In-furnace monitoring apparatus, melting furnace, and method for producing molten iron

Abstract

Provided is an in-furnace monitoring apparatus that makes it possible to clearly observe conditions in a melting furnace for melting a cold iron source. Also provided are: a melting furnace equipped with said device and capable of efficiently producing molten iron; and a method for producing molten iron using said melting furnace. The in-furnace monitoring apparatus comprises: a leading-end lens; a relay lens formed of one or more lenses; an inner tube that includes the leading-end lens and the relay lens; an outer tube that includes the inner tube; an imaging device that is disposed outside a furnace in the axial direction of the relay lens; and a band-pass filter that is provided in front of the imaging device in the imaging direction. The leading-end lens and the relay lens are far-infrared lenses. The imaging device is a far-infrared camera. The bandpass filter transmits therethrough a wavelength region that includes at least a part of the far-infrared wavelength region.

Description

In-furnace monitoring device, melting furnace, and method for producing molten iron

[0001] The present invention relates to an in-furnace monitoring device, a melting furnace, and a method for producing molten iron.

[0002] Molten iron can be produced by melting cold iron sources such as iron-based scrap using a melting furnace such as an electric furnace. At this time, the melting rate of the cold iron source in the melting chamber of the melting furnace may become non-uniform. For example, the cold iron source around an electrode melts quickly, whereas the cold iron source located away from the electrode, at a so-called cold spot, tends to melt slowly. This causes the problem that the operation of the melting furnace is rate-limited by the melting rate of the cold iron source present at the cold spot.

[0003] Accordingly, in order to melt the cold iron source throughout the melting chamber in a well-balanced manner, a method has been adopted in which a burner (combustion-supporting burner) is installed at a position where cold spots are likely to occur, and the burner promotes melting of the cold iron source present at the cold spot. For example, Patent Document 1 discloses a specific example of a combustion-supporting burner for an electric furnace for promoting melting of cold spots. By using the combustion-supporting burner, the cold iron source in the melting chamber can be melted more uniformly. However, when a combustion-supporting burner is used, if the cold iron source present at the cold spot still remains unmelted, the melting efficiency cannot be sufficiently improved. Further, if the cold iron source present at the cold spot is excessively heated, instead of eliminating the cold spot, hot spots are exacerbated, which in turn makes the temperature of molten iron in the melting chamber non-uniform. Therefore, an operator who operates the combustion-supporting burner needs to determine whether the cold iron source at the cold spot has been sufficiently melted.

[0004] Further, usually, additional charging of a cold iron source is performed in an electric furnace. At this time, if additional charging is performed in a state where the melting amount of the cold iron source before charging is insufficient, the bulk of the cold iron source exceeds the position of the furnace lid, causing a trouble that the furnace lid cannot be closed. On the other hand, if the cold iron source is completely melted before additional charging, heat loss occurs due to radiant heat from the molten steel. Therefore, the operator needs to determine the melting state of the cold iron source before additional charging.

[0005] It is difficult to directly visually check the state of the cold iron source inside the melting chamber when operating the auxiliary burner or adding additional cold iron source. For example, the state inside the melting chamber can be checked by opening the slag door or furnace lid, but when opened, excess air enters from outside the furnace into the furnace, causing significant heat loss. Furthermore, the operator needs to get close to the furnace body, which could lead to accidents if the molten iron or slag boils over. Therefore, determining whether the cold iron source has melted sufficiently relies on the operator's experience, and optimizing operational methods such as burner ignition and extinguishing and additional cold iron source charging has been virtually impossible.

[0006] Therefore, methods for monitoring the inside of a furnace using an imaging device are being considered. Patent document 2 proposes a technology that uses a furnace monitoring device to image the inside of a furnace with a television camera and monitor the internal conditions using television images.

