JP2000219906A - Gas injection method to molten iron - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method capable of achieving an improvement in tuyere life by controlling appropriate cooling conditions in accordance with the progress of blowing. SOLUTION: When agitating molten iron by blowing gas from a tuyere using one or two or more single tube nozzles, α in equation (1) is set to 0.10 to 0.60. A method of injecting gas into molten iron, wherein one or both of gas, gas flow rate and gas composition are changed. (Equation 1) Here, C is gas specific heat (kcal / m ² / K), Q is gas flow rate per single tube (Nm ³ / s), q is effective heat of reaction (kcal / Nm ³ ), T
Is the molten iron temperature (° C.), n is the conversion factor, and T _MR is the solidus temperature (° C.) of the molten metal, which is the mushroom formation temperature, with the subscript i
Indicates a gas type.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining molten iron in a top-bottom blow converter or an electric furnace, whereby a stable mushroom (metal) can be obtained by maintaining a constant cooling capacity of a bottom-blow tuyere. The present invention relates to a method of making it possible to improve the tuyere life.

[0002]

2. Description of the Related Art The technique of bottom-blowing gas from a tuyere to molten iron using one or more single-tube nozzles is widely used in converters and electric furnaces. In this case, increasing the tuyere life is the most important issue in terms of operation and refining cost, since stable gas injection is possible. In converter refining, even during one refining, the carbon concentration changes greatly from 4% or more to 0.1% or less, and the molten iron temperature also increases to 125%.
Because it changes greatly in the range from 0 ° C to 1700 ° C,
Even during one refining, proper cooling conditions vary greatly. In an electric furnace, the same control as in a converter is necessary because the carbon concentration and the molten iron temperature change greatly.

For example, Japanese Patent Application Laid-Open No. 62-96612 discloses a method in which a large number of thin metal tubes are buried in tuyere bricks to make it difficult for molten steel to be inserted at a low flow rate so as to increase the flow rate variable width. Have been. Also, JP-A-2-38
Japanese Patent Publication No. 509 discloses a molten metal container equipped with an inert gas bottom-blowing mechanism, in which a low-mass gas such as CO is bottom-blown when the bottom-blown gas flow rate is to be increased, and A
A method of bottom-blowing a high-mass gas such as r is disclosed.
Further, Japanese Patent Application Laid-Open No. 61-159520 discloses that an upper and bottom blown converter is used for an initial desiliconization section, a middle decarburization section, and a late F section.
A method is disclosed in which the amount of bottom blown gas is changed by dividing into oxidized sections and using the amount of oxygen stored in slag (Os) in each section as an index.

[0004] However, although the above prior art describes that the bottom blowing flow rate is changed in order to improve metallurgical properties, the tuyere is controlled to appropriate cooling conditions in accordance with the progress of blowing. There is no idea that the tuyere life is extremely short.

The inventors of the present invention have disclosed Japanese Patent Application Laid-Open No. 9-22792.
No. 1 discloses a technique of mixing and blowing oxygen or hydrocarbon gas according to the flow rate of an inert gas so as to maintain a healthy mushroom.

However, even with this technique, there is no idea to control the index α in consideration of the difference between the molten iron temperature and the mushroom formation temperature, and there has been a problem that the tuyere life cannot be sufficiently improved.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problem that the tuyere life of the prior art is extremely short, and provides a stable mushroom by keeping the cooling ability of the bottom blown tuyere constant during refining. It is intended to provide a method which can be generated to improve the tuyere life.

[0008]

The gist of the present invention resides in the following methods. (1) When agitating molten iron by blowing gas from a tuyere using one or more single-tube nozzles,
(1) changing one or both of the gas flow rate and the gas composition at least once during refining so that α in the formula is 0.10 to 0.60; How to blow.

[0009]

(Equation 2)

Here, C is gas specific heat (kcal / m ² / K), Q is gas flow per single tube (Nm ³ / s), and q is effective reaction heat (kc
al / Nm ³ ), T is the molten iron temperature (° C.), n is the conversion factor, T _MR is the solidus temperature (° C.) of the molten metal, which is the mushroom formation temperature, and the subscript i indicates the gas type. Further, T _MR is expressed by equation (2). T _MR = 1536-181.8 × (% C) (% C <2.14) T _MR = 1147 (% C ≧ 2.14) (2) (2) CO ₂ , C
One or two of O, nitrogen, Ar, oxygen, and hydrocarbon gas
A method for injecting gas into molten iron, characterized in that it is at least one species. Here, it is desirable that one of CO ₂ , CO, nitrogen, and Ar be the main component, and a hydrocarbon gas represented by oxygen, LPG, or LNG be mixed as necessary. (3) The method for blowing gas into molten iron according to (2), wherein one or both of a gas flow rate and a gas composition are changed based on the molten iron temperature and the carbon concentration during refining. Here, the molten iron temperature is measured by batch temperature using a sublance,
Determined using either continuous temperature measurement using an optical fiber through a dedicated observation hole provided in the furnace body, or an estimated value from regression based on past results, etc. Continuous measurement by analysis, continuous measurement using laser emission through a dedicated observation hole provided in the furnace body,
It is determined using any of the estimated values in the regression based on the past results.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that control based on carbon concentration and molten iron temperature is important for maintaining a constant cooling capacity during blowing. Equation (1) is an equation showing the control method.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

