Method for producing molten iron using electric furnace equipped with imaging device

Abstract

The present invention improves the heating efficiency of molten iron and reduces manufacturing costs. A method for producing molten iron uses an electric furnace equipped with a preheating chamber, a melting chamber, a cold iron source support capable of dividing the preheating chamber into first and second preheating chambers, an extruder, and an imaging device capable of observing the interior of the second preheating chamber. The method includes a melting step, a heating step, a preheating step, and a tapping step. During the heating step, heating of the molten iron is initiated based on visual information obtained from the imaging device regarding the interior of the second preheating chamber after the cold iron source support is closed.

Description

Technical Field

[0001] The present invention relates to a method for producing molten iron from a chilled iron source using an electric furnace equipped with an imaging device. In particular, the present invention relates to a method for producing molten iron in which the chilled iron source is separated from the melting chamber in a preheating chamber and the conditions below the preheating chamber are observed, thereby enabling the chilled iron source to be reliably supplied to the melting chamber and molten iron to be efficiently obtained. Background Art

[0002] When using an electric furnace to produce molten iron, arc heat is used to melt a cold iron source such as iron scrap to produce molten iron. This generates a problem of significant power consumption. Conventionally, methods for reducing power consumption in electric furnaces include (1) preheating the cold iron source prior to melting using high-temperature exhaust gas generated during the subsequent melting process; and (2) blowing carbon materials such as coke into the melting chamber as an auxiliary heat source.

[0003] As a specific method of (1) above, a method is known in which a preheating chamber for preheating a cold iron source is connected to the upper portion of the melting chamber, and the hot exhaust gas generated in the melting chamber in the previous process is passed through the preheating chamber filled with the cold iron source, thereby preheating the cold iron source. By melting the preheated cold iron source in this way, it is expected that the melting efficiency will be improved and the power consumption will be suppressed.

[0004] In the specific method (2) above, there is known a method of generating CO gas by reducing iron oxides injected with carbon material and burning the carbon material, and promoting the foaming of molten slag with this CO gas. This slag foaming reduces the radiant heat of the arc, which is expected to improve the melting efficiency of the cold iron source and suppress power consumption.

[0005] Examples of electric furnaces that utilize the methods (1) and (2) include the composite arc melting furnace disclosed in Patent Document 1 and the arc melting equipment disclosed in Patent Document 2.

[0006] According to Patent Document 1, a composite arc melting furnace is characterized by comprising a melting chamber and a shaft-shaped preheating chamber capable of channeling high-temperature exhaust gas generated within the melting chamber. Furthermore, in the composite arc melting furnace of Patent Document 1, the apparent bulk density of the ferrous scrap in the preheating chamber is adjusted to an appropriate range to effectively preheat the ferrous scrap filled in the preheating chamber. The diagram of Patent Document 1 discloses an openable and closable supply port provided in the upper portion of the preheating chamber. The ferrous scrap supplied through this supply port and preheated in the preheating chamber is sequentially moved into the melting chamber continuously or intermittently, depending on the rate of melting in the melting chamber.

[0007] Furthermore, Patent Document 2 describes, as prior art, a technique for continuously feeding scrap to an electric arc furnace using a pusher (extruder) and a technique for feeding scrap to an electric arc furnace by opening a stopper called a damper (a cold iron source supporter). However, the technique in Patent Document 2, which lacks scrap conveying and feeding equipment such as a pusher or damper, instead preheats the scrap by raising the exhaust gas temperature. Furthermore, Patent Document 2 melts the scrap in the melting furnace, feeding the scrap from the preheating shaft to the melting furnace.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-180560

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 10-292990 Summary of the Invention

[0012] In the production of molten iron, after the cold iron source is melted and the designed amount of molten iron accumulates in the melting chamber, the molten iron is typically heated to a predetermined temperature before tapping. This heating process is used to ensure the molten iron temperature required for the next step, such as composition adjustment or casting, after the molten iron is transported outside the electric furnace. The heating temperature is set to account for the temperature drop during the transportation to the next step. However, the inventors conducted research and discovered the following problem: the techniques of Patent Documents 1 and 2 do not address the complete separation of the next charge of ferrous scrap from the preheating chamber. As a result, during this heating process, cooler ferrous scrap enters the molten iron, reducing heating efficiency. As a result, when part of the next charge of ferrous scrap enters the molten iron, the molten iron temperature drops, prolonging the heating period and resulting in wasted energy loss, thus failing to effectively reduce power consumption.

[0013] Another problem arises: heat is transferred to a portion of the ferrous scrap in contact with the molten iron, causing the scrap in the lower portion of the preheating chamber to partially melt. This causes the scrap in the preheating chamber to collapse and flow into the melting chamber. This has also been observed in serious cases where the scrap flows into the electrodes, causing damage to the electrodes.

[0014] On the other hand, in electric furnace operation, the required composition of molten iron (e.g., the amounts of Cu, Cr, and P) varies depending on the type of steel required, and therefore, multiple chill sources are combined to adjust the composition. However, in the techniques of Patent Documents 1 and 2, when the type of chill source supplied is changed during the next charge, it is impossible to properly separate the iron-based scrap for the current melted charge and the next charge. As a result, part of the iron-based scrap for the next charge melts, making it difficult to strictly control the composition of the molten iron and the production volume.

[0015] Through the above research, the inventors of the present invention have obtained the following insights: In order to improve the heating efficiency and reduce power consumption in molten iron production, and more preferably to strictly control the composition of the molten iron produced, it is necessary to accurately separate the cold iron source in the preheating chamber from the molten iron in the melting chamber when the molten iron is heated.

[0016] Based on the above findings, the present inventors first focused on installing a chill source support device capable of holding a chill source in one area of ​​the preheating chamber, and separating the chill source in the preheating chamber from the melting chamber while the molten iron is heated.

