MXPA97003219A - Cooling device for ceiling in arc electric ovens - Google Patents

Abstract

The present invention relates to a device for cooling a roof (10) of an electric arc furnace, comprising a plurality of contiguous panels (27) positioned to cover at least a substantial part of the inner circumferential periphery of the roof (10). ), each of the panels (27) comprises at least one respective spiral-shaped cooling tube (11) to cause cooling fluid to flow therethrough, the roof (10) has at least one central opening ( 35) for inserting, positioning and moving the electrodes (28) and at least one peripheral outlet opening (16) for venting the fumes from the interior of the furnace, wherein each adjacent panel (27) covers its own defined arc of the inner circumferential periphery of the roof (10) and each spiral-shaped cooling tube (11) has windings (15) that form a spiral, the windings (15) are located in respective substantially vertical planes placed substantially Radial with respect to a vertical axis passing through the center of the roof (10), the windings (15) define a first outer layer (17) and a second inner layer (18) of tubes (11), the first layer external (17) and second inner layer (18) are separated by a hollow space (19) and function as an entrance ring to direct the emanations from inside the furnace to the outlet opening (1)

Description

COOLING DEVICE FOR CEILING IN ELECTRIC ARCH OVENS This invention relates to a device for cooling the roof of electric arc furnaces, as set out in the main claim. The cooling device according to the invention is applied in cooperation with the internal periphery of the roof in electric arc furnaces, whether they are fed with direct or alternating current, used in steel factories for melting metals. The roofs used to cover the 4 electric arc furnaces are known in the art to prevent the heat from dispersing from inside the furnace and, to avoid the spillage of harmful fumes and garbage. Typically, those ceilings have a substantially central opening for inserting, placing and moving the electrodes and a peripheral opening, called the fourth orifice, used in cooperation with the inlet and discharge ducts in order to contract the volatile emanations and debris from inside the oven and transport them to the processing and purification media and from there to the chimney. Given the working conditions within the furnace and, in particular, the extremely high temperature that develops within the furnace, there is a well-known need to provide systems for cooling the furnace, usually in cooperation with the inner surface of the roof. This cooling is usually carried out by means of pipes or conduits structured as panels where the cooling fluid circulates. An example of such cooling panels is described in EP-A-0 140 401. The function of these cooling panels is to prevent overheating of the roof and therefore protect it from wear and damage and thus extend its useful life. One problem that has had to be faced when installing those cooling devices known to the state of the art is the lack of homogeneity in the distribution of the temperatures on the internal surface of the roof. In fact, it is well known that, during the furnace operating cycle, the temperature is much more throttle in the central part of the roof, near the electrodes, than in the periphery. In addition, the temperature of the ceiling near the exit opening, or fourth orifice, is much higher than the temperature developed on the opposite side and increases progressively as it approaches the fourth orifice due to the considerable flow of incandescent emanations into this area. The input systems connected to this fourth orifice also determine a concentrated entry over a limited part of the complete furnace and, consequently, cause localized wear and damage. The systems for cooling the roof that are known in the state of the art are not always able to guarantee the optimal heat insulation and the protection that prevents the damage located in those parts of the furnace that are more exposed to overheating. In addition, these devices give a coefficient of heat exchange, or removal of heat flow, which is substantially uniform over the entire surface of the roof, with the result that above all the roof is necessary to guarantee a heat exchange coefficient at least equal to that required in the hottest part of the furnace, that is, near the fourth hole. Consequently, for a large part of the roof surface of the cooling system is out of proportion, thus causing a large energy consumption and that an excessive amount of cooling fluid is being used, considering that the hottest areas always work at a very high temperature, with the risk of breakdowns and breaks in the cooling ducts. The conduits of the state of the art may be circular, shaped as a ring or as a spiral, or may be radial from the center of the roof to the periphery or vire versa. However, these conduits, even when structured as panels, are in most cases placed substantially on an individual horizontal plane which cooperates with the internal part of the furnace. This solution does not allow, except to a very limited degree, the accumulation of insulating material such as garbage.; and an accumulation of garbage or other material could greatly assist the panels in their cooling action and heat insulation. Furthermore, all those described cooling systems exert a cooling action that is substantially uniform over the entire roof surface, given the constant flow of cooling water circulating in the ducts. The state of the art also covers the jet-type cooling devices, which uses jets of water which cooperate with the external surface of the roof, where the water is sprayed and displaced on the external surface and collected in the peripheral area. In this case it is possible to distribute the jets of water in such a way as to obtain a greater cooling in the hottest points, although then there is the problem that a greater water flow is obtained in the external peripheral area, where less removal of water is required. hot. An additional problem that affects the operational life of the cooled ceilings according to the systems known to the state of the art, is that there are welds between the individual elements of the cooling ducts.

