JPH1150160A - Semi-reduced iron agglomerate and its production method and pig iron production method - Google Patents

Abstract

[PROBLEMS] To provide a semi-reduced iron agglomerate which can be used as a raw material for a vertical furnace and can reduce the fuel ratio, a method for producing the same, and a method for producing pig iron using the same. (1) The outer shell is mainly composed of metal Fe, and the inner core is F
e-oxide and free C are semi-reduced iron agglomerates having a double structure mainly composed of 70% or more by mass% of total Fe content,
A semi-reduced iron agglomerate having a metal Fe content of 20 to 50%, a free C of 5% or more, and a volume of 20 cm ³ or more.
(2) A method for producing a semi-reduced iron agglomerate in which a mixed raw material of a powdered iron raw material and a powdered solid reducing agent is agglomerated and fired in a reduction firing furnace. By agglomerating with a double roll compressor and firing in a rotary bed furnace, high quality semi-reduced iron can be obtained at low cost. (3) Pig iron is manufactured using the above-mentioned semi-reduced iron agglomerate as a raw material in a vertical furnace having a packed bed of a massive solid reducing agent in the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel sheet comprising a metal iron (Fe) having an outer surface covered with a high-strength metallic iron (Fe) shell, and a metal Fe, an oxide of Fe and free C (carbon present as a simple substance, not as a carbide). In the present specification, a semi-reduced iron agglomerate comprising a powder containing "free C") and a method for producing the same, and the semi-reduced iron agglomerate used as a raw material for a vertical furnace And a method for producing pig iron.

[0002]

2. Description of the Related Art As a method for producing pig iron, a rigid furnace having a packed bed of a solid reducing agent is used in a furnace, an iron raw material and a solid reducing agent (fuel) are charged from the furnace top, and air is blown from the lower part of the furnace. To burn a solid reducing agent to generate heat and a reducing gas, and to react a high-temperature reducing gas with an iron raw material in a furnace. The reducing gas rises toward the upper part of the furnace, and the iron raw material and fuel gradually move (unload) toward the lower part of the furnace.
In the meantime, heat exchange is performed between the high-temperature reducing gas and the iron raw material.

A typical example of this method is a blast furnace method. That is, in the blast furnace method, iron raw materials such as massive iron ore, fired pellets, and sintered ore, and a reducing agent such as coke are alternately charged into the furnace from the top of the blast furnace, and the furnace is placed around the furnace body at the lower part of the blast furnace. High-temperature air is blown inward, burning coke to generate higher-temperature reducing gas, reducing iron oxide, the main component of iron raw materials, and melting it to produce pig iron .

[0004] The method using such a solid furnace is characterized by extremely high energy efficiency and a low fuel ratio required for producing pig iron as compared with other methods. In this method, it is important to heat the iron raw material by heat exchange with a high-temperature reducing gas, that is, to balance the heat in the furnace height direction and to secure air permeability in the furnace. is there.

[0005] In producing pig iron in a compact furnace, as a raw material for iron, in addition to massive iron ore, fired pellets, sintered ore, cold bond ore, massive scrap and reduced iron are used.

[0006] Lumpy iron ore as an iron raw material is obtained by sieving and classification. The sintered ore is obtained by sintering a raw material obtained by mixing fine iron ore and coke fine with a great travel type air suction sintering facility. It is manufactured by baking with a great travel air suction baking facility or a rotary kiln baking facility. Cold bond ore is manufactured by adding cement to fine iron ore, mixing and molding, and then performing a curing treatment. .

[0007] Reduced iron is produced by putting iron ore or calcined pellets into a shaft furnace and introducing natural gas to reduce the iron ore. It is also produced by a method in which a mixed powder of an agent (for example, pulverized coal) is granulated and reduced by a rotary kiln baking facility or a rotating bed furnace facility in which a hearth rotates horizontally.

[0008] The rotary hearth facility in which the hearth rotates horizontally (hereinafter, the rotary hearth that horizontally rotates and moves is simply referred to as "rotary hearth", and the hearth of this furnace is referred to as "rotary hearth") The method of producing reduced iron by is a method that has attracted attention in recent years,
Details will be described below.

