KR desulfurization method

Abstract

The present invention addresses the problem of providing a KR desulfurization method by which a stirring state of slag and molten iron can be quantitatively determined. In a KR desulfurization method by which molten iron (7) in a molten iron ladle (6) is mechanically stirred using an impeller (2), and an auxiliary raw material is introduced into the molten iron (7), the KR desulfurization method is provided with: an imaging step for imaging the molten surface of the molten iron (7) being stirred; a determination step for determining the entrainment state of slag (8) from the image obtained in the imaging step; and an introduction step for introducing the auxiliary raw material if it is determined, as a result of the determination, that the slag (8) is sufficiently entrained.

Description

KR desulfurization method

[0001] The present invention relates to a KR desulfurization method.

[0002] KR (Kanbara Reactor) desulfurization, a mechanical agitation type desulfurization method used in the refining of molten iron, is a process in which a desulfurization agent such as CaO is added to the molten iron and then the molten iron is mechanically agitated using an impeller or the like to remove S from the molten iron. This KR desulfurization removes S from the molten iron as slag, but the desulfurization capacity can be improved by improving the reaction efficiency between the molten iron and the desulfurization agent. Therefore, there has been a recent need to improve the reaction efficiency between the molten iron and the desulfurization agent.

[0003] For example, Patent Document 1 discloses a technique for improving desulfurization capacity in KR desulfurization, which involves adding a desulfurizing agent to the molten pig iron in a ladle and stirring the molten pig iron with an impeller. In the method of Patent Document 1, the impeller is rotated at a low speed while approaching the surface of the molten pig iron. Once the impeller enters the molten pig iron (time t1), the impeller's rotation speed is increased to distribute the slag on the molten pig iron toward the outer periphery of the vessel. Then, in this state, a desulfurizing agent is added onto the molten pig iron surface exposed near the center of the vessel (times t2 to t3). Next, with the entire impeller immersed in the molten pig iron, the added desulfurizing agent and the molten pig iron are stirred by the impeller, which is rotated at a high speed from time t3 onward. The impeller's rotation is then slowed down and stopped, and the stopped impeller is left immersed in the molten pig iron until the molten pig iron settles (times t5 to t6).

[0004] Furthermore, Patent Document 2 discloses a method for desulfurization by adding a desulfurization agent to molten iron in a molten iron vessel and stirring the mixture, in which the CaO concentration in the desulfurization slag after the treatment, as well as the shape, specific gravity, and liquid phase ratio of the desulfurization agent are set to predetermined values.

[0005] Furthermore, Patent Document 3 discloses that when molten pig iron is charged into a vessel, a desulfurization agent is added, and an impeller is immersed in the vessel, rotated, and agitated to desulfurize the molten pig iron, an impeller having a height difference in which the height of the upper ends of the blades is alternately increased and decreased is used.

[0006] Furthermore, Patent Document 4 discloses a method in which a desulfurization agent containing soda ash in a mass ratio of 2% to less than 40% with respect to quicklime and having a maximum particle size of less than 5 mm is added onto the molten pig iron before the start of desulfurization treatment or within one minute after the start of desulfurization treatment. Also, Patent Document 4 discloses a method in which a substance that generates gas upon contact with the molten pig iron is added onto the molten pig iron after the addition of the desulfurization agent is completed but before 50% of the desulfurization treatment time has elapsed.

[0007] JP 2000-1711 A JP 2003-213313 A JP 2004-204303 A JP 2013-151725 A

[0008] In the KR desulfurization process, the desulfurization agent must be added when the slag on the surface of the molten pig iron bath is sufficiently entrained in the molten pig iron. If the slag is not sufficiently entrained, that is, if a large amount of slag is present on the surface of the molten pig iron bath, the added desulfurization agent will remain in the slag, preventing contact between the desulfurization agent and the molten pig iron, thereby reducing the desulfurization processing capacity.

