U.S. patent application number 09/912498 was filed with the patent office on 2002-01-03 for method of producing reduced iron and production facilities therefor.
This patent application is currently assigned to Mitsubishi Heavy Industries, Ltd.. Invention is credited to Fujioka, Hironori, Hirata, Koichi, Itano, Shigeo, Kamikawa, Susumu, Kawamoto, Tetsumasa, Mizuki, Hideaki, Sueda, Shigeki, Teramoto, Hisao, Yamane, Takashi.
Application Number | 20020000687 09/912498 |
Document ID | / |
Family ID | 27522226 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000687 |
Kind Code |
A1 |
Fujioka, Hironori ; et
al. |
January 3, 2002 |
Method of producing reduced iron and production facilities
therefor
Abstract
Several methods and production facilities are provided in order
to solve several problems encountered in conventional methods and
facilities for producing reduced iron by reducing raw material
pellets of a mixture of an iron oxide powder and a reducing
material powder in a rotary bed-type reducing furnace and by
melting the reduced iron in a sealed-type electro-blast furnace.
Re-oxidation of reduced pellets of the mixture pellets is prevented
by introducing into a rotary bed-type reducing furnace a reduced
gas generated in an electro-blast furnace. In addition, an improved
mechanical strength of reduced pellets after direct reduction is
attained by applying rolling action to the reduced pellets. A few
method and facilities are provided for reliable utilization of wet
mixture pellets and a preferable compositions of binders for
forming the raw material mixture are selected. A novel charging
device for charging raw material pellets is developed which is
capable of charging the pellets on the rotary bed as a uniform
layer formed by piling one or more pellets.
Inventors: |
Fujioka, Hironori;
(Hiroshima, JP) ; Mizuki, Hideaki; (Hiroshima,
JP) ; Hirata, Koichi; (Hiroshima, JP) ; Itano,
Shigeo; (Hiroshima, JP) ; Kamikawa, Susumu;
(Hiroshima, JP) ; Teramoto, Hisao; (Hiroshima,
JP) ; Yamane, Takashi; (Hiroshima, JP) ;
Sueda, Shigeki; (Hiroshima, JP) ; Kawamoto,
Tetsumasa; (Hiroshima, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Mitsubishi Heavy Industries,
Ltd.
5-1, Marunouchi 2-chome
Chiyoda-ku
JP
|
Family ID: |
27522226 |
Appl. No.: |
09/912498 |
Filed: |
July 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09912498 |
Jul 26, 2001 |
|
|
|
09848280 |
May 4, 2001 |
|
|
|
09848280 |
May 4, 2001 |
|
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09386291 |
Aug 31, 1999 |
|
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Current U.S.
Class: |
266/44 ; 266/142;
266/172 |
Current CPC
Class: |
C22B 1/244 20130101;
Y02P 10/134 20151101; C21B 13/10 20130101; C21B 13/008 20130101;
C21B 13/105 20130101; C22B 1/245 20130101; C21B 13/14 20130101 |
Class at
Publication: |
266/44 ; 266/142;
266/172 |
International
Class: |
C21B 013/00; C22B
005/14; C22B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 1998 |
JP |
10-272203 |
Sep 30, 1998 |
JP |
10-294514 |
Oct 21, 1998 |
JP |
10-300167 |
Feb 19, 1999 |
JP |
11-042096 |
Mar 23, 1999 |
JP |
11-077752 |
Claims
What is claimed is:
1. A method of producing reduced iron comprising the steps of:
reducing raw material pellets obtained by pelletizing the mixture
of an oxide iron powder and a carbonaceous powder in an rotary
bed-type direct reducing furnace; melting the reduced iron pellets
obtained by said reducing process in a sealed-type electro-blast
furnace; and the method further comprising: introducing a reducing
gas composed mainly of CO.sub.2 and reproduced in said sealed-type
electro-blast furnace into said rotary bed-type direct reducing
furnace at a portion adjacent to the discharging portion of the
reduced iron pellets.
2. A production facility for producing reduced iron comprising: a
rotary bed-type direct reducing furnace for producing the reduced
iron pellets from the raw material pellets composed of the iron
oxide powder and the carbonaceous material powder; a sealed-type
electro-blase furnace for melting said reduced iron pellets; and a
reducing gas introducing means for introducing a reducing gas
composed mainly of CO.sub.2 and reproduced in said sealed-type
electro-blast furnace at the position adjacent to the reduced iron
pellets discharging portion of said rotary bed-type direct reducing
furnace.
3. A production facility according to claim 2, wherein said
reducing gas introducing means comprises: a gas holder for
collecting the reducing gas reproduced in the sealed type blast
furnace; and a nozzle which is connected with said gas holder
through a pipeline, and which is disposed passing through the
furnace wall at a position close to the reduced iron pellet
discharging portion for introducing the reducing gas into the
reduced iron discharging portion of the direct reducing
furnace.
4. A method of producing reduced iron pellets by the steps of
reducing the raw material pellets obtained by cooling the reduced
iron pellets after reducing the raw material pellets of the mixture
of a iron oxide powder and a carbonaceous material powder, the
method further comprises a step of: applying rolling to the reduced
iron pellets while being maintained within the temperature range of
800 to 1200.degree. C.
5. A method of producing reduced iron pellets according to claim 4,
wherein rolling of the reduced iron pellets is applied for more
than 3 minutes and less than 20 minutes.
6. A production facility for producing reduced iron pellets
comprises: a reducing furnace for obtaining the reduced iron
pellets by heating and reducing the raw material pellets composed
of the iron oxide powder and the carbonaceous material powder; a
heat retaining and rolling portion for executing rolling the heated
reduced iron pellets after receiving them from the reducing
furnace, while retaining the heat of the pellets; and a cooler for
cooling said reduced iron pellets after receiving from the heat
retaining and rolling portion.
7. A production facility for producing reduced iron pellets
according to claim 6, wherein said cooler is a cylindrical cooler
and said heat retaining and rolling portion is apart from said
cooler.
8. A production facility for producing reduced iron pellets
according to claim 7, wherein said heat retaining and rolling
portion is formed by lining the inside of said cooler by a
insulating material.
9. A method of reducing wet raw material pellets comprising the
steps of charging the wet raw material pellets on the rotary bed of
the rotary bed-type reducing furnace and reducing said wet raw
material pellets by heating thereof in said reducing furnace, the
method further comprising the steps of: forming a bed covering
layer by covering the rotary bed of the rotary bed-type direct
reducing furnace immediately before charging the wet raw material
pellets by insulating material particles having a higher melting
point than the heating temperature in said reducing furnace for
reducing the raw material pellets; and charging the wet raw
material pellets on said bed covering layer.
10. A method for reducing the wet raw material pellets according to
claim 9, wherein said insulating material particles are selected
from the group consisting of particles made of limestone, dolomite,
or basic oxide mixture composed of lime stone and dolomite.
11. A rotary bed-type reducing furnace comprising a wet raw
material pellets charging device for producing reduced iron pellets
by reducing the wet raw material pellets charged by said wet raw
material pellets charging device on the rotary bed of said rotary
bed-type reducing furnace, said rotary bed-type reducing furnace
further comprises: an insulating material particle supplying device
for forming a bed covering layer by covering the rotary bed with
the insulating material particles having a higher melting
temperature than the heating temperature of the reducing
furnace.
12. A rotary bed-type reducing furnace according to claim 11,
wherein said insulating material particles supplying device
comprises: a first hopper for storing said insulating material
particles; and a second hopper which receives said insulating
material particles discharged from said first hopper and which
comprises an opening at the bottom such that the opening faces to
the rotary bed of the reducing furnace leaving a space
therebetween.
13. A rotary bed-type reducing furnace according to claim 12,
wherein said insulating material particles are selected from the
group consisting of particles made of limestone, dolomite, or a
basic oxide mixture composed of lime stone and dolomite.
14. A method of forming raw material pellets comprising the steps
of forming pellets by adding adjusting water to a mixture of an
iron oxide powder, a coal powder, and a binder comprising a
hydrocarbon-type material, and drying said pellets for preparing
raw material mixed pellets; wherein the binder material is selected
from either one or both of carboxymethylcellulose and
polyvinylalcohol, and tar.
15. A method of forming raw material pellets according to claim 14,
wherein the step of drying said pellets containing adjusting water
is carried out in an atmosphere at a temperature higher than
150.degree. C.
16. A method of producing raw materials pellets according to claim
15, wherein, said binder comprises at least 0.2 wt % of either
carboxymethylcellulose or polyvinylalcohol, and more than 5 wt % of
tar.
17. A method of producing raw material pellets according to any one
of claims 14 and 15, wherein said binder comprises more than 0.2 wt
% of a mixture of carboxymethylcellulose and polyvinylalcohol.
18. A method of producing raw material pellets according to any one
of claims 14 and 15, wherein said binder comprises 4 wt % of tar
and more than 0.2 wt % of a mixture of carboxymethylcellulose and
polyvinylalcohol.
