Technical Field
[0001] The present invention relates to a method for producing a blast furnace coke and
a blast furnace coke.
Background Art
[0002] For a coke used for ironmaking in a blast furnace, three functions are roughly expected,
a function as a reducing material for iron ore (iron oxide), a function as a heat
source (fuel) and a function as a filling material for ensuring gas permeability in
a blast furnace by withstanding loads of the coke itself and the iron ore. In order
to perform these functions, certain levels of strength and reactivity (reducibility
and combustibility) are required for the above-mentioned coke.
[0003] In general, a coke is produced by baking (sometimes referred to as "carbonizing")
a coal at a high temperature of 1000°C or higher. In the case of obtaining a high-strength
coke, so-called a hard coking coal having a high caking property is used. However,
such a hard coking coal is relatively expensive. Accordingly, for a purpose of reducing
production cost of the coke, a slightly coking coal having a poor caking property
or a non-coking coal having almost no caking property (slightly coking coal and non-coking
coal are hereinafter sometimes collectively referred to as "non-coking or slightly
coking coal") is also blended in a certain amount as a raw material for the coke,
in addition to a weakly coking coal having a lower caking property than a hard coking
coal. A mechanism of producing the high-strength coke has become clear to some extent,
and methods for efficiently obtaining the high-strength coke have been variously proposed
(for example, see
WO 2010/103828).
[0004] Changes of coal particles in a carbonization process are described herein. FIG. 1A
is a view schematically expressing the changes. The left side shows a state in which
the coal particles (hard coking coal particles 1 and non-coking or slightly coking
coal particles 2) before carbonization are present in an oven body 10, and the right
side shows a state in which continuous phases 1a formed by swelling of the hard coking
particles 1 and modified components 2a of the non-coking or slightly coking coal particles
2 after carbonization are present. The hard coking coal particles 1 are melted in
the carbonization process, include generated gas to swell, and bond with the adjacent
the hard coking coal particles 1, thereby forming the continuous phases 1a containing
bubbles A. When a ratio of the hard coking coal is equivalent to or more than a certain
level and a ratio of the non-coking or slightly coking coal is small, the non-coking
or slightly coking coal particles 2 are taken into the hard coking coal in the above-mentioned
continuous phase forming process, so that defects are unlikely to occur. However,
when the ratio of the non-coking or slightly coking coal is high as shown in FIG.
1A, adhesion between the hard coking coal particles 1 is inhibited, and a low-strength
coke having coarse defects B inside is produced.
[0005] In contrast, as one of measures for increasing the strength of the coke, there is
(1) a method of increasing a bulk density of a raw material coal higher than usual
(see FIG. 1B). In such a manner, the bulk density is increased to decrease a distance
between particles, thereby filling spaces with swelling the hard coking coal, and
a high-strength coke having a few defects can be produced. Further, the strength of
the coke can also be improved by (2) blending a highly swellable hard coking coal
(see FIG. 1C). That is, the highly swellable hard coking coal particles 3 having an
extremely high swelling rate are blended, whereby pressing force acts between the
non-coking or slightly coking coal particles 2 by swelling thereof, and spaces between
the particles are effectively filled with continuous phases 3a derived from a highly
swellable hard coking coal particles 3. Accordingly, a coke strength is improved.
[0006] However, the above-mentioned production method of the high-strength coke has the
following operational problems or difficulties. First, the method of increasing the
bulk density of (1) described above requires special operations such as drying of
the coal to a high level, densification of the coal by forming a part thereof and
mechanical treatment such as stamp charging, all of which require costs. Further,
the densification of the raw coal may exert high pressure on a coke oven wall.
[0007] Then, in the method (2) of using the highly swellable hard coking coal, a probability
of occurrence of unpredictable operational troubles such as damage or breakage of
a coke oven wall and difficulty in discharging the coke from a coke oven may be increased
by occurring excess swelling. As countermeasures for improving the problems of such
a method of (2), there are proposed (3) a method of suppressing viscosity of the coal
in a molten state by using a caking additive such as tar (see
JP-A-2001-214171) and (4) a method of controlling the swelling rate of the non-coking or slightly
coking coal (see
JP-A-2008-156661). However, the method of (3) cannot avoid an increase in production cost of the coke
due to addition of the caking additive. Further, in the method of (4), a blending
step of the coal is complicated to cause an increase in production cost of the coke.
