Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND COMPOSITIONS FOR DRYING COAL
Background
Many current methods of coal mining use water to extract fine coal particles
(also called coal fines). Such particles typically can have with diameters
from
approximately 100 to 800 microns in diameter, although coal fines may have
smaller
diameters, e.g., on the order of 50 microns or less. Traditional methods of
drying the
coal particles, including centrifugation and heating technologies, can readily
dry these
coal "fines" to approximately 30% moisture. Methods of drying coal fines
beyond this
point typically employ blowers and heaters which require capital intensive
investment,
require substantial energy use, and create environmental problems and hazards
both
from energy use and from aerosolization of the coal fines.
Summary
Embodiments of this disclosure provide methods and compositions for drying
wet coal fines by employing water-collecting materials such as molecular
sieves, water
adsorbing polymeric agents, desiccants, and the like that are easily separated
from the
coal fines, for example by sieving or sifting. Such materials may remove all
or a
portion of the water from the wet fines by physical and/or chemical action.
For
example, the water-collecting materials may draw water from the wet fines by
sorption, e.g., absorption or adsorption. In embodiments of the methods and
compositions herein, the materials used for collecting water from the coal
fines can be
recycled and/or reused to dry more coal fines after removing some or all of
the water
from the water-collecting materials.
Brief Description of the Drawing
Figure 1 shows the weight of a batch of molecular sieves used to adsorb water
from six batches of coal fines. The weight of the molecular sieves are
determined after
drying each batch of coal fines and at the indicated time throughout the
drying process
weighed periodically
Detailed Description
Embodiments described herein utilize water-collecting materials such as
adsorbents and absorbents that can collect moisture from wet coal fines.
Advantageously, such materials can efficiently collect the moisture from the
coal fines,
and then can be separated from the fines, so as to reduce the amount of water
associated with the coal fines. In some embodiments, the water-collecting
materials
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then can be dried separately from the coal fines. The process may provide one
or more
desirable benefits such as a reduction in one or more of time, energy, cost,
and/or
adverse environmental impact, as compared to other processes of drying wet
coal
fines. Moreover, embodiments of this disclosure can substantially reduce the
aerosolization of coal fines by blowers, which can pose health, fire and
explosion
hazards.
Although embodiments described herein do not require the drying and reuse of
such water-collecting materials, many such materials can be efficiently dried
separately from the coal fines and reused one or more times. Embodiments
described
herein thus employ the drying and reuse water-collecting materials such as
absorbents
and adsorbents. In other embodiments all or a portion of the water-collecting
material
can be discarded, e.g., where an absorbent is degraded and cannot be
effectively
separated from the coal fines. In one embodiment, particles of water-
collecting
materials are separated by sieving or sifting to remove degraded particles
which may
be larger than particles of coal fine, but are smaller than desirable for
processing wet
coal fines. In other embodiments, some or all of the absorbent materials
employed for
use in removing moisture from coal fines may be biodegradable.
The water-collecting material also may bond with the water to cause the water
to be associated with the material instead of the coal fines.
1.0 Removing Moisture from Coal Fines
Coal fines may separated from the bulk water (water in excess of that which is
associated with coal fines when they settle, or are filtered or centrifuged
out aqueous
suspension) used in the mining /recovery process by any one or more of a
variety of
known techniques. Such techniques include, but are not limited to one or more
of,
filtration (e.g., gravity based filtration, or filtration assisted by
centrifugal force,
pressure or vacuum), settling, centrifugation and the like, which can used
singly or in
combination. Further amounts of water may optionally be removed from the coal
fines
by a second round of such treatments.
After one or more separation steps to removal bulk water, the wet coal fines
are
then mixed with particles of a water-collecting material or combination of
different
types of water-collecting materials, e.g., particles of absorbent or
adsorbent, to further
reduce the amount of water associated with the fines. In one embodiment, the
particles
of water-collecting material are large enough to be separated from the coal
fines by
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size (e.g., sifting with an appropriate size screen or mesh). In various
embodiments, to
facilitate their drying, the wet coal fines are mixed with one or more types
of water-
collecting materials including, but not limited to, molecular sieves,
particles of
hydratable polymers (e.g., polyacrylate or carboxymethyl cellulose/polyester
particles), or desiccants (e.g., silicates). The rate at which various water-
collecting
materials adsorb, absorb, or react with water present in coal fines may be
affected by
temperature. Each type of water-collecting material may have different optimum
temperatures for the rate at which they will accumulate water from the coal
fines. In
some instances, as with molecular sieves, heating/warming the molecular sieves
with
the coal fines, or heating/warming molecular sieves immediately prior to
mixing them
with coal fines, may increase the rate at which water becomes associated with
the
molecular sieves. In other embodiments, materials such as alumina particles
may
accumulate water at suitable rate from coal fines at room temperature (e.g.,
about 20-
25 C). Water-collecting materials containing water formerly associated with
the coal
fines can subsequently be removed from the coal fines a variety of means.
