U.S. patent application number 14/765722 was filed with the patent office on 2015-12-17 for method for producing reduced iron agglomerate.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). The applicant listed for this patent is KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.). Invention is credited to Takao HARADA, Shoichi KIKUCHI, Shingo YOSHIDA.
Application Number | 20150361515 14/765722 |
Document ID | / |
Family ID | 51428036 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150361515 |
Kind Code |
A1 |
KIKUCHI; Shoichi ; et
al. |
December 17, 2015 |
METHOD FOR PRODUCING REDUCED IRON AGGLOMERATE
Abstract
Provided is a method for producing a reduced iron agglomerate,
which comprises introducing an agglomerate comprising an
iron-oxide-containing substance, a carbonaceous reducing agent, a
melting point adjuster and an aid for the melting point adjuster
onto a furnace bed of a moving-bed-type heating furnace and then
heating the agglomerate on the furnace bed to reduce iron oxide in
the agglomerate; and melting the resultant product by additional
heating to cause the coalescence of an iron component, thereby
producing the reduced iron agglomerate, wherein an agglomerate
containing the melting point adjuster that has an average particle
diameter of 0.3 mm or less and in which the content of a particle
diameter of 0.5 mm or less in an amount of 55 mass % or more is
used. Thus, provided is a method which can improve the yield of a
reduced iron agglomerate having a large particle diameter and can
also reduce the amount of time required for the production of the
reduced iron agglomerate to improve the productivity of the reduced
iron agglomerate.
Inventors: |
KIKUCHI; Shoichi; (Kobe-shi,
JP) ; HARADA; Takao; (Kobe-shi, JP) ; YOSHIDA;
Shingo; (Kobe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.) |
Kobe-shi, Hyogo |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi, Hyogo
JP
|
Family ID: |
51428036 |
Appl. No.: |
14/765722 |
Filed: |
February 5, 2014 |
PCT Filed: |
February 5, 2014 |
PCT NO: |
PCT/JP2014/052665 |
371 Date: |
August 4, 2015 |
Current U.S.
Class: |
75/484 |
Current CPC
Class: |
C21B 13/008 20130101;
C21B 13/10 20130101; C21B 13/105 20130101 |
International
Class: |
C21B 13/10 20060101
C21B013/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2013 |
JP |
2013-039421 |
Claims
1. A method for producing a reduced iron agglomerate, comprising:
introducing an agglomerate comprising an iron oxide-containing
substance, a carbonaceous reducing agent, a melting-point adjuster,
and an aid for the melting-point adjuster onto a hearth of a
moving-bed heating furnace; heating the agglomerate to reduce the
iron oxide-containing substance; and melting the agglomerate by
further heating the agglomerate to coalesce an iron component,
wherein the melting-point adjuster has; an average particle
diameter of 0.3 mm or less, and a content of particles having a
diameter of 0.5 mm or less of 55% by mass or more, based on a total
mass of the melting-point adjuster.
2. The method according to claim 1, wherein the melting-point
adjuster is at least one of dolomite and limestone.
3. The method according to claim 1, wherein the aid is
fluorite.
4. The method according to claim 1, wherein the melting-point
adjuster is present in a central portion of the agglomerate.
5. A method for producing a reduced iron agglomerate, comprising
introducing an agglomerate comprising an iron oxide-containing
substance, a carbonaceous reducing agent, a melting-point adjuster,
and an aid for the melting-point adjuster onto a hearth of a
moving-bed heating furnace; heating the agglomerate to reduce the
iron oxide-containing substance; and melting the agglomerate by
further heating the agglomerate to coalesce an iron component,
wherein the aid has: an average particle diameter of 90 .mu.m or
less, and a content of particles having a diameter of 50 .mu.m or
less of 35% by mass or more, based on a total mass of the aid.
6. The method according to claim 5, wherein the melting-point
adjuster is at least one of dolomite and limestone.
7. The method according to claim 5, wherein the aid is fluorite.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing a
reduced iron agglomerate. The method includes introducing an
agglomerate made from a mixture containing an iron oxide-containing
substance and a carbonaceous reducing agent onto a hearth of a
moving-bed heating furnace and heating the agglomerate to reduce
and melt iron oxide in the agglomerate.
