JPH05171302A - Method for melting and reducing chromium ore - Google Patents

Abstract

PURPOSE:To improve the melting and reducing rates of a Cr ore and the yield of Cr. CONSTITUTION:A chromium ore sand is briquetted and introduced into a converter-type refining vessel, and the chromium ore is melted and reduced. In this case, quick lime necessary for melting and reducing is previously mixed into the chromium ore sand to briquette the sand, the briquette is introduced into the refining vessel, and the ore is melted and reduced. Since the quick lime is added along with the ore, the melting and reducing rates are increased, and the yield of chromium is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for smelting and reducing chromium ore using a converter type vessel.

[0002]

2. Description of the Related Art Generally, in a method for refining stainless steel, a method of using ferroalloy such as FeCr or stainless scrap scrap as a Cr source is adopted. FeCr is very expensive because it is produced using electric power, and it is produced by the smelting reduction method.
Studies on the production of FeCr are also being conducted.

Further, although not including FeCr, a method of smelting reduction using Cr ore as a Cr source in place of FeCr at the time of refining stainless steel is industrially carried out. Further, a method of previously mixing a flux or the like during agglomeration of Cr ore is also well known. For example, in order to obtain the strength of the agglomerated product, a small amount of quick lime, silica sand, etc. are mixed, as disclosed in JP-A-52 -46317, JP-A-61-117234 and JP-A-60-243233 are disclosed.

On the other hand, in Japanese Patent Publication No. 46-43695, silica sand,
It has been disclosed that lime or the like is added to obtain a reduced pellet having a dense and strong oxide film on the surface and a reducing layer inside, but it is assumed that the post-process is an electric furnace and low basicity Has become. The technique disclosed in JP-A-63-130728 is also used for the production of reduced pellets of chromium ore.
However, the content of CaO is small because it is limited to fixing S.

[0005]

In any of the above-mentioned conventional techniques, an electric furnace or the like is assumed as the reduction furnace, and since the converter type container is not targeted as the reduction furnace, the slag composition is low in CaO, Inadequate for protection of refractories and smelting reduction. Therefore, when applying the above-mentioned chrome ore to stainless steel refining, in any case, in order to obtain a slag composition suitable for smelting reduction, it is necessary to add a flux such as quick lime, in order to obtain a slag composition. There was a problem in that it was controlled uniformly.

On the other hand, in terms of making the slag composition uniform, it is not impossible to control the charging or blowing of quick lime from the hard side according to the amount of chromium ore or coke charged, but this is a large facility. Therefore, there was a problem that the construction cost becomes high. An object of the present invention is to provide a smelting reduction method for chromium ore that can solve the above problems.

[0007]

The present invention is intended to facilitate control of the slag composition, which is an operation point during smelting reduction in order to solve the above-mentioned problems, and its gist is as follows. is there. The present invention agglomerates the chrome ore sand, added to the converter type vessel, in the method of performing the smelting reduction of the chrome ore, in the chrome ore sand is premixed with quicklime components required for smelting reduction, agglomerate, It is a method for smelting reduction of chromium ore, which is characterized in that the smelting reduction is carried out by adding it to a converter type vessel.

[0008]

The reduction of Cr ₂ O ₃ during smelting reduction proceeds by the reaction of Cr ₂ O ₃ + 3C = 2Cr + 3CO, where C in molten iron is C.
However, the reduction is mainly due to solid C in the slag. In order to accelerate this reaction, Cr ₂ O ₃ is better to be liquid than solid, and therefore the point is how to make it slag.

CaO is added, for example, in the form of quick lime, which is (1) protection of converter refractory, (2) promotion of slag slag formation, (3) slag volume for slag formation of chromium ore. (4) It is for secondary desulfurization of molten iron. Typical raw materials and fluxes that are put into the furnace during smelting reduction are chromium ore, coke, and quick lime.
Chromium ore and coke contain an oxygen source and volatile matter as gas components, and a large amount of exhaust gas is generated at the same time when they are added to the furnace, so they can be dividedly charged, but operation controllability From the viewpoint of, it is common to continuously charge.