This rotary bed furnace is characterized by low equipment costs, unlike a traditional rotary kiln furnace (furnace used in rotary kiln baking equipment). It is necessary to pay attention to charging and discharging of products. As a typical example of the technology, a powdered iron ore is mixed with a solid reducing agent to form an agglomerate (pellet), which is heated to a high temperature to reduce iron oxide in the iron ore. (For example, U.S. Pat. No. 3,443,931 and JP-A-7-238307).

FIG. 1 is a schematic view showing an example of a conventional reduced iron production process in which heating is performed using a rotary bed furnace. As shown in the figure, bentonite as a binder is added to fine iron ore and fine coal, and water and tar are further added and mixed by a kneader. This mixed raw material is agglomerated by a pelletizer or a double-roll compressor, transferred to a raw material charging section of a rotary hearth furnace, charged into the furnace, and rotated once along with the movement of the hearth while the iron ore in the iron ore is rotated. Iron oxide is reduced at high temperature to form solid metallic iron. The obtained metallic iron is taken out from the discharge part.

In the above method for producing reduced iron, as the powdered iron raw material, in addition to the powdered iron ore, various dusts, sludges, scales, etc. containing iron generated in ironworks can be used. As the powdery solid reducing agent, coal, coke, char, oil coke and the like can be used.
These iron raw materials and solid reducing agents may be subjected to drying treatment and crushing treatment in some cases.

The powdered iron raw material and the powdered solid reducing agent are then kneaded. At this time, if necessary, water as a binder, tar, molasses, organic resin, cement, slag, bentonite, quicklime, Light dolomite and slaked lime are added.

The kneaded raw material is agglomerated into spherical pellets by a desk pelletizer or briquettes by a double roll compressor. In this case, a raw material having a particle size of 0.1 mm or less is suitable for forming a pellet, and a briquette having a particle size of 1 mm or less is suitable. . Further, in order to increase the strength of the agglomerate (refer to the above-mentioned pellets and briquettes), a drying treatment or a curing treatment may be performed after the agglomeration.

The agglomerates obtained are conveyed to the upper part of a rotary hearth on a belt conveyor, from where they are charged using a charging chute so as to be widely distributed on the rotary hearth and leveled by a leveler. Subsequently, it is reduced by heating while moving in the furnace and becomes metallic iron.

In the rotary bed furnace, a fuel gas and air are fed into the furnace and burned to maintain a furnace temperature of 1100 to 1400 ° C. The above-mentioned agglomerates are spread one by one on the hearth of this rotary hearth furnace, and the temperature is raised to 900 ° C. or more mainly by radiant heat from the furnace inner wall. The reduction sintering is performed while adjusting the rotation speed of the hearth so as to reach the rate, and the mixture is discharged from the discharge section with a screw feeder.

In the above-described method for producing pig iron using the vertical furnace, as described above, it is important to ensure air permeability in the furnace, so that the iron raw material charged from the furnace top is not powdery. It is indispensable to have a lump shape and a strength that does not cause powdering.

In addition, a large endothermic occurs during a reduction reaction in which oxygen is removed from iron oxide, which is a main component of an iron raw material, to form metallic iron, and a large amount of heat is generated during an oxidation reaction in which metallic iron becomes iron oxide. Therefore, when an iron raw material (iron oxide raw material) such as iron ore, sintered ore, and fired pellets is used, there is a problem that a reduction endothermic occurs, and the raw material charged from the upper part of the furnace is difficult to rise in temperature. To cope with this, high-temperature or oxygen-enriched air is blown from the lower part of the furnace to increase the temperature inside the furnace and raise the furnace height (that is, make it a blast furnace) to reduce the charge and the high-temperature reducing gas. To ensure the heat exchange time.