BACKGROUND ART
[0002] The following method has been developed: a direct reduction
ironmaking method for obtaining massive (including granular)
metallic iron (reduced iron) from a mixture containing an iron
oxide source (hereinafter referred to as "iron oxide-containing
substance" in some cases) such as iron ore or iron oxide and a
carbon-containing reducing agent (hereinafter referred to as
"carbonaceous reducing agent" in some cases). In the ironmaking
method, massive metallic iron (reduced iron agglomerate) is
obtained in such a manner that an agglomerate formed from the
mixture is introduced onto a hearth of a moving-bed heating furnace
and is heated by gas heat transfer or radiation heat in the heating
furnace using a heating burner, iron oxide in the agglomerate is
thereby reduced with the carbonaceous reducing agent, and obtained
reduced iron is subsequently carburized, is melted, is agglomerated
while being separated from co-produced slag, and is then solidified
by cooling.
[0003] The ironmaking method does not require a large facility such
as a blast furnace and is highly flexible in terms of sources
because of no need of coke. Therefore, in recent years, the
ironmaking method has been increasingly investigated for practical
use. However, for industrial implementation, the ironmaking method
needs to be further improved in terms of operation stability,
safety, economical efficiency, granular iron (product) quality,
productivity, and the like.
[0004] In particular, in the production of reduced iron
agglomerates, it is desired that the yield of a reduced iron
agglomerate with a large particle diameter is increased and the
production time thereof is reduced. Regarding such a technique, for
example, Patent Literature 1 proposes "a method for producing
granular metal, comprising heating a source material containing a
metal oxide-containing substance and a carbonaceous reducing agent
to reduce a metal oxide in the source material, heating a produced
metal to melt the metal, and agglomerating the melted metal while
the melted metal is separated from co-produced slag, wherein an
agglomeration promoter for co-produced slag is blended in the
source material".
[0005] In this technique, the agglomeration promoter (for example,
fluorite) is blended. Therefore, it can be expected that a granular
metal with a large particle diameter can be produced in relatively
high yield. However, in this technique, an improvement effect is
saturated; hence, a further increase in effect is desired.
CITATION LIST
Patent Literature
[0006] PTL 1: Japanese Unexamined Patent Application Publication
No. 2003-73722
SUMMARY OF INVENTION
Technical Problem
[0007] The present invention has been made in view of the above
circumstances. It is an object of the present invention to provide
a production method which increases productivity by increasing the
yield of a reduced iron agglomerate with a large particle diameter
and by reducing the production time thereof in the case where the
reduced iron agglomerate is produced in such a manner that an
agglomerate made from a mixture containing at least an iron
oxide-containing substance and a carbonaceous reducing agent is
heated in a moving-bed heating furnace and iron oxide in the
agglomerate is reduced and is melted.
Solution to Problem
[0008] A method for producing a reduced iron agglomerate according
to the present invention is capable of solving the above problem
and is summarized as follows: the method includes introducing an
agglomerate containing an iron oxide-containing substance, a
carbonaceous reducing agent, a melting-point adjuster, and an aid
for the melting-point adjuster onto a hearth of a moving-bed
heating furnace; heating the agglomerate to reduce iron oxide in
the agglomerate; and melting the resultant product by further
heating to agglomerate an iron component, wherein an agglomerate
containing the melting-point adjuster which has an average particle
diameter of 0.3 mm or less and in which the content of particles
with a diameter of 0.5 mm or less is 55% by mass or more is
used.
[0009] In the method according to the present invention, the
melting-point adjuster (one acting directly on a gangue component)
is particularly at least one of dolomite and limestone. The aid
(one promoting the reaction of the melting-point adjuster) for the
melting-point adjuster is particularly fluorite (a calcium
fluoride-containing substance).
[0010] In the method, the melting-point adjuster is present in a
central portion of the agglomerate and it is preferred that the
average particle diameter of the melting-point adjuster is 0.3 mm
or less and the content of the particles with a diameter of 0.5 mm
or less in the melting-point adjuster is 55% by mass or more. In
this case, the average particle diameter of the melting-point
adjuster, which is present in the central portion, may be
appropriately adjusted depending on the type of the melting-point
adjuster.
