JPH02179810A - Method for operating top and bottom blowing converter - Google Patents

Abstract

PURPOSE:To improve Mn yield and to reduce iron content in slag and eroding rate of furnace wall refractory by specifying a bottom blowing gas flow ratio at inner and outer of the fire point in operation of a large-scaled converter specifying the total bottom blowing gas flow rate and gas flow ratio of top blowing and bottom blowing. CONSTITUTION:Stirring gas is blown into molten steel from a single or double tube bottom blowing tuyere at furnace bottom in the large-scaled top and bottom blowing converter having 4000-8000mm furnace bottom diameter and 250-380 Ton/ch at >=0.1Nm<3>/t.min and also O2 gas jet is injected on the molten steel surface with a water cooled top blowing multi-holes lance. Then, this gas flow ratio of the top blowing and the bottom blowing is made to 0.05-0.20. In this operation, the gas flow rate from the bottom blowing tuyere at inside of fire point projecting plane under condition of the lance height at end period of the blowing, is made to 1.2-2.0 ratio to the total gas flow rate from the tuyere at outside.

Description

Detailed Description of the Invention [Industrial Application] The present invention relates to a method for operating a large top-bottom blowing converter having a bottom diameter of 4,000 to 8,000 m and a processing amount of hot metal of 250 to 380 Ton/ch. It is something.

[Conventional technology]

Conventionally, in order to improve the molten steel stirring effect using bottom blowing gas in the above-mentioned large top-bottom blowing converter, studies have been conducted on increasing the gas flow rate, selecting the gas type, optimizing the tuyere arrangement, etc. Generally, in a large top-bottom blowing converter, the total flow rate of bottom-blown gas is set to 0.1 Nbo/1-mln or more, and the ratio of the amount of gas blown from the bottom blowing to the amount of 02 gas from the top blowing is 0.05 to 0. 20, and the effect of improving the metallurgical reaction inside the converter has been obtained. Regarding the arrangement of tuyeres, Japanese Patent Publication No. 5B-16013 describes a method of arranging multiple tuyeres within the top blowing point to improve the stirring power of molten steel, and Japanese Patent Publication No. 61-36050 describes a method of arranging multiple tuyere within the top blowing point to improve the stirring power of molten steel. A method has been proposed in which two tuyeres are placed inside and outside the point to promote P removal. However, in the past, the same flow rate was assumed for each tuyere, and no mention was made of the ratio of bottom-blown gas flow rates inside and outside the ignition point.

(Problems to be Solved by the Invention) Under the operation of the above-mentioned top-bottom blowing converter, in order to suppress the yield reduction due to oxidation loss of manganese and iron at the final stage of blowing, it is necessary to increase the amount of bottom-blowing gas. It is a well-known fact that it is effective to promote supply to and from the point.However, if only the tuyere diameter is expanded, the relationship with the tuyere erosion index is shown in Figure 2, and the relationship with the tuyere erosion index is shown in Figure 3. As shown in the relationship with the furnace wall erosion index, the refractory around the tuyere is eroded due to the back attack of the discharged gas.

The amount of corrosion of the furnace wall refractories increases and the cost of the refractories increases significantly.

Note that the tuyere erosion index is expressed as a ratio of the amount of tuyere erosion per one charge of blowing (mm/ch) when the amount of erosion at the standard tuyere diameter is taken as 1, and is The index is blowing 1
This is a parameter defined as the ratio of the amount of erosion on the furnace wall per charge, when the amount of erosion at the tuyere diameter, which is the standard, is set to 1.

In addition, increasing the number of tuyeres brings the tuyere closer together, which promotes erosion of the refractory between the tuyeres due to back attack and reduces the life of the refractory. There is a limit to increasing the number of books. - On the other hand, problems such as an increase in the cost of the blown gas and a decrease in the molten steel temperature (decreased thermal margin) due to the heat removal of the blown gas arise as the flow rate of the bottom blown gas increases, so it is necessary to make effective use of the blown gas.

