JPS6187810A - Method for blowing gas into molten iron in refining vessel - Google Patents

Abstract

PURPOSE:To inhibit effectively the melt fracture of a bottom tuyere of a vessel when oxygen is blown into a molten iron bath in the vessel from the bottom tuyere, by blowing oxygen under a specified high pressure at the inlet of the tuyere. CONSTITUTION:A stainless steel pipe 4 is placed in bottom brick 2 covering the inside of the bottom iron shell 1 of a converter with tuyere brick 3 in-between, and an oxygen feeding pipe 5 is connected to the lower end of the pipe 4. When oxygen or a gas contg. oxygen is blown into a molten iron bath in the converter from the pipe 5, the pressure of the gas is regulated to at least 30kgf/cm<2> at the inlet of the tuyere 3. Thus, the molten iron is well decarburized, and the melt fracture of the tuyere 3 is effectively inhibited whether a coolant is used or not.

Description

[Detailed Description of the Invention] (Industrial Application Field) Into a bath of molten iron received into the interior of a refining vessel such as a converter through a tuyere (hereinafter referred to as bottom blowing tuyere) disposed at the bottom of the vessel, The technical content described in this specification regarding the progress of the refining reaction of the molten iron by blowing in a gas containing oxygen and the effective suppression of erosion of the bottom blowwall during the process is based on the usefulness of high-pressure blowing of the gas. It is about proposing the results of development research.

Recently, Ar and N2 have been released from the bottom of refining vessels such as converters.
The combined blowing method, in which gas is blown from the bottom and oxygen is blown from the top of the furnace using a top-blowing lance, is widely used industrially.

This composite blowing method decarburizes molten iron by 441. There is no excessive oxidation of iron even when carbon & 1 degree is used, and the iron yield is good because there is little splash, and the stirring effect of the molten iron by the bottom-blown inert gas reduces slag. - There are various benefits such as accelerated metal reaction and good refining effect.

(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 implementing this composite blowing method. There was a problem like this.

In other words, while metal pipes have the advantage of being inexpensive, there is a risk that, especially when the 7R'IL is throttled down, the molten iron in the converter may enter the hollow hole of the pipe and cause blockage of the tuyeres, reducing the flow rate. The disadvantage is that the range in which it can be adjusted by changing is narrow.

On the other hand, a porous plug as shown in Japanese Patent Application Laid-Open No. 57-200533 has the advantage that there is no risk of clogging the lining even if the flow rate is restricted, and that the flow rate can be adjusted over a wide range, but on the other hand, it is expensive. There is a drawback.

In addition, all of these tuyeres have a shorter service life when compared to the large bottom refractories of converters, and even though the bottom refractories are still sound, the lifespan of bottom blowing tuyeres is shorter than that of converter bottom refractories. In order to avoid this, the furnace body should be replaced with a new one, and the tuyeres should be closed to stop the injection of bottom-blown inert gas, and the unsatisfactory oxygen caused by blowing in only from the top-blowing run could be avoided. There is no need to carry out further refinement.

The inventors have found that the method is effective for +h before melting of the bottom blowing tuyeres, and
Regarding a method of blowing gas into molten iron in a steelmaking container, which allows the blowing flow rate to be adjusted over a wide range, a patent application filed in 1983
No. 1482 was proposed. This method uses a tuyere tube with an inner diameter of 3 mm or less, and the gas pressure at the inlet of the tuyere tube is 50 kgf during at least part of the entire blowing period.
/ cr 1 or more.

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 tuyere and extending the service life of the tuyere, but on the other hand, it has the same agitation effect as conventional blowing of inert gas from the bottom of the converter. When compared to the method of blowing oxygen into the steelmaking vessel from the bottom of the converter, which also helps increase the
Since the inert gas that controls simple stirring does not react with molten iron,
There was a problem with the economic disadvantage.

