【DESCRIPTION】
【Invention Title】
METHOD FOR RECYCLING IRON-CONTAINING BY-PRODUCTS
DISCHARGED FROM COAL-BASED MOLTENIRONMAKING PROCESS, SYSTEM
THEREFOR, AND REDUCED IRON AGGLOMERATION SYSTEM
【Technical Field】
The present disclosure relates to a method and system
for effectively agglomerating by-products containing useful
materials such as iron and discharged in the form of dust
and sludge from a coal-based molten iron making process so
as to reuse the by-products in a reduced iron agglomeration
process.
In addition, the present disclosure relates to a
method for recycling agglomerated by-products, and more
particularly, to a method and system for recycling byproducts
in a reduced iron agglomeration process.
【Background Art】
A FINEX method, a coal-based molten iron making
method, includes a fluidized reduction process for reducing
fine iron ore, an agglomeration process for agglomerating
the reduced fine iron ore, and a melting furnace process
for melting the agglomerated and reduced iron ore in a
melting furnace including a coal filling layer. Certain
amounts of by-products are discharged from each of the
3
processes.
The by-products include large amounts of materials
usable in a molten iron making process, such as iron ore,
supplementary materials, and carbon-containing materials,
and it is economically desirable to recycle the by-products
in a molten iron making process. The by-products may be
collected in the form of sludge by using water or in the
form of dust without using water.
However, it is not easy to handle by-products
collected in the form of sludge because of moisture
contained in the by-products, and a pretreatment process is
necessary before recycling the by-products. That is, it is
necessary to remove moisture from sludge-type by-products
to some degree before recycling the sludge-type by-products,
and this requires a large amount of energy.
In addition, since such by-products have a
significantly small particle size, on the level of 100μm or
less, if the by-products are directly used in a molten iron
making process, most of the by-products may be blown off.
Therefore, because of such problems, by-products are
agglomerated and then recycled in a melting furnace process.
When by-products are recycled in a melting furnace
process, dust-type by-products are agglomerated and then
inserted into a melting furnace, and sludge-type by4
products are dried, agglomerated, and then inserted into a
melting furnace. However, since agglomerated by-products
have a low degree of room-temperature strength and a low
degree of high-temperature strength (hot strength), the
agglomerated by-products are easily broken during transfer
or at the moment the agglomerated by-products are inserted
into a melting furnace having a temperature of about
1,000°C. Particles broken from the agglomerated by-products
may be blown by a reducing gas of the melting furnace and
may be discharged in the form of dust or sludge, thereby
decreasing the efficiency of recycling. In addition, if
particles broken from the agglomerated by-products remain
in the melting furnace, the particles may fill pores of
large particles, and thus the permeability of the large
particles may be decreased.
To address these problems, binders are used to
improve the coupling strength of particles, or a hightemperature
heat treatment is performed as in a pelletizing
process. In this case, however, energy consumption and
manufacturing costs are increased, and the effects of
recycling are lowered.
Because of the above-mentioned problems, by-products
are limitedly reused in molten iron making FINEX systems,
and thus most collected by-products are provided to cement
5
plants requiring iron sources free of charge or are buried
underground. Therefore, technology for recycling byproducts
using a minimum amount of energy while preventing
breakage of agglomerated by-products is required.
【Disclosure】
【Technical Problem】
An aspect of the present disclosure may provide a
method and system for agglomerating by-products discharged
from a molten iron making process in the form of sludge and
dust so as to recycle the by-products.
An aspect of the present disclosure may also provide
a method and system for effectively recycling by-products
discharged in the form of sludge and dust by agglomerating
the by-products, mixing the agglomerated by-products with
reduced iron, and agglomerating the reduced iron mixed with
the agglomerated by-products.
【Technical Solution】
According to an aspect of the present disclosure,
there may be provided a method for recycling ironcontaining
by-products discharged from a molten iron making
process in the form of dust and sludge containing moisture,
the method including: agglomerating the by-products
discharged from the molten iron making process to form byproduct
compactions; and forming reduced iron compactions
6
by mixing reduced iron with the by-product compactions and
agglomerating the reduced iron mixed with the by-product
compactions.
The agglomerating of the by-products may include:
drying a portion or all of the sludge; preparing a byproduct
mixture having a predetermined moisture content by
mixing the dried sludge with the dust or with the dust and
remaining sludge; agglomerating the by-product mixture to
form agglomerated by-products; and drying the agglomerated
by-products to form by-product compactions.
The drying of the portion or all of the sludge may
include adding the dust to the portion or all of the sludge.
The by-product mixture may have a moisture content of
30 wt% or less.
The agglomerating may be performed by an agitating
and mixing method, a pelletizing method, a briquetting
method, or an extruding method, and the agitating and
mixing method may be performed at a speed of 200 rpm to 600
rmp for 30 minutes.
The by-product compactions may have a moisture
content of 5 wt% or less.
The drying of the agglomerated by-products may be
performed by a static drying method using a belt drier or a
grate dryer.
7
The by-product compactions may have an average
particle size of 1 mm to 10 mm.
After the drying of the agglomerated by-products, the
method may further include sorting the by-product
compactions to separate by-product compactions having a
particle size of 1 mm to 10 mm, and the by-product
compactions may have a strength of 0.5 kgf or greater when
having a particle size of 5 mm.
In the forming of the reduced iron compactions, the
by-product compactions and the reduced iron may be mixed at
a weight ratio greater than 0:10 but equal to or less than
9:1.
The reduced iron may be obtained by reducing iron ore
in a reduction furnace under a reducing atmosphere.
The forming of the reduced iron compactions may
include: reducing iron ore in a fluidized reduction furnace
under a reducing atmosphere so as to form reduced iron;
discharging the reduced iron through a reduction furnace
discharge pipe; storing the reduced iron in a reduced iron
tank; supplying the reduced iron from the reduced iron tank
to a forceful transfer tank through a reduced iron supply
pipe; and supplying the reduced iron to an agglomeration
device to agglomerate the reduced iron, wherein the byproduct
compactions may be supplied to one or more of the
8
above-listed operations and mixed with the reduced iron.
The by-product compactions may be transferred using
carrier gas, gravity, or a mechanical transfer unit, and
the method may further include mixing the reduced iron with
the by-product compactions by supplying the by-product
compactions to one or more of the fluidized reduction
furnace, the reduction furnace discharge pipe, and the
reduced iron tank.
In another example, the method may further include
mixing the reduced iron with the by-product compactions by
supplying the by-product compactions to one or both of the
reduced iron supply pipe and the forceful transfer tank.
In this case, the by-product compactions may be transferred
by a flow of carrier gas and supplied to the one or both of
the reduced iron supply pipe and the forceful transfer tank
after the carrier gas is removed from the by-product
compactions by a gas-solid separation method.
According to another aspect of the present disclosure,
there may be provided a system for agglomerating ironcontaining
by-products discharged from a molten iron making
process in the form of dust and sludge containing moisture,
the system including: a sludge dryer receiving the sludge
through a pipe and drying the sludge; a by-product
agglomeration device receiving the dust and the sludge
9
dried by the sludge dryer respectively through pipes and
mixing and agglomerating the dust and sludge to form
agglomerated by-products; and a compaction dryer receiving
the agglomerated by-products from the by-product
agglomeration device and removing moisture from the
agglomerated by-products to form by-product compactions.
The sludge dryer may include an additional pipe to
receive the dust and mix and dry the sludge and the dust.
The by-product agglomeration device may be an
agitating device, a briquetting device, a pelletizer, or an
extruder, and the by-product agglomeration device may
include an additional pipe through which the sludge
containing moisture is supplied.
The compaction dryer may be a belt dryer or a grate
dryer.
