JPS5852412A - Dephosphorizing method for molten iron - Google Patents

Abstract

PURPOSE:To accelerate dephosphorization and to suppress decarburization in the stage of dephosphorizing molten iron by blowing of a coal base flux and an oxidative gas into said molten iron, by blowing a carbonaceous solid simultaneously into the molten iron. CONSTITUTION:A mixture of a coal base flux and an oxidative gas supplied from a flux supplying device 8 and an oxidative gas supplying device 9 is blown through the central part of an immersion lance 5 into the molten iron 3 contained in a pan 1. At the same time, a mixture of a solid carbonaceous material such as coke powder and a carrier gas supplied from a solid carobanaceous material supplying device 7 and a solid carbonaceous material carrier gas supplying device 6 is blown through the lance 5 into the iron 3. Then dephosphorization is accelerated and the C% at the end point of the dephoshorization is maintained at a high grade.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dephosphorizing hot metal outside a converter.

Conventionally, steelmaking methods have been used in which decarburization and dephosphorization are carried out by oxygen blowing in a converter, but recently dephosphorization has been performed outside the converter in advance, and the converter mainly performs only decarburization. The advantages of this method have been clarified, and various methods of dephosphorization outside the converter are being investigated. In this case, the principle of dephosphorization is based on basic substances such as lime.

This is a method of oxidizing phosphorus in hot metal by adding oxidizing agents such as oxygen gas and iron oxide, and solvents such as fluorite to fixing it in slag as calcium phosphate. It is similar to the dephosphorization method that has been used. The difference is that dephosphorization only needs to be considered under conditions where decarburization occurs (that is, sufficient oxygen can be supplied), whereas in dephosphorization outside the converter, suppressing decarburization is an important issue. That's true. This is because if the amount of decarburization in the converter is large during dephosphorization outside the converter, extensive equipment is required to treat the generated gas, which increases equipment costs, and the CO concentration that can be recovered in the converter is high. This is to reduce the amount of gas. Therefore, various methods have been developed to suppress decarburization during outside-furnace dephosphorization treatment and prevent the 0% level of hot metal after treatment; however, at present, 90% dephosphorization is required. In some cases, the absolute value of C has decreased by 0.7 to 0.9% or more. That is, of the 4+ h C contained in the hot metal, 15 to 20 C decreases during the dephosphorization process, and the gas produced at that time with a low CO concentration cannot be recovered and is dissipated. Therefore, if dephosphorization treatment is applied not only to a small amount of low-phosphorus steel types but also to all NM, it will pose a problem in terms of the energy balance of the steelworks. In addition, if the p value after hot metal treatment is low, the amount of heat generated in the subsequent converter will decrease, so
If the temperature of molten steel after decarburization is specified, the temperature of molten metal after dephosphorization must be increased accordingly.

However, as is well known, high treatment temperatures are disadvantageous for dephosphorization (especially in terms of equilibrium).

In view of the above-mentioned circumstances, the present invention was obtained as a result of various studies on a method for suppressing the decarburization reaction during dephosphorization treatment and increasing the C content after treatment, and its special purpose is to suppress the decarburization reaction during dephosphorization treatment. teeth,
A hot metal dephosphorization method characterized by blowing a carbonaceous solid such as coke powder into the hot metal at the same time when performing dephosphorization treatment by blowing lime-based flux and oxidizing gas into the hot metal.

Hereinafter, a detailed explanation will be given using specific examples.

FIG. 1 shows an example of equipment for implementing the present invention. In hot metal dephosphorization, from the viewpoint of simplifying equipment as much as possible, the hot metal to be treated is treated in a container for transporting between the blast furnace and the converter, such as a pot or a torpedo car. Figure 1 shows the case using a pot. A mixture of flux and oxidizing gas supplied from a flux supply device 8 and an oxidizing gas supply device 9 is blown into the hot metal 5 contained in the ladle 1 through the center of a refractory-coated immersion lance 6.

As a flux, lime (C
The following will focus on those whose main component is aO or CaCO3). In addition to the flux, it is desirable to add iron oxide, fluorite, etc. as an oxidizing agent and a solvent. The main component of the oxidizing gas is oxygen gas, but some of it is carbon.
It may be replaced with O2, N2, etc. The oxidizing gas supplies oxygen to the hot metal to oxidize phosphorus in the hot metal, and the generated iron oxide acts on lime to promote slag formation.

