U.S. patent application number 12/442966 was filed with the patent office on 2010-01-14 for method of producing ashless coal.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd). Invention is credited to Atsushi Furuya, Nobuyuki Komatsu, Noriyuki Okuyama, Naoji Tada.
Application Number | 20100006477 12/442966 |
Document ID | / |
Family ID | 39282918 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100006477 |
Kind Code |
A1 |
Okuyama; Noriyuki ; et
al. |
January 14, 2010 |
METHOD OF PRODUCING ASHLESS COAL
Abstract
A method of producing ashless coal used in caking coal for coke
for iron making includes a slurry preparation step (S1) of mixing a
solvent with coal to prepare a slurry; an extraction step (S2) of
extracting the slurry obtained in the slurry preparation step (S1)
at a temperature in the range of 400.degree. C. to 420.degree. C.
for 20 minutes or less, and then cooling the slurry to 370.degree.
C. or lower; a separation step (S3) of separating the slurry
obtained in the extraction step (S2) into a liquid portion and a
non-liquid portion; and an improved-coal-obtaining step (S4) of
separating the solvent from the liquid portion separated in the
separation step (S3) to obtain ashless coal which is improved
coal.
Inventors: |
Okuyama; Noriyuki; (Hyogo,
JP) ; Tada; Naoji; (Hyogo, JP) ; Furuya;
Atsushi; (Hyogo, JP) ; Komatsu; Nobuyuki;
(Hyogo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd)
Kobe-shi
JP
|
Family ID: |
39282918 |
Appl. No.: |
12/442966 |
Filed: |
October 11, 2007 |
PCT Filed: |
October 11, 2007 |
PCT NO: |
PCT/JP07/69833 |
371 Date: |
March 26, 2009 |
Current U.S.
Class: |
208/428 |
Current CPC
Class: |
C10L 9/10 20130101; C10L
9/02 20130101 |
Class at
Publication: |
208/428 |
International
Class: |
C10G 1/04 20060101
C10G001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 2006 |
JP |
2006-279034 |
Claims
1. A method of producing ashless coal used in caking coal for coke
for iron making, comprising: preparing a slurry by mixing a solvent
with coal; extracting the prepared slurry at a temperature of from
400.degree. C. to 420.degree. C. for 20 minutes or less, and then
cooling the slurry to a temperature of 370.degree. C. or lower;
separating the extracted slurry into a liquid portion and a
non-liquid portion; and separating the solvent from the separated
liquid portion to obtain ashless coal.
2. The method of producing ashless coal according to claim 1,
further comprising separating the solvent from the separated
non-liquid portion to obtain residue coal.
3. The method of producing ashless coal according to claim 1,
wherein extracting the prepared slurry comprises heating to and
extracting at a temperature in the range of 400.degree. C. to
420.degree. C. and then immediately cooling to a temperature of
370.degree. C. or lower.
4. The method of producing ashless coal according to claim 1,
wherein the coal is low-quality coal.
5. the method of producing ashless coal according to claim 2,
wherein the coal is low-quality coal.
6. The method of producing ashless coal according to claim 3,
wherein the coal is low-quality coal.
7. The method of producing ashless coal according to claim 2,
wherein extracting the prepared slurry comprises heating to and
extracting at a temperature in the range of 400.degree. C. to
420.degree. C. and then immediately cooling to a temperature of
370.degree. C. or lower.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of producing
ashless coal in which ashless coal used in caking coal for coke for
iron making is produced from coal.
BACKGROUND ART
[0002] Hitherto, as caking coal for coke for iron making, such as
blast furnace coke, blended coal containing high-rank caking coal
as a main component, weakly caking coal, and non- or slightly
caking coal has been used. Recently, an attempt has been made to
extract a component soluble in a solvent from coal to obtain
extracted coal having a quality higher than that of raw coal.
[0003] For example, the following method has been disclosed (see,
for example, Patent Document 1): Bituminous coal, sub-bituminous
coal, brown coal, lignite, or the like is used as raw coal and
mixed with liquefaction oil used as a solvent to prepare a slurry,
the slurry is hydrogenated at a high temperature and a high
pressure in the presence of a catalyst to liquefy the resulting
product, and solvent refined coal (SRC) that is finally produced is
separated and extracted. The SRC is used in caking coal for
coke.
[0004] In addition, the amount of caking coal resource has been
insufficient, and caking coal is expensive. Accordingly, coal such
as non- or slightly caking coal, or low-rank brown coal or
sub-bituminous coal, that is, low-quality coal has been attracting
attention. Accordingly, a development and a proposal has also been
made in which such low-quality coal is used as raw coal to produce
extracted coal having characteristics equivalent to caking coal and
the extracted coal is used as caking coal for coke.
[0005] For example, a method has been disclosed in which low-rank
coal such as brown coal or sub-bituminous coal is heat-treated in a
solvent (medium liquid) at a pressure in the range of 1 to 20 MPa
and a temperature of 400.degree. C. or lower, the solvent and the
resulting heat-treated coal are then separated to obtain
heat-treated coal, and the heat-treated coal is used as part of
caking coal for coke (see, for example, Patent Document 2).