The system may further include a classifier sorting
the by-product compactions according to particle sizes of
the by-product compactions and returning fine or coarse byproduct
compactions to the by-product agglomeration device
through a pipe.
According to another aspect of the present disclosure,
there may be provided a system for agglomerating reduced
iron obtained by reducing fine iron ore in a molten iron
making process, the system including: a fluidized reduction
10
furnace reducing iron ore to produce reduced iron; a
reduced iron tank connected to the fluidized reduction
furnace through a reduction furnace discharge pipe and
storing the reduced iron discharged from the fluidized
reduction furnace; a forceful transfer tank connected to
the reduced iron tank through a reduced iron supply pipe
and supplying the reduced iron from the reduced iron tank
to an agglomeration device; a reduced iron agglomeration
device agglomerating the reduced iron supplied from the
forceful transfer tank; and a by-product supply pipe
through which by-product compactions produced by
agglomerating by-products discharged from a molten iron
making process are transferred to the reduced iron
agglomeration device.
The by-product supply pipe may be connected to at
least one selected from the group consisting of the
fluidized reduction furnace, the reduction furnace
discharge pipe, and the reduced iron tank. In another
example, the by-product supply pipe may be connected to at
least one selected from the group consisting of the reduced
iron supply pipe and the forceful transfer tank.
The system may further include a transfer unit
transferring the by-product compactions by using a flow of
carrier gas, gravity, or a mechanical device.
11
The system may further include: a transfer unit
transferring the by-product compactions by a flow of
carrier gas; and a gas compressor generating the flow of
carrier gas.
The system may further include: a transfer unit
transferring the by-product compactions by a flow of
carrier gas; and a gas-solid separator separating the
carrier gas from the by-product compactions by a gas-solid
separation method and then supplying the by-product
compactions to the by-product supply pipe. In this case,
the gas-solid separator may be a cyclone separator.
The system may further include a transfer unit
transferring the by-product compactions, wherein the
transfer unit may be a bucket elevator or a conveyer belt.
【Advantageous Effects】
According to exemplary embodiments of the present
disclosure, by-products discharged in the form of sludge
and dust from a molten iron making process such as a FINEX
process may be efficiently agglomerated according to
factors such as the amounts, particle characteristics, and
moisture contents of the sludge and dust.
In addition, according to exemplary embodiments,
sludge and dust, by-products discharged from a molten iron
making process, are mixed with each other and agglomerated
12
with reduced iron. Thus, the moisture content of the sludge
may be controlled when the sludge is recycled, and problems
such as the loss and permeability reduction of by-products
caused by breakage of by-product compactions may not occur
when by-products are agglomerated into compactions and
recycled.
In addition, according to other exemplary embodiments
of the present disclosure, by-products discharged from a
molten iron making process in the form of sludge and dust
are agglomerated as by-product compactions and then mixed
with reduced iron and agglomerated. Therefore, breakage of
the by-product compactions may be prevented when byproducts
are recycled.
Consequently, the loss of by-products may be
prevented, and the permeability of by-products may not be
lowered when the by-products are processed in a melting
furnace.
【Description of Drawings】
FIG. 1 is a process diagram illustrating an exemplary
process for agglomerating by-products discharged in the
form of sludge and dust from a molten iron making process.
FIG. 2 is a process diagram illustrating another
exemplary process for agglomerating by-products discharged
in the form of sludge and dust from a molten iron making
13
process.
FIG. 3 is a schematic process diagram illustrating a
reduced iron agglomeration process and points to which byproducts
discharged from a molten iron making process are
supplied to the reduced iron agglomeration process,
according to an exemplary embodiment of the present
disclosure.
FIG. 4 is a schematic process diagram illustrating a
reduced iron agglomeration process and points to which byproducts
discharged from a molten iron making process are
supplied to the reduced iron agglomeration process,
according to another exemplary embodiment of the present
disclosure.
FIG. 5 is a schematic process diagram illustrating
how by-products discharged from a molten iron making
process are recycled in a reduced iron agglomeration
process.
FIG. 6 is a schematic process diagram illustrating
how compactions formed of by-products discharged from a
molten iron making process are recycled in a reduced iron
agglomeration process.
FIG. 7 is a process diagram illustrating a process
for recycling by-products discharged from a molten iron
making process, according to an exemplary embodiment of the
14
present disclosure.
【Best Mode】
Hereinafter, exemplary embodiments will be described
in detail with reference to the accompanying drawings. The
disclosure may, however, be exemplified in many different
forms and should not be construed as being limited to the
specific embodiments set forth herein. In the accompanying
drawings in which exemplary embodiments are illustrated, at
least some elements or regions may be illustrated on an
enlarged or reduced scale.
Generally, by-products of molten iron making
processes include materials such as iron ore, supplementary
materials, and carbon-containing materials that are usable
in molten iron making processes. Therefore, such byproducts
may be reused in molten iron making processes. In
the related art, such by-products are recycled by a method
of agglomerating the by-products into compactions and
supplying the compactions to a melting furnace process.
However, since the room-temperature strength and hightemperature
strength (hot strength) of the compactions are
low, the compactions are broken into fine particles while
being transferred or at the time the compactions are
inserted into a melting furnace, thereby causing problems
such as floating dust, sludge loss, or a decrease of the
15
permeability of the compactions.
Thus, the inventors have repeatedly conducted
research into methods of efficiently recycling by-products
discharged from molten iron making processes and have found
that if by-products discharged in the form of sludge and
dust from a molten iron making process are agglomerated and
mixed with reduced iron to form reduced iron compactions,
the by-products may be efficiently recycled without
problems such as sludge loss or a decrease of the
permeability of the by-products caused by floating of the
by-products during a recycling process.
An exemplary embodiment of the present disclosure
provides a method of recycling by-products discharged from
a coal-based molten iron making process. In detail, the
method includes: forming pellets by agglomerating byproducts
discharged from a molten iron making process; and
mixing the pellets with reduced iron and agglomerating the
mixture.
According to the present disclosure, by-products
discharged in the form of sludge and dust from a coal-based
molten iron making process such as a FINEX process may be
recycled. For example, sludge and dust discharged from a
FINEX process may have the following compositions and
average particle sizes shown in Table 1.
16
[Table 1]
Properties Sludge Dust
Content
(wt%)
Total Fe 53.6 63.2
Metal Fe + Fe
oxides
74.8 83.0
C 8.4 2.1
CaO 3.9 5.1
MgO 0.7 1.4
Balance 12.2 8.4
Average Particle Size (μm) 6.5 8.2
*After about 33 wt% moisture is removed from sludge, the
contents of solid components in the sludge are shown.
* The content of metal Fe and Fe oxides includes the
content of total Fe.
* The balance refers to compounds of trace elements.
Referring to Table 1, the sludge and dust include
components such as iron oxides, carbon-containing chars,
and supplementary materials such as low-quality iron ores
to which carbon and supplementary materials are added. That
is, the sludge and dust include materials that may be
sufficiently reused in the FINEX process.
In addition, the by-products discharged from the
FINEX process have an average particle size of about 10 μm
or less (90% or more of the by-products by weight have a
particle size of 30μm or less), and the main components of
17
the by-products are iron oxides, coal chars, and oxides or
carbides of calcium (Ca) and magnesium (Mg).
If the by-products are agglomerated and then recycled,
dust may not float during transfer of the by-products,
thereby preventing a decrease of the processability of the
by-products and the loss of the by-products. The byproducts
discharged from the FINEX process may easily be
agglomerated because the by-products have the abovedescribed
particle size range and component contents, and
may easily be recycled because the by-products do not
undergo rapid physicochemical reactions at high
temperatures.
It is known that if such fine by-products are mixed
with reduced iron and agglomerated, the fine by-products
are not easily agglomerated because of the reduced iron.