[Means to solve the problem]

The present invention is intended to solve the above problems, and the gist thereof is as follows.

(1) 0.00 liters of water is poured into the steel bath from the bottom blowing tuyere of a single or double pipe installed at the bottom of the furnace. Stirring gas of I Nrd/tmln or more was blown into the steel bath surface, and an oxygen gas jet was blown onto the steel bath surface using a water-cooled top-blown porous lance, and the top-bottom blowing gas flow rate ratio was set to 0.05 to 0.20. In top-bottom blowing converter operation, the ratio of the gas flow rate from the bottom blowing tuyere placed inside the hot spot projection surface to the total gas flow rate from the outside tuyeres under lance height conditions at the end of blowing is calculated. 1.2-2
．． 1. A method for operating a top-bottom blowing converter, characterized in that it is operated at zero temperature.

(2) The number of bottom blowing tuyere arranged inside the flashpoint projection plane and the number of bottom blowing tuyere arranged outside the flashpoint are the same number, and the diameter of the tuyeres inside the flashpoint is larger than the diameter of the tuyere outside the flashpoint. A method of operating a top-bottom blowing converter as described in the preceding paragraph characterized by:

(3) The number of hot spots and the number of hot spots are the same, and the tuyere diameter inside the hot spot is made larger than the outer hot spot tuyere, and the gas flow rate blown into the steel bath from each tuyere is independently controlled and independent. 3. The method of operating a top-bottom blowing converter according to item 1 or 2 above, characterized in that the control is carried out by setting a set value or by using an orifice of a different diameter or the like.

In the present invention, the bottom-blown gas flow rate refers to the gas flow rate that is ejected from the inner tube in the case of a double-pipe tuyere and from the entirety of the single-pipe tuyere.

[For production]

Conventionally, the stirring power of molten steel in the large top-bottom blowing converter was
Top blowing and bottom blowing are each determined by the total gas flow rate, and usually the bottom blowing gas flow rate is set to 0. INrrr/t-mln
It is a well-known fact that the operation is carried out at a top and bottom blowing gas flow rate ratio of 0.05 to 0.20. The distribution has not been clarified so far. Therefore, we conducted a water model experiment to investigate the effect of different bottom-blown gas injection methods on the stirring force. As shown in Figure 4, under the same total flow rate of bottom-blown gas, the center of the tank, which corresponds to the ignition point of top-blown gas, was By making the diameter of the tuyere placed in the tuyeres larger than that of the tuyere placed outside the ignition point, the amount of gas is increased from that outside the ignition point, and the ratio of the amount of gas inside and outside the ignition point is within a predetermined range.
We have found that the stirring power can be increased and the uniform mixing time can be shortened.

Furthermore, as a result of studying bottom-blown gas injection in a top-bottom blowing converter using an actual machine, it was found that it is effective to set the blowing gas flow rate from the tuyeres inside and outside the hot spot independently, as shown below. . In other words, in order to promote the reaction between slag and metal, it is effective to strengthen the slag-metal mixture by stirring outside the hot spot, and on the other hand, the Fe generated by the top-blown oxygen jet
It has been found that stirring within the hot spot is effective for reducing oxides such as O and Mn0 and suppressing oxidation. From these points of view, the present inventors particularly aimed to remove P and S by pre-treatment of hot metal.
In slagless blowing (in-furnace slag amount ≦50 kg/l) in which 10 kg or more of Mn ore is added to hot metal that has been subjected to Increase in Mn in steel by reduction of
Focusing on the fact that oxidation loss of Mn occurs at the same time in the hot spot, in order to improve the Mn yield in the furnace, we further investigated the optimal value of the amount of bottom blowing gas inside and outside the hot spot using an actual converter. It was considered in detail.

In other words, as shown in Fig. 5, increasing the ratio of powder gas at the hot point under the same total flow rate of bottom-blown gas in three cases (×, Δ, ·) not only increases the molten steel stirring force but also reduces the Mn oxidation loss. As a result, the in-furnace Mn yield is improved, and T and Fe in the slag are significantly reduced.