[0009] In the method of Patent Document 1, the rotational speed of the impeller is increased from the time when the impeller enters the molten pig iron (time t1), so that the slag on the molten pig iron is distributed toward the outer periphery of the vessel, and in this state, a desulfurization agent is poured onto the surface of the molten pig iron exposed near the center of the vessel (times t2 to t3). Therefore, the process proceeds to the next step even when the slag and molten pig iron are not sufficiently mixed, which may reduce the desulfurization treatment capacity.

[0010] Furthermore, the method of Patent Document 2 promotes the entrainment of desulfurization agent into the molten pig iron, making it possible to stably ensure a high desulfurization rate. However, because the stirring and mixing of the slag and molten pig iron is not quantified, there is a possibility that the desulfurization treatment capacity may decrease depending on the stirring conditions.

[0011] Furthermore, the method of Patent Document 3 provides a desulfurization method and apparatus that can maintain a high desulfurization rate by suppressing the entrainment of desulfurization slag into the molten pig iron and the deterioration of its dispersion, even if the desulfurization slag adheres to the impeller. However, because the stirring and mixing of the slag and the molten pig iron is not quantified, there is a possibility that the desulfurization treatment capacity will decrease depending on the stirring conditions.

[0012] Furthermore, in the method of Patent Document 4, a desulfurization agent with a maximum particle size of less than 5 mm is added onto the molten pig iron before the start of desulfurization treatment or within one minute after the start of desulfurization treatment. However, since the process proceeds to the next step even when the stirring conditions of the slag and molten pig iron are inappropriate, there is a possibility that the desulfurization treatment capacity will decrease.

[0013] In other words, the techniques of Patent Documents 1 to 4 perform the process without being able to quantify the mixing state of the slag and molten pig iron during KR desulfurization, which may reduce the desulfurization treatment capacity depending on the mixing state. Therefore, there is a need for a technique to determine whether slag, which has separated due to its specific gravity above the molten pig iron, has been entrained in the molten pig iron during molten pig iron pretreatment, particularly KR desulfurization. However, with conventional techniques, it is unclear how to determine whether the molten pig iron and slag are sufficiently mixed, or there is no method for quantitatively determining this.

[0014] Therefore, the present invention has been made in consideration of the above-mentioned problems, and aims to provide a KR desulfurization method that can quantitatively determine the stirring state of slag and molten iron.

[0015] (1) According to one aspect of the present invention, there is provided a KR desulfurization method in which molten pig iron in a molten pig iron ladle is mechanically stirred using an impeller and auxiliary materials are added to the molten pig iron, the KR desulfurization method comprising: an imaging step of imaging the bath surface of the stirred molten pig iron; a determination step of determining the state of slag entrainment from the image obtained in the imaging step; and a feeding step of feeding the auxiliary materials when it is determined as a result of the determination that the slag is sufficiently entrained.

[0016] (2) In the KR desulfurization method of (1) above, in the judgment step, the slag entrapment state is judged using a judgment model created in advance based on a teacher image.

[0017] (3) In the KR desulfurization method of (2) above, the teacher image is an image of the bath surface of the molten iron being stirred in a previous KR desulfurization process, in which an entrainment flow of the slag is formed, the area of ​​the slag decreases in accordance with the direction of rotation, and the molten iron is exposed.

[0018] (4) In the KR desulfurization method of (2) or (3) above, in the judgment step, the correlation rate between the image obtained in the imaging step and the judgment model is used as the entrainment completion rate, and the entrainment completion rate is used as an index of whether the slag is sufficiently entrained.

[0019] According to one aspect of the present invention, there is provided a KR desulfurization method that can quantitatively determine the stirring state of slag and molten iron.

[0020] 1 is a configuration diagram showing a desulfurization treatment facility according to an embodiment of the present invention; 2 is a flowchart showing a KR desulfurization method according to the present embodiment; 3 is an example of an image captured in an imaging step; 4 is a graph showing results in an example;

[0021] In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, identical or similar parts are designated by identical or similar reference numerals, and redundant explanations will be omitted. The drawings are schematic and may differ from the actual product. Furthermore, the embodiments shown below exemplify devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not specify the materials, structure, arrangement, etc. of component parts as described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims.