On the other hand, in the case of raw materials (metallic iron raw materials) such as scrap and reduced iron (DRI (direct reduced iron), HBI (hot briquette reduced iron)), there is no such problem of reduction endothermic in macroscopic view. However, there are some problems as follows. That is, the oxidizing gas such as CO ₂ and H ₂ O generated by the combustion reaction due to the blowing from the lower part of the furnace or the reduction of other iron oxides is contained in the gas generated in the hard furnace. However, especially in the upper part of the furnace, the operation of reducing the gas temperature as much as possible to protect the raw material charging equipment and the exhaust gas treatment equipment is performed, and the ratio of CO ₂ and H ₂ O in the upper part of the furnace is high. Under such conditions, scrap and reduced iron (DRI, HBI)
Such a metal iron material is reoxidized in the upper part of the furnace and generates heat, so that there is a problem that the gas temperature becomes high. In order to lower the temperature of the gas discharged at this high temperature, operations such as lowering the temperature of the lower part of the furnace are performed, but the reoxidized metallic iron is unloaded to the lower part of the furnace, where it is reduced. In this case, a problem may occur that heat is absorbed and the furnace temperature is lowered.

As described above, in a rigid furnace, an endothermic reaction is preferred in the upper part of the furnace and disliked in the lower part of the furnace. Therefore, when iron oxide raw materials such as iron ore, sintered ore, and fired pellets are used, A large reduction endothermic in the lower part of the furnace poses a problem. On the other hand, when metallic iron raw materials such as scrap and reduced iron are used, the problem is small compared to the problem with iron oxide raw materials, but the oxidative heat generation phenomenon at the upper part of the furnace and the reduction endothermic of reoxidized iron at the lower part of the furnace become problems. .

[0020]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems in producing pig iron using a vertical furnace. Its specific purpose is that when used as a raw material for a vertical furnace, it can maintain a good heat balance in the furnace without causing heat absorption in the lower part of the furnace and heat generation in the upper part of the furnace, reducing the fuel ratio. It is an object of the present invention to provide a semi-reduced iron agglomerate and a method for producing the same, and a method for producing pig iron using the semi-reduced iron agglomerate.

[0021]

As a result of various studies, the present inventors have found that the outside is covered with a high-strength metallic Fe shell, and the inside contains metallic Fe, an oxide of Fe and free C. Double structure consisting of powder, all Fe, metallic Fe
It has been confirmed that the above object can be achieved by using a semi-reduced iron agglomerate whose free C content satisfies predetermined conditions as a raw material for a vertical furnace, and has accomplished the present invention.

The gist of the present invention resides in the following (1) semi-reduced iron agglomerate, (2) its production method, and (3) pig iron production method. In addition, “%” representing the content of the component of the semi-reduced iron agglomerate means “mass% (mass%)”.

(1) The outer shell is mainly composed of metal Fe, and the inner core is a semi-reduced iron agglomerate having a double structure mainly composed of metal Fe, Fe oxide and free C, and the total Fe content is 70%. %
As described above, the semi-reduced iron agglomerate characterized in that the metal Fe content is 20 to 50%, the free C content is 5% or more, and the volume is 20 cm ³ or more.

(2) The semi-reduced iron agglomerate according to (1), wherein the mixed raw material of the powdered iron raw material and the powdered solid reducing agent is agglomerated and fired in a reduction firing furnace. Production method.

(3) A massive iron raw material containing at least the semi-reduced iron agglomerate according to the above (1), a massive solid reducing agent and a flux are provided in a furnace with a packed bed of the massive solid reducing agent. The vertical furnace is charged from the upper part of the furnace, and oxygen-containing gas is blown from the tuyeres installed at the lower part of the furnace to burn the solid reducing agent in front of the tuyeres. A method for producing pig iron, comprising dissolving ore and flux, reducing unreduced iron oxide contained in semi-reduced iron agglomerate, and carburizing.

Here, the term "powder iron raw material" refers to a powdery iron raw material containing iron oxide as a main component, and more specifically, a powdery iron ore or a dust containing iron generated at an ironworks. , Sludge (eg, sintering machine generated dust, blast furnace generated dust, converter generated dust, rolling plant generated sludge), scale, and the like. In the present invention, these can be used alone or in a mixture of two or more.

The "powder solid reducing agent" is a powder of a solid substance mainly containing carbon such as coal, coke, char, and oil coke. These can also be used alone or in combination of two or more.