[0006] Furthermore, the following method of producing ashless coal
in which ash in coal is efficiently removed has been disclosed
(see, for example, Patent Document 3). In the method, ashless coal
is extracted from raw coal by bringing the raw coal into contact
with a solvent of N-methyl-2-pyrrolidinone (NMP) or a mixed solvent
of carbon disulfide and N-methyl-2-pyrrolidinone in the presence of
chlorine or a fluorine compound. [0007] Patent Document 1: Japanese
Unexamined Patent Application Publication No. 8-269459 (paragraphs
0010 to 0032) [0008] Patent Document 2: Japanese Unexamined Patent
Application Publication No. 2003-55668 (paragraphs 0017 to 0030)
[0009] Patent Document 3: Japanese Unexamined Patent Application
Publication No. 2001-26791 (paragraphs 0009 to 0022)
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0010] However, in the above-described methods of producing
extracted coal, problems described below occur.
[0011] In the production method described in Patent Document 1, ash
and the used catalyst are concentrated in the resulting SRC, and
thus the quality of the SRC is not satisfactory when the SRC is
used in caking coal for coke for iron making. Although the SRC is
provided with thermal plasticity (i.e., softening fluidity), which
is an important quality as a binder (caking additive) for a raw
material of coke, the volatility of the SRC is too high and thus a
solidifying property at a temperature in the range of 400.degree.
C. to 500.degree. C. is not sufficient. Accordingly, even when the
SRC is used as a binder, it is difficult to produce coke having a
sufficiently high strength. Furthermore, from the standpoint of a
production method, this SRC is disadvantageous in that the method
requires expensive hydrogen and a catalyst and must be performed
under the condition of a high temperature and a high pressure, and
thus production cost and equipment cost are enormous and this
method is not economical.
[0012] Regarding the production method described in Patent Document
2, although the cost is lower than that of the above method
including liquefaction, the resulting heat-treated coal is a
mixture of a product extracted by the solvent and a non-extracted
product. Therefore, the quality such as thermal plasticity, which
is important as caking coal for coke, is not satisfactory.
[0013] In the production method described in Patent Document 3, a
component soluble in a solvent is extracted from coal using a
strong polar solvent such as NMP without adding hydrogen. However,
when a polar solvent is used as the solvent, the solvent forms a
strong bond with coal. Accordingly, the solvent is not readily
recovered, resulting in a problem of increasing production cost of
ashless coal.
[0014] The present invention has been made in view of the above
problems. It is an object of the present invention to provide a
method of producing ashless coal having an excellent quality as
caking coal used as coke for iron making with a high efficiency and
at a low cost.
Means for Solving the Problems
[0015] As a result of intensive studies on a method of producing
ashless coal used in caking coal for coke for iron making, the
inventors of the present invention found the relationship between
the temperature and the time in an extraction step wherein ashless
coal can be efficiently produced and the ashless coal can have a
quality that does not obstruct thermal plasticity (softening
fluidity) when used in blended coal. This finding led to the
invention of a method of producing ashless coal that can be used in
caking coal for coke for iron making with a high efficiency and at
a low cost.
[0016] Specifically, according to a method of producing ashless
coal in the present invention, a method of producing ashless coal
used in caking coal for coke for iron making includes a slurry
preparation step of mixing a solvent with coal to prepare a slurry;
an extraction step of extracting the slurry obtained in the slurry
preparation step at a temperature in the range of 400.degree. C. to
420.degree. C. for 20 minutes or less, and then cooling the slurry
to 370.degree. C. or lower; a separation step of separating the
slurry obtained in the extraction step into a liquid portion and a
non-liquid portion; and an improved-coal-obtaining step of
separating the solvent from the liquid portion separated in the
separation step to obtain ashless coal which is improved coal.
[0017] According to this production method, in the slurry
preparation step, a solvent is mixed with coal which is a raw
material for ashless coal to prepare a slurry. In the extraction
step, by treating the slurry obtained in the slurry preparation
step under the condition of a predetermined temperature and time,
the proportion of a coal component extracted in the solvent is
increased, the coal component is extracted in the solvent with a
high efficiency, and a resolidification temperature of the
resulting ashless coal is increased. Furthermore, in the separation
step, the slurry obtained in the extraction step is separated into
a liquid portion, which is a solution containing the coal component
extracted in the solvent, and a non-liquid portion, which is a
slurry containing a coal component insoluble in the solvent. In the
improved-coal-obtaining step, the solvent is separated from the
liquid portion separated in the separation step, thus producing
ashless coal.
[0018] In the method of producing ashless coal according to the
present invention, in the improved-coal-obtaining step, in addition
to the production of the ashless coal, the solvent is separated
from the non-liquid portion separated in the separation step to
obtain residue coal which is improved coal.
[0019] According to this production method, in the
improved-coal-obtaining step, the ashless coal is produced, and in
addition, the solvent is separated from the non-liquid portion
separated in the separation step, thus producing residue coal.
[0020] In the method of producing ashless coal according to the
present invention, in the extraction step, the slurry obtained in
the slurry preparation step is heated to and extracted at a
temperature in the range of 400.degree. C. to 420.degree. C. and
then immediately cooled to 370.degree. C. or lower.
[0021] According to this production method, in the extraction step,
the slurry obtained in the slurry preparation step is heated to and
extracted at a predetermined temperature and then immediately
cooled to 370.degree. C. or lower without maintaining the
temperature. Consequently, the proportion of the coal component
extracted in the solvent is further increased, and the coal
component is extracted in the solvent with a higher efficiency.
[0022] In the method of producing ashless coal according to the
present invention, the coal is low-quality coal.
[0023] According to this production method, by using inexpensive
low-quality coal as coal which is a raw material for ashless coal,
the ashless coal can be produced at a lower cost.
Advantages
[0024] According to a method of producing ashless coal of the
present invention, ashless coal used in caking coal for coke for
iron making can be produced with a high efficiency and at a low
cost. When this ashless coal is blended with raw coal, thermal
plasticity of the resulting blended coal can be increased, and the
amount of expensive strongly caking coal blended can be reduced.
