Shaft type electric furnace

Abstract

To provide a shaft type electric furnace equipped with a water-cooling mechanism in which water leakage hardly occurs and which can lengthen a service life of a preheating shaft.SOLUTION: A shaft type electric furnace in which a cold iron source is supplied to a furnace body through a preheating shaft includes a water-cooling box 10 disposed on an inner wall face 3Ab side of the preheating shaft. The water-cooling box 10 includes a wall plate part 11A that faces the inner wall face 3Ab of the preheating shaft and can come into contact with the cold iron source charged into the preheating shaft, a bottom plate part 11D being continuous to the lower end of the wall plate part 11A, and a water jetting section 12 that sprays water to the inner face of the wall plate part 11A, where at least the lower part of the wall plate part 11A and at least a part on the wall plate part side of the bottom plate part 11D are composed of one plate member 11F.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a shaft type electric furnace. [Background technology]

[0002] In a shaft-type electric furnace, scrap or other cold iron sources are supplied to the furnace body (electric furnace) through a preheating shaft, and the supplied cold iron sources are melted to produce molten steel. The cold iron sources supplied to the preheating shaft are preheated in the preheating shaft by utilizing the sensible heat of the exhaust gas. For this reason, shaft-type electric furnaces are highly energy-efficient electric furnaces.

[0003] For example, Patent Document 1 discloses an electric furnace (melting furnace) having a preheating shaft as a shaft-type electric furnace. In the shaft-type electric furnace described in Patent Document 1, high-temperature exhaust gas generated during melting treatment is discharged through the preheating shaft. At this time, a cold iron source such as scrap to be melted is supplied to the melting chamber through the preheating shaft, so that the cold iron source in the preheating shaft can be preheated by the exhaust gas.

[0004] Conventionally, in order to protect the frame of the preheating shaft through which the high-temperature exhaust gas passes, a tube cooler (water-cooling mechanism) may be provided at the bottom of the preheating shaft, which is heated most by the exhaust gas. Tube coolers generally perform cooling by supplying cooling water to the inside of tubes arranged along the inner surface surrounding the frame on all four sides. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-241889 Summary of the Invention [Problem to be solved by the invention]

[0006] Although tube coolers have excellent cooling efficiency, it is difficult to control the wall thickness because the cross-sectional shape of the tube is circular. Also, if the tube wall thickness becomes thin, it is prone to cracks due to collision with the cold iron source, which may cause water leakage.

[0007] In addition, in a tube cooler, the water pressure of the cooling water flowing inside the tube is increased to enhance the cooling capacity, and if a water leak occurs, the amount of water leaking will be large and will be sprayed onto the cold iron source that is being preheated.

[0008] Furthermore, since the tubes of the tube cooler have a circular cross-sectional shape, if the wall thickness becomes thin over time or if a crack occurs, it is difficult to repair by welding. Also, if the number of repairs to the tube cooler increases, the service life of the preheating shaft itself will be shortened, and there is a risk that the shaft-type electric furnace will have to stop production for a long time.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a shaft-type electric furnace equipped with a water-cooling mechanism that is less likely to cause water leakage and can extend the service life of the preheating shaft. [Means for solving the problem]

[0010] In order to solve the problem, according to one aspect of the present invention, there is provided a shaft-type electric furnace in which a cold iron source is supplied to a furnace body through a preheating shaft, the shaft-type electric furnace having a water-cooled box arranged on the inner wall surface side of the preheating shaft, the water-cooled box having a wall plate portion facing the inner wall surface of the preheating shaft and capable of contacting the cold iron source loaded into the preheating shaft, a bottom plate portion connected to a lower end of the wall plate portion, and a water spray portion for spraying water onto a surface of the wall plate portion facing the inner wall surface of the preheating shaft, the water-cooled box being constructed from a single plate material. Effect of the Invention

[0011] According to an aspect of the present invention, cooling water is sprayed onto the inner surface of the wall plate portion that can come into contact with the cold iron source, thereby cooling the wall plate portion that is heated by the exhaust gas passing through the preheat shaft. Therefore, unlike a tube cooler, the water-cooled box can prevent the internal pressure inside the water-cooled box from becoming high. Therefore, the water-cooled box is less likely to crack due to collision with the cold iron source than a tube cooler. Even if a crack occurs in the wall plate portion, the internal pressure inside the water-cooled box is not high, so even if water leaks, it is prevented from flowing into the preheat shaft as if water were to spurt out from the crack.