1.1 The Use of Molecular Sieves as Adsorbents to Reduce the Moisture
Content of Coal Fines
Molecular sieves are materials containing pores of a precise and uniform size
(pore sizes are typically from about 3 to about 10 Angstroms) that are used as
an
adsorbent for gases and liquids. Without wishing to be bound by any theory,
generally
molecules small enough to pass through the pores are adsorbed while larger
molecules
cannot enter the pores. Molecular sieves are different from a common filter in
that they
operate on a molecular level. For instance, a water molecule may not be small
enough
to pass through while the smaller molecules in the gas pass through. Because
of this,
they often function as a desiccant. Some molecular sieves can adsorb water up
to 22%
of their dry weight. Molecular sieves often they consist of aluminosilicate
minerals,
clays, porous glasses, microporous charcoals, zeolites, active carbons
(activated
charcoal or activated carbon), or synthetic compounds that have open
structures
through or into which small molecules, such as nitrogen and water can diffuse.
In
some embodiments, the molecular sieves are an aluminosilicate mineral (e.g.,
andalusite, kyanite, sillimanite, or mullite). In other embodiments, the
molecular
sieves comprise about 10%, 20%, 30%, 40%, 50%, 60%, 65%,70%, 75%, 80%, 85%,
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90%, 95%, 98%, 99% or greater (on a weigh basis) of an aluminosilicate
mineral. In
some embodiments, including those embodiments where the molecular sieves
comprise an aluminosilicate mineral, the particles of molecular sieves may
contain
other minerals, such oxides of zirconium or titanium to enhance properties
such as
strength and wear (e.g., zirconia toughened aluminosilicates or alumina-
titanate-
mullite composites). In some embodiments the molecular sieves are 3 angstrom
molecular sieves (e.g., MS3A4825 molecular sieves with 2.5 - 4.5 mm bead size
and
14 lb crush strength from Delta Enterprises, Roselle, Illinois) or 4 angstrom
molecular
sieves (e.g., MS4A4810 molecular sieves with 2.5 - 4.5 mm bead size and 18 lb
crush
strength from Delta Enterprises, Roselle, Illinois).
A variety of molecular sieves can be employed alone or in combination to
remove water or moisture from coal fines. In one embodiment, molecular sieves
may
be selected from aluminosilicate minerals, clays, porous glasses, microporous
charcoals, zeolites, active carbons, or synthetic compounds that have open
structures
through or into which small molecules, such as nitrogen and water can diffuse.
In
other embodiments, molecular sieves may be selected from aluminosilicate
minerals,
clays, porous glasses, or zeolites.
Molecular sieves with pores large enough to draw in water molecules, but
small enough to prevent any of the coal fines from entering the sieve
particles, can be
advantageously employed. Hardened molecular sieves or molecular sieves, or
those
with an especially hard shell, are useful in the methods described herein as
such sieves
will not be readily worn down and can be reused after removal of moisture.
In some embodiments molecular sieve particles are greater than 1, 1.25, 1.5,
1.75, 2.0, 2.25 or 2.5 mm in diameter and less than about 5 mm or 10 mm. In
other
embodiments the molecular sieve particles are greater than about 12, 14, 16,
18, 20,
22, 24 or 26 mm in diameter and less than about 28, 30 or 32 mm in diameter.
When
mixed with the wet coal fines having excess moisture (wet coal fines), the
molecular
sieves quickly draw the moisture from the coal fines. As the sieves are larger
than the
coal fines (e.g., over a millimeter in diameter), the mixture of sieves and
coal fines can
be lightly bounced on a fine mesh grid, where the dry coal fines can be
separated from
the molecular sieves. The separated molecular sieves can be a bit dusty and
can carry
a minute amount of coal fines with them after they have absorbed the water.
Once
separated, the molecular sieves can be passed to a heater where they can be
dried and
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sufficient moisture is removed to permit their reuse if desired. Thus, the
molecular
sieves can be employed in a close-loop system, where they are mixed with the
coal
fines, and after removing water/ moisture (drying) they are separated from the
coal
fines and passed through a heater and reused. Minimal agitation is required
during dry
the sieves.
1.2 The Use of Hydratable Polymeric Materials to Reduce the Moisture
Content of Coal Fines
Hydratable polymeric materials or compositions comprising one or more
hydratable polymers may be employed to reduce the moisture content of coal
fines
(e.g., polyacrylate or carboxymethyl cellulose/polyester particles/beads).
