Intermediate slag removal method in metal refining

Abstract

To provide an intermediate discharge method capable of rapidly discharging a prescribed amount of molten slag from a furnace in a short time without lowering the yield of molten metal when the intermediate discharge is performed by tilting a converter type refining furnace.SOLUTION: The inclination angle of a furnace body is controlled on the basis of the measured refractory shape of a converter type refining furnace (including the refractory shape in the presence of deposited metal), preferably the in-furnace shape or / and the furnace mouth shape, when tilting the furnace body in the intermediate discharge of metal refining using the converter type refining furnace. When measuring the refractory shape of a converter type refining furnace, profile measurement is performed by the measured value by a non-contact type rangefinder or / and an image taken by an imaging device.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an intermediate slag discharging method for discharging at least a part of molten slag from a furnace in metal refining using a converter-type refining furnace.

Background Art

[0002] In recent years, the required quality of steel materials has become increasingly strict, and reduction of impurity elements such as silicon and phosphorus is demanded. In order to meet such requirements, in the steelmaking process of steelworks, pretreatment is generally carried out at the stage of hot metal in advance to remove silicon and phosphorus in hot metal to some extent. In this process, after performing desiliconization treatment on the hot metal in a converter-type refining furnace (hereinafter referred to as a converter), the furnace body is tilted to perform intermediate slag discharging for discharging at least a part of the molten slag (desiliconization slag) in the furnace, and then a CaO-based solvent is charged into the furnace to perform dephosphorization treatment on the hot metal. In this process, in the intermediate slag discharging after desiliconization treatment, how to discharge a large amount of desiliconization slag in a short time is an important point in operation.

[0003] In intermediate slag discharging, in order to increase the amount of discharged desiliconization slag, for example, when the tilting angle of the furnace body is increased, a large amount of desiliconization slag is discharged, but the hot metal also flows out of the furnace mouth together with the desiliconization slag. Since the yield of iron decreases due to the outflow of hot metal, it is not preferable to increase the tilting angle of the furnace body arbitrarily to improve the intermediate slag discharging rate. Further, even if the amount of desiliconization slag generated by desiliconization treatment is the same, the surface level of the desiliconization slag differs depending on the refractory shape in the converter (the shape of the refractory worn by use of the furnace), and thus there are also significant differences in the slag discharging start angle and the slag discharging end angle (both are the tilting angles of the furnace body) at which the discharging of the desiliconization slag starts depending on the refractory shape. Therefore, it is necessary to perform intermediate slag discharging considering the refractory shape. As prior art, for example, Patent Documents 1 and 2 propose a method of correcting the tilting angle of a converter based on the number of converter heats. Further, Patent Document 3 proposes a method of estimating the mass of discharged slag using the tilting angle at which slag discharge starts and the maximum tilting angle of the refining vessel during the entire slag discharge process.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although Patent Documents 1 and 2 mention the shape of refractories depending on the number of converter heats, they do not mention the shape of refractories for each furnace campaign or each part of the converter. In actual converter operation, the wear behavior varies greatly for each furnace campaign and each part, and these effects cannot be ignored. Also, although the method of Patent Document 3 can consider the shape of refractories during operation, it does not consider the shape of refractories near the furnace mouth, which has a great influence on the slag discharge behavior, and there is a possibility of causing a large error. From the above, even when using prior technologies such as Patent Documents 1 and 2 and Patent Document 3, it is difficult to quickly discharge a predetermined amount of desiliconized slag from the converter in a short time without reducing the iron yield.

[0006] Accordingly, an object of the present invention is to solve the problems of the prior art as described above, and in the intermediate slag discharging process in metal refining using a converter-type refining furnace, when at least a part of the molten slag is discharged from the furnace by tilting the furnace, an intermediate slag discharging method is provided that can quickly discharge a predetermined amount of molten slag from the furnace in a short time without reducing the yield of the molten metal.

Means for Solving the Problems

[0007] As a result of intensive research on the influence of the refractory shape of the converter-type refining furnace on the slag discharging behavior in the intermediate slag discharging process in the converter-type refining furnace, the inventors of the present invention have found that by controlling the tilting angle of the furnace body based on the measured refractory shape, it is possible to quickly discharge a predetermined amount of molten slag from the furnace in a short time without reducing the yield of the molten metal. The present invention is based on such findings and has the following gist.

