JP7690977B2 - Intermediate slag removal method in metal refining - Google Patents

Description

The present invention relates to an intermediate slag removal method for discharging at least a portion of the molten slag from a converter-type refining furnace during metal refining.

In recent years, the quality requirements for steel products have become increasingly stringent, and there is a demand to reduce impurity elements such as silicon and phosphorus. To meet these requirements, in the steelmaking process at steelworks, it has become common to carry out pretreatment at the molten pig iron stage in advance to remove some of the silicon and phosphorus in the molten pig iron. In this process, after desiliconization of the molten pig iron in a converter-type refining furnace (hereinafter referred to as a converter), intermediate slag draining is performed by tilting the furnace body to drain at least a portion of the molten slag (desiliconization slag) in the furnace, and then a CaO-based flux is poured into the furnace to dephosphorize the molten pig iron. In this process, the key point in operation is how much desiliconization slag can be discharged in a short time in the intermediate slag draining after the desiliconization process.

In intermediate slag disposal, for example, if the tilting angle of the furnace body is increased in order to increase the amount of desiliconization slag discharged, a large amount of desiliconization slag is discharged, but the molten pig iron also flows out of the furnace throat together with the desiliconization slag. Since the iron yield decreases due to the outflow of the molten pig iron, it is not preferable to increase the intermediate slag disposal rate by simply increasing the tilting angle of the furnace body.
In addition, even if the amount of desiliconization slag generated in the desiliconization process is the same, the melt level of the desiliconization slag varies depending on the shape of the refractory in the converter (the shape of the refractory worn down by the use of the furnace), so the slag discharge start angle and slag discharge end angle (both are the tilting angles of the furnace body) at which the desiliconization slag starts to be discharged also vary greatly depending on the shape of the refractory. For this reason, it is necessary to perform intermediate slag discharge taking into account the shape of the refractory.
As prior art, for example, Patent Documents 1 and 2 propose a method of correcting the tilting angle of a converter furnace based on the number of times the converter furnace is used. Patent Document 3 also 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.

JP 2007-308773 A JP 2017-106110 A JP 2018-119195 A

However, Patent Documents 1 and 2 refer to the refractory shape depending on the number of converter furnace runs, but do not refer to the refractory shape for each furnace run or for each part of the converter. In actual converter operation, wear behavior varies greatly depending on the furnace run and each part, and the influence of these factors cannot be ignored. In addition, the method of Patent Document 3 can take into account the shape of the refractory during operation, but does not take into account the shape of the refractory near the furnace throat, which has a significant effect on the slag discharge behavior, and this may result in a large error.
For the above reasons, even if conventional techniques such as those described in Patent Documents 1, 2, and 3 are used, it is difficult to quickly discharge a predetermined amount of desiliconization slag from a converter in a short period of time without reducing the iron yield.

The object of the present invention is therefore to solve the problems of the prior art as described above, and to provide an intermediate slag removal method in the intermediate slag removal process in metal refining using a converter-type refining furnace, which allows a predetermined amount of molten slag to be quickly removed from the furnace in a short time without reducing the yield of molten metal when at least a portion of the molten slag is removed from the furnace by tilting the furnace.

The inventors conducted intensive research into the effect of the refractory shape of a converter-type refining furnace on the slag removal behavior of molten slag in the intermediate slag removal process in the converter-type refining furnace, and as a result, they discovered that by controlling the tilting angle of the furnace body based on the measured refractory shape, it is possible to quickly remove a predetermined amount of molten slag from the furnace in a short period of time without reducing the yield of molten metal.
The present invention has been made based on these findings, and has the following gist.

[1] In an intermediate slag removal process in metal refining using a converter-type refining furnace (A), when at least a portion of the molten slag is removed from the furnace by tilting the furnace body,
A method for intermediate slag removal in metal refining, characterized in that the tilting angle of the furnace body is controlled based on the actually measured refractory shape of a converter-type refining furnace (A) (including the refractory shape when there is attached bullion).
[2] The intermediate slag removal method in metal refining according to the above [1], characterized in that the refractory shape of the converter-type refining furnace (A) measured actually is the shape of the furnace interior and/or the shape of the furnace throat.
[3] The intermediate slag removal method in metal refining, wherein the furnace throat shape is a furnace throat shape that includes adhering metal, in the intermediate slag removal method in the above [2].
[4] In the intermediate slag removal method according to the above [2] or [3], when actually measuring the refractory shape of the converter-type refining furnace (A), the refractory shape including the furnace interior shape and only the furnace throat shape are measured, respectively, and the measurement frequency of the refractory shape including the furnace interior shape is made less than the measurement frequency of only the furnace throat shape.

