SPECIFICATION
TITLE OF INVENTION
METHOD OF PRODUCING SINTER
5 Field of the Invention
[0001]
The present invention relates to a method of producing a sinter. Particularly,
the present invention relates to a method of producing a sinter capable of decreasing NOx
which is contained in exhaust gas while securing or improving productivity.
10 Priority is claimed on Japanese Patent Application No. 2010-93334, filed April
14, 2010, the content of which is incorporated herein by reference.
Description of Related Art
[0002]
15 When a sinter is produced at steelworks, nitrogen oxide (NOx) occurs in exhaust
gas due to combustion of carbonaceous materials which are used as a fuel. A decrease
of NOx is an important solution in improvement of air pollution. As a method which
decreases NOx, there is an exhaust gas denitrification technology which uses ammonia as
a reducing agent.
20 However, in exhaust gas denitrification equipment according to the
above4escribed technology, operating costs are high since construction costs and the
ammonia are expensive. In addition, there is also a method in which anthracite having
low nitrogen content is used. The use of the anthracite having low nitrogen content is
limited since mining conditions have deteriorated due to a drain on resources.
25 [0003]
On the other hand, as a method of producing the sinter, in Patent Citation t, a
technique is disclosed in which NOx is removed by a catalyst of CaO^Fe O based
composite oxide which includes 5 to 50 wt.% of CaO, as a main component. In Patent
Citation 1, granules (S type) in which the catalyst is coated on the surfaces of coarse coke
5 particles or granules (P type) in which fine coke particles and fines of the catalyst are
mixed are used as a sintering feed.
In addition, in Patent Citation 2, a method is disclosed in which a granular
carbon source and a binder are mixed and granulated and a sinter containing carbon is
produced using a nowcombustion lumpy carbon source covered with the binder on the
10 surface of the mixture.
Patent Citation
[0004]
[Patent Citation t] Japanese Unexamined Patent Application, First Publication
t5 No. H8-60257
[Patent Citation 2] Japanese Unexamined Patent Application, First Publication
No. 2001-262241
SUMMARY OF THE INVENTION
20 Problems to be Solved by the Invention
[0005]
However, in Patent Citation 1, in the case of the technology in which NOx is
removed by the granules (P type) in which the fine coke particles and the fines of the
catalyst are mixed, there is a problem in that a decrease in the amount of NOx is small in
25 a low temperature region of 1,000°C or less . As described below, a large amount of
3
NOx is formed by the combustion of the coke in a low temperature region. Thereby, it
is considered that the fine coke particles in the granules (P type) are combusted in a low
temperature region and a large amount of NOx is formed, and the removal effect ofNOx
decreases. On the other hand, at the case of the technology in which NOx is removed
5 by the granules (S type) in which the catalyst is covered on the surfaces of the coarse
coke particles, if the coke surfaces are sufficiently coated with the catalyst, the
combustion rate of the coke becomes slow; and productivity of a sintering machine is
impeded.
Thereby, the coke surface should be covered with the catalyst so that a portion of
10 the coke surface is exposed, and therefore, there is a problem in that the removal effect of
NOx decreases. Moreover, since the granules are granulated with an iron ore using a
large granulator, when the amount of CaO is 5 to 50 wt.%, there is a concern that a
mixing degree or a coating area of CaO^Pe O based composite oxide catalyst may
decrease.
15 In addition, in Patent Citation 2, since almost none of the carbon source in the,
nomcombustion lumpy carbon source is combusted at the time of the sintering, it is
considered that the binder acts hardly as a catalyst even when the binder in the
non-combustion lumpy carbon source is capable of catalysis. Moreover, in Patent
Citation 2, in addition to the nowcombustion lumpy carbon source, coke is needed as a
20 sintering feed (fuel), and alarge amount of carbon sources is needed.
[0006]
An object of the present invention is to provide a method of producing a sinter
capable of (1) suppressing emission of NOx in a low temperature region and (2)
sufficiently securing or improving productivity of a sintering machine.
25
Methods for Solving the Problem
[0007]
(1) In a method of producing a sinter according to an aspect of the present
invention, a surface-coated carbonaceous material is included in a coal blend as a fuel for
5 sintering. The surface-coated carbonaceous material is coated with a coating including
36 mass% or more of Ca derived from a lime-based material on the surface of a
carbonaceous material at a ratio of more than 2 mass% and less than 50 mass% with
respect to the carbonaceous material.
(2) In the method of producing a sinter according to (1), the coal blend may
10 include 10 mass% to 100 mass% of the surface-coated carbonaceous material.
(3) in the method of producing a sinter according to (1) or (2), the lime-based
material may be calcium hydroxide, and the coating may include 67 mass% or more of
calcium hydroxide.
(4) In the method of producing a sinter according to (1) or (2),-a layer thickness
15 of the coating may be 5 μm or more and 500 μm or less on the surfaces of 0.25 mm or.
more of carbonaceous material in the carbonaceous material.
(5) The method of producing a sinter according to (1) or (2) may include:
mixing and granulating blend materials including iron ore, return fines, and an auxiliary
material; and then adding the surface-coated carbonaceous material to the mixed and
20 granulated blend materials and mixing the surface-coated carbonaceous material and the
mixed and granulated blend materials.
(6) The method of producing a sinter according to (1) or (2) may include adding
the surface-coated carbonaceous material to blend materials including iron ore, return
fines, and an auxiliary material and mixing the surface-coated carbonaceous material and
25 the blend materials after a half or more of the total mixing and granulating time elapses
S
when the blend materials are mixed and granulated , when blend materials which include
an iron ore, return fines, and an auxiliary material are mixed and granulated, the
surface-coated carbonaceous material may be added to and mixed into the blend
materials after a half or more of the total mixing and granulating time elapses.
