EP0140401A1

EP0140401A1 - Cooled panel for furnaces

Info

Publication number: EP0140401A1
Application number: EP84201172A
Authority: EP
Inventors: Andrea Pittini
Original assignee: Impianti Industriali SpA
Current assignee: Impianti Industriali SpA
Priority date: 1983-09-19
Filing date: 1984-08-14
Publication date: 1985-05-08
Also published as: IT8383463A0; IT1175125B

Abstract

This invention concerns a cooled panel (10) for furnaces, which comprises a plurality of tubes (11) arranged in a coil and connected at their ends with elbow unions (13), and in which the neighbouring tubes (11) have, at least along a tract lengthwise to the tubes themselves, a free gap (19) between them for the purpose of assisting thermal expansion in the panel (10).

Description

This invention concerns a cooled panel for furnaces which is of a type suitable to be positioned along the inner periphery of a furnace and above the bath of molten material, the furnace being advantageously an electric arc furnace.
To be more exact, the panel of the invention comprises a series of tubes arranged in a coil in a manner already known as a general principle, a cooling liquid being made to circulate within the tubes.
Panels of such a type can be formed in various ways so as to constitute parts of the side wall and/or crown of an electric arc furnace or other smelting furnace.
Such panels can be employed in particular to form the upper parts of the walls of electric furnaces, that is to say, the parts which normally lie above the highest level of the molten metal.
Panels of such a type can also be composed so as to form the crowns or a part of the crowns of such furnaces and also to form parts of the ducts which convey the fumes leaving smelting furnaces.
These panels can also be employed as heat exchangers for the recovery of energy in the form of hot water leaving the panels themselves.
Various solutions are known which are intended to provide A cooled panels to form the walls of smelting furnaces.
In one type of known solution a jacket consisting of a double wall has a flow of cooling liquid, usually water, running within it. The main shortcoming of this solution consists in the unsatisfactory behaviour of such panels with regard to thermal expansion.
In fact the wall of the furnace and therefore the panels forming that wall expand and contract in a peripheral direction as a result of the thermal cycles of the furnace, and this leads to breakage of panels thus formed owing to fatigue.
Moreover, owing to the continuous space between the two walls this solution causes unevenness in the speed of the cooling liquid within the panel and therefore uneven cooling, which provokes speedy deterioration of panels conformed in this way.
Furthermore, sediments may be created within these panels owing to the sluggish flow of the liquid.
Solutions are also known which are intended to provide panels consisting of a plurality of tubes arranged in a continuous coil.
For instance, DE 2.745.622 in the name of DEMAG is known which discloses a panel formed with a coil of tubes. This panel is specifically envisaged for being installed without refractory material in the inward side towards the furnace.
These tubes are joined together at their ends by means of specially shaped bends of a standardized type.
According to the patent cited above the arrangement of the tubes in the panel can be horizontal or vertical. If it is horizontal, the tubes have to be curved suitably beforehand so as to be adapted to the curvature of the furnace wall thus formed.
According to this DE patent the tubes of which the panel consists are arranged side by side and are joined together with a continuous weld along adjacent generating lines; this lay-out prevents good behaviour with regard to thermal expansion and also proper absorption of mechanical stresses.
Such shortcomings are a direct outcome of the resulting rigid structure, which has no space for elastic discharge of tensions and stresses and is accompanied with the occurrence of a build-up and then a sharp discharge of such tensions and stresses, which leads to sudden breakages.
Moreover, this DE patent visualises that the tubes are equipped with protrusions or projections which are welded in correspondence with the surface facing towards the inside of the furnace, so as to facilitate the attachment of slag which thus becomes a protective lining for the sole purpose of preventing thermal wear.
Patent LU 78.707 is known which discloses a type of panel like the preceding panel and comprising a coiled lay-out of tubes curved to suit the curvature of the side wall of the furnace.
In this patent the panels are not in direct contact with the inside of the furnace but are sunk within a refractory wall, the tubes of these panels being equipped with protrusions suitable for being anchored in a stable manner to the refractory structure. The tubes also have a continuous weld joining them together.
Construction of this type of panel is complex; moreover, the panel does not replace the refractory lining of the furnace but merely completes it by acting only as a means to cool the wall of the furnace.
GB 1,365,514 discloses a method to construct panels which comprise tubes. This method concerns the systems for the reciprocal positioning and anchorage of tubes located next to each other, with the possible interposing of rods or other metallic elements to join one tube to another.
The panels consisting of tubes and made in this way are employed, as in the DEMAG patent, without any lining, that is to say, they are arranged in direct cooperation with the inner walls of the furnace and face towards the inside of the furnace. These panels envisage a solution which anticipates the DEMAG invention.
Patent CA 653,798 (as US 2,179,638, EP 0025604 and SE 133.349) is known which discloses a lay-out of parallel tubes connected to the refractory wall of the furnace, with a cooling liquid running through the tubes. This system is envisaged as cooling only the crown of the furnace but can also be applied to the walls.
The tubes forming the panel have a complicated system of protrusions, which serve to anchor the panel itself to a wall of refractory material facing towards the inside of the furnace.
These panels, therefore, do not replace the traditional refractory lining but complete it by providing a supporting anchorage for it.
Patent FR 1.569.873 (as US 2,752,410, US 3,129,274, DE 3.147.337 and DE 2.943.244) discloses a cooling system with coils for the walls and crown of a furnace, the system having a very complicated structure and also being formed with one single arrangement of tubes rather than with a plurality of panels.
This entails drawbacks, especially as regards maintenance and the repair of any breakages, such maintenance and repair being operations which can be carried out more readily on a structure consisting of a plurality of panels on which corrective work can be undertaken individually.
