U.S. patent application number 09/887361 was filed with the patent office on 2001-10-18 for apparatus for producing reduced iron.
This patent application is currently assigned to Mitsubishi Heavy Industries, Ltd.. Invention is credited to Fujioka, Hironori, Hirata, Kouichi, Kamikawa, Susumu, Mizuki, Hideaki, Sato, Keiichi.
Application Number | 20010030389 09/887361 |
Document ID | / |
Family ID | 17298676 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030389 |
Kind Code |
A1 |
Kamikawa, Susumu ; et
al. |
October 18, 2001 |
Apparatus for producing reduced iron
Abstract
In the production of 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, when the temperature of reduced compacts is
900.degree. C. or higher, the oxide content in the reduced compacts
is set at 11 % or more, and the basicity of the reduced compacts is
set at 0.5 or higher.
Inventors: |
Kamikawa, Susumu;
(Hiroshima-shi, JP) ; Hirata, Kouichi;
(Hiroshima-shi, JP) ; Fujioka, Hironori;
(Hiroshima-shi, JP) ; Mizuki, Hideaki;
(Hiroshima-shi, JP) ; Sato, Keiichi;
(Hiroshima-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Mitsubishi Heavy Industries,
Ltd.
|
Family ID: |
17298676 |
Appl. No.: |
09/887361 |
Filed: |
June 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09887361 |
Jun 25, 2001 |
|
|
|
09612373 |
Jul 7, 2000 |
|
|
|
Current U.S.
Class: |
266/168 |
Current CPC
Class: |
F27B 2009/382 20130101;
F27D 2017/005 20130101; F27B 9/36 20130101; F27B 2009/3692
20130101; F27D 15/00 20130101; C22B 1/245 20130101; C22B 5/10
20130101; F27D 3/08 20130101; C21B 13/105 20130101; F27D 17/001
20130101; F27D 17/004 20130101; F27B 2009/384 20130101; F27D 13/00
20130101; F27B 9/16 20130101 |
Class at
Publication: |
266/168 |
International
Class: |
C22B 001/16 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 10, 1999 |
JP |
11-256878 |
Claims
1. 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, further including: grinding means for
grinding reduced compacts.
2. The apparatus for producing reduced iron as claimed in claim 1,
wherein: the grinding means is disposed in a discharge port of an
RHF, and the reduced compacts ground by the grinding means are
accommodated and stored in a reservoir.
3. The apparatus for producing reduced iron as claimed in claim 1,
wherein: sifting means is 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 are ground by the grinding
means.
4. The apparatus for producing reduced iron as claimed in claim 3,
wherein: the sifting means is 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.
5. The apparatus for producing reduced iron as claimed in claim 3,
wherein: reduced compacts discharged from an RHF are sifted by the
sifting means, then large lumps of the reduced compacts are ground
by the grinding means, and small lumps of the reduced compacts
sifted out by the sifting means and small lumps of the reduced
compacts formed by grinding by the grinding means are accommodated
and stored in a reservoir.
6. The apparatus for producing reduced iron as claimed in claim 3,
wherein: temporary storage means is provided for temporarily
storing the large lumps of the reduced compacts sifted out by the
sifting means, and after a predetermined amount or a larger amount
of the large lumps of the reduced compacts are stored in the
temporary storage means, all of these large lumps are ground by the
grinding means.
7. The apparatus for producing reduced iron as claimed in claim 1,
wherein: a reservoir for accommodating and storing the reduced
compacts is provided in a discharge port of an RHF, the grinding
means is disposed in a charge port for a raw material tank in a
melting furnace, and immediately before the reduced compacts in the
reservoir are charged into the raw material tank, large lumps of
the reduced compacts are ground by the grinding means.
8. The apparatus for producing reduced iron as claimed in claim 7,
wherein: sifting means for sifting the reduced compacts according
to size of the compact is provided in the charge port for the raw
material tank in the melting furnace, and large lumps of the
reduced compacts sifted out by the sifting means are ground by the
grinding means and then charged into the raw material tank.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Art
[0004] FIG. 8 outlines a production process by a conventional
apparatus for producing reduced iron.
[0005] 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 greencompacts 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.
[0006] 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.
[0007] 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.
[0008] 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.degree. 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.
[0009] 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.
[0010] Moreover, the high temperature atmosphere-i-s 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
[0011] 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.