[5] In any one of the intermediate slag removal methods according to the above [1] to [4], when actually measuring the shape of the refractory material of the converter-type refining furnace (A), a profile measurement is performed using a measurement value by a non-contact distance meter and/or an image by an imaging device.
[6] In any of the intermediate slag draining methods [1] to [5] above, the amount of molten metal and the amount of molten slag in the furnace at the time of intermediate slag draining are calculated based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), and based on the amount of molten metal and the amount of molten slag and the measured shape of the refractory material, a slag draining completion angle, which is the furnace body tilting angle at which slag draining is completed during intermediate slag draining, is calculated;
A method for intermediate slag removal in metal refining, characterized in that, during intermediate slag removal, the tilting angle of the furnace body is controlled according to the slag removal end angle.

[7] In any of the intermediate slag draining methods [1] to [5] above, the amount of molten metal and the amount of molten slag in the furnace at the time of intermediate slag draining are calculated based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), and based on the amount of molten metal and the amount of molten slag and the measured shape of the refractory material, a slag draining start angle, which is the angle of tilting the furnace body when slag draining starts during intermediate slag draining, and a slag draining end angle, which is the angle of tilting the furnace body when slag draining ends, are calculated;
A method for intermediate slag-draining in metal refining, characterized in that, during intermediate slag-draining, the tilting angle and tilting speed of the furnace body are controlled according to the slag-draining start angle and the slag-draining end angle.
[8] A method for intermediate slag discharging in metal refining according to the above item [7], characterized in that, during intermediate slag discharging, the tilting speed after the start of slag discharging is slower than the tilting speed from the start of tilting of the furnace body until the slag discharging start angle is reached, and the tilting speed is slowed down as the slag discharging completion angle is approached after the start of slag discharging, and the slag discharging completion angle is maintained for a certain period of time.

[9] A molten iron pretreatment method in which desiliconization and dephosphorization are performed in this order using one converter-type refining furnace (A) with intermediate slag removal in between,
A molten iron pretreatment method, comprising carrying out the intermediate slag removal by any one of the intermediate slag removal methods [1] to [8] above.
[10] A method for producing molten steel, comprising obtaining molten steel through the molten metal pretreatment method according to the above [9].
[11] A steelmaking method in which a single converter-type refining furnace (A) is used to carry out desiliconization, dephosphorization and decarburization in this order with intermediate slag disposal in between,
A steelmaking method, comprising the steps of: carrying out the intermediate slag removal by any one of the intermediate slag removal methods according to the above [1] to [8].

According to the present invention, in the intermediate slag removal process in metal refining using a converter-type refining furnace, when discharging at least a portion of the molten slag 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 molten metal.

An explanatory diagram showing desiliconization slag being discharged from a converter during the intermediate slag removal process in hot metal pretreatment. A schematic diagram showing the change in refractory shape depending on the number of times a converter is used FIG. 1 is an explanatory diagram showing a schematic example of a state in which a profile measurement of the refractory shape of a converter is carried out in the method of the present invention. This is a graph showing the slag volume (amount of slag) according to the slag height in a converter after a certain number of uses, comparing the slag volume calculated by the existing calculation method assuming uniform wear of the refractory with the slag volume calculated based on the profile of the refractory shape that was actually measured. An explanatory diagram showing the behavior of slag removal at each furnace body tilting angle for a refractory shape assuming uniform wear of the refractory and an actually measured refractory shape in a converter after a certain number of uses. A schematic diagram showing the change in the shape of the refractory, including the throat, depending on the number of times the converter is used. An explanatory diagram showing the refractory shape including the furnace throat in the virtual experiment FIG. 1 is an explanatory diagram showing a schematic example of a state in which a profile measurement of the converter throat shape is carried out in the method of the present invention. A schematic diagram showing the brightness distribution of the furnace port image FIG. 1 is an explanatory diagram showing a schematic example of a synthesis process in which the measurement results of the furnace interior shape and the measurement results of the furnace throat shape are synthesized to obtain the refractory shape of the entire furnace. FIG. 13 is an explanatory diagram showing a schematic example of another synthesis example in which the measurement results of the furnace interior shape and the measurement results of the furnace throat shape are synthesized to obtain the refractory shape of the entire furnace. Graph showing the average intermediate slag discharge rate and the range of variation in the intermediate slag discharge rate for the present invention and the comparative example in Example 1.