Prior Art Literature
Patent Literature
Summary of the Invention
Problems That the Invention Is to Solve
[0009] The present invention has been made in view of circumstances as described above,
and an object thereof is to provide a method for producing a blast furnace coke, by
which the high-strength coke is obtained at low cost while suppressing an influence
on a coke oven due to swelling, and such a blast furnace coke.
Means for Solving the Problems
[0010] In order to solve the above-mentioned problems, the present inventors have made intensive
studies. As a result, it has been found that when the swelling rate of a blended coal
is adjusted to 20% or less by blending with the raw coal at least a specified amount
of an ashless coal which is an extracted component obtained by solvent extraction
treatment of coal and shows high fluidity and swelling property in a molten state,
a high-strength blast furnace coke is obtained while suppressing damage and the like
of the coke oven due to swelling of the raw coal.
[0011] That is, the invention made in order to solve the above-mentioned problems is directed
to a method for producing a blast furnace coke, including a blending step of blending
an ashless coal obtained by solvent extraction treatment of coal with a coal, thereby
obtaining a blended coal, and a step of carbonizing the blended coal, wherein a blending
amount of the ashless coal in the blending step is 3 mass % or more, and a swelling
rate of the blended coal in the blending step is 20% or less
[0012] The method for producing a blast furnace coke can increase the strength of a resulting
coke, by blending the ashless coal with coal in a blending amount within the above-mentioned
range, whereby the ashless coal is melted during carbonization and fills spaces of
the raw coal. Further, the method for producing a blast furnace coke can suppress
the influence on the coke oven due to swelling of the blended coal by adjusting the
swelling rate of the blended coal to the above-mentioned range. Furthermore, the adjustment
of the swelling rate of the blended coal can be easily achieved by blending of the
ashless coal. Therefore, the method for producing a blast furnace coke does not require
another caking additive or the like. As a result, according to the method for producing
a blast furnace coke, the high-strength blast furnace coke can be obtained at low
cost while prolonging the lifetime of an oven body. The "swelling rate" is a value
measured in accordance with JIS-M8801:2004.
[0013] The swelling rate of the blended coal in the above-mentioned blending step is preferably
10% or more. By adjusting the swelling rate of the blended coal to 10% or more as
described above, the occurrence of coarse defects during carbonization can be suppressed
to further increase the strength of the resulting coke.
[0014] Coal with which the above-mentioned ashless coal is blended preferably contains the
hard coking coal and non-coking or slightly coking coal. A ratio of the hard coking
coal in the above-mentioned blended coal is preferably 20 mass % or more and 50 mass
% or less. By adjusting the ratio of the hard coking coal to such a range, a high-strength
blast furnace coke can be obtained more easily and surely at low cost. "Hard coking
coal" generally means a coal having an average maximum reflectance Ro of 1.3% or more
and 1.6% or less, and a logarithm of maximum fluidity MF (ddpm) (log MF) of 0.8 or
more and 2.5 or less, or an Ro of 1.0% or more and 1.3% or less, and a log MF of 1.5
or more and 4 or less. "Non-coking or slightly coking coal" is generally a general
term for slightly coking coal and non-coking coal, and means, for example, a coal
having an Ro of less than 0.85 and a log MF of 2.5 or less, or an Ro of 0.85 or more
and a log MF of 2 or less. Here, the "average maximum reflectance Ro" is a value measured
in accordance with JIS-M8816:1992, and the "maximum fluidity MF" is a value measured
in accordance with the Gieseler plastometer method of JIS M8801:2004.
[0015] Another invention made in order to solve the above-mentioned problems is directed
to a blast furnace coke obtained by carbonizing a blended coal prepared by blending
an ashless coal obtained by solvent extraction treatment of coal with a coal, wherein
a blending amount of the ashless coal in the blended coal is 3 mass % or more, and
a swelling rate of the blended coal is 20% or less.
[0016] For the reasons described above, the blast furnace coke has high strength and can
be produced at low cost while suppressing the influence on the coke oven due to swelling.
Advantageous Effects of the Invention
[0017] As described above, according to the method for producing a blast furnace coke of
the present invention, the high-strength blast furnace coke is obtained at low cost
while suppressing the influence on the coke oven due to swelling. Such a blast furnace
coke can be suitably used as an ironmaking material.