[0015]

[Table 4]

Table 1 shows the typical temperature during blowing and the value of α for each carbon concentration when CO ₂ is supplied alone from a ³ mmφ single tube at 1 Nm ³ / h. It can be seen that a large change in carbon and temperature results in a large change in α.
On the other hand, Table 2 shows the condition that α is constant at 0.2
Although the gas flow rate is set to 1 Nm ³ / h and the temperature and the carbon concentration during blowing are shown for a single pipe, it can be seen that a constant α can be maintained by mixing LPG. While the erosion rate of the tuyere in the case shown in Table 1 was 1.5 mm / ch, the control shown in Table 2
ch, and found the importance of cooling control based on α.

Table 3 shows typical values of α for each temperature and carbon concentration during blowing when CO ₂ is supplied alone from a 3 mmφ single pipe at 10 Nm ³ / h. However, it can be seen that a large change in carbon and temperature results in a large change in α. On the other hand, Table 4 shows that the condition where α is constant at 0.4 is that the gas flow rate is 10 Nm ³ / h in a single tube of ³ mmφ.
Although the values are shown for each of the typical temperature and carbon concentration during blowing, it can be seen that a constant α can be maintained by mixing O ₂ .
While the erosion rate of the tuyere in the case shown in Table 1 was 1.3 mm / ch, it became 0.5 mm / ch by performing the control shown in Table 4, and the mixing of LPG Α as in
The importance of cooling control on the basis of was found.

In the equation (1), the numerator indicates the amount of cooling by the sensible heat and latent heat of the gas, and the denominator indicates the amount of heat received by the mushroom from the molten iron. Further, the first term of the molecule is cooling by sensible heat of the gas, and the second term is heat of reaction (latent heat).
Cooling or heating value.

[0019]

(Equation 3)

Here, C is gas specific heat (kcal / m ² / K), Q is gas flow rate per single tube (Nm ³ / s), and q is effective reaction heat (kc
al / Nm ³ ), T is the molten iron temperature (° C.), n is the conversion factor, T _MR is the solidus temperature (° C.) of the molten metal, which is the mushroom formation temperature, and the subscript i indicates the gas type. Equation (1) includes three important factors that could not be obtained by conventional knowledge.

1) The temperature at which the mushrooms required for tuyere cooling are stably formed does not correspond to the liquidus temperature, and the solid represented by the formula (2) found by the present inventors. phase line is expressed by the temperature (T _MR). T _MR = 1536-181.8 × (% C) (% C <2.14) T _MR = 1147 (% C ≧ 2.14) (2)

2) The effective reaction heat (q) effectively acting on the cooling balance at the tuyere tip is a value dependent on the reaction rate, not the latent heat calculated thermodynamically. In other words, when the reaction rate is high, most contributes to the cooling of the tuyere tip, but when the reaction rate is low, the contribution to the cooling at the tuyere tip decreases, and the reaction takes place after the gas enters the molten iron. Will do. Here, through detailed experiments by the present inventors, the effective heat of reaction (q: kcal / Nm ³ ) of each gas was determined as follows. Here, minus indicates heat generation and plus indicates endothermic. In addition, q is zero for Ar, N ₂ , and CO that do not react with the molten iron.

CO ₂ : +65 kcal / Nm ³ LPG: +810 kcal / Nm ³ O ₂ : -4190 kcal / Nm ³ 3) The amount of heat that can be received by the mushroom is 0.
It is proportional to the cube. This indicates that, with the stirring of the molten iron by the gas supplied from the tuyere, the flow state around the mushroom changes and affects the heat transfer coefficient.
Further, since each gas reacts in the molten metal to increase the stirring power, it is necessary to multiply each gas by a conversion coefficient n, and 1 (in the case of Ar and N ₂ ) and 2 (CO, CO ₂ , O ₂ , respectively) 4) (in the case of LPG).