[0011] Another method, capable of solving the above problem,
according to the present invention is a method for producing a
reduced iron agglomerate. This method includes introducing an
agglomerate containing an iron oxide-containing substance, a
carbonaceous reducing agent, a melting-point adjuster, and an aid
for the melting-point adjuster onto a hearth of a moving-bed
heating furnace; heating the agglomerate to reduce iron oxide in
the agglomerate; and melting the resultant product by further
heating to agglomerate an iron component, wherein an agglomerate
containing the aid for the melting-point adjuster is used, the aid
having an average particle diameter of 90 .mu.m or less, the
content of particles with a diameter of 50 .mu.m or less in the aid
being 35% by mass or more.
[0012] In this method also, the melting-point adjuster is
particularly at least one of dolomite and limestone. The aid for
the melting-point adjuster is particularly fluorite (a calcium
fluoride-containing substance).
Advantageous Effects of Invention
[0013] According to the present invention, a reduced iron
agglomerate is produced in such a manner that an agglomerate made
from a mixture comprising at least an iron oxide-containing
substance, a carbonaceous reducing agent, a melting-point adjuster,
and an aid for the melting-point adjuster is introduced onto a
hearth of a moving-bed heating furnace; the agglomerate is heated
such that iron oxide in the agglomerate is reduced; and the
resultant product is melted by further heating such that an iron
component is agglomerated. The yield of a reduced iron agglomerate
with a large particle diameter is increased and the production time
thereof is reduced in such a manner that the average particle
diameter of the melting-point adjuster is reduced and the content
of particles with a predetermined diameter in the melting-point
adjuster is appropriately controlled or in such a manner that the
average particle diameter of the aid for the melting-point adjuster
is reduced and the content of particles with a predetermined
diameter in the aid is appropriately controlled. This enables
productivity to be increased.
DESCRIPTION OF EMBODIMENTS
[0014] In order to form an agglomerate from a mixture containing an
iron oxide-containing substance, a carbonaceous reducing agent, a
melting-point adjuster, and an aid for the melting-point adjuster,
the iron oxide-containing substance, the carbonaceous reducing
agent, the melting-point adjuster, and the aid being raw material
components (hereinafter referred to as "components") used to
produce a reduced iron agglomerate, both the melting-point adjuster
and the aid for the melting-point adjuster are adequately
pulverized into particles with an adequate size. However, the
influence of the size (average particle diameter) of these
components on the yield or productivity of the reduced iron
agglomerate has not been taken into account. It has been believed
that pulverizing these components into excessively fine particles
causes the dispersion of these components, prevents the
agglomeration of reduced iron, and therefore reduces
productivity.
[0015] In order to achieve the above object, the inventors have
performed investigations from various angles. In particular, the
inventors have investigated the influence of the average particle
diameter or particle size distribution (the content of particles
with a predetermined diameter) of these components on the yield and
productivity of the reduced iron agglomerate. As a result, the
inventors have found that the above object is achieved well in such
a manner that the average particle diameter of the melting-point
adjuster or the aid for the melting-point adjuster is reduced and
the content of particles with a predetermined diameter is
appropriately adjusted, thereby completing the present
invention.
[0016] In the present invention, it is necessary that the average
particle diameter of the melting-point adjuster contained in the
agglomerate is 0.3 mm or less and the content (the proportion to
the whole melting-point adjuster) of particles with a diameter of
0.5 mm or less in the melting-point adjuster is 55% by mass or
more. Alternatively, it is necessary that the average particle
diameter of the aid for the melting-point adjuster contained in the
agglomerate is 90 .mu.m or less and the content (the proportion to
the whole aid for the melting-point adjuster) of particles with a
diameter of 50 .mu.m or less in the aid is 35% by mass or more.
