JPS5816015A - Refining method for pig iron by oxygen top blown converter - Google Patents

Abstract

PURPOSE:To intensify the agitation of molten steel in the refining stage of pig iron and to reduce the losses of iron and Mn by setting the number of bottom blowing nozzles in an oxygen top blown converter at a prescribed number or above, and locating these one-sidedly only in the specific region. CONSTITUTION:Pig iron is refined by the combination use of top blowing 1 of O2 and bottom blowing of a gaseous or powdery and granular slag making agent by bottom blowing nozzles 6 by using an oxygen top blown converter which is tiltable forward and backward by a tilting shaft 2 stuck to a furnace body 3. The bottom blowing is accomplished by >=4 pieces of the nozzles 6 which are provided only in the region where the distance from a projection line 10a is apart by 1/3-1/2 the radius r of the furnace bottom on the half-moon shape side on one side in the furnace bottom where the axial center 10 of the tilting shaft is bisected by the projection line 10a perpendicular to the bottom and are disposed in series along the line 10a. As a result, the flow formed in the case of top blowing alone is disturbed and the agitation of a steel bath is intensified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining pig iron in an oxygen top-blowing converter using a combination of oxygen top-blowing using a lance and bottom-blowing using a double pipe or a single pipe.

In the oxygen top-blown converter method, hot metal, scrap, and auxiliary materials are charged into the furnace and refined by blowing oxygen onto the bath surface using a lance. However, the major problem with this refining method is that the agitation of the molten steel decreases at the final stage of refining. It is.

That is, in this method, the molten steel is stirred by carbon monoxide generated by the reaction between the molten steel and oxygen, and the carbon content in the sand and steel bath is high to some extent.

This is sufficient in the early and middle stages of refining, when the reaction between molten steel and oxygen is active and a large amount of carbon oxide is generated.

However, at the final stage of refining, the carbon content in the steel bath decreases to 0 or 1.
If the temperature is below -, less carbon monoxide is generated, the stirring of the steel bath becomes weaker, and the decarburization rate decreases. As a result, the iron oxide content in the slag increases, and the oxygen level in the round steel bath also increases rapidly, causing various problems in the past.For example, iron oxide and manganese oxide in the slag increase; There is a problem that the loss becomes large. Furthermore, there is the problem that the oxygen level in the steel bath increases rapidly, reducing the yield of ferroalloys containing silene and aluminum.

This ninth conventional article is used to solve these problems.

It has been proposed to use other stirring means in combination with top blowing by a lance. For example, a method is to install an electromagnetic stirring device near the bottom of the furnace, or to rotate or swirl a top blowing lance to stir the molten steel. .

However, the former method is more effective despite the higher equipment costs.
It is rarely used because it is not very effective.

Even with the latter method, the purpose is to strengthen the stirring of the slag, and K has not been reached until the stirring of the steel bath is strengthened.

In response to this, a new method has been proposed in which the agitation of the steel bath is strengthened by combining top blowing with bottom blowing, in which the gas is blown from below the bath surface.
This proposal is described in Japanese Patent Application Laid-open No. 55-158209 and others. The former involves changing the top-blowing oxygen supply conditions according to the gas flow rate introduced from the hearth bottom. Specifically, the higher the top-blowing gas volume from the hearth bottom, the more the top-blowing oxygen flow rate and lance height are adjusted. It is characterized by suppressing the amount of iron oxide produced in the slag by blowing weakly with K, and further improving the efficiency of the refining reaction by strengthening the stirring of the steel bath compared to bottom blowing K. On the other hand, the latter method proposes the amount of gas to be blown from below the bath surface. Specifically, one or IIa bottom blowing nozzles are installed below the bath surface, and the uniform mixing time of the steel is 2 seconds through these nozzles. that's all.

41 images are defined as blowing for 70 seconds or less.

Since both of these proposals use top blowing and bottom blowing in combination, the agitation of the steel bath is strengthened and is considered to have some effect. However, none of these proposals have carefully considered the number and arrangement of bottom blowing nozzles, and JP-A-55-158209 has two rows of 2 to 10 bottom-blowing nozzles, while Makutoku No. 148s55-188015 has only three nozzles.
It is only written as hon-ni'/toshiku. Therefore, it is thought that sufficient agitation of the steel bath cannot be obtained depending on the number and arrangement of nozzles, and there may be cases where the desired effect cannot be sufficiently achieved.