[0007] JP-A No. 10-9524 JP-A No. 07-103670

[0008] However, when we attempted to insert the furnace monitoring device disclosed in Patent Document 2 into an electric furnace to observe how the cold iron source in the cold spot was melted by the burner, visibility deteriorated while the power was on, making it impossible to continue monitoring.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a furnace monitoring device that can clearly observe the conditions inside a melting furnace in which a cold iron source is melted. Furthermore, the present invention aims to provide a melting furnace equipped with the device that can efficiently obtain molten iron, and a method for producing molten iron using the melting furnace.

[0010] As a result of diligent research, the inventors have found that the above objective can be achieved by adopting the following configuration.

[0011] 1. A furnace monitoring device comprising: a tip lens; a relay lens consisting of one or more lenses; an inner tube enclosing the tip lens and the relay lens; an outer tube enclosing the inner tube; an imaging device provided on the outside of the furnace in the axial direction of the relay lens; and a bandpass filter provided in front of the imaging device in the imaging direction, wherein the tip lens and the relay lens are far-infrared lenses; the imaging device is a far-infrared camera; and the bandpass filter transmits wavelengths including at least a portion of the far-infrared wavelength range.

[0012] 2. The in-furnace monitoring device according to claim 1, wherein the tip lens and relay lens transmit wavelengths including 7.5 to 14.0 μm, and the imaging device images wavelengths including 7.5 to 14.0 μm.

[0013] 3. The furnace monitoring device according to 1 or 2, wherein, in the transmission wavelength range of the bandpass filter, the wavelength on the short-wavelength side at which the transmittance is half of the maximum transmittance is 8.0 μm or more, and the wavelength on the long-wavelength side at which the transmittance is half of the maximum transmittance is 13.0 μm or less.

[0014] 4. The furnace monitoring device according to item 3, wherein, in the transmission wavelength range of the bandpass filter, the wavelength on the short-wavelength side at which the transmittance is half of the maximum transmittance is 11.0 μm or more, and the wavelength on the long-wavelength side at which the transmittance is half of the maximum transmittance is 12.0 μm or less.

[0015] 5. A melting furnace equipped with an in-furnace monitoring device as described in any of items 1 to 4 above.

[0016] 6. A method for producing molten iron by melting a cold iron source using the melting furnace described in item 5 above, wherein the operating conditions of the melting furnace are controlled based on images obtained from the furnace monitoring device.

[0017] According to the present invention, it is possible to provide a furnace monitoring device that allows for clear observation of the conditions inside a melting furnace in which a cold iron source is melted. Furthermore, according to the present invention, it is possible to provide a melting furnace equipped with the device that can efficiently produce molten iron, and a method for producing molten iron using the melting furnace.

[0018] This figure shows an example of a furnace monitoring device according to one embodiment of the present invention. This figure shows an example of a melting furnace according to one embodiment of the present invention. This figure shows the electric furnace used in the example. This is a graph showing the transmittance of the bandpass filter used in the example. This is an image taken using the furnace monitoring device according to the example of the invention. This is an image taken using the furnace monitoring device according to the comparative example.

[0019] The present invention will be described in detail below. The following description is an example of a preferred embodiment of the present invention, and the present invention is not limited to the embodiments described below.

[0020] [In-furnace monitoring device] An in-furnace monitoring device 1 according to one embodiment of the present invention will be described with reference to Figure 1. The in-furnace monitoring device 1 has the following components (1) to (6): (1) Tip lens 21 (2) Relay lens 22 consisting of one or more lenses (3) Inner tube 20 enclosing the tip lens 21 and the relay lens 22 (4) Outer tube 2 enclosing the inner tube 20 (5) Imaging device 30 provided on the outside of the relay lens 22 in the axial direction of the furnace (6) Bandpass filter 34 provided in front of the imaging device 30 in the imaging direction

[0021] The front lens 21 is positioned closest to the object being observed, and the relay lens 22 forms an image in the imaging device 30 from the image transmitted from the front lens 21. By having the imaging device 30 via the relay lens 22 in the furnace monitoring device 1, it is possible to install the imaging device 30 at a predetermined distance from the furnace and protect the imaging device 30 from the heat of the furnace.

