Specification
MANUFACTURING METHOD OF REDUCED IRON
Field of the Invention
[0001]
The present invention relates to a manufacturing method of reduced iron.
Priority is claimed on Japanese Patent Application No. 2010-231512, filed on
October 14, 2010, the content of which is incorporated herein by reference.
Related Art
[0002]
In the process of making pig iron or steel, iron-based dust that is produced in
blast furnaces, converters, electric furnaces, melting furnaces, or the like is reused as a
material.
[0003]
To use, as a material, a solid iron-containing cold charge such as the
aforementioned dust, a reducing agent is mixed with an iron oxide material, which is a
collected solid iron-containing cold charge. The mixture is then kneaded. After that,
the mixture is subjected to an agglomeration treatment into an agglomerated substance.
After that, the agglomerated substance is reduced, to thereby manufacture reduced iron
(for example, refer to Patent Document 1 below).
Reference Document
Patent Document
[0004]
[Patent Document l]: Japanese Unexamined Patent Application, First Publication
No. 2009-97065
Disclosure of the Invention
Problems to be Solved by the Invention
[0005]
However, in the manufacturing method of reduced iron as described above in
Patent Document 1, there are cases where in the pelletization process of performing
agglomeration treatment, it is not possible to completely agglomerate the mixture of
materials, leaving a powder. This poses a problem when a further improvement in
pelletizing ability is to be made.
[0006]
The present invention has been achieved in view of the above problem, and has
an object to provide a manufacturing method of reduced iron that is capable of further
improving the pelletizing ability when a mixture as a reduced iron material is
agglomerated.
Methods for Solving the Problem
[0007]
To solve the above problem, the present invention adopts the following aspect.
(1) Namely, a manufacturing method of a reduced iron according to an aspect of the
present invention includes: a kneading process of adding a fluid at 60°C or higher and
90°C or lower to a mixture of an iron oxide material and a reducing agent, both of which
are in a powder form, and kneading the mixture; a pelletization process of agglomerating
the mixture after the kneading process into an agglomerated substance; and a reduction
process of reducing the agglomerated substance after the pelletization process, to thereby
produce the reduced iron. The fluid in the present invention subsumes water and water
vapor.
[0008]
(2) In the kneading process according to the aspect as set forth above in (1), a binder
soluble in the fluid may be further added to the mixture.
[0009]
(3) In the case as set forth above in (2), the binder may be a liquid-like organic binder or a
powder-like organic binder.
[0010]
(4) In the case as set forth above in (3), the binder may be the powder-like organic binder,
and may be a starch of a grain selected from group consisting of a rice, a tapioca, a rye,
and a corn.
[0011]
(5) In the kneading process according to the aspect as set forth above in (1), addition of
the fluid may set a fluid content percentage of the mixture to 6% to 9%.
[0012]
(6) The mixture before kneaded in the kneading process in the aspect as set forth above in
(1) may have a minus-sieve 80% particle size of 70 um to 500 um.
[0013]
(7) The mixture before the fluid is added thereto in the kneading process in the aspect as
set forth above in (1) may have a fluid content percentage of 1% to 3%.
Effects of the Invention
[0014]
According to the aforementioned aspect of the present invention, when a mixture
i
j
including an iron oxide material and a reducing agent is pelletized, a fluid of 60°C or
higher and 90°C or lower is added to the mixture. Therefore, it is possible to make the
fluid in the mixture uniform, and hence, to further improve the pelletizing ability in the
pelletization process.
Brief Description of the Drawings
[0015]
FIG. 1 is an explanation diagram for explaining exemplary processes of
manufacturing reduced iron.
FIG. 2 is a flow chart for explaining the processes of a manufacturing method of
reduced iron according to an embodiment of the present invention.
FIG. 3 is a graph showing the time required for a fluid to penetrate into the
mixture.
FIG. 4 is a graph showing a ratio of the lumps present in the mixture.
