JP3528625B2 - Slag forming suppression method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing slag forming during hot metal pretreatment and converter blowing in a steelmaking process. 2. Description of the Related Art Conventionally, in a steelmaking process for producing molten steel from hot metal, pretreatment of hot metal and blowing in a converter are generally performed in many cases. In order to carry out these treatments more efficiently, the type of converter is mainly an upper-bottom blowing converter with a strong stirring force, and removes hot metal from the P, Si and S before blowing the converter. Also in the hot metal pretreatment process for the purpose of, etc., the use of the upper-bottom blowing converter is increasing. [0003] However, in a process using an upper-bottom blowing converter, whether the purpose is hot metal pretreatment or converter blowing, the slag forming or slopping (hereinafter referred to as slag forming or slapping) during the process is performed. It is difficult to completely suppress the occurrence of slag forming, and slag forming has a serious problem in terms of operation inhibition and yield deterioration. Conventionally, in order to solve this problem, Japanese Patent Laid-Open Nos. 62-202013 and 2-66108 disclose methods for preventing slag forming in an upper-bottom blowing converter. A method for adding carbonaceous material and a method for adding steam from above the converter disclosed in Japanese Patent Application Laid-Open No. 1-129919 are known. There are drawbacks, such as the necessity of newly installing equipment for adding a sedative such as steam and the cost of the sedative itself. As a method of suppressing forming without using a sedative, a method of increasing the amount of bottom-blown gas at the time of forming as disclosed in Japanese Patent Application Laid-Open No. 57-57820 and a method disclosed in Japanese Patent Application Laid-Open No. 2-66108 are disclosed. A method of reducing the amount of the top blown gas and a method of changing the kind of the bottom blown gas disclosed in Japanese Patent Application Laid-Open No. 57-177912 have been proposed. However, experiments conducted by the present inventors have revealed that these effects are unstable and may promote slag forming with a certain probability. However, an inexpensive and reliable method for preventing slag forming has not yet been established, and slag forming is still a major factor in hindering operation in actual operations. [0007] It is an object of the present invention to provide a method for inexpensively and surely suppressing slag forming in hot metal pretreatment or converter blowing using an upper-bottom blowing converter. The present inventors have conducted various studies on means for solving the above-mentioned problems, and as a result, have found that treatment in a top-bottom blowing converter (hot metal pretreatment, converter blowing). At that time, it was found that slag forming can be completely suppressed by appropriately adjusting the upper flow rate and the lower flow rate when slag forming occurs, and that there is a critical condition for that. That is, when the bottom flow rate at the time of occurrence of slag forming is b ₀ (Nm ³ / min) and the top flow rate is t ₀ (Nm ³ / min), b ₁ / b ₀ = B, t ₁ / Assuming that t ₀ = T, slag forming is generated by adjusting the upper flow rate t ₁ and the lower flow rate b ₁ so as to satisfy T · B ² ≦ 0.25 (where 1.0 <T or 1.0 <B). Is effectively suppressed. In this regard, as disclosed in Japanese Patent Application Laid-Open No. 57-57820, a method of increasing the amount of bottom-blown gas when slag forming occurs in an upper-bottom-blown converter has been proposed. According to the experiments of the present inventors, the effect of calming slag forming can be seen when the bottom blowing gas is increased while the top blowing condition is kept constant, but the degree of slag forming is remarkably promoted at a frequency of about 20%. There was a case. As described above, since the operation hindrance when slag forming is promoted is severe, it is difficult to apply such a method online. Therefore, the present inventors have further analyzed and found that, as shown in FIGS. 1 (a) and 1 (b), bubbles of the bottom-blown gas floating from the molten iron being processed in the upper-bottom-blown converter. When the floating point is different from the point at which the top gas reaches the molten iron surface (see Fig. 1 (b)), although the forming suppression effect is obtained, the top gas reaches the same point as the bottom gas bubble floating point. Case (Fig. 1
(See (a)), on the contrary, was found to promote forming. [0012] This is because the bottom-blown gas, which originally rises to form a gas hole in the slag, loses its rising speed due to the interference of the top-blown gas, and disperses and stays in the slag. It is because they do. In order to avoid this, it may be effective to change the position of the bottom blowing tuyere or the form of the upper blowing lance, but in the situation of slag forming, the trajectory of the jet of the upper blowing gas does not follow the initial setting. Due to its instability, it may overlap with the floating point of the bottom-blown gas with a certain probability. From these facts, it has been found that the following two points are important for suppressing forming with a high probability. The frequency of contact between the bottom-blown gas and the top-blown gas at the molten iron-slag interface is reduced. In order to actively create loopholes in the forming slag,
Increase the total amount of blown gas as much as possible. In order to satisfy only the above conditions, it is sufficient to lower the flow rate of both the top and bottom blown gases.
