Converter slag removal protection equipment and converter refining method

Abstract

To provide a protection facility for converter slag capable of opening and closing a smoke-proof shutter without deformation, and a converter refining method.SOLUTION: A protection facility for converter slag is a protection facility to prevent slag from flowing out to a front working floor of a converter when the slag is discharged with the molten iron remaining in the converter. A heat resistant plate, a heat insulating material and a shutter body are installed in this order from the converter side. A converter refining method is a method for preventing the slag from flowing out to the front working floor of the furnace by using the protection facility for converter slag when the slag is discharged while the molten iron remains in the converter, and includes a step of attaching a heat resistant plate to the converter side of a shutter body installed in front of the furnace by sandwiching a heat insulating material, and a step of removing a thermally damaged heat resistant plate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a protective equipment used when draining slag from a converter in a converter refining process for steelmaking, and to a converter refining method for preventing slag from flowing out onto a work floor in front of the converter when draining slag from the converter. [Background technology]

[0002] In conventional converter furnaces, a pair of movable walls that can be opened and closed is installed to suppress the diffusion of dust generated during refining and to prevent radiant heat and slag from flowing out onto the front work floor during converter slag removal. These movable walls are called smoke shutters. The smoke shutters are opened when charging iron sources such as molten pig iron and scrap (hereinafter simply referred to as charging), and are closed during blowing, tapping, and slag removal.

[0003] Meanwhile, in converter refining operations, so-called intermediate slag removal has traditionally been performed between blows, in which slag is removed while leaving the molten pig iron in the converter. In this case, the converter is often tilted vigorously toward the front of the furnace to remove the slag. For example, Patent Document 1 describes a method in which the slag joint of the smoke shutter is horizontally shifted from the center of the throat to prevent slag from adhering to the joint.

[0004] Furthermore, the smoke shutter is subjected to a large thermal load due to radiant heat from the furnace throat and the impact of discharged slag. For this reason, for example, in Patent Documents 2 and 3, the heat-receiving surface of the smoke shutter is made of a heat-resistant plate, and a protective wall is installed in front of the smoke shutter at the slag impact area, which is subject to a particularly large thermal load, to protect the smoke shutter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-57496 [Patent Document 2] JP 2017-66500 A [Patent Document 3] Patent Publication No. 2021-102795 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional technology has the following problem: the heat radiated from the furnace throat and the heat caused by the collision of slag are transferred from the heat-receiving heat-resistant plate to the frame that constitutes the smoke shutter. As a result, the frame is deformed or cracked due to thermal stress, making it impossible to open or close the smoke shutter.

[0007] The present invention aims to solve the above-mentioned conventional problems and to provide a converter slag waste protection system and a converter refining method in which the smoke shutter can be opened and closed without deformation. [Means for solving the problem]

[0008] The converter slag removal protective equipment of the present invention, which advantageously solves the above-mentioned problems, is protective equipment for preventing slag from flowing out onto the work floor in front of the furnace when removing slag while leaving molten iron in the converter, and is characterized by being installed in this order from the converter side: a heat-resistant plate, heat insulation material, and the shutter body.

[0009] The converter slag protection equipment according to the present invention is as follows: (a) The heat transfer coefficient K of the heat insulating material is 8W / (m 2 ·℃) or less, (b) further disposing a seal plate between the heat-resistant plate and the heat insulating material; (c) the heat-resistant plate is fastened to the shutter body with a screw, and a pipe seat through which the screw passes is embedded in the heat insulating material; (d) The heat-resistant plate is a rectangular parallelepiped with a side length in the range of 0.3 to 0.9 m and a thickness t in the range of 20 to 30 mm, and the gap between the heat-resistant plates is 6 / 1000 times or more of the side length and 1 / 2 times or less of the thickness t; This may be a preferable solution.

