ELECTRIC OVEN EQUIPPED WITH VIDEO EQUIPMENT

Abstract

For direct and clear observation of the internal state of the melting chamber in an electric furnace, the invention relates to an electric furnace equipped with a video apparatus comprising: a melting chamber; a preheating chamber; and a video apparatus for observing the internal state of the melting chamber. The video apparatus comprises: a transition lens; an inner tube containing the transition lens and having an outer diameter of 100 mm or less; an outer tube containing the inner tube; and an imaging device located at the end of the axis of the transition lens outside the furnace. The video apparatus is provided through an opening in the furnace wall or lid such that the transition lens is positioned 300 mm to 3500 mm from the highest molten iron interface in a vertically upward direction and the imaging device is positioned 300 mm or greater from the inner wall of the furnace wall or lid in an outward direction.

Description

Electric furnace with video equipment

[0001] The present invention relates to an electric furnace with a video device, and more particularly to an electric furnace with a video device that allows for the production of molten iron while directly observing the state inside a melting chamber in which a cold iron source is melted to obtain molten iron.

[0002] In general, in an electric furnace, a cold iron source such as scrap is supplied to a melting chamber and melted with arc heat generated by direct or alternating current electricity to produce molten iron. Typical methods for supplying the cold iron source include, for example, a method in which the furnace cover of the melting chamber is opened and the cold iron source is supplied discontinuously from above the melting chamber; and a method in which a preheating chamber connected to the melting chamber is provided and the cold iron source is supplied continuously from the preheating chamber to the melting chamber. Among these, the method of supplying the cold iron source from the preheating chamber to the melting chamber is widely adopted because it allows the cold iron source to be melted more efficiently.

[0003] Conventionally, when producing molten iron in an electric furnace, it has not been possible to directly observe the state inside the melting chamber, which becomes extremely hot due to the heat of the arc. Therefore, engineers control the melting conditions based on empirical rules without visually checking the state of the cold iron source and molten iron inside the melting chamber, which has posed a challenge to the efficient production of molten iron.

[0004] Methods for visually checking the inside of a furnace are discussed, for example, in Patent Documents 1 to 3. Patent Document 1 proposes a technique for monitoring the bumping of molten steel and slag in a vacuum refining furnace by installing a television camera diagonally above the ladle mouth. In the actual technique of Patent Document 1, a television camera is installed inside the top lid of the vacuum refining furnace to monitor the refractory side wall near the ladle mouth, thereby avoiding the influence of gas and dust compared to when directly looking into the molten steel surface.

[0005] Furthermore, Patent Document 2 proposes an imaging device that can observe the conditions inside a blast furnace using a color television camera. In the actual technology of Patent Document 2, the imaging device is installed in front of the tuyere outside the blast furnace, and the conditions inside the furnace are imaged through the tuyere viewing window. Furthermore, the imaging device of Patent Document 2 captures images by passing light through a pinhole instead of an objective lens while finely adjusting the optical axis angle adjustment mechanism and the optical axis movement mechanism.

[0006] Patent Document 3 proposes an in-furnace monitoring device for capturing images of the inside of a furnace such as a blast furnace with a television camera and monitoring the internal conditions on television images.

[0007] JP-A No. 08-232014 JP-A No. 50-108816 JP-A No. 07-103670

[0008] However, the technology of Patent Document 1 only observes the inside of a vacuum refining furnace, and observes the side wall near the ladle mouth, which is separated from the molten steel and slag that are actually being melted, so observations are only possible once the molten steel and slag have bumped, and it is not possible to directly observe the molten steel, which is a high-temperature radiant object, at all times during operation. The technology of Patent Document 1 can detect the presence of bumping in a vacuum refining furnace, but it cannot detect the condition of the melting chamber during actual melting.

[0009] In addition, the technology of Patent Document 2 observes the inside of a blast furnace, and moreover, images of the inside of the furnace are captured through a tuyere viewing window outside the furnace, so there are limitations to clearly grasping the state of the inside of the melting chamber during melting. Furthermore, the imaging device of Patent Document 2 has a complex optical axis angle adjustment mechanism and optical axis movement mechanism, which causes the device to become large.

[0010] Furthermore, Patent Document 3 only describes the structure of an in-furnace monitoring device that can be inserted into a furnace, and does not consider any specific or optimal conditions for what kind of furnace it should be installed in and how to observe the inside of the furnace.

[0011] As described above, it has not been possible with the prior art to clearly visually check the inside of the melting chamber of an electric furnace during operation. The present invention has been made in consideration of the above circumstances, and has as its object to provide an electric furnace equipped with a video device that produces molten iron by melting a cold iron source using arc heat, and that allows direct and clear observation of the state inside the melting chamber during operation.

