U.S. patent application number 14/607679 was filed with the patent office on 2015-05-21 for method for producing solid fuel and solid fuel produced by the method.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho. The applicant listed for this patent is Kabushiki Kaisha Kobe Seiko Sho. Invention is credited to Shigeru Kinoshita, Yutaka Mitou, Takuo Shigehisa, Satoru Sugita, Seiichi YAMAMOTO.
Application Number | 20150135584 14/607679 |
Document ID | / |
Family ID | 42100524 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150135584 |
Kind Code |
A1 |
YAMAMOTO; Seiichi ; et
al. |
May 21, 2015 |
METHOD FOR PRODUCING SOLID FUEL AND SOLID FUEL PRODUCED BY THE
METHOD
Abstract
Modified solid fuel manufacturing method and modified solid
fuels manufactured using the manufacturing method. When solid fuels
are manufactured by crushing low grade coal, mixing the crushed low
grade coal with solvent oil to prepare a slurry, heating the slurry
to at least the boiling point of water to evaporate moisture
included in the slurry, separating the solvent oil from the slurry
to produce charcoal dust and compression compacting said charcoal
dust, by heating the slurry to at least the boiling point of water,
the non-volatile components included in the low grade coal are
extracted with the solvent oil, the outer surface of the low grade
coal and the internal surfaces of the pores are coated with the
extracted non-volatile components, and the content of heavy oil
added from the outside will be less than 0.5 mass %, relative to
the solid fuel after drying.
Inventors: |
YAMAMOTO; Seiichi;
(Takasago-shi, JP) ; Shigehisa; Takuo;
(Takasago-shi, JP) ; Mitou; Yutaka; (Takasago-shi,
JP) ; Sugita; Satoru; (Takasago-shi, JP) ;
Kinoshita; Shigeru; (Takasago-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Kobe Seiko Sho |
Kobe-shi |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko
Sho
Kobe-shi
JP
|
Family ID: |
42100524 |
Appl. No.: |
14/607679 |
Filed: |
January 28, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13120369 |
Apr 1, 2011 |
|
|
|
PCT/JP09/66927 |
Sep 29, 2009 |
|
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14607679 |
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Current U.S.
Class: |
44/592 |
Current CPC
Class: |
C10L 5/04 20130101; C10L
5/32 20130101; C10L 2290/28 20130101; C10L 5/361 20130101; C10L
5/08 20130101; C10L 2200/043 20130101; C10L 2290/30 20130101; C10L
2290/08 20130101; C10L 9/10 20130101; C10L 2230/14 20130101 |
Class at
Publication: |
44/592 |
International
Class: |
C10L 5/08 20060101
C10L005/08; C10L 5/36 20060101 C10L005/36; C10L 5/04 20060101
C10L005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2008 |
JP |
2008-262513 |
Claims
1. A method for producing a solid fuel, the method comprising:
pulverizing low-rank coal; preparing a slurry by mixing the
pulverized low-rank coal with a solvent oil; evaporating water in
the slurry by heating the slurry to a boiling point of water or
more; producing fine coal by separating the solvent oil from the
slurry, while a non-volatile component contained in the low-rank
coal is not evaporated by performing solid-liquid separating
against the slurry; and briquetting the fine coal, wherein, by
heating the slurry to the boiling point of water or more, a
nonvolatile component contained in the low-rank coal is extracted
with the solvent oil and the extracted nonvolatile component covers
an outer surface of the low-rank coal and inner surfaces of pores
of the low-rank coal, and a content of a heavy oil added from
outside is made 0 mass % with respect to the solid fuel having been
dried; and in said solid-liquid separating the weight ratio of
dewatered coal, kerosene, and the coal nonvolatile component in the
solid phase is 99:33:1.
2. The method of claim 1, wherein the heavy oil is not
substantially added.
3.-4. (canceled)
5. The method of claim 1, wherein said solvent oil is a light
boiling oil.
6. The method of claim 1, wherein said solvent oil is a petroleum
oil having a boiling point of at least 100.degree. C.
7. The method of claim 6, wherein said solvent oil is a petroleum
oil having a boiling point of no more than 400.degree. C.
8. The method of claim 1, wherein said solvent oil is kerosene.
9. The method of claim 1, wherein said low-rank coal is coal having
a water content of at least 20 mass % with respect to the coal
having been dried.
10. The method of claim 1, wherein said low-rank coal is selected
from the group consisting of brown coal, lignite, and subbituminous
coal.
11. The method of claim 1, wherein said low-rank coal is brown coal
selected from the group consisting of Victoria coal, North Dakota
coal, and Beluga coal.
12. The method of claim 1, wherein said low-rank coal is
subbituminous coal selected from the group consisting of West Banko
coal, Binungan coal, and Samarangau coal.