[0012] 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 pellets, and reducing the compacts in a high temperature
atmosphere, wherein when a temperature of reduced compacts is
900.degree. C. or higher, an oxide content in the reduced compacts
is 11% or more.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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 pellets, and reducing the
compacts in a high temperature atmosphere, the apparatus further
including grinding means for grinding reduced compacts.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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 compacts formed by grinding 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.
[0022] In the apparatus for producing reduced iron according to the
invention, temporary storage means maybe provided for temporarily
storing the large lumps of the reduced compacts siftedout by the
siftingmeans, and after a predetermined amount or a larger amount
of the large lumps of the reduced compacts are stored in the
temporary storage means, all of these large lumps may be ground by
the grinding means. Thus, the large lumps of the reduced compacts
stuck together in a transport reservoir are ground by the grinding
means. Consequently, operating defects in a subsequent step due to
large lumps of the reduced compacts can be prevented reliably.
[0023] In the apparatus for producing reduced iron according to the
invention, a reservoir for accommodating and storing reduced
compacts may be provided in a discharge port of an RHF, the
grinding means may be disposed in a charge port for a raw material
tank in a melting furnace, and immediately before the reduced
compacts in the reservoir are charged into the raw material tank,
large lumps of the reduced compacts may be ground by the grinding
means. Thus, after the reduced compacts become cold, the large
lumps are ground. Consequently, the reduced compacts can be
prevented from resticking to each other.
[0024] In the apparatus for producing reduced iron according to the
invention, sifting means for sifting the reduced compacts according
to the size of the compact may be provided in the charge port for
the raw material tank in the melting furnace, and large lumps of
the reduced compacts sifted out by the sifting means may be ground
by the grinding means and then charged into the raw material tank.
Thus, after the reduced compacts become cold, only large lumps of
the reduced compacts are ground by the grinding means.
Consequently, resticking of the reduced compacts to each other can
be prevented, the amount of operation of the grinding means can be
decreased, and the efficiency of processing can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description taken in connection with the accompanying drawings, in
which:
[0026] FIG. 1 is a graph showing the relation between the basicity
and the oxide content of a reduced compact produced by a method for
producing reduced iron according to a first embodiment of the
present invention;
[0027] FIG. 2 is a schematic view showing an overall layout of a
production apparatus for carrying out the method for producing
reduced iron;
[0028] FIG. 3 is a schematic view of an apparatus for producing
reduced iron according to a second embodiment of the invention;
[0029] FIG. 4 is a schematic view of an apparatus for producing
reduced iron according to a third embodiment of the invention;
[0030] FIG. 5 is a front view of a sifter;
[0031] FIG. 6 is a plan view of the sifter;
[0032] FIG. 7 is a schematic view of an apparatus for producing
reduced iron according to a fourth embodiment of the invention;
and
[0033] FIG. 8 is a schematic view showing a production process by a
conventional apparatus for producing reduced iron.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Embodiments of the present invention will now be described
in detail with reference to the accompanying drawings, which in no
way limit the invention.
First Embodiment
[0035] A method for producing reduced iron according to the present
embodiment will be described briefly. As shown in FIG. 2, an iron
ore powder (an iron material), a coal powder (a reducing agent),
and a fluxstone (limestone) powder, which will be raw materials for
compacts, are fed from hoppers 11, 12 and 13, respectively.
Separately, a binder is fed from a hopper 14, and these materials
are mixed in a mixer 15. Then, the resulting mixed powder is
agglomerated by a pelletizer or a briquetter 16 to form green
compacts like pellets or briquetters (raw compacts). The resulting
compacts are charged into a dryer 17, where the compacts are dried
with an off-gas from an RHF 19 to be described later on. The so
dried green compacts are fed to the RHF 19 by a compact feeder 31
via a conveyor 18. The interior of the RHF 19 is maintained in a
high temperature atmosphere upon heating by burners 32, and an
off-gas inside the RHF 19 is discharged through an off-gas duct 33.
Thus, the green compacts are heated at a high temperature inside
the RHF 19 while moving in the RHF 19. Iron oxide in the iron ore
is reduced with coal to form reduced iron in compact form. The
reduced compacts are delivered from inside the RHF 19 by a compact
discharger 34, and accommodated in a reservoir 20.
