JPS613817A - Method for blowing gas into molten iron in steel making vessel - Google Patents

Abstract

PURPOSE:To prevent the erosion of a bottom blowing tuyere consisting of plural pieces of metallic pipes as gas passage holes embedded into a refractory compsn. and to regulate the rate of blowing over a wide range by decreasing the inside diameter of said pipes and using a high-pressure gas. CONSTITUTION:The tuyere 1 disposed in a furnace bottom brike 5 convering the inside of a bottom shell 4 of a converter consists of plural pieces of the stainless steel pipes 2 which have <=3mm. inside diameter and is embedded into a tuyere brick 3 as the common refractory compsn. of the furnace. The bottom end of the pipe 2 is commonly connected to a gas accumulation chamber 6 and is further communicated with a feed pipe 7 for a gas such as inert gas. The gas is blown into the molten iron in the converter by using such tuyere 1 so that the inlet pressure of the tuyere attains >=50kg/cm<2> in at least part of the entire blowing period. The erosion of the tuyere is thus prevented and the service life of the tuyere is extended. Since the flow rate of gas blowing is regulatable over a wide range, the dephosphorization and desulfurization or the blowing metting the purpose such as the improvement of an iron yield is made possible.

Description

Detailed Description of the Invention This invention relates to a method for injecting gas such as an inert gas into molten iron in a steelmaking container from a tuyere provided at the bottom of a steelmaking container such as a converter. This relates to the blowing method.

Recently, a combined blowing method in which Ar or N2 gas is bottom-blown from the bottom of the converter furnace and oxygen is blown from the top of the furnace using a top-blowing lance has been widely used industrially.

According to this combined blowing method, even if the molten iron is decarburized to a low carbon concentration, there will be no excessive oxidation of the iron.
In addition, the iron yield is good because there is little splash, and the slag-metal reaction is promoted by the stirring effect of the molten iron by the bottom-blown inert gas, which improves the refining effect. Effects can be obtained.

However, in order to carry out this composite blowing method, the metal tuyeres traditionally installed at the bottom of the converter
A pipe or a plurality of pipes or a porous refractory plug (for example, the plug described in Japanese Patent Application Laid-Open No. 47-42531) has the following problems.

In other words, a structure in which metal pipes are used as tuyeres has the advantage of being inexpensive, but if the gas flow rate is reduced, the molten iron in the converter may enter the pipes and clog the tuyeres, making it difficult to reduce the flow rate. The disadvantage is that the range in which it can be changed and adjusted is narrow. In addition, porous refractory plugs (so-called porous plugs) have the advantage that there is no risk of clogging the tuyere even if the gas flow rate is reduced, and that the flow rate can be adjusted over a wide range. There is a drawback. Furthermore,
Both the metal pipe and the porous refractory plug mentioned above have a short service life when compared to the large converter bottom, and even though the converter bottom is still healthy, the metal pipe or refractory When the tuyere of the manufactured plug reaches the end of its life, it is necessary to replace the furnace body or close the tuyere to stop the injection of bottom-blown inert gas, and the W1 injected from the top-blowing lance is replaced.
Uneconomical measures such as refining only with raw materials had to be taken.

This invention has been made in view of the above-mentioned conventional circumstances, and provides a method for blowing gas into molten iron in a steelmaking container, which can effectively prevent melting of the tuyere and at the same time, can adjust the blowing flow rate over a wide range. The purpose is to provide a method for embedding

In order to achieve the above object, the inventors of the present invention have developed a bottom-blowing blade in which a metal pipe as a gas vent is embedded in a refractory composition (so-called feather brick). After conducting extensive experiments on the opening, we found that it had a structure in which multiple metal pipes were assembled (°4, that is, a structure in which multiple metal pipes were embedded in the same tuyere brick).
By making the inner diameter of each of these metal pipes much smaller than before (3m!!1 or less) and increasing the pressure of the inert gas sent to the tuyeres, it is possible to effectively suppress the erosion of the tuyeres. I found something to gain. The reason is as follows.

