JPH09316512A - Method for melting steel using iron oxide briquette as auxiliary raw material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a melting method of a steel which efficiently charges powdery iron oxide and recovers iron content in the iron oxide in various kinds of steelmaking furnace. SOLUTION: In the steel melting method using pig iron and scrap as main raw materials and refining material, the following iron oxide briquette is used as an auxiliary raw material. The iron oxide briquette contains (a) powdery iron oxide as a main component and (b) a thermoplastic resin of 1-10wt.% based on the briquette wt. as a binder for the powdery iron oxide. As the powdery iron oxide, any one or more kinds among the iron ore, mill-scale, iron- making dust, can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steelmaking furnace, for example, a converter, an open furnace, an electric furnace, and other various steelmaking furnaces for making steel from an iron source such as hot metal or scrap and reduced iron. Briquette in which iron oxide is bonded with thermoplastics is used as an auxiliary material and is used as an iron source. In addition, hydrocarbons contained in the plastic are also used as a part of the heat source, and reusable combustion It relates to a method for melting steel, which is recovered as gas.

[0002]

2. Description of the Related Art Conventionally, in a steelmaking plant, solid iron typified by hot metal and scrap supplied from a blast furnace is used as a main raw material, and in addition to this, powdered iron oxide, such as ore, generated in a steel mill is used. Powder, OG dust, magnetic separation powder, mill scale and the like, as well as iron and steel cuttings generated in machine factories are also used as iron sources.

Effective use of the above powdery oxides among the above iron sources is to improve the yield in the steelmaking process, reduce costs,
It is also an important issue from the viewpoint of effective use of resources. Conventionally,
When using the above-mentioned powdery iron oxide in the steelmaking process, a method has been adopted in which not only coarse particles but also fine particles are directly charged into a steelmaking furnace.

However, if the above powdery oxides are directly charged into a steelmaking furnace, the powdery oxides are easily scattered, which not only deteriorates the yield but is not preferable from the viewpoint of environment and hygiene.
Further, particularly fine powders have a large amount of adsorbed water, and when charged into the furnace, the heat of vaporization / decomposition of water is deprived, which deteriorates the thermal efficiency in the steelmaking process.

As a method for solving these problems, there has been disclosed a method in which the powdered iron oxide or the carburizing material is solidified with a resin binder to form a briquette, and the briquette is put into a steelmaking furnace. For example,
In JP-A-62-158812, carboxy methyl cellulose (CMC) and polyvinyl alcohol (PVA) are disclosed.
There is disclosed a method of producing a carburizing material for metallurgy by kneading pulverized coal or the like at high speed to form a briquette by using a special binder such as. However, the binder used in this method is expensive, and thus it is not practical to use the powdery oxide as a binder for briquettes.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a briquette in which powdered iron oxide mainly generated in an iron mill is combined with plastic, for example, waste plastic, which is charged in a refining process in a steelmaking furnace to produce iron oxide. It is an object of the present invention to provide a method for smelting steel used as an auxiliary raw material which effectively acts as a heat source without loss of iron content.

[0007]

Means for Solving the Problems The inventors of the present invention charged a powdered oxide briquette bonded by plastics into a steelmaking furnace and burned carbon and hydrogen in the plastics to dissolve the main raw material and melt iron. While trying to raise the temperature of molten steel,
The inventors have obtained the finding that the iron yield in a briquette can be improved by dissolving and reducing the iron content, and the inventors have made the following invention.

The first invention provides a method for smelting steel using pig iron / scrap as a main raw material and a refining material, characterized in that the following briquette is used as an auxiliary raw material. . (A) A powdery iron oxide is contained as a main component, and (b) A thermoplastic plastic is contained as a binder of the powdery iron oxide in an amount of 1 to 10 wt% based on the weight of the briquette. By forming the powdered iron oxide into a briquette of a thermoplastic, there is an advantage that the powdered iron oxide can be charged into the steelmaking furnace with high yield. As the plastic, waste plastic is desirable from the economical aspect and the resource recycling aspect.