[0022] <Device Configuration> A desulfurization system 1 according to one embodiment of the present invention will be described. The desulfurization system 1 is a system for desulfurizing molten iron 7 contained in a molten iron ladle 6 using a KR desulfurization method (mechanical stirring type desulfurization method) in which molten iron 7 is mechanically stirred using an impeller 2. The desulfurization system 1 includes the impeller 2, a blast lance 3, an imaging device 4, and a determination device 5.

[0023] The impeller 2 is a refractory stirring blade provided at one end of the impeller shaft. The impeller 2 is immersed in the molten pig iron 7 contained in the molten pig iron ladle 6 and rotates to stir the molten pig iron 7. The impeller 2 is configured to be able to move up and down vertically and to rotate about the impeller shaft as a rotation axis by an elevating device and a rotating device (not shown) provided at the other end of the impeller shaft.

[0024] The blast lance 3 is a device that injects a desulfurization agent, which is supplied together with a carrier gas from a supply facility (not shown), into the molten iron 7. The desulfurization agent is automatically injected by a control device (not shown) of the desulfurization facility 1 at an injection timing described below.

[0025] The imaging device 4 is a device such as a camera that continuously captures images of the bath surface of the molten iron 7 from above. The imaging range of the imaging device 4 needs to capture at least the range in which the impeller 2 is rotating, but it is preferable that the entire throat of the molten iron ladle 6 is captured. The image including the bath surface of the molten iron 7 captured by the imaging device 4 is transmitted to the determination device 5.

[0026] The determination device 5 is a device that determines the state of entrapment of slag 8 on the bath surface of the molten iron 7 using images captured by the imaging device 4, and includes an acquisition unit 51 and a determination unit 52. The determination device 5 is, for example, a computer system such as a personal computer having a calculation function, and is configured with a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processing Unit), etc. The determination device 5 realizes the functions of the acquisition unit 51 and the determination unit 52 (described later) in software by executing various dedicated programs pre-stored in the ROM, etc. A method for determining entrapment of slag 8 by the determination device 5 will be described in detail later.

[0027] <KR Desulfurization Method> Next, the KR desulfurization method according to this embodiment will be described with reference to FIG. 2 . First, the impeller 2 is immersed in the molten pig iron 7 in the molten pig iron ladle 6, and stirring of the molten pig iron 7 is initiated by rotating the impeller 2 (S100). Stirring conditions, such as the rotation speed and immersion depth of the impeller 2, can be set as appropriate. The impeller 2 continues to rotate until the desulfurization treatment is completed. Prior to the desulfurization treatment, slag 8, which may include blast furnace slag and hot slag (post-desulfurization slag generated in other desulfurization treatments), is present on the surface of the molten pig iron 7. When stirring is performed by the impeller 2, the slag 8 on the surface of the molten pig iron 7 is entrained within the molten pig iron 7.

[0028] When stirring of the molten iron 7 is started, the imaging device 4 images the bath surface of the molten iron 7 (imaging step, S101). Images of the molten iron 7 are continuously taken, and the images obtained by the imaging are transmitted to the acquisition unit 51. Images of the molten iron 7 may be taken, for example, several times to several tens of times per second. Furthermore, when images are continuously taken, multiple consecutive images obtained by the imaging may be transmitted to the acquisition unit 51. An example of an image captured in the imaging step is shown in FIG. 3. As shown in FIG. 3, in the image of the bath surface of the molten iron 7 taken, the exposed molten iron 7 is displayed brightly because of its high temperature, while the slag 8 on the bath surface is displayed darkly because of its lower temperature than the molten iron 7.

[0029] After step S102, the determination unit 52 determines the state of entrapment of the slag 8 from the image acquired by the acquisition unit 51 and determines whether the entrapment is sufficient (determination step, S102). Specifically, the determination unit 52 performs a determination on the acquired image using a determination model created in advance.