[0012] The inventors of the present invention have conducted extensive research into the above-mentioned problems in an electric furnace in which a cold iron source preheated in a preheating chamber is supplied to a melting chamber, and the cold iron source is melted in the melting chamber by arc heat, and as a result, have found that by providing an imaging device having a predetermined structure at a predetermined position in the melting chamber, it is possible to directly and clearly observe the cold iron source and molten iron being melted in the melting chamber.

[0013] That is, the gist of the present invention is as follows: 1. An electric furnace equipped with a video device, comprising a melting chamber for melting a cold iron source with arc heat to obtain molten iron, and a preheating chamber for preheating the cold iron source to be supplied to the melting chamber, further comprising a video device for observing the inside of the melting chamber, the video device having a relay lens consisting of a plurality of lenses, an inner tube containing the relay lens and having an outer diameter of 100 mm or less, an outer tube containing the inner tube, and an image capturing device provided on the axial tip of the relay lens outside the furnace, the relay lens being located 300 mm to 3500 mm vertically above the highest interface of the molten iron, and the image capturing device being installed through a hole in the furnace wall or furnace lid so that the relay lens is located 300 mm or more and 3500 mm or less vertically above the highest interface of the molten iron, and the image capturing device is located 300 mm or more outside the furnace from the inner wall of the furnace wall or furnace lid that constitutes the melting chamber.

[0014] In the present invention, the "highest interface of molten iron" refers to the interface at the position where the interface of molten iron is highest in the melting chamber according to design. The position of the "highest interface of molten iron" can be calculated from the shape of the melting chamber of the electric furnace and the designed volume of molten iron obtained in the melting chamber.

[0015] 2. The electric furnace with a video device according to 1 above, further comprising a gas supply device that supplies gas between the inner tube and the outer tube at a flow rate of 50 NL / min or more and 250 NL / min or less.

[0016] According to the present invention, in an electric furnace that produces molten iron from a cold iron source using arc heat, it is possible to directly and clearly observe the cold iron source and molten iron in the melting chamber during melting. If the state inside the melting chamber of an electric furnace can be clearly observed during operation, it is possible to quickly and accurately grasp, for example, the state of supply of the cold iron source to the melting chamber and the state of melting of the cold iron source in the melting chamber. This can be effectively used to optimize operating conditions, prevent operational problems, reduce production costs, and so on, providing significant industrial benefits.

[0017] 1 is a longitudinal sectional view of an electric furnace equipped with a video device according to an embodiment of the present invention;

[0018] The following describes in detail the embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these examples.

[0019] (Electric Furnace with Visualization Device) The electric furnace with visualization device of the present invention is characterized in that a visualization device having a predetermined structure is provided at a predetermined position in the electric furnace. By providing the predetermined visualization device at a predetermined position, when producing molten iron from a cold iron source in the electric furnace, the molten cold iron source or molten iron can be tactilely and clearly observed. Preferred embodiments of the electric furnace with visualization device of the present invention will be described in detail below with reference to the drawings.

[0020] [Electric Furnace] Electric furnace 1 includes melting chamber 2 in which cold iron source 15 is melted by heat from arc 18 to obtain molten iron 16, preheating chamber 3 in which cold iron source 15 is supplied to melting chamber 2, and video device 30 installed at a predetermined position in melting chamber 2.

[0021] The raw material, cold iron sources 15, are loaded into a supply bucket 14 and transported to above a desired cold iron source supply port 19 via a traveling cart 23. Next, the cold iron source supply port 19 is opened, and the cold iron sources 15 are supplied from above into the preheating chamber 3.

[0022] The cold iron source 15 supplied to the preheating chamber 3 is preheated by any method. For example, production efficiency can be improved by preheating the cold iron source 15 by passing the high-temperature exhaust gas previously generated in the melting chamber 2 through the preheating chamber 3. The exhaust gas may be sucked through the duct 20 and passed through the preheating chamber 3, and excess exhaust gas may be exhausted through the duct 20.

[0023] The preheated cold iron source 15 is supplied to the melting chamber 2. The cold iron source 15 may be supplied to the melting chamber 2 by its own weight, or may be continuously supplied by, for example, an extruder (not shown) provided in the preheating chamber 3.