A second aspect of the present invention provides a method for smelting steel, characterized in that the powdery iron oxide of the briquette is a briquette made of one or more of iron ore, mill scale, and ironmaking dust. . Iron ore, mill scale, and iron-making dust are typical powdered iron oxides, and by using these as briquettes, it is possible to effectively utilize them.

A third aspect of the present invention provides a method for smelting steel, characterized in that the briquette is a briquette in which a part or all of the powdery iron oxide, which is the main component, is made of steel cutting dust. It is possible to manufacture a briquette using a part or all of steel scrap generated in a machine factory in place of the powdery iron oxide, and to effectively use the briquette.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally, a method of smelting steel is to smelt steel from iron sources such as pig iron, scrap, and reduced iron in various steel making furnaces such as a converter, an open furnace, and an electric furnace. That is, pig iron or scrap is used as a main raw material, and carbon in the main raw material is removed by burning with oxygen,
The heat generated by oxidation melts and refines the main raw materials.

As pig iron, generally, hot metal produced in a blast furnace or pig iron in which it is solid is generally used. Scraps include commercial scraps that can be purchased in the market, return scraps that are generated in the process of steel mills, and reduced iron that is manufactured by the direct steelmaking method. In the melting of steel, in addition to removing the carbon contained in the pig iron and scrap, a refining material such as calcined lime is charged into the furnace, phosphorus,
Impurities represented by sulfur are removed.

The above is a general melting method for steel in a steelmaking furnace. In addition to main raw materials such as pig iron, powdered iron oxides such as ore powder, OG dust, magnetic separation powder, and mill scale, Steel cuttings generated in machine shops are also used. Of these, powdered iron oxides such as ore powder, OG dust, magnetic separation powder, and mill scale are scattered if they are charged as they are in the refining process and the yield is inferior. Therefore, in the present invention, the above powdered iron oxide is molded into a briquette. Charge.

As the powdery iron oxide which is the main component of briquette, there are various candidates such as mill scale and iron ore.
The OG dust and mill scales that are generated in the steelworks and can be recycled in the steelworks are advantageous in terms of cost. The component of the powdery oxide is not particularly limited as long as it contains iron oxide as the main component, and the particle size is not particularly limited, but if it is fine powder, there is some scattering loss in the briquette manufacturing process, Since it is not necessary to make briquette if it is a grain,
Iron oxide having a particle size of 10 mm or less is desirable. Plastic and iron oxide are mixed with a mixer or the like to form a briquette with a briquette machine.

Further, in place of the above-mentioned powdery oxide, steel cutting scraps generated in a machine shop or the like can be used. From the viewpoint of improving the iron yield, cutting wastes are more advantageous than iron oxide as the iron source because the amount of input per unit heat source can be increased.

In order to produce such briquettes, the present invention uses low cost plastic as a binder. The plastic needs to be a thermoplastic. This is because the waste plastic and the powdery oxide are kneaded in the briquette manufacturing process, and the frictional heat generated during the kneading can be used to melt the plastic to act as a binder.

As the plastic, waste plastic is desirable from the economical aspect and the resource recycling aspect. If the plastic content is 1 wt% or less, the briquette strength is insufficient, and if it is 11 wt% or more, the briquette strength is excessive, which is disadvantageous in terms of manufacturing cost.
It is preferably in the range of t%. The particle size of the plastic used is preferably about 1 to 10 mm in average diameter.

This is because if it is less than 1 mm, handling loss and scattering of fine particles due to wind will occur, which is unfavorable for the environment. This is because the residence time becomes long and the productivity decreases. The type of plastic is not particularly limited as long as it is a thermoplastic plastic such as polyethylene or polypropylene. Most of these are organic compounds, mainly composed of C, H, and O.

Plastics containing halogen elements such as chlorine and fluorine can also be used, but since gases such as HCl containing halogen are produced during use in the steelmaking process, exhaust gas is wet-collected to absorb halogen elements. It is necessary to perform treatment such as neutralizing the wastewater that has been generated.

