U.S. patent application number 15/772265 was filed with the patent office on 2018-11-08 for method for producing ash-free coal.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd). The applicant listed for this patent is Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd). Invention is credited to Shigeru KINOSHITA, Noriyuki OKUYAMA, Koji SAKAI, Takuya YOSHIDA.
Application Number | 20180320097 15/772265 |
Document ID | / |
Family ID | 58764034 |
Filed Date | 2018-11-08 |
United States Patent
Application |
20180320097 |
Kind Code |
A1 |
SAKAI; Koji ; et
al. |
November 8, 2018 |
METHOD FOR PRODUCING ASH-FREE COAL
Abstract
A method for producing ash-free coal includes: pulverizing a
coal in the presence of a protection solvent; heating an extraction
solvent; mixing pulverized matter obtained after the pulverizing,
with the extraction solvent obtained after the heating; separating
a solution containing a coal component dissolved therein, from a
slurry obtained after the mixing; and evaporatively separating the
protection solvent and the extraction solvent from the solution
obtained after the separating.
Inventors: |
SAKAI; Koji; (Hyogo, JP)
; OKUYAMA; Noriyuki; (Hyogo, JP) ; YOSHIDA;
Takuya; (Hyogo, JP) ; KINOSHITA; Shigeru;
(Hyogo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) |
Kobe-shi |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd)
Kobe-shi
JP
|
Family ID: |
58764034 |
Appl. No.: |
15/772265 |
Filed: |
November 9, 2016 |
PCT Filed: |
November 9, 2016 |
PCT NO: |
PCT/JP2016/083189 |
371 Date: |
April 30, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10L 5/366 20130101;
C10L 5/04 20130101; C10L 2250/06 20130101; C10L 2290/544 20130101;
C10L 9/10 20130101; C10L 9/00 20130101 |
International
Class: |
C10L 5/36 20060101
C10L005/36; C10L 9/10 20060101 C10L009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2015 |
JP |
2015-230140 |
Claims
1. A method for producing ash-free coal, comprising: pulverizing a
coal in the presence of a protection solvent; heating an extraction
solvent; mixing pulverized matter obtained after the pulverizing,
with the extraction solvent obtained after the heating; separating
a solution containing a coal component dissolved therein, from a
slurry obtained after the mixing; and evaporatively separating the
protection solvent and the extraction solvent from the solution
obtained after the separating.
2. The method according to claim 1, wherein the pulverized matter
obtained after the pulverizing has a mean particle diameter of 0.2
mm or less.
3. The method according to claim 1, wherein in the mixing, the
pulverized matter is mixed with the extraction solvent in such a
manner that a temperature of the pulverized matter is raised at a
rate of 600.degree. C./min or higher.
4. The method according to claim 1, wherein the protection solvent
and the extraction solvent are identical solvents.
5. The method according to claim 1, wherein in the pulverizing, a
content of the protection solvent in a mixture of the coal and the
extraction solvent is greater than or equal to 20% by mass and less
than or equal to 60% by mass.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing
ash-free coal.
BACKGROUND ART
[0002] Coal finds extensive use as fuels for thermal power
generation or boilers, or as materials of chemical products. Thus,
it has been strongly desired to develop techniques for efficiently
removing ash from coal, as a measure for environmental
preservation. Attempts to use ash-free coal (hyper coal) cleared of
ash have been made as, for example, a substitute for liquid fuels
such as LNG in high-efficiency combined-cycle generation systems
driven by gas turbine combustion. Also, ash-free coal has been put
to trial use as coking coal for steelmaking, such as cokes for use
in blast furnaces.
[0003] It has been common practice to produce ash-free coal by:
mixing a coal with a solvent to prepare a slurry; heating the
slurry to allow soluble components of the coal to be dissolved in
the solvent; recovering a solution containing the soluble
components dissolved therein by solid-liquid separation; and
evaporating the solvent contained in the solution to extract only
the soluble components of the coal.
[0004] In regard to the production of ash-free coal, there have
been demands that the production efficiency of ash-free coal be
improved through increased yield by allowing a larger amount of
components of coal to be dissolved in the solvent. To increase the
yield of ash-free coal, a technique has been proposed that
accelerates dissolution of components of coal by raising the
temperature of the coal within a short time period through mixing a
preheated solvent with the coal (see, for example, Japanese
Unexamined Patent Application, Publication No. 2014-208757). It is
inferred that the rapid rise in the temperature of coal weakens the
bonds between molecules constituting the coal, and consequently
accelerates dissolution of the components, which might be otherwise
time-consuming.
