JP2624498B2 - Smelting reduction refining method of Cr oxide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a smelting reduction smelting method for Cr oxides such as Cr ore by an upper-bottom blow converter using an iron bath, and more particularly, to a method for melting the Cr oxides. It is intended to advantageously reduce dust which is inevitable during reduction refining and causes a decrease in Cr yield.

(Prior art) Cr ore or the like is placed in an iron bath such as hot metal housed in a top and bottom blown converter.
A method in which a Cr oxide is added together with a heat source and a carbon source serving as a reducing agent, and C is burned by blowing the oxygen jet from the bottom to the top to melt and reduce the Cr oxide using the iron is disclosed in, for example, The technique disclosed in 158320 is known.

(Problems to be Solved by the Invention) Incidentally, in the smelting reduction smelting according to the above-described method, a large amount of dust is generated from the converter during the smelting, and a reduction in the Cr yield in the molten iron due to this is inevitable. Table 1 shows the general Cr balance in smelting reduction using semi-reduced chromium pellets, but about 31.9% of the Cr loss escapes out of the system as dust.

Therefore, reducing dust at the time of smelting reduction refining leads to improvement of Cr yield and has economic significance.
Until now, it was difficult to deal with the problem.

It is an object of the present invention to provide a new method capable of solving the conventional problems described above and improving the Cr yield in molten iron.

(Means for Solving the Problems) The inventors have conducted various experiments and studies in order to minimize the generation of dust in the smelting reduction smelting of Cr oxide, and as a result,
It has been found that storing a predetermined amount of slag in the converter in advance is extremely effective.

 The present invention is based on the above findings.

That is, the present invention is applied to a top-blowing converter containing an iron bath.
In producing Cr-containing molten iron by supplying Cr oxide and subjecting the Cr oxide to smelting reduction smelting, prior to the smelting reduction of the Cr oxide, a slag of at least 50 kg / t is accommodated in a converter. This is a smelting reduction refining method for Cr oxide, which is characterized in that:

(Operation) In the smelting reduction of Cr oxide, first, using an 85-ton top-bottom blow converter, the amount of dust generated when smelting 10 to 20% Cr-containing molten iron by the smelting reduction method and the slag in the furnace at that time were refined. The relationship between the generation amounts was investigated. From FIG. 1 showing the relationship between the blowing time and the dust generation speed, the dust generation speed sharply increases as the Cr ore starts to be added, but after a while, the dust generation speed decreases. From FIG. 2 showing the relationship between the blowing time and the amount of generated slag, it was found that the generated slag amount increased with the elapse of the blowing time.

In particular, the mechanism of dust generation is caused by fumes, bubble bursts, or direct suction of additives.The main factors are the fumes and bubble bursts described above, both of which are caused by iron in the converter. Starting from the fire point of the oxygen blown up on the bath, it is sucked into the exhaust gas duct together with the rising airflow in the furnace.

Here, the top-blown oxygen is extremely important from the viewpoint of combustion of the added carbonaceous material, heat-up, or melting, stirring and slagging of the input ore.

Therefore, in order to cover the ignition point caused by the upwardly blown oxygen, which is the starting point of fumes and bubble bursts, without impairing the above functions, smelting reduction of Cr oxide in a converter with slag pre-existing on an iron bath Was done. As a result, it was found that the amount of slag in the furnace and the rate of dust generation had a relationship as shown in FIG.

According to the above findings, if at least 50 kg / t of slag is stored in the converter prior to the smelting reduction of Cr oxide, it is reduced to about 30% compared to when the dust generation rate is highest. You can see that.

In practicing the present invention, the smelting reduction refining of the Cr ore is performed by a specific process, and after the molten Cr-containing molten metal is discharged, at least 50 kg / t of the slag in the furnace is left and the next molten metal is melted. Iron is charged and Cr is again
If smelting reduction of ore is performed, slag of 50 kg / t or more can always be left on the bath in the converter, and as a result, the amount of generated dust is significantly suppressed.

If the amount of slag remaining or charged in the converter is too large, depending on the shape of the furnace, slopping is likely to occur during refining, and on the contrary, the Cr yield decreases. Therefore, the upper limit is preferably set to 200 kg / t or less.

(Example) For each of the conventional method (A) in which no slag is left in the converter in advance and the method (B) according to the present invention, the molten ore reduction smelting of Cr ore was performed by using an 85-ton top-bottom blow converter,
Cr-containing molten iron was manufactured, and the amount of dust generated during refining and the Cr yield were investigated.