Therefore, according to the present disclosure, by-products
are mixed with reduced iron after the by-products are
agglomerated. In this case, sludge or dust may be
agglomerated and then mixed with reduced iron. However, if
sludge and dust are mixed with each other and then
agglomerated and the agglomerated mixture of sludge and
dust is reduced iron, agglomeration may be more easily
performed.
The ratio of sludge and dust discharged from FINEX
18
processes is generally about 8:2 to about 7:3. That is,
sludge is generated in larger amounts than dust. In
addition, the content of moisture in sludge varies within
the range of about 25 wt% to 50 wt% according to the
discharged position of the sludge and the composition of
the sludge. Generally, water is added to dust so as to
prevent the dust from floating when the dust is discharged,
and thus the moisture content of dust is 15 wt% or less.
Such sludge and dust may be agglomerated and then
recycled as described above. Referring to FIGS. 1 and 2,
by-products may be agglomerated through a sludge drying
process, a by-product mixing process, an agglomeration
process, and a compaction drying process.
According to the present disclosure, by-products
discharged from a molten iron making process in the form of
sludge and dust are agglomerated. As shown in Table 1,
sludge and dust discharged from FINEX processes include
components such as iron oxides, carbon-containing chars,
and supplementary materials. Since the content of iron and
the content of carbon are 53.6% and 63.2%, respectively,
materials sufficiently reusable in FINEX processes may be
obtained from the by-products. Therefore, the mix ratio of
such by-products is not particularly limited but may be
appropriately determined. For example, if equal weights of
19
sludge and dust are mixed together, the total content of
iron is about 55 wt% or greater, and the total content of
carbon is about 4 wt%. Thus, the mixture of sludge and dust
may be suitably recycled.
The by-products may be agglomerated by drying a
portion or all of the sludge; preparing a by-product
mixture having a predetermined moisture content by mixing
the dried sludge with the dust or with the dust and
remaining sludge; agglomerating the by-product mixture to
form agglomerated by-products; and drying the agglomerated
by-products to form by-product compactions.
In this case, the sludge and dust may be agglomerated
by mixing the sludge and the dust and mechanically
processing the mixed sludge and dust. According to the
present disclosure, agglomeration may be performed using a
by-product agglomeration device, and non-limiting examples
of the by-product agglomeration device include an agitation
mixer such as an Eirich mixer, a pelletizer, a briquetting
device, or an extruder.
Although the moisture content in the by-product
mixture is varied according to a mechanical agglomeration
method used to agglomerate the by-product mixture, it may
be preferable that the moisture content in the by-product
mixture be within the range of 30 wt% or less.
20
The moisture content of the by-product mixture may be
adjusted by various methods. For example, since the sludge
and the dust have different moisture contents, the moisture
content in the by-product mixture may be adjusted by
varying the mix ratio of the sludge and the dust. In
addition, after the by-products having a sludge form, a
dust form, or a mixture form of sludge and dust are dried,
moisture may be added to the by-products or non-dried byproducts
may be added to the dried by-products so as to
adjust the moisture content of the by-product mixture.
Hereinafter, specific methods for adjusting the
content of moisture and agglomeration processes will be
described together with agglomeration devices.
If an agitation mixer such as an Eirich mixer is used
for agglomerating the by-product mixture, it may be
preferable that the total content of moisture in the byproduct
mixture be within the range of 10 wt% to 20 wt%. In
an agglomeration process performed by an agitating and
mixing method to form by-product compactions, the particle
size and apparent moisture content of the by-product
compactions are considerably affected by the total moisture
content of sludge and dust to be agitated. If a by-product
mixture having a moisture content within the abovementioned
range is agglomerated, when the by-product
21
mixture including sludge and dust is agitated, lumps of the
sludge may be pulverized, and moisture contained between
particles of the sludge may be exposed to surrounding dust.
Therefore, particles having a uniform size may be obtained.
In this case, the moisture content of the by-product
mixture may be adjusted within the above-mentioned range by
mixing the sludge and dust within a proper mix ratio range.
For example, the moisture content of the by-product mixture
may be decreased by adding more dust. The by-product
mixture may be agglomerated by an agitating and mixing
method, a pelletizing method, a briquetting method, or an
extruding method according to the moisture content of the
by-product mixture adjusted as described. By-product
agglomeration devices will be described later in more
detail. It may be necessary to dry by-products so as to
additionally adjust the moisture content of the by-products
according to the kind of by-product agglomeration device
used to agglomerate the by-products.
Although the present disclosure is not limited to
FINEX technology, most by-products discharged from molten
iron making processes using FINEX technology are in the
form of sludge having an excessive moisture content, and
thus it is difficult to agglomerate the by-products by an
agitating and mixing method. Even though dust having a
22
relatively low moisture content is mixed with the byproducts,
there is a limit to adjusting the content of
moisture to a proper value for agglomeration. In addition,
even if a proper moisture content is obtained by adding
more dust, since a large amount of sludge remains, there is
a limit to recycling the by-products.
To address this, some of the by-products may be dried
to remove moisture, and the dried by-products may be mixed
with remaining non-dried by-products. That is, a by-product
mixture of moisture-adjusted sludge and dust may be
agitated to obtain by-product compactions. In addition,
since the moisture content of dust is lower than a required
moisture content, dust may be directly supplied to an
agitation mixer to adjust the total moisture content.
For example, referring to FIG. 1, only a portion of
sludge 20 containing moisture may be dried using a sludge
dryer 240 to remove moisture, and then the dried sludge 20
may be fed into a by-product agglomeration device 230. In
addition, dust 30 and sludge 20 containing moisture may be
supplied to the by-product agglomeration device 230
respectively through supply pipes and may then be mixed
with the dried sludge 20 so that the moisture content of
whole by-products may be within a range of 10 wt% to 20 wt%.
Thereafter, the by-products may be agglomerated by an
23
agitating and mixing method.
The sludge dryer 240 for drying sludge 20 may be any
kind of dryer, and examples of the sludge dryer 240 include
a rotary kiln dryer, a fluidized bed dryer, and a belt
dryer. A drying process may be performed using air, a hot
blast stove, or a hot exhaust gas containing CO2.
Preferably, an agitation mixer having a speed range
of 200 rpm to 600 rpm, more preferably 350 rpm to 500 rpm,
may be used. If sludge 20 and dust 30 are agitated within
the speed range, the sludge 20 and dust 20 may be
agglomerated.
A time period for agitation is not particularly
limited, but may be within a range of 1 minute to 30
minutes. If the agitation time period is shorter than 1
minute, by-products may not be sufficiently agglomerated,
and the strength of agglomerated by-products may be
insufficient. On the other hand, if the agitation time
period is more than 30 minutes, it may be uneconomical
because additional effects are not obtained. For example,
by-products may be agglomerated by agitating the byproducts
for an agitation time period of 1 minute to 20
minutes, 2 minutes to 10 minutes, or 2 minutes to 6 minutes.
If by-products are agglomerated using a pelletizer,
it may be preferable that the moisture content of the by24
products be within a range of 5 wt% to 10 wt%. FIG. 2
illustrates an exemplary case in which a pelletizer is used
for agglomerating by-products.
Referring to FIG. 2, in a by-product agglomeration
process, all sludge 20 is fed into a sludge dryer 240 to
remove moisture from the sludge 20, and the dried sludge 20
is fed into a pelletizer, which is a by-product
agglomeration device 235, while dust 30 containing moisture
is supplied to the by-product agglomeration device 235 so
as to mix the dust 30 with the sludge 20. In this manner,
the total moisture content of by-products may be adjusted
within the above-mentioned range in the by-product
agglomeration process.