[0005] However, even when mixed with the high-temperature solvent,
a coal composed of large particles cannot be rapidly heated
entirely to its central portion. In this regard, the aforementioned
publication discloses the use of finely pulverized coals in which
the weight proportion of coals having a grain size of less than 1
mm is greater than or equal to 80%.
[0006] The present inventors accordingly pulverized a coal into
powder having a mean particle diameter of about 0.1 mm, in an
attempt to improve the extraction rate. However, the coal
pulverized into powder rather exhibited a lower extraction
rate.
PRIOR ART DOCUMENT
Patent Document
[0007] Patent Document 1: Japanese Unexamined Patent Application,
Publication No. 2014-208757
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0008] In view of such a circumstance, the present invention has an
object to provide a method for producing ash-free coal that enables
a relatively high rate of extraction from coal to be achieved.
Means for Solving the Problem
[0009] After a thorough investigation, the present inventors
concluded that the coal increased in surface area through
pulverization into powder, and was subjected accelerated aeration
(oxidation) through increased contact with air accordingly,
resulting in a decrease in components to be converted into ash-free
coal and thus leading to a lower extraction rate. The present
inventors therefore have accomplished the present invention in the
expectation that pulverizing a coal without aeration would improve
the extraction rate and increase the production efficiency of
ash-free coal.
[0010] According to an aspect of the invention made for solving the
aforementioned problem, a method for producing ash-free coal
includes: pulverizing a coal in the presence of a protection
solvent; heating an extraction solvent; mixing pulverized matter
obtained after the pulverizing, with the extraction solvent
obtained after the heating; separating a solution containing a coal
component dissolved therein, from a slurry obtained after the
mixing; and evaporatively separating the protection solvent and the
extraction solvent from the solution obtained after the
separating.
[0011] Due to involving pulverizing a coal in the presence of the
protection solvent, the method for producing ash-free coal of the
aspect of the invention enables the particle diameter of the coal
to be reduced, while preventing or minimizing aeration of the coal
through reduced contact with air. The method thus prevents or
minimizes loss of components to be converted into ash-free coal,
and enables the coal to be rapidly heated entirely to its central
portion by the heat of the extraction solvent preheated in the
mixing, thereby enabling a relatively high rate of extraction from
coal to be achieved. Therefore, the method for producing ash-free
coal achieves efficient production of ash-free coal.
[0012] The pulverized matter obtained after the pulverizing
preferably has a mean particle diameter of 0.2 mm or less. When
having a mean particle diameter of less than or equal to the upper
limit, the pulverized matter obtained after the pulverizing is
rapidly heated entirely to its central portion in the mixing,
thereby enabling a relatively high rate of extraction from coal to
be achieved. The term "mean particle diameter" as referred to
herein means a particle diameter corresponding to 50% on the
cumulative volumetric particle size distribution as measured by
laser diffraction.
[0013] In the mixing, the pulverized matter is preferably mixed
with the extraction solvent in such a manner that a temperature of
the pulverized matter is e at a rate of 600.degree. C./min or
higher. Mixing the pulverized matter with the extraction solvent in
the mixing in such a manner that the temperature of the pulverized
matter is raised at a rate of temperature rise of 600.degree.
C./min or higher enables a higher rate of extraction from coal to
be achieved more reliably. The "rate of temperature rise of the
pulverized matter" as referred to herein means a value determined
by dividing the temperature difference between a
temperature-stabilized slurry and the pulverized matter unmixed
with the extraction solvent, by the time between the start of the
mixing and the instant when the temperature of the extraction
solvent, i.e., the apparent temperature of the slurry, stabilized
(the time needed for the internal temperature of the pulverized
matter to conceivably reach the temperature of the extraction
solvent).
[0014] The protection solvent and the extraction solvent are
preferably identical solvents. After being separated and recovered
in the evaporatively separating, the protection solvent and the
extraction solvent that are identical solvents can be recycled as
the protection solvent or the extraction solvent.
[0015] In the pulverizing, a content of the protection solvent is
preferably greater than or equal to 20% by mass and less than or
equal to 60% by mass. In the case where the content of the
protection solvent in the pulverizing falls within the range, the
total amount of the sensible heat of the protection solvent is
reduced, and the amount of heat required for the extraction solvent
in the mixing is regulated accordingly, while aeration is prevented
more reliably during the pulverization.
Effects of the Invention
[0016] Therefore, the method for producing ash-free coal according
to the aspect of the present invention enables a relatively high
rate of extraction from coal to be achieved.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 is a flowchart of a procedure for producing ash-free
coal according to an embodiment of the present invention.
