U.S. patent application number 13/696412 was filed with the patent office on 2013-03-07 for method for producing metallic iron.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). The applicant listed for this patent is Takao Harada, Takeshi Sugiyama. Invention is credited to Takao Harada, Takeshi Sugiyama.
Application Number | 20130055853 13/696412 |
Document ID | / |
Family ID | 44903805 |
Filed Date | 2013-03-07 |
United States Patent
Application |
20130055853 |
Kind Code |
A1 |
Sugiyama; Takeshi ; et
al. |
March 7, 2013 |
METHOD FOR PRODUCING METALLIC IRON
Abstract
Disclosed is a technique for preventing the adhesive of metallic
iron and/or wustite (which is a material produced by the heat
reduction of iron oxide contained in a powder derived from an
agglomerate that comprises, as a raw material, a mixture containing
a iron-oxide-containing substance and a carbonaceous reducing
material) on a heath of a movable furnace heath type heating
furnace without largely changing the design of a facility for the
production, in the production of metallic iron by placing the
agglomerate on the heath and heating the agglomerate in the heating
furnace to reduce iron oxide contained in the agglomerate. A
heath-forming material for preventing the cohesive of metallic iron
and/or wustite (which is a material produced by the heat reduction
of iron oxide contained in the powder derived from the agglomerate)
on the heath is charged into the furnace together with the
agglomerate.
Inventors: |
Sugiyama; Takeshi;
(Kobe-shi, JP) ; Harada; Takao; (Kobe-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sugiyama; Takeshi
Harada; Takao |
Kobe-shi
Kobe-shi |
|
JP
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi, Hyogo
JP
|
Family ID: |
44903805 |
Appl. No.: |
13/696412 |
Filed: |
May 2, 2011 |
PCT Filed: |
May 2, 2011 |
PCT NO: |
PCT/JP2011/060558 |
371 Date: |
November 6, 2012 |
Current U.S.
Class: |
75/484 |
Current CPC
Class: |
C21B 13/008 20130101;
C22B 1/245 20130101; C21B 13/105 20130101 |
Class at
Publication: |
75/484 |
International
Class: |
C21B 13/10 20060101
C21B013/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2010 |
JP |
2010-106659 |
Claims
1. A method for producing metallic iron, the method comprising:
placing on a hearth of a movable hearth furnace an agglomerate
comprising a raw material mixture comprising a carbonaceous
reducing material and a substance comprising iron oxide, and
heating the agglomerate to reduce iron oxide in the agglomerate,
wherein a hearth-forming material that prevents metallic iron,
wustite, or both, from sticking to the hearth is charged into the
furnace together with the agglomerate, and wherein the metallic
iron, wustite, or both, are produced by heat reduction of iron
oxide in a powder derived from the agglomerate.
2. The method of claim 1, wherein, when a carbon content of the
agglomerate is 122 mass % or more of a carbon content required to
reduce the iron oxide in the agglomerate, the hearth-forming
material has a composition such that CaO, SiO.sub.2, and
Al.sub.2O.sub.3 contents of a total composition of the powder
derived from the agglomerate and the hearth-forming material
satisfy formulae (1) and (2): [CaO]/[SiO.sub.2]=0.25 to 1.20 (1)
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.2 to 0.7 (2) wherein each [ ] in
the formulae (1) and (2) denotes the content (% by mass) in mass %
for the component specified in the square brackets.
3. The method of claim 1, wherein when a carbon content of the
agglomerate is less than 122 mass % of a carbon content required to
reduce the iron oxide in the agglomerate, the hearth-forming
material has a composition such that a total carbon content of a
total composition of the powder derived from the agglomerate and
the hearth-forming material is 122% or more of the carbon content
required to reduce the iron oxide in the agglomerate, and CaO,
SiO.sub.2, and Al.sub.2O.sub.3 contents of the total composition of
the powder derived from the agglomerate and the hearth-forming
material satisfy formulae (3) and (4): [CaO]/[SiO.sub.2]=0.25 to
1.20 (3) [Al.sub.2O.sub.3]/[SiO.sub.2]=0.2 to 0.7 (4) wherein each
[ ] in the formulae (3) and (4) denotes the content (% by mass) in
mass % for the component specified in the square brackets.
4. The method of claim 1, wherein when a carbon content of the
agglomerate is less than 122 mass % of a carbon content required to
reduce the iron oxide in the agglomerate, the hearth-forming
material has a composition such that a total carbon content of a
total composition of the powder derived from the agglomerate and
the hearth-forming material remains less than 122% of the carbon
content required to reduce the iron oxide in the agglomerate, and
CaO, SiO.sub.2, Al.sub.2O.sub.3, and MgO contents of the total
composition of the powder derived from the agglomerate and the
hearth-forming material satisfy at least one formula selected from
the group consisting of formulae (5) to (9):
[CaO]/[SiO.sub.2]<0.25 (5) [CaO]/[SiO.sub.2]>1.20 (6)
[Al.sub.2O.sub.3]/[SiO.sub.2]<0.2 (7)
[Al.sub.2O.sub.3]/[SiO.sub.2]>0.7 (8) [MgO]/[SiO.sub.2]>0.4
(9) wherein each [ ] in the formulae (5) to (9) denotes the content
(% by mass) in mass % for the component specified in the square
brackets.
5. The production method according to of claim 2, wherein the
hearth-forming material has a composition such that a total CaO,
SiO.sub.2, and Al.sub.2O.sub.3 content is 3.0% to 7.0% by mass of
the total composition of the powder derived from the agglomerate
and the hearth-forming material.
6. The method of claim 4, wherein the hearth-forming material has a
composition such that a total CaO, SiO.sub.2, and Al.sub.2O.sub.3
content is more than 7.0% by mass of the total composition of the
powder derived from the agglomerate and the hearth-forming
material.
7. The production method according to claim 1, wherein at least 50%
by mass of the hearth-forming material has a particle diameter of
0.5 to 2 mm.
8. The method of claim 1, wherein the agglomerate has a particle
size of 5 to 50 mm.
9. The method of claim 1, wherein the agglomerate is heated in the
movable hearth furnace at a temperature of 1200.degree. C. to
1400.degree. C.
10. The method of claim 2, wherein [CaO]/[SiO.sub.2] is 0.3 to
1.1.
11. The method of claim 2, wherein [Al.sub.2O.sub.3]/[SiO.sub.2] is
0.2 to 0.6.
12. The method of claim 2, wherein [Al.sub.2O.sub.3]/[SiO.sub.2] is
0.2 to 0.4.
13. The method of claim 3, wherein [CaO]/[SiO.sub.2] is 0.3 to
1.1.
14. The method of claim 3, wherein [Al.sub.2O.sub.3]/[SiO.sub.2] is
0.2 to 0.6.
15. The method of claim 3, wherein [Al.sub.2O.sub.3]/[SiO.sub.2] is
0.2 to 0.4.
16. The method of claim 5, wherein the total CaO, SiO.sub.2, and
Al.sub.2O.sub.3 content is 4.5% to 6.5% by mass of the total
composition of the powder derived from the agglomerate and the
hearth-forming material.
17. The method of claim 5, wherein the total CaO, SiO.sub.2, and
Al.sub.2O.sub.3 content is 5.0% to 6.5% by mass of the total
composition of the powder derived from the agglomerate and the
hearth-forming material.