[0022] The tip lens 21 and relay lens 22 are protected by a double-tube structure consisting of an inner tube 20 and an outer tube 2. In this way, the furnace monitoring device 1, by having an inner tube 20 and an outer tube 2, can protect the tip lens 21 and relay lens 22 from the heat of the furnace.

[0023] It is preferable to supply cooling gas 23 between the inner tube 20 and the outer tube 2. A cooling gas supply port 24 for supplying cooling gas 23 to the gap between the inner tube 20 and the outer tube 2, and a cooling gas discharge port 25 for discharging the cooling gas 23 from the gap may be provided. A cooling gas supply device may be provided in the furnace monitoring device 1, and the cooling gas 23 may be supplied from the cooling gas supply device. By supplying cooling gas 23, the tip lens 21 and relay lens 22 and their surroundings are cooled, the effects of the high temperature of the furnace during operation are avoided, and a clearer image field of view can be secured. In addition, molten slag and other substances that may adhere to the front surface of the lens can be blown away.

[0024] The imaging device 30 is preferably installed inside the housing 3, thereby protecting the imaging device 30. It is also preferable to supply cooling gas 31 into the housing 3. A cooling gas supply port 32 for supplying cooling gas 31 into the housing 3 and a cooling gas discharge port 33 for discharging cooling gas 31 from inside the housing 3 may be provided. The furnace monitoring device 1 may also be equipped with a cooling gas supply device, and the cooling gas 31 may be supplied from the cooling gas supply device. By supplying cooling gas 31, the imaging device 30 and its surroundings are cooled, the effects of the high temperature of the furnace during operation are avoided, and a clearer image field of view can be ensured.

[0025] Since cooling gas 23 or cooling gas 31 is used in large quantities, it may be supplied by branching, extending, and connecting to gas piping that is part of the steel mill's infrastructure, or it may be supplied directly from a compressor to the furnace where it is used. Air is the most common gas, but if cost is not an issue, an inert gas such as nitrogen may also be used. It is desirable that the gas contains as little moisture as possible, because in some cases moisture may adhere to the lens surface, potentially narrowing the field of view. The cooling gas supply device is not particularly limited and includes the gas piping and compressor described above.

[0026] The tip lens 21 and relay lens 22 are far-infrared lenses, and the imaging device 30 is a far-infrared camera. The far-infrared lens transmits at least a portion of the far-infrared wavelength range, but it is preferable that the lens transmits wavelengths including 7.5 to 14.0 μm. The far-infrared camera images at least a portion of the far-infrared wavelength range, but it is preferable that it images wavelengths including 7.5 to 14.0 μm. In other words, it is preferable that the transmission wavelength range of the tip lens 21 and relay lens 22 and the imaging wavelength range of the imaging device 30 include the wavelength range of 7.5 to 14.0 μm. The far-infrared wavelength range is less susceptible to absorption of transmitted light from inside the furnace due to molten dust, water vapor, flames, etc., and the wavelength range of 7.5 to 14.0 μm is particularly less susceptible to absorption. Therefore, by using the above lenses and imaging device, the conditions inside the furnace can be clearly monitored. Known far-infrared lenses can be used as the tip lens 21 and relay lens 22, but germanium lenses are preferred. Furthermore, a known far-infrared camera can be used as the imaging device 30.

[0027] Furthermore, for similar reasons, the bandpass filter 34 is designed to transmit wavelengths that include at least a portion of the far-infrared wavelength range. In some cases, far-infrared cameras cannot separately detect the intensity of light in wavelengths with low absorbance and wavelengths with high absorbance. However, by using a bandpass filter to block a portion of the wavelength range of light incident on the camera, visibility can be improved even when using such a far-infrared camera. Hereinafter, in the transmission wavelength range of the bandpass filter 34, the wavelengths on the short-wavelength side and the long-wavelength side where the transmittance is half of the maximum transmittance will be denoted as λ1 and λ2, respectively.