In the above method (2) for producing a semi-reduced iron agglomerate, the agglomeration is carried out by molding with a double roll compressor, and the calcination is carried out in a rotary bed furnace. Mineral ore can be produced at low cost.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention (the above (1) to (1))
The invention (3) will be described in detail.

According to the invention of (1), the outer shell is a semi-reduced iron agglomerate having a double structure mainly composed of metal Fe, and the inner core is mainly composed of metal Fe, Fe oxide and free C. The total Fe content in the entire semi-reduced iron agglomerate including the inner core is 70% or more, the metal Fe content is 20 to 50%, and the free C
Is 5% or more and has a volume of 20 cm ³ or more. That is, this half-reduced iron is covered with a high-strength metallic iron shell on the outside and made of powder containing metal Fe, Fe oxide and free C, and is used as a raw material for a vertical furnace described later. When used, they are in the form of granules or lumps in order to maintain the air permeability in the furnace.

In the semi-reduced iron agglomerate of the present invention, the reason why the outer shell is made of metallic iron is that a strong impact on the semi-reduced iron occurs during transportation until charging into the solid-state furnace and handling in the furnace. Since a force is applied, a high strength to withstand this impact force is obtained.

In the semi-reduced iron of the present invention, the content of free C is set to 5% or more because if it is less than 5%, the reducing action inside the semi-reduced iron is weak, and iron oxide remains even after firing. This is because when half-reduced iron is used as a raw material for a vertical furnace, an endothermic reaction (reduction) occurs in the lower part of the furnace. Although the upper limit of the free C content is not particularly defined, the iron quality (Fe content 7
(0% or more) is preferably set to 10%.

The reason why the content of metallic Fe is set to 20 to 50% is that if it is less than 20%, the strength of the semi-reduced iron is weak because the thickness of the metallic iron of the outer shell is thin, and when used in a vertical furnace, If it exceeds 50%, on the other hand, if it exceeds 50%, the amount of iron oxide inside becomes too small, and the reaction with free C does not sufficiently occur. CO
This is because the amount of generated gas is reduced.

The reason why the total Fe content is set to 70% or more is as follows.
If the total Fe content is 70% or more, the amount of other elements contained as impurities is small, the energy consumed for reducing the oxide of the element is small, and the free C is relatively small (however, This is because the metal Fe is increased (however, 50% or less) and higher energy efficiency is obtained, and the fuel ratio of the vertical furnace can be further reduced. The upper limit is not particularly limited. This is because iron oxide is mainly composed of FeO, and the content of metallic Fe is limited to 20 to 50%, and the content of free C is limited to 5% or more (preferably 10% or less). Therefore, the upper limit is determined by itself.

The semi-reduced iron of the present invention must further have a volume of 20 cm ³ or more. It is necessary to have a certain size (particle size) as a particle or a lump from the viewpoint of securing the air permeability in the hard furnace, and if the lower limit is expressed by volume, 20 cm ³ This is because There is no particular upper limit, but 150 cm ³
The following is desirable. If it is too large, heat conduction to the center of the half-reduced iron in the lower part of the furnace will be poor, and the melting rate will be reduced.

The semi-reduced iron of the present invention is different from the cold bond ore of carbonaceous material interior which is secured with cement, and even if it is maintained at a high temperature, powdering due to brittleness of cement found in the cold bond ore is performed. Will not occur.

When the semi-reduced iron agglomerate of the present invention is used as a raw material for a vertical furnace, it is possible to maintain a good heat balance in the furnace and reduce the fuel ratio, as described later.

The invention of (2) is a method for producing a semi-reduced iron agglomerate according to the invention of (1), wherein the mixed raw material of the powdered iron raw material and the powdered solid reducing agent is agglomerated, Firing method.

As the powdered iron raw material and the powdered solid reducing agent, as described above, powdered iron ore, coal and the like can be used.

Agglomeration can be performed by pelletizing with a desk pelletizer, briquetting with a double roll compressor, etc.
What is necessary is just to carry out by the method used conventionally.