[0017] However, even with the above-mentioned method, the heating efficiency may not be significantly improved. The present inventors conducted further research to address this issue and confirmed that even when the chill source in the preheating chamber is separated from the melting chamber by a chill source support, chill source that has not been supplied to the melting chamber may remain below the chill source support (in the lower part of the preheating chamber), and this residual chill source may accidentally mix into the molten iron during heating. Therefore, they concluded that in order to reliably improve the heating efficiency of the molten iron, it is necessary to ensure that no chill source remains below the chill source support after the chill source is separated from the melting chamber by the chill source support during heating.

[0018] The present invention has been made in view of the above situation and aims to provide a method for producing molten iron using an electric furnace that can improve the heating efficiency of the molten iron and reduce the production cost. In addition, the present invention aims to better control the composition of the obtained molten iron.

[0019] The present inventors have conducted extensive research to address the above-mentioned issues and have discovered that: (1) by providing a chill source support device in the preheating chamber that can divide the preheating chamber into two parts: a chill source inlet side (usually vertically upward) and a melting chamber side (usually vertically downward), the chill source in the preheating chamber can be effectively separated from the melting chamber during heating; (2) by providing an extruder in the preheating chamber, the chill source located below the preheating chamber can be effectively supplied to the melting chamber; and (3) by further providing an imaging device that can observe the bottom of the preheating chamber, it is possible to confirm whether there is a chill source that may accidentally mix into the molten iron during heating. If the presence of such a chill source is confirmed, it is possible to take measures before the molten iron is heated, thereby accurately separating the chill source in the preheating chamber from the melting chamber during heating. It was also discovered that by preventing the accidental mixing of the chill source and heating the molten iron in this way, the heating efficiency can be improved, effectively reducing the power consumption rate in manufacturing.

[0020] The present invention has been completed based on the above findings, and the gist of the present invention is as follows.

[0021] 1. A method for producing molten iron using an electric furnace comprising a preheating chamber for preheating a cold iron source and a melting chamber for melting the preheated cold iron source to produce molten iron.

[0022] The electric furnace further comprises: a chill source support device that can open and close the preheating chamber into a first preheating chamber on the chill source introduction side and a second preheating chamber on the melting chamber side; an extruder that can move forward and backward from the second preheating chamber toward the melting chamber; and an imaging device that can observe the interior of the second preheating chamber.

[0023] The method for producing molten iron comprises the following steps:

[0024] In a melting step, with the cold iron source support device open, the cold iron source supplied to the preheating chamber and preheated is supplied to the melting chamber via the extruder, and the cold iron source supplied to the melting chamber is melted by arc heat to obtain molten iron;

[0025] In the molten iron temperature raising step, the chill source support device is closed (i.e., the first preheating chamber is isolated from the melting chamber), a new chill source (a chill source for the next charge) is introduced into the first preheating chamber, and the molten iron in the melting chamber is heated.

[0026] a preheating step of preheating the new cold iron source in the first preheating chamber by utilizing the residual heat from the heating step; and

[0027] a tapping process for discharging the heated molten iron to the outside of the electric furnace;

[0028] In the temperature raising step, the temperature of the molten iron is started based on the visual information in the second preheating chamber obtained from the imaging device after the cold iron source support machine is turned off.

[0029] 2. The method for producing molten iron according to item 1 above, further comprising a preparation step of opening the chill source support machine after the tapping step is completed to supply the preheated new chill source from the first preheating chamber to the second preheating chamber.

[0030] After the above-mentioned preparation process, the above-mentioned melting process, temperature raising process, preheating process and steel tapping process are carried out in sequence.

[0031] 3. The method for producing molten iron according to item 2 above, wherein, in the preparation step, the cold iron source support device is opened with the front end of the extruder on the melting chamber side positioned at the boundary between the second preheating chamber and the melting chamber.

[0032] 4. The method for producing molten iron according to any one of 1 to 3 above, wherein, in the temperature raising step, the temperature raising of the molten iron is started after confirming by the imaging device that no cold iron source remains in the second preheating chamber after the cold iron source support machine is closed.

[0033] 5. The method for producing molten iron according to any one of 1 to 3 above, wherein in the temperature raising step, when it is confirmed by the imaging device that the chill source remains in the second preheating chamber after the chill source support device is closed,

[0034] The remaining cold iron source is supplied to the melting chamber through the extruder, and after confirming that no cold iron source remains in the second preheating chamber, the temperature of the molten iron is started to be increased.

[0035] 6. The method for producing molten iron according to any one of 1 to 5 above, wherein in the melting step, the temperature raising step is performed after confirming that a predetermined amount of the cold iron source has been supplied to the melting chamber by the imaging device.

[0036] According to the present invention, the heating efficiency of molten iron can be improved, molten iron can be produced with high energy efficiency, and production costs can be reduced. In addition, according to the present invention, it is also possible to accurately control the composition of the obtained molten iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a longitudinal sectional view of an electric furnace equipped with an imaging device used in one embodiment of the present invention.

[0038] Figure 2A This is a conceptual diagram illustrating a preparation process according to one embodiment of the present invention.

[0039] Figure 2B This is a conceptual diagram illustrating a melting step according to one embodiment of the present invention.

[0040] Figure 2C This is a conceptual diagram illustrating a temperature raising step according to one embodiment of the present invention.

[0041] Figure 2D This is a conceptual diagram illustrating a steel tapping process according to one embodiment of the present invention. DETAILED DESCRIPTION

[0042] Next, embodiments of the present invention will be described in detail.

[0043] The following embodiment shows a preferred example of the present invention, and the present invention is not limited to these examples.

[0044] (Method for producing molten iron)

[0045] The method for producing molten iron of the present invention utilizes an electric furnace having a predetermined structure and comprises the following steps, capable of continuous operation: a melting step in which a preheated chill source in a preheating chamber is supplied to a melting chamber using an extruder, where it is melted in the melting chamber using arc heat to produce molten iron; a heating step in which the molten iron is heated while the chill source support is closed; a preheating step in which the chill source is preheated using waste heat from the heating step; and a tapping step in which the heated molten iron is discharged outside the electric furnace. Furthermore, the method for producing molten iron of the present invention may optionally include a preparation step in which, after tapping, the chill source support is opened to supply the preheated chill source from the first preheating chamber to the second preheating chamber; and may optionally include other steps. Furthermore, in the heating step of the present invention, heating of the molten iron is initiated based on visual information obtained from an imaging device for observing the interior of the second preheating chamber.

