U.S. patent application number 11/496263 was filed with the patent office on 2007-02-08 for coal particle compositions and associated methods.
This patent application is currently assigned to Primet Precision Materials, Inc.. Invention is credited to Robert J. Dobbs, Leonard E. Dolhert.
Application Number | 20070028509 11/496263 |
Document ID | / |
Family ID | 37709299 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070028509 |
Kind Code |
A1 |
Dobbs; Robert J. ; et
al. |
February 8, 2007 |
Coal particle compositions and associated methods
Abstract
Coal particle compositions are provided. The coal particle
compositions, in some cases, are characterized by having an
extremely small average particle size (e.g., 1.0 micron or less)
and a high average surface area (e.g., greater than 3 m.sup.2/g).
The small particle size and high surface area can lead to
significant property advantages including more efficient
combustion, more effective fractional distillation, and enhanced
pollution separation, amongst others. The coal particle
compositions may be produced in a milling process that uses
preferred grinding media (e.g., high density grinding media) to
reduce feed coal particles to a desired final particle size. The
coal particle compositions may be used in a variety of different
applications including fuel and non-fuel uses.
Inventors: |
Dobbs; Robert J.; (Newfield,
NY) ; Dolhert; Leonard E.; (Trumansburg, NY) |
Correspondence
Address: |
WOLF GREENFIELD & SACKS, PC
FEDERAL RESERVE PLAZA
600 ATLANTIC AVENUE
BOSTON
MA
02210-2206
US
|
Assignee: |
Primet Precision Materials,
Inc.
1005 Hudson Street Extension
Ithaca
NY
14850
|
Family ID: |
37709299 |
Appl. No.: |
11/496263 |
Filed: |
July 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60704040 |
Jul 29, 2005 |
|
|
|
Current U.S.
Class: |
44/500 |
Current CPC
Class: |
C10L 1/322 20130101;
C10L 5/00 20130101; C10L 1/326 20130101; C10L 5/366 20130101; C10L
5/04 20130101 |
Class at
Publication: |
044/500 |
International
Class: |
C10L 5/00 20060101
C10L005/00 |
Claims
1. A coal composition comprising: coal particles having an average
particle size of less than 1.0 micron.
2. A coal composition comprising: coal particles having an average
surface area of greater than 5 m.sup.2/g.
3. The composition of claim 1, wherein the average particle size is
less than 100 nm.
4. The composition of claim 1, wherein the average particle size is
less than 10 nm.
5. The composition of claim 1, wherein the average particle size is
greater than 1 nm.
6. The composition of claim 1, wherein a D.sub.90 value for the
composition is less than 250 nm.
7. The composition of claim 1, wherein a D.sub.90 value for the
composition is less than 50 nm.
8. The composition of claim 1, wherein the average surface area is
greater than 15 m.sup.2/g.
9. The composition of claim 1, wherein the average surface area is
greater than 50 m.sup.2/g.
10. The composition of claim 1, wherein the average surface area is
less than 3,000 m.sup.2/g.
11. The composition of claim 1, wherein the coal particles are
milled.
12. The composition of claim 1, wherein the coal particles include
more than one faceted surface.
13. The composition of claim 1, wherein the particles are
substantially spherical.
14. The composition of claim 1, further comprising a fluid in which
the coal particles are mixed.
15. The composition of claim 14, wherein the fluid is water.
16. The composition of claim 14, wherein the fluid is oil.
17. The composition of claim 14, wherein the fluid is a gas.
18. The composition of claim 14, wherein the fluid is a fuel.
19. The composition of claim 1, wherein the composition includes
less than 0.1% by weight of physical impurities.
20. The composition of claim 1, wherein the composition includes
less than 0.1% by weight of chemical impurities.
21. A method of producing a coal composition comprising: milling
coal feed particles to form a milled coal particle composition
having an average particle size of less than 1.0 micron.
22. The method of claim 21, comprising milling coal feed particles
to form a milled coal particle composition having an average
particle size of less than 100 nm.
23. The method of claim 21, wherein the average particle size is
less than 10 nm.
24. The method of claim 21, wherein the average particle size is
greater than 1 nm.
25. The method of claim 21, comprising milling coal feed particles
to form a milled coal particle composition having an average
surface area of greater than 15 m.sup.2/g.
26. The method of claim 21, comprising milling coal feed particles
to form a milled coal particle composition having an average
surface area of greater than 50 m.sup.2/g.
27. The method of claim 21, wherein the average surface area is
less than 3,000 m.sup.2/g.
28. The method of claim 21, comprising milling the coal feed
particles using grinding media having a density of greater than 8
grams/cm.sup.3.
29. The method of claim 21, comprising milling the coal feed
particles using grinding media having a density of greater than 10
grams/cm.sup.3.
30. The method of claim 21, comprising milling the coal feed
particles using grinding media having a density of greater than 15
grams/cm.sup.3.
31. The method of claim 21, comprising milling the coal feed
particles using grinding media comprising a metal carbide.
32. The method of claim 21, comprising milling the coal feed
particles using grinding media comprising a multi-carbide
material.
33. The method of claim 21, comprising milling the coal feed
particles using grinding media comprising a ferro-tungsten
material.
34. The method of claim 21, comprising milling the coal feed
particles using grinding media comprising a carburized
ferro-tungsten material.
35. The method of claim 21, comprising milling the coal feed
particles using grinding media having an average size of less than
about 150 microns.
36. The method of claim 21, further comprising removing impurities
from the milled coal particle composition by physical
separation.
37. The method of claim 21, comprising milling the coal feed
particles in a milling fluid capable of reacting with the coal feed
particles.