The raw material subjected to agglomeration (forming raw material) is charged into a rotary kiln or a rotary hearth furnace,
At a furnace temperature of ~ 1400 ° C, metal Fe content is 20 ~ 5
0% (that is, the metallization ratio is 20 to 50%), the residual C
It is reduced and fired until (free C) becomes 5% or more, discharged out of the furnace and quenched, or cooled using N ₂ gas so as not to be reoxidized to be semi-reduced iron.

In the above method (2) for producing a semi-reduced iron agglomerate, if the agglomeration is carried out by molding with a double roll compressor, the particle size of the raw material before compaction is greater than in the case of pelletization. However, no fine grinding equipment is required, and no drying equipment for increasing the strength of the pellets is required, so that the cost of agglomeration can be significantly reduced.

If the reduction firing is performed in a rotary bed furnace, it is easy to form a high-strength shell metal iron, and it is possible to produce a higher quality half-reduced iron. This is because when a rotary kiln furnace is used, the forming raw material is subjected to a rolling operation, whereas in a rotary bed furnace, the forming raw material can be fired while being left standing on the hearth. This makes it possible to further reduce the fuel ratio of the rigid furnace.

Further, assuming the production of semi-reduced iron having a volume of 20 cm ³ or more, it was manufactured by a double roll compressor that applies a larger force than a spherical pellet manufactured by a dish granulator. Briquettes are more densely agglomerated, so forming into briquettes with a double-roll compressor is more advantageous for producing high-strength semi-reduced iron.

The invention of (3) is a method for producing pig iron using the semi-reduced iron agglomerate of (1) as a raw material.

As a smelting furnace used in this method, as represented by a blast furnace, a massive solid reducing agent (carbon material) is contained in the furnace.
Using a vertical furnace having a packed bed of, a half-reduced iron agglomerate, a massive solid reducing agent and a flux were charged from the upper part of the furnace, and oxygen-containing gas was blown from a tuyere installed at the lower part of the furnace. The carbonaceous material in front of the tuyere is burned, the half-reduced iron and the flux are dissolved by the generated high-temperature reducing gas, and the unreduced iron oxide contained in the half-reduced iron is reduced and carburized.

When half-reduced iron is charged from the upper part of the hard furnace, CO ₂ gas and H ₂ O gas are used in the upper part of the furnace.
First, the metallic iron in the outer shell undergoes re-oxidation and generates heat. This heat is transmitted to the inside of the semi-reduced iron, where the free C reduces Fe oxide and generates CO gas. The reduction of the Fe oxide in this case involves a large endotherm, but is compensated by the heat generated by the reoxidation of the metallic iron in the outer shell. Furthermore, since the reoxidized outer shell of the semi-reduced iron that has reached the lower part of the furnace after being unloaded is reduced by the CO gas generated inside, there is almost no need for reduction by the ventilation gas in the rigid furnace, and low It can operate at the fuel ratio.

As described above, when the semi-reduced iron agglomerate of the present invention is used as a raw material in a solid furnace, free C
And the presence of Fe oxide, it is possible to maintain a better heat balance in the furnace than in the case of using reduced iron having a high metallization ratio and almost all composed of metallic iron.

Although the half-reduced iron of the present invention may be used for the whole amount of the raw materials used in the vertical furnace, a part of the raw materials may be replaced with the half-reduced iron of the present invention. Further, the half-reduced iron of the present invention may be charged into a vertical furnace at a high temperature without any problem.In fact, since the heat held by the half-reduced iron can be effectively used for reduction and melting in the vertical furnace, desirable.

The gas generated from the rigid furnace is recovered,
At least a part thereof may be used as a fuel for producing semi-reduced iron.