13. The method of claim 1, wherein said evaporating is conducted
under the application of a pressure of 1 to 40 atmospheres and
under heating to a temperature of 100.degree. C. to 250.degree.
C.
14. The method of claim 13, wherein said pressure is from 2 to 5
atmospheres.
15. The method of claim 13, wherein said temperature is from
120.degree. C. to 160.degree. C.
16. The method of claim 1, wherein said separating is mechanical
solid-liquid separation with a mechanical solid-liquid
separator.
17. The method of claim 16, wherein said mechanical solid-liquid
separator is selected from the group consisting of a centrifugal
separator, a compressor, a settling tank, and a filter.
18. The method of claim 1, wherein said briquetting is with a
briquetting device.
19. The method of claim 18, wherein said briquetting device is a
tableting device or a double-roll briquetting device.
20. The method of claim 1, wherein a content of the non-volatile
component is made in about 1 mass % with respect to the solid fuel
having been dried.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing an
improved solid fuel in which coal, in particular, low-rank coal, is
used as a raw material; and an improved solid fuel produced by the
method.
BACKGROUND ART
[0002] Solid fuel is suitably used as fuel for, for example,
thermal power generation or the like.
[0003] At present, bituminous coal is used as fuel for thermal
power generation. However, the output of bituminous coal has been
increasing year after year and there is a concern about exhaustion
of bituminous coal. Accordingly, effective use of low-rank coal
serving as an alternative to bituminous coal is an urgent
issue.
[0004] Low-rank coal has a low calorific value and a spontaneous
combustion property and hence applications of low-rank coal are
limited. As means for effectively using low-rank coal, an upgraded
brown coal process (hereafter, referred to as UBC process) has been
used. To date, several processes for improving low-rank coal have
been developed. However, it is difficult to practically use most of
these processes because of high temperature or high pressure
processing condition, which results in high apparatus cost, or
low-rank coal is chemically changed to produce waste water
containing a large amount of pyrolytic substances, which results in
high waste-water treatment cost.
[0005] The applicant of the present invention disclosed such a UBC
process in which low-rank coal is used as a raw material and an oil
mixture containing a heavy oil and a solvent oil is made to be
present in pores of the low-rank coal to thereby provide a solid
fuel in which the content of the heavy oil in weight percentage
with respect to the coal having been dewatered is 0.5% to 30%
(Patent Literature 1). In the solid fuel of Patent Literature 1,
water in pores of low-rank coal is removed and a heavy oil is made
to adhere to the inner surfaces of the pores to cover active sites.
Thus, spontaneous combustion of low-rank coal is suppressed and a
heavy oil is contained in low-rank coal to achieve a high calorie.
By dissolving a heavy oil in a solvent oil to achieve a low
viscosity, pores are sufficiently impregnated with the heavy oil
and, as a result, active sites in the pores are covered and a high
calorie is achieved.
[0006] Improved-coal powder is scarcely used without being
processed, as fuel. In general, improved-coal powder is compacted
into briquettes and the briquettes are transported to a consumption
site (for example, a thermal power plant or the like). When such
briquettes have a low strength, the briquettes are cracked or
produce powder during transportation or during loading/unloading
operations. Thus, in addition to loss of a portion of the product,
there is a concern about the increase in the probability of
spontaneous combustion. Accordingly, briquettes are required to
have a high strength.
[0007] In addition, to reduce production cost and to reduce
environmental load, the proportion of components added from the
outside is desirably made as low as possible or made zero.
Patent Literature 1: Japanese Patent No. 2776278
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0008] The present invention has been accomplished in view of what
is described above. An object of the present invention is to
provide a method for producing an improved solid fuel in which
production cost is reduced, environmental load is reduced, a high
strength is achieved for transportation or the like, and
spontaneous combustion is suppressed; and such an improved solid
fuel.
Means for Solving the Problems
[0009] The inventors of the present invention have conducted
thorough studies in view of the above-described object. As a
result, the inventors have found that, by immersing low-rank coal
in a high-temperature oil, not only water in the low-rank coal can
be evaporated but also a nonvolatile component originally contained
in the low-rank coal is extracted with the high-temperature oil and
the component can function as an alternative to a heavy oil. Like a
heavy oil, the component has a function of covering active sites in
low-rank coal to suppress spontaneous combustion. Thus, the
proportion of a heavy oil added from the outside can be
reduced.
[0010] Further study has revealed a finding that, when the heavy
oil does not adhere to the surfaces of pulverized low-rank coal,
the adhesion between fine coal particles prior to briquetting is
enhanced and the strength of briquetted solid matter can be
enhanced.
