JP2001323310A - Method for producing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reduced iron production method in which a charging quantity of an atmosphere adjusting material is reduced and the reoxidation of the reduced iron is prevented in a furnace suppressing impurities such as ash content of carbonaceous material in the reduced iron. SOLUTION: In the rear half part of a heating part in a rotary hearth furnace, the atmosphere adjusting material consisting essentially of carbon component, such as coal, is laid on the upper part of an agglomerate bed by utilizing the gravity from a space at the upper part of the agglomerate bed.

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 reduced iron by reducing agglomerates comprising a powdery iron oxide-containing substance and a powdery carbonaceous reducing material using a rotary hearth furnace. In particular, the present invention relates to a technique for preventing reoxidation of reduced iron in a reduction period.

[0002]

2. Description of the Related Art In recent years, as the production of steel products using an electric furnace has become popular, the demand for reduced iron has been increasing due to the tight supply and demand of scrap, which is the main raw material, and the demand for the production of high-grade steel in electric furnaces. .

[0003] As one of the processes for producing reduced iron, a powdered iron ore is mixed with a carbonaceous material such as powdered coal or coke to form agglomerates, for example, pellets, which are then put into a rotary hearth furnace. A method of reducing iron oxide in iron ore to obtain solid metallic iron (reduced iron) by charging and heating it to a high temperature has attracted attention (for example, Japanese Patent Application Laid-Open No. 45-19569,
JP-A-11-279611).

An example of a conventional process for producing reduced iron using a rotary hearth furnace will be described with reference to a schematic diagram of the equipment configuration of a conventional rotary hearth furnace shown in FIG.

[0005] 1) A powdered iron oxide-containing substance and a powdery carbonaceous reducing material are mixed and granulated to produce raw pellets.

[0006] 2) The raw pellets are heated to a temperature range in which flammable volatiles generated in the pellets do not ignite to remove adhering moisture, thereby obtaining dried pellets (raw material a).

[0007] 3) The dried pellets (raw material a) are supplied into a rotary hearth furnace 4 by using a suitable charging device 3 to form pellets having a thickness of about one or two pellets on the rotary hearth 1. Form a layer.

4) The pellet layer is reduced by radiant heating by combustion of a burner 5 installed in the upper part of the furnace to promote metallization.

5) The metalized pellet is cooled by the cooler 6. In this case, the cooling is performed by directly blowing gas onto the pellets, or indirectly cooling with a water-cooled jacket. It is discharged out of the furnace by (2).

6) Immediately after discharging the metalized pellets (reduced iron b), dry pellets (raw material a) are charged and the above process is repeated.

The above-mentioned dried pellets (hereinafter simply referred to as pellets) are reduced by the carbonaceous reducing material (hereinafter referred to as carbonaceous materials) in the pellets. However, since the reduction reaction is an endothermic reaction, heat is externally applied to the pellets. It needs to be supplied. Therefore, in a rotary hearth furnace, heat is supplied by combustion of a burner. In this case, when the oxidizing gas such as O ₂ required for combustion and CO ₂ or water vapor (H ₂ O) generated by combustion comes into contact with the surface of the reduced pellet, 2Fe + O ₂ → 2Fe
O, Fe + CO ₂ → FeO + CO, Fe + H ₂ O → Fe
The metal iron is rapidly reoxidized by the reaction represented by the reaction formula of O + H ₂ .

Conventionally, in order to suppress this re-oxidation, a carbon material in an amount more than necessary to reduce iron oxide is provided in the pellets, excess carbon material is left in the reduced iron, and the reduced iron surface layer is removed. There is a method of reacting the excess oxidizing gas (O ₂ , CO ₂ , water vapor (H ₂ O)) with the excess carbon material in a part, and a method of reducing the oxidizing power of the combustion gas by making the combustion of the burner incomplete combustion. Had been.

