JPH05125424A - Method for restraining slag foaming - Google Patents

Abstract

PURPOSE:To restrain foaming of slag and to prevent flow-out of the slag by observing the slag foaming height with a camera for observation arranged at near a furnace opening part at the time of executing dephosphorization and desulfurization in molten iron and injecting carbonaceous material at the time of becoming the specific foaming height. CONSTITUTION:The slag 13 is removed from a torpedo car 1 receiving the molten iron 12 and a lance 5 is inserted from the furnace hole part, and by using nitrogen gas for carrying, mixed material of fluorite-mixed lime and scale is injected into the molten iron 12 at the specific quantity to execute the dephosphorizing and desulfurizing treatments. Then, by arranging the camera 15 for observation at near the furnace opening part, the inner part of the furnace is continuously observed, and when foaming height of the slag 13 becomes about >=0.3m below the furnace opening part, coke 11 having about 1-3mm grain diameter and 0.1-<0.8kg/ton of the molten iron per one time is injected into the molten iron 12 with the carrying gas (nitrogen gas) through a lance 8 at each time. By this method, during dephosphorizing and desulfurizing works, the development of the flow-out of the slag caused by increase of the foaming height of the slag is prevented, and the operation is made to be smoothly executed in short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to hot metal such as lime, scale,
The present invention relates to a method for preventing slag foaming in a hot metal pretreatment step of performing desiliconization, dephosphorization or dephosphorization desulfurization of hot metal by adding other refining agents.

[0002]

2. Description of the Related Art When refining steel by depressurizing hot metal with or blowing high-pressure oxygen in a converter, not only decarburization in the converter but also dephosphorization desulfurization according to the target composition of the steel To do this, 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, which is generated by the desiliconization reaction at the initial stage of blowing in the converter, into a slag having a high basicity.

In recent years, in order to reduce the amount of lime used and economically perform dephosphorization and desulfurization, a so-called hot metal pretreatment method in which hot metal is previously subjected to desiliconization, dephosphorization and desulfurization in another container is widely and generally performed. ing. In this case, as a container for hot metal pretreatment, a hot metal carrier container such as a tope car or a hot metal ladle is used.Since these containers are not originally refining containers, the freeboard is small, and during desiliconization, dephosphorization, and desulfurization treatments. Often, slag foams and flows out of the reaction vessel.

As a countermeasure against such outflow of slag, two methods have been mainly used conventionally. The first is a method in which, once the slag outflow from the refining container begins, the blowing of the refining agent is suspended until the slag outflow stops. The second method is a method in which a pit for the outflow slag is dug around the hot metal pretreatment container so that the refining work is not hindered even if the slag flows out, and the outflow slag is carried out after the treatment.

These methods have the following problems. First of all, in the case of the first method of interrupting the blowing of the refining agent, the interruption of the treatment not only causes the operation time of the post-stage converter furnace to be prolonged but also has a great adverse effect of lowering the temperature, and Regarding the second method, the iron slag usually contains 10% or more of iron, so if iron in slag is not recovered, there is a problem that the iron yield will be deteriorated. It is not economical because new work such as equipment costs and slag in the pit are carried out.

[0006]

SUMMARY OF THE INVENTION 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 slag outflow, which is economical. The purpose is to perform hot metal pretreatment.

[0007]

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 desiliconization, dephosphorization and desulfurization treatments, and the foaming height is It is dominated by the stability of the slag liquid film between the bubbles, and carbon material, which is a substance that is difficult to wet with the slag, is added, and the slag liquid film between the bubbles is destroyed to promote coalescence and rupture of the bubbles. The present invention was made based on the findings of the present inventors that the height is reduced, and the gist thereof is as follows.

In the hot metal pretreatment method in which lime, scale, and other refining agents are added to hot metal to perform desiliconization, dephosphorization, or dephosphorization desulfurization of hot metal, the slag foaming height is maintained within the range of the container height. In order to control the slag bubbling height, a monitoring camera is installed near the furnace opening of the refining vessel by adding 0.1 kg or more and less than 0.8 kg of hot metal per ton of hot metal per control work. The method for preventing slag foaming is characterized by monitoring the foaming height of slag and determining when to add carbonaceous material.

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 desiliconize, dephosphorize and desulfurize the hot metal. As a refining vessel for performing hot metal pretreatment, a tope car or a hot metal ladle is usually used, but if slag outflow to the outside of the vessel or bubbling height is a problem, it may be a reactor or other reaction vessel. ..

Although lime and scale are usually mainly 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 the hot metal pretreatment is particularly problematic in the refining process for the purpose of dephosphorization and desulfurization, but even in the refining process for other purposes such as desiliconization before dephosphorization. The application of the present invention is effective as long as the slag outflow and the foaming height are problems. That is, the present invention can be applied to any hot metal pretreatment process that requires controlling the foaming height of the refining slag.