[0012] In addition, by constructing the joint between the wall plate portion and the bottom plate portion on the cold iron source side inside the preheating shaft from a single plate material, the stress on the joint is alleviated, making it less likely for water to leak from the joint.

[0013] Here, the joint between the wall panel and the bottom panel is a stress concentration area. If the plate material constituting the wall panel and the plate material constituting the bottom panel are joined by fillet welding at this joint, the welded joint is likely to crack due to the load of temperature history that occurs over time. In contrast, according to the embodiment of the present invention, there is no weld at the joint, which is the stress concentration area, and therefore the strength of the water-cooled box body over time is improved.

[0014] As a result, according to an aspect of the present invention, it is possible to provide a shaft-type electric furnace equipped with a water-cooling mechanism that is less susceptible to water leakage and can extend the service life of the preheating shaft. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 shows an example of a partially cut away shaft type electric furnace according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a cross-sectional view showing an example of the arrangement of a water-cooled box on a preheating shaft. [Diagram 3] FIG. 4 is a vertical cross-sectional view illustrating the water-cooled box. [Figure 4] FIG. 11 is a vertical cross-sectional view showing another example of the water-cooled box. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Next, an embodiment of the present invention will be described with reference to the drawings. (composition) 1, a shaft-type electric furnace 1 of this embodiment includes a furnace body 2 and a preheating shaft 3. The furnace body 2 is, for example, an electric furnace, and melts a supplied cold iron source 4, such as scrap, to produce molten steel 5. The preheating shaft 3 is a chimney-shaped shaft extending upward, and its lower part is connected to the furnace body 2 to form a guide path S for supplying the cold iron source 4 toward the furnace body 2.

[0017] In FIG. 1, the symbol R indicates an example of the flow of exhaust gas from the duct body. The exhaust gas R passes through the preheating shaft 3 and is further discharged to the outside via a dust collection duct provided at the top of the preheating shaft 3.

[0018] 2, in the shaft-type electric furnace 1 of this embodiment, a plurality of water-cooled boxes 10 are arranged on the inner wall surface 3Ab side (guide path S side) of the main frame 3A of the preheating shaft 3. Reference symbol 3Ab denotes the outer wall surface of the main frame 3A.

[0019] The multiple water-cooled boxes 10 are arranged in the circumferential direction along the inner wall surface 3Ab of the preheating shaft 3. The multiple water-cooled boxes 10 are also arranged in a stacked state in the vertical direction along the inner wall surface 3Ab of the preheating shaft 3 (see FIG. 3). Note that there may be a gap between the water-cooled boxes 10 and the inner wall surface 3Ab of the main frame 3A.

[0020] As shown in FIG. 3, the water-cooled box 10 includes a box-shaped body 11 and a water ejection unit 12 disposed within the body 11.

[0021] The main body 11 has a wall panel portion 11A facing the guide path S, a wall panel portion 11B located on the inner wall surface 3Ab side of the main body frame 3A of the preheating shaft 3, a pair of side wall portions facing each other in the width direction (the direction perpendicular to the paper surface in Figure 3), a top panel portion 11C and a bottom panel portion 11D, forming a box-shaped closed space inside.

[0022] In this specification, the wall plate portion 11A facing the guide path S side is also referred to as the cooling side wall plate portion 11A. The cooling side wall plate portion 11A is made of, for example, a flat panel material. The outer surface of the cooling side wall plate portion 11A does not have to be flat. Beads extending in the vertical direction may be provided to increase the surface area (cooling capacity). The wall plate portion 11B and the top plate portion 11C located on the inner wall surface 3Ab side of the main frame 3A of the preheating shaft 3 are not particularly limited in shape.

[0023] The outer surface of the cooling side wall plate portion 11A constitutes a surface that can come into contact with the exhaust gas R discharged from the furnace body 2 and the cold iron source 4 passing through the guide path S.

[0024] The water injection unit 12 is a device that sprays water onto the inner surface of the cooling side wall plate 11A to cool the cooling side wall plate 11A. In this embodiment, the water injection unit 12 includes a header 12A that extends vertically and a plurality of injection nozzles 12B. The injection nozzles 12B are provided in the header 12A and inject cooling water toward the inner surface of the cooling side wall plate 11A. The cooling water can be pressure-fed to each nozzle 12B through the header 12A. The water ejection unit 12 has a plurality of sets of headers 12A with nozzles 12B arranged across a pair of opposing side walls in the width direction of the body 11 (the direction perpendicular to the paper surface in FIG. 3).

