JPH04308017A - Method for preventing slag foaming - Google Patents

Abstract

PURPOSE:To effecitvely restrain foaming of slag, to prevent flow-out of the slag and to economically execute pre-treatment for a molten iron at the time of executing dephosphorization and desulfurization by adding coal, scale and the other refining agent before charging the molten iron into a converter, in which the molten iron is decarbonized and the produced steel is refined. CONSTITUTION:In the pre-treatment method, a vibrometer is disposed to an auxiliary lance differing from a lance for blowing the refining agent to continuously measure vibration strength and at the time, when the vibration strength becomes 1.4 times of the strength at the stational time, coke powder having <=3mm grain diameter is added at >=0.1kg/ton of the molten iron. At the time, when the vibration strength returns back to <1.2 times of the strength at the stational time, the addition is interrupted and by intermittently executing this operation every times, when the vibration strength is increased, the slag foaming height is controlled and the flow-out of the slag to out of the furnace is prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] In the process of decarburizing molten iron in a converter and refining steel, lime, scale, and other refining agents are added to the molten iron before it is inserted into the converter to decarburize the molten pig iron. This invention relates to a hot metal pretreatment method for phosphorus desulfurization.

0002

[Prior Art] When refining steel by decarburizing molten iron by blowing or blowing high-pressure oxygen in a converter, the converter not only decarburizes it, but also dephosphorizes and desulphurizes it according to the target composition of the steel. Therefore, it is usually necessary to add lime or other scouring agents. In this case, it is necessary to add a large amount of lime to convert the slag mainly composed of SiO2 produced by the desiliconization reaction in the early stage of converter blowing into slag with high basicity. In recent years, in order to economically perform dephosphorization and desulfurization by reducing the amount of lime used, a so-called hot metal pretreatment method in which molten iron is previously subjected to dephosphorization and desulfurization in a separate container has been widely used. In this case, a torpedo car or hot metal pot, which is a container for transporting hot metal, is used as a container for hot metal pretreatment, and since these containers are not originally used for refining, the freeboard is small, and slag is generated during the dephosphorization and desulfurization treatment. Often causes foaming and slag outflow. Conventionally, two methods have been taken as countermeasures against such slag outflow. The first method is to dig a pit for the spilled slag around the hot metal pre-treatment vessel so that the refining work will not be hindered until the slag starts flowing out, and then to transport the spilled slag in the pit after treatment. These methods have the following problems. In the case of the first method, which involves interrupting the injection of refining agents, interrupting the process results in an extension of the process time, impeding the series of smooth physical distribution from the converter to continuous casting, and ultimately leading to a deterioration in productivity. In addition, in the case of the method of arranging pits for effluent slag, since effluent slag usually contains about 10% iron, there is not only the problem that the iron yield deteriorates, but also the problem of arranging pits. This is not economical as it requires equipment costs and new work such as transporting the slag from the pit. The root cause of these problems is that during dephosphorization, CO gas is generated near the interface between hot metal and slag due to the reaction between added scale and oxygen gas and carbon in the molten iron, and these CO bubbles cause slag to grow. This is caused by foaming and the volume of the slag expanding by about 4 to 8 times. However, since there was no way to economically prevent these bubbling, the above-mentioned measures had to be taken, which caused the above-mentioned problems.

0003

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and it is an object of the present invention to effectively suppress slag bubbling, which is the root cause of the conventional problems, to prevent slag outflow, and to achieve an economical The purpose of this invention is to provide a method for pre-treating hot metal.

0004

[Means for Solving the Problems] The present invention provides that the foaming of slag is caused by the expansion of the volume of the slag due to the CO gas bubbles generated during dephosphorization treatment, and the height of the foaming is mainly determined between the bubbles. The foaming height is controlled by the stability of the slag liquid film, and the foaming height is increased by adding carbonaceous agent, which is a substance that does not easily wet the slag, to destroy the slag liquid film between the bubbles and promote bubble coalescence and bubble bursting. This was done based on the inventors' new findings that the vibration intensity decreases. When the strength increases continuously and becomes 1.4 times or more of the steady state strength, the coke powder with a particle size of 3 mm or less is added at a rate of 0.1 kg per minute per ton of hot metal.
After adding the above, when the vibration intensity returns to less than 1.2 times the steady intensity, the addition of coke powder is stopped, and this operation is performed intermittently every time the vibration intensity increases, resulting in slag foaming. This is a slag foaming prevention method characterized by controlling the height and maintaining the foaming height within the range of the container height.

