JP2000192154A - Production of partially reduced pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the metallization by charging green pellet provided with coated layer containing a specified quantity of CaO on the surface into a sintering furnace. SOLUTION: The green pellet is produced by using mixed powder of powdery iron raw material and powdery reducing agent to form the coated layer containing >=25% CaO on the surface of the green pellet. Then, after mixing with fuel carbonaceous material, this mixture is charged into the sintering furnace to form a filling layer and the ignition to the surface of the filling layer is executed and the sintering is executing by introducing the air from the upper part of the layer and sucking downward. In this way, the metallization of the pellet can be made to be >=40%. In this way, as the component except CaO, the carbonaceous material of coke powder, etc., for maintaining and strengthening the reducing atmosphere is desirable to be contained in an amount of <=20%. A method which coats the CaO, can be executed by roll-forming and granulating after charging the green pellet and CaO into a pelletizer or spraying water-slurry of CaO onto the green pellet. As the CaO-containing raw material, lime stone and smelting slag, etc., are used.

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 partially reduced pellets in which reoxidation of partially reduced pellets is prevented.

[0002]

2. Description of the Related Art Pig iron is manufactured by using a solid refining furnace, in which an iron source and fuel are charged from the furnace top and unloaded to the lower part of the furnace, and air is blown from the lower part of the furnace to burn and generate heat. And a reducing gas are created and aerated toward the upper part of the furnace, and the gas and the raw material are sufficiently reacted in the furnace. A typical example of this method is a blast furnace method.

In the blast furnace method, an iron source 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 disposed in the lower part of the blast furnace in the circumferential direction. It produces hot gas by blowing hot air from it and burning coke to produce pig iron by reducing and melting the iron source. The method using such a solid furnace is characterized by extremely high energy efficiency, and the fuel ratio required for producing pig iron is extremely low as compared with other methods.

[0004] In the case of a rigid furnace, it is important to heat the iron source by heat exchange of a high-temperature generated gas, that is, to balance heat in the furnace height direction and to secure ventilation in the furnace.

[0005] Iron raw materials used in the production of pig iron in the solid refining furnace include, in addition to massive iron ore, fired pellets, sintered ore, cold bond ore, etc. Scrap and reduced iron are used.

[0006] Lump ore is produced by sieving as an iron source material, and sinter is produced by a great travel type air suction and sintering facility of a raw material obtained by mixing fine iron ore and fine coke. The fired pellets are produced by rolling a raw material made of fine iron ore into a spherical shape and using a great travel type air suction firing device or a rotary kiln firing device.

[0007] Scrap is produced by processing into an appropriate size, and reduced iron is produced by putting iron ore or calcined pellets into a shaft furnace and introducing natural gas to reduce them.

[0008] Reduced iron is produced by granulating a mixed powder of fine iron ore and fine coal and using a rotary kiln firing facility or a rotary bed furnace facility that moves horizontally.

[0009] In such a blast furnace raw material, scrap and reduced iron are already reduced to metallic iron, so they can be said to be high quality raw materials achieving extremely high energy efficiency. However, scrap has a problem that it contains a lot of impurities, so it cannot be used in large quantities, and reduced iron uses natural gas,
The use of a rotary kiln or a horizontal rotary hearth furnace makes the production scale small and there is a problem in mass production.

On the other hand, iron ore, fired pellets, sinter, but the cold bond ore inexpensive mass-production and supply, since iron oxide (Fe ₂ O ₃₎ is composed mainly reducibility in the blast furnace (oxygen removal rate ) Greatly affects productivity and energy efficiency in blast furnace operation. Therefore, the reducibility is a very important quality index for a raw material mainly composed of iron oxide. As means for improving such reducibility, improvements in the shape, mineral structure, pore structure, etc. of sintered ores and pellets have been studied, but they are not always satisfactory.
A method for producing a large amount of partially reduced agglomerate ore and pellets having a low iron oxide ratio and a high metallization rate at low cost is being studied.

For example, Japanese Patent Publication No. Hei 8-9739 discloses a method in which fine particles of iron ore are mixed with a solvent and coarse-grained coke, mixed and granulated to produce raw pellets containing coarse-grained coke as a core.
A method is disclosed in which the raw pellets are coated with coke breeze, the obtained raw pellets are charged into a great travel type firing furnace, the surface layer is ignited, and the raw pellets are suctioned downward and fired. In addition, raw iron pellets, powdered solid reducing agents and solvents are mixed to produce raw pellets. After mixing the pellets and coke, a packed bed is formed, and after igniting the surface layer, air is discharged. A method of sucking downward and firing is disclosed.