The value of C is as follows. ^{Ar: 0.222kcal / Nm 2 / K} N 2: 0.309kcal / Nm 2 / K CO: 0.310kcal / Nm 2 / K CO 2: 0.497kcal / Nm 2 / K LPG: 1.346kcal / Nm 2 / K O ₂ ： 0.342kcal / Nm ² / K

The reasons for limiting the numerical values in each invention are shown below. In the invention according to the above (1), α is 0.10 to 0.10.
The reason for setting 0.60 is that, as shown in FIG.
If it is smaller than 10, the mushroom is small and the tuyere life is reduced, and if it is larger than 0.60, the mushroom grows excessively and the air permeability deteriorates and the required gas flow cannot be supplied. Cooling control (1)
As can be seen from the equation, it becomes possible by changing one or both of the gas flow rate and the gas composition.

The invention according to the above (2) defines the type of gas. The characteristics required for the gas to be blown are that the main gas is inexpensive and inert or weakly reactive gas, the cooling adjustment gas is inexpensive, and that even a small amount of heat and heat is large. . Therefore, CO ₂ ,
It is necessary to use one or more of CO, nitrogen, Ar, oxygen, and hydrocarbon gas. In particular, the main gases are CO ₂ , CO, nitrogen, and Ar. For cooling adjustment, it is desirable to mix oxygen or a hydrocarbon gas represented by LPG and LNG with the main gas. It is preferable that the main gas contains at least 50 vol% or more.

The invention according to the above (3) shows a cooling control method. As can be seen from equations (1) and (2), the carbon concentration and temperature of the molten iron are important factors in cooling control. Therefore, changing one or both of the gas flow rate and the gas composition based on the continuously measured molten iron temperature and carbon concentration during refining is the most stable method of the tuyere life.

[0028]

EXAMPLES The examples were carried out using a 300-ton scale top-bottom blow converter. As the upper blowing lance, a 7-hole lance of 45 mmφ was used, and the oxygen supply rate was 50,000 Nm ³ / Hr. For the bottom blowing, two tuyeres with 71 metal pipes of 3 mmφ embedded in bricks were arranged at the furnace bottom. As a main gas, CO ₂ was used, and LPG and oxygen were mixed for cooling control. The flow rate of the bottom-blown gas per tuyere was 50 to 1000 Nm ³ / Hr. The carbon concentration of the molten iron was estimated based on the exhaust gas analysis value, the exhaust gas flow rate, and the intermediate measurement value using a sublance, and the molten iron temperature was estimated by heat balance calculation. Table 5 shows the changes in temperature and carbon concentration during blowing, and the gas composition, flow rate, and
α was controlled by changing the composition and flow rate of the bottom blown gas five times during the blowing to control the melting rate of the tuyere to 0.45 mm / ch.

[Comparative Example] In Comparative Example, the operation was carried out only with CO ₂ without mixing gas. Table 6 shows changes in temperature and carbon concentration during blowing and α calculated from the gas flow rate.
Since the control of α was not performed, the erosion rate of the tuyere was 1.6.
It was 5 mm / ch.

[0030]

[Table 5]

[0031]

[Table 6]

[0032]

As described above, according to the present invention, it is possible to follow a change in the carbon concentration and the molten iron temperature in accordance with the progress of the blowing and to control the cooling conditions to an appropriate value, thereby producing a stable mushroom. The improvement of tuyere life was achieved.

[Brief description of the drawings]

FIG. 1 is an experimental result showing the relationship between α and tuyere refractory erosion rate.

Claims (3)

[Claims] When agitating molten iron by blowing gas from a tuyere using one or more single-tube nozzles, α in equation (1) is set to 0.10 to 0.60. A method of blowing gas into molten iron, wherein one or both of a gas flow rate and a gas composition are changed at least once during refining. (Equation 1) Here, C is gas specific heat (kcal / m ² / K), Q is gas flow rate per single tube (Nm ³ / s), q is effective heat of reaction (kcal / Nm ³ ), T
Is the molten iron temperature (° C.), n is the conversion factor, and T _MR is the solidus temperature (° C.) of the molten metal, which is the mushroom formation temperature, with the subscript i
Indicates a gas type. Further, T _MR is expressed by equation (2). T _MR = 1536-181.8 × (% C) (% C <2.14) T _MR = 1147 (% C ≧ 2.14) (2) 2. The method for blowing gas into molten iron according to claim 1, wherein the gas to be blown is one or more of CO ₂ , CO, nitrogen, Ar, oxygen, and a hydrocarbon gas. 3. The method of blowing gas into molten iron according to claim 2, wherein one or both of a gas flow rate and a gas composition are changed based on the molten iron temperature and carbon concentration during refining.