MXPA97001174A - Cooling device for arc electr oven - Google Patents

Abstract

The present invention relates to cooling device with panels for electric arc furnaces, which is used in an electric melting furnace in cooperation with the vertical side wall placed above the lower shell of the furnace, the furnace comprising in its part lower a lower shell to contain the melting metal bath and an upper shell defined by a plurality of panels comprising a plurality of cooling tubes, the lower shell has on its outer part a metallic containment element, the inner refractory has a upper edge located substantially at the level of the upper edge of the excoria layer contained above the melting metal bath, the sipositive which is characterized in that at least part of the external panel consists of a horizontal row of cooling tubes disposed immediately above a part of the superior refractory rim of the inferior armor

Description

COOLING DEVICE FOR ELECTRIC ARC OVENS DESCRIPTION OF THE INVENTION This invention relates to a cooling device with panels for electric arc furnaces, as set forth in the main claim. The device according to the invention is applied to electric arc melting furnaces, in cooperation with the side walls and the upper walls of the furnace and, to be more exact, to the lateral zone immediately above the refractory lower shell, which holds the bath of molten metal. The structure of electric melting furnaces, and in particular, of electric arc furnaces is known. These furnaces include in their lower part a refractory lower shell, which incorporates the heart of the furnace, and above which is included an upper shell that acts as a side wall on which the cooling panels are placed. In the state of the art, the side wall of the furnace is defined by a row of those side panels substantially spaced at the upper edge of the lower shell; this situation makes possible the last partial formation of a slag layer, which fixes itself to those panels, but it is not enough to protect the refractory material from the very violent thermal and chemical stresses found in the arc furnaces of the present. This slag layer has an insulation task to reduce the heat flow, and therefore to keep the cooling panels at least partially from premature wear. However, this arrangement is not particularly effective, since the slag fixes itself with difficulty to the internal surface of the panels, and therefore can not form a compact and uniform layer to effectively perform the task of thermal insulation. In addition, it is known that one of the biggest disadvantages that occur in a melting furnace, with the progress of the melting cycles, has to do with the progressive erosion and erosion of the refractory material that constitutes the lower shell in the area at the level of the upper edge of the slag, that is, substantially in the upper circular strip of the lower shell. In this upper zone of the lower shell, the combination of temperature and the effects of the violent chemical reactions, which take place during the melting process, leads to accentuated occurrences of erosion, which structurally damages the refractory material, in the form progressive This forces the operatives to take action between one cycle and another, in order to restore the correct conditions of refractory material efficiency, to avoid the risk of very dangerous explosions, for the safety of the personnel.

In addition, with this type of panel, the heat flow directed towards the outside of the furnace is very large, and a large amount of energy is lost. This owes to the extreme degree of the surface on which the exchanger takes place whenever the tubes forming these panels are adjacent to each other, and cover the entire side surface of the furnace in the area where there is no refractory material. GB-A-2, 270, 146 shows an electric furnace with cooling side panels, located above the shell and with cooling tubes acting on the area of the lower refractory shell. DE-C-4223109 Shows panels with a plurality of horizontal monotubes, arranged in two parallel rows and separated at regular intervals. EP-A-0699885, published after this invention was presented, shows a cooling system for the upper edge of the refractory part of the furnace. This system includes a plurality of cooled tubes arranged in a "U" shaped arrangement, with the vertical tubes facing the liquid metal bath. This arrangement causes a plurality of problems, on the one hand, because the continuous tubes, in the case of a break, become unusable, and on the other hand, because, since they look at the liquid metal bath, they are easily subjected to perforations.