[0030] (Decision Model) A method for creating the judgment model will be described. The judgment model is a model (AI program) created using images of the bath surface of the molten pig iron being stirred during a previous KR desulfurization treatment as teacher images. The teacher images are a plurality of images taken during a previous KR desulfurization treatment that are determined to have sufficient slag 8 entrainment (images determined to be good). In this embodiment, sufficient slag 8 entrainment refers to a state in which the slag 8 on the bath surface is entrained in the molten pig iron 7 to an extent that does not impede contact between the molten pig iron 7 and the desulfurization agent being added. Images that satisfy all three of the following conditions (A) to (C) are preferably used as images that are determined to be good. The number of teacher images used is preferably 50 or more, more preferably 100 or more, and even more preferably approximately 500. A small number of teacher images may result in low judgment accuracy. Furthermore, a large number of teacher images may result in overlearning, which may result in low judgment accuracy. (A) The slag 8 on the bath surface of the molten pig iron 7 rotates in the same direction as the rotation direction of the impeller 2, that is, an entrainment flow is formed in the rotation direction of the impeller 2. (B) The area of ​​the slag 8 on the bath surface of the molten pig iron 7 decreases in accordance with the rotation direction of the impeller 2. (C) The molten pig iron 7 is exposed.

[0031] Furthermore, the condition (A) is more preferably satisfied when, in the central portion of the bath surface where the slag 8 covers the bath surface of the molten pig iron 7 and the image appears dark, one or more bright streaks (portions where the molten pig iron 7 is exposed) are in the form of a swirl along the direction of rotation of the impeller 2. The condition (B) is more preferably satisfied when, upon observing the outline of the portion where the slag 8 covers the bath surface of the molten pig iron 7 and the image appears dark, the distance between the outline of the portion where the slag 8 covers the bath surface of the molten pig iron 7 and the edge of the molten pig iron ladle 6 and the image appears dark, or when multiple bright streaks appear to merge. The condition (C) is more preferably satisfied when the portion where the slag 8 covers the bath surface of the molten pig iron 7 and the image appears dark is less than about 50% of the image range of the bath surface.

[0032] It is preferable to use an image judged to be good in a treatment charge in which the desulfurization efficiency was high as a result of the desulfurization treatment.

[0033] Furthermore, it is preferable to use as the teacher images a plurality of images (images judged to be defective) that were taken during a previous KR desulfurization process and that are judged to show insufficient slag 8 entrainment. Images judged to be defective are preferably images that do not satisfy at least one of the above conditions (A) to (C). While it is possible to use only images judged to be good as the teacher images, the stirring status can be accurately determined by also using images judged to be defective.

[0034] The judgment model is created using image recognition software (e.g., DeepEye (registered trademark)) that performs image recognition using machine learning or the like. Specifically, the judgment model is created by saving images judged to be good and images judged to be bad as training images in the image recognition software and allowing the software to learn. Furthermore, a judgment may be performed using test images in which good and bad images have been clearly defined in advance using the created judgment model, and the accuracy rate of the results may be obtained and evaluated. In this case, if the accuracy rate is unsatisfactory, the judgment model may be adjusted by adding additional training images saved in the judgment model or adding test images that were judged incorrectly by the judgment model to the training images. In this way, a judgment model with high judgment accuracy can be created. The created judgment model is deployed to a judgment application and used to judge actual devices.

[0035] In step S102, the entrapment status of the slag 8 is determined using a determination model created in advance by the above-described method. Specifically, the correlation rate between the image captured in step S101 and the determination model is used as the entrapment completion rate. That is, in step S102, the entrapment completion rate is determined as the entrapment status of the slag 8. The entrapment completion rate is then used as an index of whether the slag 8 is sufficiently entrapped. For example, if the entrapment completion rate is 95% or higher, it is determined that the slag 8 is sufficiently entrapped. Furthermore, when determining whether the slag 8 is sufficiently entrapped, the determination may be made based on the entrapment completion rate of a single acquired image, or may be made based on the entrapment completion rate of multiple acquired consecutive images. For example, when multiple images are captured multiple times per second, it may be determined that the slag 8 is sufficiently entrapped if the entrapment completion rate of all images for multiple consecutive images captured for three seconds or more is equal to or higher than a predetermined value.