18. The method of claim 6, wherein the total CaO, SiO.sub.2, and
Al.sub.2O.sub.3 content is more than 7.5% by mass of the total
composition of the powder derived from the agglomerate and the
hearth-forming material.
19. The method of claim 6, wherein the total CaO, SiO.sub.2, and
Al.sub.2O.sub.3 content is more than 8% by mass of the total
composition of the powder derived from the agglomerate and the
hearth-forming material.
20. The method of claim 6, wherein the total CaO, SiO.sub.2, and
Al.sub.2O.sub.3 content is more than 7.0% and less than 10% by mass
of the total composition of the powder derived from the agglomerate
and the hearth-forming material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing
massive metallic iron by placing an agglomerate, which is produced
from a raw material mixture containing an iron oxide source, such
as iron ore or iron oxide, and a carbon-containing reducing
material, on a hearth of a movable hearth furnace and heating the
agglomerate to reduce iron oxide in the agglomerate.
BACKGROUND ART
[0002] A direct reduction ironmaking process has been developed in
which metallic iron is produced from a raw material mixture
containing an iron oxide source (hereinafter also referred to as an
iron-oxide-containing substance), such as iron ore or iron oxide,
and a carbon-containing reducing material (hereinafter also
referred to as a carbonaceous reducing material). In accordance
with this ironmaking process, an agglomerate formed of the raw
material mixture is placed on a hearth of a movable hearth furnace
and is heated in the furnace utilizing gas heat transfer or radiant
heat of a heating burner to reduce iron oxide in the agglomerate
with the carbonaceous reducing material, yielding massive metallic
iron. In the ironmaking process, however, part of the agglomerate
is pulverized to a powder by rolling, collision, or drop impact.
When the agglomerate is placed on the hearth, the powder derived
from the agglomerate accompanies the agglomerate and accumulates on
the hearth to form an accumulation layer. Like the agglomerate, the
accumulation layer is heat reduced in the furnace to form metallic
iron or wustite (FeO). Metallic iron or wustite left in the furnace
accumulates on the hearth and raises the hearth level, which makes
operation difficult. To avoid this, the accumulation layer is
usually removed with a discharger. However, because of its small
thickness, the accumulation layer on the hearth sometimes remains
on the hearth even after the removal of massive metallic iron,
which was formed by the heat reduction of iron oxide in the
agglomerate, from the furnace. Thus, the accumulation layer is
compressed with the discharger and finally forms a large solid that
cannot be discharged from the furnace. Furthermore, the discharge
of a lump formed by the aggregation of metallic iron or wustite
from the furnace sometimes forms unevenness on the hearth, which
makes operation difficult. Patent Literatures 1 to 3 propose a
technique for solving these problems.
[0003] Patent Literature 1 proposes a method for preventing the
formation of a steel sheet on a hearth. The method involves the use
of a discharger for discharging reduced iron, which is produced by
the reduction of a carbon composite iron oxide agglomerate, from a
movable hearth reduction furnace and the operation of maintaining
the gap between the surface of the moving bed and the discharger.
According to this technique, the gap can prevent a powder derived
from an agglomerate and accompanying the agglomerate in the furnace
from being pressed on the hearth and prevent the formation of a
rigid steel sheet.
[0004] Patent Literature 2 proposes a method for removing a
substance adhered on a hearth of a rotary hearth reduction furnace
from the hearth surface, which involves quenching the hearth
surface to cause cracks in the adhesive material on the hearth
before removing the adhesive material from the hearth.
[0005] Patent Literature 3 proposes a method for maintaining the
cleanliness of the hearth surface of a rotary hearth furnace by
removing a metallic iron powder left on the hearth or adhesives on
hearth bricks or by preventing the metallic iron powder from
remaining on the hearth. According to this maintenance method,
reduced iron powder left on the hearth is removed from the hearth
by blowing off the reduced iron powder with a gas jet between the
outlet for the reduced iron and the inlet for the raw
materials.
CITATION LIST
Patent Literature
[0006] PTL 1: Japanese Patent No. 3075721
[0007] PTL 2: Japanese Unexamined Patent Application Publication
No. 2002-12906
[0008] PTL 3: Japanese Unexamined Patent Application Publication
No. 11-50120
SUMMARY OF INVENTION
Technical Problem
[0009] The techniques disclosed in Patent Literatures 1 to 3
require a design change of the discharger for discharging reduced
iron from the movable hearth reduction furnace, the construction of
an apparatus for quenching the hearth surface, or the construction
of an apparatus for blowing off reduced iron powder, which
increases the capital investment.
[0010] In view of the situations described above, it is an object
of the present invention to provide a method for producing metallic
iron by placing an agglomerate, which is produced from a raw
material mixture containing an iron-oxide-containing substance and
a carbonaceous reducing material, on a hearth of a movable hearth
furnace and heating the agglomerate to reduce iron oxide in the
agglomerate. This technique prevents metallic iron or wustite,
which is produced by the heat reduction of iron oxide contained in
a powder derived from the agglomerate, from sticking to the hearth
without significantly changing the design for facilities.
Solution to Problem
[0011] A method for producing metallic iron according to the
present invention that can solve the problems described above has a
main point in that, in the production of metallic iron by placing
an agglomerate (having a particle size, for example, in the range
of 5 to 50 mm), which is produced from a raw material mixture
containing an iron-oxide-containing substance and a carbonaceous
reducing material, on a hearth of a movable hearth furnace and
heating (for example, 1200.degree. C. to 1400.degree. C.) the
agglomerate to reduce iron oxide in the agglomerate, a
hearth-forming material for preventing metallic iron and/or
wustite, which is produced by heat reduction of iron oxide
contained in a powder derived from the agglomerate, from sticking
to the hearth is charged into the furnace together with the
agglomerate.
[0012] (a) When the carbon content of the agglomerate is 122%
(which herein means % by mass) or more of the carbon content
required to reduce iron oxide in the agglomerate, the composition
of the hearth-forming material is preferably controlled such that
the CaO, SiO.sub.2, and Al.sub.2O.sub.3 contents of the total
composition of the powder derived from the agglomerate and the
hearth-forming material satisfy the following formulae (1) and
(2):
[CaO]/[SiO.sub.2]=0.25 to 1.20 (1)
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.2 to 0.7 (2)
[0013] wherein each [ ] in the formulae (1) and (2) denotes the
content (% by mass) for the component specified in the square
brackets.
[0014] In the case of (a), the composition of the hearth-forming
material is preferably controlled such that the total CaO,
SiO.sub.2, and Al.sub.2O.sub.3 content is in the range of 3.0% to
7.0% of the total composition of the powder derived from the
agglomerate and the hearth-forming material.
[0015] (b-1) When the carbon content of the agglomerate is less
than 122% of the carbon content required to reduce iron oxide in
the agglomerate, the composition of the hearth-forming material is
preferably controlled such that the total carbon content of the
total composition of the powder derived from the agglomerate and
the hearth-forming material is 122% or more of the carbon content
required to reduce iron oxide in the agglomerate and that the CaO,
SiO.sub.2, and Al.sub.2O.sub.3 contents of the total composition of
the powder derived from the agglomerate and the hearth-forming
material satisfy the following formulae (3) and (4):
[CaO]/[SiO.sub.2]=0.25 to 1.20 (3)
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.2 to 0.7 (4)
[0016] wherein each [ ] in the formulae (3) and (4) denotes the
content (% by mass) for the component specified in the square
brackets.