Brief Description of the Drawings
[0018]
[FIG. 1A] FIG. 1A is a schematic view for illustrating states before and after carbonization
of the coal in a conventional method for producing a coke using no ashless coal.
[FIG. 1B] FIG. 1B is a schematic view for illustrating states before and after carbonization
of the coal in another conventional method for producing a coke (a method of increasing
the bulk density) using no ashless coal.
[FIG. 1C] FIG. 1C is a schematic view for illustrating states before and after carbonization
of the coal in still another conventional method for producing a coke (a method of
blending hard coking coal) using no ashless coal.
[FIG. 2] FIG. 2 is a schematic view for illustrating states before and after carbonization
of the coal with which the ashless coal is blended.
Mode for Carrying Out the Invention
[0019] Embodiments of a method for producing a blast furnace coke and blast furnace coke
according to the present invention will be described below.
[Method for producing a blast furnace coke]
[0020] The method for producing a blast furnace coke is provided with a step of blending
the ashless coal obtained by solvent extraction treatment of coal with the coal (blending
step) and a step of carbonizing the above-mentioned blended coal (carbonization step).
<Blending step>
[0021] In the blending step, ashless coal is blended with coal as a raw material for the
coke, thereby obtaining the blended coal.
(Coal)
[0022] A coal used as the raw material for the coke in the method for producing a blast
furnace coke is not particularly limited, and the hard coking coal, semi-hard coking
coal, weakly coking coal, slightly coking coal, non-coking coal and the like can be
used in combination at such an appropriate ratio that fusing of the whole coal becomes
possible by carbonization. In particular, it is preferred that the raw coal contains
the hard coking coal and non-coking or slightly coking coal.
[0023] An upper limit of the ratio of the hard coking coal in raw coal is preferably 50
mass % and more preferably 40 mass %, from the viewpoint of more inexpensively producing
a high-quality coke. On the other hand, a lower limit of the ratio of the hard coking
coal in the raw coal is preferably 20 mass % and more preferably 30 mass %. When the
ratio of the hard coking coal exceeds the above-mentioned upper limit, the production
cost of the coke may be increased. Conversely, when the ratio of the hard coking coal
is less than the above-mentioned lower limit, the strength of the resulting coke may
become insufficient.
[0024] The raw coal is preferably finely pulverized into a granular form. When raw the coal
is granulated, an average particle size D20 of the raw coal is preferably 3 mm or
less. When the average particle size D20 exceeds 3 mm, miscibility with the ashless
coal and the strength of the resulting coke may become insufficient. The "average
particle size D20" means a size of an opening of a sieve at the time when an accumulated
volume of particles which have remained on the sieve reaches 20% of the volume of
all particles, in the case of screening all particles through a metal wire sieve specified
in JIS Z 8801-1:2006 from a sieve having a larger opening in order.
[0025] Although a dried coal obtained by air drying or the like may be used as a raw coal,
one in a state of containing moisture may also be used.
(Ashless coal)
[0026] An ashless coal (Hyper-coal, HPC) is a kind of modified coal obtained by modifying
a coal, and the modified coal obtained by removing ash and insoluble components as
much as possible from the coal using a solvent. However, the ashless coal may contain
ash within a range of not significantly impairing fluidity or swelling property of
the ashless coal. In general, a coal contains 7 mass % or more and 20 mass % or less
of ash. However, an ashless coal used in the method for producing a blast furnace
coke may contain ash in an amount of about 2%, and in an amount of about 5% in some
cases. "Ash content" means a value measured in accordance with JIS-M8812:2004.
[0027] Such an ashless coal can be obtained by solvent extraction treatment in which a coal
is mixed with a solvent having a high affinity for the coal to obtain an extract from
which components insoluble in the solvent, such as ash, are separated and the solvent
is removed from this extract. As a specific method of the solvent extraction treatment,
there can be used, for example, a method disclosed in Japanese Patent No.
4045229. The ashless coal obtained by such solvent extraction treatment does not substantially
contain ash, and contains large amounts of organic substances which are soluble in
solvent and show softening and melting properties. Structurally, the ashless coal
has a wide molecular weight distribution ranging from a component with a relatively
low molecular weight having two or three fused aromatic rings to a component with
a high molecular weight having about five or six fused aromatic rings. Accordingly,
the ashless coal shows high fluidity under heating, and generally melts at 150°C or
more and 300°C or less regardless of the grade of the coal used as the raw material.