However, if the gas ratio in the flashing point is further increased, the slag
As the metal stirring effect fades, the Mn yield decreases and T and Fe in the slag rapidly increase. In other words, it has been found that a flow rate ratio of powder gas at the hot point of 1.2 to 2.0 is most suitable as a bottom blowing gas injection method.

As a means of achieving the above-mentioned optimal blowing method, it is possible to use tuyeres of the same diameter and change the number of tuyeres arranged inside and outside the spark point. In addition, if there is a limit to the number of tuyere arrangement due to refractory corrosion etc., the diameter of the tuyere located inside and outside the fire point can be changed from inside the fire point to outside the fire point (
(hereinafter referred to as "different diameter"), it is possible to adjust the gas flow rate between inside the fire point and outside the fire point.

In the case of flow control method 2, in which the flow rate of each tuyere cannot be set independently, by installing an appropriate orifice for each tuyere diameter in the middle of the supply pipe, the gas flow rate can be adjusted according to the different diameters of the tuyere. can be changed. The ratio of the blown gas flow rate inside and outside the fire point changes slightly during operation due to the adhesion of pine mushrooms to the tip of the tuyere, which usually results in an aperture ratio of 0.8 or less. It is preferable to determine the initial setting value so that the value is between . By installing orifices according to each tuyere diameter shown in the table, the inter-tuyere flow rate deviation caused by flow rate fluctuation due to changes in tuyere tip pine mushroom pressure loss can be reduced to about 6% at most (when the inner pipe back pressure is ±10%).

In addition, Figure 6 shows the case where the tuyere pore area ratio fluctuates in the direction of decreasing (
It shows the flow rate between each tuyere (which is called a blockage), and the flow rate deviation is expressed as a percentage when the reference value for each tomorrow is set to 100%.

Table 1 Using a blowing converter, the amount of top blowing oxygen is 3 to 4 Nrr in the initial to middle stages.
f/t-min, 2-3 Nnr/t in the final stage
・min.

The distance between the ransuru molten metal surfaces at the final stage of blowing was 2.5 to 3.0 m. In addition, hot metal is represented by the temperature and composition shown in Table 2.
Pretreated hot metal that had been previously subjected to Si, P, and S removal treatments was used, and the amount of slag in the converter was set to 50 kg/or less.

Table 2 〔Example〕 Examples of the present invention are shown below.

All furnaces have 3407on top and bottom blowing tuyeres with a bottom diameter of 6.200 mm, with a maximum of six tuyeres operating simultaneously, and a ratio of the tuyere flow rate at the hot spot to the tuyere flow rate outside the hot spot to 0.7. ~2, 1,
Bottom blowing gas total flow rate 0.16 to 0.18 Nnf/t-
Tests were conducted at each level between win. Table 3 shows the bottom blow conditions at each level. In addition, in the initial stage of blowing, Mn ore is 5
-35 kg/mu of Mn ore was added, and 1-8 kg/mu of quicklime was added to adjust the basicity to match the amount of gangue of Mn ore.

Figures 7 and 8 show an example of the metallurgical effect in the blow-off slag (
The effect of improving the Mn yield in the converter is shown.

Here, in FIG. 7, the horizontal axis shows the blow-off (C) amount, and the vertical axis shows the blow-off slag (T, Fe). Further, in FIG. 8, the horizontal axis shows the total amount of Mn introduced into the furnace, and the vertical axis shows the in-furnace Mn yield.

φ22X4 (0,15Nrrf/t-min
) to φ24X4 (0,18Nrrf/l -min
) by increasing the total flow rate of bottom-blown gas
The effect of reducing Mn (Fig. 7) and the effect of improving Mn yield (Fig. 8) are observed.

Comparing Comparative Example 7 and Example 5, which have the same total flow rate of bottom blowing gas, T, Fe
A 0.8% reduction in Mn yield and a 4% improvement in Mn yield were observed. The improvements in the metallurgical effects of Examples 1 to 3 and Comparative Examples 1 to 6 under other conditions are collectively shown in FIG.