First, according to the method (A), hot metal (C: 4.20 wt%, Si: tr, Mn: 0.02 wt%, P: 0.009 wt%, S:
Refining was performed using 58.8 tons of 0.021 wt% (Cr: tr).

 The results are described below.

1. In-top brand / quantity Hot metal: 58.8 tons Coke: 25.58 tons Lightly fired dolomite: 2.4 tons Semi-reduced chromium pellets (T.Cr: 32.18%, T.Fe: 22.23%,
Al ₂ O ₃ : 17.28%, MgO: 10.29%, reduction ratio 69.89)%: 33.01
Tons Calcined lime: 5.70 tons Blowing oxygen: 19045Nm ³ (Bottom tuyere: 4.001Nm ³ ) Propane: 301Nm ³ Blowing time: 66.7 minutes 2. Output brand / quantity Crude molten chrome steel: 71.0 tons 3. Steel temperature (° C), component composition (wt%) 4. Slag composition at tapping (%) 5.Dust generation: 80kg / ton 6.Steel yield and Cr yield Next, following the blowing by the above method (A), the hot metal (C: 4.20 wt%, Si: tr, M
n: 0.03 wt%, P: 0.012 wt%, S: 0.021 wt%, Cr: tr) 65.2
Refining using tons was performed. The results are described below. In the method (B), after the molten steel obtained by the method (A) is tapped, when the waste is discharged, the tilt angle of the discharge side of the converter is set to 10 degrees.
5 kg (furnace upright 0 kg) was used and 53 kg / t of slag was left in the converter.

1. Input brand / quantity Hot metal: 65.2 tons Coke: 25.55 tons Lightly burnt dolomite: 2.31 tons Semi-reduced chromium pellets: 31.38 tons Burnt lime: 5.70 tons Blowing oxygen: 18667Nm ³ (Bottom blowing tuyere: 4152Nm ³ ) Propane: 311Nm ³ Blowing time: 69.5 minutes 2. Output brand / quantity Molten chrome molten steel: 77.8 tons 3. Molten steel temperature (℃), component composition (wt%) 4. Slag composition at tapping (%) 5. Dust generation: 55kg / ton 6. Tapping yield and Cr yield Tapping yield: 94.99% Cr yield: 92.99% In this example, semi-reduced chromium pellets that were partially preliminarily reduced as Cr ore were used. However, from the above results, in the smelting reduction refining, in the method (B) in which slag is left in the bath in the furnace in advance, compared with the method (A) in which no slag remains (J), jet water is added to the bare water particularly at the beginning of blowing. It was confirmed that the amount of initial dust generated by the action of decreased by about 36%, the amount of total dust generated decreased by about 20 kg / ton, and the Cr yield increased by about 1.0%.

FIG. 4 is a comparison diagram of the blowing time and the dust generation speed, and FIG.
Fig. 6 shows the relationship between the total blowing time and the total amount of dust generated, and Fig. 6 shows the relationship between the Cr pellet input amount and the Cr yield.

(Effects of the Invention) According to the present invention, in the production of molten iron containing Cr in the smelting reduction smelting of Cr oxide, the generation of dust that causes a decrease in Cr yield can be suppressed as much as possible. Operational troubles such as dust clogging in the OG hood and troubles in the OG dust collection water treatment facility were eliminated or reduced.

[Brief description of the drawings]

Fig. 1 is a graph showing the relationship between the dust generation speed and the blowing time, Fig. 2 is a graph showing the relationship between the slag generated in the furnace and the blowing time, and Fig. 3 is a graph showing the relationship between the dust generation speed and the slag generated in the furnace. Fig. 4 is a graph showing the relationship between the dust generation speed and the blowing time, Fig. 5 is a graph showing the relationship between the total dust amount and the blowing time, and Fig. 6 is a graph showing the relationship between the Cr yield and the amount of Cr pellet charged.

Continuing from the front page (72) Inventor Keizo Taoka 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Ichiichi Mada 1 Kawasaki-cho, Chiba-shi Chiba Prefecture Kawasaki Steel Corporation Chiba Works (56) References JP-A-63-28812 (JP, A)

Claims (1)

(57) [Claims] 1. A Cr oxide is supplied into an upper-bottom blow converter containing an iron bath, and the Cr oxide is melted and refined to contain the Cr oxide.
In producing Cr molten iron, at least the converter must be
A smelting reduction refining method for Cr oxide, characterized by containing 50 kg / t of slag.