[0036] The off-gas discharged through the off-gas duct is cooled by
a water spray type primary cooler 21, and then sent to a heat
exchanger 22, where the cooled off-gas is heat exchanged with air
fed by a fan 23. Then, the off-gas is cooled again by a water spray
type secondary cooler 24. The air heated in the heat exchanger 22
is carried to the RHF 19, and fed into the furnace together with
fuel. The off-gas cooled in the secondary cooler 24 is sent to the
dryer 17 by a fan 25 to become drying air for the green compacts,
as stated earlier. The off-gas discharged from the dryer 17 is
cleaned by a dust collector 26, sent to a stack 28 by an off-gas
fan 27 for desulfurization, and then released into the
atmosphere.
[0037] Compacts before reduction (may be hereinafter referred to as
"unreduced compacts"), i.e., green compacts, contain a considerable
amount of iron oxide Fe.sub.2O.sub.3 contained in the iron ore as
the iron material, carbon C in the coal as the reducing agent,
small amounts of other iron ore components (gangue mineral
components) contained in the iron ore, coal and binder, such as
calcium oxide CaO, magnesium oxide MgO, potassium oxide K.sub.2O,
sodium oxide Na.sub.2O, silicon oxide SiO.sub.2, aluminum oxide
Al.sub.2O.sub.3, and boron oxide B.sub.2O.sub.3. The reduced
compacts, on the other hand, are composed of iron Fe reduced from
iron oxide, and small amounts of iron ore components, including ash
produced by combustion of carbon. The volume of the reduced
compacts decreases by the amount of carbon which has vanished
because it is converted to a combustion gas.
[0038] Of the above-mentioned gangue mineral components, calcium
oxide CaO, magnesium oxide MgO, potassium oxide K.sub.2O, and
sodium oxide Na.sub.2O are alkaline oxides, while the other
components, i.e., silicon oxide SiO.sub.2, aluminum oxide
Al.sub.2O.sub.3, and boron oxide B.sub.2O.sub.3, are acidic oxides.
Thus, the basicity of the gangue mineral components remaining in
the reduced compacts is determined by dividing the amount of the
alkaline oxides by the amount of the acidic oxides.
[0039] The inventor of the present invention experimentally
investigated changes which occur in compacts during the heating and
reduction of the compacts in the RHF 19. As a result, the inventor
found that the sticking of reduced compacts to each other occurred
upon melting of gangue mineral components present around reduced
iron during the reduction process, and this sticking was related to
the amount, and degree of dispersion, of the gangue mineral
components (including ash) present around iron obtained by
reduction. That is, it has become clear that when the proportion of
the gangue mineral type oxide components in the compact composition
is less than a certain value, sticking occurs easily, but when this
proportion is higher than the certain value, sticking minimally
occurs.
[0040] It has also been shown that when the basicity of the gangue
mineral type oxides in the compact composition is lower than a
certain value, the melting point lowers and sticking occurs easily,
and when the basicity is higher than the certain value, the melting
point rises and sticking occurs minimally. In detail, compacts
undergo a heat history at a reduction temperature of 1,200.degree.
C. or higher. Thus, to curtail sticking, a mixture of the gangue
mineral components has been found to require a melting point of
1,200.degree. C. or higher.
[0041] By fulfilling the above-described two requirements, it has
been found that reduced compacts at 900.degree. C. or higher can be
hot direct charged without the need to be cooled.
[0042] By conducting experiments based on the foregoing theory, the
inventor worked out a method capable of hot direct charging reduced
compacts reduced at a required high temperature of 900.degree. C.
or higher without need to cool the compacts. That is, the inventor
devised a method for preventing sticking when green compacts
comprising a mixed powder of iron ore, coal, fluxstone, and a
binder in a high temperature atmosphere in the RHF 19. According to
the method, when the temperature of reduced compacts is 900.degree.
C. or higher, the oxide content in the reduced compacts is set at
11% or more, and the basicity of the reduced compacts is set at 0.5
or higher in order to raise the softening temperature during
reduction.
[0043] FIG. 1 is a graph for evaluating sticking of reduced
compacts produced, with a combination of the temperature, oxide
content, and basicity of the reduced compacts being varied. In FIG.
1, .circle-solid. represents a sample without sticking at a
temperature of up to 750.degree. C., .tangle-solidup. represents a
sample without sticking at a temperature of up to 850.degree. C.,
.DELTA. represents a sample without sticking at a temperature of up
to 900.degree. C., and .largecircle. represents a sample without
sticking at a temperature of up to 1,250.degree. C. In reducing
green compacts in the RHF 19, a temperature of 900.degree. C. or
higher is necessary to ensure quality. Thus, the optimal region is
a region demarcated by a one-dot chain line in FIG. 1, i.e., a
region in which the oxide content in the reduced compacts is 11% or
higher, and the basicity is 0.5 or higher.