[0011] The present invention has been accomplished on the basis of
the finding. An aspect of the present invention is a method for
producing a solid fuel, the method including: a step of pulverizing
low-rank coal; a step of preparing a slurry by mixing the
pulverized low-rank coal with a solvent oil; a step of evaporating
water in the slurry by heating the slurry to a boiling point of
water or more; a step of producing fine coal by separating the
solvent oil from the slurry; and a step of briquetting the fine
coal,
[0012] wherein, by heating the slurry to the boiling point of water
or more, a nonvolatile component contained in the low-rank coal is
extracted with the solvent oil and the extracted nonvolatile
component covers an outer surface of the low-rank coal and inner
surfaces of pores of the low-rank coal, and
[0013] a content of a heavy oil added from outside is made less
than 0.5 mass %, preferably substantially 0 mass %, with respect to
the solid fuel having been dried.
[0014] The present invention also provides a solid fuel produced by
briquetting pulverized low-rank coal, wherein an outer surface of
the low-rank coal and inner surfaces of pores of the low-rank coal
are covered with a nonvolatile component contained in the low-rank
coal, and a content of a heavy oil is less than 0.5 mass %,
preferably substantially 0 mass %, with respect to the solid
fuel.
Advantageous Effects of Invention
[0015] According to the present invention, a nonvolatile component
originally contained in low-rank coal is dissolved with
high-temperature oil and the component can function as an
alternative to a heavy oil. Thus, the proportion of a heavy oil
added from the outside can be reduced; production cost can be
reduced; and adverse effects on the environment can be suppressed.
Furthermore, according to the present invention, as described
above, the proportion of a heavy oil added, the heavy oil degrading
the adhesion between fine coal particles, can be reduced. As a
result, the strength of briquetted solid matter can be
enhanced.
[0016] Accordingly, the present invention can provide a method for
producing an improved solid fuel in which production cost is
reduced, environmental load is reduced, and the strength of the
solid fuel is enhanced for transportation or the like; and an
improved solid fuel produced by the method.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 illustrates a process flow of a method for producing
an improved solid fuel according to the present invention.
[0018] FIG. 2 is a schematic diagram illustrating an example of an
apparatus for producing an improved solid fuel in which a method
for producing an improved solid fuel according to the present
invention is carried out.
[0019] FIG. 3 is a graph about a coal nonvolatile component
dissolved in kerosene.
[0020] FIG. 4 illustrates a process flow in a steady state.
[0021] FIG. 5 is a graph illustrating the relationship between the
mass fraction (percentage with respect to dewatered coal) [mass %]
of a heavy oil (specifically, asphalt) and briquette strength
[kg-wt].
REFERENCE SIGNS LIST
[0022] 1 mixing tank [0023] 2 pump [0024] 3 preheater [0025] 4
preheater [0026] 5 gas-liquid separator [0027] 6 pump [0028] 7
evaporator [0029] 8 compressor [0030] 9 oil-water separator [0031]
10 centrifugal separator [0032] 11 screw press [0033] 12 dryer
[0034] 13 condenser [0035] 14 pump [0036] 15 cooler [0037] 16
heater
BEST MODES FOR CARRYING OUT THE INVENTION
[0038] Hereinafter, a method for producing an improved solid fuel
according to the present invention and an improved solid fuel
produced by the production method will be described in detail with
reference to the drawings. However, embodiments described below are
examples of the present invention and are not viewed as limiting
the present invention. Note that common parts or components in the
drawings are designated with like reference signs and redundant
descriptions are omitted.
First Embodiment
[0039] A method for producing an improved solid fuel according to
the present invention includes pulverizing low-rank coal; preparing
a slurry by mixing the pulverized low-rank coal with a solvent oil;
evaporating water in the slurry by heating the slurry to a boiling
point of water or more; producing fine coal by separating the
solvent oil from the slurry; and briquetting the fine coal,
wherein, by heating the slurry to the boiling point of water or
more, a nonvolatile component contained in the low-rank coal is
extracted with the solvent oil and the extracted nonvolatile
component covers an outer surface of the low-rank coal and inner
surfaces of pores of the low-rank coal, and a content of a heavy
oil added from outside is made less than 0.5 mass %, preferably
substantially 0 mass %, with respect to the solid fuel having been
dried (that is, in percentage with respect to the coal having been
dewatered).