38. The method of claim 37, wherein the milling fluid reacts with
the coal feed particles to form fuel.
39. The method of claim 37, wherein the milling fluid reacts with
the coal feed particles at a temperature greater than 100.degree.
C.
40. The method of claim 37, wherein the milling fluid reacts with
the coal feed particles at a temperature greater than 300.degree.
C.
41. The method of claim 21, comprising milling the coal feed
particles in a milling fluid comprising a light cycle oil
(LCO).
42. The method of claim 21, comprising milling the coal feed
particles in a milling fluid comprising a hydrocarbon fuel.
43. The method of claim 21, comprising milling the coal feed
particles in a milling fluid comprising petroleum.
44. The method of claim 21, comprising milling the coal feed
particles in a milling fluid comprising a hydrogen donor.
45. The method of claim 21, further comprising processing the
milled coal particle composition in a fractional process.
46. The method of claim 21, further comprising mixing the milled
coal particle composition in a liquid.
47. A method of producing a coal composition comprising: milling a
coal feed particle composition to form a milled coal particle
composition from the coal feed particles; and separating coal
molecules from the milled coal particle composition at a
temperature of less than 100.degree. C., the separated coal
molecules having a total weight of greater than 25% the weight of
the coal feed particle composition.
48. The method of claim 47, wherein the separated coal molecules
have a total weight of greater than 90% the weight of the coal feed
particle composition.
49. The method of claim 47, further comprising collecting the
molecular separated coal molecules.
50. The method of claim 47, comprising separating coal molecules
from the milled coal particle composition at a temperature of less
than 50.degree. C.
51. The method of claim 47, separating coal molecules from the
milled coal particle composition at about room temperature.
Description
RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 60/704,040, filed Jul. 29, 2005, which is
incorporated herein by reference.
FIELD OF INVENTION
[0002] The invention relates generally to coal and, more
particularly, to coal particle compositions and methods associated
with the same.
BACKGROUND OF INVENTION
[0003] Coal is a brown to black rock comprised primarily of carbon.
Coal is formed by the accumulation and physical/chemical alteration
of vegetation over long periods of time. Mining operations are used
to unearth coal from the ground.
[0004] Coal may be used as a solid fuel to produce heat by
combustion. The heat may be used to create steam which may power
generators, for example, to produce electricity. Coal also has a
number of non-fuel uses. For example, coal may be separated into
smaller molecules in separation processes (e.g., fractional
distillation) and then used to synthesize a variety of other types
of chemicals and materials including polymeric materials,
pharmaceuticals, specialty chemicals and oils, amongst others.
[0005] In certain processes, it may be desirable to process coal
into particles. For example, fine coal particles may be mixed with
a liquid to form a slurry for use as a fuel. Such slurries may be
pumped through lines and pipes to facilitate transport and delivery
of the fuel to desired locations.
SUMMARY OF INVENTION
[0006] Coal particle compositions and methods associated with the
same are described.
[0007] In one aspect, a coal composition is provided. The
composition comprises coal particles having an average particle
size of less than 1.0 micron.
[0008] In another aspect, a coal composition is provided. The
composition comprises coal particles having an average surface area
of greater than 5 m.sup.2/g.
[0009] In another aspect, a method of producing a coal composition
is provided. The method comprises milling coal feed particles to
form a milled coal particle composition having an average particle
size of less than 1.0 micron.
[0010] In another aspect, a method of producing a coal composition
is provided. The method comprises milling coal feed particles to
form a milled substantially non-porous coal particle composition
having an average surface area of greater than 3 m.sup.2/g.
[0011] In another aspect, a method of producing a coal composition
is provided. The method comprises milling coal feed particles using
grinding media having a density of greater than 6 grams/cm.sup.3
and an average size of less than 250 micron.
[0012] In another aspect, a method of producing a coal composition
is provided. The method comprises milling a coal feed particle
composition to form a milled coal particle composition from the
coal feed particles; and, separating coal molecules from the milled
coal particle composition at a temperature of less than 100.degree.
C. The separated coal molecules have a total weight of greater than
25% the weight of the coal feed particle composition.
[0013] Other aspects, embodiments and features of the invention
will become apparent from the following detailed description when
considered in conjunction with the accompanying drawings. The
accompanying figures are schematic and are not intended to be drawn
to scale. For purposes of clarity, not every component is labeled
in every figure. Nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. All
patent applications and patents incorporated herein by reference
are incorporated by reference in their entirety. In case of
conflict, the present specification, including definitions, will
control.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a copy of an SEM micrograph of milled coal
particles produced in Example 1.
DETAILED DESCRIPTION
[0015] The invention provides coal particle compositions. The coal
particle compositions, in some cases, are characterized by having
an extremely small average particle size (e.g., 1 micron or less)
and a high average surface area (e.g., greater than 3 m.sup.2/g).
The small particle size and high surface area can lead to
significant property advantages including more efficient
combustion, more effective separation processes, and enhanced
impurity removal, amongst others. As described further below, the
coal particle compositions may be produced in a milling process
that uses preferred grinding media (e.g., high density grinding
media) to reduce feed coal particles to a desired final particle
size. The coal particle compositions may be used in a variety of
different applications including fuel and non-fuel
applications.
[0016] Coal particle compositions of the present invention may be
produced at very small particle sizes. In some embodiments, the
average particle size of the coal composition is less than 20
microns; in some embodiments, less than 10 microns; and, in some
embodiments, less than 1.0 micron (e.g., between 10 nm and 1.0
micron). In certain embodiments, the average particle size may be
even smaller. For example, the average particle size may be less
than 600 nm, less than 250 nm, or less than 100 nm. In some cases,
it is even possible to produce coal particle compositions having an
average particle size of less than 50 nm, or less than 10 nm. Such
particle sizes may be obtained, in part, by using grinding media
having certain preferred characteristics, as described further
below.