[0008] [1] In the intermediate slag discharging process in metal refining using a converter-type refining furnace (A), when at least a part of the molten slag is discharged from the furnace by tilting the furnace body, An intermediate slag discharging method in metal refining, characterized in that the tilting angle of the furnace body is controlled based on the measured refractory shape of the converter-type refining furnace (A) (including the refractory shape when there is adhering metal). [2] The intermediate slag discharging method according to [1] above, characterized in that the measured refractory shape of the converter-type refining furnace (A) is the furnace inner shape and / or the furnace mouth shape. [3] The intermediate slag discharging method according to [2] above, characterized in that the furnace mouth shape is a furnace mouth shape including adhering metal. [4] In the intermediate slag discharging method according to [2] or [3] above, when measuring the refractory shape of the converter-type refining furnace (A), the measurement of the refractory shape including the furnace inner shape and the measurement of only the furnace mouth shape are each performed, and the measurement frequency of the refractory shape including the furnace inner shape is made less than the measurement frequency of only the furnace mouth shape.

[0009] [5] In any of the intermediate slag discharging methods of [1] to [4] above, when measuring the refractory shape of the converter-type refining furnace (A), profile measurement is performed based on the measurement value by a non-contact distance meter and / or the image by an imaging device. An intermediate slag discharging method in metal refining is characterized by this. [6] In any of the intermediate slag discharging methods of [1] to [5] above, based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), etc., the amount of molten metal and the amount of molten slag in the furnace during intermediate slag discharging are calculated. Based on this amount of molten metal and molten slag and the actually measured refractory shape, the slag discharging end angle, which is the tilting angle of the furnace body when slag discharging ends during intermediate slag discharging, is obtained. During intermediate slag discharging, an intermediate slag discharging method in metal refining is characterized by controlling the tilting angle of the furnace body according to the slag discharging end angle.

[0010] [7] In any of the intermediate slag discharging methods of [1] to [5] above, based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), etc., the amount of molten metal and the amount of molten slag in the furnace during intermediate slag discharging are calculated. Based on this amount of molten metal and molten slag and the actually measured refractory shape, the slag discharging start angle, which is the tilting angle of the furnace body when slag discharging starts during intermediate slag discharging, and the slag discharging end angle, which is the tilting angle of the furnace body when slag discharging ends, are obtained. During intermediate slag discharging, an intermediate slag discharging method in metal refining is characterized by controlling the tilting angle and tilting speed of the furnace body according to the slag discharging start angle and the slag discharging end angle. [8] In the intermediate slag discharging method of [7] above, during intermediate slag discharging, the tilting speed after slag discharging start is made lower compared to the tilting speed from the start of tilting of the furnace body to the slag discharging start angle, and the tilting speed is decreased as it approaches the slag discharging end angle after slag discharging start, and is held for a certain time at the slag discharging end angle. An intermediate slag discharging method in metal refining is characterized by this.

[0011] [9] In a hot metal pretreatment method using one converter-type refining furnace (A) and performing desiliconization treatment and dephosphorization treatment in this order with intermediate slag discharging in between. A hot metal pretreatment method characterized by performing the intermediate slag removal by any one of the intermediate slag removal methods [1] to [8] above.

[10] A method for producing molten steel, characterized by obtaining molten steel through hot metal pretreatment by the hot metal pretreatment method [9] above.

[11] In a steelmaking method using one converter-type refining furnace (A) and performing desiliconization / phosphorus removal treatment and decarburization treatment in this order with intermediate slag removal in between, A steelmaking method characterized by performing the intermediate slag removal by any one of the intermediate slag removal methods [1] to [8] above. [Effect of the Invention]

[0012] According to the present invention, in the intermediate slag removal step in metal refining using a converter-type refining furnace, when at least a part of the molten slag is discharged from the furnace by tilting the furnace body, it is possible to quickly discharge a predetermined amount of molten slag from the furnace in a short time without reducing the yield of the molten metal. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0014] Figure 1 shows the state of discharging desiliconized slag from the converter in the intermediate slag discharge process in hot metal pretreatment. In the figure, A is a converter (converter type refining furnace), 1 is hot metal (hot metal), 2 is desiliconized slag, 3 is a slag ladle, and 4 is a slag ladle trolley. At the time when the desiliconization treatment process is completed, the desiliconized slag 2 in the converter A contains CO gas bubbles generated by the reaction between the oxygen-containing gas supplied from the top blowing lance and carbon in the hot metal, and its apparent volume increases by several times or more compared to the case without bubbles, that is, it is in a so-called forming state. After that, the converter A is tilted and the desiliconized slag 2 is discharged from the furnace mouth toward the slag ladle 3 installed under the furnace.