In addition, the ashless coal swells while generating a large amount of volatile matter
in an initial stage of carbonization at about 300°C or more and 500°C or less. Further,
the ashless coal is obtained through dewatering of a mixture (slurry) of the coal
and the solvent. Therefore, the moisture content thereof is from about 0.2 mass %
or more and 3 mass % or less, and the ashless coal has a sufficient calorific value.
[0028] As described above, the ashless coal has excellent fluidity and high caking property,
so that it can compensate a caking property of the non-coking or slightly coking coal.
Specifically, as shown in FIG. 2, by dispersing and blending the ashless coal particles
4 with the raw coal particles (hard coking coal particles 1 and non-coking or slightly
coking coal particles 2), the ashless coal particles 4 start to flow at a temperature
lower than that of the raw coal particles in the coke oven, and continuous phases
4a derived from the ashless coal particles 4 are almost uniformly formed, including
a central portion of the oven in which a temperature rise is slow. Thereby, continuous
phases 1a derived from the hard coking coal particles 1 and modified components 2a
of the non-coking or slightly coking coal particles 2 are connected to fill spaces
between the particles. Further, the ashless coal has a higher swelling property than
the hard coking coal, so that the ashless coal particles 4 swell even in a lower part
of the coke oven, in which a large load is applied, thereby connecting the coal particles
to fill spaces between the particles. As a result, the defects such as occurrence
of poor adhesion between the coal particles (macrocracks) and occurrence of excessive
swells (coarse pores), which may act as starting points for breakage of the coke,
can be reduced, and it is possible to suppress variations in a coke quality depending
on a position in the coke oven. On the other hand, the viscosity of the ashless coal
in a molten state is low compared to that of the hard coking coal, so that the swelling
rate of the blended coal obtained by blending the ashless coal with the raw coal is
not excessively increased. Therefore, suppression of an increase in the swelling rate
of the blended coal and improvement in the strength of the coke can be made compatible
by blending the ashless coal. As described above, by using the ashless coal as a caking
additive, the high-strength blast furnace coke can be obtained at low cost while prolonging
a lifetime of the coke oven.
[0029] A lower limit of the blending amount of the ashless coal in this blending step is
3 mass %, preferably 4 mass % and more preferably 5 mass %. On the other hand, an
upper limit of a blending amount of the ashless coal is preferably 15 mass %, more
preferably 12 mass % and still more preferably 10 mass %. When the blending amount
of the ashless coal is less than the above-mentioned lower limit, a connecting effect
of the coal particles described above is not sufficiently obtained, and the strength
of the coke may become insufficient. Conversely, when the blending amount of the ashless
coal exceeds the above-mentioned upper limit, the swelling rate of the blended coal
is excessively increased, which may have the influence on the oven body and increases
the production cost of the coke.
[0030] Further, 3 mass % of the above-mentioned lower limit can be calculated as described
below. First, a porosity at the time of carbonizing the raw coal free from the ashless
coal is about 10% by volume. It becomes a problem whether or not the ashless coal
can fill the spaces. Here, the ashless coal is extremely high in fluidity in a molten
state compared to an ordinary coal, so that measurement of the swelling rate according
to the JIS method cannot be applied. Then, the swelling rate of the ashless coal is
measured by the following method. First, a quartz test tube having an inner diameter
of 15 mm is filled with 1.8 g of an anthracite pulverized into a particle size of
2 mm or less and 0.2 g of the ashless coal pulverized into a particle size of 200
µm or less, followed by heat treatment to 500°C at 3°C/min, and the swelling rate
V
10% (%) is determined from a ratio of a height of a sample after heating to a height
of the sample before heating. Next, similarly, a quartz test tube having an inner
diameter of 15 mm is filled with 1.6 g of an anthracite pulverized into a particle
size of 2 mm or less and 0.4 g of the ashless coal pulverized into a particle size
of 200 µm or less, followed by heat treatment to 500°C at 3°C/min, and the swelling
rate V
20% (%) is determined from the ratio of the height of the sample after heating to the
height of the sample before heating. The swelling rate D (%) of the ashless coal is
determined from the following formula (1):
[0031] The swelling rate of the ashless coal measured by this method is about 300% (from
200% or more and 500% or less), although it depends on the raw material or production
conditions of the ashless coal. Accordingly, a volume of the ashless coal necessary
for filling most of the spaces, for example, 80% of the spaces, is 10×0.8/300×100%=2.6%
by volume. A mass ratio of the ashless coal for filling the above-mentioned spaces
is considered to be 3 mass %, because a specific gravity of the ashless coal and the
specific gravity of the raw coal are assumed to be substantially equal to each other.