[0017] The preferred average particle size of the coal composition
typically depends on the intended application. In certain
applications, it may be desired for the average particle size to be
extremely small (e.g., less than 100 nm); while, in other
applications, it may be desired for the average particle size to be
slightly larger (e.g., between 100 nm and 1 micron). In general,
milling parameters may be controlled to provide a desired particle
size, though in certain cases it may be preferable for the average
particle size to be greater than 1 nm to facilitate milling. For
example, the average particle size of the milled coal material may
be controlled by a number of factors including grinding media
characteristics (e.g., density, size, hardness, toughness), as well
as milling conditions (e.g., energy, time).
[0018] It should be understood that the average particle size of a
coal composition may be determined by measuring an average
cross-sectional dimension (e.g., diameter for substantially
spherical particles) of a representative number of coal particles.
The particle size may be measured using a laser particle
measurement instrument, a scanning electron microscope or other
conventional techniques.
[0019] It should also be understood that coal compositions having
average particle sizes outside the above-described ranges (e.g.,
greater than 20 micron) may be useful in certain embodiments of the
invention.
[0020] The coal particle compositions of the present invention may
also be relatively free of large particles. That is, the coal
particle compositions may include only a small concentration of
larger particles. For example, the D.sub.90 values for the
compositions may be any of the above-described average particle
sizes. Though, it should be understood that the invention is not
limited to such compositions.
[0021] Coal particle compositions of the present invention may also
have a very high average surface area. The high surface area is, in
part, due to the very small particle sizes noted above. In certain
embodiments, the coal particles may have surface pores (which may
or may not extend through the particle) which can also contribute
significantly to the surface area. Although, it should be
understood that, in some cases, the coal particles are
substantially non-porous being substantially free of such surface
pores.
[0022] The average surface area of coal particle compositions may
be greater than 1 m.sup.2/g; in other cases, greater than 5
m.sup.2/g; and, in other cases, greater than 50 m.sup.2/g. In some
cases, the coal particles may have extremely high average surface
areas of greater than 100 m.sup.2/g; or, even greater than 500
m.sup.2/g. It should be understood that these high average surface
areas are even achievable in particles that are substantially
non-porous. Such high surface areas may be obtained, in part, by
using grinding media having certain preferred characteristics, as
described further below.
[0023] Similar to particle size, the preferred average surface area
of the coal composition typically depends on the intended
application. In certain applications, it may be desired for the
average surface area to be extremely large (e.g., greater than 50
m.sup.2/g); while, in other applications, it may be desired for the
average surface area to be slightly smaller (e.g., between 50
m.sup.2/g and 1 m.sup.2/g). In general, milling parameters may be
controlled to provide a desired surface area, though in certain
cases it may be preferable for the average surface area to be less
than 3,000 m.sup.2/g (e.g., for substantially non-porous
particles). For example, the average surface area of the milled
coal material may be controlled by a number of factors including
grinding media characteristics (e.g., density, size, hardness,
toughness), as well as milling conditions (e.g., energy, time).
[0024] The coal compositions of the invention are not limited to
specific types of coal. That is, the invention encompasses all
types of coal known in the art including sub-bituminous,
bituminous, semi-bituminous, semi-anthracite and anthracite. "Coal
compositions", as used herein, may also refer to oil shale. "Coal
compositions", as used herein, are not meant to refer to
compositions that have been precipitated from a solution comprising
dissolved coal species. Although, it should be understood that
"coal compositions" may include coal compositions that have been
processed (e.g., during milling as described further below) to
remove species from the coal composition.
[0025] One aspect of the invention is the discovery that coal
particle compositions having the very small particle sizes (and
high surface areas) described above can be produced in a milling
process. The particle sizes (and surface areas) are achievable by
using grinding media having particular characteristics. For
example, in certain processes, it is preferred for the grinding
media to have a very high density. It has been found that very high
density grinding media can greatly enhance the efficiency of the
milling process and can enable production of coal particle
compositions having small particle sizes and high surface
areas.
[0026] As described further below, the coal particles of the
present invention can be produced in a milling process. Thus, these
coal particle compositions may be described as having a
characteristic "milled" morphology. Those of ordinary skill in the
art can identify "milled particles," which, for example, can
include one or more of the following microscopic features: multiple
sharp edges, faceted surfaces, and being free of smooth rounded
"corners" such as those typically observed in
chemically-precipitated particles.
[0027] It should be understood that the milled particles described
herein may have one or more of the above-described microscopic
features, while being substantially spherical, for example, when
viewed at lower magnifications. In certain embodiments, it may be
preferred for coal particles of the invention to be substantially
spherical. In other cases, the milled particles may have platelet,
oblate spheroid, and/or lens shapes. Other particle shapes are also
possible.
[0028] It should be understood that not all embodiments of the
invention are limited to milled particles or milling processes.
[0029] In some embodiments, it may be preferable for the particles
to have a platelet shape. In these cases, the particles may have a
relatively uniform thickness across the length of the particle. The
particles may have a substantially planar first surface and a
substantially planar second surface with the thickness extending
therebetween. The particle thickness may be smaller than the
particle width and particle length. In some embodiments, the length
and width may be approximately equal; however, in other embodiments
the length and width may be different. In cases where the length
and width are different, the platelet particles may have a
rectangular box shape. In certain cases, the particles may be
characterized as having sharp edges. For example, the angle between
a top surface (e.g., first planar surface) of the particle and a
side surface of the particle may be between 75.degree. and
105.degree.; or between 85.degree. and 95.degree. degrees (e.g.,
about 90.degree.). However, it should be understood that the
particles may not have platelet shapes in all embodiments and that
the invention is not limited in this regard. For example, the
particles may have a substantially spherical or oblate spheroid
shape, amongst others. It should be understood that within a milled
coal particle composition, individual particles may be in the form
of one or more of the above-described shapes.