[0015] The furnace body of converter A undergoes refractory wear due to repeated blowing, and its shape gradually changes. Figures 2(a) to (c) schematically show the changes in the refractory shape (furnace interior shape and furnace mouth shape) of converter A according to the number of uses. In the figures, 10 is the refractory that constitutes the furnace body. The solid line indicates the refractory shape at each number of converter uses, and the dashed line (the dashed lines in Figures 2(b) and (c)) indicates the refractory shape at 0 uses (new furnace). When the number of uses of converter A is relatively small, it shows a refractory shape close to that of a new furnace. However, when the number of uses of converter A increases, local refractory wear progresses, resulting in a non-uniform wear state. This wear state changes each time the furnace age of converter A changes and also varies depending on the daily operating conditions.

[0016] Therefore, in the present invention, the refractory shape of converter A (including the refractory shape when there is an attached backing metal) is regularly measured, and when tilting the furnace body to perform intermediate slag removal, the tilting angle of the furnace body is controlled based on the measured refractory shape. Specifically, in order to grasp the daily-changing wear state as described above, means such as a non-contact distance meter or an imaging device are used to regularly (for example, daily) measure the profile of the refractory shape. Based on the measured values of the refractory shape obtained from this measurement, the tilting angles of the furnace body (slag removal start angle, slag removal end angle) during intermediate slag removal are determined, and based on this, the tilting angle of the furnace body is controlled. Further, if necessary, the tilting speed may be controlled as described later. Figure 3 schematically shows an example of the implementation status of the profile measurement of the refractory shape. It shows the case where the profile measurement of the refractory shape is performed using a non-contact distance meter 5 (for example, a laser distance meter, etc.) arranged facing the furnace mouth a of converter A. In this case, after the treatment in converter A is completed, tapping of the molten iron and slag removal are performed. Then, converter A is tilted so that the furnace mouth a faces the non-contact distance meter 5 (in the figure, 6 is a tripod) arranged near converter A. As shown in Figure 3, with the furnace body tilted until the inside of the furnace can be observed from the furnace mouth a, the non-contact distance meter 5 measures the distances to a plurality of measurement points inside the furnace and at the furnace mouth, and the profile measurement device 7 acquires the measured data of the refractory shape from these measurement values.

[0017] Here, as the refractory shape that affects the relationship between the tilting angle of the furnace body and the slag discharge amount during intermediate slag discharge, there are the furnace inner shape (furnace inner profile) and the furnace mouth shape (furnace mouth profile). The furnace mouth a of converter A is subject to wear of the refractory, while the ingot (solidified molten iron) is likely to adhere. The shape and size also change due to this ingot adhesion, which affects the relationship between the tilting angle of the furnace body and the slag discharge amount. Therefore, in the profile measurement of the refractory shape of converter A as shown in FIG. 3, as the refractory shape, the furnace inner shape or / and the furnace mouth shape are measured. Also, when there is ingot adhering to the furnace mouth a, the measured furnace mouth shape is the furnace mouth shape including the adhering ingot. Also, as a means for performing the profile measurement of the refractory shape, an imaging device may be used. For example, instead of the non-contact distance meter 5 in FIG. 3, an imaging device is arranged, and the profile of the refractory shape (furnace inner shape or / and furnace mouth shape) is measured by the imaging device to obtain the actual measurement data of the refractory shape. The method for obtaining the actual measurement data of the refractory shape from the image captured by the imaging device will be described later.

[0018] In the present invention, based on the refractory shape actually measured as described above, the tilting angle of the furnace body during intermediate slag discharge is obtained and controlled. Specifically, for example, the following control is performed. The amount of molten iron and the amount of slag in the furnace during intermediate slag discharge can be calculated from the amount of hot metal charged into the converter (amount of molten material to be refined), the amount of refining agent, etc. Based on this amount of molten iron - slag amount and the actually measured refractory shape, the tilting angle of the furnace body (slag discharge start angle) when slag discharge (slag discharge) starts and the tilting angle of the furnace body (slag discharge end angle) when slag discharge ends (immediately before the start of molten iron discharge) are obtained when the converter is tilted. Therefore, during intermediate slag discharge, the tilting angle of the furnace body is controlled so that the converter is gradually tilted until this slag discharge end angle is reached. By thus controlling the tilting angle of the furnace body according to the slag discharge end angle obtained based on the actually measured refractory shape, it is possible to quickly discharge a large amount of slag (perform slag discharge) without discharging as much molten iron as possible. Preferably, during intermediate slag discharge, the tilting angle and tilting speed of the furnace body are controlled according to the slag discharge start angle and the slag discharge end angle. For example, during intermediate slag discharge, the tilting angle of the furnace body is controlled so that the converter is gradually tilted until the slag discharge end angle is reached. However, compared with the tilting speed from the start of tilting of the furnace body after the end of the previous blowing (start of tilting from the upright state with a tilting angle of 0 degrees) to the slag discharge start angle, the tilting speed after the start of slag discharge is lowered, and after the start of slag discharge, the tilting speed is decreased as it approaches the slag discharge end angle, and it is held at the slag discharge end angle for a certain period of time. Thereby, the purpose of discharging as much slag as possible quickly (discharging slag) without discharging molten iron as much as possible can be achieved at a higher level.

