Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2000-07-07
2002-09-17
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S481000
Reexamination Certificate
active
06451085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for producing reduced iron by mixing a powder of an iron material and a powder of a reducing agent to form a mixed powder, agglomerating the mixed powder to form compacts like briquettes or pellets, and reducing the compacts in a high temperature atmosphere.
2. Description of the Related Art
FIG. 8
outlines a production process by a conventional apparatus for producing reduced iron.
In a conventional apparatus for producing reduced iron, as shown in
FIG. 8
, an iron ore powder, a coal powder, and a binder are mixed in a mixer (not shown) . The resulting mixed powder is agglomerated by a pelletizer or a briquetter
001
to form green compacts (raw compacts). Then, the green compacts are charged into a dryer
002
, where they are dried with an off-gas from a reducing furnace (a rotary hearth furnace, RHF)
004
to be described later on. The so dried green compacts are fed to the RHF
004
by a compact feeder
003
. The interior of the RHF
004
is heated by burners
005
, and thereby maintained in a high temperature atmosphere. The off-gas inside the RHF
004
is discharged from an off-gas duct
006
.
The green compacts are heated with the radiant heat of a high temperature gas while they are moving in the RHF
004
. Iron oxide in the iron ore is reduced with coal to form reduced iron in compact form. The reduced compacts are discharged by a compact discharger
007
, and accommodated into a reservoir
008
. The off-gas discharged through the off-gas duct
006
is cooled by a primary cooler
009
, and then sent to a heat exchanger
010
, where the cooled off-gas is heat exchanged. Air heated upon heat exchange is sent to the RHF
004
, and fed into the furnace together with fuel. On the other hand, the off-gas is cooled again by a secondary cooler
011
, and a part of the off-gas is sent to the dryer
002
as drying air for the green compacts, as stated earlier. The off-gas discharged from the dryer
002
is cleaned by a dust collector
012
, and then released into the atmosphere.
The reservoir
008
accommodating the reduced compacts is passed on to a subsequent step. That is, the reduced compacts in the reservoir
008
are supplied to a raw material tank (hopper)
013
, and charged into a melting furnace
015
via a chute feeder
014
for melting.
The RHF
004
of the foregoing apparatus for producing reduced iron requires that the residence time of the green compacts in the high temperature atmosphere be minimized for increased productivity. Thus, the interior of the RHF
004
needs to be heated to a high temperature of 1,200 to 1,300° C. The reduced compacts discharged from the compact discharger
007
are accommodated at a high temperature directly into the reservoir
008
. In the reservoir
008
, the reduced compacts stick to each other under their own weight. When the reduced compacts are charged from the reservoir
008
into the melting furnace
015
through the chute feeder
014
, large lumps of the reduced compacts stuck together may clog the chute feeder
014
.
Hence, it has been common practice to dispose a rotary drum type cooler immediately below the compact discharger
007
of the RHF
004
, cool the hot temperature reduced compacts to ordinary temperature in this cooler, and then accommodate them into the reservoir
008
. This necessitates equipment cost for the cooler, and requires a cooling time for cooling the reduced compacts to ordinary temperature. Thus, the productivity is decreased, and the forced cooling of the high temperature reduced compacts wastes the heat that the compacts per se retain.
Moreover, the high temperature atmosphere is unstable during an initial period of operation of the RHF
004
. In this case, the reduced compacts are reoxidized, and heat generation during this reoxidation results in partial melting. As a result, the reduced compacts stick to each other, forming large lumps. In this case as well, when the reduced compacts are charged from the reservoir
008
into the melting furnace
015
through the chute feeder
014
, large lumps of them may clog the chute feeder
014
, as stated previously.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problems. It is an object of this invention to provide a method and an apparatus for producing reduced iron, which eliminate operating defects in a subsequent step due to large lumps of reduced compacts, and prevent a decrease in the efficiency of production.
A method for producing reduced iron according to the present invention, as a means of attaining the above-mentioned object, is a method for producing reduced iron by agglomerating a mixed powder of an iron material and a reducing agent to form compacts like briquettes or pellets, and reducing the compacts in a high temperature atmosphere, wherein when a temperature of reduced compacts is 900° C. or higher, and an oxide content in the reduced compacts is 11% or more.
Thus, mutual sticking of the reduced compacts can be suppressed to eliminate operating defects in a subsequent step due to large lumps of the reduced compacts, and prevent a decrease in the efficiency of production.
In the method for producing reduced iron according to the invention, basicity of the reduced compacts may be 0.5 or more. Since the basicity of the reduced compacts is 0.5 or more, mutual sticking of the reduced compacts can be suppressed reliably.
In the method for producing reduced iron according to the invention, the compacts maybe formed, with the amount of limestone mixed with the mixed powder of the iron material and the reducing agent being adjusted so that the oxide content in the reduced compacts will be 11% or higher. Thus, the adjustment can be made easily and highly accurately so that the oxide content in the reduced compacts will be appropriate.
An apparatus for producing reduced iron according to the invention is an apparatus for producing reduced iron by agglomerating a mixed powder of an iron material and a reducing agent to form compacts like briquettes or pellets, and reducing the compacts in a high temperature atmosphere, the apparatus further including grinding means for grinding reduced compacts.
Since large lumps of reduced compacts stuck together are ground by the grinding means, operating defects in a subsequent step due to large lumps of the reduced compacts can be eliminated, and a decrease in the efficiency of production can be prevented.
In the apparatus for producing reduced iron according to the invention, the grinding means may be disposed in a discharge port of an RHF, and the reduced compacts ground by the grinding means may be accommodated and stored in a reservoir. Thus, the reduced compacts in a high temperature state can be easily ground, and can be stored without being oxidized again.
In the apparatus for producing reduced iron according to the invention, sifting means may be provided for sifting the reduced compacts according to size of the compact, and large lumps of the reduced compacts sifted out by the sifting means may be ground by the grinding means. Since only large lumps of the reduced compacts are ground by the grinding means, the amount of operation of the grinding means can be decreased, and the efficiency of processing can be increased.
In the apparatus for producing reduced iron according to the invention, the sifting means may be composed of a plurality of sieves, and a vibrator for vibrating the sieves, each of the sieves being composed of a plurality of rods supported at predetermined intervals and in an inclined state on an upper portion of a body. Thus, the structure of the sifting means can be simplified and made lightweight.
In the apparatus for producing reduced iron according to the invention, reduced compacts discharged from an RHF may be sifted by the sifting means, then large lumps of the reduced compacts may be ground by the grinding means, and small lumps of the reduced compacts sifted out by the sifting means and small lumps of the reduced c
Fujioka Hironori
Hirata Kouichi
Kamikawa Susumu
Mizuki Hideaki
Sato Keiichi
Mai Ngoclan
Mitsubishi Heavy Industries Ltd.
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