FIG. 5 is a graph showing a percentage change in dissolution of the cornstarch
into the fluid.
FIG. 6 is a graph showing a change in strength of the agglomerated substance
after drying.
Embodiments of the Invention
[0016]
Hereunder is a detailed description of an embodiment of the present invention
with reference to the drawings. In the following description, a fluid subsumes water and
water vapor.
[0017]
< Processes of manufacturing reduced iron>
Before describing a manufacturing method of reduced iron according to the
present embodiment, the processes of manufacturing reduced iron will be described in
detail with reference to FIG. 1. FIG. 1 is an explanation diagram for explaining
exemplary processes of manufacturing reduced iron.
[0018]
An iron oxide material such as iron dust collected from each facility in the steel
plant or iron ore, and a reducing agent such as coal, coke, or fine carbon are previously
contained in hoppers 11 or the like. The iron oxide material and the reducing agent are
combined so as to be in a preset combination ratio, and are then charged into a grinder mill
13.
[0019]
The grinder mill 13 represented by a vibrational mill such as a ball mill grinds the
charged iron oxide material and reducing agent to a predetermined particle size while
mixing them. The particle size of the iron oxide material and the reducing agent after
grinding may be appropriately set according to the value suitable for a reduction furnace
such as a rotary hearth furnace or rotary kiln used for the manufacture of reduced iron.
The mixture made of the ground iron oxide material and reducing agent is carried to a
kneading machine 15.
[0020]
The kneading machine 15 receives and kneads the mixture that has been ground
to a predetermined particle size by the grinder mill 13. When kneading a mixture, the
kneading machine 15 often performs a moisture-adjusting treatment of adding water to the
mixture until the amount of water becomes suitable for the mixture to be charged into the
reduction furnace used for the manufacture of reduced iron. As an example of the
kneading machine 15, a mix muller can be listed. However, other than this, a variety of
kneading machines may be utilized. The mixture kneaded by the kneading machine 15 is
carried to a molding machine 17.
[0021]
The molding machine 17, such as a pan pelletizer (disc-type pelletizer), a double
roll squeezer (briquetting machine), or an extruder, receives and molds the mixture
containing the iron oxide material and the reducing agent into an agglomerated substance,
for example, pellets or briquettes. Here, the agglomerated substance refers to pellets,
briquettes, molded pieces formed by extrusion and cutting, and a granular
substance/grainy substance such as a grainy substance whose particle size is adjusted.
After a drying/heating reduction (described later), the molding machine 17 agglomerates
the aforementioned mixture so as to have a size that will not be flown apart by an
in-furnace rising gas flow when, for example, the mixture is hot-charged into a melting
furnace 23. A produced agglomerated substance is charged into a drying machine 19.
[0022]
The drying machine 19 receives and dries the agglomerated substance from the
molding machine 17, to thereby adjust the agglomerated substance to a fluid content
percentage suitable for a heating reduction process (described later) (in other words, to a
fluid content percentage for each reduction furnace used for the manufacture of reduced
iron: for example, 1% or less). The agglomerated substance adjusted to a predetermined
fluid content percentage is carried to a reduction furnace 21 (described later).
[0023]
The reduction furnace 21 such as a rotary hearth furnace: RHF or a rotary kiln
heats and reduces the charged agglomerated substance under a heating atmosphere by use
of an LNG burner, COG burner, or the like into reduced iron. The reduction furnace
heats the agglomerated substance to, for example, approximately 1000 to 1300°C.
Thereby, the reduction furnace reduces the agglomerated substance to manufacture
reduced iron. The manufactured reduced iron is carried to a melting furnace 23.
[0024]
The melting furnace 23 melts the reduced iron, which is supplied in a form of, for
example, high-temperature pellets from the reduction furnace 21, into molten metal. The
molten metal thus produced in the melting furnace 23 is carried by use of ladles or the like,
and is then subjected to a desulfurization/refining treatment. After that, the treated
, molten metal is utilized as crude molten steel.
