JPH0445564B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial application field) Blowing gas containing oxygen into a bath of molten iron received into the inside of a smelting vessel such as a converter through a tuyere (hereinafter referred to as bottom blowing tuyere) placed at the bottom of the vessel. The technical contents described in this specification regarding the progress of the refining reaction of the molten iron and the effective suppression of melting loss of the bottom blowing tuyere during this process propose the results of development research on the usefulness of high-pressure blowing of the gas. It's there. Recently, from the bottom of a refining vessel such as a converter,
The combined blowing method, in which Ar or N ₂ gas is blown from the bottom while oxygen is blown from the top of the furnace using a top-blowing lance, is widely used industrially. According to this composite blowing method, even if the molten iron is decarburized to a low carbon concentration, the iron will not be excessively oxidized, and since there is little splash, iron retention is good. The slag-metal reaction is promoted by the stirring effect of the molten iron by the bottom-blown inert gas, and various benefits such as a good refining effect are obtained. (Prior art) Metal pipes and so-called porous plugs made of porous refractories have been used as the bottom blowing tuyere, which is essential for carrying out this composite blowing method. I had a problem like this. In other words, while metal pipes have the advantage of being inexpensive, there is a risk that, especially when the flow rate is reduced, molten iron in the converter may enter the hollow hole of the pipe and clog the tuyeres, making it difficult to change the flow rate. The disadvantage is that the range in which it can be adjusted is narrow. On the other hand, the porous plug shown in Japanese Patent Application Laid-Open No. 57-200533 has the advantage that there is no risk of clogging the tuyere even if the flow rate is restricted, and the flow rate can be adjusted over a wide range, but it is expensive. There is a drawback that it sticks. In addition, all of these tuyeres have a shorter service life when compared to the bottom refractory of a converter, and even though the bottom refractory is still sound, the lifespan of the bottom blowing tuyere is In addition to uneconomically replacing the furnace body, the tuyeres are blocked to stop the injection of bottom-blown inert gas, which causes unsatisfactory oxygen flow only from the top-blowing run. I am forced to continue refining. The inventors found that the method is effective in preventing erosion of the bottom blowing tuyere,
In addition, we previously proposed in Japanese Patent Application No. 1982-61482 a method for blowing gas into molten iron in a steelmaking vessel, which allows the blowing flow rate to be adjusted over a wide range. This method is
Use a tuyere pipe with an inner diameter of 3 mm or less, and inject a gas such as an inert gas so that the gas pressure at the inlet of the tuyere pipe is 50 Kgf/cm ² or more during at least a part of the entire blowing period. It is something to be instilled. In this method, the gas blowing flow rate can be adjusted over a wide range, and therefore blowing can be carried out according to the purpose, such as improving the dephosphorization and desulfurization rate or iron yield. It has the advantage of preventing melting of the bottom blowing tuyeres for blowing active gas, etc., and extending the service life of the tuyere, but on the other hand, it is similar to the conventional blowing of inert gas from the bottom of the converter. Compared to the method of blowing oxygen into the steelmaking vessel from the bottom of the converter, which also helps to enhance the stirring effect, this method was economically inferior because the inert gas that merely controls stirring does not react with the molten iron. In addition, when blowing oxygen that reacts with the molten iron in the refining vessel while enhancing the stirring effect, a cooling gas (hereinafter referred to as coolant) is required to cool the bottom blowing tuyere and prevent its melting. From an economical perspective, it is desirable to use a small amount of this coolant. (Problems to be Solved by the Invention) The present invention provides a method for appropriately blowing oxygen or a gas containing oxygen into molten iron charged into a smelting vessel, which is effective in preventing erosion of the bottom blowing tuyeres. The purpose is to give. (Means for Solving the Problems) The above objectives are advantageously achieved by the following methods. 1. When bottom-blowing a gas containing 60 vol% or more of oxygen into the molten iron bath in the refining container from the tuyere installed at the bottom of the container, the tuyere is used to cool the tuyere and the oxygen-containing gas surrounding it. Gas blowing into molten iron in a refining vessel characterized by supplying oxygen-containing gas under high pressure of at least 30 Kgf/cm ² at the tuyere inlet using a multi-tube tuyere serving for concentric ejection of molten iron. 2. When bottom-blowing a gas containing 60 vol% or more of oxygen into the molten iron bath in the refining container from the tuyere arranged at the bottom of the container, the gas is A method for blowing gas into molten iron in a smelting vessel, characterized in that a high pressure of at least 50 Kgf/cm ² is maintained at the inlet of the molten iron through a smelting vessel during substantially the entire blowing period. (Second invention) Here, the gas containing oxygen means that at least 60 vol% of pure oxygen or _O2 is present, and the remainder is, for example,