Fig. 1 shows the process of discharging desiliconization slag from a converter in the intermediate slag removal process of hot metal pretreatment. In the figure, A is a converter (converter-type refining furnace), 1 is molten iron (hot metal), 2 is desiliconization slag, 3 is a slag ladle, and 4 is a slag cart.
At the end of the desiliconization process, the desiliconization 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 the carbon in the molten iron, and its apparent volume increases to several times that of the case without the bubbles, in a so-called foaming state. After this, the converter A is tilted to discharge the desiliconization slag 2 from the throat toward the slag ladle 3 installed below the furnace.

The refractory wear of the converter A furnace body occurs as a result of repeated blowing, and the shape gradually changes. Figures 2(a) to (c) show schematic diagrams of the change in refractory shape (furnace interior shape and furnace throat shape) depending on the number of times converter A is used. In the figures, 10 is the refractory that makes up the furnace body, the solid lines show the refractory shape at each converter use count, and the dashed lines (dashed lines in Figures 2(b) and (c)) show the refractory shape at zero uses (new furnace). When converter A is used relatively few times, the refractory shape is close to that of a new furnace, but when converter A is used many times, the refractory wear progresses locally, resulting in an uneven wear state. This wear state changes every time the furnace price of converter A changes, and also changes depending on the daily operating conditions.

Therefore, in the present invention, the shape of the refractory of the converter A (including the shape of the refractory when there is attached metal) is measured periodically, and when the furnace body is tilted to perform intermediate slag discharge, 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, the profile of the refractory shape is measured periodically (for example, every day) using a means such as a non-contact type distance meter or an image pickup device, and the tilting angle of the furnace body during intermediate slag discharge (slag discharge start angle, slag discharge end angle) is obtained based on the actual value of the refractory shape obtained by this measurement, and the tilting angle of the furnace body is controlled based on this. Furthermore, if necessary, the tilting speed may be controlled as described later.
Fig. 3 is a schematic diagram showing an example of a state in which a profile measurement of a refractory shape is carried out, and shows a case in which the profile measurement of the refractory shape is carried out using a non-contact type distance meter 5 (e.g., a laser distance meter, etc.) arranged toward the throat a of the converter A. In this case, after the treatment in the converter A is completed, the molten iron is tapped and the slag is removed, and then the converter A is tilted so that the throat a faces the non-contact type distance meter 5 (in the figure, 6 is a tripod) arranged near the converter A. As shown in Fig. 3, in a state in which the furnace body is tilted until the inside of the furnace can be observed from the throat a, the non-contact type distance meter 5 measures distances to a plurality of measurement points in the furnace and at the throat, and the profile measurement device 7 obtains actual measurement data of the refractory shape from the measured values.

Here, the refractory shape that affects the relationship between the tilting angle of the furnace body and the amount of slag discharged during intermediate slag discharge includes the furnace interior shape (furnace interior profile) and the furnace throat shape (furnace throat profile). The furnace throat a of the converter A is subject to refractory wear, but is also prone to adhesion of metal (solidified molten iron), and this adhesion of metal also changes the shape and size, affecting the relationship between the tilting angle of the furnace body and the amount of slag discharged. Therefore, in the profile measurement of the refractory shape of the converter A as shown in Figure 3, the furnace interior shape and/or the furnace throat shape are measured as the refractory shape. Furthermore, when metal is attached to the furnace throat a, the measured furnace throat shape is the furnace throat shape including the attached metal.
An imaging device may be used as a means for measuring the profile of the refractory shape, for example, an imaging device is provided instead of the non-contact type distance meter 5 in Fig. 3, and the imaging device is used to measure the profile of the refractory shape (furnace interior shape and/or furnace opening shape) and obtain measured data of the refractory shape. A method for obtaining measured data of the refractory shape from an image captured by the imaging device will be described later.