In this case, as described above, since the moisture
content of by-products is preferably 5 wt% to 10 wt% for
the case of using a pelletizer, a predetermined amount of
dust 30 may be supplied to the sludge dryer 240 together
with sludge 20 for reducing the moisture content of the byproducts,
and the remaining dust 30 may be supplied to the
by-product agglomeration device 235 for controlling the
moisture content of the by-products.
Alternatively, in a by-product agglomeration process,
a by-product agglomeration device 235 such as a briquetting
device or an extruder may be used so as to agglomerate by25
products while applying pressure to the by-products. In a
case in which a briquetting device is used, it may be
preferable that the moisture content of by-products be
within a range of 10 wt% or less, more preferably within a
lower range. In a case in which an extruder is used, it
may be preferable that the moisture content of by-products
be within a range of 10 wt% to 30 wt%.
Although the by-product agglomeration process using a
briquetting device or an extruder has not been described in
detail, those having ordinary skill in the art will easily
adjust the moisture content of by-products in the byproduct
agglomeration process according to an agglomeration
system used to perform the by-product agglomeration process,
and will easily manufacture by-product compactions by
referring to the descriptions given above with reference to
FIGS. 1 and 2.
According to the present disclosure, by-product
compactions may be made by agglomerating by-products using
a mixer as described above or using any other by-product
agglomeration device or method such as a mechanically
extruding method, an extruding method using a mold, or a
cohesion method using an inclined rotary fan or drum.
As illustrated in FIGS. 1 and 2, if necessary, in a
by-product agglomeration process, an additive 60 such as
26
water, a by-product having a different particle size, or a
binder may be supplied to the agglomerate system to
increase the strength of by-product compactions and the
recovery rate of by-products, and another by-product, ore,
or coal containing a large amount of iron or carbon may be
supplied to the agglomeration device to increase the
recycling efficiency of by-products.
In more detail, according to the present disclosure,
when by-products are agglomerated, at least one selected
from the group consisting of water, binders, and additives
may be added to the by-products.
Water may be added to by-products for easily mixing
the by-products and increasing cohesion between particles
of the by-products. A binder may be added to by-products
for improving the cohesive efficiency, room-temperature
strength, and high-temperature strength of compactions
formed of the by-products. An additive may be added to byproducts
for facilitating the reduction of iron oxides of
the by-products or increasing the iron content of the byproducts.
Examples of the binder include an inorganic
binder such as bentonite or water glass, and an organic
binder such as starch or molasses.
Examples of the additive include coal or carboncontaining
waste for facilitating the reduction of iron
27
oxides, and ores or iron-containing wastes for increasing
the content of iron. Alternatively, an additive such as
limestone or white mica may be added to the by-products so
as to facilitate the formation of slag in a later melting
process in which the by-products are mixed with reduced
iron.
According to the present disclosure, by-products
containing carbon may facilitate the reduction of iron
oxides included as main components in by-products of a
melter gasifier, and thus reduced iron having a low
reduction rate may also be recycled without causing
problems such as an increase in fuel costs. In this case,
if coal or waste containing carbon are additionally added,
the reduction of iron oxides may be markedly improved, and
thus the above-mentioned problems may be more surely
prevented.
According to exemplary embodiments of the present
disclosure, the moisture content of agglomerated byproducts
obtained through an agglomeration process may be
varied within a range of 30 wt% or less according to
process conditions. According to the present disclosure,
by-product compactions 90 obtained as described above may
be mixed with reduced iron in a reduced iron agglomeration
process so as to produce reduced iron compactions.
28
In this case, if the by-product compactions 90
supplied to the reduced iron agglomeration process have a
high moisture content, reduced iron may easily be reoxidized
by moisture contained in the by-product
compactions 90, and the formability of reduced iron
compactions may be lowered due to the generation of gas.
For this reason, the by-product compactions 90 obtained in
the by-product agglomeration process may be processed
through a compaction drying process.
In the drying process, preferably, the by-product
compactions 90 may be dried until the moisture content of
the by-product compactions 90 is decreased to less than 5
wt%. If the moisture content of the by-product compactions
90 is 5 wt% or higher, the reduction rate of reduced iron
may be undesirably lowered by 1% or more. Therefore, it may
be preferable that the moisture content of the by-product
compactions 90 be within a range of 5 wt% or less, and it
may be more preferable if the by-product compactions 90
have a lower moisture content.
Any kind of compaction dryer 245 may be used to dry
the by-product compactions 90. For example, the sludge
dryer 240 used to dry sludge 20 may be used. However, since
there is a possibility that the by-product compactions 90
may break into fine particles while being dried, a static
29
dryer such as a belt dryer or a grate dryer may be used
rather than using a dynamic dryer such as a rotary kiln
dryer or a fluidized bed dryer so as to prevent the byproduct
compactions 90 from breaking into fine particles.
According to exemplary embodiments of the present
disclosure, the by-product compactions 90 may be formed
using by-products discharged in the form of sludge 20 and
dust 30 from a molten iron making process. The by-product
compactions 90 produced as described above may be supplied
to a fine reduced iron agglomeration process so as to
produce reduced iron compactions by mixing the by-product
compactions 90 with reduced iron.
To produce reduced iron compactions as described
above, the by-product compactions 90 may be required to
have a proper degree of strength and a proper particle size
so that the by-product compactions 90 may not be broken
when being transferred to a reduced iron agglomeration
process. If the by-product compactions 90 have a strength
of 0.5 kgf or greater based on the case in which the byproduct
compactions 90 have a spherical particle shape
having a diameter of 5 mm, the by-product compactions 90
may be minimally broken when being transferred or stored.
The strength of the by-product compactions 90 may
preferably be 1 kgf or greater, and, more preferably, 2 kgf
30
or greater.
Since the by-product compactions 90 are more
effectively prevented from breaking in smaller pieces if
the by-product compactions 90 have a higher degree of
strength, the upper limit of the strength of the by-product
compactions 90 is set to a particular value. However, if
the by-product compactions 90 have an excessively high
degree of strength, it may be undesirable in terms of
process economics or energy consumption. Thus, the strength
of the by-product compactions 90 may be adjusted to be
equal to or less than 20 kgf, 10 kgf, 7 kgf, 5 kgf, or 3
kgf.
In addition, the particle size of the by-product
compactions 90 may preferably be within a range of 1 mm to
10 mm, but is not limited thereto. If the particle size of
the by-product compactions 90 is less than 1 mm, poor
formability may be caused when the by-product compactions
90 are mixed with reduced iron. Even if some of the byproduct
compactions 90 have a particle size less than 1 mm,
if a fraction thereof is controlled to be less than 50 wt%,
the formability of reduced iron compactions may be
maintained. Conversely, if the particle size of the byproduct
compactions 90 is greater than 10 mm, it may be
difficult to transfer the by-product compactions 90 and
31
supply the by-product compactions 90 to a reduced iron
agglomeration process.
Therefore, if necessary, the by-product compactions
90 may be sorted according to the particle size thereof so
as to separate by-product compactions having a particle
size within the above-mentioned range. To this end, the byproduct
compactions 90 may be sorted using a classifier 250.
After undergoing a sorting process using the
classifier 250, by-product compactions 90 having a particle
size within the above-mentioned range may be reused as
described above in a process such as a reduced iron
agglomeration process. In addition, fine by-product
compactions 95 having a particle size smaller than the
above-mentioned range may be supplied back to the byproduct
agglomeration device 230 or 235, and by-product
compactions 90 having a particle size greater than the
above-mentioned range may be broken into smaller pieces
having a particle size within the above-mentioned range by
using a crusher and may then be reused.