[0025]
•

Based on the above description, a manufacturing method of reduced iron
according to the present embodiment will be described in detail below.
[0026]
[Outline of manufacturing method of reduced iron according to present embodiment]
In the manufacturing method of reduced iron according to the present
embodiment, the agglomerated substance molded from the mixture of the iron oxide
material and the reducing agent is subjected to a heat/reduction treatment as described
above, to thereby manufacture reduced iron. The iron oxide material according to the
present embodiment may be appropriately selected from iron dust (for example, converter
dust that is produced in a converter for melting iron-containing cold charge, a converter
for refining, a converter for melting dust, or the like and is collected by a wet-type dust
collector or the like; dust from a blast furnace; mill scale; dust from an electric furnace; or
other dust), non-ferrous dust from smelting, and ore. As the reducing agent according to
the present embodiment, for example coal such as powder coal, coke, or carbon material
such as fine carbon may be used.
[0027]
Here, in the processes of manufacturing reduced iron of the present embodiment,
there were cases where, in the pelletization process using a pelletizing machine or, it was
not possible to completely agglomerate the mixture of the materials, leaving a powder.
Such remaining of a powder, prevents the improvement in pelletizing ability in the
pelletization process. Therefore, as a result of extensive investigation with a view to
| improving the pelletizing ability in the pelletization process, the present inventor arrived at
a conclusion that, with the addition of a fluid at a temperature of 60°C or higher and 90°C
or lower to the mixture of materials in the pelletization process, it is possible to improve
the pelletizing ability in the pelletization process.
[0028]
As will be described in detail later, the investigation by the present inventor has
made clear the following. Utilization of a fluid at a temperature of 60°C or higher and
90°C or lower in the pelletization process decreases the surface tension, increasing the
hydrophilicity. This activates the molecular movements, functioning as repulsive forces
among the molecules. This makes it possible to improve the penetrating ability of the
fluid into the mixture containing the iron oxide material and the reducing agent, and hence,
• to significantly improve the diffusional efficiency of the fluid into the mixture. With this
improvement in the diffusional efficiency, it is possible to make the distribution of the
fluid present in the mixture containing the iron oxide material and the reducing agent more
uniform than the conventional case, and hence, to improve the pelletizing ability at the
time of pelletization.
[0029]
Furthermore, as a result of the investigation by the present inventor, it has also
been revealed that utilization of a fluid at a temperature of 60°C or higher and 90°C or
lower in the pelletization process makes it possible to improve not only the pelletizing
ability but also improve the strength of the manufactured agglomerated substance more
than the conventional case. In the conventional manufacturing method of reduced iron as
described above, it has been a common practice to add various binders to the mixture
made of the oxide material and the reducing agent in order to improve the strength of the
agglomerated substance. However, with the addition of a fluid at a temperature of 60°C
or higher and 90°C or lower in the pelletization process is as the case with the
manufacturing method of reduced iron according to the present embodiment, the
diffusional efficiency of the fluid into the mixture significantly improves. This causes
the fluid to instantaneously penetrate deeper into the mixture. As a result, it is possible
to further improve the strength of the manufactured agglomerated substance without
increasing the amount of the added binder. Moreover, in the pelletization process, not
only the addition of a fluid at 60°C or higher and 90°C or lower but also the addition of a
binder to the mixture makes it possible to further improve the strength of the
manufactured agglomerated substance.
. [0030]
[Flow of manufacturing method of reduced iron according to present embodiment]
t
Hereunder is a detailed description of an exemplary flow of the manufacturing
method of reduced iron according to the present embodiment based on the knowledge as
described above, with reference to FIG. 2. FIG. 2 is a flow chart showing a flow of the
manufacturing method of reduced iron according to the present embodiment.