Incidentally, the term "average particle diameter" as used herein
refers to the particle diameter (hereinafter referred to as "D50"
in some cases) where the number of particles corresponds to 50% by
mass (the cumulative value is 50% by mass) as counted from the
smallest particle size. The use of the fined melting-point adjuster
or the fined aid for the melting-point adjuster to form the
agglomerate increases the yield and productivity of the obtained
reduced iron agglomerate. The reason for this can be inferred as
described below.
[0017] The agglomerate is reduced and melted at a high temperature
of 1,200.degree. C. to 1,500.degree. C. In the initial stage of the
reduction reaction, reaction proceeds through the direct contact of
the iron oxide-containing substance with the carbonaceous reducing
agent. Pulverizing the melting-point adjuster, such as limestone or
dolomite ore, or the aid, such as fluorite, for the melting-point
adjuster into fine particles reduces the distance between a gangue
component contained in the iron oxide-containing substance and the
surface of the melting-point adjuster or the aid for the
melting-point adjuster (increases the probability of the presence
of the gangue component near the surface of the melting-point
adjuster or the aid for the melting-point adjuster) and is unlikely
to prevent the agglomeration of the reduced iron agglomerate
(hereinafter referred to as "granular reduced iron" in some cases)
because the gangue component is likely to come into contact with
the melting-point adjuster or the aid for the melting-point
adjuster to produce a melt. That is, it is conceivable that a
phenomenon completely opposite to a conventionally recognized
finding may occur.
[0018] In order to effectively exhibit such an effect, the
melting-point adjuster which has an average particle diameter of
0.3 mm or less and in which the content of the particles with a
diameter of 0.5 mm or less is 55% by mass or more needs to be used
to form the agglomerate. Alternatively, the aid for the
melting-point adjuster needs to be used to form the agglomerate,
the aid having an average particle diameter of 90 .mu.m or less,
the content of the particles with a diameter of 50 .mu.m or less
being 35% by mass or more. Incidentally, the content of the
particles with a diameter of 0.5 mm or less in the melting-point
adjuster is preferably 60% by mass or more and more preferably 65%
by mass or more (may be 100% by mass). The content of the particles
with a diameter of 50 .mu.m or less in the aid for the
melting-point adjuster is preferably 40% by mass or more and more
preferably 45% by mass or more (may be 100% by mass).
[0019] In the present invention, the iron oxide-containing
substance may be iron ore, iron sand, nonferrous refining residue,
or the like. The carbonaceous reducing agent may be, for example, a
carbon-containing substance such as coal or coke.
[0020] The agglomerate may contain another component such as a
binder, a MgO-containing substance, or a CaO-supplying substance.
The binder may be, for example, a polysaccharide (for example,
starch such as cornstarch, rice flour, or wheat flour). The
MgO-containing substance may be, for example, a MgO powder, natural
ore, a Mg-containing substance extracted from seawater, magnesium
carbonate (MgCO.sub.3), or the like. The CaO-supplying substance
may be, for example, quicklime (CaO) or the like.
[0021] The shape of the agglomerate is not particularly limited and
may be, for example, a pellet shape, a briquette shape, or the
like. The size of the agglomerate is not particularly limited. The
diameter (maximum diameter) of the agglomerate is preferably 50 mm
or less. Excessively increasing the diameter of the agglomerate
impairs the efficiency of granulation and also impairs the transfer
of heat to a lower portion of a pellet to reduce productivity.
Incidentally, the lower limit of the diameter of the agglomerate is
about 5 mm.
[0022] The whole of the melting-point adjuster in the agglomerate
need not be fined. A portion (for example, 10% by mass or more) of
the melting-point adjuster to be used may meet specified
requirements (the average particle diameter is 0.3 mm or less and
the content of the particles with a diameter of 0.5 mm or less is
55% by mass or more). A form meeting such requirements is, for
example, the presence of the fined melting-point adjuster only in
at least a central portion of the agglomerate. That is, when the
agglomerate is heated from outside, the increase in temperature of
the central portion of the agglomerate is slow as compared to the
periphery thereof and the reaction of the central portion is also
slow. In order to mitigate this phenomenon, fining the
melting-point adjuster present in the central portion of the
agglomerate is effective. Incidentally, the term "central portion"
refers to a portion ranging from the center of a sphere to a
location satisfying the above content (a portion outside the
location is referred to as "peripheral portion") when the
agglomerate has, for example, a spherical shape (a dry pellet
described below).