Patent FR 2.455.719 discloses a cover cooled with a liquid for the crown of a furnace. This cover includes a plurality of panels conformed coil-wise, each panel consisting of a plurality of tubes joined to each other with bends.
The system thus disclosed has the tubes in close contact with each other and can therefore lead to problems resulting from thermal expansion.
Patent GB 958,348 discloses a system for the union of neighbouring tubes by means of a bar or other metallic element interposed between and welded to the tubes themselves. The panels which can be constructed in this way are intended for use without a refractory lining.
DE-OS-2.032.829 and DE-PS-1.013.680 disclose panels consisting of tubes arranged in a coil on at least two parallel planes, the continuity of the tube passing alternately from one plane to the other.
Such systems create strong tensions in the coils since the thermal loads are too highly differentiated within restricted spaces; moreover, the space employed is considerable as also is the complexity of the embodiment.
DE-PS-3.202.574 discloses a panel in which the tubes are kept spaced apart. This type of panel is expensive owing to the types of tubes and connecting bends employed; moreover, the connection system is such that it makes possible the cracking and/or breakage of at least the welds.
It is the purpose of our present invention to provide a type of panel consisting of tubes arranged in a coil and joined together at their ends by elbow unions, thus offering a considerably simplified structure together with excellent behaviour under even the severest thermal stresses.
According to one embodiment of the invention, lengths of tubes are arranged substantially parallel to the axis of the furnace so as to form together a curved wall.
This eliminates the need to have the tubes curved beforehand so as to follow the curvature of the furnace wall, as happens instead in panels having their tubes substantially horizontal.
According to the invention the tubes are arranged vertically with a gap between them, thus permitting immediate adaptation to the curvature of the wall which it is wished to form with the panels of this invention.
Reciprocal anchorage of the tubes is obtained with welds between one tube and another. These welds are not continuous but are made with tracts of a short extent. The welds between neighbouring tubes are made advantageously at staggered positions.
This permits excellent behaviour with regard to thermal expansion owing to the free gaps between the tubes and to the cooperation of these gaps with the connecting welds, which permit an accordion-wise compensation.
The gaps between the tubes may vary between 0.5 millimetres and 2 millimetres in width, depending on the power of the furnace and on the usage parameters of the same. Such a value of the gaps enables the panel to expand freely in a direction circumferential to the furnace (or radial to the furnace if the panels form its crown).
In this way the panel can easily withstand even the severest thermal cycles, which cause in the panel only very small mechanical stresses as compared to those in known solutions, where the tubes are closely adjacent to each other and/or are rigidly welded to each other.
Moreover, in a preferred embodiment the elbows which join the ends of the tubes are arranged at a suitable angle, so that an accordion-wise or bellows-wise disposition of the tubes is thus obtained. This disposition is much more elastic than that in which the tubes are merely positioned side by side.
In this way mechanical thermal expansions are absorbed also by elastic deformation of the bellows-wise structure thus formed, that is to say, by the variations in the angle at which the parts lie in relation to each other.
According to the invention excellent compensation for thermal and mechanical expansions is obtained in this way without any damage to the panels.
The discontinuous surface positioned towards the inside of the furnace in such an arrangement of the tubes provides excellent anchorage for the slag, which thus forms a protective lining having advantageously a thickness of a few centimetres.
This makes it possible to obviate the prior arrangement of specific anchorages, such as projections, protrusions or others, welded to the inner wall of the panel, for such anchorages create dangerous thermal points and also the risk of a concentration of mechanical stresses.
In this way the panel is solid and stable, can be constructed more simply and therefore can be made at a lower cost.
In the event that the tubes are arranged accordion-wise, the spaces between the tubes will be smaller since their function is performed by the special arrangement of the tubes themselves.
If the tubes are merely positioned side by side, it is envisaged in the invention, as we said earlier, that the tubes are not placed in close contact with each other but that a free gap is left between neighbouring tubes.This gap, which is closed at the tracts of the welds, allows thermal expansion of the panel in the peripheral direction with accordion-wise mechanical compensation.
The main advantages inherent in this invention are as follows.
The panel of the invention can work without refractory linings on its side facing the inside of the furnace, such refractory linings being subject to wear by abrasion caused by the charges of scrap introduced from time to time and also to wear caused by thermal stresses.
The panels of the invention permit excellent compensation for thermal expansion, this being a thing which is not possible in panels forming a continuous wall, in panels having their tubes welded continuously along their whole length and in panels having neighbouring tubes positioned side by side in contact with each other.
Furthermore, the geometric shapes which can be obtained with the panel of the invention can be readily adapted to any conformation of the furnace.
Next, the bellows-wise staggered lay-out of the tubes enables panels of any size to be embodied without being restricted by the diameter of the tubes employed.
Moreover, the panels of the invention can be readily repaired in the event of damage since they can be removed individually and since the individual tracts of tubes can be replaced with great ease.
This invention is therefore embodied with a cooled panel for furnaces which comprises a plurality of tubes arranged in a coil and connected at their ends with elbow unions, and in which the neighbouring tubes have, at least along a tract lengthwise to the tubes themselves, a free gap between them for the purpose of assisting thermal expansion in the panel.
We shall describe hereinafter, as a non-restrictive example, some preferred embodiments of the invention with the help of the attached figures, in which:-