[0018] FIG. 2 is a graph showing the extraction rate and the
particle diameter of coal for each of Example, Control Example and
Comparative Examples of the present invention.
DESCRIPTION OF EMBODIMENTS
[0019] An embodiment of the present invention will be described in
detail with appropriate references to the drawings.
Method for Producing Ash-Free Coal
[0020] With reference to FIG. 1, a method for producing ash-free
coal includes: pulverizing a coal in the presence of a protection
solvent (Step S1: Pulverizing Step); heating an extraction solvent
(Step S2: Heating Step); mixing pulverized matter obtained after
the pulverizing step, with the extraction solvent obtained after
the heating step (Step S3: Mixing Step); separating a solution
containing a coal component dissolved therein, from a slurry
obtained after the mixing step (Step S4: Solution Separating Step);
and evaporatively separating the protection solvent and the
extraction solvent from the solution obtained after the separating
step (Step S5: Evaporatively Separating Step).
[0021] Pulverizing Step
[0022] In Step S1, the pulverizing step is performed to pulverize a
coal in the presence of the protection solvent, which covers the
surfaces of pulverized coals to keep the surfaces (cross sections)
exposed by the pulverization of the coal from contact with air
(oxygen, in particular).
[0023] The pulverizing may be carried out by using, for example, a
planetary mill, a ball mill, an impact mill, a ring rolling mill or
a ball race mill.
[0024] Pulverizing a coal premixed with the protection solvent in
the pulverizing step prevents aeration of the coal more reliably.
Alternatively, a coal may be mixed with the protection solvent
while being pulverized in a particular type of mills, such as a
batch mill, so that the surfaces of coal particles are covered with
the protection solvent.
[0025] The pulverizing step is preferably performed under an
atmospheric pressure in light of equipment costs and energy costs.
In the pulverizing step, the upper limit of the temperature of the
coal and the protection solvent is preferably 100.degree. C., more
preferably 80.degree. C., and still more preferably 50.degree. C.
Although the lower limit of the temperature of the coal and the
protection solvent in the pulverizing step is not limited, cooling
that would lead to unnecessary increases in cost is not preferred.
In the case where the temperature of the coal and the protection
solvent in the pulverizing step is greater than the upper limit,
the bonds between molecules constituting the coal may not be
weakened in the mixing step, resulting in insufficient improvement
effect on the extraction rate.
[0026] The lower limit of the mean particle diameter of the
pulverized matter obtained after the pulverizing step is preferably
0.01 mm, and more preferably 0.02 mm. The upper limit of the mean
particle diameter of the pulverized matter obtained after the
pulverizing step is preferably 0.2 mm, and more preferably 0.1 mm.
In the case where the mean particle diameter of the pulverized
matter is less than the lower limit, the improvement effect on the
extraction rate produced by the pulverization of a coal into small
particles may plateau, and this may lead to unnecessary increases
in cost. Conversely, in the case where the mean particle diameter
of the pulverized matter is greater than the upper limit, the
improvement effect on the extraction rate may be insufficient.
[0027] The upper limit of the particle diameter corresponding to 90
on the cumulative volumetric particle size distribution of the
pulverized matter obtained after the pulverizing step is preferably
0.5 mm, and more preferably 0.2 mm. The lower limit of the particle
diameter corresponding to 90 on the cumulative volumetric particle
size distribution of the pulverized matter obtained after the
pulverizing step is not limited, and may be any value falling
within the range of the mean particle diameter. In the case where
the particle diameter corresponding to 90 on the cumulative
volumetric particle size distribution of the pulverized matter is
greater than the upper limit, the improvement effect on the
extraction rate may be insufficient.
[0028] Coal
[0029] Coal feedstock according to the method for producing
ash-free coal is not limited to particular coals, and may be coals
of various ranks. For example, bituminous coal with a high
extraction rate, or less expensive low-quality coals (subbituminous
coal and lignite) may be suitably used. A combination of different
types of coals may be used as coal feedstock. These coals may be
dried beforehand by, for example, air-drying, or may contain the
moisture when being used.
[0030] Protection Solvent
[0031] The protection solvent for covering the surfaces of coals in
the pulverizing step may be any solvent that is miscible with the
extraction solvent (described below) and removable through
pyrolysis or evaporative separation in the evaporatively separating
step. In particular, a solvent having a strong affinity for coals
(capable of easily wetting coals) at normal temperature is
preferred.