[0013]

In order to suppress re-oxidation, the strength of raw pellets and dried pellets is reduced when pellets contain more carbon material than is necessary to reduce iron oxide. Then, it is easy to pulverize at the time of transfer to a dryer or a reduction furnace or at the time of charging, and since excess carbon material remains, the strength of the reduced iron is also reduced and easily pulverized at the time of discharge from the reduction furnace. Furthermore, there is a problem that the carbonaceous ash content in the reduced iron increases and the grade of the reduced iron decreases.

[0014] Further, if the combustion of the burner is regarded as incomplete combustion in order to reduce the oxidizing power of the combustion gas, the temperature of the combustion gas decreases and the unit consumption of fuel increases.

Japanese Patent Application Laid-Open No. H11-217613 proposes a method of reducing the linear velocity of a combustion gas near a pellet in order to prevent an oxidizing gas from contacting the pellet.
In order to generate a high temperature, it is necessary to generate a large amount of combustion gas, and it is substantially difficult to control to a low linear velocity.

Furthermore, Japanese Patent Application Laid-Open No. H11-269521 proposes a method of spraying methane or a methane-containing gas onto the surface of a pellet in order to reduce the oxidizing power of the gas near the pellet, but requires expensive methane or the like. In addition, heat loss increases due to the necessity of expensive water-cooling structure blowing equipment for spraying methane and the like onto the pellet surface, and the necessity of installing this water-cooling structure equipment in a rotary hearth furnace. There are problems such as things.

Further, in Japanese Patent Application Laid-Open No. 11-61215, in order to reduce the amount of interior carbonaceous material, an exterior carbonaceous material together with pellets is charged into a rotary hearth furnace, and the pellets are buried in at least half of their diameter in this exterior carbonaceous material. However, it is necessary to cool a large amount of the exterior carbonaceous material once heated in the furnace and circulate it for use. There is a large loss of sensible heat.

Furthermore, Japanese Patent Application Laid-Open No. Hei 10-251723 proposes a method of charging pellets coated with a carbon material into a rotary hearth furnace, which complicates the granulation process and adds carbon to reduced iron. Grade decreases due to increase in ash content.

Accordingly, the present invention provides a reduction method which can reduce the amount of an atmosphere control material such as a carbon material and prevent reoxidation of reduced iron in a furnace without increasing impurities such as carbon material ash of reduced iron. An object of the present invention is to provide an iron manufacturing method.

[0020]

According to a first aspect of the present invention, a rotary hearth furnace is used to reduce and reduce agglomerates formed by mixing a powdery iron oxide-containing substance and a powdery carbonaceous reducing material. A method for producing reduced iron, wherein an atmosphere adjusting material is placed on the agglomerate bed in the method for producing iron.

The invention according to claim 2 is characterized in that the portion on which the atmosphere adjusting material is placed is the latter half of the heating section in the rotary hearth furnace.

A third aspect of the present invention is characterized in that the atmosphere adjusting material is a material having a carbon component as a main component.

The invention according to a fourth aspect is characterized in that the atmosphere adjusting material is coal and has a volatile content of 40% or less.

According to a fifth aspect of the present invention, the ash content of the coal is 30%.
% Or less and the melting point of the ash is 1200 ° C. or more. The “%” of volatile and ash means “% by mass on a dry basis by industrial analysis”, and the melting point of ash is J
According to IS-M8812.

The invention of claim 6 is characterized in that the atmosphere adjusting material introduced into the rotary hearth furnace is placed on the agglomerate bed by using gravity from the space above the agglomerate bed. And

The invention according to claim 7 is characterized in that the particle size of the atmosphere control material is in the range of 0.05 to 10 mm.

As described above, since the atmosphere adjusting material is preferentially reacted with the oxidizing gas by being placed on the agglomerate bed, reoxidation of reduced iron in the furnace can be prevented even with a small amount of the atmosphere adjusting material. .

Further, by placing the atmosphere adjusting material in the latter half of the heating section in the rotary hearth furnace, the atmosphere adjusting material can be used as compared with the case where it is placed before entering the heating section or in the first half of the heating section. Attrition can be greatly reduced, and the maximum amount of reduced iron reoxidation can be prevented with the minimum amount of atmosphere control material at the site where the agglomerates are almost reduced to reduced iron.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below in detail with reference to FIG. 1 which is a schematic diagram of the equipment configuration of a reduced iron production process using a rotary hearth furnace according to the present invention.