[0010] The converter refining method of the present invention, which advantageously solves the above-mentioned problems, is a converter refining method that, when slag is discharged while leaving molten iron in the converter, uses any of the above-mentioned converter slag discharge protective equipment to prevent slag from flowing out onto the work floor in front of the furnace, and is characterized by including the steps of attaching a heat-resistant plate to the converter side of the shutter body installed in front of the furnace, with heat insulating material sandwiched between them, and removing the heat-resistant plate damaged by heat. [Effects of the Invention]

[0011] The converter slag protection equipment and converter refining method of the present invention can prevent the temperature of the smoke shutter frame from exceeding a certain value, and can prevent the smoke shutter from becoming unable to move due to thermal deformation of the frame. In addition, deformation and cracks in the heat-resistant plate can be managed and replaced during periodic maintenance, which reduces the impact on production due to problems and is extremely useful in industry. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a converter slag protection system according to one embodiment of the present invention. [Figure 2] FIG. 4 is a schematic cross-sectional view showing an example of a method for connecting a heat-resistant plate and a frame according to the embodiment. [Figure 3] 1A and 1B are partial front views illustrating the state of the heat-resistant plate after the converter slag removal work, where (a) shows the heat-resistant plate of a conventional panel, and (b) shows the heat-resistant plate of a segmented panel. [Figure 4] 10 is a graph showing the relationship between the thickness and thermal conductivity of the heat insulating material used in the embodiment. [Figure 5] 1 is a graph showing an example of a temperature transition of a heat-resistant plate during converter refining. [Figure 6] Schematic diagrams showing the temperature distribution based on actual measurement results and finite element method (FEM) analysis, where (a) shows the heat-resistant plate and (b) shows the frame. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes in detail embodiments of the present invention. Note that the drawings are schematic and may differ from the actual embodiments. Furthermore, the following embodiments exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0014] FIG. 1 is a schematic diagram showing a converter slag removal protection system according to one embodiment of the present invention. The converter system includes a converter installation section where a converter 1 is located and a furnace front section adjacent to the converter installation section where molten iron and other materials are charged. A furnace front-side work platform 4 is provided at the furnace front section. FIG. 1 shows the state during slag removal, with slag S above the molten iron L being discharged to the furnace front side. In this embodiment, the converter 1 is tilted to the furnace front side while the molten iron L remains in the converter 1, and the slag S is discharged, i.e., intermediate slag removal is performed.

[0015] A pair of smoke shutters 2 are provided in front of the converter to isolate the front-side work floor 4 from the converter 1 during operation. The smoke shutters 2 are opened and closed by moving on a traveling rail using a traveling device consisting of wheels and an electric motor. In this embodiment, a heat-resistant plate 3 is attached to the frame 2A (shutter body) of the smoke shutter 2.

[0016] As shown in FIG. 2 , the heat-resistant plate 3 according to this embodiment is connected and fixed to the frame 2A via a heat insulating material 5. The heat-resistant plate 3 blocks, for example, radiant heat from the throat of the converter 1 toward the front-side working floor 4 and outflowing slag during intermediate slag removal. The heat-resistant plate 3 is preferably made of ductile cast iron or heat-resistant cast steel. Furthermore, the thickness of the heat-resistant plate 3 is set to 20 mm or more because casting becomes difficult and the risk of material defects increases if the thickness is less than 20 mm. Furthermore, the thickness of the heat-resistant plate 3 is set to 30 mm or less because the temperature difference between the front and back surfaces increases and the risk of cracks due to thermal stress increases if the thickness exceeds 30 mm. Furthermore, when ductile cast iron is used for the heat-resistant plate 3, for example, its thermal expansion coefficient is 10.0 × 10 -6 / K. If the temperature rise of the heat-resistant plate due to the heat load from the converter is assumed to be about 600°C, it is preferable to provide a gap of 6 mm or more between adjacent heat-resistant plates 3 for every 1000 mm of side length of the heat-resistant plate 3, taking thermal expansion into consideration. If the gap is too wide, molten slag or sparks may leak from the gap, so it is preferable to make the gap no more than half the thickness of the heat-resistant plate (no more than 10 mm if the heat-resistant plate thickness is 20 mm).