[0028] The gas generated inside the electric furnace was collected and its absorption spectrum was analyzed. As a result, abrupt changes in absorbance were observed at wavelengths of 8.0 μm and 13.0 μm. That is, the absorbance was low in the wavelength range from 8.0 μm to 13.0 μm, while the absorbance was high (light was not easily transmitted) in the wavelength range below 8.0 μm or above 13.0 μm. Therefore, it is preferable to set λ1 to 8.0 μm or greater. This allows for blocking the shorter wavelengths within the high absorbance wavelength range. It is even more preferable to set λ1 to 10.0 μm or greater. Furthermore, it is preferable to set λ2 to 13.0 μm or less. This allows for blocking the longer wavelengths within the high absorbance wavelength range. In addition, the above analysis showed that the absorbance was close to zero in the wavelength range of 11.0 to 12.0 μm. Therefore, from the viewpoint of monitoring the furnace with as little influence as possible from absorbance, it is even more preferable to set λ1 to 11.0 μm or greater. Similarly, it is even more preferable that λ2 be 12.0 μm or less. However, λ2 may also be 11.0 μm or less. λ2-λ1 is not particularly limited and may be greater than 0 μm, but by increasing λ2-λ1 and widening the observable wavelength range, the resolution can be improved, enabling clearer in-furnace monitoring. Therefore, λ2-λ1 is preferably 1.0 μm or more, and more preferably 4.0 μm or more. λ1 and λ2 can be determined by considering the balance between resolution and the influence of absorbance.

[0029] The bandpass filter 34 is located in front of the imaging device 30. This allows for the blocking of a specific wavelength range of light incident on the imaging device. The position of the bandpass filter 34 is not particularly limited as long as it is in front of the imaging device 30, but by placing it behind the front lens 21, it can be used even if the bandpass filter does not have heat resistance. Also, by placing it in a position other than between the lenses, optical design is not required, and maintenance and replacement of the bandpass filter become easier. Based on the above, it is preferable that the bandpass filter 34 be placed between the relay lens 22 and the imaging device 30.

[0030] The imaging device 30 should capture images via the front lens 21, relay lens 22, and bandpass filter 34. The type of image captured by the imaging device 30 (still image or moving image) is not particularly limited and should be determined according to the user's needs. Furthermore, as described later, the captured images may be saved. Whether the images are saved continuously or in batches should also be determined according to the user's requirements. Additionally, if the object of observation is bright, the images may be captured via an ND filter or the like.

[0031] To prevent poor visibility due to deposits, the furnace monitoring device 1 may have an automatic cleaning mechanism such as an air blower or wiper. The automatic cleaning mechanism may be provided, for example, in the tip lens or bandpass filter. This enables stable monitoring over a long period of time.

[0032] As described above, the furnace monitoring device 1 according to this embodiment has the components (1) to (6) above. Furthermore, the tip lens 21 and relay lens 22 are far-infrared lenses, the imaging device 30 is a far-infrared camera, and the bandpass filter 34 transmits wavelengths including at least a portion of the far-infrared wavelength range. Therefore, by using the furnace monitoring device 1, the conditions inside the melting furnace where the cold iron source is melted can be clearly observed.

[0033] Although Figure 1 shows an embodiment in which the number of components such as the imaging device and bandpass filter is one, the number of each component is not particularly limited in this embodiment.

[0034] For example, the optical path may be split using a beam splitter or the like after the relay lens 22, and a bandpass filter 34 and an imaging device 30 may be placed in each optical path. This makes it possible to perform simultaneous observation with different types of imaging devices. It also makes it possible to perform simultaneous imaging in different wavelength bands for the same field of view.