[0017] (b-2) When the carbon content of the agglomerate is less
than 122% of the carbon content required to reduce iron oxide in
the agglomerate, the composition of the hearth-forming material is
preferably controlled such that the total carbon content of the
total composition of the powder derived from the agglomerate and
the hearth-forming material remains less than 122% of the carbon
content required to reduce iron oxide in the agglomerate and that
the CaO, SiO.sub.2, Al.sub.2O.sub.3, and MgO contents of the total
composition of the powder derived from the agglomerate and the
hearth-forming material satisfy at least one of the following
formulae (5) to (9):
[CaO]/[SiO.sub.2]<0.25 (5)
[CaO]/[SiO.sub.2]>1.20 (6)
[Al.sub.2O.sub.3]/[SiO.sub.2]<0.2 (7)
[Al.sub.2O.sub.3]/[SiO.sub.2]>0.7 (8)
[MgO]/[SiO.sub.2]>0.4 (9)
[0018] wherein each [ ] in the formulae (5) to (9) denotes the
content (% by mass) for the component specified in the square
brackets.
[0019] In the case of (b-2), the composition of the hearth-forming
material is preferably controlled such that the total CaO,
SiO.sub.2, and Al.sub.2O.sub.3 content is more than 7.0% of the
total composition of the powder derived from the agglomerate and
the hearth-forming material.
[0020] A hearth-forming material having a particle diameter in the
range of 0.5 to 2 mm preferably constitutes 50% by mass or more of
the total amount of hearth-forming material charged in the
furnace.
Advantageous Effects of Invention
[0021] According to the present invention, a hearth-forming
material charged into a hearth of a movable hearth furnace together
with an agglomerate can prevent metallic iron or wustite, which is
produced by heat reduction of iron oxide contained in a powder
derived from the agglomerate, from sticking to the hearth. This can
prevent a large adhesive material, such as a steel sheet, that
cannot be discharged from the furnace from being formed on the
hearth and prevent the rising of the hearth level. Thus, metallic
iron can be efficiently produced without significantly changing the
design for facilities.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a graph showing the relationship between
temperature and deformation ratio when a pellet is reduced at
different [MgO]/[SiO.sub.2] ratios.
[0023] FIG. 2 is a photograph substituted for drawing of a cross
section of a reduced pellet.
[0024] FIG. 3 is a graph of 40% contraction temperature as a
function of [MgO]/[SiO.sub.2].
[0025] FIG. 4 is a graph of 40% contraction temperature as a
function of [CaO]/[SiO.sub.2].
[0026] FIG. 5 is a SiO.sub.2--MgO--FeO ternary equilibrium
diagram.
[0027] FIG. 6 is a CaO--SiO.sub.2--MgO ternary equilibrium
diagram.
[0028] FIG. 7 is a CaO--SiO.sub.2--Al.sub.2O.sub.3 ternary
equilibrium diagram.
DESCRIPTION OF EMBODIMENTS
[0029] The techniques proposed in Patent Literatures 1 to 3 require
significant design changes of facilities and significant capital
investments. Thus, the present inventors have made extensive
studies in order to provide a method for efficiently producing
metallic iron with a minimum capital investment, in which metallic
iron or wustite produced by heat reduction of iron oxide contained
in a powder derived from an agglomerate in a furnace is prevented
from sticking to a hearth, which prevents the formation of a large
adhesive material, such as a steel sheet, that cannot be discharged
from the furnace on the hearth and prevents the rising of the
hearth level. As a result, it was found that a hearth-forming
material can be charged into the furnace together with the
agglomerate. More specifically, the present invention was completed
by finding that, with consideration given to the carbon content of
the agglomerate charged into the furnace and the carbon content
required to reduce iron oxide contained in the agglomerate, the
hearth-forming material can be charged into the furnace while the
composition of the hearth-forming material is appropriately
controlled such that the total composition of a powder derived from
the agglomerate and the hearth-forming material satisfies
predetermined conditions.
[0030] A method for producing metallic iron according to the
present invention is characterized in that a hearth-forming
material for preventing metallic iron and/or wustite, which is
produced by heat reduction of iron oxide contained in a powder
derived from an agglomerate, from sticking to a hearth is charged
into a furnace together with the agglomerate. The powder derived
from the agglomerate adhered on the hearth is based on a powder
accompanying the agglomerate charged into the furnace and a powder
produced by disintegration of the agglomerate caused by rapid
heating in the furnace. Thus, when the agglomerate is charged into
the furnace together with a hearth-forming material, the
hearth-forming material can be mixed with the powder derived from
the agglomerate on the hearth. Appropriate control of the
composition of the hearth-forming material in consideration of the
composition of the powder derived from the agglomerate can prevent
metallic iron or wustite produced by heat reduction of iron oxide
contained in the powder derived from the agglomerate from sticking
to the hearth. This can prevent the formation of an adhesive
material, such as a steel sheet, or the rising of the hearth level,
thus increasing the metallic iron production efficiency.
[0031] The hearth-forming material is added before the agglomerate
is charged into the furnace and preferably when the hearth-forming
material is blended with the agglomerate.
[0032] When the hearth-forming material is added before the
agglomerate is charged, for example, the hearth-forming material
may be added to the agglomerate on a conveyor for charging the
agglomerate into a hopper, and a mixture of the agglomerate and the
hearth-forming material may be placed on the hearth. Among the
charged mixture, a powder derived from the agglomerate and granules
of the hearth-forming material accumulate on a lower portion of the
agglomerate and move as a mixture when the agglomerate is leveled
off with a leveler.
[0033] A material for preventing metallic iron or wustite produced
by heat reduction of iron oxide contained in a powder derived from
an agglomerate from sticking to a hearth may be charged as the
hearth-forming material. More specifically, paying attention to the
carbon content of the agglomerate, the hearth-forming material may
be charged into the furnace while the composition of the
hearth-forming material is controlled in a manner that depends on
whether the carbon content is (a) 122% or more or (b) less than
122% of the carbon content required to reduce iron oxide in the
agglomerate. When the carbon content of the agglomerate is 100% of
the carbon content required to reduce iron oxide in the
agglomerate, this means that the iron oxide in the agglomerate is
entirely (100%) reduced. When the carbon content is 122% of the
carbon content required to reduce iron oxide in the agglomerate,
this means that the carbon content is in excess of 22%, and the
carbon content of 22% corresponds to approximately 5% of the
residual carbon in the agglomerate after reduction.
[0034] The carbon content of the agglomerate and the carbon content
required to reduce iron oxide in the agglomerate can be calculated
from the composition of the raw material mixture composing the
agglomerate. The carbon content of the agglomerate after heat
reduction of iron oxide in the agglomerate can be determined, for
example, by charging the agglomerate into an electric furnace,
heating the agglomerate in an inert atmosphere (for example,
N.sub.2 atmosphere) at 1300.degree. C. (representative
temperature), and measuring the amount of residual carbon in the
agglomerate after reduction reaction by infrared analysis. The
carbon content of the agglomerate before heating can be calculated
backwards from the total of this analytical value and the carbon
content required to reduce iron oxide in the agglomerate.