On the other hand, quick lime is generally charged in portions. A typical example is shown in FIG. Change of basicity CaO / SiO ₂ is an example showing changes of the slag composition, Come to along the time axis although at the target value Come to a temporal average value, CaO / SiO ₂ is repeated height You can see that The smelting reduction has the above-mentioned role of CaO.
There is an optimum value of basicity CaO / SiO ₂ as shown in (Fig. 1
Then CaO / SiO ₂ = 2.5 to 3.5 is the optimum range). Therefore,
In the conventional charging method as shown in Fig. 4, CaO / SiO ₂
Will be lost, and the reducing ability will be reduced.

On the other hand, according to the present invention, the chrome ore sand is made to agglomerate by previously containing the necessary quicklime, so that the slag composition can be easily controlled throughout the entire time. As a means for agglomerating, conventional means such as pelletizing or briquetting is sufficient. Figure 2
The method of the present invention in which limestone is mixed in advance with chrome ore so as to have a basicity of 2.5 to 3.5 at the time of smelting reduction refining, and the limestone is lumped and used, and quick lime is used as a conventional method shown in FIG. It is shown in comparison with the apparent reduction rate constant K ₁ of the chromium ore by the method of.

Here, the apparent reduction rate constant K ₁ is expressed by the following equation. d (T · Cr) / dt = K ₁ (T · Cr) T · Cr: Total Cr concentration in slag In the method of the present invention, there is no variation in slag formation as compared with the conventional method, so that the apparent reduction rate is You can see that it is improving. Further, FIG. 3 shows the T / Cr (%) in the slag after the addition of the specified amount of Cr pellets (10 t · Cr) as a result of the result. According to the method of the present invention, T / Cr in the slag is shown. Since the amount is lower than that of the conventional method, the effect of the present invention can be clearly understood.

[0013]

EXAMPLE A smelting reduction of Cr ore was carried out using an 85t top-bottom blow converter. The following two types of Cr ores were used for comparison. (A) Cr ore only fired and pelletized (conventional method whose components are shown in Table 1) (B) Cr ore to which quicklime is added (Cr ore: CaO = 1: 0.
18) and then pelletized by firing (the method of the present invention whose components are shown in Table 2) In this experiment, all the Cr ore sands used were those previously reduced by a rotary kiln.

[0014]

[Table 1]

[0015]

[Table 2]

The smelting reduction conditions are as follows. 1. Hot metal charge 60t 2. Melt reduction temperature 1550 ℃ constant 3. C 5.5% in molten reduced molten iron 4. Blowing O ₂ flow rate 300Nm ³ / min 5. Cr ore addition rate 900kg / min 6. Coke addition rate 400kg / min 7. Quick lime addition rate (only in case of A) Cr ore added every 1400kg /, 250kg / every 8. Final slag composition basicity 310 Cr ore was unified with Cr pure content of 10 t / charge (Cr ore 30 t / charge). According to the results of this experiment, T.Cr in the slag after the completion of refining by the method of the present invention was 1.87 wt%, whereas T.Cr was 5.2% by the conventional method. From this result, the reduction yield of Cr was improved by the method of the present invention as compared with the conventional method, and its effectiveness was found.

[0017]

According to the present invention, over the entire period of blowing,
Since the slag composition can be controlled to be constant, the apparent reduction rate and the Cr reduction yield can be improved.

[Brief description of drawings]

[Figure 1] Basicity CaO / SiO ₂ in slag and T ・ Cr in slag
It is a graph which shows the relationship of (wt%).

FIG. 2 is a graph showing an apparent reduction rate constant K ₁ when the Cr ore (B) according to the present invention is used and when the conventional Cr ore (A) is used.

FIG. 3 shows the case where Cr ore (B) according to the present invention is used,
It is a graph which shows T * Cr concentration (wt%) in slag when the conventional Cr ore (A) is used.

FIG. 4: Basicity CaO / Si in slag during conventional refining
It is a graph which shows changes of O ₂ .

Claims (1)

[Claims] 1. A method in which chrome ore sand is lumped and added to a converter-type refining vessel to perform smelting reduction of chrome ore, and the lime ore sand necessary for smelting reduction is mixed in advance to form lumps. A method for smelting and reducing chromium ore, which comprises liquefying and adding it to a converter-type refining vessel to perform smelting reduction.