[0031]
In the manufacturing method of reduced iron according to the present
embodiment, an iron oxide material is firstly selected from the group consisting of iron
dust produced in the iron-making treatment and iron ore. The selected iron oxide is
mixed with a reducing agent (step S101), and is then charged from hoppers 11 into a
grinder mill 13. As a powder coal used for the reducing agent, for example one with a
minus-sieve 80% particle size of approximately 5 mm to 10 mm and with a fluid content
percentage of approximately 8 to 12% may be used. The combination ratio between the
iron oxide material and the reducing agent is adjusted in consideration of preferable
conditions for obtaining reduced iron favorable in a reduction process (described later).
It is possible to set the mass ratio between the iron oxide material and the reducing agent
to, for example, approximately 90:10. The mixture has a particle size of, for example,
approximately 4 mm when it is charged into the grinder mill.
[0032]
Subsequently, the mixture of the iron oxide material and the reducing agent is
ground by the grinder mill 13 to a particle size (minus-sieve 80% particle size) of, for
example, 70 um to 500 um, and preferably to a particle size of 150 um to 300 urn (step
SI03). With the mixture having a particle size of 70 um to 500 um, it is possible to
manufacture reduced iron high in degree of metallization and low in the variations in
degree of metallization (for example, not more than approximately 6%). In addition,
with the lower limit of its particle size being set to 70 um, it is possible to suppress the
explosive fracture of the agglomerated substance in the reduction process. Furthermore,
with the mixture having a particle size of 150 um to 300 um, it is possible to manufacture
reduced iron with a high degree of metallization and extremely low in the variations in
degree of metallization (for example, not more than approximately 3%). In addition,
with the lower limit of its particle size being set to 150 um, it is possible to avoid the
explosive fracture of the agglomerated substance in the reduction process.
[0033]
In the grinding process (step SI03), it is preferable that a fluid content percentage
of the mixture made of the iron oxide material and the reducing agent be adjusted to
approximately 1% to 3%. With this fluid content percentage, it is possible to maintain
favorable kneading ability in a kneading process (described later).
[0034]
As a grinder mill that grinds the mixture, for example, a vibrational mill such as a
ball mill or a rod mill may be used. To set the particle size of the mixture to the
aforementioned range and set the fluid content percentage of the mixture to approximately
1% to 3% on the outlet side of the vibrational mill such as a ball mill, the processing speed
of the ball mill or the like used for the grinding may be appropriately set. For example,
firstly a grinding ratio is calculated from the target value of the particle size on the outlet
side of the vibrational mill (ball mill) and the particle size on the inlet side of the
vibrational mill. Then, by utilizing the calculated grinding ratio and the theoretical curve
of grinding ability of the vibrational mill indicated at the target value of the fluid content percentage on the outlet side of the vibrational mill as described in Patent Document 1, it
is possible to determine the processing speed of the vibrational mill.
i
[0035]
In the manufacturing method of reduced iron according to the present
embodiment, the iron oxide material is dried before it is mixed. Therefore, it is possible j
to maintain the fluid content percentage of the mixture when the mixture is charged into
the grinder mill at a value at which the vibrational mill indicates a proper grinding ability.
This eliminates the necessity of constantly modifying the control over the vibrational mill at the time of grinding. Furthermore, even if the fluid content percentage of the iron
oxide material fluctuates due to various causes, it is possible to maintain the grinding
ability of the vibrational mill at a preferable value through appropriate control over the ;
settings of the drying machine 12 at the time of drying before mixture.
I
[0036]
After completion of the grinding of the mixture, the ground mixture is charged
into the kneading machine 15 such as a mix muller. After water is added to the mixture
so that the fluid content percentage is at a value proper for kneading (for example,
approximately 6 to 9%), the mixture is kneaded (step SI05). When the mixture is
kneaded, a predetermined binder may be added in order to improve the strength of the
manufactured agglomerated substance.