19. A method of producing raw material pellets according to any one
of claims 14 and 15, wherein said binder comprises more than 0.2 wt
% of a mixture of carboxymethylcellulose and polyvinylalcohol, and
bentonite in a range of 0.3 to 0.6 wt %.
20. A pellet charging device for charging the raw material pellets
on the rotary bed of the rotary bed-type reducing furnace, the
device comprising: a rotating drum having a truncated conical side
surface rotatable around the central axis, located beyond the
rotary bed of the reducing furnace; a hopper for supplying the raw
material pellets on the side surface of said rotating drum; and
furthermore, the central axis of the rotating drum is located
within a plane including the rotational axis of the rotary bed, the
rotating drum is inclined toward the rotary bed such that the upper
cross-line between said side surface of the rotating drum and said
plane is parallel to the rotary bed, and the vertical angle of the
conical rotating drum is set such that the ratio of the rotating
directional speeds of side surfaces beyond the inside and outside
peripheries of the rotary bed coincides with the ratio of rotating
directional-speeds of the rotary bed at both inside and outside
peripheries.
21. A pellet charging device according to claim 20, wherein said
hopper comprises a supplying port, which opens facing toward the
rotary bed of the reducing furnace, for supplying the raw material
pellets, wherein a distance between the ports and the rotary bed is
set such that the raw material pellets supplied from the port are
arranged to form a layer of pellets on the surface of the rotating
drum.
22. A pellet charging device according to any one of claims 20 and
21, wherein the rotating directional speed of said rotating drum is
established such that each point on the upper side surface of said
rotating drum is equal or an integer times of the moving speed of
the rotary bed, and the rotational direction of the rotating drum
is opposite to the rotational direction of the rotating drum.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of producing
reduced iron and production facilities therefor, and particularly
relates to production facilities for annexing a rotary bed-type
direct reducing furnace with a sealed-type electro-blast furnace, a
pellet production facility including the rotary bed-type direct
reducing furnace and a few improved methods of producing pellets
containing reducing materials, and a production facility and method
for supplying the pellets into a rotary bed-type direct reducing
furnace, and further relates to compositions of raw materials and
binders for producing pellets.
[0003] 2. Background Art
[0004] Conventionally, reducing iron is obtained by the steps of
forming pellets using mixed raw materials of iron ore and a
carbonaceous material by means of pellet production facilities, and
by reducing the pellets by means of a direct reducing furnace.
[0005] The reduced iron pellets are obtained by forming raw
material pellets which are a mixture of raw materials such as an
oxide particulate of iron ore and a particulate of carbonaceous
material like coal and by heating these pellets at high temperature
in a rotary bed-type direct reducing furnace. The thus produced
reduced iron pellets are then placed into a melting furnace for
meting the reduced pellets and for producing pig iron.
Conventionally, a sealed type blast furnace, a so-called submerged
arc-furnace is used as the melting furnace, and will be described
later.
[0006] Production of reduced iron by the rotary bed-type furnace is
advantageous in many respects such as (1) it is possible to utilize
coal with a reduced cost as the reducing agent, (2) it is possible
to acquire a favorable heat economy, since preheating of the raw
material pellets prepared by raw materials is not necessary, (3)
the reduction reaction can be completed within a short time
(approximately 10 min.), because the materials to be reacted (the
iron ore powder and the carbonaceous material powder) are in close
contact with each other. Therefore, it is possible to construct the
rotary bed-type direct reducing furnace in a simple structure and
at a reduced cost.
[0007] Hereinafter, a conventional rotary bed-type direct reducing
furnace will be explained in detail with reference to FIGS. 15 and
16.
[0008] FIG. 15 is a perspective view of the conventional rotary
bed-type direct reducing furnace (hereinafter, referred to as a
reducing furnace). The reference numeral 101 is the reducing
furnace, 122 is a burner provided through the side wall of the
reducing furnace, 113 is a transporting device for charging the
pellets into the reducing furnace, 102 is a conveyer such as a
reciprocating conveyer for charging the pellets in a uniformly
layer on the rotary bed, 124 is a pellet discharging device such as
a screw-type discharging device for discharging reduced pellets
(reduced iron pellets) from the reducing furnace, 104 is a
container for temporary storing the reduced iron pellets, and 105
is an exhaust gas duct for discharging the combustion gas in the
reducing furnace.
[0009] The raw material pellets produced by mixing the iron ore
powder as the oxide material and a coal powder as the carbonaceous
material is supplied to the reciprocating conveyer 102 through the
transporting device 113. The raw material pellets are charged into
the reducing furnace 101 uniformly as one or two layers on the
rotary bed 127. This pellet filled layer is heated by the burner
122 at about 1200.degree. C. and reduced during turning one round
in the direction shown by an arrow (clockwise revolution in FIG.
15) in the reducing furnace 101, and the reduced pellets are
discharged by the screw type discharging device 124 from the
reducing furnace 101, and stored in the container 4. The combustion
gas in the reducing furnace 101, after heating the raw material
pellets, is discharged through the exhaust dust 105 to the outside
the reducing furnace 101, and released into the atmosphere.
[0010] FIG. 16 is a cross-sectional developed diagram along the
center of the reducing furnace clockwise showing the pellet
charging portion and the reduced pellet discharging portion. In
FIG. 16, the reference numeral 103 denotes a reduced iron pellets
discharging chamber (discharging portion) for discharging the
reduced iron pellet layer 128. The rotary bed 127 of the reducing
furnace 101 is made of a refractory, its bottom is constructed by a
steel member, and wheels are annexed under the steel member. The
reference numeral 131 is a rail for these wheels. The rotary bed
127 of the rotary bed-type reducing furnace 101 rotates such that
it moves from left to right in a cross-sectional and developed
diagram along the center axis of the reducing furnace. The burner
122 is used for heating the raw material pellets and air for
combustion is supplied to the burner through an air line 123. The
reference numeral 134 is a combustion flame, and 125 is a cooling
device for cooling the pellet layer indirectly in order to prevent
the reduced iron pellet layer from burning. The reference numeral
126 is a damper for sealing the gas flow between the reduced iron
pellet discharge chamber and the raw material pellet charging
chamber 102.
[0011] As hereinabove described, a conventional facility for
producing the reduced iron pellets having high mechanical strength
is described in detail. Although the reduced iron pellets are
produced by the above-described rotary bed-type direct reducing
furnace, the other systems may be used for producing reduced iron
which comprises a few annexed equipment.
[0012] FIG. 17 illustrates a facility containing a perspective view
of the rotary bed-type direct reducing furnace 201, wherein the raw
material pellets are supplied onto the rotary bed 206 by a charging
conveyer 202 through a charging conveyer 204. The inside chamber of
the rotary bed-type direct reducing furnace 210 is heated by use of
a plurality of burners (not shown).
[0013] As shown in FIG. 17, a reduced iron pellet production
facility comprises a conventional rotary bed-type direct reducing
furnace 201, shown as a cross sectional developed diagram, for
producing the reduced iron pellets by heating the raw material
pellets P1 at high temperatures, and a rotary cylinder-type cooler
202 for cooling the reduced iron pellets P2 preserved at high
temperature after receiving them at a transfer portion 208 during
rolling.
[0014] The reference numeral 203 denotes a pelletizer for producing
pellets of the mixture of the raw materials comprising an iron ore
powder and a coal powder. The reference numeral 204 denotes a
transporting device such as a belt conveyer, 205 denotes a pellet
charging device for charging pellets on the bed 206 into a uniform
pellet layer 207.
[0015] The reference numeral 208 denotes a discharging device for
discharging the heated reduced iron pellets P2 into the rotary
cylinder-type cooler 202, and 209 denotes an exhaust gas duct for
discharging the combustion gas.
[0016] The reference numeral 210 shown in FIG. 4 denotes a
cylindrical chute for delivering the reduced iron pellets P2 heated
at a temperature of 1100.degree. C. into the rotary cylinder-type
cooler 202 and 211 denotes a gas sealing hood.
[0017] The reference numeral 212 denotes spray nozzles for spraying
cooling water on the outside surface of the rotary cylinder-type
cooler 202, and 213 denotes a spray nozzle for spraying cooling
water directly on the reduced iron pellets located near the exit
port of the cooling cylinder 102. The reference numerals 214 and
215 denote rubber-rollers for supporting the rotating
rotary-cylinder-type cooler 202, and 216 denotes a gear for driving
the rotary cylinder-type cooler. The numeral 217 denotes a hood as
well as a hopper, 218 denotes a sieving screen, and 219 denotes an
exhaust duct of water vapor.
[0018] Conventionally, although the same rotary base-type reducing
furnace as shown in FIG. 15 is used, another method for producing
reduced iron pellets is known, in which, wet raw material pellets
formed by adding water, mixing, and pelletizing are heated and
reduced, without prior drying, in the rotary bed-type reducing
furnace shown in FIG. 18 which is the same as that shown in FIG.
15.