[0019] In order to confirm that the method of the present invention can accurately grasp the slag situation in the converter compared with the existing method (a method of determining the tilting angle of the furnace assuming that the refractory uniformly wears according to the number of uses), the following tests were conducted. The techniques of Patent Documents 1 and 2 cited above are based on the assumption that the refractory uniformly wears according to the number of uses. Table 1 shows the results of comparing the slag volume calculated under such an assumption (slag volume by the existing calculation method assuming uniform wear) with the slag volume calculated based on the profile of the refractory shape (refractory shape including the shape inside the furnace) measured as in the present invention. Figure 4 shows the results in a graph. In this test, in a converter with 1844 uses, the slag volume corresponding to various slag heights was determined. In Table 1 and Figure 4, the slag volume by the existing calculation method assuming uniform wear is denoted as "uniform wear", and the slag volume calculated based on the profile of the refractory shape measured as in the present invention is denoted as "measured value".

[0020]

Table 1

[0021] According to Table 1 and Figure 4, when the slag height is small, there is no difference in the slag volume between the two. However, when the slag height is large, it has been found that the existing calculation method assuming uniform wear overestimates the slag volume. That is, the actual wear of the converter refractory is less compared to the case assuming uniform wear. Here, the difference at 1844 uses is shown, but for other numbers of uses and furnace generations, the existing calculation method assuming uniform wear does not always overestimate the slag volume. There were also cases of underestimation. From the above results, it is difficult to accurately grasp the situation of the slag in the converter using the existing calculation method assuming uniform wear. On the other hand, it can be seen that the calculation method based on the actually measured refractory shape can accurately grasp the situation of the slag in the converter.

[0022] In addition, the influence of the refractory shape assuming uniform wear by the existing method and the actually measured refractory shape on the slag discharge behavior was also examined. Figure 5 shows the slag discharge behavior for each tilting angle in a converter with 2749 uses, for the refractory shape assuming uniform wear and the actually measured refractory shape (refractory shape including the in-furnace shape). Here, the molten iron volume and the slag volume are the same for both. In Figure 5, the refractory shape assuming uniform wear is denoted as "uniform wear", and the actually measured refractory shape is denoted as "measured value". According to Figure 5, in the case of the refractory shape assuming uniform wear by the existing method, slag discharge starts when the tilting angle reaches 50 degrees, while in the case of the actually measured refractory shape, slag discharge starts when the tilting angle reaches 60 degrees. That is, it has been found that the slag volume is underestimated in the case of the refractory shape assuming uniform wear by the existing method. Here, the difference at 2749 uses is shown, but for other numbers of uses and furnace generations, the calculation method assuming uniform wear does not always underestimate the slag volume. There were also cases of overestimation as in the case of the converter with 1844 uses shown earlier. That is, it can be seen that it is difficult to accurately reproduce the situation of the slag in the converter even with the existing calculation method assuming uniform wear.

[0023] Next, a case where the measured refractory shape is the furnace interior shape and the furnace mouth shape (furnace mouth shape including the adhering metal) in a preferred embodiment of the present invention will be described. The shape change of the converter occurs not only due to the wear of the refractory, but especially at the furnace mouth, where metal and the like adhere and the shape constantly changes. When the adhesion of the metal becomes excessive, operations such as oxygen blowing are performed to remove the metal. Fig. 6 schematically shows the change in the refractory shape including the furnace mouth according to the number of times the converter is used (exemplified). In the figure, 10 is the refractory constituting the furnace body, 11 is the metal adhering to the furnace mouth, the solid line indicates the refractory shape at each number of times the converter is used, and the dashed line indicates the refractory shape at 0 times of use (new furnace). This Fig. 6 shows that at the 307th use (Fig. 6(a)), there is almost no adhesion of the metal near the furnace mouth, but at the 337th use (Fig. 6(b)), the adhesion of the metal 11 near the furnace mouth has become excessive, so an example of removal by oxygen blowing is shown. In this case, although the furnace body shapes at the 307th use (Fig. 6(a)) and the 338th use (Fig. 6(c)) are relatively similar, the furnace body shape at the 337th use (Fig. 6(b)) is significantly different. Therefore, it is desirable that the control of the tilting angle of the furnace body during intermediate slag tapping takes into account not only the change in the refractory shape due to wear but also the temporary change in the furnace body shape due to the adhesion of the metal at the furnace mouth and the like.