[0024] The melting chamber 2 is partitioned by a furnace wall 4 and a furnace lid 5, and may be equipped with an electrode 6 for generating an arc 18 for heating, an oxygen blowing lance 7 and a carbonaceous material blowing lance 8 for maintaining the desired high temperature, and a burner 9 for locally heating low-temperature areas. A cold iron source 15 supplied to the melting chamber 2 is melted by the heat of the arc to form molten iron 16 and molten slag 17. The resulting molten iron 16 can be tapped from the tapping port 12 by opening the tapping door 21. The molten slag 17 can be discharged from the slag discharge port 13 by opening the slag discharge door 22.

[0025] In the present invention, as will be described later, a video device 30 capable of observing the inside of the melting chamber 2 is installed at an optimum position in the electric furnace, so that the state of the cold iron source 15 being supplied and the state of the cold iron source 15 being melted to become molten iron 16 can be clearly observed. Therefore, this is useful for preventing operational troubles and improving production efficiency in the molten iron production process.

[0026] The cold iron source 15 typically includes, but is not limited to, in-house scrap generated at steelworks, scrap generated in the market, and pig iron solidified from molten pig iron. Examples of in-house scrap generated at steelworks include unsteady portions of slabs cast by continuous casting or ingot casting (portions generated at the beginning or end of casting), and crops generated during the rolling of steel materials such as steel strips. Examples of scrap generated in the market include recycled materials such as construction steel (e.g., H-beams), automotive steel, and cans. Pig iron solidified from molten pig iron is obtained by tapping and solidifying molten pig iron obtained from raw materials such as iron ore and coke in a blast furnace or other smelting furnace.

[0027] [Imaging Device] The imaging device 30 includes a relay lens 31 made up of multiple lenses, an inner tube 33 containing the relay lens 31 and having an outer diameter of 100 mm or less, an outer tube 32 containing the inner tube 33, and an imaging device 36 provided outside the furnace at the axial tip of the relay lens 31. The imaging device 36 is typically a camera, and is preferably protected by a housing 35.

[0028] 1 , the imaging device 30 is installed facing the melting chamber 2 through a hole provided in the furnace wall 4 or furnace lid 5, more preferably via a jig 34 for fixing the imaging device 30 in a predetermined position, and the relay lens 31 and the imaging device 36 are arranged in this order from the melting chamber 2 toward the outside of the furnace. In this way, since the imaging device 30 has the imaging device 36 via the relay lens 31, the length of the relay lens 31 can be used to install the imaging device 36 at a predetermined distance from the electric furnace 1, and the imaging device 36 can be protected from the heat of the electric furnace 1.

[0029] Furthermore, the relay lens 31 is protected by a double-tube structure consisting of a predetermined inner tube 33 and an outer tube 32. Having the predetermined inner tube 33 and outer tube 32 in the imaging device 30 also protects the relay lens 31 from the heat of the electric furnace 1. It is particularly important to narrow the outer diameter of the inner tube 33 to 100 mm or less. Molten iron or molten slag may splash onto the tip lens of the relay lens 31, the lens closest to the melting chamber 2. Increasing the outer diameter of the inner tube 33 would widen the field of view, but this risk increases. Narrowing the inner tube 33 reduces the risk of molten iron or molten slag splashing from the melting chamber 2 and ensures a clear imaging field of view. Furthermore, gas such as air is sometimes blown toward the melting chamber 2 to repel splashing molten iron or molten slag. Narrowing the inner tube 33 increases the flow rate of this gas, effectively preventing adhesion of the splashed material to the lens. The outer diameter of the inner tube 33 is preferably 90 mm or less, and is usually 20 mm or more.

[0030] As long as the outer diameter of the inner tube 33 is as described above, the inner diameters of the inner tube 33, the inner diameter of the outer tube 32, and the outer diameter of the outer tube 32 are not particularly limited, and can be determined, for example, as follows. That is, the inner diameter of the inner tube 33 is determined based on the determined outer diameter of the inner tube 33, taking into consideration the wall thickness of the inner tube 33 in consideration of the required strength and the size of the lens to be used, and is usually 16 mm or more, preferably 20 mm or more, preferably 90 mm or less, and more preferably 86 mm or less. Furthermore, the inner diameter of the outer tube 32 is determined based on the determined outer diameter of the inner tube 33, taking into consideration the gap between the inner tube 33 and the outer tube 32 in consideration of the desired flow rate and flow rate of the cooling gas, and is preferably 30 mm or more, preferably 110 mm or less, and more preferably 100 mm or less. The outer diameter of the outer tube 32 is determined based on the determined inner diameter of the outer tube 32, taking into consideration the thickness of the outer tube 32 in light of the required strength, and is preferably 40 mm or more, preferably 120 mm or less, and more preferably 110 mm or less.