[0030] As noted above, it may be preferred to use grinding media
having specific characteristics. However, it should be understood
that not every embodiment of the invention is limited in this
regard.
[0031] In some embodiments, the grinding media is formed of a
material having a density of greater than 6 grams/cm.sup.3; in some
embodiments, greater than 8 grams/cm.sup.3; in some embodiments,
the density is greater than 10 grams/cm.sup.3; or greater than 15
grams/cm.sup.3; or, even, greater than 18 grams/cm.sup.3. Though,
in certain embodiments, the density of the grinding media may be
less than 22 grams/cm.sup.2, in part, due to difficulties in
producing suitable grinding materials having greater densities. It
should be understood that conventional techniques may be used to
measure grinding media material density.
[0032] In certain embodiments, it also may be preferable for the
grinding media to be formed of a material having a high fracture
toughness. For example, in some cases, the grinding media is formed
of a material having a fracture toughness of greater than 6
MPa/m.sup.1/2; and in some cases, the fracture toughness is greater
than 9 MPa/m.sup.1/2. The fracture toughness may be greater than 12
MPa/m.sup.1/2 in certain embodiments. Conventional techniques may
be used to measure fracture toughness. Suitable techniques may
depend, in part, on the type of material being tested and are known
to those of ordinary skill in the art. For example, an indentation
fracture toughness test may be used. Also, a Palmqvist fracture
toughness technique may be suitable, for example, when testing hard
metals.
[0033] It should be understood that the fracture toughness values
disclosed herein refer to fracture toughness values measured on
bulk samples of the material. In some cases, for example, when the
grinding media are in the form of very small particles (e.g., less
than 150 micron), it may be difficult to measure fracture toughness
and the actual fracture toughness may be different than that
measured on the bulk samples.
[0034] In certain embodiments, it also may be preferable for the
grinding media to be formed of a material having a high hardness.
It has been found that media having a high hardness can lead to
increased energy transfer per collision with product material
which, in turn, can increase milling efficiency. In some
embodiments, the grinding media is formed a material having a
hardness of greater than 75 kgf/mm.sup.2; and, in some cases, the
hardness is greater than 200 kgf/mm.sup.2. The hardness may even be
greater than 900 kgf/mm.sup.2 in certain embodiments. Conventional
techniques may be used to measure hardness. Suitable techniques
depend, in part, on the type of material being tested and are known
to those of ordinary skill in the art. For example, suitable
techniques may include Rockwell hardness tests or Vickers hardness
tests (following ASTM 1327). It should be understood that the
hardness values disclosed herein refer to hardness values measured
on bulk samples of the material. In some cases, for example, when
the grinding media are in the form of very small particles (e.g.,
less than 150 micron), it may be difficult to measure hardness and
the actual hardness may be greater than that measured on the bulk
samples.
[0035] It should be understood that not all milling processes of
the present invention use grinding media having each of the
above-described characteristics.
[0036] Milling processes of the invention may use grinding media
having a wide range of dimensions. In general, the average size of
the grinding media is between about 0.5 micron and 10 cm. The
preferred size of the grinding media used depends of a number of
factors including the size of the coal feed particles, desired size
of the milled coal particle composition, grinding media
composition, and grinding media density, amongst others.
[0037] In certain embodiments, it may be advantageous to use
grinding media that are very small. It may be preferred to use
grinding media having an average size of less than about 250
microns; or, less than about 150 microns (e.g., between about 75
and 125 microns). In some cases, the grinding media may have an
average size of less than about 100 microns; or even less than
about 10 microns. Grinding media having a small size have been
shown to be particularly effective in producing coal particle
compositions having very small particle sizes (e.g., less than 1
micron). In some cases, the grinding media may have an average size
of greater than 0.5 micron.
[0038] It should be understood that the average size of grinding
media used in a process may be determined by measuring the average
cross-sectional dimension (e.g., diameter for substantially
spherical grinding media) of a representative number of grinding
media particles. The grinding media size may be measured using
conventional techniques such as suitable microscopy techniques or
standard sieve size screening techniques.
[0039] The grinding media may also have a variety of shapes. In
general, the grinding media may have any suitable shape known in
the art. In some embodiments, it is preferred that the grinding
media be substantially spherical (which may be used herein
interchangeably with "spherical"). Substantially spherical grinding
media have been found to be particularly effective in obtaining
desired milling performance.
[0040] It should also be understood that any of the grinding media
used in methods of the invention may have any of the
characteristics (e.g., properties, size, shape, composition)
described herein in combination with one another. For example,
grinding media used in methods of the invention may have any of the
above-noted densities and above-noted average sizes (e.g., grinding
media may have a density of greater than about 6 grams/cm.sup.3 and
an average size of less than about 250 micron).
[0041] The above-described grinding media characteristics (e.g.,
density, hardness, toughness) are dictated, in part, by the
composition of the grinding media. In certain embodiments, the
grinding media may be formed of a metallic material including metal
alloys or metal compounds. In one set of embodiments, it may be
preferred that the grinding media are formed of ferro-tungsten
material (i.e., Fe--W). In some cases, the compositions may
comprise between 75 and 80 weight percent iron and between 20 and
25 weight percent tungsten. In some cases, ferro-tungsten grinding
media may be carburized to improve wear resistance.