[0025] In the water-cooled box 10 of this embodiment, at least the lower part of the cooling side wall plate portion 11A and at least the part of the bottom plate portion 11D of the cooling side wall plate portion 11A are configured from a single plate material 11F. The plate material 11F is also referred to as a connecting plate 11F.

[0026] The connecting plate 11F is L-shaped (angle-shaped) and includes a rising portion 11Fa extending vertically, a horizontal portion 11Fc extending laterally, and an arc-shaped curved portion 11Fb connecting the rising portion 11Fa and the horizontal portion 11Fc. The angle formed by the rising portion 11Fa and the horizontal portion 11Fc does not have to be 90 degrees. The connecting plate 11F may be formed by bending a plate material to form the curved portion 11Fb.

[0027] From the viewpoint of stress relaxation, the radius of curvature of the arc shape of the bent portion 11Fb is preferably, for example, 20 mm or more.

[0028] In the example of Fig. 3, the cooling side wall plate portion 11A is composed of a vertical plate 11E made of a plate material extending vertically, and a rising portion 11Fa of a connecting plate 11F. In this example, the lower end of the vertical plate 11E and the upper end of the rising portion 11Fa are joined by butt welding. Reference symbol D2 indicates the position of the butt welding. The lower end of the vertical plate 11E and the upper end of the rising portion 11Fa may be joined by a method other than welding, such as bolt joining.

[0029] Here, the vertical plate 11E and the connecting plate 11F may be formed from a single plate material. In this case, the lower part of the plate material may be bent to form the bent portion 11Fb. When the cooling side wall plate portion 11A is formed from the vertical plate 11E and the rising portion 11Fa of the connecting plate 11F as shown in FIG. 3, the dimensions of the plate material (connecting plate 11F) to be bent become smaller and easier to process. However, welding at the point D2 is required.

[0030] 3, the bottom plate portion 11D is composed of a horizontal plate 11G extending laterally and a horizontal portion 11Fc of a connecting plate 11F. The horizontal plate 11G and the horizontal portion 11Fc of the connecting plate 11F are butt-welded to each other at the position indicated by reference symbol D1. The horizontal plate 11G and the connecting plate 11F may be formed from a single plate material.

[0031] Here, the bent portion 11Fb constitutes a joint between the cooling side wall plate portion 11A and the bottom plate portion 11D, and therefore the bent portion 11Fb is also referred to as a joint.

[0032] Moreover, the water-cooled box 10 of this embodiment has a baffle plate 13 that prevents the cooling water sprayed from the water spraying portion 12 from directly hitting the bent portion 11Fb. 3, the baffle plate 13 is provided below the lowest nozzle 12B and above the bent portion 11Fb, protruding obliquely downward from the inner surface of the cooling side wall plate portion 11A. The shape of the baffle plate 13 does not need to be a flat plate, and the tip of the baffle plate 13 may be close to or in contact with the bottom plate portion 11D.

[0033] Incidentally, a rubber material or other cushioning material may be disposed on the inner surface side of the bent portion 11Fb to further prevent the cooling water from directly contacting the bent portion 11Fb. In FIG. 3, reference numeral 14 denotes a drain pipe, which is a pipe for discharging water that has fallen onto the bottom plate portion 11D to the outside.

[0034] (Operation etc.) The cold iron source 4 supplied to the furnace body 2 through a guide passage S in the preheating shaft 3 is preheated by exhaust gas R flowing from the bottom to the top through the preheating shaft 3.

[0035] At this time, by arranging a water-cooled box 10 on the inner surface side of the preheating shaft 3 through which the exhaust gas R passes, the main frame 3A of the preheating shaft 3 is prevented from being heated by the exhaust gas R, thereby improving the life of the preheating shaft 3.

[0036] In the water-cooled box 10 of this embodiment, the cooling side wall plate 11A is cooled by spraying cooling water onto the inner surface of the cooling side wall plate 11A that comes into contact with the cold iron source 4 and the exhaust gas R. As a result, unlike a tube cooler, the water-cooled box 10 of this embodiment can prevent the internal pressure in the water-cooled box 10 from becoming high, so that cracks are less likely to occur in the cooling side wall plate 11A due to collision with the cold iron source 4 compared to a tube cooler.