[0031] It is also preferable to provide a gap between the inner tube 33 and the outer tube 32 and supply a gas 39, such as air, into this gap at a flow rate of 50 NL / min to 250 NL / min. The electric furnace 1 may further include a gas supply device (not shown), which can supply the gas 39. The tips of the outer tube 32 and the inner tube 33 are significantly heated by radiant heat, primarily from the molten iron being observed. Thermal conduction can cause the relay lens 31 contained within the inner tube 33 to exceed its heat-resistant temperature. This can result in damage such as lens distortion, preventing images from reaching the imaging device 36, or even lens cracking. The heat-resistant temperature of the imaging device 30 is typically 60°C, and it is important to control the temperature so as not to exceed this temperature. If the temperature of the imaging device 30 exceeds 60°C, the lens may become distorted, making it impossible to capture images. While the only method for cooling the relay lens 31 is by using gas 39, supplying gas 39 at or above the lower limit effectively cools the relay lens 31, further reducing the effects of the high temperature of the melting chamber during operation and ensuring a clearer image field. Furthermore, the tip lens of the relay lens 31 closest to the object of observation is likely to be exposed to high-temperature radiation, to have slag scattered during electric furnace operation, or to be approached by slag or molten iron when the electric furnace is tilted during tapping. Therefore, it is preferable to appropriately control the flow rate of gas 39 in order to effectively blow away scattered molten iron or slag and prevent it from adhering to the lens. A flow rate of 100 NL / min or more is more preferable.

[0032] On the other hand, if the flow rate of the gas 39 exceeds 250 NL / min, the problem of adhesion of molten steel and slag is eliminated, but the running costs increase, and a large amount can be used. Furthermore, a high flow rate may cause condensation due to excessive cooling. Therefore, from the viewpoint of suppressing production costs and condensation, it is preferable to set the flow rate below the upper limit, and more preferably below 200 NL / min. Here, "NL / min" is a unit commonly used in the field of the present invention and refers to a flow rate under atmospheric pressure of 1 atm. Generally, the unit "NL / min" can be interpreted as "L / min." Typically, the gas flows from the outside of the electric furnace toward the inside of the electric furnace (see FIG. 2).

[0033] Similarly, it is preferable to supply gas 38, such as air, between the jig 34, which can be used when attaching the electric furnace, and the outer tube 32. The electric furnace 1 may further include a gas supply device, which can supply gas 38. Because the outer tube 32 is exposed to heat transmitted from the furnace wall 4 or furnace lid 5 through the jig 34, supplying gas 38 further cools the imaging device 30, further avoiding the effects of the high temperature of the melting chamber during operation and ensuring a clearer imaging field of view. It also effectively blows away molten slag that may adhere to the front surface of the lens. The flow rate of gas 38 depends on the outer diameter of the outer tube 32 and the design size of the gap between the jig 34 and the outer tube 32. From the above-mentioned viewpoints, however, it is preferable that the flow rate be 400 NL / min or more, preferably 600 NL / min or less, and more preferably approximately 500 NL / min. Alternatively, since the furnace wall 4 and the furnace cover 5 are generally water-cooled, the flow rate of the gas 38 may be relatively small compared to the flow rate of the gas 39 described above.

[0034] Similarly, it is preferable to supply a gas 37 such as air into the housing 35. The electric furnace 1 may further include a gas supply device, which can supply the gas 37. Supplying the gas 37 further cools the imaging device 36, further avoids the effects of the high temperature of the melting chamber during operation, and ensures a clearer image field. The flow rate of the gas 37 depends on the design size of the housing 35, but from the above-mentioned viewpoint, it is preferably 200 NL / min or more, preferably 300 NL / min or less, and more preferably about 260 NL / min.

[0035] Since a large amount of gas is used for cooling, it may be connected by branching or extending gas pipes supplied as part of the steelworks' infrastructure, or it may be supplied directly from a compressor to the electric furnace side. Air is a typical example of the gas, but if cost is not an issue, an inert gas such as nitrogen may also be used. It is desirable that the gas contain as little moisture as possible, as moisture may adhere to the lens surface in some cases, narrowing the field of view. The gas supply device provided in the electric furnace 1 is not particularly limited, and may include the gas pipes and compressors described above.