[0046] By appropriately and timely controlling the molten iron temperature environment based on the visual information in the second preheating chamber, it is possible to prevent the cold iron source from accidentally mixing into the molten iron during the temperature rise process, and to effectively improve the temperature rise efficiency of the molten iron.

[0047] [Electric stove]

[0048] Hereinafter, an electric furnace that can be preferably used in the present invention will be described in detail with reference to the drawings.

[0049] The electric furnace 1 includes a melting chamber 2, in which heat from an electric arc 18 melts a chill source 15 to produce molten iron 16; a vertical preheating chamber 3 connected to the melting chamber 2 to preheat the chill source 15 and supply the preheated chill source 15 to the melting chamber 2 via an extruder 10; and an imaging device 30, which is located at an arbitrary position. An openable and closable chill source support 11 is located at an arbitrary position vertically relative to the preheating chamber 3. The chill source support 11 can be opened and closed, for example, in the cross-sectional or horizontal direction of the electric furnace 1. Opening the chill source support 11 allows the preheating chamber 3 to have a single space. Conversely, closing the chill source support 11 allows the preheating chamber 3 to have two spaces: a first preheating chamber 3a on the chill source inlet side (vertically upper side) and a second preheating chamber 3b on the melting chamber side (vertically lower side). The extruder 10 is usually installed in the second preheating chamber 3b, and its front end can be moved forward and backward to any position between the second preheating chamber 3b and the adjacent melting chamber 2. The imaging device 30 can be used to check the situation in the second preheating chamber 3b at any time as needed.

[0050] The cold iron source 15 as a raw material is temporarily placed in a scrap storage yard, for example, according to its type, and is mixed with the appropriate type and mass ratio corresponding to the steel grade of the molten iron to be manufactured. The mixed cold iron source 15 is loaded into the bottom-opening supply hopper 14 and transported to the desired position above the cold iron source supply port 19 via the traveling trolley 23. Next, the cold iron source supply port 19 is opened, and the cold iron source 15 is supplied to the preheating chamber 3 from above. At this time, since the cold iron source support machine (baffle) 11 that can be opened and closed and is provided in the approximate middle section of the preheating chamber 3 is in an open state, the supplied cold iron source 15 is filled in the first preheating chamber 3a that can occupy the upper part of the cold iron source support machine 11 and the second preheating chamber 3b that can occupy the lower part of the cold iron source support machine 11.

[0051] The supply of the cold iron source 15 can be carried out by loading the cold iron source 15 in multiple batches into the supply bucket 14. For example, if the design of the cold iron source 15 is 130 tons per charge, and this is supplied from the supply bucket 14 in 13 batches, the total is 130 tons (10 tons x 13 times), with 10 tons supplied each time.

[0052] Examples of the cold iron source 15 include, but are not limited to, internal scrap generated in ironworks, urban scrap, and pig iron obtained by solidifying molten iron. The cold iron source 15 may also contain organic matter (e.g., plastic, rubber, biomass).

[0053] On the other hand, examples of slag-forming materials for forming the molten slag 17 include, but are not limited to, calcined lime and limestone. Lightly burned dolomite or recycled slag from steelmaking, etc., may also be used as the slag-forming material. The slag-forming material can be supplied from a secondary raw material chute (not shown) provided above the melting chamber 2.

[0054] In the preheating chamber 3 (the first preheating chamber 3a and the second preheating chamber 3b), the filled cold iron source 15 is preheated by any method. For example, if the cold iron source 15 is preheated by passing the high-temperature exhaust gas previously generated in the melting chamber 2 through the first preheating chamber 3a and the second preheating chamber 3b, it is possible to improve the manufacturing efficiency, so it is preferred. At this time, an exhaust duct 20 can also be provided on the upper side of the preheating chamber 3, and the duct 20 can be connected to a suction fan (not shown). The high-temperature exhaust gas generated in the melting chamber 2 can flow into the preheating chamber 3 and pass through it by suction of the suction fan, rise in the preheating chamber 3, and then be exhausted from the duct 20. A dust collector (not shown) can also be provided in the middle of the duct 20.

[0055] The high-temperature exhaust gas suitable for preheating is generated by the arc heating part as the main heat source, the carbon material as the auxiliary heat source, and the melting and heating by the burner 9, etc., and may contain CO, CO2, unreacted O2 and external air flowing in from the opening, etc.

[0056] The second preheating chamber 3b is provided with an extruder 10 (an impeller) for extruding and supplying the preheated chill source 15 within the second preheating chamber 3b into the melting chamber 2 connected to the preheating chamber 3. The extruder 10 can be arranged to penetrate the side wall of the melting chamber 2 and be able to advance and retreat toward the arc heating portion generated by the arc 18 (in this embodiment, the approximate center of the melting chamber). This extruder 10 can thereby extrude the preheated chill source 15 from the second preheating chamber 3b toward the arc heating portion of the melting chamber 2. The extruder 10 can also be driven by a drive device (not shown).

[0057] The boundary between the melting chamber 2 and the preheating chamber 3 (second preheating chamber 3 b ) is an imaginary surface extending vertically downward from a portion of the side wall of the preheating chamber 3 connected to the furnace cover 5 constituting the melting chamber 2 .

[0058] The melting chamber 2 is divided by a furnace wall 4 and a furnace cover 5. The furnace wall 4 is preferably water-cooled, and the furnace cover 5 is preferably an openable and closable water-cooled structure. Multiple electrodes 6 are inserted from above through the furnace cover 5 in the approximately horizontal center of the melting chamber 2. An arc 18 is generated between these electrodes 6, thereby forming an arc heating unit that serves as the main heat source for melting the cold iron source 15. The electrodes 6 are typically made primarily of graphite and are movable up and down.

