Specialized metallurgical processes – compositions for use therei – Compositions – Solid treating composition for liquid metal or charge
Reexamination Certificate
2000-05-17
2004-01-27
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Solid treating composition for liquid metal or charge
C075S322000, C075S769000
Reexamination Certificate
active
06682583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing sintered ore used as a raw material in ironmaking and sintered ore produced by means of the process and particularly, to a process for producing the sintered ore which product shows improved strength, and sintered ore produced by means of the process.
2. Description of the Prior Art
Production of sintered ore used as a raw material in ironmaking is generally performed in a preliminary process for a sintering raw material shown in FIG.
5
. This preliminary process includes steps of: mixing and granulation with raw material tanks
1
and a drum mixer
2
; and sintering with an ore feed hopper
3
and a sintering machine
4
. The sintering raw material is composed of: iron ore powder of about 10 mm or less in particle size; auxiliary materials, such as lime stone, quick lime, silica rock and serpentine; and solid fuel, such as coke, and components of the sintering raw material are stored in the raw material tanks
1
. The components of the sintering raw material are charged into the drum mixer
2
at a predetermined composition, then, a proper amount of water is added thereto and the components are mixed and granulated in the drum mixer
2
. Granules thus formed are packed on a pallet of a sintering machine (for example, a Dwight-Lloyd sintering machine)
4
to a predetermined height by the ore feed hopper
3
and solid fuel in a top surface section of the packed raw material is ignited. After the ignition, burning of the solid fuel is continued while the air is sucked downward and the sintering raw material is sintered by a combustion heat to form a sinter cake. This sinter cake is pulverized, followed by particle size adjustment to obtain a sintered ore product of 3 mm or more in particle size.
A sintered ore product requires high strength as a raw material in ironmaking. This is to prevent not only reduction in production yield due to pulverization of sintered ore in the course of charging it into a blast furnace but deterioration in blast furnace operating conditions due to reduction in air flowing-through property through a blast furnace from pulverization of sintered ore in the furnace.
In order to improve the strength of the sintered ore product, it is important that a high temperature is generated in the granules packed on the pallet of the sintering machine by combustion of solid fuel in the granules and this high temperature is maintained, so that a sufficient amount of a melt for sintering of iron ore powder is formed in a uniform manner in the bulk of the sintering raw material.
The melt is formed by a slag reaction between iron ore and the auxiliary materials, the melt being, in general, a multi-component system calcium-ferrite. With the melt, liquid phase sintering of iron ore powder is effected and after cooling, bonds between particles of the iron ore powder are formed.
It has widely been known that the strength of a sintered ore product is increased either when a bond is wide or when bonds are constructed in a network structure.
For this reason, it has been understood that the strength of a sintered ore product can be improved when a sufficient amount of a melt for sintering iron ore powder is produced to extend a width of a bond and in addition, the melt is produced in a uniform manner in the bulk of the sintering raw material to achieve a uniform network structure of bond.
An air flowing-through resistance of a granule bed packed on the pallet of the sintering machine has generally been reduced in order that a high temperature is generated and maintained by combustion of solid fuel included in the granules as described above. With the reduced air flowing-through resistance, much of air can be passed through the bed and the solid fuel can be efficiently burned in a uniform manner, thereby enabling a high temperature at which a high strength sintered ore product can be produced (sintered) to be achieved and maintained.
It has been adopted, in order to reduce an air flowing-through resistance, that a sintering raw material is prepared so as to be of coarse granules by either making primary particles of the sintering raw material larger in size or promoting a granulating nature of the sintering raw material and thereby improving a degree of agglomeration.
In order to promote the granulating nature of the sintering raw material, a binder, such as quick lime, bentonite, cement or cement clinker in powder, has been added to the raw material.
However, in company with recent decrease in output of good quality iron ore, the number of brands of iron ores in use has increased and thereby, a granulating nature of a sintering raw material is largely affected by characteristics of brands. To be detailed, a granulating nature of a sintering raw material has recently decreased with decrease in content of a coarse raw material, use of iron ore of a brand poorer in granulating nature, and increase in content of return sintered ore also poorer in granulating nature. As a result, there has been arisen a problem, since an air flowing-through property of a sintering raw material is degraded, thereby decreasing the strength of a sintered ore product.
In such circumstances, much of a binder has been added to a sintering raw material in order to improve a granulating nature.
However, there has arisen a problem in which a process where much addition of a binder into a sintering raw material leads to increase in production cost of sintered ore. Besides, addition of a large amount of a binder to a sintering raw material makes a composition of an ironmaking raw material fall off a scope allowed as the raw material, thereby influencing operation of a blast furnace adversely.
In addition to the above described problems associated with a binder, an improvement effect on the granulating nature of a sintering raw material has a maximum in regard to an additive amount of a binder and if the binder is added more than the maximum, the granulating nature of the sintering raw material has a chance of degradation.
OBJECT AND SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a process for producing sintered ore in which a small amount of a water-soluble compound (a sintering aid) is added to iron ore powder and, thereby, which product shows an improved strength and no adverse influence as an ironmaking raw material either without any increase in content of an auxiliary material (CaO) serving as a binder.
The present invention to achieve the above described object is directed to a process for producing sintered ore in which an aqueous solution is added to iron ore powder and an auxiliary raw material and the iron ore powder and the auxiliary raw material are kneaded to form a mixture, and the mixture is granulated to form granules, followed by sintering the granules, wherein the aqueous solution contains a water-soluble compound reacting with the iron ore powder to form a reaction product having a melting point of 1200° C. or lower.
Since a compound reacting with iron ore powder to form a reaction product having a melting point of 1200° C. or lower and preferably 1150° C. or lower is soluble in water, an aqueous solution containing the water-soluble compound makes wet surfaces of particles of the iron ore powder with certainty, so that coating of the surfaces of the particles of the iron ore powder with the compound can be ensured when drying the iron ore powder prior to sintering in a sintering step. As a result, the water-soluble compound and the iron ore powder can efficiently react with each other.
Therefore, the reaction between the water-soluble compound and the iron ore powder can be efficiently performed at a conventional sintering temperature ranging from 1150° C. to 1200° C. for sintered ore to form a melt, with the result that melt formation through a slag reaction between the iron ore powder and the auxiliary material is accelerated in the presence of the melt from the water-soluble compound and thereby, a sufficient amount of a melt for sint
Kiguchi Jyunpei
Matsumura Toshihide
Morioka Kouichi
Andrews Melvyn
Kabushiki Kaisha Kobe Seiko Sho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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