Refers to a highly concentrated oxygen-containing gas consisting of a mixture of inert gases such as N ₂ and Ar. Regarding the mixing ratio of O ₂ and inert gas, it is advantageous for the proportion of O ₂ to exceed 60 vol % in the total blown gas as follows. In other words, as the O ₂ ratio increases, even at the same flow rate, it reacts with C in the steel bath and becomes CO gas with twice the amount of oxygen, so the stirring power increases. Furthermore, since it is cheaper than inert gas, it is advantageous in terms of cost. On the other hand, it is generally disadvantageous to increase the amount of O ₂ because the reaction heat of O ₂ increases the amount of erosion in the tuyere. The gas pressure on the side was set to high pressure. Although this high-pressure injection increases equipment costs and running costs, considering the above advantages and disadvantages, it is desirable that the proportion of O ₂ in the total blown gas exceeds 60 Vol%. be. The inventors have conducted various experimental studies and found that it is possible to suppress the erosion of the tuyere by reducing the diameter of the bottom blowing tuyere and increasing the pressure of oxygen or oxygen-containing gas. I found out. Possible reasons for this are as follows. First, when the pressure of the oxygen-containing gas sent to the tuyere is increased, the heat absorption effect due to the expansion of the oxygen-containing gas at the tuyere outlet is large, and the cooling effect of the tuyere is improved. In other words, by reducing the diameter of the tuyere and applying high pressure, the mass flow rate per unit cross-sectional area of the tuyere increases, which improves the cooling effect of the tuyere by oxygen-containing gas, and the high-pressure gas has a high flow rate. Therefore, the heat transfer coefficient between the gas and the inner wall of the tube of the bottom blowing tuyere increases, which also improves the effectiveness of the gas in cooling the tuyere. Second, when the pressure of the oxygen-containing gas sent to the tuyere is increased, solidified iron, called pine room, is generated at the tuyere tip due to the endothermic effect caused by the expansion of the oxygen-containing gas at the tuyere tip. It is noteworthy that That is, the inventors conducted a hot model experiment using molten steel and found that the pressure of oxygen-containing gas
When we investigated the effects on pine room formation in the case of 100 Kgf/cm ² and in the case of 10 to 15 Kgf/cm ² , we found that the sensible heat of the gas mentioned above affects the pine room, as seen in Figure 1 A and B. It was found that there was a significant difference in the cooling effect. As shown in Figure 1A, the pressure is 30~100Kg.
The cooling effect of the above gas on the pine room in the case of f/cm ² is as shown in Figure 1B when the pressure is 10 to 20.
It is much larger than the case of Kgf/cm ² .
For this reason, especially when the pressure is set to 30 to 100 kg/ ^cm2 , the cooling effect of the gas on the pine room becomes greater than the radiation from the fire point or the convective heat transfer from the molten steel, and a stable pine room forms at the tip of the tuyere. properly generated. On the other hand, when the pressure is set to 10 to 15 Kg/ ^cm2 , the cooling effect on the pine room becomes smaller than the radiation from the fire point and the convective heat transfer from the molten steel, and a satisfactory pine room cannot be generated at the tip of the tuyere. do not have. Generally, when blowing oxygen from the bottom blowing tuyere, if a pine room is not stably generated at the tip,
The radiation from the fire point and the iron oxide produced at the fire point cause the refractory near the tuyere to erode faster than the refractory in other parts, and as a result, the tuyere itself erodes faster. That will happen. Thirdly, due to the difference in the behavior of the jet flow of oxygen-containing gas blown into the molten iron from the tuyere, the higher the pressure of the blown gas, the less the erosion of the tuyere. That is, from the hot model experiment already mentioned, there are cases where the pressure is 30 to 100 Kgf/ ^cm2 and cases where the pressure is 10 to 15 Kgf/ ^cm2.