The most important work in applying the present invention is
When the slag foaming height was monitored with a monitoring camera installed near the furnace mouth and it was determined that the foaming height reached the outflow, coke powder with an average particle size of 0.1 to 3 mm was used as a suppressor. 0.1k per ton of hot metal per control work
The point is to add at least g and less than 0.8 kg, and repeat this operation as necessary. Considering the time margin from the start of addition of carbonaceous material to the suppression effect, it is empirically considered that the foaming height at which the addition of carbonaceous material is started should be added at the latest when it reaches 0.3 m below the furnace mouth. Is desirable.

Coke powder is most effective as the foaming inhibitor to be added, but depending on the purpose, coal may be used instead of coke powder, or a mixture of coke powder and other powder such as calcium carbonate may be used. You can also Even in that case, by adding 0.1 kg or more of the total amount of carbon components in the powder to be added per ton of hot metal, the same effect as adding only the coke powder can be obtained. As shown in Fig. 4, the amount of coke powder added is 0.1 kg per ton of hot metal.
If it is more than the above, the longer the foam-suppressing effect lasts, the more preferable it is. However, if it is too large, the coke consumption rate increases, which is not economical and the coke added as shown in FIG. Since FeO in the steel is reduced, it adversely affects the efficiency of dephosphorization and oxygen reduction. Therefore, the upper limit of addition is less than 0.8 kg per ton of hot metal. On the other hand, if the addition amount is less than 0.1 kg per ton of hot metal, it may not be possible to suppress slag outflow even if coke is added, which is not preferable. In addition, when adding the suppressor, it is desirable that the suppressor is continuously blown instead of being added all at once so as to be uniformly blown into the slag. At this time, it should be noted that the degree of forming suppression changes depending on the addition rate of the carbonaceous material. According to the results of the suppression experiment using the tope car of the present inventors, when the carbonaceous material addition rate is less than 5 kg / min, it is impossible to suppress the forming even if the carbonaceous material is added, and thus it is possible to go outside the tope car. Could not prevent the outflow of slag. Similarly, when the carbonaceous material addition rate is set to 100 kg / min, the exhaust gas temperature rises, which causes problems such as a decrease in dust collection efficiency due to an increase in the heat load of the dust collector and a thermal deformation crack of the dust collection duct, which hinders the operation. Therefore, it is desirable that the upper limit of the amount of carbon material added be 100 kg / min.

As described above, it is desirable that the addition of the foaming suppressing material such as coke is limited to the minimum necessary from the viewpoint of economical efficiency and avoidance of adverse effects on dephosphorization, and therefore, the amount of coke powder per slag outflow suppressing operation is reduced. It is possible to suppress the foaming of slag by limiting the addition amount as described above and repeating this operation as necessary.

If the particle size of the coke powder is too large, the number of powder particles will decrease with respect to the amount added, and it will take time for the foaming suppressing effect to appear, so the upper limit is made 3 mm. As shown in FIG. 6, according to the experiments conducted by the present inventors, the smaller the particle size of the powder, the better the immediate effect of the foaming suppressing effect. On the other hand, if the particle diameter is too small, there is a problem that the duration of the suppressing effect becomes short as shown in FIG. 4, but there is no particular problem as long as it is continuously blown. Also, if the particle size is too small, there is a problem that the powder will be scattered and loss of the powder will occur, but if the conditions for ensuring that the powder is added to the foaming slag are secured and the manufacturing cost can be ignored, the particle size can be reduced. It is not necessary to specify the lower limit of the above, but from the viewpoint of manufacturing cost, 0.1 mm or more is practically desirable.

The most preferable method of adding the coke powder is to blow it into the foaming slag from the lance with a carrier gas such as nitrogen gas, but if it can be surely dispersed in the slag, it is blown from the lance together with the carrier gas. It does not matter if it is other than the method. According to the experiments conducted by the present inventors, the foaming suppressing effect is not sufficient by simply adding the bag-filled carbonaceous material from above, and in order to reliably disperse the powder in the slag, it is necessary to measure 500 mm from the hot metal surface. It is desirable that the coke powder is surely blown into the upper layer portion of the foaming slag below the surface of the foaming slag at a position of 2000 mm to 2000 mm.

Although it is not impossible to judge the timing of adding the coke powder by visual observation from the operation room of the hot metal pretreatment equipment installed at the position facing the refining reaction vessel, the rise of the foaming height of the slag Since it is abrupt, it is difficult to judge the start of carbonaceous material addition at a proper time when the slag does not flow out of the reaction vessel. Therefore, in order to enable the start of carbonaceous material addition at an appropriate time, in the operation room, the image taken by the monitoring camera 15 installed at a position near the furnace mouth where the slag foaming condition near the furnace mouth can be accurately observed is provided. It is important to observe.