A reason for using an anthracite in the above-mentioned measuring method is as follows.
Among coals, an anthracite is in a class having the highest degree of coalification,
and is often used as a part of raw coal for an ironmaking coke production. However,
it has no caking property and no fluidity at all. That is just the reason for using
an anthracite in the above-mentioned measuring method. That is, an anthracite is neither
melted nor swelled in the carbonization process, and therefore, it is expected that
the swelling rate in the course of mixing ashless coal with the coal particles and
performing carbonization can be estimated with a higher accuracy.
[0032] Coal acting as a raw material for ashless coal used in the method for producing blast
a furnace coke is not particularly limited in quality. Further, ashless coal preferably
has a granular shape with a small particle size, from a viewpoint of enhancing dispersibility
to increase the strength of the coke. An upper limit of a maximum diameter of the
ashless coal particles is preferably 1 mm. When the maximum diameter of the ashless
coal particles exceeds the above-mentioned range, the connecting effect of the coal
particles described above is not sufficiently obtained, and the strength of the coke
may become insufficient. The maximum diameter of the ashless coal particles means,
for example, a maximum length (maximum distance between two points) of the outer shape
of an ashless coal particles photographed under an electron microscope or the like.
(Blended coal)
[0033] A lower limit of the logarithm of the maximum fluidity (log MF) of blended coal obtained
by blending ashless coal with raw coal is preferably 1.8, more preferably 2 and still
more preferably 2.1. On the other hand, an upper limit of log MF of blended coal is
preferably 3, more preferably 2.5 and still more preferably 2.3. When log MF of blended
coal is less than the above-mentioned lower limit, the fluidity of blended coal is
insufficient, and the strength of the resulting coke may become insufficient. Conversely,
when log MF of the blended coal exceeds the above-mentioned upper limit, the fluidity
become excessive, and bubbles may become liable to occur in the coke. The maximum
fluidity MF mainly indicates a magnitude of heat fluidity, and log MF of the blended
coal means a weighted average value of log MF of the whole coal and the ashless coal
contained in the raw coal.
[0034] A lower limit of an average maximum reflectance Ro of the blended coal is preferably
0.95 and more preferably 1. On the other hand, an upper limit of the average maximum
reflectance Ro of the blended coal is preferably 1.3 and more preferably 1.2. When
the average maximum reflectance Ro of the blended coal is less than the above-mentioned
lower limit, swelling and fusing of the coal or the ashless coal become insufficient
due to the low degree of coalification of the blended coal, and the strength of the
resulting coke may become insufficient. Conversely, when the average maximum reflectance
Ro of the blended coal exceeds the above-mentioned upper limit, the swelling rate
of the blended coal is excessively increased, which may have the influence on the
oven body. The average maximum reflectance Ro mainly indicates the degree of coalification,
and Ro of blended coal means a weighted average value of Ro of the whole coal and
the ashless coal contained in raw the coal.
[0035] An upper limit of the swelling rate of the blended coal is 20%, preferably 19% and
more preferably 18%. On the other hand, a lower limit of the swelling rate of the
blended coal is preferably 10%, more preferably 12% and still more preferably 14%.
When the swelling rate of the blended coal exceeds the above-mentioned upper limit,
damage of the coke oven due to swelling of the blended coal may occur. Conversely,
when the swelling rate of the blended coal is less than the above-mentioned lower
limit, swelling and fusing of the coal or ashless coal become insufficient due to
the low degree of coalification of the blended coal, and the strength of the resulting
coke may become insufficient. A swelling phenomenon of coal is affected by an interaction
between the coal particles. Therefore, the swelling rate of the blended coal is not
a weighted average of the swelling rate of the coal and ashless coal contained in
the blended coal, and accurate prediction thereof is said to be difficult.