(a) 122% or More
[0035] When the carbon content of the agglomerate is 122% or more
of the carbon content required to reduce iron oxide in the
agglomerate, the composition of the hearth-forming material may be
controlled such that the CaO, SiO.sub.2, and Al.sub.2O.sub.3
contents of the total composition of the powder derived from the
agglomerate and the hearth-forming material satisfy the following
formulae (1) and (2):
[CaO]/[SiO.sub.2]=0.25 to 1.20 (1)
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.2 to 0.7 (2)
[0036] wherein each [ ] in the formulae (1) to (2) denotes the
content (% by mass) for the component specified in the square
brackets.
[0037] Thus, when the carbon content of the agglomerate is higher
than the required carbon content, and carbon remains after heat
reduction, iron oxide contained in the agglomerate is completely
reduced, and the resulting metallic iron forms separate fine
granules. Furthermore, excessive carbon in the agglomerate promotes
the carburization of metallic iron through heat reduction, thus
separating one metallic iron granule from another with a hard and
brittle slag phase. Thus, even if an adhesive material, such as a
steel sheet, is formed on the hearth, the adhesive material can be
easily crushed and removed from the furnace.
[0038] Thus, when the carbon content of the agglomerate is 122% or
more of the required carbon content, it is effective to further
promote the granulation of metallic iron so as to facilitate the
discharge of metallic iron from the furnace. In order to promote
the granulation of metallic iron, the present invention focuses on
slag associated with the production of metallic iron, and the
melting point of the slag is decreased to promote the aggregation
and granulation of metallic iron. More specifically, the
composition of the hearth-forming material is controlled such that
the CaO, SiO.sub.2, and Al.sub.2O.sub.3 contents of the total
composition of the powder derived from the agglomerate and the
hearth-forming material satisfy the formulae (1) and (2).
Regarding Formula (1)
[0039] When [CaO]/[SiO.sub.2] is preferably in the range of 0.25 to
1.20, the melting point of the slag can be decreased to promote the
granulation of metallic iron. [CaO]/[SiO.sub.2] is more preferably
0.3 or more and 1.1 or less.
Regarding Formula (2)
[0040] When [Al.sub.2O.sub.3]/[SiO.sub.2] is preferably in the
range of 0.2 to 0.7, the melting point of the slag can be decreased
to promote the granulation of metallic iron.
[Al.sub.2O.sub.3]/[SiO.sub.2] is more preferably 0.6 or less, still
more preferably 0.4 or less.
[0041] When the carbon content of the agglomerate is 122% or more
of the required carbon content, the composition of the
hearth-forming material is preferably controlled such that the
total CaO, SiO.sub.2, and Al.sub.2O.sub.3 content is in the range
of 3.0% to 7.0% of the total composition of the powder derived from
the agglomerate and the hearth-forming material. A higher amount of
molten slag results in promotion of the carburization of metallic
iron after heat reduction. Thus, when the total amount of the
components described above is preferably 3.0% or more, the
granulation of metallic iron can be promoted. The total amount is
more preferably 4.5% or more, still more preferably 5.0% or more.
However, the total amount of more than 7.0% results in excessively
increased molten slag, which may flow downward and erode the
hearth. Thus, the total amount is preferably 7.0% or less, more
preferably 6.5% or less.
(b) Less Than 122%
[0042] When the carbon content of the agglomerate is less than 122%
of the required carbon content,
[0043] (b-1) the composition of the hearth-forming material is
controlled such that the total carbon content of the total
composition of the powder derived from the agglomerate and the
hearth-forming material is 122% or more of the required carbon
content, or
[0044] (b-2) the composition of the hearth-forming material is
controlled such that the total carbon content of the total
composition of the powder derived from the agglomerate and the
hearth-forming material remains less than 122% of the required
carbon content.
[0045] In the case of (b-1), it is important that the composition
of the hearth-forming material is controlled such that the total
carbon content of the total composition of the powder derived from
the agglomerate and the hearth-forming material is 122% or more of
the required carbon content, and the composition of the
hearth-forming material is controlled such that the CaO, SiO.sub.2,
and Al.sub.2O.sub.3 contents of the total composition of the powder
derived from the agglomerate and the hearth-forming material
satisfy the following formulae (3) and (4):
[CaO]/[SiO.sub.2]=0.25 to 1.20 (3)
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.2 to 0.7 (4)
[0046] wherein each [ ] in the formulae (3) and (4) denotes the
content (% by mass) for the component specified in the square
brackets.
[0047] More specifically, when the carbon content of the
agglomerate is less than 122% of the required carbon content, this
results in slightly insufficient carbon, and part of iron oxide
contained in the powder derived from the agglomerate may remain
unreduced, for example, as wustite. This also results in less
carbon involved in the carburization of metallic iron and promotes
the formation of a metallic iron sheet instead of the granulation
of metallic iron. Thus, in order to completely reduce iron oxide in
the powder derived from the agglomerate and sufficiently carburize
the iron oxide for granulation, a carbonaceous reducing material is
blended as the hearth-forming material, the deficiency in the
carbon content of the agglomerate is compensated for, and the
composition of the hearth-forming material is controlled such that
the total carbon content of the total composition of the powder
derived from the agglomerate and the hearth-forming material is
122% or more of the required carbon content.
[0048] In this case, the CaO, SiO.sub.2, and Al.sub.2O.sub.3
contents of the total composition of the powder derived from the
agglomerate and the hearth-forming material must satisfy the
formulae (3) and (4). The formulae (3) and (4) are the same as the
formulae (1) and (2) and are defined on the basis of the same
finding. More specifically, the melting point of the slag can be
decreased to further promote the granulation of the metallic iron,
thus facilitating the removal of the metallic iron from the
furnace.
[0049] In the case of (b-2), it is important that the composition
of the hearth-forming material is controlled such that the total
carbon content of the total composition of the powder derived from
the agglomerate and the hearth-forming material remains less than
122% of the required carbon content, and that the CaO, SiO.sub.2,
Al.sub.2O.sub.3, and MgO contents of the total composition of the
powder derived from the agglomerate and the hearth-forming material
satisfy at least one of the following formulae (5) to (9):
[CaO]/[SiO.sub.2]<0.25 (5)
[CaO]/[SiO.sub.2]>1.20 (6)
[Al.sub.2O.sub.3]/[SiO.sub.2]<0.2 (7)
[Al.sub.2O.sub.3]/[SiO.sub.2]>0.7 (8)
[MgO]/[SiO.sub.2]>0.4 (9)
[0050] wherein each [ ] in the formulae (5) to (9) denotes the
content (% by mass) for the component specified in the square
brackets.
[0051] When no carbonaceous reducing material is blended as the
hearth-forming material, and the total carbon content of the total
composition of the powder derived from the agglomerate and the
hearth-forming material remains less than 122% of the required
carbon content, it is effective to appropriately control the
composition of gangue components. More specifically, the melting
point of the gangue components can be increased to form solid
gangue between metallic iron or wustite particles and thereby
increase the distance between the metallic iron or wustite
particles, which can prevent the aggregation of the metallic iron
or wustite particles. This can prevent the metallic iron or wustite
particles from sticking to the hearth or sticking to the hearth and
forming a lump to raise the hearth level.