[0040] In a method for producing a solid fuel according to the
present invention, an oil mixed with pulverized low-rank coal
serves as a solvent oil; a nonvolatile component originally
contained in the low-rank coal is extracted with the oil at a high
temperature; and the nonvolatile component functions as an
alternative to a heavy oil. Accordingly, the proportion of a heavy
oil added from the outside can be reduced. In addition, although
the amount of the heavy oil added is reduced, the nonvolatile
component contained in the low-rank coal is used as the alternative
and the nonvolatile component covers active sites in pores of the
low-rank coal. Thus, spontaneous combustion can be suppressed as in
the cases where the heavy oil is added. Furthermore, by a method
for producing a solid fuel according to the present invention, the
proportion of such a heavy oil added can be reduced, the heavy oil
reducing the adhesion between fine coal particles. Thus, the
strength of briquetted solid matter can be enhanced.
[0041] FIG. 1 illustrates a process flow of a method for producing
an improved solid fuel according to the present invention. A method
for producing an improved solid fuel according to the present
invention will be described in detail with reference to FIG. 1.
FIG. 2 is a schematic diagram illustrating an example of an
apparatus for producing an improved solid fuel in which a method
for producing an improved solid fuel according to the present
invention is carried out. A method for producing an improved solid
fuel according to the present invention includes a low-rank coal
pulverization and slurry preparation step; a dewatering step; a
solid-liquid separation step; and a briquetting step. In addition,
the method may further include a cooling step for cooling dried
solid content between the solid-liquid separation step and the
briquetting step.
[0042] The step of preparing a slurry of pulverized low-rank coal
corresponds to a mixing section in the process flow in FIG. 1 and
is conducted in a mixing tank 1 in the apparatus for producing an
improved solid fuel in FIG. 2. The dewatering step corresponds to a
dewatering section in the process flow in FIG. 1 and is conducted
in an evaporator 7 and a gas-liquid separator 5 in the production
apparatus in FIG. 2. The solid-liquid separation step corresponds
to solid-liquid separation sections (mechanical separation and
thermal separation) in the process flow in FIG. 1 and is conducted
in a mechanical solid-liquid separator (centrifugal separator) 10,
a screw press 11, and a dryer 12 in the production apparatus in
FIG. 2. The briquetting step corresponds to a briquetting section
in the process flow in FIG. 1 and is conducted in a briquetting
device (not shown) in the production apparatus. The apparatus for
producing an improved solid fuel in which a method for producing an
improved solid fuel according to the present invention is carried
out includes the mixing tank 1 in which an oil mixture containing a
solvent oil is mixed with low-rank coal to prepare a raw material
slurry; the evaporator 7 and the gas-liquid separator 5 in which
the raw material slurry is subjected to a water evaporation
treatment; the mechanical solid-liquid separator (centrifugal
separator) 10, the screw press 11, and the dryer 12 in which the
slurry having been subjected to the water evaporation treatment is
subjected to solid-liquid separation; and the briquetting device
(not shown) in which the dried solid fuel in the form of a powder
is briquetted to produce a briquetted solid fuel.
[0043] Hereinafter, the steps will be described in detail.
1. Low-Rank Coal Pulverization and Slurry Preparation Step
[0044] As illustrated in FIGS. 1 and 2, low-rank coal serving as a
raw material is pulverized and then supplied to the mixing section,
that is, the mixing tank 1. The pulverized low-rank coal is mixed
with an oil containing a solvent oil in the mixing tank 1 to
prepare a raw material slurry. Various oils may be used as the
solvent oil mixed with low-rank coal as long as a nonvolatile
component contained in low-rank coal can be extracted with the
oils. The solvent oil is preferably a light boiling oil in view of
compatibility with a nonvolatile component and a heavy oil, ease of
handling of a slurry, ease of entry into pores, and the like. In
view of stability at a water evaporation temperature, the solvent
oil is suitably a petroleum oil having a boiling point of
100.degree. C. or more and preferably 400.degree. C. or less.
Examples of such a petroleum oil include kerosene, light oil, and
heavy oil. Alternatively, coal liquid may be used. Preferably,
kerosene can be used.
[0045] Although the solvent oil may contain a heavy oil, it is
important that the amount of a heavy oil added by addition of an
oil into the mixing tank 1 is adjusted such that the adhesion
amount of the heavy oil in a solid fuel (that is obtained by
subjecting a cake provided by solid-liquid separation to an oil
evaporation treatment with a dryer) is less than 0.5 mass %,
preferably substantially 0 mass %, with respect to low-rank coal
(improved coal) having been dried in the solid fuel, that is, in
percentage with respect to the coal having been dewatered.
[0046] As illustrated in FIG. 1, an oil and the like ejected from
the dewatering section, the solid-liquid separation section
(mechanical separation), and the solid-liquid separation section
(thermal separation) may be circulated as a circulation oil to the
mixing section. A solvent oil and a heavy oil may be added to the
circulation oil. In this case, as in the above-described case, it
is also important that the amount of a heavy oil added is adjusted
such that the adhesion amount of the heavy oil in a solid fuel
(that is obtained by subjecting a cake provided by solid-liquid
separation to an oil evaporation treatment with a dryer) is less
than 0.5 mass %, preferably substantially 0 mass %, with respect to
low-rank coal (improved coal) having been dried in the solid fuel,
that is, in percentage with respect to the coal having been
dewatered.