Figs.1 give views of a panel according to the invention with tubes arranged accordion-wise;
Fig.2 gives a view from above of a panel with tubes positioned side by side;
Fig.3 shows a possible anchorage of a panel to act as a side wall;
Figs.4 show some forms of wall panels according to the invention;
Figs.5 show forms of panels to be used for the crown of the furnace.

In Figs.1 a wall panel 10 of an electrical furnace consists of a plurality of lengths of tube 11, which here are positioned vertically.
In the embodiment of Fig:1a these lengths of tube 11 are joined together by welds 12 so as to form the panel 10.
As can be seen in the figure, the whole panel 10 has a curvature corresponding to the curvature of the furnace wall in which the panel 10 is to be used.
The tubes 11 forming the panel 10 are joined together at their ends with elbow unions 13, which are suitably shaped so as to minimize losses of load and to obtain an assemblage as compact as possible.
The various tubes 11 forming the panel 10 are joined together with tracts of welds 12. These welds 12 can be all at the same height as those on neighbouring tubes 11, as shown on the lefthand side in Fig.1a, or can be staggered, as shown on the righthand side in Fig.1a; the latter arrangement provides a better behaviour during thermal expansion.
A free gap 19 is left between one weld 12 and the next one and can vary from 0.5 millimetres up to 2 millimetres in width, thus allowing the tubes 11 to be deformed freely in their tract along the free gap 19 during thermal cycles of the furnace.
The value of this free gap 19 depends on a plurality of factors, of which we may cite, as an example, the power of the furnace, the working cadence, the sizes of the panels and tubes, the thicknesses of the tubes, the type of cooling liquid, etc.
In the example of Fig.1a the elbows 13 are arranged at such an angle as to obtain an accordion-wise or bellows-wise arrangement of the various tubes 11 forming the panel 10.
This arrangement is shown particularly clearly in Fig.lb; the angled arrangement of the elbows 13 and therefore the staggered arrangement of the tubes 11 forming the panel 10 are particularly evident in this figure. An outer wall 14 of the furnace can also be seen here.
Fig.1a also shows upper coupling and support plates 15 and a protruding eyelet 16 for lower anchorage. An inlet 17 and outlet 18 for the cooling fluid can also be seen.
The inlet and outlet unions 17-18 respectively are positioned on the same side of the panel 10 and in its lower part in this instance. Noteworthy simplicity of hydraulic connection is obtained for the panel 10 in this way.
As can be noted and as has been mentioned already in another part of the description, the accordion-wise structure of the embodiments of Figs.1a and 1b together with the presence of the free gaps 19 between neighbouring tubes 11 leads to excellent behaviour of the panel 10 during thermal expansion.
The panel 10 thus formed is, in fact, even less rigid than a panel 10 with tubes 11 positioned side by side as in Fig.2.
In the embodiment of Fig.2 the tubes 11 are positioned side by side but a free gap 19 is left between them in correspondence with welded bridges 12 which can be seen in this figure. For this kind of panel 10 too a staggered distribution of the welded bridges 12 can be adopted whenever required. This kind of panel 10 also has an inlet 17 and outlet 18 for the cooling fluid.
Fig.3 shows a possible method of anchorage of panels 10 positioned next to the inside of the wall of the furnace, the wall being indicated with 14. In this case the panels 10 are shown diagrammatically and are of the type of Fig.2.
In the embodiment of Fig.3 the panels 10 are anchored to the wall 14 with upper coupling plates 15, which in our example are H-shaped and are two in number for each panel 10 but which could be in any required number.
These coupling plates 15 cooperate with an upper edge 114 of the wall 14 of the furnace. The wall 14 also comprises a lateral rib 20, which supports below itself a manifold 21 feeding cooling fluid.
The inlets 17 for cooling fluid in the individual panels 10 are connected to the manifold 21 with connecting tubes which are not shown here.
Anchorage of the panels 10 is carried out at their lower end with a fixture eyelet 16, which has already been shown in Figs.1 and which cooperates with a clamping wedge 22.
