U.S. patent application number 10/289290 was filed with the patent office on 2003-04-03 for method and apparatus for making metallic iron.
This patent application is currently assigned to KABUSHIKI KAISHA KOBE SEIKO SHO. Invention is credited to Inaba, Shinichi, Ito, Shuzo, Kikuchi, Shoichi, Kobayashi, Isao, Kujirai, Takashi, Kunii, Kazuo, Matsumura, Toshihide, Negami, Takuya, Shimizu, Masataka, Sugiyama, Kimio, Takenaka, Yoshimichi, Tsuchiya, Osamu, Uragami, Akira.
Application Number | 20030061909 10/289290 |
Document ID | / |
Family ID | 27572515 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030061909 |
Kind Code |
A1 |
Negami, Takuya ; et
al. |
April 3, 2003 |
Method and apparatus for making metallic iron
Abstract
A method of making metallic iron in which a compact, containing
iron oxide such as iron ore or the like and a carbonaceous
reductant such as coal or the like, is used as material, and the
iron oxide is reduced through the application of heat, thereby
making metallic iron. In the course of this reduction, a shell
composed of metallic iron is generated and grown on the surface of
the compact, and slag aggregates inside the shell. This reduction
continues until substantially no iron oxide is present within the
metallic iron shell. Subsequently, heating is further performed to
melt the metallic iron and slag. Molten metallic iron and molten
slag are separated one from the other, thereby obtaining metallic
iron with a relatively high metallization ratio. Through the
employment of an apparatus for making metallic iron of the present
invention, the above-described method is efficiently carried out,
and metallic iron having a high iron purity can be made
continuously as well as productively not only from iron oxide
having a high iron content but also from iron oxide having a
relatively low iron content.
Inventors: |
Negami, Takuya; (Tokyo,
JP) ; Kunii, Kazuo; (Tokyo, JP) ; Inaba,
Shinichi; (Hyogo, JP) ; Shimizu, Masataka;
(Hyogo, JP) ; Kobayashi, Isao; (Osaka, JP)
; Takenaka, Yoshimichi; (Hyogo, JP) ; Matsumura,
Toshihide; (Hyogo, JP) ; Uragami, Akira;
(Osaka, JP) ; Kujirai, Takashi; (Osaka, JP)
; Tsuchiya, Osamu; (Hyogo, JP) ; Sugiyama,
Kimio; (Osaka, JP) ; Ito, Shuzo; (Osaka,
JP) ; Kikuchi, Shoichi; (Osaka, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA KOBE SEIKO
SHO
Hyogo
JP
|
Family ID: |
27572515 |
Appl. No.: |
10/289290 |
Filed: |
November 7, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10289290 |
Nov 7, 2002 |
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09891653 |
Jun 26, 2001 |
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6506231 |
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09891653 |
Jun 26, 2001 |
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09478409 |
Jan 6, 2000 |
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6432533 |
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09478409 |
Jan 6, 2000 |
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08818954 |
Mar 14, 1997 |
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6036744 |
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Current U.S.
Class: |
75/485 ; 266/177;
75/500 |
Current CPC
Class: |
C21B 13/105 20130101;
C21B 13/0046 20130101 |
Class at
Publication: |
75/485 ; 75/500;
266/177 |
International
Class: |
C21B 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 1996 |
JP |
HEI 8-257114 |
Sep 27, 1996 |
JP |
HEI 8-257115 |
Sep 27, 1996 |
JP |
HEI 8-257116 |
Sep 27, 1996 |
JP |
HEI 8-257117 |
Sep 27, 1996 |
JP |
HEI 8-257118 |
Mar 15, 1996 |
JP |
HEI 8-59801 |
Claims
1. A method, comprising: heating a first compact, thereby forming a
reduced compact; wherein said first compact comprises (i) iron
oxide, and (ii) a carbonaceous reducing agent; and said reduced
compact comprises (iii) a shell, comprising metallic iron, and (iv)
molten slag, inside said shell.
2. The method of claim 1, wherein substantially no iron oxide is
present within said shell.
3. The method of claim 1, further comprising heating said reduced
compact, thereby allowing said slag to flow out from inside said
shell.
4. The method of claim 3, wherein during said further heating part
of said shell is melted, thereby separating molten slag from said
metallic iron.
5. The method of claim 4, wherein during said further heating said
metallic iron is carburized, thereby reducing the melting point of
said metallic iron.
6. The method of claim 1, further comprising heating said reduced
compact, thereby melting said metallic iron and separating said
metallic iron from said slag.
7. The method of claim 6, wherein during said further heating said
metallic iron is carburized, thereby reducing the melting point of
said metallic iron.
8. The method of claim 1, further comprising allowing said slag to
form aggregates, and separating said aggregates from said metallic
iron.
9. The method of claim 1, wherein said heating is performed at a
maximum temperature of not less than the melting point of said
slag, and not more than the melting point of said metallic
iron.
10. The method of claim 1, wherein during said heating said iron
oxide is reduced first by solid phase reduction, followed by liquid
phase reduction, and said heating is continued until substantially
no iron oxide is present.
11. The method of claim 1, wherein said reduced compact comprises
5% by weight or less of FeO.
12. The method of claim 11, wherein said reduced compact comprises
2% by weight or less of FeO.
13. The method of claim 1, wherein said slag comprises 5% by weight
or less of FeO.
14. The method of claim 13, wherein said slag comprises 2% by
weight or less of FeO.
15. The method of claim 1, wherein said shell is closed and
continuous.
16. The method of claim 1, wherein said beating is performed at a
temperature of 1350-1540.degree. C.
17. An object, comprising; (a) a shell comprising metallic iron,
and (b) slag, inside said shell.
18. The object of claim 17, wherein said slag is molten.
19. The object of claim 17, wherein said slag comprises 5% by
weight or less of FeO.
20. The object of claim 17, wherein said slag comprises 2% by
weight or less of FeO.
21. The method of claim 1, wherein said first compact is in the
form of grains or aggregates and undergoes reduction through the
application of heat while being moved in a horizontal
direction.
22. The method of claim 21, wherein said first compact is placed on
an iron belt having edge portions comprising walls formed at said
edge portions thereof to prevent said first compact from falling
off said iron belt, and said first compact undergoes reduction
through the application of heat while being moved in a horizontal
direction.
23. The method of claim 1, wherein said first compact is in the
form of grains or aggregates and undergoes reduction through the
application of heat while being placed on a horizontal plane.
24. The method of claim 1, wherein said first compact is in the
form of grains or aggregates and undergoes reduction through the
application of heat while being rolled.
25. The method of claim 1, wherein said first compact is in the
form of grains or aggregates and undergoes reduction through the
application of heat while falling downward.
26. The method of claim 1, wherein said first compact is in an
elongated form, and undergoes reduction through the application of
heat while being moved downward in an upright position.
27. The method of claim 26, wherein said first compact is
continuously formed into an elongated form and fed to a section
where reduction is performed through the application of heat.
28. The method of claim 26, wherein said first compact comprises
iron mesh serving as a support therefor.
29. The method of claim 26, wherein said first compact comprises an
iron bar or wire serving as a core thereof.
30. The method of claim 1, wherein said first compact is in an
elongated form and undergoes reduction through the application of
heat while being moved downward along a slope.
31. The method of claim 30, wherein said first compact is
continuously fed on an iron belt to a section where reduction is
performed through the application of heat.
32. An apparatus for manufacturing metallic iron by reducing a
compact of iron oxide containing a carbonaceous reducing agent,
comprising: a thermal reduction apparatus for reducing the compact
through the application of heat, thereby forming a shell comprising
metallic iron and slag inside the shell; a beat-melting apparatus
for melting the shell and the slag; and a separator for separating
the molten iron from the molten slag.
33. The apparatus of claim 32, wherein the compact is in the form
of grains or aggregates and said thermal reduction apparatus
comprises a mechanism for reducing the compact through the
application of heat while moving the compact in a horizontal
direction.
34. The apparatus of claim 33, wherein said mechanism comprises an
endless rotary member and a hearth located on said member and used
for placing the compact thereon.
35. The apparatus of claim 34, wherein said hearth is provided with
separating members at certain intervals on said hearth to prevent
the compact from adhering to another compact.
36. The apparatus of claim 35, wherein said separating members
includes a desulfurizing agent.
37. The apparatus of claim 32, wherein said heat-melting apparatus
comprises a sloped floor for melting the compact by application of
heat while tumbling or sliding the compact thereon.
38. The apparatus of claim 32, wherein the compact is in the form
of grains or aggregates and said thermal reduction apparatus
comprises a mechanism for reducing the compact through the
application of heat while the compact is placed on a horizontal
plane.
39. The apparatus of claim 38, wherein said thermal reduction
apparatus comprises a feeding member having a horizontal plane for
intermittently feeding the compact placed on said horizontal plane,
a discharging member for discharging the compact from said feeding
member, and a heating mechanism for heating the compact.
40. The apparatus of claim 39, wherein said discharging member is a
tilting member for making the position of said feeding member
alternate between a horizontal position and a sloped position.
41. The apparatus of claim 39, wherein said discharging member is a
pushing member for pushing out the compact from said feeding
member.
42. The apparatus of claim 39, wherein an iron support is placed on
said feeding member and adapted to be discharged together with the
compact.
43. The apparatus of claim 39, wherein separating members are
provided on said feeding member at certain intervals to prevent the
compact from adhering to another compact.
44. The apparatus of claim 43, wherein said separating members
includes a desulfurizing agent.
45. The apparatus of claim 39, wherein said heat-melting apparatus
comprises a sloped floor for melting the compact by application of
heat while tumbling or sliding the compact thereon.
46. The apparatus of claim 32, wherein the compact is in the form
of grains or aggregates and said thermal reduction apparatus
comprises a mechanism for reducing the compact through the
application of heat while tumbling the compact.
47. The apparatus of claim 46, wherein said thermal reduction
apparatus comprises a tumbling mechanism and a thermal reduction
member for heating the compact, said tumbling mechanism comprising
a surface for tumbling the compact thereon and a discharging unit
for discharging the compact from said surface.
48. The apparatus of claim 47, comprising a thermal
reduction-melting apparatus, comprising an integrated unit of said
thermal reduction apparatus and said heat-melting apparatus,
wherein said thermal reduction-melting apparatus comprises a
tumbling mechanism and a mechanism for reducing and melting the
compact through the application of heat, said tumbling mechanism
including a sloped surface for gradually tumbling down the compact
along a sloped direction and a discharging unit for discharging the
compact from said sloped surface.
49. The apparatus of claim 47, wherein said surface of tumbling is
formed of the interior surface of a channel-like member.
50. The apparatus of claim 49, wherein the interior surface of said
channel-like member has an arc-shape, V-shape, or U-shape.
51. The apparatus of claim 47, wherein said surface comprises the
interior surface of a channel-like member having an arc-shape,
V-shape, or U-shape and is sloped along the length of the
channel-like member.
52. The apparatus of claim 32, wherein the compact is in the form
of grains or aggregates and said thermal reduction apparatus
reduces the compact through the application of heat while the
compact is falling downward.
53. The apparatus of claim 52, comprising a thermal
reduction-melting apparatus, comprising an integrated unit of said
thermal reduction apparatus and said heat-melting apparatus,
wherein said thermal reduction-melting apparatus comprises a space
of falling for allowing the compact in the form of grains to fall
downward and a heating member for reducing and melting the compact
in the form of grains through the sequential application of heat
while the compact in the form of grains is falling.
54. The apparatus of claim 53, wherein said separator comprises a
submerged weir for receiving molten slag and molten iron falling
from above on one side thereof and for releasing the molten slag
from one side thereof and the molten iron from the other side
thereof.
55. The apparatus of claim 32, wherein the compact is in an
elongated form, and said thermal reduction apparatus reduces the
compact through the application of beat while moving the compact
downward in an upright position.
56. The apparatus of claim 32, wherein the compact is in an
elongated form, and said thermal reduction apparatus comprises a
downward sloped surface for reducing the compact through the
application of heat while moving the compact downward along said
downward sloped surface.
57. The apparatus of claim 55, wherein there is provided an
apparatus for continuously forming an elongated compact on the
material feed side of said thermal reduction apparatus.
58. The apparatus of claim 32, further comprising means for feeding
an iron belt operable to convey the compact thereon, the compact
placed on said iron belt being subjected to reduction and melting
through the application of heat.
59. The apparatus of claim 58, wherein the compact is in the form
of grains Or agglomerates, and said iron belt has edge portions and
comprises walls formed at said edge portions thereof to prevent the
compact from falling off said iron belt and conveys the compact
thereon in a horizontal direction within said thermal reduction
apparatus for reducing the compact through the application of
heat.
60. The apparatus of claim 58, wherein the compact is in an
elongated form, further comprising forming means for continuously
forming the compact in an elongated form and for feeding the
compact in an elongated form onto said iron belt.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of obtaining
metallic iron by subjecting iron oxides contained in iron ore or
the like to reduction through the application of heat using a
carbonaceous material as a reductant. More specifically, the
invention relates to a method of efficiently making high purity
metallic iron in which iron oxides are efficiently reduced into
metallic iron while slag components including gangue and the like
contained in an iron oxide source, such as iron ore, are melted and
separated properly from metallic iron, and to a method and
apparatus for industrially making metallic iron based on this
method
BACKGROUND ART
[0002] A conventional method of making direct reduced iron is where
iron ore or pellets which contain iron oxide are directly reduced
using a reducing gas to obtain reduced iron An example is a shaft
furnace method represented by the Midrex process. In this type of
method of making direct reduced iron, a reducing gas made from
natural gas or the like, is forced into a shaft furnace from a
tuyere located at the bottom portion thereof to reduce iron oxides,
thereby obtaining reduced iron.
[0003] In recent years, of particular interest has been a process
of manufacturing reduced iron in which a carbonaceous material,
such as coal, is used as a reductant in place of natural gas. Such
a method has already been put into practice and is referred to as
an SL/RN method in which indurated pellets manufactured from iron
ore are subjected to reduction through the application of heat
using coal as a reductant.
[0004] Another reducing iron-making process is disclosed in U.S.
Pat. No. 3,443,931, in which a mixture of pulverized iron ore and
pulverized coal are agglomerated, and the agglomerated mass is
subject to reduction through the application of heat on a rotary
hearth, in high temperature atmosphere, yielding reduced iron.
[0005] Reduced iron obtained using the above-mentioned methods is
charged into an electric furnace directly as source iron or in the
form of briquettes. With the increasing trend of recycling scrap in
recent years, this reduced iron is of particular interest, since it
may be used as a diluent of impurities contained in the scrap.
[0006] A conventional method, however, does not involve separating
slag components such as SiO.sub.2, Al.sub.2O.sub.3, and CaO
contained in the iron ore or the like and in the carbonaceous
material (coal or the like), from the molten iron produced.
Therefore, the resultant reduced iron has a relatively low iron
content (iron purity of metallic iron) In actual practice, these
slag components are separated and removed during a subsequent
refining process. However, an increase in the amount of slag not
only decreases yield of refined molten iron, but significantly
increases the running cost of an electric furnace. Therefore,
reduced iron is required to be iron rich and have a relatively low
content of slag components. In order to meet this requirement, it
is necessary for the above-mentioned conventional reducing
iron-making methods to use iron-rich iron ore, which narrows the
choice of source materials for making iron.
[0007] Furthermore, a goal of the conventional methods described
above is to obtain a reduced solid product as an intermediate
product in an iron making process. Therefore, additional steps such
as conveyance, storage, forming briquettes, and cooling are
required before reduced iron is sent to the next refining process.
These steps involve a large energy loss, and a briquetting step
requires excess energy and a special apparatus.
[0008] In addition, a smelting reduction process such as the DIOS
method is known in which iron oxides are directly reduced to obtain
molten iron. In this method, iron oxides are pre-reduced to an iron
purity of approximately 30 to 50%, and then molten iron in an iron
bath is subjected to a direct reducing reaction with carbon, to
obtain metallic iron. However, this method has problems; since two
steps are required, pre-reduction and final reduction within an
iron bath, the work is complicated, and in addition, due to direct
contact between molten iron oxide (FeO) present in an iron bath and
the refractory of a furnace, the refractory is significantly
damaged.
[0009] Japanese Patent Publication (kokoku) No 56-19366 discloses a
method in which an agglomerate of metal oxide, a solid carbonaceous
material, and slag materials is reduced through the application of
heat to thereby enclose reduced metal with slag shell while
maintaining the shape of the agglomerate, and then the slag shell
is melted to separate metal from slag. This method must generate a
sufficient amount of slag to completely enclose reduced metallic
iron in order to prevent the metallic iron from being re-oxidized.