By-product compactions 90 produced as described above
may be mixed with reduced iron in a reduced iron
agglomeration process. In this manner, the by-product
compactions 90 may be reused. As described above, byproducts
are agglomerated by mixing the by-products with
32
reduced iron and are then supplied to a melting furnace,
thereby preventing secondary problems such as the loss of
the by-products or a decrease in the permeability of the
by-products caused by breakage of the by-products when the
by-products are recycled under a high-temperature
atmosphere.
Generally, a coal-based molten iron making method
includes a fluidizing reduction process in which fine iron
ore is reduced, an agglomeration process in which the
reduced fine iron ore is agglomerated into reduced iron
compactions, and a melting process in which the reduced
iron compactions are melted in a melting furnace. Among the
processes, the fluidizing reduction process and the
agglomeration process will now be schematically described
with reference to FIGS. 3 and 4.
Referring to FIGS. 3 and 4, fine iron ore is reduced
in a fluidized reduction furnace 110 to obtain reduced iron.
The fluidized reduction process using the fluidized
reduction furnace 110 is performed under a reducing
atmosphere at a high temperature of 600°C, and thus the
reduced iron has a high temperature of about 550°C to 850°C
after passing through the fluidized reduction furnace 110.
The reduced iron is discharged from the fluidized reduction
furnace 110 through a reduction furnace discharge pipe 115
33
and is then supplied to a reduced iron tank 120, for
example, by using a pressure difference.
Referring to FIG. 3, by-product compactions may be
mixed with the reduced iron having a high temperature while
making contact with the reduced iron for a sufficient time
period, and thus the by-product compactions may be heated
to a temperature similar to the temperature of the reduced
iron, thereby improving formability in the reduced iron
agglomeration process.
That is, as described above, the reduced iron to be
mixed with the by-product compactions is produced at a high
temperature of 600°C or higher, and thus has a temperature
within the range of 550°C to 850°C. In this case, although
the by-product compactions are rapidly heated to about
600°C while being mixed with the reduced iron, since the
by-product compactions are processed under high-temperature
conditions and have a very low moisture content and a small
particle size, the by-product compactions may not be
subjected to or undergo physiochemical reactions, thermal
impact, or breakage.
Therefore, the by-product compactions may be supplied
to the fluidized reduction furnace 110 in which the reduced
iron is produced, the reduction furnace discharge pipe 115
through which the reduced iron is discharged, or the
34
reduced iron tank 120 in which the reduced iron is
temporarily stored.
In addition, if the by-product compactions are
supplied to the fluidized reduction furnace 110, the
reduction furnace discharge pipe 115, or the reduced iron
tank 120 as described above, the by-product compactions may
be naturally mixed with the reduced iron because the
reduced iron is being moved to the position to which the
by-product compactions are supplied. In addition, the byproduct
compactions may be additionally mixed with the
reduced iron while the reduced iron is transferred to the
next equipment. Therefore, although an additional mixer for
mixing the by-product compactions with the reduced iron is
not used, the by-product compactions and the reduced iron
may be uniformly mixed together. If the reduced iron and
the by-product compactions are uniformly mixed with each
other, reduced iron compactions may easily be formed.
Thus, a by-product supply pipe 200 may be installed
so as to supply the by-product compactions to at least one
selected from the group consisting of the fluidized
reduction furnace 110, the reduction furnace discharge pipe
115, and the reduced iron tank 120.
The by-product compactions transferred as described
above may be mixed with the reduced iron by a pneumatic
35
method. For example, a high-pressure carrier gas may be
blown to transfer the by-product compactions to the reduced
iron by a steam of the carrier gas. The carrier gas may be
any kind of gas. For example, compressed air or nitrogen
gas may be used, or gases generated or discharged during a
FINEX process may be used. A gas compressor 380 may be used
to blow the carrier gas at a high pressure.
Alternatively, a storage bin may be installed at a
halfway point, and a predetermined amount of the by-product
compactions may be fed by gravity. In addition, a
mechanical device such as a bucket elevator or a conveyer
belt may be used for transferring and supplying the byproduct
compactions.
A mixture of by-product compactions and reduced iron
may be supplied to an agglomeration process through a
reduced iron supply pipe 125 by one or more of the abovedescribed
methods. In this case, if necessary, the mixture
of by-product compactions and reduced iron may be first
supplied to a forceful transfer tank 130, and then the
mixture may be forcefully supplied from the forceful
transfer tank 130 to a reduced iron agglomeration device
140 which agglomerates the mixture into reduced iron
compactions.
The reduced iron compactions obtained as described
36
above are finally inserted into a melter gasifier and
melted. In this manner, the by-products may be reused in a
molten iron making process.
Referring to FIG. 4, by-product compactions may be
supplied from the reduced iron tank 120 in the middle of an
agglomeration process. That is, the by-product compactions
may be supplied to the reduced iron supply pipe 125 through
which reduced iron is supplied from the reduced iron tank
120 to the forceful transfer tank 130. In addition, the byproduct
compactions may be supplied to the forceful
transfer tank 130 used to forcefully supply reduced iron.
After the reduced iron is supplied to the forceful
transfer tank 130 through the reduced iron pipe 125 as
described above, the reduced iron may be processed through
an agglomeration process. Therefore, the state of reduced
iron supplied to the reduced iron pipe 125 and the forceful
transfer tank 130 may be closely related with the
formability of reduced iron compactions. Therefore, during
an agglomerate process, the shape of reduced iron
compactions, that is, the formability of reduced iron
compactions may be observed to control the formability of
the reduced iron compactions by varying the supply amount
of by-product compactions. That is, the formability of
reduced iron compactions may be improved by rapidly taking
37
action according to process situations.
In addition, since by-product compactions are mixed
with reduced iron in a reduced iron agglomeration process
after the by-product compactions are minimally processed,
the breakage of the by-product compactions may be minimized,
and thus the formability of reduced iron compactions may be
further improved.
According to the above-described embodiments, the
temperature of reduced iron compactions is not sufficiently
increased. However, the formability of reduced iron
compactions may be improved by controlling the amount of
by-product compactions, and thus problems that may be
caused due to low-temperature conditions may be compensated
for.
As described above, by-product compactions may be
transferred to reduced iron by a pneumatic method using a
carrier gas and may be mixed with the reduced iron. In this
case, any kind of carrier gas may be used. For example,
compressed air or nitrogen gas may be used, or gases
generated or discharged during a FINEX process may be used.
Alternatively, a storage bin may be installed at a
halfway point, and a predetermined amount of the by-product
compactions may be fed by gravity. Alternatively, a
mechanical device such as a bucket elevator or a conveyer
38
belt may be used for transferring and supplying the byproduct
compactions.
A mixture of by-product compactions and reduced iron
may be supplied to the forceful transfer tank 130 as
described above and may then be supplied to the reduced
iron agglomeration device 140 to form reduced iron
compactions from the mixture.
The reduced iron compactions obtained as described
above are finally inserted into a melter gasifier and
melted. In this manner, by-products may be reused in a
molten iron making process.
As long as by-product compactions are obtained using
an existing by-product agglomeration device and are then
mixed with reduced iron at the above-described positions,
the present disclosure does not limit the kind or type of
by-product compactions.
According to the present disclosure, the mix ratio of
by-product compactions and reduced iron is not limited.
However, the mix ratio of by-product compactions and
reduced iron may be preferably greater than 0:10 but equal
to or less than 9:1. Since reduced iron is generally in the
form of particles of which surfaces are reduced as iron and
is kept at a high temperature of about 600°C, even though
the reduced iron is mixed with by-product compactions
39
within the above-mentioned mix ratio range, agglomeration
of the reduced iron may not be affected. The mix ratio of
by-product compactions and reduced iron may be more
preferably within a range of 1:9 to 4:6 by weight, and even
more preferably within a range of 1:9 to 3:7 by weight or
within a range of 1.5:8.5 to 2.5:7.5 by weight.