[0018]

OPERATION AND EXAMPLES The effects of the present invention will be described below based on examples.

Example A schematic view during hot metal treatment is shown in FIG. 260 tons of the hot metal 12 tapped from the blast furnace was received by the Topedecar 1, at which time a scale was added to make the silicon content in the hot metal 0.36%.
To 0.12%, the slag 13 is discharged, and the lance 5 is inserted into the hot metal 12 from the furnace opening of the toped car to obtain lime and scale mixed with 20% of fluorite using nitrogen gas as a carrier gas. In a mixed state, 22 kg and 16 kg of hot metal tonnes were blown and dephosphorized and desulfurized.
By this treatment, the phosphorus content in the hot metal is changed from 0.15% to 0.024%, and the sulfur content is changed from 0.019% to 0.024%.
It fell to 06%. As shown in the figure, as a result of continuously observing the furnace opening with the monitoring camera 15, 8 minutes, 18 minutes, and 25 minutes after the start of the treatment, the slag foaming height was 0.3 m below the furnace opening. As described above, fine coke having an average particle size of 220 μm was used in each case, and a total of 80 kg was obtained from the carbonaceous material injection lance 5 for about 1.5 minutes using nitrogen gas as a carrier gas.
It was blown in to suppress the foaming of the slag. During this period, the blowing of lime and scale for dephosphorization and desulfurization could be carried out without interruption, and the total treatment time required for dephosphorization and desulfurization was 35 minutes.

As a carbonaceous material addition method, the method of FIGS. 2 and 3 in which a carbonaceous material injection hole 14 is provided in the middle of the refining agent injection lance 5 is also the same as that of the method shown in FIG. The effect of is expected. In the figure, 2 is a pressure feeding tank, 3 is a pressure feeding pipe, 4 is a weighing machine, 6 is an inlet, 7 is a carbon material storage hopper, 9 is a pressure feeding gas supply source, 10 is a refining agent blowing hopper,
Reference numeral 16 denotes a monitor TV.

Comparative Example Desiliconization and dephosphorization desulfurization were performed in the same manner as in the example.
During the dephosphorization process, four slag outflows occurred from the furnace opening, so that the lime and scale injections were interrupted until the slag outflow stopped each time, and as a result, the phosphorus content was 0.15% to 0%. 0.024%, sulfur content 0.0
Although the phosphorus and sulfur contents were reduced from 20% to 0.005% within the target composition range, the total processing time required for dephosphorization and desulfurization was 48 minutes. As a result, the loading of the hot metal into the converter is delayed, waiting time occurs in the converter, and continuous casting is impossible in the continuous casting, which is the casting process. As a result, the iron yield of the continuous cast slab is 2.5%. Fell.

[0022]

From the above Examples and Comparative Examples, according to the method of the present invention, it is possible to effectively carry out the refining reaction in the hot metal pretreatment, and as a result, the slag outflow occurs due to the increase in the slag foaming height. It became possible to carry out operations smoothly in a short time without incident.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the amount of coke added per suppression work and the duration of the suppression effect, and the effect of coke powder particle size on the duration of the suppression effect.

FIG. 5 is a graph showing the relationship between the amount of coke added per depressing operation and the dephosphorization efficiency.

FIG. 6 is a graph showing the influence of the coke powder particle size on the suppression effect expression time.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Toped car (mixed pig metal) 2 ... Pressure-feeding tank 3 ... Pressure-feeding piping 4 ... Weighing machine 5 ... Refining agent blowing lance 6 ... Injection port 7 ... Carbon material storage hopper 8 ... Carbon material blowing lance 9 ... Pressure feeding gas supply source 10 ... Refining agent blowing hopper 11 ... Carbon material 12 ... Hot metal 13 ... Slag 14 ... Carbon material addition hole 15 ... Surveillance camera

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[Procedure amendment]

[Submission date] March 10, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

Front page continuation (72) Inventor Eiji Aida Kimitsu 1 Kimitsu, Nippon Steel Co., Ltd. Kimitsu Steel Works (72) Inventor Kenji Tomita Kimitsu, Kimitsu City 1 Nippon Steel Co., Ltd. Kimitsu Steel Works

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, dephosphorization or dephosphorization desulfurization of hot metal, the slag foaming height falls within the range of the container height. In order to maintain the slag foaming height, add a monitoring camera near the furnace mouth of the refining vessel by adding 0.1 kg or more and less than 0.8 kg per ton of hot metal per control work so that it is maintained. A method for suppressing slag foaming, which comprises installing and monitoring the foaming height of slag to determine when to add carbonaceous material.