[0051]

EXAMPLE After mixing the fine iron ore shown in Table 1 and the fine coal shown in Table 2 at the mixing ratio shown in Table 3, the mixture was formed into pellets or briquettes, and then reduced and calcined (using a rotary kiln or rotary bed furnace). ), And sintering was performed with the sintering time changed to produce semi-reduced iron agglomerate. The rotary kiln used had a diameter of 5 m, a length of 80 m, a rotation speed of 8 rpm, and a furnace temperature of 1200 ° C. Table 4 shows the equipment specifications and operating conditions of the rotary bed furnace. The half-reduced iron thus obtained is charged into a compact furnace (capacity: 820 t / d) together with a carbon material (coke) and a flux (limestone), and reduced and melted to produce pig iron. The fuel ratio was determined for each of the production conditions and compared. In this case, half reduced iron was used for the entire amount of the raw material of the vertical furnace.

Table 5 shows the production conditions and properties of the semi-reduced iron used in the comparative study.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

Sample No. 1 and sample no. 2 is
This is semi-reduced iron obtained by producing pellets having different volumes from a fine iron ore and fine coal by using a 7.5 m diameter dish-shaped pelletizer, and calcining the pellets in a rotary kiln for varying firing times.

Sample No. 3 to sample no. 9 is
This is semi-reduced iron obtained by producing a Macek-type briquette with a double roll compressor and firing it in a rotary bed furnace. In this case, the sample No. 3 to sample no. In No. 8, the metallization ratio of the outer shell of the semi-reduced iron and the residual amount of C in the inner core were adjusted by changing the firing time, and the total Fe content, metal Fe content, and free C The content was changed. In addition, the sample No. In No. 9, the volume was changed to a large briquette.

Next, using each of these samples as a raw material, a compact furnace was operated under the conditions shown in Table 6 to produce pig iron. Table 7 shows the fuel ratio of the vertical furnace at this time.

[0061]

[Table 6]

[0062]

[Table 7]

When a raw material composed of iron oxide such as sinter or pellets or iron ore is used, the fuel ratio is usually 480.
550 kg / p (pig iron) -t,
o. 1 to No. In the case of using reduced iron as shown in FIG.
As shown, pig iron can be produced with a very low fuel ratio.

In particular, it can be seen that semi-reduced iron agglomerates satisfying the conditions defined in the present invention are extremely effective in reducing the fuel ratio of the solid-state furnace. Alternatively, briquettes are manufactured from a mixed powder of coal and iron ore using a double-roll compressor, and then baked in a rotary bed furnace to form semi-reduced iron.Then, pelletized using a dish-shaped pelletizer, and baked in a rotary kiln. This is more effective in reducing the fuel ratio than when using half reduced iron.

[0065]

According to the present invention, if the semi-reduced iron agglomerate of the present invention is used as a raw material for a vertical furnace and pig iron is manufactured, the heat balance in the furnace can be prevented without heat absorption at the lower part of the furnace and heat generation at the upper part of the furnace. Can be kept good, and the fuel ratio of the vertical furnace can be reduced. This semi-reduced iron agglomerate can be easily produced by the method of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a conventional reduced iron production process performed using a rotary hearth furnace.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Masahiko Hoshi 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Inside Sumitomo Metal Industries, Ltd.

Claims (3)

[Claims] 1. The outer shell is mainly made of metal Fe, and the inner core is made of metal F
e, a reduced iron agglomerate having a double structure mainly composed of Fe oxides and free C, and having a total Fe content of 7% by mass.
A semi-reduced iron agglomerate characterized by having a metal Fe content of 0% or more, a Fe content of 20 to 50%, a free C content of 5% or more, and a volume of 20 cm ³ or more. 2. The method for producing a semi-reduced iron agglomerate according to claim 1, wherein the mixed raw material of the powdered iron raw material and the powdered solid reducing agent is agglomerated and fired in a reduction firing furnace. . 3. A block-shaped iron raw material containing at least the semi-reduced iron agglomerate according to claim 1, a block-shaped solid reducing agent and a flux, and a furnace having a packed layer of the block-shaped solid reducing agent in a furnace. The furnace is charged from the upper part of the furnace, the oxygen-containing gas is blown from the tuyeres installed in the lower part of the furnace, and the solid reducing agent in front of the tuyeres is burned. A method for producing pig iron, comprising dissolving a flux, reducing unreduced iron oxide contained in semi-reduced iron agglomerate, and carburizing the iron oxide.