FIGS. 5 and 6 are schematic views illustrating a
method of forming reduced iron compactions by supplying byproduct
compactions to a reduced iron agglomeration process.
Referring to FIG. 5, dust and sludge, solid
substances of by-products discharged from a FINEX process,
are mixed with each other and agglomerated to form byproduct
compactions, and the by-product compactions are
supplied to a by-product tank 310 where the by-product
compactions are mixed and then discharged through a screw
feeder 320. The by-product compactions are transferred to a
by-product intermediate tank 330 using a bucket elevator
325 and are then transferred to a by-product pneumatic
transfer tank 340. Then, the by-product compactions are
discharged from the by-product pneumatic transfer tank 340
through a rotary feeder 350 and are supplied to a reduced
iron agglomeration process through a by-product supply pipe
200 by using a carrier gas blown from a gas compressor 380.
In the example shown in FIG. 5, the by-product
40
compactions are pneumatically transferred to the reduced
iron tank 120 in which reduced iron discharged from a
fluidized reduction furnace 110 is stored for an
agglomeration process. However, as described above, the byproduct
compactions may be supplied to the fluidized
reduction furnace 110 or a reduction furnace discharge pipe
115 through which reduced iron discharged from the
fluidized reduction furnace 110 is supplied to the reduced
iron tank 120 by a discharge pressure difference.
Referring to FIG. 6, dust and sludge, solid
substances of by-products discharged from a FINEX process,
are mixed with each other and agglomerated to form byproduct
compactions, and the by-product compactions are
supplied to a by-product tank 310 where the by-product
compactions are mixed and then discharged through a screw
feeder 320. The by-product compactions are transferred to a
by-product intermediate tank 330 using a bucket elevator
325 and are then transferred to a by-product pneumatic
transfer tank 340. Then, the by-product compactions are
discharged from the by-product pneumatic transfer tank 340
through a rotary feeder 350 and are supplied to a reduced
iron agglomeration process through a by-product supply pipe
200 by using a carrier gas blown from a gas compressor 380.
In this case, if the by-product compactions are
41
supplied to the reduced iron agglomeration process together
with the carrier gas, the reduced iron agglomeration
process may be negatively affected. Therefore, the carrier
gas may be separated from the by-product compactions by a
gas-solid separation method using a cyclone separator 360,
and then the by-product compactions may be temporarily
stored in a by-product supply tank 370 and then supplied to
the reduced iron agglomeration process through the byproduct
supply pipe 200 by using the rotary feeder 350. At
this time, the by-product compactions may be supplied
through the by-product supply pipe 200 by gravity or a
mechanical transfer device.
In the example shown in FIG. 6, when reduced iron
discharged from a fluidized reduction furnace 110 and
stored in a reduced iron tank 120 is supplied to a forceful
transfer tank 130 through a reduced iron supply pipe 125,
by-product compactions are supplied to the reduced iron
supply pipe 125. However, as described above, the byproduct
compactions may be supplied to the forceful
transfer tank 130 or both the reduced iron supply pipe 125
and the forceful transfer tank 130.
FIG. 7 illustrates an exemplary process of recycling
by-products discharged from a molten iron making process,
according to an exemplary embodiment of the present
42
disclosure.
Referring to FIG. 7, sludge 20 and dust 30 generated
from a molten iron making process are respectively stored
in a sludge tank 210 and a dust tank 220. Then, the sludge
20 and the dust 30 are mixed with each other at a weight
ratio of 1:1 and supplied to a by-product agglomeration
device 230. Before an agglomeration process is performed in
the by-product agglomeration device 230, a binder 50 and an
additive 60 may be added to the mixture of the sludge 20
and dust 30 so as to improve cohesive efficiency and
facilitate the reduction of iron.
The mixture of the sludge 20 and the dust 30 may then
be agglomerated into spherical by-product compactions. Then,
the by-product compactions may be optionally processed in a
compaction dryer 245 to remove moisture therefrom. If the
average particle size of the by-product compactions is not
within a proper range or not suitable for recycling, the
by-product compactions may be sorted using a classifier 250,
and fine by-product compactions may be supplied back to the
by-product agglomeration device 230 through a fine byproduct
recirculation pipe 255.
Thereafter, the by-product compactions are
transferred to a storage/supply device 260 and then to a
reduced iron tank 120 in which reduced iron obtained by
43
reducing fine ore 10 in a fluidized reduction furnace 110
is stored. In the reduced iron tank 120, the by-product
compactions and the reduced iron are mixed with each other
at a predetermined ratio.
Thereafter, a mixture of the by-product compactions
and the reduced iron is transferred to a reduced iron
agglomeration device 140 and is agglomerated using the
reduced iron agglomeration device 140. At this time, fine
particles of the reduced iron generated when the mixture is
agglomerated may be transferred back to the reduced iron
tank 120 through a fine reduced iron recirculation pipe 145.
Then, the rest of the agglomerated mixture is transferred
to a melter gasifier 150 and melted, and slag 70 and molten
iron 80 are discharged from the melter gasifier 150.
As described above, if the method and system of the
present disclosure are used, compactions formed of byproducts
discharged from a molten iron making process may
be recycled without the loss of the by-products or a
decrease in the permeability of the compactions caused by
breakage of the compactions.
【Mode for Invention】
EXAMPLES
Hereinafter, the present disclosure will be described
more specifically with reference to examples. The following
44
examples are for illustrative purposes only and are not
intended to limit the scope of the present invention.
Example 1
In Example 1, sludge and dust generated from a FINEX
process for making molten iron (molten iron making FINEX
process) were agglomerated through a by-product
agglomeration process shown in FIG. 1.
In detail, sludge 20 having a moisture content of
about 40 wt% and dust 30 having a moisture content of about
15 wt%, which were by-products discharged from a molten
iron making FINEX process, were prepared at a weight ratio
of 7:3.
Half the sludge 20 was supplied to the sludge dryer
(rotary kiln furnace) 240 in which the half of the sludge
20 was heated to remove moisture.
Then, the half of the sludge 20 which was heat-dried
was supplied to the by-product agglomeration device 230
being an agitation mixer, and the other half of the sludge
20 which was not dried was directly supplied to the
agitation mixture to mix the non-dried half of the sludge
20 with the dried half of the sludge 20. In addition, the
dust 30 was supplied to the agitation mixer.
The by-products (the sludge 20 and the dust 30) mixed
45
in the agitation mixer had a moisture content of about 18
wt% based on the total weight of the by-products.
The agitation mixer was continuously agitated at a
speed of 400 rpm for about 4 minutes to agglomerate the byproducts
as by-product compactions.
Thereafter, the by-product compactions were
transferred from the agitation mixer to the compaction
dryer 245 in which the by-product compactions were fully
dried, and the dried by-product compactions were sorted
using the classifier 250 to collect by-product compactions
90 having a particle size within a range of 1 mm to 10 mm.
The weight of the by-product compactions 90 was
measured to be about 85% of the weight of the by-products
supplied to the agitation mixer. In addition, the strength
of the by-product compactions 90 was about 1 kgf.
Example 2
In Example 2, sludge and dust generated from a molten iron
making FINEX process were agglomerated through a by-product
agglomeration process shown in FIG. 2.
The same by-products as the by-products used in
Example 1 were prepared from a molten iron making FINEX
process.
All sludge 20 was supplied to the sludge dryer
46
(rotary kiln furnace) 240, and the sludge 20 was heated in
the sludge dryer 240 to remove moisture.
The dried sludge 20 was supplied to the agglomeration
device 235 being a pelletizer, and dust 30 was also
supplied to the pelletizer. The by-products (the sludge 20
and the dust 30) mixed in the pelletizer had a moisture
content of about 5 wt% based on the total weight of the byproducts.