[0019] A facility for producing the reduced iron pellets by use of
wet raw material pellets is shown in FIG. 19, including the rotary
bed-type reducing furnace 301.
[0020] Referring to FIG. 19, the reference numeral 306 denotes a
storage tank for the iron oxide powder such as the iron ore powder,
307 a storage tank for the carbonaceous powder such as a coal
powder, and 308 a storage tank for a binder material such as
bentonite. A kneading machine 309 kneads materials weighed and
collected from these storage tanks 206, 207, and 208, while adding
water, and a pelletizing machine 310 produces wet pellets by adding
water to the kneaded powders as the material for production of
reduced iron pellets. On the other hand, the reference numeral 301
denotes the rotary base-type reducing furnace which is the same as
that shown in FIG. 16. The wet raw material pellets are charged
continuously on the rotary bed 320 by a pellet charging machine 302
such as a conveyer through a transporting device 311 so as to form
a uniform wet pellet layer 312.
[0021] As the rotary bed rotates (the rotational direction is shown
by an arrow A), wet raw material pellets 312 on the rotary bed 320
are heated and reduced. The numeral 303 denotes a discharging
portion of the reduced iron pellets at high temperature, 304
denotes a container for temporary storing the heated pellets, and
305 a exhaust gas duct for discharging the combustion gas in the
reducing furnace 201.
[0022] In order to improve the mechanical strength in terms of the
falling distance of the raw material pellets without being
fractured, the type and added amounts were studied. When the raw
material pellets are formed as described above, generally, the iron
ore powder which mainly contains Fe.sub.2O.sub.3 and
Fe.sub.2O.sub.4 and the carbonaceous material powder such as coal
or coke powders are mixed and pelletized into pellets by addition
of a binder. As the binder for forming pellets, usually bentonite
is incorporated in a range of 0.5 to 1 wt %.
[0023] The raw material pellets containing the reducing material,
after being pelletized by the pelletizing machine and dried by a
drying machine, is charged into the reduced iron producing machine,
which is the same rotary base-type direct reducing furnace as that
shown in FIGS. 15 or 16. Accordingly, the raw material pellets
undergo various mechanical impact during transportation or charging
on the rotary bed.
[0024] FIG. 21 is a diagram for explaining the process using the
rotary bed-type reducing furnace. The reference numeral 401 denote
a reducing furnace, which has the same structure as shown in FIG.
15. The cross-sectional view of the reducing furnace 401 is shown
in FIG. 21. The rotary bed 412 is a disc formed from a belt-like
plate, and wheels 413 are provided beneath the rotary bed so as to
engage with the rail 414 constructed concentrically about the
center axis of the rotary bed. The rotary bed 412 is driven by a
driving mechanism (not shown) and rotates on the rail at a certain
rotating speed.
[0025] As shown in FIG. 21, fine powders of the iron ore and the
coal are mixed with the binder, pelletized into pellets (10 to 12
mm in diameter) by a pelletizing machine 402, and dried by a drying
machine 403. After being dried, the raw material mixed pellets are
charged on the rotary bed of the reducing furnace 401 by a charging
machine 404 which will be described later. The pellets moves
together with the movement of the rotary bed.
[0026] As shown in FIG. 23, a plurality of burners 407 are provided
along the outside periphery of the reducing furnace, and a high
temperature combustion gas is generated by combustion of a fuel.
The high temperature combustion gas circulates in the furnace in
the direction opposite to that of the rotational direction (shown
by an arrow A) of the furnace, and the inside of the reducing
furnace is maintained at high temperature. This high temperature
atmosphere reduces Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4 in the iron
ore and the combustion gas is then discharged to a preheater 409 of
primary air for combustion and released to the air after passing
through a dust collector 410.
[0027] The raw material pellets are directly reduced during one
circulation in the rotary bed reducing furnace and the thus reduced
pellets containing reduced iron are discharged from the reducing
furnace by means of a screw-type discharging machine 405 (FIG. 24)
located near the pellet charging portion and the reduced pellets
are supplied to the subsequent process after being cooled by a
cooler 406.
[0028] A pellet charging machine 404 is provided for charging the
raw material pellets on the rotary bed as a layer of pellets having
a uniform thickness (the thickness of one or two pellets
layer).
[0029] Here, the raw material pellets charging machine for charging
the raw material on the rotary bed of the rotary bed-type direct
reducing furnace will be described.
[0030] FIGS. 24 and 24 show the pellet charging machine, which
comprises a receiving portion 516 of the raw material pellets, an
inclined plate 516b for guiding the pellets discharged from the
receiving bin 516, and a pair of partition plates 517 and 518 for
controlling the thickness of the pellet laminate layer. The height
of the opening H3 at the bottom of the receiving portion 516, the
intervals H2 and H1 under the partition plates are set as
H3>H2>H1. The pellets in the receiving bin 516 is supplied
onto the rotary bed 512 after passing through intervals of H3, H2,
and H1 which becomes sequentially smaller.
[0031] A first problem arises in the conventional rotary bed-type
direct reducing furnace 1 as shown, for example, in FIGS. 15 and 16
in that the inner pressure of the raw material pellet charging
portion 150 is made negative by an exhaust fan for discharging the
combustion gas, because the pellet charging portion 150 is close to
the exhaust duct 105 and is opened to the outside atmosphere. In
addition, a space is formed in between the pellet charging portion
150 and the charging conveyer 102, and it is likely to cause air
flows in the directions 153 and 154.
[0032] Even though a damper 126 is formed to prevent air from
flowing between the pellet charging portion 102 and the reduced
iron pellet discharging portion 103, the leak air is flown into the
pellet discharging portion as shown by an arrow 155 due to
insufficient seal. Thereby, the first problem encountered is that
the reduced iron pellets at high temperature are again oxidized
according to the following chemical reactions caused by the leak
air flown into the reducing furnace 101.
Fe (reduced iron)+1/2 O.sub.2.fwdarw.FeO (1)
Fe (reduced iron)+3/4 O.sub.2.fwdarw.1/2Fe.sub.2O.sub.3 (2)
[0033] Sometimes, the combustion gas is made to flow into the
pellet discharging portion 103, because the internal pressure
balance in the pellet charging portion 150 and the pellet
discharging portion 103 is destroyed due to the air flow 55. Since
the combustion gas is an oxidizing gas containing CO.sub.2 gas and
H.sub.2O gas, the reduced iron is re-oxidized by the following
chemical reactions.
Fe+CO.sub.2.fwdarw.FeO+CO (3)
Fe+H.sub.2O.fwdarw.FeO+H.sub.2 (4)
[0034] The second problem concerns the mechanical strength of the
reduced iron pellets discharged from the reducing furnace. That is,
the reduced iron pellets produced in the rotary bed-type direct
reducing furnace have a very low density and a very low crushing
strength, corresponding to very low mechanical strength.
Practically, the crushing strength of one reduced iron pellet with
a diameter of 10 mm is as low as approximately 30 kgf, which is too
fragile to be shattered when such pellets are thrown in a blast
furnace as the raw material.
[0035] The reason for the weak strength is because the gas phase
including oxygen, carbon, and a volatile component (when coal is
used as the carbonaceous material) is released from the raw
material pellets and also because the reduction time in the
reducing furnace 1 is too short to sinter the pellets after the gas
release.
[0036] The third problem concerns the wet raw material pellets. If
the wet raw material pellets are charged onto the rotary bed 227
heated more than 700.degree. C. of the rotary bed-type reducing
furnace 201, the wet raw material pellets will be fractured by the
explosion of steam generated by the rapid heating of the wet raw
material pellet. This fracture by the steam explosion is called
bursting, and the bursting naturally reduces the yield of the
reduced iron product.
[0037] In order to avoid such a bursting phenomenon, the surface
temperature at the charging portion (Ti) of the rotary bed is
reduced below 700.degree. C. as shown in FIG. 20. As shown in FIG.
20, the surface temperature at the discharging portion (To) is as
high as 1100.degree. C. In order to establish the temperature
gradient between the discharging portion (To) and the charging
portion (Ti), it is necessary to have a considerable distance
between the charging portion and the discharging portion, which
requires the expanded rotary bed and the increased cost of
equipment, which constitute the third problem. The point (b) in
FIG. 9 represents the point where the wet pellets are dried and the
temperature at the point (b) in the furnace is the lowest.
[0038] The fourth problem is related to the composition of the raw
material pellets, because the conventional raw material pellets
additionally containing bentonite are likely to be fractured by
mechanical shocks applied to the raw material pellets during
transportation. When dried, the downfall strength of the raw
material pellets containing bentonite becomes so weak that almost
all of the pellets are fractured when they are dropped from a
height of 300 mm. If the raw material pellets are fractured or
subjected to surface peeling, the diameters of the pellets becomes
uneven which causes uneven reduction in the reducing furnace and
which also causes uneven quality of the reduced iron. In order to
eliminate the fracture of the raw material pellets, the
conventional transportation equipment are designed so as to reduce
the falling height of pellets when transporting or charging, which
results in reducing the degree of freedom in designing the
transportation and charging apparatuses. It is an object of the
present invention to provide a method of obtaining the raw material
pellets having a high downfall strength.