(7) In the method of producing a sinter according to (1) or (2), the carbonaceous
material may have a size distribution in which there are 20 mass% or less of particles
having a particle size of less than 0.5 mm and 40 mass% or more of particles having a
particle size of 0.5 mm or more and 3 mm or less.
10 Effects of the Invention
[0008]
By controlling the combustion of the carbonaceous material, at the time of the
production of the sinter, formation of NOx is suppressed and productivity of the sintering
machine can be sufficiently secured and improved.
15
BRIEF DESCRIPTION OF THE DRAWINGS
[0009]
FIG. I is a graph showing a relationship between NOx conversion and
temperature.
20 FIG. 2 is a graph showing a relationship between particle size (diameter) of coke
and amount of formed NOx.
FIG. 3 is a.schematic view of an apparatus for pot test.
FIG. 4 is a graph showing a relationship between amount of a coating and Ca
concentration in a coating layer, and NOx conversion (i1NO).
25 FIG. SA is a photomicrograph of surface- coated coke including a coating layer
6
having a layer thickness of 500 μm or less which is used in a pot test.
FIG. SB is a photomicrograph of surface-coated coke including a coating layer
having alayer thickness more than 500 μm which is used in a pot test.
FIG. 6 is a graph showing a relationship between layer thickness of the coating
S and NOx conversion.
FIG. 7 is a graph showing a relationship between a kind of the coating and a
ratio of the cohesive coating.
FIG. 8 is a graph showing a relationship between feeding time of the
surface-coated coke and NOx conversion.
10 FIG. 9 is a graph showing a relationship between blending ratio of the
surface-coated coke with respect to total coal blend and NOx conversion.
FIG. 10 is a graph showing a relationship between kind of the coating layer and
productivity of the sinter:
FIG. 11 is a schematic view showing a process corresponding to an addition
15 before granulation.
FIG. 12 is a schematic view showing a process corresponding to an addition
after granulation.
FIG. 13 is a view showing an EPMA analysis result in a case where a normal
coke is added to other blend materials before a first mixer.
20 FIG. 14 is a view showing an EPMA analysis result of the surface-coated coke in
a case where the surface-coated coke is added to other blend materials before the first
drum mixer.
FIG 15 is a view showing an EPMA analysis result of the surface-coated coke in
a case where the surface-coated coke is added to other blend materials at a latter half of a
25 second drum mixer.
7
FIG. 16 is a graph showing test results of an actual operation test.
DETAILED DESCRIPTION OF THE INVENTION
[0010]
5 Hereinafter, a preferable embodiment of the present invention will be described
with reference to the accompanying drawings.
FIG I shows a relationship between NOx conversion and temperature due to
coke combustion.
[0011]
10 The NOx conversion is aratio (mole percentage) in which nitrogen atoms in
combusted fuel are converted into NOx. Specifically, the NOx conversion is calculated
by Equation (1) described below.
[0012]
Mainly, nitrogen in a carbonaceous material is oxidized at the time of sintering
15 and NOx forms. Particularly, as show in FIG 1, it is confirmed that a large amount of
NOx forms at a low temperature of 1,000°C or less. Therefore, in order to suppress
formation of NOx, it is important to combust the carbonaceous material at a high
temperature as far as possible.
Here, the carbonaceous material indicates coke, anthracite, and other solid fuel
20 used for producing the sinter.
[0013]
Moreover, fines in the carbonaceous material are combusted at a low
temperature, which increases NOx. FIG. 2 shows a relationship between a particle size
of the carbonaceous material (particle size of coke) and an amount of formed NOx. It is
25 considered that NOx increases since a combustion rate of the fines in the carbonaceous
8
material is rapid and the combustion is completed at a low temperature. Thereby, it is
considered that the amount of formed NOx decreases if the fine carbonaceous material
having a particle size of 0.5 mm or less can be removed.
[0014]
5 Specifically, in order to further decrease the amount of formed,NOx in the
sintering process, the mass percentage of the carbonaceous material (particles) having a
particle size of more than 0 mm and less than 0.5 mm is preferably 20 mass% or less,
more preferably 11 mass% or less, and most preferably 5 mass% or less. The reason is
because a large amount of NOx forms from the carbonaceous material having a particle
10 size of less than 0.5 mm as shown in FIG 2.
Moreover, the mass percentage of the carbonaceous material (particles) having a
particle size of 0.5 mm or more and 3 mm or less is preferably 40 mass% or more, and
more preferably 70 mass% or more. This s because it is possible to decrease a
combustion time in a low temperature region and to secure or improve productivity of the
15 sintering sufficiently while effects of decrease of NOx are secured since the
carbonaceous material having a particle size of 0.5 mm or more and 3 mm or less has a
sufficient combustion rate (combustion efficiency). Thereby, it is preferable to use the
carbonaceous material having the above-described size distribution. In addition, if the
particle size of the carbonaceous material increases too much, the combustion rate
20 decreases, the combustion time in a low temperature region increases easily, and effects
of the decrease of NOx approach a limit. An upper limit or a. lower limit of each class
in the size distribution is not particularly limited, the upper limit is 100 mass% and the
lower limit is 0 mass%.