Consequently, the cost of the raw coal for coke for iron making can
be reduced. Furthermore, by improving the caking property of the
blended coal, the strength of coke for iron making can also be
improved. Furthermore, in addition to the ashless coal, residue
coal can also be produced with a high efficiently and at a low
cost.
BRIEF DESCRIPTION OF DRAWINGS
[0025] [FIG. 1] FIG. 1 is a flowchart illustrating steps of a
method of producing ashless coal.
[0026] [FIG. 2] FIG. 2 is a schematic view showing a sold-liquid
separator for performing a gravitational settling method.
[0027] [FIG. 3] FIG. 3 is a graph showing Gieseler curves obtained
by a Gieseler plastometer test in Example 1.
[0028] [FIG. 4] FIG. 4 is a graph showing the relationship between
the extraction temperature and the resolidification temperature of
prepared ashless coal c in the case where an extraction treatment
was performed with an extraction time of one hour using
sub-bituminous coal C was used as raw coal in Example 2.
[0029] [FIG. 5] FIG. 5 is a graph showing the relationship between
the extraction time and the extraction yield in the case where
sub-bituminous coal C was heated to an extraction temperature of
370.degree. C., 400.degree. C., or 420.degree. C. with a preheater,
and kept in an extractor for a predetermined time, and then rapidly
cooled to 360.degree. C. to perform an extraction treatment in
Example 3.
REFERENCE NUMERALS
[0030] S1 slurry preparation step
[0031] S2 extraction step
[0032] S3 separation step
[0033] S4 improved-coal-obtaining step
[0034] 1 coal slurry preparation tank
[0035] 2 pump
[0036] 3 preheater
[0037] 4 extraction chamber
[0038] 5 gravity settling chamber
[0039] 6 solid-concentrated liquid receiver
[0040] 7 cooler
[0041] 8 filter unit
[0042] 9 supernatant receiver
[0043] 10 stirrer
[0044] 100 sold-liquid separator
BEST MODE FOR CARRYING OUT THE INVENTION
[0045] Next, a method of producing ashless coal according to the
present invention will be described in detail with reference to the
drawings. In the drawings to be referred, FIG. 1 is a flowchart
illustrating steps of the method of producing ashless coal, and
FIG. 2 is a schematic view showing a sold-liquid separator for
performing a gravitational settling method.
<<Method of Producing Ashless Coal>>
[0046] As shown in FIG. 1, the method of producing ashless coal
includes a slurry preparation step (S1), an extraction step (S2), a
separation step (S3), and an improved-coal-obtaining step (S4).
[0047] The steps will be described below.
<Slurry Preparation Step (S1)>
[0048] The slurry preparation step (S1) is a step of mixing coal
with a solvent to prepare a slurry.
[0049] As a solvent for dissolving coal, a monocyclic aromatic
compound such as benzene, toluene, or xylene; or a polar solvent
such as N-methyl-pyrrolidone (NMP) or pyridine is generally used.
However, in the present invention, a non-hydrogen-donor solvent,
examples of which mainly include bicyclic aromatic compounds, is
used.
[0050] Non-hydrogen-donor solvents are coal derivatives which are
mainly bicyclic aromatic solvents which are mainly obtained by
purifying a coking product of coal. Such non-hydrogen-donor
solvents are stable even in a heated state and have good affinity
with coal. Therefore, a proportion of a coal component extracted in
such a solvent (hereinafter, also referred to as "extraction
yield") is high, and such a solvent can be easily recovered by a
distillation method or the like. In addition, the recovered solvent
can be recycled in order to improve the economical efficiency.
[0051] Examples of the non-hydrogen-donor solvent mainly include
bicyclic aromatic compounds such as naphthalene, methylnaphthalene,
dimethylnaphthalene, and trimethylnaphthalene. Examples thereof
also include naphthalenes having an aliphatic side chain, biphenyl,
and alkylbenzenes having a long aliphatic side chain.
[0052] The non-hydrogen-donor solvent preferably has a boiling
point in the range of 180.degree. C. to 330.degree. C. When the
boiling point is lower than 180.degree. C., pressures necessary in
the extraction step (S2) and the separation step (S3) are high, and
a loss due to volatilization is increased in the step of recovering
the solvent, thereby decreasing the rate of recovery of the
solvent. Furthermore, the extraction yield in the extraction step
(S2) is decreased. On the other hand, when the boiling point is
higher than 330.degree. C., it is difficult to separate the solvent
from a liquid portion and a non-liquid portion described below,
thereby decreasing the rate of recovery of the solvent.
[0053] As described above, by performing thermal extraction using
the non-hydrogen-donor solvent, the extraction yield of coal can be
increased. Furthermore, unlike polar solvents, the solvent can be
easily recovered, and thus the solvent can be readily recycled. In
addition, expensive hydrogen or a catalyst need not be used, and
thus coal can be solubilized at a low cost to obtain ashless coal,
thus improving the economical efficiency.
[0054] As coal (hereinafter, also referred to as "raw coal") used
as a raw material for ashless coal, low-quality coal, which hardly
has thermal plasticity, such as non- or slightly caking coal,
steaming coal, or low-rank coal, e.g., brown coal or sub-bituminous
coal, is preferably used. By using such inexpensive coal, the
ashless coal can be produced at a lower cost, and thus the
economical efficiency can be further improved. However, the coal
used is not limited to such low-quality coal, and caking coal may
be used according to need.