[0024] The inventors of the present invention clarified by virtual experiments of slag tapping by numerical analysis that not only the furnace interior shape (the refractory shape inside the furnace) but also the furnace mouth shape in the refractory shape of the entire furnace greatly affects the slag tapping property. In this experiment, assuming a 1 / 20 scale of the actual machine, a converter vessel with a furnace height of 500 mm and a furnace diameter (barrel diameter) of 300 mm was used. In this converter vessel, a liquid 1 (virtual molten iron) with a depth of about 100 mm (3.4 kg) from the furnace bottom and a liquid 2 (virtual slag) with an upper layer of about 235 mm (2.1 kg) were held. The refractory shape including the furnace mouth was set to four types shown in Figs. 7(a) to (d). In the experiment, first, the furnace body was tilted at a speed of 2 degrees / s until 30 seconds from the start, and then at a speed of 0.35 degrees / s, and the slag tapping start angle was examined. Also, the slag tapping rate was examined when the tilting angle reached 115 degrees after the start of tilting. Here, the slag tapping rate indicates the ratio of the slag weight discharged outside the converter by slag tapping to the slag weight before slag tapping.

[0025] The results of examining the slag discharge start angle are shown in Table 2, and the results of examining the slag discharge rate are shown in Table 3, respectively. According to these, the slag discharge start angle and the slag discharge rate greatly depend on the furnace mouth shape, and depend more on the opening dimension than on the detailed shape such as whether there is a step at the furnace mouth. Thus, it can be understood that in evaluating the slag discharge property, the furnace mouth shape is also an important factor among the refractory shapes of the whole furnace, and it is also important to accurately grasp the furnace mouth shape.

Table 2

Table 3

[0026] The measurement of the furnace mouth shape (including the furnace mouth shape with the attached backing metal) and the furnace inner shape can be carried out by the method described above (Figure 3). For example, when performing the profile measurement of the furnace mouth shape using the non-contact distance meter 5 as shown in Figure 3, the measurement time can be shortened by limiting the measurement scanning range to the furnace mouth. Also, when using an imaging device, as shown in Figure 8, from two or more images taken by two or more imaging devices 9 (cameras) installed at different positions, photogrammetry, that is, selecting each pixel of the points common to the plurality of images, obtaining the correspondence of each pixel based on the principle of triangulation measurement, calculating the three-dimensional coordinates of the target points, and obtaining the distance to the target points, the profile measurement of the furnace mouth shape can be carried out. As another method, as shown in Figure 9, from the luminance information of the image of the furnace mouth, the luminance region where the backing metal exists (the gray part in the figure) is extracted to obtain the backing metal region of the furnace mouth, and the profile measurement of the furnace mouth shape can be carried out. Here, in Figure 9, 100 is the luminance region indicating the periphery of the furnace mouth, 101 is the luminance region indicating the attachment of the furnace mouth backing metal, and 102 is the luminance region indicating the furnace bottom refractory.

[0027] In the present invention, even when the measured refractory shape is the furnace interior shape and the furnace mouth shape (the furnace mouth shape including the attachment ingot), there is no change in controlling the tilting angle of the furnace body based on the measured refractory shape. The specific example is as described above, and the tilting angle (and further the tilting speed) of the furnace body is controlled according to the slag discharge start angle and the slag discharge end angle obtained based on the measured refractory shape. Thereby, it is possible to discharge as much slag as possible quickly (perform slag discharge) without discharging molten iron as much as possible.

[0028] In practicing the present invention, measurement of the refractory shape is carried out. However, since the measurement of the refractory shape is carried out during operation, if the measurement frequency is high, it will affect the production efficiency (furnace operation rate). On the other hand, compared with the shape change of the furnace mouth, the shape change due to the wear of the refractory in the furnace is relatively slow. Therefore, even if the measurement frequency of the refractory shape including the furnace interior shape is made lower than the measurement frequency of only the furnace mouth shape, there is no major problem in sequentially obtaining the measured values of the refractory shape. Therefore, when actually measuring the refractory shape in the present invention, measurement of the refractory shape including the furnace interior shape (usually the refractory shape of the entire furnace including the furnace interior shape; the same applies hereinafter) and measurement of only the furnace mouth shape are respectively carried out, and the measurement frequency of the refractory shape including the furnace interior shape can be made lower than the measurement frequency of only the furnace mouth shape. Thereby, while suppressing the influence on the production efficiency, it is possible to control the tilting angle of the furnace body during intermediate slag discharge based on the actually measured refractory shape. There are no particular restrictions on the measurement frequency of the refractory shape including the furnace interior shape and the measurement frequency of only the furnace mouth shape, and they may be determined in consideration of the influence on production efficiency, the work load required for measurement, etc. For example, the measurement frequency can be set such that the measurement of the refractory shape including the furnace interior shape is carried out every 300 to 700 charges, and the measurement of only the furnace mouth shape is carried out every 10 to 30 charges.