Thus, the slag materials content must be increased. Furthermore,
this method is likely to generate slag having a relatively high FeO
content, which raises a serious problem, in practical application,
of significantly damaging the refractory lining of equipment.
[0010] Thus, it is quite important to realize a method of making
metallic iron having a relatively low content of slag components,
since such a method adds more value to a metallic iron product,
reduces the running cost of an electric furnace, and provides a
flexible choice of source materials.
[0011] Since slag having a relatively large iron oxide content
melts refractory, it is very important for industrial feasibility
of this kind of iron-making process to reduce the iron oxide
content of slag, generated accompanyingly in a process of
reduction, in order to minimize damage to refractory.
DISCLOSURE OF INVENTION
[0012] The present invention has been achieved in view of the
foregoing. AD object of the present invention is to provide a
method and apparatus of making metallic iron in which metallic
iron, in either solid or molten form, having a very high purity, is
readily and efficiently made from iron ore having a relatively low
iron content or having a relatively high iron content, without
damaging the refractory of a furnace via direct contact with molten
iron oxide.
[0013] In the method of making metallic iron according to the
present invention, iron oxide compacted with a carbonaceous
reductant is subjected to reduction through the application of heat
to yield metallic iron, the method having the following
aspects:
[0014] (1) A shell containing metallic iron is generated and grown
via reduction through the application of heat. The reduction
normally is continued until substantially no iron oxide is present
within the shell, during which slag aggregates within the
shell.
[0015] (2) A metallic iron shell is generated and grown via
reduction through the application of heat, the reduction is
continued until substantially no iron oxide is present within the
shell, and heating is further continued to allow slag generated
within the shell to flow out from inside the shell.
[0016] (3) A metallic iron shell is generated and grown via
reduction through the application of beat, the reduction is
continued until substantially no iron oxide is present within the
shell, and heating is further continued to allow molten metallic
iron to separate from molten slag.
[0017] (4) A metallic iron shell is generated and grown via
reduction through the application of heat, and the reduction is
continued until substantially no iron oxide is present within the
shell, during which slag aggregates within the shell, and then the
aggregated slag is separated from metallic iron.
[0018] In order to embody aspect (2) described above, part of the
metallic iron shell may be melted to allow molten slag to flow out
from inside the shell. In this case or in order to embody aspect
(3) described above, carburization may be continued within the
metallic iron shell in the presence of a carbonaceous reductant so
as to reduce the melting point of the metallic iron shell, thereby
readily melting part or the entirety of the metallic iron shell
When any of aspects (1) to (4) described above is embodied, a
maximum temperature of heating for reduction may be controlled to
be not less than the melting point of the accompanying slag and not
more than the melting point of the metallic iron shell, so as to
more efficiently conduct the reaction of generating metallic iron.
This reducing step may be solid phase reduction, through which an
iron oxide is reduced, and liquid phase reduction which is
continued until substantially no iron oxide, composed mainly of
FeO, is present, whereby the purity of the metallic iron obtained
can be efficiently improved.
[0019] As used herein, the term "reduction is continued until
substantially no iron oxide is present within the metallic iron
shell" means, on a quantitative basis, that the reduction through
the application of heat is continued until the content of iron
oxide, composed mainly of FeO, is preferably reduced to 5% by
weight or less, more preferably to 2% by weight or less. From a
different point of view, this means that the reduction through the
application of heat is continued until the content of iron oxide,
composed mainly of FeO in the slag separated from metallic iron, is
preferably not more than 5% by weight, more preferably 2% by weight
or less.
[0020] The thus-obtained metallic iron having a high iron purity
and accompanying slag may be melted by further heating so as to
separate one from the other through differences in their specific
gravities. Alternatively, they may be solidified by chiling, and
then crushed to separate the metallic iron from the slag
magnetically, or by any other screening method. Thus, it is
possible to obtain metallic iron having a high iron purity, with a
metallization ratio of not less than 95%, or in some cases of not
less than 98%.
[0021] In carrying out the above-described method of the present
invention, the compact of iron oxide containing a carbonaceous
reductant may be granular or agglomerate, and be reduced through
the application of heat in a manner having any of the following
aspects:
[0022] 1) The compact is moved in a horizontal direction.
[0023] 2) The compact is placed on an iron belt, comprising walls
formed at both edge portions thereof to prevent the compact from
falling off the iron belt, and is moved in a horizontal
direction.
[0024] 3) The compact is placed on a horizontal surface.
[0025] 4) The compact is tumbled.
[0026] 5) The compact falls downward.
[0027] In addition, the compact may be elongated and reduced
through the application of heat in a manner having any of the
following aspects:
[0028] 6) The elongated compact is moved downward in a vertical
position.
[0029] Aspect 6) may be embodied as follows:
[0030] 6-1) The elongated compact is continuously prepared and fed
into a section where reduction is performed through the application
of heat, the elongated compact comprising:
[0031] 6-1-1) a support mesh made of iron and wrapping the
elongated compact, or
[0032] 6-1-2) an iron bar serving as a core thereof.
[0033] The above iron mesh or bar is preferably employed because it
prevents the elongated compact from breaking at an intermediate
position thereof due to its own weight while the elongated compact
is moving downward.
[0034] 7) The elongated compact is moved downward along a sloped
surface.
[0035] Aspect 7) may be embodied as follows:
[0036] 7-1) The elongated compact is placed on an iron belt and
continuously fed into a section where reduction is performed
through the application of heat.
[0037] Through employment of any of the above aspects, the
aforementioned method of making metallic iron is more efficiently
carried out.
[0038] An apparatus for making metallic iron according to the
present invention carries out the above-described method of making
metallic iron and has the following basic structure An apparatus
for making metallic iron by reducing a compact of iron oxide
containing a carbonaceous reducing agent through the application of
heat comprises:
[0039] a thermal reduction apparatus for reducing the compact
through the application of heat, thereby forming a shell comprising
metallic iron and slag inside the shell;
[0040] a melting apparatus for melting the shell and the slag;
and
[0041] a separator for separating the molten iron from the molten
slag.
[0042] In the above-described apparatus for making metallic iron,
when the compact is granular or agglomerate, the above-described
thermal reduction apparatus may comprise a mechanism for reducing
the compact through the application of heat while moving the
compact in a horizontal direction. A preferred embodiment of the
mechanism is an endless rotary member, comprising an endless rotary
member and a hearth located on the member and used for placing the
compact thereon. Separating members may be provided on the hearth
at certain intervals to prevent the compact from adhering to
another compact. The separating members are preferably formed of a
desulfurizing agent, so that desulfurization can also be performed
in a process of reduction through the application of heat.
[0043] The above-described mechanism may also be embodied in the
form of an iron belt, comprising walls formed at both edge portions
thereof to prevent the compact from falling off the iron belt, for
conveying thereon the compact in a horizontal direction and for
subjecting the compact to reduction through the application of heat
during the horizontal conveyance of the compact.
[0044] A preferred embodiment of the above-described melting
apparatus may comprise a sloped floor for tumbling or sliding the
reduced compact thereon and for melting the tumbling or sliding
compact through the application of heat.
[0045] When the compact is granular or agglomerate, another
preferred embodiment of the thermal reduction apparatus may
comprise a feeding member, comprising a horizontal plane, for
intermittently feeding in the compact placed on the horizontal
plane, a discharging member for discharging the compact from the
feeding member, and a heating mechanism for heating the compact.
The discharging member may be a tilting member for malting the
position of the feeding member alternate between a horizontal
position and a sloped position, or a pushing member for pushing out
the compact from the feeding member, thereby smoothly discharging
the compact.
[0046] An iron support may be placed on the feeding member and
adapted to be discharged together with the compact. Separating
members (preferably formed of a desulfurizing agent) are preferably
provided on the feeding member at certain intervals to prevent the
compact from adhering to another compact.
[0047] A preferred embodiment of the feeding member may comprise an
iron belt for continuously conveying the compact thereon and for
subjecting the compact to reduction through the application of
heat. This avoids a problem that part of the reduced compact melts
and adhesively accumulates on the internal surface of a furnace.
When this embodiment is employed, the iron belt used for feeding in
the compact is melted with reduced metallic iron to become molten
iron.
[0048] A preferred embodiment of the aforementioned melting
apparatus may comprise a sloped floor for melting the compact by
application of heat while tumbling or sliding the compact
thereon.
[0049] For more efficient reduction through the application of
best, the aforementioned thermal reduction apparatus may preferably
comprise:
[0050] a mechanism for reducing the compact through the application
of heat while tumbling the compact, or
[0051] a mechanism of tumbling, comprising a tumbling surface for
tumbling the compact thereon and a discharging unit for discharging
the compact from the tumbling surface, and a thermal reduction
member for heating the compact.
[0052] The above-described thermal reduction apparatus and the
melting apparatus may be integrated into a thermal
reduction-melting apparatus, which comprises a mechanism of
tumbling, comprising a sloped tumbling surface for gradually
tumbling down the compact along a sloped direction and a
discharging section for discharging the compact from the sloped
tumbling surface, and a mechanism for reducing and melting the
compact through the application of heat. This enables reduction and
melting through the application of heat to be performed
continuously and efficiently.
[0053] In the above-described thermal reduction-melting apparatus,
the tumbling surface preferably comprises the interior surface of a
channel-like member having an arc-shape, V-shape, or the like
recess and is sloped along the length of the channel-like member.
This enables smoother reduction and melting through the application
of heat.
[0054] A further embodiment of the thermal reduction apparatus
which receives the granular or agglomerate compact may comprise a
mechanism for allowing the compact to fall downward and for
reducing the falling compact through the application of heat.
Alternatively, the thermal reduction-melting apparatus integrally
comprising the thermal reduction apparatus and the melting
apparatus may further comprise a space for allowing the granular
compact to fall downward and a heating member for reducing and
melting the granular compact through the sequential application of
heat while the granular compact is falling.
[0055] The separator preferably comprises a submerged weir for
receiving molten slag and molten iron falling from above on one
side thereof and for releasing the molten slag from one side
thereof and the molten iron from the other side thereof. Thus, the
molten iron and the molten slag are continuously and readily
separated one from the other.
[0056] When an elongated compact is used, the thermal reduction
apparatus may comprise a mechanism for reducing the elongated
compact through the application of beat while moving the elongated
compact downward in a vertical position or along a downward sloped
surface. This allows the elongated compact to be continuously
reduced through the application of heat while it moves downward in
a vertical position or along the downward sloped surface.
[0057] When the elongated compact is used, the elongated compact
may be continuously fed onto an iron belt through an feeder, so
that the elongated compact on the iron belt is continuously
conveyed into a thermal reduction apparatus, where the elongated
compact is reduced through the application of heat. In this case,
the iron belt is also melted in a melting process with metallic
iron generated in the reducing process, and collected in the form
of molten iron.
[0058] Preferably, the apparatus for making metallic iron according
to the present invention may further comprises means for feeding an
iron belt for conveying the compact thereon, thereby feeding the
compact on the iron belt into the thermal reduction apparatus and a
melting apparatus for reducing and melting the compact through the
application of heat In this case, when the compact is granular or
agglomerate, the iron belt may comprise walls formed at both edge
portions thereof to prevent the compact from falling off the iron
belt and may convey the compact thereon in a horizontal direction
within the thermal reduction apparatus for reducing the compact
through the application of heat. When the compact is in an
elongated form, there may be provided forming means for
continuously forming the elongated compact and for feeding the
elongated compact onto the iron belt, thereby continuously forming
the elongated compact and subjecting it to reduction and melting
through the application of heat. The iron belt used is melted in
the melting apparatus to thereby be merged with metallic iron,
generated through reduction, and collected in the form of molten
iron.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same become better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0060] FIGS. 1(A) to (F) are cross-sectional views of a compact
schematically illustrating the progress of a reducing reaction when
a method of the present invention is carried out;
[0061] FIG. 2 is a set of photographs showing cross-sections of
pellets subjected to reduction through the application of heat at
different temperatures;
[0062] FIG. 3 is a set of photographs showing a change in the
appearance of a reduced pellet observed when the reducing time is
varied at a reducing temperature-of 1500.degree. C.;
[0063] FIG. 4 is a graph showing a change in the metallization
ratio of reduced pellets with reducing time at a reducing
temperature of 1500.degree. C.;
[0064] FIG. 5 is a graph showing a change in the content of slag
constituents with reducing time at a reducing temperature of
1500.degree. C.;
[0065] FIG. 6 is a graph showing a change in the FeO content of
reduced pellets with reducing time at a reducing temperature of
1500.degree. C.;
[0066] FIG. 7 is a graph showing a change in the carbon content of
reduced pellets with reducing time at a reducing temperature of
1500.degree. C. and
[0067] FIG. 8 is a schematic flow chart illustrating a reducing
iron-making process according to an embodiment of the present
invention.
[0068] FIG. 9 is a schematic cross-sectional view showing an
embodiment 2 of an apparatus for making metallic iron according to
the present invention;
[0069] FIG. 10 is a schematic top sectional view showing an
embodiment 3 of an apparatus for making metallic iron according to
the present invention;
[0070] FIG. 11 is a schematic cross-sectional view taken along
lines Z-Z and Y-Y of FIG. 10;
[0071] FIG. 12 is a schematic cross-sectional view showing an
embodiment 4 of an apparatus for making metallic iron according to
the present invention;
[0072] FIG. 13 is a schematic cross-sectional view taken along line
A-A of FIG. 12;
[0073] FIG. 14 is a schematic cross-sectional view showing an
embodiment 5 of a method and apparatus for making metallic iron
according to the present invention;
[0074] FIG. 15 is a schematic cross-sectional view showing an
embodiment 6 (employing a suspension method) of a method and
apparatus for making metallic iron according to the present
invention;
[0075] FIG. 16 is a schematic cross-sectional view showing an
embodiment 7 (utilizing, as fuel, a reducing gas generated in a
reducing process) of a method and apparatus for making metallic
iron according to the present invention,
[0076] FIG. 17 is a schematic cross-sectional view showing an
embodiment 8 of a method and apparatus for making metallic iron
according to the present invention;
[0077] FIG. 18 is a schematic cross-sectional view showing an
embodiment 9 of a method and apparatus for making metallic iron
according to the present invention;
[0078] FIG. 19 is a schematic cross-sectional view showing an
embodiment 10 of an apparatus for making metallic iron according to
the present invention;
[0079] FIG. 20 is a schematic cross-sectional view showing an
embodiment 11 of an apparatus for making metallic iron according to
the present invention;
[0080] FIG. 21 is a schematic cross-sectional view showing an
embodiment 12 of an apparatus for making metallic iron according to
the present invention; and
[0081] FIG. 22 is a schematic plan view showing the embodiment 12
of an apparatus for making metallic iron according to the present
invention,
BEST MODE FOR CARRYING OUT THE INVENTION
[0082] A method of making metallic iron according to the present
invention, involves compacting the pulverized mixture, composed of
iron ore which contains iron oxides and coal or the like acting as
a carbonaceous reductant, to grains, pellets, or to any other
forms. A feature of the method is that a metallic iron shell is
generated and grown via reduction through the application of heat
The reduction is continued until substantially no iron oxide is
present within the shell.
[0083] In the process of studying a new method of making metallic
iron, which may replace both indirect iron making methods such as a
method using a blast furnace, and direct iron making methods such
as the heretofore mentioned SL/RN method, the present inventors
found that when compacts, in grains, pellets, or in any other form,
of pulverized iron oxides and carbonaceous reductant are heated in
a non-oxidizing atmosphere, the following phenomenon occur. When a
compact is heated, the carbonaceous reductant contained in the
compact reduces iron oxides in the following manner: the reduction
continues from the periphery of the compact, and metallic iron
generated during the incipient stage of the reduction diffuse and
join together on the surface of the compact to form a metallic iron
shell on the periphery of the compact. Subsequently, reduction of
iron oxides by the carbonaceous reductant progresses efficiently
within the shell, so that a state is established within a very
short period of time such that substantially no iron oxide is
present within the shell The thus generated metallic iron adheres
to the inner surface of the shell, and the shell grows accordingly.
On the other hand, most of the by-product slag, which is derived
from both gangue contained it an iron oxide source, such as iron
ore, and the ash content of a carbonaceous reductant, aggregates
within the metallic iron shell. Thus, metallic iron having a
relatively high iron purity and constituting the shell can be
efficiently separated from the aggregated slag.