These welds form critical points and create stresses along the conduit that can not be completely eliminated even by heat treatments such as tempering. These stresses, together with the particular conditions of high temperature to which the pipes are subjected, can cause the welds to break with the resulting spill of the cooling water inside the furnace. Given the high pressure of the water circulating in the cooling ducts, the amount of water that enters the furnace in this case is very high, and as soon as it comes into contact with the molten metal evaporates very quickly, with the consequent sudden rise in the pressure that can cause an explosion. Such a situation requires that the furnace be shut down immediately, with all the technical and economic problems that this entails, apart from the potential damage to the workers. The applicants hereof have designed, tested and modalized this invention to overcome the disadvantages of the state of the art and to achieve additional advantages. This invention is established and characterized in the main claim, while the dependent claims describe variants of the idea of the main mode. The purpose of this invention is to provide a ceiling cooling device in electric arc furnaces which makes it possible to obtain optimum furnace heating insulation and better performance, with a resulting reduction in production costs and a much lower risk of localized wear and damage. A further purpose of the invention is to provide a cooling device with a considerably lower risk of breakage than conventional devices, increasing the useful life of the device and reducing the interruptions required for maintenance between one cycle and the next to carry out repairs, whose arrests require the furnace to be closed. Still another purpose of the invention is to ensure a homogeneous and uniform entry of the fumes over the entire furnace, thus avoiding the problems derived from a concentrated entry over a limited area and, reducing to a minimum any loss in density of the fumes as move to the fourth hole. The cooling device according to the invention comprises a system of adjacent panels and in communication, each of which consists of at least one spiral pipe, with the windings placed on a substantially vertical plane, to define together a double layer of pipes, one external and one internal. These internal and external layers are placed on their respective planes and are separated by a hollow space inside which an annular circulation of the concentrated emanations is created, the hollow space being located on a plane that is suitable for the conformation of the roof. The windings of the spiral are positioned substantially in a radial direction in cooperation with the circumferential periphery of the roof. Each double-layer panel covers a defined arc of the circumferential periphery and all of the panels together form a structure that is suitable for shaping the upper section of the furnace. According to one embodiment of the invention, each panel, formed by a pipe of individual spiral shape, is joined at the ends to the adjacent panel to form a continuous cooling conduit. According to a variant, the joints between the ends of the pipes are welded at points outside the furnace and, therefore, are not subjected to stress by particular heat. In this way, a continuous tubular structure is obtained, without any welding at critical points and, therefore, not subject to the previously described problems, possibly with an individual entry and an individual exit of the cooling water. According to a variant, there are several inputs and outputs for the cooling water, so that if a panel breaks, it does not compromise the cooling action on the entire internal surface of the roof surface.

To make this freestanding structure, in accordance with a variant, the spiral-shaped pipe is reinforced with the appropriate supporting elements. With the double layer panels according to the invention, the waste suspended in the fumes sets itself in an extremely short time (approximately two casting cycles) to the pipes, thus creating a continuous insulator that covers at least the first outer layer. According to a variant, there are means of anchoring and securing on at least part of the tubes, which favors that the garbage fixes itself to the tubes and therefore forms the cover and protective layer. The second inner layer of the double layer panels is also partially covered by the garbage to form an insulating layer, although the continuous flow of the concentrated fumes through the hollow space between the two layers prevents the space between two adjacent contiguous windings to close completely, thus guaranteeing the free entry of the emanations. The density of the windings of the cooling pipe along the inner circumference of the roof can be varied at will, to obtain a higher or lower coefficient of heat exchange and, therefore, the greater or lesser cooling of a particular peripheral area. of the roof in accordance with the need and also according to the conformation of the roof and the furnace.