[0029] Also, when the measurement frequency of the refractory shape including the furnace interior shape is made lower than the measurement frequency of only the furnace mouth shape, the measurement result of only the furnace mouth shape with a high measurement frequency is combined with the measurement result of the refractory shape including the furnace interior shape with a low measurement frequency to obtain a refractory shape to be used for the intermediate slag discharge of the charge. Then, based on this combined refractory shape, the tilting angle of the furnace body for each charge is controlled. Figures 10 and 11 schematically show such synthesis examples. For the measurement results of the refractory shape including the furnace inner shape with low measurement frequency shown in each figure (a), the measurement results of only the furnace mouth shape with high measurement frequency shown in each figure (b) are synthesized to obtain the refractory shape shown in each figure (c). In this case, correction may be performed by adding to each figure (a) the prediction of the change over time of the furnace inner shape from the time of measurement in each figure (a) to the current operation charge. For example, assuming that the refractory wear occurs at a constant rate, correction is performed by subtracting a constant value (wear amount) corresponding to the number of charges from the measured value in figure (a).

[0030] Also, when the scrap removal operation is performed, it is desirable to measure only the furnace mouth shape, but the furnace mouth shape measured when the scrap removal was most recently performed can also be used. In that case, correction such as subtracting a constant value (wear amount) corresponding to the number of charges from the measured furnace mouth shape may be added. The measurement frequency of only the furnace mouth shape is desirably carried out at a high frequency to such an extent that it does not affect the production efficiency, but it is preferably at a higher frequency than the frequency of scrap removal. For example, when the scrap removal operation is carried out every 30 charges, it is preferable to carry out the measurement of only the furnace mouth shape one or more times during that period.

[0031] In the above-described embodiments (such as Figure 1), an example of applying the method of the present invention to the intermediate slag removal in the hot metal pretreatment was shown, but the method of the present invention can be widely applied to metal refining using a converter-type refining furnace, and for example, it is also applicable to non-ferrous metal refining such as converter steelmaking, electric furnace steelmaking, and copper refining. In the hot metal pretreatment to which the method of the present invention is applied, for example, when the desiliconization treatment and the dephosphorization treatment are carried out in this order with the intermediate slag removal in between, the intermediate slag removal is carried out by the above-described method. The hot metal that has undergone such a hot metal pretreatment is decarburized to become molten steel. Also, when the method of the present invention is applied to converter steelmaking, for example, when the desiliconization / dephosphorization treatment and the decarburization treatment are carried out in this order with the intermediate slag removal in between, the intermediate slag removal is carried out by the above-described method. Molten steel is obtained from hot metal by such converter steelmaking.

Example

[0032] [Example 1] In the pretreatment of hot metal using a 300-ton converter, the method of the present invention (example of the present invention) and the conventional method (comparative example) were each carried out 100 times (N = 100 times), and the slag discharge rate (intermediate slag discharge rate) in the intermediate slag discharge was compared. In determining the slag discharge rate, the slag weight before the intermediate slag discharge was taken as the slag generation amount obtained by the calculation of the blowing model. Also, for the slag weight discharged outside the converter during the intermediate slag discharge, a weighing device using a load cell system was installed on the slag transfer trolley that transports the discharged slag. After performing pretreatment such as air bagging of the slag ladle on the trolley, the slag weight discharged was determined from the weight at the completion of slag discharge. In the example of the present invention, the shape of the refractory in the furnace was measured by a laser distance meter at the start of the test (0 times) and after 50 times had elapsed. For the charge in which the refractory shape was not measured, the wear amount of the furnace body refractory was set at a constant 0.2 mm / times, and the furnace shape measured most recently was corrected.

[0033] Based on the amount of hot metal and the amount of refining agent charged into the converter, etc., the amount of molten iron and slag in the furnace at the time of intermediate slag discharge were calculated. Based on this amount of molten iron and slag and the measured refractory shape, the slag discharge start angle and the slag discharge end angle were determined. Then, during the intermediate slag discharge, while controlling the tilt angle of the furnace body so that the converter is gradually tilted until the slag discharge end angle is reached, the tilt speed from the start of tilting of the furnace body to the slag discharge start angle was increased, and in contrast, the tilt speed was decreased after the start of slag discharge. Further, as it approached the slag discharge end angle, the tilt speed was decreased, and it was set to be held for a certain period of time at the slag discharge end angle. In the comparative example, the wear amount of the furnace body refractory was set at a constant 0.2 mm / times, and intermediate slag discharge was carried out with the operator visually tilting the converter. Fig. 12 shows the average intermediate slag discharge rate and the width of the variation in the intermediate slag discharge rate in the example of the present invention and the comparative example. The intermediate slag discharge rate of the comparative example was about 45%, whereas the intermediate slag discharge rate of the example of the present invention was about 64%. Also, in the example of the present invention, the variation in the slag discharge amount in each time could be reduced as compared with the comparative example.

