JPS629161B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a converter steel manufacturing method, and more particularly to a steel manufacturing method using top and bottom blowing in which stirring gas is blown from below the surface of the molten steel along with oxygen top blowing.

A pure oxygen top-blown converter stirs molten steel using an O ₂ jet blown from the top and CO bubbles generated in the bath, thereby promoting the reaction, but as converters have become larger in recent years, There was a problem that the O ₂ jet did not reach deep into the molten steel, which delayed the reaction.

In order to solve this problem, in recent years, in addition to top-blowing oxygen, a tuyere is provided below the surface of the molten steel, and stirring gas is blown through the tuyere, thereby promoting the stirring of the molten steel and the reaction. Upper and lower blowing is becoming more common.

In this top-bottom blowing, an inert gas such as Ar gas or CO ₂ gas is generally used as the bottom-blowing stirring gas.

However, the production costs of inert gas and CO ₂ gas are high, and since they are generally produced in remote areas, it is necessary to transport them by truck or pipeline, which limits the amount of use and also increases the transportation cost. There were some problems, such as the cost. Therefore, there is a method to reduce costs by diverting a portion of the O ₂ gas for top blowing to the bottom blowing without using a new inert gas as the stirring gas for the bottom blowing, but in this case, the O 2 gas is directly used for the bottom blowing. Since blowing ₂ gas from below the surface of the steel bath water will cause melting of the tuyere, the tuyere has a double pipe structure, and O ₂ gas is blown into the inner pipe and slit gas is used as slit gas from the outer pipe, such as inert gas or kerosene. Alternatively, it is necessary to cool the tuyere by blowing propane gas or the like.

Furthermore, a method of blowing N ₂ gas or air downward is also considered, but both of these methods are inappropriate because they cause nitridation.

As described above, at present, each stirring gas for downward blowing has its advantages and disadvantages, and at present no method of upward blowing has been proposed that is inexpensive and does not easily damage the tuyeres.

In view of this problem, the present applicant has already proposed a converter steel manufacturing method in which costs are reduced by recovering LD gas and using it as under-blowing gas in a patent application filed in 1973.
It has already been proposed in No. 113497.

Furthermore, in the past, when blowing the stirring gas downward, sufficient consideration has not been given to the relationship between the downward blowing position and the stirring performance, and this has sometimes caused problems in the stirring performance of slag, etc.

The object of the present invention is to provide a converter steel manufacturing method that can further reduce costs in addition to the above-mentioned proposed inventions and also provides good stirring performance.

For this reason, the present invention sprays oxygen from the top of the molten steel, and also blows a stirring mixed gas prepared by diluting inert gas and/or CO ₂ gas with O ₂ from the tuyere provided at the bottom of the furnace. When injecting gas, regarding the bottom of the furnace, (a) the area between the projection line of the outer periphery of the fire point on the bottom of the furnace and the curve drawn by a point half the distance between the projection line and the furnace wall is called area A. (b) When the area between the above curve and the furnace wall is defined as area B, a plurality of tuyeres are formed in each of area A and area B, and the mixed gas for stirring is injected from these tuyeres. It is characterized by the fact that

FIG. 1 shows the basic configuration for implementing the method of the present invention. 1 is the converter furnace body, 2 is the top blowing lance,
3 is molten steel, and 4 is a tuyere provided below the surface of the molten steel. FIG. 2 shows the arrangement of this tuyere 4. In the example shown in the figure, four tuyeres 4 are provided at the hearth bottom. Of the four tuyeres, two tuyeres 4a and 4b are provided in area A, and tuyeres 4c and 4d are provided in area B.
Area A is an area between a projection line 5 of the outer periphery of the flashing point and a curve 6 drawn by a point half the distance between this projection line 5 and the furnace wall 1'. Area B is the area between this curve 6 and the furnace wall 1'. By distributing the tuyeres 4 in such regions A and B, good slag agitation performance can be obtained. In other words, with this arrangement, the tuyere provided in area A can stir the molten steel, and the tuyere provided in area B can stir the slag, which prevents the slag from staying around the furnace wall without being stirred. can be prevented from happening. Further, it is preferable in terms of stirring efficiency that the tuyeres in zone A and the tuyere in zone B are not lined up in a straight line.

If the number of tuyeres 4 is too large, the stirring gas will rise up from the entire surface of the molten steel, and the molten steel and gas bubbles will simply be exchanged, preventing the formation of a flow of molten steel and the stirring effect will not be improved, so 30 or less tuyeres are preferable.

Note that the structure of each tuyere 4 does not need to be a double pipe in the present invention, and a single pipe structure is also possible by adjusting the dilution ratio with O ₂ gas.