[0023] When the fined melting-point adjuster is present in at least
the central portion of the agglomerate, it is a basic form that the
fined melting point adjuster is present only in the central portion
of the agglomerate as specified in the present invention and the
melting-point adjuster with a usual average particle diameter (not
fined) is present in a peripheral portion. The case where the whole
of the melting-point adjuster used meets the requirements specified
in the present invention is included in embodiments of the present
invention.
[0024] The present invention is further described below in detail
with reference to examples. The examples are not intended to limit
the present invention. Appropriate changes may be made within the
scope adaptable to the gist described above and below and are
included in the technical scope of the present invention.
[0025] This application claims benefits of priority to Japanese
Patent Application No. 2013-039421 filed on Feb. 28, 2013. The
entire contents of Japanese Patent Application No. 2013-039421
filed on Feb. 28, 2013 are incorporated herein by reference.
EXAMPLES
Example 1
[0026] An agglomerate was prepared from a mixture containing an
iron oxide-containing substance, a carbonaceous reducing agent,
melting-point adjusters, an aid for the melting-point adjusters,
and a binder. The agglomerate was introduced onto a hearth of a
moving-bed heating furnace and was heated. Iron oxide in the
agglomerate was reduced and was melted, whereby a reduced iron
agglomerate (granular reduced iron) was produced.
[0027] The iron oxide-containing substance used was iron ore having
a composition shown in Table 1 below. The carbonaceous reducing
agent used was coal having a composition shown in Table 2 below.
The melting-point adjusters used were limestone having a
composition shown in Table 3 below and dolomite having a
composition shown in Table 4 below. The aid for the melting-point
adjusters used was fluorite having a composition shown in Table 5
below. Agglomerates were produced by varying the average particle
diameter (D50) and particle size distribution (the content of
particles with a predetermined diameter) of each of the
melting-point adjusters and the aid for the melting-point adjusters
(Table 7 below). In particular, wheat flour used as the binder was
mixed with each of mixtures containing the melting-point adjusters
(limestone and dolomite) and the aid (fluorite) for the
melting-point adjusters, the melting-point adjusters and the aid
being different in average particle diameter and particle size
distribution, at a blending ratio shown in Table 6 below. An
adequate amount of water was added to each of the mixtures,
followed by producing raw pellets with a diameter of 19 mm using a
tire-type pelletizer. The obtained raw pellets were introduced into
a dryer and were heated at 180.degree. C. for 1 hour such that
contained water was completely removed, whereby pellet-shaped
agglomerates (spherical dry pellets) were prepared.
TABLE-US-00001 TABLE 1 Composition of iron ore (mass percent)
T.cndot.Fe FeO SiO.sub.2 CaO Al.sub.2O.sub.3 MgO S 66.62 0.12 2.24
0.07 0.96 0.03 0.008
TABLE-US-00002 TABLE 2 Composition of coal (mass percent) Fixed
carbon Volatile matter Ash Total 79.5 15.97 4.53 100.00
TABLE-US-00003 TABLE 3 Composition of limestone (mass percent)
SiO.sub.2 CaO Al.sub.2O.sub.3 MgO S 0.16 55.59 0.22 0.26
<0.001
TABLE-US-00004 TABLE 4 Composition of dolomite (mass percent)
SiO.sub.2 CaO Al.sub.2O.sub.3 MgO S 0.84 30.0 0.28 20.44 0.062
TABLE-US-00005 TABLE 5 Composition of fluorite (mass percent)
SiO.sub.2 T.Ca Al.sub.2O.sub.3 MgO F 10.58 44.01 1.36 0.1 43.63
TABLE-US-00006 TABLE 6 Blending ratio (mass percent) Iron ore Coal
Limestone Dolomite Fluorite Binder Total 75.05 18.0 2.9 2.35 0.8
0.9 100.00
[0028] The dry pellets were introduced into a moving-bed reduction
heating furnace in which a carbon material (anthracite with a
maximum particle diameter of 2 mm or less) was spread and were
heated at 1,450.degree. C. in a nitrogen atmosphere, followed by
measuring the time (reaction time) necessary for reduction and
melting.