[0052] Metallic iron produced by the reduction of iron oxide
contained in the powder derived from the agglomerate is minute and
has very low cohesion. Depending on the composition of gangue
components, such as CaO, SiO.sub.2, and Al.sub.2O.sub.3, the
resulting slag may have a low melting point, and the formation of
molten slag during heat reduction facilitates the movement of Fe
atoms on the metallic iron surface in the vicinity of the molten
slag, which promotes the coalescence of metallic iron to form a
reticulated metallic iron coalescence layer. The compression of the
metallic iron coalescence layer results in the formation of a dense
metal steel sheet (adhesive material), making it difficult to
remove metallic iron from the furnace.
[0053] Insufficient reduction of iron oxide also results in the
formation of wustite (FeO). Even in this case, the presence of the
molten slag facilitates the movement of Fe atoms on the wustite
surface and promotes the coalescence of wustite to form coarse
wustite particles. The coarse wustite particles forms large blocks
with the molten slag and become difficult to remove from the
furnace.
[0054] Thus, it is believed that the prevention of coalescence
between metallic iron or wustite particles or between metallic iron
particles and wustite particles facilitates the removal of metallic
iron or wustite from the hearth. On the basis of such findings,
when no carbonaceous reducing material is blended as the
hearth-forming material, and the total carbon content of the total
composition of the powder derived from the agglomerate and the
hearth-forming material remains less than 122% of the required
carbon content, it is important to increase the melting point of
the resulting slag to reduce the formation of molten slag.
Formulae (5) and (6)
[0055] When [CaO]/[SiO.sub.2] is preferably less than 0.25 or more
than 1.20, the resulting slag can have a high melting point, which
can prevent the coarsening of metallic iron or wustite particles.
[CaO]/[SiO.sub.2] is more preferably 0.20 or less or 1.25 or
more.
Formulae (7) and (8)
[0056] When [Al.sub.2O.sub.3]/[SiO.sub.2] is preferably less than
0.2 or more than 0.7, the resulting slag can have a high melting
point, which can prevent the coarsening of metallic iron or wustite
particles. [Al.sub.2O.sub.3]/[SiO.sub.2] is more preferably 0.18 or
less, still more preferably 0.16 or less, or more preferably 0.8 or
more.
Formula (9)
[0057] MgO can reduce the formation of molten slag and prevent the
coarsening of metallic iron or wustite particles. Among gangue
components, a component having a lower melting point melts earlier
during temperature rise. Dissolution of a component that can
increase the melting point in the gangue components solidifies the
molten component. Repetition of these yields molten gangue. Thus,
even when the average composition of gangue has a high melting
point, a bonded substance may be partly formed. Since MgO can
easily diffuse into solid FeO, a higher MgO content results in a
higher melting point of slag. Thus, MgO can reduce the formation of
molten slag.
[0058] As is clear from FIG. 5 described below, the melting point
of molten slag changes greatly with [MgO]/[SiO.sub.2]. Thus, the
MgO content may be controlled while the balance between the MgO
content and the SiO.sub.2 content is taken into consideration. More
specifically, when [MgO]/[SiO.sub.2] is preferably more than 0.4,
the formation of molten slag can be reduced to increase solid slag.
[MgO]/[SiO.sub.2] is more preferably 0.45 or more, still more
preferably 0.5 or more. [MgO]/[SiO.sub.2] is 0.9 or less, for
example.
[0059] At least one of the formulae (5) to (9) may be satisfied to
increase the melting point of the resulting slag.
[0060] When the carbon content of the agglomerate is less than 122%
of the required carbon content, and the total carbon content of the
total composition of the powder derived from the agglomerate and
the hearth-forming material remains less than 122% of the required
carbon content, the composition of the hearth-forming material is
preferably controlled such that the total CaO, SiO.sub.2, and
Al.sub.2O.sub.3 content is more than 7.0% of the total composition
of the powder derived from the agglomerate and the hearth-forming
material. When the total amount is more than 7.0%, the amount of
gangue can be increased, and the solid slag can be increased. This
can prevent metallic iron or wustite from becoming coarse through
aggregation and adhering to the hearth to raise the hearth level.
The total amount is more preferably 7.5% or more, still more
preferably 8% or more. The total amount is 10% or less, for
example.
[0061] A material serving as a CaO source, a SiO.sub.2 source, an
Al.sub.2O.sub.3 source, or a MgO source may be blended as the
hearth-forming material. Examples of the CaO source include calcium
oxide (CaO) and limestone (main component: CaCO.sub.3). Examples of
the SiO.sub.2 source include silica sand and mixtures with other
components, such as serpentinite. Examples of the Al.sub.2O.sub.3
source include bauxite and mixtures with other components, such as
alumina-containing iron ore. Examples of the MgO source include
MgO-containing slag, Mg-containing substances extracted from
seawater, magnesium carbonate (MgCO.sub.3), and dolomite.
[0062] In order to control the composition of the hearth-forming
material such that the total composition of the powder derived from
the agglomerate and the hearth-forming material satisfies the
requirements described above, the mass of the powder derived from
the agglomerate must be measured.
[0063] Examples of the powder derived from the agglomerate include
powders of two types: a powder that is produced by disintegration
of part of an agglomerate produced from a raw material mixture
containing an iron-oxide-containing substance and a carbonaceous
reducing material or disintegration due to impact or abrasion of
the agglomerate (hereinafter also referred to as a powder I) or a
powder that is produced by disintegration of the agglomerate during
heat reduction in a furnace (hereinafter also referred to as a
powder II).
[0064] The mass of the powder I is measured, for example, by
measuring the total mass of agglomerate charged into a furnace and,
after classification into the agglomerate and the powder derived
from the agglomerate, directly measuring the mass of the powder
derived from the agglomerate. In the present invention, a powder is
defined to have a particle diameter of 3 mm or less.
[0065] The method for directly measuring the mass of the powder
derived from the agglomerate cannot be applied to cases where the
characteristics of the agglomerate vary while the agglomerate is
continuously charged into a furnace. As described in an example
described below, a rotation strength test that simulates a transfer
process up to charging a formed agglomerate into a furnace may be
performed to measure the mass of a powder having a particle
diameter of 3 mm or less and estimate the mass of the powder
derived from the agglomerate.
[0066] The mass of the powder II may be measured by heating the
agglomerate in an electric furnace and measuring the mass of a
powder having a particle diameter of 3 mm or less produced by rapid
heating (for example, a heating rate of 10.degree. C./min or more)
to estimate the mass of the powder derived from the
agglomerate.