In the present invention, the tilting angle of the furnace body during intermediate slag draining is calculated based on the shape of the refractory measured as described above, and the angle is controlled. Specifically, for example, the following control is performed. The amount of molten iron and slag in the furnace during intermediate slag draining can be calculated from the amount of molten iron (amount of molten material to be refined) and the amount of refining agent charged into the converter. Based on the amount of molten iron and slag and the measured shape of the refractory, the tilting angle of the furnace body when slag draining (slag discharge) starts as the converter is tilted (slag discharge start angle) and the tilting angle of the furnace body when slag discharge ends (just before molten iron discharge starts) are calculated. Therefore, during intermediate slag draining, the tilting angle of the furnace body is controlled so that the converter is gradually tilted until it reaches this slag discharge end angle. In this way, by controlling the tilting angle of the furnace body in accordance with the slag discharge end angle obtained based on the actually measured shape of the refractory, it is possible to quickly discharge (discharge) as much slag as possible while minimizing the discharge of molten iron.
Also, preferably, during intermediate slag dumping, the tilting angle and tilting speed of the furnace body are controlled according to the slag dumping start angle and the slag dumping end angle. For example, during intermediate slag dumping, the tilting angle of the furnace body is controlled so that the converter is gradually tilted until the slag dumping end angle is reached. However, the tilting speed after the start of slag dumping is slower than the tilting speed from the start of tilting of the furnace body after the end of the early blowing (tilting start from an upright state with a tilting angle of 0 degrees) until the slag dumping start angle, and after the start of slag dumping, the tilting speed is slowed as the slag dumping end angle is approached, and the slag dumping end angle is held for a certain period of time. This makes it possible to more highly achieve the objective of quickly discharging (discharging) as much slag as possible without discharging as much molten iron as possible.

In order to confirm that the method of the present invention can accurately grasp the state of slag in a converter and tilt the converter at an appropriate tilting angle during intermediate slag removal, as compared with the existing method (a method in which the tilting angle of the furnace is determined on the assumption that the refractories wear uniformly depending on the number of times they are used), the following tests were carried out.
The techniques of Patent Documents 1 and 2 cited above are based on the assumption that the refractory wears uniformly depending on the number of uses. Table 1 shows a comparison of the slag volume calculated based on such an assumption (slag volume calculated by the existing calculation method assuming uniform wear) with the slag volume calculated based on the profile of the refractory shape (including the shape inside the furnace) measured as in the present invention. FIG. 4 is a graph showing the results. In this test, slag volumes corresponding to various slag heights were obtained in a converter that had been used 1,844 times. In Table 1 and FIG. 4, the slag volume calculated based on the existing calculation method assuming uniform wear is indicated as "uniform wear", and the slag volume calculated based on the profile of the refractory shape measured as in the present invention is indicated as "actual measurement value".

According to Table 1 and Figure 4, when the slag height is small, there is no difference in the slag volume between the two, but when the slag height is large, it was found that the existing calculation method assuming uniform wear overestimates the slag volume. In other words, the actual wear of the converter refractory was less than when uniform wear was assumed. Here, the difference at 1,844 uses is shown, but for other uses and furnace costs, the existing calculation method assuming uniform wear does not necessarily always overestimate the slag volume, and there were also cases where it was underestimated. From the above results, it is clear that the existing calculation method assuming uniform wear makes it difficult to accurately grasp the condition of the slag in the converter, while the calculation method based on the actually measured refractory shape can accurately grasp the condition of the slag in the converter.

We also investigated the influence of the refractory shape assuming uniform wear according to the existing method and the actually measured refractory shape on the slag discharge behavior. Figure 5 shows the slag discharge behavior for each tilting angle for the refractory shape assuming uniform wear and the actually measured refractory shape (including the furnace interior shape) in a converter that had been used 2,749 times. Here, the molten iron volume and 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 "actual value".
According to Fig. 5, in the case of the refractory shape assuming uniform wear according to the existing method, slag discharge starts when the tilting angle reaches 50 degrees, whereas in the case of the measured refractory shape, slag discharge starts when the tilting angle reaches 60 degrees. That is, in the case of the refractory shape assuming uniform wear according to the existing method, it was found that the slag volume was underestimated. Here, the difference at 2749 uses was shown, but in other uses and furnace costs, the calculation method assuming uniform wear did not always underestimate the slag volume, and there were also cases where the slag volume was overestimated, as in the case of the converter with 1844 uses shown above. That is, it is found that even with the existing calculation method assuming uniform wear, it is difficult to accurately reproduce the state of the slag in the converter.

Next, a preferred embodiment of the present invention will be described in which the refractory shape to be actually measured is the furnace interior shape and the furnace throat shape (furnace throat shape including the deposited metal).
The shape of the converter changes due to reasons other than the wear of the refractory. In particular, the shape of the throat is constantly changing due to the adhesion of metals and the like. When the adhesion of metals becomes excessive, the work of removing the metals is carried out by blowing oxygen or the like. Figure 6 is a schematic (illustrative) diagram showing the change in the shape of the refractory, including the throat, depending on the number of times the converter is used. In the figure, 10 is the refractory constituting the furnace body, 11 is the metals attached to the throat, the solid lines show the refractory shapes at each number of times the converter is used, and the dashed lines show the refractory shapes at 0 times of use (new furnace). This Figure 6 shows an example in which there is almost no adhesion of metals near the throat in the 307th use (Figure 6(a)), but the adhesion of metals 11 near the throat became excessive in the 337th use (Figure 6(b)), so the metals were removed by blowing oxygen. In this case, the furnace body shapes for the 307th use (Fig. 6(a)) and the 338th use (Fig. 6(c)) are relatively similar, but the shape of the furnace body for the 337th use (Fig. 6(b)) is significantly different. Therefore, when controlling the tilting angle of the furnace body during intermediate slag draining, it is desirable to take into consideration 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 base metal to the throat.

