9 or claim 10, further comprising regulating valves in the pipes and tubes.

1 2. A cover according to any of the preceding claims, wherein one or more openings in the furnace cover are delimited by annular tubes which carry cooling water and which are provided on the radial pipes.

1 3. A cover according to any of the preceding claims, wherein the cooling rim serves as a lining frame for the central portion.

1 4. A cover according to any of the preceding claims, wherein the cooling rim is of substantially frusto-conical shape.

1 5. A cover according to any of the preceding claims, wherein the cooling elements are secured in position by means of brackets attached to the supporting structure, the brackets being adapted to allow the cooling elements to undergo thermal deformation.

1 6. A cover according to claim 15, further comprising a sealing system of resiliently deformable, heat resisting material inside the securing brackets.

1 7. A cover according to any of the preceding claims, further comprising a sheet metal covering.

18. A cover substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.