In addition, when injecting 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 blowwall and prevent it from melting. It is economically desirable to use less coolant.

(Problems to be Solved by the Invention) This invention provides a method that is effective for preventing erosion of the bottom blowing tuyeres, and in particular, appropriately blows N9 cable or gas containing oxygen into molten iron charged into a smelting vessel. The purpose is to give

(Means for solving problems) The above objects are advantageously achieved by the following methods.

1. When bottom-blowing oxygen or a gas containing oxygen into the molten iron bath in the refining container from the tuyere provided at the bottom of the container, the gas must be supplied under high pressure of at least 30 kgf/cJ at the tuyere inlet. A method for injecting gas into molten iron in a refining vessel (first invention), characterized in that the tuyere is a concentric arrangement of a gas containing an enzyme or oxygen and a tuyere cooling gas surrounding it. A preferred embodiment is the use of multi-tube tuyeres to assist in ejection.

2. When bottom-blowing oxygen or a gas containing oxygen into the molten iron bath in the refining container from the tuyere provided at the bottom of the container, the gas must be passed through the single pipe siding at the inlet at a rate of at least 50 kgf/
A method for blowing gas into molten iron in a refining vessel, the method comprising supplying gas while maintaining a high pressure of ci throughout the entire blowing period (second invention). Alternatively, a gas containing oxygen refers to a gas containing pure oxygen or 02, which accounts for at least 1% of GOVo, and the remainder is a mixed gas such as an inert gas such as Nz or Ar. Regarding the mixing ratio of C1 and inert gas, it is advantageous for the proportion of 02 to exceed 60 VO 1% in the total blown gas as follows.

The higher the 02 ratio, the higher the Ω in the steel bath even at the same flow rate.
The stirring power increases because CO bagasse reacts with the amount of oxygen and becomes twice as much as the amount of oxygen. Furthermore, since it is cheaper than inert gas, it is advantageous in terms of cost.

On the other hand, since the reaction heat of 02 increases the amount of melting loss of the tuyeres, it is generally considered disadvantageous to increase the amount of 02, and in this invention, the gas pressure on the inlet side of the tuyere is reduced to reduce this melt 10. The pressure was high.

Note that this high-pressure injection will increase equipment costs and running costs (but the above advantages and disadvantages [-
Taking these into account, the proportion of 02 in the total blown gas is 6.
Therefore, it is desirable that the voltage exceeds 0Vo1%.

The inventors have conducted various experimental studies and found that it is possible to suppress the melting of the tuyere by particularly reducing the diameter of the bottom blown tuyere and increasing the pressure of oxygen or oxygen-containing gas. Ta.

Possible reasons for this are as follows.

First, by increasing the pressure of the oxygen-containing gas sent to the tuyere, the heat absorption effect due to the expansion of the oxygen-containing gas at the tuyere outlet increases, and the cooling effect of the tuyere improves. In other words, when the diameter of the tuyere is reduced and high pressure is applied, the suspended flow standard per unit cross-sectional area of the tuyere increases, which improves the cooling effect of the tuyere by oxygen-containing gas. This increases the heat transfer coefficient between the gas and the inner wall of the tube of the bottom blowing tuyere, 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 mushroom, is generated at the C-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 was 30 to 100 kg.
FI2 g to pine mushroom production for f/cJ case and 10-15 kgf/cJ case
However, as shown in FIGS. 1(A) and 1(B), it was discovered that there was a significant difference in the cooling effect on the pine mushroom due to the sensible heat of the gas.

As shown in Figure 1 (A), the pressure is 30 to 100 kg.
The cold J,l'l effect of the gas on the pine mushroom in the case of r/c+/ is much larger than that in the case where the pressure is 10-20 kgf/cvr as shown in FIG. 1(B). For this reason, the pressure should be increased from 30 to 100k8.
/cf, the cooling effect of the gas on the pine mushroom becomes greater than the radiation from the fire point and the convection heat transfer from the molten steel, and a stable pine mushroom is appropriately generated at the tip of the tuyere.