[0015]
25 Although the fines (for example, less than 0.5 mm) are removed from the
9
carbonaceous material, in order to suppress the formation of NO is necessary to
combust the carbonaceous material at a high temperature as much as possible. Thereby,
if the surface of the carbonaceous material is covered with a coating layer (coating)
which melts in a high temperature region and ambient atmospheric oxygen can be
5 blocked at a low temperature region, the formation of NOx can be suppressed.
In Patent Citation 1, NOx which forms at the time of the combustion is reduced
or decomposed and removed by the catalysis of the CaO-Fe^O based composite oxide
using the carbonaceous material in which the CaO-Fe O based composite oxide
including 5 to 50 wt.% of CaO is coated on the surface. In the CaO-FexO based
10 composite oxide in which the amount of CaO is limited to 50 mass% or less, since the
melting point of the composite oxide is low and the composite oxide melts at a high
temperature of 1200°C or more, the effects of decrease of NOx is partly expected when
the composite oxide is covered on the surface of the carbonaceous material. However,
since the lime-based material and the iron ore are formed.so as to be melted and the
15 CaO-Fe^O based composite oxide is produced, the composite oxide is expensive
compared to the lime-based material which is used as the auxiliary material in a normal
sintering.
In the embodiment, the lime-based material which is used as the auxiliary
material in a normal sintering is used as the coating of the surface of the carbonaceous
20 material without using the expensive oxide described above. Particularly, in the
embodiment, a surface-coated carbonaceous material on which a coating including 35
mass% or more of Ca is coated is used in at least a portion of a coal blend which is
charged into a sintering machine as a fuel, and therefore, NOx formed at the time of
combusting the carbonaceous material can decrease. Here, the coal blend is a
25 carbonaceous material which is mixed with the sintering feed (blend materials) other than
10
the coal blend before being charged into the sintering machine and is used as a solid fuel
(sintering fuel).
In the embodiment, it is preferable that the coating layer on the surface of the
carbonaceous material include at least one kind selected from a group consisting of
5 calcium hydroxide, calcium carbonate, calcium oxide, and calcium fluoride. In this
case, for example, lime-based materials such as calcium hydroxide (slaked lime), calcium
carbonate (limestone), milk of lime, and fluorite and mixtures thereof can be used.
Since the lime-based material easily reacts with iron ore fines which exist in the
periphery at a high temperature and forms calcium ferrite having a low melting point, the
10 lime-based material functions as a solvent. If the calcium ferrite melts at a high
temperature, since oxygen is supplied to the surface of the carbonaceous material, the
combustion of the carbonaceous material is promoted, and the carbonaceous material can
be combusted at a high temperature. Moreover, a solid ash which remains on the
surface during the combustion of the carbonaceous material dissolves in the calcium
15 ferrite (melt), which further promotes the combustion of the carbonaceous material at a
high temperature. It is more preferable that the lime-based material contained in the
coating layer be calcium hydroxide. Since calcium hydroxide acts as a binder and a
coating layer which strongly adheres the surface of the carbonaceous material is formed,
at the time of the mixing with other blend materials and in a transportation process up to
20 charging of the materials into the sintering machine, separation of the coating of the
surface of the carbonaceous material can be suppressed.
It is preferable that the coating of the surface of the carbonaceous material
contain 36 mass% or more of Ca derived from a lime-based material. When the amount
of Ca in the coating is less than 36 mass%, since a reaction rate between the iron ore
25 around the coating and the coating (lime-based material in the coating) is not sufficient,
11
the melt reaction on the surface of the carbonaceous material becomes slow, and the
effects decrease which promote the combustion of the carbonaceous material at a high
temperature.
When the calcium hydroxide is used in the lime-based material, the coating
5 contains preferably 67 mass% or more of calcium hydroxide, and more preferably 100
mass% of calcium hydroxide. In addition, when calcium carbonate, milk of lime,
fluorite, or the like are used as the lime-based material, the coating contain preferably 90
mass% or more of these lime-based materials or mixtures thereof, and more preferably
100 mass% of these lime-based materials or mixture thereof.
10 [0016]
Since NOx forms by the combustion of the carbonaceous material at a low
temperature of 1,000°C or less, in order to suppress the formation of NOx at the time of
sintering, it is necessary to combust the carbonaceous material at a high temperature as
far as possible while suppressing the combustion of the carbonaceous material at a low
15 temperature.
Since the surface of the carbonaceous material is coated with the coating layer in
a low temperature region of 1,000°C or less, the combustion of the carbonaceous
material is suppressed and the formation of the NOx can be suppressed. However, in
the high temperature region of 1,200°C or more, CaO derived from the lime-based
20 material in the coating layer reacts with the ores around the CaO, and the melt of the
calcium ferrite having a low melting point is formed and runs down. At this time, the
solid ash which exists on the surface of the carbonaceous material can be absorbed into
the melt. In this way, when the coating layer of the surface of the carbonaceous
material forms the melt of the calcium ferrite, since the combustion temperature of the
25 carbonaceous material has already reached the high temperature region of 1,200°C or
12
more, the formation of NOx decreases , the carbonaceous material can be actively
combusted, and productivity can be improved. That is, in the embodiment, a
combustion starting temperature of the carbonaceous material increases apparently, a
rapid combustion of the carbonaceous material at the high temperature region can be
5 realized, and a maximum temperature at the time of the combustion of the carbonaceous
material can be effectively increased.
[0017]
A mixing and granulating method of the blend materials in the embodiment will
be described. Here, the blend materials are materials which are mixed before being
10 charged into the sintering machine and then used.
