JPH0816242B2 - Pressure forming prevention method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the process of decarburizing molten iron in a converter to refine steel, adding lime, scale and other refining agents before inserting molten iron into the converter to remove molten iron. The present invention relates to a hot metal pretreatment method for performing phosphorus desulfurization.

[0002]

2. Description of the Related Art When molten steel is decarburized by blowing or blowing high-pressure oxygen in a converter to smelt steel, not only decarburization is performed in the converter but also dephosphorization and desulfurization according to the target composition of the steel. In addition, it is usually necessary to add lime and other refining agents. In this case, it is necessary to add a large amount of lime in order to change the slag containing SiO ₂ as a main component generated by the desiliconization reaction in the initial stage of the converter blowing into a slag having a high basicity.
In recent years, in order to reduce the amount of lime used and economically perform dephosphorization desulfurization treatment, a so-called hot metal pretreatment method in which molten iron is preliminarily desulfurization desulfurization treatment in a separate container is widely performed. In this case, the hot metal pre-treatment container is a hot metal carrier, such as a pigeon car or a hot metal ladle.Since these containers are not originally refining vessels, the freeboard is small and slag is not generated during the dephosphorization and desulfurization process. Frequent foaming and slag spillage. Conventionally, two methods have been taken as measures against such slag outflow. The first is a method of interrupting the blowing of the refining agent until the outflow of slag begins. Another method is to carry out the outflowing slag in the pit after the refining process even if the slag flows out. These methods have the following problems. First, in the case of the first method of interrupting the blowing of the refining agent, the interruption of the treatment leads to the extension of the treatment time, which obstructs the smooth flow of a series of products from the converter to the continuous casting, resulting in the deterioration of the productivity. Also, in the case of the method of arranging the pit for the outflow slag,
Since the slag slag usually contains about 10% of iron content, there is not only a problem that the iron yield is deteriorated, but also equipment costs for pit placement and a new slag in the pit are taken out. It requires work and is not economical.
The root cause of these problems is that during dephosphorization, CO gas is generated in the vicinity of the interface between the hot metal and slag due to the reaction between the added scale and oxygen gas and carbon in the molten iron, and the CO bubbles generate slag. This is due to bubbling and expansion of the slag volume by about 4 to 8 times. However, since there was no method for economically preventing these bubbles, the above measures were taken without fail, and the above problems were caused thereby.

[0003]

The present invention has been made in view of the above circumstances, and effectively suppresses the foaming of slag, which is the root cause of the conventional problems, to prevent the outflow of slag, which is economical. The purpose of the present invention is to provide a method for performing hot metal pretreatment.

[0004]

According to the present invention, the foaming of the slag is caused by the expansion of the volume of the slag by the CO gas bubbles generated during the dephosphorization treatment, and the foaming height is mainly between the bubbles. It is controlled by the stability of the slag liquid film and the atmospheric pressure.The higher the atmospheric pressure, the smaller the bubbling height, and the addition of a carbonizing agent, which is a substance that is difficult to wet with the slag, destroys the slag liquid film between the bubbles and creates bubbles. According to the present invention, the foaming height is lowered by promoting the coalescence of the particles and the rupture of the bubbles, and the foaming height during the dephosphorization treatment can be estimated by the vibration intensity of the vibrometer installed in the auxiliary lance. It was made based on the new knowledge of the researchers, and the main point is that the inside of the refining vessel is a closed type and a vibrometer is attached to the auxiliary lance inside the refining vessel different from the lance for blowing the refining agent. Location and the vibration intensity continuously measured, by controlling the pressure in the vessel in accordance with an increase in the vibration intensity as foaming slag height is maintained within a range of container height,
After the refining, a coke powder having a particle diameter of 3 mm or less is added in an amount of 0.1 kg or more per ton of hot metal, and then the internal pressure of the container is restored to normal pressure, which is a method for preventing slag foaming.