[0037]
Here, as described before, in the manufacturing method of reduced iron according
to the present embodiment, the fluid at a temperature of 60°C or higher and 90°C or lower
is utilized to adjust the fluid content percentage of the mixture. By utilizing this fluid, it
is possible to improve the penetrating ability of the fluid into the mixture, and hence, to
significantly improve the diffusional efficiency of the fluid into the mixture. This makes
it possible to make the fluid present in the mixture further uniform, and hence, to improve
the pelletizing ability at the time of pelletization.
[0038]
Furthermore, in the manufacturing method of reduced iron according to the
present embodiment, a fluid at a temperature of 60°C or higher and 90°C or lower is
utilized in a humidification treatment for adjusting the fluid content percentage. Thereby,
it is possible not only to improve the pelletizing ability but also to significantly improve
the strength of the manufactured agglomerated substance. Therefore, according to the
manufacturing method of reduced iron according to the present embodiment, it is possible
to enhance the strength of the manufactured agglomerated substance without increasing
the amount of the added binder.
[0039]
As a binder used in the kneading process, any binder may be used so long as it is
soluble in the fluid at 60°C or higher and 90°C or lower. Such binders include liquid-like
organic binders and powder-like organic binders. Examples of liquid-like organic binder
include molasses and lignin. Examples of powder-like organic binder include starch of
. • • ' •
• 12
grain such as rice, tapioca, rye, or corn. Of these organic binders, a powder-like one is
better than a liquid-like one because, if a binder is added in a slurry addition system to the
required fluid in the kneading process, viscosity is added, preventing good blending in the
kneading process. Organic blenders gasify at the time of reduction, contributing the
improvement in reduction. Therefore, especially a powder-like organic binder is
preferably utilized.
[0040]
Utilization of a binder soluble in the fluid at 60°C or higher and 90°C or lower
improves the solubility of the binder itself in the fluid, leading to an improvement in
dispersion efficiency of the binder. As a result, the binder itself spreads all over in the
mixture. This makes it possible to further improve the strength of the manufactured
agglomerated substance.
[0041]
In addition to the aforementioned organic binder, an inorganic binder such as
cement, bentonite, or fly ash may be further added.
[0042]
As for the amount of the binder to be added to the mixture, the more it is added,
the stronger the manufactured agglomerated substance can be made. However, from the
viewpoint of manufacturing costs, it is preferable that, when dry, the amount of the binder
be not more than 2% with respect to the whole mass of the mixture to be kneaded.
[0043]
On completion of the kneading by the kneading machine 15, the mixture is
charged into a molding machine 17, which is a pan pelletizer (disc-type pelletizing
machine), a double roll squeezer (briquetting machine), an extruder, or the like, where it is
pelletized (step SI07) into an agglomerated substance.
[0044]
The produced agglomerated substance is dried by the drying machine 19 so as to
have a fluid content percentage of, for example, not more than 1% (step SI09). The
dried agglomerated substance is charged into a reduction furnace 21 such as an RHF, •
i
where it is subjected to a reduction treatment. As a result of the use of a fluid at 60°C or
higher and 90°C or lower in the kneading process, the agglomerated substance according
to the present embodiment not only shows favorable pelletizability but also shows
favorable crushing strength. Therefore, also in the reduction process, the agglomerated
substance is unlikely to be cracked in the reduction furnace 21. This makes it possible to
sufficiently reduce the volume of the agglomerated substance. For example, in the case
of using an RHF as the reduction furnace 21, the temperature in the reduction furnace 21
may be set to, for example, approximately 1350°C, and the speed of the rotary hearth may
be set so that the reduction treatment finishes in approximately 15 minutes. With this
reduction treatment, it is possible to efficiently manufacture the reduced iron that is hard
to crack and is also high in degree of metallization.
[0045]
As described above, according to the manufacturing method of reduced iron
according to the present embodiment, it is possible not only to improve the pelletizing
ability in the pelletization process but also to manufacture the reduced iron that is hard to
crack and is high in degree of metallization. Therefore, it is possible to improve the
basic unit for oxygen used for the converter for melting reduced iron, and furthermore, to
maintain the productivity of molten metal at a high level.