[0037] In addition, even if a crack occurs in the cooling side wall plate portion 11A, the internal pressure in the water-cooled box 10 is not high, so that it is possible to prevent water from gushing out from the crack into the guide path S side, and the influence on the preheated cold iron source 4 passing through the preheating shaft 3 can be made smaller than that of a tube cooler.

[0038] In this embodiment, the curved portion 11Fb, which is the joint between the cooling side wall plate portion 11A and the bottom plate portion 11D on the side of the cold iron source 4 in the preheating shaft 3, is made of a single plate material. This reduces the stress applied to the curved portion 11Fb and makes it difficult for water to leak from the curved portion 11Fb.

[0039] Here, the joint (bent portion 11Fb) between the cooling side wall plate portion 11A and the bottom plate portion 11D becomes a stress concentration portion. If the plate material constituting the cooling side wall plate portion 11A and the plate material constituting the bottom plate portion 11D were joined at this joint position by fillet welding, cracks would easily occur at the welded joint due to the load of temperature history that occurs over time.

[0040] In contrast, in the present embodiment, there is no welded portion at the joint position where stress is concentrated, and therefore the strength of the joint against temperature history over time is improved accordingly. Moreover, by forming the joint portion to have an arc-shaped cross section, the stress concentration at the joint portion can be further alleviated.

[0041] As a result, in this embodiment, water leakage is less likely to occur in the body 11 of the water-cooled box 10, so a shaft-type electric furnace 1 equipped with a water-cooling mechanism can be provided that can extend the service life of the preheating shaft 3.

[0042] Furthermore, in this embodiment, the baffle plate 13 prevents the cooling water from directly contacting the bent portion 11Fb, thereby reducing the stress applied to the bent portion 11Fb, which is the joint, and further extending the life of the water-cooled box 10. When the bent portion 11Fb is spray-cooled, high stress is generated at the bent portion 11Fb. This is prevented by the baffle plate 13.

[0043] (Modification) FIG. 4 shows a modified example of the water-cooled box 10 of this embodiment.

[0044] 4, the bottom plate portion 11D is inclined so that the side of the main frame 3A of the preheating shaft 3 is lower than the side of the joint portion 11Fb. That is, the bottom plate portion 11D is inclined downward as it moves away from the cooling side wall plate portion 11A, that is, as it approaches the inner wall surface of the preheating shaft 3. The inclination angle is not particularly limited, but has a depression angle of 5 degrees or more and 45 degrees or less with respect to the horizontal, for example.

[0045] When the bottom plate portion 11D is tilted as shown in FIG. 4, water that falls onto the bottom plate portion 11D is more likely to flow toward the drain pipe 14. In addition, the bending angle of the bent portion 11Fb is smaller than that in the case of FIG. 3, which leads to the reduction of stress concentration at the bent portion 11Fb.

[0046] (others) The present disclosure may also have the following configuration. (1) A shaft-type electric furnace in which a cold iron source is supplied to the furnace body through a preheating shaft, A water-cooled box is disposed on the inner wall surface side of the preheating shaft, the water-cooled box includes a wall plate portion facing an inner wall surface of the preheating shaft and capable of contacting a cold iron source loaded in the preheating shaft, a bottom plate portion connected to a lower end of the wall plate portion, and a water spray portion spraying water onto a surface of the wall plate portion facing the inner wall surface of the preheating shaft; At least the lower part of the wall panel and at least the part of the bottom panel facing the wall panel are constructed from a single plate material. (2) The plate material is curved into an arc shape at a joint between the wall plate portion and the bottom plate portion, The bottom plate portion is formed by butt-welding an end of another plate material to an end of the plate material on the bottom plate portion side. (3) A baffle plate is provided to prevent the cooling water sprayed from the water spraying portion from directly hitting the joint between the wall plate portion and the bottom plate portion. (4) The bottom plate portion is inclined so that the inner wall surface side of the preheating shaft is lower than the wall plate portion side. EXAMPLES

[0047] A heat transfer and thermal stress analysis (FEM analysis) was performed by CAE on the water-cooled box 10 having the shape shown in Fig. 3 described in this embodiment, and the stress applied to the bent portion 11Fb was obtained. Note that MSC.Marc was used as the analysis software for performing the analysis.