[0035] Alternatively, a configuration may be used in which multiple independent optical systems, such as a front lens 21, a relay lens 22, an inner tube 20, an outer tube 2, an imaging device 30, and a bandpass filter 34, are arranged in parallel inside a single housing. This allows for simultaneous monitoring of different directions or different objects of observation.

[0036] Furthermore, multiple bandpass filters 34 may be provided, and a switching mechanism may be provided to switch between the bandpass filters 34 in the optical path. By switching the bandpass filters as needed, different wavelength bands can be observed with a single imaging device.

[0037] [Melting Furnace] A melting furnace according to one embodiment of the present invention is equipped with the furnace monitoring device 1 described above. An example of a melting furnace is shown in Figure 2. An electrode 40 is inserted into the melting furnace 4, and molten iron m is produced by melting a cold iron source x with arc heat from the electrode 40. By producing molten iron using this melting furnace and monitoring the inside of the furnace with the furnace monitoring device 1, it is possible to get a good grasp of how the cold iron source x is supplied and how the cold iron source x melts into molten iron m. Therefore, it is useful in preventing operational troubles and improving production efficiency in the molten iron production process.

[0038] Cold iron sources x typically include, but are not limited to, on-site scrap generated at steel mills, scrap generated from the market, and pig iron produced by solidifying molten iron. On-site scrap generated at steel mills includes, for example, the non-steady parts of slabs cast by continuous casting or ingot-making methods (parts generated at the start and end of casting), and crops produced during the rolling of steel materials such as steel strips. Scrap generated from the market includes recycled materials such as construction steel (H-beams, etc.), automobile steel, and cans. Pig iron produced by solidifying molten iron is produced by tapping molten iron obtained from iron ore and coke in a blast furnace or other blast furnace and then solidifying it.

[0039] The installation angle of the furnace monitoring device 1 is not particularly limited and should be appropriately determined according to the position of the object to be observed and the installation height on the furnace wall or furnace lid. For example, when installing on the furnace wall to observe the cold iron source x and molten iron m, it should be installed at a downward angle to the horizontal, as shown in Figure 1. On the other hand, when installing on the furnace wall to observe the condition of molten slag adhering to the underside of the furnace lid, or to observe the furnace lid becoming overheated and reaching high temperatures, it should be installed at an upward angle to the horizontal. The installation angle can be adjusted in the horizontal range of -90° to 90°, and this can be appropriately adjusted, for example, by controlling the structure of the jig according to the relative positional relationship between the part to be observed and the hole.

[0040] In addition, the number of furnace monitoring devices 1 in the melting furnace 4 is not particularly limited, and there may be multiple furnace monitoring devices 1. By arranging multiple furnace monitoring devices 1 at different positions or angles, blind spots inside the furnace can be reduced, enabling monitoring from a wider area and multiple viewpoints. Furthermore, by analyzing (for example, combining) the obtained multiple images using image analysis technology such as AI, the accuracy of understanding the furnace state can be further improved.

[0041] [Method for producing molten iron] A method for producing molten iron according to one embodiment of the present invention is a method for producing molten iron by melting a cold iron source using the melting furnace, wherein the operating conditions of the melting furnace are controlled based on images obtained from the furnace monitoring device.

[0042] Examples of operating conditions of the melting furnace to be controlled include the timing of turning on and off the auxiliary combustion burner, and the amount and timing of additional charging of cold iron sources. For example, the melting state of the cold iron source near the auxiliary combustion burner may be determined from an image obtained from the above-mentioned in-furnace monitoring device, and the auxiliary combustion burner may be turned on or off according to the determination result. Alternatively, the bulk of the cold iron source in the melting furnace may be determined from an image obtained from the above-mentioned in-furnace monitoring device, and the amount and timing of additional charging of the cold iron source may be determined according to the determination result. Furthermore, when the melting furnace is provided with an oxygen blowing lance or a carbonaceous material blowing lance, the amount of oxygen blown from the oxygen blowing lance or the amount of carbonaceous material blown from the carbonaceous material blowing lance can be controlled. For example, the melting-down state of the cold iron source may be determined from an image obtained from the above-mentioned in-furnace monitoring device, and the blowing amount of oxygen or carbonaceous material may be changed according to the determination result. Furthermore, when the melting furnace is provided with an electrode, the amount of power input to the electrode can be controlled. For example, the melting-down state of the cold iron source may be determined from an image obtained from the above-mentioned in-furnace monitoring device, and the amount of input power may be changed according to the determination result.