Otherwise, if these tubes were protected, they would never acquire the desired effect. Applicants hereby have designed, tested and modalized this invention to overcome these problems, which have been the subject of complaints by businessmen in this field for some time, and also to obtain additional advantages. This invention is set forth and characterized in the main claim, while the dependent claims describe variants of the idea of the main mode. The purpose of the invention is to provide a cooling device with panels in electric ovens, the device allowing the problem of progressive wear of the refractory material in the upper circular strip of the lower shell to be avoided or at least greatly reduced. A further purpose of the invention is to modalize a cooling device with panels, which allows the insulation properties of the slag layer, to be exploited in a very efficient manner, thus preserving the panels against progressive consumption and wear, and for therefore, increasing the working life of those panels, considerably. Still, another purpose of the invention is to obtain a cooling device with panels, in which the crucial points are reduced to a minimum along the hydraulic circuit defined by the cooling panels, and, therefore, the possibility of discharges. and cracking of the cooling device is reduced. According to the invention, the cooling device with panels comprises at least one row of cooling tubes, arranged substantially horizontally, or even partially inclined downwards and outwards, in cooperation with the upper edge of the refractory lower shell , which holds the fusion bath. This substantially horizontal row of tubes is easily covered by the slag, which protects it and has the purpose of cooling the upper zone made of refractory material of the lower shell substantially at the upper level of the slag present on the liquid metal bath, this area is thus subject to the wear and erosion caused by the slag during the progress of the melting cycle. The cooling action of this substantially horizontal row of tubes, drastically reduces the wear on the refractory material of the lower shell, made by the slag on the liquid metal bath. According to the invention, the row of tubes, which cooperates with the upper edge of the refractory material of the lower shell, consists of panels, that is, of autonomous elements, each of which covers a certain round angle of the circular crown defined by the edge.

According to a variant, the upper zone of the lower shell is shaped as a refractory ring having a larger diameter than the lower part of the furnace. The height of the ring can be substantially equal to the height of the slag layer on the liquid metal bath; according to another variant, the height of the ring is greater than the height of the slag layer. The inclusion of this ring allows the surface of the heat exchanger to be increased between the upper refractory zone of the lower shell and the panel cooling device, according to the invention. According to this embodiment, the refractory ring is cooled by at least one of the rows of tubes, substantially horizontal or even partially inclined downward and outward, which covers the entire upper surface of the ring and then extends outward from the upper side wall of the oven. According to a variant, the ring is also cooled along its vertical side, in order to increase the amount of heat flow removed by the cooling device. According to an additional variant, the ring is cooled, also, at least partially at its lower edge, and up to the outer edge of the lower shell. According to these two last modalities, a plurality of holes are provided in the element containing an external surface of metal sheet, for the discharge of water in case of the rupture of one or more of the cooling tubes. According to another variant, the external surface of sheet metal, which mechanically protects and contains the refractory ring, placed in cooperation with the slag layer above the liquid metal bath, is cooled by a plurality of jets of water. According to this variant, the water, which covers the external surface, evaporates in the environment and removes the heat from the refractory ring without causing problems. According to this variant, it is also possible to use a closed system, in which the water sprayed by these jets is collected and reused. The substantially horizontal row of cooling tubes, according to the invention, is situated, in relation to the melting bath, above the zone that is considered the safety zone, and is protected by its horizontal position, which allows to be covered quickly by the scum; this contributes to the increase of the reliability ratio of the panel, with respect to any breakage and loss of water in an area, which is especially close to the fusion bath. According to the invention, in cooperation with the horizontal row of tubes, which cools the upper edge of the lower shell and above the row, the cooling device comprises a double layer of cooling tubes organized as panels.