f% First, if the pressure of the inert gas sent to the tuyere is increased, the heat absorption effect due to the expansion of the inert gas at the tuyere outlet increases, and the cooling effect of the tuyere is improved. This is because that. In other words, by reducing the diameter of the via 1 as the gas passage hole in the tuyere and using high-pressure gas, the mass flow rate of gas per unit area of the inner wall of each pipe of the tuyere increases, and the cooling effect of the gas on the tuyere is increased. will improve. In addition, the high-pressure gas has a high flow velocity, which increases the heat transfer coefficient between the gas and the inner wall of the tuyere pipe, which also improves the effectiveness of the gas in cooling the tuyere. Furthermore, since the structure is made up of multiple pipes, the surface area of the entire gas flow area of the tuyere is larger than that of a single pipe, which promotes heat exchange between the gas passing through the pipe and the surrounding refractories. Cooling of the cap body is maintained.

Secondly, due to the slow behavior of the jet flow of the inert gas blown into the molten iron from the tuyeres, the higher the pressure of the blown gas, the less the erosion of the tuyeres. That is, according to the cold model experiment using water by the present inventors, Fig. 1(A)
and (B), the gas pressure is 50-100
It has been found that there are differences in the jet area and the bubble area H of the gas blown into the water in the case of k(J/c!lr and in the case of 10 to 20 kMar. Figure 1 (A)
Gas pressure is 50-100kg/alr as shown in
In this case, the gas blown from the tuyere 1 travels a considerable distance in the form of a jet, and then floats up as bubbles. Therefore, the jet area work is long. Compared to this, '11
As shown in Figure (8), the gas pressure is 10 to 20 kg/
In the case of CD, the distance that the gas blown in from the tuyere 1 travels in a jet shape, that is, one area I + -1 shorter than the distance x7. In general, the lower the injected gas pressure, the shorter the jet-shaped region (■), and when the jet-shaped region (■) is short, bubbles of the injected gas are generated near the tuyere exit. However, the bubbles generate turbulence in the water near the tuyere outlet, increasing the flow velocity of the water flow. Therefore, in an actual converter, the flow velocity of molten iron on the surface of the refractory near the tuyere outlet is accelerated by the generation of such turbulence, and as a result, the refractory near the tuyere outlet is affected by the refractories in other parts. It is more likely to be eroded than 〒. In addition, the tuyeres themselves are subject to accelerated wear and tear. Note that Figures (Δ) and (B) show an example of a tuyere 1 in which a plurality of metal pipes 2 are embedded in the same tuyere brick 3 in accordance with the present invention.

This invention j:1. This was done based on the above knowledge, and a tuyere consisting of a metal pipe embedded in a refractory composition as a gas vent is installed at the bottom of the steelmaking container, and the steelmaking process is carried out through the tuyere. In a method of blowing gas into molten iron in a steelmaking container in which gas is bottom-blown into molten iron in the container, a plurality of metal pipes are embedded in a common refractory composition as the tuyeres, and The inner diameter of each pipe is 31
A tuyere with a pressure below Il is used, and the gas pressure at the inlet of the tuyere is 50 ka/'c! for at least part of the entire blowing period. ! J which is equal to or more than r: Characterized by blowing sea urchin gas.

The method of the present invention will be explained in more detail below with reference to Examples.

FIG. 2 shows the structure of a tuyere used for carrying out the invention. In FIG. 2, a tuyere 1, which is characteristic of the present invention, is disposed on a hearth brick 5 covering the inside of a bottom shell 4 of a converter. This tuyere 1 has an inner diameter 3a as a metal pipe and a tuyere brick 3 as a common refractory composition of the tuyere.
A plurality of stainless steel pipes 2 with a length of +m or less are embedded. The lower ends of these stainless steel pipes 2 are commonly connected to the air storage chamber 6 and further communicated with an inert gas feed pipe 7.

Using one such mm tuyere, the inner diameter and number of stainless steel pipes 2 of the tuyere were set variously, and the method of the present invention was carried out as follows. The tit of each stainless steel pipe 2 is 5LJS304. The diameter of the bulbs 2 in the first embodiment was 0.8 m11 and 28 pieces, in the second example there were 8 pieces with a diameter of 1.51 mm, and in the third example there were 2 pieces with a diameter of 3I.