[0067] On the basis of such estimation of the mass of the powder
derived from the agglomerate, the total composition of the powder
derived from the agglomerate and the hearth-forming material can be
represented by the following formulae (21) to (24):
CaO(kg/h):
H.sub.CaO=(L.sub.CaO.times.W.sub.L+C.sub.CaO.times.CW.sub.L+S.sub.CaO.tim-
es.SW.sub.L+A.sub.CaO.times.AW.sub.L+M.sub.CaO.times.MW.sub.L)/100
(21)
SiO.sub.2(kg/h):
H.sub.SiO2=(L.sub.SiO2.times.W.sub.L+C.sub.SiO2.times.CW.sub.L+S.sub.SiO2-
.times.SW.sub.L+A.sub.SiO2.times.AW.sub.L+M.sub.SiO2.times.MW.sub.L)/100
(22)
Al.sub.2O.sub.3(kg/h):
H.sub.Al2O3=(L.sub.Al2O3.times.W.sub.L+C.sub.Al2O3.times.CW.sub.L+S.sub.A-
l2O3.times.SW.sub.L+A.sub.Al2O3.times.AW.sub.L+M.sub.Al2O3.times.MW.sub.L)-
/100 (23)
MgO(kg/h):
H.sub.MgO=(L.sub.MgO.times.W.sub.L+C.sub.MgO.times.CW.sub.L+S.sub.MgO.tim-
es.SW.sub.L+A.sub.MgO.times.AW.sub.L+M.sub.MgO.times.MW.sub.L)/100
(24)
[0068] In the formulae (21) to (24), L.sub.CaO, L.sub.SiO2,
L.sub.Al2O3, and L.sub.MgO denote the percentage (% by mass) of
CaO, SiO.sub.2, Al.sub.2O.sub.3, and MgO, respectively, in the
agglomerate, and W.sub.L denotes the mass (kg) of the powder
derived from the agglomerate charged into a furnace per unit time
(h).
[0069] C.sub.CaO, C.sub.SiO2, C.sub.Al2O3, and C.sub.MgO denote the
percentage (% by mass) of CaO, SiO.sub.2, Al.sub.2O.sub.3, and MgO,
respectively, in the CaO source of the hearth-forming material, and
CW.sub.L denotes the mass (kg) of the CaO source in the
hearth-forming material charged into a furnace per unit time
(h).
[0070] S.sub.CaO, S.sub.SiO2, S.sub.Al2O3, and S.sub.MgO denote the
percentage (% by mass) of CaO, SiO.sub.2, Al.sub.2O.sub.3, and MgO,
respectively, in the SiO.sub.2 source of the hearth-forming
material, and SW.sub.L denotes the mass (kg) of the SiO.sub.2
source in the hearth-forming material charged into a furnace per
unit time (h).
[0071] A.sub.CaO, A.sub.SiO2, A.sub.Al2O3, and A.sub.MgO denote the
percentage (% by mass) of SiO.sub.2, CaO, Al.sub.2O.sub.3, and MgO,
respectively, in the Al.sub.2O.sub.3 source of the hearth-forming
material, and AW.sub.L denotes the mass (kg) of the Al.sub.2O.sub.3
source in the hearth-forming material charged into a furnace per
unit time (h).
[0072] M.sub.CaO, M.sub.SiO2, M.sub.Al2O3, and M.sub.MgO denote the
percentage (% by mass) of CaO, SiO.sub.2, Al.sub.2O.sub.3, and MgO,
respectively, in the MgO source of the hearth-forming material, and
MW.sub.L denotes the mass (kg) of the MgO source in the
hearth-forming material charged into a furnace per unit time
(h).
[0073] When the target compositions are represented by the
following formulae (25) to (28), the total composition of the
powder derived from the agglomerate and the hearth-forming material
is represented by the following formulae (29) to (32) on the basis
of the formulae (21) to (24):
[CaO]/[SiO.sub.2]=1.3 (25)
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.3 (26)
[MgO]/[SiO.sub.2]=0.5 (27)
CaO+Al.sub.2O.sub.3+SiO.sub.2=7 (28)
H.sub.CaO/H.sub.SiO2=1.3 (29)
H.sub.Al2O3/H.sub.SiO2=0.3 (30)
H.sub.MgO/H.sub.SiO2=0.5 (31)
(H.sub.CaO+H.sub.Al2O3+H.sub.SiO2)/(W.sub.L+CW.sub.L+SW.sub.L+AW.sub.L+M-
W.sub.L).times.100=7 (32)
[0074] Since no SiO.sub.2 source is generally added as the
hearth-forming material, SW.sub.L may be 0. When the SiO.sub.2
source is added, the SiO.sub.2 source is set at a temporary value,
and another additive amount that gives the target component ratio
is determined. When the result does not reach the target value, the
amount of SiO.sub.2 source to be added is changed until the
solution is obtained.
[0075] With respect to the hearth-forming material, a
hearth-forming material having a particle diameter in the range of
0.5 to 2 mm preferably constitutes 50% by mass or more of the total
amount of hearth-forming material charged into a furnace. Although
the hearth-forming material having a smaller particle diameter is
easier to mix with the powder derived from the agglomerate, the
hearth-forming material having an excessively small particle
diameter is blown off by wind while the hearth-forming material is
charged into a furnace or heated in the furnace and cannot achieve
the intended effects. Thus, the hearth-forming material having a
particle diameter of 0.5 mm or more preferably constitutes 50% by
mass or more. However, the hearth-forming material having an
excessively large particle diameter is difficult to mix with the
powder derived from the agglomerate and cannot achieve the intended
effects. In order to rapidly melt CaO or MgO in molten gangue when
the gangue begins to melt and thereby promote the solidification of
slag, it is recommended that the hearth-forming material have an
increased surface area. Thus, the hearth-forming material having a
particle diameter of 2 mm or less preferably constitutes 50% by
mass or more.
[0076] The agglomerate is produced by shaping a raw material
mixture containing an iron-oxide-containing substance and a
carbonaceous reducing material. The iron-oxide-containing substance
may be iron ore, iron sand, or a nonferrous smelting residue. The
carbonaceous reducing material may be a carbon-containing
substance, for example, coal or coke.
[0077] The raw material mixture may contain another component, such
as a binder, a MgO source, or a CaO source. The binder may be a
polysaccharide (for example, starch, such as wheat flour). The MgO
source or the CaO source may be one exemplified as the MgO source
or the CaO source to be blended into the hearth-forming
material.
[0078] The agglomerate may have any shape, for example, a pellet or
briquette form. The agglomerate may have any size and may have a
particle size (maximum diameter) of 50 mm or less. The particle
size is approximately 5 mm or more. The particle size of the
agglomerate in a briquette form may be a sphere-equivalent
diameter.
[0079] The agglomerate may be heated in the furnace to an
agglomerate temperature in the range of 1200.degree. C. to
1400.degree. C. to reduce iron oxide in the raw material
mixture.
[0080] The furnace may be a movable hearth furnace, for example, a
rotary hearth furnace.
[0081] The temperature of the agglomerate is particularly
preferably 1250.degree. C. or more. At an agglomerate temperature
of 1250.degree. C. or more, the melting time of metallic iron and
slag can be decreased. However, an excessively high agglomerate
temperature may result in erosion of a hearth with molten metallic
iron, raising the hearth level. Thus, the temperature of the
agglomerate is preferably 1350.degree. C. or less.
[0082] The agglomerate may be heated with a burner, and the
temperature of the agglomerate may be controlled with the
combustion conditions of the burner.
[0083] Although the present invention is more specifically
described in the following examples, the present invention is not
limited to these examples. Various modifications may be made to
these examples without departing from the gist described above and
below. These modifications are also within the technical scope of
the present invention.
