JPS63183113A - Pretreatment of molten iron - Google Patents

Abstract

PURPOSE:To improve the yield of an iron-component and to reduce the consumption unit of a refining agent by blowing gaseous oxygen into molten iron flow on the down stream of a refining agent blowing position in a tapping spout. CONSTITUTION:The molten iron 8 tapped from a blast furnace is subjected to a desiliconization treatment before a skimmer 2 and thereafter, a dephosphorizing material is blown from a non-immersed upward facing lance 6 into the molten iron 8. The gaseous oxygen is blown to the molten iron from an immersion lance 7 on the down stream thereof. The oxygen blown into the molten iron 8 floats in the form of gaseous CO which stirs and heats up slag 9. As a result, the flow characteristics of the slag is improved and the contact characteristic of the dephosphorizing material and the molten iron 8 is improved, by which the reaction efficiency is improved. The iron-component in the slag is acceleratively settled, by which the iron-component in the slag is separated and the yield of the iron-component is improved. The position where the gaseous oxygen is blown is preferably in a range from the refining agent blowing position up to the position 3-5m apart therefrom toward the down stream.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for preliminary treatment such as desiliconization and dephosphorization of hot metal in a blast furnace tap runner, and more specifically to a method for injecting a refining agent with a non-immersed top blowing lance. The present invention relates to a hot metal pretreatment method that aims to improve the unit consumption of refining agent and the iron yield in the pretreatment method.

Technical background The composition of hot metal tapped from a blast furnace greatly affects the refining efficiency and quality of steel in the next steelmaking process, so in order to streamline the steelmaking process and make operations easier, the composition of hot metal and the type of steel produced are determined. Various hot metal pretreatment methods are appropriately adopted depending on the situation. Preliminary treatment of hot metal includes desiliconization, dephosphorization, desulfurization, etc., and these processes are carried out in blast furnace tap runners, hot metal ladles, torpedo cars, etc.

BACKGROUND ART As a method for pre-treating hot metal, such as dephosphorization, in a blast furnace tap runner, a method is known in which blast furnace slag is removed by a skimmer and then treated by the method shown below.

■ A method in which powder flux is added to the hot metal in the tap hole to perform desiliconization and nq* treatment. In other words, in this method, powder flux is placed on top of the hot metal flowing in the tap hole, and the natural mixing as it flows together is used to perform desiliconization and dephosphorization treatment (overlay method). ).
810 etc.). However, in this method, the powder flux added to the hot metal tends to flow while floating on the hot metal, so the natural mixing described above does not mix sufficiently in the tap hole.
The reaction efficiency between hot metal and powder flux is low.

■ Injection method in which powder flux is blown along with carrier gas from a lance immersed in hot metal in the tap runner or from a bottom blowing nozzle (Special Publication No. 50-33010゜Special Publication No. 53)
-33935. Special Publication No. 60-35408, etc.). This method is an improved method of adding powder flux in order to eliminate the above-mentioned drawback (2). In particular, the method using an immersion lance has good contact between the powder flux and hot metal and has high reaction efficiency.

However, this method has the disadvantage that the immersion lance is severely damaged by erosion and the cost of preliminary treatment is high. In addition, the method using a bottom blowing nozzle not only suffers from significant nozzle erosion, but also requires significant improvement of the tap culvert, resulting in high equipment costs. The flux floats to the surface before it comes into sufficient contact with the hot metal, making it impossible to expect a significant improvement in reaction efficiency.

■ A method of blowing powder flux together with carrier gas using a non-immersed top-blowing lance (Japanese Patent Application Laid-open No. 58-130208,
JP-A-60-184611, etc.). This method is called the so-called blasting method, and was proposed as a method to reduce the erosion of the immersion lance and bottom-blowing nozzle mentioned in ① above.Since there is no direct contact with the hot metal, the erosion of the lance is prevented. The reaction efficiency is significantly reduced compared to the immersion method, and the reaction efficiency is also high because the effect of stirring the hot metal flow is obtained.

Problems to be Solved by the Invention Among the conventional pretreatment methods mentioned above, the blasting method in which a refining agent is injected using a non-immersed top blowing lance has the following problems: This method has the effect of improving the contact between the hot metal and the refining agent due to the stirring effect of the hot metal and increasing the reaction efficiency. When the iron falls onto the generated slag and is captured by the slag, Fi@ in the slag increases and the iron yield decreases.Also, the bath depth is generally 1.
Because it is shallow (less than 0m), the refining agent floats to the surface before it comes into sufficient contact with the hot metal, and many of the refining agents are discharged with the slag without reacting.As a result, the refining agent consumption rate (input refining agent @
/ amount of molten pig iron treated) increases, which is not only disadvantageous in terms of cost, but also a significant improvement in reaction efficiency cannot be expected. moreover,
If the iron content in the slag is high, the quality of the slag will deteriorate, and depending on the use of the slag for recycling, it may be out of specification, necessitating a special slag purification process.

Purpose of the Invention This invention was made to solve the problems of the conventional blasting method, and improves the iron yield by injecting oxygen gas during the refining agent injection process using a non-immersed lance. The purpose of this paper is to propose a hot metal pretreatment method that reduces the consumption of refining agents.

Means for Solving the Problems The present invention provides a means for solving the above-mentioned problems in the conventional method of pre-treating hot metal by blasting in a blast furnace tap runner. When a refining agent is blown in using a blowing lance for preliminary treatment, oxygen gas is blown into the hot metal flow downstream from the refining agent injection position.