[0034] [Example 2] In the pretreatment of hot metal using a 300-ton converter, the two-level inventive method (Inventive Examples 1 and 2) and the conventional method (Comparative Example) were each carried out 100 times (N = 100 ch), and the slag discharge rate (intermediate slag discharge rate) in the intermediate slag discharge was compared. The intermediate slag discharge rate was determined in the same manner as in Example 1. Note that the conventional method (Comparative Example) is the same as [Example 1]. In Inventive Example 1, the refractory shape including the furnace interior shape (the refractory shape of the entire furnace including the furnace interior shape) was measured every 50 ch by the method shown in Fig. 3, and only the furnace mouth shape was measured every 10 ch by the method described in Fig. 9. In Inventive Example 2, the refractory shape including the furnace interior shape (the refractory shape of the entire furnace including the furnace interior shape) was measured every 50 ch by the method shown in Fig. 3, and only the furnace mouth shape was measured every 1 ch by the method described in Fig. 9. In both Inventive Examples 1 and 2, for charges where the refractory shape including the furnace interior shape was not measured, the wear amount of the furnace body refractory was set at a constant 0.2 mm / ch, and the furnace interior shape measured most recently was corrected.

[0035] Based on the amount of hot metal charged into the converter, the amount of refining agent, etc., the amount of molten iron and slag in the furnace during intermediate slag discharge was calculated, and the slag discharge start angle and the slag discharge end angle were determined based on this amount of molten iron and slag and the measured refractory shape. Then, during intermediate slag discharge, the tilting angle of the furnace body was controlled so that the converter was gradually tilted until the slag discharge end angle was reached, the tilting speed was increased from the start of tilting of the furnace body until the slag discharge start angle was reached, and the tilting speed was decreased after the start of slag discharge. Further, the tilting speed was decreased as the slag discharge end angle was approached, and it was held for a certain period of time at the slag discharge end angle. In this example, in the Comparative Example, the intermediate slag discharge rate was about 45%, and the width of the variation in the intermediate slag discharge rate for each ch was about 30%. In contrast, in Inventive Example 1, the intermediate slag discharge rate was about 65%, and the width of the variation for each ch was about 10%. In Inventive Example 2, the intermediate slag discharge rate was about 69%, and the width of the variation for each ch was about 7%. That is, in Inventive Examples 1 and 2, the intermediate slag discharge rate was improved compared with the Comparative Example, and the variation in the intermediate slag discharge rate could also be reduced. Also, when comparing Inventive Example 1 and Inventive Example 2, it can be seen that even if the measurement frequency of the refractory shape including the furnace interior shape is the same, the higher the measurement frequency of only the furnace mouth shape, the more the intermediate slag discharge rate is improved and the variation in the intermediate slag discharge rate is reduced.

[0036] [Example 3] In the preliminary treatment of hot metal using a 300-ton converter, the present invention method at two levels (present invention examples A and B) was carried out 100 charges each, and the slag discharge rate (intermediate slag discharge rate) and production efficiency in the intermediate slag discharge were compared. The intermediate slag discharge rate was determined in the same manner as in Example 1. In present invention example A, the refractory shape including the furnace interior shape (the refractory shape of the entire furnace including the furnace interior shape) was measured by the method of FIG. 3 every 10 charges, and only the furnace mouth shape was measured by the method described in FIG. 9 every 10 charges. In present invention example B, the refractory shape including the furnace interior shape (the refractory shape of the entire furnace including the furnace interior shape) was measured by the method of FIG. 3 every 50 charges, and only the furnace mouth shape was measured by the method described in FIG. 9 every 10 charges. In both present invention examples A and B, for charges where the refractory shape including the furnace interior shape was not measured, the loss amount of the furnace body refractory was set at a constant of 0.2 mm / charge, and the furnace interior shape measured most recently was corrected.