[0036] A blending method of an ashless coal with the raw coal is not particularly limited.
For example, there can be used a method of feeding the raw coal and ashless coal from
each hopper into a known mixer, followed by stirring while pulverizing by an ordinary
method. By using this method, not only secondary particles formed by coagulation of
the ashless coal are pulverized, but also the raw coal can be pulverized into a granular
shape. Further, the coal and ashless coal which are pulverized in advance may be mixed.
[0037] Furthermore, a caking additive other than the ashless coal may be added to the raw
coal. However, in the method for producing a blast furnace coke, the coal particles
are connected with the ashless coal as described above. It is therefore unnecessary
to add the caking additive. For this reason, the blended coal preferably contains
no caking additive other than the ashless coal, from a viewpoint of cost reduction.
<Carbonization step>
[0038] In the carbonization step, the above-mentioned blended coal is charged into the coke
oven, and carbonized, thereby obtaining the coke. As this coke oven, there can be
used, for example, one having an oven body which can be charged with 30 tons per oven.
[0039] A lower limit of the bulk density of the blended coal at the time of charging into
the coke oven is preferably 720 kg/m
3 and more preferably 730 kg/m
3. On the other hand, an upper limit of the above-mentioned bulk density is preferably
850 kg/m
3 and more preferably 800 kg/m
3. When the above-mentioned bulk density is less than the above-mentioned lower limit,
the strength of the coke may become insufficient. Conversely, when the above-mentioned
bulk density exceeds the above-mentioned upper limit, a pressure applied to the oven
body is increased, which may cause damage of the oven body, or operations for improving
the bulk density of the blended coal may increase the production cost of the coke.
The "bulk density" means the bulk density measured in accordance with JIS-K2151:2004.
[0040] A lower limit of a carbonization temperature of the blended coal is preferably 950°C
and more preferably 1000°C. On the other hand, an upper limit of the carbonization
temperature is preferably 1200°C and more preferably 1050°C. When the carbonization
temperature is less than the above-mentioned lower limit, melting of the coal becomes
insufficient, and the strength of the coke may be decreased. Conversely, when the
carbonization temperature exceeds the above-mentioned upper limit, the production
cost may be increased, from a viewpoint of heat resistance of the oven body or fuel
consumption.
[0041] A lower limit of the carbonization time of the blended coal is preferably 8 hours
and more preferably 10 hours. On the other hand, an upper limit of the carbonization
time is preferably 24 hours and more preferably 20 hours. When the carbonization time
is less than the above-mentioned lower limit, melting of the coal becomes insufficient,
and the strength of the coke may be decreased. Conversely, when the carbonization
time exceeds the above-mentioned upper limit, the production cost may be increased,
from a viewpoint of fuel consumption.
<Advantages>
[0042] The method for producing a blast furnace coke can increase the strength of the resulting
coke, by blending the ashless coal with coal so that the blending amount is within
the above-mentioned range, whereby the ashless coal is melted during carbonization
and fills spaces of the raw coal. Further, the method for producing a blast furnace
coke can suppress the influence on the coke oven due to swelling of the blended coal
by adjusting the swelling rate of blended coal to the above-mentioned range. Furthermore,
the adjustment of the swelling rate of the blended coal can be easily achieved by
blending of the ashless coal. Therefore, the method for producing a blast furnace
coke does not require another caking additive or the like. As a result, according
to the method for producing a blast furnace coke, the high-strength blast furnace
coke can be obtained at low cost while prolonging the lifetime of the oven body.
[Blast furnace coke]
[0043] The blast furnace coke of the present invention is produced by carbonizing the blended
coal prepared by blending the ashless coal obtained by solvent extraction treatment
of coal with the coal. In the blast furnace coke, the blending amount of the above-mentioned
ashless coal and the swelling rate of the blended coal in the above-mentioned blended
coal are within the above-mentioned respective ranges. Therefore, the blast furnace
coke has high strength despite low cost.
Examples
[0044] The present invention will be described in more detail below with reference to examples,
but the present invention should not be construed as being limited thereto.