Moreover, in the description below, an example is described in which a fine iron
ore in addition to the lime-based material is used as the coating in the surface-coated
carbonaceous material. However, the present invention is not limited to this example.
That is, if the amount of Ca derived from a lime-based material in the coating is 36
15 mass% or more, the fine iron ore and other auxiliary materials can be used as the coating
material in addition to the lime-based material. Here, the other auxiliary materials mean
auxiliary materials (silica rock, serpentine, peridotite, or the like) other than the
lime-based material.
First, the blend materials (hereinafter, referred to "first blend materials") except
20 for the materials which are used to produce the surface-coated carbonaceous material are
granulated by a mix granulator such as a drum mixer. The first blend materials include
at least the iron ore, return fines, and the auxiliary material. Here, the first blend
materials do not include a bedding ore. In addition, a coal blend maybe included in the
first blend materials.
25 [0018]
13
Next, the materials (hereinafter, referred to as "second blend materials") which
are used to produce the surface-coated carbonaceous material, that is, a carbonaceous
material, the lime-based material, and the iron ore fines are mixed and granulated using a
coarse carbonaceous material as nuclei, and therefore, the surface-coated carbonaceous
5 material is produced. The iron ore fines may include dust which is formed in
steelworks. In a method which mixes the carbonaceous material with the iron ore fines
and the lime-based material and granulates them, a mix granulator such as a drum mixer
and a granulator using a centrifugal force can be used. Thereby, the surface-coated
carbonaceous material in which the lime-based material and the iron ore fines are coated
10 on the coarse carbonaceous material (nuclei) is formed. When calcium carbonate, milk
of lime, fluorite, or the like which have almost no binder function are used as the
lime-based material, it is preferable that a binder be added to these. An organic binder
such as CMC (carboxymethyl cellulose) or gum arabic and an inorganic binder such as
water glass may be used as the binder. Since the coating layer which strongly adheres
15 to the surface of the carbonaceous material by the addition of the binder is formed, at the
time of the mixing with the first blend materials and in the transportation process up to
charging of the materials into the sintering machine, separation of the coating of the
surface of the carbonaceous material is suppressed, and NOx which forms at the time of
the sintering can be stably decreased.
20 Regarding the second blend materials, the carbonaceous material and the
lime-based material are mixed and granulated, and therefore, the surface-coated
carbonaceous material may be produced. In this case, the coating layer of the
surface-coated carbonaceous material is formed from only the lime-based material.
[0019]
25 The amount of the surface-coated carbonaceous material in the carbonaceous
14
material (coal blend) which is mixed and used for the sinter production is not particularly
limited. However, the surface-coated carbonaceous material needs to be included in the
coal blend. That is, a portion of the coal blend needs to be a surface-coated
carbonaceous material. Particularly, in order to stably decrease NOx which forms at the
5 time of the sintering, it is preferable that the coal blend include 10 mass% or more and
100 mass% or less of the surface-coated carbonaceous material. In order to decrease
differences in the combustion time for each kind of the carbonaceous materials as much
as possible and stably perform the combustion in the sintering machine at a high
temperature, the amount of the surface-coated carbonaceous material with respect to the
10 total amount of the coal blend is preferably 50 mass% or more, more preferably 70
mass% or more, and most preferably 80 mass% or more. In addition, if a large amount
of coal blend is used as the solid fuel of the sintering, a large amount of melt which is
formed by the sintering reaction of the sintering feed is formed on a sintering pallet,
permeability of a sintering feed bed is deteriorated, and productivity of the sinter may
15 decrease. Therefore, in order to supply an appropriate amount of heat for making the
sintering reaction of the sintering feed favorably proceed using the coal blend as a solid
fuel, it is preferable that the amount of the coal blend with respect to the iron ore and the
auxiliary material (auxiliary material excluding the lime-based material used in the
surface-coated carbonaceous material) be 14 mass% or less, for example. In this case,
20 the permeability of the sintering feed bed can be sufficiently secured. Moreover, for
example, the amount of the coal blend with respect to the iron ore and the auxiliary
material (auxiliary material excluding the lime-based material used in the surface-coated
carbonaceous material) is not particularly limited. However, considering the amount of
the heat which is required for the sintering reaction of the sintering feed, the amount of
25 the coal blend may be 1 mass% or more.
15
[0020]
A timing at which the surface-coated carbonaceous material is added to the first
blend materials and mixed is not particularly limited. However, it is preferable that the
surface-coated carbonaceous material be added to and mixed with the first blend
5 materials after the first blend materials are mixed and granulated (addition after the
granulation). The surface-coated carbonaceous material is added to and mixed with the
first blend materials according to the above-described timing, and thereby, collapse or
separation of the coating on the surface of the carbonaceous material can be suppressed.
In this case, the first blend materials may consist of the iron ore, the return fines, the
10 auxiliary material, and the coal blend other than the surface-coated carbonaceous
material, and may consist of the iron ore, the return fines, and the auxiliary material.
However, the surface-coated carbonaceous material is added to the first blend
materials before the first blend materials are mixed and granulated (addition before the
granulation), the granulation conditions are controlled so that the coating of the
15 surface-coated carbonaceous material does not separate,, and the first blend materials and
the surface-coated carbonaceous material may be mixed and granulated. In this case,
the first blend materials may consist of the iron ore, the return fines, the auxiliary
material, and the coal blend.
