JPH10251729A - Smelting reduction method for chromium ore - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smelting reduction method for chromium ore by which chromium reduction yield and carbonaceous material yield are improved by using a converter type smelting reduction furnace having combination-blown function. SOLUTION: At the time of producing molten chromium-containing metal by adding the chromium ore together with the carbon-containing material into the converter type smelting reduction furnace having combination-blown function and supplying oxygen, a material having <=0.5H/C value (the ratio of number of atoms of hydrogen to that of carbon in terms of carbon-containing material), and >=85% fixed carbon content, is used and further, the bottom-blown oxygen flow rate is regulated to 0.3-0.8Nm<3> /min.t.

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 by adding a carbon-containing substance to chromium ore and smelting and reducing chromium ore.

[0002]

2. Description of the Related Art Conventionally, smelting of stainless steel has been carried out using ferrochrome produced by carbon reduction of chromium ore or the like in an electric furnace. As a result, the production cost of stainless steel has been increased. In order to solve this problem, there has been known a method of melting a chromium-containing molten metal by reducing carbon in a pre-reduced semi-reduced chromium pellet using a top-bottom blowing converter without using electric power. ing.
In addition, a method has been proposed in which the chromium ore is directly reduced to obtain a chromium-containing molten metal. (JP-A-58-9
Japanese Unexamined Patent Application Publication No. 7-41872 discloses a method of using a carbon material having thermal degradability to prevent metal particles from adhering to the carbon material. Discloses a method for reducing metal loss and increasing the rate of reduction reaction.

[0003]

The smelting reduction method of semi-reduced chromium pellets requires equipment for producing chromium pellets, and has a problem that the cost is higher than the method of smelting reduction of chromium ore directly. . On the other hand, in the smelting reduction method of chromium ore, the oxide (Cr ₂ O ₃ , Fe
Since the charging rate of O) increases, there is a problem that the reduction reaction rate must be increased in order to make the amount of chromium reduction per unit time the same as in the conventional method. For this purpose, it is effective to increase the surface area of the carbon-containing substance, which is the main reduction reaction interface, but when the same carbon-containing substance as in the past is used, it is necessary to increase the amount of the carbon-containing substance added. . This increase in the amount of the carbon-containing material added causes not only the increase in the amount of addition itself to increase the cost, but also the carbon-containing material remaining in the treated slag.
It is also harmful because it has an adverse effect on slag recycling, and greatly reduces the benefits of the smelting reduction method of chromium ore.

[0004] An object of the present invention is to provide a method for smelting and reducing chromium ore which increases the surface area of a carbon-containing material without increasing the amount of the carbon-containing material added, and provides a high reduction reaction rate. Although the above object can be solved by using a carbonaceous material having a fine particle size, the use of such a fine carbonaceous material has a problem that the addition yield is low and the amount of dust generated increases. On the other hand, JP-A-7-4187
No. 2 discloses a method in which the carbon material is caught in the slag or metal before the thermal collapse of the carbon material by adjusting the charging method so that the carbon material reaches the slag or metal at a temperature of 800 ° C or less. It is shown.

However, when the present inventors conducted experiments by changing the carbon material input height, the yield of the carbon material did not change even under the condition that the surface temperature could be kept at 800 ° C. or less, and the flow rate of the exhaust gas was simply changed. There was a tendency for the carbonaceous material yield to decrease with the increase. In addition, blowing of carbonaceous powder was observed near the furnace port during the experiment due to the pulsation of the furnace pressure, and a large amount of carbonaceous material was observed above the slag based on observations inside the furnace and sampling results of the slag after the experiment. Was observed. From these results, it is estimated that some of the carbon material charged into the furnace was caught in the slag and metal, but most of it was floating on the slag or suspended in the space inside the furnace. Was. For this reason, it is considered that the scattering of the carbonaceous material does not decrease even when a treatment for preventing the thermal collapse during the charging is performed.

As described above, the method of adding a fine carbonaceous material has a problem that the addition yield is low.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies with the aim of improving the chromium reduction yield and carbon material yield in the smelting reduction process using a converter, and found that the chromium reduction yield was added. Greatly affected by the type of carbon-containing material (carbon material)
The chromium reduction yield was dramatically improved with the use of certain carbon-containing materials, and the carbon material yield was greatly affected by the bottom-blown oxygen flow rate, and there was an optimum range of the bottom-blown oxygen flow rate. I learned.