As a comparative example, the inner diameter of stainless steel pipe 2 is 41, and 6
I collected the books. Further, the surface of the tuyere brick in the tuyere light control was circular in all examples, and its diameter was 100 mm.

Then, blowing of hot metal was performed using each of the above-mentioned tuyeres. , In each example and comparative example, the moisture content of the i8 pig to be refined is 1270 to 1350°C, m tit at the time of blowing, 14
~17 minutes, output w4 waterfall temperature is 1660-1720℃). In addition, 1. In each example, the inert gas injection conditions are as follows:
The gas flow rate was 0.01 to 0.03 N-/t, and the gas pressure was 50 to 100 kL'ct. On the other hand, in the comparative example, the gas flow rate was 0.01 to 0.03 N m',
, /nm·t, and the gas pressure was 5 to 20 kg/d.

Hot metal was blown under each of the above conditions, and the remaining length of the tuyeres in each example and comparative example was measured at predetermined charging intervals to determine the erosion rate of the tuyeres.

As a result, the erosion rate in the first example was 0.1711
11 to 0.21 +ue,/charge, 0.16 to 0.24 mm/charge in the second example, and 0.19 to 0.24 n+m/charge in the third example.

On the other hand, the erosion rate in the comparative example was 0.32-0.
It was 591111/charge. The results are shown in Table 1.

As is clear from the results in Table 1 and above, the erosion rate in each example is 3! compared to the erosion rate in the comparative example! The degree is much smaller, and each stainless steel pipe 2 is completely penetrated even after blowing. On the other hand, in the comparative example, two of the six stainless steel pipes 2 were blocked and gas did not flow.

As carried out in each of the above embodiments, in the method of blowing gas into molten iron in a steelmaking container of the present invention, the pressure at the tuyere inlet of the gas blown into the molten iron is 50 kQ/cllr or more. The gas pressure at the inlet of the tuyere is kept at 50 bg, z′C during the entire period during which gas is blown into the molten iron.
It is not necessary to keep the gas pressure at the inlet of the tuyere at 50 ka, *'at or more, and it can be set arbitrarily depending on the purpose of blowing gas from the bottom of the converter into the flash-molten iron of the converter. be able to.

In general, the injection of inert gas from the bottom of the converter is carried out as follows (
1) -, -(3') is carried out for the purpose of -.

(1) Even if the carbon moisture content of molten iron is low, the decarburization reaction takes precedence over the oxidation of iron, 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.

Regarding the injection of inert gas from the bottom of the converter, see (1) above.
), it is necessary to increase the flow rate of inert gas in the latter half of blowing. On the other hand, II of (2) above
When promoting the RP reaction, it is necessary to reduce the inert gas flow rate in the second half of blowing #A. That is, if the inert gas flow rate is large in the latter half of blowing, oxidation of iron will be reduced, the concentration of iron oxide in the slag will be reduced, and dephosphorization will not be carried out well.

Therefore, when aiming at (2) and (3) above, it is necessary to inject a large amount of inert gas in the first half of blowing, and reduce the inert gas injection flow rate in the second half.

According to the method of the present invention, since a plurality of metal pipes with an inner diameter of 31 mm or less are used, the flow rate of the blown gas can be easily adjusted for the purposes of (2) and (3) above. That is, in the conventional method of blowing low-pressure gas using a large-diameter nozzle, if the flow rate of the blowing gas was significantly reduced during blowing, there was a risk that the tuyeres would be clogged with molten iron. However, according to the method of the present invention, there is no such fear, and the gas flow rate can be significantly reduced during the blowing process.

The above is clear from each of the above embodiments.

That is, in Examples 1 to 3, the gas pressure was set to 50.
Even if it is 100 kg/l・shi, the gas flow rate is 0.01~0.
03Nrn''/+Yen・+Pi! degree, it does not flow excessively.

On the other hand, if you use the 4nu++ stainless steel pipe in the soil comparison example, the gas IF force will be 0.0 at 5 to 20 kg/cllr.
A gas flow rate of 1 to 0.03 N m'/'輔・() flowed, and two pipes were blocked. This means that at low pressure, tuyere blockage would occur even at the same flow rate.
It is clear that the flow Q (L!fi) under low pressure is an operational problem.