[0084] This phenomenon, which occurs during reduction and will be
described later with reference to photos, is believed to occur in
the following manner. FIGS. 1(A) to 1(F) show cross-sectional views
of a compact schematically illustrating the phenomenon which occurs
when the method of the present invention is carried out. When a
compact 1 composed of an iron oxide-containing material and a
carbonaceous reductant and having a form shown in FIG. 1(A) is
heated, for example, to a temperature of 1450 to 1500.degree. C. in
a nonoxidizing atmosphere, the reduction of iron oxides progresses
from the periphery of the compact 1, and metallic iron generated
diffuses and joins together to form a metallic iron shell 1a (FIG.
1(B)). Subsequently, as heating continues, iron oxides within the
shell 1a are quickly reduced, as shown in FIG. 1(C), through
reduction by the carbonaceous reductant present within the shell 1a
and reduction by CO generated by a reaction between the
carbonaceous reductant and iron oxides. The thus generated metallic
iron Fe adheres to the inner surface of the shell, and the shell
grows accordingly. On the other hand, as shown in FIG. 1(D), most
of the by-product slag Sg derived from the above-mentioned gangue
and the like aggregates within the cavity defined by the shell
1a.
[0085] The reduction through the application of heat is represented
by the following schemes:
FeO.sub.x+xC.fwdarw.Fe+xCO (1)
FeO.sub.x+(x/2)C.fwdarw.Fe+(x/2)CO2 (2)
Y=y.sub.1+y.sub.2 (3)
[0086] where
[0087] Y: chemical equivalent (mol) of carbon required for
reduction
[0088] y.sub.1: amount (mol) of carbon required for reaction
represented by scheme (1)
[0089] y.sub.2: amount (mol) of carbon required for reaction
represented by scheme (2)
[0090] When compacts are prepared using an iron oxide, containing
material and a carbonaceous reductant, the mixing ratio between
iron oxides and the carbonaceous reductant is adjusted such that
the amount of the carbonaceous reductant is not less than a
theoretical equivalent expressed by scheme (3). This allows
reduction through the application of heat to progress
efficiently.
[0091] As described above, according to the present invention, the
metallic iron shell 1a is formed on the periphery of the compact 1
during the incipient stage of reduction through the application of
heat, and the reduction progresses further within the cavity
defined by the shell 1a, thereby significantly improving the
efficiency of the reduction. Preferably, an ultimate temperature of
heating for reduction may be controlled so as to be not less than
the melting point of the accompanying slag and not more than the
melting point of the metallic iron shell 1a. If the ultimate
temperature of heating is equal to or greater than the melting
point of the metallic iron shell 1a, generated metallic iron will
immediately fuse and aggregate; consequently, the metallic iron
shell 1a will not form and the subsequent reducing reaction will
not progress efficiently. Also, if non-reduced molten iron oxide
flows out from inside the metallic iron shell 1a, it may be highly
likely to damage the refractory of the furnace. On the other hand,
when the ultimate temperature of heating for reduction is
controlled so as to be not less than the melting point of the
accompanying slag, the by-product slag fuses and aggregates, and
metallic iron diffuses and joins together intensively;
consequently, the metallic iron shell 1a grows accordingly while
slag Sg is separating from the shell 1a as shown in FIGS. 1(C) and
(D).
[0092] As described above, a key feature of the present invention
is that "a metallic iron shell is formed within which a reducing
reaction progresses efficiently," which is not employed in
conventional indirect and direct iron-making methods and which
significantly enhanced reduction through the application of heat.
The metallic iron shell 1a grows as a carbonaceous reductant
contained in the compacts progressively reduces the compacts. Once
the metallic iron shell 1a is formed, the carbonaceous reductant
and the generated CO continue reduction within the shell 1a Hence,
the atmosphere for reduction through the application of heat does
not need to be reducing, but may be a non-oxidizing atmosphere such
as a nitrogen gas atmosphere. This is a significant difference from
the conventional methods
[0093] All the reducing agent necessary for reducing the iron oxide
is present in the pellet. No external reducing agent is needed;
neither solid nor gaseous reducing agents need to be added during
the reduction process. The reducing agent used in the process may
be only the carbonaceous reductant present in the compact.
Furthermore, the metallic iron shell may be in contact with the
atmosphere in the furnace; there is no need to coat or cover the
shell.
[0094] Basically, the above-stated reduction through the
application of heat progresses in the form of a solid phase
reduction, which does not cause the metallic iron shell 1a to melt.
Conceivably, liquid phase reduction also progresses at the latter
or end stage of the reducing reaction for the following reason. The
interior of the metallic iron shell la is believed to maintain a
highly reducing atmosphere because of the presence of a
carbonaceous reductant and CO generated by the reducing reaction of
the reductant, resulting in a significant rise in reduction
efficiency. In such a highly reducing atmosphere, metallic iron
generated within the shell 1a is subjected to carburization, so
that its melting point gradually reduces. As a result, at the
latter or end stage of the reducing reaction, part of the compacts
melt, so that iron oxides undergo liquid phase reduction. By
setting a relatively low reducing temperature, reduction can be
carried out entirely in the solid phase. However, the higher the
reducing temperature, the higher the reaction ratio of reduction,
and so a relatively high reducing temperature is advantageous to
complete the reducing reaction within a short period of time.
Hence, it is desirable that the reducing reaction ends with liquid
phase reduction.
[0095] Whether or not the above-mentioned reducing reaction is
completed can be confirmed by measuring the concentration of CO or
CO.sub.2 contained in the atmosphere of gas produced by the
reduction through the application of beat. In other words, the gas
generated is extracted at appropriate intervals of time from inside
the furnace of the reducing reaction. When no CO or CO.sub.2 is
detected from the gas, it indicates the completion of the reducing
reaction. This method uses the fact that the reduction through the
application of heat involves a reducing reaction carried out by a
carbonaceous reductant itself and a reducing reaction carried out
by the CO gas which is generated by the reaction between the
carbonaceous reductant and iron oxides. After the iron oxides are
all reduced, CO and CO.sub.2 are no longer generated.
[0096] In actual practice, there is no need to continue the
reaction until the release of the CO and CO.sub.2 gases terminates
completely The present inventors have confirmed that it depends on
the inner volume of the furnace used for the reaction, but when the
concentration of the CO and CO.sub.2 gases in the furnace gas diops
to approximately 2 volume % or less, not less than 95% by weight of
iron oxides are reduced; when the gas concentration drops to about
1 volume % or less, not less than 98% by weight of iron oxides are
reduced.
[0097] In the state shown in FIG. 1(D), iron oxides composed mainly
of FeO and contained in the compact are substantially all reduced
to metallic iron (iron oxide content, indicative of the progress of
the reduction, is usually not more than 5% by weight and is
experimentally confirmed to be not more than 2% by weight or not
more than 1% by weight), and some iron oxides composed mainly of
FeO and fused into the internal aggregate of molten slag Sg are
also mostly reduced (content of iron oxides composed mainly of FeO
contained in the slag, indicative of the progress of the reduction,
is usually not more than 5% by weight and is experimentally
confirmed to be not more than 2% by weight or not more than 1% by
weight). Accordingly, metallic iron having a relatively high iron
purity can be efficiently obtained by chilling compacts in the
state of FIG. 1(D), crushing their metallic iron shell 1a with a
crusher, and magnetically selecting metallic iron from slag.
Alternatively, heating at the same temperature or a higher
temperature may be continued subsequently to the establishment of
the state of FIG. 1(D), whereby part or all of the metallic iron
shell 1a is melted so as to separate the slag from metallic iron,
which will be described below.
[0098] When heating is continued at a slightly higher temperature,
as needed, subsequent to the establishment of the state of FIG.
1(D), part of the metallic iron shell 1a melts, for example, as
shown in FIG. 1(E). This allows the accompanying slag Sg to flow
out from inside the shell 1a, thereby facilitating the separation
of metallic iron from the slag. Alternatively, heating may be
continued to establish the state shown in FIG. 1(E), whereby the
entire metallic iron shell 1a melts and aggregates, in order to be
separated from the slag Sg which had previously melted and
aggregated. Then, the thus prepared mass in the state shown in FIG.
1(E) or (F) is processed by a crusher or the like to crush the
fragile slag only, leaving metallic iron in agglomerates. The
crushed mass is then subjected to screening using a screen having
an appropriate mash or to magnetic separation, thereby readily
obtaining metallic iron having a relatively high iron purity. In
addition, the difference in specific gravity between metallic iron
and slag may be used to separate molten metallic iron from molten
slag.
[0099] The metallic iron shell can be melted not only by heating at
a higher temperature subsequently to the completion of the reducing
reaction but also by reducing the melting point of the metallic
iron shell through carburization. At the last stage of the
reduction progressing within the metallic iron shell, the internal
atmosphere, which is strongly reducing, causes reduced iron to be
carburized with a resultant reduction in the melting point of the
reduced iron. Hence, even by maintaining the reducing temperature,
the metallic iron shell can be melted due to the reduction in its
melting point.
[0100] Carbonaceous reductants usable with the present invention
include coal, coke or other similar carbonaceous materials treated
by dry distillation, petroleum coke, and any other form of
carbonaceous materials. In actual use, mined coal is pulverized and
screened to obtain coal powder for use, and coke is also
pulverized. In addition, for example, blast furnace dust may be
used which is collected as waste which contains carbonaceous
materials. However, in order to efficiently progress the reaction
of reduction through the application of heat, a carbonaceous
reductant to be used contains carbon preferably not less than 70%
by weight, more preferably not less than 80% by weight. However,
such matter containing iron oxides and carbonaceous reductant
therein as blast furnace dust is not limited to this amount. For
example, in the case of blast furnace dust, it may be possible to
contain carbon not less than 20% by weight. In addition, in order
to increase the specific surface area of the carbonaceous
reductant, its grain size is preferably not more than 2 mm, more
preferably not more than 1 mm. Likewise, in order to improve the
efficiency of a reducing reaction through an increase in the
specific surface area of iron ore or iron oxide-containing
materials, its grain size is preferably not more than 2 mm, more
preferably not more than 1 mm.
[0101] In the present embodiment, an iron oxide and a carbonaceous
reductant and, as needed, a binder, are homogeneously mixed and
then formed into agglomerates, grains, briquettes, pellets, bars,
or other forms of compacts, and the resulting compacts are
subjected to reduction through the application of heat. The amount
of the carbonaceous reductant to be mixed in is not less than a
theoretical chemical equivalent required for a reducing reaction
represented by the aforesaid schemes (1) to (3). The amounts of y1
and y2 represented by schemes (1) and (2) vary with material
conditions (chemical composition, grain size, pellet size, etc.)
and reduction temperature. However, the theoretical chemical
equivalent is determined by measuring the CO and CO.sub.2 density
of gases which is generated in a small reduction apparatus where
pellets are reduced at a specified temperature. The pellets are
added with carbonaceous reductant slightly more than a necessary
amount for an assumed reduction case of scheme (1) only.
Preferably, the carbonaceous reductant is used in excess, in
consideration of the amount consumed or carburization to lower the
melting point of the metallic iron shell.
[0102] As heretofore mentioned, preferably, an ultimate temperature
during reduction through the application of heat is not less than
the melting point of the by-product slag and not more than the
melting point of the metallic iron shell. However, it is not
necessarily adequate to absolutely predetermine the ultimate
temperature because the temperature of slag varies depending on the
amount gangue contained in iron ore or other iron oxide sources and
depending on the amount of iron oxide contained in the slag.
Nevertheless, the reducing temperature falls preferably in the
range of 1350 to 1540.degree. C., preferably in the range of 1400
to 1540.degree. C., more preferably in the range of 1430 to
1500.degree. C. Such a temperature range of reduction provides
metallic iron having as high an iron purity of not less than 95% by
weight in metallization ratio, usually not less than 98% by weight,
and in excellent cases not less than 99% by weight.
[0103] As for the by-product slag, its content of iron oxides
composed mainly of FeO can be reduced to not more than 5% by
weight, usually not more than 2% by weight, or under more adequate
conditions of reduction through the application of heat, not more
than 1% by weight. This feature is advantageous to prevent damage
to the refractory wall of a furnace caused by direct contact with
molten iron oxide. According to the heretofore mentioned
conventional reducing iron-making methods, when iron oxides
contained in iron ore or the like are subjected to reduction
through the application of heat using a carbonaceous material, or
when metallic iron obtained through reduction is separated from
accompanying slag, a considerable amount of iron oxides composed
mainly of FeO is left unreduced in the slag, causing damage to the
refractory of the furnace. According to the present invention, iron
oxides composed mainly of FeO contained in slag are mostly reduced,
so that almost no iron oxide or only a very small amount of iron
oxide, if any, is left unreduced in the slag. Thus, the problem of
damage to the refractory of a furnace does not occur, not only at
the reducing step, but also at the subsequent slag separating
step.
[0104] Since the thus obtained metallic iron has a relatively high
iron purity and does not contain constituents of slag, it can be
used intact as long as it is used as a diluent in a steel malting
process. However, since the metallic iron contains a considerable
amount of impurities such as sulfur and phosphorus it needs to be
refined so as to reduce the impurities, if the impurities raise any
problems. In addition, the metallic iron allows its carbon content
to be adjusted.
[0105] The metallic iron may form a continuous closed shell. In
this form, most, if not all, of the reduced iron is in a single
piece or mass, separate from the slag. Even after the shell has
been partially or completely melted most of the reduced iron is in
the form of a single piece or mass.
[0106] When the present invention is carried out, preferably, a
grown metallic iron shell is not allowed to melt while molten slag
is aggregating, and also at the subsequent step of separating slag
from metallic iron, the metallic iron is not allowed to melt. This
practice minimizes the amount of sulfur and phosphorus contained in
the obtained metallic iron The mechanism of this practice is
described below. After completion of reduction, if metallic iron,
together with slag, is melted, part of the sulfur and phosphorus
contained in the molten slag may mingle with the molten metallic
iron. However, if at the reducing step and the subsequent slag
separating step, metallic iron is held in the solid state and only
slag is melted for separation from the metallic iron, sulfur and
phosphorus contained in the carbonaceous reductant, such as coal,
melt into the molten slag and are removed together with the slag,
thereby minimizing entry of sulfur and phosphorus into the metallic
iron.
[0107] The present invention will next be described in detail by
way of embodiments, which should not be construed as limiting the
invention. Variations and modifications are possible without
deviating from the gist of the invention.
[0108] Embodiment 1:
[0109] Coal powder (carbonaceous reductant), iron ore
(iron-containing material), and binder (bentonite), each having a
composition shown in Table 1 and an average grain diameter of not
more than 45 .mu.m, were mixed in the mixing ratio shown in Table
1. The resulting mixture was formed into substantially
spherical-pellets having 17 mm diameters. The thus formed pellets
were subjected to reduction through the application of heat in a
non-oxidizing atmosphere (nitrogen gas atmosphere) for 20 minutes
at 1400.degree. C., 1450.degree. C., and 1500.degree. C., followed
by cooling. The cross-sections of the reduced pellets were
observed. FIG. 2 shows typical photographs of their cross-sections.
In the tables "T." stands for "total", and "M." stands for
"metallic".
1TABLE 1 Pellet Making Conditions Iron ore Mixing T. Fe FeO
SiO.sub.2 Al.sub.2O.sub.3 CaO Ratio (%) (%) (%) (%) (%) 0.5 (%)
80.3 69.7 38.5 1.7 0.44 Coal Mixing Total Fixed Volatile Ash Ratio
Carbon Carbon matter Content (%) 18.5 (%) (%) (%) (%) 83.5 78.4
17.1 4.5 Binder Mixing SiO.sub.2 Al.sub.2O.sub.3 CaO Ratio (%) (%)
(%) 0.9 (%) 1.2 69.2 14.7 Pellet T. Fe Total Volatile (%) 56.1
Carbon matter SiO.sub.2 Al.sub.2O.sub.3 CaO (%) (%) (%) (%) (%) 0.5
15.4 14.4 3.3 0.9
[0110] As seen from FIG. 2, in pellets subjected to reduction
through the application of heat at a temperature of 1400.degree. C.
and 1450.degree. C., a metallic iron shell is formed on their
surface while metallic iron adheres to the internal surface of the
shell as it accumulates, and slag agglomerates separately from the
shell in an internal space defined by the shell. In a pellet
subjected to reduction through the application of heat at a
temperature of 1500.degree. C., it seems that once formed, the
metallic iron shell melted after the reducing reaction had
completed, and then the molten metallic iron and molten slag
solidified to mutually separated metallic iron having metallic
luster, and a vitreous mass, respectively (the corresponding
photograph in FIG. 2 show only metallic iron obtained by removing
slag after crushing). Table 2 shows the chemical composition of the
reduced pellets, and Table 3 shows the chemical composition of the
vitreous slag.