[0036] [Location of the Imaging Device] In the present invention, the location of the imaging device 30 is extremely important. Unless the imaging device 30 is installed in a predetermined position in the electric furnace 1, direct and clear observation of the high-temperature interior of the melting chamber 2 during operation is impossible. Specifically, the imaging device 30 requires that the relay lens 31 be installed in the melting chamber 2 at a vertical position 300 mm to 3,500 mm above the highest molten iron interface. The installation position of the relay lens 31 is based on the center of the tip lens closest to the melting chamber 2. The "highest molten iron interface" is as defined above, and can be calculated by a skilled artisan based on the shape of the melting chamber 2 and the volume of molten iron 16 produced in the melting chamber 2, which are determined when the electric furnace 1 is installed. If the relay lens 31 is not installed at a height of 300 mm or more above the highest molten iron interface, the lens will be covered with slag and / or molten iron when the molten iron interface fluctuates or when the electric furnace is tilted to remove slag or tap molten iron. Furthermore, the thermal load on the relay lens 31 due to radiation from the molten iron increases, making it difficult to ensure a good viewing field. Furthermore, if the relay lens 31 is located more than 3,500 mm away from the highest interface of the molten iron, the thermal load due to radiation from the molten iron is reduced, but the field of view for observing, for example, the movement of the cold iron source 15 extruded from the preheating chamber 3 becomes narrow, making it difficult to accurately grasp the overall status of the melting chamber 2. The installation position of the video device 30 is preferably such that the relay lens 31 is located vertically above the highest interface of the molten iron at a distance of 400 mm or more, and preferably 1,500 mm or less. As long as the above-mentioned specified installation position is satisfied, the video device 30 may be installed on the furnace lid 5. However, because the furnace lid is opened and closed, care must be taken when protecting and routing the cable used to transmit the video. Therefore, it is preferable to install the video device 30 on the furnace wall 4.

[0037] Furthermore, the imaging device 30 must be installed so that the imaging device 36 is located at least 300 mm away from the inner wall of the furnace wall 4 or furnace lid 5 of the melting chamber toward the outside of the furnace. By locating the imaging device 36 at least 300 mm away from the outside of the furnace, the thermal load on the imaging device 36 can be sufficiently reduced, ensuring a clear imaging field of view. Furthermore, repair or replacement of the imaging device 36 in the event of a malfunction is simplified, and the flow rate of the gas 37 used to cool the imaging device 36 can be reduced, thereby reducing manufacturing costs. The distance between the imaging device 36 and the inner wall of the furnace wall 4 or furnace lid 5 is the shortest distance L, or a distance equivalent thereto, from the intersection P of the central axis O of the relay lens 31 and the line segment R connecting the inner wall edge of the hole in the furnace wall 4 or furnace lid 5 at the maximum diameter to the imaging device 36. In FIG. 2 , the relay lens 31, protected by the outer tube 32 and the inner tube 33, is inserted into the hole in the furnace wall 4. The above-mentioned installation position can be controlled by, for example, adjusting the length of the relay lens 31 of the imaging device 30 or the length of the inner tube 33 that contains it.

[0038] The installation angle of the imaging device 30 is not particularly limited and may be appropriately determined depending on the position of the object to be observed and the installation height on the furnace wall 4 or furnace lid 5. For example, when installing the imaging device 30 on the furnace wall 4 to observe the molten slag 17 and molten iron 16, the imaging device 30 may be installed at a downward angle relative to the horizontal, as shown in FIG. 1. On the other hand, when installing the imaging device 30 on the furnace wall 4 to observe the condition of molten slag adhering to the underside of the furnace lid 5 or the condition of the furnace lid 5 being overheated and reaching a high temperature, the imaging device 30 may be installed at an upward angle relative to the horizontal. The installation angle can be adjusted within a range of -90° to 90° horizontally, and this may be appropriately adjusted, for example, by controlling the structure of the jig depending on the relative positional relationship between the area to be observed and the hole.

[0039] The images captured by the imaging device 30 are generally connected via cables (not shown) to a monitor or recording device (neither of which are shown) in an operation room operated by an operator.

[0040] The imaging device 36 only needs to be able to capture images via the relay lens 31, and the images may be recorded and saved within the imaging device 36 itself. Alternatively, a video cable (not shown) may be extended to the rear, installed in a room with little dust, and the images may be captured on a separate recording device. The format of still or video images may be determined according to the user's needs, and whether the images are saved continuously or in batches may also be determined according to the user's desires. Furthermore, if the object being observed is bright, it may be advisable to take the image through an ND filter or other suitable device.

[0041] The inner tube 33 may be any material capable of fixing the relay lens 31. It may also be connected to the housing 35. The inner tube 33 may be tubular, and the material may be appropriately selected in relation to the ambient temperature to be used and the strength of the installation location. From the viewpoint of cost, it is desirable to select carbon steel, stainless steel, or the like.