On the other hand, when the pressure is set to 10 to 15 kg/cJ, the cooling effect on the pine mushroom is smaller than the radiation from the fire point and the convective heat transfer from the molten steel, and a satisfactory pine mushroom is produced at the tip of the tuyere. cannot be generated.

Generally, when blowing oxygen through a bottom-blown tuyere, if pine mushrooms are not stably generated at the tip, radiation from the fire point and iron oxide generated at the fire point will damage the refractory near the tuyere. It will melt down faster than the refractory, and therefore the siding itself will melt away faster.

Thirdly, due to the difference in the behavior of the jet flow of oxygen-containing gas that is blown into the molten iron from the tuyere, the higher the pressure of the blown gas, the less the molten metal 10 in the tuyere.

That is, from the hot model experiment already mentioned, the pressure is 30
As can be seen in Figure 2 (A) and (B) in the case of ~100 kg f/c+i and the case of 10 to 15 dazzling f/cm2, there are side effects due to radiation from the flame point when oxygen is blown into the flame. It was found that there is a difference in the heat flux to the

As shown in Figure 2 (A), the pressure is 30 to 100 kg.
f/cl, 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 region, while when the pressure is 10-15 kgf/cl, the gas jet region As shown in Figure 2 (B), the heat flux to the tuyere due to radiation from the fire point increases.

Therefore, the melting IQ of the tuyere is 30 to 100 J f
The pressure is 10 to 15 years compared to /C case 7/
In the case of cl, it will be accelerated.

The cooling effect on the pine mushroom shown in Figure 1 (A>) and the effect of reducing the heat flux to the bottom blowing tuyere shown in Figure 2 (A) are both more effective as the pressure of oxygen or oxygen-containing gas is higher. Generally, according to the above experimental results, in order for the cooling effect to exceed the heat flux and to ensure proper pine mushroom formation at the tuyere tip, the oxygen-containing gas supply pressure should be at least 30 kg f/ cmf, and in this case, if the bottom blower is a multi-pipe system represented by a so-called double-pipe siding, in which the bottom blower ejects the oxygen-containing gas concentrically with the coolant enclosing it, In particular, better siding protection is achieved even at the minimum pressure limits mentioned above.Suitable siding cooling gases here include hydrocarbons, carbon oxides, carbon dioxide and inert gases, but under the high pressure blowing mentioned above, The flow rate can be significantly reduced compared to the conventional case where tuyere cooling was completely dependent on it.

When the bottom blowing tuyere is a single pipe type made of metal pipe,
Taking into consideration the lack of other means to assist in cooling the siding, it is necessary to set the supply pressure of oxygen-containing gas to at least 50 kgf/c in order to obtain the same effect as the multi-pipe 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 if the carbon concentration of the molten ore becomes low, the decarburization reaction occurs before the oxidation of iron, thereby preventing excessive oxidation of iron and improving the iron yield.

(2) Promote desulfurization and dephosphorization reactions between slag and molten iron,
Increases impurity removal effect.

(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 injection from the bottom of the converter, see (1) above.
If this is the purpose, it is necessary to increase the flow rate in the latter half of blowing. On the other hand, if the purpose is to promote the P dephosphorization reaction in (2) above, it is necessary to reduce the flow rate in the latter half of blowing. This is because the iron oxide concentration in the slag decreases and dephosphorization cannot be performed satisfactorily.

Therefore, if the purpose is (2) above,
As in the case of 3), in the first half of the blowing process,
In the second half, it is necessary to reduce the blowing flow rate.

According to the method of this invention, the above (2
) and (3) can be easily adjusted by changing the ratio of oxygen to gas.