[0029] The results are shown in Table 7 together with the average
particle diameter and particle size distribution of components
(iron ore, coal, limestone, dolomite, and fluorite) used (regarding
iron ore, the average particle diameter thereof only is shown and
the same applies hereinafter). Common properties (such as apparent
density and dry pellet analytical data) of the dry pellets are also
shown in Table 7. A measurement method and standards for main items
among items shown in Table 7 are as described below.
(Productivity (Productivity Index))
[0030] The productivity where granular reduced iron is produced in
such a manner that the dry pellets are heated and iron oxide is
reduced and is melted is evaluated through the production (tons) of
granular reduced iron per hearth area (m.sup.2) per unit time
(hour) as represented by the following Equation (1):
Productivity (tons/m.sup.2/hour)=productivity of granular reduced
iron (tons/hour)/hearth area (m.sup.2)tm (1).
[0031] In Equation (1), the production (tons/hour) of granular
reduced iron is represented by the following Equation (2):
Productivity of granular reduced iron (tons-granular reduced
iron/hour)=amount of introduced agglomerates (dry pellets)
(tons-agglomerates/hour).times.mass of granular reduced iron
produced from a ton of agglomerates (tons-granular reduced
iron/ton-agglomerates).times.product recovery rate (2).
[0032] In Equation (2), the product recovery rate is calculated as
the mass ratio [mass % of +3.35 mm granular iron/amount % of
granular reduced iron.times.100 (%)] of granular reduced iron with
a diameter of 3.35 mm or more to the amount of obtained granular
reduced iron (shown as "Yield of +3.35 mm granular iron (%)" in
Table 7). In Table 7, in order to quantitatively evaluate effects
of the present invention, agglomerates (dry pellets) of Experiment
No. 1 are used as standard agglomerates and the productivity where
other agglomerates are used is expressed as a relative value
(productivity index) on the basis that the productivity where the
standard agglomerates are used is 1.00.
TABLE-US-00007 TABLE 7 Experiment No. 1 2 3 4 5 Average particle
diameter (D50) Iron ore (.mu.m) 37 37 37 37 37 Coal (.mu.m) 21 21
21 21 21 Limestone (.mu.m) 1102 276 1102 1102 1102 Dolomite (.mu.m)
1155 1155 204 99 1155 Fluorite (.mu.m) 103 103 103 103 85 Content
of -500 .mu.m in limestone (mass percent) 22 59 22 22 22 Content of
-500 .mu.m in dolomite (mass percent) 20 20 63 81 20 Content of -50
.mu.m in fluorite (mass percent) 34 34 34 34 38 Dry pellets
Apparent density (g/cm.sup.3) 2.181 2.313 2.287 2.272 2.275
Reaction time (minutes) 11.15 10.56 11.00 10.24 10.88 Analytical
data of dry pellets Total iron (%) 51.11 51.39 51.24 50.73 51.16
Granular reduced iron Yield of +3.35 mm granular iron (%) 85.73
92.4 90.97 94.83 89.84 Analytical data of granular reduced iron C
(%) 3.10 2.98 2.90 3.09 2.97 Productivity index (--) 1.00 1.21 1.13
1.25 1.12
[0033] As is clear from the results, it is understandable that when
the average particle diameter (D50) of limestone used as a
melting-point adjuster is 0.3 mm or less (300 .mu.m or less) and
the content of particles with a diameter of 0.5 mm or less (shown
as "-500 .mu.m") is 55% by mass or more (Experiment No. 2) or when
the average particle diameter (D50) of dolomite used as a
melting-point adjuster is 0.3 mm or less (300 .mu.m or less) and
the content of particles with a diameter of 0.5 mm or less (shown
as "-500 .mu.m") is 55% by mass or more (Experiment Nos. 3 and 4),
the yield of granular reduced iron is increased and the
productivity thereof is significantly increased. On the other hand,
it is understandable that when the average particle diameter (D50)
of fluorite used as an aid for a melting-point adjuster is 90 .mu.m
or less and the content of particles with a diameter of 50 .mu.m or
less (shown as "-50 .mu.m") is 35% by mass or more (Experiment No.