In accordance with one embodiment of the invention, this density of the windings varies uniformly from a point of maximum coefficient to a point of minimum coefficient of heat exchange. According to this embodiment, the maximum heat exchange coefficient point is placed in the area or in the vicinity of the opening, or fourth hole, of the emanation inlet conduit and, the point of minimum coefficient of heat exchange matches with the coldest point of the roof, located in a position diametrically opposite to that of the maximum point. This differential distribution of the winding density allows a differentiated cooling of the roof, which gives a considerable improvement in the efficiency of the furnace. In addition, this differentiated distribution of the density of the windings makes it possible to correlate the entity of the cooling action to the higher or lower temperatures that develop in the specific areas of the roof, which allows to make considerable energy and energy savings. More general, savings in operating costs of the cooling device. Furthermore, with this modality, it is not necessary to overdevelop the cooling action of the cooling device and, at the same time, maintain a high level of safety and efficiency. An additional advantage of the differential distribution of the density of the d evanados, due to the presence of the emanation inlet in the space between the two layers of the internal and external panels, is that the emanations are uniformly concentrated from all the surface of the roof. This is because the spaces between two contiguous windings in the second inner panel, which allows the emanations to be concentrated by the entrance ring between the two layers of panels, are smaller in the area where the depression is greater, in correspondence with or in proximity to the fourth hole, as they are larger in the area where the depression is smaller, thus achieving a substantial balance in the flow of emanations in each part of the roof. For this purpose, according to a variant, the distance between the two layers of panels, or the size of the section of the winding, can also vary from a maximum gas flow point, which coincides substantially with the inlet opening , up to a point of minimum gas flow, located in a diametrically opposite position. This variation in the distance between the two layers, external and internal, causes a different flow towards the emanation inlet ring, allowing a more even distribution of the emanation entry on the roof surface. An additional advantage obtained by the radial arrangement of the windings towards the center of the roof is that the density of the cooling pipes, in the central part of the roof, is greater than that in the periphery, thus obtaining a more efficient cooling in the roof. area adjacent to the electrodes, compared to the outer peripheral area. In addition, the presence of a double cooling panel makes it possible to have a heat insulation decidedly better than that which can be obtained with a traditional cooling system, with considerable improvement in the furnace field. Since there are no welds in the critical points of the furnace, it is possible to avoid the problems described above that derive from the presence of welds; This considerably extends the life of the furnace and also considerably reduces the costs and production times. In accordance with a further variant, there is a double-inlet spiral that causes the fumes to be directed along a symmetrical path over the two halves of the inner circumference of the roof. This solution gives an even more homogeneous entry and also reduces the loss of waste from the emanations. The attached figures are given as a non-restrictive example and show the most preferred embodiments of the invention as follows: Fig. 1 shows a plan view, in partial cross-section, of a roof associated with a cooling device in accordance with the invention; Fig. 2 shows a cross section from the side of the roof in Fig. 1 .