[0032] The upper limit of the kinetic viscosity of the protection
solvent at 20.degree. C. is preferably 100 mm.sup.2/s, and more
preferably 10 mm.sup.2/s. The lower limit of the kinetic viscosity
of the protection solvent at 20.degree. C. is not limited. In the
case where the kinetic viscosity of the protection solvent at
20.degree. C. is greater than the upper limit, films formed of the
protection solvent may be likely to get ripped on the surfaces of
coals, failing to sufficiently prevent aeration of the coals. It is
to be noted that the term "kinetic viscosity" as referred to herein
means a value measured in accordance with JIS-K2283 (2000).
[0033] Examples of the protection solvent include: monocyclic
aromatic compounds such as benzene, toluene and xylene; bicyclic
aromatic compounds such as naphthalene, methylnaphthalene,
dimethylnaphthalene and trim ethylnaphthalene; and the like.
[0034] The protection solvent may contain additives such as a
surfactant for improving wettability of coal. Additives that will
be pyrolyzed in the mixing step or the evaporatively separating
step are preferred for easy recycling of solvents.
[0035] In the pulverizing step, the lower limit of the content of
the protection solvent (the proportion of the protection solvent in
the mixture of the coal and the protection solvent) on a dry
ash-free basis (daf) is preferably 20% by mass, and more preferably
30% by mass. The upper limit of the content of the protection
solvent in the pulverizing step is preferably 60% by mass, and more
preferably 50% by mass. In the case where the content of the
protection solvent in the pulverizing step is less than the lower
limit, the protection solvent may fail to cover the surfaces of
coals, and consequently, may fail to sufficiently prevent aeration
of the coals. In addition, such a solvent may impart poor fluidity
to the pulverized matter, making it less easy to handle.
Conversely, in the case where the content of the protection solvent
in the pulverizing step is greater than the upper limit, a greater
amount of heat may be required for the solvent in the mixing step
(described below) to offset the sensible heat load of the
protection solvent, leading to unduly low production efficiency of
ash-free coal.
[0036] The pulverized matter obtained in the pulverizing step is
preferably pasty, for improved handleability in the mixing step
(described below). The lower limit of the viscosity of the
pulverized matter in the form of a paste at 30.degree. C. is
preferably 0.5 Pa.s, and more preferably 1 Pa. s. The upper limit
of the viscosity of the pulverized matter in the form of a paste is
preferably 1,000 Pa.s, and more preferably 600 Pa.s. In the case
where the viscosity of the pulverized matter in the form of a paste
is less than the lower limit, the proportion of the protection
solvent in the pulverized matter in the form of a paste may be
excessively large, and thus, the rate of temperature rise in the
mixing step (described below) may not be high enough for producing
sufficient improvement effect on the extraction rate. Conversely,
in the case where the viscosity of the pulverized matter in the
form of a paste is greater than the upper limit, the pulverized
matter in the form of a paste may be less easy to handle.
[0037] Heating Step
[0038] In Step S2, the heating step is performed to preheat the
extraction solvent. A heating process of the extraction solvent is
not limited, and for example, in-line heating by a heat exchanger
may be performed. The heat exchanger may be of, for example, the
multitubular, plate or spiral type.
[0039] Extraction Solvent
[0040] The extraction solvent is not limited, and may be any
solvent in which coal can be dissolved. Examples of the extraction
solvent include: monocyclic aromatic compounds such as benzene,
toluene and xylene; bicyclic aromatic compounds such as
naphthalene, methylnaphthalene, dimethylnaphthalene and
trimethylnaphthalene; and the like. Of these, coal-derived bicyclic
aromatic compounds such as methylnaphthalene and naphthalene, which
are oils obtained by distilling oils being by-products of
carbonizing coal in coke production, are suitably used. The
bicyclic aromatic compounds have a basic structure similar to that
of structural molecules of coal, and thus have a strong affinity
for coal. This feature enables a relatively high extraction rate to
be achieved.
[0041] The extraction solvent and the protection solvent are
preferably identical solvents. After being separated and recovered
in the evaporatively separating step (described below), the
protection solvent and the extraction solvent that are identical
solvents can be recycled as the protection solvent and the
extraction solvent directly, thereby leading to a reduction in the
cost of ash-free coal production.
[0042] The boiling point of the extraction solvent is not limited.