[0021]
20 In general, if the addition of the carbonaceous material such as the coke is
performed after the granulation, since diffusion of oxygen in the carbonaceous material
becomes faster, the. combustion of the carbonaceous material starts at a low temperature,
a solid ash covers the surface of the carbonaceous material during the combustion of the
carbonaceous material, and thereby, the combustion of the carbonaceous material is
25 impeded. Therefore, in this case, the amount of NOx increases significantly.
16
On the other hand, if the surface-coated carbonaceous material is used, even
though either the addition before the granulation or the addition after the granulation is
performed, the amount ofNOx can be suppressed. Particularly, if the addition of the
surface-coated carbonaceous material after the granulation is performed, since the
5 collapse and the separation of the coating can be suppressed, shielding effects against
oxygen in the atmosphere in a low temperature region and melting effects of the ash at a
high temperature region can be enhanced, and the amount of NOx can be significantly
suppressed. In this case, a feeding time is preferably 0.5 (half) or more, is more
preferably 0.8 or more, and the feeding time is defined by a ratio of the mixing time of
10 the carbonaceous material (the adding and mixing time of the surface-coated
carbonaceous material to the first blend materials) with respect to the total mixing and
granulating time of the sintering feed (total of the mixing and granulating time of only
the first blend materials and the adding and mixing time of the surface-coated
carbonaceous material to the first blend materials). For example, when the sintering
15 feed is mixed and granulated through a single unit, the surface-coated carbonaceous
material may be added to and mixed into the sintering feed in the unit. Moreover, for
example, when the sintering feed is mixed and granulated through a plurality of units, the
surface-coated carbonaceous material may be added and mixed in the unit in which the
feeding time reaches a predetermined value (for example, 0.5 or more).
20 [0022]
In the surface-coated carbonaceous material of the embodiment, it is necessary
to coat the coating on the surface of the carbonaceous material with a ratio of more than 2
mass% and less than 50 mass% by mass percentage with respect to the carbonaceous
material (the amount of the coating with respect to the carbonaceous material). When
25 the mass percentage of the coating with respect to the carbonaceous material is 2 mass%
7
or less, a sufficient formation of the coating layer which covers the entire surface of the
carbonaceous material is difficult, a portion of the surface of the carbonaceous material is
exposed,. and thereby, the effects of decrease of NOx due to the shielding against oxygen
in the atmosphere in a low temperature region cannot be obtained. In addition, when
5 the mass percentage of the coating with respect to the carbonaceous material is 50 mass%
or more, rate at which the calcium ferrite is formed from the lime-based material at a
high temperature region decreases, the combustion efficiency of the carbonaceous
material decreases, and thereby, productivity of the sintering machine decreases. Here,
in order to further enhance effects of decrease of NOx, the mass percentage of the
10 coating with respect to the carbonaceous material is preferably 3 mass% or more, more
preferably S mass% or more, and most preferably 10 mass% or more. Moreover in
order to further increase the combustion efficiency of the carbonaceous material, it is
preferable that the mass percentage of the coating with respect to the carbonaceous
material be 40 mass% or less.
15 In addition, it is preferable that the thickness of the coating layer be 5 μm or
more and 500 μm or less on the surface of the carbonaceous material of 0.25 mm or more
in the carbonaceous material which forms the surface-coated carbonaceous uterial.
Here, the thickness of the coating layer means an average thickness of the coating layer
on the surface of the carbonaceous material of 0.25 mm or more. Moreover, it is more
20 preferable that the thickness of the coating layer with respect to each piece of
surface-coated carbonaceous material be 5 pm or more and 500 pm or less. In addition,
when 20 or more pieces of the surface-coated carbonaceous material are observed with a
microscope, the layer thickness of 5 positions or more in the coating layers of each
surface-coated carbonaceous material are measured, the average of these layer
25 thicknesses is calculated, and therefore, the thickness of the coating layer can be
19
obtained.
When the thickness of the coating layer is 5 μm or more, the separation of the
coating layer can be suppressed in the mixing process of the first blend materials (iron
ore, return fines, or the like) and the surface-coated carbonaceous material or the
5 subsequent handling process, and the effects of suppression of NOx by the coating layer
on the surface of the carbonaceous material can be sufficiently secured. Moreover, if
the thickness of the coating layer is 500 pm or less, the calcium ferrite is rapidly formed
from the lime-based material in a high temperature region, the carbonaceous material can
be effectively combusted at a high temperature region, and productivity of the sintering
10 machine can be sufficiently secured or improved.
[0023]
As described above, in the embodiment, the coating containing 36 mass% or
more of Ca derived from a lime-based material is coated on the surface of the
carbonaceous material so that the mass percentage of the coating with respect to the
15 carbonaceous material is more than 2 mass% and less than 50 mass%, the surface-coated
carbonaceous material is prepared, and the surface-coated carbonaceous material can be
combusted in the sintering machine as a sintering fuel. Moreover, in the embodiment,
the surface-coated carbonaceous material is included in the coal blend. That is, the
surface-coated carbonaceous material is used as the coal blend. In addition, the coal
20 blend is mixed with the blend materials which include the iron ore, the return fines, and
the auxiliary material until the coal blend is charged into the sintering machine.
In this way, the surface-coated carbonaceous material is combusted in the
sintering machine as the sintering fuel, thereby, the combustion of the carbonaceous
material can be controlled, the formation of NOx is suppressed, and productivity of the
25 sintering machine can be sufficiently secured or improved.
19
[Example]
[0024]
Next, an example of the present invention will be described. However, the
present invention is not limited thereto.