<Production of ashless coal>
[0045] Using a Hyper-coal continuous production facility (Bench Scale Unit), an ashless
coal was produced by a following method. First, a bituminous coal produced in Australia
was used as a raw coal for the ashless coal, and 5 kg of the raw coal (in terms of
dried coal) and 1-methylnaphthalene (manufactured by Nippon Steel Chemical Co., Ltd.)
as a solvent in four times the volume (20 kg) of the raw coal were mixed to prepare
a slurry. This slurry was placed in a batch-type autoclave with an inner volume of
30 L, and nitrogen was introduced therein to increase the pressure to 1.2 MPa, followed
by heating at 370°C for one hour. This slurry was separated into a supernatant and
a solid-content concentrated liquid in a gravity settling tank maintaining the temperature
and the pressure described above, and the solvent was separated and recovered from
the supernatant by distillation to obtain 2.7 kg of the ashless coal F. The ash content
of the resulting ashless coal F was 0.9 mass %, and the logarithm of the maximum fluidity
(log MF) and the average maximum reflectance Ro were as shown in Table 1. The ashless
coal F was pulverized so that all (100% by mass) thereof had a maximum diameter of
3 mm or less.
<Examples 1 to 4 and Comparative Example 8>
[0046] Using the ashless coal F produced as described above, the blast furnace coke of Examples
1 to 4 and Comparative Example 8 was produced by a following procedure.
(Blending step)
[0047] The above-mentioned ashless coal F and various kinds of the raw coal having properties
shown in Table 1 were each adjusted to a moisture content of 7.5 mass %, and mixed
at the blending ratios shown in Table 2, on the dry coal basis, to obtain the blended
coal. At this time, there was used the raw coal all (100 mass %) of which was pulverized
so as to have a maximum diameter of 3 mm or less. The maximum fluidity MF (dppm) of
the coal and ashless coal shown in Table 1 was measured by the Gieseler plastometer
method in accordance with JIS-M8801:2004. Further, the average maximum reflectance
Ro (%) was measured in accordance with JIS-M8816:1992, and the swelling rate (%) was
measured in accordance with JIS-M8801:2004.
[0048] For the above-mentioned blended coal, the maximum fluidity MF was calculated from
the respective blending ratios of various kinds of the coal and ashless coal. Furthermore,
the swelling rate of the blended coal was measured in accordance with JIS-M8801:2004.
These values are shown in Table 2.
(Carbonization step)
[0049] The above-mentioned blended coal was arranged in a retort made of steel, and vibration
was applied to the retort, thereby adjusting the bulk density as shown in Table 2.
Then, the retort was placed in an electric furnace of a both-side heating type, and
carbonization was performed under a nitrogen stream. The carbonization conditions
were heating at 1,000°C for 20 minutes after the temperature was raised at 3°C/min.
After the carbonization, the retort was taken out of the electric furnace and left
to cool naturally. Thus, the blast furnace coke was obtained.
<Comparative Examples 1 to 7>
[0050] The raw coal was blended at the blending ratios shown in Table 2 by the same procedure
as in Examples 1 to 4 and Comparative Example 8 described above, except that no ashless
coal was added, and the blended coal was carbonized to obtain the blast furnace coke
of Comparative Examples 1 to 7.
<Comparative Examples 9 to 11 >
[0051] The raw coal was blended at the blending ratios shown in Table 2 by the same procedure
as in Examples 1 to 4 and Comparative Example 8 described above, except for that the
ashless coal M obtained by the same procedure as in the case of the above-mentioned
ashless coal F and having properties shown in Table 1 was used, and that the raw coal
shown in Table 1 and different from one used in Examples 1 to 4 and Comparative Examples
1 to 8 described above was used, and the blended coal was carbonized to obtain the
blast furnace coke of Comparative Examples 9 to 11. These Comparative Examples 9 to
11 are some parts of Examples described in
JP-A-2014-015502.
<Evaluation>
[0052] For the blast furnace coke of Examples 1 to 4 and Comparative Examples 1 to 11 described
above, a drum strength index DI was measured. Specifically, in accordance with JISK2151:2004,
the blast furnace coke was rotated in a drum for 150 revolutions, and thereafter,
screened using a metal plate sieve with an opening of 15 mm, which is specified in
JIS-Z8801-2:2006, and a mass ratio (DI 15015) of the blast furnace coke remaining
on the sieve was determined. The acceptability criterion for strength is set to DI>84.5%.
The blast furnace coke satisfying this was acceptable and evaluated as A, and the
blast furnace coke not satisfying this was unacceptable and evaluated as B. These
results are shown in Table 2.