In one embodiment the hydratable polymeric materials is polyacrylate (e.g., a
sodium salt of polyacrylic acid). Polyacrylate polymers are the
superabsorbents
employed in a variety of commercial products such as in baby's diapers,
because of
their ability to absorb up to 400% of their weight in water. Polyacrylates can
be
purchased as a come a translucent gel or in a snowy white particulate form.
Suitable
amounts of polyacrylic acid polymers (polyacrylates) sufficient to adsorb the
desired
amounts of water from coal fines can be mixed with the fines, to quickly dry
coal. The
polyacrylate, which swells into particles or "balls," may be separated from
the coal
fines on suitable size filters or sieves. The particles or "balls" can either
be discarded
or recycled by drying using any suitable method (direct heating, heating by
exposure to
microwave energy, and the like).
The properties of hydrateable polymers, including polyacrylate polymers, may
be varied depending on the specifics of the process being employed to dry the
coal
fines. A skilled artisan will recognize that the properties (gel strength,
ability to absorb
water, biodegradability etc.) are controlled to a large degree by the type and
extent of
the cross-linking that is employed in the preparation of hydratable polymers.
A skilled
artisan will also recognize that it may be desirable to match the degree of
cross-linking
with the mechanical vigor of the process being used dry the coal fines and the
number
of times, if any, that the particles are intended to be reused in drying
batches of coal
fines. Typically, the use of more cross-linked polymers, which are typically
mechanically more stable/rigid, will permit their use in more mechanically
vigorous
processes and the potential reuse of the particles.
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In another embodiment the hydratable polymer composition employed is a
combination of carboxymethylcellulose (CMC) and polyester (e.g., CMC gum
available from Texas Terra Ceramic Supply, Mount Vernon, TX). Such
compositions,
or other super adsorbent hydratable polymeric substances, can be used to
remove water
from coal fines in a manner similar to that described above for molecular
sieves or
polyacrylate polymer compositions.
1.3 The Use of Desiccants to Reduce the Moisture Content of Coal Fines
In other embodiments, desiccants are used as water-collecting materials to dry
coal fines. A variety of desiccation agents (desiccants) may be employed to
reduce the
moisture content of coal fines including, but not limited to, silica, alumina,
and
calcium sulfate (Drierite, W.A. Hammond Drierite Col Ltd Xenia, OH) and
similar
materials. Desiccants, like the compositions described above can be used to
remove
water from coal fines in a manner similar to that described above for
molecular sieves
or polyacrylate polymer compositions.
In some embodiments, the desiccant material is comprised of activated
alumina, a material that is effective in absorbing water. Without wishing to
be bound
by any theory, activated alumina's efficiency as a desiccant is based on the
large and
highly hydrophilic surface area of activated alumina (on the order of 200
m2/g) and
water's attraction (binding) to the activated alumina surface. Other materials
having
high-surface areas that are hydrophilic are contemplated, e.g., materials that
have
hydrophilic surfaces and surface areas greater than 50 m2/g, 100 m2/g or 150
m2/g. In
some embodiments the desiccant comprises about 10%, 20%, 30%, 40%, 50%, 60%,
65%,70%, 75%, 80%, 85%, 90%, 95%, 98%, 99% or greater (on a weigh basis) of
alumina.
Activated alumina is a very hard, durable ceramic capable of withstanding
significant abrasion and wear, however, the wear resistance and mechanical
properties
of activated alumina may be enhanced by introducing other materials into
particles of
water-collecting materials that comprise alumina. In some embodiments,
desiccants
comprising alumina may contain about 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%,
10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% or more of other
minerals, such oxides of zirconium or titanium to enhance properties such as
strength
and wear (e.g., zirconia alumina or zirconia toughened alumina ZTA).
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1.4 Particles of Water Collecting Materials
As described above, a variety of water-collecting materials may be employed in
systems for removing water from wet (or moist) coal fines. Such water-
collecting
materials include those that absorb water, those that adsorbs water, and those
that
bonds or react with water. Typically the water-collecting materials will be in
the form
of particles that can be of any shape suitable for forming an admixture with
the wet (or
moist) coal fines and that are capable of being recovered. Such particles may
be
irregular in shape, or have a regular shape. Where particles are not irregular
in shape
they may be of virtually any shape. In one embodiment, particles that are
generally or
substantially spherical, or generally or substantially oblate, or prolate may
be
employed. Suitable particle shapes also include cylindrical or conical
particles, in
addition to regular polygons such as icosahedral particles, cubic particles
and the like.