As seen in Figure 2 A and B,
It was found that there is a difference in the heat flux to the tuyere due to radiation from the fire point when oxygen is blown into the tuyere. As shown in Figure 2A, the pressure is 30~100Kg.
f/cm ² , the heat flux to the tuyeres due to radiation from the fire point moves away from the fire point due to the long gas jet area, while when the pressure is 10-15 Kgf/cm ² , the gas jet area is As shown in Figure 2B, the heat flux to the tuyere due to radiation from the fire point increases. Therefore, the erosion of the tuyeres occurs when the pressure is 30 to 100 kg.
When the pressure is 10 to 15 kgf/cm ² , the speed is accelerated compared to when the pressure is 10 to 15 kgf/cm ² . The cooling effect on the pine room shown in Figure 1A and the effect of reducing the heat flux to the bottom blowing tuyere shown in Figure 2A are both more effective as the pressure of oxygen or oxygen-containing gas is higher; According to the experimental results, the cooling effect exceeds the heat flux,
In order to ensure the formation of an appropriate pine room at the tip of the tuyere, the supply pressure of the oxygen-containing gas must be at least 30 kgf/ ^cm2 , and at this time, the bottom blowing tuyere must be supplied with the oxygen-containing gas. On the other hand, in the case of a multi-tube system represented by a so-called double-tube tuyere, which performs concentric jetting with the surrounding coolant, more sufficient tuyere protection can be achieved even at the above-mentioned minimum pressure limit. Hydrocarbons, carbon monoxide, carbon dioxide, and inert gases are suitable as the tuyere cooling gas, but under the above-mentioned high-pressure injection, the flow rate is lower than in the conventional case where tuyere cooling was completely dependent on it. Significant savings can be made. When the bottom blowing tuyere is a single-pipe type consisting of a metal pipe, the supply pressure of the oxygen-containing gas should be set to at least 50°C, taking into account the lack of other means to assist in cooling the tuyere.
Kgf/cm ² is necessary in order to obtain the same effect as the multi-tube system. Generally, stirring gas (sometimes also containing oxygen gas) is injected from the bottom of the converter for the following purposes (1) to (3). (1) Even when the carbon concentration of molten iron is low, decarburization takes precedence over iron oxidation, preventing excessive oxidation of iron and improving iron yield. (2) Promotes desulfurization and dephosphorization reactions between slag and molten iron, increasing the effect of removing impurities. (3) Aim to prevent slopping in the first half of blowing. By the way, regarding the injection of gas containing oxygen from the bottom of the converter, the decarburization reaction of the molten iron is promoted by the oxygen itself. It is also done for the sake of Here, regarding the blowing from the bottom of the converter, if the above objective (1) is to be achieved, it is necessary to increase the flow rate in the latter half of the blowing. On the other hand, if the purpose is to promote the dephosphorization reaction in (2) above, it is necessary to reduce the flow rate in the latter half of blowing, because if the flow rate is high in the latter half of blowing, oxidation of iron will be reduced This is because the iron oxide concentration in the slag decreases and dephosphorization cannot be performed satisfactorily. Therefore, when aiming at the above (2), it is necessary to blow a large amount in the first half of the blowing and reduce the blowing flow rate in the second half, as in the case of the above (3). According to the method of the present invention, in a multiple pipe, the flow rate of the blown gas for the purposes of (2) and (3) above can be easily adjusted by changing the flow rate ratio of oxygen to gas. In other words, using a conventional large diameter nozzle,
In the method of blowing low-pressure gas, there was a risk that the tuyere would be clogged with molten iron if the flow rate of the blowing gas was significantly reduced during blowing, but the method of the present invention eliminates this risk. There is no flow rate at all, and the flow rate can be significantly reduced during blowing. In order to clarify the above, we used stainless steel pipes with inner diameters of 2.0 mm, 4 mm and 6 mm.