Example
[0046]
Hereunder is a further description of the manufacturing method of reduced iron
according to the present invention with reference to examples and comparative examples. f
The examples shown below are only specific examples of the present invention. j
Therefore, the present invention is not limited only to the example shown below I
[0047] [
In the examples and comparative examples described below, an agglomerated I
substance was manufactured according to the procedure shown in FIG 2. In the grinding
process (step SI03), a ball mill (diameter x length: 3.3 m x 6.0 m, injection amount: 40
ton/h, motor capacity: 700 KW, ball: 49 ton) was used. In the kneading process (step
SI05), a mix muller was used. In the pelletization process (step SI07), a double roll
squeezer was used. In the drying process (step SI09), a band drying machine was used.
[0048]
In the examples and comparative examples described below, dust from a steel
plant including dust from a converter and dust from a blast furnace was used as an iron
oxide material, and coal was used as a reducing agent. Furthermore, in the examples and I
comparative examples described below, the iron oxide material and the reducing agent
were mixed so as to be in a mass ratio of 87:13, to thereby form a mixture. The mixture
t
had a particle size of not more than 300 urn with a minus-sieve 80% particle size. In the
water addition treatment in the kneading process, a fluid was added so that the mixture
had a fluid content percentage of 8.0%. The difference between the examples and the
comparative examples described below lies in the temperature of the fluid used in the
kneading process.
[0049]
[Penetration time of fluid into mixture]
Firstly, a change in the penetration time of fluids into the mixture will be
described with reference to FIG 3. ['
The penetration time of fluids into the mixture was measured as follows. Firstly,
20 g of the mixture, in which the iron oxide material and the reducing agent were mixed at j
the aforementioned ratio, before addition of water and kneading was collected. Then, to
this mixture, fluids corresponding to a fluid content percentage of 8% were added. At
this time, the time for the added fluid to completely penetrate into the mixture was [
l
(•
measured to obtain the penetration time. Here, the added fluids were at five different [
temperatures: 0°C, 15°C, 60°C, 80°C, and 90°C. FIG 3 shows relative periods of time [
with reference to the time for the fluid at 15°C to completely penetrate into the mixture.
[0050]
As is clear when reference is made to FIG 3, in the case where the fluid at 0°C in j
ice water was added, the penetration time of the fluid into the mixture was longer than that
of the case where the fluid at 15°C was added. In the case where the fluids at 60°C,
80°C, and 90°C were added, the penetration time of the fluid into the mixture was shorter
than that of the case where the fluid at 15°C was added. These show that the higher the
temperature of a fluid, the shorter the penetration time. As shown in FIG. 3, with the
addition of the fluid at 90°C to the mixture, the fluid penetrates in 60% of the time of the
case where the fluid at 15°C was added, revealing that the penetration time of the fluid
into the mixture was reduced by 40%. Thus, with the addition of a fluid at 60°C or
higher and 90°C or lower (in the present examples, fluids at 60°C, 80°C, and 90°C) to the
mixture, it is possible to significantly reduce the penetration time of a fluid into the
mixture.
[0051]
•
[Existence ratio of lumps]
Next is a description of a change in the ratio of the lumps present in the mixture ;
after kneading (and before pelletizing) with reference to FIG. 4. In the following
description, a "lump" refers to a clump with a particle size of not less than 5 mm that
remains when the mixture is sieved. In the present embodiment, four sets of mixtures
after kneading (and before pelletizing) to which fluids at four different temperatures: 15°C,
60°C, 80°C, and 90°C were respectively added were collected, and were then sieved.
After that, the total weight of the lumps containing the fluid with a particle size of not less
than 5 mm was measured. FIG. 4 shows ratios with reference to the weight of the lumps
in the case where the fluid at a temperature of 15°C was added in the kneading process.