[0042] In other embodiments, the grinding media may be formed of a
ceramic material such as a carbide material. In some embodiments,
the grinding media to be formed of a single carbide material (e.g.,
iron carbide (Fe.sub.3C), chromium carbide (Cr.sub.7C.sub.3),
molybdenum carbide (MO.sub.2C), tungsten carbide (WC, W.sub.2C),
niobium carbide (NbC), vanadium carbide (VC), and titanium carbide
(TiC)). In some cases, it may be preferred for the grinding media
to be formed of a multi-carbide material. A multi-carbide material
comprises at least two carbide forming elements (e.g., metal
elements) and carbon.
[0043] A multi-carbide material may comprise a multi-carbide
compound (i.e., a carbide compound having a specific stoichiometry;
or, a blend of single carbide compounds (e.g., blend of WC and
TiC); or, both a multi-carbide compound and a blend of single
carbide compounds. It should be understood that multi-carbide
materials may also include other components such as nitrogen,
carbide-forming elements that are in elemental form (e.g., that
were not converted to a carbide during processing of the
multi-carbide material), amongst others including those present as
impurities. Typically, but not always, these other components are
present in relatively minor amounts (e.g., less than 10 atomic
percent).
[0044] Suitable carbide forming elements in multi-carbide grinding
media of the invention include iron, chromium, hafnium, molybdenum,
niobium, rhenium, tantalum, titanium, tungsten, vanadium,
zirconium, though other elements may also be suitable. In some
cases, the multi-carbide material comprises at least two of these
elements. For example, in some embodiments, the multi-carbide
material comprises tungsten, rhenium and carbon; in other cases,
tungsten, hafnium and carbon; in other cases, molybdenum, titanium
and carbon.
[0045] Suitable grinding media compositions have been described,
for example, in U.S. Patent Publication No. 2006/0003013, which is
incorporated herein by reference and is based on U.S. patent
application Ser. No. 11/193,688, filed Jan. 5, 2006.
[0046] In some embodiments, it may be preferred for the
multi-carbide material to comprise at least tungsten, titanium and
carbon. In some of these cases, the multi-carbide material may
consist essentially of tungsten, titanium and carbon, and is free
of additional elements in amounts that materially affect
properties. Though in other cases, the multi-carbide material may
include additional metal carbide forming elements in amounts that
materially affect properties. For example, in these embodiments,
tungsten may be present in the multi-carbide material in amounts
between 10 and 90 atomic %; and, in some embodiments, in amounts
between 30 and 50 atomic %. The amount of titanium in the
multi-carbide material may be between 1 and 97 atomic %; and, in
some embodiments, between 2 and 50 atomic %. In these embodiments
that utilize tungsten-titanium carbide multi-carbide material, the
balance may be carbon. For example, carbon may be present in
amounts between 10 and 40 atomic %. As noted above, it should also
be understood that any other suitable carbide forming elements can
also be present in the multi-carbide material in these embodiments
in addition to tungsten, titanium and carbon. In some cases, one or
more suitable carbide forming elements may substitute for titanium
at certain sites in the multi-carbide crystal structure. Hafnium,
niobium, tantalum and zirconium may be particularly preferred as
elements that can substitute for titanium. Carbide forming elements
that substitute for titanium may be present, for example, in
amounts of up to 30 atomic % (based on the multi-carbide material).
In some cases, suitable multi-carbide elements may substitute for
tungsten at certain sites in the multi-carbide crystal structure.
Chromium, molybdenum, vanadium, tantalum, and niobium may be
particularly preferred as elements that can substitute for
tungsten. Carbide forming elements that substitute for tungsten may
be present, for example, in amounts of up to 30 atomic % (based on
the multi-carbide material).
[0047] It should also be understood that the substituting carbide
forming elements noted above may completely substitute for titanium
and/or tungsten to form a multi-carbide material free of tungsten
and/or titanium.
[0048] It should be understood that grinding media compositions
that are not disclosed herein but have certain above-noted
characteristics (e.g., high density) may be used in embodiments of
the invention. Also, it should be understood that milling processes
of the present invention are not limited to the grinding media
compositions and/or characteristics described herein. Other
suitable grinding media may also be used.
[0049] In general, any suitable process for forming grinding media
compositions may be used. In some cases, the processes involve
heating the components of the composition to temperatures higher
than the respective melting temperatures of the components followed
by a cooling step to form the grinding media. A variety of
different heating techniques may be used including a thermal plasma
torch, melt atomization, and arc melting, amongst others. For
example, one suitable process involves admixing fine particles of
the elements intended to comprise the grinding media in appropriate
ratios. The stability of the mixture may be enhanced by
introduction of an inert binding agent (e.g., which burns off and
does not form a component of the grinding material). The mixture
may be subdivided into a plurality of aggregates (e.g., each having
a mass approximately equal to that of the desired media particle to
be formed). The aggregates may be heated to fuse (e.g., to 90% of
theoretical density) and, eventually, melt individual aggregates to
form droplets that are cooled to form the grinding media.
[0050] In some embodiments, the grinding media may be formed of two
different materials. For example, the grinding media may be formed
of a blend of two different ceramic materials (e.g., a blend of
high density ceramic particles in a ceramic matrix); or a blend of
a ceramic material and a metal (e.g., a blend of high density
ceramic materials in a metal matrix).
[0051] In some embodiments in which the grinding media comprises
more than one material component, the grinding media may comprise
coated particles. The particles may have a core material and a
coating formed on the core material. The coating typically
completely covers the core material, but not in all cases. The
composition of the core and coating materials may be selected to
provide the grinding media with desired properties such as a high
density. For example, the core material may be formed of a high
density material (e.g., greater than 8 grams/cm.sup.3). The core,
for example, may be formed of a metal such as steel or depleted
uranium; or a ceramic such as a metal carbide.