A tuyere of mm was made, and the relationship between the pressure injected from the tuyere and the flow rate in an actual converter was measured.
The results are shown in FIG. As is clear from the figure, even if the pressure is increased in the tuyeres with inner diameters of 2 mm and 4 mm, the gas flow rate does not increase excessively; on the contrary, the molten iron flows backwards and The flow rate can be reduced while maintaining a pressure that does not cause oral obstruction. On the other hand, for a tuyere with an inner diameter of 6 mm,
If the pressure is increased, the flow rate increases excessively, and in order to reduce the flow rate below a certain level, the pressure must be greatly reduced, which causes molten iron to flow backwards and clog the tuyere. (Example) Now, FIGS. 4A and 4B illustrate the structure of a bottom blowing tuyere used for carrying out the present invention. In FIG. 4A, a stainless steel pipe 4 is installed through a tuyere brick 3 to a hearth brick 2 covering the inside of the bottom shell 1 of the converter, and oxygen is supplied to the lower end of the stainless steel pipe 4. A gas supply pipe 5 containing the gas is connected. In addition, in FIG. 4B, a double pipe 6 is installed through a tuyere brick 3 to the hearth brick 2 that covers the inside of the bottom shell 1 of the converter, and the lower end of this double pipe 6 is connected to the inside of the bottom shell 1. An oxygen supply pipe 7 is connected to the pipe, and a coolant supply pipe 8 is connected to the outer pipe. Using two types of bottom blowing tuyere with such a structure,
The number of these bottom blowing tuyeres arranged at the bottom of the converter,
In the case of FIG. 4A, the inner diameter of the stainless steel pipe 4, and in the case of FIG. 4B, the inner diameter of the double pipe 6 were set variously. In the first embodiment, the stainless steel pipe 4
In the second and third embodiments, the inner diameter of the stainless steel pipe 4 was 4.0 mm and the number of pipes was 3. In the fourth embodiment, the inner diameter of the double pipe 6 is
2.0 mm, and the number of pipes arranged is 8. In the fifth and sixth embodiments, the inner diameter of the double pipe 6 is set to 4.0 mm, and the number of pipes arranged is 5. I did some refining. In each of the examples, SUS 304 was used as the outer tube material of the stainless steel pipe 4 and the double tube 6, and copper pipe was used as the inside material of the double tube 6. On the other hand, as first and second comparative examples, 10 stainless steel pipes 4 each made of SUS 304 were installed at the bottom of the converter, and as a third comparative example, the inner diameter of the double pipe 6 was 4.0 mm. Ten of them were installed at the bottom of the converter, and the hot metal was subjected to blowing in the same manner as in each of the above examples. In each example and comparative example, the temperature of the hot metal that was refined was 1250°C to 1330°C, and the blowing time was 13 to 16°C.
The tapping temperature was 1650-1730℃. The blowing conditions are summarized in Table 1.

[Table] In each Example and Comparative Example, the remaining length of the tuyere was measured at a predetermined charge interval, and the erosion rate of the tuyere was determined. The results are also shown in Table 1. Burnback in Table 1 refers to a phenomenon in which the tuyere material reacts with oxygen and is rapidly eroded. As is clear from the above results, the single pipe tuyere is 50
Kgf/cm ² or more, and the double pipe tuyere is 30 Kgf/cm ² or more, the erosion rate in each example is much lower than that of the comparative example, and its variation is also reduced. In particular, the fourth and fifth embodiments using double pipes have a lower melting rate and less variation than the first and second embodiments using single pipes. Therefore, if you expect the same erosion rate as a single pipe, 30 kg during the entire suction period.