[0042] The outer tube 32 is usually larger in outer diameter than the inner tube 33, and preferably can supply the gas 39 at the above-mentioned flow rate between the outer tube 32 and the inner tube 33 toward the tip of the relay lens 31 on the melting chamber 2 side. If the gap between the outer tube 32 and the inner tube 33 is too wide, the flow rate of the supplied gas increases, so it is desirable to appropriately adjust the diameter of the outer tube 32 to ensure that flow rate is met. The outer tube 32 can be tubular, and its material may be appropriately selected depending on the relationship between the ambient temperature to be used and the strength of the installation location. From the viewpoint of cost, it is desirable to select carbon steel, stainless steel, or the like.

[0043] The jig 34 for fixing the outer pipe 32 to the furnace wall 4 or furnace lid 5 can be flanged and fixed with bolts to connect the furnace wall 4 or furnace lid 5 to the outer pipe 32. Of course, the furnace wall 4 or furnace lid 5 and the jig 34 can also be fixed by welding, but from the viewpoint of ease of maintenance, flange fixing is preferable.

[0044] The housing 35 can be used to house and properly install the imaging device 36. To prevent a rise in temperature inside the housing 35 and protect the imaging device 36 from heat, it is preferable to have a structure in which a cooling gas 37 can be circulated inside the housing 35. As with the outer pipe 32 and the inner pipe 33, the material of the housing 35 may be determined depending on the atmosphere in which it will be installed, but from the viewpoints of good connection and high strength, it is desirable to select carbon steel or stainless steel.

[0045] The present invention will be specifically described below based on examples. Note that the following examples are merely preferred examples of the present invention and are not intended to limit the present invention in any way. Furthermore, the following examples can be modified within the scope of the present invention, and such modifications are also included within the technical scope of the present invention.

[0046] Molten iron was produced by melting a cold iron source in an electric furnace equipped with a melting chamber 2 and a preheating chamber 3 shown in Figure 1, equipped with a video device 30 shown in Figure 2 in the melting chamber 2, and conforming to the conditions shown in Table 1. The equipment specifications of this electric furnace are as follows: Molten iron capacity in the melting chamber: 190 tons; Power: AC 50 Hz; Transformer capacity: 75 MVA; Number of electrodes: 3; Diameter of the melting chamber: 5 m; Highest molten iron interface: 1.3 m vertically above the bottom of the furnace.

[0047] The imaging devices 30 were equipped with inner tubes 33 having various outer diameters as shown in Table 1. The imaging devices 30 were installed via jigs through holes drilled in the furnace wall 4 at various heights (vertical distances upward) from the highest molten iron interface, as determined by the design based on the shape of the electric furnace 1 and the molten iron capacity of 190 tons, as shown in Table 1. Cooling gases 37, 38, and 39 were all supplied to the inlets of the imaging devices 30 via flexible hoses from gas piping provided at the steelmaking plant. An air dryer was installed midway to remove water vapor that may be contained in the cooling gas. The state of the melting chamber during actual molten iron production was observed on a monitor through the imaging devices 30, and the imaging device was evaluated for clarity of the field of view and protection from heat as follows. The results are shown in Table 1.

[0048] Inventive Example 1, the outer diameter of the inner tube of the imaging device was 80 mm. A hole was drilled in the furnace wall, 500 mm vertically above the highest designed molten iron interface, and the imaging device was installed in the hole. The camera (imaging device) was positioned 320 mm away from the inner wall of the furnace toward the outside of the furnace. Air was used as the gas supplied between the inner and outer tubes at a flow rate of 150 NL / min. The air temperature was 12°C. When molten iron was produced, the cold iron source and the molten iron in the melting chamber could be clearly visually monitored. Furthermore, when the furnace was tilted, no adhesion of molten iron or slag to the lens due to the blowing of oxygen from the oxygen blowing lance was observed, and this was completely prevented, ensuring a clear imaging field of view. The temperature of the imaging device averaged 26°C, which did not exceed the allowable temperature of 60°C, and the imaging device was well protected from the high temperature in the melting chamber. The cost of the cooling gas supplied between the inner and outer pipes was determined based on the total amount of gases 37 to 39 actually used, compared to the total flow rate of 1,000 NL / min of cooling gas that can be supplied from the compressor during normal operation. In this example, the actual total amount used was 910 NL / min, which was at an acceptable level without the need to operate a spare compressor and thus did not increase costs.

[0049] Inventive Example 2: Molten iron was produced under the same conditions as in Inventive Example 1, except that the flow rate of the gas supplied between the inner and outer tubes was changed to 40 NL / min. Despite the reduced cooling gas flow rate, the status of the cold iron source and molten iron in the melting chamber during the melting process could be clearly monitored visually. Although some molten iron and slag were observed to adhere to the lens due to scattering, this did not interfere with monitoring the melting chamber, and a clear image field was ensured. The average temperature of the imaging device was 58°C, temporarily exceeding the allowable temperature of 60°C, causing some image distortion. However, the overall operation was not affected, and the imaging device was protected. The cost of the cooling gas supplied between the inner and outer tubes was within acceptable limits, with the actual total usage of gases 37 to 39 being 800 NL / min, which did not result in an increase in cost.