For example, the lower limit of the boiling point of the extraction
solvent is preferably 180.degree. C., and more preferably
230.degree. C. The upper limit of the boiling point of the
extraction solvent is preferably 300.degree. C., and more
preferably 280.degree. C. In the case where the boiling point of
the extraction solvent is below the lower limit, the recovery rate
of the extraction solvent may be low due to a great loss of the
extraction solvent to be recovered in the evaporatively separating
step (described below). Conversely, in the case where the boiling
point of the extraction solvent is above the upper limit, the
solvent-soluble components may be less separable form the
extraction solvent, and the recovery rate of the extraction solvent
may be low as in the above case.
[0043] The lower limit of the temperature of the heated extraction
solvent is preferably 330.degree. C., and more preferably
380.degree. C. The upper limit of the temperature of the heated
extraction solvent is preferably 450.degree. C., and more
preferably 430.degree. C. In the case where the temperature of the
heated extraction solvent is below the lower limit, the extraction
solvent may fail to sufficiently raise the temperature of the
pulverized coals in the mixing step (described below), resulting in
an insufficient extraction rate. Conversely, in the case where the
temperature of the heated extraction solvent is above the upper
limit, pyrolysis radicals generated in pyrolytic reactions of coal
in the mixing step may recombine, also resulting in a low
extraction rate.
[0044] Mixing Step
[0045] In Step S3, the mixing step is performed to mix the
pulverized matter including the protection solvent having been
blended therein in the pulverizing step, with the extraction
solvent having been heated to high temperatures in the heating
step, thereby rapidly raising the temperatures of the individual
coal particles in the pulverized matter. This step provides a
slurry containing coal particles dispersed in the extraction
solvent.
[0046] In the mixing step, the lower limit of the rate of
temperature rise of the pulverized matter is preferably 600.degree.
C./min, and more preferably 1,000.degree. C./min. The upper limit
of the rate of temperature rise of the pulverized matter in the
mixing step is not limited, and is preferably 200,000.degree.
C./min, and more preferably 100,0000.degree. C./min. In the case
where the rate of temperature rise of the pulverized matter in the
mixing step is below the lower limit, sufficient improvement effect
on the extraction rate, which might be otherwise produced by a
rapid temperature rise, may not be achieved. Conversely, in the
case where the rate of temperature rise of the pulverized matter in
the mixing step is above the upper limit, throughput may be
excessively regulated, and/or the equipment cost may be unduly
increased.
[0047] Examples of the process for mixing the pulverized matter
with the extraction solvent include a process that involves, as
disclosed in Japanese Unexamined Patent Application, Publication
No. 2014-208757, pressurizing and feeding the pulverized matter by
a lock hopper, into a pipe through which an extraction solvent is
flowing. As an alternative to the lock hopper, a pump or another
feeding unit may be used to feed the pulverized matter into a
pipe.
[0048] The lock hopper is used in the following manner. The
pulverized matter in the form of a paste is fed into the hopper,
which can be internally pressurized by supply of gas. Then, the
hopper is closed and supplied with gas so as to be internally
pressurized, whereby the pulverized matter in the form of a paste
is squeezed out by the force of the gas. The lock hopper may be
part of a pipe partitioned by two valves.
[0049] Examples of the pump that may be used as the feeding unit
include a mohno pump, a sine pump, a diaphragm pump, a bellows pump
and a rotary pump.
[0050] For mixing the pulverized matter with the extraction
solvent, the pulverized matter may be fed all at once into a tank
equipped with a mixer having a sufficient mixing power and
retaining the extraction solvent. Alternatively, the extraction
solvent may be fed all at once into a tank containing the
pulverized matter, and may be stirred in the tank.
[0051] The lower limit of the ratio of the mass of the extraction
solvent mixed with the pulverized matter to the mass of coal in the
pulverized matter is preferably 2, and more preferably 3. The upper
limit of the ratio of the mass of the extraction solvent mixed with
the pulverized matter to the mass of coal in the pulverized matter
is preferably 10, and more preferably 8. In the case where the
ratio of the mass of the extraction solvent mixed with the
pulverized matter is less than the lower limit, the coal components
may not be sufficiently extracted. Conversely, in the case where
the ratio of the mass of the extraction solvent mixed with the
pulverized matter is greater than the upper limit, the solution may
contain ash-free coal components in small concentrations, leading
to unduly low production efficiency.