7 is an inert gas or CO ₂ gas source, 8 is O ₂
It is a gas source. Ar gas or the like is preferable as the inert gas. The inert gas and CO ₂ gas may be used as a mixture, or each may be used alone. When using CO ₂ gas, it reacts with molten steel [C]
It causes a decomposition reaction of CO ₂ + C → 2CO, which cools and protects the tuyere 4, doubles the volume, increases the stirring effect of molten steel, and acts as an oxidizing agent to lower the O ₂ consumption rate. The effects are great, such as:

This inert gas and/or CO ₂ gas is diluted with O ₂ gas and blown into the molten steel 3 through the tuyeres 4a to 4d. Since top-blown O ₂ gas can be directly used as O ₂ gas, the basic unit of stirring gas is reduced by the dilution of O ₂ gas. Therefore, the higher the dilution ratio of O ₂ gas, the better _in terms of cost reduction.
If the amount is too large, the cooling effect will be lost and tuyere melting will become a problem. Figure 3 shows the relationship between O ₂ gas amount and tuyere erosion rate. α indicates the case where CO ₂ gas is diluted with O ₂ gas, and β indicates the case where inert gas is diluted with O ₂ gas. In addition, A shows the limit of O ₂ amount when the tuyere is a single pipe, and B shows the limit of O ₂ amount when the tuyere is a double pipe. As can be seen from this graph, when using CO ₂ gas, it is possible to dilute O ₂ up to approximately 80% with a single tube and approximately 90% with a double tube. Furthermore, when inert gas is used, it is possible to dilute O ₂ up to approximately 65% with a single tube and approximately 75% with a double tube.

In addition, if the O ₂ amount is less than 20%, although it is not impossible to operate, the effect of reducing the unit consumption will not be improved and the problem of nozzle clogging will occur, making the operation unstable.

Further, it is efficient that the total amount of the downwardly blown gas is in the range of about 1/3 to 1/3000 of the upwardly blown oxygen amount. The stirring effect of molten steel does not appear below 1/3000, and about 1/3
In this case, the basic unit of the downward blowing gas becomes large, which is disadvantageous in terms of cost, and furthermore, even if the amount of downward blowing gas is increased further, no improvement in the stirring effect can be expected.

Next, examples will be shown.

Example A 180TON converter was used, and four tuyeres were installed at the bottom of the converter. Each tuyere is a single stainless steel pipe with a diameter of 10 mm, and its installation location is 2 in area A shown in Figure 2.
Two books were placed in Area B. The bottom blowing gas is CO ₂ 160Nm ³ /Hr and O ₂ 110Nm ³ /Hr for each tuyere, and O ₂ % is
The plant operated at 40% capacity. As a result, the basic unit of stirring gas was reduced, and the tuyere life was 1,150 times with an average of 0.54 mm/charge loss.

As explained above, in the converter steel manufacturing method according to the present invention, inert gas, CO ₂ gas, or a mixture thereof is diluted with O ₂ gas, and this is blown downward as stirring gas, so stirring is not required. It is possible to reduce the gas consumption rate. Furthermore, by adjusting the mixing ratio of O ₂ , it also has secondary effects such as prevention of tuyere melting and prevention of tuyere clogging. In addition, in the present invention, the furnace bottom is divided into a specific inner region and an outer specific region, and by blowing downward from a plurality of tuyeres provided in each region, extremely good stirring of molten steel and slag can be achieved. It is possible to obtain the desired characteristics and perform efficient blowing.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the configuration of an apparatus for carrying out the method of the present invention, Fig. 2 is a plan view thereof, and Fig. 3 is a
It is a graph showing the relationship between O ₂ amount and tuyere erosion rate. In the figure, 1 is the converter furnace body, 1' is the furnace wall, 2 is the lance, 3 is the molten steel, 4, 4a, 4b, 4c, 4d are the tuyeres, 5 is the projected line of the outer periphery of the hot spot, 6 is the curved line, 7 indicates an inert gas and/or CO ₂ gas source, and 8 indicates an O ₂ gas source.

Claims (1)

[Claims] 1. Blowing oxygen from above the molten steel,
Inert gas and/or
A stirring mixed gas made by diluting CO ₂ gas with O ₂ is blown into the furnace bottom surface. If the area between the curve drawn by a point that is 1/2 of the distance between the walls is Area A, and the area between the above curve and the furnace wall is Area B, then there are multiple areas in Area A and Area B. A converter steel manufacturing method characterized by forming tuyeres and blowing a stirring mixed gas through these tuyeres.