[0052]
As is clear from FIG. 4, by utilizing fluids at temperatures of 60°C, 80°C, and
90°C in the kneading process, the existence ratios of lumps were lower than that of the
case where the fluid at a temperature of 15°C was utilized. In addition, it is shown that
the higher the temperature of the fluid is, the more the existence ratio of lumps decreases.
Furthermore, it is shown that by utilizing the fluid at 90°C in the kneading process, the
existence ratio of lumps is decreased to approximately 87% of that of the case where the
fluid at 15° was utilized. These results reveal that by utilizing a fluid at 60°C or higher
;
;
and 90°C or lower (in the present examples, fluids at 60°C, 80°C, and 90°C), the fluid
diffuses into the mixture more uniformly, thus actualizing the uniform distribution of the
fluid in the mixture and improving the pelletizing ability.
[0053]
[Dissolution ratio of cornstarch]
Next, in the present example, how the dissolution ratio of the cornstarch, which
had been utilized as an organic binder, into the fluid changed depending on the change in
temperature of the fluid was actually measured. In this measurement, 5.0 g of cornstarch
was added to 500 mL of fluids (fluids at four different temperatures: 20°C, 60°C, 80°C,
and 90°C), and the amount of unsolved solute (g) was measured, to thereby calculate the
dissolution ratio.
[0054]
The obtained results are shown in FIG. 5. As is clear from FIG. 5, while the
I'
ratio of the cornstarch dissolved in the fluid at a temperature of 20°C was 40%, the ratio of
the cornstarch dissolved in the fluid at a temperature of 60°C was approximately 48%, the
ratio of the cornstarch dissolved in the fluid at a temperature of 80°C was approximately
70%, and the ratio of the cornstarch dissolved in the fluid at a temperature of 90°C was
approximately 96%.
[0055]
These results show that, with the temperature of the fluid to be added in the
kneading process being set to 60°C or higher and 90°C or lower, the solubility of the
binder itself into the fluid improves, and also that, with the binder being dissolved in the
fluid, the dispersion efficiency of the binder improves.
[0056]
[Change in strength of agglomerated substance]
Next, crushing strengths of plural types of agglomerated substance after drying
were measured. The agglomerated substances were manufactured according to the
processes as described above. The measurement of crushing strength was taken f
according to the measurement method of crushing strength out of the measurement
•
*
methods of strength defined in JIS Z-8841.
[0057]
Crushing strength was measured on 14 types of agglomerated substances:
agglomerated substances to which fluids at temperatures of 15°C, 60°C, 80°C, 90°C,
120°C, 160°C, and 200°C were added; and agglomerated substances manufactured by
further adding (externally adding) 1% of cornstarch to the above mixtures and then adding
the fluids at the above temperatures. Other than theses, crushing strength was measured
similarly on an agglomerated substance manufactured by adding the fluid at 90°C to a
mixture whose amount of added binder was reduced by 13%, and on an agglomerated
substance manufactured by adding the fluid at 90°C to a mixture whose amount of added
binder was reduced by 21%. Note that the manufactured agglomerated substances had
an elliptic shape whose major radius is 20 to 30 mm.
[0058]
The obtained results are shown in FIG. 6. FIG. 6 shows relative strengths, where
a crushing strength for the case in which the fluid at 15°C is added to a mixture without an
added binder is regarded as 1.
[0059]
As is clear from FIG. 6, both in the case where a binder was not added and in the
case where a binder was added, the crushing strength significantly improved when the
added fluid was at a temperature of 60°C or higher. Thus, with an addition of a fluid at
60°C or higher in the kneading process, it is possible not only to improve the pelletizing
ability in the pelletization process, but also to improve the strength of the manufactured
agglomerated substance. Furthermore, both in the case where a binder was not added
and in the case where a binder was added, the crushing strength is at a substantially
constant value when the added fluid was at a temperature of 90°C to 200°C. Because, as
for the upper limit of the temperature of the fluid to be added to the mixture, the
dissolution ratio of the binder into the fluid in FIG. 5 is almost 100% when the fluid is at a
temperature of 90°C, and also because of the heatproof temperature of the facilities used
in the kneading process and the processes subsequent to the kneading process, because of
••• v.
f;
t )
• 18
equipment restrictions in the vapor supply facilities, and for other reasons, the optimal [
temperature of the fluid at which the strength of the manufactured agglomerated substance j
is improved is 60°C or higher and 90°C or lower.