First, an experiment on which the present invention is based will be described. In a 5 ton test converter, chromium ore and various carbon-containing substances were added to the converter, and oxygen was supplied to perform smelting reduction of chromium ore, and the reduction rate of chromium ore was investigated. As a result, as shown in FIG. 2, it has been found that a high chromium ore reduction rate can be obtained only when the added carbon-containing substance is finely divided at the time of addition in the furnace. In addition, the carbon-containing substance to be added is charged in advance on carbon-saturated hot metal in a 30 kg-class small melting furnace, the disintegration of these substances is investigated, and the added carbon-containing substance is instantaneously granulated at the time of charging. As shown in FIG. 4, it has been confirmed that the particle size distribution is divided into two types: one in which the particle size distribution changes and one in which the particle size is hardly reduced.

Next, the present inventors investigated the characteristics of the various carbon-containing substances that were tested, and found that the destructibility of the carbon-containing substance upon introduction into the furnace showed the ratio of the number of atoms of hydrogen and carbon contained in the substance,
It has been found that the H / C value is closely related to the fixed carbon amount. That is, as shown in FIG.
Carbon-containing substances having a carbon content of 5 or less and having a fixed carbon content of 85% or more are refined when charged into the furnace, but carbon-containing substances outside the above range hardly become fine.

Further, the present inventors put chromium ore and a carbon-containing substance (carbonaceous material) into the converter in a 5 ton test converter, make the total oxygen supply flow rate constant, and make the bottom blown oxygen flow rate various. The smelting reduction was carried out by changing, and the carbon material yield and the chromium reduction yield were investigated. As a result, as shown in FIG. 3, it was found that both the chromium reduction yield and the carbonaceous material yield could be increased by adjusting the bottom blown oxygen flow rate within a certain range. That is, from FIG. 3, the bottom blown oxygen flow rate is set to 0.3 to 0.8 Nm ³ / min.
・ By setting it within the range of t, both the carbon material yield and the chromium reduction yield increase to 85% or more.

The present invention has been made based on the above findings. That is, the present invention relates to a chromium ore smelting reduction method for adding a chromium ore together with a carbon-containing material to a converter type smelting reduction furnace having a top-bottom blowing function and supplying oxygen to smelt a chromium-containing molten metal, As the carbon-containing substance, the ratio of the number of atoms of hydrogen and carbon and the H / C value are
Use a substance with a fixed carbon content of 85% or less and 0.5 or less,
Further, there is provided a method for smelting and reducing chromium ore, wherein the flow rate of bottom-blown oxygen is 0.3 to 0.8 Nm ³ / min · t.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a converter type smelting reduction furnace having a top-bottom blowing function is used. The chromium ore is added to the converter together with the carbon-containing material, and the carbon-containing material is burned by supplying oxygen by top and bottom blowing, and the heat of combustion melts and reduces the chromium ore to melt the chromium-containing molten metal.

[0013] The use of the top-bottom blow converter allows a large amount of oxygen gas to be supplied from both the top and bottom to enable high-productivity smelting reduction,
It is also effective from the viewpoint of increasing the reduction reaction rate of the metal oxide in the slag by vigorous stirring by the bottom blow gas. In the present invention, as a carbon-containing substance to be added to the converter,
A substance having an atomic ratio of hydrogen to carbon, an H / C value of 0.5 or less, and a fixed carbon amount of 85% or more is used.

When the H / C value of the carbon-containing substance exceeds 0.5, the carbon-containing substance is not instantaneously refined when it is charged into the furnace, so that the reaction interface area of the carbon-containing substance does not increase,
The rate of the reduction reaction is low, and therefore the chromium ore reduction rate decreases. For this reason, the ratio of the number of atoms of hydrogen and carbon contained in the carbon-containing substance to be added and the H / C value are limited to 0.5 or less. Further, if the H / C value of the carbon-containing substance to be added is 0.5 or less and the fixed carbon amount is less than 85%, the carbon-containing substance has low disintegration and is hard to be granulated when put into a furnace. Therefore, the ratio of the number of atoms of hydrogen and carbon contained in the carbon-containing substance to be added, the H / C value is 0.5 or less, and the fixed carbon amount is 85%.
%. In addition, it can be inferred that the ratio between the number of atoms of hydrogen and carbon in the carbon-containing material and the relationship between the fixed carbon amount and the tendency to refine the carbon-containing material are closely related to the internal structure of the carbon-containing material. Is unknown.

Examples of the carbon-containing substance suitable in the present invention include anthracite, semi-anthracite and the like, among which anthracite is preferred. It goes without saying that these substances satisfy the ratio of the number of atoms of hydrogen to carbon, the H / C value, of 0.5 or less and the fixed carbon content of 85% or more. In the present invention, the carbon-containing substance to be charged is limited as described above, and the flow rate of the bottom-blown oxygen is set to 0.3 to 0.8 Nm ³ / min · t.

