JPH04308016A - Method for preventing pressure foaming - Google Patents

Abstract

PURPOSE:To effectively restrain the foaming of a 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 refining vessel is made to a closed condition and vibrometer is installed to an auxiliary lance differing from a lance for blowing the refining agent to continuously measure vibration strength and pressure in the vessel is controlled according to the increase in the vibration strength so as to maintain the slag foaming height in the range of vessel height. After completing the refining, coke powder having >=3mm grain diameter is charged at >=1.0kg/ton of the molten iron and then, by returning back the pressure in the vessel to the normal pressure, the slag foaming is prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is used in the process of decarburizing molten iron in a converter to refine steel. 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. 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 temporarily suspend the injection of the refining agent until the slag begins to flow out. Another method is to transport the slag out of the pit after the refining process even if the slag flows out. 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 spilled slag, since the spilled slag usually contains about 10% iron, there is a problem that not only the iron yield deteriorates, but also
This is not economical because it requires equipment costs for arranging the pit and new work such as carrying out the slag in 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. It is controlled by the stability of the slag liquid film and the atmospheric pressure, and the higher the atmospheric pressure, the smaller the foaming height, and the addition of carbonaceous 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 reduced by promoting coalescence and bursting of bubbles, and the foaming height during dephosphorization treatment can be estimated by the vibration intensity of a vibration meter installed in the auxiliary lance. This was done based on the new knowledge of the researchers, and its gist is that the inside of the refining vessel should be sealed,
In addition, a vibration meter was installed in the auxiliary lance inside the refining vessel, which is different from the lance for blowing the refining agent, and the vibration intensity was continuously measured.
The pressure inside the container is controlled according to the increase in vibration intensity so that the slag bubbling height is maintained within the range of the container height, and after the completion of refining, coke powder with a particle size of 3 mm or less is produced per ton of hot metal.
．． This method of preventing slag foaming is characterized by restoring the pressure inside the container to normal pressure after adding 1 kg or more.

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. As long as foaming height is a problem,
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 refining slag.

The most important task in applying the present invention is
The inside of the refining vessel is sealed, and a vibration meter is installed in the auxiliary lance inside the refining vessel, which is different from the lance for blowing refining agent, to continuously measure the vibration intensity, and the height of slag bubbling is within the range of the height of the vessel. The pressure inside the vessel is controlled according to the increase in vibration intensity so that the pressure is maintained, and after the completion of refining, the pressure inside the vessel is restored to normal pressure after adding 0.1 kg or more of coke powder with a particle size of 3 mm or less per ton of hot metal. At the point. First, we will discuss the estimation of foaming height. Methods for estimating the foaming height include the electrical resistance method and the furnace observation method using a fiberscope, but the measurement reliability is poor and is not practical. As a result of various experiments, the present inventors found that the most reliable method was to install a vibration meter on an auxiliary lance different from the refining agent injection lance and measure the vibration intensity. It is important that the lance where the vibration meter is installed is separate from the lance where the refining agents such as lime and scale are injected. When the present inventors installed a vibration meter on the refining agent injection lance,
There is no correlation between the slag foaming height and the vibration intensity, but if an auxiliary lance is provided separately from the lance and a vibration meter is installed on this auxiliary lance, the slag foaming height and vibration intensity will change as shown in Figure 1. A clear correlation was found between the vibration intensities. 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.

The second important point in the present invention is based on the inventors' knowledge that the height of slag foaming can be suppressed by increasing the atmospheric pressure inside the container, as shown in FIG. be. Therefore, by estimating the slag foaming height using a vibration meter and controlling the atmosphere in the container according to the result, the slag foaming height can be made to be within the range of the container height. According to the findings of the present inventors, the required pressure at this time is about 4 atmospheres at most, and the height of slag bubbling can be controlled at an industrially feasible pressure level.

The third important point in the present invention is that when the lance is pulled up after the completion of the refining work, it is necessary to restore the pressure inside the container to normal pressure, and at this time there is a means to prevent the slag from bubbling and flowing out from the furnace mouth. It is related to. By adding an appropriate amount of coke powder after the completion of refining, the present inventors
It is possible to prevent slag from flowing out from the furnace mouth when the pressure is restored to normal pressure, and the conditions for this are as shown in Figure 3, the size of the coke powder must be 3 mm or less in particle diameter, and the amount added must be equal to or less than 1 ton of hot metal. It has been found that 0.1 kg or more is required per unit. 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 0.5 kg or more per ton of hot metal. If the size of the coke powder is too large, the number of powder particles will be small relative to the amount added, and the effect of calming the foaming slag will be insufficient, so the upper limit was set to 1 mm. As shown in Figure 3, when the size of coke powder is 3 mm or less, the incidence of slag outflow due to slag foaming at the time of pressure recovery after adding 0.1 kg of coke per ton of hot metal is 0. If the size of the coke powder exceeds 3 mm, there is a high probability that slag will flow out even if the amount of coke powder added is increased. 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. In addition, the coke powder injection position is 300mm from the furnace mouth.
The position between 600 mm and 600 mm was the best, and the amount of coke powder added to obtain the same effect was the smallest and was effective. This is because the powder was reliably dispersed in the slag. 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 was reduced from 3% to 0.023%, and the sulfur content was reduced from 0.020% to 0.007%.On the other hand, an acceleration vibrometer was installed in advance on an auxiliary lance that was installed separately from the one for injecting the refining agent. The vibration intensity was continuously measured during the treatment, and the values were recorded on an automatic recorder. At the same time, the value of the vibration intensity is processed by a computer, and the resulting intensity is 1/1 of the original intensity.
．． A system was previously created to automatically control the pressure inside the container so that it was maintained within a range of 0 to 1.5 times, and the pressure inside the container was controlled by this system. The system operates as designed, and the pressure inside the container gradually increases from about 9 minutes after the start of the process, reaching a peak of 1.8 atm after about 22 minutes, and then gradually decreases to 1 atm at the end of the process. The pressure was .3 atm. Thereafter, finely divided 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 inside the container was restored to normal pressure. No slag leakage from the furnace mouth was observed during pressure recovery, and the process was completed smoothly. Note that this amount of coke added corresponds to 0.18 kg per ton of hot metal.

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% to 0.02
The sulfur content decreased from 0.019% to 0.006%, achieving the target phosphorus and sulfur content, but 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]

[Figure 1] Diagram showing the relationship between vibration intensity and slag foaming height,

[Figure 2] Diagram showing the relationship between slag foaming height and container pressure,

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

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, the inside of the refining vessel is closed, and a lance for blowing the refining agent is used. Vibration meters were installed in the auxiliary lances in different smelting vessels to continuously measure the vibration intensity during the smelting process, and the slag foaming height was maintained within the range of the vessel height according to the increase in vibration intensity. Controls the pressure inside the container,
A method for preventing slag foaming, which comprises adding coke powder with a particle size of 3 mm or less in an amount of 0.1 kg or more per ton of hot metal after completion of refining, and then restoring the pressure inside the vessel to normal pressure.