The inventors have clarified through a virtual experiment of slag removal using numerical analysis that not only the furnace interior shape (the refractory shape in the furnace) but also the furnace opening shape has a large effect on slag removal performance among the refractory shapes of the entire furnace. In this experiment, a converter vessel with a furnace height of 500 mm and a furnace diameter (body diameter) of 300 mm was used, assuming a scale of 1/20 of the actual machine, and liquid 1 (virtual molten iron) with a depth of about 100 mm (3.4 kg) from the bottom of the furnace and liquid 2 (virtual slag) with a depth of about 235 mm (2.1 kg) above it were held in the converter vessel. The refractory shapes including the furnace opening were four types shown in Figures 7 (a) to (d). In the experiment, the furnace body was tilted at a speed of 2 degrees/s for the first 30 seconds and then at a speed of 0.35 degrees/s to examine the slag removal start angle. In addition, the slag removal rate was examined when the tilting angle reached 115 degrees after the start of tilting. Here, the slag discharge rate refers to the ratio of the weight of slag discharged outside the converter by slag discharge to the weight of slag before slag discharge.

The results of the investigation of the slag discharge start angle are shown in Table 2, and the results of the investigation of the slag discharge rate are shown in Table 3. According to these, the slag discharge start angle and the slag discharge rate are greatly dependent on the furnace throat shape, and are more dependent on the opening dimensions than on the detailed shape such as whether the throat has a step or not. Thus, in order to evaluate the slag discharge performance, the throat shape is also an important factor among the refractory shapes of the entire furnace, and it is clear that it is also important to accurately grasp the throat shape.

The throat shape (thrust shape including the deposited metal) and the shape inside the furnace can be measured by the method described above (FIG. 3). For example, when measuring the profile of the throat shape using a non-contact distance meter 5 as shown in FIG. 3, the measurement time can be reduced by limiting the measurement scanning range to the throat.
In addition, when an imaging device is used, as shown in Fig. 8, from two or more images taken by two or more imaging devices 9 (cameras) installed at different positions, photogrammetry, i.e., selecting pixels of points common to a plurality of images, determining the correspondence of each pixel by the principle of triangulation, calculating the three-dimensional coordinates of the target point, and acquiring the distance to the target point, can be used to perform profile measurement of the throat shape. As another method, as shown in Fig. 9, a brightness area where bare metal exists (gray area in the figure) can be extracted from brightness information of an image taken of the throat to determine the bare metal area of the throat, and the throat shape profile can be measured. Here, in Fig. 9, 100 is a brightness area indicating the vicinity of the throat, 101 is a brightness area indicating the attachment of bare metal to the throat, and 102 is a brightness area indicating the hearth refractory.

In the present invention, even when the measured refractory shape is the furnace interior shape and the furnace mouth shape (furnace mouth shape including the attached base metal), the tilting angle of the furnace body is still controlled based on the measured refractory shape. Specific examples are as described above, and the tilting angle of the furnace body (and the tilting speed) is controlled according to the slag discharge start angle and slag discharge end angle determined based on the measured refractory shape. This makes it possible to discharge (discharge) as much slag as possible quickly while minimizing the discharge of molten iron.

In carrying out the present invention, the refractory shape is measured. However, since the measurement of the refractory shape is carried out between operations, if the measurement frequency is high, it will affect the production efficiency (furnace operating rate). On the other hand, since the shape change due to wear of the refractory in the furnace is relatively gradual compared to the shape change of the furnace throat, even if the measurement frequency of the refractory shape including the furnace inner shape is made less than the measurement frequency of only the furnace throat shape, there is no big problem in sequentially obtaining the actual value of the refractory shape. Therefore, when actually measuring the refractory shape in the present invention, the measurement of the refractory shape including the furnace inner shape (usually the refractory shape of the entire furnace including the furnace inner shape; the same applies below) and the measurement of only the furnace throat shape are performed, and the measurement frequency of the refractory shape including the furnace inner shape can be made less than the measurement frequency of only the furnace throat shape. This makes it possible to control the tilt angle of the furnace body at intermediate slag discharge based on the measured refractory shape while suppressing the influence on the production efficiency.
There is no particular restriction on the frequency of measurement of the refractory shape including the furnace interior shape and the frequency of measurement of only the furnace opening shape, and these may be determined taking into consideration the impact on production efficiency and the workload required for the measurements. For example, the measurement frequency can be set so that the measurement of the refractory shape including the furnace interior shape is performed every 300 to 700 ch, and the measurement of only the furnace opening shape is performed every 10 to 30 ch.