[0055] Note that, the term "low-quality coal" used here refers to
coal such as non- or slightly caking coal, steaming coal, low-rank
coal (such as brown coal and sub-bituminous coal). The term
"low-rank coal" refers to coal that contains moisture in an amount
of 20% or more and that is desirably dehydrated. Examples of the
low-rank coal include brown coal, lignite, and sub-bituminous coal.
Specific examples of the brown coal include Victorian coal, North
Dakota coal, and Berga coal. Examples of the sub-bituminous coal
include West Banco coal, Binungan coal, and Samarangau coal. The
low-rank coal is not limited to the above examples. Any coal that
contains a large amount of moisture and that is desirably
dehydrated is included in the low-rank coal in the present
invention.
[0056] The concentration of the coal relative to the solvent is
preferably in the range of 10 to 50 mass percent, and more
preferably in the range of 20 to 35 mass percent on the basis of
dry coal, though it depends on the type of raw coal. If the
concentration of the coal relative to the solvent is less than 10
mass percent, the ratio of a coal component extracted in the
solvent to the amount of solvent is low, which is not economical.
The coal concentration is preferably as high as possible. However,
if the coal concentration exceeds 50 mass percent, the prepared
slurry has a high viscosity, and thus transfer of the slurry and
separation of a liquid portion and a non-liquid portion in the
separation step (S3) tend to be difficult.
<Extraction Step (S2)>
[0057] The extraction step (S2) is a step of extracting
(hereinafter, also referred to as "heating") the slurry obtained in
the slurry preparation step at a temperature in the range of
400.degree. C. to 420.degree. C. for 20 minutes or less, and then
cooling the slurry to 370.degree. C. or lower.
[0058] The heating temperature of the slurry in the extraction step
(S2) is in the range of 400.degree. C. to 420.degree. C. If the
heating temperature is lower than 400.degree. C., a bond between
molecules constituting coal is not sufficiently weakened.
Accordingly, in the case where low-quality coal is used as the raw
coal, a resolidification temperature of the resulting ashless coal
cannot be increased to a temperature equivalent to the
resolidification temperature of strongly caking coal. On the other
hand, if the heating temperature exceeds 420.degree. C., a thermal
decomposition reaction of the coal becomes very active and
generated thermal decomposition radicals are recombined, thereby
decreasing the extraction yield.
[0059] In the heating temperature range of 400.degree. C. to
420.degree. C., as the extraction time increases, the thermal
decomposition reaction is excessively carried out and radical
polymerization proceeds, thus decreasing the extraction yield.
However, a relatively high extraction yield can be maintained in an
extraction time of 20 minutes or less. In addition, at a
temperature of 370.degree. C., the extraction yield becomes the
maximum in an extraction time of 30 minutes or more. Even if the
extraction time is then prolonged to several hours, the
resolidification temperature of the resulting ashless coal is not
increased, though the extraction yield is not significantly
changed. Accordingly, in order to increase the resolidification
temperature of the resulting ashless coal and to improve the
extraction yield, the most preferable condition is heating at a
temperature in the range of 400.degree. C. to 420.degree. C. for 20
minutes or less, and then cooling to 370.degree. C. or lower.
[0060] The lower limit of the temperature in the cooling is
preferably 350.degree. C. If the temperature is decreased to lower
than 350.degree. C., a dissolving power of the solvent decreases,
and reprecipitation of an extracted coal component occurs, thereby
decreasing the yield of the ashless coal.
[0061] As described below, in the extraction step (S2), for
example, the temperature of an extraction chamber may be increased
to 400.degree. C. to 420.degree. C., and the extraction chamber may
then be cooled immediately. The lower limit of the extraction time
is not determined uniquely, but is preferably determined to be one
minute from the standpoint of the operation of the extraction
chamber. That is, in this case, the extraction time is preferably
in the range of 1 to 20 minutes.
[0062] After heating is performed at a temperature in the range of
400.degree. C. to 420.degree. C. for 20 minutes or less, cooling is
immediately performed to 370.degree. C. or lower. This is because
if it takes a long time to cool to 370.degree. C. or lower, the
extraction yield is decreased accordingly.
[0063] Here, the phrase "cooling is performed immediately" means
that cooling is performed by performing a cooling treatment as soon
as possible. For example, it means that cooling is performed as
soon as possible by a cooling treatment until the slurry is
transferred to a gravity settling chamber described below.
[0064] The shorter the heating time (extraction time) at a
temperature in the range of 400.degree. C. to 420.degree. C., the
higher the extraction yield. Accordingly, in order to further
improve the extraction yield, the heating time (extraction time) is
preferably 15 minutes or less, more preferably 10 minutes or less,
and further preferably 5 minutes or less. Furthermore, zero minutes
are preferable, more specifically, it is preferable that the
temperature be increased to 400.degree. C. to 420.degree. C. to
perform extraction, and immediately decreased to 370.degree. C. or
lower.
[0065] Furthermore, in the temperature range of 400.degree. C. to
420.degree. C., a temperature close to 400.degree. C. is
preferable, and 400.degree. C. is preferable. The reason for this
is that, as the temperature is close to 400.degree. C., the
extraction yield increases.
[0066] In the extraction in this extraction step (S2), components
that are rich in aromatic components having an average boiling
point (Tb50: 50% distillation temperature) mainly in the range of
200.degree. C. to 300.degree. C. are produced by the thermal
decomposition of the coal, and the components can be suitably used
as a part of the solvent.
[0067] The extraction step (S2) is preferably performed in the
presence of an inert gas.