[0050] Inventive Example 3, molten iron was produced under the same conditions as in Inventive Example 1, except that the flow rate of the gas supplied between the inner and outer tubes was changed to 260 NL / min. The status of the cold iron source and molten iron in the melting chamber during the melting process could be clearly monitored visually. Furthermore, adhesion of molten iron and slag to the lens due to scattering was completely prevented, ensuring a clear visual field. Furthermore, the average temperature of the imaging device was 4°C, never exceeding the allowable temperature of 60°C, effectively protecting the imaging device from the high temperature of the melting chamber. The cost of the cooling gas supplied between the inner and outer tubes was 1,020 NL / min in total for gases 37 to 39, and the operation of a spare compressor increased costs. However, there were no problems with the operation itself.

[0051] Inventive Example 4, molten iron was produced under the same conditions as in Inventive Example 1, except that the relay lens was positioned at a vertical distance of 1,500 mm above the highest molten iron interface. The cold iron source and molten iron status in the melting chamber were clearly visible during the melting process. Furthermore, no adhesion of molten iron or slag to the lens due to scattering was observed, completely preventing this and ensuring a clear visual field. Furthermore, the average temperature of the imaging device was 17°C, never exceeding the allowable temperature of 60°C, effectively protecting the imaging device from the high temperatures in the melting chamber. The cost of the cooling gas supplied between the inner and outer tubes was an acceptable level, with the actual total usage of gases 37 to 39 being 910 NL / min, which did not result in any additional costs.

[0052] Inventive Example 5, molten iron was produced under the same conditions as in Inventive Example 1, except that the outer diameter of the inner tube was changed to 50 mm. The flow rate of the cooling gas supplied between the inner and outer tubes was maintained at 150 NL / min, resulting in a higher flow rate than in Inventive Example 1, allowing for clearer visual monitoring of the cold iron source and molten iron in the melting chamber during the melting process. Furthermore, no adhesion of molten iron or slag to the lens due to scattering was observed, completely preventing it and ensuring a clear viewing field. Furthermore, the average temperature of the imaging device was 14°C, never exceeding the allowable temperature of 60°C, effectively protecting the imaging device from the high temperatures in the melting chamber. The cost of the cooling air supplied between the inner and outer tubes was 910 NL / min, the actual total usage of gases 37 to 39, which was within acceptable limits and did not result in increased costs.

[0053] Inventive Example 6, molten iron was produced under the same conditions as in Inventive Example 1, except that the gas supplied between the inner and outer tubes was changed to nitrogen gas. The status of the cold iron source and molten iron in the melting chamber during the melting process could be clearly monitored visually. Furthermore, no adhesion of molten iron or slag to the lens due to scattering was observed, and this was completely prevented, ensuring a clear visual field. Furthermore, the temperature of the imaging device averaged 29°C, never exceeding the allowable temperature of 60°C, effectively protecting the imaging device from the high temperatures in the melting chamber. The cost of the cooling air supplied between the inner and outer tubes increased due to the use of nitrogen, although the actual total usage of gases 37 to 39 was 910 NL / min, less than 1,000 NL / min. However, there were no problems with the operation itself.

[0054] Comparative Example 1: Molten iron was produced under the same conditions as in Example 1, except that the relay lens was positioned at a vertical distance of 290 mm above the highest interface of the molten iron. When the furnace was tilted, excessive amounts of molten iron and slag scattered by the oxygen blowing lance adhered to the lens, gradually narrowing the field of view and making it impossible to observe the interior of the melting chamber over time. The average temperature of the imaging device was 74°C, exceeding the allowable temperature of 60°C, which not only caused problems with debris adhesion but also distorted the image, making it impossible to observe the interior of the melting chamber. The cost of the cooling gas supplied between the inner and outer tubes was 910 NL / min, a total of 910 NL / min for gases 37 to 39, which did not increase costs and was within the acceptable range.

[0055] Comparative Example 2: Molten iron was produced under the same conditions as in Example 1, except that the relay lens was positioned at a vertical distance of 3600 mm above the highest interface of the molten iron. No adhesion of molten iron or slag to the lens due to scattering was observed, but the molten iron, which was the object of observation, was not in the field of view, and the desired imaging field of view could not be secured. However, the temperature of the imaging device averaged 14°C and never exceeded 60°C, so the imaging device was well protected from the high temperature of the melting chamber. The cost of the cooling gas supplied between the inner and outer tubes was an acceptable level, with the actual total usage of gases 37 to 39 being 910 NL / min, which did not result in an increase in cost.