2TABLE 2 Chemical Composition of Reduced Pellets Reducing time: 20
minutes Unit: % by weight Reducing Temperature 1400.degree. C.
1450.degree. C. 1500.degree. C. T.Fe 94.20 94.33 99.10 M.Fe 89.42
93.02 98.88 FeO 4.70 0.79 0.28 SiO.sub.2 2.21 1.44 0.22
Al.sub.2O.sub.3 1.02 0.45 0.01 CaO 0.43 0.20 0.01 Total carbon 0.60
0.42 0.49 S 0.062 0.068 0.072 Metallization ratio (%) 94.93 98.61
99.78
[0111]
3TABLE 3 Chemical Composition of Vitreous Matter Unit: % by weight
M.Fe FeO CaO SiO.sub.2 Al.sub.2O.sub.3 8.46 0.18 4.47 57.53
1.55
[0112] As seen from Table 2, in pellets subjected to reduction at a
temperature of 1500.degree. C., solidified metallic iron (see FIG.
2) having an elliptical shape and metallic luster contains almost
no slag constituents, and the reduced metallic iron having a
metallization ratio of not less than 99% by weight is substantially
completely separated from the slag. On the other hand, in pellets
subjected to reduction at a temperature of 1400.degree. C. or
1450.degree. C., a metallic iron shell still remains, and their
chemical compositions seem to indicate that reduction of iron oxide
is insufficient. However, as seen from FIG. 2, in those pellets, a
metallic iron shell is already separated from aggregated slag
within the shell. This implies that granular metallic iron having a
relatively high iron purity can be obtained by: crushing reduced
pellets and collecting metallic iron through magnetic separation;
continuing heating at a higher temperature to melt part of the
metallic iron shell to thereby allow molten slag to flow out from
inside the shell, followed by separation of metallic iron from
slag; or continuing heating at a higher temperature to melt the
entire metallic iron shell and then allowing molten metallic iron
and molten slag to aggregate separately from each other.
[0113] FIG. 3 shows a change in appearance of a pellet observed
when reducing time is varied from 3 minutes through 15 minutes at a
reducing temperature of 1500.degree. C. Table 4 shows the chemical
composition of each reduced pellet corresponding to each reducing
time FIGS. 4 to 7 show a change in metallization ratio, content of
slag constituents, iron oxide content, and carbon content,
respectively, with reducing time.
4TABLE 4 Effect of Reducing Time on Chemical Composition of Reduced
Pellet Unit: % by weight Reducing time (min) 3 5 6 9 12 15 T.Fe
83.75 92.35 98.50 98.75 99.03 98.98 M.Fe 71.75 92.16 98.04 98.08
98.30 98.40 FeO 14.01 0.23 0.27 0.29 0.20 0.34 SiO.sub.2 4.04 3.42
0.22 0.18 0.27 0.27 Al.sub.2O.sub.3 1.49 1.34 0.29 0.01 0.01 0.01
CaO 0.64 0.56 0.03 0.01 0.01 0.01 Total carbon 5.57 0.79 0.51 0.46
0.48 0.68 S 0.061 0.064 0.066 0.066 0.071 0.074 Metalization 85.67
99.79 99.53 99.32 99.26 99.41 ratio (%)
[0114] As seen from FIG. 3, 3 minutes after heating has started, no
particular change in appearance is observed with the pellet.
However, as seen from Table 4, reduction of iron oxide is
considerably progressed in the pellet. 5 minutes after heating has
started, the pellet surface exhibits an apparent metallic luster
indicative of a metallic iron shell being formed. In addition, the
T. Fe content of the metallic iron is in excess of 90% by weight. 6
minutes later, the T. Fe content of the metallic iron is as high as
not less than 98% by weight as shown in Table 4.
[0115] At this point of time, it is observed that part of the
metallic iron shell melts to allow molten slag to flow out from
inside the shell. 9 minutes later, most of the metallic iron shell
melts and aggregates in a fried egg like shape, in which metallic
iron agglomerates in the position corresponding to the yolk, and
vitreous slag aggregates around the metallic iron in the position
corresponding to the white of the egg. After this point of time,
the shape of the metallic iron and slag varies somewhat, but as
seen from Table 4, the T. Fe concentration in the metallic iron
shows almost no further increase. This indicates that the reducing
reaction of iron oxides contained in a pellet progresses quickly
and is almost completed while the metallic iron shell is formed
and, once the metallic iron shell is formed, under an enhanced
reducing condition established within the shell, after which the
separation of the metallic iron from slag progresses with time. As
seen from Table 4 and FIGS. 4 to 7, 6 minutes after reduction
through the application of heat starts, the slag and FeO content of
the obtained metallic iron is reduced to a very low level, whereby
metallic iron having a metallization ratio of not less than 99% is
obtained.
[0116] As will be easily understood, if the compact composed of an
iron oxide-containing material and a carbonaceous reductant
contains as much carbonaceous reductant as equal to or greater than
the equivalent required for reducing iron oxides contained in the
compact, then when the compact is heated at a temperature of about
1400.degree. C. or higher, a metallic iron shell will form on the
periphery of the compact at the incipient stage of heating, and
subsequently iron oxide will be quickly reduced within the metallic
iron shell, while molten slag is separated from metallic iron. When
the reducing temperature is increased to 1500.degree. C., a
reducing reaction and the separation of metallic iron from slag
progress within a very short period of time, whereby metallic iron
having a very high iron purity is obtained at a relatively high
yield.
[0117] FIG. 8 shows a flow chart illustrating an embodiment of the
present invention. Pulverized iron oxide-containing material and
pulverized carbonaceous reductant, together with binder, are mixed
and formed into pellets or other forms of compacts. The thus formed
pellets or the like are subjected to reduction through the
application of heat at a temperature of not less than 1400.degree.
C. in a furnace. During the reducing step, a metallic iron shell is
formed during the incipient stage of reduction, and then a reducing
reaction progresses within the shell while molten slag aggregates
within the shell. At the separating step, reduced masses are
chilled to solidify, and then the resulting solidified masses are
crushed, followed by collection of metallic iron through magnetic
separation or the like. Alternatively, heating may be further
continued to melt metallic iron so as to separate molten metallic
iron from molten slag utilizing a difference in the specific
gravity between them. If needed, the collected metallic iron may be
refined to remove impurities such as sulfur and phosphorus and in
addition, the carbon content of the metallic iron can be
adjusted.
[0118] The above-described method of making metallic iron will next
be described by way of embodiment. The method and apparatus of the
present invention may be embodied in an industrial scale as
described below.
[0119] Embodiment 2:
[0120] In a method of making metallic iron according to Embodiment
2 of the present invention, a granular or agglomerate compact
(hereinafter may be referred to as a compact) of iron oxide which
contains a carbonaceous reductant is reduced through the
application of heat, thereby making metallic iron. Specifically,
the above-mentioned compact is reduced through the application of
heat while being conveyed in a horizontal direction. In the course
of this reduction, a shell composed of metallic iron is generated
and grown, and slag aggregates inside the shell. This reduction is
continued until substantially no iron oxide is present inside the
shell. Subsequently, the compact in the form of the shell with a
slag aggregate contained inside is discharged from the end portion
of a conveying member into the subsequent melting process, in which
the shell and the slag aggregate are melted, followed by separation
into molten slag and molten iron.
[0121] Since a carbonaceous reductant is contained in a compact,
reduction advances within the compact itself, thereby generating
metallic iron (shell) and slag (inside the shell). The resulting
substance is melted, followed by separation into molten iron and
molten slag through the utilization of difference in specific
gravity therebetween.
[0122] The amount of a carbonaceous reductant contained in the
compact must be at least an amount required for reducing iron
oxide, preferably plus an amount required for carburizing reduced
iron, so that generation of reduced iron (metallic iron) can be
accompanied by carburization. Solid (unmolten) reduced iron,
composing a shell, has a porous form and thus is likely to be
re-oxidized. This re-oxidization can be prevented by the presence
of the carbonaceous reductant in the compact more than the
above-described "amount required for reducing source iron
oxide+amount required for carburizing reduced iron." This is
because the CO gas generated from the compact establishes a
non-oxidizing atmosphere around the compact. That is, the compact
most preferably contains the carbonaceous reductant in "amount
required for reducing source iron oxide+amount required for
carburizing reduced iron+amount of loss associated with
oxidation."
[0123] Furthermore, in Embodiment 2, a carbonaceous reductant is
preferably additionally supplied while the compact is being
conveyed in a horizontal direction and reduced through the
application of heat.
[0124] In the above-described process, a carbonaceous reductant is
previously contained in the compact in "amount required for
reducing source iron oxide" plus "amount required for carburizing
reduced iron+amount of loss associated with oxidation."However, the
carbonaceous reductant may be contained in the compact in "amount
required for reducing source iron oxide," and the carbonaceous
reductant may be additionally supplied from outside in "amount
required for carburizing reduced iron+amount of loss associated
with oxidation" during reduction through the application of heat.
Alternatively, the carbonaceous reductant may be contained in the
compact in "amount required for reducing source iron oxide+amount
required for carburizing reduced iron," and the carbonaceous
reductant may be additionally supplied from outside in "amount of
loss associated with oxidation" during reduction through the
application of heat. In such a manner, the carbonaceous reductant
may be additionally supplied to compensate a shortage. In any of
these cases, the carbonaceous reductant in "amount required for
reducing source iron oxide" allows a metallic iron shell to be
generated in a good manner while slag aggregates inside the
shell.
[0125] Through the use of a powdery carbonaceous reductant, the
powdery carbonaceous reductant may be attached to the compact
surface, thereby preventing the compacts from sintering together to
become a relatively large agglomerate or sinteringly adhering to a
furnace wall, and thus facilitating the handling of the
compacts.
[0126] A carbonaceous reductant in "amount required for carburizing
reduced iron" or "amount of loss associated with oxidation" may be
additionally supplied while metallic iron (reduced iron) is being
melted. In this case, carburization advances during the melting
process, and the CO gas generated from the carbonaceous reductant
maintains a non-oxidizing atmosphere around the compact, thereby
preventing metallic iron from being re-oxidized.
[0127] An apparatus of making metallic iron according to Embodiment
2 implements the above-described method of making metallic iron.
That is, there is provided an apparatus of making metallic iron by
reducing a granular or agglomerate compact of iron oxide which
contains a carbonaceous reductant, comprising: a thermal reduction
apparatus having a conveying member for conveying the compact in a
horizontal direction and a thermal reduction mechanism for heating
the compact; a melting apparatus having a melting mechanism for
melting, through the application of heat, the compact which is
discharged from the conveyance end portion of the conveying member
in the thermal reduction apparatus; and a separator, disposed
subsequent to the melting apparatus, for separating molten slag and
molten iron one from the other.
[0128] Through the use of the apparatus of Embodiment 2, molten
iron can be continuously made from the compacts.
[0129] Further, in Embodiment 2, the conveying member for conveying
the compact in a horizontal direction preferably employs an endless
belt system and has a hearth on which the compact is placed.
[0130] Also, in Embodiment 2, the hearth preferably has separating
members, arranged thereon at certain intervals, for preventing the
compacts from adhering together. Examples of the separating members
include plate-shaped refractories. Through employment of the
separating members, the compacts can be prevented from sintering
together to become a relatively large agglomerate, thereby
facilitating the handling of the compacts.
[0131] Furthermore, the separating member is more preferably made
of a desulfurizer. In this case, the separating member (a
desulfurizer) is constructed to be readily separable from the
hearth, so that the desulfurizer, together with the reduced
compact, is charged into the melting apparatus. Therefore,
desulfurization can be performed in the melting apparatus. The
separating member made of a desulfurizer may be, for example,
plate-shaped or in the form of a heap of powder.
[0132] A powdery desulfurizer may be used which is attached to the
surface of the compact. This prevents the compacts from sintering
together to become a relatively large agglomerate or sinteringly
adhering to a furnace wall. In addition, since the powdery
desulfurizer adhering to the compact is charged into the melting
apparatus, desulfurization can be performed within the melting
apparatus. Examples of such a desulfurizer include limestone.
[0133] In Embodiment 2, the melting apparatus preferably has a
sloped floor, so that the compacts are melted through the
application of heat while tumbling or sliding on the sloped
floor.
[0134] Through the employment of such a sloped floor, the compacts
smoothly move within the melting apparatus toward the subsequent
separator. As the compacts move downward on the sloped floor, their
degrees of melting increase and become substantially uniform (no
mixed presence of the compacts of different degrees of melting),
thereby efficiently melting the compacts.
[0135] Embodiment 2 will next be described in detail with reference
to FIG. 9.
[0136] FIG. 9 is a schematic sectional view showing Embodiment 2 of
a metallic iron-making apparatus according to the present
invention.
[0137] The metallic iron-making apparatus has a thermal reduction
apparatus 123, a melting apparatus 112, and a separator 113. The
thermal reduction apparatus 123 has, as a conveying member, hearths
146 for placing compacts 104 thereon and a roller 147 for
horizontally moving the hearth 146. This conveying member employs
an endless belt system in which the pallet type hearths 146 are
mounted on a belt conveyor, and the roller 147 is rotated by an
external drive unit (not shown). The thermal reduction apparatus
123 has, as a thermal reduction mechanism, a reducing burner 148
for heating the interior of thermal reduction furnaces 150 enclosed
by furnace walls 105 made of refractory to a predetermined
temperature. The hearths 146 carrying the compacts 104 pass through
the interior of the thermal reduction furnaces 150, thereby
horizontally conveying the compacts 104. As shown in FIG. 9, three
thermal reduction furnaces 150 are provided, each being able to be
regulated to a desired temperature in accordance with a stage of
reduction.
[0138] The thermal reduction apparatus 123 is followed by a melting
apparatus 112, located at an end of conveyance on the hearths 146
(downstream of the conveying member). The melting apparatus 112
has, as a melting mechanism, a melting burner 161 for heating the
interior of the melting apparatus 112 enclosed by a furnace wall
106 made of refractory The melting apparatus 112 also has a sloped
floor 151 for leading the compacts 104 to the next process
(separator 113). A weir 152 is located between the melting
apparatus 112 and the following separator 113. The separator 113
collects molten iron 154 and molten slag 153. The separator 113 has
a slag outlet 155 and a molten iron outlet 156
[0139] The thermal reduction furnaces 150 and the melting apparatus
112 have exhaust gas outlets 149 and 157, respectively.
[0140] Next, a process of making metallic iron will be described
with reference to FIG. 9.
[0141] A pulverized mixture, composed of a carbonaceous reductant
such as coal or the like and iron oxide such as iron ore or the
like, is compacted to grains, for example. The thus-formed compact
contains the carbonaceous reductant in "amount required for
reducing source iron oxide+amount required for carburizing reduced
iron+amount of loss associated with oxidation."
[0142] The compacts 104 are placed onto the hearths 146 at the
entrance (at the left of FIG. 9) of the thermal reduction apparatus
123 and then conveyed through the thermal reduction furnaces 150
one after the other (toward the right of FIG. 9). The internal
temperature of the thermal reduction furnaces 150 is regulated by
adjusting flame intensity of the reducing burner 148 so as to be
less than a melting temperature of a metallic iron shell to be
generated and not less than a melting temperature of slag to be
generated Through this application of heat, the compacts 104 are
reduced.
[0143] In this thermal reduction process, reduction first advances
at the peripheral portion of the compact 104, thereby forming a
shell composed of metallic iron. Subsequently, through reduction by
carbon monoxide, which is generated inside the shell from the
carbonaceous reductant itself and through pyrolization of the
carbonaceous reductant, a reducing reaction of iron oxide
efficiently advances inside the shell. Accordingly, generated
metallic iron aggregates to grow the shell, and generated slag also
fuses to aggregate. As a result, in this thermal reduction process,
a metallization ratio considerably increases, and the amount of
iron oxide mixed into the slag considerably decreases.