[0068] The reason for this is that contact with oxygen in the
extraction step (S2) is hazardous because of a fear of ignition,
and that use of hydrogen increases the cost.
[0069] As the inert gas used in the extraction step (S2),
inexpensive nitrogen is preferably used, but the inert gas is not
particularly limited thereto. The pressure in the extraction step
(S2) depends on the temperature during extraction and the vapor
pressure of the solvent used, but is preferably in the range of 1.0
to 2.0 MPa. If the pressure is lower than the vapor pressure of the
solvent, the solvent vaporizes and is not confined in a liquid
phase, and thus extraction cannot be performed. In order to confine
the solvent in the liquid phase, a pressure higher than the vapor
pressure of the solvent is necessary. On the other hand, if the
pressure is excessively high, the cost of the apparatus and the
operation cost increase, which is not economical.
<Separation Step (S3)>
[0070] The separation step (S3) is a step of separating the slurry
obtained in the extraction step (S2) into a liquid portion and a
non-liquid portion.
[0071] Here, the term "liquid portion" refers to a solution
containing a coal component extracted in a solvent, and the term
"non-liquid portion" refers to a slurry containing a coal component
that is insoluble in the solvent (coal containing ash, i.e., ash
coal).
[0072] A method of separating the slurry into the liquid portion
and the non-liquid portion in the separation step (S3) is not
particularly limited, but a gravitational settling method is
preferably used.
[0073] Various types of filtering methods and methods of
centrifugal separation are generally known as a method of
separating a slurry into a liquid portion and a non-liquid portion.
However, in the methods of filtration, it is necessary to change a
filter aid frequently. In addition, in the methods of centrifugal
separation, clogging due to an undissolved coal component readily
occurs. Therefore, it is difficult to carry out these methods on an
industrial scale. Accordingly, the gravitational settling method,
in which a continuous operation of a fluid can be performed, which
can be performed at a low cost, and thus which is suitable for
treatment of a large amount, is preferably used. Thereby, a liquid
portion (hereinafter, also referred to as "supernatant"), which is
a solution containing a coal component extracted in the solvent,
can be obtained from an upper portion of a gravity settling
chamber, and a non-liquid portion (hereinafter, also referred to as
"solid-concentrated liquid"), which is a slurry containing a coal
component insoluble in the solvent, can be obtained from an lower
portion of the gravity settling chamber.
[0074] An example of the gravitational settling method will now be
described with reference to FIGS. 1 and 2.
[0075] As shown in FIG. 2, in the gravitational settling method, in
a sold-liquid separator 100, first, powdery coal which is a raw
material for ashless coal is mixed with a solvent in a coal slurry
preparation tank 1 to prepare a slurry (slurry preparation step
(S1)). Next, a predetermined amount of the slurry is supplied from
the coal slurry preparation tank 1 to a preheater 3 using a pump 2,
and the slurry is heated to a temperature in the range of
400.degree. C. to 420.degree. C. The heated slurry is then supplied
to an extraction chamber (extractor) 4. The slurry is heated at a
temperature in the range of 400.degree. C. to 420.degree. C. for 20
minutes or less under stirring with a stirrer 10, and then
immediately cooled to 370.degree. C. or lower with a cooler 7
(extraction step (S2)). Note that, in order to immediately perform
cooling, a cooling mechanism is preferably provided in the
extraction chamber 4. The term "20 minutes or less" used here means
the total of the heating time in the preheater 3 and the heating
time in the extraction chamber 4, that is, the time from the start
of heating in the preheater 3 at a temperature in the range of
400.degree. C. to 420.degree. C. to the immediate cooling to
370.degree. C. or lower. The slurry obtained after this extraction
treatment is supplied to a gravity settling chamber 5, and the
slurry is separated into a supernatant and a solid-concentrated
liquid (separation step (S3)). The solid-concentrated liquid
settled in a lower portion of the gravity settling chamber 5 is
discharged to a solid-concentrated liquid receiver 6, and a
predetermined amount of supernatant in an upper portion thereof is
discharged to a filter unit 8.
[0076] Here, in order to prevent reprecipitation of a solute eluted
from the coal of the raw material, the gravity settling chamber 5
is preferably maintained at a temperature in the range of
350.degree. C. to 370.degree. C., i.e., a temperature cooled after
the heating of the slurry, and the pressure therein is preferably
controlled to be in the pressured range of 1.0 to 2.0 MPa.
[0077] The time during which the slurry is maintained at the cooled
temperature in the gravity settling chamber 5 is a time required
for separating the slurry into the supernatant and the
solid-concentrated liquid. This time is generally in the range of
60 to 120 minutes, but is not particularly limited.
[0078] By increasing the number of gravity settling chambers 5, a
component soluble in the solvent contained in the
solid-concentrated liquid can be recovered. In order to efficiently
recover the component, the gravity settling chambers 5 are
preferably arranged in two stages.
[0079] The supernatant discharged from the gravity settling chamber
5 is filtered through the filter unit 8 according to need, and is
recovered to a supernatant receiver 9.
[0080] Next, as described below, the solvent is separated and
recovered from the liquid portion and the non-liquid portion by a
distillation method or the like, and ashless coal which is improved
coal not containing ash is obtained from the liquid portion
(improved-coal-obtaining step (S4)). Furthermore, residue coal
which is improved coal containing concentrated ash can be obtained
from the non-liquid portion, as required.
<Improved-Coal-Obtaining Step (S4)>
[0081] The improved-coal-obtaining step (S4) is a step of
separating the solvent from the liquid portion separated in the
separation step (S3) to obtain ashless coal which is improved coal
(ashless coal-obtaining step).