The features of these methods are that the pellet raw material composed of the powder mixture of the powdered iron raw material and the powdered solid reducing agent can be easily reduced from iron oxide to metallic iron by heating at 900 ° C. or more. The purpose is to form a packed bed with the added pellet raw material, ignite the surface layer, suck air, burn the added coke, and heat and calcine the raw pellets using the generated heat.

[0013]

Although these methods can produce agglomerate ore in a large amount and inexpensively in the form of a combination of partially reduced pellets, the metallization rate (metal iron Fe concentration / total Fe concentration) is 10%. The following were low.

An object of the present invention is to provide a method for obtaining partially reduced pellets having a high metallization ratio of 40% or more or agglomerates in the form of combined pellets.

[0015]

The present inventors have obtained the following (A) to (H) regarding the reason why the above-mentioned conventional method cannot obtain a high reduction rate and the solution thereof.

(A) Even if the pellet surface is coated with coke, if the coated coke disappears due to combustion, a re-oxidation phenomenon occurs due to the supplied air. Therefore, even if a carbon material such as coke is added, it does not help to prevent re-oxidation.

(B) Since the reoxidation phenomenon is an exothermic reaction, it is not easily cooled. For this reason, it is necessary to further supply air to cool, and a vicious cycle of increasing the degree of reoxidation occurs.

(C) As a means for preventing the above reoxidation, it is effective to coat the surface of the raw pellets with one containing CaO.

(D) When the raw pellet surface is coated with a material containing CaO, CaO functions as a flux for producing a low melting point compound, and reacts with reduced iron or iron oxide to form a melt layer. , Can function to cut off contact with supply air.

(F) In general, iron and iron oxide have a high melting point and a temperature of 1350 ° C. or higher. However, when a CaO component is added thereto, the melting point decreases and the CaO content becomes 12.5% by weight (hereinafter simply expressed as%). ), The temperature can drop to about 1200 ° C. Therefore, when a film containing 12.5% or more of CaO is formed on the raw pellet surface, a liquid layer is formed at a high temperature zone of 1200 to 1300 ° C in a firing furnace. Can be.

(G) The liquid layer is first formed from the film portion. Since the liquid layer is a liquid layer, the reduced iron layer and the Ca
O reacts to decrease the CaO content in the film, so that 25%, which is about twice the limit CaO content of 12.5%.
% Or more of CaO is required in the coating.

(H) If the CaO content in the film is 25% or more, a melt having a low melting point and a very good wettability is formed at about 1200 ° C., and the surface portion is thinly and widely covered, and air A surface film having a high barrier effect can be formed, and the metallization ratio of the pellet can be maintained at 40% or more.

The present invention has been made on the basis of the above findings, and the gist of the invention is that "raw pellets produced using a powder mixture of a powdered iron raw material and a powdered solid reducing agent are sintered in a firing furnace. And producing a partially reduced pellet, wherein a raw pellet having a coating layer containing 25% by weight or more of CaO on the surface of the raw pellet is charged into a firing furnace. The method. "

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is to produce a raw pellet using a powder mixture of a powdery iron raw material and a powdery solid reducing agent, and to form a coating layer containing at least 25% CaO on the surface of the raw pellet. After being applied and mixed with the fuel carbon material, the mixture is charged into a firing furnace to form a packed bed, and the surface of the packed bed is ignited, air is fed from above the packed bed, and baked by suctioning downward. This is a method for producing partially reduced pellets having a high metallization ratio.

When the CaO content in the film is 25% or more, a film having a sufficiently high blocking effect can be formed, and the metallization ratio of the pellet can be 40% or more. in this case,
Components other than CaO are not particularly limited, but mainly contain Fe oxides because they are iron raw materials.
In order to maintain and strengthen the reducing atmosphere, it is preferable that a carbon material such as coke powder is partially contained at 20% or less.

The coating method is a method in which the raw pellets and the coating material are put into a pelletizer, and the surface of the raw pellets is coated by tumbling granulation. A mixture of water and the coating material is sprayed onto the raw pellets to coat the raw pellets. And a method in which water and the coating material are mixed, and the raw pellets are immersed in a slurry-like material, and the raw pellets are lifted up to perform coating.

Although the upper limit of the CaO content in the coating layer is not particularly defined, it is preferable that the CO content be reduced from the viewpoint of the target quality of the product partially reduced pellets.
What is necessary is just to select the aO content concentration appropriately.