[0043] [In-furnace Monitoring System] An in-furnace monitoring system according to another embodiment of the present invention is a system for monitoring the interior of a melting furnace 4, and includes the in-furnace monitoring device 1. The configuration of the in-furnace monitoring system will be described below. Note that, for example, the in-furnace monitoring device 1 may have the configuration and functions of the in-furnace monitoring system described later, and in this case, the in-furnace monitoring device 1 may function as the in-furnace monitoring system.

[0044] The in-furnace monitoring system may be provided with one or both of a display unit that displays captured images and a storage unit that stores captured images. The display unit is typically a monitor provided in an operation room where an operator who operates the melting furnace 4 is stationed. The storage unit may include, for example, any one of a semiconductor memory, a magnetic memory, and an optical memory. The storage unit may be provided in the main body of the imaging device 30, or may be provided in a room with low dust. The imaging device 30 may be connected to the display unit and the storage unit by wire via a cable (particularly a video cable) or the like, or may be connected wirelessly.

[0045] It should be noted that the display unit is not limited to the above-described embodiment, and may function as a display unit by displaying images captured via a network, for example, on a display device provided at a remote location other than an operation room. This enables an operator to safely and efficiently grasp the state inside the furnace without entering high-temperature or dangerous environments, contributing to the improvement of safety of the working environment and the flexibility of operations. Further, the storage unit is not limited to the above-described embodiment, and may function as a storage unit by storing captured images in one or more server devices capable of communicating with each other (for example, a cloud server, a server on an in-house network, etc.). Accumulating video data in a server on a network in this manner facilitates utilization for operation history management, trouble analysis, quality control and the like.

[0046] The furnace monitoring system may include an image analysis unit that analyzes images captured by the imaging device 30. The method for analyzing the images is not particularly limited, and any image analysis technology (e.g., AI) can be used. Furthermore, the furnace monitoring system may further include an operating condition control unit that automatically controls the operating conditions of the monitored melting furnace (e.g., ignition and extinguishing of auxiliary burners, oxygen injection amount, carbon injection amount, etc.) based on the results of the image analysis by the image analysis unit. This enables more advanced and efficient operational management that does not depend on the operator's experience, and contributes to the automation and reduction of manpower in operations. The specific control of operating conditions can be carried out in the same way as in the molten iron manufacturing method described above. In addition, the furnace monitoring system may include an abnormal condition detection unit for detecting abnormal conditions based on the results of the image analysis by the image analysis unit, and an alert generation unit for issuing alerts based on the detection results. This enables early detection and rapid response to operational troubles, further enhancing the safety and efficiency of operations. Examples of detectable abnormal conditions include delayed dissolution of the cold iron source and abnormal slag adhesion. The video analysis unit includes at least one processor (e.g., a CPU). The operating condition control unit includes at least one processor (e.g., a CPU). The abnormal condition detection unit includes at least one processor (e.g., a CPU). The video analysis unit, operating condition control unit, and abnormal condition detection unit can be implemented as any general-purpose electronic device such as a PC (Personal Computer), but are not limited to this, and may be implemented as one or multiple server devices capable of communicating with each other. The alert generation unit includes an optional output interface, such as a display.