In addition, when the measurement frequency of the refractory shape including the furnace interior shape is set lower than the measurement frequency of only the furnace opening shape, the measurement results of the refractory shape including the furnace interior shape that is measured less frequently can be combined with the measurement results of only the furnace opening shape that is measured more frequently to obtain the refractory shape to be used for intermediate slag removal of the charge. Then, the tilting angle of the furnace body for each charge is controlled based on this combined refractory shape.
Figures 10 and 11 are schematic diagrams showing such synthesis examples, in which the measurement results of the refractory shape including the furnace interior shape, which is measured less frequently, shown in each figure (a), are synthesized with the measurement results of only the furnace opening shape, which is measured more frequently, shown in each figure (b), to obtain the refractory shape shown in each figure (c). In this case, a correction may be made by adding a prediction of the change in the furnace interior shape over time from the measurement time of each figure (a) to the current operational charge to each figure (a). For example, a correction is made by assuming that the refractory wear occurs at a constant rate and subtracting a constant value (amount of wear) according to the number of charges from the measurement value in figure (a).

Although it is desirable to measure only the throat shape when the metal removal work is performed, the throat shape measured when the metal removal work was performed most recently can be used. In that case, a correction such as subtracting a fixed value (loss amount) according to the number of charges from the measured throat shape may be performed.
The frequency of measurement of only the throat shape is desirably performed as frequently as possible without affecting production efficiency, but is preferably higher than the frequency of metal removal. For example, when metal removal is performed every 30 charges, it is preferable to measure only the throat shape at least once during that time.

In the above-described embodiment (FIG. 1, etc.), an example has been shown in which the method of the present invention is applied to intermediate slag removal in molten iron pretreatment. However, the method of the present invention can be widely applied to metal refining using a converter-type refining furnace, and can also be applied to, for example, converter steelmaking, electric furnace steelmaking, copper refining, and other non-ferrous metal refining processes.
In the hot metal pretreatment to which the present invention is applied, for example, when desiliconization and dephosphorization are performed in this order with intermediate slag removal in between, the intermediate slag removal is performed by the above-mentioned method. After such hot metal pretreatment, the hot metal is decarburized to become molten steel.
When the method of the present invention is applied to converter steelmaking, for example, when desiliconization/dephosphorization and decarburization are performed in this order with intermediate slag removal in between, the intermediate slag removal is performed by the above-mentioned method. Molten steel is obtained from molten pig iron by such converter steelmaking.

[Example 1]
In the hot metal pretreatment using a 300 ton converter, the present invention (example) and the conventional method (comparison example) were carried out with N=100ch each, and the slag removal rate at intermediate slag removal (intermediate slag removal rate) was compared. In calculating the slag removal rate, the weight of slag before intermediate slag removal was taken as the amount of slag generated calculated by the blowing model. In addition, the weight of slag discharged from the converter in intermediate slag removal was calculated by installing a load cell type weighing device on the slag transfer cart that transports the discharged slag, and after pretreatment such as taring the slag ladle on the cart, the weight of the discharged slag was calculated from the weight at the time of completion of slag discharge.
In the present invention, the shape of the refractory inside the furnace was measured by a laser distance meter at the start of the test (0 ch) and after 50 ch. In the charge in which the refractory shape was not measured, the wear rate of the furnace body refractory was set constant at 0.2 mm/ch, and the most recently measured shape inside the furnace was corrected.

The amount of molten iron and slag in the converter during intermediate slag draining was calculated from the amount of molten iron and refining agents charged into the converter, and the start and end angles of slag draining were calculated based on the amount of molten iron and slag and the measured shape of the refractories. During intermediate slag draining, the tilting angle of the converter was controlled so that the converter was gradually tilted until it reached the end angle of slag draining, and the tilting speed was increased from the start of tilting the converter until it reached the start angle of slag draining, while the tilting speed was decreased after slag draining had started. Furthermore, the tilting speed was decreased as the end angle of slag draining was approached, and the end angle of slag draining was maintained for a certain period of time.
In the comparative example, the wear rate of the furnace body refractory was set constant at 0.2 mm/ch, and intermediate slag removal was performed by tilting the converter under visual inspection by an operator.
Figure 12 shows the average intermediate slag discharge rate and the range of variation in the intermediate slag discharge rate in the present invention example and the comparative example. The intermediate slag discharge rate in the comparative example was about 45%, while the intermediate slag discharge rate in the present invention example was about 64%. In addition, the present invention example was able to reduce the variation in the amount of slag discharged in each channel compared to the comparative example.