[0052] The lower limit of the ratio of the mass of the extraction
solvent mixed with the pulverized matter to the mass of the
protection solvent in the pulverized matter is preferably 3, and
more preferably 4. The upper limit of the ratio of the mass of the
extraction solvent mixed with the pulverized matter to the mass of
the protection solvent in the pulverized matter is preferably 15,
and more preferably 12. In the case where the ratio of the mass of
the extraction solvent to the mass of the protection solvent is
less than the lower limit, the rate of temperature rise of
pulverized coals may not be high enough due to the sensible heat
load in the heating of the protection solvent. Conversely, in the
case where the ratio of the mass of the extraction solvent to the
mass of the protection solvent is greater than the upper limit, the
solution may contain ash-free coal components in small
concentrations, leading to unduly low production efficiency.
[0053] The lower limit of the temperature of a slurry (i.e., the
temperature of pulverized coals) obtained after the mix step is
preferably 300.degree. C., and more preferably 350.degree. C. The
upper limit of the temperature of the slurry is preferably
450.degree. C., and more preferably 400.degree. C. In the case
where the temperature of the slurry is below the lower limit, the
bonds between molecules constituting the coal may not be
sufficiently weakened, resulting in a low extraction rate.
Conversely, in the case where the temperature of the slurry is
above the upper limit, pyrolytic reactions of coal may be very
active, and pyrolysis radicals generated in the reactions may
recombine, resulting in a low extraction rate.
[0054] The slurry obtained in the mixing step is preferably held at
the same temperature (extraction temperature) for a certain period
of time until the coal components are dissolved. In the case where
the pulverized matter is mixed with the extraction solvent in such
a manner that the pulverized matter is pressurized and fed into the
pipe through which the extraction solvent is flowing, the slurry is
preferably fed into an extraction vessel (tank) equipped with a
mixer, and then is preferably retained in the extraction vessel for
a certain period of time to allow soluble components of coal to be
dissolved. The extraction temperature is preferably equal to the
temperature of the slurry obtained after the mixing step. For easy
control and/or reduction of energy costs, however, the extraction
temperature may be slightly different from the temperature of the
slurry obtained after the mixing step.
[0055] The lower limit of the duration that the temperature is
maintained (the extraction time) is preferably 5 minutes, and more
preferably 20 minutes. The upper limit of the duration that the
temperature is maintained is preferably 3 hours, and more
preferably 2 hours. In the case where the duration that the
temperature is maintained is shorter than the lower limit, the
extraction rate may be insufficient. Conversely, in the case where
the duration that the temperature is maintained is longer than the
upper limit, extended cycle time may be required, leading to unduly
low production efficiency.
[0056] It is preferred that the mixing of the pulverized matter
with the extraction solvent, and the maintaining of the temperature
of the resulting slurry are carried out in a non-oxidizing
atmosphere. Specifically, it is preferred that the mixing of the
slurry, and the maintaining of the temperature are carried out in
the presence of an inert gas such as nitrogen. By using the inert
gas such as nitrogen, the slurry is kept from contact with oxygen
and thus is prevented from igniting while the mixing is performed
and the temperature is maintained.
[0057] The pressure at which the pulverized matter is mixed with
the extraction solvent and the temperature of the slurry thus
obtained is maintained is selected according to the temperature
and/or the vapor pressure of the extraction solvent employed, and
may be, for example, greater than or equal to 1 MPa and less than
or equal to 3 MPa. In the case where the mixing step is performed
at a pressure below the vapor pressure, the extraction solvent may
volatilize, and thus the soluble components of coal may not be
sufficiently extracted. Meanwhile, the extraction with the addition
of heat at unduly high pressures causes increases in equipment
costs and operating costs associated with production
apparatuses.
[0058] Solution Separating Step
[0059] In Step S4, the solution separating step is performed to
separate the slurry obtained after the mixing step, into: a
solution containing soluble components of coal dissolved therein;
and solid matter containing insoluble components of coal. Although
the solution separating step does not require thorough solid-liquid
separation, it is desired to separate the largest possible amount
of solution containing substantially no solid matter. Examples of
the process for separating the solution include gravitational
settling, filtration and centrifugal separation. Of these, the
gravitational settling, which is suited for continuous treatments,
is suitably employed. In the case where the gravitational settling
is employed, solid matter in the slurry settles by gravitation,
whereby the slurry is separated into a supernatant liquor
containing substantially no solid matter and solid-content
concentrate containing solid matter having settled therein.
[0060] Evaporatively Separating Step
[0061] In Step S5, the evaporatively separating step is performed
to evaporatively separate the protection solvent and the extraction
solvent from the solution separated in the solution separating
step, whereby ash-free coal (hyper coal) is obtained.