This double layer of cooling tubes, mainly an inner layer and an outer layer, respectively, in relation to the internal part of the furnace, develops substantially vertically in order to cover a substantial part of the internal wall of the furnace above the surface of the furnace. the lower shell. According to the invention, the outer layer of each individual panel, i.e. the layer that cooperates with the external part of the furnace, is composed of tubes arranged substantially in contact with each other, thus substantially forming a continuous wall. Also according to the invention, the inner layer of cooling tubes is rarified and is positioned at a distance from the outer layer, and may be parallel or inclined with respect to it. The rarification of the inner layer tubes, therefore, leaves wide open spaces between one tube and the other. The external cooling tubes are continuous for each panel or, according to a variant, subdivided into several autonomous circuits. The internal cooling tubes are continuous and usually constitute an individual circuit. The inclusion of this double layer of cooling panels allows the slag to enter and be retained; it also makes possible a better fixation of the slag to the panels, with the result of a thicker, more compact, and more uniform layer formation, in the interspace between the two layers of the panel, in order to function as protection and a heat accumulator. Actually, the slag in the space between the two layers of panels is maintained at a temperature lower than the melting temperature because of the heat exchanger with the tubes. Therefore, this slag is not easily removed, even during the loading steps of the furnace, when the mechanical stresses cause the release and fall of slag from the panels in the ovens present. In addition, this slag remains hot during the bleeding step, and the stored energy is then produced towards the new charge, thus making possible a great saving of energy. According to the invention, at least the inner layer of the tubes includes means for supporting and anchoring the slag. This slag, which anchors itself on the inner layer, has a temperature of about 1350 ° C, corresponding to the melting temperature; in addition, this molten slag, which has a higher thermal conductivity than that of the solid slag present between the inner and outer layer of the panel, prevents local overheating due to arc discharges. In addition, this molten slag distributes the thermal and mechanical stresses, due to those discharges over a large area, and transfers them downwards during its emptying on the panels. The too cold refractory edge of the lower shell is further protected by the slag, which continues to empty over that edge as long as the slag flow does not run out, but continues to be fed by the slag pool accumulated between the inner and outer layers of the slag. individual panel. This solution leads to considerable advantages with respect to the protection against wear and consumption of the same panels; It also has advantages in terms of duration and energy saving. In the embodiment according to the invention, the slag layer between the two layers of a panel can reach a thickness of up to 200 mm. In order to avoid the excessive emptying of the liquid slag from the tubes of the two caps of each individual panel, and to help anchoring the new slag, those tubes can be equipped with elements to anchor the slag, which are of a traditional type, such as, for example, metal hooks. However, the traditional hooks placed on the tubes of the internal panels, usually damage and melt and can not withstand a large flow of heat, which suffer because of the insufficient heat exchange coefficient of the metai of which they consist . To avoid this problem, a variant of the invention provides the use of anchoring elements consisting of a series of cold rings of a material having a high thermal conductivity, such as copper, for example, these rings not only allow the slag to be anchored, but also which make possible a large flow of heat towards the cold tube. The shape of the ring according to the invention can be toroidal or serrated, in order to improve the anchoring of the slag. The cold rings can be welded to the tube or can be fixed to the tube without welding, when the coefficients of thermal expansion of the tube and the ring are such that they allow their surfaces to be in contact with each other. According to another variant, the elements for anchoring the slag consist of hooks having any shape and comprising elements of a material having a high thermal conductivity. The internal layer of tubes of the individual panel is secured to the outer layer by means of hooks of fixation, to obtain a connection and a reciprocal placement. These hooks, even if they are protected by the slag that forms in the interspace between the two layers of panels, suffer from enormous mechanical and thermal stresses and have a certain limit of maximum length, which, therefore, also limits the maximum thickness of the slag insulation layer. According to a variant of the invention, these connection hooks are modalized with a bimetallic structure suitable for improving their