Water was supplied to the pelletizer to adjust the
moisture content of the by-products to be 8 wt%, and then
the by-products were agglomerated as pellets using the
pelletizer.
Thereafter, the pellets were transferred from the
pelletizer to the compaction dryer 245 in which the pellets
were fully dried, and the dried pellets were sorted using
the classifier 250 to collect pellets having a particle
size within the range of 1 mm to 10 mm.
The weight of the pellets (by-product compactions)
was measured to be about 95% of the weight of the byproducts
supplied to the pelletizer. In addition, the
strength of the by-product compactions was about 1.5 kgf.
Example 3
Equal weights of sludge and dust generated from a
47
molten iron making FINEX process and having the
compositions shown in Table 1 were mixed with each other
for about 3 minutes using an Eirich mixer. In this manner,
pellets having an average particle size of 2 mm were
obtained.
The pellets were dried in an oven dryer at 105°C for
24 hours to fully remove moisture from the pellets.
Thereafter, the pellets were mixed with reduced iron
at a weight ratio of 2:8 to form a mixture sample, and 100g
of the mixture sample was agglomerated at 600°C while
applying a pressure of 150 MPa to the mixture sample to
form disk-shaped compactions. Then, the compressive
strength of the disk-shaped compactions (sample) was
measured.
After excluding abnormal values, 10 measured values
were averaged. The average compressive strength is shown in
Table 2.
Comparative Example 1
The same reduced iron as that used in Example 3 was
agglomerated as disk-shaped compactions by the same method
as that used in Example 3, except that by-products were not
mixed with the reduced iron, and the compressive strength
of the disk-shaped compactions (sample) was measured. The
48
measured compressive strength is shown in Table 2.
[Table 2]
Sample Comparative Example 1 Example 3
Compressive
Strength (kg/cm2)
575 682
Referring to Table 2, the compressive strength of the
compactions prepared by mixing pellets (by-products) and
reduced iron with each other in Example 3 is greater than
the compressive strength of the compactions prepared only
using reduced iron in Comparative Example 1. Therefore,
when the compactions formed by mixing by-products and
reduced iron are inserted into a melting furnace, problems
such as breakage of the compactions may not be caused.
Example 4
Fine iron ore was reduced at about 750°C in the
fluidized reduction furnace 110 to obtain reduced iron.
Then, the reduced iron was discharged from the fluidized
reduction furnace 110 through the reduction furnace
discharge pipe 115 and was supplied to the reduced iron
tank 120 by a pressure difference.
Sludge and dust discharged from a molten iron making
FINEX process and having the compositions shown in Table 1
49
were mixed together and agglomerated at a weight ratio of
1:1 to obtain by-product compactions, and the by-product
compactions were stored in the by-product tank 310 shown in
FIG. 5.
Thereafter, the by-product compactions were
discharged from the by-product tank 310 using the screw
feeder 320 and transferred to the by-product intermediate
tank 330 using the bucket elevator 325.
Next, the by-product compactions were transferred to
the by-product pneumatic transfer tank 340 and were
discharged a predetermined amount at a time to the byproduct
supply pipe 200 connected to the reduced iron tank
120 by using the rotary feeder 350. High-pressure nitrogen
gas was blown to the reduced iron tank 120 through the byproduct
supply pipe 200 by the gas compressor 380.
The by-product compactions discharged to the byproduct
supply pipe 200 were transferred to the reduced
iron tank 120 by a stream of the nitrogen gas. At that time,
the by-product compactions were transferred to the reduced
iron tank 120 such that the content of the by-product
compactions in a mixture of the by-product compactions and
the reduced iron might be about 7 wt% based on the total
weight of the mixture.
Thereafter, the mixture of the by-product compactions
50
and the reduced iron was compressed using the reduced iron
agglomeration device 140 to form compactions.
The density and hot strength of the compactions were
compared with the density and hot strength of hot compacted
iron (HCI) formed of only reduced iron, and comparison
results are shown in Table 3.
After, a drum test was performed on the compactions
and the HCI at a temperature of 1000°C and a speed of 30
rmp, and the percentage (%) of particles having a size of
2.8 mm or less (fine particle percentage) that might
decrease the permeability of the compactions and the HCI
were measured as a factor of the hot strength of the
compactions and the HCI.
The percentage of particles having a size of 2.8 mm
or less (fine particle percentage) of the HCI was about 10%
before the drum test, and based on this fine particle
percentage, the variations of hot strength of the
compactions and the HCI could be estimated after the drum
test. A large variation of the fine particle percentage
indicates a low degree of hot strength.
[Table 3]
HCI Example 4
Density (g/cm3) 3.73 3.57
Fine Particle Percentage (%) 15 17
51
Referring to Table 3, although the compactions
prepared according to the present disclosure had the byproduct
compactions as impurities, the increase of the fine
particle percentage of the compactions was less than the
increase of the fine particle percentage of the HCI formed
of only reduced iron. That is, the hot strength of the
compactions of the present disclosure was substantially not
decreased when compared with the HCI.
Therefore, although the compactions including the byproduct
compactions are inserted into a melting furnace,
by-products may not break, and thus by-products may be
recycled without problems.
Example 5
Fine iron ore was reduced at about 750°C in the
fluidized reduction furnace 110 to obtain reduced iron.
Then, the reduced iron was discharged from the fluidized
reduction furnace 110 through the reduction furnace
discharge pipe 115 and was supplied to the reduced iron
tank 120 by a pressure difference.
Sludge and dust discharged from a molten iron making
FINEX process and having the compositions shown in Table 1
were mixed together and agglomerated at a weight ratio of
1:1 to obtain by-product compactions, and the by-product
52
compactions were stored in the by-product tank 310 as shown
in FIG. 6.
Thereafter, the by-product compactions were
discharged from the by-product tank 310 using the screw
feeder 320 and transferred to the by-product intermediate
tank 330 using the bucket elevator 325.
Next, the by-product compactions were transferred to
the by-product pneumatic transfer tank 340, and the byproduct
compactions were discharged to the gas supply pipe
355 through the rotary feeder 350. At the same time, highpressure
nitrogen gas was supplied from the gas compressor
380.
The by-product compactions transferred through the
gas supply pipe 355 using the nitrogen gas was supplied to
the cyclone separator 360 to separate the nitrogen gas from
the by-product compactions, and then the by-product
compactions were supplied by gravity to the reduced iron
supply pipe 125 through the by-product supply pipe 200
connected to the reduced iron supply pipe 125. At that time,
the by-product compactions were supplied such that the
content of the by-product compactions in a mixture of the
by-product compactions and reduced iron might be about 7
wt% based on the total weight of the mixture.
Thereafter, the mixture of the by-product compactions
53
and the reduced iron was compressed using the reduced iron
agglomeration device 140 to form compactions. The hot
strength of the compactions was measured as shown in Table
4.
The density and hot strength of the compactions were
compared with the density and hot strength of HCI formed of
only reduced iron, and results of comparison are shown in
Table 4.
After, a drum test was performed on the compactions
and the HCI at a temperature of 1000°C and a speed of 30
rmp, and the percentage (%) of particles having a size of
2.8 mm or less (fine particle percentage) that might
decrease the permeability of the compactions and the HCI
was measured as a factor of the hot strength of the
compactions and the HCI.
The percentage of particles having a size of 2.8 mm
or less (fine particle percentage) of the HCI was about 10%
before the drum test, and based on this fine particle
percentage, the variations of hot strength of the
compactions and the HCI could be estimated after the drum
test. A large variation of the fine particle percentage
indicates a low degree of hot strength.