[0044] In the reduction process for the green compacts in the RHF
19, the produced compacts are actually classified into those
reducible easily and those reducible with difficulty, depending on
the quality of the iron ore or coal. Thus, a reduction temperature
of 1,300.degree. C. at the highest, or a lower temperature than
that may be sufficient. In the reduction step for the green
compacts in the RHF 19, therefore, the temperature of the reduced
compacts to be discharged from the compact discharger 34 is about
900 to 1,250.degree. C. This means that the oxide content in the
reduced compacts is desirably 11% or higher, and the basicity is
optimally 0.5% or higher.
[0045] As noted above, in the method for producing reduced iron
according to the present embodiment, when the temperature of
reduced compacts is 900.degree. C. or higher, the oxide content in
the reduced compacts is set at 11% or more, and the basicity of the
reduced compacts is set at 0.5 or higher. This is achieved by
grasping the proportions of iron ore and coal which will be powdery
raw materials for green compacts, and mixing fluxstone, etc. so
that reduced compacts will have the aforementioned composition.
Thus, mutual sticking of reduced compacts is suppressed, large
lumps of reduced compacts do not clog the chute feeder, etc., and-a
decline in the production efficiency can be prevented.
[0046] In the above-described embodiment, clogging of the chute
feeder, etc. with large lumps of reduced compacts is inhibited by
preventing sticking itself. However, it is difficult for this
method to prevent sticking of reduced compacts completely. In
embodiments to be explained below, therefore, large lumps of
reduced compacts are subjected to sieving or grinding to prevent
clogging of the chute feeder, etc.
Second Embodiment
[0047] In an apparatus for producing reduced iron according to the
present embodiment, as shown in FIG. 3, an RHF 19 has a compact
feeder 31 and a compact discharger 34, and also has burners 32 for
maintaining compacts in a high temperature atmosphere and an
off-gas duct 33 for discharging an off-gas. To the compact
discharger 34, a discharge chute 41 is mounted. In an exit portion
of the discharge chute 41, a grinder 42 for grinding reduced
compacts is disposed, and a reservoir 20 for accommodating the
ground reduced compacts is installed.
[0048] Thus, green compacts formed from a mixed powder of iron ore,
coal, fluxstone and a binder are fed to the RHF 19 by the compact
feeder 31. While the green compacts are moving in the RHF 19, they
are heated to a high temperature. Iron oxide in the iron ore is
reduced with the coal to form reduced iron in compact form. The
reduced compacts, which have been delivered from inside the RHF 19
by the compact discharger 34, are sent to the grinder 42. Large
lumps of the reduced compacts stuck together are ground by the
grinder 42, and accommodated in the reservoir 20.
[0049] The reservoir 20 accommodating the reduced compacts is
passed on to a subsequent step. That is, the reduced compacts in
the reservoir 20 are supplied to a raw material tank (hopper) 43,
charged into a melting furnace 45 via a chute feeder 44, and melted
there.
[0050] In the apparatus for producing reduced iron according to the
present embodiment, as described above, the reduced compacts, which
have been discharged by the compact discharger 34 of the RHF 19,
are ground by the grinder 42, and accommodated in the reservoir 20.
Hence, even if the reduced compacts stick to each other, lumps
formed by the sticking are ground by the grinder 42. Consequently,
the reduced compacts are not accommodated in the reservoir 20 as
large lumps, so that when the reduced compacts inside the reservoir
20 are charged into the melting furnace 45 from the raw material
tank (hopper) 43, they do not clog the chute feeder 44.
Third Embodiment
[0051] In an apparatus for producing reduced iron according to the
present embodiment, as shown in FIG. 4, a sifter 51 is disposed in
a discharge portion of a compact discharger 34 in an RHF 19. The
sifter 51 can sift the reduced compacts to pick up large lumps of
the reduced compacts that have been formed by mutual sticking.
Beside a discharge portion of the sifter 51 for the reduced
compacts passing through the sifter 51, a reservoir 20 is disposed.
Beside a discharge portion of the sifter 51 for large lumps of the
reduced compacts sifted out by the sifter 51, a container 52 is
disposed for temporarily accommodating the large lumps of the
reduced compacts. Adjacent to the container 52, there are mounted a
grinder 42 for grinding the large lumps of the reduced compacts,
and a reservoir 20 for accommodating the reduced compacts after
grinding.