[0059] Electric furnaces 1 can be of either direct current or alternating current types. The electric furnace 1 illustrated in this embodiment is of the alternating current type and includes the aforementioned electrodes 6. Alternatively, when the electric furnace 1 is of the direct current type, electrodes may be provided at the furnace bottom and at the upper portion of the melting chamber, respectively, so that arcs are generated between these electrodes to melt the cold iron source. The present invention is also applicable to the production of molten iron using a direct current electric furnace.

[0060] An oxygen injection lance 7 and a carbon material injection lance 8 can be inserted from above into the melting chamber 2 through the furnace roof 5. The carbon material injection lance 8 can inject a carbon material composed of one or more of coke, charcoal, coal, charcoal, graphite, etc., serving as an auxiliary heat source, into the molten slag 17 using a transport gas such as air or nitrogen. Furthermore, the oxygen injection lance 7 can supply oxygen (pure oxygen, for example, an oxygen-containing gas mixed with air) by jetting, pushing the molten slag 17 away and injecting oxygen directly into the molten iron 16. The molten iron 16 injected with oxygen is decarburized to a desired carbon content.

[0061] As a method for adding oxygen and carbon material, in addition to blowing with a lance, other methods may be used, such as injection from above the melting chamber 2 into the bath (molten iron 16 or molten slag 17), or bottom blowing injection using a dedicated nozzle installed at the furnace bottom. Furthermore, the oxygen and carbon material injection lances 7 and 8 may be immersed in the molten iron 16 and molten slag 17, respectively. However, as in the embodiment shown in FIG2 , they may be arranged not to be immersed in the molten iron 16 and molten slag 17 but to follow the liquid level (interface) of the molten iron 16 and molten slag 17 above the interface in response to fluctuations in their height. Alternatively, oxygen injection lance 7 may be installed at the furnace wall 4 to inject oxygen from the furnace wall 4.

[0062] In the melting chamber 2, a burner 9 can also be inserted from above through the furnace cover 5 and / or from obliquely above through the furnace wall 4. The burner 9 acts as a combustion-supporting burner that uses combustion-supporting gas (oxygen, air or oxygen-enriched air) to burn fossil fuels such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas. When the molten iron 16 is tapped, it is necessary to be in a state where no unmelted cold iron source 15 remains in the molten iron 16. Here, the cold iron source around the electrode melts earlier, but the cold iron source at a place far away from the electrode, that is, at the so-called cold spot, melts slower, and sometimes the melting rate of the cold iron source in the melting chamber becomes uneven. In such a case, for example, the burner 9 can be used in the heating process to effectively assist in the melting of the unmelted cold iron source 15. The burner 9 is preferably arranged in a position near the top of the water outlet 12 described later, in other words, a position where a cold spot is likely to occur.

[0063] In the melting chamber 2, a water outlet 12 may be further provided at the furnace bottom on the side opposite to the preheating chamber 3, and a slag outlet 13 may be provided on the furnace wall 4 above the water outlet 12. In processes other than the steel tapping process, the slag outlet 13 is closed by a slag tapping door 22. In addition, in processes other than the steel tapping process, the water outlet 12 is closed by a water outlet door 21 that squeezes the sand and slurry filled inside and squeezes them outside the furnace. The obtained molten iron 16 can be tapped from the water outlet 12 by opening the water outlet door 21. In addition, the molten slag 17 generated along with the production of the molten iron 16 can be discharged from the slag tapping door 13 by opening the slag tapping door 22.

[0064] The interior of the second preheating chamber can be observed using an imaging device 30. The imaging device 30 is not particularly limited; any device capable of capturing an image of the object being observed will suffice, typically comprising a lens and a camera. A cooling gas of any flow rate is preferably passed around a lens (not shown) located at the front end of the imaging device 30. Proper cooling of the imaging device 30 allows it to withstand the high temperatures within the electric furnace and prevents the field of view from being narrowed by the scattering of slag and molten steel. Examples of the cooling gas include air and inert gases such as nitrogen.

[0065] To better understand the conditions within the second preheating chamber 3b, the imaging device 30 is preferably installed on a side wall forming the second preheating chamber 3b. In this case, the side wall of the preheating chamber 3b is preferably also cooled by water or air. While the installation method is not particularly limited, if the imaging device 30 is installed on the side wall of the second preheating chamber 3b, it is preferable to install the imaging device 30 through a hole (not shown) in the side wall. This allows the lens to be located within the second preheating chamber 3b while the camera is located outside the electric furnace 1, achieving both a clear field of view and ease of operation. The images captured by the imaging device 30 are typically connected via a cable (not shown) to a monitor or recording device (neither shown) in the operator's operating room.

[0066] Furthermore, although not shown, it is preferable to utilize an imaging device to monitor the conditions within the first preheating chamber 3a. If the conditions within the first preheating chamber 3a can also be visually monitored, for example, the level of the chill source 15 filling the preheating chamber can be monitored while the chill source is supplied to maintain that level within a certain range. This allows for more efficient preheating of the chill source. To monitor the conditions within the first preheating chamber 3a, for example, an additional imaging device can be installed on a side wall constituting the first preheating chamber 3a.

[0067] [Melting process]

[0068] In the melting step of the present invention, referring to Figure 2B With the chill source support 11 open, the extruder 10 supplies chill source 15 preheated in the preheating chamber 3 to the melting chamber 2. Arc heat melts the chill source 15 supplied to the melting chamber 2, producing molten iron 16. By repeatedly moving the extruder 10 forward and backward in the direction of the arrows in Figure 2, the chill source 15 filling the second preheating chamber 3b is gradually lowered. Simultaneously, the chill source 15 filling the preheating chamber 3 gradually descends, and accordingly, the supply of new chill source 15 from the supply bucket 14 to the preheating chamber 3 is repeated. This allows the chill source for a single charge to be melted.

[0069] From the perspective of manufacturing efficiency, it is preferable to allow high-temperature exhaust gas generated in the melting chamber during melting to flow into the preheating chamber 3, for example, as described above with respect to the electric furnace, to effectively preheat the cold iron source 15 filling the preheating chamber 3. In this embodiment, the temperature of the exhaust gas flowing into the preheating chamber 2 is approximately 1000-1500°C.