Next, by using the method described above, (2) is actually carried out.
An example in which blowing was carried out for the purpose of (3) and (3) will be described.

The conditions for blowing, such as the diameter and number of Stella 1 nozzle pipes in the tuyere, are as follows:
In the same manner as in the first embodiment of this invention described above, and in order to compare the results, blowing was carried out for the purposes of (2) and (3) also by the method of the comparative example for each of the above embodiments. .

The components of the target hot metal are 4.3 to 4.4% C, 3i
is 0.12 to 0.40%, Mn is 0.35 ・-0.4
5%, P 0.10-0.12%, S 0go02-0.
03%, and the C concentration of the molten steel component at the end of blowing is 0.0.
4-0.09%, fJ jI 4J 1680 =-
'I 730 C de Atsu Iko.

In blowing using the method of this invention, during the entire period from the start of blowing to the end of blowing III, during 70% of the time from the start of blowing I, the gas pressure in the prisoner is set at 60 to 90 kilI/
d, average gas flow rate 0, 03 N m'/ra
Then, the ridge gas pressure was reduced to 10-15Ω7・d, and the gas flow rate was adjusted to an average of 0.003 to 0.005 Nm.
The weight was reduced to 'z'wi-1. On the other hand, in the comparative example, the gas pressure during 70% of the period from the start of blowing was set at 10 to 20 ka.
iai, the gas flow Ω is on average 0603N as in the above example.
m'/sieve/seal, then reduce the gas pressure to 3 to 5 ko/d, and adjust the gas flow rate to the minimum tRIra 0.0.m' required to prevent hot metal from flowing into the tuyere and clogging the tuyere. 0
1-0.02 Nm3/lll-t 1. :m1i
b.

In the above Examples and Comparative Examples, the components of the molten steel at the end of blowing were analyzed, and the relationship between carbon concentration and ms degrees was determined. ,
(The results are shown in Figure 3.
It can be seen that the actual R example of the present invention, in which the gas flow rate at the final stage of blowing is large, has a lower P4 concentration than the comparative example, 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 to, for example, W4 smelting.

As described above, according to this invention, the inner diameter is 3+II! 11
A tuyere in which the following multiple metal pipes are embedded in a common tuyere brick is used, and the inlet pressure of the tuyere is 50 k.

By blowing gas into the molten iron in the steel making container so that the molten iron reaches 7 ci or more, it is possible to prevent the tuyere from melting and damage and extend the useful life of the tuyere.

Furthermore, when carrying out the method of the present invention, the gas blowing flow rate can be adjusted to r:I over a wide range, so that blowing can be carried out according to purposes such as dephosphorization and desulfurization or improving iron yield. It can be done.

[Brief explanation of the drawing]

Figures 1 (A) and (B) are schematic diagrams showing the relationship between the pressure of gas blown into water and the behavior of the blown gas jet, and Figure 2 is a tuyere used for the actual state of this invention. FIG. 3 is a diagram showing the relationship between carbon concentration and phosphorus concentration at the end of blowing SPi. DESCRIPTION OF SYMBOLS 1...Tuyere, 2...Metal pipe (stainless steel pipe), 3...Refractory composition (tuyere brick), N...Inert gas feed pipe.

Claims (1)

[Scope of Claims] A tuyere consisting of a metal pipe embedded in a refractory composition as a gas vent is installed at the bottom of the steelmaking container, and gas is pumped through the tuyere into the molten iron in the steelmaking container. In a method for blowing gas into molten iron in a blowing steelmaking container, as the tuyere, a plurality of metal pipes are embedded in a common refractory composition, and each pipe has an inner diameter of 3 m.
m or less, and the gas pressure at the inlet of the tuyere is 50 kg during at least part of the entire blowing period.
A method for blowing gas into molten iron in a steelmaking container, characterized by blowing gas into molten iron in a steel making container so that the gas is blown into molten iron at a pressure of /cm^2 or more.