[0144] The above-described reduction continues until substantially
no iron oxide is present within the compact 104. The moving speed
of the hearths 146 is adjusted in accordance with time required for
this reduction. Since the amount of iron oxide mixed into the slag
can be reduced through sufficient execution of reduction, the
refractory (furnace wall) of the subsequent melting apparatus 112
can be prevented from being damaged by iron oxide when the compacts
104 are melted in the melting apparatus 112. The length of the
thermal reduction furnace 150, through which the hearths 146 move,
may be determined based on time required for reduction and the
moving speed of the hearths 146.
[0145] As previously described, during reduction within the thermal
reduction furnaces 150, the carbonaceous reductant contained in the
compact 104 carburizes reduced iron, and the CO gas generated from
the compact 104 establishes a non-oxidizing atmosphere around the
compact 104, thereby preventing reduced iron from again being
oxidized.
[0146] Upon substantial end of reduction, the compact 104 is
composed of the metallic iron shell and a slag aggregate inside the
shell and conveyed on the moving hearth 146 to the melting
apparatus 112 while at least the shell is in a solid state. In the
melting apparatus 112, tumbling or sliding downward on the sloped
floor 151 (toward the separator 113), the compacts 104 are exposed
to heat to melt. The interior of the melting apparatus 112 is set
to a temperature for melting not only the slag but also the
shell.
[0147] Even when a small amount of unreduced portion remains in the
compact 104 led into the melting apparatus 112 (reduction is
performed within the thermal reduction furnace 150 until
substantially no iron oxide is present in the metallic iron shell,
but iron oxide may remain in an amount of not more than 5% by
weight or not more than 2% by weight in some cases), such an
unreduced portion is reduced through the application of heat during
the melting process. In this case, the melting apparatus 112 may be
replenished with a carbonaceous reductant.
[0148] The melting compacts 104 stay behind the weir 152, and a
molten substance overflows the weir 152 to he collected in the
separator 113.
[0149] Since the molten slag 153 and the molten iron 154 are
different in specific gravity, they separate one from the other in
the separator 113 such that the molten slag 153 collects on the
molten iron 154 to form two layers. The thus-separated slag 153 is
released from the slag outlet 155 while the molten iron 154 is
released from the molten iron outlet 156.
[0150] As described above, highly reduced metallic iron can be
efficiently obtained in the form of molten iron, with a
metallization ratio of not less than 95%, or in some cases of not
less than 98%. Furthermore, as a result of highly advanced
reduction of iron oxide in the thermal reduction process, the
amount of iron oxide mixed into the accompanying molten slag is
significantly small. Therefore, the refractory of the melting
apparatus 112 can accordingly be prevented from damagingly being
melted by iron oxide mixed into the molten slag
[0151] The separator 113 may preferably be provided with a heating
burner or an electric heating apparatus for further heating the
molten slag 153 and the molten iron 154 to a higher temperature to
thereby increase their fluidity, so that the molten slag 153 and
the molten iron 154 can be more readily separated one from the
other, thereby facilitating their separate release.
[0152] Since an exhaust gas discharged from the exhaust gas outlets
149 and 157 has a high temperature and contains combustible gas,
the exhaust gas may be utilized as a fuel gas to be fed to the
burners 148 and 161 The exhaust gas may also be used as a heat
source for drying or preheating the compacts 104 or for preheating
fuel and combustion air. Also, the exhaust gas may be released
without being utilized.
[0153] Embodiment 3:
[0154] In a method of making metallic iron according to Embodiment
3 of the present invention, a granular or agglomerate compact
(hereinafter may be referred to as a compact) of iron oxide which
contains a carbonaceous reductant is reduced through the
application of heat, thereby making metallic iron. Specifically,
the above-mentioned compact is reduced through the application of
heat while being placed on a horizontal surface. In the course of
this reduction, a shell composed of metallic iron is generated and
grown, and slag aggregates inside the shell. This reduction is
continued until substantially no iron oxide is present inside the
shell. Subsequently, the compact in the form of the shell with a
slag aggregate contained inside is discharged from the horizontal
surface, followed by further heating for melting The resulting
molten substance is separated into molten slag and molten iron.
[0155] As previously described, since a carbonaceous reductant is
contained in a compact, reduction advances within the compact
itself, thereby generating metallic iron (shell) and slag (inside
the shell). The resulting substance is melted, followed by
separation into molten iron and molten slag through the utilization
of difference in specific gravity therebetween.
[0156] Like Embodiment 2, the amount of a carbonaceous reductant
contained in the compact must be at least an amount required for
reducing iron oxide, preferably plus an amount required for
carburizing reduced iron. More preferably, the amount of a
carbonaceous reductant is "amount required for reducing source iron
oxide+amount required for carburizing reduced iron+amount of loss
associated with oxidation."
[0157] Also, in Embodiment 3, a carbonaceous reductant is
preferably additionally supplied while the compact, placed on a
horizontal surface, is being reduced through the application of
heat.
[0158] Further, like Embodiment 2, a carbonaceous reductant may be
contained in the compact in "amount required for reducing source
iron oxide," and the carbonaceous reductant may be additionally
supplied from outside in "amount required for carburizing reduced
iron+amount of loss associated with oxidation" during reduction
through the application of heat. Alternatively, the carbonaceous
reductant may be contained in the compact in "amount required for
reducing source iron oxide+amount required for carburizing reduced
iron," and the carbonaceous reductant may be additionally supplied
from outside in "amount of loss associated with oxidation" during
reduction through the application of heat. In such a manner, the
carbonaceous reductant may be additionally supplied to compensate a
shortage.
[0159] Further, like Embodiment 2, through the use of a powdery
carbonaceous reductant, the powdery carbonaceous reductant may be
attached to the compact surface, thereby preventing the compacts
from sintering together to become a relatively large agglomerate or
sinteringly adhering to a furnace wall, and thus facilitating the
handling of the compacts.
[0160] Further, as previously described, a carbonaceous reductant
in "amount required for carburizing reduced iron" or "amount of
loss associated with oxidation" may be additionally supplied while
metallic iron (reduced iron) is being melted. In this case,
carburization advances during the melting process, and the CO gas
generated from the carbonaceous reductant maintains a non-oxidizing
atmosphere around the compact, thereby preventing metallic iron
from being re-oxidized.
[0161] An apparatus of making metallic iron according to Embodiment
3 implements the above-described method of making metallic iron.
That is, there is provided an apparatus of making metallic iron by
reducing a granular or agglomerate compact of iron oxide which
contains a carbonaceous reductant, comprising: a thermal reduction
apparatus having a feeding member for intermittently feeding the
compact in while carrying the compact on a horizontal surface, a
discharging member capable of discharging the compact from the
feeding member, and a thermal reduction mechanism for heating the
compact; a melting apparatus having a melting mechanism for
melting, through the application of heat, the compact which is
discharged from the thermal reduction apparatus; and a separator,
disposed subsequent to the melting apparatus, for separating molten
slag and molten iron one from the other.
[0162] Through the use of the apparatus of Embodiment 3, molten
iron can be continuously made from the compacts.
[0163] Further, in Embodiment 3, the discharging member is
preferably a tilting member for alternating the position of the
feeding member between a horizontal position and a sloped position.
Alternatively, the discharging member is preferably a pushing
member for pushing out the compact from the feeding member. The
feeding member is also preferably a tilting member and has a
pushing member. Through the employment of a tilting member or
pushing member as the discharging member, the compacts can smoothly
be led into the melting apparatus even when the compacts sinter
together to become a relatively large agglomerate during reduction
through the application of heat.
[0164] Like Embodiment 2, in Embodiment 3, an iron support may be
placed on the feeding member, so that the iron support, together
with the compacts, can be discharged. Also, in this case, the
compacts can be smoothly led into the melting apparatus even when
the compacts sinter together to become a relatively large
agglomerate or adhere to the iron support during reduction through
the application of heat.
[0165] Furthermore, the feeding member preferably has separating
members, arranged thereon at certain intervals, for preventing the
compacts from adhering together. Examples of the separating members
include plate-shaped refractories. Through employment of the
separating members, the compacts can be prevented from sintering
together to become a relatively large agglomerate, thereby
facilitating the handling of the compacts.
[0166] Further, as previously described, the separating member is
more preferably made of a desulfurizer. In this case, the
separating member (a desulfurizer) is constructed to be readily
separable from the hearth, so that the desulfurizer, together with
the reduced compact, is charged into the melting apparatus.
Therefore, desulfurization can be performed in the melting
apparatus. The separating member made of a desulfurizer may be, for
example, plate-shaped or in the form of a heap of powder.
[0167] A powdery desulfurizer may be used which is attached to the
surface of the compact. This prevents the compacts from sintering
together to become a relatively large agglomerate or sinteringly
adhering to a furnace wall. In addition, since the powdery
desulfurizer adhering to the compact is charged into the melting
apparatus, desulfurization can be performed within the melting
apparatus Examples of such a desulfurizer include limestone.
[0168] In Embodiment 3, the melting apparatus preferably has a
sloped floor, so that the compacts are melted through the
application of heat while tumbling or sliding on the sloped
floor.
[0169] Through the employment of such a sloped floor, the compacts
smoothly move within the melting apparatus toward the subsequent
separator. As the compacts move downward on the sloped floor, their
degrees of melting gradually increase, and thus the compacts of
different degrees of melting are not mixedly present (the degrees
of melting are substantially uniform at each position on the sloped
floor), thereby efficiently melting the compacts.
[0170] Embodiment 3 will next be described in detail with reference
to FIGS. 10 and 11.
[0171] FIGS. 10 and 11 show Embodiment 3 of a metallic iron-making
apparatus according to the present invention, wherein FIG. 10 shows
a horizontal section of the apparatus as viewed from above, and
FIG. 11 shows a sectional view of the apparatus taken along lines
Z-Z and Y-Y of FIG. 10.
[0172] The apparatus of making metallic iron has a thermal
reduction apparatus 223, a melting apparatus 212, and a separator
213. The thermal reduction apparatus 223 is composed of preparatory
compact chambers 202 and 209 and a thermal reduction furnace 210.
The thermal reduction apparatus 223 has a cart (feeding member) 207
to carry the compacts 204, and the cart 207 moves between the
preparatory compact chambers 202 and 209 and the thermal reduction
furnace 210. The cart 207 has a tilting member (not shown) for
alternating the position of a compact-carrying plane (hearth)
between a horizontal position and a sloped position. The
preparatory compact chambers 202 and 209 have feed ports 217 and
218, respectively, for feeding the compacts 204 therethrough from
the exterior of the preparatory compact chambers 202 and 209. The
thermal reduction furnace 210 has a reducing burner 211 (thermal
reduction mechanism) and an exhaust gas outlet 221 for releasing a
generated exhaust gas.
[0173] The melting apparatus 212 is located on the outlet side of
the thermal reduction furnace 210 and has a melting burner 216
(heat-melting mechanism) and an exhaust gas outlet 222. The melting
apparatus 212 also has a sloped floor 224, which leads the compacts
204 toward the next process (separator 213).
[0174] The separator 213, following the melting apparatus 212,
collects molten slag 254 and molten iron 253 and has a slag outlet
219 and a molten iron outlet 220.
[0175] Next, a process of making metallic iron will be described
with reference to FIGS. 10 and 11.
[0176] A pulverized mixture, composed of a carbonaceous reductant
such as coal or the like and iron oxide such as iron ore or the
like, is compacted in advance. As in the above-described Embodiment
2, The thus-formed compact contains the carbonaceous reductant in
"amount required for reducing source iron oxide+amount required for
carburizing reduced iron+amount of loss associated with oxidation."
Furthermore, in Embodiment 3, a powdery desulfurizer such as
powdery limestone or the like adheres to the compact surface.
[0177] The compacts 204 are fed into the preparatory compact
chamber 202 through the feed port 217 to be placed on the cart 207
(in a horizontal position). The cart 207 carrying the compacts 204
moves into the thermal reduction furnace 210. The compacts 204 are
reduced through the application of heat within the thermal
reduction furnace 210, whose maximum temperature is regulated by
the reducing burner 211 so as to be not less than the melting point
of generated slag and not more than the melting point of a metallic
iron shell. During this reduction, the cart 207 maintains its
horizontal position, i.e. the compacts 204 are reduced through the
application of heat while being placed on a horizontal plane
(hearth).
[0178] In this thermal reduction process, reduction first advances
at the peripheral portion of the compact 204, thereby forming a
shell composed of metallic iron. Subsequently, through reduction by
carbon monoxide, which is generated inside the shell from the
carbonaceous reductant itself and through pyrolization of the
carbonaceous reductant, a reducing reaction of iron oxide
efficiently advances inside the shell. Accordingly, generated
metallic iron aggregates to grow the shell, and generated slag also
fuses to aggregate. That is, as reduction advances, the compact 204
generates and grows the metallic iron shell while slag aggregates
inside the shell. As a result, in this thermal reduction process, a
metallization ratio considerably increases, and the amount of iron
oxide mixed into the slag considerably decreases.
[0179] The above-described reduction continues until substantially
no iron oxide is present within the compact 204. Since the amount
of iron oxide mixed into the slag can be reduced through sufficient
execution of reduction, the refractory (furnace wall) of the
subsequent melting apparatus 212 can be prevented from being
damaged by iron oxide when the compacts 204 are melted in the
melting apparatus 212.
[0180] Because of adhesion of a powdery desulfurizer to the surface
of the compacts 204 as previously described, the compacts 204 are
prevented from sintering together to become a relatively large
agglomerate or sinteringly adhering to the furnace wall during this
reduction.
[0181] Furthermore, as previously described, during reduction
within the thermal reduction furnaces 250, the carbonaceous
reductant contained in the compact 204 carburizes reduced iron, and
the CO gas generated from the compact 204 establishes a
non-oxidizing atmosphere around the compact 204, thereby preventing
reduced iron from again being oxidized.
[0182] Upon substantial end of reduction, the compact 204 is
composed of the metallic iron shell and a slag aggregate inside the
shell. At this stage, the cart 207 is sloped by the tilting member
(as represented by the dotted line of FIG. 11). Since at least the
shell of the compact 204 is in a solid state, the compacts 204 move
downward on the sloped hearth of the cart 207 to be discharged from
the thermal reduction furnace 210 into the melting apparatus 212.
The emptied cart 207 returns to the preparatory compact chamber 202
to be fed again with the compacts 204 through the feed port
217.
[0183] In the present invention, since the cart 207 is tilted for
leading the compacts 204 from the thermal reduction furnace 210 to
the melting apparatus 212, even when no powdering desulfurizer is
employed with a resultant formation of relatively large
agglomerates of the compacts 204 which have been subjected to
reduction through the application of heat, the thus-agglomerated
compacts 204 can be smoothly led into the melting apparatus
212.
[0184] Since the interior of the melting apparatus 212 is set to a
temperature for melting not only the slag but also the metallic
iron shell, the compacts 204 melt within the melting apparatus 212.
Rolling or sliding downward on the sloped floor 224 (toward the
separator 213), the compacts 204 are exposed to heat to melt. The
resulting molten substance is led into the separator 213.
[0185] Even when a small amount of unreduced portion remains in the
compact 204 led into the melting apparatus 212 (reduction is
performed within the thermal reduction furnace 250 until
substantially no iron oxide is present in the metallic iron shell,
but iron oxide may remain in an amount of not more than 5% by
weight or not more than 2% by weight in some cases), such an
unreduced portion is reduced through the application of heat during
the melting process. In this case, the melting apparatus 212 may be
replenished with a carbonaceous reductant.
[0186] Since the molten slag 254 and the molten iron 253 are
different in specific gravity, they separate one from the other in
the separator 213 such that the molten slag 254 collects on the
molten iron 253 to form two layers. The thus-separated slag 254 is
released from the slag outlet 219 while the molten iron 253 is
released from the molten iron outlet 220.
[0187] As described above, highly reduced metallic iron can be
efficiently obtained in the form of molten iron, with a
metallization ratio of not less than 95%, or in some cases of not
less than 98%. Furthermore, as a result of highly advanced
reduction of iron oxide in the thermal reduction process, the
amount of iron oxide mixed into the accompanying molten slag is
significantly small. Therefore, the refractory of the melting
apparatus 212 can accordingly be prevented from damagingly being
melted by iron oxide mixed into the molten slag.
[0188] As in the aforementioned Embodiment 2, the separator 213 may
preferably be provided with a heating burner or an electric heating
apparatus for further heating the molten slag 254 and the molten
iron 253 to a higher temperature to thereby increase their
fluidity, so that the molten slag 254 and the molten iron 253 can
be more readily separated one from the other, thereby more
facilitating their separate release.