[0048] At this time, the shape of the inner surface of the joint (bent portion 11Fb) was changed to obtain the stress generated in the bent portion 11Fb. In addition, the analysis was performed with two types of plate thickness of the cooling side wall plate portion 11A, 50 mm and 32 mm.

[0049] The results are shown in Table 1. [Table 1]

[0050] Here, the column "shape of bent portion" in Table 1 indicates the shape of the inner surface of the bent portion 11Fb. "Right angle" refers to the case where the inner surface of the bend 11Fb is a right angle. "Fill leg length 16 mm" refers to a shape where the fillet is padded with a leg length of 16 mm on the right angle. "R20" refers to the case where the shape of the inner surface of the bend 11Fb is an arc with a curvature radius of 20 mm. "Right angle" simulates the case where the cooling side wall plate portion 11A and the bottom plate portion 11D are fillet welded at the bend 11Fb, "fillet leg length 16 mm" simulates the case where the fillet weld is padded on the inside to increase the thickness, and "R20" simulates the case where the bend 11Fb is made of a single plate material curved into an arc shape.

[0051] In the heat transfer analysis, the initial temperature was set to 30°C, and the temperature was increased by receiving radiant heat from a heat source of 1300°C for 10 hours. The analysis was an elastic-plastic calculation.

[0052] As can be seen from Table 1, it was found that stress is reduced and cracks are less likely to occur at the joint when a single plate material is bent to form the bent portion 11Fb (joint) compared to when the joint between the cooling side wall plate portion 11A and the bottom plate portion 11D is constructed by welding.

[0053] It was also confirmed by a heat transfer and thermal stress analysis that a high stress concentration occurs in the curved portion 11Fb, as compared with the flat cooling side wall plate portion 11A.

[0054] It was also found that the thinner the cooling side wall plate portion 11A, the smaller the stress at the bent portion 11Fb. However, since the cold iron source 4 such as scrap hits the cooling side wall plate portion 11A, durability (strength) is required to withstand the cold iron source 4, and therefore the thickness of the cooling side wall plate portion 11A may be appropriately set in consideration of the required durability (strength). [Explanation of symbols]

[0055] 1 Shaft type electric furnace 2. Furnace body 3 Preheat shaft 3A Body Frame 3Ab Inner wall 4 cold iron source 5. Molten Steel 10 Water Cooling Box 11 Body 11A Cooling side wall plate part 11D Bottom plate part 11E Vertical plate (cooling side wall plate) 11F connecting plate (plate material) 11Fa rising part (cooling side wall plate part) 11Fb Bend (joint) 11Fc Horizontal part (bottom plate part) 11G Horizontal plate (bottom plate) 12 Water injection part 12A Header 12B Injection nozzle 13 Baffle Plate 14 Drain pipe R Exhaust gas (flow) S Guideway

Claims

1. A shaft-type electric furnace in which a cold iron source is supplied to a furnace body through a preheating shaft, A water-cooled box is disposed on the inner wall surface side of the preheating shaft, the water-cooled box includes a wall plate portion facing an inner wall surface of the preheating shaft and capable of contacting a cold iron source loaded in the preheating shaft, a bottom plate portion connected to a lower end of the wall plate portion, and a water spray portion spraying water onto a surface of the wall plate portion facing the inner wall surface of the preheating shaft; At least the lower part of the wall panel portion and at least the part of the bottom panel portion on the wall panel portion side are made of a single plate material. A shaft type electric furnace characterized by:

2. The plate material is curved into an arc shape at a joint between the wall plate portion and the bottom plate portion, An end of another plate material is butt-welded to an end of the plate material on the bottom plate portion side to form the bottom plate portion.

2. A shaft type electric furnace according to claim 1.

3. a baffle plate for preventing the cooling water sprayed from the water spraying portion from directly hitting the joint between the wall plate portion and the bottom plate portion; 3. A shaft type electric furnace according to claim 1 or 2.

4. The bottom plate portion is inclined so that the inner wall surface side of the preheating shaft is lower than the wall plate portion side.

3. A shaft type electric furnace according to claim 1 or 2.

5. The bottom plate portion is inclined so that the inner wall surface side of the preheating shaft is lower than the wall plate portion side.

4. A shaft type electric furnace according to claim 3.

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