The eyelet 16 and wedge 22 can be replaced with equivalent means. For instance, anchorage can be performed with screws of any type. The type of anchorage chosen will be the one which permits the fastest installation and dismantling of the panel 10 and the employment of surfaces with a rough finish, thus enabling the costs of production and installation of the panel 10 to be reduced.
Plates 23 to protect the manifold 21 can also be seen in the figure.
Figs.4 show possible forms of embodiment of panels 10, according to the invention, which form the side wall of the furnace.
The example of Fig.4a shows a normal panel 10 to form the wall of the furnace. In this example the inlet 17 and outlet 18 of the cooling fluid are positioned next to each other in the middle portion of the panel 10, this lay-out being different from that shown in Figs.1 and 2 in which the inlets and outlets 17-18 lie at the respective ends of the panel 10 itself.
In the embodiment of Fig.4a the panel 10 has a substantially rectangular shape.
Fig.4b shows a panel 10 provided with an opening 24 suitable for the passage of a lance to blow in oxygen. This is obtained by envisaging the inclusion of some lengths of tube 111 shorter than the other normal lengths of tube 11.
The panel 10 in Fig.4c has an asymmetric shape forming a half of the door of the furnace.
Lastly, Figs.5 show various types of panels 110 intended to form the crown of the furnace. The panel 110 shown in Fig.5a has a shape substantially of a sector of a circular crown.
The inlet 17 and outlet 18 for the cooling liquid can be seen clearly.
In this embodiment the tubes 11 forming the panel 110 are curved according to the substantially circular-crown or truncated-cone shape of the crown of the furnace.
This embodiment has the purpose of permitting minimum rigidity of the panel 110 in a direction radial to the crown. Indeed, the crown, as we said before in another part of this description, expands "dome-wise" and the panel is deformed preferentially in a radial direction or along a generating line of the crown.
A supplementary lateral tube 211 can be seen which runs in a radial direction and serves to position the outlet 18 of the cooling fluid in correspondence with the outer periphery of the furnace.
Fig.5b shows a like panel 110 in which the tubes 11 are distributed substantially in a coil with an arrangement which becomes progressively smaller as it proceeds inwards.
In this case too the inlet 17 and outlet 18 of the cooling fluid are located near each other and the tubes 11 are so arranged as to leave within them a space 26 intended as an outlet for fumes.
The panel 110 of Fig.5c has a side portion missing, this portion corresponding to the space 26 for the outlet of fumes.
Alongside this panel 110 is placed a symmetrical counterpart panel, so that the union of the two panels leaves the whole space 26 open.
In these panels 110, as in the panels 10 shown in Figs.4, it is also possible to use either an accordion-wise arrangement of tubes 11 as in Figs.1 or a side-by-side arrangement of tubes 11 as in Fig.2.
As regards the distribution of welds in panels 110 intended to form the crown, the anchorage of one tube 11 to another is provided with welded tracts as shown in Figs.1 and 2 or with like methods, according to the invention.
We have described here some preferred embodiments of the invention, but variants are possible without departing thereby from the scope of the invention itself.
Thus, for instance, panels 10-110 can be embodied with shapes and sizes different from those shown and described, depending on the specific covering and/or dimensional requirements of the furnace to be built.
In the same way it is possible to envisage mechanical connections between one panel and another or between panels and the outer wall of the furnace, these connections being different from those shown.
Likewise the circuit to feed the cooling fluid can have any required development and arrangement, several panels being connected in series or in parallel, according to the specific requirements for flow and/or speed of the fluid.
Further variants are possible for a person skilled in this field without departing thereby from the scope of this invention.