[0036] If it is determined in step S102 that the slag 8 is not sufficiently entrained, the process of step S101 is performed again. That is, the imaging step of step S101 and the determination step of step S102 are repeated until the slag 8 is sufficiently entrained.

[0037] On the other hand, if it is determined in step S102 that the slag 8 is sufficiently entrained, a desulfurization agent is injected into the molten pig iron 7 via the blast lance 3 (S103, injection step). In the injection step, the timing at which it is determined in the determination step that the slag 8 is sufficiently entrained is set as the injection timing, and the desulfurization agent is automatically injected by the control device of the desulfurization equipment 1. The amount of desulfurization agent injected is appropriately set depending on the temperature and composition of the molten pig iron 7, the target composition after desulfurization, etc. The desulfurization agent is an auxiliary material used in the desulfurization process and mainly contains lime.

[0038] After step S103, the impeller 2 continues stirring for a preset treatment time, and the desulfurization treatment by the desulfurization equipment 1 is completed.

[0039] According to the KR desulfurization method of this embodiment, the stirring state of the slag 8 and the molten pig iron 7 can be quantitatively determined by determining the entrainment state of the slag 8 from the image obtained in the imaging process. Therefore, it is possible to accurately determine whether the slag 8 is sufficiently entrained, and the desulfurization agent can be added at an appropriate timing. In the KR desulfurization method, as described above, if the addition timing is too early, a large amount of slag 8 is present on the bath surface of the molten pig iron 7, resulting in a poor yield of the added desulfurization agent and a decrease in desulfurization treatment capacity. Furthermore, if the addition timing is too late, it takes too long to add the desulfurization agent, which may result in an insufficient stirring time after addition, thereby decreasing the desulfurization treatment capacity. Furthermore, the extended desulfurization treatment time may result in a decrease in production capacity and a decrease in the molten pig iron temperature. In contrast, according to this embodiment, the addition timing can be appropriately determined, thereby improving the desulfurization treatment capacity and preventing a decrease in production capacity. In particular, by using a determination model created in advance based on a training image, the accuracy of determining the addition timing can be further improved. Furthermore, by using an image that satisfies the three conditions (A) to (C) as an image that is considered to be a good teacher image, the accuracy of the judgment can be further improved.

[0040] Furthermore, in the KR desulfurization process, the amount of slag 8 before desulfurization varies for each treatment charge, making it difficult to determine the appropriate timing for adding slag 8 based solely on the mixing time. However, in this embodiment, the determination is made based on the captured images as described above, so the timing for adding slag 8 can be appropriately determined regardless of differences in the conditions for each treatment charge. Furthermore, when an operator visually judges the captured images or video, the operator must make the judgment within a short period of time, which can lead to variability depending on the individual's level of skill. However, in this embodiment, the determination is made based on the captured images as described above, and a judgment model using a teacher image that indicates sufficient mixing is used, thereby reducing the variability in the judgment.

[0041] <Modifications> Although the present invention has been described above with reference to specific embodiments, it is not intended that the invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention that include various modifications in addition to the disclosed embodiments will be apparent to those skilled in the art. Therefore, it should be understood that the embodiments of the invention described in the claims also encompass embodiments that include these modifications described herein, either alone or in combination.

[0042] For example, in the above embodiment, the desulfurizing agent is introduced by blasting using the blast lance 3, but the present invention is not limited to this example. For example, the cut-out desulfurizing agent may be introduced by gravity falling through a chute.