[Example 2]
In the hot metal pretreatment using a 300 ton converter, two levels of the present invention (Invention Examples 1 and 2) and a conventional method (Comparative Example) were carried out with N = 100 ch each, and the slag removal rate in intermediate slag removal (intermediate slag removal rate) was compared. The intermediate slag removal rate was obtained in the same manner as in Example 1. The conventional method (Comparative Example) was the same as [Example 1].
In Example 1 of the present invention, the refractory shape including the furnace internal shape (the refractory shape of the entire furnace including the furnace internal shape) was measured every 50 channels using the method of Fig. 3, and only the furnace throat shape was measured every 10 channels using the method described in Fig. 9. In Example 2 of the present invention, the refractory shape including the furnace internal shape (the refractory shape of the entire furnace including the furnace internal shape) was measured every 50 channels using the method of Fig. 3, and only the furnace throat shape was measured every 1 channel using the method described in Fig. 9. In both Examples 1 and 2 of the present invention, in charges in which the refractory shape including the furnace internal shape was not measured, the wear amount of the furnace body refractory was set constant at 0.2 mm/ch, and the furnace internal shape measured most recently was corrected.

The amount of molten iron and slag in the converter during intermediate slag draining was calculated from the amount of molten iron and refining agents charged into the converter, and the start and end angles of slag draining were calculated based on the amount of molten iron and slag and the measured shape of the refractories. During intermediate slag draining, the tilting angle of the converter was controlled so that the converter was gradually tilted until it reached the end angle of slag draining, and the tilting speed was increased from the start of tilting the converter until it reached the start angle of slag draining, while the tilting speed was decreased after slag draining had started. Furthermore, the tilting speed was decreased as the end angle of slag draining was approached, and the end angle of slag draining was maintained for a certain period of time.
In this embodiment, the intermediate slag discharge rate in the comparative example was about 45%, and the variation in the intermediate slag discharge rate in each channel was about 30%, while the intermediate slag discharge rate in the present invention example 1 was about 65%, and the variation in the intermediate slag discharge rate in each channel was about 10%, and the intermediate slag discharge rate in the present invention example 2 was about 69%, and the variation in the intermediate slag discharge rate in each channel was about 7%. That is, the intermediate slag discharge rate in the present invention examples 1 and 2 was improved and the variation in the intermediate slag discharge rate was reduced compared to the comparative example. In addition, when the present invention example 1 and the present invention example 2 are compared, it can be seen that the intermediate slag discharge rate is improved and the variation in the intermediate slag discharge rate is reduced when the measurement frequency of only the furnace opening shape is higher, even if the measurement frequency of the refractory shape including the furnace interior shape is the same.

[Example 3]
In the hot metal pretreatment using a 300 ton converter, two levels of the method of the present invention (Invention Examples A and B) were carried out with N = 100 ch each, and the slag removal rate at intermediate slag removal (intermediate slag removal rate) and production efficiency were compared. The intermediate slag removal rate was obtained in the same manner as in Example 1.
In Example A, the refractory shape including the furnace internal shape (the refractory shape of the entire furnace including the furnace internal shape) was measured every 10 ch using the method of Fig. 3, and only the furnace throat shape was measured every 10 ch using the method described in Fig. 9. In Example B, the refractory shape including the furnace internal shape (the refractory shape of the entire furnace including the furnace internal shape) was measured every 50 ch using the method of Fig. 3, and only the furnace throat shape was measured every 10 ch using the method described in Fig. 9. In both Examples A and B, in charges where the refractory shape including the furnace internal shape was not measured, the wear amount of the furnace body refractory was set constant at 0.2 mm/ch, and the furnace internal shape measured most recently was corrected.