[0037] The amount of molten iron and slag in the furnace at the time of intermediate slag discharge was calculated from the amount of hot metal charged into the converter, the amount of refining agent, etc., and the slag discharge start angle and slag discharge end angle were determined based on this molten iron amount - slag amount and the actually measured refractory shape. Then, at the time of intermediate slag discharge, while controlling the tilting angle of the furnace body so that the converter is gradually tilted until the slag discharge end angle is reached, the tilting speed from the start of tilting of the furnace body to the slag discharge start angle is increased, and on the other hand, the tilting speed is decreased after the start of slag discharge. Further, the tilting speed is decreased as it approaches the slag discharge end angle, and it is held for a certain time at the slag discharge end angle. In this example, in both present invention examples A and B, the intermediate slag discharge rate was about 62%, and the range of variation in the intermediate slag discharge rate for each charge was about 11%, showing almost no change. On the other hand, regarding production efficiency, present invention example A, where the measurement frequency of the refractory shape including the furnace interior shape and the measurement frequency of only the furnace mouth shape are the same, had an average daily treatment of 45 charges, while present invention example B, where the measurement frequency of the refractory shape including the furnace interior shape was made less than the measurement frequency of only the furnace mouth shape, had an average daily treatment of 50 charges, and a higher production efficiency was obtained compared to present invention example A.

Explanation of Signs

[0038] 1 Molten iron 2 Desiliconized slag 3 Converter pan 4 Converter trolley 5 Non-contact distance meter 6 Tripod 7 Profile measuring device 8 Arithmetic unit 9 Imaging device 10 Refractory 11 Ingots 100 Luminance area indicating the vicinity of the furnace mouth 101 Luminance area indicating the adhesion of ingots to the furnace mouth 102 Luminance area indicating the bottom refractory of the furnace A Converter (Converter type refining furnace) a Furnace mouth

Claims

1. In the intermediate slag discharge process in metal refining using a converter-type refining furnace (A), when at least a part of the molten slag is discharged from the furnace by tilting the furnace body, Based on the actually measured refractory shape of the converter-type refining furnace (A) (including the refractory shape when there is an adhering ingot), the tilting angle of the furnace body is controlled, When actually measuring the refractory shape of the converter-type refining furnace (A), the measurement of the refractory shape including the inner furnace shape and the measurement of only the furnace mouth shape are each performed, and the measurement frequency of the refractory shape including the inner furnace shape is made less than the measurement frequency of only the furnace mouth shape. A method for intermediate slag discharge in metal refining is characterized by this.

2. The method for intermediate slag discharge in metal refining according to claim 1, wherein the furnace mouth shape is a furnace mouth shape including an adhering ingot.

3. When actually measuring the refractory shape of the converter-type refining furnace (A), profile measurement is performed by a measurement value by a non-contact distance meter and / or an image by an imaging device. The method for intermediate slag discharge in metal refining according to claim 1 or 2 is characterized by this.

4. Based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), the amount of molten metal and the amount of molten slag in the furnace during intermediate slag discharge are calculated. Based on this amount of molten metal and molten slag and the actually measured refractory shape, the slag discharge end angle, which is the tilting angle of the furnace body when slag discharge ends during intermediate slag discharge, is obtained. During intermediate slag discharge, the tilting angle of the furnace body is controlled according to the slag discharge end angle. The method for intermediate slag discharge in metal refining according to claim 1 or 2 is characterized by this.

5. Based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), the amount of molten metal and the amount of molten slag in the furnace during intermediate slag discharge are calculated. Based on this amount of molten metal and molten slag and the actually measured refractory shape, the slag discharge start angle, which is the tilting angle of the furnace body when slag discharge starts during intermediate slag discharge, and the slag discharge end angle, which is the tilting angle of the furnace body when slag discharge ends, are obtained. During intermediate slag discharge, the tilting angle and tilting speed of the furnace body are controlled according to the slag discharge start angle and the slag discharge end angle. The method for intermediate slag discharge in metal refining according to claim 1 or 2 is characterized by this.

6. During intermediate slag discharge, compared with the tilting speed from the start of tilting of the furnace body to the slag discharge start angle, the tilting speed after slag discharge start is made lower, and after slag discharge start, the tilting speed is decreased as it approaches the slag discharge end angle, and is held for a certain time at the slag discharge end angle. The method for intermediate slag discharge in metal refining according to claim 5 is characterized by this.

7. In a hot metal pretreatment method in which one converter type refining furnace (A) is used and desiliconization treatment and dephosphorization treatment are carried out in this order with intermediate slag removal in between, A hot metal pretreatment method characterized by performing the intermediate slag removal by the intermediate slag removal method according to claim 1 or 2.

8. A method for producing molten steel, characterized by obtaining molten steel through hot metal pretreatment by the hot metal pretreatment method according to claim 7.

9. In a steelmaking method in which one converter type refining furnace (A) is used and desiliconization / dephosphorization treatment and decarburization treatment are carried out in this order with intermediate slag removal in between, A steelmaking method characterized by performing the intermediate slag removal by the intermediate slag removal method according to claim 1 or 2.

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