INDEX

10 - panel for side wall of furnace
110 - panel for crown of furnace
11 - tube
111 - short length of tube
211 - lateral tube
12 - welded bridges
13 - elbow unions
14 - furnace wall
114 - upper edge
15 - coupling plates
16 - fixture eyelet
17 - inlet for fluid
18 - outlet for fluid
19 - free gap between tubes
20 - lateral rib
21 - manifold to feed fluid
22 - wedge
23 - protective plate
24 - opening for lance
25 - asymmetrical portion
₂6 - opening for outlet of fumes.

Claims

1 - Cooled panel (10) for furnaces, which comprises a plurality of tubes (11) arranged in a coil and connected at their ends with elbow unions (13), and in which the neighbouring tubes (11) have, at least along a tract lengthwise to the tubes themselves, a free gap (19) between them for the purpose of assisting thermal expansion in the panel (10).

2 - Cooled panel (10) for furnaces as claimed in Claim 1, in which the tubes (11) are arranged substantially on one plane but are offset in relation to that plane substantially in the manner of a flattened accordion (Fig.lb) to assist thermal expansion.

3 - Cooled panel (10) for furnaces as claimed in Claim 1, in which the tubes (11) are arranged substantially side by side (Fig.2).

4 - Cooled panel (10) for furnaces as claimed in any claim hereinbefore, in which welded tracts (12) are arranged substantially in corresponding positions on the various tubes (11).

5 - Cooled panel (10) for furnaces as claimed in any of Claims 1 to 3 inclusive, in which the welded tracts (12) are arranged in a staggered manner.

6 - Cooled panel (10) for furnaces as claimed in any claim hereinbefore, in which the width of the free gap (19) has a value that can vary from a half millimetre up to two millimetres.

7 - Cooled panel (10) for furnaces as claimed in any claim hereinbefore, which has at its upper end coupling means (15) cooperating with appropriate seatings in a wall (14) of the furnace.

8 - Cooled panel (10) for furnaces as claimed in any claim hereinbefore, which has fixture means (16-22) in a position offset in a lengthwise direction.

9 - Cooled panel (10) for furnaces as claimed in any claim hereinbefore, in which an inlet pipe (17) and outlet pipe (18) for fluid are positioned at its lower end and are pointing in a backwards direction.

10 - Cooled panel (10) for furnaces as claimed in any claim hereinbefore, which assumes any morphological conformation.