The raw materials used include iron oxide-containing substances,
Coal, coke, oil coke and the like can be used as carbonaceous reducing agents such as iron ore, blast furnace dust, steelmaking dust, electric furnace dust and mill scale. The mixing ratio of the carbonaceous reducing agent to the agglomerate may be such that only the amount of carbon necessary to reduce iron oxide in the agglomerate to metallic iron is incorporated. For example, when iron ore is used as the iron oxide-containing substance and coal is used as the carbonaceous reducing agent, the iron ore is blended in an amount of about 23 to 18% by mass with 77 to 82% by mass of iron ore according to their chemical composition. What is necessary is just to adjust a ratio. If necessary, these are pulverized to about -0.1 mm, pulverized and mixed, and formed into pellets or briquette-like agglomerates a having a size of about 10 to 25 mm to form a rotary hearth furnace 4.
To charge. At the time of molding, a binder such as bentonite, starch, slaked lime, and an organic binder may be added as necessary. When water is added at the time of molding, the carbonaceous reducing agent may be dried at a temperature of about 200 ° C. or less at which it does not ignite, and then charged into a rotary hearth furnace.

The agglomerate a is supplied to the rotary hearth furnace 4 by using a suitable charging device 3 and the agglomerate 1 is placed on the rotary hearth 1.
Form an agglomerate bed having a thickness of about 2 or so.
The agglomerate bed is heated up to about 1350 ° C. by the radiant heat of the combustion gas of the burner 5 installed above the furnace in the furnace with the rotation of the hearth. It is reduced and becomes reduced iron b in 7 to 13 minutes. The reduced iron b is cooled down to 1000 ° C. or less in the furnace and discharged out of the furnace, and then directly charged into the melting furnace, heated into briquettes, or temporarily stored in a storage tank and completely stored. After being cooled down, it is divided into products that become products as they are.

When the temperature of the agglomerate becomes 1000 ° C. or more, the agglomerate containing the carbonaceous material becomes C + CO 2 as shown in FIG.
_The solution loss reaction expressed by the reaction formula of ₂ → 2CO is activated, and a large amount of CO-rich gas is generated from the agglomerate, so that the agglomerate in the agglomerate bed is less affected by the burner combustion gas atmosphere. The iron oxide is metallized without reduction. However, the amount of gas generated from the agglomerates decreases rapidly from the latter half of the reduction to the last stage of the reduction, and the surface layer of the agglomerates is reoxidized by the combustion gas from the burner, so the metallization rate decreases. .

According to the present invention, an agglomerated material is placed on the agglomerate bed by causing the oxidizing gas in the combustion gas to preferentially react with the atmosphere adjusting material in the final stage of reduction. The metal iron in the surface layer has little oxidizing power or is prevented from being reoxidized by being covered with a reducing gas to improve the metallization ratio. In the conventional method of burying part of the agglomerate in the exterior carbon material, the thickness of the exterior carbon material was required to be at least half the diameter of the agglomerate in order to prevent the re-oxidation of the surface layer portion of the agglomerate. However, in the present invention, since it is placed on the agglomerate, reoxidation can be prevented with a small amount of the atmosphere adjusting material.

It is desirable that the atmosphere adjusting material be placed on the agglomerate bed in the latter half of the heating section in the rotary hearth furnace. Here, the “heating unit” refers to a region that receives radiant heating by burner combustion. In the first half of the heating section, the burner is completely burned in order to raise the temperature of the agglomerate in the shortest possible time.
Since air for secondary combustion of O is blown in, a gas atmosphere having a strong oxidizing power is consumed in this portion, so that an atmosphere adjusting material to be mounted is consumed. In order to avoid this, if an atmosphere adjusting material is placed in the latter half of the heating section, reoxidation of reduced iron in the final stage of the reduction period can be effectively prevented. FIG. 4 shows a region in the second half of the heating unit where the atmosphere adjusting material is placed.