5), the yield of granular reduced iron is increased and the
productivity thereof is significantly increased.
Example 2
[0034] Dry pellets having a double structure were prepared using a
mixture (the blending ratio was the same as that shown in Table 6)
containing an iron oxide-containing substance, carbonaceous
reducing agent, melting-point adjusters (limestone and dolomite),
aid for the melting-point adjusters (fluorite), and binder each
having the same composition as that used in Example 1. In
particular, wheat flour used as a binder was mixed with a mixture
containing iron ore, limestone, and fluorite each having an average
particle diameter and particle size distribution shown in the
column "central portion" in Table 8 below and an adequate amount of
water was added to this mixture, followed by producing spherical
raw pellets with a diameter of 9.5 mm using a tire-type pelletizer.
A mixture containing limestone having different average particle
diameters and particle size distributions was concentrically formed
on the periphery (a peripheral portion) of each spherical raw
pellet using the spherical raw pellet as a core, whereby raw
pellets with a diameter of 19.0 mm were produced (the mixture
content of a central portion was about 12% by mass of each pellet).
The obtained raw pellets were introduced into a dryer and were
heated at 180.degree. C. for 1 hour such that contained water was
completely removed, whereby pellet-shaped agglomerates
(double-structured pellets) were prepared.
[0035] The double-structured pellets were introduced into a
moving-bed reduction heating furnace in which a carbon material
(anthracite with a maximum particle diameter of 2 mm or less) was
spread and were heated at 1,450.degree. C. in a nitrogen
atmosphere, followed by evaluating the time (reaction time)
necessary for reduction and melting in the same manner as that
described in Example 1. The results are shown in Table 8 together
with the average particle diameter (D50) and particle size
distribution of components (iron ore, coal, limestone, dolomite,
and fluorite) used. Incidentally, items evaluated in Examples 1 and
2 are also shown in Table 8 (an evaluation method is the same as
that described in Example 1).
TABLE-US-00008 TABLE 8 Experiment No. 6 Position Peripheral Central
portion portion Average particle diameter (D50) Iron ore (.mu.m) 37
37 Coal (.mu.m) 21 21 Limestone (.mu.m) 276 1102 Dolomite (.mu.m)
1155 1155 Fluorite (.mu.m) 103 103 Content of -500 .mu.m in
limestone 59 22 (mass percent) Content of -500 .mu.m in dolomite 20
20 (mass percent) Content of -50 .mu.m in fluorite 34 34 (mass
percent) Dry pellets Apparent density (g/cm.sup.3) 2.275 Reaction
time (minutes) 10.76 Analytical data of dry pellets Total iron (%)
51.55 Granular reduced iron Yield of +3.35 mm granular iron (%)
93.53 Analytical data of granular reduced iron C (%) 2.91
Productivity index (--) 1.19
[0036] As is clear from the results, it is understandable that the
effect of increasing the yield of granular reduced iron is achieved
in such a manner that the whole of each pellet is not fined but the
central portion only is primarily fined, that is, an effect of the
present invention is achieved even in such a state that the amount
of a fined component is small.
INDUSTRIAL APPLICABILITY
[0037] The present invention provides a method for producing a
reduced iron agglomerate. The method includes introducing an
agglomerate containing an iron oxide-containing substance, a
carbonaceous reducing agent, a melting-point adjuster, and an aid
for the melting-point adjuster onto a hearth of a moving-bed
heating furnace; heating the agglomerate to reduce iron oxide in
the agglomerate; and melting the resultant product by further
heating to agglomerate an iron component, wherein an agglomerate
containing the melting-point adjuster which has an average particle
diameter of 0.3 mm or less and in which the content of particles
with a diameter of 0.5 mm or less is 55% by mass or more is used.
This enables the following method to be provided: a method which
increases productivity by increasing the yield of a reduced iron
agglomerate with a large particle diameter and by reducing the
production time thereof.
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