As described above, when performing glazing by blowing lime-based flux and oxidizing gas into hot metal, the feature of the present invention is that carbonaceous solids such as coke powder are injected simultaneously with lime-based flux and oxidizing gas through the immersion lance 5. It's about instilling. One way to do this is to use a double-pipe immersion lance, in which lime/based flux and oxidizing gas are blown into the center as described above, and carbonaceous solids such as coke powder are blown into the outer pipe.
An inert gas such as N2 or a hydrocarbon gas is blown into the hot metal as a carrier. The supply of carbonaceous solids is as follows:
It is desirable to start when the Si content of the hot metal is 0.2% or less. The reason for this is that when Sl > 0.1%, decarburization is difficult to occur even if carbonaceous solids are not supplied, and when the hot metal temperature is low, if carbonaceous solids are supplied at 5i) 0.2%. This is because formation of quiche graphite occurs. When 81<0.2%, decarburization tends to occur, so
Supply of carbonaceous solids is necessary and kick-starting to suppress decarburization.

There is no need to worry about graphite formation.

Dephosphorization rate Figure 2 shows the effect of promoting dephosphorization and suppressing decarburization (represented by dephosphorization)
and the appropriate supply amount of carbonaceous solids. in this case,
Decarburization amount ΔC is C analysis value before and after treatment: C3+C
(It is calculated from the formula % formula % (1) from the C upti: ΔC2 (4) when 100 g of the injected carbon is carburized into hot metal. As a carbonaceous solid The most inexpensively available coke powder (less than 1 so-called φ) was used.Also, the unit of lime was constant #'11skq/l hot metal, and the amount of sulfur supplied in 02 was 2Nnt'/l, 4N
There were two levels: m''/l.

Injecting carbon (spring solid) at the same time during the dephosphorization process, which is oxidation refining, is contrary to conventional wisdom, but if the appropriate amount of carbon is selected from Figure 2, dephosphorization can be promoted and decarburization can be suppressed. The reasons for this are as follows.

(1) The temperature of hot metal near the oxidizing gas injection point is lowered by the sensible heat and heat of dissolution (both are endothermic) of the carbonaceous solid. This suppresses the decarburization reaction and, as a result, screens the oxygen potential, creating conditions favorable for dephosphorization.

(1 Li 9> At 4%, the higher 9 is, the higher the dissolved oxygen level is, which is advantageous for dephosphorization. Also, the higher 9 is, the greater the phosphorus activation coefficient is, both of which are advantageous for progress of dephosphorization reaction. Become.

(i) When a carbonaceous solid with gangue content, such as coke, is injected, the gangue content remaining in the molten steel promotes the slag formation of the injected lime, thereby promoting the Yue-rin reaction.

GV) Cooling of the blow nozzle tip with carbonaceous solid.

The protective effect stabilizes the blowing conditions, which is advantageous for dephosphorization.

In this way, decarburization is suppressed (decarburization is reduced by reducing dephosphorization speed and dephosphorization processing time is reduced by promoting dephosphorization), and a small amount of decarburization is also achieved by carburizing by injecting carbonaceous solids. To compensate, the C% at the end of the dephosphorization process can be maintained at a high level. As a result, if the temperature of molten steel after decarburization is specified, the temperature of molten metal at the end of dephosphorization can be lowered, further promoting dephosphorization and
It becomes possible to suppress decarburization.

EXAMPLE In the apparatus shown in FIG. 1, phosphorus was carried out by injecting epsilon ash-based fur, cous, oxidizing gas, and coke powder into hot metal under the following conditions.

The components and temperature of the hot metal after treatment were as follows.

Assuming that all of the injected coke powder has once attached to the hot metal, the actual amount of decarburization was 0.05%. Note that among the above conditions, only the injection of coke powder was excluded. As a result, the amount of decarburization was 0.8 inches. It is recognized that the addition of coke powder has the effect of promoting dephosphorization and suppressing decarburization.

As described above, the present invention achieves the effect of promoting hot metal dephosphorization and suppressing decarburization by introducing a new method of injecting carbonaceous solids at the same time in bath metal desorption/treatment using lime-based flaring. As a result, the steelmaking process consisting of the combination of the hot metal dephosphorization process and the decarburization process can be rationalized, which has great industrial effects.

[Brief explanation of drawings]

Figure 1 shows one of the facilities for carrying out the present invention using a hot metal ladle.
An explanatory diagram showing an example, Figure 2 is a dephosphorization promotion/body (coke)
FIG. 1: Pot, 2: Freeboard, 3: Hot metal, 4: 7-do, 5
: Immersion lance, 6: Solid carbonaceous carrier gas supply device, 7:
Solid carbonaceous supply device, 8: Flux supply device, 9: Oxidizing gas supply device, 10: Sub-material charging device, 11': Air bubbles.

Claims (1)

[Claims] A hot metal dephosphorization method characterized by blowing a carbonaceous solid such as coke powder into the hot metal at the same time as performing dephosphorization treatment by blowing lime-based flux and oxidizing gas into the hot metal.