If the bottom blown oxygen flow rate is less than 0.3 Nm ³ / min · t, the carbon material is not sufficiently entrained in the slag and metal,
Since the reduction does not proceed sufficiently, the chromium reduction yield decreases, and the scattering of the carbonaceous material increases, and the carbonaceous material yield also decreases. On the other hand, when the bottom-blown oxygen flow rate exceeds 0.8 Nm ³ / min · t, the spitting amount increases and the chromium reduction yield decreases. For this reason,
The bottom-flow oxygen flow rate was 0.3 to 0.8 Nm ³ / min · t.

In the operation of the smelting reduction method of the present invention, oxygen is blown downward and upward. In the present invention, it is not necessary to define particularly for top-blown conditions of oxygen top-blown oxygen, the primary combustion of the carbonaceous material is controlled in consideration of the secondary combustion to the generated CO gas until CO ₂ It is desirable. If secondary combustion is used, a large amount of energy can be obtained without increasing the amount of carbon material used, and the productivity of the converter can be increased. In order to improve the secondary combustion efficiency, the height of the upper blowing lance, the upper blowing oxygen,
It is known that the flow velocity decreases. Needless to say, these methods can be suitably used in the present invention.

[0018]

EXAMPLE Using a 5-ton scale converter-type smelting reduction furnace having a top-bottom blowing function, a carbon-containing substance having a hydrogen / carbon atomic weight ratio (H / C ratio) and a fixed carbon content shown in Table 1 was prepared. The chromium ore was melted and reduced at a flow rate shown in Table 1 to obtain a chromium-containing molten metal. During operation,
Adjust the height of the upper blowing lance and adjust the secondary combustion rate (CO ₂ / CO ₂ + CO
) Was kept constant at 20%.

After the operation, the components of the obtained chromium-containing molten metal,
The chromium reduction yield was determined from the weight and the amount of added chromium ore, and the carbon material yield was determined from the amount of generated dust component and the added carbon-containing material.

[0020]

[Table 1]

From Table 1, it can be seen that the examples (test Nos. 1 and 2) in which the carbon-containing material within the scope of the present invention was used and operated at the bottom-blown oxygen flow rate within the scope of the present invention were all the reduction of chromium ore. The yield is over 90%, and the carbon material yield is over 98%. On the other hand, a comparative example using a carbon-containing substance outside the scope of the present invention (Test No. 3,
No. 4) and the comparative examples (test No. 5 and No. 6) operated with the bottom-blown oxygen flow rate outside the range of the present invention, the reduction yield of chromium ore was remarkably low at 60 to 70%, and , Test No. 5, N
In o.6, the carbon material yield is as low as 85-88%.

FIG. 4 shows an example of the particle size distribution before and after the collapse of the carbon-containing substance added in Test No. 1. It can be seen that the fine particles are formed by the collapse.

[0023]

According to the present invention, the carbon-containing material becomes finer after addition in the furnace, the surface area of the carbon material increases without increasing the amount of the carbon material added, and the reduction reaction speed can be increased. In addition to these, it is possible to obtain a high chromium reduction yield and thereby achieve a great industrial effect of enabling a smelting reduction operation of chromium ore capable of obtaining a high carbon material yield.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the fixed carbon amount of a carbon-containing substance, the ratio of the number of atoms of hydrogen and carbon, the H / C value, and the grain refinement.

FIG. 2 is a graph showing the relationship between the chromium ore reduction rate and the refinement of carbon-containing substances.

FIG. 3 is a graph showing a relationship between a carbon material yield, a chromium reduction yield, and a bottom-blown oxygen flow rate.

FIG. 4 is a graph showing an example of a particle size distribution before and after the collapse of a carbon-containing substance.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Nagayasu, Nagayasu 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. Kawasaki Steel Corporation Chiba Works (72) Inventor Yasuo Kishimoto 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works

Claims (1)

[Claims] 1. A method for smelting and reducing chromium ore, comprising adding chromium ore together with a carbon-containing substance to a converter type smelting reduction furnace having a top-bottom blowing function and supplying oxygen to melt the chromium-containing molten metal. As the carbon-containing material, a material having a ratio of the number of atoms of hydrogen and carbon, H / C of 0.5 or less and a fixed carbon amount of 85% or more, is used.
A method for smelting and reducing chromium ore, wherein the method is 0.3 to 0.8 Nm ³ / min · t.