[0039] Furthermore, the fifth problem remains which is related to
the charging apparatus of the raw material pellets. As shown
schematically in FIG. 10, a problem of the conventional charging
apparatus arises in that the raw material pellets are easily broken
when the thickness of the pellet layer is controlled by means of
the partition plates.
[0040] That is, since it is necessary for the charging apparatus to
charge a comparatively large amount of pellets onto the rotary bed
of the rotary bed-type reducing furnace, the raw material pellets
are subjected to a large amount of tensile stress, when pellets are
damed by the partition plates 317, 318 for reducing the thickness
of the pellet layer, until the pellets are supplied onto the rotary
base 327. Therefore, when the pellet charging machine is used, the
raw material pellets are broken or the surfaces of the pellets are
peeled off. The fracture, breakage, or the surface peeling make
pellet diameters uneven, which results in uneven reduction of
pellets in the rotary base reducing furnace and this in turn
results in making it difficult to maintain the quality of the
reduced iron pellets.
[0041] As shown in FIG. 7, when the thickness of the charged pellet
layer is controlled by the partition plates 317, 318, since the
rotary base is in a form of circular belt type, the outer
peripheral speed of the rotary base differs from that of the inner
peripheral speed, which results in changing the density of the
resultant reduced iron pellets. That is, when the conventional
pellet charging machine is used, the distribution along the radial
direction changes, so that the raw material pellets cannot be
uniformly distributed on the rotary base of the reducing furnace.
Thereby, the quality of the reduced iron can not be preserved due
to the uneven diameters of the pellets by the fracture or peeling
of the pellets.
SUMMARY OF THE INVENTION
[0042] It is therefore objects of the present invention to provide
improved apparatuses and methods for solving the above five
problems.
[0043] The first embodiment of the present invention provides an
apparatus for solving the first problem wherein the air flows from
outside into the reduced pellet discharging portion and the reduced
iron pellets are likely to be re-oxidized. The first aspect of the
present invention is characterized in that a reducing gas mainly
composed of CO.sub.2 gas, reproduced in the sealed-type blast
furnace for melting the reduced iron pellets produced in the direct
reducing furnace from raw material pellets, is introduced into a
pellet discharging portion of the direct reducing furnace.
[0044] The apparatus of the first embodiment comprises a rotary
bed-type direct reducing furnace for producing the reduced iron
pellets from the raw material pellets composed of the iron oxide
powder and the carbonaceous material powder and a sealed-type
electro-blast furnace for melting the reduced iron pellets, and a
reducing gas introducing means. The reducing gas introducing means
comprises a gas holder for collecting the reducing gas reproduced
in the sealed-type blast furnace, and a nozzle which is connected
with said gas holder through a pipe line, and which is disposed so
as to go through the furnace wall in front of the reduced iron
pellet discharging portion for introducing the reducing gas into
the reduced iron discharging portion of the direct reducing
furnace.
[0045] The second embodiment of the present invention provides an
apparatus and method for solving the second problem wherein the
reduced iron pellets produced in the rotary bed-type direct
reducing furnace have a very low density and a very low fracture
strength. The second embodiment is characterized in that a rolling
action is applied to the heated reduced iron pellets in a
temperature range of 800 to 1200.degree. C. just after being
discharged from the direct reducing furnace in a heat retaining and
rolling portion provided in the cooling cylinder before
annealing.
[0046] According to the first aspect of the second embodiment,
since the deformation resistance of the reduced iron pellets in a
temperature range of 800 to 1200.degree. C. is very small, the
rolling action applied to the reduced iron pellets in the cooling
cylinder gives pellets a sintering effect which makes the reduced
iron pellets denser.
[0047] According to this method, the rolling of the pellets is
carried out in the cooling cylinder for more than 3 min. and less
than 20 min., in order to execute sintering and densification of
the pellets sufficiently.
[0048] According to the third aspect of the second embodiment, a
production facility for producing the reduced iron pellets
comprises a reducing furnace for obtaining the reduced iron pellets
by heating and reducing the raw material pellets composed of the
iron oxide powder and the carbonaceous material powder, a heat
retaining and rolling portion for executing rolling on the heated
reduced iron pellets after receiving them from the reducing
furnace, while retaining the heat of the pellets and a cooler for
cooling these reduced iron pellets after receiving from the heat
retaining and rolling portion.
[0049] The above facility according to the third aspect, the raw
material pellets are heated and reduced in the reducing furnace,
and the thus produced reduced iron pellets are exposed to the
rolling action in the heat retaining and rolling portion for
producing sintered heated pellets, and the sintered reduced iron
pellets are collected after being cooled by the cooler.
[0050] According to the fourth aspect of the second embodiment, the
heat retaining and rolling portion for receiving the heated reduced
pellets rotates together with the rotary cylinder-type cooler.
[0051] According to the fifth aspect of the second embodiment, the
heat retaining and rolling portion is formed by lining a part of
the inside of the rotary cylinder-type cooler with an insulating
material. The insulating material lining suppresses the heat of the
pellets from dissipating from the cooler wall.
[0052] The third embodiment of the present invention provides an
apparatus and a method of heating and reducing the wet raw material
pellets in the reducing furnace.
[0053] According to the first aspect of the third embodiment, the
method of using the wet raw material pellets comprises the steps of
forming a bed covering layer on the rotary bed by use of heat
insulating particles having a higher melting point than the heating
temperature of the raw material pellets, and subsequently supplying
the wet raw material pellets on the bed covering layer. Examples of
the heat insulating particles includes particles of lime stone or
dolomite or basic oxide particles obtained by mixing these
particles.
[0054] According to the second aspect of the third embodiment, the
rotary bed-type direct reducing furnace, provided with a wet raw
material pellet charging device for charging the wet raw material
on the rotary bed of the reducing furnace, comprises a bed covering
particle supplying device for covering the rotary bed by a bed
covering particle layer by use of the heat insulating material
particles. The heat insulating material particle supplying device
comprises a first hopper for storing the heat insulating material
particles and a second hopper which receives the heat insulating
particles discharged from the first hopper and which is provided
with an opening at the bottom end such that the opening faces
toward the rotary bed of the reducing furnace leaving a space
therebetween.
[0055] The bed covering particle layer formed by spreading the
insulating material particles having a high melting point on the
rotary bed before charging the wet raw material pellets acts as the
insulating layer for the wet raw material pellets. In this case,
the surface of the rotary bed is only required to be cooled to a
level of 1000.degree. C. until the wet raw material pellets are
charged after the reduced pellets are discharged, a shorter
distance is necessary between the discharging portion of the
reduced pellets and charging portion of the raw material pellets
than the distance in the conventional reducing furnace in which the
surface temperature of the rotary bed at the charging portion is
700.degree. C.
[0056] The wet raw material pellets are mainly composed of the iron
oxide powder and the wet raw material pellets are usually heated at
a level of 1300.degree. C. for reduction. Thus, the insulating
material particles should have a melting point of more than
1300.degree. C. so as not to be melted during heating (temperature
in the furnace), and it is preferable for the insulating material
particles to have a melting point of more than 1400.degree. C.
[0057] In addition, since the basic oxide materials such as lime
stone or dolomite have a considerably low thermal conductivity and
a comparatively high specific heat, the bed covering layer formed
by use of these particles constitutes a quite effective insulating
layer for the wet raw material pellets. Furthermore, these
insulating material particles are not only stable in the high
temperature reducing atmosphere, but also functions as a
desulphurization agent in the subsequent melting process of the
reduced iron pellets after being discharged into the container
together with the reduced iron pellets.
[0058] The fourth embodiment of the present invention provides a
method and compositions of the raw material pellets composed of the
iron oxide powder, the reducing material powder, and binders in
order to improve the mechanical strength of the raw material
pellets. According to the first aspect, the method of forming the
raw material pellets comprises the steps of forming raw material
pellets by combining and mixing the iron oxide powder, a reducing
material powder, a binder material, and a predetermined amount of
adjusting water; wherein the binder material is selected from
either or both of carboxymethylcellulose and polyvinylalcohol, and
tar.
[0059] According to this aspect, the raw pellets are produced by a
pelletizing machine and the like, after mixing the iron ore powder,
the coal powder, and a binder powder and after adjusting the water
content. The raw material pellets are produced by drying the
above-described raw pellets. The present embodiment allows the
dried raw material pellets to have a dramatically improved
mechanical strength such as the falling strength by the use of
carboxymethylcellulose, polyvinylalcohol, and tar.
Carboxymethylcellulose and polyvinylalcohol may be used alone or as
a combination.
[0060] The second aspect of the fourth embodiment provides a method
of producing the raw material pellets by drying the raw pellets in
an atmosphere higher than 150.degree. C. after forming the raw
pellets, because it is confirmed that a superior falling strength
of the raw material pellets is obtained by drying in an atmosphere
higher than 150.degree. C.