[0017] In order to suppress the thermal stress that causes cracks and deformation in the heat-resistant plate 3, it is effective to reduce the temperature difference within the heat-resistant plate 3. In the smoke shutter 2, the main thermal loads are radiant heat and molten slag collisions. In the case of radiant heat, the temperature of the heat-resistant plate 3 rises uniformly, so temperature differences are unlikely to occur. On the other hand, in the case of molten slag collisions, a large temperature difference occurs between the parts with and without molten slag. This increases the thermal stress generated in the heat-resistant plate 3. Therefore, by dividing the heat-resistant plate into smaller parts in the area that is hit by molten slag, it is possible to suppress the damage area and the amount of deformation per plate.

[0018] An example of how a heat-resistant plate 3 panel can be subdivided is shown in Figure 3. Figure 3(a) shows a conventional panel, a square panel 3A with side lengths of 0.9m x 0.9m. In the example of Figure 3(a), four panels are partially within the slag impact area D, i.e., four 0.9m x 0.9m panels 3C are damaged. Figure 3(b) shows a subdivided panel 3B, which is 0.3m x 0.9m. Although the slag impact area D is the same as in Figure 3(a), the damaged panels 3C are now six 0.3m x 0.9m panels. Therefore, the area of ​​the damaged panels 3C is halved by subdividing the heat-resistant plate.

[0019] Therefore, the heat-resistant plate 3 is preferably a rectangular parallelepiped with a side length in the range of 0.3 to 0.9 m and a thickness in the range of 20 to 30 mm. If the side length is below the lower limit, the number of heat-resistant plates 3 to be installed will be too large, which may lead to an increase in the number of work steps.

[0020] The thickness and physical properties of the heat insulating material 5 used in this embodiment must be selected depending on the expected heat load. The mechanical strength of SS400, the material of the frame 2A, drops sharply when it exceeds 300 to 400°C. Therefore, it is preferable to design the frame so that the temperature is 200°C or less. Figure 4 shows the relationship between the thermal conductivity λ and thickness t of the heat insulating material 5. In the inventor's study, based on the results of actual temperature measurements during operation, it was found that in order to keep the temperature of the frame 2A below 200°C, the overall heat transfer coefficient K (=λ / t) of the heat insulating material 5 must be set to 8W / (m 2 It was found that the temperature must be kept below 100°C.

[0021] Insulation material 5 is classified into fixed insulation material and irregular insulation material. When fixed insulation material is used, the heat-resistant plate and the insulation material are not glued together, making replacement easy. Special molds are required to manufacture fixed insulation material, which is costly. For irregular insulation material, methods such as pouring or spraying are commonly used. If irregular insulation material is directly installed between the heat-resistant plate 3 and the frame 2A, it will adhere to the heat-resistant plate 3. Therefore, by installing a seal plate 6 between the heat-resistant plate 3 and the insulation material 5 and installing irregular insulation material on the seal plate 6, it becomes possible to replace the heat-resistant plate 3 alone.

[0022] Furthermore, much of the insulation 5 is made of brittle material and may break under the tightening force of the bolts 7. Therefore, by fastening the bolts 7 through pipe seats 9 that are longer than the thickness of the insulation, it is possible to prevent the application of tightening force to the insulation. With this method, the insulation will rattle due to vibrations when the smoke shutter 2 is in motion, so it is preferable to adhere the insulation to the frame with adhesive or the like. [Example]

[0023] To clarify the thermal load on smoke shutter 2 in a plant with a converter facility configured as shown in Figure 1, a heat-resistant plate for temperature measurement was installed on the existing smoke shutter 2 and temperature measurements were conducted. The converter operation method used during the measurements was the double slag (WS) method, which is the method with the highest thermal load. Specifically, the converter is charged with molten iron, desiliconized and phosphorus-removed as the first blow, dephosphorized slag discharged as intermediate slag removal (Rm), decarbonized as the second blow, tapped steel, and finally slag removal (Rf). Smoke shutter 2 is subjected to thermal loads due to radiation from the throat (throat temperature 1600°C) and slag impingement during the intermediate slag removal (Rm) (7–10 min) and final slag removal (Rf) processes. The measurements were conducted on the panel of heat-resistant plate 3, which is the part of the converter that receives the greatest thermal load from the slag impingement, in front of the throat where the radiant heat is greatest. Figure 5 shows an example of the temperature measurement results for this one cycle. From this result, it can be seen that temperature peaks appear at the time of intermediate slag discharge Rm and final slag discharge Rf. It was found that the smoke shutter 2 gradually accumulates heat through continuous operation, and when the amount of heat received and the amount of heat released balances, the temperature of the heat-resistant plate 3 reaches a maximum of approximately 600°C. Based on these measurement results, a finite element method (FEM) analysis was performed to select the insulation material 5. Figure 6 shows the analysis results for insulation material 5 with a thermal conductivity λ = 0.2 W / (m°C) and a thickness of 30 mm. The overall heat transfer coefficient of this insulation material 5 is 6.67 W / (m°C), as plotted in Figure 4. 2 The maximum temperature of the heat-resistant plate 5 was 600°C, while the maximum temperature of the frame 2A was 150°C, which was a good result.