[0070] The molten slag 17 in the melting process sometimes contains iron oxide (FeO) generated by the injection of oxygen. Therefore, it is preferable to inject a carbon material into the molten slag 17 in accordance with the above-mentioned method to reduce the FeO. In addition, it is preferable to generate CO gas by burning the injected carbon material, thereby forming a so-called "slag foaming" state in which the molten slag 17 foams. The slag foaming reduces the radiation heat of the arc 18, and the melting efficiency of the cold iron source 15 can be further improved. By shortening the melting time with higher melting efficiency, the time during which the slag foaming state can be stably maintained can be extended, and energy efficiency can be further improved.

[0071] In the melting step, it is preferred that the supply of a predetermined amount of the chill source 15 for a single charge to the melting chamber 2 be visually confirmed by the imaging device 30 before the process shifts to the next heating step and the chill source support device 11 is turned off. Thus, by confirming, using the imaging device 30, that the predetermined amount of the chill source 15 for a single charge has been supplied to the melting chamber 2, it is possible to further prevent the chill source 15 from accidentally entering the molten iron during the subsequent heating of the molten iron 16, allowing the next heating step to be carried out more efficiently.

[0072] It should be noted that, at the start of a certain charging operation in the electric furnace 1 (i.e., at the initial supply of the chill source 15), in order to uniformly supply the chill source 15 to the melting chamber 2, the chill source 15 and, if necessary, the carbon material may be pre-supplied into the space of the melting chamber 2 opposite the preheating chamber 3 (to the right of the electrode 6 in FIG. 2 ) with the furnace lid 5 open. Alternatively, molten iron may also be supplied to the melting chamber 2 at the same time as the chill source 15 is supplied. The molten iron may be supplied to the melting chamber 2 via a supply ladle (not shown) or a molten iron tank (not shown) connected to the melting chamber 2.

[0073] [Heating process]

[0074] In the temperature raising step of the present invention, Figure 2CWith the chill source support 11 closed and the first preheating chamber 3a isolated from the melting chamber 2, the molten iron 16 obtained in the previous melting step is further heated to the desired temperature. After the heating step, the molten iron 16 is tapped and transferred to the next step outside the electric furnace, such as composition adjustment and casting, and must maintain the desired high temperature required for that next step. Therefore, during the heating step, the molten iron 16 must be heated to a temperature specified by the design, taking into account the temperature drop after the tapping step when transferring to the next step outside the electric furnace. If the molten iron 16 is not heated to the specified temperature, tapping will not be possible. Furthermore, during the heating step, with the chill source support 11 closed and the first preheating chamber 3a isolated from the melting chamber 2, a new chill source 15 for the next charge is introduced into the first preheating chamber 3a. During this heating step, it is important to initiate heating of the molten iron 16 based on the visual information obtained from the imaging device 30 within the second preheating chamber 3b after the chill source support 11 is closed. For example, if the chill source 15 remains in the second preheating chamber 3b after the chill source support device 11 is turned off and has not been supplied to the melting chamber 2, if the temperature is increased in this state, the relatively low-temperature chill source 15 will undesirably mix into the relatively high-temperature molten iron 16 being heated, causing the temperature of the molten iron 16 to drop. This reduces the efficiency of the heating process, which consumes a lot of electricity, and leads to increased manufacturing costs. Therefore, it is necessary to visually confirm the situation in the second preheating chamber 3b before starting the heating process.

[0075] In the prior art, the condition of the second preheating chamber 3b could not be visually confirmed, so the timing of heating was determined based on the operator's experience. However, the present invention uses visual information to confirm that there are no factors hindering heating efficiency and then determines the timing of heating. This significantly improves heating efficiency and, by extension, manufacturing efficiency.

[0076] Based on the above viewpoint, during the heating process, it is preferred to visually confirm, using the imaging device 30, that no chill 15 remains in the second preheating chamber 3b after the chill support device 11 is closed, before starting to heat the molten iron 16. Once the imaging device 30 confirms that no chill 15 remains, heating can be started immediately.

[0077] On the other hand, when it is confirmed by the imaging device 30 that the cold iron source 15 remains in the second preheating chamber 3b after the cold iron source support machine 11 is turned off, it is preferred to forcibly supply the remaining cold iron source 15 to the melting chamber 2 through the extruder 10, and then start heating the molten iron 16 after confirming that no cold iron source 15 remains in the second preheating chamber 3b.

[0078] In this manner, by heating the molten iron 16 without the presence of the cold iron source 15 in the second preheating chamber 3 b , the heating efficiency can be further improved without lowering the temperature of the molten iron 16 being heated.

[0079] As in the melting process, it is also preferable to maintain a stable slag foaming state during the heating process to further improve energy efficiency. In the prior art, there are cases where the cold iron source 15 flows from the preheating chamber 3 into the melting chamber 2 during the heating process, causing the slag foaming to subside. This can cause the arc 18 to become unstable, thereby reducing the heating efficiency. In contrast, in this embodiment, the cold iron source 15 in the first preheating chamber 3a during the heating process is physically and completely isolated from the melting chamber 2 by the cold iron source support device 11, and the state of the second preheating chamber 3b suitable for starting the heating process can be visually confirmed. Therefore, the influx of the cold iron source 15 during the heating process can be reliably suppressed, and the slag foaming and arc 18 can be stably maintained, thereby improving the heating efficiency.

[0080] Here, during the heating process, the chill source 15 for the next charge is supplied to the first preheating chamber 3a. During the heating process, the chill source support device 11 is closed, isolating the first preheating chamber 3a from the melting chamber 2, and the conditions in the second preheating chamber can be visually confirmed. Therefore, even if the chill source 15 for the current charge remains in the second preheating chamber 3b, it can be accurately separated from the chill source 15 for the next charge in the first preheating chamber 3a. In the prior art, due to the lack of a chill source support device 11 or the inability to visually confirm the conditions in the second preheating chamber 3b, the separation of the chill source 15 for the current charge from the next charge is performed based on operator experience. However, the present invention includes a chill source support device 11, an image processing device 30, and an extruder 10 capable of forcibly supplying the remaining chill source 15 to the melting chamber 2. This allows accurate separation of the chill source 15 for the current charge without mixing with the chill source 15 for the next charge. This is particularly useful when, in the next charge, hot metal 16 is to be produced having a composition or properties different from those of the current charge.