[0061] The third aspect of the third embodiment provides a method
of producing the raw materials pellets comprises incorporating at
least 0.2 wt % of either carboxymethylcellulose or
polyvinylalcohol, and more than 5 wt % of tar. That is, when one
binder among carboxymethylcellulose and a polyvinylalcohol is used,
it is preferable to add more than 0.2 wt %; and when the tar is
used, it is preferable to add more than 5 wt % of tar, in order to
obtain the raw material pellets having a particularly preferable
falling strength.
[0062] The fourth aspect of the fourth embodiment provides a method
of incorporating more than 0.2 wt % of a mixture of
carboxymethylcellulose and polyvinylalcohol. The falling strength
of the raw material pellets is remarkably improved by addition of
more than 0.2 wt % of a mixture of carboxymethylcellulose and
polyvinylalcohol, when both chemicals are used in combination.
[0063] The fifth aspect of the fourth embodiment provides a method
of incorporating, as the binder, 4 wt % of tar and more than 0.1 wt
% of either carboxymethylcellulose or polyvinylalcohol, or more
than 0.1 wt % of the mixture of carboxymethylcellulose and
polyvinylalcohol. The addition of binders of 4 wt % of tar and more
than 0.1 wt % of either carboxymethylcellulose or polyvinylalcohol,
or more than 0.1 wt % of the mixture of carboxymethylcellulose and
polyvinylalcohol is effective in obtaining the superior falling
strength of the raw material pellets.
[0064] The sixth aspect of the fourth embodiment provides a method
of incorporating, as the binder, more than 0.2 wt % of either
carboxymethylcellulose or polyvinylalcohol, and bentonite within a
range of 0.3 to 0.6 wt %. The addition of binders of more than 0.2
wt % of a mixture of carboxymethylcellulose and polyvinylalcohol,
and within a certain range of bentonite is further effective in
obtaining the superior falling strength of the raw material
pellets.
[0065] The fifth embodiment of the present invention provides a
charging device for uniformly charging the raw material pellets
onto a rotary bed of a rotary bed-type reducing furnace in a
uniform one pellet layer or a pellet layer formed by piling two
pellets. The raw material pellet charging apparatus according to
the first aspect comprising a rotating drum, having a truncated
conical side surface rotatable around the central axis, located
beyond the rotary bed of the reducing furnace, and a hopper for
supplying the raw material pellets on the side surface of the
rotating drum; wherein the central axis of the rotating drum is
located within a plane including the rotational central axis of the
rotary bed, and the rotating drum is disposed inclined such that
the upper cross-line in cross-lines between the side surface of the
rotating drum and the plane is parallel to the rotary bed, and the
vertical angle of the conical rotating drum is set such that the
ratio of the rotating speed of the side surface of the rotating
drum to the rotating speed of the rotating drum beyond the inner
portion of the rotary bed coincides with the ratio of rotating
speeds at both outside and inside peripheries of the rotary
bed.
[0066] According to the first aspect, the rotating drum of the
pellet discharging apparatus has a conical side surface and rotates
around the central axis of the conical drum which traverse the
rotary bed. The raw material pellets are supplied from above on the
rotating side surface of the rotating drum. Therefore, the pellet
supplying apparatus constitutes a rotary feeder without using the
partition plates. The central axis of the rotating drum of the
present invention is disposed inclined against the rotary bed such
that the upper surface of the rotating drum is parallel to the
rotary bed, and the upper surface of the rotating drum receives the
raw material pellets. Since the vertical angle of the truncated
conical rotating drum is set such that the rotating speed of each
position of the rotary bed coincides with the rotating speed of the
rotary bed of each position beneath each position of the rotating
drum.
[0067] Consequently, the amount of raw material pellets supplied on
each point of the rotary bed becomes proportional to the rotating
speed of each corresponding point of the rotating drum just below
each points of the rotating drum. This charging apparatus allows
distributing the raw material pellets uniformly on the rotary bed
of the reducing furnace, irrespective of the radial variation of
the rotating speed on the rotary bed. This apparatus also allows
preventing friction or pressing being caused between the pellets
and the fracture, damage, or surface peeling of the pellets are
avoided.
[0068] According to the second aspect, the hopper is provided
comprising a supplying port, which opens facing to the rotary bed
of the reducing furnace, for supplying the raw material pellets,
wherein a distance between the ports and the rotary bed is set such
that the pellets supplied from the port forms a layer having a
thickness of a pellet on the surface of the rotating drum.
[0069] That is, since the pellets are supplied from the discharging
port as a one pellet layer on the rotating drum, the pellets
discharged on the rotary bed becomes uniform. According to the
third aspect, the rotating speed of the rotating drum is set such
that the rotating speed at a point on the surface of the rotating
drum coincide with a integer times of the rotating directional
speed at a point just beneath the point on the rotating drum.
Therefore, it becomes possible to control the thickness of the
pellet layer supplied on the rotary bed of the reducing furnace.
For example, if supplying the pellets at a thickness of one pellet
is desired, the rotating speed of the rotating drum at one point is
set so as to coincide with that of the rotating directional speed
of the rotary bed just beneath that point. If the rotating speed of
the rotating drum is set two times larger than the rotating
directional speed of the rotary bed, the pellets are charged by a
two pellets layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0070] FIG. 1 is a schematic diagram showing the whole facility for
producing reduced iron, including a reducing furnace and an
electro-blast furnace, wherein a reducing gas generated in the
electro-blast furnace is introduced into the reducing furnace.
[0071] FIG. 2 is a developed diagram showing a part of the rotary
bed-type reducing furnace, indicating disposition nozzles for
introducing the reducing gas.
[0072] FIG. 3 is a developed diagram showing a part of the rotary
bed-type reducing furnace indicating another disposition of nozzles
for introducing the reducing gas.
[0073] FIG. 4 is a developed diagram showing a part of the rotary
bed-type reducing furnace indicating the other disposition of
nozzles for introducing the reducing gas.
[0074] FIG. 5 is a diagram showing the facility for producing
reduced iron pellets having a high density and a high mechanical
strength.
[0075] FIG. 6 is a partially opened cross-sectional view of the
rotary bed-type direct reducing furnace provided with the raw
material pellets forming and charging apparatuses.
[0076] FIG. 7 is a diagram showing the facility for producing
reduced iron pellets including the raw material pellet forming
facility and the rotary bed-type reducing furnace.
[0077] FIG. 8 is a diagram showing the relationship between the
surface temperature of the rotary bed and the location on the
rotary bed.
[0078] FIG. 9 is a diagram showing a relationship between a
thickness of the bed coating layer and the permissible surface
temperature of the rotary bed.
[0079] FIG. 10 is a diagram showing a facility for producing
reduced iron pellets from wet raw material pellets composed of an
iron oxide powder, a reducing material powder, and a binder.
[0080] FIG. 11 shows the relationship between the contents of the
tar (binder 1) in the raw pellets and the falling distance of the
raw material pellets.
[0081] FIG. 12 is a diagram showing the pellet charging device
according to the fifth embodiment of the present invention.
[0082] FIG. 13 is a diagram of the pellet charging device viewed
from above as shown by arrows marked by II and II.
[0083] FIG. 14 is a side view of the pellet charging device viewed
from side as shown by arrows marked by III and III.
[0084] FIG. 15 is a schematic perspective view of a conventional
rotary bed-type direct reducing furnace.
[0085] FIG. 16 is a partial cross-sectional and developed view
along the central axis of the conventional rotary bed-type direct
reducing furnace shown in FIG. 1.
[0086] FIG. 17 is a schematic perspective view of a conventional
rotary bed-type direct reducing furnace and a cooling cylinder.
[0087] FIG. 18 is a diagram showing a top view of the conventional
rotary bed-type direct reducing furnace.
[0088] FIG. 19 is a schematic diagram showing the reduced iron
pellets producing facility including the raw material processing
facility and a conventional rotary bed-type direct reducing furnace
shown as the cross-sectional and developed view.
[0089] FIG. 20 is a diagram showing a relationship between the
surface temperatures of the rotary bed of the conventional reducing
furnace and the rotating directional positions of the rotary
bed.
[0090] FIG. 21 is a schematic diagram showing a reduced iron pellet
producing system including a reducing furnace and accessories.
[0091] FIG. 22 is a schematic diagram showing locations of devices
of a conventional rotary bed-type direct reducing furnace and
accessories.
[0092] FIG. 23 is a side view of the reduced iron pellet
discharging device of the conventional rotary bed-type reducing
furnace.
[0093] FIG. 24 is a diagram showing a conventional charging
apparatus for charging raw material pellets in the rotary bed-type
reducing furnace.
[0094] FIG. 25 is a diagram showing the conventional charging
apparatus when the raw material pellets are loaded.
[0095] FIG. 26 shows a positional relationship of various
accessories in the rotary bed direct reducing furnace.