In order to satisfy both conditions, an upper limit is set for the total amount of blown gas, the amount of top blown gas is reduced when the amount of bottom blown gas is increased, and the amount of bottom blown gas is reduced when the amount of top blown gas is increased. It can be seen that the technique of reducing is appropriate. Therefore, when the flow rate of the upper blowing gas is increased as described in JP-A-57-57820, or when the flow rate of the upper blowing oxygen is reduced as described in JP-A-2-66108. In this case, the effect of suppressing the forming means that only one of the above effects is seen, so that the effect is not only insufficient,
In some cases, abnormal forming often occurred, and the practical problem was large. For example, in Japanese Patent Laid-Open No. 57-57820, as shown in FIG. 2 of the publication, the amount of bottom blown gas is reduced from 0.1 Nm ³ / min / ton to 0.13 Nm ³ / min / ton when slag forming occurs. In this case, when the above equation (1) is used for calculation, T · B ² = 1.69. Similarly, in Japanese Patent Application Laid-Open No. 2-66108, as shown in FIG. 4 of the publication, the amount of bottom blown gas is changed from 0.05 Nm ³ / min / ton to 0.07 Nm ³ / min / ton when slag forming occurs.
In this case, when calculated by the above equation (1), T · B ² = 1.96. On the other hand, in the method of changing the gas type disclosed in Japanese Patent Application Laid-Open No. 57-177912, a certain slag forming suppression effect may be obtained due to the influence of flow hunting or the like at the moment when the gas type is changed. Unless the above two conditions were satisfied, the effect was unstable, and there were many problems such as occurrence of abnormal slopping. However, the prior art and literature only enumerate individual elements for suppressing slopping and accidental success experiences, and there are cases where inappropriate combination thereof promotes forming. Since the potential points were not taken into account, the accuracy of the effect was extremely poor even when put to practical use. The present inventors have found through experiments the optimal relationship between the upper flow rate and the lower flow rate for suppressing slag forming, and completed the present invention. Here, according to the present invention, when slag forming occurs, the bottom flow rate is b ₀ (Nm ³ / min) and the top flow rate is t ₀ (Nm ³ / mi).
When b ₁ / b ₀ = B and t ₁ / t ₀ = T when n), T · B ² ≦ 0.25 (where 1.0 <T or 1.0 <B)... (1) In addition, a method for suppressing slag forming, characterized by adjusting the upper flow rate t ₁ and the lower flow rate b ₁ . As described above, the feature of the present invention is that the optimal balance between the flow rates of the top and bottom blown gas, which has not been clarified, has been found and quantified. As a result, the precision of forming suppression has been dramatically improved, and its practical significance is great. According to the present invention, controlling the upper flow rate and the lower flow rate based on the above equation (1) is almost completely effective in suppressing slag forming. An unexpected effect that abnormal forming, which has conventionally been a problem, does not occur at all is obtained. This equation (1) has no effect unless the top blow flow rate is significantly reduced if the bottom blow flow rate is increased. If it is desired to increase the top blow flow rate, the bottom blow flow rate is greatly reduced. It means what to do. This means that the frequency of contact between the top and bottom blown gas at the molten iron-slag interface is reduced as described above. The condition of 1.0 <T or 1.0 <B indicates that either the top blowing gas or the bottom blowing gas increases more than immediately before. This also meets the condition that a larger total gas amount is more effective as described above. Preferably, 1.0 <T or 1.0 <B, and T ≠ 1 and B ≠ 1. In addition, the time for controlling the flow rate within the above range may be any number of minutes, but in actual operation it is 0.5 minutes.
It is appropriate that the time is not less than about 12 minutes. The effect of the present invention as described above depends only on the change in the blow flow rate, and does not depend on the type of blow gas. That is, most of the top blowing gas is usually oxygen, but the bottom blowing gas is carbon dioxide, carbon monoxide, nitrogen,
Any one of commonly used bottom-blown gases such as hydrocarbons and oxygen may be used, or a combination of two or more of them may be used.