[Table 4]
HCI Example 5
54
Density (g/㎤) 3.73 3.50
Fine particle percentage (%) 15 18
Referring to Table 4, although the compactions
prepared according to the present disclosure had the byproduct
compactions as impurities, the increase of the fine
particle percentage of the compactions of the present
disclosure was less than the increase of the fine particle
percentage of the HCI formed of only reduced iron. That is,
the hot strength of the compactions of the present
disclosure was substantially not decreased when compared
with the HCI.
Therefore, although the compactions including the byproduct
compactions are inserted into a melting furnace,
by-products may not break, and thus by-products may be
recycled without problems.

WE CLAIM:
【Claim 1】
A method for recycling iron-containing by-products
discharged from a molten iron making process in the form of
dust and sludge containing moisture, the method comprising:
agglomerating the by-products discharged from the
molten iron making process to form by-product compactions;
and
forming reduced iron compactions by mixing reduced
iron with the by-product compactions and agglomerating the
reduced iron mixed with the by-product compactions.
【Claim 2】
The method of claim 1, wherein the agglomerating of
the by-products comprises:
drying a portion or all of the sludge;
preparing a by-product mixture having a predetermined
moisture content by mixing the dried sludge with the dust
or with the dust and remaining sludge;
agglomerating the by-product mixture to form
agglomerated by-products; and
drying the agglomerated by-products to form byproduct
compactions.
【Claim 3】
The method of claim 2, wherein the drying of the
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portion or all of the sludge comprises adding the dust to
the portion or all of the sludge.
【Claim 4】
The method of claim 2, wherein the by-product mixture
has a moisture content of 30 wt% or less.
【Claim 5】
The method of claim 4, wherein the agglomerating is
performed by an agitating and mixing method, a pelletizing
method, a briquetting method, or an extruding method.
【Claim 6】
The method of claim 5, wherein the agitating and
mixing method is performed at a speed of 200rpm to 600rmp
for 30 minutes.
【Claim 7】
The method of claim 1, wherein the by-product
compactions have a moisture content of 5 wt% or less.
【Claim 8】
The method of claim 2, wherein the drying of the
agglomerated by-products is performed by a static drying
method using a belt drier or a grate dryer.
【Claim 9】
The method of claim 1, wherein the by-product
compactions have an average particle size of 1 mm to 10 mm.
【Claim 10】
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The method of claim 2, wherein after the drying of
the agglomerated by-products, the method further comprises
sorting the by-product compactions to separate by-product
compactions having a particle size of 1 mm to 10 mm.
【Claim 11】
The method of claim 1, wherein the by-product
compactions has a strength of 0.5 kgf or greater when
having a particle size of 5 mm.
【Claim 12】
The method of claim 1, wherein in the forming of the
reduced iron compactions, the by-product compactions and
the reduced iron are mixed at a weight ratio greater than
0:10 but equal to or less than 9:1.
【Claim 13】
The method of claim 1, wherein the reduced iron is
obtained by reducing iron ore in a reduction furnace under
a reducing atmosphere.
【Claim 14】
The method of claim 1, wherein the forming of the
reduced iron compactions comprises:
reducing iron ore in a fluidized reduction furnace
under a reducing atmosphere so as to form reduced iron;
discharging the reduced iron through a reduction
furnace discharge pipe;
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storing the reduced iron in a reduced iron tank;
supplying the reduced iron from the reduced iron tank
to a forceful transfer tank through a reduced iron supply
pipe; and
supplying the reduced iron to an agglomeration device
to agglomerate the reduced iron,
wherein the by-product compactions are supplied to
one or more of the above-listed operations and mixed with
the reduced iron.
【Claim 15】
The method of claim 14, wherein the by-product
compactions are transferred using carrier gas, gravity, or
a mechanical transfer unit.
【Claim 16】
The method of claim 14, further comprising mixing the
reduced iron with the by-product compactions by supplying
the by-product compactions to one or more of the fluidized
reduction furnace, the reduction furnace discharge pipe,
and the reduced iron tank.
【Claim 17】
The method of claim 14, further comprising mixing the
reduced iron with the by-product compactions by supplying
the by-product compactions to one or both of the reduced
iron supply pipe and the forceful transfer tank.
59
【Claim 18】
The method of claim 17, wherein the by-product
compactions are transferred by a flow of carrier gas and
supplied to the one or both of the reduced iron supply pipe
and the forceful transfer tank after the carrier gas is
removed from the by-product compactions by a gas-solid
separation method.
【Claim 19】
A system for agglomerating iron-containing byproducts
discharged from a molten iron making process in
the form of dust and sludge containing moisture, the system
comprising:
a sludge dryer receiving the sludge through a pipe
and drying the sludge;
a by-product agglomeration device receiving the dust
and the sludge dried by the sludge dryer respectively
through pipes and mixing and agglomerating the dust and
sludge to form agglomerated by-products; and
a compaction dryer receiving the agglomerated byproducts
from the by-product agglomeration device and
removing moisture from the agglomerated by-products to form
by-product compactions.
【Claim 20】
The system of claim 19, wherein the sludge dryer
60
comprises an additional pipe to receive the dust and mixes
and dries the sludge and the dust.
【Claim 21】
The system of claim 19, wherein the by-product
agglomeration device is an agitating device, a briquetting
device, a pelletizer, or an extruder.
【Claim 22】
The system of claim 19, wherein the by-product
agglomeration device comprises an additional pipe through
which the sludge containing moisture is supplied.
【Claim 23】
The system of claim 19, wherein the compaction dryer
is a belt dryer or a grate dryer.
【Claim 24】
The system of claim 19, further comprising a
classifier sorting the by-product compactions according to
particle sizes of the by-product compactions and returning
fine or coarse by-product compactions to the by-product
agglomeration device through a pipe.
【Claim 25】
A system for agglomerating reduced iron obtained by
reducing fine iron ore in a molten iron making process, the
system comprising:
a fluidized reduction furnace reducing iron ore to
61
produce reduced iron;
a reduced iron tank connected to the fluidized
reduction furnace through a reduction furnace discharge
pipe and storing the reduced iron discharged from the
fluidized reduction furnace;
a forceful transfer tank connected to the reduced
iron tank through a reduced iron supply pipe and supplying
the reduced iron from the reduced iron tank to an
agglomeration device;
a reduced iron agglomeration device agglomerating the
reduced iron supplied from the forceful transfer tank; and
a by-product supply pipe through which by-product
compactions produced by agglomerating by-products
discharged from a molten iron making process are
transferred to the reduced iron agglomeration device.
【Claim 26】
The system of claim 25, wherein the by-product supply
pipe is connected to at least one selected from the group
consisting of the fluidized reduction furnace, the
reduction furnace discharge pipe, and the reduced iron tank.
【Claim 27】
The system of claim 25, wherein the by-product supply
pipe is connected to at least one selected from the group
consisting of the reduced iron supply pipe and the forceful
62
transfer tank.
【Claim 28】
The system of claim 25, further comprising a transfer
unit transferring the by-product compactions by using a
flow of carrier gas, gravity, or a mechanical device.
【Claim 29】
The system of claim 25, further comprising:
a transfer unit transferring the by-product
compactions by a flow of carrier gas; and
a gas compressor generating the flow of carrier gas.
【Claim 30】
The system of claim 27, further comprising:
a transfer unit transferring the by-product
compactions by a flow of carrier gas; and
a gas-solid separator separating the carrier gas from
the by-product compactions by a gas-solid separation method
and then supplying the by-product compactions to the byproduct
supply pipe.
【Claim 31】
The system of claim 30, wherein the gas-solid
separator is a cyclone separator.
【Claim 32】
The system of claim 28, further comprising a transfer
unit transferring the by-product compactions, wherein the
63
transfer unit is a bucket elevator or a conveyer belt.