[0096] FIGS. 27A and 27B are diagrams showing the conventional
pellet charging device, in which FIG. 27A shows the structure and
FIG. 27B shows when pellets are charged by the device.
DETAILED DESCRIPTION OF THE INVENTION
[0097] Hereinafter, the details of the present invention will be
described according to the embodiments of the present invention
with reference to the attached drawings.
[0098] First Embodiment:
[0099] FIG. 1 is a schematic diagram showing the whole facility for
producing reduced iron production, and the same rotary bed-type
direct reducing furnace shown in FIG. 21 is used in the production
facility shown in FIG. 1.
[0100] Referring to FIG. 2, the reference numeral 1 denotes a
rotary bed-type direct reducing furnace and FIG. 1 is obtained by
developing the circular furnace shown in FIG. 1. The numeral 2
denotes a charging device (e. g. a reciprocating conveyer) of raw
material pellets, 3 a discharging portion for discharging the
reduced iron pellets to the outside of the reducing furnace, 4 a
container for discharging the reduced iron pellets, 5 a exhaust
duct for discharging the exhaust gas in the reducing furnace 1. The
rotary bed-type direct reducing furnace 1 is the same as the
conventional reducing furnace shown in FIG. 1 and the operation of
the reducing furnace is also the same as the conventional reducing
furnace.
[0101] The reference numeral 14 denotes a sealed type electro-blast
furnace (synonym: a submerged arc furnace), in which, when the
container 4 storing the reduced iron pellet is transported on the
top of the electro-blast furnace 14, the reduced iron pellets are
placed into a hopper 16 of the electro-blast furnace 14 without
contacting with air and charged into the electro-blast furnace 14
through a chute 17. The reduced iron pellets thus charged into the
electro-blast furnace 14 are melted in sequence by applying
currents between electrodes 18. The molten pig iron at this stage
contains a considerable amount of carbon. This molten pig iron is
intermittently discharged into a ladle and it is converted into a
molten steel through desulfuration and decarburization
treatments.
[0102] The reduced iron pellets after the heating and reducing
treatments in the rotary bed-type direct reducing furnace still
contain remaining unreduced iron oxide (FeO) and CO gas is
generated when the unreduced iron oxide is exposed to the strong
reducing atmosphere in the sealed-type electro-blast furnace. The
amount of CO gas generated in the electro-blast furnace is 30 to 40
Nm.sup.3 per a ton of the reduced iron pellets and the CO gas
reproduced in the electro-blast furnace is discharged through the
exhaust pipe 19 and stored in a gas holder 20 after washing. The CO
gas in the gas holder 20 is introduced into the rotary CO gas
bed-type direct reducing furnace 1 through the pipe line 21
inserted near the discharging portion of the reducing furnace
1.
[0103] The detail of this embodiment is described hereinafter with
reference to FIG. 2. FIG. 2 is a developed cross-sectional view of
the rotary bed-type direct reducing furnace 1 wherein the top end
of the pipe line 21 is branched into two ends, each of which is
connected to the gas introducing nozzles 32 and 33. These gas
introducing nozzles 32 and 33 are inserted obliquely through the
furnace wall of the reducing furnace 1 at both sides of the cooling
device 25.
[0104] As described above, the gas holder 20 is a collecting means
for the reducing gas generated in the electro-blast furnace 14, and
the reducing gas introducing means is constructed by the gas holder
20, pipe line 21, and the gas introducing nozzles 32 and 33. It is
possible to construct the reducing gas introducing means by
connecting lines 21 and 21a directly for introducing the reducing
gas into the reducing furnace 1. It is also possible to increase
the number of nozzles from one to two or more.
[0105] A case of producing about 50 tons per hour of the reducing
iron pellet will be described hereinafter as an operational
example. The sealed-type elecrtro-blast furnace regenerates about
2200 Nm.sup.3 of the reducing exhaust gas mainly composed of CO gas
and this reducing exhaust gas is introduced into the reduced iron
pellet discharge portion 3 of the reducing furnace 1. Thereby, the
reduced iron pellets just before discharge are blown by the
reducing gas, and at the same time, the reducing gas effectively
reduces the partial pressures of oxidizing gases (O.sub.2,
CO.sub.2, and H.sub.2O) in the combustion gas, and thus the
re-oxidization of the reduced iron pellets can be suppressed. An
analysis of the reduced iron in the container 4 for storing the
reduced iron pellets has revealed that the metal ratio of the
reduced iron has increased more than 3% in average.
[0106] The reducing gas introduced in the reducing furnace can be
utilized as a fuel gas; thus the reducing gas contributes to the
fuel economy. Practically, the fuel consumption through a series of
burners can be reduced by 10%.
[0107] A modified example of the first embodiment is described.
[0108] As shown in FIG. 3, a reducing gas introducing nozzle 40 is
inserted obliquely through the furnace wall (top wall), instead of
the two nozzles 32 and 33 in the former example. More practically,
the gas nozzle 40 is connected with the gas holder 20 through the
pipe line 21.
[0109] A screw-type reduced iron pellet discharging machine 24 is
provided and the reducing gas is inserted such that the reducing
gas flow on the surface of the screw in the direction in conformity
with the tangential direction of the rotation of the screw.
Accordingly, the screw is effectievely cooled by the reducing gas
at almost room temperature. The working life of the reduced iron
pellet screw charger can be extended for more than 20%, since the
reducing gas flow effectively reduce the corrosion of the screw. In
this case, the metal ratio of the reduced iron pellets sampled from
the container 4 showed a high ratio of more than 2%. The
introduction of the reducing gas reduces the fuel consumption by
about 8%.
[0110] The other modified example of this first embodiment is shown
in FIG. 4. In this example, the pipeline 21 is branched into two
lines and each branched line is connected to respective nozzles 33
and 40, instead of the first example of two nozzles 32 and 33. Out
of 2200 Nm.sup.3/hour of the reduced gas generated in the
electro-blast furnace, about 30% is discharged through the nozzle
32 and 70% is discharged through the nozzle 40 and the gas streams
35 and 41 are formed. The working life of the screw discharging
machine is extended for more than 15% and the fuel gas consumption
is reduced more than 9% over that of the conventional
structure.
[0111] Second embodiment
[0112] The second embodiment of the present invention provides a
method and facility for producing the reduced iron pellets having a
high density and a higher mechanical strength.
[0113] FIG. 5 is a diagram showing the facility for producing
reduced iron pellets having a high density and a high mechanical
strength. This facility comprises a rotary bed-type direct reducing
furnace 201 for reducing the raw material pellets into the reduced
iron pellets, a heat retaining and rolling portion 272a for
receiving the reduced iron pellets and executing rolling of the
pellets, a rotary cylinder-type cooler 272 for receiving the rolled
pellets and cooling the rolled reduced iron pellets, and a
container 217. The heat retaining and rolling portion 222a is
formed by lining a part of the rotary cylinder 222 with an
insulating material i. The heat retaining and rolling portion 222a
occupies about 1/3 of the total length of the rotary cylinder
222.
[0114] The reference numeral 233 denotes a pelletizing machine for
producing the raw material pellets P1 by pelletizing the mixture of
the iron ore powder and the carbonaceous material powder. The
numeral 223 denotes a conveying device, 224 a pellet charging
machine for charging the raw material pellets on the rotary bed 247
of the reducing machine 201, 228 a pellet layer formed on the
rotary bed 227, 244 a reduced iron pellets discharging machine for
discharging the high temperature pellets from the reducing furnace
201 to the heat retaining and rolling portion, and 225 a combustion
gas exhaust duct for discharging the combustion gas to the outside
of the reducing furnace 201.
[0115] The reference numeral 230 denotes a chute for supplying the
reduced iron pellets into the heat retaining and rolling portion
222a, 231 a gas sealing hood for sealing gas, 232 a series of spray
nozzles for spraying water on the outer surface of the rotary
cylinder, 233 a spray nozzle for spraying water directly on the
rolled reduced iron pellets near the exit of the rotary cylinder
222. The numerals 234 and 235 denote tire rolls for rotating the
rotary cylinder 222, 236 a gear for driving rotation of the rotary
cylinder, and 239 a hood as well as a hopper, 238 a screen, and 239
an exhaust duct for discharging waste gas.
[0116] Hereinafter, a method of producing reduced iron will be
described.
[0117] The raw material pellets P1, formed by pelletizing the
mixture of the iron ore powder and the reducing material powder by
the pelletizing machine 223, are transported to the pellet charging
machine 224 and charged on the rotary bed 227 of the reducing
furnace 201 to form the pellet layer 228. The pellet layer is
usually a two pellet layer because the pellet layer is usually
heated mainly by radiation. The raw material pellets P1 are reduced
by being heated at about 1200.degree. C. on the rotary bed 227 of
the reducing furnace 201 and converted into the reduced iron
pellets P2. The high temperature reduced iron pellets P2 discharged
from the reducing furnace 201 are delivered to the heat retaining
and rolling portion 222a. The temperature of the reduced iron
pellets P2 delivered into the heat retaining and rolling portion
222a is at about 1100.degree. C. and the reduced iron pellets as
discharged have a density of about 2 g/cm.sup.3. The reduced iron
pellets discharged are subjected to the rolling motion for more
than 3 min. to less than 20 min. Since the deformation resistance
of the reduced iron pellets are very low under this temperature
condition, the high temperature reduced iron pellets P2 undergo the
sintering action and the reduced iron pellets are made further
denser becoming compacted reduced iron pellets P2'.