However, with the conventional method of blowing low-pressure gas using a large-diameter nozzle, there was a risk that the tuyeres would become clogged with molten iron if the flow rate of the blowing gas was significantly reduced during blowing. According to the method of the invention, there is no such fear at all, and the flow rate can be significantly reduced during blowing.

In order to clarify this, we used stainless steel pipes with inner diameters of 2.0 mm, 4 mm and 6 mm.
A tuyere was made and the relationship between the pressure blown into the blade and the flow rate was measured in an actual converter.

The results are shown in FIG.

As is clear from the figure, even if the pressure is increased, the gas flow ω does not increase excessively in the case where the inner diameter is 2 mm and 4n+m.On the contrary, the molten iron flows backward and the bottom blowing blade The flow rate can be reduced while maintaining a pressure that does not cause oral obstruction.

On the other hand, in a tuyere with an inner diameter of 6 mm, when 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 reduced manually, so The water flows backwards and the tuyeres become blocked.

(Example) Figures 4 (A> and (B) illustrate the structure of the bottom blowing tuyeres used for carrying out the present invention. Figure 4 <A) shows the bottom iron shell of the converter. A stainless steel pipe 4 is disposed through a tuyere brick 3 to a hearth brick 2 covering the inside of the furnace, and a gas supply pipe 5 containing oxygen is connected to the lower end of the stainless steel pipe 4.

In addition, in Fig. 4 (8), the inside of the bottom shell 1 of the converter is DI
The double pipe 6 is connected to the hearth brick 2 through the tuyere brick 3.
At the lower end of this double pipe 6, an oxygen supply pipe 7 is connected to the inner pipe, and a coolant supply pipe 8 is connected to the outer pipe.

In the case of Fig. 4 (A), the inner diameter of the stainless steel vibrator 4 and In the case of FIG. 4(B), the inner diameter of the double tube 6 was set variously.

In the first embodiment, the inner diameter of the stainless steel vibrator 4 is 2.0 mm, and the number of vibrators disposed is 8. In the second and third embodiments, the inner diameter of the stainless steel vibrator 4 is 4.0 mm. Omm In the fourth embodiment, the inner diameter of the double pipe 6 is 2.0 mm, and the number of pipes is 8. In the fifth and sixth embodiments, the number of pipes is 3. In this case, the inner diameter of the double pipe 6 is set to 4. The following refinement was carried out using a multi-single tube system in which the number of tubes was set to 5. In each of the examples, 5US304 was used as the material for the outer tube of the stainless steel vibrator 4 and the double tube 6, and copper pipe was used as the material for the inner tube of the double tube 6.

On the other hand, as first and second comparative examples, ten stainless steel vibrators 4 made of 5US304 and each having an inner diameter of 4.0111111 were installed at the bottom of the converter, and as a third comparative example, the inner diameter of the double pipe 6 was 4.0111111. 10 mm at the bottom of the converter.
After the actual installation, 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, the blowing time was 13 to 16 minutes,
The tapping temperature was 1650 to 1730°C.

The blowing conditions are summarized in Table 1.

In each of the Examples and Comparative Examples, the remaining length of the tuyere was measured at predetermined charging intervals, 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 has a weight of 50 kgf.
lcJ or more, and the motorcycle control port is 30 kgf/c1 or more, the erosion rate in each example is much lower than that in the comparative example, and its variation is also reduced.

In particular, the M4 embodiment in the double pipe and the fifth embodiment are the M4 embodiment in the double pipe and the M4 embodiment in the single pipe. The erosion rate is roughly smaller than that of the second embodiment, and the variation is also small. Therefore, if you expect the same erosion rate as the LIi tube, it is not necessary to use 30 dazzling f/c during the entire suction period, but only for a part of the period. Also, the first embodiment in a single pipe,
The erosion rate of the second example was also much lower than that of Comparative Examples 1 and 3, which had a single tube, and was especially lower than that of Comparative Example 2, which had a double tube in which the coolant was flowing from the outer tube. There is.