[0043] Furthermore, in the above embodiment, it is preferable to use an image that satisfies all of the conditions (A) to (C) as an image that is judged to be good, but the present invention is not limited to such an example. For example, when it is determined that the desulfurization agent was added with sufficient slag 8 entrained as a result of the desulfurization treatment, an image of the bath surface of the molten pig iron 7 immediately before the desulfurization agent is added may be used as an image that is judged to be good. An example of a case where it is determined that the desulfurization agent was added with sufficient slag 8 entrained is when the desulfurization efficiency (the proportion of the desulfurization agent that contributed to desulfurization) is high relative to the S concentration in the molten pig iron 7 before the desulfurization treatment. Furthermore, an image that is judged to be bad may be used as an image that is judged to be good when it is determined that the desulfurization agent was not added with sufficient slag 8 entrained.

[0044] Furthermore, in the above embodiment, the desulfurization agent is added in step S103, but the present invention is not limited to this example. In step S103, it is sufficient to add an auxiliary material for the desulfurization treatment, and in addition to the desulfurization agent, a solvent such as alumina for forming a molten layer in the slag may also be added.

[0045] Next, an example conducted by the present inventor will be described. In the example, desulfurization was performed in an actual desulfurization treatment facility 1 using the KR desulfurization method according to the above embodiment, that is, a method of determining the timing of adding a desulfurization agent using images captured in an imaging process. In the example, images that satisfied the three conditions (A) to (C) were used as teacher images that were determined to be good, and images that did not satisfy at least one of the conditions (A) to (C) were used as teacher images that were determined to be bad. In addition, as a comparative example, the timing of adding a desulfurization agent was determined by the visual judgment of an operator, and desulfurization was performed.

[0046] Figure 4 shows the relationship between tapped pig iron S (%) and desulfurization lime efficiency as a result of an example. Tapped pig iron S corresponds to the S concentration in the molten pig iron 7 before desulfurization treatment. Desulfurization lime efficiency indicates the proportion of lime in the added desulfurization agent that actually contributed to desulfurization, based on the change in S concentration before and after desulfurization treatment. The example shown in Figure 4 also shows the results of sorting under the following conditions: (Sorting conditions) - Hot slag used - No scrap placed in the molten pig iron ladle 6 - Tapped pig iron temperature 1500°C to 1540°C - T. CaO (amount of CaO (kg) in the desulfurization agent per ton of molten pig iron) 9 kg / t to 11 kg / t

[0047] As shown in Figure 4, it was confirmed that the KR desulfurization method according to the above embodiment improves the desulfurization efficiency of lime and reduces variation compared to the comparative example. This is because, based on the visual judgment of the operator in the comparative example, there are cases where the desulfurization agent is added when the mixing is insufficient, that is, when a large amount of slag 8 remains on the bath surface. On the other hand, it was confirmed that the KR desulfurization method according to the above embodiment stabilizes the desulfurization efficiency at a high value.

[0048] REFERENCE SIGNS LIST 1 Desulfurization treatment equipment 2 Impeller 3 Blast lance 4 Imaging device 5 Determination device 51 Acquisition unit 52 Determination unit 6 Molten iron ladle 7 Molten iron 8 Slag

Claims

1. A KR desulfurization method in which molten pig iron in a molten pig iron ladle is mechanically stirred using an impeller and auxiliary materials are added to the molten pig iron, the KR desulfurization method comprising: an imaging step of imaging the bath surface of the stirred molten pig iron; a determination step of determining the state of slag entrainment from the image obtained in the imaging step; and a feeding step of feeding the auxiliary materials when it is determined as a result of the determination that the slag is sufficiently entrained.

2. The KR desulfurization method according to claim 1, wherein the determination step determines the state of slag entrapment using a determination model created in advance based on a teacher image.

3. The KR desulfurization method according to claim 2, wherein the teacher image is an image of the bath surface of the molten pig iron being stirred in a past KR desulfurization process, in which an entrainment flow of the slag is formed, the area of ​​the slag is reduced in accordance with the direction of rotation, and the molten pig iron is exposed.

4. A KR desulfurization method according to claim 2 or 3, wherein in the judgment process, the correlation rate between the image obtained in the imaging process and the judgment model is used as an entrapment completion rate, and the entrapment completion rate is used as an index of whether the slag is sufficiently entrapped.

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