The atmosphere adjusting material is an oxidizing gas (O ₂ , CO ₂₎ .
_2. Any solid substance that easily reacts with water vapor (H ₂ O) can be used, for example, coal, coke, oil coke, waste plastic, aluminum dross containing metal Al, metal Si containing carbon as a main component. Inexpensive materials and wastes, such as waste silicon wafers containing as a main component, can be used. In particular, when a substance mainly composed of a carbon component is used, the oxidizing gas is changed to 2C + O ₂ → 2CO, C + CO
₂ → 2CO, C + H ₂ O → CO + H _{2 The} reaction represented by the reaction formula is reformed into CO and H ₂ as reducing gases, so that the effect of preventing re-oxidation is further enhanced.

When coal is used as the atmosphere control material, the volatile content is 40% in order to reduce a decrease in the atmospheric temperature due to a pyrolysis reaction in which volatiles are vaporized when the coal is charged into the furnace. Below, preferably 30% or less, more preferably 20% or less. Furthermore, when coal is charged into the furnace, the coal adheres to the reduced iron so that adhesion to the furnace wall is reduced as much as possible and the separated iron and coal after discharge from the furnace are easily separated. In order to avoid this, the ash content of the coal is 30% or less, preferably 20% or less, more preferably 15% or less, and the melting point of the ash is 1200 ° C or more, preferably 1300 ° C or more, more preferably 1400 ° C or more. I just need.

The required amount of the atmosphere adjusting material varies depending on the type, the particle size, and the portion to be charged of the atmosphere adjusting material. However, even when the reduced iron is discharged, the atmosphere adjusting material remains to some extent, and the metallization ratio of the reduced iron is reduced. What is necessary is just to adjust suitably within the range which can be maintained high.

As shown in FIG. 2, for example, as shown in FIG. 2, the atmosphere adjusting material is quantitatively cut out from a hopper 8 installed above a portion corresponding to a heating section of a rotary hearth furnace by a commonly used cutting device 9 such as a vibration feeder or a drum feeder. The chute 10 provided at the lower part of the cutting device 9 and covering the entire furnace width of the hearth disperses from the ceiling part 12 of the rotary hearth furnace to the hearth upper space in the furnace so as to be substantially uniform over the entire furnace width. Supply. The supplied atmosphere adjusting material c descends by gravity and is placed on the agglomerate bed a over the entire furnace width. Note that the burner 5 is used so that the atmosphere adjusting material c is not oxidized and consumed as much as possible in the space above the hearth.
It should be supplied from a site that does not come into direct contact with the flame. When the furnace width is wide, a plurality of supply devices and chutes may be installed in the furnace width direction. As shown in FIG. 3, instead of the supply from the rotary hearth furnace ceiling 12, the atmosphere is adjusted using the carrier gas d from the outer peripheral wall and / or the inner peripheral furnace wall 13 of the rotary hearth furnace. The material c may be blown into the upper space of the agglomerate bed a and placed on the agglomerate bed by gravity drop. By appropriately adjusting the position (height from the upper surface of the agglomerate bed) of the inlet 14 of the furnace wall 13, the blowing angle, the carrier gas flow rate, etc., according to the furnace width and the particle size configuration of the atmosphere adjusting material c. The atmosphere control material c can be dispersed and placed over the entire furnace width direction. However, in this method as well, it is necessary to avoid a blowing position, a blowing angle, and the like that directly contact the flame of the burner 5 as described above.

The particle size of the atmosphere control material is 0.05 to 10 m
m, preferably 0.1 to 5 mm, more preferably 0.1 to 5 mm.
What is necessary is just to set it as the range of 2-3 mm. If the particle size is too small, the amount of scattering loss outside the system together with the rotary hearth furnace exhaust gas without being placed on the agglomerate bed increases.On the other hand, if the particle size is too large, This is because the specific surface area of the mounted atmosphere adjusting material is reduced, so that the amount of reaction with the oxidizing gas is reduced, and the effect of preventing reoxidation of reduced iron is reduced.