During use and reuse the particles may become abraded altering their shape.
Particles for use in the methods and systems for removing water (e.g.,
reducing
the moisture content) of from coal fines described herein can be of a variety
of sizes.
In one embodiment, where the water-collecting materials are in the form of
particles,
the particles have an average size that is at least: 2, 3, 4, 6, 7, 8; 9, 10,
12, 14, 16, 18,
20, 25, or 30 times greater than the average size of the coal fines, which are
typically
in the range of 100 to 800 microns. In one embodiment the difference in size
is based
upon the difference in the average size of the largest dimension of the
particles and
coal fines.
Particles of water-collecting materials, including those that are spherical or
substantially spherical, may have an average diameter (or largest dimension)
that is at
least: 1, at least 1.25, at least 1.5, at least 1.75, at least 2.0, at least
2.25, at least 2.5
mm, or at least 4 mm where the average diameter (or largest dimension) is less
than
about 5 mm, 7.5mm, lOmm or 15 mm. In another embodiment, the systems may
employ particles that have an average diameter (or largest dimension) that is
greater
than about 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 or 26 mm and less than
about 28, 30
or 32 mm.
In embodiments where particles have an irregular shape, or are not spherical
or
substantially spherical, they may have a largest dimension that is at least:
1, at least
1.25, at least 1.5, at least 1.75, at least 2.0, at least 2.25, at least 2.5
mm, or at least 4
mm, and less than about 5 mm, 7.5 mm, lOmm or 15 mm. In another embodiment,
the
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methods and systems described herein may employ irregular or non-spherical
particles
that have a largest dimension that is greater than about one of 4, 5, 6, 8,
10, 12, 14, 16,
18, 20, 22, 24 or 26 mm and less than about one of 28, 30 or 32 mm.
In one embodiment the water-collecting materials are desiccants, such as
activated alumina desiccants, which are manufactured in multiple forms. In
some
embodiments the desiccants particles used for water-collecting materials,
which may
be spherical or substantially spherical, are greater than about 1, 1.25, 1.5,
1.75, 2.0,
2.25 or 2.5 mm in diameter and less than about 5 mm or 10 mm in diameter. In
other
embodiments the desiccant particles have an average diameter or greatest
dimension
that is greater than about 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 or 26 mm
in and less
than about 28, 30 or 32 mm. In one set of embodiments the desiccant particles
are
spheres (or substantially spherical) with diameters (e.g., average diameters)
in those
size ranges. In other embodiments, the desiccant particles are spheres (or
substantially
spherical) in sizes up to or about 6mm in diameter. In other embodiments the
desiccants are spherical or substantially spherical particles comprised of
alumina
having a size in a range selected from: about 2mm to about 4 mm, about 4 mm to
about 8 mm, about 8 mm to about 16 mm, about 16 mm to about 32 mm, about 5 mm
to about 10 mm, about 8 mm to about 20 mm, and about 16 mm to about 26 mm. In
still other embodiments, the water collecting materials are spherical or
substantially
spherical alumina particles having an average diameter of about: 4, 6, 8, 10,
12, 14, 16,
18, 20, 22, 24, 26, 28, 30, or 32 mm.
2.0 Separation by Size and/or Magnetic Means
Water-collecting materials may be separated from coal fines by any suitable
technique including filtering, sieving or sifting, or the use of a stream of
gas to carry
coal fines away from larger and/or heavier particles water-collecting
materials.
The separation of all types of water-collecting materials (e.g., molecular
sieves,
desiccants, or hydratable polymers) may also be accomplished using magnetic
separation equipment where the water-collecting materials comprise material
capable
of, or susceptible to, being attracted by a magnet. Materials that render
water-
collecting materials capable of being attracted by a magnet include magnetic
material
and ferromagnetic material (e.g., iron, steel, or neodymium-iron-boron). Water-
collecting materials need only comprise sufficient magnetic materials to
permit their
separation from coal fines. The amount of magnetic material employed permit
the
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separation of water-collecting particles from coal fines will vary depending
on, among
other things, the strength of the magnet, the size of the particles, and the
depth of the
bed of coal fines from which the particles are to be collected. The amount of
magnetic
material may be greater than about 10%, 20%, 30%, 40%, 50%, 60%, 65%, 70%,
75%,
80%, 85%, or 90% of the total weight of the water-collecting material on a dry
weight
basis. In some embodiments the magnetic materials will be iron or an iron
containing
material such as steel.