[0052] The sifter 51, as shown in FIGS. 5 and 6, is composed of a
plurality of rods mounted at predetermined intervals and in an
inclined state on an upper portion of a body 53, e.g., three sieves
54, 55 and 56, and a vibrator 57 for vibrating these sieves 54, 55
and 56. These sieves 54, 55 and 56 have rod-to-rod gaps each
measuring, for example, about 100 mm. Reduced compacts having a
diameter smaller than this gap fall through this gap, while large
lumps of reduced compacts having a greater diameter than this gap
roll on an inclined surface and fall forward.
[0053] Thus, when green compacts are reduced in a high temperature
atmosphere inside the RHF 19, they are delivered by the compact
discharger 34, and sent to the sifter 51. In the sifter 51, reduced
compacts are fed from the direction of an arrow A onto the sieves
54, 55 and 56 vibrated by the vibrator 57. Reduced compacts, which
have not stuck to each other, fall through the rod-to-rod gaps of
the sieves 54, 55 and 56 in the direction of an arrow C, and are
then accommodated in the reservoir 20. Whereas large lumps of
reduced compacts stuck together roll on the inclined surface on the
sieves 54, 55 and 56, fall in the direction of an arrow B, and are
then accommodated in the container 52. After the large lumps of the
reduced compacts in the container 52 are heaped to a certain
extent, they are sent to the grinder 42. The large lumps are ground
by the grinder 42 and accommodated in the reservoir 20. Then, the
reservoir 20 accommodating the reduced compacts is passed on to a
subsequent step. That is, the reduced compacts in the reservoir 20
are supplied to a raw material tank 43, charged into a melting
furnace 45 via a chute feeder 44, and melted there.
[0054] In the apparatus for producing reduced iron according to the
present embodiment, reduced compacts discharged from the compact
discharger 34 of the RHF 19 are separated by the sifter 51 into
reduced compacts which have not stuck to each other, and large
lumps of reduced compacts formed by mutual sticking. The large
lumps of reduced compacts are temporarily heaped in the container
52, ground altogether by the grinder 42, and accommodated in the
reservoir 20. Hence, only large lumps of reduced compacts are
ground by the grinder 42. Compared with the preceding embodiment,
the amount of operation of the grinder 42 can be decreased, and the
processing efficiency can be increased. As in the preceding
embodiment, moreover, clogging of the chute feeder 44 can be
prevented when the reduced compacts in the reservoir 20 are charged
into the melting furnace 45 from the raw material tank 43.
Fourth Embodiment
[0055] In an apparatus for producing reduced iron according to the
present embodiment, as shown in FIG. 7, a sifter 51 for sifting
reduced compacts in a reservoir 20 is disposed beside a supply
portion of a raw material tank 43 from which reduced compacts are
charged into a melting furnace 45 via a chute feeder 44. A grinder
42 is disposed beside a discharge portion of the sifter 51 for
large lumps of the reduced compacts sifted out by the sifter
51.
[0056] Thus, when green compacts are reduced in a high temperature
atmosphere inside an RHF 19, they are delivered by a compact
discharger 34, and accommodated in the reservoir 20. Then, the
reservoir 20 accommodating the reduced compacts is passed on to a
subsequent step. That is, the reduced compacts in the reservoir 20
are sent to the sifter 51 before their supply to the raw material
tank 43. In the sifter 51, reduced compacts, which have not stuck
to each other, fall downward, and accommodated in the raw material
tank 43. Whereas large lumps of reduced compacts stuck together are
sent to the grinder 42, and after being ground by the grinder 42,
they are charged into the raw material tank 43. The reduced
compacts are charged from the raw material tank 43 into the melting
furnace 45 via the chute feeder 44, and melted there.
[0057] In the apparatus for producing reduced iron according to the
present embodiment, as described above, reduced compacts inside the
reservoir 20 are separated by the sifter 51 into reduced compacts
which have not stuck to each other, and large lumps of reduced
compacts formed by mutual sticking. The large lumps of reduced
compacts are ground by the grinder 42, and then charged into the
raw material tank 43. Thus, even large lumps of reduced compacts
formed by mutual sticking in the reservoir 20 are ground by the
grinder 42, and then charged into the raw material tank 43.
Consequently, clogging of the chute feeder 44 can be prevented.
[0058] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
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