The present invention will be explained in more detail below. First, a process to which this invention is applied will be explained. 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 the hot metal to perform dephosphorization and desulfurization of the hot metal. A torpedo car or a hot metal ladle is usually used as the refining vessel for hot metal pretreatment, but if slag leakage outside the vessel or high foaming is a problem, other vessels such as a converter may also be used. Although lime and scale are usually used as refining agents, it goes without saying that the present invention is also applicable to other refining agents such as soda carbonate. In addition, slag outflow during hot metal pretreatment is a particular problem in the refining process for the purpose of dephosphorization and desulfurization, but even in refining processes for other purposes, such as desiliconization treatment before dephosphorization, slag outflow is a problem. Application of the present invention is effective as long as foaming and foaming height are a problem. That is, the present invention can be applied to any hot metal pretreatment process that requires control of the foaming height of refining slag.

The most important task in applying the present invention is
A vibration meter is installed on the auxiliary lance in the refining vessel to continuously measure the vibration intensity, and when the vibration intensity increases continuously and becomes 1.4 times or more of the steady state intensity, the particle size is 3 mm or less. Adding at least 0.1 kg of coke powder per minute per ton of hot metal,
The point is that the addition of coke powder is stopped when the vibration intensity returns to less than 1.2 times the steady-state intensity, and this operation is performed intermittently every time the vibration intensity increases. Coke powder is the most effective foaming suppressant to be added, but depending on the purpose, coal may be used instead of coke powder, or coke powder mixed with other powders such as calcium carbonate may also be used. Even in that case, the same effect as when only coke powder is added can be obtained by adding the C component in the powder in an amount of 0.1 kg or more per ton of hot metal. As shown in FIG. 1, the amount of coke powder added per minute is preferably 0.1 kg or more per ton of hot metal, because the foaming suppressing effect can be exerted more quickly. On the other hand, if the amount added is less than 0.1 kg per minute per ton of hot metal, it is not preferable because even if coke is added, no significant slag outflow suppressing effect can be expected. If the size of coke powder is too large, the number of powder particles will be small relative to the amount added, resulting in insufficient foaming suppression effect, so the upper limit is set at 3 mm.
And so. As shown in Figure 1, the size of coke powder is 3mm.
If the amount exceeds the amount, the suppressing effect will be insufficient even if the amount added per minute is increased, which is not preferable. On the other hand, if the size is too small, there is a problem of powder scattering and powder loss, but if conditions can be ensured for the powder to foam and be added to the slag, the lower limit of the size can be specified. There is no particular need to do so. The most preferable method for adding the material is to blow it into the bubbling slag using a carrier gas such as nitrogen gas from a lance, but other methods may be used as long as it is possible to reliably disperse the material into the slag. According to the experiments conducted by the present inventors, simply charging the bagged powder from above is insufficient to suppress foaming, and it is necessary to reliably disperse the powder in the slag. Furthermore, the best blowing position for coke powder was 300 mm to 600 mm from the furnace mouth, and the amount of coke powder added to obtain the same effect was the smallest. This is because the powder was reliably dispersed in the slag.

Next, a method for determining when to add coke powder will be explained. The timing of adding the coke powder used in the present invention must be before the bubbling slag flows out from the furnace opening of the refining vessel, and the timing can be determined by observing the state of slag scattering from the furnace opening. However, in the case of visual judgment, the timing for addition is often missed, resulting in slag outflow. Additionally, observation personnel are required to visually determine the state of slag scattering. In order to solve these problems, it is preferable to continuously measure the slag height during refining. As a result of various experiments conducted by the present inventors regarding means for this purpose, it was found that the vibration method can effectively predict the phenomenon before the slag overflows from the furnace mouth. In these methods, a vibration meter is installed in an auxiliary lance in a refining vessel to continuously measure the vibration intensity, and the vibration intensity increases when the slag begins to bubble. In this case, it is important that the lance to which the vibration meter is attached is provided separately from the lance to which the refining agent, such as lime or scale, is blown. When the present inventors installed a vibration meter on the refining agent injection lance, there was no correlation between the slag foaming height and the vibration intensity; however,
It has been found that when an auxiliary lance is provided separately from the lance and a vibration meter is installed on this auxiliary lance, there is a clear correlation between the height of slag bubbling and the vibration intensity. It is important that this auxiliary lance is not a lance for blowing refining powder; there is no problem if only gas is blown; for example, it may be a lance for blowing gaseous oxygen.