[0189] Since the thermal reduction apparatus 223 has also the
preparatory compact chamber 209, the compacts 204 are also fed into
the preparatory compact chamber 209 through the feed port 218 to be
placed on the cart 207 (in a horizontal position). The cart
carrying the compacts 204 moves into the thermal reduction furnace
210, where the compacts 204 are subjected reduction through the
application of heat in the similar manner described above. The
compacts 204 (carried on the cart 207) are intermittently led into
the thermal reduction furnace 210 from the preparatory compact
chambers 202 and 209 in an alternating manner. While the compacts
204 fed from either of the preparatory compact chambers 209 and 202
is being reduced, the compacts 204 may be fed into the other
preparatory compact chamber 209 or 202, thereby reducing time
required for feeding and reducing the compacts 204.
[0190] Since an exhaust gas discharged from the exhaust gas outlets
221 and 222 has a high temperature and contains combustible gas,
the exhaust gas may be utilized as a fuel gas to be fed to the
burners 211 and 216. The exhaust gas may also be used as a heat
source for drying or preheating the compacts 204 or for preheating
fuel and combustion air. Also, the exhaust gas may be released
without being utilized.
[0191] In the apparatus of making metallic iron of FIGS. 10 and 11,
the thermal reduction apparatus 223 uses a tilting member, as a
discharging member, which changes the position of the cart 207 (a
feeding member) from a horizontal position to a sloped position to
thereby discharge the compacts 204 from the thermal reduction
apparatus 223 into the melting apparatus 212. The discharging
member is not limited thereto, but may be, for example, a pushing
member for pushing out the compacts 204 on the cart 207 to thereby
discharge the compacts 204 from the thermal reduction apparatus
223. Alternatively, an iron support may be placed on the cart 207,
and the compacts 204 may be placed on the support, so that the
compacts 204, together with the iron support, may be discharged
from the thermal reduction apparatus 223. Such a method that the
compacts 204 are discharged by the pushing member or together with
the iron support can smoothly lead the compacts 204 into the
melting apparatus 212 even when the compacts 204 agglomerate to a
considerably large size.
[0192] Embodiment 4:
[0193] In Embodiment 4, a granular or agglomerate compact
(hereinafter may be referred to as a compact) of iron oxide which
contains a carbonaceous reductant is reduced through the
application of heat, thereby making metallic iron. Specifically,
the above-mentioned compact is rolled to be uniformly heated so as
to be efficiently be reduced. In the course of this reduction, a
shell composed of metallic iron is generated and grown, and slag
aggregates inside the shell. This reduction is continued until
substantially no iron oxide is present inside the shell.
Subsequently, the compact in the form of the shell with a slag
aggregate contained inside is further heated to be melted, followed
by separation into molten slag and molten iron. Since the compacts
are rolled, the compacts are prevented from sintering together to
become a relatively large agglomerate or sinteringly adhering to a
furnace wall during reduction through the application of heat.
[0194] FIG. 12 is a schematic sectional view showing an embodiment
4 of an apparatus of making metallic iron according to the present
invention. FIG. 13 shows a sectional view of the apparatus of
making metallic iron taken along line A-A of FIG. 12. In FIGS. 13
and 12, reference numeral 301 denotes a thermal reduction-melting
apparatus, and-reference numeral 302 denotes a separator. The
thermal reduction-melting apparatus 301 and the separator 302 are
constructed of or lined with refractory.
[0195] The thermal reduction-melting apparatus 301 is composed of a
channel-like member 303 and a cover member 304. The channel-like
member 303 has an arc-shaped inner surface, i.e. a sloped surface
for tumbling 308 and is sloped along the length of a channel (in a
right-left direction of FIG. 12). The channel-like member 303 is
supported by support rollers 307 and rocks in the direction of
arrow B. Therefore, the sloped surface for tumbling 308 rocks
accordingly. Rolling on the rocking sloped surface for tumbling
308, compacts 305 gradually move downward along the direction of
inclination (toward the right of FIG. 12). A burner 306 serving as
a thermal reduction-melting member is provided in the thermal
reduction-melting apparatus 301 on the bottom side of the slope (at
the right-hand side of FIG. 12). The burner 306 establishes a
thermal reduction atmosphere (the left-hand region of FIG. 12) and
a melting atmosphere (the right-hand region of FIG. 12) within the
thermal reduction-melting apparatus 301. In FIG. 12, reference
numeral 309 denotes an exhaust gas outlet for releasing an exhaust
gas generated by the burner 306.
[0196] The compacts 305 are formed by compacting a mixture,
composed of a carbonaceous reductant such as coal or the like and
iron oxide such as iron ore or the like. The thus-prepared compacts
305 are charged into the thermal reduction-melting apparatus 301
through a feed port 310. As described above, the compacts 305
gradually move downward along the direction of inclination (toward
the right of FIG. 12) while tumbling, during which the compacts 305
are reduced and melted through the application of heat of the
burner 306. A resulting molten substance 315 is discharged through
a discharging section 311, formed at the bottom end portion of the
sloped surface for tumbling 308, into the separator 302. The
internal temperature of the thermal reduction-melting apparatus 301
is regulated such that the thermal reduction region has a
temperature of less than the melting point of a generated metallic
iron shell and not less than the melting point of generated slag
and such that the melting region has a temperature at which both
reduced metallic iron and the generated slag melt.
[0197] In a thermal reduction process within the thermal
reduction-melting apparatus 301, reduction first advances at the
peripheral portion of the compact 305, thereby forming a shell
composed of metallic iron. Subsequently, through reduction by
carbon monoxide, which is generated inside the shell from the
carbonaceous reductant itself and through pyrolization of the
carbonaceous reductant, a reducing reaction of iron oxide
efficiently advances inside the shelf. Accordingly, generated
metallic iron aggregates to grow the shell, and generated slag also
fuses to aggregate. As a result, in this thermal reduction process,
a metallization ratio considerably increases, and the amount of
iron oxide mixed into the slag considerably decreases.
[0198] The above-described reduction continues until substantially
DO iron oxide is present within the compact 305. The moving speed
(lowering speed) of the compacts 305 is adjusted in accordance with
time required for this reduction. The moving speed of the compacts
305 may be effectively adjusted through the adjustment of angle of
inclination of the sloped surface for tumbling 308 or through the
formation of a plurality of elongated bumps on the sloped surface
for tumbling 308 in a direction perpendicular to the direction of
inclination of the sloped surface for tumbling 308. The compacts
305, which have been reduced and thus are each composed of a
metallic iron shell and a slag aggregate inside the shell, are
melted through the application of high-temperature heat in the
downstream region of the thermal reduction-melting apparatus 301,
as previously described.
[0199] In the separator 302, since molten slag S, having a smaller
specific gravity, separately floats on the surface of molten iron
F, separated molten slag S may be released through a slag outlet
321 while molten iron F may be released through a molten iron
outlet 322.
[0200] In the above-described Embodiment 4, the compacts 305 are
reduced and melted through the application of heat within the
thermal reduction-melting apparatus 301 having the sloped surface
for tumbling 308 Alternatively, the thermal reduction-melting
apparatus 301 may be constructed as a thermal reduction apparatus
wherein the burner 306 is only used as a thermal reduction member
for reducing the compacts 305 and the compacts 305 undergoes only
reduction through the application of heat. In this case, the
separator 302 may be provided with a burner, an electric heating
apparatus or the like to thereby have functions of a melting
apparatus, or a melting apparatus may be provided between the
thermal reduction apparatus and the separator so as to perform
melting within the separate melting apparatus. In addition, a
plurality of the burners 306 may be provided such that some burners
306 are used to maintain a thermal reduction atmosphere while other
burners 306 are used to maintain a melting atmosphere. The
separator 302 may preferably be provided with a heating burner or
an electric heating apparatus for further heating molten slag S and
molten iron F to a higher temperature to thereby increase their
fluidity, so that molten slag S and molten iron F can be more
readily separated one from the other, thereby more facilitating
their separate release.
[0201] In the above-described Embodiment 4, the sloped surface for
tumbling 308 is provided so that the compacts 305 naturally move
downward in the direction of inclination. The surface for tumbling
is not limited to a sloped surface, but may be movably constructed
such that it maintains a horizontal position during reduction of
the compacts 305 and is sloped upon completion of reduction of the
compacts 305. Alternatively, certain mechanical means may be
provided to send the reduced compacts 305 to the separator side
while the surface remains horizontal. The above-described sloped
surface for tumbling 308 (or a horizontal surface for tumbling) is
formed into an arc shape, but is not limited thereto. It may be
formed into any shape, including a V shape and a U-shape, so long
as the compacts 305 can roll thereon.
[0202] The amount of a carbonaceous reductant contained in the
compact 305 must be at least an amount required for reducing iron
oxide, preferably plus an amount required for carburizing reduced
iron, so that generation of reduced iron can be accompanied by
carburization. Solid (unmolten) reduced iron, composing a shell,
has a porous form and thus is likely to be re-oxidized. This
re-oxidization can be prevented through containment of an
additional amount of the carbonaceous reductant in the compact 305
since the CO gas generated from the compact 305 establishes a
non-oxidizing atmosphere around the compact 305. That is, the
compact 305 most preferably contains the carbonaceous reductant in
"amount required for reducing source iron oxide+amount required for
carburizing reduced iron+amount of loss associated with
oxidation."
[0203] Also, in Embodiment 4, a carbonaceous reductant is
preferably additionally supplied while the compact is being rolled
and reduced through the application of heat.
[0204] In the above-described proposal, a carbonaceous reductant is
previously contained in the compact in "amount required for
reducing source iron oxide+amount required for carburizing reduced
iron+amount of loss associated with oxidation." However, like
Embodiment 2 or the like, the carbonaceous reductant may be
contained in the compact in "amount required for reducing source
iron oxide," and the carbonaceous reductant may be additionally
supplied from outside in "amount required for carburizing reduced
iron+amount of loss associated with oxidation" during reduction
through the application of heat. Alternatively, the carbonaceous
reductant may be contained in the compact in "amount required for
reducing source iron oxide+amount required for carburizing reduced
iron," and the carbonaceous reductant may be additionally supplied
from outside in "amount of loss associated with oxidation" during
reduction through the application of heat. In such a manner, the
carbonaceous reductant may be additionally supplied to compensate a
shortage.
[0205] As previously described, through the use of a powdery
carbonaceous reductant, the powdery carbonaceous reductant may be
attached to the compact surface, thereby preventing the compacts
from sintering together to become a relatively large agglomerate or
sinteringly adhering to a furnace wall, and thus facilitating the
handling of the compacts.
[0206] While metallic iron (reduced iron) is being melted, the
thermal reduction-melting apparatus 301 may be replenished with a
carbonaceous reductant to compensate a shortage of the carbonaceous
reductant, so that the CO gas generated from the carbonaceous
reductant maintains a non-oxidizing atmosphere around the compacts
305, thereby preventing metallic iron from again being oxidized.
Thus, it is preferable that during the melting of metallic iron, a
carbonaceous reductant be additionally fed in the amount of
compensating a shortage or that the carbonaceous reductant is
previously contained in the compact 305 in excess of a required
amount, so that even when some iron oxide remains due to incomplete
reduction in a reducing process, the remaining iron oxide can
completely be reduced in a melting process.
[0207] According to the above description of Embodiment 4, the
compacts 305 are not subjected to any treatment before they are
charged into the thermal reduction-melting apparatus 301 (or a
thermal reduction apparatus). In order to reduce the length of the
surface of tumbling of the thermal reduction-melting apparatus 301
(i.e. the length in the direction of inclination in FIG. 12) to
thereby shorten time required for reduction through the application
of heat, the compacts 305 may be prereduced before they are charged
into the thermal reduction-melting apparatus 301. In this case, a
prereducing apparatus must be provided upstream of the thermal
reduction-melting apparatus 301 (or a thermal reduction
apparatus).
[0208] Embodiments 5 to 7:
[0209] In Embodiments 5 to 7, a granular or agglomerate compact of
iron oxide which contains a carbonaceous reductant is reduced
through the application of heat, thereby making metallic iron.
Specifically, the above-mentioned compact is reduced through the
application of heat while falling downward. In the course of this
reduction, a shell composed of metallic iron is generated and
grown, and slag aggregates inside the shell. This reduction is
continued until substantially no iron oxide is present inside the
shell. The compact in the form of the shell with a slag aggregate
contained inside is further heated to be melted in the course of
the fall, followed by separation into molten slag and molten iron.
Further, by adding a preceding process of continuously forming the
granular compacts to the process of reduction through the
application of heat, it becomes possible to continuously perform a
series of processes of preparing granular compacts serving as
material for metallic iron, reducing the compacts through the
application of heat, and separating metallic iron generated through
the reduction from slag.
[0210] In the above-described process of reduction through the
application of heat, reduction, first, advances from the surface of
the granular compact, thereby forming a shell composed of metallic
iron. Subsequently, due to a reducing action of carbon monoxide
generated from the carbonaceous reductant itself and through
pyrolization of the carbonaceous reductant, the reducing reaction
of CO with iron oxide efficiently advances inside the shell.
Accordingly, generated metallic iron adheres together to aggregate
while generated slag is melted to aggregate. As a result, in this
thermal reduction process, a metallization ratio considerably
increases, and the amount of iron oxide mixed into the slag
considerably decreases.
[0211] In a section located underneath the section of reduction
through the application of beat, further heating is performed to
melt the metallic iron shell. The resulting molten substance falls
into a separator located underneath, where molten iron and molten
slag are separated one from the other due to their different
specific gravities. Thus, highly reduced metallic iron can be
efficiently obtained in the form of molten iron Furthermore, since
iron oxide is intensively reduced in the thermal reduction process,
the amount of iron oxide mixed into the accompanying molten slag is
significantly small. Therefore, the refractory of a melting
apparatus can accordingly be prevented from damagingly being melted
by iron oxide mixed into the molten slag.
[0212] FIG. 14 shows a schematic sectional view of Embodiment 6 of
the present invention, illustrating a typical method and apparatus
for making metallic iron. In FIG. 14, reference numeral 401 denotes
a screw-shaped conveying apparatus; numeral 402 denotes a
reducing-melting furnace having a space of falling for conducting
heating, reduction, and melting; numeral 403 denotes a heating
section for indirectly heating the reducing-melting furnace 402
from outside; and numeral 404 denotes a separator furnace for
receiving molten slag and molten metallic iron, falling from above,
and for separating them one from the other. For use in this
apparatus of making metallic iron, a mixture, composed of a
carbonaceous reductant such as coal or the like and iron oxide such
as iron ore or the like and, as needed, a binder, is compacted to
grains, thereby forming granular compacts D. The granular compacts
D are fed into the conveying apparatus 401, so that they are
continuously charged from the tip portion of the conveying
apparatus 401 into the top portion of the reducing-melting furnace
402.
[0213] In FIG. 14, the previously prepared granular compacts D are
continuously charged into the reducing-melting furnace 402 through
the use of the conveying apparatus 401. Alternatively, a continuous
compacting apparatus such as a disk pelletizer may be installed
upstream of the conveying apparatus 401, so that the granular
compacts D are continuously prepared and fed to the
reducing-melting furnace 402 via the conveying apparatus 401. This
arrangement is particularly preferable since a series of processes
of preparing, conveying, and reducing through the application of
heat the granular compacts D can be continuously conducted.
[0214] The reducing-melting furnace 402 is indirectly heated by the
heating section 403 provided therearound. While the charged
granular compacts D are falling downward by their own weight within
the reducing-melting furnace 402, reduction advances from the
surface of each granular compact D, thereby forming a shell,
composed mainly of metallic iron generated through reduction, on
the surface. Carbon monoxide generated from a carbonaceous
reductant and through pyrolization of the carbonaceous reductant
establishes an intensive reducing atmosphere within the shell,
thereby sharply accelerating reduction of iron oxide inside the
shell. Therefore, by properly determining the length of the
reducing-melting furnace 402 and a heating temperature in
accordance with the falling speed of the granular compacts D, the
intensive reducing atmosphere established within the metallic iron
shell efficiently reduces iron oxide inside the shell, thereby
obtaining a metallization ratio of not less than 95%, or in some
cases of not less than 98%.