That is, in this invention, by injecting oxygen gas downstream from the refining agent injection position, the injected oxygen becomes CO gas and floats, stirring the slag and heating it up.
This improves the fluidity of the slag and reduces the amount of unreacted agents. It also promotes the settling of iron (granular iron) in the slag, which separates the iron in the slag and improves the iron yield. It was measured.

DISCLOSURE OF THE INVENTION BASED ON DRAWINGS FIG. 1 is a schematic diagram showing an example in which the present invention is applied to a conventional seed type continuous refining method, in which (1) is a tap sluice, and (2) is a taper.

(3) is a skimmer, (4), <5) is a slag outlet, (6
) indicates a non-immersed top blowing lance for blowing refining agent, ('7) indicates a submerged lance for blowing oxygen gas, (8) indicates hot metal, and (9) indicates slag.

In other words, in the case of seed type continuous refining method, skinmer (21,
This is a method of pre-treating the hot metal (8) in the gutter divided by (3) by injecting a refining agent from a non-immersed top-blowing lance (6).This invention is a method for pre-treating the hot metal (8) in the gutter divided by (3).
This is a method in which an immersion lance for oxygen gas injection (7) is installed downstream of the refining agent injection position by the non-immersed top blowing lance (6), and oxygen gas is blown into the hot metal from this lance.

Here, the oxygen gas injection position is preferably within a range of 3 to 5 meters downstream from the refining agent injection position. This is because the area where the refining agent blown from the non-immersed top blowing lance (6) floats approximately corresponds to a position 3 to 5 meters downstream from the refining agent injection position.

In the above configuration, when the hot metal tapped from the blast furnace is subjected to dephosphorization treatment after desiliconization, for example, the desiliconization treatment is performed before the skinmer (2), and then the dephosphorization agent is applied from the non-immersed top blowing lance (6). At the same time as blowing into the hot metal (8), there is an immersion lance for oxygen gas blowing downstream (forcefully blows oxygen gas into it. When oxygen gas is blown downstream from the refining agent injection position, the oxygen gas is blown into the hot metal. Oxygen becomes CO gas and floats to the surface, stirring the slag and raising its temperature.

As a result, the fluidity of the slag is improved, the contact between the dephosphorizing agent and the hot metal is improved, the amount of unreacted agent is reduced, the reaction efficiency is improved, and the precipitation of iron in the slag is promoted. The iron content in the slag is separated and the yield of iron content is improved.

Note that oxygen gas is added while measuring the temperature of the produced slag. This depends on the temperature of the produced slag and the Fθ content in the slag.
This is because the amount changes. FIG. 2 is a diagram showing the relationship between the slag upper surface temperature and the Fs content in the slag, which was experimentally determined by the inventor. The temperature on the top surface of the slag was measured using a radiation thermometer that can easily carry out continuous measurements, and was carried out immediately before the slag outlet downstream of the oxygen gas injection position. As is clear from this figure,
It can be seen that as the slag upper surface temperature increases, the F8 content in the slag decreases. Therefore, when blowing oxygen gas, the temperature of the generated slag is measured.

Here, as an example, an example in which dephosphorization of hot metal was carried out by the method of the present invention is shown below.

Example 20CaO-10CaF was applied to dephosphorizable hot metal (IO/m1n) having the composition shown in Table 1 after desiliconization, tapped from a blast furnace, and slag having the composition shown in Table 2.
A dephosphorizing agent having a composition of 270Fa203 was injected at a rate of 58 kg/unit together with a carrier gas (air), and the inner diameter was 12 rn at a position 1 m downstream from the dephosphorizing agent injection position.
Three oxygen lances made of mφ steel pipes and protected with refractories on the outside are immersed in the hot metal to a depth of 100 mm to supply oxygen gas at a rate of 30 Nm3/min when the slag temperature is below 800°C.
20 Nm'/m between 800 and 1000℃! n
.

ONm3/minNm3/ for 1000'C or more.

The hot metal components after the dephosphorization treatment in this example are shown in Table 1, and the generated slag composition is compared with that of the conventional blasting method in Table 3.
Each is shown in the table.

In this example, the slag temperature was about 800°C,
As is clear from the composition of the produced slag shown in Table 3, the Fs content in the slag was significantly reduced to 4.2%. It can be inferred that this is because the oxygen blown into the hot metal became CO gas, floated up, stirred the slag, and raised the temperature, resulting in an effect more than simply heating. In addition, the hot metal temperature has increased by about 30 to 40 degrees Celsius compared to conventional processing (160 to 770 degrees Celsius).
The effect of preventing temperature drop through continuous treatment was also obtained.

Table 1 Hot metal composition (%) Table 2 Slag composition (%) As described in detail, according to the method of this invention, the slag-metal is stirred by oxygen gas injection in the refining agent injection process. And, due to the heating effect, reaction efficiency and slag fluidity can be improved, and the yield of iron in hot metal can be improved. Moreover, since such an effect can be obtained by a simple means of blowing oxygen gas, the effect brought about in linear refining is enormous.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the slag upper surface temperature and the F8 content in the slag in the present invention. 1... Tapping trough, 2, 3... Skinmer, 4.5...
・Slag discharge port, 6... Non-immersed top blowing lance for blowing refining agent, 1...
Immersion lance for oxygen gas injection, 8...Hot metal, 9.
...Slag. Figure 1 Figure 2 Slag top surface temperature (''C)

Claims (1)

[Claims] A hot metal pretreatment method in which a refining agent is injected together with a carrier gas into the hot metal flow in a blast furnace tap runner from a lance installed above the hot metal surface, characterized by injecting oxygen gas downstream from the refining agent injection position. A method for pre-treatment of hot metal.