JPS61272305A - Pretreatment of molten iron - Google Patents

Abstract

PURPOSE:To utilize scraps and to prevent a decrease in the temp. of molten iron effectively by oxidizing and melting scraps in a melting furnace with an oxygen-contg. gas, then adding the melt to the molten iron charged in a pretreating furnace and desiliconizing the molten iron. CONSTITUTION:Scraps are charged into a melting furnace, an oxygen-contg. gas such as an oxygen-enriched gas is blown in to oxidize the scraps and the scraps are melted by the heat of oxidation. Meanwhile, the molten iron obtained in a blast furnace is charged into a pretreating furnace and the melt obtained in the melting furnace and contg. molten oxides is added to the molten iron in the pretreating furnace. Consequently, the molten iron is desiliconized. Subsequently, the melt is further added, as required, to dephosphorize the molten iron. A decrease in the temp. of the molten iron is prevented by the addition of the melt at high temp. The pretreated molten iron is desulfurized, then charged into a converter and refined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot metal pretreatment method that can effectively utilize scrap (iron scraps).

[Conventional technology and its problems] Conventionally, scrap generated in Nanchu and scrap generated as defective parts in the processing stage at steelworks is input into a converter and consumed as part of the converter charge. Alternatively, it is melted in an electric furnace or shaft furnace and used for manufacturing castings.

However, in recent years, before charging hot metal into a converter, hot metal pretreatment is carried out to remove silicon, dephosphorize, and desulfurize. This reduces the heat source in the converter, making it difficult to feed scrap into the hot metal in the converter.

On the other hand, even if scrap is melted in a shaft furnace, its use is limited to castings because the shaft furnace does not have a refining function.

As described above, in the current situation where the uses of scrap are decreasing, there is a tendency for the generation of scrap in cloth to increase, and there is a demand for the development of a steel manufacturing process that uses this scrap in multiple layers.

In addition, in hot metal pretreatment, iron oxide (Fe
Since the block d) is introduced, the temperature of the hot metal decreases, and carbon in the hot metal may precipitate.

[Means for Solving the Problems] The present invention has been made in view of the above circumstances, and provides a hot metal pretreatment that can effectively utilize scrap and prevent the temperature of hot metal from decreasing. The purpose is to provide a method.

The hot metal pretreatment method according to the present invention includes charging scrap into a melting furnace, oxidizing the scrap with oxygen-containing gas, and melting the scrap with the heat of oxidation, while charging the hot metal into the pretreatment furnace, The method is characterized in that the molten metal containing molten oxide obtained by melting scrap in the melting furnace is added to the molten pig iron in the pretreatment furnace to desiliconize the molten pig iron.

Further, by adding the molten metal obtained in the melting furnace to the desiliconized hot metal and dephosphorizing the hot metal, it is possible to effectively utilize scrap to dephosphorize the hot metal.

Conventionally, when melting scrap in a shaft furnace, the scrap and coke are charged from the top of the shaft furnace, air is blown through the tuyere installed at the bottom of the shaft furnace, and the coke is combusted by oxygen gas. The scrap is melted by the heat of oxidation. In this case, if molten iron oxide is produced, it will be of no use and the yield will be reduced, so the amount of oxygen in the gas blown into the shaft furnace is kept to an amount sufficient to oxidize the input coke. The present invention was made as a result of intensive research into methods for effectively utilizing scrap, and contrary to the conventional wisdom of scrap melting, a large amount of oxygen gas is blown into the melting furnace to melt coke, etc. In addition to the oxidation of the exothermic substance, the scrap itself is oxidized, and a large amount of oxidation heat generated by this is used to melt the scrap.

This molten iron oxide is added to the hot metal in the pretreatment of the hot metal to oxidize and remove silicon (S i ) or phosphorus (P) from the hot metal. This results in
Scrap can be used effectively, and since high-temperature molten iron oxide is used in the pretreatment of hot metal, a drop in temperature can be prevented.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a flowchart showing a hot metal pretreatment method according to an embodiment of the present invention, and FIG. 2 is a schematic diagram thereof. In a blast furnace, ore, coke, and limestone are charged, and hot air is blown into the blast furnace by heating the air through the blast furnace tuyeres. The hot metal obtained by reducing the ore is stored in a ladle, a torpedo car, or the like, and is subjected to hot metal preliminary treatment.

On the other hand, in a melting furnace such as a shaft furnace, scrap and coke are charged, and air enriched with oxygen gas is blown into the melting furnace through the tuyeres at the lower part of the melting furnace. Then, due to the oxidation reaction of the coke, heat is generated as shown in (1) below.

C+02-CO2+ 7830kcal/kgCC+1
/2 ・02→CO+2200kcal/kac...
(1) In this way, by oxidizing coke (C) by 11 cI, a heat amount of 7830 kcal or 2200 kcal is generated. This amount of heat causes some of the scrap to melt.

On the other hand, the oxygen gas in the gas blown into the melting furnace oxidizes the molten iron through the reaction shown in equation (2) below.
1310 kcal of heat is generated per 1 kg of iron.