[0062] Examples of the process for evaporatively separating the
extraction solvent and the protection solvent from the solution
containing soluble components of coal dissolved therein include
well-known separation processes such as a distillation process and
an evaporation process (e.g. spray drying). After being separated
from the solution, the extraction solvent and the protection
solvent are recovered in the evaporatively separating step, thereby
being repetitively usable as at least a part of a solvent for the
extraction solvent and the protection solvent.
[0063] The ash-free coal thus obtained has an ash content of 5% by
mass or less or of 3% by mass or less, i.e., contains almost no ash
matter, with absolutely no moisture. The ash-free coal has a
caloric value higher than that of, for example, coal feedstock.
Furthermore, the ash-free coal has greatly improved plasticity and
fusibility, which is a particularly important quality of coking
coal for steelmaking. The ash-free coal exhibits fluidity extremely
superior to that of, for example, coal feedstock. The ash-free coal
obtained according to the method for producing ash-free coal is
therefore suitably used as a coal blend for coke making.
[0064] Advantages
[0065] Due to involving pulverizing a coal in the presence of the
protection solvent in the pulverizing step, the method for
producing ash-free coal of the embodiment of the invention enables
the particle diameter of the coal to be reduce, while preventing or
minimizing aeration of the coal through reduced contact with air.
The method thus prevents loss of components to be converted into
ash-free coal, and enables the coal to be rapidly heated entirely
to its central portion by the heat of the extraction solvent
preheated in the mixing step, thereby enabling a relatively high
rate of extraction from coal to be achieved. Therefore, the method
for producing ash-free coal enables efficient production of
ash-free coal.
Other Embodiments
[0066] The above-described embodiment does not limit the
constituent features of the present invention. Therefore,
constituent elements of each part of the above-described embodiment
may be omitted, replaced or added based on the description in the
present specification and the common technical knowledge, and such
omission, replacement and addition should be construed as falling
within the scope of the present invention.
EXAMPLES
[0067] The present invention will be described below in detail by
way of Example. It is to be noted that Example should not be
construed as limiting the present invention.
Example
[0068] Ash-free coal was prepared as a sample product according to
the method for producing ash-free coal of the embodiment of the
invention by using, as coal feedstock, bituminous coal that had
been subjected to preliminary pulverization to have a mean particle
diameter of 0.3 mm, and by using 1-methylnaphthalene as the
protection solvent and the extraction solvent.
[0069] First, 30 g of the coal was mixed with 20 g of the
protection solvent to prepare a pasty mixture. The mixture was
charged into a planetary mill, and then was subjected to secondary
pulverization, in which coals in the mixture were pulverized to
have a mean particle diameter of 0.04 mm. Consequently, pulverized
matter in the form of a paste was obtained.
[0070] Then, 160 g of the extraction solvent was charged into a
heating-and-pressurizing apparatus equipped with a stainless steel
filter and having a capacity of 500 cc, where the extraction
solvent was heated to 400 .degree. C. at a pressure of 2.0 MPa.
[0071] The pulverized matter was added to the heated extraction
solvent, and then, the pulverized matter and the extraction solvent
were instantaneously mixed to give a slurry, whose temperature was
380 .degree. C. The rate of temperature rise of the pulverized
matter in this process was about 1,500.degree. C./min.
[0072] After being held at 380.degree. C. for 1 hour, the slurry
was filtered through the stainless filter of the
heating-and-pressurizing apparatus to be separated into: a solution
containing soluble components of coal dissolved therein; and filter
residues (solid matter), which were undissolved components of
coal.
[0073] The solution was dried to obtain ash-free coal of Example of
the present invention. The filter residues were dried to determine
the weight thereof, and thus, the rate of extraction (expressed in
% by mass) on a dry ash-free basis (daf) of soluble components from
coal in Example of the present invention was determined.
Control Example
[0074] As Control Example, ash-free coal was prepared as a sample
product according to a conventional production method involving a
rapid rise in the temperature of coal. In Control Example, the
ash-free coal was prepared as a sample product under the same
conditions as those of Example, except that the mixture of coals
and the protection solvent was not subjected to the secondary
pulverization before use. Then, the rate of extraction of soluble
components from coal was determined.
Comparative Example 1
[0075] As Comparative Example 1, ash-free coal was prepared as a
sample product under the same conditions as those of Example,
except that a coal was pulverized to have a mean particle diameter
of 0.06 mm in a mortal with no protection solvent charged therein,
and thereafter was mixed with the protection solvent to give
pulverized matter in the form of a paste. Then, the rate of
extraction of soluble components from coal was determined.