[0118] The thus compacted reduced iron pellets P2' are transferred
and cooled into a temperature of less than 600.degree. C., while
the compacted reduced iron pellets are cooled by the cooling water
spray and by the heat dissipating into the furnace wall of the
rotary cylinder 222. The compacted reduced iron pellets P3' are
further cooled directly by the sprayed water from the spray nozzle
233 to 100.degree. C., and finally collected as the compacted
reduced iron pellets P4'.
[0119] The collapsing strength of the thus obtained compacted
reduced iron pellets increases until a value of 100 kgf per a
pellet. In the conventional method, the collapsing strength of the
reducing iron pellets has been about 30 kgf for a pellet with a
diameter of 10 mm, and thus, it is possible to increase the
collapsing strength of a reducing pellet more than three times by
the use of the new apparatus and new method described above.
[0120] Therefore, the high temperature reduced iron pellets
discharged from the reducing furnace can be compacted by the
sintering effect obtained by rolling at a temperature range of
800.degree. C. to 1200.degree. C. for more than 3 min. and less
than 30 min. and it has been proven that the compacted pellets are
not fragile and are suitable for use in the electro-blast
furnace.
[0121] Third embodiment
[0122] Hereinafter, the third embodiment of the present invention
will be described which is related to the use of wet raw material
pellets. A new facility is provided for the use of wet raw material
pellets.
[0123] The present embodiment will be described with reference to
FIGS. 7 and 8. FIG. 7 is a diagram showing the facility for
producing reduced iron pellets including the raw material pellet
forming facility and the rotary bed-type reducing furnace, and FIG.
8 is a diagram showing the relationship between the surface
temperature of the rotary bed and the location on the rotary
bed.
[0124] As shown in FIG. 7, since reference numerals 306, 307, and
308 denotes hoppers for storing an iron oxide powder, a reducing
material powder and a binder, respectively. 309 denotes a mixer and
310 a pelletizer.
[0125] Furthermore, referring to FIG. 7, the reference numeral 321
is a hopper for storing the insulating particles 323 such as lime
stone particles used for the bed covering layer, 322 a second
particle hopper having an opening at the bottom end facing toward
the rotary bed 320 of the reducing furnace leaving a specified
interval therebetween. These first and second hoppers 321 and 322
constitutes an insulating material supplying device 300 for
covering the rotary bed to form a bed covering layer 324 (the heat
insulating layer) of the insulating particles 323 having a high
melting point, prior to charging the wet raw material pellets. In
order to avoid melting, the insulating particles are required to
have a higher melting temperature than the heating temperature
(1300.degree. C.) of the wet raw material pellets, preferably more
than 1400.degree. C. Examples of the high melting point particles
include limestone particles, dolomite particles, or basic oxide
particles composed of their mixture.
[0126] In the rotary bed direct reducing furnace, as shown in FIG.
7, the insulating particles 323 such as limestone particles are
supplied through the second particle hopper 322 on the rotary bed
320 uniformly at a point A to form the bed covering layer 324.
Since the insulating particles supplying device 300 is constructed
by the first hopper 321 and the second hopper 322, the continuous
supply of the insulating particles will never be interrupted for a
long time even if one of both hoppers is blocked by the
particles.
[0127] As shown in FIG. 9, the appropriate particle size of the
insulating particle is preferably in a range of 1 to 5 mm in
diameter. In addition, the appropriate layer thickness of the
insulating particles is estimated to be in a range of 1 to 5 mm.
The wet raw material pellets are charged on the rotary bed just
after the insulating particle layer is formed on the rotary bed 320
of the reducing furnace 301, and a layer of the wet raw material
pellets are formed. In this case, an appropriate size of the wet
raw material pellets is from 7 to 20 mm in general, and single
pellet layer or double pellet layer is usually formed.
[0128] The wet raw material pellet layer 312 are heated during
passing in the reducing furnace, the wet raw material pellets are
first dried, the reducing reaction takes place by heating to a high
temperature, and the raw material pellets are finally converted
into the reduced iron pellets which are discharged by a reduced
iron pellets discharging machine 303 at point (C) in FIG. 7 into
the container 304. Thereafter, the reduced metal pellets are
charged into the electro-blast furnace to be melted and refined
into the refined molten metal.
[0129] The surface temperature (To) of the rotary bed after
discharging of the reduced iron pellets is normally 1100.degree. C.
In the conventional reducing furnace, a time consuming operation
has been carried out to cool down the surface temperature of the
rotary bed below 700.degree. C. However, if the surface of the
rotary bed is covered by the insulating particle layer, the wet raw
material pellets may be charged without suffering bursting, even if
the surface temperature of the rotary bed (Ti) for charging the wet
pellets is as high as 1000.degree. C. In addition to the above
effect, the advantageous features of the present embodiment include
that, even when one hopper of the insulating particles is blocked
or becoming empty, it is possible to avoid a discontinuation in the
supply of the insulating particles, because two stage hoppers are
provided.
[0130] Fourth Embodiment
[0131] The fourth embodiment, relating to an improvement of the
falling strength of the raw material pellets, will be described
hereinafter with reference to attached drawings.
[0132] The reduced iron pellets are usually produced by the
reducing facility shown in FIG. 10, including a rotary bed-type
direct reducing furnace 401.
[0133] The iron ore 421 as a raw material of the reduced iron and
the coal or coke 422 as the reducing material are weighed to adjust
the content of the coal to 2 wt %, and both materials are supplied
to each pulverizer 421a and 422a for obtaining powders of each
material with the powder size of tens of microns. The pulverized
powders of both iron ore and coal are supplied to the pelletizer
402 after these powders are mixed with a viscous binder composed of
hydro carbon-type compounds (described in a later section) by a
mixer 425.
[0134] The powders 421 and 422, and a binder are mixed with a small
amount of water (about 10 wt %) by a pelletizing machine 402 and
the mixture is pelletized into raw pellets having a diameter in a
range of 10 to 20 mm.
[0135] This raw pellets are supplied to the drying machine 403. The
raw pellets are preserved in an atmosphere maintained at more than
150.degree. C., preferably in a range of 150 to 170.degree. C.
Thereby, the raw pellets are dried and the raw material pellets are
formed through the dehydration reaction of a part of hydrogen and
oxygen.
[0136] The raw material pellets after drying are charged on the
rotary bed of the reducing furnace, and these pellets are reduced
in the reducing furnace by heating in a reducing atmosphere. The
combustion gas circulate in the reducing furnace in a direction
opposite to that of the rotation of the rotary bed, as shown in the
dotted arrow in FIG. 10 and discharged from the exhaust duct 408 to
the heat exchange device. The exhaust gas is discharged into the
air after preheating the primary air used in the burners 407.
[0137] The rotary bed 412 in the reducing furnace 401 rotates in
the direction shown by the arrow shown in FIG. 9 once around every
ten minutes. The reduced pellets are discharged to the outside of
the reducing furnace by a screw-type discharging machine 405
disposed near the charging machine 404 and the reduced iron pellets
are cooled into room temperature by a cooling device 406 to be
supplied to the next process.
[0138] As described above, the raw material pellets undergo various
mechanical impacts before they are charged on the rotary bed of the
reducing furnace. The conventional raw material pellets formed by
use of bentonite do not have sufficient falling strength, so that
the freedom of the design is considerably restricted in order to
minimize the falling distance of the raw material pellets.
[0139] The present embodiment has solved the above problem by the
use of particular binders shown below.
[0140] In this embodiment, it has been clarified from experimental
research that hydrocarbon compounds having a certain viscosity such
as carboxymethylcellulose (CMC), polyvinylalcohol (PVA), and tar
are preferable as binders in order to improve the falling strength
of the raw material pellets.
[0141] Table 1 shows the relationship between the content of the
binders (content in the raw pellets) and the falling distance of a
pellet without fracturing the raw material pellets obtained after
drying the raw pellets.
[0142] As shown in Table 1, when the tar is used alone as a binder,
addition of more than 5 wt % ensures the falling strength (falling
distance) of more than 400 mm.
[0143] FIG. 11 shows the relationship between the contents of the
tar (the binder 1) in the raw pellets and the falling strength and
the raw material pellets. The failing distance of the raw material
pellets can be secured if the content of the tar is more than 5 wt
%. As shown in FIG. 11, as the content of the tar increases, the
region wherein the raw material pellets are not broken expands and
the falling distances of the raw material pellets becomes higher.