The amount of molten iron and slag in the converter during intermediate slag draining was calculated from the amount of molten iron and refining agents charged into the converter, and the start and end angles of slag draining were calculated based on the amount of molten iron and slag and the measured shape of the refractories. During intermediate slag draining, the tilting angle of the converter was controlled so that the converter was gradually tilted until it reached the end angle of slag draining, and the tilting speed was increased from the start of tilting the converter until it reached the start angle of slag draining, while the tilting speed was decreased after slag draining had started. Furthermore, the tilting speed was decreased as the end angle of slag draining was approached, and the end angle of slag draining was maintained for a certain period of time.
In this example, the intermediate slag discharge rate was about 62% for both Invention Examples A and B, and the variation in the intermediate slag discharge rate for each channel was about 11%, which was almost the same. On the other hand, with regard to production efficiency, Invention Example A, in which the measurement frequency of the refractory shape including the furnace inner shape was the same as the measurement frequency of only the furnace opening shape, had an average daily processing rate of 45 channels, whereas Invention Example B, in which the measurement frequency of the refractory shape including the furnace inner shape was less than the measurement frequency of only the furnace opening shape, had an average daily processing rate of 50 channels, and thus achieved a higher production efficiency than Invention Example A.

REFERENCE SIGNS LIST 1 molten iron 2 desiliconization slag 3 slag ladle 4 slag trolley 5 non-contact distance meter 6 tripod 7 profile measuring device 8 computing device 9 imaging device 10 refractory 11 ingot 100 brightness area showing vicinity of furnace throat 101 brightness area showing ingot adhesion to furnace throat 102 brightness area showing hearth refractory A converter (converter-type refining furnace)
a Hearth mouth

Claims (9)

In an intermediate slag removal process in metal refining using a converter-type refining furnace (A), when at least a portion of the molten slag is removed from the furnace by tilting the furnace body,
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 attached metal);
This method for intermediate slag removal in metal refining is characterized in that, when measuring the refractory shape of a converter-type refining furnace (A), the refractory shape including the furnace interior shape and only the furnace opening shape are measured, and the measurement frequency of the refractory shape including the furnace interior shape is made less than the measurement frequency of only the furnace opening shape. The method for intermediate slag removal in metal refining according to claim 1 , characterized in that the furnace throat shape is a furnace throat shape that includes adherent bullion. The intermediate slag removal method in metal refining according to claim 1 or 2, characterized in that when measuring the refractory shape of the converter-type refining furnace (A), profile measurement is performed using measurement values from a non-contact distance meter and/or an image from an imaging device. The amount of molten metal and the amount of molten slag in the furnace at the time of intermediate slag draining are calculated based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), and the amount of molten metal and the amount of molten slag in the furnace at the time of intermediate slag draining is calculated based on the amount of molten metal and the amount of molten slag and the measured shape of the refractory material, and the slag draining completion angle, which is the furnace body tilting angle at which slag draining is completed during intermediate slag draining, is calculated.
3. The method for intermediate slag removal in metal refining according to claim 1 , wherein the tilting angle of the furnace body is controlled according to the end angle of the intermediate slag removal. The amount of molten metal and the amount of molten slag in the furnace at the time of intermediate slag discharge are calculated based on the amount of molten material to be refined and the amount of refining agent charged into the converter-type refining furnace (A), and based on the amount of molten metal and the amount of molten slag and the measured shape of the refractory material, the slag discharge start angle, which is the angle of tilting the furnace body when slag discharge starts during intermediate slag discharge, and the slag discharge end angle, which is the angle of tilting the furnace body when slag discharge ends, are calculated;
3. The method for intermediate slag removal in metal refining according to claim 1 or 2 , characterized in that, during intermediate slag removal, the tilting angle and the tilting speed of the furnace body are controlled according to the slag removal start angle and the slag removal end angle. 6. The method for intermediate slag discharging in metal refining according to claim 5, characterized in that, during intermediate slag discharging, the tilting speed after the start of slag discharging is slower than the tilting speed from the start of tilting the furnace body until the slag discharging start angle is reached, and the tilting speed is slowed down as the slag discharging end angle is approached after the start of slag discharging, and the slag discharging end angle is held for a certain period of time. A molten iron pretreatment method using one converter-type refining furnace (A) and carrying out desiliconization and dephosphorization in this order with intermediate slag removal in between, comprising:
A molten iron pretreatment method, comprising the steps of: carrying out the intermediate slag removal by the intermediate slag removal method according to claim 1 or 2 . A method for producing molten steel, comprising obtaining molten steel through a molten metal pretreatment method according to claim 7 . A steelmaking method using one converter-type refining furnace (A) and carrying out desiliconization, dephosphorization and decarburization in this order with intermediate slag disposal in between,
A steelmaking method, comprising the steps of: carrying out the intermediate slag removal by the intermediate slag removal method according to claim 1 or 2 .

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