resistance to heat, and mechanical strength. When the working conditions require a slag thickness, a greater distance between the inner and outer layers of the individual panel will be necessary, a variant of the invention provides for the insertion of a third intermediate layer, which likewise does not cover the entire surface of the panel, in order to reduce the length of the hooks and, at the same time, cool them in a correct way. According to a further variant, the connection hooks are internally cooled by the circulation of a cooling fluid. According to the invention, the tubes used are of a type without welding, thus considerably reducing the critical points more subject to thermal stresses and greatly increasing the working life of the panels. The tubes that form the panels, can have, according to another variant, sections with a non-circular shape, in order to optimize the heat exchange coefficient by adjusting the speed of the cooling water and reducing the total speed of the water flow , making the water only circulate in the part of the tube exposed to the flow of heat. According to this variant, the modalities can be used to provide for the insertion of a tube into another tube, or to include half-moon sections or other types of sections. The part of the tube in which the cooling water does not circulate, «It can be filled with a suitable material or fluid, or left empty. The appended figures are presented as a non-restrictive example and show some preferred embodiments of the invention, and are as follows: Figure 1 shows a portion of the lower portion of an electric furnace equipped with a cooling device with combs according to the invention; Figure 2 shows a first variant of Figure 1; Figure 3 shows a second variant of Figure 1; Figure 4 shows a third variant of Figure 1; Figure 5 shows a front view of an inner layer of cooling tubes, according to the invention; Figure 6 shows an example of a hook for connecting the inner and outer layers; Figure 7 shows a variant of Figure 6; Figures 8 and 9 show, respectively, a front view and a top view of the cooling tube with a double layer of cooling tubes according to the invention; Figure 10 shows a cross section of a cooling tube equipped inwards with a second tube to reduce the flow rate; Figure 11 shows a variant of Figure 10; Figure 12 is a side view of a cooling tube equipped with elements for anchoring the slag; and Figure 13 shows a variant of Figure 12. An electric furnace, of which the lower portion is partially shown in Figures 1 to 4, comprises a lower shell 1 1 consisting of a refractory material and acting as a container for a bath 12 of molten metal. This molten metal bath 12 has an upper level 13, above which a slag layer 14 is included. The lower shell 11 cooperates, on its outside, with a metallic support and containment element 15. The furnace comprises, above of the lower shell 1 1, a circular upper shell defined by a plurality of cooling panels 16, comprising a plurality of adjacent tubes, within which a cooling liquid circulates. This plurality of cooling panels 16, which are maintained substantially vertical above the lower shell 11, constitutes the cooling device 10. The cooling device 10, according to the invention, also includes a panel, or a portion of panel 16, composed of a plurality of adjacent cooling tubes cooperating directly with the upper refractory edge 19 of the lower shell 1 1. These cooling tubes, or horizontal row 18, have the task of intensively cooling the upper zone of the lower shell 1 1, said area being located substantially at the level of the slag layer 14, which is above the molten metal bath 12. This refractory zone of the lower shell 1 1, as is well known, is subjected to further progressive wear and erosion during the progress of the fusion cycle. In the embodiment of Figure 1, the panel consisting of the cooling tubes 18, cooperates with a plurality of tubes 1 7 placed substantially in contact therebetween; the plurality of tubes 1 7 constitutes the outer layer 1 16 of the panel 16, and extends vertically above the upper edge 19 of the lower shell 1 1, and towards the substantially external periphery of the lower shell 1 1. The panel 16, in this case, comprises, above the horizontal row 18, a double layer of cooling tubes, respectively, the outer layer 1 16 and the inner layer 22. The two layers of the cooling tubes, 16 and 22, which constitute the vertical walls of the panel 16, define between them an interspace 23, within which the slag accumulates to form an insulating layer that protects the layers 1 16, 22, and the horizontal row 1 8, of the consumption and wear. The structure with the two layers 1 16 and 22 of the panels 16, makes it possible for the slag to be retained and anchored within the interspace 23, and in this way form a slag layer of the desired thickness, which is compact, or niform and it constitutes a heat accumulator. The distance between the two layers 16, 22 is advantageously between about 50 mm and about 150 mm; With such a structure, the thickness of the slag layer can reach as much as 200 mm. Figure 1 shows an example of a liquid slag 31 running down from the panels 16.