[0215] Slag, generated in the course of generation of metallic
iron, melts inside the metallic iron shell of the granular compact
D at a lower temperature than metallic iron does. The thus-molten
slag and the metallic iron shell fuse together in a separated
state. As the granular compact D falls further downward within the
reducing-melting furnace 402 and is heated further, the metallic
iron shell also melts. The molten metallic iron, together with the
molten slag, falls into the separator furnace 404 located
underneath. In the separator furnace 404, molten slag S having a
smaller specific gravity separately floats on the surface of molten
iron F. Thus, the molten slag S is released from the separator
furnace 404 at a location in the vicinity of the surface of the
molten iron F while the molten iron F is released from the bottom
portion of the separator furnace 404.
[0216] In Embodiment 5, a submerged weir 408 is provided within the
separator furnace 404. Due to difference in specific gravity
between the molten slag S and the molten iron F, the molten slag S
floats on the surface of the molten iron F on one side of the
submerged weir 408 and is released from the separator furnace 404
at a location in the vicinity of the molten iron surface. The
molten surface F flows under the submerged weir 408 to the other
side of the submerged weir 408 (to the right-hand side of FIG. 14)
and is released from the bottom portion of the separator surface
404. This arrangement more efficiently separates the molten iron F
from the molten slag S.
[0217] In addition to the above-described arrangement in which the
submerged weir 408 is provided so that a molten substance of the
granular compacts D falls and accumulates on one side of the
submerged weir 408, a heating arrangement may be employed for
heating the molten slag S accumulated on that side of the submerged
weir 408. In this case, even when the molten substance of the
granular compacts D, with some portion being insufficiently
reduced, falls into the separator furnace 404, the molten slag
layer is again heated, thereby completing a reducing reaction.
Accordingly, a metallization ratio is further improved.
[0218] In FIG. 14, reference numeral 406 denotes exhaust gas
outlets. Exhaust gases may be released through the corresponding
exhaust gas outlets 406 without any utilization thereof. However,
since the exhaust gases have a high temperature and contains
combustible gas, they may be utilized as fuel gases to be fed to
burners 405 located at the heating section 403, resulting in a
reduced fuel consumption associated with heating. In the above
description, the reducing-melting furnace 402 is indirectly heated
from outside. However, burners may be mounted inside the
reducing-melting furnace 402 for directly heating the granular
compacts D.
[0219] The present invention is desirably embodied such that while
the granular compacts D are falling by their own weight within the
reducing-melting furnace 402, reduction is substantially completed
and such that the thus-reduced iron is melted at the lower portion
of the reducing-melting furnace 402 and falls, in the molten state,
into the separator furnace 404. To this end, in order to secure a
sufficient residence time in accordance with the falling speed of
the granular compacts D, the reducing-melting furnace must be
vertically elongated to a considerably large length. Furthermore,
it may be effective to provide baffle plates within the
reducing-melting furnace 402 in order to reduce the falling speed
of the granular compacts D, or to provide guides to make the
granular compacts D whirl down. However, if falling-speed control
members such as these baffle plates or guides are mounted at the
lower portion of the reducing-melting furnace 402, metallic iron,
which has been generated through reduction through the application
of heat and has begun to melt through the further application of
heat, may adhere to and accumulate on the falling-speed control
members, resulting in the risk of hindering continuous operation.
Therefore, these falling-speed control members are desirably
mounted above a position where metallic iron begins to melt.
[0220] FIG. 15 shows a schematic sectional view of Embodiment 6 of
the present invention, which is constructed such that the falling
speed of granular compacts D can be reduced with no requirement to
mount falling-speed control members or the like. In Embodiment 6, a
separator furnace 404 is integrally formed at the bottom portion of
a reducing-melting furnace 402. Furthermore, a high-temperature
non-oxidizing gas is fed into the thus-constructed furnace at
positions just above the boundary between the reducing-melting
furnace 402 and the separator furnace 404, thereby forcibly
suspending the falling granular compacts D by an ascending current
of the non-oxidizing gas. As a result, the residence time of the
granular compacts D within the reducing-melting furnace 402 can be
increased. In this case, while the suspended granular compacts D
are subjected to reduction through the application of heat, a
metallic iron shell is formed on the surface of the granular
compact D, and a reducing reaction advances inside the shell.
Subsequently, when the thus-formed metallic iron is melted through
the further application of heat, molten iron fuses together to
grow. The thus-grown molten iron falls downward. Accordingly, by
adequately regulating the flow rate of the non-oxidizing gas in
accordance with the resistance of the granular compacts D against
the ascending current, the residence time of the granular compacts
D within the reducing-melting furnace 402 can be regulated as
desired. Therefore, while the granular compacts D are resident
within the reducing-melting furnace 402, reduction through the
application of heat can sufficiently be advanced. This application
of heat for reduction may be attained by direct heating through the
feed of a high-temperature non-reducing gas or by indirect heating
through the use of burners or the like arranged around the
reducing-melting furnace 402.
[0221] FIG. 16 shows a schematic sectional view of Embodiment 7 of
the present invention. Embodiment 7 is constructed such that a
reducing gas generated within the reducing-melting furnace 402 can
be utilized as a fuel for indirectly heating the reducing-melting
furnace 402. Since the granular compacts D used in the present
invention contain a large amount of a carbonaceous reductant to
effectively conduct a reducing agent as previously described, a gas
within the reducing-melting furnace 402 contains combustible gas,
and thus may be effectively used as a fuel gas. Therefore, this
Embodiment 7 is constructed in the following manner to utilize the
combustible gas. The reducing-melting furnace 402 is indirectly
heated from outside with burners 405, and the reducing gas is
extracted through the upper wall of the reducing-melting furnace
402 and led into a surrounding burner section 403, where the
combustible gas is used as a fuel. The resulting exhaust gas is
released through an exhaust outlet 406. This arrangement is
preferable since the amount of a fuel used for heating can be
reduced.
[0222] Also, in Embodiments 5 to 7, as described above in other
Embodiments, the carbonaceous reductant contained in the
above-described granular compact D is consumed, first, through
reduction of iron oxide in a reducing process, and then through
carbonization of metallic iron, generated through the reduction.
Solid reduced iron to undergo a melting process has a porous form
and thus is likely to be re-oxidized. In order to prevent the
reduced iron from being re-oxidized, the carbonaceous reductant
must be contained in the granular compact D sufficiently against
re-oxidization, so that the CO gas generated through combustion of
the carbonaceous reductant establishes a non-oxidizing atmosphere
around the granular compact D falling within the reducing-melting
furnace 402. To attain this end, the granular compact D must
contain the carbonaceous reductant in at least "amount required for
reducing source iron oxide+amount consumed for carburizing reduced
iron+amount of loss associated with oxidation within the furnace."
In addition, in order to prevent reduced iron from being
re-oxidized, the carbonaceous reductant or the CO gas may be
additionally supplied in the amount of compensating a shortage into
the lower portion of the reducing-melting furnace 402 or the
separator furnace 404.
[0223] By employing a method of replenishing the separator furnace
404 with a carbonaceous reductant or previously containing the
carbonaceous reductant in excess of a required amount in the
granular compact D, even when some iron oxide which has not
completely been reduced within the reducing-melting furnace 402
falls into the separator furnace 404, such iron oxide can be
completely reduced within the separator furnace 404.
[0224] According to the above-described Embodiments 5 to 7, the
granular compacts D are not subjected to any treatment before they
are charged into the reducing-melting furnace 402. In order to
reduce the length of the reducing-melting furnace 402 to thereby
shorten time required for reduction through the application of
heat, the granular compacts D may be prereduced before they are
charged into the reducing-melting furnace 402. In this case, a
prereducing apparatus must be provided upstream of the
reducing-melting furnace 402.
[0225] Also, in Embodiments 5 to 7, as described above in other
Embodiments, the separator furnace 404 may preferably be provided
with a heating burner or an electric heating apparatus for further
heating molten slag and iron to a higher temperature to thereby
increase their fluidity, so that molten slag and molten iron can be
more readily separated one from the other, thereby facilitating
their separate release.
[0226] Embodiments 8 and 9:
[0227] In Embodiments 8 and 7, an elongated compact of iron oxide
which contains a carbonaceous reductant is reduced through the
application of heat, thereby making metallic iron. Specifically,
the above-mentioned elongated compact is reduced through the
application of heat while being moved downward in a vertical
position. In the course of this reduction, a shell composed of
metallic iron is generated and grown, and slag aggregates inside
the shell. Subsequently, the metallic iron shell with a slag
aggregate contained inside is further heated to be melted in the
course of downward movement, followed by separation into molten
slag and molten iron. Further, by adding a preceding process of
continuously forming the elongated compact to the process of
reduction through the application of heat, it becomes possible to
continuously perform a series of processes of preparing the
elongated compact serving as material for metallic iron, reducing
the elongated compact through the application of heat, and
separating metallic iron generated through the reduction from
slag.
[0228] In the above-described process of reduction through the
application of heat, reduction, first, advances from the surface of
the elongated compact, thereby forming a shell composed of metallic
iron. Subsequently, due to a reducing action of carbon monoxide
generated from the carbonaceous reductant itself and through
pyrolization of the carbonaceous reductant, the reducing reaction
of CO with iron oxide efficiently advances inside the shell.
Accordingly, generated metallic iron adheres together to aggregate
while generated slag is melted to aggregate. As a result, in this
thermal reduction process, a metallization ratio considerably
increases, and the amount of iron oxide mixed into the slag
considerably decreases.
[0229] In a section located underneath the section of reduction
through the application of heat, further heating is performed to
melt the metallic iron shell The resulting molten substance,
composed of molten iron and molten slag, falls into a separator
located underneath, where molten iron and molten slag are separated
one from the other due to their different specific gravities. Thus,
highly reduced metallic iron can be efficiently obtained in the
form of molten iron. Furthermore, since iron oxide is intensively
reduced in the thermal reduction process, the amount of iron oxide
mixed into the accompanying molten slag is significantly small.
Therefore, the refractory of a melting apparatus can accordingly be
prevented from damagingly being melted by iron oxide mixed into the
molten slag.
[0230] FIG. 17 shows a schematic sectional view of Embodiment 8 of
the present invention, illustrating a method and apparatus for
making metallic iron. In FIG. 17, reference numeral 501 denotes a
material hopper, numeral 502 denotes compacting-feeding rollers
(having functions of both a compacting apparatus and a feeding
apparatus); numeral 503 denotes a thermal reduction furnace; and
numeral 504 denotes a separator furnace serving as a separator. A
mixture E, composed of a carbonaceous reductant such as coal or the
like and iron oxide such as iron ore or the like and, as needed, a
binder, is fed into the hopper 501 in the direction of arrow H. The
compacting-feeding rollers 502 continuously compact the mixture E
into an elongated compact G having a certain shape (usually a plate
shape, a square bar shape, or a round bar shape) and certain
dimensions, and feed the elongated compact G, maintained in a
vertical position, into the thermal reduction furnace 503. The
"vertical position" basically means a hanging position, but may
somewhat (for example, =5.degree.) incline at a feeding section due
to accuracy of a feeding apparatus without departing from the
spirit of the present invention.
[0231] The thermal reduction furnace 503 has burners 505 serving as
a heating member. As the elongated compact G lowers within the
thermal reduction furnace 503, the elongated compact G is directly
heated by flames of the burners 505. As a result, reduction
advances from the surface of the elongated compact G toward the
interior thereof, thereby forming a shell, composed mainly of
metallic iron generated through reduction, on the surface as
previously described. Carbon monoxide generated from a carbonaceous
reductant and through pyrolization of the carbonaceous reductant
establishes an intensive reducing atmosphere within the shell,
thereby sharply accelerating reduction of iron oxide inside the
shell. Therefore, by properly controlling the lowering speed of the
elongated compact G and heating conditions in accordance with the
length of the thermal reduction furnace 503, the intensive reducing
atmosphere established within the metallic iron shell efficiently
reduces iron oxide inside the shell, thereby obtaining a
metallization ratio of not less than 95%, or in some cases of not
less than 98%.
[0232] Slag, generated in the course of generation of metallic
iron, melts inside the metallic iron shell at a lower temperature
than metallic iron does. The thus-molten slag and the metallic iron
shell fuse together in a separated state. As the elongated compact
G further advances toward the lower portion of the thermal
reduction furnace 503 and is heated further, the metallic iron
shell also melts. The molten metallic iron, together with the
molten slag, falls into the separator furnace 504 located
underneath. In the separator furnace 504, molten slag S having a
smaller specific gravity separately floats on the surface of molten
iron F. Thus, the molten slag S is released from the separator
furnace 504 at a location in the vicinity of the surface of the
molten iron F while the molten iron F is released from the bottom
portion of the separator furnace 504.
[0233] In FIG. 17, reference numeral 506 denotes exhaust gas
outlets. As previously described, an exhaust gas may be released
through the exhaust gas outlets 506 without any utilization
thereof. However, since the exhaust gas has a high temperature and
contains combustible gas, it may preferably be utilized as a fuel
gas to be fed to the burners 505. In FIG. 17, reference numeral 507
denotes a gas seal portion.
[0234] The present invention may be embodied such that the
aforementioned mixture is compacted to the elongated compact G
merely through the application of pressure. Preferably, as shown in
FIG. 17, the mixture is compacted through the application of
pressure while being surrounded by a support mesh K made of iron,
so that there is no risk that the elongated compact G would break
while it is continuously lowering. The support mesh K is finally
melted together with metallic iron, generated through reduction
through the application of heat, and falls into the separator
furnace 504. Therefore, the support mesh K is desirably made of
iron. In place of an exterior reinforcement through the use of the
support mesh K, an iron core (a stranded wire, or an iron wire
having a rugged surface for increasing the effect of support may
also be acceptable) may be inserted as reinforcement in the central
portion of the elongated compact G.
[0235] Embodiment 9:
[0236] FIG. 18 shows a schematic sectional view of Embodiment 9 of
the present invention. Embodiment 9 is basically similar to
Embodiment 8 except that a mixture E, composed of a carbonaceous
reductant, iron oxide, and a binder, is fed to compacting-feeding
rollers 502 through a screw feeder 501a and that a thermal
reduction furnace 503 is indirectly heated by burners 505 arranged
therearound.
[0237] In the above-described Embodiments 8 and 9, the
compacting-feeding rollers 502 simultaneously compact the mixture E
to and feed the elongated compact G. However, separate apparatuses
may be used for compacting and feeding. Alternatively, the
elongated compact G may be previously prepared using a separate
apparatus, and the thus-prepared elongated compact G may be fed
into the thermal reduction furnace 503.
[0238] The carbonaceous reductant contained in the above-described
elongated compact G is consumed first, through reduction of iron
oxide in a reducing process, and then through carburization of
metallic iron, generated through the reduction. Solid reduced iron
to undergo a melting process has a porous form and thus is likely
to be re-oxidized. In order to prevent the reduced iron from being
re-oxidized, as previously described, the carbonaceous reductant
must be contained in the granular compact D sufficiently against
re-oxidization, so that the CO gas generated through combustion of
the carbonaceous reductant establishes a non-oxidizing atmosphere
around the elongated compact G moving downward within the thermal
reduction furnace 503. To attain this end, the elongated compact G
must contain the carbonaceous reductant in at least "amount
required for reducing source iron oxide+amount consumed for
carburizing reduced iron+amount of loss associated with oxidation
within the furnace." In addition, in order to prevent reduced iron
from being re-oxidized, the carbonaceous reductant or the CO gas
may be additionally supplied in the amount of compensating a
shortage into the lower portion of the thermal reduction furnace
503 or the separator furnace 504.
[0239] As previously described, by employing a method of
replenishing the separator furnace 504 with a carbonaceous
reductant or previously containing the carbonaceous reductant in
excess of a required amount in the elongated compact G, even when
some iron oxide which has not completely been reduced within the
thermal reduction furnace 503 falls into the separator furnace 504,
such iron oxide can be completely reduced within the separator
furnace 504.
[0240] In the above-described Embodiments 8 and 9, the elongated
compact G is not subjected to any treatment before it is charged
into the thermal reduction furnace 503. In order to reduce the
length of the thermal reduction furnace 503 to thereby shorten time
required for reduction through the application of heat, the
elongated compact G may be prereduced before it is charged into the
thermal reduction furnace 503. In this case, a prereducing
apparatus must be provided upstream of the thermal reduction
furnace 503. Also, as shown in FIG. 18. a submerged weir 508 may be
provided within the separator furnace 504, thereby efficiently
separating molten iron F and molten slag S one from the other.
[0241] Also, in Embodiments 8 and 9, the separator furnace 504 may
preferably be provided with a heating burner or an electric heating
apparatus for further heating molten slag and iron to a higher
temperature to thereby increase their fluidity, so that molten slag
and molten iron can be more readily separated one from the other,
thereby more facilitating their separate release.