Using the above-mentioned briquette as an iron source, the mixing ratio varies depending on the type of steelmaking furnace. In a converter, the content of scrap is usually up to about 15 wt% of the charged iron source, so that it is possible to charge up to this limit. However, in the electric furnace, 1
It is possible to charge up to 100 wt% scrap, so it is possible to charge up to this limit.

The charging timing is as follows:
Both can be performed during decarburization blowing, but when charging during blowing, it is necessary to complete charging a predetermined time before the end of blowing in order to secure the dissolution / reduction time. This predetermined time varies depending on the blowing conditions of the converter and the properties of the briquette, but it is generally about 3 to 5 minutes.

Since hydrogen is contained in the plastic as described above, hydrogen gas is generated if the plastic is decomposed after being put into the furnace. Therefore, when charging during decarburization blowing, the exhaust gas is sucked as OG gas, so that the concentration of CO gas generated by decarburization is stable and the oxygen concentration in the gas is high so that the gas composition does not fall within the explosion range. It is important to throw in when it is decreasing.

The critical oxygen concentration of explosion for hydrogen is 5 vo
It is conventionally known that the concentration is 1%, and if oxygen falls below this concentration, no explosion will occur. In a normal actual operation of a steelmaking furnace, the oxygen concentration in the furnace gas is 5 vol% or less, so there is no danger of the explosion.

On the other hand, in the case of an electric furnace, since electric power is used as a heat source, it is possible in principle to use up to 100% by weight, but coke or Fe-Si is used as a reducing agent for reducing iron oxide.
Since it is necessary to charge, etc., 30 wt.
Up to about% is realistic. In an electric furnace, the briquette is usually charged before the melting and refining process, but the present invention is not limited thereto. As in the case of the converter, if the time for dissolution and reduction is secured, there is no problem in charging during the melting and refining process.

[0025]

EXAMPLE As an example of the present invention, an example of using a briquette bonded with polyethylene as a plastic in melting steel in a converter will be described below. Table 1 shows the components of polyethylene, which is a waste plastic, and Table 2 shows the components of OG dust, which is mainly used as powdered iron oxide. These were kneaded with a high-speed kneader, and then compressed and molded with a press roll to produce a briquette.

The briquette has a standard grain size of 20 mm,
5 mm and 50 mm were also manufactured. The mixing ratio of the waste plastics was 1, 4, 6 or 9 wt% by weight. This is the economical mixing ratio for briquette production found during repeated tests in the briquette production process as described above.

There were two methods for charging briquettes into the converter. In the first method, before the molten iron was charged into the converter, it was charged into the furnace by using a scrap charging chute. In the second method, hoisting to the hopper-top of the converter,
It was added from above the furnace during decarburization blowing, that is, while blowing oxygen into the furnace.

Table 3 shows the facility capacity of the 250 ton top and bottom blowing converter used in this example. Table 4 shows the operating conditions and typical hot metal components in the examples of the present invention. In order to facilitate the comparison of iron yield improvement in the results shown here, the temperature of the molten iron charged and the temperature of the molten steel tapped are constant, and the scrap mixing ratio to the amount of molten hot metal is constant at 2 wt%. The amount was changed. Accordingly, the input amount of iron ore changed due to heat balance.

Next, a procedure for implementing the present invention will be described. If necessary, the hot metal after blast furnace tapping was subjected to a pretreatment using a mechanical stirring type desulfurization facility. In the first method, 25
A 0 ton converter was charged with 5 or 10 tons of the briquette, and ordinary scrap was also charged at the same time.

Subsequently, hot metal was charged, 4.6 tons of calcined lime and 4.6 tons of light-burnt dolomite were added as refining materials, and decarburization blowing was started. In the second method, decarburization blowing is started after charging scrap, hot metal and refining material as in the first method, and the CO concentration in the OG gas is about 78 vol after about 5 minutes from the start of blowing. %, When the oxygen concentration reached about 1 vol%, the briquette was charged at a rate of about 1 ton / min to 1
Tons or 4 tons was added.