[0052] As noted above, coal particle compositions may be produced
in a milling process that use grinding media as described herein.
The processes may utilize a wide range of conventional mills having
a variety of different designs and capacities. Suitable types of
mills include, but are not limited to, ball mills, rod mills,
attritor mills, stirred media mills, pebble mills and vibratory
mills, among others.
[0053] In some cases, conventional milling conditions (e.g.,
energy, time) may be used to process the coal particle compositions
using the grinding media described herein. In other cases, the
grinding media described herein may enable use of milling
conditions that are significantly less burdensome (e.g., less
energy, less time) than those of typical conventional milling
processes, while achieving a superior milling performance (e.g.,
very small average particle sizes).
[0054] One aspect of the invention is that the small coal particle
compositions of the invention may be produced using very low
specific energy input (i.e., energy consumed in milling process per
weight of feed material).
[0055] Milling processes of the invention can involve the
introduction of a slurry of feed coal material (e.g., feed
particles) and a milling fluid (e.g., water or others described
further below) into a processing space in a mill in which the
grinding media are confined. The viscosity of the slurry may be
controlled, for example, by adding additives to the slurry such as
dispersants. The mill is rotated at a desired speed and coal
material particles mix with the grinding media. Collisions between
the coal particles and the grinding media can reduce the size of
the coal particles. In certain processes, it is believed that the
mechanism for particle size reduction is dominated by wearing of
coal particle surfaces; while, in other processes, it is believed
the mechanism for particle size reduction is dominated by coal
particle fracture. The particular mechanism may affect the final
characteristics (e.g., morphology of the milled coal particle
composition). The coal particles are typically exposed to the
grinding media for a certain mill time after which the milled coal
material is separated from the grinding media using conventional
techniques, such as washing and filtering, screening or gravitation
separation.
[0056] It should be understood that, in certain methods, the goal
of the milling process may be to accelerate a reaction involving
coal particles rather than to reduce particle size. In these
methods, coal particle size also may be reduced, though the
particle size reduction may be negligible in some cases. In methods
that accelerate reactions with coal particles, reactivity may be
enhanced by wearing particle surfaces and, thus, exposing reactive
species. In some cases, layer(s) on the coal particles that may
otherwise impede reactions may be removed in the milling
process.
[0057] In some processes, the coal slurry is introduced through a
mill inlet and, after milling, recovered from a mill outlet. The
process may be repeated and, a number of mills may be used
sequentially with the outlet of one mill being fluidly connected to
the inlet of the subsequent mill.
[0058] In certain processes, it is possible to reduce the size of
coal particles and solid impurity particles (e.g., pyrite) at
different rates. For example, coal particles may be reduced at a
much higher rate than solid impurity particles (e.g., pyrite) and,
in certain processes, the impurity particles may be only be
negligibly reduced. In this manner, the milled coal composition may
include small coal particles and larger impurity particles. This
enables efficient removal of the coal particles from the impurities
by conventional physical separation techniques such as screening or
density floatation methods.
[0059] This selective particle size reduction may be accomplished
by controlling milling parameters such as the rotational speed
(rpm) of the mill which is a measure of milling intensity. For
example, the rotational speed (or milling intensity) can be
selected so as to efficiently reduce the size of the coal
particles, while not efficiently reducing the size of the impurity
particles. Though suitable rotational speeds (or milling
intensities) may depend on the specific process (e.g., specific
type of coal being processed), those of ordinary skill in the art
can readily determine suitable values by varying the rotational
speed and observing the effect on the wear rate of the coal and
impurity particles.
[0060] The small coal particle sizes and high surface areas also
enable efficient removal of chemical impurities including organic
impurities (e.g., organic sulfur) and/or low vapor pressure
impurities. For example, the small particle size and high surface
area enhances access to such chemical impurities by suitable
chemicals which can react with the impurities to form reactants
that are subsequently removed from particle surfaces. Also, the
small particle size and high surface area promotes removal of low
vapor pressure impurities from the particles (e.g., by desorption)
which may be at particle surfaces or can readily diffuse to
surfaces. The chemical impurities may be removed during, or after,
the milling process.
[0061] Accordingly, processes of the invention enable production of
coal particle compositions having low levels of both physical and
chemical impurities. For example, processes of the invention may
reduce impurities such that the compositions include less than 0.1%
by weight of such impurities. Although, it should be understood,
that not all compositions of the invention have such low impurity
levels.
[0062] In certain processes, the milling fluid may be selected to
provide additional functions. For example, the milling fluid may be
capable of reacting with the small coal particles during the
milling process, itself (i.e., a reactive milling process). This
can eliminate additional processing steps and can limit handling of
fine coal particles which may be advantageous in certain cases.
[0063] The milling fluid may be a suitable solvent that is capable
of extracting desired chemical species from the coal. For example,
the milling fluid (e.g., light cycle oil (LCO)) may be capable of
extracting a refined chemical oil (RCO) from the coal. The
resulting product obtainable from the milling process can include
small coal particles, as well as a mixture of RCO and the milling
fluid (e.g., LCO). Such a product can be used to produce jet fuel
(e.g., JP-900)
[0064] In certain embodiments, a gas may be dissolved in the
milling fluid. The gas may be capable of reacting with the coal
particles.
[0065] In another process, the milling fluid may be a hydrocarbon
fuel, such as petroleum. The mixture of the small coal particle
composition and the fuel can be processed to form a high quality
coke.