Comparative Example 2
[0076] As Comparative Example 2, ash-free coal was prepared as a
sample product under the same conditions as those of Example,
except that a coal was not subjected to the secondary pulverization
and thereafter was mixed with 180 g of the extraction solvent at
normal temperature to give a slurry, and that the slurry was heated
to 380.degree. C. at a rate of temperature rise of 5.5.degree.
C./min by the heating-and-pressurizing apparatus and thereafter was
held at the temperature for 1 hour. Then, the rate of extraction of
soluble components from coal was determined. The production method
in this Comparative Example was similar to an ash-free coal
production method that had been commonly employed before the
establishment of the production method involving a rapid rise in
the temperature of coal.
Comparative Example 3
[0077] As Comparative Example 3, ash-free coal was prepared as a
sample product under the same conditions as those of Example,
except that a mixture of a coal and the protection solvent was
pulverized into a paste by a planetary mill and thereafter was
mixed with 160 g of the extraction solvent at normal temperature to
give a slurry, and that the slurry was heated to 380.degree. C. at
a rate of temperature rise of 5.5.degree. C./min by the
heating-and-pressurizing apparatus and thereafter was held at the
temperature for 1 hour. Then, the rate of extraction of soluble
components from coal was determined.
Comparative Example 4
[0078] As Comparative Example 4, ash-free coal was prepared as a
sample product under the same conditions as those of Example,
except that a coal was pulverized to have a mean particle diameter
of 0.06 mm in a mortal with no protection solvent charged therein
and thereafter was mixed with 180 g of the protection solvent at
normal temperature to give a slurry, and that the slurry was heated
to 380.degree. C. at a rate of temperature rise of 5.5.degree.
C./min by the heating-and-pressurizing apparatus and thereafter was
held at the temperature for 1 hour. Then, the rate of extraction of
soluble components from coal was determined.
[0079] FIG. 2 provides a summary of the relationships between the
particle diameter and the rate of extraction from coal determined
in Example, Control Example, and Comparative Examples 1 to 4.
[0080] Comparisons were made among Example, Control Example and
Comparative Example 1 that all involved the mixing of a coal in the
form of a paste with the extraction solvent so as to rapidly
raising the temperature of the coal. The extraction rate determined
in Example that involved the secondary pulverization of coal in the
presence of the protection solvent was higher than the extraction
rate determined in Control Example that did not involve the
secondary pulverization. Although the particle diameter was reduced
in Comparative Example 1 that involved the secondary pulverization
of coal in a state of contacting with air in the absence of the
protection solvent, the extraction rate determined in Comparative
Example 1 was lower than the extraction rate determined in Control
Example.
[0081] Control Example, Example and Comparative Example 1 that all
involved a rapid rise in the temperature of coal were compared
respectively to Comparative Examples 2, 3 and 4 that all involved a
slow rise in the temperature of coal. Given the same process for
pulverizing the coal, the extraction rate obtained after the rapid
rise in the temperature of coal was higher than the extraction rate
obtained after the slow rise in the temperature of coal.
[0082] Also, comparisons were made among cases that involved a slow
rise in the temperature of coal. There was almost no difference in
the extraction rates between Comparative Example 2 that did not
involve pulverization of coal and Comparative Example 3 that
involved pulverization of coal in the presence of the protection
solvent. The extraction rate determined in Comparative Example 4
that involved pulverization of coal in the absence of the
protection solvent was lower than the extraction rates determined
in Comparative Example 2 and Comparative Example 3.
[0083] The foregoing results revealed that pulverizing a coal in
the presence of the protection solvent prevented loss of soluble
components of the coal, and that adding the heated solvent so as to
rapidly raise the temperature of the coal yielded enhanced effect
of improving the extraction rate.
[0084] While the present invention has been described in detail and
with reference to the specific embodiment, it would be apparent to
one of ordinary skill in the art that various alterations and
modifications can be made without departing from the spirit and
scope of the present invention.
[0085] The present application claims priority to Japanese Patent
Application No. 2015-230140, filed on Nov. 25, 2015, and the
contents of which are incorporated herein by reference in their
entirety.
INDUSTRIAL APPLICABILITY
[0086] The method for producing ash-free coal according to the
present invention is widely applicable to the production of
ash-free coal to be used as, for example, fuels or feedstocks for
coke making.
EXPLANATION OF THE REFERENCE SYMBOLS
[0087] S1 Pulverizing Step
[0088] S2 Heating Step
[0089] S3 Mixing Step
[0090] S4 Solution Separating Step
[0091] S5 Evaporatively Separating Step
* * * * *