The present invention will be described in more detail below. First, the steps to which the present invention is applied will be described. The process to which the present invention is applied is a hot metal pretreatment process in which lime, scale, and other refining agents are added to hot metal to dephosphorize and desulfurize the hot metal. As a refining vessel for performing the hot metal pretreatment, a tope car or a hot metal ladle is usually applied, but if slag outflow to the outside of the vessel or bubbling height is a problem, it may be another vessel such as a converter. Although lime and scale are usually used as the refining agent, it goes without saying that the present invention can be applied to other refining agents such as sodium carbonate. The slag outflow during hot metal pretreatment is particularly problematic in the refining process for the purpose of dephosphorization and desulfurization, but even for refining processes for other purposes such as desiliconization before dephosphorization, slag outflow And foam height is a problem,
The application of the present invention is effective. That is, the present invention can be applied to any hot metal pretreatment process that requires control of the foaming height of the refining slag.

The most important work in applying the present invention is
The refining vessel is sealed and the vibrometer is installed on the auxiliary lance inside the refining vessel that is different from the refining agent blowing lance to continuously measure the vibration intensity, and the slag foaming height is within the range of the vessel height. The pressure in the container is controlled according to the increase of the vibration intensity so as to be maintained, and after the refining, 0.1 kg or more of coke powder with a particle size of 3 mm or less is added per ton of hot metal, and then the pressure in the container is returned to normal pressure. In point. First, the estimation of the foaming height will be described. As a method for estimating the foaming height, there are an electric resistance method, a furnace observation method using a fiberscope, and the like, but the reliability of the measurement is poor and it is not practical. As a result of various experiments conducted by the present inventors, it was found that a method of measuring vibration intensity by installing a vibrometer on an auxiliary lance different from the refining agent blowing lance is the most reliable. It is important that the lance for installing the vibrometer is provided separately from the lance for blowing the refining agent such as lime or scale. When the present inventors installed a vibrometer on the refining agent blowing lance,
Although there is no correlation between the slag foaming height and the vibration intensity, when an auxiliary lance is provided separately from the lance and a vibrometer is installed on this auxiliary lance, as shown in FIG. It was found that there was a clear correlation between vibration intensities. Note that it is important that this auxiliary lance is not a lance for blowing powder for refining, as long as it blows only gas, it may be a lance for blowing gaseous oxygen.

The second important point in the present invention is based on the finding by the present inventors that the slag foaming height can be suppressed low by increasing the atmospheric pressure in the container as shown in FIG. is there. Therefore, it is possible to make the slag foaming height fall within the range of the container height by estimating the slag foaming height by the vibrometer and controlling the atmosphere in the container according to the result. According to the knowledge of the present inventors, the required pressure at this time is at most about 4 atm, and the slag foaming height can be controlled at a pressure level that can be industrially realized.

A third important point in the present invention is that the pressure inside the container must be restored to normal pressure when the lance is pulled up after the refining work is completed, and at this time, means for preventing the slag from bubbling out of the furnace opening. It is about. The present inventors by adding an appropriate amount of coke powder after the refining,
It is possible to prevent the slag from flowing out of the furnace opening when the pressure is restored to normal pressure, and the conditions at this time are as shown in Fig. 3 that the size of the coke powder is 3 mm or less and the addition amount is hot metal ton It has been found that 0.1 kg or more is required per unit. Although coke powder is the most effective foam inhibitor to be added, coal may be used instead of coke powder, or coke powder mixed with other powder such as calcium carbonate may be used depending on the purpose. Even in that case, by adding the amount of the component C in the powder to be added to 0.5 kg or more per ton of hot metal, the same effect as adding only the coke powder can be obtained. If the size of the coke powder is too large, the number of powder particles decreases with respect to the amount added, and the calming effect of the foaming slag becomes insufficient. Therefore, the upper limit was made 1 mm. As shown in FIG. 3, when the size of the coke powder is 3 mm or less, the occurrence rate of slag outflow due to slag foaming at the time of recompression after adding 0.1 kg of coke per ton of hot metal is 0. When the size of the coke powder is more than 3 mm, slag outflow occurs with a considerable probability even if the amount of the coke powder added is increased. On the other hand, if the size is too small, there is a problem that the powder will scatter and lose the powder, but if the condition that the powder is reliably added to the foaming slag can be secured, the lower limit of the size is specified. There is no particular need to do it. The most preferable addition method is a method in which a carrier gas such as nitrogen gas is blown from the lance and blown into the slag, but a method other than the lance may be used as long as it can be surely dispersed in the slag. According to the experiments conducted by the inventors of the present invention, the foaming suppressing effect is not sufficient by simply adding the packed powder from above, and it is necessary to surely disperse the powder in the slag. The coke powder injection position is 300m from the furnace opening
The position of m to 600 mm was the best, and the amount of coke powder added to obtain the same effect was the smallest and effective. This is because the powder was surely dispersed in the slag. The effects of the present invention will be described below based on Examples.