[0082] As a method of separating the solvent from the supernatant
(liquid portion), a general distillation method, evaporation method
(such as a spray drying method), or the like can be employed. The
solvent recovered by the separation can be circulated in the coal
slurry preparation tank 1 (see FIG. 2) and used repeatedly. By
separating and recovering the solvent, ashless coal that does not
substantially contain ash can be obtained from the supernatant.
[0083] This ashless coal hardly contains ash, is free of moisture,
and has a heat value higher than that of the raw coal. Furthermore,
thermal plasticity, which is a particularly important quality as a
raw material for coke for iron making, is markedly improved, and
the ashless coal exhibits a performance (fluidity) superior to that
of the raw coal. Accordingly, this ashless coal can be used as
blended coal for a raw material for coke. In addition, the ashless
coal can also be used as blended coal by mixing with the residue
coal.
[0084] According to need, in the improved-coal-obtaining step (S4),
in addition to the production of the ashless coal, residue coal
which is improved coal may be produced by separating the solvent
from the non-liquid portion separated in the separation step (S3)
(residue-coal-obtaining step).
[0085] As a method of separating the solvent from the
solid-concentrated liquid (non-liquid portion), a general
distillation method or an evaporation method can be employed as in
the ashless coal-obtaining step described above. The solvent
recovered by the separation can be circulated in the coal slurry
preparation tank 1 (see FIG. 2) and used repeatedly. By separating
and recovering the solvent, residue coal in which ash is
concentrated can be obtained from the solid-concentrated
liquid.
[0086] This residue coal contains ash, but is free of moisture and
has a sufficient heat value. The residue coal does not exhibit
thermal plasticity, but an oxygen-containing functional group is
eliminated from the residue coal. Therefore, in the case where the
residue coal is used as blended coal, the residue coal does not
obstruct thermal plasticity of other coal contained in the blended
coal. Accordingly, this residue coal can be used as part of blended
coal for a raw material for coke as in general non- or slightly
caking coal. Alternatively, the residue coal can be used as various
types of fuels instead of being used in caking coal for coke.
[0087] Only the ashless coal not containing ash may be produced
from the liquid portion as caking coal for coke. Only the solvent
may be recovered from the non-liquid portion, and the residue coal
in which the ash is concentrated may be disposed of without being
recovered.
[0088] The present invention has been described above. However,
when the present invention is carried out, as long as the
above-described steps are not adversely affected, other steps such
as a coal-crushing step of crushing raw coal, a removing step of
removing undesired substances such as contaminations, and a drying
step of drying the prepared ashless coal may be performed between
the steps or before or after the steps.
EXAMPLES
[0089] Next, a method of producing ashless coal according to the
present invention will be specifically described using
Examples.
Example 1
[0090] In Example 1, in the case where an extraction temperature in
an extraction step was 370.degree. C., changes in thermal
plasticity (softening fluidity), a resolidification temperature,
and the like of raw coal samples and ashless coal samples obtained
from the raw coal samples were examined (Experimental Example
1).
[0091] Strongly caking coal A, strongly caking coal B, and
sub-bituminous coal C having industrial analysis values and
elemental analysis values shown in Table 1 were used as raw coal
samples. Five kilograms of each of the raw coal samples was mixed
with 20 kg (fourfold) of a solvent (1-methylnaphthalene (produced
by Nippon Steel Chemical Co., Ltd.) to prepare slurries. Extraction
was performed by pressing each of the slurries with nitrogen at a
pressure of 1.2 MPa in an autoclave having an internal volume of 30
L at 370.degree. C. for one hour. Each of the slurries was
separated into a supernatant and a solid-concentrated liquid in a
gravity settling chamber in which the same temperature and the same
pressure were maintained. The solvent was separated and recovered
from the supernatant by a distillation method. Ashless coal a was
prepared from the strongly caking coal A, ashless coal b was
prepared from the strongly caking coal B, and ashless coal c was
prepared from the sub-bituminous coal C. Industrial analysis values
and elemental analysis values of these samples are shown in Table
1.
[0092] Next, for the strongly caking coal A, the strongly caking
coal B, the sub-bituminous coal C, the ashless coal a, the ashless
coal b, and the ashless coal c, a Gieseler plastometer test defined
in JIS M 8801 was performed.
[0093] The test results are shown in Table 1. FIG. 3 is a graph
showing Gieseler curves obtained by the Gieseler plastometer
test.
TABLE-US-00001 TABLE 1 Industrial analysis value Heat Results of
Gieseler plastometer test Volatile value Softening Maximum Log
Total Ash component Elemental analysis value (HV) staring fluidity
(maximum Resolidification moisture [Wt %] [Wt %] (daf C H N S O
[kcal/kg] temperature temperature fluidity) temperature [Wt %] (db)
basis) [Wt %] (daf basis) (gross) [.degree. C.] [.degree. C.]