The atmosphere control material placed on the agglomerate bed reacts preferentially with the oxidizing gas and prevents reoxidation of the reduced iron, thereby obtaining reduced iron with a high metallization ratio. The atmosphere control material remaining at the upper part of the agglomerate bed without reacting with the oxidizing gas is discharged out of the furnace together with the metallized agglomerate (reduced iron) and separated from the reduced iron by sieving or magnetic separation. It is reused as an adjusting material, an agglomerated interior reducing material (when the atmosphere adjusting material is a material mainly containing a carbon component such as coal), and the like.

[0041]

As described above, according to the method for producing reduced iron according to the present invention, in which the atmosphere adjusting material is placed on the agglomerate bed, the amount of the atmosphere adjusting material used can be reduced. In addition, reoxidation of reduced iron can be effectively prevented, and reduced iron can be produced at low cost with a high metallization ratio and low carbon material ash.

Further, by placing the atmosphere adjusting material in the latter half of the reduction period in the rotary hearth furnace, the consumption of the atmosphere adjusting material can be reduced, and the reoxidation of the reduced iron can be more effectively prevented.

Since the oxidizing gas is reformed into a reducing gas by using a material having a carbon component as a main component, such as coal, as an atmosphere adjusting material, the effect of preventing reoxidation of reduced iron is further enhanced.

By placing the atmosphere adjusting material on the agglomerate bed by using gravity from the space above the agglomerate bed, the above effects can be obtained with simple equipment.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an equipment configuration of a reduced iron production process using a rotary hearth furnace according to the present invention.

FIG. 2 is a schematic cross-sectional view of a method for supplying an atmosphere adjusting material according to the present invention from a rotary hearth furnace ceiling.

FIG. 3 is a schematic cross-sectional view of a method for supplying the atmosphere adjusting material according to the present invention from the outer peripheral wall and / or the inner peripheral furnace wall of the rotary hearth furnace.

FIG. 4 is a diagram showing, over time, the center temperature of the pellet, the amount of CO gas generated from inside the pellet, and the amount of CO ₂ gas generated due to the reduction of iron oxide during the reduction of the carbon material-containing pellet.

FIG. 5 is a schematic diagram of a facility configuration of a reduced iron production process using a conventionally used rotary hearth furnace.

[Explanation of symbols]

1: Rotary hearth 2: Reduced iron discharger
3: Raw material charging device 4: Rotary hearth furnace 5: Burner
6: Cooler 7: Atmosphere adjusting material supply device 8: Hopper
9: Cut-out device 10: Chute 11: Blow-in device
12: Ceiling 13: Furnace wall 14: Inlet a: Raw material (agglomerate, agglomerate bed) b: Reduced iron
c: Atmosphere adjusting material

Claims (7)

[Claims] 1. A method for producing reduced iron by reducing agglomerates formed by mixing a powdery iron oxide-containing substance and a powdery carbonaceous reducing material using a rotary hearth furnace, comprising: A method for producing reduced iron, wherein an atmosphere adjusting material is placed on an upper part. 2. The method for producing reduced iron according to claim 1, wherein the portion on which the atmosphere adjusting material is placed is a latter half of a heating unit in a rotary hearth furnace. 3. The method for producing reduced iron according to claim 1, wherein the atmosphere adjusting material is a material containing a carbon component as a main component. 4. The method for producing reduced iron according to claim 1, wherein the atmosphere adjusting material is coal having a volatile content of 40% or less. 5. The method for producing reduced iron according to claim 4, wherein the ash content of the coal is 30% or less, and the melting point of the ash is 1200 ° C. or more. 6. The method according to claim 1, wherein the atmosphere adjusting material introduced into the moving bed type heating furnace is placed on the agglomerate bed by using gravity from a space above the agglomerate bed. Item 3. The method for producing reduced iron according to any one of Items 1 or 2. 7. The particle size of the atmosphere control material is 0.05 to 1
A range of 0 mm, wherein
7. The method for producing reduced iron according to any one of 3, 4, and 6.