In addition, when using a double-tube tuyere, in order to suppress the increase in the amount of tuyere erosion due to the enlargement of the diameter of the inner fire point cavity, the outer tube cooling gas is a mixed gas of t, pc + coz, and the linear flow rate of the outer tube gas is A new method has been adopted in which the bubbles are raised to the bubble receding and disappearing region.

On the other hand, it has been confirmed that similar effects can be obtained when stirring is performed by blowing inert gas through a single tube.

〔Effect of the invention〕

As described above, according to the present invention, Mn in the furnace is
The yield can be significantly improved and the use of expensive Mn alloys can be reduced. In addition, the iron concentration in the slag (T.

This greatly reduces Fe) and improves the iron yield.

On the other hand, by reducing the amount of blown gas in the outer circumference, which is outside the fire point, it is also possible to reduce the amount of erosion of the furnace wall refractories at the same time. It is also possible to equalize the lifespan of multiple tuyeres by reducing the diameter of the tuyeres in areas where the amount of erosion is large.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing an example of a top-bottom blowing converter for carrying out the present invention, FIGS. 2 and 3 are views showing the tuyere diameter and melting rate of each part, and FIG. The figure shows the uniform mixing time in a 1/10 water model experiment when four tuyeres were placed at positions assumed to be inside the fire point and outside the fire point so that the flow rate ratio of both was 1.1.4. Figure 5 shows the effect of the ratio of flow rates inside and outside the spark point on the metallurgical effect under each total flow rate of bottom-blown gas. Figure 6 is a diagram showing the results in a bottom-blowing converter, and Figure 6 is a diagram showing the calculated effect of changes in the nozzle tip aperture ratio on the flow rate of each tuyere when the tuyere diameter of each tuyere is changed. Figures 7 and 8 are examples of actual machine top-bottom blowing when the bottom-blown total gas is 18Nrrr/1-mln and the flow rate inside the hot spot/flow rate outside the hot spot is 1.1.4. It is a figure comparing the results in a furnace. H1 yield (o7o) Fig. 1 Upper ψ shi cools down, acid seat jet fire point Zuteg 5''! A4! 4 c Large point force peeling lower fire 5 color external use port N4rne 9 Fig. 3 Blowing gas #, t (Nm' = Pure 1. Main 9 ψ16 硲 - Oblique -28 Tuyere diameter C-type υ #/6 φ2D p-ψJ Tomoko outsider Yuatsu Fig. 6 1 @ Clever Figure 7 (C) (Z) Figure 8 Total amount of Mn in the reactor (x/(7-'Z)

Claims (3)

[Claims] (1) Stirring gas of 0.1 Nm^3/t・min or more is blown into the steel bath from the bottom blowing tuyere of a single or double tube installed at the bottom of the furnace, and the steel bath is cooled with water. In a top-bottom blowing converter operation in which an oxygen gas jet is blown by a blowing porous lance and the top-bottom blowing gas flow rate ratio is set to 0.05 to 0.20, the fire point projection surface under lance height conditions at the end of blowing. The ratio of the gas flow rate from the bottom blowing tuyeres placed inside to the total gas flow rate from the outside tuyeres is 1.2 to 2.0.
1. A method of operating a top-bottom blowing converter, characterized in that it is operated at. (2) The number of bottom blowing tuyere arranged inside the fire point projection surface is the same as the number of bottom blowing tuyere arranged outside the fire point, and the diameter of the tuyere inside the fire point is larger than the diameter of the tuyere outside the fire point. 2. The method of operating a top-bottom blowing converter according to claim 1. (3) The number of tuyeres inside the hot spot and the number outside the hot spot are the same, and the diameter of the tuyere inside the hot spot is made larger than the tuyere outside the hot spot, and the gas flow rate blown into the steel bath from each tuyere is independently controlled. 3. The method of operating a top-bottom blowing converter according to claim 1, wherein control is performed using independent set values or by using orifices of different diameters.