It is not necessary to set it to f/cm ² and only a part of the period is sufficient. In addition, the erosion rate of the first and second embodiments, which are single tubes, is much lower than that of Comparative Examples 1 and 3, which are also single tubes.Especially, the comparison made with double tubes in which coolant is flowing from the outer tube. It is also smaller than Example 2. As demonstrated in the above embodiments, according to the present invention, in the single pipe method, the pressure inside the tuyere pipe of the gas sucked into the molten iron is set to be 50 Kgf/cm ² or more during substantially the entire suction period, and on the other hand, In the case of multiple pipes, the period during which the pressure inside the tuyere pipe for blowing gas into the molten iron is maintained at 30 Kgf/cm ^{2 or} more can be arbitrarily set depending on the purpose. Next, the blowing conditions such as the diameter of the tuyere and the number of tuyeres installed are as follows.
As in the fourth embodiment described above, mainly slag and
Blowing was carried out as follows for the purpose of promoting the dephosphorization reaction between metals and preventing slopping. The target hot metal components are C 4.2% to 4.4%,
Si 0.15%~0.38%, Mn 0.31%~0.48%, P
0.09% to 0.11%, S 0.02% to 0.04%, and the C concentration of the molten steel component after blowing is 0.05% to 0.11%.
The temperature was 1690°C to 1720°C. In blowing using the method of this invention, the pressure during 70% of the time from the start of blowing to the end of blowing is 60 to 90 kg.
f/cm ² , the average gas flow rate is 0.05Nm ³ /min・t,
Thereafter, the pressure was reduced to 10 to 15 Kgf/cm ² and the flow rate was reduced to 0.003 to 0.005 Nm ³ /min·t. On the other hand, as a comparison method, the pressure during 70% of the time from the start of blowing was set to 10 to 20 Kgf/cm ² and the flow rate was set to an average of 0.05 Nm ³ /min·t as in the above example.
Thereafter, the pressure was reduced to 3 to 5 Kgf/cm ² to reduce the flow rate to 0.01 to 0.02 Nm ³ /min·t, which is the minimum flow rate necessary to prevent the tuyere from clogging. The components of the molten steel at the end of blowing were analyzed, and the relationship between carbon concentration and phosphorus concentration was determined. The results are shown in FIG. As shown in the figure, it can be seen that the method of the present invention can lower the phosphorus concentration compared to the comparative method, and that the method of the present invention has excellent dephosphorization properties. Note that the method of the present invention is applicable not only to converters, but also for ladle refining, for example. (Effect of the invention) By blowing oxygen-containing gas under high pressure into the molten iron bath in the refining vessel, it not only contributes to the decarburization reaction of the molten iron, but also reduces the erosion of the tuyere depending on whether or not coolant is used. In particular, according to the second invention, the service life of the tuyere can be extended while more effectively preventing melting damage when no coolant is used.

[Brief explanation of the drawing]

Figure 1 is a graph showing the influence of pressure on the relationship between the cooling effect on the pine room due to gas sensible heat and the blown gas flow rate, and Figure 2 is a graph showing the heat flux to the tuyere due to radiation from the fire point and the blown gas flow rate. Figure 3 is a graph showing the effect of pressure on the relationship between The cross-sectional view shown in FIG. 5 is a comparison diagram of dephosphorization characteristics.

Claims (1)

[Scope of Claims] 1. When a gas containing 60 vol% or more of oxygen is bottom-blown into a bath of molten iron in a refining container from a tuyere provided at the bottom of the container, the gas containing oxygen and the outer envelope thereof are used as the tuyeres. in the refining vessel, characterized in that the oxygen-containing gas is supplied at the tuyere inlet under a high pressure of at least 30 Kgf/cm ² by means of a multi-tube tuyere serving for concentric ejection with the tuyere cooling gas. Method of blowing gas into molten iron. 2. When bottom-blowing a gas containing 60 vol% or more oxygen into the molten iron bath in the refining vessel from the tuyere located at the bottom of the vessel, the gas shall be passed through the single-pipe tuyere to a rate of at least 50 kgf at its inlet. 1. A method for blowing gas into molten iron in a refining vessel, the method comprising supplying gas while maintaining a high pressure of /cm ² during substantially the entire blowing period.