[0047] In the present invention, the term "low-rank coal" denotes a
coal that contains a large amount of water and is desirably
dewatered, for example, a coal that has a water content of at least
20 mass % with respect to the coal having been dried. Naturally,
such low-rank coal may contain high-rank coal or the like. Examples
of such low-rank coal include brown coal, lignite, and
subbituminous coal. Examples of brown coal include Victoria coal,
North Dakota coal, and Beluga coal. Examples of subbituminous coal
include West Banko coal, Binungan coal, and Samarangau coal.
Low-rank coal is not restricted to the above-described examples and
low-rank coal according to the present invention encompasses any
coal that has a large water content and is desirably dewatered.
[0048] In the present invention, the term "nonvolatile component"
denotes a nonvolatile oil that is originally contained in low-rank
coal and, after being extracted, covers the outer surface of the
low-rank coal and the inner surfaces of pores of the low-rank coal.
Thus, the nonvolatile component covers active sites in pores of
low-rank coal and hence suppresses spontaneous combustion. An
example of such a nonvolatile component is an aromatic organic
polymer compound.
[0049] In the present invention, the term "heavy oil" denotes a
heavy fraction that substantially does not exhibit vapor pressure
at, for example, 400.degree. C., such as vacuum residual oil or an
oil containing such a heavy fraction. As with the nonvolatile
component, the heavy oil has a function of covering active sites in
pores of low-rank coal and hence suppresses spontaneous combustion.
Examples of such a heavy oil include petroleum asphalt, native
asphalt, aliphatic organic polymer compounds, and aromatic organic
polymer compounds.
[0050] In the present invention, the term "solvent oil" denotes an
oil that can dissolve a heavy oil to reduce the viscosity of the
heavy oil to thereby facilitate entry of the heavy oil into pores
of low-rank coal, and that can extract a nonvolatile component
contained in low-rank coal. Such a solvent oil can also dissolve a
nonvolatile component to reduce the viscosity of the nonvolatile
component to thereby facilitate entry of the nonvolatile component
into pores of low-rank coal.
[0051] However, when a solid fuel in the form of a powder is
briquetted, such a heavy oil reduces the mechanical strength of the
briquetted solid fuel. Accordingly, the amount of the heavy oil is
preferably as small as possible. As described above, the amount of
a heavy oil added is preferably adjusted such that the adhesion
amount of the heavy oil in a solid fuel (that is obtained by
subjecting a cake provided by solid-liquid separation to an oil
evaporation treatment with a dryer) is less than 0.5 mass %,
preferably substantially 0 mass %, with respect to low-rank coal
(improved coal) having been dried in the solid fuel (in percentage
with respect to the coal having been dewatered). FIG. 5 illustrates
the relationship between the mass fraction (percentage with respect
to dewatered coal) [mass %] of a heavy oil (specifically, asphalt)
and briquette strength [kg-wt]. The abscissa axis indicates the
mass fraction (percentage with respect to dewatered coal) [mass %]
of a heavy oil (specifically, asphalt). The ordinate axis indicates
briquette strength [kg-wt]. As illustrated in FIG. 5, by making the
adhesion amount of a heavy oil in a solid fuel be 0 to 0.5 mass %,
the strength of a briquetted solid fuel can be made about 68 kg-wt
to about 87 kg-wt. In particular, when the adhesion amount is 0
mass %, the briquetted solid fuel has the highest strength of about
87 kg-wt, which is preferred. When a briquetted solid fuel produces
powder, the probability of the contact between active sites of the
solid fuel and the air increases and there is a concern about the
increase in the probability of spontaneous combustion. However, as
described above, when the strength of a briquetted solid fuel is
increased by making the adhesion amount of a heavy oil be 0 to 0.5
mass %, spontaneous combustion can be suppressed.
[0052] The type of a mixing tank according to the present invention
is not particularly restricted and various mixing tanks may be
used. However, in general, an axial mixer or the like is preferably
used.
[0053] In the low-rank coal pulverization and slurry preparation
step, a raw material slurry can be prepared by mixing pulverized
low-rank coal with an oil containing a solvent oil.