As demonstrated in the above embodiments, according to the present invention, in the single pipe system, the pressure inside the tuyere pipe of the gas sucked into the molten iron is set to be 8f/c1 or more during substantially the entire blowing period, On the other hand, in the case of multiple pipes, the internal pressure of the siding pipe that blows gas into the molten iron is 30 kgf/cr! The above period can be arbitrarily set depending on the purpose.

Next, the conditions for blowing, such as the diameter of the slats and the number of slats, are the same as in the fourth embodiment described above. was carried out as follows.

The target hot metal components are C4, 2% to 4.4%, 3i
0.15%~0.38%, MnO, 31%~
0.48%, P 0909%~0.11%, 30.0
The C temperature of the molten steel component after blowing is 0.05% to 0.11%, and the temperature is 1690°C to 17%.
Hot at 20℃.

In blowing in which the method of this invention is carried out, seven days from the start of blowing out of the entire period from the start of blowing to the end of blowing.
60~90kgrlc pressure in a certain amount of time! , the gas flow rate was set to an average of 0.05 Nm 3/min -t, the subsequent pressure was reduced to 10 to 15 kgf/c/, and the flow n was set to 0.003 to 0,005 Nm 3/i+in
−t. On the other hand, as a comparison method, the pressure during 70% of the time from the start of blowing is set at 10 to 20 kgf/
The average flow rate at cJ was 0.05 N as in the above example.
m3/n+1n-t, then increase the pressure to 3 to 5 kgf
0.01 to 0.02 Nm, which is the minimum flow rate necessary to reduce the pressure to /d and prevent the tuyere from clogging.
The weight was reduced to /1n・[.

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 can also be applied to, for example, steel refining.

(Effect of the invention) By blowing oxygen-containing gas into the molten iron bath in the refining vessel under high pressure, in addition to contributing to the IIR coal reaction of the molten iron, 1q of the molten iron in the tuyere is blown into the molten iron bath with or without coolant. In particular, according to the second aspect of the present invention, it is possible to effectively prevent melting damage and extend the service life of the siding even when no coolant is used.

[Brief explanation of drawings]

Figure 1 is a graph showing the influence of pressure on the relationship between the cooling effect on pine mushrooms due to gas sensible heat and the flow rate of blown gas. Figure 2 is a graph showing the relationship between the heat flux to the siding due to radiation from the fire point and the flow rate of blown gas. The graph does not show the influence of pressure on the relationship. Figure 3 is a flow rate and pressure correlation diagram of the blown gas with the inner pipe diameter of the bottom blowing tuyere as a parameter, and Figure 4 is a typical example of a bottom blowing tuyere. FIG. 5 is a cross-sectional view of a hailstone, and FIG. 5 is a comparison diagram of dephosphorization characteristics. Fire point, Kaden On # J Yuzuka to the tuyere (KW) 05 20 40 60 Bo
f00 Blow-in pressure (K and a Fig. 4 (A) Fig. 4 (B) Blow-off C coal production (%

Claims (1)

[Claims] 1. When bottom-blowing oxygen or a gas containing oxygen into the molten iron bath in the refining container from the tuyere provided at the bottom of the container, the gas is supplied at a rate of at least 30 kgf/cm^ at the tuyere inlet. 2. A method for blowing gas into molten iron in a refining vessel, characterized by supplying the gas under high pressure. 2. The method according to 1, in which a multi-tube tuyere is used as the tuyere, which serves for concentric ejection of oxygen or a gas containing oxygen and a tuyere cooling gas surrounding the same. 3. When bottom-blowing oxygen or a gas containing oxygen into the molten iron bath in the refining vessel from the tuyere provided at the bottom of the vessel, the gas is passed through the single-tube tuyere and at least 50 kgf/ c.
A method for blowing gas into molten iron in a refining vessel, characterized by supplying gas while maintaining a high pressure of m^2 over substantially the entire blowing period.