5 (Example 1)
A test was performed in order to examine influences of the amount of the
coating in the surface-coated coke and Ca concentration in the coating layer on the
amount of formed NOx. FIG. 3 is a schematic view of an apparatus for pot test which
was used in this test.
10 The apparatus for pot test includes an ignition furnace 1, a sintering pot 2, a
wind box 3, a blower 4, and an analyzer 5.
In this apparatus for pot test, the sintering feed including the surface-coated
carbonaceous material is charged into the sintering pot 2, and the sintering feed is heated
by the ignition using the ignition furnace 1. Simultaneously, the blower 4 starts, exhaust
15 gas formed in the sintering pot 2 is discharged via the wind box 3, and the exhaust gas is
analyzed at the analyzer 5. The sintering pot 2 has a diameter of 300 into and a height
of 600 mm and analyzes CO, CO2, 02, NOx, and SOx in the exhaust gas.
7.5 mass% (outer percentage) of water was added to the iron ore fines (iron ore),
the auxiliary material, and the carbonaceous material, and these materials were mixed
20 and granulated for 5 minutes using a drum mixer having the diameter of 1,000 mm.
Moreover, 9.0 mass% (outer percentage) of water was added to the coke and the coating,
and the surface-coated coke (surface-coated carbonaceous material) was produced using
a universal kneading machine. The sintering feed which was mixed and granulated was
charged into the apparatus for pot test and was sintered under a constant condition of a
25 firing time of 90 seconds and suction negative pressure of 15 kPa. Ratios of each blend
20
5
material which was used in the test are shown in Table 1, and the size distribution of the
coke is shown in Table 2.
[0025]
[Table 1]
Material Iron Ore Limestone Quicklime Serpentine 'Dotal Return Fines Coke
15.0% 4.5%
Percentage 82.85% 13.10% 1.00% 3.05% 1.00% (Outer (Outer
Percentage) Percentage)
[0026]
[Table 2]
Size Class Average
5.0-3.0 3.0-1.0 1.0-0.5 0.5-0.25 -0.25 Total
Level (nun) (nm)
Base 0.0-5.0 24.0% 27.9% 27.0% 8.2% 12.9% 100% 1.78
[0027]
10 FIG. 4 shows a relationship between the amount of a coating and Ca
concentration in a coating layer, and NOx conversion (11NO). If the Ca concentration in
the coating layer is 36 mass% or more, effects of sufficient decrease of NOx could be
obtained. Moreover, when the Ca concentration in the coating layer were adjusted to
approximately 54 mass% using only calcium hydroxide as the coating, effects of
15 decrease-ofNOx were further enhanced . In addition, if the mass percentage of the
coating with respect to the coke (the coke for the surface-coated carbonaceous material)
was more than 2 mass% and less than 50 mass %, the effects of decrease of NOx were
confirmed. Particularly, when the mass percentage of the coating with respect to the
coke was 10 to 40 mass%, effects of decrease of NOx could be further enhanced.
20 [0028]
[Equation (1)]
21
r1NO = 100 x NOx / ((CO + CO2) • Nc0KE / (CLPG + CcoicE + CLS)) / 10000
Where, 11NO: NOx conversion (mol%), NOx: NOx (ppm) in exhaust gas, CO:
CO (mol%) in exhaust gas, CO2: CO2 (mol%) in exhaust gas, Ncoi : N (mol) in coke,
CLPG: C (mol) in ignition gas, CcoijE: C (mot) in coke, and CLS:C (mot) in limestone.
5 [0029]
(Example 2)
In order to examine influences of the layer thickness of the coating layer of the
surface-coated carbonaceous material on the effects of decrease of NOx, the pot test
similar to Example 1 was performed. Only the calcium hydroxide was used for the
10 coating of the surface-coated coke. FIGS. 5A and 5B show photomicrographs of the
surface-coated coke used in the pot test in which each thickness of the coating layer is
different, Moreover, FIG. 6 shows a relationship between the thickness of the coating
layer (coating layer thickness) and the NOx conversion. As shown in FIG 6, when the
surface-coated coke having the coating layer of the layer thickness of 500 μm or less
15 shown in FIG 5A was used, compared to a case where the surface-coated coke having the
coating layer of the layer thickness of more than 500 μm shown in FIG. SB was used, the
effects of decrease ofNOx (NOx conversion) were improved. Thereby, it was
confirmed that the layer thickness of the coating is preferably adjusted to 500 μm or less.
[0030]
20 (Example 3)
In order to examine influences of a kind of the lime-based material on
coatability (adhesion) to the coke of the coating layer, tests for producing the
surface-coated coke in which only the calcium carbonate was used in the coating and the
surface-coated coke in which only the calcium hydroxide was used in the coating were
22
performed. The mass percentage of the coating with respect to the coke was adjusted to
15 mass% before the carbonaceous material and each coating were mixed, FIG. 7
shows ratios of coating material adhered on the surface of the coke after drying in a case
where each coating was used. The ratio of the calcium carbonate adhered on the surface
5 of the coke was about 20 mass%. On the other hand, the ratio of the calcium hydroxide
adhered on the surface of the coke was more than 80 mass%. In this way, when the
surface-coated coke is produced , it is considered that the binder function of the calcium
hydroxide can be effectively used and effects of great suppression of NOx can be
obtained.
10 [0031]
(Example 4)
In order to examine influences of the feeding time (feeding position) of the
surface-coated coke on the amount of formed NOx, the pot test was performed. As
described above, the feeding time is a ratio of the mixing time of the carbonaceous
15 material with respect to the total mixing and granulating time of the sintering feed.