2. Dewatering Step
[0054] The thus-prepared raw material slurry is transported to
preheaters 3 and 4 by a pump 2 and preheated with the preheaters 3
and 4. After that, the raw material slurry is heated with the
evaporator 7. In the evaporator 7, dewatering in oil is conducted
under the application of a pressure of 1 to 40 atmospheres
(preferably, 2 to 5 atmospheres) and under heating to a temperature
of 100.degree. C. to 250.degree. C. (preferably, 120.degree. C. to
160.degree. C.). In the evaporator 7, the raw material slurry is
heated to the boiling point of water or more as described above
and, as a result, moisture is removed and a nonvolatile component
contained in low-rank coal is extracted with a solvent oil
contained in the raw material slurry. Thus, a nonvolatile component
contained in low-rank coal is extracted and the nonvolatile
component functions as an alternative to a heavy oil. Accordingly,
as described above, the amount of a heavy oil added can be
reduced.
[0055] Thus, the raw material slurry is transported to the
gas-liquid separator 5 and water in the raw material slurry is
removed in the form of moisture in the gas-liquid separator 5.
After the separation of moisture, the slurry is drawn through the
bottom and transported toward the centrifugal separator 10 by a
pump 6. A portion is branched at an intermediate position of a
transportation line, heated by being passed through the evaporator
7, and then transported back to the gas-liquid separator 5. The
pressure of a vapor-phase fraction obtained by subjecting moisture
generated in the evaporator 7 to gas-liquid separation is increased
by being passed through a compressor 8 and the resultant thermal
energy is used to heat the slurry in the evaporator 7 to thereby
dewater the slurry in oil. The vapor-phase fraction is subsequently
transported to the preheater 3, used as a preheating source for the
raw material slurry, and then subjected to oil-water separation in
an oil-water separator 9. The resultant water is discarded. The oil
collected in the oil-water separation is returned to the mixing
tank 1 and reused.
[0056] In the dewatering step, since a dewatering treatment is
conducted, the raw material slurry is required to be heated to the
boiling point of water or more. In addition, since it is necessary
to extract and extract a nonvolatile component with a solvent oil
contained in the raw material slurry, the raw material slurry is
preferably heated to 100.degree. C. or more. To evaporate water at
normal pressure, heating at least to 100.degree. C. is required.
However, to reduce the size of an apparatus, operation may be
performed at a pressure higher than normal pressure. As a result,
vapor-phase volume is reduced. To make the size of a compressor be
reasonable, process may be performed at a pressure higher than
normal pressure. When the pressure is increased, since the boiling
point of water increases, the heating temperature needs to be made
100.degree. C. or more. For example, when operation is performed
under pressurization at 0.4 MPa, heating to 145.degree. C. or more
is required to evaporate water. However, when the temperature is
increased to an unnecessarily high value, not only water but also a
solvent oil evaporates. In the process, evaporation of a solvent
oil needs to be reduced as much as possible. Accordingly, it is
reasonable to perform operation at a temperature about several
degrees centigrade higher than the boiling point of water at an
operation pressure. Note that, in view of extracting a nonvolatile
component of coal, a higher temperature is preferred.
[0057] The type of the evaporator 7 according to the present
invention is not particularly restricted and various evaporators
may be used: for example, a heating evaporator, a decompression
evaporator, a heating-decompression evaporator, and the like. For
example, a flash vaporization evaporator, a coil evaporator, a
forced-circulation vertical-tube evaporator, or the like may be
used. In general, for example, a forced-circulation evaporator
equipped with a heat exchanger is preferably used.
[0058] As described above, in the dewatering step, water contained
in low-rank coal is evaporated to thereby remove moisture and a
nonvolatile component contained in the low-rank coal is extracted
with a solvent oil contained in a raw material slurry.
3. Solid-Liquid Separation Step
[0059] As described above, after the water evaporation treatment is
performed, the slurry having been subjected to the water
evaporation treatment is transported to the solid-liquid separation
section (mechanical separation) and subjected to solid-liquid
separation with a mechanical solid-liquid separator. The type of
such a mechanical solid-liquid separator is not particularly
restricted and various separators may be used: for example, a
centrifugal separator, a compressor, a settling tank, a filter, and
the like. In the present embodiment, concentration with the
centrifugal separator 10 is firstly performed and then compression
with the screw press 11 is performed. However, only a centrifugal
separator or a screw press may be used. Instead of a centrifugal
separator, sedimentation may be employed. Instead of compression,
vacuum filtration may be employed. An oil obtained by the
solid-liquid separation may be returned as a circulation oil to the
mixing tank 1.
[0060] The thus-separated solid matter (cake) is transported to the
solid-liquid separation section (thermal separation) and heated in
the dryer 12 under a carrier-gas flow to thereby evaporate the oil.
As a result, a solid fuel is obtained.
[0061] In the thermal separation step, the surface of coal and
pores of the coal are covered with a nonvolatile component.