The present invention is not particularly limited. The method for suppressing slag forming according to the present invention is effective in all processes using an upper-bottom blowing converter. For example, when blowing an upper-bottom blower as a normal converter, it is effective even when forming occurs, and the upper-bottom is used for hot metal pretreatment for the purpose of hot metal de-P or Si removal. According to the present invention, the forming can be effectively suppressed even in the case of using the blow furnace. FIG. 2 shows the behavior when the converter blowing is carried out in an upper-bottom blowing converter. Oxygen gas was used as the top blowing gas, and carbon dioxide gas was used as the bottom blowing gas. Forming occurred in the early stage of blowing 2 minutes after the start of blowing, but after 5 minutes, the bottom flow rate was reduced by 1.5 times and the top flow rate was reduced to 10%. It has succeeded in suppressing slag forming. The degree of forming was determined by indexing the forming height. In this example, B = 1.5, T = 0.1, and T · B ² = 0.225 in equation (1). Table 1 shows the composition of the molten metal before and after the treatment. [Table 1] FIG. 3 shows a case where the top-bottom blowing converter is used for the purpose of removing hot metal. In this case, oxygen is used as the top blowing gas and carbon dioxide gas is used as the bottom blowing gas. Forming occurs at the end of processing, but at that time, the bottom flow rate is increased by 30% and the top flow rate is reduced to 0%, forming is remarkably suppressed, and subsequent tapping work is carried out smoothly. It became possible to do. In this example, B = 1.3, T = 0, T · B ² =
It was 0. Table 2 shows the composition of the molten metal before and after the treatment. [Table 2] FIG. 4 shows a comparison between the method of the present invention and the conventional method. Using oxygen as the top blowing gas and nitrogen gas as the bottom blowing gas, converter blowing was performed in a bottom blowing converter, and when forming occurred, the following actions were taken to compare the two. Conventional method: bottom-blown gas is increased by 30%, top-blown gas is not changed. Inventive method: bottom-blown gas is increased by 30%, top-blown gas is reduced to 10%. In the present invention, the probability that forming can be reduced is 100. In contrast, in the conventional method, although the forming was reduced with a probability of 80%, the forming was promoted with a probability of 20%, and it was found that an abnormal reaction occurred. This is because the bottom blow gas and the top blow gas interfere with a certain probability as shown in FIG. In the present example, the conventional example uses the equation (1) where B = 1.
3, T = 1.0 and T · B ² = 1.69, but in the present invention, B = 1.3, T = 0.1 and T · B ² = 0.169.
Table 3 shows the composition of the molten metal before and after the treatment. [Table 3] FIG. 5 shows the suppression of forming when an experiment was conducted when the upper and lower blower was used for the purpose of removing hot metal. When forming occurred at the end of de-P blowing, the flow rate of the top blowing gas (oxygen) and the bottom blowing gas (carbon dioxide gas) was changed to confirm the forming sedation level. From the graph of FIG. 5 which is the result of this experiment, it was found that the forming can be surely reduced in the range of T · B ² ≦ 0.25 (where 1.0 <T or 1.0 <B) which is the basic formula of the present invention. Table 4 shows the composition of the molten metal before and after the treatment. [Table 4] According to the present invention, the slag forming of the upper-bottom blower can be suppressed inexpensively and reliably. As a result, we succeeded in greatly reducing losses such as operation hindrance and yield deterioration due to slag forming. The effect of the present invention is very large.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are schematic diagrams for explaining the relationship between the interference of upper and lower blowing gases and the degree of forming. FIG. 2 is a graph showing the effect when the method according to the present invention is applied to converter blowing with a top-bottom blowing converter. FIG. 3 is a graph showing the effect when the method according to the present invention is applied to hot metal de-P treatment by an upper-bottom blower. FIG. 4 is a graph showing the effect of the present invention in comparison with the conventional method in the example. FIG. 5 is a graph showing an effect of suppressing forming due to a change in upper and lower blowing flow rates when the method according to the present invention is performed.

Claims (1)

(57) [Claims] [Claim 1] In refining in an upper-bottom blowing converter, the bottom blowing flow rate at the time of occurrence of slag forming is b ₀ (Nm ³ / min), and the upper blowing flow rate is t ₀ (Nm ³ / min) and _{when, b 1 / b 0 = B} , t 1 / t 0 = T
Then, a method for suppressing slag forming characterized by adjusting the upper flow rate t ₁ and the lower flow rate b ₁ so that T · B ² ≦ 0.25 (where 1.0 <T or 1.0 <B) is satisfied. .