Moreover, the apparatus for pot test and the test method were similar to Example I.
FIG. 8 shows a relationship between the feeding time of the surface-coated coke
and the NOx conversion . In a condition in which the feeding time of the surface-coated
coke was 0.5 or more, particularly, was 0.8 or more, the amount of formed NOx (NOx
20 conversion) was significantly decreased. In this case, it is considered that the sintering
feed charged into the sintering pot can be prepared while the collapse of the coating or
the separation or the coating from the surface of the coke is suppressed.
[0032]
(Example 5)
25 In order to examine influences of the amount of the surface-coated coke in the
23
coal blend and the feeding time of the surface-coated coke on the amount of formed NOx,
the pot test was performed . Moreover, the apparatus for pot test and the test method
were similar to Example 1. However, the Ca concentration in the coating layer was
adjusted to about 54 mass%, and the mass percentage of the coating with respect to the
5 coke was adjusted to 15 mass%, using only the calcium hydroxide as the coating.
FIG 9 is a graph showing a relationship between the amount of the
surface-coated coke in the coal blend and the feeding time of the surface -coated coke,
and NOx conversion . It was possible to suppress the amount of formed NOx by
increasing the blending ratio of the surface-coated coke with respect to the entire coke
10 and increasing the feeding time. As shown in FIG 9, it was confirmed that when 50
mass% or more of the surface-coated coke was blended into the coal blend, and the
feeding time was controlled so as to be 0.5 or more , the effects of suppression of NOx
could be further enhanced.
[0033]
15 In order to examine influences of the surface -coating layer on the productivity of
the sinter, the pot test was performed. Moreover, the apparatus for pot test and the test
method were similar to Example 1. However, when only the calcium hydroxide was
used in the coating, the mass percentage of the coating with respect to the coke was
adjusted to 15 mass%, and when calcium hydroxide and Pilbara Blend fines were used in
20 the coating, the mass percentage of the coating with respect to the coke was adjusted to
30 mass%. When only the calcium hydroxide was used in the coating, the Ca
concentration in the coating layer was about 54 mass%. In addition, when calcium
hydroxide and Pilbara Blend fines were used in the coating, the Ca concentration in the
coating layer was about 36 mass%. The surface-coated coke was used for the total
25 amount of the coke (blend material) and the feeding time was controlled to be 0.85.
24
The results of the productivity of the obtained sinter are shown in FIG. 10.
Compared with a case where the coke which did not have the coating layer was used,
when the surface-coated coke having the coating layer which included the calcium
hydroxide was used, the productivity of the sinter was improved . In this way, it was
5 confirmed that when the surface-coated coke having the coating layer which includes the
calcium hydroxide is used, the sintering operation can be performed with a low NOx
conversion at a high productivity.
[0034]
(Example 6)
10 In order to confirm the effects of decrease of NOx of the surface-coated coke, an
actual operation test was performed twice over five days for each in a large-sized
sintering machine of 660 m2. The size distribution of the coke (cokes a to c and cokes A
to C) which was used for performing the actual operation test is shown in Table 3. In
the cokes A to C, the surface of the coke was covered with the calcium hydroxide in an
15 amount of about 14 mass% with respect to the amount of the coke (coke for the
surface-coated coke), and thereby, the surface-coated coke was produced. Moreover,
cokes a to c were normal cokes to which the surface coating was not applied.
Here, the coke a (base) was a coke which was obtained by a size distribution
control so that the ratio of particles of less than 0.5 mm was more than 20 mass% and the
20 ratio of particles of 0.5 mm or more and 3 mm or less was less than 40 %. The coke A
(surface-coated coke A) was a coke in which the surface of the coke a was covered with
the calcium hydroxide. The coke b was a coke which was obtained by the size
distribution control so that the ratio of particles of less than 0.5 mm was more than 20
mass% and the ratio of particles of 0.5 mm or more and 3 mm or less was 40 mass% or
25 more. The coke B (surface-coated coke B) was a coke in which the surface of the coke
25
b was covered with the calcium hydroxide. The coke c was a coke which was obtained
by the size distribution control so that the ratio of particles of less than 0.5 mm was 11
mass% or less . The coke C (surface-coated coke C ) was a coke in which the surface of
the coke c was covered with the calcium hydroxide.
5 [0035]
Based on a normal actual operation (using the coke a), tests for the following
cases were performed . ( 1) A case where the surface-coated coke and other sintering
feed were simultaneously granulated (addition before the granulation) and (2) a case
where the surface-coated coke was added after the sintering feed other than the
10 surface-coated coke were granulated once (addition after the granulation ). FIG I I is a
schematic view of a process of (1) the addition before the granulation . FIG. 12 is a
schematic view of a process of (2) the addition after the granulation.
In FIGS. 11 and 12, the coke and the calcium hydroxide were fed from a coke
tank l I and a calcium hydroxide tank (lime-based material tank) 12 and supplied to a
15 granulator 13, and thereby, the surface-coated coke was produced.
In FIG. 11, the granulated surface-coated coke was taken out from a
surface-coated coke tank 19, and the granulated surface-coated coke was sequentially
mixed and granulated at a first mixer 15 and a second mixer 16 along with the materials
(ore, auxiliary material, return fines, or the like) which were fed from a material tank 14.
20 This case is the addition before the granulation in which the surface-coated coke is
simultaneously mixed and granulated with other materials.