Specifically, while a solvent oil is evaporated, a nonvolatile
component (heavy oil) contained in the coal is not evaporated and
hence remains on the surface of the coal and in pores of the
coal.
[0062] The drying is preferably performed by a fluid-bed process or
a rotary dryer process. The oil that is transported and separated
with a carrier gas may be fed to a condenser 13, collected as an
oil, and then returned as a lubricating oil to the mixing tank
1.
[0063] As described above, in the solid-liquid separation step, a
slurry is subjected to solid-liquid separation with a mechanical
solid-liquid separator and an oil contained in the solid matter is
evaporated with a dryer. As a result, a solid fuel in the form of a
powder can be obtained.
4. Briquetting Step
[0064] The thus-obtained solid fuel in the form of a powder is
transported from the dryer to the briquetting section and
briquetted with a briquetting device (not shown) into a briquetted
solid fuel. Examples of such a briquetting device include a
tableting device (tableting) and a double-roll briquetting device
(roll press). In general, a double-roll briquetting device is
preferably used. In the briquetting step, a briquetted solid fuel
can be produced.
[0065] According to the above-described method, although the amount
of a heavy oil added is reduced, spontaneous combustion can be
suppressed as in the cases where a heavy oil is added and the
strength of briquetted solid matter can be enhanced.
EXAMPLES
Example 1
Regarding Properties of Nonvolatile Component Contained in Low-Rank
Coal
[0066] It has been reported that, when coal is dewatered in oil, by
making a nonvolatile heavy oil such as asphalt be present with the
coal, asphalt effectively adheres to pores of the coal and
spontaneous combustion is suppressed (Japanese Patent No.
2776278).
[0067] The inventors of the present invention have considered that,
since a nonvolatile component that is a portion of coal is
dissolved in a high-temperature oil and extracted, the dissolved
nonvolatile component functions as an alternative to asphalt.
[0068] Then, the solubility of a coal (Indonesian brown coal) in a
high-temperature solvent oil (kerosene) was measured. The following
procedures were employed.
[0069] 1) Pulverized coal (the amount of particles having a
diameter of 1 mm or more is 10 mass % or less) was mixed with
kerosene in a round bottom flask at room temperature.
[0070] 2) The round bottom flask was placed in a heater and the
sample was gradually heated to 140.degree. C. over 2 hours. At this
time, to make the atmosphere in the flask be inert, nitrogen gas
was supplied at 200 cm.sup.3/min. In addition, at this time, water
evaporated from the coal was drawn in the form of moisture from the
top of the round bottom flask, condensed with a cooling tube, and
drawn in the form of liquid (water) outside the system. The sample
in the round bottom flask was held at 140.degree. C. for an
hour.
[0071] 3) Subsequently, the sample in the round bottom flask was
filtered under the application of a pressure (pressurized with a
nitrogen gas at 0.1 MPa) in the high-temperature state to separate
the sample into the solid phase and the liquid phase.
[0072] 4) The separated liquid phase was temporarily cooled, then
poured into a flask of distillation equipment, subjected to
distillation under reduced pressure under conditions described
below to evaporate and draw kerosene outside the system. An
evaporation residue, that is, a coal nonvolatile component having
been dissolved in kerosene was collected.
[0073] Pressure: 10 mmHg
[0074] Heating rate: 2.degree. C./min
[0075] Final temperature: 159.degree. C. (after the final
temperature is reached, the temperature is maintained until
generation of moisture stops: 60 minutes)
[0076] FIG. 3 illustrates measurement results: s/c represents the
ratio of the weight of kerosene charged to the weight of coal
(having been dried); and coal weight reduction percentage
represents the weight fraction of a component dissolved in kerosene
with respect to the dry weight of the coal charged. As illustrated
in FIG. 3, it has been found that at least 1% of a raw material
coal dissolves in kerosene at 140.degree. C.
[0077] For another coal, it has also been found that at least 1% of
a raw material coal dissolves in kerosene at 140.degree. C.
[0078] The coal component dissolving in kerosene was a nonvolatile
heavy oil and had properties very similar to those of heavy oils
such as asphalt that are added from the outside in existing
techniques. Accordingly, it has been found that a low-rank coal
improvement process can be achieved without adding a heavy oil from
the outside.
Example 2
Regarding Process Flow
[0079] Next, FIG. 4 illustrates an example of a process flow in a
steady state together with a material balance. The numeral values
in FIG. 4 represent mass flow rate. DC represents dewatered coal;
SC represents a nonvolatile component contained in coal; W
represents water; and O represents kerosene. About 1% of a raw
material coal can dissolve in kerosene and the concentration
increases over time in circulating kerosene. In the dewatering
section, 1% of coal dissolves in high-temperature kerosene. In the
solid-liquid separation section (mechanical separation), a portion
of kerosene remains on the surface and in pores of coal. The
kerosene contains about 3% of a coal component that can dissolve in
kerosene, that is, a nonvolatile component contained in coal. Thus,
in the subsequent solid-liquid separation section (thermal
separation), while kerosene is evaporated and separated, the coal
nonvolatile component that can dissolve in kerosene remains on the
surface and in pores of coal.