[0066] Some processes involve milling the coal particles in an
environment that provides hydrogen capable of reacting with the
coal particles. In such cases, the milling fluid may be a hydrogen
donor such as tetralin or dihydrophenathrene. In some cases, the
hydrogen donor may be a gas dissolved in the milling fluid (e.g.,
gas comprising hydrogen species, or hydrogen). Such processes
promote hydrogenation of the coal which may be useful, for example,
in producing a liquid hydrocarbon fuel such as gasoline.
[0067] It should also be understood that other embodiments of the
invention may involve dispersing coal particles after the milling
process in any of the "milling" fluids described above. In these
embodiments, the fluid used in the milling process may be a
conventional milling fluid such as water, or other inert milling
fluids.
[0068] In certain embodiments, the milling step may occur at
temperatures above room temperature (e.g., greater than 30.degree.
C.). In some cases, the temperatures may be up to about 300.degree.
C. At elevated temperatures, reactions between coal and other
components (e.g., milling fluid) may be enhanced. In certain
processes, these high temperatures promote separation (e.g., by
vaporization) of coal molecules which can be collected. Such
molecules may be used, for example, in fuel or non-fuel uses.
[0069] In some embodiments, the milling step may occur at
temperatures below room temperatures (e.g., less than 15.degree.
C.). Lower temperatures may be advantageous in collecting certain
components that are separated from coal (e.g., in separation
processes) that may have glass transition temperatures above that
of the milling temperature, but below room temperature. Such
molecules may be used, for example, in fuel or non-fuel uses.
[0070] In some methods, swelling agents may be added to the coal
particles during, or after, the milling step. Suitable swelling
agents are known to those of skill in the art. The swelling agents
may cause the coal particles to swell in size, for example, by
increasing particle porosity. The increased porosity can enable
reactive species within the coal to escape from the coal particle
prior to reaction completion and, thus, increasing the amount of
reaction taking place external of the particle which may be
advantageous.
[0071] The above-described small particle sizes and high surface
areas lead to a number of advantages that may be found in coal
particle compositions of the present invention. For example, the
small particles sizes and high surface areas may significantly
enhance the reactivity of the coal compositions. Thus, processes
that involve reactions with the coal particles (e.g., combustion,
extraction, etc.) can be accelerated. This can improve and/or
simplify and/or reduce cost of certain existing coal processes and
may enable new processes.
[0072] The combustion (i.e., burning) efficiency may be
substantially increased using coal particle compositions of the
present invention. For example, the small particles and high
surface areas can lead to rapid combustion which may be nearly
instantaneous. This can enhance performance of coal in fuel
applications and, in particular, when coal is dispersed in a fluid
to form a mixture (e.g., slurry) which can be used as a fuel. Such
slurries may also include high solid loadings (e.g., greater than
or equal to about 50%) because of the small particle sizes.
Suitable fluids may be water, other liquid fuels (e.g., hydrocarbon
fuels such as gasoline) oil, or even gas (e.g., air, argon). In
particular, coal particles at larger particle sizes typically
cannot be effectively transferred using gas (e.g., air); however,
the very small particle sizes of coal compositions of the present
invention may enable transfer in a gas (e.g., through a powder
bed).
[0073] Also, the coal particles of the present invention having
small particle sizes and high surface areas may enhance separation
processes (such as fractional distillation). Such processes
liberate molecules from coal which can be used in a variety of
applications including fuels (e.g., gasoline), pharmaceuticals,
specialty chemicals, plastics and oils. In particular, at the very
small dimensions described above (e.g., less than 1000 nm, 500 nm
or 100 nm), separation processes may be utilized to obtain specific
relatively low molecular weight molecular components (i.e.,
fractions) which can be particularly valuable in the above-noted
applications and which may not be as readily obtained in other
conventional processes. The small particles can also lead to
substantial cost reductions in separation processes.
[0074] The milling process, itself, may be used as a separation
process. For example, coal feed particles may be milled to the
small dimensions noted above which can lead directly to the
separation of coal-based molecules from the feed particles. Such
separation may be enhanced by the presence of certain agents and/or
heat, though such agents and/or heat are not required. The
coal-based molecules may be collected and used in a variety of fuel
and non-fuel-based applications as described further below. Such
separation may be quantified by measuring the total weight of the
coal feed particle composition before and after separation. The
difference in the weight is generally due to the separation of
coal-based molecules from the coal feed particles. In some
embodiments, the separated coal molecules having a total weight of
greater than 25% the weight of the coal feed particle composition.
In other embodiments, the separated coal molecules have a total
weight of greater than 50%, 70%, or even 90% the weight of the coal
feed particle composition. The actual degree of separation, may
depend on the specific process conditions and particle size of the
milled coal particles.
[0075] For example, raw coal typically contains pure coal material
and non-coal material. The non-coal material may include, for
example, pyrite, other aluminosilicate materials, sulfur-containing
materials including sulfides, sulfates, organic sulfur, inorganic
sulfur (e.g., pyrite sulfur, sulfate sulfur, and the like),
minerals such as clays, carbonates, quartz, biotite, rutile,
feldspars, hemetite, and various non-combustible ash-forming
impurities. The presence of large amounts of these non-coal
materials can create problems during combustion. For example,
sulfur-containing materials the present in the coal may produce
sulfur dioxide when burned. Some methods of the invention may
separate the pure coal material from the non-coal material,
producing a relatively clean coal product and reducing the
production of excessive pollutants.