Powdered iron raw materials include iron ore, dust generated by steelworks (dust generated by a sintering machine, dust generated by a blast furnace, dust generated by a converter, sludge generated by a rolling mill), and coal and coke as powdered solid reducing agents. , Char, oil coke and the like are used.

[0029] Raw pellets are produced by mixing the powdered iron raw material and the powdered solid reducing agent. If necessary, water, tar, molasses, organic resin, cement, slag, bentonite, quicklime, lightly burnt dolomite may be used as a binder. Add slaked lime.

As the CaO-containing raw material to be coated on the surface of the raw pellet, limestone, smelting slag, cement, slaked lime,
Examples include quicklime, dolomite, and calcined dolomite.

Although coke is exemplified as an additive to the packed bed, it is not necessarily limited to coke.
Solid fuel such as coal and char may be used.

As the firing process to which the present invention is applied,
After charging the raw materials to form a packed bed, the surface layer is ignited by an ignition burner while sucking with a blower from the wind box provided at the bottom, and the suction is continued downward after ignition, and the air is sucked from the surface layer and fired. The apparatus may be a batch Grinnwald-type sintering furnace, but from the viewpoint of inexpensive mass production, a great travel-type sintering furnace (DL sintering machine) widely used for sinter production is desirable. .

[0033]

EXAMPLE The method of the present invention and the conventional method were compared and examined using a sintering pot test apparatus made of alumina fiber walls having a diameter of 90 mm.

After blending and mixing under the raw material conditions shown in Table 1, using a disk pelletizer having a diameter of 500 mm, water was added and the particle size was 10 to 14 mm and 14 to 16 m.
m of raw pellets were produced. The raw pellets were coated under the conditions shown in Table 2 to compare and evaluate the metallization ratio of the products.

[0035]

[Table 1]

[0036]

[Table 2]

As a coating method, the raw pellets and the dried coating material are put into a pelletizer, and the surface of the raw pellets is coated by tumbling granulation. And a method of mixing by coating water and a coating material, immersing raw pellets in a slurry, and pulling up.

In mixing the raw materials of the pellets 5, the same raw materials as the pellets 4 were simultaneously charged into a ball mill and mixed and pulverized for about 1 hour.

Next, a 6 m floor was placed on the plate of the firing furnace.
A layer of alumina balls with a diameter of m is laid, and raw material obtained by adding 4% coke as fuel to raw pellets
m. Thereafter, the mixture was sucked from the wind box and the surface layer of the pot was ignited with a gas burner, and air was sucked into the packed bed for firing. In addition, the case where fuel coke was replaced with coal was also tested.

Case 1 is a conventional example and the metallization ratio of the fired product is as low as 6%. On the other hand, cases 2 and below (cases 12, 1
9 is an example of the present invention, and in each case, the metallization ratio is 4
Over 0%, the quality of the product was improved.

A comparison of Case 2 to Case 10 reveals that the best coating method is a method of immersing in a slurry, then a method of spraying the slurry is excellent, and the effect of the rolling method using a pelletizer is low. Was.

As for the type of the additive, it was found that the influence of the CaO concentration in the coating material was small unless the amount of CaO was changed. The addition of coke to the coating resulted in a higher metallization rate and was more effective.

The effect of the CaO concentration of the coating was
(Ca0 = 25.2%), Case 12 (CaO = 21.
6%), when the CaO concentration is 25% or less, the product metallization rate is significantly reduced to 23%, and the CaO concentration of the coating agent is 25% or more in order to secure the improvement effect. I found it necessary.

Next, in Cases 13 to 18, the effects of the powdered iron raw material and the powdered solid reducing agent of the pellet raw material were examined, but the influence of the difference between the hematite reagent and the iron ore, and the difference between the graphite powder and the coal powder was small. I understand.

Case 19 is a case where the surface of the raw pellets is coated only with coke breeze, but the reoxidation resulted in a low metallization ratio.

[0046]

According to the method of the present invention, reoxidation of pellets can be prevented, and it is possible to obtain partially reduced pellets having a high metallization ratio of 40% or more.

Claims (1)

[Claims] 1. A method for producing a partially reduced pellet by sintering a raw pellet produced using a powder mixture of a powdered iron raw material and a powdered solid reducing agent in a firing furnace, wherein the surface of the raw pellet is CaO content A method for producing partially reduced pellets, comprising charging raw pellets provided with a coating layer containing 25% by weight or more into a firing furnace.