[0080] A heavy component (asphalt) is added in existing techniques
for the purpose of suppressing spontaneous combustion of product
coal. Accordingly, for example, the proportion of a mass component
remaining in a product is made 1 mass %. Then, to provide another
product having an equal quality, 1 mass % of a coal nonvolatile
component that can dissolve in kerosene is made to remain in the
product. To achieve this, the mechanical solid-liquid separation
step (centrifugal separation) in FIG. 4 is performed such that, in
the solid phase, the weight ratio of dewatered coal (DC) to a
nonvolatile component (SC) that can dissolve in kerosene is 99:1.
At this time, the mass ratio of the nonvolatile component to
kerosene in the slurry supplied to the mechanical solid-liquid
separation step (centrifugal separation) is 4.5:157, that is, about
3:100. Accordingly, when the ratio of dewatered coal to kerosene in
the solid phase is made about 99:33 (99:34.5 in FIG. 4), the weight
ratio of dewatered coal, kerosene, and the coal nonvolatile
component is 99:33:1. For the solid phase containing kerosene,
while most of the kerosene is evaporated and separated in the
subsequent heating step (drying step), the nonvolatile component
that can dissolve in kerosene is heavy and hence is not separated
and remains on the surface of the coal. In a continuous centrifugal
separator, parameters that mainly determine the capability of
separating a solid phase and a liquid phase from each other are the
number of revolutions and average residence time. The larger the
number of revolutions and the longer the average residence time,
the less the amount of a liquid phase remaining in a solid phase
becomes. Continuous centrifugal separators are of various sizes and
types and the number of revolutions and average residence time for
achieving a desired solid-liquid separation capability vary and
cannot be generally determined. However, in the present invention,
by performing solid-liquid separation as described above, about 1
mass % of a nonvolatile component can be made to remain in
dewatered coal and addition of a heavy oil can be preferably
eliminated.
Example 3
Regarding Strength of Briquetted Solid Fuel
[0081] In an existing technique (Japanese Patent No. 2776278), at
least 0.5 mass % of a heavy oil is added in a mass percentage with
respect to dewatered coal.
[0082] Asphalt was selected as a heavy oil and a low-rank coal
(Indonesian brown coal) was improved while an asphalt mass fraction
(percentage with respect to dewatered coal) was varied. After that,
solid fuels in the form of a briquette were produced with a
double-roll briquetting device (K-205, manufactured by Furukawa
Otsuka Co., Ltd.). The number of revolutions of the double-roll
briquetting device was made 8 rpm. The strength was measured with a
crush strength meter (XA-500, manufactured by Furukawa Otsuka Co.,
Ltd.).
[0083] The results are illustrated in FIG. 5. FIG. 5 is a graph
illustrating the relationship between the mass fraction (percentage
with respect to dewatered coal) [mass %] of a heavy oil
(specifically, asphalt) and briquette strength [kg-wt]. The
abscissa axis indicates the mass fraction (percentage with respect
to dewatered coal) [mass %] of a heavy oil (specifically, asphalt).
The ordinate axis indicates briquette strength [kg-wt]. As
illustrated in FIG. 5, by making the adhesion amount of a heavy oil
in a solid fuel be 0 to 0.5 mass %, the strength of a briquetted
solid fuel can be made about 68 kg-wt to about 87 kg-wt. In
particular, when the adhesion amount is 0 mass %, a briquetted
solid fuel has the highest strength of about 87 kg-wt. When a
briquetted solid fuel produces powder, the probability of the
contact between active sites of the solid fuel and the air
increases and there is a concern about the increase in the
probability of spontaneous combustion. However, as described above,
when the strength of a briquetted solid fuel is increased by making
the adhesion amount of a heavy oil be 0 to 0.5 mass %, spontaneous
combustion can be suppressed. From FIG. 5, it has been found that,
the lower the asphalt mass fraction, the higher the briquette
strength is; and, in particular, the highest strength is achieved
at 0 mass % in which no asphalt is added. To increase the briquette
strength, the adhesion between fine coal particles to be briquetted
is preferably high. However, asphalt adheres to the surface of the
coal and, as a result, the adhesion is probably degraded. Although
the detailed mechanism is not clear, it can be considered that
asphalt is petroleum-based (aliphatic series) and hence has low
compatibility (adhesion) with coal (aromatic series).
* * * * *