Fe(1)+1/2・02 (Q) −+FeO(1)+1310kcal/kgFe−(2
) Furthermore, 1. S and Q indicate liquid, solid, and gas states, respectively. This heat of reaction is used to melt the scrap. The amount of heat required in this case is shown by the reaction equation (3) below.

Fe(S)at25℃ 1'Fe(+)at1600℃-309kcal/ka
F e...(3) In other words, as is not clear from equations (2) and (3), 1
By oxidizing ka of iron, 4.2 kO of iron (scrap) can be dissolved. In other words, the molten R iron oxide is 1
kg and 4.2 ka of molten iron will be produced from scrap with a heat balance of O.

Note that the scrap contains silicon <S i ) and manganese (Mn), and these 3i and Mn
The oxidation reaction of is also an exothermic reaction. Therefore, the oxidation of 81 and Mn in the scrap can promote the dissolution of the scrap.

Fe(+) and FeO(1) discharged from the melting furnace are added to hot metal tapped from the blast furnace,
81 of the hot metal is removed according to the reaction formula shown in equation (4) below.

S i +2FeO-+S ioz +2Fe ・
- (4) This desiliconized hot metal is taken out of the melting furnace again after removing the slag generated during the desiliconization process.

FeO(1) and Fe(1) are added, and also quicklime (Cab) is added. As a result, the hot metal is as follows (
5) Dephosphorization treatment is carried out according to the reaction formula shown in the formula.

2P+4CaO+5FeO -+40aO-P20g +5 Fe...(
5) After the pretreated hot metal is transferred to a steel plate, the slag on the hot metal is removed by, for example, a slag dragger. Next, this hot metal is charged into a converter and subjected to oxygen blowing.

In the hot metal pretreatment method configured as described above, scrap is melted in a melting furnace, and molten iron F6(+) and molten iron oxide Fe0(1) are obtained. In this case, if coke is not used as the exothermic substance, the heat balance will be O
In this state, iron oxide and iron are dissolved at a ratio of 1:4.2, respectively.

The molten iron and molten iron thus obtained are added to hot metal tapped from a blast furnace. Hot metal during tapping is, for example,
As shown in Figure 2, 3i is 0.40% and P is 0.110%.
%, and its temperature is 1500°C. This hot metal is desiliconized by the reaction shown in the above formula (4) by adding 1:eo(I), and the concentration of Si is, for example, 0.10.
%. This desiliconized hot metal is subjected to a dephosphorization process as shown in the above equation (5) by adding Fe0(1) together with CaO again. In this case, the desiliconization reaction also progresses, and 81 and P(7) a a Gt of the hot metal, respectively, t
r (fine I) and decreases to 0.020%. In addition, in such desiliconization and dephosphorization treatment, in the present invention, molten iron oxide can be used and so-called hot charging of iron oxide can be performed. Therefore, it is possible to avoid the endotherm shown in the following reaction formula (7), and it is possible to suppress the temperature drop of the hot metal.

Fe0(s)at25℃ -+ Fe Oat1500℃-860kcal/k
(IFe.-(7) Furthermore, since a decrease in the concentration of hot metal can be suppressed, precipitation of carbon (C) in the hot metal can be prevented.

This hot metal is treated with sulfur by adding quicklime, etc., if necessary. After that, the slag on the hot metal is removed and the hot metal is charged into a converter.

This invention is not limited to the above embodiments, and various modifications can be made within the technical scope of this invention. In particular, the objects of the invention can be achieved even when molten iron oxide is used only for the desiliconization treatment. In addition, Fe produced in a melting furnace
Since O(1) and Fe(I) are separated by specific gravity into 211, after separating them, only FeO(l) may be added to the hot metal and subjected to preliminary treatment.

[Effects of the Invention] According to the present invention, scrap can be melted using a large amount of heat generated during oxidation of iron, and the generated molten iron oxide can be used for desiliconization and dephosphorization of hot metal. I can do it. Therefore, scrap that is expected to increase the number of generated layers can be effectively utilized. In addition, since molten iron oxide can be added to hot metal, the oxidation reaction of 3i and P by oxygen in iron oxide progresses rapidly, and
It is possible to prevent the temperature of the hot metal from decreasing and avoid its heat loss. In this way, since inexpensive scrap can be used and a drop in the temperature of the hot metal can be prevented, according to the present invention, the cost of preliminary treatment of the hot metal is reduced.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a hot metal pretreatment method according to an embodiment of the present invention, and FIG. 2 is a schematic diagram thereof. Applicant's representative Patent attorney Takehiko Suzue No. 1! ! I

Claims (2)

[Claims] (1) Charge scrap into a melting furnace, oxidize the scrap with oxygen-containing gas, and melt the scrap with the heat of oxidation, charge hot metal into a pretreatment furnace, and A hot metal pretreatment method characterized by adding molten metal containing molten oxide obtained by melting scrap to hot metal in a pretreatment furnace to desiliconize the hot metal. (2) A hot metal reserve according to claim 1, characterized in that molten metal containing molten oxides obtained in the melting furnace is added to the desiliconized hot metal to dephosphorize the hot metal. Processing method.