[0076] In some methods, it may even be possible to separate coal
molecules from coal particles at low temperatures including less
than 100.degree. C., less than 50.degree. C., or even at about room
temperature (e.g., about 30.degree. C.). Such temperature ranges
may be used to obtain the above-noted weight percentage. Certain
prior art techniques, which do not involve milling (e.g., Low
Temperature Carbonization, chemical processes using gases such as
hydrogen, nitrogen, chlorine, steam, air, and the like, or with
solutions such as sodium hydroxide, ferric sulfate, cupric sulfate,
and the like), for obtaining such molecules were conducted at
significantly higher temperatures (e.g., greater than 400.degree.
C.). The milling processes described herein enable separation of
certain molecules because of the ability to reduce particle size to
such small values (e.g., less than 250 nm, less than 100 nm).
[0077] In some embodiments, the milling process may be a reactive
milling process. For example, a chemical reaction between the coal
particles and the milling fluid may occur during the milling
process to form a desired product (e.g., a fuel). In some cases,
the coal particles are milled with a milling fluid capable of
reacting with the coal feed particles at elevated temperatures
(e.g., greater than about 100.degree. C., greater than about
300.degree. C.). The milled coal particles can react with the
milling fluid and/or with another chemical species within the fluid
(e.g., a gas bubbled through the milling fluid).
[0078] The small coal particles may enable equipment advantages.
Coal water slurries may be used in systems for electricity
generation significantly smaller and less complex than certain
conventional systems. For example, small coal particle compositions
having low levels of pollution can limit, or even eliminate, the
need for scrubbers which otherwise would be used to reduce
pollution levels. Smaller coal particles also may lead to less
abrasion to equipment that may further process such coal particles
(e.g., motors).
[0079] Because of the ability of milling processes of the invention
to produce very small particles, it may be possible to use coal
"fines", which are a waste product in certain conventional coal
processes, as the feed material. Such fines may have an average
particle size between 30 and 100 microns and generally have not
been used as feed material in typical conventional milling
processes. By utilizing a waste product, thus, processes of the
invention may have a positive environmental impact.
[0080] Coal particles of the invention may be used in a variety of
applications including fuel and non-fuel-based applications. The
non-fuel based applications include, but are not limited to,
additives to other materials (e.g., such as modifiers/fillers in
polymeric materials) and use in separation processes to produce
components used to synthesize polymeric materials, pharmaceuticals,
specialty chemicals, and oils. It should also be understood that
coal particle compositions of the present invention may have a
variety of other uses beyond those described herein.
[0081] Coal particles of the invention may be further processed for
certain applications. For example, the coal particles of the
invention may be processed to form coal films. In some cases, the
films may be very thin (e.g., less than 10 micron, less than 1
micron, or less than 100 nm) because of the very small coal
particle sizes obtainable using methods of the invention. In some
cases, coal films may even be used as molecular thin films. Coal
films may be used in electronic applications as semiconductor
layers, conductive layers or shielding layers (e.g.,
electromagnetic shielding).
[0082] The coal particles described herein may also have excellent
electrostatic properties and may be used in applications that
utilize such properties. For example, the coal particles may be
used in electrostatic printing applications (e.g., laser printers,
copiers). The small particles sizes obtainable using the methods
described herein are particularly important in such applications.
In these applications, the coal particles may have an average
particle size of less than 1 micron and, in some applications,
between about 1 nm and 50 nm. Because of differences between the
properties (e.g., triboelectric properties) of coal and other
materials used in these applications such as carbon, it is possible
to design printing equipment that is compatible with coal particles
but incompatible with other types of carbon particles. This enables
a manufacturer of printer equipment (e.g., printer cartridges) to
limit "after market" sales of such equipment to that which is
compatible with coal which may give such manufacturers a
competitive advantage.
[0083] Coal particles described herein may also be used in ink and
dye applications. For example, the coal particles may be used in
inks for ink-jet printers and dye formulations for inks.
[0084] The following example is meant to be illustrative of certain
embodiments of the invention and are not meant to be limiting.
EXAMPLE 1
[0085] This example illustrates production of a coal particle
composition having an extremely small particle size.
[0086] Anthracite coal particles having an average particle size of
about 50 microns was used as the feed material. The coal particles
were mixed with water to form a slurry which was introduced into a
1.5 inch diameter stirred media mill with 1.8 mm diameter zirconia
beads as the grinding media. The particles were milled for about 20
minutes at 3,000 rpm to obtain a coal particle composition having
an average particle size of about 10 microns.
[0087] The slurry was introduced into a 3 inch diameter stirred
media mill with grinding media having a tungsten-titanium carbide
composition (i.e., (W:Ti)C including about 10% by weight W) with a
density of 16 grams per cubic centimeter. The grinding media had an
average particle size between 75 micron and 125 micron. The
particles were milled for 1 hour at 2,200 RPM to produce a milled
coal particle composition having an average particle size of about
160 nm.
[0088] A sample of the slurry of coal and water was collected by
evaporating the water at room temperature until the sample was
dried. The weight of the dried sample was measured and compared to
the weight of the wet sample prior to drying. The measurements
indicated that 81 wt % of the coal mass evaporated along with the
water. This mass is attributed to the mass of coal molecular
species separated from the coal particles during milling. FIG. 1 is
a micrograph of representative milled coal particles obtained using
SEM analysis.
[0089] This example establishes that coal particle compositions
having an extremely small particle size can be produced and that
coal molecules may be effectively separated from each other at such
small particles sizes with substantial amounts of separation being
obtainable even at low temperatures (e.g., less than 100.degree.
C.).
[0090] Having thus described several aspects of at least one
embodiment of this invention, it is to be appreciated various
alterations, modifications, and improvements will readily occur to
those skilled in the art. Such alterations, modifications, and
improvements are intended to be part of this disclosure, and are
intended to be within the spirit and scope of the invention.
Accordingly, the foregoing description and drawings are by way of
example only.
* * * * *