[0242] Embodiment 10:
[0243] In a method of making metallic iron according to Embodiment
10 of the present invention, a granular (including pellet-like) or
agglomerate compact of iron oxide which contains a carbonaceous
reductant is conveyed on an iron belt and reduced through the
application of heat, thereby making metallic iron. In the course of
this reduction, a shell composed of metallic iron is generated and
grown on the surface of the compact, and slag aggregates inside the
shell. Subsequently, the compact in the form of the shell with a
slag aggregate contained inside is further heated while being
conveyed on the iron belt, so that the metallic iron shell, slag,
and the iron belt used for conveyance are melted. The resultant
molten substance is separated into molten slag and molten iron
According to the present embodiment, there can also be performed
continuously a series of processes of reducing the compact through
the application of beat, melting generated metallic iron and slag
through the further application of heat, and separating molten iron
and molten slag one from the other.
[0244] FIG. 19(a) is a schematic cross-sectional view showing an
apparatus for making metallic iron for carrying out the
above-described method. In FIG. 19(a), reference numeral 601
denotes an iron belt; numeral 602 denotes an annealing furnace;
numeral 603 denotes a forming section; numeral 604 denotes a
material hopper; numeral 605 denotes a thermal reduction furnace;
numeral 606 denotes a melting furnace; and numeral 607 denotes a
separator furnace.
[0245] The present embodiment uses an iron belt 601 as means for
conveying material compact. The iron belt 601 is annealed to be
softened while passing through the annealing furnace 602. The
thus-annealed iron belt 601 is formed at the forming section 603
into a gutter-like shape with both edges bent upright (see a
partial transverse cross-section shown in FIG. 19(b)). The
thus-formed iron belt 601 is continuously fed into the thermal
reduction furnace 605. A mixture, composed of a carbonaceous
reductant such as coal or the like and iron oxide such as iron ore
or the like and, as needed, a binder, is compacted to a certain
form such as pellets, thereby forming material compacts. The
thus-prepared material compacts are placed onto the iron belt 601
through the material hopper 604 located at the upstream side of the
thermal reduction furnace 605. The material compacts are
continuously fed on the iron belt 601 toward the right of FIG. 19.
Heating burners (not shown) are provided on side walls or ceiling
portion of the thermal reduction furnace 605 so as to sequentially
dry and reduce the material compacts through the application of
heat. As previously described, in this thermal reduction process,
reduction progresses from the surface of each compact due to a
solid reductant contained in the compact, thereby forming a shell,
composed mainly of metallic iron generated through reduction, on
the surface of the compact. In addition, carbon monoxide generated
from a carbonaceous reductant and through pyrolization of the
carbonaceous reductant establishes an intensive reducing atmosphere
within the shell, thereby sharply accelerating reduction of iron
oxide inside the shell. Therefore, by properly determining the
moving speed of the iron belt 601, heating conditions, etc. in
accordance with the length of the thermal reduction furnace 605,
the intensive reducing atmosphere established within the metallic
iron shell efficiently reduces iron oxide inside the shell, thereby
obtaining a metallization ratio of not less than 95%, or in some
cases of not less than 98% Slag, generated in the course of
generation of metallic iron, melts inside the metallic iron shell
at a lower temperature than metallic iron does. The thus-molten
slag aggregates inside and separately from the metallic iron shell.
As the compact in the form of the metallic iron shell with a slag
aggregate contained inside is further heated in the melting furnace
606 located downstream of the thermal reduction furnace 605, the
metallic iron shell, slag inside the shell, and the iron belt 601
are all melted. The resulting molten substance flows toward the
separator furnace 607 In the separator furnace 607, molten slag S
having a smaller specific gravity separately floats on the surface
of molten iron F. Thus, the molten slag S is released from the
separator furnace 607 at a location in the vicinity of the surface
of the molten iron F while the molten iron F is released from the
bottom portion of the separator furnace 607.
[0246] In FIG. 19, reference numeral 608 denotes an exhaust gas
outlet. An exhaust gas may be released through the gas outlet 608
without any utilization thereof. However, since the exhaust gas has
a high temperature and contains combustible gas, it may desirably
be utilized as a fuel gas to be fed to the burners of the thermal
reduction furnace 605 and melting furnace 606, or as a heat source
for preheating the combustion air. Material compacts fed from the
material hopper 604 are preferably in the form of pellets and
pre-dried, more preferably further pre-reduced since the length of
the thermal reduction furnace 605 is reduced through the use of
pre-reduced compacts. A compacting apparatus for preparing the
material compacts in the form of pellets or the like may be
disposed in the vicinity of the hopper 604, so that the material
compacts prepared in the compacting apparatus are fed into the
hopper 604. Through the employment of this arrangement, a process
of preparing material compacts and a process of reduction through
the application of heat is combined into a continuous process.
[0247] The actual design of the above-described apparatus for
making metallic iron may be adequately modified so long as no
deviation from the above-stated gist of the present invention is
involved. Of course, such modifications are encompassed by the
technological scope of the present invention. In operation, the
above-described conditions and settings (operating temperature, the
amount and form of use of a carbonaceous reductant, utilization of
an exhaust gas, etc.) may adequately be selected.
[0248] Embodiment 11:
[0249] In a method of making metallic iron according to Embodiment
11 of the present invention, an elongated material compact of iron
oxide which contains a carbonaceous reductant is continuously
prepared, conveyed, like Embodiment 10 described above, on an iron
belt into a thermal reduction furnace, and reduced through the
application of heat in the thermal reduction furnace, thereby
making metallic iron. Accordingly, a series of processes of
reduction through the application of heat, melting through the
application of heat, and separation of molten iron is continuously
performed. While the elongated compact conveyed on the iron belt is
subjected to reduction through the application of heat, a shell
composed of metallic iron is generated and grown on the surface of
the elongated compact, and slag aggregates inside the shell.
Subsequently, the compact in the form of the shell with a slag
aggregate contained inside is further heated while being conveyed
on the iron belt, so that the metallic iron shell, slag, and the
iron belt used for conveyance are melted. The resultant molten
substance is separated into molten slag and molten iron.
[0250] FIG. 20(a) is a schematic cross-sectional view showing an
apparatus for making metallic iron for carrying out the
above-described method. In FIG. 20(a), reference numeral 601
denotes an iron belt; numeral 603 denotes a forming section;
numeral 609 denotes a screw feeder; numeral 605 denotes a thermal
reduction furnace; numeral 606 denotes a melting furnace; and
numeral 607 denotes a separator furnace.
[0251] An elongated compact is continuously prepared and placed on
the iron belt 601 so as to be conveyed on the iron belt 601 into
the thermal reduction furnace 605. That is, as shown in FIG. 20,
the screw feeder 609 is combined with the forming section 603. A
mixture, composed of a carbonaceous reductant, iron oxide, and
binder, is fed into the screw feeder 609, which feeds the mixture
toward the forming section 603. Being fed with the mixture and the
iron belt 601, the forming section 603 forms the kneaded mixture
into an elongated form having a certain cross-section and placed on
the iron belt 601 (see a partial transverse cross-section shown in
FIG. 20(b)), and feeds the thus-formed elongated compact, together
with the iron belt 601, into the thermal reduction furnace 605. The
elongated compact may have a flat plate or bar shape, but is
preferably shaped such that elongated projections and depressions
are formed in a longitudinal direction in order to increase the
surface area for efficient drying and reduction through the
application of heat.
[0252] In the present embodiment, since the compact in an elongated
form is continuously placed on the iron belt 601, there is no fear
that the compact will tumble off the iron belt 601. Accordingly,
the iron belt 601 may be flat. In addition, the iron belt 601 may
be fed not only in a horizontal direction but also in an
appropriately downward sloped direction for smooth conveyance.
[0253] The thermal reduction furnace 605 comprises an upstream
drying section and a downstream thermal reduction section. Heating
burners (not shown) are provided on side walls and ceiling portions
of the drying and thermal reduction sections so as to sequentially
dry and reduce the elongated compact through the application of
heat. As previously described, in this thermal reduction process,
reduction progresses from the surface of the elongated compact due
to a solid reductant contained in the elongated compact, thereby
forming a shell, composed mainly of metallic iron generated through
reduction, on the surface of the elongated compact. In addition,
carbon monoxide generated from a carbonaceous reductant and through
pyrolization of the carbonaceous reductant establishes an intensive
reducing atmosphere within the shell, thereby sharply accelerating
reduction of iron oxide inside the shell. Therefore, by properly
determining the moving speed of the iron belt 601, heating
conditions, etc. in accordance with the length of the thermal
reduction furnace 605, the intensive reducing atmosphere
established within the metallic iron shell efficiently reduces iron
oxide inside the shell.
[0254] Slag, generated in the course of generation of metallic
iron, melts inside the metallic iron shell at a lower temperature
than metallic iron does. The thus-molten slag aggregates inside and
separately from the metallic iron shell. As the elongated compact
in the form of the metallic iron shell with a slag aggregate
contained inside is further heated in the melting furnace 606
located downstream of the thermal reduction furnace 605, the
metallic iron shell, slag inside the shell, and the iron belt 601
are all melted. The resulting molten substance flows toward the
separator furnace 607. In the separator furnace 607, molten slag S
and molten iron F are separated one from the other in a manner as
described previously.
[0255] The actual design of the above-described apparatus for
making metallic iron may be adequately modified so long as no
deviation from the above-stated gist of the present invention is
involved. Of course, such modifications are encompassed by the
technological scope of the present invention. In operation, the
above-described conditions and settings (operating temperature, the
amount and form of use of a carbonaceous reductant, utilization of
an exhaust gas, etc.) may adequately be selected.
[0256] Embodiment 12:
[0257] In a method of making metallic iron according to Embodiment
12 of the present invention, a number of elongated compacts of iron
oxide which contains a carbonaceous reductant are continuously
prepared in parallel by a number of compacting apparatuses disposed
in parallel. The thus-prepared elongated compacts are continuously
fed in parallel along a sloped surface into a heat-drying-reducing
furnace, and reduced through the application of heat therein.
Subsequently, metallic iron generated through reduction and
accompanying slag are led into a melting furnace. The resultant
molten substance is led into a separator, where molten iron and
molten slag are separated one from the other, thereby obtaining
metallic iron.
[0258] FIG. 21 is a schematic cross-sectional view showing an
apparatus of making metallic iron for carrying out the
above-described method, and FIG. 22 is a schematic plan view of the
apparatus. In FIGS. 21 and 22, reference numeral 701 denotes a
material hopper; numeral 702 denotes compacting devices; numeral
703 denotes a heating furnace serving as drying, reducing, and
melting furnaces; numeral 704 denotes a separator furnace; and
numeral 705 denotes elongated compacts.
[0259] In the present embodiment, as shown in FIGS. 21 and 22, the
heating furnace 703 having a sloped surface, sloping down toward
the separator furnace 704, is provided on one side or both sides
(on one side in FIGS. 21 and 22) of the elongated separator furnace
704. Each heating furnace 703 is provided with a heating burner
apparatus and a number of the compacting devices 702 across the
width thereof (in a direction perpendicular to the paper surface of
FIG. 21) at the upper end portion thereof as shown in FIG. 22. Each
heating furnace 703 prepares plate- or bar-like elongated compacts
705, feeds these elongated compacts 705 into the heating furnace
703 along the sloped surface of the heating furnace 703. Moving
downward along the sloped surface, the elongated compacts 705 are
dried and reduced through the application of heat. As previously
described, in this thermal reduction process, reduction progresses
from the surface of each elongated compact 705 due to a solid
reductant contained in the elongated compact 705, thereby forming a
shell, composed mainly of metallic iron generated through
reduction, on the surface of the elongated compact 705. In
addition, carbon monoxide generated from a carbonaceous reductant
and through pyrolization of the carbonaceous reductant establishes
an intensive reducing atmosphere within the shell, thereby sharply
accelerating reduction of iron oxide inside the shell.
[0260] The metallic iron generated through reduction and
accompanying slag are further heated and melted at the downstream
portion of the heating furnace 703. The resulting molten substance
flows into the separator furnace 704. A number of the elongated
compacts 705 fed into the heating furnace 703 concurrently undergo
the above-described reduction and melting through the application
of heat.
[0261] Therefore, by properly determining the moving speed of the
elongated compacts 705, heating conditions, etc. in accordance with
the length of the heating furnace 703, a metallic iron shell is
generated on the surface of each elongated compact 705, and the
intensive reducing atmosphere established within the metallic iron
shell efficiently reduces iron oxide inside the shell, thereby
obtaining a metallization ratio of not less than 95%, or in some
cases of not less than 98%. The thus-generated metallic iron and
accompanying slag are further heated and melted. The resulting
molten substance flows into the separator furnace 704.
[0262] In the separator furnace 704, molten slag S having a smaller
specific gravity separately floats on the surface of molten iron F.
Thus, the molten slag S is released from the separator furnace 704
at a location in the vicinity of the surface of the molten iron F
while the molten iron F is released from the bottom portion of the
separator furnace 704.
[0263] The above-described apparatus allows a user to adjust, as
desired, the production of metallic iron per unit time through
adjustment of the size, number, feeding rate, etc. of elongated
compacts in accordance with the scale or heating capability of the
heating section of the heating furnace 703, or to readily design
and construct an apparatus in accordance with a target
production.
[0264] The actual design of the above-described apparatus for
making metallic iron may be adequately modified so long as no
deviation from the above-stated gist of the present invention is
involved. Of course, such modifications are encompassed by the
technological scope of the present invention. In operation, the
above-described conditions and settings (operating temperature, the
amount and form of use of a carbonaceous reductant, utilization of
an exhaust gas, etc.) may adequately be selected.
[0265] When the present invention is embodied as described above in
Embodiments 2 to 12. in a thermal reduction process, slag generated
must melt at a lower temperature than does metallic iron generated
through reduction in order to successfully reduce iron oxide in a
solid-phase state, as previously described. To meet this
requirement, the composition of slag components (gangue components
mixed in iron ore, generally used as source iron oxide, and a
carbonaceous reductant) contained in a compact (or an elongated
compact) must be controlled such that the melting point of
generated slag is lower than that of reduced iron before and after
carburization. Therefore, it may be desirable in some cases that
Al.sub.2O.sub.3, SiO.sub.2, CaO, etc. be added to a source mixture
of the compact (or the elongated compact) in a compacting process
to thereby reduce the melting point of generated slag.
[0266] The present invention is not limited to the above-described
embodiments. Numerous modifications and variations of the present
invention are possible in light of the spirit of the present
invention, and they are not excluded from the scope of the present
invention.
INDUSTRIAL APPLICABILITY
[0267] As has been described above, according to the present
invention, compacts of iron oxide containing a carbonaceous
reductant are subjected to reduction through the application of
heat, at the incipient stage of which a metallic iron shell is
formed. Once the metallic iron shell is formed, iron oxides are
reduced under an enhanced reducing condition which is established
within the metallic iron shell, whereby the reducing reaction
progresses quickly and efficiently. Therefore, the method of the
invention can efficiently produce, via reduction through the
application of heat and in a short period of time, metallic iron
having such a high iron purity, with a metallization ratio of not
less than 95%, or in some cases of not less than 98%, which cannot
be attained by conventional direct iron making methods. The thus
obtained metallic iron having a relatively high iron purity and
accompanying slag may be solidified by chilling and then crushed to
separate metallic iron from slag magnetically or by any other
screening method or may be melted by further heating so as to
separate one from the other through a difference in their specific
gravities.
[0268] Further, the method of the present invention can make the
iron oxide content of slag relatively small, so that it does not do
damage to the refractory of a furnace, which would normally result
from contact of molten iron oxide with the refractory.
[0269] The apparatus for making metallic iron according to the
present invention can efficiently carry out, in an industrial
scale, the above-proposed new technique for making metallic iron,
and can productively and effectively produce high-purity metallic
iron having a metallization ratio of not less than 95%, or in some
cases of not less than 98%. in a relatively short period of time
from source iron oxide having a high iron content, even from an
iron source having a low iron content, such as iron ore or the
like. Through the employment of the above-described method and
apparatus for making metallic iron, the amount of iron oxide mixed
into slag accompanyingly generated in a process of reduction
considerably decreases, thereby minimizing damage caused by molten
iron oxide to the refractory lining of a thermal reduction
apparatus, melting apparatus, separator, separator furnace, and the
like.
* * * * *