[0009]

[Example] 250 tons of hot metal discharged from a blast furnace was received in a toped car, at which time scale was added to reduce the silicon content in the hot metal from 0.35% to 0.13%, and then slag was discharged. , Lance was inserted into the hot metal from the furnace opening of the tope car, and nitrogen gas was used as a carrier gas for fluorspar.
In the mixed state of 0% mixed lime and scale, 21 kg and 15 kg of hot metal tons were blown to perform dephosphorization desulfurization treatment. By this treatment, the phosphorus content in the hot metal is 0.1
Sulfur content decreased from 3% to 0.023% and sulfur content from 0.020% to 0.007%, while an accelerometer was installed on an auxiliary lance installed separately from the refining agent injection. The vibration intensity was continuously measured during the treatment, and the value was recorded in an automatic recorder. At the same time, the value of the vibration intensity is processed by a computer, and the pressure inside the container is automatically controlled so that the intensity is maintained within the range of 1.0 to 1.5 times the original intensity. Was prepared and the pressure inside the container was controlled by this system. The system operates as designed, and after about 9 minutes from the start of the treatment, the pressure inside the container gradually increases and reaches a peak of 1.8 atm after about 22 minutes, and then gradually decreases to 1 at the end of the treatment. It was 0.3 atm. Then, fine coke having a particle size of 100 mesh or less was blown into the container at a rate of 80 kg per minute for 30 seconds, and then the pressure in the container was restored to normal pressure. No slag outflow was seen from the furnace opening when the pressure was restored, and the process was completed smoothly. The amount of coke added corresponds to 0.18 kg per ton of hot metal.

[0010]

Comparative Example As in Example 1, desiliconization and dephosphorization desulfurization treatments were performed. During the dephosphorization process, a total of four slag outflows from the furnace mouth occurred, so that the lime and scale blowing was interrupted until the slag outflow started each time, and as a result, the phosphorus content in the hot metal was 0. 13% to 0.02
At 2%, the sulfur content decreased from 0.019% to 0.006% and the target phosphorus and sulfur contents were obtained, but the total treatment time required for dephosphorization and desulfurization was 45 minutes. . As a result, the transport of the hot metal to the converter was delayed, waiting time was generated in the converter, and continuous casting was impossible in the continuous casting, which is the casting process. As a result, the iron yield of the continuously cast slab decreased by 2%.

[0011]

According to the method of the present invention, it is possible to effectively carry out the dephosphorization desulfurization treatment in the hot metal pretreatment from the above-mentioned Examples and Comparative Examples, and as a result, the flow of the entire steelmaking process including the casting process is improved. It is clear that this is an economical method that not only smoothes but also increases the iron yield in the entire steel making process.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between vibration intensity and slag foaming height,

FIG. 2 is a diagram showing the relationship between the slag foaming height and the pressure inside the container,

FIG. 3 is a diagram showing the influence of the amount of coke added and the size of coke powder on the outflow of slag at the time of recompression upon the end of treatment.

Claims (1)

[Claims] 1. In a hot metal pretreatment method in which lime, scale or other refining agent is added to hot metal to perform desiliconization or dephosphorization desulfurization of hot metal, the refining vessel is closed and the refining agent blowing lance is Vibrometers are installed on different lances in different refining vessels to continuously measure the vibration intensity during refining process, depending on the increase in vibration intensity so that the slag foaming height is maintained within the vessel height range. Control the pressure in the container,
After completion of refining, a coke powder having a particle diameter of 3 mm or less was supplied from the lance by a carrier gas such as nitrogen gas to 0.1 kg per ton of hot metal.
A method for preventing slag foaming, which comprises restoring the internal pressure of a container to normal pressure after the above addition.