[0060]
Next, attention is paid to the strength for the case where the fluid at 15°C was
added to the binder-added mixture and the strength for the case where the fluid at 90°C !
was added to the mixture whose amount of the added binder was reduced. As is clear
from FIG. 6, between the agglomerated substances to which fluids at the same temperature
of 90°C were added, reduction in the amount of additional binder results in decrease in
crushing strength. However, as is seen, the crushing strength of the agglomerated
substance whose amount of additional binder was reduced by 13% and to which the fluid
at 90°C was added had a value substantially the same as that of the crushing strength for
the case where the fluid at 80°C was added to the binder-containing mixture, and the
crushing strength of the agglomerated substance whose amount of additional binder was
reduced by 21% and to which the fluid at 90°C was added had a value substantially the
same as that of the crushing strength for the case where the fluid at 15° was added to the
binder-containing mixture. These results show that addition of the fluid at 60°C or
higher and 90°C or lower makes it possible to control the amount of binder to be added,
and suggest that by use of the manufacturing method of reduced iron according to the
present embodiment, it be possible to offer a wider variety of operations for manufacturing
reduced iron.
[0061]
While a preferred embodiment of the present invention has been described in
detail above with reference made to the attached drawings, the present invention is not
limited solely to the above-described embodiment. It is obvious that those with ordinary
skill in the field of art to which the present invention belongs can conceives variety of
modifications and corrections within the scope of the technical idea described in the
appended claims. Therefore, it is understood that these obviously belong to the technical
scope of the present invention as well.
Industrial Applicability
[0062]
According to the manufacturing method of reduced iron of the present invention,
it is possible to further improve the pelletizing ability when the mixture as a reduced iron
material is agglomerated.
•
Reference Symbol List
[0063]
11: hopper
•
12: drying machine
13: grinder mill
15: kneading machine
17: molding machine
19: drying machine
21: reduction furnace
23: melting furnace
':
%
J.

CLAIMS
1. A manufacturing method of a reduced iron, the method comprising:
a Icneading process of adding a fluid at 60°C or higher and 90°C or lower to a
mixture of an iron oxide material and a reducing agent, both of which are in a powder
form, and kneading the mixture;
a pelletization process of agglomerating the mixture after the kneading process
into an agglomerated substance; and
a reduction process of reducing the agglomerated substance after the pelletization
process, to thereby produce the reduced iron.
2. The manufacturing method of the reduced iron according to claim 1, wherein
in the kneading process, a binder soluble in the fluid is further added to the
mixture.
3. The manufacturing method of the reduced iron according to claim 2, wherein
the binder is a liquid-like organic binder or a powder-like organic binder.
4. The manufacturing method of the reduced iron according to claim 3, wherein
the binder is the powder-like organic binder, and is a starch of a grain selected
from group consisting of a rice, a tapioca, a rye, and a com.
5. The manufacturing method of the reduced iron according to claim 1, wherein
in the kneading process,, addition of the fluid sets a fluid content percentage of the
mixture to 6% to 9%.
6. The manufacturing method of the reduced iron according to claim 1, wherein
the mixture before kneaded in the kneading process has a minus-sieve 80%
particle size of 70 nm to 500 )xm.
21
7. The manufacturing method of the reduced iron according to claim 1, wherein
the mixture before the fluid is added thereto in the kneading process has a fluid
content percentage of 1% to 3%.