[ddpm] [.degree. C.] Strongly 1.6 10.4 27.8 88.4 5.6 2.4 0.7 2.9
7340 397 462 2.79 496 caking coal A Ashless 0.0 0.03 26.9 89.3 5.0
2.5 0.6 2.6 8510 330 447 3.86 508 coal a Strongly 1.6 10.3 32.1
87.0 5.5 2.3 0.7 4.6 7590 425 455 2.08 483 caking coal B Ashless
0.0 0.05 29.8 86.6 5.0 1.9 0.7 5.9 8590 320 443 3.47 488 coal b
Sub- 5.8 8.2 40.8 76.4 5.5 1.9 0.9 15.4 7030 392 423 0.78 445
bituminous coal C Ashless 0.0 0.08 49.1 81.2 5.8 1.8 0.8 10.4 8560
183 297 to 427 >4.48 463 coal c
[0094] As shown in Table 1, the ashless coal a, the ashless coal b,
and the ashless coal c did not contain moisture, and the ash
contents thereof were very small as compared with those of the raw
coal samples. In addition, the ashless coal a, the ashless coal b,
and the ashless coal c exhibited heat values higher than those of
the raw coal samples. The oxygen concentration of the
sub-bituminous coal C was high; more than 15%. In addition,
although the oxygen concentration of the ashless coal c was
decreased to about 10%, a relatively high oxygen concentration was
maintained.
[0095] Here, in the results of the Gieseler plastometer test, the
resolidification temperatures of the raw coal samples will be
discussed. The resolidification temperature of the strongly caking
coal A was 496.degree. C., and the resolidification temperature of
the strongly caking coal B was 483.degree. C. In contrast, the
resolidification temperature of the sub-bituminous coal C was low;
445.degree. C. If the sub-bituminous coal C was used as one
component of blending coal for coke, the lower resolidification
temperature obstructs the melting state of the whole blending coal
in the coking process. Accordingly, the sub-bituminous coal C
cannot be used as caking coal for coke for iron making.
[0096] Referring to the values of the maximum fluidity shown in
FIG. 3 and Table 1, as for thermal plasticity, the ashless coal a,
the ashless coal b, and the ashless coal c obtained from the above
raw coal samples exhibited satisfactory thermal plasticity
significantly higher than that of corresponding raw coal
samples.
[0097] However, as for the resolidification temperatures of the
prepared ashless coal samples, the ashless coal a obtained from the
strongly caking coal A was 508.degree. C., and the ashless coal b
obtained from the strongly caking coal B was 488.degree. C. That
is, the ashless coal a and the ashless coal b were solidified at
temperatures higher than those of the strongly caking coal A and
the strongly caking coal B, respectively, which were raw coal
samples of the ashless coal samples. The resolidification
temperature of the ashless coal c obtained from the sub-bituminous
coal C was higher than that of the sub-bituminous coal C, which was
a raw coal sample, but was relatively low; 463.degree. C.
[0098] Here, in the case where the ashless coal c is added to
caking coal for coke for iron making and coked as blended coal, the
ashless coal c is solidified at 463.degree. C., during which
strongly caking coal maintains the fluidity, thus obstructing the
fluidity of the whole blended coal. As a result, the strength of
the resulting coke is decreased.
[0099] According to the above results, in the case where
low-quality coal such as sub-bituminous coal is used as raw coal,
even when ashless coal is produced under the above conditions, the
ashless coal is not particularly excellent as caking coal for coke
for iron making.
[0100] When strongly caking coal (or caking coal) is used as raw
coal, the resulting ashless coal exhibited thermal plasticity
superior to that of the raw coal and can be used as caking coal for
coke for iron making. However, strongly caking coal is expensive,
and thus the raw material cost cannot be reduced.
Example 2
[0101] In Example 2, the relationship between the extraction
temperature when an extraction treatment of the sub-bituminous coal
C used in Example 1 was performed and the resolidification
temperature of the ashless coal c obtained from the sub-bituminous
coal C was examined (Experimental Example 2).
[0102] FIG. 4 shows the relationship between the extraction
temperature and the resolidification temperature of the prepared
ashless coal c in the case where an extraction treatment was
performed with an extraction time of one hour (60 minutes) using
the sub-bituminous coal C was used as raw coal.
[0103] The method of producing ashless coal was performed in
accordance with Example 1 except that the extraction temperature
was changed.
[0104] As shown in FIG. 4, at extraction temperatures exceeding
about 360.degree. C., as the extraction temperature increased, the
resolidification temperature of the ashless coal c increased. At an
extraction temperature of 400.degree. C., the resolidification
temperature was about 490.degree. C., that is, the resolidification
temperature was increased to substantially the same as the
resolidification temperature of the above strongly caking coal. The
resolidification temperature further increased at temperatures
exceeding 400.degree. C. Accordingly, it was found that the
resolidification temperature of the resulting ashless coal was
increased by increasing the extraction temperature of coal to
400.degree. C. or higher.
[0105] According to the above results, in the case where
low-quality coal such as sub-bituminous coal is used as raw coal,
by controlling the extraction temperature to be 400.degree. C. or
higher, the resulting ashless coal can be used as caking coal of
coke for iron making.
Example 3
[0106] In Example 3, the relationships between the extraction
temperature, the extraction time, and the extraction yield in the
case where an extraction treatment of the sub-bituminous coal C
used in Example 1 was performed were examined (Experimental Example
3).
[0107] FIG. 5 shows the relationship between the extraction time
and the extraction yield in the case where the sub-bituminous coal
C was heated to an extraction temperature of 370.degree. C.,
400.degree. C., or 420.degree. C. with a preheater, and kept in an
extractor for a predetermined time, and then rapidly cooled to
360.degree. C. to perform an extraction treatment. In the
experiment at 420.degree. C., the time required for increasing the
temperature from 400.degree. C. to 420.degree. C. in the preheater
was eight minutes. Accordingly, in FIG. 5, extraction times which
also include the eight minutes, which corresponds to an extraction
time from 400.degree. C. to 420.degree. C., in the preheater are
shown.
[0108] The method of producing ashless coal was performed in
accordance with Example 1 except that the extraction temperature
and the extraction time were changed.