On the other hand, there is a proposal in Japanese Patent Laid-Open No. 455-65313 as a method in which the arrangement of bottom-blowing nozzles is slightly taken into account. This proposal is characterized by installing a bottom blowing nozzle at the bottom of a concentric circle within 3/4 of the maximum inner diameter of the furnace, and allows the arrangement pattern to be arbitrarily selected during papermaking and blowing. .

However, with this type of nozzle arrangement, the bottom blowing nozzle may be located below the bath surface when charging hot metal into the furnace or during tapping after refining, and in that case, the hot metal or molten steel may flow into the nozzle. It is necessary to blow gas for nozzle retention to prevent intrusion. Therefore, in the case of this method, refining Ki[! If a large amount of unrelated gas is consumed, it will also have an adverse effect on the temperature of the molten steel. Also, as mentioned above, K
If gas is blown from the bottom of the furnace when the flow of 11m1 pig iron or molten steel is low, a large amount of gas may be scattered from the furnace mouth, resulting in a decrease in iron yield and the formation of a large powder layer.

In addition, in both of the above proposals, the bottom blowing nozzle is arranged so that its blowing direction is opposite to the blowing direction of the lance, so that they mutually suppress the stirring flow, and this also reduces the stirring effect. There are concerns.

The present invention provides a method for refining pig iron that eliminates the problems and drawbacks of the conventional proposals as described above.

The present inventors have repeatedly conducted various experimental studies regarding the number and arrangement of bottom blowing nozzles in an oxygen top-blowing converter. A friend discovered that if the number of these rods exceeds a predetermined number and agitating force is applied, the flow in the steel bath will be severely disturbed.

That is, in the present invention, in the oxygen top-blowing converter method that uses bottom blowing, when the tilting shaft axis is projected perpendicularly to the bottom surface,
It is a semi-circular shape on one side that is divided into two parts by the projection line, and the distance from the projection line is 1/4 to 1/ of the radius of the hearth bottom! Four or more bottom-blowing nozzles are provided only in the Separate Nine area, and bottom-blowing is performed with them arranged in a row with one projection line Kff, thereby disturbing the flow that would be formed when there is only top-blowing. The aim is to strengthen the stirring of the steel bath.

The present invention will be explained in detail below.

Figures 1.2 of the attached drawings show an example of the oxygen top-blowing converter used in the implementation of this project. - It is a cross-sectional view at A'. In Fig. 1, 1 is a top blow lance, 2 is a pair of tilting shafts fixed to the outside of the furnace body 3, and the furnace body 3 uses this tilting shaft 2 as the rotation axis, and its front end tilts backward. 4 is a slag bath, and 5 is a steel bath. Reference numeral 6 denotes a double-tube bottom blowing nozzle that is provided through the furnace bottom 7 and is unevenly distributed from the center of the furnace bottom. Oxygen for refining filling or granular slag forming agent is blown into the inner pipe 8, and air or inert gas is blown in during hot metal charging or tapping. During refining, hydrocarbon gas is injected from the inner pipe 8 while pure oxygen or granular slag is injected, and air or an inert gas such as nitrogen is injected during charging or tapping of molten iron. 8 and outer pipe 9 are each connected to a gas tank for each gas via flow rate adjustment equipment. In this embodiment, a double pipe is shown as the bottom blowing nozzle, but a single pipe may be used, and in this case, an inert gas such as argon is used as the blowing gas.

Figure 2 shows the uneven distribution of bottom blowing nozzles.
The bottom blowing nozzle 6 connects the tilting shaft axis 10 (Fig. 1) to the bottom surface KI.
When the projection is 9, 5 are provided on one semicircular side divided by the projection -l. Then, these bottom blowing nozzles 6 are connected to the furnace bottom radius r (center of the furnace!7) from the projection line 10a.
Distance to FIIK) 01/3~1/! The projection lines IQa and Kura are arranged in a row, preferably in parallel, with a distance of t.

Therefore, the stirring of the steel bath 5 by the bottom-blowing nozzle 6 forms a circulating flow throughout the bath as shown by the arrows starting from the installation part of one nozzle, as shown in FIGS. 3 and 4. In other words, the flow is disturbed by the top blow lance IK, that is, the stirring in the present invention is carried out by disturbing the flow by the top blow lance from the side. This is a stirring method that is completely different from conventional methods and is a feature of the present invention.

In addition, in the case of the present invention, each bottom blowing nozzle 60 projection line toe19
If the distance is less than 1/3 r of the furnace bottom radius r, the formation of circulation flow will be poor, and if the distance exceeds 1/2, the nozzle will be located below the bath surface during hot metal charging or molten steel tapping. In some cases, various problems arise as in the conventional method. Therefore, it is placed within the area.