[0047] The in-furnace monitoring system may have an input section that receives input for manually controlling the in-furnace monitoring device. The input section includes at least one input interface (e.g., a physical key). The input section may be located, for example, in the control room, or an input device located in a remote location outside the control room may function as the input section by transmitting input via a network. This allows operators to perform control safely and efficiently without entering high-temperature, hazardous environments, contributing to improved safety in the work environment and greater operational flexibility.

[0048] The furnace monitoring system may also be equipped with other sensors such as temperature sensors, pressure sensors, and gas analyzers. By integrating these sensors to create a comprehensive furnace monitoring system, more advanced operational management and quality assurance can be achieved.

[0049] The present invention will be described in detail below based on examples. The following examples are merely preferred examples of the present invention and do not limit it in any way. Furthermore, the following examples can be modified to the extent that they are consistent with the spirit of the present invention, and such modifications are also included within the technical scope of the present invention.

[0050] (Example 1) Molten iron was produced by melting a cold iron source using an electric furnace 4a schematically shown in Figure 3. The electric furnace 4a had a furnace diameter of approximately 6.3 m, a furnace height of 4.1 m, and a tapping capacity of approximately 120 tons. It was a DC type furnace with one electrode 40 installed approximately at the horizontal center of the furnace. The furnace monitoring devices 1 (#1, #2) shown in Figure 1 were installed one at each of the two opposing locations, penetrating the furnace wall. A water-cooled oxygen injection lance 42 and a carbon injection lance 43 were installed inside the furnace from above. The auxiliary combustion burners 41 (#1, #2, #3) were installed one at each of the three locations, which divided the outer circumference of the furnace body into approximately three equal parts, penetrating the furnace wall.

[0051] As the front lens 21 and relay lens 22, far-infrared lenses that transmit wavelengths including 7.5 to 14.0 μm were used. As the imaging device 30, a far-infrared camera that images wavelengths including 7.5 to 14.0 μm was used. As the bandpass filter 34, a bandpass filter having the transmittance shown in Figure 4 was used. As shown in Figure 4, the wavelength λ1 on the short-wavelength side where the transmittance is half of the maximum transmittance %Tmax was 8.4 μm, and the wavelength λ2 on the long-wavelength side was 12.8 μm.

[0052] The basic operating conditions for the electric furnace are as follows: Cold iron source supply per charge: approximately 130 tons Cold iron source supply per batch: approximately 65 tons Number of cold iron source batches per charge: 2 Cold iron source type: Heavy H2 (from the Japan Iron and Steel Association's "Unified Standards for Inspection and Acceptance of Iron Scrap") Amount of steel tapped per charge: approximately 120 tons Target tapping temperature: 1580°C Target tapping carbon concentration: 0.060% Coke lump supply (auxiliary material): 1000 kg Lime supply (auxiliary material): 500 kg Oxygen injection flow rate (pure oxygen): 0-5000 Nm ３ / hr Charcoal material blowing speed (powdered coke): 0-100 kg / min, Charcoal material conveying gas flow rate (air): approx. 350 Nm ３ / hr Flow rate of gaseous fuel (LNG) per burner: 0-350 Nm ３ Flow rate of combustion-supporting gas (pure oxygen) per burner: 0-770 Nm³ / hr ３ / hr Flow rate of lens cooling medium (air) per burner: 8 Nm ３ / hr

[0053] The cold iron source was supplied to the electric furnace 4a from a bucket in two stages: before operation and during operation. In addition, before operation, coke lumps, which are auxiliary fuel, and lime, which is a slag-forming material, were supplied to the electric furnace 4a from an auxiliary material input chute (not shown) as auxiliary raw materials. The cold iron source was melted while pure oxygen and powdered coke were supplied from the oxygen injection lance 42 and the carbon material injection lance 43, respectively.