As shown as examples 2 and 3 in Table 1, when CMC and PVA are used
alone, the falling distance of 500 mm can be secured by addition of
more than 0.2 wt % of CMC or PVA. As shown for examples 5, 6, 8 and
9 in Table 1, it has been confirmed that the falling strength of
the raw material pellets increases as the amounts of CMA and PVA
are increased.
[0144] When a mixture of CMC and PVA is used, the falling distance
of more than 500 mm is secured if the content of the mixture
exceeds 0.2 wt %. The falling distance of more than 500 mm is
secured if more than 4 wt % of tar and a mixture of more than 0.1
wt % of CMC and PVA are incorported.
[0145] Furthermore, even when the conventional bentonite is used as
the binder, addition of more than 0.2 wt % of CMC and PVA makes it
possible to secure the galling distance of 500 mm (FIG. 11,
examples 12 to 14).
[0146] In the repetitive falling experiment, it has been confirmed
that the raw material pellets containing more than 5 wt % of tar
and more than 0.2 wt % of CMC or PVA show at least two times of the
falling distance of 300 mm. The above results are obtained for the
raw material pellets after drying, the raw pellets before drying
show a falling distance of 400 mm for more than four times, which
indicates that the raw pellets of the present embodiment are three
times higher than the conventional raw pellets containing only
bentonite.
[0147] As shown above, the present embodiment showed that it is
possible to remarkably improve the strength of the raw material
pellets by selecting types and amounts of binders used for
producing the raw material pellets.
[0148] Fifth Embodiment
[0149] The fifth embodiment of the present invention provides an
improved pellet charging device which is capable of charging the
raw material pellets on the rotary bed of the rotary bed-type
direct reducing furnace.
[0150] FIG. 12 is a diagram showing the pellet charging device
according to the fifth embodiment of the present invention, FIG. 13
is a bird eye view from the directions of II and II shown by
arrows, and FIG. 14 is a side view of the pellet charging device
from the direction of III and III shown by arrows.
[0151] As shown in FIGS. 12, 13 and 14, the pellet charging device
of the present embodiment 504 comprises a rotating drum 521 and a
hopper 511 for supplying the raw material pellets 511 onto the
rotating drum 521.
[0152] As shown in FIG. 14, the rotating drum is in a shape of a
truncated cone, and a side surface of the truncated cone shaped
rotating drum is disposed facing toward the rotary bed 512 such
that the top surface 521a at the small diameter side of the
truncated cone 521 is disposed facing toward the inner periphery of
the rotary bed 512. The lower surface 512c of the rotating drum 512
faces to the rotary bed 512.
[0153] In this embodiment, the truncated surface of the rotating
drum 521 is disposed parallel to the plane including the central
axis of the rotary bed, and the rotating drum is disposed to have
an angle of inclination (shown by .alpha. in FIG. 14) such that the
side surface 512c of the rotating drum 521 becomes horizontal at
the highest point of the rotating drum 521 (shown as A in FIG. 12)
as shown in FIG. 14 to the bottom surface of the hopper 522.
Thereby, the side upper surface of the rotating drum 521 becomes
horizontal. In this embodiment, the rotating drum 521 is driven so
as to be rotated in the direction shown by an arrow B in FIG. 12 by
an electric motor (not shown) such that the tangential direction of
the rotating drum becomes opposite to the moving direction of the
rotary bed 512 (the direction of the rotary bed is shown by an
arrow in FIG. 12).
[0154] Since the rotating drum 521 is in the shape of the truncated
cone, the circumferential speed of the side surface of the rotating
drum 521c varies depending on the rotating radius of the rotating
drum. In the present embodiment, the vertical angle (the angle
.beta. shown in FIG. 13) of the side surface of the rotating drum
is determined such that the ratio of the circumferential speed at
the large diameter of the rotating cone to that of the small
diameter of the rotating cone coincides with the ratio of the
rotational speed of the rotary bed just beneath the large diameter
521b of the rotating drum 521 and that of the rotary bed just
beneath the small diameter 521a of the rotating drum 521. That is,
when the radius of the vertical angle .beta. is r1, a radius of the
bottom surface 21b is R1, the radius of the inner periphery of the
rotary bed is r, and the radius of the outer periphery is R (see
FIG. 13), the vertical angle of the rotating drum is set so as to
satisfy an equation, R1/r1=R/r. Accordingly, the circumferential
speed at each position of the upper side surface A of the rotating
drum 521 coincides with the rotating speed at the each radial
position of the rotary bed. For example, when the number of
revolutions of the drum 521 is determined such that the
circumferential speed of the bottom surface 521b of the drum 521
coincides with the rotating speed of the outer periphery of the
rotary bed, the circumferential speeds at each position of the side
surface of the drum 521 coincide with rotating speeds towards
opposite direction of the rotary bed at each position just beneath
each point of the drum 521.
[0155] The rotating drum 521 is disposed so as to leave a space
corresponding to two or three layers of pellets. The hopper 522 is
provided with an exit opening 522a, and the hopper 522 and the drum
surface 521c are spaced so as to allow one layer of pellets to pass
therethrough.
[0156] In the present embodiment, the raw material pellets 511 are
placed in a hopper 522 and the pellets are delivered as a layer of
pellets from an exit opening 522a on the rotating drum. The raw
material pellets delivered from the hopper 522 slide over the side
surface 521c of the drum 521, fall on the rotary bed 512, and are
transferred below the rotating drum 521 by the movement of the
rotary bed 512.
[0157] Assuming that a circumferential speed at a point on the side
surface 521c of the rotating drum 521 is V, the moving speed of the
rotary bed just beneath this point is also V. Therefore, the raw
material pellets supplied on the rotary bed by one pellet layer
move as one layer of pellets. In addition, in this embodiment, the
central axis of the rotating drum is inclined such that the
circumferential speed at each point of the rotating drum surface
521c becomes proportional to the moving speed of the rotary bed 512
at each point just beneath the point of the rotating drum surface
521c. Thus, the circumferential speed at a point on the rotating
drum surface 521c coincides with the moving speed of the rotary
bed.
[0158] Assuming that a circumferential speed at a point on the side
surface 521c of the rotating drum 521 is V, the moving speed of the
rotary bed just beneath this point is also V. Therefore, the raw
material pellets supplied on the rotary bed by one pellet layer
move as one layer of pellets. In addition, in this embodiment, the
central axis of the rotating drum is inclined such that the
circumferential speed at each point of the rotating drum surface
521c becomes proportional to the moving speed of the rotary bed 512
at each point just beneath the point of the rotating drum surface
521c. Thus, the circumferential speed at a point on the rotating
drum surface 521c coincides with the moving speed of the rotary
bed.
[0159] Consequently, since the circumferential speed of the
rotating drum coincides with the moving speed of the rotary bed,
the raw material pellets delivered from the hopper 522 are placed
on the rotary bed as one pellet layer.
1TABLE 1 Ex- Iron bento- height am- ore coal tar CMC PVA nite
without ple (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) fracture 2 75
20 5 -- -- -- 400 mm 3 79.8 20 -- 0.2 -- -- 500 mm 4 79.8 20 -- --
0.2 -- 500 mm 5 65 15 20 -- -- -- 1000 mm 6 75 20 -- 5 -- -- 800 mm
7 75 20 -- -- 5 -- 800 mm 8 70 20 10 -- -- -- 500 mm 9 78 21 -- 1
-- -- 600 mm 10 78 21 -- -- 1 -- 500 mm 11 76 19.5 4 -- -- 0.5 400
mm 12 76 19.6 4 -- -- 0.4 400 mm 13 78 21.8 -- 0.05 0.15 -- 500 mm
14 75 20.9 4 0.1 -- -- 600 mm 15 75 20.9 4 -- 0.1 -- 500 mm 16 78
21.4 -- 0.15 0.05 0.4 500 mm 17 77 22.2 -- 0.1 0.1 0.6 500 mm 18 77
22.5 -- 0.1 0.1 0.3 500 mm
[0160] The case described above is that in which the
circumferential speed of the drum coincides with the moving speed
of the rotary bed. However, when the revolution frequency is set
such that the circumferential speed of the rotating drum is an
integer times as large as the moving speed of the rotary bed, it
becomes possible to form a piled layer of pellets having any
numbers of pellet layers. For example, if the circumferential speed
of the rotating drum is set two times or three times as large as
the moving speed of the rotary bed beneath the rotating drum, a
layer in which two or three layers of pellet are piled may be
formed uniformly on the rotary bed.
[0161] Since the raw material pellets do not incur any damage by
being pressed by, for example, a dam, in this embodiment, an
advantageous feature is further obtained that the raw material
pellets may be prevented from suffering fracture or surface
peeling.
[0162] According to the present embodiment, advantageous effects
are obtained such that the present charging device allows charging
the raw material pellets without incurring fracture, fracture, or
surface peeling, and also allows charging the raw material pellets
in a layer in which any numbers of pellets are piled. Thus, the
reduced iron pellets obtaining by processing the thus charged raw
material pellets has a uniform quality that is suitable and
advantageous for subsequent processing.
* * * * *