[0008] In this way, the vibration intensity is continuously measured, and when a continuous decreasing trend in the vibration intensity is confirmed, coke powder is added to effectively control the foaming height as shown in Fig. 2. It is possible to do so. In this case it is necessary to eliminate false positives. In other words, it is necessary to reliably determine the increase in the foaming height, which is a sign of slag outflow. According to experiments conducted by the present inventors, when the vibration intensity shows a monotonous increasing trend over time and increases to 1.5 times or more of the initial steady intensity level, approximately 100
% slag outflow occurs, and if the vibration intensity decreases to less than 1.2 times the initial value by adding coke powder, the coke has increased to the extent that it can be considered that the slag foaming height has essentially returned to its initial value. It was found that the effect of adding flour persisted. Therefore, by incorporating this criterion into the system, it is possible to automatically perform a stable hot metal pretreatment operation that does not cause slag outflow. In addition, if the amount of coke added is larger than necessary, it not only increases the coke consumption rate and is not economical, but also has negative effects such as deterioration of the dephosphorization rate because the added coke reduces FeO in the slag. However, in the method of the present invention, the addition of coke powder is stopped when the vibration intensity returns to less than 1.2 times the level before adding coke, so there is no risk of adding a larger amount of coke powder than necessary. . As a result of numerous experiments conducted by the present inventors, it was found that in the case of the method according to the present invention, no decrease in the dephosphorization rate was observed due to the addition of coke powder. The effects of the present invention will be described below based on Examples.

[0009]

[Example] 250 tons of hot metal tapped from a blast furnace was received in a torpedo car, and after adding scale to reduce the silicon content in the hot metal from 0.35% to 0.13%, the slag was discharged. , a lance is inserted into the hot metal from the furnace opening in the torpedo car, and 2 fluorites are transported using nitrogen gas as a transport gas.
Dephosphorization and desulfurization treatment was carried out by blowing 21 kg and 15 kg of 0% mixed lime and scale per ton of hot metal, respectively. This treatment reduces the phosphorus content in hot metal to 0.1
The sulfur content decreased from 3% to 0.023% and from 0.020% to 0.007%. During this treatment, an acceleration vibrometer was installed on an auxiliary lance that was installed separately from the one for injecting the refining agent, and the vibration intensity was continuously measured using this and the value was recorded on an automatic recorder. At the same time, the vibration intensity value is processed by a computer, and when the vibration intensity increases continuously for more than 2 minutes and reaches 1.4 times or more of the steady-state intensity, the coke powder is automatically removed. A system was created in advance so that coke powder is blown into the slag, and the blowing of coke powder is automatically interrupted when the strength returns to less than 1.2 times the steady state strength. Coke was intermittently blown in from a separately installed auxiliary lance. As a result of checking the vibration intensity with an automatic recorder,
The system worked as designed and approximately 9 minutes after starting the process, 1
80 kg/min after 3 minutes, 18 minutes, 22 minutes, 27 minutes
Fine coke was automatically blown a total of 5 times for 0.8 to 1.7 minutes at a blowing rate of . The total processing time required for dephosphorization and desulfurization was 30 minutes, but during this time there was no slag flowing out from the furnace mouth, and lime and scale injection for dephosphorization and desulfurization could be carried out without interruption. .

0010

[Comparative Example] Desiliconization, dephosphorization, and desulfurization treatments were carried out in the same manner as in Example 1. During the dephosphorization process, slag flowed out from the furnace mouth a total of four times, so the injection of lime and scale was interrupted each time until the slag flow started, and as a result of this process, the phosphorus content in the hot metal was reduced to 0.13. or% to 0.02
2%, sulfur content from 0.0190% to 0.006%
Although the target phosphorus and sulfur content was achieved,
The total processing time required for dephosphorization and desulfurization was 45 minutes. As a result, the transportation of hot metal to the converter was delayed, resulting in waiting time in the converter, making continuous casting impossible in the casting process, and as a result, the iron yield of continuously cast slabs decreased by 2%.

[0011]

[Effects of the Invention] As can be seen from the above-mentioned Examples and Comparative Examples, according to the method of the present invention, dephosphorization and desulfurization treatment in hot metal pretreatment can be carried out effectively, and as a result, the logistics of the entire steelmaking process including the casting process can be improved. It is clear that it is an economical method that not only facilitates but also increases the iron yield in the entire steelmaking process.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of coke powder added per minute and the onset time of the slag outflow suppressing effect, and the influence of coke powder size on the onset time of the slag outflow suppressing effect,

[
FIG. 2 is a diagram showing an example of the change in vibration intensity over time when slag outflow is prevented by adding coke powder and when slag outflow occurs without adding coke powder.

Claims (1)

[Claims] Claim 1: In a hot metal pretreatment method in which lime, scale, and other refining agents are added to hot metal to desiliconize or dephosphorize and desulfurize the hot metal, a vibration meter is installed in an auxiliary lance in the refining vessel that is different from the refining agent injection lance. The vibration intensity was continuously measured during the refining process, and when the vibration intensity increased continuously and became 1.4 times or more of the steady state intensity, the particle size
0.1 kg or more of coke powder of 0.1 mm or less per ton of hot metal is added per minute, and when the vibration intensity returns to less than 1.2 times the steady state intensity, the addition of coke powder is stopped, and the operation is continued to increase the vibration intensity. A slag foaming prevention method characterized by controlling the slag foaming height intermittently every time an increase in slag foaming occurs, and maintaining the foaming height within the range of the container height.