[0024] The heat-resistant plate 3 must cover the area that is subject to the impact of molten slag and the radiant heat from the furnace opening, so it is preferable that it be about twice the diameter of the furnace opening. In this example, the heat-resistant plate area is 9.5 m × 10.0 m for a furnace opening diameter of 4.6 m.

[0025] Furthermore, if the heat-resistant plate 3 is divided into too many pieces, for example, in the case of a panel measuring 0.1 m x 0.1 m, the number of bolts required will be 4 per panel x 1296 panels, for a total of 5184 bolts, which is significantly more than when the heat-resistant plate of 0.9 m x 0.3 m of this embodiment is used. Increasing the number of bolts not only increases the labor required to install the heat-resistant plate 3, but also increases the bolt area relative to the heat-receiving surface, leading to a deterioration in heat-resistance performance.

[0026] Without the insulation material 5, the temperature of frame 2A would reach approximately 550°C, and the rise in temperature would cause the tensile strength of the SS400 material of frame 2A to drop from 400 MPa to approximately 150 MPa. SS400, the material of frame 2A, has low creep resistance, so it is generally not recommended for use as a structure in environments above 350°C. If heat-resistant steel were used in consideration of creep resistance, the cost would be significantly higher than that of SS400. [Explanation of symbols]

[0027] 1 Converter 2 Smokeproof shutter 2A (Smoke shutter) frame 3 Heat-resistant plate 3A (traditional) panel 3B (Subdivided) Panel 3C (damaged) panel 4 (Furnace front side) Work floor 5. Insulation 6 Seal plate 7 flat head bolts 8 nuts 9 Tube seat L Molten steel S slug D (Slag) Collision Range Rm Intermediate sludge removal Rf final slag

Claims

1. This is a protective equipment for preventing slag from flowing out onto the furnace front work floor when removing slag while leaving molten iron in the converter. The protective equipment includes smoke shutters, which are a pair of movable walls that can be opened and closed; From the converter side, a metal heat-resistant plate, a heat insulating material with a heat transfer coefficient K of 8 W / (m 2 ·°C) or less, and the shutter body are installed in this order. The heat-resistant plates in the area that will be hit by the slag are vertically long rectangular parallelepiped panels with side lengths in the range of 0.3 to 0.9 m and thicknesses t in the range of 20 to 30 mm, and are protective equipment for converter slag discharge.

2. The converter slag protection equipment according to claim 1, further comprising: an insulating material that is an amorphous insulating material; and a seal plate that prevents adhesion between the heat-resistant plate and the insulating material, disposed between the heat-resistant plate and the insulating material.

3. 2. The converter slag protection equipment according to claim 1, wherein the heat-resistant plate is fastened to the shutter body with a screw, and a pipe seat through which the screw passes is embedded in the heat insulating material.

4. 2. The converter slag protection equipment according to claim 1, wherein the gap between the heat-resistant plates is 6 / 1000 times or more of the side length and 1 / 2 times or less of the thickness t.

5. A converter refining method for preventing slag from flowing out to a furnace front side working floor by using the converter slag removal protective equipment according to any one of claims 1 to 4 when removing slag while leaving molten iron in the converter, A process of attaching a heat-resistant plate to the converter side of the shutter body installed in front of the furnace, sandwiching an insulating material between them. and removing the heat-damaged refractory plate.

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