Furthermore, if the number of bottom blowing nozzles is less than three, the formation of a circulating flow will be poor and the flow will not reach the entire bath, and sufficient stirring will not be strengthened, so it is preferable to use four or more bottom blowing nozzles.

Furthermore, the nozzles are arranged in rows, preferably in parallel, since a circulating flow over the entire bath cannot be formed unless they are arranged in rows along the projection line Kfa-).

In addition, when the furnace is tilted during charging of hot metal and tapping of molten steel, the bath surface is at the position of line 11 in Fig. 2, so that it does not reach the position of the bottom blowing nozzle 6 and gases that are not directly involved in refining are removed. It doesn't have to be consumed.

Next, the present invention will be explained with reference to Examples.

Example 1 Oxygen top blowing and simultaneous KI of 256 Nd/Bim
Blow argon gas at the bottom of ON//ml to reach the end point [0
The steel was refined from 0.04 to 0.25 inches.

Main raw material: 85 tons of hot metal 15 tons of scrap Copper raw material: 5 tons of quicklime Fluorite 1 ton Sintered ore 0.9 tons Pellets 0.2 tons Comparative example.”

As shown in Figure 5, a bottom blowing nozzle (single pipe, inner diameter 10+1
6) was refined under the same conditions as Example 1 using a furnace in which three furnaces were arranged symmetrically.

Comparative Example 1 Using the furnace of Example 1, bottom blowing was stopped and s 25ONme
Only oxygen top blowing of /mln was performed.

The end point after blowing in these Examples and Comparative Examples [0
Figures 6 and 7 show the relationships between oxidation and oxygen in the slag, as well as the teotaae (T, F) in the slag and oxygen in the molten steel.Table IK shows typical refining results.

According to the present invention, T, h in the slag at the end point is compared to the case where only oxygen top blowing (Comparative Example 2) and the case where bottom blowing is used together but no special consideration is given to the nozzle arrangement (Comparative Example 1). It can be seen that the loss of iron and manganese is reduced, with a decrease in i and an increase in i. In the case of the present invention, a decrease in oxygen in the molten steel is also observed, and it can be seen that the amount of Al 1=um added decreases accordingly.

Table 1 As described above, according to the present invention, the conventional K<rape circulation flow is formed in the molten steel, and the stirring of the molten steel is strengthened, so that the loss of iron and manganese during product value can be reduced. Furthermore, the yield of added alloy iron can also be improved.

[Brief explanation of drawings]

Figures 1 and 2 show an embodiment of the oxygen top blowing converter used in the practice of the present invention, so Figure 1 is a longitudinal cross-sectional view thereof, and Figure 2 is a cross-sectional view taken along line AA' in Figure 1. It is a diagram. FIG. 3 is a longitudinal cross-sectional view of an oxygen top-blowing converter showing the circulating flow of molten steel produced in the present invention, and FIG. 4 is a cross-sectional view taken along line B-B' in FIG. 3. FIG. 5 is a cross-sectional view of the oxygen top-blowing converter used in Comparative Example 1, and FIGS. It is a figure showing the relationship with oxygen in molten steel. 1... Top blowing lance, 2... Tilting shaft, 3-... Furnace body,
4... Slag, 5... Steel bath, 6... Bottom blowing nozzle, 7... Furnace bottom, 8... Inner tube, 9... Outer tube, 10
...Tilt axis axis, 10 fields...Projection line. Patent Applicant Nissin Steel Co., Ltd. Agent No. 1 Fig. 2! ,Shi,,-. Figure 30 Y5 Figure 1000 Figure 4 Figure 7 A-B, shrimp, [cJ tzn

Claims (1)

[Claims] An oxygen top-blowing converter is used, which is fixed to the furnace body and can be tilted back and forth through nine tilting shafts. Oxygen is top-blown by a lance, and gas or powder is supplied by a nine-bottom blowing nozzle installed at the bottom of the furnace. In a method for refining pig iron using bottom blowing of a granular slag agent, the bottom blow is such that when the axis of the tilting shaft is projected directly onto the bottom surface, the projection IIi! ) The distance from the projection line on one semicircular side of the hearth bottom, which is divided into two, is 1 to 1/ of the hearth center meridian! A method for refining pig iron using an oxygen top-blowing converter, characterized in that four or more hawk-blowing nozzles are provided only in separated areas, and they are arranged in a row along the projection line Kfa.