Fig. 3 shows a variant of Fig. 2; Fig. 4 shows a detail of the double layer of panels according to the invention; Figs. 5a and 5b show a perspective view from above and below of a roof associated with a double spiral cooling device according to the invention and suitable for an AC furnace including a single upper electrode; Fig. 6 shows the cooling device of Figures 5a and 5b. The reference numeral 10 in the accompanying figures generally denotes a chilled roof of electric arc furnaces in its entirety. The roof 10 in this case is associated with a cooling device 30 comprising a plurality of contiguous panels 27 that cover together the entire inner circumferential periphery of the roof 10. Each panel 27 consists in this case of a continuous pipe wound in a spiral whose individual windings 15, placed adjacent on a substantially vertical plane, define a first outer layer 17 and a second inner layer 18 separated by a hollow space 19 which is located on a substantially horizontal plane. In this case, the pipes 1 1 of each individual panel 27 are joined together by means of the ends 12, to form a substantially continuous conduit with an individual inlet 13 and an individual outlet 14 for the cooling water. According to a variant, each tube 1 1 constituting the individual panel 27 has input and output intercept means that intervene in the event of a break of the panel 27 and interrupts the flow of water. In the embodiment shown, the density of the windings 15 formed by the tube 1 1 varies progressively, along both circumferences of the roof 10, from an area 24 where the density is at its maximum, substantially coinciding with the opening 16 of the exit of discharge emanations, or fourth hole of the furnace and, an area 25 where the density is at its minimum, located in a diametrically opposite position. This differentiated distribution of the density of the windings 15 guarantees a greater and more intense cooling action where it is more necessary, that is, where the temperatures are higher due to the flow of emanations from the fourth orifice 16. In the intermediate areas 26 between the two areas 24 and 25, the density of the windings 15 is substantially at an intermediate value between the minimum and maximum values. The discharge emanations coming from the furnace enter the hollow space 19 or entry ring through the openings 20 in the adjacent windings of the second inner layer of the panels 18.

In a short time, these discharge emanations cause the formation of a waste coating layer 31 which attaches itself to the tubes 11 until it completely seals the first outer layer 17 of panels 27 as shown in Fig. . This waste liner 31 fixed to the tubes 11 considerably improves the insulation and the heat protection of the furnace, reducing the thermal stresses on the roof 10 of the furnace and therefore reduces the wear and damage. This waste also protects the tubes 11 from any overheating, which can lead to damage and breakage. The second inner layer 18 of the panels 27, on the other hand, is only partially covered by the waste, due to the continuous flow of emanations through the openings 20 which prevents the waste from forming a continuous, homogeneous layer. The different size of the apparatus 20, directly proportional to the distance between two adjacent windings 15 and therefore to the distribution density of the windings 15, allows the discharge emanations to be concentrated uniformly and homogeneously from inside the furnace. In the area 24 located near the entry opening 16 or fourth orifice, where the depression caused by the inlet of the emanations is at its maximum, the size of the opening 20 is minimal, as the density of the adjacent windings 15 is at its maximum.

In the area 25 located on the opposite side and therefore further away from the entry opening, where the depression is minimal, the size of the openings 20 is at its maximum, since the density of the windings 15 is at its minimum . This different arrangement of the windings 15 allows a substantially constant flow of emanations along each section of the hollow space or the inlet ring 19. Furthermore, this avoids problems arising due to the concentrated entry of the emanations into a part. limited of the whole furnace and to the different flow of the fumes, which may cause them to be supplied in a non-optimal way.

According to a variant of the invention shown in Fig. 3, the section of the windings 15 or, the distance between the first outer layer 17 and the second inner layer 18, varies from the maximum sectional area, located in correspondence with the opening 16 of the inlet duct, where the flow of emanations is at its maximum, towards the area 25 of the minimum section, where the flow of the emanations is at its minimum. The differential cooling of the roof 10 and the uniform entry of the discharge emanations give a considerable improvement in the performance of the furnace, with an obvious reduction in the operating costs of both the furnace and the cooling device.