[Table 1]
|
Log MF |
Ro |
Swelling Rate |
|
- |
% |
% |
Hard coking coal A |
1.70 |
1.41 |
65 |
Hard coking coal B |
2.80 |
1.19 |
36 |
Semi-hard coking coal C |
3.50 |
0.86 |
51 |
Non-coking or slightly coking coal D |
1.60 |
0.82 |
-15 |
Non-coking or slightly coking coal E |
0.60 |
0.75 |
-20 |
Ashless coal F |
6.00 |
0.97 |
- |
Hard coking coal G |
0.81 |
1.60 |
102 |
Hard coking coal H |
2.20 |
1.35 |
42 |
Semi-hard coking coal I |
3.10 |
0.78 |
53 |
Non-coking or slightly coking coal J |
0.99 |
1.05 |
5 |
Non-coking or slightly coking coal K |
2.58 |
0.75 |
-11 |
Non-coking or slightly coking coal L |
0.02 |
1.22 |
-18 |
Ashless coal M |
4.78 |
0.95 |
- |
[0053] As shown in Table 1, the blast furnace coke of Examples 1 to 4 in which 3 mass %
or more of the ashless coal is blended has a drum strength index DI of 84.5% or more
and has high strength, and the swelling rate of the blended coal is 20% or less. Therefore,
damage to the coke oven can be prevented. Further, Examples 1 to 4 are excellent in
production cost, because the bulk density is as relatively low as 740 kg/m
3.
[0054] On the other hand, the blast furnace coke of Comparative Example 1 in which the ratio
of the hard coking coal is high has excellent strength, but the swelling rate of the
blended coal is as high as 34%. Therefore, the coke oven may be damaged. The blast
furnace coke of Comparative Examples 2, 6 and 7 in which the ratios of the non-coking
or slightly coking coal are increased has insufficient strength, although the swelling
rate of the blended coal is small. The blast furnace coke of Comparative Example 3
in which the ratio of the highly swellable hard coking coal A is increased provides
high strength, but the swelling rate of the blended coal is as high as 26%. Therefore,
the coke oven may be damaged. In addition, the cost is high, because the hard coking
coal A is much used. The blast furnace coke of Comparative Example 4 in which the
bulk density is increased has sufficient strength and a small probability of damaging
the coke oven. However, cost increase cannot be avoided, because filling treatment
is needed. The blast furnace coke of Comparative Example 5 in which the bulk density
is similarly increased is insufficient in strength, and cost increase cannot be avoided,
similarly to Comparative Example 4. In the blast furnace coke of Comparative Example
8, the ashless coal is blended. However, the blending amount thereof is less than
3 mass %, so that sufficient strength cannot be secured. Also in the blast furnace
coke of Comparative Examples 9 to 11, the ashless coal is blended. However, the swelling
rate of the hard coking coal G is extremely high, so that the swelling rate of the
blended coal is also high. From a long-term view, therefore, the probability of damaging
the coke oven is increased.
[0055] The results of Table 2 reveal that there is no direct correlation between log MF
and the swelling rate, and between log MF and the drum strength index. It is therefore
difficult to obtain the blast furnace coke having high strength and a small influence
on the coke oven at low cost, using log MF as an index.
[0056] While the present invention has been described in detail with reference to the specific
embodiments thereof, it is apparent to one skilled in the art that various changes
and modifications can be made without departing from the spirit and scope of the present
invention.
[0057] The present application is based on Japanese Patent Application No.
2014-110159 filed on May 28, 2014, the contents of which are incorporated herein by reference.
Industrial Applicability
[0058] As described above, according to the method for producing a blast furnace coke of
the present invention, the high-strength blast furnace coke is obtained at low cost
while suppressing the influence on the coke oven due to swelling. Such a blast furnace
coke can be suitably used as an ironmaking material.
Description of Reference Numerals and Signs
[0059]
- 1:
- Hard coking coal particle
- 1a:
- Continuous phase
- 2:
- Non-coking or slightly coking coal particle
- 2a:
- Modified component
- 3:
- Highly swellable hard coking coal particle
- 3a:
- Continuous phase
- 4:
- Ashless coal particle
- 4a:
- Continuous phase
- 10:
- Oven body
- A:
- Bubble
- B:
- Coarse defect