EXAMPLES
[0084] In Experimental Example 1, an agglomerate produced from a
raw material mixture containing an iron-oxide-containing substance
and a carbonaceous reducing material was heated in a furnace to
reduce iron oxide in the raw material mixture, producing metallic
iron. The composition and strength of the metallic iron were
determined to examine the relationship between fixation on a hearth
and the composition. In Experimental Example 2, the effects of CaO,
SiO.sub.2, and MgO on the deformation ratio of agglomerate were
examined to determine the relationship between the composition and
the formation behavior of molten slag. In Experimental Example 3, a
ternary phase diagram was used to examine the relationship between
the melting temperature of an Al.sub.2O.sub.3 slag component and
the composition.
Experimental Example 1
[0085] An agglomerate having the composition listed in the
following Table 1 was produced as an agglomerate produced from a
raw material mixture containing an iron-oxide-containing substance
and a carbonaceous reducing material. The shape of the agglomerate
was a pillow-shaped briquette having a sphere-equivalent diameter
(maximum diameter) in the range of approximately 22 to 26 mm for
Nos. 1, 6, and 7 and a spherical pellet having a particle size
(maximum diameter) in the range of approximately 12 to 20 mm for
Nos. 2 to 5 in Table 1. In Table 1, TFe denotes the total iron
content, TC denotes the carbon content (in Table 1, the total
carbon content of the agglomerate), and FC denotes the percentage
of carbon that is not converted into gas at 970.degree. C. Table 1
lists [CaO]/[SiO.sub.2], [Al.sub.2O.sub.3]/[SiO.sub.2],
[MgO]/[SiO.sub.2], and [CaO]+[Al.sub.2O.sub.3]+[SiO.sub.2] based on
the composition of the agglomerate.
[0086] The agglomerate was heated in a furnace to 1300.degree. C.
to reduce iron oxide contained in the agglomerate, thus yielding
metallic iron. The heating time in the furnace was listed in the
following Table 2.
[0087] Table 2 listed the measurements of the composition of the
agglomerate after heating. In Table 2, MFe denotes the metallic
iron content, TC denotes the carbon content (in Table 2, the total
carbon content after heating), TC/TFe.times.100 denotes the ratio
of the total carbon content to the total iron content, and Metal Fe
denotes the metallization ratio [=metallic iron content (%)/total
iron content (%).times.100].
[0088] In Table 2, RCs denotes the carbon content of the residue
(agglomerate) after heating based on the carbon content of the
agglomerate before heating. Subtracting RCs from TC of the
agglomerate before heating yields the carbon content used for
reduction (RedC). Table 2 lists the ratio of the residual carbon
after heating to carbon required for reduction
(RCs/RedC.times.100). As is clear from Table 2, the carbon content
at which the residual carbon after heating is approximately 5% of
the carbon content required for reduction is approximately 22%.
[0089] The strength of massive metallic iron (agglomerate) after
heating was measured in a rotation strength test.
Rotation Strength Test
[0090] The residue was sieved in a rotating container at a total
number of revolutions of 500 in accordance with three particle
diameters: 1 mm or less, more than 1 mm and 2 mm or less, and more
than 2 mm. The rotating container is a cylinder having a diameter
of 113 mm and a length of 205 mm and has two barrels, which rotate
at a rotation speed of 30 rpm.
[0091] Table 2 lists the ratio of a powder having a particle
diameter of 1 mm or less to the mass of the sieved powders. An
increase in the percentage of the powder having a particle diameter
of 1 mm or less indicates that the residue can be easily
pulverized, is not adhered on a hearth, and has good removability.
In the present invention, removability is considered to be
excellent when the percentage of the powder having a particle
diameter of 1 mm or less is 29% or more (working examples) and poor
when the percentage is less than 29% (comparative examples).
[0092] The following are discussions based on Table 2. With respect
to Nos. 1, 2, 3, and 5, the carbon content of the residue is 5% or
more (RCs/RedC.times.100 is 22% or more), and the carbon content of
the agglomerate is 122% or more of the carbon content required to
reduce iron oxide contained in the agglomerate. With respect to
Nos. 1, 2, and 3 of these, among the compositions of the
agglomerate, [CaO]/[SiO.sub.2] is in the range of 0.25 to 1.20, and
[Al.sub.2O.sub.3]/[SiO.sub.2] is in the range of 0.2 to 0.7, which
satisfy the formulae (1) and (2). Thus, Nos. 1, 2, and 3 are weakly
adhered on the hearth. In contrast, with respect to No. 5, among
the compositions of the agglomerate, [CaO]/[SiO.sub.2] is 0.23,
which does not satisfy the formula (1). No. 5 also has a total CaO,
Al.sub.2O.sub.3, and SiO.sub.2 content of less than 3.0%, and
metallic iron is easily sintered. Thus, residue removability is not
improved.
[0093] With respect to Nos. 4, 6, and 7, the carbon content of the
residue is less than 5% (RCs/RedC.times.100 is less than 22%), and
the carbon content of the agglomerate is less than 122% of the
carbon content required to reduce iron oxide contained in the
agglomerate. With respect to No. 6 of these, among the compositions
of the agglomerate, [CaO]/[SiO.sub.2] is 0.14, which satisfies the
formula (5). Thus, slag has an increased melting point, and the
residue has low cohesion, is easily separable, and has good
removability. With respect to Nos. 4 and 7, among the compositions
of the agglomerate, [CaO]/[SiO.sub.2] is in the range of 0.25 to
1.20, [Al.sub.2O.sub.3]/[SiO.sub.2] is in the range of 0.2 to 0.7,
and [MgO]/[SiO.sub.2] is 0.4 or less, which do not satisfy the
formulae (5) to (9). Thus, Nos. 4 and 7 are strongly sticked on the
hearth.
TABLE-US-00001 TABLE 1 Composition of agglomerate (% by mass) [CaO]
+ [Al.sub.2O.sub.3] + No. TFe FeO TC FC CaO SiO.sub.2
Al.sub.2O.sub.3 MgO [CaO]/[SiO.sub.2] [Al.sub.2O.sub.3]/[SiO.sub.2]
[MgO]/[SiO.sub.2] [SiO.sub.2] 1 46.24 0.32 21.55 17.35 2.11 2.44
1.44 0.31 0.86 0.59 0.13 5.99 2 47.95 0.34 20.65 17.99 1.98 2.50
1.49 0.25 0.79 0.60 0.10 5.97 3 52.19 3.42 16.61 14.47 1.14 1.96
1.33 0.08 0.58 0.68 0.04 4.43 4 53.68 25.02 17.10 14.96 1.32 2.22
0.92 0.40 0.59 0.41 0.18 4.46 5 53.57 23.09 17.53 15.34 0.38 1.62
0.61 0.29 0.23 0.38 0.18 2.61 6 46.96 1.21 16.21 10.95 0.55 3.82
1.62 0.12 0.14 0.42 0.03 5.99 7 46.96 0.72 16.18 10.93 1.86 5.54
1.56 0.12 0.34 0.28 0.02 8.96
TABLE-US-00002 TABLE 2 Time Composition after heating (% by mass)
Percentage of Carbon content (% by mass) No. (min) TFe FeO MFe TC
TC/TFe .times. 100 MetalFe 1 mm or less (%) RCs Red C RCs/Red C
.times. 100 1 16.00 80.1 0.51 79.47 11.0 13.73 99.2 68.30 6.37
15.18 42 2 16.00 81.1 0.28 80.16 10.5 12.95 98.8 86.20 6.21 14.44
43 3 16.00 87.2 0.53 86.58 5.0 5.73 99.3 29.31 2.98 13.63 22 4
16.00 88.0 0.50 87.20 3.6 4.09 99.1 7.12 2.19 14.91 15 5 16.00 86.6
0.40 86.26 5.1 5.89 99.6 0.40 3.16 14.37 22 6 9.95 84.1 0.90 83.11
3.1 3.69 98.8 67.24 1.73 14.48 12 7 8.83 80.9 0.92 80.13 1.3 1.61
99.0 5.82 0.75 15.43 5 MetalFe = MFe/TFe .times. 100
Experimental Example 2
[0094] It is difficult to accurately observe the formation behavior
of molten slag in the reduction of iron oxide in the presence of
CaO, SiO.sub.2, and MgO. Because of the coexistence of solid and
liquid states and nonuniform presence of each oxide, it is not
clear what state of molten slag contributes to metallic iron
sintering and the promotion of coarse coalescence of wustite.