[0081] [Preheating process]

[0082] In the preheating process of the present invention, the new cold iron source (cold iron source for the next charge) 15 in the first preheating chamber 3a is preheated by the residual heat from the heating process. Therefore, the preheating process and the heating process are carried out approximately simultaneously. Preheating can be carried out by, for example, allowing the residual heat such as high-temperature exhaust gas generated during the heating process to flow into the first preheating chamber 3a by the method described above for the electric furnace. In the heating process, the melting chamber 2 is brought to a high temperature state of, for example, about 1600°C, so that the cold iron source 15 for the next charge filled in the first preheating chamber 3a can be effectively preheated, thereby improving the melting efficiency of the next charge. In the preheating process, the temperature of the exhaust gas flowing into the first preheating chamber 3a is about 1000-1600°C.

[0083] After the molten iron 16 is heated to a set temperature, it is transferred to the next steel-making process.

[0084] [Steel tapping process]

[0085] In the steel-discharging process of the present invention, referring to Figure 2D With the cold iron source support 11 closed, the heated molten iron 16 is led out of the electric furnace 1. In this way, a single charge of molten iron 16 can be obtained. The specific tapping method can be the same as that described above for the electric furnace.

[0086] Furthermore, during the steel tapping process, it is preferable to continue preheating the chill source 15 for the next charge within the first preheating chamber 3a. During the steel tapping process, the chill source 15 for the next charge within the first preheating chamber 3a can be preheated by, for example, allowing residual heat, such as high-temperature exhaust gas remaining from the heating process, to continue flowing into the first preheating chamber 3a using the method described above for electric furnaces. The temperature of the exhaust gas flowing into the first preheating chamber 3a is approximately 1100-1600°C.

[0087] [Preparation process]

[0088] In the preparatory step that the manufacturing method of the present invention may optionally have, refer to Figure 2A After the tapping process is complete, the chill source support 11 is opened, and a new chill source (the chill source for the next charge) 15, preheated during the heating process and, if necessary, the tapping process, is supplied from the first preheating chamber 3a to the second preheating chamber 3b. This completes the preparations for the next charge. The melting, heating, preheating, and tapping processes are then repeated sequentially for the chill source 15 for the next charge, enabling continuous operation for multiple charges. The chill source 15 supplied to the second preheating chamber 3b during the preparation process is already sufficiently preheated, allowing for efficient subsequent melting and subsequent processes.

[0089] In the preparation process, it is preferable to place the front ends of the melting chamber of the extruder 10 at the boundary between the second preheating chamber 3b and the melting chamber 2 (see Figure 2A ), open the cold iron source support machine 11. This can prevent the cold iron source 15 from rushing into the melting chamber 2 during the next melting step, prevent a decrease in melting efficiency, and prevent damage to the electrodes, etc.

[0090] [Other processes]

[0091] The other steps are not particularly limited, and an example thereof includes a slag discharge step of discharging the generated molten slag 17 out of the electric furnace. The slag discharge step can be performed, for example, according to the method described above with respect to the electric furnace.

[0092] Example

[0093] Below, based on embodiment, the present invention is specifically described.It should be noted that the following examples represent a preferred example of the present invention and do not limit the present invention in any way.In addition, the following examples can also be changed and implemented within the scope that can meet the gist of the present invention, and such a mode is also included in the technical scope of the present invention.

[0094] Invention Examples

[0095] exist Figure 1 The electric furnace shown includes a melting chamber 2, a preheating chamber 3, a chill source support 11, an extruder 10, and an imaging device 30 installed in the second preheating chamber 3b. The chill source is melted to produce molten iron. The equipment specifications of the electric furnace are shown below.

[0096] Melting chamber: furnace diameter 7m, furnace height 5m

[0097] Preheating chamber: width 3m, depth 4m, height 8m

[0098] Furnace capacity: 210 tons

[0099] Power: AC 50Hz

[0100] Transformer capacity: 75MVA

[0101] Number of electrodes: 3

[0102] In addition, the basic operating conditions of the electric furnace are shown below.

[0103] Supply volume of cold iron source per charge: approximately 130 tons

[0104] Supply of cold iron source per time: about 10 tons

[0105] Number of times each charge of the cold iron source is supplied: 13 times

[0106] Steel output per charge: approximately 120 tons

[0107] Oxygen consumption rate of oxygen blown into the spray gun: about 20Nm 3 / Ton of steel

[0108] Carbon material consumption rate of carbon material blown into the lance: about 20kg / ton of steel

[0109] Lime consumption rate as slag material: about 18.8kg / ton of steel

[0110] Among them, "steel-producing ton" refers to the capacity of molten iron produced by steel (unit: ton), and " / steel-producing ton" refers to the molten iron produced per 1 ton of steel.

[0111] The cold iron source was prepared according to the raw materials specified in the "Unified Standards for Acceptance of Iron-Based Scrap" of the Japan Iron Source Association, and was used in the following blending (total blending ratio: 100%).

[0112] Heavy scrap iron (grade: H2), mix ratio 60%

[0113] Factory scrap (grade: raw material A), mixing ratio 20%

[0114] Crusher (grade: A), mixing ratio 10%

[0115] Cast iron scrap (grade: A), mix ratio 5%

[0116] Lathe grinding steel powder (grade: A), mixing ratio 5%

[0117] When producing molten iron of the same composition continuously in 20 charges, 210 tons of cold iron source 15 are first supplied to the melting chamber 2 and preheating chamber 3, and melting is performed with the cold iron source 15 continuously present in the melting chamber 2 and preheating chamber 3. The temperature is raised after approximately 200 tons of molten iron 16 is generated in the melting chamber 2. Then, 80 tons of molten iron 16 remain in the melting chamber 2, and the 120 tons of molten iron 16 from the first charge is discharged from the outlet 12 into a ladle outside the furnace.