[0056] Comparative Example 3: Molten iron was produced under the same conditions as in Example 1, except that the outer diameter of the inner tube was changed to 110 mm. In this case, increasing the diameter of the inner tube inevitably increases the diameter of the outer tube, thereby increasing the cross-sectional area through which the cooling gas flows. In Comparative Example 3, the cooling gas flow rate was maintained at 150 NL / min, resulting in a cooling gas flow rate approximately half that of Example 1. Since cooling capacity generally depends heavily on flow rate, the temperature of the inner tube rose, resulting in a significant increase in the temperature of the imaging device. The average temperature of the thermocouple (not shown) installed in the inner tube was 67°C, exceeding the allowable temperature of 60°C, causing the relay lens to expand and crack. As a result, neither the imaging field of view nor the imaging device could be protected from high heat was ensured. The cost of the cooling gas supplied between the inner and outer tubes was within acceptable limits, with the actual total usage of gases 37 to 39 being 910 NL / min, which did not result in an increase in cost.

[0057] Comparative Example 4: Molten iron was produced under the same conditions as Example 1, except that the distance from the inner wall of the furnace wall where the imaging device was located to the outside of the furnace was changed to 290 mm. In this case, the imaging device was moved 30 mm closer to the electric furnace compared to Example 1, but the image was distorted and some parts were unclear. This is presumably due to the imaging device being heated more than expected by radiant heat from the molten steel being observed, resulting in insufficient cooling of the inner tube. Furthermore, the temperature of the imaging device rose to an average of 77°C, exceeding the allowable temperature of 60°C, and the imaging device could not be protected from the high heat. The cost of the cooling gas supplied between the inner and outer tubes was an acceptable level, with the actual total usage of gases 37 to 39 being 910 NL / min, which did not result in an increase in cost.

[0058]

[0059] As is clear from Table 1, by installing a video device with a specified structure in a specified position in an electric furnace having a melting chamber and a preheating chamber, it is possible to directly and clearly monitor the behavior inside the melting chamber during operation. This is useful for preventing operational problems before they occur. Operational problems not only shut down the electric furnace for an extended period of time, halting production, but also require repair costs, so observing the inside of the melting chamber and preventing operational problems is extremely effective.

[0060] According to the present invention, in an electric furnace that produces molten iron from a cold iron source using arc heat, the state inside the melting chamber during melting can be directly and clearly observed.

[0061] REFERENCE SIGNS LIST 1 Electric furnace (with imaging device) 2 Melting chamber 3 Preheating chamber 4 Furnace wall 5 Furnace cover 6 Electrode 7 Oxygen blowing lance 8 Carbon material blowing lance 9 Burner 12 Tap hole 13 Slag outlet 14 Supply bucket 15 Cold iron source 16 Molten iron 17 Molten slag 18 Arc 19 Cold iron source supply port 20 Duct 21 Tap door 22 Slag outlet door 23 Traveling cart 30 Imaging device 31 Relay lens 32 Outer tube 33 Inner tube 34 Jig 35 Housing 36 Imaging device (camera) 37 Gas (air for cooling housing) 38 Gas (air for cooling outer tube) 39 Gas (air for cooling relay lens) O Central axis of relay lens P Intersection R Line segment connecting the opening edges at the maximum diameter L Clearance distance

Claims

1. An electric furnace comprising a melting chamber for melting a cold iron source by arc heat to obtain molten iron, and a preheating chamber for preheating the cold iron source supplied to the melting chamber, further comprising an imaging device for observing the inside of the melting chamber, the imaging device having a relay lens composed of a plurality of lenses, an inner tube containing the relay lens and having an outer diameter of 100 mm or less, an outer tube containing the inner tube, and an imaging device provided outside the furnace at the axial tip of the relay lens, the relay lens being positioned 300 mm or more and 3500 mm or less vertically above the highest interface of the molten iron, and the imaging device being positioned 300 mm or more away from the inner wall of the furnace wall or furnace lid constituting the melting chamber in the furnace-outward direction, the imaging device being provided through a hole in the furnace wall or furnace lid. An electric furnace with an imaging device.

2. The electric furnace with an imaging device according to claim 1, further comprising a gas supply device for supplying gas at a flow rate of 50 NL / min or more and 250 NL / min or less between the inner tube and the outer tube.

Images