In this case, the outer side of the lower shell 1 1 is cooled with jets of water by means of suitable nozzles 32.

According to the variant of Figures 2, 3 and 4, the upper refractory portion of the lower shell 1 1 is configured as a ring 20, which has an outer diameter greater than the outer diameter of the containment element 15. This portion upper portion configured as a ring 20, has a height at least equal to the height of the slag layer 14. The upper refractory portion configured as a ring 20, has its own containment, protection, and support element, 1 15, which is made of metal. This upper refractory portion configured as a ring 20 cooperates at least for the length of its upper horizontal degree (Figure 2) with the first horizontal row 18 of cooling tubes, thus increasing the heat exchange surface in the critical zone and a greater removal of heat flow. According to the variant of Figure 3, a vertical row 218 of cooling tubes is also included. According to the invention, there is a plurality of discharge holes 21 included in the external containment element 1 15, and which have the purpose of discharging the cooling liquid, in the case of ruptures or discharges in the cooling circuit. According to another variant shown in Figure 4, there is also a lower horizontal row 318 of cooling tubes.

According to the invention, the inner layer 22 of the panel 16 can have a development substantially parallel to the outer layer 16 (Figures 1 and 2), or it can have a parallel development in its first lower segment, that is, the closest one to the lower shell 1 1, where the insulation is more important, and then it tilts towards the outer layer 1 16 in its upper segment (Figure 3), or it can also have an inclined development along its entire length (Figure 4). In these cases, the inclination of the inner layer 22 towards the outer layer 1 16 of the cooling tubes 17, defines an angle "a" between 8o and 30 °, the angle "a" being able to vary from the panel 16 to the panel 16. The greater or lesser inclination of the inner layer 22 may also depend on the proximity, or otherwise, of the oven electrodes. The anchoring of the slag to form the insulating layer on the outer layer 1 16 and / or the inner layer 22, is assisted by the inclusion of anchoring elements 24 (Figure 5), distributed substantially along the entire surface, and also by the inclusion of connection hooks 25 between the inner layer 22 and the outer layer 1 16. Figure 12 shows a cooling tube 17 equipped with anchoring elements 24, consisting of cooling rings of a material possessing a high Thermal conductivity. Figure 13 shows a variant of Figure 13, the anchoring elements 24 consisting of hooks of a material having a high thermal conductivity, and possibly modalized with a bimetallic structure. The layers constituting the panel 16 are modalized using tubes 17 devoid of welding, thus eliminating the critical points due to the welding and especially subjected to thermal stresses during the work of the furnace. In this case, the tubes 17 are formed by bending in the hot state. The hooks 25, which connect the inner layer 22 to the outer layer 1 16 of the panel, have to be especially resistant to mechanical and thermal stresses. The greatest distance between the layers 1 16 and 22, and therefore, the thickness of the slag layer that is formed in the interspace 23, is linked to the resistance capacity of the hooks 25, which are especially subjected to efforts in its central zone, mainly the farthest zone of layers 1 16 and 22, and therefore less cold. In this example, the hooks 25 are modalized with a copper core 26, which has a high thermal conductivity and with an external steel lining 27, which has high mechanical strength properties and is capable of making the hooks 25 impact resistant and allows easier connection to the walls of the tubes 17 which constitute layers 1 16,22. Each hook 25 has a critical temperature, above which its central zone can not be carried without great risks of ruptures and discharges, and this fact dictates the maximum distance at which the layers 1, 16, 22 can be placed between them . Where the working conditions of the furnace require an increase in the distance between the layers 1 16, 22, it is possible to include a third intermediate layer 28 of cooling tubes and reduce the length of the hooks 25 and at the same time cool them (Figure 7). According to a variant, which is not shown, the connecting hooks 25 are internally cooled by the circulation of a cooling fluid. Figure 9 also shows a coupling hook 29, which allows the panels 16 to be easily handled. In accordance with the embodiment of the invention shown in Figures 10 and 11, the tubes 17 have different sections to a circular section and / or cooperate internally with dividing means. For example, the dividing means consist of a second tube 30 in order to restrict the flow rate of cooling water in the less hot spots, thus obtaining energy savings and improved oven efficiency.