[0118] During the temperature increase described above, with the chill source support device 11 closed, a single batch of approximately 10 tons (or a multiple of that amount) of chill source 15 is supplied to the first preheating chamber 3a. At this time, the temperature increase process for the previous charge is already underway, and the chill source 15 in the first preheating chamber 3a is being preheated using the exhaust gas from the melting chamber 2. During the subsequent tapping process for the previous charge, the chill source 15 in the first preheating chamber 3a continues to be preheated using the exhaust gas from the melting chamber 2.

[0119] <Preparation process>

[0120] After the tapping process of the previous charge is completed, the cold iron source support device 11 is opened to supply the preheated cold iron source 15 from the first preheating chamber 3a to the second preheating chamber 3b. At this time, the front ends of the melting chamber of the extruder 10 are located at the boundary between the second preheating chamber 3b and the melting chamber 2.

[0121] Melting process

[0122] With the cold iron source support 11 open, the cold iron source 15 in the second preheating chamber 3b is supplied to the melting chamber 2 via the extruder 10. The cold iron source 15 is melted by the heat of the arc 18 generated by the electrode 6 (graphite electrode) to produce molten iron 16. Oxygen is blown into the lance 7 at a speed of 3000 to 5000 Nm 3Pure oxygen is supplied at a rate of 40-80 kg / min from the carbon material injection lance 8. The coke powder has a fixed carbon content of 85% or more, a moisture content of 1.0% or less, a volatile content of 1.5% or less, and an average particle size of 5 mm or less. Quicklime, used as a slag-forming material, is supplied from a secondary raw material chute (not shown) located in the furnace roof 5.

[0123] During the melting process, the interior of the second preheating chamber 3b was monitored by a video device 30. As the chill source 15 in the melting chamber 2 melted and extruded by the extruder 10, the chill source 15 in the preheating chamber 3 gradually decreased. Approximately 10 tons of new chill source 15, delivered from the supply hopper 14, was replenished from the chill source supply port 19 into the preheating chamber 3, maintaining the chill source 15 filling level within a certain range. This process was repeated 13 times, allowing melting to proceed with the chill source 15 continuously present in the melting chamber 2 and preheating chamber 3. A total of approximately 130 tons of chill source 15, a primary charge, was melted in the melting chamber 2.

[0124] In fact, including the 80 tons of molten iron 16 remaining in the melting chamber 2 from the previous charge, approximately 200 tons of molten iron 16 are accumulated in the melting chamber 2. If it is desired to change the composition of the molten iron obtained before and after the charge, the molten iron 16 from the previous charge can be melted without leaving it in the melting chamber 2.

[0125] <Heating process>

[0126] When approximately 200 tons of molten iron 16 accumulates in the melting chamber 2, the chill source support 11 is shut down, and the condition of the second preheating chamber 3b is checked using the imaging device 30. Visual information obtained from the imaging device 30 confirms that the chill source 15 remains in the second preheating chamber 3b. Therefore, heating is not immediately initiated, and the extruder 10 repeatedly advances and retreats until the remaining chill source 15 is supplied to the melting chamber 2 and no longer visible in the second preheating chamber 3b. After confirming that the chill source 15 is no longer present in the second preheating chamber 3b, heating is initiated. After approximately 3 to 4 minutes of heating, a temperature measuring probe is inserted into the molten iron 16 to measure its temperature. If the molten iron temperature reaches the designed heating temperature of 1600°C, the process proceeds to the tapping step. If the heating temperature has not yet been reached, the temperature is further increased for approximately 1 minute, and the molten iron temperature is measured again to repeatedly confirm whether tapping is possible.

[0127] In the temperature raising step, with the chill source supporter 11 closed, a chill source 15 of about 10 tons as a first charge for the next charge is supplied to the first preheating chamber 3a.

[0128] <Preheating process>

[0129] The next charge supplied to the first preheating chamber 3a is preheated by the cold iron source 15 simultaneously with the temperature raising process, and is preheated by the preheat (exhaust gas) from the melting chamber 2 generated by the temperature raising.

[0130] <Steel tapping process>

[0131] After heating, 80 tons of the approximately 200 tons of molten iron 16 remain in the melting chamber 2, and 120 tons of molten iron 16, equivalent to a single charge, is tapped from the tapping port 12 into a ladle outside the furnace. During the tapping process, the exhaust gas from the melting chamber 2 continues to preheat the cold iron source 15 in the first preheating chamber 3a. The temperature of the molten iron 16 at the time of tapping is approximately 1600°C. The carbon concentration in the molten iron is controlled to a target of 0.060 mass%. After the tapping process, oxygen and coke are injected while maintaining the state of the molten iron 16, and the above-mentioned <preparation process> and subsequent charging steps are repeated a total of 20 times.

[0132] Comparative Example 1

[0133] During the heating process, the chiller 11 and the imaging device 30 were not used (i.e., the chiller 11 was kept open during all steps and the conditions inside the furnace were not visually checked). The extruder 10 was operated based on the operator's experience to increase the temperature. Otherwise, the same charging process as in the inventive example was repeated 20 times.

[0134] Comparative Example 2

[0135] In the heating process, the imaging device 30 was not used (ie, the condition inside the furnace was not visually checked), and the operator operated the cold iron source support device 11 and the extruder 10 based on their experience to increase the temperature.

[0136] For the inventive examples and comparative examples, the average time (minutes) required for each step during 20 charges, the average power consumption rate (kWh / t) required for the entire manufacturing process, the frequency of mixing of the cold iron source into the molten iron during the heating process (times / charge), the average noise level (dB) in the operating electric furnace, and the average carbon concentration (mass %) in the molten iron were evaluated. The results are shown in Table 1.

[0137] Here, the average power consumption rate was calculated as the amount of power used per ton of the volume of molten iron for 20 charging tappings.