The simple presence of the two layers of panels 27, external 17 and internal 18, gives an improvement in the insulation and heat protection of the roof 10. In the embodiments shown in the figures, the roof 10 comprises support elements 21 to do so. freestanding The support elements 21 cooperate in this case with two peripheral cooling rings 21 and with a cover skin 23. In the central part of the roof, in correspondence with the electrodes 28, there is a cover 29 of the type known for the state of the technique, peripherally cooled and having an opening for placing the electrodes 28. In the embodiment shown in Figs. 5a, 5b and 6, the cooling device has a double spiral shape with two outlets, respectively 32a and 32b, connected to the inlet opening. In accordance with the invention there can also be an individual output. This double spiral conformation causes the emanations to follow a symmetrical route in the two semi-circumferences of the inner periphery of the roof 10, which ensures an even more homogeneous entrance of the emanations along the entrance ring 19 between the first outer layer 17 and second inner layer 18. in the mode shown in Fig. 6 can be seen as the density of the windings 15 and the section of the windings 1 5 can have a lower value in the intermediate areas 26 between the area 24 of the fourth hole and the diametrically opposite area 25, in accordance with the particular technology and / or the construction requirements of the furnace or roof 10. In Figs. 5a and 5b the device 30 is placed in a support structure 33 to constitute a movable roof for an electric furnace, of the type that rotates laterally on its axis 34. Since the support structure 33 has an individual hole 35 in its center, It is obvious that it is for a CD oven; however, this support structure 33 may also have holes for the three electrodes necessary for CA ovens. Fig. 5b shows the additional cooling device 36 consisting of panels 37 where the cooling fluid circulates and placed substantially coaxial and concentric towards the opening 35 through which the electrodes are inserted. Fig. 5a shows how the support structure 33 cooperates with the cooling device 30.

Claims (10)

1 . Device for cooling the roof (10) in electric arc furnaces, of the type comprising a plurality of contiguous panels (27) positioned to cover at least a substantial part of the inner circumferential periphery of the roof (10), each of the panels (27) consisting of at least one tube (1 1) in which the cooling fluid flows, the roof (10) having at least one central opening (35) for inserting, placing and moving the electrodes (28) and at least one peripheral opening or fourth orifice (16) for venting the fumes from inside the furnace, the device being characterized in that each cooled panel (27) covers its own defined arc of the inner circumferential ring of the roof (10) and it is composed of a spiral-shaped cooling tube (11), the windings (15) of which spiral are located on respective vertical planes placed substantially radially with respect to the center of the roof (10), the windings (1) 5) defining a first outer layer (17) and a second internal layer (18) of tubes (11), the first outer layer (17) and the second inner layer (18) being separated by a hollow space (19) that it is located on a suitable plane for shaping the roof (10) of the furnace and functioning as an entrance ring to direct the emanations from the front of the furnace towards the exit opening (16).

2. The cooling device as in claim 1, wherein the spiral-shaped tube (11) of each panel (27) is composed of a single continuous tube without solder.

3. The cooling device as in any preceding claim, wherein the density of the windings (15) of the spiral is variable along the circumference of the roof (10).

4. The cooling device as in any previous claim, in which the density of the windings (15) reaches its maximum in correspondence with the opening (16, 32) to vent the emanations.

5. The cooling device as in any previous claim, in which the density of the windings (15) is at its minimum in correspondence with the furthest area from the area where the opening (16, 32) is to ventilate the emanations .

6. The cooling device as in any preceding claim, wherein the free section of the hollow space (19) defined by the windings (15) is variable along the circumference of the roof (10).

7. The cooling device as in any preceding claim, in which the free section of the windings (15) is at its maximum in correspondence with the opening (16) to vent the fumes.

8. The cooling device as in any preceding claim, wherein each individual spiral shaped tube (1 1) comprising the panel (27) comprises its own inlet (13) and its own outlet (14) for the cooling water. The cooling device as in any preceding claim, in which each individual panel (27) has its own means of interception at the inlet and / or outlet of the cooling liquid. 10. The cooling device as in any previous claim, wherein the spiral-shaped tubes (1 1) comprising the individual panels (27) are joined at their ends (12) along the outer periphery to form a substantially continuous tube (11). eleven . The cooling device as in any preceding claim, which includes peripheral cooling rings (22) positioned outward in cooperation with the panels (27). 12. The cooling device as in any preceding claim, which includes central cooling panels (37). 13. The cooling device as in any previous claim, which includes a circular circulation of the emanations. 14. The cooling device as in any preceding claim, wherein the opening for venting the emanations is defined by the exit hollow space (32) of the windings (15). 15. The cooling device as in any preceding claim, which includes two hollow exit spaces (32).