Claims (9)

1. CLAIMS 1. - A cooling device with panels for electric arc furnaces, which is used in an electric melting furnace in cooperation with the vertical side wall placed above the lower shell (11) of the furnace, the furnace comprising in its lower part, a lower shell (11), to contain the bath (12) of fusion metal, and an upper shell defined by a plurality of panels (16) comprising a plurality of cooling tubes (17), the lower shell (1) 1) having on its external part a metallic containment element (15), the internal refractory material having an upper edge (19) located substantially at the level of the upper edge of the slag layer (14) contained above the bath (12) of fusion metal, the device being characterized in that each panel (16) consists of a horizontal row (18) of the cooling tubes (17), arranged immediately above a substantial part of the upper refractory rim r (19) of the lower shell (11).
2. 2. The cooling device of claim 1, wherein the upper portion of the lower shell (11) includes a refractory ring (20) extending outward, beyond the perimeter of the containment element (15) and having a upper edge (19) covered by an external panel (16) composed of a horizontal row (1 18) of cooling tubes (17).
3. 3. The cooling device of claim 2, wherein the refractory ring (20) has a height at least equal to the level height of the slag layer (14), located above the melting bath (12). ).
4. 4. The cooling device of claim 2 or 3, wherein the outer vertical wall of the refractory ring (20) cooperates with an external panel (16) that includes a vertical row (218) of cooling tubes (17).
5. 5. The cooling device of any of claims 2 to 4, inclusive, wherein the lower wall of the refractory ring (20) above the lower shell (11) cooperates with an outer panel (16), which includes a horizontal row (318) of cooling tubes (17).
6. 6. The cooling device of any of claims 2 to 5, inclusive, wherein the refractory ring (20) cooperates with an external metal containment element (1 15).
7. 7. The cooling device of claim 6, wherein the external containment element (115) contains at least one hole (21) in a lower position of the same element. (115).
8. 8. The cooling device of any of the preceding claims, wherein the outer panel (16) includes an outer layer (16) and at least one inner layer (22) of cooling tubes (17), the layers (1 16, 22) developing vertically and separated by an interspace (23).
9. 9. The cooling device of any of the preceding claims, wherein the outer layer (16) of the outer panel (16) includes the cooling tubes (17) adjacent to each other, and substantially covering the entire surface of the same panel. (16) 10. The cooling device of any of the preceding claims, wherein the inner layer (22) of the panel (16) includes the cooperation tubes (17) separated from each other by wide spaces. 1 .- The cooling device of any of claims 1 to 10, inclusive, wherein the inner layer (22) is at least partially parallel to the outer layer (116). 12. The cooling device of any of claims 1 to 10, inclusive, wherein the inner layer (22) is at least partially inclined by an angle "a" between 8o and 30 ° towards the outer layer (1). 16). 13. The cooling device of any of the preceding claims, wherein at least the inner layer (22) is modeled with a continuous tube. 14. The cooling device of any of the preceding claims, wherein the inner layer (22) and the outer layer (16) of the panels (16) are connected to each other by hooks (25). 15. The cooling device of claim 14, wherein the connecting hooks (25) have an internal copper core (26) and an outer steel jacket (27). 16. - The cooling device of claim 14 or 15, wherein the connecting hooks (25) include a conduit for the circulation of cooling fluid. 17. The cooling device of any of the preceding claims, wherein at least the inner layer (22) comprises on its surface means for anchoring and coupling (24) the slag. 18. The cooling device of claim 17, wherein the anchoring and coupling means (24) are made of a material having a high thermal conductivity. 19. The cooling device of any preceding claim wherein the cooling tubes (17) contain internal division means (30), which define a first zone for the passage of cooling water, this zone being exposed to the zone of removal of the thermal flow and at least a second zone not affected by the passage of the cooling water. 20. The cooling device of any of the preceding claims, wherein between the inner layer (22) and the outer layer (1 16), there is at least one intermediate layer (28) of cooling tubes (17).