Table 5 shows the results of melting steel under these conditions. As is clear from Table 5, the iron yield was improved and the OG gas recovery was increased as compared with the conventional operation. Secondary combustion ratio in the converter furnace (= (CO ₂ + H ₂ O) / (CO + CO ₂ +
H ₂ + H ₂ O)) is about 5 vol%, and the combustion ratio (= H ₂ O / (H ₂ + H ₂ O)) focusing only on hydrogen is about 1
It was 8 vol%.

In the present invention, the use of the briquette reduces the amount of iron ore used for heat balance.
However, the iron source in the briquette required less heat per unit amount of iron than the iron ore to dissolve and reduce, and it was possible to use more iron sources than the reduction in the amount of iron ore used.

In addition to that, there is an effect that the heat generated by the partial combustion of carbon and hydrogen in the waste plastic used as the binder in the furnace heats the molten iron / molten slag.
Further use of the briquette was possible. In this example, as a result of analyzing the heat balance, the heat deposition efficiency of the burned portion of the waste plastic was about 80%.

As a result of using extra oxygen for burning carbon and hydrogen in the waste plastic, the oxygen transfer time was extended within a range that does not hinder the operation, but the amount of OG gas recovered increased, The heat source in the waste plastic was recovered without waste, and the result was advantageous even when combined with the raw material of briquette and the manufacturing cost.

As is clear from Table 5, the effect of briquette charging did not depend on the charging method or particle size, but on the charging amount within the range of this embodiment. Further, when the mixing ratio of the waste plastics is increased, the iron yield tends to decrease, but the OG gas recovery amount increases, and the mixing ratio can be selected according to the situation.

In Example 13 of the present invention in which cutting waste was used as the iron source in addition to OG dust, and briquettes containing 40 wt% of iron in the briquette were used, in comparison with Example 11 of the present invention in which only OG dust was used. The yield is greatly improved. This is because in the case of cutting waste, the amount of heat required for melting is small, so that the amount of iron ore used due to the introduction of the briquette is small, and the iron content in the briquette is high.

In Example 14 of the present invention in which a powdery iron ore was used as an iron source, a calorie was required to dissolve and reduce the ore, so that the amount of iron ore used was greatly reduced as compared with Example 11 of the present invention. Therefore,
Although the amount of improvement in iron yield is also small, powdery iron ore is inevitably generated in the iron making process, and the fact that it can be used is a great industrial effect.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

[Table 5]

[0043]

As described above, according to the present invention,
In the steel smelting method that is usually carried out, by combining powdered iron oxide, which has been used alone as it is, with plastic and charging it into the steelmaking furnace as a briquette, it is possible to charge it into the steelmaking furnace with good yield. This is a very useful invention because hydrocarbon contained in plastic such as waste plastic can be used as a part of a heat source and can be recovered as reusable fuel gas.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Nakatsugawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Steel Tube Co., Ltd. (72) In-house 1-2-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd. (72) Inventor Shinichi Okimoto 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd. (72) Inventor Masafumi Ikeda 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Inside Steel Pipe Co., Ltd. (72) Hideo Futagawa, 429 Shinjo-dori Shijo-Kamitana-cho, Shinmachi-dori, Nakagyo-Ku, Kyoto Prefecture, Keihan Co., Ltd. Keihan Co., Ltd.

Claims (3)

[Claims] 1. A method for smelting steel using pig iron scrap and a refining material as main raw materials, wherein the following iron oxide briquette is used as an auxiliary raw material. (A) A powdery iron oxide is contained as a main component, and (b) A thermoplastic plastic is contained as a binder of the powdery iron oxide in an amount of 1 to 10 wt% based on the weight of the briquette. 2. The briquette powdered iron oxide is iron ore,
The method for smelting steel according to claim 1, characterized in that it comprises at least one of a mill scale and iron-making dust. 3. The method for smelting steel according to claim 1, wherein the briquette is a briquette in which a part or all of the powdery iron oxide as a main component is cutting scraps of steel.