Regardless of the magnetic material employed to render water-collecting
materials susceptible to magnetic collection, the magnetic materials may be
arranged
in the water-collecting material as a solid core or as dispersed particles or
layers within
the water-collecting materials. Where dispersed particles employed are
employed,
they may be spread uniformly throughout the water-collecting material. In one
embodiment the magnetic material is comprises iron containing particles that
are
admixed with water-collecting materials such as alumina or mullite prior to
forming
into pellets that will fired into a ceramic type of material. In still other
embodiments
the water-collecting materials may contain layers of materials that render the
particles
susceptible to attraction by a magnet (e.g. iron or steel). Examples of
magnetic
alumina particles that may be used as water-collecting materials may be found
in US
Patent No. 4,438,161 issued to Pollock titled Iron-containing refractory balls
for
retorting oil shale.
3.0 Separation Systems and Methods
The present disclosure also includes and provides for systems and methods for
removing water from wet coal fines. The systems and methods described herein
may
employ any of the above-described water-collection materials or particles of
water
collecting materials for removing water from coal fines. As described above
the
water-collecting materials may comprise molecular sieve, a hydratable polymers
or
desiccants. And as also described above, regardless of the type, size and
shape of
particles of water-collecting material, the particles also may include
materials that
render the particles susceptible to attraction by a magnet to facilitate
magnetic
separation of the particles from coal fines.
In one embodiment such systems and methods comprise:
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a first location in which the wet coal fines are admixed with at least one
water-
collecting material to form an admixture of wet coal fines and said water-
collecting
material, and
a second location where at least a portion of said water-collecting material
is
removed from said admixture.
In one embodiment the second location is configured to provide size-based
separation. In another embodiment, the second location is configured to
provide a
treatment selected from the group consisting of filtering, sieving or sifting,
and the use
of a stream of gas to carry coal fines away from larger and/or heavier water-
collecting
materials.
The second location may also be configured to provide magnetic separation of
water-collecting materials from the coal fines. Magnetic separation may be
employed
alone or in combination with any one or more of filtering, sieving or sifting,
and the
use of a stream of gas to separate coal fines from particles of water-
collecting
materials.
Systems and methods for collecting water from coal fines may further comprise
a third location where at least a portion of the water is removed from the
water-
collecting material. In addition, the systems may further comprising a
transporter for
transporting at least a portion of the water-collecting material obtained from
the third
location back to the first location for admixture with wet coal fines. Where
particles
having materials that are susceptible to attraction by a magnetic are used,
such
transport systems also may include magnetic transport equipment.
In one embodiment, following the step of forming an admixture of the coal
fines with the water-collecting material, at least 25% of the water (by
weight) in the
composition is associated with the water-collecting material. In other
embodiments,
the amount of water by weight that is associated with the water-collecting
material is at
least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least
55%, at least
60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or
at least
90%.
Example 1
Coal fines (15 g) with a moisture content of 30% by weight are mixed with
molecular sieves having a pore sizes of 3 angstroms (15 g, product MS3A4825
2.5-4.5
mm bead size from Delta Adsorbents, which is a division of Delta Enterprises,
Inc.,
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Roselle, Illinois) for about 60 minutes thereby drying the coal fines to <5%
moisture
by weight. After separating the coal fines from the sieves by sifting, the
molecular
sieves were weighed and dried in a 100 C oven. The coal fines were weighed
periodically to determine the length of time necessary to drive off the water
absorbed
from the coal. The data is plotted in Figure 1 for the first batch of coal.
The process is
repeated using the same molecular sieves with a second through sixth batch of
coal
fines. The graph in Figure 1 shows the weight measurements for the molecular
sieves
throughout the drying process after drying the first through sixth batches of
coal fines.
Figure 1 demonstrates that the molecular sieves can be effectively reused.
Example 2
Coal fines (15 g) with a moisture content of 30% by weight are mixed with a
polyacrylate polymer (0.5 g Online Science Mall, Birmingham, Alabama) for
about 1
minute thereby drying the coal fines to <5% moisture by weight. After
separating the
coal fines from the polymer gently sifting the mix, the molecular polyacrylate
polymer
particles are recovered for reuse after drying.
Example 3
Coal fines (100g) with a moisture content of 21% by weight are mixed with
activated alumina beads (6mm diameter, AGM Container Controls, Inc, Tucson,
AZ)
for about 10 minutes, thereby drying the coal fines to about 7% moisture by
weight.
After separating the coal fines from the polymer gently sifting the mix, the
activated
alumina beads are recovered for reuse after drying.
The invention(s) as defined by the appended claims is/are not to be limited in
scope by the embodiments disclosed herein. Indeed, various modifications of
the
embodiments shown and described herein will become apparent to those skilled
in the
art from the foregoing description and thus should be deemed to fall within
the scope
of the appended claims.
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