[0095] A MgO source magnesite and a CaO source limestone were
blended with iron ore containing SiO.sub.2 as a gangue component to
form a pellet (agglomerate). The pellet was fired in the air in an
electric furnace at 1300.degree. C. for 10 minutes. While the
pellet was reduced with a gas, the deformation ratio of the pellet
was measured. The effects of CaO, SiO.sub.2, and MgO on the
deformation of the pellet were examined. The results were described
in "High Temperature Reduction and Softening Properties of Pellets
with Magnesite" (Transactions of the Iron and Steel Institute of
Japan, issued by The Iron and Steel Institute of Japan, vol. 23
(1983), No. 2, p. 153).
[0096] The reduction of the fired pellet with a gas was performed
under a load of 0.5 kg/pellet with a reducing gas (CO gas:N.sub.2
gas=30% by volume:70% by volume) while the fired pellet was heated
to 1500.degree. C. at 10.degree. C./min. The SiO.sub.2 content of
the pellet was 0.3%, and [MgO]/[SiO.sub.2] was changed in the range
of 0.01 to 1.32. The deformation ratio of the pellet was measured
before and after reduction. The results were described in the
literature described above. FIG. 1 shows the results.
[0097] The deformation of the pellet is based on contraction
resulting from the reduction of iron oxide to metallic iron and
deformation resulting from the formation of molten slag.
Deformation at 1100.degree. C. or more predominantly results from
the latter deformation. This is demonstrated by observing structure
photographs of a cross section of the pellet described in the
literature. FIG. 2 shows structure photographs described in the
literature. FIG. 2 shows photographs substituted for drawing of a
cross section of a pellet reduced by heating a fired pellet in
which SiO.sub.2 is 4.5% and [MgO]/[SiO.sub.2]=0.59 to 1300.degree.
C. FIG. 2(1) shows the outer area of the pellet, and FIG. 2(2)
shows the inner area of the pellet. (1) includes much metallic iron
shown in white, and (2) includes wustite shown in gray and molten
slag shown in black. The wustite particles are coarse and have a
molten round surface. Thus, it is clear that deformation at
1100.degree. C. or more results from the formation of molten
slag.
[0098] In the literature, the effects of the pellet composition on
the deformation of the pellet are examined by measuring the
temperature for 40% contraction (hereinafter also referred to as
40% contraction temperature) of the pellet. FIGS. 3 and 4 show the
results.
[0099] FIG. 3 shows the results for different [MgO]/[SiO.sub.2]
with a SiO.sub.2 content of 4.4% (circles) or 8.3% (crosses)
without CaO. FIG. 4 shows the results for different
[CaO]/[SiO.sub.2] with [MgO]/[SiO.sub.2]=0.72.
[0100] As is clear from FIG. 3, in the absence of CaO, the 40%
contraction temperature monotonously increases with
[MgO]/[SiO.sub.2]. In the presence of CaO, the 40% contraction
temperature is lowest at [CaO]/[SiO.sub.2]=0.45. The composition at
which the 40% contraction temperature is 1350.degree. C. is
[MgO]/[SiO.sub.2] of more than 0.4 in the absence of CaO as
illustrated in FIG. 3 or [CaO]/[SiO.sub.2] of less than 0.18 or
more than 1.05 in the presence of CaO as illustrated in FIG. 4.
Although this result is different from the range described above in
the presence of CaO and MgO, regarding the results of Example 1 as
important, [CaO]/[SiO.sub.2] is defined to be less than 0.25 or
more than 1.20.
[0101] It is also qualitatively clear from a ternary equilibrium
diagram that such a way of thinking is reasonable.
[0102] FIG. 5 is a SiO.sub.2--MgO--FeO ternary equilibrium diagram.
In FIG. 5, [MgO]/[SiO.sub.2]=0.4 gives a straight line, and the
melting point under this condition is 1450.degree. C. even for
different FeO contents, indicating that the melting point
monotonously decreases with [MgO]/[SiO.sub.2].
[0103] Even having a melting point of 1450.degree. C., for example,
all the gangue components are not necessarily solid at 1350.degree.
C. Since part of the gangue components melt at approximately
1200.degree. C. or more, a higher melting point is only indicative
of a smaller amount of melt.
[0104] FIG. 6 is a CaO--SiO.sub.2--MgO ternary equilibrium diagram.
In FIG. 6, [MgO]/[SiO.sub.2]=0.4, [MgO]/[SiO.sub.2]=0.72,
[CaO]/[SiO.sub.2]=0.25, [CaO]/[SiO.sub.2]=0.45, and
[CaO]/[SiO.sub.2]=1.20 give straight lines. Even when
[MgO]/[SiO.sub.2] is constant, with a change in [CaO]/[SiO.sub.2],
[CaO]/[SiO.sub.2] of 0.45 almost results in a compound
CaO.MgO.2SiO.sub.2 having a melting point of approximately
1400.degree. C. Thus, getting closer to the composition of a
low-melting-point compound, the molten gangue increases. As shown
by the dotted lines in FIG. 6, in order for the melting point of
the slag to be approximately 1450.degree. C. or more,
[CaO]/[SiO.sub.2] may be less than 0.25 or more than 1.20.
Experimental Example 3
[0105] The effects of Al.sub.2O.sub.3 on the deformation of the
pellet was examined in Experimental Example 2.
[0106] FIG. 7 is a CaO--SiO.sub.2--Al.sub.2O.sub.3 ternary
equilibrium diagram. In FIG. 7, [Al.sub.2O.sub.3]/[SiO.sub.2]=0.2,
[Al.sub.2O.sub.3]/[SiO.sub.2]=0.7, [CaO]/[SiO.sub.2]=0.25, and
[CaO]/[SiO.sub.2]=1.20 give straight lines. In a region surrounded
by these straight lines, a low-melting-point slag having a melting
point of approximately 1250.degree. C. is partly formed. Outside
this region is a high-melting-point region. Thus, the amount of
molten slag can be decreased in the outside of this region.
INDUSTRIAL APPLICABILITY
[0107] According to the present invention, a large adhesive
material, such as a steel sheet, that cannot be discharged from a
furnace can be prevented from being formed on a hearth, and the
hearth level can be prevented from being raised. Thus, metallic
iron can be efficiently produced without significantly changing the
design for facilities.
* * * * *