[0054] Molten iron was produced using the electric furnace 4a by three different methods. In method No. 1, the operating conditions of the auxiliary burner 41 were controlled based on empirical judgment without using the furnace monitoring device 1. In method No. 2, the furnace was monitored using the furnace monitoring device 1, and the operating conditions of the auxiliary burner 41 were controlled based on the video feed from the furnace monitoring device 1. In method No. 3, the furnace was monitored using the furnace monitoring device 1, and the operating conditions of the auxiliary burner 41, oxygen injection lance 42, and carbon injection lance 43 were controlled based on the video feed from the furnace monitoring device 1. The results are shown in Table 1. In the table, " / ton" means per ton of molten iron extracted. By controlling the operating conditions using methods No. 2 and 3, molten iron could be obtained efficiently.

[0055]

[0056] (Example 2) Molten iron was manufactured and the inside of the furnace was monitored using an electric furnace 4a having the same furnace monitoring device 1 as in Example 1 (Inventive Example). Figure 5 shows an image captured using the furnace monitoring device according to the Inventive Example. As a comparative example, molten iron was manufactured and the inside of the furnace was monitored with a modified configuration of the furnace monitoring device. In the furnace monitoring device according to the comparative example, the tip lens and the relay lens consisting of one or more lenses were visible light lenses, the imaging device was a visible light camera, and it did not have a bandpass filter that transmits wavelengths including at least a part of the far-infrared wavelength range. Figure 6 shows an image captured using the furnace monitoring device according to the comparative example. In the image shown in Figure 6, it is difficult to distinguish between molten iron and unmelted cold iron source, but in the image shown in Figure 5, it is easy to distinguish between unmelted cold iron source and molten iron. Thus, by using the furnace monitoring device according to the Inventive Example, it was possible to clearly observe the conditions inside the melting furnace.

[0057] 1 Furnace monitoring device 2 Outer tube 20 Inner tube 21 Tip lens 22 Relay lens 23 Cooling gas 24 Cooling gas supply port 25 Cooling gas outlet 3 Housing 30 Imaging device 31 Cooling gas 32 Cooling gas supply port 33 Cooling gas outlet 34 Bandpass filter 4 Melting furnace 4a Electric furnace 40 Electrode 41 Combustion booster burner 42 Oxygen injection lance 43 Carbon injection lance x Cold iron source m Molten iron

Claims

1. A furnace monitoring device comprising: a tip lens; a relay lens consisting of one or more lenses; an inner tube enclosing the tip lens and the relay lens; an outer tube enclosing the inner tube; an imaging device provided on the outside of the furnace in the axial direction of the relay lens; and a bandpass filter provided in front of the imaging device in the imaging direction, wherein the tip lens and the relay lens are far-infrared lenses; the imaging device is a far-infrared camera; and the bandpass filter transmits wavelengths including at least a portion of the far-infrared wavelength range.

2. The in-furnace monitoring device according to claim 1, wherein the tip lens and relay lens transmit wavelengths including 7.5 to 14.0 μm, and the imaging device images wavelengths including 7.5 to 14.0 μm.

3. The furnace monitoring device according to claim 1 or 2, wherein, in the transmission wavelength range of the bandpass filter, the wavelength on the short-wavelength side at which the transmittance is half of the maximum transmittance is 8.0 μm or more, and the wavelength on the long-wavelength side at which the transmittance is half of the maximum transmittance is 13.0 μm or less.

4. The furnace monitoring device according to claim 3, wherein, in the transmission wavelength range of the bandpass filter, the wavelength on the short-wavelength side at which the transmittance is half of the maximum transmittance is 11.0 μm or more, and the wavelength on the long-wavelength side at which the transmittance is half of the maximum transmittance is 12.0 μm or less.

5. A melting furnace equipped with an in-furnace monitoring device according to any one of claims 1 to 4.

6. A method for producing molten iron by melting a cold iron source using the melting furnace described in claim 5, wherein the operating conditions of the melting furnace are controlled based on images obtained from the furnace monitoring device.

Images