[0138] The mixing frequency of the chill source was calculated by dividing the number of loud noises produced when the chill source collapsed, which was confirmed by ear, by the number of charges.

[0139] The noise level of the electric furnace is measured using a decibel meter placed 5 meters from the furnace. The noise level of the electric furnace is an indicator of the quality of slag foaming; lower noise levels indicate more stable arcs. Measurements are performed during the melting and heating steps, and the average value is calculated.

[0140] The carbon concentration in the molten iron was measured by inserting a carbon concentration measuring probe into the molten iron together with the temperature measuring probe, and the average value of all the charges was calculated.

[0141]

[0142] Table 1 shows that, compared to Comparative Examples 1 and 2, the inventive example significantly shortens the time required for the melting and heating steps, thereby shortening the time required for the entire production process and reducing power consumption. While power consumption is 385 kWh / t in Comparative Example 1 and 380 kWh / t in Comparative Example 2, the inventive example is as low as 365 kWh / t, enabling power-efficient operation (where t is the volume of molten iron, i.e., tons).

[0143] The reduction in power consumption in the inventive example is primarily due to the use of an imaging device, which enables appropriate control of the chill support mechanism to reliably suppress the collapse and influx of the chill during the heating process. This effectively prevents unintended mixing of the chill into the molten iron during the heating process, thereby significantly shortening the heating process. Furthermore, it is speculated that the reduced noise level in the inventive example also resulted in improved slag foaming and melting efficiency. Furthermore, it is speculated that the additional imaging device installed on the side wall of the first preheating chamber 3a during the melting process allows the chill filling level in the preheating chamber 3 to be confirmed and appropriately maintained within a certain range. This improves the efficiency of exhaust gas heating the chill, thereby enhancing melting efficiency.

[0144] Furthermore, with respect to the carbon concentration in the molten iron, the target carbon concentration of 0.060 mass% was 0.055 mass% in Comparative Example 1, 0.057 mass% in Comparative Example 2, and 0.059 mass% in the inventive example. These values ​​are closer to the target carbon concentration of 0.060 mass%, making it possible to more easily and accurately control the carbon concentration in the molten iron. It should be noted that the decrease in carbon concentration in the comparative example is presumably due to the mixing of the cold iron source 15 into the molten iron 16 during the heating process, thereby reducing the heating efficiency.

[0145] Industrial applicability

[0146] According to the present invention, the temperature-raising efficiency of molten iron can be improved, and molten iron can be produced with high energy utilization efficiency.

[0147] Explanation of symbols

[0148] 1 electric stove

[0149] 2 Melting Chamber

[0150] 3 Preheating chamber

[0151] 3a First preheating chamber

[0152] 3b Second preheating chamber

[0153] 4 Furnace wall

[0154] 5 Furnace cover

[0155] 6 electrodes

[0156] 7 Oxygen blowing into the spray gun

[0157] 8 Carbon material blown into the spray gun

[0158] 9 Burner

[0159] 10 Extruder (propeller)

[0160] 11. Cold iron source support machine (baffle)

[0161] 12 Water outlet

[0162] 13 slag outlet

[0163] 14 Supply bucket

[0164] 15 Cold Iron Source

[0165] 16 molten iron

[0166] 17 Molten slag

[0167] 18 Arc

[0168] 19 Cold iron source supply port

[0169] 20 Pipeline

[0170] 21 Water outlet door

[0171] 22 Slag discharge door

[0172] 23 Traveling trolley

[0173] 30 video installations.

Claims

1. A method for producing molten iron using an electric furnace comprising a preheating chamber for preheating a cold iron source and a melting chamber for melting the preheated cold iron source to produce molten iron. The electric furnace also has: a cold iron source support device, which divides the preheating chamber into a first preheating chamber on the cold iron source introduction side and a second preheating chamber on the melting chamber side and is openable and closable; an extruder capable of moving forward and backward from the second preheating chamber toward the melting chamber; as well as an imaging device, disposed on a side wall of the second preheating chamber, capable of observing conditions within the second preheating chamber; The method for producing molten iron comprises the following steps: a melting step in which, with the cold iron source support device turned on, the cold iron source supplied to the preheating chamber and preheated is supplied to the melting chamber by the extruder, and the cold iron source supplied to the melting chamber is melted by arc heat to obtain molten iron; a heating step of closing the cold iron source support machine, introducing a new cold iron source into the first preheating chamber, and heating the molten iron in the melting chamber; a preheating step of preheating the new cold iron source in the first preheating chamber by utilizing the residual heat from the heating step; and a tapping process of discharging the heated molten iron to the outside of the electric furnace; In the temperature raising step, the temperature of the molten iron is started to be raised based on the visual information in the second preheating chamber obtained from the imaging device after the cold iron source support machine is closed.

2. The method for producing molten iron according to claim 1, wherein: The method further comprises a preparation step of opening the cold iron source support machine after the steel tapping step is completed and supplying the preheated new cold iron source from the first preheating chamber to the second preheating chamber. After the preparation process, the melting process, the temperature rising process, the preheating process and the steel tapping process are carried out in sequence.

3. The method for producing molten iron according to claim 2, wherein: In the preparation step, the cold iron source support device is opened in a state where the front end of the extruder on the melting chamber side is located at a boundary between the second preheating chamber and the melting chamber.

4. The method for producing molten iron according to any one of claims 1 to 3, wherein: In the temperature raising step, the temperature of the molten iron is started after confirming through the imaging device that no chill source remains in the second preheating chamber after the chill source supporting machine is turned off.

5. The method for producing molten iron according to any one of claims 1 to 3, wherein: In the heating process, when it is confirmed by the imaging device that the cold iron source remains in the second preheating chamber after the cold iron source support machine is turned off, The remaining cold iron source is supplied to the melting chamber by the extruder, and after confirming that the cold iron source does not remain in the second preheating chamber, the temperature of the molten iron is started to be increased.

6. The method for producing molten iron according to any one of claims 1 to 3, wherein: In the melting step, the temperature raising step is performed after confirming that a predetermined amount of the cold iron source has been supplied to the melting chamber using the imaging device.

Images