[0109] The extraction yield of coal was determined from the amount
of separated solid residue coal.
[0110] Specifically, the extraction yield was determined using a
formula of (raw coal-residue coal)/raw coal.times.100. Note that
the amounts of raw coal and residue coal were determined on the
basis of the amount of anhydrous ashless coal.
[0111] Herein, the term "extraction time" means the following
temperature-maintaining time: In the case where the temperature is
increased to a predetermined temperature, the temperature is
maintained, and the temperature is then decreased to 370.degree. C.
or lower, the time during which the predetermined temperature is
maintained is referred to as "extraction time". The term
"extraction time zero" means a case where the temperature is
increased to a predetermined temperature, and a cooling treatment
is then immediately performed without maintaining the
temperature.
[0112] As shown in FIG. 5, at an extraction temperature of
370.degree. C., the maximum extraction yield was obtained at an
extraction time of 30 minutes. Even when the extraction time was
prolonged for several hours, the extraction yield of coal did not
significantly changed. In contrast, at temperatures of 400.degree.
C. and 420.degree. C., which are in a temperature range in which
thermal decomposition of coal rapidly occurs, when the temperature
was maintained for a relatively long time, the extraction yield was
significantly decreased by, for example, a repolymerization
reaction of radicals generated by the thermal decomposition of the
coal. Accordingly, it was found that maintaining the temperature
for a long time was not economical.
[0113] It is known that, at temperatures exceeding 420.degree. C.,
the thermal decomposition significantly occurs, thereby decreasing
the extraction yield. Therefore, experiments at such temperatures
were omitted here.
[0114] Specifically, at an extraction temperature of 400.degree.
C., the extraction yield was hardly changed in an extraction time
in the range of 0 to 20 minutes, and an extraction yield of about
60% or more could be achieved. However, when the extraction time
reached 60 minutes, the extraction yield was decreased to about
50%. In addition, it was found that even when the extraction
temperature was increased to 420.degree. C., a relatively high
extraction yield (about 52% or more) could be maintained within an
extraction time of 20 minutes.
[0115] Note that, in general, an extraction yield of about 52% or
more can be considered to be as a relatively high extraction
yield.
[0116] The above results showed that in the case where the
extraction temperature was in the range of 400.degree. C. to
420.degree. C. and the time before the temperature was cooled to
370.degree. C. or lower was 20 minutes or less, ashless coal could
be obtained at a high efficiency.
[0117] Ashless coal obtained under an extraction condition of
400.degree. C. for zero minutes had a resolidification temperature
of 483.degree. C., and ashless coal obtained under an extraction
condition of 400.degree. C. for 10 minutes had a resolidification
temperature of 490.degree. C. Ashless coal obtained under an
extraction condition of 420.degree. C. for zero minutes had a
resolidification temperature of 487.degree. C., and ashless coal
obtained under an extraction condition of 420.degree. C. for 22
minutes had a resolidification temperature of 486.degree. C.
Accordingly, the resolidification temperatures of the above ashless
coal samples obtained by heating low-quality coal such as
sub-bituminous coal at a temperature in the range of 400.degree. C.
to 420.degree. C. for 20 minutes or less and then cooling to
370.degree. C. or lower were comparable to the resolidification
temperature of the above strongly caking coal. Accordingly, even
when such ashless coal is added to caking coal for coke for iron
making to prepare blended coal, the fluidity of strongly caking
coal contained in the blended coal is not obstructed and the
fluidity of the whole blended coal is not obstructed.
[0118] On the other hand, at an extraction temperature of
370.degree. C., a resolidification temperature of about 460.degree.
C. is merely achieved. Accordingly, even though the extraction
yield is high, as described above, the resulting ashless coal is
not particularly excellent as caking coal for coke for iron
making.
[0119] According to the results of Examples 1 to 3, it was found
that, in the case where low-quality coal such as inexpensive non-
or slightly caking coal is used as a raw material, conditions for
obtaining ashless coal having a high resolidification temperature
at a high efficiency are as follows: As an extraction temperature,
the temperature is increased to 400.degree. C. to 420.degree. C.,
heating is performed at the temperature for 20 minutes or less, and
the temperature is then decreased to 370.degree. C. or lower. In
addition, the time (extraction time) during which the temperature
is maintained in the range of 400.degree. C. to 420.degree. C. is
preferably 15 minutes or less, and more preferably 10 minutes or
less. Furthermore, the extraction time is preferably as short as
possible.
[0120] In addition, even when ashless coal thus obtained is added
to caking coal for coke for iron making to prepare blended coal,
the strength of the coke is not degraded.
[0121] In Examples 2 and 3, cases where low-quality coal is used as
a raw material have been described. Alternatively, in the case
where caking coal (strongly caking coal) is used as a raw material,
the resulting ashless coal has a quality higher than the ashless
coal produced using low-quality coal as the raw material.
Furthermore, the resulting ashless coal has a quality higher than
the caking coal used as raw coal. Accordingly, in order to produce
ashless coal having a higher quality, caking coal is used as a raw
material. However, in the case where a reduction in the cost of raw
coal for coke is important, inexpensive low-quality coal is
preferably used as the raw material.
[0122] A method of producing ashless coal according to the present
invention has been described in detail using the best mode and
Examples. However, the purpose of the present invention is not
limited to the features described above, and the scope of right of
the present invention should be widely interpreted on the basis of
the description of Claims. It is to be understood that the features
of the present invention can be widely modified and changed on the
basis of the above description.
* * * * *