On the other hand, in FIG 12, after the surface-coated coke which was taken out
from the granulator 13 was further granulated in a pan pelletizer 18, the surface-coated
coke was added to and mixed with the other materials which were mixed and granulated
25 in the first mixer 15 and the second mixer 16 at the latter half of the second mixer 16.
26
This case is the addition after the granulation in which the mixing of the surface-coated
coke is performed after the mixing and granulating of other materials.
FIGS. 13 to 15 shows EPMA analysis results of the surface -coated coke in
which the surface of the coke (coke a) was coated with the calcium hydroxide. FIG 13
5 is an EPMA analysis result in a case where the normal coke was added to the blend
material before the first mixer (first drum mixer).
FIG. 14 is an EPMA analysis result in a case where the surface -coated coke was
added to the blend material before the first drum mixer. It was observed that the
surface-coating layer (calcium hydroxide layer) of the surface-coated coke was broken,
10 and there were separated particles. If the surface-coated coke and the blend material are
simultaneously mixed and granulated at the first mixer and the second mixer (second
drum mixer), it is considered that the coating of the surface -coated coke is easily broken.
FIG. 15 is an EPMA analysis result in a case where the surface -coated coke was
added to other sintering feed in the latter half of the second drum mixer. In this case, it
15 was observed that the layer of the coating (calcium hydroxide) having the layer thickness
of 5 to 500 μm was secured on the surface of the coke.
[0036]
FIG 16 shows test results of the actual operation test. Compared to a base
period of the actual operation (addition before the granulation) which used the coke a, in
20 an operation period of the actual operation (addition after the granulation) which used the
surface-coated coke A, NOx in the exhaust gas decreased by 25 ppm. Moreover,
compared to the base period, in an operation period of the actual operation (addition after
the granulation) which used the surface-coated coke B, NOx in the exhaust gas decreased
by 30 ppm. Compared to the coke a which was used in the surface-coated coke A, in
25 the coke b which was used in the surface-coated coke B, the mass percentage of the
27
particles (class) of 0.5 mm or more and 3 mm or less was high. Thereby, compared to
the case where the surface-coated coke A was used , in the case where the surface-coated
coke B was used, it could be considered that the amount of formed NOx decreased. In
addition, compared to the base period, in an operation period of the actual operation
5 (addition after the granulation) which used the surface -coated coke C, NOx in the
exhaust gas decreased by 42 ppm. Compared to the coke a which was used in the
surface-coated coke A, in the coke c which was used in the surface -coated coke C, the
mass percentage of the particles (class) of less than 0.5 mm was low. Thereby,
compared to the case where the surface -coated coke A was used, in the case where the
10 surface-coated coke C was used , it could be considered that the amount of formed NOx
decreased.
[0037]
[Table 3]
15
Coke
Average
size
(mm)
-0.5mm
(%)
0.5-3mn
N) Coating
a 2.12 31.8 38. 6 No Coating
b 1.54 25.4 59. 7 No Coating
c 2.89 8.5 37. 6 No Coating
A 2.66 10.3 52. 5 Slaked Lime Coating
B 1.66 13.3 71.6 Slaked Line Coating
C 3.09 2.0 41.5 Slaked Line Coating
Industrial Applicability
forma
[0038]
It is possible to provide a method of producing a sinter which suppresses
on of NOx by controlling the combustion of the carbonaceous material and is
28
capable of sufficiently securing or improving productivity of a sintering machine.
Reference Symbol List
[0039]
5 1: Ignition furnace
2: Sintering pot
3: Wind box
4: Blower
5: Analyzer
10 11: Colce tank
12: Slaked lime tank (Lime-based material tank)
13: Granulator
14: Material tank
15: First mixer
15 16: Second mixer
18: Pan pelletizer
19: Surface-coated coke tank

What is claimed is:
1. A method of producing a sinter,
wherein a coal blend includes a surface-coated carbonaceous material as a fuel
for sintering, the surface-coated carbonaceous material being coated with a coating
including 36 mass% or more of Ca derived from a lime-based material on a surface of a
carbonaceous material at a ratio of more than 2 mass% and less than 50 mass% with
respect to the carbonaceous material.
10 2. The method of producing the sinter according to claim 1,
wherein the coal blend includes 10 mass% to 100 mass% of the surface-coated
carbonaceous material.
3. The method of producing the sinter according to claim 1 or 2,
15 wherein the lime-based material is a calcium hydroxide, and the coating includes
67 mass% or more of the calcium hydroxide.
The method of producing the sinter according to claim 1 or 2,
wherein a layer thickness of the coating is 5 μm or more and 500 μm or less on a
20 surfaces of 0.25 mm or more of carbonaceous material in the carbonaceous material.
5. The method of producing the sinter according to claim I or 2, the method
comprising:
mixing and granulating a blend material including an iron ore, return fines, and
25 an auxiliary material; and
30
'thereafter, adding the surface-coated carbonaceous material to the mixed and
granulated blend material and mixing the surface-coated carbonaceous material and the
mixed and granulated blend material.
5 6. The method of producing the sinter according to claim 1 or 2, the method comprising
adding the surface-coated carbonaceous material to a blend material including an iron ore,
return fines, and an auxiliary material and mixing the surface-coated carbonaceous
material and the blend material after a half or more of a total mixing and granulating time
elapses when the blend material is mixed and granulated.
10
7. The method of producing the sinter according to claim 1 or 2,
wherein the carbonaceous material has a size distribution in which there is 20
mass% or less of particles having a particle size of less than 0.5 mm and 40 mass% or
more of particles having a particle size of 0.5 mm or more and 3 mm or less.